Hello, everyone
I was confused with the function of JointReaction Analysis tool in OpenSim 2.2.
when I use RRA setting and results files as input for JointReaction Tool, it seems to give me the results of Joint reaction force.
when I use CMC setting and results files as input for JointReaction Tool, it seems to give me the results of Joint contact force.
So, does that mean the Jointreaction Tool can give us both joint reaction force and contact force depend on the input files we give OpenSim.
Thanks very much for any help.
JointReaction Analysis Tool
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Matt DeMers
- Posts: 16
- Joined: Mon Oct 08, 2007 8:36 pm
RE: JointReaction Analysis Tool
Hi Hang Xu,
The JointReaction Analysis simply reports the reaction forces occurring at a joint due to the structure, or definition of that joint. For example, JoinReaction will only report 3 non-zero forces and two moments for a pin joint, and will report 3 non-zero moments for a ball joint.
I'm going to abandon the reaction force vs contact force distinction because, depending on your joint model, these could be identical. A more appropriate distinction when comparing RRA to CMC is the difference between intersegmental loads and internal joint loads. JoinReaction does not distinguish between the two and will always calculate the resultant of all inertial forces and actuator forces, which corresponds to the internal joint load. It will compute the joint resultant loads based on the model kinematics, external loads, and the actuator forces provided by the user.
Let's assume, as in your case, that the same model, kinematics, and ground forces are used to produce RRA and CMC solutions. If the RRA solution contains just coordinate actuators, these actuators simply represent joint torques. JointReactions computes the resultant loads at the joint, which happen to be equivalent to the intersegmental loads in this case because the model is entirely torque driven. The CMC solution will include muscle actuators so JointReactions computes a joint resultant load that balances these muscle forces. In this case, the internal joint loads are equivalent to bone-on-bone loads. In either case, JointReaction is computing the internal joint force as the resultant of inertial forces and actuator forces. It's up to the user to decide what type of actuators to include.
Matt
The JointReaction Analysis simply reports the reaction forces occurring at a joint due to the structure, or definition of that joint. For example, JoinReaction will only report 3 non-zero forces and two moments for a pin joint, and will report 3 non-zero moments for a ball joint.
I'm going to abandon the reaction force vs contact force distinction because, depending on your joint model, these could be identical. A more appropriate distinction when comparing RRA to CMC is the difference between intersegmental loads and internal joint loads. JoinReaction does not distinguish between the two and will always calculate the resultant of all inertial forces and actuator forces, which corresponds to the internal joint load. It will compute the joint resultant loads based on the model kinematics, external loads, and the actuator forces provided by the user.
Let's assume, as in your case, that the same model, kinematics, and ground forces are used to produce RRA and CMC solutions. If the RRA solution contains just coordinate actuators, these actuators simply represent joint torques. JointReactions computes the resultant loads at the joint, which happen to be equivalent to the intersegmental loads in this case because the model is entirely torque driven. The CMC solution will include muscle actuators so JointReactions computes a joint resultant load that balances these muscle forces. In this case, the internal joint loads are equivalent to bone-on-bone loads. In either case, JointReaction is computing the internal joint force as the resultant of inertial forces and actuator forces. It's up to the user to decide what type of actuators to include.
Matt
RE: JointReaction Analysis Tool
Thank you very much for the explaination which helps me a lot.
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Jonathan Walter
- Posts: 8
- Joined: Fri Mar 28, 2008 7:05 am
RE: JointReaction Analysis Tool
Matt,
Does the JointReactions analysis take into account the loads from a CustomForce as well?
Also, does the Inverse Dynamics class include the actuator ( and customForce ) loads?
Where would I look in the actual code to figure this out?
Jonathan
Does the JointReactions analysis take into account the loads from a CustomForce as well?
Also, does the Inverse Dynamics class include the actuator ( and customForce ) loads?
Where would I look in the actual code to figure this out?
Jonathan