JP2009069665A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately scrape off each respective foreign matter such as discharge products stuck to each image carrier with different charging mechanisms. <P>SOLUTION: The image forming apparatus is provided with each photoreceptor drum 11Y, 11M, 11C and 11K which are for yellow, magenta, cyan and black and an intermediate transfer belt 20 which is arranged in contact with the same drums. A non-contact type charging unit 12K is fitted to the photoreceptor drum 11K, and contact type charging units 12Y, 12M and 12C are fitted to the photoreceptor drums 11Y, 11M and 11C. In a full color mode, the photoreceptor drum 11K is set to a second black circumferential velocity VK2, the photoreceptor drums 11Y, 11M and 11C are set to a color circumferential velocity VC higher than the second black circumferential velocity VK2, and the intermediate transfer belt 20 which is arranged in contact with each photoreceptor drum 11Y, 11M, 11C and 11K is set to a second belt circumferential velocity VB2 lower than the second black circumferential velocity VK2 or the color circumferential velocity VC. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image.

  As an image forming apparatus such as a printer or a copying machine, for example, an image formed on a plurality of photoconductor drums arranged side by side is primary-transferred sequentially to an intermediate transfer belt, and then the image primarily transferred to the intermediate transfer belt is paper Those that undergo secondary transfer are known. When the electrophotographic method is employed, an image is formed on each photosensitive drum through known charging, exposure, and development processes. Here, Patent Document 1 discloses a technique of driving while making a speed difference between each photosensitive drum and the intermediate transfer belt. Patent Document 2 discloses a technique for switching the image forming speed when a single color (for example, black) image is formed faster than when forming a plurality of colors (for example, yellow, magenta, cyan, and black). It is disclosed.

JP 2004-93864 A JP-A-5-330130

By the way, for example, when the image forming speed at the time of forming a single color image is set to be higher than that at the time of forming a plurality of color images, the charging performance of the photosensitive drum that forms a single color image at the time of forming a single color image becomes insufficient. There is a fear. For this reason, it is conceivable that a charging device having a higher performance than that of a photosensitive drum for forming an image of another color is attached to the photosensitive drum for forming a monochrome image.
On the other hand, it is known that in the charging operation, a discharge product generated along with discharge adheres to the photosensitive drum. When the discharge product adheres to the photoreceptor drum in this way, the characteristics of the photoreceptor at the site where the discharge product is adhered differ from the non-adhered site, resulting in a reduction in image quality.

Therefore, when a charging device having a different configuration is attached to the photosensitive drum for a single color and the photosensitive drum for the other color, the amount of discharge product adhered to the photosensitive drum for the single color and the photosensitive drum for the other color is increased. It will change. Then, the image quality of the image formed on the photosensitive drum on the side where the discharge product is attached is lower than the image formed on the photoconductor drum on the side where the discharge product is attached.
Here, providing a predetermined speed difference between each photosensitive drum and the intermediate transfer belt or the like is an effective technique for scraping discharge products adhering to each photosensitive drum. However, if an appropriate speed difference is set in accordance with the photosensitive drum on the side where the discharge product adheres more, the photosensitive drum on the side where the discharge product is less will be scraped, resulting in a decrease in life. . On the other hand, when an appropriate speed difference is set in accordance with the photosensitive drum on the side where the amount of discharge product attached is small, the discharge product that could not be scraped off remains on the photosensitive drum on the side where the discharge product is large. End up.

  An object of the present invention is to appropriately rub off foreign matters such as discharge products adhering to image holding bodies having different charging mechanisms.

According to a first aspect of the present invention, there is provided a first image carrier that rotates at a first peripheral speed, a first charging unit that charges the first image carrier, and the first that is charged by the first charging unit. The first image forming means for forming an image on the image holding body, the second image holding body rotating at a second peripheral speed, and the first charging means have different configurations, and charge the second image holding body. A second charging means for making contact, a second image forming means for forming an image on the second image holding body charged by the second charging means, and a contact with the first image holding body and the second image holding body. However, the speed difference between the second circumferential speed and the third circumferential speed is larger than the speed difference between the rotating speed rotating at the third circumferential speed and the first circumferential speed and the third circumferential speed. An image forming apparatus including setting means for setting the first peripheral speed, the second peripheral speed, and the third peripheral speed. .
According to a second aspect of the present invention, the first charging unit includes a non-contact type charging device arranged in non-contact with the first image holding member, and the second charging unit is arranged in contact with the second image holding member. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a contact type charging device.
According to a third aspect of the present invention, the first image forming means and the second image forming means collectively use a single rotating polygonal mirror to collect a plurality of light flux groups each consisting of a plurality of light fluxes emitted from a light source. After the scanning operation, the light beam group is separated and guided to the corresponding first image holding body and second image holding body, respectively, and the first image holding body and the second image holding body are main-scanned. A correction unit that includes an optical scanning device and corrects the light amounts of a plurality of light beams constituting the light beam group guided to the first image carrier or corrects the number of the plurality of light beams constituting the light beam group; The image forming apparatus according to claim 1, further comprising:

According to a fourth aspect of the present invention, a first image holding body that holds a first image and rotates at a first peripheral speed, and a first image that charges the first image holding body when forming the first image. A first image forming unit including a charging member, a second image holding body that holds a second image and rotates at a second peripheral speed, and has a configuration different from that of the first charging member. A second image forming unit including a second charging member that charges the second image carrier when forming an image; and a third circumference while contacting the first image carrier and the second image carrier. A rotating member that rotates at a speed, and the first mode for forming the first image sets the third peripheral speed at a higher speed than the second mode for forming the second image together with the first image; A speed difference is set between the third circumferential speed and the first circumferential speed, and the third mode is used in the second mode. Setting means for setting the speed lower than that in the first mode and setting different speed differences between the third peripheral speed and the first peripheral speed and between the third peripheral speed and the second peripheral speed. And an image forming apparatus.
According to a fifth aspect of the present invention, in the first mode, the second image holding body and the rotating member are separated from each other, and in the second mode, the contacting / separating means for bringing the second image holding body and the rotating member into contact with each other. The image forming apparatus according to claim 4, further comprising:
According to a sixth aspect of the present invention, the first image forming unit and the second image forming unit collectively collect a plurality of light flux groups each consisting of a plurality of light fluxes emitted from a light source by a single rotary polygon mirror. After the scanning operation, the light beam group is separated and guided to the corresponding first image holding body and second image holding body, respectively, and the first image holding body and the second image holding body are main-scanned. An optical scanning device is provided in common, and in the first mode, adjacent to the rotation direction of the first image carrier in the interval between a plurality of light beams constituting the light beam group guided to the first image carrier. The image forming apparatus according to claim 4, wherein intervals between the light beams at a boundary between the two light beam groups are matched.
According to a seventh aspect of the present invention, the first image forming unit and the second image forming unit collect a plurality of light beam groups each consisting of a plurality of light beams emitted from a light source by a single rotating polygon mirror. After the scanning operation, the light beam group is separated and guided to the corresponding first image holding body and second image holding body, respectively, and the first image holding body and the second image holding body are main-scanned. An optical scanning device is provided in common, and in the second mode, adjacent to the rotation direction of the second image carrier in the interval between a plurality of light beams constituting the light beam group guided to the second image carrier. The image forming apparatus according to claim 4, wherein intervals between the light beams at a boundary between the two light beam groups are matched.
According to an eighth aspect of the present invention, in the second mode, the light quantity of a plurality of light beams constituting the light beam group guided to the first image carrier is corrected, or the number of the plurality of light beams constituting the light beam group is determined. 8. The image forming apparatus according to claim 7, further comprising a correcting unit for correcting.

According to the first aspect of the present invention, it is possible to appropriately scrape foreign matters such as discharge products adhering to the respective image carriers having different charging means.
According to the second aspect of the present invention, the charging performance of the first image carrier can be improved as compared with the second image carrier.
According to the third aspect of the present invention, it is possible to suppress periodic unevenness generated in the electrostatic latent image formed on the first image holding member, as compared with the case where this configuration is not provided.
According to the fourth aspect of the present invention, foreign matters such as discharge products adhering to the respective image holding bodies having different charging members can be scraped appropriately.
According to the fifth aspect of the present invention, it is possible to suppress the second image carrier from being rubbed by the rotating member in the first mode.
According to the invention described in claim 6, in the first mode, it is possible to suppress periodic unevenness generated in the electrostatic latent image formed on the first image carrier.
According to the seventh aspect of the present invention, in the second mode, it is possible to suppress periodic unevenness that occurs in the electrostatic latent image formed on the second image carrier.
According to the eighth aspect of the invention, in addition to the effect of the seventh aspect, in the first mode, it is possible to suppress periodic unevenness generated in the electrostatic latent image formed on the first image holding member.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Embodiment 1>
FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied.
The image forming apparatus includes, for example, a plurality (four in the present embodiment) of image forming units 10 (yellow unit 10Y, magenta unit 10M, cyan unit 10C, and black unit 10K) that form toner images of each color component by electrophotography. ). In addition, the image forming apparatus includes an intermediate transfer belt 20 that sequentially transfers the color component toner images formed by the image forming units 10 in order. Further, this image forming apparatus has a secondary transfer device 30 for secondary transfer of the superimposed image transferred to the intermediate transfer belt 20 onto the paper P, and a fixing device 45 for fixing the secondary transferred image onto the paper P. is doing. In addition, the image forming apparatus is provided with a control unit 70 that controls the image forming operation.

  The yellow unit 10Y includes a photosensitive drum 11Y that rotates in the direction of arrow A, a charging device 12Y, a developing device 14Y, a primary transfer roll 15Y, and a drum cleaner 16Y that are provided around the photosensitive drum 11Y in the rotational direction. It has. The magenta unit 10M includes a photosensitive drum 11M that rotates in the direction of arrow A, a charging device 12M, a developing device 14M, a primary transfer roll 15M, and a drum cleaner 16M that are provided around the photosensitive drum 11M in the rotational direction. It has. The cyan unit 10C includes a photosensitive drum 11C that rotates in the direction of arrow A, a charging device 12C, a developing device 14C, a primary transfer roll 15C, and a drum cleaner 16C that are provided around the photosensitive drum 11C in the rotational direction. It has. The black unit 10K includes a photosensitive drum 11K that rotates in the direction of arrow A, a charging device 12K, a developing device 14K, a primary transfer roll 15K, and a drum cleaner 16K that are provided around the photosensitive drum 11K in the rotational direction. It has. In the present embodiment, the black unit 10K functions as the first image forming unit, and the yellow unit 10Y, the magenta unit 10M, and the cyan unit 10C function as the second image forming unit, respectively. In addition, the photosensitive drum 11K serves as a first image holding body that holds a first image, that is, a black image, and the photosensitive drums 11Y, 11M, and 11C hold second images, that is, yellow, magenta, and cyan images. Each functions as a two-image carrier.

  An exposure device 13 is provided above each image forming unit 10. The exposure apparatus 13 includes a yellow beam group LY for the photosensitive drum 11Y, a magenta beam group LM for the photosensitive drum 11M, a cyan beam group LC for the photosensitive drum 11C, and a photosensitive drum. 11K is irradiated with the black beam group LK.

  Here, each of the photosensitive drums 11Y, 11M, 11C, and 11K has a photosensitive layer (not shown), and a surface layer having higher wear resistance than the photosensitive layer is provided outside the photosensitive layer. Yes. As a surface layer, for example, a known charge transfer agent and a filler such as alumina are appropriately added to a thermoplastic resin such as polycarbonate, or a charge that can be cross-linked with these resins to a thermosetting resin such as a phenol resin or a melamine resin. A transporting agent and, if necessary, a conductive agent dispersed therein are used. In this example, the outer diameter of the photosensitive drum 11K is larger than those of the other photosensitive drums 11Y, 11M, and 11K.

  For each of the charging devices 12Y, 12M, and 12C functioning as the second charging unit, a roll charger that is disposed in contact with the corresponding photosensitive drum 11Y, 11M, and 11C is used. On the other hand, a scorotron charger disposed in a non-contact manner with respect to the photosensitive drum 11K is used as the charging device 12K that functions as the first charging unit.

  Each of the developing devices 14Y, 14M, 14C, and 14K includes a corresponding color toner, and includes a developing roll that is disposed to face the corresponding photosensitive drums 11Y, 11M, 11C, and 11K. In the present embodiment, the exposure device 13 and the developing device 14K function as first image forming means, and the exposure device 13 and the developing devices 14Y, 14M, and 14C function as second image forming means.

The primary transfer rolls 15Y, 15M, 15C, and 15K are arranged to face the corresponding photosensitive drums 11Y, 11M, 11C, and 11K with the intermediate transfer belt 20 interposed therebetween. Each primary transfer roll 15Y, 15M, 15C, 15K is pressed toward the intermediate transfer belt 20 by a spring (not shown).
Each of the drum cleaners 16 </ b> Y, 16 </ b> M, 16 </ b> C, and 16 </ b> K includes a cleaning member that is disposed in contact with the photosensitive drum 11.

Next, the intermediate transfer belt 20 will be described.
The intermediate transfer belt 20 as a kind of rotating member is composed of an endless belt having semiconductivity. Then, the intermediate transfer belt 20 is wound around the drive roll 21, the advance / retreat roll 22, the fixed roll 23, the transfer roll 24, the correction roll 25 and the backup roll 26, and rotates in the arrow B direction.

Among these, the drive roll 21 is provided on the upstream side in the rotation direction of the intermediate transfer belt 20 with respect to the image forming units 10Y, 10M, 10C, and 10K. The driving roll 21 is rotated by applying a driving force to the intermediate transfer belt 20. Further, the advancing / retreating roll 22 is provided between the magenta unit 10M and the cyan unit 10C, and is in contact with the inner side of the intermediate transfer belt 20 to push out the intermediate transfer belt 20 (referred to as an advance direction) or from the intermediate transfer belt 20. Move away (referred to as retraction direction). The fixed roll 23 is provided between the cyan unit 10 </ b> C and the black unit 10 </ b> K, and is disposed so as to be in contact with the inner surface of the intermediate transfer belt 20 while being fixed at the same position, unlike the forward / backward roll 22. The transfer roll 24 is provided on the downstream side in the rotation direction of the intermediate transfer belt 20 with respect to the black unit 10K. The correction roll 25 has a function of correcting the meandering in the direction substantially orthogonal to the rotation direction of the intermediate transfer belt 20 while the intermediate transfer belt 20 is wound around. The backup roll 26 hangs around the intermediate transfer belt 20 and functions as a constituent member of the secondary transfer device 30.
A belt cleaner 27 having a cleaning member disposed in contact with the intermediate transfer belt 20 is attached to a position facing the drive roll 21 with the intermediate transfer belt 20 interposed therebetween.

  The secondary transfer device 30 includes a secondary transfer roll 31 disposed in contact with the outer surface of the intermediate transfer belt 20, that is, the toner image holding surface side, and a secondary transfer roll 31 disposed on the inner surface side of the intermediate transfer belt 20. And a backup roll 26 serving as a counter electrode.

Further, the paper transport system includes a paper storage unit 40, a feeding roll 41, a separating unit 42, a registration roll 43, and a paper transport belt 44. The paper storage unit 40 has, for example, a box shape, and stores the paper P therein. The feeding roll 41 is disposed on the upper portion of the paper storage unit 40 and is disposed so as to contact the uppermost paper P in the bundle of papers P stored in the paper storage unit 40. The separation unit 42 is provided on the downstream side in the paper transport direction with respect to the feeding roll 41, and includes, for example, a feed roll that is rotatably provided and a retard roll whose rotation direction is restricted. The registration roll 43 is provided on the downstream side in the paper transport direction with respect to the separation unit 42, and is constituted by a pair of roll members, for example. The paper transport belt 44 is provided downstream of the secondary transfer device 30 in the paper transport direction and upstream of the fixing device 45 in the paper transport direction. For example, the paper transport belt 44 is connected to an endless belt stretched around a plurality of roll members. Configured.
The fixing device 45 includes a heating roll having a heating source therein and rotatably arranged, and a pressure roll rotating in contact with the heating roll.

  FIG. 2 is a view showing a detailed configuration of the exposure apparatus 13 shown in FIG. FIG. 2 also shows the photosensitive drums 11Y, 11M, 11C, and 11K that are irradiated with the beam groups LY, LM, LC, and LK for the respective colors by the exposure device 13. However, the relationship between the sizes of the photosensitive drums 11Y, 11M, 11C, and 11K is different from the actual one.

  An exposure apparatus 13 as a kind of optical scanning apparatus includes a surface emitting laser array chip 50 that is a light source having a plurality of light emitting points, and a scanning optical system 60. The surface emitting laser array chip 50 emits a yellow beam group LY, a magenta beam group LM, a cyan beam group LC, and a black beam group LK as four luminous flux groups for each of Y, M, C, and K colors. To do. The scanning optical system 60 scans the respective color beam groups LY, LM, LC, and LK emitted from the surface emitting laser array chip 50, and beams corresponding to the photosensitive drums 11Y, 11M, 11C, and 11K, respectively. Lead groups LY, LM, LC, LK.

  The surface emitting laser array chip 50 constituting the exposure apparatus 13 is a surface emitting laser device in which a plurality of light emitting points by surface emitting laser diodes are arranged on a substrate in a two-dimensional matrix. Details of the surface emitting laser array chip 50 will be described later.

  The scanning optical system 60 constituting the exposure apparatus 13 includes a pre-deflection optical system 61, a polygon mirror 62 that is a rotary polygon mirror, and a post-deflection optical system 63. Here, the deflection scanning direction by the rotation of the polygon mirror 62 is the main scanning direction, and the direction orthogonal to the deflection scanning direction is the sub-scanning direction. That is, the rotation axis direction in each of the photosensitive drums 11Y, 11M, 11C, and 11K is the main scanning direction, and the rotation direction orthogonal to the rotation axis direction is the sub-scanning direction.

  The pre-deflection optical system 61 includes a coupling lens 61A, an aperture 61B, and a cylinder lens 61C. Then, the beam groups LY, LM, LC, and LK for each color emitted from the surface emitting laser array chip 50 are condensed by the coupling lens 61A, passed through the opening of the aperture 61B while being truncated, and by the cylinder lens 61C. The principal ray is incident on the polygon mirror 62 in parallel with or in the sub-scanning direction. This pre-deflection optical system 61 is common to the beam groups LY, LM, LC, and LK for each color.

  The polygon mirror 62 has six deflection surfaces 62A, and is driven to rotate by a DC motor (not shown), for example, at a speed of 30,000 revolutions per minute. Then, the beam groups LY, LM, LC, and LK for each color incident from the pre-deflection optical system 61 are deflected by the respective deflection surfaces 62A, and scanning operations are performed on the respective photosensitive drums 11Y, 11M, 11C, and 11K.

  The post-deflection optical system 63 includes an aspheric lens 63A, a first plane mirror 63B (63BY, 63BM, 63BC, 63BK), a second plane mirror 63C (63CY, 63CM, 63CC, 63CK), and a toroidal lens 63D (63DY). , 63DM, 63DC, 63DK). Both the aspheric lens 63A and the toroidal lens 63D have positive power, and the aspheric lens 63A is configured to have an fθ characteristic in cooperation with the toroidal lens 63D in the main scanning direction. The aspheric lens 63A is common to the beam groups LY, LM, LC, and LK for each color, and the first plane mirror 63B, the second plane mirror 63C, and the toroidal lens 63D are beam groups LY, LM, LC, and It is provided for each LK.

  Then, the post-deflection optical system 63 separates the aspherical lens 63A by crossing the optical paths of the beam groups LY, LM, LC, and LK for each color deflected and scanned by the polygon mirror 62 at the rear focal position, respectively. The light enters the first flat mirrors 63BY, 63BM, 63BC, and 63BK. The aspheric lens 63A corrects the aberrations of the beam groups LY, LM, LC, and LK for each color passing through a position away from the optical axis, and the sub-lenses of the beam groups LY, LM, LC, and LK for each color. The imaging magnification in the scanning direction is substantially the same.

Each of the first plane mirrors 63BY, 63BM, 63BC, 63BK and each of the second plane mirrors 63CY, 63CM, 63CC, 63CK reflects and deflects the beam groups LY, LM, LC, LK for each color, and each corresponding photoconductor. Guide to drums 11Y, 11M, 11C, 11K.
The toroidal lens 63D focuses the beam groups LY, LM, LC, and LK for the respective colors reflected by the second plane mirrors 63CY, 63CM, 63CC, and 63CK onto the photosensitive drums 11Y, 11M, 11C, and 11K. At that time, each of the toroidal lenses 63DY, 63DM, 63DC, and 63DK corrects the beam position variation due to the surface tilt of the deflection surface 62A of the polygon mirror 62.
Thereby, in the exposure apparatus 13, the beam groups LY, LM, LC, and LK for the respective colors emitted from the surface emitting laser array chip 50 are imaged on the respective photosensitive drums 11Y, 11M, 11C, and 11K, and the rotation thereof. The scanning is performed in the axial direction, that is, the main scanning direction.

FIG. 3 is a diagram for explaining the configuration of the surface-emitting laser array chip 50 described above.
This surface emitting laser array chip 50 includes a substrate 51 and a total of 32 light emitting points LP provided on one surface of the substrate 51. On the substrate 51, the light emitting points LP are arranged in 8 points × 4 rows. The rows of the light emission points LP are a yellow light emission point group LPY, a magenta light emission point group LPM, a cyan light emission point group LPM, and a black light emission point group LPK one by one in the horizontal order from the lower side in the figure. Yes. Here, the light emission point groups LPY, LPM, LPC, and LPK for each color are arranged side by side in the main scanning direction, and the light emission points LP that constitute the light emission point groups for each color LPY, LPM, LPC, and LPK are arranged in the sub scanning direction. Is done. In the following description, the light emission points LP constituting the light emission point groups LPY, LPM, LPC, and LPK for the respective colors are denoted by reference numerals 1 to 8 in order from the color name and one end portion in the sub-scanning direction. It expresses with. Therefore, for example, the eight light emission points LP constituting the black light emission point group LPK are expressed as the first black light emission point LPK1 to the eighth black light emission point LPK8 in order from the left side in the drawing. For the other colors, the first yellow light emission point LPY1 to the eighth yellow light emission point LPY8, the first magenta light emission point LPM1 to the eighth magenta light emission point LPM8, and the first cyan light emission point LPC1 to the first cyan light emission point LPC8, respectively. It is expressed as a light emission point LPC8 for 8 cyan.

  The yellow light emitting point group LPY emits a yellow beam group LY composed of eight beams. In the following description, beams as a plurality of light beams emitted from the first yellow light emission point LPY1 to the eighth yellow light emission point LPY8 are referred to as a first yellow beam LY1 to an eighth yellow beam LY8, respectively. The magenta light emission point group LPM emits a magenta beam group LM composed of eight beams. In the following description, beams as a plurality of light beams emitted from the first magenta light emission point LPM1 to the eighth magenta light emission point LPM8 are referred to as a first magenta beam LM1 to an eighth magenta beam LM8, respectively. Further, the cyan light emitting point group LPC emits a cyan beam group LC composed of eight beams. In the following description, beams as a plurality of light beams emitted from the first cyan light emission point LPC1 to the eighth cyan light emission point LPC8 are referred to as a first cyan beam LC1 to an eighth cyan beam LC8, respectively. Furthermore, the black light emitting point group LPK emits a black beam group LK composed of eight beams. In the following description, beams as a plurality of light beams emitted from the first black light emission point LPK1 to the eighth black light emission point LPK8 are referred to as a first black beam LK1 to an eighth black beam LK8, respectively.

FIG. 4 shows a block diagram of the control unit 70 shown in FIG.
A CPU (Central Processing Unit) 71 of the control unit 70 functioning as a setting unit exchanges data appropriately with a RAM (Random Access Memory) 73 in accordance with a program stored in a ROM (Read Only Memory) 72. Execute the process. In addition, information related to an instruction for an image forming operation is input to the control unit 70 from a UI (user interface) 80 via the input / output interface 74. Information relating to the instruction of the image forming operation includes, for example, a monochrome mode as a first mode for forming a monochrome image using only black toner, or a full color image using yellow, magenta, and cyan toners in addition to black. In the full color mode as the second mode for forming the image. The control unit 70 also outputs control signals to the YMC drum drive motor 81, the K drum drive motor 82, the belt drive motor 83, the advance / retreat drive motor 84, and the laser drive signal creation unit 85 via the input / output interface 74. To do.

  Here, the YMC drum driving motor 81 is mechanically connected to the photosensitive drums 11Y, 11M, and 11C, and rotationally drives the photosensitive drums 11Y, 11M, and 11C. On the other hand, the K drum drive motor 82 is mechanically connected to the photosensitive drum 11K, and rotationally drives the photosensitive drum 11K. That is, in the present embodiment, the drive system for the photoconductive drums 11Y, 11M, and 11C and the drive system for the photoconductive drum 11K are separated. The belt drive motor 83 is mechanically connected to the drive roll 21 and rotationally drives the intermediate transfer belt 20 via the drive roll 21. Furthermore, the advance / retreat drive motor 84 is mechanically connected to the advance / retreat roll 22 and moves the advance / retreat roll 22 from the advanced position to the retracted position or from the retracted position to the advanced position. In the present embodiment, the advance / retreat drive motor 84 and the advance / retreat roll 22 function as contact / separation means. The laser drive signal generator 85 is electrically connected to the exposure device 13 and outputs a drive signal for outputting the beam groups LY, LM, LC, and LK for each color to the exposure device 13.

  Next, an image forming operation by the image forming apparatus shown in FIG. 1 will be described. In this image forming apparatus, since the preparation before the image forming operation and the procedure of the image forming operation are different between the monochrome mode and the full color mode, this will also be described.

FIG. 5 is a flowchart for explaining the preparation process for the image forming operation.
When an instruction to start an image forming operation is received via the UI 80 (step 101), the control unit 70 determines whether or not the received instruction is a monochrome mode (step 102). When it is determined that the received instruction is the monochrome mode, the control unit 70 sends a control signal to the advance / retreat drive motor 84, and the advance / retreat drive motor 84 receives the control signal and moves the advance / retreat roll 22 to the retracted position. (Step 103). Subsequently, the control unit 70 sends a control signal to the K drum drive motor 82, and the K drum drive motor 82 receives the control signal and sets the peripheral speed of the black photosensitive drum 11K to the first black peripheral speed VK1. (Step 104). In the monochrome mode, since the photosensitive drums 11Y, 11M, and 11C are not used, it is not necessary to rotate the photosensitive drums 11Y, 11M, and 11C. For this reason, the control unit 70 does not send a control signal to the YMC drum drive motor 81 in the monochrome mode. Next, the control unit 70 sends a control signal to the belt drive motor 83, and the belt drive motor 83 receives the control signal and changes the peripheral speed of the drive roll 21, that is, the peripheral speed of the intermediate transfer belt 20, to the first belt peripheral. The speed VB1 is set (step 105).
Then, after the above setting is completed, the control unit 70 starts an image forming operation in the monochrome mode (step 106).

On the other hand, when it is determined that the instruction received in step 102 is not the monochrome mode, that is, when it is determined that the instruction is the full color mode, the control unit 70 sends a control signal to the advance / retreat drive motor 84, In response to the control signal, the advance / retreat roll 22 is moved to the advanced position (step 107). Subsequently, the control unit 70 sends a control signal to the K drum drive motor 82, and the K drum drive motor 82 receives the control signal and sets the peripheral speed of the photosensitive drum 11K to the second black peripheral speed VK2 ( Step 108). Further, the control unit 70 sends a control signal to the YMC drum drive motor 81, and the YMC drum drive motor 81 receives the control signal and sets the peripheral speed of the photosensitive drums 11Y, 11M, and 11C to the color peripheral speed VC. (Step 109). Next, the control unit 70 sends a control signal to the belt drive motor 83, and the belt drive motor 83 receives the control signal and changes the peripheral speed of the drive roll 21, that is, the peripheral speed of the intermediate transfer belt 20, to the second belt peripheral speed. The speed VB2 is set (step 110).
Then, after the above setting is completed, the control unit 70 starts an image forming operation in the full color mode (step 106).

Here, FIG. 6A is a diagram for explaining the settings of the photosensitive drums 11Y, 11M, 11C, and 11K and the intermediate transfer belt 20 in the monochrome mode.
As described with reference to FIG. 5, in the monochrome mode, the advance / retreat roll 22 moves downward in the figure and stops at the retracted position. Then, the position of the primary transfer surface of the intermediate transfer belt 20 is lowered, and the intermediate transfer belt 20 is separated from the photosensitive drums 11Y, 11M, and 11C. In addition, since the advancing / retreating roll 22 moves to the retracted position, the fixed roll 23 does not move, so that the photosensitive drum 11K is kept in contact with the intermediate transfer belt 20. Therefore, in the monochrome mode, only the photosensitive drum 11K comes into contact with the intermediate transfer belt 20.

  In the monochrome mode, the peripheral speed of the photosensitive drum 11K, that is, the first peripheral speed is set to the first black peripheral speed VK1, and the peripheral speed of the intermediate transfer belt 20, that is, the third peripheral speed is set to the first belt peripheral speed VB1. The Here, the first black peripheral speed VK1 is 0.3% higher than the first belt peripheral speed VB1 (VK1 = 1.003 × VB1). That is, in the monochrome mode, the photosensitive drum 11K and the intermediate transfer belt 20 are rotationally driven with a speed difference of 0.3%. In the following description, the speed difference between the photosensitive drum 11K and the intermediate transfer belt 20 in the monochrome mode is referred to as a first black speed difference ΔVK1.

On the other hand, FIG. 6B is a diagram for explaining the settings of the photosensitive drums 11Y, 11M, 11C, 11K and the intermediate transfer belt 20 in the full color mode.
As described with reference to FIG. 5, in the full color mode, the advance / retreat roll 22 moves upward in the drawing and stops at the advanced position. Then, the position of the primary transfer surface of the intermediate transfer belt 20 is raised, and the intermediate transfer belt 20 comes into contact with the photosensitive drums 11Y, 11M, and 11C. Further, since the position of the fixed roll 23 is not different from the monochrome mode, the photosensitive drum 11K is kept in contact with the intermediate transfer belt 20. Accordingly, in the full color mode, all the photosensitive drums 11Y, 11M, 11C, and 11K come into contact with the intermediate transfer belt 20.

  In the full color mode, the peripheral speed of the photosensitive drum 11K, that is, the first peripheral speed is set to the second black peripheral speed VK2, and the peripheral speed of the photosensitive drums 11Y, 11M, and 11C, that is, the second peripheral speed is set to the color peripheral speed VC. Thus, the peripheral speed of the intermediate transfer belt 20, that is, the third peripheral speed, is set to the second belt peripheral speed VB2. Here, the second black peripheral speed VK2 is lower than the first black peripheral speed VK1 in the monochrome mode, and the second belt peripheral speed VB2 is lower than the first belt peripheral speed VB1 in the monochrome mode. The second black peripheral speed VK2 is 0.3% higher than the second belt peripheral speed VB2 (VK2 = 1.003 × VB2), and the color peripheral speed VC is 3% higher than the second belt peripheral speed VB2. Yes (VC = 1.03 × VB2). Accordingly, the color peripheral speed VC is higher than the second black peripheral speed VK2. That is, in the full color mode, the photosensitive drum 11K and the intermediate transfer belt 20 are rotationally driven with a speed difference of 0.3%, while the photosensitive drums 11Y, 11M, and 11C and the intermediate transfer belt 20 are rotated. Is driven to rotate with a speed difference of 3%. In the following description, the speed difference between the photosensitive drum 11K and the intermediate transfer belt 20 in the full color mode is referred to as a second black speed difference ΔVK2, and the speed difference between the photosensitive drums 11Y, 11M, and 11C and the intermediate transfer belt 20 is described. Is referred to as a color speed difference ΔVC. As is apparent from the above-described relationship, the color speed difference ΔVC is larger than the second black speed difference ΔVK2.

Now, an image forming operation in the monochrome mode will be specifically described.
In the monochrome mode, the surface of the photosensitive drum 11K rotating at the first black peripheral speed VK1 is charged to a predetermined potential by the charging device 12K. Next, the exposure device 13 selectively irradiates the photosensitive drum 11K with the black beam group LK based on the black drive signal, and as a result, a predetermined electrostatic latent image is formed on the photosensitive drum 11K. . Subsequently, the developing device 14K develops the electrostatic latent image formed on the photosensitive drum 11K with black toner, and forms a black toner image on the photosensitive drum 11K. The black toner image formed on the photosensitive drum 11K is primarily transferred to the intermediate transfer belt 20 rotating at the first belt peripheral speed VB1 using the primary transfer roll 15K. The residual toner remaining on the photosensitive drum 11K after the primary transfer is removed by the black drum cleaner 16K.

Next, the black toner image primarily transferred to the intermediate transfer belt 20 is conveyed toward the secondary transfer device 30 as the intermediate transfer belt 20 rotates.
On the other hand, the paper P stored in the paper storage unit 40 is fed out by a feeding roll 41 and conveyed in a state where the paper P is rolled up one by one by a winding unit 42. Then, the conveyed paper P is temporarily blocked by the resist roll 43 and is re-conveyed at the timing when the toner image on the intermediate transfer belt 20 enters the secondary transfer device 30.
Then, the toner image on the intermediate transfer belt 20 is secondarily transferred to the paper P by the secondary transfer device 30. The sheet P on which the toner image has been transferred is further conveyed by the sheet conveying belt 44, and then the toner image is fixed on the sheet P by the fixing device 45, and is conveyed to a sheet discharge unit (not shown). The residual toner remaining on the intermediate transfer belt 20 after the secondary transfer is removed by the belt cleaner 27.

Next, an image forming operation in the full color mode will be specifically described.
In the full color mode, the photosensitive drums 11Y, 11M, and 11C rotating at the color peripheral speed VC are charged to a predetermined potential by the corresponding charging devices 12Y, 12M, and 12C. Further, the surface of the photosensitive drum 11K rotating at the second black peripheral speed VK2 is charged to a predetermined potential by the charging device 12K. Next, the exposure device 13 applies the yellow beam group LY based on the yellow drive signal to the photoconductive drum 11Y, the magenta beam group LM based on the magenta drive signal to the photoconductive drum 11M, and the cyan drive signal to the photoconductive drum 11C. Are selectively irradiated with the cyan beam group LC based on the above, and the photosensitive drum 11K is selectively irradiated with the black beam group LK based on the drive signal. As a result, predetermined electrostatic latent images are formed on the respective photosensitive drums 11Y, 11M, 11C, and 11K. Subsequently, each of the developing devices 14Y, 14M, 14C, and 14K develops the electrostatic latent image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11K with a corresponding color toner, and then develops the photosensitive drum 11Y. A yellow toner image, a magenta toner image on the photosensitive drum 11M, a cyan toner image on the photosensitive drum 11C, and a black toner image on the photosensitive drum 11K are formed. The yellow toner image formed on the photoreceptor drum 11Y is formed on the photoreceptor drum 11C using the primary transfer roll 15Y, and the magenta toner image formed on the photoreceptor drum 11M is formed on the photoreceptor drum 11C using the primary transfer roll 15M. The intermediate transfer belt 20 that rotates at the second belt peripheral speed VB2 using the primary transfer roll 15C and the black toner image formed on the photosensitive drum 11K using the primary transfer roll 15C. The primary transfer is performed sequentially. The residual toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11K after the primary transfer is removed by the corresponding drum cleaners 16Y, 16M, 16C, and 16K.

  Next, the yellow, magenta, cyan, and black toner images primarily transferred to the intermediate transfer belt 20 are conveyed toward the secondary transfer device 30 as the intermediate transfer belt 20 rotates. Since the subsequent steps are the same as those in the monochrome mode, detailed description thereof is omitted.

  As described above, in the present embodiment, the first belt peripheral speed VB1 in the monochrome mode is made faster than the second belt peripheral speed VB2 in the full color mode, so that the image forming speed in the monochrome mode is made higher than that in the full color mode. Yes. Thereby, the productivity of the image in the monochrome mode is improved as compared with the full color mode. In the present embodiment, the photosensitive drums 11Y, 11M, and 11C are separated from the intermediate transfer belt 20 in the monochrome mode. As a result, wear of the protective layer provided on the photosensitive layers of the photosensitive drums 11Y, 11M, and 11C is suppressed.

  In the present embodiment, as the image forming speed in the monochrome mode is higher than that in the full color mode, the first black peripheral speed VK1 in the monochrome mode of the photosensitive drum 11K is changed to the second black peripheral speed VK2 in the full color mode. It is faster than. For this reason, the photosensitive drum 11K in the monochrome mode is less likely to be charged than in the full color mode. Therefore, in the present embodiment, a scorotron charger having higher charging performance than the roll charger used as the other charging devices 12Y, 12M, and 12C is used as the charging device 12K. As a result, the photosensitive drum 11K obtains good charging characteristics in both the monochrome mode and the full color mode.

  By the way, in such a charging process, a part of discharge products such as nitrogen oxides generated by the charging devices 12Y, 12M, 12C, and 12K adhere to the corresponding photosensitive drums 11Y, 11M, 11C, and 11K. There are things to do. As a result, for example, the charging performance of the photosensitive layer changes between the portion where the discharge product is attached and the portion where the discharge product is not attached, and as a result, the image quality of the obtained toner image is deteriorated.

Therefore, in the present embodiment, the discharge product adhering to each of the photosensitive drums 11Y, 11M, 11C, and 11K is configured to be scraped off by the intermediate transfer belt 20. That is, in this image forming apparatus, a predetermined speed difference is provided between each of the photosensitive drums 11Y, 11M, 11C, and 11K and the intermediate transfer belt 20.
Specifically, for example, in the monochrome mode, the first black speed difference ΔVK1 is provided between the photosensitive drum 11K and the intermediate transfer belt. On the other hand, in the full color mode, the second black speed difference ΔVK2 is between the photosensitive drum 11K and the intermediate transfer belt 20, and the color speed difference ΔVC is between the photosensitive drums 11Y, 11M, and 11C and the intermediate transfer belt. Provided.

  In this embodiment, as described above, a scorotron charger, which is a kind of non-contact charger, is used as the charging device 12K, whereas a contact charger is used as the charging devices 12Y, 12M, and 12C. A kind of roll charger is used. In general, it is known that when a contact charger is used, the discharge product adheres more to the photoreceptor than when a non-contact charger is used. This is presumably because the contact type charger discharges closer to the photoreceptor than the non-contact type charger. That is, in this image forming apparatus, it can be said that discharge products are more likely to adhere to the photosensitive drums 11Y, 11M, and 11C as compared to the photosensitive drum 11K.

  Therefore, in the present embodiment, in the full color mode, the second black speed difference ΔVK2 is set between the photosensitive drum 11K and the intermediate transfer belt 20, and the photosensitive drums 11Y, 11M, and 11C and the intermediate transfer belt 20 are set. A color speed difference ΔVC having a speed difference larger than the second black speed difference ΔVK2 is set therebetween. Thereby, the discharge product adhering to the photoconductor drums 11Y, 11M, and 11C and the discharge product adhering to the photoconductor drum 11K are appropriately scraped off and removed. Therefore, image defects caused by discharge products locally adhering to the respective photosensitive drums 11Y, 11M, 11C, and 11K are suppressed.

  By the way, in this image forming apparatus, in the full color mode, as described above, a speed difference is provided between the color peripheral speed VC of the photosensitive drums 11Y, 11M, and 11C and the second black peripheral speed VK2 of the photosensitive drum 11K. (VK2 <VC). Further, in this image forming apparatus, the yellow, magenta, cyan, and black color beam groups LY, LM, LC, and LK irradiated to the photosensitive drums 11Y, 11M, 11C, and 11K will be described with reference to FIG. As described above, deflection scanning is performed using a single polygon mirror 62. Therefore, in the full color mode, an electrostatic latent image (toner image) formed on the photosensitive drums 11Y, 11M, and 11C and an electrostatic latent image (toner image) formed on the photosensitive drum 11K are A difference occurs in the magnification in the sub-scanning direction in one scanning.

Now, the difference in magnification in the sub-scanning direction among yellow, magenta, cyan and black in the full color mode will be specifically described.
FIG. 7 shows an example of a laser drive signal supplied to the surface emitting laser array chip 50 (see FIG. 3) of the exposure apparatus 13 in the full color mode. FIG. 7 exemplifies a laser drive signal when a so-called process black halftone image is formed by superimposing yellow, magenta, cyan, and black toners.

  Here, the laser drive signals are eight first yellow drive signals Y1 to eighth yellow drive supplied to the first yellow light emission points LPY1 to LPY8 constituting the yellow light emission point group LPY. It has a signal Y8. The laser drive signals are the eight first magenta drive signals M1 to eighth magenta drive supplied to the first magenta light emission point LPM1 to the eighth magenta light emission point LPM8 constituting the magenta light emission point group LPM. It has a signal M8. Further, the laser drive signals are eight first cyan drive signals C1 to 8th cyan drive supplied to the first cyan light emission point LPC1 to the eighth cyan light emission point LPC8 constituting the cyan light emission point group LPC. It has a signal C8. Furthermore, the laser drive signals are eight first black drive signals K1 to 8th black supplied to the first black light emission points LPK1 to LPK8 constituting the black light emission point group LPK. It has a drive signal K8.

  The laser drive signals Y1 to Y8, M1 to M8, C1 to C8, and K1 to K8 for each color are output one line at a time in the main scanning direction in synchronization with a predetermined period T. The period T is set to be 1/6 of the rotation period of the polygon mirror 62 because the polygon mirror 62 of the present embodiment has six deflection surfaces 62A.

  In this embodiment, since a so-called tandem image forming apparatus is used, the positions of the photosensitive drums 11Y, 11M, 11C, and 11K with respect to the intermediate transfer belt 20 as shown in FIG. It is displaced in the scanning direction. More specifically, the photosensitive drum 11M is provided at a position preceding the photosensitive drum 11Y in the sub-scanning direction. Similarly, the photoconductor drum 11C is provided at a position preceding the photoconductor drum 11M in the sub-scanning direction, and the photoconductor drum 11K is provided at a position preceding the photoconductor drum 11C in the sub-scanning direction. For this reason, the surface emitting laser array chip 50 is supplied with a laser drive signal in consideration of the distance in the sub-scanning direction of each of the photosensitive drums 11Y, 11M, 11C, and 11K in the same cycle.

  For example, as shown in FIG. 7, the first yellow driving signal Y1 to the eighth yellow driving signal Y8 corresponding to the Nth set are supplied to the first yellow light emitting point LPY1 to the eighth yellow light emitting point LPY8. Shall. One set is composed of drive signals for eight lines in the sub-scanning direction. At this time, the first magenta light emission point LPM1 to the eighth magenta light emission point LPM8 are Na-set first magenta driving signal M1 to eighth magenta driving signal preceding the yellow by a line in the sub-scanning direction. M8 is supplied. Further, the first cyan light emission point LPC1 to the eighth cyan light emission point LPC8 have Nb-th first cyan drive signal C1 to eighth cyan drive signal C8 preceding the yellow by b lines in the sub-scanning direction. Is supplied. Further, the first black light emission point LPK1 to the eighth black light emission point LPK8 have the Nc set first black drive signal K1 to eighth black drive signal K8 preceding the yellow by c lines in the sub-scanning direction. Is supplied. Here, a <b <c, and the number of lines a, b, and c is determined in advance based on the sub-scanning direction distances of the photosensitive drums 11Y, 11M, 11C, and 11K.

  FIG. 8 shows each color beam group LY when the N-th set of yellow beam groups LY (first yellow beam LY1 to eighth yellow beam LY8) is irradiated from the surface emitting laser array chip 50 in the full color mode. It is a schematic diagram for demonstrating the behavior of LM, LC, and LK. As is apparent from FIG. 7, at this time, the surface emitting laser array chip 50 has a Na-set magenta beam group LM (first magenta beam LM1 to eighth magenta beam LM8) and Nb-set cyan. The beam group LC (first cyan beam LC1 to eighth cyan beam LC8) and the Nc-th set black beam group LK (first black beam LK1 to eighth black beam LK8) are also irradiated at the same time. .

  The color beam groups LY, LM, LC, and LK irradiated from the surface emitting laser array chip 50 at the same period are deflected and scanned in the main scanning direction by a predetermined deflecting surface 62A of the polygon mirror 62. The respective color beam groups LY, LM, LC, and LK that have been deflected and scanned are irradiated to the corresponding photosensitive drums 11Y, 11M, 11C, and 11K through the post-deflection optical system 63 (see FIG. 2). The

  In the full color mode, the photosensitive drum 11Y rotates in the sub-scanning direction at the color peripheral speed VC. The N-th set of the first yellow beam LY1 to the eighth yellow beam LY8 reflected from the predetermined deflection surface 62A is exposed to the photosensitive drum 11Y while moving in the main scanning direction. Further, the photosensitive drum 11M also rotates in the sub-scanning direction at the color peripheral speed VC similarly to the photosensitive drum 11Y. The Na-set first magenta beam LM1 to eighth magenta beam LM8 reflected from the predetermined deflection surface 62A are exposed to the photosensitive drum 11M while moving in the main scanning direction. Further, the photosensitive drum 11C is also rotated in the sub-scanning direction at the color peripheral speed VC similarly to the photosensitive drums 11Y and 11M. Then, the first cyan beam LC1 to the eighth cyan beam LC8 of the Nb set reflected from the predetermined deflection surface 62A are exposed to the photosensitive drum 11C while moving in the main scanning direction. On the other hand, the photosensitive drum 11K rotates in the sub-scanning direction at the second black peripheral speed VK2. Then, the first black beam LK1 to the eighth black beam LK8 of the Nc set reflected from the predetermined deflection surface 62A are exposed to the photosensitive drum 11K while moving in the main scanning direction.

  Here, the adjacent interval of the first yellow beam LY1 to the eighth yellow beam LY8 on the photosensitive drum 11Y and the first magenta beam LM1 to the eighth magenta on the photosensitive drum 11M in the same set. The adjacent interval of the beam LM8 and the adjacent interval of the first cyan beam LC1 to the eighth cyan beam LC8 on the photosensitive drum 11C are all the same in-set gap G. Further, the adjacent gap between the first black beam LK1 to the eighth black beam LK8 on the photosensitive drum 11K in the same set is also the in-set gap G. That is, the interval between adjacent beams in the set is the same regardless of the peripheral speed of the drum.

  FIG. 9 shows electrostatic latent images formed on the photosensitive drums 11Y, 11M, 11C, and 11K when the surface emitting laser array chip 50 is driven in the full color mode with the laser drive signal shown in FIG. It is a figure for demonstrating. Here, FIG. 9A shows an electrostatic latent image formed on the photosensitive drums 11Y, 11M, and 11C, and FIG. 9B shows an electrostatic latent image formed on the photosensitive drum 11K. ing.

As shown in FIG. 9A, the photosensitive drum 11Y (photosensitive drum 11M, photosensitive drum 11C) has an N−− beam by a yellow beam group LY (magenta beam group LM, cyan beam group LC). The electrostatic latent images of the first set (Na-1 set, Nb-1 set), N set (Na set, Nb set), and N + 1 set (Na + 1 set, Nb + 1 set) are synchronized. However, they are sequentially formed in the sub-scanning direction.
In the formed yellow, magenta, and cyan electrostatic latent images, the adjacent intervals of the color beams LY1 to LY8, LM1 to LM8, and LC1 to LC8 in the same set become the in-set gap G as described above. In this example, the eighth yellow beam LY8, the first yellow beam LY1, the eighth magenta beam LM8, and the second yellow beam at the boundary between two sets (for example, N-1 set and N set) adjacent in the sub-scanning direction. The adjacent spacing of the 1 magenta beam LM1, the eighth cyan beam LC8, and the first cyan beam LC1 is the color set gap GC. In this example, it is assumed that the in-set gap G and the color set gap GC are set in advance to be equal.

  Therefore, when exposure is performed using the laser drive signal shown in FIG. 7 in the full color mode, the potentials of the photosensitive drums 11Y, 11M, and 11C charged to the predetermined charging potential VH are uniformly reduced. Accordingly, a uniform electrostatic latent image is formed on each of the photosensitive drums 11Y, 11M, and 11C in the sub-scanning direction.

On the other hand, as shown in FIG. 9B, the electrostatic latent images of the Nc−1th set, the Ncth set, and the Nc + 1th set are sub-scanned on the photosensitive drum 11K by the black beam group LK. Sequentially formed in the direction. Here, the Nc-1th electrostatic latent image is a yellow N-1th electrostatic latent image, and the Ncth electrostatic latent image is a yellow Nth electrostatic latent image. , The Nc + 1th set of electrostatic latent images are synchronized with the N + 1th set of electrostatic latent images for yellow, respectively.
In the black electrostatic latent image to be formed, the adjacent interval between the black beams LK1 to LK8 in the same set becomes the in-set gap G as described above. On the other hand, a gap GK between black sets, which is an adjacent interval between the eighth black beam LK8 and the first black beam LK1, at the boundary between two sets (for example, Nc-1 set and Nc set) adjacent in the sub-scanning direction is The gap G within the set (= gap GC between color sets) becomes narrower. In this example, since each color beam group LY, LM, LC, LK is scanned by a single polygon mirror 62 as described above, the period T for creating the electrostatic latent image of each set is common to each color. (See FIG. 7). In the full color mode, the second black peripheral speed VK2 of the photoconductor drum 11K is set lower than the color peripheral speed VC of the photoconductor drums 11Y, 11M, and 11C. For this reason, the distance moved between the sets in the sub-scanning direction is different between the photoconductive drums 11Y, 11M, and 11C and the photoconductive drum 11K, and as a result, the gap between the sets is different.

  Here, when the speed difference between the color peripheral speed VC and the second black peripheral speed VK2 in the full color mode is small, the difference between the in-set gap G and the color set gap GC and the black set gap GK is negligible. Therefore, no particular problem occurs. On the other hand, if the speed difference between the color peripheral speed VC and the second black peripheral speed VK2 increases to some extent, when exposure is performed using the laser drive signal shown in FIG. 7 in the full color mode, the charge is charged to a predetermined charging potential VH. A phenomenon appears in which the potential of the photosensitive drum 11K is lower than the other parts at the boundary between sets. This is due to the fact that the eighth black beam LK8 of the previous set approaches the first black beam LK1 of the next set at the boundary between the sets. Since such a boundary between sets occurs every 8 lines in the sub-scanning direction, for example, when a black halftone image is to be formed, it appears as striped density unevenness in the black image. End up.

Therefore, in the present embodiment, by correcting the first black drive signal K1 to the eighth black drive signal K8 supplied to the surface emitting laser array chip 50, the density unevenness of the black image in the full color mode is suppressed. Yes.
FIG. 10 is a block diagram showing a configuration of the laser drive signal creation unit 85 shown in FIG.
Image data D (YMCK) is input to the laser drive signal generator 85 from, for example, a scanner device or a computer device (both not shown). Further, the laser drive signal creation unit 85 creates drive signals Y1 to Y8, M1 to M8, C1 to C8, and K1 to K8 for each color based on the input image data D (YMCK), and the exposure apparatus 13. The light is output to the light emitting points LPY1 to LPY8, LPM1 to LPM8, LPC1 to LPC8, and LPK1 to LPK8 of the surface emitting laser array chip 50 provided in (see FIG. 1). Here, the laser drive signal creation unit 85 outputs a total of 32 drive signals for each color, 8 in parallel.

  The laser drive signal creation unit 85 includes an image data separation unit 91, an image data development unit 92, and a drive signal output unit 93. The laser drive signal creation unit 85 further includes a black data correction unit 94 and a correction data storage unit 95.

The image data separation unit 91 separates image data D (YMCK) input from the outside for each color, and outputs the image data as yellow image data DY, magenta image data DM, cyan image data DC, and black image data DK.
The image data expansion unit 92 expands the input image data DY, DM, DC, DK for each color in the main scanning direction and the sub-scanning direction, respectively. Then, the image data development unit 92 outputs the image data DY, DM, DC, and DK for each color as a set for every 8 lines that are continuous in the sub-scanning direction. More specifically, the image data development unit 92 generates the first yellow data DY1 to the eighth yellow data DY8 based on the yellow image data DY, and the first magenta data DM1 to the eighth magenta based on the magenta image data DM. The magenta data DM8 is repeatedly output from the first cyan data DC1 to the eighth cyan data DC8 based on the cyan image data DC and from the first black data DK1 to the eighth black data DK8 based on the black image data DK.

  A black data correction unit 94 as a kind of correction means corrects the black data DK1 to DK8 input from the image data development unit 92 for each line in the sub-scanning direction, and the corrected black data DK1 to DK1. DK8 is output. Here, the correction data storage unit 95 stores correction values used by the black data correction unit 94 as a table. Then, the black data correction unit 94 reads a table to be used from the correction data storage unit 95 based on a control signal input via the control unit 70 (see FIG. 4), and uses the read table to read each black data. Corrections by multiplication are applied to DK1 to DK8, respectively. Details of the table will be described later.

  The drive signal output unit 93 includes first yellow data DY1 to eighth yellow data DY8, first magenta data DM1 to eighth magenta data DM8, first cyan data DC1 to eighth cyan data input from the image data development unit 92. Corresponding to each light emission point LP (see FIG. 3) based on the DC8 and the corrected first black data DK1 to eighth black data DK8 input from the image data development unit 92 via the black data correction unit 94. Create and output a laser drive signal. Specifically, the drive signal output unit 93 performs the first yellow drive for one set, that is, for eight lines in the continuous sub-scanning direction, based on the input first yellow data DY1 to eighth yellow data DY8. A signal Y1 to an eighth yellow drive signal Y8 are generated and output in parallel. Here, for example, the first yellow drive signal Y1 created based on the first yellow data DY1 in one set is the first on the most upstream side in the sub-scanning direction in the yellow light emission point group LPY shown in FIG. The light is supplied to the yellow light emitting point LPY1. For example, the eighth yellow drive signal Y8 created based on the eighth yellow data DY8 is applied to the eighth yellow light emission point LPY8 on the most downstream side in the sub-scanning direction in the yellow light emission point group LPY shown in FIG. Supplied. Further, the second yellow driving signal Y2 to the seventh yellow driving signal Y7 of the second to seventh lines generated based on the other second yellow data DY2 to seventh yellow data DY7 are the corresponding second yellow light emitting points. LPY2 to the seventh yellow emission point LPY7 are supplied. Further, the first magenta drive signal M1 to the eighth magenta drive signal M8 created based on the first magenta data DM1 to the eighth magenta data DM8 are the first magenta constituting the magenta light emitting point group LPM shown in FIG. The light emission point LPM1 is supplied to the eighth magenta light emission point LPM8. Further, the first cyan drive signal C1 to the eighth cyan drive signal C8 created based on the first cyan data DC1 to the eighth cyan data DC8 are the first cyan constituting the cyan light emission point group LPC shown in FIG. The light emission points LPC1 to LPC8 are respectively supplied to the light emission points LPC1 to LPC8. Furthermore, the first black drive signal K1 to the eighth black drive signal K8 created on the basis of the corrected first black data DK1 to eighth black data DK8 are obtained by changing the black light emission point group LPK shown in FIG. The light is supplied to the first black light emission point LPK1 to the eighth black light emission point LPK8, respectively.

FIG. 11 shows an example of a table stored in the correction data storage unit 95. In this table, the first black data DK1 to the eighth black data DK8 in one set are associated with the full color correction value XC used in the full color mode and the monochrome correction value XM used in the monochrome mode. .
Here, in the full color correction value XC, 1.0 is set for the second black data DK2 to the seventh black data DK7, while it is 0 for the first black data DK1 and the eighth black data DK8. .6 is set. That is, lower values are set for the most upstream side and the most downstream side in the sub-scanning direction corresponding to the boundary between sets than for the central side in the sub-scanning direction. On the other hand, in the monochrome correction value XM, 1.0 is set for all of the first black data DK1 to the eighth black data DK8. The correction values for the first black data DK1 and the eighth black data DK8 in the full color correction value XC may be set as appropriate based on the difference between the in-set gap G and the inter-black set gap GK.

Next, the operations of the laser drive signal generation unit 85 and the exposure device 13 (surface emitting laser array chip 50) in the image forming operation will be specifically described.
First, the full color mode will be described. In the full color mode, the control unit 70 sends a control signal to the black data correction unit 94, and the black data correction unit 94 receives the control signal and receives the correction value for full color shown in FIG. XC is being read.

In the full color mode, image data D (YMCK) including each color data is input to the laser drive signal creation unit 85. Therefore, the image data separation unit 91 outputs predetermined yellow image data DY, magenta image data DM, cyan image data DC, and black image data DK based on the image data D (YMCK).
Further, the image data development unit 92 converts the first yellow data DY1 to the eighth yellow data DY8 based on the yellow image data DY, the first magenta data DM1 to the eighth magenta data DM8 based on the magenta image data DM, and cyan. First cyan data DC1 to eighth cyan data DC8 are sequentially output based on the image data DC, and first black data DK1 to eighth black data DK8 are sequentially output based on the black image data DK.

  The black data correction unit 94 multiplies each of the input first black data DK1 to eighth black data DK8 using the full-color correction value XC, and the result is corrected first black data DK1. To 8th black data DK8. As shown in FIG. 11, the full color correction value XC is 1.0 for the second black data DK2 to the seventh black data DK7 corresponding to the central portion in the sub-scanning direction in one set. The first black data DK1 and the eighth black data DK8 corresponding to both ends in the sub-scanning direction are 0.6.

  Here, FIG. 12A shows an example of the first black data DK1 to the eighth black data DK8 before correction input from the image data development unit 92 to the black data correction unit 94 in the full color mode. FIG. 12B shows the corrected first black data DK1 to DK1 output from the black data correction unit 94 when the black data before correction shown in FIG. 12A is input in the full color mode. 8 black data DK8 is shown. Here, black data when a black halftone image is formed is illustrated. In the full color mode, as shown in FIG. 12, the black data correction unit 94 makes 0.6 times the first black data DK1 and the eighth black data DK8 before correction for the first and eighth lines in the sub-scanning direction. For the second to seventh lines in the sub-scanning direction, the same values as the second black data DK2 to the seventh black data DK7 before correction are respectively output.

  Then, the drive signal output unit 93 outputs the yellow drive signals Y1 to Y8 created based on the yellow data DY1 to DY8, the magenta drive signals M1 to M8 created based on the magenta data DM1 to DM8, and the cyan data. The cyan drive signals C1 to C8 created based on DC1 to DC8 and the black drive signals K1 to K8 created based on the corrected black data DK1 to DK8 are output in parallel.

  Thereafter, in the surface emitting laser array chip 50 of the exposure apparatus 13, the yellow beam group LY is generated from the corresponding yellow light emission points LPY1 to LPY8 based on the yellow drive signals Y1 to Y8, and based on the magenta drive signals M1 to M8. Magenta light emission points LPM1 to LPM8 corresponding to magenta beam groups LM, cyan light emission points LPC1 to LPC8 corresponding to cyan light beam groups LC based on cyan drive signals C1 to C8, and black drive signals K1. Based on ˜K8, the black beam group LK is irradiated from the corresponding black light emission points LPK1 to LPK8 while being synchronized.

  FIG. 13 is a diagram for explaining electrostatic latent images formed on the photosensitive drums 11Y, 11M, 11C, and 11K in the full color mode. Here, FIG. 13A shows an electrostatic latent image formed on the photosensitive drums 11Y, 11M, and 11C, and FIG. 13B shows an electrostatic latent image formed on the photosensitive drum 11K. ing. Here, a case where a process black halftone image using yellow, magenta, cyan, and black is formed will be described as an example.

  As shown in FIG. 13A, the photosensitive drums 11Y, 11M, and 11C have yellow and magenta colors in the in-set gap G and the color set gap GC as in the case of FIG. 9A. The electrostatic latent images are sequentially formed by the cyan beam groups LY, LM, and LC. Here, the color set gap GC in the full color mode is set to be equal to the in-set gap G (GC = G). When exposure is performed using the yellow, magenta, and cyan beam groups LY, LM, and LC, the potentials of the photosensitive drums 11Y, 11M, and 11C charged to the predetermined charging potential VH are uniform. descend. Therefore, in the full color mode, a uniform electrostatic latent image is formed on each of the photosensitive drums 11Y, 11M, and 11C in the sub-scanning direction.

  On the other hand, as shown in FIG. 13 (b), the photosensitive drum 11K has a static by the black beam group LK in the in-set gap G and the black-set gap GK, as in FIG. 9 (b). An electrostatic latent image is formed. Here, the gap GK between black sets in the full color mode becomes narrower than the gap G within the set (GK <G).

  However, in the full color mode, as shown in FIG. 12, the black data correction unit 94 performs correction to reduce the values of the first black data DK1 and the eighth black data DK8 to 60%. Accordingly, the first black drive signal K1 and the eighth black drive signal K8 created based on the first black data DK1 and the eighth black data DK8 are also set to 60% of the value to be originally output. Is done. For this reason, even if the exposure position by the eighth black beam LK8 of the previous set and the exposure position by the first black beam LK1 of the next set approach each other at the boundary between the sets, the amount of light at the boundary is different. It becomes almost equal to the part. When exposure is performed with the black beam group LK obtained by performing such correction, the potential of the photosensitive drum 11K charged to the predetermined charging potential VH is reduced substantially uniformly. Therefore, by using the method of the present embodiment, a substantially uniform electrostatic latent image is formed on the photosensitive drum 11K in the sub-scanning direction in the full color mode.

  In the full color mode, as can be seen from FIG. 13, electrostatic latent images (toner images) formed on the photosensitive drums 11Y, 11M, and 11C and electrostatic latent images (toner images) formed on the photosensitive drum 11K. ) And the extension in the sub-scanning direction are different. More specifically, the electrostatic latent image formed on the photosensitive drum 11K is contracted more than the electrostatic latent images formed on the other photosensitive drums 11Y, 11M, and 11C. Here, in the present embodiment, the second black peripheral speed VK2 of the photosensitive drum 11K in the full color mode is set to be lower than the color peripheral speed VC of the other photosensitive drums 11Y, 11M, and 11C. Therefore, when the toner images of the respective colors formed on the photosensitive drums 11Y, 11M, 11C, and 11K are primarily transferred to the intermediate transfer belt 20 that rotates at the second belt peripheral speed VB2, the sub-scanning direction is set. The expansion and contraction will be corrected.

  Next, the monochrome mode will be described. In the monochrome mode, the control unit 70 sends a control signal to the black data correction unit 94, and the black data correction unit 94 receives the control signal and reads the monochrome correction value XM from the correction data storage unit 95. Yes.

In the monochrome mode, image data D (YMCK) including only black data is input to the laser drive signal creation unit 85. Therefore, the image data separation unit 91 outputs empty yellow image data DY, magenta image data DM, and cyan image data DC based on the image data D (YMCK), and outputs predetermined black image data DK.
Further, the image data development unit 92 sequentially outputs the first black data DK1 to the eighth black data DK8 based on the black image data DK. Further, since the yellow image data DY, the magenta image data DM, and the cyan image data DC are empty, the image data developing unit 92 is empty, each of the yellow data DY1 to DY8, each of the magenta data DM1 to DM8, and each of the cyan data. DC1 to DC8 are also output.

  The black data correction unit 94 multiplies each of the input first black data DK1 to eighth black data DK8 using the monochrome correction value XM, and the result is corrected first black data DK1. To 8th black data DK8. As shown in FIG. 11, the monochrome correction value XM is 1.0 for all of the first black data DK1 to the eighth black data DK8.

  Here, FIG. 14A shows an example of the first black data DK1 to the eighth black data DK8 before correction input from the image data development unit 92 to the black data correction unit 94 in the monochrome mode. FIG. 14B shows the corrected first black data DK1 to DK1 output from the black data correction unit 94 when the black data before correction shown in FIG. 14A is input in the monochrome mode. 8 black data DK8 is shown. Here, as in the example shown in FIG. 12, black data when a black halftone image is formed is illustrated. In the monochrome mode, the black data correction unit 94 outputs the same values as the first black data DK1 to the eighth black data DK8 before correction for all of the first to eighth lines in the sub-scanning direction.

  And the drive signal output part 93 outputs each black drive signal K1-K8 produced based on each black data DK1-DK8 after correction | amendment in parallel. Further, since the yellow data DY1 to DY8, the magenta data DM1 to DM8, and the cyan data DC1 to DC8 are empty, the drive signal output unit 93 has empty yellow, magenta, and cyan drive signals Y1 to Y1, respectively. Y8, M1 to M8, and C1 to C8 are also output.

  Thereafter, the surface emitting laser array chip 50 of the exposure apparatus 13 irradiates the black beam group LK from the corresponding black light emission points LPK1 to LPK8 based on the respective black drive signals K1 to K8. In the monochrome mode, the yellow, magenta, and cyan drive signals Y1 to Y8, M1 to M8, and C1 to C8 are all empty, so the yellow beam group LY, the magenta beam group LM, and the cyan beam group LC. Is not irradiated.

  FIG. 15 is a diagram for explaining an electrostatic latent image formed on the photosensitive drum 11K in the monochrome mode. Here, a case where a halftone image using black is formed will be described as an example.

  As shown in FIG. 15, an electrostatic latent image is formed on the photosensitive drum 11K by the black beam group LK at the in-set gap G and the black set gap GK. Here, the black set gap GK in the monochrome mode is set to be equal to the in-set gap G (GK = G). This is because the photosensitive drums 11Y, 11M, and 11C are not used in the monochrome mode, and therefore, appropriate exposure conditions (for example, the rotational speed of the polygon mirror 62) are set for the first black peripheral speed VK1 of the photosensitive drum 11K. This is because it becomes possible. When exposure is performed with the black beam group LK, the potential of the photosensitive drum 11K charged to the predetermined charging potential VH is uniformly reduced. Therefore, in the monochrome mode, a uniform electrostatic latent image is formed on the photosensitive drum 11K in the sub-scanning direction.

  In the present embodiment, the apparent correction by multiplication is performed by the black data correction unit 94 even in the monochrome mode. However, the present invention is not limited to this. For example, in the monochrome mode, the first black data DK1 to the eighth black data DK8 output from the image data expansion unit 92 are directly input to the drive signal output unit 93, while in the full color mode, the first black data DK1 output from the image data expansion unit 92 are output. The first black data DK1 to the eighth black data DK8 may be corrected by the black data correction unit 94 and then input to the drive signal output unit 93.

<Embodiment 2>
In the first embodiment, the method suitable for the case where the black set gap GK in the black electrostatic latent image is smaller than the in-set gap G in the full color mode has been described. On the other hand, in the present embodiment, in the full color mode, the exposure position by the eighth black beam LK8 of the previous set and the exposure position by the first black beam LK1 of the next set are almost equal at the boundary between the sets. A case will be described, which is suitable when the gap between black sets GK approaches 0. Note that the gap between black sets GK varies depending on the speed difference between the color peripheral speed VC of the photosensitive drums 11Y, 11M, and 11C and the second black peripheral speed VK2 of the photosensitive drum 11K in the full color mode.

FIG. 16 shows an example of a table stored in the correction data storage unit 95 in the present embodiment. In this table, as in the first embodiment, the first black data DK1 to the eighth black data DK8 in one set, the full color correction value XC used in the full color mode, and the monochrome correction value used in the monochrome mode. XM is associated.
Here, in the full color correction value XC, 1.0 is set for the first black data DK1 to the seventh black data DK7, while 0.0 is set for the eighth black data DK8. Yes. On the other hand, as for the monochrome correction value XM, 1.0 is set for all of the first black data DK1 to the eighth black data DK8, as in the first embodiment.

  Next, the operations of the laser drive signal generation unit 85 and the exposure device 13 (surface emitting laser array chip 50) in the image forming operation will be specifically described. However, since the monochrome mode is the same as that of the first embodiment, only the full color mode will be described here. In the full color mode, the control unit 70 sends a control signal to the black data correction unit 94, and the black data correction unit 94 receives the control signal and receives the correction value for full color shown in FIG. XC is being read.

In the full color mode, image data D (YMCK) including each color data is input to the laser drive signal creation unit 85. Therefore, the image data separation unit 91 outputs predetermined yellow image data DY, magenta image data DM, cyan image data DC, and black image data DK based on the image data D (YMCK).
Further, the image data development unit 92 converts the first yellow data DY1 to the eighth yellow data DY8 based on the yellow image data DY, the first magenta data DM1 to the eighth magenta data DM8 based on the magenta image data DM, and cyan. First cyan data DC1 to eighth cyan data DC8 are sequentially output based on the image data DC, and first black data DK1 to eighth black data DK8 are sequentially output based on the black image data DK.

  The black data correction unit 94 multiplies each of the input first black data DK1 to eighth black data DK8 using the full-color correction value XC, and the result is corrected first black data DK1. To 8th black data DK8. As shown in FIG. 16, the full color correction value XC is 1.0 for all of the first black data DK1 to the seventh black data DK7 in one set, but on the most downstream side in the sub-scanning direction. The corresponding 8th black data DK8 is 0.0.

  Here, FIG. 17A shows an example of the first black data DK1 to the eighth black data DK8 before correction input from the image data development unit 92 to the black data correction unit 94 in the full color mode. FIG. 17B shows the corrected first black data DK1 to DK1 output from the black data correction unit 94 when the black data before correction shown in FIG. 17A is input in the full color mode. 8 black data DK8 is shown. Here, black data when a black halftone image is formed is illustrated. In the full color mode, as shown in FIG. 17B, the black data correction unit 94 has the same values as the first black data DK1 to the seventh black data DK7 before correction for the first to seventh lines in the sub-scanning direction. For the eighth line in the sub-scanning direction, a value obtained by multiplying each of the uncorrected eighth black data DK8 by 0.0, that is, a value of 0 is output.

  Then, the drive signal output unit 93 outputs the yellow drive signals Y1 to Y8 created based on the yellow data DY1 to DY8, the magenta drive signals M1 to M8 created based on the magenta data DM1 to DM8, and the cyan data. The cyan drive signals C1 to C8 created based on DC1 to DC8 and the black drive signals K1 to K8 created based on the corrected black data DK1 to DK8 are output in parallel.

  Thereafter, in the surface emitting laser array chip 50 of the exposure apparatus 13, the yellow beam group LY is generated from the corresponding yellow light emission points LPY1 to LPY8 based on the yellow drive signals Y1 to Y8, and based on the magenta drive signals M1 to M8. Magenta light emission points LPM1 to LPM8 corresponding to magenta beam groups LM, cyan light emission points LPC1 to LPC8 corresponding to cyan light beam groups LC based on cyan drive signals C1 to C8, and black drive signals K1. Based on ˜K8, the black beam group LK is irradiated from the corresponding black light emission points LPK1 to LPK8 while being synchronized.

  FIG. 18 is a diagram for explaining electrostatic latent images formed on the photosensitive drums 11Y, 11M, 11C, and 11K in the full color mode. Here, FIG. 18A shows an electrostatic latent image formed on the photosensitive drums 11Y, 11M, and 11C, and FIG. 18B shows an electrostatic latent image formed on the photosensitive drum 11K. ing. Here, a case where a process black halftone image using yellow, magenta, cyan, and black is formed will be described as an example. Here, the content shown in FIG. 18A is the same as that described with reference to FIG. 13A in the first embodiment, and a detailed description thereof will be omitted.

  As shown in FIG. 18B, an electrostatic latent image is formed on the black photosensitive drum 11K by the black beam group LK at the in-set gap G and the black-set gap GK. However, in this example, as described above, the gap between black sets GK is almost 0, and therefore, for the eighth black at the boundary between two sets (for example, Nc-1 set and Nc set) adjacent in the sub-scanning direction. The exposure position by the beam LK8 and the exposure position by the first black beam LK1 substantially coincide.

  However, in the full color mode, as shown in FIG. 17, the black data correction unit 94 performs correction to change the value of the eighth black data DK8 to zero. Accordingly, the eighth black drive signal K8 created based on the eighth black data DK8 is also set to 0, not a value that should be output. That is, the eighth black beam LK8 is not irradiated in each set. For this reason, even if the exposure position by the eighth black beam LK8 in the previous set substantially coincides with the exposure position by the first black beam LK1 in the next set at the boundary between the sets, the amount of light at the boundary is different in other parts. Is almost equal to At this time, the apparent black set gap GK ′, which is the adjacent interval between the previous set of the seventh black beam LK7 and the next set of the first black beam LK1 at the boundary between sets, is the in-set gap. Equal to G (GK ′ = G). When exposure is performed with the black beam group LK obtained by performing such correction, the potential of the black photosensitive drum 11K charged to the predetermined charging potential VH is reduced substantially uniformly. Therefore, by using the method of the present embodiment, a substantially uniform electrostatic latent image is formed on the photosensitive drum 11K in the sub-scanning direction in the full color mode.

In the present embodiment, correction for changing the value of the eighth black data DK8 on the most downstream side in the sub-scanning direction to 0 in one set is performed, but the present invention is not limited to this. For example, the same result can be obtained when correction is performed to change the first black data DK1 on the most upstream side in the sub-scanning direction in the set in place of the eighth black data DK8 to 0.
In the present embodiment, the first black data DK1 to the eighth black data DK8 are corrected by multiplication in the full color mode. However, the present invention is not limited to this. For example, in the full color mode, the same result can be obtained even if the black data correction unit 94 passes the first black data DK1 to the seventh black data DK7 as it is and blocks the eighth black data DK8.

  In the first and second embodiments, in the full color mode, the second black peripheral speed VK2 of the black photosensitive drum 11K is set to the color peripheral speed VC of the yellow, magenta, and cyan photosensitive drums 11Y, 11M, and 11C. Although it was set to low speed, it is not restricted to this. That is, if necessary, the second black peripheral speed VK2 may be set higher than the color peripheral speed VC. However, in this case, the second belt peripheral speed VB2 in the full color mode needs to be lower than the color peripheral speed VC and the second black peripheral speed VK2.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. It is a figure which shows the detailed structure of exposure apparatus. It is a figure for demonstrating the structure of a surface emitting laser array chip. It is a block diagram of a control part. 5 is a flowchart for explaining a preparation process for an image forming operation. (A) is a diagram for explaining setting of each photosensitive drum and intermediate transfer belt in a monochrome mode, and (b) is a full color mode. It is a figure which shows an example of the laser drive signal supplied to a surface emitting laser array chip | tip in full color mode. It is a schematic diagram for explaining the behavior of each color beam group when the N-th set of yellow beam groups are irradiated from the surface emitting laser array chip in the full color mode. It is a figure for demonstrating the electrostatic latent image formed on each photoconductive drum when a surface emitting laser array chip is driven using the uncorrected laser drive signal in a full color mode. It is a block diagram of a laser drive signal preparation part. It is a figure which shows an example of the table stored in a correction data storage part. (A) is a figure which shows an example of each black data before correction | amendment input into a black data correction part in a full color mode, (b) is an example of each black data after correction | amendment output from a black data correction part. FIG. 5 is a diagram for explaining an electrostatic latent image formed on each photosensitive drum when a corrected laser drive signal is used in the full color mode. (A) is a figure which shows each example of each black data before correction | amendment input into a black data correction part in monochrome mode, (b) is each black data after correction | amendment output from a black data correction part. FIG. 6 is a diagram for explaining an electrostatic latent image formed on a black photosensitive drum when a corrected laser drive signal is used in the monochrome mode. It is a figure which shows an example of the table stored in a correction data storage part. (A) is a figure which shows an example of each black data before correction | amendment input into a black data correction part in a full color mode, (b) is an example of each black data after correction | amendment output from a black data correction part. FIG. 5 is a diagram for explaining an electrostatic latent image formed on each photosensitive drum when a corrected laser drive signal is used in the full color mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image forming unit, 11 ... Photosensitive drum, 12 ... Charging device, 13 ... Exposure device, 14 ... Developing device, 15 ... Primary transfer roll, 16 ... Drum cleaner, 20 ... Intermediate transfer belt, 30 ... Secondary transfer device 50 ... Surface emitting laser array chip, 60 ... scanning optical system, 61 ... pre-deflection optical system, 62 ... polygon mirror, 63 ... post-deflection optical system, 70 ... control unit, 80 ... UI, 81 ... YMC drum drive motor, 82 ... K drum drive motor, 83 ... belt drive motor, 84 ... advance / retreat drive motor, 85 ... laser drive signal creation unit, 91 ... image data separation unit, 92 ... image data development unit, 93 ... drive signal output unit, 94 ... Black data correction unit, 95 ... correction data storage unit

Claims (8)

A first image carrier that rotates at a first peripheral speed;
First charging means for charging the first image carrier;
First image forming means for forming an image on the first image carrier charged by the first charging means;
A second image carrier that rotates at a second circumferential speed;
A second charging unit having a configuration different from that of the first charging unit and charging the second image carrier;
Second image forming means for forming an image on the second image carrier charged by the second charging means;
A rotating member that rotates at a third peripheral speed while contacting the first image carrier and the second image carrier;
The first peripheral speed, the second peripheral speed, and the second peripheral speed so that a speed difference between the second peripheral speed and the third peripheral speed is larger than a speed difference between the first peripheral speed and the third peripheral speed. An image forming apparatus including setting means for setting the third peripheral speed. The first charging means comprises a non-contact type charging device arranged in non-contact with the first image carrier.
The image forming apparatus according to claim 1, wherein the second charging unit includes a contact type charging device disposed in contact with the second image holding member. The first image forming means and the second image forming means scan a plurality of light flux groups each consisting of a plurality of light fluxes emitted from a light source by a single rotating polygonal mirror, and then the light fluxes. An optical scanning device that separates each group and guides the first image holding body and the second image holding body to the corresponding first image holding body and main scanning of the first image holding body and the second image holding body is provided. ,
The correction means for correcting the light quantity of the plurality of light beams constituting the light beam group guided to the first image carrier or correcting the number of the plurality of light beams constituting the light beam group. The image forming apparatus according to 1. A first image holding body that holds a first image and rotates at a first peripheral speed, and a first charging member that charges the first image holding body when forming the first image. An image forming unit;
A second image carrier that holds the second image and rotates at a second peripheral speed, and the second image carrier that has a configuration different from that of the first charging member and forms the second image. A second image forming unit comprising a second charging member to be charged;
A rotating member that rotates at a third peripheral speed while contacting the first image carrier and the second image carrier;
In the first mode for forming the first image, the third peripheral speed is set to be higher than that in the second mode for forming the second image together with the first image, and the third peripheral speed and the first A speed difference is set between the first peripheral speed, the third peripheral speed is set lower than the first mode in the second mode, and the third peripheral speed is set between the first peripheral speed and the first peripheral speed. An image forming apparatus including setting means for setting a different speed difference between a third peripheral speed and the second peripheral speed.   In the first mode, the second image holding body and the rotating member are separated from each other, and in the second mode, contact / separation means for bringing the second image holding body and the rotating member into contact with each other is further included. The image forming apparatus according to claim 4. The first image forming unit and the second image forming unit scan a plurality of light flux groups each consisting of a plurality of light fluxes emitted from a light source by a single rotating polygonal mirror, and then the light fluxes. An optical scanning device that separates each group and guides the first image holding body and the second image holding body to the corresponding first image holding body and main scanning of the first image holding body and the second image holding body is provided. ,
In the first mode, the light flux at the boundary between the two light flux groups adjacent to each other in the rotation direction of the first image carrier in the interval between the plurality of light fluxes constituting the light flux group guided to the first image carrier. The image forming apparatus according to claim 4, wherein the intervals are matched. The first image forming unit and the second image forming unit scan a plurality of light flux groups each consisting of a plurality of light fluxes emitted from a light source by a single rotating polygonal mirror, and then the light fluxes. An optical scanning device that separates each group and guides the first image holding body and the second image holding body to the corresponding first image holding body and main scanning of the first image holding body and the second image holding body is provided. ,
In the second mode, the light flux at the boundary between the two light flux groups adjacent to each other in the rotation direction of the second image carrier is disposed in the interval between the plurality of light fluxes constituting the light flux group guided to the second image carrier. The image forming apparatus according to claim 4, wherein the intervals are matched.   In the second mode, the image processing apparatus further includes a correction unit that corrects the light amount of the plurality of light beams constituting the light beam group guided to the first image carrier or corrects the number of the plurality of light beams constituting the light beam group. The image forming apparatus according to claim 7.

Images