Force-tracking impedance control for manipulators mounted on compliant bases

The paper presents a control law for interaction tasks with environments of unknown geometrical and mechanical properties by manipulators mounted on compliant bases. Based on force-tracking impedance controls, the control strategy allows the execution of such class of tasks using the estimation of base position as a feedback in the control loop, requiring at the same time the on-line estimation of the environment stiffness. The properties of the control using non co-located sensors and the dynamic configuration of the coupled base-robot-environment system are studied. An Extended Kalman Filter is used for the estimation of the environment because of measurement uncertainties and errors in compound interaction model. The base is modelled as a second-order physical system with known parameters (offline identification before the task execution) and the base position is estimated from the measure of interaction forces. The grounding position estimation and the defined control law are validated in simulation and with experiments, especially dedicated to an insertion-assembly task. Control laws with and without the base compensation in the feedback loop are compared, verifying the effectiveness of the developed control law.