Joint Reaction Analysis errors (extremely large forces)

[Ryan Byrne]

Hi all,

I am working on a lumbar spine model consisting of several joints (moving joint centers), ligaments, and muscles. The general flow of the process is IK > SO > JRA. I am using the forces.sto and muscle control files from SO, motion file from IK, actuators files, and ground reaction forces to run JRA.

Sometimes the results from JRA are realistic. However, at times I get joint reaction forces that are nearly infinity at every joint (around 100 zeros on the end of the numbers). When this occurs, I close the active states corresponding to the joint reaction analysis I just ran (pic attached). I then re-link the files (controls, motion, etc.), re-run the JRA and get realistic values.

I was hoping someone could make sense of why this might be occurring. It is really hindering my ability to trust the results and move forward efficiently. Perhaps there are values store in memory somewhere that are messing with my solution, or something of that nature? It may also be worth noting that the input files are scattered across many folders.

Thanks,
Ryan

[jimmy d]

My suggestion would be that there is an error in the files that get specified in the GUI (mismatching force and kinematics files).