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8/12/2019 Technical Seminar On ultrasonic motors
1/22
Technical Seminaron
ULTRASONIC PIEZOELECTRIC MOTOR Submitted by
Name: Akhil Adarsh S
H.T. no.: 10E31A0253
Students signature:
Guides signature:
HODs signature:
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ABSTRACT
ULTRASONIC MOTOR
An utrasoni! motoris a type of electric motor powered
by the ultrasonic ibration of a component! the stator!
placed a"ainst another component! the rotor or slider
dependin" on the scheme of operation #rotation or lineartranslation$. %ltrasonic motors differ
from pie&oelectric actuators in seeral ways! thou"h both
typically use some form of pie&oelectric material! most
often lead &irconate titanate and occasionally lithium
niobate or other sin"le'crystal materials. (he most obious
difference is the use of resonance to amplify the ibration
of the stator in contact with the rotor in ultrasonic motors.
%ltrasonic motors also offer arbitrarily lar"e rotation or
slidin" distances! while pie&oelectric actuators are limited
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by the static strain that may be induced in the pie&oelectric
element.
)ne common application of ultrasonic motors is in camera
lenses where they are used to moe lens elements as part of
the auto'focus system. %ltrasonic motors replace the noisier
and often slower micro'motor in this application.
"R#S#NT#$ B%&
A'HIL A$ARSH S
ONTENTS Utrasoni! Motors
Introduction
Objectives
Structure and Operating Principlesof Motor
Finite lement !nal"sis
Set#$p For The %haracterisation OfThe Motor
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o &stDesign
o 'ndDesign
o (rdDesign
Driving %ircuit
%onclusion
INTRODU TION
* An ultrasonic motor #%S+$ conerts ultrasonicibrations into linear or rotary motion.
* %S+s plays an important role a few markets where
the si&e! tor,ue! speed or other re,uirements could not
be satisfied by the traditional E+ motor
(he two lar"est markets for %S+s are cameras and
automotie but they are also found in medical e,uipment
#+-s$ and as robotic sero motors.
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* %ltrasonic motors! which hae superior characteristics
like hi"h tor,ue at low speed! absence of ma"netic
interference! and compactness in si&e! are "oodcandidates for medical applications! automation!
robotics! aerospace en"ineerin" and arious other
fields. +any different types of ultrasonic motors hae
been proposed up to date 1'5.
* (he stator of an ultrasonic motor that is ecited bypie&oelectric elements in ultrasonic fre,uency ran"e
deelops different kinds of ibrations dependin" on its
structure. rom the way of creatin" an elliptical
motion on the stator! ultrasonic motors were classified
into two ma4or "roups! such as standin" wae and
traelin" wae types.
* urther classifications include mode'conersion!
multi'mode !6!7 and mode'rotation types of motors
8 that are suitable for miniaturi&ation and can be
manufactured less costly.
* %ltrasonic motors are of "reat interest due to the
fleibility of miniaturi&ation in comparison with
conentional electroma"netic motors whose efficiency
decreases si"nificantly. Especially in information
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systems / and medical industry 10! compact si&e of
these motors makes them find wider applications.
Objective(he miniaturi&ation of a mechatronic deice depends on the
si&e of the motor e,uipped in the deice to run it.
+iniaturi&ation of conentional electroma"netic motors
to seeral millimeters with hi"h efficiency is difficult since
a "ear mechanism is re,uired to obtain a hi"h tor,ue from
the electroma"netic motor. (his mechanism adds additional
mass! olume and compleity and also increases the
number of components of the system! which decreases the
motor system reliability. )n the other hand! pie&oelectric
ultrasonic motors are suitable for miniaturi&ation in termsof their compactness and low power consumption.
)ur main ob4ectie is to desi"n! fabricate and characteri&e
pie&oelectric ultrasonic motors for micromechatronic
deices. (he approach in desi"nin" these pie&oelectric
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motors were as followsi. (o simplify the structure
includin" the polin" confi"uration of pie&oelectric element
used in stator. . (o reduce the number of components in
order to decrease the cost and enhance the driin"reliability.
(he desi"ned motors are a multi'mode'sin"le'ibrator
ecitation type! which uses two ortho"onal bendin" modes
of a hollow cylinder. Since the structure and polin"
confi"uration of the actie pie&oelectric elements used in
the stator are simple! these motor structures are ery
suitable for miniaturi&ation. +oreoer! a sin"le driin"
source can ecite two bendin" modes at the same time! thus"enerate a wobble motion. (here are 3 types of ultrasonic
motors. (he pie&oelectric stator structure is the same for all
of these motors. 9oweer! the dimensions of the motor are
reduced by almost 50 percent. Startin" with a 10 mm lon"
stator! we reached down to / mm in the last model. (he
initial diameter was 2./ mm and it went down to 1. mm.
n the final desi"n! the rotor part of the motor had beenchan"ed and this resulted in a reduction in the number of
components. n terms of driin" circuit! a sin"le driin"
source was enou"h to run the motor and a conentional
switchin" power supply type resonant '; circuit was
used
Structures and Operating Principles ofMotors
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A s,uare beam has two ortho"onal bendin" modes whose
resonance fre,uencies are e,ual to each other. (he first
bendin" mode fre,uencies in any direction for circular
cylinders are also e,ual to each other. (he stator of themotor combines the circular and s,uare cross'sections. (he
outside surface of a hollow metal cylinder was flattened on
two sides at 80'de"rees to each other and two uniformly
electroded rectan"ular pie&oelectric plates were bonded
onto these two flattened surfaces #i".1 #a$$. (he basic
confi"uration of the motor is shown in i".1 #b$. Since the
stator is symmetric with respect to the
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inite Ele!ent "nal#sis.(he behaior of the free stator was simulated usin" A(A
finite element software to erify the conceptual operation
principle. (ailorin" dimensions of the metal and
pie&oelectric ceramics e,uated the two ortho"onal bendin"
mode fre,uencies of the stator. (he pie&oelectric plates on
the surface of the cylinder were placed in such a way that
one pie&oelectric plate can ecite the two ortho"onal
bendin" modes of the stator. i".2 #a$ shows the two
ortho"onal bendin" mode shapes when only the plate on
the 'ais #plate @$ was ecited! while the electrode of theplate was short'circuited. ?obble motion was "enerated
on the cylinder when only one pie&oelectric plate is ecited
at a fre,uency between the two ortho"onal bendin" modes
fre,uencies #i".2
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#b$$. ?hen the other pie&oelectric plate was ecited at the
same fre,uency! the direction of wobble motion was
reersed.
Set$up for t%e %aracteri&ation of t%eMotors(he performance of the motors was measured usin" a
transient characteri&ation method! which was initiallyproposed by Bakamura 11. (he principle of this method
is mountin" a load #usually a disk whose moment of inertia
is known$ onto the motor! at 61 k9& at 6/ k9& runnin" the
motor! and! finally! analy&in" the transient speed obtained
as a function of time. +ore eplicitly! the an"ular
acceleration of the motor is calculated from the speed
measurement by Bewton
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onto the stator and the motor is then drien with an A;
olta"e. (he position of the rotatin" disk is detected
throu"h an optical encoder. (he transient position data
were then conerted into olta"e si"nal usin" a fre,uencyto'olta"e conerter. Since the output olta"e of the
conerter is proportional to the input fre,uency!
the speed of the motor was obtained. (he an"ular
acceleration of the motor was estimated usin" the
deriatie of the an"ular speed. inally! the transient tor,ue
was calculated by multiplyin" the an"ular acceleration with
the moment of inertia of the rotatin" disk.Structural
Croperties and ;haracteristics of the +otors So far! 3motors were fabricated. (able 1 summari&es the structural
properties of these motors. As can be seen from (able 1!
there is a "radual reduction in the dimensions and reduction
in the total len"th of the whole motor structure.
'st Design(he outside surface of the metal cylinder was "round on
two sides at 80'de"rees to each other to obtain two
ortho"onal flat surfaces. (he CD( plates! which were
electroded uniformly and poled in the thickness direction!
were bonded onto the flat ortho"onal surfaces of the
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cylinder usin" an epoy. (he rotor was a cylindrical rod
and it was pressed by a sprin" usin" a pair of stainless steel
ferrules. A picture of this motor can be seen in i".3.
As a first step to clarify the behaior of the stator! the
admittance spectra i" 3. 1st desi"n when plate @ or was
ecited. ?hen plate @ was ecited while short'circuitin"
the electrode of plate to the "round! the stator had two
de"enerated bendin" mode resonance fre,uencies around
61.7 and 6/.0 k9&. ?hen plate was ecited! the stator
showed a similar behaior.
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(he wobble motion in the @'plane was also erified by
measurin" the ma"nitude of the ibration elocity in andy directions at the same time. A function "enerator
#9C33120A$ and a power amplifier #B/010$ were used to
ecite the stator. y ecitin" either plate @ or plate ! the
elliptical displacements in and y directions were
measured with two laser fiber optic interferometers.
irst! plate @ was ecited at fre,uencies of 60.6! 61.! 62.2!
63! 6/! 65! 6 k9&! with an input olta"e of 112.0 F p'to'p.
(he results are plotted in i".5 #a$. (he measurements wererepeated by ecitin" only plate and the results are shown
in i".5
i".5. Elliptical displacements at fre,uencies 60.6! 61.!
62.2! 63! 6/! 65 and 6 k9& #a$ when plate @ was ecited
and! #b$ when plate was ecited. Elliptical >isplacement
when Clate ecited
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60.6 61. 62.2 >isp.@ 65 6 k9& Elliptical >isplacement
when Clate ecited 60.6 61. 62.2 >isp.@ 65 6 k9& (he
interestin" points here are: i$ the direction of wobble
motion when only plate @ was ecited was clockwise! andcounterclockwise when only plate was ecited! ii$ the
wobble motion! when only plate @ was ecited! was almost
identical to the wobble motion when only plate was
ecited at the same fre,uency. n conclusion! the desi"ned
motor can be drien with a sin"le A; source and ecitin"
either plate @ or ! the direction of the rotation can be
reersed. n terms of load characteristics of the motor!
transient speed! tor,ue and efficiency were measured andcalculated. A load! a metal disk #0 "$ with a diameter of
3/ mm and moment of inertia #7. k"mm2$ was mounted
onto the stator. As shown in i".! the steady state speed
reached 7 rad=sec in 6 sec. A startin" tor,ue of 1.7 mBm
at 120 Folt is similar to other bulk pie&oelectric cylindrical
type micro motors in literature and almost one order of
ma"nitude hi"her than that of a thin film motor with asimilar si&e 12'1/
1/
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(he product of output tor,ue with output speed "ies the
output power. A maimum power of 0 m? was obtained
at a speed of 0 rad=sec and a tor,ue of 1 mBm. (hemaimum efficiency of 25 G #i".6$ at 120 F is similar to
other bulk cylindrical type micro pie&oelectric motor 1/.
(nd Design(he principle is the same as the preious motor. (he
important improement is in the reduction of thedimensions of the stator almost by half of the preious one.
abricated motor can be seen in i".7.
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Simulation of the stator was performed by A(A finite
element software to determine the bendin" modes of the
structure. (he two ortho"onal bendin" fre,uencies
were obsered at 127 k9& and 132 k9&. Eperimental set'
up for measurin" load characteristics is the same as the
preious one and the results are as follows. (he steady state
speed was obtained as 6 rad=sec in 6 sec. A maimum
tor,ue of 0.76 mBm was obtained. (he motor reached a
maimum power of /5 m? at a speed of /5 rad=sec. (hemaimum efficiency was 12 G. (he power of the motor is
dependent on the si&e of the pie&oelectric ceramics used.
As the thickness and the len"th of the components were
reduced! a lower output power was obtained.
)rd Design(his motor is the smallest of all three desi"ns. (hediameters of the stator part are the same as that of 2nd
motor. 9oweer! the len"th is reduced to / mm and also the
rotor part has chan"ed completely. nstead of a solid metal
rod! a sprin" was used as a shaft.
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(his sprin" acts as a rotor and as a pre'stress element! as
well. Apparently! the number of components was
minimi&ed. A picture of this motor can be seen in i".8.
(he resonance fre,uency of the stator is in the ran"e of
230'2/5 k9&. As the len"th of the ceramic plates reduced
down to / mm! the workin" fre,uency increased
relatiely. +aimum tor,ue and power are 0.3 mBm and
25 m?! respectiely. (able 2 summari&es the important
characteristics of all motors.Tabe (. C%aracteristics of t%e !otors
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(o summari&e! (able 3 compares the structural differences
of all fabricated motors. (he ob4ecties to miniaturi&e and
to simplify the structure of the proposed motor desi"n were
achieed successfully.
Tabe ). Co!parison of t%e designs
Driving ircuit;urrent trend for driin" ultrasonic motors consists ofusin" switchin" amplifiers. (he reason is that they
considerably reduce the heat "enerated by the pie&oelectric
element. or the 3rd desi"n! a switchin" power amplifier
type driin" circuit was used. +a4or feature of this kind of
circuit is that it acts as a olta"e re"ulator. As load
re,uirements chan"e! olta"e ariations also occur. (his
kind of olta"e re"ulator circuit is capable of establishin"and maintainin" a nearly constant dc output olta"e.
A schematic dia"ram of the circuit is shown in i". 10.
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onclusion
(he desi"n! fabrication and characteri&ation of a
pie&oelectric ultrasonic micromotor hae been inesti"ated.
(he pie&oelectric motor makes use of two ortho"onal
bendin" modes of a hollow cylinder. (he ibratin" element!
stator! of the motor consists of a brass tube and two
pie&oelectric plates bonded to two flattened surfaces of the
tube. (hree different motors were fabricated. n the first
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two desi"ns! a solid stainless steel was used as a shaft! a
sprin" as a pre'stress and a ferrule to hold the rod and the
sprin". +a4or improement of the 2nd motor with respect
to the 1st one was the reduction in the dimensions of thestator. 3rd motor was the smallest in len"th of all and the
shaft was replaced with a sprin". ;onse,uently!
miniaturi&ation and simplification of the proposed desi"n
were achieed.All three motors were characteri&ed
indiidually. Admittance spectra of the free
stators! tor,ue! power and efficiency alues of each motor
were presented. >riin" of the motor was enabled by a
switchin" power supply. t is conentionaland cheap.
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