JP2009173005A - Exposure head, and image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for suppressing the occurrence of poor exposure caused by the difference of a spot forming position in a first direction. <P>SOLUTION: An image formation device includes a latent image supporter which moves in the first direction SD, an exposure head 29 which has a first image formation optical system LS<SB>-</SB>1, a second image formation optical system LS<SB>-</SB>2 arranged at the first direction side of the first image formation optical system LS<SB>-</SB>1, a light emitting device which emits a light image-formed on the latent image supporter by the first image formation optical system, and a light emitting device which emits a light image-formed on the latent image supporter by the first image formation optical system, and a light emitting device which emits a light image-formed on the latent image supporter by a second image formation optical system, and a control unit which controls the quantity of the light of the light emitting device for generating the light to be image-formed on the latent image supporter by the first image formation optical system LS<SB>-</SB>1 in response to the image formation characteristic of the first image formation optical system LS<SB>-</SB>1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exposure head that emits light from a light emitting element to form a spot, and an image forming apparatus using the exposure head.

  2. Description of the Related Art Conventionally, a technique is known in which spots are formed by a line head (exposure head) on an image plane that moves in the sub-scanning direction and the image plane is exposed. In addition, as such a line head, for example, a line head described in Patent Document 1 in which a plurality of light emitting elements are arranged in the main scanning direction orthogonal or substantially orthogonal to the sub-scanning direction is used. it can. That is, in the exposure operation using such a line head, a plurality of light emitting elements included in the line head emit light, and a plurality of spots arranged in the main scanning direction are formed on the image plane. Then, the spot forming operation is repeatedly executed to expose the entire image plane.

Japanese Patent Laid-Open No. 2-4546

  In order to achieve higher resolution, a line head in which a plurality of light emitting elements are arranged at different positions in the moving direction of the image plane (first direction) can be used. However, in such a line head, the light emitting elements arranged at different positions in the first direction form spots at different positions in the first direction. In addition, various exposure failures may occur due to the difference in the spot formation position in the first direction.

  The present invention has been made in view of the above problems, and an object thereof is to provide a technique for suppressing the occurrence of exposure failure due to a difference in spot formation position in the first direction.

  In order to achieve the above object, an image forming apparatus according to the present invention has a latent image carrier that moves in a first direction, a first imaging optical system, and a first imaging optical system on a first direction side. The arranged second imaging optical system, the light emitting element for emitting the light imaged on the latent image carrier by the first imaging optical system, and the latent image carrier by the second imaging optical system The exposure head having a light emitting element that emits the light to be imaged and the light quantity of the light emitting element that emits the light imaged on the latent image carrier by the first imaging optical system are the same as those of the first imaging optical system. And a control unit that performs control according to the imaging characteristics.

  In order to achieve the above object, an exposure head according to the present invention is arranged on the first image forming optical system and a first direction side in which an exposed surface moves with respect to the first image forming optical system. The second imaging optical system, a light emitting element that emits light imaged by the first imaging optical system, a light emitting element that emits light imaged by the second imaging optical system, And a controller that controls the amount of light emitted from the light emitting element that emits light imaged by the first imaging optical system in accordance with the imaging characteristics of the first imaging optical system. .

  In the invention thus configured (exposure head, image forming apparatus), the first imaging optical system and the second imaging optical system are provided, and the latent image carrier that moves in the first direction is provided. Each imaging optical system images light. Moreover, the second imaging optical system is disposed on the first direction side of the first imaging optical system. Therefore, the position of the imaging light of the first imaging optical system and the position of the imaging light of the second imaging optical system are different in the first direction, which is caused by the difference in the position of the imaging light. As a result, the first imaging optical system cannot be exposed in the same manner as the second imaging optical system, and there is a possibility that an exposure failure may occur. In contrast, the present invention provides a control unit that controls the light amount of the light emitting element that emits light imaged by the first imaging optical system in accordance with the imaging characteristics of the first imaging optical system. Good exposure can be realized.

  In this case, the imaging characteristic may be an area of light imaged on the latent image carrier by the first imaging optical system. Alternatively, the imaging characteristic may be the diameter in the first direction of the light imaged on the latent image carrier by the first imaging optical system. By adjusting the light amount of the light emitting element in accordance with the image formation characteristics, good exposure can be performed.

  The latent image carrier may be a photosensitive drum. By the way, such a photosensitive drum has a curvature shape. As a result, an exposure failure may occur due to the fact that the position where the light is imaged differs depending on the imaging optical system. Therefore, it is preferable to apply the present invention to an apparatus provided with a photosensitive drum.

  Further, the imaging characteristic may be the position of the light imaged on the latent image carrier by the first imaging optical system. By adjusting the light amount of the light emitting element in accordance with the image formation characteristics, good exposure can be performed.

  A charging unit that charges the latent image carrier may be provided, and the latent image carrier charged to the charging unit may be configured to expose the exposure head to form a latent image. By the way, as will be described later, the latent image formed in this way tends to spread with time. Therefore, the control by the control unit is such that the light amount of the light emitting element that emits the light imaged at the first position of the latent image carrier by the first imaging optical system is changed by the second imaging optical system. The light quantity of the light emitting element that emits light that is imaged at the second position where the distance between the charging position and the charging position is longer than the distance between the position 1 and the charging section may be reduced. This is because good exposure can be realized regardless of the spread of the latent image of the spot with time.

  Further, a developing unit that develops the latent image formed on the latent image carrier by the exposure head may be provided. Incidentally, as described later, in such a configuration, there is a case where an image formation defect occurs due to the fact that the distance between the imaging light and the development position differs depending on the imaging optical system. Therefore, the distance between the image formation position of the latent image carrier of the light imaged by the first image forming optical system and the development position of the latent image formed by the light of the developing unit is defined as an image formation characteristic. The light amount of the light emitting element may be adjusted. This is because it is possible to suppress image formation defects caused by the difference between the imaging light and the development position depending on the imaging optical system.

  A light emitting element that emits light imaged on the latent image carrier by the first imaging optical system, and a light emitting element that emits light imaged on the latent image carrier by the second imaging optical system May be provided on the substrate. Furthermore, the control unit may also be provided on the substrate. At this time, the control unit can be constituted by a TFT.

  The light-shielding member is provided between the substrate and the imaging optical system, and the light-shielding member includes a light emitting element that emits light imaged by the first imaging optical system, and the first imaging optical system. And a second light guide disposed between the light-emitting element that emits light imaged by the second imaging optical system and the second imaging optical system. You may comprise so that it may have a hole.

  A light emitting element that emits light imaged on the latent image carrier by the first imaging optical system, and a light emitting element that emits light imaged on the latent image carrier by the second imaging optical system May be an organic EL element. At this time, the organic EL element may be a bottom emission type.

  In order to achieve the above object, an image forming apparatus according to the present invention forms an image on a latent image carrier by a latent image carrier that moves in the first direction, an imaging optical system, and an imaging optical system. An exposure head having a light emitting element that emits the emitted light, and a control unit that adjusts the amount of light of the light emitting element according to the position in the first direction of the imaging optical system that images the light of the light emitting element It is characterized by.

  In the image forming apparatus configured as described above, the light amount of the light emitting element is adjusted according to the position in the first direction of the imaging optical system that forms an image of the light of the light emitting element. Therefore, good exposure can be realized.

  In order to achieve the above object, the line head according to the present invention includes a head substrate in which a plurality of light emitting elements are arranged at different positions in the first direction which is the moving direction of the image plane, and the light emitting elements emit light. A spot is formed on the image plane, and each light emitting element arranged at a different position in the first direction forms a spot at a different position in the first direction of the image plane. It is characterized in that it is adjusted according to the position in the first direction of the spot to be formed.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a line having a latent image carrier whose surface moves in a first direction and a head substrate in which a plurality of light emitting elements are arranged at different positions in the first direction. A light emitting element that emits light to form a spot on the image plane, and each light emitting element arranged at a different position in the first direction has a spot at a different position in the first direction on the surface of the latent image carrier. The surface of the latent image carrier carries a spot latent image formed by spots, and the light amount of the light emitting element is adjusted according to the position of the spot formed by the light emitting element in the first direction. It is characterized by.

  In the invention thus configured (line head, image forming apparatus), the light amount of the light emitting element is adjusted according to the position of the spot formed by the light emitting element in the first direction. Therefore, it is possible to suppress the occurrence of exposure failure due to the difference in the spot formation position in the first direction and to realize good exposure.

  The image plane is a surface of a latent image carrier that carries a spot latent image formed by spots, and each light emitting element arranged at a different position in the first direction emits light at a timing according to the movement of the image plane. Therefore, it is particularly preferable to apply the present invention to a configuration in which a plurality of spot latent images arranged in a second direction orthogonal or substantially orthogonal to the first direction are formed.

  That is, in the above-described line head, the light emitting elements arranged at different positions in the first direction form spots at different positions in the first direction on the surface of the latent image carrier, and the spot latent image is formed on the image plane by this spot. Is formed. Therefore, in order to form a plurality of spot latent images side by side in the second direction, each light emitting element emits light at a timing corresponding to the movement of the image plane. Thereby, spots are formed in order from the upstream spot in the first direction, and a plurality of spot latent images arranged in the second direction are formed. However, this spot latent image tends to become larger with time. Therefore, among the multiple spot latent images formed side by side in the second direction, the spot latent image formed by the upstream spot in the first direction is the spot latent image formed by the downstream spot in the first direction. In some cases, the time after the formation becomes longer, and therefore becomes larger. As a result, the size of the plurality of spot latent images formed side by side in the second direction may vary. On the other hand, when the present invention is applied, the amount of light of the light emitting element is adjusted according to the position of the spot formed by the light emitting element in the first direction, so that variation in the size of the spot latent image is suppressed. Thus, good exposure can be realized.

  At this time, of the two light emitting elements that form spots at different positions in the first direction, the light emitting element that forms the spot on the upstream side in the first direction is the upstream light emitting element and the spot is formed on the downstream side. When the light emitting element is a downstream light emitting element, the light quantity of the upstream light emitting element may be adjusted to a value smaller than the light quantity of the downstream light emitting element. When configured in this way, it is possible to suppress variations in a plurality of spot latent images formed side by side in the second direction without depending on the spread of the spot latent image over time, and to realize good exposure. Become.

  Further, in the configuration including the developing means for developing the spot latent image on the surface of the latent image carrier at the development position downstream in the first direction with respect to each spot formed on the surface of the latent image carrier, the following is provided. Problems may occur. That is, between the spots formed at different positions in the first direction, the distance between the spot and the development position in the first direction is different. Therefore, the spot latent image formed by the upstream spot in the first direction and the spot latent image formed by the downstream spot may differ in size at the development position, in other words, the development position. In some cases, the size or the like of the spot latent image varies. Therefore, the light amount of the light emitting element may be adjusted according to the distance in the first direction between the spot formed by the light emitting element and the development position. This is because such a configuration suppresses variations in the spot latent image at the development position, and develops a spot latent image with such a small variation, thereby enabling good image formation.

  In addition, it is particularly preferable to apply the present invention to a configuration in which the image plane has a curvature shape in a cross section in the first direction and is a surface of a latent image carrier that carries a spot latent image formed by spots. is there. That is, as described above, in the line head of the present invention, the light emitting elements arranged at different positions in the first direction form spots at different positions in the first direction on the surface of the latent image carrier. Therefore, when the image plane has a curvature shape, the distance between the light emitting element and the spot formed by the light emitting element may be different between the light emitting elements arranged at different positions in the first direction. However, as will be described later, the spot latent image formed by this spot may show a tendency to increase as the distance between the element spots increases. Here, the distance between element spots is the distance between the light emitting element and the spot formed by the light emitting element. As a result, the size may vary among a plurality of spot latent images formed by spots at different positions in the first direction. On the other hand, when the present invention is applied, the amount of light of the light emitting element is adjusted according to the position of the spot formed by the light emitting element in the first direction, so that variation in the size of the spot latent image is suppressed. Thus, good exposure can be realized.

  At this time, among the two light emitting elements in which the spots are formed in different positions in the first direction and the distance between the element spots is different from each other, the light amount of the light emitting element with the long distance between the element spots is the light emitting element with the short distance between the element spots. It may be configured to be adjusted to a value smaller than the amount of light. When configured in this manner, variations in spot size can be suppressed regardless of the distance between element spots, and good exposure can be realized.

  Hereinafter, terms used in the present specification will be described first (see “A. Explanation of Terms”). Following the explanation of this term, the basic configuration of the image forming apparatus equipped with the line head to which the present invention is applied (see “B. Basic Configuration”), and the basic operation of the line head (“C. (Refer to “Operation” section). Then, following description of these basic configurations and basic operations, embodiments of the present invention will be described.

A. Explanation of Terms FIG. 1 and FIG. 2 are explanatory diagrams of terms used in this specification. Here, the terms used in this specification will be organized using these drawings. In this specification, the transport direction of the surface (image surface IP) of the photosensitive drum 21 is defined as a sub-scanning direction SD, and a direction orthogonal or substantially orthogonal to the sub-scanning direction SD is defined as a main scanning direction MD. . The line head 29 is arranged with respect to the surface (image surface IP) of the photosensitive drum 21 so that the longitudinal direction LGD corresponds to the main scanning direction MD and the width direction LTD corresponds to the sub-scanning direction SD. Has been.

  A set of a plurality of (eight in FIG. 1 and FIG. 2) light emitting elements 2951 arranged on the head substrate 293 in a one-to-one correspondence with the plurality of lenses LS included in the lens array 299 is defined as a light emitting element group 295. To do. That is, in the head substrate 293, the light emitting element group 295 including the plurality of light emitting elements 2951 is disposed for each of the plurality of lenses LS. A set of a plurality of spots SP formed on the image plane IP by the light beam from the light emitting element group 295 being imaged by the lens LS corresponding to the light emitting element group 295 is defined as a spot group SG. That is, the plurality of spot groups SG can be formed in one-to-one correspondence with the plurality of light emitting element groups 295. In each spot group SG, the most upstream spot in the main scanning direction MD and the sub-scanning direction SD is particularly defined as the first spot. The light emitting element 2951 corresponding to the first spot is particularly defined as the first light emitting element.

  Further, as shown in the column “on image plane” in FIG. 2, a spot group row SGR and a spot group column SGC are defined. That is, a plurality of spot groups SG arranged in the main scanning direction MD are defined as spot group rows SGR. The plurality of spot group rows SGR are arranged side by side in the sub-scanning direction SD at a predetermined spot group row pitch Psgr. A plurality (three in the figure) of spot groups SG arranged at the spot group row pitch Psgr in the sub-scanning direction SD and at the spot group pitch Psg in the main scanning direction MD are defined as a spot group column SGC. The spot group row pitch Psgr is a distance in the sub-scanning direction SD between the geometric centroids of two spot group rows SGR adjacent to each other in the sub-scanning direction SD. The spot group pitch Psg is the distance in the main scanning direction MD of the geometric centroids of two spot groups SG adjacent to each other in the main scanning direction MD.

  Lens rows LSR and lens columns LSC are defined as shown in the “lens array” column of FIG. That is, a plurality of lenses LS arranged in the longitudinal direction LGD are defined as a lens row LSR. The plurality of lens rows LSR are arranged side by side in the width direction LTD at a predetermined lens row pitch Plsr. A plurality (three in the figure) of lenses LS arranged at the lens row pitch Plsr in the width direction LTD and at the lens pitch Pls in the longitudinal direction LGD are defined as a lens row LSC. The lens row pitch Plsr is a distance in the width direction LTD of the geometric centroids of two lens rows LSR adjacent to each other in the width direction LTD. The lens pitch Pls is a distance in the longitudinal direction LGD between the geometric centroids of the two lenses LS adjacent to each other in the longitudinal direction LGD.

  As shown in the column “Head Substrate” in the drawing, a light emitting element group row 295R and a light emitting element group column 295C are defined. That is, a plurality of light emitting element groups 295 arranged in the longitudinal direction LGD is defined as a light emitting element group row 295R. The plurality of light emitting element group rows 295R are arranged side by side in the width direction LTD at a predetermined light emitting element group row pitch Pegr. In addition, a plurality of (three in the figure) light emitting element groups 295 arranged at the light emitting element group row pitch Pegr in the width direction LTD and at the light emitting element group pitch Peg in the longitudinal direction LGD are defined as a light emitting element group column 295C. The light emitting element group row pitch Pegr is a distance in the width direction LTD between the geometric centroids of two light emitting element group rows 295R adjacent to each other in the width direction LTD. The light emitting element group pitch Peg is the distance in the longitudinal direction LGD between the geometric centers of gravity of two light emitting element groups 295 adjacent to each other in the longitudinal direction LGD.

  As shown in the “light emitting element group” column of FIG. 2, a light emitting element row 2951R and a light emitting element column 2951C are defined. That is, in each light emitting element group 295, a plurality of light emitting elements 2951 arranged in the longitudinal direction LGD is defined as a light emitting element row 2951R. The plurality of light emitting element rows 2951R are arranged side by side in the width direction LTD at a predetermined light emitting element row pitch Pelr. A plurality of (two in the figure) light emitting elements 2951 arranged in the width direction LTD at the light emitting element row pitch Pelr and at the longitudinal direction LGD in the longitudinal direction LGD are defined as a light emitting element row 2951C. The light emitting element row pitch Pelr is a distance in the width direction LTD of the geometric centroids of two light emitting element rows 2951R adjacent to each other in the width direction LTD. The light emitting element pitch Pel is a distance in the longitudinal direction LGD between the geometric centroids of two light emitting elements 2951 adjacent to each other in the longitudinal direction LGD.

  As shown in the column “Spot Group” in the figure, a spot row SPR and a spot column SPC are defined. That is, in each spot group SG, a plurality of spots SP arranged in the longitudinal direction LGD are defined as spot rows SPR. The plurality of spot rows SPR are arranged side by side in the width direction LTD at a predetermined spot row pitch Pspr. Further, a plurality of (two in the figure) spots arranged at the spot pitch Pspr in the width direction LTD and at the spot pitch Psp in the longitudinal direction LGD are defined as a spot row SPC. The spot row pitch Pspr is a distance in the sub-scanning direction SD between the geometric centroids of two spot rows SPR adjacent to each other in the sub-scanning direction SD. The spot pitch Psp is a distance in the longitudinal direction LGD between the geometric centroids of two spots SP adjacent to each other in the main scanning direction MD.

B. Basic Configuration FIG. 3 is a diagram showing an example of an image forming apparatus equipped with a line head to which the present invention is applied. FIG. 4 is a diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus uses a color mode in which four color toners of black (K), cyan (C), magenta (M), and yellow (Y) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. FIG. 3 is a diagram corresponding to the execution of the color mode. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC and also outputs an image forming command. Corresponding video data VD is supplied to the head controller HC. The head controller HC controls the line head 29 for each color based on the video data VD from the main controller MC, the vertical synchronization signal Vsync from the engine controller EC, and parameter values. As a result, the engine unit EG executes a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  An electrical component box 5 containing a power circuit board, a main controller MC, an engine controller EC, and a head controller HC is provided in the housing main body 3 of the image forming apparatus. An image forming unit 7, a transfer belt unit 8, and a paper feed unit 11 are also disposed in the housing body 3. In FIG. 3, a secondary transfer unit 12, a fixing unit 13, and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feeding unit 11 is configured to be detachable from the apparatus main body 1. The paper feed unit 11 and the transfer belt unit 8 can be removed and repaired or exchanged.

  The image forming unit 7 includes four image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality of images of different colors. Each of the image forming stations Y, M, C, and K is provided with a cylindrical photosensitive drum 21 having a surface with a predetermined length in the main scanning direction MD. Each of the image forming stations Y, M, C, and K forms a corresponding color toner image on the surface of the photosensitive drum 21. The photosensitive drum is arranged so that the axial direction is substantially parallel to the main scanning direction MD. Each photosensitive drum 21 is connected to a dedicated drive motor and is driven to rotate at a predetermined speed in the direction of arrow D21 in the figure. As a result, the surface of the photosensitive drum 21 is conveyed in the sub-scanning direction SD that is orthogonal or substantially orthogonal to the main scanning direction MD. A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. Therefore, when the color mode is executed, the toner images formed at all the image forming stations Y, M, C, and K are superimposed on the transfer belt 81 of the transfer belt unit 8 to form a color image, and the monochrome mode is executed. In some cases, a monochrome image is formed using only the toner image formed at the image forming station K. In FIG. 3, the image forming stations of the image forming unit 7 have the same configuration, and therefore, for convenience of illustration, only some image forming stations are denoted by reference numerals, and the other image forming stations are omitted. .

  The charging unit 23 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to rotate in contact with the surface of the photosensitive drum 21 at the charging position, and at a peripheral speed in the driven direction with respect to the photosensitive drum 21 as the photosensitive drum 21 rotates. Followed rotation. The charging roller is connected to a charging bias generator (not shown). The charging roller is supplied with the charging bias from the charging bias generator and is charged at the charging position where the charging unit 23 and the photosensitive drum 21 come into contact with each other. The surface of 21 is charged.

  The line head 29 is disposed with respect to the photosensitive drum 21 such that the longitudinal direction thereof corresponds to the main scanning direction MD and the width direction thereof corresponds to the sub-scanning direction SD. Is substantially parallel to the main scanning direction MD. The line head 29 includes a plurality of light emitting elements arranged side by side in the longitudinal direction, and is spaced apart from the photosensitive drum 21. Then, light is emitted from these light emitting elements to the surface of the photosensitive drum 21 charged by the charging unit 23, and an electrostatic latent image is formed on the surface.

  The developing unit 25 has a developing roller 251 on which toner is carried. The charged toner is developed at a developing position where the developing roller 251 and the photosensitive drum 21 come into contact with each other by a developing bias applied to the developing roller 251 from a developing bias generator (not shown) electrically connected to the developing roller 251. Is moved from the developing roller 251 to the photosensitive drum 21, and the electrostatic latent image formed by the line head 29 becomes obvious.

  The toner image that has been made visible at the developing position in this way is conveyed in the rotational direction D21 of the photosensitive drum 21, and then a primary transfer position TR1 at which each of the photosensitive drums 21 comes into contact with the transfer belt 81, which will be described in detail later. 1 is primarily transferred to the transfer belt 81.

  In this embodiment, the photosensitive drum cleaner 27 is provided in contact with the surface of the photosensitive drum 21 on the downstream side of the primary transfer position TR1 in the rotational direction D21 of the photosensitive drum 21 and on the upstream side of the charging unit 23. It has been. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to clean and remove toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 3, and a stretched direction of these rollers in the direction of the arrow D81 (conveying direction). And a transfer belt 81 that is driven to circulate. Further, the transfer belt unit 8 is disposed on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations Y, M, C, and K when the photosensitive cartridge is mounted. Four primary transfer rollers 85Y, 85M, 85C, and 85K are provided. Each of these primary transfer rollers 85 is electrically connected to a primary transfer bias generator (not shown). As will be described in detail later, when the color mode is executed, as shown in FIG. 3, all the primary transfer rollers 85Y, 85M, 85C, 85K are positioned on the image forming stations Y, M, C, K side. Then, the transfer belt 81 is pushed and brought into contact with the photosensitive drums 21 included in the image forming stations Y, M, C, and K, so that the primary transfer position TR1 is set between each photosensitive drum 21 and the transfer belt 81. Form. Then, by applying a primary transfer bias from the primary transfer bias generator to the primary transfer roller 85 at an appropriate timing, the toner images formed on the surfaces of the photosensitive drums 21 correspond respectively. A color image is formed by transferring to the surface of the transfer belt 81 at the primary transfer position TR1.

  On the other hand, when the monochrome mode is executed, among the four primary transfer rollers 85, the color primary transfer rollers 85Y, 85M, and 85C are separated from the image forming stations Y, M, and C facing each other, and the monochrome primary transfer is performed. By bringing only the roller 85K into contact with the image forming station K, only the monochrome image forming station K is brought into contact with the transfer belt 81. As a result, the primary transfer position TR1 is formed only between the monochrome primary transfer roller 85K and the image forming station K. Then, by applying a primary transfer bias from the primary transfer bias generator to the monochrome primary transfer roller 85K at an appropriate timing, the toner image formed on the surface of each photosensitive drum 21 is subjected to primary transfer. A monochrome image is formed by transferring to the surface of the transfer belt 81 at a position TR1.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed on the downstream side of the monochrome primary transfer roller 85K and on the upstream side of the driving roller 82. Further, the downstream guide roller 86 is formed between the primary transfer roller 85K and the photosensitive drum 21 at the primary transfer position TR1 formed by the monochrome primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station K. It is configured to contact the transfer belt 81 on a common inscribed line.

  The driving roller 82 circulates and drives the transfer belt 81 in the direction of the arrow D81 in the figure, and also serves as a backup roller for the secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the driving roller 82, and secondary transfer is omitted by grounding through a metal shaft. The conductive path of the secondary transfer bias supplied from the bias generation unit via the secondary transfer roller 121 is used. When the rubber layer having high friction and shock absorption is provided on the driving roller 82 in this way, the sheet enters the contact portion (secondary transfer position TR2) between the driving roller 82 and the secondary transfer roller 121. Is difficult to be transmitted to the transfer belt 81, and image quality deterioration can be prevented.

  The sheet feeding unit 11 includes a sheet feeding unit having a sheet feeding cassette 77 capable of stacking and holding sheets and a pickup roller 79 that feeds sheets one by one from the sheet feeding cassette 77. The sheet fed from the sheet feeding unit by the pickup roller 79 is fed to the secondary transfer position TR2 along the sheet guide member 15 after the sheet feeding timing is adjusted by the registration roller pair 80.

  The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 13 includes a heating roller 131 that includes a heating element such as a halogen heater and is rotatable, and a pressure unit 132 that presses and biases the heating roller 131. Then, the sheet on which the image is secondarily transferred is guided to a nip portion formed by the heating roller 131 and the pressure belt 1323 of the pressure portion 132 by the sheet guide member 15, and in the nip portion, a predetermined value is provided. The image is heat-fixed at temperature. The pressure unit 132 includes two rollers 1321 and 1322 and a pressure belt 1323 stretched between them. A nip portion formed by the heating roller 131 and the pressure belt 1323 by pressing the belt tension surface stretched by the two rollers 1321 and 1322 against the peripheral surface of the heating roller 131 among the surfaces of the pressure belt 1323. Is configured to be widely taken. Further, the sheet thus subjected to the fixing process is conveyed to a paper discharge tray 4 provided on the upper surface of the housing body 3.

  Further, in this apparatus, a cleaner portion 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner and paper dust remaining on the transfer belt after the secondary transfer by bringing the tip of the cleaner blade 711 into contact with the blade facing roller 83 via the transfer belt 81. The foreign matter removed in this way is collected in a waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are integrally formed with the blade facing roller 83. Therefore, when the blade facing roller 83 moves as will be described below, the cleaner blade 711 and the waste toner box 713 also move together with the blade facing roller 83.

  FIG. 5 is a perspective view showing an outline of the line head according to the present invention. FIG. 6 is a cross-sectional view in the width direction of the line head shown in FIG. As described above, the line head 29 is arranged with respect to the photosensitive drum 21 such that the longitudinal direction LGD corresponds to the main scanning direction MD and the width direction LTD corresponds to the sub-scanning direction SD. The longitudinal direction LGD and the width direction LTD are orthogonal or substantially orthogonal to each other. The line head 29 includes a case 291, and positioning pins 2911 and screw insertion holes 2912 are provided at both ends of the case 291 in the longitudinal direction LGD. Then, the positioning pin 2911 covers the photosensitive drum 21 and is fitted into a positioning hole (not shown) formed in a photosensitive cover (not shown) positioned with respect to the photosensitive drum 21, thereby The head 29 is positioned with respect to the photosensitive drum 21. Further, the line head 29 is positioned and fixed with respect to the photosensitive drum 21 by screwing and fixing a fixing screw into a screw hole (not shown) of the photosensitive member cover through the screw insertion hole 2912.

  The case 291 holds the lens array 299 at a position facing the surface of the photosensitive drum 21, and includes a light shielding member 297 and a head substrate 293 in the order close to the lens array 299. The head substrate 293 is formed of a material (for example, glass) that can transmit a light beam. Further, on the back surface of the head substrate 293 (the surface opposite to the lens array 299 among the two surfaces of the head substrate 293), as will be described later, there are a plurality of light emitting element groups 295 in which a plurality of light emitting elements 2951 are grouped. Has been placed. Each light emitting element 2951 is a bottom emission type organic EL (Electro-Luminescence) element. The light beams emitted from the respective light emitting element groups 295 are transmitted from the back surface to the front surface of the head substrate 293 and directed to the light shielding member 297.

  A plurality of light guide holes 2971 are formed in the light shielding member 297 on a one-to-one basis with respect to the plurality of light emitting element groups 295. Further, the light guide hole 2971 is formed as a substantially cylindrical hole penetrating the light shielding member 297 with a line parallel to the normal line of the head substrate 293 as a central axis. Therefore, among the light beams emitted from the light emitting element group 295, the light beams that are directed to other than the light guide hole 2971 corresponding to the light emitting element group 295 are blocked by the light blocking member 297. Thus, all the light emitted from one light emitting element group 295 is directed to the lens array 299 through the same light guide hole 2971, and interference between light beams emitted from different light emitting element groups 295 is prevented by the light shielding member 297. The Then, the light beam that has passed through the light guide hole 2971 formed in the light shielding member 297 is imaged by the lens array 299, and a spot is formed on the surface of the photosensitive drum 21.

  As shown in FIG. 6, the back cover 2913 is pressed against the case 291 via the head substrate 293 by the fixing device 2914. That is, the fixing device 2914 has an elastic force that presses the back cover 2913 toward the case 291, and presses the back cover with the elastic force, thereby making the inside of the case 291 light-tight (that is, from the inside of the case 291. It is sealed so that light does not leak and so that light does not enter from the outside of the case 291. Note that a plurality of fixing devices 2914 are provided in the longitudinal direction of the case 291. The light emitting element group 295 is covered with a sealing member 294.

  FIG. 7 is a perspective view schematically showing the lens array. FIG. 8 is a cross-sectional view of the lens array in the longitudinal direction LGD. The lens array 299 has a lens substrate 2991. The first surface LSFf of the lens LS is formed on the back surface 2991B of the lens substrate 2991, and the second surface LSFs of the lens LS is formed on the surface 2991A of the lens substrate 2991. The first surface LSFf and the second surface LSFs of the lenses facing each other and the lens substrate 2991 sandwiched between these two surfaces function as one lens LS. The first surface LSFf and the second surface LSFs of the lens LS can be formed of, for example, a resin.

  In the lens array 299, a plurality of lenses LS are arranged so that their optical axes OA are substantially parallel to each other. The lens array 299 is arranged so that the optical axis OA of the lens LS is substantially orthogonal to the back surface of the head substrate 293 (the surface on which the light emitting element 2951 is disposed). The lenses LS are provided one-on-one with respect to the light emitting element group 295, and a plurality of lenses LS are two-dimensionally arranged corresponding to the arrangement of the light emitting element groups 295 described later. That is, a plurality of lens rows LSC in which three lenses LS are arranged at different positions in the width direction LTD are arranged along the longitudinal direction LGD.

  FIG. 9 is a diagram showing the configuration of the back surface of the head substrate, which corresponds to the case where the back surface is viewed from the front surface of the head substrate. FIG. 10 is a diagram showing the arrangement of light emitting elements in each light emitting element group. In FIG. 9, the lens LS is indicated by a two-dot chain line. This is for indicating that the light emitting element groups 295 are provided in one-to-one relationship with the lens LS. It does not indicate that it is arranged on the back surface of the head substrate. As shown in FIG. 9, a plurality of light emitting element group columns 295C in which three light emitting element groups 295 are arranged at different positions in the width direction LTD are arranged in the longitudinal direction LGD. In other words, the light emitting element group row 295R in which the plurality of light emitting element groups 295 are arranged along the longitudinal direction LGD is arranged in three rows in the width direction LTD at the light emitting element group row pitch Pegr (= 1.7 [mm]). Yes. At this time, the light emitting element group rows 295R are shifted from each other in the longitudinal direction LGD so that the light emitting element groups 295 do not overlap with each other in the longitudinal direction LGD. Here, reference numerals 295R_A, 295R_B, and 295R_C are attached to the three light emitting element group rows in order from the upstream side in the width direction LGD.

  In each light emitting element group 295, two light emitting element rows 2951R in which four light emitting elements 2951 are arranged along the longitudinal direction LGD are arranged in the width direction LTD at a light emitting element row pitch Pelr (= 63.5 [μm]). (Fig. 10). At this time, the light emitting element rows 2951R are shifted from each other in the longitudinal direction LGD so that the light emitting elements 2951 do not overlap with each other in the longitudinal direction LGD. As a result, eight light emitting elements 2951 are arranged in a staggered manner. Also, as shown in FIG. 10, each light emitting element group 295 is arranged symmetrically with respect to the optical axis OA of the corresponding lens LS. That is, the eight light emitting elements 2951 constituting the light emitting element group 295 are arranged symmetrically with respect to the optical axis OA. Therefore, a light beam from the light emitting element 2951 relatively far from the optical axis OA can be imaged with little aberration.

  Corresponding to each light emitting element group row 295R_A, 295R_B, 295R_C, drive circuits DC_A (for each light emitting element group row 295R_A), DC_B (for each light emitting element group row 295R_B), DC_C (for each light emitting element group row 295R_C) These drive circuits DC_A and the like are configured by TFTs (Thin Film Transistors), for example (FIG. 9). Each drive circuit DC_A and the like is disposed on one side in the width direction LTD of the corresponding light emitting element group 295R_A and the like, and is connected to the light emitting element 2951 such as the light emitting element group 295R_A by the wiring WL. When the drive circuit DC_A or the like gives a drive signal to each light emitting element 2951, each light emitting element 2951 emits light beams having the same wavelength. The light emitting surface of the light emitting element 2951 is a so-called perfect diffusion surface light source, and the light beam emitted from the light emitting surface follows Lambert's cosine law.

  The light beam emitted from the light emitting element 2951 is imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum 21 (the surface of the photosensitive drum). On the other hand, as described above, the surface of the photosensitive drum is charged by the charging unit 23 prior to spot formation. Therefore, the area where the spot SP is formed is neutralized, and the spot latent image Lsp is formed. The spot latent image Lsp thus formed is conveyed downstream in the sub-scanning direction SD while being carried on the surface of the photosensitive drum. Then, as described in the section “C. Basic operation”, the spots SP are formed at a timing according to the movement of the surface of the photosensitive drum, and a plurality of spot latent images Lsp aligned in the main scanning direction MD are formed. Is done.

C. Basic Operation FIG. 11 is a perspective view for explaining spots formed by the line head. In FIG. 11, the description of the lens array 299 is omitted. As shown in FIG. 11, each light emitting element group 295 can form spot groups SG in different exposure regions ER in the main scanning direction MD. Here, the spot group SG is a set of a plurality of spots SP formed by simultaneously emitting light from all the light emitting elements 2951 of the light emitting element group 295. As shown in the drawing, the three light emitting element groups 295 capable of forming the spot group SG in the exposure region ER continuous in the main scanning direction MD are arranged so as to be shifted from each other in the width direction LTD. That is, for example, the three light emitting element groups 295_1, 295_2, 295_3 capable of forming spot groups SG_1, SG2, SG3 in the exposure regions ER_1, ER_2, ER3 continuous in the main scanning direction MD are mutually connected in the width direction LTD. They are staggered. These three light emitting element groups 295 constitute a light emitting element group column 295C, and a plurality of light emitting element group columns 295C are arranged along the longitudinal direction LGD. As a result, as described in the description of FIG. 9, the three light emitting element group rows 295R_A, 295R_B, and 295R_C are arranged in the width direction LTD, and the light emitting element group rows 295R_A and the like are mutually connected in the sub scanning direction SD. Spot groups SG are formed at different positions.

  That is, in the line head 29, the plurality of light emitting element groups 295 (for example, the light emitting element groups 295_1, 295_2, and 295_3) are arranged at different positions in the width direction LTD. The light emitting element groups 295 arranged at different positions in the width direction LTD form spot groups SG (for example, spot groups SG_1, SG_2, SG_3) at different positions in the sub-scanning direction SD.

  In other words, in the line head 29, a plurality of light emitting elements 2951 are arranged at different positions in the width direction LTD (for example, the light emitting elements 2951 belonging to the light emitting element group 295_1 and the light emitting elements belonging to the light emitting element group 295_2). 2951 are arranged at different positions in the width direction LTD). The light emitting elements 2951 arranged at different positions in the width direction LTD form spots SP at different positions in the sub-scanning direction LTD (for example, the spots SP belonging to the spot group SG_1 and the spot group SG_2). The spots SP are formed at different positions in the sub-scanning direction SD).

  As described above, the formation position of the spot SP in the sub-scanning direction SD differs depending on the light emitting element 2951. Therefore, in order to form a plurality of spot latent images Lsp side by side in the main scanning direction MD (that is, to form a plurality of spot latent images Lsp at the same position in the sub-scanning direction SD), It is necessary to consider the difference. Therefore, in the line head 29, each light emitting element 2951 emits light at a timing according to the movement of the surface of the photosensitive drum.

  FIG. 12 is a diagram showing a spot forming operation by the above-described line head. Hereinafter, the spot forming operation by the line head will be described with reference to FIG. 9, FIG. 11, and FIG. Schematically, the surface of the photosensitive drum (latent image carrier surface) moves in the sub-scanning direction SD, and the head control module 54 (FIG. 4) controls the light emitting element 2951 at a timing according to the movement of the photosensitive drum surface. By emitting light, a plurality of spot latent images Lsp arranged in the main scanning direction MD are formed.

  First, among the light emitting element rows 2951R (FIG. 10) belonging to the most upstream light emitting element group 295_1, 295A4, etc. in the width direction LTD, the light emitting element rows 2951R on the downstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Note that the lens LS has an inverted characteristic, and the light beam from the light emitting element 2951 is inverted to form an image. Thus, the spot latent image Lsp is formed at the position of the “first” hatching pattern in FIG. In the figure, a white circle represents a spot latent image that has not yet been formed and is scheduled to be formed in the future. In the same figure, the spot latent images labeled with reference numerals 295_1 to 295_4 indicate spot latent images formed by the light emitting element groups 295 corresponding to the reference numerals assigned thereto.

  Next, among the light emitting element rows 2951R belonging to the light emitting element groups 295_1, 295A4, etc., the light emitting element row 2951R on the upstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp is formed at the position of the “second” hatching pattern in FIG. Here, the reason why light is emitted in order from the light emitting element row 2951R on the downstream side in the width direction LTD is to correspond to the fact that the lens LS has an inverted characteristic.

  Next, among the light emitting element rows 2951R belonging to the second light emitting element group 295_2 and the like from the upstream side in the width direction, the light emitting element rows 2951R on the downstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp is formed at the position of the “third” hatching pattern in FIG.

  Next, among the light emitting element rows 2951R belonging to the second light emitting element group 295_2 and the like from the upstream side in the width direction, the light emitting element rows 2951R on the upstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp is formed at the position of the “fourth” hatching pattern in FIG.

  Next, among the light emitting element rows 2951R belonging to the third light emitting element group 295_3 and the like from the upstream side in the width direction, the light emitting element rows 2951R on the downstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp is formed at the position of the “fifth” hatching pattern in FIG.

  Finally, among the light emitting element rows 2951R belonging to the third light emitting element group 295_3 from the upstream side in the width direction, the light emitting element row 2951R on the upstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp is formed at the position of the “sixth” hatching pattern in FIG. As described above, by executing the first to sixth light emission operations, the spot SP is formed in order from the spot SP on the upstream side in the sub-scanning direction SD, and a plurality of spot latent images Lsp aligned in the main scanning direction MD. Is formed.

  By the way, in the line head 29, the light emitting elements 2951 arranged at different positions in the width direction LTD form spots SP at different positions in the sub-scanning direction SD (FIG. 11). In addition, various exposure failures may occur due to such a difference in spot formation position in the sub-scanning direction SD.

  Specifically, for example, as shown in the first and second embodiments, the surface of the photosensitive drum has a bright attenuation characteristic as shown in FIG. 13, and therefore the spot latent image tends to become larger with time. Therefore, among the plurality of spot latent images Lsp formed side by side in the sub-scanning direction SD, the spot latent image Lsp formed by the upstream spot SP in the sub-scanning direction is caused by the spot SP downstream in the sub-scanning direction SD. In some cases, the spot latent image Lsp becomes larger than the formed spot latent image Lsp because of a longer time after the formation. As a result, the size of the multiple spot latent images Lsp formed side by side in the main scanning direction MD may vary.

  Alternatively, as shown in the third embodiment, the surface of the photosensitive drum has a curvature shape in a sub-scanning direction cross section (sub-scanning cross section). Therefore, the distance between the light emitting elements 2951 and the spots SP formed by the light emitting elements 2951 (element spot distance) may be different between the light emitting elements 2951 arranged at different positions in the width direction LTD. However, as will be described later, the spot latent image formed by the spots SP may tend to spread as the distance between the element spots increases. As a result, the size may vary among a plurality of spot latent images formed by the spots SP at different positions in the sub-scanning direction SD.

  On the other hand, in the line head 29 shown in the following embodiment, the light amount of the light emitting element 2951 is adjusted according to the position of the spot SP formed by the light emitting element 2951 in the sub-scanning direction SD. Accordingly, it is possible to suppress the occurrence of exposure failure due to the difference in the spot SP formation position in the sub-scanning direction SD and to realize good exposure.

D-1. First Embodiment FIG. 13 is a diagram showing the light attenuation characteristics of the surface of the photosensitive drum. The horizontal axis represents time [seconds] and the vertical axis represents the potential [V] of the surface of the photosensitive drum. Here, the bright attenuation characteristic is a characteristic representing a change of the surface potential of the photosensitive drum with respect to time. As shown in the figure, at time 0 [second], the surface potential of the photosensitive drum charged to a predetermined negative potential increases with time. As described above, the surface of the photosensitive drum cannot maintain a constant surface potential, and the surface potential increases with time.

  On the other hand, as described with reference to FIGS. 11 and 12, the spot SP is formed in order from the spot SP on the upstream side in the sub-scanning direction SD, and a plurality of spot latent images Lsp aligned in the main scanning direction MD are formed. . Accordingly, among the plurality of spot latent images Lsp formed side by side in the main scanning direction MD, the spot latent image Lsp formed by the upstream spot SP in the sub scanning direction SD is the downstream spot SP in the sub scanning direction SD. In some cases, the spot latent image Lsp is larger than the spot latent image Lsp formed by the above-described method, because the time from the formation is longer, resulting in variations in the formed spot latent image.

  FIG. 14 is a diagram schematically showing variations in spot latent images. In the drawing, spot latent images formed by the respective light emitting elements 2951 of the light emitting element groups 295_1, 295_2, and 295_3 are schematically shown. As can be seen from the above description, the light emitting element 2951 of the light emitting element group 295_1 forms a spot SP upstream of the light emitting element 2951 of the light emitting element groups 295_2 and 295_3 in the sub-scanning direction SD. The light emitting element 2951 of the light emitting element group 295_2 forms a spot SP on the upstream side in the sub-scanning direction SD from the light emitting element 2951 of the light emitting element group 295_3. At this time, as shown in the column “Relationship between light quantities” in the figure, assuming that the light quantity of each light emitting element 2951 is constant regardless of the position of the spot SP to be formed, the field “Spot latent image” in the figure is used. Spot latent images Lsp as shown are formed side by side in the main scanning direction MD. Here, the hatching pattern of each spot latent image Lsp has the same meaning as the hatching pattern of FIG.

That is, the spot latent image Lsp formed by the upstream spot SP in the sub-scanning direction SD is larger than the spot latent image Lsp formed by the downstream spot SP. More specifically, the spot latent image Lsp_1 formed by the light emitting elements 2951 of the light emitting element group 295_1 is larger than the spot latent images Lsp_2 and Lsp_3 formed by the light emitting elements 2951 of the light emitting element groups 295_2 and 295_3. Further, the spot latent image Lsp_2 formed by the light emitting element 2951 of the light emitting element group 295_2 is larger than the spot latent image Lsp_3 formed by the light emitting element 2951 of the light emitting element group 295_3. In particular, in the example of the figure, the magnitude relationship between the diameters Dlm_1, Dlm_2, and Dlm_3 in the main scanning direction MD of the spot latent images Lsp_1, Lsp_2, and Lsp_3 is
Dlm_1>Dlm_2> Dlm_3
It has become. Therefore, in order to cope with such a problem, in the first embodiment, the light amount of the light emitting element 2951 is adjusted as follows.

  FIG. 15 is a diagram schematically illustrating an example of a light emitting element light amount adjustment mode according to the first embodiment. As shown in the figure, in the first embodiment, the light amount of the light emitting elements 2951 of the light emitting element group 295 that forms the spot SP on the upstream side is set to be smaller (smaller). Specifically, the light amount of the light emitting element 2951 of the light emitting element group 295_1 is adjusted to a value smaller than the light amount of the light emitting element 2951 of the light emitting element groups 295_2 and 295_3, and the light amount of the light emitting element 2951 of the light emitting element group 295_2 is The light amount of the light emitting element 2951 of the light emitting element group 295_3 is adjusted to a value smaller than that of the light emitting element group 295_3 (see the column of “Relationship of light amount” in the figure). As a result, as shown in the column “Spot Latent Image” in the figure, variations in the spot latent images Lsp_1, Lsp_2, and Lsp_3 are suppressed, and the diameters Dlm_1 of the spot latent images Lsp_1, Lsp_2, and Lsp_3 in the main scanning direction MD are suppressed. , Dlm_2 and Dlm_3 are also reduced.

  As described above, in the first embodiment, the light amount of the light emitting element 2951 is adjusted according to the position of the spot SP formed by the light emitting element 2951 in the sub-scanning direction SD. Therefore, it is possible to suppress the occurrence of exposure failure due to the difference in the spot formation position in the sub-scanning direction SD and to realize good exposure.

  In the first embodiment, of the two light emitting elements 2951 that form the spots SP at different positions in the sub scanning direction SD, the light emitting elements that form the spots upstream in the sub scanning direction SD are referred to as upstream light emitting elements. In addition, when a light emitting element that forms a spot on the downstream side is a downstream light emitting element, the light amount of the upstream light emitting element is adjusted to a value smaller than the light amount of the downstream light emitting element. Specifically, the light amount of the light emitting element 2951 (upstream light emitting element) of the light emitting element group 295_1 is adjusted to a value smaller than the light amount of the light emitting element 2951 (downstream light emitting element) of the light emitting element group 295_2. The light amount of the light emitting element 2951 (upstream light emitting element) in the light emitting element group 295_2 is adjusted to a value smaller than the light amount of the light emitting element 2951 (downstream light emitting element) in the light emitting element group 295_3. Therefore, variations in the plurality of spot latent images Lsp formed side by side in the main scanning direction MD can be suppressed regardless of the spread of the spot latent image Lsp with time, and good exposure can be realized.

D-2. Second Embodiment FIG. 16 is an explanatory diagram of an image forming apparatus according to a second embodiment. Hereinafter, the second embodiment will be described with reference to FIG. In the image forming apparatus 1 equipped with the line head 29 as described above, when the line head 29 forms a spot SP on the surface of the photosensitive drum charged by the charging unit 23, an area where the spot SP is formed. Is neutralized to form a spot latent image Lsp. The spot latent image Lsp is developed with toner by the developing unit 25 at the developing position DP. Here, the developing position DP is a position where the spot latent image Lsp is developed with toner, and in this embodiment, the position where the developing roller 251 and the photosensitive drum 21 abut corresponds to the developing position DP.

On the other hand, when the distance in the sub-scanning direction SD between the spot SP and the development position DP is defined as a spot development distance DT, the line head 29 has, between the spots SP formed at different positions in the sub-scanning direction SD, The distance DT between spot developments is different. That is, the position in the sub scanning direction SD of the spot SP formed by the light emitting element 2951 of the light emitting element group 295_1 is defined as the position LC_1, and the position of the spot SP formed by the light emitting element 2951 in the light emitting element group 295_2 is defined in the sub scanning direction SD. When the position LC_2 is the position in the sub scanning direction SD of the spot SP formed by the light emitting elements 2951 of the light emitting element group 295_3, the position LC_3 is the position LC_1, LC_2, LC_3 and the development position DP in the sub scanning direction SD. The distances DT_1, DT_2, and DT3 (spot development distance DT) are different from each other and have the following magnitude relationship: DT_1>DT_2> DT3
(See FIG. 16). Therefore, the potential of the spot latent image Lsp formed by the upstream spot SP in the sub-scanning direction SD and the potential of the spot latent image Lsp formed by the downstream spot SP may be different at the development position DP. It was.

A more specific simulation result is shown and described. When the potentials of the spot latent images Lsp_1, Lsp_2, and Lsp_3 at the development position DP are the potentials VT_1, VT_2, and VT_3,
VT_1 = -105.9 [V]
VT_2 = -102.4 [V]
VT_3 = -99.3 [V]
In some cases, the potentials varied. In this simulation, the photosensitive drum diameter = 40 [mm], the photosensitive member linear velocity = 212 mm / second, the exposure development angle AG = 68 °, and the light emitting element group row pitch Pegr = 1.7 [mm]. Performed under conditions. Note that the exposure development angle AG is an angle formed by intersecting a straight line extending from the rotation axis CP21 of the photosensitive drum 21 to the spot formation position LC_2 of the light emitting element group 295_2 and a straight line extending from the rotation axis CP21 to the development position DP. There is (FIG. 16). Further, the surface of the photosensitive drum is assumed to have the bright attenuation characteristic shown in FIG.

  Therefore, the spot latent image Lsp formed by the upstream spot SP in the sub-scanning direction SD and the spot latent image Lsp formed by the downstream spot SP may differ in size at the development position DP. In other words, the size or the like of the spot latent image Lsp may vary at the development position DP. Therefore, in order to cope with such a problem, in the second embodiment, the light amount of the light emitting element 2951 is adjusted as follows.

  FIG. 17 is a diagram schematically illustrating an example of a light emitting element light amount adjustment mode according to the second embodiment. As shown in the figure, the light emitting element 2951 of the light emitting element group 295 having a longer (large) distance DT from the positions LC_1, LC_2, LC_3 of the spot SP to the development position DP is set to have a smaller (smaller) light amount. . Specifically, the light amount of the light emitting element 2951 of the light emitting element group 295_1 is adjusted to a value smaller than the light amount of the light emitting element 2951 of the light emitting element groups 295_2 and 295_3, and the light amount of the light emitting element 2951 of the light emitting element group 295_2 is The light amount of the light emitting element 2951 of the light emitting element group 295_3 is adjusted to a value smaller than that of the light emitting element group 295_3 (see the column of “Relationship of light amount” in the figure). As a result, as shown in the column “Spot Latent Image at Development Position DP” in the figure, variations in spot latent images Lsp_1, Lsp_2, and Lsp_3 at development position DP are suppressed. For example, spot latent images Lsp_1, Variations in the diameters Dlm_1, Dlm_2, and Dlm_3 in the main scanning direction MD of Lsp_2 and Lsp_3 are also suppressed.

  As described above, also in the second embodiment, the light amount of the light emitting element 2951 is adjusted according to the position of the spot SP formed by the light emitting element 2951 in the sub-scanning direction SD. Therefore, it is possible to suppress the occurrence of exposure failure due to the difference in the spot formation position in the sub-scanning direction SD and to realize good exposure.

  In the second embodiment, the light amount of the light emitting element 2951 is adjusted according to the distance DT between the spot SP formed by the light emitting element 2951 and the development position DP in the sub scanning direction SD. Therefore, it is possible to suppress the variation of the spot latent image Lsp at the development position DP and to form a good image.

D-3. Third Embodiment By the way, the surface of the photosensitive drum 21 has a curvature shape in a cross section (sub-scanning cross section) in the sub-scanning direction SD (FIG. 18 and the like). In this specification, the shape of the cylindrical peripheral surface is defined as a “curvature shape”. In addition, as described above, in the line head 29, the light emitting elements 2951 of the light emitting element groups 295 arranged at different positions in the width direction LTD have spots SP at different positions in the sub scanning direction SD on the surface of the photosensitive drum. Form. Therefore, the distance between the light emitting element 2951 and the spot SP formed by the light emitting element 2951 (element spot distance Les) may be different between the light emitting element groups 295 arranged at different positions in the width direction LTD. However, the spot latent image Lsp formed by the spot SP may show a tendency to increase as the element spot distance Les increases. In other words, due to the curvature shape of the surface of the photosensitive drum, the image formation position of the light beam may deviate from the surface of the photosensitive drum, and the light beam of the light emitting element 2951 with a short element spot distance Les is the photosensitive drum. While the image is formed on the surface, the light beam of the light emitting element 2951 having a long element spot distance Les may be formed at a position shifted from the surface of the photosensitive drum. In this case, the spot SP that can be formed on the surface of the photosensitive drum by the light emitting element 2951 having a long element spot distance Les spreads. As a result, the size may vary among the plurality of spot latent images Lsp formed by the spots SP at different positions in the sub-scanning direction SD.

FIG. 18 is a diagram schematically showing variations in spot latent images. As shown in the column “Side view of line head” in the figure, the element spot distance Les is different among the light emitting element groups 295. Specifically, the distance between the light emitting element 2951 of the light emitting element group 295_1 and the spot formation position LC_1 of the light emitting element 2951 is an element spot distance Les_1, and the light emitting element 2951 of the light emitting element group 295_2 When the distance from the spot formation position LC_2 of 2951 is the element spot distance Les_2, the relationship between the element spot distances Les_1 and Les_2 is expressed by the following equation: Les_1> Les_2
It has become. As a result, the spot latent image Lsp_1 formed by the light emitting element 2951 of the light emitting element group 295_1 is larger than the spot latent image Lsp_2 formed by the light emitting element 2951 of the light emitting element group 295_2 (see “Photosensitive member in FIG. (See the “Drum surface plan” column). In particular, in the example of the figure, the diameter Dls_1 of the spot latent image Lsp_1 in the sub-scanning direction SD is larger than the diameter Dls_2 of the spot latent image Lsp_2 in the sub-scanning direction SD. In the third embodiment, the distance between the light emitting element 2951 of the light emitting element group 295_3 and the spot formation position LC_3 of the light emitting element 2951 is substantially equal to the element spot distance Les_1 corresponding to the light emitting element group 295_1. In order to cope with such variations in the spot latent image, in the third embodiment, the light quantity of the light emitting element 2951 is adjusted as follows.

  FIG. 19 is a diagram schematically illustrating an example of a light emitting element light amount adjustment mode in the third embodiment. In the third embodiment, the light amount of the light emitting elements in the light emitting element group 295 having a longer element spot distance Les is set to be smaller (smaller). Specifically, the light amount of the light emitting element 2951 of the light emitting element group 295_1 (295_3) is adjusted to a value smaller than the light amount of the light emitting element 2951 of the light emitting element group 295_2. As a result, as shown in the “plan view of the photosensitive drum surface” in FIG. 19, the diameter Dls_1 of the spot latent image Lsp_1 in the sub-scanning direction SD and the diameter Dls_2 of the spot latent image Lsp_2 in the sub-scanning direction SD are substantially equal. The variation of the spot latent image as shown in FIG. 18 is suppressed.

  As described above, in the third embodiment, the light amount of the light emitting element 2951 is adjusted according to the position of the spot SP formed by the light emitting element 2951 in the sub-scanning direction SD. Therefore, it is possible to suppress the occurrence of exposure failure due to the difference in the spot formation position in the sub-scanning direction SD and to realize good exposure.

  In particular, in the third embodiment, among the two light emitting elements 2951 having the spot SPs formed at different positions in the sub-scanning direction SD and having the element spot distances Les different from each other, the light emitting element 2951 having the long element spot distance Les. The amount of light is adjusted to be smaller than the amount of light of the light emitting element 2951 having a short element spot distance Les. Specifically, the light amount of the light emitting element 2951 of the light emitting element group 295_1 is adjusted to a value smaller than the light amount of the light emitting element 2951 of the light emitting element group 295_2. Therefore, variation in the size of the spot latent image Lsp can be suppressed regardless of the element spot distance Les, and good exposure can be realized.

D-4. Fourth Embodiment In the present embodiment, after explaining the spot variation that occurs when the line head 29 is displaced in the width direction LTD with respect to the photosensitive drum 21, the influence of the spot variation on latent image formation is suppressed. The technology to do is explained.

  FIG. 20 is a diagram showing spot variation when the line head is displaced in the width direction with respect to the photosensitive drum. The three light emitting element groups 295_1 to 295_3 shown in the column of “side view of line head etc.” in the same figure constitute the same light emitting element group row 295C, and the three lenses LS_1 to LS_3 are the same lens row. Configure the LSC. Then, the light emitted from each of the light emitting element groups 295_1 to 295_3 is imaged by the corresponding lens among the lenses LS_1 to LS_3, and a spot is formed on the surface of the photosensitive drum 21.

  In the drawing, since the line head 29 is shifted in the width direction LTD, the spot formation positions LC_1 to LC_3 of the lenses LS_1 to LS_3 are shifted in the sub-scanning direction SD by the shift amount Δsft. On the other hand, since the surface of the photosensitive drum 21 has a curvature shape, when the spot forming positions LC_1 to LC_3 are shifted in the sub-scanning direction SD by the shift amount Δsft, the distance between the spot forming positions LC_1,. Fluctuates. Specifically, the distance between the lens LS_1 and the spot formation position LC_1 becomes short, while the distance between the lens LS_2 and the spot formation position LC_2 becomes long. As a result, some spots SP may spread. In the example shown in FIG. 20, the spot SP_1 formed by the lens LS_1 is not so wide, but the spot SP_2 formed by the lens LS_2 is widened (see the “plan view showing spot variation” in FIG. 20). reference). As a result, the light density (light quantity per unit area) is reduced at the spot SP_2, and the spot latent image may not be stably formed by the spot SP_2. As a result, there is a possibility that the size of the latent image formed by the spot SP_1 and the spot SP_2 may vary.

  That is, the spot SP may spread depending on the position where it is formed (spot formation position), and as a result, a good latent image may not be formed. Therefore, in order to deal with such a problem, depending on the spot formation position LC_1,... (In other words, depending on the position in the lens width direction LTD), the spot formation position LC_1,. What is necessary is just to adjust the light quantity of the light emitting element which forms. Specifically, the light amount of the light emitting element that forms the spot SP_2 may be increased as compared with the light emitting element that forms the spot SP_1. As a result, both the spot SP_1 and the spot SP_2 can form a uniform latent image.

  As described above, in this embodiment, the line head 29 (exposure head) includes the lens LS_1 (first imaging optical system) and the lens LS_2 (second imaging optical) disposed on the width direction LTD side of the lens LS_1. System). And the light quantity of a light emitting element is adjusted according to the lens which focuses the light of the said light emitting element. Therefore, good exposure can be realized and a good image can be formed. The light amount adjustment of the light emitting element may be performed by a drive circuit DC_A or the like (control unit) provided on the head substrate 293 (FIG. 9), or may be performed by a head controller HC (control unit). (FIG. 4).

E. Others As described above, in the above embodiment, the line head 29 corresponds to the “exposure head” of the present invention, the photosensitive drum 21 corresponds to the “latent image carrier” of the present invention, and the sub-scanning direction SD and the width direction LTD. Corresponds to the “first direction” of the present invention, the lens LS corresponds to the “imaging optical system” of the present invention, and the head substrate 293 corresponds to the “substrate” of the present invention. The surface of the photosensitive drum 21 corresponds to the “exposed surface” of the present invention. Further, when the lens LS for imaging light from the light emitting element group 295_1 is the “first imaging optical system” of the present invention, the lens LS for imaging light from the light emitting element groups 295_2, 295_3 is the present invention. When the lens LS for imaging the light from the light emitting element group 295_2 is the “first imaging optical system” of the present invention, the light emitting element group 295_3 The lens LS for imaging light corresponds to the “second imaging optical system” of the present invention. The spot SP corresponds to “light imaged by the imaging optical system” of the present invention. In the first embodiment, the light-emitting elements of the light-emitting element group 295_1 emit light that is imaged at the first position of the latent image carrier by the first imaging optical system of the present invention. The second light emitting element of light emitting element group 295_2 is the second position where the distance from the charging part is longer than the distance between the first position and the charging part by the second imaging optical system of the present invention. Corresponds to a “light emitting element that emits light focused on”. In the third embodiment, the diameter of the light (spot SP) imaged on the photosensitive drum 21 by the lens LS in the sub-scanning direction SD corresponds to the “imaging characteristic of the imaging optical system” of the present invention. ing. In the fourth embodiment, the position of the light (spot SP) formed by the lens LS on the photosensitive drum 21 corresponds to the “imaging characteristic of the imaging optical system” of the present invention. In the second embodiment, the distance between the position LC_1 of the light imaged on the photosensitive drum 21 by the lens LS and the development position DP corresponds to the “imaging characteristics of the imaging optical system” of the present invention. ing.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. In the above embodiment, three light emitting element group rows 295R are arranged in the width direction LTD. However, the number of light emitting element group rows 295R is not limited to three, and may be two, for example.

  In the above embodiment, the light emitting element group 295 includes two light emitting element rows 2951R. However, the number of light emitting element rows 2951R constituting the light emitting element group 295 is not limited to two, and may be, for example, one.

  In the above embodiment, the light emitting element row 2951R includes four light emitting elements 2951. However, the number of the light emitting elements 2951 constituting the light emitting element row 2951R is not limited to four.

  In the above embodiment, an organic EL element is used as the light emitting element 2951. However, an element other than the organic EL element may be used as the light emitting element 2951. For example, an LED (Light Emitting Diode) may be used as the light emitting element 2951.

  In the above embodiment, toner development is performed by a contact development method in which the developing roller 251 is brought into contact with the surface of the photosensitive drum. However, the toner development method is not limited to this. The toner development is performed by a non-contact development method in which the development roller is spaced from the surface of the photosensitive drum and the toner is ejected from the development roller to the surface of the photosensitive drum. You may do it.

  In the first and second embodiments, the technique for adjusting the amount of imaging light for each lens row LSR has been described. However, the amount of imaging light between lenses belonging to the same lens row LSR is particularly important. Did not mention. However, as will be described below, when the line head 29 warps in the longitudinal direction LGD (main scanning direction MD), the imaging light amount may be adjusted between lenses belonging to the same lens row LSR. .

  FIG. 21 is a diagram illustrating spot variation when the line head is warped in the longitudinal direction. In the column of “side view of line head or the like” in the drawing, the light beam LB imaged by each lens in one lens row LSR is indicated by a one-dot chain line. Further, the end lens LS_e at the end in the longitudinal direction LGD of the lens row LSR and the central lens LS_m at the center in the longitudinal direction LGD (second direction) of the lens row LSR belong to the same lens row LSR.

  In the figure, the line head 29 is warped in the longitudinal direction LGD so as to be convex with respect to the surface of the photosensitive drum 21. As a result, the distance between the spot formation position and the lens differs depending on the lens. Specifically, the distance between the end lens LS_e and the spot formation position LC_e is longer than the distance between the center lens LS_m and the spot formation position LC_m. As a result, the spot formed may spread from the center to the end. Specifically, the spot SP_e formed by the end lens LS_e is wider than the spot SP_m formed by the center lens LS_m. As a result, the light density is reduced as the spot is closer to the end, and the spot latent image may not be formed stably. Therefore, in order to cope with such a problem, the light quantity of the corresponding light emitting element 2951 may be increased as the lens LS closer to the end. Thereby, a uniform latent image can be formed.

  In addition, the line head 29 and the plurality of light emitting elements 2951 in the above embodiment are grouped to form a light emitting element group 295, and a lens LS is provided for each light emitting element group 295. However, the configuration of the line head 29 is not limited to this, and may be configured as follows, for example.

  22 is a cross-sectional view in the width direction showing another configuration of the line head, and FIG. 23 is a plan view showing the back surface of the head substrate included in the line head of FIG. In FIG. 23, the lens arrays 299s_1 and 299s_2 are indicated by two-dot chain lines, but this is for showing the positional relationship between the lens arrays 299s_1 and 299s_2 and the light emitting elements, and the lens arrays 299s_1 and 299s_2. Does not indicate that it is arranged on the back surface of the head substrate. In the following description, differences from the above-described line head will be mainly described, and common portions will be denoted by corresponding reference numerals and description thereof will be omitted.

  As shown in FIG. 23, two rows of light emitting element lineups LUs_1 and LUs_2 are arranged in the width direction LTD on the back surface of the head substrate 293. In the light emitting element lineup LU, a plurality of light emitting elements 2951 are arranged in the longitudinal direction LGD. Moreover, the light emitting element lineups LUs_1 and LUs_2 are shifted from each other in the longitudinal direction LGD so that the positions of the light emitting elements 2951 are different in the width direction LTD. Further, two lens arrays LA are arranged to face each other in a one-to-one correspondence with the light emitting element lineups Ls_1 and LUs_2 (FIGS. 22 and 23). This lens array LA is configured by stacking a plurality of gradient index lenses, and has optical characteristics of erecting equal magnification.

  As described above, the light emitting element 2951 of the light emitting element lineup LUs_1 and the light emitting element 2951 of the light emitting element lineup LUs_2 are disposed at different positions in the width direction LTD. The light emitting element lineups LUs_1 and LUs_2 form spots SP at different positions LCs_1 and LCs_2 in the sub-scanning direction SD. Therefore, in order to form a plurality of spot latent images side by side in the main scanning direction MD, the light emitting element lineups LUs_1 and LUs_2 arranged at different positions in the width direction LTD are at timings according to the movement of the surface of the photosensitive drum. Emits light.

  FIG. 24 is a diagram showing a spot latent image forming operation executed by the line head shown in FIG. In FIG. 24, the spot latent image Lsps_1 is a spot latent image formed by the light emitting elements 2951 of each light emitting element lineup LUs_1, and the spot latent image Lsps_2 is formed by the light emitting elements 2951 of each light emitting element lineup LUs_2. It is a spot latent image. That is, in the line head 29 according to another configuration, first, the light emitting element lineup LUs_1 on the upstream side in the width direction LTD emits light to form a spot latent image Lsps_1. Subsequently, the light emitting element lineup LUs_2 on the downstream side in the width direction LTD emits light, and a spot latent image Lsps_2 is formed. In this way, a plurality of spot latent images arranged in the main scanning direction MD are formed (FIG. 24).

  As described above, also in the line head 29 shown in FIG. 22, the spots SP are formed in order from the upstream spot SP in the sub-scanning direction SD, and a plurality of spot latent images Lsp aligned in the main scanning direction MD are formed. . Therefore, in the same manner as shown in the first embodiment and the like, there are cases where variations occur in the formed spot latent images. Therefore, by applying the present invention to the line head 29 shown in FIG. 22, the light quantity of the light emitting element 2951 can be adjusted according to the position of the spot SP formed by the light emitting element 2951 in the sub-scanning direction SD. desirable. This is because the occurrence of variations in spot latent images can be suppressed and good exposure can be realized.

  Further, as can be seen from FIG. 22, the surface of the photosensitive drum 21 has a curvature shape in a section (sub-scanning section) in the sub-scanning direction SD. Moreover, as described above, the light emitting elements 2951 of the light emitting element lineups LUs_1 and LUs_2 arranged at different positions in the width direction LTD are spot SPs at positions LCs_1 and LCs_2 that are different from each other in the sub scanning direction SD on the surface of the photosensitive drum. Form. Therefore, the distance between the light emitting element 2951 and the spot SP formed by the light emitting element 2951 (element spot distance Less_1, Less_2) may be different between the light emitting element lineups LUs_1 and LUs_2. Therefore, in the same way as shown in the third embodiment, there are cases where the size varies among the plurality of spot latent images formed by the spots SP at different positions in the sub-scanning direction SD.

  Therefore, by applying the present invention to the line head 29 shown in FIG. 22, the light quantity of the light emitting element 2951 can be adjusted according to the position of the spot SP formed by the light emitting element 2951 in the sub-scanning direction SD. desirable. This is because the occurrence of variations in spot latent images can be suppressed and good exposure can be realized.

Explanatory drawing of the term used by this specification. Explanatory drawing of the term used by this specification. 1 is a diagram illustrating an example of an image forming apparatus according to the present invention. FIG. 4 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 3. The perspective view which shows the outline of the line head concerning this invention. FIG. 6 is a cross-sectional view in the width direction of the line head shown in FIG. 5. The perspective view which shows the outline of a lens array. Sectional drawing of the longitudinal direction LGD of a lens array. The figure which shows the structure of the back surface of a head board | substrate. The figure which shows arrangement | positioning of the light emitting element in each light emitting element group. The perspective view for demonstrating spot formation operation | movement. The figure which shows the spot formation operation | movement by a line head. The figure which shows the light attenuation | damping characteristic of the photoreceptor drum surface. The figure which shows the dispersion | variation in a spot latent image typically. The figure which showed typically an example of the adjustment aspect of the light emitting element light quantity in 1st Embodiment. Explanatory drawing of the image forming apparatus in 2nd Embodiment. The figure which showed typically an example of the adjustment aspect of the light emitting element light quantity in 2nd Embodiment. The figure which shows the dispersion | variation in a spot latent image typically. The figure which showed typically an example of the adjustment aspect of the light emitting element light quantity in 3rd Embodiment. FIG. 6 is a diagram illustrating a case where the line head is displaced in the width direction with respect to the photosensitive drum. The figure which shows the spot dispersion | variation when a line head curves in the longitudinal direction. The width direction sectional view showing another composition of a line head. The top view showing the back surface of the head substrate which the line head of FIG. 22 has. The figure which shows the spot latent image formation operation which the line head shown in FIG. 22 performs.

Explanation of symbols

  21Y, 21K ... photosensitive drum (latent image carrier), 25 ... developing part (developing means), 251 ... developing roller, 29 ... line head, 293 ... head substrate, 295 ... light emitting element group, 2951 ... light emitting element, 299 ... lens array, LS ... lens, SP ... spot, Lsp ... spot latent image, MD ... main scanning direction (second direction), SD ... sub-scanning direction (first direction), LGD ... longitudinal direction (second direction), LTD: width direction (first direction), DP: development position

Claims (15)

A latent image carrier that moves in a first direction;
A first imaging optical system, a second imaging optical system disposed on the first direction side of the first imaging optical system, and the latent image carrier by the first imaging optical system. An exposure head having a light emitting element that emits light to be imaged, and a light emitting element that emits light to be imaged on the latent image carrier by the second imaging optical system;
A control unit that controls the amount of light of a light emitting element that emits light imaged on the latent image carrier by the first imaging optical system according to the imaging characteristics of the first imaging optical system;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the imaging characteristic is an area of light imaged on the latent image carrier by the first imaging optical system.   The image forming apparatus according to claim 1, wherein the imaging characteristic is a diameter in the first direction of light imaged on the latent image carrier by the first imaging optical system.   The image forming apparatus according to claim 2, wherein the latent image carrier is a photosensitive drum.   The image forming apparatus according to claim 1, wherein the imaging characteristic is a position of light imaged on the latent image carrier by the first imaging optical system. A charging unit for charging the latent image carrier;
The control by the control unit is such that the light amount of the light emitting element that emits the light imaged at the first position of the latent image carrier by the first imaging optical system is changed to the second imaging optical system. The light amount of the light emitting element that emits light that is imaged at a second position that is longer than the distance between the first position and the charging unit is longer than the distance between the first position and the charging unit. The image forming apparatus described in 1. A developing unit that develops the latent image formed on the latent image carrier by the exposure head;
The imaging characteristic is defined as a distance between an imaging position of the latent image carrier of light imaged by the first imaging optical system and a developing position of the latent image formed by the light of the developing unit. The image forming apparatus according to claim 5, wherein   A light emitting element that emits light imaged on the latent image carrier by the first imaging optical system and a light imaged on the latent image carrier by the second imaging optical system. The image forming apparatus according to claim 1, wherein the light emitting element is provided on a substrate. The image forming apparatus according to claim 8, wherein the control unit is provided on the substrate.   The image forming apparatus according to claim 9, wherein the control unit includes a TFT. A light shielding member provided between the substrate and the imaging optical system;
The light shielding member includes a first light guide hole disposed between the light emitting element that emits light imaged by the first imaging optical system and the first imaging optical system; 11. The image formation according to claim 9, further comprising: a second light guide hole disposed between the light emitting element that emits light imaged by the two imaging optical system and the second imaging optical system. apparatus.   A light emitting element that emits light imaged on the latent image carrier by the first imaging optical system and a light imaged on the latent image carrier by the second imaging optical system The image forming apparatus according to claim 1, wherein the light emitting element is an organic EL element.   The image forming apparatus according to claim 12, wherein the organic EL element is a bottom emission type. A latent image carrier that moves in a first direction;
An imaging optical system, and an exposure head having a light emitting element that emits light imaged on the latent image carrier by the imaging optical system;
A control unit that controls the light amount of the light emitting element according to the position in the first direction of the imaging optical system that forms an image of the light of the light emitting element;
An image forming apparatus comprising: A first imaging optical system;
A second imaging optical system disposed on a first direction side in which an exposed surface moves with respect to the first imaging optical system;
A light emitting element that emits light imaged by the first imaging optical system;
A light emitting element that emits light imaged by the second imaging optical system;
A control unit that controls the amount of light of a light emitting element that emits light imaged by the first imaging optical system according to the imaging characteristics of the first imaging optical system;
An exposure head comprising:

Images