simtk.org

Hi,
for my thesis work, I decide to use the upper extremity model by Holzbaur et al. (2005).
The aim is to apply scale tool, IK and CMC for some movements, in order to compare muscle's activations with sEMG signal.
Scale tool and IK work well but I've a problem with CMC tool. For CMC I base my setup files on the Gait2354 example and I don't use forces data. When I lanch the simulation i don't see any error and the program starts to calculate. For solving the initial frame time the software takes a little less 2 hous; furthermore, for the second frame time, the simulation seems to stop here without write any error(many hours later the message is always: executing computed muscle control).
Any suggestion?
Should I use the RRA?

Thank you.
Giuliano

Hi Giuliano,

The model you're referring to is a bit old and is not setup to do dynamics (lots of extra/phantom bodies and wrapping objects to match kinematics). The authors have been working on a new model that is much simpler and is more dynamics-capable, so I'd suggest contacting them (they have a project on simtk.org) to see if the new model is available.

For the model you have, you may want to play with the integration tolerance to see how it affects the running time.

Generally, RRA is not needed unless you have measured external forces that maybe inconsistent with the dynamics implied by the model and motion, so it's not indicated in your case.

Hope this helps,
-Ayman

Thank you very much Ayman, yuor help is precious!
Giuliano

Hello

For my master thesis i also would need an upper extremity model thats capable of dynamic simulations like CMC. I allready contacted one of the project administrators of the dynamic upper extremity model project but without any answer yet.

But i've tried to reduce the kinematic model from Holzbaur et al.. So i get rid of all unwanted joints and replaced them by weldjoint. I also deleted unnecessary constraints and wrapping objects. What i've archieved is dramatically faster IK-computation however CMC still has the same problems described by the thread-starter.
So, does anyone have suggestions on how to further reduce/modify the kinematic model to make it capable of dynamic simulations?

Thanks in advance
Thomas

I am just starting to use CMC on the Holzbaur upper limb model and I've noticed that PECM1 is extremely noisy. I get very large (>1000 N) "bumps" in my simulation. PECM1 will have very little muscle force, jump up to 1200N or so, then immediately return. Has anyone else encountered this before?