Experimental Evaluation of Nonlinear Feedback and Feedforward Control Schemes for Manipulators

Abstract

The manipulator trajectory tracking control problem revolves around computing the torques to be applied to achieve accurate tracking. This problem has been extensively studied in simulations, but real-time results have been lacking in the robotics lilerature. In this paper, we present the experimental results of the real-time pe$ormance of model-based control algorithms. We compare the computed-torque control scheme with the feedforward dynamics compensation scheme. The feedforward scheme compensates for the manipulator dynamics in the fiedforward path, whereas the computed-torque scheme uses the dynamics in the feedback loop for linearization and decoupling. The parameters in the dynamics model for the computed-torque and feedforward schemes were estimaled by using an identification algorithm. Our experiments underscore the importance of including the ofldiagonal terms of the manipulator inertia matrix in the torque computation. This observation is further supported by our analysis of the dynamics equations. The manipulator control schemes have been implemented on the CMU DD arm 11 with a sampling period of 2 ms.