Motor and apparatus using the same motor

Details Motor and apparatus using the same motor Motor and apparatus using the same motor

2002-02-27

2003-12-09

Ramirez, Nestor (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S091000, C310S090000, C310S154010, C310S049540

Reexamination Certificate

active

06661131

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a motor to be used for recording and/or reproducing information stored in a compact disc or a video disc, and an apparatus using the same motor. More particularly, it relates to a motor structure which can improve oil-holding performance of oil-impregnated metal, and a motor structure which can restrain a rotor from moving and vibrating axially due to axial attraction from an attracting magnet.
BACKGROUND OF THE INVENTION
Recently, oil-impregnated metal made of porous metal has been widely used for a bearing in order to meet a requirement of lowering cost of motors that drive optical discs or optical-magneto discs for recording and/or reproducing information stored therein. However, an apparatus such as a compact-disc player or a videodisc player runs at a speed higher than ever, and this trend reduces long-term reliability of the bearing, and thus the motors encounter the following problems:
necessity of an oil-holding structure of the oil-impregnated metal which forms the bearing; and
measures against oil splashing from the oil-impregnated metal.
If a rotor moves or vibrates axially when the motor is driven at a high speed, errors could occur in reading/writing information from/to a disc.
A conventional motor is disclosed in Japanese Published Unexamined Patent Application No. H08-289523.
FIG. 9
shows a construction of conventional motor. In
FIG. 9
, shaft
101
transmits rotation. Ring-shaped rotor-magnet
103
is press-fitted or rigidly bonded to an inner wall of frame
102
. Magnet
103
is multipolar magnetized in a circumferential direction. A burring process is applied to a central section of frame
102
, and shaft
101
is directly press-fitted into the burring-processed section. Rotor
111
comprises shaft
101
, frame
102
and magnet
103
.
Bracket
104
made of magnetic material is formed by press working, and has a burring-processed section
112
that projects like steps at an approximately central portion thereof. Burring-processed section
112
works as bearing housing
123
accommodating a bearing. Bracket
104
includes burring-processed section
112
with which mounting-base
113
is unitarily formed. Mounting-base
113
is used for mounting a motor to an apparatus.
On an inner wall of burring-processed section
112
, oil-impregnated metal
105
is press-fitted for supporting shaft
101
rotatably. On the other hand, on an outer wall of burring-processed section
112
, stator core
114
is press-fitted. On stator core
114
, copper wire
106
is wound via an insulator made of resin.
Printed circuit board
107
, which includes at least a part of circuits driving and controlling the motor, is rigidly bonded to mounting-base
113
with double-faced adhesive tape (not shown). An end of copper wire
106
is connected onto board
107
.
Stopper
108
, for preventing rotor
111
from coming off in a thrust direction, is formed by metal pressing work. Stopper
108
is press-fitted onto an end of shaft
101
. Bottom plate
109
bears load of rotor
111
in the thrust direction via resin board
110
exhibiting abrasion resistance. Bottom plate
109
is press-fitted into an inner wall of burring-processed section
112
.
A plurality of through-holes
116
are punched in a top plate of frame
102
. When bottom plate
109
is press-fitted into section
112
, face “P” of stator core
114
can be supported with a jig (not shown) extending through holes
116
, so that a force caused by press-fitting is restrained from being applied to mounting-base
113
.
However, the structure discussed above allows oil leaked from a top of oil-impregnated metal
105
to splash outwardly during rotation of rotor
111
. The oil splashed moves to stator core
114
, travels on the inner wall of frame
102
and arrives at magnet
103
.
As a result, the oil impregnated in metal
105
decreases, which lowers reliability of the bearing spinning at a high speed. Thus, the motor is not suited for an apparatus demanded to spin at a higher speed.
In the conventional motor discussed above, attraction force (called magnetic thrust) working axially between stator
115
and rotor
111
is produced by deviation between a center of an axial length of stator core
114
and a center of an axial length of rotor magnet
103
. In other words, the attraction force can be produced by shifting magnetic center H
1
appropriately. This attraction force working between stator
115
and rotor
111
allows a disc to vibrate less in an axial direction, thereby preventing read/write errors.
Another conventional motor, having different structure to produce an attraction force, is disclosed in Japanese Published Unexamined Patent Application No. H11-55900. The motor disclosed in this application comprises the following elements:
a rotary shaft;
a bearing for journaling the rotary shaft;
a hub fixed to the rotary shaft;
a stopper, for preventing a motor from coming off, made of magnetic material and fixed to the hub;
an attracting magnet mounted to the stopper;
a bracket for holding the bearing; and
a coil assembly fixed to the bracket.
The attracting magnet faces a core of the coil assembly. The stopper slides with the bearing only when a rotating body moves. This structure prevents the motor from coming off, and restrains vibrations in both a radial and a thrust direction.
However, according to the publication discussed above, oil leaked from an oilless bearing cannot be collected or returned to the bearing per se; therefore, it is difficult to further improve reliability of the motor spinning at a higher speed. Major magnetic field produced by a driving current running through the coil is affected by magnetic flux from the attracting magnet because the attracting magnet is disposed closely to the coil assembly, and the major magnetic field produces magnetic interference.
Still another conventional motor is disclosed in Japanese Published Unexamined Patent Application No. 2000-245116. This conventional motor comprises the following elements:
a stationary member;
a rotor rotatable with respect to the stationary member;
a bearing disposed between the stationary member and the rotor;
a rotor magnet mounted to the rotor; and
a stator mounted to the stationary member.
The rotor includes a cup-shaped rotor made of magnetic material. The cup-shaped rotor has an annular wall and an end wall disposed on a first end of the annular wall. The rotor magnet is formed of a sheet-like rubber magnet. This rubber magnet is mounted forming a ring shape on an inner face of the annular wall. Magnetic energizing structure, for energizing the rotor axially, is mounted to the stationary member, wherein the magnetic energizing structure includes a sintered magnet of ferrite system and faces the end wall of the cup-shaped rotor. This structure allows the conventional motor to be manufactured at a lower cost and obtain desirable energizing force.
However, this structure needs additionally a holder as an element of the magnetic energizing structure, and yet, this structure cannot collect oil leaked from an oilless bearing or return the oil to the bearing per se. Therefore, it is difficult for this structure to further improve reliability of the bearing spinning at a higher speed. Furthermore, since the energizing structure is placed above the stator core, this structure is not suited for a motor used in a slim apparatus.
SUMMARY OF THE INVENTION
The present invention addresses the problems discussed above, and aims to provide a motor suitable for a disc driving apparatus which records and/or reproduces information stored in a compact disc, videodisc, optical disc, optical magneto disc or the like, and an apparatus using the same motor.
To be more specific, the present invention aims to provide a motor structure that meets a requirement of downsizing and lowering of profile of an apparatus as well as improves reliability of a motor-bearing spinning at a higher speed. At the same time, the present invention aims to provide a motor in a simple construction which prevents a disc from moving or vi

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