JP2001100129A - Optical writing scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unify the polarization directions of plural laser beams in a main scanning direction. SOLUTION: The two laser beams P1 and P2 generated from a multi beam semiconductor laser 11 are scan-deflected by a rotary polygon mirror 3, and image-formed on the photoreceptor on a rotating drum 5 through an image forming lens 4. When the polarization directions of the beams P1 and P2 are different from each other, a spot diameter on the drum 5 is deformed, and light quantity irregularity occurs, so that the polarization directions of the beams P1 and P2 obtained after the beams P1 and P2 are transmitted through a polarizing plate 1a become the same direction of the main scanning direction by the mirror 3 by integrally providing the plate 1a with a cylindrical lens 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing / scanning apparatus used for a laser beam printer, a digital copying machine, or the like.

[0002]

2. Description of the Related Art In recent years, in an electrophotographic apparatus such as a laser beam printer, an optical writing / scanning apparatus for simultaneously writing a plurality of lines using a plurality of light beams has been developed.

In this method, a plurality of light beams separated from each other are simultaneously scanned. As shown in FIG. 7, two light beams are emitted from a multi-beam semiconductor laser 111 which is a light source of a multi-beam light source unit 101. Beam P
₁ and P ₂ are generated, and the collimator lens 112
After being collimated by the cylindrical lens 10
Then, the light is irradiated onto the reflection surface 103a of the rotary polygon mirror 103 through the imaging lens 104 to form an image on the photosensitive member on the rotating drum 105 via the imaging lens 104.

The two laser beams P ₁ and P ₂ are incident on the reflection surface 103 a of the rotary polygon mirror 103, are scanned in the main scanning direction, and are scanned by the rotation of the rotary polygon mirror 103 and the rotation of the rotary drum 105. An electrostatic latent image is formed on the photoconductor with the sub-scan.

The cylindrical lens 102 transmits the laser beams P ₁ and P ₂ to the reflecting surface 1 of the rotating polygon mirror 103.
The light is condensed linearly on 03a. This has a function of preventing the point image formed on the photoconductor from being distorted due to the tilting of the rotary polygon mirror 103 as described above, and the imaging lens 104 has a spherical lens unit. It has a function of preventing the distortion of a point image on the photoconductor similarly to the cylindrical lens 102, and has a function of correcting the point image to be scanned at a constant speed in the main scanning direction on the photoconductor. Having.

[0006] The two laser beams P ₁ and P ₂ are separated by a detection mirror 106 at the end of the main scanning plane, respectively, introduced into the optical sensor 107 on the opposite side of the main scanning plane, and written by a controller (not shown). The signal is converted into a signal and transmitted to the multi-beam semiconductor laser 111.
Upon receiving the write start signal, the multi-beam semiconductor laser 111 starts write modulation of both laser beams P ₁ and P ₂ .

By adjusting the timing of the write modulation of the two laser beams P ₁ and P _{2 in} this manner, the write start (write) position of the electrostatic latent image formed on the photoconductor on the rotating drum 105 is controlled. .

[0008] The cylindrical lens 102, the rotating polygon mirror 103, the imaging lens 104 and the like are mounted on the bottom wall of the optical box 108. After assembling the optical components into the optical box 108, the upper opening of the optical box 108 is closed by a lid member (not shown).

The multi-beam semiconductor laser 111 emits a plurality of laser beams P ₁ and P ₂ at the same time as described above, and is integrally connected to a lens barrel 112a containing a collimator lens 112 via a laser holder 111a. Is assembled on the side wall 108a of the optical box 108.

When assembling the multi-beam light source unit 101, the laser holder 111a holding the multi-beam semiconductor laser 111 is attached to the side wall 108 of the optical box 108.
a into the opening 108b provided in the laser holder 1
The lens barrel 112a of the collimator lens 112 is placed over the lens holder 11a, the focus of the collimator lens 112 is adjusted and the optical axis is adjusted.
Then, the entire multi-beam light source unit 101 including the laser holder 111a is rotated by a small angle θ as shown in FIG.

This involves adjusting the beam interval between the _two laser beams P ₁ and P ₂ generated from the multi-beam semiconductor laser 111 as shown in FIG. This is an adjustment operation for adjusting the separation distance S in the main scanning direction and the separation distance in the sub-scanning direction, that is, the line interval T, of A ₁ and A ₂ to the designed value. After performing this operation, the laser holder 111a is fixed to the side wall 108a of the optical box 108 using screws or the like.

[0012]

However, according to the above-mentioned prior art, a multi-beam semiconductor laser, which is a light source having a plurality of light-emitting points, is not suitable for manufacturing or structural reasons.
There is a problem that the polarization direction (polarization plane) does not always match for each of these light emitting points. In the above-described writing optical system, the difference in the polarization direction of each light beam makes the reflection and transmission characteristics of optical components such as a rotary polygon mirror and an imaging lens different, and each light beam is individually exposed to the photosensitive drum of the rotating drum. This causes unevenness in light amount of spots to be written on the top, irregularities in spot diameters, etc., and also deteriorates scanning pitch accuracy and the like, causing print quality to be significantly impaired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned unresolved problems of the prior art, and has been made in consideration of the non-uniform light amount and spot of a point image due to a difference in polarization direction of a plurality of light beams generated from a multi-beam semiconductor laser. An object of the present invention is to provide an optical writing / scanning apparatus capable of realizing stable and high image quality such as scanning pitch accuracy while avoiding irregular diameters and the like.

[0014]

In order to achieve the above object, an optical writing / scanning apparatus according to the present invention comprises a light source having a multi-beam semiconductor laser for generating a plurality of light beams, and a light source for deflecting the plurality of light beams. A scanning imaging optical system for deflecting and scanning by the scanning means to form an image on an imaging surface; and a polarizing plate disposed on an optical path of the plurality of light beams from the multi-beam semiconductor laser to the deflection scanning means. The polarizing plates are configured so that the polarization planes of the plurality of light beams are unified in the same direction.

Preferably, the polarizing plate is integrated with a cylindrical lens for condensing a plurality of light beams in a linear manner.

[0016] The polarizing plate may be provided in the vicinity of the collimator lens constituting the light source together with the multi-beam semiconductor laser.

[0017] The polarizing plate may be arranged in the vicinity of the optical stop constituting the light source together with the multi-beam semiconductor laser.

[0018] A polarizing plate may be provided at the window of the multi-beam semiconductor laser.

[0019]

A polarizing plate that transmits only energy in the same polarization direction to a cylindrical lens, a collimator lens, an optical aperture, or a window of a multibeam semiconductor laser in an optical path from a multibeam semiconductor laser to a deflection scanning means such as a rotary polygon mirror. To unify the polarization planes of a plurality of light beams generated from the multi-beam semiconductor laser in the same direction.

It is possible to avoid the occurrence of uneven light quantity and the irregular spot diameter due to the difference in the polarization direction of a plurality of light beams, and to realize a very high quality printing performance which is clear and has stable scanning pitch accuracy. .

[0021]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an optical writing and scanning apparatus according to an embodiment, which is composed of two light beams, ie, laser beams P ₁ and P ₁ from a multi-beam semiconductor laser 11 of a multi-beam light source unit 1 as a light source. P ₂ is generated,
After being collimated by the collimator lens 12, the cylindrical lens 2 is integrated with the polarizing plate 1a.
Through the reflecting surface 3a of the rotary polygon mirror 3, which is a deflection scanning means.
To form an image on a photosensitive member which is an image forming surface on a rotating drum 5 via an image forming lens 4 which forms a scanning image forming optical system 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 and are respectively scanned in the main scanning direction.
The electrostatic latent image is formed on the photosensitive member with the sub-scanning due to the rotation of.

The cylindrical lens 2 condenses the laser beams P ₁ and P ₂ linearly on the reflection surface 3 a of the rotary polygon mirror 3. This has the function of preventing the point image formed on the photoreceptor from being distorted due to the tilting of the rotary polygon mirror 3 as described above, and the imaging lens 4 is provided with a spherical lens unit. A function of preventing a distortion of a point image on the photoconductor, similarly to the cylindrical lens 2, and a function of correcting the point image to be scanned at a constant speed in the main scanning direction on the photoconductor. Having.

The two laser beams P ₁ and P ₂ are separated by the detection mirror 6 at the end of the main scanning plane, respectively.
The light is introduced into the optical sensor 7 on the opposite side of the main scanning surface, converted into a write start signal by a controller (not shown), and transmitted to the multi-beam semiconductor laser 11. Upon receiving the write start signal, the multi-beam semiconductor laser 11 starts write modulation of both laser beams P ₁ and P ₂ .

By adjusting the timing of the write modulation of the two laser beams P ₁ and P _{2 in} this manner, the write start (write) position of the electrostatic latent image formed on the photoconductor on the rotating drum 5 is controlled. .

A cylindrical lens 2, a rotary polygon mirror 3,
The imaging lens 4 and the like are mounted on the bottom wall of the optical box 8 as a housing. After assembling each optical component into the optical box 8,
The upper opening of the optical box 8 is closed by a lid member (not shown).

The multi-beam semiconductor laser 11 has the above-described structure.
So that multiple laser beams P₁ , P _Two Flash at the same time
And a collimator lens via a laser holder 11a.
Unit 12 integrally connected to a lens barrel 12a containing
Of the optical box 8 together with the laser drive circuit board 13
It is assembled to the side wall 8a.

When assembling the multi-beam light source unit 1, a laser holder 11a for holding the multi-beam semiconductor laser 11 is inserted into an opening 8b provided on the side wall 8a of the optical box 8, and the mirror of the collimator lens 12 is mounted on the laser holder 11a. After three-dimensional adjustment such as focus adjustment and optical axis alignment of the collimator lens 12 is performed by covering the cylinder 12a, the lens barrel 12a is bonded to the laser holder 11a.

As shown in FIG. 2, the multi-beam semiconductor laser 11 has a submount 21 integrated with a stem 21.
a laser chip 22 fixed to a
A photodiode 23 for monitoring the light emission amounts of the laser beams P ₁ and P ₂ emitted from the two light emitting points 22a and 22b, and an energizing terminal 24 for energizing the laser chip 22 and the like. Is covered by a cap 25.

In the step of assembling the multi-beam light source unit 1 into the optical box 8, the multi-beam light source unit 1 is rotated so that the two laser beams P ₁ and P _{2 form} respective image forming points (spots) on the rotating drum 5. An adjustment operation is performed to match the line spacing of ()) with the design value.

The polarizing plate 1a integrated with the cylindrical lens 2 cuts the energy components of the laser beams P ₁ and P _{2 having} different polarization directions to unify the polarization directions when forming an image on the photosensitive member. belongs to.

As shown in (a) of FIG. 3, the multi-beam semiconductor laser 11 having a sub-mount 21a on the laser chip 22 and the electrode 21b is emits light with a linear polarization, the laser beams P _1, The direction of the electric vector of P ₂ , that is, the polarization direction is basically the direction of arrows Da and Db just beside the laser crystal stacking direction (vertical direction in the drawing), which is a desired normal one.

In practice, however, as shown in FIG. 3 (b), the direction of polarization is often not at the side of the light perpendicular to the crystal stacking direction but at a certain angle for each light emitting point.
The polarization directions of the actual laser beams P ₁ and P ₂ are different in angle from the arrow directions D ₁ and D _2, and a relative difference is generated. These are due to residual stress when the laser chip 22 is attached by soldering, and that the laser structure itself is distorted during crystal growth and internal stress is generated. That is, when various mechanical stresses are applied to the individual light emitting points, the polarization directions become non-uniform.

When the polarization direction varies from one light emitting point to another as described above, the light amount of the writing beam for scanning the photosensitive member is not constant due to the influence of the transmission characteristics of the imaging lens and the like, and the spot diameter of the light beam is not uniform. This causes a problem that the pitch of the scanning lines is not uniform.

Therefore, in this embodiment, a plurality of laser beams P are added by adding a polarizing plate 1a to the optical path from the multi-beam semiconductor laser 11 to the rotary polygon mirror 3.
₁ and P ₂ are unified in the same polarization direction.

By mounting the polarizing plate 1a in close contact with the cylindrical lens 2, as shown in FIG. 4, the initial polarization directions D ₁ and D ₂ can be aligned in the same direction as Da and Db, respectively.

The polarizing plate 1a used here transmits only the same polarization component whose polarization direction Da, Db is the same as the main scanning direction of the rotating polygon mirror 3 and the imaging lens 4 thereafter, and each laser It is important to play the role of unifying the polarization directions of the beams P ₁ and P ₂ . By unifying the polarization directions of the laser beams P ₁ and P _{2 in} the main scanning direction in this way, it is possible to obtain extremely high print quality.

After each laser beam has passed through the polarizing plate, the energy (light amount) of the remaining component cannot be transmitted because a specific polarized component is transmitted. Since the amounts thereof depend on the degree of the angle of the polarization direction before transmission, the light amount of the device is preferably set to a desired specified value after passing through the polarizing plate.

When a plurality of light-emitting points of a multi-beam semiconductor laser are arranged in a straight line, the whole is inclined at a small angle in order to adjust the line interval of the scanning lines as described above. Since this angle is minute and almost parallel, it can be considered that the polarization direction of the polarizing plate is substantially the same in practical use. Therefore, the loss in light quantity is not large.

FIG. 5 shows a configuration in which the polarizing plate 31 a is assembled in contact with the collimator lens 12 or the optical stop 14 of the multi-beam light source unit 1. The optical diaphragm 14 is a component indispensably used in the multi-beam light source unit 1. A polarizing plate 31a is added thereto with an adhesive or the like, and the polarization direction of the laser beam immediately after being parallelized is defined as the main scanning direction. A function of aligning the polarization directions in the same direction Da and Db is provided.

Alternatively, as shown in FIG. 6, a polarizing plate 41a is provided on the window of the cap 45 of the multi-beam semiconductor laser 41.
May be provided. In this case, the polarizing plate 31a is attached in close contact with a flat glass window, which is a window of the multi-beam semiconductor laser 41, or integrally with the glass window.

The polarization direction of each laser beam can be aligned with the main scanning direction, as in the case where the laser beam is mounted on an optical stop or the like.

The arrangement of the light emitting points of the multi-beam semiconductor laser is not limited to those arranged linearly, but a multi-beam semiconductor laser arranged two-dimensionally may be used.

[0045]

Since the present invention is configured as described above, the following effects can be obtained.

By unifying the polarization planes of a plurality of light beams in the same direction, it is possible to avoid unevenness in the amount of light of a point image on the photoreceptor, irregularities in the spot diameter, and a decrease in scanning pitch accuracy.

As a result, it is possible to realize an optical writing / scanning apparatus having high printing quality and excellent printing performance without variation in scanning pitch.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an optical writing scanning device according to an embodiment.

FIG. 2 is an enlarged perspective view showing the multi-beam semiconductor laser of the apparatus of FIG. 1 in an enlarged manner.

FIG. 3 is a diagram illustrating a polarization direction of each laser beam.

FIG. 4 is a diagram illustrating a polarization direction of a laser beam that has passed through a polarizing plate.

FIG. 5 is a diagram showing a modification.

FIG. 6 is a diagram showing another modification.

FIG. 7 is a schematic plan view showing an optical writing / scanning device according to a conventional example.

FIG. 8 is a diagram illustrating an operation of adjusting a beam interval in the apparatus of FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multi-beam light source unit 1a, 31a, 41a Polarizer 2 Cylindrical lens 3 Rotating polygon mirror 4 Imaging lens 8 Optical box 11, 41 Multi-beam semiconductor laser 12 Collimator lens 14 Optical diaphragm 21 Stem 22 Laser chip 25, 45 Cap

Continued on the front page F term (reference) 2C362 AA03 AA13 AA14 AA45 AA48 BA58 BA61 BA83 BA84 BA90 DA03 2H045 AA01 BA22 CA88 CA98 CB02 CB22 CB24 CB33 DA02 DA04 DA24

Claims (7)

[Claims] A light source having a multi-beam semiconductor laser for generating a plurality of light beams; a scanning image forming optical system for deflecting and scanning each of the plurality of light beams by a deflecting scanning means to form an image on an image forming surface; A polarizing plate disposed on an optical path of the plurality of light beams from the multi-beam semiconductor laser to the deflection scanning unit, whereby the polarizing planes of the plurality of light beams are unified in the same direction. An optical writing / scanning device characterized by being configured as described above. 2. The optical writing and scanning device according to claim 1, wherein the polarizing plate is integrated with a cylindrical lens that condenses each of the plurality of light beams linearly. 3. The optical writing / scanning device according to claim 1, wherein the polarizing plate is disposed near a collimator lens constituting a light source together with the multi-beam semiconductor laser. 4. The optical writing / scanning device according to claim 1, wherein the polarizing plate is disposed near an optical stop constituting a light source together with the multi-beam semiconductor laser. 5. The optical writing and scanning device according to claim 1, wherein the polarizing plate is provided in a window of the multi-beam semiconductor laser. 6. The optical writing scanning device according to claim 1, wherein the multi-beam semiconductor laser has light emitting points arranged two-dimensionally. 7. The optical writing / scanning apparatus according to claim 1, wherein the polarization planes of the plurality of light beams are configured to be unified in the main scanning direction by a polarizing plate. .