Framus Unlimited Inc.
100 Institute Rd.
Worcester, Massachusetts
Memorandum
To: Young Swans Design Group
From: Chief Swan
Subject: Hell on Heels (ME 3310 Project 3 Term C-91)
Date: Assigned 2/18/91 – Final report due on 2/28/91 @ 4 Pm
O’Sullivan’s Rubber Heels Inc. has asked us to design a rubber heel-testing machine for their quality control department. The chief engineer has given some thought to this problem and has come up with a design concept for you to investigate. Figure P9-3 on p391 in Design of Machinery shows a cam-driven mechanism which will do the job. Project problem P9-3 on p390 describes the problem. A hydraulic pump and cylinder has been chosen and its pressure-volume characteristic is as shown in the figure. Your task is to design the cam-follower system to drive the pump so as to obtain as close an approximation to the force-time function of a typical human’s foot on the tested heel as shown in the figure. Though a human’s walking pace is fairly slow, they want to do an accelerated test on these boot heels. You should design your cam to run as fast as is reasonable in respect to the system’s resulting accelerations, velocities and jerks. The moving pump parts weigh about 2 pounds and the weight of the working fluid (oil) will depend on the length of your tubes. The damping ratio (z) can be assumed to be between 0.1 and 0.2.
As with any design problem, there is an infinity of solutions possible. You are expected to come up with the best solution you can design. To do so you will have to try out many alternate designs and iterate to your 'best' solution. You should expect to typically go through at least ten iterations before arriving at an acceptable one. Some measures of "better" designs will be: (for any particular design speed) lower peak accelerations, smoother jerk, smaller physical cam size, good pressure angles and reasonable follower size. You may use either a flat faced or roller follower. You are required to compute the s, v, a, j functions, the pressure angles and radii of curvature of the entire cam and draw the cam profile. Also compute the dynamic force on the follower and select a spring to close the joint. Spring data can be found in Appendix C of Design of Machinery. All of these tasks can be accomplished with program Dynacam. Please note that a bug was found in Dynacam. The new REV 11 of version 5.3, dated 2/17 91 corrects the bug. Please update your copy before doing this project as the old version will not read its data files correctly.
You are also required to document your solution in a professional engineering report which adheres to the "Project Report Specifications" document previously 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. Note that unreferenced and un-discussed computer or other illustrations will be considered to be report "filler" and be ignored. Do not put anything in the report unless you discuss its meaning. NO model of your design is required. But, do include a computer disk with your DYNACAM solution files on it.
For this project, no background research is required beyond your textbook. See chapters 9 and 17 and section 2-15. Begin your report with the design description phase of the design process. Do not include research, goal statement or task specifications. They will not be read even if you do include them. The report must include the following figures IN THE ORDER LISTED!
- S-V-A-J diagrams in one plot
- separate S, V, A, J plots (4 figures)
- pressure angle plot
- radius of curvature plot
- dynamic force plot
- the (3) boundary condition tables for each of your segments
- a cam profile
- any other data you think necessary
IMPORTANT! IMPORTANT!
YOU HAVE ONLY (10) DAYS for this project!
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 new Word Processing Lab in Fuller Laboratories. 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.
Now please re-read this document to ensure you understand what is being requested. If you are the least bit confused, ASK QUESTIONS IN CLASS OR SECTION MEETING. Above all, Have Fun!