JP2008036938A - Line head and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique of enabling realization of good spot formation by suppressing distortion of a spot shape in a line head which uses a plurality of light emitting elements. <P>SOLUTION: The line head is equipped with a plurality of the light emitting elements arranged two-dimensionally, and an imaging lens which forms spots by imaging light beams from each of a plurality of the light emitting elements to a face to be scanned. When an intersection between a luminous flux center of the light beam emitted from a surface of the light emitting element and the surface is defined as a luminous flux center point of the light emitting element, the light emitting element whose luminous flux center point is farthest from an optical axis of the imaging lens among a plurality of the light emitting elements is defined as the outermost element, an intersection between a perpendicular line drawn from the luminous flux center point of the outermost element to the optical axis and the optical axis is defined as an element side intersection, and an intersection between a plane of incidence of the imaging lens and the optical axis is defined as an incidence plane side intersection, a distance L from the luminous flux center point of the outermost element to the optical axis and a distance Mr from the element side intersection to the incidence plane side intersection satisfy the following inequality L/Mr<0.08. <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, for example, as described in Japanese Patent Application Laid-Open No. H10-260260, a light emitting element array configured by linearly arranging a plurality of light emitting elements at a constant pitch in the main scanning direction has been proposed. ing. In such a line head, a light beam emitted from each of the plurality of light emitting elements included in the light emitting element array is imaged on the scanned surface by an imaging lens, thereby forming a spot on the scanned surface.

JP 2000-158705 A

  However, in the line head that forms an image on the surface to be scanned with the light beams emitted from the plurality of light emitting elements by the imaging lens, the following problems may occur. That is, in such a line head, the light beam from the light emitting element forms an image on the surface to be scanned as a spot, but the spot shape by the light emitting element disposed at a position far from the optical axis of the imaging lens is distorted, and a good spot is obtained. It may be difficult to form. Further, when an image is formed using this line head, there arises a problem that image quality is deteriorated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of suppressing spot shape distortion and realizing good spot formation in a line head using a plurality of light emitting elements. And

A first aspect of the line head according to the present invention is a line head that forms a spot by forming an image of a light beam on a surface to be scanned. In order to achieve the above object, a light beam can be emitted from each surface. And a plurality of light emitting elements that are two-dimensionally arranged so that their positions in the main scanning direction are different from each other, and a plurality of light emitting elements that are arranged to face the plurality of light emitting elements and are incident on the incident surface thereof And an imaging lens that forms a spot by forming an image of the light beam from each element on the surface to be scanned, and the intersection of the center of the light beam emitted from the surface of the light emitting element and the surface is the light flux of the light emitting element The center point is defined, and the light emitting element whose light beam center point is farthest from the optical axis of the imaging lens among the plurality of light emitting elements is defined as the outermost element. Intersection of vertical line and optical axis When the intersection point between the incident surface of the imaging lens and the optical axis is defined as the incident surface side intersection point, the distance L from the light beam center point of the outermost element to the optical axis is defined as the element side intersection point and the element side intersection point. The distance Mr to the incident surface side intersection is the following inequality L / Mr <0.08
It is characterized by satisfying.

  In the line head configured as described above, the light emitting elements are two-dimensionally arranged. Therefore, unlike the line head described in Patent Document 1 in which the light emitting elements are linearly arranged in the main scanning direction, the distance from the optical axis to the light emitting element has not only the main scanning direction component but also the sub scanning direction component. . As a result, in the line head in which the light emitting elements are two-dimensionally arranged, the distance from the optical axis to the light emitting element tends to be longer than that in the line head in which the light emitting elements are linearly arranged. That is, in the line head in which the light emitting elements are two-dimensionally arranged, the above spot shape distortion may become a more serious problem.

On the other hand, in the first aspect of the line head according to the present invention, the distance L from the light beam center point of the outermost element to the optical axis and the distance Mr from the element side intersection to the incident surface side intersection are expressed by the following inequality. L / Mr <0.08
It is configured to satisfy. Therefore, although the light emitting elements are two-dimensionally arranged, the above-described distortion of the spot shape is suppressed, and favorable spot formation can be realized.

A second aspect of the line head according to the present invention is a line head for forming a spot by forming an image of a light beam on a surface to be scanned. In order to achieve the above object, a light beam is emitted from each surface. A plurality of light emitting elements that can be emitted and are two-dimensionally arranged so that their positions in the main scanning direction are different from each other, and a plurality of light emitting elements that are arranged to face the plurality of light emitting elements and are incident on the incident surface An image forming lens that forms a spot by forming an image of a light beam from each of the light emitting elements on the surface to be scanned, and a plurality of light emitting elements and the image forming lens, and the inside of which can transmit the light beam. A transparent member is defined, and the intersection of the light beam center of the light beam emitted from the surface of the light emitting element and the surface is defined as the light beam center point of the light emitting element, and the light beam center point of the plurality of light emitting elements forms an image. From the optical axis of the lens The distant light-emitting element is defined as the outermost element, the intersection of the perpendicular line drawn from the light flux center point of the outermost element to the optical axis and the optical axis is defined as the element-side intersection, and the incident surface of the imaging lens and the optical axis Is defined as the incident surface side intersection point, the distance L from the light beam center point of the outermost element to the optical axis, and the distance Mv from the virtual image of the element side intersection point by the transparent member to the incident surface side intersection point are as follows: Inequality L / Mv <0.08
It is characterized by satisfying.

  Also in the second aspect of the line head according to the present invention, the light emitting elements are two-dimensionally arranged. Therefore, also in the second aspect, the above-described spot shape distortion may become a more serious problem as compared with a line head in which light emitting elements are linearly arranged. Further, unlike the line head of the first aspect, the line head of the second aspect includes a transparent member that is disposed between the plurality of light emitting elements and the imaging lens and through which the light beam can be transmitted. . That is, in the line head according to the second aspect, due to the presence of the transparent member, a refractive index distribution is generated in a space extending between the plurality of light emitting elements and the imaging lens.

Therefore, the second aspect of the line head according to the present invention is configured as follows in consideration of the refractive index distribution by the transparent member. That is, the distance L from the light flux center point of the outermost element to the optical axis and the distance Mv from the virtual image of the element side intersection by the transparent member to the incident surface side intersection are expressed by the following inequality L / Mv <0.08.
It is configured to satisfy. Therefore, although the light emitting elements are two-dimensionally arranged, the above-described distortion of the spot shape is suppressed, and favorable spot formation can be realized.

  Here, it is desirable to arrange the plurality of light emitting elements symmetrically with respect to the optical axis of the imaging lens. The reason is that the distance L becomes the smallest due to the symmetrical arrangement, which is advantageous for satisfying the above inequality.

  In order to achieve the above object, the 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 with the surface of the latent image carrier as the 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. Thus, by forming spots on the surface of the latent image carrier using the above-described line head, it is possible to form favorable spots with suppressed distortion.

  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. The configuration of the line head 29 corresponding to the first and second embodiments of the present invention will be described in detail later.

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

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

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

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

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

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

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed downstream of the monochrome primary transfer roller 85K and upstream of the driving roller 82. 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 schematically showing a first embodiment of a line head (exposure means) according to the present invention. FIG. 4 is a sectional view in the sub-scanning direction of the first 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). In other words, the plurality of light emitting element groups 295 are two-dimensionally arranged on the surface of the substrate 293 so as to be separated from each other by a predetermined distance in the main scanning direction XX and the sub scanning direction YY. Here, each of the plurality of light emitting element groups 295 is configured by two-dimensionally arranging a plurality of light emitting elements, which will be described later. In the present embodiment, an LED (Light Emitting Diode) is used as the light emitting element. That is, in this embodiment, LEDs are arranged as light emitting elements on the surface of the substrate 293. The light beam emitted from each of the plurality of light emitting elements toward the photosensitive drum 21 is directed directly to the light shielding member 297.

  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. Therefore, 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 the light beams emitted from different light emitting element groups 295 is obtained. Is prevented by the light shielding 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 2913 via the substrate 293 by the fixing device 2914. That is, the fixing device 2914 has an elastic force that presses the back cover 2913 toward the case 291, and presses the back cover with the elastic force, thereby making the inside of the case 291 light-tight (that is, from inside the case 291. It is sealed so that light does not leak and so that light does not enter from the outside of the case 291. Note that a plurality of fixing devices 2914 are provided in the longitudinal direction of the case 291. The light emitting element group 295 is covered with a sealing member 294.

  FIG. 5 is a perspective view schematically showing the microlens array. FIG. 6 is a cross-sectional view of the microlens array in the main scanning direction. The microlens array 299 includes a glass substrate 2991 and a plurality of lens pairs configured by two lenses 2993A and 2993B arranged one-on-one so as to sandwich the glass substrate 2991. These lenses 2993A and 2993B can be formed of resin.

  That is, a plurality of lenses 2993A are arranged on the front surface 2991A of the glass substrate 2991, and a plurality of lenses 2993B are arranged on the back surface 2991B of the glass substrate 2991 so as to correspond to the plurality of lenses 2993A on a one-to-one basis. Further, the two lenses 2993A and 2993B constituting the lens pair share a common optical axis OA. The plurality of lens pairs are arranged one-on-one in the plurality of light emitting element groups 295. That is, the plurality of lens pairs are two-dimensionally arranged at a predetermined interval in the main scanning direction XX and the sub-scanning direction YY corresponding to the arrangement of the light emitting element groups 295.

  FIG. 7 is a diagram illustrating an arrangement of a plurality of light emitting element groups. In the present embodiment, a light emitting element row L2951 in which four light emitting elements 2951 are arranged at predetermined intervals in the main scanning direction XX is formed. In addition, two light emitting element rows L2951 configured as described above are arranged in the sub-scanning direction YY. Thus, one light emitting element group 295 is configured. That is, eight light emitting elements 2951 corresponding to a microlens ML (described in detail later) indicated by a two-dot chain line in FIG. The plurality of light emitting element groups 295 are arranged as follows. That is, the light emitting element group rows (295A1, 295A2, 295A3,...), (295B1, 295B2, 295B3), (295C1, 295C2, 295C3,...) Configured in a predetermined number in the main scanning direction XX The light emitting element groups 295 are arranged so that three are 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 gravity center point of the light emitting element 2951 is set as the position of the light emitting element 2951, and the geometric gravity center of all the light emitting element positions belonging to the same light emitting element group 295 is set as the position of the light emitting element group 295. In addition, the main scanning direction position and the sub scanning direction position mean the main scanning direction component and the sub scanning direction component at the position of interest, respectively.

  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 showing the arrangement of the light emitting elements in the light emitting element group. FIG. 9 is a diagram showing an imaging state of the light beam emitted from the light emitting element. As shown in FIG. 8, in each light emitting element group 295, eight light emitting elements 2951 are arranged symmetrically with respect to the optical axis OA of the lens pair. As shown in FIG. 9, the light beam emitted from each light emitting element 2951 forms an image on the surface of the photosensitive drum (scanned surface) through the microlens ML. In this specification, “microlens ML” means an optical system including a pair of lenses 2993A and 2993B that form a one-to-one pair and a glass substrate 2991 sandwiched between the pair of lenses. In addition, FIG. 9 illustrates an imaging state when a light beam is emitted from the optical axis center (element side intersection DI2951) of the light emitting element group 295 for reference. In addition, reference numerals OM2951, CB2951, DI2951, and EI in FIG. 8 and FIG. 9 indicate the following technical matters, respectively.

Reference numeral OM2951 denotes the light emitting element 2951 that is the farthest from the optical axis OA of the microlens ML (imaging lens). Hereinafter, the light emitting element 2951 is referred to as the “outermost element”. Two outermost elements OM2951 exist because eight light emitting elements are arranged symmetrically in the center.
Reference numeral CB2951 indicates an intersection between the surface of the light emitting element 2951 and the light beam center of the light beam emitted from the surface. Hereinafter, the light beam center point CB2951 is referred to as a “light beam center point”. Is equivalent to
Reference numeral DI2951 indicates an intersection of a perpendicular drawn from the light beam central point CB2951 of the outermost element to the optical axis OA and the optical axis OA, and hereinafter referred to as an “element-side intersection”.
Reference numeral EI indicates an intersection between the optical axis OA and the incident surface EF of the microlens ML (imaging lens), and is hereinafter referred to as an “incident surface side intersection”.

  9, the light beam emitted from the element side intersection DI 2951 is emitted from the surface of the photosensitive drum 21 and the optical axis OA of the microlens ML (in other words, the light beams of the lenses 2993A and 2993B). An image is formed at the intersection I0 with the axis OA). As described above, this is because the element side intersection DI2951 is on the optical axis OA of the microlens ML. In addition, the light beam emitted from the light emitting element 2951 disposed at a distance L from the element side intersection DI 2951 forms an image at a position I 1 on the surface of the photosensitive drum 21. In other words, the light beam emitted from the light emitting element arranged in a predetermined direction with respect to the optical axis OA is opposite to the arrangement direction across the optical axis OA of the lenses 2993A and 2993B (the optical axis OA of the microlens ML). The image is formed at the position I1. That is, the microlens ML is a so-called reversal optical system having reversal characteristics. The microlens ML has a magnification (optical magnification) corresponding to a ratio between the distance L and the distance between the positions I0 and I1 on the surface of the photosensitive drum.

The point to be noted here is that the distance L from the optical axis OA to the light emitting element 2951 differs depending on the arrangement position of each light emitting element 2951 as is apparent from FIG. That is, the distance L related to the light emitting element 2951 relatively close to the optical axis OA is close to zero, and the light beam emitted from the light emitting element 2951 is imaged on the surface of the photosensitive drum near the optical axis OA via the microlens ML. And a good spot shape can be obtained. On the other hand, the spot shape is distorted as the distance from the optical axis OA increases, that is, the distance L increases. Then, the distance L to the light emitting element farthest from the optical axis OA, that is, the outermost element OM2951, becomes maximum, and the spot shape corresponding to the outermost element OM2951 may be distorted, and it may be difficult to form a favorable spot. In particular, in the line head 29 according to this embodiment, since the light emitting elements 2951 are two-dimensionally arranged, the distance L from the optical axis OA to the light emitting elements 2951 has not only a main scanning direction component but also a sub scanning direction component. It will be. As a result, in the line head 29 in which the light emitting elements 2951 are two-dimensionally arranged, the distance L is longer than in the line head in which the light emitting elements 2951 are linearly arranged as in the apparatus described in Patent Document 1, for example. . That is, in the line head 29 in which the light emitting elements 2951 are two-dimensionally arranged, the above-described distortion of the spot shape may become a more serious problem. Therefore, even when the light emitting elements 2951 are two-dimensionally arranged, the inventors of the present application perform various optical analyzes and simulations in order to suppress spot shape distortion and enable favorable spot formation. It was. As a result, in the first embodiment, the following inequality L / Mr <0.08
However, Mr is the distance from the element side intersection DI2951 to the incident surface side intersection EI.
The inventors of the present application have found that it is desirable to configure the line head 29 to satisfy the above. Hereinafter, the reason for the conclusion will be described.

FIG. 10 is a diagram schematically showing the relationship between the arrangement of the light emitting elements and the incident angle. The inventors of the present application have obtained an analysis result that the phenomenon that the spot shape caused by the light emitting element disposed at a position far from the optical axis OA of the imaging lens is distorted is related to the incident angle of the light beam to the microlens ML. . That is, as the position of the light emitting element becomes farther from the optical axis OA, the incident angle θ of the light beam emitted from the light emitting element to the microlens ML increases and causes distortion of the spot shape. Therefore, a simulation was performed on the relationship between the distance LL and the distance Mr directly related to the incident angle θ and the spot distortion. That is, the angle θ was changed by changing the ratio LL / Mv, and the spot diameters on the meridional plane and the sagittal plane were examined by simulation. Here, the length LL in the main scanning direction is positive when the outermost element is on the main scanning direction XX side as viewed from the element side intersection DI2951, and is negative when the outermost element is on the opposite side of the main scanning direction XX. In this case, the length is from the light flux center point of the outermost element to the optical axis OA. That is, the relationship between the length LL in the main scanning direction from the light beam center point of the outermost element to the optical axis OA and the distance L from the light beam center point of the outermost element to the optical axis OA is expressed by the following equation: L = | LL ｜
It becomes. That is, L is given by the absolute value of LL.

Simulation SM1
Table 1 is a table showing optical system specifications in the simulation SM1. That is, in the simulation SM1, the diameter of the light emitting element (light emitting pixel diameter) was set to 30 μm, and the wavelength of the light beam emitted from the light emitting element was set to 760 nm. The magnification (optical magnification) of the imaging lens was set to 1. Table 2 is a table showing lens data in the simulation SM1. FIG. 11A is a diagram illustrating an imaging state in the simulation SM1. The line head in the simulation SM1 uses LEDs as light emitting elements. FIG. 5A shows an image formation state when the distance L is set to 0.152 mm and the distance Mv is set to 2.11 mm, that is, L / Mv = 0.072. FIG. 11B shows the result of the simulation SM1. That is, FIG. 11B is a diagram in which the spot diameters of the meridional surface and the sagittal surface on the surface to be scanned (S4) are plotted while changing the ratio LL / Mv.

Simulation SM2
Table 3 is a table showing optical system specifications in the simulation SM2. That is, in the simulation SM2, the diameter of the light emitting element (light emitting pixel diameter) was set to 30 μm, and the wavelength of the light beam emitted from the light emitting element was set to 760 nm. The magnification (optical magnification) of the imaging lens was 0.75 times. Table 4 is a table showing lens data in the simulation SM2. FIG. 12A is a diagram illustrating an imaging state in the simulation SM2. The line head in the simulation SM2 uses LEDs as light emitting elements. FIG. 9A shows an image formation state when the distance L is set to 0.202 mm and the distance Mv is set to 2.96 mm, that is, L / Mv = 0.068. FIG. 12B shows the result of the simulation SM2. That is, FIG. 12B is a diagram in which the spot diameters of the meridional surface and the sagittal surface on the surface to be scanned (S4) are plotted while changing the ratio LL / Mv.

Simulation SM3
Table 5 is a table showing optical system specifications in the simulation SM3. That is, in the simulation SM3, the diameter of the light emitting element (light emitting pixel diameter) was set to 30 μm, and the wavelength of the light beam emitted from the light emitting element was set to 760 nm. The magnification (optical magnification) of the imaging lens was 0.5. Table 6 is a table showing lens data in the simulation SM3. FIG. 13A is a diagram illustrating an imaging state in the simulation SM3. The line head in the simulation SM3 uses LEDs as light emitting elements. FIG. 9A shows an image formation state when the distance L is set to 0.202 mm and the distance Mv is set to 2.96 mm, that is, L / Mv = 0.068. FIG. 13B shows the result of the simulation SM3. That is, FIG. 13B is a diagram in which the spot diameters of the meridional surface and the sagittal surface on the surface to be scanned (S4) are plotted while changing the ratio LL / Mv.

  The inventors of the present invention have conducted the following studies on the simulations SM1 to SM3. First, as shown in FIGS. 11 (b), 12 (b), and 13 (b), in the range where the ratio LL / Mv is small, the spot diameter of the sagittal surface and the spot diameter of the meridional surface are substantially the same. It is. That is, in the range where the ratio LL / Mv is small, the spot shape is kept in a good shape with uniform distortion and little distortion. On the other hand, when the absolute value of the ratio LL / Mv exceeds 0.08, the spot diameter on the sagittal surface tends to decrease, whereas the spot diameter on the meridional surface increases rapidly. That is, when the absolute value of the ratio LL / Mv is 0.08 or more, it can be seen that the difference between the spot diameter on the sagittal surface and the spot diameter on the meridional surface increases rapidly, and the spot shape starts to be distorted rapidly.

  Therefore, the inventors of the present application decided to arrange the outermost element OM2951 as described above in view of the above consideration. That is, the outermost element is arranged in a range where the absolute value of the ratio LL / Mv is less than 0.08. This is because in such a range, the difference between the spot diameter of the sagittal surface and the spot diameter of the meridional surface is small, so that distortion of the spot shape on the surface to be scanned is suppressed, and favorable spot formation can be realized. .

  FIG. 14 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 14. 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 imaged on the surface of the photosensitive drum at a predetermined magnification while being inverted by the microlens ML having the above-described inversion characteristics. 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 emission operation are imaged on the surface of the photosensitive drum at a predetermined magnification while being inverted by the microlens ML having the above-described inversion characteristics. That is, a spot is formed at the position of the “second” hatching pattern in FIG. Here, while the conveyance direction of the surface of the photosensitive drum 21 is the sub-scanning direction YY, the light emitting element rows L2951 on the downstream side in the sub-scanning direction YY are sequentially arranged (that is, at the positions Y1 and Y2 in the sub-scanning direction). The reason why the light is emitted in order is that the microlens ML has a reversal characteristic.

  Next, the light emitting elements 2951 of the light emitting element row L2951 in the sub scanning direction position Y3 belonging to the second light emitting element group 295B1, 295B2, 295B3,. The plurality of light beams emitted by the light emission operation are imaged on the surface of the photosensitive drum at a predetermined magnification while being inverted by the microlens ML having the above-described inversion characteristics. 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 emission operation are imaged on the surface of the photosensitive drum at a predetermined magnification while being inverted by the microlens ML having the above-described inversion characteristics. 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 emission operation are imaged on the surface of the photosensitive drum at a predetermined magnification while being inverted by the microlens ML having the above-described inversion characteristics. 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 imaged on the surface of the photosensitive drum at a predetermined magnification while being inverted by the microlens ML having the above-described inversion characteristics. That is, a spot is formed at the position of the “sixth” hatching pattern in FIG. In this way, by performing the first to sixth light emitting operations, a plurality of spots are formed side by side on a straight line extending in the main scanning direction XX.

As described above, in the line head 29 according to this embodiment, the light emitting elements 2951 are two-dimensionally arranged. Therefore, for example, as in Patent Document 1 described above, the distortion of the spot shape may be a more serious problem compared to a line head in which light emitting elements are linearly arranged. On the other hand, the line head 29 of the first embodiment has the above inequality L / Mv <0.08.
It is configured to satisfy. Therefore, although the light emitting elements 2951 are two-dimensionally arranged, the above-described distortion of the spot shape is suppressed, and favorable spot formation can be realized.

  By the way, in said 1st Embodiment, although LED was used as the light emitting element 2951, the specific structure of the light emitting element 2951 is not restricted to this, For example, an organic EL (Electro-Luminescence) element is used as the light emitting element 2951. Also good. Therefore, a line head using an organic EL element as the light emitting element 2951 will be described with a focus on differences from the first embodiment, while description of common configurations and operations will be omitted.

  FIG. 15 is a sectional view in the sub-scanning direction showing a second embodiment of a line head (exposure means) according to the present invention. That is, the line head of FIG. 15 uses an organic EL as a light emitting element. The main difference from the line head shown in FIG. 4 using LEDs as the light emitting elements is the location of the light emitting elements. That is, as shown in FIG. 4, in the line head illustrated in FIG. 4 using LEDs as light emitting elements, the light emitting elements are arranged on the surface of the substrate 293. On the other hand, in a line head using an organic EL element as a light emitting element, a light emitting element (light emitting element group 295) is arranged on the back surface of the glass substrate 293. In addition, since the line head of FIG. 4, FIG. In addition, as the arrangement mode of the light emitting elements 2951 in the plane of the substrate 293, the same arrangement mode as in the case of the LED can be adopted in the case of the organic EL element. That is, also in the second embodiment, “light flux center point”, “outermost element”, “element side intersection”, and “incident surface side intersection” can be defined as in the first embodiment.

  FIG. 16 is a diagram illustrating an imaging state of the microlens in the second embodiment, and is a diagram illustrating an imaging state of the light beam emitted from the light emitting element (organic EL element). As indicated by a two-dot chain line in the figure, the light beam emitted from the element side intersection DI 2951 is the surface of the photosensitive drum 21 and the optical axis OA of the microlens ML (in other words, the optical axes OA of the lenses 2993A and 2993B). And an image at an intersection I0 with (). In addition, the light beam emitted from the light emitting element 2951 disposed at a distance L from the element side intersection DI 2951 forms an image at a position I 1 on the surface of the photosensitive drum 21. In other words, the light beam emitted from the light emitting element arranged in a predetermined direction with respect to the optical axis OA is opposite to the arrangement direction across the optical axis OA of the lenses 2993A and 2993B (the optical axis OA of the microlens ML). The image is formed at the position I1. As described above, the microlens ML has a magnification (optical magnification) corresponding to the ratio between the distance L and the distance between the positions I0 and I1 on the surface of the photosensitive drum.

The point to be noted here is that, as in the first embodiment, the distance L from the optical axis OA to the light emitting element 2951 differs depending on the arrangement position of each light emitting element 2951, and the light emitting element 2951 is two-dimensionally arranged. It is a point that is arranged. By adopting such a configuration, the spot shape corresponding to the outermost element OM2951 may be distorted, and it may be difficult to form a favorable spot. Therefore, even when the organic EL element is two-dimensionally arranged as the light emitting element 2951, the inventors of the present application have made various optical analyzes in order to suppress the distortion of the spot shape and enable favorable spot formation. And simulated. As a result, in the second embodiment, M1 is the thickness of the glass substrate 293 in the optical axis OA direction, M2 is the distance between the glass substrate 293 and the incident surface side intersection EI on the optical axis OA, and N1 is the glass substrate 293. In terms of refractive index, the following inequality L / Mv <0.08
However, Mv = (M1 / N1) + M2,
The inventors of the present application have found that it is desirable to configure the line head 29 to satisfy the above. Hereinafter, the reason for the conclusion will be described.

  The optical analysis (FIG. 10) regarding the phenomenon that the spot shape is distorted by the light emitting element disposed at a position far from the optical axis OA of the imaging lens is as described above. However, in the second embodiment, the light beam emitted from the light emitting element 2951 enters the microlens ML via the glass substrate 293. Therefore, the optical analysis described above cannot be directly applied to the second embodiment. Therefore, the inventors of the present application performed an optical analysis corresponding to the second embodiment. The optical analysis and simulation will be described in detail with reference to FIG. 10 and FIG.

FIG. 17 is a diagram schematically showing the optical path of the light beam on the glass substrate. The glass substrate 293 has a predetermined refractive index N1. Therefore, when an organic EL element is used as the light emitting element, a refractive index distribution is generated in a space extending between the light emitting element and the microlens ML. As a result, as shown in FIG. 17, when the element-side intersection DI2951 is viewed from the microlens ML, the element-side intersection DI2951 appears as a “virtual image of DI2951” in FIG. Here, the “virtual image of DI2951” is a virtual image of the element side intersection DI2951 by the glass substrate 293. That is, the distance from the element side intersection DI2951 to the incident surface side intersection EI apparently changes to the distance from the virtual image of the element side intersection DI2951 to the incident surface side intersection EI. When the refractive index N1 of the glass substrate 293 is spatially uniform, the following formula Mv = (M1 / N1) + M2 (Formula 1)
Thus, the distance Mv from the virtual image of the element side intersection DI2951 to the incident surface side intersection EI can be obtained. Then, the angle θ is changed by changing the ratio LL / Mv between the distance Mv obtained by Equation 1 and the length LL in the main scanning direction from the light beam center point CB2951 to the optical axis OA of the outermost element OM2951; The spot diameters on the meridional surface and the sagittal surface were examined. Hereinafter, specific simulation contents performed by the inventors will be described.

Simulation SM4
Table 7 is a table showing optical system specifications in the simulation SM4. That is, in the simulation SM4, the diameter of the light emitting element (light emitting pixel diameter) was set to 30 μm, and the wavelength of the light beam emitted from the light emitting element was set to 760 nm. The magnification (optical magnification) of the imaging lens was 0.5. Table 8 is a table showing lens data in the simulation SM4. FIG. 18A is a diagram illustrating an imaging state in the simulation SM4. The line head in the simulation SM4 uses an organic EL element as a light emitting element. 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. FIG. 5A shows the imaging state when the distance L is set to 0.304 mm and the distance Mv obtained by the above equation 1 is set to 4.66 mm, that is, L / Mv = 0.065. ing. FIG. 18B shows the result of the simulation SM4. That is, FIG. 18B is a diagram in which the spot diameters on the meridional surface and the sagittal surface on the surface to be scanned (S6) are plotted while changing the ratio LL / Mv.

  The inventors of the present application have made the following examination on the simulation. First, as shown in FIG. 18B, in the range where the ratio LL / Mv is small, the spot diameter of the sagittal surface and the spot diameter of the meridional surface are substantially the same value. That is, in the range where the ratio LL / Mv is small, the spot shape is kept in a good shape with uniform distortion and little distortion. On the other hand, when the absolute value of the ratio LL / Mv exceeds 0.08, the spot diameter on the sagittal surface tends to decrease, whereas the spot diameter on the meridional surface increases rapidly. That is, when the absolute value of the ratio LL / Mv is 0.08 or more, it can be seen that the difference between the spot diameter on the sagittal surface and the spot diameter on the meridional surface increases abruptly, and the spot shape starts to be abruptly distorted.

  Therefore, the inventors of the present application decided to arrange the outermost element OM2951 as described above in view of the above consideration. That is, the outermost element is arranged in a range where the absolute value of the ratio LL / Mv is less than 0.08. This is because in such a range, the difference between the spot diameter of the sagittal surface and the spot diameter of the meridional surface is small, so that distortion of the spot shape on the surface to be scanned is suppressed, and favorable spot formation can be realized. .

As described above, in the line head 29 according to this embodiment, the light emitting elements 2951 are two-dimensionally arranged. Therefore, for example, as in Patent Document 1 described above, the distortion of the spot shape may be a more serious problem compared to a line head in which light emitting elements are linearly arranged. On the other hand, the line head 29 of the first embodiment has the above inequality L / Mv <0.08.
It is configured to satisfy. Therefore, although the light emitting elements 2951 are two-dimensionally arranged, the above-described distortion of the spot shape is suppressed, and favorable spot formation can be realized. Further, when image formation is performed using the line head 29 configured as described above, a spot forming operation similar to that in the first embodiment can be performed. That is, by performing the spot forming operation shown in FIG. 14, a plurality of spots can be formed side by side on a straight line extending in the main scanning direction XX.

<Others>
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the second embodiment, a glass substrate 293 having a refractive index of N1 and a uniform refractive index is used as the transparent member. However, a member that can be used as the transparent member is not limited to the glass substrate 293. That is, it is possible to use a transparent member whose refractive index is spatially distributed. In short, the distance Mv from the virtual image of the element side intersection DI2951 to the incident surface side intersection by such a transparent member is obtained, and the following inequality L / Mv <0.08
By configuring the line head so as to satisfy the above, it is possible to suppress the distortion of the spot shape and to achieve the effect of realizing a good spot shape.

  In the above embodiment, a plurality of spots are formed in a straight line in the main scanning direction XX as shown in FIG. 14 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.

  In the above embodiment, two light emitting element arrays L2951 configured by arranging four light emitting elements 2951 at predetermined intervals in the main scanning direction XX are arranged in the sub scanning direction YY. However, the configuration and arrangement mode of the light emitting element row L2951 (in other words, the arrangement mode of the plurality of light emitting elements) is not limited to this. That is, three light emitting element rows L2951 configured by arranging five light emitting elements 2951 at predetermined intervals in the main scanning direction XX may be arranged in the sub scanning direction YY, or six at a predetermined interval in the main scanning direction XX. Four light emitting element rows L2951 configured by arranging the light emitting elements 2951 may be arranged in the sub-scanning direction YY. In short, the outermost element of the plurality of light emitting elements may be arranged as in the first and second embodiments.

  In the above embodiment, the light emitting element array L2951 configured by arranging a predetermined number of light emitting elements 2951 in the main scanning direction XX is used, but the light emitting element array L2951 is not an essential requirement of the present invention. That is, it is not necessary to arrange the plurality of light emitting elements 2951 so as to form the light emitting element row L2951. Therefore, for example, the light emitting elements may be arranged side by side so as to have a predetermined angle in the main scanning direction XX, or may be arranged in a zigzag shape or a wave shape. May be arranged as in the first and second embodiments.

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

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 showing an outline of a first embodiment of a line head according to the invention. FIG. 2 is a sub-scan sectional view of the first 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 arrangement | positioning of the light emitting element in a light emitting element group. The figure which shows the imaging state of the light beam in 1st Embodiment. The figure which shows typically the relationship between arrangement | positioning of a light emitting element, and an incident angle. The figure which shows simulation SM1. The figure which shows simulation SM2. The figure which shows simulation SM3. The figure which shows the spot formation operation | movement by a line head. FIG. 6 is a sub-scan sectional view of a second embodiment of the line head according to the invention. The figure which shows the imaging state of the light beam in 2nd Embodiment. The figure which shows typically the optical path of the light beam in the glass substrate The figure which shows simulation SM4.

Explanation of symbols

  21Y, 21M, 21C, 21K ... photosensitive drum (latent image carrier), 29 ... line head (exposure means), 295 ... light emitting element group, 2951 ... light emitting element, CB2951 ... light flux center point, OM2951 ... outermost element, DI2951 ... element side intersection, L2951 ... light emitting element array, 293 ... substrate, glass substrate, 299 ... microlens array, 2991 ... glass substrate, 2993A, 2993B ... lens, OA ... optical axis, ML ... microlens (imaging lens) EF ... incidence surface (of the imaging lens), EI ... incidence surface side intersection, XX ... main scanning direction, YY ... sub-scanning direction

Claims (4)

In a line head that forms a spot by imaging a light beam on a surface to be scanned,
A plurality of light emitting elements that can emit light beams from the respective surfaces and are two-dimensionally arranged so that the positions in the main scanning direction are different from each other;
An imaging lens disposed opposite to the plurality of light emitting elements and forming a spot by forming an image of a light beam from each of the plurality of light emitting elements incident on the incident surface on the surface to be scanned; ,
The intersection of the light beam center of the light beam emitted from the surface of the light emitting element and the surface is defined as the light beam center point of the light emitting element, and the light beam center point of the plurality of light emitting elements is separated from the optical axis of the imaging lens. The farthest light emitting element is defined as the outermost element, and the intersection of the optical axis with the perpendicular drawn from the light flux center point of the outermost element to the optical axis is defined as the element side intersection, When the intersection of the incident surface and the optical axis is defined as the incident surface side intersection,
The distance L from the light beam center point of the outermost element to the optical axis and the distance Mr from the element side intersection point to the incident surface side intersection point are expressed by the following inequality L / Mr <0.08.
A line head characterized by satisfying In a line head that forms a spot by imaging a light beam on a surface to be scanned,
A plurality of light emitting elements that can emit light beams from the respective surfaces and are two-dimensionally arranged so that the positions in the main scanning direction are different from each other;
An imaging lens that is arranged to face the plurality of light emitting elements and forms a spot by forming an image of a light beam from each of the plurality of light emitting elements incident on the incident surface on the surface to be scanned;
A transparent member disposed between the plurality of light emitting elements and the imaging lens, and capable of transmitting a light beam therein;
The intersection of the light beam center of the light beam emitted from the surface of the light emitting element and the surface is defined as the light beam center point of the light emitting element, and the light beam center point of the plurality of light emitting elements is separated from the optical axis of the imaging lens. The farthest light emitting element is defined as the outermost element, and the intersection of the optical axis with the perpendicular drawn from the light flux center point of the outermost element to the optical axis is defined as the element side intersection, When the intersection of the incident surface and the optical axis is defined as the incident surface side intersection,
The distance L from the light flux center point of the outermost element to the optical axis and the distance Mv from the virtual image of the element side intersection by the transparent member to the incident surface side intersection are expressed by the following inequality L / Mv <0.08
A line head characterized by satisfying   The line head according to claim 1, wherein the plurality of light emitting elements are arranged symmetrically with respect to an optical axis of the imaging lens. A latent image carrier whose surface is conveyed in the sub-scanning direction;
An exposure means having the same configuration as the line head according to claim 1, wherein spots are 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