• It has been known for more than 30 years.• The first ultrasonic motor was introduce by v.v lavrinko in 1965.• An Ultrasonic motor is a type of electric motor formed from the ultrasonic vibration of a component, the stator being placed against another, the rotor depending on the scheme of operation.• Conversion of electric energy into motion by inverse piezoelectric effect.
• To obtain the levels of torque speed characteristics of USM using conventional motors we require to add a gear system to reduce the speed.• These characteristics of USM makes them attractive for robotic applications where small motions are required.• This motor achieves high speed and drive forces, while still permitting the moving part to be positioned with high accuracy.
The piezoelectric effect is understood as the linearelectromechanical interaction between the mechanical and theelectrical state in crystalline materials with no inversionsymmetry.• Piezoelectricity – generation of voltage in response of mechanical stress.• 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) lead zirconate titanate and occasionally lithium niobate .
Electromagnetic motors are notorious for consuming high amount of power and creating high ambient motor temperatures respect to USMThe electromagnetic motors produce strong magnetic fields which cause interference. Ultrasonic motors use piezoelectric effect and hence no magnetic interference.Electromagnetic motor has high input to output energy loss ratiosUSM High positional accuracy respect to Electromagnetic Motor.
• 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
Ultrasonic motor Standing Traveling wave wavebidirectional unidirectional
This type of motors use three groups of crystals: two of which are Locking and one Motive. First, one group of locking crystals is activated — this gives one locked side and one unlocked side of the sandwich. Next, the motive crystal group is triggered and held — the expansion of this group moves the unlocked locking group along the motor path. This is the only stage where motor movement takes place.
This type of motor commonly known under the names of Inchworm, Piezo LEGS or PiezoWalk motors
• Superposition of multiple standing wave create a traveling wave.• Representation of travelling wave U(x ,p)= A cos(k x) cos(wt) + A cos(k x - 90) cos (wt-90).• Phase difference is 90 degree
•The active material excites a traveling flexural wave within thestator that leads to elliptical motion of the surface particles.•Teeth are used to enhance the speed that is associated with thepropelling effect of these particles.•The rectification of the micro-motion an interface is provided bypressing the rotor on top of the stator and the frictional force betweenthe two causes the rotor to spin.
• Camera auto focus lenses• Driving fluid• Watch motors and compact paper handling.• Optoelectronics area• In micro surgery and sensor scanning.
Hence the ultrasonic motors, which is a new stepin the miniaturized electrical technology has gotmany applications in small appliances because ofits high torque at low density.