Motor apparatus

Details Motor apparatus Motor apparatus

2002-03-01

2003-05-06

Lam, Thanh (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S268000, C310SDIG003

Reexamination Certificate

active

06559565

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a motor apparatus preferable for use in a flexible disk drive, having a structure of a frequency generator which outputs a FG signal for detecting a rotational velocity of a spindle, and particularly relates to a motor apparatus being compact in size and having high controllability and high noise resistance.
2. Description of Related Art
FIGS.
7
(
a
) and
7
(
b
) are perspective views of a motor apparatus having a frequency generator for detecting a rotational velocity of a spindle in accordance with the related art. Such the motor apparatus is used for a flexible disk drive having a spindle being a rotating shaft of the motor, which is so called a direct drive structure.
FIG.
7
(
a
) shows a perspective view of a rotor portion of a motor apparatus. A circle shaped rotor
101
having a diameter “D” includes a FG magnet
102
placed on the outer circumference of the rotor
101
. The FG magnet
102
is formed by mixing magnetic powder with nylon resin (so called “plastic magnet”) and having residual flux density “Br” of 0.18 T (Tesla).
FIG. 8
shows an enlarged view of a rotor shown in FIG.
7
(
a
).
FIG. 9
shows a side view of a motor apparatus. In
FIG. 8
, forty-eight (48) magnetic poles of FG magnetic pole
102
a
are provided on the rotor
101
in radial direction thereof. The diameter “D” of the rotor
101
in this case is 46 mm and a pitch “W” of the magnetic pole is 3 mm (&pgr;·46/48=3).
FIG.
7
(
b
) shows a stator of the motor apparatus. A stator
105
includes a stator base
103
, a FG coil
104
, a driving coil
108
and a shaft bearing
106
. The FG coil
104
is placed on the circumference of the circle of which center is the shaft bearing
106
. The stator base
103
is formed with a copper foiled printed circuit board through an insulative layer laminated over a base plate of soft magnetic material such as cold rolling iron and silicon steel. The FG coil
104
has a folded pattern with a folded pitch of 7.5° (360/48=7.5) and opposing to the magnetic pole of the plastic magnet described above.
In FIGS.
7
(
a
) and
7
(
b
), a rotating shaft not shown is fixed in the center of the rotor
101
, and is supported by the shaft bearing
106
at the center of the stator
105
, and the FG magnet
102
opposes to the FG coil
104
with a gap “G” of 2 mm.
As the magnetic flux of the FG magnetic pole
102
a
shown in
FIG. 8
interlinks to the FG coil
104
, an FG signal is generated in the FG coil
104
by rotation of the rotor
104
in accordance with the Fleming's rule. The frequency of the FG signal is in proportion of the rotational velocity. The structure described above constitutes a frequency generator.
The rotor
101
has disciform driving magnet (field magnet)
107
having sixteen (16) field magnetic poles, and the stator
105
has nine (9) driving coils
108
respectively. The rotational magnetic field occurs in the driving coil
107
by passing driving current through the driving circuit not shown, then the rotational force for the rotor
101
occurs by the interaction with field magnetic pole formed by the driving magnet
107
.
The FG signal described above is converted to a voltage commensurate to the frequency by velocity controlling circuit not shown, and the converted voltage is given feedback to the driving circuit to control the rotational velocity of the motor constant.
However, the motor apparatus described above has following problems.
(1) The motor apparatus has problem of rotational control that the generated FG signal is very weak. Actually, the magnetic flux generated by the FG magnetic pole
102
a
reaches to the FG coil
104
for only 0.02 T. Accordingly, the magnetic flux leaked from the driving coil
108
adversely impact the magnetic flux of the FG coil
104
.
The magnetic flux leaked from the driving coil
108
causes noise in the output of FG signal when it interlinks to the FG coil. Consequently, the velocity controlling circuit can not operate properly and the rotation of the motor fluctuates. Eventually, the rotation of the disk drive adversely impact the read-out/write-on operation of the flexible disk drive.
(2) The motor apparatus has disadvantage in miniaturization. The FG coil
104
and the driving coil
108
should be kept away from each other to suppress the impact of magnetic flux leaked from the driving coil
108
, which causes the size of the motor apparatus bigger.
If the FG coil
104
and the driving coil
108
are kept away in horizontal direction, the diameter of the motor apparatus becomes bigger, and if the coils are kept away in vertical direction, the thickness of the motor apparatus becomes thicker.
In either case, the motor apparatus can not be miniaturized and the flexible disk drive having such the motor apparatus can not be miniaturized and the final product incorporating such the flexible disk drive can not be miniaturized.
(3) The FG coil is influenced by leaked magnetic flux coming from outside. The FG coil
104
is placed in the outer circumference of the motor which position is most sensitive for any leaked magnetic flux coming from outside. Leaking of magnetic flux can be blocked by magnetic shield. However, the magnetic shield is costly and needs more room for installation.
SUMMARY OF THE INVENTION
Accordingly, in consideration of the above-mentioned problems of the related art, an object of the present invention is to provide a motor apparatus a motor apparatus having a rotor placed rotatably on a stator base and provided with an FG signal for controlling the rotation of the rotor, the motor apparatus including, a driving magnet having an even number of magnetic poles evenly placed on the outer circumference of the rotor, wherein the even number is not less than 12 and not more than 32, and having a magnetic flux density pattern superposed with an “n”th (n is either one of 3 and 5) harmonic component, wherein the driving magnet is made of Nd—Fe—B system material, and wherein a peak value of the magnetic flux density pattern of the driving magnet is in the range of 0.2 to 0.6 T (Tesla) in order to suppress rotational fluctuation caused by controlling the rotation of rotor within 5%, and an FG coil provided on the circumference of the stator base in the position opposing to each of the magnetic poles of the driving magnet with keeping a predetermined gap between the FG coil and the driving magnet, wherein the FG coil has a folding pattern of being folded alternately in the radial direction by a fold pitch angle of 1
of a pitch angle of the driving magnet.
According to another aspect of the present invention, there provided a motor apparatus having a rotor placed rotatably on a stator base and provided with an FG signal for controlling the rotation of the rotor, the motor apparatus including, a driving magnet having an even number of magnetic poles evenly placed on the outer circumference of the rotor, wherein the even number is not less than 12 and not more than 32, and having a magnetic flux density pattern superposed with an “n”th (n is either one of 3 and 5) harmonic component, wherein the driving magnet is made of Nd—Fe—B system material, and an FG coil provided on the circumference of the stator base in the position opposing to each of the magnetic poles of the driving magnet with keeping a predetermined gap between the FG coil and the driving magnet, wherein the FG coil has a folding pattern of being folded alternately in the radial direction by a fold pitch angle of 1
of a pitch angle of the driving magnet, the motor apparatus further satisfying an equation of 4≦&pgr;D/(PG)≦15 in order to suppress rotational fluctuation caused by controlling the rotation of rotor within 5%, wherein &pgr; is circular constant, D is a diameter of the driving magnet, P is a number of magnetic pole of the driving magnet, and G is a gap length between the driving magnet and the FG coil.
Other object and further features of the present invention will be apparent from the following detailed description when lea

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