An exponentially stable adaptive control for force and position tracking of robot manipulators

The problem of controlling a robot manipulator while the end effector is in contact with all environment of finite but unknown stiffness is considered in this paper. An exponentially stal,le control law is derived starting fr ont a passivity-based position control algorithm. The original position tra jectory is scaled along the interaction direction so as to achieve force tr acking as well as position tracking: along: the unconstrained directions. A passivity-based adaptive algorithm is designed to avoid the explicit compu tation of the scaling factor, which depends on the unknown stiffness of the environment, leading to time-varying PID control actions on the force erro r.