Modelling backlash in joints SIMSCAPE (Multibody)

Question

Adam Green 2020-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/506868-modelling-backlash-in-joints-simscape-multibody

回答： Alexandr Kovalenko 2023-10-23

mockup.png

I have imported a CAD model of a 4 bar linkage into Simscape Multibody which moves perfectly but I am unable to figure out how to make it take into account backlash.

I've attached an image showing a mock up of the sort of thing I'm looking at.

Main problem: How do you take into account backlash in the joint? I set the pin to be 46mm and the hole to be 50mm meaning there is a 4mm gap (at max) which needs to be overcome when you put a force on the system but that's just being ignored and moving it as if it was touching.

I've tried lots of things such as:

Modelling the pin joint in CREO to act in the centre, but through two slot constraints be freehanging in the centre so in CREO you can drag it all around the cylinder but when you import that to Simscape multibody it does not like the joint constraints and fixes it rigidly.

I've tried just applying the pin constraint on the pin like you can see in the image but again it's ignoring the backlash

Any ideas are appreciated thank you.

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Answer 1

Steve Miller 2021-10-20

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For a square hole, you can just enable joint limits.

For a round (or other shaped) hole, you place a planar joint at connection between the two parts and put a custom force law on the x- and y- degrees of freedom.

From the joint block, output the x- and y- positions and velocities
Calculate the radial distance of the F frame from the B Frame (sqrt(x^2+y^2)) and the radial velocity.
If the distance is larger than your backlash, apply a force pushing back towards the center.
Calculate a spring-damper force (for example, stiffness * radial distance, damping * radial velocity)
Multiply that times a unit vector to get the x- and y- components
Apply those forces back at the joint.

--Steve