Hitachi, Ltd.

Nobuyoshi Ushijima

Norikazu Takayama

Akira Ishibashi

Hiroshi Masuda

Masahiko Sato

Toshiyuki Haruna

Tetsuzo Kobashi

Yoshinobu Kudou

Kousuke Fujii

Yoshihiko Yano

Jun Isozaki

Masahiko Satou

Yoshinobu Kudoh

A control method for brushless DC motor having a rotor, a plurality of magnetic poles and coils of a plurality of phases involves sequentially applying a current to one phase for a prescribed time, stopping the current temporarily and then reapplying the current to the same phase. The state of the rise of the current when it begins to flow to the phase, is measured. The position of one of the magnetic poles located at a position opposite to the particular phase is detected based on the measured state of the rise of the current. In response to the position of the magnetic pole, it is determined whether the flow of the current is to be switched over to the following phase or not. If so, the current is switched over the following phase and the process is repeated. Constant speed control may be accomplished by reading information from a driven disk to determine speed, comparing the speed to a fixed speed, and selectively applying by time sharing a normal current, a brake current and an acceleration current.

Control system for brushless DC motor

A method of forming servo information in a magnetic disk apparatus of a sector servo system. Servo information is recorded in advance at the beginning of each of the sectors, and includes a DC erase signal, a track address signal and a burst signal. The track address signal indicates on which track of the magnetic disk the sector is located, and is formed by expressing the track address in Gray code and interleaving a dummy code into the Gray code. Servo information is recorded using an NRZI system or an RLL coding method. Servo information in which the dummy code is interleaved is decoded after the dummy code is removed at the time of demodulation.

Magnetic disk apparatus

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Odawara, Japan

Nobuyoshi Ushijima