1. Field of the Invention
The present invention relates to a technology for controlling driving of a motor of a storage medium, depending on a rotational state of the motor.
2. Description of the Related Art
In a magnetic disk device, a spindle motor is used to drive a magnetic disk. Two driving mode are used when driving the magnetic disk. One is a start-up mode in which the magnetic disk is driven from a non-rotating state and the other is a spin-up mode in which an already rotating magnetic disk is driven still faster.
Specifically, the start-up mode is a normal mode by which a spindle motor is driven. Through the start-up mode, a start-up control is performed for implementing control of phase switching (commutation) by which an electric current flows, from different directions, through coils forming the spindle motor, and when the spindle motor starts to rotate adequately, a spin-up control (or a BEMF(back electromotive force) control) is performed based on BEMF signals produced by the spindle motor.
The spin-up mode, on the other hand, includes driving the spindle motor after the magnetic disk is activated from a sleep state. In this case, the BEMF signals can be detected as the spindle motor is already in an inertial rotating state, and the BEMF control can be directly performed without going through the start-up control step.
Various technologies have been proposed to assuredly drive the spindle motor as well as to reduce a start-up time of the spindle motor. For example, Japanese Patent Application Laid-open No. H7-226016 discloses a technology for reducing the start-up time in the start-up mode, by stopping a steadily rotating motor, checking relative positions of a rotor and stator members, restarting the motor, and performing synchronous control. Specifically, the start-up time for the next Spin-On operation (at a time of starting up rotation) can be reduced by performing a brake operation and an aligning operation during Spin-Off operation (at a time of stopping rotation).
However, when the spindle motor is not rotating adequately for proceeding an operation to the spin-up mode. (to perform a BEMA control), a longer start-up time is required compared to a time required when the spindle motor is rotating adequately, because it is necessary to retry the start-up operation repeatedly and perform a start-up control after the spindle motor is stopped.
With the conventional technology described above, although the start-up time is reduced for the Spin-On operation (at a time of starting up the rotation) only in the start-up mode, operation time cannot be reduced in the spin-up mode.