ULTRASONIC MOTOR

Abstract:

An ultrasonic motor is a type of electric motor formed from the ultrasonic vibration of a component, the stator, placed against another, the rotor or slider depending on the scheme of operation (rotation or linear translation). Piezoelectric ultrasonic motors are a new type of actuator. They are characterized by high torque at low rotational speed, simple mechanical design and good controllability. They alsoprovide a high holding torque even if no power is applied. Compared to electromagnetic actuators the torque per volume ratio of piezoelectric ultrasonic motors can be higher by an order of magnitude. Many different types of ultrasonic motors have been proposed up to date.  Ultrasonic motors are of great interest due to the flexibility of miniaturization in comparison with conventional electromagnetic motors whose efficiency decreases significantly. Especially in information systems and medical industry, compact size of these motors makes them find wider applications. This paper describes the advantages of ultrasonic motors over the conventional electromagnetic motors, several types of piezoelectricultrasonic motors. The basic working principle; the mechanism of the ultrasonic motor are also explained. Finally, its applications and the only disadvantage are discussed.

INTRODUCTION

An ultrasonic motor is a type of electric motor formed from the ultrasonic vibration of a component, the stator, placed against another, the rotor or slider depending on the scheme of operation (rotation or linear translation). Ultrasonic motors differ from piezoelectric actuators in several ways, though both typically use some form of piezoelectric material, most often lead zirconate titanate and occasionally lithium niobate or other single-crystal materials. The most obvious difference is the use of resonance to amplify the vibration of the stator in contact with the rotor in ultrasonic motors. Ultrasonic motors also offer arbitrarily large rotation or sliding distances, while piezoelectric actuators are limited by the static strain that may well be induced in the piezoelectric element.

Piezoelectric ultrasonic motors are a new type of actuator. They are characterized by high torque at low rotational speed, simple mechanical design and good controllability. They also provide a high holding torque even if no power is applied. Compared to electromagnetic actuators the torque per volume ratio of piezoelectric ultrasonic motors can be higher by an order of magnitude.

The ultrasonic motor is characterized by a “low speed and high torque”, contrary to the “high speed and low torque” of the electromagnetic motors. Two categories of ultrasonic motors are developed at our laboratory: the standing wave type and the traveling wave type.

The standing wave type is sometimes referred to as a vibratory-coupler type, where a vibratory piece is connected to a piezoelectric driver and the tip portion generates flat-elliptical movement. Attached to a rotor or a slider, the vibratory piece provides intermittent rotational torque or thrust. The travelling-wave type combines two standing waves with a 90¡-phase difference both in time and space. By means of the traveling elastic wave induced by the thin piezoelectric ring, a ring-type slider in contact with the surface of the elastic body can be driven.

ULTRASONIC MOTOR