Hsm Canon

Ultrasonic Motor

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 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. 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 that operate using 50 MHz surface acoustic wave (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 Dr. 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 lenses for the Canon EF lens mount. Numerous patents on ultrasonic motors have been filed by Canon, its chief lensmaking rival Nikon, and other industrial concerns since the early 1980s. 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, Sony SSM, SuperSonic Motor

Nikon SWM, Silent Wave Motor

Olympus SWD, Supersonic Wave Drive

Panasonic XSM, Extra Silent Motor

Pentax SDM, Supersonic Drive Motor

Sigma HSM, Hyper Sonic Motor

References

^ Ueha, S.; Tomikawa, Y.; Kurosawa, M.; Nakamura, N. (December 1993), Ultrasonic Motors: Theory and Applications, Clarendon Press, ISBN 0-1985-9376-7 

^ 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, 50, IEEE, pp. 376385 

^ 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, 48, issue 3, IEEE, pp. 699708 

^ Hu, Junhui; Nakamura, Kentaro; Ueha, Sadauki (May 1997), "An analysis of a noncontact ultrasonic motor with an ultrasonically levitated rotor", Ultrasonics, 35, Elsevier, pp. 459467 

^ 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, 3, IEEE, pp. 15381541 

External links

Ultrasonic Actuators, Motors and Sensors page, from NASA JPL

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

Institute of Piezomechanics, Kaunas University of Technology, Lithuania

Disassembly of a Canon EF lens, revealing an ultrasonic motor

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Electric motors

Broad Motor Categories

Synchronous motor AC motor DC motor

Conventional

Electric Motors

Induction Brushed DC Brushless DC Stepper Linear Unipolar Reluctance

Novel Electric Motors

Ball bearing Homopolar Piezoelectric Ultrasonic Electrostatic Switched Reluctance

Motor

Controllers

Adjustable-speed drive Amplidyne Direct torque control Direct on line starter Electronic speed control Metadyne Motor controller Variable-frequency drive Vector control Ward Leonard control Thyristor drive

See also

Barlow's Wheel Nanomotor Traction motor Lynch motor Mendocino motor Repulsion motor Inchworm motor Booster (electric power) Brush (electric) Electrical generator Alternator

Categories: Electric motorsHidden categories: Wikipedia articles needing clarification from October 2009 | All Wikipedia articles needing clarification
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