JP2009119666A - Line head and image forming apparatus using line head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique enabling excellent spot formation by suppressing variance in positional relation of a lens surface in a line head using a plurality of lens rows. <P>SOLUTION: In the lens array, a plurality of lens rows where a plurality of lenses are arranged in a first direction are arranged in a second direction orthogonal to or substantially orthogonal to the first direction, and also the respective lens rows are provided to be displaced each other in the first direction such that the positions of the respective lenses are different from each other in the first direction, then the lens has one or more lens surfaces formed on a plane of a lens substrate. When performing labeling that the lens surfaces are numbered in order from a light emitting element group side to the lenses, the lens surfaces having the same number are formed on the same plane of the lens substrate each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a line head that forms an image of a light beam emitted from a light emitting element with a lens, and an image forming apparatus using the line head.

  As this type of line head, one that forms a spot on an image plane by forming an image of a light beam emitted from a light emitting element with a lens is known. Further, for example, in Patent Document 1, a line head using a plurality of lens rows (“monocular lens array” in the same document) in which a plurality of lenses are arranged in the longitudinal direction is proposed in order to form a spot with high resolution. Has been. That is, in this line head, a plurality of lens rows are arranged in a direction substantially orthogonal to the longitudinal direction, and these lens rows are shifted from each other in the longitudinal direction so that the positions of the lenses are different from each other in the longitudinal direction. Are arranged.

JP-A-6-278314

  By the way, in the line head, one lens is constituted by two lens surfaces, and the light beam emitted from the light emitting element enters the first lens surface counted from the light emitting element side and then enters the second lens surface. The light is emitted from the lens surface and imaged as a spot on the image surface. However, in the above line head, between lenses belonging to different lens rows, lens surfaces corresponding to the same number (for example, the first lens surfaces counted from the light emitting element side) are formed on different planes. Therefore, the positional relationship between these lens surfaces tends to vary, and as a result, spot formation may not be performed satisfactorily.

  The present invention has been made in view of the above problems, and in a line head that uses a plurality of lens rows, provides a technique that enables favorable spot formation by suppressing variations in the positional relationship of the lens surfaces as described above. With the goal.

  In order to achieve the above object, the line head according to the present invention forms an image of a head substrate provided with a plurality of light emitting elements grouped for each light emitting element group and a light beam from the light emitting elements of the light emitting element group. A lens array in which a lens forming a spot is opposed to each light emitting element group, and in the lens array, a lens row in which a plurality of lenses are arranged in the first direction is a second direction orthogonal or substantially orthogonal to the first direction. The lens rows are arranged so as to be shifted from each other in the first direction so that the positions of the lenses are different from each other in the first direction, and the lens has one lens surface formed on the plane of the lens substrate. As described above, when labeling is performed on each lens in order from the light emitting element group side, the lens surfaces with the same number It is characterized by being formed on the same lens substrate plane.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a latent image carrier, a head substrate provided with a plurality of light emitting elements grouped for each light emitting element group, and light emission of the light emitting element group. A line head having a lens array that forms a spot latent image on the surface of the latent image carrier by forming a light beam from the element as a spot, and a lens array facing each light emitting element group. The lens rows are arranged in a first direction so that a plurality of lens rows are arranged in a second direction orthogonal to or substantially orthogonal to the first direction, and the positions of the lenses are different from each other in the first direction. The lens has one or more lens surfaces formed on the plane of the lens substrate, and the lens surfaces in order from the light emitting element group side are provided. Labeling denoted with the number in was performed on the lens, the lens surface of the same numbers is characterized by being formed on the same lens substrate plane with each other.

  In the invention thus configured (line head, image forming apparatus), the lens surfaces with the same number are formed on the same lens substrate plane. Here, the “number” is a number assigned to the lens surface when labeling is performed on each lens in order from the light emitting element group side. Therefore, the lens surfaces corresponding to the same number are formed on the same lens substrate plane regardless of the lens row to which the lens surface belongs. Therefore, variation in the positional relationship between lens surfaces corresponding to the same number is suppressed, and favorable spot formation is possible. Further, in the image forming apparatus, it is possible to form a good spot latent image by forming a spot latent image with such a good spot.

  Each lens is composed of two lens surfaces formed on a single lens substrate. The first lens surface is formed on one plane on the light emitting element group side of the lens substrate, and the second lens surface. May be formed on the other plane of the lens substrate. In such a configuration, the first lens surface and the second lens surface constituting the lens are respectively formed on the front and back of the same lens substrate. Therefore, since the distance between the first lens surface and the second lens surface is determined only by the thickness of the substrate, the distance can be set with high accuracy. As a result, spot formation can be performed satisfactorily.

  By the way, the lens substrate may cause a large thermal shrinkage depending on the material. When the lens substrate undergoes thermal shrinkage in this way, the positional relationship between the lens surfaces formed on the lens substrate may change. Therefore, the lens substrate may be formed of glass. This is because glass has a smaller thermal expansion coefficient than that of resin or the like, and thus it is possible to suppress the positional variation of the lens surface due to temperature change, which is advantageous in favor of spot formation.

  In order to form a spot more favorably, it is desirable to form each light emitting element while suppressing variation in positional relationship between the light emitting elements. Therefore, each light emitting element may be configured to be formed on the same head substrate plane. This is because in such a configuration, variation in the positional relationship between the light emitting elements is suppressed, and better spot formation is possible.

  The light emitting element may be an organic EL element formed on the head substrate plane. This is because such an organic EL element can be formed with high positional accuracy by a semiconductor process, which is advantageous for good spot formation.

  In the image forming apparatus that can form a spot latent image satisfactorily, the spot latent image may be developed with a liquid developer. That is, the liquid developer can develop the latent image with relatively high accuracy. Therefore, it is preferable that the development of the spot latent image formed favorably in the image forming apparatus is performed with a liquid developer.

A. Explanation of Terms Before explaining embodiments of the present invention, terms used in this specification will be explained.

  1 and 2 are explanatory diagrams of terms used in this specification. Here, the terms used in this specification will be organized using these drawings. In this specification, the transport direction of the surface (image surface IP) of the photosensitive drum 21 is defined as a sub-scanning direction SD, and a direction orthogonal or substantially orthogonal to the sub-scanning direction SD is defined as a main scanning direction MD. . The line head 29 is arranged with respect to the surface (image surface IP) of the photosensitive drum 21 so that the longitudinal direction LGD corresponds to the main scanning direction MD and the width direction LTD corresponds to the sub-scanning direction SD. Has been.

  A set of a plurality of (eight in FIG. 1 and FIG. 2) light emitting elements 2951 arranged on the head substrate 293 in a one-to-one correspondence with the plurality of lenses LS included in the lens array 299 is defined as a light emitting element group 295. To do. That is, in the head substrate 293, the light emitting element group 295 including the plurality of light emitting elements 2951 is disposed for each of the plurality of lenses LS. Further, the light beam from the light emitting element group 295 is imaged toward the image plane IP by the lens LS corresponding to the light emitting element group 295, whereby a set of a plurality of spots SP formed on the image plane IP is obtained. It is defined as group SG. That is, the plurality of spot groups SG can be formed in one-to-one correspondence with the plurality of light emitting element groups 295. In each spot group SG, the most upstream spot in the main scanning direction MD and the sub-scanning direction SD is particularly defined as the first spot. The light emitting element 2951 corresponding to the first spot is particularly defined as the first light emitting element.

  Further, as shown in the column “on image plane” in FIG. 2, a spot group row SGR and a spot group column SGC are defined. That is, a plurality of spot groups SG arranged in the main scanning direction MD are defined as spot group rows SGR. The plurality of spot group rows SGR are arranged side by side in the sub-scanning direction SD at a predetermined spot group row pitch Psgr. A plurality (three in the figure) of spot groups SG arranged at the spot group row pitch Psgr in the sub-scanning direction SD and at the spot group pitch Psg in the main scanning direction MD are defined as a spot group column SGC. The spot group row pitch Psgr is a distance in the sub-scanning direction SD between the geometric centroids of two spot group rows SGR adjacent to each other in the sub-scanning direction SD. The spot group pitch Psg is the distance in the main scanning direction MD of the geometric centroids of two spot groups SG adjacent to each other in the main scanning direction MD.

  Lens rows LSR and lens columns LSC are defined as shown in the “lens array” column of FIG. That is, a plurality of lenses LS arranged in the longitudinal direction LGD are defined as a lens row LSR. The plurality of lens rows LSR are arranged side by side in the width direction LTD at a predetermined lens row pitch Plsr. A plurality (three in the figure) of lenses LS arranged at the lens row pitch Plsr in the width direction LTD and at the lens pitch Pls in the longitudinal direction LGD are defined as a lens row LSC. The lens row pitch Plsr is a distance in the width direction LTD of the geometric centroids of two lens rows LSR adjacent to each other in the width direction LTD. The lens pitch Pls is a distance in the longitudinal direction LGD between the geometric centroids of the two lenses LS adjacent to each other in the longitudinal direction LGD.

  As shown in the column “Head Substrate” in the drawing, a light emitting element group row 295R and a light emitting element group column 295C are defined. That is, a plurality of light emitting element groups 295 arranged in the longitudinal direction LGD is defined as a light emitting element group row 295R. The plurality of light emitting element group rows 295R are arranged side by side in the width direction LTD at a predetermined light emitting element group row pitch Pegr. In addition, a plurality of (three in the figure) light emitting element groups 295 arranged at the light emitting element group row pitch Pegr in the width direction LTD and at the light emitting element group pitch Peg in the longitudinal direction LGD are defined as a light emitting element group column 295C. The light emitting element group row pitch Pegr is a distance in the width direction LTD between the geometric centroids of two light emitting element group rows 295R adjacent to each other in the width direction LTD. The light emitting element group pitch Peg is the distance in the longitudinal direction LGD between the geometric centers of gravity of two light emitting element groups 295 adjacent to each other in the longitudinal direction LGD.

  As shown in the “light emitting element group” column of FIG. 2, a light emitting element row 2951R and a light emitting element column 2951C are defined. That is, in each light emitting element group 295, a plurality of light emitting elements 2951 arranged in the longitudinal direction LGD is defined as a light emitting element row 2951R. The plurality of light emitting element rows 2951R are arranged side by side in the width direction LTD at a predetermined light emitting element row pitch Pelr. A plurality of (two in the figure) light emitting elements 2951 arranged in the width direction LTD at the light emitting element row pitch Pelr and at the longitudinal direction LGD in the longitudinal direction LGD are defined as a light emitting element row 2951C. The light emitting element row pitch Pelr is a distance in the width direction LTD of the geometric centroids of two light emitting element rows 2951R adjacent to each other in the width direction LTD. The light emitting element pitch Pel is a distance in the longitudinal direction LGD between the geometric centroids of two light emitting elements 2951 adjacent to each other in the longitudinal direction LGD.

  As shown in the column “Spot Group” in the figure, a spot row SPR and a spot column SPC are defined. That is, in each spot group SG, a plurality of spots SP arranged in the longitudinal direction LGD are defined as spot rows SPR. The plurality of spot rows SPR are arranged side by side in the width direction LTD at a predetermined spot row pitch Pspr. Further, a plurality of (two in the figure) spots arranged at the spot pitch Pspr in the width direction LTD and at the spot pitch Psp in the longitudinal direction LGD are defined as a spot row SPC. The spot row pitch Pspr is a distance in the sub-scanning direction SD between the geometric centroids of two spot rows SPR adjacent to each other in the sub-scanning direction SD. The spot pitch Psp is a distance in the longitudinal direction LGD between the geometric centroids of two spots SP adjacent to each other in the main scanning direction MD.

B. Embodiment FIG. 3 is a diagram showing an example of an image forming apparatus according to the present invention. FIG. 4 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. 3 is a diagram corresponding to the execution of the color mode. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC and also outputs an image forming command. Corresponding video data VD is supplied to the head controller HC. The head controller HC controls the line head 29 for each color based on the video data VD from the main controller MC, the vertical synchronization signal Vsync from the engine controller EC, and parameter values. As a result, the engine unit EG executes a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  An electrical component box 5 containing a power circuit board, a main controller MC, an engine controller EC, and a head controller HC is provided in the housing main body 3 of the image forming apparatus. An image forming unit 7, a transfer belt unit 8, and a paper feed unit 11 are also disposed in the housing body 3. In FIG. 3, a secondary transfer unit 12, a fixing unit 13, and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feeding unit 11 is configured to be detachable from the 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 cylindrical photosensitive drum 21 having a surface with a predetermined length in the main scanning direction MD. Each of the image forming stations Y, M, C, and K forms a corresponding color toner image on the surface of the photosensitive drum 21. The photosensitive drum is arranged so that the axial direction is substantially parallel to the main scanning direction MD. 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 SD that is orthogonal or substantially orthogonal to the main scanning direction MD. 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. 3, 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 is disposed with respect to the photosensitive drum 21 such that the longitudinal direction thereof corresponds to the main scanning direction MD and the width direction thereof corresponds to the sub-scanning direction SD. Is substantially parallel to the main scanning direction MD. The line head 29 includes a plurality of light emitting elements arranged side by side in the longitudinal direction, and is spaced apart from the photosensitive drum 21. Then, light is emitted from these light emitting elements to the surface of the photosensitive drum 21 charged by the charging unit 23, and an electrostatic latent image is formed on the surface.

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

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

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

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 3, and a stretched direction of these rollers in the direction of the 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. 3, all the primary transfer rollers 85Y, 85M, 85C, 85K are positioned on the image forming stations Y, M, C, 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 on the downstream side of the monochrome primary transfer roller 85K and on the upstream side of the driving roller 82. The downstream guide roller 86 is formed between the primary transfer roller 85K and the photosensitive drum 21 at the primary transfer position TR1 formed by the monochrome primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station K. It is configured to contact the transfer belt 81 on a common inscribed line.

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

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

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

  Further, in this apparatus, a cleaner portion 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner and paper dust remaining on the transfer belt after the secondary transfer by bringing the tip of the cleaner blade 711 into contact with the blade facing roller 83 via the transfer belt 81. The foreign matter removed in this way is collected in a waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are integrally formed with the blade facing roller 83. Therefore, when the blade facing roller 83 moves as will be described below, the cleaner blade 711 and the waste toner box 713 also move together with the blade facing roller 83.

  FIG. 5 is a perspective view showing an outline of the line head according to the present invention. FIG. 6 is a cross-sectional view in the width direction of the line head shown in FIG. As described above, the line head 29 is arranged with respect to the photosensitive drum 21 such that the longitudinal direction LGD corresponds to the main scanning direction MD and the width direction LTD corresponds to the sub-scanning direction SD. The longitudinal direction LGD and the width direction LTD are substantially orthogonal to each other. The line head 29 includes a case 291, and positioning pins 2911 and screw insertion holes 2912 are provided at both ends of the case 291 in the longitudinal direction LGD. 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 lens array 299 at a position facing the surface of the photosensitive drum 21, and includes a light shielding member 297 and a head substrate 293 in the order close to the lens array 299. The head substrate 293 is formed of a material (for example, glass) that can transmit a light beam. A plurality of bottom emission organic EL (Electro-Luminescence) elements are arranged as light emitting elements 2951 on the back surface of the head substrate 293 (the surface opposite to the lens array 299 of the two surfaces of the head substrate 293). ing. The plurality of light emitting elements 2951 are arranged in groups for each light emitting element group 295, as will be described later. The light beams emitted from the respective light emitting element groups 295 are transmitted from the back surface to the front surface of the head substrate 293 and directed 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 penetrating the light shielding member 297 with a line parallel to the normal line of the head substrate 293 as a central axis. Therefore, among the light beams emitted from the light emitting element group 295, the light beams that are directed to other than the light guide hole 2971 corresponding to the light emitting element group 295 are blocked by the light blocking member 297. Thus, all the light emitted from one light emitting element group 295 is directed to the lens array 299 through the same light guide hole 2971, and interference between light beams emitted from different light emitting element groups 295 is prevented by the light shielding member 297. The 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 lens array 299.

  As shown in FIG. 6, the back cover 2913 is pressed against the case 291 via the head substrate 293 by the fixing device 2914. That is, the fixing device 2914 has an elastic force that presses the back cover 2913 toward the case 291, and presses the back cover with the elastic force, thereby making the inside of the case 291 light-tight (that is, from the inside of the case 291. It is sealed so that light does not leak and so that light does not enter from the outside of the case 291. Note that a plurality of fixing devices 2914 are provided in the longitudinal direction of the case 291. The light emitting element group 295 is covered with a sealing member 294.

  FIG. 7 is a plan view schematically showing the lens array, and corresponds to a case where the lens array is viewed from the image plane side. As shown in the figure, the lens array 299 is provided with a plurality of lenses LS as follows. In this lens array 299, a plurality of lenses LS are arranged in the longitudinal direction LGD to form a lens row LSR, and three lens rows are arranged in the width direction LTD. These three lens rows LSR1 to LSR3 are shifted from each other in the longitudinal direction LGD so that the positions of the lenses LS are different from each other in the longitudinal direction LGD. More specifically, in each of the lens rows LSR1 to LSR3, a plurality of lenses LS are arranged in the longitudinal direction at 3 times the lens pitch (Pel × 3). Moreover, the lens rows LSR1 to LSR3 are shifted from each other in the longitudinal direction LGD by the lens pitch Pel. As a result, the positions LSldg of the lenses LS in the longitudinal direction LGD are different from each other. In the figure, the position of the lens LS is represented by the center position CP of the lens LS, and the position of the lens LS in the longitudinal direction LGD is lowered from the center position CP of the lens LS to the longitudinal axis. It is represented as a vertical leg. Further, the center position CP of the lens LS can be obtained, for example, as the most convex portion of the lens surface (that is, the portion closest to the image surface) facing the image surface (the surface of the photosensitive drum 21).

  In addition, the lens array LSC will be described for later explanation. From a different viewpoint, the plurality of lenses LS of the lens array 299 described above are arranged as follows. That is, a plurality of lens rows LSC are arranged in the longitudinal direction LGD, in which three lenses arranged at the lens pitch Pel in the longitudinal direction LGD are arranged at different positions in the width direction LTD. Next, a cross-sectional structure of such a lens array 299 will be described.

  FIG. 8 is a cross-sectional view of the lens array in the longitudinal direction, and corresponds to a case where the lens array is viewed in a cross section including the center position of each lens. FIG. 9 is a cross-sectional view of the lens array in the lens array direction, and corresponds to a case where the lens array is viewed in a cross section including the lens center positions. In these drawings, the upper side is the image plane side, and the lower side is the light emitting element group side. A number is attached to the lens surface code LSF, and this number represents the “number” of the lens surface. Incidentally, the “number” is a number assigned to the lens surface LSF when labeling for assigning a number to the lens surface LSF in order from the light emitting element group side is performed on each lens LS. That is, the lens surface LSF1 is the first lens surface, and the lens surface LSF2 is the second lens surface. Further, the lens array direction Dlsc in FIG. 9 is a direction in which the three lenses LS are arranged in the lens array LSC.

  As shown in these drawings, in the lens array 299, one lens substrate LB made of glass is provided, and two lens surfaces LSF1, LSF2 arranged in the optical axis OA direction so as to sandwich the lens substrate LB. Thus, the lens LS is configured. These lens surfaces LSF1, LSF2 can be formed of, for example, a photocurable resin. Of the two lens surfaces, the lens surface LSF1 is formed on the back surface LBF1 of the lens substrate LB, and the lens surface LSF2 is formed on the surface LBF2 of the lens substrate LB. That is, the lens surface LSF1 is formed on one plane on the light emitting element group side of the lens substrate LB, and the lens surface LSF2 is formed on the other plane. Further, the lens rows LSR are configured by arranging the lenses LS in the longitudinal direction LGD (FIG. 8). Further, the lenses LS of the lens rows LSR1 to LSR3 are arranged in the lens column direction Dlsc (FIG. 9). Here, the notation “LS / LSR1” and the like in FIG. 9 indicates that the lens LS belongs to the lens LSR1 and the like. In this embodiment, the lens surfaces having the same number are formed on the same lens substrate plane regardless of the lens row LSR (or lens column LSC) to which the lens surfaces belong. Specifically, the first lens surface LSF1 is formed on the lens substrate back surface LBF1, and the second lens surface LSF2 is formed on the lens substrate surface LBF2.

  FIG. 10 is a diagram showing the configuration of the back surface of the head substrate, which corresponds to the case where the back surface is viewed from the front surface of the head substrate. In FIG. 9, the lens LS is indicated by a two-dot chain line. This is for indicating that the light emitting element groups 295 are provided in one-to-one relationship with the lens LS. It does not indicate that it is arranged on the back surface of the head substrate. As shown in FIG. 10, a plurality of light emitting element group columns 295C in which three light emitting element groups 295 are arranged at different positions in the width direction LTD are arranged along the longitudinal direction LGD. In other words, three light emitting element group rows 295R in which a plurality of light emitting element groups 295 are arranged along the longitudinal direction LGD are arranged in the width direction LTD. At this time, the light emitting element group rows 295R are shifted from each other in the longitudinal direction LGD so that the positions of the light emitting element groups 295 are different from each other in the longitudinal direction LGD. Here, reference numerals 295R_A, 295R_B, and 295R_C are attached to the three light emitting element group rows in order from the upstream side in the width direction LGD.

  As shown in the drawing, light emitting element rows 2951R in which four light emitting elements 2951 are arranged in the longitudinal direction are arranged in even rows (two rows in the figure) in the width direction LTD. The respective light emitting element rows 2951R are arranged so as to be shifted from each other by the light emitting element pitch Pel in the width direction LTD, and the respective light emitting elements 2951 are at different positions in the width direction LTD. When a drive circuit (not shown) gives a drive signal to each light emitting element 2951, each light emitting element 2951 emits light beams having the same wavelength. The light emitting surface of the light emitting element 2951 is a so-called perfect diffusion surface light source, and the light beam emitted from the light emitting surface follows Lambert's cosine law.

  FIG. 11 is a diagram showing a spot forming operation by the above-described line head. The spot forming operation by the line head in this embodiment will be described below with reference to FIGS. In order to facilitate understanding of the invention, a case where a line latent image is formed by arranging a plurality of spots on a straight line extending in the main scanning direction MD will be described. In summary, in the latent image forming operation, a plurality of light emitting elements are caused to emit light at a predetermined timing by the head control module 54 while transporting the surface of the photosensitive drum 21 in the sub scanning direction SD (width direction LTD). A plurality of spots are formed side by side on a straight line extending in the main scanning direction MD (longitudinal direction LGD). Details will be described below.

  First, among the light emitting element rows 2951R belonging to the most upstream light emitting element groups 295A1, 295A2,... In the width direction LTD, the light emitting element rows 2951R on the downstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. In the present embodiment, the lens LS has an inverted characteristic, and the light beam from the light emitting element 2951 is imaged while being inverted. Thus, 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, among the light emitting element rows 2951R belonging to the light emitting element groups 295A1, 295A2,..., The light emitting element row 2951R on the upstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. In this way, a spot is formed at the position of the “second” hatching pattern in FIG. Here, the reason why light is emitted sequentially from the light emitting element row 2951R on the downstream side in the width direction WD is to correspond to the fact that the microlens ML has an inverted characteristic.

  Next, among the light emitting element rows 2951R belonging to the second light emitting element group 295B1,... From the upstream side in the width direction, the light emitting element rows 2951R on the downstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. Thus, a spot is formed at the position of the “third” hatching pattern in FIG.

  Next, among the light emitting element rows 2951R belonging to the second light emitting element group 295B1,... From the upstream side in the width direction, the light emitting element row 2951R on the upstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. Thus, a spot is formed at the position of the “fourth” hatching pattern in FIG.

  Next, among the light emitting element rows 2951R belonging to the third light emitting element group 295C1,... From the upstream side in the width direction, the light emitting element rows 2951R on the downstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. Thus, a spot is formed at the position of the “fifth” hatching pattern in FIG.

  Finally, among the light emitting element rows 2951R belonging to the third light emitting element group 295C1,... From the upstream side in the width direction, the light emitting element row 2951R on the upstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. Thus, a spot is formed at the position of the “sixth” hatching pattern in FIG. In this way, by performing the first to sixth light emission operations, a plurality of spots are formed side by side on a straight line extending in the longitudinal direction LGD (main scanning direction MD).

  As described above, in the line head 29 of the above-described embodiment, the lens surfaces LSF with the same number are formed on the same lens substrate plane. Therefore, variation in the positional relationship between the lens surfaces LSF corresponding to the same number is suppressed, and favorable spot formation is possible. Further, in the image forming apparatus 1 equipped with such a line head 29, it is possible to form a good spot latent image by forming a spot latent image with such a good spot.

  In the above embodiment, each lens LS is composed of two lens surfaces LSF1 and LSF2 formed on a single lens substrate LB, and the first lens surface LSF1 is formed on the back surface LBF1 of the lens substrate LB. The second lens surface LSF2 is formed on the surface LBF2 of the lens substrate LB. Accordingly, since the distance between the first lens surface LSF1 and the second lens surface LSF2 is determined only by the thickness of the lens substrate LB, the distance can be set with high accuracy. As a result, spot formation can be performed satisfactorily.

  Incidentally, the lens substrate LB may cause a large thermal contraction depending on the material. When the lens substrate LB is thermally contracted in this way, the positional relationship between the lens surfaces LSF formed on the lens substrate LB may be changed. On the other hand, the above embodiment is preferable because the lens substrate LB is formed of glass. Since glass has a smaller coefficient of thermal expansion than resin or the like, it is possible to suppress the positional fluctuation of the lens surfaces LSF1 and LSF2 due to temperature change, which is advantageous in favor of spot formation. It is.

  In order to form spots more favorably, it is desirable that each light emitting element 2951 is also formed while suppressing variation in positional relationship between the light emitting elements 2951. On the other hand, in the above embodiment, each light emitting element 2951 is formed on the same head substrate plane 293, which is preferable. This is because variation in the positional relationship among the light emitting elements 2951 is suppressed, and better spot formation is possible.

  Moreover, the said embodiment forms the light emitting element 2951 with the organic EL element, and is suitable. This is because such an organic EL element can be formed with high positional accuracy by a semiconductor process, which is advantageous for good spot formation.

  Thus, in the above embodiment, the longitudinal direction LGD corresponds to the “first direction” of the present invention, the width direction LTD corresponds to the “second direction” of the present invention, and the photosensitive drum 21 corresponds to the “latent direction” of the present invention. The surface of the photosensitive drum 21 corresponds to the “image surface” of the present invention.

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 above embodiment, the lens LS is formed by the two lens surfaces LSF1, LSF2 formed on the front and back surfaces of one lens substrate LB. However, the number of lens substrates LB and the number of lens surfaces constituting the lens LS are not limited to this, and for example, a line head can be configured as follows.

  12 is a perspective view schematically showing a line head according to another embodiment, and FIG. 13 is a cross-sectional view in the width direction of the line head shown in FIG. In the following description, differences from the above-described embodiment will be mainly described, and common portions will be denoted by corresponding reference numerals and description thereof will be omitted. As shown in these drawings, in the line head 29 of another embodiment, two lens substrates LBa and LBb are provided so as to overlap each other. A lens LS is constituted by three lens surfaces LSF1 to LSF3 formed on these lens substrates LBa and LBb. Details are as follows.

  FIG. 14 is a longitudinal sectional view of a lens array according to another embodiment, and corresponds to a case where the lens array is viewed in a cross section including the center position of each lens. FIG. 15 is a cross-sectional view of the lens array in another embodiment in the lens array direction, and corresponds to a case where the lens array is viewed in a cross section including each lens center position. In these drawings, the upper side is the image plane side, and the lower side is the light emitting element group side. As shown in these drawings, in the lens array 299, two lens substrates LBa and LBb are provided so as to overlap in the direction of the optical axis OA. A first lens surface LSF1 is formed on the back surface LSF1 of the lens substrate LBa on the light emitting element group side, and a second lens surface LSF2 is formed on the surface LSF2 of the lens substrate LBa. A third lens surface LSF3 is formed on the lens substrate LBb on the image surface side. Thus, the three lens surfaces LSF1 to LSF3 from No. 1 to No. 3 are arranged on the optical axis OA to constitute one lens LS. The light beam emitted from the light emitting element group 295 is imaged by the lens LS.

  As described above, also in the line head 29 of another embodiment, the lens surfaces LSF with the same number are formed on the same lens substrate plane (for example, the third lens surface LSF3 is the back surface LSF3 of the lens substrate LBb). Formed). Therefore, variation in the positional relationship between the lens surfaces LSF corresponding to the same number is suppressed, and favorable spot formation is possible.

  In the above embodiment, the light emitting element group 295 is composed of two light emitting element rows 2951R arranged in the width direction LTD. However, the number of light emitting element rows 2951R is not limited to two.

  In the above embodiment, the light emitting element group 295 is configured by the eight light emitting elements 2951. However, the number of the light emitting elements 2951 constituting the light emitting element group 295 is not limited to eight.

  In the above embodiment, the lens array 299 is provided with three lens rows LSR1 to LSR3. However, the number of lens rows LSR is not limited to this, and may be plural.

  In the above embodiment, the latent image is developed with so-called dry toner to form an image. However, the latent image may be developed with a liquid developer. FIG. 22 is a diagram showing an outline of an apparatus for developing with a liquid developer. Since the difference between the apparatus shown in FIG. 3 and the apparatus shown in FIG. 3 is mainly the structure of the developing unit, the following description will mainly describe the developing unit, and the other parts will be denoted by the same reference numerals and description thereof will be omitted. .

  Four developing units 90Y (for yellow), 90M (for magenta), 90C (for cyan), and 90K (for black) corresponding to each toner color are arranged side by side along the conveyance direction of the intermediate transfer belt 81. ing. In each developing unit 90K and the like, an oil container 901 that stores carrier oil, a toner container 902 that stores high-concentration toner, and a stirrer 903 are provided. In the agitator 903, the carrier oil supplied from the oil container 901 and the high-concentration toner supplied from the toner container 902 are agitated to generate a liquid developer whose density is adjusted. The liquid developer thus generated is supplied to the developer container 904. A supply roller 905 and an anilox roller 906 are provided inside the developer container 904. The lower part of the supply roller 905 is immersed in the liquid developer inside the developer container 904. The supply roller 905 rotates in the direction of the arrow in the drawing to draw up the liquid developer and convey it to the anilox roller 906. The anilox roller 906 rotates in the direction of the arrow in the figure, and applies the liquid developer conveyed from the supply roller 905 to the developing roller 907.

  The developing roller 907 is in contact with the photosensitive drum 21 at the developing position. The developing roller 907 is rotatable in the direction of the arrow in the figure, and the liquid developer supplied from the anilox roller 906 is carried on the surface of the developing roller 907 and supplied to the developing position. The toner contained in the liquid developer supplied in this manner adheres to the latent image on the surface of the photosensitive drum, and development is executed.

  A cleaner blade 908 is in contact with the developing roller 907 on the downstream side of the developing position in the rotation direction of the developing roller 907. The liquid developer is peeled off from the surface of the developing roller 907 by the cleaner blade 908 and recovered in the recovery container 909. Further, the liquid developer recovered in the recovery container 909 is returned to the agitator 903 and reused.

  In the rotational direction D21 of the photosensitive drum, two photosensitive squeeze rollers 910 are provided in contact with the surface of the photosensitive drum 21 on the downstream side of the developing position. The photoconductor squeeze roller 910 peels off the carrier oil from the surface of the photoconductor drum 21, thereby adjusting the amount of carrier oil contained in the liquid developer on the surface of the photoconductor drum 21. Further, the peeled carrier oil is once collected in the collection container 911 and then returned to the agitator 903 for reuse.

  An image obtained by developing the latent image at the development position is transferred to the intermediate transfer belt 81 at the primary transfer position TR1. In the transport direction D81 of the intermediate transfer belt 81, a belt squeeze roller 912 is in contact with the downstream side of the primary transfer position TR1. The belt squeeze roller 912 peels off the carrier oil from the surface of the intermediate transfer belt 81, so that the amount of carrier oil contained in the liquid developer on the surface of the intermediate transfer belt 81 is adjusted. Further, the stripped carrier oil is collected in a collection container 913.

  The image primarily transferred in this way is secondarily transferred to the paper. This secondary transfer operation is executed by two secondary transfer rollers 82 and a backup roller 121 disposed opposite to each secondary transfer roller 82. Each backup roller 121 is provided with a cleaner blade 1211 in contact therewith, and the liquid developer remaining on the backup roller 121 is peeled off by the cleaner blade 1211 and collected in a collection container 1212.

  Thus, in the apparatus of FIG. 22, the latent image is developed (liquid development) by the liquid developer. By the way, in general, such liquid development can perform latent image development with relatively high accuracy. Therefore, it is preferable that the development of the spot latent image formed favorably by the above invention is performed by liquid development.

Explanatory drawing of the term used by this specification. Explanatory drawing of the term used by this specification. 1 is a diagram illustrating an example of an image forming apparatus according to the present invention. FIG. 4 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 3. The perspective view which shows the outline of the line head concerning this invention. FIG. 6 is a cross-sectional view in the width direction of the line head shown in FIG. 5. The top view which shows the outline of a lens array. Sectional drawing of the longitudinal direction of a lens array. Sectional drawing of the lens array direction of a lens array. The figure which shows the structure of the back surface of a head board | substrate. The figure which shows the spot formation operation | movement by a line head. The perspective view which shows the outline of the line head concerning another embodiment. FIG. 13 is a cross-sectional view in the width direction of the line head shown in FIG. 12. Sectional drawing of the longitudinal direction of the lens array in another embodiment. Sectional drawing of the lens array direction of the lens array in another embodiment. FIG. 2 is a diagram illustrating an outline of an apparatus that performs development with a liquid developer.

Explanation of symbols

  21Y, 21K ... photosensitive drum (latent image carrier), 29 ... line head, 293 ... head substrate, 295 ... light emitting element group, 295R ... light emitting element group row, 2951 ... light emitting element, 2951R ... light emitting element row, 299 ... Lens array, LS ... lens, LSF1 to LSF3 ... lens surface, LB, LBa, LBb ... lens substrate, MD ... main scanning direction, SD ... sub-scanning direction, LGD ... longitudinal direction (first direction), LTD ... width direction ( Second direction),

Claims (7)

A head substrate provided with a plurality of light emitting elements grouped for each light emitting element group;
A lens array that forms a spot by forming an image of a light beam from the light emitting element of the light emitting element group, and a lens array facing each light emitting element group;
In the lens array, a plurality of lens rows in which a plurality of the lenses are arranged in the first direction are arranged in a second direction that is orthogonal or substantially orthogonal to the first direction, and the positions of the lenses are mutually in the first direction. Differently, each lens row is provided offset from each other in the first direction,
The lens has one or more lens surfaces formed on the plane of the lens substrate, and when performing labeling for each lens in order from the light emitting element group side, A line head characterized in that lens surfaces having the same number are formed on the same lens substrate plane.   Each of the lenses is composed of two lens surfaces formed on a single lens substrate, and the first lens surface is formed on one plane of the lens substrate on the light emitting element group side. The line head according to claim 1, wherein the surface is formed on the other flat surface of the lens substrate.   The line head according to claim 1, wherein the lens substrate is made of glass.   The line head according to claim 1, wherein the light emitting elements are formed on the same head substrate plane.   The line head according to claim 4, wherein the light emitting element is an organic EL element formed on the head substrate plane. A latent image carrier;
A head substrate provided with a plurality of light emitting elements grouped for each light emitting element group, and a spot latent image formed on the surface of the latent image carrier by imaging a light beam from the light emitting elements of the light emitting element group as a spot. A line head having a lens array facing each of the light emitting element groups.
In the lens array, a plurality of lens rows in which a plurality of the lenses are arranged in the first direction are arranged in a second direction that is orthogonal or substantially orthogonal to the first direction, and the positions of the lenses are mutually in the first direction. Differently, each lens row is provided offset from each other in the first direction,
The lens has one or more lens surfaces formed on the plane of the lens substrate, and when performing labeling for each lens in order from the light emitting element group side, An image forming apparatus, wherein lens surfaces having the same number are formed on the same lens substrate plane. The image forming apparatus according to claim 6, wherein the latent image is developed with a liquid developer.

Images