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Joint Stop

Joint Stop

(OP)
Hello,

Are there any possibilities in the ADAMS to stop a joint motion in a specified joint positon like for example in the ProEngineer/ProMechanism? With or without restitution?

An example: there is a revolution joint, hinge like, and one wants to prescribe, that the motion to be limited in a 0-120deg revolution angle, related to the initial position. If the motion reaches one of the limit (0 or 120 deg) it stops (if restitution is not defined or zero), or begins to move back some kind of velocity according to the restitution value.

I can solve the problem with the combination of a joint and some kind of contact, but maybe there is more simple way.

I hope, may problem is clear,
thank you for any help or suggestion

dezsit

RE: Joint Stop

Easy peasy way is to define a non linear torsional spring. This has the advantage that you can shape the force vs deflection curve to represent the real stiffness of your end stops. If you do this right you'll end up with much faster solve times than if you use contacts.

It will be difficult to add damping or friction to that system without using contacts, but there may be a clever way similar to the method at the end of this note.

Using contacts isn't very difficult, it is just numerially unstable, and rather hard to calibrate.

An alternative approach is like this, where a bumper only exerts a force when it is in vertical contact, and also has damping only when it is in contact. Note that this formulation explicitly does not use contact for speed and robustness.

VARIABLE/118971,
,FUNC=(DZ(118971,118775,118775)+ABS(DZ(118971,118775,118775)))/2.0
!  bumper elastic force
VFORCE/118971,I=118775,JFLOAT=1189711, RM=118775
,   FX=0\FY=0\FZ=ABS(AKISPL(VARVAL(118971),0,118971))

VARIABLE/118775,FUNC=VZ(118971,118775,118775,118775)
! bumper damping force
VFORCE/118775,I=118775,JFLOAT=1189712, RM=118775
,   FX=0\FY=0\FZ=STEP(VARVAL(118971),0,0,.1,0.1*(VARVAL(118775)))

Cheers

Greg Locock

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RE: Joint Stop

(OP)
Hello,

Thank you for your answer. Yes, my problem is the calibration of the contact, not its using.

I will try the nonlinear spring, this solution probably has also calibration problem, but maybe easier to solve it, because my joint stop device (in the real design) is a bumper, a rubber like material.

And thanks for the last suggestion, I will test it.

Dezsit

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