Passive Bilateral Control of Nonlinear Mechanical Teleoperators

In this paper, a passive bilateral control law is proposed for a teleoperator consisting of a pair of n-DOF nonlinear robotic systems. The control law ensures energetic passivity of the closed-loop teleoperator with power scaling, coordinates motions of the master and slave robots, and installs useful task-specific dynamics for inertia scaling, motion guidance and obstacle avoidance. Consequently, the closed-loop teleoperator behaves like a common passive mechanical tool. A key innovation is the energy preserving passive decomposition of the 2n-DOF nonlinear teleoperator dynamics into two robot-like systems: a n-DOF shape system representing the master-slave position coordination aspect (n-DOF holonomic constraint) and a n-DOF locked system representing the dynamics of the coordinated teleoperator. The master-slave position coordination is then achieved by regulating the shape system, while programmable apparent inertia of the coordinated teleoperator is achieved by scaling the effect of the environmental and human forces on the locked system. Passive velocity field control (PVFC) and artificial potential field control are used to implement guidance and obstacle avoidance for the coordinated teleoperator. A special passive control implementation structure is used to ensure the energetic passivity of the closed-loop teleoperator even in the presence of model parametric uncertainties and inaccurate force sensing. Experimental results are presented to validate the properties of the proposed control framework.