Title: Multi-beam scanning apparatus
Abstract: A multi-beam scanning apparatus has a multi-beam semiconductor laser which emits a plurality of laser beams, a laser holder holding the multi-beam semiconductor laser, a multi-beam light source unit having the multi-beam semiconductor laser and the laser holder, scanning imaging unit for scanning a plurality of laser beams emitted by the multi-beam semiconductor laser to form an image on a surface to be scanned, and a housing supporting the scanning imaging unit and the multi-beam light source unit. The multi-beam semiconductor laser is fixed to the laser holder with an inclination at or near a predetermined rotational angle for adjusting a beam interval between the plurality of laser beams.
Patent Number: 6,992,690 Issued on 01/31/2006 to Mogi, et al.
| Inventors:
|
Mogi; Shin (Kashiwa, JP);
Naruge; Yasutaka (Toride, JP)
|
| Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
392626 |
| Filed:
|
September 9, 1999 |
Foreign Application Priority Data
| Sep 14, 1998[JP] | 10-279352 |
| Nov 30, 1998[JP] | 10-355353 |
| Current U.S. Class: |
347/238 |
| Current Intern'l Class: |
B41J 2/45 (20060101) |
| Field of Search: |
347/238,241-242,256-257,237,245,247,263
359/641,819,821,822,826
372/107
|
References Cited [Referenced By]
U.S. Patent Documents
| 4800401 | Jan., 1989 | Sato et al.
| |
| 4993801 | Feb., 1991 | Sarraf.
| |
| 5408493 | Apr., 1995 | Aoki.
| |
| 5774248 | Jun., 1998 | Komatsu.
| |
| 5786594 | Jul., 1998 | Ito et al.
| |
| 5999345 | Dec., 1999 | Nakajima et al.
| |
| Foreign Patent Documents |
| 0 804 015 | Oct., 1997 | EP.
| |
| 06-242160 | Sep., 1994 | JP.
| |
| 9-243944 | Sep., 1997 | JP.
| |
| 09329754 | Dec., 1997 | JP.
| |
| 10-10447 | Jan., 1998 | JP.
| |
| 10-244707 | Sep., 1998 | JP.
| |
Primary Examiner: Pham; Hai
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Claims
What is claimed is:
1. A multi-beam scanning apparatus comprising:
a light source unit comprising a laser light source, a holder holding said laser
light source and a driving circuit board for driving said laser light source, said
laser light source including a laser chip having a plurality of emission points
for emitting laser beams and a terminal for energizing the laser chip, said driving
circuit board being connected to the terminal of said laser light source;
scanning means for scanning a surface to be scanned with the laser beams emitted
by said light source unit; and
a housing having a wall,
wherein said housing contains said scanning means and supports said light source
unit on the wall,
wherein said holder has a reference portion and said laser light source is fixed
to said holder such that a hypothetical straight line connecting the plurality
of emission points is inclined with respect to the reference portion so as to have
an inclination angle equal to or close to a predetermined angle, and
wherein said holder holding said laser light source is fixed to the wall of said
housing after the inclination angle of the hypothetical straight line is finally
adjusted by rotating said holder.
2. An apparatus according to claim 1, wherein said driving circuit board has
a substantially rectangular shape.
3. An apparatus according to claim 1, wherein the plurality of emission points
of said laser light source is arranged linearly.
4. An apparatus according to claim 1, wherein the plurality of emission points
of said laser light source is arranged two-dimensionally.
5. An apparatus according to claim 1, wherein said light source unit further
comprises a collimator lens for collimating the laser beams emitted from said laser
light source and a lens barrel holding said collimator lens, said lens barrel being
integrated with said holder.
6. An apparatus according to claim 1, wherein said laser light source is a multi-beam
semiconductor laser.
7. An apparatus according to claim 1, wherein said scanning means comprises a
rotary polygon mirror for deflecting the laser beams emitted by said light source
unit and an imaging lens for focusing the laser beams deflected by said rotary
polygon mirror.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-beam scanning apparatus used for a laser
beam printer, digital copying machine, and the like.
2. Related Background Art
In recent years, multi-beam scanning apparatuses for simultaneously writing a
plurality of lines using a plurality of laser beams are being developed in electrophotographic
apparatuses such as a laser beam printer.
The multi-beam scanning apparatus simultaneously scans a plurality of laser beams
apart from each other. As shown in FIG. 1, in the multi-beam scanning apparatus,
a multi-beam semiconductor laser
111 serving as a light source for a multi-beam
light source unit
101 emits two laser beams P
1 and P
2.
The laser beams P
1 and P
2 are collimated by a collimator
lens
112, irradiate a reflecting surface
103a of a rotary
polygon mirror
103 via a cylindrical lens
102, and form an image
on a photosensitive member on a rotary drum
105 via an imaging lens
104.
The two laser beams P
1 and P
2 are incident on the reflecting
surface
103a of the rotary polygon mirror
103, scanned in
the main scanning direction, and form an electrostatic latent image on the photosensitive
member along with main scanning by rotation of the rotary polygon mirror
103
and subscanning by rotation of the rotary drum
105.
The cylindrical lens
102 linearly focuses the laser beams P
1
and P
2 on the reflecting surface
103a of the rotary polygon
mirror
103. The cylindrical lens
102 has a function of preventing
a point image formed on the photosensitive member in the above manner from being
distorted due to surface tilt of the rotary polygon mirror
103. The imaging
lens
104 is made up of a spherical lens and toric lens. The imaging lens
104 has a function of preventing distortion of a point image on the photosensitive
member, similar to the cylindrical lens
102, and a correction function of
scanning the point image on the photosensitive member in the main scanning direction
at a constant speed.
The two laser beams P
1 and P
2 are respectively split by
a detection mirror
106 at the end of the main scanning plane (X-Y plane),
guided to a photosensor
107 on an opposite side to the main scanning plane,
and converted into write start signals in a controller (not shown) to be transmitted
to the multi-beam semiconductor laser
111. The multi-beam semiconductor
laser
111 receives the write start signals to start write modulation of
the two laser beams P
1 and P
2.
By adjusting the write modulation timings of the two laser beams P
1
and P
2, the write start (write) position of an electrostatic latent
image formed on the photosensitive member on the rotary drum
105 is controlled.
The cylindrical lens
102, rotary polygon mirror
103, imaging lens
104, and the like are mounted on the bottom wall of an optical box
108.
After the respective optical components are mounted in the optical box
108,
the upper opening of the optical box
108 is closed with a lid (not shown).
As described above, the multi-beam semiconductor laser
111 simultaneously
emits the laser beams P
1 and P
2. The multi-beam semiconductor
laser
111 is integrated via a laser holder
111a with a lens
barrel
112a incorporating the collimator lens
112, and the
integral unit is mounted on a sidewall
108a of the optical box
108
together with a laser driving circuit board
113.
In mounting the multi-beam light source unit
101, the laser holder
111a
holding the multi-beam semiconductor laser
111 is inserted into an opening
108b formed in the sidewall
108a of the optical box
108. The laser holder
111a is fitted in the lens barrel
112a
of the collimator lens
112, the focal point and optical axis of the
collimator lens
112 are adjusted, and the lens barrel
112a is
adhered to the laser holder
111a. As shown in FIG. 2A, the laser
holder
111a is rotated through a predetermined angle θ to adjust
a straight line connecting the emission points of the laser beams P
1
and P
2, i.e., the inclination angle of a laser array N. More specifically,
as shown in FIG. 2B, the beam interval between the laser beams P
1 and
P
2 emitted by the multi-beam semiconductor laser
111 is adjusted
to make a pitch S between imaging points A
1 and A
2 on the
rotary drum
105 in the main scanning direction, and a pitch, i.e., line
interval T in the subscanning direction coincide with design values. After this
adjustment, the laser holder
111a is fixed to the sidewall
108a
of the optical box
108 with a screw or the like.
In the prior art, however, when the multi-beam light source unit is to be fixed
to the optical box, the whole multi-beam light source unit is rotated through the
predetermined angle θ together with the laser driving circuit board, thereby
obtaining the line interval T. To realize this, a space enough to rotate the large-area
laser driving circuit board must be prepared outside the optical box, which interferes
with downsizing of the whole apparatus.
Further, an error allowable value for adjustment of the line interval T
is as strict as several μm or less. If the angular adjustment range in assembling
the multi-beam light source unit to the optical box is wide, high-precision adjustment
is difficult to complete within a short time. The multi-beam light source unit
cannot be assembled with high working efficiency and high reliability.
SUMMARY OF THE INVENTION
The present invention has been made to eliminate the conventional drawbacks,
and has as its object to provide a multi-beam scanning apparatus which can be downsized
and allows adjusting of the beam interval within a short time with high precision.
To achieve the above object, according to the present invention, there is provided
a multi-beam scanning apparatus comprising a multi-beam light source unit having
a multi-beam semiconductor laser and a laser holder holding the multi-beam semiconductor
laser, scanning imaging means for scanning a plurality of laser beams emitted by
the multi-beam semiconductor laser to form an image on a surface to be scanned,
and a housing supporting the scanning imaging means and the multi-beam light source
unit. The multi-beam semiconductor laser is fixed to the laser holder with an inclination
at or near a predetermined rotational angle for adjusting a beam interval between
the plurality of laser beams.
In the multi-beam scanning apparatus, the multi-beam semiconductor laser preferably
has a laser array fixed with an inclination with respect to a reference surface
of the laser holder.
The multi-beam semiconductor laser preferably has a plurality of aligned emission points.
The multi-beam semiconductor laser preferably has a plurality of two-dimensionally
arrayed emission points.
The laser holder is preferably integrated with a lens barrel holding a collimator lens.
In mounting the laser holder in the housing after the multi-beam semiconductor
laser is fixed to the laser holder, the whole multi-beam light source unit is inclined
(rotated) to adjust the beam interval. In this arrangement, however, angular adjustment
is difficult to perform precisely, and takes a long time. In addition, an extra
space is required to incline the large-area laser driving circuit board mounted
on the multi-beam light source unit. To avoid this, in a unit assembly step of
assembling the multi-beam semiconductor laser to the laser holder, the multi-beam
semiconductor laser is rotated (inclined) through an angle necessary for adjusting
the beam interval or an angle approximate to the necessary angle. In this state,
the multi-beam semiconductor laser is fixed to the laser holder into a unit.
In mounting the multi-beam light source unit in the housing, the whole multi-beam
light source unit is rotated through a small angle in order to finally adjust a
small error arising from the component precision and the like.
Since final angular adjustment in mounting the multi-beam light source unit
in the housing is done within a small angular range, the angle can be quickly adjusted
with high precision.
Since the large-area laser driving circuit board need not be greatly inclined,
the whole apparatus can be downsized.
The present invention has been made to eliminate the conventional drawbacks,
and has as its object to provide a low-cost, high-performance multi-beam scanning
apparatus which can easily ensure the installation positional precision of the
multi-beam light source unit in terms of the structure, can improve the adjustment
precision of the multi-beam line interval, can efficiently mount the multi-beam
light source unit, and can maintain high image quality without generating any error
upon mounting.
To achieve the above object, according to the present invention, there is provided
a multi-beam scanning apparatus comprising a multi-beam light source unit having
a multi-beam semiconductor laser and a laser holder holding the multi-beam semiconductor,
scanning imaging means for scanning a plurality of laser beams emitted by the multi-beam
semiconductor laser to form an image on a surface to be scanned, a housing supporting
the scanning imaging means and the multi-beam light source unit, and fixing means
for fixing the multi-beam light source unit to the housing after the rotational
angle of the multi-beam light source unit is adjusted, the fixing means having
a plurality of fixing portions. The center of the rotation of the multi-beam light
source unit and a plurality of emission points of the multi-beam semiconductor
laser are located on a straight line connecting two of the plurality of fixing
portions or a planar region defined by straight lines connecting all the plurality
of fixing portions.
The fixing means preferably has at least three fixing portions.
The fixing means preferably has a fixing portion fastened by a screw.
The fixing means preferably has a fixing portion adhered with an adhesive.
The multi-beam semiconductor laser preferably has a plurality of aligned emission points.
The multi-beam semiconductor laser preferably has a plurality of two-dimensionally
arrayed emission points.
The laser holder is preferably integrated with a lens barrel holding a collimator lens.
In mounting the multi-beam semiconductor laser in the housing, the whole multi-beam
light source unit is rotated to adjust the line interval. Thereafter, screws or
the like are tightened to fix the multi-beam light source unit to the housing.
A plurality of fixing portions by screws or the like are set. The emission points
of laser beams and the center of rotation of the multi-beam light source unit are
located on a straight line connecting two of the fixing portions or a planar region
defined by straight lines connecting all the fixing portions. Accordingly, the
multi-beam light source unit can be very firmly, stably fixed to the housing.
Hence, no rotational shift occurs in the multi-beam light source unit due
to shock or the like after the multi-beam light source unit is fixed to the housing.
Trouble such as a shift of the rotational angle of the multi-beam light source
unit due to free running during screw tightening operation does not occur. Thus,
the assembly efficiency and precision can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic plan view showing a conventional multi-beam scanning apparatus;
FIGS. 2A and 2B are views for explaining line interval adjustment in the multi-beam
scanning apparatus in FIG. 1;
FIG. 3 is a schematic plan view showing a multi-beam scanning apparatus according
to the present invention;
FIG. 4 is an enlarged perspective view showing the first embodiment of a multi-beam
light source unit in the multi-beam semiconductor laser of the apparatus in FIG. 3;
FIGS. 5A and 5B are views for explaining line interval adjustment;
FIG. 6 is a perspective view showing a laser holder temporarily fixed to an
optical box;
FIG. 7 is a view for explaining final line interval adjustment;
FIG. 8 is a schematic view showing the second embodiment of the multi-beam light
source unit;
FIG. 9 is a schematic view showing a multi-beam semiconductor laser in FIG.
8 together with a laser driving circuit board;
FIG. 10 is a schematic view showing the third embodiment of the multi-beam light
source unit;
FIGS. 11A and 11B are views showing the fourth embodiment of the multi-beam
light source unit, in which FIG. 11A is a plan view showing the layout of three
fixing portions, and FIG. 11B is a sectional view showing the fixing portions; and
FIG. 12 is a schematic view showing the fifth embodiment of the multi-beam light
source unit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be described below with reference
to the accompanying drawings.
FIG. 3 shows a multi-beam scanning apparatus according to the present invention.
In this multi-beam scanning apparatus, a multi-beam semiconductor laser
11
serving as a light source for a multi-beam light source unit
1 emits two
laser beams P
1 and P
2. The laser beams P
1 and
P
2 are collimated by a collimator lens
12, irradiate a reflecting
surface
3a of a rotary polygon mirror
3 via a cylindrical
lens
2, and form an image on a photosensitive member on a rotary drum
5
serving as a surface to be scanned via an imaging lens
4 which constitutes
a scanning imaging means together with the rotary polygon mirror
3.
The two laser beams P
1 and P
2 are incident on the reflecting
surface
3a of the rotary polygon mirror
3, scanned in the
main scanning direction, and form an electrostatic latent image on the photosensitive
member along with main scanning by rotation of the rotary polygon mirror
3
and subscanning by rotation of the rotary drum
5.
The cylindrical lens
2 linearly focuses the laser beams P
1
and P
2 on the reflecting surface
3a of the rotary polygon
mirror
3. The cylindrical lens
2 has a function of preventing a point
image formed on the photosensitive member in the above manner from being distorted
due to surface tilt of the rotary polygon mirror
3. The imaging lens
4
is made up of a spherical lens and toric lens. The imaging lens
4 has a
function of preventing distortion of a point image on the photosensitive member,
similar to the cylindrical lens
2, and a correction function of scanning
the point image on the photosensitive member in the main scanning direction at
a constant speed.
The two laser beams P
1 and P
2 are respectively split by
a detection mirror
6 at the end of the main scanning plane (X-Y plane),
guided to a photosensor
7 on an opposite side to the main scanning plane,
and converted into write start signals in a controller (not shown) to be transmitted
to the multi-beam semiconductor laser
11. The multi-beam semiconductor laser
11 receives the write start signals to start write modulation of the two
laser beams P
1 and P
2.
By adjusting the write modulation timings of the two laser beams P
1
and P
2, the write start (write) position of an electrostatic latent
image formed on the photosensitive member on the rotary drum
5 is controlled.
The cylindrical lens
2, rotary polygon mirror
3, imaging lens
4,
and the like are mounted on the bottom wall of an optical box
8 serving
as a housing. After the respective optical components are mounted in the optical
box
8, the upper opening of the optical box
8 is closed with a lid
(not shown).
As described above, the multi-beam semiconductor laser
11 simultaneously
emits the laser beams P
1 and P
2. The multi-beam semiconductor
laser
11 is integrated via a laser holder
11a with a lens
barrel
12a incorporating the collimator lens
12, and the integral
unit is mounted on a sidewall
8a of the optical box
8 together
with a laser driving circuit board
13.
In mounting the multi-beam light source unit
1, the laser holder
11a
holding the multi-beam semiconductor laser
11 is inserted into an opening
8b formed in the sidewall
8a of the optical box
8.
The laser holder
11a is fitted in the lens barrel
12a of
the collimator lens
12, three-dimensional adjustment such as focus adjustment
and optical axis adjustment of the collimator lens
12 is done, and the lens
barrel
12a is adhered to the laser holder
11a.
As shown in FIG. 4, the multi-beam semiconductor laser
11 comprises a
laser
chip
22 fixed to a pedestal
21a integrated with a stem
21,
a photodiode
23 for monitoring the emission amounts of laser beams P
1
and P
2 emitted from two emission points
22a and
22b
on the laser chip
22, and an enerigization terminal
24 for energizing
the laser chip
22 and the like. The laser chip
22 and the like are
covered with a cap
25.
In a unit assembly step of mounting the multi-beam semiconductor laser
11
in the laser holder
11a, the multi-beam semiconductor laser
11
is rotated through a predetermined rotational angle θ or angle approximate
to the angle θ with respect to a reference surface V of the laser holder
11a, as shown in FIG. 5A, thereby adjusting in advance the inclination
angle of a straight line, i.e., laser array N connecting the emission points of
the laser beams P
1 and P
2. More specifically, the beam interval
between the laser beams P
1 and P
2 emitted by the multi-beam
semiconductor laser
11 is adjusted to make a pitch S between imaging points
A
1 and A
2 on the rotary drum
5 in the main scanning
direction, and a pitch, i.e., line interval T in the subscanning direction coincide
with design values in advance (see FIG. 5B). After this adjustment, the multi-beam
semiconductor laser
11 is fixed to the laser holder
11a to
obtain a unit.
After the lens barrel
12a of the collimator lens
12 is
adhered to the laser holder
11a, as described above, the laser holder
11a is temporarily fixed to the sidewall
8a of the
optical box
8 with screws
11b fitted in slots of the laser
holder
11a, as shown in FIG. 6. While emitting the laser beams P
1
and P
2, the laser holder
11a is rotated through a small
angle Δθ for final adjustment of the line interval T in order to compensate
for the precision of each apparatus component and an error at the fit portion of
the multi-beam semiconductor laser
11 itself. In practice, as indicated
by the broken line in FIG. 7, this adjustment is done after the laser driving circuit
board
13 is mounted on the laser holder
11a. Upon the final
adjustment, the screws
11b are tightened to fix the laser holder
11a to the optical box
8.
The line interval T on the rotary drum must be adjusted with submicron-order
precision. In the first embodiment, when the multi-beam semiconductor laser is
mounted in the laser holder, the laser array N is roughly adjusted to or near to
the predetermined inclination angle θ. When the laser holder is mounted in
the optical box together with the laser driving circuit board, the angle is finally
slightly adjusted to correct an assembly error and the like. Therefore, the final
line interval adjustment precision is very high, and the adjustment time can be
greatly shortened compared to the conventional wide-range angular adjustment on
the optical box. In addition, the large-area laser driving circuit board need not
be rotated outside the optical box, and the apparatus can be downsized.
As a result, this embodiment can realize a small-size, high-precision multi-beam
scanning apparatus with low assembly cost.
Note that this embodiment uses the laser chip with two emission points. However,
the number of emission points, i.e., laser beams can be arbitrarily changed. The
assembly procedure of the laser driving circuit board, lens barrel, collimator
lens, and the like can also be arbitrarily changed. The laser holder can be fixed
to the optical box not only with a fastening means such as a screw, but also by
another method such as adhesion.
FIG. 8 shows the second embodiment of the multi-beam light source unit. This
multi-beam light source unit uses a disk-like laser holder
31a instead
of the rectangular laser holder
11a having a reference surface V
as an end face. In this case, a reference surface U with a rotational angle θ
in mounting a multi-beam semiconductor laser
31 in the laser holder
31a
is defined at a notched portion
31b at the circumferential portion
of the laser holder
31a.
As shown in FIG. 9, a laser driving circuit board
33 is mounted on the
laser holder
31a such that an upper end face
33a serves
as an attachment reference for an optical box (not shown).
The edge-emission-type multi-beam semiconductor lasers
11 and
31
on each of which a plurality of emission points are aligned may be replaced with
a multi-beam semiconductor laser
41 having a surface-emission-type laser
chip
42 on which a plurality of emission points
42a to
42d
are two-dimensionally arrayed, as shown in FIG. 10. This multi-beam semiconductor
laser
41 can advantageously reduce optical aberration because all the emission
points can be made close to the optical axis of the collimator lens. A positioning
hole
41b is formed in a disk-like laser holder
41a as
a positioning reference used to adjust the rotational angle θ for adjusting
beam intervals T
1 to T
3.
The surface-emission-type laser can increase the degree of freedom for the positions
of the emission points to facilitate distribution of the mounting tolerance.
As described above, in the multi-beam scanning apparatus of the present invention,
the two laser beams P
1 and P
2 emitted by the multi-beam semiconductor
laser
11 are scanned by the rotary polygon mirror inside the optical box
8, and form an image on the photosensitive member on the rotary drum via
the imaging lens. To adjust the line interval T and the like on the photosensitive
member, when the multi-beam semiconductor laser
11 is to be mounted in the
laser holder
11a, the multi-beam semiconductor laser
11 is
rotated to incline the laser array N at the predetermined inclination angle θ.
Then, the multi-beam semiconductor laser
11 is fixed to the laser holder
11a. In mounting the multi-beam light source unit
1 in the
optical box
8, the whole multi-beam light source unit
1 is only slightly
inclined to compensate for the component precision and the like.
With this arrangement, the present invention exhibits the following effects.
The beam interval between a plurality of laser beams emitted by the multi-beam
semiconductor laser can be adjusted within a short time with high precision. Accordingly,
the apparatus can attain high resolution, the assembly cost can be greatly reduced,
and the whole apparatus can be downsized.
The fourth embodiment of the present invention will be described below. FIGS.
11A and 11B are schematic views showing the fourth embodiment of the multi-beam
light source unit. The whole arrangement of the multi-beam scanning apparatus is
the same as that shown in FIG. 3, and a description thereof will be omitted. The
multi-beam light source unit will be explained.
As shown in FIGS. 11A and 11B, after a lens barrel
12a of a collimator
lens
12 is adhered to a laser holder
11a, the laser holder
11a is temporarily fixed to a sidewall
8a of an optical
box
8 with screws
14 (see FIGS. 11A and 11B) serving as fixing means
fitted in holes in the laser holder
11a. While emitting laser beams
P
1 and P
2, the laser holder
11a is rotated
to adjust the inclination angle θ in order to adjust the line interval T,
as shown in FIG. 5A.
This adjustment is to adjust the beam interval between the two laser beams P
1
and P
2 emitted by the multi-beam semiconductor laser
11, i.e.,
to make the pitch S between imaging points A
1 and A
2 on a
rotary drum
5 in the main scanning direction, and a pitch, i.e., line interval
T in the subscanning direction coincide with design values.
After the angular adjustment, the screws
14 are tightened to fix the
laser holder
11a to the optical box
8.
In this adjustment, the laser holder
11a is rotated while the spot
positions, i.e., imaging points A
1 and A
2 of the two laser
beams P
1 and P
2 that displace in submicron order are monitored
with a CCD camera or the like.
As shown in FIG. 11A, the three screws
14 fasten the laser holder
11a
to the sidewall
8a of the optical box
8. Fixing portions
14a to
14c surround the emission points of the laser
beams P
1 and P
2. That is, the three screws
14 are
laid out to locate the emission points of the laser beams P
1 and P
2
on straight lines L
1 to L
3 connecting the fixing portions
14a to
14c or within a planar region N (shadow portion)
defined by the straight line L
1 to L
3.
The laser holder
11a has a cylindrical boss
11c.
As shown in FIG. 11B, the boss
11c is fitted in a cylindrical opening
8b in the sidewall
8a of the optical box
8 so
as to rotate the laser holder
11a. The center O of rotation is also
positioned on the straight lines L
1 to L
3 connecting the
fixing portions
14a to
14c or within the planar region
N defined by the straight lines L
1 to L
3.
With this layout, the emission points of the two laser beams P
1 and
P
2 always fall within the range defined by lengths obtained by converting
the intervals between the fixing portions
14a to
14c into
main scanning and subscanning components. The wide range including the center O
of rotation can be firmly fixed to effectively prevent vertical and horizontal
tilt of the multi-beam light source unit
1.
Particularly, when the screws
14 are used as fixing means, the
laser holder
11a and the sidewall
8a of the optical
box
8 are pressed against each other via a fastening surface M. A clearance
K is set as an adjustment margin for angular adjustment rotation. The laser holder
11a is moved within this range.
The fastening surface M at the fixing portions
14a to
14c
of the screws
14 provides the highest fastening reliability and high
stability because the laser holder
11a and sidewall
8a
contact each other at fastening pressure generation positions. Note that if
the fastening surface M does not completely coincide with the positions of the
screws
14, the same effects can be obtained so long as they are close to
each other. The position and shape of the fastening surface M and the number of
fastening surfaces M need not be limited.
The fourth embodiment adopts the screws as fixing means, but may adopt an adhesion
means with an ultraviolet-curing adhesive or the like. The number of emission points
is not limited and may be arbitrarily set to two or more.
The collimator lens is adhered to the lens barrel preferably with the ultraviolet-curing
adhesive, but may be adhered with another adhesive.
According to the fourth embodiment, the multi-beam light source unit is
fastened to the sidewall of the optical box with screws at three or more fixing
portions. The center of rotation of the multi-beam light source unit and the emission
points of respective laser beams locate on straight lines connecting the fixing
portions or within the planar region defined by straight lines connecting all the
fixing portions. Thus, the multi-beam light source unit can be stably, firmly mounted
in the optical box.
The fourth embodiment can realize a low-cost, high-performance multi-beam scanning
apparatus capable of effectively avoiding troubles such as a rotational shift of
the multi-beam light source unit upon high-precision line interval adjustment,
and free running during fastening upon adjustment.
FIG. 12 shows the fifth embodiment of the multi-beam light source unit. When
the position of the emission point of a multi-beam semiconductor laser
11
is greatly offset from the center O of rotation of a laser holder
11a
due to low component precision, the multi-beam semiconductor laser
11
is adjusted again in the laser holder
11a. To realize this, an adjustment
member
15 for adjusting the relative position is used and fastened to the
laser holder
11a with screws
16.
The adjustment member
15 is relatively moved together with the multi-beam
semiconductor laser
11 with respect to the laser holder
11a to
adjust a laser array connecting laser beams P
1 and P
2 so
as to pass through the center O of rotation. Then, the adjustment member
15
is fastened to the laser holder
11a with the screws
16.
Even if the positional precision of emission points varies in the component,
the adjustment member
15 can adjust the positions of the emission points
to locate them on straight lines L
1 to L
3 connecting fixing
portions
14a to
14c or within the planar region N defined
by all the straight lines L
1 to L
3, as shown in FIG. 11A.
The package shape of the multi-beam semiconductor laser can advantageously be
selected from a wide range.
The edge-emission-type multi-beam semiconductor laser
11 on which a plurality
of emission points are aligned may be replaced with a multi-beam semiconductor
laser
41 having a surface-emission-type laser chip
42 on which a
plurality of emission points
42a to
42d are two-dimensionally
arrayed, as shown in FIG. 10. This multi-beam semiconductor laser
41 can
advantageously reduce optical aberration because all the emission points can be
made close to the optical axis of the collimator lens. A positioning hole
41b
is formed in a disk-like laser holder
41a as a positioning reference
used to adjust the inclination angle θ for adjusting line intervals T
1
to T
3.
The surface-emission-type laser can increase the degree of freedom for the positions
of the emission points to facilitate distribution of the mounting tolerance.
As described above, in the multi-beam scanning apparatus of the present invention,
the two laser beams P
1 and P
2 emitted by the multi-beam semiconductor
laser are scanned by the rotary polygon mirror inside the optical box
8,
and form an image on the photosensitive member on the rotary drum via the imaging
lens. To adjust the line interval and the like on the photosensitive member, the
laser holder
11a is fixed to the sidewall
8a of the
optical box
8 after rotation through a predetermined angle. The fixing portions
14a to
14c are set to locate the emission points of
the laser beams P
1 and P
2 and the center O of rotation on
straight lines connecting the fixing portions
14a to
14c
by the screws
14 or within the planar region N defined by these lines.
The laser holder
11a is firmly, stably mounted with high positional precision.
With this arrangement, the present invention exhibits the following effects.
The line interval between a plurality of laser beams emitted by the multi-beam
semiconductor laser can be adjusted with high precision, and the laser holder can
be firmly, stably mounted.
The present invention can realize a low-cost, high-performance multi-beam scanning
apparatus free from any multi-beam line interval error.
*
