Ultrasonic Motor Utilizing a Wave Spring

3D Render of ultrasonic motor with Rotor Clip single-turn wave spring

Ultrasonic motors are small motors, some measured in millimeters, often used in the auto focus feature on modern DSLR camera lenses. Other applications are usually seen in the automotive industry in headrests or side mirrors, surgical equipment and now common in robotics movement. What made ultrasonic motors groundbreaking in the 1970’s and relevant today is the ability to create a motor that is extremely small, compact and virtually silent, without sacrificing torque.

This ultrasonic motor is used in a camera lens for autofocusing. It consists of a stator, a rotating rotor and an output ring. A stator is a stationary part of a motor or turbine. The rotor is a non-stationary part of the motor, fitting inside or against the stator. A single-turn closed wave spring is utilized to maintain the necessary pressure against the stator, holding the rotor in place since there are no screws or bolts in ultrasonic motors. The wave spring is a better choice in this application over coil or washer type springs. The wave spring is light-weight, compact and still manages the low to medium loads required of it while keeping its spring.

The stator of an ultrasonic motor is piezoelectric, meaning it has ceramic elements which when energized by AC voltage creates vibrations at the ultrasonic level. The vibrations of the stator and the pressure of the wave spring against the stator create friction which rotates the rotor that turns the output ring. The output ring is the transmission of the ultrasonic motor. It receives the “input” of the motor which then focuses the lens of the camera. The great advantage to using ultrasonic motors is that they are almost silent when in motion. This is excellent for cameras zooming in and out when taking video. Furthermore, the ultrasonic motor is extremely responsive for quick zooms or because of the high torque of the motor; it can slowly move the lens, allowing for just the right movement to correct itself and focus for the photographer.

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