JP2010173225A - Exposure head, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique which enables simplification of control of a light emission timing in an exposure head which forms a latent image by selectively switching a plurality of light emitting elements arranged in a sub-scan direction. <P>SOLUTION: The exposure head has first light emitting elements, second light emitting elements arranged in a first direction of the first light emitting elements and in a second direction orthogonal to the first direction, third light emitting elements arranged in a second direction of the first light emitting elements, fourth light emitting elements arranged in the second direction of the second light emitting elements, and an optical part which images the light from the first light emitting elements, second light emitting elements, third light emitting elements and fourth light emitting elements on an exposure surface. A distance in the second direction between the first light emitting element and the third light emitting element is equal to a distance in the second direction between the second light emitting element and the fourth light emitting element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exposure head that exposes a latent image carrier with light from a light emitting element, and an image forming apparatus using the exposure head.

  As such an exposure head, there is known an exposure head that exposes the surface (exposed surface) of a latent image carrier by imaging light from a plurality of light emitting elements by an optical member. For example, in the exposure head of Patent Document 1, a light emitting element group including a plurality of light emitting elements arranged in the main scanning direction is provided, and light from each light emitting element of the light emitting element group is imaged by an optical member, A spot group composed of a plurality of spots arranged in the scanning direction is formed. Then, the surface of the latent image carrier is exposed by the spot group, and a latent image for one line is formed in the main scanning direction. In addition, each light emitting element repeatedly emits light at a timing according to the movement of the surface of the latent image carrier in the sub-scanning direction orthogonal to the main scanning direction, thereby forming a plurality of latent images for the previous line in the sub-scanning direction. Thus, a latent image for one page is formed.

  Here, as the light emitting element, an LED (Light Emitting Diode) element, an organic EL (Electro Luminescence) element, or the like can be used. However, these elements may be consumed while emitting light many times, and may not be able to emit light with a sufficient amount of light for latent image formation. Therefore, the exposure head of Patent Document 1 arranges a plurality of light emitting element groups side by side in the sub-scanning direction, and forms a latent image by causing one light emitting element group selected from the plurality of light emitting element groups to emit light. When the light emitting elements of the light emitting element group used for forming the latent image are consumed, the light emitting element group used for forming the latent image is switched to another light emitting element group.

Japanese Patent Laying-Open No. 2005-096259

  By the way, since each of the plurality of light emitting element groups is arranged at a different position in the sub-scanning direction, each of these light emitting element groups forms a spot group at a different position in the sub-scanning direction. Therefore, the spot group formation position varies before and after switching of the light emitting element groups. Therefore, if the light emission timings of the light emitting element groups are the same before and after the switching of the light emitting element groups, the latent image formation position is shifted in the sub-scanning direction on the surface of the latent image carrier. Therefore, it is conceivable to control the shift of the light emission timing of the light emitting element group before and after switching of the light emitting element group to suppress the shift of the latent image forming position. However, the arrangement mode of the plurality of light emitting elements in each light emitting element group is not limited to a straight line as described in Patent Document 1, and the plurality of light emitting elements may be arranged in a staggered manner, for example. If the plurality of light emitting elements are not arranged in a straight line, the light emission timing control of the light emitting elements may be complicated. This will be described by comparing a case where a plurality of light emitting elements are arranged in a straight line with a case where the plurality of light emitting elements are not aligned (FIG. 10).

  FIG. 10 is a diagram comparing a configuration in which a plurality of light emitting elements are arranged in a straight line (in the “straight line” column in the figure) and a configuration in which it is not (in the “staggered” column in the figure). In the drawing, as an example of a configuration in which a plurality of light emitting elements are not arranged in a straight line, a configuration in which a plurality of light emitting elements are arranged in a staggered pattern is shown (in the column “staggered” in the figure). In the “Linear” column of the same figure, a light emitting element group is composed of a plurality of light emitting elements arranged in a straight line in the main scanning direction MD, and two rows of light emitting element groups are arranged in the sub scanning direction SD. ing. Then, for example, a latent image is formed using each light emitting element E11, E12,... Of the light emitting element group in the first row, and when these light emitting elements E11, E12,. The light emitting element group is switched to each light emitting element E21, E22,. Thus, the light emitting element E21 is exposed after switching the portion exposed by the light emitting element E11 before switching, and similarly, the light emitting element E22 is exposed after switching the portion exposed by the light emitting element E12 before switching.

  In addition, as shown in the “staggered” column of the figure, even in a configuration in which a plurality of light emitting elements are arranged in a staggered manner, two rows of light emitting element groups are provided. Therefore, the light emitting element group used for latent image formation can be switched according to the consumption of the light emitting elements. As described above, the configuration in which the plurality of light emitting elements are arranged in a straight line and the configuration in which the light emitting elements are arranged in a staggered manner are common in that a plurality of light emitting element groups are provided and a light emitting element group used for forming a latent image is selectively switched. . However, at the time of this switching operation, in order to suppress the shift of the latent image forming position, the light emission timings of the light emitting elements E21, E22,. There is a problem peculiar to the configuration in which the light emitting elements are arranged in a staggered manner.

  That is, such light emission timing control is a time corresponding to a distance (for example, distance P1) in the sub-scanning direction of two light emitting elements (for example, light emitting elements E1, E2) that expose the same portion before and after switching. Only the light emission timings of the light emitting elements E21, E22,. As shown in the “Linear” column, in the configuration in which a plurality of light emitting elements are arranged in a straight line, the distance in the sub-scanning direction of the two light emitting elements that expose the same portion before and after the switching is as follows. E21, E22, ... are equal. Therefore, the light emission timing shift time can be shared by the light emitting elements E21, E22,. On the other hand, as shown in the “staggered” column, in a configuration in which a plurality of light emitting elements are arranged in a staggered manner, the distance in the sub-scanning direction of two light emitting elements that expose the same portion before and after switching. Is different between the light emitting elements E21 and E22 (distance P1 ≠ distance P2), for example. Therefore, the light emission timing shift time cannot be made common to the light emitting elements E21, E22,..., And the light emission timing control may be complicated.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to simplify light emission timing control in an exposure head that selectively switches a plurality of light emitting elements arranged in the sub-scanning direction to form a latent image. The purpose is to provide technology.

  In order to achieve the above object, an exposure head according to the present invention is arranged in a first light emitting element and a first direction of the first light emitting element and a second direction orthogonal to the first direction. Second light emitting element, a third light emitting element disposed in the second direction of the first light emitting element, and a fourth light emitting element disposed in the second direction of the second light emitting element. A first light emitting element comprising: an element; and an optical unit that images light from the first light emitting element, the second light emitting element, the third light emitting element, and the fourth light emitting element on an exposed surface. The distance in the second direction between the first light emitting element and the third light emitting element is equal to the distance in the second direction between the second light emitting element and the fourth light emitting element.

  The invention thus configured (exposure head) includes a first light emitting element and a second light emitting element. In addition, the third light emitting element is disposed in the second direction of the first light emitting element (the direction in which the exposed surface moves), and the fourth direction in the second direction of the second light emitting element. The light emitting element is arranged. In other words, the third light emitting element and the fourth light emitting element are arranged in the second direction of the first light emitting element and the second light emitting element. Therefore, the exposure head has a configuration capable of switching and executing the exposure operation by the first light emitting element and the second light emitting element and the exposure operation by the third light emitting element and the fourth light emitting element. Yes. However, the second light emitting element is a first direction (side) orthogonal to the direction in which the surface to be exposed moves with respect to the first light emitting element, and the first direction with respect to the first light emitting element. Is disposed in a second direction (side) orthogonal to the. That is, the first light emitting element and the second light emitting element are not arranged linearly in the first direction orthogonal to the moving direction of the exposed surface. Therefore, as described with reference to FIG. 10, there is a possibility that the light emission timing control accompanying the switching of the light emitting elements used for the exposure operation may be complicated. On the other hand, in the present invention, the distance in the second direction between the first light emitting element and the third light emitting element, and the second distance between the second light emitting element and the fourth light emitting element. The direction distance is equal. Therefore, the shift time of the light emission timing of the third light emitting element with respect to the light emission timing of the first light emitting element and the shift time of the light emission timing of the fourth light emitting element with respect to the light emission timing of the second light emitting element are the same. Thus, the light emission timing control is simplified.

  As described above, the exposure head according to the present invention can switch and execute the exposure operation by the first light emitting element and the second light emitting element and the exposure operation by the third light emitting element and the fourth light emitting element. It has a configuration. Therefore, a first exposure operation for exposing the exposed surface using the first light emitting element and the second light emitting element, and a first exposure operation for exposing the exposed surface using the third light emitting element and the fourth light emitting element. A control unit that performs switching between the two exposure operations may be provided.

  The exposure head according to the present invention includes a shift time of a light emission timing of the third light emitting element with respect to a light emission timing of the first light emitting element and a light emission timing of the fourth light emitting element with respect to the light emission timing of the second light emitting element. It has a configuration that can make the shifting time the same. Therefore, the control unit shifts the light emission timing of the third light emitting element in the second exposure operation with respect to the light emission timing of the first light emitting element in the first exposure operation for the first time, and The light emission timing of the fourth light emitting element in the second exposure operation may be configured to be shifted by the first time with respect to the light emission timing of the second light emitting element in the exposure operation.

  In addition, a light emission time measuring unit that measures the accumulated light emission time of the first light emitting element and the accumulated light emission time of the second light emitting element is provided, and the control unit performs the first exposure operation based on the measurement result of the light emission time measuring unit. It may be configured to switch from the first exposure operation to the second exposure operation. With this configuration, when the first light-emitting element or the second light-emitting element is consumed, switching from the first exposure operation to the second exposure operation can be reliably performed.

  In order to achieve the above object, an image forming apparatus according to the present invention is arranged in a first light emitting element and a second direction orthogonal to the first direction in the first direction of the first light emitting element. The second light emitting element, the third light emitting element disposed in the second direction of the first light emitting element, the fourth light emitting element disposed in the second direction of the second light emitting element, An exposure head having an optical part that forms an image of light from the first light emitting element, the second light emitting element, the third light emitting element, and the fourth light emitting element, and a latent image is formed by the exposure head A latent image carrier that moves in the second direction, the distance between the first light emitting element and the third light emitting element in the second direction, and the second light emitting element and the fourth light emitting element. The distance between the element and the second direction is equal.

  The invention (image forming apparatus) configured in this manner includes a first light emitting element and a second light emitting element. In addition, a third light emitting element is disposed in the second direction of the first light emitting element (the side in which the latent image carrier moves), and in the second direction of the second light emitting element. 4 light emitting elements are arranged. In other words, the third light emitting element and the fourth light emitting element are arranged in the second direction of the first light emitting element and the second light emitting element. Therefore, the image forming apparatus has a configuration capable of switching and executing the exposure operation by the first light emitting element and the second light emitting element and the exposure operation by the third light emitting element and the fourth light emitting element. ing. However, the second light emitting element is on the first direction side orthogonal to the direction in which the latent image carrier moves with respect to the first light emitting element and in the first direction with respect to the first light emitting element. It is disposed on the side of the second direction orthogonal to each other. That is, the first light emitting element and the second light emitting element are not arranged linearly in the first direction orthogonal to the moving direction of the latent image carrier. Therefore, as described with reference to FIG. 10, there is a possibility that the light emission timing control accompanying the switching of the light emitting elements used for forming the latent image may be complicated. On the other hand, in the present invention, the distance in the second direction between the first light emitting element and the third light emitting element, and the second direction between the second light emitting element and the fourth light emitting element. The distance is equal. Therefore, the shift time of the light emission timing of the third light emitting element with respect to the light emission timing of the first light emitting element and the shift time of the light emission timing of the fourth light emitting element with respect to the light emission timing of the second light emitting element are the same. Thus, the light emission timing control is simplified.

  As described above, the image forming apparatus according to the present invention can switch and execute the exposure operation by the first light emitting element and the second light emitting element and the exposure operation by the third light emitting element and the fourth light emitting element. It has a configuration that can. Therefore, a first exposure operation for forming a latent image on the latent image carrier using the first light emitting element and the second light emitting element, and a latent image carrier using the third light emitting element and the fourth light emitting element. You may comprise so that the control part which switches and performs the 2nd exposure operation | movement which forms a latent image in a body may be provided.

  Further, the developing unit that develops the latent image, the transfer unit that transfers the image developed by the developing unit to the recording material, the conveying unit that conveys the recording material, and the number of recording materials conveyed by the conveying unit are measured. And a control unit that calculates the number of recording materials onto which the latent image formed by the first exposure operation is transferred from the measurement result from the number measurement unit, and based on the calculated result It may be configured to switch from the first exposure operation to the second exposure operation. With this configuration, when the light emitting element is consumed, the switching from the first exposure operation to the second exposure operation can be reliably performed.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a view showing the arrangement of image forming stations in the image forming apparatus of FIG. FIG. 3 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 yellow (Y), magenta (M), cyan (C) and black (K) 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. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main body controller MC having a CPU, a memory, and the like, the main body controller MC performs exposure systems EP-Y, EP-M, An image corresponding to an image formation command is performed on a sheet as a recording material such as a copy sheet, a transfer sheet, a sheet, and an OHP transparent sheet by controlling each part of the apparatus such as EP-C and EP-K. Form.

  In the housing main body 3 of the image forming apparatus according to this embodiment, an electrical component box 5 containing a power circuit board, a main body controller MC, a head controller HC, a counter CT, and a memory MM is provided. An image forming unit 2, a transfer belt unit 8, and a paper feed unit 7 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 feed unit 7 is configured to be detachable from the housing body 3. The paper feeding unit 7 and the transfer belt unit 8 can be removed and repaired or exchanged.

  The image forming unit 2 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan) and 2K (for black) that form a plurality of images of different colors. In FIG. 1, since the image forming stations of the image forming unit 2 have the same configuration, only some of the image forming stations are denoted by reference numerals for convenience of illustration, and the reference numerals are omitted for other image forming stations. To do.

  Each of the image forming stations 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. The photosensitive drum 21 is disposed so that its axial direction is parallel to the main scanning direction (direction perpendicular to the paper surface of FIG. 1). 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 moves in the sub-scanning direction orthogonal to the main scanning direction. A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction thereof. Then, a charging operation, an exposure operation, and a toner developing operation are executed by these functional units. When the color mode is executed, the toner images formed by all the image forming stations 2Y, 2M, 2C, and 2K are superimposed on the transfer belt 81 provided in the transfer belt unit 8 to form a color image. When the monochrome mode is executed, only the image forming station 2K is operated to form a black monochrome image.

  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 is driven to rotate as the photosensitive drum 21 rotates. 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 to a predetermined surface potential.

  The line head 29 is disposed opposite to the photosensitive drum 21 so that the longitudinal direction thereof is parallel to the main scanning direction. In addition, the line head 29 includes a plurality of light emitting elements arranged in the longitudinal direction (main scanning direction). Then, light is emitted from these light emitting elements toward the surface of the photosensitive drum 21 charged by the charging unit 23 to form an electrostatic latent image 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. Moves from the developing roller 251 to the photosensitive drum 21, and the electrostatic latent image formed on the surface thereof is visualized.

  The toner image made visible at the developing position is conveyed in the rotational direction D21 of the photosensitive drum 21, and then is transferred to the transfer belt 81 at a primary transfer position TR1 where the photosensitive belt 21 comes into contact with the transfer belt 81 described later in detail. Primary transcription.

  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. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to remove the toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 1, and an arrow D81 illustrated by rotation of the driving roller 82 stretched between these rollers. And a transfer belt 81 that is circulated in the direction (conveyance direction). Further, four transfer belt units 8 are arranged 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 2Y, 2M, 2C, and 2K when the cartridge is mounted. Primary transfer rollers 85Y, 85M, 85C and 85K. Each of these primary transfer rollers is electrically connected to a primary transfer bias generator (not shown).

  When the color mode is executed, as shown in FIGS. 1 and 2, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations 2Y, 2M, 2C, and 2K, so that the transfer belt 81 is imaged. A primary transfer position TR1 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 2Y, 2M, 2C, and 2K. Then, by applying a primary transfer bias from the primary transfer bias generating unit to the primary transfer roller 85Y or the like at an appropriate timing, the toner images formed on the surface of each photosensitive drum 21 are respectively transferred to the corresponding primary transfer positions. Transfer is performed on the surface of the transfer belt 81 in TR1. That is, in the color mode, the single color toner images of the respective colors are superimposed on the transfer belt 81 to form a color image.

  In the so-called tandem image forming apparatus, the primary transfer position where the toner image is primarily transferred from the photosensitive drum 21 to the transfer belt 81 is different for each image forming station. In this embodiment, the yellow image forming station 2Y, the magenta image forming station 2M, the cyan image forming station 2C, and the black image forming station 2K are arranged in this order along the moving direction of the transfer belt 81. . Therefore, the yellow primary transfer position TR1y and the magenta primary transfer position TR1m are the distance Lym, the magenta primary transfer position TR1m and the cyan primary transfer position TR1c are the distance Lmc, and the cyan primary transfer position TR1c and the black primary transfer position TR1k are only the distance Lck. Separated.

  On the other hand, during the monochrome mode, among the four primary transfer rollers, the primary transfer rollers 85Y, 85M, and 85C are separated from the image forming stations 2Y, 2M, and 2C, which face each other, and the primary transfer roller corresponding to the black color. By bringing only 85K into contact with the image forming station 2K, only the monochrome image forming station 2K is brought into contact with the transfer belt 81. As a result, the primary transfer position TR1k is formed only between the primary transfer roller 85K and the image forming station 2K. Then, by applying a primary transfer bias to the primary transfer roller 85K from the primary transfer bias generation unit at an appropriate timing, a black toner image formed on the surface of the photosensitive drum 21 provided in the image forming station 2K is obtained. A monochrome image is formed by transferring to the surface of the transfer belt 81 at the primary transfer position TR1k.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed on the downstream side of the black primary transfer roller 85K and on the upstream side of the driving roller 82. The downstream guide roller 86 is common to the primary transfer roller 85K and the black photosensitive drum 21 (K) at the primary transfer position TR1 formed by the primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station 2K. It is configured to contact the transfer belt 81 on the tangent line.

  A sensor 89 is provided to face the surface of the transfer belt 81 wound around the downstream guide roller 86. The sensor 89 is formed of, for example, a reflection type photosensor, and optically detects a change in reflectance on the surface of the transfer belt 81, so that the position of the registration mark formed on the transfer belt 81 and the density of the patch image are obtained as necessary. Etc. are detected.

  The paper feed unit 7 includes a paper feed unit having a paper feed cassette 77 capable of stacking and holding sheets and a pickup roller 79 that feeds the sheets one by one from the paper feed cassette 77. The sheet fed from the sheet feeding unit by the pickup roller 79 is adjusted in sheet feeding timing by the registration roller pair 80, and then the drive roller 82 and the secondary transfer roller 121 abut along the sheet guide member 15. Paper is fed to the secondary transfer position TR2.

  The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 13 includes a heating roller 131 that includes a heating element such as a halogen heater and is rotatable, and a pressure unit 132 that presses and biases the heating roller 131. The sheet on which the image is secondarily transferred is guided to a nip formed by the heating roller 131 and the pressure belt 1323 of the pressure unit 132 by the sheet guide member 15, and in the nip, a predetermined value is formed. The image is heat-fixed at temperature. The pressure unit 132 includes two rollers 1321 and 1322 and a pressure belt 1323 stretched between them. A nip portion formed by the heating roller 131 and the pressure belt 1323 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.

  The drive roller 82 described above 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. 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. Thus, by providing the driving roller 82 with a rubber layer having high friction and shock absorption, image quality deterioration caused by transmission of the impact to the transfer belt 81 when the sheet enters the secondary transfer position TR2. Can be prevented.

  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 81 after the secondary transfer by abutting 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. Further, the cleaner blade 711 and the waste toner box 713 are configured integrally with the blade facing roller 83.

  In this embodiment, the photosensitive drum 21, the charging unit 23, the developing unit 25, and the photosensitive cleaner 27 of each of the image forming stations 2Y, 2M, 2C, and 2K are integrated into a unit as a cartridge. The cartridge is configured to be detachable from the apparatus main body. Each cartridge is provided with a nonvolatile memory for storing information related to the cartridge. Then, wireless communication is performed between the main body controller MC and each cartridge. By doing so, information about each cartridge is transmitted to the main body controller MC, and information in each memory is updated and stored. Based on these pieces of information, the usage history of each cartridge and the lifetime of consumables are managed.

  A cooperative operation between the main body controller MC configured as described above and the exposure systems EP-Y, EP-M, EP-C, and EP-K corresponding to the respective colors will be described with reference to FIG. When an image forming command is given from the external device to the main body controller MC, the main body controller MC performs predetermined signal processing on the image data included in the image forming command, and generates video data VD for each toner color. At the same time, the main body controller MC starts initialization and warm-up of each part of the apparatus. When these are completed and the image forming operation can be executed, the main body controller MC outputs a synchronization signal Vsync that triggers the start of the image forming operation to the head controller HC that controls each line head 29. With the reception of the synchronization signal Vsync, the head controller HC sequentially outputs the horizontal request signal Hreq to the main body controller MC. Each time the main body controller MC receives the horizontal request signal Hreq, the main body controller MC outputs one line of video data VD to the head controller HC in the main scanning direction MD, and the head controller HC outputs the line head 29 based on the received video data VD. The light emitting element emits light. At this time, the light emission timing of the light emitting element is controlled by the timing control circuit 210, which will be described in detail later.

  FIG. 4 is a partial cross-sectional view in the width direction of the line head. FIG. 5 is a plan view showing the arrangement of the light emitting elements provided in the line head, and shows a case where a back surface of a head substrate 293 described later is seen through from the front surface of the head substrate 293. In these drawings, a main scanning direction MD, a sub-scanning direction SD, a longitudinal direction LGD of the line head 29, and a width direction LTD of the line head 29 are illustrated. The width direction LTD of the line head 29 is a direction perpendicular to the longitudinal direction LGD of the line head 29 and is parallel to the sub-scanning direction SD.

  The line head 29 includes a case 291 elongated in the longitudinal direction LGD (main scanning direction MD), and a head substrate 293 and an optical member 295 are provided in the case 291. In addition, two light emitting element groups (a first light emitting element group EG1 and a second light emitting element group EG2) are arranged on the back surface of the head substrate 293. Since the first and second light emitting element groups EG1 and EG2 have the same configuration, the configuration of the first light emitting element group EG1 will be mainly described here, and the configuration of the second light emitting element group EG2 will be described. Are denoted by the same reference numerals in the drawings and description thereof is omitted as appropriate. As shown in FIG. 5, the first light emitting element group EG1 is composed of a plurality of light emitting elements E arranged in a zigzag pattern in the main scanning direction MD. That is, these light emitting elements E are arranged in the main scanning direction MD at the main scanning pixel pitch Rm, and two light emitting elements E (for example, the light emitting elements E1, E1, etc.) arranged at the main scanning pixel pitch Rm in the main scanning direction MD. E2) are shifted from each other by the sub-scanning pixel pitch Rs in the sub-scanning direction SD.

  Here, the main scanning pixel pitch Rm is the pixel pitch in the main scanning direction MD, the sub-scanning pixel pitch Rs is the pixel pitch in the sub-scanning direction SD, and the resolution of the image that forms any pixel pitch Rm, Rs. It depends on. In FIG. 5, the position of each light emitting element E is indicated by the intersection of two broken lines, and the main scanning pixel pitch Rm and the sub-scanning pixel pitch Rs both start from the position of the target light emitting element E or Shown as end point. The position of the light emitting element E can be obtained as the geometric center of gravity of the light emitting surface of the light emitting element E.

  As described above, the first light emitting element group EG1 and the second light emitting element group EG2 thus configured have the same configuration. Further, in the present embodiment, the first light emitting element group EG1 and the second light emitting element group EG2 have a translational symmetry relationship with respect to the main scanning direction MD. Therefore, the first light emitting element group EG1 translated in the main scanning direction MD by the distance De overlaps with the second light emitting element group EG2. Then, the two light emitting elements (for example, the light emitting elements E1, E3 or the light emitting elements E2, E4) overlapping by such translation operation can expose the same portion of the surface of the photosensitive drum 21.

  Each of the light emitting elements E constituting the first and second light emitting element groups EG1 and EG2 is a bottom emission type organic EL (Electro-Luminescence) element, and emits light having the same wavelength. The head substrate 293 is a light transmissive substrate (for example, a glass substrate) that can transmit light from the light emitting element E. Therefore, the light from each light emitting element E passes through the head substrate 293 and travels toward the optical member 295.

  The optical member 295 includes two lens arrays (a first lens array LA1 and a second lens array LA2). Each of the first and second lens arrays LA1 and LA2 is configured by stacking a plurality of gradient index lenses, and functions as an imaging optical system having imaging characteristics of erecting equal magnification. The first lens array LA1 is disposed to face the first light emitting element group EG1, and forms an image of light from each light emitting element E of the first light emitting element group EG1. Thus, the first spot group SG1 is formed with a plurality of spots arranged in the main scanning direction MD. A latent image is formed on the surface of the photosensitive drum 21 exposed by the first spot group SG1. Similarly, the second lens array LS2 is disposed so as to face the second light emitting element group EG2, and forms an image of light from each light emitting element E of the second light emitting element group EG2 to form a second spot group. SG2 is formed. A latent image is formed on the surface of the photosensitive drum 21 exposed by the second spot group SG2.

  Thus, in the line head 29 of this embodiment, the two light emitting element groups EG1 and EG2 are arranged in the sub scanning direction SD. Then, one of the light emitting element groups EG1 and EG2 selectively performs an exposure operation. Specifically, the switching circuit 220 of the head controller HC shown in FIG. 3 first selects the first light emitting element group EG1, and the first light emitting element group EG1 executes the exposure operation (first exposure operation). ) And a latent image is formed on the surface of the photosensitive drum 21 (first exposure operation). In parallel with this exposure operation, the counter CT measures the accumulated light emission time of each light emitting element E of the line head 29, and the measurement result of this counter CT is stored in the memory MM for each issuing element. If the accumulated light emission time of any one of the light emitting elements E exceeds a predetermined time while the exposure operation of the first light emitting element group EG1 is performed many times, the main body controller MC switches the switching circuit 220. Is given a command to switch the light emitting element group. Upon receiving the switching command, the switching circuit 220 switches the light emitting element group for executing the exposure operation from the first light emitting element group EG1 to the second light emitting element group EG2. Thereby, the second light emitting element group EG2 executes an exposure operation (second exposure operation), and forms a latent image on the surface of the photosensitive drum 21 (second exposure operation). As described above, the life of the line head 29 is extended by selectively performing the exposure operation (exposure operation) by one of the two light emitting element groups EG1 and EG2. The head controller HC is provided for each color line head 29, and the switching operation of the light emitting element groups EG1 and EG2 is performed independently for each line head 29.

  Incidentally, as already described, in the tandem type image forming apparatus, the plurality of image forming stations 2Y, 2M, 2C, and 2K are arranged in the transfer direction of the transfer belt 81. As shown in FIG. 2, the primary transfer positions TR1y, TR1m, TR1c, and TR1k at which the image forming stations 2Y, 2M, 2C, and 2K transfer the toner image onto the transfer belt 81 are different from each other. Therefore, in order to superimpose toner images formed at the respective image forming stations 2Y, 2M, 2C, and 2K at the same position on the transfer belt 81, the timing control circuit 210 (FIG. 3) determines the interval between the primary transfer positions. The timing of the exposure operation by each line head 29 is adjusted according to the distance.

FIG. 6 is a timing chart showing the start time of the exposure operation by each line head. This figure corresponds to the case where all of the line heads 29 of the respective colors execute the exposure operation with the first light emitting element group EG1 to form a latent image for one page. As shown in the figure, the yellow (Y) line head 29 starts the exposure operation at time tsy1, and the magenta (M) line head 29 performs the exposure operation at time tsm1 with a time difference Tym from time tsy. Start. Similarly, the cyan (C) and black (K) line heads 29 start the exposure operation at times tsc1 and tsk1, respectively. In addition, the time differences Tym, Tmc, Tck provided between the exposure operation start times of the line heads 29 of the respective colors are set according to the distances between the primary transfer positions TR1y, TR1m, TR1c, TR1k. For example, the time difference Tym between the exposure operation start time tsy of the yellow (Y) line head 29 and the exposure operation start time tsm of the magenta (M) line head 29 is expressed by the following equation:
Tym = Lym / V81
It is set to satisfy. Here, the speed V81 is the moving speed of the transfer belt 81. The other time differences Tmc and Tck are set in the same manner. That is, the timing control circuit 210 according to the present embodiment adjusts the exposure operation start times tsy1, tsm1, tsc1, and tsk1 of the line heads 29 of the respective colors so as to satisfy the time differences Tym, Tmc, and Tck thus obtained.

  In each line head 29, the first light emitting element group EG1 sequentially emits light for a predetermined time Tp from the exposure operation start time. Thereby, a latent image for one page corresponding to each color (Y), (M), (C), (K) is formed (FIG. 7). Here, FIG. 7 is a timing chart showing an exposure operation for the line head of each color to form a latent image for one page. Then, the latent image for one page of each color (Y), (M), (C), (K) is developed as a corresponding color toner image, and the toner image for one page of each color is transferred. Overlapping on the belt 81, a color image for one page is completed. As described above, in this embodiment, by adjusting the timing of the exposure operation of the line head 29 for each color (Y), (M), (C), and (K), each image forming station 2Y, 2M, 2C, The toner images formed by 2K are superimposed on each other at the same position on the transfer belt 81.

  By the way, since each of the first light emitting element group EG1 and the second light emitting element group EG2 is arranged at a different position in the sub scanning direction SD, each of these light emitting element groups EG1, EG2 is in the sub scanning direction SD. Spot groups SG1 and SG2 are formed at different positions (FIG. 4). Therefore, the spot group formation position varies before and after switching of the light emitting element groups. Therefore, the latent image formation position may be shifted in the sub-scanning direction SD on the surface of the photosensitive drum 21 before and after switching of the light emitting element groups. Therefore, in the present embodiment, when the light emitting element group is switched, the timing control circuit 210 changes the timing of the exposure operation of the light emitting element group.

  FIG. 8 is a timing chart showing exposure operation start times before and after switching of the light emitting element groups. The chart “before switching” in the figure corresponds to the case where all the line heads 29 of the respective colors perform the exposure operation with the first light emitting element group EG1. Further, the “after switching” chart in the figure corresponds to the case where the light emitting element group performing the exposure operation is switched to the second light emitting element group EG2 in the line head 29 of magenta (M). In the operation shown in the “after switching” chart of the same drawing, each line head 29 other than magenta (M) performs the exposure operation with the first light emitting element group EG1. That is, the light emitting element group of the magenta (M) line head 29 is switched between the “before switching” chart and the “after switching” chart.

In “before switching”, each line head starts an exposure operation at times tsy1, tsm1, tsc1, and tsk1 shown in FIG. On the other hand, in “after switching”, the magenta (M) line head 29 corresponds to the fact that the light emitting element group performing the exposure operation in the magenta (M) line head 29 is switched to the second light emitting element group EG2. The exposure operation start time is changed. Specifically, the exposure operation start time is shifted to time tsm2 that is earlier than time tsm1 by time Δtsm. This shift time Δtsm corresponds to the exposure position by the first light emitting element group EG1 (formation position of the first spot group SG1) and the exposure position by the second light emitting element group EG2 (formation position of the second spot group SG2). Is set in accordance with a distance L21 in the sub-scanning direction SD (a distance L21 on the surface of the photosensitive drum 21 (FIG. 4)).
Δtsm = L21 / V21
The shift time Δtsm can be set based on the above. The distance L21 and the speed V21 may be obtained in advance at the time of factory shipment and stored in the memory.

  In the magenta (M) line head 29, the second light emitting element group EG2 emits light sequentially from the time tsm2 after the change to the time Tp (FIG. 9). FIG. 9 is a timing chart showing an exposure operation for the magenta line head to form a latent image for one page. FIG. 9 shows the exposure operation of the magenta (M) and yellow (Y) line heads 29. The chart “(Y) before switching” indicates that the light emitting element group of the magenta (M) line head is switched. The exposure operation of the yellow (Y) line head before switching is shown, and the chart “(M) before switching” shows the magenta (M) line head before the switching of the light emitting element group of the magenta (M) line head. The exposure operation is shown. The chart “After (Y) switching” shows the exposure operation of the yellow (Y) line head after the light emitting element group of the magenta (M) line head is switched. The “after” chart shows the exposure operation of the magenta (M) line head after the light emitting element group of the magenta (M) line head is switched.

  As shown in FIG. 9, in response to switching of the light emitting element group used for the exposure operation by the magenta (M) line head 29, the light emission timing of the light emitting element group used for the exposure operation is shifted by Δtsm. ing. As a result, displacement of the latent image forming position on the surface of the magenta (M) photosensitive drum 21 is prevented. Then, the toner image obtained by developing the latent image corresponding to magenta (M) and the latent image corresponding to other colors such as yellow (Y) formed in this way is accurately superimposed on the surface of the transfer belt 81. Therefore, it is possible to form a good color image.

  As described above, in the present embodiment, the light emission timing of the first light emitting element group EG1 in the first exposure operation is different from the light emission timing of the second light emitting element group EG2 in the second exposure operation. Make it. Accordingly, it is possible to suppress the shift of the latent image forming position and to form a good latent image.

  In particular, for the tandem type image forming apparatus as described above, the light emission timing of the first light emitting element group EG1 in the first exposure operation and the second light emitting element group EG2 in the second exposure operation. A configuration in which the light emission timing is different is suitable. The reason for this is as follows. As described with reference to FIGS. 2, 6, and 7, in order to form a good color image with a tandem type image forming apparatus, the toner images of the respective colors can be accurately superimposed on the surface of the transfer belt 81. It becomes important. However, when the position of forming the latent image corresponding to the one color is shifted by switching from the first exposure operation to the second exposure operation for one of the plurality of colors, The toner images of the respective colors are not accurately superimposed on the surface of the transfer belt 81, and color misregistration may occur in the formed color image. On the other hand, in this embodiment, the light emission timing of the first light emitting element group EG1 in the first exposure operation and the light emission timing of the second light emitting element group EG2 in the second exposure operation are different. Thus, since the shift of the latent image formation position before and after switching from the first exposure operation to the second exposure operation is suppressed, it is possible to obtain a good color image without color shift. Yes.

  Further, as can be seen from the above discussion, the shift of the latent image formation position is formed by the spot formed by the light emitting element E of the first light emitting element group EG1 and the light emitting element E of the second light emitting element group EG2. This is because the positions of the spots differ. On the other hand, in the present embodiment, the distance L21 (FIG. 4) between the spot formed by the light emitting elements of the first light emitting element group EG1 and the spot formed by the light emitting elements E of the second light emitting element group. Accordingly, the light emission timing of the first light emitting element group EG1 in the first exposure operation is different from the light emission timing of the second light emitting element group EG2 in the second exposure operation. Thereby, the shift of the latent image forming position is reliably suppressed, and a better latent image can be formed.

  Further, the moving speed of the surface of the photosensitive drum 21 also affects the formation position of the latent image on the surface of the photosensitive drum 21. On the other hand, the second light emission timing is made different from the first light emission timing in accordance with the moving speed V21 of the surface of the photosensitive drum 21 in this embodiment. Thereby, the shift of the latent image forming position is reliably suppressed, and a better latent image can be formed.

  By the way, in this embodiment, the arrangement | positioning aspect of the several light emitting element E in each light emitting element group EG1 and EG2 is not linear, but arrange | positions several light emitting elements in zigzag form, for example. Therefore, as described with reference to FIG. 10, the light emission timing control may be complicated before and after the switching of the light emitting element groups EG1 and EG2. On the other hand, in the above embodiment, the first light emitting element group EG1 and the second light emitting element group EG2 have a translational symmetry relationship with respect to the main scanning direction MD. As a result, it is possible to simplify the light emission timing control. The reason for this will be described with reference to the light emitting elements E1, E2, E3, and E4 shown in FIG.

  As described above, as the light emitting element groups EG1 and EG2 are switched, the light emitting element E3 exposes the portion exposed by the light emitting element E1 instead of the light emitting element E1, and the light emitting element E4 exposes the light emitting element E2. The exposed portion is exposed instead of the light emitting element E2. In order to suppress the shift of the latent image forming position, the light emission timing of the light emitting element E3 is a time corresponding to the distance (spot distance) between the spot formed by the light emitting element E3 and the spot formed by the light emitting element E1. It is shifted with respect to the light emission timing of the light emitting element E1. Similarly, the light emission timing of the light emitting element E4 is set with respect to the light emission timing of the light emitting element E2 only for a time corresponding to the distance (spot distance) between the spot formed by the light emitting element E4 and the spot formed by the light emitting element E2. It is shifted. Here, since the light emitting element groups EG1 and EG2 are translationally symmetric in the sub-scanning direction SD, the distance between the light emitting element E1 and the light emitting element E3 and the distance between the light emitting element E2 and the light emitting element E4 are both distance De. equal. Therefore, the distance between the spot formed by the light emitting element E3 and the spot formed by the light emitting element E1, and the distance between the spot formed by the light emitting element E4 and the spot formed by the light emitting element E2 are also equal. Therefore, the shift time of the light emission timing of the light emitting element E3 with respect to the light emission timing of the light emitting element E1 and the shift time of the light emission timing of the light emitting element E4 with respect to the light emission timing of the light emitting element E2 are both the same time (time Δtsm in the above embodiment). It can be. As described above, in this embodiment, the light emission timing shift time before and after the switching of the light emitting element groups EG1 and EG2 can be made common to each light emitting element E, and the light emission timing control is simplified. Furthermore, the configuration of the timing control circuit 210 that executes the light emission timing control can be simplified.

  In the above embodiment, the counter CT for measuring the cumulative light emission time of each light emitting element E of the first light emitting element group EG1 is provided, and the first exposure operation to the second exposure operation are performed based on the measurement result of the counter CT. Switching to. Therefore, when the light emitting element E of the first light emitting element group EG1 is consumed, the switching from the first exposure operation to the second exposure operation can be surely executed.

  Thus, in this embodiment, the line head 29 functions as the “exposure head” of the present invention. The light emitting element E1 corresponds to the “first light emitting element” of the present invention, the light emitting element E2 corresponds to the “second light emitting element” of the present invention, and the light emitting element E3 corresponds to the “third light emitting element” of the present invention. The light emitting element E4 corresponds to the “fourth light emitting element” of the present invention. Further, the main scanning direction MD and the longitudinal direction LGD correspond to the “first direction” of the present invention, and the sub-scanning direction SD and the width direction LTD correspond to the “second direction” of the present invention. Further, the main body controller MC and the head controller HC cooperate to function as the “control unit” of the present invention, and the counter CT functions as the “light emission time measuring unit” of the present invention. The time Δtsm corresponds to the “first time” 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-described embodiment, the second exposure using the second light emitting element group EG2 from the first exposure operation using the first light emitting element group EG1 at the timing based on the accumulated light emission time of the light emitting element E. Although switching to the exposure operation, the switching operation of the light emitting element groups EG1, EG2 is not limited to this. Therefore, the counter CT functions as a latent image number measuring unit that measures the number of latent images formed in the first exposure operation, and the first exposure operation starts from the measurement result of the latent image number measuring unit of the counter CT. It may be configured to switch to the second exposure operation. Also with this configuration, when the light emitting element E is consumed, the switching from the first exposure operation to the second exposure operation can be surely performed.

  Alternatively, the number of recording materials conveyed by the paper feeding unit 7 (conveyance unit) is measured by the counter CT (number measurement unit), and the latent image formed by the first exposure operation from the measurement result from the counter CT. It is also possible to calculate the number of recording materials onto which the toner image has been transferred and to switch from the first exposure operation to the second exposure operation based on the calculated result. With this configuration, when the light emitting element is consumed, the switching from the first exposure operation to the second exposure operation can be reliably performed.

  In the above-described embodiment, the first exposure operation by the first light emitting element group EG1 is switched to the second exposure operation by the second light emitting element group EG2. Not limited. Therefore, the second exposure operation by the second light emitting element group EG2 may be switched to the first exposure operation by the first light emitting element group EG1. Alternatively, it may be configured such that the user confirms and switches the formed image.

In the above embodiment, the shift time Δtsm is expressed by the following equation:
Δtsm = L21 / V21
Set based on. However, the method for setting the shift time Δtsm is not limited to this. In other words, as described above, in the tandem type image forming apparatus, the formation position shift of the latent image before and after the switching of the light emitting element groups EG1 and EG2 appears as the color shift of the color image. Therefore, a registration mark is formed on the transfer belt 81 while changing the shift time Δtsm stepwise, and the degree of color shift is obtained from the result of detecting the registration mark by the sensor 89, and the shift time Δtsm is based on this result. May be set.

  In the above embodiment, in each of the light emitting element groups EG1 and EG2, the plurality of light emitting elements E are arranged in a two-row zigzag pattern, but the plurality of light emitting elements E may be arranged in a zigzag pattern of three or more columns. These may be arranged in a manner other than these.

In the above-described embodiment, the light emitting element E is composed of a bottom emission type organic EL element. However, the light emitting element E is a top emission type organic EL element or LED (Light
(Emitting Diode) may be used.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating an arrangement of image forming stations in the image forming apparatus of FIG. 1. FIG. 2 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 1. The width direction fragmentary sectional view of a line head. The top view which shows arrangement | positioning of the light emitting element with which a line head is provided. 6 is a timing chart showing the start time of an exposure operation by each line head. 6 is a timing chart showing an exposure operation for forming a latent image for one page. The timing chart which shows before and after switching of the light emitting element group. 6 is a timing chart showing an exposure operation for forming a latent image for one page. The figure which shows the structure etc. which have arrange | positioned the several light emitting element in the straight line form.

  DESCRIPTION OF SYMBOLS 21 ... Photosensitive drum, 210 ... Timing control circuit, 220 ... Switching circuit, 29 ... Line head, 295 ... Optical member, CT ... Counter, E, E1, E2, E3, E4 ... Light emitting element, EG1 ... First light emission Element group, EG2 ... second light emitting element group, EP-Y, EP-M, EP-C, EP-K, exposure system, HC, head controller, LGD, longitudinal direction, LTD, width direction, MD, main scanning Direction, SD ... sub-scanning direction, MM ... memory

Claims (7)

A first light emitting element;
A second light emitting element disposed in a first direction of the first light emitting element and in a second direction orthogonal to the first direction;
A third light emitting element disposed in the second direction of the first light emitting element;
A fourth light emitting element disposed in the second direction of the second light emitting element;
An optical unit that images light from the first light-emitting element, the second light-emitting element, the third light-emitting element, and the fourth light-emitting element on an exposed surface;
With
The distance in the second direction between the first light emitting element and the third light emitting element is the distance in the second direction between the second light emitting element and the fourth light emitting element. An exposure head characterized by being equal to   A first exposure operation in which the exposed surface is exposed using the first light emitting element and the second light emitting element; and the exposed surface using the third light emitting element and the fourth light emitting element. The exposure head according to claim 1, further comprising a control unit that switches and executes a second exposure operation for exposing the first exposure operation.   The control unit shifts the light emission timing of the third light emitting element in the second exposure operation with respect to the light emission timing of the first light emitting element in the first exposure operation for a first time, and The exposure head according to claim 2, wherein the light emission timing of the fourth light emitting element of the second exposure operation is shifted from the light emission timing of the second light emitting element of the first exposure operation by the first time. A light emission time measuring unit for measuring a cumulative light emission time of the first light emitting element and a cumulative light emission time of the second light emitting element;
4. The exposure head according to claim 2, wherein the control unit switches from the first exposure operation to the second exposure operation based on a measurement result of the light emission time measurement unit. A first light emitting element, a second light emitting element disposed in a second direction orthogonal to the first direction in the first direction of the first light emitting element, and the first light emitting element of the first light emitting element. A third light emitting element disposed in the direction of 2, a fourth light emitting element disposed in the second direction of the second light emitting element, and the first light emitting element and the second light emitting element. An exposure head having an optical part for imaging light from the element, the third light emitting element and the fourth light emitting element;
A latent image is formed by the exposure head and moves in the second direction;
With
The distance in the second direction between the first light emitting element and the third light emitting element is the distance in the second direction between the second light emitting element and the fourth light emitting element. An image forming apparatus characterized by being equal to   Using the first light emitting element and the second light emitting element to form a latent image on the latent image carrier, and using the third light emitting element and the fourth light emitting element. The image forming apparatus according to claim 5, further comprising a control unit that switches and executes a second exposure operation for forming a latent image on the latent image carrier. A developing unit for developing the latent image;
A transfer portion for transferring the image developed by the developing portion to a recording material;
A transport unit for transporting the recording material;
A sheet number measuring unit for measuring the number of the recording materials conveyed by the conveying unit,
The control unit calculates the number of the recording materials onto which the latent image formed by the first exposure operation is transferred from the measurement result from the number measurement unit, and based on the calculated result, the first The image forming apparatus according to claim 6, wherein the exposure operation is switched to the second exposure operation.

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