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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. 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 The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric m ...
, 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 '' ...
motors in several ways, though both typically use some form of piezoelectric material, most often lead zirconate titanate and occasionally lithium niobate or other single-crystal 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 force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscil ...
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 Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...
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 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 ...
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 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 (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 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: * Canon – 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 professional ...
– SSM, Super Sonic wave Motor (ring motor) *
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 ...
– SWM, Silent Wave Motor *
Olympus Olympus or Olympos ( grc, Ὄλυμπος, link=no) may refer to: Mountains In antiquity Greece * Mount Olympus in Thessaly, northern Greece, the home of the twelve gods of Olympus in Greek mythology * Mount Olympus (Lesvos), located in Le ...
– 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 – SDM, Supersonic Dynamic Motor * Samyang – DLSM, Dual Linear Sonic Motor *
Sigma Sigma (; uppercase Σ, lowercase σ, lowercase in word-final position ς; grc-gre, σίγμα) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used a ...
– HSM, Hyper Sonic Motor *
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 professional ...
- DDSSM, Direct Drive Super Sonic wave Motor (linear motor) * Tamron - USD, Ultrasonic Silent Drive; PZD, Piezo Drive *
Actuated Medical, Inc. An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) an ...
- Direct Drive, MRI Compatible Ultrasonic Motor


See also

* Piezoelectric motor *
Linear actuator A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as ...
*
Stepper motor A stepper motor, also known as step motor or stepping motor, is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any posi ...
*
Ultrasonic homogenizer A sonicator at the Weizmann Institute of Science during sonicationSonication is the act of applying sound energy to agitate particles in a sample, for various purposes such as the extraction of multiple compounds from plants, microalgae and seawe ...


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