IK Tasks

[Saeed-Mansouri]

Dear Dr. Caron,
I have encountered an issue with the IK for which I appreciate your help. As you said in your paper, IK is solved based on six tasks:

1- Maintain foot contact(s)
2- CoM position and velocity tracking
3- Swing foot position and velocity tracking
4- Bend the chest to a prescribed angle
5- Keep the pelvis upright
6- Regularizing half-sitting joint configuration

I know that the IK is in the acceleration level. However, I cannot find a damping coefficient for some tasks. Would you please explain it?
The first task "Maintain foot contact(s)" means keep support foot in contact with the ground and is a PD regulation. In the codes, mc_tasks::coptask is used to define the first and third tasks. Why don't you use a PositionTask instead of COPTask? What does mc_tasks::coptask do?

[stephane-caron]

However, I cannot find a damping coefficient for some tasks. Would you please explain it?

What tasks cannot you find a damping coefficient for?

Why don't you use a PositionTask instead of COPTask?

The CoPTask implements foot damping control, which is described in Section III.A of the paper. If we used a position task here, we wouldn't get the force control we need for balance. Here is an overall picture of what balance control is:

In the stabilizer, force control is implemented by the CoPTasks, updateFootForceDifferenceControl() and updateCoMTaskZMPCC() functions. They correspond to the three admittance control strategies described in the paper and summarized at the bottom of this overview poster.

What does mc_tasks::coptask do?

Take a look at the documentation comments in CoPTask.h, as well as in the header file of its parent classes. Feel free to reopen this issue and ask further questions if anything is not explained or badly explained there.