CONSISTENT TASK SPECIFICATION FOR MANIPULATION SYSTEMS WITH GENERAL KINEMATICS

Although most of the literature bn manipulation systems deals with sys tems with as many degrees of freedom ns the dimension of their task sp ace, or even with more (redundant manipulators), kinematically defecti ve manipulation systems are often encountered in robotics, in particul ar when dealing with simple industry-oriented grippers, or when the wh ole surface of the manipulator limbs is exploited to constrain the man ipulated object, as in ''whole-arm'' manipulation. Kinematically defec tive systems differ from nondefective and redundant manipulation syste ms in many ways, some of which have been addressed in the literature. In this paper, we focus on one of the central problems of manipulation , i.e., controlling the manipulator in order to track a desired object trajectory, while guaranteeing that contact forces are controlled so as to comply with contact constraints (friction bounds, etc.) at every instant. We attack this problem by an unified approach that is approp riate for manipulation systems with general kinematics. When dealing w ith kinematically defective systems, it is not possible to assign arbi trary trajectories of object motions and contact forces. To understand what restrictions position and force reference trajectories Should ex hibit in order to be feasible by a given system, is the central issue of this work.