Multiple Working Mode Control of Mobile Serial Robot with Online Mode Switching for Operations on Mechanisms with Unmodelled Constraints

In this paper, a multiple working mode approach is proposed to control a mobile serial robot manipulator to perform operations on mechanisms with unmodelled constraints. A constrained robot manipulator is an over-actuated system in which kinematic modelling errors lead to high internal and external reaction forces. With the proposed approach, problems caused by modelling inaccuracies are avoided by reducing the number of position-controlled joints during task execution. As a result, the manipulator becomes a minimally actuated system, where the uncontrolled generalized variables are task-actuated (passive), and the remaining (active) variables are assigned to a priority-based task hierarchy. Three practical criteria are derived for the assignment of active and passive control modes; two based on the coordinate partitioning method for multibody dynamics, and another based on minimizing task friction forces. The proposed control method is implemented on a mobile reconfigurable robot, performing constrained motion along an elliptical trajectory, similar to door-opening task. The experimental results have demonstrated the effectiveness of the proposed control approach.