JP2011042039A - Exposure head, image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for enabling good exposure by suppressing uneven exposure, even if design errors occur in an imaging optical system, or even if the imaging optical system and a light emitting element are arranged to be misaligned, for example. <P>SOLUTION: On an exposed surface, a first spot imaged by a first imaging optical system overlaps a third spot imaged by the first imaging optical system seen from a direction orthogonal to a first direction. A second spot imaged by the first imaging optical system overlaps a fourth spot imaged by a second imaging optical system seen from the direction orthogonal to the first direction. A first light emitting element and a third light emitting element are made to emit light with the same or almost the same amount of light. A second light emitting element and a fourth light emitting element are made to emit light with a smaller amount of light than the light amount of the first light emitting element. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exposure head that forms an image of light from a light emitting element on an exposed surface by an imaging optical system and an image forming apparatus including the exposure head.

  Conventionally, as described in Patent Document 1, exposure including a plurality of light emitting element groups (light emitting element groups of the same document) provided in a one-to-one correspondence with a plurality of imaging lenses of a lens array. A head (line head of the same document) has been proposed. That is, in the light emitting element group of this exposure head, a plurality of light emitting elements are arranged in the first direction (longitudinal direction in the same document) corresponding to the main scanning direction. Each light emitting element emits light at a timing corresponding to the movement of the exposed surface (scanned surface in the same document) in the sub-scanning direction, and the light is different from each other in the main scanning direction of the exposed surface by the imaging lens. The spot is formed on the exposed surface by the light, and the exposed surface is exposed. Such exposure is performed for each light emitting element group, and as a result, a plurality of spots are formed side by side in the main scanning direction of the exposed surface for each light emitting element group. In Patent Document 1, such a plurality of spots formed for each light emitting element group is referred to as a spot group, and a plurality of spot groups are formed corresponding to the plurality of light emitting element groups.

  By the way, as pointed out in Patent Document 1, the positional relationship between a plurality of spot groups may be shifted due to various causes. For example, the lens formation position in the lens array may vary within a range of manufacturing errors. Can be mentioned. In this way, with the positional relationship between the spot groups shifted from each other, spot groups are sequentially formed while moving the exposed surface in the sub-scanning direction and developed to form a toner image. Vertical streaks in the sub-scanning direction appear at corresponding positions in between, causing a reduction in image quality. Therefore, in Patent Document 1, multiple spot exposure is partially performed in spot groups formed adjacent to each other in the main scanning direction. That is, the spot by the light from the light emitting element at the end of one light emitting element group adjacent to the first direction and the spot by the light from the light emitting element at the end of the other light emitting element group are They overlap each other in the main scanning direction. In this way, two spot groups formed by different imaging optical systems are partially overlapped. This prevents vertical stripes from appearing in the toner image even when the positional relationship between the spot groups is shifted from each other.

JP 2008-173889 A

  However, for example, if a design error occurs in the imaging optical system of the exposure head, or if the imaging optical system and the light emitting element are shifted, the spot due to the light from the light emitting element is shifted in the main scanning direction. There is. Accordingly, in the exposure head described in Patent Document 1, for example, when the imaging optical system and the light emitting element are arranged to be shifted, the multiple exposure region, that is, two spots by light from the two light emitting elements. In the region where the two are overlapped in the main scanning direction, the spots are shifted from each other in the main scanning direction, so that the influence of the shift that the exposure is somewhat blurred appears. On the other hand, in a region where multiple exposure is not performed, that is, a region where spots do not overlap, there is no overlap of spots, and thus the above-described influence due to the shift does not appear. Therefore, a difference due to the presence or absence of the influence of the deviation occurs between these areas, and this difference becomes exposure unevenness. In an image forming apparatus using such an exposure head, uneven density of the toner image due to uneven exposure occurs.

  The present invention has been made in view of the above problems. In an exposure head that forms an image of light from a light emitting element on an exposed surface by an imaging optical system and an image forming apparatus including the exposure head, for example, imaging optics Even if a design error occurs in the system or the imaging optical system and the light emitting element are shifted from each other, it is an object of the present invention to provide a technique capable of suppressing exposure unevenness and realizing good exposure.

  In order to achieve the above object, an exposure head according to the present invention forms a first spot formed by a first imaging optical system that forms an image of light on a surface to be exposed and a first imaging optical system. Is formed in the first direction of the first light emitting element, and is imaged by the first imaging optical system to be a second spot. Is formed on the exposed surface by a second light emitting element that emits light and the first imaging optical system, and the third spot overlaps with the first spot when viewed from the direction orthogonal to the first direction. A third light-emitting element that emits light that forms a spot on the exposed surface, a second image-forming optical system that forms light on the exposed surface, and a second image-forming optical system. , A fourth light emitting element that emits light that forms a fourth spot on the exposed surface that overlaps the second spot when viewed from a direction orthogonal to the first direction. The element, the first light emitting element, and the third light emitting element emit light with the same or substantially the same light amount, and the second light emitting element and the fourth light emitting element emit light with a light amount smaller than the light amount of the first light emitting element. And a control unit.

  In the invention configured as described above, the first image is formed by the first image forming optical system, the first spot is formed on the exposed surface, and the first image forming optical system forms an image. A third spot that overlaps the first spot when viewed from a direction orthogonal to the direction is formed on the exposed surface. In addition, an image is formed by the first imaging optical system and a second spot is formed on the exposed surface, and an image is formed by the second imaging optical system from a direction orthogonal to the first direction. A fourth spot that overlaps with the second spot when viewed is formed on the exposed surface. That is, the second spot imaged by the first imaging optical system and the fourth spot imaged by the second imaging optical system, that is, each spot by a different imaging optical system is the first spot. It does not only overlap when viewed from the direction orthogonal to the direction. The first spot imaged by the first imaging optical system and the third spot imaged by the first imaging optical system also overlap each other when viewed from a direction orthogonal to the first direction. That is, each spot imaged by the same imaging optical system is overlapped when viewed from a direction orthogonal to the first direction, and multiple exposure is performed in any of them. Therefore, for example, when the imaging optical system and the light emitting element are arranged so as to be shifted, the two spots subjected to multiple exposure are shifted from each other. In any of the spots imaged by the imaging optical system, the influence of the deviation that the exposure is somewhat blurred appears. At this time, compared to multiple exposure using the same imaging optical system, multiple exposure using different imaging optical systems is more affected by the deviation between the imaging optical system and the light-emitting element, so the amount of deviation also increases and exposure is increased. The degree of blur becomes large. That is, the deviation amount between the second spot and the fourth spot is larger than the deviation amount between the first spot and the third spot. This is because, for example, the multiple exposure is guided by a different imaging optical system compared to the distance between the first light emitting element and the third light emitting element that are guided by the same imaging optical system and subjected to multiple exposure. One possible cause is that the distance between the second light emitting element and the fourth light emitting element may be larger. Therefore, in the present invention, the control unit causes the first light emitting element and the third light emitting element to emit light with the same or substantially the same light amount, and the second light emitting element and the fourth light emitting element are connected to the first light emitting element. The light is emitted with a light amount smaller than the light amount. That is, the light amounts of the second and fourth light emitting elements guided by different imaging optical systems are smaller than the light amounts of the first and third light emitting elements guided by the same imaging optical system. As a result, the blurring degree of multiple exposure by different imaging optical systems is suppressed, and as a result, the difference in influence due to the shift is reduced, so that uneven exposure is suppressed. Thus, in the present invention, even if the imaging optical system and the light emitting element are arranged to be shifted, for example, it is possible to suppress exposure unevenness and realize good exposure.

  In addition, the distance between the second light emitting element and the fourth light emitting element may be larger than the distance between the first light emitting element and the third light emitting element. According to this configuration, the influence of the shift between the imaging optical system and the light emitting element is greater in the multiple exposure using different imaging optical systems, compared to the multiple exposure using the same imaging optical system. Therefore, the amount of deviation of overlapping spots also increases, and the degree of blurring of exposure also increases. That is, the shift amount of the second and fourth spots is larger than the shift amount of the first and third spots. However, since the light amounts of the second and fourth light emitting elements guided by different imaging optical systems are smaller than the light amounts of the first and third light emitting elements guided by the same imaging optical system, different image formation The blurring degree of multiple exposure by the optical system is suppressed. As a result, the difference in influence due to the shift is reduced, so that exposure unevenness is suppressed.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a latent image carrier that moves in a direction orthogonal to the first direction, and first imaging optics that forms light on the latent image carrier. A first light emitting element that emits light that is imaged by the first imaging optical system to form a first latent image on the latent image carrier, and is disposed in the first direction of the first light emitting element. A second light-emitting element that emits light that is imaged by the first imaging optical system to form a second latent image on the latent image carrier, and is imaged by the first imaging optical system. A third light emitting element that emits light to form a third latent image on the latent image carrier that overlaps the first latent image by the movement of the latent image carrier, and a second that forms light on the latent image carrier. Light is emitted to form a fourth latent image on the latent image carrier that is imaged by the imaging optical system and the second imaging optical system and overlaps the second latent image by the movement of the latent image carrier. The exposure head having four light-emitting elements, the first light-emitting element, and the third light-emitting element emit light with the same or substantially the same light amount, and the second light-emitting element and the fourth light-emitting element are connected to the first light-emitting element. And a control unit that emits light with a light amount smaller than the light amount.

  In the invention configured as described above, an image is formed by the first image forming optical system to form the first latent image on the latent image carrier, and an image is formed by the first image forming optical system. A third latent image overlapping the first latent image is formed on the exposed surface by the movement of the latent image carrier. In addition, the second image is formed on the latent image carrier by the first image forming optical system, and the second image is formed on the latent image carrier by the movement of the latent image carrier. A fourth latent image overlapping the second latent image is formed on the latent image carrier. That is, the second latent image formed by the first image forming optical system and the fourth latent image formed by the second image forming optical system, that is, each latent image by different image forming optical systems, Not only does it overlap due to the movement of the latent image carrier. The first latent image formed by the first image forming optical system and the third latent image formed by the first image forming optical system also overlap each other due to the movement of the latent image carrier. That is, the latent images formed by the same image forming optical system are also overlapped by the movement of the latent image carrier, and multiple exposure is performed in any case. Therefore, for example, when the imaging optical system and the light emitting element are arranged so as to be shifted, the two latent images to be subjected to multiple exposure are shifted from each other. In any of the latent images formed by the same image forming optical system, the influence of the deviation that the exposure is slightly blurred appears. At this time, compared to multiple exposure using the same imaging optical system, multiple exposure using different imaging optical systems is more affected by the deviation between the imaging optical system and the light-emitting element, so the amount of deviation also increases and exposure is increased. The degree of blur becomes large. That is, the shift amount between the second latent image and the fourth latent image is larger than the shift amount between the first latent image and the third latent image. This is because, for example, the multiple exposure is guided by a different imaging optical system compared to the distance between the first light emitting element and the third light emitting element that are guided by the same imaging optical system and subjected to multiple exposure. One possible cause is that the distance between the second light emitting element and the fourth light emitting element may be larger. Therefore, in the present invention, the control unit causes the first light emitting element and the third light emitting element to emit light with the same or substantially the same light amount, and the second light emitting element and the fourth light emitting element are connected to the first light emitting element. The light is emitted with a light amount smaller than the light amount. That is, the light amounts of the second and fourth light emitting elements guided by different imaging optical systems are smaller than the light amounts of the first and third light emitting elements guided by the same imaging optical system. As a result, the blurring degree of multiple exposure by different imaging optical systems is suppressed, and as a result, the difference in influence due to the shift is reduced, so that uneven exposure is suppressed. Thus, in the present invention, even if the imaging optical system and the light emitting element are arranged to be shifted, for example, it is possible to suppress exposure unevenness and realize good exposure.

1 is a diagram illustrating an example of an image forming apparatus to which the present invention can be applied. FIG. 2 is a block diagram showing an electrical configuration provided in the image forming apparatus of FIG. 1. The perspective view which shows the outline of the line head of 1st Embodiment. The partial top view which planarly viewed the head substrate from the thickness direction. The fragmentary sectional view of the line head in the AA line of FIG. The figure which shows the spot formation position when a line head is inclined and arrange | positioned. The figure which shows the exposure operation | movement by a line head. The figure which shows the light quantity of each light emitting element.

A. Embodiment FIG. 1 is a diagram illustrating an example of an image forming apparatus to which the present invention is applicable. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus shown in FIG. This apparatus uses a color mode in which four color toners of black (K), cyan (C), magenta (M), and yellow (Y) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. FIG. 1 is a diagram corresponding to the execution of the color mode. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC and also outputs an image forming command. Corresponding video data VD is supplied to the head controller HC. At this time, every time the main controller MC receives the horizontal request signal HREQ from the head controller HC, the main controller MC supplies video data VD for one line to the head controller HC in the main scanning direction MD. 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 ENG 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 feeding unit 11 are also disposed in the housing body 3. In FIG. 1, a secondary transfer unit 12, a fixing unit 13, and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feeding unit 11 is configured to be detachable from the apparatus main body 1. The paper feed unit 11 and the transfer belt unit 8 can be removed and repaired or exchanged.

  The image forming unit 7 includes four image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality of images of different colors. Each of the image forming stations Y, M, C, and K is provided with a 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 21 is arranged so that the axial direction is parallel or 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. 1, the image forming stations of the image forming unit 7 have the same configuration, and therefore, for convenience of illustration, only some image forming stations are denoted by reference numerals, and the other image forming stations are omitted. .

  The charging unit 23 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to be driven to rotate in contact with the surface of the photosensitive drum 21 at a charging position, and is rotated 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 a 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 spaced apart from the photosensitive drum 21, the longitudinal direction of the line head 29 is parallel or substantially parallel to the main scanning direction MD, and the width direction of the line head 29 is the sub-scanning direction SD. Parallel or substantially parallel to The line head 29 includes a plurality of light emitting elements, and each light emitting element emits light according to video data VD from the head controller HC. The surface of the photosensitive drum 21 is irradiated with light from the light emitting element, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 21.

  The developing unit 25 has a developing roller 251 that carries toner on the surface thereof. 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. Moves from the developing roller 251 to the photosensitive drum 21, and the electrostatic latent image formed by the line head 29 is made visible.

  The toner image that has been made visible at the developing position as described above is conveyed in the rotational direction D21 of the photosensitive drum 21, and then transferred to the transfer belt 81 at the primary transfer position TR1 where the photosensitive belt 21 abuts. Primary transfer.

  In this embodiment, a photoreceptor cleaner 27 is provided in contact with the surface of the photoreceptor drum 21 on the downstream side of the primary transfer position TR1 in the rotation direction D21 of the photoreceptor drum 21 and on the upstream side of the charging unit 23. It has been. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to 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. 1, and the direction of an arrow D81 (conveying direction) stretched around these rollers. 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 the respective 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). When the color mode is executed, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations Y, M, C, and K as shown in FIG. A primary transfer position TR 1 is formed between each photosensitive drum 21 and the transfer belt 81 by being pushed and brought into contact with the photosensitive drum 21 included in each of the forming stations Y, M, C, and K. Then, by applying a primary transfer bias from the primary transfer bias generating unit to the primary transfer roller 85 at an appropriate timing, the toner images formed on the surface of each photosensitive drum 21 correspond to each. 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, which face 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 being in contact with the photosensitive drum 21 of the image forming station K. It is configured to contact the transfer belt 81 on a common inscribed line.

  The drive roller 82 circulates and drives the transfer belt 81 in the direction of the arrow D81 in the figure, and also serves as a backup roller for the secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the drive 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 manner, the sheet enters the contact portion (secondary transfer position TR2) between the driving roller 82 and the secondary transfer roller 121. Is difficult to be transmitted to the transfer belt 81, and image quality deterioration can be prevented.

  The paper feed unit 11 includes a paper feed unit having a paper feed cassette 77 capable of stacking and holding sheets and a pickup roller 79 for feeding sheets one by one from the paper feed cassette 77. The sheet fed from the sheet feeding unit by the pickup roller 79 is fed to the secondary transfer position TR2 along the sheet guide member 15 after the 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 out of the surface 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 portion of the housing body 3.

  Further, in this apparatus, a cleaner unit 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 contacting the tip of the cleaner blade 711 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.

  FIG. 3 is a perspective view schematically showing an embodiment of the line head. In the drawing, in order to facilitate understanding of the configuration of the line head 29 in the thickness direction TKD, the end of the line head 29 in the longitudinal direction LGD (the lower left end in FIG. 3) is shown in cross section. Here, the thickness direction TKD is a direction perpendicular or substantially perpendicular to the longitudinal direction LGD and the width direction LTD, and a light emitting element E to be described later emits light (that is, a side from the line head 29 toward the photosensitive drum 21). ). The line head 29 arranges the head substrate 293, the light shielding member 297, the first lens array LA1 and the second lens array LA2 in this order in the thickness direction TKD, and from the back surface of the head substrate 293 (strictly speaking, the head substrate A rigid member 299 (from the back surface of the sealing member 294 provided on 293) has a schematic configuration that supports these members. Then, the light from the light emitting element E of the head substrate 293 passes through the light guide hole 2971 of the light shielding member 297 and is imaged by the lenses LS1 and LS2 of the first and second lens arrays LA1 and LA2. Next, the detailed configuration of each member will be described with reference to FIGS. 3, 4, and 5. In the description of the embodiment, the downstream side in the thickness direction TKD (upper side in FIG. 3) is referred to as “one side in the thickness direction TKD”, and the upstream side in the thickness direction TKD (lower side in FIG. 3). Is referred to as “the other side (in the thickness direction TKD)”. In addition, one surface of the substrate or the flat plate is referred to as a front surface, and the other surface of the substrate or the flat plate is referred to as a back surface.

  FIG. 4 is a partial plan view of the head substrate 293 viewed from the thickness direction TKD, and corresponds to a case where the back surface 293-t of the head substrate 293 is seen through from one side of the thickness direction TKD (upper side in FIG. 3). To do. FIG. 5 is a partial cross-sectional view of the line head of this embodiment, taken along line AA in FIG. 4, and corresponds to a case where the cross section is viewed from the longitudinal direction LGD (main scanning direction MD). This AA line cross section has a distance Dg in the longitudinal direction LGD and a distance Dt in the width direction LTD, and each center of gravity of the two light emitting element groups EG arranged in a row (or two lenses LS1, etc.). Pass through the center of each lens). Moreover, the direction Dlsc shown in FIGS. 4 and 5 is a direction parallel to the line AA. Further, FIG. 4 shows the positional relationship between the light emitting element group EG formed on the head substrate 293, the first lens LS1 formed on the first lens array LA1, and the second lens LS2 formed on the second lens array LA2. For this reason, the first lens LS1 and the second lens LS2 are shown together with alternate long and short dash lines. Incidentally, the description of the first lens LS1 and the second lens LS2 in the drawing is for showing the positional relationship between them, and the first lens LS1 and the second lens LS2 are the back surface 293-t of the head substrate (FIG. 5). It does not indicate that it is formed. In FIG. 5, a member that is light transmissive (that is, transparent) is hatched with a set of points.

  The head substrate 293 is formed of a glass substrate (light transmissive substrate) that transmits light, and a plurality of light emitting elements E that are bottom emission type organic EL (Electro-Luminescence) elements are formed on the back surface 293-t of the head substrate. At the same time, it is sealed by a sealing member 294 (FIGS. 3 and 5). The plurality of light emitting elements E have the same emission spectrum, and emit a light beam toward the surface of the photosensitive drum 21. As shown in FIG. 4, the arrangement of the plurality of light emitting elements E formed on the head substrate back surface 293-t has a group structure. That is, 34 light emitting elements E are arranged in two rows in the longitudinal direction LGD to form one light emitting element group EG, and a plurality of light emitting element groups EG are discretely arranged in two rows in the longitudinal direction LGD. Is arranged.

  In more detail, this arrangement | positioning aspect can be demonstrated as follows. That is, the light emitting element group rows GRa and GRb are configured such that a plurality of light emitting element groups EG are arranged discretely along the longitudinal direction LGD with a distance Peg between the groups. Further, the two light emitting element group rows GRa and GRb are discretely arranged at different positions in the width direction LTD with a distance Dt therebetween, and the light emitting element group rows GRa and GRb are separated by a distance Dg in the longitudinal direction LGD. Are just shifted from each other. Thus, the two light emitting element groups EG are arranged in a line in the direction Dlsc with a distance Dg in the longitudinal direction LGD and a distance Dt in the width direction LTD.

  In each light emitting element group EG, two light emitting element rows in which the light emitting elements E are arranged in a line in the longitudinal direction LGD with an interelement distance Pel are provided at different positions in the width direction LTD. That is, each light emitting element group EG of the light emitting element group row GRa has light emitting element rows GRa1 and GRa2, and each light emitting element group EG of the light emitting element group row GRb has light emitting element rows GRb1 and GRb2. The light emitting element row GRa1 has 15 light emitting elements E, the light emitting element row GRa2 has 19 light emitting elements E, and the positions of the 15 light emitting elements E in the light emitting element row GRa1 in the longitudinal direction LGD are The positions of the 15 light emitting elements E at the center of the light emitting element row GRa2 are the same as the positions in the longitudinal direction LGD. The light emitting element row GRb1 has 19 light emitting elements E, the light emitting element row GRb2 has 15 light emitting elements E, and the positions of the 15 light emitting elements E in the light emitting element row GRb2 in the longitudinal direction LGD are The positions of the 15 light emitting elements E in the center of the light emitting element row GRb1 in the longitudinal direction LGD are the same. In other words, in each light emitting element group EG, a pair of light emitting element pairs EP is constituted by two light emitting elements having the same position in the longitudinal direction LGD, and 15 pairs of light emitting element pairs EP in the longitudinal direction LGD. Are lined up.

  Further, among the 19 light emitting elements E in the light emitting element row GRa2, the position of the rightmost two light emitting elements E in FIG. 4 in the longitudinal direction LGD is the light emission of the right light emitting element group EG adjacent to the longitudinal direction LGD. The positions of the two light emitting elements E at the left end of the element row GRb1 are the same as the positions in the longitudinal direction LGD. For example, the position in the longitudinal direction LGD of the two light emitting elements E at the right end of the light emitting element row GRa2 of the light emitting element group EGa2 is the longitudinal direction LGD of the two light emitting elements E at the left end of the light emitting element row GRb1 of the light emitting element group EGb2. The positions are the same. Also, among the 19 light emitting elements E in the light emitting element row GRa2, the leftmost two light emitting elements E in FIG. 4 are positioned in the longitudinal direction LGD of the left light emitting element group EG adjacent to the longitudinal direction LGD. The positions of the two light emitting elements E at the right end of the element row GRb1 are the same as the positions in the longitudinal direction LGD. For example, the position in the longitudinal direction LGD of the two light emitting elements E at the left end of the light emitting element row GRa2 of the light emitting element group EGa2 is the longitudinal direction LGD of the two light emitting elements E at the right end of the light emitting element row GRb1 of the light emitting element group EGb1. The positions are the same. In other words, each light-emitting element group EG has two light-emitting elements E adjacent to each other in the longitudinal direction LGD and two light-emitting elements E located at the same position in the longitudinal direction LGD at both ends of the longitudinal direction LGD. is doing.

  In each light emitting element group EG, each light emitting element row is separated from the line parallel to the longitudinal direction LGD passing through the point corresponding to the optical axis of the corresponding lens LS1, LS2 by the same distance Dr in the width direction LTD. It is provided at the position. That is, the 15 light emitting elements E in the light emitting element row GRa1 and the 15 light emitting elements E in the center of the light emitting element row GRa2 are line symmetric with respect to a line parallel to the longitudinal direction LGD. The 15 light emitting elements E in the light emitting element row GRb2 and the 15 light emitting elements E in the center of the light emitting element row GRb1 are line symmetric with respect to a line parallel to the longitudinal direction LGD. Further, in each light emitting element group EG, each light emitting element row is line symmetric with respect to a line parallel to the width direction LTD passing through a point corresponding to the optical axis of the corresponding lens LS1, LS2. That is, the central light emitting element E of the 15 light emitting elements E of the light emitting element rows GRa1 and GRb2 is located on a line parallel to the width direction LTD, and the 19 light emitting elements E of the light emitting element rows GRa2 and GRb1 are arranged. The center light emitting element E is located on a line parallel to the width direction LTD.

  Here, the inter-element distance Pel can be obtained as a distance in the longitudinal direction LGD between the geometric centroids of the two light emitting elements E to be processed. Further, the inter-group distance Peg is the geometric center of gravity of the light emitting element E at the other end of the light emitting element group EG on one side in the longitudinal direction LGD, and the longitudinal direction LGD of the two target light emitting element groups EG. The distance in the longitudinal direction LGD with the geometric center of gravity of the light emitting element E at the one end of the other light emitting element group EG can be obtained. Further, the distance Dg can be obtained as a distance in the longitudinal direction LGD between the centers of two light emitting element groups EG adjacent to each other in the longitudinal direction LGD. The distance Dt can be obtained as the distance in the width direction LTD between the centers of the two light emitting element groups EG whose positions in the width direction LTD are adjacent. Further, the distance Dr is a line parallel to the longitudinal direction LGD passing through a point corresponding to the optical axis of the corresponding lens LS1, LS2, and a line passing through the geometric center of gravity of each light emitting element E in the target light emitting element row. It can be obtained as a distance in the width direction LTD. Note that the center of the light emitting element group EG is a position corresponding to the optical axis of the corresponding lens LS1, LS2. Here, as described above, each light emitting element row in the light emitting element group EG is identical in the width direction LTD from a line parallel to the longitudinal direction LGD passing through a point corresponding to the optical axis of the corresponding lens LS1, LS2. They are provided at positions separated by a distance Dr, and are symmetrical with respect to a line parallel to the width direction LTD passing through a point corresponding to the optical axis of the corresponding lens LS1, LS2. Therefore, the center of the light emitting element group EG coincides with the midpoint between the geometric center of gravity of one light emitting element row and the geometric center of gravity of the other light emitting element row. The geometric center of gravity of the light emitting element row is the geometric center of gravity of all the light emitting elements E arranged in the light emitting element row.

  In addition, by applying the technology described in Japanese Patent Application Laid-Open No. 2004-082330, this embodiment includes a configuration for detecting the light amount of each light emitting element E in advance in order to help control the light amount of each light emitting element E. Yes. Specifically, on each of both sides of the head substrate back surface 293-t in the width direction LTD, a plurality of optical sensors SC are arranged in a line in the longitudinal direction LGD at a predetermined interval. Thus, the rows of the optical sensors SC are arranged on both sides in the width direction LTD with the plurality of light emitting element groups EG interposed therebetween. Each optical sensor SC outputs the result of detecting the light amount from the light emitting element E to the head controller HC, and the head controller HC controls the light amount of the light emitting element E thereafter based on the received light amount signal.

  Thus, the light emitting element group EG and the optical sensor SC are arranged on the back surface 293-t of the head substrate 293. On the other hand, a light shielding member 297 is disposed on the surface 293-h of the head substrate 293. The light shielding member 297 is formed with a light guide hole 2971 that penetrates in the thickness direction TKD. The light guide hole 2971 has a circular shape in plan view from the thickness direction TKD, and the inner wall has a black color. It is plated. One light guide hole 2971 is formed for each light emitting element group EG. That is, one light guide hole 2971 is opened for one light emitting element group EG. Thus, the light shielding member 297 is fixed in contact with the head substrate surface 293-h in a state where the light guide hole 2971 is opened in the light emitting element group EG.

  The purpose of providing such a light shielding member 297 is to prevent so-called stray light from entering the lenses LS1 and LS2. That is, each light emitting element group EG is provided with a dedicated imaging optical system composed of a pair of lenses LS1 and LS2. In such a configuration, it is desirable that the light beam is incident only on the imaging optical systems LS1 and LS2 provided in the light emitting element group EG which is its own emission source, and is imaged. However, some of the light beams may become stray light without being directed to the imaging optical systems LS1 and LS2 provided in the light emitting element group EG that is the emission source. If such stray light enters the imaging optical systems LS1 and LS2 provided in the light emitting element group EG that is not its own emission source, a so-called ghost may occur. On the other hand, in this embodiment, a light shielding member 297 is provided between the light emitting element group EG and the imaging optical systems LS1 and LS2. The light shielding member 297 is provided with a light guide hole 2971 whose inner wall is black-plated so as to open to the light emitting element group EG. Therefore, most of the stray light is absorbed by the inner wall of the light guide hole 2971. As a result, the above-described ghost can be suppressed and a good exposure operation can be realized.

  In addition, on one side of the light shielding member 297 in the thickness direction TKD, the first lens array LA1 is supported at a distance from the light shielding member 297. The first lens array LA1 is supported by a metal first spacer SP1 provided on the surface 293-h of the head substrate 293. The first lens array LA1 includes a plurality of first lenses LS1 formed of a photocurable resin on the back surface of a rhombus-shaped glass substrate SB whose both ends in the longitudinal direction LGD are cut obliquely (parallel to the direction Dlsc). Are arranged in an array. The plurality of first lenses LS1 are arranged in a zigzag manner in two rows corresponding to the arrangement of the opposing light emitting element groups EG (FIG. 4). The head substrate 293 and the first spacer SP1, and the first spacer SP1 and the first lens array LA1 are fixed by a method using an adhesive or the like.

  Furthermore, on one side of the thickness direction TKD of the first lens array LA1, the second lens array LA2 is supported at a distance from the first lens array LA1. The second lens array LA1 is supported by a metal second spacer SP2 provided on the surface of the glass substrate SB of the first lens array LA1. The second lens array LA2 includes a plurality of second lens arrays LA2 formed on a back surface SB-t of a rhombus-shaped glass substrate SB whose both ends in the longitudinal direction LGD are cut obliquely (parallel to the direction Dlsc). It has a configuration in which two lenses LS2 are arranged in an array. The plurality of second lenses LS2 are arranged in a two-row zigzag pattern corresponding to the arrangement of the first lenses LS1 facing each other (FIG. 4). The first lens array LA1 and the second spacer SP2, and the second spacer SP2 and the second lens array LA2 are fixed by a method using an adhesive or the like.

  Thus, the lens LS1 of the first lens array LA1 and the lens LS2 of the second lens array LA2 are arranged in the thickness direction TKD to constitute one imaging optical system, and light from each light emitting element E is sent to the photosensitive drum 21. To the surface of the substrate to form spots on the surface. This imaging optical system forms an inverted reduced image, and its magnification is negative and has an absolute value of less than 1. A line latent image extending in the main scanning direction MD can be formed by controlling the light emission of each light emitting element E according to the movement of the surface of the photosensitive drum 21 in the sub scanning direction SD.

  FIG. 6 is a diagram showing the spot formation position when the line head is disposed at an angle. FIG. 6A shows the angle θ with respect to the main scanning direction MD of the photosensitive drum 21 by the line head 29 of the present embodiment. FIG. 5B is a diagram showing spot formation positions when they are disposed at an inclination only, and FIG. 5B shows a conventional line head in which only spots guided by different imaging optical systems overlap each other (for example, a line head described in Patent Document 1). It is a figure which shows the spot formation position when it arrange | positions only the angle (theta) with respect to main scanning direction MD of the body drum. Here, referring to FIG. 6, an explanation will be given of the case where the spot formation position is shifted as mentioned in the section “Problems to be Solved by the Invention” with reference to FIG. FIG. 6 shows spots formed on the surface of the photosensitive drum 21 when the light emitting elements E are turned on simultaneously. Further, the deviation of the spot formation position is not limited to when the line head is disposed at an inclination, but when the light emitting element group EG and the lens LS1 are displaced, when the light emitting element group EG and the lens LS2 are displaced, This occurs when a design error occurs in the lenses LS1 and LS2.

  When the longitudinal direction LGD of the line head 29 of the present embodiment is arranged without being inclined with respect to the main scanning direction MD of the photosensitive drum 21, each spot is subjected to main scanning as described later with reference to FIG. It overlaps the direction MD without shifting. However, as shown in FIG. 6A, when the longitudinal direction LGD of the line head 29 is disposed at an angle θ with respect to the main scanning direction MD of the photosensitive drum 21, the same lenses LS1 and LS2 are used. The spot SP_1 and the spot SP_3 formed by being guided are shifted by a distance d1 in the main scanning direction MD. Similarly, the spots SP_5 and SP_6 guided and formed by the same lenses LS1 and LS2 are also shifted by the distance d1 in the main scanning direction MD. Further, the spot SP_2 and the spot SP_4 guided and formed by different lenses LS1 and LS2 are shifted by a distance d2 in the main scanning direction MD. In this way, the spots formed by being guided by the same imaging optical system (lenses LS1, LS2) and the spots formed by being guided by different imaging optical systems (lenses LS1, LS2) overlap each other. Each spot is shifted in the main scanning direction MD by the distance d1 or d2. Therefore, in both cases, the exposure (latent image) becomes somewhat blurred, but the exposure unevenness is suppressed. Here, d2> d1, which will be described later.

  On the other hand, as shown in FIG. 6B, when a conventional line head is disposed at an angle θ with respect to the main scanning direction MD, it is guided by different lenses LS1 and LS2. The spot SP_11 and the spot SP_12 are shifted by a distance d3 in the main scanning direction MD. On the other hand, the spot SP_13 and the spot SP_14 do not overlap with other spots, so that a deviation in the main scanning direction MD does not appear. Therefore, only the portion where the spot SP_11 and the spot SP_12 overlap is slightly blurred in the exposure (latent image), but the other portion, that is, the spot SP_13 and the spot SP_14 are those in which the exposure (latent image) is blurred. Therefore, exposure unevenness occurs between these portions. Then, in each of these portions, one pixel equivalent is developed with toner, and when the developed areas are compared, the exposure is somewhat blurred in the multiple-exposed region (1 pixel in the multiple-exposed region)> (One pixel in a region where multiple exposure is not performed). As a result, toner image density unevenness occurs.

  FIG. 7 is a diagram showing an exposure operation by the line head of this embodiment, and FIG. 8 is a diagram showing the light amount of each light emitting element. Hereinafter, the exposure operation by the line head in the present embodiment will be described with reference to FIGS. 2, 4, 7, and 8. In order to facilitate understanding of the invention, a case where a line-shaped latent image extending in the main scanning direction MD is formed will be described here. In the present embodiment, a plurality of light emitting elements E are caused to emit light at a predetermined timing by the head controller HC while conveying the surface (exposed surface) of the photosensitive drum 21 (image carrier) in the sub scanning direction SD. A line-shaped latent image extending in the main scanning direction MD is formed.

  That is, in the line head of this embodiment, four light emitting element rows GRa1, GRa2, GRb1, and GRb2 are arranged side by side in the width direction LTD corresponding to the sub-scanning direction SD (FIG. 4). Thus, in the present embodiment, the light emitting element rows at the same width direction position emit light at substantially the same timing, and the light emitting element rows at different width direction positions emit light at different timings. More specifically, the light emitting elements E are caused to emit light in the order of the light emitting element rows GRa2, GRa1, GRb2, GRb1. And while conveying the surface of the photosensitive drum 21 in the sub scanning direction SD, the light emitting elements E emit light in the above-described order, thereby forming a line-like latent image extending in the main scanning direction MD on the surface. Here, while the conveyance direction of the surface of the photosensitive drum 21 is the sub-scanning direction SD, the light emitting element rows on the downstream side in the width direction LTD are sequentially arranged (that is, the order of the light emitting element rows GRa2, GRa1 and the light emission). The reason for emitting light (in the order of the element rows GRb2 and GRb1) is to correspond to the fact that the imaging optical system composed of the lenses LS1 and LS2 has reversal characteristics.

  The head controller HC includes two light emitting elements E on both ends on one side and the other side in the longitudinal direction LGD of the light emitting element row GRa2, and both ends on one side and the other side in the longitudinal direction LGD of the light emitting element row GRb1. The light quantity of each light emitting element E is controlled so that the light quantity with each of the two light emitting elements E is smaller than the light quantity of the other light emitting elements E. That is, the head controller HC adjusts the light amount of each light emitting element E of the same light emitting element group EG in which the spots formed by being guided by the same lenses LS1 and LS2 overlap each other in the main scanning direction MD on the surface of the photosensitive drum 21. In comparison, the light amounts of the light emitting elements E of the light emitting element groups EG adjacent to each other in the longitudinal direction LGD in which the spots formed by different lenses LS1 and LS2 overlap each other in the main scanning direction MD on the surface of the photosensitive drum 21. The light quantity of each light emitting element E is controlled so as to be small. The reason will be described later.

  In the exposure operation by the line head 29 of the present embodiment, first, the light emitting elements E in the downstream light emitting element row GRa2 among the light emitting element rows belonging to the upstream light emitting element groups EGa1, EGa2,. Make it emit light. The plurality of light beams emitted by the light emission operation are reduced while being inverted by the imaging optical system having the above-described inversion reduction characteristics, and are guided to the surface of the photosensitive drum. That is, a spot is formed at the position of the “first” hatching pattern in FIG. In the figure, white circles represent spots that have not yet been formed and are to be formed in the future. Further, in the figure, the spots labeled with symbols EGa1, EGb1, and EGa2 indicate spots formed by light from the light emitting element groups EG corresponding to the symbols assigned thereto. That is, at the first time, 19 spots are formed by the light from the light emitting elements E of the light emitting element rows GRa2 of the light emitting element groups EGa1 and EGa2. At this time, the 15 light emitting elements E at the center of each light emitting element row GRa2 of the light emitting element groups EGa1 and EGa2 emit light with a light amount of 50%, and the two light emitting elements E at the left and right ends of each light emitting element row GRa2 are It emits light with a light quantity of 44%. Note that the total amount of light with respect to the surface of the photosensitive drum 21 is 100%. That is, when there is a light emitting element that does not perform multiple exposure as in the conventional case, the light amount of the light emitting element is 100%.

  Next, among the light emitting element rows belonging to the same light emitting element group EGa1, EGa2,..., The light emitting element E in the upstream light emitting element row GRa1 is caused to emit light. The plurality of light beams emitted by the light emission operation are reduced while being inverted by the imaging optical system having the above-described inversion reduction characteristics, and are guided to the surface of the photosensitive drum. As a result, a spot is formed at the position of the “second” hatching pattern in FIG. That is, the “second” spot is formed so as to overlap the “first” spot. That is, the spot is formed by the light from the 15 light emitting elements E of the light emitting element row GRa1 of the light emitting element group EGa1 and the light from the 15 light emitting elements E of the light emitting element row GRa1 of the light emitting element group EGa2. Are formed so as to overlap the spot formed at the first time. At this time, each light emitting element E emits light with a light amount of 50%. Therefore, the total amount of light with respect to the surface of the photosensitive drum 21 is 100%.

  Next, the light emitting elements E in the downstream light emitting element row GRb2 among the light emitting element rows belonging to the downstream light emitting element group EGb1,. The plurality of light beams emitted by the light emission operation are reduced while being inverted by the imaging optical system having the above-described inversion reduction characteristics, and are guided to the surface of the photosensitive drum. As a result, a spot is formed at the position of the “third” hatching pattern in FIG. That is, 15 spots are formed by the light from the 15 light emitting elements E in the light emitting element row GRb2 of the light emitting element group EGb1,. At this time, each light emitting element E emits light with a light amount of 50%.

  Finally, the light emitting elements E in the upstream light emitting element row GRb1 among the light emitting element rows belonging to the downstream light emitting element group EGb1,... In the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emission operation are reduced while being inverted by the imaging optical system having the above-described inversion reduction characteristics, and are guided to the surface of the photosensitive drum. As a result, a spot is formed at the position of the “fourth” hatching pattern in FIG. 7. That is, the “fourth” spot is formed so as to overlap the “first” and “third” spots. That is, among the light emitting elements E in the light emitting element row GRb1 of the light emitting element group EGb1, the light from each of the two light emitting elements E at the one end and the other end in the longitudinal direction LGD overlaps the spot formed at the first time. As such, spots are formed. At this time, each of these two light emitting elements E emits light with a light quantity of 44%. Therefore, the total amount of light with respect to the surface of the photosensitive drum 21 is 88%. Further, among the light emitting elements E in the light emitting element row GRb1 of the light emitting element group EGb1, the spots are overlapped with the spots formed in the third time by the light from the 15 light emitting elements E in the center in the longitudinal direction LGD. It is formed. At this time, these 15 light emitting elements E emit light with a light amount of 50%. Therefore, the total amount of light with respect to the surface of the photosensitive drum 21 is 100%.

  That is, the partial latent image EX1 in FIG. 7 is obtained from the 15 light emitting elements E of the light emitting element row GRa1 of the light emitting element group EGa1 and the 15 light emitting elements E of the light emitting element row GRa2 of the same light emitting element group EGa1. The multiple exposure is performed with the light. The partial latent image EX2 includes light from the two light emitting elements E in the light emitting element row GRa2 of the light emitting element group EGa1, and light from the two light emitting elements E in the light emitting element row GRb1 of the different light emitting element group EGb1. Thus, multiple exposure is performed. The partial latent image EX3 includes light from the 15 light emitting elements E in the light emitting element row GRb1 of the light emitting element group EGb1, and light from the 15 light emitting elements E in the light emitting element row GRb2 of the same light emitting element group EGb1. Thus, multiple exposure is performed. The partial latent image EX4 includes light from the two light emitting elements E in the light emitting element row GRb1 of the light emitting element group EGb1, and light from the two light emitting elements E in the light emitting element row GRa2 of the different light emitting element group EGa2. Thus, multiple exposure is performed. The partial latent image EX5 includes light from the 15 light emitting elements E of the light emitting element row GRa2 of the light emitting element group EGa2, and light from the 15 light emitting elements E of the light emitting element row GRa1 of the same light emitting element group EGa2. Thus, multiple exposure is performed. As described above, by executing the first to fourth light emission operations, a line-like latent image extending in the main scanning direction MD is formed. The line-shaped latent image is formed such that the spots from the light from the two light emitting elements E overlap each other. That is, not only the partial latent images EX2 and EX4 are formed by multiple exposure with the light from each light emitting element E guided by different lenses LS1 and LS2, but also the light from each light emitting element E guided by the same lens LS1 and LS2. Are subjected to multiple exposure to form partial latent images EX1, EX3, and EX5.

  Next, the reason why there is a difference in the light amount of each light emitting element E will be described with reference to FIGS. 4 and 6A. That is, in this embodiment, as described above, the light quantity of each light emitting element E of the same light emitting element group EG that is guided by the same lens LS1, LS2 and subjected to multiple exposure is guided by the different lenses LS1, LS2. The light quantity of each light emitting element E of the light emitting element group EG adjacent to the longitudinal direction LGD to be exposed is reduced. The reason will be described below.

  As described with reference to FIG. 6A, when the longitudinal direction LGD of the line head 29 is arranged to be inclined with respect to the main scanning direction MD of the photosensitive drum 21, it is guided by the same lenses LS1 and LS2. Each spot formed and each spot guided by different lenses LS1 and LS2 are shifted in the main scanning direction MD. That is, as shown in FIG. 6A, the spots SP_1 and SP_3 are shifted by a distance d1 in the main scanning direction MD, and the spots SP_5 and SP_6 are also shifted by a distance d1 in the main scanning direction MD. Further, the spot SP_2 and the spot SP_4 are shifted by a distance d2 in the main scanning direction MD. Here, d2> d1. That is, even if the line head 29 is inclined with respect to the photosensitive drum 21 by the same angle θ, the influence of the inclination is different from the spots LS 1 and LS 2 formed by the same lenses LS 1 and LS 2. It appears in the direction of each spot formed by This is because, for example, the distance between the light emitting elements E that emit light forming the spots SP_2 and SP_4 is larger than the distance between the light emitting elements E that emit light forming the spots SP_1 and SP_3. This is thought to be due to the large size.

  That is, as shown in FIG. 4, the distance between each light emitting element E that emits light that is guided by the same lens LS1, LS2 to form overlapping spots, that is, the distance between the light emitting element row GRa1 and the light emitting element row GRa2, The distance between the light emitting element row GRb1 and the light emitting element row GRb2 is 2Dr. On the other hand, the distance between the light emitting elements E that emit light that forms the overlapping spots guided by different lenses LS1 and LS2, that is, the distance between the light emitting element row GRa2 and the light emitting element row GRb1 is (Dt−2Dr). . These relationships are 2Dr <(Dt−2Dr) as can be seen from FIG. Thus, when the distance between the light emitting elements E subjected to multiple exposure is large, it is considered that the influence of the inclination of the line head 29 with respect to the photosensitive drum 21 appears greatly. Further, when the line head 29 is disposed, the longitudinal direction LGD of the line head 29 may be inclined with respect to the main scanning direction MD of the photosensitive drum 21 within an allowable error range. However, even if the inclination angle θ is a minute value within the allowable error range, the influence of the inclination appears, and each spot formed by being guided by the different lenses LS1 and LS2 becomes the main scanning direction MD. It may shift to. On the other hand, when the inclination angle θ is a minute value within the allowable error range, the spots formed by the same lenses LS1 and LS2 are hardly displaced in the main scanning direction MD. For this reason, only the exposure (latent image) of each spot formed by being guided by different lenses LS1 and LS2 may be somewhat blurred. As described above, the deviation of the spot formation position is not limited to when the line head is disposed at an inclination. When the light emitting element group EG and the lens LS1 are displaced, the light emitting element group EG and the lens LS2 are displaced. This occurs when the lens is shifted or a design error occurs in the lenses LS1 and LS2. Therefore, for example, even when the light emitting element group EG and the lens LS1 are shifted within the allowable error range, only the exposure (latent image) by each spot formed by being guided by the different lenses LS1 and LS2 is somewhat blurred. It can be a thing.

  Therefore, in the present embodiment, compared to the amount of light of each light emitting element E of the same light emitting element group EG forming the overlapping spot guided by the same lens LS1, LS2, the overlapping spot guided by different lenses LS1, LS2 is formed. The light quantity of each light emitting element E of the light emitting element group EG adjacent in the longitudinal direction LGD is reduced. That is, in this embodiment, when the total light quantity with respect to the surface of the photosensitive drum 21 is 100%, the former light emitting elements E emit light with a light quantity of 50%, while the latter light emitting elements E are 44%. The light is emitted with the amount of light. That is, the total amount of light with respect to the surface of the photosensitive drum 21 by the respective light emitting elements E of the same light emitting element group EG guided by the same lenses LS1 and LS2 becomes 100%, whereas the longitudinal direction guided by different lenses LS1 and LS2 is used. The total amount of light with respect to the surface of the photosensitive drum 21 by each light emitting element E of the light emitting element group EG adjacent in the direction LGD is 88%. This reduces the degree of blurring of exposure (latent image) by each spot formed by being guided by different lenses LS1 and LS2. As a result, exposure unevenness is suppressed.

  As described above, in the line head 29 according to the present embodiment, the latent image formed on the photosensitive drum 21 is formed so that the spots from the light from the two light emitting elements E overlap each other in the main scanning direction MD. Forming. That is, not only each spot by the light from the two light emitting elements E guided by the different lenses LS1 and LS2, but also each spot by the light from the two light emitting elements E guided by the same lens LS1, LS2. They overlap each other in the scanning direction MD. Therefore, when the longitudinal direction LGD of the line head 29 is arranged to be inclined with respect to the main scanning direction MD of the photosensitive drum 21, spots from the light from the two light emitting elements E are in the main scanning direction MD. Since they are shifted from each other, the influence of the shift occurs that the exposure (latent image) becomes somewhat blurred. However, since all the partial latent images EX1 to EX5 are similarly affected by the deviation, the difference in the influence due to the deviation between the respective parts is reduced. Further, since the influence of the inclination of the line head 29 with respect to the photosensitive drum 21 appears more greatly in each spot guided by the different lenses LS1 and LS2 than in each spot by the same lens LS1 and LS2, the degree of exposure blurring is increased. Also grows. Therefore, in the present embodiment, the light amounts of the light emitting elements E that form the overlapping spots guided by the different lenses LS1 and LS2 are set to the light emitting elements E that form the overlapping spots guided by the same lenses LS1 and LS2. It is smaller than the light quantity. This suppresses the difference in influence due to deviation, that is, the difference in the degree of blurring of exposure. Thus, in this embodiment, it is possible to suppress exposure unevenness due to a difference in influence due to deviation, and it is possible to realize good exposure. Here, when a latent image in which exposure unevenness has occurred is developed to form a toner image, density unevenness occurs, but toner image density unevenness is easily noticeable to the human eye. Therefore, even if the exposure (latent image) becomes somewhat blurred, the toner image formed by the line head 29 of the present embodiment in which uneven exposure is suppressed can suppress the deterioration in image quality. .

  Furthermore, in the line head 29 of this embodiment, in each light emitting element group EGa1, EGa2,..., 15 light emitting elements E in the light emitting element row GRa1 and 15 light emitting elements E in the center of the light emitting element row GRa2 are Are symmetrical with respect to a line parallel to the longitudinal direction LGD passing through a point corresponding to the optical axis of the corresponding lens LS1, LS2. In each of the light emitting element groups EGb1, EGb2,..., The 15 light emitting elements E in the light emitting element row GRb2 and the 15 light emitting elements E in the center of the light emitting element row GRb1 are light beams of the corresponding lenses LS1, LS2. The line is symmetrical with respect to a line parallel to the longitudinal direction LGD passing through a point corresponding to the axis. For this reason, the spots due to the light from each of the 15 light emitting elements E can be suitably overlapped on the photosensitive drum 21 in the main scanning direction MD.

  Further, in the line head 29 of the present embodiment, each light emitting element group EG includes a light emitting element E of the light emitting element group EG adjacent in the longitudinal direction LGD and a light emitting element E having the same position in the longitudinal direction LGD. There are two at each end of the LGD. That is, for example, in FIG. 4 of the light emitting element row GRa2 of the light emitting element group EGa2, the position of the rightmost two light emitting elements E in the longitudinal direction LGD is the two light emitting elements at the left end of the light emitting element row GRb1 of the light emitting element group EGb2. The position of the element E in the longitudinal direction LGD is the same. Moreover, in each light emitting element group EG, each light emitting element row is line symmetric with respect to a line parallel to the width direction LTD passing through a point corresponding to the optical axis of the corresponding lens LS1, LS2. That is, for example, the light emitting element E at the center of the 19 light emitting elements E of the light emitting element rows GRa2 and GRb1 is located on a line parallel to the width direction LTD. Therefore, the light spot from the light emitting element E of the light emitting element group EG (for example, the two rightmost light emitting elements E in FIG. 4 in the light emitting element row GRa2 of the light emitting element group EGa2) and the light emitting element adjacent in the longitudinal direction LGD. Light spots from the light-emitting elements E of the group EG (for example, the two leftmost light-emitting elements E in FIG. 4 in the light-emitting element row GRb1 of the light-emitting element group EGb1) are spotted by the lenses LS1 and LS2 constituting the reversing optical system. The photosensitive drum 21 can be suitably overlapped in the main scanning direction MD.

  Further, in the line head 29 of the present embodiment, each of the light emitting element groups EGa1, EGa2,... Has the same light emitting element E in the longitudinal direction LGD as the light emitting element E of the light emitting element group EG adjacent in the longitudinal direction LGD. Are provided at both ends of the light emitting element row GRa2 instead of at both ends of the light emitting element row GRa1. Further, each of the light emitting element groups EGb1, EGb2,... Has a light emitting element E adjacent to the light emitting element group EG in the longitudinal direction LGD, and a light emitting element E having the same position in the longitudinal direction LGD at both ends of the light emitting element row GRb2. There are two light emitting element rows GRb1 at both ends. Therefore, it is possible to reduce the distance between the light emitting elements E that emit the light that is guided by the different lenses LS1 and LS2 to form the overlapping spots, and thereby the influence of the inclination of the line head 29 with respect to the photosensitive drum 21. Can be suppressed.

B. Others As described above, in the above embodiment, the longitudinal direction LGD corresponds to the “first direction” of the present invention. The photosensitive drum 21 corresponds to the “latent image carrier” of the invention, the surface of the photosensitive drum 21 corresponds to the “exposed surface” of the invention, and the line head 29 corresponds to the “exposure head” of the invention. The head controller HC corresponds to the “control unit” of the present invention. The 15 light emitting elements E of the light emitting element row GRa1 of the light emitting element groups EGa1, EGa2,... Correspond to the “third light emitting element” of the present invention, and the 15 light emitting elements in the center of the light emitting element row GRa2. E corresponds to the “first light emitting element” of the present invention, and each of the two light emitting elements E at both ends of the light emitting element row GRa2 corresponds to the “second light emitting element” of the present invention, and the light emitting element group EGa1, The lenses LS1, LS2 corresponding to EGa2,... Correspond to the “first imaging optical system” of the present invention. Each of the two light emitting elements E at both ends of the light emitting element row GRb1 of the light emitting element groups EGb1, EGb2,... Corresponds to the “fourth light emitting element” of the present invention, and corresponds to the light emitting element groups EGb1, EGb2,. The lenses LS1, LS2 that correspond to the “second imaging optical system” of the present invention. The spots SP_1, SP_2, SP_3 and SP_4 correspond to “first, second, third and fourth spots” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention. For example, in the above embodiment, when the total light amount with respect to the surface of the photosensitive drum 21 is 100%, the light amount of each light emitting element E that emits light that forms the respective spots guided by the same lenses LS1 and LS2. Is 50%, whereas the light quantity of each light emitting element E that emits light that is guided by different lenses LS1 and LS2 to form overlapping spots is 44%, but is not limited thereto. For example, depending on the size of the distance (Dt−2Dr) between the light emitting elements E that emit the light that is guided by the different lenses LS1 and LS2 to form overlapping spots, the characteristics of the photosensitive drum 21, etc. Can be made larger or smaller. In short, the amount of light emitted from each light-emitting element E that emits light that is guided by different lenses LS1 and LS2 to form overlapping spots is emitted from the light emitting element E that is guided by the same lenses LS1 and LS2 to emit light that forms overlapping spots. What is necessary is just to be smaller than the light quantity of the light emitting element E.

  In the above embodiment, the light emitting element rows GRa1, GRa2, GRb1, and GRb2 are configured by the light emitting elements E arranged in one line in the longitudinal direction LGD, but the present invention is not limited to this. For example, the light emitting element rows GRa1, GRa2, GRb1, and GRb2 may be configured by the light emitting elements E arranged in the four rows and staggered, and the arrangement form of the light emitting elements E is arbitrary.

  Moreover, in the said embodiment, although the light emitting element group EG is arrange | positioned by 2 rows zigzag, it is not restricted to this. For example, as in Example 2 to be described later, the light emitting element groups may be arranged in three rows and staggered, and the arrangement of the light emitting element groups is arbitrary. Similarly, in the above embodiment, the lenses are arranged in a zigzag pattern in each of the lens arrays LA1 and LA2. However, the arrangement of the lenses is not limited to this, and it is only necessary to correspond to the light emitting element group EG.

  In the above embodiment, the 15 light emitting elements E constitute the light emitting element rows GRa1 and GRb2, and the 19 light emitting elements E constitute the light emitting element rows GRa2 and GRb1. That is, each light emitting element group EG has 15 light emitting element pairs EP at the center in the longitudinal direction LGD. Further, the light emitting element E and the spot of the adjacent light emitting element group EG are main-scanned on one side in the longitudinal direction LGD of the 15 light emitting element rows GRa2 and GRb1 constituting the 15 light emitting element pairs EP. It has two light emitting elements E that overlap in the direction MD, and two light emitting elements E in which spots and light spots of adjacent light emitting element groups EG overlap in the main scanning direction MD on the other side. However, the number of light emitting elements E constituting the light emitting element row and the number of light emitting element pairs EP are not limited thereto.

  In the above embodiment, a bottom emission type organic EL element is used as the light emitting element E. However, a top emission type organic EL element may be used as the light emitting element E, or an LED (Light Emitting Diode) other than the organic EL element may be used as the light emitting element E.

  In addition, the imaging optical system including the lenses LS1 and LS2 of the above embodiment forms an inverted reduced image, and its magnification is negative and has an absolute value of less than 1. The magnification of the imaging optical system is not limited to this, and may be positive or may have an absolute value of 1 or more.

  In the above embodiment, the lenses LS1 and LS2 are formed on the back surfaces of the lens arrays LA1 and LA2. However, for example, the lenses LS1 and LS2 may be formed on the surfaces of the lens arrays LA1 and LA2.

  In the above embodiment, the lens arrays LA1 and LA2 are formed by forming the resin lenses LS1 and LS2 on the glass transparent substrate SB. However, the lens arrays LA1 and LA2 can be integrally formed of one material.

  Various changes can be made to the shape and size of the lens arrays LA1 and LA2.

  In addition to the above, the arrangement of the optical sensor SC can be variously changed, and the optical sensor SC may not be provided.

  21 ... photosensitive drum, 29 ... line head, E ... light emitting element, EG ... light emitting element group, GRa1, GRa2, GRb1, GRb2 ... light emitting element row, HC ... head controller, LS1, LS2 ... lens, LGD ... longitudinal direction, LTD: Width direction, MD: Main scanning direction, SD: Sub scanning direction, SP_1 to SP_4: Spot

Claims (3)

A first imaging optical system for imaging light on an exposed surface;
A first light emitting element that emits light that is imaged by the first imaging optical system to form a first spot on the exposed surface;
Second light emission that is disposed in the first direction of the first light emitting element and emits light that forms an image by the first imaging optical system and forms a second spot on the exposed surface. Elements,
A first light that is imaged by the first imaging optical system and that forms a third spot on the exposed surface that overlaps the first spot when viewed from a direction orthogonal to the first direction. 3 light emitting elements;
A second imaging optical system that images light on the exposed surface;
A first light that is imaged by the second imaging optical system and that forms a fourth spot on the exposed surface that overlaps the second spot when viewed from a direction orthogonal to the first direction. 4 light emitting elements;
The first light emitting element and the third light emitting element emit light with the same or substantially the same light amount, and the second light emitting element and the fourth light emitting element have a light amount smaller than the light amount of the first light emitting element. A control unit that emits light,
An exposure head comprising:   The exposure head according to claim 1, wherein a distance between the second light emitting element and the fourth light emitting element is larger than a distance between the first light emitting element and the third light emitting element. A latent image carrier that moves in a direction perpendicular to the first direction;
A first imaging optical system that forms light on the latent image carrier, and emits light that is imaged by the first imaging optical system to form a first latent image on the latent image carrier. A first light emitting element is disposed in the first direction of the first light emitting element, and is imaged by the first imaging optical system to form a second latent image on the latent image carrier. A second light emitting element that emits light to be emitted, and a third latent image that is imaged by the first imaging optical system and that overlaps the first latent image by the movement of the latent image bearing member. A third light emitting element for emitting light to be formed on the body, a second image forming optical system for forming light on the latent image carrier, and the latent image formed by the second image forming optical system. An exposure head having a fourth light emitting element that emits light to form a fourth latent image on the latent image carrier that overlaps the second latent image by movement of the carrier;
The first light emitting element and the third light emitting element emit light with the same or substantially the same light amount, and the second light emitting element and the fourth light emitting element have a light amount smaller than the light amount of the first light emitting element. A control unit that emits light,
An image forming apparatus comprising:

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