R. L. Norton, 11/5/92

Assigned 11/6/92 ----- Due 11/20/92 (14 days!)

    It is well-known that for the best in abrasives one turns to Norton. A company by that name has requested that the Legitimate Engineering Group provide them with the design of a superior hand-held sanding/polishing machine to utilize their abrasive/polishing products.

    Many such devices exist on the market. Some have a simple pure-rotation motion which creates an undesireable pattern of rotary scratches on the affected surface. Others have an ineffective random vibration motion of very small amplitude. Still others have more complicated motions. What is desired in this product is a more sophisticated motion pattern which will provide a superior finish.

    It is also critical that this new machine provide smoother and quieter operation than any non-rotary devices now on the market. Most current non-rotary polishing machines deliver significant vibratory forces to the user's hands. The new design should minimize the effects of vibratory forces as felt by the user. In addition, it should require the smallest possible input torque (and thus power) from its electric motor.

    The ability of the human to accommodate forces delivered to the hands is documented in the human-factors literature. You can obtain some human factors information from the books on reserve for ME3311 in Gordon Library. Electric motor information is also on reserve.

    Your assignment is to design a sander/polisher mechanism based on the fourbar Grashof crank-rocker linkage which mechanism will provide suitable motions to the platen of the sander/polisher, and to arrange the shapes, sizes and materials of the parts such that the reaction forces applied to the user of the device are as small as possible. The driving-torque fluctuations are also of concern as they will rob energy from the drive mechanism and thus should be minimized. The pivot pins must be sized against failure, and the dimensions and materials of the links specified.

    Luckily for you, Norton has provided a computer program developed for abrasive research called "DYNAFOUR" (supplied with your text and available in the Aptlab and other Labs). This program will calculate all the forces and torques on a fourbar linkage for multiple positions. You must supply to it the link dimensions, masses, and moments of inertia for your design's elements, and also supply the crank input angular velocity, and any external forces or torques. Note that DYNAFOUR imposes a constant angular velocity on that driving crank, which assumes that the motor used has sufficient torque available at all speeds. You also have to specify what horsepower will be required of this motor, and the required diameter of the pivot pins based on the dynamic pin forces in your linkage and their material strength. TKSolver and/or the Aries solids modelling system will be an invaluable aid for calculating masses and moments of inertia of your links.

    As with any design problem, there is an infinity of solutions possible. You are expected to come up with one solution which will work and, most importantly, to understand how it works. If it doesn’t work, you should at least be able to explain in good engineering detail why it doesn’t! To do this you will have to try out many alternate designs and iterate to your 'best' solution. You should expect to go through at least ten iterations before arriving at any acceptable solution. You will need to do some paper and pencil (or preferably TKSolver) calculations for masses and moments of inertia of your proposed links before going to the computer to use DYNAFOUR. The entire project including its kinematics can be designed using only DYNAFOUR but the kinematic accelerations can be more quickly calculated with program FOURBAR. Program DYNAFOUR can then be used for the force and torque calculations. Note that a Fourbar data file can be read into DYNAFOUR as well.

    You are also required to document your solution in a professional engineering report which adheres to the Project Report Specifications document which will be distributed. This report will document the process by which you iterated to your final design as well as the design itself. Do not just describe the final result. Rather show me how you arrived at it, including the failures encountered along the way. This will demonstrate to me that you understand the engineering concepts and the relevant course material. A working cardboard model of at least one plane (one side) of your design is required. Your report should include titled (labeled) plots and tables from program 'DYNAFOUR'. These graphics should be imported to your word processor file using the GRAB.COM package. Remember, one purpose of the project report is to convince me that you understand your solution well enough to have been the real designer thereof!

    You are also required to submit a progress report (see the Progress Report Specifications) on Friday, 11/13 which describes your concepts and the work done to that date. This progress report is limited to three (3) typed pages MAXIMUM plus any number of figures, sketches and plots. This progress report must, at a minimum, contain two plots of your linkage showing its coupler curves and polar plots of the forces at points of interest. If this progress report is submitted on time, I will return it to you with comments and suggestions no later than Monday, 11/16.

Some suggestions to get you started:

1. Do research before trying to solve the problem! Don't 'shoot from the hip'. Avoid BFI (Brute Force and Ignorance). Engineer it.

2. Investigate the dynamic and friction factors involved.

3. Mr. Hrones and Mr. Nelson will definitely help.

4. Reading the textbook might even help.

5. Cardboard models make designing much easier.

6. Do some simple table-top experiments to develop needed data such as friction coefficients.

7. THINK about the theory discussed in class and in your text. It IS applicable to this problem!

IMPORTANT! IMPORTANT!

IT IS CRUCIAL THAT YOU START THIS PROJECT RIGHT AWAY! Do not kid yourself that you can knock this off over the weekend before it is due! You cannot! This type of problem requires incubation periods. Work on it until stumped, then put it aside and do other coursework. Then come back to this problem after your subconscious has had a chance to work on it. You'll be surprised how effective this 'time-sharing' of your tasks can be. Read The Design Process in Chapter 1 for more information on this phenomenon. Incubation really does work. You should plan to have all the design work done at least 2 days before the due date, and use that time to write it up. It will take about three times longer to write up the report than you think it will. Allow at least two days for the write-up.

    The report must be word processed and spell checked! WordPerfect (with built-in spell checker) is available in the ADP Word Processing Lab in Fuller Laboratories. Use the GRAB.COM package to incorporate graphics into the report. If you have your own PC and word processor, that's fine too. Letter quality output is NOT required, but DARK type is. Use a good printer ribbon, or better yet, take your disk to CCC and laser print the final draft.

Regarding cooperation between students: This is a very gray area. I do not object to your discussing the problem with your classmates or others. Much learning can take place by 'bouncing' ideas off other technically competent people (including your instructors). So you do not need to work on these projects in a vacuum. BUT, and this is a very large BUT, the final result must be your own. Any duplication of results or designs in the final reports will be quite obvious and will result in a very tense confrontation between you and me. So, brainstorm ideas among yourselves if that helps, but make sure that the final result is your own and that you fully explain its intricacies in your report. This is NOT a group project.