RRA pelvic drift and high residual force in the y direction
Posted: Wed Jun 03, 2015 2:34 am
To whom it may concern
I am performing a modeling pipeline on opensim for over ground walking specifically during stance phase. The pipeline is as follows:
Scale - IK - ID - RRA - CMC
I only perform the analyses for 0.69 seconds which includes the toe off of the right foot, full stance of the left foot and heel strike to midstance of the right foot (in that order). I have been able to scale my model within the specified error boundaries to an extent that when I run the IK with all the markers activated it produces errors below the IK error boundaries in the first run. Therefore I have relevant confidence in these steps.
I have a grf file which applies a 3D ground force to both feet during the trial as well as a free y-torque on both feet. When I run the RRA my model experiences pelvic drift in both the y and z direction. I then apply the body segment weight changes advised by the RRA tool and the residual forces decrease but the maximum and rms residual forces are still too high. The residual moments are within the specified range however. The model still experiences pelvic drift in both the y and z direction after adjusting the body segment masses.
It is important to note that the pelvic drift and increase in residual forces starts when the left foot (which does a complete stance) gets to midstance. The model then begins to lift and the residual forces increase. Then when the right foot takes the next step, at heel strike the model lifts more and drifts more in the z-direction.
I have tried altering the kp and Kv values as well as reducing the optimal residual forces. Although this does drop the residual forces, it seems to increase the pelvic drift. I would also like to note that my model does move forward in the x-direction when walking, so the pelvis will displace in the x-direction. I have checked that my ground forces are acting on my model and they seem to be if I use the preview experimental data tool. I see in the gait2392 example that their ground forces COP is acting at -0.075m in the y-direction. Is this necessary?
I have run out of ideas to reduce the residual force and pelvis drift and any advice or help would be very welcome. I have a feeling it has to do with the grfs. I would like to note that I used the gait2392 generic model (which I scaled) and also the RRA files are adapted from the gait2392 example. I have changed the pelvis COM on the xml file.
Thank you in advance for your help.
Kind regards,
Bruce de Jongh
I am performing a modeling pipeline on opensim for over ground walking specifically during stance phase. The pipeline is as follows:
Scale - IK - ID - RRA - CMC
I only perform the analyses for 0.69 seconds which includes the toe off of the right foot, full stance of the left foot and heel strike to midstance of the right foot (in that order). I have been able to scale my model within the specified error boundaries to an extent that when I run the IK with all the markers activated it produces errors below the IK error boundaries in the first run. Therefore I have relevant confidence in these steps.
I have a grf file which applies a 3D ground force to both feet during the trial as well as a free y-torque on both feet. When I run the RRA my model experiences pelvic drift in both the y and z direction. I then apply the body segment weight changes advised by the RRA tool and the residual forces decrease but the maximum and rms residual forces are still too high. The residual moments are within the specified range however. The model still experiences pelvic drift in both the y and z direction after adjusting the body segment masses.
It is important to note that the pelvic drift and increase in residual forces starts when the left foot (which does a complete stance) gets to midstance. The model then begins to lift and the residual forces increase. Then when the right foot takes the next step, at heel strike the model lifts more and drifts more in the z-direction.
I have tried altering the kp and Kv values as well as reducing the optimal residual forces. Although this does drop the residual forces, it seems to increase the pelvic drift. I would also like to note that my model does move forward in the x-direction when walking, so the pelvis will displace in the x-direction. I have checked that my ground forces are acting on my model and they seem to be if I use the preview experimental data tool. I see in the gait2392 example that their ground forces COP is acting at -0.075m in the y-direction. Is this necessary?
I have run out of ideas to reduce the residual force and pelvis drift and any advice or help would be very welcome. I have a feeling it has to do with the grfs. I would like to note that I used the gait2392 generic model (which I scaled) and also the RRA files are adapted from the gait2392 example. I have changed the pelvis COM on the xml file.
Thank you in advance for your help.
Kind regards,
Bruce de Jongh