constraints with a gap...

[PAULKORENKIEWIC]

Guru's,

We have an application where I would like to some how simulate a "gap" in a constraint. Essentially, we have a shaft with three bearing supports (not my design, and we have already tried to convince the customer to redesign it to a more appropriate bearing application design) where the desire is to design in a small gap into one of the bearings with the theory that it will engage at some level of shaft displacement. What I have been asked to do is to simulate this with various gaps to help determine the bearing loads so appropriate parts can be specified.

IS there a way to simulate this? Obviously, I can simulate the shaft with all it's external loads and then constrain the three bearing surfaces on the shaft appropriately (one in all direction and the other two only radially leaving them free to move on the axis). This captures the stiffness of the shaft and the resulting reaction forces at the constraints can be measured. IS there a way to model a "gap" on one of the bearings?

Thanks in advance...

Paul Korenkiewicz
FEV, Inc.
4554 Glenmeade
Auburn Hills, MI., 48326


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[ChrisKaswer]

Paul,

You should be able to use contact - just set-up the dimensions appropriately for your gap. To avoid an assembly analysis, another option is to use a spring - now I'm going to throw out a "guess" since I haven't applied it yet to see how it works, but it should be up and running with WF5 or Creo 1. You create a non-linear spring to support the shaft at the location(s) your shaft would contact the bearing, you can have it simulate the gap. Just make the spring very weak for the distance it has to move before contacting the bearing (race or rolling element), then increase the stiffness and you should have your gap constraint.

Cheers,

Chris

Christopher Kaswer
Staff Engineer
Covidien
Research and Development, Surgical Solutions

[JonathanHodgson]

There's nothing inherently wrong with a three-bearing shaft - this
arrangement is often used in transmissions. Since both the shaft and
the bearings have a finite (if non-linear) stiffness, the reactions can
be solved numerically.



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