## Search found 166 matches

- Wed Jun 12, 2013 8:02 pm
- Forum: OpenSim
- Topic: Can the Vicon PluginGait marker set be used in OpenSim?
- Replies:
**3** - Views:
**1653**

### Re: Can the Vicon PluginGait marker set be used in OpenSim?

Opensim uses full-body inverse kinematics (IK) and does not need three markers on each segment. It estimates all kinematic variables simultaneously by minimizing the sum of squared distances between simulated marker positions and measured marker positions. Most joints do not have 6 DOF so a surprisi...

- Tue Dec 18, 2012 3:25 pm
- Forum: OpenSim
- Topic: Inverse Kinematics...implementation
- Replies:
**7** - Views:
**2204**

### Re: Inverse Kinematics...implementation

As far as I know, SIMM's inverse kinematic solver uses a Levenberg-Marquardt algorithm ( http://www.netlib.org/minpack/lmdif.f ) so it could solve fast enough for real time applications. If you use the exact same model, the same marker placements, and the same least-squares criterion in Opensim, wit...

- Fri Nov 23, 2012 8:34 am
- Forum: OpenSim
- Topic: kinematic constraint forces
- Replies:
**7** - Views:
**1815**

### Re: kinematic constraint forces

Sherm, I think we have the same idea, just different ways to formalize it. I did not include your eq. (2), which states that the kinematic constraints must be satisfied for the accelerations. I assumed that this would already have been taken care of in the preceding inverse kinematics or forward kin...

- Wed Nov 21, 2012 1:49 pm
- Forum: OpenSim
- Topic: kinematic constraint forces
- Replies:
**7** - Views:
**1815**

### Re: kinematic constraint forces

I do not use Opensim for inverse dynamics but the problem seems somewhat fundamental and not limited to Opensim. We are working on inverse dynamic analysis of the shoulder mechanism. There is a closed kinematic chain (thorax-clavicle-scapula-thorax) and therefore more unknown joint moments than equa...

- Tue Nov 15, 2011 7:28 am
- Forum: OpenSim
- Topic: Extract Muscle Force Vectors (Lines of action)
- Replies:
**13** - Views:
**3332**

### Re: Extract Muscle Force Vectors (Lines of action)

Yes, your understanding is correct. In the Opensim GUI, you can generate a graph of x,y,z components of the line of action vector, as a function of time within the gait cycle, just as you would do with moment arms. Use Tools->Plot->Y-Quantity->moment arm to generate the three curves. Then you can ex...

- Thu Nov 10, 2011 8:02 am
- Forum: OpenSim
- Topic: Extract Muscle Force Vectors (Lines of action)
- Replies:
**13** - Views:
**3332**

### Re: Extract Muscle Force Vectors (Lines of action)

Laurence, If the muscle has via points or wrapping, the line of action changes direction. I assume that you want the line of action where it crosses a joint. There is a trick to get this line of action out of a model. We have done this with SIMM and I think it will work with Opensim too. If you add ...

- Thu Dec 09, 2010 7:02 am
- Forum: OpenSim
- Topic: ID calculations
- Replies:
**6** - Views:
**571**

### RE: ID calculations

<t>There is yet another way to accomplish this.<br/> <br/> Take the 3D acceleration data of snowboard, expressed in Earth XYZ axes (as discussed before). Integrate the signals twice to get XYZ displacement. Initial position and velocity do not matter, so zeros can be used there.<br/> <br/> Then use ...

- Wed Dec 08, 2010 8:41 am
- Forum: OpenSim
- Topic: ID calculations
- Replies:
**6** - Views:
**571**

### RE: ID calculations

<t>I think this changes the situation somewhat and makes me more optimistic.<br/> <br/> You have absolute orientations (relative to earth) as function of time, and a kinematic model to convert these orientations into position/velocity/acceleration data relative to the snowboard. The only thing that ...

- Tue Dec 07, 2010 8:52 am
- Forum: OpenSim
- Topic: ID calculations
- Replies:
**6** - Views:
**571**

### RE: ID calculations

<t>Andreas,<br/> <br/> A long time ago I did some inverse dynamics work on skiing, with inertial sensors (van den Bogert et al., J Biomech 1996). Your first question is one I thought about a lot at that time.<br/> <br/> I suspect that you are using the newer inertial measurement units that give you ...

- Thu Aug 09, 2007 10:32 am
- Forum: Efficient Methods for Multi-Domain Biomechanical Simulations
- Topic: Teleconference - All Teams
- Replies:
**12** - Views:
**2215**

### RE: REMINDERS

<r>Agenda for 8/9/2007<br/> <br/> 1. Year 2 funding (Ton)<br/> 2. Infrastructure (Ahmet)<br/> 3. Foot modeling and testing (Ahmet)<br/> 4. Surrogate modeling (Jason)<br/> 5. Gait optimization (Marko)<br/> 6. Utah update<br/> 7. Stanford update<br/> <br/> Voice instructions:<br/> <br/> 1. At the spec...