Preliminary Design Proposal for the Design and … · Web viewFinal Design Report for the Automatic Dental Bur Loading Device Project 99.06 Design Team Members: Jason Dickey [email protected]

Final Design Report for the Automatic Dental Bur Loading Device

Project 99.06

Design Team Members:

Jason Dickey [email protected] (302) 368-4509 11 Lincoln Dr., Newark, DE 19711Greg Frantz [email protected] (302) 837-8147 102 Squire Hall, Newark, DE 19717Allison Martin [email protected] (302) 737-1252 385 S. College Ave., Newark, DE 19711Nancy Meyer [email protected] (302) 837-1321 214 Pencader G, Newark, DE 19717

Sponsor:David Berezowski

Dentsply/CaulkL.D. Caulk Division38 W. Clarke Ave.

P.O. Box 359Milford, DE 19963-0359

(302) 422-4511Dave_Berezowski/[email protected]

NCDADental Products Development Group

mailto:[email protected]




Executive Summary

Our sponsor, L.D. Caulk, is looking for a cost effective way to automate the loading

process of dental burs, which is currently done manually. Our top customer wants consist of

minimizing the final cost of the loader, simplicity of the loader, and the consistency of the

loader. While designing the loader there are several constraints we need to follow. The final

prototype must be under budget, the quality of burs produced must not decrease, and the cycle

time must not increase. There are basically only two system benchmarks for our project. These

are of the Yamaha automatic bur loader and humans, which is currently used. The Yamaha is

not a valid solution for Caulk because it is unreliable and is over budget.

We began brainstorming concepts and developed twelve ideas that did not seem to

violate any constraints and satisfied the customer wants. We were able to throw out four of the

designs immediately because of space constraints, the position of the grinder, and the

impossibility of rear loading. This left us with eight concepts that we compared to our metrics.

After finishing SSD, we were left with our top three designs including a linear screw driven, a

linear piston driven, and a swing arm design. Since the ranking on SSD was close we decided to

split our concepts into six specific functions. After we compared our functions and defined our

three concepts, we compared them against our benchmarks to find our best concept. This turned

out to be the swing arm because of its simplicity due to its one-degree of freedom, its low cost,

consistency of loading the bur, and its percentage of parts from standard vendors.

In conclusion, the prototype proved the feasibly of our design. Almost every customer

want was successfully meet. The prototype and per unit budget, load time, and operator steps

metrics all were well below their target values. The only metric not meet was the percentage of

incorrect loads. With the enclosed proposed design revisions, this value should be easily meet.

Introduction

Our sponsor, L.D. Caulk, has come to Team06 of New Castle Design Associates

(NCDA) Dental Products Development Group (DPDG) with a senior design project in attempt to

reduce manufacturing costs of dental burs. They are looking to cost effectively automate the

loading process, which is currently done manually, for the final fluting of the dental bur. L.D.

Caulk currently has 27 bur grinding machines and feels that automation of the loading and

unloading stages of their dental bur grinding machines is a possible way of cutting

manufacturing costs.

Project Definition

The goal of this project is to automate the load-unload process for the final fluting

process in the manufacturing of the dental bur. The loading and unloading process is repetitive

and relatively simple and therefore lends itself easily to automation. The grinding process begins

by taking the unfinished bur and manually loading it into the grinder by hand. The operator must

place the bur into the collet, tighten the collet, and raise a rest for the bur to be supported on

while grinding. Once the automated grinding cycle begins, the operator is able to load another

machine. At the completion of the automated grinding cycle, the grinder stops, and the operator

can release the support and collet. The finished bur can then be removed from the grinder and

another one loaded.

By automating the machines, the only interactions between the machine and the operators

will be loading a quantity of the blank burs, removing the finished burs from a storage container,

and monitoring the machines. Caulk expects that the labor force can be reduced from three

people per shift to one. Running two shifts per day, this comes out to a reduction of four

operators per day. This reduction in labor cost is the benefit that L.D. Caulk desires. While

there are numerous wants and constraints, L.D. Caulk’s main goal is overall cost savings.

Mission

We have developed a mission statement to describe our project and the goals we plan to

achieve. Our mission statement is as follows:

“To develop a cost effective dental bur automatic loading and unloading device, while

fulfilling as many of the customer and team wants as possible, within the specified time

and budget constraints.”

We plan to remain within the prototyping budget, while delivering a consistently working

prototype to L.D. Caulk before the end of the 1999 spring semester.

Customer -- Wants and Constraints

We have done an in-depth search of customers and their wants. A full listing of our

findings is included in Appendix 1. For our customer selection process, we looked at who would

benefit from the automation of the bur grinders and the associated cost savings. At the top of our

list is L.D. Caulk, our sponsor, who came to us with the idea that automation will save them

money. We also considered the people who would want to assure that the machines met all

applicable codes. The recipient of the dental bur is also an important customer. Dentists are the

representative customers for users of the burs. Since the automatic loader will be specific to the

machine as well as designed only for a very small range of use, the customers were limited here.

Other companies could benefit from an automatic loader; however, the costs associated with

fitting such a dedicated piece of equipment to another process would be too high. The summary

of our top customers wants can be seen in Figure 1 – Top 10 Customer Wants below.

Final

Ranking

Want Description Rate of

Importance

Performance

Goal

1 Minimize Final Per Unit Cost of Upgrading to

Automatic Loaders

18.12 5

2 Simplicity of Automatic Grinder Operation for Operator 14.02 3

3 Consistency of Automated Bur Unloading/Loading

Operation

11.33 5

4 Easy to Diagnose and Repair Problems 11.00 4

5 Minimize Unscheduled Down Time 9.39 3

6 Comply with regulations 8.95 3

7 Reduce Bur Production Cost 7.77 5

8 Complete Required Documentation 7.55 5

9 Match Dentsply/Caulk Engineering Philosophy 6.47 2

10 Decrease Bur Unload/Load Cycle Time 5.39 1

Figure 1: Top 10 Customer Wants

Our top ten wants were determined by calculating a rate of importance. This number was

computed by first multiplying the rank of the customer and the weight of the want. These were

summed for the number of times the want appeared in the customer data and wants as shown in

Appendix 1. The weight of the want decreased from 0.45 for the first want to 0.05 for the fifth

want of each customer. After this number was determined for each want, it was divided by the

total to get the rank of importance in terms of a percentage. This process is shown in Figure 2 –

Ranking of Wants.

Figure 2 – Ranking of Wants

L.D. Caulk has requested that a documentation package be included with the prototype.

This is listed as a want under complete documentation. For the final delivered prototype,

training aides will be required for operators of the grinders. Standard operating procedures

(SOPs) will also be required for the prototype, included in Appendix 4. The final piece of

written material will be a preventative maintenance program, included in Appendix 5. This

program should coincide with the preventative maintenance schedule of the grinder. In addition

to the above documentation, all technical material including fabrication information, assembly

drawings, and component lists will be included. The component list should include model

numbers, prices, etc. for each piece of equipment in the automatic loader, Appendix 3.

Besides the customer wants, there are also constraints that effect the project. The

constraints on the project are listed below.

Must be under budget

Quality of burs produced must not decrease

Cycle time must not increase

Must have operational interlock

Must perform design and equipment validation

Voltage and air pressure requirements

Must be able to load all 4 bur families

The constraints for our project came from our sponsors at L.D. Caulk. For our automatic

loader to be economical in terms of replacing the current operators, it must be under budget. To

be effective, the cycle time can not exceed thirteen seconds, which is the average time it takes

the operator to load and unload the bur. The sponsors want operational interlocks in order to

assure each step is complete before the next step is initiated. The voltage requirement is 240 3-

phase and the air pressure requirement is 80 psi, which is currently installed on the machine. In

order to install the automatic loader on all twenty-seven loaders at Caulk, it must be able to load

all four bur families.

Benchmarking

System benchmarking is limited but each individual function can be benchmarked. Our

system benchmarks include the manual loading of the machine, as it is now, and the Yamaha

automatic loader (Dentsply previous attempt to automate the loading/unloading process). The

Yamaha is a benchmark, but is not a serious competitor because it does not measure well

compared to the metrics. It is too costly to implement the machine on all the loaders, the

percentage of incorrect loads is high, and the cycles between failure is low. The Yamaha is very

costly and unreliable.

The best system benchmark that has target values that we can aim for and try to beat is

the manual loading. The manual loading of the machine is our main competitor, because it is

people that Caulk is trying to replace. If our machine is not as good as if not better than humans

are prototype is not worth implementing on all 27 machines. It is from the current operators that

we derived our target values.

We looked at several different functional benchmarks for the various functions. The

different ways of performing these functions are discussed in the concept selection section.

Metrics

From our customer’s wants we contrived related metrics. We used SSD to compare the

correlation between our wants and metrics. From this comparison we narrowed the list of metric

to eleven. The chart below, Figure 3, shows the correlation between the wants and metrics and

the associated target values. Following the chart is an explanation of how the target values were

derived.

Top Ten Wants Associated Metrics Metric Target Value

Minimize Final Per Unit Cost of Upgrading to Automatic Loaders

(1)Design Cost (2)Initial Per Unit Cost and Setup

$25,000 $8,000

Simplicity of Automated Grinder Operation for Operator

(3)Number of Steps Needed By Operator 7

Consistency of Automated Bur Unloading / Loading Operation

(4)Percentage of Incorrect Loads (11)(# of interlocks)/(# of positions)

0.02% (~1 per shift) 1/1

Easy to Adjust, Diagnose and Repair Problems

(5)Number of Status Indicators (6)Contains Documentation/Drawings (7)% of parts from Standard Vendors or made In-House

Equal to Number of Interlocks Yes

100%

Minimize Unscheduled Down Time (8)Cycles Between Failure (6)Contains Documentation/Drawings (11)(# of interlocks)/(# of positions)

250,000 Yes 1/1

Comply With Regulations (9)Noise Level (6)Contains Documentation/Drawings

80 dB Yes

Reduce Bur Production Cost (3)Number of Steps Required By Operator 7

Complete Required Documentation

(6)Contains Documentation/Drawings Yes

Match Denstply / Caulk Engineering Philosophy

(7)% of parts from Standard Vendors or made In-House

100%

Decrease Bur Unloading / Loading Cycle Time

(10)Unload / Load Cycle Time (11)(# of interlocks)/(# of positions)

13 seconds 1/1

Figure 3 – Top Ten Wants

$10,000

$8,000

The metrics are a way of measuring the customers’ wants. Associated with the metrics

are target values in order to see if the wants and metrics are achieved. The design cost metric is

a way to measure the monies spent on the initial design and prototyping. The associated target

value arise from the fact that the customer usually estimates that design and prototyping for them

is usually just over three times the final per unit cost. For this project this value represents the

maxim that that can be spent.

The initial per cost and setup metric is a way to measure the monies spent on the cost of

fabrication and installation of the final design on all twenty seven bur grinders. The target value

of $8,000 was given to us by our sponsor and represents the number that makes replacing the

human operator with an automatic loader.

The number of steps needed by the operator metric is a way of measuring the simplicity

of routine operation of the machine. The metric is the number of different steps the operator has

to do to make one bur. The target value is the current best from the benchmarks. Our project is

to decrease the number of steps needed per bur. We hope to improve this value by reducing it to

one.

The percentage of incorrect loads metric is a way of measuring the consistency of the

loading and unloading operation. The target value is from the current best benchmark which is

manual loading. It is estimated that there is currently one misload per shift.

The number of status indicators metrics is a way of measuring the ease to adjust,

diagnose, and repair problems. It is hoped that with more visual feedback, an operator will

quickly locate problems and broken parts. This is important since the operation will be

controlled by a PLC and problems may not be readily apparent. The target value is that the

number of indicators will equal the number of interlocks. Therefore, the PLC runs through the

program and the completion of each step can be seen with a visual feedback.

The ‘contains documentation/drawings’ metric is a way to measure the quantity of

documentation during prototyping and finished documents after. It is hoped that better

documentation would help make diagnosing and repairing problems easier. Better documentation

will also help our sponsor meet ISO certification. Our target value is to completely satisfy all

our sponsors wants in the way of documentation. The current list of wanted documentation is

standard operating procedures, preventive maintenance plan, technical drawings, component list,

and a complete wiring diagram.

The (# of interlocks)/(# of positions) metric is a way of measuring the amount of

feedback the PLC is receiving and can then be outputted to a display. This extra data can help

prevent unscheduled downtime, by monitoring of wear on the machinery, and increase the

load/unload cycle time. The target value is to have one interlock for every position that the

machinery goes through.

The noise level metric is a way to measure the increase in the generated sound by the

machinery before and after installation of an automatic loader. The target value is set at 80dB

which is an OSHA standard. The shop floor is currently over the 80dB limit.

The % of parts from standard vendors or made in-house metric is a way of measuring the

ease of repairing a problem and the time it would take to fix a problem. Since the sponsor wants

to minimize down time and repair, being able to quickly make a part or ordering it from our

customers standard vendors is important. This would also match Denstply/Caulk engineering

philosophy in that all parts should be able to be made in house or order quickly from a standard

vendor. Thus, the target value is for the machinery to be 100% made or ordered by Caulks’

vendors.

The cycles between failure metric is a way to measure the chance of an unscheduled

down time. The target value represents the number of cycles in a two-year period. This also

represents the time of at least two maintenance cycles.

The unload/ load cycle time metric is a way of measuring the time it takes to replace a

finished bur in the collet with a blank bur. The current best benchmark is thirteen seconds, which

is the average time for an operator to load and unload a bur. This time must be met or broken in

order for automation to be competitive with a human.

Concept Generation

The following sections will take us down the path to final concept generation. The next

section will start us on our path with brainstorming system concepts.

1) Linear Screw Drive

This unit mounts on the side of the head of the bur grinder. At the start, the screw drive is

retracted towards the back of the collet. Here, parallel grippers are used to pick up the bur from

a tray. By way of a screw drive, the grippers move forward, parallel to the head unit. At a given

point, the grippers rotate 180 degrees where the bur is in line with the opening of the collet. The

screw drive then moves back along the head unit, loading the bur into the collet and a pancake

cylinder will be used to fasten the bur in the collet. To avoid any contact with the grippers, an air

cylinder will be used to lower and raise the steady rest, replacing the existing cam. Once the bur

is in place, the grippers open and return to the start position to clear the bur grinding area.

2) Swing Arm

This loader is mounted on the side of the head unit. The loading arm begins parallel to the

head unit, facing away from the collet. Angular grippers will be used to grab the bur from a

stationary tray. An air cylinder is used to lower the steady rest about an inch in order for the

grippers and arm to clear it. The arm is attached to a bearing and swings 180 degrees to the front

of the head. While the grippers are stationary, the collet opens by the force of a pancake

cylinder. As the collet opens, it moves forward and extends over the bur sitting in the grippers.

The grippers open and the air cylinder is again activated to pull the collet back, fastening the bur

into the collet. To clear the bur grinding area, the grippers are returned to their starting position.

3) Rear Load Push Rod

From a magazine, a bur is loaded through the back of the collet. A piston, driven by an air

cylinder is used to drive the bur through the head. A front stop will be used to hold the bur in

place while the collet is tightened on the bur. The grinding process will then begin.

4) Rear Load Chain Driven

A bur is fed into the back of the collet, where two parallel chains pinch the bur and move it

into the head. The chain drives the bur all the way through the head and then through a reduction

in the distance between the chains, the bur is held while grinding. The position of the bur and

the loading and unloading process is done through the control of the chains.

5) Top Loader

Another idea is to mount the grippers and arm to the top of the head unit. This way, the

burs could be fed into a tray where a swing arm could flip 180 degrees and pick up the bur.

Once the grippers grab the bur, it swings 180 degrees toward the front of the head, loading the

bur in one continuous motion. The grinding process will begin once the collet and steady rest are

tightened and raised.

6) Conveyor Belt

This is a front loading idea in which the bur will be loaded into the collet by the use of a

conveyor belt. The belt will be attached to the bottom base of the grinder. The conveyor belt

will have a groove down the center in which the bur will sit. Back stops and front guides will

hold the bur while it is led into the open collet. The steady rest will have to be lowered quite a

bit in order for the belt to clear it. After the bur is loaded and fastened, the conveyor belt will be

retracted away from the collet. The steady rest will be raised and the collet will be fastened by

an air cylinder and the grinding process will start.

7) Linear Piston

This device will be attached to the side of the head unit. A linear piston with guides for

precision begins retracted where a bur is picked up with parallel grippers, which are facing away

from the head. The piston extends to a point such that the grippers and bar will clear the head

and collet. Next, a rotary actuator rotates the gripper 180 degrees, aligning the bur with the

collet. The piston retracts, facing the bur into the collet (opened by another actuator). The collet

closes, the grippers release and rotate 180 degrees out of the way. The linear piston then retracts

to clear the grinding area completely.

8) Eliminate Head Unit—Grippers Only

This concept requires the redesigning of the entire unit. The existing head unit and collet

will be eliminated and replaced by grippers. These will hold the bur in place during the grinding

process. The grippers will still be attached to the indexer in order for the bur to be rotated in the

correct grinding positions.

9) Robotic Arm

The robotic arm will be attached to the base of the grinder. The arm will be extremely

advanced and precise in that it can pick up the bur from a tray and place it into the collet in one

continuous motion. Air cylinders would be used to raise and lower the steady rest and to open

and close the collet.

10) Four-Bar Mechanism

With a four bar mechanism, the transfer of the bur from a bur magazine to the collet will be

done with a four bar linkage mechanism with a dwell. It will be mounted to the base and be

setup for each bur family. The mechanism and the collet will be controlled with pneumatic

cylinders. This would pick up the bur and move the bur in an arc to the front of the collet. Once

the bur is in the collet, the dwell would allow the bur to move straight back.

11) Replace Steady Rest with Grippers

Currently, there is a steady rest that is used after the bur is loaded and tightened into the

collet. The steady rest is used to hold the bur in place during the grinding process. We proposed

that the steady rest and collet could be replaced by a set of grippers which would load the bur

and hold the bur during the grinding process.

12) Monkey

This option represents a method that is non-mechanical. It is feasible because it has been

shown in the past the monkeys can be trained to perform repetitive tasks. In addition, it is viable

because it does not violate any of our wants or constraints. The monkey will sit on a platform

above the head unit of the bur grinder. It will be responsible for grabbing a bur, loading it into

the collet, tightening the collet, raising the steady rest, and pressing a start button to begin the

grinding process.

Narrowing Concepts

Since our brainstorming was done before receiving the bur grinder head, four of our

concepts were immediately eliminated. Because of the logistics of the bur grinder, we were not

able to receive the entire machine. Instead, we were given the critical unit of the machine, the

head, which we did not receive until the middle of November. After becoming more familiar

with the head unit we found that one of our concepts failed a constraint. The concept that failed

was a rear loading push rod because it could not accommodate all four families. The fourth bur

family could not fit through the collet. The rear load chain driven system was impossible

because the chains interfered with the rotation of the bur in the grinding process. After driving to

Caulk a second time we were able to eliminate two more concepts. The top loader would be an

impossible design because during the grinding process the top of the head unit becomes almost

flush with the grinder wheel casing. After looking at the space between the grinding wheel and

the head unit we realized that there was not enough room for the expected size of the conveyor

belt.

Of the remaining eight concepts we used SSD to compare the concepts to the metrics in

Figure 4: For the ranking: 1=best and 8=worst

Figure 4: Concept Comparison

From the chart, three concepts scored well below the others. These included the linear screw

drive, the linear piston drive, and the swing arm. The three concepts scored fairly even against

the metrics. All three of these concepts are mounted to the head unit. The mounting position is

important because one of the problems with the Yamaha loader is that it is mounted to more than

one frame of reference. The frame of reference determines the ease with which the loader can be

Figure 4 Initial Concepts

adjusted. If the loader is mounted to the head, it can also minimized unscheduled downtime the

simplicity of the loader.

To better compare the concepts we broke them down into their functions and compared

them. We broke our design into six comparable functions. First, the bur needs to be delivered to

the tray in order for the grippers to pick up the bur. Second, the collet needs to be released and

tightened. Third, the steady rest needs to be lowered and returned to its operating position.

Fourth, the bur needs to be loaded into the collet. Finally, the finished bur needs to be stored.

These functions must have a control/feedback system. With a control system we can reduce the

number of steps by the operator and the cycle time. In addition, it makes the loader easier to

adjust. Both of these points are reflected in our metrics.

Four of these functions could be interchangeable with any of the three concept ideas.

These included opening the collet, storage of the finished bur, grippers and the feedback/control

system. The last two functions, the lowering of the steady rest and the tray holding the uncut

bur, were dependent upon the concept. This will play part of the concept design later on.

The following paragraphs and charts compare the functions that were independent of the

concept to the metrics to develop the best solution.

Many types of grippers were investigated because they are a critical part of the design.

One type is pneumatic grippers which are used to precisely position and control the movement of

the bur. Pneumatic grippers are available in compact sizes that are ideal for our project.

Pneumatic grippers are able to open either parallel or angular. We also looked at ways of using

magnetic grippers to grip the shaft or vacuum grippers used to suction and hold the bur. The

consistency of loading is a major concern with using these types of grippers. The following

chart compares the different grippers against the metrics. It was shown from Figure 5 that the

pneumatic grippers would be the best choice.

Figure 5 -- Grippers

For the final storage of the bur, baskets were considered. The basket needs to be small

enough so that it is not in the way and large enough to hold many burs and not require exact

positioning of the grippers above the basket. Instead of using a basket, an indexed x-y tray could

be used. Different ways of indexing trays were studied. The above chart compares the possible

storage of the finished bur to the metrics. From the chart, the best choice would be a direct drop

into a basket as shown in Figure 6.

Figure 6 – Basket Storage

Once again, we compared our metrics to the opening of the collet. The collet holds the

bur during the grinding process. The way it holds the bur is identical to a chuck. The spring at

the back of the is under pulling collet back into the head. This forces the collet to grip the bur.

When a compressive force is applied to the spring, it causes the collet to move away from the

head and release its grip on the bur. Currently the spring is being compress by a manual screw

press system. To automate the compression of the spring, we have looked several different

systems including; air cylinders mount in different positions, electro-server, and electro-magnet

Figure 7 – Opening of the Collet

From figure 7, the easiest way to open the collet would be an air cylinder to compress the

spring. Comparing it to the metrics it was the cheapest, easiest to design, with one of the lowest

load/unload cycle times, and the air cylinder would be a standard vendor part.

This leads us to our last independent function which is the feedback/control system. For

automation of the bur grinder we need a system to control the entire process. This could be done

through several different methods that we found, such as PLCs, LabView , or other computer

software such as Machine Vision.

Figure 8 – Feedback/Control System

When finding information on PLCs we found that PLCs can control everything that we

need to have controlled. Also for ease of programming and implementation it was determined

that if PLCs were used the PLC should be the same type as already used by Caulk. Instead of

using, PLCs LabVIEW could be used but this becomes very expensive because of all the

components that need to be bought. Machine Vision is used as a method of location sensing, but

this too becomes expensive. For the feedback/control system the PLC appears to be the best

choice, as demonstrated in Figure 8. The design cost and the initial cost is low do to the fact that

they are currently using PLCs.

In all three cases a bur will be delivered to the loading tray similar to current one on the

Yamaha loader. After talking to the customer and comparing it to the metrics this method is

cheap, reliable and simple. We performed an experiment to compare different types of flexible

tubing to deliver the bur to the tray. We found that ordinary flexible PVC tubing had a high

coefficient of friction and burs become stuck inside the tube. Stiffer, but flexible nylon tubing

allows the burs to slide through the tube without binding.

For the first design, the linear screw drive, has two degrees of freedom. To transfer the

bur from the tray to the collet a linear and rotational movement is required. The loading tray will

have an opening in the middle where the grippers will reach in from the top and grab the bur.

The tray will have to be on a linear system, moving in the z-direction (a possible third degree of

alignment needed) so the grippers can clear the tray on the return. There will be linear motion to

the front of the head and then rotational movement is needed in order to get the bur lined up with

the collet.

The swing arm uses a simple beam which is attached to the side of the head by a pivot.

This design has only one degree of freedom because the radial swing of the arm is all that is

needed to get the bur from the tray to the collet opening. Unlike the linear designs, this concept

takes advantage of the movement of the collet to place the bur in the opening. The linear designs

add another degree of freedom by not utilizing the motion of the collet. The bur is lifted into

grippers on the swing arm by the motion of the tray. At the middle of the tray a square notch will

be removed so that the grippers can pass by the side of the tray. Angular grippers will be used in

this design in order to clear the tray on the return.

The linear piston will have three degrees of freedom. For this design the tray will be

completely stationary. Because the grippers can move in three directions, there is no need for the

tray to move. This is beneficial in that the steady rest will not have to be redesigned. In the

other two concepts, the steady rest needs to be redesigned to allow for a greater space and range

of motion. Unlike the screw driven device, this concept moves in a completely linear manner.

We have now discussed the functions of motions for the three designs, and compared the

concepts for the different interchangeable functions. At this point, we are ready to compare our

three concepts to our benchmarks using the metrics. Figure 9 was derived from SSD.

Figure 9 -- SSD

As it turns out, the swing arm design clearly beats out the benchmarks and the two other

competing designs. Of the mechanical devices, the swing arm is the cheapest to develop because

of its simplicity. In addition, it is also the cheapest to build and setup on the per unit basis

because of the simplicity and the percentage of standard vendor parts. Because the design only

requires one degree of freedom, we found it the easiest to come back to the same point every

time. We demonstrated this by a single beam attached to the head unit and compared it to a x-y

slider.

The lowest ranking of the Yamaha with the metrics seems to correlate with the current

situation. Currently, the amount of work put in to the Yamaha is greater than the amount of

work that is being saved. Because it is attached to the base of the grinder, it consistently has

problems with the alignment, which can take weeks to fix. The Yamaha also costs forty-

thousand dollars which is much greater than the budget available to Caulk. This design is a

prototype and came with incomplete technical drawings which is basically useless.

Working Model

After SSD was completed, we were left with our three top concepts. The feasibility of

the three models were proven with working models and simulation of the individual system

functions. First, the idea of flexible tubing for the delivery of the bur to the tray was tested.

After examining several styles of tubing, we found that burs were able to slide through the tubing

at minimum angles and the help of gravity. Although possible, we learned that there were

binding issues in the tube when multiple burs were used. Therefore, a two stage bur release

system would need to be implemented. Another critical function included the ability of the collet

to extend and grab the bur from the grippers. To ensure only one degree of freedom, the collet

needed to extend without the movement of the grippers back to the collet. This process was

demonstrated by the use of pliers, acting as grippers. The collet would extend, grabbing the bur,

and then retract while the grippers remain stationary. This is shown in Figure 10 – collet

extension. This proved to be a valid option for loading the bur into the collet.

Figure 10 – Collet Extension

Fabrication

Caulk expressed an interest in manufacturing many of the parts. They wanted to

guarantee the part would be made correctly and they could determine early on the ease and

feasibility of making the part. Since one of Caulks’ top wants was the percentage of in-house

parts be close to one-hundred percent, it was determined that materials readily available to them

would be used in machining the parts. For this reason, all but two parts were made from a hot or

cold-rolled carbon steel. The grippers, due to potential wear, were made from a hardened tool

Step 1 of Collet Load Step 2 of Collet Load

steel. The copper tubing in the bur release was chosen because it was readily available. This

tubing is in a high-wear position because of the carbide bur tip. However, it is in position with

plastic tubing that will wear as well, so it can all be replaced more frequently then other parts in

the system. The blue tubing worked well because it was flexible and maintained its shape. The

clear tubing was stiff, and was well chosen to hold the burs. Both of these tubings were readily

available to Caulk.

Assembly

The assembly can be broken into four separate units. First is the Bur Release Assembly.

The base (NCDA 24) is bolted to the support bracket extending from the grinder. Next, the

cylinders for the bur release (already modified as per NCDA 26) are bolted to the bur release

cylinder support. This assembly is then bolted to the bur release base, with the cylinders

extending into the large holes on the top of the bur release base. Take a short one-inch piece of

1/8” hard plastic tubing and insert it into the copper tubing (NCDA 27) so that it rests between

the holes drilled in it. Next, the copper tubing is inserted into the bur release base and secured

with the set screw so that the cylinders line up with the holes in the bur release. Next, the plastic

sleeve (NCDA 28) is pressed onto the lower end of the copper tubing and the other end of the

sleeve is connected to the blue metric tubing. The air fittings and flow controls can be mounted

to the air cylinders at this time, as can the magnetic reed switches for position sensing. The other

end of the flexible blue tubing will be connected to the tray in a later step.

The steady rest is the next portion of assembly. The steady rest middle mount (NCDA

18) and the steady rest cylinder support (NCDA 17) are mounted to the steady rest that has been

modified as per NCDA 16. The air cylinder is then attached to the cylinder mount using the

clevis bracket and to the steady rest middle mount using the rod pivot. The air fittings and hall

effect switches can then be mounted to the cylinder.

The third assembly portion is for modifications to the draw bar and indexer. The draw

bar is modified as per NCDA 08. The indexer / collet assembly is reassembled and the manual

collet extension is replaced with NCDA 06, supported by the tubes in NCDA 07.

The main unit is the final assembly step. First, the rotary cylinder (modified as per

NCDA 22) is mounted to the main support using the spacer (NCDA 23). Next the main support

is mounted to the head as per the modifications in NCDA 01 to the main head. Next, the U-

Bracket (NCDA 05) is mounted to the head as well as through the spacer (NCDA 04) to the

collet cylinder support bracket (NCDA 03). The other end of the support bracket is mounted to

the main support through an adjustable bracket (NCDA 02). The collet extension cylinder is

then mounted to the support and the fittings and hall effect switches attached. Next, the tray

cylinder is mounted to the 45 degree bracket which is attached to the Y-adjustment bracket

(NCDA 11). This bracket is attached to the middle tray bracket (NCDA 12) which is, in turn,

attached to the X-adjustment bracket (NCDA 13). Finally, the X-adjustment bracket is attached

to the elbow bracket (NCDA 14), and that is attached to the Z-adjustment bracket (NCDA 15).

This bracket is then attached to the main support bracket. Next, the tray (NCDA 09) is mounted

to the tray cylinder, as are the fittings, flow controls, and the hall effect switches. The tray cover

(NCDA 10) is attached to the tray, as is the flexible blue tubing. Now, the top and bottom

fingers (NCDA 19 & 20) are attached to the grippers, which is then attached to the swing arm

(NCDA 21). The swing arm is then mounted to the rotary air cylinder installed in the first step

of this paragraph.

Testing and Results

For a detailed test plan see Appendix 6. Below is a summary of the test plan followed.

Functional Testing

Each component of the system was tested individually to make sure that it functioned

properly.

The first component that we tested was the PLC logic. In order to test the PLC, we

checked to make sure that the sensors and air cylinders were hooked up correctly. We also

checked to make sure that the PLC still operated the grinder correctly.

The first function that we tested was the grippers. They were tested to insure that they

were able to hold the bur properly. We also made sure that the grippers meet correctly. Next we

checked the collet extension and retraction. This allowed the collet to move out far enough to

pick up the bur. At this time we also checked to make sure that the steady rest moved far enough

out of the way.

After we were satisfied with the collet and steady rest performance, we began our testing

of the tray. We tested to make sure that the bur fit into the tray, the tray could move to the

desired positions, and the grippers could pick up the bur from the tray. This is when we tested

the swing arm cylinder to insure that it had the stated range of motion.

The final function that we tested was the bur release mechanism. We tested to make sure

that the bur was not being damaged by the air cylinders. We also checked to make sure only one

bur was released at a time and burs could not be released when the cylinder was blocking the

passage. We also tested the bur release mechanism with several different types of tubing to

insure that binding of the burs in the tube would not occur.

As a result of this testing slight modifications were made and these changes are discussed

in the redesign and modifications section of the report. After each function was tested

individually the functions were integrated together and tested.

Function Integration

Before the system testing could occur, several of the functions needed to be integrated

together. The grippers had to be aligned with the collet, this process is described in the SOP.

The grippers also had to be aligned with the tray. This procedure is also in the SOP. During

this function integration the PLC delays were optimized.

System Testing

Once the functions were integrated together, the system testing could begin. The system

testing was used to obtain values to compare to our metrics and target values. After over 200

system tests adjustments were made and a few parts were redesigned. Testing was again run to

make sure that everything still worked and to get the updated target values.

During at run the cycle time was recorded. This time was averaged after every 20 tests

and these averages were averaged to obtain the final cycle time. The number of steps required to

start the cycle was also measured each time.

Each time the tests were run we checked to see if the bur loaded correctly. If it did not

load correctly, we checked to see where the error occurred and adjustments were made. We used

the number of incorrect loads to determine the percentage of incorrect loads.

Results

From our testing the following results were obtained. They are summarized in Figure 11

below.

Metric Target Value Actual ValuePrototype Cost <$10,000 $6,500Per Unit Cost <$8,000 $6,500

Number of Steps by the Operator

<7 2

Percentage of Incorrect Loads

<0.5% <4%

Ratio of Interlocks to Positions

=1/1 1/1

Number of Status Indicators

# of Indicators 1, 47

Completeness of Documentation

=100% 85%

Number of Cycles Between Failure

>250,000 TBD

Noise Level <80 dB <65 dB% of Standard or In-House Parts

=100% 99%

Unload/Load Cycle Time <13 seconds <6 seconds

Figure 11: Test Results

The prototype cost was determined from an ordered parts cost of $3,500 plus an

estimated cost of labor by Caulk to make the parts. It was estimated that Caulk spend about 100

hours working on our parts. This brings the total prototype cost to $6,500.

Currently the per unit cost is the same as the prototype cost, because the cost of assembly

will offset the cost of the purchased parts that are not being used.

In order to start the grinder the operator needs to load the bur feed tube and press the start

button twice. These steps are only to start the machine. Once the machine starts the machine

will continue to run as long as it still has burs.

The percentage of incorrect loads was measured to be 5%. Several modifications were

made to the bur release mechanism and the tray in order to decrease this percentage even further.

More tests need to be run but the percent of incorrect loads is currently about 4%.

There is an operational interlock for each step in the process. This is to insure that the

next step in the loading process will not occur until the previous step is complete.

On the machine there is one status indicator, the big red light, showing that the machine

is operational. On each of the Hall Effect Sensors there is an indicator showing if the switch is

triggered or not. There are two sensors on each air cylinder to allow the exact state of the air

cylinder to be verified. These indicators are used to aid in troubleshooting when something goes

wrong. This brings the total number if status indicators to 47.

Our complete documentation consists of the standard operation procedure, the

preventative maintenance plan, the technical drawings, wiring diagrams, and the PLC operating

guide. These are in Appendixes 4, 5, 7, 8, and 9, respectively.

The number of cycles between failure is going to be determined by Caulk when they run

it for 6-8 months as part of their prototype testing procedure.

We measured the noise level of our loader and it raised the sound level by less than 5 dB.

Most of the parts were either made by Caulk or bought from their vendor. The only part

that wasn’t was the shock that is being used for damping. We did not have time to try and

purchase this part through their vendor. This could be replaced with a shock that their vendor

could supply.

We were able to greatly reduce the cycle time. We were able to reduce the cycle time to

6 seconds. This is faster than it takes a human operator to unload and load the bur once he

arrives at the machine.

Re-Design/Suggested Modifications

There were several modifications, which became apparent during testing, that needed to

be made in order for the final prototype to work. The first change was the main support bracket.

After the bracket was attached to the head unit, the grippers were not aligned with the tray. The

branch of the support bracket for the bur holding tray needed to be cut and reattached with three

steel links which allowed for alignment in the x, y, and z-directions.

The air cylinder that controlled the motion of the steady rest was too long to allow motion

of the head for all four of the bur families. The cylinder would dip into the coolant and possibly

hit the coolant collection tray. To remedy this, the cylinder was replaced with a cylinder of equal

bore and stroke, but a shorter length. The mounting bracket was then altered for the shorter

length and wider width of the new cylinder.

The two cylinders that controlled the release of the burs were two small to contain a

magnet in the piston for magnetic position sensing. For this reason, larger air cylinders were

needed for the two-stage bur release. However, these cylinders needed to be modified by

grinding the tips of the threaded rods down to allow them to fit in the bur release tubing. This

was easily accomplished and enabled magnetic position sensing on the bur release.

After the grippers were aligned with the collet and tray, the motion of the rotary arm was

introduced. The velocity of the swing arm was too high and the rotary cylinder was unable to

dampen the downward swing of the arm. For this reason, we attached a shock absorber from the

support bracket to the swing arm. This was an effective method to control the deceleration of the

arm at the ends of the stroke. By selecting a shock absorber with the correct extended to

compressed length, the shock was able to be mounted on the centerline of the rotary cylinder,

enabling it to work effectively in both the clockwise and counterclockwise directions.

After the support bracket was mounted and the tray was aligned, we activated the

pancake cylinder on the back of the support bracket, that moves the collet forward and back.

Because of the force of the cylinder, it caused a high degree of flexion in the support bracket.

For this reason, a second bracket was designed to mount the free side of the support bracket to

the head unit. This reduced the flexion in the bracket and we were able to get full extension from

the collet.

Once we determined the full extension of the collet, and aligned the grippers, we realized

there was not enough extension in the collet to grab the bur. Therefore, the collet was put on the

lathe to reduce the shaft diameter in two places. This allowed the collet to extend from the

original 0.25 inches to the 0.375 inches needed to grab the bur from the grippers and ensure

seating against the positive stop.

Initially, the flexible tubing into the tray was fed through the two-stage bur release. After

several successful runs of the automatic loader, the bur release became very unreliable. The

tubing began to deform from the compression due to the air cylinders, preventing the release of

the burs. Therefore, the flexible tubing was replaced with brass tubing in the bur release system

and connected to the flexible tubing at the bottom of the release with a plastic sleeve.

Our main problem was the delivery of the bur into the tray. The bur would line up

correctly only about a third of the time. Mostly, the bur would be stuck in the slot of the tray or

would bounce out of the tray completely. To solve this problem, we first attached a piece of

sheet metal from the support bracket that plugged the groove of the tray in the lower position. In

order for the tray to clear the metal in its upward stroke, the bottom of the tray was cut out with

an endmill. This greatly improved the accuracy of the bur into the tray. Since the delivery of the

bur was not a hundred percent, adjustments still had to be made. A new piece was designed,

again using sheet metal attached to the support bracket, which rather than being flat had sides

which were contour to the tray. This was a highly effective correction for the bur delivery to the

tray. To solve the problem of the bur bouncing out of the tray, a piece of sheet metal was

designed to cover the tray. The metal would be placed on the top of the tray with a groove,

identical to the tray, for the grippers to clear.

Conclusions

The prototype that we developed is very good when compared to our metrics. We were

able to produce the prototype far under the given budget. The per unit cost is also over $1,500

below the desired cost given to us by Caulk. We were able to reduce the number of steps

required by the operator to two in order to start the machine. We were able to greatly reduce the

unload load cycle time. The six seconds that our prototype takes to unload and load the bur is

less than half the time it previously took. While this is a lower level want, the automated cycle

now occurs quicker than the manual cycle can. For the percentage of incorrect loads, we have

found a design that should reduce that number but currently more testing needs to be performed

to determine the exact number.

This project proved to be a very good learning tool as well. Along the way to meeting

our customer wants, much was learned about industry and industrial equipment as well as

teamwork. Everyone from Caulk was extremely helpful in making sure that all needs were met

in a timely fashion. In return for their help, they will receive a design that exceeds all of their

wants and target values by the time of delivery.

Appendix 1: Customers and their Wants

Appendix 2: Budget

Appendix 3: Bill of Materials

Appendix 4: Standard Operating Procedures

Appendix 5: Preventative Maintenance Plan

Appendix 6: Test Plan

Appendix 7: Technical Drawings

Appendix 8: Wiring Diagrams

Appendix 9: PLC Technical Manual

Appendix 1

Project Title: Automatic LoaderMission “To develop a cost effective dental bur automatic loading and unloading device, while fulfilling as

Statement: many of the customer and team wants as possible, within the specified time and budget constraints.”

Customer Information Want Information

Name & 10 0.45 0.25 0.15 0.1 0.05Title Organization Rank 1st Want 2nd Want 3rd Want 4th Want 5th Want

Dave Berezowski - Bur Area Manager

Dentsply/Caulk 10


Decrease Bur Unloadin / Loading Cycle Time

Easy to Diagnose and Repair Problems


Reduce Bur Production Cost

Dave Berezowski - Bur Area Manager

Dentsply/Caulk 9

Consistancy of Automated Bur Unloading / Loading Operation

Minimize Unscheduled Down Time


Comply With Regulations


Gene Anthony - Machine Repairman

Dentsply/Caulk 8Easy to Diagnose and Repair Problems


Consistancy of Automated Bur Unloading / Loading Operation



Kevin Barkley - Bur Area Operator

Dentsply/Caulk 7



Remain w/in Footprint of Machine


Dave Brown - Manager

Dentsply/Caulk 7


Reduce Bur Production Cost



Brian Huntington - Safety & HAZMAT Officer

Dentsply/Caulk, Osha

5 Comply With Regulations

James Agnew - ISO Auditor

ISO 9000 4 Complete Required Documentation

Comply With Regulations

Brian Melonakis - General Manager

Dentsply/Caulk 3 Reduce Bur Production Cost


Dr. Donald Bond - Dentist

Private Practice 3 Continue Using Same Type of Bur

Cost Effective to Dispose of After

One UseConstant Quality

Sustained Sharpness Maximize Profits

Customer Data and Wants Formulation

Appendix 2

Budget

Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $3,500

Caulk Shop Time:

100 hours @ 30 $/hour . . . . . . . . . . . . . . . $3,000

Our Shop Time:

100 hours @ 0 $/hour . . . . . . . . . . . . . . . . $0

Engineering Hours:

1600 hours @ 0 $/hour . . . . . . . . . . . . . . . $0

-------------------------

Total Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . $6,500

Appendix 3

Appendix 4

Standard Operating Procedures

Start Up Procedure

At the start of the shift, the bur feed tube needs to be filled with burs. The burs are to be

placed rear first into the tube. Next the bur tray, fingers, and the collet need to be inspected to be

free of dirt and grease. If the machine has been shut off, the initial cycle needs to be run in

manual mode. Upon completion of the first cycle, loader should be switched to automatic mode.

The system should immediately begin a load/unload cycle. A bur may not appear in the tray in

the first few load/unload cycles. This due to the fact it takes one to two cycles for a bur to work

it’s way through the bur advance. The first time the automatic load/unload cycle runs the

operator should watch the loading cycle to insure that the loader loads correctly. Pay attention

that the grippers do not open before clearing the tray as the arm goes to unload the collet. Also,

look at the alignment of the grippers with the collet.

Running Procedure

When the system is running in automatic load/unload mode, only periodic filling of the

feed tube and emptying of the finished bur basket is needed.

Shut Down Procedure

Under normal operating conditions, it is best to stop the machine at the end of the

grinding cycle. In an emergency, the machine can be stopped at any place in the cycle. Note the

program running the machine will restart in the same place it was stopped. Once the machine has

stopped, the power may be shut-off. Turning off the air pressure is not recommended.

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Connecting and Disconnecting Air Pressure

Before attaching air pressure to the system, turn the regulator supplying the automatic

loader to zero PSI. Check to make sure that all pneumatic cylinders are in their home position

and the power is off. Next plug the airline in and slowly increase the air pressure to 78 PSI.

When shutting off the air pressure a similar process is followed. First power down the machine.

Then slowly decrease the air pressure using the regulator supplying the automatic loader to zero

PSI and then disconnect the airline.

If Something Goes Wrong

1) If the grippers are not aligned with the collet:

a) First the machine needs to be set to manual mode

b) Adjust the back most set screw on the swing arm air cylinder until the centerline of a bur

in the grippers aligns with the centerline of the collet

c) Solenoid number 3 needs to be fired and held in order to align the grippers and the collet

d) While solenoid 3 is still held the collet release switch needs to be switched

i) If the collet picks up the bur:

(1) Retract the collet, release solenoid 3, fire solenoid 3, extend collet

(2) If the collet picks up the bur the collet and grippers are now aligned

ii) If the collet does not pick up the bur return to step (b)

2) If the grippers are not aligned with the tray, but are aligned with the collet:

a) The machine should be set in manual mode to make this adjustment

b) Adjust the front most set screw on the swing arm air cylinder until the grippers are able to

pick up a bur without hitting the tray

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c) Solenoid number 7 needs to be fired to move the tray into the upper position

3) If the collet is not extending far enough to pick up the bur:

a) The machine needs to be set in manual mode

b) Solenoid 3 needs to be fired and held and a bur needs to be in the grippers

c) The collet release switch needs to be switched and the distance that the collet needs to be

moved forward needs to be measured

d) The collet release switch is switched so that the collet is now retracted

e) The set screws on the bracket holding the collet cylinder are used to adjust the position

f) The air cylinder needs to be moved forward by the distance measured in step (c)

g) Once the set screws are tightened down the collet needs to be extended to insure that the

collet is correctly picking up the bur

When Changing Between Bur Families

The loader needs to be realigned when the bur family is changed. The position of the tray

can be adjusted in the x, y, and z directions with a series of set screws. The only time that these

screws should have to be adjusted is when changing bur families. The correct sized bur feed tube

needs to be install in the bur advance.

Appendix 5

PREVENTATIVE MAINTENANCE PLAN

Daily

Clean tray

Clean rotary cylinder

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Clean grippers

Oil the shock

Check if the grippers are aligned with the collet and tray

Monitor the set screw in the collet

Check for correct pressure

Monthly

Check wear on the grippers

Check wear on the tray

Check wear on the tubing from the bur release to the tray

Check wear on the tubing that holds the burs

Check the copper tubing in the bur release for wear

Check the magnetic reed switches

Every Two Years

Replace the air cylinders

Appendix 6

Automatic Dental Bur Loader Test Plan

NCDA Team 06Jason Dickey

Page 51

Greg FrantzAllison MartinNancy Meyer

This document is a supplement to the two-page test sequence spreadsheet attached as the last two

pages. The first spreadsheet test page is the sheet to record data for items to be completed before

system testing begins and can be found as Figure 3. The second spreadsheet test sheet is a

checklist to be used during system testing to identify problems and see how the metrics that were

not compared in the pre system test compare to the target vales. This spreadsheet is Figure 4.

This document explains what must be accomplished for each test that is required. It also tells

how to integrate the functional tests into the system tests. Included at the end is a schedule for

testing and fabrication, if necessary, that includes all items to be completed before delivery of the

automatic loader to Caulk.

The spreadsheet checklists are easily followed when used in conjunction with this document.

This document explains what is required by each of the tests before it is considered complete.

The column headings of the spreadsheet list the test or trial number, and this document lists the

required number of good, consecutive trials. For the pre system checklist (Figure 3), each row

requires it’s own set of functional tests. The sheet should be completed in the order shown on

both the sheet and in this document. The system test checklist (Figure 4) has each column filled

out for each test, and this document explains what is required for each test to be passing. Again,

it also tells the number of good, consecutive tests required. As more sheets will probably be

needed than are included, photocopies can be made of the test spreadsheets.

The test plan for the prototype will be broken down into initial fit & assembly, functional testing,

and system testing. The tests will be performed using all four required bur families. First, all the

parts will be assembled to ensure that general fit is accomplished. For the initial fit portion of

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testing it will be verified that all parts have the proper general alignment. It will be verified that

all bolt holes line up properly. Each part will also be moved to ensure that there is no

interference between any parts of the automatic loader assembly. All wiring will be checked for

continuity using a multimeter and for correctness. All air connections will be checked for

correctness as well. Initial fit & assembly will be completed by 3 March 1999, assuming power

is received for the grinder so the head can be mounted to the base and the unit rewired.

Next, the functional tests will be performed. These individual tests will be performed to test the

alignment of the function and repeatability of the functions operation. These functional tests will

be performed a minimum of five (5) times. However, five (5) consecutive good tests must be

performed before the test is considered complete. The functional testing will be completed by 2

April 1999. This is the most difficult portion so the most time must be given to the functions

testing.

Functions will then added together until the whole system can be tested, again for alignment and

repeatability. Then system testing will be performed to compare the results to our metrics. With

the data collected, alterations to timing will be made to increase the efficiency and decrease the

load time of the burs. These tests will be performed repeatedly, simulating a typical operating

day. System testing will be given until 11 April 1999. This is a little more than one week worth

of testing. Since functional integration will already have occurred, this last week of testing

should flow smoothly. If not, there is a week of cushion uncase a problem should arise.

Items that are not part of the grinder, but part of the project, such as those considered parts of

complete documentation, will be completed jointly with the assembly and testing of the grinder.

A documentation package for review will be delivered to Caulk by 12 April 1999. A final report

draft will be delivered on 22 April 1999.

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Functional Testing

As stated in the introduction, the first testing will be of individual functions. The order of testing

of the functions will be as follows:

PLC Logic – Does activation of each sensor cause the desired result as an output from the PLC?

Does the PLC properly control the indexing and grinder operation that was added when the

mechanical counter was eliminated? Does the PLC respond properly to user inputs from the

switch panel (Does the manual mode work as expected?)? Each switch will be manually

activated to verify that the correct solenoid is triggered. We will also check the air cylinders

during this segment to make sure they work properly.

Collet Extension / Retraction – Does the collet fully retract when desired? Does the fully

extended collet extend out far enough to allow the bur to slide completely in?

Steady Rest Raising and Lowering – Does the steady rest lower far enough to allow the grippers

to clear? When raised, the force applied equivalent to that supplied by the original spring?

Tray Raising and Lowering – Does the tray raise and lower to the desired positions? When

lowered, is it out of the way of the grippers? When raised is the centerline of the ready bur in

line with the centerline of the grippers?

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Grippers – Do the grippers hold the bur with enough force to prevent the collet from shifting the

bur? Do the upper and lower gripper meet properly?

Gripper Alignment w/ Collet – When the grippers are closed and in the forward position, does

the centerline of the grippers match up with the centerline of the collet (Horizontal, vertical, and

angular alignment is critical.)?

Gripper Alignment w/ Tray – When the tray is raised and the grippers are in the back position,

does the centerline of the grippers match up with the centerline of the bur in the tray (Horizontal,

vertical, and angular alignment is critical.)?

Rotary Cylinder Range of Motion – Is the range of motion acceptable? Does the cylinder stop

with the gripper centerline lined up with the collet in the forward position and the bur ready in

the tray in the back position (Horizontal, vertical, and angular alignment is critical.)?

Bur Ready Mechanism – Does the upper cylinder compress but not damage the pressed bur.

Does the lower cylinder close far enough to stop the lower bur from passing by? Do burs pass

freely when the cylinders are open, or is there any binding in the setup? When a bur is released,

does it properly land in the bur ready tray or does it get stuck or bounce out (Position of the bur

ready tray is critical.)?

For each of the above functions, alignment will consist of fitting and measuring the difference

between where a piece is located and where it needs to be. Corrections will then be made to the

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loader and the drawings adjusted accordingly. During each of the above stages, the sensors will

also be mounted as needed to the cylinders. This way, they can be set to trigger when needed.

Figure 2 is a list of sensors and which cylinder they belong with. When each function is adjusted

to where it needs to be, integration to a complete system should be fairly easy.

Function Integration

Once all of the individual functions are tested, we will combine the functions together

step by step to test the whole system. We will integrate the required functions step by step, in

the order of occurrence, until all of the steps are completed. The next step will not be added to

the system until all of the previous steps occur correctly. Each step is being added one at a time

in order to make any adjustments that are needed. The system will be tested after the addition of

each step a minimum of five (5) times assuming that there is not a problem with any function

involved in the current test.

The order of addition will be as follows. First, the grippers will be integrated with the

rotary cylinder and will rotate from the front position to the back position on the rotary cylinder.

After this works, the tray will be added to ensure that the alignment is good between the grippers

and they can consistently land in the same locations. Once this works, the steady rest will be

added, ensuring it clears the grippers each time. With this much of the system working, the

collet extension can be added and a bur can be placed in the grippers to see if it aligns properly in

both the front and back positions of the grippers. Finally, in terms of mechanical components,

the bur release mechanism can be added to the system. To top of the whole thing, the PLC will

be powered up to test the entire operation under the control of the PLC. The sensors will be

attached to the proper cylinders, etc. and their adjustments fine-tuned (see Figure 2). This will

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allow the PLC to trigger the proper step at the correct time in the sequence. This will test the

functionality of all the sensors in connection with the operating automatic loader. A spreadsheet

of the sensors and what triggers them is located at the end of this documentation.

To finish off the pre system testing and functional integration, some of the metrics can be

evaluated before system testing begins. A list of metrics, target values and test values can be

found as Figure 1. Complete documentation is not something that can be checked with a test, but

we will send our documentation to Caulk with enough time for them to make revisions and

inform us if they need more details. The percent of parts from standard vendors and in house

will be determined separate of testing. At this time all of the parts are from Caulk’s vendors or

made by Caulk. The prototype and per unit cost will be determined once the redesign is

complete. The ratio of interlocks to positions and the number of status indicators will also be

determined before final system testing. Noise level testing can be done at any point in testing,

since we are only concerned with the loader part of the grinder.

System Testing

Once it is determined that all of the functions operate correctly together, the system will

be tested and the results will be compared with the metrics listed at the end of this document.

The system testing will be run for a minimum of fifty (50) tests. However, adjustment will be

made whenever there is an incorrect load and the tests restarted until fifty (50) good cycles are

completed of the automatic load / unload process. After these fifty (50) good tests occur, it will

be marked that the adjustment is correct and the dimensions of the loader are in good tolerance.

With the working loader, a system test will begin, running a minimum of ten (10) tests to check

the functionality of the entire grinding cycle, since it too is PLC controlled. Once it runs through

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ten (10) consecutive tests with no errors, the system is considered good and the repeatability

testing will begin. It will be set to grind and load for a simulated workday. Any fine-tuning will

occur at this stage until it can load for a workday within the percentage of incorrect loads given

by the metrics. This value, along with all the values for the other metrics can be recorded in

Figure1 for comparison.

During each test the cycle time will be recorded for the load / unload operation. This time will

be averaged for all of the tests after the final redesign. The number of steps required by the

operator will be recorded for each trial. This number will be the same unless something goes

wrong in the cycle. To determine the percentage of incorrect loads we will take the number of

incorrect loads and divide by the total runs. A minimum of 200 tests need to be run to determine

if the percentage of incorrect loads. This will easily be reached in the workday simulation. As a

part of determining if the bur is loaded correctly we will check several things during the initial

system testing. We will make sure the:

steady rest moves out of the way and returns

grippers open, close and can sense a bur

rotary arm moves to the required positions

bur release mechanism operates correctly

tray moves correctly

collet grabs and releases bur

Recording these six items for each trial is a way to locate and fix problem spots in the loader.

The system will also be checked to make sure nothing broke during the tests.

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Appendix 7

Technical Drawings

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2.0

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0.38

0.98

0.38

0.64

0.61

0.21

0.40

0.88

0.130.520.19

0.28

0.250.25

0.25

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1.10

1.10

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Appendix 8

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Appendix 9

PLC Technical Manual

Introduction

Welcome to the wonderful world of trying to control the automatic bur loader through

ladder logic. The purpose of this manual is help in the understanding of the code used to control

the automatic bur loader, so that changes to the operation of loader can be quick and simple. This

will be done by going into detail about the different steps and motions the loader goes through,

and lastly the meanings and recommendations for the constants used in the timers and counters.

This manual assumes that the reader understands and is familiar ladder logic, the LSS software

by Omron, Inc. and the C40K PLC. If the reader is not familiar with anything listed above the

reference section has some suggested reading.

Quick FAQ

How do you change the number of steps in the cutting process?

On line 12 of the code the counter prox switch is connected to a counter call CNT 000.

This counter is what determines the number of cuts a bur receives during grinding process. The

motors will run as long as the CNT 000 is false. Note: When in automatic mode, the PLC has to

tell the motors to run between load cycles in order for the program to function correctly. This is

because the code depends on the motor running input (IR 00206) to reset some of the keep

states. Therefore, the counter must always be set to one or higher.

Loader operation and steps

To understand the code a good understanding the operation of the loader is needed first.

The operation of the grinder is broken down into three modes, grinding the bur mode, manual

load mode, and automatic load mode. In order to prevent the code from seeing the two loading

modes jumps statements where used to single out each section. The bur grinding mode code is

present at all times and relies on variables in keep states to know when to run. For safety, an

interlock is attached to the stop button. When the interlock is triggered, it causes all code

between the interlock rungs to be ignored and all outputs to be turned off. This means that all

motors are stopped and all pistons return to their home position. Note: This doesn’t cause any

variables to be reset just temporally turn off the outputs.

Automatic Load Mode

The automatic load mode is design so that it completely independent of a user and that

the only choice the operator has is, on or off. Listed below are all the mechanical steps the

system has to go through. Due to inaccuracy of the proximity switches, delays are needed to

insure that machine is in the position that the prox switches say it is in. They are not included in

the list below because, they add complexity and hinder the understanding of the code. One note

of caution. The swing arm cannot leave or return to the home (Clock –wise) position with the

grippers open, because the fingers will jam into the tray (even in the down position) and cause

the alignment to go off.

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Step 0

Bur advance starts ( should finish before tray raises in step 2)

Steady rest is lowered

The swing arm is rotated counter-clock wise and before reaching the final location the

gripper opens

Collet is extended (open)

Step 1

Grippers are closed

Collet retracted

Arm rotated clock-wise

Step 2

Grippers open

Tray raises

Step 3

Grippers Close

Tray is lowered

Arm rotates counter-clock wise

Step 4

Collet extend

Grippers open

Clear the Bur Done Variable

Signal new bur Loaded.

Bur Advance

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Lower bur cylinder opens and closes

Upper bur cylinder opens and closes

Delay while new bur slides down tube to tray.

Variables, Counters, and Timers

Listed below are explanation of the most important counters and timers. Then followed by a

complete listing of all variables, timers and counters.

CNT 000 - On line 12 of the code the counter prox switch is connected to a counter call

CNT 000. This counter is what determines the number of cuts a bur receives during

grinding. The motors will run as long as the CNT 000 is false. Note: When in automatic

mode, the PLC has to tell the motors to run between load cycles in order for the program to

function correctly. This is because the code depends on the motor running input (IR 00206)

to reset some the keep states. Therefore, the counter must be set to one or higher.

TIM 001 - Used in the manual load mode to give a delay between sending the collet home

and turning on the grinding process. Currently set at two seconds (4/25/99).

TIM 002 – Used in automatic mode to give a delay to allow the bur time to slide past the

lower cylinder. Upon completion, the lower cylinder is closed and the upper cylinder is

opened. Currently set at two seconds (4/25/99).

TIM 101 – Used in the automatic mode to allow for the time it takes the bur to slide from the

bur advance to the tray. Currently set at two seconds (4/25/99)

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Code

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References

WWW.PLCS.NET - An excellent source for understanding Ladder Logic and how to program

in ladder logic.

Ladder Support Software Operation Manual by Omron, Inc. Just about everything you want to

know about the software, but nothing about what ladder logic is.

C20K, C28K, C40K, C60K Installation Guide by Omron, Inc. Just about everything you wanted

to know about the physical attributes of the PLC. Also there is an appendix listing the ladder

logic commands available for the PLC.

WWW.RITEAID.COM – An excellent source for aspirin and earplugs. The LSS software will

try to drive you insane. The use of the above products helps to keep your sanity.

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http://WWW.RITEAID.COM/

http://WWW.PLCS.NET/

Documents

Preliminary Design Proposal for the Design and … · Web viewFinal Design Report for the Automatic Dental Bur Loading Device Project 99.06 Design Team Members: Jason Dickey [email protected]