Effect of Point Constraint in kinematics of the ankle

[Catarina Ribeiro]

Hello,
I have inserted an AFO with a self-align mechanism that is fixed to the left foot of the gait2354 model by a Point Constraint defined in the toes.
Then, I ran the Inverse Kinematics tool, one with the Point Constraint enabled and other with this constraint disabled. The figure attached next shows the kinematics curves of the ankle. My question is if it's normal that this constraint limits this much the ankle angle? And how can I fix this, if possible?
Note that I've already ran the RRA tool, so the results are dynamically consistent.

OpenSimForum(1).png (39.15 KiB) Viewed 227 times

Another thing that I can't quite understand is how the curve of kinetics (total ankle moment (AFO+muscles)) with the Point Constraint enabled can show a similar behaviour relatively to the curve of normal gait ("NoAFO").

OpenSimForum(2).png (55.15 KiB) Viewed 227 times

I would very much appreciate any help here.

Thanks in advance and hope you are all well and safe from this pandemic.

Catarina Ribeiro

[Ayman Habib]

Hi Catarina,

A point constraint enforces that two locations on two different bodies are coincident, can you explain what are the two points/bodies you're using? and if you get the correct kinematics? Can you also explain what you mean by self-align? A diagram or picture would be very helpful.

Thank you,
-Ayman

[Catarina Ribeiro]

Hello Ayman, thanks for the response.

The two bodies are the AFO_foot and the toes of the left foot of the model. After extensive try and error, the points that best defined visually were the mass center of the calcaneus the gait2354 model and a changed mass center of the AFO foot. If I defined the mass center of the toes, the AFO wouldn't fix to the foot.
The mechanism it's presented in the attached figure. The underlined joints are pin joints that allow for the rotation in the sagittal plane. The rest of the mechanism' joints were defined as weldjoints.

Forum.PNG (382.37 KiB) Viewed 189 times

Thank you for the help,
Catarina