# Simulink Simscape joint ignores specified limits

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Milando il 7 Feb 2022
Commentato: Steve Miller il 10 Mag 2023
Hi, I'm trying to simulate the kinematics of two connected systems. One of them moves through some defined motion input. The other system (with 3 different joints) has to follow the first system. The joints of the second system have defined lower and upper limits, but ignores them every time through the motion of the first system, and it distorts the simulation of movement.
I need to "hard stop" the joints between some limits. The upper and lower limit for the joints only works, if there is no motion input in the second system.
I already tried it with the Simscape Multibody Multiphysics Library. But still it ignores the limitations.
Is there any possibility to set this kind of limit?
Thanks!
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Milando il 18 Feb 2022
Since I couldn't find any solution for my issue, I will add an example.
The green System is moved by the yellow system, but the joints in the green system are ignoring the limits.

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### Risposte (1)

Steve Miller il 12 Mar 2023
In the model you attached, you are driving the joint with a motion input. That motion will provide whatever force or torque is necessary to move the mechanism, including pushing through joint limits. If you want the joint limits to be obeyed, you need to actuate your joint with a force or a torque, not a motion input.
--Steve
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Patrick Schneider il 9 Mag 2023
Hello Steve,
thank you very much for your answer. However, the limits are exceeded even though I use torque as input. Do you have any other idea what could be the problem?
Best
Patrick
Steve Miller il 10 Mag 2023
When I change this to torque driven, Revolute Joint will go only slightly outside the range of 45 to -90 degrees. The joint limits are spring-dampers, so the limits will get compressed a bit. If you make the spring-damper stiffer, the joints will stay closer to the defined limit. You could also make the limits slightly narrower, recognizing that some compression of the springs will occur. See images and model below.
--Steve

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