Hello.
I am Hrishi Shah, a graduate student at SUNY, Buffalo and am currently
on an independent study that examines the effect of an exo-knee on the
actual knee.
I aim to make a model with two actual Leg segments and two exoskeleton
leg segments attached to the leg segments nodes via fixed joints. The
exo-knee and the actual knee are the only revolute joints in the whole
setup.
However, in the first phase itself, when I tried to cut out the pelvis
and foot from the foot model by copying their nodes to the Upper leg
and shank segments resp., it comes up with an error in Inverse Dynamic
Analysis saying that its “Kinetically over constrained”. I have
already removed many muscles that are used for movements other than
the knee movements. Could someone please point out what the error is?
The files are in Simplistic_Leg.zip.
Thanking in anticipation.
Regards,
Hrishi Shah
Hi Hrishi Shah,
The same question have been ask about this model being kinetically over
constrained by Shivaswamy Anirudh some days ago, one of your colleague I
suppose?
Well here is the answer I gave him:
"The model being kinetically over-constrained means that there are too much
reaction forces.
In your case the Reaction.Type of the hip joint and knee joint are switched
On. So all the load is carried by the artificial force of the drivers and
therefore the muscles are not activated. You have to free at least one dof.
As there are no muscles around the hip joint it is indicated to keep the
Reaction.Type On on this joint, but the Reaction.type of the knee joint must
be switched Off in order to load the muscles."
Once this is done I noticed a second issue that will prevent the model to
run the inverse dynamic analysis. The problem is that the Soleus muscle has
its origin and insertion at the same node, it is just a “point” muscle with
no length. The muscle cannot be recruited in such configuration. You should
either remove or modify this muscle.
Also the tibialis anterior and the gluteus maximus are doing some kind of
loop with the origin and insertion at the same node, I think you should
reconsider the definition of those 2 muscles.
Best regards,
Sylvain, AnyBody Support
From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf
Of hrishi_shah2002
Sent: 16. januar 2009 00:36
To: anyscript@yahoogroups.com
Subject: [AnyScript] Simplistic yet kinetically overconstrained Leg model
Hello.
I am Hrishi Shah, a graduate student at SUNY, Buffalo and am currently
on an independent study that examines the effect of an exo-knee on the
actual knee.
I aim to make a model with two actual Leg segments and two exoskeleton
leg segments attached to the leg segments nodes via fixed joints. The
exo-knee and the actual knee are the only revolute joints in the whole
setup.
However, in the first phase itself, when I tried to cut out the pelvis
and foot from the foot model by copying their nodes to the Upper leg
and shank segments resp., it comes up with an error in Inverse Dynamic
Analysis saying that its “Kinetically over constrained”. I have
already removed many muscles that are used for movements other than
the knee movements. Could someone please point out what the error is?
The files are in Simplistic_Leg.zip.
Thanking in anticipation.
Regards,
Hrishi Shah
[Non-text portions of this message have been removed]