Servo Control; Servo Control Circuit; Block Diagram Of Servo Control Circuit - Fujitsu MAB3091FC Series Maintenance Manual

5.7

Servo Control

The servomechanism is controlled using a digital servo technique by the firmware in the
digital signal processor (DSP).
DPS carries out VCM control. Control of the voice coil motor consists of track-following
operation control and seek operation control. Track-following operation is controlled to center
the data-head-mounted actuator over the target cylinder for read/write operation. The seek
operation moves the actuator to a different target cylinder at high speed. For stable operation,
a variety of calibration is done (see Section 5.5).
5.7.1

Servo control circuit

Figure 5.8 is the block diagram of the servo control circuit. The following explains each
function of the servo control circuit.
Servo system block diagram
Data surface
signal
Data Servo
bus8
head demodulator
bus8
HDC
Figure 5.8
(1) Digital signal processor-application specific IC (DSP-ASIC)
A DSP controls the spindle motor and the voice coil motor. The SCSI sends an instruction to
the DSP through the SCSI control MPU and native interface. The DSP is a 1-chip DSP-ASIC,
and also contains an analog-to-digital converter, a digital-to-analog converter, RAM, and other
logic circuits.
(2) Servo demodulator
As explained in 5.7.2, servo signals consist of a training segment, a Servo Mark segment, a
Position segment and a Gray Code segment, and there are 86 frames arranged around the
circumference. In the servo demodulator, the Gray Code and Position signals from the servo
signal are demodulated and used to control head positioning.
5 - 16
DSP
Core
bus16
Control signal
(PWM)
Drive
bus16
I/F LSI
bus8
MCU
9000x
Control signal

Block diagram of servo control circuit

C141-F028-01EN
DSP controlled actuator servo system
MCU controlled spindle servo system
FET × 2
SPM/VCM
combo
FET × 3
VCM
Spindle
motor