• It has been known for more than 30 years.
• The first ultrasonic motor was introduce by
v.v lavrinko in 1965.
• An Ultrasonic motor is a type of electric
motor formed from the ultrasonic vibration of
a component, the stator being placed
against another, the rotor depending on the
scheme of operation.
• Conversion of electric energy into motion by
inverse piezoelectric effect.
• To obtain the levels of torque speed
characteristics of USM using conventional
motors we require to add a gear system to
reduce the speed.
• These characteristics of USM makes them
attractive for robotic applications where small
motions are required.
• This motor achieves high speed and drive
forces, while still permitting the moving part to
be positioned with high accuracy.
• Piezoelectricity – generation of voltage in response of
• The word is derived from the Greek piezein, which means to
squeeze or press.
• This effect is also reversible.
• Deformation is only 0.1 % of the original dimension.
• Piezoelectric material- quartz(SiO2), barium titanate (BaTiO3)
lead zirconate titanate and occasionally lithium niobate .
The piezoelectric effect is understood as the linear
electromechanical interaction between the mechanical and the
electrical state in crystalline materials with no inversion
Electromagnetic motors are notorious for consuming high
amount of power and creating high ambient motor
temperatures respect to USM
The electromagnetic motors produce strong magnetic
fields which cause interference. Ultrasonic motors use
piezoelectric effect and hence no magnetic interference.
Electromagnetic motor has high input to output energy loss
USM High positional accuracy respect to Electromagnetic
• Generation of gross mechanical motion through the
amplification and repetition of micro-deformations of
• The active material induces an orbital motion of the
stator at the rotor contact points .
• Frictional interface between the rotor and stator
rectifies the micro-motion to produce macro-motion of
• Working frequency-20 KHz to 10 MHz
• Amplitude of the actuator motion – 20 to 200nm
EQUIVALENT CIRCUIT OF USM
Cd is the capacitance due to
the dielectric property of piezo
crystal i.e tank capacitance.
Rm,Cm,Lm are the resistance
,capacitnce & inductance of
Their combined impedance is
( + 1 / + ).
a) Based on the use of reverse piezo-electric effect
for continuous conversion of electric power into
b) The process of energy conversion can be
seperated into two parts:
Ultrasonic vibration generation
Conversion of this vibration into the slider(rotor)
When a voltage is applied to a peizoelectric-
ceremic element,alternating expansion and
contraction occur either in the ceremic body itself
or in the elastic body
The magnitude of this oscilation is very small
The conversion of ultrasonic vibration in the rotor
movement is based on the elliptic motion
displacement of the surface points of the contact
zone between stator and rotor
The displacement can be produced
independently through two individual vibrating
bodies or by a single vibrator
This type of motors use three groups of
crystals: two of which are Locking and
First, one group of locking crystals is
activated — this gives one locked side
and one unlocked side of the 'sandwich'.
Next, the motive crystal group is
triggered and held — the expansion of
this group moves the unlocked locking
group along the motor path. This is the
only stage where motor movement takes
Standing wave USM
Representation u( x, t) = A coskx coswt
It is also referred as vibratory coupler type or
wood pecker type.
A vibrator is connected to the piezoelectric
driver,it produces bending, so its tip produces flat
elliptical motion to drive the rotor.
LINEAR TYPE STANDING WAVE
card or paper senders.
ROTATING TYPE STANDING WAVE
Provides high speed
than linear motors
because of high
Provides speed of 1500
rpm, torque of 0.08 Nm
& efficiency of 80%.
This type of motor commonly known under the names
of Inchworm, Piezo LEGS or PiezoWalk motors
STANDING WAVE USM
one vibration source
TRAVELING WAVE USM
Superposition of multiple standing wave create a
Representation of travelling wave
U(x ,t)= A cos(k x) cos(wt) + A cos(k x - 90)
Phase difference is 90 degree
• Superposition of multiple standing wave
create a traveling wave.
• Representation of travelling wave
U(x ,p)= A cos(k x) cos(wt) + A cos(k x - 90)
• Phase difference is 90 degree
•The active material excites a traveling flexural wave within the
stator that leads to elliptical motion of the surface particles.
•Teeth are used to enhance the speed that is associated with the
propelling effect of these particles.
•The rectification of the micro-motion an interface is provided by
pressing the rotor on top of the stator and the frictional force between
the two causes the rotor to spin.
TRAVELLING WAVE USM
Requires two vibrating source.
Controllable in both direction.
Silent operation, so suitable to video cameras
Thinner design, leading to space saving.
Use of high frequency
Supppression of heat
• Camera auto focus lenses
• Driving fluid
• Watch motors and compact
• Optoelectronics area
• In micro surgery and sensor
These motors are advantageous.
Electromagnetic interference is not there.
It is in great demand in the area of automation &
Light weight & compact size