Nonlinear effect analysis and compensation based on improved friction observer for torque rotating stage

In semiconductor precision packaging and other applications involving alignment of automated equipment, the nonlinear motion caused by structural characteristics and friction effects on torque-type rotating motion stages seriously affects output accuracy and stability. To solve this problem, the motion characteristics of a rotating stage and the mechanism by which friction nonlinearity influences accuracy are analyzed in detail. In addition, a compound control strategy based on a kinematic model and the Stribeck friction model is designed. A friction disturbance observer based on output position feedback is improved for simple parameter tuning. Finally, an experimental system is constructed to carry out validation tests, including identification of nonlinear characteristics and performance comparisons. The experimental results show that the linear tracking error of the torque-type rotating stage is less than 1.47 µm after adoption of the proposed model-based composite control strategy, and the corresponding rotary angle deviation is less than 0.0153°. The linearity of output motion is increased to 97.59% and the error compensation effect is improved by 51.6% compared with the PID control method. The experimental results confirm that the analysis method adopted here and the proposed compensation strategy can effectively reduce frictional nonlinearity and improve motion accuracy. The proposed method can also be applied to other precision electromechanical systems.