Trouble with Inverse Dynamics with exoskeletons

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Guillermo Muñoz
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Joined: Sat Nov 23, 2019 11:08 am

Trouble with Inverse Dynamics with exoskeletons

Post by Guillermo Muñoz » Fri Jun 18, 2021 8:49 am

Hello everyone. My name is Guillermo, and I started to work with OpenSim and Moco some months ago. I would like to ask for some piece of help for a project I'm involved in. I am working with the 3D model, subject_walk_armless.osim, and I've built an exoskeleton on it, as it can be seen in the picture.

Image.

The exoskeleton is composed of two bodies in each leg, the upper bodies are connected to the hip through CustomJoints with 3 DOF each, all of them rotations, while the lower bodies are connected to the tibia through PointConstraints so as to close the loop.

First of all, I performed a Inverse Kinematic analysis in OpenSim by loading marker_trajectories.trc, obtaining the evolution of generalized coordinates in time. Then, I tried to perform a dynamical analysis in Moco so as to obtain generalized forces and torques. For that purpose, I built a Matlab script based in exampleMocoInverse.m, adapted to my problem, using my .osim model, and the .mot file I obtained by doing the Inverse Kinematics. The file can be seen in this picture.

Image

Here the problems arrive. When I make the optimization problem begin, it never reaches a solution, the problem takes so many iterations until reaching the maximum number of iterations allowed, and I don't know what could be happening. I tried to reduce the time interval in the Moco script, and increase the mesh interval, but none of these worked to obtain a solution. Please, could someone give me an idea to solve this problem? Thank you very much.

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