Improvement of Low-Speed Precision Control of a Butterfly-Shaped Linear Ultrasonic Motor

The control performance of a butterfly-shaped linear ultrasonic motor is not good when the target speed is less than 1 mm/s by traditional methods. To improve low-speed controlling characteristics of linear ultrasonic motor, a closed-loop control strategy by using both the step control and the fuzzy PID control was proposed. The controller was constructed with the function of providing a closed-loop control of the speed by adjusting the driving voltage amplitude in stepping driving mode. The corresponding step controlling parameters were determined by experiments. Comprehensive experiments on the developed control strategy were conducted under different target speeds. There was a maximum of 24.5% speed error at the target speed of 10 μm/s, meanwhile, the coefficient of variation and the response time were 16.3% and 0.11 s, respectively. With the triangular or sinusoidal waves speed tracking curves at amplitude of 1 mm/s, the maximum speed tracking error were 0.1 mm/s and 0.15 mm/s respectively. Thus, a good speed tracking performance was obtained. These results support the functional ability and potential of the proposed method as a low-speed precision control method for linear ultrasonic motors.