JP2007118196A - Image forming apparatus, exposure device, and light source of exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which rationally increases the number of light-emitting points for black by suppressing an increase in cost and which increases a process speed by performing scanning more lines through one scanning operation, and also to provide an exposure device, and a light source of the exposure device. <P>SOLUTION: This image forming apparatus employs the exposure device 12 which collectively scans a plurality of beams from the plurality of light-emitting points of a surface emitting laser array chip 20 by using a polygon mirror. In the image forming apparatus, the chip 20 as the light source is equipped with the total of thirty-five light-emitting points LP which are provided in such a manner that sets of seven points are arranged in five lines. In light-emitting point groups LPY, LPM and LPC for respective colors, that is, yellow, magenta and cyan, the respective seven light-emitting points LP are provided in each line, and the group LPK for black is constituted in such a manner that two lines LPK1 and LPK2 of the light-emitting points have the fourteen light-emitting points LP. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine, and more particularly to an image forming apparatus capable of forming a color image.

Recently, color image forming apparatuses are widely used in image forming apparatuses such as printers and copiers. As a general image forming apparatus of this type, for example, an image forming unit provided for each color of black (K), yellow (Y), magenta (M), and cyan (C) is a transfer medium (intermediate transfer member). 2. Description of the Related Art A so-called tandem type image forming apparatus is known which is arranged to face a transfer belt or a recording sheet. In the tandem type image forming apparatus, images of different colors formed in the respective image forming units are sequentially transferred to a traveling transfer medium and multiplexed to form a color image.
Such a tandem-type image forming apparatus includes an exposure apparatus having a similar configuration for each color image forming unit. If these exposure apparatuses can be shared, the entire apparatus can be reduced in size and the manufacturing cost can be reduced.

In view of this, an image forming apparatus using a so-called multi-beam (multiple beam) exposure apparatus in which a plurality of laser beams are collectively scanned by a rotary polygon mirror (polygon mirror) has been proposed. (For example, see Patent Document 1)
The image forming apparatus disclosed in Patent Document 1 includes a light source having a plurality of light emitting points for each color of yellow (Y), magenta (M), cyan (C), and black (K). Then, the laser beam for each color emitted from these light emitting points is deflected by a single polygon mirror to perform scanning operation and separated for each color by the subsequent optical system, and each of the image forming units for each color It is configured to lead to a photosensitive drum.
The light source is a surface emitting laser array provided with a group of light emitting points each consisting of eight light emitting points for four colors, and is configured in one chip. The eight light-emitting points constituting each light-emitting point group are arranged in a straight line inclined with respect to the main scanning direction or the sub-scanning direction, and scanning operation for each color is performed once for each color by the laser beam from these light-emitting points. Thus, 8 rows can be scanned.

Japanese Patent Laid-Open No. 2005-70067

  By the way, a color image forming apparatus is usually configured to be able to switch between a color mode and a monochrome mode in order to enable rational image formation according to a document. When forming a color image, the amount of toner transferred to the recording paper is large, and the fixing action takes time compared to the case of forming a black and white image. For this reason, the upper limit of the process speed is mainly defined by the capability of the fixing device, and the process speed is also changed when switching between the color mode and the monochrome mode. That is, in the monochrome mode, the process speed is set faster than in the color mode.

Here, in the image forming apparatus using the conventional multi-beam exposure apparatus, the surface emitting laser array of the light source has the same number and arrangement of light emitting points in the light emitting point group for each color for all colors. It has become.
FIG. 7A shows a plan view of a surface emitting laser array chip as a light source. In the surface emitting laser array chip shown in the figure, eight light emitting points LP in which eight light emitting points LP are linearly arranged at predetermined intervals are arranged in four rows in the vertical direction in the figure, and the rows are arranged in order from the upper side in the figure. Light emission point groups LPY, LPM, LPC, and LPK for yellow (Y), magenta (M), cyan (C), and black (K) are configured.
In the case of such a light source configuration, it is necessary to change the main scanning speed in order to switch the process speed between the color mode and the monochrome mode. However, for that purpose, the rotational speed of the polygon mirror must be changed, and a special circuit for switching the rotational speed of the polygon mirror is required. Moreover, it must be rotated stably at a plurality of rotational speeds, and advanced control for maintaining high rotational accuracy is required. As a result, the exposure apparatus is significantly increased in cost. In addition, when the difference in process speed between the color mode and the monochrome mode is large, the rotation speed of the polygon mirror must be significantly increased in the monochrome mode, but there is a limit to the increase in the speed.
Therefore, the number of light emitting points LP is increased only for the light emitting point group LPK for black than the light emitting point groups LPY, LPM, and LPC for other colors, and in the black and white mode, the number of rows is increased by one scanning operation. A configuration for improving the process speed by performing the main scanning is conceivable.

However, when the number of light emitting points LP arranged in a row is simply increased, only the light emitting point group LPK for black has a light emitting point row length longer than the light emitting point groups LPY, LPM, and LPC for other colors. become longer.
FIG. 7B is a plan view of an example of a surface emitting laser array chip in which the number of light emitting points for black is increased in the arrangement direction. This assumes that the process speed in the color mode is 200 mm / s and the process speed in the monochrome mode is 325 mm / s. For other colors corresponding to the speed ratio (about 1: 1.6). The number of light emission points LP of the light emission point group LPK of the black light emission point group LPK is 13 with respect to the number of light emission point LPs of the light emission point groups LPY, LPM, and LPC of 8.
Thus, when the number of light emitting points LP arranged in a row is simply increased, the overall shape of the surface emitting laser array chip is the arrangement of the light emitting points LP of the light emitting point groups LPY, LPM, LPC, LPK. Longer in the direction. As a result, a wasted area as shown by hatching in FIG. 7B is generated, the chip area is unreasonably increased, the number of wafers is reduced in the manufacturing process, the yield is deteriorated, and the cost is increased. There is a problem of being invited.

  The present invention has been made to solve such a technical problem, and can increase the number of light emitting points for black reasonably while suppressing an increase in cost, and more by one scanning operation. It is an object of the present invention to provide an image forming apparatus, an exposure apparatus, and a light source thereof that can improve the process speed by scanning the number of rows.

In order to achieve the above object, an image forming apparatus according to the present invention includes a plurality of image carriers including a black image carrier provided corresponding to a plurality of colors, and a plurality of light emitting points. A light source including a black light-emitting point group for each of a plurality of colors and a light beam group for each color emitted from each light-emitting point group of the light source are collectively collected by a scanning deflection unit. A scanning optical system that performs scanning operation and separates each color and guides it to each image carrier, and the black light emitting point group of the light source has the number of light emitting points for other colors. More, the arrangement of the light emitting points is different from the light emitting point group for other colors.
Here, the light emitting point groups for each color are arranged in a row with the same light emitting points, and the black light emitting point group has more columns than the light emitting point groups for the other colors. Features. In addition, the row of light emitting points constituting the light emitting point for black is provided in parallel in a direction substantially perpendicular to the direction in which the light emitting points are arranged.

Further, in addition to the above-described configuration, a color mode for forming an image using a plurality of image carriers and a monochrome mode for forming an image using only a black image carrier, It is characterized by comprising control means for controlling the light emitting points to be driven more in the monochrome mode than in the color mode.
As another configuration, the monochrome mode includes control means for controlling to drive more rows of light emitting points for black than in the color mode.
Here, in the black-and-white mode having such a configuration, when a plurality of black light emission point columns scan image data discontinuously, inter-row image data between the scanned image data of the light emission point columns is stored. Inter-column image data storage means is provided. As the inter-column image data storage means, a color deviation correction storage means for storing data for color deviation correction in the color mode can be used.

  The exposure apparatus of the present invention includes a light source having a plurality of light emitting point groups each corresponding to a plurality of colors, each composed of a plurality of light emitting points, and a light flux group for each color emitted from each light emitting point group of the light source. And a scanning optical system that separates the colors for each color by a scanning deflection unit such as a rotating polygon mirror, and the specific light emitting point group of the light source has other light emitting points in other numbers. More than the light emission point group, the arrangement of the light emission points is different from the other light emission point groups.

  The light source of the exposure apparatus of the present invention emits a plurality of light beams for a plurality of colors to a scanning optical system that collectively scans a plurality of light beams for a plurality of colors by a scanning deflection unit and separates the light beams into a light beam group for each color. A light source comprising a plurality of light emission points for each color, and a specific light emission point group in the light emission point group has a larger number of light emission points than other light emission point groups, The light emitting point group is different from the arrangement of the light emitting points.

  According to the image forming apparatus, the exposure apparatus, and the light source of the present invention configured as described above, the number of black light emitting points can be increased reasonably while suppressing an increase in cost. Thereby, when forming a black image, the main scanning of a larger number of rows can be performed by a single scanning operation to improve the process speed.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus 1 to which the exemplary embodiment is applied.
The illustrated image forming apparatus 1 is a so-called tandem type digital color machine that forms a color image by a plurality of image forming units 10 (10Y, 10M, 10C, 10K) using an electrophotographic method. The image forming apparatus 1 includes an image forming unit 10 that forms an image of each color, an exposure device 12 that exposes a photosensitive drum 11 that is an image carrier of each image forming unit 10 to form an electrostatic latent image, and And a transfer belt 13 serving as an intermediate transfer member that superposes and carries a toner image carried on the photosensitive drum 11. Four sets of image forming units 10 are provided corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K). Hereinafter, when it is necessary to distinguish between them, they are referred to as image forming units 10Y, 10M, 10C, and 10K. When they are not necessary to be distinguished, they are simply referred to as image forming units 10. Similarly, the photosensitive drum 11 is expressed as the photosensitive drums 11Y, 11M, 11C, and 11K only when necessary, and is expressed as the photosensitive drum 11 in other cases. The photosensitive drum 11K is the black image carrier in the present embodiment.

A primary transfer roll 14 for carrying an image on the transfer belt 13 is provided inside the transfer belt 13 at a position facing the photosensitive drum 11 of each image forming unit 10. In addition, a secondary transfer roll 16 and a counter roll 15 provided inside the transfer belt 13 are disposed opposite to each other at a secondary transfer position where the toner image carried on the transfer belt 13 is transferred to a recording sheet as a recording medium. Has been. Further, a paper feed cassette 17 for storing recording paper and a fixing device 18 for fixing the transferred paper are provided.
Further, the image forming apparatus 1 includes a control unit 40, and all the drive control is performed by the control unit 40.

The image forming unit 10 is configured by arranging various devices for image formation around a photosensitive drum 11 which is an image carrier. That is, a charging device that charges the photosensitive drum 11 around the photosensitive drum 11 along the rotation direction thereof, a developing device that develops a toner image on the photosensitive drum 11 exposed by the exposure device 12, and a transfer belt 13. A cleaner that removes residual toner remaining on the photosensitive drum 11 after the transfer of the toner image to is provided.
Four sets of image forming units 10Y, 10M, 10C, and 10K having such a configuration are provided at regular intervals in a substantially horizontal direction with respect to a substantially linear upper circulation path portion of a transfer belt 13 described later. ing. In this embodiment, the yellow image forming unit 10Y, the magenta image forming unit 10M, the cyan image forming unit 10C, and the black image forming unit 10K are arranged in this order from the upstream side to the downstream side in the moving direction of the transfer belt 13. It is installed.

  As will be described in detail later, the exposure apparatus 12 receives a surface emitting laser array chip 20 (see FIG. 2) having a light emitting point group composed of a plurality of light emitting points, and a plurality of laser beams emitted from the surface emitting laser array chip 20. This is a so-called multi-beam scanning device constituted by a scanning optical system 30 (see FIG. 2) that performs a scanning operation collectively. Then, the photosensitive drums 11Y, 11M, 11C, and 11K are exposed to a plurality of laser beams emitted from the surface emitting laser array chip 20 to form latent images. The driving is performed based on a digital image signal supplied via the control unit 40.

  The transfer belt 13 is formed in an endless belt shape by a synthetic resin film such as polyimide having flexibility. The transfer belt 13 is stretched in a loop by the drive roll 13A, the backup roll 13B, and the like so that the upper circulation path is substantially linear. The four-color image forming portions 10Y, 10M, 10C, and 10K are disposed on the substantially linear upper circulation path of the transfer belt 13 as described above. A primary transfer roll 14 is disposed at a position facing the photosensitive drum 11 of each image forming unit 10 with the transfer belt 13 in between.

The control unit 40 collectively controls the driving of each mechanism of the image forming apparatus 1, converts image information input from an image reading apparatus (IIT), a PC (personal computer), or the like into a digital image signal, and performs exposure. The image is supplied to the apparatus 12, and writing is performed on the transfer belt 13 via each image forming unit 10.
Further, the control unit 40 generates an image signal such as a pattern image for color misregistration control, supplies the image signal to the exposure device 12, causes writing to the transfer belt 13 via each image forming unit 10, and color The detection result of the color misregistration control pattern is acquired from the misregistration sensor 53, the color misregistration amount is analyzed based on the acquired information, and necessary correction is performed.
These functions in the control unit 40 are realized by, for example, a program-controlled CPU (Central Processing Unit). The configuration and function of the control unit 40 will be described in detail later.

  Then, the image forming apparatus 1 is controlled and driven by the control unit 40, and images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K by exposure by the exposure device 12 are transferred onto the transfer belt 13 according to the movement thereof. By superimposing in order, a color toner image is formed. The color toner image formed on the transfer belt 13 is a secondary image in which a secondary transfer roll 16 and a counter roll 15 are arranged to face each other on a recording paper P that is conveyed in synchronization with the movement of the transfer belt 13. Transferred at the transfer section. Thereafter, the recording paper P on which the color toner image has been transferred is conveyed to the fixing device 18 where the color toner image is fixed in the fixing device 18 and discharged to a paper discharge tray provided outside the housing of the image forming apparatus 1. It is what is done.

Next, the configuration of the exposure apparatus 12 will be described in detail.
FIG. 2 is a perspective view showing the overall conceptual configuration of the exposure apparatus 12. 3 is a plan view of the surface emitting laser array chip 20, and FIG. 4 is a diagram for explaining multi-beam scanning by the surface emitting laser array chip 20. As shown in FIG.
The exposure apparatus 12 includes a surface emitting laser array chip 20 as a light source that emits laser beam groups LY, LM, LC, and LK as four luminous flux groups for each color, and the laser beam groups LY, LM, LC, and The scanning optical system 30 is configured to scan the LK and guide the photosensitive drums 11Y, 11M, 11C, and 11K of the image forming units 10Y, 10M, 10C, and 10K, respectively.

The surface emitting laser array chip 20 is a surface emitting laser device in which a plurality of light emitting points LP by surface emitting laser diodes are disposed on a substrate 21. In the illustrated embodiment, a total of 35 light emitting points LP are provided in an array (arrangement shape) of 7 points × 5 rows.
The scanning optical system 30 includes a pre-deflection optical system 31, a polygon mirror 32 that is a rotary polygon mirror as a deflecting unit, and a post-deflection optical system 33. The deflection scanning direction by the rotation of the polygon mirror 32 of the scanning optical system 30 is called a main scanning direction, and the direction orthogonal to the deflection scanning direction is called a sub-scanning direction. That is, the rotation axis direction of the photosensitive drum 11 is the main scanning direction, and the movement direction of the peripheral surface perpendicular to the rotation direction is the sub-scanning direction.

  The pre-deflection optical system 31 includes a coupling lens 31A, an aperture 31B, and a cylinder lens 31C. Then, the laser beam groups LY, LM, LC, and LK for the respective colors emitted from the surface emitting laser array chip 20 are condensed by the coupling lens 31A, passed through the opening of the aperture 31B while being truncated, and the cylinder lens 31C. As a result, the principal ray is incident on the polygon mirror 32 in parallel or in the direction corresponding to the sub-scanning direction. This pre-deflection optical system 31 is common to the laser beam groups LY, LM, LC, and LK.

  The polygon mirror 32 has six deflection surfaces 32A, and is rotationally driven by a DC motor with high rotational accuracy, for example, at a speed of 30,000 revolutions per minute. Then, the laser beam groups LY, LM, LC, and LK incident from the pre-deflection optical system 31 are deflected by the respective deflection surfaces 32A and, for example, are scanned on the photosensitive drums 11 at a speed of 254 mm / s.

  The post-deflection optical system 33 includes an aspheric lens 33A, a first plane mirror 33B (33BY, 33BM, 33BC, 33BK), a second plane mirror 33C (33CY, 33CM, 33CC, 33CK), and a toroidal lens 33D (33DY). , 33DM, 33DC, 33DK). Both the aspherical lens 33A and the toroidal lens 33D have positive power, and the aspherical lens 33A is configured to have an fθ characteristic in cooperation with the toroidal lens 33D in the main scanning direction. The aspherical lens 33A is common to the laser beam groups LY, LM, LC, and LK, and the first plane mirror 33B, the second plane mirror 33C, and the toroidal lens 33D are each of the laser beam groups LY, LM, LC. , Provided for each LK.

In the post-deflection optical system 33, the aspherical lens 33A crosses and separates the optical paths of the laser beam groups LY, LM, LC, and LK that have been deflected and scanned by the polygon mirror 32 at the rear focal position, The light enters the first flat mirrors 33BY, 33BM, 33BC, and 33BK. The aspherical lens 33A corrects aberrations of the laser beam groups LY and LK that pass through positions away from the optical axis, and the imaging magnification in the sub-scanning corresponding direction of the laser beam groups LY, LM, LC, and LK. Are substantially the same.
Each of the first plane mirrors 33BY, 33BM, 33BC, 33BK and each of the second plane mirrors 33CY, 33CM, 33CC, 33CK reflects and deflects each of the laser beam groups LY, LM, LC, LK, and each photoreceptor drum 11Y. , 11M, 11C, 11K.
The toroidal lens 33D focuses the laser beam groups LY, LM, LC, and LK reflected by the second plane mirrors 33CY, 33CM, 33CC, and 33CK onto the photosensitive drums 11Y, 11M, 11C, and 11K. At this time, each toroidal lens 33D (33DY, 33DM, 33DC, 33DK) corrects the beam position variation due to the surface tilt of the deflection surface 32A of the polygon mirror 32.
As a result, the laser beam groups LY, LM, LC, and LK emitted from the surface emitting laser array chip 20 are transferred to the photosensitive drums 11Y, 11M, 11C, and 11K of the image forming units 10Y, 10M, 10C, and 10K, respectively. Then, the main scanning operation is performed in the rotation axis direction.

Here, the surface emitting laser array chip 20 is provided with a total of 35 light emitting points LP of 7 points × 5 columns as described above.
As shown in FIG. 3, the light emission point LP columns form a yellow light emission point group LPY, a magenta light emission point group LPM, and a cyan light emission point group LPC in order from the upper side in the figure. The lowermost two rows constitute the light emitting point group LPK (LPK1, LPK2) for black. In other words, the light emission point groups LPY, LPM, and LPC for each color of yellow, magenta, and cyan have one light emission line LP each having seven light emission points LP, and only the light emission point group LPK for black has the same configuration. The point sequence is two rows (first light emission point group LPK1, second light emission point group LPK2), and has 14 light emission points LP.
With such a configuration of the surface emitting laser array chip 20, the exposure device 12 uses the photosensitive drums 11 </ b> Y, 11 </ b> M, 11 </ b> M, 11 </ b> Y, 11 </ b> Y, 11 </ b> M, 11 </ b> 11C is scanned, and the photosensitive drum 11K is scanned with two sets of laser beam groups LPK1 and LPK2 each having seven laser beams for black. That is, the photosensitive drum 11K is scanned with a total of 14 laser beams for black only.

In FIG. 2, the surface emitting laser array chip 20 has the black light emitting point group LPK on the upper side. This is because the optical path of the laser beam groups LY, LM, LC, and LK is changed by the scanning optical system 30. This is because it flips up and down. In FIG. 3 and FIG. 4 conceptually shown, in order to facilitate understanding of the correspondence between the light emitting point groups LPY, LPM, LPC, LPK of the surface emitting laser array chip 20 and the photosensitive drums 11Y, 11M, 11C, 11K. The surface emitting laser array chip 20 has the light emitting point group LPK for black as the lower side, and directly corresponds to the photosensitive drums 11Y, 11M, 11C, and 11K.
In the present embodiment, the light emission points LP constituting the light emission point groups LPY, LPM, LPC, and LPK are arranged in parallel to the upper and lower sides of the rectangular substrate 21. The arrangement direction of the image forming points on the photosensitive drum 11 of the laser beam groups LY, LM, LC, and LK from LPY, LPM, LPC, and LPK has a predetermined angle with respect to the main scanning direction. . Then, as shown in FIG. 4, the main scanning lines by the adjacent light emitting points LP constituting the same light emitting point group LPY, LPM, LPC, LPK are arranged on the photosensitive drum 11 between the columns in the sub scanning direction (for example, If the resolution is 2400 dpi, the interval is set to 10.58 μm. This is configured such that the surface emitting laser array chip 20 is inclined at a predetermined angle or the arrangement direction is inclined by the scanning optical system 30.

The intervals in the sub-scanning direction of the light emitting point groups LPY, LPM, LPC, LPK on the surface emitting laser array chip 20 are the laser beam groups LY, LM, emitted from the light emitting point groups LPY, LPM, LPC, LPK. LC and LK are set to an interval that can be easily separated by the scanning optical system 30 (post-deflection optical system 33).
Further, the interval between the two light emitting point groups LPK1 and LPK2 constituting the black light emitting point group LPK is such that the main scanning region by the first light emitting point group LPK1 and the main scanning region by the second light emitting point group LPK2 are arranged. Are preferably set to be continuous in the sub-scanning direction as shown in FIG. However, in such a setting, the light emission point group LPK1 in the first row and the light emission point group LPK2 in the second row may be extremely close to each other on the substrate 21 and may be difficult to configure. In this case, the distance between the main scanning region by the light emitting point group LPK1 in the first row and the main scanning region by the light emitting point group LPK2 in the second row is such that the light emitting point groups LPK1 and LPK2 have sub-spaces on the surface of the photosensitive drum 11K. It is set to be twice the scanning width. Then, the intervals set in this way are also applied to the intervals between the light emitting point groups LPY, LPM, LPC for each color, and the intervals of all the light emitting point groups LPY, LPM, LPC, LPK are made equal. The surface emitting laser array chip 20 can be configured to be rational and easy to manufacture. However, in such an arrangement configuration, in the black and white mode in which image formation is performed using the two black light emitting point groups LPK1 and LPK2, the laser beams from the light emitting point groups LPK1 and LPK2 are respectively used. So-called skip scanning in which main scanning is performed every other column in the sub-scanning direction must be performed, and complicated scanning control is required. This will be described later. As shown in FIG. 4, when the main scanning region by the first light emitting point group LPK1 and the main scanning region by the second light emitting point group LPK2 are continuous in the sub-scanning direction, skip scanning is not performed. Scanning can be continued (without complicated operation control).

In the surface emitting laser array chip 20 configured as described above, the light emitting point group LPK for black has twice as many light emitting points LP as the light emitting point groups LPY, LPM, and LPC for other colors. . Thus, the main scanning by the laser beam groups LY, LM, and LC from the light emission point groups LPY, LPM, and LPC of other colors is performed by one scanning operation of the laser beam group LK from the black light emission point group LPK. The main scanning can be performed with twice the number of rows. That is, even if the main scanning speed is the same, the sub scanning speed is doubled. Further, the light emitting point group LPK for black is composed of two rows of light emitting point groups LPK1 and LPK2 having the same configuration as the light emitting point groups LPY, LPM, and LPC for other colors. By performing main scanning only with (light emitting point group LPK1 or LPK2), the main scanning conditions are the same as those for other colors.
Therefore, in the color mode, the main scanning is performed by only one of the light emitting point groups LPK1 and LPK2 for black, so that an image can be formed in synchronization with other colors. In the black and white mode, main scanning is performed with all the light emitting point groups LPK1 and LPK2, so that the image is formed at a sub-scanning speed twice that in the color mode without changing the rotational speed of the polygon mirror 32. It becomes possible. For example, the process speed in the color mode can be 210 mm / s, and the process speed in the monochrome mode can be 420 mm / s.

  Note that the speed ratio between the color mode and the black-and-white mode required for the fixing capability is not necessarily doubled. For example, if the process speed in the color mode is 210 mm / s and the process speed in the black and white mode is 330 mm / s, the simple ratio calculation may be performed in the black and white mode if the main scan is performed at 7 points in the color mode. In this case, main scanning may be performed at 11 points. Therefore, if the light emission point group LPK1 in the first row has 7 light emission points LP, the light emission point group LPK2 in the second row only needs to have 4 light emission points LP. However, from the viewpoint of space efficiency of the surface emitting laser array chip 20, there is no merit that only the four light emitting points LP of the light emitting point group LPK2 in the second row are used. In the case of a configuration in which there is an interval (not continuous in the sub-scanning direction) with the scanning region by the light emission point group LPK2 in the second column, continuous sub-scanning cannot be performed. For this reason, even if the speed ratio is as described above, a configuration like the present configuration example in which the light emission points LP are the same in the first light emission point group LPK1 and the second light emission point group LPK2 is preferable. In the case where the main scanning region by the light emission point group LPK1 in the first row and the main scanning region by the light emission point group LPK2 in the second row are continuous in the sub-scanning direction, the sub-scanning can be performed continuously, and thus such a configuration is also possible. It is.

Next, the configuration of the control unit 40, the switching of the process speed and the control of the exposure apparatus 12 when the control unit 40 switches between the color mode and the monochrome mode will be described.
FIG. 5 is a block diagram showing the configuration of the control unit 40.
The control unit 40 includes each of the image forming apparatuses 1 (see FIG. 1) such as a drum drive motor that rotationally drives the photosensitive drum 11 of each image forming unit 10 and a belt drive motor that rotationally drives the drive roll 13A of the transfer belt 13. Drive control of the mechanism part.
The control unit 40 includes a controller 50 that controls image processing, an image processing unit 51, and an image output unit 52. Then, under the control of the controller 50, the image processing unit 51 digitally converts the image information of each color of Y, M, C, and K, performs color correction and image processing, and the image output unit 52 generates the image information by the image processing unit 51. The obtained digital image signal is output to the exposure device 12 at an appropriate timing. Further, the controller 50 controls color misregistration and density misalignment detection, correction operations, and the like.

In addition, the control unit 40 includes a nonvolatile ROM (Read Only Memory) 41, a readable / writable RAM (Random Access Memory) 42 as a memory, and a flash that enables data rewriting and data retention after the power is turned off. And a non-volatile memory (NVM) 43 that is a non-volatile memory such as a memory.
The ROM 41 stores a software program for controlling an image forming operation, color misregistration detection and correction operation, etc. executed by the controller 50, color misregistration control pattern image information, and the like.
The RAM 42 stores various types of information acquired as the image forming apparatus 1 operates, such as various counter values, the number of job executions, and execution information (time information and the like) of the previous color misregistration detection process. Further, when adjusting the color registration by changing the skew and the magnification, the image information is temporarily stored and functions as a storage unit for color misregistration correction.
Further, the NVM 43 stores information on the writing timing for color registration adjustment acquired at a predetermined timing, for example, when the image forming apparatus 1 is shipped from the factory, when the power is turned on, or several times a day. . The exposure position of the exposure device 12 and the image forming units 10Y, 10M, 10C, and 10K for each color is controlled in accordance with information stored in the NVM 43.

Then, the control unit 40 controls to switch the process speed between the color mode and the monochrome mode. That is, the color mode and the black and white mode are used to change and control various processes for image formation including the exposure device 12 and the conveyance speed of the recording paper. Next, control by the control unit 40 will be described. Refer to FIG. 2 to FIG.
When switching the process speed between the color mode and the monochrome mode, the control unit 40 controls the light emission point groups LPY, LPM, LPC, and LPK of the surface emitting laser array chip 20 of the exposure apparatus 12 as follows.
In the monochrome mode, all the light emission points LP of the black light emission point group LPK (light emission points LP of the first light emission point group LPK1 and the second light emission point group LPK2) are driven. In the color mode, only the first light emission point group LPK1 is driven out of the light emission point group LPK for black.
As a result, even in the case where the scanning speed of the main scanning is constant, the speed in the sub-scanning direction twice as high as that in the color mode can be obtained in the monochrome mode. That is, if the ratio of the process speed between the color mode and the monochrome mode is 1: 2, as in the case where the process speed in the color mode is 210 mm / s and the process speed in the monochrome mode is 420 mm / s, for example, The rotation speed may be constant. Accordingly, it is possible to cope with a change in process speed without changing the rotation speed of the polygon mirror 32. As a result, there is no need for complicated control of the drive DC motor and special control circuit for making the rotation speed of the polygon mirror 32 variable, and it is possible to suppress an increase in the cost of the entire apparatus due to the provision thereof.

Next, the control unit 40 (controller 50) when the main scanning area of the first light emitting point group LPK1 and the second light emitting point group LPK2 of the black light emitting point group LPK is not continuous in the sub-scanning direction. ) Will be described. Refer to FIG. 1 to FIG. 5 for the reference numerals of each component.
FIG. 6 is a diagram for explaining a scanning step when the interval between the light emitting point groups LPK1 and LPK2 is set to twice the width of both the light emitting point groups LPK1 and LPK2 in the sub-scanning direction. In the figure, S1 indicates a main scanning region by a laser beam from the light emitting point group LPK1, and S2 indicates a main scanning region by a laser beam from the light emitting point group LPK2.

That is, the interval in the sub-scanning direction between the main scanning region S1 by the laser beam from the first light emitting point group LPK1 and the main scanning region S2 by the laser beam from the second light emitting point group LPK2 is the main scanning region S1, When it is set to twice the width (main scanning column width) W of S2 in the sub-scanning direction, as shown in FIG. 6 (a), in the first main scanning operation, the first light emission point group LPK1. A region (gap G1, G2) not subjected to main scanning corresponding to the width of the two main scanning columns is generated between the main scanning region S1 by the main scanning region S2 by the second light emitting point group LPK2.
Here, since the peripheral speed (sub-scanning speed) of the photosensitive drum 11K is twice that in the color mode, the region located in the gap G2 on the front side in the sub-scanning direction (the lower side in the figure) is shown in FIG. As shown in (b), in the second main scanning operation, the scanning is performed by the laser beam from the first light emitting point group LPK1 located in the main scanning region S1. At that time, the region main-scanned by the second light emission point group LPK2 during the first main-scanning operation is positioned in the gap G1 so as to be continuous forward in the sub-scanning direction. For this reason, the unmain-scanned region between the main scan regions S1 and S2 is only a region located in the gap G2 corresponding to one main scan column width.
In the third main scanning operation, as shown in FIG. 6C, the non-main scanning region located in the gap G2 during the previous second main scanning operation is located in the scanning region S1, and the first main scanning operation is performed. Main scanning is performed by the laser beam from the light emitting point group LPK1.
Hereinafter, for each main scanning operation, the lower gap G2 is not subjected to main scanning, and the portion is subjected to main scanning by the first light emitting group LPK1 in the next main scanning operation, and this is repeated in the sub scanning direction. The main scanning can be performed continuously.

In such scanning control, there is a difference of two main scans between the main scan by the laser beam from the first light emission point group LPK1 and the main scan by the laser beam from the second light emission point group LPK2. . Therefore, the main scanning by the laser beam from the first light emitting point group LPK1 always draws image information delayed by two main scannings from the main scanning by the laser beam from the second light emitting point group LPK2. For this reason, it is necessary to store image information for two main scans in the meantime.
A memory for storing the image information for the two main scans may be newly provided. Here, the controller 50 uses the RAM 42 to store the image information for the two main scans.
The RAM 42 temporarily stores image information in order to adjust the color registration in the color mode, but it is not necessary to adjust the color registration in the monochrome mode. Therefore, in this black and white mode, image data for two main scans is stored using the RAM 42 in the idle state. According to this, since it is not necessary to provide a new memory, a rational configuration can be achieved without incurring an increase in cost.

  The memory for storing the image information for the two main scans is not limited to the RAM 42 in the circuit configuration as described above. In other words, in the actual circuit, the circuit for each color of the image processing unit 51 of the control unit 40 is configured by an IC (ASIC) having a specific function including a memory for storing image information at the time of color registration adjustment. Is done. In that case, the black IC is also rationally configured using the same IC as the other colors. In such a configuration, if the color registration adjustment is performed with the black reference, the black IC memory is not used. Therefore, a configuration may be adopted in which image information for two main scans is stored using this memory. Even with such a circuit and control configuration, it is not necessary to provide a new memory and can be rationally configured.

As described above in detail, according to the present embodiment, the image forming apparatus 1 using the exposure apparatus 12 that collectively scans a plurality of beams from the plurality of light emitting points LP of the surface emitting laser array chip 20 with the polygon mirror 32. In this case, the number of black light emitting points LP of the surface emitting laser array chip 20 can be increased without incurring a cost increase due to a deterioration in yield. Thereby, in the monochrome mode, the main scanning is performed with a larger number of rows by a single scanning operation, and the process speed is improved compared to the color mode without changing the rotation speed of the polygon mirror 32. It is something that can be done.
In addition, this invention is not limited to the structure of the said embodiment, It can change suitably. For example, in the above embodiment, the surface emitting laser array chip 20 provided with a plurality of light emitting points LP by the surface emitting laser diodes on the substrate 21 is used as the light source. However, the light source configuration is not limited to this, for example, an edge emitting laser is integrated. May be configured.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. It is a perspective view which shows the conceptual structure of the whole exposure apparatus. It is a top view of a surface emitting laser array chip. It is a figure explaining the multi-beam scanning by a surface emitting laser array chip. It is a block diagram which shows the structure of a control part. It is a figure explaining a scanning step. It is a top view of the surface emitting laser array chip as a conventional example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 (10Y, 10M, 10C, 10K) ... Image forming part, 11 ... Photosensitive drum (image carrier), 11Y, 11M, 11C ... Photosensitive drum (Image carrier for other colors) ), 11K ... photosensitive drum (black image carrier), 12 ... exposure device, 13 ... transfer belt, 20 ... surface emitting laser array chip (light source), 30 ... scanning optical system, 32 ... polygon mirror (rotating multi-sided) Mirror, deflection scanning means) 40... Control section, 42... RAM (color shift correction storage means, inter-column image data storage means) 50... Controller (control means) 51. LP ... light emission point, LPY, LPM, LPC ... light emission point group (light emission point group for other colors), LPK (LPK1, LPK2) ... light emission point group for black, LY, LM, LC, LK ... laser beam group (Flux group)

Claims (14)

A plurality of image carriers including an image carrier for black provided corresponding to each of a plurality of colors;
A light source provided with a plurality of light emission points each including a light emission point group for black, including a light emission point group for black,
A scanning optical system that scans the luminous flux groups for the respective colors emitted from the respective light emitting point groups of the light source in a lump by the scanning deflecting means and separates the light flux groups for the respective colors and guides them to the respective image carriers; With
The black light emitting point group of the light source has a larger number of light emitting points than the light emitting point group for other colors, and the arrangement of the light emitting points is different from the light emitting point group for the other colors. Image forming apparatus.   The light emitting point groups for each color are arranged in a row with the same light emitting points, and the black light emitting point group has more columns than the light emitting point groups for the other colors. The image forming apparatus according to claim 1.   3. The image forming apparatus according to claim 2, wherein the row of the light emitting points constituting the black light emitting point group is provided in parallel in a direction substantially perpendicular to a direction in which the light emitting points are arranged. . A color mode for forming an image using the plurality of image carriers, and a monochrome mode for forming an image using only the black image carrier,
The image forming apparatus according to claim 1, further comprising a control unit that controls the number of light emitting points of the black light emitting point group to be driven more in the monochrome mode than in the color mode.   A color mode for forming an image using the plurality of image carriers, and a monochrome mode for forming an image using only the image carrier for black, and the monochrome mode is more in the color mode than in the color mode. The image forming apparatus according to claim 2, further comprising a control unit that controls to drive the row of light emitting points for black.   In the black and white mode, when the row of the plurality of light emitting points for black scans the image data discontinuously, the inter-row image data storage for storing the inter-row image data between the scanned image data by the row of the light emitting points The image forming apparatus according to claim 5, further comprising a unit. A color misregistration correction storage unit for storing data for color misregistration correction in the color mode;
In the black-and-white mode, when the row of the plurality of light emitting points for black scans the image data discontinuously, the inter-row image data between the scanned image data by the row of the light emitting points is stored in the color misregistration correction memory. 6. The image forming apparatus according to claim 5, further comprising control means for controlling to store in the means. A light source having a plurality of light emitting point groups each corresponding to a plurality of colors, each composed of a plurality of light emitting points;
A scanning optical system that performs a scanning operation of the luminous flux groups for the respective colors emitted from the respective light emitting point groups of the light source in a lump by the scanning deflection unit, and separates for each of the colors; and
The specific light emitting point group of the light source has a larger number of the light emitting points than the other light emitting point groups, and the arrangement of the light emitting points is different from the other light emitting point groups.   The light emitting point groups for the respective colors are arranged in rows with the same light emitting points, and the specific light emitting point group has more columns than the light emitting point groups for the other colors. The exposure apparatus according to claim 8, characterized in that:   10. The exposure apparatus according to claim 9, wherein the row of the light emitting points constituting the specific light emitting point group is provided in parallel in a direction substantially orthogonal to the direction in which the light emitting points are arranged.   The exposure apparatus according to claim 10, wherein the scanning deflection unit is a rotary polygon mirror. A light source for emitting a plurality of light beams for a plurality of colors to a scanning optical system that causes a plurality of light beams for a plurality of colors to be collectively scanned by a scanning deflection unit and separated into a light beam group for each color,
The light emitting point group is composed of a plurality of light emitting points for each color, and the specific light emitting point group in the light emitting point group has a larger number of light emitting points than the other light emitting point groups, and the other light emitting point group And a light source of an exposure apparatus, wherein the arrangement of the light emitting points is different.   The light emitting point groups for each color are arranged in a row with the same light emitting points, and the specific light emitting point group has more columns than the other light emitting point groups. The light source of the exposure apparatus according to claim 12.   14. The light source of the exposure apparatus according to claim 13, wherein the row of the light emitting points constituting the specific light emitting point group is provided in parallel in a direction substantially perpendicular to the arrangement direction of the light emitting points. .

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