JP2008201123A - Printing head and image forming apparatus using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make constant a length ratio between a length between proximate spots and a constant spot pitch. <P>SOLUTION: A diaphragm DH with a center axis nearly coincident with an optical axis OA of an imaging lens is prepared at a front side focal position FP of the imaging lens of a light guide hole 2971. Most of loci LL (for example, a locus LLa and a locus LLb) of a principal ray among loci of a plurality of light beams that pass the diaphragm DH pass a front side focal point F. Therefore, most of the loci LL of the principal ray ejected from the imaging lens become nearly parallel to the optical axis OA of the imaging lens and enter nearly perpendicularly to a surface to be scanned 211. Loci L (for example, a locus L1 and a locus L2, or a locus L3 and a locus L4) of light beams other than the principal ray pass the imaging lens, and consequently converge on the loci LL of the principal ray. The length ratio between the length between proximate spots and the constant spot pitch can be made constant accordingly. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  As a light emitting element having an optical lens that can be used for a print head, for example, a light emitting element described in Patent Document 1 has been proposed. The light emitting element described in Patent Document 1 is formed on an opening on one surface of a substrate on which a light guide hole which is a through hole is formed. An imaging lens, which is an optical lens, is bonded to the opening on the other surface. Here, the light guide holes are columnar holes perpendicular to the one surface and the other surface of the substrate. In the print head using the above-described light emitting element, the light beam emitted from the light emitting element is guided to the imaging lens through the light guide hole, and is imaged by the imaging lens to form a spot on the surface to be scanned.

Japanese Patent Laid-Open No. 2002-170662 (Items 6 to 7, FIG. 8)

  However, in the print head as described above, since the light guide hole is a columnar hole perpendicular to the one surface and the other surface of the substrate, the inner diameter of the light guide hole is constant in the thickness direction. Therefore, the opening on the other surface of the light guide hole that is in contact with the imaging lens, which is an optical lens, serves as a diaphragm that defines the light beam that is directly incident on the imaging lens. In this way, the stop is located closer to the imaging lens than the position of the front focal point of the imaging lens. As a result, of the light beam that passes through the opening (diaphragm) on the other surface of the light guide hole, most of the locus of the principal ray that passes through the center of the light beam of the light beam does not pass through the front focal point. Therefore, most of the trajectory of the chief ray emitted from the imaging lens is not substantially parallel to the optical axis of the imaging lens but enters the surface to be scanned at various angles. Then, the trajectory of the light beam other than the chief ray converges to the chief ray trajectory by passing through the imaging lens. Accordingly, one of the two light emitting elements closest to each other belonging to each of the two light emitting element groups having the smallest group pitch as the length between the imaging lens and the surface to be scanned varies. The ratio of the length between the spot on the scanned surface corresponding to the light emitting element and the length between adjacent spots, which is the length between the spots on the scanned surface corresponding to the other light emitting element, and a constant spot pitch Fluctuates. As a result, there is a problem in that a plurality of spots having different spot pitches and adjacent spot lengths are formed on the surface to be scanned. And in an image forming apparatus using such a print head, there is a problem that an unnecessary shading pattern is likely to occur and the image is likely to deteriorate.

  In order to solve the above problems, a print head according to the present invention includes a plurality of light emitting elements grouped for each light emitting element group, and an optical for imaging a light beam emitted from the light emitting element group on a surface to be scanned. A lens array having a system for each light-emitting element group, and a light-shielding member for each light-emitting element group having a light guide hole for guiding the light beam emitted from the light-emitting element group to the optical system. A stop portion provided at a position and having a central axis that substantially coincides with or coincides with the optical axis of the optical system is provided for each light emitting element group.

  In order to solve the above problems, an image forming apparatus of the present invention includes a latent image carrier whose surface is conveyed in a predetermined conveyance direction, and a print head which forms a latent image on the surface of the latent image carrier. The print head includes, for each light emitting element group, a plurality of light emitting elements grouped for each light emitting element group and an optical system that forms an image of the light beam emitted from the light emitting element group on the latent image carrier. And a light-shielding member provided for each light-emitting element group with a light guide hole for guiding the light beam emitted from the light-emitting element group to the optical system. A stop portion having a central axis substantially coincident with or coincident with the optical axis is provided for each light emitting element group.

  According to the present invention (printing head and image forming apparatus), a diaphragm portion that is provided at the front focal position of the optical system and has a central axis that substantially coincides with or coincides with the optical axis of the optical system is provided for each light emitting element group. ing. As a result, among the trajectories of the plurality of light beams that pass through the aperture, most of the trajectories of the chief rays pass through the front focal point. Therefore, most of the trajectory of the chief ray emitted from the optical system is substantially parallel to the optical axis of the optical system, and the surface to be scanned and the surface of the latent image carrier (hereinafter collectively referred to as “scanned surface”). ) Is incident substantially perpendicularly. Then, the trajectory of the light beam other than the principal ray converges on the trajectory of the principal ray by passing through the optical system. For these reasons, regardless of the variation in the length between the optical system and the surface to be scanned, the two light emitting element groups that belong to each of the two light emitting element groups having the smallest group pitch in the arrangement direction and are closest to each other. A spot on the scanned surface corresponding to one of the light emitting elements, a length between adjacent spots that is a length between spots on the scanned surface corresponding to the other light emitting element, and a predetermined spot pitch It is possible to make the ratio of the lengths constant. As a result, it is possible to form a plurality of spots on the surface to be scanned, in which the spot pitch and the length between adjacent spots are substantially equal.

  Here, the aperture portion may be provided in the light guide hole, whereby the print head can be reduced in size in the optical axis direction of the optical system.

  In addition, it is preferable that the light guide hole has an inner surface that does not block the trajectories of the plurality of light beams in contact with the inner edge of the front aperture portion.

  In this invention, since the inner surface of the light guide hole that does not block the trajectories of the plurality of light beams in contact with the inner edge of the aperture portion is provided, it is possible to avoid the shielding of the plurality of light beams on the inner surface. .

  In the present invention, the light shielding member is preferably a laminate of a plurality of thin plates. When the light shielding member is configured in this way, drilling to a thin plate before stacking is performed in a relatively short time with less processing shape restrictions compared to drilling to a thick plate. A print head provided with a light shielding member provided with light guide holes of various shapes can be obtained relatively easily.

  Moreover, when such a laminated body is used, what provided the opening in one sheet | seat can be used as an aperture | diaphragm | squeeze part. In this case, the thin plate has the functions of the light shielding member and the diaphragm portion, and the number of parts is smaller than in the case where the light shielding member and the diaphragm portion are formed independently, which is advantageous in terms of cost.

  The configuration of the optical system is not particularly limited as long as it has an imaging characteristic that forms an image of the light beam emitted from the light emitting element group on the scanned surface. For example, the optical system may be configured with a single lens or a plurality of lenses. Can be configured. In addition, the lens surface of the optical system that faces the latent image carrier can be a flat surface, thereby preventing particles such as scattered toner from adhering and depositing on the lens surface. Can do. Therefore, the invention configured as described above is preferable because it is possible to suppress the occurrence of the problem (the amount of transmitted light beam is reduced) due to the above-described scattered toner or the like.

  You may comprise so that the cleaning means which cleans the lens surface facing a to-be-scanned surface may be provided. This is because even if particles such as scattered toner adhere to the lens surface facing the surface to be scanned, the attached particles can be removed by the cleaning means.

  You may comprise so that the aperture area of an aperture | diaphragm | squeeze part may become smaller than the light guide hole area by the side of a light emitting element with respect to an aperture stop part, and the light guide hole area by the side of an optical system. As a result, stray light existing in the light guide hole can be blocked to suppress the occurrence of ghost.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a first 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. The image forming apparatus 1 includes 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 black (K) toner. This is an image forming apparatus 1 that can selectively execute a monochrome mode in which a monochrome image is formed using only a monochrome image. FIG. 1 is a diagram corresponding to the execution of the color mode. As shown in FIG. 2, in this image forming apparatus 1, 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 sends a control signal to the engine controller EC. And the video data VD corresponding to the image formation command is supplied to the head controller HC. The head controller HC controls the line head 29 as a print head 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 a copy sheet, a transfer sheet, a sheet, and an OHP transparent sheet.

  As shown in FIG. 1, an electrical component box 5 containing a power circuit board, a main controller MC, an engine controller EC, and a head controller HC is provided in the housing body 3 of the image forming apparatus 1 according to the present embodiment. ing. An image forming unit 7, a transfer belt unit 8, and a paper feeding unit 11 are also disposed in the housing body 3. A secondary transfer unit 12, a fixing unit 13, and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feeding unit 11 is configured to be detachable from the image forming apparatus 1. The sheet feeding unit 11 and the transfer belt unit 8 can be removed and repaired or replaced.

  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 different color images. Each of the image forming stations Y, M, C, and K is provided with a photosensitive drum 21 as a latent image carrier on which the respective color toner images are 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 each photosensitive drum 21 is conveyed in the sub-scanning direction. Further, a charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are arranged around each photoconductor 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, as shown in FIG. 2, a head controller HC is provided to control the line heads 29 for each color, and based on video data VD from the main controller MC and signals from the engine controller EC. Each line head 29 is controlled. 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 control 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. Moves from the developing roller 251 onto the surface of 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 to an arrow D21 that is the rotation direction of the photosensitive drum 21, and then a primary belt in which the transfer belt 81, which will be described in detail later, contacts each photosensitive drum 21. Primary transfer is performed on the transfer belt 81 at the transfer position TR1.

  In this embodiment, the photosensitive drum 21 is in contact with the surface of the photosensitive drum 21 on the downstream side of the primary transfer position TR1 of the arrow D21 that is the rotation direction of the photosensitive drum 21 and on the upstream side of the charging unit 23. 27 is provided. The photoconductor cleaner 27 is in contact with the surface of the photoconductor drum 21 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 (hereinafter also referred to as a blade facing roller 83) disposed on the left side of the driving roller 82 in FIG. And a transfer belt 81 that is circulated and driven in the (conveying direction). 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 85 (85Y, 85M, 85C, 85K) are provided. Each of these primary transfer rollers 85 is electrically connected to a primary transfer bias generator (not shown). As described later in detail, when the color mode is executed, as shown in FIG. 1, all the primary transfer rollers 85 (85Y, 85M, 85C, 85K) are connected to the image forming stations Y, M, C, K side. Is positioned so that the transfer belt 81 is pressed against and brought into contact with the photosensitive drum 21 of each of the image forming stations Y, M, C, and K, and the primary between the photosensitive drum 21 and the transfer belt 81. A transfer position TR1 is formed. 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 surface of each photosensitive drum 21 correspond to each. A color image is formed by transferring to the surface of the transfer belt 81 at the primary transfer position TR1.

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

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed downstream of the monochrome primary transfer roller 85K and upstream of the driving roller 82. Further, the downstream guide roller 86 includes the monochrome primary transfer roller 85K and the photosensitive drum 21 at the primary transfer position TR1 formed by the monochrome primary transfer roller 85K being in contact with the photosensitive drum 21 of the image forming station K. Are configured to abut against the transfer belt 81 on the 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 drive 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, when the sheet enters the contact portion (secondary transfer position TR2) between the driving roller 82 and the secondary transfer roller 121. Is difficult to transmit 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.

  In the image forming apparatus 1, a cleaner unit 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 81 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 schematically showing an embodiment of a print head (line head) according to the present invention. FIG. 4 is a cross-sectional view in the sub-scanning direction of an embodiment of a print head (line head) 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 to be scanned 211 that is the surface of the photosensitive drum 21, and includes a light shielding member 297 and a transparent substrate in the order close to the microlens array 299. A glass substrate 293 is provided. 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 side of the two surfaces of the glass substrate 293). In the present embodiment, an organic EL (Electro-Luminescence) element is used as the light emitting element. That is, the organic EL element is arranged as a light emitting element on the back surface of the glass substrate 293. A light beam emitted from each of the plurality of light emitting elements toward the photosensitive drum 21 is directed to the light shielding member 297 via the glass substrate 293. Here, the light emitting element group 295 of the organic EL elements is formed by utilizing techniques such as thin film formation, photolithography, and precision etching. Therefore, the light emitting element group 295 is excellent in dimensional accuracy between organic EL elements and between organic EL element groups.

  Further, 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 2913 with the elastic force, so that the inside of the case 291 is light-tight (that is, inside the case 291). From the outside of the case 291 so that no light leaks from 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 an exploded perspective view showing an embodiment of the light shielding member before lamination according to the present invention. As shown in FIG. 5, the light shielding member 297 is made of thin plates TP1 to TP8. The thin plates TP1 to TP7 include a plurality of holes TP1a to TP7a penetrating the thin plates TP1 to TP7 around a line parallel to the normal line of the glass substrate 293, and alignment holes AH1 at both ends of the thin plates TP1 to TP7. AH7 (only one end is shown and the other is not shown) is formed one by one. A hole TP4a of one thin plate TP4 in the thin plate is the throttle portion DH. The thin plate TP8 includes an opening OH that passes through the thin plate TP8 with a line parallel to the normal line of the glass substrate 293 as a central axis, and alignment holes AH8 (only one end is illustrated) corresponding to the above-described alignment holes AH1 to AH7. The other end is not shown), but one is formed at each end of the thin plate TP8. The opening OH has an area larger than the area of the region divided by the outermost tangent line CL of the plurality of holes TP7a. By applying the thin plate TP8 having an appropriate thickness, the above-described stop DH is adjusted so as to be at the front focal position of the imaging lens.

  Here, the thin plates TP1 to TP8 are made of metal such as carbon steel or titanium. Further, the processing of shaping the thin plates TP1 to TP8 including the holes TP1a to TP7a and the opening OH can be performed by a press method or an etching method. In the present embodiment, carbon steel is used for the thin plates TP1 to TP8, and the shaping process is performed by a press method. Moreover, the light shielding member 297 which is a laminated body is formed by bonding the thin plates TP1 to TP8 with an adhesive containing a gap agent or the like.

  FIG. 6 is a cross-sectional view of an embodiment of a print head (line head) according to the present invention in a specific direction ZZ shown in FIG. 9 described later. The light guide hole 2971 is formed as a hole penetrating the light shielding member 297 with a line parallel to the normal line of the glass substrate 293 as a central axis. Further, the optical axis OA of the imaging lens substantially coincides with the central axis of the stop DH.

  An example of the locus of the light beam of the most upstream light emitting element 295a that is the most upstream light emitting element belonging to the light emitting element group 295 is a locus L1 that is the locus of the first light beam incident on the most upstream side of the imaging lens. , And a locus L2 that is a locus of the second light beam incident on the most downstream side of the imaging lens. An example of the locus of the light beam of the most downstream light emitting element 295b, which is the most downstream light emitting element belonging to the light emitting element group 295, is the locus of the third light beam incident on the most upstream side of the imaging lens. A locus L3 and a locus L4 that is a locus of the fourth light beam incident on the most downstream side of the imaging lens. An inner edge that is in contact with the locus L1, the locus L2, the locus L3, and the locus L4 for defining the locus L1, the locus L2, the locus L3, and the locus L4 is an inner edge DH1 of the aperture DH. This diaphragm portion DH is at the front focal position FP of the imaging lens between the one surface 2972 and the other surface 2973 of the light shielding member 297. Further, the inner surface 2971A of the light guide hole 2971 does not block the locus L1, the locus L2, the locus L3, and the locus L4.

  An example of the locus LL of the principal ray of the light beam emitted from the most upstream light emitting element 295a and passing through the diaphragm DH is the locus LLa. The locus LLa passes through the front focal point F of the imaging lens and enters the imaging lens. Thereafter, the light exits from the imaging lens, becomes substantially parallel to the optical axis OA of the imaging lens, and enters the position Ia of the scanned surface 211 substantially perpendicularly. And the locus | trajectory L1 and the locus | trajectory L2 which are examples of the locus | trajectory L of light beams other than a principal ray converge on the locus | trajectory LLa by passing through an imaging lens. Thus, the light beam emitted from the most upstream light emitting element 295a is imaged as a spot at the position Ia. An example of the locus LL of the principal ray of the light beam emitted from the most downstream light emitting element 295b and passing through the diaphragm DH is the locus LLb. The locus LLb passes through the front focal point F of the imaging lens and enters the imaging lens. Thereafter, the light is emitted from the imaging lens, and is substantially parallel to the optical axis OA of the imaging lens and enters the position Ib of the scanned surface 211 substantially perpendicularly. The trajectory L3 and the trajectory L4, which are examples of the trajectory L of the light beam other than the principal ray, converge on the trajectory LLb by passing through the imaging lens. Thus, the light beam emitted from the most downstream light emitting element 295b is imaged as a spot at the position Ib.

  FIG. 7 is a perspective view schematically showing the microlens array. FIG. 8 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 each including 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 one-to-one to the plurality of lenses 2993A. 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. In this specification, an optical system including a pair of lenses 2993A and 2993B forming a one-to-one pair and a glass substrate 2991 sandwiched between the pair of lenses is referred to as a “microlens ML”. The plurality of lens pairs (microlenses ML) are two-dimensionally arranged corresponding to the arrangement of the light emitting element groups 295.

  FIG. 9 is a diagram illustrating an arrangement of a plurality of light emitting element groups. In the present embodiment, a light emitting element array L2951 configured by arranging four light emitting elements 2951 in the main scanning direction XX as an example at a constant element pitch DP such as an element pitch DP1, DP2, DP3, DP4 is arranged in the sub scanning direction. Two light emitting element groups 295 are formed by arranging two rows at a constant interval in YY. That is, eight light emitting elements 2951 corresponding to the microlens ML indicated by a two-dot chain line circle in FIG. The plurality of light emitting element groups 295 are arranged as follows.

  That is, two light emitting element groups 295 are arranged such that three light emitting element group rows L295 (group rows) configured by arranging a predetermined number (two or more) of light emitting element groups 295 in the main scanning direction XX are arranged in the sub scanning direction YY. Dimensionally arranged. All the light emitting element groups 295 are arranged at different positions in the main scanning direction. Further, the sub-groups of the light emitting element groups (for example, the light emitting element group 295C1 and the light emitting element group 295B1) in which the group pitch GP in the main scanning direction XX, which is one arrangement direction WW in which the light emitting element groups 295 are arranged, have a minimum length relationship. The plurality of light emitting element groups 295 are arranged so that the positions in the scanning direction are different from each other. Here, each of the element pitches DP is a constant value, and each of the group pitches GP is also a constant value. Note that in this specification, the geometric center of gravity of the light emitting element 2951 is defined as the position of the light emitting element 2951. Therefore, the distance between the two light emitting elements means the distance between the geometric centers of gravity of the respective light emitting elements. Further, in this specification, the “geometric centroid of light emitting element group” means the geometric centroid of all light emitting element positions belonging to the same light emitting element group 295. Further, the position in the main scanning direction XX and the position in the sub scanning direction YY mean the main scanning direction component and the sub scanning direction component of the position of interest, respectively.

  Corresponding to the arrangement of the light emitting element groups 295, a light guide hole 2971 is formed in the light shielding member 297, and a lens pair including 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, the central axis of the diaphragm portion DH, and the optical axis OA of the lens pair configured by the lenses 2993A and 2993B , Are configured to substantially match.

  FIG. 10 is a diagram illustrating an imaging state of the light beam emitted from the light emitting elements of the light emitting element array according to the present embodiment by the microlens array. Also, in the figure, in order to show 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, which are both ends in the left-right direction of the figure separated from the geometric center of gravity E0 by a predetermined interval. Among the light beams emitted from E2, the locus LL of the principal ray is represented by a one-dot chain line, and the locus L of the light beam other than the principal ray is represented by a broken line. As shown by the locus, the light beam emitted from each position is incident from the back surface of the glass substrate 293, passes through the glass substrate 293, and is emitted from the front surface side. The light beam emitted from the surface of the glass substrate 293 reaches the surface of the photosensitive drum 21 (scanned surface 211) via the microlens array 299. Note that the light emitting element at the position E2 and the position I2 correspond to the most upstream light emitting element 295a and the position Ia shown in FIG.

  As shown in FIGS. 8 and 10, the light beam emitted from the geometric center of gravity E0 of the light emitting element group is imaged at the intersection I0 between the surface of the photosensitive drum 21 and the optical axis OA of the lenses 2993A and 2993B. As described above, this is because, in the present embodiment, the geometric center of gravity E0 of the light emitting element group 295 (the position 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 XX, and the light beam emitted from the position E2 is In the main scanning direction XX, an image is formed at a position I2 on the opposite side across the optical axis OA of the lenses 2993A and 2993B. That is, an imaging lens composed of 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 having reversal characteristics.

  Further, as shown in FIG. 10, the distance between the position I1 where the light beam is imaged and the intersection point I0 is longer than the distance between the position E1 and the geometric center of gravity E0. That is, the absolute value of the magnification (optical magnification) of the optical system in the present embodiment is a predetermined multiple greater than 1. That is, the optical system in the present embodiment is a so-called magnifying optical system having magnifying characteristics. As described above, in the present embodiment, the microlens ML, which is an optical system composed of the lens pair including the lenses 2993A and 2993B having the common optical axis OA and the glass substrate 2991 sandwiched between the lens pairs, is It functions as an “optical system” or “imaging lens” in the invention.

  FIG. 11 is a diagram showing a spot forming operation by the above-described line head. Hereinafter, the spot forming operation by the line head and the spots to be formed according to the present embodiment will be described with reference to FIGS. 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, a plurality of light emitting elements 2951 are caused to emit light at a predetermined timing by the head control module 54 while conveying the surface (scanned surface 211) of the photosensitive drum 21 in the sub-scanning direction YY. A plurality of spots are formed side by side on a straight line extending to 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. 9). 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. Then, the light emitting element array L2951 is caused to emit light in the above-described order while conveying the surface (scanned surface 211) of the photosensitive drum 21 in the sub-scanning direction YY, so that the surface of the photosensitive drum 21 extends in the main scanning direction XX. A plurality of spots are formed side by side.

  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,. The plurality of light beams emitted by the light emission operation are enlarged by a predetermined magnification while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics, and the surface of the photosensitive drum 21 (scanned surface 211). Is imaged. 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 the light emitting element groups 295C1, 295B1, 295A1, and 295C2 are 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 light emitting element groups 295A1, 295A2, 295A3,. The plurality of light beams emitted by the light emission operation are enlarged by a predetermined magnification while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics, and are imaged on the surface of the photosensitive drum 21. 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 (scanned surface 211) is the sub-scanning direction YY, the light emitting element array L2951 on the upstream side in the sub-scanning direction YY is sequentially (that is, sub-scanning). The reason for emitting light (in the order of the directional positions Y1 and Y2) is to respond to the “imaging lens” having reversal characteristics.

  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,... From the most upstream side in the sub scanning direction YY are caused to emit light. The plurality of light beams emitted by the light emission operation are enlarged by a predetermined magnification while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics, and the surface of the photosensitive drum 21 (scanned surface 211). Is imaged. 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 array L2951 in the sub-scanning direction position Y4 belonging to the light emitting element groups 295B1, 295B2, 295B3,. The plurality of light beams emitted by the light emission operation are enlarged by a predetermined magnification while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics, and the surface of the photosensitive drum 21 (scanned surface 211). Is imaged. 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 array L2951 in the sub scanning direction position Y5 belonging to the light emitting element groups 295C1, 295C2, 295C3,. The plurality of light beams emitted by the light emission operation are enlarged by a predetermined magnification while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics, and the surface of the photosensitive drum 21 (scanned surface 211). Is imaged. 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,. The plurality of light beams emitted by the light emission operation are enlarged by a predetermined magnification while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics, and the surface of the photosensitive drum 21 (scanned surface 211). Is imaged. 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.

  Each of the spot pitches SP1, SP2, and SP3, which are examples of the spot pitch SP in the main scanning direction XX of the surface (scanned surface 211) of the photosensitive drum 21 shown in FIG. 11, is an element pitch DP shown in FIG. Each of the pitches DP1, DP2 and DP3 is a predetermined multiple. Further, each of the light-emitting element group 295C1 and the light-emitting element group 295B1, the light-emitting element group 295B1 and the light-emitting element group 295A1, the light-emitting element group 295A1 and the light-emitting element group 295C2 is arranged in the same manner as shown in FIG. The light emitting element groups having the shortest group pitch GP in the main scanning direction XX which is the direction WW. Further, in the light emitting element groups having the shortest group pitch relationship, the light emitting elements adjacent to each other in the relationship between the most downstream light emitting element in one light emitting element group and the most upstream light emitting element in the other light emitting element group The element C1b, the light emitting element B1a, the light emitting element B1b, the light emitting element A1a, the light emitting element A1b, and the light emitting element C2a. An example of the inter-proximity element length DD, which is the length between the above-mentioned adjacent light-emitting elements, is the inter-proximity element length DD1, DD2, DD3. The values of the predetermined multiples of the inter-proximity element lengths DD1, DD2, and DD3 are inter-proximity spot lengths SD1, SD2, and SD3, which are examples of the inter-proximity spot length SD shown in FIG. Here, the spot pitches SP1, SP2, SP3 and the adjacent spot lengths SD1, SD2, SD3 are substantially equal in length.

  In the above-described embodiment, the following effects can be obtained.

  (1) Since the front focal position FP of the imaging lens in the light guide hole 2971 is provided with a diaphragm DH having a central axis substantially coincident with the optical axis OA of the imaging lens, it passes through the diaphragm DH. Among the trajectories of the plurality of light beams, most of the principal ray trajectories LL (for example, the trajectory La and the trajectory Lb) pass through the front focal point F. Therefore, most of the locus LL of the principal ray emitted from the imaging lens is substantially parallel to the optical axis OA of the imaging lens and is incident on the scanned surface 211 substantially perpendicularly. The trajectory L (for example, the trajectory L1 and the trajectory L2 or the trajectory L3 and the trajectory L4) of the light beam other than the chief ray converges on the chief ray trajectory LL by passing through the imaging lens. For these reasons, regardless of the variation in the length between the imaging lens and the surface to be scanned 211, the group pitch GP belongs to each of the two light emitting element groups 295 having the smallest relationship, and the two closest to each other. The adjacent spot length SD, which is the length between the spot on the scanned surface 211 corresponding to one of the light emitting elements and the spot on the scanned surface 211 corresponding to the other light emitting element; The ratio of the length to the constant spot pitch SP can be made constant. As a result, a plurality of spots in which the spot pitch SP and the length SD between adjacent spots are substantially equal can be formed on the scanned surface 211.

  (2) By providing the inner surface 2971A of the light guide hole 2971 that does not block the trajectories of the plurality of light beams in contact with the inner edge DH1 of the aperture section DH, the light shielding of the plurality of light beams on the inner surface 2971A is avoided. Can do.

  (3) Since the light shielding member 297 is a laminated body of a plurality of thin plates TP, the drilling processing to the thin plates TP before stacking has fewer restrictions on the processing shape compared to the drilling processing to thick plates. Since it is carried out in a relatively short time, the line head 29 as a print head provided with the light shielding member 297 provided with the light guide holes 2971 of various shapes can be relatively easily obtained.

  (4) Since the front focal position FP of the imaging lens in the light guide hole 2971 is provided with a diaphragm DH having a central axis substantially coinciding with the optical axis OA of the imaging lens, it passes through the diaphragm DH. Among the trajectories of the plurality of light beams, most of the principal ray trajectories LL (for example, the trajectory La and the trajectory Lb) pass through the front focal point F. Therefore, most of the locus LL of the principal ray emitted from the imaging lens is substantially parallel to the optical axis OA of the imaging lens and is incident on the scanned surface 211 substantially perpendicularly. The trajectory L (for example, the trajectory L1 and the trajectory L2 or the trajectory L3 and the trajectory L4) of the light beam other than the chief ray converges on the chief ray trajectory LL by passing through the imaging lens. For these reasons, regardless of the variation in the length between the imaging lens and the surface to be scanned 211, the group pitch GP belongs to each of the two light emitting element groups 295 having the smallest relationship, and the two closest to each other. A spot on the scanned surface 211 corresponding to one of the light emitting elements, a length SD between adjacent spots on the scanned surface 211 corresponding to the other light emitting element, and a constant spot pitch SP. The length ratio can be made constant. As a result, a plurality of spots in which the spot pitch SP and the adjacent spot length SD have substantially the same length can be formed on the scanned surface 211. In the image forming apparatus 1 using such a line head 29 as an exposure unit, the occurrence of unnecessary shading patterns is reduced, and the image can be hardly deteriorated.

  (5) An image that avoids the shielding of the plurality of light beams on the inner surface 2971A by providing the inner surface 2971A of the light guide hole 2971 that does not block the trajectories of the plurality of light beams that are in contact with the inner edge DH1 of the aperture section DH. The forming apparatus 1 can be obtained.

  (6) Since the light shielding member 297 is a laminated body of a plurality of thin plates TP, the drilling of the thin plate TP before stacking has less restrictions on the processing shape compared to the drilling processing of the thick plate. Since it is carried out in a relatively short time, the image forming apparatus 1 including the light shielding member 297 provided with the light guide holes 2971 having various shapes can be provided relatively easily.

  (7) As shown in FIG. 6, the aperture area of the diaphragm DH is the light guide hole area on the light emitting element side (lower side of the figure) and the optical system side (upper side of the figure) with respect to the diaphragm part DH It is configured to be smaller than the light guide hole area. As a result, stray light existing in the light guide hole is blocked, and generation of ghost can be suppressed.

  As a specific example of a line head (printing head) having such effects, lenses having lens data shown in Table 1 can be used. The surface numbers S1 to S6 in the table will be described with reference to FIG. The surface number S1 corresponds to the object surface, that is, the back surface of the glass substrate 293 on which the light emitting element 2951 is arranged. The surface number S2 corresponds to the surface of the glass substrate 293. The surface number S3 corresponds to the aperture portion DH. As described above, the diaphragm DH is disposed at the front focal point F of the imaging lens ML, and image-side telecentricity is realized. The surface number S4 corresponds to the first surface MLf of the imaging lens ML. The surface number S5 corresponds to the second surface MLs of the imaging lens ML. The surface number S6 corresponds to the surface to be scanned 211, that is, the surface of the photosensitive drum (latent image carrier). Here, the sum of the surface intervals from surface numbers S1 to S3 gives the lens position. Further, the surface distance of the surface number S4 gives the lens thickness.

  Table 2 shows the aspheric coefficients of the aspheric surfaces S4 and S5. Equation 1 is an expression that gives an aspherical shape. That is, the shapes of the aspheric surfaces S4 and S5 (in other words, the lens shape of the imaging lens ML) are determined by Table 2 and Equation 1.

  Table 3 shows the specifications of the optical system used in the specific examples. Here, the wavelength is the wavelength of the light beam emitted from the light emitting element. The lens diameter is the diameter of the exit surface of the imaging lens ML, that is, the second surface MLs. The light source diameter is the diameter of the light emitting element 2951. Further, the object height of 0.6 mm in the same specification means that the simulation was performed under the condition that the light beam was emitted from the virtual light emitting element having the object height of 0.6 mm. At this time, since the magnification is −0.5, the image height is −0.3 mm.

(Second Embodiment)
FIG. 12 is a diagram showing a second embodiment of the print head (line head) according to the present invention, and more specifically, one modification of the print head (line head) according to the present invention in the specific direction ZZ shown in FIG. It is sectional drawing of an example. Thus, the second embodiment will be described. However, the same contents as those of the embodiment will be omitted, and different contents will be described. As shown in FIG. 12, the light shielding member 297 includes thin plates TP1 to TP8 (TP8 is not shown). The holes TP1b to TP3b of the thin plates TP1 to TP3 have substantially the same size as the holes TP4b of the thin plate TP4. In the image forming apparatus 1 including the line head 29 provided with the light shielding member 297 provided with the inner surface 2971B having the shape shown in this modification and the exposure unit having the same configuration as the line head 29, the same effects as in the first embodiment are provided. The effect is obtained.

(Third embodiment)
FIG. 13 is a diagram showing a third embodiment of the print head (line head) according to the present invention. More specifically, FIG. 13 shows another print head (line head) according to the present invention in the specific direction ZZ shown in FIG. It is sectional drawing of a modification. Thus, the third embodiment will be described. However, the same contents as those of the first embodiment and the second embodiment will be omitted, and different contents will be described. As shown in FIG. 13, the holes TP2c and TP1c of the thin plates TP2 and TP1 are sequentially smaller than the hole TP4c of the thin plate TP4. The hole TP3c of the thin plate TP3 is the same as the hole TP4c of the thin plate TP4. Further, the holes TP5c to TP7c of the thin plates TP5 to TP7 are sequentially larger than the holes TP4c of the thin plate TP4. In the image forming apparatus 1 including the line head 29 provided with the light shielding member 297 provided with the inner surface 2971C having the shape shown in this modification and the exposure unit having the same configuration as the line head 29, the first embodiment and the second embodiment. The same effect as the effect in the form can be obtained.

(Fourth embodiment)
FIG. 14 is a diagram showing a fourth embodiment of a print head (line head) according to the present invention. Thus, although the fourth embodiment will be described, the same content as the first embodiment and the second embodiment will be omitted, and different content will be described. In the fourth embodiment, as shown in FIG. 14, the microlens array 299 has a configuration in which two lens arrays 299A and 299B are combined. That is, in the lens array 299A, the lens ML1 is provided for each light emitting element group on the light source side surface (the lower surface in the figure) of the glass substrate. On the other hand, in the lens array 299B, the lens ML2 is provided for each light emitting element group on the light source side surface (the lower surface in the figure) of the glass substrate. An imaging lens ML is configured by the lenses ML1 and ML2 corresponding to each light emitting element group. That is, the imaging lens ML has a function of forming an image of the light beam emitted from the light emitting element on the scanned surface 211 (the surface of the photosensitive drum 21) by combining two plano-convex lenses. In this respect, the imaging lens (optical system) is greatly different from the first to third embodiments in which a single lens is used.

  The light shielding member 297 is made of thin plates TP1 to TP10. These thin plates TP1 to TP10 are aligned with both ends of the plurality of holes TP1a to TP10a penetrating the thin plates TP1 to TP10 with a line parallel to the normal line of the glass substrate 293 as the central axis, and the thin plates TP1 to TP10. One hole (not shown) is formed one by one. A hole TP7a of one thin plate TP7 in the thin plate is the throttle portion DH. In addition, the hole TP10a of the thin plate TP10 closest to the optical system (microlens array 299) among the thin plates has the same or slightly larger diameter as the lens ML1, and the microlens array 299 is fitted into the lens ML1. The light blocking member 297 and the microlens array 299 are positioned in the optical axis direction and the direction orthogonal to the optical axis.

  In this embodiment, the holes TP1a to TP6a formed in the thin plates TP1 to TP6 positioned on the light emitting element side with respect to the diaphragm portion DH all have the same diameter. A side light guide hole "is configured. On the other hand, the holes TP8a to TP10a formed in the thin plates TP8 to TP10 positioned on the optical system (microlens array 299) side with respect to the diaphragm DH all have the same diameter, and thus the “optical” of the present invention. A system-side light guide hole "is configured. When the area of the light guide hole thus formed is compared with the opening area of the diaphragm DH, the aperture area of the diaphragm DH is smaller than the light guide hole area on the light emitting element side and the light guide hole area on the optical system side. Yes. In addition, by optimizing the number and thickness of the thin plates TP8 to TP10, the above-described stop portion DH is adjusted to be the front focal position of the imaging lens ML.

  As an example of the fourth embodiment configured as described above, a lens having lens data shown in Table 4 can be used. The surface numbers S1 to S7 in the table will be described with reference to FIG. The surface number S1 corresponds to the object surface, that is, the back surface of the glass substrate 293 on which the light emitting element 2951 is arranged. The surface number S2 corresponds to the aperture portion DH. As described above, the diaphragm DH is disposed at the front focal point F of the imaging lens ML, and image-side telecentricity is realized. The surface number S3 corresponds to the first surface ML1f of the first lens ML1. The surface number S4 corresponds to the second surface ML1s of the first lens ML1. The surface number S5 corresponds to the first surface ML2f of the second lens ML2. The surface number S6 corresponds to the second surface ML2s of the second lens ML2. The surface number S7 corresponds to the surface to be scanned 211, that is, the surface of the photosensitive drum (latent image carrier).

  As is apparent from the table, the lenses ML1 and ML2 are both plano-convex lenses, and the lens surfaces S3 and S5 are aspherical surfaces. Table 5 shows the aspheric coefficients of the lens surfaces S3 and S5. Equation 1 is an equation that gives an aspherical shape. That is, the shapes of the aspheric surfaces S3 and S5 (in other words, the lens shape of the imaging lens ML) are determined by Table 5 and Equation 1.

  Table 6 shows the specifications of the optical system used in the specific examples. Here, the wavelength is the wavelength of the light beam emitted from the light emitting element. The number of rows in which lenses are arranged in the arrangement direction WW, that is, the number of lens rows is three as in the case shown in FIG. In the same specification, the object height of 0.2 mm means that the simulation was performed under the condition that the light beam was emitted from the virtual light emitting element having the object height of 0.2 mm. At this time, since the magnification is −0.5, the image height is −0.4 mm. Further, the maximum field angle is 4.46 °, and the optical path length is 9.815 mm.

  In the fourth embodiment configured as described above, the same function and effect as in the first embodiment can be obtained. In addition, in the present embodiment, the surface S6 of the microlens array 299 that faces the surface of the photosensitive drum is a flat surface, so that the following effects can be further obtained. That is, adhesion and accumulation of scattered toner on the surface of the microlens array 299 is suppressed. Therefore, the line head 29 configured as described above is preferable because it is possible to suppress the occurrence of problems caused by the scattered toner. Further, after configuring the line head 29 in this way, the following cleaning mechanism (cleaning means) may be provided.

(Fifth embodiment)
FIG. 16 is a perspective view of the cleaning mechanism. The cleaning mechanism 60 cleans the surface of the microlens array 299 on the photosensitive drum surface side. Specifically, the cleaning mechanism 60 includes a cleaning pad 601 and a handle portion 602. The material of the cleaning pad 601 is artificial leather. Here, EXSEINE (registered trademark) manufactured by Toray Industries, Inc. can be used as the artificial leather. Further, the cleaning pad 601 and the handle portion 602 are connected by a connecting member 603. Further, a hollow portion 6031 is formed in the connection member 603.

  FIG. 17 is a diagram illustrating a cleaning operation by the cleaning mechanism. As shown in the figure, the cleaning mechanism 60 is arranged with respect to the line head 29 so that the extending direction of the connecting member 603 is parallel to the main scanning direction XX. Further, the cleaning pad 601 is in contact with the surface S6 of the microlens array 299 on the photosensitive drum surface side (latent image carrier surface side). When the operator moves the handle portion 602 in the longitudinal direction, the cleaning pad 601 moves in a direction corresponding to the main scanning direction XX while being in contact with the surface S6. Therefore, the scattered toner adhering to the lens surface S6 is scraped off and removed by the cleaning pad 601.

  As described above, the configuration further including the cleaning mechanism 60 cleans the toner adhering to the lens surface S6 even if the scattered toner adheres to the transparent member surface on the photosensitive drum surface side of the microlens array 299. It can be removed by the mechanism 60, which is preferable.

  In addition, this invention is not limited to the above-mentioned embodiment and modification, A various change other than the above-mentioned content is possible unless it deviates from the main point. In the embodiment and the modification described above, a plurality of light emitting element groups 295 including a plurality of light emitting elements 2951 are arranged as shown in FIG. As an example, four light emitting elements 2951 in the main scanning direction XX are arranged at a constant element pitch DP such as element pitches DP1, DP2, DP3, and two light emitting element rows L2951 are arranged at constant intervals in the sub scanning direction YY. One light emitting element group 295 is formed side by side. That is, eight light emitting elements 2951 corresponding to the microlens ML indicated by a two-dot chain line circle in FIG. However, the number of the light emitting elements 2951 constituting the light emitting element group 295, the number of the light emitting element rows L2951, and the arrangement of the plurality of light emitting elements 2951 and the plurality of light emitting element rows L2951 are not limited thereto, and can be appropriately changed. is there. However, as described above, the arrangement of the plurality of light emitting elements 2951 is preferable in that good spot formation can be easily realized by adopting the symmetrical arrangement.

  Further, as shown in FIG. 9, the plurality of light emitting element groups 295 are arranged as follows. That is, two light emitting element groups 295 are arranged such that three light emitting element group rows L295 (group rows) configured by arranging a predetermined number (two or more) of light emitting element groups 295 in the main scanning direction XX are arranged in the sub scanning direction YY. Dimensionally arranged. However, the arrangement of the plurality of light emitting element groups 295 is not limited to this and can be changed as appropriate.

  Moreover, in the above-mentioned embodiment and modification, although the light emitting element 2951 was an organic EL element, it is not limited to this, A light emitting diode other than an organic EL element may be sufficient.

  In the above-described embodiment and modification, the plurality of light-emitting elements 2951 and the plurality of light-emitting element groups 295 are formed on the back surface of the glass substrate 293. However, the present invention is not limited to this and depends on the type of the light-emitting elements 2951. Then, it may be formed on the surface of the glass substrate 293. Further, when the plurality of light emitting elements 2951 and the plurality of light emitting element groups 295 are formed on the surface of the substrate, a substrate made of metal or ceramic other than the glass substrate may be used.

  In the above-described embodiment and modification, the inner surfaces 2971A, 2971B, and 2971C have the shapes shown in FIGS. 6, 12, or 13, but the inner surface is not limited to this, and the inner edge DH1 of the throttle portion DH. It is sufficient that the trajectory of the light beam in contact with is not obstructed, and can be changed as appropriate.

  In the above-described embodiments and modifications, the magnifying optical system is employed as the imaging lens, but this is not an essential requirement for the present invention. That is, a reduction optical system having a magnification (optical magnification) of less than 1 or a 1 × optical system having a magnification of approximately 1 may be used as the imaging lens.

  In the above-described embodiment and modification, the present invention is applied to the image forming apparatus 1 for color image formation. However, the application target of the present invention is not limited to this, and a so-called single-color image is formed. The present invention can also be applied to an image forming apparatus for forming a monochrome image.

1 is a diagram illustrating a first 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. The perspective view which shows the outline of 1st Embodiment of a print head (line head). FIG. 3 is a cross-sectional view in the sub-scanning direction showing the first embodiment of the print head (line head). The disassembled perspective view which shows one Embodiment of the light shielding member before lamination | stacking. Sectional drawing which shows 1st Embodiment of the printing head (line head) of the specific direction ZZ. The perspective view which shows the outline of a microlens array. Sectional drawing of the main scanning direction 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 by a micro lens array. The figure which shows the spot formation operation | movement by a line head. The figure which shows 2nd Embodiment of the printing head (line head) concerning this invention. The figure which shows 3rd Embodiment of the print head (line head) concerning this invention. The figure which shows 4th Embodiment of the print head (line head) concerning this invention. The figure which shows the image formation state by a micro lens array. The perspective view of a cleaning means. The figure which shows the cleaning operation | movement by the cleaning means.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 21 ... Photosensitive drum as a latent image carrier, 211 ... Scanned surface, 60 ... Cleaning means, XX ... Main scanning direction, YY ... Sub-scanning direction, 29 ... Line head (printing head) Head), 295 ... light emitting element group, 2951 ... light emitting element, L2951 ... light emitting element array, WW ... arrangement direction, DP, DP1, DP2, DP3, DP4 ... element pitch, GP ... group pitch, SP ... spot pitch, ML ... Microlens (imaging lens), OA ... optical axis (center axis of diaphragm), FP ... front focal position, 297 ... light shielding member (laminate), 2971 ... light guide hole, 2971A, 2971B, 2971C ... inner surface, 2972 ... One side, 2973 ... The other side, DH ... Restriction, DH1 ... Inner edge, TP1, TP2, TP3, TP4, TP5, TP6, TP7, TP8 ... Thin plate, L , LLa, LLb ... locus of the principal ray of the light beam, L, L1, L2, L3, L4 ... trajectory of light beams other than the principal ray of the light beam.

Claims (20)

A plurality of light emitting elements provided in groups for each light emitting element group;
A lens array having, for each light emitting element group, an optical system that forms an image of a light beam emitted from the light emitting element group on a scanned surface;
A light guide hole for guiding the light beam emitted from the light emitting element group to the optical system, and a light shielding member provided for each light emitting element group,
A print head, wherein a stop portion provided at a front focal position of the optical system and having a central axis that substantially coincides with or coincides with the optical axis of the optical system is provided for each light emitting element group. The print head according to claim 1.
The print head according to claim 1, wherein the aperture is provided in the light guide hole. The print head according to claim 1 or 2,
The print head according to claim 1, wherein the light guide hole has an inner surface that does not block a trajectory of the plurality of light beams in contact with an inner edge of the aperture portion. The print head according to any one of claims 1 to 3,
The print head, wherein the light shielding member is a laminate of a plurality of thin plates. The print head according to claim 4.
The print head according to claim 1, wherein the aperture portion has an opening in one of the plurality of thin plates. The print head according to any one of claims 1 to 5,
The print head according to claim 1, wherein the optical system is a single lens. The print head according to any one of claims 1 to 5,
The print head according to claim 1, wherein the optical system includes a plurality of lenses. The print head according to claim 6 or 7,
The print head according to claim 1, wherein the lens surface of the optical system that faces the scanned surface is a flat surface. The print head according to claim 8.
A printing head comprising a cleaning means for cleaning a lens surface facing the surface to be scanned. The print head according to any one of claims 1 to 9,
An opening area of the diaphragm portion is smaller than the light guide hole area on the light emitting element side and the light guide hole area on the optical system side with respect to the diaphragm portion. The print head according to claim 10.
The print head, wherein the light guide hole area on the light emitting element side is smaller than the light guide hole area on the optical system side. A latent image carrier whose surface is conveyed in a predetermined conveyance direction;
A print head for forming a latent image on the surface of the latent image carrier,
The print head is
A plurality of light emitting elements provided in groups for each light emitting element group;
A lens array having, for each light emitting element group, an optical system that images the light beam emitted from the light emitting element group onto the latent image carrier;
A light guide hole for guiding the light beam emitted from the light emitting element group to the optical system, and a light shielding member provided for each light emitting element group,
2. An image forming apparatus according to claim 1, wherein a stop portion provided at a front focal position of the optical system and having a central axis substantially coinciding with or coincident with the optical axis of the optical system is provided for each light emitting element group. The image forming apparatus according to claim 12.
The image forming apparatus, wherein the aperture is provided in the light guide hole. The image forming apparatus according to claim 12 or 13,
The image forming apparatus according to claim 1, wherein the light guide hole has an inner surface that does not block a trajectory of the plurality of light beams in contact with an inner edge of the aperture portion. The image forming apparatus according to any one of claims 12 to 14,
The image forming apparatus, wherein the light shielding member is a laminate of a plurality of thin plates. The image forming apparatus according to any one of claims 12 to 15,
The image forming apparatus, wherein the optical system is a single lens. The image forming apparatus according to any one of claims 12 to 15,
The image forming apparatus, wherein the optical system includes a plurality of lenses. The image forming apparatus according to claim 16 or 17,
An image forming apparatus, wherein a lens surface facing the latent image carrier among the lens surfaces of the optical system is a flat surface. The image forming apparatus according to claim 18.
An image forming apparatus comprising: cleaning means for cleaning a lens surface facing the latent image carrier. The image forming apparatus according to any one of claims 12 to 19,
2. An image forming apparatus according to claim 1, wherein an aperture area of the aperture portion is smaller than the light guide hole area on the light emitting element side and the light guide hole area on the optical system side with respect to the aperture portion.

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