Abstract: Aiming at the problem of decreased control accuracy caused by uncertainties such as nonlinear mechanical friction,external disturbances,and model errors in the dual-axis cradle turntable system,an improved sliding mode control law was designed using an extended state observer. Firstly,the spatial coordinate system relationship among the base,cradle and turntable of the dual-axis cradle turntable was analyzed,and the dynamic models of the cradle and turntable were established. Then,the uncertainty in the system was extended to the system state,and the designed extended state observer was used to estimate the uncertainty. Finally,the improved sliding mode control law was designed to dynamically compensate for the influence of uncertainty,effectively suppressing the phenomenon of chattering and achieving high-precision control of the dual-axis cradle turntable. The simulation results show that the designed extended state observer can accurately estimate the uncertainty in the dual-axis cradle turntable,and the maximum estimation error is only 0.01 (°)/s². The maximum tracking errors of the improved sliding mode control law for turntable rotation angular velocity and cradle rotation angular velocity are only 0.02 (°)/s and 0.03 (°)/s,respectively. The test results show that the proposed improved sliding mode control method has stronger robustness and higher accuracy compared to adaptive iterative learning control method and command filtered adaptive backstepping control method,and the maximum positioning errors for turntable rotation angle and cradle rotation angle are only 0.04° and 0.05°,respectively,greatly improving the control accuracy of the dual-axis cradle turntable.

Key words: dual-axis cradle turntable, servo motor, model error, mechanical friction, uncertainty, extended state observer, sliding mode control law