DESIGN AND FABRICATION OF THREE AXIS MECHANISM WITH AC

SERVO MOTOR IN APPLICATION OF PERSONAL COMPUTER NUMERICAL

CONTROL

LIM LIANG HEONG

A report submitted in partial fulfilment of the

requirements for the award of the degree of

Bachelor of Mechanical Engineering7

r Faculty of Mechanical Enginering

Universiti Malaysia Pahang

NOVEMBER 2007

ABSTRACT

This project was carried out to develop the accuracy and efficiency of the

three axis mechanism with AC servomotor in application of personal computer

numerical control. For running the incremental forming rig test is the main objective

of this project. This three axis mechanism prototyping had been involved designed,

analyzed, simulation approach, fabrication and assemble work. The structure part is

one most important design part to minimize the vibration and friction. Extension

simulations were performed to consider the failure analysis of the structure. The

table structure found that it is strong enough to support the force and load which

cause it bends about 3.11 mm and maximum stress applied is 5.11 MPa. The

ultimate tensile strength is far higher than maximum stress applied. This three axis

mechanism machine is successful develop. High technology electrical devices and

good control system used to increase the accuracy and efficiency of the product.

V

ABSTRAK

Projek im dibangunkan adalah bertujuan membangunkan mesin pergerakan

tiga paksi yang jitu dan cekap dengan berbantuan arus ulang alik dan diapplikasikan

"Servomotor" dalam computer peribadi. Tujuan pembagunan mesin mi adalah untuk

menjalankan eksperimen pembentukan berperingkat. Projek mi dimulakán dengan

melakar model projek, melukis model dalam perisian komputer, menganalisis sistem

model, proses simulasi dan proses fabrikasi. Struktur mesin adalah bahagian yang

paling penting supaya getaran dan geseran antara bahagian-bahagian dapat

dikurangkan. Kerja simulasi harus dijalankan supaya dapat mengawal had kegagalan

struktur mesin itu. Dalam menganalisis struktur mi, didapati bahawa tekanan

maksimum yang dialami oleh struktur adalah sebanyak 5.11 MPa dan lenturan

sebanyak 3.11 mm sahaja. Jika dibandingkan dengan maklumat tekanan maksimum

sebenar, didapati struktur adalah cukup tegtih untuk meriyokong eksperimen mi.

Kesimpulannya, mesin tiga paksi pergerakan itii berjaya dihasilkan. Alat tekñologi

elektrikal yang canggih dan sistem kawalan yang mantap digunakan untuk

meningkatkan kejituan dan kecekapan produk.

"I

TABLE OF CONTENTS

CHAPTER

TITLE

PAGES

TITILE 1

STUDENT DECLARATION 11

DEDICATION ill

ACKNOWLEGDEMENT

iv

ABSTRACT ki

ABSTRAK Vi

TABLE OF CONTENTS Vii

LIST OF TABLE Xi

LIST OF EQUATION xi'

LIST OF FIGURE xi"

LIST OF APPENDICES xv

1 INTRODUCTION

1.1 Project Objective 1

1.2 Project Scopes 1

1.3 Project Background 2

1.4 Problem Statement 3

Vii

vi"

2 LITERATURE REVIEW

2.1 Components 4

2.1.1 Linear Slides 4

2.1.1 .1 Ball Bearing Slides (Ball Slides) 6

2.1.1.2 Dovetail Slides 7

2.1.1.3 Machines Slides 8

2.1.1.4 Roller Slides 9

2.1.1.5 Roller Tables 9

2.1.1.6 XYTable 11

2.1.2 Ball Screw 12

2.1.2.1 Lead Screw 14

2.1.2.2 ACME Screw 15

2.1.2.3 Jack Screw 16

2.1.3 Introduction of Motor 17

2.1.3.1 DC Motor 19

2.1.3.2 AC Motor 19

2.1.3.3 Servomotors 20

2.1.3.3.1 AC Servomotors 21

2.1.3.3.2 DC Servomotors 22

2.1.3.4 Stepper Motor 22

2.2 Mechanism of Ball Screw 24

2.3 Friction of Slide Guide (Table Moving) 27

2.4 Thermal Effect to Linear Slide 29

2.5 Finite Element Analysis (ALGOR) 32

3

METHODOLOGY

3.1 Concept Design 34

3.2 Mechanical Design 36

3.3 Fabrication of Components of Three Axes

Mechanism Machine 36

3.3.1 Fabrication of Coupler for Ball Screw 36

3.3.1.1 Milling Process 37

3.3.1.2 Drilling ProcesS 38

3.3.1.3 Simulation of Milling and

Drilling Process 39

3.3.2 Cutting Process 40

3.3.3 Drilling Process 40

3.3.4 Turning Process 42

3.4 Assemble of Three Axes Mechanism Machine 43

3.4.1 Structure Part 43

3.4.2 Motion Part 43

3.4.3 Control Part 45

3.5 Test Running 46

4 RESULT AND DISCUSSION

4.1 Introduction 47

4.2 Ball Screw Analysis 47

4.3 Selection of Gear Box 49

4.4 Structure of Table Extrude Aluminum Bar Analysis 51

4.5 AC Servomotor Sizing Selection 55

4.6 AC Servomotor Analysis 63

ix

CONCLUSION AND RECOMMENDATION

5.1 Conclusion 64

5.2 Recommendation 67

REFERENCES 68

APPENDIX 71-94

LIST OF TABLES

xi

TABLE NO TITLE

Table 2.1 Comparison Advantage and Disadvantage

Between AC and DC Motor

Table 2.2 Advantage and Disadvantage of Stepper Motor

Table 3.1 Motion Part Components

Table 3.2 ContMl Part Components

• PAGE

20

24

46

47

LIST OF EQUATIONS

EQUATION NO EQUATION PAGE

2.1 L=N1p 25

2.2 tan 2= ± 26

2.3 ARB/A=LAOA •26

2.4 VB,A 'A 26

xii

2.5 aBIA =

2.6(FD

2.7

ZA 26

r(L+D)1

)L(' —pL)j26

[(2rDcosa_,JL)1 27 L(r1uD + L cos a)]

2.8 27

LIST OF FIGURES

FIGURE NO TITLE PAGE

Figure 2.1 Ball Bearing Slides 6

Figure 2.2 Dovetail Slides 7

Figure 2.3 Machine Slides 8

Figure 2.4 Roller Slides 9

Figure 2.5 Roller Table 10

Figure 2.6 XY Table 11

Figure 2.7 Power Screw Thread Forms (Juvinall, Marshek, 2006) 13

Figure 2.8 Example of Ball Screw 13

Figure 2.9 ACME Screw 16

Figure 2.10 Jack Screw 17

Figure 2.11 Basic Configuration of Load-Raising Power Screw

(Collin, 2003) 25

Figure 2.12 The Efficiency of ACME Screw Threads When Collar

Friction Is Negligible (Juvinall, Marshek, 2006) 28

Figure 2.13 Friction Coefficient versus Speed According to Preload

(Lee et al, 2003) 30

Figure 2.14 Measurement of thermal Effect (Lee et al, 2003) 31

Figure 2.15 Thermal Displacement of the Slide Guide versus Time

(Lee et al, 2003) 31

Figure 2.16 Temperature of the slide guide versus running time

(Lee et a!, 2003) 32

xlii

xiv

Figure 2.17 Thermal deformation of the table and slide guide

(Lee et al, 2003) 33

Figure 3.1 Flowchart of overall methodology 37

Figure 3.2 CNC Milling Machine 39

Figure 3.3 Horizontal Bandsaw 42

Figure 3.4 Pillar Drill 43

Figure 3.5 Lathe Machine 44

Figure 4.1 Three Axis Mechanism Model 53

Figure 4.2 Table Structure with Bracket 54

Figure 4.3 Nodal Displacement of Extrude Aluminum Bar in Z-axis 55

Figure 4.4 Axial Stress of Extrude Aluminum Bar in Z-axis 56

Figure 4.5 Reduction Gear Setting 57

Figure 4.6 Coupling Setting 58

Figure 4.7 Ball Screw Horizontal Setting 58

Figure 4.8 Simple Linear Load Setting 59

Figure 4.9 Linear Motion External Force Factor Setting For Both 59

Figure 4.10 Velocity Pattern of MotOr 60

Figure 4.11 Selection of Motor 60

Figure 4.12 Reduction Gear Setting 61

Figure 4.13 Coupling Setting 62

Figure 4.14 Ball Screw Horizontal Setting 62

Figure 4.15 Simple Linear Load Setting 63

Figure 4.16 Linear Motion External Force Factor Setting For Both 63

Figure 4.17 Velocity Pattern of Motor 64

Figure 4.18 Selection of Motor 64

LIST OF APPENDICES

APPENDIX TITLE

PAGE

A Data analysis for table structure extrude 71

Aluminum bar

B Drawing of three axis mechanism parts 76

C HAAS (-'NC milling machine language 83

D Final Product 94

CHAPTER 1

INTRODUCTION

1.1 Project Objective

(a) Design and fabricate the three axis mechanism of incremental forming rig test by

applying personal computer numerical control.

(b) Analyzing the three axis mechanism structure.

1.2 Project Scopes

The scopes of the project are cover from

(a) data collecting for the conceptual design such as linear motion guide

(b) geometry measurement of the components of the three axis mechanism

machine such as AC servo motor and ball screw

(c) design the algorithm by using Solid Work and Computer Aid Manufacturing

(CAM)

(d) analysis the velocity, life of the linear guide motion and ball screw by

numerical method

(e) result validation while performing the project test running

1.3 Project Background

Nowadays, three axis mechanism machine has been widely use in this

world. A lot of applications are using this mechanism and make the engineering

process easier and efficiencies. Machine such as lathe, turning, milling and grinding

are using this mechanism by applying automatic control system and applied

engineering devices with some sensors.

The introduction of three axis mechanism machine has changed the

manufacturing industry by increasing the automation of manufacturing process

which the improvements in consistency and quality has been achieved. In addition,

these machines are more flexibility in time to produce different components.

Incremental forming, which is a variety of forming processes

characterized by the fact that the product is not formed as a whole, but that at any

time only a small part is actually being deformed. For special interest is called

incremental sheet forming (1SF) of which several varieties exist, that are carried out

by moving a steel punch or roller by a CNC-machine over a metal sheet.

The principal directions in forming are an orthogonal set of directions in

the material that remain orthogonal in the forming Operation. The strains in these

principal directions are called principal strains. This may seem academically to

many readers but it is of importance when one wants to carry out a more

fundamental analysis of the process, specially if this is related to material behaviour.

3

1.4 Problem Statement

Problem statement of the project:

(a) High demand for more and more complex products to be forming.

(b) Cost of making the tool is high; therefore, the cost of the products will be

higher also.

(c) Incremental forming also applies high vibration force and pressure to the

tool platform of three axis mechanism machine.

CHAPTER 2

LITERATURE REVIEW

2.1 Components

In order to fabricate a three axis mechanism machine for incremental

forming rig test, there is a need to determine which the components have to utilized

so that it can perform smoothly and efficiency.

2.1.1 Linear Slides

Linear slides is a precision products designed to control the physical

movement of a manufacturing robot or an intermediate product under assembly. It

can turn motion or torque into thrust. The actual directions and commands for the

product positioning come from a computer that effectively controls the entire

manufacturing process. Application of the linear slides is to move mounted

mechanisms across a given axis either in one direction or combine of three or more

directions. Complete linear slides normally consist of at least a base, a saddle,

adjusting screws and a straight gib. Linear slides are resistant to contamination,

extremely durable in shock load conditions and run smoothly on lightweight frames.

5

By using linear slides,

(a) Products that having a wide range of weights, from lightweight miniatures

to payloads of several hundred pounds can be move easily.

(b) Products can be move in distances that range from as little as 2.5

millimeters to 1.5 meters.

(c) Rapidly position their loads.

(d) They position their loads so precisely, that the final positioning can be

measured in microns (millionths of a meter).

There are two principle types of linear slides:

(i) Ball bearing auto-slide (the most common variety)

(ii) Auto-slide uses crossed rollers.

Linear slides assemblies use non-recirculating precision balls and rollers that

move against highly polished and hardened rod ways, greatly reducing friction.

For immense loads and safe operation, dovetail linear slides will be appropriate.

Ball bearing slides would be an appropriate choice if a self-lubricating slide with a

smaller maximum load carrying capacity is required.

Industries that require linear slides for high levels of precision in their

manufacturing:

(a) Industrial robots and machine tool assembly

(b) Fiber optics and photonics component building

(c) Manufacturing semiconductor and electronic equipment

(d) Medical equipment manufacture

2.1.1.1 Ball Bearing Slides (Ball Slides)

Most commons type of linear slides due to their self-lubricating qualities,

which increase their reliability. Ball bearing slides are composed of two rows of

balls on both sides of the base, the rows being contained by four rods. Functions of

two rows of balls are to eliminate play and roil along the rods to create smooth,

accurate, and low-friction motion. Thus, it can perform with a smooth linear motion;

typically use four hardened and ground shafts that surround the balls at four different

points.

The base length, base height, carriage length, carriage width, and top height

are important specification to choose a particular ball slides. Larger slides can

handle bigger loads, but the slide has to be able to fit into the housing or drive

system. Ball bearing slides mostly use for delicate instrumentation, high-cycle

applications, and clean room environments.

Figure 2.1: Ball Bearing Slides

7

2.1.1.2 Dovetail Slides

Dovetail slides are used in high load applications that require long travel

distances and/or damping. Dovetail slides consist of a saddle or flaring tenon and a

fixed base.

Dovetail slides represent the simplest type of linear translation stages. They

have relatively high stiffness and load capacity, and they can provide long travel.

Dovetail slides are more resistant to shock than other bearings, and they are mostly

immune to contamination.

Compare to ball bearing slides, dovetail slides have direct contact between

the base and saddle. Because of this fact, a greater force is necessary to move the

saddle and thus slowing acceleration rates. The amount of surface contact allows

dovetail slides to be used in heavy load applications and various industrial uses.

However, dovetail slides should not be used for high precision applications.

The dynamic load carrying ability, the number Of inches per revolution of the

screw (in dovetail slides with Acme, ball, or lead screws), maximum linear velocity

of the carriage required, and the rate and distance of linear movement are an

important specification when choosing a particular dovetail slide.

Figure 2.2: Dovetail Slides

8

2.1.1.3 Machine Slides

Machine slides are a type of linear slide that are used on various machines

mostly in CNC machining. They are precision-designed to have close tracking

tolerances. By using machine slides, high rigidity can be retained, which creates

accurate linear motion for all applications. For machine slides, its have an adjustable

gibs in order to make up for any irregular movements that may develop throughout

an application.

Machine slides can be single, double, or multi-axis, depending on their

intended use. Mostly machine slides will conjunction with ball screws, lead screws,

air cylinders, or hydraulic cylinders. Some of the standard types of machine slides

include dovetail slides, hardened way slides, linear guide slides, and more.

Dovetail machine slides are used when occasional movement is needed in a

positioning application for manual or powered movement. Hardened way machine

slides are used in production for high-usage and heavy loads with little required

maintenance for years. Of all machine slides, linear guide machine slides hold the

highest load capacities for their size and have the lowest amount of friction.

Figure 2.3: Machine Slides

2.1.1.4 Roller Slides

Roller slides, or crossed roller slides have a simple construction, which use

perpendicular rollers with a stationary base and moving carriage with higher load

capacity than ball bearing. Its utilize rollers that crisscross each other at a 900 angle

and move between the four semi-flat and parallel rods that surround the rollers. The

rollers are between "V" grooved bearing races, one being on the top carriage and the

other on the base. The design of crossed roller slides allows them to carry up to

twice the load of ball bearing slides and to absorb larger impacts or stackable to

create multi-axis linear motion. In addition, roller slides are very versatile, as they

can be adjusted for different uses.

Figure 2.4: Roller Slides

2.1.1.5 Roller Tables

Roller tables are the quietest type of bearing table and made up of a front

sliding surface and rear sliding surface that are longitudinally aligned. For secure to

rear supporting group, lifting levers are pivoted on a bearing bar. The levers have

feeler pins engaged in sliding manners along guiding grooves, which are shaped so

that when the front and rear supporting groups are moved away from each other, the

10

rollers are lifted one by one and led to the level of the front and rear sliding surfaces.

This allows the roller table to support a product between the spaced sliding surfaces

while it is working.

Roller tables are the quietest type due to the containing linear bearings that

provide the least mechanical noise of any bearing table. By using the cylindrical

rollers and rods rather than balls, roller tables can handle twice the load capacity as

ball bearing tables. Industries such as building assembly, inspection, dispensing,

pick and place, milling, drilling, material handling, and industrial automation

equipment are using roller tables.

Many roller tables are also adjustable to fit different applications and have

the ability to be assembled into multi-axis systems. Benefits of using roller tables:-

(a) Low cost

(b) high accuracy

(c) high load capacity

(d) resistance to corrosion

Fi2ure 2.5: Roller Table

ii

2.1.1.6 XYTabIe

XY tables are composed of forcers and platens that usually contain motor

mounting plates, couplings, lead screws, and a large base and top plate. The forcer

glides over the platen on frictionless air bearings and moves continuously in a linear

motion across the platen. It is because of linear motoring modules, typically between

two and four, responding to currents.

Variations among XY tables include the ways and the drive mechanism.

While the drive mechanisms determine smoothness and speed, the ways determine

load capacity, straight-line accuracy, and stiffness. Other factors imperative to XY

tables are the accuracy, repeatability, and resolution required, as well as the

appropriate motor for the application and whether or not an encoder is needed.

XY tables are most often mounted horizontally. Mostly used in applications

such as water jet cutting, milling, and table sawing. XY tables may also be used in

microelectronics assembly, laser machining and factory automation but depending

on the specifications.

Figure 2.6: XY Table

12

2.1.2 Bail Screw

Ball screws are used in the conversion of rotary movement to linear

movement, which translates torque into thrust. Assemblies of ball screw consists a

screw and a nut. In order to produce a rolling friction between the nut and screw, a

steel ball is encased within the round nut. The nut itself can be made of either plastic

or metal. The ball screw assembly is powered by a motor. While the motor generates

torque, the rotating screw pushes the nut along the screw shaft and producing linear

thrust. Figure 2.7 illustrates most of the standard thread forms used for ball screws.

There are a few variations of ball screws available for use in industrial

settings. The most common are ACME, Lead and Ground ball screws. Each of them

differ in size and efficiency output on application.

(a) Lead screws do not actually use rollers to create movement but are placed in the

same category as ball screws due to their similar function and capacities.

(b) ACME screws most widely used power screw and are a type of lead screw

which creates friction btween ball and nut.

Industries that utilize ball screw in product application including aerospace,

computer, electronic, automotive, and medical industries. Most of its used in

medical equipment, material handling equipment, conveyors and machine tools,

among many other product applications.

The most common use for ball screws is in aspects where linear motion is

needed. They are often used alongside linear slides and linear actuators to create

movement necessary to move parts and devices along a single axis. Ball screws

remain beneficial for a variety of reasons. For example:-

(i) Ball screw assemblies maintain high levels of efficiency, measuring