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Repetitive position tracking performance enhancement of linear ultrasonic motor with sliding mode-cum-iterative learning control

Abstract:

The ultrasonic motors are finding increasing demand in high precision positioning applications due to their superior tracking performance compared to electromagnetic motors. The motors have simple construction, but exhibit highly nonlinear characteristics such as deadzone and hysteresis. Moreover motor parameters are time varying due to change in temperature when motor is running. Due to all these nonlinearities it is very difficult to come up with an exact model of the motor. When conventional linear controllers such as PI/PID are used for position control, they do not provide satisfactory performance. In this paper position control of the linear ultrasonic motor(LUSM) is carried out using sliding mode control(SMC) technique. An approximate model of the motor is being used and the SMC technique can give comparatively improved tracking performance and robustness than the traditional linear controllers. For repetitive position tracking the periodic error can be further reduced by augmenting a plug-in iterative learning controller (ILC) to the existing SMC. In such a hybrid scheme, SMC is dominant during transient period while ILC takes over most of the control action during steady state period resulting in improved tracking performance during transient as well as steady state operations. Experimental results obtained show tracking error can be reduced by a factor of at least ten as compared to scheme with SMC alone validating the efficacy of the proposed control scheme.