Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-07-01
2002-04-23
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S243000
Reexamination Certificate
active
06377293
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a scanning unit of a laser printer and a magnetic bearing apparatus therein, more particularly, to a scanning unit of a laser printer in which a cover is provided on a scanning motor so that the scanning motor is isolated from an outside and an inner portion of the cover is maintained in a vacuum state and in which the scanning motor is provided with a magnetic bearing having a repulsive force in thrust and radial directions, and to the magnetic bearing apparatus used in the scanning unit.
2. Description of the Related Art
Generally, a laser printer used in a laser component and a photo scanning and recording apparatus, etc. employs a semiconductor laser. In the laser printer, a light source or laser beam is irradiated to a rotating polygon mirror so as to scan a recording face formed on a hologram disk.
At this time, it a refracting speed of the laser beam by each face of the polygon mirror is increased, the scanning speed can be also increased.
FIG. 1
shows a structure of a scanning unit of a conventional laser print.
As shown in
FIG. 1
, the scanning unit of the conventional laser print comprises a semiconductor laser diode
100
for irradiating a laser beam as a light source of the laser printer, a collimator lens
200
, a cylindrical lens
300
, a polygon mirror
400
, a scanning motor
500
, lenses
600
for forming an image, a reflecting mirror
700
, a horizontal synchronizing mirror
900
and a light sensor
1000
. The collimator lens
200
makes the laser beam irradiated from the semiconductor laser diode
100
be parallel with an optical axis. The cylindrical lens
300
converts the parallel light passed through the collimator lens
200
into a linear light which is in a horizontal direction with respect to a sub-irradiation direction. The polygon mirror
400
moves the linear light at a constant linear velocity to perform a scanning operation. Therefore, the linear light has a negative refractive index with respect to the optical axis. The scanning motor
500
rotates the polygon mirror
400
at a constant velocity. The lenses
600
for forming an image polarize the linear light reflected from the polygon mirror
400
in a main scanning direction so as to compensate a spherical aberration of the lenses and focus on a scanning face. The reflecting mirror
700
reflects perpendicularly the laser beam passed through the lenses
600
so as to form the image on a surface of a photosensitive drum
600
. The horizontal synchronizing mirror
900
reflects horizontally the laser beam passed through the lenses
600
. The light sensor
1000
receives the laser beam reflected by the horizontal synchronizing mirror
900
so as to synchronize a point of time of forming the image on the photosensitive drum
800
with a point of time of transferring a printing data.
The lenses
600
include a spherical lens
610
for compensating the spherical aberration and a toric lens
620
. The spherical lens
610
concentrates and polarizes the laser beam refracted by the polygon mirror
400
. The toric lens
620
polarizes the laser beam in the main scanning direction, in which the spherical aberration is compensated by the spherical lens
610
.
The operation of the conventional semiconductor laser scanning unit is described more fully.
If the laser beam as a light source is irradiated from the semiconductor laser diode
100
, the laser beam is adjusted to be parallel with respect Lo the optical axis by the collimator lens
200
. The laser beam passed through the collimator lens
200
is converted into the linear light in the horizontal direction with respect to the sub-irradiation direction by the cylindrical lens
300
. The linear light passed through the cylindrical lens
300
is moved at a constant linear velocity by the polygon mirror
400
which is rotatably mounted on a rotating shaft of the scanning motor
500
to be rotated at a constant angular velocity, and forms an image of a point shape on the surface of the photosensitive drum
800
.
That is, if the linear light of the horizontal direction is transferred to the polygon mirror
400
, since the polygon mirror
400
is rotated at the constant angular velocity by the scanning motor
500
, the linear light is refracted and moved at the constant linear velocity according to the refracting angle of the polygon mirror
400
and is concentrated by the lenses
600
for forming the image. The lenses
600
compensate an error of the spherical aberration f&thgr; and polarize the concentrated light to the main scanning direction, wherein f is a focal distance and &thgr; is a scanning angle. Then, the laser beam passed through the lenses
600
is perpendicularly refracted by the refracting mirror
700
so as to form the point shape image on the surface of the photosensitive drum
800
.
Meanwhile, the scanning motor
500
for rotating the polygon mirror
400
simultaneously supports a radial load and a thrust load, and a half-spherical bearing device which is a fluid bearing device is employed in the scanning motor
500
. Referring to
FIG. 2
, the scanning motor
500
is described more fully.
The scanning motor using the half-spherical bearing device comprises a fixed shaft
510
which is a rotating center of the polygon mirror
400
, half-spherical bearings
520
,
521
through which the fixed shaft
510
is inserted, a bush
530
for supporting the radial and thrust loads, a motor rotor
540
, a motor stator
541
, a hub
550
and a housing
560
.
The fixed shaft
510
is inserted in the housing
560
. The hub
550
is provided on an outer peripheral surface so that the polygon mirror
400
and the motor rotor
540
can be mounted thereon. The motor stator
541
is disposed apart from the motor rotor
540
at an interval.
The bush
530
for supporting the radial and thrust loads of the half-spherical bearings
520
,
521
is provided with a through hole at the center thereof. The through hole has a larger diameter than that of the fixed shaft
510
. Half-spherical grooves
531
,
532
having the same radius of curvatures as those of the half-spherical bearings
520
,
521
are defined on both ends of the bush
530
. Further, a spacer
570
is provided in the through hole of the bush
530
in order to adjust a clearance between the half-spherical bearing
520
,
521
and the half-spherical grooves
531
,
532
.
In the scanning motor as described above, when a power source is applied to the motor rotor
540
and the motor stator
541
and the motor rotor
540
and the motor stator
541
are rotated, the lower half-spherical groove
531
of the bush
530
is moved downward by a load applied to the bush
530
and is closely contacted with the lower half-spherical bearing
520
.
At this time, if the lower half-spherical groove
531
of the bush
530
is closely contacted with the lower half-spherical bearing
520
, the clearance(&mgr;m) is defined between the upper half-spherical groove
532
and the upper half-spherical bearing
521
. Therefore, the clearance between the upper half-spherical groove
532
and the upper half-spherical bearing
521
is lager than that between the lower half-spherical groove
531
and the lower half-spherical bearing
520
.
Meanwhile, a plurality of spiral grooves are formed on the outer face of each half-spherical bearing
520
,
521
. If the bush
530
is rotated, a dynamic pressure is generated by air flowed in the spiral grooves. At this time, the dynamic pressure generated in the lower half-spherical bearing
520
is greater than that generated in the upper half-spherical bearing
521
. Therefore, the bush
530
is risen upwardly by the dynamic pressure.
However, if the bush
530
is risen, upwardly, the clearance between the lower half-spherical groove
531
and the lower half-spherical bearing
520
is gradually increased. On the contrary, the clearance between the upper half-spherical groove
532
and the upper half-spherical bearing
521
is gradually decreased, whereby the dynamic pressure between the upper half-sphe
Kim Young-Chul
Koh Byeong-Cheon
Lee Chang-Woo
LandOfFree
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