CMC ERROR Message

[Anna Ventura]

Hi!
I am trying to obtain the results from CMC tool, but OpenSim write: "CMC.computeControls: t = 5
CMC::computeControls WARNING- small force range for ECU (200.867 to 200.867)

SimTK Exception thrown at InteriorPointOptimizer.cpp:261:
Optimizer failed: Ipopt: Infeasible problem detected (status 2)
OPTIMIZATION FAILED...".
I tried to change the max value of excitation of the muscles in the controlconstraint file, to decrease the weight in the other files but I can't find the way to solve this problem...
I thought it could be a problem due to the way I wrote the CMC_Tasks file, so I added the lines of description of the muscle but I don't know which informations to add... Infact, I am using the file of the model already in OpenSim but in my model the muscle is a Schutte1993Muscle_Deprecated and in the example file the muscle is a ThelenMuscle2003.
Can you help me?
Thank you very much!
Anna

[Carmichael Ong]

The small (and non-zero) force range seems to indicate that the muscle is stretched so that it's generating all passive force and can't generate any active force. This means that in that specific set of coordinate values, that force will always be generating that exact force value given in the warning message. Thus, changing the weighting factors won't affect this problem, and these high passive forces might prevent a problem from being solved.

It might be good to check that you are using a model that is validated within the range of motion that you are studying. You could also look to literature to see if there are any normal values of passive resistance to check if the model might have some problems for your study.