A linear/rotary ultrasonic motor, which is driven using a friction force, generally requires a preload mechanism between the slider/rotor and the stator. The preload mechanism is of considerable importance to the motor's ability to produce a practical thrust/torque because the output thrust/torque is dependent on the friction force. However, the preload mechanism generally occupies a relatively large space as a proportion of the space for the entire motor, which may limit motor miniaturization. To overcome this limitation, a linear ultrasonic motor has been developed in this work with a slider that has an inherent preloading capability. The ultrasonic motor is composed of a phosphor bronze stator with piezoelectric ceramic plates and a U-shaped stainless steel slider. The stator is inserted into the slider with an interference fit, which means that the preload between the slider and the stator is applied mechanically. By selective excitation of the second or third resonance vibration modes of the stator, the slider can be driven bidirectionally. The maximum velocity, thrust and output power values of the proposed motor are 62.5 mm/s, 0.12 N and 1.01 mW, respectively. This simple but effective solution, which eliminates the need for an external preload mechanism, will contribute to progress in ultrasonic motor research and design.
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