JP2009006581A - Line head, line head control method, and image forming apparatus using the line head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique that suppresses generation of gaps between adjacent irradiation regions even in the occurrence of positional deviation of chips. <P>SOLUTION: The line head includes a substrate in which chips are provided emitting a light beam from a light emitting element and an optical system which makes the light beam from the light emitting element form an image to a moving image plane. In the substrate, a plurality of chips are arrayed in a first direction corresponding to the moving direction of the image plane. Each of the plurality of chips is provided with an element assembly in which light emitting elements are installed in mutually different positions in a second direction corresponding to a direction orthogonal to the moving direction. The light beams outgoing from the element assembly are emitted to the image plane, in accordance with the movement of the image plane, through the optical system to form irradiation regions. The light emitting elements of the element assembly emit light so that the irradiation regions are linked together which are formed by the mutually different chips and adjacent in the orthogonal direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a line head that irradiates an image surface with a light beam, a control method for the line head, 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 surface and irradiates the image surface with the light beam 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 irradiates an image surface with a light beam emitted from the LEDs of each LED array chip. In this way, each of the plurality of LED array chips irradiates a light beam to a region corresponding to the LED array chip in the image plane.

Japanese Patent Laid-Open No. 2-4546

  By the way, in the above-described line head, since a plurality of LED array chips (chips) are provided on the substrate by using a bonding technique such as die bonding, the position of the chip is shifted from a desired position on the substrate (chip chip). When the position shift occurs), the position of the region (irradiation region) irradiated with the light beam by the chip also shifts the desired position. As a result, a gap may be generated between two adjacent irradiation regions. As described above, in a line head that irradiates an image surface with a light beam using a plurality of chips, there is a possibility that a gap is generated between adjacent irradiation regions when the position of the chip is shifted from a desired position. 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 the generation of a gap between adjacent irradiation regions even when a chip position shift occurs.

  In order to achieve the above object, a line head according to the present invention provides 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 an image that moves the light beams from the light emitting elements. And an optical system that forms an image toward the surface. The substrate has a plurality of chips arranged in a first direction corresponding to the moving direction of the image surface, and each of the plurality of chips corresponds to an orthogonal direction orthogonal to the moving direction. The device has a set of light-emitting elements at different positions in the second direction, and forms an irradiation area by irradiating the image plane with a light beam emitted from the set as the image plane moves. In addition, the light emitting elements of the element set emit light so that irradiation regions formed by different chips and adjacent in the orthogonal direction are connected.

  In order to achieve the above object, the line head control method according to the present invention emits light from a light emitting element of a chip provided on a substrate and irradiates a moving image plane with a light beam emitted from the light emitting element. A plurality of chips arranged in a first direction corresponding to the moving direction of the image plane, and each of the plurality of chips is arranged in a second direction corresponding to an orthogonal direction orthogonal to the moving direction. It has element sets with light emitting elements at different positions, and emits a light beam from the element set according to the movement of the image plane to form an irradiation area on the image plane. In the light irradiation process, it is formed with different chips In addition, the light emission of the light emitting elements of the element set is controlled so that adjacent irradiation regions in the orthogonal direction are connected.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a latent image carrier whose surface moves, a chip on which a plurality of light emitting elements for emitting a light beam are formed, and a plurality of chips. A substrate, an optical system for focusing the light beam from the light emitting element toward the surface of the latent image carrier, and a control means for controlling the light emission of the light emitting element. A plurality of chips are arranged in the corresponding first direction, and each of the plurality of chips has an element set in which light emitting elements are provided at different positions in the second direction corresponding to the orthogonal direction orthogonal to the moving direction. The light beam emitted from the element set according to the movement of the image carrier surface is irradiated onto the surface of the latent image carrier through the optical system to form an irradiation area, and the control means is formed by different chips and orthogonal to each other. Adjacent in direction As the irradiation region is connected, it is characterized by controlling the light emission of the light emitting element of the element set.

  In the invention thus configured (line head, line head control method and image forming apparatus), a light beam is emitted from the light emitting element to the image plane (latent image carrier surface). Such a chip is provided on the substrate. That is, on the substrate, a plurality of chips are arranged in the first direction corresponding to the moving direction of the image plane (latent image carrier surface). Each of the plurality of chips has an element set in which light emitting elements are provided at different positions in the second direction corresponding to the orthogonal direction orthogonal to the moving direction, and is emitted from the element set in accordance with the movement of the image plane. An irradiated area is formed by irradiating the image plane with the light beam.

  In the invention described above, the light emitting elements of the element set emit light so that irradiation regions formed by different chips and adjacent in the orthogonal direction are connected. Therefore, even if the position of the chip is slightly shifted, it is possible to suppress the generation of a gap between adjacent irradiation regions, and a good light beam irradiation 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.

  Here, in each of the plurality of chips, the element set includes more light emitting elements than the number necessary for forming the irradiation region, and some of the light emitting elements included in the element set emit light. The line head is preferably configured so that an irradiation region is formed.

  That is, in the line head having such a configuration, the element region of each chip has in advance more light emitting elements 2951 than the number necessary to form the irradiation region. In actual operation, only the light emitting elements necessary for forming the irradiation region are caused to emit light to form the irradiation region. Therefore, even when the position of the chip is slightly shifted, the irradiation region is formed at an appropriate position, and the above-described problems such as vertical stripes can be effectively suppressed.

  Here, from the viewpoint of effectively suppressing the generation of gaps in the irradiation region due to the chip position shift, a part of the plurality of light emitting elements included in the chip element set emits light according to the chip position shift. The line head may be configured as described above.

  Further, a line head in which an irradiation region is formed by arranging a plurality of spots in an orthogonal direction when a chip emits a light beam from a light emitting element of an element set may be configured as follows. That is, the line head may be configured such that the light emitting element emits light so that the pitch between spots formed in different chips and adjacent in the orthogonal direction is equal to or less than the maximum pitch. In other words, such a line head is formed by different chips and is formed by different chips and adjacent in the orthogonal direction, requiring that the pitch between spots adjacent in the orthogonal direction is not more than the maximum pitch. The irradiation areas to be connected are connected. As a result, in such a line head, it is possible to suppress the generation of a gap between adjacent irradiation regions even if the position of the chip is slightly shifted, and a good light beam irradiation is realized.

  In addition, the line head may be configured such that the light emitting element emits light so that the pitch between spots formed in different chips and adjacent in the orthogonal direction is equal to or greater than the minimum pitch. This is because, by configuring in this way, it is possible to suppress excessive overlap of spots formed adjacent to each other, thereby realizing better light beam irradiation.

  In addition, it is particularly preferable to apply the above invention to a line head in which the absolute value of the magnification of the optical system is greater than 1. That is, in a line head in which the absolute value of the magnification of the optical system is larger than 1, even if the position of the chip on the substrate is slight, the position is enlarged and the irradiation 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, it is particularly preferable to apply the above-described invention to suppress the generation of a gap in the irradiation region.

  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 bonded to the surface of the head substrate 293 (the surface on the microlens array side of the two surfaces of the head substrate 293). That is, for example, as disclosed in Japanese Patent Application Laid-Open No. 2002-314191, a chip CP (a laser array of the same publication) is bonded to a head substrate 293 (a package substrate of the same publication). Further, in the line head 29 shown in FIGS. 3 and 4, in each chip CP, 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. It is bonded to the surface of the head substrate 293 so that

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 CLG) 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 a line-emitting element row 2951R in which a plurality of (four in FIG. 3) light-emitting elements 2951 are arranged in a line in the longitudinal direction LGD (chip major axis CLG). Two are arranged side by side in 29 width directions LTD (chip end axis CLT). 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 each spot group SG, 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 in the longitudinal direction LGD at a predetermined pitch (= twice the element pitch Pel) 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.

  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. Thus, 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 2951R of the light emitting element group 295_C1,
(b) Timing T02: lighting timing of the lower light emitting element row 2951R of the light emitting element group 295_C1,
(c) Timing T03: lighting timing of the upper light emitting element row 2951R of the light emitting element group 295_B1,
(d) Timing T04: lighting timing of the lower light emitting element row 2951R of the light emitting element group 295_B1,
(e) Timing T05: lighting timing of the upper light emitting element row 2951R of the light emitting element group 295_A1 and the light emitting element group 295_A2,
(f) Timing T06: The lighting of the light emitting element row 2951R is controlled based on the lighting timing of the lower light emitting element row 2951R 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.

  As described above, each of the plurality of chips CP provided on the head substrate 293 forms an irradiation region by irradiating the region corresponding to the chip CP with the light beam as the spot SP. That is, the chip CP_A can form the irradiation regions IR_A1 and IR_A2 by forming the spot groups SG_A1 and SGA2 in the region corresponding to the chip CP_A. Similarly, the chip CP_B can form the irradiation region IR_B1 by forming the spot group SG_B1 in the region corresponding to the chip CP_B. Further, the chip CP_C can form the irradiation region IR_C1 by forming the spot group SG_C1 in the region corresponding to the chip CP_C.

  As is clear from FIGS. 11 and 12, all the spots SP irradiated on the surface of the photosensitive member are at different positions in the main scanning direction MD, and all the spots SP in the main scanning direction MD are spot pitches ( Psp = m · Pel). Therefore, when the chip CP is displaced from the desired position (displacement of the chip CP occurs), the position of the irradiation region formed by the chip CP is also shifted, and a gap may be generated between the adjacent irradiation regions. is there. When the latent image forming operation is executed in such a state where a gap is generated in the irradiation area 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 no displacement occurs in the chip CP, there is no displacement in the irradiation area. That is, the adjacent irradiation areas are connected without gaps in the main scanning direction MD, and the plurality of irradiation areas IR_A1, IR_B1, and IR_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, as shown in FIG. 13B, for example, when the chip CP_B is displaced from the chip CP_A in the longitudinal direction LGD, a gap is generated between the irradiation region IR_A1 and the irradiation region IR_B1 in the main scanning direction MD. When the latent image forming operation is executed in such a state where a gap is generated in the irradiation area as described above, vertical stripes are generated.

Embodiment FIG. 14 is a perspective view showing a line head in an embodiment. FIG. 15 is a diagram illustrating an arrangement of chips on a substrate in the embodiment. In the following description of the embodiment, differences from the above-described basic configuration will be mainly described, and common configurations and operations will be denoted by corresponding reference numerals and description thereof will be omitted. As shown in these figures. A plurality of chips CP_A, CP_B, CP_C, CP_D,... Are arranged on the surface of the head substrate 293. Each chip CP is arranged such that the major axis CLG is parallel to the longitudinal direction LGD and the minor axis CLT is parallel to the width direction LTD. Each chip CP is formed with an element set 2951SET including a plurality of light emitting elements 2951. 14 and 15, a plurality (three in this embodiment) of chips CP (for example, chips CP_A, CP_B, CP_C) are aligned in the width direction LTD and shifted from each other in the longitudinal direction LGD. Have been placed. Therefore, the element set 2951SET of chips adjacent to the width direction LTD (for example, chips CP_A and CP_B) partially overlap in the longitudinal direction LGD.

  In the element set 2951SET formed in each chip CP, a plurality of light emitting elements 2951 are arranged at the light emitting element pitch Pel in the longitudinal direction LGD (chip major axis CLG) of the line head 29. Specifically, the element set 2951SET includes two light emitting element lines 2951L in which a predetermined number of light emitting elements 2951 are linearly arranged in the longitudinal direction LGD at a predetermined pitch (= twice the element pitch Pel) in the width direction LTD. Moreover, the shift amount of the light emitting element line 2951L in the longitudinal direction LGD is the element pitch Pel. For this reason, in the element set 2951SET, all the light emitting elements 2951 are arranged in a staggered manner with the element pitch Pel at different chip major axis positions (longitudinal position). Thus, in the element set 2951SET, a plurality of light emitting elements 2951 are laid out in the longitudinal direction LGD with the element pitch Pel.

  A plurality (three in this embodiment) of microlenses ML are provided to face such an element set 2951SET. That is, in the present embodiment, the three microlenses ML are arranged to face the chip CP. These three microlenses ML are arranged at a predetermined pitch (a pitch three times the lens pitch Pls) on the chip major axis CLG of the chip CP facing each other. Specifically, for example, the three microlenses ML_A1, ML_A2, and ML_A3 face the chip CP_A, and these three microlenses ML_A1, ML_A2, and ML_A3 are three times the lens pitch Pls on the chip major axis of the chip CP_A. Line up on the pitch. Each microlens ML forms an image of the light beam emitted from the light emitting element 2951 of the opposing chip CP on the surface of the photoconductor to form a spot group SG on the surface of the photoconductor.

  By the way, although it explains in full detail through description of subsequent spot formation operation | movement, in this embodiment, each spot group SG consists of eight spots. That is, each microlens ML forms an image of the light beams emitted from the eight light emitting elements 2951 to form one spot group SG. On the other hand, the element set 2951SET facing each microlens ML has a configuration in which a plurality of light emitting elements 2951 as described above are spread. Therefore, in the range where the microlenses ML of the element set 2951SET face each other, more than eight light emitting elements 2951, which is the number necessary to form the spot group SG, are arranged in the longitudinal direction LGD (chip major axis). They exist side by side at the element pitch Pel. Therefore, as will be described later, the line head 29 of this embodiment selects eight light emitting elements 2951 suitable for forming an irradiation region from a plurality of light emitting elements 2951 included in the element set 2951SET to emit light.

  FIG. 16 is a diagram illustrating an imaging state of the microlens array. In the figure, the light shielding member 297 is omitted. Further, in the drawing, in order to facilitate understanding of the imaging characteristics of the microlens array 299, the position of the element set 2951SET on the optical axis OA (OA1 to OA3) of the microlens ML (ML1 to ML3). (E1_0, E2_0, E3_0), a position (E1_1, E2_1, E3_1) separated from the position on the optical axis by a predetermined distance in the longitudinal direction LGD, and the opposite side of the longitudinal direction LGD from the position on the optical axis The trajectory of the light beam emitted from the position (E1_2, E2_2, E3_2) separated by a predetermined interval toward the. 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.

  More specifically, a light beam emitted from a position (for example, positions E1_0, E1_1, E1_2) facing the microlens ML1 is imaged by the microlens ML1 as follows. That is, the light beam emitted from the position E1_0 is imaged at the intersection I1_0 between the surface of the photoconductor and the optical axis OA1 of the microlens ML1. The light beams emitted from the positions E1_1 and E1_2 are imaged at positions I1_1 and I1_2 on the surface of the photosensitive drum 21, respectively. That is, the light beam emitted from the position E1_1 is imaged at a position I1_1 on the opposite side across the optical axis OA1 of the microlens ML1 in the main scanning direction MD, and the light beam emitted from the position E1_2 is the main beam. In the scanning direction MD, an image is formed at a position I1_2 on the opposite side across the optical axis OA1 of the microlens ML1. Thus, the microlens ML1 has a reversal characteristic (in other words, the magnification m of the microlens ML1 has a negative value). As shown in the figure, the distance between the positions I1_1 and I1_0 where the light beam is imaged is longer than the distance between the positions E1_1 and E1_0. That is, the absolute value of the magnification of the microlens ML1 is greater than 1.

  Similarly to the image formation by the microlens ML1, the light beam emitted from the position (for example, positions E2_0, E2_1, E2_2) facing the microlens ML2 is positioned on the surface of the photosensitive member (by the microlens ML2. Light beams emitted from positions (for example, positions E3_0, E3_1, E3_2) that are imaged at positions I2_0, I2_1, I2_2) and the microlens ML3 are opposed to each other by the microlens ML3. I3_0, I3_1, I3_2).

  FIG. 17 is a diagram showing the positions of spots formed on the surface of the photoreceptor by the line head. FIG. 17 corresponds to the case where all the chips CP are in a desired position and no chip position deviation occurs. 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. In order to facilitate understanding of the invention, the figure shows the case where the spot SP is formed with the surface of the photoconductor stationary. Therefore, the spots SP in the spot group SG are two-dimensionally arranged. However, as described with reference to FIG. 12, the actual spot forming operation is performed by moving the photosensitive member surface in the sub-scanning direction SD and causing the light emitting element 2951 to emit light according to the movement of the photosensitive member surface. The 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. The contents described with reference to FIG. 17 are the same for FIGS. 18 to 21 described later.

  Of the three stages separated by the two-dot chain line, the spot SP in the upper stage is a spot SP that can be formed by the chip CP_A. Further, in the figure, among the spots SP that can be formed by the chip CP_A, the spot SP that can be formed by the microlens ML_A2 that faces the chip CP_A and the spot SP that can be formed by the microlens ML_A3 that faces the chip CP_A. It shows.

  Of the plurality of stages separated by the two-dot chain line, the spot SP in the middle stage is a spot SP that can be formed by the chip CP_B. Further, in the figure, among the spots SP that can be formed by the chip CP_B, the spot SP that can be formed by the microlens ML_B2 that faces the chip CP_B and the spot SP that can be formed by the microlens ML_B3 that faces the chip CP_B. It shows.

  Further, the spot SP in the lower stage among the plurality of stages separated by the two-dot chain line is a spot SP that can be formed by the chip CP_C. Further, in the figure, among the spots SP that can be formed by the chip CP_C, the spot SP that can be formed by the microlens ML_C1 that faces the chip CP_C and the spot SP that can be formed by the microlens ML_C2 that faces the chip CP_C. It shows.

  As shown in the figure, each chip CP forms only a spot SP (shaded spot in the figure) selected from a plurality of spots SP that can be formed. That is, in the range shown in the figure, the chip CP_A actually forms only 16 spots SP among the plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_A selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 opposed to the micro lens ML_A2 to emit light, thereby allowing a plurality of spots that can be formed by the micro lens ML_A2. Among them, eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A2 is formed) to form the irradiation region IR_A2. Further, the chip CP_A selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_A3 to emit light, so that eight spots SP7 among the plurality of spots that can be formed by the microlens ML_A3. To SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A3 is formed) to form the irradiation region IR_A3.

  In the range shown in the figure, the chip CP_B actually forms only eight spots SP out of a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_B selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_B2 to emit light, thereby allowing a plurality of spots that can be formed by the microlens ML_B2. Among them, eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, the spot group SG_B2 is formed) to form the irradiation region IR_B2. Further, in the range shown in the figure, the chip CP_C actually forms only eight spots SP among a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_C selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the micro lens ML_C2 to emit light, and thereby, among the spots that can be formed by the micro lens ML_C2. Eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, a spot group SG_C2 is formed) to form an irradiation region IR_C2.

  In the drawing, only two spot groups SG_A2 and SG_A3 are shown as the spot group SG formed by the chip CP_A, and only the spot group SG_B2 is shown as the spot group SG formed by the chip CP_B. Only the spot group SG_C2 is shown as the spot group SG formed by the chip CP_C. However, each of the three microlenses ML facing each chip CP can form a spot group SG. Therefore, in practice, three spot groups SG can be formed by one chip CP.

  It should be noted here that the light emission of the element set 2951SET of each of the chip CP_A and the chip CP_B so that the irradiation region IR_A2 formed by the chip CP_A and the irradiation region IR_B2 formed by the chip CP_B are connected in the main scanning direction MD. The element 2951 emits light. That is, the chip CP_A causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_A2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. Accordingly, the irradiation region IR_A2 and the irradiation region IR_B2 adjacent in the main scanning direction MD are connected.

  Similarly, the light emitting element 2951 of the element set 2951SET of each of the chip CP_B and the chip CP_C so that the irradiation area IR_B2 formed by the chip CP_B and the irradiation area IR_C2 formed by the chip CP_C are connected in the main scanning direction MD. Is emitting light. That is, the chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_C causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_C2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. As a result, the irradiation region IR_B2 and the irradiation region IR_C2 adjacent in the main scanning direction MD are connected.

As described above, in the present embodiment, the light emission of the light emitting elements 2951 of the element set 2951SET is controlled so that the irradiation regions adjacent to each other in the main scanning direction MD are formed with different chips CP. In particular, in the present embodiment, in order to connect the irradiation regions satisfactorily, the light emitting element is formed such that the pitch between adjacent spots SP formed by different chips CP is not more than the maximum pitch and not less than the minimum pitch. 2951 emission is controlled. Specifically, a spot pitch between adjacent spots SP formed in the same chip and in the main scanning direction MD is defined as an in-chip spot pitch Psp_in, and formed with different chips CP and in the main scanning direction MD. When the spot pitch between adjacent spots SP is defined as an off-chip spot pitch Psp_out, the following formula 0.5 × Psp_in ≦ Psp_out ≦ 1.5 × Psp_in Formula 1
Light emission of the light emitting element 2951 of the element set 2951SET is controlled so as to satisfy the above. The control of the light emitting element 2951 as described above can be executed by, for example, the head control module 54 (control unit) of the head controller HC.

  In FIG. 17, the spot outside pitch Psp_out between the irradiation area IR_A2 and the irradiation area IR_B2 is the same as the spot inside pitch Psp_in. Further, the spot outside pitch Psp_out between the irradiation region IR_B2 and the irradiation region IR_C2 is also the same as the spot inside pitch Psp_in.

  FIG. 18 is a diagram showing the positions of spots formed on the surface of the photoreceptor by the line head. 18 shows that the position of the chip CP_B is shifted from the desired position in the longitudinal direction LGD, and as a result, the position of the spot that can be formed by the chip CP_B is 0 on the spot pitch Psp_in in the chip on the upstream side in the main scanning direction MD. Corresponds to a case where it is shifted by 4 times (that is, 0.4 · Psp_in). Due to such a positional deviation of the chip, for example, a spot SP7 that can be formed by the microlens ML_A2 and a spot SP15 that can be formed by the microlens ML_B2 that have the same position in the main scanning direction in a state where there is no positional deviation (FIG. 17). In the main scanning direction MD, the positional deviation is caused by 0.4 times the in-chip spot pitch Psp_in. Further, in the state where there is no positional deviation (FIG. 17), the spot SP7 that can be formed by the microlens ML_B2 and the spot SP15 that can be formed by the microlens ML_C2 whose positions in the main scanning direction coincide with each other in the main scanning direction MD. The positional deviation is caused by 0.4 times the inner spot pitch Psp_in. In the following description of FIG. 18, differences from FIG. 17 will be mainly described, and common parts with FIG.

  As shown in the figure, each chip CP forms only a spot SP (shaded spot in the figure) selected from a plurality of spots SP that can be formed. That is, in the range shown in the figure, the chip CP_A actually forms only 16 spots SP among the plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_A selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 opposed to the micro lens ML_A2 to emit light, thereby allowing a plurality of spots that can be formed by the micro lens ML_A2. Among them, eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A2 is formed) to form the irradiation region IR_A2. Further, the chip CP_A selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_A3 to emit light, so that eight spots SP7 among the plurality of spots that can be formed by the microlens ML_A3. To SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A3 is formed) to form the irradiation region IR_A3.

  In the range shown in the figure, the chip CP_B actually forms only eight spots SP out of a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_B selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_B2 to emit light, thereby allowing a plurality of spots that can be formed by the microlens ML_B2. Among them, eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, the spot group SG_B2 is formed) to form the irradiation region IR_B2. Further, in the range shown in the figure, the chip CP_C actually forms only eight spots SP among a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_C selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the micro lens ML_C2 to emit light, and thereby, among the spots that can be formed by the micro lens ML_C2. Eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, a spot group SG_C2 is formed) to form an irradiation region IR_C2.

  It should be noted here that the light emission of the element set 2951SET of each of the chip CP_A and the chip CP_B so that the irradiation region IR_A2 formed by the chip CP_A and the irradiation region IR_B2 formed by the chip CP_B are connected in the main scanning direction MD. The element 2951 emits light. That is, the chip CP_A causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_A2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. Accordingly, the irradiation region IR_A2 and the irradiation region IR_B2 adjacent in the main scanning direction MD are connected.

  Similarly, the light emitting element 2951 of the element set 2951SET of each of the chip CP_B and the chip CP_C so that the irradiation area IR_B2 formed by the chip CP_B and the irradiation area IR_C2 formed by the chip CP_C are connected in the main scanning direction MD. Is emitting light. That is, the chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_C causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_C2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. As a result, the irradiation region IR_B2 and the irradiation region IR_C2 adjacent in the main scanning direction MD are connected.

  In FIG. 18, the outside-spot pitch Psp_out between the irradiation region IR_A2 and the irradiation region IR_B2 is 0.6 times the in-spot pitch Psp_in (that is, Psp_out = 0.6 · Psp_in). Further, the pitch Psp_out outside the spot between the irradiation region IR_B2 and the irradiation region IR_C2 is 1.4 times the pitch Psp_in within the spot (that is, Psp_out = 1.4 · Psp_in). As described above, both the pitch Psp_out outside the spot between the irradiation region IR_A2 and the irradiation region IR_B2 and the pitch Psp_out outside the spot between the irradiation region IR_B2 and the irradiation region IR_C2 satisfy the condition of the above formula 1. The light emission of the light emitting elements of the element set 2951SET is controlled.

  FIG. 19 is a diagram showing the positions of spots formed on the surface of the photoreceptor by the line head. In FIG. 19, the position of the chip CP_B is shifted from the desired position in the longitudinal direction LGD. As a result, the position of the spot that can be formed by the chip CP_B is 0 on the spot pitch Psp_in in the chip on the upstream side in the main scanning direction MD. Corresponds to a case of deviation by 7 times (that is, 0.7 · Psp_in). Due to the positional deviation of the chip, for example, a spot SP7 that can be formed by the microlens ML_A2 and a spot SP15 that can be formed by the microlens ML_B2 that have the same position in the main scanning direction in a state where there is no positional deviation (FIG. 17). In the main scanning direction MD, the positional deviation is caused by 0.7 times the spot pitch Psp_in in the chip. Further, in the state where there is no positional deviation (FIG. 17), the spot SP7 that can be formed by the microlens ML_B2 and the spot SP15 that can be formed by the microlens ML_C2 whose positions in the main scanning direction coincide with each other in the main scanning direction MD. The positional deviation is caused by 0.7 times the inner spot pitch Psp_in. Further, in the following description of FIG. 19, differences from FIG. 17 will be mainly described, and common parts with FIG.

  As shown in the figure, each chip CP forms only a spot SP (shaded spot in the figure) selected from a plurality of spots SP that can be formed. That is, in the range shown in the figure, the chip CP_A actually forms only 16 spots SP among the plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_A selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 opposed to the micro lens ML_A2 to emit light, thereby allowing a plurality of spots that can be formed by the micro lens ML_A2. Among them, eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A2 is formed) to form the irradiation region IR_A2. Further, the chip CP_A selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_A3 to emit light, so that eight spots SP7 among the plurality of spots that can be formed by the microlens ML_A3. To SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A3 is formed) to form the irradiation region IR_A3.

  In the range shown in the figure, the chip CP_B actually forms only eight spots SP out of a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_B selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_B2 to emit light, thereby allowing a plurality of spots that can be formed by the microlens ML_B2. Among them, eight spots SP6 to SP13 are arranged in the main scanning direction MD (that is, the spot group SG_B2 is formed) to form the irradiation region IR_B2. Further, in the range shown in the figure, the chip CP_C actually forms only eight spots SP among a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_C selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the micro lens ML_C2 to emit light, and thereby, among the spots that can be formed by the micro lens ML_C2. Eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, a spot group SG_C2 is formed) to form an irradiation region IR_C2.

  It should be noted here that the light emission of the element set 2951SET of each of the chip CP_A and the chip CP_B so that the irradiation region IR_A2 formed by the chip CP_A and the irradiation region IR_B2 formed by the chip CP_B are connected in the main scanning direction MD. The element 2951 emits light. That is, the chip CP_A causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_A2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP6 to SP13 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light.

  In particular, in FIG. 19, the chip CP_B does not form the spot SP14 formed in FIGS. 17 and 18 in order to connect the irradiation region IR_B2 to the irradiation region IR_A2 of the chip CP_A. In other words, in order to connect the irradiation region IR_A2 and the irradiation region IR_B2, among the plurality of light emitting elements 2951 included in the element set 2951SET of the chip CP_B, the element set so that the light emitting element 2951 corresponding to the spot SP14 does not emit light. The emission of 2951 SET is controlled. That is, in FIG. 19, the light emission of the light emitting elements of the element set 2951SET of the chip CP_B is controlled according to the positional deviation of the chip CP_B. As a result, the irradiation region IR_A2 and the irradiation region IR_B2 adjacent in the main scanning direction MD are connected to each other in spite of the positional deviation of the chip CP_B.

  Similarly, the light emitting element 2951 of the element set 2951SET of each of the chip CP_B and the chip CP_C so that the irradiation area IR_B2 formed by the chip CP_B and the irradiation area IR_C2 formed by the chip CP_C are connected in the main scanning direction MD. Is emitting light. That is, the chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP6 to SP13 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_C causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_C2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light.

  In particular, in FIG. 19, the chip CP_B forms a spot SP6 that is not formed in FIGS. 17 and 18 in order to connect the irradiation region IR_B2 to the irradiation region IR_C2 of the chip CP_C. In other words, in order to connect the irradiation region IR_C2 and the irradiation region IR_B2, among the plurality of light emitting elements 2951 included in the element set 2951SET of the chip CP_B, the element set 2951 corresponding to the spot SP6 is issued. The emission of 2951 SET is controlled. That is, in FIG. 19, the light emission of the light emitting elements of the element set 2951SET of the chip CP_B is controlled according to the positional deviation of the chip CP_B. As a result, the irradiation region IR_B2 and the irradiation region IR_C2 that are adjacent in the main scanning direction MD are connected to each other in spite of the positional deviation of the chip CP_B.

  In FIG. 19, the outside spot pitch Psp_out between the irradiation region IR_A2 and the irradiation region IR_B2 is 1.3 times the in-spot pitch Psp_in (that is, Psp_out = 1.3 · Psp_in). Further, the pitch Psp_out outside the spot between the irradiation region IR_B2 and the irradiation region IR_C2 is 0.7 times the pitch Psp_in within the spot (that is, Psp_out = 0.7 · Psp_in). As described above, both the pitch Psp_out outside the spot between the irradiation region IR_A2 and the irradiation region IR_B2 and the pitch Psp_out outside the spot between the irradiation region IR_B2 and the irradiation region IR_C2 satisfy the condition of the above formula 1. The light emission of the light emitting elements of the element set 2951SET is controlled.

  FIG. 20 is a diagram showing the positions of spots formed on the surface of the photoreceptor by the line head. In FIG. 20, the position of the chip CP_B is shifted from the desired position in the longitudinal direction LGD. As a result, the position of the spot that can be formed by the chip CP_B is 1 on the spot pitch Psp_in in the chip on the upstream side in the main scanning direction MD. Corresponds to a case where the deviation is four times (that is, 1.4 · Psp_in). Due to such a positional deviation of the chip, for example, a spot SP7 that can be formed by the microlens ML_A2 and a spot SP15 that can be formed by the microlens ML_B2 that have the same position in the main scanning direction in a state where there is no positional deviation (FIG. 17). In the main scanning direction MD, the positional deviation is caused by 1.4 times the in-chip spot pitch Psp_in. Further, in the state where there is no positional deviation (FIG. 17), the spot SP7 that can be formed by the microlens ML_B2 and the spot SP15 that can be formed by the microlens ML_C2 whose positions in the main scanning direction coincide with each other in the main scanning direction MD. The position is shifted by 1.4 times the inner spot pitch Psp_in. In the following description of FIG. 20, the difference from FIG. 17 will be mainly described, and the common parts with FIG.

  As shown in the figure, each chip CP forms only a spot SP (shaded spot in the figure) selected from a plurality of spots SP that can be formed. That is, in the range shown in the figure, the chip CP_A actually forms only 16 spots SP among the plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_A selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 opposed to the micro lens ML_A2 to emit light, thereby allowing a plurality of spots that can be formed by the micro lens ML_A2. Among them, eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A2 is formed) to form the irradiation region IR_A2. Further, the chip CP_A selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_A3 to emit light, so that eight spots SP7 among the plurality of spots that can be formed by the microlens ML_A3. To SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A3 is formed) to form the irradiation region IR_A3.

  In the range shown in the figure, the chip CP_B actually forms only eight spots SP out of a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_B selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_B2 to emit light, thereby allowing a plurality of spots that can be formed by the microlens ML_B2. Among them, eight spots SP6 to SP13 are arranged in the main scanning direction MD (that is, the spot group SG_B2 is formed) to form the irradiation region IR_B2. Further, in the range shown in the figure, the chip CP_C actually forms only eight spots SP among a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_C selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the micro lens ML_C2 to emit light, and thereby, among the spots that can be formed by the micro lens ML_C2. Eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, a spot group SG_C2 is formed) to form an irradiation region IR_C2.

  It should be noted here that the light emission of the element set 2951SET of each of the chip CP_A and the chip CP_B so that the irradiation region IR_A2 formed by the chip CP_A and the irradiation region IR_B2 formed by the chip CP_B are connected in the main scanning direction MD. The element 2951 emits light. That is, the chip CP_A causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_A2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP6 to SP13 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light.

  In particular, in FIG. 20, the chip CP_B does not form the spot SP14 formed in FIGS. 17 and 18 in order to connect the irradiation region IR_B2 to the irradiation region IR_A2 of the chip CP_A. In other words, in order to connect the irradiation region IR_A2 and the irradiation region IR_B2, among the plurality of light emitting elements 2951 included in the element set 2951SET of the chip CP_B, the element set so that the light emitting element 2951 corresponding to the spot SP14 does not emit light. The emission of 2951 SET is controlled. That is, in FIG. 20, the light emission of the light emitting elements of the element set 2951SET of the chip CP_B is controlled according to the positional deviation of the chip CP_B. As a result, the irradiation region IR_A2 and the irradiation region IR_B2 adjacent in the main scanning direction MD are connected to each other in spite of the positional deviation of the chip CP_B.

  Similarly, the light emitting element 2951 of the element set 2951SET of each of the chip CP_B and the chip CP_C so that the irradiation area IR_B2 formed by the chip CP_B and the irradiation area IR_C2 formed by the chip CP_C are connected in the main scanning direction MD. Is emitting light. That is, the chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP6 to SP13 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_C causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_C2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light.

  In particular, in FIG. 20, the chip CP_B forms a spot SP6 that is not formed in FIGS. 17 and 18 in order to connect the irradiation area IR_B2 to the irradiation area IR_C2 of the chip CP_C. In other words, in order to connect the irradiation region IR_C2 and the irradiation region IR_B2, among the plurality of light emitting elements 2951 included in the element set 2951SET of the chip CP_B, the element set 2951 corresponding to the spot SP6 is issued. The emission of 2951 SET is controlled. That is, in FIG. 20, the light emission of the light emitting elements of the element set 2951SET of the chip CP_B is controlled according to the positional deviation of the chip CP_B. As a result, the irradiation region IR_B2 and the irradiation region IR_C2 that are adjacent in the main scanning direction MD are connected to each other in spite of the positional deviation of the chip CP_B.

  Further, in FIG. 20, the pitch Psp_out outside the spot between the irradiation region IR_A2 and the irradiation region IR_B2 is 0.6 times the spot pitch Psp_in (that is, Psp_out = 0.6 · Psp_in). Further, the pitch Psp_out outside the spot between the irradiation region IR_B2 and the irradiation region IR_C2 is 1.4 times the pitch Psp_in within the spot (that is, Psp_out = 1.4 · Psp_in). As described above, both the pitch Psp_out outside the spot between the irradiation region IR_A2 and the irradiation region IR_B2 and the pitch Psp_out outside the spot between the irradiation region IR_B2 and the irradiation region IR_C2 satisfy the condition of the above formula 1. The light emission of the light emitting elements of the element set 2951SET is controlled.

  FIG. 21 is a diagram showing the positions of spots formed on the photoreceptor surface by the line head. FIG. 21 shows that the position of the chip CP_B is shifted from the desired position in the longitudinal direction LGD, and as a result, the position of the spot that can be formed by the chip CP_B is 1 of the spot pitch Psp_in in the chip on the upstream side in the main scanning direction MD. This corresponds to a case of deviation by 7 times (that is, 1.7 · Psp_in). Due to such a positional deviation of the chip, for example, a spot SP7 that can be formed by the microlens ML_A2 and a spot SP15 that can be formed by the microlens ML_B2 that have the same position in the main scanning direction in a state where there is no positional deviation (FIG. 17). In the main scanning direction MD, the positional deviation is caused by 1.7 times the in-chip spot pitch Psp_in. Further, in the state where there is no positional deviation (FIG. 17), the spot SP7 that can be formed by the microlens ML_B2 and the spot SP15 that can be formed by the microlens ML_C2 whose positions in the main scanning direction coincide with each other in the main scanning direction MD. The position is shifted by 1.7 times the inner spot pitch Psp_in. Further, in the following description of FIG. 21, differences from FIG. 17 will be mainly described, and common parts with FIG.

  As shown in the figure, each chip CP forms only a spot SP (shaded spot in the figure) selected from a plurality of spots SP that can be formed. That is, in the range shown in the figure, the chip CP_A actually forms only 16 spots SP among the plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_A selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 opposed to the micro lens ML_A2 to emit light, thereby allowing a plurality of spots that can be formed by the micro lens ML_A2. Among them, eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A2 is formed) to form the irradiation region IR_A2. Further, the chip CP_A selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_A3 to emit light, so that eight spots SP7 among the plurality of spots that can be formed by the microlens ML_A3. To SP14 are arranged in the main scanning direction MD (that is, the spot group SG_A3 is formed) to form the irradiation region IR_A3.

  In the range shown in the figure, the chip CP_B actually forms only eight spots SP out of a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_B selects a plurality of light emitting elements 2951 from the plurality of light emitting elements 2951 facing the microlens ML_B2 to emit light, thereby allowing a plurality of spots that can be formed by the microlens ML_B2. Among them, eight spots SP5 to SP12 are arranged in the main scanning direction MD (that is, the spot group SG_B2 is formed) to form the irradiation region IR_B2. Further, in the range shown in the figure, the chip CP_C actually forms only eight spots SP among a plurality of spots SP that can be formed in the actual spot forming operation. In order to execute the spot forming operation, the chip CP_C selects eight light emitting elements 2951 from the plurality of light emitting elements 2951 facing the micro lens ML_C2 to emit light, and thereby, among the spots that can be formed by the micro lens ML_C2. Eight spots SP7 to SP14 are arranged in the main scanning direction MD (that is, a spot group SG_C2 is formed) to form an irradiation region IR_C2.

  It should be noted here that the light emission of the element set 2951SET of each of the chip CP_A and the chip CP_B so that the irradiation region IR_A2 formed by the chip CP_A and the irradiation region IR_B2 formed by the chip CP_B are connected in the main scanning direction MD. The element 2951 emits light. That is, the chip CP_A causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_A2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP5 to SP12 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light.

  In particular, in FIG. 21, the chip CP_B does not form the spot SP14 formed in FIGS. 17 and 18 in order to connect the irradiation region IR_B2 to the irradiation region IR_A2 of the chip CP_A. Further, the spot SP13 formed in FIGS. 17 to 20 is not formed. In other words, in order to connect the irradiation region IR_A2 and the irradiation region IR_B2, among the plurality of light emitting elements 2951 included in the element set 2951SET of the chip CP_B, the light emitting elements 2951 corresponding to these spots SP13 and SP14 do not emit light. The light emission of the element set 2951SET is controlled. That is, in FIG. 21, the light emission of the light emitting elements of the element set 2951SET of the chip CP_B is controlled in accordance with the positional deviation of the chip CP_B. As a result, the irradiation region IR_A2 and the irradiation region IR_B2 adjacent in the main scanning direction MD are connected to each other in spite of the positional deviation of the chip CP_B.

  Similarly, the light emitting element 2951 of the element set 2951SET of each of the chip CP_B and the chip CP_C so that the irradiation area IR_B2 formed by the chip CP_B and the irradiation area IR_C2 formed by the chip CP_C are connected in the main scanning direction MD. Is emitting light. That is, the chip CP_B causes only the eight light emitting elements 2951 corresponding to the spots SP5 to SP12 that irradiate the irradiation region IR_B2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light. The chip CP_C causes only the eight light emitting elements 2951 corresponding to the spots SP7 to SP14 that irradiate the irradiation region IR_C2 among the plurality of light emitting elements 2951 included in the element set 2951SET to emit light.

  In particular, in FIG. 21, the chip CP_B forms a spot SP6 that is not formed in FIGS. 17 and 18 in order to connect the irradiation area IR_B2 to the irradiation area IR_C2 of the chip CP_C. Further, a spot SP5 that is not formed in FIGS. 17 to 20 is also formed. In other words, in order to connect the irradiation region IR_C2 and the irradiation region IR_B2, among the plurality of light emitting elements 2951 included in the element set 2951SET of the chip CP_B, the light emitting elements 2951 corresponding to the spots SP5 and SP6 are issued. The light emission of the element set 2951SET is controlled. That is, in FIG. 21, the light emission of the light emitting elements of the element set 2951SET of the chip CP_B is controlled in accordance with the positional deviation of the chip CP_B. As a result, the irradiation region IR_B2 and the irradiation region IR_C2 that are adjacent in the main scanning direction MD are connected to each other in spite of the positional deviation of the chip CP_B.

  Further, in FIG. 21, the spot outside pitch Psp_out between the irradiation area IR_A2 and the irradiation area IR_B2 is 1.3 times the spot pitch Psp_in (that is, Psp_out = 1.3 · Psp_in). Further, the pitch Psp_out outside the spot between the irradiation region IR_B2 and the irradiation region IR_C2 is 0.7 times the pitch Psp_in within the spot (that is, Psp_out = 0.7 · Psp_in). As described above, both the pitch Psp_out outside the spot between the irradiation region IR_A2 and the irradiation region IR_B2 and the pitch Psp_out outside the spot between the irradiation region IR_B2 and the irradiation region IR_C2 satisfy the condition of the above formula 1. The light emission of the light emitting elements of the element set 2951SET is controlled.

  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 “movement direction” in the present invention, and the main scanning direction MD corresponds to the “orthogonal direction” in the present invention. The photosensitive drum 21 corresponds to the “latent image carrier” of the invention. Further, the width direction LTD corresponds to the “first direction” of the present invention, and the longitudinal direction LGD corresponds to the “second direction” of the present invention. The photosensitive drum 21 corresponds to the “latent image carrier” of the invention.

  As described above, the line head 29 in the above embodiment irradiates the surface of the photoconductor with the light beam to form an irradiation region (light irradiation step). In the line head 29, the light emitting elements 2951 of the element set 2951SET are formed so that irradiation regions (for example, irradiation region IR_A2 and irradiation region IR_B2) that are formed by different chips CP and are adjacent in the main scanning direction MD are connected. Emits light. Therefore, even if the position of the chip CP is slightly deviated, it is possible to suppress the generation of gaps and vertical stripes between adjacent irradiation regions as shown in FIG. 13, and perform good light beam irradiation. be able to. Further, in the image forming apparatus 1 using such a line head 29, it is possible to form a good latent image on the surface of the photoreceptor.

  By the way, in the line head 29 of the above-described embodiment, the element set 2951SET of each chip CP has a larger number of light emitting elements 2951 than the number necessary for forming the irradiation region arranged in the longitudinal direction LGD (chip major axis) at the element pitch Pel. Have. Then, some of the light emitting elements 2951 of the plurality of light emitting elements 2951 included in the element set 2951SET emit light to form an irradiation region.

  More specifically, as shown in FIG. 15, in the element set 2951SET, a plurality of light emitting elements 2951 are laid out at the element pitch Pel in the longitudinal direction LGD, and the element set 2951SET of the chip CP is necessary to form an irradiation region. A larger number of light emitting elements 2951 are arranged in the longitudinal direction LGD. Then, as described with reference to FIGS. 18 to 21, in actual operation, only the light emitting element 2951 necessary for forming the irradiation region is selected to emit light to form the irradiation region. That is, when forming the irradiation region, the chip CP selectively selects only a part of the light emitting elements 2951 suitable for forming the irradiation region among the plurality of light emitting devices 2951 included in the element set 2951SET of the chip CP. Make it emit light. Therefore, even when the position of the chip is slightly deviated, by selecting a light emitting element that emits light according to the position deviation (in other words, controlling the light emission of the light emitting element in accordance with the position deviation of the chip). ), An irradiation region can be formed at an appropriate position. In other words, the light emission of the light emitting elements 2951 of the element set 2951SET can be controlled so that the irradiation regions adjacent to each other in the main scanning direction MD are formed by different chips CP, and the above-described problems such as vertical stripes occur. Can be suppressed.

  In the above-described embodiment, as described with reference to FIGS. 18 to 21, a part of the plurality of light emitting elements 2951 included in the element set 2951SET of the chip CP emits light according to the positional deviation of the chip CP. Therefore, it is possible to effectively suppress the occurrence of a gap in the irradiation region due to the positional deviation of the chip CP, and the above embodiment is suitable.

  In the above embodiment, the pitch Psp_out between the spots SP formed by different chips CP and adjacent in the main scanning direction is equal to or less than the maximum pitch (1.5 · Psp_in in the above embodiment) and the minimum pitch. (In the above embodiment, the light emitting element 2951 emits light so as to be 0.5 · Psp_in) or more. That is, the light emitting elements of the element set 2951SET emit light so as to satisfy the above formula 1. As described above, since the pitch Psp_out between the spots SP that are formed by different chips CP and adjacent in the main scanning direction is equal to or less than the maximum pitch, the irradiation that is formed by different chips and is adjacent in the orthogonal direction. The areas can be connected well. Further, the pitch Psp_out between the spots SP which are formed by different chips CP and are adjacent to each other in the main scanning direction MD is equal to or larger than the minimum pitch, thereby suppressing excessive overlap of the spots SP which are formed adjacently. Thus, better light beam irradiation is realized.

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 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 substrate 293 is slight, the positional deviation is enlarged and the surface of the photoconductor is enlarged. This is a deviation of the irradiation area. Therefore, in the line head provided with such a microlens ML, the problem of the gap as described above is likely to occur. Therefore, in such a line head 29, it is particularly preferable to apply the above-described invention to suppress the generation of a gap in the irradiation region.

  In the above embodiment, two light emitting element lines 2951L are arranged in the chip minor axis CLT (width direction LTD) to form the element set 2951SET. It is not limited.

  In the above embodiment, three microlenses ML are provided to face the element set 2951SET. However, the number of microlenses ML provided to face the element set 2951SET is limited to three. Absent.

  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 perspective view which shows the line head in embodiment. The figure which shows arrangement | positioning of the chip | tip on the board | substrate in embodiment. The figure which shows the image formation state of a micro lens array. 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. 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. FIG. 4 is a diagram showing the positions of spots formed on the surface of a photoreceptor by a line head.

Explanation of symbols

  21Y, 21K ... photosensitive drum (latent image carrier), 29 ... line head, 2951 ... light emitting element, 2951SET ... element assembly, 293 ... head substrate (substrate), 299 ... micro lens array (optical system), ML ... micro Lens, CP ... chip, IR_A2, IR_A3, IR_B2, IR_C2 ... irradiation region, MD ... main scanning direction (orthogonal direction), SD ... sub-scanning direction (moving direction), LGD ... longitudinal direction (second direction), LTD ... width Direction (first direction), CLG: chip major axis, CLT: chip minor axis

Claims (8)

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 forms an image toward the moving image plane of the light beam from the light emitting element,
A plurality of the chips are arranged in a first direction corresponding to the moving direction of the image plane on the substrate, and each of the plurality of chips is at a different position in a second direction corresponding to an orthogonal direction orthogonal to the moving direction. Having an element set provided with the light emitting elements, and irradiating the image plane with a light beam emitted from the element set according to the movement of the image plane to form an irradiation region;
The line head according to claim 1, wherein the light emitting elements of the element set emit light such that the irradiation regions adjacent to each other in the orthogonal direction are formed by different chips.   In each of the plurality of chips, the element set includes more light emitting elements than the number necessary for forming the irradiation region, and some of the light emitting elements of the plurality of light emitting elements included in the element set are included. The line head according to claim 1, wherein the irradiation region is formed by emitting light.   The line head according to claim 2, wherein a part of the plurality of light emitting elements included in the element set of the chip emits light in accordance with the positional deviation of the chip. When the chip emits a light beam from the light emitting element of the element set, a plurality of spots are arranged in the orthogonal direction to form the irradiation region,
4. The line head according to claim 2, wherein the light emitting element emits light so that a pitch between the spots formed by different chips and adjacent in the orthogonal direction is equal to or less than a maximum pitch. 5.   The line head according to claim 4, wherein the light emitting element emits light so that a pitch between the spots formed by the different chips and adjacent in the orthogonal direction is equal to or greater than a minimum pitch.   The line head according to any one of claims 1 to 5, wherein an absolute value of magnification of the optical system is larger than one. A light irradiation step of emitting a light emitting element included in a chip provided on a substrate and irradiating a moving image plane with a light beam emitted from the light emitting element;
In the substrate, the plurality of chips are arranged in a first direction corresponding to the moving direction of the image plane, and each of the plurality of chips is different from each other in a second direction corresponding to an orthogonal direction orthogonal to the moving direction. An element set provided with the light emitting element, and a light beam is emitted from the element set according to the movement of the image plane to form an irradiation area on the image plane,
In the light irradiation step, the light emission of the light emitting element of the element set is controlled so that the irradiation areas adjacent to each other in the orthogonal direction are formed by the chips different from each other. . A latent image carrier whose surface moves;
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 for imaging a light beam from the light emitting element toward the surface of the latent image carrier;
Control means for controlling light emission of the light emitting element,
On the substrate, a plurality of the chips are arranged in a first direction corresponding to the moving direction of the surface of the latent image carrier, and each of the plurality of chips is in a second direction corresponding to an orthogonal direction orthogonal to the moving direction. It has an element set provided with the light emitting elements at different positions, and irradiates the surface of the latent image carrier through the optical system with a light beam emitted from the element set according to the movement of the surface of the latent image carrier. To form an irradiated area,
The image forming apparatus, wherein the control unit controls light emission of the light emitting elements of the element set so that the irradiation regions adjacent to each other in the orthogonal direction are formed by the chips different from each other.

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