JP2009160740A - Line head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique which enables realizing good exposure by suppressing adhesion of foreign substances to a lens array with a plurality of lenses disposed in two dimensions. <P>SOLUTION: The line head is equipped with both the lens array in which a plurality of lens rows each with a plurality of lenses arranged in a first direction for ejecting the light incident from a plane of incidence out of an ejection plane are disposed in a second direction orthogonal or nearly orthogonal to the first direction, and a head substrate in which a light emitting element group of a grouped plurality of light emitting elements is set correspondingly for each lens. In the head substrate, the light emitting element group is set oppositely to the plane of incidence of the corresponding lens, and ejects the light towards the plane of incidence of the lens. The plane of incidence of the lens is a convex surface, and the ejection plane of the lens is a flat surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a line head including a lens array in which a plurality of lenses provided for each light emitting element group are arranged, and an image forming apparatus using the line head.

  As such a line head, there is provided a line head that provides one lens for a plurality of light emitting elements and forms an image of light from the light emitting elements by the lens to expose an image surface such as a latent image carrier surface. Are known. For example, in the line head described in Patent Document 1, a plurality of light emitting element groups obtained by grouping a plurality of light emitting elements (corresponding to a plurality of light emitting diodes provided in the light emitting diode element array in the same patent document) are arranged in the longitudinal direction. It has been. On the other hand, in the lens array, a lens is provided for each light emitting element group. Accordingly, the light beam emitted from the light emitting element group enters the incident surface of the lens, and the lens emits the incident light beam while forming an image of the incident light beam. Thus, the image plane is exposed.

Japanese Patent No. 2801835 JP 2005-276849 A

  By the way, for the purpose of suppressing the vignetting by increasing the lens aperture, a plurality of lenses are arranged in the longitudinal direction (first direction) to form a lens row, and the plurality of lens rows are arranged in the width direction (second direction). ) Can be used. That is, this line head has a plurality of lenses arranged two-dimensionally. Therefore, when the exit surface of the lens is a convex surface, the region where the exit surfaces of the lens are arranged in the lens array has a two-dimensional uneven shape. However, since the region where the exit surfaces of the lens are arranged is arranged to face the image surface, if the region has a two-dimensional uneven shape, foreign matters such as toner and dust scattered from the image surface are incident on the lens array. There was a case where the problem of adhering occurred. As a result, a good exposure operation may not be performed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of realizing good exposure by suppressing foreign matter adhesion to a lens array in which a plurality of lenses are two-dimensionally arranged. .

  In order to achieve the above object, the line head according to the present invention has a plurality of lenses arranged in the first direction for emitting light incident from the incident surface in the first direction, and the lens rows are orthogonal or substantially orthogonal to the first direction. A plurality of lens arrays arranged in the second direction, and a head substrate provided with a light emitting element group in which a plurality of light emitting elements are grouped corresponding to each lens, wherein the light emitting element group is incident on a corresponding lens The lens is provided so as to face the surface and emits light toward the entrance surface of the lens. The entrance surface of the lens is a convex surface and the exit surface of the lens is a plane.

  In order to achieve the above object, the image forming apparatus according to the present invention includes a plurality of lenses arranged in the first direction that emit light incident from the incident surface in the first direction, and the lens rows are orthogonal to the first direction. A line head having a plurality of lens arrays arranged in a substantially orthogonal second direction, a head substrate provided with a light emitting element group obtained by grouping a plurality of light emitting elements corresponding to each lens, and an exit surface of the lens of the line head And a latent image carrier that is exposed by light emitted from the exit surface.In the head substrate, the light emitting element group is provided to face the entrance surface of the corresponding lens and the entrance surface of the lens. Light is emitted toward the lens, and the entrance surface of the lens is a convex surface, and the exit surface of the lens is a flat surface.

  In the invention thus configured (line head, image forming apparatus), the exit surface of each of the plurality of lenses included in the lens array is a plane. Therefore, the region where the exit surfaces of the lenses are arranged in the lens array does not have an uneven shape. Therefore, the adhesion of foreign matter to the lens array is suppressed and good exposure can be realized.

  Further, the incident surface may be an aspherical surface. This is because, by forming the incident surface as an aspherical surface, the imaging characteristics of the lens are improved and good exposure is possible.

  Further, the incident surface may be configured to be a rotationally symmetric surface having the optical axis of the lens as a rotationally symmetric axis. By configuring the entrance surface with a rotationally symmetric surface in this way, the lens configuration can be simplified.

  Moreover, you may comprise so that the cross-sectional shape in the 1st direction of an incident surface may differ from the cross-sectional shape in the said 2nd direction of an incident surface. When the entrance surface is configured in this way, the imaging characteristics of the lens can be changed in the first direction and the second direction, so that the imaging characteristics of the lens are appropriately adjusted according to the configuration of the line head and the like. It becomes possible.

  Particularly, for a line head having a light emitting element row in which a plurality of light emitting elements are arranged in a first direction, the light emitting element group has a cross sectional shape in a first direction of an incident surface and a cross sectional shape in the second direction of the incident surface. It is preferable to configure so that they are different. This is because the imaging characteristics of the lens can be adjusted appropriately according to the configuration of the light emitting element group.

  Further, a stop may be provided at the front focal point of the lens. With this configuration, the image side is telecentric. Therefore, even if the position variation occurs on the image plane, the influence of the position variation on the image can be suppressed, and good exposure can be performed.

  In the following, terms used in this specification will be described first. Following the explanation of this term, an embodiment of the present invention will be explained.

Explanation of Terms FIG. 1 and FIG. 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. A set of a plurality of spots SP formed on the image plane IP by the light beam from the light emitting element group 295 being imaged by the lens LS corresponding to the light emitting element group 295 is defined as a spot 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.

Embodiment FIG. 3 is a diagram showing an example of an image forming apparatus equipped with a line head to which the present invention is applied. 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. 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 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 orthogonal or 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.

  Inside the case 291, a head substrate 293, a diaphragm plate 298 and a lens array 299 are arranged. The inside of the case 291 is in contact with the front surface 293A of the head substrate 293, while the back cover 2913 is in contact with the back surface 293B of the head substrate 293. The back cover 2913 is pressed into the case 291 through 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 inside of the case 291 (upper side in FIG. 6), and the back cover is pressed by the elastic force, so that the inside of the case 291 is It is hermetically sealed (in other words, light does not leak from the inside of the case 291 and 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 LGD of the case 291.

  A light emitting element group 295 in which a plurality of light emitting elements are grouped is provided on the back surface 293B of the head substrate 293. The head substrate 293 is formed of a light transmissive member such as glass, and the light beam emitted from each light emitting element of the light emitting element group 295 can be transmitted from the back surface 293B of the head substrate 293 to the front surface 293A. This light emitting element is a bottom emission type organic EL (Electro-Luminescence) element and is covered with a sealing member 294.

  The head substrate 293 and the diaphragm plate 298 are arranged to face each other via a pedestal 296A, and the diaphragm plate 298 and the lens array 299 are arranged to face each other via a pedestal 296B. That is, in FIG. 6, a pedestal 296A is disposed on the head substrate surface 293A, and a diaphragm plate 298 is disposed on the pedestal 296A. A pedestal 296B is disposed on the diaphragm plate 298, and a lens array 299 is disposed on the pedestal 296B. In the lens array 299, a lens LS that forms an image of the light beam from the light emitting element group 295 is provided for each light emitting element group 295. A diaphragm plate 298 between the head substrate 293 and the lens array 299 is formed with a diaphragm opening 2981 for each light emitting element group 295. Therefore, among the light beams emitted from the light emitting element group 295, the light beam that has passed through the aperture opening 2981 is incident on the lens LS.

  FIG. 7 is a longitudinal sectional view of the lens array, the diaphragm plate, etc., and shows a longitudinal sectional view including the optical axis OA of the lens LS. The lens array 299 includes a lens substrate 2991 and a plurality of lens surfaces LSF provided on the back surface 2991B of the lens substrate 2991. Each lens surface LSF is a convex surface and has a curvature. The lens array 299 is formed by a method described in, for example, Japanese Patent Application Laid-Open No. 2005-276849. That is, a mold having a concave portion corresponding to the convex shape of the lens surface LSF is brought into contact with a light-transmitting substrate as the lens substrate 2991. For example, a glass substrate can be used as the light transmissive substrate. When the photocurable resin is filled between the mold and the light transmissive substrate, the light curable resin is irradiated with light, and the lens surface LSF is formed on the light transmissive substrate. Then, the mold is released at the timing when the photocurable resin is cured.

  Thus, in the present embodiment, one lens LS is configured by one lens surface LSF and the lens substrate 2991 on which the lens surface LSF is formed. In other words, the lens LS has a flat exit surface. This is a convex flat lens. Then, as indicated by the broken line in the figure, the lens LS emits the light beam incident from the lens surface LSF (incident surface) from the lens substrate surface 2991A (exit surface). The lens substrate surface 2991A is opposed to the surface of the photosensitive drum. Thus, the light beam emitted from the light emitting element group 295 is imaged by the lens LS and the surface of the photosensitive drum (image surface) is exposed.

  FIG. 8 is a plan view of the lens array, which corresponds to a case where the lens array is viewed from the image plane side (upper side in FIG. 7). As shown in the drawing, in the lens array 299, a plurality of lens rows LSC made up of three lenses LS arranged at different positions in the width direction LTD are arranged in the longitudinal direction LTD. In other words, in the 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 LSR are provided in the width direction LTD. The lens rows LSR are arranged so as to be shifted from each other in the longitudinal direction LGD, and the positions PTL of the lenses LS in the longitudinal direction LGD are different from each other. Thus, in the lens array 299, the plurality of lenses LS are two-dimensionally arranged, and the lens array is configured by arranging the lenses LS (convex flat lenses LS) in an array. In the figure, the position of the lens LS is represented by the apex of the lens surface LSF of the lens LS, and the position PTL in the longitudinal direction LGD of the lens LS is lowered from the position of the lens LS to the longitudinal axis LGD. It is represented by a vertical foot.

  FIG. 9 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. FIG. 10 is a diagram showing the arrangement of light emitting elements in each light emitting element group. 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. 9, 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 in the longitudinal direction LGD. In other words, a plurality of light emitting element groups 295 are arranged in the longitudinal direction LGD to form a light emitting element group row 295R, and three light emitting element group rows 295R are provided in the width direction LTD. The light emitting element group rows 295R are arranged so as to be shifted from each other in the longitudinal direction LGD, and the positions PTE of the light emitting element groups 295 in the longitudinal direction LGD are different from each other. As described above, the plurality of light emitting element groups 295 are two-dimensionally arranged on the head substrate 293. In the drawing, the position of the light emitting element group 295 is represented by the center of gravity of the light emitting element group 295, and the position PTE in the longitudinal direction LGD of the light emitting element group 295 is the longitudinal axis from the position of the light emitting element group 295. It is represented by a vertical leg down to LGD.

  In the light emitting element group 295, four light emitting elements 2951 are arranged along the longitudinal direction LGD to form a light emitting element row 2951R, and two light emitting element rows 2951R are provided in the width direction LTD (FIG. 10). . The respective light emitting element rows 2951R are shifted from each other in the longitudinal direction LGD, and the positions of the respective light emitting elements 2951 in the longitudinal direction LGD are different from each other. The light emitting element group 295 configured as described above has a light emitting element group width W295 in the longitudinal direction LGD. The light emitting element group width W295 is defined as follows. That is, when the light emitting elements 2951 positioned at both ends in the longitudinal direction LGD are the end light emitting elements 2951X, the light emitting element group width W295 is the pitch of the end light emitting elements 2951X in the longitudinal direction LGD.

Thus, each light emitting element 2951 provided on the head substrate 293 is, for example, a TFT (Thin
Film Transistor) is driven by a circuit or the like and 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.

  The light beam emitted from the light emitting element 2951 is imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum 21 (the surface of the photosensitive drum). On the other hand, as described above, the surface of the photosensitive drum is charged by the charging unit 23 prior to spot formation. Therefore, the area where the spot SP is formed is neutralized, and the spot latent image Lsp is formed. The spot latent image Lsp thus formed is conveyed downstream in the sub-scanning direction SD while being carried on the surface of the photosensitive drum. As will be described next, the spots SP are formed at a timing corresponding to the movement of the surface of the photosensitive drum, and a plurality of spot latent images Lsp arranged in the main scanning direction MD are formed.

  FIG. 11 is a perspective view for explaining spots formed by the line head. In FIG. 11, the description of the lens array 299 is omitted. As shown in FIG. 11, each light emitting element group 295 can form spot groups SG in different exposure regions ER in the main scanning direction MD. Here, the spot group SG is a set of a plurality of spots SP formed by simultaneously emitting light from all the light emitting elements 2951 of the light emitting element group 295. Further, as shown in the figure, three light emitting element groups 295 belonging to different light emitting element group rows 295R (in other words, three light emitting element groups 295 arranged to be shifted from each other in the width direction LTD), Spot groups SG are formed in three exposure regions ER that are continuous in the main scanning direction MD. That is, spot groups SG_1, SG2, and SG3 are formed in the exposure regions ER_1, ER_2, and ER3 continuous in the main scanning direction MD by the light emitting element groups 295_1, 295_2, and 295_3 belonging to the different light emitting element group rows 295R.

  Incidentally, as shown in FIG. 9, the three light emitting element group rows 295R are arranged at different positions in the width direction LTD. Therefore, the light emitting element groups 295 belonging to different light emitting element group rows 295R form spot groups SG at different positions in the sub-scanning direction SD. Therefore, in order to form a plurality of spot latent images Lsp side by side in the main scanning direction MD (that is, to form a plurality of spot latent images Lsp at the same position in the sub-scanning direction SD), It is necessary to consider the difference. Therefore, in the line head 29, each light emitting element 2951 emits light at a timing according to the movement of the surface of the photosensitive drum.

  FIG. 12 is a diagram showing a spot forming operation by the above-described line head. Hereinafter, the spot forming operation by the line head will be described with reference to FIG. 9, FIG. 11, and FIG. Schematically, the surface of the photosensitive drum (latent image carrier surface) moves in the sub-scanning direction SD, and the head control module 54 (FIG. 4) controls the light emitting element 2951 at a timing according to the movement of the photosensitive drum surface. By emitting light, a plurality of spot latent images Lsp arranged in the main scanning direction MD are formed.

  First, among the light emitting element rows 2951R (FIG. 10) belonging to the most upstream light emitting element group 295_1, 295_4, etc. in the width direction LTD, the light emitting element row 2951R on the downstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Note that the lens LS has an inverted characteristic, and the light beam from the light emitting element 2951 is inverted to form an image. Thus, the spot latent image Lsp is formed at the position of the “first” hatching pattern in FIG. In the figure, a white circle represents a spot latent image that has not yet been formed and is scheduled to be formed in the future. In the same figure, the spot latent images labeled with reference numerals 295_1 to 295_4 indicate spot latent images 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 same light emitting element group 295_1, 295_4, etc., 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 emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp is formed at the position of the “second” hatching pattern in FIG. Here, the reason why light is emitted in order from the light emitting element row 2951R on the downstream side in the width direction LTD is to correspond to the fact that the lens LS has an inverted characteristic.

  Next, among the light emitting element rows 2951R belonging to the second light emitting element group 295_2 and the like 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 emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp 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 295_2 and the like from the upstream side in the width direction, the light emitting element rows 2951R on the upstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp 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 295_3 and the like 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 emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp 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 295_3 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 emission operation are imaged by the lens LS, and a spot SP is formed on the surface of the photosensitive drum. Thus, the spot latent image Lsp is formed at the position of the “sixth” hatching pattern in FIG. As described above, by executing the first to sixth light emission operations, the spot SP is formed in order from the spot SP on the upstream side in the sub-scanning direction SD, and a plurality of spot latent images Lsp aligned in the main scanning direction MD. Is formed.

  As described above, in the line head 29 according to the present embodiment, the surface 2991A of the lens substrate 2991 functions as the “lens exit surface” in the present invention, and the exit surfaces of the plurality of lenses LS included in the lens array 299 ( 2991A) is a plane. Therefore, the region where the exit surfaces of the lenses LS are arranged in the lens array 299 does not have an uneven shape. Therefore, the adhesion of foreign matter to the lens array 299 is suppressed and good exposure can be realized.

  Further, even if foreign matter adheres to a region where the exit surfaces of the lenses LS are arranged in the lens array 299, the shape of this region is a flat shape and not an uneven shape, so that the foreign matter can be easily removed. .

  In the line head 29 according to the present embodiment, a plurality of (three) lens rows LSR are arranged in the width direction LTD. Therefore, the line head 29 according to the present embodiment can suppress vignetting due to the lens LS and can perform good exposure as compared with the line head 29 having only one lens row LSR. ing. That is, when there is vignetting due to the lens LS, vignetting occurs in the light beam passing through the lens LS. As a result, the incident angle to the image plane of the principal ray of the light beam emitted from the lens LS may increase.

  Therefore, in the present embodiment, a plurality of (three) lens rows LSR are arranged in the width direction LTD, so that the aperture of the lens LS can be increased. That is, when the pitch between the lenses LS adjacent to each other in the longitudinal direction LGD in the lens row LSR is set to the pitch Δls, as shown in FIG. 13, the three lens rows LSR than the line head having one lens row LSR are used. A line head having a larger pitch Δls can be obtained. Here, FIG. 13 is a diagram comparing a line head having three lens rows and a line head having one lens row. Therefore, vignetting due to the lens LS can be suppressed, and good exposure is possible.

  In the present embodiment, the line head 29 is configured by superimposing three members of the head substrate 293, the diaphragm plate 298, and the lens array 299 via the bases 296A and 296B. Therefore, adjustment of the positional relationship among the light emitting element group 295, the diaphragm aperture 2981, and the lens LS can be performed simply by matching the arrangement of these three members, and the assemblability of the line head 29 is improved.

Others As described above, 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 “first direction” of the present invention. The surface of the photosensitive drum 21 corresponds to the “image surface” of the present invention. The lens surface LSF corresponds to the “incident surface” of the present invention, and the lens substrate surface 2991A corresponds to the “exit surface” of the present invention.

  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 array 299 is formed by forming a photocurable resin as the lens surface LSF on the light-transmitting substrate as the lens substrate 2991. However, the method of forming the lens array 299 is not limited to this, and the lens array 299 may be formed by the following method described in Japanese Patent Application Laid-Open No. 2005-276849. In this forming method, the mold is pressed and adhered to the resin substrate in a state where the substrate made of a thermoplastic resin (resin substrate) is maintained at a temperature equal to or higher than the transition temperature. Then, the mold is released from the resin substrate at a timing when the resin substrate and the mold are cooled to the transition temperature of the resin substrate or lower. That is, when forming the lens array in the present invention by the forming method described in the publication, the lens surface LSF only needs to be formed only on the back surface of the resin substrate by press-contacting the mold only on the back surface of the resin substrate. This is because the exit surface of the lens LS (surface of the resin substrate) of the lens array 299 configured in this way is a flat surface, and the region where the exit surfaces of the lenses LS are arranged in the lens array 299 does not have an uneven shape. Therefore, foreign matter adhesion to the lens array 299 is suppressed, and good exposure can be realized.

  In the above embodiment, the three light emitting element group rows 295R are arranged in the width direction LTD. However, the number of light emitting element group rows 295R is not limited to three and may be two or more.

  In the above embodiment, the light emitting element group 295 includes two light emitting element rows 2951R. However, the number of light emitting element rows 2951R constituting the light emitting element group 295 is not limited to two, and may be one, for example.

  In the above embodiment, the light emitting element row 2951R includes four light emitting elements 2951. However, the number of the light emitting elements 2951 constituting the light emitting element row 2951R is not limited to four.

  In the above embodiment, an organic EL element is used as the light emitting element 2951. However, an element other than the organic EL element may be used as the light emitting element 2951. For example, an LED (Light Emitting Diode) may be used as the light emitting element 2951.

  Next, examples of the present invention will be shown. However, the present invention is not limited by the following examples as a matter of course, and it is of course possible to implement the present invention with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. They are all included in the technical scope of the present invention.

  In the above embodiment, the lens array is configured by arranging the convex flat lenses LS in an array. Therefore, the following embodiment shows data of an optical system employing the convex flat lens LS and evaluates the imaging characteristics of the convex flat lens.

Example 1
FIG. 14 is a diagram illustrating data of the optical system according to the first example. FIG. 15 is an optical path diagram of the optical system according to the first example and illustrates a cross section in the main scanning direction including the optical axis of the lens LS. FIG. 16 is a diagram illustrating a spot diagram of the optical system according to the first example.

  In FIG. 15, the light beam emitted from the object point OP0 on the optical axis of the lens LS (solid line in the figure) and 0.21 [mm] (= light emitting element group width W295) from the object point OP0 in the longitudinal direction LGD. The optical path diagram of the light beam (broken line in the figure) emitted from the object point OP1 separated by / 2) is shown. That is, FIG. 15 corresponds to the case where the width W295 of the light emitting element group 295 is 0.42 [mm], and the light beam emitted from the object point OP1 is emitted at the longitudinal end of the light emitting element group 295. This corresponds to the light beam emitted from the element 2951. The object point OP0 and the object point OP1 are both object points that exist on the cross section in the main scanning direction including the optical axis of the lens LS.

  In FIG. 16, the position of the spot on the image plane is represented by the image height corresponding to the main scanning direction MD. Further, the incident angle in the figure indicates the incident angle of the principal ray of the light beam forming the spot with respect to the entrance pupil.

  The focal length of the optical system is 1.1043 [mm], whereas the distance from the stop DIA to the incident surface LSF of the lens LS is 1.103753 [mm]. Accordingly, the stop DIA is disposed at a substantially front focal point, and the image side is substantially telecentric (FIG. 15). Specifically, the incident angle (end portion incident angle) of the light beam (dashed line in FIG. 15) from the end portion in the longitudinal direction LGD of the light emitting element group 295 with respect to the image plane of the principal ray is about 0.3 [degree]. It is. In this optical system, the end incident angle can be suppressed to about 1 [degree] by suppressing the deviation between the position of the stop DIA and the front focal point to about 10% of the focal length. At this time, for example, even if the image plane is deviated by ± 50 μm, the deviation of the position of the spot is about 0.9 μm, which is a level with no practical problem. That is, in the present embodiment, when the deviation between the position of the diaphragm DIA and the front focal point is within 10% of the focal length, it can be said that the diaphragm DIA is substantially provided at the front focal point.

  As shown in FIGS. 14 and 15, the lens LS is a convex and convex lens having a flat exit surface, and the surface of surface number S3 corresponding to the entrance surface of the lens LS is a convex surface and has a curvature, while the exit of the lens LS. The surface number S4 corresponding to the surface is a plane. Therefore, by arranging the lenses LS in the first embodiment in an array and configuring the lens array 299, it is possible to suppress adhesion of foreign matter to the lens array 299.

  In Example 1, since the incident surface LSF of the lens LS is aspherical, the end incident angle can be easily set to approximately 0 [degree], and good imaging characteristics can be realized. .

  Further, in Example 1, as can be seen from the aspherical definition formula of FIG. 14, the incident surface LSF of the lens LS is a rotationally symmetric surface with the optical axis OA of the lens LS as the rotationally symmetric axis, and the lens configuration is simplified. Is possible.

Example 2
FIG. 17 is a diagram illustrating data of the optical system according to the second example. FIG. 18 is an optical path diagram of the optical system according to the second example and illustrates a cross section in the main scanning direction including the optical axis of the lens LS. FIG. 19 is a diagram illustrating a spot diagram of the optical system according to the second example. In FIG. 17, the coordinate x corresponds to the main scanning direction MD, and the coordinate y corresponds to the sub-scanning direction SD.

  In FIG. 18, a light beam emitted from an object point OP0 on the optical axis of the lens LS (solid line in the figure) and 0.21 [mm] (= light emitting element group width W295) from the object point OP0 in the longitudinal direction LGD. The optical path diagram of the light beam (broken line in the figure) emitted from the object point OP1 separated by / 2) is shown. That is, FIG. 17 corresponds to the case where the width W295 of the light emitting element group 295 is 0.42 [mm], and the light beam emitted from the object point OP1 is emitted at the longitudinal end of the light emitting element group 295. This corresponds to the light beam emitted from the element 2951. The object point OP0 and the object point OP1 are both object points that exist on the cross section in the main scanning direction including the optical axis of the lens LS. In Example 2, the focal length of the optical system is 1.1185 [mm].

  In FIG. 19, the position of the spot on the image plane is represented by the image height corresponding to the main scanning direction MD. Further, the incident angle in the figure indicates the incident angle of the principal ray of the light beam forming the spot with respect to the entrance pupil.

  As shown in FIGS. 17 and 18, the lens LS is a convex and convex lens having a flat exit surface, and the surface of the surface number S3 corresponding to the entrance surface of the lens LS is a convex surface and has a curvature, while the exit of the lens LS. The surface number S4 corresponding to the surface is a plane. Therefore, by arranging the lenses LS in the second embodiment in an array and configuring the lens array 299, it is possible to suppress foreign matter adhesion to the lens array 299.

  In Example 2, as can be seen from the aspherical definition formula of FIG. 17, the incident surface LSF is a non-rotationally symmetric aspheric surface, and the cross-sectional shape of the incident surface LSF in the main scanning direction MD (or the longitudinal direction LGD) The cross-sectional shape of the incident surface in the sub-scanning direction SD (or the width direction LTD) is different. Accordingly, since the imaging characteristics of the lens LS can be changed between the main scanning direction MD and the sub-scanning direction SD, it is possible to appropriately adjust the imaging characteristics of the lens LS according to the configuration of the line head 29 and the like. It has become.

  In particular, as in the above embodiment, when the light emitting element group 295 has the light emitting element row 2951R in which the plurality of light emitting elements 2951 are arranged in the longitudinal direction LGD, the cross-sectional shape of the incident surface LSF in the longitudinal direction LGD and the width of the incident surface LSF. It is preferable that the cross-sectional shape in the direction LTD is different. This is because the imaging characteristics of the lens LS can be appropriately adjusted according to the configuration of the light emitting element group 295.

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. Sectional drawing of the longitudinal direction, such as a lens array and an aperture plate. The top view of a lens array. The figure which shows the structure of the back surface of a head board | substrate. The figure which shows arrangement | positioning of the light emitting element in a light emitting element group. The perspective view for demonstrating the spot formed with a line head. The figure which shows the spot formation operation | movement by a line head. The comparison figure of the structure which has three lens rows, and the structure which has one lens row. FIG. 3 is a diagram illustrating data of the optical system according to the first example. 1 is an optical path diagram of an optical system according to Example 1. FIG. 1 is a diagram showing a spot diagram of an optical system according to Example 1. FIG. FIG. 6 is a diagram showing data of an optical system according to Example 2. FIG. 6 is an optical path diagram of the optical system according to the second example. FIG. 6 is a diagram showing a spot diagram of an optical system according to Example 2.

Explanation of symbols

  21Y, 21K ... photosensitive drum (latent image carrier), 29 ... line head, 293 ... head substrate, 295 ... light emitting element group, 2951 ... light emitting element, 299 ... lens array, LS ... lens, LSF ... incident surface, 2991 ... lens substrate, MD ... main scanning direction, SD ... sub-scanning direction, LGD ... longitudinal direction (first direction), LTD ... width direction (second direction)

Claims (7)

A lens array in which a plurality of lenses emitting light incident from an incident surface is emitted from an exit surface in a first direction, and a plurality of lens rows are arranged in a second direction orthogonal or substantially orthogonal to the first direction;
A head substrate provided with a light emitting element group in which a plurality of light emitting elements are grouped corresponding to each lens;
In the head substrate, the light emitting element group is provided facing the incident surface of the corresponding lens and emits light toward the incident surface of the lens,
The line head according to claim 1, wherein the entrance surface of the lens is a convex surface and the exit surface of the lens is a plane.   The line head according to claim 1, wherein the incident surface is an aspherical surface.   The line head according to claim 1, wherein the incident surface is a rotationally symmetric surface having an optical axis of the lens as a rotationally symmetric axis.   The line head according to claim 1, wherein a cross-sectional shape of the incident surface in the first direction is different from a cross-sectional shape of the incident surface in the second direction.   The line head according to claim 4, wherein the light emitting element group has a light emitting element row in which a plurality of light emitting elements are arranged in the first direction.   The line head according to claim 1, wherein a stop is provided at a front focal point of the lens. A lens array in which a plurality of lenses emitting light incident from an incident surface is emitted from an exit surface in a first direction, and a plurality of lens rows are arranged in a second direction orthogonal or substantially orthogonal to the first direction, and a plurality of light emitting elements A line head having a head substrate provided with a group of light emitting element groups corresponding to each lens,
A latent image carrier that is exposed by light emitted from the exit surface opposite to the exit surface of the lens of the line head;
In the head substrate, the light emitting element group is provided facing the incident surface of the corresponding lens and emits light toward the incident surface of the lens,
2. The image forming apparatus according to claim 1, wherein the entrance surface of the lens is a convex surface and the exit surface of the lens is a plane.

Images