A limitation of position based impedance control in static force regulation: theory and experiments

This paper documents explanation of an experimentally observed behavior suggesting basic limitation to the implementation of position-based impedance control in a static force control application. It is shown that finite positioning accuracy will lead to recurring oscillatory behavior if the static component of the target impedance is less than twice the stiffness of the combined environment and force sensor. Experiments demonstrate this limitation, and show that application-specific compensation methods can be used to decrease the apparent manipulator stiffness without compromising stability. The experiments were performed on a Unimate MK-II hydraulic research robot