Imposing motion constraints to a force reflecting telerobot through real-time simulation of a virtual mechanism

In a teleoperation system, assistance can be given to the operator by constraining the telerobot position to remain within a restricted subspace of its workspace. A new approach to motion constraint is presented in this paper. The control law is established simulating a virtual ideal mechanism acting as a jig, and connected to the master and slave arms via springs and dampers. Using this approach, it is possible to impose any (sufficiently smooth) motion constraint to the system, including non-linear constraints (complex surfaces) involving coupling between translations and rotations. Physical equivalence ensures that the controller is passive. Experimental results obtained with a 6-DOF teleoperation system are given. Other applications of the virtual mechanism concept include hybrid position-force control and haptic interfaces