simtk.org

Hi,
Our laboratory specializes in biomechanical analysis of upper limbs, especially the shoulder. Our current analysis focuses on a handling task where the subject lift a box with a force sensor on the right handle.

Since this is not a force platform, I cannot express the ground reaction force.
Is there a way to express the sensor data (Fx, Fy, Fz, Mx, My and Mz) in the global coordinate system as input in inverse dynamics? (Knowing that the sensor is moving)
I tried the following solution in matlab:

1. Define the local frame of the sensor
2. Get the rotranslation matrix for each frame
3. Express the force in the global frame with:
Force in global frame = rotation matrix* force in local frame
4. Express the moment in the global frame with:
Moment in global frame = (rotation matrix * moment in local frame) + cross product of rotation matrix and force in global

I get Fx, Fy, Fz, Mx, My, Mz in the global frame of VICON. But I have doubts about how to proceed once on opensim.
Thank you,
-Romain

You can define this as an external force similar with the ground reaction forces (see examples in model folder). Moreover it is possible to prescribe a force and a torque expressed in the local frame of the body applied at a specific point defined in the local frame of the body.

Best