"Ultrasonic Motors"

Inventors: K. Uchino, et al.

PSU Invention Disclosure No. 96-1633

Issued U.S. Patent No. 5,955,820

There have been many different designs proposed for ultrasonic motors. The commercialized motors by Shinsei Industries and Seiko Instruments, and most of the reported motors utilize traveling wave bending modes excited on a ring-type unimorph piezoelectric element. These conventional ultrasonic motor designs have a limitation of the size reduction because of a complexity of the structure. Furthermore, the traveling wave type requires two power supplies for sine and cosine voltages.

The subject invention is a bi-directional rotary type ultrasonic motor, which consists of only one type of element driven by a single-phase power supply. The invention has only three components; a rotor, a bearing and a stator. In addition to a simple structure of the stator and a simple driving circuit, the volume of the proposed embodiment can be reduced to a cylinder three (3) mm in diameter and less than three (3.0) mm in height. The combination of longitudinal and angular vibrations makes an elliptical motion at the periphery and side surface of the top endcap of the stator generating a rotational force on the rotor.

Several prototypes of varying sizes have been produced and tested by the Penn State researchers. The prototypes have shown the following desirable characteristics: 1) minimum number of components, 2) high generative force to volume ratio, 3) high efficiency, and 4) simple driving circuitry. The enclosed figure shows a torque vs. speed and an applied AC voltage vs. no-load speed characteristics of a rotary motor. This invention is applicable for linear motor applications. In this case the stator component of the rotary motor is used as a moving slider element. By changing the frequency of the ac power supply, back and forward movement can be obtained.

The inventors envision that this motor in the size range of 3 - 8 mm will have commercial value for most office equipment, such as floppy disk drives, printers, plotters, CD and tape recorders, and for camera and video camera drives. Smaller sized motors may have medical application within micro-surgery and sensor scanning. The researchers estimate that initial raw material costs are low and that the final price range per unit will be significantly reduced (~ $3) upon increased demand. Consequently, the inventor believes that electromagnetic motors shall not be competitive against this miniaturized motor technology.