Real-Time Implementation and Evaluation of Computed-Torque Scheme

This paper presents the experimental results of the real-time performance of model-based control algorithms. We compare the computed-torque scheme which utilizes the complete dynamics model of the manipulator with the independent joint control scheme which assumes a decoupled and linear model of the manipulator dynamics. The two manipulator control schemes have been implemented on the CMU DD Arm I1 with a sampling period of 2 ms. We discuss the design of controller gains for both the computed-torque and the independent joint control schemes and establish a framework for comparing their trajectory tracking performance Our investigation shows that the computed-torque scheme outperforms the independent joint control scheme as long as there is no torque saturation in the actuators. Based on our experimental results, we conclusively establish the importance of compensating for the nonlinear Coriolis and centrifugal forces even at low speeds of operation. This represents an important result because it serves to resolve the controversy about the need to compensate for these forces at low speeds of operation.