Model-based control of a class of voltage-driven robot manipulators with non-passive dynamics

A class of voltage-driven robot manipulators is addressed in this paper. Such a class includes those manipulators actuated by direct current (DC) motors with servo-amplifiers in current mode. For those robots, it is assumed that the control inputs to the manipulator are the servo-amplifier input voltages, in:stead of the applied torques. And even though it is common to consider that the applied torque in each joint is proportional to the servo-amplifier input voltage, in: this paper it is assumed that the voltage-to-torque conversion constant is unknown. Notwithstanding, the robot model parameters may still be computed using standard identification methods. An important fact of the class of robots considered in the present study is that the robot dynamics is not passive from the servo-amplifier input voltage to the joint velocity. The paper shows how this drawback can be overcome by using a model-based trajectory tracking controller, which makes the closed-loop system passive from an auxiliary control input to a filtered error signal. To confirm the theoretical conclusions, real-time experiments are carried out in a two-degree-of-freedom direct-drive manipulator. Two known control strategies are compared with respect to the proposed controller. The success of the implementations is based on real-time computing, which ensures that the access to I/O ports and the computation of the control algorithms meet timing requirements accurately.