High-precision control algorithm for velocity and position of ultrasonic motor

In order to improve speed/position control accuracy and overcome nonlinearity accompanied by a multivariable coupling effect, the targeted speed and position control of the ultrasonic motor was proposed in this paper. Firstly, the control mechanism of the ultrasonic motor was demonstrated from the perspectives of continuous macroscopic motion and microscopic stepwise motion. Then, the sources of velocity fluctuation errors were clarified, and a multiparameter speed control model was established; the amplitude and frequency were integrated into the model by combining steady and dynamic links. In order to predict stepwise displacements, a two-stage second-order speed model was also constructed from the microscopic dimension. Then, the double-loop compound control algorithm was used to realize high-stability speed control, while high-resolution position control could be achieved through driving parameter optimization. Finally, a piecewise approximation strategy was adopted to combine the continuous and stepwise motion for high-precision positioning. The experimental results show that speed stability under dual-loop compound control is 0.44%, which is two times better than that of single-loop control. In terms of position control, the open-loop position resolution of the ultrasonic motor reached 0.375 μrad, and a positioning accuracy of 1.7 μrad is achieved. The proposed control strategy integrates the control characteristics of different parameters and loops, which effectively improves the speed and position control accuracy of the ultrasonic motor. This work lays the foundation for extended applications in advanced precision equipment. © 2020, Science Press. All right reserved.