Control Electronics, Head disk assembly

3 Fixed disk subsystem description

3.1Control Electronics

The drive is electronically controlled by a microprocessor, several logic modules, digital/analog modules, and various drivers and receivers. The control electronics performs the following major functions:

Controls and interprets all interface signals between the host controller and the drive.

Controls read write accessing of the disk media, including defect management and error recovery.

Controls starting, stopping, and monitoring of the spindle.

Conducts a power-up sequence and calibrates the servo.

Analyzes servo signals to provide closed loop control. These include position error signal and estimated velocity.

Monitors the actuator position and determines the target track for a seek operation.

Controls the voice coil motor driver to align the actuator in a desired position.

Constantly monitors error conditions of the servo and takes corresponding action if an error occurs.

Monitors various timers such as head settle and servo failure. Performs self-checkout (diagnostics).

3.2Head disk assembly

The head disk assembly (HDA) is assembled in a clean room environment and contains the disks and actuator assembly. Air is constantly circulated and filtered when the drive is operational. Venting of the HDA is accomplished via a breather filter.

The spindle is driven directly by an in-hub, brushless, sensorless DC drive motor. Dynamic braking is used to quickly stop the spindle.

3.3Actuator

The read/write heads are mounted in the actuator. The actuator is a swing-arm assembly driven by a voice coil motor. A closed-loop positioning servo controls the movement of the actuator. An embedded servo pattern supplies feedback to the positioning servo to keep the read/write heads centered over the desired track.

The actuator assembly is balanced to allow vertical or horizontal mounting without adjustment.

When the drive is powered off, the actuator automatically moves the head to the actuator ramp outside of the disk where it parks.

- Hitachi hard disk drive specifications –

HCS721016CLA382, HCS721050CLA382, HCS721025CLA382, HDP725050GLA360, HUA722050CLA330/1 specifications

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