This document provides an overview of ultrasonic motors. It begins with introducing the principle of piezoelectricity that ultrasonic motors are based on. It then describes the typical construction of an ultrasonic motor including the actuator, stator, rotor and casing. The working principle involves generating ultrasonic surface waves on the stator using the actuator that causes friction with the rotor, rotating it. It classifies ultrasonic motors and discusses their advantages like high torque and efficiency, and disadvantages like requiring high frequency power. It concludes by describing some applications like in cameras and automobiles.

1. ULTRASONIC
MOTORS
SONAL MAHESHWARI
B110986EE

2. CONTENTS
 INTRODUCTION
 PRINCIPLE OF OPERATION
 CONSTRUCTION
 WORKING
 FRICTIONAL COUPLING
 CLASSIFICATION
 CONTROL TECHNIQUE
 ADVANTAGES
 DISADVANTAGES
 APPLICATIONS
 CONCLUSION
2

3. INTRODUCTION
 Motor is a device that converts electrical energy to mechanical energy.
 Almost all the motors work on the principle of Faraday’s Law of Electromagnetic Induction.
 The energy conversion in such motors involves two stages, electrical energy to magnetic
energy and further magnetic to mechanical energy.
 Because of two-stage energy conversion, electromagnetic motor suffer from several losses
that lead to a rigorous energy wastage.
 The electromagnetic motors that are widely used in home, industrial and other sectors suffer
from several disadvantages –
1. Noisy operations
2. Surge currents and spikes
3. Magnetic losses
3

4. Contd..
4. High power consumption
5. Low power factor
6. Comparatively lesser efficiency
 Therefore, a new class of motors using high power ultrasonic energy, ultrasonic motors were
introduced.
 The ultrasonic motors belong to the class of piezoelectric motors, which directly convert
electric energy to mechanical energy.
 USM plays an important role in few niche markets, where the size, torque, speed or other
requirements couldn’t be satisfied by electromagnetic motors.
 USMs replaced not only the EM motors, but also the servomotors, stepper motors and
synchronous motors.
4

5. PRINCIPLE OF OPERATION
 Before learning about USMs it is required to know about piezoelectric effect.
 Piezoelectric effect was discovered by Jacques Curie & Pierre Curie [France-
1880].
 It was found that in certain types of crystals when a pressure is applied across a
pair of opposite faces, an equivalent potential difference is developed across the
other pair of opposite faces.
 Further, if we reverse the direction of application of force, the polarity of the
potential difference developed also reverses.
5

6.  In figure given below, a compressive force is applied across the crystal and we obtain a
potential difference as shown but if the compressive force is replaced by an elongation
force, the polarity reverses.
 It was later discovered that the converse of this phenomenon is also possible.
Piezoelectric Effect
6

7. Converse Piezoelectric Effect
 When a potential difference is applied across the pair of opposite faces, compressions or
elongations are obtained across the other pair of opposite faces depending upon the polarity
of the applied PD.
 Further, the application of AC voltage across these faces resulted in alternating
compressions and elongations (mechanical vibrations) across the other pair of faces. This is
the driving force behind the USMs.
 Crystals that exhibit the above phenomenon are called piezoelectric materials.
 In short, the Ultrasonic Motors works on the principle of converse piezoelectric effect.
7

8. CONSTRUCTION
 Ultrasonic motor construction tends to be simpler than EM type
motors.
 Fewer assembly parts mean fewer moving parts and consequently less
wear.
 The number of components required to construct an USM is small
thereby minimizing the number of potential failure points.
8

9. Contd..
The Ultrasonic Motors constitutes mainly four parts, viz.
1. Actuator
2. Stator
3. Rotor
4. Casing
1. ACTUATOR
• It is a driving unit of USM.
• It is made up of piezoelectric material such as Quartz, Barium Titanate, Tourmaline,
Rochelle salt, etc.
• It is fixed on the stator using thin metal sheets and bearings.
• It is directly connected to the supply mains.
9

10. Contd..
2. STATOR
• Stator is the stationary but vibrating part.
• It is constructed using a malleable material, usually steel.
• It can be of ring, cylindrical or rod shaped.
3. ROTOR
• It is the rotating part, which acquires the energy conversion and produces the desired
torque on the shaft.
• It is made of the same material as that of the stator and does have the same shape.
10

11. Contd..
4. CASING
• To provide protection against abrasive forces, external interferences and extreme
environmental conditions.
• They are made of non- corrosive alloys or fiber.
• Cylindrical, disc or box shaped.
11

12.  Comb tooth grooves are created on the stator surface that adheres to the rotor.
 These are devised to make the amplitude of elliptic motion large and to reduce
abrasions.
 Further feature of comb tooth is to amplify vibrations.
 The grooves also allow the dust created by friction to escape and thus keep the
contact surface dust free.
 So the USMs are well known for their low speed operation.
 Torque ratings averaging 10 times greater than a comparably sized electromagnetic
motor can be achieved.
 Voltage inputs vary piezo-crystal assembly. That is, if the piezo-ring assembly is of
a thinner design, the voltage requirements will be less than that of a thicker type
piezo-ring assembly.
 Power requirements for the USM usually rate in the low range.
12

13. FUNDAMENTAL CONSTRUCTION
OF USM
► Figure shows the basic construction of
USMs, which consist of a high-
frequency power supply, a vibrator
and a slider.
► Further, the vibrator is composed of a
piezoelectric driving component and
an elastic vibratory part.
► The slider is composed of an elastic
moving part and a friction coat.
13

14. ULTRASONIC MOTOR BY
BARTH
 The practical ultrasonic motor was proposed
firstly by H V Barth of IBM in 1973.
 As shown in figure, the rotor was pressed
against two horns placed at different locations.
 By exciting one of the horns, the rotor was
driven in one direction, and by exciting the
other horn, the rotation direction was reversed.
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15. WORKING OF USM
 When the supply is switched ON, the actuator starts vibrating owing to
converse piezoelectric effect.
 The particles of the stator receive energy from the actuator and starts
vibrating in the plane. This results in the formation of a surface wave.
 The stator and rotor are placed so close to each other that their surfaces
almost grazes upon each other.
 The surface waves so produced have a frequency in the ultrasonic range and
are not visible by our bare eyes. These waves cause the stator to slide against
the rotor.
15

16. Contd..
 As the wave propagates, the rotor is pulled
back in the opposite direction of movement
of the wave.
 In the figure, the surface wave produced is
propagating in the anti-clockwise direction,
whereby, the rotor is pulled to rotate in the
clockwise direction.
 The shaft, upon which the rotor is mounted,
now rotates and the output torque is thus
obtained.
 From the figure, it is evident that the stator
and rotor always possess the same shape.
The figure depicts a rotational USM.
16

17. The above figure is the schematic diagram of a linear USM driven by dual actuators.
17

18. FRICTIONAL COUPLING
 As we have discussed in the working of USM that a surface wave is generated in the
stator, by the converse piezoelectric effect occurring in the actuator.
 As the wave propagates through the stator, the rotor is pulled back in the opposite
direction.
 Now, there is a chance that the rotor may get slipped off from the stator. To avoid this
hitch, the surface of contact between rotor and stator is made rough or rather uneven.
This method of coupling of rotor and stator is known as frictional coupling.
 The grooves are designed in such a shape as to toss away the dust produced by this
process.
 During the design of frictional grooves, care is to be taken that during slow speeds,
interlocking of rotor and stator doesn’t occur.
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19. CLASSIFICATION OF USMs
 There are several classifications for ultrasonic motors depending upon their shape, size,
type of motion, application etc.
 The USMs are also classified according to the type of wave that is being generated in the
stator.
 If the wave produced in the stator has its particles vibrating only in the vertical direction,
(standing wave), such type of motors are called Standing Wave type USMs.
 And, if the wave produced in the stator has its particles vibrating both in the vertical
direction as well as horizontal direction (travelling wave), such type of motors are called
Travelling Wave type USMs.
 Even though the type of wave produced is different, both these types of USMs has got the
same construction and working principles.
 However, the Travelling Wave-type USMs are found to have better operating
characteristics.
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20.  The other methods of classifications of ultrasonic motors are,
1. Mode of operation:
a. Static
b. Resonant
2. Type of motion:
a. Rotary
b. Linear
c. Spherical
3. Shape of implementation:
a. Beam
b. Rod
c. Disk
20

21. ► If we categorize them from the
vibrator shape, there are
• Rod type
• π-shaped
• Ring (square)
• Cylinder types.
21

22. TYPES OF ULTRASONIC
MOTORS
ULTRASONIC
MOTOR
STANDING
WAVE TYPE
LINEAR
MOTOR
ROTARY
MOTOR
TRAVELLING
WAVE TYPE
LINEAR
MOTOR
ROTARY
MOTOR
22

23. STANDING WAVE TYPE USM
 The first ultrasonic standing wave motor was proposed by H.V. Barth in 1973.
 The standing-wave type is sometimes referred to as a vibratory-coupler type or a
woodpecker type.
 A vibratory piece is connected to a piezoelectric driver and the tip portion generates
flat elliptical movement.
Fig: Vibratory coupler type motor (a) and its tip locus (b).
23

24. ► When a vibration displacement:
u(x) = u0 sin(ωt +α)
is excited at the piezoelectric vibrator, the vibratory piece generates bending because
of restriction by the rotor,
► So that the tip moves along the rotor face between A → B, and freely between B →
A.
► If the vibratory piece and the piezo-vibrator are tuned properly, they form a
resonating structure.
► Therefore, only the duration A → B provides a unidirectional force to the rotor
through friction, i.e. intermittent rotational torque or thrust.
24

25. LINEAR TYPE STANDING WAVE
USM
 K Uchino et al invented a π-shaped linear motor.
 This linear motor is equipped with a multilayer piezoelectric
actuator and fork-shaped metallic legs.
 Since there is a slight difference in the mechanical resonance
frequency between the two legs, the phase difference between
the bending vibrations of both legs can be controlled by
changing the drive frequency.
 A test motor 20×20×5 mm 3in dimension exhibited a maximum
speed of 20 cm/s and a maximum thrust of 0.2 kgf with a
maximum efficiency of 20%, when driven at 98 kHz at 6 V
(actual power = 0.7 W).
25

26.  The figure given below shows the motor characteristics of the linear motor.
 Applications of linear standing wave type motors are paper or card senders.
26

27. ROTATING TYPE STANDING
WAVE USM
 The torsional coupler consisting of two legs which transform
longitudinal vibration.
 Extruder is aligned with a certain cant angle to the legs, which
transforms the bending to a torsion vibration.
 This transverse moment coupled with the bending up–down
motion leads to an elliptical rotation on the tip portion.
 The optimum pressing force to obtain the maximum thrust is
obtained, when the ellipse locus is deformed roughly by half.
27

28.  However, this type provides only
unidirectional rotation.
 Even though the drive of the motor is
intermittent, the output rotation becomes very
smooth because of the inertia of the rotor.
 Provides high speed than linear motors
because of high frequency (160kHz)&
amplified vibration.
 Provides speed of 1500 rpm, torque of 0.08
Nm and efficiency of 80%.
28

29.  The standing-wave type is
• Low in cost (one vibration source) and
• High efficiency (up to 98% theoretically)
• But lack of control in both clockwise and counterclockwise directions.
29

30. TRAVELLING WAVE USM
 The propagating-wave type combines two standing waves with a 90
degree phase difference both in time and in space.
 Representation of travelling wave
U(x ,t)= A cos(k x) cos(wt) + A cos(k x - 90) cos (wt-90)
 A surface particle of the elastic body draws an elliptical locus due to the
coupling of longitudinal and transverse waves.
30

31. LINEAR TYPE TRAVELLING WAVE
USM
 Linear motor using bending vibration.
 The two piezoelectric vibrators installed at
both ends of a transmittance steel rod
excite and receive the traveling transverse
wave.
 Adjusting a load resistance in the receiving
vibrator leads to a perfect traveling wave.
31

32.  Exchanging the role of exciting and receiving piezo-components provided a
reverse moving direction.
 The bending vibration transmitting via the rail rod.
 Low efficiency around 3% because the whole rod must be excited even when
only a small portion is utilized for the output.
32

33. ROTARY TYPE TRAVELLING
USM
 Two voltage sources are used to produce
travelling wave.
 Vibrations of the piezoelectric material is
amplified by the stator teeth.
 Due to frictional forces rotor rotates.
 Resonant frequency- 46kHz.
33

34.  The travelling-wave type-
• Requires two vibrating source.
• Controllable in both direction.
• Silent operation, so suitable to video cameras with
microphone.
• Thinner design, leading to space saving.
• Low efficiency(not more than 50%)
• Energy saving.
34

35. Comparison of the motor characteristics of the vibration coupler standing
wave type, surface propagating wave type and a compromised ‘teeth’
vibrator type.
35

36. CONTROL TECHNIQUE OF
USM
 PWM control is used.
 Motor is operated at
resonance frequency(low
impedance) to reduce losses &
to reduce pressure on
piezoelectric material.
 Various control methods are :
36

37. Block diagram of the total ultrasonic drive system
37

38. ESTIMATIONS FOR SMALLER
USMs
 The output force is proportional to the force factor A.
 The relationship between the force factor and stator dimensions-
 Force factor is expressed as-
where ƛ is a constant equivalent to 4.730, R0 is outer radius of piezoelectric
material, Ri is inner radius of piezoelectric material, l is length and e is
piezoelectric coefficient.
 Maximum output force, Fmax is expressed as AV and the maximum output torque
is proportional to FmaxRo.
38

39.  Calculation results for micro ultrasonic motors with various
diameters
39

40. 40

41. ADVANTAGES
 They have got high output torque & efficiency.
 They exhibit high torque to weight ratio.
 Good positioning accuracy
 Capable of working in extreme environmental conditions.
 No magnetic interference.
 Simple construction
 Compact size and Low cost
 Energy saving
41

42. DISADVANTAGES
 Requires high frequency power supply(kHz range).
 Piezoelectric material is expensive.
 Ultrasonic noise occurs.
 Drooping torque-speed characteristics.
 Suppression of heat is required.
 Less constancy.
42

43. APPLICATIONS
 Auto focusing & optical zooming in digital cameras &
surveillance cameras.
 In the automobile industry, the USMs are used for the operation
of power steering, power windows, tilt steering, ORVMs, car
seat adjustment, etc.
 The disk heads of hard disks, floppies & CD drives can be
controlled by the USM.
 Wrist watches & Clocks
 Robotics
 Aerospace
 Medicine
43

44. CONCLUSION
 The above prose has gone through almost all the fundamental details of this
modern technology machine. Hence the ultrasonic motors, which is a new
step in the miniaturized electrical technology has got many applications in
small appliances because of its high torque at low density. Though USMs are
not widely used for heavy motoring activities because of the requirement of a
larger & expensive piezoelectric material that causes the production cost to
shoot up double fold. However, researches are in progress to improve the
technology to meet the heavy industrial requirements and also to minimize
the problems caused by ultrasonic noise. A world might be expected in the
near future that replaces the futile electromagnetic motors by the proficient
ultrasonic motors.
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45. REFERENCES
 http://www.noliac.com/Files/Billeder/Pdf/Pdf%20%20external/
Piezoelectric_ultrasonic_motors.pdf
 http://www.americanpiezo.com/piezo_theory /piezo_theory.pdf
 http://www.slideshare.net
 www.pdf-searchengine.com
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47. Questions?