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INTROUCTION
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.
DRAWBACKS
OF ELECTROMAGNETIC MOTORS
Electromagnetic motors rely on the attraction and repulsion of magnetic fields
for their operation. Without good noise suppression circuitry, their noisy electrical
operation will affect the electronic components inside it. Surges and spikes from
these motors can cause disruption or even damage in nonmotor related items such
as CRTs and various types of receiving and transmitting equipments. Also , electromagnetic
motors are notorious for consuming high amount of power and creating high ambient
motor temperatures. Both are undesirable from the efficiency point of view. Excessive
heat energy is wasted as losses. Even the efficiently rated electromagnetic motor
has high input to output energy loss ratios.
Replacing these by ultrasonic motors would virtually eliminate these undesirable
effects. The electromagnetic motors produce strong magnetic fields which cause
interference. Ultrasonic motors use piezoelectric effect and hence no magnetic
interference.
PRINCIPLE
OF OPERATION PIEZOELECTRIC
EFFECT Many
polymers, ceramics and molecules are permanently polarized; that is some parts
of the molecules are positively charged, while other parts are negatively charged.
When an electric field is applied to these materials, these polarized molecules
will align themselves with the electric field, resulting in induced dipoles within
the molecular or crystal structure of the material. Further more a permanently
polarized material such as Quartz(SiO2) or Barium Titanate(BaTiO3) will produce
an electric field when the material changes dimensions as a result of an imposed
mechanical force. These materials are piezoelectric and this phenomenon is known
as Piezoelectric effect. Conversely, an applied electric field can cause a piezoelectric
material to change dimensions. This is known as Electrostriction or Reverse piezoelectric
effect. Current ultrasonic motor design works from this principle, only in reverse. When
a voltage having a resonance frequency of more than 20KHz is applied to the piezoelectric
element of an elastic body (a stator),the piezoelectric element expands and contracts.
If voltage is applied, the material curls. The direction of the curl depends on
the polarity of the applied voltage and the amount of curl is determined by how
many volts are applied.
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