In this paper, we present implementation of a nonlinear disturbance observer algorithm to estimate disturbance torques on a wrist rehabilitation robot. The ultimate goal is to enable accurate estimation of user interaction torques without force/torque sensors. A dynamic model of the Wrist Gimbal two degree-of-freedom forearm and wrist exoskeleton is developed. A nonlinear disturbance observer (NDO) algorithm that incorporates the robot dynamics is implemented. Friction models for both joints of the robot are identified. The robot dynamic model and the accuracy of the disturbance torque estimations are experimentally verified under closed-loop trajectory tracking scenarios.
Abstract. The method of controlled Lagrangians is a technique for stabilizing relative equilibria of mechanical systems with symmetry. This paper develops a modification of kinetic shaping technique in the theory of controlled Lagrangians. The main idea is that the dynamics associated with the controlled Lagrangian is amended by non-conservative forces that act in the shape directions; this gives additional freedom and hence applicability to the method. The usefulness of this methodology is demonstrated on the pendulum on a rotor arm.
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