Design and evaluation of a micro linear ultrasonic motor

We propose a micro linear ultrasonic motor, which is one of the smallest linear actuators that can generate practical force. Such a small actuation mechanism can be used for a wide range of applications, such as auto-focus systems used in thinner cell phones and smaller endoscopes. In this paper, we design the micro linear ultrasonic motor and evaluate the performance of the prototype motor. The size of the prototype stator with piezoelectric elements measures 2.6 mm in height, 2.6 mm in width, and 2.2 mm in depth (the length in slider travel direction). There is a hole of 1.4 mm in diameter at the stator center, and the slider inserted into the hole moves back and forth when voltages are applied to the piezoelectric elements. By optimizing the preload between the stator and slider experimentally, the motor thrust force has been improved to over 10 mN, which is a practical force for moving small objects. Experiments clarify the output characteristics in response to the input voltages. Finally, a maximum thrust force of 20 mN has been obtained at applied voltages with an amplitude of 150 V_p−p.