Segment definition

[mehrdad davoodi]

Hi
I am Mehrdad Davoodi, and master student in Sharif university in Tehran.
I am intrested in the joint moments, and muscle forces than my model, and i will test with force plate, how i use force plate data in opensim?
and i have a full body model that upper limbs ( especially shoulder ,..), where is suchlike this model in opensim?

and,** is it possible to definition a segment like a bar( or flexible pole ) in opensim that has a motion (like cos diagram) and model hold it in his hand to transfer bar's vibration to body?

Best,
M.D

[Dimitar Stanev]

Hi,

Have look at the user guide to get familiar with the tool.

http://simtk-confluence.stanford.edu:80 ... %27s+Guide

You would like to perform Scale->Inverse Kinematics->Inverse Dynamics in order to compute the moments. The force plate data can be used in OpenSim and there are scripts for matlab that can help you convert the data.

https://simtk.org/projects/motonms

Here are all available model (there are also some in the SimTK project):

http://simtk-confluence.stanford.edu:80 ... tal+Models

is it possible to definition a segment like a bar( or flexible pole ) in opensim that has a motion (like cos diagram) and model hold it in his hand to transfer bar's vibration to body?

OpenSim does not support flexible bodies (you can model it with a rigid body, but you will not get the vibrations). Otherwise, if you are able to somehow estimate the effect of the bar on the hand, you can always apply an external force f(t) on the hand body.

Regards

[mehrdad davoodi]

Hi Demitar
thank you very much.
i have some questions about your reply, please answer me

-please look at image that attached, my segment is a grip with two wing, also they are rigid, but their connection is like spherical joint of 3 dof, and grip hold by hand, and hand also has a little linear motion, i should definition a linear motion for grip( that transfer to hand) and a similar and simultaneous motion for two wings, like cos Fourier Series,
can i build this collection? and if yes, how?

-in opensim models, which model is best for upper extremity muscles analysis?

-and opensim support kistler' force plate? what i do,when i have not c3d format ( like .txt or .csv format ) ? and after converting to this open sim format how include(attach) data to model ? i have this questions also about test with markers.

i'm sorry for this many and long questions, with them large range of issue.

Best Regards,
Mehrdad davoodi

[Dimitar Stanev]

It seems a complex setup. You would like to think not only about how to model this but also about your simulation. What question you want to answer (e.g. what are the muscle forces?)? In your experiment setup do you record the motion of the object that your hand is griping and the forces applied by the wind?

If that is the case then you need to model an extra free body (with proper mass parameters) and attach it to the hand by a constraint. Then you need to apply your recorded motion to Inverse Kinematics. After that you can perform static optimization but you need to account for any external force acting on the system (ground reaction forces, wind forces, etc.).

On the other hand if you are trying to simulate the effect that the object have on your body assuming some perturbations, you need to construct some kind of controller to keep a balance and consequently apply the forces and see what is going on (very difficult).

An alternative approach would be to use inverse dynamics and static optimization, without any motion and to assume some kind of perturbation force. You would need to implement a controller again that keeps the body in some configuration so that you can predict the motion and use it latter.

Here are all the available models. There are some models if you search in the project.

http://simtk-confluence.stanford.edu:80 ... tal+Models

I would suggest you to simplify the setup as possible as you can.

https://simtk.org/projects/up-ext-model

opensim support kistler' force plate?

Yes

https://simtk.org/projects/motonms

Regards

[mehrdad davoodi]

Hi
Thank you dear Dimitar.

i will record body(hand,..) and bar motion (marker tracking) , and have a force plat ( grf,moment and cop), wind forces are not my test results.
my purpose is evaluation muscle moment arms.
{ 2 question:
-i can plot moment arms in opensim (image) , but i want to attach model result(moment arms) to MATLAB, how do this connection? and can i save my result in another format( txt, csv,..)?
-moment arms are dependent to motion or independent of tasks?
}

"""""then you need to model an extra free body"""": how i do it? please introduce me some exact refrence for this porpuse.

"""""you can perform static optimization but you need to account for any external force acting on the system (ground reaction forces, wind forces, etc.)."""" please explain this statement.

Best,
Mehrdad Davoodi

[Dimitar Stanev]

i can plot moment arms in opensim (image) , but i want to attach model result(moment arms) to MATLAB, how do this connection? and can i save my result in another format( txt, csv,..)?

You can export your the plot to a data file (right click). Otherwise you would have to do it programmatically through scripting and calling OpenSim API.

moment arms are dependent to motion or independent of tasks?

Moment arm is a function of the generalized coordinates R(q). So if you have different poses your moment arm changes. What the plot tool does is to span a single coordinate and measure the moment arm of the muscle. Also the moment arm may depend on multiple coordinates (e.g. r_soleus(q1, q2, q5)).

"""""then you need to model an extra free body"""": how i do it? please introduce me some exact refrence for this porpuse.

If you open the .osim file you would see how a body is attached to the parent body through a joint. In the same way you will introduce a body attached to the ground by a free joint (6DOFs). Then you would constraint this body's point to the hand by a constraint. Have a look at the documentation and you will find plenty of examples.

"""""you can perform static optimization but you need to account for any external force acting on the system (ground reaction forces, wind forces, etc.)."""" please explain this statement.

When you have the equation of motion, and you would like to solve for the unknown torques knowing the motion (acceleration) you can ignore any other force that is acting on your model, but you will underestimate the actual torques. For example if you are pushing something, the torques will be small, but the actual torques that generate the movement and the force to push are different.

[mehrdad davoodi]

Hi Dimitar
Thank you very much. your helps was very useful.
Best Regards
Mehrdad

[mehrdad davoodi]

Hi
I decided to instead of modeling of flexible pole, measure the perpendicular forces applied by the grip to the hand by FSR sensors. i will record forces per time as real time and synchronized to my setup and then i want to simulate this measured force in opensim as the force applied to specified point in hand to evaluate the moment arms and .., is this simulation possible in opensim and how add this force and build specific point in palm ?

please advise me to achieve this aim.
Best Regards
Mehrdad

this part of user guide is proper for me?
http://simtk-confluence.stanford.edu:80 ... ernalLoads
"A point force (most commonly used) is a force applied at a specified point" -->for filling Point Columns box, can i place marker on grip ? how i fill "Force and point Expressed In" box?

also this part appear good for me, but for forces that are per times (times series?) appear not enough :
http://simtk-confluence.stanford.edu:80 ... eXMLMarker

<!--Apply a force at a point in the direction specified in the body frame -->
<PointActuator name="FY_residual">
<!--Name of Body to which this actuator is applied.-->
<body> pelvis </body>
<!--Location of application point; in body frame unless point_is_global=true-->
<point> 0 0 0</point>
<!--Interpret point in Ground frame if true; otherwise, body frame.-->
<point_is_global> false </point_is_global>
<!--Force application direction; in body frame unless force_is_global=true.-->
<direction> 1 0 0</direction>
<!--Interpret direction in Ground frame if true; otherwise, body frame.-->
<force_is_global> true </force_is_global>
<!--The maximum force produced by this actuator when fully activated.-->
<optimal_force> 8.0 </optimal_force>
</PointActuator>

8 is constant, but i have a excel file of force ! in opensim model exist >hand< body to define <000> point ?where?

[Dimitar Stanev]

Hi,

You can define a body, where you apply your force, if you are unable to record the point. Then you define the 3 components of the force measured in ground frame. Also, you can define a torque force, but I am not sure if you are recording it.

[mehrdad davoodi]

Thank you very much Dimitar
but if i have not a constant force, force is depend to time, how write code for this?