U.S. patent application number 09/345762 was filed with the patent office on 2002-02-14 for scanning unit of laser printer and magnetic bearing apparatus therein.
Invention is credited to KIM, YOUNG-CHUL, KOH, BYEONG-CHEON, LEE, CHANG-WOO.
Application Number | 20020018113 09/345762 |
Document ID | / |
Family ID | 19542659 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018113 |
Kind Code |
A1 |
KOH, BYEONG-CHEON ; et
al. |
February 14, 2002 |
SCANNING UNIT OF LASER PRINTER AND MAGNETIC BEARING APPARATUS
THEREIN
Abstract
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 a magnetic bearing apparatus using in the scanning unit,
whereby the noise is lowered and the structure of the scanning unit
can be simplified.
Inventors: |
KOH, BYEONG-CHEON;
(KYONGGI-DO, KR) ; LEE, CHANG-WOO; (KYONGGI-DO,
KR) ; KIM, YOUNG-CHUL; (SEOUL, KR) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS PLLC
2100 PENNSYLVANIA AVENUE N W
WASHINGTON
DC
200373202
|
Family ID: |
19542659 |
Appl. No.: |
09/345762 |
Filed: |
July 1, 1999 |
Current U.S.
Class: |
347/261 |
Current CPC
Class: |
F16C 32/0431 20130101;
G02B 26/122 20130101 |
Class at
Publication: |
347/261 |
International
Class: |
B41J 027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 1998 |
KR |
26355/1998 |
Claims
What is claimed is:
1. A scanning unit of a laser printer comprising; a semiconductor
laser diode for irradiating a laser beam; a collimator lens for
making the laser beam irradiated from the semiconductor laser diode
to be parallel with an optical axis; a cylindrical lens for
converting the parallel light passed through the collimator lens
into a linear light which is in a horizontal direction with respect
to a sub-irradiation direction; a polygon mirror for moving the
linear light passed through the cylindrical lens at a constant
linear velocity to perform a scanning operation; a scanning motor
for rotating the polygon mirror at a constant velocity; a lens for
forming an image, which polarizes the linear light reflected by the
polygon mirror in a main scanning direction and compensates a
spherical aberration and focuses on a scanning face; a reflecting
mirror for reflecting perpendicularly the laser beam passed through
the lens for forming an image so as to form the image on a surface
of a photosensitive drum; a horizontal synchronizing mirror for
reflecting horizontally the laser beam passed through the lens; a
light sensor for receiving the laser beam reflected by the
horizontal synchronizing mirror so as to synchronize a point of
time of forming the image on the photosensitive drum with a point
of time of transferring a printing data; and a cover for covering
the polygon mirror and scanning motor; wherein the scanning motor
is a magnetic bearing type motor.
2. The scanning unit according to claim 1, wherein the cylindrical
lens is integrally formed on the cover which is in an incidence
course of the laser beam.
3. The scanning unit according to claim 1, wherein the lens for
forming an image is integrally formed on the cover which is in the
irradiation course of the laser beam.
4. The scanning unit according to claim 1, wherein an inner portion
of the cover is maintained in a vacuum state.
5. The scanning unit according to claim 1, wherein the scanning
motor comprises a fixed shaft which is a rotating center of the
polygon mirror; a housing through which the fixed shaft is
inserted; a fixed thrust magnet which is fixed on an outer face of
the fixed shaft; a fixed radial magnet which is fixed on an upper
face of the housing; a hub on which the polygon mirror is mounted;
a rotating thrust magnet and a rotating radial magnet which are
respectively mounted in the hub corresponding to the fixed thrust
and radial magnet so that the hub maintains a constant clearance
with respect to the housing and the fixed shaft; and a motor stator
and a motor rotor for driving the polygon mirror.
6. The scanning unit according to claim 5, wherein the rotating
thrust magnet corresponding to the fixed thrust magnet is disposed
so that the poles of the rotating thrust magnet are respectively
corresponded to the opposite poles of the fixed thrust magnet, and
the rotating radial magnet corresponding to the fixed radial magnet
is disposed so that the poles of the rotating radial magnet are
respectively corresponded to the opposite poles of the fixed radial
magnet.
7. A magnetic bearing apparatus comprising; a fixed shaft which is
a rotating center of a rotary body; a housing through which the
fixed shaft is inserted; a fixed thrust magnet which is fixed on an
inner face of the fixed shaft; a fixed radial magnet which is fixed
on an upper face of the housing; a hub on which the rotary body is
mounted; and a rotating thrust magnet and a rotating radial magnet
which are respectively mounted in the hub corresponding to the
fixed thrust and radial magnet so that the hub maintains a constant
clearance with respect to the housing and the fixed shaft.
8. The magnetic bearing apparatus according to claim 7, wherein The
rotating thrust magnet corresponding to the fixed thrust magnet is
disposed so that the poles of the rotating thrust magnet are
respectively corresponded to the opposite poles of the fixed thrust
magnet, and the rotating radial magnet corresponding to the fixed
radial magnet is disposed so that the poles of the rotating radial
magnet are respectively corresponded to the opposite poles of the
fixed radial magnet.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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 using
in the scanning unit.
[0003] 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.
[0004] At this time, if a refracting speed of the laser beam by
each face of the polygon mirror is increased, the scanning speed
can be also increased.
[0005] FIG. 1 shows a structure of a scanning unit of a
conventional laser print.
[0006] 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 to 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 800. 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.
[0007] 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.
[0008] The operation of the conventional semiconductor laser
scanning unit is described more fully.
[0009] 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 to 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.
[0010] 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.theta. and polarize the concentrated light to the main scanning
direction, wherein f is a focal distance and .theta. 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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 is 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.
[0015] 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.
[0016] 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 (.mu.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.
[0017] 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.
[0018] 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-spherical groove 532
and the upper half-spherical bearing 521 is gradually
increased.
[0019] The upper and lower clearances is varied for a while
according to the movement of the bush 530. Finally, the bush 530
recovers a balance at a rotating place where the difference between
the upper and lower dynamic pressures is the same as the weight of
the bush 530.
[0020] However, in the conventional scanning unit as described
above, there is a problem that, since the scanning unit employs an
air pressure type bearing, a noise is generated when the scanning
motor is rotated at a high speed.
[0021] Further, since the components of the scanning motor are so
many, it is difficult to simplify the structure of the scanning
unit.
SUMMARY OF THE INVENTION
[0022] It is therefore an object of the present invention to
provide a scanning unit using a magnetic bearing, which can lower
the noise according to the rotation of the scanning motor.
[0023] The other object of the present invention is to provide a
scanning unit of which the structure is simplified, thereby
miniaturizing the product.
[0024] To achieve the above objects and other advantages, there is
provided a scanning unit of a laser printer comprising a
semiconductor laser diode for irradiating a laser beam; a
collimator lens for making the laser beam irradiated from the
semiconductor laser diode to be parallel with an optical axis; a
cylindrical lens for converting the parallel light passed through
the collimator lens into a linear light which is in a horizontal
direction with respect to a sub-irradiation direction; a polygon
mirror for moving the linear light passed through the cylindrical
lens at a constant linear velocity to perform a scanning operation;
a scanning motor for rotating the polygon mirror at a constant
velocity; a lens for forming an image, which polarizes the linear
light reflected by the polygon mirror in a main scanning direction
and compensates a spherical aberration and focuses on a scanning
face; a reflecting mirror for reflecting perpendicularly the laser
beam passed through the lens for forming an image so as to form the
image on a surface of a photosensitive drum; a horizontal
synchronizing mirror for reflecting horizontally the laser beam
passed through the lens; a light sensor for receiving the laser
beam reflected by the horizontal synchronizing mirror so as to
synchronize a point of time of forming the image on the
photosensitive drum with a point of time of transferring a printing
data; and a cover for covering the polygon mirror and scanning
motor, wherein the scanning motor is a magnetic bearing type
motor.
[0025] Preferably, the cylindrical lens is integrally formed on the
cover which is in an incidence course of the laser beam.
[0026] Preferably, the scanning unit according to claim 1, wherein
the lens for forming an image is integrally formed on the cover
which is in the irradiation course of the laser beam.
[0027] Further, it is preferable that an inner portion of the cover
is maintained in a vacuum state.
[0028] In addition, the scanning motor comprises a fixed shaft
which is a rotating center of the polygon mirror; a housing through
which the fixed shaft is inserted; a fixed thrust magnet which is
fixed on an outer face of the fixed shaft; a fixed radial magnet
which is fixed on an upper face of the housing; a hub on which the
polygon mirror is mounted; a rotating thrust magnet and a rotating
radial magnet which are respectively mounted in the hub
corresponding to the fixed thrust and radial magnet so that the hub
maintains a constant clearance with respect to the housing and the
fixed shaft; and a motor stator and a motor rotor for driving the
polygon mirror.
[0029] Further, the rotating thrust magnet corresponding to the
fixed thrust magnet is disposed so that the poles of the rotating
thrust magnet are respectively corresponded to the opposite poles
of the fixed thrust magnet, and the rotating radial magnet
corresponding to the fixed radial magnet is disposed so that the
poles of the rotating radial magnet are respectively corresponded
to the opposite poles of the fixed radial magnet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The above object and other advantages of the present
invention will become more apparent by describing in detail the
preferred embodiments thereof with reference to the accompanying
drawings, in which:
[0031] FIG. 1 is a perspective view showing a structure of a
scanning unit of a conventional laser printer;
[0032] FIG. 2 is a sectional view of a scanning motor in FIG.
1;
[0033] FIG. 3 is a perspective view showing one embodiment of a
structure of a scanning unit of a laser printer according to the
present invention;
[0034] FIG. 4 is a sectional view showing one embodiment of a
scanning motor according to the present invention;
[0035] FIG. 5 is an enlarged detail of a magnetic thrust bearing
using in the scanning motor in FIG. 4; and
[0036] FIG. 6 is an enlarged detail of a magnetic radial bearing
using in the scanning motor in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown.
[0038] The scanning unit of the laser print according to the
present invention comprises a semiconductor laser diode 1 for
irradiating a laser beam, a collimator lens 2, a cylindrical lens
3, a polygon mirror 4, a scanning motor 5, a lens 6 for forming an
image, a reflecting mirror 7, a horizontal synchronizing mirror 9
and a light sensor 10. The collimator lens 2 makes the laser beam
irradiated from the semiconductor laser diode 1 to be parallel with
an optical axis. The cylindrical lens 3 converts the parallel light
passed through the collimator lens 2 into a linear light which is
in a horizontal direction with respect to a sub-irradiation
direction. The polygon mirror 4 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 5 rotates the polygon mirror 4
at a constant velocity. The lens 6 for forming an image polarizes
the linear light reflected from the polygon mirror 4 in a main
scanning direction so as to compensate a spherical aberration of
the lenses and focus on a scanning face. The reflecting mirror 7
reflects perpendicularly the laser beam passed through the lens 6
so as to form the image on a surface of a photosensitive drum 8.
The horizontal synchronizing mirror 9 reflects horizontally the
laser beam passed through the lens 6. The light sensor 10 receives
the laser beam reflected by the horizontal synchronizing mirror 9
so as to synchronize a point of time of forming the image on the
photosensitive drum 8 with a point of time of transferring a
printing data.
[0039] In addition, a cover 11 is provided on an upper portion of
the polygon mirror 4 and the scanning motor 5 The cylindrical lens
3 is integrally formed on the cover 11 which is in an incidence
course of the laser beam from the semiconductor laser diode 1. The
lens 6 is integrally formed on the cover 11 which is in the
irradiation course of the laser beam. An inner portion of the cover
is in a vacuum state.
[0040] Further, the cover 11 is engaged with the housing 12 by
means of a hook. A rubber packing 13 is interposed between the
cover 11 and the housing 12, thereby intercepting a noise.
[0041] In the scanning motor according to the present invention, a
magnetic bearing is applied. The magnetic bearing type scanning
motor comprises a fixed shaft 14 which is a rotating center of the
polygon mirror 4, a fixed thrust magnet 15 through which the fixed
shaft 14 is inserted, a fixed radial magnet 16 which is fixed on an
upper face of the housing 12, a hub 17 on which the polygon mirror
4 is mounted, a rotating thrust magnet 18, a rotating radial magnet
19, a motor stator 20 and a motor rotor 21 for driving the polygon
mirror 4. The rotating thrust and radial magnets 18, 19 are
respectively mounted in the hub 17 corresponding to the fixed
thrust and radial magnet 15, 16 and improve a levitation force of
the polygon mirror 4. And a reference numeral 22 is an
adhesive.
[0042] The rotating thrust magnet 18 which is mounted on an inner
face of the hub 17 corresponding to the fixed thrust magnet 15 is
disposed so that the poles of the rotating thrust magnet 18 are
respectively corresponded to the opposite poles of the fixed thrust
magnet 15.
[0043] In addition, The rotating radial magnet 19 which is mounted
on the upper face of the housing 12 corresponding to the fixed
radial magnet 16 is disposed so that the poles of the rotating
radial magnet 19 are respectively corresponded to the opposite
poles of the fixed radial magnet 16.
[0044] Hereinafter, the attachment structure of each magnet is
described more fully referring to FIG. 5. As shown in FIG. 5, a
first fixed magnet 15a and a second fixed magnet 15b of the fixed
thrust magnet 15 serving as a magnetic thrust bearing are contact
with each other and are fixed to a yoke 15c provided on a side
portion of the fixed shaft 14, while poles of the first fixed
magnet 15a are corresponded to the opposite poles of the second
fixed magnet 15b.
[0045] By the same manner, a first rotating magnet 18a and a second
rotating magnet 18b of the rotating thrust magnet 18 are contact
with each other and are fixed to a yoke 18c provided on a side
portion of the hub 17, while poles of the first rotating magnet 18a
are corresponded to the opposite poles of the second rotating
magnet 18b.
[0046] As shown in FIG. 6, a first fixed magnet 16a and a second
fixed magnet 16b of the fixed radial magnet 16 serving as a
magnetic radial bearing are contact with each other and are fixed
to a yoke 16c provided on the upper face of the housing 12, while
poles of the first fixed magnet 16a are corresponded to the
opposite poles of the second fixed magnet 16b. And a first rotating
magnet 19a and a second rotating magnet 19b of the rotating radial
magnet 19 are contact with each other and are fixed to a yoke 19c
provided on a lower face of the hub 17, while poles of the first
rotating magnet 19a are corresponded to the opposite poles of the
second rotating magnet 19b.
[0047] The operation of the scanning unit of the laser printer
according to the present invention will be described.
[0048] If the laser beam as a light source is irradiated from the
semiconductor laser diode 1, the laser beam is adjusted to be
parallel with respect to the optical axis by the collimator lens 2.
The laser beam passed through the collimator lens 2 is converted
into the linear light in the horizontal direction with respect to
the sub-irradiation direction by the cylindrical lens 3 which is
integrally formed with the cover 11. The linear light passed
through the cylindrical lens 3 is refracted by the polygon mirror 4
which is rotatably mounted on a rotating shaft of the scanning
motor 5.
[0049] The lens 6 which is integrally formed with the cover 11
compensates an error of the spherical aberration f.theta. and
polarizes the concentrated light to the main scanning direction.
Then, the laser beam passed through the lens 6 is perpendicularly
refracted by the refracting mirror 7 so as to form the point shape
image on the surface of the photosensitive drum 8.
[0050] The operation of the scanning motor is as follows.
[0051] A repulsive force is generated between the fixed radial
magnet 16 mounted on the upper face of the housing 12 and the
rotating radial magnet 19 mounted on the lower potion of the hub 17
due to their magnetic flux density.
[0052] At this time, since the fixed radial magnet 16 is fixed and
the rotating radial magnet 19 can be moved to the axial direction,
the repulsive force generated by the fixed radial magnet 16 and the
rotating radial magnet 19 is upwardly applied against the weight of
the hub 17 and the loads in a gravity direction by the motor stator
20, the motor rotor 21 and the polygon mirror 4.
[0053] Therefore, the loads in a gravity direction is set off by
the repulsive force of the fixed radial magnet 16 and the rotating
radial magnet 19, whereby the hub 17 maintains a constant clearance
with the housing 12.
[0054] If a power source is applied to the motor stator 20 and the
motor rotor 21 and the motor rotor 21 is rotated, while the hub 17
maintains a constant clearance with the housing 12, the hub 17 is
also rotated. At this time, since a repulsive force is also
generated between the fixed thrust magnet 15 mounted on the outer
face of the fixed shaft 14 and the rotating thrust magnet 18
mounted on the inner face of the hub 17, a clearance is generated
between the fixed shaft 14 and the hub 17. Therefore, the hub 17 is
rotated, while maintaining the constant clearance with respect to
the housing 12 and the fixed shaft 14 during the driving of the
motor stator 20 and the motor rotor 21.
[0055] In the of the scanning unit of the laser printer of the
present invention, as described above, the scanning motor employs a
magnetic bearing and the inner portion of the scanning motor is
maintained in a vacuum state, whereby the noise is lowered.
[0056] In addition, the lenses used in the scanning unit is
integrally formed with the cover, whereby the structure of the
scanning unit can be simplified.
[0057] This invention has been described above with reference to
the aforementioned embodiments. It is evident, however, that many
alternative modifications and variations will be apparent to those
having skill in the art in light of the foregoing description.
Accordingly, the present invention embraces all such alternative
modifications and variations as fall within the spirit and scope of
the appended claims.
* * * * *