Miniature Cantilever-Type Ultrasonic Motor Using Pb-Free Multilayer Piezoelectric Ceramics

A Miniature cantilever-type ultrasonic motor was fabricated using multilayer piezoelectric ceramics (MLPC) made of (Sr,Ca) 2 NaNb 5 O 15 (SCNN), a Pb-free piezoelectric material, and the electrical driving properties were investigated. The displacement of SCNN-MLPC was 177 nm at 100 V, which was 10-fold the voltage of MLPC made of Pb(Zr,Ti)O 3 –Pb(Ni,Nb)O 3 –Pb(Zn,Nb)O 3 (PZT). The ultrasonic motor using SCNN-MLPC started to rotate at 3.8 V p–p , and showed the following characteristics: a revolution speed of Ω 0 =517 rpm, a torque of T 0 =1.4 µN m, and an efficiency of η=7% at 13.4 V p–p . The power consumption, in this case, was 0.3 mW, which is not so high. On the other hand, an ultrasonic motor of the same form made of PZT-MLPC showed Ω 0 =610 rpm, T 0 =1.6 µN m, and η=9% at 1.9 V p–p , and the same power consumption as the SCNN motor. That is, it was found that the SCNN motor was not so different from the PZT motor in terms of their characteristics; however, the SCNN motor needed 10 times as high a voltage as the PZT motor in electrical driving. In conclusion, it can be said that we succeeded in realizing a miniature cantilever-type ultrasonic motor using Pb-free MLPC.