Ultrasonic Motor EEE Engineering


          All of us know that motor is a machine which produces or imparts motion, or in detail it is an arrangement of coils and magnets that converts electric energy into mechanical energy and ultrasonic motors are the next generation motors.

          In 1980,the world’s first ultrasonic motor was invented which utilizes the piezoelectric effect in the ultrasonic frequency range to provide its motive force resulting in a motor with unusually good low speed, high torque and power to weight characteristics.

          Electromagnetism has always been the driving force behind electric motor technology. But these motors suffer from many drawbacks. The field of ultrasonic seems to be changing that driving force.

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          When a voltage having a resonance frequency of more than 20 KHz is applied to the piezoelectric element of an elastic body(a stator),the piezoelectric element expands and  expands and contracts. The piezoelectric ring is divided into two groups of alternated polarities, which are driven simultaneously by cyclic signals that are ninety degrees out of phase, to produce a traveling wave of flexural vibrations. The third input lead is ground and attached to the ring itself. It acts as a common return to both  the out of phase input leads.

A stator and a rotor (dynamic body) are coupled to form an ultrasonic motor. The dynamic body is pressed against the side of the stator metal surface which the piezoelectric ceramic is  not glued on.Comb tooth grooves are created on this side. The rotor (dynamic body) is pressed tightly against this side of the stator metal surface so that they are adhered together closely. As the progressive wave travels and undulates through this contact surface, some areas of the surface of the rotor which is tightly adhered to the stator are contacted by the vertices of the wave and some areas are not. At this time, at the vertices of the progressive wave that contacts the rotor surface, an elliptic motion is generated.                    

          The locus of the elliptic motion points to the opposite direction of the progressive wave traveling on the stator surface. At the same time, it has a vertical elliptic motion in contrast to the horizontal undulation of the progressive wave that travels on the stator surface. Reversing the polarity of the input power will reverse the direction of rotation.

          The rotor and stator are pressed against each other with strong pressure to create tight adhesion. The progressive wave travels along the circumference of the stator while undulating. Only the vertexes of the progressive wave contact the rotor surface and an elliptic rotary motion is generated at each vertex. Affected by the elliptic rotary motion, the rotor is impelled to rotate. As the direction of the locus of the elliptic motion is opposite to the direction of the progressive wave, the rotor affected by it also rotates in the opposite direction of the progressive wave. When   the progressive wave travels along the circumference of the stator clockwise (CW), a counterclockwise (CCW) elliptic rotary motion is generated at the vertex of the wave contacting the rotor surface. The rotor contacting the vertex is impelled by the CCW elliptic rotary motion and rotates CCW.

Absence Of Magnetic Motion

          As the ultrasonic motor does not use coil or magnets as its driving force, it does not generate magnetism. It can be operated without influence of magnetism even in strong magnetic fields.

Compact, Lightweight And Noiseless

          As the  USM does not require coils, it has a simple and lightweight structure. Further more, as it doesn’t require reduction gear due to its low speed, and uses ultrasonic vibrations in ranges not audible to the human ear, its running noise is extremely quiet. Only 2 ms are needed to start the motor from zero.