Connecting exoskeleton to human body

Hello,

I have a problem with the implementation of my exoskeleton system.
The system consists of a belt, attached to the hip and 2 brackets, which are connected to the belt by a revolute joint. However, they should be able to rotate freely. The movement is given by the person, so the brackets should touch the person at the shoulder blades and move in the same way. I don't understand why the simulation behaves so strangely. If I use other joint definitions, the system does not work at all. Can you please help me how to define the dependencies correctly? I haven't defined the contact forces on the belt and shoulder blades respectively, because I don't know yet how to do it.

I wanted to upload it, but it is not possible for new user. Is there another way I can provide you the model?

Thanks,
Anna

Hi @mannanas and welcome to the forum :slight_smile:

First of all, the upload function should be available to you on your next forum post - it is just to avoid spam.

So you want your bracket revolute joints to be spherical joints ?

  • how do you currently connect the brackets to the shoulder?
  • what error message do you get?

A good approach is to model in a iterative approach so you start by adding one object at a time and implement simplified constraints so it can run, then you start moving towards the correct joint, contacts etc. one DoF at a time.

Best regards,
Bjørn

Hello Bjorn,

the joints at the harness should be revolute joints and the joints at the shoulder spherical joints. I don't know if it is possible to model the contact points on the shoulder without a joint...a spherical joint seemed logical to me.
At the moment I don't get an error, but the model is moving in a strange way (see attachment). The exo isn't connecting to the body, but the body moves strangely to connect to the exo.

Probably the fixation of the harness is wrong, maybe you have a better suggestion than implemented.
All of the implementation of the system is done in the file "Exo_02.any".

Best regards,
Anna
Model_with_Exo.zip (3.7 MB)

Hello Bjorn,

is it possible that I define a contact point at the shoulders, so the bars have to move with the given motion and the revolute joint on the hips move automatically due to the given motion? Or do I need to define a driver for them too?
If it is possible, how can do I implement this? I tried a lot of different things, but nothing is working...

Kind regards,
Anna

Hi @mannanas

It seems that your harness is rotated when connecting to the hips?
try and look into aligning the two coordinate systems so the harness sits correctly as a belt around the hip. Your spehrical joints connect the two but it does not ensure that it is rotated correctly.
You can pick three nodes on the harness and the three corresponding nodes on the hips. Then create a reference system based on the three and use those for connecting.

A good advice is to keep the Exo.main.any file working without the body. This way you can test the Exo alone without including the body.

Best regards,
Bjørn