JP5070839B2 - Line head and image forming apparatus using the line head - Google Patents

Description

  The present invention relates to a line head that scans a surface to be scanned with a light beam and an image forming apparatus using the line head.

  As this type of line head, for example, as described in Japanese Patent Application Laid-Open No. H10-260260, a light emitting element array configured by linearly arranging a plurality of light emitting elements at a constant pitch in the main scanning direction has been proposed. ing. In such a line head, a light beam emitted from each of a plurality of light emitting elements included in the light emitting element array is imaged on a scanned surface while being magnified at a predetermined magnification by an imaging optical system, thereby forming a spot on the scanned surface. Is forming.

JP 2000-158705 A (FIG. 1)

  However, in the line head disclosed in Patent Document 1, light emitting elements are linearly arranged in the main scanning direction (in other words, one-dimensionally), and the surface to be scanned is formed by an imaging optical system having an absolute value of 1 or more. A spot is formed. Therefore, in realizing high resolution, the amount of light beams related to spot formation is reduced, and there is a case where it becomes difficult to realize good spot formation.

  That is, in order to realize high resolution, it is necessary to reduce the size of the spot formed on the surface to be scanned. However, the conventional line head uses an imaging optical system (that is, an enlargement optical system) having an absolute value of magnification larger than 1. Therefore, in order to reduce the spot, it is necessary to reduce the size of the light emitting element itself. As a result, as the size of the light emitting element is reduced, the amount of light beams related to spot formation is also reduced, which may cause a problem that it is difficult to realize good spot formation.

  The present invention has been made in view of the above problems, and in a line head and an image forming apparatus using a plurality of light emitting elements, a sufficient spot is obtained by securing a sufficient amount of light beams for spot formation even at high resolution. The object is to provide a technique that enables the realization of formation.

  In order to achieve the above object, the line head according to the present invention has a microlens array in which a plurality of microlenses having an absolute value of magnification less than 1 are arranged in the main scanning direction of the surface to be scanned, and the plurality of microlenses. A plurality of light emitting element groups provided in a one-to-one correspondence relationship with each other, and in each of the plurality of light emitting element groups, the plurality of light emitting elements are arranged at different positions in the main scanning direction, Each of the plurality of light emitting elements emits light at a timing according to the movement of the scanned surface in the sub-scanning direction, and light beams emitted from the plurality of light emitting elements are on the scanned surface at different positions in the main scanning direction. A plurality of spots are formed side by side in the main scanning direction, and each of the plurality of light emitting element groups includes the light emitting element group. Among the plurality of light emitting elements which is characterized by being disposed at different positions two light emitting elements to emit light in the sub-scanning direction to form a spot adjacent to each other.

  Further, the latent image carrier whose surface according to the present invention is conveyed in the sub-scanning direction, and a plurality of spots are formed on the surface of the latent image carrier in the main scanning direction substantially orthogonal to the sub-scanning direction. A line head for forming a latent image and developing means for developing the latent image on the latent image carrier with toner, and the line head has an absolute value of magnification in the main scanning direction of the surface to be scanned. A plurality of light emitting element groups, each having a microlens array in which a plurality of microlenses less than 1 are arranged, and a plurality of light emitting element groups provided in a one-to-one correspondence with the plurality of microlenses. In each of the above, a plurality of light emitting elements are arranged at different positions in the main scanning direction, and the plurality of light emitting elements respectively emit light at a timing according to the movement of the latent image carrier in the sub scanning direction. A plurality of spots are formed side by side in the main scanning direction by forming light beams emitted from a plurality of light emitting elements on the latent image carrier at positions different from each other in the main scanning direction. In each of the light emitting element groups, among the plurality of light emitting elements constituting the light emitting element group, two light emitting elements that emit light to form adjacent spots are arranged at different positions in the sub-scanning direction. It is characterized by being.

  In the invention thus configured (line head and image forming apparatus including the line head), the light beam emitted from the light emitting element is converted into a microlens (that is, a reduction optical system) whose absolute value of magnification is less than 1. Is formed on the surface to be scanned. Thereby, it is possible to form an image of a light beam emitted from a large light emitting element into a small spot. That is, a small spot can be formed by a light beam having a large amount of light. And in this invention, after employ | adopting such a microlens, it comprises as mentioned above with a microlens, a light emitting element group. For this reason, it is possible to realize high resolution while ensuring a sufficient amount of light beam for spot formation, and it is possible to realize favorable spot formation even at high resolution. The reason is as follows.

  In a conventional device using a magnifying optical system, for example, the device described in Patent Document 1, in order to increase the resolution, it is necessary to reduce the diameter of the light emitting element. However, it is difficult in manufacturing to reduce the element diameter while securing a desired amount of emitted light. Further, the driving of the light emitting element becomes unstable, and a good spot cannot be formed on the surface to be scanned (the surface of the latent image carrier). In particular, the image forming apparatus is one of the main factors that cause image quality degradation.

  On the other hand, in the present invention, since the reduction optical system microlens is used, the diameter of the light emitting element can be set large. Moreover, in the present invention, the light emitting elements are arranged as described above in the light emitting element group. That is, in each light emitting element group, the light emitting elements are arranged at different positions in the main scanning direction, and two light emitting elements that emit light to form adjacent spots are arranged at different positions in the sub scanning direction. Yes. Therefore, even when the interval between spots formed on the surface to be scanned (the surface of the latent image carrier) is small, the interval between the light emitting elements can be increased. In this way, (a) the point using the reduction optical system and (b) the arrangement of the light emitting elements in the light emitting element group are sufficient to obtain a desired amount of emitted light in a relatively wide space. A light-emitting element having a large element diameter can be formed. Therefore, element formation becomes easy. Further, the driving of the light emitting element can be stabilized, and a good spot can be formed on the surface to be scanned (the surface of the latent image carrier). Furthermore, by applying this to an image forming apparatus, it is possible to form a toner image with excellent image quality.

  Here, the following modes can be adopted for the arrangement of the light emitting elements in each light emitting element group. That is, in each of the plurality of light emitting element groups, a plurality of light emitting element arrays in which a plurality of light emitting elements are arranged in the main scanning direction are arranged in the sub scanning direction of the surface to be scanned, and the light emitting elements constituting the light emitting element group You may comprise so that it may be arrange | positioned. In this case, in each of the plurality of light emitting element arrays, the plurality of light emitting elements constituting the light emitting element array emit light at a timing according to the movement of the scanned surface in the sub-scanning direction, and the plurality of spots are aligned in the main scanning direction. Can be formed. Therefore, the light emission timing adjustment can be simplified, which is preferable.

  The light emitting element groups adjacent to each other in the main scanning direction partially overlap in the main scanning direction. On the other hand, in each light emitting element group, the light emitting elements in the main scanning direction among the plurality of light emitting elements constituting the light emitting element group. You may comprise so that the nearest light emitting element nearest to the other light emitting element group adjacent to a group may be arrange | positioned in a different position from another light emitting element group in a subscanning direction. That is, when the light emitting element groups adjacent to each other in the main scanning direction are configured as described above, the space for arranging the light emitting elements can be expanded (see FIG. 10 described later). In addition, the degree of freedom in arrangement can be increased.

  In a line head in which a plurality of light emitting elements are provided on a substrate and a driving circuit for driving a plurality of light emitting element groups is further provided on the substrate, the plurality of light emitting elements and the driving circuit are electrically connected to each other through wiring. Can be connected. In such a line head, by adopting the configuration (b), wiring can be provided between the light emitting elements, and the degree of freedom of wiring on the substrate can be increased. This effect cannot be obtained simply by using a reduction optical system (see comparison of FIGS. 10B and 10C described later).

  Further, a plurality of microlenses arranged in a main scanning direction may be arranged in a plurality of sub-scanning directions so that a plurality of microlenses are arranged in a staggered manner. In addition, two light emitting element groups provided corresponding to microlenses adjacent to each other in the sub-scanning direction may partially overlap in the main scanning direction. In this case, the microlens and the light emitting element group can be efficiently arranged with a high degree of design freedom while using the reduction optical system.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. 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. Thus, the engine unit EG executes a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet such as a copy sheet, a transfer sheet, a sheet, and an OHP transparent sheet.

  In the housing main body 3 of the image forming apparatus according to this embodiment, an electrical component box 5 is provided that incorporates a power circuit board, a main controller MC, an engine controller EC, and a head controller HC. An image forming unit 7, a transfer belt unit 8, and a paper feeding unit 11 are also disposed in the housing body 3. In FIG. 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 Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality of images of different colors. Each of the image forming stations Y, M, C, and K is provided with a photosensitive drum 21 on which a 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 Y, M, C, and K are superimposed on the transfer belt 81 of the transfer belt unit 8 to form a color image, and the monochrome mode is executed. In some cases, a monochrome image is formed using only the toner image formed at the image forming station K. In FIG. 1, the image forming stations of the image forming unit 7 have the same configuration, and therefore, for convenience of illustration, only some image forming stations are denoted by reference numerals, and the other image forming stations are omitted. .

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

  The line head 29 includes a plurality of light emitting elements arranged in the axial direction of the photosensitive drum 21 (direction perpendicular to the paper surface of FIG. 1), and is spaced apart from the photosensitive drum 21. From these light emitting elements, the surface of the photosensitive drum 21 charged by the charging unit 23 is irradiated with light to form a latent image on the surface. In this embodiment, a head controller HC is provided to control the line heads 29 for the respective colors, and each line head 29 is controlled based on the video data VD from the main controller MC and a signal from the engine controller EC. ing. That is, in this embodiment, the image data included in the image formation command is input to the image processing unit 51 of the main controller MC. Various image processing is performed on the image data to create video data VD for each color, and the video data VD is given to the head controller HC via the main-side communication module 52. In the head controller HC, the video data VD is given to the head control module 54 via the head side communication module 53. As described above, the head controller module 54 is supplied with the signal indicating the parameter value related to the latent image formation and the vertical synchronization signal Vsync from the engine controller EC. Based on these signals, video data VD, and the like, the head controller HC creates a signal for controlling element driving for the line head 29 of each color, and outputs the signal to each line head 29. Thus, the operation of the light emitting elements is appropriately controlled in each line head 29, and a latent image corresponding to the image formation command is formed.

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

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

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

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

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. And a transfer belt 81 that is driven to circulate. Further, the transfer belt unit 8 is disposed on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations Y, M, C, and K when the photosensitive cartridge is mounted. Four primary transfer rollers 85Y, 85M, 85C, and 85K are provided. Each of these primary transfer rollers 85 is electrically connected to a primary transfer bias generator (not shown). As will be described in detail later, when the color mode is executed, as shown in FIG. 1, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations Y, M, C, and K side. Then, the transfer belt 81 is pushed and brought into contact with the photosensitive drums 21 included in the image forming stations Y, M, C, and K, so that the primary transfer position TR1 is set between each photosensitive drum 21 and the transfer belt 81. Form. Then, by applying a primary transfer bias from the primary transfer bias generator to the primary transfer roller 85 at an appropriate timing, the toner images formed on the surfaces of the photosensitive drums 21 correspond respectively. A color image is formed by transferring to the surface of the transfer belt 81 at the primary transfer position TR1.

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

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

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

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

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

  Further, in this apparatus, a cleaner portion 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The 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 an embodiment of a line head (exposure means) according to the present invention. FIG. 4 is a sectional view in the sub-scanning direction of an embodiment of the line head (exposure means) according to the present invention. The line head 29 according to the present embodiment includes a case 291 whose longitudinal direction is the main scanning direction XX, and positioning pins 2911 and screw insertion holes 2912 are provided at both ends of the case 291. Then, the positioning pin 2911 covers the photosensitive drum 21 and is fitted into a positioning hole (not shown) formed in a photosensitive cover (not shown) positioned with respect to the photosensitive drum 21, thereby The head 29 is positioned with respect to the photosensitive drum 21. Further, the line head 29 is positioned and fixed with respect to the photosensitive drum 21 by screwing and fixing a fixing screw into a screw hole (not shown) of the photosensitive member cover through the screw insertion hole 2912.

  The case 291 holds the microlens array 299 at a position facing the surface of the photosensitive drum 21, and includes a light shielding member 297 and a glass substrate 293 in the order close to the microlens array 299. In addition, a plurality of light emitting element groups 295 are provided on the back surface of the glass substrate 293 (the surface opposite to the microlens array 299 among the two surfaces of the glass substrate 293). That is, the plurality of light emitting element groups 295 are two-dimensionally arranged on the back surface of the glass substrate 293 so as to be separated from each other by a predetermined distance in the main scanning direction XX and the sub scanning direction YY. Here, each of the plurality of light emitting element groups 295 is configured by two-dimensionally arranging a plurality of light emitting elements, which will be described later. In the present embodiment, a bottom emission type organic EL (Electro-Luminescence) element is used as the light emitting element. That is, in this embodiment, the organic EL element is disposed as a light emitting element on the back surface of the glass substrate 293. When each light emitting element is driven by a drive circuit (reference numeral D295 in FIG. 7 later) formed on the glass substrate 293, a light beam is emitted from the light emitting element in the direction of the photosensitive drum 21. This light beam is directed to the light shielding member 297 through the glass substrate 293. Note that the structures of the light emitting element group 295 and the drive circuit described above will be described later.

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

  As shown in FIG. 4, the back cover 2913 is pressed against the case 291 through the glass substrate 293 by the fixing device 2914. That is, the fixing device 2914 has an elastic force that presses the back cover 2913 toward the case 291, and presses the back cover with the elastic force, thereby making the inside of the case 291 light-tight (that is, from inside the case 291. It is sealed so that light does not leak and so that light does not enter from the outside of the case 291. Note that a plurality of fixing devices 2914 are provided in the longitudinal direction of the case 291. The light emitting element group 295 is covered with a sealing member 294.

  FIG. 5 is a perspective view schematically showing the microlens array. FIG. 6 is a cross-sectional view of the microlens array in the main scanning direction. The microlens array 299 includes a glass substrate 2991 and a plurality of lens pairs configured by 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 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 a predetermined interval in the main scanning direction XX and the sub-scanning direction YY corresponding to the arrangement of the light emitting element groups 295. More specifically, in this microlens array 299, an imaging optical system composed of a lens pair composed of lenses 2993A and 2993B and a glass substrate 2991 sandwiched between the lens pair corresponds to the microlens of the present invention. Yes. A plurality of microlenses ML arranged in the main scanning direction XX are arranged in a plurality of rows (“3” in the present embodiment) in the subscanning direction YY, and the plurality of microlenses ML are staggered. Has been placed.

  FIG. 7 is a diagram showing the arrangement and wiring of each part in the line head. Hereinafter, the arrangement of the light emitting element group, the arrangement of the drive circuit that drives each light emitting element, the wiring that electrically connects the drive circuit and the light emitting element, and the control signal line that controls the light emitting element will be described in order. In the present embodiment, one light emitting element group 295 is formed by arranging two light emitting element rows L2951 arranged in the main scanning direction XX at predetermined intervals and arranging two light emitting element rows L2951 in the sub scanning direction YY. Yes. That is, a total of 16 light emitting elements 2951 surrounded by a two-dot chain line in FIG. 7 constitute a light emitting element group 295. The plurality of light emitting element groups 295 are arranged as follows.

  That is, the light emitting element groups 295 are arranged such that three light emitting element group columns 295L arranged in the main scanning direction XX are arranged in the sub scanning direction YY. Further, all the light emitting element groups 295 are arranged at different main scanning direction positions. Further, the plurality of light emitting element groups 295 are arranged so that the sub scanning direction positions of the light emitting element groups (for example, the light emitting element group 295C1 and the light emitting element group 295B1) whose main scanning direction positions are adjacent to each other are different. Here, the light emitting element rows L2951 belonging to each of two light emitting element groups adjacent in the main scanning direction are arranged so as to overlap each other in the main scanning direction XX in each part. Depending on the reason. That is, as will be described later, in this embodiment, a light beam emitted from the light emitting element 2951 by the reduction optical system having a magnification of less than 1 is imaged on the surface of the photosensitive drum 21 (hereinafter referred to as “photosensitive member surface”). To do. Therefore, in order to form a plurality of spots in the main scanning direction XX on the surface of the photoreceptor, the light emitting element array L2951 is arranged as described above. Note that in this specification, the geometric gravity center point of the light emitting element 2951 is set as the position of the light emitting element 2951, and the geometric gravity center of all the light emitting element positions belonging to the same light emitting element group 295 is set as the position of the light emitting element group 295. In addition, the main scanning direction position and the sub scanning direction position mean the main scanning direction component and the sub scanning direction component at the position of interest, respectively.

  In this embodiment, a part of the driving circuit D295 including a TFT (Thin Film Transistor) for driving the light emitting element 2951 arranged as described above, and the driving circuit D295 and the light emitting element 2951 are electrically connected. A part of the wiring WL to be connected is disposed on the substrate 295 as shown in FIG. For example, in a gap region surrounded by the light emitting element groups 295C1, 295C2, and 295B1, a driving circuit (TFT) D295 for driving the light emitting element group 295B1 is disposed, and the driving circuit D295 and the light emitting element group 295B1 are The wirings WL are electrically connected. In the other gap region, the drive circuit D295 and the wiring WL are formed in the same manner as described above. Note that reference symbol CL in the figure denotes a control signal line for transmitting a control signal for controlling the light emitting element 2951 to the drive circuit D295.

  Corresponding to the arrangement of the light emitting element groups 295 described above, a light guide hole 2971 is formed in the light shielding member 297, and a lens pair including the lenses 2993A and 2993B is arranged. That is, in the present embodiment, the gravity center position of the light emitting element group 295, the central axis of the light guide hole 2971, and the optical axis OA of the lens pair configured by the lenses 2993A and 2993B are configured to substantially coincide. ing. The light beams emitted from the light emitting elements 2951 of the light emitting element group 295 enter the microlens array 299 through the corresponding light guide holes 2971 and are spotted on the surface of the photosensitive drum 21 by the microlens array 299. Is imaged.

  FIG. 8 is a diagram illustrating an imaging state of the microlens array in the present embodiment. That is, this figure is a cross-sectional view when the light emitting element group 295, the glass substrate 293, and the microlens array 299 are cut in the main scanning direction XX so as to include the optical axes OA of the lenses 2993A and 2993B. Further, in the same figure, in order to show the imaging state of the microlens array 299, the light is emitted from the virtual light emitting elements at the geometric center of gravity position E0 of the light emitting element group 295 and at both ends E1, E2 in the main scanning direction of the light emitting element group 295. Represents the trajectory of the emitted light beam. As shown by the locus, the light beam emitted from the virtual light emitting element is incident on the back surface of the glass substrate 293 and then emitted from the surface of the glass substrate 293. Then, the light beam emitted from the surface of the glass substrate 293 reaches the photosensitive member surface (scanned surface) via the microlens array 299. Here, the glass substrate 293 and the microlens array 299 each have a predetermined relative refractive index.

  As shown in FIG. 8, the light beam emitted from the virtual light emitting element at the geometric gravity center position E0 of the light emitting element group is connected to the intersection I0 between the surface of the photosensitive drum 21 and the optical axis OA of the lenses 2993A and 2993B. Imaged. As described above, this is because, in the present embodiment, 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 virtual light emitting elements at both ends E1 and E2 in the main scanning direction of the light emitting element group 295 are imaged at positions I1 and I2 on the surface of the photosensitive drum 21, respectively. That is, the light beam emitted from the virtual light emitting element at 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 XX, and at the position E2. The light beam emitted from the virtual light emitting element forms an image at a position I2 on the opposite side across the optical axis OA of the lenses 2993A and 2993B in the main scanning direction XX. That is, an optical system composed of a glass substrate 293, a lens pair composed of lenses 2993A and 2993B having a common optical axis, and a glass substrate 2991 sandwiched between the lens pairs, that is, the microlens ML has inversion characteristics. A so-called reversal optical system.

  As shown in the figure, the distance between the positions I1 and I0 where the light beam is imaged is shorter than the distance between the positions E1 and E0 where the virtual light emitting elements are present. That is, the absolute value of the magnification of the optical system in the present embodiment is less than 1. That is, the optical system (microlens ML) in the present embodiment is a so-called reduction optical system having reduction characteristics.

  FIG. 9 is a diagram showing details of the arrangement of the light emitting elements in the present embodiment. As shown in the figure, in this embodiment, two light emitting element rows L2951 configured by arranging eight light emitting elements at predetermined intervals in the main scanning direction XX are arranged in the sub scanning direction YY. In the same light emitting element group, the positions of the plurality of light emitting elements 2951 in the main scanning direction XX are different from each other, and two light emitting elements 2951 whose positions in the main scanning direction XX are adjacent to each other are in different light emitting element rows L2951. To belong, these two light emitting element rows L2951 are arranged in the sub-scanning direction. Therefore, in the present embodiment, a plurality of light emitting elements 2951 are arranged in the same light emitting element group so that the sub scanning direction positions of two light emitting elements 2951 adjacent in the main scanning direction position are different from each other. . That is, for example, when attention is paid to the two light emitting elements 2951A and 2951B in the drawing, the positions of these two light emitting elements 2951A and 2951B in the main scanning direction are positions XA and XB, respectively, which are adjacent to each other. The sub-scanning direction positions of the two light emitting elements 2951A and 2951B adjacent to each other in the main scanning direction are positions YA and YB, which are different from each other.

  Further, as shown in FIG. 9, in the present embodiment, in the same light emitting element group, two light emitting elements 2951 whose positions in the main scanning direction are adjacent to each other partially overlap each other in the main scanning direction XX. Further, a plurality of light emitting elements 2951 are arranged. That is, for example, when attention is paid to the two light emitting elements 2951A and 2951B in the figure, the positions of these two light emitting elements 2951A and 2951B in the main scanning direction are adjacent to each other as described above. The two adjacent light emitting elements 2951A and 2951B overlap each other by a width W in the main scanning direction XX in a part of each.

  In addition, the light emitting element groups adjacent to each other in the main scanning direction XX partially overlap in the main scanning direction XX, while each light emitting element group includes a plurality of light emitting elements 2951 constituting the light emitting element group in the main scanning direction XX. , The closest light emitting element closest to another light emitting element group adjacent to the light emitting element group is arranged at a position different from the other light emitting element groups in the sub-scanning direction YY. For example, considering the light emitting element group 295C1, the light emitting element group 295B1 is adjacent to the light emitting element group 295C1 while partially overlapping in the main scanning direction XX. In the light emitting element group 295C1, the light emitting element 2951C is closest to the light emitting element group 295B1 and corresponds to the “closest light emitting element” of the present invention. The light emitting element 2951C is a light emitting element group in the sub-scanning direction YY. It is arranged at a position different from 295B1. For this reason, as shown in FIGS. 7 and 8, the interval between the light emitting elements 2951 can be increased not only in the same light emitting element group but also between adjacent light emitting element groups. By adopting such an arrangement configuration, the degree of freedom in arrangement of the light emitting element groups and the light emitting elements 2951 can be increased. Further, as will be described below, the wiring WL can be routed between the light emitting elements, and the degree of freedom of wiring can be increased.

  Next, the spot forming operation by the line head configured as described above will be described. Here, first, the spot forming operation by each light emitting element group will be described with reference to FIG. 10 and FIG. Thereafter, the spot forming operation by the line head will be described in detail.

  FIG. 10 is a schematic diagram showing the relationship between the configuration of the light emitting element group and the spot formation position. FIG. 11 is a schematic view showing a spot forming operation by the light emitting element group of the present embodiment. FIG. 10A shows the arrangement of light emitting elements and the spot formation position in the conventional example. In the conventional example, the light emitting elements 2951 are arranged in a line in the main scanning direction XX, and the light beams from the respective light emitting elements 2951 are spot-imaged on the surface of the photosensitive member by the magnifying optical system (optical magnification m> 1). Therefore, in order to reduce the spot SP and increase the resolution, it is necessary to reduce the size of the light emitting element 2951 itself, but it is difficult to secure a sufficient amount of light beam.

  On the other hand, it can be considered that the optical magnification m is less than 1, that is, a reduction optical system is used ((b) in the figure). In this case, the light beam emitted from the large light emitting element 2951 can be imaged to the small spot SP, and the small spot SP can be formed by the light beam having a large amount of light. Furthermore, in this embodiment, since the arrangement of the light emitting elements 2951 is devised as described above, the degree of freedom of arrangement of the light emitting elements 2951 and the degree of freedom of the wiring WL can be increased ((c) in the figure). ). However, as shown in FIG. 3C, when the light emitting elements 2951 arranged in a staggered manner are turned on at the same time, the spots SP formed on the surface of the photoreceptor are also two-dimensionally arranged.

  Therefore, in this embodiment, as shown in FIG. 11, in each of the light emitting element rows L2951, the light emitting elements 2951 constituting the light emitting element row L2951 emit light at a timing according to the rotational movement of the photosensitive drum 21. It is composed. That is, the lighting timing of the upper light emitting element array (FIG. 1A) is different from the lighting timing of the lower light emitting element array (FIG. 1B) corresponding to the rotational movement of the photosensitive drum 21. Therefore, only by this timing adjustment, the spot SP formed by the upper light emitting element array and the spot SP formed by the lower light emitting element array can be formed side by side in the main scanning direction XX. Thus, the spots SP can be formed in a line in the main scanning direction XX by simple light emission timing adjustment.

  FIG. 12 is a diagram showing a spot forming operation by the above-described line head. Hereinafter, the spot forming operation by the line head in this embodiment will be described with reference to FIGS. 2, 7, 11, and 12. In order to facilitate understanding of the invention, here, a case where a plurality of spots are formed side by side on a straight line extending in the main scanning direction XX will be described. In the present embodiment, the head control module 54 causes a plurality of light emitting elements to emit light at a predetermined timing while transporting the surface (scanned surface) of the photosensitive drum 21 (latent image carrier) in the sub-scanning direction YY. A plurality of spots are formed side by side on a straight line extending in the main scanning direction XX.

  That is, in the line head of this embodiment, six light emitting element rows L2951 are arranged side by side in the sub-scanning direction YY corresponding to each position of the sub-scanning direction positions Y1 to Y6 (FIG. 7). Therefore, in this embodiment, the light emitting element rows L2951 at the same sub-scanning direction position emit light at substantially the same timing, and the light emitting element rows L2951 at different sub-scanning direction positions emit light at different timings. More specifically, the light emitting element rows L2951 are caused to emit light in the order of the sub-scanning direction positions Y1 to Y6. A plurality of spots are formed side by side on a straight line extending in the main scanning direction XX of the surface by causing the light emitting element array L2951 to emit light in the order described above while transporting the surface of the photosensitive drum 21 in the sub scanning direction YY. To do.

  Such an operation will be described with reference to FIGS. First, the light emitting elements 2951 of the light emitting element row L2951 in the sub scanning direction position Y1 belonging to the most upstream light emitting element groups 295A1, 295A2, 295A3,. Then, the plurality of light beams emitted by the light emission operation are reduced while being inverted by the microlens ML having the above-described inversion reduction characteristics, and are imaged on the surface of the photoreceptor. That is, a spot is formed at the position of the “first” hatching pattern in FIG. In the figure, white circles represent spots that have not yet been formed and are to be formed in the future. In the same figure, the spots labeled with reference numerals 295C1, 295B1, 295A1, and 295C2 indicate spots formed by the light emitting element groups 295 corresponding to the reference numerals assigned thereto.

  Next, the light emitting elements 2951 of the light emitting element row L2951 in the sub-scanning direction position Y2 belonging to the same light emitting element group 295A1, 295A2, 295A3. Then, the plurality of light beams emitted by the light emission operation are reduced while being inverted by the microlens ML having the above-described inversion reduction characteristics, and are imaged on the surface of the photoreceptor. That is, a spot is formed at the position of the “second” hatching pattern in FIG. Here, while the conveyance direction of the surface of the photosensitive drum 21 is the sub-scanning direction YY, the light emitting element rows L2951 on the downstream side in the sub-scanning direction YY are sequentially arranged (that is, at the positions Y1 and Y2 in the sub-scanning direction). The reason why the light is emitted in order is that the microlens ML has a reversal characteristic.

  Next, the light emitting elements 2951 of the light emitting element row L2951 in the sub scanning direction position Y3 belonging to the second light emitting element group 295B1, 295B2, 295B3,. Then, the plurality of light beams emitted by the light emission operation are reduced while being inverted by the microlens ML having the above-described inversion reduction characteristics, and are imaged on the surface of the photoreceptor. That is, a spot is formed at the position of the “third” hatching pattern in FIG.

  Next, the light emitting elements 2951 of the light emitting element row L2951 in the sub-scanning direction position Y4 belonging to the light emitting element groups 295B1, 295B2, 295B3. Then, the plurality of light beams emitted by the light emission operation are reduced while being inverted by the microlens ML having the above-described inversion reduction characteristics, and are imaged on the surface of the photoreceptor. That is, a spot is formed at the position of the “fourth” hatching pattern in FIG.

  Next, the light emitting elements 2951 of the light emitting element row L2951 in the sub scanning direction position Y5 belonging to the light emitting element groups 295C1, 295C2, 295C3. Then, the plurality of light beams emitted by the light emission operation are reduced while being inverted by the microlens ML having the above-described inversion reduction characteristics, and are imaged on the surface of the photoreceptor. That is, a spot is formed at the position of the “fifth” hatching pattern in FIG.

  Finally, the light emitting elements 2951 of the light emitting element row L2951 in the sub-scanning direction position Y6 belonging to the light emitting element groups 295C1, 295C2, 295C3. Then, the plurality of light beams emitted by the light emission operation are reduced while being inverted by the microlens ML having the above-described inversion reduction characteristics, and are imaged on the surface of the photoreceptor. That is, a spot is formed at the position of the “sixth” hatching pattern in FIG. In this way, by performing the first to sixth light emitting operations, a plurality of spots are formed side by side on a straight line extending in the main scanning direction XX.

  As described above, in this embodiment, in the light emitting element group, a plurality of light emitting elements 2951 are arranged at different positions in the main scanning direction XX, and two light emitting elements that emit light to form adjacent spots. Are arranged at different positions in the sub-scanning direction YY. Then, the light emitting elements 2951 are caused to emit light at timings corresponding to the movement of the photosensitive drum 21 in the sub-scanning direction YY, and the light beams emitted from the light emitting elements 2951 are connected to the surface of the photoreceptor at different positions in the main scanning direction XX. The spots SP are formed side by side in the main scanning direction XX.

  Further, the light beam emitted from the light emitting element 2951 is imaged on the surface of the photoreceptor (scanned surface) by a micro lens (that is, a reduction optical system) ML having an absolute value of magnification of less than 1. This makes it possible to form an image of a light beam emitted from the large light emitting element 2951 into a small spot. That is, a small spot can be formed by a light beam having a large amount of light. Therefore, high resolution can be realized while ensuring a sufficient amount of light beam for spot formation, and good spot formation can be realized even at high resolution. The reason is as follows.

  For example, in the conventional apparatus using the magnifying optical system as shown in FIG. 10A, it is necessary to reduce the diameter of the light emitting element 2951 in order to increase the resolution. However, it is difficult in manufacturing to reduce the element diameter while securing a desired amount of emitted light. Further, the driving of the light emitting element 2951 becomes unstable, and a good spot cannot be formed on the surface of the photoreceptor. In particular, the image forming apparatus is one of the main factors that cause image quality degradation.

  On the other hand, since the apparatus according to the present embodiment uses the microlens ML of the reduction optical system, the diameter of the light emitting element 2951 can be set large. In addition, since the light emitting elements 2951 are arranged in the light emitting element group as described above, the distance between the light emitting elements 2951 can be widened even when the distance between spots formed on the surface of the photoreceptor is small. As described above, (a) the reduction optical system is used, and (b) the arrangement of the light emitting elements 2951 in the light emitting element group is devised to obtain a desired light emission amount in a relatively wide space. A light-emitting element 2951 having a sufficient element diameter can be formed. Therefore, element formation becomes easy. Further, the driving of the light emitting element 2951 can be stabilized, and a favorable spot can be formed on the surface of the photoreceptor. As a result, an excellent image quality toner image can be formed.

  By the way, in this type of line head, spots are formed at predetermined positions on the surface of the photoreceptor (scanned surface) by adjusting the light emission timing of each of the light emitting elements 2951. On the other hand, the line head of this embodiment uses a light emitting element array L2951 configured by arranging a predetermined number (eight) of light emitting elements 2951 at predetermined intervals in the main scanning direction XX. That is, the light-emitting elements 2951 belonging to one light-emitting element array L2951 are configured to have substantially the same position in the sub-scanning direction. Therefore, in the case of using the line head of this embodiment to form spots formed by the light beams emitted from the respective light emitting elements 2951 in the main scanning direction XX, for the light emitting elements 2951 belonging to one light emitting element row L2951. Therefore, it is preferable to apply substantially the same light emission timing, and the light emission timing adjustment can be simplified.

  The image forming apparatus of the present embodiment using the above-described line head forms spots on the surface of the photosensitive member (latent image carrier surface) using the line head. That is, a latent image can be formed by forming a sufficient amount of light beam as a small spot on the surface of the photoreceptor. Therefore, a favorable high resolution image can be realized, which is preferable.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, a plurality of spots are arranged in a straight line in the main scanning direction XX as shown in FIG. 12 by a line head having two light emitting element rows L2951. However, the spot forming operation is an example of the operation of the line head according to the present invention, and the operation that can be executed by the line head is not limited thereto. That is, the formed spots do not need to be formed in a straight line along the main scanning direction XX. For example, the spots may be formed side by side with a predetermined angle in the main scanning direction XX, You may form in a waveform. That is, the two light emitting elements 2951 that emit light to form the adjacent spots SP may be arranged at different positions in the sub-scanning direction YY. In this case, the light emitting element emits light at a timing according to the movement of the scanned surface in the sub-scanning direction, and light beams emitted from the light emitting elements are imaged on the scanned surface at different positions in the main scanning direction. A plurality of spots may be formed side by side in the main scanning direction.

  In the above embodiment, two light emitting element rows L2951 configured by arranging eight light emitting elements 2951 at predetermined intervals in the main scanning direction XX are arranged in the sub scanning direction YY. However, the configuration and arrangement mode of the light emitting element row L2951 (in other words, the arrangement mode of the plurality of light emitting elements) is not limited to this. That is, three light emitting element rows L2951 configured by arranging five light emitting elements 2951 at predetermined intervals in the main scanning direction XX may be arranged in the sub scanning direction YY, or six at a predetermined interval in the main scanning direction XX. Four light emitting element rows L2951 configured by arranging the light emitting elements 2951 may be arranged in the sub-scanning direction YY. The point is that the plurality of light emitting elements 2951 are arranged so that the positions in the main scanning direction XX are different from each other, and two light emitting elements 2951 that emit light to form adjacent spots SP are arranged in the sub scanning direction. What is necessary is just to arrange | position to a mutually different position in YY.

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

  FIG. 13 is a sectional view in the sub-scanning direction of another embodiment of the line head (exposure means) according to the present invention. That is, the line head of FIG. 13 uses LEDs as light emitting elements. The main difference from the line head shown in FIG. 4 using an organic EL as the light emitting element is the location of the light emitting element. That is, as shown in FIG. 4, in a line head using an organic EL as a light emitting element, the light emitting element (light emitting element group 295) is arranged on the back surface of the glass substrate 293. On the other hand, in the line head shown in FIG. 13 using LEDs as the light emitting elements, the light emitting elements are arranged on the surface of the substrate 293. In other configurations, the line heads shown in FIGS. 4 and 13 are common to each other, and thus the same reference numerals are given and description thereof is omitted. In addition, as an arrangement mode of the light emitting elements 2951 in the plane of the substrate 293, the same arrangement mode as in the case of the organic EL can be adopted also in the case of the LED.

  FIG. 14 is a diagram illustrating an imaging state of a microlens array according to another embodiment. That is, this figure is a cross-sectional view showing an imaging state of a line head using LEDs as light emitting elements. In addition, the cut surface in the figure is a cross section when the light emitting element group 295, the glass substrate 293, and the microlens array 299 are cut in the main scanning direction XX so as to include the optical axes OA of the lenses 2993A and 2993B. Further, in the same figure, in order to show the imaging state of the microlens array 299, the light is emitted from the virtual light emitting elements at the geometric center of gravity position E0 of the light emitting element group 295 and at both ends E1, E2 in the main scanning direction of the light emitting element group 295. Represents the trajectory of the emitted light beam. As described above, in a line head using LEDs as light emitting elements, the light emitting elements (light emitting element group 295) are formed on the surface of the substrate 293. Therefore, the light beam emitted from the light emitting element (LED) enters the microlens array 299 without passing through the glass substrate. That is, in a line head using LEDs as light emitting elements, the light emitted from the light emitting elements is directly incident on the microlens array 299 and is imaged on the surface of the photoreceptor (scanned surface) by the microlens array 299. The In this way, in a line head using LEDs, the light beam emitted from the light emitting element does not pass through the substrate 293 on which the light emitting element is disposed. Therefore, the material of the substrate 293 is not limited to a transparent material such as glass.

  As shown in FIG. 14, the light beam emitted from the virtual light emitting element at the geometric gravity center position E0 of the light emitting element group is connected to the intersection point I0 between the surface of the photosensitive drum 21 and the optical axis OA of the lenses 2993A and 2993B. Imaged. 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 virtual light emitting elements at both ends E1 and E2 in the main scanning direction of the light emitting element group 295 are imaged at positions I1 and I2 on the surface of the photosensitive drum 21, respectively. That is, the light beam emitted from the virtual light emitting element at 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 XX, and at the position E2. The light beam emitted from the virtual light emitting element forms an image at a position I2 on the opposite side across the optical axis OA of the lenses 2993A and 2993B in the main scanning direction XX. That is, an optical system (microlens ML) constituted by a lens pair composed of lenses 2993A and 2993B having a common optical axis and a glass substrate 2991 sandwiched between the lens pairs is a so-called reversal optical system.

  As shown in the figure, the distance between the positions I1 and I0 where the light beam is imaged is shorter than the distance between the positions E1 and E0 where the virtual light emitting elements are present. That is, the absolute value of the magnification of the optical system in this embodiment is less than 1. That is, the optical system in this embodiment is a reduction optical system.

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

  Next, examples of the present invention will be shown. However, the present invention is not limited by the following examples as a matter of course, and it is needless to say that the present invention can be implemented with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. These are all included in the technical scope of the present invention. In the following embodiments, specific examples of the microlens ML applicable to the present invention, that is, the microlens ML having an absolute value of magnification of less than 1, will be described.

<First embodiment>
Table 1 shows lens data of the line head in the first example. FIG. 15 is a diagram showing an imaging state of the microlens in the first embodiment. The line head in the first embodiment uses an organic EL as a light emitting element. As described in the above embodiment, the organic EL light emitting element is disposed on the back surface of the glass substrate 293. Therefore, the light emitting surface (surface number S1) of the light emitting element and the back surface (surface number S2) of the glass substrate 293 are opposed to each other with a surface interval of zero.

  The light beam emitted from the position E0 on the object plane is imaged at a position I0 on the surface to be scanned (image plane) via the glass substrate 293 and the microlens ML. The light beam emitted from the position E1 on the object plane is imaged at a position I1 on the surface to be scanned (image plane) via the glass substrate 293 and the microlens ML. Here, both the position E0 and the position I0 are on the optical axis of the microlens ML. As shown in the figure, the distance between the image plane positions I0 and I1 is shorter than the distance between the object plane positions E0 and E1. That is, the absolute value of the magnification of the optical system composed of the glass substrate 293 and the microlens ML is less than 1, specifically 0.5.

<Example 2>
Table 2 shows lens data of the line head in the second example. FIG. 16 is a diagram showing an imaging state of the microlens in the second embodiment. The line head in the second embodiment uses LEDs as light emitting elements. As described in the above embodiment, the LED light emitting element is disposed on the surface of the substrate 293. Therefore, the light beam emitted from the light emitting element enters the microlens ML without passing through the substrate 293.

  The light beam emitted from the position E0 on the object plane is imaged at a position I0 on the surface to be scanned (image plane) via the microlens ML. The light beam emitted from the position E1 on the object plane is imaged at a position I1 on the surface to be scanned (image plane) via the microlens ML. Here, both the position E0 and the position I0 are on the optical axis of the microlens ML. As shown in the figure, the distance between the image plane positions I0 and I1 is shorter than the distance between the object plane positions E0 and E1. That is, the absolute value of the magnification of the optical system including the microlens ML is less than 1, specifically 0.5.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 1. 1 is a perspective view schematically showing an embodiment of a line head according to the present invention. FIG. 3 is a sub-scan sectional view of an embodiment of the line head according to the invention. The perspective view which shows the outline of a microlens array. The main scanning sectional view of a micro lens array. The figure which shows arrangement | positioning of a several light emitting element group. The figure which shows the image formation state of a micro lens array. The figure which shows the detail of arrangement | positioning of a light emitting element. The schematic diagram which shows the relationship between the structure of a light emitting element group, and a spot formation position. The schematic diagram which shows the spot formation operation | movement by the light emitting element group of this embodiment. The figure which shows the spot formation operation | movement by the line head concerning this invention. FIG. 6 is a sub-scan sectional view of another embodiment of the line head according to the invention. The figure which shows the image formation state of the micro lens array in another embodiment. The figure which shows the image formation state of the micro lens in 1st Example. The figure which shows the image formation state of the micro lens in 2nd Example.

Explanation of symbols

  21Y, 21M, 21C, 21K ... photosensitive drum (latent image carrier), 29 ... line head (exposure means), 295 ... light emitting element group, 2951 ... light emitting element, 295L ... light emitting element group row, L2951 ... light emitting element row 293 ... Substrate, glass substrate (microlens), 299 ... microlens array, 2991 ... glass substrate, 2993A, 2993B ... lens (microlens), ML ... microlens, MLA ... microlens array, MLL ... lens array, OA ... optical axis, XX ... main scanning direction, YY ... sub-scanning direction

Claims (7)

A microlens array in which a plurality of microlenses having an absolute value of magnification of less than 1 are arranged in the main scanning direction of the surface to be scanned;
A plurality of light emitting element groups provided in a one-to-one correspondence with the plurality of microlenses,
In each of the plurality of light emitting element groups, the plurality of light emitting elements are arranged at different positions in the main scanning direction,
Each of the plurality of light emitting elements emits light at a timing corresponding to movement of the scanned surface in the sub-scanning direction, and the scanned surface is at a position where light beams emitted from the plurality of light emitting elements are different from each other in the main scanning direction. A plurality of spots that are imaged above are formed side by side in the main scanning direction, and
In each of the plurality of light emitting element groups, among the plurality of light emitting elements constituting the light emitting element group, two light emitting elements that emit light to form adjacent spots are located at different positions in the sub-scanning direction. A line head characterized by being arranged. In each of the plurality of light emitting element groups, the light emitting elements that constitute the light emitting element group by arranging a plurality of light emitting element arrays in which the light emitting elements are arranged in the main scanning direction are arranged in the sub scanning direction of the surface to be scanned. Are arranged in a staggered pattern,
2. The line head according to claim 1, wherein in each of the plurality of light emitting element arrays, the plurality of light emitting elements constituting the light emitting element array emit light at a timing corresponding to movement of the scanned surface in the sub-scanning direction.   The light emitting element groups adjacent to each other in the main scanning direction partially overlap in the main scanning direction, while each light emitting element group includes the light emitting element groups in the main scanning direction among the plurality of light emitting elements constituting the light emitting element group. 3. The line head according to claim 1, wherein a closest light emitting element closest to another light emitting element group adjacent to the light emitting element group is disposed at a position different from the other light emitting element group in the sub-scanning direction.   The plurality of light emitting elements are provided on a substrate, and a drive circuit for driving the plurality of light emitting element groups is further provided on the substrate, and is electrically connected to the plurality of light emitting elements through wiring. Item 4. The line head according to any one of Items 1 to 3.   5. The microlens array according to claim 1, wherein a plurality of lens arrays in which a plurality of the microlenses are arranged in the main scanning direction are arranged in the sub-scanning direction, and the plurality of microlenses are arranged in a staggered manner. The line head according to any one of the above.   The line head according to claim 5, wherein the two light emitting element groups provided corresponding to the microlenses adjacent to each other in the sub-scanning direction partially overlap in the main scanning direction. A latent image carrier whose surface is conveyed in the sub-scanning direction;
A line head for forming a latent image by forming a plurality of spots on the surface of the latent image carrier in a main scanning direction substantially perpendicular to the sub-scanning direction;
Developing means for developing the latent image on the latent image carrier with toner,
The line head has a one-to-one correspondence relationship with a microlens array in which a plurality of microlenses having an absolute value of magnification less than 1 are arranged in the main scanning direction of the surface to be scanned, and the plurality of microlenses. A plurality of light emitting element groups provided, and in each of the plurality of light emitting element groups, the plurality of light emitting elements are arranged at different positions in the main scanning direction, and each of the plurality of light emitting elements is the latent image. A plurality of light beams emitted at timings corresponding to the movement of the carrier in the sub-scanning direction and emitted from the plurality of light emitting elements are formed on the latent image carrier at different positions in the main scanning direction. Are formed side by side in the main scanning direction, and in each of the plurality of light emitting element groups, among the plurality of light emitting elements constituting the light emitting element group, Image forming apparatus characterized by two light-emitting element which emits light to form a spot adjacent to the have are located at different positions in the sub-scanning direction.

Images