Flexible Link modelling for Robots in Isaac Sim

Omniverse Isaac Sim
1

Hello NVIDIA Forum,

is it possible to model flexible Links for Robots? I have seen that is flexible Body simulation possible with PhysX but is this also possible for the Links of the Robot or do these have to be rigid bodies? The Joints can be configures to be flexible with stiffness and damping coeffictients.

Thanks in advance!

2

Hello @claudiusbirk ,

I am not sure I understand your question. Indeed usually one would try to model the flexible joint using regular joints in the articulation. If there is an advantage to model the joint using a deformable, that should be achievable as well, but the simulation wouldn’t converge as well (so might need more iterations/smaller time steps etc). One could use attachments between deformable bodies and rigid bodies.

3

Hello @SimonPhysX

I want to create a hight fidelity dynamics model of a industrial robot.
When observing the motion of a robot with a precise measurement device and trying to model the precise movement of the robot these increasingly more complex abstractions can be used:

  1. level of abstraction: The robot movement can be modeled by non deformable rigid bodies and rigid joints. No deformation and perfect transmission all the way.

  2. level of abstraction: The robots links (the body parts between the drives) are assumed to be rigid but there is some flexibilty in the joints.

  3. level of abstraction: The Robots links can not be assumed to be rigid and they behave like a soft body with slight movement and the joints also have some flexibility.

By increasing the level of abstraction one can explain the movement measured with the precise measurment device in more detail.

This is also explained here: https://www.sciencedirect.com/science/article/abs/pii/S0094114X06000292

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I have attached two images which should help to explain.

Basically i want to know which level of abstraction is possible in NVIDIA Isaac sim.

As far as i can tell the robots joints parameters have some stiffness and some damping parameter. Wich means the joints can be modeled as flexible with 1 spring damper pair.
And the Links are modeled as rigid bodies as far as i can tell.

Can you tell me what kind of options there are in order to create a high fidelity robot model in NVIDIA Isaac Sim?

Thanks in advance!

4

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@SimonPhysX

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@SimonPhysX

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6

@claudiusbirk Thanks for the clarifications!

I see that deformables could in principle be useful for abstraction 3). However, our current volume deformable model is not accurate enough to simulate the elastic and plastic deformation of very rigid parts.
I think for abstraction 2) one can work with joint degrees of freedom (spring and damper). How to define this especially in Isaac Sim, I am not sure. Let me refer to my college @philipp.reist.

Cheers,
Simon

7

Hi @claudiusbirk - Agree with Simon here that Abstraction 2 is your best bet - model the deformation of the link with an additional revolute or spherical joint with high stiffness. We do not support deformable objects being part of articulations.