Over constrained system

[Jakob Pflugbeil]

Hello,

 

I am trying to simulate a robotic movement where the robot has two arms, in the initial state the end effectors are fixed. Meaning the robotic structure creates a closed loop and an over constrained mechanism. But this results in the simulation in a oscillating movement, see attached file, which should not be present.

The robots body is initialy fixed, but this is deactivated shortly after the start.

 Is there a possibility to avoid these oscillations i.e. solver or stepper settings?

-Jakob

[Radu Serban]

Hi Jakob,

 

First, a closed loop does not necessarily mean an over-constrained system.  Second, if you do have an over-constrained system, the question is if you have redundant or conflicting constraints.  Most Chrono solvers can deal with redundant constraints (one exception is the Pardiso solver).

 

You will have to carefully analyze your system in terms of DOFs and constraints to decide if any of the above is the case.

If there’s no issue at the kinematics level, then the most likely cause of unexpected oscillations is that the solution is not properly converged. I see that you are using the Barzilai-Borwein solver. Try increasing the number of maximum iterations allowed in the iterative solver (the default is 50). Start with something significantly larger (say, 200) and, if that resolves the issue, start reducing it until you strike a balance between accuracy and performance.

 

--Radu

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