JP2009000827A - Line head and image forming apparatus using line head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique to suppress occurrence of a gap between exposure areas even when a chip is positionally deviated. <P>SOLUTION: A line head includes a substrate provided with a plurality of chips to emit a light beam from a light emitting element, and an optical system to form an image onto an image surface with the light beam emitted from the light emitting element. Each of the plurality of chips irradiates the image surface with the light beam via the optical system so as to expose the exposure area corresponding to the chip out of the image surface. Then, the adjacent exposure areas corresponding to the chips different from each other are partially overlapped to form the overlapped exposure area. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a line head for exposing a light beam to an image surface and an image forming apparatus using the line head.

  2. Description of the Related Art Conventionally, a line head that forms an image of a light beam emitted from a light emitting element toward an image plane and exposes the image plane is known. Patent Document 1 proposes a line head using LEDs (Light Emitting Diodes) as light emitting elements. That is, the line head of Patent Document 1 has a plurality of LED array chips on which LEDs are formed, and exposes an image plane with a light beam emitted from the LEDs of each LED array chip. That is, each of the plurality of LED array chips exposes a region corresponding to the LED array chip in the image plane.

Japanese Patent Laid-Open No. 2-4546

  By the way, the above-described line head has a plurality of LED array chips (chips) provided on a substrate using a bonding technique such as die bonding. Here, if the position of the chip is shifted on the substrate, the position of the exposure area exposed by the chip is also shifted. As a result, a gap may occur between two adjacent exposure areas. That is, when two adjacent exposure areas are exposed by different chips, there is a possibility that a gap is generated between the two exposure areas due to the positional deviation of the chips. In particular, in an image forming apparatus that forms a latent image on the surface of a latent image carrier using a line head having such a problem, the latent image may not be formed satisfactorily.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for suppressing generation of a gap between exposure regions even when a positional deviation of a chip occurs.

  In order to achieve the above object, a line head according to the present invention images a chip on which a plurality of light emitting elements that emit light beams are formed, a substrate on which a plurality of chips are provided, and a light beam emitted from the light emitting elements. An optical system that forms an image toward the surface, and each of the plurality of chips can irradiate the image surface with a light beam through the optical system to expose an exposure area corresponding to the chip on the image surface. There is a feature in that overlapping exposure regions corresponding to different chips and adjacent exposure regions partially overlap to form overlapping exposure regions.

  In addition, an image forming apparatus according to the present invention includes a latent image carrier that forms a latent image on the exposed portion when the surface is exposed, a chip on which a plurality of light emitting elements that emit light beams are formed, and a chip A plurality of substrates, and an optical system that forms an image of the light beam emitted from the light emitting element toward the surface of the latent image carrier, each of the plurality of chips carrying a latent image via the optical system. The exposure surface corresponding to the chip can be exposed on the surface of the latent image carrier by irradiating the body surface with a light beam, and the adjacent exposure areas corresponding to different chips and overlapping partially overlap each other. An exposure region is formed.

  The invention thus configured (line head and image forming apparatus) includes a substrate provided with a plurality of chips for emitting light beams from the light emitting elements, and an image plane (latent image carrier) for the light beams emitted from the light emitting elements. And an optical system that forms an image toward the surface. Each of the plurality of chips can irradiate an image surface with a light beam through an optical system to expose an exposure area corresponding to the chip on the surface of the latent image carrier. Here, in the line head configured as described above, adjacent exposure areas corresponding to different chips are partially overlapped to form an overlapping exposure area. Therefore, even if the position of the chip is slightly shifted, it is possible to suppress the generation of a gap between adjacent exposure regions, and good exposure can be performed. In addition, in an image forming apparatus using such a line head, it is possible to form a good latent image on the surface of the latent image carrier.

  The optical system forms an image of the light beam emitted from the light emitting element toward the image plane moving in the first direction, and each of the plurality of chips emits light from the light emitting element at a timing according to the movement of the image plane. In a line head in which a beam is emitted and exposure areas adjacent in the first direction can be exposed to each other by the same chip, it is preferable to configure as follows. In other words, the line head is configured so that the exposure areas corresponding to different chips and adjacent in the second direction orthogonal to the first direction partially overlap in the second direction to form an overlapping exposure area. Is preferred.

  In the line head configured as described above, each of the plurality of chips performs an exposure operation by emitting a light beam from the light emitting element at a timing according to the movement of the image plane. By the way, in such a line head, since the exposure areas adjacent in the first direction can be exposed by the same chip, there is almost no displacement between the exposure areas adjacent in the first direction. However, in the second direction orthogonal to the first direction, adjacent exposure regions may be exposed by different chips. Therefore, in the line head to which the present invention is not applied, there is a possibility that a gap is generated between the exposure areas adjacent in the second direction. In such a situation where a gap in the second direction has occurred, if the exposure operation is performed while moving the image plane in the first direction, the gap may continue in the first direction, causing a so-called vertical stripe. There is.

  On the other hand, the above-described line head is configured so as to correspond to mutually different chips and adjacent exposure areas in the second direction orthogonal to the first direction partially overlap to form an overlapping exposure area. ing. Therefore, the generation of gaps between adjacent exposure areas in the second direction is suppressed, and as a result, the generation of vertical stripes can be suppressed.

  In addition, it is particularly preferable to apply the above-described invention to a line head configured such that exposure areas adjacent in the second direction correspond to different chips. That is, when the exposure area adjacent in the second direction is an adjacent exposure area pair, in the line head configured in this way, the exposure area constituting the adjacent exposure area pair in any adjacent exposure area pair is Corresponds to different chips. That is, the gap described above occurs in any pair of adjacent exposure areas, and as a result, the above-described vertical streak may occur in each exposure area. In particular, in an image forming apparatus using such a line head, a vertical line pattern in which vertical lines are arranged in a constant cycle in the second direction is unintentionally generated in the latent image formed on the surface of the latent image carrier. There is a case. Therefore, in such a line head, as in the above-described invention, the exposure areas corresponding to different chips and adjacent in the second direction orthogonal to the first direction partially overlap to form an overlapping exposure area. It is particularly preferable to configure so as to.

  Further, the line head may be configured such that each of the plurality of chips can expose a plurality of exposure regions arranged in the second direction. That is, a plurality of exposure areas may be exposed with one chip. This is because by configuring the line head in this way, the number of chips to be used can be reduced, and the number of steps for bonding the chips to the substrate can be reduced. As a result, the cost and time required for assembling the line head can be reduced.

  In addition, it is particularly preferable to apply the above-described invention to a line head in which the absolute value of the magnification of the optical system is greater than 1. In other words, in the case of a line head having an absolute value of the magnification of the optical system larger than 1, even if the positional deviation of the chip on the substrate is slight, the positional deviation is enlarged and the exposure area is shifted on the image plane. Become. Therefore, in the line head provided with such an optical system, the above-described gap problem is likely to occur. Therefore, in such a line head, as in the above-described invention, the exposure areas corresponding to different chips and adjacent in the second direction orthogonal to the first direction partially overlap to form an overlapped exposure area. It is particularly preferable to configure this.

  By the way, in the above-described line head having an overlapped exposure region, light beams are emitted from all the light emitting elements formed on the chip, in other words, all the light emitting elements do not contribute to the exposure operation, and the gaps described above are not. It may be possible to suppress the occurrence. Therefore, the overlapping exposure area is selected from a plurality of light emitting elements that can be exposed, and when exposing the overlapping exposure area, an exposure operation to the overlapping exposure area is performed by emitting a light beam only from the selected light emitting elements. The line head may be configured to execute

  Hereinafter, embodiments of the present invention will be described. Before a specific embodiment, a line head to which the present invention is applicable and a basic configuration of an image forming apparatus using the line head will be described. Then, following the description of the basic configuration, an embodiment of the present invention will be described.

Basic Configuration FIG. 1 is a diagram showing a configuration of an image forming apparatus to which the present invention is applicable. FIG. 2 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. 1 is a diagram corresponding to the execution of the color mode. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC and also outputs an image forming command. Corresponding video data VD is supplied to the head controller HC. The head controller HC controls the line head 29 for each color based on the video data VD from the main controller MC, the vertical synchronization signal Vsync from the engine controller EC, and parameter values. As a result, the engine unit EG executes a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  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 feed unit 11 are also disposed in the housing body 3. In FIG. 1, 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. 1, since the image forming stations of the image forming unit 7 have the same configuration, only a part of the image forming stations is given a sign for convenience of illustration, and the sign is omitted for the other image forming stations. .

  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. 1), 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 of the respective colors, and the line heads 29 are controlled based on video data VD from the main controller MC and signals 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 of 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 signals for controlling the element driving for the line heads 29 of the respective colors and outputs the signals to the line heads 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, which will be described in detail later. 1 is primarily transferred to the transfer belt 81.

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

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 1, and stretched around these rollers in a 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 on the downstream side of the monochrome primary transfer roller 85K and on the upstream side of the driving roller 82. Further, the downstream guide roller 86 is formed between the primary transfer roller 85K and the photosensitive drum 21 at the primary transfer position TR1 formed by the monochrome primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station STK. It is configured to contact the transfer belt 81 on a common inscribed line.

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

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

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

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

  FIG. 3 is a perspective view showing an outline of the line head. FIG. 4 is a cross-sectional view of the line head in the width direction. The surface of the photosensitive drum 21 facing the line head 29 is conveyed in the sub scanning direction SD orthogonal to the main scanning direction MD. The line head 29 has a surface on the surface of the photosensitive drum 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. Are arranged opposite to each other. That is, 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 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 head substrate 293 in the order close to the microlens array 299. A plurality of chips CP are provided on the surface of the head substrate 293 (the surface on the microlens array side of the two surfaces of the head substrate 293). Each chip CP is bonded to the surface of the head substrate 293 so that the chip major axis CLG is parallel to the longitudinal direction LGD of the line head 29 and the chip minor axis CLT is parallel to the width direction LTD of the line head 29. ing. That is, for example, as disclosed in Japanese Patent Application Laid-Open No. 2002-314191, the chip CP (laser array of the same publication) is bonded to the head substrate 293 (package substrate of the same publication).

The chip CP is a light emitting element 2951 LED (Light
A so-called LED array having a plurality of (Emitting Diodes), for example, a configuration in which a plurality of LEDs are formed on a small piece of silicon substrate, such as an LED array described in Japanese Patent Application Laid-Open No. 2002-2222988 and 2003-347581 have. The chip CP has a configuration as shown in the broken line in FIG. That is, each chip CP has a plurality (three in FIG. 3) of light emitting element groups 295 arranged at a predetermined pitch in the longitudinal direction LGD (chip major axis LGD) of the line head 29. Each of the plurality of light emitting element groups 295 includes a plurality (eight in FIG. 3) of light emitting elements 2951. More specifically, each light emitting element group 295 includes an issue element row 2951R formed by linearly arranging a plurality (four in FIG. 3) of light emitting elements 2951 in the longitudinal direction LGD (chip major axis CLG). Two are arranged side by side in 29 width directions LTD (chip end axis CTD). At this time, in each light emitting element group 295, the positions of the eight light emitting elements 2951 in the longitudinal direction LGD (chip major axis CLG) are different from each other. As a result, these eight light emitting elements 2951 are arranged in a staggered manner.

  The plurality of chips CP are two-dimensionally arranged on the head substrate 293 so as to be separated from each other in the longitudinal direction LGD and the width direction LTD, so that the plurality of light emitting element groups 295 are formed on the surface of the head substrate 293 in the longitudinal direction LGD. And they are two-dimensionally arranged apart from each other in the width direction LTD. At this time, the positions of the plurality of light emitting element groups 295 in the longitudinal direction LGD are different from each other. When a light emitting element 2951 of the light emitting element group 295 is driven by a drive circuit (not shown) formed on the head substrate 293, a light beam is emitted from the light emitting element 2951 toward the photosensitive drum 21. Then, this light beam is directed to the light shielding member 297.

  The light shielding member 297 is disposed to face the surface of the head substrate 293 and is separated from the surface of the head substrate 293. Such a separation interval is set according to the thickness of the chip CP. In other words, the contact between the light shielding member 297 and the chip CP is prevented by providing the separation interval. A plurality of light guide holes 2971 are formed in the light shielding member 297 on a one-to-one basis with respect to the plurality of light emitting element groups 295. Further, the light guide hole 2971 is formed as a substantially cylindrical hole penetrating the light shielding member 297 with a line parallel to the normal line of the head substrate 293 as a central axis. 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. 4, the back cover 2913 is pressed against the case 291 via the head substrate 293 by the fixing device 2914. That is, the fixing device 2914 has an elastic force that presses the back cover 2913 toward the case 291, and presses the back cover with the elastic force, thereby making the inside of the case 291 light-tight (that is, from the inside of the case 291. It is sealed so that light does not leak and so that light does not enter from the outside of the case 291. Note that a plurality of fixing devices 2914 are provided in the longitudinal direction of the case 291.

  FIG. 5 is a perspective view schematically showing the microlens array. FIG. 6 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 arranged at predetermined intervals in the longitudinal direction LGD and the width direction LTD corresponding to the arrangement of the light emitting element groups 295. More specifically, in the microlens array 299, a microlens ML is configured by a lens pair including lenses 2993A and 2993B and a glass substrate 2991 sandwiched between the lens pairs. Then, a plurality of lens rows MLR in which a plurality of these microlenses ML are arranged in the longitudinal direction LGD are arranged in a plurality of rows (“3” in FIG. 5) in the width direction LTD, and the plurality of microlenses ML are located in different longitudinal positions. Is arranged. All the microlenses ML have the same configuration and the same magnification m. As will be described later, in the present embodiment, the microlens ML having a negative value of the magnification m is used, but it goes without saying that the magnification m may be set to a positive value.

  FIG. 7 is a diagram illustrating an imaging state of the microlens array. In the figure, the light shielding member 297 is omitted. Further, in the same figure, in order to facilitate understanding of the imaging characteristics of the microlens array 299, the geometric center of gravity E0 of the light emitting element group 295 and the positions E1, E2 separated from the geometric center of gravity E0 by a predetermined distance in the longitudinal direction LGD. It represents the locus of the light beam emitted from E2. As indicated by the locus, the light beam emitted from each position reaches the surface of the photosensitive drum 21 (photosensitive member surface) via the microlens array 299. That is, the light beam emitted from the chip CP provided on the surface of the head substrate 293 is imaged on the surface of the photoreceptor by the microlens ML of the microlens array 299.

  As shown in FIG. 7, the light beam emitted from the geometric gravity center position E0 of the light emitting element group 295 forms an image at the intersection point I0 between the photosensitive member surface and the optical axis OA of the lenses 2993A and 2993B. This is because the geometric gravity center position E0 of the light emitting element group 295 is on the optical axis OA of the lenses 2993A and 2993B. The light beams emitted from the positions E1 and E2 are imaged at positions I1 and I2 on the surface of the photosensitive drum 21, respectively. That is, the light beam emitted from the position E1 is imaged at the position I1 on the opposite side across the optical axis OA of the lenses 2993A and 2993B in the main scanning direction MD, and the light beam emitted from the position E2 is In the main scanning direction MD, an image is formed at a position I2 on the opposite side across the optical axis OA of the lenses 2993A and 2993B. Thus, the microlens ML has a reversal characteristic (in other words, the magnification m of the microlens ML has a negative value). As shown in the figure, the distance between the positions I1 and I0 where the light beam is imaged is longer than the distance between the positions E1 and E0. That is, the absolute value of the magnification of the microlens ML is larger than 1.

  8 and 9 are explanatory diagrams of terms used in this specification. Here, the terms used in this specification will be organized using these drawings. In the present specification, as described above, the transport direction of the surface (image surface IP) of the photosensitive drum 21 is defined as the sub-scanning direction SD, and the direction orthogonal to the sub-scanning direction SD is defined as the main scanning direction MD. Yes. 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. 8 and FIG. 9) light emitting elements 2951 arranged on the head substrate 293 in a one-to-one correspondence with the plurality of microlenses ML 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 microlenses ML. Further, the light beam from the light emitting element group 295 is imaged toward the image plane IP by the microlens ML 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 a spot group SG. That is, the plurality of spot groups SG can be formed in one-to-one correspondence with the plurality of light emitting element groups 295. In each light emitting element group 295, the most upstream light emitting element 2951 in the longitudinal direction LGD and the width direction LTD is particularly defined as a first light emitting element. In the spot group SG to be written, the spot SP corresponding to the first light emitting element 2951 is particularly defined as the first spot.

  8 and 9 show the case where the spot SP is formed in a state where the image plane IP is stationary so that the correspondence relationship among the light emitting element group 295, the microlens ML, 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. 9, 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 arranged at the same pitch. The spot group pitch Psg is a distance in the main scanning direction MD between the geometric centroids of two spot groups SG arranged at the same pitch.

  Lens rows MLR and lens columns MLC are defined as shown in the “lens array” column of FIG. That is, a plurality of microlenses ML arranged in the longitudinal direction LGD are defined as a lens row MLR. The plurality of lens rows MLR are arranged side by side in the width direction LTD at a predetermined lens row pitch Plsr. A plurality (three in the figure) of microlenses ML 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 array MLC. The lens row pitch Plsr is a distance in the width direction LTD between the geometric centroids of two lens rows MLR arranged at the same pitch. The lens pitch Pls is a distance in the longitudinal direction LGD between the geometric centroids of the two microlenses ML arranged at the same pitch.

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

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

  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 main scanning direction MD are defined as spot rows SPR. The plurality of spot rows SPR are arranged side by side in the sub-scanning direction SD at a predetermined spot row pitch Pspr. Further, a plurality of (two in the figure) spots arranged at the spot pitch Pspr in the sub-scanning direction SD and at the spot pitch Psp in the main scanning direction MD are defined as spot rows SPC. The spot row pitch Pspr is the distance in the sub-scanning direction SD between the geometric centroids of two spot rows SPR arranged at the same pitch. The spot pitch Psp is the distance in the main scanning direction MD between the geometric centroids of two spots SP arranged at the same pitch.

  FIG. 10 is a diagram showing the arrangement of chips on the substrate. As shown in the figure. A plurality of chips CP_A, CP_B, CP_C,... Are arranged on the surface of the head substrate 293. Each chip CP is arranged such that the major axis is parallel to the longitudinal direction LGD and the minor axis is parallel to the width direction LTD. Here, in the present specification, when it is not specified which of the plurality of chips is simply referred to as a chip CP. In each chip CP, three light emitting element groups 295 are formed. For example, the chip CP_A includes light emitting element groups 295_A1 to 295_A3, the chip CP_B includes light emitting element groups 295_B1 to 295_B3, and the chip CP_C includes light emitting element groups 295_C1 to 295_C3. Has been.

  At this time, as shown in the figure, 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 295R. Here, in the present specification, when it is not specified which light-emitting element group of the plurality of light-emitting element groups is simply referred to as a light-emitting element group 295. These light emitting element group rows 295R are arranged in a plurality of rows (“3” rows in FIG. 10) in the width direction LTD. The three light emitting element group rows 295R are arranged with a predetermined pitch shift in the longitudinal direction LGD. As a result, the plurality of light emitting element groups 295 are two-dimensionally arranged, and the positions of the plurality of light emitting element groups 295 in the longitudinal direction are different from each other. A plurality of microlenses ML are arranged in a one-to-one correspondence with the plurality of light emitting element groups 295 arranged as shown in FIG.

  As shown also in FIG. 3, each light emitting element group 295 has eight light emitting elements 2951, 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 at predetermined intervals (= twice the element pitch Pel) in the longitudinal direction LGD to form a light emitting element row 2951R. The light emitting element rows 2951R are arranged in two rows 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 Pel. For this reason, in each light emitting element group 295, all the light emitting elements 2951 are arranged at element pitches Pel at different longitudinal positions. Accordingly, when each light emitting element group 295 emits light beams from all eight light emitting elements 2951, the light beams emitted from the eight light emitting elements 2951 are different from each other in the main scanning direction MD by the microlens ML. An image is formed toward the surface of the photoreceptor. That is, the light emitting element group 295 causes all eight light emitting elements 2951 to emit light, thereby forming a spot group in which eight spots are arranged in the main scanning direction MD. In this way, the area where the spot group is formed on the surface of the photoreceptor is exposed.

  11 and 12 show the positions of spots formed on the surface of the photosensitive member by the line head. Spots are formed by four light emitting element groups, for example, the light emitting element groups 295_A1, 295_B1, 295_C1, and 295_A2 in FIG. The state of being done is shown schematically. 11 and 12, a spot group SG_A1 represents a group of spots SP formed by the light emitting element group 295_A1, a spot group SG_B1 represents a group of spots SP formed by the light emitting element group 295_B1, and a spot group SG_C1 Indicates a group of spots SP formed by the light emitting element group 295_C1, and the spot group SG_A2 indicates a group of spots SP formed by the light emitting element group 295_A2. That is, the spot group SG_A1 and the spot group SG_A2 are formed by the chip CP_A, the spot group SG_B1 is formed by the chip CP_B, and the spot group SG_C1 is formed by the chip CP_C. As shown in FIG. 11, when the light emitting elements 2951 are turned on at the same time, spot groups SG_A1, SG_B1, SG_C1, and SG_A2 formed on the surface of the photoreceptor are also two-dimensionally arranged.

  Therefore, as shown in FIG. 12, in each of the light emitting element rows 2951R, at the timing according to the rotational movement of the photosensitive drum 21, that is, at the timing according to the movement of the photosensitive member surface in the sub-scanning direction SD. The light emitting elements 2951 constituting the light emitting element row 2951R are configured to emit light. Specifically, the lighting timings of the light emitting element rows 2951R constituting the light emitting element groups 295_A1, 295_B1, 295_C1, and 295_A2 are made different according to the rotational movement of the photosensitive drum 21 as follows.

That means
(a) Timing T01: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_C1,
(b) Timing T02: lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_C1,
(c) Timing T03: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_B1,
(d) Timing T04: lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_B1,
(e) Timing T05: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_A1 and the light emitting element group 295_A2,
(f) Timing T6: The lighting of the light emitting element row 2951R is controlled based on the lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_A1 and the light emitting element group 295_A2. 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.

  Thus, each of the plurality of chips CP provided on the head substrate 293 can form a spot on the exposure area corresponding to the chip to expose the exposure area. That is, each chip CP has a light emitting element group 295. Accordingly, each chip CP can expose an exposure region exposed by the light emitting element group 295 included in the chip CP. In addition, each chip CP has a plurality of (three in FIG. 10) light emitting element groups 295, and the plurality of light emitting element groups 295 can expose different exposure regions. That is, in the line head 29 shown in FIG. 10, each chip CP can expose three different exposure areas.

  The description will be continued with reference to FIGS. 11 and 12. The chip CP_A can expose the exposure areas EX_A1 and EX_A2 by forming spot groups SG_A1 and SG_A2 with respect to the exposure areas EX_A1 and EX_A2 corresponding to the chip CP_A. Similarly, the chip CP_B can expose the exposure area EX_B1 by forming a spot group SG_B1 with respect to the exposure area EX_B1 corresponding to the chip CP_B. Furthermore, the chip CP_C can expose the exposure area EX_C1 by forming a spot group SG_C1 with respect to the exposure area EX_C1 corresponding to the chip CP_C.

  Further, as is apparent from FIGS. 11 and 12, the exposure regions are connected in the main scanning direction MD without overlapping each other. Accordingly, all the spots SP formed on the photosensitive member surface are at different positions in the main scanning direction MD, and all the spots SP are formed at a spot pitch (Psp = m · Pel) in the main scanning direction MD. Therefore, when a position shift occurs in the chip CP, the position of the exposure area corresponding to the chip CP is also shifted, and a gap may be generated between the adjacent exposure areas. If the exposure operation is executed in such a state where a gap is generated in the exposure region in this way, so-called vertical stripes may be caused.

  FIG. 13 is a diagram for explaining a problem caused by the positional deviation of the chip. When there is no positional deviation in the chip CP, there is no positional deviation in the exposure area. That is, adjacent exposure areas are connected without gaps in the main scanning direction MD, and the plurality of exposure areas EX_A1, EX_B1, and EX_C1 are continuously connected in the main scanning direction MD. As a result, adjacent spot groups are continuously connected to form a favorable spot (see FIG. 13A). However, in FIG. 5A, the adjacent exposure areas corresponding to different chips CP do not overlap each other. That is, the exposure areas EX_A1 and EX_B1 that correspond to different chips and are adjacent to each other do not overlap each other. Further, the exposure areas EX_B1 and EX_C1 that correspond to different chips and are adjacent to each other do not overlap each other. Therefore, for example, when the chip CP_B is displaced from the chip CP_A in the direction away from the longitudinal direction LGD, a gap is generated between the exposure area EX_A1 and the exposure area EX_B1 in the main scanning direction MD. When a gap is generated in the exposure area as described above and a spot group is formed in the exposure area and an exposure operation is performed, vertical stripes are generated.

  That is, in the line head 29, each of the plurality of chips CP emits a light beam from the light emitting element 2951 at a timing according to the movement of the surface of the photoreceptor, and exposes an exposure region corresponding to the chip CP. By the way, in such a line head 29, since the exposure areas adjacent in the sub-scanning direction SD can be exposed by the same chip CP, the positional deviation hardly occurs between the exposure areas adjacent in the sub-scanning direction SD. However, in the main scanning direction MD that is orthogonal to the sub-scanning direction SD, adjacent exposure regions may be exposed by different chips CP. Therefore, there is a possibility that a gap is generated between the adjacent exposure areas in the main scanning direction MD. Then, in such a situation in which a gap in the exposure area in the main scanning direction MD is generated, an exposure operation is performed on the exposure area while moving the surface of the photoconductor in the sub scanning direction SD (that is, the spot group SG is changed). Once formed), the gap in the exposure area continues in the sub-scanning direction SD on the surface of the photoreceptor. Then, since the gaps continuous in the sub-scanning direction SD are not exposed, vertical stripes are generated in the latent image formed on the surface of the photoreceptor (see FIG. 13B). Therefore, in order to deal with the problem of the vertical stripe, the line head 29 of the first embodiment has the following configuration.

First Embodiment FIG. 14 is a diagram showing the arrangement of chips on a substrate in the first embodiment. As shown in the figure. A plurality of chips CP_A, CP_B, CP_C,... Are arranged on the surface of the head substrate 293. Each chip CP is arranged such that the major axis is parallel to the longitudinal direction LGD and the minor axis is parallel to the width direction LTD. Each chip CP includes a plurality (three in the first embodiment) of light emitting element groups 295 arranged at a predetermined pitch in the longitudinal direction LGD (chip major axis LGD) of the line head 29. That is, for example, the chip CP_A includes the light emitting element groups 295_A1 to 295_A3, the chip CP_B includes the light emitting element groups 295_B1 to 295_B3, and the chip CP_C includes the light emitting element groups 295_C1 to 295_C3. Is formed.

  At this time, as shown in the figure, 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 295R. These light emitting element group rows 295R are arranged in a plurality of rows (“3” rows in the first embodiment) in the width direction LTD. The three light emitting element group rows 295R are arranged with a predetermined pitch shift in the longitudinal direction LGD. As a result, the plurality of light emitting element groups 295 are two-dimensionally arranged, and the positions of the plurality of light emitting element groups 295 in the longitudinal direction are different from each other. A plurality of microlenses ML are arranged in a one-to-one correspondence with the plurality of light emitting element groups 295 arranged as shown in FIG.

  In the first embodiment, 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 Pel) in the longitudinal direction LGD to form a light emitting element row 2951R. The light emitting element rows 2951R are arranged in two rows 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 Pel. For this reason, in each light emitting element group 295, all the light emitting elements 2951 are arranged at element pitches Pel at different longitudinal positions. Accordingly, when each light emitting element group 295 emits light beams from all ten light emitting elements 2951, the light beams emitted from the ten light emitting elements 2951 are exposed to different positions in the main scanning direction MD by the microlens ML. An image is formed on the body surface. That is, the light emitting element group 295 causes all ten light emitting elements 2951 to emit light, thereby forming a spot group in which ten spots are arranged in the main scanning direction MD. Then, an area where the spot group is formed on the surface of the photoreceptor is exposed.

  15 and 16 are views showing the positions of spots formed on the surface of the photosensitive member by the line head. Spots are formed by four light emitting element groups, for example, the light emitting element groups 295_A1, 295_B1, 295_C1, and 295_A2 in FIG. The state of being done is shown schematically. In the figure, a spot group SG_A1 indicates a group of spots SP formed by the light emitting element group 295_A1, a spot group SG_B1 indicates a group of spots SP formed by the light emitting element group 295_B1, and the spot group SG_C1 indicates a light emitting element. A group of spots SP formed by the group 295_C1 is shown, and a spot group SG_A2 shows a group of spots SP formed by the light emitting element group 295_A2. That is, the spot group SG_A1 and the spot group SG_A2 are formed by the chip CP_A, the spot group SG_B1 is formed by the chip CP_B, and the spot group SG_C1 is formed by the chip CP_C. As shown in FIG. 15, when the light emitting elements 2951 are turned on simultaneously, the spot groups SG_A1, SG_B1, SG_C1, and SG_A2 formed on the surface of the photosensitive member are also two-dimensionally arranged.

  Therefore, in the first embodiment, as shown in FIG. 16, in each of the light emitting element rows 2951R, the photosensitive drum 21 is moved in the sub-scanning direction SD at a timing corresponding to the rotational movement of the photosensitive drum 21. The light emitting element 2951 constituting the light emitting element row 2951R emits light at a corresponding timing. Specifically, the lighting timings of the light emitting element rows 2951R constituting the light emitting element groups 295_A1, 295_B1, 295_C1, and 295_A2 are made different according to the rotational movement of the photosensitive drum 21 as follows.

That means
(a) Timing T11: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_C1,
(b) Timing T12: lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_C1,
(c) Timing T13: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_B1,
(d) Timing T14: lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_B1,
(e) Timing T15: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_A1 and the light emitting element group 295_A2,
(f) Timing T16: The lighting of the light emitting element row 2951R is controlled based on the lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_A1 and the light emitting element group 295_A2. By adjusting the timing in this way, the spots SP can be formed in a line in the main scanning direction MD.

  As shown in FIGS. 15 and 16, in the first embodiment, the exposure areas corresponding to the different chips CP and adjacent in the main scanning direction MD are partially overlapped in the main scanning direction MD. Region EX_OR is formed. Specifically, the exposure area EX_A1 corresponds to the chip CP_A, the exposure area EX_B1 corresponds to the chip CP_B, and the exposure area EX_A1 and the exposure area EX_B1 correspond to different chips CP. Further, the exposure area EX_A1 and the exposure area EX_B1 are adjacent in the main scanning direction MD. In the first embodiment, the exposure area EX_A1 and the exposure area EX_B1 having such a relationship partially overlap in the main scanning direction MD to form an overlapping exposure area EX_OR. In the first embodiment, the width of the overlapped exposure region EX_OR in the main scanning direction MD is equal to or greater than the spot pitch (Psp = m · Pel) in the main scanning direction MD (in FIG. 15 and FIG. 16, twice the spot pitch (2 Psp = 2 · m · Pel)).

  Further, in FIG. 15 and FIG. 16, the following overlapping exposure region EX_OR is formed. That is, the exposure area EX_B1 and the exposure area EX_C1 that correspond to different chips CP and that are adjacent in the main scanning direction MD partially overlap in the main scanning direction MD to form an overlapping exposure area EX_OR. Further, the exposure area EX_C1 and the exposure area EX_A2 corresponding to different chips CP and adjacent in the main scanning direction MD partially overlap in the main scanning direction MD to form an overlapping exposure area EX_OR.

  As described above, in the line head 29 in the first embodiment, the exposure areas corresponding to the different chips CP and adjacent in the main scanning direction MD partially overlap in the main scanning direction MD to form an overlapping exposure area EX_OR. ing. Therefore, even if the position of the chip CP is slightly deviated, the generation of a gap between adjacent exposure regions is suppressed.

  Furthermore, in the first embodiment, the spot forming operation is performed using such a line head 29 to form the overlapping spot region OR. That is, the line head 29 in the first embodiment has the overlapping exposure region EX_OR. In addition, with respect to the overlapping exposure region EX_OR, different spots CP can overlap to form a spot SP. Therefore, in the first embodiment, the overlapping spot region OR is formed in the overlapping exposure region EX_OR by forming spots overlapping with the different chips CP with respect to the overlapping exposure region EX_OR.

  FIG. 17 is a diagram illustrating a two-dimensional latent image obtained when an overlapping spot region is formed with respect to an overlapping exposure region. That is, when the overlapping spot region OR is formed with respect to the overlapping exposure region EX_OR, a two-dimensional latent image LI as shown in FIG. 17 can be obtained. In the first embodiment, since the width of the overlapping exposure area EX_OR in the main scanning direction MD is twice the spot pitch, two spots SP are formed side by side in the main scanning direction MD in each of the overlapping spot areas OR. (See spot SP_OR in FIG. 16). Therefore, it is possible to prevent a gap from being generated between the spot groups SG even if the position deviation of the chip CP occurs as well as the case where the position deviation of the chip CP does not occur (FIG. 1A). 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.

  As described above, in the above embodiment, the head substrate 293 corresponds to the “substrate” of the present invention, the microlens array 299 corresponds to the “optical system” of the present invention, and the surface of the photoreceptor is the “image plane” of the present invention. It corresponds to. The sub-scanning direction SD corresponds to the “first direction” of the present invention, and the main scanning direction MD corresponds to the “second direction” of the present invention. The photosensitive drum 21 corresponds to the “latent image carrier” of the invention.

  By the way, in the first embodiment, all the spots that can be formed on the overlapping exposure region EX_OR are actually formed on the overlapping exposure region EX_OR, thereby forming the overlapping spot region OR. However, it is not essential to form the overlapping spot region OR with respect to the overlapping exposure region EX_OR in this way, and the line head 29 may be configured as described in the next second embodiment.

Second Embodiment FIG. 18 is an explanatory diagram of spots that can be formed inside the overlapped exposure region EX_OR. Prior to the description of the specific contents of the second embodiment, the spots that can be formed inside the overlapped exposure area EX_OR will be described. That is, spots that can be formed inside the overlapping exposure region EX_OR are defined as shown in FIG. That is, in the main scanning direction MD, when the center CTP of the spot SP is within the overlap exposure area EX_OR, the spot is inside the overlap exposure area EX_OR. On the other hand, when the center CTP of the spot SP is outside the overlapped exposure area EX_OR, the spot SP is outside the overlapped exposure area EX_OR. More specifically, the spots SPc, SPd, and SPe are inside the overlapping exposure area EX_OR, and the spots SPa, SPb, SPf, and SPg are outside the overlapping exposure area EX_OR.

  19, 20, 21, and 22 are explanatory diagrams of the exposure operation in the second embodiment. The second embodiment is different from the first embodiment in that the exposure areas corresponding to the different chips CP and adjacent to each other in the main scanning direction MD partially overlap in the main scanning direction MD to form the overlapping exposure area EX_OR. Although it is the same, it differs from 1st Embodiment by the point of the spot formation operation | movement with respect to this overlap exposure area | region EX_OR. That is, as will be described below, the line head 29 in the second embodiment selects a spot SP that is actually formed from a plurality of spots SP that can be formed inside the overlapping exposure region EX_OR, and performs an exposure operation. Execute.

  FIG. 19 corresponds to the case where there is no displacement of the chip CP. In this case, the width in the main scanning direction MD of the overlapping exposure region EX_OR1 between the exposure region corresponding to the chip CP_A and the exposure region corresponding to the chip CP_B is twice the spot pitch Psp (2 · Psp). There are four spots that can be formed in the exposure area EX_OR1, that is, the spot SP9 and the spot SP10 of the spot group SG_A1 and the spot SP1 and the spot SP2 of the spot group SG_B1. In FIG. 19, among these four spots that can be formed in the exposure area EX_OR1, only the spot SP9 and spot SP10 of the spot group SG_A1 are actually formed in the exposure area EX_OR1, and the spot SP1 and spot of the spot group SG_B1. SP2 is not formed. Here, the solid line circles in the figure indicate the spots SP that can be formed. Of these solid line circles, a solid line circle whose inside is filled with diagonal lines indicates a spot that is actually formed, and a solid line circle whose interior is blank indicates a spot that is not actually formed. Hereinafter, the meaning of the solid circle is the same in FIGS. In this way, in FIG. 19, the spot SP that is actually formed is selected from the plurality of spots SP that can be formed for the overlapping exposure region EX_OR1, and the exposure operation is executed.

  For the overlapped exposure areas EX_OR2 and EX_OR3, the spot SP that is actually formed is selected from a plurality of spots SP that can be formed for these overlapped exposure areas, and the exposure operation is executed. Specifically, among the plurality of spots that can be formed in the exposure area EX_OR2, only the spot SP9 and spot SP10 of the spot group SG_B1 are actually formed in the exposure area EX_OR1, and the spot SP1 and spot SP2 of the spot group SG_C1 are formed. do not do. Of the plurality of spots that can be formed in the exposure area EX_OR3, only the spot SP9 and spot SP10 of the spot group SG_C1 are actually formed in the exposure area EX_OR3, and the spot SP1 and spot SP2 of the spot group SG_A2 are not formed.

  FIG. 20 corresponds to the case where the chip position is shifted by 0.4 times the spot pitch Psp. That is, the chip CP_B is displaced in the longitudinal direction LGD with respect to the chip CP_A and the chip CP_C. As a result, the exposure area corresponding to the chip CP_B is 0.4 times the spot pitch Psp in the main scanning direction MD (0.4・ Psp) is shifted. In this case, the width in the main scanning direction MD of the overlapping exposure region EX_OR1 between the exposure region corresponding to the chip CP_A and the exposure region corresponding to the chip CP_B is 2.4 times (2.4 · Psp) the spot pitch Psp. . There are four spots that can be formed in the exposure area EX_OR1, that is, the spot SP9 and the spot SP10 of the spot group SG_A1 and the spot SP1 and the spot SP2 of the spot group SG_B1. In FIG. 20, of these four spots that can be formed in the exposure area EX_OR1, only the spot SP9 and spot SP10 of the spot group SG_A1 are actually formed in the exposure area EX_OR1, and the spot SP1 and spot of the spot group SG_B1. SP2 is not formed.

  In FIG. 20, the width in the main scanning direction MD of the overlapping exposure region EX_OR2 between the exposure region corresponding to the chip CP_B and the exposure region corresponding to the chip CP_C is 1.6 times the spot pitch Psp (1.6 · Psp). ) There are four spots that can be formed in the exposure area EX_OR2, that is, a spot SP9 and a spot SP10 of the spot group SG_B1, and a spot SP1 and a spot SP2 of the spot group SG_C1. In FIG. 20, among these four spots that can be formed in the exposure area EX_OR2, only the spot SP9 and spot SP10 of the spot group SG_B1 are actually formed in the exposure area EX_OR2, and the spot SP1 and spot of the spot group SG_C1. SP2 is not formed.

  Furthermore, in FIG. 20, the width in the main scanning direction MD of the overlapping exposure region EX_OR3 of the exposure region corresponding to the chip CP_C and the exposure region corresponding to the chip CP_A is twice the spot pitch Psp (2 · Psp). There are four spots that can be formed in the exposure area EX_OR3, that is, the spot SP9 and the spot SP10 of the spot group SG_C1, and the spot SP1 and the spot SP2 of the spot group SG_A2. In FIG. 20, among these four spots that can be formed in the exposure area EX_OR3, only the spot SP9 and spot SP10 of the spot group SG_C1 are actually formed in the exposure area EX_OR3, and the spot SP1 and spot of the spot group SG_A2 SP2 is not formed.

  FIG. 21 corresponds to the case where the chip position shift occurs by 0.7 times the spot pitch Psp. That is, the chip CP_B is displaced in the longitudinal direction LGD with respect to the chips CP_A and CP_C, and as a result, the exposure area corresponding to the chip CP_B is 0.7 times the spot pitch Psp in the main scanning direction MD (0.7・ Psp) is shifted. In this case, the width in the main scanning direction MD of the overlapping exposure region EX_OR1 between the exposure region corresponding to the chip CP_A and the exposure region corresponding to the chip CP_B is 2.7 times (2.7 · Psp) the spot pitch Psp. . And there are six spots that can be formed for the exposure area EX_OR1, that is, the spot SP8, the spot SP9 and the spot SP10 of the spot group SG_A1, and the spot SP1, the spot SP2 and the spot SP3 of the spot group SG_B1. In FIG. 21, among these six spots that can be formed in the exposure area EX_OR1, only the spot SP8, spot SP9, and spot SP10 of the spot group SG_A1 are actually formed in the exposure area EX_OR1, and the spot of the spot group SG_B1. SP1, spot SP2, and spot SP3 are not formed.

  In FIG. 21, the width in the main scanning direction MD of the overlapping exposure region EX_OR2 of the exposure region corresponding to the chip CP_B and the exposure region corresponding to the chip CP_C is 1.3 times the spot pitch Psp (1.3 · Psp). ) Then, there are two spots that can be formed for the exposure area EX_OR2: a spot SP10 of the spot group SG_B1 and a spot SP1 of the spot group SG_C1. In FIG. 21, of these two spots that can be formed in the exposure area EX_OR2, only the spot SP10 of the spot group SG_B1 is actually formed in the exposure area EX_OR2, and the spot SP1 of the spot group SG_C1 is not formed.

  Furthermore, in FIG. 21, the width in the main scanning direction MD of the overlapping exposure region EX_OR3 of the exposure region corresponding to the chip CP_C and the exposure region corresponding to the chip CP_A is twice the spot pitch Psp (2 · Psp). There are four spots that can be formed in the exposure area EX_OR3, that is, the spot SP9 and the spot SP10 of the spot group SG_C1, and the spot SP1 and the spot SP2 of the spot group SG_A2. In FIG. 21, among these four spots that can be formed in the exposure area EX_OR3, only the spot SP9 and spot SP10 of the spot group SG_C1 are actually formed in the exposure area EX_OR3, and the spot SP1 and spot of the spot group SG_A2 SP2 is not formed.

  FIG. 22 corresponds to the case where the chip position shift occurs by 1.4 times the spot pitch Psp. That is, the chip CP_B is displaced in the longitudinal direction LGD with respect to the chip CP_A and the chip CP_C. As a result, the exposure area corresponding to the chip CP_B is 1.4 times the spot pitch Psp in the main scanning direction MD (1.4.・ Psp) is shifted. In this case, the width in the main scanning direction MD of the overlapping exposure region EX_OR1 between the exposure region corresponding to the chip CP_A and the exposure region corresponding to the chip CP_B is 3.4 times (3.4 · Psp) the spot pitch Psp. . And there are six spots that can be formed for the exposure area EX_OR1, that is, the spot SP8, the spot SP9 and the spot SP10 of the spot group SG_A1, and the spot SP1, the spot SP2 and the spot SP3 of the spot group SG_B1. In FIG. 22, among these six spots that can be formed in the exposure area EX_OR1, only the spot SP8, the spot SP9, and the spot SP10 of the spot group SG_A1 are actually formed in the exposure area EX_OR1, and the spot of the spot group SG_B1. SP1, spot SP2, and spot SP3 are not formed.

  In FIG. 22, the width in the main scanning direction MD of the overlapping exposure region EX_OR2 between the exposure region corresponding to the chip CP_B and the exposure region corresponding to the chip CP_C is 0.6 times the spot pitch Psp (0.6 · Psp). ) Then, there are two spots that can be formed for the exposure area EX_OR2: a spot SP10 of the spot group SG_B1 and a spot SP1 of the spot group SG_C1. In FIG. 22, of these two spots that can be formed in the exposure area EX_OR2, only the spot SP10 of the spot group SG_B1 is actually formed in the exposure area EX_OR2, and the spot SP1 of the spot group SG_C1 is not formed.

  Furthermore, in FIG. 22, the width in the main scanning direction MD of the overlapping exposure region EX_OR3 of the exposure region corresponding to the chip CP_C and the exposure region corresponding to the chip CP_A is twice the spot pitch Psp (2 · Psp). There are four spots that can be formed in the exposure area EX_OR3, that is, the spot SP9 and the spot SP10 of the spot group SG_C1, and the spot SP1 and the spot SP2 of the spot group SG_A2. In FIG. 22, among these four spots that can be formed in the exposure area EX_OR3, only the spot SP9 and spot SP10 of the spot group SG_C1 are actually formed in the exposure area EX_OR3, and the spot SP1 and spot of the spot group SG_A2 SP2 is not formed.

  As described above, also in the second embodiment, similar to the first embodiment, the exposure areas corresponding to the different chips CP and adjacent in the main scanning direction MD partially overlap in the main scanning direction MD. An exposure area EX_OR is formed. Therefore, even if the position of the chip CP is slightly deviated, the generation of a gap between adjacent exposure regions is suppressed. And the line head 29 in 2nd Embodiment can suppress generation | occurrence | production of the vertical stripe resulting from the clearance gap of this exposure area | region.

  In addition, the line head 29 in the second embodiment selects the spot SP that is actually formed from the plurality of spots SP that can be formed inside the overlapping exposure region EX_OR, and executes the exposure operation. In other words, the overlapping exposure area EX_OR is selected from a plurality of light emitting elements 2951 that can be exposed, and when exposing the overlapping exposure area EX_OR, a light beam is emitted only from the selected light emitting elements to overlap the exposure area. Spots are formed on EX_OR (that is, an exposure operation is executed). Thereby, the following effects are produced. That is, the occurrence of a situation where the number of spots contributing to the exposure of the overlapped exposure region EX_OR is made appropriate and the overlapped exposure region EX_OR is excessively exposed is suppressed. By forming an image using such a line head 29, a good image can be formed.

Third Embodiment FIG. 23 is a perspective view showing an outline of a line head in a third embodiment. FIG. 24 is a diagram showing the arrangement of chips on the substrate in the third embodiment. The following description of the third embodiment will be mainly made on the differences from the first and second embodiments described above, and the common parts will be denoted by the same reference numerals and omitted.

  The third embodiment is the same as the first and second embodiments in that a so-called LED array having a plurality of LEDs (Light Emitting Diodes), which are light emitting elements 2951, is used as the chip CP. 1. Different from the second embodiment. That is, the differences between the line head 29 of the third embodiment and the line heads 29 of the first and second embodiments are the configuration of the chip CP and the manner of arrangement of the chip CP on the head substrate 293. More specifically, the chip CP of the third embodiment is formed with a light emitting element array 295C composed of three light emitting element groups 295. At this time, in the light emitting element row 295C, the direction D295C in which the light emitting element row 295C extends (that is, the arrangement direction D295C of the light emitting element group 295 in the light emitting element row 295C) and the chip major axis CLG of the chip CP are parallel. , Formed on the chip CP.

  A plurality of chips CP are arranged on the head substrate 293 in the longitudinal direction LGD. At this time, each chip CP is bonded to the surface of the head substrate 293 so that the chip major axis CLG is parallel to the direction D295C, so that the chip major axis CLG of the chip CP is in relation to the longitudinal direction LGD of the line head 29. The chip minor axis CLT of the chip CP is inclined with respect to the width direction LTD of the line head 29.

  As shown in FIG. On the surface of the head substrate 293, 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 295R. These light emitting element group rows 295R are arranged in a plurality of rows (“3” rows in the first embodiment) in the width direction LTD. The three light emitting element group rows 295R are arranged with a predetermined pitch shift in the longitudinal direction LGD. As a result, the plurality of light emitting element groups 295 are two-dimensionally arranged, and the positions of the plurality of light emitting element groups 295 in the longitudinal direction are different from each other. A plurality of microlenses ML are arranged in a one-to-one correspondence with the plurality of light emitting element groups 295 arranged as shown in FIG.

  And in 3rd Embodiment, the three light emitting element groups 295 which comprise each light emitting element row | line | column 295C are each comprised as follows. In each light emitting element row 295C, the most upstream light emitting element group 295 located at the most upstream in the direction D295C has ten light emitting elements 2951, and the light emitting elements 2951 are arranged as follows. That is, in the most upstream light emitting element group 295, five light emitting elements 2951 are arranged at predetermined intervals (= twice the element pitch Pel) in the longitudinal direction LGD to form a light emitting element row 2951R. The light emitting element rows 2951R are arranged in two rows 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 Pel. For this reason, in the most upstream light emitting element group 295, all the light emitting elements 2951 are arranged at element pitches Pel at different longitudinal positions. Therefore, when the most upstream light emitting element group 295 emits light beams from all ten light emitting elements 2951, 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 ML. An image is formed on the surface of the photoreceptor. That is, when the most upstream light emitting element group 295 causes all ten light emitting elements 2951 to emit light, a spot group in which ten spots are arranged in the main scanning direction MD can be formed. Then, an area where the spot group is formed on the surface of the photoreceptor is exposed.

  On the other hand, in each light emitting element row 295C, the light emitting element group 295 located at a position other than the most upstream in the direction D295C has eight light emitting elements 2951, and the light emitting elements 2951 are arranged as follows. That is, in these light emitting element groups 295, four light emitting elements 2951 are arranged at predetermined intervals (= twice the element pitch Pel) in the longitudinal direction LGD to form a light emitting element row 2951R. The light emitting element rows 2951R are arranged in two rows 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 Pel. For this reason, in the light emitting element group 295, all the light emitting elements 2951 are arranged at element pitches Pel at different longitudinal positions. Therefore, when the light emitting element group 295 emits light beams from all eight light emitting elements 2951, the light beams emitted from the eight light emitting elements 2951 are photoconductors at different positions in the main scanning direction MD by the microlens ML. Imaged on the surface. That is, the light emitting element group 295 causes all eight light emitting elements 2951 to emit light, thereby forming a spot group in which eight spots are arranged in the main scanning direction MD. Then, an area where the spot group is formed on the surface of the photoreceptor is exposed.

  25 and 26 are diagrams showing the positions of spots formed on the surface of the photosensitive member by the line head. Spots are formed by four light emitting element groups, for example, the light emitting element groups 295_A1, 295_A2, 295_A3, and 295_B1 in FIG. The state of being done is shown schematically. In the figure, a spot group SG_A1 indicates a group of spots SP formed by the light emitting element group 295_A1, a spot group SG_A2 indicates a group of spots SP formed by the light emitting element group 295_A2, and the spot group SG_A3 indicates a light emitting element. A group of spots SP formed by the group 295_A3 is shown, and a spot group SG_B1 shows a group of spots SP formed by the light emitting element group 295_B1. That is, the spot groups SG_A1 to SG_A3 are formed by the chip CP_A, and the spot group SG_B1 is formed by the chip CP_B. As shown in FIG. 25, when the light emitting elements 2951 are turned on simultaneously, the spot groups SG_A1, SG_A2, SG_A3, and SG_B1 formed on the surface of the photosensitive member are also two-dimensionally arranged.

  Therefore, in the third embodiment, as shown in FIG. 26, in each of the light emitting element rows 2951R, the photosensitive drum 21 is moved in the sub-scanning direction SD at the timing according to the rotational movement of the photosensitive drum 21. The light emitting element 2951 constituting the light emitting element row 2951R emits light at a corresponding timing. Specifically, the lighting timings of the light emitting element rows 2951R constituting the light emitting element groups 295_A1, 295_A2, 295_A3, and 295_B1 are made different in correspondence with the rotational movement of the photosensitive drum 21 as follows.

That means
(a) Timing T31: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_A3,
(b) Timing T32: lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_A3,
(c) Timing T33: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_A2,
(d) Timing T34: lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_A2,
(e) Timing T35: lighting timing of the upper light emitting element row 2951L of the light emitting element group 295_A1 and the light emitting element group 295_B1,
(f) Timing T36: The lighting of the light emitting element row 2951R is controlled based on the lighting timing of the lower light emitting element row 2951L of the light emitting element group 295_A1 and the light emitting element group 295_B1. By adjusting the timing in this way, the spots SP can be formed in a line in the main scanning direction MD.

  As shown in FIGS. 25 and 26, in the third embodiment, the exposure areas corresponding to different chips CP and adjacent in the main scanning direction MD are partially overlapped in the main scanning direction MD. Region EX_OR is formed. Specifically, the exposure area EX_A3 corresponds to the chip CP_A, the exposure area EX_B1 corresponds to the chip CP_B, and the exposure area EX_A3 and the exposure area EX_B1 correspond to different chips CP. Further, the exposure area EX_A3 and the exposure area EX_B1 are adjacent in the main scanning direction MD. In the third embodiment, the exposure area EX_A3 and the exposure area EX_B1 having such a relationship partially overlap in the main scanning direction MD to form an overlapping exposure area EX_OR. In the third embodiment, the width of the overlapped exposure region EX_OR in the main scanning direction MD is equal to or larger than the spot pitch (Psp = m · Pel) in the main scanning direction MD (in FIG. 25 and FIG. 26, twice the spot pitch (2 Psp = 2 · m · Pel)).

  As described above, in the line head 29 according to the third embodiment, the exposure areas corresponding to the different chips CP and adjacent in the main scanning direction MD partially overlap in the main scanning direction MD to form an overlapping exposure area EX_OR. ing. Therefore, even if the position of the chip CP is slightly deviated, the generation of a gap between adjacent exposure regions is suppressed.

  Further, in the third embodiment, the spot forming operation is performed using such a line head 29 to form the overlapping spot region OR. That is, the line head 29 in the third embodiment has an overlapping exposure area EX_OR. In addition, with respect to the overlapping exposure region EX_OR, different spots CP can overlap to form a spot SP. Therefore, in the third embodiment, the overlapping spot area OR is formed in the overlapping exposure area EX_OR by forming spots overlapping with the different chips CP with respect to the overlapping exposure area EX_OR.

  FIG. 27 is a diagram showing a two-dimensional latent image obtained when an overlapping spot region is formed with respect to an overlapping exposure region. That is, when the overlapping spot region OR is formed with respect to the overlapping exposure region EX_OR, a two-dimensional latent image LI as shown in FIG. 27 can be obtained. In the third embodiment, since the width of the overlapping exposure region EX_OR in the main scanning direction MD is twice the spot pitch, two spots SP are formed side by side in the main scanning direction MD in each of the overlapping spot regions OR. (See the spot SP_OR in FIG. 26). Therefore, it is possible to prevent a gap from being generated between the spot groups SG even if the position deviation of the chip CP occurs as well as the case where the position deviation of the chip CP does not occur (FIG. 1A). 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.

  By the way, in the said 3rd Embodiment, all the spots which can be formed with respect to the overlap exposure area | region EX_OR are actually formed with respect to the overlap exposure area | region EX_OR, and the overlap spot area | region OR is formed. However, it is not essential to form the overlapping spot region OR with respect to the overlapping exposure region EX_OR in this way, and the line head 29 may be configured as described in the next fourth embodiment.

Fourth Embodiment FIG. 28, FIG. 29, FIG. 30 and FIG. 31 are explanatory views of an exposure operation in the fourth embodiment. The fourth embodiment is different from the third embodiment in that the exposure areas corresponding to the different chips CP and adjacent in the main scanning direction MD partially overlap in the main scanning direction MD to form the overlapping exposure area EX_OR. Although the same, it is different from the third embodiment in the spot forming operation for the overlapped exposure region EX_OR. That is, as will be described below, the line head 29 in the fourth embodiment selects a spot SP that is actually formed from a plurality of spots SP that can be formed inside the overlapping exposure region EX_OR, and performs an exposure operation. Execute.

  FIG. 28 corresponds to the case where there is no displacement of the chip CP. In this case, the width in the main scanning direction MD of the overlapping exposure region EX_OR1 between the exposure region corresponding to the chip CP_A and the exposure region corresponding to the chip CP_B is twice the spot pitch Psp (2 · Psp). There are four spots that can be formed in the exposure area EX_OR1, that is, a spot SP7 and a spot SP8 of the spot group SG_A3 and a spot SP1 and a spot SP2 of the spot group SG_B1. In FIG. 28, among these four spots that can be formed in the exposure area EX_OR1, only the spot SP7 and spot 8 of the spot group SG_A3 are actually formed in the exposure area EX_OR1, and the spot SP1 and spot of the spot group SG_B1. SP2 is not formed. Here, the solid line circles in the figure indicate the spots SP that can be formed. Of these solid line circles, a solid line circle whose inside is filled with diagonal lines indicates a spot that is actually formed, and a solid line circle whose interior is blank indicates a spot that is not actually formed. Hereinafter, the meaning of the solid circle is the same in FIGS. 29 to 31. In this way, in FIG. 28, the spot SP that is actually formed is selected from the plurality of spots SP that can be formed for the overlapping exposure region EX_OR1, and the exposure operation is executed.

  FIG. 29 corresponds to the case where the chip position shift occurs by 0.4 times the spot pitch Psp. That is, the chip CP_B is displaced in the longitudinal direction LGD with respect to the chip CP_A. As a result, the exposure area corresponding to the chip CP_B is 0.4 times (0.4 · Psp) the spot pitch Psp in the main scanning direction MD. It is only shifted. In this case, the width in the main scanning direction MD of the overlapping exposure region EX_OR1 between the exposure region corresponding to the chip CP_A and the exposure region corresponding to the chip CP_B is 1.6 times (1.6 · Psp) the spot pitch Psp. . There are four spots that can be formed in the exposure area EX_OR1, that is, a spot SP7 and a spot SP8 of the spot group SG_A3 and a spot SP1 and a spot SP2 of the spot group SG_B1. In FIG. 29, of these four spots that can be formed in the exposure area EX_OR1, only the spot SP7 and spot 8 of the spot group SG_A3 are actually formed in the exposure area EX_OR2, and the spot SP1 and spot of the spot group SG_B1 are formed. SP2 is not formed.

  FIG. 30 corresponds to the case where the chip position shift occurs by 0.7 times the spot pitch Psp. That is, the chip CP_B is displaced in the longitudinal direction LGD with respect to the chip CP_A, and as a result, the exposure area corresponding to the chip CP_B is 0.7 times (0.7 · Psp) the spot pitch Psp in the main scanning direction MD. It is only shifted. In this case, the width in the main scanning direction MD of the overlapping exposure region EX_OR1 between the exposure region corresponding to the chip CP_A and the exposure region corresponding to the chip CP_B is 1.3 times (1.3 · Psp) the spot pitch Psp. . And there are two spots that can be formed for the exposure area EX_OR1, a spot SP8 of the spot group SG_A3 and a spot SP1 of the spot group SG_B1. In FIG. 30, of these two spots that can be formed in the exposure area EX_OR1, only the spot SP8 of the spot group SG_A3 is actually formed in the exposure area EX_OR1, and the spot SP1 of the spot group SG_B1 is not formed.

  FIG. 31 corresponds to the case where the chip position shift occurs by 1.4 times the spot pitch Psp. That is, the chip CP_B is displaced in the longitudinal direction LGD with respect to the chip CP_A. As a result, the exposure area corresponding to the chip CP_B is 1.4 times the spot pitch Psp (1.4 · Psp) in the main scanning direction MD. It is only shifted. In this case, the width in the main scanning direction MD of the overlapping exposure region EX_OR1 between the exposure region corresponding to the chip CP_A and the exposure region corresponding to the chip CP_B is 0.6 times (0.6 · Psp) the spot pitch Psp. . And there are two spots that can be formed for the exposure area EX_OR1, a spot SP8 of the spot group SG_A3 and a spot SP1 of the spot group SG_B1. In FIG. 31, of these two spots that can be formed in the exposure area EX_OR1, only the spot SP8 of the spot group SG_A3 is actually formed in the exposure area EX_OR1, and the spot SP1 of the spot group SG_B1 is not formed.

  As described above, also in the fourth embodiment, similar to the third embodiment, the exposure areas corresponding to the different chips CP and adjacent in the main scanning direction MD partially overlap in the main scanning direction MD. An exposure area EX_OR is formed. Therefore, even if the position of the chip CP is slightly deviated, the generation of a gap between adjacent exposure regions is suppressed. And the line head 29 in 4th Embodiment can suppress generation | occurrence | production of the vertical stripe resulting from the clearance gap of this exposure area | region.

  Further, the line head 29 in the fourth embodiment selects the spot SP that is actually formed from the plurality of spots SP that can be formed inside the overlapping exposure region EX_OR, and executes the exposure operation. In other words, the overlapping exposure area EX_OR is selected from a plurality of light emitting elements 2951 that can be exposed, and when exposing the overlapping exposure area EX_OR, a light beam is emitted only from the selected light emitting elements to overlap the exposure area. Spots are formed on EX_OR (that is, an exposure operation is executed). Thereby, the following effects are produced. That is, the occurrence of a situation where the number of spots contributing to the exposure of the overlapped exposure region EX_OR is made appropriate and the overlapped exposure region EX_OR is excessively exposed is suppressed. By forming an image using such a line head 29, a good image can be formed.

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, the chip CP in the above embodiment is a so-called LED array having a plurality of LEDs (Light Emitting Diodes) as the light emitting elements 2951, but the chip CP is not limited to this. That is, a chip CP having a surface emitting laser called a VCSEL (Vertical Cavity Surface Emitting Laser) may be used as a light emitting element. As a chip having such a surface emitting laser, for example, a two-dimensional surface emitting laser array described in JP-A-2001-358411 is known.

  In the first embodiment, adjacent exposure regions in the main scanning direction MD correspond to different chips. However, it is not essential for the present invention that the exposure areas adjacent in the main scanning direction MD correspond to different chips CP. That is, for example, in FIG. 28 shown in the third embodiment, the exposure area EX_A1 and the exposure area EX_A2 are adjacent to each other in the main scanning direction MD, but both correspond to the chip CP_A. However, it is particularly preferable to apply the present invention to the line head 29 of the first embodiment corresponding to chips in which the exposure areas adjacent in the main scanning direction MD are different from each other.

  That is, in the line head 29 of the first embodiment, when the exposure areas adjacent to each other in the main scanning direction MD are set as the adjacent exposure area pairs, the exposure areas constituting the adjacent exposure area pairs in any adjacent exposure area pair. Corresponds to different chips CP. That is, the gap described above occurs in any pair of adjacent exposure areas, and as a result, the above-described vertical streak may occur in each exposure area. In particular, in the image forming apparatus 1 using such a line head 29, a vertical line pattern in which vertical lines are arranged at regular intervals in the main scanning direction MD is unintentionally generated in the latent image formed on the surface of the photoreceptor. May end up. Therefore, in the line head 29 described in the first embodiment, as described above, the exposure areas corresponding to the different chips CP and adjacent in the main scanning direction MD partially overlap to form the overlapping exposure area EX_OR. It is particularly preferable to configure so as to.

  In addition, the chip CP of the above embodiment can expose three exposure regions arranged in the main scanning direction MD. That is, for example, in the first embodiment, the chip CP can be exposed to three exposure areas (exposure areas EX_A1, EX_A2,... Corresponding to the chip CP_A) that are spaced apart from each other in the main scanning direction MD. In the second embodiment, the chip CP can be exposed to three exposure areas (exposure areas EX_A1, EX_A2, and EX_A3 corresponding to the chip CP_A) arranged in the main scanning direction MD. However, the number of exposure regions corresponding to one chip CP is not limited to three, and may be two or four. However, the line head 29 capable of exposing a plurality of exposure areas with one chip CP is preferable in the following points. That is, by configuring the line head 29 in this way, the number of chips CP to be used can be reduced and the number of steps for bonding the chips CP to the substrate can be reduced. As a result, the cost and time required for assembling the line head 29 can be reduced.

  In the above embodiment, the absolute value of the magnification of the microlens ML included in the microlens array 299 (optical system) is larger than 1. However, the magnification of the micro lens ML is not limited to this. For example, the absolute value of the magnification may be 1 or less. However, it is particularly preferable to apply the present invention to a line head in which the absolute value of the magnification of the microlens ML is larger than 1. That is, in the line head 29 in which the absolute value of the magnification of the microlens ML is larger than 1, even if the positional deviation of the chip CP on the head 293 substrate is slight, the positional deviation is enlarged and the surface of the photoconductor is enlarged. Of the exposure area. Therefore, in the line head 29 provided with such a microlens array 299, the above-described gap problem is likely to occur. Therefore, in the line head 29, as described above, the exposure areas corresponding to the different chips CP and adjacent in the main scanning direction MD are partially overlapped to form the overlapping exposure area EX_OR. It is particularly preferred to do this.

  Further, in the above embodiment, two light emitting element rows 2951R configured by arranging four or five 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. The point is that the plurality of light emitting elements 2951 may be arranged so that the positions in the longitudinal direction LGD are different from each other.

  In the above 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.

1 is a diagram illustrating a configuration of an image forming apparatus to which the present invention can be applied. FIG. 2 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 1. The perspective view which shows the outline of a line head. Sectional drawing of the width direction of a line head. The perspective view which shows the outline of a micro lens array. Sectional drawing of the longitudinal direction of a micro lens array. The figure which shows the image formation state of a micro lens array. Explanatory drawing of the term used by this specification. Explanatory drawing of the term used by this specification. The figure which shows arrangement | positioning of the chip | tip on a board | substrate. 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 the positions of spots formed on the surface of a photoreceptor by a line head. The figure explaining the malfunction resulting from position shift of a chip. The figure which shows arrangement | positioning of the chip | tip on the board | substrate in 1st Embodiment. 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 the positions of spots formed on the surface of a photoreceptor by a line head. The figure which shows the latent image obtained by forming an overlap spot area | region in an overlap exposure area | region. Explanatory drawing of the spot which can be formed in the inside of an overlap exposure area | region. Explanatory drawing of the exposure operation | movement in 2nd Embodiment. Explanatory drawing of the exposure operation | movement in 2nd Embodiment. Explanatory drawing of the exposure operation | movement in 2nd Embodiment. Explanatory drawing of the exposure operation | movement in 2nd Embodiment. The perspective view which shows the outline of the line head in 3rd Embodiment. The figure which shows arrangement | positioning of the chip | tip on the board | substrate in 3rd Embodiment. 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 the positions of spots formed on the surface of a photoreceptor by a line head. The figure which shows the latent image obtained by forming an overlap spot area | region in an overlap exposure area | region. Explanatory drawing of the exposure operation | movement in 4th Embodiment. Explanatory drawing of the exposure operation | movement in 4th Embodiment. Explanatory drawing of the exposure operation | movement in 4th Embodiment. Explanatory drawing of the exposure operation | movement in 4th Embodiment.

Explanation of symbols

  21Y, 21K ... photosensitive drum (latent image carrier), 29 ... line head, 295 ... light emitting element group, 2951 ... light emitting element, 295C ... light emitting element group column, 2951R ... light emitting element row, 293 ... head substrate (substrate) 299 ... Microlens array (optical system), ML ... Microlens, CP ... Chip, EX_A1, EX_A2, EX_A3, EX_B1, EX_C1 ... Exposure area, EX_OR, EX_OR1, EX_OR2, EX_OR3 ... Overlapping exposure area, MD ... Main scanning direction (Second direction), SD ... sub-scanning direction (first direction, LGD ... longitudinal direction, LTD ... width direction, CLG ... chip long axis, CLT ... chip short axis

Claims (7)

A chip formed with a plurality of light emitting elements for emitting a light beam;
A substrate provided with a plurality of the chips;
An optical system that focuses the light beam emitted from the light emitting element toward an image plane;
Each of the plurality of chips can irradiate the image plane with a light beam through the optical system, and can expose an exposure area corresponding to the chip in the image plane,
The line head according to claim 1, wherein the adjacent exposure areas corresponding to different chips are partially overlapped to form an overlapping exposure area. The optical system forms an image of the light beam emitted from the light emitting element toward the image plane moving in a first direction;
Each of the plurality of chips emits a light beam from the light emitting element at a timing according to the movement of the image plane, and the exposure areas adjacent in the first direction can be exposed by the same chip.
2. The line according to claim 1, wherein the exposure areas corresponding to the different chips and adjacent in a second direction orthogonal to the first direction partially overlap in the second direction to form the overlapping exposure area. head.   The line head according to claim 2, wherein the exposure areas adjacent in the second direction correspond to the chips different from each other.   4. The line head according to claim 2, wherein each of the plurality of chips is capable of exposing a plurality of exposure regions arranged in the second direction.   The line head according to claim 1, wherein the absolute value of the magnification of the optical system is greater than 1. 5.   The overlapping exposure area is selected from a plurality of light emitting elements that can be exposed, and when the overlapping exposure area is exposed, a light beam is emitted only from the selected light emitting elements to perform an exposure operation on the overlapping exposure area. The line head according to claim 1, which is executed. A latent image carrier on which a latent image is formed on the exposed portion when the surface is exposed;
A chip formed with a plurality of light emitting elements for emitting a light beam;
A substrate provided with a plurality of the chips;
An optical system that images the light beam emitted from the light emitting element toward the surface of the latent image carrier,
Each of the plurality of chips can irradiate the surface of the latent image carrier with a light beam through the optical system, and can expose an exposure area corresponding to the chip on the surface of the latent image carrier,
An image forming apparatus, wherein the adjacent exposure areas corresponding to different chips are partially overlapped to form an overlapping exposure area.

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