Bearing/Rolling Cam analysis tools 1

[eedave]

I am an electrical engineer who has been asked to come up with a mathematical model to simulate the mechanics of one of my company's products. The product is called an expansion chuck and it operates on a cam like principle. The chuck consists of a center hub and three "jaws" - the jaws are supported on the hub by a series of rollers. When a torque is transmitted via the jaws, the rollers ride up a ramp feature on the center hub thus causing the jaws to expand out. I want to come up with a model that predicts the expansion force as a function of actuating torque.<br>
My guess is that the math involved is similar to that used to predict starting torques in bearings.<br>
I would appreciate any thoughts on:<br>
1. Mechanical engineering text books or other references that<br>
discuss bearings, cams or other related subjects.<br>
2. Simulation software that would be useful for implementing such a model.<br>
<br>
Thanks in advance<br>
eedave

 

[JEFF1]

I'm not completely clear on the geometry that you've described. But when I was in college 25 years ago, the textbooks that I would have used would have been "Vector Mechanics for Engineers- Dynamics" and "Vector Mechanics for Engineers - Dynamics", both by Beer and Johnston, (McGraw-Hill). I don't know if these books are still in publication, but they're excellent. The people who studied mechanisms used "Kinematic Analysis of Mechanisms" by Shigley. This was part of the "McGraw-Hill Series in Mechanical Engineering". I didn't take the course, but I think the book is probably pretty good. As an electrical engineer, you probably worked a lot with vector algebra, and these books shouldn't be too difficult.

 

[MikeVV]

&gt; 1. Mechanical engineering text books or other <br>
&gt; references that discuss bearings, cams or other <br>
&gt; related subjects.<br>
<br>
There are many to choose from - this is a basic machine design problem. Marks handbook for Mechanical Engineers is a good general reference for all aspects including machine design. Machinery's Handbook is the best general reference for your situation that I've ever come across. Both should be available from McGraw-Hill. Shigley's text book is a good reference for this type of problem because it teaches you how to solve the individual <br>
problems associated with it (torque to linear force, drag/friction effects, contact stress, torsional stress, etc). <br>
<br>
Look for those topics that describe free-body diagrams and force vector calculations - these are the analysis techniques that allow you to determine how much force is acting on each individual component in the device. It sounds like you have a simple ramp with roller(s) that acts as a force multiplier - you also have an arrangement that allows you to convert torque into linear motion.<br>
<br>
&gt; 2. Simulation software that would be useful for<br>
&gt; implementing such a model.<br>
<br>
There appear to be three major questions involved with this design - how much expansion force is delivered for a given device torque, what are the loads on the individual parts of the device at these torques and what are the critical stresses in each part of the device. The first question involves a prediction of the device's efficiency - how much torque is lost to friction. The second question requires free-body diagrams of each part and the third is a comparison of each part's strength to load to determine <br>
strucutral safety factors.<br>
<br>
Each of the three questions can be modelled using software. Some computer programs can handle all three questions. A finite element analysis program that processes 3d elements and has a full suite of pre and post processing functions such as SDRC-Ideas, Algor, MSC-NASTRAN, etc will work - the hitch is that you will need a year to learn how to use them if you are a novice now. <br>
Computer programs that are limited to each of the basic questions also exist - Look at the American Society of Mechanical Engineer's (ASME) site - they have links to other sites that supply these types of programs. <br>
<br>
This type of problem is generally solved in three steps - 1) make rough estimates of the device stress situation with closed-form (equations) analysis, 2) zero-in on the critical parts of the device to perform a detailed analysis using closed-form and numerical analysis techniques, and 3) verify the results of your analysis with an independant check (from another engineer or using an other approach) and/or testing in the field.<br>
<br>
This type of analysis should be followed by a check of fatigue and vibration / balancing issues. The mass and distribution thereof needs to be checked to ensure that the device is balanced while rotating. <br>
<br>
MJVanVoorhis@Compuserve.com<br>
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