Iterative learning of impedance control from the viewpoint of passivity

This paper proposes an iterative learning control scheme for impedance cont rol of robotic tasks when the tool endpoint covered by soft and deformable material presses a rigid object or environment at a prescribed periodic for ce pattern. To this end, an iterative learning control scheme for a class o f linear dynamical systems with a negative feedback structure is analysed a nd convergence of the proposed learning update law after a sufficient numbe r of repetitions is proved. It is shown that this convergence realizes impe dance matching in a sense of electric circuit theory if the feedback system can be expressed as a lumped-parameter electric circuit. The iterative lea rning control scheme is then applied for a case of impedance control of rob otic tasks when the characteristics of reproducing force of the deformable material is nonlinear in its displacement and unknown and the tool mass is uncertain. Simulation results are also presented, which show effectiveness of the proposed learning control scheme. Copyright (C) 2000 John Wiley & So ns, Ltd.