Abstract
To overcome the influence of the nonlinear friction on the gimbal servo-system of a double gimbal control moment gyro with harmonic drivers,the methods of modeling and compensation of the nonlinear friction are proposed.Firstly,the relationships between the nonlinear friction torque and the angle acceleration of a gimbal motor and the friction torque and the current of the gimbal motor are deduced according to the mathematical model of gimbal servo-system.Then,based on the angle position measured by encoders,the angle velocities of the motor and loader sides are calculated and an angle acceleration estimator is designed to estimate the angle accelerations of the motor and loader sides.Furthermore,the nonlinear friction torque is calculated and modeled as the Coulomb,viscous and Stribeck friction model.Finally,a feedforward compensation controller based on the model is designed to restrain the nonlinear friction and to improve the control precision.Experimental results indicate that compared with those of the conventional PID control method,the peak-peak value of angle velocity error curve has decreased by 28.2% and the mean squared error decreased by 25.7% after the feedforward compensation controller is added.It concludes that the feedforward compensation controller decreases the angle velocity error caused by nonlinear friction and improves the control precision of the servo-system.
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