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9.2
MOTOR OPERATION
1 Motor Construction
1.The
PXM-067
is an
outer-rotor
brushless
DC
motor with 6 poles and 9 slots.
2. Motor windings are arranged in a 3-phase Y con-
figuration.
For
detection
of the platter posi-
tion, 3 Hall elements are mounted at AO° inter-
vals.
5. The inner surface of the rotor magnet possesses
6 magnetic poles. As shown in Fig.17, these are
tilted by 22.0° relative to the vertical axis.
Hall Element
Speed Detection Plate
2. Principlé of Motor Rotation
1.
Let us assume
that the motor is at standstill,
in the position shown in Fig. 3.
41
8.
When
the
unit
is switched
on,
the
output
voltages of the respective Hall elements will be
as shown in Fig. 25-a, page 47.
4.
The
Hall
element
output
is applied
to the
Position Signal Combination Circuit contained
in IC PA-2005 and utilized to control the cur-
rent flowing to the motor drive coils.
For further details, see paragraph
''Drive Cir-
cuit."
5.
The output from the Hall elements undergoes
waveform
formation
in the
Position
Signal
Combination circuit. The resulting waveforms
are shown in Fig. 25-b, page 47.
6.
These composite signals are used to switch the
drive current
in such a way that
each
motor
winding receives the proper current to polarize
the magnetic poles for north, south, or OFF in
the correct sequence.
In actual rotation, this happens as follows.
7.
As the pole of coil La becomes a south pole,
that of Lz becomes north, and Le, neutral.
8.
Repulsion
between
the S pole at La, and the
rotor S pole, and attraction between
the Lg N
pole and the rotor S pole exert a propulsive
force on the rotor.
9. As the rotor turns through 20°
of arc, the
output from the Hall elements changes.
10. Lg now
enters
OFF
state,
L~ becomes
a N
pole, and L, aS
pole.
11. The
L¢ N pole now attracts the rotor S pole,
and the La S pole attracts the rotor N pole.
Rotation continues.
Fig. 18
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