Force tracking in impedance control

Two simple and computationally efficient schemes for force tracking using impedance control are presented. The schemes generate the reference position trajectory required to produce a desired contact force despite lack of knowledge of the environmental stiffness and location. The first scheme uses direct adaptive control to generate the reference position on-line as a function of the force tracking-error. The second scheme utilizes an indirect adaptive strategy in which the environmental parameters are estimated on-line, and the required reference position is computed based on these estimates. Simulation studies are presented for a 7-degrees-of-freedom (DOF) robotics research arm using full arm dynamics. It is shown that the adaptive schemes are able to compensate for uncertainties in both the environmental stiffness and location, so that the end-effector applies the desired contact force while exhibiting the specified impedance dynamics