Forums Anyscript.org  

Go Back   Forums Anyscript.org > Self-Supported Forum > Debug model

Notices

Reply
 
Thread Tools Display Modes
  #1  
Old 10-22-2014, 08:41 PM
Stijnugent Stijnugent is offline
Junior Member
 
Join Date: Sep 2014
Posts: 3
Default Hinge model of the knee

Dear all

I am trying to program a hinge model (representing a knee) for validation of our Oxford Knee rig.
-The model has 2 segments, a femur and a tibia. Both parts are connected by a hinge.
-The femur segment is attached to our rig with a hinge, while the ankle (bottom part of the tibia) is only positioned in the xy-plane.
-The axis of the hip-hinge and the knee-hinge is the z-axis so we can do the analyses in 2D
While running the InverseDynamics, I get the message :
'There are fewer unknown forces (muscles and reactions) than dynamic equations.'

Hopefully this is enough information to understand the model.
Does anybody has a suggestion on this?

Stijn
Attached Files
File Type: txt teststijn3.txt (2.8 KB, 6 views)
File Type: any HingeModel-V9.any (4.5 KB, 7 views)

Last edited by Stijnugent; 10-22-2014 at 08:47 PM.
Reply With Quote
  #2  
Old 10-27-2014, 09:01 AM
mkjung9980's Avatar
mkjung9980 mkjung9980 is offline
Senior Member
 
Join Date: Aug 2009
Posts: 886
Default

Hi Stijn,

First of all, there is no problem in your model in terms of kinematics.

You defined same number of kinematics constraints as the number of DoFs.

But there is not enough reaction forces in your model.

You removed all the joint constraint reactions in your two revolute joints.

Also you removed the reactions in your drivers. Then you should define some external reaction forces or muscles.

You should clarify how you would like to arrange the force elements in your model.

Best regards,
Moonki
__________________

Moon Ki Jung, Ph.D, Application Engineer, AnyBody Technology A/S.

※ AnyScript™ Reference Manual is the bible.
※ AnyScript™ wiki page is the best supplementary information(http://wiki.anyscript.org).
※ When you would upload your models, please write information about your AMS and AMMR versions.
※ If you want to get more intensive support, please update your information(profile, organization and signature).
Reply With Quote
  #3  
Old 10-27-2014, 05:35 PM
Stijnugent Stijnugent is offline
Junior Member
 
Join Date: Sep 2014
Posts: 3
Default

Dear Moonki,


Thanks for your reply.

When I activate the reaction forces of the driver, then I have a kinetically over-constrained mechanical system. Looking at the system description, I have 12 constraints (2 segments) and 12 active reaction forces. I found it strange that this gives no solution.

The objective of the model is to receive the reaction forces in the ankle.

(Later on I will implement a quadriceps force. But to validate our Knee Rig I will only analyse the influence of gravitation.)

Best regards,
Stijn
Reply With Quote
  #4  
Old 10-29-2014, 09:23 AM
mkjung9980's Avatar
mkjung9980 mkjung9980 is offline
Senior Member
 
Join Date: Aug 2009
Posts: 886
Default

Dear Stijn,

If you turn on all reaction forces in your model, then you can see the following message:
Code:
WARNING(OBJ.MCH.MUS1) :   C:/W..E/AMMR/A..3/F..m/K..g/HingeModel-V10.any(156)  :   HingeStudy  :  The muscles in the model are not loaded due to kinetically over-constrained mechanical system.
NOTICE(OBJ1) :   C:/W..E/AMMR/A..3/F..m/K..g/HingeModel-V10.any(156)  :   HingeStudy.InverseDynamics  :  No muscles in the model.
This means that because there are 12 reactions in 12 DOFs, there is no need for muscles to do any work.
Muscles in AnyBody are lazy. They will only work when it is needed.

I tried to modify your model. Instead of turning on the reactions in your driver, I tried to create a hip and a knee torque.

But I tried to implement that in two different ways.
One is using the AnyReacForce object and the other is using AnyGeneralMuscle object.

In the model which used AnyGeneralMuscle object, you will not see any warning message.

But if you compare the calculated knee and hip torques between two models then you can see that those values are same.

I hope this may help you.

Best regards,
Moonki
Attached Files
File Type: any HingeModel-V10.any (4.9 KB, 2 views)
File Type: any HingeModel-V11.any (5.6 KB, 8 views)
File Type: txt teststijn3.txt (2.8 KB, 2 views)
__________________

Moon Ki Jung, Ph.D, Application Engineer, AnyBody Technology A/S.

※ AnyScript™ Reference Manual is the bible.
※ AnyScript™ wiki page is the best supplementary information(http://wiki.anyscript.org).
※ When you would upload your models, please write information about your AMS and AMMR versions.
※ If you want to get more intensive support, please update your information(profile, organization and signature).
Reply With Quote
  #5  
Old 11-04-2014, 10:23 PM
Stijnugent Stijnugent is offline
Junior Member
 
Join Date: Sep 2014
Posts: 3
Default

Dear Moonki,

Thanks again for your response ! It was very useful.

I used both methods in 2 different models. For your information, I add both models.

Thanks for all your help.

Stijn
Attached Files
File Type: zip HingeModel-V14.zip (132.0 KB, 16 views)
File Type: zip HingeModel-WhitoutQ-force.zip (3.0 KB, 6 views)
Reply With Quote
  #6  
Old 11-05-2014, 10:02 AM
mkjung9980's Avatar
mkjung9980 mkjung9980 is offline
Senior Member
 
Join Date: Aug 2009
Posts: 886
Default

Hi Stijn,

Your model look very interesting. Hope that you can make good models for future!

Best regards,
Moonki
__________________

Moon Ki Jung, Ph.D, Application Engineer, AnyBody Technology A/S.

※ AnyScript™ Reference Manual is the bible.
※ AnyScript™ wiki page is the best supplementary information(http://wiki.anyscript.org).
※ When you would upload your models, please write information about your AMS and AMMR versions.
※ If you want to get more intensive support, please update your information(profile, organization and signature).
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +2. The time now is 05:59 PM.