JP2009063759A - Exposure apparatus and image forming apparatus - Google Patents

Abstract

An object of the present invention is to suppress the influence of distortion of the shape of each beam spot caused by passing through a rod lens array, to improve the uniformity of printing density, and to suppress the occurrence of unevenness in the printing result.
A plurality of light emitting elements 20A arrayed on a substrate at predetermined intervals, a drive circuit provided for the plurality of light emitting elements 20A and driving each light emitting element to emit light by passive matrix driving, and a plurality of light emitting elements In an exposure apparatus that includes a rod lens array that includes a plurality of rod lenses arranged in an array facing the element 20A, and forms an image of light emitted from the plurality of light emitting elements 20A on a photosensitive member, the light emitting element 20A is driven by a drive circuit. The photosensitive drum is configured such that light is emitted a plurality of times during the dot formation period, and the shape of the light emitting element 20A has a long side in the array arrangement direction, which is the main scanning direction, and a long / short side ratio determined by the number of times of light emission. The width of the beam spot formed on the circumferential surface of 1 is configured to be equal to the width in the main scanning direction and the width in the sub scanning direction.
[Selection] Figure 7

Description

  The present invention relates to an electrophotographic exposure apparatus and an image forming apparatus including the same, and more particularly to an exposure apparatus using a light emitting element as an exposure light source and an image forming apparatus including the exposure apparatus.

In an electrophotographic image forming apparatus (printing apparatus), various plans and products using light emitting elements such as organic electroluminescence (hereinafter referred to as “organic EL”) as light sources have been developed and commercialized. In the apparatus, a light-emitting element array composed of a plurality of light-emitting elements and a photoconductor are arranged at a certain distance through a lens, and light emitted from each light-emitting element is focused through the lens, and is placed on the photoconductor. In this configuration, an electrostatic latent image is formed by irradiation (for example, Patent Document 1).
JP 2004-327217 A

  In general, including the technique described in Patent Document 1, the light emitter of the light emitting element is formed in a substantially square shape. Ideally, the light emission becomes a substantially circular beam spot through the lens, and the peripheral surface of the photosensitive drum. Designed to be imaged on top.

  Here, as a lens used in such an image forming apparatus, a rod lens array composed of a plurality of rod lens groups arranged in an array is used. In such a rod lens array, it is very difficult to make the optical characteristics such as the refractive index distribution of each rod lens and the tilt angle of the optical axis uniform in manufacturing. For this reason, the shape of the beam spot imaged through each rod lens that actually constitutes the rod lens array causes distortion inherent to each rod lens, and as a result, the print density for each light emitting element is uniform. There is a problem that the printing performance is impaired and the printing result may be uneven.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to suppress the influence of the distortion of the shape of each beam spot caused by passing through the rod lens array, and to make the print density uniform. It is an object of the present invention to provide an exposure apparatus and an image forming apparatus provided with the same that can improve the image quality and suppress the occurrence of unevenness in the printing result.

  According to a first aspect of the present invention, there is provided an exposure apparatus for performing exposure by irradiating light to a rotating photosensitive drum, wherein a plurality of light emitting elements having a light emitting portion are linearly arranged at predetermined intervals on a substrate. An array, a driving circuit that drives each light emitting element of the light emitting element array with a predetermined dot formation period as a cycle, and drives the light emitting elements to emit light a predetermined number of times within the dot formation period, and the light emitting element array A plurality of lenses arranged opposite to each other on the light emitting surface side of the plurality of light emitting elements and arranged in an array, and the light emitted from the plurality of light emitting elements is imaged on the peripheral surface of the photosensitive drum. A lens array that forms a beam spot on the peripheral surface, and the light emitting portion of each light emitting element has a long side in the arrangement direction of the light emitting elements, which is the main scanning direction, and is orthogonal to the main scanning direction. Sub-scan It has a rectangular shape that the direction and short sides, the ratio of the short side and the long side of the light emitting unit is characterized in that it is set to a value corresponding to the number of light emission within the dot formation period.

  According to a second aspect of the present invention, in the first aspect of the present invention, the ratio of the short side to the long side of each light emitting element is determined by each of the plurality of light emitting elements by the plurality of times of light emission. The width of the beam spot formed on the circumferential surface on the photosensitive drum in the sub-scanning direction is set to a value equal to the width of the main scanning method.

  The invention according to claim 3 is the invention according to claim 1, wherein the ratio of the short side to the long side of the light emitting part of each light emitting element is when the number of times of light emission in the dot formation period is n. , 1 / n.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, each of the light emitting elements is an organic EL element.

  According to a fifth aspect of the present invention, there is provided an image forming apparatus for performing exposure by irradiating light on a rotating photosensitive drum based on image data and performing printing by an electrophotographic method, wherein a plurality of light emitting elements each having a light emitting portion are provided. Based on the light emitting element array linearly arranged on the substrate at a predetermined interval and the image data, the light emitting elements of the light emitting element array are driven with a predetermined dot forming period as a period, and the dot forming period A drive circuit that is driven so as to emit light a predetermined number of times, and a plurality of lenses arranged in an array, provided facing the light emitting surface side of the plurality of light emitting elements of the light emitting element array, A lens array that images light emitted from the plurality of light emitting elements on the peripheral surface of the photosensitive drum to form a beam spot on the peripheral surface, and the light emitting portion of each light emitting element includes: The light emitting element has a rectangular shape in which the arrangement direction of the light emitting elements, which is the main scanning direction, is a long side, and the sub scanning direction orthogonal to the main scanning direction is a short side, and the ratio of the short side to the long side of the light emitting unit is It is set to a value corresponding to the number of times of light emission within the dot formation period.

  The invention according to claim 6 is the invention according to claim 5, wherein the ratio of the short side to the long side of each light emitting element is determined by each of the plurality of light emitting elements by the plurality of times of light emission. The width of the beam spot formed on the circumferential surface on the photosensitive drum in the sub-scanning direction is set to a value equal to the width of the main scanning method.

  The invention according to claim 7 is the invention according to claim 5, wherein the ratio of the short side to the long side of the light emitting part of each light emitting element is when the number of times of light emission in the dot formation period is n. , 1 / n.

  The invention according to claim 8 is the invention according to any one of claims 5 to 7, wherein each of the light emitting elements is an organic EL element.

  According to the present invention, it is possible to suppress the influence of the distortion of the shape of each beam spot generated through the rod lens array, improve the uniformity of the print density, and suppress the occurrence of unevenness in the print result.

An exposure apparatus and an image forming apparatus (printing apparatus) according to an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus using the exposure apparatus according to the present embodiment. In the figure, the image forming apparatus includes a photosensitive drum 1, an exposure device 2 integrally provided with a case portion 2A and a rod lens array portion 2B, a charging roller 3, an eraser light source photoconductor 4, and a cleaning member 5. A developing device 6 including a developing roller 6 a, a transfer roller 8, a fixing roller 9, and a conveying belt 11. Note that reference numeral 7 denotes printing paper.

  The rod lens array unit 2B is a lens array in which, for example, Selfoc (registered trademark) lenses are arranged in a single row or a plurality of rows, and a lens that forms incident light on the photosensitive drum 1 as an equal-magnification erect image. Part.

  The photosensitive drum 1 is a negatively charged OPC (Organic Photo Conductor) photosensitive member (organic photosensitive member), and the charging roller 3 is a negative charger correspondingly. The exposure apparatus 2 is configured by arranging a plurality of light emitting elements in an array, as will be described in detail later.

  In the image forming apparatus shown in FIG. 1, printing is generally performed by the following steps. First, when the charging roller 3 comes into contact with the surface of the rotating photosensitive drum 1, the contacted surface of the photosensitive drum 1 is uniformly charged with a negative potential.

  Subsequently, the exposure device 2 irradiates the photosensitive drum 1 with light, and an electrostatic latent image is formed on the photosensitive drum 1. Thereafter, toner is attached to the electrostatic latent image by the developing device 6.

  Then, the toner attached to the electrostatic latent image is transferred to the printing paper 7 by the transfer roller 8. Hereinafter, such a printing process will be described in detail.

  First, a negative high voltage supplied from a charging power source (not shown) is applied to the photosensitive drum 1 by the charging roller 3. As a result, the peripheral surface of the photosensitive drum 1 is uniformly negatively charged, and is in an initialized charged state that is initialized in terms of potential.

  Then, optical writing (exposure) according to the printing information is performed by the exposure device 2 on the photosensitive drum 1 whose peripheral surface is in an initialized charged state. As a result, an electrostatic latent image composed of a negative high potential portion due to initialization charging and a negative low potential portion of about −50 [V] due to exposure is formed on the peripheral surface of the photosensitive drum 1.

  Here, the toner charged in the developing unit 6 and charged to a weak negative potential is rotated and conveyed by the developing roller 6a to the facing portion between the developing roller 6a and the photosensitive drum 1. At this time, a developing bias voltage of about −250 [V], for example, is applied to the developing roller 6a from a power source (not shown). Accordingly, between the developing roller 6a to which the developing bias voltage of −250 [V] is applied and the minus low potential portion of about −50 [V] of the electrostatic latent image on the photosensitive drum 1 is about 200 [V]. Is formed.

  Due to the potential difference from the developing voltage in these electrostatic latent images, the negatively charged potential portion in the electrostatic latent image that has a positive polarity relative to the developing roller 6a has a negatively charged toner. Is transferred to form a toner image. The toner image is conveyed to a transfer portion where the photosensitive drum 1 and the transfer roller 8 are opposed to each other by the rotation of the photosensitive drum 1.

  Note that the toner adhesion amount in the toner image formed as described above, that is, the density of the developed image, is generated according to the exposure amount of the photosensitive drum 1 by the light emitting element of the exposure device 2. It is determined by the amount of potential attenuation on the circumferential surface.

  Next, when the toner image is conveyed to the transfer unit as described above, the printing paper 7 is conveyed to the transfer unit by the conveyance belt 11. In the transfer portion, the toner image is transferred onto the printing paper 7 by the transfer roller 8.

  The printing paper 7 onto which the toner image has been transferred in this manner is conveyed further downstream by the conveying belt 11, and after the toner image is thermally fixed by the fixing roller 9, the printing paper 7 is discharged to the outside of the image forming apparatus. The

  Further, after the toner image is transferred onto the printing paper 7, the residual toner is removed from the peripheral surface of the photosensitive drum 1 by the cleaning member 5, and is further uniformly 0 (zero) [V] by the eraser light source photosensitive member 4. To be charged for the charging roller 3.

  In the case unit 2A of the exposure apparatus 2, a large number of light emitting elements are arranged in a line along the axial direction of the photosensitive drum 1, which is the main scanning direction of exposure scanning on the photosensitive drum 1 shown in FIG. An organic EL array is provided as a light emitting element array disposed in the.

Hereinafter, the basic structure of the organic EL element 20 which is a light emitting element will be described with reference to FIG.
In FIG. 2, for example, a pixel electrode (anode) 22, a hole transport layer (HTL) 23, a light emitting layer (EL) 24, an electron transport layer (ETL) 25, and a counter electrode (cathode) are formed on a transparent substrate made of a glass substrate 21. ) 26 are formed in this order. Further, a counter substrate (not shown) for sealing these components may be provided.

  Here, the bottom emission structure in which the light emitted from the light emitting layer 24 is emitted from the transparent substrate 21 side is illustrated, but the top emission structure in which the light is emitted to the opposite side to the transparent substrate 21 side is employed. May be.

  The pixel electrode 22 functions as an anode, and in the case of the illustrated bottom emission structure, tin doped indium oxide (ITO), zinc doped indium oxide, or the like is used to transmit light emitted from the light emitting layer 24. It consists of a transparent conductive metal oxide film having a transparent electrode material.

  In this case, the counter electrode 26 functioning as a cathode is composed of an electron injection layer having a low signal function such as barium, magnesium and lithium on the lower layer side and a metal layer having a high signal function such as light-reflective aluminum located on the upper layer side. By constituting with a laminated reflective structure or with a single layer of a reflective metal layer such as an aluminum alloy, the light L from the light emitting layer 24 is reflected as shown in the figure, and as a result, is emitted from the transparent substrate 21 side. The counter electrode 26 is preferably a single electrode shared by a plurality of light emitting elements arranged in an array constituting the exposure apparatus 2.

When the top emission structure is used instead of the bottom emission structure shown in FIG. 2, the counter electrode 26 is an anode and the pixel electrode 22 is a cathode, and the components of the counter electrode 26 and the pixel electrode 22 described above are replaced. it can.
In this case, the carrier transport layer in contact with the pixel electrode 22 is an electron transport layer, and the carrier transport layer in contact with the counter electrode 26 is a hole transport layer.

  The light emitting layer 24 includes an organic material that emits light by recombining holes transported from the hole transport layer (HTL) 23 and electrons transported from the electron transport layer (ETL) 25.

  Although the organic EL element 20 has been described as having a three-layer structure of the hole transport layer 23, the light emitting layer 24, and the electron transport layer 25, the present invention is not limited to this, and for example, the hole transport layer and the electron transport Two-layer structure of layers, single-layer structure of hole transport / electron transport, two-layer structure of hole transport layer-emitting layer and electron transport layer, or other carrier transport layer interposed between them, It does not limit the structure.

  In the present embodiment, the carrier transport layers such as the hole transport layer 23, the light emitting layer 24, and the electron transport layer 25 are collectively referred to as an EL layer.

  However, when a predetermined voltage is applied between the pixel electrode 22 and the counter electrode 26, holes from the pixel electrode 22 and electrons from the counter electrode 26 are injected into the light emitting layer 24. The holes and electrons recombine and emit light.

In the case of a bottom emission structure as shown in the figure, the light L generated by this light emission passes through the pixel electrode 22 and the transparent substrate 21 and is completely diffused and emitted. In the case of the top emission structure, the light L from the light emitting layer 24 is completely diffused and radiated through the counter electrode 26. As described above, in the electrophotographic image forming apparatus, the photosensitive drum 1 is exposed. The apparatus 2 performs optical writing in accordance with the printing information, but the photosensitive drum 1 is separated by a distance of about several millimeters without any imaging optical system structure only on the case portion 2A side constituting the exposure apparatus 2. It is difficult to form a light spot with a small diameter on the photoconductor and to create a light spot for resolving each dot. Therefore, in the present invention, a light spot is realized by combining the rod lens array portion 2B with the case portion 2A.

The detailed configuration of the exposure apparatus 2 will be described below with reference to FIGS.
FIG. 3 is a view showing an external configuration of the exposure apparatus 2 as an organic EL head. As shown in the drawing, in the exposure apparatus 2, a plurality of light-emitting elements (not shown) are arranged in a line in an array in the main scanning direction of recording scan (the axial direction of the photosensitive drum 1). The organic EL array has a print density of 1200 [dpi] to fill the width of the image forming apparatus so that the vertical direction of, for example, A4 size (vertical 297 mm × horizontal 210 mm) printing paper coincides with the axial direction of the photosensitive drum 1. ], 14,000 organic EL elements 20 are provided.

  A pulse voltage according to print information output from a host device (not shown) externally connected to the image forming apparatus is applied to each of the organic EL elements 20. That is, the light emission of each organic EL element 20 is selectively controlled.

  As shown in FIG. 3, the organic EL element 20 is electrically connected to the host device described above by control cables 31A and 31B.

FIG. 4 is a sectional view showing the structure of the exposure apparatus 2 as seen from the side.
The transparent substrate 21 is fixed to the front case 41 constituting a part of the case portion 2A with an adhesive resin (not shown). As shown in the figure, the front case 41 is fitted with a rear case 42 that constitutes a part of the case portion 2A. In other words, the transparent substrate 21 is enclosed and fixed in a housing composed of the front case 41 and the back case 42.

  On the surface side of the transparent substrate 21 on which the organic EL element 20 is provided, a sealing glass 27 constituting a counter electrode for sealing the organic EL element 20 is provided, and the sealing glass 27 is avoided, A plurality of driver ICs 43 are provided. These driver ICs 43 are electrically connected to the pixel electrode 22 and the counter electrode 26 shown in FIG.

  The driver IC 43 receives a synchronization signal, a clock signal, an image signal, and the like from a controller (not shown), and the driver IC 43 controls the pixel electrode 22 and the counter electrode 26 based on these signals.

  In the present embodiment, because of the structure of the image forming apparatus, the exposure apparatus 2 is a single device apparatus. Therefore, some external force may be applied to the connection wiring during assembly or replacement. Therefore, in order to make the cable outside the case part 2A higher in strength and excellent in workability by making the cable different between the inside and the outside of the case part 2A, as shown in FIG. A relay connector 44 is provided on the rear case 42.

  Then, the external cable 45 is connected to the outside of the exposure apparatus 2 via the relay connector 44 by providing a relay cable 46 for connecting the relay connector 44 and the driver IC 43 on the transparent substrate 21. 44 and the relay cable 46 constitute the control cables 31A and 31B in FIG.

  By the way, the front case 41 is provided with a convex portion 51 directed toward the photosensitive drum 1. An opening is formed in the convex portion 51, and the rod lens array portion 2B is fitted into the opening portion so as to face each organic EL element 20, and a gap between the opening portion and the rod lens array portion 2B is not shown. Sealed and fixed with an agent.

  For this reason, even if the front case 41 is opaque to visible light, the light emitted from the organic EL element 20 is incident on the rod lens array portion 2B through the sealed space formed in the convex portion 51. become.

  Note that the organic EL element 20 shown in FIG. 4 has a bottom emission structure in which the transparent substrate 21 faces the rod lens array portion 2B, but the sealing glass 27 that is the opposite substrate has a rod lens array portion. A top emission structure that faces 2B may be adopted.

Next, a passive matrix driving method for driving the organic EL elements 20 to emit light will be described with reference to FIGS.
FIG. 5A shows the driving principle of the passive matrix. A row driver 81 and a column driver 82 are used, and a predetermined number of scanning electrodes and signal electrodes crossing in the row (row) and column (column) directions are determined. By sequentially applying a bias voltage at this timing, the organic layer of the organic EL element 20 that is the intersection of the electrodes is caused to emit light.

  Assuming that the number of scanning electrodes is m and the number of signal electrodes is n (m and n are natural numbers of 2 or more, respectively), a matrix having m × n intersections is formed, and the number of organic EL elements 20 is the number. It will be possible to arrange as much as possible.

  In the actual case portion 2A in which the organic EL elements 20 are arrayed, the matrix-shaped organic EL elements 20 shown in FIG. 5A are rearranged in one or a plurality of columns as described above. For example, FIG. 5B illustrates a configuration when m × n organic EL elements 20 are arranged in a line.

  FIG. 6A shows an example of dot wiring in the case of the configuration shown in FIG. As shown in FIG. 6A, each organic EL element 20 is composed of m EL element groups 20G1 to 20Gn, and each group 20Gi (i = Each element 20 belonging to 1, 2,..., N) is controlled to be turned on once in one scanning line in synchronization with the pulse signal.

  FIG. 6B shows the driving timing of the organic EL element 20 by the row driver 81 and the column driver 82 shown in FIG. The row driver 81 sequentially activates the scan electrode rows 1, 2,..., M during one scan line time with a horizontal synchronization signal Hsync (not shown) as a reference, and the column driver 82 outputs data based on the print information during that time. The amount of light emission is controlled by writing to the signal electrode.

  For example, while the row driver 81 makes the scan electrode row 1 active, the column driver 82 corresponds to the scan electrode row 1 by writing data based on the print information to the signal electrode columns 1, 2,. The amount of light emitted from the organic EL element 20 located at each intersection is controlled.

Next, a specific shape of the organic EL element 20 and a driving method thereof will be described.
FIG. 7 shows the shape of the light emitter 20A portion of the organic EL element 20 and the driving method thereof in comparison with the case of a light emitter of an organic EL element having a conventional general shape.

  FIG. 7F shows the shape of a light-emitting body of a light-emitting element generally used conventionally. That is, as shown in the figure, the conventional light emitter PA has a substantially square shape, the width in the array arrangement direction, which is the main scanning direction, corresponding to the horizontal direction in the figure, and L in the figure. The width in the sub-scanning direction perpendicular to the main scanning direction, corresponding to the direction, is L, and the widths of both are substantially equal.

  FIG. 7G is formed on the peripheral surface of the photosensitive drum 1 to be irradiated by instantaneous light emission for a short time by the conventional light emitter through a rod lens array having an ideal lens configuration. FIG. 7H shows the shape of the beam spot, and FIG. 7H shows the shape of the beam spot formed by the conventional light emitter through the actual rod lens array.

  That is, in the conventional configuration, the light emitting element is driven to emit light instantaneously, and the rod spot array is ideal for the shape of the beam spot formed on the peripheral surface of the photosensitive drum 1 at this time. In this case, since an equal-size erect image is obtained, the width in the main scanning direction (lateral direction in the drawing) and the width in the sub-scanning direction (vertical direction in the drawing) are both L as shown in FIG. Are substantially circular shapes.

  However, in an actual rod lens array, a large number of individual rod lenses are arranged in an array, and the optical images formed by the lenses overlap with each other at the periphery. In addition, the positional relationship between each lens and the light emitter is not strictly uniform, and there are variations in optical characteristics such as the refractive index distribution and the angle of the optical axis between the lenses.

  For this reason, the beam spot actually formed on the peripheral surface of the photosensitive drum 1 is both L in the main scanning direction and L in the sub scanning direction, but is distorted from a circular shape. For example, FIG. ), And the shape and area of the beam spot with respect to each light emitting element of the light emitting element array are not uniform. When these uneven beam spots are continuously arranged, the print density is uneven.

  On the other hand, FIG. 7 (A) shows the shape of the light emitter 20A of the organic EL element 20 in the embodiment of the present invention. That is, as shown in FIG. 7A, the shape of the light emitter 20A of the organic EL element 20 in this embodiment is such that the width of the light emitting element array side in the light emitting element array in the main scanning direction is L. It has a rectangular shape with a long side and a sub-scanning direction orthogonal to the main scanning direction with a short side of M shorter than L in width.

  FIG. 7B shows the shape of a beam spot formed on the peripheral surface of the photosensitive drum 1 by instantaneous light emission of the light emitter 20A through a rod lens array having an ideal lens configuration. FIG. 7D shows the shape of a beam spot formed by customary light emission of the light emitter 20A via an actual rod lens array.

  That is, when the rod lens array is ideal, the shape of the beam spot formed on the peripheral surface of the photosensitive drum by the instantaneous light emission of the light emitter 20A is as shown in FIG. The width in the main scanning direction is L, the width in the sub scanning direction is M, and an oval shape having a width in the sub scanning direction shorter than the width in the main scanning direction is obtained.

  On the other hand, the shape of the beam spot formed by the customary light emission of the light emitter 20A through the actual rod lens array is, for example, as shown in FIG. As shown in D), the width in the main scanning direction is L and the width in the sub-scanning direction is M, but the distortion occurs.

  However, in the present embodiment, the light emitter 20A is further driven to emit light a plurality of times at a predetermined light emission interval within the dot formation period assigned to printing of one line, and the actual beam spot shape by the rod lens array. The effect of distortion is suppressed.

  That is, in the conventional configuration, each light emitter of the light emitting element array is configured to emit light only once in one light emission cycle with the dot formation period as the light emission cycle. The light is emitted a plurality of times during the cycle.

  In this case, since the photosensitive drum 1 rotates at a constant speed, when the light emitter 20A emits light a plurality of times, the position of the beam spot formed on the peripheral surface of the photosensitive drum 1 by each light emission is the light emission interval. As a result, the shape of the beam spot formed on the peripheral surface of the photosensitive drum 1 is formed by a plurality of times of light emission of the light emitter 20A. The plurality of beam spots to be overlapped are shifted by the moving distance of the peripheral surface of the photosensitive drum 1 corresponding to the light emission interval.

  In this embodiment, the shape of the beam spot formed on the peripheral surface of the photosensitive drum 1 by the light emitting body 20A emitting light a plurality of times in this way is the width in the sub-scanning direction (vertical direction in the drawing). The number of times of light emission and the shape of the light emitter 20A (the ratio of the short side to the long side) are set so that the shape is substantially equal to the width L in the main scanning direction (the horizontal direction in the drawing).

  As a result, even if the beam spot shape by the rod lens array is distorted, the influence can be reduced, and the uniformity of the print density for each light emitting element can be improved and the unevenness in the print result can be reduced. It can be done. This will be described in more detail below.

  In FIG. 7C, as shown in FIG. 7B, when the rod lens array is ideal and an elliptical beam spot is obtained, the light emitter 20A is spaced at a constant interval. The shape of the beam spot formed on the circumferential surface of the photosensitive drum 1 when the light is emitted five times is illustrated.

  On the other hand, in FIG. 7E, as shown in FIG. 7D, when the beam spot shape distorted by the actual rod lens array is obtained, the light emitter 20A emits light five times at regular intervals. This is an example of the shape of the beam spot formed on the peripheral surface of the photosensitive drum 1 when it is applied.

  The shape of the beam spot formed on the peripheral surface of the photosensitive drum 1 according to the present embodiment is the same as the shape of the beam spot formed on the peripheral surface of the photosensitive drum by the instantaneous light emission of the light emitter 20A. This is determined by the distance that the peripheral surface of the photosensitive drum 1 moves during the light emission interval by the rotation of the drum 1 and the number of times of light emission.

  Here, a plurality of times of light emission is performed, for example, at equal intervals, and at this time, the light emission interval is set to a time obtained by dividing the dot formation period by the number of times of light emission. The shape of the beam spot formed on the peripheral surface of the photosensitive drum 1 by a plurality of light emissions is such that the vertical width in the sub-scanning direction is substantially equal to the horizontal width L in the main scanning direction. By setting the shape of the light emitter 20A and the number of times of light emission, it is possible to obtain a printing result similar to the conventional one.

  In this case, as shown in FIG. 7E, even if the beam spot shape due to instantaneous light emission by the rod lens array is distorted, the beam spot due to instantaneous light emission shown in FIG. As a result, the shape of the beam spot formed on the peripheral surface of the photosensitive drum 1 is not much different from the case where the shape is not distorted.

  Thereby, even if each rod lens constituting the rod lens array has a variation in optical characteristics, a beam spot shape with respect to each light emitting element of the light emitting element array, that is, a variation in printing density, is suppressed, resulting in a printing result. Generation of unevenness can be suppressed.

  Next, the relationship between the shape set for the rectangular light emitter 20A and the number of times of light emission will be described. As described above, the shape of the light emitter 20A in the present embodiment is a rectangular shape in which the main scanning direction is the long side (width L) and the sub-scanning direction orthogonal to the main scanning direction is the short side (width M). It is what you have. The ratio of the short side to the long side (M: L) of the rectangle is determined according to the number of times of light emission during the dot formation period.

  That is, when the dot formation period is 1, when the number of times of light emission is 2, the light emission interval is 0.5. At this time, the ratio of the short side: long side (M: L) of the light emitter 20A is 0.5: Assuming that the width of the beam spot formed by two light emission in the sub-scanning direction is 1, the width of the long side is 1, 0.5 + 0.5 = 1, and the aspect ratio is 1: 1. A beam spot can be obtained.

  When the number of times of light emission is four, the light emission interval is 0.25. At this time, if the ratio of the short side: long side of the light emitter 20A is 0.25: 1, a beam formed by four times of light emission. The width M in the sub-scanning direction of the spot shape is 0.25 + 0.25 × 3 = 1, where the width of the long side is 1, and in this case also, a beam spot having a 1: 1 aspect ratio can be obtained. it can. That is, the ratio of the short side to the long side (M: L) of the light emitter 20A is (1 / number of continuous light emission): 1.

  As described above, in the present embodiment, the light-emitting body 20A of the organic EL element 20 is formed in a rectangular shape with the long side on the main scanning direction side that is the array arrangement direction and the short side on the sub-scanning direction orthogonal to the main scanning direction. It was driven to emit light a plurality of times during the dot formation period by matrix driving, and the ratio of the short side to the long side of the light emitter 20A was determined according to the number of times of light emission during the dot formation period.

  As a result, the light emitted from the light emitter 20 </ b> A is combined on the peripheral surface of the photosensitive drum 1 by a combination with the individual lenses constituting the rod lens array unit 2 </ b> B for imaging the peripheral surface of the photosensitive drum 1. Even if the shape of the instantaneous beam spot to be imaged is distorted, the shape of the beam spot formed on the peripheral surface of the photosensitive drum 1 as a result of exposure by multiple times of light emission is as described above. This reduces the influence of the distortion, thereby improving the uniformity of the printing density for each light emitting element of the light emitting element array and suppressing the occurrence of unevenness in the printing result.

  In the above-described embodiment, the case where the organic EL element 20 has a bottom emission structure has been described.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention in the implementation stage. In addition, the functions executed in the above-described embodiments may be implemented in appropriate combination as much as possible. The above-described embodiment includes various stages, and various inventions can be extracted by an appropriate combination according to a plurality of disclosed structural requirements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, if the effect is obtained, a configuration from which the constituent requirements are deleted can be extracted as an invention.

1 is a diagram illustrating a configuration example of an image forming apparatus using an exposure apparatus according to an embodiment of the present invention. The figure which shows the basic structure of the organic EL element which concerns on this embodiment. FIG. 2 is a perspective view showing an external configuration of an exposure apparatus according to the present embodiment. FIG. 6 is a cross-sectional view showing a structure viewed from the side of the exposure apparatus according to the present embodiment. The figure for demonstrating the circuit structure of the passive matrix drive which concerns on this embodiment. The figure explaining the circuit structure of the passive matrix drive concerning this embodiment. The figure which shows the shape of the light emission part of the organic EL element which concerns on this embodiment, and its driving method in contrast with the case of the light emission body of the organic EL element of the conventional general shape.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Exposure apparatus, 2A ... Case part, 2B ... Rod lens array part, 3 ... Charging roller, 4 ... Eraser light source photoconductor, 5 ... Cleaning member, 6 ... Developing device, 6a ... Developing roller, DESCRIPTION OF SYMBOLS 7 ... Printing paper, 8 ... Transfer roller, 9 ... Fixing roller, 11 ... Conveyor belt, 20 ... Organic EL element, 20A ... Light-emitting body, 20G1-20Gn ... EL element group, 21 ... Transparent substrate, 22 ... Pixel electrode (ITO) ), 23... Hole transport layer (HTL), 24. Light emitting layer (EL), 25. Electron transport layer (ETL), 26. Counter electrode, 27... Sealing glass, 31 A, 31 B. Case: 42 ... Back case, 43 ... Driver IC, 44 ... Relay connector, 45 ... External cable, 46 ... Relay cable, 51 ... Projection, 81 ... Row (row) driver, 82 ... Column (column) driver Bar, L ... light.

Claims (8)

In an exposure apparatus that performs exposure by irradiating light to a rotating photosensitive drum,
A light emitting element array in which a plurality of light emitting elements each having a light emitting portion are linearly arranged at predetermined intervals on a substrate;
A drive circuit that drives each light emitting element of the light emitting element array with a predetermined dot formation period as a cycle, and drives the light emitting elements to emit light a plurality of times within the dot formation period;
The light emitting element array includes a plurality of lenses arranged facing the light emitting surface side of the plurality of light emitting elements, and emits light from the plurality of light emitting elements to the peripheral surface of the photosensitive drum. A lens array that forms a beam spot on the peripheral surface by focusing on the surface;
With
The light emitting section of each light emitting element has a rectangular shape having a long side in the arrangement direction of the light emitting elements, which is the main scanning direction, and a short side in the sub scanning direction orthogonal to the main scanning direction. The ratio of the short side to the long side is set to a value corresponding to the number of times of light emission within the dot formation period.   The ratio of the short side to the long side of the light-emitting portion of each light-emitting element is determined by the subordinate of the beam spot formed on the circumferential surface on the photosensitive drum by each of the plurality of light-emitting elements by the plurality of times of light emission. 2. The exposure apparatus according to claim 1, wherein the width in the scanning direction is set to a value equal to the width of the main scanning method.   The ratio of the short side to the long side of the light emitting part of each light emitting element is set to 1 / n, where n is the number of times of light emission in the dot formation period. The exposure apparatus described.   The exposure apparatus according to claim 1, wherein each of the light emitting elements is an organic EL element. An image forming apparatus that performs exposure by irradiating light on a rotating photosensitive drum based on image data, and performing printing by an electrophotographic method,
A light emitting element array in which a plurality of light emitting elements each having a light emitting portion are linearly arranged at predetermined intervals on a substrate;
A driving circuit that drives each light emitting element of the light emitting element array with a predetermined dot formation period as a period based on the image data, and drives the light to emit light a predetermined number of times within the dot formation period;
The light emitting element array includes a plurality of lenses arranged facing the light emitting surface side of the plurality of light emitting elements, and emits light from the plurality of light emitting elements to the peripheral surface of the photosensitive drum. A lens array that forms a beam spot on the peripheral surface by focusing on the surface;
With
The light emitting section of each light emitting element has a rectangular shape having a long side in the arrangement direction of the light emitting elements, which is the main scanning direction, and a short side in the sub scanning direction orthogonal to the main scanning direction. The ratio of the short side to the long side is set to a value corresponding to the number of times of light emission within the dot formation period.   The ratio of the short side to the long side of the light-emitting portion of each light-emitting element is the sub-portion of the beam spot formed on the circumferential surface on the photosensitive drum by each of the plurality of light-emitting elements by the plurality of times of light emission. The image forming apparatus according to claim 5, wherein a width in a scanning direction is set to a value equal to a width of the main scanning method.   The ratio of the short side to the long side of the light-emitting portion of each light-emitting element is set to 1 / n, where n is the number of times of light emission in the dot formation period. The image forming apparatus described.   The image forming apparatus according to claim 5, wherein each of the light emitting elements is an organic EL element.

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