Seiko Instruments (SII) and the Furukawa Laboratory, Tokyo University of Agriculture and Technology (TUAT) jointly developed the world’s smallest* micromotor, 0.95 mm in diameter. The development was based on an invention by Tadashi Moriya, Honorary Professor at Tokyo Metropolitan University and Yuji Furukawa, Dean of the Graduate School of Technology Management, TUAT.
Using conventional techniques, reducing the size of a micromotor with a diameter smaller than 1mm has been extremely difficult. Electromagnetic motors have practical limitations to reducing the coil and magnet size, and ultrasonic motors require advanced design of the piezoelectric device and preload mechanism.
The new motor is classified as an ultrasonic motor because it employs an external ultrasonic oscillator. Using a 50μm diameter metal wire as a waveguide, ultrasonic waves are propagated from the wire tip to a coiled stator to rotate a cylindrical rotor attached to the stator. Because of the use of an external oscillator and the motor’s simpler structure compared to conventional designs, it requires fewer parts and the motor size was significantly reduced. The metal waveguide wire is made of SPRON, which was originally developed by SII for use in the mechanical wristwatch springs and is currently used for a wide range of applications.
Another advantage is that the motor can be operated while submersed in liquid, because it rotates based on the application of ultrasonic oscillations directly from the external oscillator to the motor body instead of using electrical signals.
Seiko Instruments, taking advantage of its time-honored, high-precision processing technologies cultivated through watch development and manufacturing, successfully developed the micromotor as a manufacturable device. SII will explore potential applications in a wide range of fields, while further improving the micromotor performance.
*As of March 15,2007,researched by SII
[Draft Specification]
Size: 0.95mm in diameter, 3.6mm in length (except the rotor axis)
Output speed: 2000 to 4000 rpm
Torque: less than 0.2μN·m
This is a preliminary specification for your reference.
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Seiko Instruments Inc.
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