technical seminar on ultrasonic motors

8/12/2019 Technical Seminar On ultrasonic motors

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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/

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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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technical seminar on ultrasonic motors

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