forces in joints

[Uwe Mittag]

I could make a lot by checking the clamping mark. IK now works fine. But the results of ID ist strange: Without locking the freejoints all joints are shifted. When locking all joints I have only one big shifts (translation in x and z) in the lower joint.

Best regards
Uwe

[Vahidreza Jafari]

Hello everyone,
I'm writing in reference to one of mechanical aspects called angular momentum during human motion. Is Opensim capable of calculating this factor in three dimension?

Thanks

[Uwe Mittag]

After a longer break I am able to proceed with my problem. Because nobody had answered me months ago again my question again:

My segmented tibiamodel (included into a standard gait model) works fine for Inverse Kinematics but I am getting strange results for Inverse Dynamics. The lowest joint only shows a large displacement. Is there any way to upload a picture?

I am using Free Joints with very narrow range specifications for my tibia joints. The problem arises independently of using bushing forces for the joints.

Best regards
Uwe

[Uwe Mittag]

Here a Picture of the displaced "Joint".

Best regards
Uwe

[Ayman Habib]

Hi Uwe,

Wonderful to hear from you again. Your picture didn't post but here's a general comment that should help clarify.

Generally speaking, IK should solve for all coordinates (respecting coordinate limits since these are built into the problem), InverseDynamics does not respect coordinate limits since these are not dynamical (they don't produce forces when you reach the coordinate range limit).

I'd expect that if you feed IK solution as a motion to ID then you'll have the correct behavior, we just need to make sure InverseDynamics is accounting for the BushingForces and other forces in the model (usually excluding muscles).

Hope this helps,
-Ayman

[Uwe Mittag]

Thanks Ayman,

the IK of my model based on a gait looks pretty good. I fed that into the ID but got this diplacement in one "joint" of my Tibia. I tried to upload a picture with my last post but could not it in the post. Can you see it?

Best regards
Uwe

[Uwe Mittag]

I see two Points where Problems could be. I saw that I have for my five Special Joints:
first is that I have Joint coordinates from child perspective identical to the coordinates from parent perspective.
second: for the bushing Joints Definition I use the same coordinate definitions.
why isnt it possible to assign bushing Forces directly to a known Joint?

Sorry for the strange upper/lower case choices. I do not feel like correcting the auto-upper-case Settings of this Editor.

[jimmy d]

What joints are you using to divide the tibia? WeldJoints? Freejoints? I think it would be best if you zip up all the relevant model and setup files and attach to your next post. The descriptions of your problem seem to provide little insight into what you are actually doing.

On another note, you have been getting a lot of help from the user community. Please do not say that nobody answered you months ago, you had many people trying to help you and it is disrespectful to them that you suggested otherwise.

[Uwe Mittag]

Sorry I did not want to be disrespectful and I - of course - am happy over any Kind of help from this Forum. You guys brought me, the newby, already several pretty steps ahead. Thanks for that.

What I want to do: I want to see the Deformation on the Tibia coming from the Dynamics of the Body during different exercises. The idea is to have a flexible Tibia model that allows for adjusting the "Joint" properties in a way that it reflects the mechanical behaviour of a real Tibia including compression, bending and axial torsion. We have Deformation data from a study, could scale the model to the different test subjects, overlay the Motion data that are available and then compare reality and model to achieve a better understanding of what is going on. For that I will Need plots of bending angles and diplacements inside my different "Joints" along the exercises (Walking, squatting, jumping,...). With FE in parallel we can get stress/strain data that we Need for our bone Adaptation simulations. I want to start from an existing model like gait2354. Perhaps in a later step we will have do work on a finer model of muscles and the role of the fibula. Let us see whether I expect too much from Opensim.

For my "Joints" I am using freejoints. I will - try to - upload my model together with the geometry files. All the rest should be taken from the original gait2354 model. My IK configuration is in the gait_06_16.xml. At the Moment I am sticking with a strange behaviour of the model when running the inverse Dynamics sequence. In the kinematics Animation all segments stay together as expected. In the ID there is a big displacement between Segment 5 and 6. Only the positioning of the segments is tuned up to now. Bushing Forces are set to high values to force the segments together for the first tests.

Thanks in advance for your help.

Kind regards
Uwe

PS: I cannot see my uploaded files in the preview. I hope they will come along anyway.

[jimmy d]

Uwa, please try to post your files again.

-j