On Tuesday, October 4, 2005, at 11:59 AM, graywolf wrote:
I believe the ultrasonic comes in because the linear motor uses ultrasonic frequency AC current to operate. Using AC in the 30KHz to 100KHz range allows for a much smaller motor than DC or normal AC does. BTW the switching power supply in your computer uses ultrasonic AC, but they don't hype it like Canon does. Consider it an advertising buzz word and don't get excited over it.
Ultrasonic vibrations from a piezo generator are transferred to two mating rings in an ultrasonic motor. Varying the frequency allows control of the speed at which one ring rotates on the other, and the direction of rotation. One ring is attached to the lens body, one to the moving part of the helical. The mating surfaces of the rings are specially treated.
Bob
