JP2008036939A - Line head and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-resolution and compact line head and an image forming apparatus equipped with the line head. <P>SOLUTION: A plurality of light emitting element groups 295 are arranged in two dimensions, and light beams emitted from each light emitting element group 295 are imaged on a photoreceptor drum surface (face to be scanned) by a micro-lens (imaging lens) ML of an enlarging optical system. An arrangement interval of the light emitting element groups 295 at a substrate 293 is widened, so that a relatively wide clearance region AR is formed. A driving circuit D295 and a wiring line WL are arranged in each clearance region AR. Full driving circuit space and wiring line space can be secured on the substrate 293 without increase of a substrate size even if the number of light emitting elements 2951 is increased to enhance the resolution. <P>COPYRIGHT: (C)2008,JPO&INPIT

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, one using a plurality of organic EL (electroluminescence) elements has been proposed, as described in Patent Document 1, for example. In such a line head, a plurality of organic EL elements are arranged on a chip-on-board substrate, and a plurality of driver ICs (corresponding to the “driving circuit” of the present invention) are arranged apart from the formation region of the organic EL elements. Has been. The chip-on-board substrate and the driver IC and the driver IC and the organic EL element are electrically connected by bonding wires.

Japanese Patent Laid-Open No. 9-226171 (FIG. 1)

  However, in the line head of Patent Document 1, a plurality of organic EL elements and a driver IC are separately disposed on a chip-on-board substrate, and bonding wires are electrically connected therebetween. For this reason, the mounting area of an organic EL element, a driver IC, etc. has become large. Further, in recent years, the number of organic EL elements to be mounted on a substrate in order to increase the resolution has dramatically increased, and accordingly, the number of driver ICs to be mounted also increases. For this reason, the mounting space of the driver IC is reduced, and there is a problem that a sufficient driving current for driving the organic EL element cannot be obtained. Furthermore, it has become difficult to secure wiring space due to the increase in organic EL elements and driver ICs. As a result, due to these factors, it is difficult to satisfy simultaneously the miniaturization and high resolution of the line head.

  The present invention has been made in view of the above problems, and an object thereof is to provide a high-resolution, small-sized line head and an image forming apparatus equipped with the line head.

  The line head according to the present invention forms an image of a light beam emitted from a plurality of light emitting elements formed on a substrate on a surface to be scanned that is conveyed in the sub scanning direction by an imaging optical system, and is substantially orthogonal to the sub scanning direction. A line head for forming a latent image in a line extending in the main scanning direction, and a drive circuit provided on a substrate for driving a plurality of light emitting elements, a drive circuit and a plurality of light emitting elements, in order to achieve the above object A plurality of light emitting element groups that are separated from each other in the main scanning direction and have a light emitting element row in which two or more light emitting elements are arranged in the main scanning direction. A plurality of light emitting element groups are two-dimensionally arranged with a plurality of group lines spaced apart from each other in the sub-scanning direction, and the imaging optical system has a one-to-one correspondence with the plurality of light emitting element groups. Set up And a plurality of imaging lenses having an optical magnification exceeding 1, each of the plurality of imaging lenses images a light beam emitted from a corresponding light emitting element group at the optical magnification, and all of the wiring Alternatively, a part is arranged between a plurality of light emitting element groups on the substrate.

  In the invention configured as described above, a plurality of light emitting element groups are two-dimensionally arranged, and an imaging lens is arranged corresponding to each light emitting element group. That is, the same number of imaging lenses as the light emitting element groups are provided, and the plurality of light emitting element groups and the plurality of imaging lenses are arranged in a one-to-one correspondence relationship. When a light beam is emitted from the light emitting elements constituting each light emitting element group, the light beam is imaged on the surface to be scanned by the imaging lens corresponding to the light emitting element group to form a spot. Thus, by arranging the light emitting element groups two-dimensionally, the interval between the adjacent light emitting element groups becomes wider than when the light emitting element groups are arranged linearly. Moreover, in the present invention, the imaging lens has an optical magnification exceeding 1, that is, a magnifying optical system. For this reason, the arrangement | positioning space | interval of the light emitting element group in a board | substrate has expanded. Wirings are arranged between these light emitting element groups. Therefore, even if the number of light emitting elements is increased in order to increase the resolution, a sufficient wiring space can be ensured on the substrate without increasing the substrate size. Therefore, it is possible to satisfy both the miniaturization and the high resolution of the line head at the same time.

  Further, a part or all of the drive circuit may be disposed in a gap region surrounded by a plurality of light emitting element groups adjacent to each other. Thus, by arranging the drive circuit in the gap region, the size of the line head can be further reduced. Here, the gap region has an inter-group region sandwiched between two light emitting element groups adjacent to each other in the group row. Therefore, a circuit for driving a light emitting element constituting a group column adjacent to the group column in the drive circuit may be arranged in the inter-group region. By disposing the driving circuit in this manner, the distance from the light emitting element driven by the driving circuit is reduced, and the wiring space can be efficiently used. As a result, the line head can be further reduced in size and resolution.

  In addition, a control signal line that transmits a control signal for controlling the light emitting element may be connected to the drive circuit. In this case, it is preferable to extend the control signal line in the main scanning direction between adjacent group columns. By adopting such a wiring structure, the control signal line can be made the shortest, and the wiring space for wiring the control signal line can be narrowed, which greatly contributes to miniaturization and high resolution of the line head. is there.

  In addition, a drive circuit may be provided adjacent to an element formation zone in which a plurality of light emitting element groups are provided. By adopting such an arrangement structure, the distance between the light emitting element and the drive circuit is shortened, and the line head can be further reduced in size and resolution.

  An LED (Light Emitting Diode) or the like can be used as the light emitting element, but the usefulness of the present invention is particularly conspicuous when a bottom emission type organic EL element is used as the light emitting element. This is because in this organic EL element, a transparent substrate such as glass is used as a substrate, and a light emitting element is formed on the back side of the transparent substrate. The light beam emitted from the light emitting element passes through the transparent substrate and travels from the substrate surface toward the imaging lens. Therefore, it is not allowed that the light emitting element overlaps with the wiring or the driving circuit in plan view. This is because such a restriction on the arrangement structure is one of the main factors that increase the size of the line head. On the other hand, in the present invention, it is possible to reduce the size of the line head while satisfying such restrictions.

  In addition, for each of the plurality of light emitting element groups, a plurality of light emitting element rows may be arranged in a two-dimensional manner with a plurality of light emitting element rows spaced apart in the sub-scanning direction. As a result, the interval between the light-emitting elements constituting the light-emitting element array is widened, and the degree of freedom with respect to the arrangement of wiring and drive circuits in the gap region is increased.

  Furthermore, in order to achieve the above object, an image forming apparatus according to the present invention has a latent image carrier whose surface is conveyed in the sub-scanning direction, and the latent image carrier having the surface of the latent image carrier as a surface to be scanned. And an exposure unit having the same configuration as that of the line head for forming spots on the body surface. Since the image forming apparatus configured as described above is equipped with the high-resolution line head configured as described above and miniaturized, it is possible to form a high-resolution image while being small.

  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 and the upstream side of the charging unit 23 in the rotation direction D21 of the photoreceptor drum 21. 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. 1, and stretched around these rollers in a direction indicated by an arrow D81 (conveying direction). And a transfer belt 81 that is driven to circulate. Further, the transfer belt unit 8 is disposed inside the transfer belt 81 so as to be opposed to the respective photosensitive drums 21 of 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 image formed on the surface of each photosensitive drum 21 is transferred to the primary transfer position. In TR1, the image is transferred to the surface of the transfer belt 81 to form a monochrome image.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed downstream of the monochrome primary transfer roller 85K and upstream of the driving roller 82. Further, the downstream guide roller 86 is formed between the primary transfer roller 85K and the photosensitive drum 21 at the primary transfer position TR1 formed by the monochrome primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station 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. 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. 9) formed on the glass substrate 293, a light beam is emitted from the light emitting element toward 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 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 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. 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 at predetermined intervals in the main scanning direction XX and the sub-scanning direction YY, corresponding to the arrangement of the light emitting element groups 295.

  FIG. 7 is a diagram illustrating an arrangement of a plurality of light emitting element groups. In the present embodiment, one light emitting element group 295 is configured 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, eight light emitting elements 2951 corresponding to the microlens ML indicated by the two-dot chain line 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. 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. 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. 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.

  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, 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. Also, in the figure, in order to show the imaging characteristics of the microlens array 299, the light beams emitted from the geometric center of gravity E0 of the light emitting element group 295 and the positions E1 and E2 separated from the geometric center of gravity E0 by a predetermined interval. Represents the trajectory. As shown by the locus, the light beam emitted from each position is incident on the back surface of the glass substrate 293 and then emitted from the surface of the glass substrate 293. The light beam emitted from the surface of the glass substrate 293 reaches the surface of the photosensitive drum (scanned surface) via the microlens array 299.

  As shown in FIG. 8, the light beam emitted from the geometric gravity center position E0 of the light emitting element group forms an image 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 this embodiment, the geometric gravity center position E0 (the position of the light emitting element group 295) 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. In other words, 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 the figure, the distance between the positions I1 and I0 where the light beam is imaged is longer than the distance between the positions E1 and E0. That is, the absolute value of the magnification (optical magnification) of the optical system in the present embodiment is 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 that is an optical system including the lens pair including the lenses 2993A and 2993B having the same optical axis and the glass substrate 2991 sandwiched between the lens pairs is used in the present invention. It functions as an “imaging lens”. A microlens array 299 including a plurality of microlenses ML corresponds to the “imaging optical system” of the present invention.

  As this micro lens (imaging lens) ML, for example, a lens having the optical system specifications shown in Table 1 and the lens data shown in Table 2 can be adopted. Here, a bottom emission type organic EL element is used as the light emitting element constituting the line head. As described in the above embodiment, the organic EL 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 E 0 on the object plane is imaged at a position I 0 on the surface to be scanned (image plane) via the glass substrate 293 and the microlens array 299. 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 array 299. Here, both the position E0 and the position I0 are on the optical axis of the microlens ML. As shown in FIG. 8, the distance between the image plane positions I0 and I1 is wider than the distance between the object plane positions E0 and E1. That is, the absolute value of the optical magnification of the imaging lens composed of the glass substrate 293 and the microlens array 299 exceeds 1 and specifically is 2.

  FIG. 9 is a diagram showing the arrangement and wiring of each part in the line head. Hereinafter, 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 with reference to FIG. In this embodiment, the plurality of light emitting element groups 295 are two-dimensionally arranged such that three group rows L295 in which the four light emitting element groups 295 are arranged in the main scanning direction XX are arranged in the sub scanning direction YY while being separated from each other. Is arranged. Further, in the plurality of light emitting elements 2951 belonging to the same light emitting element group 295, the light emitting element rows L2951 configured by arranging the four light emitting elements 2951 in the main scanning direction XX are arranged apart from each other in the sub scanning direction YY. Are two-dimensionally arranged. Thus, the plurality of light emitting element groups 295 are two-dimensionally arranged. For this reason, the gap area AR surrounded by the plurality of light emitting element groups 295 is greatly expanded on the substrate.

  Therefore, in this embodiment, a part of the drive circuit D295 including a TFT (Thin Film Transistor) for driving the light emitting element 2951 and a part of the wiring WL that electrically connects the drive circuit D295 and the light emitting element 2951. Are arranged in the gap area AR. For example, in the gap area AR 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 in an inter-group area sandwiched between the light emitting element groups 295C1 and 295C2. In addition, the drive circuit D295 and the light emitting element group 295B1 are electrically connected by the wiring WL. In the other gap region AR, the drive circuit D295 and the wiring WL are formed as described above. As described above, the inter-group region of the gap region AR is a region sandwiched between two light-emitting element groups 295 adjacent to each other in the group row L295. In the inter-group region, light emission that constitutes one of the group rows in the drive circuit. A circuit for driving the element is arranged. Consider, for example, a group row L295 composed of light emitting element groups 295C1, 295C2,.

  In this group row L295, a plurality of drive circuits D295 are provided so as to be sandwiched between the light emitting element groups 295C1, 295C2,. These drive circuits D295 are circuits for driving the light emitting elements 2951 constituted by the light emitting element groups 295B1,... Forming the adjacent group row L295. In each gap region AR, a wiring WL that electrically connects the driving circuit D295 to the light emitting element groups 295B1,. In particular, in the present embodiment, as shown in the figure, the drive circuit D295 and the light emitting element groups 295B1,... Accordingly, the distance between the drive circuit D295 and the corresponding light emitting element 2951 is shortened, and the wiring WL connecting the two is also shortened. As a result, the gap area AR can be used efficiently, which is advantageous for downsizing and increasing the resolution of the line head 29.

  In this embodiment, a control signal line CL for transmitting a control signal for controlling the light emitting element 2951 is connected to the drive circuit D295. Each control signal line CL extends in the main scanning direction XX between adjacent group columns 295 as shown in FIG. For example, a control signal line CL located at the center of the figure is connected to the drive circuit D295 that drives the light emitting element groups 295B1,. By adopting such a wiring structure, the control signal line CL can be made the shortest. In other words, the wiring structure enables efficient use of the gap area AR, which is advantageous for downsizing and increasing the resolution of the line head 29.

  FIG. 10 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, and 10. 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,. The plurality of light beams emitted by the light emission operation are enlarged while being reversed and imaged on the surface of the photosensitive drum by the “microlens (imaging lens) ML” having the above-described reverse magnification characteristic. 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,. The plurality of light beams emitted by the light emitting operation are enlarged while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics and imaged on the surface of the photosensitive drum. 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, Y2 in the sub-scanning direction). The reason (in order) is that the “imaging lens” corresponds to having 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,. The plurality of light beams emitted by the light emitting operation are enlarged while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics and imaged on the surface of the photosensitive drum. 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,. The plurality of light beams emitted by the light emitting operation are enlarged while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics and imaged on the surface of the photosensitive drum. 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,. The plurality of light beams emitted by the light emitting operation are enlarged while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics and imaged on the surface of the photosensitive drum. 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 emitting operation are enlarged while being inverted by the “imaging lens” having the above-described inversion enlarging characteristics and imaged on the surface of the photosensitive drum. 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, according to this embodiment, the plurality of light emitting element groups 295 are two-dimensionally arranged, and the light beam emitted from each light emitting element group 295 is expanded into a microlens (imaging lens) ML of an expanding optical system. Thus, an image is formed on the surface of the photosensitive drum (surface to be scanned). For this reason, the arrangement | positioning space | interval of the light emitting element group 295 in the board | substrate 293 spreads, and the comparatively wide clearance gap area AR is formed. A drive circuit D295 and a wiring WL are disposed in each gap area AR. Therefore, even if the number of light-emitting elements 2951 is increased in order to increase the resolution, sufficient drive circuit space and wiring space can be secured on the substrate 293 without increasing the substrate size. As a result, it is possible to satisfy both the miniaturization and the high resolution of the line head 29 at the same time. Further, by adopting such a line head 29, it is possible to reduce the size of the image forming apparatus.

  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. That is, in the above embodiment, the light emitting element group 295 is configured as shown in FIG. 7, but the configuration of the light emitting element group 295 is not limited thereto. In short, two or more light emitting elements 2951 are arranged in the main scanning direction XX to form a light emitting element group 295 including the light emitting element row L2951, and a plurality of the light emitting element groups 295 are two-dimensionally arranged to form the gap region AR. Can be formed. And in order to make these clearance gap area AR wider, the micro lens ML can be comprised with an expansion optical system. Thus, a relatively wide gap area AR can be formed by combining the two-dimensional arrangement of the light emitting element groups 295 and the micro lens ML of the magnifying optical system. For example, as shown in FIG. 11, a (6 × 2) light emitting element group 295 forms a group column extending in the main scanning direction XX, and only two such group columns are formed to form the light emitting element group 295 as an element forming band. You may arrange two-dimensionally with FM.

  Also, the arrangement position of the drive circuit D295 is not limited to the gap area AR. For example, each drive circuit D295 may be arranged adjacent to the element formation band FM as shown in FIG. In particular, when the driving circuit D295 and the light emitting element group 295 are arranged in a one-to-one relationship so as to face each other, the wiring WL that electrically connects them can be shortened, and the wiring WL is formed in the gap region AR. Can be efficiently routed. As a result, the line head 29 can be reduced in size and resolution.

  In the above embodiment, a lens having an optical magnification of 2 is exemplified as the micro lens (imaging lens) ML of the magnifying optical system. However, the configuration of the micro lens ML is not limited to this, and other magnifying optics. A system can be adopted. For example, as the micro lens (imaging lens) ML, for example, one having the optical system specifications shown in Table 3 and the lens data shown in Table 4 can be adopted.

  Further, in the above embodiment, a plurality of spots are arranged in a straight line in the main scanning direction XX as shown in FIG. 10 using the line head according to the present invention. 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.

  Furthermore, 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 also to a monochrome image forming apparatus that forms a so-called single-color image. The present invention can be applied.

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 arrangement | positioning and wiring of each part in a line head. The figure which shows the spot formation operation | movement by a line head. The figure which shows other embodiment of the line head concerning this invention.

Explanation of symbols

  21Y, 21M, 21C, 21K ... photosensitive drum (latent image carrier), 29 ... line head (exposure means), 295 ... light emitting element group, L295 ... group row, 2951 ... light emitting device, L2951 ... light emitting device row, 293 ... Glass substrate, 299 ... Microlens array (imaging optical system), 2991 ... Glass substrate, 2993A, 2993B ... Lens, AR ... Gap area, CL ... Control signal line, D295 ... Drive circuit, FM ... Element formation zone, ML ... micro lens (imaging lens), OA ... optical axis, WL ... wiring, XX ... main scanning direction, YY ... sub-scanning direction

Claims (9)

A line extending in a main scanning direction substantially orthogonal to the sub-scanning direction by forming an image of light beams emitted from a plurality of light emitting elements formed on a substrate on a scanning surface conveyed in the sub-scanning direction by an imaging optical system In a line head that forms a latent image in a shape,
A drive circuit provided on the substrate and driving the plurality of light emitting elements;
A wiring for electrically connecting the driving circuit and the plurality of light emitting elements;
Two or more light emitting elements have a light emitting element row arranged in the main scanning direction, and a plurality of light emitting element groups are spaced apart from each other in the main scanning direction to form a group row, and further the group row A plurality of light emitting element groups are two-dimensionally arranged with a plurality of being spaced apart from each other in the sub-scanning direction,
The imaging optical system includes a plurality of imaging lenses provided in a one-to-one correspondence with the plurality of light emitting element groups and having an optical magnification exceeding 1, and each of the plurality of imaging lenses corresponds to it. The light beam emitted from the light emitting element group is imaged at the optical magnification, and
A line head wherein all or part of the wiring is disposed between the plurality of light emitting element groups on the substrate.   The write head according to claim 1, wherein a TFT is used in the drive circuit.   The line head according to claim 1, wherein a part or all of the driving circuit is disposed in a gap region surrounded by the plurality of light emitting element groups.   The gap region has an inter-group region sandwiched between two light emitting element groups adjacent to each other in the group column, and the inter-group region constitutes a group column adjacent to the group column in the drive circuit. The light head according to claim 3, wherein a circuit for driving the light emitting element is disposed. A control signal line that is electrically connected to the drive circuit and transmits a control signal for controlling the plurality of light emitting elements;
5. The line head according to claim 3, wherein the control signal line extends in the main scanning direction between adjacent group columns.   The line head according to claim 1, wherein the drive circuit is provided adjacent to an element formation band in which the plurality of light emitting element groups are provided.   The line head according to claim 1, wherein the light emitting element is a bottom emission type organic EL element.   8. The light emitting element group according to claim 1, wherein in each of the plurality of light emitting element groups, a plurality of the light emitting element rows are spaced apart in the sub-scanning direction, and the plurality of light emitting elements are two-dimensionally disposed. Line head. A latent image carrier whose surface is conveyed in the sub-scanning direction;
An exposure unit having the same configuration as the line head according to claim 1, wherein a spot is formed on the surface of the latent image carrier using the surface of the latent image carrier as a surface to be scanned. Image forming apparatus.

Images