A NEW SCHEME FOR HYBRID FORCE-POSITION CONTROL

Many robotic tasks require the end-effector to come into contact with the external environment. In such complex tasks, the manipulator is constrained by the environment, and certain DOFs are lost for motion. The contact forces must be controlled in constraint directions, while the tip position is simultaneously controlled in the free directions. Among the various control laws which have been proposed, Salisbury's active compliance scheme1 and Craig and Raibert's force/position scheme2 are the most used. Although it seems that a parallel force/position scheme is very valuable and consistent concept, some difficulties have been encountered when implementing a hybrid control law. A new approach to hybrid force/position control has been recently developed3 based on an original architecture; the force control loop is closed around an internal position loop in a hierarchical way. The main results of this methodology are presented in this paper, where a detailed comparison with classical methods proved the effectiveness of this new scheme.