Principle Of Motor Operation; Pole Position Detector - Pioneer PL-51A Service Manual

3.
PRINCIPLE OF MOTOR OPERATION
Construction of motor
control
for
the
PL-51A
is
depicted in Fig.
2.
1. Applying power sets
the
oscillator into
operation.
Output
of
this circuit
passes to
the pole position
detecting
circuit
(L1-LG).
2.
Here,
assume
that
coupling between
L1
and
L4 is the
tightest.
Voltage induced
in L4
is
rectified and applied
to
Q106/Q109
in
the
driver.
3.
Q109
in
turn
conducts and
causes
current to
flow in the
associated drive
coil (A-1).
The
rotor
moves
in
the direction shown by arrow
in
Fig. 1.
The magnetic pole affixed
to
the
rotor
induces
a
voltage
proportional to
rotor
movement,
in
the
sensing
coil (A-4).
4.
Voltage induced
in
A-4
is
rectified by
a
diode
in
the
speed sensor
and applied
to
Q103
in
the control
stage.
This point
is also
fed from the
reference voltage
generator
(voltage Es)through
a
fine
speed
control pot.
5.
Voltage applied
to
the
base
of
Q103
in
the
control
stage
controls current
that
flows
in
Q104.
6.
Q104
serves as
a constant current
source
for
Q106 through
Ql1
1 in the
driver
and
therefore controls current flow in
the
drive
coils.
7. When ambient
temperature
change
causes
driver current
to
rise,
the
speed
of
rotation
increases above
the rated
value. Q104 current
increases and
Q106-Q111
currents decrease.
pOLE pOStTtON
As a
result, the
speed
of
rotation
falls
off.
DETECTOR
OSCI
LLATOR
REFERENCE VOLTAGE
GENERATOR
POLE POSITION
DETECTOR
Pole Position Detector
Fig.
1
shows a
simplified
view
of
the drive
and
sense
coils. With
power applied and
coupling
between
L1
and
L4 high,
Q109
causes
current
to flow
through A-1.
As a result, the rotor
end
of coil A-i
becomes
a south pole (S1)
and
attracts
N1.
The
rotor
moves
in the
direction
shown
by arrow.
Coupling factor
between
L2
and L5
increases
and operatior,
of
Q110
causes
current
to flow
in coil A-2.
Pole S2 attracts pole
N2
and
rotor rotation
continues.
In the
same
manner,
53
attracts Pole
N3. Continuation of
this
process causes
the
rotor to turn
on
a
steady
basis.
DIRECTION
OF
ROTATION
CONTROL
STAGE
Fig.
1
DRIVE
SENSING
cotLS cotLs
sPEED SENSO
ROTOR
Lr
Lz
L3
DRIVER
Fig.2