In teleoperation of manipulators, the positions and velocities of the slave actuators should resemble those of the master controls to help the operator project his presence into the slave space. Direct viewing by TV has been in-corporated into teleoperator design based on this philosophy, and then becomes a most common sensor subsystem of teleoperator. Force reflection to the operator is also recognized as a useful sensory correspondence for enhancing the operator's identification with the task at hand. Several exoskeletal devices have been proposed as the master arms for the force reflection. However, the mechanisms become complicated because the arms should have the same number of active joints as the slave manipulators; moreover, those provide not only the required sensory feedbacks on the operator but also uncomfortable constraints. So as to overcome this difficulty, we propose a new man-machine interface in which functional electrical stimulation is used to present the reaction forces to the operator. Three small electrodes and two small position/orientation sensors are attached on the skin of the upper limb of the operator. Force reflection from the slave manipulator to the operator is achieved by functional electrical stimulation through the surface electrodes. There is no mechanical element in our master subsystem because the upper limb of the operator works as the master arm by itself. It is shown in this paper that the proposed structure of master subsystem allows the operator to be released from the unnecessary constraints of exoskeletal devices. The effectiveness of the proposed teleoperator is illustrated by several experiments with a seven axis slave manipulator.
