Constructions and characteristics of a tiny piezoelectric linear motor using radial mode vibrations

A tiny ultrasonic linear motor with a structure has been developed, and various shaft materials were tested in the motor in order to improve its dynamic properties. We found that the shaft material has direct influence on efficiency, reliability and quality of the motors and their dynamic properties and is crucial to the achievement of high motor performance. The use of shafts of various materials such as stainless steel, stainless steels coated with DLC (Diamond Like Carbon) and PTFE (Teflon), a Pyrex, and a graphite, can make it possible to improve dynamic properties of the motors over a wide range of tribological conditions. In a motor with a stainless steel shaft coated with DLC driven at 44 kHz, its velocity was 4 mm/s with a force of 75 mN. When a motor used the Pyrex shaft was used a force of 110 mN was attained at 51 kHz. Thus the maximum force produced by a motor with a graphite shaft is estimated to be 120 mN with a velocity of 8 mm/s. We found that graphite has the appropriate surface conditions and directional texture to promote the linear motion of the moving element. Finally, the use of a cap resulted in significant improvements in the stability of the motor's operation. Motor with graphite and Pyrex shafts were found to exhibit very stable operation and improved dynamic characteristics.