| Ultrasonic motor has many advantages, such as low noise, no electromagnetism interference, small inertia, rapid response etc, and shall replace traditional electromagnetism motor in some application field. The wide use of ultrasonic motor is depending on its whole drive/control system performance improving and suitable control strategy research. However, the on-line control of ultrasonic motor becomes complex because of coupling among its control variables.This paper does some research of low-frequency PWM control methods of ultrasonic motor, analyses the principle of ON/OFF, Forward/Backward and Forward/Backward/Stop three low-frequency PWM control methods, works over the realization means of these three low-frequency PWM control methods which is based on the driving and controlling platform of DSP and CPLD combination of two-phase traveling wave ultrasonic motor; and compares the similarities and differences and control effect of three low-frequency PWM control methods from many aspects, such as the stator traveling wave vibration status, open-loop speed control characteristics and input power etc. This paper regards low-frequency ON/OFF PWM which has better performance as bottom control method, designs and realizes close-loop speed control of ultrasonic motor which takes the duty-ratio of low-frequency PWM as control object, studies on its control characteristics. On this base, it researches the basic thoughts and means of its whole system efficiency optimization, and carries through the initial investigation.The experiment makes clear that low-frequency PWM control strategy can realize speed effective control, besides it can separate the control variables of driving-voltage amplitude, frequency, phase difference of ultrasonic motor, it is propitious to make this kind of efficiency optimization close-loop control of more aims realization easier, and may becomes an effective means to realize high performance motion control using ultrasonic motor. |
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