Resonance frequency ratio control with an additional inductor for a miniaturized resonant-type SIDM actuator

• The adjusting method of the resonant frequency ratio in the piezoelectric transducer is proposed.
• The method relies on inserting an electrical inductor in series with the transducer.
• The controllability of the resonant frequency ratio with the additional inductor was examined.
• The bearing rotation speed and the output force were improved by the method.

A smooth impact drive mechanism (SIDM) is one type of piezoelectric actuator that converts a saw-shaped piezoelectric displacement to linear (or rotational) motion. For sufficient displacement, a soft-type multilayered piezoelectric element is essential; however, such a piezoelectric element prevents efficient driving due to its low quality factor. To overcome this problem, we proposed a resonant-type SIDM using a hard-type single-layered piezoelectric element. In this resonant-type SIDM, the first and third longitudinal resonant sinusoidal vibration modes were combined to obtain a quasi-saw-shaped waveform. To realize such a saw-shaped waveform, precise adjustment of the resonance frequency ratio is essential. However, it is not easy to regulate the resonance frequency ratio by just the transducer design because of the fabrication error. As a solution for this issue, this study proposes to adjust the frequency ratio by inserting an electrical inductor in series with the piezoelectric transducer. With this method, the resonance frequency ratio was controlled, and the rotor velocity increased as expected.