JP2009190397A - Exposure head and image forming apparatus - Google Patents

Abstract

Provided is a technique that enables a good exposure by taking a lot of light into a lens.
A light-transmitting substrate 2991 having a length W1 in a first direction LGD and a length W2 in a second direction orthogonal to the first direction LGD and having a relationship of W1>W2; A lens array 299 having a first lens LS11 disposed on a transmissive substrate 2991 and a second lens LS12 disposed in a first direction LGD of the first lens LS11 on a light transmissive substrate 299 is provided. The first lens LS11 and the second lens LS12 are connected in the first direction LGD.
[Selection] Figure 16

Description

  The present invention relates to an exposure head and an image forming apparatus using a lens array having a plurality of lenses.

  As such a lens array, for example, as described in FIG. 2 of Patent Document 1, an array in which a plurality of lenses are arranged at a predetermined pitch in the longitudinal direction is known. In this lens array, lenses adjacent in the longitudinal direction are arranged at a predetermined interval from each other, and each lens forms an image of incident light. Then, a latent image carrier such as a photosensitive drum is exposed by the light formed by each lens to form a latent image.

JP-A-6-278314

  By the way, from the viewpoint of good exposure, it is preferable that the amount of light incident on the lens is large. Therefore, for example, it is conceivable to increase the diameter of the lens. However, when the diameter of the lens is increased in the above configuration in which the lenses are arranged at a predetermined interval in the longitudinal direction (first direction), the lens pitch in the longitudinal direction (first direction) increases, and a desired resolution is obtained. Could not be obtained. In other words, in the conventional technique, the resolution may decrease in exchange for increasing the amount of light incident on the lens.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique that enables a good exposure by taking a lot of light into a lens even at a high resolution.

  In order to achieve the above object, the exposure head according to the present invention has a length in the first direction W1, a length in the second direction orthogonal to the first direction is W2, and W1> W2. A light-transmitting substrate having a relationship, a first lens disposed on the light-transmitting substrate, and a lens array having a second lens disposed on the light-transmitting substrate in the first direction of the first lens And a head substrate having a first light emitting element that emits light to the first lens and a second light emitting element that emits light to the second lens, and the first lens and the second lens Are connected in the first direction.

  In the exposure head configured as described above, the first lens and the second lens are connected in the first direction. Therefore, more light can be taken into the first lens and the second lens without widening the distance between the first lens and the second lens in the first direction, and good exposure can be performed. It has become.

  The lens array has a third lens disposed on the light transmissive substrate on the second direction side of the first lens, and the third lens and the first lens are connected to each other. It may be configured. With this configuration, more light can be taken into the third lens and the first lens without widening the distance between the third lens and the first lens, and good exposure is possible. Become.

  Further, the third lens and the second lens may be connected. With this configuration, more light can be taken into the third lens and the first lens without widening the distance between the third lens and the second lens, and good exposure is possible. Become.

  As described above, in the configuration in which the first lens or the second lens and the third lens arranged on the second direction side of these lenses are connected, the first lens or the second lens and the third lens are connected. A large amount of light can be taken into the lens without increasing the distance from the lens. In other words, this is a configuration that can suppress the width of the lens array in the second direction. As a result, the area where the light emitting element is arranged corresponding to each lens can also be relatively space-saving in the second direction. Therefore, a space can be provided on both sides in the second direction in the head substrate on which the light emitting element is disposed. Therefore, it is preferable to provide a drive circuit for driving the light emitting element in this empty space. That is, the head substrate is preferably configured to have a drive circuit for driving the first light emitting element and the second light emitting element on the second direction side of the first light emitting element and the second light emitting element. At this time, the drive circuit can be composed of TFTs.

  In addition, it is particularly preferable to apply the present invention to a configuration in which the light emitting element is an organic EL element. That is, when the organic EL element is used as the light emitting element, the light amount of the light emitting element is less than that when the LED or the like is used. This is especially true when a bottom emission type organic EL element is used as a light emitting element. Therefore, it is preferable to apply a large amount of light to the lens by applying the present invention to such a configuration.

  The lens array substrate may be formed of glass. That is, glass has a relatively small linear expansion coefficient. Therefore, by forming the lens array substrate from glass, deformation of the lens array due to temperature change can be suppressed, and good exposure can be realized regardless of temperature.

  The lens may be formed of a photocurable resin. That is, the photocurable resin is cured by irradiating light. Therefore, since the lens array can be easily manufactured by forming the lens from the photocurable resin, the cost of the lens array can be suppressed.

  Further, the lens may be configured to be a free-form surface lens. This is because by employing a free-form surface lens, the imaging characteristics of the lens are improved and better exposure can be realized.

In order to achieve the above object, the exposure head according to another aspect of the present invention has a length in the first direction of W1 and a length in the second direction orthogonal to the first direction of W2. A light transmitting substrate having a relationship of W1> W2, a first lens disposed on the light transmitting substrate, and a second lens disposed on the light transmitting substrate in the first direction of the first lens. A lens array having a lens; a light emitting element that emits light imaged by the first lens; and a light emitting element that emits light imaged by the second lens; When the position is the first position, x: position in the first direction with the first position as the origin, y: position in the second direction with the first position as the origin, h: first position Height from the light transmitting substrate to the apex of the first lens, f (x, y): the first lens at coordinates (x, y) Others from the lens surface of the second lens to the first position height, p: interval in the first direction of the first lens and the second lens, the following equation,
f (p / 2, 0) <h
It is characterized by having the relationship.

  In the exposure head configured as described above, the first lens and the second lens are connected in the first direction. Therefore, more light can be taken into the first lens and the second lens without widening the distance between the first lens and the second lens in the first direction, and good exposure can be performed. It has become.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a latent image carrier and an exposure head that exposes the latent image carrier, and the exposure head has a length in the first direction. A light-transmitting substrate having a relationship of W1 and a length in a second direction orthogonal to the first direction being W2 and W1> W2, a first lens disposed on the light-transmitting substrate, and light A lens array having a second lens disposed in a first direction of the first lens on a transparent substrate, and a first light emission for emitting light imaged on the latent image carrier by the first lens And a head substrate having a second light emitting element that emits light formed on the latent image carrier by the second lens, and the first lens and the second lens are in the first direction. It is characterized by being connected to.

  In the image forming apparatus configured as described above, the first lens and the second lens are connected in the first direction. Therefore, more light can be taken into the first lens and the second lens without widening the distance between the first lens and the second lens in the first direction, and good exposure can be performed. It has become.

  In the configuration in which the latent image carrier is a photosensitive drum, the photosensitive drum has a cylindrical shape. Therefore, if the first lens and the third lens have the same shape, the imaging position may be different depending on the lens. In some cases, the surface of the photosensitive drum may be displaced. As a result, good exposure may not be performed. Therefore, the lens array has a third lens disposed on the light transmitting substrate on the second direction side of the first lens, and the head substrate forms an image on the latent image carrier by the third lens. A third light emitting element that emits the emitted light, an image formation position of the light from the first light emitting element imaged by the first lens, and a third light emission imaged by the third lens The shapes of the first lens and the third lens may be configured such that the image formation position of light from the element is a position corresponding to the shape of the photosensitive drum.

  Further, the third lens and the first lens may be connected. With this configuration, more light can be taken into the third lens and the first lens without widening the distance between the third lens and the first lens, and good exposure is possible. Become.

  Further, the third lens and the second lens may be connected. With this configuration, more light can be taken into the third lens and the first lens without widening the distance between the third lens and the second lens, and good exposure is possible. Become.

  As described above, in the configuration in which the first lens or the second lens and the third lens arranged on the second direction side of these lenses are connected, the first lens or the second lens and the third lens are connected. A large amount of light can be taken into the lens without increasing the distance from the lens. In other words, this is a configuration that can suppress the width of the lens array in the second direction. Therefore, it is possible to reduce the width of the exposure head and make a space around the latent image carrier. As a result, other functional units can be arranged in this empty space, and the image forming apparatus can be downsized.

  In order to achieve the above object, a lens array according to the present invention has a light transmissive lens array substrate, and the lens array substrate is provided with a lens row in which a plurality of lenses are arranged in a first direction. In the lens row, lenses adjacent in the first direction are connected to each other.

  In order to achieve the above object, the line head according to the present invention emits light from a head substrate on which a plurality of light emitting element groups in which a plurality of light emitting elements are grouped and a light-transmitting lens array substrate. And a lens array in which a plurality of lenses are arranged in the first direction on the lens array substrate, and adjacent lenses in the first direction are connected to each other in the lens row. It is characterized by that.

  In order to achieve the above object, the image forming apparatus according to the present invention has a head substrate on which a plurality of light emitting element groups in which a plurality of light emitting elements are grouped, and a light transmitting lens array substrate. A line head having a lens array arranged for each light emitting element group; and a latent image carrier on which a latent image is formed by exposure by the line head. A plurality of lenses are arranged in a first direction on the lens array substrate. Lined lens rows are provided, and the lens rows are characterized in that lenses adjacent in the first direction are connected to each other.

  In the invention thus configured (lens array, line head, image forming apparatus), a plurality of lenses are provided on a light transmissive lens array substrate. In this lens array substrate, a lens row in which a plurality of lenses are arranged in the first direction is provided. In the lens row, adjacent lenses in the first direction are connected to each other. In other words, in the present invention, there is no gap as in the prior art between lenses adjacent in the first direction, and these adjacent lenses are connected to each other. Therefore, a large amount of light can be taken into the lens even at high resolution, and good exposure is possible.

  In addition, the lens array substrate is configured such that a plurality of lens rows are arranged in a second direction orthogonal or substantially orthogonal to the first direction, and lenses in adjacent lens rows in the second direction are connected to each other. May be. As described above, since the lens is connected also in the second direction, more light can be incident on the lens, and better exposure can be performed.

  The lens array substrate may be formed of glass. That is, glass has a relatively small linear expansion coefficient. Therefore, by forming the lens array substrate from glass, deformation of the lens array due to temperature change can be suppressed, and good exposure can be realized regardless of temperature.

  The lens may be formed of a photocurable resin. That is, the photocurable resin is cured by irradiating light. Therefore, since the lens array can be easily manufactured by forming the lens from the photocurable resin, the cost of the lens array can be suppressed.

  Further, the lens may be configured to be a free-form surface lens. This is because by employing a free-form surface lens, the imaging characteristics of the lens are improved and better exposure can be realized.

  Hereinafter, terms used in the present specification will be described first (see “A. Explanation of Terms”). Following the explanation of this term, an embodiment of the present invention will be described (see the sections of “B. First Embodiment”, “C. Second Embodiment”, etc.)

A. 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.

B-1. First 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 in the first embodiment. FIG. 6 is a partial cross-sectional view taken along line AA of the line head shown in FIG. The AA line is a line including the optical axis of each lens constituting a lens array described later, and FIG. 6 is a cross section including the AA line and parallel to the optical axis of the lens. As described above, the line head 29 is disposed 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. As will be described later, in the line head 29, a plurality of light emitting elements are formed on the head substrate 293, and each light emitting element emits a light beam toward the surface of the photosensitive drum 21. Therefore, in this specification, a direction perpendicular to the longitudinal direction LGD and the width direction LTD and directed from the light emitting element to the surface of the photosensitive drum is defined as a light beam traveling direction Doa. The traveling direction Doa of the light beam is parallel or substantially parallel to an optical axis OA described later.

  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 light shielding member 297, and two lens arrays 299 (299A, 299B) are arranged. The inside of the case 291 is in contact with the front surface 293-h of the head substrate 293, while the back cover 2913 is in contact with the back surface 293-t 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 293-t 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 293-t of the head substrate 293 to the front surface 293-h. is there. This light emitting element is a bottom emission type organic EL (Electro-Luminescence) element and is covered with a sealing member 294. Details of the arrangement of the light emitting elements on the back surface 293-t of the head substrate 293 are as follows.

  FIG. 7 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. 8 is a diagram showing a configuration of a light emitting element group provided on the back surface of the head substrate. As shown in FIG. 7, the light emitting element group 295 is configured by grouping eight light emitting elements 2951. In each light emitting element group 295, eight light emitting elements 2951 are arranged as follows. That is, as shown in FIG. 8, 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 arranged in the width direction LTD. Are arranged side by side with the light emitting element row pitch Pelr. The light emitting element rows 2951R are shifted from each other by the element pitch Pel in the longitudinal direction LGD, and the positions of the light emitting elements 2951 in the longitudinal direction LGD are different from each other.

  In addition, on the back surface 293-t of the head substrate 293, a plurality of light emitting element groups 295 configured as described above are arranged. That is, the three light emitting element groups 295 are arranged at different positions in the width direction LTD to form the light emitting element group column 295C, and the plurality of light emitting element group columns 295C are arranged along the longitudinal direction LGD. In each light emitting element group column 295C, the three light emitting element groups 295 are shifted from each other by the light emitting element group pitch Peg in the longitudinal direction LGD. As a result, the position PTE in the longitudinal direction LGD of each light emitting element group 295 is Different from each other. In other words, on the back surface 293-t of the head substrate 293, 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 arranged in the width direction LTD. Is provided. Further, the light emitting element group rows 295R are arranged so as to be shifted from each other in the longitudinal direction LGD by the light emitting element group pitch Peg, and as a result, the positions PTE of the light emitting element groups 295 in the longitudinal direction LGD are different from each other. As described above, in the present embodiment, 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.

  Thus, each light emitting element 2951 formed on the head substrate 293 emits light beams having the same wavelength, for example, driven by a TFT (Thin Film Transistor) circuit or the like. 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.

  Returning to FIG. 5 and FIG. A light shielding member 297 is disposed in contact with the surface 293-h of the head substrate 293. The light shielding member 297 is provided with light guide holes 2971 for each of the plurality of light emitting element groups 295 (in other words, a plurality of light guide holes 2971 are provided one-on-one with respect to the plurality of light emitting element groups 295. ) Each light guide hole 2971 is formed in the light shielding member 297 as a hole penetrating in the light beam traveling direction Doa. Two lens arrays 299 are arranged in the light beam traveling direction Doa on the upper side of the light shielding member 297 (on the opposite side of the head substrate 293).

  As described above, the light shielding member 297 provided with the light guide hole 2971 for each light emitting element group 295 is arranged between the light emitting element group 295 and the lens array 299 in the traveling direction of the light beam Doa. Accordingly, the light beam emitted from the light emitting element group 295 passes through the light guide hole 2971 corresponding to the light emitting element group 295 and travels toward the lens array 299. In other words, among the light beams emitted from the light emitting element group 295, the light beam directed to other than the light guide hole 2971 corresponding to the light emitting element group 295 is shielded by the light shielding 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. ing.

  FIG. 9 is a plan view of the lens array in the first embodiment, and corresponds to the case where the lens array is viewed from the image plane side (light beam traveling direction Doa side). In addition, each lens LS in the same figure is formed in the back surface 2991-t of the lens array board | substrate 2991, and the same figure has shown the structure of this lens array board | substrate back surface 2991-t. In addition, in the same figure, the light emitting element group 295 is described, but this is for showing the correspondence between the light emitting element group 295 and the lens LS, and the light emitting element group 295 is provided on the rear surface 2991-t of the lens array substrate. It does not indicate that In the lens array 299, a lens LS is provided for each light emitting element group 295. That is, in the lens array 299, the lens array LSC is configured by arranging three lenses LS arranged at different positions in the width direction LTD, and a plurality of lens arrays LSC are arranged along the longitudinal direction LTD. . In each lens row LSC, three lenses are arranged so as to be shifted from each other by a lens pitch Pls in the longitudinal direction LGD. As a result, the positions PTL of the lenses LS in the longitudinal direction LGD are different from each other.

  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 by the lens pitch Pls 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. In the figure, the position of the lens LS is represented by the apex of the lens LS (that is, the point where the sag is maximum), and the position PTL in the longitudinal direction LGD of the lens LS is long from the apex of the lens LS. It is represented by a leg with a perpendicular line down to the direction axis LGD.

  As shown in FIG. 9, in this embodiment, in each lens row LSR, the lenses LS adjacent in the longitudinal direction LGD are connected to each other. On the other hand, in the width direction LTD, an interval (clearance) CL is provided between the lens rows LSR, and the lens rows LSR are arranged apart from each other.

  Further, as shown in FIG. 9, the shape of the lens LS differs depending on the lens row LSR. That is, in the width direction LTD, each of the upstream lens LS-u belonging to the most upstream lens row LSR and the downstream lens LS-d belonging to the most downstream lens row LSR has a shape in which a circular arc is connected to a rectangle. is doing. Further, the shape of the central lens LS-m belonging to the middle lens row LSR in the width direction LTD is substantially rectangular. Further, as shown in FIG. 5, the light guide hole 2971 has a shape corresponding to the corresponding lens LS. That is, each of the light guide hole 2971-u corresponding to the upstream lens LS-u and the light guide hole 2971-d corresponding to the downstream lens LS-d has a shape in which a circular arc is connected to a rectangle. . The shape of the light guide hole 2971-m corresponding to the center lens LS-m is substantially rectangular.

  FIG. 10 is a longitudinal sectional view of the lens array, the head substrate, and the like, and shows a longitudinal sectional view including the optical axis of the lens LS formed in the lens array. The lens array 299 has a light transmissive lens array substrate 2991. In this embodiment, the lens array substrate 2991 is made of glass having a relatively small linear expansion coefficient. Of the front surface 2991-h and back surface 2991-t of the lens array substrate 2991, a lens LS is formed on the lens array substrate 2991 back surface 2991-t. 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 shape of the lens LS is brought into contact with a glass substrate as the lens array substrate 2991. A photocurable resin is filled between the mold and the light transmissive substrate. When this photocurable resin is irradiated with light, the photocurable resin is cured and a lens LS is formed on the light transmissive substrate. Then, when the photocurable resin is cured and the lens LS is formed, the mold is released. As described above, in the present embodiment, the lens LS is formed of a photocurable resin that can be quickly cured by irradiation with light. Therefore, since the lens LS can be easily formed, the manufacturing process of the lens array 299 is simplified, and the cost of the lens array 299 can be reduced. In addition, since the lens array substrate 2991 is formed of glass having a small linear expansion coefficient, deformation of the lens array 299 due to a temperature change is suppressed, and good exposure can be realized regardless of the temperature.

  In the line head 29, two lens arrays 299 having such a configuration are arranged side by side in the traveling direction Doa of the light beam (299A, 299B), and two lenses LS1, LS2 aligned in the traveling direction Doa of the light. Is arranged for each light emitting element group 295 (FIGS. 5, 6, and 10). Also, the optical axis OA (the two-dot chain line in FIG. 10) passing through the center of each of the first lens LS1 and the second lens LS2 corresponding to the same light emitting element group 295 is orthogonal to or substantially the back surface 293-t of the head substrate 293. Orthogonal. Here, the lens LS of the lens array 299A upstream of the light beam traveling direction Doa is the first lens LS1, and the lens LS of the lens array 299B downstream of the light beam traveling direction Doa is the second lens LS2. . Thus, in this embodiment, since the plurality of lens arrays 299 are arranged in the light beam traveling direction Doa, the degree of freedom in optical design can be improved.

  As described above, the line head 29 includes an optical system having the first and second lenses LS1 and LS2. Therefore, the light beam emitted from the light emitting element group 295 is imaged by the first lens LS1 and the second lens LS2, and a spot SP is formed on the surface (image 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. As shown in the drawing, the three light emitting element groups 295 capable of forming the spot group SG in the exposure region ER continuous in the main scanning direction MD are arranged so as to be shifted from each other in the width direction LTD. That is, for example, the three light emitting element groups 295_1, 295_2, 295_3 capable of forming the spot groups SG_1, SG2, SG3 in the exposure regions ER_1, ER_2, ER3 continuous in the main scanning direction MD are mutually connected in the width direction LTD. They are staggered. These three light emitting element groups 295 constitute a light emitting element group column 295C, and a plurality of light emitting element group columns 295C are arranged along the longitudinal direction LGD. As a result, as described in the description of FIG. 7, the three light emitting element group rows 295R_A, 295R_B, and 295R_C are arranged in the width direction LTD, and the light emitting element group rows 295R_A and the like are mutually connected in the sub scanning direction SD. Spot groups SG are formed at different positions.

  That is, in the line head 29, the plurality of light emitting element groups 295 (for example, the light emitting element groups 295_1, 295_2, and 295_3) are arranged at different positions in the width direction LTD. Then, the light emitting element groups 295 arranged at different positions in the width direction LTD form spot groups SG (for example, spot groups SG_1, SG_2, SG_3) at different positions in the sub-scanning direction SD.

  In other words, in the line head 29, a plurality of light emitting elements 2951 are arranged at different positions in the width direction LTD (for example, the light emitting elements 2951 belonging to the light emitting element group 295_1 and the light emitting elements belonging to the light emitting element group 295_2). 2951 are arranged at different positions in the width direction LTD). The light emitting elements 2951 arranged at different positions in the width direction LTD form spots SP at different positions in the sub-scanning direction SD (for example, the spots SP belonging to the spot group SG_1 and the spot group SG_2). The spots SP are formed at different positions in the sub-scanning direction SD).

  As described above, the formation position of the spot SP in the sub-scanning direction SD differs depending on the light emitting element 2951. 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. 7, 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. 11) belonging to the most upstream light emitting element group 295_1, 295A4, etc. 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 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 light emitting element groups 295_1, 295A4, 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 first embodiment, the light transmissive lens array substrate 2991 is provided with a plurality of lenses LS. In the lens array substrate 2991, a lens row LSR in which a plurality of lenses LS are arranged in the longitudinal direction LGD (first direction) is provided. In the lens row LSR, the lenses LS adjacent to each other in the longitudinal direction LGD are connected to each other. In other words, in the first embodiment, there is no gap between the lenses LS adjacent in the longitudinal direction LGD as in the prior art, and these adjacent lenses LS are connected to each other. Therefore, a large amount of light can be taken into the lens even at high resolution, and good exposure is possible.

  By the way, in the said embodiment, since the organic EL element is used as the light emitting element 2951 and this organic EL element has little light quantity compared with LED (Light Emitting Diode) etc., the light quantity which can be taken in into the lens LS tends to become small. It is in. In particular, when a bottom emission type organic EL element is used, a part of the light beam emitted from the organic EL element is absorbed by the head substrate 293, so that the amount of light that can be captured by the lens LS is further reduced. On the other hand, in the above embodiment, the lenses LS adjacent to each other in the longitudinal direction LGD are connected to each other, so that a lot of light can be taken into the lens LS. Therefore, even in a configuration using a bottom emission type organic EL element as the light emitting element 2951, good exposure is possible.

B-2. Second Embodiment FIG. 13 is a perspective view showing an outline of a line head in a second embodiment. FIG. 14 is a plan view of the lens array in the second embodiment, and corresponds to a case where the lens array is viewed from the image plane side (light beam traveling direction Doa side). Each lens LS in FIG. 14 is formed on the back surface 2991-t of the lens array substrate 2991. FIG. 14 shows the configuration of this lens array substrate back surface 2991-t. In addition, in the same figure, the light emitting element group 295 is described, but this is for showing the correspondence between the light emitting element group 295 and the lens LS, and the light emitting element group 295 is provided on the rear surface 2991-t of the lens array substrate. It does not indicate that In the following, differences between the second embodiment and the first embodiment will be mainly described, and common portions are denoted by corresponding reference numerals and description thereof is omitted.

  As shown in FIG. 14, also in the second embodiment, 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 by the lens pitch Pls in the longitudinal direction LGD, and the positions PTL of the lenses LS in the longitudinal direction LGD are different from each other. In each lens row LSR, the lenses LS adjacent to each other in the longitudinal direction LGD are connected to each other. On the other hand, in the second embodiment, the interval CL as in the first embodiment is not provided between the lens rows, and the lenses LS of the lens rows LSR adjacent in the width direction LTD are connected to each other.

  As shown in FIG. 14, also in the second embodiment, the shape of the lens LS differs depending on the lens row LSR. That is, in the width direction LTD, each of the upstream lens LS-u belonging to the most upstream lens row LSR and the downstream lens LS-d belonging to the most downstream lens row LSR has an arc in a pentagon (home base pentagon). It has a connected shape. Further, the shape of the central lens LS-m belonging to the middle lens row LSR in the width direction LTD is a substantially hexagonal shape. Moreover, as shown in FIG. 13, the light guide hole 2971 has a shape corresponding to the corresponding lens LS. That is, each of the light guide hole 2971-u corresponding to the upstream lens LS-u and the light guide hole 2971-d corresponding to the downstream lens LS-d has a shape in which an arc is connected to a home base pentagon. Have. The shape of the light guide hole 2971-m corresponding to the central lens LS-m is substantially hexagonal.

  As described above, also in the second embodiment, in the lens row LSR, the lenses LS adjacent to each other in the longitudinal direction LGD (first direction) are connected to each other. That is, there is no gap between the lenses LS adjacent in the longitudinal direction LGD as in the prior art, and these adjacent lenses LS are connected to each other. Therefore, a large amount of light can be taken into the lens even at high resolution, and good exposure is possible.

  In the second embodiment, the lens array substrate 2991 has a plurality of lens rows LSR arranged in the width direction LTD (second direction), and the lenses LS of the lens rows LSR adjacent to the width direction LTD are connected to each other. ing. That is, in the second embodiment, the lens LS is connected not only in the longitudinal direction LGD but also in the width direction LTD. Therefore, more light can be incident on the lens LS, and better exposure is possible.

B-3. In the configuration shown in FIG. 14, the lens LS-u (first lens, second lens) and the lens LS-m (third lens) are connected to each other. A large amount of light can be taken into the lens without increasing the distance between the lens LS-u and the lens LS-m. The lens LS-m (first lens, second lens) and the lens LS-d (third lens) are connected to each other, and the distance between the lens LS-m and the lens LS-d. A large amount of light can be taken into the lens without widening. In other words, the configuration in FIG. 14 is a configuration that can suppress the width of the lens array 299 in the width direction LTD (second direction). As a result, the area where the light emitting elements 2951 are arranged corresponding to the respective lenses LS on the head substrate 293 can also be saved in the width direction LTD. Therefore, in the head substrate 293 on which the light emitting element 2951 is disposed, a space can be provided on both sides in the width direction LTD. Therefore, it is preferable to arrange a drive circuit for driving the light emitting element in this vacant space. Specifically, it is as follows.

  FIG. 15 is a plan view showing the configuration of the head substrate of the third embodiment. As shown in the figure, the drive circuit DC composed of TFTs is disposed in the space vacated on both sides in the width direction LTD of the head substrate 293. This drive circuit DC is connected to the light emitting elements 2951 by wirings WL, and gives a drive signal to each light emitting element 2951. As described above, the drive circuit DC can be arranged relatively close to the light emitting element 2951 by arranging the drive circuit DC in the space that is vacant on both sides of the head substrate 293 in the width direction LTD. Therefore, the wiring WL can be shortened, and a driving signal with less dullness due to the floating capacitance of the wiring WL can be supplied to the light-emitting element 2951 so that a favorable exposure operation can be performed.

B-4. Fourth Embodiment FIG. 16 is a plan view showing a configuration of a lens array according to a fourth embodiment. The lens array 299 includes a lens array substrate 2991 (light transmissive substrate) whose base material is glass. This lens array substrate 2991 has a length W1 in the longitudinal direction LGD and a width W2 (length W2) in the width direction LTD. Further, the length W1> the width W2, and the lens array substrate 2991 is long in the longitudinal direction LGD. On the surface 2991-h of the lens array substrate 2991, a plurality of lenses LS are two-dimensionally arranged. In each lens row LSR, adjacent lenses LS in the longitudinal direction LGD with an interval p are connected to each other in the longitudinal direction LGD. Further, in the drawing, a flat region where the lens LS is not formed is shown as a flat region Ap (first region) on the lens array substrate surface 2991-h.

  Further, in FIG. 16, xy coordinates (x, y) are shown in order to indicate the position on the lens array substrate surface 2991-h. The x axis is a coordinate axis parallel or substantially parallel to the longitudinal direction LGD, the y axis is a coordinate axis parallel or substantially parallel to the width direction LTD, and the x axis and the y axis are orthogonal to each other. Further, in the xy coordinates, the origin is the vertex Lt11 of the lens LS11 in the upper left of the figure (the position on which it is projected onto the xy plane). The vertex Lt of the lens LS is a position where the height of the lens LS from the flat area Ap is the highest. Thus, x indicates the position in the longitudinal direction LGD with the vertex Lt11 as the origin, and y indicates the position in the width direction LTD with the vertex Lt11 as the origin. The lens surface of each lens LS is configured as follows.

  FIG. 17 is a diagram illustrating the configuration of the lens surface of the lens. The “plan view” in FIG. 17 corresponds to a plan view from the traveling direction Doa of the light beam, and the “cross-sectional view” in FIG. It is longitudinal direction LGD sectional drawing containing the vertex Lt. In the drawing, in order to show the relationship between two lenses LS adjacent to each other in the longitudinal direction LGD, the lens LS11 and the lens LS are representatively shown. Hereinafter, the lens LS11 is referred to as a “first lens” and the lens LS12 is referred to as a “second lens” as necessary.

The symbol h shown in “Cross-sectional view” in the figure indicates the height from the flat region Ap at the position (vertex Lt) at which the height from the flat region Ap is highest on the lens surface of each lens LS. . That is, the symbol h is the height from the flat area Ap (in other words, the lens array substrate surface 2991-h) of the lens vertex Lt of each lens LS, and each lens LS has the same height h. The function f (x, y) is the height from the lens surface at coordinates (x, y) to the vertex Lt (first position) of the lens LS. And in this embodiment,
f (p / 2, 0) <h
Is satisfied. That is, the first lens LS11 and the second lens LS12 are connected to each other in the longitudinal direction LGD, and the boundary BD between the first lens LS11 and the second lens LS12 has a height Δ (from the flat region Ap. = H−f (p / 2, 0)> 0).

  Thus, also in this embodiment, the lenses LS adjacent in the longitudinal direction LGD are connected to each other. Therefore, more light can be taken into the lens LS without increasing the distance p between the lenses LS. This will be described in detail as follows.

  FIG. 18 is an explanatory diagram of the effect of the present invention. The “unconnected” column in the figure corresponds to the case where the adjacent lens LS is not connected in the longitudinal direction LGD, and the “connected” column in the figure has the lens LS connected in the longitudinal direction LGD. This corresponds to the case (that is, the case where the present invention is applied). In addition, the area surrounded by the two-dot chain line circle in the figure shows the effective area LSe of the lens LS, and the solid line circle in the figure shows the lens outer periphery LSc of the lens LS. In general, the surface accuracy in the vicinity of the lens outer periphery LSC cannot be guaranteed. Therefore, it is necessary to provide a margin d between the lens outer periphery LSC and the effective area LSe of the lens LS. As shown in the column “Not Connected”, when the lens LS adjacent in the longitudinal direction LGD is not connected, it is necessary to provide a margin d over the entire circumference of the lens outer periphery LSC. On the other hand, as shown in the “connection” column, by connecting the lenses LS adjacent to each other in the longitudinal direction LGD, it is not necessary to provide a margin d in the longitudinal direction LGD. As a result, the lens effective area LSe can be expanded without changing the lens interval p.

  In addition, the configuration in which the boundary BD of the lenses LS connected to each other has a height Δ as in the present embodiment has the following advantages. That is, when the lens array 299 is formed using the above-described mold, the photocurable resin that is the base material of the lens LS is filled between the mold and the lens array substrate 2991. At this time, in order to form a lens LS having a highly accurate surface shape, it is desirable to distribute the photocurable resin over substantially the entire lens array substrate 2991. For this purpose, the flow of the photocurable resin is desired. It is important to ensure sex. On the other hand, in this embodiment, since the boundary BD has a height Δ, the mold also has a predetermined height at a portion corresponding to the boundary BD. Therefore, the photocurable resin can be flowed through the portion corresponding to the boundary BD, and as a result, the lens LS having a highly accurate surface shape can be formed.

  Furthermore, in this embodiment, there is no need to increase the distance p between the lenses LS, in other words, the distance p between the lenses can be kept short. As a result, the present embodiment can achieve the following effects. FIG. 19 is an explanatory diagram of further effects of the present invention. As described above, the line head 29 is arranged so that the longitudinal direction LGD of the line head 29 is parallel to the axial direction of the photosensitive drum 21 (that is, the main scanning direction MD). However, in some cases, the longitudinal direction LGD of the line head 29 may be attached skewed with respect to the main scanning direction MD. As a result, as shown in FIG. 19, in the sub-scanning direction SD between the plurality of spot latent images Lsp formed by the first lens LS11 and the plurality of spot latent images Lsp formed by the second lens LS12. A step g is generated. In FIG. 19, the spot latent image by the first lens LS11 is denoted by reference numeral 295_1 and the spot latent image by the second lens LS12 is denoted by reference numeral 295_4 corresponding to the notation in FIG. . As described above, although the step g is generated due to the occurrence of the skew, in the present embodiment, since the interval p between the lenses LS is suppressed to be short, the step g can be suppressed to be relatively small. As a result, it is possible to execute a good exposure operation regardless of the occurrence of skew.

C. Others As described above, in the above-described embodiment, the longitudinal direction LGD and the main scanning direction MD correspond to the “first direction” of the present invention, and the width direction LTD and the sub scanning direction SD correspond to the “second direction” of the present invention. The photosensitive drum 21 corresponds to the “latent image carrier” of the present invention. The line head 29 corresponds to the “exposure head” 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 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. Therefore, the light emitting element group 295 can be configured as shown below.

  FIG. 20 is a plan view showing another configuration of the light emitting element group. FIG. 21 is a diagram showing the configuration of the back surface of the head substrate in which a plurality of light emitting element groups of FIG. 20 are arranged, and corresponds to the case where the back surface is viewed from the front surface of the head substrate. In another configuration shown in FIG. 20, 15 light emitting elements 2951 are arranged in the longitudinal direction LGD to form a light emitting element row 2951R. In the light emitting element row 2951R, the light emitting elements 2951 are arranged at a pitch (= 0.084 [mm]) that is four times the element pitch Pel (= 0.021 [mm]). The four light emitting element rows 2951R thus configured are arranged in the width direction LTD (2951R-1, 2951R-2, 2951R-3, 2951R-4). In the width direction LTD, the pitch between the light emitting element row 2951R-4 and the light emitting element row 2951R-1 is 0.1155 [mm], and between the light emitting element row 2951R-4 and the light emitting element row 2951R-2. The pitch is 0.084 [mm], and the pitch between the light emitting element row 2951R-4 and the light emitting element row 2951R-3 is 0.0315 [mm]. When a straight line that passes through the center (center of gravity) of the light emitting element group 295 and is parallel to the width direction LTD is a center line CTL, each of the light emitting element row 2951R-1 and the light emitting element row 2951R-4 and the center line CTL The pitch is 0.05775 [mm].

  In FIG. 20, two rows 2951R-1 and 2951R-2 above the center line CTL constitute one light emitting element row set 2951RT, and two rows 2951R-3 and 2951R- below the center line CTL. 4 constitutes one light emitting element row set 2951RT. In each of the light emitting element row sets 2951RT, the two light emitting element rows 2951R are shifted from each other by twice the element pitch Pel (= 0.021 [mm]) (= 0.042 [mm]) in the longitudinal direction LGD. Moreover, the two light emitting element row groups 2951RT are shifted from each other by the element pitch Pel (= 0.021 [mm]) in the longitudinal direction LGD. Therefore, the four light emitting element rows 2951R are displaced from each other by the element pitch Pel (= 0.021 [mm]) in the longitudinal direction LGD. As a result, the positions of the respective light emitting elements 2951 in the longitudinal direction LGD are different. Yes. Here, when the light emitting elements 2951 positioned at both ends in the longitudinal direction LGD of the light emitting element group 295 are end light emitting elements 2951x, the pitch between the end light emitting elements 2951x in the longitudinal direction LGD is 1.239 [mm] The pitch between the end light emitting element 2951x and the center of the light emitting element group 295 in the longitudinal direction LGD is 0.6195 [mm].

  In the example shown in FIG. 21, the light emitting element groups 295 shown in FIG. 20 are two-dimensionally arranged. As shown in FIG. 21, a plurality of light emitting element groups 295 are arranged in the longitudinal direction LGD to form a light emitting element group row 295R. In the light emitting element group row 295R, the light emitting element groups 295 are arranged at a pitch (= 1.778 [mm]) three times the light emitting element group pitch Peg. The three light emitting element group rows 295R thus configured (295R-1, 295R-2, 295R-3) in the width direction LTD are light emitting element group row pitches Pegr (= 1.77 [mm]). Are lined up. The light emitting element group rows 295R are shifted from each other by the light emitting element group pitch Peg (about 0.593 [mm]) in the longitudinal direction LGD. That is, the light emitting element group row 295R-1 and the light emitting element group row 295R-2 are shifted by 0.59275 [mm] in the longitudinal direction LGD, and the light emitting element group row 295R-2 and the light emitting element group row 295R-3 are disposed. Is shifted by 0.5925 [mm] in the longitudinal direction LGD, and the light emitting element group row 295R-3 and the light emitting element group row 295R-1 are shifted by 0.59275 [mm] in the longitudinal direction LGD. . Therefore, the light emitting element group row 295R-1 and the light emitting element group row 295R-3 are shifted by 1.18525 [mm] in the longitudinal direction LGD.

  In the above embodiment, the lens array 299 is configured by forming the lens LS on the back surface 2991-t of the lens array substrate. However, the configuration of the lens array is not limited to this. That is, the lens array 299 may be formed by forming the lens LS on the surface 2991-h of the lens array substrate, or the lens array may be formed by forming the lens LS on both surfaces 2991-t and 2991-h of the lens array substrate. 299 may be configured.

  In the above embodiment, the three lens rows LSR are arranged in the width direction LTD. However, the number of lens rows LSR is not limited to three, and may be one, for example.

  In the above embodiment, two lens arrays 299 are used, but the number of lens arrays 299 is not limited to this.

  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.

  FIG. 22 is a diagram showing an optical system in the embodiment, and shows a cross section in the main scanning direction MD. In this embodiment, a stop DIA is provided in front of the first lens LS1 in the light beam traveling direction Doa, and the light beam stopped by the stop DIA is incident on the first lens LS1. In the figure, the optical path of the light beam that emerges from the object point OB0 on the optical axis OA and forms an image at the image point IM0, and the light beam that emerges from the object point OB1 different from the optical axis OA and forms an image at the image point IM1. The optical path is shown. The configuration other than the diaphragm DIA is substantially the same as that shown in the first embodiment, and the three lenses LS-u, LS-m, and LS in the AA line direction shown in FIGS. The optical systems including the respective lenses LS are arranged so that −d forms a lens array.

  FIG. 23 is a partial cross-sectional view taken along line AA of the line head and the photosensitive drum in the first embodiment. As shown in the figure, the line head including the light emitting element group 295, the diaphragm DIA, and the lens arrays 299A and 299B is disposed to face the photosensitive drum 21. The photosensitive drum 21 has a substantially cylindrical shape centered on the rotation axis CC21, and the surface of the photosensitive drum has a finite curvature. Here, the shape of the surface of the photoreceptor is particularly referred to as “curvature shape”.

  In this embodiment, the optical systems are arranged at equal pitches in the horizontal direction in FIG. 23, and the optical axis OA of the optical system including the central lens LS-m passes through the rotation axis CC21 of the photosensitive drum 21. Therefore, in order to make the optical beam imaging position of each optical system substantially coincide with the surface of the photosensitive drum, it is necessary to adjust the imaging position in the light beam traveling direction Doa (optical axis OA direction) for each optical system. is there. In the example shown in FIG. 23, the imaging positions FP in the traveling direction Doa of the light beam are equal between the optical system including the upstream lens LS-u and the optical system including the downstream lens LS-d. On the other hand, the imaging position in the traveling direction Doa of the light beam differs from the optical system including the upstream lens LS-u (or the downstream lens LS-d) by a distance ΔFP. Therefore, as shown in the following data, in this embodiment, the configuration differs between the optical system including the lenses LS-u and LS-d and the optical system including the lens LS-m.

  FIG. 24 is a diagram showing optical system specifications in the embodiment. As shown in the figure, the wavelength of the light beam emitted from the light emitting element is 690 [nm]. The diameter of the photoreceptor is 40 [mm]. FIG. 25 is a diagram illustrating data of the optical system including the central lens. As shown in the figure, in the optical system including the central lens LS-m, the lens surface (surface number S4) of the first lens LS1 and the lens surface (surface number S7) of the second lens LS2 are both free-form surfaces (XY). Polynomial surface). FIG. 26 is a diagram showing the definition formula of the XY polynomial surface. The lens surface shape of the first lens LS1 is given by the same definition formula and the coefficient shown in FIG. 27, and the lens surface shape of the second lens LS2 is the same definition formula. It is given by the coefficient shown in FIG. Here, FIG. 27 is a diagram illustrating coefficient values of the surface S4 of the optical system including the central lens, and FIG. 28 is a diagram illustrating coefficient values of the surface S7 of the optical system including the central lens.

  FIG. 29 is a diagram illustrating data of an optical system including an upstream lens and a downstream lens. As shown in the figure, also in the optical system including the upstream lens LS-u and the downstream lens LS-d, the lens surface (surface number S4) of the first lens LS1 and the lens surface (surface number S7) of the second lens LS2. Are free-form surfaces (XY polynomial surfaces). The lens surface shape of the first lens LS1 is given by the definition formula of FIG. 26 and the coefficient shown in FIG. 30, and the lens surface shape of the second lens LS2 is given by the definition formula and the coefficient shown in FIG. Here, FIG. 30 is a diagram illustrating coefficient values of the surface S4 of the optical system including the upstream lens and the downstream lens, and FIG. 31 is a diagram illustrating coefficient values of the surface S7 of the optical system including the upstream lens and the downstream lens. .

  Thus, in the above embodiment, the lens LS of the lens array 299 is a free-form surface lens. Here, the free-form surface lens is a lens whose lens surface is a free-form surface. Therefore, the imaging characteristics of the lens are improved, and better exposure can be realized.

  In this embodiment, the lenses LS are not connected in the width direction LTD, that is, the lenses LS-u, LS-m, and LS-d are not connected. However, the lenses LS-u, LS-m, and LS-d may be connected to each other in the width direction LTD. Accordingly, a large amount of light can be taken into the lenses LS-u, LS-m, and LS-d without increasing the interval in the width direction LTD of the lenses LS-u, LS-m, and LS-d. In other words, the width of the lens array 299 in the width direction LTD can be suppressed. As a result, the width of the line head 29 can be reduced, and a space can be made around the photosensitive drum 21. Therefore, other functional units can be concentrated and arranged in this empty space, and the image forming apparatus can be downsized.

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 in 1st Embodiment. FIG. 6 is a partial cross-sectional view taken along line AA of the line head illustrated in FIG. 5. The figure which shows the structure of the back surface of a head board | substrate. The figure which shows the structure of the light emitting element group provided in the head substrate back surface. The top view of the lens array in 1st Embodiment. Sectional drawing of a longitudinal direction, such as a lens array and a head board | substrate. The perspective view for demonstrating the spot formed with a line head. The figure which shows the spot formation operation | movement by the above-mentioned line head. The perspective view which shows the outline of the line head in 2nd Embodiment. The top view of the lens array in 2nd Embodiment. The top view which shows the structure of the head substrate of 3rd Embodiment. The top view which shows the structure of the lens array concerning 4th Embodiment. The figure which shows the structure of the lens surface of a lens. Explanatory drawing of the effect of this invention. Explanatory drawing of the further effect of this invention. The top view which shows another structure of a light emitting element group. The figure which shows the head substrate back surface which has arranged the light emitting element group of FIG. The figure which shows the optical system in an Example. FIG. 3 is a partial cross-sectional view taken along line AA of the line head and the like in the first embodiment. The figure showing the optical system item in an Example. The figure which shows the data of the optical system containing a center lens. The figure which shows the definition formula of an XY polynomial surface. The figure which shows the coefficient value of surface S4 of the optical system containing a center lens. The figure which shows the coefficient value of surface S7 of the optical system containing a center lens. The figure which shows the data of the optical system containing an upstream lens and a downstream lens. The figure which shows the coefficient value of surface S4 of the optical system containing an upstream lens and a downstream lens. The figure which shows the coefficient value of surface S7 of the optical system containing an upstream lens and a downstream lens.

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, 299A, 299B ... lens array, 2991 ... lens array substrate, LS, LS1, LS2 ... lens, SP ... spot, Lsp ... spot latent image, MD ... main scanning direction (first direction), SD ... sub-scanning direction (second direction), LGD ... longitudinal direction (first direction), LTD: width direction (second direction)

Claims (15)

A light-transmitting substrate having a relationship of W1> W2 in which the length in the first direction is W1, the length in the second direction orthogonal to the first direction is W2, and W1> W2 is disposed on the light-transmitting substrate. A lens array comprising: a first lens provided; and a second lens disposed on the light transmissive substrate in the first direction of the first lens;
A head substrate having a first light emitting element that emits light to the first lens, and a second light emitting element that emits light to the second lens;
With
An exposure head, wherein the first lens and the second lens are connected in the first direction. The lens array includes a third lens disposed on the light transmissive substrate on the second direction side of the first lens,
The exposure head according to claim 1, wherein the third lens and the first lens are connected.   The exposure head according to claim 2, wherein the third lens and the second lens are connected.   The head substrate has a drive circuit for driving the first light emitting element and the second light emitting element on the second direction side of the first light emitting element and the second light emitting element. 4. The exposure head according to 3.   The exposure head according to claim 4, wherein the driving circuit is constituted by a TFT.   The exposure head according to claim 1, wherein the first light emitting element and the second light emitting element are organic EL elements.   The exposure head according to claim 6, wherein the organic EL element is a bottom emission type.   The exposure head according to claim 1, wherein the light transmissive substrate is made of glass.   The exposure head according to claim 1, wherein the first lens and the second lens are formed of a photocurable resin.   The exposure head according to claim 1, wherein the first lens and the second lens are free-form surface lenses. A light-transmitting substrate having a relationship of W1> W2 in which the length in the first direction is W1, the length in the second direction orthogonal to the first direction is W2, and W1> W2 is disposed on the light-transmitting substrate. A lens array comprising: a first lens provided; and a second lens disposed on the light transmissive substrate in the first direction of the first lens;
A light emitting element that emits light imaged by the first lens;
A light emitting element that emits light imaged by the second lens,
When the position of the vertex of the first lens is the first position,
x: a position in the first direction with the first position as an origin,
y: position in the second direction with the first position as the origin,
h: a height from the light transmissive substrate to the apex of the first lens at the first position;
f (x, y): the height from the lens surface of the first lens or the second lens to the first position at coordinates (x, y),
p: The distance between the first lens and the second lens in the first direction is expressed by the following equation:
f (p / 2, 0) <h
An exposure head having the following relationship: A latent image carrier;
An exposure head for exposing the latent image carrier,
The exposure head includes a light transmissive substrate having a length of W1 in a first direction and a length of W2 in a second direction orthogonal to the first direction, and having a relationship of W1> W2. A first lens disposed on a transmissive substrate; a lens array having a second lens disposed on the light transmissive substrate in the first direction of the first lens; and the first A first light emitting element that emits light imaged on the latent image carrier by a lens; and a second light emitting element that emits light imaged on the latent image carrier by the second lens. A head substrate, and
The image forming apparatus, wherein the first lens and the second lens are connected in the first direction. The latent image carrier is a photosensitive drum;
The lens array includes a third lens disposed on the light transmissive substrate on the second direction side of the first lens,
The head substrate includes a third light emitting element that emits light imaged on the latent image carrier by the third lens,
The imaging position of light from the first light emitting element imaged by the first lens and the imaging position of light from the third light emitting element imaged by the third lens are the photosensitivity. The image forming apparatus according to claim 12, wherein the shapes of the first lens and the third lens are configured so as to be positioned according to the shape of the body drum.   The image forming apparatus according to claim 13, wherein the third lens and the first lens are connected.   The image forming apparatus according to claim 14, wherein the third lens and the second lens are connected.

Images