Geneva Mechanism – Effect Of Friction

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Areas covered:

  • Use of a Multi-Body-Dynamics (MBD) Model to simulate a mechanism.
  • Design Of Experiment.
  • Construction of an Approximation.
  • Use of Monte Carlo methods for stochastic analysis.

 

Description of the Problem: A Geneva Mechanism is a widely used indexing mechanism. It relies on friction between the crank and the slotted-disk for the indexing. Friction is hard to pin down perfectly. At best, we can estimate the range between which the friction coefficient can vary. Further complicating the issue, there is more than one “kind” of friction coefficient the designer has to grapple with. We have static friction at the initiation of motion, dynamic friction when the mechanism is running, and “stiction” or stick-friction, which can be a nightmare for a designer. With this, what is the reliability of the design? There are two areas the designer is interested in. First, the forces on the crank during motion. If these can be evaluated, a stress analysis can be carried out to ensure that the crank is safe for all ranges of expected forces. That is, at the best and worst case friction-coefficient scenarios. Second, which ranges of coefficients are the worst and best case scenarios? We perform a Monte Carlo study to investigate the behavior of the mechanism given the designer’s interest.

The Solution-Summary can be viewed on any computer that has an AVI or VLC  player (e.g. VLC media player 2.0.3) installed.

Right-click on each of the links below, choose “Save As” and save the files to a folder on your computer. Then use a “zip” application to extract the contents to your folder.
HTML and IGES
Introduction
DOE
Approximation
Stochastics
Solution
Study Setup
Planning

After you extract the files, open the HTML file titled HS_FrictionStochastics.html and use the menus to access the instructions in sequence.