Impedance control of manipulators carrying a heavy payload

A heavy payload attached to the wrist force/moment (F/M) sensor of a manipulator can fail the conventional impedance controller to establish a desired impedance due to the non-contact components of the force measurement, i.e., the inertial and gravitational forces of the payload. This paper proposes an impedance control scheme for such a manipulator to accurately shape its force-response without needing any acceleration measurement. Therefore, no wrist accelerometer or a dynamic estimator for compensating the load inertial forces are required. The impedance controller is further developed using an inner/outer loop feedback approach that allows not only to overcome the robot dynamics uncertainty, but also to specify the target impedance model in a general form, e.g., a nonlinear model. The stability and convergence of the impedance controller are analytically investigated, and the results show that that control input remains bounded provided that the desired inertia is selected to be different from the payload inertia. Experimental results demonstrate that the proposed impedance controller is able to accurately shape the impedance of a manipulator carrying a relatively heavy load according to a desired impedance model.