An ultrasonic motor is a type of piezoelectric motor powered by the ultrasonic

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

of a component, the

stator The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors, or biological rotors (such as bacterial flagella or ATP synthase). Energy flows through a stator to or from the rotat ...

, placed against another component, the

rotor ROTOR was an elaborate air defence radar system built by the British Government in the early 1950s to counter possible attack by Soviet bombers. To get it operational as quickly as possible, it was initially made up primarily of WWII-era syst ...

or slider depending on the scheme of operation (rotation or linear translation). Ultrasonic motors differ from other

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied stress (mechanics), mechanical s ...

motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gene ...

s in several ways, though both typically use some form of piezoelectric material, most often

lead zirconate titanate Lead zirconate titanate, also called lead zirconium titanate and commonly abbreviated as PZT, is an inorganic compound with the chemical formula . It is a ceramic perovskite material that shows a marked piezoelectric effect, meaning that the comp ...

and occasionally

lithium niobate Lithium niobate () is a synthetic salt consisting of niobium, lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperatur ...

or other single-crystal materials. The most obvious difference is the use of

resonance Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...

to amplify the vibration of the stator in contact with the rotor in ultrasonic motors. Ultrasonic motors also offer arbitrarily large rotation or sliding distances, while piezoelectric actuators are limited by the static strain that may be induced in the piezoelectric element. One common application of ultrasonic motors is in camera lenses where they are used to move lens elements as part of the auto-focus system. Ultrasonic motors replace the noisier and often slower micro-motor in this application.

Mechanism

Dry friction is often used in contact, and the ultrasonic vibration induced in the stator is used both to impart motion to the rotor and to modulate the frictional forces present at the interface. The friction modulation allows bulk motion of the rotor (i.e., for farther than one vibration cycle); without this modulation, ultrasonic motors would fail to operate. Two different ways are generally available to control the friction along the stator-rotor contact interface, traveling-wave vibration and standing-wave vibration. Some of the earliest versions of practical motors in the 1970s, by Sashida, for example, used standing-wave vibration in combination with fins placed at an angle to the contact surface to form a motor, albeit one that rotated in a single direction. Later designs by Sashida and researchers at Matsushita, ALPS, and

Canon Canon or Canons may refer to: Arts and entertainment * Canon (fiction), the material accepted as officially written by an author or an ascribed author * Literary canon, an accepted body of works considered as high culture ** Western canon, th ...

made use of traveling-wave vibration to obtain bi-directional motion, and found that this arrangement offered better efficiency and less contact interface wear. An exceptionally high-torque 'hybrid transducer' ultrasonic motor uses circumferentially-poled and axially-poled piezoelectric elements together to combine axial and torsional vibration along the contact interface, representing a driving technique that lies somewhere between the standing and traveling-wave driving methods. A key observation in the study of ultrasonic motors is that the peak vibration that may be induced in structures occurs at a relatively constant ''vibration velocity'' regardless of frequency. The vibration velocity is simply the

time derivative A time derivative is a derivative of a function with respect to time, usually interpreted as the rate of change of the value of the function. The variable denoting time is usually written as t. Notation A variety of notations are used to denote th ...

of the vibration displacement in a structure, and is not (directly) related to the speed of the

wave propagation In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. '' Periodic waves'' oscillate repeatedly about an equilibrium (resting) value at some f ...

within a structure. Many engineering materials suitable for vibration permit a peak vibration velocity of around 1 m/s. At low frequencies — 50 Hz, say — a vibration velocity of 1 m/s in a

woofer A woofer or bass speaker is a technical term for a loudspeaker driver designed to produce low frequency sounds, typically from 50 up to 200 Hz. The name is from the onomatopoeic English word for a dog's deep bark, " woof" (in contrast to a ' ...

would give displacements of about 10 mm, which is visible. As the frequency is increased, the displacement decreases, and the acceleration increases. As the vibration becomes inaudible at 20 kHz or so, the vibration displacements are in the tens of micrometers, and motors have been built that operate using 50 MHz

surface acoustic wave A surface acoustic wave (SAW) is an acoustic wave traveling along the surface of a material exhibiting elastic (solid mechanics), elasticity, with an amplitude that typically decays exponentially with depth into the material, such that they are c ...

(SAW) that have vibrations of only a few nanometers in magnitude. Such devices require care in construction to meet the necessary precision to make use of these motions within the stator. More generally, there are two types of motors, contact and non-contact, the latter of which is rare and requires a working fluid to transmit the ultrasonic vibrations of the stator toward the rotor. Most versions use air, such as some of the earliest versions by Hu Junhui. Research in this area continues, particularly in near-field acoustic levitation for this sort of application. (This is different from far-field acoustic levitation, which suspends the object at half to several wavelengths away from the vibrating object.)

Applications

Canon was one of the pioneers of the ultrasonic motor, and made the "USM" famous in the late 1980s by incorporating it into its

autofocus An autofocus (AF) optical system uses a sensor, a control system and a motor to focus on an automatically or manually selected point or area. An electronic rangefinder has a display instead of the motor; the adjustment of the optical system h ...

lenses for the

Canon EF lens mount The EF lens mount is the standard lens mount on the Canon EOS family of SLR film and digital cameras. EF stands for "Electro-Focus": automatic focusing on EF lenses is handled by a dedicated electric motor built into the lens. Mechanically, it i ...

. Numerous patents on ultrasonic motors have been filed by Canon, its chief lensmaking rival

Nikon (, ; ) is a Japanese optics and photographic equipment manufacturer. Nikon's products include cameras, camera lenses, binoculars, microscopes, ophthalmic lenses, measurement instruments, rifle scopes, spotting scopes, and equipment related to S ...

, and other industrial concerns since the early 1980s. Canon has not only included an ultrasonic motor (USM) in their DSLR lenses, but also in the Canon PowerShot SX1 IS bridge camera. The ultrasonic motor is now used in many consumer and office electronics requiring precision rotations over long periods of time. The technology has been applied to photographic lenses by a variety of companies under different names.

References

;General * Certificate of authorship #217509 "Electric Engine", Lavrinenko V., Necrasov M., application #1006424 from 10 May 1965. * US Patent #4.019.073, 1975. * US Patent #4.453.103, 1982. * US Patent #4.400.641, 1982. * Piezoelectric motors. Lavrinenko V., Kartashev I., Vishnevskyi V., "Energiya" 1980. * V. Snitka, V. Mizariene and D. Zukauskas The status of ultrasonic motors in the former Soviet Union, Ultrasonics, Volume 34, Issues 2–5, June 1996, Pages 247-250 * Principles of construction of piezoelectric motors. V. Lavrinenko, , "Lambert", 2015, 236p.

External links

Ultrasonic Actuators, Motors and Sensors page, from NASA JPL

Design and performances of high torque ultrasonic motor for application of automobile

Design of miniature ultrasonic motors

Ultrasonic Lens Motor

Micro/Nano Physics Research Laboratory, with research on ultrasonic piezoelectric actuators by Dr James Friend

Institute of Piezomechanics, Kaunas University of Technology, Lithuania

* ttps://web.archive.org/web/20110822234835/http://nano.ktu.lt/text/research/precision.php/ Research Center for Microsystems and Nanotechnology, KTU, Lithuania {{Electric motor Electric motors de:Ultraschallmotor hi:पराश्रव्य मोटर ru:Ультразвуковой мотор

Mechanism

Applications

See also

References

External links