Experimental Evaluation of Nonlinear Feedback and Feedforward Control Schemes for Manipulators

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Abstract
The manipulator trajectory tracking control problem revolves around computing the torques to be applied to achieve accu rate tracking. This problem has been extensively studied in simulations, but real-time results have been lacking in the robotics literature. In this paper, we present the experimental results of the real-time performance 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 dy namics in the feedforward path, whereas the computed-torque scheme uses the dynamics in the feedback loop for lineariza tion and decoupling. The parameters in the dynamics model for the computed-torque and feedforward schemes were esti mated by using an identification algorithm. Our experiments underscore the importance of including the off-diagonal terms of the manipulator inertia matrix in the torque compu tation. This observation is further supported by our analysis of the dynamics equations. The manipulator control schemes have been implemented on the CMU DD arm II with a sam pling period of 2 ms.

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