A flexible ultrasonic motor (FUSM), which generates linear motion as a novel soft actuator, has been born out of research led by Dr Tomoaki Mashimo, Associate Professor of the Department of Mechanical Engineering at Toyohashi University of Technology (TUT), and Dr Ayato Kanada, Assistant Professor of the Department of Mechanical Engineering at Kyushu University.
This motor consists of a single metal cube stator with a hole and an elastic elongated coil spring inserted into the hole. When voltages are applied to piezoelectric plates on the stator, the coil spring moves back and forward as a linear slider.
In the FUSM that uses the friction drive as the principle, the most important parameter for optimizing its output is the preload between the stator and slider. The coil spring has a slightly larger diameter than the stator hole and generates the preload by expanding in a radial direction.
The coil springs act not only as a flexible slider but also as a resistive positional sensor. Changes in the resistance between the stator and the coil spring end are converted to a voltage and used for position detection.