GRF Prediction

[Melanie Hook]

Hello everyone,
I have been trying to predict ground reaction forces and moments during walking gait using the zero moment point method described in this paper: https://www.sciencedirect.com/science/a ... 9015005278.

In the paper, they run ID without ground reaction forces applied then transform the resultant forces and moments at the pelvis to the ground. I have been using the raw data values from ID (pelvis tx, ty, tz, tilt, list, rotation) in the calculations described in the paper but am not sure if this is correct. Using the gait2392 model and comparing my calculated results to the provided ground reaction data, my GRF results seem reasonable but GRM do not. I know that residual actuators need to be added to the pelvis for RRA so maybe a similar process is required in this case? I am not very familiar with the concept of residual actuators or how to implement them. If anyone has any suggestions on how to obtain the correct resultant forces and moments at the pelvis, please let me know!

Also, if you know of an easier way to predict GRF, please help! I have mainly been focusing on this paper but also have looked into these methods:

Fluit et al. : https://www.sciencedirect.com/science/a ... via%3Dihub#! - not sure if contact spheres with Hunt-Crossley forces are sufficient or what to do once the contact model is implemented

Contact force static optimization plugin: https://simtk.org/projects/statopt-contact - model won't show up in OpenSim visualizer once contacts are added but no error messages are provided

Thank you so much for your help!
Melanie Hook
melaniehook@vt.edu

[Thomas Mokadim]

Hi Melanie,

I am also working on such topic. Did you manage to get trough your issue ? Finally what solution is the best to estimate GRF regarding the original dataset ?

Thank you so much.

Regards,
Thomas

[Johannes Amend]

Hey guys,

did you find a solution yet? I have a similar problem.

Regards, Johannes

[Adrián Schmedling]

Hello,

I am also researching this topic, I have found the following related posts on the forum, maybe you can find some information here:

viewtopicPhpbb.php?f=91&t=7095&p=34452&start=0&view=
viewtopicPhpbb.php?f=91&t=11946&p=33745&start=0&view=
viewtopicPhpbb.php?f=91&t=8675&p=23903&start=0&view=
viewtopicPhpbb.php?f=91&t=8457&p=23214&start=0&view=
viewtopicPhpbb.php?f=91&t=7785&p=20709&start=0&view=
viewtopicPhpbb.php?f=91&t=6840&p=17734&start=0&view=

Apparently there are 3 ways to solve the problem of obtaining the GRF from a known motion.
1) Applying the calculus described in the article above. Using the ID tool, obtain the forces applied on the CoM and translate them to the ZMP (CoP).
2) Create a ground contact model of the feet with the ground and use the FD tools.
3) Add a constraint of the foot with the ground to obtain the generated forces. This case is only valid for studies where the foot is not moving (doing squats, evaluating balance, weight lifting, etc).

[Johannes Amend]

Hello Adrian,
Thank you for your answer, i will give it a look.

[Adrián Schmedling]

3) Add a constraint of the foot with the ground to obtain the generated forces. This case is only valid for studies where the foot is not moving (doing squats, evaluating balance, weight lifting, etc).

It seems this is technically correct, but it's very tricky to deal with in practice. So the first two options are better approaches