ULTRASONICPIEZOELECTRIC

MOTOR

RAKESH REEE-S746

MOTOR

• Device that converts electrical energy to mechanical energy.

• ELECTROMAGNETIC MOTORS Current carrying conductor kept in a magnetic field

experiences a force or torque (Faraday’s law of EMI).

Electrical energy Magnetic energy Mechanical energy

Drawbacks of Electromagnetic Motors

• Noisy operation.• Surge currents and spikes.• Electromagnetic interference.• Magnetic losses (Eddy currents & Hysteresis).• High power consumption & high temperature.• Low power factor.• Comparatively lesser efficiency.

ULTRASONIC MOTOR (USM)

• A pressure applied across a pair of opposite faces of a crystal, results in a PD developed across the other pair.

PIEZOELECTRIC EFFECT

+ + + ++ + + +

_ _ _ __ _ _ _

Mechanical Pressure

Mechanical Pressure

Potential Difference

• When an AC is applied across a pair of opposite faces, alternating compressions and elongations (mechanical vibrations) are obtained across the other pair of opposite faces.

• As a result, a surface wave is formed over the crystal driving force of the USM

Working Principle : CONVERSE PIEZOELECTRIC EFFECT

Construction• ACTUATOR A piezoelectric material (Quartz, Barium Titanate,

Tourmaline, Rochelle Salt) is used as actuator. Actuator is fixed on the stator using thin metal

sheets and bearings. Actuator is directly connected to the supply

mains.

• STATOR Stator is made of any malleable material Steel. Ring, Cylindrical or Rod shaped.

Contd…

• ROTOR Same material as that of the stator. Same shape as that of the stator(Ring, Cylindrical

or Rod). Frictional coupling.

• CASING Cylindrical, Disc or Box shaped. Non- corrosive alloys or Fiber. To provide protection against abrasion & external

interferences.

Contd…

Working

Linear USM with double stators

Stator

StatorRotor

Actuator

Actuator

Coupling of Rotor & Stator

• Surface of contact b/w rotor & stator is made uneven, so that they never slip off frictional coupling.

• During motion, rotor is levitated from the stator in the perpendicular direction less wear & tear.

• Care is to be taken that friction doesn't cause the interlocking of rotor & stator.

Types of USM• Travelling Wave type

If the wave produced in the stator causes the particles to experience both horizontal and vertical movement.Produced by double actuators.

• Standing Wave typeIf the wave produced in the stator causes the particles

to experience only vertical movement.Single actuator is required.

NB: 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.

Advantages & DisadvantagesAdvantages

• High o/p torque & efficiency.• High power to weight ratio.• Good positioning accuracy.• Capable of working in

extreme environmental conditions.

• No magnetic interference.• Simple construction.• Small size, light weight, less

noise.

Disadvantages

• Requires high frequency power supply(kHz range).

• Piezoelectric material is expensive.

• Ultrasonic noise occurs.• Drooping torque-speed

characteristics.

Applications• Auto focusing & optical zooming in digital

cameras & surveillance cameras.• Wrist watches & Clocks.• Power steering, Power windows, Tilt steering,

ORVM, Car seat adjustment etc.• Robotics.• Aerospace.• Medicine• Hardware positioning (Hard disks, Floppy & CD

Drives) etc.

Conclusion

The above mentioned advantages and applications, concludes the scope of USMs in the day-to-day life.

However the disadvantages brings up the need for further researches in the field.

Additional Info

• Piezoelectric effect was discovered by Jacques Curie & Pierre Curie [France-1880].

• 1st Ultrasonic Motor was developed by V V Lavrinenko [Russia-1965].

THE END