High-Precision Angular Speed Tracking Control of Gimbal System with Harmonic Reducer

In this article, a composite controller based on an extended state observer (ESO) and sliding-mode control (SMC) is presented in order to deal with the angular speed fluctuation caused by the kinematic error of a harmonic reducer in the gimbal system of a control moment gyro. First, based on the analysis of the kinematic error derived from the relationship between the angular speed of the motor and that of the load, a second-order gimbal system model is established based on the Lagrange function and the Rayleigh dissipation function. Second, a three-order linear ESO is designed to observe the uncertain disturbances of the gimbal system, and the disturbances are rejected via the proposed composite controller combining the ESO with SMC. Third, we prove the overall system stability by using the Lyapunov approach and the final value theorem. Finally, both simulation and experimental results verify the effectiveness of the proposed method in attenuating gimbal system disturbances.