How to add my exoskeleton model to gait2354simbody?

[Marta Carrilho]

Hello,

I am still trying to do this.

I am editing an xml model. So, with that in mind, I tried to add some contact forces. I have a model where I am trying to use Elastic Foundation Model and other one with Bushing Forces.

My question now is, with these forces two bodies might be connected or is it wrong? For example, if I have a foot and a footplate connected trough a Bushing Force, when I move the foot in Coordinates panel, the foot plate should follow the movement, right? Just like it happens in "Simulation-Based Design to Prevent Ankle Injuries" (http://simtk-confluence.stanford.edu:80 ... e+Injuries).

Thank you,
Marta

[Thomas Uchida]

with these forces two bodies might be connected or is it wrong? For example, if I have a foot and a footplate connected trough a Bushing Force, when I move the foot in Coordinates panel, the foot plate should follow the movement, right? Just like it happens in "Simulation-Based Design to Prevent Ankle Injuries"

You have described a model that differs from the model used in the "Simulation-Based Design to Prevent Ankle Injuries" example. In the example, the AFO consists of two bodies: r_AFO_footplate and r_AFO_cuff. The footplate is welded to the calcn_r body and therefore will move when the foot moves. Similarly, the cuff is welded to the tibia_r body. The bushing applies forces between the r_AFO_footplate and r_AFO_cuff bodies.

In your model, it seems that the footplate is not rigidly attached to the foot. Note that changing the pose in the Coordinates tab does not run a simulation; joints and kinematic constraints are respected, but contact forces are not computed. (You can see this in the example by adjusting the pelvis_ty coordinate to move the foot through the platform without generating contact forces.) Thus, if you connect a footplate to the foot with a bushing, you will be able to move the footplate arbitrarily far from the foot by adjusting the values of the coordinates. When you begin a forward simulation, however, the bushing is likely to generate very high forces which may affect the numerical stability of your simulation.

You may want to start off with a simple two-block "proof-of-concept" model to get a better feel for how the OpenSim components work before diving into a more complex model.

[zheng xiaojuan]

the "Simulation-Based Design to Prevent Ankle Injuries" example.

I can't understand that why did add the bush force between the tibia_l and calcn_l in the toy landing model.

[Thomas Uchida]

why did add the bush force between the tibia_l and calcn_l in the toy landing model.

There is a References section at the bottom of the "Simulation-Based Design to Prevent Ankle Injuries" Confluence page (http://simtk-confluence.stanford.edu:80 ... e+Injuries). The first reference is to the following paper:

DeMers, M.S., Hicks, J.L., Delp, S.L. (2017) Preparatory co-activation of the ankle muscles may prevent ankle inversion injuries. Journal of Biomechanics 52:17–23. http://nmbl.stanford.edu/wp-content/upl ... rs2017.pdf

From the Methods section:

The passive mechanics measured in cadaver ankles were represented in the model as a three-dimensional torsional bushing. The bushing acted like a set of three uncoupled, nonlinear torsional springs between the distal tibia and the calcaneus, crossing the talocrural and subtalar joints. […] The bushing captured the passive response of all ligaments and soft structures that cross the ankle, excluding musculature.

[Janek Butzer]

Dear all,

I'm trying to model the connection between an exoskeleton and the Arnold Hamner Running Hybrid model to test the alignement of the joint axes of the human model and the exoskeletons joints.
I've alredy combined the the model of the exoskeleton and the human model into one .osim-file and used weld constraints to connect the exoskeleton to the human body. I was able to run inverse kinematics with the model and the results look promising.
Now I would like to model the connection as some kind of spring-damper connection to simulate the orthopaedic cushions that will be used in the real system. I thought of using bushing forces for this application.
Have I understood correctly that to see the effects of the bushing forces I need to run a forward dynamic simulation?
Is it possible to run a forward dynamic simulation without ground reaction forces? Unfortunately I only have experimental marker position data but no data about the ground reaction forces.
I hope it is clear what I would like to do. I'm thankful for any advice on how to proceed.

All the best,
Janek

[Jason Liu]

Hello,

I'm just wondering have you figure this question out? Because I'm now working on it. I have launched some .STL and .XML files but I don't know how to put them in the right position. Can they be calculated automatically? or do I have to try the coordinates one by one? Your quick reply will be highly appreciated.

Yours sincerely,
Thank you.

[rui zhou]

I have the same question with you