Index Position Detecting Method of Spindle Motor for Slim Floppy Disk Drive

Abstract

Slim Floppy Disk Drive, which could be mounted on a Hand-held personal computer, is now under intensive study in Japan. Spindle motor for Floppy Disc Drive has a index position detecting means, a index magnet attached to the outer wall of the periphery of the rotor yoke, and a magnetic sensor detecting the magnetic flux from the index magnet. As a result, spaces for providing the index magnet and the magnetic sensor prevent the motor from being made smaller in size and thinner in thickness.
This paper describes the method for detecting index position of a spindle motor without both the index magnet and the magnetic sensor. This method detects a index position per rotation from two different kinds of frequency generating signals (Main FG and Sub FG) through a index detecting circuit. The thin spindle motor applied this index detecting method performed a smaller degree of rotational speed variation compared with another wellknown one without both the index magnet and the magnetic sensor. This index detecting method is most suitable for less-inatia-thin spindle motor, and is easy to assemble.