Implementing contact tasks involving position uncertainty with impedance controlled robots

This paper discusses a high bandwidth, six degree of freedom impedance controller for a Puma 562 robot which is used to perform contact tasks. We focus on how impedance control can be exploited to perform contact tasks with rigid objects in the presence of positioning uncertainty. Our work has shown that the permissible deviation between the nominal and actual trajectory in performing these tasks is significantly greater with impedance control. By using impedance control in such cases, the interface forces between the manipulator and its environment are kept well within acceptable levels. Selection of appropriate impedance elements and nominal trajectory generation are discussed. Based on a knowledge of the task, we define constrained and unconstrained subspaces and select the robot impedance to complement the environment along these axis. Our work has concentrated on tasks associated with workpiece and tool manipulation at a machining center using a robot mounted on a wheeled mobile platform which moves from workcell to workcell. Experimental results for turning a kinematically constrained crank are described