Abstract
A surface acoustic wave (SAW) linear motor is a kind of ultrasonic motor. The advantages of the SAW linear motor are thin structure, high thrust force, high velocity and precise positioning. The relationship between applied current and output velocity is, however, unstable in the low velocity range due to the friction drive principle. Therefore the SAW linear motor cannot obtain stable driving without feedback control in the low-velocity region. In this research, to realize low velocity, a pulse width modulation (PWM) control and flexible slider structure are employed. Flexible structure is installed to cancel vibration due to the PWM carrier wave. A lower velocity in the unstable range is realized. Moreover we change the calculation algorithm for the slider velocity measurement. As a result, the SAW linear motor can be driven at an ultra low velocity of 30μm/s. Additionally, driving characteristics are improved using a feedforward controller.
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