JP2009149007A - Line head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of inferior light exposure caused by difference in spot group forming positions of a plurality of light emitting element groups arranged at different positions each other in a first direction. <P>SOLUTION: A line head is equipped with a head substrate wherein a plurality of light emitting element groups in which a plurality of light emitting elements are made into groups are arranged, and an optical array wherein an imaging optical system for imaging a light emitted by the light emitting element of the light emitting element group and forming a spot on an image face moving in the first direction is arranged on each light emitting element group. On the head substrate, a plurality of the light emitting element groups are arranged at different positions each other in the first direction. The light emitting element groups emit lights and a spot group being an assembly of the spots is formed on the image face. A plurality of the light emitting element groups arranged at different positions each other in the first direction form the spot groups at different positions each other in the first direction. The amount of the light of the light emitting element is adjusted in accordance with the position in the first direction of the light emitting element group to which the light emitting element belongs. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a line head that forms a spot by forming an image of light from a light emitting element, and an image forming apparatus using the line head.

  Conventionally, a technique is known in which a spot is formed by a line head on an image plane moving 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 further higher resolution, the following line head can be used. That is, in this line head, a plurality of light emitting elements are grouped to form a light emitting element group, and the plurality of light emitting element groups are arranged at different positions in the image plane movement direction (first direction). When the light emitting element group emits light, a spot group that is a set of spots is formed. However, in such a line head, the light emitting element groups arranged at different positions in the first direction form spot groups at different positions in the first direction. Then, various exposure failures may occur due to the difference in the spot group formation position in the first direction.

  The present invention has been made in view of the above problems, and provides a technique for suppressing the occurrence of exposure failure due to differences in spot group formation positions of a plurality of light emitting element groups arranged at different positions in the first direction. With the goal.

  In order to achieve the above object, a line head according to the present invention forms an image of a head substrate on which a plurality of light emitting element groups in which a plurality of light emitting elements are grouped, and light emitted from the light emitting elements of the light emitting element group. An imaging optical system that forms a spot on an image plane that moves in a first direction, and an optical system array that is arranged for each light emitting element group, and the head substrate has a plurality of light emitting element groups at different positions in the first direction. A plurality of light emitting element groups arranged in different positions in the first direction are formed at positions different from each other in the first direction. A spot group is formed, and the light quantity of the light emitting element is adjusted according to the position in the first direction of the light emitting element group to which the light emitting element belongs. There.

  In order to achieve the above object, an image forming apparatus according to the present invention has a latent image carrier whose surface moves in a first direction, a head substrate on which a plurality of light emitting element groups each having a plurality of light emitting elements arranged, A line head having an optical system array in which an image forming optical system for forming a spot on the surface of the latent image carrier by forming an image of light emitted from the light emitting elements of the light emitting element group is arranged for each light emitting element group. In the substrate, a plurality of light emitting element groups are arranged at different positions in the first direction, the light emitting element groups emit light, and spot groups, which are sets of spots, are formed on the image plane, and are located at different positions in the first direction. The plurality of arranged light emitting element groups form spot groups at different positions in the first direction, and the light quantity of the light emitting element is the first direction of the light emitting element group to which the light emitting element belongs. It is characterized in that it is adjusted in accordance with the position in the.

  In the invention thus configured (line head, image forming apparatus), the light amount of the light emitting element is adjusted according to the position in the first direction of the light emitting element group to which the light emitting element belongs. Therefore, it is possible to suppress the occurrence of exposure failure due to the difference in the spot group formation positions of the plurality of light emitting element groups arranged at different positions 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 group emits a light emitting element at a timing according to the movement of the image plane. 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 that is orthogonal or substantially orthogonal are formed.

  That is, in the above-described line head, a plurality of light emitting element groups are arranged at different positions in the first direction. Accordingly, in order to form a plurality of spot latent images side by side in the second direction, each light emitting element group causes the light emitting elements to emit light at a timing according to the movement of the image plane. As a result, spots are sequentially formed from the light emitting element group on the upstream side 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 plurality of spot latent images formed side by side in the second direction, the spot latent image formed by the light emitting element group on the upstream side in the first direction is formed by the light emitting element group on the downstream side in the first direction. In some cases, the spot latent image becomes larger than the spot latent image because of a longer time after the formation. 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, since the light amount of the light emitting element is adjusted according to the position in the first direction of the light emitting element group to which the light emitting element belongs, the variation in the size of the spot latent image. Is suppressed, and good exposure can be realized.

  At this time, of the two light emitting element groups that form spot groups at different positions in the first direction, the light emitting element group that forms the spot group on the upstream side in the first direction is the upstream light emitting element group and the downstream side. When the light emitting element group forming the spot group is a downstream light emitting element group, the light amount of the light emitting element of the upstream light emitting element group is adjusted to be smaller than the light amount of the light emitting element of the downstream light emitting element group. You may comprise. 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 provided with 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 from each spot group formed on the surface of the latent image carrier, the following is provided. Problems may occur. That is, the distance between the spot group and the development position in the first direction is different between the spot groups formed at different positions in the first direction. Therefore, the spot latent image formed by the upstream spot group in the first direction and the spot latent image formed by the downstream spot group may differ in size at the development position, in other words, In some cases, the size or the like of the spot latent image varies at the development position. Therefore, the light quantity of the light emitting element may be adjusted according to the distance in the first direction between the spot group formed by the light emitting element group to which the light emitting element belongs 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 element groups arranged at different positions in the first direction form spot groups 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 group and the spot group formed by the light emitting element group may be different between the light emitting element groups arranged at different positions in the first direction. . However, as will be described later, the spot latent image formed by this spot group may show a tendency to increase as the distance between the element spot groups increases. Here, the element spot group distance is a distance between the center of gravity of the light emitting element group and the center of gravity of the spot group formed by the light emitting element group. As a result, there may be a variation in size between spot latent images formed by spot groups 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 in the first direction of the light emitting element group to which the light emitting element belongs, thereby suppressing variation in the size of the spot latent image. Thus, good exposure can be realized.

  At this time, the light quantity of the light emitting element of the light emitting element group having a long distance between the element spot groups among the two light emitting element groups in which the spot groups are formed at different positions in the first direction and the distance between the element spot groups is different You may comprise so that it may be adjusted to a value smaller than the light quantity of the light emitting element of a light emitting element group with short distance between element spot groups. When configured in this manner, it is possible to suppress variations in spot size regardless of the element spot group distance, and it is possible to realize good exposure.

  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.

  As described above, the formation position of the spot group SG in the sub-scanning direction SD differs depending on the light emitting element group 295. 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), the spot group formation position It is necessary to consider the difference. Therefore, in the line head 29, each light emitting element group 295 causes the light emitting elements 2951 to emit 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.

  In the line head 29, the light emitting element groups 295 arranged at different positions in the width direction LTD form spot groups SG at different positions in the sub-scanning direction SD (FIG. 11). In addition, various exposure failures may occur due to the difference in the spot group 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 spot group SG on the upstream side in the sub-scanning direction SG is the spot on the downstream side in the sub-scanning direction SD. Since the time after the formation is longer than the spot latent image Lsp formed by the group SG, it sometimes becomes larger. 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, when the light emitting element groups 295 arranged at different positions in the width direction LTD have different distances between the light emitting element groups 295 and the spot groups SG formed by the light emitting element groups 295 (element spot group distances). There is. However, as will be described later, the spot latent image formed by the spot group SG may tend to spread as the distance between the element spot groups increases. As a result, there may be a variation in size between spot latent images formed by spot groups SG 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 in the width direction LTD of the light emitting element group 295 to which the light emitting element 2951 belongs. Accordingly, it is possible to suppress the occurrence of exposure failure due to the difference in the spot group formation positions of the plurality of light emitting element groups 295 arranged at mutually different positions in the width direction LTD, 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 spots SP are sequentially formed from the light emitting element group on the upstream side in the width direction LTD, and a plurality of spot latent images Lsp aligned in the main scanning direction MD are formed. . Therefore, 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 light emitting element group 295 on the upstream side in the width direction LTD is the light emitting element on the downstream side in the width direction LTD. In some cases, the spot latent image formed by the group 295 is larger than the spot latent image Lsp formed due to a long time since the spot latent image Lsp is formed, and the formed spot latent image varies.

  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 group 295_1 forms a spot group SG upstream of the light emitting element groups 295_2 and 295_3 in the sub-scanning direction SD. In addition, the light emitting element group 295_2 forms a spot group SG upstream of the light emitting element group 295_3 in the sub-scanning direction SD. 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 light emitting element group 295, as shown in the column “Spot latent image” in the figure. Spot latent images Lsp 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 light emitting element group 295 in the sub-scanning direction SD is larger than the spot latent image Lsp formed by the downstream light emitting element group 295. More specifically, the spot latent image Lsp_1 formed by the light emitting element group 295_1 is larger than the spot latent images Lsp_2 and Lsp_3 formed by the light emitting element groups 295_2 and 295_3. Further, the spot latent image Lsp_2 formed by the light emitting element group 295_2 is larger than the spot latent image Lsp_3 formed by 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 element 2951 of the light emitting element group 295 that forms the spot group SG 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 in the width direction LTD of the light emitting element group 295 to which the light emitting element 2951 belongs. Accordingly, it is possible to suppress the occurrence of exposure failure due to the difference in the spot group formation positions of the plurality of light emitting element groups 295 arranged at mutually different positions in the width direction LTD, and to realize good exposure.

  In the first embodiment, of the two light emitting element groups 295 that form the spot group SG at different positions in the sub scanning direction SD, the light emitting element group 295 that forms the spot group SG on the upstream side in the sub scanning direction SD. Is the upstream side light emitting element group and the light emitting element group 295 that forms the spot group SG on the downstream side is the downstream side light emitting element group, the light quantity of the light emitting element 2951 of the upstream side light emitting element group is that of the downstream side light emitting element group. It is adjusted to a value smaller than the light amount of the light emitting element 2951. 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 between the spot group SG and the development position DP in the sub-scanning direction SD is the spot group development distance DTg, the line head 29 is arranged between the spots SP formed at different positions in the sub-scanning direction SD. Thus, the distance DTg between spot developments is different. That is, the position in the sub scanning direction SD of the spot group SG formed by the light emitting element group 295_1 is defined as a position LCg_1, and the position of the spot group SG formed by the light emitting element group 295_2 in the sub scanning direction SD is defined as a position LCg_2. When the position in the sub-scanning direction SD of the spot group SG formed by the group 295_3 is defined as a position LCg_3, the distances DTg_1, DTg_2, DTg3 (spot development) between the positions LCg_1, LCg_2, LCg_3 and the development position DP in the sub-scanning direction SD. The distance DTg is different from each other, and the following magnitude relationship DTg_1>DTg_2> DTg3
(See FIG. 16). Note that the position of the spot group SG can be obtained as the center of gravity of the spot group SG. That is, for each spot SP constituting the spot group SG, the position where the light intensity distribution reaches a peak can be obtained as the peak position of the spot SP, and the geometric center of gravity of these peak positions can be obtained as the position of the spot group SG.

Accordingly, the potential of the spot latent image Lsp formed by the upstream spot group SG and the potential of the spot latent image Lsp formed by the downstream spot group SG in the sub-scanning direction SD are different at the development position DP. was there. 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. The simulation is performed under the conditions of 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]. I did it. 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 group formation position LCg_2 of the light emitting element group 295_2 and a straight line extending from the rotation axis CP21 to the development position DP. (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 group SG in the sub-scanning direction SD and the spot latent image Lsp formed by the downstream spot SP may differ in size or the like at the development position DP. In other words, the spot latent image Lsp may vary in size 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 DTg from the position LCg_1, LCg_2, LCg_3 of the spot group SG to the developing position DP is set to have a smaller (smaller) light amount. Yes. 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 in the width direction LTD of the light emitting element group 295 to which the light emitting element 2951 belongs. Accordingly, it is possible to suppress the occurrence of exposure failure due to the difference in the spot group formation positions of the plurality of light emitting element groups 295 arranged at mutually different positions in the width direction LTD, and to realize good exposure.

  In the second embodiment, the light amount of the light emitting element 2951 is adjusted according to the distance DTg between the spot group SG formed by the light emitting element group 295 to which the light emitting element 2951 belongs and the development position DP in the sub scanning direction SD. Yes. 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”. Moreover, as described above, in the line head 29, the light emitting element groups 295 arranged at different positions in the width direction LTD form spot groups SG at different positions on the surface of the photosensitive drum in the sub scanning direction SD. Therefore, the distance between the light emitting element group 295 and the spot group SG formed by the light emitting element group 295 (element spot group distance Lesg) is different between the light emitting element groups 295 arranged at different positions in the width direction LTD. There is a case. Here, the element spot group distance Lesg is a distance between the center of gravity of the light emitting element group 295 and the center of gravity of the spot group SG formed by the light emitting element group 295. The center of gravity of the light emitting element group 295 can be obtained as the geometric center of gravity of the plurality of light emitting elements 2951 included in the light emitting element group 295, and as shown in FIG. The barycentric point of the light emitting element group 295 in which the elements 2951 are arranged symmetrically coincides with the symmetry center (in other words, the optical axis OA). The center of gravity of the spot group SG can be obtained as follows. That is, for each spot SP constituting the spot group SG, the position at which the light amount distribution reaches a peak can be obtained as the peak position of the spot SP, and the geometric center of gravity of these peak positions can be obtained as the center of gravity of the spot group SG.

  However, the spot latent image Lsp formed by the spot SP may tend to spread as the element spot group distance Lesg increases. In other words, due to the curvature shape of the surface of the photosensitive drum, the imaging position of the light beam may deviate from the surface of the photosensitive drum, and the light beam of the light emitting element group 295 having a short element spot group distance Lesg is photosensitive. While the image is formed on the surface of the photosensitive drum, the light beam of the light emitting element group 295 having a long element spot group distance Lesg may be formed at a position shifted from the surface of the photosensitive drum. In such a case, each spot SP of the spot group SG that can be formed on the surface of the photosensitive drum by the light emitting element group 295 having a long element spot group distance Lesg spreads. As a result, the size may vary among the plurality of spot latent images Lsp formed by the spot groups SG 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 group distance Lesg differs among the light emitting element groups 295. Specifically, the distance between the light emitting element group 295_1 and the spot group formation position LCg_1 of the light emitting element group 295 is defined as an element spot group distance Lesg_1, and the light emitting element group 295_2 and the spot group of the light emitting element group 295 When the distance to the formation position LCg_2 is the element spot group distance Lesg_2, the relationship between the element spot group distances Lesg_1 and Lesg_2 is expressed by the following equation: Lesg_1> Lesg_2
It has become. The spot group formation position LCg corresponds to the center of gravity of the spot group SG. As a result, the spot latent image Lsp_1 formed by the light emitting element group 295_1 is larger than the spot latent image Lsp_2 formed by the light emitting element group 295_2 (in the column “plan view of the surface of the photosensitive drum” in FIG. reference). 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 group 295_3 and the spot group formation position LCg_3 of the light emitting element group 295_3 is substantially equal to the element spot group distance Lesg_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 quantity of the light emitting element group 295 having a longer element spot group distance Lesg 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 in the width direction LTD of the light emitting element group 295 to which the light emitting element 2951 belongs. Accordingly, it is possible to suppress the occurrence of exposure failure due to the difference in the spot group formation positions of the plurality of light emitting element groups 295 arranged at mutually different positions in the width direction LTD, and to realize good exposure.

  In particular, in the third embodiment, among the two light emitting element groups 295 having the spot group SG formed at different positions in the sub-scanning direction SD and having the element spot group distance Lesg different from each other, the element spot group distance Lesg is long. The light amount of the light emitting element 2951 of the light emitting element group 295 is configured to be adjusted to a value smaller than the light amount of the light emitting element 2951 of the light emitting element group 295 having the short element spot group distance Lesg. 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 group distance Lesg, and good exposure can be realized.

E. Others As described above, in the above embodiment, the sub-scanning direction SD and the width direction LTD correspond to the “first direction” of the present invention, and the main scanning direction SD and the longitudinal direction LGD correspond to the “second direction” of the present invention. The photosensitive drum 21 corresponds to the “latent image carrier” of the present invention, the surface of the photosensitive drum 21 corresponds to the “image plane” of the present invention, and the lens LS corresponds to the “imaging optical system” of the present invention. The lens array 299 corresponds to the “optical system array” of the present invention.

  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.

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.

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 (7)

A head substrate in which a plurality of light emitting element groups in which a plurality of light emitting elements are grouped are arranged;
An image forming optical system that forms an image of light emitted from the light emitting element of the light emitting element group and forms a spot on an image plane that moves in the first direction; and an optical system array that is arranged for each light emitting element group. ,
In the head substrate, the plurality of light emitting element groups are arranged at different positions in the first direction,
The light emitting element group emits light and a spot group which is a set of spots is formed on the image plane, and the plurality of light emitting element groups arranged at different positions in the first direction are different from each other in the first direction. Forming the spot group in position,
The line head, wherein the light quantity of the light emitting element is adjusted according to a position in the first direction of the light emitting element group to which the light emitting element belongs.   The image plane is a surface of a latent image carrier that carries a spot latent image formed by the spots, and each light emitting element group causes the light emitting elements to emit light at a timing according to the movement of the image plane. The line head according to claim 1, wherein the plurality of spot latent images arranged in a second direction orthogonal to or substantially orthogonal to the first direction are formed.   Of the two light emitting element groups that form the spot group at different positions in the first direction, the light emitting element group that forms the spot group upstream in the first direction is an upstream light emitting element group. When the light emitting element group that forms the spot group on the downstream side is a downstream light emitting element group, the light amount of the light emitting element of the upstream light emitting element group is smaller than the light amount of the light emitting element of the downstream light emitting element group. The line head according to claim 2, wherein the line head is adjusted.   2. The line head according to claim 1, wherein the image plane is a surface of a latent image carrier having a curvature shape in a section in the first direction and carrying a latent spot image formed by the spots.   When the distance between the barycentric point of the light emitting element group and the barycentric point of the spot group formed by the light emitting element group is the distance between the element spot groups, the spot groups are formed at different positions in the first direction. Among the two light emitting element groups having different distances between the element spot groups, the light amount of the light emitting elements in the light emitting element group having the long distance between the element spot groups is short in the distance between the element spot groups. The line head according to claim 4, wherein the line head is adjusted to a value smaller than a light amount of the light emitting elements of the group. A latent image carrier whose surface moves in the first direction;
A head substrate in which a plurality of light emitting element groups are arranged in which a plurality of light emitting elements are grouped, and imaging optics for forming a spot on the surface of the latent image carrier by imaging light emitted from the light emitting elements of the light emitting element group A line head having an optical system array in which a system is arranged for each light emitting element group,
In the head substrate, the plurality of light emitting element groups are arranged at different positions in the first direction,
The light emitting element group emits light and a spot group which is a set of spots is formed on the image plane, and the plurality of light emitting element groups arranged at different positions in the first direction are different from each other in the first direction. Forming the spot group in position,
An image forming apparatus, wherein the light amount of the light emitting element is adjusted according to a position in the first direction of the light emitting element group to which the light emitting element belongs. A developing means for developing the spot latent image on the surface of the latent image carrier at a development position downstream of the spot groups formed on the surface of the latent image carrier in the first direction;
The image forming apparatus according to claim 6, wherein a light amount of the light emitting element is adjusted according to a distance in the first direction between the spot group formed by the light emitting element group to which the light emitting element belongs and the development position.

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