I am trying to use a bushing force to model the stiffness/damping of a thin film placed across the front of the patella. Intuitively, I had assumed flexing the knee (moving in the -z direction) should cause the spring to generate a positive moment in the z direction which should result in an increase in the knee_angle_moment found using inverse dynamics.
But I am seeing a decrease in the value of knee_angle_moment.
Can you please help me understand two things:
1. What is the knee_angle_moment actually telling me?
2. Am I implementing the Bushing force improperly? Are the angles specified in radians or degrees? Is there a way to change the sign of the stiffness so that it effects the knee joint in the proper way?
Thank you for your help,
Heather Lai
Here is the code I used to implement the bushing force:
<BushingForce name="KneeJointBushing_l">
<body_1> femur_l </body_1>
<body_2> tibia_l </body_2>
<location_body_1> 0.03 -0.04 0.000 </location_body_1>
<orientation_body_1> 0.0000 0.000 0.0000 </orientation_body_1>
<location_body_2> 0.0000 0.0000 0.0000 </location_body_2>
<orientation_body_2> 0.000 0.000 0.000 </orientation_body_2>
<rotational_stiffness> 0.000 0.000 0.7155 </rotational_stiffness>
<translational_stiffness> 0.0000 0.000 0.000 </translational_stiffness>
<rotational_damping> 0.000 0.000 0.00089 </rotational_damping>
<translational_damping> 0.0000 0.000 0.000 </translational_damping>
</BushingForce>