simtk.org

OpenSim team,

I am experiancing an issue with the CMC tool. When I attempt to simulate trials based on jump-landing or sidestep-cutting kinematics the process fails to complete and I continually receive the error "Optimizer failed: Ipopt: Search direction becomes too small (status 3)"

I am using inverse kinematics exported into .mot files by Visual3D. I have successfully used this process to simulate gait motion through CMC. Also, prior to the failure of the CMC simulation I am able to complete RRA analyses of the jump and cut kinematics. Thus, I would doubt this is an issue of improperly exporting from Visual3D. I have also have tried to greatly increase force values within my CMC_Actuators.xml file, but this does not correct the simulation failure. I have been using the gait2392_simbody.osim model to conduct RRA and CMC.

I would appreciate it if someone could explain:
1. What this error indicates?
2. How I can correct this problem?

Thanks,
-Nate Bates

Hi Nate,

One possible issue is that your muscle are not strong enough.

Try to increase MIF (maximum Isometric force) of your muscle in .OSIM file.

It may help you run the the simulation
Hossein

Hossein,

Thank you for your reply, I have worked with adjusting the .OSIM file to increase maximum isometric force across the muscles. This did resolve some of the CMC simulation failures.

However, this was not true for all cases as some files still crash the simulation. Since adjusting the model, the error message has changed during the crash and now appears as "Optimizer failed: Ipopt: Restoration failed (status -2)". Do you know what is causing this error and how to troubleshoot? Is this more of the same problem, do I just need to further increase .OSIM muscle forces?

Thanks,
Nate

Hi Nat,

You can try increasing it untill you get the results and at the same time check the kinematics and ID , or RRA results. Have a look at them and see if they are smooth enough. Check your GRF as well if they are applied cottectly.
Hossein