| Mechanism | | | | and requires a working fluid to transmit the ultrasonic |
| Dry friction is often used in contact, and the | | | | vibrations of the stator toward the rotor. Most |
| ultrasonic vibration induced in the stator is used both | | | | versions use air, such as some of the earliest |
| to impart motion to the rotor and to modulate the | | | | versions by Dr. Hu Junhui. Research in this area |
| frictional forces present at the interface. The friction | | | | continues, particularly in near-field acoustic levitation |
| modulation allows bulk motion of the rotor (i.e., for | | | | for this sort of application. (This is different from |
| farther than one vibration cycle); without this | | | | far-field acoustic levitation, which suspends the object |
| modulation, ultrasonic motors would fail to operate. | | | | at half to several wavelengths away from the |
| Two different ways are generally available to control | | | | vibrating object.) |
| the friction along the stator-rotor contact interface, | | | | Applications |
| traveling-wave vibration and standing-wave vibration. | | | | Canon was one of the pioneers of the ultrasonic |
| Some of the earliest versions of practical motors in | | | | motor, and made the "USM" famous in the late 1980s |
| the 1970s, by Sashida, for example, used | | | | by incorporating it into its autofocus lenses for the |
| standing-wave vibration in combination with fins | | | | Canon EF lens mount. Numerous patents on ultrasonic |
| placed at an angle to the contact surface to form a | | | | motors have been filed by Canon, its chief |
| motor, albeit one that rotated in a single direction. | | | | lensmaking rival Nikon, and other industrial concerns |
| Later designs by Sashida and researchers at | | | | since the early 1980s. The ultrasonic motor is now |
| Matsushita, ALPS, and Canon made use of | | | | used in many consumer and office electronics |
| traveling-wave vibration to obtain bi-directional | | | | requiring precision rotations over long periods of time. |
| motion, and found that this arrangement offered | | | | The technology has been applied to photographic |
| better efficiency and less contact interface wear. An | | | | lenses by a variety of companies under different |
| exceptionally high-torque 'hybrid transducer' ultrasonic | | | | names: |
| motor uses circumferentially-poled and axially-poled | | | | Canon USM, UltraSonic Motor |
| piezoelectric elements together to combine axial and | | | | Minolta, Sony SSM, SuperSonic Motor |
| torsional vibration along the contact interface, | | | | Nikon SWM, Silent Wave Motor |
| representing a driving technique that lies somewhere | | | | Olympus SWD, Supersonic Wave Drive |
| between the standing and traveling-wave driving | | | | Panasonic XSM, Extra Silent Motor |
| methods. | | | | Pentax SDM, Supersonic Drive Motor |
| A key observation in the study of ultrasonic motors | | | | Sigma HSM, Hyper Sonic Motor |
| is that the peak vibration that may be induced in | | | | References |
| structures occurs at a relatively constant vibration | | | | ^ Ueha, S.; Tomikawa, Y.; Kurosawa, M.; Nakamura, |
| velocity regardless of frequency. The vibration | | | | N. (December 1993), Ultrasonic Motors: Theory and |
| velocity is simply the time derivative of the vibration | | | | Applications, Clarendon Press, ISBN 0-1985-9376-7 |
| displacement in a structure, and is not (directly) | | | | ^ Shigematsu, T.; Kurosawa, M.K.; Asai, K. (April |
| related to the speed of the wave propagation within | | | | 2003), "Nanometer stepping drives of surface |
| a structure. Many engineering materials suitable for | | | | acoustic wave motor", IEEE Transactions on |
| vibration permit a peak vibration velocity of around 1 | | | | Ultrasonics, Ferroelectrics and Frequency Control, 50, |
| m/s. At low frequencies 50 Hz, say a vibration | | | | IEEE, pp. 376385 |
| velocity of 1 m/s in a woofer would give | | | | ^ Hu, Junhui; Li, Guorong; Lai Wah Chan, Helen; Loong |
| displacements of about 10 mm, which is visible to | | | | Choy, Chung (May 2003), "A standing wave-type |
| the eye. As the frequency is increased, the | | | | noncontact linear ultrasonic motor", IEEE Transactions |
| displacement decreases, and the acceleration | | | | on Ultrasonics, Ferroelectrics and Frequency Control, |
| increases. As the vibration becomes inaudible at | | | | 48, issue 3, IEEE, pp. 699708 |
| 20 kHz or so, the vibration displacements are in the | | | | ^ Hu, Junhui; Nakamura, Kentaro; Ueha, Sadauki (May |
| tens of micrometers, and motors have been built | | | | 1997), "An analysis of a noncontact ultrasonic motor |
| that operate using 50 MHz surface acoustic wave | | | | with an ultrasonically levitated rotor", Ultrasonics, 35, |
| (SAW) that have vibrations of only a few | | | | Elsevier, pp. 459467 |
| nanometers in magnitude. Such devices require care in | | | | ^ Koyama, D.; Takeshi, Ide; Friend, J.R.; Nakamura, K.; |
| construction to meet the necessary precision to | | | | Ueha, S. (September 2005), "An ultrasonically |
| make use of these motions within the stator. | | | | levitated non-contact sliding table with the traveling |
| More generally, there are two types of motors, | | | | vibrations on fine-ceramic beams", 2005 IEEE |
| contact and non-contact, the latter of which is rare | | | | Ultrasonics Symposium, 3, IEEE, pp. |