Micro Linear Ultrasonic Motor With a Hall Sensor-Based Feedback Control System

We propose a one-millimeter-scale linear ultrasonic motor and its feedback control system with a Hall sensor. The size of the stator measures 1.6 mm in height, 1.6 mm in width, and 0.3 mm in thickness, and there is a hole with a diameter of 0.6 mm at the center, which is one of the smallest linear motors reported to date. A similar-sized Hall sensor detects the displacement of the slider inserted into the stator hole for position control. In this paper, we build the prototype motor and evaluate its basic performance measures, such as electrical impedance characteristics and mechanical output characteristics. The optimization of the preload between the stator and slider has improved the thrust force of the motor to the maximum value of 7.6 mN, resulting in a higher force-to-volume ratio than existing miniature linear motors. We combine the motor with a Hall sensor having a similar scale to the motor and construct a feedback system with a burst-wave control. The feedback control succeeded in removing the steady-state error that remains in the open-loop system.