Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-02-21
2003-08-05
Le, N. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C310S06800R
Reexamination Certificate
active
06603304
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an index position detector for a spindle motor which rotates rotating recording media such as floppy disks, and also relates to a motor apparatus including the index position detector.
2. Description of the Related Art
With regard to spindle motors which rotate rotating recording media, for example, floppy disks, an index signal which provides one pulse for each rotation is required to determine the starting point for writing data. The index signal is also used for detecting the rotational condition of the floppy disk, or the motor, so as to provide a ready signal for writing or reading. In addition, the index signal is also used to start writing in the process of formatting tracks, and to stop the writing when the rotation stops.
FIGS. 10
to
12
conceptually show a construction of a motor apparatus including an index position detector which detects the index position of the spindle motor. Referring to the figures, the motor apparatus includes a mount
101
, a circuit board
102
which is mounted on the mount
101
, and a rotor yoke
103
. The mount
101
is constructed of a metal plate, and is provided with three attachment tabs
101
a
at the periphery thereof. Each of the attachment tabs
101
a
is formed unitarily with the mount
101
and is bent upward in an L-shape. In addition, the attachment tabs
101
a
are provided with attachment holes
101
b
for fixing the mount
101
to a housing of a floppy disk drive (FDD) by screws or by other means. The mount
101
is also provided with four restraining hooks
101
c
at the periphery thereof. The restraining hooks
101
c
are shaped approximately like the letter L and project upward. As shown in
FIGS. 10 and 11
, a part of each of the restraining hooks
101
c
is bent in the horizontal direction so as to press downward and hold the circuit board
102
, which is disposed on the mount
101
.
The circuit board
102
is constructed with an insulated substrate on which wiring patterns and circuit components such as a driver circuit and a driver control circuit (not shown) are mounted. The circuit board
102
is provided with a bearing hole
102
a
at the center thereof, through which a bearing
104
having a shaft hole
104
a
is inserted. The bearing
104
is attached to the mount
101
, and is provided with an iron-core member
105
. The iron-core member
105
has twelve pole pieces
105
a
which are arranged radially at even intervals, and stator coils
106
are formed around the pole pieces
105
a.
The stator coils
106
may be divided into three types for applying three phases, U-phase, V-phase, and W-phase. Three coil terminals
106
a
for the three types of the stator coils
106
and one common coil terminal
106
b
are soldered on lands
102
b
provided on the circuit board
102
. The iron-core member
105
is constructed of, for example, a laminated iron core formed by punching out a plurality of magnetic steel plates, such as ferrosilicon plates, and stacking them. In addition, a Hall device
107
for detecting the index position of a rotating recording media is mounted on the circuit board
102
, so as to oppose one of the pole pieces
105
a.
As shown in
FIGS. 13 and 14
, the rotor yoke
103
has a shape like a shallow dish inverted on the circuit board
102
, including a flange portion
103
a
at the periphery thereof. A ring-type rotor magnet
108
is affixed on the inner wall of the flange portion
103
a
. The rotor magnet
108
is constructed of a resin, such as a rubber or a plastic, containing magnetic material. The rotor magnet
108
is equally divided along the periphery thereof into, for example, sixteen portions, which are magnetized so as to alternate S-pole and N-pole. In addition, a window portion
103
b
having a predetermined width is formed in the flange portion
103
a
. A pair of dipolar magnets
108
a
and
108
b
is provided to the rotor magnet
108
so as to project out through the window portion
103
b
beyond the periphery of the flange portion
103
a
. Alternatively, the dipolar magnets
108
a
and
108
b
may be separated from the rotor magnet
108
and be stuck on the periphery of the rotor magnet
108
.
The rotor yoke
103
is also provided with a shaft
109
which penetrates through the center thereof, and the lower side of the shaft is inserted through the shaft hole
104
a
formed in the bearing
104
. Accordingly, the rotor yoke
103
is rotatably disposed above the circuit board
102
as shown in
FIG. 10
so as to cover the stator coils
106
, in a manner such that the Hall device
107
opposes the flange portion
103
a
at the periphery thereof. Although not shown in the figures, a thrust bearing is disposed under the shaft hole
104
a
so as to support the shaft
109
at the bottom end. Thus, the shaft
109
can smoothly rotate while being supported by the shaft hole
104
a
and the thrust bearing. In addition, a chucking device for receiving and holding the floppy disk at the center hub thereof (not shown in the figure) is mounted on the rotor yoke
103
.
The operation of the index position detector for the spindle motor will be described below. First, a three-phase AC power supply applies a three-phase alternating current to the stator coils
106
of three types for U-phase, V-phase and W-phase, by switching the current in a predetermined order. Accordingly, magnetic opposing force is continuously generated between the stator coils
106
and the rotor magnet
108
, so that the rotor yoke
103
rotates above the circuit board
102
, which is a part of the stator. The switching of the current is performed by detecting the rotational position using position detectors, for example, three Hall devices disposed between the stator coils
106
, and by using the detection signal as a switching control signal.
When the rotor yoke
103
of the spindle motor rotates as described above, the dipolar magnets
108
a
and
108
b
also rotate along with the rotation of the rotor yoke
103
. Accordingly, the dipolar magnets
108
a
and
108
b
periodically move toward and away from the Hall device
107
. When the dipolar magnets
108
a
and
108
b
are away, the Hall device
107
receives a small amount of magnetic flux, so that the detection output is approximately 0. When the dipolar magnets
108
a
and
108
b
are in proximity, the Hall device
107
receives sufficient magnetic flux, so that the detection output increases or decreases in accordance with the movement of the dipolar magnets
108
a
and
108
b
. The detected output V
f
obtained from the Hall device
107
is calculated by V
f
=k
&PHgr;
, so that the detection output V
f
is proportional to an amount of the magnetic flux which affects the Hall device
107
, as shown in FIG.
15
. The detection output is then compared with a predetermined reference voltage to obtain a square wave signal representing the result of the comparison. The square wave signal is used for generating an index signal which provides a pulse at the same time when, for example, the square wave signal provides a rising edge.
The conventional index position detector for the spindle motor, however, has the following problems. That is, an expensive Hall device
107
is required for detecting the magnetic flux from the dipolar magnets
108
a
and
108
b
with high sensitivity. In addition, the window portion
103
b
must be formed in the flange portion
103
a
of rotor yoke
103
, and the end portions of the dipolar magnets
108
a
and
108
b
must project far beyond the window portion
103
b
. Accordingly, high processing cost is incurred when the dipolar magnets
108
a
and
108
b
are combined with the rotor magnet
108
. When the dipolar magnets
108
a
and
108
b
are independently provided, and are affixed on the ring-type rotor magnet
108
, there is also a problem in that the gap loss of the magnetic flux density occurs, which degrades the detection sensitivity of the Hall device
107
. Additionally, variations in the ambient temperature result in variations in the a
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kinder Darrell
Le N.
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