JP2008201121A - Line head and image forming apparatus using the line head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology which can achieve favorable spot formation in a line head that uses a plurality of light emitting elements and in an image forming apparatus. <P>SOLUTION: In each light emitting element group, a plurality of the light emitting elements are arranged at different positions in a longitudinal direction. The light emitting elements of the light emitting element group emit light at respective timing according to movement in the sub-scanning direction Y of a photoreceptor surface. Light beams ejected from the light emitting elements of the light emitting element group are image-formed on the photoreceptor surface at different positions in a main scanning direction X, and a plurality of spots SP are formed while being arranged in the main scanning direction X while forming spot groups SG1 and SG2. Moreover, the spot groups SG1 and SG2 adjoining in the main scanning direction X partially overlap with each other, whereby an overlapping spot region OR is formed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a line head that has a plurality of light emitting elements and forms an image of a light beam emitted from each light emitting element on an image plane, and an image forming apparatus using the line head.

  As this type of line head, one using a light emitting element array has been proposed as described in Patent Document 1, for example. In this light emitting element array, a plurality of light emitting elements are linearly arranged at a constant pitch in the longitudinal direction corresponding to the main scanning direction. In addition, a plurality of light emitting element arrays configured as described above are provided, and lenses are arranged in one-to-one correspondence with each light emitting element array. In each light emitting element array, a light beam is emitted from each of the plurality of light emitting elements included in the array, and further, the light beam is imaged on an image plane by a lens arranged corresponding to the array. As a result, spots are formed in a line shape in the main scanning direction on the image plane.

JP 2000-158705 A (FIG. 1)

  By the way, a group of spots is formed on the image plane by the light emitting elements constituting the light emitting element array to form a spot group. In this spot group, the relative positional relationship of the spots is constant. However, in the line head of Patent Document 1, since the plurality of light emitting element arrays are arranged in a direction corresponding to the main scanning direction, the position of the light emitting elements may be shifted in units of arrays. When this positional shift occurs, the spot positions are relatively shifted between the spot groups, and a gap is generated between the spot groups. In particular, in an image forming apparatus in which a latent image is formed on a photoreceptor using a line head having such a problem and a toner image is formed by developing the latent image, vertical stripes appear in the toner image. The quality will be degraded. Further, in the line head of Patent Document 1, since the lenses are not integrally formed, the relative position error of each lens is large. Therefore, the spot position on the image plane is shifted between the spot groups, and the same problem as described above may occur.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of realizing good spot formation in a line head and an image forming apparatus using a plurality of light emitting elements.

  In order to achieve the above object, the line head according to the present invention images a plurality of light emitting elements provided in groups for each light emitting element group and a light beam emitted from the light emitting element group facing the light emitting element group. A lens array for each light emitting element group, which has a lens that forms an image on a surface to form a spot group, and has a plurality of light emitting element groups in different first and second directions. The spot groups adjacent to each other in the direction corresponding to the first direction are formed on the image plane so as to partially overlap in the direction corresponding to the second direction.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a latent image carrier whose surface is conveyed in a predetermined conveyance direction, and a line head which forms a latent image on the surface of the latent image carrier. The line head includes a plurality of light emitting elements grouped for each light emitting element group, and a light beam emitted from the light emitting element group facing the light emitting element group and formed on a latent image carrier. A lens array having a lens forming a group for each light emitting element group, and a plurality of light emitting element groups arranged in M × N (M and N are integers of 2 or more) in different first and second directions The spot group adjacent to each other in the direction corresponding to the first direction is formed on the latent image carrier so as to partially overlap in the direction corresponding to the second direction.

  In the invention thus configured (line head and image forming apparatus), a plurality of light emitting element groups are provided in the first direction. In each light emitting element group, the light beam emitted from the light emitting element group is imaged on an image plane such as a latent image carrier by a lens facing the light emitting element group to form a spot group. For this reason, a plurality of spot groups are formed in a direction corresponding to the first direction. Therefore, if the spot groups adjacent to each other in the direction corresponding to the first direction are relatively displaced, a gap is generated between the spot groups. However, in the present invention, spot groups adjacent to each other in the direction corresponding to the first direction are formed on the image plane so as to partially overlap in the direction corresponding to the second direction. As a result, even if these spot groups are relatively displaced, no gap is generated between the spot groups, and favorable spot formation can be performed. Further, by forming an image using such a line head, a high-quality toner image can be formed without generating vertical stripes.

  Here, by controlling the light emission timing of the light emitting element, a plurality of spots can be formed side by side in a direction corresponding to the first direction to form a spot group. In this case, the spot groups adjacent in the direction corresponding to the first direction may partially overlap each other to form an overlapping spot region. By forming overlapping spot regions in this way, even if the mutual positional relationship between the light emitting element groups and the lenses is slightly deviated, there is no gap between the spot groups, and favorable spot formation can be performed. Further, by forming an image using such a line head, a high-quality toner image can be formed without generating vertical stripes.

  Moreover, you may comprise so that the element diameter of the light emitting element which forms an overlap spot area | region among several light emitting elements may become smaller than the element diameter of the remaining light emitting elements. Since the light emitting elements forming the overlapping spot region among the plurality of light emitting elements constituting each light emitting element group are arranged on the end side of the light emitting element group, the angle of view of the light beam emitted from the light emitting element with respect to the lens Becomes bigger. As a result, the spot diameter formed by the light beam increases. Therefore, by setting the element diameter as described above, it is possible to prevent the spot diameter from greatly differing between the overlapping spot region and the other spot areas. That is, the spot diameter can be made uniform.

  Moreover, you may comprise so that the emitted light quantity of the light emitting element which forms an overlap spot area | region among several light emitting elements may become smaller than the emitted light quantity of the remaining light emitting elements. In the overlapping spot area, the two spots overlap, so the light amount of the overlapping spot area increases. Therefore, by setting the light emission amount of the light emitting element as described above, it is possible to suppress the light amount of the overlapping spot region from becoming larger than the other light amounts. That is, the amount of light can be made uniform.

  Further, in the center spot group among the three spot groups adjacent in the direction corresponding to the first direction, a part of the center spot group overlaps with the upstream spot group and the rest overlaps with the downstream spot group. You may comprise so that the whole center spot group may become an overlap spot area | region. In this case, the overlapping spot area coincides with the center spot group, and it is possible to reliably prevent the occurrence of vertical stripes even when the positional deviation or magnification error becomes large.

  In addition, there are a plurality of combinations of spot groups adjacent to each other in the direction corresponding to the first direction, but the spot group partially overlaps in the direction corresponding to the second direction for some of these combinations. You may comprise so that it may be formed. Also in this case, even if the mutual positional relationship between the light emitting element groups and the lenses is slightly shifted in the first direction, no gap is generated between the spot groups, and favorable spot formation can be performed. Further, by forming an image using such a line head, a high-quality toner image can be formed without generating vertical stripes.

  As the lens array, a combination of a plurality of lens substrates having lenses can be used. However, in the lens array configured as described above, the paired lenses may be relatively displaced with respect to the lens substrate combination position due to an assembly error of the lens substrate. When a relative positional shift occurs between the lens pairs forming the spot groups adjacent to each other in the direction corresponding to the first direction among the lens pairs, a gap is generated between the spot groups. Therefore, in a line head or an image forming apparatus employing such a lens array, spot groups adjacent to each other in the direction corresponding to the first direction are formed in the second direction by a pair of lenses that sandwich the lens substrate combination position. It is desirable that the image plane is formed so as to overlap in the corresponding direction, whereby a high-quality toner image can be formed without generating vertical stripes.

  Also, when a plurality of element substrates having light emitting element groups are combined, the same problem as in the case of a lens array in which a plurality of lens substrates are combined may occur. Therefore, the spot groups adjacent to each other in the direction corresponding to the first direction are formed on the image plane so that the spot groups adjacent to each other in the direction corresponding to the first direction are overlapped by the light emitting element group pairs that are paired across the combination position of the element substrates. It is desirable to configure. As a result, a high-quality toner image can be formed without generating vertical stripes.

  The same problem as described above may also occur in a line head having a lens array configured as follows. That is, in a lens array in which a plurality of lens rows arranged in the first direction are arranged in a second direction different from the first direction with N columns (N is an integer of 3 or more), the first lens in the second direction The lenses constituting the rows and the lenses constituting the Nth lens row in the second direction are widely separated in the second direction. Therefore, a lens constituting the first lens row in the second direction and a lens constituting the Nth lens row in the second direction may be relatively displaced due to a manufacturing error or the like. When a relative positional shift occurs between the lens pairs that form the spot groups adjacent to each other in the direction corresponding to the first direction among the lens pairs constituted by these lenses, a gap is generated between the spot groups. End up. Therefore, in a line head or an image forming apparatus that employs such a lens array, a lens composed of a lens constituting the first lens row in the second direction and a lens constituting the Nth lens row in the second direction. It is desirable that the pair of spot groups adjacent to each other in the direction corresponding to the first direction is formed on the image plane so as to overlap in the direction corresponding to the second direction, thereby generating no vertical stripes. A high quality toner image can be formed.

  Moreover, you may comprise so that the element diameter of the light emitting element which forms an overlap area | region among several light emitting elements may become smaller than the element diameter of the remaining light emitting elements. Since the light emitting elements forming the overlapping region among the plurality of light emitting elements constituting each light emitting element group are arranged on the end side of the light emitting element group, the angle of view of the light beam emitted from the light emitting elements with respect to the lens is growing. As a result, the spot diameter formed by the light beam increases. Therefore, by setting the element diameter as described above, it is possible to prevent the spot diameter from greatly differing between the overlap region and the other regions. That is, the spot diameter can be made uniform.

  Moreover, you may comprise so that the emitted light amount of the light emitting element which forms an overlap area | region among several light emitting elements may become smaller than the emitted light amount of the remaining light emitting elements. In the overlapping area, two spots are formed, so that the amount of light in the overlapping area increases. Therefore, by setting the light emission amount of the light emitting element as described above, it is possible to suppress the light amount in the overlapping region from becoming larger than the other light amounts. That is, the amount of light can be made uniform.

  Further, in the center spot group among the three spot groups adjacent in the direction corresponding to the first direction, a part of the center spot group overlaps with the upstream spot group and the rest overlaps with the downstream spot group. You may comprise so that the whole center spot group may become an overlap area | region. In this case, the overlapping area coincides with the center spot group, and it is possible to reliably prevent the occurrence of vertical stripes even when the positional deviation or the magnification error becomes large.

  All the combinations of spot groups adjacent to each other in the direction corresponding to the first direction may be formed on the image plane so as to partially overlap in the direction corresponding to the second direction.

  The configurations of the light emitting element group and the lens may all be the same, but may be configured such that the magnifications of the lenses are different from each other. By adopting such a configuration, the lens arrangement can be arbitrarily set, the degree of design freedom can be increased, and for example, an effect of being able to easily secure a wiring space can be obtained.

  Moreover, the following aspect can be employ | adopted about arrangement | positioning of the light emitting element in each light emitting element group. That is, in each of the plurality of light emitting element groups, a plurality of light emitting element arrays in which a plurality of light emitting elements are arranged in the first direction are arranged in the second direction, and the light emitting elements constituting the light emitting element group are arranged in a staggered manner. You may comprise as follows. In this case, in each of the plurality of light emitting element arrays, the plurality of light emitting elements constituting the light emitting element array emit light at a timing corresponding to the movement of the image plane in the direction corresponding to the second direction, and the plurality of spots are emitted. They can be formed side by side in a direction corresponding to the first direction. Therefore, the light emission timing adjustment can be simplified, which is preferable.

  Further, the lens array may be configured such that a plurality of lenses are arranged in a staggered manner by arranging N lens rows in which M lenses are arranged in the first direction in the second direction. Accordingly, the lens and the light emitting element group can be efficiently arranged with a high degree of design freedom.

  Further, when the pitches of the spots formed on the image plane in the direction corresponding to the first direction are made the same, the spot pitches formed on the image plane become equal, and spot formation can be performed better. it can. Further, by forming an image using such a line head, a high quality image can be obtained.

A. Explanation of Terms Before explaining embodiments of the present invention, terms used in this specification will be explained.

  1 and 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. Further, the light beam from the light emitting element group 295 is imaged toward the image plane IP by the lens LS corresponding to the light emitting element group 295, whereby a set of a plurality of spots SP formed on the image plane IP is obtained. It is defined as 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.

  1 and 2 show the case where the spot SP is formed in a state where the image plane is stationary so that the correspondence between the light emitting element group 295, the lens LS, and the spot group SG can be easily understood. Therefore, the formation position of the spot SP in the spot group SG is substantially similar to the arrangement position of the light emitting element 2951 in the light emitting element group 295. However, as will be described later, the actual spot forming operation is performed while conveying the image plane IP (the surface of the photosensitive drum 21) in the sub-scanning direction SD. As a result, the spots SP formed by the plurality of light emitting elements 2951 included in the head substrate 293 are formed on a straight line substantially parallel to the main scanning direction MD.

  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 “head substrate” column of the same figure, 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. Further, 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 column of “light emitting element group” in the drawing, 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. In addition, a plurality of (two in the figure) light emitting elements 2951 arranged at the light emitting element row pitch Pelr in the width direction LTD and at the light emitting element pitch Pel in the longitudinal direction LGD are defined as a light emitting element column 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 the 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. First Embodiment FIG. 3 is a diagram showing a first embodiment of an image forming apparatus according to the present invention. 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. Thus, 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 a copy sheet, a transfer sheet, a sheet, and an OHP transparent sheet.

  In the housing main body 3 of the image forming apparatus according to this embodiment, an electrical component box 5 is provided that incorporates a power circuit board, a main controller MC, an engine controller EC, and a head controller HC. An image forming unit 7, a transfer belt unit 8, and a paper feeding 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 STY (for yellow), STM (for magenta), STC (for cyan), and STK (for black) that form a plurality of images of different colors. Each image forming station STY, STM, STC, STK is provided with a photosensitive drum 21 on which the toner image of each color is formed. 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. 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 STY, STM, STC, STK 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 STK. 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 includes a plurality of light emitting elements arranged in the axial direction of the photosensitive drum 21 (direction perpendicular to the paper surface of FIG. 3), and is spaced from the photosensitive drum 21. From these light emitting elements, the surface of the photosensitive drum 21 charged by the charging unit 23 is irradiated with light to form a latent image on the surface. In this embodiment, a head controller HC is provided to control the line heads 29 for the respective colors, and each line head 29 is controlled based on the video data VD from the main controller MC and a signal from the engine controller EC. ing. That is, in this embodiment, the image data included in the image formation command is input to the image processing unit 51 of the main controller MC. Various image processing is performed on the image data to create video data VD for each color, and the video data VD is given to the head controller HC via the main-side communication module 52. In the head controller HC, the video data VD is given to the head control module 54 via the head side communication module 53. As described above, the head controller module 54 is supplied with the signal indicating the parameter value related to the latent image formation and the vertical synchronization signal Vsync from the engine controller EC. Based on these signals, video data VD, and the like, the head controller HC creates a signal for controlling element driving for the line head 29 of each color, and outputs the signal to each line head 29. Thus, the operation of the light emitting elements is appropriately controlled in each line head 29, and a latent image corresponding to the image formation command is formed.

  In this embodiment, the photoconductive drum 21, the charging unit 23, the developing unit 25, and the photoconductive cleaner 27 of each image forming station STY, STM, STC, STK are unitized as a photoconductive cartridge. Each photoconductor cartridge is provided with a nonvolatile memory for storing information related to the photoconductor cartridge. Then, wireless communication is performed between the engine controller EC and each photoconductor cartridge. In this way, information on each photoconductor cartridge is transmitted to the engine controller EC, and information in each memory is updated and stored.

  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 described in detail later. 1 is primarily transferred to the transfer belt 81.

  In this embodiment, a photoreceptor cleaner 27 is provided in contact with the surface of the photoreceptor drum 21 on the downstream side of the primary transfer position TR1 in the rotation direction D21 of the photoreceptor 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 remove the 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 indicated by an arrow D81 (conveying direction). And a transfer belt 81 that is driven to circulate. Further, the transfer belt unit 8 is disposed inside the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in each of the image forming stations STY, STM, STC, STK 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, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations STY, STM, STC, and STK as shown in FIG. Then, the transfer belt 81 is pushed and brought into contact with the photosensitive drums 21 included in the image forming stations STY, STM, STC, STK, and 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 STY, STM, and STC that face each other and the monochrome primary transfer is performed. By bringing only the roller 85K into contact with the image forming station STK, only the monochrome image forming station STK 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 STK. 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 transferred to the primary transfer position. In TR1, the image is transferred to the surface of the transfer belt 81 to form a monochrome image.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed downstream of the monochrome primary transfer roller 85K and upstream 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 STK. It is configured to contact the transfer belt 81 on a common inscribed line.

  The drive 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 paper feed unit 11 includes a paper feed unit having a paper feed cassette 77 capable of stacking and holding sheets and a pickup roller 79 for feeding sheets one by one from the paper feed 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. The sheet on which the image has been secondarily transferred is guided to a nip formed by the heating roller 131 and the pressure belt 1323 of the pressure unit 132 by the sheet guide member 15, and in the nip, a predetermined value is formed. 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 is formed by pressing the belt tension surface stretched by the two rollers 1321 and 1322 out of the surface of the pressure belt 1323 against the peripheral surface of the heating roller 131. 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 portion 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 tip of the cleaner blade 711 comes into contact with the blade facing roller 83 via the transfer belt 81 to remove foreign matters such as toner and paper dust remaining on the transfer belt after the secondary transfer. 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 schematically showing a first embodiment of the line head according to the present invention. FIG. 6 is a cross-sectional view in the width direction of the first embodiment of the line head according to the invention. In the present embodiment, the line head 29 is arranged such that the longitudinal direction LGD of the line head 29 is parallel to the main scanning direction MD and the width direction LTD substantially orthogonal to the longitudinal direction LGD is parallel to the sub-scanning direction SD. It is arranged to face the surface of the photosensitive drum. That is, in this embodiment, the main scanning direction MD and the sub-scanning direction SD on the photosensitive drum 21 side correspond to the longitudinal direction LGD and the width direction LTD on the line head 21 side, respectively. In the present embodiment, the longitudinal direction LGD corresponds to the “first direction” of the present invention, the width direction LTD corresponds to the “second direction” of the present invention, and the main scanning direction MD corresponds to the “first direction” of the present invention. It corresponds to “direction corresponding to direction”.

  The line head 29 includes a case 291 extending in parallel with the longitudinal direction LGD, and positioning pins 2911 and screw insertion holes 2912 are provided at both ends of the case 291. 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 microlens array 299 at a position facing the surface of the photosensitive drum 21, and includes a light shielding member 297 and a glass substrate 293 in the order close to the microlens array 299. In addition, a plurality of light emitting element groups 295 are provided on the back surface of the glass substrate 293 (the surface opposite to the microlens array 299 among the two surfaces of the glass substrate 293). That is, the plurality of light emitting element groups 295 are two-dimensionally (M × N) arranged on the back surface of the glass substrate 293 so as to be separated from each other in the longitudinal direction LGD and the width direction LTD of the case 291 by a predetermined distance. Here, each of the plurality of light emitting element groups 295 is configured by two-dimensionally arranging a plurality of light emitting elements, which will be described later. In the present embodiment, a bottom emission type organic EL (Electro-Luminescence) element is used as the light emitting element. That is, in this embodiment, the organic EL element is disposed as a light emitting element on the back surface of the glass substrate 293. When each light emitting element is driven by a drive circuit (not shown) formed on the glass substrate 293, a light beam is emitted from the light emitting element in the direction of the photosensitive drum 21. This light beam is directed to the light shielding member 297 through the glass substrate 293. In the present embodiment, all the light emitting elements are configured so that the wavelengths of light emitted from the respective light emitting elements are equal to each other.

  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 that penetrates the light shielding member 297 with a line parallel to the normal line of the glass substrate 293 as a central axis. Accordingly, all the light emitted from the light emitting elements belonging to one light emitting element group 295 is directed to the microlens array 299 through the same light guide hole 2971, and interference between light beams from different light emitting element groups 295 is blocked. This is prevented by the member 297. Then, the light beam that has passed through the light guide hole 2971 formed in the light shielding member 297 is imaged as a spot on the surface of the photosensitive drum 21 by the microlens array 299. The specific configuration of the microlens array 299 and the imaging state of the light beam by the microlens array 299 will be described in detail later.

  As shown in FIG. 6, the back cover 2913 is pressed against the case 291 through the glass 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 inside 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 microlens array. FIG. 8 is a longitudinal sectional view of the microlens array. The microlens array 299 has a glass substrate 2991 and a plurality of lens pairs each composed of two lenses 2993A and 2993B arranged one-on-one so as to sandwich the glass substrate 2991. These lenses 2993A and 2993B can be formed of, for example, resin.

  That is, a plurality of lenses 2993A are arranged on the front surface 2991A of the glass substrate 2991, and a plurality of lenses 2993B are arranged on the back surface 2991B of the glass substrate 2991 so as to correspond to the plurality of lenses 2993A on a one-to-one basis. . Further, the two lenses 2993A and 2993B constituting the lens pair share a common optical axis OA. The plurality of lens pairs are arranged one-on-one in the plurality of light emitting element groups 295. That is, the plurality of lens pairs are two-dimensionally (M × N) spaced apart from each other by a predetermined distance in the longitudinal direction LGD and the width direction LTD corresponding to the arrangement of the light emitting element groups 295. More specifically, in this microlens array 299, a microlens LS composed of a lens pair composed of lenses 2993A and 2993B and a glass substrate 2991 sandwiched between the lens pair corresponds to the “lens” of the present invention. Yes. A plurality of these microlenses LS arranged in the longitudinal direction LGD are arranged in a plurality of columns (in this embodiment, “3” columns) in the width direction LTD, and the plurality of microlenses LS are staggered. They are arranged at different longitudinal positions. In particular, in this embodiment, the microlens LS is arranged so that the distance P between the optical axes in the longitudinal direction LGD is constant. (FIG. 7). All the micro lenses LS have the same configuration and the same magnification m. In this embodiment, the microlens LS having a negative value for the magnification m is used, but it goes without saying that the magnification m may be set to a positive value.

  FIG. 9 is a diagram showing the arrangement relationship between the light emitting element groups and the microlenses in the line head. In this line head, a plurality of light emitting element groups 295 having the same configuration are arranged in a one-to-one correspondence with the microlenses LS arranged as described above. That is, a predetermined number of light emitting element groups 295 are arranged while being spaced apart from each other in the longitudinal direction LGD to form a light emitting element group row 295R. The light emitting element group rows 295R are arranged in a plurality of columns (in the present embodiment, “3” columns) in the width direction LTD, and the plurality of light emitting element groups 295 are arranged in a staggered manner. The distance between the light emitting element groups 295 adjacent to each other in the longitudinal direction LGD is equal to the distance P between the optical axes of the microlenses LS.

  Each light emitting element group 295 has ten light emitting elements 2951, and the light emitting elements 2951 are arranged as follows. That is, in each light emitting element group 295, five light emitting elements 2951 are arranged at predetermined intervals (= twice the element pitch dp) in the longitudinal direction LGD to form a light emitting element row 2951R. The light emitting element rows 2951R are arranged in two columns in the width direction LTD. Moreover, the shift amount of the light emitting element row 2951R in the longitudinal direction LGD is the element pitch dp (= Pel). For this reason, in each light emitting element group 295, all the light emitting element groups 295 are arrange | positioned by the element pitch dp in the mutually different longitudinal direction position. Accordingly, in each light emitting element group 295, the light beams emitted from the ten light emitting elements 2951 are different from each other in the main scanning direction MD by the microlens LS on the surface of the photosensitive drum 21 (hereinafter referred to as “photosensitive member surface”). Is imaged. Thereby, 10 spots are formed side by side in the main scanning direction MD to form a spot group.

  Furthermore, in this embodiment, the line head 29 is configured such that spot groups formed adjacent to each other in the main scanning direction MD partially overlap each other. In particular, in this embodiment, the magnification m of the microlens LS is set to (−1), and the both ends of each light emitting element group 295 are arranged so as to overlap the ends of the adjacent light emitting element groups 295 in the longitudinal direction LGD. Has been. Here, with reference to FIG. 9, the arrangement relationship will be described in detail with a focus on three light emitting element groups 259A to 259C adjacent in the longitudinal direction LGD. The light emitting element group 295A is located on the upstream side (left hand side in the figure) with respect to the light emitting element group 295B, while the light emitting element group 295C is located on the downstream side (right hand side in the figure). As indicated by the broken line in the figure, in the longitudinal direction LGD, two of the 10 light emitting elements 2951 constituting the light emitting element group 295B are positioned at the downstream end of the light emitting element group 295A. It arrange | positions so that it may overlap with two light emitting elements. On the other hand, the two most downstream elements are arranged so as to overlap the two light emitting elements located at the upstream end of the light emitting element group 295C.

  FIG. 10 is a diagram showing the positions of spots formed on the surface of the photoreceptor by the line head, and schematically shows how spots are formed by two light emitting element groups, for example, the light emitting element groups 295A and 295B in FIG. Show. In addition, “spot group SGa” in the figure indicates a group of spots SP formed by the light emitting element group 295A on the upstream side (left hand side in FIG. 9), while “spot group SGb” indicates the downstream side (in FIG. 9). A group of spots SP formed by the light emitting element group 295B on the right hand side) is shown. As shown in the upper part of the figure, when the light emitting elements 2951 are turned on at the same time, the spot groups SGa and SGb formed on the surface of the photoreceptor are also two-dimensionally arranged.

  Therefore, in the present embodiment, as shown in the lower part of the figure, in each of the light emitting element rows 2951R, the light emitting elements 2951 constituting the light emitting element row 2951R emit light at a timing according to the rotational movement of the photosensitive drum 21. It is configured as follows. That is, the lighting timings of the light emitting element rows 2951R constituting the light emitting element groups 295A and 295B are made different in correspondence with the rotational movement of the photosensitive drum 21 as follows.

(a) Timing T1: lighting of the upper light emitting element row 2951R of the light emitting element group 295A,
(b) Timing T2: lighting of the lower light emitting element row 2951R of the light emitting element group 295A,
(c) Timing T3: lighting of the upper light emitting element row 2951R of the light emitting element group 295B,
(d) Timing T4: lighting of the lower light emitting element row 2951R of the light emitting element group 295B,
Therefore, only by this timing adjustment, the spot SP formed by the upper light emitting element array and the spot SP formed by the lower light emitting element array can be formed side by side in the main scanning direction MD. Thus, the spots SP can be formed in a line in the main scanning direction MD by simple light emission timing adjustment.

  Here, it should be noted that spot groups SGa and SGb formed adjacent to each other in the main scanning direction MD in this embodiment partially overlap each other to form an overlapping spot region OR. That is, in this overlapping spot region OR, a part of the spots by the light emitting element group 295A (spots SPa1, SPa2 in FIG. 10) and a part of the spots by the light emitting element group 295B (spots SPb1, SPb2 in FIG. 10) Are overlapping. In this specification, the spots SPa1, SPa2, SPb1, and SPb2 constituting the overlapping spot region OR are referred to as “overlapping spots”.

  When the surface of the photosensitive member is exposed using the line head 29 configured as described above, a two-dimensional latent image LI as shown in FIG. 11 is obtained. That is, adjacent spot groups partially overlap to form an overlapping spot region OR. Therefore, not only when there is no positional deviation or magnification error (FIG. 5A), it is also assumed that the mutual positional relationship between the light emitting element group 295 and the microlens LS is slightly shifted, or the magnification error of the microlens LS occurs. In addition, it is possible to prevent a gap from being generated between the spot groups SG, and a favorable spot formation can be performed. Further, by forming an image using such a line head 29, it is possible to form a high-quality toner image without generating vertical stripes.

  FIG. 12 is a diagram showing a comparative example of the line head. FIGS. 13 and 14 are views showing the state of spots formed by the comparative example of FIG. Here, the effect by having employ | adopted the said structure is demonstrated using these drawings.

  In this comparative example, as shown in the lower part of FIG. 12, in each light emitting element group 295, four light emitting elements 2951 are arranged at predetermined intervals (= twice the element pitch dp) in the longitudinal direction LGD. Row 2951R is formed. The light emitting element rows 2951R are arranged in two columns in the width direction LTD. Moreover, the shift amount of the light emitting element row 2951R in the longitudinal direction LGD is the element pitch dp. In the comparative example, when the light emitting element 2951 is turned on, as is apparent from the upper part of the figure, all the spots SP are formed at different positions in the main scanning direction MD and at a spot pitch (m · dp).

  Therefore, when the spot SP is formed on the surface of the photosensitive member by the line head according to the comparative example, adjacent spot groups are continuously connected and good spot formation is performed when no positional deviation or magnification error occurs (FIG. 13). (See (a) and FIG. 14 (a)). However, if the mutual positional relationship between the light emitting element group 295 and the microlens LS is slightly shifted and a positional shift occurs, the spot groups SG1 and SG2 are separated from each other as shown in FIG. End up. Also, when a magnification error occurs in the microlens array 299, as shown in FIG. 14B, the spot groups SG1 to SG3 are separated from each other and vertical stripes are generated.

  On the other hand, as described above, according to the present embodiment, the line head 29 is configured to form the overlapping spot region OR, so that it is possible to form spots without causing these problems. it can. An image forming apparatus using the thus configured line head 29 as an exposure unit can form a high-quality image.

C. Second Embodiment By the way, since the angle of view of the light beam from the light emitting element 2951 positioned at the end of the light emitting element group 295 with respect to the microlens LS is increased, the diameter of the spot SP increases due to the aberration deterioration of the microlens LS. In addition, the amount of light may decrease. When it is necessary to consider such a problem, it is desirable to configure each light emitting element group 295 as follows.

  FIG. 15 is a view showing a second embodiment of the line head according to the present invention. In this embodiment, the light emitting elements constituting the light emitting element group 295 are divided into two different types of light emitting elements. One of them is a light emitting element 2951b which is located at the end of the light emitting element group 295 and forms an overlapping spot. The other is the remaining light emitting element 2951a, each of which forms an independent spot. In this embodiment, the element diameter of the light emitting element 2951b is smaller than the element diameter of the light emitting element 2951a.

  When the light emitting element group 295 configured as described above is used, the diameter of the spot formed by the light emitting element 2951b, that is, the overlapping spot increases due to the aberration deterioration of the microlens LS. Therefore, the diameter of the overlapping spot is substantially the same as the spot SP formed by the light emitting element 2951a, and the spot diameter can be made uniform. Further, by reducing the element diameter of each light emitting element 2951b, the light amount of each overlapping spot is also reduced. However, in the overlapping spot region OR, overlapping spots formed by the light emitting elements 2951b of the light emitting element groups adjacent to each other in the longitudinal direction LGD (for example, the light emitting element groups 295A and 295B in the figure), that is, the two light emitting elements 2951b are overlapped. The As a result, the same amount of light as the spot SP formed by the light emitting element 2951a can be obtained. Accordingly, it is possible to eliminate a decrease in the amount of light due to the aberration deterioration of the microlens LS.

  As described above, according to the line head according to this embodiment, even when the aberration of the microlens LS is deteriorated, the spot diameter and the light amount can be made uniform. In addition, it is not necessary to require extremely strict optical characteristics for the design of the microlens LS, so that a relatively large design freedom can be obtained and the cost of the microlens array 299 can be reduced. Such a configuration can also be applied to an apparatus for forming the overlapping spot region OR and the overlapping region WR in the fifth to eighth embodiments, which will be described in detail later, and the same effects can be obtained.

D. Third Embodiment Further, regarding the problem that the light amount in the overlapping spot region OR is larger than the light amount in other regions, it is desirable to configure as follows. Hereinafter, a description will be given with reference to FIG.

  FIG. 16 is a view showing another embodiment of the line head according to the present invention. Also in this embodiment, as in the embodiment shown in FIG. 15, the light emitting element group 295 includes a light emitting element 2951b that forms overlapping spots and a light emitting element 2951a that forms independent spots. In this embodiment, the light emission amount of the light emitting element 2951b is smaller than the light emission amount of the light emitting element 2951a. Accordingly, in the overlapping spot region OR, overlapping spots formed by the two light emitting elements 2951b are overlapped, but the light amount in the overlapping spot region OR is changed in other regions (regions where spots are formed by the light emitting elements 2951a). The amount of light is almost the same. Therefore, even if the overlapping spot region OR is provided, the amount of light on the surface of the photoreceptor can be made uniform. Such a configuration can also be applied to an apparatus for forming the overlapping spot region OR and the overlapping region WR in the fifth to eighth embodiments, which will be described in detail later, and the same effects can be obtained.

  In the above embodiment, a part of the light emitting elements constituting the light emitting element group 295 functions as a light emitting element for forming overlapping spots. However, as shown in FIG. 17, all the light emitting elements for forming overlapping spots are used. May function as

  FIG. 17 is a diagram showing a third embodiment of a line head according to the present invention. In this embodiment, each light emitting element group 295 has 16 light emitting elements 2951. More specifically, in each light emitting element group 295, eight light emitting elements 2951 are arranged at predetermined intervals (= twice the element pitch dp) in the longitudinal direction LGD to form a light emitting element row 2951R. The light emitting element rows 2951R are arranged in two columns in the width direction LTD. Moreover, the shift amount of the light emitting element row 2951R in the longitudinal direction LGD is the element pitch dp. For this reason, in each light emitting element group 295, all the light emitting element groups 295 are arrange | positioned by the element pitch dp in the mutually different longitudinal direction position. Of course, also in this embodiment, it operates as shown in FIG. 18 and all the light emitting elements 2951 form overlapping spots.

  FIG. 18 is a diagram showing the positions of spots formed on the surface of the photoreceptor by the line head of FIG. In the drawing, spots SP formed by the three light emitting element groups 295A to 295C shown in FIG. 17 are shown. As shown in FIG. 17, these three light emitting element groups 295A to 295C are provided corresponding to the three microlenses LS adjacent to each other, and are also adjacent to each other in the longitudinal direction LGD. Therefore, the light emitting element groups 295A to 295C correspond to the “upstream light emitting element group”, “central light emitting element group”, and “downstream light emitting element group” of the present invention, respectively.

  In each of the light emitting element rows 2951R, the light emitting elements 2951 constituting the light emitting element row 2951R emit light at a timing according to the rotational movement of the photosensitive drum 21. That is, the lighting timings of the light emitting element rows 2951R constituting the light emitting element groups 295A to 295C are made different in correspondence with the rotational movement of the photosensitive drum 21 as follows.

(a) Timing T1: lighting of the upper light emitting element row 2951R of the light emitting element group 295A,
(b) Timing T2: lighting of the lower light emitting element row 2951R of the light emitting element group 295A,
(c) Timing T3: lighting of the upper light emitting element row 2951R of the light emitting element group 295B,
(d) Timing T4: lighting of the lower light emitting element row 2951R of the light emitting element group 295B,
(e) Timing T5: lighting of the upper light emitting element row 2951R of the light emitting element group 295C,
(f) Timing T6: lighting of the lower light emitting element row 2951R of the light emitting element group 295C,
Therefore, the spot SP formed by the upper light emitting element array and the spot SP formed by the lower light emitting element array can be formed side by side in the main scanning direction MD only by this timing adjustment. Thus, the spots SP can be formed in a line in the main scanning direction MD by simple light emission timing adjustment. Further, the overlapping spot region OR formed in this way matches the spot region formed by the light emitting element group 295B. Further, in this embodiment, the overlapping spot region OR is expanded as compared with the first embodiment and the like, and the occurrence of vertical stripes can be reliably prevented even when the positional deviation or the magnification error becomes large. Such a configuration can also be applied to an apparatus for forming the overlapping spot region OR and the overlapping region WR in the fifth to eighth embodiments, which will be described in detail later, and the same effects can be obtained.

E. Fourth Embodiment In the above embodiment, the light emitting element group 295 has the same configuration, and the microlens LS has the same configuration. However, for example, as shown in FIG. 19, the magnification may be different for each microlens LS. In the embodiment shown in the figure, the magnification m of the uppermost and lowermost microlenses LS in the width direction LTD is set to “−2 times”, while the magnification m of the middle microlens LS is set to “−1 times”. It is set (in the parenthesis in the figure indicates the magnification m). As described above, the microlens LS having different magnifications m of the microlens LS may be provided. Also in such a line head, by forming an overlapping spot region, the same as in the above embodiment. The effect of this can be obtained. Moreover, the magnification m of the microlens LS can be arbitrarily set in this way. As a result, the degree of freedom in design can be increased, and for example, a space suitable for routing the wiring formed on the glass substrate 293 can be easily secured. When changing the magnification m for each microlens LS, it is desirable to change the element diameter of the light emitting element 2951 in consideration of the magnification m, as shown in FIG. That is, it is desirable to increase the element diameter as the absolute value of the magnification m is smaller. This is because the spot diameters on the surface of the photoreceptor are made uniform. Such a configuration can also be applied to an apparatus for forming the overlapping spot region OR and the overlapping region WR in the fifth to eighth embodiments, which will be described in detail later, and the same effects can be obtained.

F. Fifth Embodiment However, in the above embodiment, the overlapping spot regions OR are formed for all the combinations of the spot groups SG adjacent to each other. An overlapping spot region OR may be formed at the same time. For example, when a lens array in which a plurality of lens substrates having lenses is combined is used, a pair of lenses may be relatively displaced with the lens substrate combination position interposed due to an assembly error of the lens substrate. . When a relative positional shift occurs between the lens pairs forming spot groups adjacent to each other in the longitudinal direction LGD among the lens pairs, a gap is generated between the spot groups SG. Therefore, in a line head or an image forming apparatus that employs such a lens array, the overlap spot region OR is formed by configuring the inter-lens distance Pi of the lenses constituting the lens pair so as to satisfy a relational expression (1) described later. It is desirable to form. Hereinafter, a description will be given with reference to FIGS.

  FIG. 20 is a perspective view schematically showing a fifth embodiment of the line head according to the invention. FIG. 21 is a sectional view in the width direction of a fifth embodiment of the line head according to the invention. In the present embodiment, the line head 29 is arranged such that the longitudinal direction LGD of the line head 29 is parallel to the main scanning direction MD and the width direction LTD substantially orthogonal to the longitudinal direction LGD is parallel to the sub-scanning direction SD. It is arranged to face the surface of the photosensitive drum. That is, in this embodiment, the main scanning direction MD and the sub-scanning direction SD on the photosensitive drum 21 side correspond to the longitudinal direction LGD and the width direction LTD on the line head 21 side, respectively. The line head 29 of the present embodiment is greatly different from that of the first embodiment in the following two points. That is, the first point is that a split lens configuration in which a plurality of lens substrates are combined is adopted. The second point is formed on the surface of the photoconductor (image plane) so that spot groups adjacent to each other in the main scanning direction MD overlap with each other in the sub-scanning direction SD by a pair of lenses that sandwich the lens substrate combination position. This is the point. Since the other configuration is the same as that of the first embodiment, the difference will be mainly described.

  In FIG. 20, the line head 29 includes a case 291 whose longitudinal direction is parallel to the main scanning direction MD, and positioning pins 2911 and screw insertion holes 2912 are provided at both ends of the case 291. The line head 29 is positioned with respect to the photosensitive drum 21 shown in FIG. 3 by fitting the positioning pin 2911 into a positioning hole formed in a photosensitive member cover (not shown). The photoconductor cover covers the photoconductor drum 21 and is positioned with respect to the photoconductor 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.

  20 and 21, the case 291 holds the microlens array 299 in which the imaging lenses are arranged at a position facing the surface 211 of the photosensitive drum 21, and in the order close to the microlens array 299. Thus, a light shielding member 297 and a head substrate 293 as a substrate are provided. The head substrate 293 is a transparent glass substrate. A plurality of light emitting element groups 295 are provided on the back surface 2932 of the head substrate 293 (the surface opposite to the surface 2931 facing the light shielding member 297 out of the two surfaces of the head substrate 293). As shown in FIG. 20, the plurality of light emitting element groups 295 are two-dimensionally and discretely arranged in the longitudinal direction LGD and the width direction LTD at a predetermined interval, as shown in FIG. . Here, the light emitting element group 295 is configured by two-dimensionally arranging a plurality of light emitting elements 2951 as shown in a circled portion in FIG. Their arrangement will be described later in detail.

  In the present embodiment, an organic EL is used as the light emitting element. That is, in this embodiment, the organic EL is disposed as the light emitting element 2951 on the back surface 2932 of the head substrate 293. Light emitted from each of the plurality of light emitting elements 2951 toward the photosensitive drum 21 is directed to the light shielding member 297 via the head substrate 293. In the present embodiment, all the light emitting elements are configured so that the wavelengths of light emitted from the respective light emitting elements are equal to each other. Further, although the organic EL is used as the light emitting element 2951, the specific configuration of the light emitting element 2951 is not limited thereto, and for example, an LED (Light Emitting Diode) may be used as the light emitting element 2951. In this case, the substrate 293 may not be a glass substrate, and the LED can be provided on the surface 2931 of the substrate 293.

  20 and 21, the light shielding member 297 includes a plurality of light guide holes 2971 that correspond one-to-one to the plurality of light emitting element groups 295. Light emitted from the light emitting elements 2951 belonging to the light emitting element group 295 is guided to the microlens array 299 through the light guide holes 2971 corresponding to the light emitting element groups 295 on a one-to-one basis. Then, the light passing through the light guide hole 2971 is imaged as a spot on the surface 211 of the photosensitive drum 21 by the microlens array 299 as indicated by a two-dot chain line.

  As shown in FIG. 21, the back cover 2913 is pressed against the case 291 via the head substrate 293 by the fixing device 2941. That is, the fixing device 2941 has an elastic force that presses the back cover 2913 toward the case 291, and presses the back cover 2913 with the elastic force, thereby making the inside of the case 291 light-tight (that is, inside the case 291). From the outside of the case 291 and so that light does not enter from the outside of the case 291). Note that a plurality of fixing devices 2941 are provided in the longitudinal direction LGD of the case 291 shown in FIG. The light emitting element group 295 is covered with a sealing member 294.

  FIG. 22 is a schematic partial perspective view of the microlens array. FIG. 23 is a partial cross-sectional view of the microlens array in the longitudinal direction. FIG. 24 is a plan view of the microlens array. 22 and 23, the microlens array 299 includes a glass substrate 2991 as a transparent substrate and a plurality (eight in this embodiment) of plastic lens substrates 2992. Since these figures are partial views, not all parts are shown.

  22 and 23, the plastic lens substrate 2992 is provided on both surfaces of the glass substrate 2991. That is, as shown in FIG. 24, four plastic lens substrates 2992 are combined in a straight line on one surface of the glass substrate 2991 and adhered by an adhesive 2994. The shape of the microlens array 299 when viewed in plan is a rectangle. On the other hand, the plastic lens substrate 2992 has a parallelogram shape, and a gap portion 2995 is formed between the four plastic lens substrates 2992. As shown in FIGS. 23 and 24, the gap portion 2995 may be filled with a light absorbing material 2996, and the light absorbing material 2996 has a characteristic of absorbing a light beam emitted from the light emitting element 2951. For example, a resin containing fine particles of carbon can be used. In the circle in FIG. 24, an enlarged view of the vicinity of the gap 2995 is shown.

  The lenses 2993 are arranged so as to form three lens rows LSR1 to LSR3 in the longitudinal direction LGD of the microlens array 299. Each row is arranged with a slight shift in the longitudinal direction LGD, and the lens columns LSC are arranged obliquely with respect to the short side of the rectangle when the microlens array 299 is viewed in plan. The gap 2995 is formed between the lens rows LSC along the lens row LSC, and corresponds to the “combination position” of the present invention.

  Each gap 2995 is formed so as not to cover the lens effective range LE of the lens 2993. The effective range LE of the lens is an area through which light emitted from the light emitting element group 295 is transmitted. As a method of forming the gap portion 2995 so as not to cover the effective range LE of the lens, a method of forming an end surface of the plastic lens substrate so as not to cover the effective range LE of the lens, and a plurality of plastic lenses. There is a method in which the substrate is integrally molded and then cut so as not to reach the effective range LE of the lens.

  Also, the four plastic lens substrates 2992 are bonded to the other surface side by an adhesive 2994 corresponding to the four lens substrates 2992. In this way, the biconvex lens is configured as an imaging lens by the two lenses 2993 arranged one-on-one so as to sandwich the glass substrate 2991. The plastic lens substrate 2992 and the lens 2993 can be integrally formed by resin injection molding using a mold.

  The two lenses 2993 constituting the imaging lens share a common optical axis OA indicated by a one-dot chain line in the drawing. Further, the plurality of lenses are arranged one-on-one in the plurality of light emitting element groups 295 shown in FIG. In this specification, an optical system including two lenses 2993 and a glass substrate 2991 sandwiched between the lenses 2993 is referred to as a “microlens LS”. The microlens LS as the imaging lens corresponds to the arrangement of the light emitting element groups 295 in the longitudinal direction LGD (direction corresponding to the main scanning direction MD) and the width direction LTD (direction corresponding to the sub scanning direction SD). They are arranged two-dimensionally (M × N) at a predetermined interval.

  When the gap portion 2995 is provided as described above, that is, when the lens array 299 is formed by combining a plurality of lens substrates 2992, it is difficult to combine the lens substrates 2992 as designed, and the gap portion 2995 is sandwiched. A relative positional shift may occur in the lens LS arranged at. Therefore, in the present embodiment, a plurality of light emitting element groups 295 are arranged in a one-to-one correspondence relationship with the microlenses LS arranged as described above, and the vicinity (combination position) where the lens substrates 2992 are combined. The device configuration is different between the vicinity of the device and the other devices. Hereinafter, the apparatus configuration and operation will be described separately.

FIG. 25 is a diagram showing the arrangement relationship between the microlenses on the lens substrate and the light emitting element groups corresponding to the microlenses. In this line head, a predetermined number of light emitting element groups 295 are arranged while being separated from each other in the longitudinal direction LGD to form a light emitting element group row (reference numeral 295R in FIG. 2). These light emitting element group rows are arranged in a plurality of columns (“3” columns in this embodiment) in the width direction LTD, and a plurality of light emitting element groups 295 are arranged in a staggered manner. The distance between the light emitting element groups 295 adjacent to each other in the longitudinal direction LGD is equal to the distance between the optical axes of the microlenses LS. For example, as shown in FIG. 25, in the longitudinal direction LGD, the first lens LS ₁ and the second lens LS ₂ are distance P ₁ , the second lens LS ₂ and the third lens LS _3. And the distances P ₂ ,... Have the same value. Further, the distance in the longitudinal direction LGD between the light emitting element groups 295 corresponding to the lenses LS _{1 to} LS ₃ also coincides with them.

The light emitting element group 295 includes eight light emitting elements 2951 except for a light emitting element group related to a special lens pair described later, and the light emitting elements 2951 are arranged as follows. That is, in each light emitting element group 295, four light emitting elements 2951 are arranged in each (2-fold = element pitch dp _i) a predetermined distance in the longitudinal direction LGD light emitting element row (reference numeral 2951R in Fig. 1) is formed Has been. Further, two light emitting element rows are arranged in the width direction LTD. Moreover, the shift amount of the light emitting element rows in the longitudinal direction LGD is in the element pitch dp _i. Therefore, they are arranged in the respective light emitting element groups 295, all of the light emitting element groups 295 elements in the different longitudinal positions pitch dp i ₍₌ Pel). Accordingly, in each light emitting element group 295, the light beams emitted from the eight light emitting elements 2951 are placed on the surface of the photosensitive drum 21 (hereinafter referred to as “photosensitive member surface”) at different positions in the main scanning direction MD by the microlens LS. Is imaged. Thus, eight spots are formed side by side in the main scanning direction MD to form a spot group SG. More specifically, the spot group SG is formed as follows.

FIG. 26 is a diagram showing the positions of spots formed on the surface of the photoconductor by the line head. For example, the light emitting element group 295_1 corresponding to the _first lens LS1 in FIG. A mode that a spot is formed with the light emitting element group 295_2 corresponding to the _2nd lens LS2 is shown typically. In the figure, “spot group SG ₁ ” indicates a group of spots SP formed by the light emitting element group 295_1 on the upstream side (left hand side in FIG. 25), while “spot group SG ₂ ” indicates the downstream side (FIG. 25 shows a group of spots SP formed by the light emitting element group 295_2 on the right hand side of 25). As shown in the upper part of the figure, when the light emitting elements 2951 are simultaneously turned on, the spot groups SG ₁ and SG ₂ formed on the surface of the photosensitive member are also two-dimensionally arranged.

  Therefore, in the present embodiment, as shown in the lower part of the figure, in each of the light emitting element rows, the light emitting elements 2951 constituting the light emitting element row emit light at a timing according to the rotational movement of the photosensitive drum 21. It is composed. That is, the lighting timings of the light emitting element rows constituting the light emitting element group 295 are made different according to the rotational movement of the photosensitive drum 21 as follows.

(a) Timing T1: lighting of the upper light emitting element row of the light emitting element group 295_1,
(b) Timing T2: lighting of the lower light emitting element row of the light emitting element group 295_1,
(c) Timing T3: lighting of the upper light emitting element row of the light emitting element group 295_2,
(d) Timing T4: lighting of the lower light emitting element row of the light emitting element group 295_2,
Therefore, the spot SP formed by the upper light emitting element row and the spot SP formed by the lower light emitting element row can be formed side by side in the main scanning direction MD only by this timing adjustment. Thus, the spots SP can be formed in a line in the main scanning direction MD by simple light emission timing adjustment.

FIG. 27 is a diagram showing the arrangement relationship between the microlenses and the light emitting element groups in the vicinity of the combination position. Even in the vicinity of the combination position, the arrangement and operation of the microlens and the light emitting element group are basically the same as those shown in FIG. That is, in order to form spot groups adjacent to each other in the main scanning direction MD, a plurality of lens pairs, for example, the lens LS _i-1 and the lens LS _{i in} FIG. 27 are formed on the same lens substrate 2992. A spot group is formed by the lens pair in the same manner as the lens pair (lens LS ₁ , LS ₂ ). However, a pair of lenses (hereinafter referred to as a “special lens pair”) that form a spot group adjacent to each other in the main scanning direction MD, for example, a lens LS _i and a lens LS _{i + 1 in} FIG. The lens pair configured by is different from the lens pair shown in FIG. 25 (hereinafter referred to as “normal lens pair”). That is, as shown in FIG. 27, in the light emitting element group 295 corresponding to the lens LS _i , two extra light emitting elements 2951 are provided. That is, the light emitting element group 295_I, 5 pieces of aligned light-emitting element row every (2 times = element pitch dp _i) the light emitting element 2951 is predetermined intervals in the longitudinal direction LGD (code 2951R in FIG. 2) is formed ing. Further, two light emitting element rows are arranged in the width direction LTD. Moreover, the shift amount of the light emitting element rows in the longitudinal direction LGD is in the element pitch dp _i.

FIG. 28 is a diagram showing the positions of spots formed on the surface of the photoreceptor by the special lens pair and the light emitting element group corresponding to the lens pair. In this embodiment, the inter-lens distance P _i of the lenses LS _i and LS _{i + 1} constituting the special lens pair is given by

ｍ_ｉはレンズＬＳ_ｉの光学倍率であり、
Ｌ_ｉはレンズＬＳ_ｉに対向する発光素子グループの長手方向ＬＧＤの幅であり、
ｄｐ_ｉはレンズＬＳ_ｉに対向する発光素子グループでの長手方向ＬＧＤにおける発光素子２９５１のピッチであり、
ｍ_ｉ＋１はレンズＬＳ_ｉ＋１の光学倍率であり、
Ｌ_ｉ＋１はレンズＬＳ_ｉ＋１に対向する発光素子グループの長手方向ＬＧＤの幅であり、
ｄｐ_ｉ＋１はレンズＬＳ_ｉ＋１に対向する発光素子グループでの長手方向ＬＧＤにおける発光素子２９５１のピッチであり、
を満たしている。なお、ピッチｄｐ_ｉ、ｄｐ_ｉ＋１は予め設計した値や実測値の平均ピッチなどを用いることができる。

m _i is the optical magnification of the lens LS _i ,
L _i is the width in the longitudinal direction LGD of the light emitting element group facing the lens LS _i ,
dp _i is the pitch of the light emitting elements 2951 in the longitudinal direction LGD in the light emitting element group facing the lens LS _i,
m _{i + 1} is the optical magnification of the lens LS _{i + 1} ,
L _{i + 1} is the width in the longitudinal direction LGD of the light emitting element group facing the lens LS _{i + 1} ,
dp _{i + 1} is the pitch of the light emitting elements 2951 in the longitudinal direction LGD in the light emitting element group facing the lens LS _{i + 1} ,
Meet. Note that pitches dp _i and dp _{i + 1} may be values designed in advance or average pitches of actually measured values.

When the spot is formed by the special lens pair configured as described above, the spot groups SG _i and SG _{i + 1} formed adjacent to each other in the main scanning direction MD partially overlap each other to form an overlapping spot region OR. Is done. That is, in the overlapping spot region OR, spot portion of the spot by the light emitting element group 295 (spot _SP a in FIG. 28, SP _b) and, by the light emitting element group 295 corresponding to the lens _{LS i + 1} corresponding to the lens LS _i Part (spots SP _aa , SP _{bb in} FIG. 28) overlap. In this specification, the spots SP _a , SP _b , SP _aa and SP _bb constituting the overlapping spot region OR are referred to as “overlapping spots”.

When the surface of the photosensitive member is exposed using the thus configured line head 29, a two-dimensional latent image LI as shown in FIG. 29 is obtained. That is, adjacent spot groups partially overlap to form an overlapping spot region OR. Therefore, the following effects can be obtained. That is, when the lens array 299 is manufactured, the lenses LS _i and LS _{i + 1} that are paired with the lens substrate 2992 assembling position (gap portion 2995) between the lens substrates 2992 and the like may be relatively shifted due to an assembly error of the lens substrate 2992. is there. When a relative positional shift occurs in the special lens pair, a gap is generated between the spot groups ((a) in the figure). On the other hand, in the present embodiment, since the special lens pair is configured to satisfy the relational expression (1), spots can be formed without causing these problems (FIG. b)). An image forming apparatus using the thus configured line head 29 as an exposure unit can form a high-quality image.

As described above, according to the fifth embodiment, a lens pair (lens LS _k and lens LS _{k + 1} : k = 1, 2, 3,...) That forms spot groups SG adjacent to each other in the main scanning direction MD. Among these, the special lens pair (the lens LS _i and the lens LS _{i + 1 in} FIG. 27) is configured such that the inter-lens distance P _{i of} the lenses LS _i and LS _{i + 1} constituting the lens pair satisfies the relational expression (1). is doing. As a result, the spot groups SG _i and SG _{i + 1} adjacent to each other in the main scanning direction MD are formed on the photoconductor surface (image plane) by the special lens pair so as to partially overlap in the sub-scanning direction SD. It is formed. Therefore, even if a relative positional shift occurs between the special lens pair, it is possible to prevent a gap from being generated between the spot groups SG _i and SG _{i + 1} . Therefore, an image forming apparatus employing such a lens array 299 can form a high-quality toner image without generating vertical stripes.

In the above embodiment, the value (m _k dp _k ) and the value (m _{k + 1} dp _{k + 1} ) are the same in all spot groups SG _k (k = 1, 2, 3,...). Therefore, the spot pitch Psp in each spot group SG becomes equal, and spot formation can be performed better. Further, by forming an image using such a line head, a high quality image can be obtained.

Here, the configuration is such that the relational expression (1) is established only for the special lens pair, but the lens pair (the lens LS _k and the lens LS _{k + 1)} forming the spot groups SG adjacent to each other in the main scanning direction MD. : However, the relational expression (1) may be established for all k = 1, 2, 3,. In this case, as in the first embodiment, an overlapping spot region OR is formed between adjacent spot groups SG.

In the fifth embodiment, in order to form the overlapping spot region OR, the number of the light emitting elements 2951 constituting the light emitting element group 295_i is increased by two to form the overlapping spot region OR. Here, the number of light emitting elements in the light emitting element group 295_i + 1 corresponding to the other lens LS _{i + 1} constituting the special lens pair is increased by two, or one in each of the light emitting element groups 295_i and 295_i + 1 as shown in FIG. May increase. Further, the number of light emitting elements 2951 to be overlapped is not limited to “2”, and is arbitrary.

  In the fifth embodiment, the lens array 299 is formed by combining four lens substrates 2992 in a straight line. However, a line in which a lens array is formed by combining a plurality of lens substrates in an arbitrary form. The present invention can be applied to the entire head. In other words, in a line head in which a plurality of lens substrates are combined, among the lens pairs forming a pair with the lens substrate combination position interposed therebetween, they are adjacent to each other in the direction corresponding to the longitudinal direction (first direction) LGD (main scanning direction MD). The lens pair forming the spot group to be configured can be configured such that the expression (1) is satisfied. Thereby, the spot groups SG adjacent to each other in the main scanning direction MD are formed on the photosensitive member surface (image plane) by the special lens pair so as to partially overlap in the sub scanning direction SD, thereby forming an overlapping spot region OR. Therefore, even in the line head and the image forming apparatus configured as described above, the same effects as those in the above-described embodiment can be obtained.

G. Sixth Embodiment In the fifth embodiment, the lens array 299 is configured by the division / assembly method. However, the head substrate 293 may be configured by the division / assembly method, and a line head using the head substrate and The present invention can be applied to an image forming apparatus. For example, as shown in FIG. 31, a head substrate 293 may be configured by combining element substrates 2933 and 2934 on which light emitting element groups 295 are formed. In this case, at the combination position 2935 of the two element substrates 2933 and 2934, a problem similar to the case where the lens array is configured by the division / assembly method may occur due to an assembly error or the like. That is, vertical stripes may occur between spot groups adjacent to each other in the main scanning direction MD. Therefore, in the line head and the image forming apparatus configured as described above, the same effects as those of the above-described embodiment can be obtained by configuring as follows. That is, spot groups adjacent to each other in the main scanning direction MD corresponding to the longitudinal direction (first direction) LGD are formed among the pair of lenses facing the pair of light emitting element groups sandwiching the combination position 2935 of the element substrate 2932. The special lens pair (lens LS _i , LS _{i + 1} ) to be configured is configured to satisfy the expression (1). As a result, the spot groups SG _i and SG _{i + 1} adjacent to each other in the main scanning direction MD are formed on the photoconductor surface (image plane) by the special lens pair so as to partially overlap in the sub-scanning direction SD. It is formed. Therefore, even if the positional deviation of the light emitting element group at the combination position 2935 occurs, good spot formation can be performed, and the occurrence of vertical stripes can be reliably prevented.

H. Seventh Embodiment The present invention can also be applied to a line head and an image forming apparatus using a lens array 299 and a head substrate 293 manufactured without using a division / assembly method. For example, in the apparatus shown in FIG. 32, the lenses LS are arranged so that three lens rows LSR1 to LSR3 are formed in the longitudinal direction LGD of the microlens array 299. In the lens array 299 having such an arrangement, the same problem as in the above embodiment may occur. That is, the lens constituting the first lens row LSR1 and the lens constituting the third lens row in the width direction (second direction) LTD are separated from each other in the width direction LTD. Therefore, the two lenses may be relatively displaced due to a manufacturing error or the like. Among the lens pairs constituted by these lenses, the lens pair is formed of a lens pair forming spot groups adjacent to each other in the main scanning direction MD corresponding to the longitudinal direction LGD, for example, a lens LS _i and a lens LS _{i + 1} in FIG. When a relative positional shift occurs in the lens pair, a gap is generated between the spot groups. Therefore, in a line head or an image forming apparatus employing such a lens array, the inter-lens distance P _i between the lens LS _i and the lens LS _{i + 1} is configured to satisfy the above formula (1), and a special lens pair is used. It is desirable that the spot groups SG _i and SG _{i + 1} adjacent to each other in the main scanning direction MD are formed on the photoreceptor surface (image plane) so as to partially overlap in the sub-scanning direction SD to form an overlapping spot region OR. As a result, a high-quality toner image can be formed without generating vertical stripes.

In this embodiment, the present invention is applied to an apparatus having three lens rows, that is, N = 3. However, the present invention can be applied to an apparatus having four or more columns. That is, spot groups adjacent to each other in the main scanning direction MD are formed in the sub-scanning direction by the lens pair of the lens constituting the first lens row in the width direction LTD and the lens constituting the Nth lens row in the width direction LTD. By forming on the surface of the photoreceptor (image surface) so as to overlap with SD, the same effects as those of the above-described embodiment can be obtained.

I. Eighth Embodiment In the above embodiment, the spots SP constituting the adjacent spot groups SG in the main scanning direction MD are configured to overlap in the overlapping spot region OR, but the spot SP is shifted in the sub-scanning direction SD. Even if formed, the same effect as described above can be obtained. For example, when a screen-processed gradation pattern is formed by a conventional technique (comparative example), a latent image LI shown in FIG. 33 is formed on the surface (image surface) of the photoreceptor. That is, when no positional deviation or the like occurs, spot groups SG _i and SG _{i + 1} adjacent to each other in the main scanning direction MD are continuously formed as shown in FIG. However, when a positional shift or the like occurs, as shown in FIG. 5B, the spot groups SG _i and SG _{i + 1} are separated from each other to generate vertical stripes.

In contrast, in the eighth embodiment of the present invention, the spot groups partially overlap in the sub-scanning direction SD with respect to some or all of the combinations of spot groups adjacent in the main scanning direction MD. It is formed. As a result, as shown in FIG. 34, an overlapping region WR is formed between the spot groups SG _i and SG _{i + 1} . Therefore, not only when there is no positional deviation or magnification error (FIG. 5A), it is also assumed that the mutual positional relationship between the light emitting element group 295 and the microlens LS is slightly shifted, or the magnification error of the microlens LS occurs. Further, it is possible to prevent a gap from being generated between the spot groups SG, and it is possible to form a good screen-processed latent image LI. Further, by performing image formation using such a line head 29, it is possible to form a good gradation image without generating vertical stripes.

J. et al. Others 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. For example, in the above embodiment, two light emitting element rows 2951R configured by arranging four, five or eight light emitting elements 2951 at predetermined intervals in the longitudinal direction LGD are arranged in the width direction LTD. However, the configuration and arrangement mode of the light emitting element row 2951R (in other words, the arrangement mode of the plurality of light emitting elements) is not limited to this. In short, as the arrangement mode of the plurality of light emitting elements 2951, they may be arranged so that the positions in the longitudinal direction LGD are different from each other.

  In the above embodiment, the organic EL is used as the light emitting element 2951. However, the specific configuration of the light emitting element 2951 is not limited thereto, and for example, an LED (Light Emitting Diode) may be used as the light emitting element 2951. .

  In the above embodiment, the surface of the photosensitive drum 21 is the “image plane” of the present invention, but the application target of the present invention is not limited to this. For example, as shown in FIG. 35, the present invention can be applied to an apparatus using a photosensitive belt.

  FIG. 35 is a schematic view showing an image forming apparatus equipped with a line head according to the present invention. The point that this embodiment differs greatly from the embodiment of FIG. 3 is the mode of the photoconductor. That is, in this embodiment, a photosensitive belt 21B is used instead of the photosensitive drum 21. In addition, since the other structure is the same as that of the said embodiment, about the same structure, the same or equivalent code | symbol is attached | subjected and description of a structure is abbreviate | omitted.

  In this embodiment, the photosensitive belt 21B is stretched between two rollers 28 extending in the main scanning direction MD. The photosensitive belt 21B is rotationally moved in a predetermined rotational direction D21 by a drive motor (not shown). A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductor belt 21B along the rotation direction D21. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units.

  In this embodiment, the line head 29 is arranged corresponding to the position where the photosensitive belt 21B becomes flat. Therefore, the light beam for exposure from the line head 29 is vertically irradiated onto the surface of the photosensitive belt 21B to form a spot. Therefore, the spot is always irradiated on the surface of the flat photosensitive member, and the spot formation can be further improved. This is because when the photoconductor drum 21 is used as the surface to be scanned, the surface of the photoconductor has a curvature surface, so that the deformation of the spot SP is inevitable. On the other hand, in the apparatus using the photoreceptor belt 21B, the surface of the photoreceptor is flat, the deformation of the spot SP can be prevented, and better spot formation is possible.

  In the above-described embodiment, the present invention is applied to a color image forming apparatus. However, the application target of the present invention is not limited to this, and it is also applicable to a monochrome image forming apparatus that forms a so-called monochromatic image. The present invention can be applied.

Explanatory drawing of the term used by this specification. Explanatory drawing of the term used by this specification. 1 is a diagram illustrating a first embodiment 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. 1 is a perspective view showing an outline of a first embodiment of a line head according to the invention. Sectional drawing of the width direction of 1st Embodiment of the line head concerning this invention. The perspective view which shows the outline of a microlens array. The main scanning sectional view of a micro lens array. The figure which shows arrangement | positioning and a structure of a several light emitting element group. FIG. 4 is a diagram showing the positions of spots formed on the surface of a photoreceptor by a line head. FIG. 4 is a diagram showing a two-dimensional latent image formed on the surface of the photoreceptor by a line head. The figure which shows the comparative example of a line head. The figure which shows the mode of the spot formed by the comparative example of FIG. The figure which shows the mode of the spot formed by the comparative example of FIG. The figure which shows 2nd Embodiment of the line head concerning this invention. The figure which shows another embodiment of the line head concerning this invention. The figure which shows 3rd Embodiment of the line head concerning this invention. The figure which shows the position of the spot formed with the line head of FIG. The figure which shows 4th Embodiment of the line head concerning this invention. The perspective view which shows the outline of 5th Embodiment of the line head concerning this invention. Sectional drawing of the width direction of 5th Embodiment of the line head concerning this invention. The schematic partial perspective view of a micro lens array. The fragmentary sectional view of the micro lens array in the longitudinal direction. The top view of a micro lens array. The figure which shows the arrangement | positioning relationship between a microlens and a light emitting element group. FIG. 4 is a diagram showing the positions of spots formed on the surface of a photoreceptor by a line head. The figure which shows the arrangement | positioning relationship of the lens and light emitting element group in the vicinity of a combination position. FIG. 3 is a diagram showing the positions of spots formed on the surface of a photoreceptor. The figure which shows the function of an overlap spot area | region. FIG. 6 is a diagram showing another embodiment of the image forming apparatus according to the present invention. FIG. 10 is a diagram illustrating a sixth embodiment of an image forming apparatus according to the invention. FIG. 10 is a diagram showing an image forming apparatus according to a seventh embodiment of the invention. The figure which shows the screen pattern formed with the conventional image forming apparatus. The figure which shows the screen pattern formed in 8th Embodiment of this invention. 1 is a schematic diagram showing an image forming apparatus equipped with a line head according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Photosensitive drum (latent image carrier), 29 ... Line head, 293 ... Head substrate, 2933, 2934 ... Element substrate, 295 ... Light emitting element group, 2951 ... Light emitting element, 295R ... Light emitting element group row, 299 ... Micro Lens array, 2991 ... glass substrate, 2992 ... plastic lens substrate, 2993 ... lens, 2995 ... gap (combination position), D21 ... transport direction, IP ... image plane, LGD ... longitudinal direction (first direction), LS ... micro Lens, LSR ... Lens row, LTD ... Width direction (second direction), MD ... Main scanning direction, SD ... Sub scanning direction (conveyance direction), SG ... Spot group, SP ... Spot

Claims (20)

A plurality of light emitting elements provided in groups for each light emitting element group;
A lens array for each of the light emitting element groups, and a lens that forms a spot group by imaging a light beam emitted from the light emitting element group facing the light emitting element group on an image plane;
The plurality of light emitting element groups are provided in an arrangement of M × N (M and N are integers of 2 or more) in different first and second directions,
The line head, wherein spot groups adjacent to each other in a direction corresponding to the first direction are formed on the image plane so as to partially overlap in a direction corresponding to the second direction. In each spot group, a plurality of spots are formed side by side in a direction corresponding to the first direction by controlling the light emission timing of the light emitting element,
The line head according to claim 1, wherein the spot groups adjacent in a direction corresponding to the first direction partially overlap each other to form an overlapping spot region.   The line head according to claim 2, wherein an element diameter of a light emitting element forming the overlapping spot region among the plurality of light emitting elements is smaller than an element diameter of the remaining light emitting elements.   The line head according to claim 2, wherein a light emission amount of a light emitting element forming the overlapping spot region among the plurality of light emitting elements is smaller than a light emission amount of the remaining light emitting elements.   Among the three spot groups adjacent in the direction corresponding to the first direction, in the central spot group, a part of the central spot group overlaps with the upstream spot group and the rest overlaps with the downstream spot group. The line head according to any one of claims 2 to 4, wherein the entire center spot group is an overlapping spot region.   The spot group is formed on the image plane such that a spot group partially overlaps in a direction corresponding to the second direction for a part of a combination of the spot groups adjacent to each other in a direction corresponding to the first direction. The line head according to 1. In the lens array, a plurality of lens substrates having the lens are combined,
The spot groups adjacent to each other in a direction corresponding to the first direction are formed on the image plane such that spot groups adjacent to each other in a direction corresponding to the first direction are overlapped in a direction corresponding to the second direction by a pair of lenses sandwiching the combination position of the lens substrates. Item 7. The line head according to Item 6. A plurality of element substrates having the light emitting element group are combined,
Spot groups adjacent to each other in a direction corresponding to the first direction are formed on the image plane by a pair of light emitting element groups that are paired across the combination position of the element substrates so as to overlap in a direction corresponding to the second direction. The line head according to claim 6. In the lens array, lens rows in which M lenses are arranged in the first direction are provided in N columns (N is an integer of 3 or more) in the second direction,
Spots adjacent to each other in a direction corresponding to the first direction by a lens pair of a lens constituting the first lens row in the second direction and a lens constituting the Nth lens row in the second direction. The line head according to claim 6, wherein groups are formed on the image plane so as to overlap in a direction corresponding to the second direction. When the region where the spot group partially overlaps in the direction corresponding to the second direction is an overlapping region,
The line head according to any one of claims 6 to 9, wherein an element diameter of a light emitting element forming the overlapping region among the plurality of light emitting elements is smaller than an element diameter of the remaining light emitting elements. When the region where the spot group partially overlaps in the direction corresponding to the second direction is an overlapping region,
The line head according to any one of claims 6 to 9, wherein a light emission amount of a light emitting element forming the overlapping region among the plurality of light emitting elements is smaller than a light emission amount of the remaining light emitting elements. When the region where the spot group partially overlaps in the direction corresponding to the second direction is an overlapping region,
Among the three spot groups adjacent in the direction corresponding to the first direction, in the central spot group, a part of the central spot group overlaps with the upstream spot group and the rest overlaps with the downstream spot group. The line head according to any one of claims 6 to 9, wherein the entire center spot group is an overlapping region.   The line head according to claim 1, wherein all the combinations of spot groups adjacent to each other in a direction corresponding to the first direction are formed on the image plane so as to partially overlap in a direction corresponding to the second direction.   The line head according to any one of claims 1 to 13, wherein the plurality of lenses are provided with the lenses having different magnifications of the lenses. In each of the plurality of light emitting element groups, a plurality of light emitting element arrays in which the light emitting elements are arranged in the first direction are arranged in the second direction so that the light emitting elements constituting the light emitting element group are staggered. Arranged,
2. The plurality of light emitting elements constituting the light emitting element array emit light at a timing corresponding to the movement of the image plane in a direction corresponding to the second direction in each of the plurality of light emitting element arrays. The line head according to any one of 14.   16. The lens array according to any one of claims 1 to 15, wherein the plurality of lenses are arranged in a staggered manner by arranging N lens rows in which M lenses are arranged in the first direction in the second direction. The line head according to one item.   The line head according to any one of claims 1 to 16, wherein the pitches of spots formed on the image plane in a direction corresponding to the first direction are the same. A latent image carrier whose surface is conveyed in a predetermined conveyance direction;
A line head for forming a latent image on the surface of the latent image carrier,
The line head is
A plurality of light emitting elements provided in groups for each light emitting element group;
A lens array for each light emitting element group, and a lens that forms a spot group by imaging a light beam emitted from the light emitting element group facing the light emitting element group on the latent image carrier,
The plurality of light emitting element groups are provided in an arrangement of M × N (M and N are integers of 2 or more) in different first and second directions,
The image forming apparatus, wherein the latent image carrier is formed such that spot groups adjacent to each other in a direction corresponding to the first direction partially overlap in a direction corresponding to the second direction. In each spot group, a plurality of spots are formed side by side in a direction corresponding to the first direction by controlling the light emission timing of the light emitting element,
The image forming apparatus according to claim 18, wherein the spot groups adjacent in a direction corresponding to the first direction partially overlap each other to form an overlapping spot region.   In the latent image carrier, a spot group partially overlaps in a direction corresponding to the second direction for a part of the combination of the spot groups adjacent to each other in a direction corresponding to the first direction. The image forming apparatus according to claim 18, wherein the image forming apparatus is formed.

Images