Squeegee Me!
WPI ME 3311 Project 1
Term B-94

Assigned 11/4/94 ----- Due 11/18/94 (14 days!)

    The Autoroll Co. makes bottle printing machines. These use a silk-screen process to apply label information to bottles in an automatic assembly machine. A videotape is available for viewing that shows one of their machines in operation. A new machine is being designed. They have subcontracted a small portion of its design to WPI.

    A mechanism is needed that will move the squeegee (also called a knife) in an approximate straight line across the top of the silk screen while the bottle is rolled against the underside of the screen. It is also preferred that the velocity of the knife be as uniform as possible during the print stroke. The useable print stroke is a maximum of 6 inches long. The knife is 5 inches wide, 1 inch high and can flex up to 0.1 inches in the vertical direction. Its spring constant is 20 lb/in. It only needs to wipe in one direction. There is an effective coefficient of friction between knife and screen of about 1.5. The desired production rate is 80 bottles per minute. The bottle-motion mechanism is not a part of this contract.

    Your assignment is to design a squeegee-driving mechanism based on a fourbar linkage which will provide suitable motions and velocities and to arrange the shapes, sizes and materials of the parts such that the reaction forces applied to the machine frame are as small as possible. The driving-torque requirements are also of concern as they will require 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. A multi-view, overall assembly drawing must be supplied which shows how the mechanism mounts to the machine.

    Luckily for you, WPI has provided a computer program called DYNAFOUR available in the Aptlab - (note that the version supplied with your text has a bug which has been corrected in the lab versions). This program will calculate all the forces and torques on a fourbar linkage over 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 device used has sufficient torque available at all speeds. You also have to specify what power will be required of this device. TKSolver and/or the Aries solids modeling 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.

    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 preferably 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!

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 can help.

4. Reading the textbook might even help.

5. Cardboard models make designing much easier.

6. 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.