Multiple working mode approach to manipulation of unknown mechanisms using a serial robot: A special case of constrained motion with active and passive joints

Tasks for robots such as opening doors and drawers, and operation of cranks and levers in an unstructured environment pose a challenge for robot control due to unmodelled constraints. A constrained robot manipulator is an over-actuated system in which kinematic modelling errors lead to high internal and external reaction forces. In this work, problems caused by modelling inaccuracies are avoided by reducing the number of position-controlled joints during task execution, such that the number of generalized inputs matches the task degrees of freedom. In this configuration, the manipulator is a minimally actuated system, where the uncontrolled generalized coordinates are task-actuated (passive). We present two criteria for the assignment of active and passive control modes; one based on the coordinate partitioning method for multibody dynamics, and another that that minimizes task friction forces. Simulation results are presented for the case of 1-DOF constrained motion along an elliptical trajectory, similar to a crank turning task.