On the stability of manipulators performing contact tasks

Manipulation requires contact with the object being manipulated, and the full potential of robots can only be realized when they are applied to contact tasks. One of the difficulties engendered by contact tasks is that they require intimate dynamic interaction between the robot and its environment. That interaction changes the performance of the robot and can jeopardize the stability of its control system. A discussion is presented of the problem of preserving the stability of a manipulator's control system during contact tasks. It will be shown that contact stability may be guaranteed if the control system provides the manipulator with an appropriately structured dynamic response to environmental inputs. Two aspects of one implementation of such a controller will be considered. Robustness to large errors in the manipulator kinematic equations and to unmodeled interface dynamics is shown.>