Phase Four Final Report

Transcription

1 Team Delaware Diamond Knives Phase Four Final Report University of Delaware Daniel Ruhlman, Greg Specht, Winston Arnold, Pete Trainer, Nick Damiani 12/12/2009

2 Table of Contents Phase 4 Executive Summary Page 3 Fixture Design Page 4 Proof of Concept Model Page5 Testing Page 7 Areas of Improvement Page 8 Commercial Application Page 8 Path Forward Page 9 Proof of Concept to Mass Production Page 10 Appendix Page 11 2

3 Executive Summary Phase 4 Through an iterative design process, an automated diamond grinding fixture was developed with the intent of increasing process accuracy and repeatability while reducing the need for operator attention and skill level. A proof of concept model was created in order to test the validity of the design. Ideal testing could not be completed due to the absence of a critical control system component that was ordered over 5 weeks in advance. The proof of concept model was tested manually, with an operator acting as a temporary control system. Initial testing revealed some desired changes in the final design, but also indicated that the design is functional and, with some minor adjustments, is capable of improving the overall diamond grinding process.the proof of concept model is an example of a single fixture in a larger overall process. The final design would include six fixtures per table, increasing production capability by 50% while still reducing operator attention time. Many of the final parameters could not be fully tested, but the theory of the design, overall functionality and benefits to the sponsor could be witnessed through only preliminary testing. 3

4 Fixture Design Phase 4 The design process was conducted in a manner that focused on meeting customer wants and metrics while striving to reduce costs and improve the overall process. The first step in the design process was determining customer wants and the metrics involved in the diamond grinding process. Each want and metric was based off of communication with the sponsor and comparison to benchmarked values and the current system. The current system uses a fixture originally designed for precious gem polishing and moves in an orientation that does not maintain the constant parallel position of the diamond to the lap wheel and thus requires frequent operator attention. Minimal defects, repeatability and ease of use were the top three wants for the design while the top three metrics include thickness measurements, leveling accuracy and operator attention time. The final design can be seen below with key components labeled (figure 1). Motor Mount Motor Pin Linear Encoder Linear Stage Tilt Stage Rotation Stage Upper Force Mount Lower Force Mount Shank Holder Linkages Stand Shank Base Slide Lap Wheel Figure 1: Final Design 4

5 The theoretical design was completed on the computer before implementation. Once a computer model was created using the specifications for purchased parts and parts manufactured by the team, the proof of concept model was constructed. The pictures below (figure 2) show the realization of the final design into a proof of concept model. Phase 4 Figure 2: Computer Model and Proof of Concept Proof of Concept Model The proof of concept was assembled using a number of purchased parts as well as manufactured parts. A full parts list can be found in the appendix. The exploded view below (figure 3) gives a general idea of the process used to assemble the proof of concept model. Figure 3: Exploded View 5

6 Phase 4 The intended operation of the proof of concept model is to have an automated design in which an operator can set a desired diamond thickness and desired force to be applied and then allow the process to finish automatically. The automated process uses inputs from a force sensor and a linear encoder driving a linear stage. The flow chart in Appendix 1, outlines the coordinated functions of the force sensor and linear encoder as they work to complete the diamond grinding process. The model also incorporates lockable tilt and rotation stages that allow an operator to level a diamond with respect to a lap wheel and lock it in place. The leveling process is very important and the angles must be adjusted to assure that diamond thickness on one side of a diamond sample is similar to that of the opposite side. In general, the linear encoder is capable of sensing position and is programmed to move down until the first force is detected. Once a force is picked up by the force sensor, a zero position for the encoder is set. The encoder allows the diamond to press onto the lap wheel with a desired force until the specified final diamond thickness is reached. One a desired diamond thickness is reached, the encoder lifts the diamond from the lap wheel to prevent grinding a diamond too thin or beyond specification. As mentioned above, a flow chart describing this process can be found in Appendix 1. The photograph below (Figure 4) shows a completed version of the proof of concept model with a manual linear actuator in place of a linear encoder. Figure 4: Proof of Concept Model 6

7 Testing Phase 4 Due to complications with vendors, the control system for the fixture was unable to be completed (see Appendix 2: The Ealing Journey). Without the control system in effect, a series of tests were done manually using a slab of silicon. The silicon slab was used as an initial test because it is less expensive and softer then diamond. Therefore the silicon slab was less likely to damage a lap wheel or lose the company money in the case of failure. Using an operator in lieu of a control system, the exact control flow chart (shown in Appendix 1) was followed. Initial testing showed that all components in the system were fully functional. The tilt and rotation stages were used to level the shank, diamond and lap wheel. The diamond was manually lowered until it made initial contact with the lap wheel. This process was tested several times and the force sensor was able to detect initial contact and could thus set initial position. Once the diamond was brought into contact with the lap wheel, the force was increased to the desired amount in the experiment. A correlation between the force sensor output values and equivalent grams applied to the diamond can be seen in the table below (Figure 5). Figure 5: Force Sensor Output Vs. Gram Values Grams Number Grams Number Grams Number

8 Areas of Improvement Phase 4 The linear stage we chose exceeds the necessary travel distance. It is advisable for the company to save money they go with a 25 millimeter stage instead of the 50 millimeter stage. The system as a whole has too much movement especially in the force sensor. For the next one it would be advised to use a purchased force sensor instead of making one ourselves. This would also give us a more accurate force sensor. There appeared to be a problem with the motor during use. It started to heat up to temperatures that were hot to the touch. It would be advised to use a different motor for future use. Commercial Application The objective of the project was to provide some benefit to the company by designing a replacement fixture. The fixture that was designed, while having its own flaws, still has several advantages over the current fixture. Due to the design of the new fixture and how it can be set-up as a system on the lap wheel table, it will be possible to fit a total of six fixtures on the table (Figure 6). Currently, only four fixtures can fit on the table. With the new layout for the replacement fixtures, simply on the ratio of fixtures, there will be an increase in production rate by fifty percent. DDK can take advantage of this increased production rate in a few ways. First, they can keep the same number of lap wheel tables and still have an overall increase of production by fifty percent. The second option is to one remove one lap wheel table while maintaining the same production rate. Currently, there are four lap wheel tables with four fixtures on each, which means that sixteen diamonds can be grinded at once. By keeping the same number of tables, twentyfour diamonds can be grinded at a time. If one table is removed, the number of diamonds that can be grinded at one time with the new fixture and its set-up is the same as that of the current set-up and fixture. Thereby, the new production rate will either allow DDK to make more diamonds at once or free up more space on the production floor for other systems. Figure 6: Six Arms on Table 8

9 Phase 4 While it was not implemented in the Proof of Concept due to difficulties with a supplier, the fixture implemented by the sponsor would include a computer operated control system. The control system will reduce the amount of operator attention time. While the operator is still required to manually orient the diamond and shank through the tilt and rotation stages incorporated in the fixture, just as was required for the current fixture, the new fixture will not require the operator to periodically check the diamond. Two problems of the current system associated with checking the thickness of the diamond are that the diamond/shank must be removed from the fixture to measure the thickness, which requires its own break-down/set-up time, and depending upon when the diamond thickness is checked, it is possible for the diamond to be grinded too long and no longer be of a useful thickness. The control system will eliminate the need to remove the diamond/shank from the fixture to measure the thickness of the diamond and it will eliminate the possibility of removing too much material. The fixture will also be easier to use and understand than the current system because of automation. Orienting the diamond/shank will still be roughly the same, but afterwards, all the operator needs to do is enter the initial thickness and the desired thickness into the computer and it will grind the diamond down to the correct thickness. This, coupled with the reduced operator attention time, means that the operators will not need to be as skilled or need to devote as much time to the system while grinding the diamonds and thereby can focus on other tasks. Overall, the new fixture offers several benefits to the company that should improve their business. Path Forward When our group finishes with the sponsor the company will need to continue building 10-18fixtures. In order to complete this task they will need to do the following. The company must look at replacing parts that were purchased by Ealing Company, which were the linear stage, encoder driver, and PCI card. This is because Ealing continuously mailed us wrong and faulty parts, and no software to comply with the parts we order. This caused major setbacks in the completion of our projected and resulted in a delay of over three weeks. The parts that were ordered from Ealing may be directly order from Precision Microcontrol Corporations who Ealing is a distributor for. Our original choice to go with Ealing was because they offered a package deal reducing the price and simplifying the ordering process. Now that we know exactly what parts we need the price discount did not overcompensate the difficulty when dealing with the company. All production and assembly of machined parts was done at Delaware Diamond Knives facilities except welding. One of our group members completed the welding because Delaware Diamond Knives did not have the proper equipment to complete it. In order to fabricate these welded parts the company will need to find a proper facility to complete the welding. It will require a significant amount of time to complete the work which can be done by one of the employs. Unfortunately he is very busy with multiple things. We advise them to hire 1 or 2 people to complete the assembly of these arms. By following these suggestions, and the ones listed above in Areas of Improvement, Delaware Diamond Knives will be able to produce a fixture even better then our proof of concept fixture. 9

10 Phase 4 Proof of Concept to Increased Production This new grinding arm will replace 18 of the current fixtures within Delaware Diamond Knives. The new grinding arm is not going to be sold outside of the company so these fixtures are going to be all hand made within the company. This means that traditional mass production techniques will not be used. Instead there will only be slight adjustments made between our proof of concept fixture and the fixtures that will be used on the floor (as discussed in Areas of Improvement). As stated above in Path Forward Delaware Diamond Knives will have to talk directly with the manufacturer of the linear stage and all its components, Precision Microcontrol Corporations, to get new parts for the final fixtures. All of the steel parts for the stand will have to be outsourced to a fabrication company to be welded. The milled aluminum parts can easily be made inside of Delaware Diamond Knives because only 18 of these arms are being made and there are only three machined aluminum parts for each arm. 10

11 Appendix Phase 4 Appendix 1: Control Flow Chart 11

12 Phase 4 Appendix 2: The Ealing Journey After significant research, benchmarking and deliberation, the decision to use an Ealing encoder driver to provide motion to the automated grinding fixture was made. An encoder driver, linear stage, PCI board (for motion control), and a program similar to Labview was purchase from a California based optic company by the name of Ealing. Because this system was imperative to the control of the grinding fixture and process, it was among the first set of parts ordered. Unfortunately, three and a half weeks later it was the last to arrive. When the part first arrived, the linear stage was the only satisfactory component despite some damage to the surface of the stage. The linear encoder provided in the package was not the one that was ordered and was also not compatible with the correct linear stage. A mother board and daughter board came as expected, but there was no included software to be found. Our team contacted Ealing and ensured that new parts would be delivered quickly. A few days later, the correct encoder arrived along with a copy of the control software. Unfortunately, the copy of the software was out of date, and entirely dysfunctional. Once again, Ealing was contacted, and a new copy of the software was sent. This time, the software was correct enough to reveal another Ealing shortcoming. The new software was able to detect that the entire mother board and daughter board assembly used in the control system were faulty. Ealing was contacted again and another debacle ensued. The manufacturer of the circuit board, another California based company called PCI, was made aware of the situation, but required a minimum of one week to inspect the board for issues before issuing any returns or replacement parts. After a shipping mix up, Ealing finally decided to admit their poor business practices and send us a new board. Unfortunately this entire exchange took over a month and the final step leaves us in our current state. Because of the lack of a central control system, testing had to be completed by hand and the project will continue slightly past the due date. For the future implantation of a system of fixtures, the sponsor will be advised to use a different vendor. 12

13 Phase 4 Appendix 3: Wire Diagram Wire Diagram Force Sensor Voltage Divider Phidget Control Board The force sensor, used to sense the amount of force on the diamond, is connected directly to the Voltage Divider. The voltage divider senses force by calculating a voltage drop in the force The Phidget control board is connected to the voltage divider and to the computer. The control board is connected to the computer via a USB connection and provides an interface within the computer so that the force sensor information can be seen and used. Computer The computer is setup so that values can be input into a control system to provide the desired functions. The computer also uses a version of lab view to control the encoder driver with response to inputs from the force sensor. Encoder Driver and PCI board The linear encoder drives the linear stage. The PCI board is connected into the PCI slot of the computer. The board allows the linear stage to be controlled and the encoder provides the motion to the stage. 13

14 Phase 4 Appendix 4: Cost Analysis When deciding the parts for the arm we tried to obtain parts that fit the goals of the project while being as economical as possible. The maximum amount of money that was supplied to us by Delaware Diamond Knives for the project was $10,000. While our target value price was $5,000. Throughout contacting many companies for quotes and weighing our options the final price our arm is $4, This as you could see is as under our target value and sufficiently under our maximum value. When the finalized cost was presented to our sponsor they were accepting or our cost analysis. Part section Part name Part # Price Company Contact Info Load cell 6 port hub C-200-P1019 $97.15 Trossen Robotics Load cell Load cell S FSRKT5 $14.25 Trossen Robotics Motor stage Encoder Drive $1, Ealing Catalogs Motor stage Encoder controller card $1, Ealing Catalogs Motor stage Stage and motor $ Ealing Catalogs Linear Rail Linear rail 2HWE6 $ Grainger angle stage tilt stage 36 $ Newport bearings 2 bearings 60355K851 $5.78 McMaster-carr Geared motor motor $ Bison Gear engineering Machined parts $ Computer desktop Inspiron-546mt $ Dell Dell.com Monitor monitor HANNS.G HH-181APB $ newegg newegg.com $5, Price per arm for 6 arms around table $4,