Small movement in robot when I set d->ctrl to d->qfrc_bias

Discussion in 'Support requests' started by Isaac, Aug 12, 2019.

  1. Hello,

    I want to implement an impedance controller in task space for my robot. But when I set the d->ctrl signals to d->qfrc_bias, I see movement in the arm. I think it should be without any movement. Am I wrong?
     
  2. Emo Todorov

    Emo Todorov Administrator Staff Member

    There are also passive forces from any springs and dampers, as well as constraint forces from any contacts, joint limits etc.

    Note also that ctrl is the control signal. How it maps to force depends on the actuation model. I am assuming you are using the "motor" shortcut with gear ratio of 1 so in that case ctrl=force.
     
  3. Thank you for your answer. Yes that's true. I use motor tag with gear=1. then set the d->ctrl value using controller. When I use controller in joint space it works fine and the arm is fixed. but when I use controller in task space and then multiply it by J^T and add qfrc_bias, It has some small movement at first and then come back to it's location. the change is about 2-3 cm. Now at the first moment which the error is zero, my controller doesn't generate any force and I only set the qfrc_bias and it cannot hold the arm in a fixed position. I cannot remove it.
     
    Last edited: Aug 13, 2019