An ultrasonic motor is a type of

piezoelectric motor A piezoelectric motor or piezo motor is a type of electric motor based on the change in shape of a piezoelectric material when an electric field is applied, as a consequence of the converse piezoelectric effect. An electrical circuit makes acousti ...

vibration Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, su ...

of a component, the stator, placed against another component, the

rotor Rotor may refer to: Science and technology Engineering * Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element so called the stator *Helicopter rotor, the rotary wing(s) of a rotorcraft ...

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 mechanical stress. The word '' ...

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 g ...

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

lead zirconate titanate Lead zirconate titanate is an inorganic compound with the chemical formula (0≤''x''≤1), commonly abbreviated as PZT. Also called lead zirconium titanate, it is a ceramic perovskite material that shows a marked piezoelectric effect, meaning ...

and occasionally

lithium niobate Lithium niobate () is a non-naturally-occurring salt consisting of niobium, lithium, and oxygen. Its single crystals are an important material for optical waveguides, mobile phones, piezoelectric sensors, optical modulators and various other linea ...

or other

single-crystal In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries In m ...

materials. The most obvious difference is the use of

resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied Periodic function, periodic force (or a Fourier analysis, Fourier component of it) is equal or close to a natural frequency of the system ...

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 Strain may refer to: Science and technology * Strain (biology), variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes * Strain (chemistry), a chemical stress of a molecule * Strain (injury), an injury to a mu ...

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 conceptual material accepted as official in a fictional universe by its fan base * Literary canon, an accepted body of works considered as high culture ** Western ca ...

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 Wave propagation is any of the ways in which waves travel. Single wave propagation can be calculated by 2nd order wave equation ( standing wavefield) or 1st order one-way wave equation. With respect to the direction of the oscillation relative to ...

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 Hz up to 1000 Hz. The name is from the onomatopoeic English word for a dog's bark, " woof" (in contrast to th ...

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 elasticity, with an amplitude that typically decays exponentially with depth into the material, such that they are confined to a depth of about ...

(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 Near field may refer to: * Near-field (mathematics), an algebraic structure * Near-field region, part of an electromagnetic field * Near field (electromagnetism) ** Magnetoquasistatic field, the magnetic component of the electromagnetic near fi ...

for this sort of application. (This is different from

far-field acoustic levitation Acoustic levitation is a method for suspending matter in air against gravity using acoustic radiation pressure from high intensity sound waves. It works on the same principles as acoustic tweezers by harnessing acoustic radiation forces. However ...

, which suspends the object at half to several wavelengths away from the vibrating object.)

Applications

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 (or 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 ...

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 ...

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

Nikon (, ; ), also known just as Nikon, is a Japanese multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging products. The companies held by Nikon form the Nikon Group. Nikon's products include cameras, camera ...

, 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 The PowerShot products is a line of consumer and prosumer grade digital cameras, launched by Canon in 1996. () In 1996 a model of PowerShot was introduced to the market, The Powershot 600. The production of The PowerShort came shortly after Can ...

SX1 IS

bridge camera Bridge cameras are cameras that fill the niche between relatively simple point-and-shoot cameras and interchangeable-lens cameras such as mirrorless cameras and single-lens reflex cameras (SLRs). They are often comparable in size and weight t ...

. 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: *

– USM, UltraSonic Motor *

Minolta was a Japanese manufacturer of cameras, camera accessories, photocopiers, fax machines, and laser printers. Minolta Co., Ltd., which is also known simply as Minolta, was founded in Osaka, Japan, in 1928 as . It made the first integrated aut ...

Konica Minolta is a Japanese multinational corporation, multinational technology company headquartered in Marunouchi, Chiyoda, Tokyo, Chiyoda, Tokyo, with offices in 49 countries worldwide. The company manufactures business and industrial imaging products, in ...

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professiona ...

– SSM, Super Sonic wave Motor (ring motor) *

– SWM, Silent Wave Motor * Olympus – SWD, Supersonic Wave Drive *

Panasonic formerly between 1935 and 2008 and the first incarnation of between 2008 and 2022, is a major Japanese multinational conglomerate corporation, headquartered in Kadoma, Osaka. It was founded by Kōnosuke Matsushita in 1918 as a lightbulb ...

– XSM, Extra Silent Motor *

Pentax is a brand name used primarily by the Japanese multinational imaging and electronics company Ricoh for DSLR cameras, lenses, sport optics (including binoculars and rifle scopes), and CCTV optics. The Pentax brand is also used by Hoya Corporatio ...

– SDM, Supersonic Dynamic Motor * Samyang – DLSM, Dual Linear Sonic Motor * Sigma – HSM, Hyper Sonic Motor *

- DDSSM, Direct Drive Super Sonic wave Motor (linear motor) *

Tamron is a Japanese company manufacturing photographic lenses, optical components and commercial/industrial-use optics. Tamron Headquarters is located in Saitama City in the Saitama Prefecture of Japan. The name of the company came from the surna ...

- USD, Ultrasonic Silent Drive; PZD, Piezo Drive * Actuated Medical, Inc. - Direct Drive, MRI Compatible Ultrasonic Motor

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