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An ultrasonic motor is a type of electric motor formed from the ultrasonic vibration of a component, the stator, placed against another, the rotor or slider depending on the scheme of operation (rotation or linear translation). An electric motor uses Electrical energy to produce Mechanical energy. Vibration refers to mechanical Oscillations about an equilibrium point. The stator is the stationary part of an Electric generator or Electric motor. The rotor is the non-stationary part of a rotary Electric motor or Alternator, which rotates because the wires and magnetic field of the motor are arranged so Ultrasonic motors differ from piezoelectric actuators 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. Lead zirconate titanate ( 0 x Ceramic Perovskite material that shows a marked piezoelectric effect. Lithium niobate ( is a compound of Niobium, Lithium, and Oxygen. A single crystal, also called monocrystal, is a Crystalline Solid in which the Crystal lattice of the entire sample is continuous and unbroken The most obvious difference is the use of resonance to amplify the vibration of the stator in contact with the rotor in ultrasonic motors. In Physics, resonance is the tendency of a system to Oscillate at maximum Amplitude at certain frequencies, known as the system's 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.

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. Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e 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. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. A standing wave, also known as a stationary wave, is a Wave that remains in a constant position Some of the earliest versions of practical motors in the 1970s, by Sashida,[1] 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 of the vibration displacement in a structure, and is not (directly) related to the speed of the wave propagation within a structure. 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 Wave propagation is any of the ways in which waves travel through a Waveguide. 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 would give displacements of about 10 mm, which is visible to the eye. 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[2] that operate using 50 MHz surface acoustic wave (SAW) that have vibrations of only a few nanometers in magnitude. A surface acoustic wave ( SAW) is an Acoustic wave traveling along the surface of a material having some elasticity, with an Amplitude that 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 Dr. Hu Junhui. [3][4] Research in this area continues, particularly in near-field acoustic levitation for this sort of application. [5] (This is different from far-field acoustic levitation, which suspends the object at half to several wavelengths away from the vibrating object. )

Canon was one of the pioneers of the ultrasonic motor, and made the "USM" famous in the 1980s by incorporating it into its autofocus lenses for the Canon EF lens mount. is a Japanese Multinational corporation that specializes in imaging and optical products including Cameras photocopiers and Computer printers Autofocus (or AF) is a feature of some Optical systems that allows them to obtain (and in some systems to also continuously maintain correct focus on a The EF lens mount allows all the Canon EF lenses to be used on any of the Canon EOS line of Cameras made by Canon Inc Numerous patents on ultrasonic motors have been filed by Canon, its chief lensmaking rival Nikon, and other industrial concerns since the early 1980s. ( also known as Nikon or Nikon Corp, is a Multinational corporation headquartered in Tokyo Japan specializing in Optics 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

  1. ^ Ueha, S. ; Tomikawa, Y. ; Kurosawa, M. & Nakamura, N. (December 1993), Ultrasonic Motors: Theory and Applications, Clarendon Press, ISBN 0-1985-9376-7 
  2. ^ Shigematsu, T. ; Kurosawa, M. K. & Asai, K. (April 2003), “Nanometer stepping drives of surface acoustic wave motor”, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 50, issue 4, IEEE, pp. 376-385 
  3. ^ Hu, Junhui; Li, Guorong; Lai Wah Chan, Helen & Loong Choy, Chung (May 2003), “A standing wave-type noncontact linear ultrasonic motor”, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 48, issue 3, IEEE, pp. 699-708 
  4. ^ Hu, Junhui; Nakamura, Kentaro & Ueha, Sadauki (May 1997), “An analysis of a noncontact ultrasonic motor with an ultrasonically levitated rotor”, Ultrasonics, vol. 35, issue 6, Elsevier, pp. 459-467 
  5. ^ Koyama, D. ; Takeshi, Ide; Friend, J. R. ; Nakamura, K. & Ueha, S. (September 2005), “An ultrasonically levitated non-contact sliding table with the traveling vibrations on fine-ceramic beams”, 2005 IEEE Ultrasonics Symposium, vol. 3, IEEE, pp. 1538-1541 

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