On the control of biologically and kinematically redundant manipulators

One of the key problems in motor control concerns the apparent redundancy of muscles and joints. This biological and kinematic redundancy has been an object of study since long. In this paper we will give a review of the various approaches which have been proposed to solve this problem. We will give a comparison of the results of these approaches with special emphasis on recent models, which try to deal with this problem by eliminating the number of degrees of freedom. This reduction will be achieved by imposing constraints, which follow from the biomechanics of the system under study or from some plausible requirements on the behaviour of these systems in various motor tasks. Since this problem is a key issue both in the control of biological and artificial robot manipulators, we will also discuss models from the robotics community, as well as the possible relevance of biological models for robotics. Most biological limbs have a large flexibility in terms of degrees of freedom due to the relatively large number of joints, and due to the fact that the number of muscles acting across a joint usually exceeds the number of degrees of freedom in that joint. Yet, this same flexibility is one of the most complex problems in understanding motor performance, since a kinematically redundant limb allows a movement to be made by a large