JP2010253895A - Exposure head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for enabling favorable exposure by making small an angle of light incident on an exposure surface, and stabilizing a position of the light incident on the exposure surface. <P>SOLUTION: The exposure head includes a first light emitting element, a first lens on which light from the first light emitting element is made incident, a second lens on which light projected from the first lens is made incident, a second light emitting element, a third lens on which light from the second light emitting element is made to incident, and a fourth lens on which light projected from the third lens is made to incident. First light emitted by the first light emitting element and passing through the first lens and the second lens, and second light emitted by the second light emitting element and passing through the third lens and the fourth lens are incident on different positions in a first direction of the exposure surface which has a radius of curvature. A distance Dls1 in the first direction between the first lens and the third lens is different from a distance Dls2 in the first direction between the second lens and the fourth lens. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  Conventionally, in order to expose a surface to be exposed, an exposure head that uses a light emitting element and a lens to focus light on the surface to be exposed has been proposed. For example, in the exposure head described in Patent Document 1 (line head in the same document), a plurality of lenses are arranged in an array on both surfaces of a glass substrate, and two lenses sandwiching the glass substrate from the thickness direction form a pair. It is made. In addition, each lens pair has a predetermined number of light emitting elements that are arranged to face each other, and each light emitting element emits light toward the opposing lens pair. Then, light incident on the lens pair from the light emitting element is converged on the exposed surface by receiving the optical action of each lens constituting the lens pair.

JP 2008-036937 A

  Incidentally, the exposed surface exposed by the exposure head described in Patent Document 1 is the peripheral surface of a cylindrical photosensitive drum. The photosensitive drum has a rotation axis parallel to the main scanning direction, and the circumferential surface of the photosensitive drum rotates around the rotation axis, and as a result, moves in the sub-scanning direction orthogonal to the main scanning direction. To do. However, due to reasons such as the rotational axis slightly deviating from the center of the photoconductive drum or the cross section of the photoconductive drum is not a perfect circle, the photoconductor is rotated along with the rotation of the photoconductive drum. There are cases where the distance between the drum peripheral surface and the exposure head varies. At this time, if the incident angle of the convergent light (its principal ray) to the circumferential surface of the photosensitive drum is large, the converged light enters the circumferential surface of the photosensitive drum according to the variation in the distance between the circumferential surface of the photosensitive drum and the exposure head. The incident position varies greatly. Therefore, from the viewpoint of stabilizing the incident position of the convergent light on the circumferential surface of the photosensitive drum, it is desirable that the incident angle of the convergent light on the circumferential surface of the photosensitive drum is as small as possible.

  However, in the above exposure head, it may be difficult to keep the incident angle of the convergent light small. That is, in this exposure head, a plurality of (3 in the same patent document) lens pairs are arranged so that the positions in the sub-scanning direction are different from each other, and each of these lens pairs is located in a position different in the sub-scanning direction. To converge light. That is, in the exposure by this exposure head, a plurality of convergent lights are incident on the circumferential surface of the photosensitive drum at different positions in the sub-scanning direction. Moreover, the respective convergent lights (principal rays) by the exposure head are parallel to each other or slightly inclined with respect to each other. In contrast, the peripheral surface of the photosensitive drum has a finite radius of curvature in the sub-scanning direction (in other words, curved in the cross section in the sub-scanning direction). For this reason, all or a part of the plurality of convergent lights is inclined with respect to the normal line of the circumferential surface of the photosensitive drum in the cross section in the sub-scanning direction, and enters the circumferential surface of the photosensitive drum at a relatively large incident angle. In some cases, it was incident.

  As described above, in an exposure head in which a plurality of lights are incident on the surface to be exposed at different positions in a direction in which the surface to be exposed has a finite curvature, all or a part of the plurality of lights is large. In some cases, the light incident on the surface to be exposed at an incident angle. As a result, the incident position of light is not stable, and there is a possibility that exposure cannot be performed satisfactorily.

  The present invention has been made in view of the above problems, and an exposure head that makes a plurality of light incident on an exposed surface at different positions in a direction in which the exposed surface has a finite radius of curvature, and image formation using the exposure head An object of the present invention is to provide a technique that makes it possible to perform good exposure by reducing the incident angle of each light to the exposed surface and stabilizing the incident position of each light on the exposed surface.

  In order to achieve the above object, an exposure head according to the present invention includes a first light emitting element, a first lens into which light from the first light emitting element is incident, and light emitted from the first lens. Is incident on the second lens, the second light emitting element, the third lens on which the light from the second light emitting element is incident, and the fourth lens on which the light emitted from the third lens is incident. The first light emitted from the first light emitting element and transmitted through the first lens and the second lens, and the third light emitted from the second light emitting element and the fourth lens. The second light transmitted through the light is incident at different positions in the first direction of the exposed surface having a radius of curvature, and a distance Dls1 in the first direction between the first lens and the third lens; The distance Dls2 in the first direction between the second lens and the fourth lens is different from each other.

  In the invention (exposure head) configured as described above, the first light transmitted from the first light emitting element through the first lens and the second lens, and the third light emitting element from the second light emitting element and the fourth light are transmitted. The exposed surface is exposed with the second light transmitted through the lens. However, the surface to be exposed has a curvature, and the first light and the second light are incident on the surface to be exposed at different positions in the first direction. Therefore, if the first light and the second light are parallel to each other or slightly tilted with respect to each other, both or one of the first light and the second light are covered at a large incident angle. In some cases, the light enters the exposure surface. On the other hand, in the present invention, the distance Dls1 between the first lens and the third lens in the first direction, and the distance Dls2 between the second lens and the fourth lens in the first direction. Is different. As a result, the first light and the second light can be tilted sufficiently and appropriately, and as a result, the incident angles of the first light and the second light on the exposed surface can be reduced. . In this way, it is possible to stabilize the incident positions of the first light and the second light on the exposed surface and realize good exposure.

  At this time, when the center of curvature of the exposed surface is on the opposite side of the exposed surface with respect to the second lens and the fourth lens, the exposure head is preferably configured such that the distance Dls2 is shorter than the distance Dls1. As a result, the incident angles of the first light and the second light on the exposed surface can be reduced, and the incident positions of the first light and the second light on the exposed surface can be stabilized. It is possible to realize good exposure.

  Further, when the peripheral surface of a cylindrical drum having a rotation axis in a second direction orthogonal to the first direction and rotating on the rotation axis is an exposed surface, the present invention is applied to this exposure head. Is preferred. This is because, in such a case, the gap between the drum peripheral surface and the exposure head is likely to change due to the above-described reason. Therefore, by applying the present invention to the exposure head, the first light and the second light respectively. This is because it is preferable to reduce the incident angle of the first light and the second light to stabilize the incident positions of the first light and the second light on the exposed surface, thereby achieving good exposure. .

  At this time, the exposure head may be configured such that the first light is emitted toward the rotation axis and the second light is emitted toward the rotation axis. Thereby, the incident angles of the first light and the second light on the exposed surface can be surely reduced, and the incident positions of the first light and the second light on the exposed surface can be further increased. It is possible to achieve stable and very good exposure.

  By the way, in order to direct both the first light and the second light to the rotation axis of the drum, it is required to manufacture each lens so that the above-mentioned distance Dls1 and distance Dls2 satisfy predetermined accuracy. . Therefore, the first lens and the third lens are disposed on the same surface of the first lens substrate, and the first lens and the third lens are disposed on the same surface of the second lens substrate. Thus, an exposure head may be configured. In this way, the first lens and the third lens can be simply arranged so that the distance Dls1 satisfies a predetermined accuracy by adopting a configuration in which the first lens and the third lens are arranged on the same surface. It can be produced. Further, by adopting a configuration in which the second lens and the fourth lens are arranged on the same surface, the second lens and the fourth lens can be easily manufactured so that the distance Dls2 satisfies a predetermined accuracy. It becomes possible.

  A first aperture stop disposed between the first light emitting element and the first lens; and a second aperture stop disposed between the second light emitting element and the third lens. An exposure head may be configured to provide. Accordingly, the amount of light incident on the first lens can be appropriately adjusted by the first aperture stop, and the amount of light incident on the third lens is appropriately adjusted by the second aperture stop. Therefore, such an exposure head is advantageous for good exposure.

  In order to achieve the above object, the image forming apparatus according to the present invention includes a first light emitting element, a first lens on which light from the first light emitting element is incident, and light emitted from the first lens. An incident second lens, a second light emitting element, a third lens to which light from the second light emitting element is incident, and a fourth lens to which light emitted from the third lens is incident An exposure head, and an image carrier that receives light emitted from the second lens and light emitted from the fourth lens and has a radius of curvature in the first direction. The first light emitted from the element and transmitted through the first lens and the second lens, and the second light emitted from the second light emitting element and transmitted through the third lens and the fourth lens are the first light Are incident on the image carrier at different positions in the directions of the first lens and the third lens. The distance Dls1 in a first direction, and being different from the first distance in the direction Dls2 between the second lens and the fourth lens.

  The invention (image forming apparatus) configured in this manner includes the first light transmitted from the first light emitting element through the first lens and the second lens, and the third light emitting element from the second light emitting element and the third lens. The image carrier is exposed with the second light transmitted through the lens 4. However, the image carrier has a curvature, and the first light and the second light are incident on the image carrier at different positions in the first direction. Therefore, if the first light and the second light are parallel to each other or are slightly inclined with respect to each other, both or one of the first light and the second light is imaged at a large incident angle. In some cases, the light enters the carrier. On the other hand, in the present invention, the distance Dls1 between the first lens and the third lens in the first direction, and the distance Dls2 between the second lens and the fourth lens in the first direction. Is different. Accordingly, the first light and the second light can be tilted sufficiently and appropriately, and as a result, the incident angles of the first light and the second light on the image carrier can be reduced. . In this manner, it is possible to stabilize the incident positions of the first light and the second light on the image carrier and to realize good exposure.

  At this time, the image carrier is an image carrier drum that rotates on a rotating shaft, and when the exposure head is disposed on the outer peripheral side of the image carrier drum, the exposure head is configured such that the distance Dls is shorter than the distance Dda. Good. Thereby, the incident angles of the first light and the second light on the image carrier can be reduced, and the incident positions of the first light and the second light on the image carrier can be stabilized. It is possible to realize good exposure.

1 is a diagram showing an example of an image forming apparatus equipped with a line head according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. FIG. 3 is a perspective view illustrating a schematic configuration of a photosensitive drum. The perspective view which shows the outline of a line head. The partial top view which planarly viewed the head substrate from the thickness direction. FIG. 6 is a step sectional view of the line head taken along line AA shown in FIG. 5. The figure which showed the positional relationship of a 1st lens array and a 2nd lens array. The figure which showed the convergent light by a line head in the AA line step cross section. Explanatory drawing of the problem which may generate | occur | produce when making a several convergent light enter into a to-be-exposed surface. The figure explaining the example of the effect of the line head of a 1st embodiment. The figure which partially showed the line head of 2nd Embodiment in the AA line step cross section. The figure which showed the line head of 3rd Embodiment partially in the AA line step cross section. The conceptual diagram for demonstrating the light which faces the rotation center vicinity of a photoconductive drum. The figure which partially showed the line head of the Example in the AA line step cross section. The figure which summarized the optical system specification of the upstream image formation optical system as a table | surface. The figure which summarized the optical system specification of the central imaging optical system as a table | surface. The figure which summarized the optical-system item of the downstream image formation optical system as a table | surface. FIG. 6 is a ray diagram of the upstream imaging optical system in the sub-scanning direction cross section. The light ray figure of the center image formation optical system in the subscanning direction section. The ray diagram of the downstream image formation optical system in the sub-scanning direction section. The light ray figure in a main scanning direction cross section. The figure which shows the lens data of an upstream imaging optical system and a downstream imaging optical system. The figure which shows the data of the S4 surface of the lens data of FIG. The figure which shows the data of the S7 surface of the lens data of FIG. The figure which shows the lens data of a center image formation optical system. The figure which shows the data of the S4 surface of the lens data of FIG. The figure which shows the data of the S7 surface of the lens data of FIG. The figure which shows the definition formula of an XY polynomial surface.

First Embodiment FIG. 1 is a view showing an example of an image forming apparatus equipped with a line head according to a first embodiment of the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus uses a color mode in which four color toners of black (K), cyan (C), magenta (M), and yellow (Y) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. FIG. 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 includes a cylindrical photosensitive drum 21 having a peripheral surface (surface) having 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 peripheral surface of the photosensitive drum 21.

  FIG. 3 is a perspective view showing a schematic configuration of the photosensitive drum. As shown in the figure, the photosensitive drum 21 is provided with a drum shaft rod RS21. More specifically, the drum shaft RS21 is formed so as to penetrate the cylindrical center of the photosensitive drum 21, and one end thereof protrudes from the side surface of the photosensitive drum 21. The photosensitive drum 21 is arranged so that the drum shaft RS21 is parallel to the main scanning direction MD. Each photosensitive drum 21 is provided with a dedicated drive motor, and this drive motor is connected to the drum shaft RS21 of the photosensitive drum 21 directly or via a gear. When the drive motor applies a rotational driving force to the drum shaft RS21, the photosensitive drum 21 rotates at a predetermined speed in the direction of the arrow D21 in the drawing together with the drum shaft RS21. As a result, the circumferential surface of the photosensitive drum 21 is conveyed in the sub-scanning direction SD orthogonal to the main scanning direction MD. Then, the peripheral surface of the photosensitive drum 21 having a finite radius of curvature (or curvature) in the sub-scanning direction SD (in other words, having a finite radius of curvature (or curvature) in the cross section in the sub-scanning direction SD) is exposed. As a surface, the line head 29 performs exposure. The center of curvature of the photosensitive drum 21 is given by a cylindrical center line, and is located on the opposite side of the circumferential surface (exposed surface) of the photosensitive drum 21 with respect to the line head 29.

  Further, a charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductor drum 21 (on the outer peripheral side) along the rotation direction D21. 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 rotate in contact with the surface of the photosensitive drum 21 at the charging position, and at a peripheral speed in the driven direction with respect to the photosensitive drum 21 as the photosensitive drum 21 rotates. Followed rotation. The charging roller is connected to a charging bias generator (not shown). The charging roller receives power 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 to the main scanning direction MD, and the width direction of the line head 29 is parallel to the sub-scanning direction SD. is there. 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.

  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 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 each of the photosensitive drums 21 included in the image forming stations Y, M, C, and K when the photosensitive cartridge is mounted. Four primary transfer rollers 85Y, 85M, 85C, and 85K are provided. Each of these primary transfer rollers 85 is electrically connected to a primary transfer bias generator (not shown). 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 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.

  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. 4 is a perspective view showing an outline of the line head. In the drawing, a part of the line head 29 is shown in a cross section in order to facilitate understanding of the configuration of the line head 29 in the thickness direction TKD. Here, the thickness direction TKD is a direction perpendicular to the longitudinal direction LGD and the width direction LTD, and faces the side from which the light emitting element E described later emits light (that is, the side from the line head 29 toward the photosensitive drum 21). It is assumed that the direction was. The line head 29 includes a head frame 291 that is long in the longitudinal direction LGD. The line head 29 can be positioned and fixed with respect to the photosensitive drum 21 by positioning pins 2991 and screw insertion holes 2912 provided at both ends of the head frame 291 in the longitudinal direction LGD. That is, the photoconductor cover (not shown) that covers the photoconductor drum 21 is positioned with respect to the photoconductor drum 21 and has a positioning hole. Therefore, the line head 29 is positioned with respect to the photosensitive drum 21 by fitting the positioning pins 2991 of the head frame 291 into the positioning holes of the photosensitive cover. Further, the line head 29 is fixed to the photosensitive drum 21 by screwing a fixing screw into the screw hole of the photosensitive member cover through the screw insertion hole 2912.

  In the head frame 291, a head substrate 293, a light shielding member 297, a first lens array LA1, and a second lens array LA2 are arranged in this order in the thickness direction TKD. Next, these members will be described with reference to FIGS. 4, 5, and 6. In the description of this embodiment, the downstream side in the thickness direction TKD (upper side in FIG. 4) is referred to as “one side in the thickness direction TKD”, and the upstream side in the thickness direction TKD (the lower side in FIG. 4). ) 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. 5 is a partial plan view of the head substrate 293 in plan view from the thickness direction, and corresponds to a case where the back surface 293-t of the head substrate 293 is seen through from the downstream side in the thickness direction TKD (upper side in FIG. 4). . FIG. 6 is a step sectional view of the line head taken along line AA shown in FIG. 5 and corresponds to a case where the section is viewed from the longitudinal direction LGD (main scanning direction MD). In FIG. 5, the light emitting element group EG formed on the head substrate 293, the first lens LS1 (LSa1, LSb1, LSc1) formed on the first lens array LA1, and the second lens array LA2 formed on the second lens array LA2. In order to show the positional relationship between the two lenses LS2 (LSa2, LSb2, LSc2), the first lens and the second lens are indicated by a one-dot chain line. Note that the descriptions of the first lens and the second lens in the drawing are for showing the positional relationship between them, and the first lens and the second lens are formed on the back surface 293-t (FIG. 6) of the head substrate. It does not indicate that there is.

  The head substrate 293 is formed of a glass 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. The plurality of light emitting elements E emit light beams having the same wavelength toward the surface of the photosensitive drum 21. As shown in FIG. 5, the arrangement of the plurality of light emitting elements E formed on the back surface 293-t of the head substrate has a group structure. That is, 15 light emitting elements E are arranged in a staggered manner in 3 rows in the longitudinal direction LGD to form one light emitting device group EG, and a plurality of light emitting device groups EG are dispersed in a staggered manner in 3 rows in the longitudinal direction LGD. Are arranged.

  In more detail, this arrangement | positioning aspect can be demonstrated as follows. That is, in each light emitting element group EG, 15 light emitting elements E are arranged at different positions in the longitudinal direction LGD, and the longitudinal direction LGD of two light emitting elements E and E whose positions in the longitudinal direction LGD are adjacent to each other. Is the inter-element distance Pel (in other words, in each light emitting element group EG, 15 light emitting elements E are arranged in the longitudinal direction LGD with a pitch Pel). Further, in each light emitting element group EG, five light emitting elements E are linearly arranged along the main scanning direction MD to form one light emitting element row, and three light emitting element rows ERa, ERb and ERc are arranged at different positions in the sub-scanning direction SD while being shifted from each other by the inter-element distance Pel in the main scanning direction MD.

  A plurality of light emitting element groups EG are discretely arranged along the longitudinal direction LGD with a group distance Peg longer than the element distance Pel to form one light emitting element group row GRa and the like. Further, three light emitting element group rows GRa, GRb, GRc are discretely arranged at different positions in the width direction LTD with a distance Dt therebetween, and each of the light emitting element group rows GRa, GRb, GRc is: They are mutually shifted by a distance Dg in the longitudinal direction LGD.

  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. The distance Dg can be obtained as a distance in the longitudinal direction LGD between the geometric centroids of two light emitting element groups EG whose positions in the longitudinal direction LGD are adjacent to each other. The distance Dt can be obtained as the distance in the width direction LTD between the geometric centroids of the two light emitting element groups EG whose positions in the width direction LGD are adjacent to each other.

  Thus, the plurality of light emitting element groups EG are discretely arranged on the back surface 293-t of the head substrate 293. On the other hand, as shown in FIG. 6, a light shielding member 297 is disposed on the surface 293-h of the head substrate 293. The other side of the light shielding member 297 is fixed to the head substrate surface 293-h with an adhesive. The light shielding member 297 is formed with a light guide hole 2971 that penetrates in the thickness direction TKD, and the light guide hole 2971 has a circular shape in plan view from the thickness direction TKD. Further, the inner wall of each light guide hole 2971 is plated with black. In the light shielding member 297, 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. ing.

  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, as will be described later, dedicated lenses LS1 and LS2 are provided for each light emitting element group EG. In such a configuration, it is desirable that the light beam be incident only on the lenses LS1 and LS2 provided in the light emitting element group EG which is its own emission source. However, some of the light beams may become stray light without being directed to the lenses LS1 and LS2 provided in the light emitting element group EG that is the emission source. If such stray light enters the lenses 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, a light shielding member 297 is provided between the light emitting element group EG and the lenses LS1 and LS2, and the light guiding hole 2971 whose inner wall is plated with black is provided in the light shielding member 297. An opening is provided in the group EG. Therefore, most of the stray light is absorbed by the inner wall of the light guide hole 2971. In this way, ghost suppression is achieved.

  The first lens array LA1 is disposed on one side of the light shielding member 297 in the thickness direction TKD. The first lens array LA1 has a substantially flat plate shape elongated in the longitudinal direction LGD, and is sandwiched by the head frame 291 from the width direction LTD. Further, on the back surface of the first lens array LA1, one first lens LS1 (FIG. 4) is formed for each light emitting element group EG, that is, one sheet for one light emitting element group EG. The first lens LS1 (FIG. 4) faces each other. Thus, in the first lens array LA1, the plurality of first lenses LS1 are arranged in a three-row zigzag pattern. In other words, three first lenses LS1 (LSa1, LSb1, LSc1) whose positions in the main scanning direction MD are adjacent to each other. ) Are different from each other in the sub-scanning direction SD. Therefore, in FIG. 5 and FIG. 6, the first lens LS1 is shown separately according to the position in the sub-scanning direction SD. In other words, the first lens LS1 that is in the uppermost stream in the sub-scanning direction SD is labeled with a symbol LSa1, and the first lens LS1 that is in the center in the sub-scanning direction SD is labeled with a symbol LSb1. Reference sign LSc1 is assigned to the first lens LS1 located on the most downstream side in SD.

  Furthermore, on the one side in the thickness direction TKD of the first lens array LA1, the second lens array LA2 is opposed in a state of being separated from the first lens LA1. The second lens array LA2 has a substantially flat plate shape elongated in the longitudinal direction LGD, and is sandwiched by the head frame 291 from the width direction LTD. On the back surface of the second lens array LA2, one second lens LS2 (FIG. 4) is formed for each light emitting element group EG, that is, one sheet for one light emitting element group EG. The second lens LS2 (FIG. 4) faces each other. Thus, in the second lens array LA2, the plurality of second lenses LS2 are arranged in a three-row zigzag pattern. In other words, three second lenses LS2 (LSa2, LSb2, LSc2) whose positions in the main scanning direction MD are adjacent to each other. ) Are different from each other in the sub-scanning direction SD. Therefore, in FIG. 5 and FIG. 6, the second lens LS2 is shown separately according to the position in the sub-scanning direction SD. That is, the second lens LS2 that is in the uppermost stream in the sub-scanning direction SD is denoted by the symbol LSa2, the second lens LS2 that is in the center in the sub-scanning direction SD is denoted by the symbol LSb2, and the sub-scanning direction Reference sign LSc2 is assigned to the second lens LS2 which is the most downstream in SD. In this way, the two lenses LS1 and LS2 facing the same light emitting element group EG form an inverted image reduced in cooperation.

  As described above, in the line head 29, the light guide hole 2971, the first lens LS1, and the second lens LS2 are disposed so as to face each light emitting element group EG. Therefore, the light beam from the light emitting element group EG enters the first lens LS1 and the second lens LS2 after passing through the light guide hole 2971. In addition, since the first lens LS1 and the second lens LS2 cooperate to form one imaging optical system (LS1, LS2), when the light emitting element E of the light emitting element group EG emits light, the photosensitive drum Spots are formed on the peripheral surface of 21. Therefore, the line head 29 can form a latent image on the peripheral surface of the photosensitive drum 21 in the same manner as the exposure operation described in FIG. 11 of Japanese Patent Laid-Open No. 2008-036937. That is, a plurality of spots can be formed side by side in the main scanning direction MD by causing each light emitting element E to emit light at a timing corresponding to the movement of the circumferential surface of the photosensitive drum 21 in the sub scanning direction SD.

  By the way, in such an exposure operation, convergent lights LBa, LBb, and LBc that have received the optical action of the first lens LS1 and the second lens LS2 are incident on the circumferential surface of the photosensitive drum 21 at different positions in the sub-scanning direction SD. The line head 29 according to the first embodiment has a configuration described below in order to stabilize the position where the convergent lights LBa, LBb, and LBc are incident on the photosensitive drum 21.

  FIG. 7 is a diagram showing a positional relationship between the first lens array and the second lens array in the step AA line cross section. Hereinafter, if necessary, the first lens LSa1 positioned at the most upstream end of the first lens array LA1 in the sub-scanning direction SD is referred to as an “upstream first lens LSa1”, and the first lens array LA1 in the sub-scanning direction SD is referred to as “first upstream lens LSA1”. The first lens LSb1 positioned at the center is referred to as “center first lens LSb1”, and the first lens LSc1 positioned at the most downstream end of the first lens array LA1 in the sub-scanning direction SD is referred to as “downstream first lens LSc1”. I will call it. Further, the second lens LSa2 positioned at the most upstream end of the second lens array LA2 in the sub-scanning direction SD is referred to as “upstream second lens LSa2”, and is positioned in the center of the second lens array LA2 in the sub-scanning direction SD. The second lens LSb2 is referred to as a “center second lens LSb2”, and the second lens LSc2 located at the most downstream end of the second lens array LA2 in the sub-scanning direction SD is referred to as a “downstream second lens LSc2”. .

  As shown in the figure, the first lens array LA1 has a first light-transmitting substrate SB1 made of glass, and a first lens made of resin is placed on the back surface SB1-t of the first light-transmitting substrate SB1. LSa1, LSb1, and LSc1 are formed. Similarly, the second lens array LA2 has a second light-transmitting substrate SB2 made of glass, and the second lenses LSa2 and LSb2 made of resin are disposed on the back surface SB2-t of the second light-transmitting substrate SB2. , LSc2 is formed. In each of the lens arrays LA1 and LA2, these lenses are arranged at a predetermined inter-lens distance in the sub scanning direction SD. The inter-lens distance in the sub scanning direction SD is the distance of the center line of each lens in the sub scanning direction SD. Specifically, it is as follows.

  The inter-lens distance between the upstream first lens LSa1 and the central first lens LSb1 in the sub scanning direction SD is the sub scanning direction between the center line Ca1 of the upstream first lens LSa1 and the center line Cb1 of the central first lens LSb1. It is calculated | required as a distance to SD, and is the 1st distance Dls1.

  The inter-lens distance in the sub-scanning direction SD between the central first lens LSb1 and the downstream first lens LSc1 is the sub-scanning direction between the center line Cb1 of the central first lens LSb1 and the center line Cc1 of the downstream first lens LSc1. It is calculated | required as a distance to SD, and is the 1st distance Dls1.

  The inter-lens distance in the sub-scanning direction SD between the upstream second lens LSa2 and the central second lens LSb2 is the sub-scanning direction between the center line Ca2 of the upstream second lens LSa2 and the center line Cb2 of the central second lens LSb2. It is calculated | required as a distance to SD, and is 2nd distance Dls2.

  The inter-lens distance in the sub scanning direction SD between the center second lens LSb2 and the downstream second lens LSc2 is the sub scanning direction between the center line Cb2 of the center second lens LSb2 and the center line Cc2 of the downstream second lens LSc2. It is calculated | required as a distance to SD, and is 2nd distance Dls2.

  As shown in FIG. 7, the center line Cb1 of the center first lens LSb1 and the center line Cb2 of the center second lens LSb2 coincide with each other. Further, the central first lens LSb1 and the central second lens LSb2 are arranged so that these center lines Cb1, Cb2 (extension lines thereof) intersect with the rotation center Ccy (FIG. 8) of the photosensitive drum 21. The positional relationship between the upstream lenses LSa1, LSa2 and the downstream lenses LSc1, LSc2 is different from the positional relationship between the central lenses LSb1, LSb2. That is, the center line Ca2 of the upstream second lens LSa2 is decentered by a distance ΔDls downstream of the sub scanning direction SD with respect to the center line Ca1 of the upstream first lens LSa1. Further, the center line Ca2 of the downstream second lens LSb2 is decentered by the distance ΔDls upstream of the sub-scanning direction SD with respect to the center line Cc1 of the downstream first lens LSc1. Therefore, the inter-lens distance Dls2 in the second lens array LA2 is shorter than the inter-lens distance Dls1 in the first lens array LA1. With this configuration, the convergent light LBa by the upstream imaging optical system (LSa1, LSa2), the convergent light LBb by the central imaging optical system (LSb1, LSb2), and the downstream imaging optical system (LSc1) , LSc2), the convergent light LBc (the principal ray thereof) can be tilted with respect to each other.

  FIG. 8 is a diagram showing convergent light by the line head in the AA line step cross section. The three convergent lights LBa, LBb, and LBc shown in the figure are as follows. That is, the upstream convergent light LBa is converged by being emitted from the light emitting element E on the center line Ca1 of the upstream first lens LSa1 and receiving the optical action of the upstream first lens LSa1 and the upstream second lens LSa2. Light. The central convergent light LBb is convergent light emitted from the light emitting element E on the center line Cb2 of the central first lens LSb1 and subjected to the optical action of the central first lens LSb1 and the central second lens LSb2. Further, the convergent light LBc on the downstream side is emitted from the light emitting element E on the center line Cc1 of the first downstream lens LSc1 and converged by the optical action of the downstream first lens LSc1 and the downstream second lens LSc2. Light. Further, in the same figure, the principal rays PRa, PRb, and PRc are shown together with the convergent lights LBa, LBb, and LBc by a one-dot chain line.

  As shown in FIG. 8, the upstream imaging optical system (LSa1, LSa2), the central imaging optical system (LSb1, LSb2), and the downstream imaging optical system (LSc1, LSc2) are all optical beams that converge the light beam. Has a positive effect. Further, the upstream imaging optical system (LSa1, LSa2) and the downstream imaging optical system (LSc1, LSa2) also have an optical function of bending the principal ray of the light beam toward the rotation center Ccy of the photosensitive drum 21. That is, since the upstream second lens LSa2 is decentered by the distance ΔDls on the rotation center Ccy side (downstream in the sub-scanning direction SD) with respect to the upstream first lens LSa1, the upstream constituting the upstream imaging optical system. The first side lens LSa1 and the second upstream lens LSa2 converge the light beam while bending the principal ray of the light beam toward the rotation center Ccy of the photosensitive drum 21. Further, since the downstream second lens LSc2 is decentered by the distance ΔDls on the rotation center Ccy side (upstream side in the sub-scanning direction SD) with respect to the downstream side first lens LSc1, the downstream side constituting the downstream imaging optical system. The first side lens LSc1 and the second downstream lens LSc2 converge the light beam while bending the principal ray of the light beam toward the rotation center Ccy of the photosensitive drum 21.

  By such optical action of each imaging optical system, the principal ray PRa of the upstream convergent light LBa and the principal ray PRb of the central convergent light LBb are inclined with respect to each other by an angle θab, and the principal ray PRb of the central convergent light LBb The downstream convergent light LBc is inclined by an angle θbc with respect to the principal ray PRc. As a result, the principal ray PRa of the upstream convergent light LBa is inclined toward the rotation center Ccy of the photosensitive drum 21, and the principal ray PRc of the downstream convergent light LBc is inclined toward the rotation center Ccy of the photosensitive drum 21.

  In particular, in the first embodiment, all of the convergent lights LBa, LBb, and LBc face the rotation center Ccy of the photoreceptor drum 21 and are incident on the circumferential surface of the photoreceptor drum 21 (in other words, convergent light). All of LBa, LBb, and LBc are emitted to the rotation center Ccy of the photosensitive drum 21). Here, when the extension lines VLa, VLb, and VLc of the principal rays PRa, PRb, and PRc of the convergent lights LBa, LBb, and LBc intersect with the rotation center Ccy of the photosensitive drum 21, the convergent lights LBa, LBb, and LBc rotate. It is assumed that it faces the center Ccy (emits the rotation center Ccy).

  As described above, in the first embodiment, the circumferential surface (exposed surface) of the photosensitive drum 21 has a finite radius of curvature (or curvature) in the sub-scanning direction SD, and the line head 29 is in the sub-scanning direction. The convergent lights LBa, LBb, and LBc are incident on the circumferential surface of the photosensitive drum 21 at different positions on the SD. Therefore, if the convergent lights LBa, LBb, and LBc (the principal rays PRa, PRb, and PRc thereof) are parallel to each other or slightly tilted, all or part of the convergent lights LBa, LBb, and LBc. May enter the surface to be exposed at a large incident angle, and the incident position of the convergent light on the surface to be exposed may not be stable. This problem will be described in detail.

  FIG. 9 is an explanatory diagram of a problem that may occur when a plurality of convergent lights are incident on the exposed surface at different positions in the sub-scanning direction. In the figure, the chief rays PRa, PRb, and PRc of the convergent lights are parallel to each other. The lower part of the figure shows the case where there is no fluctuation in the distance between the circumferential surface of the photosensitive drum 21 and the line head 29, and the upper part of the figure shows the case where there is a fluctuation in the distance between the circumferential surface of the photosensitive drum 21 and the line head 29. Yes. That is, as described above, the interval between the circumferential surface of the photosensitive drum 21 and the line head 29 may vary with time, and the upper part of FIG.

  First, the case where there is no interval variation in the lower part of the figure will be described. In this case, the upstream convergent light LBa is incident on the circumferential surface of the photosensitive drum 21 at the position SIa (left column). Further, the downstream convergent light LBc is incident on the circumferential surface of the photosensitive drum 21 at the position SIc (right column). As described above, when there is no change in the distance between the photosensitive drum 21 and the line head 29, the convergent lights LBa and LBc can be incident on the circumferential surface of the photosensitive drum 21 at the positions SIa and SIc designed in advance. .

  On the other hand, as shown in the upper part of the figure, when the position of the circumferential surface of the photosensitive drum 21 changes from the solid curve to the two-dot chain curve and the distance between the photosensitive drum 21 and the line head 29 changes, the convergent light LBa, The incident position of LBc will fluctuate. That is, as shown in the left column, the upstream convergent light LBa (the principal ray PRa thereof) is inclined with respect to the normal line NL of the circumferential surface of the photosensitive drum 21. In other words, the circumference of the photosensitive drum 21 with a large incident angle. Incident on the surface. Therefore, the upstream convergent light LBa that should be incident on the circumferential surface of the photosensitive drum 21 at the position SIa is incident on the circumferential surface of the photosensitive drum 21 at the position Sra that is shifted from the position SIa by the distance d in the circumferential direction. . The same thing occurs for the downstream convergent light LBc. That is, as shown in the right column, the downstream-side convergent light LBc (the principal ray PRc thereof) is inclined with respect to the normal line NL of the circumferential surface of the photosensitive drum 21. Incident on the surface. Accordingly, the downstream-side convergent light LBc that should be incident on the circumferential surface of the photosensitive drum 21 at the position SIc is incident on the circumferential surface of the photosensitive drum 21 at the position Src that is shifted from the position SIc by the distance d in the circumferential direction. .

  For such a problem, in the first embodiment, the inter-lens distance Dls1 in the sub-scanning direction SD of the first lenses LSa1, LSb1, and LSc1 disposed in the first lens array LA1 and the second lens array LA2 are used. Is different from the inter-lens distance Dls2 in the sub-scanning direction SD of the second lenses LSa2, LSb2, and LSc2 disposed in the lens. As a result, the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc can be tilted sufficiently and appropriately. As a result, the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc respectively. The incident angle to the circumferential surface of the photosensitive drum 21 can be reduced. Accordingly, it is possible to stabilize the incident positions of the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc on the circumferential surface of the photosensitive drum 21 and realize good exposure. This effect will be described with a specific example as follows.

  FIG. 10 is a diagram for explaining the effect of the line head according to the first embodiment with a specific example. Also in FIG. 10, as in FIG. 9, the solid curve represents the circumferential surface of the photosensitive drum 21 with no variation in the distance to the line head 29, and the two-dot chain curve represents the photosensitive drum with a variation in the spacing with the line head 29. This represents the 21 circumferential surface. In the line head 29 shown in FIG. 10, unlike the line head shown in FIG. 9, the upstream-side convergent light LBa (its principal ray PRa) substantially coincides with the normal line NL, and is incident on the circumferential surface of the photosensitive drum 21 with a very small incident angle. (Left column). Accordingly, the original incident position SIa and the actual incident position Sra can be substantially matched in the circumferential direction of the photosensitive drum 21, and the incident position of the upstream convergent light LBa can be stabilized. Similarly, the downstream convergent light LBc (the principal ray PRc thereof) substantially coincides with the normal line NL, and is incident on the circumferential surface of the photosensitive drum 21 with a very small incident angle (right column). Accordingly, the original incident position SIc and the actual incident position Src can be made to substantially coincide with each other in the circumferential direction of the photosensitive drum 21, and the incident position of the downstream convergent light LBc can be stabilized. Thus, good exposure is achieved.

  In particular, as described above, the center of curvature of the peripheral surface of the photosensitive drum 21 is sensitive to the line head 29 (in other words, the upstream second lens LSa2, the central second lens LSb2, and the downstream second lens LSc2). Located on the opposite side of the peripheral surface of the body drum 21. Therefore, in the line head according to the first embodiment, the first lens LSa1, LSb1, LSc1 disposed in the first lens array LA1 is arranged in the second lens array LA2 more than the inter-lens distance Dls1 in the sub-scanning direction SD. The inter-lens distance Dls2 in the sub-scanning direction SD of the provided second lenses LSa2, LSb2, and LSc2 is set short. As a result, the incident angles of the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc on the circumferential surface of the photosensitive drum 21 are reduced, and the circumference of the photosensitive drum 21 around the convergent lights LBa, LBb, and LBc. It is possible to stabilize the incident position on the surface and realize good exposure.

  Further, as described above, when the exposure is performed by the line head 29 with the peripheral surface of the cylindrical photosensitive drum 21 having the rotation center Ccy in the main scanning direction MD and rotating at the rotation center Ccy as an exposed surface, It is preferable to apply the present invention to the line head 29. This is because, in such a case, the gap between the circumferential surface of the photosensitive drum 21 and the line head 29 is likely to occur due to the reasons described above. Therefore, by applying the present invention to the line head 29, the upstream side convergent light LBa. The incident angles of the central convergent light LBb and the downstream convergent light LBc on the circumferential surface of the photosensitive drum 21 are reduced, and the incident positions of the convergent lights LBa, LBb, and LBc on the circumferential surface of the photosensitive drum 21 are stabilized. This is because it is preferable to achieve good exposure.

  At this time, as in the first embodiment, the line head 29 may be configured so that the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc are directed to the rotation center Ccy of the photosensitive drum 21. good. Thereby, the incident angles of the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc to the peripheral surface of the photosensitive drum 21 can be surely reduced, and the photoreceptors of the convergent lights LBa, LBb, LBc. The incident position on the circumferential surface of the drum 21 can be further stabilized to achieve extremely good exposure.

  By the way, in order to direct the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc toward the rotation center Ccy of the photosensitive drum 21, the first distance Dls1 and the second distance Dls2 described above each have a predetermined accuracy. It is required to manufacture each lens LSa1, LSb1, LSc1, LSa2, LSb2, and LSc2 so as to satisfy the above. In contrast, in the first embodiment, the upstream first lens LSa1, the central first lens LSb1, and the downstream first lens LSc1 are all disposed on the back surface SB1-t of the first light-transmitting substrate SB1, The upstream second lens LSa2, the central second lens LSb2, and the downstream second lens LSc2 are all disposed on the back surface SB2-t (same surface) of the second light transmitting substrate SB2. In this way, the upstream first lens LSa1, the central first lens LSb1, and the downstream first lens LSc1 are arranged on the same plane SB1-t so that these distances Dls1 satisfy a predetermined accuracy. In addition, the upstream first lens LSa1, the central first lens LSb1, and the downstream first lens LSc1 can be easily manufactured. Further, the upstream second lens LSa2, the central second lens LSb2, and the downstream second lens LSc2 are arranged on the same plane SB2-t so that these distances Dls2 satisfy a predetermined accuracy. The upstream second lens LSa2, the central second lens LSb2, and the downstream second lens LSc2 can be easily manufactured.

  In this way, in order to direct the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc toward the rotation center Ccy of the photosensitive drum 21, the upstream first lens LSa1 and the upstream second lens LSa2 are used. It is further preferable that the alignment of the first central lens LSb1 and the central second lens LSb2 and the alignment of the downstream first lens LSc1 and the downstream second lens LSc2 can be easily performed. . In contrast, the line head 29 of the first embodiment includes a first light-transmitting substrate SB1 and a second light-transmitting substrate SB2, and further includes an upstream first lens LSa1, a central first lens LSb1, and The plane on which the downstream first lens LSc1 is disposed is the back surface SB1-t of the first light transmissive substrate SB1, and the upstream second lens LSa2, the central second lens LSb2, and the downstream second lens LSc2 are disposed. The formed plane is the back surface SB2-t of the second light-transmitting substrate SB2. Thereby, for example, when the line head 29 is assembled, the position of the first light-transmitting substrate SB1 and the position of the second light-transmitting substrate SB2 are respectively adjusted, so that the alignment of the respective lenses is easily executed. be able to.

Second Embodiment FIG. 11 is a diagram partially showing a line head according to a second embodiment in the AA line step cross section. Hereinafter, differences between the first embodiment and the second embodiment will be mainly described, and portions common to both embodiments will be denoted by common reference numerals and description thereof will be omitted as appropriate.

  The main differences between the first embodiment and the second embodiment are that the upstream first lens LSa1, the central first lens LSb1, the downstream first lens LSc1, the upstream second lens LSa2, the central second lens LSb2, and the downstream side. The second lens LSc2 is disposed on the front and back surfaces of one lens array LA. That is, the upstream first lens LSa1, the central first lens LSb1, and the downstream first lens LSc1 are disposed on the back surface LA-t of the lens array LA, while the upstream second lens LSa2, the central second lens LSb2, and the like. The downstream second lens LSc2 is disposed on the surface LA-h of the lens array LA.

  Similarly to the first embodiment, in the second embodiment, compared to the inter-lens distance Dls1 in the sub-scanning direction SD of the upstream first lens LSa1, the central first lens LSb1, and the downstream first lens LSc1, The inter-lens distance Dls2 in the sub-scanning direction SD of the upstream second lens LSa2, the central second lens LSb2, and the downstream second lens LSc2 is short. As described above, the line head 29 according to the second embodiment having the same configuration as that of the line head 29 according to the first embodiment can achieve the same effects as those of the line head 29 according to the first embodiment described above.

Third Embodiment FIG. 12 is a view partially showing a line head according to a third embodiment in a step cross section taken along line AA. Hereinafter, differences between the first embodiment and the third embodiment will be mainly described, and portions common to both embodiments will be denoted by common reference numerals, and description thereof will be omitted as appropriate.

  The main difference of the third embodiment from the first embodiment is that the third lens array LA3 is provided between the second lens array and the light emitting element E. The third lens array LA3 has the same configuration as the second lens array LA2, that is, on the back surface of the third lens array LA3, an upstream third lens LSa3, a central third lens LSb3, and a downstream third lens LSC3. Are arranged at different positions in the sub-scanning direction SD, and the distances of the upstream third lens LSa3, the central third lens LSb3, and the downstream third lens LSc3 in the sub-scanning direction SD are the first distance Dls1. Therefore, the upstream convergent light LBa is convergent light subjected to the optical action of the three lenses LSa3, LSa1, and LSa2, and the central convergent light LBb is subject to the optical action of the three lenses LSb3, LSb1, and LSb2. This is convergent light, and the downstream convergent light LBc is convergent light subjected to the optical action of the three lenses LSc3, LSc1, and LSc2.

  As in the first embodiment, in the third embodiment, compared to the inter-lens distance Dls1 in the sub-scanning direction SD of the upstream first lens LSa1, the central first lens LSb1, and the downstream first lens LSc1, The inter-lens distance Dls2 in the sub-scanning direction SD of the upstream second lens LSa2, the central second lens LSb2, and the downstream second lens LSc2 is short. As described above, the line head 29 according to the third embodiment having the same configuration as the line head 29 according to the first embodiment can achieve the same effects as the effects of the line head 29 according to the first embodiment described above.

Fourth Embodiment In the above-described embodiment, the convergent lights LBa, LBb, and LBc face the rotation center Ccy of the photosensitive drum 21. However, the convergent lights LBa, LBb, and LBc do not need to be accurately directed to the rotation center Ccy. For example, the convergent lights LBa, LBb, and LBc are directed to the vicinity of the rotation center Ccy (in other words, each convergent light is The line head 29 may be configured so that LBa, LBb, and LBc are emitted in the vicinity of the rotation center Ccy).

  FIG. 13 is a conceptual diagram for explaining light directed to the vicinity of the rotation center of the photosensitive drum. The distance Dy in the figure is the distance between the light emitting elements E corresponding to different optical systems in the sub-scanning direction SD (that is, the light emitting element E corresponding to the upstream imaging optical system (DAa, LSa1, LSa2) and the center. The distance in the sub-scanning direction SD between the light emitting element E corresponding to the optical system (DAb, LSb1, LSb2) or the light emitting element E corresponding to the central imaging optical system (DAb, LSb1, LSb2) and the downstream optical System (DAc, LSc1, LSc2) corresponding to the light emitting element E in the sub-scanning direction SD). In other words, the distance Dy corresponds to the distance Dt (FIG. 5) in the sub-scanning direction SD of the two light emitting element groups EG, and in particular, the light emitting element is located at the geometric center of gravity of the light emitting element group EG illustrated in FIG. In the configuration in which E exists, the distance Dt in the sub-scanning direction SD between the light emitting elements E at the geometric center of gravity of the two light emitting element groups EG can be obtained.

  A range where the distance from the rotation center Ccy of the photosensitive drum 21 is shorter than the distance Dy (less than the distance Dy) is in the vicinity of the rotation center Ccy of the photosensitive drum 21. Therefore, the light whose extension of the principal ray passes through the distance range shorter than the distance Dy from the rotation center Ccy is directed to the vicinity of the rotation center Ccy and is incident on the circumferential surface of the photosensitive drum 21 (in other words, the rotation center). The light is emitted in the vicinity of Ccy). Specifically, light whose chief ray extension lines are alternate long and short dash lines VL1_1 and VL_2 are incident on the circumferential surface of the photosensitive drum 21 facing the vicinity of the rotation center Ccy. On the other hand, light whose chief ray extension lines are alternate long and short dash lines VL1_3 and VL_4 does not face the vicinity of the rotation center Ccy.

  Then, by configuring the line head 29 so that the convergent light is directed to the vicinity of the rotation center Ccy of the photoconductive drum 21, the incident angle of the convergent light to the peripheral surface of the photoconductive drum 21 can be suppressed, and the convergent light. It is possible to stabilize the incident position on the circumferential surface of the photosensitive drum 21 and achieve good exposure.

Others As described above, in the above embodiment, the line head 29 corresponds to the “exposure head” of the present invention. In addition, when the upstream first lens LSa1 is the “first lens” of the present invention, the upstream second lens LSa2 corresponds to the “second lens” of the present invention, and the central first lens LSb1 is the present invention. And the center second lens LSb2 corresponds to the “fourth lens” of the present invention, and the light emitting element E that emits the light incident on the upstream first lens LSa1 of the present invention. The light emitting element E that corresponds to the “first light emitting element” and emits the light incident on the central first lens LSb1 corresponds to the “second light emitting element” of the present invention, and the convergent light LBa is the “first light emitting element” of the present invention. 1 "and the convergent light LBb corresponds to" second light "of the present invention. The sub-scanning direction SD corresponds to the “first direction” of the present invention, and the main scanning direction MD corresponds to the “second direction” of the present invention. In the first embodiment, the first light-transmitting substrate SB1 corresponds to the “first lens substrate” of the present invention, and the second light-transmitting substrate SB2 corresponds to the “second lens substrate” of the present invention. The first light transmissive substrate back surface SB-t corresponds to the “first plane” of the present invention, and the second light transmissive substrate back surface SB-t corresponds to the “second plane” of the present invention. The photosensitive drum 21 corresponds to the “image carrier” of the present invention. The center of rotation Ccy corresponds to the “rotary axis” 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, all of the convergent lights LBa, LBb, and LBc are directed to the rotation center Ccy of the photosensitive drum 21 or the vicinity thereof. However, such a configuration is not essential.

  In the above embodiment, the lenses are arranged in a three-row zigzag manner in each of the lens arrays LA1, LA2, and LA3. However, the lens arrangement is not limited to this. Therefore, for example, the lenses may be arranged in other arrangement modes such as a two-row zigzag.

  In the above embodiment, the lenses LS1, LS2, and LS3 are formed on the back surfaces of the lens arrays LA1, LA2, and LA3. However, for example, the lenses LS1, LS2, and LS3 may be formed on the surfaces of the lens arrays LA1, LA2, and LA3.

  In the above embodiment, the lens arrays LA1, LA2, and LA3 are formed by forming the resin lenses LSa1 and LSa2 on the glass transparent substrate SB. However, the lens arrays LA1, LA2, and LA3 can be integrally formed of one material.

  Moreover, in the said embodiment, although the several light emitting element group EG was arrange | positioned by 3 rows zigzag, the arrangement | positioning aspect of the some light emitting element group EG is not restricted to this.

  In the above embodiment, the light emitting element group EG is composed of 15 light emitting elements E. However, the number of light emitting elements E constituting the light emitting element group EG is not limited to this.

  Moreover, in the said embodiment, in the light emitting element group EG, although the some light emitting element E was arrange | positioned by 3 rows zigzag, the arrangement | positioning aspect of the some light emitting element E in the light emitting element group EG is restricted to this. Absent.

  Various changes can be made to the light shielding member 297 as well. That is, for example, as described in Japanese Patent Application Publication No. 2008-307885, a light shielding plate is formed by a thin flat plate having one hole for each light emitting element group EG, and the light shielding plate is spaced apart in the thickness direction TKD. The light shielding members 297 arranged side by side can also be used.

  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 the above embodiment, the photosensitive drum 21 is rotatably supported by the shaft rod RS21. However, the rotation support mechanism of the photosensitive drum 21 is not limited to this, and may be a mechanism using a flange as disclosed in JP 2001-305911 A, for example.

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

  FIG. 14 is a diagram partially showing the line head according to the embodiment in the cross section taken along line AA. The line head according to the example has substantially the same configuration as the line head according to the first embodiment, but the diaphragm plate 295 is provided between the light emitting element E and the first lens array LA1. Different from line head. The aperture plate 295 is provided with aperture stops DA, DA, DA facing the lenses LSa1, LSb1, LSc1 of the first lens array LA1. These aperture stops DA, DA, DA are arranged at a first distance Dls1 in the sub-scanning direction SD. Note that the distance between the aperture stops DA in the sub-scanning direction SD is the distance of the center line of each aperture stop DA in the sub-scanning direction SD.

  These aperture stops DA, DA, DA limit the amount of light incident on the opposing lenses LSa1, LSb1, LSc1. As described above, the line head 29 according to the embodiment can appropriately adjust the amount of light incident on each of the lenses LSa1, LSb1, and LSc1 by the aperture stop DA, which is advantageous in performing good exposure.

  In the following, each of the imaging optics was calculated with the curvature radius of the image plane set to 20 [mm] (R21 = 20 [mm]) and other optical system specifications as values shown in FIGS. The ray diagram and lens data of the system are shown.

  FIG. 15 is a table summarizing the optical system specifications of the upstream imaging optical system (LSa1, LSa2) as a table. FIG. 16 is a table summarizing the optical system specifications of the central imaging optical system (LSb1, LSb2) as a table. FIG. 17 is a table summarizing the optical system specifications of the downstream imaging optical system (LSc1, LSc2) as a table. 14 and 15 to 17, positions in the sub-scanning direction with the center of the central imaging optical system (in other words, the lens center line Cb1, Cc2 or the optical axis of the central imaging optical system) as the origin. The negative direction is taken to the right in FIG. 14, and the positive direction is taken to the left in FIG. As in the embodiment, the center line Cb1 of the center first lens LSb1 and the center line Cb2 of the center second lens LSb2 coincide with each other.

  First, the optical system specifications of the upstream imaging optical system (LSa1, LSa2) will be described using the table of FIG. The center position of the upstream first lens LSa1 in the sub-scanning direction SD is 1.71 [mm] (the item “lens position in the sub-scanning direction”), and the subordinate of the upstream second lens LSa2 with respect to the upstream first lens LSa1. The amount of eccentricity ΔDls in the scanning direction SD is −0.1724 [mm] (item “second lens eccentricity”). The lens diameter of each lens LSa1, LSa2 is 1.66 [mm] (item “lens diameter”), and the diameter of the aperture stop DA is 0.8 [mm] (item “diaphragm diameter”). Further, the inclination θab of the principal ray PRa of the convergent light by the upstream imaging optical systems LSa1 and LSa2 is −4.5 ° (item “θab”), and the principal ray PRa faces the rotation center CT21 (that is, The extension line VLa of the principal ray PRa intersects the rotation center CT21). The imaging position in the sub-scanning direction SD of the upstream imaging optical system (LSa1, LSa2) is 1.57 [mm] (item “imaging position in the sub-scanning direction”). The light emitting element E is on the center line Ca1 of the upstream first lens LSa1 (item “object height (sub-scanning direction)”), and emits light having a wavelength of 690 [nm] (item “wavelength”). ).

  Next, the optical system specifications of the central imaging optical system (LSb1, LSb2) will be described using the table of FIG. The central position of the central first lens LSb1 in the sub-scanning direction SD is 0 [mm] (item “lens position in the sub-scanning direction”), and the central second lens LSb2 with respect to the central first lens LSb1 in the sub-scanning direction SD. The amount of decentering is 0 [mm] (item “second lens decentering amount”). The lens diameter of each lens LSb1 and LSb2 is 1.66 [mm] (item “lens diameter”), and the diameter of the aperture stop DA is 0.8 [mm] (item “diaphragm diameter”). Further, the principal ray PRb of the convergent light from the central imaging optical systems LSb1 and LSb2 faces the rotation center CT21 (that is, the extension line VLb of the principal ray PRb intersects the rotation center CT21). The imaging position in the sub-scanning direction SD of the central imaging optical system (LSb1, LSb2) is 0 [mm] (item “imaging position in the sub-scanning direction”). The light emitting element E is on the center line Cb1 of the central first lens LSb1 (item “object height (sub-scanning direction)”), and emits light having a wavelength of 690 [nm] (item “wavelength”). .

  Finally, the optical system specifications of the downstream imaging optical system (LSc1, LSc2) will be described using the table of FIG. The center position of the downstream first lens LSc1 in the sub-scanning direction SD is −1.71 [mm] (the item “lens position in the sub-scanning direction”), and the downstream second lens LSc2 with respect to the downstream first lens LSc1. The amount of eccentricity ΔDls in the sub-scanning direction SD is 0.1724 [mm] (item “second lens eccentricity”). The lens diameter of each lens LSc1, LSc2 is 1.66 [mm] (item “lens diameter”), and the diameter of the aperture stop DA is 0.8 [mm] (item “diaphragm diameter”). Further, the inclination θbc of the principal ray PRc of the convergent light by the downstream imaging optical systems LSc1 and LSc2 is 4.5 ° (item “θbc”), and the principal ray PRc faces the rotation center CT21 (ie, the principal ray). The extension line VLc of the ray PRc intersects the rotation center CT21). The imaging position in the sub-scanning direction SD of the downstream imaging optical system (LSc1, LSc2) is −1.57 [mm] (item “imaging position in the sub-scanning direction”). The light emitting element E is on the center line Cc1 of the downstream first lens LSc1 (item “object height (sub-scanning direction)”) and emits light having a wavelength of 690 [nm] (item “wavelength”). ).

  When the ray diagram and lens data of each imaging optical system were obtained so as to satisfy the above specifications of the optical system, it was as follows. FIG. 18 is a ray diagram of the upstream imaging optical system (LSa1, LSa2) in the cross section in the sub-scanning direction. FIG. 19 is a ray diagram of the central imaging optical system (LSb1, LSb2) in the sub-scanning direction cross section. FIG. 20 is a ray diagram of the downstream imaging optical system (LSc1, LSc2) in the sub-scanning direction cross section. FIG. 21 is a ray diagram in the cross section in the main scanning direction. The ray diagram in the cross section in the main scanning direction is common to the upstream imaging optical system (LSa1, LSa2), the central imaging optical system (LSb1, LSb2), and the downstream imaging optical system (LSc1, LSc2). FIG. 22 is a table showing lens data of the upstream imaging optical system (LSa1, LSa2) and the downstream imaging optical system (LSc1, LSc2) as a table. FIG. 23 is a table showing the S4 surface data of the lens data of FIG. FIG. 24 is a table showing the data on the S7 surface of the lens data of FIG. FIG. 25 is a table showing lens data of the central imaging optical system (LSb1, LSb2). FIG. 26 is a table showing the S4 surface data of the lens data of FIG. 24 as a table. FIG. 27 is a table showing the S7 surface data of the lens data of FIG. 24 as a table. FIG. 28 is a diagram illustrating a definition formula of an XY polynomial surface.

  Thus, also in the present embodiment, the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc can be sufficiently and appropriately tilted (that is, the upstream convergent light LBa and the central convergent light LBb are , Θab = −4.5 °, and the central convergent light LBb and the downstream convergent light LBc are inclined θbc = 4.5 °). As a result, the incident angles of the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc on the circumferential surface of the photosensitive drum 21 can be reduced. Accordingly, it is possible to stabilize the incident positions of the upstream convergent light LBa, the central convergent light LBb, and the downstream convergent light LBc on the circumferential surface of the photosensitive drum 21 and realize good exposure.

DESCRIPTION OF SYMBOLS 21 ... Photosensitive drum, 29 ... Line head, 291 ... Head frame, 293 ... Head substrate, 295 ... Diaphragm flat plate, DA ... Aperture stop, 297 ... Light-shielding member, 2971 ... Light guide hole, CT21 ... Center of rotation, D21 ... Rotation Direction, E ... Light emitting element, EG ... Light emitting element group, LA1 ... First lens array LA1, LA2 ... Second lens array, LA ... Lens array, LS1 ... First lens, LS2 ... Second lens, LSa1 ... Upstream first 1 lens, LSb1... Center first lens LSb1, LSc1... Downstream first lens, LSa2... Upstream second lens, LSb2... Center second lens, LSc2 .. downstream second lens, LBa .. upstream convergent light, LBb ... center convergent light, LBc ... downstream convergent light, Dls1 ... first distance, Dls2 ... second distance, LGD ... longitudinal direction LGD, LTD ... width direction, MD ... main scanning direction, SD ... Scanning direction, NL ... normal, RS21 ... drum axle, SB1 ... first light transmissive substrate, SB2 ... second light transmitting substrate

Claims (8)

A first light emitting element;
A first lens into which light from the first light emitting element is incident;
A second lens on which light emitted from the first lens is incident;
A second light emitting element;
A third lens into which light from the second light emitting element is incident;
A fourth lens on which light emitted from the third lens is incident;
With
The first light emitted from the first light emitting element and transmitted through the first lens and the second lens, and the third light and the fourth lens emitted from the second light emitting element. The transmitted second light is incident at different positions in the first direction of the exposed surface having a radius of curvature,
The distance Dls1 in the first direction between the first lens and the third lens and the distance Dls2 in the first direction between the second lens and the fourth lens are An exposure head characterized by being different.   2. The exposure head according to claim 1, wherein a center of curvature of the exposed surface is opposite to the exposed surface with respect to the second lens and the fourth lens, and the distance Dls2 is shorter than the distance Dls1. .   3. The exposure head according to claim 2, wherein a peripheral surface of a cylindrical drum having a rotation axis in a second direction orthogonal to the first direction and rotating around the rotation axis is the exposed surface.   The exposure head according to claim 3, wherein the first light is emitted toward the rotation axis, and the second light is emitted toward the rotation axis. The first lens and the third lens are disposed on the same surface of the first lens substrate;
The exposure head according to claim 4, wherein the first lens and the third lens are disposed on the same surface of the second lens substrate.   A first aperture stop disposed between the first light emitting element and the first lens; and a second aperture stop disposed between the second light emitting element and the third lens. An exposure head according to any one of claims 1 to 5, further comprising: A first lens that receives light from the first light-emitting element, a second lens that receives light emitted from the first lens, a second light-emitting element, An exposure head having a third lens on which light from the second light emitting element is incident, and a fourth lens on which light emitted from the third lens is incident;
An image carrier that receives the light emitted from the second lens and the light emitted from the fourth lens and has a radius of curvature in a first direction;
With
The first light emitted from the first light emitting element and transmitted through the first lens and the second lens, and the third light and the fourth lens emitted from the second light emitting element. The transmitted second light is incident on the image carrier at a different position in the first direction,
A distance Dls1 in the first direction between the first lens and the third lens, and a distance Dls2 in the first direction between the second lens and the fourth lens. An image forming apparatus characterized by being different from the above. The image carrier is an image carrier drum having a rotation axis,
The image forming apparatus according to claim 7, wherein the exposure head is disposed on an outer peripheral side of the image carrier drum, and the distance Dls2 is shorter than the distance Dls1.

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