Presentation on theme: "PIEZOELECTRIC ULTRASONIC MOTOR"— Presentation transcript:
1PIEZOELECTRIC ULTRASONIC MOTOR BYNEENA SKARIAEdited BySarath S Nair
2CONTENTS Need for USM Principle of operation Working of USM Travelling wave USMEquivalent circuit of USMSpeed characteristics of USMComparison with electromagnetic motorConclusionReference
3NEED FOR USMFor applications such as industrial, medical, robotic, space, automotive etc market research indicates that tiny motors smaller than 1 cm3 is of great demand.Electromagnetic motors smaller than 1 cm3 are difficult to produce with sufficient energy efficiency.With smaller parts, an increasing percentage of power is converted into heat instead of motion.A new class of motors using high power ultrasonic energy— ultrasonic motors—is gaining widespread attention
4Ultrasonic motorUSM is newly developed motor that uses ultrasonic vibration of a piezoelectric material as its drive source.The working frequency of ultrasonic motor ranges from 20Khz to 10Mhz (quiet in operation ).The torque of an USM is 10 to 100 times larger than electromagnetic motors of the same size or weightUSM are emerging as an alternative to electromagnetic motors where miniaturization, low power use, and high reliability are required.
5converse PIEZOELECTRIC EFFECT Basic principle of operation –converse piezoelectric effectthe production of stress / strain when an electric field is applied to a piezoelectric material.
7If a voltage of the same polarity as the poling voltage is applied to a ceramic element, in the direction of the poling voltage, the element will lengthen and its diameter will become smaller.If a voltage of polarity opposite that of the poling voltage is applied, the element will become shorter and broader.If an alternating voltage is applied, the element will lengthen and shorten cyclically, at the frequency of the applied voltage
9In the operation of the USMs two-stage energy conversion is formed. 1)Electromechanical energy conversionelectrical energy is converted into mechanical energy by excitation of the piezoelectric ceramic with ultrasonic range frequency.2)mechanical energy conversionmechanical vibrations are converted to linear or rotary motion by friction force generated in stator–rotor interface.
10CLASSIFICATIONThere are various categories to classify ultrasonic motorssuch as(1) Operation: Rotary type and linear type(2) Device geometry: Rod type, π-shaped, ring and cylinder types(3) Generating wave: Standing wave type and travelling wave type.
11Direction of USM opposite to direction of travelling wave TRAVELLING WAVE USMDirection of USM opposite to direction of travellingwave
12The ellipse of movement allows us to calculate speed of rotor The velocity in the highest point of ellipse determines the speed of contact between stator and rotor which is the speed of the rotor itself
13GENERATION OF TRAVELLING WAVE Standing wave is expressed asu s (x, t) = A cos kx . cos ωtTravelling wave is expressed asu t (x, t) = A cos ( kx – ωt)Using a trigonometric relation, u t (x, t) can be transformed asut (x, t) = A cos kx . cos ωt + A cos ( kx – π/2) cos ( ωt -π/2)Travelling wave can be generated by superimposing two standing waves whose phases differ by 90 degree from each other both in time and in space
15To generate a travelling-wave within the stator, it is necessary to have control of 2 mechanical orthogonal modes.Electrode pattern A provides cos(kθ)and pattern B provides sin(kθ). By driving these 2 modes 90 degree out of phase temporally a travelling-wave is produced.Patterns A and B provide a standing wave individually. The superposition of standing waves produces a travelling-waveBy changing the sign of one of the drives signals the direction of the travelling-wave and the direction of the rotor changes.
16Relation b/w feedback electrode and speed Feedback electrode produces high frequency AC voltage when mechanical vibrations act on the stator surface which is proportional to motor speed.
17USR 60 (TRAVELLING WAVE USM) USR 60 is rotary travelling wave USMnameplate of USR60 USMDrive frequency kHzDrive voltage VrmsDrive current 53mARated torque 0.4 NmRated power 4 WRated speed 10 rad/sWeight 0.23 kg
18ESTIMATION OF MOTOR CHARACTERISTICS Three methods have proposed to estimate motor characteristics.1)Finite element method-----( where no electrical parameters are considered).2)Energy conversion method (which is too complicated to estimate motor characteristics under different driving frequencies).3) Equivalent circuit model (ECM)If there is a sufficiently applicable equivalent circuit model (ECM) for expression of practical operations of the USMs, it will be very useful for the design and the estimation of motor characteristics.
19F = force at mechanical terminal EQUIVALENT CIRCUITWhere, F=AV-ZvI=YdV+AvYd=1/jwCdA = force factorF = force at mechanical terminalv = velocity at the mechanical terminalZ= the mechanical impedance of piezoelectric ceramic
21Where s =spring constant of stator, m= mass of metal assembly and ceramic of stator,A =force factorr = mechanical resistanceUSM should be driven at frequency creating resonance between Cm and Lm in the equivalent circuit.The mechanical resonance frequency is expressed as
22Damping admittance Yd and motional admittance Ym of the equivalent circuit are found as follows Current flowing into the motional branch causes motor movement called motional current, which is expressed byIm= V×Ym
23EQUIVALENT CIRCUIT PARAMETERS OF USR60 Cd = 9 nF rd = 20 k Lm = 0.1 H r0 = 150 Cm = 168 Pf
24SPEED characteristics of twusm Speed of USM is time varying due to changes in1)temperature- internal losses- frictional interface b/w stator & rotor2)drive operating conditions-driving frequency,-source voltage-load torque.
25SPEED FREQUENCY CHARACTERISTIC Speed of USR60 is controlled in kHz frequency range
27SPEED CONTROLSpeed of an ultrasonic motor can be contolled in 3 ways 1)drive frequency control, 2)applied voltage control, 3) phase difference control of applied voltages
28Comparison with electromanetic motor simple structurefaster response timesmaller packaging capabilityhigh torque at low speedhigh dynamic resolutionvery low inertiahigh power to weight ratiolow speed without additional gear or spindle mechanisms,
29good control characteristics at start and stop noiseless operationgood control characteristics at start and stophigh dynamics and very good positioning accuracyrequire no winding.not affected by magnetic field
30Necessity for a high frequency power supply. limitationsThey suffer from potential wear at the rotor / stator interface due to friction which tends to shorten service lifeNecessity for a high frequency power supply.Sensitive to temperature variations.Difficult to derive a complete mathematical model of USM.
31APPLICATIONS Computer disc drives Camera autofocus Robotic positioning Pharmaceuticals handlingMedical cathetes placementMicropositioning stagesFibre optic positioningManufacturing process controlSemiconductor test equipment
32SUMMARYThis paper focuses on a new class of motors using high power ultrasonic energy—ultrasonic motors.Equivalent circuit for an ultrasonic motor is developed.The operation and characteristics of a travelling wave USM is discussed taking into consideration USR60Piezoelectric motors are emerging as an alternative to electromagnetic motor where miniaturization, low power use, and high reliability are required.USMs are presently being widely used for industrial, medical, robotic, space and automotive applications
33REFERENCE Güngör Bal Erdal Bekiroglu “Characteristics Estimation Of Travelling-WaveUltrasonic Motor Using Equivalent Circuit Model” Eleco’2001 InternationalConference on Electrical and Electronics Engineering 7-11 November 2001,Bursa/TURKEY Yoichi Ogahara, Takashi Maeno”Torque Characteristics Analysis of aTravelling Wave Type Ultrasonic Motor Impressed High Load Torque in LowSpeed Range” IEEE International Ultrasonics, Ferroelectrics, and FrequencyControl Joint 50th Anniversary Conference2004 Ming Hao and Weishan Chen ” Analysis and Design of a Ring-type TravelingWave Ultrasonic Motor” Proceedings of the 2006 IEEE International Conferenceon Mechatronics and Automation June , 2006, Luoyang, China Güngör Bal, Member, IEEE, and Erdal Bekiro˘glu, “A Highly Effective LoadAdaptive Servo Drive System for Speed Control of Travelling-Wave UltrasonicMotor”, IEEE Transactions On Power Electronics, Vol. 20, No. 5, September
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