Introduction
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.
Working
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.
0 comments: