Adaptive force control of robot arm with estimation of environmental stiffness

Working robots may encounter and interact with various objects, whose dynamical characteristics are unknown; linear or nonlinear and their strength of stiffness. The interaction includes such processes as collision of arm with environments, hand gripping of objects, holding human body in medical case etc. These processes consist of free motion before touching the objects, and constrained motion after then. An adaptive force control is proposed to manage these conditions mentioned above. The environment is modeled by linear or nonlinear spring with unknown stiffness. The impedance parameters are tuned through the use of stiffness estimation for both linear and nonlinear spring. The conventional recursive least squares method is modified so that the nonlinearity can be detected with high sensitivity.