Speed Fluctuation Suppression Method for Gimbal Servo System With Harmonic Drive by Disturbance Observer Based Sliding Mode Control

The torque accuracy of a control moment gyro (CMG) relies heavily on the speed accuracy of the gimbal servo system, where kinematic error from harmonic drive cause significant speed fluctuations. To address this problem, a sliding mode control (SMC) feedback controller based on the disturbance observer (DOB) containing the $\mathbf{W}$ matrix (WDOB) was proposed. It not only meets the response requirements of the system, but also suppresses the chattering phenomenon of the SMC. Since kinematic error has periodic changes and varies with angular velocity, existing DOBs are ineffective for accurate estimation. An exogenous system matrix $\mathbf{W}$ that adapts to angular velocity, is embedded in a DOB to improve the disturbance estimation accuracy. Both simulation and experimental results show that the proposed WDOB-SMC can effectively suppress the speed fluctuations and enhance the dynamic performance of the system.