Hello Denmark!
Now, I must ask you, when will optimization be implemented?
btw, you can’t ski here just yet…but any day now…
/jokke (who just might update the webpage for the 5th workshop one
day)
Hi Jokke,
Good to hear from you. I hope your skiing model is coming along.
For the other members of the group let me just explain that the
optimization facility is what is also sometimes described as inverse-
inverse dynamics. It enables the system to identify partially
unknown movements and peform ergonomic optimization.
Anyway, this facility has been pending yet another and somewhat
delayed restructuring of the basic datastructure of the system. This
hopefully final restructuring will allow for a facility called
AnyFunction necessary to define objective and constraint functions
in a uniform way. After that, the next step is automatic parameter
studies that can vary model parameters systematically and evaluate
the results. Finally, this will become an optimization facility for
automatic identification of the best combination of the variable
parameters.
AnyFunction will be available in the fourth beta release scheduled
for the beginning of December. Parameter studies and optimization
will come after that, but it is unlikely that we can include them in
version 1.0. However, registered users will have access to beta
releases of version 2.0 as soon as they are ready. This will
hopefully be shortly into 2004.
Best regards and happy skiing.
John
— In anyscript@yahoogroups.com, “joakim_holmberg”
<joakim_holmberg@y…> wrote:
> Hello Denmark!
>
> Now, I must ask you, when will optimization be implemented?
>
> btw, you can’t ski here just yet…but any day now…
>
> /jokke (who just might update the webpage for the 5th workshop one
> day)
Hello
I have a question concerning the optimization approach to minimizes
muscles activities (=muscle force divided by the current muscle
strength): I understood, that the MAXIMAL muscle activity of all
muscles is minimized and not the sum of all maximal muscles activies,
i.e. it is opimized in a sense, that NO single muscle gets overloaded.
Is that right?
By the way I did not introduced myself. My interests are in shoulder
biomechanics in spinal cord injured individuals and I am working in
the Instiute of Biomechanics at the ETH Zurich, Switzerland.
Thanks in advance for the answer,
Heidi
Hi Heidi
Welcome to the group!
The basic optimality assumption in the AnyBody Modeling System is that the
body attempts to use its muscles in such a way that fatigue is postponed as
far as possible. This leads to the idea of minimizing maximum muscle
activity.
In other words the optimizer will always try to lower the activity of the
muscle which is maximally loaded, so it is correct that is not the sum of
the activities. This do not ensure however that no muscles is overloaded,
you may have a problem where the activities will be higher than one, but
using the min max formulation you can be sure that there is not other
solution that will be able lower the activities any further.
It is possible however to add a penalty to the objective function which will
add a fraction of the sum of the activities to the objective function,
please see below
Minimize
(maximum muscle activity)
- e1*(sum of activities)
- e2*(sum of squared activities)
Subject to
- Equilibrium equations fulfilled
- Muscles are not allowed to push
In the tutorials you can find a simple arm example illustrating the use of
this.
<http://www.anybodytech.com/514.0.html>
http://www.anybodytech.com/514.0.html
Best regards
Søren, AnyBody Support
From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf
Of heidi_knuesel
Sent: 6. september 2006 16:36
To: anyscript@yahoogroups.com
Subject: [anyscript] Optimization
Hello
I have a question concerning the optimization approach to minimizes
muscles activities (=muscle force divided by the current muscle
strength): I understood, that the MAXIMAL muscle activity of all
muscles is minimized and not the sum of all maximal muscles activies,
i.e. it is opimized in a sense, that NO single muscle gets overloaded.
Is that right?
By the way I did not introduced myself. My interests are in shoulder
biomechanics in spinal cord injured individuals and I am working in
the Instiute of Biomechanics at the ETH Zurich, Switzerland.
Thanks in advance for the answer,
Heidi
[Non-text portions of this message have been removed]