Chris,
It is the weekend here, and you will probably receive an answer that
more directly addresses your questions early next week. However, I
think I should say a few words about driving models in general and
the shoulder model in particular for the benefit of all the members.
In general, AnyBody is neither a forward nor an inverse kinematics
system. AnyBody allows you to drive the model by any combination of
forward and inverse type drivers.
You are right that the “natural” way to drive a model is to start
proximaly and progress along the extremities, and to some extent this
is the way the standing model and the free posture model in the
repository work. But this is a modeling issue and not a system issue.
Now about the shoulder model: It does indeed have all the natural
degrees of freedom of a shoulder, i.e. the scapular-thoracic movement
and the gleno-humeral movement. But the repository models do not
provide access to the scapular-thoracic movement through the
mannequin file. This does not mean that the scapula is welded to the
thorax in a kinetic sense - only that the model specifies that this
movement is zero; the model will still recruit the necessary muscle
forces to keep the scapula stationary.
To control the scapular-thoracic movement you must go to the
JointsAndDrivers file of your model. A bit down you will finde the
sterno-clavicular joint driver. To obtain scapular-thoracic movement
you must either control the angle of the clavicle wrt. the sternum as
it is done in the existing JointsAndDrivers setup, or remove one or
more of these existing drivers and replace them by other driver
strategies. A popular way to drive the scapula is to create a linear
measure between the thorax and the acromion and create two drivers on
this measure driving elavation and protraction/retraction.
I hope this clarifies some of the general issues.
Best regards,
John
— In anyscript@yahoogroups.com, “chrisjgatti” <cjgatti@…> wrote:
>
> Søren,
>
> Thanks for the response. I have a couple additional questions, just
to
> make sure things are clear.
>
> I understand that the shoulder model is ‘driven’ by angles of the
> humerus with respect to the thorax, as opposed to driving distal
> segments in a sequential order (thorax to clavicle to scapula to
> humerus, for example). After playing with the model (comparing the
> scapula position in 0 degrees abduction with 90 degrees abduction)
and
> reading the code, the scapula position and orientation doesn’t seem
to
> be affected by the motion of the humerus. Is this correct? How does
> the elliptical gliding plane of the scapula come into the model
then?
> How does this allow for changes in muscle lengths which span the
> thorax and scapula then?
>
> Also, the referenced information regarding the coordinate system
> information
>
(http://www.fbw.vu.nl/research/Lijn_A4/shoulder/isg/proposal/protocol.
htm)
> states that the origin of the scapular coordinate system is located
at
> the AC joint. In the AnyBody model though, this coordinate system
> seems to be floating over approximately where the acromion meets the
> main body of the scapula, which is posterior to the AC joint. I am
> curious if this difference affects the locations of the muscle
origin
> and insertion points that are defined in the scapular coordinate
> system, such that those points that were originally defined in the
> Dutch shoulder model may be slightly translated in the current
AnyBody
> model.
>
> Thanks again,
>
> Chris
>
> — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
wrote:
> >
> > Hi Chris
> >
> > Please see posting #1445 in this group, this is also about
> > coordinate systems in the shoulder and there are references to
> > several other postings on this topic.
> >
> > Please ask again if this do not answer your questions
> >
> > Best regards
> > Søren, AnyBody Support
>