Functional Surfaces in Mechanical Handling of Micropartsetd.dtu.dk/thesis/192973/12_15_2006_Povilas_Pocius_Master_Thesis.pdf · Gripper employing the Bernoulli ... Functional surfaces

Functional Surfaces in Mechanical Handling of Microparts

Povilas Pocius, s021524

Supervisor: Prof. Leonardo De Chiffre

Co-supervisor: Ph.D. student Asta Gegeckaite

IPL publication

December, 2006

Abstract The present thesis investigates functional surfaces on a mechanical gripping device, in

order to improve the handling of micro objects. The projects will focus on different

techniques for surface modifications with the applications on micro handling and

assembly. The gripper had been tested on robot MELFA RV-1A/ Mitsubishi for handling

operation of micro-specimens. Functional surface of gripper was measured by several

optical measuring machines, evaluated with powerful image metrology programs and the

conclusions had been drawn regarding the suitability for the gripping devices for the

micro applications.

Analysis of functional surfaces for mechanical handling of microparts is needed in order

to evaluate the impact of tacking surface area ration and different surface parameters.

These parameters can strongly affect the functional behaviour of handling process of

microobjects. For this reason it is a need to develop different techniques for surface

modifications.

Mechanical grippers are traditional used for manipulating large objects. Due to this

scaling behaviour manipulation in microscale is completely different from manipulation

in the macro scale. Adhesive forces between gripper and object can be significant, if

compared to the gravitation force. These adhesive forces arrives primary from

electrostatic attraction, van der Waals and surface tension forces. The balance between

these forces depends on the environmental conditions, such as humidity, temperature,

surrounding medium, surface condition, material and relative motion.

Design, mathematical modelling and surface structure of griper grasping parts must be

developed in order to avoid or decrease influence of surface, material and motion.

Preface

The thesis has been prepared as the requirement of the Master Science Degree in

Department of Manufacturing Engineering and Management at Technical University of

Denmark.

The work has been carried out during the period June 1st, 2006 to December15th, 2006 at

IPL-DTU under supervision of Prof. Leonardo De Chiffre and Ph.D. student Asta

Gegeckaite. During the project I have become indebted to number of people whose

help I could not have been without. Firstly, I would like to thank my supervisors

Professor Leonardo De Chiffre and Ph.d. student Asta Gegeckaite for the input to the

thesis work and a great supervision.

Special thanks are for Ph.D. Giuliano Bissaco for huge support in experiment task and

preparation of experiments equipment. Thanks to René Sobieski for his help, suggestions

for metrology, evaluations and his kind advice.

Thanks to all people who have contributed significantly to the present work and

especially I would like to thank the: Peter, Giudo, Jimmy, Rasmus, Tomasso, Chistoffer.

I would like to thank my friends and colleagues Danila and Vladimir for comprehensive

help and great time we had together and the friendly atmosphere accompanied our days.

Finally it is very important to me to thank to all IPL staff for grate atmosphere and a lot

of advice.

Kgs. Lyngby, December 2006 Povilas Pocius

Nomenclature Symbol Description Standard Unit Ref-

ere-nce

Amplitude parameters: Sa Roughness Average DIN 4768 [nm] Sq Root Mean Square ISO 4287/1 [nm] Ssk Surface Skewness ISO 4287/1 Sku Surface Kurtosis ANSI B.46.1 Sy Peak-Peak ISO 4287/1 [nm] Sz Ten Point Height ANSI B.46.1 [nm] Hybrid Parameters: Ssc Mean Summit Curvature [1/nm] [6] Sti Texture Index [7] Sdq Root Mean Square Slope [1/nm] [6] Sdr Surface Area Ratio [6] Functional Parameters: Sbi Surface Bearing Index [6] Sci Core Fluid Retention Index [6] Svi Valley Fluid Retention Index [6] Spk Reduced Summit Height DIN 4776 [nm] Sk Core Roughness Depth DIN 4776 [nm] Svk Reduced Valley Depth DIN 4776 [nm] Sdcl-h l-h% height intervals of Bearing Curve ISO 4287 [nm] Spatial Parameters: Sds Density of Summits [1/mm2] [6] Std Texture Direction [deg] [6] Stdi Texture Direction Index [7] Srw Dominant Radial Wave Length [nm] [7] Srwi Radial Wave Index [7] Shw Mean Half Wavelength [nm] The table lists the roughness parameters by their symbol, name, corresponding 2D standard and unit.

Povilas Pocius Functional surfaces in mechanical handling of microparts

Table of contents Table of contents........................................................................................................................ 1 1. Micromanufacture and microhandling. Review of gripping devices................................. 2

1.1. Gripping principles .................................................................................................... 3 1.2. Factors, influencing microhandling ........................................................................... 4

1.2.1. Room conditions ................................................................................................ 5 1.2.2. Gravitation ......................................................................................................... 6 1.2.3. Van der Waals force........................................................................................... 7 1.2.4. Electrostatic force .............................................................................................. 7 1.2.5. Surface tension................................................................................................... 8 1.2.6. Comparison between the forces ......................................................................... 9

1.3. Classification of gripping devices............................................................................ 10 1.4. Requirements for gripping devices .......................................................................... 11 1.5. Gripping design of devices and handling process performance ............................... 12

1.5.1. Design of mechanical gripping devices ........................................................... 12 1.5.2. Adhesive gripper.............................................................................................. 14 1.5.3. Vacuum gripper ............................................................................................... 15 1.5.4. Gripper employing the Bernoulli effect........................................................... 16

1.6. Microobjects ............................................................................................................ 17 1.6.1. Definition of the microobject........................................................................... 17 1.6.2. Design .............................................................................................................. 17 1.6.3. Factors influencing handling process............................................................... 18

2. Microassembly with mechanical gripper ......................................................................... 22 2.1. Definition of mechanical grippers ........................................................................... 22

3. Mathematical modeling ................................................................................................... 24 3.1. Modeling of part and gripper interaction ................................................................. 24 3.2. Equilibrium forces ................................................................................................... 26

4. Design and manufacturing of the gripper surfaces .......................................................... 36 4.1. Existing gripper: Study on functional surfaces in gripper ....................................... 36 4.1. Existing gripping device ............................................................................................... 37 4.2. Development of new gripper functional surfaces .................................................... 38

5. Metrology......................................................................................................................... 41 5.1 Robot limits and uncertainty analysis ............................................................................ 41

5.1.1. Error analysis ................................................................................................... 43 5.1.2. Measurement uncertainty evaluation ............................................................... 45

5.2. Existing gripper functional surface evaluation ........................................................ 46 5.3. Grippers evaluation by optical measuring machine................................................. 50 5.4. Measuring procedures with De Meet....................................................................... 53 5.5. Roughness Parameters ............................................................................................. 54 5.6. Results...................................................................................................................... 58

6. Experiments. Testing of gripping devices ....................................................................... 60 6.1 Experiment procedure and results.................................................................................. 60

7. Conclusion ..................................................................................................................... 101 References.............................................................................................................................. 102

Master thesis Page 1


1. Micromanufacture and microhandling. Review of gripping

devices

Micro handling and assembly is as the discipline of transportation, positioning,

orienting and assembling of micro-scale components into complex micro systems and

covers. In this chapter a review of possible techniques for handling and assembly, as

well as review of gripping devices will be given.

This report consists of seven chapters. Chapter 1 gives a general introduction to

microhandling problem and all influence factors which performed with them and description

of microobjects.

Chapter 2 describes mechanical grippers, process of handling microparts and suitability of

microapplication. There main task is to define and specify the requirements of the mechanical

gripper fingers (for micro applications), by using many different methods for gripping device.

This has been done by performing mathematical modelling of the micropart. So, the purpose

of chapter 3 is a mathematical modelling of handling operation influencing factors and

method of theoretical calculation. Chapter 4 experimental parts to evaluate existing gripper

functional surface, develop new grippers for microapplication. There additional profile was

provided in form of design and manufactured gripper surfaces. Represented development and

modification of new gripper functional surface.

Chapter 5 represents metrological point of view. All measurement and evaluation what occurs

in the project are represented in this chapter. Mostly all the measurement was done by optical

measuring machines: UBM, DeMeet, Stemi 200C Microscope and evaluated by SPIP and

Dix/microscope programs. Surface values related to microhandling problem are evaluated and

analyzed for father suggestions. There is also going to be performed evaluation of functional

surfaces of the grippers, their repeatability, compatibility and variability concerning

appropriate micro parts.

Chapter 6 represents experiments of handling of microobjects, robotic programming,

alignment, handling process and results of suitability and repeatability.



The purpose of chapter 7 is discussion and conclusion of the results. There will be find

suggestions to what could be done to improve micro handling processes.

1.1. Gripping principles

Handling of micro parts is an issue facing new problems that were not encountered in

conventional size production. However, an increasing number of micro components

based on different materials and with complex geometries need to be handled with

micrometer precision. A significant number of specialized micro grippers are

developed for specific applications, but a homogeneous strategy for specification and

selection of the grippers seem to be missing. Manual placement of micro mechanical

parts by contact and non-contact gripping devices is extremely slow, troublesome and

inaccurate. The need for highly flexible automatic solutions is therefore evident

although they usually require large investment in tooling.

In this paper, micro handling is defined as the handling and subsequent assembly of

micro mechanical parts of dimensions below 1 millimeter as well as parts larger than 1

millimeter with denned microstructures of sub-millimeter size [1].

These main parts will be discussed in this paper:

• The object,

• The handling functionality

• The gripping principle.

The object is defined by means of dimension, geometry, material and weight. The

handling functionality is an attempt to describe the handling situation and the related

necessary operations. Handling scenario consists of the sequential steps of picking,

transportation, orientation and releasing. Furthermore, in order to focus on a possible

assembly operation coming immediately after the physical handling, the assembly process

is considered as a part of the handling functionality. Finally, the gripping principle is

described [2].



The methodology for choosing a gripping principle based on the object geometry and a

handling functionality would be the following:

• Define the micro object characteristics (weight, material, geometry, dimensions);

• Choose the functionality of the micro handling process.

The functionality of the micro handling process depends also on the number of the micro

object to be manipulated, that gives a beed to define and plan the handling strategy. One

of the important factors is the speed of operation, as precision and control of the process

can be easily lost with high speeds. After all the factors, influencing the micro handling

process are summarized and consideration of the properties of the micro object itself are

done, the qualified micro gripping principle can be selected among the list from known

principles.

1.2. Factors, influencing microhandling In this paragraph of factors, influencing the microhandling will be summarized. A survey

of the forces influencing microobject during the handling will be presented. A particular

attention will be on the forces, working at the microscale.

For the parts with masses of several grams, the gravitational force usually will dominate

adhesive forces and parts will drop when the gripper opens. When parts to be handled are

very small (relative diameter less when 1 mm) adhesive forces between gripper and object

will become larger than gravitational forces. Then the object will adhere to the gripper

and after the gripper will be opened will not drop down, but has to be removed by specific

techniques. These surface forces can be used in grippers as an adhesive force to pick up

the object. These forces are almost not controllable and they are more likely to disturb the

process rather than improve it. It shows that grippers using adhesive forces to pick up

objects have been developed.

Adhesive force arises primarily from:

• van der Waals forces;



• electrostatical forces;

• surface tension.

These adhesive forces arise primarily from electrostatic attraction, van der Waals forces

and surface tension. The balance between these forces depends on the environmental

conditions, such as humidity, temperature, surrounding medium, surface condition,

material, and relative motion [2],[3]. In the figure 1.1 it is shown common pick and place

operations.

Figure 1.1: Pick-and-place operation with micro-parts. Due to sticking effects, parts may be attracted to the gripper during approach and release phase, causing inaccurate placement [4]

1.2.1. Room conditions In a high humidity environment, or with hydrophilic surfaces, there may be a liquid film

between the spherical object [4]. Figure…



vv Figure 1.2: Micro-gripper holding spherical objects

γπrFtens 4= ( 1.1 )

where r is the object radius ,γ is the surface tension ( γ =73 mNm-1 1 for water).

Assuming hydrophilic surfaces and a separation distance much smaller than the object

radius.

1.2.2. Gravitation Gravitation is a physical force that is responsible for interactions between objects with

mass. For a spherical part of silicon the gravitational force is:

gsrF igrav ρπ 3

34

= ( 1.2 )

where isρ = 2300Kgm-3 is the density of silicon. For accurate placement, adhesion forces

should be an order of magnitude less than gravitational forces. More about gravitation

force will be discussed in chapter 2.1.



1.2.3. Van der Waals force Van der Waals force is a force that arises from the instantaneous polarization of atoms

and molecules into dipoles when they are set close. Even if van der Waals force is much

weaker than other intermolecular forces, like ionic interactions, hydrogen bonding or

permanent dipole-dipole interactions, it is able to hold together many molecules that are

too stable to become an integral part, as noble gases. The van der Waals force between a

sphere and a flat gripper can be approximated by [5] and [6]:

28 zhrFvdw π

= z<<r (1.3)

where H is the Hamaker constant, z is the distance between the surfaces and r is the radius

of the sphere. This formula is assuming atomically smooth surfaces. Severe corrections

need to be made for the rough surfaces. In fact the van der Waals force falls off very

rapidly with increase of distance between two surfaces, but it is only significant for gaps

less than about 100 µm.

Since the tolerances on the billetare r 6 µrn, the distance between the lateral surface of the

billet and a cylindrical bore cannot be kept less than 0.1 µm, for this reason the van der

Waals force results prevented.

1.2.4. Electrostatic force

The electrostatic forces arise from charge generation (triboelectrification) or charge

transfer during contact. Consider the force between a spherical object and a plane (such as

one finger of the grippe). The approximate force between a charged sphere and a

conducting plane is given by:

( )2

2

24 rqFelec∈

=π

(1.4)



where q is charge, ∈ is the permittivity of the dielectric, and r is object radius. The

assumed charge density is approximately 1.6 x 10-6 Cm-2.

The attractive force per unit area between two parallel plates is [5]:

εσ

ε22

1 22 SEp == ( 1.5)

where p is the pressure in Pascal, ε is the permittivity of the air, E the electric field

strength and σs the surface charge density. At atmospheric pressure and centimeter-size

gaps, the breakdown strength of the air (about 3-106 V/m) limits the maximum surface

charge density to about 3x10-5C/m2. Such a value of the surface charge density sets a limit

to the pressure at about 50 Pa[6].

When a gap is very small (in the order of 10µm) maximum fields of gap can increase by

one order of magnitude or even more.

For the specific process to be performed, no relevant charging affects are considered or

easily achievable: therefore, the electrostatic force was not comprised between the

eligible methods for billet gripping.

1.2.5. Surface tension

When two objects are exposed to the environment, a thin film of water or contaminant

(e.g. oil, lubricant, etc .) is formed on their surfaces. When they are brought together very

closely, the films touch and melt together. In this way the two objects stick because of the

surface tension. This attractive force increases because of high humidity environment,

large radius of curvature, long contact time and hydrophilic surfaces. The force can be

calculated through the following expression [5]:

dA

Ftens)cos(cos 21 θθγ +

= (1.6)

where: γ is the surface tension, A is the shared area, d is the gap between surfaces and θ1 ,

θ2, are the contact angles between the liquid and the surfaces.



1.2.6. Comparison between the forces Adhesive forces and the gravitational force are compared in Figure 1.3 [reference]. It is

assumed that the object is a silicon sphere picked up by a gripper with flat jaw surfaces.

Forces are expressed as a function of the object radius.

For accurate gripping, adhesive forces should be an order of magnitude higher than

gravitational forces. From the comparison, it can be highlighted that surface tension

forces are the biggest ones. For this reason the attention was focused on these surface

tension forces, considered as the most stable, repeatable and accurate.

On the other hand, van der Waals forces can start to be significant when spheres of radius

>100µm have to be handled. Similarly, electrostatic forces can be of interest task for the

manipulation when operating with parts less than 10 µm in size.

Figure 1.3: Gravitation, electric, van der Waals and surface tension forces

Capillary forces dominate and must be prevented to allow accurate placement. Van der

Waals forces start to be significant (with smooth surfaces) at about 100 µm radius and

generated electric charges from contacts could prevent dry manipulation of parts less than

10µm in size.



Figure 1.3 shows electrostatic to be the least significant force except for gravity, it can be

argued that it is actually the most significant force for grasping and manipulation of W/m

to 1 mm parts [4]. First, van der Waals force is only significant when a gap is less than

100nm, unless objects surface is very smooth. Then the effective distance, between the

object and the gripper will be large except at a few points of contact. Finally, the

electrostatic forces can be active over ranges of the order of the object radius. Surface

roughness is much less important for electrostatic forces than for van der Waals.

1.3. Classification of gripping devices Gripping devices, depending on the principle used to hold the micropart, can be divided

into two categories:

• Contact;

• Non-contact.

Contact grippers are a group of grippers which have direct contact with the object.

Contact grippers especially gripers for micro assembly can be divided in categories

depending of work principle:

• Mechanical gripper;

• Vacuum gripper;

• Adhesive gripper;

• Biological gripper;

• Distributed motion gripper.

Non-contact grippers are a group of grippers which have no direct contact with the object;

it means that handling process is without any direct contact with the object. That is

important when it is needed to avoid a damage of microobject (due to very small

dimensions of the object or resistance of the object material). Micro non-contact grippers

are divided into following categories depending of the working principle:

• Magnetic gripper;

• Electrostatic gripper;

• Optical gripper;



• Bernouli effect gripper

1.4. Requirements for gripping devices Requirements for the gripping devices are to match related gripping application. In our case

will be examined a gripping devices for micro application.

Many micro-operations demand sensor control in the execution to compensate for several

types of errors like part dimension variations. It might be possible to compensate for

inaccuracies in part gripper relations in this way as well.

When diminishing part dimensions, the influence of adhesive forces increases.

Electrostatic force fields are known to be disturbing in the pick-and-place cycle. In

particular when direct physical contact exists between gripper and part, surface tension

forces and van der Waals forces may play a role as well. The sensitivity for adhesive

forces needs therefore to be considered when selecting a griping principle. The part

weight, e.g. the relative importance of adhesive forces compared to gravity, is essential

here. Measures can be taken to diminish the effect of adhesive forces, e.g. drying the

environment or adding hydrophobic coatings to parts reduces the influence of surface

tension forces. Adding surface roughness reduces the influence of van der Waals forces

and electrostatic forces can be reduced by using conductive materials. Other approaches

can be: overcoming the surface forces during the release task such as for example by

gluing the component at the right place, using dynamic release using a needle blowing

away the handled component

The mechanical micro grippers have to fulfil these requirements [3]:

• Parallel opening or closing of the gripper tip:

• Non planar design of the gripper:

• Small dimension of the gripper;

• Relatively high surface roughness for easy gripping of micro structures;

• Material according to the applications of the gripper device.



1.5. Gripping design of devices and handling process performance One of the main difficulties in production of microsystems is handling and assembly. These

process steps of the fabrication sequence are predominantly done manually by skilled human

operators. The automation in this area by assisting the human operator in picking-up

microscopically small structures, holding them and placing on the right position improves

the operators working conditions, decrease the production costs, increase both, the process

reliability and the product quality after assembly [7]. In this section the important designs of

micro-grippers and micro-assembly process solutions will be presented.

1.5.1. Design of mechanical gripping devices Microgripper is robotic tool used for microhandling or microassembling operation to

grabb or manipulate microobject. Generally defined for grabbing a product with

dimensions in the micrometer range.

Mechanical grippers is group of grippers where handling process is performed by using to

the grasping force. Forces acting in this micro-environment will be properly discussed in

chapter 2.1. Many different kind of microgrippers have been developed.

One of the examples is electrostatically driven mechanical gripper which has a total

length of 400µm and a thickness of 2.5µm (see Figure 1.4) [8]. The gripper closes

completely by applying a voltage of 45V. The maximum force is equal to 0,1µN and it is

reached at 50V. The gripper has been used to pick up microscopic objects, such as 2.7µm

diameter polystyrene spheres. However, sticking problems have been observed.





Figure 1.4: Electrostatic microgripper [1].

Suzumori et al. [7] developed a pneumatically or hydraulically driven gripper. In such a

gripper, one of the jaws is a flexible chamber, while the other is a rigid jaw. When the

flexible chamber is pressurized, it bends towards the rigid jaw. The prototype is 8 mm

wide, 18 mm long and has a gripping force of 2N.

Keller et al. [11] made a thermal gripper, based on differential thermal expansion. By

pushing the elastic structure which holds the jaws, a longitudinally expanding beam

element allows the opening motion (see Figure 1.5). It can be provided with different

types of tweezers tips, depending on the application. The gripping device is about 2 mm

wide and 9 mm long.

Figure 1.5: Thermal microtweezers [16]

1.5.2. Adhesive gripper Adhesion is the molecular attraction between the two bodies in contact. Adhesive gripper

is based on this principle. As it is described in the section 1.2 sticktion or adhesion also

can be used to build a gripper. In this case, objects are picked up by means of surface

tension forces. This kind of forces, arising from air humidity, can be controlled by

incorporating a microheater in the gripper [6]. In the cold condition, the object can be

picked up simply by touching it.



To release the object, the heater evaporates the moisture layer that keeps the object stuck

to the gripper. Instead of using natural moisture layers, some adhesive grippers have a

dispenser that forms a small drop at the gripper's surface. When the gripper is brought in

contact with the object, the surface tension centers the component to the surface of the

gripper. The disadvantage of such gripper is that the spreading of the drop takes some

time and the micro part has to be resistant to the liquids.

1.5.3. Vacuum gripper A vacuum gripper is a very simple gripper, as it consists mainly of a thin tube or pipette

connected to a vacuum pump. This makes this kind of gripper cheap and easy to replace.

The suction principle enables the grippingg of objects with different shapes, dimensions

surface quality and material. (see figure 1.6).

Figure 1.6: Vacuum gripper

The vacuum gripper and the working platform, carrying the microstructures, should have

the same electric potential (grounding) to avoid electrostatic loading between the gripper

and handled microstructures. After sputtering, the glass-pipette is connected with the

holder and the vacuum controller. Due to the fact that we have used for experiments

pipettes with different dimensions, a direct connection with the vacuum controller was not

possible. To solve this problem a polymer-microloader was used (as shown in Fig. 10),

enabling at the same time mechanical flexibility between the glass-pipette and the

connection of the vacuum controller. To handle larger structures (>500 µm), very fine

medical injection needles (e.g. with 0,3 mm diameter) can be used as metallic vacuum

grippers (Fig. 1.6) [4] and [8].



1.5.4. Gripper employing the Bernoulli effect Bernoulli's principle states that for fluid (or air) flow an increase in velocity occurs

simultaneously with decrease in pressure. That means that the only cause of the change in

fluid velocity is the difference in pressures either side of it. Due to difference between

pressures specimen will be lifted without any touch with gripper. This type of grippers

can lift and transport delicate silicon wafers (or similar 2½D microobjects, e.g.

membranes, etc.). The gripping device mainly consists of a circular plate with a hole

through which the air is blown. It lifts the wafers by blowing gently on the wafer upper

surface so that the aerodynamic lift is created (see Figure 1.7).

Figure 1.7 - Bernoulli effect employing gripper [12].

By blowing through the central hole, the air flows radially between the circular plate and

the wafer. The air high velocity induces a dynamic pressure decrease (Bernoulli effect)

that leads to an attractive force between the wafer and the circular plate.



1.6. Microobjects

1.6.1. Definition of the microobject

Microobject is an object with dimensions in the micrometer range, or object that has structures

in the micro range, which have affect for handling or assembly of a product. Due to consideration of the micro object classification, many different aspects have to be

taken into the account. The object which is going to be handled is the main part of the

handling and assembly process, so it is critically important to classify micro parts. The

literature study about the micro products shows that there is no clear classification and

united system to separate the micro objects into the specifics classes [10].

In order to have a better understanding, why different products require specific handling

process, the classification has to be done. In the microobject classification, the different

properties will be explained, by introducing the different object characteristics and

concluding how these characteristics influence the micro handling and assembly process.

1.6.2. Design A design of the micro product is closely dependent on the required functionality of the

product, specifications and final tolerances of the separated components and the final

products. While designing a micro product, the different functionalities are related to the

different, components, which are optimized to the specific function, with respect to shape,

weight, materials, dimensions and surface properties. These properties will be examined

in the following section .

The approach of the design would be the desired functionality of a product, resolved into

a logical structure. The easiest way to do it is to decompose the product into the separate

objects and to prospect separate parts of the process and object itself. An extreme case in

functionality integration is the monolithic design, where the micro product is constituted

of only one component, having all the functionalities, with the displacements obtained

only through the flexibility of its features. When designing a microproduct, the

specification meets the specified requirements for a product, thus controlling the design

process [9].



Several constrain due to the incompatibilities of materials, processes and geometries have

to be considered while defining a manufacturing sequence. Since each process step

influences the results of both the previous and the following process steps the process

sequence has to be checked and incompatibilities has to be identified.

1.6.3. Factors influencing handling process

Geometry Geometry of the micro product is one of the critical parameters which influence the

handling and assembly process. From a geometrical point of view micro products can be

organized into three groups [9]:

• Two-dimensional structures (2D). Examples of the products could be different

types of optical lenses or micro mirrors.

• Two- dimensional structures with a third dimension also called two and a half

dimension (2½D). Examples could be: fluid sensors where the structure of the

channel system itself is two-dimensional, but since the channels have a finite depth

they can be characterized as 2½D|.

• Real three-dimensional structures (3D). Typical examples of 3D structure can be

components of various shapes, found for example in hearing aids [8] or in micro

motors [10].

Dimensions Depending on the dimensions of the microobject, these are separated into these groups:

<lmm (real micro products);

>lmm, but having micro structures, which can effect handling process.

Importance of dimensional classification is to explain the definition of the microobject

and to show the differ ence between micro object and the "macro" object with the micro

structures.



Materials A full understanding of the properties of the materials, used for micro applications is

important in order to future develop the micro components. Depending on the

functionality of the microparts, material characterization may take the form of evaluation:

mechanical, optical, etc. Material properties also influence the handling process. While

going to the smaller sizes of the products, from macro to micro and even to the nano

sizes, it very important to choose the right material for the product, as it is probably one

of the easiest things to change. Depending on the specific properties, existing materials

can be divided into groups of:

• Ceramic and glasses;

• Metals and alloys;

• Polymers and elastometers

• Hybrids: composites, foams and natural materials

Ceramics and Glasses.

A generic term of so called earth materials: (clay. sand, etc.) processed by firing, or

baking. The classification includes pottery, earthenware, glass, abrasives. Chemically

materials of this class have a combination of metallic (light blue) and non- metallic

aterials. Predominantly ionic bonding is influencing the properties, mainly because of the

Coulomb interaction between the positive and negative ions. The difference between

Ceramic and glasses is a morphologic structure: Ceramic has crystalline and glasses has

amorphous structure. The most commonly used ceramics is silicon. It is a semiconductor

material used to fabricate most transistors and integrated circuits. Pure silicon is used to

make almost all the semiconductor chips currently sold on the market. Silicon is not the

only semiconductor which can be used to make integrated circuits, but it does have many

properties that make it quite a bit better for this purpose than the other known

semiconductors. It has been separated from ceramics, as silicon is one of the materials

which is mostly used in the micro technology [15].



Metals and alloys.

About 80% of the known elements are metals. Any of a class of chemical elements that

have a luster and can conduct heat and electricity. In water quality, these elements (in

high enough concentrations) can be considered toxic. Specific physical property of

metals is metallic bonding (positive ions in the soup of the valence electrons) [10] and

[13].

Polymers and elastometers.

High molecular weight, chemical compounds formed by repeated linking of smaller

chemical units called monomers. Polymers from which fibers are made are long chain

molecules in which the monomers are linked end-to-end linearly. Synthetic polymers used

for carpet fibre include nylon-6,6 and nylon-6 (polyamides), polyester, polypropylene and

polyacrylonitrile (acrylics). In popular terminology, polymers are also called plastics or

resins.

Mechanical properties of the materials influencing the final properties of the material are:

• Stiffness - elastic modulus or Youngs modulus (MPa);

• Strength - yield, ultimate, fracture, proof, offset yield measured as stress (MPa);

• Ductility - measure of ability to deform plastically without fracture - elongation,

fracture:

• Strain toughness, resilience - measure of ability to absorb energy (J/m3);

• Hardness - resistance to indentation/abrasion (Various scales, e.g.: Rockwell.

Brinell, Vickers).

Weight The weight of the part can be defined as a the vertical force exerted by a mass as a result

of gravity. A model for a weight calculation is introduced for a product, having few parts,

connected in together. Each part has a weight associated with it which the engineer can

estimate, or calculate, using Newton's weight equation:

w = m x g (1.7)



where w is the weight, m is the mass, and g is the gravitational constant which is 9.8 m/s

in metric units. The mass of an individual component can be calculated if we know the

size of the component and its chemical composition.

Every material has a unique density. Density r is defined to be the mass divided by the

volume v:

r = m/v (1.8)

If we can calculate the volume of the component, then:

m= r x v (1.9)

The total weight of the part W is simply the sum of the weight of all of the individual

components [12].

The weight of the micropart is important, to know, as it is used later in the calculations of

the gripping devices and also it can influence the handling and assembly principle. Also

gravity force depends on the weight of the microobject.

Topography Surface properties plays an important role in determining the applicability of a griping

principle. For instance, in case of applying the van der Waals principle, the surface

roughness is determining for the force value [15, 16]. Another example is if surfaces can

easily be damaged, direct physical contact between the gripper and the part may be

undesirable. In this case it is better to use non-contact gripping devices.



2. Microassembly with mechanical gripper

2.1. Definition of mechanical grippers Mechanical grippers is group of grippers where handling process is performed with the

help of grabbing force. Force generated from motor through the drives is transformed to

two or more jaws, when jaws are compressed in interaction between them emerge grasp

force. This force is calculated:

drgg knNG ⋅⋅= (2.1)

here: - grasp force; gG

– one jaws grasp force ; gN

n – number of jaws;

- empirical coefficient due to jaws material; drk

Mechanical grippers are based on the friction principle (see Figure 2.1) and they are

generally used for manipulating large object. In the microworld, mechanical grippers have

to deal with these problems:

• too high forces damage the object or the object may jump away and be lost;

• too low forces lead to lose the object.

Therefore, the force applied by the gripper has to be precisely controlled [1].



NgNg

Ffr Ffr

Figure 2.1: Main forces, friction principle

Gs

ss mgG ⋅= (2.2)

( )tenselecvdwfrgs FFFFNG ++++< µ2

(2.3)

where: -gravitation force of the specimen; sG

- friction force between specimen jaw surface; frF

- van der Waals forces; vdwF

- electrostatic forces; elecF

- surface tension forces; tensF

- mass of specimen; sm

µ -friction coefficient between the object and jaw; The best way to grasp micro-objects is to use a microgripper where grasp force and jaws

size match the requirements.



3. Mathematical modeling The force analysis of manipulation systems for robots has two points of consideration:

• the control of the robot in particular industrial environment [16], [17] and [18],

• the second point, which can be considered from design point of view [19].

It is necessary to control the actuated joint force and torques in case of force control based

upon the information of external environment forces. The force control might be

associated with a non-deformation grasping. Link dimensions, bearings, motors and other

elements have to be chosen during the design of the robot, based on the knowledge of the

external load and the reaction forces obtained in the joints. In many cases the external

load might be considered as static or as a function of the position of the end-effector of

the robot.

3.1. Modeling of part and gripper interaction

Grippers are the object of considerable research. The kinematics and force control

problems engendered by these devices here will be analyzed. Force control for this system

requires the specification of contact forces between the fingers and the gripped object.

Fgrav

Ffr

Fvdw, Ftent, FelecFvdw, Ftent, Felec

T

Figure 3.1. Model of interaction between the object and the gripper functional surface

An equilibrium forces are the forces required to maintain the object in equilibrium

without squeezing it. The interaction force between two fingers is defined as the



component of the difference of the finger contact forces along the lines joining the two

contact points. The equilibrating forces have no interaction force components.

Fgrav

Ffr

Fvdw, Ftent, Felec

Fvdw, Ftent, Felec

Fvdw, Ftent, Felec Figure 3.2. Model of the objevct and gripper interaction, if the gripper would have three fingers. In a legged locomotion system or a walking machine it is essential to compute the support

forces required at the feet to maintain equilibrium with the force of gravity and the inertial

forces [22], [24]. The support forces are equilibrating forces. They are similar to the

scalar internal forces which characterize the pinch between two jaws [20].

Instead, a suboptimal solution to this problem is proposed in this paper. This method is

attractive in its speed and efficiency. Contacts are modeled as point contacts [20] which

means that a finger can apply any three force components but no moments. A quasi-static

approach to the problem has been adopted. That is, the load wrench, which is the resultant

of the inertial forces on the object and all external forces excluding the finger forces, is

always balanced by the finger contact forces.

Formulation

Let Xe-Ye-Ze be a reference frame fixed with respect to the earth. Consider a reference

frame Xg-Yg-Zb with the origin at the grasp centroid, the centroid of the support/contact



points, (Exi, Eyj, Ezj,), and the Zb axis parallel to the wrench axis [25]. The leading

superscripts e and b refer to the earth and body (object) fixed reference frames

respectively.

This problem of determining the contact forces may be decomposed into two sub-

problems:

a) Determination of the forces required to maintain the equilibrium of the gripped body

assuming that the finger interaction forces are absent.

b) Determination of the interaction forces needed to produce the finger forces computed

in step a) without violating the friction angle constraints.

The following sections elaborate on procedures for steps a) and b).

The force analysis of manipulation systems for robots has two points of consideration: the

control of the robot in particular industrial environment [3], [6] and [7], and the second

point, which can be considered from design point of view [5]. It is necessary to control

the actuated joint force and torques in case of force control based upon the information of

external environment forces. The force control of the robots might be associated with a

non-deformation grasping [1]. Link dimensions, bearings, motors and other elements have

to be chosen during the design of the robot, based on the knowledge of the external load

and the reaction forces obtained in the joints. In many cases the external load might be

considered as static or as a function of the position of the end-effector of the robot.

3.2. Equilibrium forces The force distribution must satisfy the six equations of equilibrium (see eq.3.1, 3.2). It is

convenient to decompose this system of equilibrating forces into two force fields. One

force field consists of forces parallel to the load wrench axis (parallel to Zb) and the other

is comprised of forces perpendicular to the load wrench. Two methods of solving the two

problems to find the equilibrating forces are described in the following subsections.



(3.1)

(3.2)

It will be presented as methods:

A. Method I

The set of six equations in (3.1) can be decomposed into two sets of equations. Three out

of the six equations of equilibrium, involving the x and y components may be written as

(3.3)

where Fix and Fiy are the x and y components of Fi and the xi and yi, coordinates refer to

the i-th finger contact point. The matrix equation (3.3) represents an undetermined set of

equations with only three equations in 2n unknowns. There are clearly 2n-3 degrees of

freedom in this system. However, in accordance with the definition of the equilibrating

forces, the vector difference between any two contact forces should have no component

along the line joining the two contact points [24]. Mathematically, this condition is

expressed as

(Fi - Fj) • (pi -pj) = 0, i, j = 1 ,•••,n (3.4)

The matrix equation (3.3) can now be solved subject to the restriction (3.4) and this yields

a simple solution given by



(3.5a)

(3.5b)

where

The forces on the X-Y plane are thus given by (3.5a) and (3.5b) and it is easy to verify by

substitution that they satisfy (3.3) and (3.4). All forces are perpendicular to the

corresponding position vector

(Fixi+Fiyj) • pi = 0. (3.6)

This force field is analogous to the velocity field of a rigid body where the velocity of any

point is perpendicular to the position vector if the origin is coincident with the velocity

center [24]. Thus the centroid of the contact points may be introduced as a force center

similar to the velocity center in instantaneous kinematics.

If (3.3) is rewritten as

Gr = w (3.7)

where G is the 3* 2n coefficient matrix, r is the 2n * 1 unknown force vector, and w is a

known 3*1 vector, then this system of equations can also be solved by taking the Moore-

Penrose Generalized Inverse of G [26]. If G+ is the pseudo-inverse of G, then for a full

rank matrix (one in which the rank of G is the minimum of the number of rows and the

number of columns)

G+=GT(GGT)-1 (3.8a)

and r can be found from the equation



r = G + * w. (3.8b)

In the event G is not of full rank, the pseudo-inverse can still be found by using the LU

decomposition scheme or the Householder algorithm [26]. In this case, the pseudo-inverse

can be analytically derived and it is interesting to note that the solution thus obtained from

(3.8a) and (3.8b) is identical to (3.5a) and (3.5b).

This, in fact, provides a physical interpretation of the pseudo-inverse. The null space of

the coefficient matrix G consists of all possible interaction force vectors and the row

space of G comprises of all the equilibrating force vectors with zero interaction force

components. The pseudo-inverse seeks the solution vector with the least Euclidean norm

(length) and hence the force vector which lies completely in the row space of the

coefficient matrix (which has no interaction force components). A rigorous proof for the

general case, in which all three components of forces are considered, is presented

elsewhere [25], [26].

Having found the finger forces in the x and y directions the three remaining equations of

equilibrium, (3.1) can be applied to solve the second subproblem involving the z

components

(3.9)

The F^ and Fiy quantities on the right-hand side in (3.9) are known quantities (see (3.5))

and it should be noted that (3.3) has to be solved before the right-hand side of (3.9) is

known—the two sets of equations are not decoupled. This system of three equations and n

unknowns can be solved again by using the pseudo-inverse which serves to minimize the

norm of the Fz vector. (A physical interpretation for the pseudo-inverse can be made in

terms of the fingers having equal compliances in the Z direction.) The zero interaction

force hypothesis is not used here as it would require all the z components to be equal and

would thus overconstrain the problem. The Fiz force field obtained by the pseudo-inverse

is described by a planar force distribution and is of the form



Fiz=A+B(xi-xs) + C(yi-ys). (3.10)

This is because the pseudo-inverse solution has to belong to the row space of the

coefficient matrix in (3.9). The coefficients A, B, and C can be obtained by Gaussian

elimination performed on a 3 x 3 system of equations. Alternatively, analytical

expressions can be written for the three constants

where

This completes one method for finding the equilibrating forces (step a).

Method II

This method decouples the problems of finding forces parallel to the x-y plane and forces

parallel to the wrench axis completely. This time, (3.l) are used to solve for Fix and

Fiy.



(3.11)

The pseudo-inverse solution can be obtained with some algebraic manipulation

(3.12)

(3.13)

where

The z components of the forces are found by considering (3.1) through. The terms ΣziFix

and ΣziFiy in (3.9) are zero by (3.11). Again, an analytical inversion for (8) is possible and

the Fiz are given by:

(3.14)



Equations (.12) and (3.13) do not describe a force field with zero interaction forces ((3.4)

does not hold). The interaction forces on the x-y plane can be found to be

(3.15)

Unfortunately, this quantity is not zero, unless the contact points are all on the same plane

perpendicular to the wrench axis or along the same line parallel to the wrench axis. But,

on the other hand, the complete decoupling of (3.9) and (3.11) which are required to find

the two force fields is an advantage. It is difficult to say which of the two methods is

better as in either case, the solution is suboptimal.

It should be noted that the forces computed by either of these two methods are not really

equilibrating forces. However, as mentioned earlier, the pseudo-inverse solution is

identical to the equilibrating force solution in the general case. Thus both these method

yield solutions which are, in fact, approximations to the equilibrating force vector.

The forces computed by either of the two methods described earlier are Fiz(i = 1, , n)

which are parallel to the wrench axis Fix, Fiy(i = 1, ... , n) which lie on plane perpendicular

to the wrench axis. It is assumed that method I is used and the resultant of the forces Fix

and Fiy is perpendicular to the vector p, (see Fig. 2). Let the total interaction force exerted

by the ith finger on the object be Ffl. Then

(3.16)

(3.17)



The net resultant of the interaction forces has to be zero for equilibrium to be maintained.

It is easy to see that for a two-fingered grasp, the interaction forces must be equal and

opposite in direction. For a three-fingered grasp, the interaction forces must be coplanar

and concurrent [24]. If the number of fingers are greater than 3, it is not easy to arrive at

such simple conclusions. However, if the lines of action of the interaction forces pass

through a point of concurrence, (3.17) is automatically satisfied. The condition of

concurrency is a necessary and sufficient condition for n < 3 but only a sufficient

condition for n > 3.

Nevertheless, this condition yields useful simplifications in the procedure of

determination of interaction forces. The desired situation is one in which the lines of

action are along the normal to the surface of the gripped object at the contact points. In a

practical situation, the normal at the contact points are unknown and, in general, are not

concurrent. It is proposed that the point of concurrence be chosen as the centroid of the

contact of points, namely, the origin. This choice is merely a convenience and, in

principle, any other point could be chosen. The reader is requested to bear with this gross

assumption—its validity is discussed later. Now the unit normals et at all the « contact

points are given by

eix=xi/di eiy=yi/di and eiz = zi/di (3.18)



(3.19)

For n = 3, (3.19) is a system of three homogeneous linear equations in three unknowns

and the only solution seems to be a trivial one. This is not the case since the rank of the

system of three equations in (3.19) is only 2. This is because any three points and their

centroid are coplanar, and hence, the determinant of the coefficient matrix formed by the e/'s

is always zero for n = 3. Thus (3.19) has only one degree of freedom. If n = 4 there are three

independent equations (in general the points are not coplanar, unless the grip is planar, and

the rank is 3) and again there is one degree of freedom. For n > 4 there are n - 3 degrees of

freedom. In Fig. 3.2, if

Fit = Fixj+ Fiyj

then

Fi = Fit + Fiz + Fil.

The net contact force Fi may be resolved along the normal et (postulated normal) to get

Fin and on to the plane perpendicular to the normal to get Fin.

The friction angle, at the i-th contact point is defined as



(3.20)

In (3.20) it has been assumed that (3.6) is satisfied. That is, Fit is perpendicular to ef

which is true only if method I is adopted. If method n is used Fit has to be resolved along

and perpendicular to ei and accordingly (3.19) and (3.20) are modified.



4. Design and manufacturing of the gripper surfaces

The design of production systems is generally based on economic considerations, which are

related to certain technical criteria, such as capacity, availability, and reliability. To realize a

cost-effective design, these technical and economic criteria should be considered in their

mutual coherence during the conceptual design process.

This chapter focuses on a productivity of model, which is related to this subject. This model

allows an opinion to be formed about the technical and economic performance of conceptual

robotic assembly cells, during the process of design. First, the system design process is

discussed in brief, after which the productivity variables are presented. All models are used to

assess the technical and economical behaviour.

4.1. Existing gripper: Study on functional surfaces in gripper

130°

1.29±0.01

2

Measuring directions

Figure 4.1. Surface roughness measuring direction by stylus instrument



Figure 4.2. Gripper surface roughness. After filtering surface error.

Figure 4.3.Rough profile. Exsisting gripper functional surface. (see appendix)

4.1. Existing gripping device

Existing gripping device is shown in the following picture




The design of the gripping devices and the experimental setup is represented in the following tables

4.2. Development of new gripper functional surfaces

Figure 4.4. Existing gripping device


Table 4.1. Plan of the experiment gripper’s testing GRIPPER \ SPECIMEN

Cylindrical surface

Plane surface (polished)

Plane surface (rough)

LBM surface

EDM horizontal surface

EDM vertical surface

Shape

R1.15

0.1Ra

Ra≈0.28µm

Ra

Ra≈1.2µm

0.120.06

0.02

0.05

0.07

0.04

0.05

0.07

0.03

Sketch of grabbing

Plastic specimen

No

+

+

+

No

+

Micro screw

+

+

+

+

+

No


Povilas Pocius

Master thesis

Functional surfaces in mechanical handling of microparts

Page 40

Table 4.1 . Gripper/ Specimen

Cylindrical surface

Plane surface (polished)

Plane surface (rough)

LBM surface

EDM horizontal surface

EDM vertical surface

Shape

R1.15

0.1

Ra

Ra≈0.28µm

Ra

Ra≈1.2µm

0.120.06

0.02

0.05

0.07

0.04

0.05

0.07

0.03

Manufacture procedure

Preparation

milling

milling

milling

milling

milling

milling

Modification

milling

-

-

LBN

EDM

EDM

Surface finish

polishing

polishing

-

polishing

-

-

Contact area

100 %

Measuring and evaluation equipments

UBM

UBM

UBM

UBM, DeMeet, Stemi 2000C

UBM, Stemi 2000C


5. Metrology

5.1 Robot limits and uncertainty analysis The most important characteristic for our object is accuracy and repeatability. This defines

and estimates the robot ability of coming back to the same position within coordinate system

with the same movements made n-times, is a measure of variability of measuring results

when the same quantity is measured more times. Usually that the parameter that estimates the

repeatability is defined in a statistic mode, using for example the deviation standard, often the

interval that define the repeatability

Another characteristic of the robot performance the quality of robot performance is accuracy:

it is the error between the nominal position and the average of the obtained positions.

The standards do not specify what type of instrumentation shall be used for the test.

With the data of test we can evaluate the pose accuracy in 3D so:

APp= 222 )()()( ZcZYcYXcX −+−+−

Xc = commanded position

APp= position accuracy

Xai= position attained

X = average of attained positions

And the pose repeatability so :

RP1= l±3Si

li= ( ) ( ) ( )222ZZYYXX aiaiai −+−+−



l = ∑=

N

iil

N 1

1

Sl=( )

11

2

−

−∑=

N

llN

ii

For a linear test the accuracy become:

accuracy

APp = ( )cXX −

with

∑=N

iXN

X1

1

Thus, the differential change in length ln,1, caused by position errors, (Dx, Dy, Dz), is

obtained as:

( ) ( ) ( )212

12

11, ZZYYXXl pppn −+−+−=

Then, by following the same procedure, two additional measurements at point (xp, yp, zp),

are

, where is the length measured by LVDT. 1,1,1 na lll −=∆ 1.al



5.1.1. Error analysis There are many reasons for which a robot does not reach the position or orientation wanted.

In this section is presented an overview of all possible error sources and a several manners

how these errors appear, in particular considering the circular test. After considering the main

errors a mathematical model to evaluate and correct these errors: this part is not present in

this section.

Mechanics Kinematics Dynamics

gear errors:

backlash,

compliance

static, dynamic

and thermal

deformation

angle transmission error

link length

deviation

displacement of

axes

zero error

dynamic of the

real system

following error

simplified joint

controller

Table 5.1 Summary of main error sources.

Geometric errors.

This type of errors depends mainly by inaccuracy of the robot mechanic structure as arm

length arm, axis position, zero position and by the components for movement like motors,

bearing, stiffness of the drive…it’s possible remove to them only by increasing the accuracy

of working phase. They appear like translation, rotation, parallelism or squareness error. The

effects that produce angular errors are the most heavier because the arm length enlarge these

arms giving large position errors.

Dynamic errors.

These error origin from dynamic forces or mechanic resonances driven by movement. Often

these are only present during the transitory phase and depends by the length of this phase. To

remove these errors the robot needs a computer-power bigger than actually used in industries.



Thermal errors.

Are due from thermal expansion of metal. The sources can be internal(motors, bearing) or

external(environment causes). These errors produce a non-linear effects on the structure, very

hard to analyze.

System errors.

This categories includes all errors that come from a bad calibration, control algorithms and

non-synchronism between the measurement system and robot controller, errors in the basic or

system software, in particular considering a circular path errors of interpolation,

imperfections from the sensors, death band or transmission components. Only identifying the

sources of these errors it possible remove these ones.

Instrumentation/equipment.

Some errors can derive from inaccuracy, positioning and human errors.

The robot’s joints are all revolute joints, thus in particular it is possible to recognize some

particulars errors like:

• Tumbling: imperfections in the roundness of the axis, the bearings, and shells will

introduce a motion of ideally in itself moving axis;

• Errors at the encoder: this depends by resolution of encoder

• Link deflection: is directly related to link extension and causes inclinations of and of

each link;

• Human errors: adherence to all recommendations and instructions for use the robot or

the measuring instrumentation, inaccuracy of robot positioning, inexperience etc…

• The loads that the robot carries and moves influences this performance: there are two

types of load to be considered : static load(weight of workpiece etc…) and dynamic

(force due acceleration).

• Vibrations are divided in two types: self-exited vibrations(e.g. by eccentric load),

forced vibration(e.g. stimulation by other machines or robots via foundation) and

chatter(stimulation of the robot by automatic process).



5.1.2. Measurement uncertainty evaluation

All types of measurement are subjects to some uncertainty. A measurement is complete only

if it is accompanied by an estimate of uncertainty. There are a lot of uncertainty sources as

equipment uncertainty, from operator, environmental influence etc. This parameter is

evaluated using statistical analysis following definite rules.

The complete sequence of passages in order at an estimate of the uncertainty is the following:

Identifications of the influence components: environment of measurement, reference element

of measurement equipment, measurement equipment, measurement setup, software and

calculation, metrologist, object to be measured, measuring procedure, physical constant and

conversion factors.

Modelling: this operation consist of express in mathematical terms the dependence of output

quantity (Y) on the input quantity (X)

Correction: defined the systematic error model a correction can be carried out. Error sources

which can not be corrected will contribute to the uncertainty of measurement.

Analysis of uncertainty sources: is needed to know these sources, uncertainties of a

measurement process are a mix of a lot of contributors

First type of evaluation of standard uncertainty: this type of estimate is applied when several

independent observations have been made for one of the input quantities under the same

conditions of measurement; if s is the deviation standard of our sample the uncertainty u

equal to s : s=u

Second type of evaluation of standard uncertainty: is associated with an estimate xi of an

input quantity Xi by means other then the statistical analysis of a series of observations. The

standard uncertainty u(xi) is evaluated by scientific judgement based on all available

information (from literature or past experiences) about the variability of Xi . This type of

standard uncertainty is obtained assuming a density function based on the degree of belief



that even will occur. The density function usable are the Gaussian(normal), triangular,

rectangular, U-shaped.

Calculate the combined standard uncertainty u(c): is the standard uncertainty of an output y

obtained from the values of a number of other quantities. Is the results of the combined

variance obtained from all variance and covariance components; if the quantities are not

correlated

if the quantities are correlated

Calculate the expanded measurement uncertainty: the object of this parameter is to provide an

interval about the results of a measurement that may be expected to encompass a large

fraction of values that could be reasonable to attribute to the measurand. Expanded

uncertainty is a multiplying the combined standard uncertainty u(c) by a coverage factor k .

U=k*u

The standard coverage factor is k=2 that presents a level of confidence of 95,45%.

5.2. Existing gripper functional surface evaluation

Analysis of topography can be based on two or three dimensions. Since the topographies of the project case are inherently three-dimensional, the focus in the following will mainly be on three-dimensional surface topography analysis.



Various methods for quantitative and semi-quantitative topography analysis have been established as reviewed in reference [?]. These methods include: • Height distributions and Abbott curves • Topography parameters • Fourier transform analysis (FT analysis) • Fractal methods • Wavelets • Motif analysis • Change trees Despite their appeal FT analysis, fractal methods, wavelets, Motif analysis, and change trees do not have the same industrial importance as topography parameter. The Abbot curve, also known as bearing area curve, illustrates the relationship between height and the bearing area of the surface. The Abbott curve also corresponds to a cumulative height distribution. In the two-dimensional regime topography parameters are well established and standardised as in ISO 4287. A similar body of standards have not yet been established for three-dimensional parameters. Fourier transform analysis involves decomposing the surface into a series of sinusoidal and calculating the root-mean-square height for each wave [6]. The resulting FT spec shows the relationship between wave frequency and root-mean-square height (see 3.5). For noncyclical topographies, FT analysis has less intuitive appeal, but can provide useful information [9]. Topographical evaluation could also be based on topography-dependent functional properties such as friction or roughness. Typically, such topography-dependent functional properties also depend on other factors and we would not expect universal relationships between topography and functional properties. The definition of parameters able to characterize and quantify the microgeometry of the surface has been a topic of great interest in the last decades. The availability of 3D data, allowed by the new generations of measuring instruments, has stimulated research in many fields. One of the most impressive achievements has concerned the visualization techniques and image manipulation able to provide realistic representations of the surface. The usefulness of such an approach for a qualitative characterization is well recognised [5], [12]: often the image inspection, possibly aided by some enhancement techniques, can be assumed as the only aim of the analysis. Indeed, the image conveys a vast amount of information, which can be easily interpreted by an experienced observer. When quantitative information is required, the adoption of parameters becomes essential. But parameters are inherently synthetic and can not completely describe the complex reality of a surface; each parameter can give only information on some specific features of the microgeometrical texture and requires a sound interpretation. In this work 2D parameters are those that are calculated from a single profile, while parameters calculated over an area are referred



to as 3D, with a further subdivision into areal parameters, derived by 2D parameters, and uniquely 3D parameters. At present, 3D surface texture measurement is not yet covered by international standards, but it is the object of on-going research projects in Europe and abroad; standards concerning this area are expected to appear in the future. In the research carried out within the European Program [12] a set of fourteen 3D parameters has been proposed (Table 5.2). These parameters are denoted by "S" instead of "R" to indicate that they are calculated over a surface. Strictly speaking, most of the parameters of the set are derived from the corresponding 2D parameters, while only three are uniquely devised for surface characterisation. The definitions of these latter are below: Table 5.2: The primary parameter set proposed in [5].

SQSZSsqSku

SdsStrSalStd

SqSscSdr

SbiSciSvi

Surface bearing indexCore fluid retention indexValley fluid retention index

Functional parameters

Hybrid parametersRoot mean square slopeArithmetic mean summit curvatureDeveloped surface area ratio

Density of summitsTexture aspect ratioFastest decay autocorrelation lengthTexture direction

Amplitude parametersRoot mean square deviationTen point heightSkewness of height distributionKurtosis of height distribution

Spatial parameters

While the main objectives of the these efforts originally were there to create network reproductions of the surfaces in three dimensions, several features as coloured plots, extensive filtering facilities, computation of three-dimensional parameters, as well as volume and area computation facilities, ftnave been added and are now in use in different [7] Two groups of surface parameters have been found to be most relevant: (i) Sa, St and Ssk that are related to the general roughness of the surface, and (ii) Spk, Sk, Svk, which are related to specific functional properties - primarily tribological properties. These parameters, which correspond to the two-i dimensional parameters Ra, Rt (DIN), Rsk, Rpk, Rk and Rvk, are defined in.



Another set of parameters that are under development comprises surface high peaks count, furrow and pit identification, furrow separation and other texture identification entities. SPIP™ is a comprehensive product containing many generic analytical and visualization tools that can be applied on various types of images and curve data, for example images from electron-, interference-, and optical microscopes. In particularly SPIP™ has specialized tools for correcting and analyzing Scanning Probe Microscope (SPM) data including force curve analysis and Continuous Imaging Tunneling Spectroscopy (CITS). Fourier Measurement The Measure tab of the Fourier menu is used for measuring systematic periodicities in the image by analysis of the associated Fourier peaks at sub-pixel level. Periodicities are most often part of the true surface in which case we may want to use SPIP to detect and measure the lattice structure and maybe perform a calibration when the reference values are known. However, periodicities may also originate from coherent noise or vibration problems during the scanning process, in which case you can use SPIP to diagnose the problem and determine the time domain frequency in Hz. Fourier analysis The Fourier transform is a powerful tool for image analysis. This is true in particular for analysis of repeated patterns such as pitch standards and molecular or atomic structures. Fourier images reflect repeated patterns as narrow peaks, the co-ordinates of which describe their periodicity and direction. Such peaks are easy to detect by image processing without any pre-knowledge of the features form or periodicity. Furthermore, the repeat distances can be measured very accurately by determining the Fourier peak co-ordinates at sub-pixel level.

Pict. Fourier

1D Fourier Analysis



The Fourier transform of a profile is calculated when right clicking on one of the Fourier functions in a profile window. The 1D Fourier window has strong tools for analyzing periodic structures and diagnosing noise or vibration problems. To achieve the highest accuracy it will be an advantage to apply the Fourier X 16 (Requires the Calibration Module) function of the Profile context menu. The cursors can be used to measure a periodic distance (pitch) by moving a cursor to the first harmonic peak. Then the corresponding wavelength is calculated and written in the text field of the window and next the first cursor, see example below. The MX/M1 fields are used for testing the harmonic numbers; SPIP automatically divides the wavelength of the different cursors with the wavelength of curser M1. In this example, M1 points to the first harmonic, i.e., the pitch, M2, M3 and M4 are pointing to the 2nd, 3rd and 4th harmonics respectively, which is confirmed by the M2/M1, M3/M1, and M4/M1 fields. The higher harmonics can be used for getting a statically estimate of the pitch by multiplying the wavelength values by their harmonic numbers.

5.3. Grippers evaluation by optical measuring machine Influencing factors in optical measuring machine

Results influencing measurement in optical measurement machines

Measurement Strategy

•Evaluation criteria•Probing method

•Number of sampling points•Distribution of sampling

points•Filter

Measuring Instrument

•Measuring range•Algorithms

•Coordinate system•Measurement and evaluation

software•Probing system

Operator

•Planning•Alignment

•Probe configuration•Tidiness

Workpiece

•Material•Size•Color•Gloss

•Roughness•Waviness

•Value of form deviation•Type of form deviation

Environment

•Humidity•Temperature

•Temperature evaluation•Vibration

•Dirt particles

Results influencing measurement in optical measurement machines




points•Filter




points•Filter









Operator



Operator



Workpiece




Workpiece




Environment



•Dirt particles

Environment



•Dirt particles

Figure 5.1. Influencing factors on the results of coordinate measurement



Figure 5.1.shows the basic factors for coordinate measuring machines and the results of their measurements. All these factors are usually divided into two parts, de-pending on the source of the factor. The factors coming from the machine and from the machines systems are called internal source errors. In this case, the measuring instru-ment and all factors in this part are coming from internal sources. The coordinate system most significant internal factor consists in the deviations of the real coordinate system with regard to the ideal machine coordinate system. These deviations are caused by distortions in the shape and orientation of the guideways and relative parts. OMM have a control unit and computer with special algorithms to handle the readings and to introduce corrections, calculate distances and all geometrical features. The algorithms that carry out these functions can have unexpected behavior if they are used near their validity range. Another type of factors that are showed in Fig.xx are the external factors. Tem-perature is the most difficult factor to control. Temperature modifies the shape of the parts base of a OMM, and alters them configuration. Temperature changes in time in a determined place or has different values according to each place. The reference temperature for all kinds of di-mensional measurements is 20ºC. Environmental humidity also influences the result of a measurement. It can expand the volume of the granite table. Dusts can rest on the ob-ject or the measuring probe and change the results of a measurement too. Earthquakes are transmitted to the machine through the foundations. The atmosphere can also transmit vibration. Light Among the external factors, influencing the accuracy of measurement is the operator. He can misrepresent the results of the measurements for any reason (i.e. competence, tiredness etc.). In addition, the operator can have very big influence on the temperature and dimensions of an item if he touches the object. Limitation The optical measuring systems (UBM, De Meet, Stemi 2000C microscope) of coordinate measuring machines have more limitations of measurement, compared with mechanical probing system. The factors that were described in section 1.4.1 are valid for optical probes too. However, optical sensors have more factors that mostly are coming from external source. Table 5.3.



RV 1-A Mitsubishi Axis movemets 6 Speed 2.2m/s** Load capacity 1.5Kg Repeatability* ± 0.02 Arm weight 19Kg Max.P-point 418mm Allow movement 1.44Nm Using Pallet insertion assembly

Dimension The length measurement uncertainty u is specified in a simple form as a length – dependent parameter (VDI/VDA 2617): There A, K and B are constants, and L is measured length. This equation can be represented in the graph called the length measurement uncertainty diagram The environmental conditions have a significant influence on the error source of a OMM. All these conditions from measurements of a reference artefact are to be re-corded and taken into account as reference environment condition for assumption the OMM deviation as measuring uncertainties. The limits of difference between reference and real measurement conditions shall be stated in the calibration certificate. The calibration using the error synthesis method usually consists of three steps: The firs step is estimation of the OMM’s parametric errors. These errors can be assessed for each of the axes (Table5.4) of the machine six degrees of freedom: three rotational and three translational errors. During this estimation, only the error sources that are active and have influence for the specific measurement task need to be estimated. Usually this involves the assessment of the geometric and probing errors of the OMM and their response to variations in the environmental conditions as specified in certificate. Second step is calculations of the errors for the measured coordinates of each measured point specified in the measurement strategy, as obtained using a well-known probing strategy, under specified environmental conditions. These errors are obtained by superposition of the parametric errors. Table 5.4 specification of scale GB – A /2.1/

Measuring range 50 – 475 mm Smallest readable value 0,1 micrometer Accuracy ± 1 to 3 micrometer (depends on measuring area) Measuring axis Diameter 2 mm Total length Measuring area + 100 mm

The standard uncertainty of y is obtained by appropriately combining the standard uncertainties of the input estimates x1, x2... xn. This combined standard uncertainty of the



estimate y is denoted by u(y) and it can be find from positive square root of the combined variance , which is given by/16/: ( )yuc

2

( ) 2

1)(

ix

n

i i

uxfyu ⋅

∂∂

= ∑=

The total standard uncertainty of measurement is calculated by equation: kuU ⋅= Where ‘k’ is the coverage factor .

5.4. Measuring procedures with De Meet

1. Planarity between basic and functional plane (two distance); 2. Holes for pins and screw hole measuring (diameter, tolerance); 3. Holes in gripper plate measuring (5 holes 3mm diameter, 2 with 2 mm diameter); 4. Distance between holes in gripper plate ( corresponding to drawing);

• if hole axis is alignment;

5. Distance between holes in grippers heads ( corresponding to drawing); [see drawing] 6. Alignment between hole axis on gripper head and basic axis ( on gripper plate), find

angle α

α



Figure 5.2 angle 7. Alignment between the holes on gripper plate (claiming holes of gripper head) with

basic axis (find angle γ)

γ

Figure 5.3. angle

8. Alignment between basic axis and gripper head sharp angle line (and distance); 9. Gripper head dimensions (just shown in the figure);

Figure 5.4. Gripper

5.5. Roughness Parameters Most parameters are general and valid for any M ´ N rectangular image. However, for some parameters related to the Fourier transform we assume that the image is quadrangular (M=N). Before the calculation of the roughness parameters we recommend carrying out a slope correction by a 2nd or 3rd order polynomial plane fit. Note, also that roughness values



depends strongly on measurement conditions especially scan range and sample density. It is therefore important to include the measurement conditions when reporting roughness data. The Roughness Average, Sa , is defined as:

|),(|1 1

0

1

0µ−= ∑∑

−

−

−

−lk

N

l

M

ka yxz

MNS R 1

Where µ is the mean height:

),(1 1

0

1

0lk

N

l

M

k

yxzMN ∑∑

−

−

−

−

=µ

The Root Mean Square Sq, is defined as:

[ ]21

0

1

0),(1 µ−= ∑∑

−

−

−

−lk

N

l

M

kq yxz

MNS

Note, that the mean value µ is not subtracted from the height values before squaring. It is therefore necessary to perform a proper plane correction or high pass filtering of the image before calculating the Sq. The Peak-Peak Height, Sy, is defined as the height difference between the highest and lowest pixel in the image. minmax zzSy −= The Ten Point Height, Sz , is defined as the average height of the five highest local maximums plus the average height of the five lowest local minimums:

, 5

)()(5

1

5

1∑∑−−

−+−= i

vii

pi

z

zzS

µµ

where zpi and zvi are the height of the ith highest local maximum and the ith lowest local minimum respectively. Only positive maximums and negative minimums are valid. When there are less than five valid maximums or five valid minimums, the parameter is not defined.



The Surface Skewness, Ssk , describes the asymmetry of the height distribution histogram, and is defined as:

[ ]∑∑−

−

−

−

−=1

0

1

0

33 ),(1 M

k

N

llk

qsk yxz

MNSS µ

If Ssk = 0, a symmetric height distributions is indicated, for example, a Gaussian like. If Ssk < 0, it can be a bearing surface with holes and if Ssk > 0 it can be a flat surface with peaks. Values numerically greater than 1.0 may indicate extreme holes or peaks on the surface. The Surface Kurtosis, Sku , describes the peaked-ness of the surface topography, and is defined as:

[ ]∑∑−

−

−

−

−=1

0

1

0

44 ),(1 M

k

N

llk

qku yxz

MNSS µ

For Gaussian height distributions Sku approaches 3.0 when increasing the number of pixels. Smaller values indicate broader height distributions and visa versa for values greater than 3.0. Hybrid parameters There are three hybrid parameters. These parameters reflect slope gradients and their calculations are based on local z-slopes. The Mean Summit Curvature, Ssc, is the average of the principal curvature of the local maximums on the surface, and is defined as:

∑−

⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟⎠

⎞⎜⎜⎝

⎛−=

n

tsc y

yxzx

yxzn

S1

2

2

2

2 ),(),(2

1δ

δδ

δ

for all local maximums where dx and dy are the pixel separation distances. The Root Mean Square Slope, Sdq , is the RMS-value of the surface slope within the sampling area, and is defined as:

∑∑−

−

−

−

−−⎟⎟⎠

⎞⎜⎜⎝

⎛ −+⎟

⎠⎞

⎜⎝⎛ −

−−=

1

0

1

0

21

21 ),(),(),(),(

)1)(1(1 M

k

N

l

lklklklkdq y

yxzyxzx

yxzyxzNM

Sδδ

R 8

The Surfaces Area Ratio, Sdr , expresses the ratio between the surface area (taking the z height into account) and the area of the flat xy plane:



, %100)1)(1(

)1)(1(2

0

2

0

yxNM

yxNMAS

M

k

N

lkl

dr δδ

δδ

−−

−−−⎟⎠

⎞⎜⎝

⎛

=∑∑−

−

−

−

where

( )( )2

11122

12

2111

221

2

)),(),(()),(),((

)),(),(()),(),((41

++++

++++

−++−+

⋅−++−+=

lklklklk

lklklklkkl

yxzyxzyyxzyxzy

yxzyxzyyxzyxzyA

δδ

δδ

For a totally flat surface, the surface area and the area of the xy plane are the same and Sdr = 0 %. Functional parameters for characterizing bearing and fluid retention properties The functional parameters for characterizing bearing and fluid retention properties are described by six parameters. All six parameters are defined from the surface bearing area ratio curve shown in the figures below.

Figure 1: Bearing curve illustrating the calculation of Surface Bearing Index, Core Fluid Retention Index and Valley Fluid Retention Index



5.6. Results

0,0E+00

1,0E+03

2,0E+03

3,0E+03

4,0E+03

5,0E+03

6,0E+03

7,0E+03

LBM EDM Cylindrical Plane-Polished

Existing Plane rough

Functional surface

Spk,

Sk,

Svk

[nm

]

SpkSkSvk

0,0E+00

5,0E+02

1,0E+03

1,5E+03

2,0E+03

2,5E+03

3,0E+03

3,5E+03

4,0E+03



Functional surface

Spk,

Sk,

Svk

[nm

]

SpkSkSvk



0,0E+00

5,0E+02

1,0E+03

1,5E+03

2,0E+03

2,5E+03



Functional surface

Sa, [

nm]

0,0E+00

5,0E+02

1,0E+03

1,5E+03

2,0E+03

2,5E+03



Functional surface

Sq, [

nm]



6. Experiments. Testing of gripping devices

6.1 Experiment procedure and results

Methodology of experiment. The methodology of experiment is formed in order to select the

appropriate and optimal plan of experiment from the viewpoints of time, precision of results,

price and technologies. It means that it is needed to assess how to perform that in

technological way in order to obtain the needed results, how to eliminate the undesirable

factors from the experiments that they would not influence the results, the number of tests

regarding to the relation of the precision of results and time, the price of experiments, this is

the ratio of price of experiment operations (equipments, materials, operator’s time) and time

required to perform the needed experiments.

Assessing all these factors while testing and changing some of the parameters (it was

observed how much time it takes, how to perform it better, how to decrease the influence of

outside factors and etc.) it was performed the methodology of experiment plan. The results

showed that it was purposeful to use the slightly different sequence of handling operation

experiments for different micro-specimens. It is almost the same experiments only there are

used different “hole” positional plates for different micro-specimens and the number of

experiments differs too. The latter dimension changed because of the complexity of

operation, the number of occurring mistakes and time needed to perform one operation.

Alignment of positions in the “hole” plate

Plan of experiment is to assess the handling operation while taking a plastic specimen for the

ending specimen part of small diameter and putting it into a positioning hole in the plate

mentioned above. In this way it is to prepare the plastic specimen to assembly operation with

micro-screw. Our investigated micro-specimens can be assembled by cranking the micro-

screw into plastic specimen part of small diameter.

Experiment was performed at the “hole” position plate, which dimensions and data of holes is

(see Picture 6.1)



Y

X

P1

P12P3

2*4stk. ø2

4stk. ø1.9

P10

15

15

Picture 6.1 “Hole” position plate

For this reason the handling of plastic specimen operation over small diameter ending part

due to high deformation was cancelled and the priority was given to the handling operation

for the main part. In this experiment there was used twelfth hole positioning plate (see above).

Four positions x-axis direction and three y-axis. Diameters of the holes are 1.9mm in first

position for each line of operation and 2mm respectively.

. Farther there follows the sequence according to the experiment plan:

• The robot program is written according to the experiment handling operation that was

determined in advance.

• The plastic specimens are putted manually with tweezers to every position. Also the

small diameter part should be above. This helps to perform the alignment of position

plate in original x, y-axis of the robot, as the external diameter of plastic specimen is

similar to the diameter of the hole. Also the small part hole of specimen is of the

similar diameter as the calibration stick angle, and the central axis of specimen’s small

part hole coincides with the axis of position hole. This makes it easy to determine the

exact position of holes in the robot’s positions measured position plate in three

marginal positions of x, y- axis (xx) and are recorded and converted in computer

positioned list.

• Calibration stick mounted on the robot jaws

• Then it is compared with the robot’s original x, y axis and the alignment of position

plate is performed after the above indicated coordinates are checked several times;

• Putting gripper on the robot jaws;



• With mounted gripper all the positions are checked, and then it is adjusted if needed.

For positioning we used grippers with plane (rough) surface and small diameter ending

specimen.

Plane (rough) surface gripper is defined by a functional surface unmodified after it’s

manufacturing. During manufacturing surface of this gripper was milled with high speed, as

it’s aluminum alloy material allows such high speed operations. Due to this fact functional

surface of gripper has uniform grooves.

Experiments performed with plane surfaces showed the following results:

Conclusion. The more pressure grippers applied to the plastic specimen (forced influenced)

the more difficult it is to remove the specimen from its position (hole) in the plate. This leads

to increase in error numbers, which can be explained by deformation of the plastic specimen

due to the exceedingly strong forced influenced.

We observed that adhesive force (stickiness) is not dependant of “hole” position alignment

(on the position plate). The experiments show us that the error frequency is the same for

experimental operations for on all 4 different lines. At the same time we observed a high level

of dependence from how good specimen placement was in second position in each line. Good

specimen placement in this case means placement without specimen falling out or sticking

effect, which causes misalignment. After that the program needs to be stopped in order to

correct position of the specimen, otherwise misalignment makes it very difficult to continue

with proper insertion of the specimen into the next position.

Conclusion. Experiment shows that increasing specimen position in one operation

summarizes uncertainty for each position.

The higher position in the row (see Picture 6.1) the more frequently we observe specimen

stickiness to the functional surface of gripper.



Heavy deformation influence due to elasticity and force relations. Specimen endings with

small diameter and thin walls elasticity too big for handling force. This leads to deformation

of this part, which increases touching with gripper surface size. This explains more frequent

stickiness of deformed specimens to gripper surface.

This project task is to evaluate of grippers different functional surfaces influence in the

handling process of these specimens, so that is not our part to found optimal procedure of

assembly. For this reason handling operation with the small diameter ending plastic specimen

is not enough related to project goal.

For the future handling evaluation was used a new positioning hole plate with smaller hole

diameters.

Experiment was performed using plastic specimen to evaluate plane-surface grippers. The

platform for experiment was a plate with 12 positions. (see Picture 6.2)

Y

X

P1

P12

P3

4 stk ø1.3x0.6

2 * 4 stk ø1.3 * 0.7

P10

15

15

Picture 6.2 Positions “hole” plate with 12 positions

Alignment of two gripper “holding” surfaces.

The two gripper functional surfaces must be aligned to each other in order for gripper to

properly grab the specimen. The functional surfaces must be parallel to each other to avoid



premature release of the specimen. The lower ends of the grippers must be on the same level,

e.g. z-axis’ value of these ends must be equal in order for gripper to touch plate properly.

Gripper functional surface alignment is done by performing the following steps:

1) Gripper is lightly fixed with screws to the robot jaws

2) A G-block is placed between two gripper functional surfaces

3) Gripper closes and the G-block is held tightly by it. Due to lightly fixed screws and

automatic force control (constant load) this action aligns the gripper functional

surfaces in planar positions

4) Gripper moves carefully down in z-axis direction to a G-block put on the plate. This

corrects the gripper with parallel position of the hole plate.

5) The screws are then tightened in this two alignment positions

Experiment plan

Experiment for plastic specimen evaluation consisted of following steps: (see picture 6.3)

1) Open gripper jaws

2) Move gripper to first position (in each line), which is described in position list *.pos

3) Gripper grabs the specimen

4) Gripper arches the specimen to a point above second position

5) Gripper opens jaws (releases the specimen)

6) Operator evaluates, whether adhesive force effect is present

a. If present then error is marked. Program must be stopped and alignment must

be corrected.

b. If not present then experiment continues

7) Move gripper to second position

8) Gripper grabs the specimen

9) Gripper arches the specimen to a point above third position

10) Gripper opens jaws (releases the specimen)

11) Operator evaluates, whether adhesive force effect is present



a. If present then error is marked. Program must be stopped and alignment must

be corrected.

b. If not present then experiment continues

12) Gripper moves to next line or positions and experiment is repeated

Picture 6.3. Experiment plan for plastic specimen evaluation

Experiment for micro screw specimen evaluation consist a similar step. Due to cost of

operation and high frequency of occurring handling errors there is two positions and two

line of handling operation. Experiment operation is represented in picture below (see

Picture 6.4).

Picture 6.4 Plan of experiments for micro screw specimen evaluation

In order to prepare for the experiments operator performs the following steps:



• Checks all positions on the plate

• Checks the gripper jaw handling program

• Places specimens into 1st position of each line of the plate

Conditions of experiment

To limit the impact of temperature and humidity on experiments all experiments must be

performed in temperature controlled room. In the room where all handling operation

experiments were performed a temperature controlling device is present. But due to strong

deviations in the atmosphere of the room temperature control was insufficient to completely

avoid temperature and humidity impact. For this reason the temperature and humidity levels

were recorded prior to each experiment.

Certain corrections are done to position the holes of the plate more precisely. Operator does

this by changing appropriate coordinates in the robot positioning program.

This process was performed in order to avoid gripper manufacturing uncertainty. It was

observed that after the alignment procedure of gripper position mostly in z-axis direction was

changed. This can be explained by gripper manufacturing uncertainty, e.g. in hole centricity.

In this experiment the temperature of 21.1oC and humidity level of 51% were recorded in the

robot laboratory.

Grippers with plane (rough) surface.

Experiments performed with plane (rough) surface grippers showed the following results:

Repeatability of handling experiment was 100%, when distance between the gripper and

position hole plate is 0.5 or 1 mm. Accuracy of the experiments decreased rapidly, when

distance was increased to 2mm and more. During the course of all experiments z-axis position

of the gripper (distance from the plate to gripper) did not affect the adhesive force and/or

stickiness effect on the specimen held by the gripper. This fact was observed in all

experiments, regardless of the functional surface of the gripper used in the given experiment.

For all further experiments the distance between the gripper and positioning hole plate was

chosen to provide the operator with optimal conditions for observing the release phase of the



handling procedure, at the same time minimizing the possible error due to “falling” distance

[See picture 6.3].

“Falling” distance error can be explained by specimen turning during the fall and only

touching the hole with one side, e.g. asymmetrically. The kinetic force accumulated by the

specimen during the fall becomes potential force on the moment of impact with the plate. If

the potential force is stronger than specimen’s gravitational force (Fspec.pot.> Gs), the specimen

bounces off the surface of the positioning plate. In cases with specimen falling

asymmetrically, it turns further and does not properly fit into the positioning hole, e.g. falls

out of it. Following the handling program must be stopper and the operator has to place the

specimen into the correct position manually.

To avoid this disturbance several trials were performed prior to the experiments. During those

trials it has been determined that the optimal distance between the gripper and the position

place is from 0.75 to 1 mm. Therefore all experiments with plastic specimens were performed

with 1mm distance.

Following to the same logic and trials as above with the plastic specimens, the distance

between the gripper and the position plate was set to 2mm for experiments with micro-

screws.

There appeared a question as to which influence caused this effect. We suppose that this is, as

well as in the aforementioned paragraph, an effect of electrostatic force relations of plate and

gripper. It could also be influence of elasticity of specimens and potential force, (which

occurs due to kinetic force of falling specimen) after bouncing off the surface.

Plane (rough) surface of gripper with plastic specimen.

From the beginning handling process showed 100% repeatability, but after some time during

experiment adhesive force effects appeared. This processes cannot be explained by anything

else than electrostatic force influence. Because other parameters which have influence the

handling process were unchanged during subsequent experiments. Electrostatic force could

be conducted to plate or gripper by the human operator during the manual placement with

tweezers of specimens into first position in each line. This can affect generation of different

electrostatic charges between gripper and position “hole” plate.



Load number 15

The experiment using gripper with rough surface had several errors in repeatability of

handling operations. Grabbing the specimen from the first positions in each operation was

100% accurate. However steps following the first release were in some cases erroneous. This

can be explained by severe roughness and uniform profile errors due to milling, as peaks on

rough functional surface grab the specimen in ununiformed manner (from different unaligned

angles and varying touching surface areas). During this experiment stickiness effect was not

observed. Adhesive force influence occurred several times but without clear pattern. Results

represented in table bellow (see Table 6.1).

Table 6.1

1 2 3 4 Mean value St.DevFirst 100 100 100 100 100,0 0,0Second 80 70 70 77 74,3 5,1Third 66 60 50 50 56,5

76,9 19,3

Stiching occasion 1

Plane-Rough - plastic specimen (load number 15)

Correct operation percentage in all positions %Operation line on the position plate

Ope

ratio

n

posi

tions

Of all positions7,9

Plane-Rough - plastic specimen

40,0

60,0

80,0

100,0

1 2 3

Position in each line

Rel

ease

, % load 15load 20load 25

Figure 6.1 Plane-Rough-plastic specimen

Load number 20.



The results of experiment with load number were similar. However the overall number of

errors has decreased (26.7%’ received when minus successfully numbers of handling

operation). This result can be explained by higher load force lightly deforming the specimen

and creating more stable touching surface area. (see Table 6.2)

Table 6.2


73,3 19,1

Stiching occasion 3

Ope

ratio

n

posi

tions

Of all positions

Operation line on the position plate

Plane-Rough- plastic specimen (load number 20)

Correct operation percentage in all positions %

3,6

Load number 25.

Experiment with plane (rough) surface grippers with load number 25 and plastic specimens

was different from the previous ones, as there was a higher number of errors (35.2%).

Stickiness effects were observed several times. This can be explained by a higher level of

specimen deformation, increase of touching surface area due to this deformation and profile

error (waviness). (see Table 6.3)

Table 6.3

1 2 3 4 Mean value St.DevFirst 80 90 90 90 87,5Second 55 50 60 60 56,3 4,8Third 58 50 50 44 50,5

64,8 17,6

Stiching occasion 7


Ope

ratio

n

posi

tions

Of all positions

Plane-Rough - plastic specimen (load number 25)


5,0

5,7

Experiments with plane (polished) surface grippers with load number 15



Plane (polished) surface of gripper was produced by polishing the previous plane (rough)

surface with 4000 quality sandpaper.

Experiments performed with plane surfaces showed the following results:

Load number 15.

The experiment using gripper with polished surface gave good results and repeatability

during the first attempts. However after several handlings adhesive force effects started to

occur. Adhesive force effect can be explained as the electrostatic force influence. We can

conclude this because no deformation or other force influences was observed. Due to

significant roughness of plastic specimen there could not be influence by other forces such as

Van der Waals force. Surface tension can also be neglected due to light load.

The most likely source of the electrostatic force conduction, as in the previous experiments,

could be the human operator. This explains the cumulatively growing adhesive force

influence with repeating number of handling operations during the experiment.

Load number 15

However after several handlings adhesive force effects started to occur. Adhesive force effect

can be explained as the electrostatic force influence. We can conclude this because no

deformation or other force influences was observed. Due to significant roughness of plastic

specimen there could not be influence by other forces such as Van der Waals force. Surface

tension can also be neglected due to light load.

The most likely source of the electrostatic force conduction, as in the previous experiments,

could be the human operator. This explains the cumulatively growing adhesive force

influence with repeating number of handling operations during the experiment. (see Table

6.4).

Table 6.4




78,3 18,3

Stiching occasion 8


Ope

ratio

n

posi

tions

Of all positions

Plane-Polished - plastic specimen (load number 15)


9,2

Plane-Polished - plastic specimen

40,0

60,0

80,0

100,0

1 2 3


Rel

ease

, %

load 15load 20load 25

Figure 6.2 Plane-Polished-plastic specimen

Load number 20

With increased load the effects of adhesive force became more frequent, as additionally to the

electrostatic force influence the touching surface area has increased. This can be explained by

higher load deforming (squeezing) the plastic specimen. Though the level of deformation

with this load could not be visible by eye. (see Table 6.5)

Table 6.5




75,0 18,5

Stiching occasion 6


Ope

ratio

n

posi

tions

Of all positions



5,4

Load number 25.

Plane (polished) surface of gripper and plastic specimen showed slightly higher adhesive

force effects, compared to the previous load. At the same time the effects of deformation of

the plastic specimen became clearly visible. Such relatively low increase of adhesive force

influence compared to the large increase in the touching surface area and can be explained by

rapid increase in the tension force of the plastic specimen. (see Table 6.6)

Table 6.6


65,8 24,4

Stiching occasion 7

Of all positions

Ope

ratio

n

posi

tions



5,3

Conclusions:

• Grippers with plane (polished) functional surface can be used for handling operations

with plastic specimens, however conduction of electrostatic force from external

“generators” must be eliminated.



• This experiment has clearly showed the influence of load force on handling

operations, because there no other significant forms of influence were present

Plane (polished) surface of gripper with chamfer surface of microscrew

In order to better evaluate fitting of the plane (polished) surface gripper for handling

operations with microscrew, the process was divided into two different holding techniques.

• Gripper grabs the chamfer surface of screw head;

• Gripper grabs the cylindrical surface of the screw head

The test was performed on the new position hole plate (see figure 6.3) with 4holes ø0.6x1.5

dimensions, because diameters of holes in the plate must be related to screw diameter.

Y

X

P3

P2P4

2*2 stk ø0.6x1.5P1

15

15

Figure 6.3 Position “hole” plate for micro-screw handling operation

Load number 15.

This experiment showed mediocre handling operation quality with some errors in holding, as

well as adhesive force influence. No deformation on plane (polished) gripper surface or

microscrew chamfer surface was visible. Results represented in table bellow (see Table 6.7).

Table 6.7



1 2 Mean value St.DevFirst position 80 80 80,0 0,0Second position 55 60 57,5 3,5

68,8 13,1

Stiching occasion 6

Operation line

Of all positions

Chamfer screw surfaceCorrect operation %

Plane-Polished - micro-screw (chamfer)

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

1 2


Rel

ease

, %

load 15load 20

Figure 6.4 Plane-Polished microscrew (chamfer).

Load number 20.

With load number 20 there appeared significant visible deformation on functional surface of

the gripper. However the number of proper handling operations has also significantly

increased. This can be explained by deformation providing an “optimal” level of touching

surface area, e.g. not too large to graven adhesive force influence, but large enough for proper

holding. (see Table 6.8)

Table 6.8


78,8 7,5

Stiching occasion 2


Of all positions

Operation line



Load number 25.

Further increase in load rapidly escalated the level of plane (polished) gripper surface

deformation. After several handling the surface area was completely worn down, preventing

further handling operations.

Plane (polished) surface of gripper with cylindrical surface of microscrew.

Load number 15.

The experiment with the cylindrical surface of the microscrew operated with plane (polished)

surface of the gripper was conducted under the same conditions as the one with chamfer

surface of microscrew. In the same way, as with previous experiments with different gripper

surfaces, the coordinates were changed in the gripper operating program in order to avoid

using the part of gripper’s functional surface damaged by experiments with the chamfer

surface of the microscrew.

In this case, comparing to the experiments with the chamfer part of the microscrew, the

handling operation error margin became generally lower with no adhesive force influence.

However the microscrew was slipping relatively more often out of the grip. (see Table 6.9)

Table 6.9

1 2 Mean valueSt.DevFirst position 70 70 70,0 0,0Second positio 60 50 55,0 7,1

62,5 9,6

Stiching occasion 0

Operation line

Of all positions

Cylindrical screw surfaceCorrect operation %



Plane-Polished - micro-screw (cylindrical)

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

1 2


Rel

ease

, %

load 15load 20

Figure 6.5 Plane-Polished-micro-screw (cylindrical).

Load number 20.

In the first handing operations with load number 20 the results were very good. However

deformation started occurring to the functional surface of the gripper. After more repetitive

operations the plane (polished) surface of the gripper became completely deformed and could

no longer function. (see Table 6.10).

Table 6.10


74,5 8,3

Stiching occasion 0


Of all positions

Operation line

No experiments with load number 25 were conducted, as the functionality of the gripper was

completely disabled.

Conclusions:

• During experiments with plane (polished) surface of gripper best results were

achieved when handling chamfer surfaces of the microscrews with load number 20.

• Handling experiments with cylindrical surface of microscrews also showed very good

results with load number 20, but due to the soft material of the gripper surface

repeatability was limited by durability of gripper surface.



• In order to achieve optimal microscrew handling results harder material should be

used for gripper with plane (polished) surface.

LBM and plastic specimen

When carrying out the experiment for the evaluation of the handling operation of plastic

specimen with the functional surface of the modified LBM (Laser beam machining) gripper,

the robot load number 15 was used in the first case.

Load number 15

The test was performed on the same position “hole” plate as in the analogous experiment. In

this case, the results have shown that gripping mistakes occur at the moment of holding

operation, which was not observed before (see Table 6.11). This could be explained by

insufficient squeezing force of the gripper – i.e., the micro-object was simply not gripped

with enough force. Also, some mistakes were observed at the point of release operation: the

tested micro-object falls out at a wrong time. One presumes that electrostatic and van der

Waals forces might contribute to this. Their total values are not sufficient to ensure stable

stickiness effects to the gripper functional surface, but are enough to offset the influence of

the elasticity force of the specimen. The total amount of mistakes does not exceed 21.9%.

Table 6.11


78,1 14,0

Stiching occasion 1

LBM - plastic specimen (load number 15)


Ope

ratio

n

posi

tions

Of all positions7,0



LBM - plastic specimen

40,0

60,0

80,0

100,0

1 2 3


Rel

ease

, %


Figure 6.6 LBM-plastic specimen.

Load number 20

The experiment, using the robot load number 20, is performed in the same way as the

previous one. The results demonstrated that the handling operation is performed in a much

more exact way. Moreover, in comparison to the previous experiment, no cases of the object

falling out due to insufficient grip were observed. Repeatability of holding operation from the

first position in each line was at the 100% level during the experiment. However, there were

mistakes in the second and third operation positions. Also, several cases were observed with

the stickiness effect. This can be explained by the increased influence of the adhesive force.

When the squeezing force is bigger, the elastic plastic specimen deforms which leads to an

increased touching surface between it and the gripper surface and the reduction of roughness.

That leads to the increase of van der Waals and surface tension force and its influence to the

micro-specimen handling operation. (see Table 6.12).

Table 6.12



1 2 3 4 Mean value St.DevFirst 100 100 100 100 100,0 0,0Second 80 60 60 50 62,5 12,6Third 50 77 70 62,5 64,9 11,5

75,8 20,0

Stiching occasion 5

Of all positions



Correct operation percentage in all positions %O

pera

tion

posi

tions

Load number 25

The experiment, using the robot load number 25, showed that results were poorer compared

with the load number 20 test. Due to the increased influence of the forces, mentioned in the

description of the previous experiment, the number of mistakes grew, and the influence of the

stickiness effect was observed more frequently. (see Table 6.13).

Table 6.13

1 2 3 4 Mean value St.DevFirst 90 80 90 90 87,5Second 77 50 70 50 61,8 13,9Third 60 77 50 42 57,3 15,1

68,8 17,7

Stiching occasion 14

Of all positions



Ope

ratio

n

posi

tions

5,0

Conclusion. The results of this experiment have shown that the best results of handling plastic

micro-specimen are achieved with the load numbers 15 and 20. The difference is that, using

load 15, there is not enough force to fully grip the specimen consistently, while at load 20, the

influence of the adhesive force manifests quite strongly.

The use of the functional surface of modified LBM gripper (using such modification

parameters), despite quite good observed results, is not expedient.



LBM – Screw

Chamfer profile of screw.

Evaluation of handling operation while using chamfer surface of a screw head with a LBM

gripper. (Theoretical touching surface of a rectangle. See Chapter 3)

Load number 15.

During handling operations chamfer surface of microscrew head with LBM gripper stickiness

not occurred most of the times. (see Table 6.14). Mostly this happened due to adhesive force

influence. At the same time light deformation of the gripper functional surfaces took place,

due to hard microscrew material and soft gripper surface. This means that functional surface

area increased slightly from nominal.

Table 6.14


69,0 14,3

Stiching occasion 0

Chamfer screw surface

Operation lineCorrect operation %

Of all positions

LBM - micro-screw (chamfer)

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

1 2


Rel

ease

, %


Figure 6.7 LBM-micro-screw (chamfer).



Load number 20.

Stickiness occurrence not frequency between chamfer surface of microscrew of head and

LBM gripper remained on the same level during handling operations with load number 20, if

compared to ones with load number 15. (see Table 6.15). But due to the aforementioned

differences in material hardiness of microscrew and grippers the level of gripper surface

deformation has greatly increased. The total touching surface area increased respectively.

Increase in the total touching surface and the unchanged level of stickiness shows us that

adhesive force influence has reduced. This happened due to increase of touching surface

profile error and roughness, because each microscrew makes handling process scratches or

deformation.

Table 6.15


71,8 8,9

Stiching occasion 1


Operation line

Of all positions

Load number 25.

Frequency of stickiness occurrence between chamfer surface of microscrew head and LBM

gripper has reduced during handling operations with load number 25, when compared to

previous loads. Adhesive force influence was not recorded. This can be explained by high

level of set deformation occurring due to high pressure on the small surface. After that the

gripper surface “received” form of wear scar, shaped as the head of the microscrew. (see

Table 6.16).

Table 6.16


61,8 13,9

Stiching occasion 1


Operation line

Of all positions



Furthermore, due to positioning error and increased roughness of the gripper’s functional

surfaces, gripper had less touching with microscrews surface. Wear scar radius became

greater than the microscrew head and their contact surface was due to peak of roughness. This

explains the low level of stickiness and inexistent adhesive force effect.

Conclusion. The increased surface deformation during trials with load 25 has reduced the

influence of the adhesive force. In the following operations screw handling error margin

became even higher.

Cylindrical profile of screw with LBM gripper functional surface

Evaluation of handling operation while using cylindrical surface of screw head with a LBM

gripper (theoretical touching profile line. See Chapter 3.2.)

For this experiment the positioning coordinates in the gripper operating program were

changed, due to deformation caused to the LBM gripper by previous operations with the

chamfer surface of microscrews. The coordinates for the functional surface of LBM gripper’s

contact with the microscrew were moved by 0.75mm from the original gripper axis. This

could be done, because the width of functional surface of the LBM gripper is 2mm. In

essence this means that a “new” gripper surface was used for the experiment, in order to

avoid influence of the deformation caused by the previous experiment. (see picture 6.5 below)

Picture 6.5 LBM gripper functional surface after the handling operation



Load number 15.

During handling operations cylindrical surface of microscrew head with LBM gripper

percentage of error while handling the microscrew after the first position in the line was very

high (%). However when the handling process was proper neither stickiness, nor adhesive

force influence was observed. This can be explained by very small touching surface size.

During the course of this operation some level of gripper LBM surface deformation occurred.

This effect was similar to the one described in the above section regarding the chamfer

surface of the microscrew. (see Table 6.17).

Table 6.17


74,5 12,2

Stiching occasion 2


Operation line

Of all positions

LBM - micro-screw (cylindrical)

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

1 2


Rel

ease

, %

load 15load 20

Figure 6.8 LBM-microscrew (cylindrical).

Load number 20.

During handling operations cylindrical surface of microscrew head with LBM gripper

percentage of error while handling the microscrew after the first position in the line was even



higher (%). Handling of cylindrical microscrew has become much more difficult, due to

increase in LBM gripper surface deformation with this load.

In continuation of the same experiment handling it has become virtually impossible to

successfully grab and move the microscrew, as the microscrew was slipping out of the gripper

all the time. (see Table 6.18).

Table 6.18


48,3 6,2

Stiching occasion 0


Operation line

Of all positions

Further operations with load number 25 were not performed, due to anticipated high level of

further deformation of the LBM gripper surfaces without positive handling results.

Conclusion. LBM gripper surface is insufficient for grabbing the cylindrical surface of the

microscrew, due to too small touching area. For this reason frequent slipping was observed.

Friction coefficient is very small and adhesive force effects were not observer. Also the level

of deformation caused to the functional surface of the LBM gripper while operating

cylindrical surface of the microscrew was higher than the one caused with the same loads

while operating the chamfer surface of the microscrew.

EDM vertical modified functional gripper surface with plastic specimen.

This experiment was performed in order to evaluate influence of EDM (electro-discharge

machining) in vertical direction (See Chapter 4.3) gripper surface on handling operations with

plastic specimens.

The same “hole” plane plate was used for this experiment, as the one used for grippers with

plane surface.



Load number 15.

In the course of this experiment handling operations with plastic specimen by EDM vertical

gripper functional surface showed very good results. Handling was correct and precise both

with holding and releasing the plastic specimen, though sticking effect occurred just a one

times. (see Table 6.19).

Table 6.19


90,4 10,3

Stiching occasion 1

Ope

ratio

n

posi

tions

Of all positions


EDMvert. - plastic specimen (load number 15)

8,3

EDMvert. - plastic specimen

40,0

60,0

80,0

100,0

1 2 3


Rel

ease

, %


Figure 6.9 EDM vertical-plastic specimens

Load number 20.

Handling operations were similar with load number 20 with even smaller number of handling

errors, compared to load number 15. (see Table 6.20).

Table 6.20




94,0 6,8

Stiching occasion 0

Ope

ratio

n

posi

tions

Of all positions




4,8

Load number 25.

During handling operations with load 25 the error margin during the release phase of the

handling operation was higher than with the previous loads (see Table 6.21).

Table 6.21


84,8 13,1

Stiching occasion 0

Ope

ratio

n

posi

tions

Of all positions



6,0

At the moment of the release by gripper plastic specimen fell down out of “hole” position.

This can be explained by tension force of the plastic specimen generated due to high pressure

load of the EDM surface of the gripper. Theoretically in this case the tension force of the

specimen should be equal values and moving in opposite (180o) direction. In our case the

micro-peaks on the parallel gripper surfaces made by EDM are not aligned with each other

(See Picture 6.6 below).



FSTFT

FT

∑∑→→

≠ STST FF FSTFT

FT

∑∑→→

= STST FF

FST FT

FTFT

FT

Picture 6.6 Representation of how tension force is generated

These micro-peaks generate tension force to different directions. The summary tension forces

in both sides are not parallel with each other, due to this fact the plastic specimen did not fall

down straight into the position hole.

Conclusion. Handling plastic specimen with EDM vertical surface gripper shows very good

results and repeatability. We can conclude that EDM vertical surface gripper provided the

best results out of the gripper surfaces used this far in the experiments. For this gripper

surface type the optimal load force number is 20. With EDM vertical surface only light

adhesive force influence was observed with load number 15, but in load number 20 that was

made obsolete with light tension force. Load number 25 is too high for this type of gripper

functional surface due to occurring undesirable force (tension force etc).

EDM vertical modified functional gripper surface with micro-screw.

This experiment was performed in order to evaluate influence of EDM (electro-discharge

machining) in vertical direction (See Chapter XX) gripper surface on handling operations

with microscrew. During this experiment the external temperature in the robot room was

21.1oC and humidity level was 50%.



Chamfer profile of screw with EDM vertical surface gripper.

Evaluation of handling operation while using chamfer surface of microscrew head with an

EDM vertical modified gripper surface.

Load number 15.

The experiment with handling operations with chamfer surface of microscrew by EDM

vertical gripper showed quite good results with both grabbing and holding percentages

(62,0%). However the margin of correct releases was very low due to high stickiness level (9

times). (see Table 6.22). After occurrence of such stickiness the operator had to stop the

handling program and to remove the microscrew from the gripper functional surface. Set

deformation appeared on the peaks of EDM vertical surfaces of the gripper, where chamfer

area of the peaks was completely smashed.

Table 6.22


62,0 27,9

Stiching occasion 9

Operation line

Of all positions

Correct operation %Chamfer screw surface



EDMvert. - micro-screw (chamfer)

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

1 2


Rel

ease

, %load 15load 20

Figure 6.10 EDM vertical-microscrew (chsmfer).

Load number 20.

The handling with load number 20 showed better results compared to those with load number

15. This was especially significant during the release phase of the operation, as the stickiness

effect has disappeared. However it became more difficult for the gripper to hold and raise the

microscrew in the beginning of the operation due to increased heavy damage to the EDM

vertical modified surface. (see Table 6.23).

Table 6.23


50,8 3,0

Stiching occasion 1

Of all positions


Operation line



Cylindrical profile of screw with EDM vertical surface gripper.

Evaluation of handling operation while using cylindrical surface of microscrew head with an

EDM vertically modified gripper surface.

In the same way, as with the experiments performed with LBM surface gripper (See above),

the level of deformation sustained during experiments with chamfer surface of the

microscrew was too heavy. Analogically the coordinates for the functional surface of EDM

vertical gripper’s contact with the microscrew were altered by 0.75mm.

Load number 15.

The experiment with handling the cylindrical surface of the microscrew had fewer stickiness

occurrences than respective experiment with chamfer surfaces (See Table 6.24). The lower

level of stickiness can be explained by relatively smaller touching area of the cylindrical

microscrew surface compared to the chamfer one. At the same time the number of errors with

holding was about the same.

Table 6.24


38,8 17,0

Stiching occasion 3

Of all positions


Operation line



EDMvert. - micro-screw (cylindrical)

20,0

25,0

30,0

35,0

40,0

45,0

50,0

55,0

1 2


Rel

ease

, %load 15load 20

Figure 6.11 EDM vertical microscrew (cylindrical).

Load number 20.

Handling operation with EDM vertical surface gripper and load number 20 on cylindrical

surface of microscrew showed worse results than those shown with load number 15 for same

surface, as well as number 20 with chamfer surface of the microscrew. This is explained by

heavy deformation, as after several repeated handling operations the gripper functional

surface was no longer functional, e.g. handling operation could no longer be performed. (see

Table 6.25).

Table 6.25


39,0 14,7

Stiching occasion 3

Of all positions

Operation line


Note on load number 25.

In cases with both chamfer and cylindrical surfaces of microscrew further operations with

load number 25 were not performed, due to anticipated high level of further deformation of

the EDM vertical gripper surfaces without improved handling results.



Conclusion. Best results were showed in experiments with chamfer surface of the microscrew

and load number 20, as well as cylindrical microscrew surface and load number 15. In general

usage of EDM vertical modified gripper surface is not suitable for handling microscrews in

all possible ways. There is large difference in hardiness of metals and the fragile triangular

peaks of EDM surface are easily destroyed.

For this reason usage of EDM gripper surface modification on such metal type during

microscrew handling operations is too expensive and not reasonable.

Cylindrical profile surface gripper and plastic specimen

No handling experiments with cylindrical profile surface gripper and plastic specimen,

because no expedience to increase tacking surface area for handling operation of the plastic

micro-specimen. Also the diameter of gripper cylindrical functional surface and plastic

specimen not related.

Cylindrical profile surface gripper with micro-screw.

All dimensions and reason for this experiment was explained in chapter 4. Cylindrical profile

of the surface gripper is made with the same radius as the diameter of microscrew. Because of

that gripper with this surface type can only be used in experiments with microscrews and not

with plastic specimens. In order to properly handle the microscrews this gripper needs to be

especially properly aligned.

Alignment of two cylindrical profile functional surfaces of gripper.

Two cylindrical profile functional surfaces of gripper must be aligned to each other in order

for gripper to properly grab the specimen. These surfaces must be parallel to each other to

avoid premature release of the specimen and radius centers on cylindrical curves must be in

the same point. Also the lower ends of the grippers must be on the same level, e.g. z-axis’

value of these ends must be equal in order for gripper to touch plate properly.



In order to achieve the abovementioned conditions the operator must perform the following

steps:

1) Gripper is lightly fixed with screws to the robot jaws

2) Take a bore with the same diameter as the cylindrical microscrew profile

3) A hole in position plate is covered with multiple levels.

4) The bore is put through the tape and thereby fixed vertical position. The tape makes it

possible to move the bore in all three axes

5) Two G-blocks are placed on both sides of the bore tip

6) Grip closes with high load and the bore is held tightly by it. Due to lightly fixed

screws and automatic force control (constant load) this action aligns the gripper

functional surfaces in planar positions

7) Gripper moves carefully down in z-axis direction to the two G-blocks put on the plate.

This sets the gripper tips on the parallel level with the position hole plate

8) The screws are then tightened in this two alignment positions

All further experiment preparation procedures are the same as in the previous experiment. To

reduce manufacturing uncertainty of gripper all positions of holes on the plate must be

checked and corrected in the position list of the handling program by the operator.

Experiment cylindrical profile surface gripper with microscrew.

Load number 15.

During the experiment with cylindrical profile surface gripper and microscrew handling

operation frequent errors were observed in grabbing and holding phases of the process. Upon

release of the screw stickiness occurred frequently (10 times). (see Table 6.26). The two

possible reasons for such large amount of errors are:

• Theoretically large touching area, compared to the previous experiments

• Possible error in radius of cylindrical gripper profile or in diameter of microscrews

No deformation to the gripper surface was observed.

Table 6.26




38,5 19,6


Operation line

Of all positions


Cylindrical func. surface - micro-screw

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

1 2


Rel

ease

, %

load 15load 20

Figure 6.12 Cylindrical functional surface –microscrew.

Load number 20

In comparison with the previous, lighter load this handling experiment provided superior

results, especially in holding procedure. However the level of stickiness to the cylindrical

surface of the gripper has increased.

This can be the effect of higher load, which negated the influence of errors in radius of

cylindrical gripper profile and in diameter of microscrews.

Another reason for that is the deformation of cylindrical gripper surface. As a result the

microscrews in handling started rotating under the load force thus increasing their touching

surface with the touching surface of the gripper and by that stabilize the position in the hold.

This supported the stickiness effect. (see Table 6.27).

Table 6.27




65,8 22,2


Of all positions

Correct operation %Operation line

Cylindrical screw surface

Conclusions

• Handling microscrews with cylindrically surfaced gripper was best with load number

15

• The large circular touching area did not guarantee the microscrew turning away from

the original axis

• Too large touching surface proves to have negative effect on handling operation in

form of high stickiness level

• The soft gripper material was relatively quickly and lightly deformed allowing the

screw to turn into erroneous position

• Using cylindrically surfaced gripper made of this kind of material for handling

microscrews is inefficient

Existing gripper

The existing gripper is the griper, which was built at IPL by supervision of Asta Gegeckaite.

And used in all the previous experiments before this project. For more information about it

see in the chapter 4.

Existing gripper evaluation test is performed in order to ascertain the existing relevance

degree of gripper for micro-handling process with samples that interest us. Also to compare

how much the handling process has improved or worsened while leveling with newly

produced and modified functional surfaces of grippers. Existing gripper handling operation

experiment with plastic micro-specimen was performed applying the analogous procedure as

for the experiment of grippers of new design.

Experiment with existing gripper surface with load number 15 and plastic specimens showed

results with a high number of errors (30.6%). (see Table 6.28).



Table 6.28


69,4 13,5

Stiching occasion 4

Ope

ratio

n

posi

tions


Of all positions


5,8

5,7

Existing gripper - plastic specimen

40,0

60,0

80,0

100,0

1 2 3


Rel

ease

, %


Figure 6.13 Existing gripper-plastic specimen

The test was performed on the same position “hole” plates as in the analogous experiments.

In this case, the results have shown that gripping mistakes occur at the moment of holding

operation. Plastic specimen stickiness to the existing gripper surface is possible to explain by

too great touching surface influencing gripper functional surfaces geometry. It is of triangle

shape with the cut with 130 degrees angle, thus while taking the element it touches to four

planes of the gripper (see picture 6.7). This increases the grabbing area by a long way

comparing with the flat surface of the gripper.



Picture 6.7 Functional surface of existing gripper

Some mistakes were observed at the point of release operation: the tested micro-object falls

out at a wrong time. One presumes that electrostatic and van der Waals forces might

contribute to this. Their total values are not sufficient to ensure stable stickiness effects to the

gripper functional surface, but are enough to offset the influence of the elasticity force of the

specimen.

The experiment, using the robot load number 20, is performed in the same way as the

previous one. The results demonstrated that the handling operation is performed in a much

more exact way.

Repeatability of holding operation from the first position in each line was at the 100% level

during the experiment. However, there were mistakes in the second and third operation

positions. Also, several cases were observed with the stickiness effect. This can be explained

by the increased influence of the adhesive force. When the squeezing force is bigger, the

elastic plastic specimen deforms which leads to an increased touching surface between it and

the gripper surface and the reduction of roughness. That leads to the increase of van der

Waals and surface tension force and its influence to the micro-specimen handling operation.

(see Table 6.29).

Table 6.29


65,9 16,9

Stiching occasion 6

Of all positions

Ope

ratio

n

posi

tions


5,0

7,9



The experiment, using the robot load number 25, showed that results were poorer compared

with the load number 20 test. Due to the increased influence of the forces, mentioned in the

description of the previous experiment, the number of mistakes grew, and the influence of the

stickiness effect was observed more frequently. (see Table 6.30).

Table 6.30


58,9 20,0


Ope

ratio

n

posi

tions

Of all positions

Operation line on the position plateCorrect operation percentage in all positions %

Existing gripper - plastic specimen (load number 25)

5,8

5,0

The plastic specimen stickiness with existing gripper surface can be explain due to

immoderate touching surface area with four points gripper functional surfaces.

Micro-screw handling operation with existing gripper experiment was performed applying the

same methodology and on the analogous hole position plate. Experiments of the load number

15 and 20 showed the analogous results, thus here they are analyzed together. Results

indicated that only 3 operations out of 40 were successful. This is explained by the total

variance of geometrical functional surfaces of both gripper and micro-screw. From the

viewpoint of geometrical sense the common grabbing of gripper of lozenge profile totally

misfits the grabbing of chamber micro-screw surface. The grabbing of micro-screw of

cylindrical surface is possible only under certain favorable conditions. These conditions mean

that the micro-screw position, to be precise, the turning of micro-screw cap has to be ideally

proportional regarding the existing functional surface of the gripper.

In opposite case the different asymmetric forces will affect the functional surfaces of the

gripper. Knowing that the width of grabbing surfaces is very small, alignment of micro-screw

xy plane is very easily vulnerable. And in this case it is overbalanced by the affecting

asymmetric forces, thus the micro-screw merely slips out of the existing gripper functional



surface. In this way the impropriety of the existing gripper for the micro-screw handling

operation is explained.

Conclusion is that existing gripper with its triangle functional surface misfits for the plastic

specimen handling operation because of too great area of the touching surface. Thus too great

adhesive forces having negative influence for handling operation operate there. But this

geometrical solution of form of functional surface of existing gripper has it own advantages.

Grabbing by four points on the cylindrical or spherical surfaces performs the automatic

alignment of position (that is very important). (see Picture 6.8)

Picture 6.8 Geometrical solution

Also after the automatic alignment the grabbing of the object is performed by four

symmetrical points (when the specimens are cylindrical or spherical surfaces) with regard to

each other and applying the proportional forces. This means that if there is a different

structure or material of functional surface of existing gripper when influence of van der

Waals, electrostatic and surface tension forces is decreased to minimum, then it would the

optimal solution from the geometrical point of view for handling operation specimens with

cylindrical or spherical surfaces. Existing gripper with its own triangle functional surface

totally misfits the micro-screw handling operation because of the geometrical inadequacy.

The modification of surface or selection of other material would not solve the problem of the

micro-screw handling. It would require the functional surface of gripper of totally other

design and geometry.



50

60

70

80

90

100

LM EDM Plane-Polished

Plane-Rough Existing

Functional surface

Rel

eas

(%)

load nr 15load nr 20load nr 25

0

10

20

30

40

50

60

70

80

90

LBMchamfer

LBMcylind

EDMchamfer

EDMcylind

Cylindrical Plane-Polishedchamfer

Plane-Polishedcylind

Plane-Rough

chamfer

Plane-Roughcylind

Functional surface

Real

es (%

)

load nr 15load nr 20load nr 25



7. Conclusion

Analysis of functional surfaces for mechanical handling of microparts was presented in theis

thesis. In was done in order to evaluate the impact of tacking surface area ration and different

surface parameters. These parameters can strongly affect the functional behaviour of handling

process of microobjects. For this reason it is a need to develop different techniques for

surface modifications.

These grippers were important to be investigate, as the ones working at the macroscale,

cannot be used in the microscale

Design, mathematical modelling and surface structure of griper grasping parts are developed

in order to avoid or decrease influence of surface, material and motion.



References

1. Petrovic, D., Popovic, G., Chatzitheodoridis, E., Medico, O., Almansa, A., Sümecz, F., Brenner, W., Detter, H. 2002 Gripping tools for handling and assembly of microcomponents Proc. 23rd. International conference on microelectronics (Miel 2002), Vol. 1., Yugoslavia, 12-15 May 247- 250

2. Petrovic, D., Popovic, G., Chatzitheodoridis, E., Del Medico, O., Almanasa, A., Detter, H., Brenner, W. 2001 Mechanical gripper system for handling and assembly in MEMS Micromachining and microfabrication process technology VII. SPIE P. 151-155

3. Bleuler H., Clavel R., Breguet J., Langen H., Belleouard Y. 2001 Applications of microrobotics and microhandling First Japan-Switzerland Bilateral Symposium on Science and Technology in Micro/Nano Scale issue 36 26-28 microrobotics and microhandling

4. Fearing R.S., 1995 Survey of Sticking effects for micro parts handling IEEE 212-217

5. Zhou Y., Nielson B.J. 1998 Adhesion force modeling and measurement for micromanipulation Part of SPIE Conference on microrobotics and micromanipulation 169-180

6. Weck, M., Petersen, B. 2001 Adhesion problems during handling of micro parts- vibration assisted release of objects Euspen international conference 148-151

7. Dechev, N., Cleghorn, W.L., Mills, J.K. 2004 Microassembly of 3-D microstructures using a compliant, passive microgripper Juornal of microelectronical systems, vol. 13, no.2 176-189

8. Development of tools for handling and assembling microcomponents J Ansel, Y., Schmitz, F., Kunz, S., Gruber, H.P., Popovic, G. 2002 . Micromech. Microeng. 12 430- 437

9. Austin, B.M. 1969 Handling miniature parts; Automation 66-69 micohandling 10. Alting L., Kimura, F., Hansen H.N., Bissacco G. 2003 Micro engineering Annals

of CIRP vol. 2003 11. López-Sáncez, J., Miribel- Catala, P., Montare, E., Puig- Vidal, M., Bota, S.A.,

Samitier, J. 2001 High accuracy piezoelectric- based microrobot for biomedical applications IEEE 603- 609

12. Miller A.T. Allen P.K. 2004 Grasp it! A versatile simulation for robotics grasping IEEE 110-122

13. Fleischer, J., Bouchholz, C., Weule, H. 2003 Automation of the powder injection moulding process for micro mechanical parts Annals of the CIRP Vol. 52/1 419- 422

14. Rollot Y., Régnier S., Giunot J.C. 1999 Simulation of micro-manipulations: adhesion forces and specifics dynamics models International journal of adhesion and adhesives nr. 19 35-48

15. Liu Y., Starr G., Lumia W.R. 2005 Spatial grasp synthesis for complex objects using model-based simulation Industrial robot: an international journal 24-31



16. Ikonomopoulos A., Dritsas L., Force control in Robot Finishing, Proc. of 25th ISIR, Hanover, Germany, 1995

17. Shim S., Kramer B., A Force-controlled Approach to Robotics Deburring, ASME Press, New York, 1988

18. Whitney D. E., Quasi-static Assembly of compliantly Supported Rigit Parts, Trans. ASME I. Dyn. Syst. Meas Control, 104. (3), 1982, pp. 65-77.]

19. Shahinpoor, M., A Robot Engineering Textbook, Harper and Row, Publishers, New York, 1987.

20. J. K. Salisbury and B. Roth, "Kinematic and force analysis of articulated mechanical hands," J. Mech. Transmiss. Automat, in Des., vol. 105, pp. 35-41, Mar. 1983

21. W. Holzmann and J. M. McCarthy, "Computing the friction forces associated with a three fingered grasp,'' in Proc. 1985 IEEE Con/, on Robotics and Automation (St. Louis, MO, 1985), pp. 594-600. Also IEEE J. Robotics Automat., vol. RA-1, pp. 206-221, Dec. 1985.

22. C. A. Klein, K. W. Olson, and D. R. Pugh, "Use offeree and altitude sensors for locomotion of a legged vehicle over irregular terrain," I, 1983.

23. R. B. McGhee and D. E. Orin, "A mathematical programming approach to control of joint position and torques in legged locomotion systems," in Theory and Practice of Robots and Manipulators, A. Morecki and K. Kedzior, Eds. New York, NY: Elsevier, 1977, pp. 225-232.

24. K. J. Waldron, "Force and motion management in legged locomotion, IEEE J. Robotics Automat., vol. RA-2, no. 4, pp. 214-220, Dec. 1986.

25. K. H. Hunt, Kinematic Geometry of Mechanisms. Oxford, UK:Clarendon Press, 1978.


Apendix content: WRITE HEADING 1....................................................................................................................................................... II

PLANE SURFACE (ROUGH) ................................................................................................................................ II EXISTING GRIP (ALL SURF)............................................................................................................................... III EXISTING GRIP (SMALL AREAS) .......................................................................................................................IV LBM SURFACE WITHOUT POLISHING (ALL SURF) ..........................................................................................V LBM SURFACE WITHOUT POLISHING (SMALL AREAS) .................................................................................VI LBM SURFACE POLISHED (ALL SURF)............................................................................................................VII LBM SURFACE POLISHED (SMALL AREAS)...................................................................................................VIII EDM VERTICAL SURFACE (ALL SURF).............................................................................................................IX EDM VERTICAL SURFACE (SMALL AREAS)......................................................................................................X CYLINDRICAL SURFACE (ALL SURF) ...............................................................................................................XI PLANE SURFACE POLISHED (ALL SURF) .......................................................................................................XII

WRITE HEADING 1....................................................................................................................................................XIII LBM – PLASTIC SPECIMEN..............................................................................................................................XIII LBM – MICRO-SCREW..................................................................................................................................... XIV EDMVERT. - PLASTIC SPECIMEN ................................................................................................................... XV EDMVERT. - MICRO-SCREW........................................................................................................................... XVI CYLINDRICAL FUNCTIONAL SURFECE........................................................................................................ XVII PLANE-POLISHED - PLASTIC SPECIMEN.................................................................................................... XVIII PLANE-POLISHED - MICRO-SCREW.............................................................................................................. XIX PLANE-ROUGH - PLASTIC SPECIMEN ........................................................................................................... XX EXISTING GRIPPER - PLASTIC SPECIMEN.................................................................................................. XXII EXISTING GRIPPER - MICRO-SCREW ......................................................................................................... XXIII

WRITE HEADING 1

Plane surface (rough) Measuring values [nm] [nm] Surface parameters

[units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 1145 1254 1177 1195 1205 1195,2 40,01 Sq [nm] 1385 1484 1405 1396 1455 1425 42,49 Ssk 0,0663 0,0446 0,0643 0,0553 0,0601 0,05812 0,01 Sdr % 3,94 4,1 4 4,2 3,84 4,016 0,14 Spk [nm] 1349 1202 1349 1349 1349 1319,6 65,74 Sk [nm] 3965 4215 3995 3785 4365 4065 226,83

Svk [nm] 800 746 810 804 780 788 26,04

Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 1164 1168 1214 1150 1210 1181,2 28,93 Sq [nm] 1389 1381 1348 1421 1358 1379,4 28,59 Ssk -0,165 -0,145 -0,151 -0,148 -0,154 -0,1526 0,01 Sdr % 2,5 2,22 2,35 2,2 2,3 2,314 0,12 Spk [nm] 1428 1095 1227 1295 1287 1266,4 120,71 Sk [nm] 3474 3423 3488 3412 3444 3448,2 32,45

Svk [nm] 1229 1192 1212 1183 1210 1205,2 18,05

Existing grip (all surf) Measuring values [nm] [nm] Surface parameters

[units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 1497 1294 1304 1340 1471 1381,2 95,83 Sq [nm] 1883 1672 1848 1741 1683 1765,4 95,87 Ssk -0,0686 0,18 0,051 0,14 -0,02 0,05648 0,10 Sdr % 7,02 4,02 5,35 6,2 4,3 5,378 1,26 Spk [nm] 1883 1862 1827 1895 1887 1870,8 27,35 Sk [nm] 4802 4811 4488 4512 4344 4591,4 206,63

Svk [nm] 2158 2131 2212 2183 1910 2118,8 120,51

Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 1026 768 1014 850 810 893,6 119,05 Sq [nm] 1368 978 1148 1021 1199 1142,8 154,83 Ssk 0,622 0,623 0,524 0,553 0,708 0,606 0,07 Sdr % 4,3 2,3 2,95 3,2 4,1 3,37 0,83 Spk [nm] 2216 1516 1527 2195 1857 1862,2 342,12 Sk [nm] 2863 2346 2488 2612 2700 2601,8 197,71

Svk [nm] 1369 761 1112 1183 910 1067 237,16

Existing grip (small areas) Measuring values [nm] [nm] Surface parameters

[units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 479 398 427 448 425 435,4 30,15 Sq [nm] 655 550 601 590 612 601,6 37,94 Ssk 0,215 0,476 0,284 0,366 0,401 0,3484 0,10 Sdr % 1,56 1,34 1,5 1,41 1,39 1,44 0,09 Spk [nm] 1036 939 1011 983 949 983,6 40,88 Sk [nm] 1319 1142 1340 1101 1228 1226 105,27

Svk [nm] 831 569 801 562 760 704,6 129,48

Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 891 724 789 812 825 808,2 60,44 Sq [nm] 1182 884 1008 943 1113 1026 121,74 Ssk 0,0809 0,477 0,342 0,105 0,376 0,27618 0,17 Sdr % 2,89 1,43 1,34 2,5 2,64 2,16 0,72 Spk [nm] 1632 1080 1458 1514 1109 1358,6 249,35 Sk [nm] 2536 2232 2337 2520 2302 2385,4 135,67

Svk [nm] 1422 477 887 946 1102 966,8 343,58

LBM surface without polishing (all surf) Measuring values [nm] [nm] Surface

parameters [units] 1 2 3 4 5 Mean value St.Dev

Sa [nm] 5179 4768 4018 4850 3920 4547 551 Sq [nm] 6604 5974 5142 6021 5349 5818 583 Ssk 0,0568 0,152 0,278 0,0539 0,178 0,14374 0,09 Sdr % 22,8 2,3 2,95 3,2 4,1 7,07 8,82 Spk [nm] 8177 7216 6927 8026 7852 7639,6 540,94 Sk [nm] 15700 12486 12518 14212 13709 13725 1335,10

Svk [nm] 6212 5765 4178 5133 4945 5246,6 782,07

Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev

Sa [nm] 3082 4079 3141 3210 3367 3375,8 407,28

Sq [nm] 3782 3210 4242 4079 4352 3933 457,68 Ssk -0,811 -0,121 0,278 0,041 -0,231 -0,1688 0,41 Sdr % 12,3 10,1 7,95 13,2 16,3 11,97 3,16 Spk [nm] 3418 2516 3227 3698 4151 3402 605,08 Sk [nm] 8761 8414 6218 11210 8711 8662,8 1770,53

Svk [nm] 4475 4178 3165 5121 4692 4326,2 734,51

LBM surface without polishing (small areas) Measuring values [nm] [nm] Surface

parameters [units] 1 2 3 4 5 Mean value St.Dev

Sa [nm] 3126 2646 4000 2812 3226 3162 524 Sq [nm] 4128 3327 4957 3943 4153 4102 583 Ssk 0,746 0,527 0,737 0,525 0,676 0,6422 0,11 Sdr % 20,6 14,8 16,8 2,5 2,64 11,468 8,39 Spk [nm] 8549 5110 8331 7214 8009 7443 1399 Sk [nm] 7460 7275 10473 8520 8202 8386 1275

Svk [nm] 3388 1838 1731 2446 2100 2301 668


Sa [nm] 2592 3491 2646 3126 2817 2934,4 374,40 Sq [nm] 3372 4824 3327 3327 3943 3758,6 650,21 Ssk -1,15 -1,95 0,527 -0,68 0,746 -0,5014 1,14 Sdr % 15,3 20,3 14,8 17,2 15,9 16,7 2,20 Spk [nm] 3086 1328 5110 2573 3497 3118,8 1379,66 Sk [nm] 6040 5930 7275 6824 6192 6452,2 575,66

Svk [nm] 5589 10214 1838 4485 6731 5771,4 3074,79

LBM surface polished (all surf) Measuring values [nm] [nm] Surface parameters

[units] 1 2 3 4 5 Mean value St.Dev


Svk [nm] 1446 1395 1516 1435 1527 1463,8 56,12


Sa [nm] 786 894 679 755 812 785,2 78,66 Sq [nm] 1196 1242 1136 1145 1011 1146 86,66 Ssk -3,61 -2,84 0,954 -2,62 -0,432 -1,71 1,90 Sdr % 2,84 3,41 0,848 2,54 3,54 2,64 1,08 Spk [nm] 1076 1042 1671 987 9,26 957,05 597,97 Sk [nm] 2193 1842 2140 2298 1947 2084 185,84

Svk [nm] 1905 2195 1716 1853 2159 1965,6 205,35

LBM surface polished (small areas) Measuring values [nm] [nm] Surface parameters


Sa [nm] 339 340 287 331 398 339 39,53 Sq [nm] 425 422 358 452 470 425,4 42,58 Ssk 0,254 0,343 0,215 0,348 0,284 0,2888 0,06 Sdr % 0,814 0,811 1,34 0,544 0,734 0,8486 0,30 Spk [nm] 721 870 892 765 741 797,8 77,92 Sk [nm] 1042 1136 1011 1198 1036 1084,6 79,21

Svk [nm] 324 305 284 365 287 313 33,19


Sa [nm] 705 606 699 768 679 691,4 58,22 Sq [nm] 895 782 888 812 864 848,2 49,29 Ssk -0,435 -0,7 2,68 0,0243 0,457 0,40526 1,35 Sdr % 2,47 2,09 1,34 2,21 1,94 2,01 0,42 Spk [nm] 995 821 1023 874 995 941,60 88,66 Sk [nm] 2093 1753 2077 1843 1942 1941,60 147,09

Svk [nm] 1015 1069 1140 1097 1014 1067,00 54,19

EDM vertical surface (all surf) Measuring values [nm] [nm] Surface parameters


Sa [nm] 1984 1888 1915 2153 1810 1950 129,45 Sq [nm] 2242 2478 1975 2121 2199 2203 184,30 Ssk -0,0542 -0,0864 0,0524 -0,214 0,08 -0,04444 0,12 Sdr % 5,41 6,3 5,95 5,6 5,1 5,672 0,47 Spk [nm] 1127 1016 1241 1195 1051 1126 94,49 Sk [nm] 6211 6044 4678 5612 6700 5849 761,69

Svk [nm] 1203 1351 1112 1183 1110 1191,8 98,24



Svk [nm] 1213 1035 1182 1267 1294 1198,2 101,28

EDM vertical surface (small areas) Measuring values [nm] [nm] Surface parameters


Sa [nm] 1033 1344 1152 1279 1221 1205,8 119,84 Sq [nm] 1318 1693 1456 1594 1498 1511,8 141,82 Ssk -0,903 -0,949 0,0253 -0,9412 -0,652 -0,68398 0,41 Sdr % 7,45 4,77 7,62 6,34 5,11 6,258 1,31 Spk [nm] 560 1197 784 946 897 876,8 232,75 Sk [nm] 2749 2316 2314 2687 2704 2554 219,35

Svk [nm] 2196 3564 3145 3013 2265 2836,6 590,01


Sa [nm] 1224 777 1164 945 1034 1028,8 178,07 Sq [nm] 1500 999 1452 1367 1294 1322,4 197,31 Ssk -0,552 -0,761 -0,194 0,0487 -0,0971 -0,31108 0,34 Sdr % 6,02 4,56 4,21 5,33 6,04 5,232 0,83 Spk [nm] 405 713 527 634 551 566 116,08 Sk [nm] 3645 1619 2434 2264 2931 2578,6 758,64

Svk [nm] 1669 1710 1730 1645 1634 1677,6 41,33

Cylindrical surface (all surf) Measuring values [nm] [nm] Surface parameters


Sa [nm] 1314 1355 1278 1362 1426 1347 55,63 Sq [nm] 1827 1875 1768 1794 1867 1826,2 46,02 Ssk 0,531 0,458 0,376 0,675 0,464 0,5008 0,11 Sdr % 6,39 6,47 6,12 6,75 5,94 6,334 0,31 Spk [nm] 3036 3108 3204 3123 3009 3096 76,98 Sk [nm] 3451 3534 3462 3514 3442 3480,6 40,86

Svk [nm] 2052 2140 2002 2134 2167 2099 69,19


Sa [nm] 965 960 945 976 931 955,4 17,62 Sq [nm] 1315 1296 1276 1304 1379 1314 39,03 Ssk 0,535 0,344 0,366 0,434 0,513 0,4384 0,09 Sdr % 4,23 4,11 3,94 3,76 4,35 4,078 0,23 Spk [nm] 2185 2152 2046 2246 2234 2172,6 80,25 Sk [nm] 2828 2827 2714 2768 2887 2804,8 65,93

Svk [nm] 1571 1627 1594 1616 1647 1611 29,44

Plane surface polished (all surf) Measuring values [nm] [nm] Surface parameters


Sa [nm] 287 281 346 372 296 316,4 40,32 Sq [nm] 374 368 476 501 397 423,2 61,23 Ssk 0,0929 0,1 0,24 0,076 0,149 0,13158 0,07 Sdr % 0,698 0,673 0,631 0,449 0,864 0,663 0,15 Spk [nm] 519 528 587 603 632 573,8 48,77 Sk [nm] 853 833 954 978 828 889,2 71,24

Svk [nm] 404 389 492 426 356 413,4 50,78


Sa [nm] 474 465 368 467 385 431,8 50,95 Sq [nm] 639 612 544 586 633 602,8 38,88 Ssk -0,377 -0,58 0,064 0,0741 -0,247 -0,21318 0,28 Sdr % 1,7 1,7 1,1 0,94 1,54 1,396 0,35 Spk [nm] 604 604 566 542 522 567,6 36,70 Sk [nm] 1334 1316 1298 1235 1364 1309,4 48,21

Svk [nm] 911 858 824 876 801 854 43,18

WRITE HEADING 1

LBM – plastic specimen LBM - plastic specimen (load number 15)

Correct operation percentage in all positions % Operation line on the position plate

1 2 3 4 Mean value St.Dev

First 90 100 90 100 95,0 5,8

Second 80 60 70 70 70,0 8,2

Ope

ratio

n po

sitio

ns

Third 60 70 77 70 69,3 7,0

Of all positions 78,1 14,0

Stiching occasion 1 LBM - plastic specimen (load number 20)



First 100 100 100 100 100,0 0,0

Second 80 60 60 50 62,5 12,6

Ope

ratio

n po

sitio

ns

Third 50 77 70 62,5 64,9 11,5


Stiching occasion 5 LBM - plastic specimen (load number 25)



First 90 80 90 90 87,5 5,0

Second 77 50 70 50 61,8 13,9

Ope

ratio

n po

sitio

ns

Third 60 77 50 42 57,3 15,1



LBM – micro-screw LBM - micro-screw (load number 15)

Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %

Operation line Operation line

1 2Mean value St.Dev 1 2Mean value St.Dev

First position 90 60 75,0 21,2First position 70 60 65,0 7,1

Second position 60 66 63,0 4,2


Of all positions 69,0 14,3 Of all positions 74,5 12,2

Stiching occasion 0 Stiching occasion 2

LBM - micro-screw (load number 20)









LBM - micro-screw (load number 25)

Chamfer screw surface Cylindrical screw surface -no recorded resultsCorrect operation %

Operation line

1 2Mean value St.DevFirst position 70 50 60,0 14,1Second position 77 50 63,5 19,1


Stiching occasion 1

EDMvert. - plastic specimen EDMvert. - plastic specimen (load number 15) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 100 100 100 100 100,0 0,0 Second 90 90 100 88 92,0 5,4

Ope

ratio

n po

sitio

ns

Third 80 70 90 77 79,3 8,3 Of all positions 90,4 10,3 Stiching occasion 1 EDMvert. - plastic specimen (load number 20) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 100 100 100 100 100,0 0,0 Second 100 90 100 90 95,0 5,8

Ope

ratio

n po

sitio

ns

Third 90 80 90 88 87,0 4,8 Of all positions 94,0 6,8 Stiching occasion 0 EDMvert. - plastic specimen (load number 25) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 100 100 100 100 100,0 0,0 Second 90 88 77 77 83,0 7,0

Ope

ratio

n po

sitio

ns

Third 80 70 66 70 71,5 6,0 Of all positions 84,8 13,1 Stiching occasion 0

EDMvert. - micro-screw EDMvert. - micro-screw (load number 15)









EDMvert. - micro-screw (load number 20)









EDMvert. - micro-screw (load number 25)

No experiments due to high deformation

Cylindrical functional surface Cylindrical func. surface - micro-screw (load number 15) Cylindrical screw surface

Correct operation % Operation line

1 2 Mean value St.Dev First position 50 60 55,0 7,1Second position 20 24 22,0 2,8

Of all positions 38,5 19,6 Stiching occasion 10 Cylindrical screw surface (load 20)

Correct operation % Operation line

1 2 Mean value St.Dev First position 80 88 84,0 5,7Second position 55 40 47,5 10,6

Of all positions 65,8 22,2 Stiching occasion 12

Plane-Polished - plastic specimen Plane-Polished - plastic specimen (load number 15) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 100 90 100 100 97,5 5,0 Second 80 90 70 77 79,3 8,3

Ope

ratio

n po

sitio

ns

Third 66 66 50 50 58,0 9,2 Of all positions 78,3 18,3 Stiching occasion 8 Plane-Polished - plastic specimen (load number 20) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 90 100 90 100 95,0 5,8 Second 77 80 70 80 76,8 4,7

Ope

ratio

n po

sitio

ns

Third 55 50 60 48 53,3 5,4 Of all positions 75,0 18,5 Stiching occasion 6 Plane-Polished - plastic specimen (load number 25) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 100 100 100 90 97,5 5,0 Second 60 50 55 60 56,3 4,8

Ope

ratio

n po

sitio

ns


Plane-Polished - micro-screw

Plane-Polished - micro-screw (load number 15)




First position 80 80 80,0 0,0 First position 70 70 70,0 0,0

Second position 55 60 57,5 3,5Second position 60 50 55,0 7,1



Plane-Polished - micro-screw (load number 20)








Plane-Polished - micro-screw (load number 25)Experiment not succeed

Plane-Rough - plastic specimen Plane-Rough - plastic specimen (load number 15) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 100 100 100 100 100,0 0,0 Second 80 70 70 77 74,3 5,1

Ope

ratio

n po

sitio

ns

Third 66 60 50 50 56,5 7,9 Of all positions 76,9 19,3 Stiching occasion 1 Plane-Rough- plastic specimen (load number 20) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 90 100 90 100 95,0 5,8 Second 77 64 70 80 72,8 7,2

Ope

ratio

n po

sitio

ns

Third 55 50 55 48 52,0 3,6 Of all positions 73,3 19,1 Stiching occasion 3 Plane-Rough - plastic specimen (load number 25) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev

First 80 90 90 90 87,5 5,0 Second 55 50 60 60 56,3 4,8

Ope

ratio

n po

sitio

ns


Plane-Rough - micro-screw (load number 15)



1 2Mean valueSt.Dev 1 2Mean value St.Dev





Plane-Rough - micro-screw (load number 20)



1 2Mean valueSt.Dev 1 2Mean value St.Dev





Plane-Rough- micro-screw (load number 25)

Experiment not succeed

Existing gripper - plastic specimen Existing gripper - plastic specimen (load number 15)



First 80 90 90 80 85,0 5,8

Second 70 60 70 70 67,5 5,0

Ope

ratio

n po

sitio

ns

Third 55 48 60 60 55,8 5,7


Stiching occasion 4 Existing gripper - plastic specimen (load number 20)



First 90 90 90 80 87,5 5,0

Second 60 50 55 50 53,8 4,8

Ope

ratio

n po

sitio

ns

Third 50 50 60 66 56,5 7,9


Stiching occasion 6 Existing gripper - plastic specimen (load number 25)



First 90 80 90 80 85,0 5,8

Second 40 50 48 55 48,3 6,2

Ope

ratio

n po

sitio

ns

Third 44 38 50 42 43,5 5,0



Existing gripper - micro-screw

Existing gripper - micro-screw (load number 20)

Cylindrical screw surface

Correct operation %

Operation line

1 2 Mean value St.Dev

First position 20 10 15,0 7,1



Stiching occasion 0

Documents

Functional Surfaces in Mechanical Handling of Micropartsetd.dtu.dk/thesis/192973/12_15_2006_Povilas_Pocius_Master_Thesis.pdf · Gripper employing the Bernoulli ... Functional surfaces