JP2002139884A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an image forming device having compact and inexpensive constitution capable of improving productivity in a black-and-white mode and easily aligning a write position in a color mode. SOLUTION: In this image forming device, an optical write device 5 is equipped with a light source unit for black 54 having multibeam constitution and three light source units for color 52, 53 and 55 having one-beam constitution, and uses only the light source unit for black so as to write a latent image by plural light beams on an image carrier for black 4 in the black-and-white mode, and uses the light source unit for black and three light source units for color so as to write the latent image on the image carriers 1 to 4 in the color mode. In the color mode, the light source unit for black uses only one previously regulated beam out of plural light beams so as to align the write position by three light beams for color L1 to L3 by setting the write position by the light beam L4 as reference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes an optical writing device for writing a latent image by irradiating a light beam onto a surface to be scanned of a plurality of image carriers arranged in parallel, and forming the image on the plurality of image carriers. The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a plotter that forms a multicolor image by developing latent images formed with developers of different colors and sequentially transferring the latent images to transfer materials.

[0002]

2. Description of the Related Art Conventionally, light beams emitted from a plurality of light sources are applied to four image bearing members (for example, photosensitive drums) arranged side by side to write a latent image thereon, and each image bearing member is subjected to writing. After the latent images formed on the sheet are developed with respective developers of different colors (for example, yellow, magenta, cyan, and black toners) to be visualized, the transfer of a recording sheet or the like carried on a transfer conveyance belt or the like is performed. The material is sequentially conveyed to the transfer section of each image carrier, and the visible images of each color formed on each image carrier are superimposed and transferred on the transfer material, and then the image transferred on the transfer material is fixed. A tandem type color image forming apparatus that obtains a multicolor image by using a tandem type is known. In such a tandem type color image forming apparatus, a type in which a latent image is written on each image carrier separately by an optical writing device individually provided for each image carrier is conventionally known. An optical writing device using an optical deflector composed of a polygon mirror and a motor for driving the polygon mirror is relatively expensive. Providing an optical writing device individually for each image carrier is costly in terms of parts costs and manufacturing costs. There's a problem. In addition, a large installation space is required to install a plurality of optical writing devices each having an optical deflector corresponding to the number of image carriers, and thus there is a problem that the entire image forming apparatus becomes large.

In order to reduce the cost and size of the tandem type color image forming apparatus, an optical deflector is shared by a plurality of light sources as a means for performing optical writing on a plurality of image carriers. 2. Description of the Related Art There is known an optical writing apparatus that deflects and scans light beams from a plurality of light sources at the same time by an optical deflector and irradiates a plurality of image carriers with light to perform optical writing.

[0004]

As described above, an optical writing apparatus for simultaneously deflecting and scanning light beams from a plurality of light sources and irradiating a plurality of image carriers with one optical deflector to perform optical writing is described below. A plurality of light source units, one optical deflector, and a plurality of light beams which are arranged symmetrically in two directions about the optical deflector and which are deflected and scanned by the optical deflector are respectively guided on the corresponding surfaces to be scanned. And a configuration in which these optical members are housed in one housing, so that the number of parts can be reduced compared to a configuration having a plurality of conventional optical writing devices, and installation is possible. Since the space can be reduced, the cost and size of the image forming apparatus can be reduced.

[0005] In the case of an image forming apparatus provided with the optical writing device having the above-described configuration and forming a full-color image, usually, a plurality of light source units for black and three light source units for color ( For example, light source units for cyan, magenta, and yellow are provided. In the black and white mode for forming a black and white image, only the light source unit for black is used. In the color mode for forming a color image, the above four light source units are used. used. In the color mode, four light source units for black and color are used, and light beams from the four light source units are simultaneously deflected and scanned by one optical deflector to irradiate four image carriers. Optical writing is performed. In this case, it is important to match the writing positions by the four beams, and if the writing positions are shifted, it causes color shift. For this reason, the four light source units usually have one light source with one light source so that the writing position can be easily adjusted.

[0006] Even in the color image forming apparatus having the above-described configuration, since it is usually frequently used to form a black-and-white image such as a document or a diagram, the productivity (printing per unit time) in the black-and-white mode is high. There is a demand to improve the number. Therefore, in order to improve the productivity in the black and white mode, a multi-beam configuration having a plurality of light sources (semiconductor lasers) only for the black light source unit is used to increase the writing speed. However, there is a problem in that it is difficult to align the position with the writing position of the beam from the three light source units, which causes a color shift.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, has a small and low-cost configuration, can improve productivity in a monochrome mode, and can easily align a writing position in a color mode. It is an object of the present invention to provide an image forming apparatus having a configuration capable of performing the operation. In addition, the present invention provides an image forming apparatus having a configuration in which the pixel density can be switched in addition to the above object, and the writing position can be easily aligned in the color mode even when the pixel density is switched. With the goal.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a plurality of image carriers arranged side by side, and a light beam is irradiated on a surface to be scanned of the plurality of image carriers. Optical writing means for irradiating and writing a latent image; developing means for developing the latent image formed on each image carrier with a developer of a different color to make it a visible image; Transfer transfer means for sequentially transferring the transfer material and transferring the visible image of each color formed on each image carrier on the transfer material by superimposing, and fixing means for fixing the image transferred on the transfer material, As the optical writing means,
The light beams from the plurality of light source units are distributed in one symmetrical direction by one optical deflector and deflectively scanned, and a plurality of light beams are transmitted through the optical system symmetrically arranged in the two directions with respect to the optical deflector. An image forming apparatus comprising an optical writing device configured to guide a light beam onto a scan surface of a corresponding image carrier to form an image, wherein the optical writing device includes a plurality of light source units as a light source unit for black. And three light source units for color, the light source unit for black has a multi-beam configuration having a plurality of light sources, and the three light source units for color have a one-beam configuration having one light source each. In the black-and-white mode, using only the black light source unit, writing a latent image with a plurality of light beams on the black image carrier,
In the color mode, a black light source unit and three color light source units are used to write latent images of each color on four image carriers. In the color mode, the black light source is used. The unit uses only one predefined beam of the plurality of light beams, and positions the writing positions of the light beams of the three light source units for color on the basis of the writing position of the light source unit for black by the light beam. Is performed.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the pixel density can be switched between the black and white mode and the color mode. Means for switching the beam pitch of the beam in the sub-scanning direction in accordance with the pixel density; in the color mode, the beam pitch of the black light source unit is fixed at a beam pitch of a predetermined pixel density; Using only one specified beam, the writing positions of the light beams of the three color light source units are aligned with reference to the writing position of the black light source unit by the light beam. According to the third aspect of the invention, in the image forming apparatus according to the first aspect, it is possible to switch the pixel density between the first pixel density and the second pixel density in both the black and white mode and the color mode. In the color mode, the beam pitch of the plurality of light beams in the sub-scanning direction of the light source unit for black is the first regardless of the selected pixel density.
Fixed at a beam pitch at a pixel density of 3 pixels, using only one predetermined beam among a plurality of light beams, and three color light sources based on the writing position of the black light source unit by the light beam. The writing position of the light beam of the unit is aligned.

[0010] Further, in the invention according to claim 4, claim 1 is provided.
In the image forming apparatus described above, it is possible to switch the pixel density in both the monochrome mode and the color mode, and the light source unit for black adjusts the beam pitch in the sub-scanning direction of a plurality of light beams in the monochrome mode according to the pixel density. In the color mode, the black light source unit uses only a predetermined one of a plurality of light beams, and based on the writing position of the black light source unit by the light beam, the color light source unit is used as a reference. The configuration is such that the writing positions of the light beams of the three light source units are electrically adjusted. According to a fifth aspect of the present invention, in the image forming apparatus of the first aspect, it is possible to switch the pixel density in both the black and white mode and the color mode, and the light source unit for black includes a plurality of light beams in the black and white mode. Means for switching the beam pitch in the sub-scanning direction according to the pixel density with reference to the position of one light beam defined in advance. In the color mode, the light source unit for black becomes the reference among a plurality of light beams. The position of the light beam writing position of the three color light source units is adjusted using the light beam of the position and the writing position of the black light source unit by the light beam as a reference.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction, operation and operation of an image forming apparatus according to the present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is a schematic configuration diagram of an image forming apparatus showing an embodiment of the present invention, and FIG. 2 is a diagram showing an example of an optical writing apparatus provided in the image forming apparatus shown in FIG. FIG. 3 is a plan view showing the configuration of the upper surface side of the substrate of the apparatus, and FIG.
FIG. 3 is a cross-sectional view illustrating a cross-sectional configuration taken along line AA ′ of the optical writing device illustrated in FIG. 2. FIG. 4 shows a light source unit, an optical deflector and an optical system extracted from the configuration of the optical writing apparatus shown in FIG. 2 and shows the arrangement thereof. FIG. 5 shows the arrangement of the optical writing apparatus shown in FIG. FIG. 2 shows an arrangement configuration of an optical deflector and an optical system extracted from the configuration.

The image forming apparatus shown in FIG. 1 is a full-color image forming apparatus in which a plurality of drum-shaped photoconductive photosensitive members (hereinafter, photosensitive drums) 1, 2, 3, and 4 are arranged as a plurality of image carriers. And the four photosensitive drums 1, 2, 3,
Reference numeral 4 denotes, for example, for forming images corresponding to yellow (Y), magenta (M), cyan (C), and black (Bk) in order from the right to the figure (the order of the colors is It is possible to set it arbitrarily instead of as much as possible). A charging unit (a charging roller, a charging brush, a charging charger, and the like) for forming an image by an electrophotographic process is provided around each of the four photosensitive drums 1, 2, 3, and 4.
6, 7, 8, 9 and the light beam L1,
L2, L3, L4 exposure part and development part (Y, M, C, B
k, developing devices for each color) 10, 11, 12, 13 and transfer means (transfer rollers, transfer brushes, etc.) 14, 15, 16, 17 disposed on the transfer / conveying belt 22 a and the back surface thereof.
And a cleaning unit (cleaning blade, cleaning brush, etc.) 18, 19,
Reference numerals 20, 21 and the like are provided so that images of respective colors can be formed on the respective photosensitive drums 1, 2, 3, and 4.

More specifically, in FIG. 1, when the Z direction in FIG. 1 is a vertical upward direction and the X and Y directions are horizontal directions, the direction in which the four photosensitive drums 1, 2, 3, 4 are juxtaposed is The transfer conveyance device 22 is inclined with respect to the horizontal plane (in FIG. 1, inclined with respect to the X direction). The transfer material is arranged so as to be inclined with respect to the horizontal plane so as to be parallel, and the transfer material is fed from the lower side in the direction of inclination and the four photosensitive drums 1, 2, 3, and 4 are directed upward by the transfer conveyor belt 22a. The fixing device 26 is disposed on the downstream side in the conveying direction of the transfer material and on the upper side in the inclined direction. The optical writing device 5 is disposed obliquely above an image forming unit in which four photosensitive drums 1, 2, 3, and 4 are juxtaposed, and the housing 50 of the optical writing device 5 includes four photosensitive drums. The drums 1, 2, 3, 4 are arranged obliquely with respect to a horizontal plane (X direction in the figure) so as to be substantially parallel to the juxtaposition direction of the body drums 1, 2, 3, 4.
30.

Here, the optical writing device 5 is shown in FIGS.
5, four light source units 52, 5
3, 54, 55, and the light beam L from each light source unit
An optical deflector 62 for deflecting and scanning the light beam L1, L2, L3, and L4 in two symmetrical directions, and symmetrically arranged in the two directions with the optical deflector 62 as a center to be deflected and scanned by the light deflector 62. An optical system (imaging lenses 63, 64, and 6) for guiding the plurality of light beams L1, L2, L3, and L4 onto the scanned surfaces of the corresponding photosensitive drums 1, 2, 3, and 4 to form an image.
9, 70, 71, 72, optical path turning mirrors 65, 6
6,67,68,73,74,75,76,77,7
8, 79, 80 etc.).
These components are housed in one housing 50.

More specifically, the housing 50 includes a base 50A on which the optical deflector 62 and the optical system are disposed, and a base 50A.
A has a frame-shaped side wall 50B surrounding the periphery of A, and a base 50A is provided at a substantially central portion of the side wall 50B to partition the housing 50 up and down. The four light source units 52, 53, 54, 55 Side wall 50B of housing 50
And the optical deflector 62 is mounted on the base 50 of the housing 50.
An optical member (imaging lenses 63, 64, 69, 70, 71, 72,
Optical path turning mirrors 65, 66, 67, 68, 73,
74, 75, 76, 77, 78, 79, 80, etc.) are disposed separately on both surfaces (upper surface side and lower surface side) of the base 50A. A cover 8 is provided on the upper and lower parts of the housing 50.
The lower cover 87 is provided with an opening through which a light beam passes, and dustproof glass 83, 84, 85, 86 is attached to the opening.

In the optical writing device 5, color-separated image data input from a document reading device (scanner) (not shown) or an image data output device (a personal computer, a word processor, a facsimile receiving unit, etc.) is used for driving a light source. The light source (semiconductor laser (LD)) in each of the light source units 52, 53, 54, 55 is driven in accordance with the signal to emit a light beam. The light beams emitted from each of the light source units 52, 53, 54, 55 are converted into cylindrical lenses 56, 57,
After passing through 58 and 59, the light reaches a light deflector 62 directly or via mirrors 60 and 61, and is deflected and scanned in two symmetrical directions by two-stage polygon mirrors 62a and 62b rotated at a constant speed by a polygon motor 62c. . In the configurations shown in FIGS. 3 and 5, the polygon mirrors are used for the light beams L2 and L3, and for the light beams L1 and L3.
Although the configuration is divided into two upper and lower stages for four light beams, a configuration in which deflection scanning is performed by one thick polygon mirror may be employed.

The polygon mirrors 62a, 62 of the optical deflector 62
The light beams deflected and scanned in two directions by two beams in 2b respectively pass through first imaging lenses 63 and 64 composed of, for example, an upper-lower two-layer fθ lens and the like, and are returned to first folding mirrors 65 and 66, respectively. After being folded by 67 and 68 and passing through the opening of the base 51, the second imaging lenses 69, 70, 71, which are composed of, for example, a long toroidal lens, etc.
72, the second folding mirrors 73, 75, 77,
79, the third folding mirrors 74, 76, 78, 80, and dustproof glasses 83, 84, 85, 86 irradiate the surfaces of the photosensitive drums 1, 2, 3, and 4 for the respective colors to be scanned to form an electrostatic latent image. Write the image.

In the optical writing device 5 having the above configuration, for example, the light source unit 52 is used for the magenta light source unit 53.
Are for yellow, the light source unit 54 is for black, the light source unit 55 is for cyan, and the three light source units 52, 53, 55 for color are one semiconductor laser (LD) as a light source and emission of the semiconductor laser. The light source unit 54 for black, which is composed of a collimating lens for collimating a light beam and integrally incorporated in a holding member such as a holder, is often used in a monochrome mode (black and white image formation). In order to enable high-speed writing for the purpose of improving productivity in the mode, a multi-beam configuration in which a set of two or more light sources (LD) and a collimating lens is integrally held by a holding member. The black light source unit 54 includes means for switching the beam pitch of the plurality of light beams in the sub-scanning direction in the monochrome mode according to the pixel density. Since the three color light source units 52, 53, and 55 have a single beam configuration, only one predefined beam among a plurality of beams is used as the black light source unit 54 in the color mode. The pixel density can be changed even in the color mode. In this case, the pixel density is changed by changing the linear speed of the photosensitive drum, the rotation speed of the optical deflector, or the writing speed of the light source unit.

Here, an example of a multi-beam light source unit used as the light source unit 54 for black is shown in FIGS. FIG. 6 is an exploded perspective view showing the configuration of the multi-beam light source unit, and FIG. 7 is a sectional view of a main part of the multi-beam light source unit. 6 and 7, semiconductor lasers 111 and 112 as light sources are supported on supports 113 and 11 respectively.
4 and using screws 118, 119, etc., with the optical axes of collimating lenses 116, 117 to be described later on the back surface of a base (collimating lens holder) 115 serving as a holding member via the supports 113, 114. Joined.
The collimating lenses 116 and 117 are housed in a lens barrel,
Fitting holes 115a, 11 of collimating lens holder 115
5b are respectively engaged with the semiconductor lasers 111 and 112 so as to be aligned with each other, and are bonded with an adhesive to convert each light beam into a parallel light beam. Further, the collimating lenses 116 and 11
An aperture plate 120 for obtaining a predetermined beam diameter with respect to each emitted light is provided on the emission side of 7, and a beam combining means 121 including a prism or the like is provided in front of the aperture plate 120. .

The two semiconductor lasers 111 and 112 are arranged on the same plane so that their pn junction surfaces coincide with each other.
Either beam (the beam of the semiconductor laser 111 in this example) has its polarization plane rotated by 90 ° by the half-wave plate 122 attached to the incident surface of the beam synthesis means 121, and the beam synthesis means 121 Pass through the polarizing beam splitter surface 121b. Then, the beam of the semiconductor laser 112 is internally reflected by the inclined surface 121 a of the beam combining means 121, reflected by the polarization beam splitter surface 121 b of the beam combining means 121, and becomes a reference semiconductor laser 111.
Near the optical axis of the semiconductor laser 111. A series of optical axes of the semiconductor lasers 111 and 112 are set to be shifted from each other by an angle θ shown on the output side of the beam combining means 121 so as to correspond to a position slightly shifted in the main scanning direction. Have been.

The beam combining means 121 and the aperture plate 120 are
The flange member 123 is supported at a predetermined position on the back surface, and the flange member 123 is fixed to a base (collimating lens holder) 115 by screws 124 and 125. The flange member 123 and / or the base 115 are fixed to a substrate 126 on which a driving circuit for the semiconductor lasers 111 and 112 is formed by screws or the like (not shown).
Each member of the optical path reaching 23 is integrally fixed to the substrate 126 to constitute a light source unit. The cylindrical portion 123a erected on the emission side of the flange member 123 is inserted into the hole 132a of the optical frame 132 provided on the side wall 50B of the housing 50 of the optical writing device 5 and passes through the spring 130. Pass through the hole 131a of the spring pressing plate 131. In this state, the light source unit 54 in which the members from the semiconductor lasers 111 and 112 to the flange member 123 are assembled to the substrate 126 is pulled in the direction of the arrow α in the drawing, and the spring pressing plate 131 is rotated by 90 °. The protrusion 131b of the spring pressing plate 131 is connected to the cylindrical portion 123a.
Hook on the projection 123b. Thereby, the light source unit 54 is mounted on the optical frame 132 by the flange member 1.
It is attached rotatably around the center (optical axis) of the cylindrical portion 123a of 23.

Next, an example of pitch changing means for changing the interval (beam pitch) between light spots in the sub-scanning direction on the photosensitive drum by rotating the light source unit 54 around the optical axis will be described. In FIG. 6, reference numeral 127 denotes a sliding member, and 128 denotes a feed screw. The feed screw 128 is provided with a male screw having a nominal diameter of M3, and the sliding member 127 is provided with an M3 female screw inside. . Also, the sliding member 12
The outer shape of 7 is substantially D-shaped. The male screw of the feed screw 128 is previously inserted into the female screw of the sliding member 127 by rotation, and the sliding member 127 slides in the D-shaped hole of the column 132b provided on the optical frame 132 side of the housing. It can be inserted freely. At this time, the rotary shaft 129a of the pitch variable stepping motor 129 is inserted into the hole of the cylindrical column 132b of the optical frame 132, and the lower end of the feed screw 128 is press-fitted and fixed to the tip of the rotary shaft 129a. It has become so. The pitch variable stepping motor 129 is fixed to the optical frame 132, and by rotating the stepping motor 129, the feed screw 128 press-fitted into the rotation shaft 129a of the motor rotates. Since the hole is D-shaped, the sliding member 127 slides vertically without rotating.

On the other hand, the flange member 1 of the light source unit 54
An arm 123 extends in the direction of the sliding member 127 and abuts on the upper end of the sliding member 127 at the tip.
c is provided between the arm 123c and the optical frame 132. A spring 135 is provided between the arm 123c and the optical frame 132, and the arm 123c is pulled downward by the spring 135. Is the sliding member 12
7 is pressed against a hatched portion which is a plane portion. Therefore, when the sliding member 127 slides in the vertical direction due to the rotation of the stepping motor 129 for changing the pitch, the arm 123c of the flange member 123 is rocked in the vertical direction, and the light source unit 53 is moved to the cylindrical portion of the flange member 123. Rotate around the center of 123a.

As means for controlling the rotation angle of the light source unit 54, an optical home position sensor 133 comprising a photo interrupter having a light emitting portion 133a and a light receiving portion 133b is provided on the optical frame 132 side of the housing.
Are fixed by screws or the like (not shown), and on a part of the flange member 123 on the side opposite to the arm 132b,
A filler 123d having an edge 123e capable of shielding between the light emitting unit 133a and the light receiving unit 133b of the home position sensor 133 is provided. Then, the edge 123e of the filler 123d of the flange member 123
However, the position at the moment when the light emitting unit 133a and the light receiving unit 133b of the home position sensor 133 are shielded is set to be the home position (HP) position.
It is a reference for rotation adjustment.

FIG. 8 shows a method of changing the beam pitch in the sub-scanning direction by adjusting the rotation of the light source unit 54 shown in FIGS. In FIG. 8, the positions of the light emitting portion 133 a and the light receiving portion 133 b of the home position sensor 133 are indicated by broken lines, and the edge 123 e of the shielding filler 123 d provided on the flange member 123 is connected to the light emitting portion 133 a as described above. The position at the moment when the space between the light receiving units 133b is shielded is the home position (HP) position. A position A in the figure is a position where the light source unit 54 is rotated from the home position (HP) by θ ₁ around the cylindrical portion 123 a as a rotation center. In order to obtain this rotation angle θ ₁ , a stepping motor for changing the pitch is used. 129 rotates a predetermined number of pulses, moves the above-mentioned sliding member 127 upward by a predetermined amount, and rotates the light source unit 54. Similarly, in the position B in the figure, the light source unit 54 moves from the home position (HP) to θ ₂ with the cylindrical portion 123a as the rotation center.
This is the rotated position.

FIGS. 9A and 10A show the home position (HP) and the positions A and B, respectively.
FIG. 9A shows an example of the position of the two light spots on the photosensitive drum at the time of FIG. 9A. FIG. 9A shows the center position between the two light beams (first beam and second beam) as the rotation center. FIG. 10A shows an example in which the rotation is adjusted in accordance with the center of rotation with reference to the position of one of the beams from the two semiconductor lasers (first beam). The beam pitch in the sub-scanning direction of the light spot on the photosensitive drum corresponding to the rotation angles θ ₁ and θ ₂ is P1 and P2. That is, by changing the amount of rotation from the home position (HP), the interval (beam pitch) between light spots on the photosensitive drum can be changed, and the amount of rotation is controlled by the stepping motor 129.
H. P. Can be easily controlled by the number of drive pulses from

In the normal case, the beam pitch of the light spot on the photosensitive drum in the sub-scanning direction is changed in accordance with the pixel density.
i) the beam pitch when the: H. when setting the P ₁ = 42 .mu.m P. The number of pulses from: Pa and the sub-scanning direction of the beam pitch when the second pixel density (e.g. 1200 dpi): H. when setting the P ₂ = 21 [mu] m P. Is stored in a memory or the like of a control unit in the image forming apparatus, the stepping motor 129 is rotated according to the required pixel density at the time of image formation, and the light on the photoreceptor is rotated. The beam pitch of the spot in the sub-scanning direction can be easily switched.

Normally, when the power of the image forming apparatus is turned on, the light source unit 54 is positioned at a predetermined position, for example, 600 d.
The rotation is controlled to the rotation angle (position A) at the pixel density of pi. This is because H.O. P. After homing to the position, the number of pulses Pa drives the stepping motor 129 in a predetermined direction, the sub-scanning direction of the beam pitch of the light spot on the photosensitive drum is a light source unit 54 is rotated such that P _1. Thereafter, the rotation angle of the light source unit 54 is recognized in a memory such as in a CPU (Central Processing Unit) of the control unit. When a pixel density of 1200 dpi is required, the stepping motor 129 is moved from the position at 600 dpi to [Pb −Pa], the beam pitch of the light spot on the photoconductor is changed to P _2.
Can be changed to

Next, in the optical writing device 2 having the configuration shown in FIGS. 2 to 5, the optical paths of the light beams L1, L2, L3, and L4 are provided for taking out the light beam at the scanning start position in the main scanning direction. There is provided a synchronization detecting mirror which is not provided, and the light beam reflected by the synchronization detecting mirror is received by the synchronization detectors 81 and 82 as shown by broken lines in FIG. 5, and a synchronization signal for starting scanning is output. . Further, as shown in FIG.
Skew adjusting stepping motors 92, 93 and 94 are provided on the third folding mirrors 74, 76 and 78 arranged on the optical path of the light beam L2 and L3, respectively, with reference to the scanning line position of the light beam L4. Thus, the displacement of the scanning line positions of the light beams L1, L2, and L3 is corrected. The scanning direction of the light beam deflected by the optical deflector 62 is the main scanning direction, which is the axial direction of each photosensitive drum. The direction orthogonal to the main scanning direction is the sub-scanning direction, which is the direction of rotation of the photoconductor drum (the direction of movement of the surface of the photoconductor drum), and the direction of conveyance of the transfer conveyance belt 22a described later. . That is, the width direction of the transfer conveyance belt 22a is the main scanning direction, and the conveyance direction is the sub-scanning direction.

Next, as shown in FIG. 1, below the four photosensitive drums 1, 2, 3 and 4 arranged in parallel, a transfer transport belt 22a stretched over a driving roller and a plurality of driven rollers is arranged. And is conveyed by a driving roller in a direction indicated by an arrow in the figure. Further, a plurality of paper feed units 23 and 24 containing a transfer material such as recording paper are installed in a lower part of the main body of the image forming apparatus. The transfer material stored in the paper feed units 23 and 24 Roller, transport roller, registration roller 25
Is fed to the transfer / transport belt 22a via the transfer belt 22a, and is carried and transported by the transfer / transport belt 22a.

Each of the photosensitive drums 1 and 2 is
Each of the latent images formed on 2, 3, and 4 is developed by each of the developing units 10, 1
Y, M, C, and B are developed with toner of each color of Y, M, C, and Bk to be visualized, and the visualized Y, M, C, and B are developed.
The toner image of each color of k is transferred to the transfer conveyor belt 22 a by the transfer units 14, 15, 16 and 17 of the transfer conveyor 22.
The image is transferred by being superimposed on the transfer material carried thereon.
Then, the transfer material on which the four color images are transferred is fixed to the fixing device 26.
After the image is fixed by the fixing device 26, the image is discharged onto a discharge tray 28 by a discharge roller 27. still,
In the black and white mode, writing is performed only by the black light source unit 54 of the optical writing device 5, and the above-described image forming operation is performed on the black photosensitive drum 1.

As described above, the configuration of the image forming apparatus according to the present invention
Although the operation has been described, in the image forming apparatus having the configuration shown in FIG. 1, the image forming unit in which the four photosensitive drums 1, 2, 3, and 4 are juxtaposed, the optical writing device 5, and the transfer / conveyance device 22 perform image transfer. Since it is compactly housed in the main body of the forming apparatus and is installed obliquely with respect to the horizontal direction (X direction in the figure), the installation space is smaller than in the conventional horizontal arrangement, and a tandem-type collar is provided. Further miniaturization of the image forming apparatus can be achieved.

By the way, in the image forming apparatus having the above-described configuration, as the plurality of light source units, a black light source unit 54 and three color light source units (for example, light source units for magenta, yellow and cyan) 5
2, 53, and 55 are provided. In the black-and-white mode for forming a black-and-white image, only the black light source unit 54 is used, and in the color mode for forming a color image, four light source units 52 to 55 are used. . And
In color mode, a total of 4 for black and 4 for color
Light beams L1 to L4 from the two light source units 52 to 55
Are simultaneously deflected and scanned by one optical deflector 62 to irradiate four photosensitive drums 1, 2, 3, and 4 to perform optical writing.
In this case, it is important to match the writing positions of the four beams L1 to L4. In the image forming apparatus having the above-described configuration, the black light source unit 54 has a multi-beam configuration having two light sources (semiconductor lasers) 111 and 112 in order to improve productivity in the black-and-white mode. But in this case,
In the color mode, three light source units 5 for color are used.
It is necessary to specify which of the two black beams should be used to align the light beam from 2, 53, 55 with the writing position.

Therefore, in the present invention, in the color mode,
The black light source unit 54 uses only one of the two light beams, and three color light source units 52 and 53 based on the writing position of the black light source unit 54 by the light beam. , 55
The writing position of the light beam is adjusted. That is, of the two light sources (semiconductor lasers) 111 and 112 of the black light source unit 54, the light source used in the color mode is defined in advance, and only one beam is used. Based on the writing position by the beam, 3
If the writing positions of the light beams of the two light source units 52, 53, 55 are aligned, the writing positions can be easily adjusted.

However, when the light source unit 54 for black has means for switching the beam pitch according to the pixel density as shown in FIGS. 6 to 8, the light of the light source unit 54 for black is changed by switching the pixel density. Since the writing position of the beam may be shifted, it is necessary to adopt a configuration in which the writing position in the color mode can be easily adjusted even when the pixel density is switched. For example, FIG.
As shown in (A), the light source unit 54 for black is used.
However, in a configuration in which the beam pitch is rotationally adjusted around the center position between two light beams (the first beam and the second beam) as the rotation center, the pixel density is 600 dpi and 1200 dpi.
In both cases, the writing position moves from position A to position B for both the first beam and the second beam.
A position shift by P occurs. For this reason, for example, 600 dpi
The three light source units 52, 5 for color are based on the position of the light beam of the light source unit 54 for black at the time of.
When the pixel density is switched to 1200 dpi in the color mode when the writing positions of the 3,55 light beams have been aligned, the position of the black light beam is shifted to the position A.
From position to position B, and is shifted by ΔP in the sub-scanning direction, causing color shift.

Therefore, according to the present invention, when the black light source unit 54 has means for switching the beam pitch of the two light beams in the sub-scanning direction according to the pixel density in the black and white mode, the black light source unit 54 in the color mode. The beam pitch of the light source unit 54 is set to a predetermined pixel density (for example, 6
00dpi), and uses only one of the two light beams defined in advance. The three light source units for color are used with reference to the writing position of the black light source unit 54 by the light beam. 52,
In this configuration, the writing positions of the light beams 53 and 55 are aligned. More specifically, as shown in FIG. 9B, in the color mode, the selected pixel density (600
Irrespective of dpi, 1200 dpi), the beam pitch in the sub-scanning direction of the two light beams of the light source unit 54 for black is fixed to the beam pitch P1 at a pixel density of, for example, 600 dpi, and is defined in advance among the two light beams. The three light source units 52, 53, and 55 for color are used by using only one beam (for example, the first beam) and using the writing position (position A) of the black light source unit 54 by the first beam as a reference. The writing position of the light beam is adjusted. In this manner, as shown in FIG. 9B, in the color mode, only the first beam of the black light source unit 54 is used, and the writing position is at the position A regardless of the pixel density. The three light source units 52, 5 for color are fixed based on the writing position.
If the writing positions of the 3,55 light beams are aligned, even if the pixel density is switched in the color mode, the writing position does not shift, and color shift can be prevented.

As another means different from the above method, three color light source units 52 and 5 are set based on the writing position of the black light source unit 54 by the light beam.
A configuration may also be adopted in which the writing positions of the 3,55 light beams are electrically adjusted. That is, FIG.
In the case where the writing positions of the light beams of the three light source units 52, 53, 55 for color are aligned with reference to the position of the light beam of the light source unit 54 for black when the pixel density is 600 dpi, When the pixel density is switched to 1200 dpi in the color mode, the position of the light beam for black moves from position A to position B and shifts by ΔP in the sub-scanning direction. Three light source units 5 for color
By electrically shifting the writing timings of the light beams 2, 53, and 55 in the sub-scanning direction, it is possible to match the writing position of the black light beam. More specifically, when the writing positions of the light beams of the three color light source units 52, 53, and 55 are aligned, the pixel density is 600 dpi.
When the pixel density is switched to 1200 dpi, the three light source units 52 for color are moved in accordance with the movement of the position of the light beam for black when the pixel density is switched to 1200 dpi. , 53, and 55, the writing position of the black light beam and the color light beam can be matched even if the pixel density is changed, and the color shift can be achieved. Can be prevented from occurring.

By the way, as shown in FIG.
In the case where the black light source unit 54 is configured to adjust the rotation of the first light beam in accordance with the rotation center with reference to the position of one of the beams (first beams) of the two semiconductor lasers. The alignment of the writing position of the color light beam can be performed more easily.
That is, in the case where the black light source unit 54 switches the beam pitch of the plurality of light beams in the sub-scanning direction in the black and white mode in accordance with the pixel density based on the position of the first beam defined in advance, the color mode Sometimes, as shown in FIG. 10B, the light source unit 5 for black is used.
4 is a reference position (center of rotation) of the two light beams
Light source unit 5 for the black using the first beam of
The writing position of the light beam of the three light source units 52, 53, 55 for color is aligned based on the writing position by the first beam of No. 4. In this configuration, even if the pixel density is switched from 600 dpi to 1200 dpi, the writing position of the first beam is fixed and does not move. Therefore, even when the pixel density is switched in the color mode, the position of the first beam for black is shifted. Without
Since there is no deviation between the light beam writing positions of the three light source units 52, 53, 55 for color, it is possible to prevent the occurrence of color deviation.

[0039]

As described above, in the image forming apparatus according to the first aspect, the optical writing device includes a plurality of light source units for black and a plurality of light source units for color.
The light source unit for black has a multi-beam configuration having a plurality of light sources, and the three light source units for color have a one-beam configuration having one light source. Uses only the light source unit for black, writes latent images with multiple light beams on the image carrier for black, and uses the light source unit for black and three light source units for color in color mode In the color mode, the black light source unit uses only one predefined light beam among a plurality of light beams, and the black Write position of light beam of three color light source units based on write position of light source unit for light beam by light beam Since a structure for aligning, it can be aligned in the writing position of the color mode it is possible to easily form an image without color deviation.

In the image forming apparatus according to the second aspect,
In addition to the configuration of claim 1, it is possible to switch the pixel density in both the black and white mode and the color mode. In the black and white mode, the light source unit for black changes the beam pitch of the plurality of light beams in the sub-scanning direction to the pixel density. In the color mode, the beam pitch of the light source unit for black is fixed at a beam pitch of a predetermined pixel density, and only one of a plurality of light beams is used. The writing position of the light beam of the three light source units for color is aligned with reference to the writing position of the light source unit of the light source unit, so that the writing position shifts even when the pixel density is switched in the color mode. This does not occur, and the occurrence of color shift can be prevented.

In the image forming apparatus according to the third aspect,
In addition to the configuration of claim 1, the pixel density can be switched between the first pixel density and the second pixel density in both the black and white mode and the color mode. Regardless, the beam pitch of the plurality of light beams of the black light source unit in the sub-scanning direction is fixed to the beam pitch at the first pixel density, and only one predefined light beam of the plurality of light beams is used. Since the writing positions of the light beams of the three light source units for color are aligned with reference to the writing position of the light source unit for black using the light beam, writing is performed even when the pixel density is switched in the color mode. It is possible to prevent the occurrence of color shift without causing a position shift.

In the image forming apparatus according to the fourth aspect,
In addition to the configuration of claim 1, it is possible to switch the pixel density in both the black and white mode and the color mode. In the black and white mode, the light source unit for black changes the beam pitch of the plurality of light beams in the sub-scanning direction to the pixel density. In the color mode, the light source unit for black uses only one of a plurality of light beams, which is defined in advance. The writing positions of the light beams of the three light source units are electrically adjusted, so that the writing positions of the black light beam and the color light beam can be matched even when the pixel density is switched. And the occurrence of color misregistration can be prevented.

In the image forming apparatus according to the fifth aspect,
In addition to the configuration of claim 1, it is possible to switch the pixel density in both the monochrome mode and the color mode, and the light source unit for black defines the beam pitch of a plurality of light beams in the sub-scanning direction in the monochrome mode in advance. Means for switching in accordance with the pixel density with reference to the position of one light beam; in the color mode, the light source unit for black uses the light beam at the reference position among the plurality of light beams, and Since the writing position of the light beam of the three light source units for color is adjusted based on the writing position of the light source unit by the light beam, the reference for black is maintained even when the pixel density is switched in the color mode. Since there is no shift in the position of the light beam, the light beam writing position of the three light source units for color Without occurs, the occurrence of color shift can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus showing one embodiment of the present invention.

FIG. 2 is a plan view illustrating an example of an optical writing device included in the image forming apparatus illustrated in FIG. 1 and illustrating a configuration of a top surface side of a base of the optical writing device.

FIG. 3 is a cross-sectional view showing a cross-sectional configuration taken along line AA ′ of the optical writing device shown in FIG. 2;

FIG. 4 is a schematic configuration diagram showing a light source unit, an optical deflector, and an optical system extracted from the configuration of the optical writing device shown in FIG.

FIG. 5 is a schematic configuration diagram showing an arrangement configuration of an optical deflector and an optical system extracted from the configuration of the optical writing device shown in FIG. 3;

FIG. 6 is an exploded perspective view showing a configuration example of a multi-beam light source unit used for a light source unit for black.

FIG. 7 is a cross-sectional view of a main part showing the assembled state of the multi-beam light source unit.

8 is an explanatory diagram of a method of switching the beam pitch in the sub-scanning direction by adjusting the rotation of the multi-beam light source unit having the configuration shown in FIGS.

FIG. 9 is a diagram showing an example of a case where a multi-beam light source unit having the configuration shown in FIGS. 6 to 8 is used to rotate and adjust a beam pitch with a center position between two beams as a rotation center; FIG. 4B is an explanatory diagram in a monochrome mode, and FIG. 4B is an explanatory diagram in a color mode.

FIG. 10 shows a multi-beam light source unit having the configuration shown in FIGS. 6 to 8, in which the beam pitch is rotated by adjusting the position of one of the beams from the two semiconductor lasers (first beam) to the center of rotation. FIGS. 7A and 7B are diagrams illustrating an example of adjustment, in which FIG. 7A is an explanatory diagram in a monochrome mode, and FIG. 7B is an explanatory diagram in a color mode.

[Explanation of symbols]

1, 2, 3, 4: photosensitive drum (image carrier) 5: optical writing device 6, 7, 8, 9: charging unit 10, 11, 12, 13: developing unit (Y, M, C, Bk) 14, 15, 16, 17: transfer means 18, 19, 20, 21: cleaning unit 22: transfer / conveyance device (transfer / conveyance unit) 22a: transfer / conveyor belt 23, 24: paper supply unit 25: Registration rollers 26: Fixing device (fixing unit) 27: Discharge roller 28: Discharge tray 29, 30: Inclined frame of image forming apparatus main body 50: Housing 50A: Base 50B: Side wall 52, 53, 55: For color ( (M, Y, C) light source unit 54: black light source unit 56, 57, 58, 59: cylindrical lens 60, 61: mirror 62: optical deflector 62a, 62b: polygon mirror 62c: Ligon motors 63, 64: first imaging lenses 65, 66, 67, 68: first folding mirrors 69, 70, 71, 72: second imaging lenses 73, 75, 77, 79: second folding Mirrors 74, 76, 78, 80: Third folded mirrors 81, 82: Synchronous detectors 83, 84, 85, 86: Dustproof glass 87, 88: Covers 111, 112: Semiconductor lasers 113, 114: Support body 115: Base (Collimate lens holder) 116, 117: Collimate lens 120: Aperture plate 121: Beam combining means 122: 1/2 wavelength plate 123: Flange member 126: Substrate 127: Sliding member 129: Pitch variable stepping motor (Pitch variable means 130: Spring 131: Spring pressing plate 132: Optical frame of housing 133: Home positive Yonsensa (photo-interrupter)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04N 1/113 H04N 1/04 D 1/23 103 104A F-term (reference) 2C362 BA51 BA53 BA57 BA68 BA70 BA71 BB28 BB46 CA22 CA39 CB02 CB06 CB08 CB14 CB62 2H030 AA01 AB02 AD07 AD08 AD17 BB02 BB16 BB44 BB63 2H076 AB05 AB06 AB12 AB22 AB75 EA01 5C072 AA03 BA01 BA19 HA02 HA06 HA13 HB01 QA14 QA17 XA01 XA05 5C07A02 DDB26ADD DD26 GG12 HH02

Claims (5)

[Claims] A plurality of image carriers arranged side by side; an optical writing means for irradiating a light beam onto a surface to be scanned of the plurality of image carriers to write a latent image; Developing means for developing the formed latent image with a developer of a different color to form a visible image; and sequentially transferring the transfer material to the position of each image carrier, and visualizing each color formed on each image carrier. A transfer unit configured to transfer the image by superimposing the image on the transfer material; and a fixing unit configured to fix the image transferred onto the transfer material. The optical writing unit transmits light beams from a plurality of light source units to one light. The light is deflected and scanned in two directions symmetrical by a deflector, and a plurality of light beams are respectively scanned on the corresponding image carriers through optical systems arranged symmetrically in the two directions with respect to the optical deflector. An image forming apparatus including an optical writing device configured to guide and form an image on a surface, wherein the optical writing device is As a plurality of light source units, a light source unit for black and three light source units for color are provided, and the light source unit for black has a multi-beam configuration having a plurality of light sources, and the three light source units for color are Each of them has a one-beam configuration having one light source. In the black-and-white mode, only the black light source unit is used, a latent image is written on the black image carrier by a plurality of light beams, and in the color mode, A black light source unit and three color light source units, and write latent images of each color on four image carriers. In the color mode,
The black light source unit uses only one predefined beam of the plurality of light beams, and writes the light beams of the three color light source units based on the writing position of the black light source unit by the light beam. An image forming apparatus for performing position alignment. 2. The image forming apparatus according to claim 1, wherein the pixel density can be switched between the monochrome mode and the color mode, and the light source unit for black is provided with a plurality of light beams in the sub-scanning direction in the monochrome mode. A means for switching the beam pitch according to the pixel density is provided. In the color mode, the beam pitch of the black light source unit is fixed at a beam pitch of a predetermined pixel density, and only one of a plurality of light beams is defined in advance. And an image forming apparatus for adjusting the writing positions of the light beams of the three light source units for color with reference to the writing positions of the light source units for black using the light beams. 3. The image forming apparatus according to claim 1, wherein the pixel density can be switched between a first pixel density and a second pixel density in both the black and white mode and the color mode. Regardless of the selected pixel density, the beam pitch of the plurality of light beams of the black light source unit in the sub-scanning direction is fixed to the beam pitch at the first pixel density, and is defined in advance among the plurality of light beams. Using only one beam, the color light source unit is used as a reference for the writing position by the light beam, and the color 3
An image forming apparatus for performing alignment of writing positions of light beams of two light source units. 4. The image forming apparatus according to claim 1, wherein the pixel density can be switched between the black and white mode and the color mode, and the light source unit for black is provided in the black and white mode in the sub-scanning direction of a plurality of light beams. Means for switching the beam pitch in accordance with the pixel density; in the color mode, the black light source unit uses only a predetermined one of a plurality of light beams, and the black light source unit writes with the light beam An image forming apparatus characterized in that, based on the positions, the positions of the writing positions of the light beams of the three light source units for color are electrically adjusted. 5. The image forming apparatus according to claim 1, wherein the pixel density can be switched in both the monochrome mode and the color mode, and the black light source unit in the black-and-white mode in the sub-scanning direction of a plurality of light beams. Means for switching according to the pixel density with reference to the position of one light beam whose beam pitch is defined in advance, and in the color mode, the black light source unit switches the light beam at the reference position among a plurality of light beams. An image forming apparatus, wherein, based on a writing position of a light source unit for black using a light beam as a reference, a writing position of a light beam of three light source units for color is aligned.