Stability margins and passivity for the control of robots operating in varying-impedance environments

It is well-known that if the robot with its end-effector force control is passive, the closed loop system consisting of the robot and an arbitrary passive environment is asymptotically stable. Passive robot control, however, limits the achievable robot impedance reduction. Recently, [1] (Buerger and Hogan, 2007) investigated what performance can be achieved with non-passive control when uncertainty bounds for the environment are known, but unfortunately neglected stability margins. Here we present a robust force control design with stability margins for Buerger and Hogan's example.