JP2012166448A - Exposure apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure apparatus that reduces variations in light quantity on an exposed surface and an image forming apparatus with the exposure apparatus to form a high-quality image.SOLUTION: The exposure apparatus includes: a lens array which includes a plurality of rod lenses arranged along a first direction and having incident end faces located within a first plane, and which forms an erect equal-magnification image on an exposed surface by collecting light beams entering through the incident end faces; and a light emitting element array which consists of a plurality of light emitting elements, which are larger in number than the rod lenses, arranged in a second plane opposite to the first plane along the first direction, the light emitting elements being displaced, from a center line extending in the first direction, in a second direction intersecting the first direction so that the light quantity of the erect equal-magnification image corresponding to the light emitting elements is greater than that in the case where the plurality of light emitting elements are arranged on the center line extending in the first direction.

Description

  The present invention relates to an exposure apparatus and an image forming apparatus.

  Patent Document 1 discloses an optical recording head having a light emitting element array in which a plurality of light emitting element blocks in which a predetermined number of light emitting elements are arranged in a row in the main scanning direction are arranged in a row in the main scanning direction, and the optical recording head. And a photosensitive member that is sensitive to light emitted from the light emitting element, the light emitting element having a slow light emission timing in the light emitting element block is selected according to the light emission timing. The image forming apparatus is characterized in that the image forming apparatus is arranged so as to be shifted downstream in the sub-scanning movement direction.

Japanese Patent Laid-Open No. 2007-062019

  An object of the present invention is to provide an exposure apparatus that can reduce the variation in the amount of light on the surface to be exposed, and an image forming apparatus that can form a high-quality image by including the exposure apparatus. is there.

  In order to achieve the above object, the invention described in each claim has the following configuration.

  The invention according to claim 1 is a lens array in which a plurality of rod-shaped lenses are arranged along a first direction, wherein each incident end surface of the plurality of rod-shaped lenses is located in a first plane, A lens array for condensing each light incident from each incident end surface to form an erecting equal-magnification image on the exposed surface, and the plurality of rod-shaped lenses in a second surface facing the first surface A light emitting element array in which a larger number of light emitting elements are arranged along the first direction, wherein each of the plurality of light emitting elements is disposed on a center line extending in the first direction. A light emitting element array arranged so as to be shifted from the center line in a second direction intersecting the first direction so that the light amount of an erecting equal-magnification image corresponding to the light emitting element is larger than the case; Is an exposure apparatus.

  According to a second aspect of the present invention, in the lens array, the plurality of rod-shaped lenses are periodically arranged, and the light-emitting element array includes the plurality of light-emitting elements according to an arrangement period of the plurality of rod-shaped lenses. 2. The exposure apparatus according to claim 1, wherein each of the plurality of light emitting elements is arranged to be shifted from the center line in the second direction so that the amount of shift in the second direction periodically varies. It is.

  According to a third aspect of the present invention, the exposure apparatus according to the first or second aspect is disposed apart from the exposure apparatus by an operating distance, and the first direction with respect to the exposure apparatus is provided. An image forming apparatus including a photosensitive member that is relatively moved in a second direction that intersects, is scanned and exposed in accordance with image data by the exposure device, and is written with an image.

  According to the invention described in each claim of the present invention, the following effects are obtained.

  According to the first aspect of the present invention, there is an effect that the variation in the amount of light on the exposed surface can be reduced as compared with the case where the present invention is not used.

  According to the second aspect of the invention, there is an effect that it is possible to effectively reduce the variation in the amount of light on the exposed surface.

  According to the third aspect of the present invention, there is an effect that a high-quality image can be formed as compared with the case where the present invention is not used.

1 is a schematic diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. It is a schematic perspective view which shows an example of a structure of the LED print head which concerns on embodiment of this invention. It is a schematic perspective view which shows an example of a structure of a rod lens array. It is a schematic diagram which shows a mode that an erecting equal-magnification image is formed. It is a top view which shows the arrangement | positioning relationship between the light emitting element and rod lens before correction | amendment. It is a graph which shows the light quantity distribution of the main scanning direction in an imaging surface. It is a top view which shows the position of the main scanning direction of the light emitting element used as a measuring object. It is a graph which shows the light quantity distribution of the subscanning direction in an imaging surface. It is a top view which shows the arrangement | positioning relationship between the light emitting element after correction | amendment, and a rod lens. It is a graph which shows the light quantity distribution of the main scanning direction in an imaging surface.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

<Image forming apparatus>
FIG. 1 is a schematic diagram showing an example of the configuration of an image forming apparatus according to an embodiment of the present invention. This device is an image forming device that forms an image by an electrophotographic method, and is equipped with an LED type exposure device (LED print head, abbreviated as “LPH”) using a light emitting element such as a light emitting diode (LED) as a light source. ing. LED printheads have the advantage that no mechanical drive is required.

  The image forming apparatus is a so-called tandem digital color printer. The image forming process unit 10 as an image forming unit that forms an image corresponding to image data of each color, and a control for controlling the operation of the image forming apparatus. And an image processing unit 40 that is connected to the image reading device 3 and an external device such as a personal computer (PC) 2 and performs predetermined image processing on image data received from these devices. ing.

  The image forming process unit 10 includes four image forming units 11Y, 11M, 11C, and 11K that are arranged in parallel at regular intervals. Each of the image forming units 11Y, 11M, 11C, and 11K forms yellow (Y), magenta (M), cyan (C), and black (K) toner images. The image forming units 11Y, 11M, 11C, and 11K are collectively referred to as “image forming unit 11” as appropriate.

  Each of the image forming units 11 includes a photosensitive drum 12 as an image holding body that forms an electrostatic latent image and holds a toner image, and a charger 13 that uniformly charges the surface of the photosensitive drum 12 with a predetermined potential. , An LED print head (LPH) 14 as an exposure device for exposing the photosensitive drum 12 charged by the charger 13, a developing unit 15 for developing the electrostatic latent image obtained by the LPH 14, and the photosensitive drum 12 after transfer. A cleaner 16 for cleaning the surface is provided.

  The LPH 14 is a long print head having substantially the same length as the length of the photosensitive drum 12 in the axial direction. In the LPH 14, a plurality of light emitting elements are arranged in an array (row shape) along the length direction. The LPH 14 is disposed around the photosensitive drum 12 so that the length direction thereof faces the axial direction of the photosensitive drum 12. As will be described later, the LPH 14 includes the light emitting element array and a rod lens array in which a plurality of rod lenses are arranged in an array. Each light emitted from the plurality of light emitting elements is condensed by the rod lens and imaged on the photosensitive drum.

  The image forming process unit 10 also intermediate-transfers each color toner image of each image forming unit 11 and the intermediate transfer belt 21 onto which the toner images of each color formed on the photosensitive drum 12 of each image forming unit 11 are transferred in a multiple manner. A primary transfer roll 22 that sequentially transfers (primary transfer) to the belt 21; a secondary transfer roll 23 that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 21 to a sheet P that is a recording medium; and A fixing device 25 for fixing the secondary transferred image on the paper P is provided.

Next, the operation of the image forming apparatus will be described.
First, the image forming process unit 10 performs an image forming operation based on a control signal such as a synchronization signal supplied from the control unit 30. At that time, the image data input from the image reading device 3 or the PC 2 is subjected to image processing by the image processing unit 40 and supplied to each image forming unit 11 via the interface.

  For example, in the yellow image forming unit 11Y, the surface of the photosensitive drum 12 uniformly charged at a predetermined potential by the charger 13 is emitted by the LPH 14 that emits light based on the image data obtained from the image processing unit 40. As a result of exposure, an electrostatic latent image is formed on the photosensitive drum 12. That is, each light emitting element of the LPH 14 emits light based on the image data, so that the surface of the photoconductive drum 12 is main-scanned, and the photoconductive drum 12 is rotated to perform sub-scanning. An electrostatic latent image is formed. The formed electrostatic latent image is developed by the developing device 15, and a yellow toner image is formed on the photosensitive drum 12. Similarly, magenta, cyan, and black toner images are formed in the image forming units 11M, 11C, and 11K.

  Each color toner image formed by each image forming unit 11 is sequentially electrostatically attracted and transferred by the primary transfer roll 22 onto the intermediate transfer belt 21 that rotates in the direction of arrow A in FIG. 1 (primary transfer). A superimposed toner image is formed on the intermediate transfer belt 21. The superimposed toner image is conveyed to a region (secondary transfer portion) where the secondary transfer roll 23 is disposed as the intermediate transfer belt 21 moves. When the superimposed toner image is conveyed to the secondary transfer unit, the paper P is supplied to the secondary transfer unit in accordance with the timing at which the toner image is conveyed to the secondary transfer unit.

  The superimposed toner images are collectively electrostatically transferred onto the conveyed paper P (secondary transfer) by the transfer electric field formed by the secondary transfer roll 23 in the secondary transfer portion. The sheet P on which the superimposed toner image has been electrostatically transferred is peeled off from the intermediate transfer belt 21 and conveyed to the fixing device 25 by the conveyance belt 24. The unfixed toner image on the paper P conveyed to the fixing device 25 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 25. The paper P on which the fixed image is formed is discharged to a paper discharge tray (not shown) provided in the discharge unit of the image forming apparatus.

<LED print head (LPH)>
FIG. 2 is a schematic perspective view showing an example of the configuration of an LED print head as an exposure apparatus according to the present embodiment. As shown in FIG. 2, the LED print head (LPH 14) includes a light emitting element array 50 in which a plurality of light emitting elements 52 are arranged, and a rod lens array 60 in which a plurality of rod lenses 62 are arranged. The number of rod lenses 62 constituting the rod lens array 60 is smaller than the number of light emitting elements 52 constituting the light emitting element array 50. For example, eight rod lenses 62 are arranged for about 20 light emitting elements 52 arranged with the same length as the diameter of one rod lens 62.

  The plurality of light emitting elements 52 are mounted on a long substrate 54 together with a drive circuit (not shown) for driving each of the light emitting elements 52. The rod lens array 60 is supported by a support member (not shown) and is disposed on the light emitting side of the light emitting element array 50. Each of the light emitting elements 52 is disposed on the main surface 54A of the substrate 54 with the light emitting surface facing the rod lens array 60 side. In addition, each of the light emitting elements 52 is arranged such that the interval between the two light emitting elements 52 adjacent to each other in the main scanning direction is a constant interval. That is, the arrangement direction of the light emitting elements 52, that is, the length direction of the LPH 14 is the “main scanning direction”. Further, since the sub-scanning is performed by the rotation of the photosensitive drum 12, the direction orthogonal to the “main scanning direction” is the “sub-scanning direction”.

In the example shown in FIG. 2, the plurality of light emitting elements 52 are arranged along the main scanning direction. The nth light emitting element 52 is referred to as “light emitting element 52 _n ”. In addition, when it is not necessary to distinguish each, these are named "the light emitting element 52" generically. In FIG. 2, an example in which a plurality of light emitting elements 52 are arranged in a row is illustrated. However, as described later, in the present embodiment, each of the plurality of light emitting elements 52 has an amount of light on the imaging surface. In order to increase, they are shifted from the center line in the sub-scanning direction (see FIGS. 9 and 10).

  Note that FIG. 2 only schematically illustrates a part of the LPH 14 in which a plurality of light emitting elements 52 are arranged. In an actual image forming apparatus, thousands of light emitting elements 52 are arranged in accordance with the resolution in the main scanning direction.

In the rod lens array 60, a plurality of rod lenses 62 are arranged in m rows. The n-th rod lens 62 in the m row is denoted as “rod lens 62 _mn ”. In addition, when it is not necessary to distinguish each, these are named generically as the “rod lens 62”. In FIG. 2, an example in which a plurality of rod lenses 62 are arranged in a staggered manner in two rows is illustrated, but the present invention is not limited to this. The plurality of rod lenses 62 may be arranged in one row, or may be arranged in three or more rows.

  FIG. 3 is a schematic perspective view showing an example of the configuration of the rod lens array. As shown in FIG. 3, the rod lens array 60 further includes a holding member, and a plurality of rod lenses 62 are held by the holding member. The holding member includes a first flat plate member 64A, a second flat plate member 64B, and a separation member 66. The first flat plate member 64 </ b> A and the second flat plate member 64 </ b> B are disposed so as to face each other, and are separated by a predetermined distance by a separation member 66. The plurality of rod lenses 62 are sandwiched between these parallel flat plates. A gap between the plurality of rod lenses 62 and the holding member is filled with a light absorbing material 68 such as black resin.

  The rod lens 62 is a rod-shaped lens that forms an erecting equal-magnification image. As the rod lens 62, a gradient index rod lens such as SELFOC (registered trademark) may be used. The refractive index distribution type rod lens has a cylindrical shape, and has a refractive index distribution symmetrical to the optical axis in a direction orthogonal to the optical axis. The refractive index at the optical axis is the highest, and the refractive index decreases as the distance from the optical axis increases. The light incident on the rod lens is bent in a direction having a high refractive index and propagates while meandering. For example, in SELFOC (registered trademark), incident light travels along a sinusoidal optical path. Therefore, when the length of the rod lens is determined according to the refractive index distribution, a rod-shaped lens that forms an erecting equal-magnification image is obtained.

  Each of the plurality of rod lenses 62 has the same length. Since the plurality of rod lenses 62 are held by the holding member, the incident end faces of the rod lens 62 are arranged in the same plane, and the emission end faces of the rod lens 62 are arranged in the same plane. That is, the rod lens array 60 has a light incident surface 60A and a light emitting surface 60B. An incident end face of the rod lens 62 is arranged on the light incident face 60A, and an outgoing end face of the rod lens 62 is arranged on the light outgoing face 60B.

  The rod lens array 60 is disposed on the substrate 54 on which the light emitting elements 52 are arranged so that the light incident surface 60A faces the main surface 54A of the substrate 54. The light incident surface 60A of the rod lens array 60 is separated from the main surface 54A by a predetermined distance so that the main surface 54A is positioned on the “object plane” of each rod lens 62 (see FIGS. 2 and 4). ). Further, the photosensitive drum 12 is separated from the light emitting surface 60B of the rod lens array 60 by a predetermined distance so that the surface 12A of the photosensitive drum 12 is positioned on the “imaging plane” of each rod lens 62. Are arranged (see FIG. 4).

  Although not shown, the LPH 14 is supported by a support member such as a housing or a holder, and is attached to a predetermined position in the image forming unit 11 shown in FIG. Moreover, LPH14 may be comprised so that it may move by adjustment means, such as an adjustment screw (not shown). The mounting position is adjusted by the adjusting means so that the image forming position by the rod lens 62 is positioned on the surface of the photosensitive drum 12.

<Operation of LED print head>
FIG. 4 is a schematic diagram showing how an erecting equal-magnification image is formed by the LPH 14. As shown in FIG. 4, when each of the light emitting elements 52 of the light emitting element array 50 is caused to emit light, the light emitted from the light emitting elements 52 is irradiated onto the light incident surface 60 </ b> A of the rod lens array 60. Each rod lens 62 propagates light incident from the incident end surface exposed to the light incident surface 60A to the output end surface. Each rod lens 62 emits the propagated light from the exit end face exposed at the light exit surface 60B. The light emitted from the light emitting surface 60B of the rod lens array 60 converges in the direction of the photosensitive drum 12, and forms an erecting equal-magnification image on the surface 12A of the photosensitive drum 12.

  As shown in FIG. 4, a plurality of condensing points 70 corresponding to each of the plurality of light emitting elements 52 are formed on the surface 12 </ b> A of the photosensitive drum 12. The plurality of condensing points 70 formed on the “imaging plane” are erecting equal-magnification images of the optical image formed on the “object plane” by the plurality of light emitting elements 52. Therefore, the condensing point 70 has the same shape as the light emitting region of the light emitting element 52. The plurality of condensing points 70 are arranged in the main scanning direction at the same interval as the plurality of light emitting elements 52.

  For example, in an image forming apparatus capable of printing up to A3 width, in order to obtain a resolution of 1200 spots per inch, 14848 light emitting elements 52 are arranged on the substrate 54 at intervals of 21 μm. Accordingly, 14848 condensing points 70 are formed on the surface 12A of the photosensitive drum 12 so as to be arranged in the main scanning direction at intervals of 21 μm.

<Correction of position where light emitting element is arranged>
Next, a method for correcting the position where the light emitting element 52 is arranged will be described. FIG. 5 is a plan view showing an arrangement relationship between the light emitting element and the rod lens before position correction. FIG. 5 is a diagram in which the plan view of the light incident surface 60 </ b> A of the rod lens array 60 is superimposed on the plan view of the main surface 54 </ b> A of the substrate 54. Within the light incident surface 60A, the incident end surfaces of the plurality of rod lenses 62 are arranged along the main scanning direction and are arranged in two rows in the sub-scanning direction. Each of the plurality of incident end faces has a circular shape and is arranged in a triangular lattice shape.

  A straight line passing through the center of the rod lens array 60 in the sub scanning direction and extending in the main scanning direction is the center line of the rod lens array 60. Further, the projection projected onto the main surface 54 </ b> A of the substrate 54 corresponding to the center line of the rod lens array 60 is the “center line” of the light emitting element array 50. As described above, the “center line” of the light emitting element array 50 is determined according to the center line of the rod lens array 60. In FIG. 5, the two “center lines” overlap each other. Hereinafter, the center line of the light emitting element array 50 is referred to as a “center line” that serves as a reference when the light emitting elements 52 are arranged.

In FIG. 5, two-dimensional coordinates (XY coordinates) are set with one rod lens 62C as a reference. One rod lens 62C is positioned at the center in the main scanning direction of the eight rod lenses 62 arranged in groups of four in two rows. The X axis is on the “center line”, and the Y axis is on the “tangent” at one end of the rod lens 62C in the main scanning direction. The origin of the XY coordinates is the intersection of these “center line” and “tangent”. A plurality of light emitting elements 52 are arranged along the “center line”. In the example shown in FIG. 5, 15 light emitting elements 52 _{1 to} 52 ₁₅ are arranged in a length of the diameter Φ = 0.45 mm of the rod lens 62C. Among the light emitting element 52 ₁ of the left end, is placed on the origin of the XY coordinates.

  Therefore, the “X coordinate” represents the position of the light emitting element 52 in the X axis direction (main scanning direction), and the “Y coordinate” represents the position of the light emitting element 52 in the Y axis direction (sub scanning direction). Here, the “position in the main scanning direction” means a distance from the origin in the main scanning direction. The “position in the sub-scanning direction” means a distance from the center line in the sub-scanning direction, that is, a shift amount in the sub-scanning direction. As shown in FIG. 5, before the position correction is performed, the plurality of light emitting elements 52 are arranged on the “center line” of the light emitting element array 50 at regular intervals. That is, before the position correction is performed, the amount of deviation in the sub-scanning direction is set to zero for each of the plurality of light emitting elements 52.

  FIG. 6 is a graph showing the light quantity distribution in the main scanning direction on the imaging plane. The horizontal axis represents the X coordinate, that is, the distance (unit: mm) from the origin in the X-axis direction. A condensing point is formed at the position of the X coordinate of the “imaging plane” corresponding to the light emitting element 52 arranged at the X coordinate of the “object plane”. The vertical axis represents the amount of light on the “imaging plane”. The amount of light is represented by the relative intensity when the maximum amount of light is 1. The graph shown in FIG. 6 shows the result of measuring the light quantity distribution on the imaging plane by causing each of the plurality of light emitting elements 52 to emit light in the arrangement relationship before the position correction shown in FIG.

The condensing point sequence formed on the “imaging plane” is an erecting equal-magnification image of the light image by the light emitting element array 50. In the example shown in FIG. 5, 15 light emitting elements 52 _{1 to} 52 ₁₅ are arranged immediately below one rod lens 62C located in the center. Eight rod lenses 62 are arranged for the ₁₅ light emitting elements 52 _{1 to} 52 ₁₅ . By the eight rod lenses 62, the light emitted from the _fifteen light emitting elements 52 _{1 to} 52 15 arranged immediately below the rod lens 62C is imaged.

When caused to emit light 15 light-emitting elements ₅₂ 1 _{to 52 15} which are arranged in X = 0mm~0.45mm the "object plane", a range of X = 0mm~0.45mm the "imaging plane" is scanned and exposed The The amount of light on the “imaging plane” changes so as to draw two peaks along the X-axis direction, the maximum distance is 0.11 mm and 0.34 mm in the X-axis direction, and the distance in the X-axis direction is 0 mm. The minimum value is “0.95” at 0.23 mm and 0.45 mm. That is, the light amount variation of 5% occurs within the scanning exposure range.

  The light quantity distribution on the imaging surface, that is, “light quantity” and “light quantity variation” are the diameter Φ, the refractive index distribution, the arrangement, the number of light emitting elements 52 associated with the rod lens 62 constituting the rod lens array 60, and the arrangement. It changes by etc. In the present embodiment, each of the plurality of light emitting elements 52 is arranged at regular intervals in the main scanning direction, and is shifted in the sub scanning direction to change the light amount distribution on the imaging plane (FIG. 9). FIG. 10). The X coordinate of the light emitting element 52 is made constant, and the Y coordinate (distance from the center line in the sub scanning direction) is changed to change the position of the light emitting element 52 in the sub scanning direction. For the light emitting elements 52 having different X coordinates, when the Y coordinate is changed and the amount of light on the “imaging plane” is measured, it can be seen that the amount of light changes according to the Y coordinate.

For example, as illustrated in FIG. 7, among the ₁₅ light emitting elements 52 _{1 to} 52 15 illustrated in FIG. 5, the five light emitting elements 52 _{4 to} 52 ₈ illustrated in black are used as measurement targets, and the “object plane” is used. The amount of light on the “imaging plane” is measured while changing the Y coordinate. Emitting element 52 _4, when shifting the position to place along a straight line L1 extending in the sub-scanning direction, while the X-coordinate constant, Y-coordinate is changed. Similarly, the light-emitting element 52 ₅ is arranged along a straight line L2, the light emitting element 52 ₆ are disposed along the straight line L3. The light emitting element 52 ₇ are arranged along a straight line L4, the light emitting element 52 ₈ is arranged along a straight line L5.

  FIG. 8 is a graph showing the light quantity distribution in the sub-scanning direction on the image plane. The horizontal axis represents the Y coordinate, that is, the distance (unit: mm) from the center line in the sub-scanning direction. The vertical axis represents the amount of light on the “imaging plane”. The amount of light is represented by the relative intensity when the maximum amount of light is 1. A condensing point is formed at the Y coordinate position of the “imaging plane” corresponding to the light emitting element 52 disposed at the Y coordinate position of the “object plane”. While changing the Y coordinate of the “object plane”, each of the plurality of light emitting elements 52 emits light, and the amount of light on the “imaging plane” is measured.

As shown in FIG. 8, by moving the light emitting element 52 ₄ in the sub-scanning direction along a straight line L1, the light amount is maximized in the "image plane" distances from the center line at 0mm position. That is, when the light emitting element 52 ₄ disposed on the center line, the amount of the image plane is maximized. On the other hand, each of the light emitting elements 52 _{5 to} 52 ₈ has the maximum amount of light on the “imaging plane” at a position away from the center line as indicated by an arrow. In other words, each of the light emitting elements 52 _{5 to} 52 ₈ is arranged so as to be shifted from the center line in the sub-scanning direction, and the amount of light on the imaging surface is increased as compared to the case where the light emitting elements 52 _{5 to} 52 ₈ are arranged on the center line.

  Accordingly, if each of the plurality of light emitting elements 52 is shifted in the sub-scanning direction so as to increase the amount of light on the imaging plane, the variation in the amount of light is reduced. Further, when each of the plurality of light emitting elements 52 is shifted in the sub-scanning direction so that the amount of light on the imaging plane is maximized, the variation in the amount of light is reduced most and the total amount of light is increased most.

For example, among the light-emitting element 52 _{5-52 8,} the amount of light in the image plane is most reduced when placed on the center line is a light-emitting element 52 _8. Moving in the sub-scanning direction along the light-emitting element 52 ₈ linear L5, light intensity (relative intensity) of the image plane is the center line is 0.95, 0.08 mm is the distance from the center line It becomes 0.97 and the maximum at the position.

This remains light-emitting element 52 ₈ is arranged on the center line is to generate a light quantity variation of 5%, when arranged offset only 0.08mm light-emitting element 52 ₈ from the center line, the light quantity variation is up to 3% It means to be reduced. If each of the plurality of light emitting elements 52 is arranged so as to be shifted in the sub-scanning direction so that the amount of light on each imaging plane is larger than the amount of light when arranged on the center line, the amount of light is raised, Variability is reduced.

  FIG. 9 is a plan view showing the positional relationship between the light emitting element and the rod lens after position correction. The arrangement relationship shown in FIG. 9 is the same as the arrangement relationship shown in FIG. 5 except that the position where the light emitting element 52 is arranged is shifted in the sub-scanning direction. The description is omitted. In addition, the position of the light emitting element before position correction is written together with a white square. FIG. 10 is a graph showing the light amount distribution in the sub-scanning direction on the imaging plane. The dotted line indicates the light amount distribution before position correction, and the solid line indicates the light amount distribution after position correction. The horizontal axis represents the X coordinate, that is, the distance (unit: mm) from the origin in the X-axis direction. The vertical axis represents the amount of light (relative intensity).

  As shown in FIG. 9, the plurality of rod lenses 62 are periodically arranged along the main scanning direction. In this case, when position correction is performed and each of the plurality of light emitting elements 52 is arranged so that the amount of light on each imaging plane is maximized, the Y coordinate ( The distance from the center line in the sub-scanning direction) changes periodically. In other words, the position of each of the plurality of light emitting elements 52 in the sub-scanning direction is determined according to the arrangement period of the plurality of rod lenses 62 in the main scanning direction. Therefore, it is not necessary to determine the position in the sub-scanning direction by measuring the light amount for each light emitting element 52.

  As shown by the dotted line in FIG. 10, when the light emitting element 52 is arranged on the center line, the amount of light in the main scanning direction on the imaging plane is periodically drawn so as to draw two “mountains” per diameter Φ of the rod lens 62. Change. Between the two “mountains”, a “valley” in which the amount of light falls is formed. On the other hand, after the position correction of the light emitting element 52, as shown by a solid line in FIG. 10, the light amount is raised at the “valley” portion, and the light amount variation is reduced. Periodic light quantity variations degrade the print quality in the image forming apparatus. Therefore, the reduction of the periodic light quantity variation leads to the improvement of the printing quality in the image forming apparatus and is more effective.

<Other variations>
In addition, although the example provided with the LED print head provided with several LED was demonstrated above, it replaced with LED and you may use other light emitting elements, such as an electroluminescent element (EL) and a laser diode (LD).

  In the above description, the image forming apparatus is a tandem type digital color printer, and the LED print head as an exposure apparatus that exposes the photosensitive drum of each image forming unit has been described. Any image forming apparatus in which an image is formed by imagewise exposing a medium may be used, and the present invention is not limited to the above application examples.

  For example, the image forming apparatus is not limited to an electrophotographic digital color printer. The exposure apparatus of the present invention may be mounted on a writing apparatus such as a silver salt type image forming apparatus or optical writing type electronic paper. The photosensitive image recording medium is not limited to the photosensitive drum. The exposure apparatus according to the above application example may also be applied to exposure of a sheet-shaped photoreceptor, a photographic material, a photoresist, a photopolymer, and the like.

2 PC
3 Image Reading Device 10 Image Forming Process Unit 11 Image Forming Unit 12 Photosensitive Drum 12A Surface 13 Charger 14 LED Print Head 15 Developer 16 Cleaner 21 Intermediate Transfer Belt 22 Primary Transfer Roll 23 Secondary Transfer Roll 24 Conveying Belt 25 Fixing Device 30 control unit 40 image processing unit 50 light emitting element array 52 light emitting element 54 substrate 54A main surface 60 rod lens array 60A light incident surface 60B light emitting surface 62 rod lens 64A first flat plate member 64B second flat plate member 66 spacing member 68 Light absorbing material 70 Condensing point

Claims (3)

A lens array in which a plurality of rod-shaped lenses are arranged along a first direction, each incident end surface of the plurality of rod-shaped lenses being located in the first surface, and each light incident from each incident end surface is A lens array that focuses and forms an erect life-size image on the exposed surface;
A light emitting element array in which a plurality of light emitting elements larger in number than the plurality of rod-shaped lenses are arranged along the first direction in a second surface facing the first surface, Compared with the case where each of the light emitting elements is arranged on the center line extending in the first direction, the first erect image corresponding to the light emitting element has a light quantity that is larger from the center line than the first light emitting element. A light emitting element array arranged to be shifted in a second direction intersecting the direction of
An exposure apparatus comprising: In the lens array, the plurality of rod lenses are periodically arranged,
The light emitting element array is configured such that each of the plurality of light emitting elements is configured so that a shift amount of the plurality of light emitting elements in the second direction periodically varies according to an arrangement period of the plurality of rod-shaped lenses. Arranged in the second direction from the center line,
The exposure apparatus according to claim 1. An exposure apparatus according to claim 1 or 2,
The exposure apparatus is disposed apart from the exposure apparatus by a working distance, is moved relative to the exposure apparatus in a second direction intersecting the first direction, and is subjected to scanning exposure according to image data by the exposure apparatus. A photoconductor on which an image is written,
An image forming apparatus including: