PREPARED BY:- CHANDAN BEHERA ELECTRICAL ENGINEERING DEPARTMENT REGISTRATION NO:-0901106167COLLEGE OF ENGINEERING & TECHNOLOGY BHUBANESWAR
CONTENTS1. INTRODUCTION2. ELECTROSTICTION NOTION3. POLING4. ULTRASONICMOTOR NOTION5. EQUATIONS6. BASIC PRINCIPLE7. CONSTRUCTION8. PARTS OF ULTASONIC MOTOR9. TYPES OF ULTRASONIC MOTOR10. DRIVER CIRCUIT OF ULTRASONIC MOTOR11. CONTROL TECHNIQUE OF ULTRASONIC MOTOR12. MAJOR APPLICATION13. ADVANTAGES & DISADVANTAGES14. CONLUSION15. REFERENCE
INTRODUCTION The first ultrasonic motor was developed by V.V lavrinko in 1965. Conversion of electric energy into motion by inverse piezoelectric effect. In this tpye of motor efﬁciency is insensitive to size,& these are superior in the mm-sized motor area.
ELECTROSTICTION NOTION Inverse piezoelectricity – generation of mechanical stress in response to electric voltage. 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),PZT(Lead-Zirconium-Titanium).
HOW IT OCCURS?? When voltage is applied across the crystal, the atoms experience electrcal pressure. So they move to rebalance themselves, & thus deformation is produced. If the voltage is applied in the direction of poling voltage the material will elongate & its diameter reduces else length decreases & diameter increases. If AC is applied then the material will lengthen & shorten cyclically, at the frequency of applied voltage.
POLING It is process of polarization of the piezoelectric material.
EQUATIONS The relationships between an applied voltage & the corresponding increase or decrease in a piezoelectric ceramic elements thickness, length, or width are: Δh = d33v S = d33E Δl / l = d31E Δw / w = d31E where l: initial length of ceramic element w: initial width of ceramic element Δh: change in height (thickness) of ceramic element Δl: change in length of ceramic element Δw: change in width of ceramic element d31,d33: piezoelectric charge constants in different direction V: applied voltage S: strain (change in height / original height of element) E: electric field
ULTRASONICMOTOR NOTION It is named so ,as it uses voltage of frequency higher than 20kHz. It is based on inverse piezoelectricty. It can be abbreviated as USM. It is driven by ultrasonic vibration of transducer. The ultrasonic vibration is transformed into output torque (in rotary USM) or thrust (in linear USM) by the friction between the stator and the rotor (in rotary USM) or the moving part (in linear USM).
BASIC PRINCIPLE Generation of gross mechanical motion through the amplification and repetition of micro- deformations of active material. 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 the ROTOR. Working frequency-20 KHz to 10 MHz Amplitude of the actuator motion – 20 to 200nm
PARTS OF ULTRASONIC MOTOR The Stator part transmits vibration. Stator consists of: The Piezo-Electric Ceramics which generate vibration. The Stator metal which makes vibration amplify. The Friction material which contacts with a rotor. The Rotor which is a rotation part. The Shaft which transmits rotation. The Bearing.
WORKING•If voltage is made to apply to piezo-electric ceramics, the shapeof piezo-electric ceramics will be changed or distorted. Themodification amplifies and spreads with stator metal, andgenerates a traveling wave on the surface of stator metal.•Here, the stator metal touches the rotor only at each peak of atraveling wave, and each of that peak carries out ellipticalmovement. A rotor rotates in response to the influence of theelliptical movement.•The direction of movement of this ellipse is in accordance to thedirection which a traveling wave follows. And a rotor rotates in thedirection contrary to a traveling wave under the influence.•So, When a traveling wave progresses in the clockwise direction(CW) on the circumference of a stator, each peak of the travelingwave in contact with a rotor carries out elliptical movement in theclockwise direction (CW).And the rotor in contact with the peak ofthe wave rotates in the counterclockwise direction (CCW).Bycontrolling the speed and direction of this traveling wave, controlof an Ultrasonic Motor is possible
TYPES OF ULTRASONIC MOTOR ULTRASONIC MOTOR STANDING TRAVELLING WAVE TYPE WAVE TYPE LINEAR ROTARY LINEAR ROTARY MOTOR MOTOR MOTOR MOTOR
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 USM Rectangular plate ultrasonic motor. Resonant frequency- 98kHz. Efficiency-65% Applications-card or paper senders.
ROTATING TYPE STANDING WAVE USM Torsional coupler ultrasonic motor. Provides high speed than linear motors because of high frequency (160kHz)& amplified vibration. Provides speed of 1500 rpm, torque of 0.08 Nm & efficiency of 80%.
STANDING WAVE USM Low cost one vibration source High efficiency Unidirectional
TRAVELING WAVE USM Superposition of multiple standing wave create a traveling wave. Representation of travelling wave U(x ,t)= A cos(k x) cos(wt) + A cos(k x - 90) cos (wt-90). Phase difference is 90 degree
LINEAR TYPE TRAVELLING WAVE USM Linear motor using bending vibration. Consists of two piezoelectric vibrators installed at both the ends. Load resistance is adjusted for perfect travelling wave.
ROTARY TYPE TRAVELLING WAVE USM Two voltage sources are used to produce travelling wave. Vibrations of the piezoelectric material is amplified by the stator teeths. Due to frictional forces rotor rotates. Resonant frequency- 46kHz.
TRAVELLING WAVE USM 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.
EQUIVALENT CIRCUIT OF USM STATOR 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 stator. Their combined impedance is given by( +1/ + ).
DRIVER CIRCUIT OF USM Nref and Uref are the given value of rotating speed and amplitude of driving voltage, respectively. An optoelectric encoder, E, is used to measure the rotating speed of ultrasonic motor. 1 ∼ 8 are power MOSFETs, T1 and T2 are transformers, and L1 and L2 are series compensating inductances. PWM1~PWM8 are the PWM control signals for 1 ∼ 8. DSP is used to implement the control strategies & CPLD is used to produce the phase-shift PWM control signals PWM1 ~ PWM8 for H-bridge.
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 :
MAJOR APPLICATION Camera auto focus lenses Watch motors and compact paper handling. Conveying machine parts In micro surgery and sensor scaning.
ADVANTAGES DISADVANTAGES Low cost Use of high frequency High efficiency power supply No magnetic Less constancy interference Drooping torque Compact size speed characteristic High torque/weight Supppression of heat ratio is required Energy saving
CONCLUSION These motors are advantageous. Electromagnetic interference is not there. It is in great demand in the area of automation & miniaturiztion. Energy efficient. Light weight & compact size