Sharp FDD-412A - Page 34

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FDD412A/B

2.5.6

Operations

Related

to

Spindle

Motor

Drive

Mechanism

(1)

Interface

signal

None

(automatic

control

initiated

upon

power

application)

(2)

Outline

of

operation

Applying

power

immediately

rotates

the

spindle

motor.

The

mechanism

automatically

keeps

the

rotational

speed

constant

(360

rpm)

through

a

feedback

loop.

(3)

Block

diagram

of

spindle

motor

drive

mechanism

MTR

SPD

OK

Phase

com-

Power

pensator

amplifier

t

t

'

!

Position

detection

(HALL

IC)

|

1

'

amplifier

Frequency

oe

S

generator

‘

(FG)

:

CP

ri

Ro

aes

prec

|

a

oe

es

Motor

coil

|

Fig.

2.28

Block

Diagram

of

Spindle

Motor

Drive

Mechanism

(4)

Operating

principles

of

spindle

motor

drive

mechanism

(a)

Drive

section

The

S

pole

of

the

rotary

magnet

is

detected

by

a

position

detecting

element

(HALL

IC).

In

the

setup

of

Fig.

2.29,

Hy

detects

the

S

pole.

This

‘drives

amplifier

Vw,

allows

current

Ip

to

flow,

and

rotates

the

rotor.

With

the

rotor

rotating

H,,

Hy

and

Hy

detects

the

S

pole

in

turn

to

generate

drive

voltages

(Fig.

2.30)

for

motor

drive.

(b)

Feedback

section

The

frequency

generator

generates

frequencies

proportionate

to

the

rotor

revolutions.

The

generator

output

and

crystal

oscillator

output

are

compared

in

phase

shift

and

frequency

to

calculate

rotation

correction

values.

—

28—