Hi Sarah
The orientation of the coordinate systems on segments in the
shoulder follows the following guidelines
http://www.fbw.vu.nl/research/Lijn_A4/shoulder/isg/proposal/protocol.
htm
If you would like to have the reactions in the GH joint given in a
locally defined coordinate system on humerus some vector algebra
needs to be applied. Here is a description on how this can be done:
1: Create a new node on humerus its location (sRel) is not important
but it’s orientation (ARel) must be defined to obtain the desired
orientation. I have uploaded a small example named “RotateNode.any”
to the file section. This small sample shows how to rotate a node
based on two user defined points. The script will change the
orientation of the node so that the Z axis will point from point p2
towards p1.
2: Next step is to measure the force in gobal coordinates, this can
be done using the function AnyForceMomentMeasure, please see the
file "RotatedNode.any " for details
3: We now have force GHReaction.F in global coordinates and we now
need to transform it into the user defined coordinate system. For
this we will now open the folder InverseAnalysis in the study,
please see the file "RotatedNode.any " for details
This way of transforming the forces into a new coordinate system can
be applied whitout making changes to the Brep. Alternatively the
coordinate system of humerus should have been changed.
The ARel’s numbers which are not 0 and 1 most mostly comes from
similar transformations as given in the sample. Typically we would
like a cylinder to follow a part of a bony surface. We will then
define two nodes on this surface which will be used for calculating
ARel. Please see the file BRep/Arm3D/shoulderArm.root for details
about where the data originates from.
Best regards
AnyBody Support
— In anyscript@yahoogroups.com, “Sarah R. Sullivan”
<sarsulli@e…> wrote:
>
>
> First off, I wanted to let you know that I am now driving the
> wheelchair model with actual patient force and moment push-rim
data,
> and I wanted to thank you for your help with it!
>
> I will be moving on to also driving the model with kinematics, but
> right now I am most concerned with making sure that my joint
reaction
> force results are physiologically valid for what I am concerned
with.
> I want to be able to find the compression and shear forces in the
> shoulder, which means making sure the axes of the bones in the
model
> are correct and in reference to local coordinates (compression
being
> the forces along the y-axis of the humerus and shear being the
forces
> along the z-axis). I want the y-axis of the model to be along the
> long bone of the humerus (for example) and vertical, the x-axis to
be
> medial/lateral and horizontal to the ground, and the z-axis to be
> anterior/posterior and horizontal to the ground. As the subject
> moves, I want the y-axis to always remain along the length of the
> bone. I don’t want the information to be with respect to the
global
> coordinates, but instead with respect to the local coordinates.
>
> Knowing that, I am not sure where you are getting numbers for
example,
> in the seg file in the BRep repository of the model. Looking at
the
> humerus again, where do the following numbers come from?
>
> AnyRefNode art_tub_minus_tub_majus = {
> sRel = ({…Sign*-.001379, 0.008999, -0.009119}+.Soffset)*.Smat;
> ARel = {{0,1,0},{0,0,1},{1,0,0}};
> };
>
> Where do all the sRel and ARel numbers come from, especially when
the
> ARel numbers aren’t 0 and 1? And do you have any suggestion about
how
> to make the y-axis of the humerus, for example, the difference
between
> the joint center of the elbow minus the joint center of the humeral
> head?
>
> Thank you for your time!
> Sarah Sullivan