Real-time implementation and evaluation of the computed-torque scheme

Experimental results on the real-time performance of model-based control algorithms are presented. The computed-torque scheme which utilizes the complete dynamics model of the manipulator was compared to 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 Carnegie-Mellon University DD (direct-drive) Arm II with a sampling period of 2 ms. The authors 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 performances. It is shown that the computed-torque scheme outperforms the independent joint control scheme as long as there is not torque saturation in the actuators. Based on the experimental results, the authors conclusively establish the importance of compensating for the nonlinear Coriolis and centrifugal forces even at low speeds of operation.>