Light-emitting component and optical writing device and image forming device using the same

Abstract

To reduce the arrangement interval between adjacent light emitting points of light emitting devices arranged side by side in a main scanning direction, while ensuring the light emitting area of the light emitting devices arranged side by side in the main scanning direction.SOLUTION: A light emitting component includes a first light emitting device row 2 consisting of light emitting devices 4 arranged in a main scanning direction, and a second light emitting device row 3 that is arranged in the main scanning direction to be deviated in a sub scanning direction from the first light emitting device row 2 and located between the light emitting devices 4 of the first light emitting device row 2. A light emitting point area WA1 of each of the light emitting devices 4 in the first light emitting device row 2 and a light emitting point area WA2 of each of the light emitting devices 4 in the second light emitting device row 3 are arranged to overlap with respect to the main scanning direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light emitting component, and an optical writing device and an image forming apparatus using the same. [Background technology]

[0002] Conventionally, this type of image forming apparatus has often adopted a method in which an image is written by light onto a photoconductor or a dielectric body using an optical writing device. As this type of optical writing device, for example, the device described in Patent Document 1 is already known. Patent Document 1 provides a light-emitting element array in which light-emitting elements are arranged along the main scanning direction as a light-emitting component used in an optical writing device. This light-emitting element array is configured such that light-emitting points of the light-emitting elements are not arranged in a single row in the main scanning direction, but are arranged in two staggered rows. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5862404 (Form for carrying out the invention, FIG. 4) Summary of the Invention [Problem to be solved by the invention]

[0004] The technical problem that the present invention aims to solve is to provide a light-emitting component that makes it possible to narrow the arrangement spacing between adjacent light-emitting points of light-emitting elements arranged in the main scanning direction while ensuring the light-emitting area of ​​the light-emitting elements arranged in the main scanning direction, and an optical writing device and an image forming device using the same. [Means for solving the problem]

[0005] The invention according to claim 1 includes a first light-emitting element row consisting of light-emitting elements arranged in a main scanning direction, and a second light-emitting element row arranged in the main scanning direction so as to be biased in the sub-scanning direction with respect to the first light-emitting element row and to be located between each light-emitting element of the first light-emitting element row,an arrangement pitch in a main scanning direction between a light emitting point of each light emitting element of the first light emitting element row and a light emitting point of each light emitting element of the second light emitting element row is equal to or smaller than 1 / 2 of an arrangement pitch in the main scanning direction between the light emitting points of each light emitting element of the first and second light emitting element rows; A light-emitting point region, which is a region where each light-emitting element of the first light-emitting element row emits light, and a light-emitting point region, which is a region where each light-emitting element of the second light-emitting element row emits light, are arranged so as to overlap with each other in the main scanning direction. the light emitting point regions of adjacent light emitting elements between the first and second light emitting element rows overlap in the main scanning direction by 30 to 70%, and a light emitting beam region in which light is emitted toward an object from a portion of the light emitting point region, which is a region in which each light emitting element of the first light emitting element row emits light, other than the non-transparent electrodes arranged around the light emitting point region, and a light emitting beam region in which light is emitted toward an object from a portion of the light emitting point region, which is a region in which each light emitting element of the second light emitting element row emits light, other than the non-transparent electrodes arranged around the light emitting point region, are arranged so as to have no gap in the main scanning direction, and the light emitting beam regions of adjacent light emitting elements between the first and second light emitting element rows overlap in the main scanning direction by 0 to 10%. It is a light emitting component characterized by the above.

[0007] Claim 2 The invention according to claim 1 In the light-emitting component relating to the above, an arrangement pitch along the sub-scanning direction between the light-emitting points of each light-emitting element in the first light-emitting element row and the light-emitting points of each light-emitting element in the second light-emitting element row is an integer N times the spacing between image-forming lines.

[0008] Claim 3 The invention according to claim 1 or 2 and an imaging means for focusing light emitted from each light-emitting element of the light-emitting component onto an image holding means capable of holding an image formed by light, and writing an image formed by light onto the image holding means. Claim 4 The invention according to claim 3 In the optical writing device according to the present invention, the imaging means is Each light-emitting element and the second light emitting element row Each light-emitting element In the optical writing device, refractive index distribution lenses having a diameter larger than the difference between the diameters in the sub-scanning direction and the diameters in the main scanning direction are arranged. Claim 5 The invention according to claim 4 In the optical writing device according to the above, the first light-emitting element row and the second light-emitting element row are arranged so that emitted light is incident on the refractive index distribution lens at different positions in the sub-scanning direction. Claim 6 The invention according to claim 5In the optical writing device relating to the above, there are a plurality of light-emitting element chips including the first light-emitting element row and the second light-emitting element row, the plurality of light-emitting element chips are arranged with a bias in the sub-scanning direction and the main scanning direction, the imaging means is an array of the refractive index distribution lenses adjacent to each other in a plurality of rows in the main scanning direction, and light from each light-emitting element of the same light-emitting element chip is incident on the refractive index distribution lenses in the same row aligned in the main scanning direction, and light from each light-emitting element of adjacent light-emitting element chips is incident on the refractive index distribution lenses in different rows.

[0009] Claim 7 The invention according to claim 3 ~ 6 An image forming apparatus includes any one of the optical writing devices and an image holding unit that is provided opposite the optical writing device and holds an image formed by light and written by the optical writing device. Claim 8 The invention according to claim 7 In the image forming apparatus relating to the above, the optical writing device is characterized in that when a linear image along the main scanning direction is written onto the image holding means using light emitted from each light-emitting element of the first light-emitting element row and the second light-emitting element row, the imaging beam areas corresponding to adjacent light-emitting points in the main scanning direction are arranged to overlap. Effect of the Invention

[0010] Claim 1 According to the invention, it is possible to narrow the arrangement interval between adjacent light-emitting points of the light-emitting elements aligned in the main scanning direction while ensuring the light-emitting area of ​​the light-emitting elements aligned in the main scanning direction. especially, The substantial arrangement pitch of the light emitting points of the light emitting components can be narrowed to 1 / 2 or less of the arrangement pitch in the main scanning direction between the light emitting points of the light emitting elements of the first and second light emitting element rows. Also, By appropriately selecting the overlap of the light emitting spot areas, the resolution can be increased while maintaining the same light output. Furthermore,By appropriately selecting the overlap of the emission beam areas, it is possible to increase the resolution while maintaining the same light output. 。 Claim 2 According to the invention, the amount of deviation in the sub-scanning direction caused by the first light-emitting element row and the second light-emitting element row can be appropriately selected. Claim 3 According to the invention, it is possible to provide an optical writing device including a light-emitting component that makes it possible to narrow the arrangement spacing between adjacent light-emitting points of light-emitting elements arranged in the main scanning direction while ensuring the light-emitting area of ​​the light-emitting elements arranged in the main scanning direction. Claim 4 According to the invention, even if the imaging means has tilt or arrangement tolerance, it is possible to reduce the variation in the optical path from each light emitting element in the first and second light emitting element rows. Claim 5 According to the invention, the influence of variations in the incidence position can be suppressed compared to the case where the light from the first light-emitting element row and the second light-emitting element row is incident on the same position on the refractive index distribution lens. Claim 6 According to the invention, the influence of variations in the refractive index distribution lenses for each row can be suppressed compared to the case where multiple rows of refractive index distribution lenses are not assigned to the optical path from each of the offset-arranged light-emitting element row chips. Claim 7 According to the invention, it is possible to provide an image forming apparatus equipped with an optical writing device including a light-emitting component that enables narrowing the arrangement spacing between adjacent light-emitting points of light-emitting elements arranged in the main scanning direction while ensuring the light-emitting area of ​​the light-emitting elements arranged in the main scanning direction. Claim 8 According to the invention, the effects of variations in the light-emitting characteristics of each light-emitting element can be suppressed compared to an embodiment in which the imaging beam diameters corresponding to adjacent light-emitting points in the main scanning direction are arranged so as not to overlap. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1A is an explanatory diagram showing an overview of an embodiment of an image forming apparatus to which the present invention is applied; FIG. 1B is an explanatory diagram showing an example of the configuration of a light-emitting component used in FIG. 1A; and FIG. 1C is an explanatory diagram showing a main part of the light-emitting component. [Diagram 2] FIG. 1 is an explanatory diagram showing an overall configuration of an image forming apparatus according to a first embodiment. [Diagram 3] FIG. 2 is an explanatory diagram showing an example of an optical writing device used in the image forming apparatus according to the first embodiment. [Figure 4] 4 is a perspective view illustrating a configuration example of the optical writing device illustrated in FIG. 3. FIG. [Diagram 5] FIG. 2A is an explanatory diagram showing a light-emitting element array used in an optical writing device, and FIG. 2B is an explanatory diagram showing a configuration example of a light-emitting chip used in the light-emitting element array. [Figure 6] 1A is an explanatory diagram showing an example of the configuration of a light-emitting chip of a light-emitting element array used in comparative form 1, and FIG. 1B is an explanatory diagram showing an example of the configuration of a light-emitting chip of a light-emitting element array used in comparative form 1, in which the arrangement pitch of the light-emitting element row of the light-emitting chip shown in FIG. [Figure 7] FIG. 5(a) is an explanatory diagram showing a main part of FIG. 5(b), and FIG. 5(b) is an explanatory diagram showing a schematic diagram of a beam emitted from a light-emitting element. [Figure 8] FIG. 2 is an explanatory diagram showing a configuration example of a light-emitting element used in the first embodiment. [Figure 9] 1A is an explanatory diagram showing an example of a wiring structure of a light-emitting element used in embodiment 1, FIG. 1B is an explanatory cross-sectional view taken along line BB in FIG. 1A, and FIG. 1C is an explanatory cross-sectional view taken along line CC in FIG. [Figure 10] 10 is a flowchart showing an example of drive control of the light-emitting element array. [Figure 11] FIG. 2A is an explanatory diagram showing a configuration example of an imaging lens of an optical writing device used in the first embodiment, and FIG. 2B is a view seen from a direction indicated by an arrow B in FIG. [Figure 12] 2 is an explanatory diagram showing a schematic diagram of an object point (a light emitting point of a light emitting element) and an image point (an image formed by an imaging lens) of the optical writing device used in the first embodiment. FIG. [Figure 13]FIG. 2A is an explanatory diagram showing an example of an image formed by the optical writing device used in the first embodiment, and FIG. 2B is an explanatory diagram showing an example of an image formed by the optical writing device used in the first comparative embodiment. [Figure 14] 1A is an explanatory diagram showing the incident state of light emitted from the light-emitting element array of embodiment 1 and comparative embodiment 1 when the imaging lens is installed in the ideal position, and FIG. 1B is an explanatory diagram showing the incident state of light emitted from the light-emitting element array of embodiment 1 and comparative embodiment 1 when the imaging lens is shifted from the ideal position. [Figure 15] 1A is an explanatory diagram showing the state in which light emitted from an offset-positioned light-emitting chip in an light-emitting element array used in embodiment 1 is incident on an imaging lens, and FIG. 1B is an explanatory diagram showing the state in which light emitted from an offset-positioned light-emitting chip in an light-emitting element array used in comparative embodiment 1 is incident on an imaging lens. [Figure 16] FIG. 13 is an explanatory diagram showing a main part of a light-emitting element array used in the first modified embodiment. [Figure 17] FIG. 2A is an explanatory diagram showing a light amount profile when a 2400 dpi image is formed on a photoconductor using the optical writing device according to the first embodiment, and FIG. 2B is an explanatory diagram showing an enlarged photograph of the print sample. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Overview of the embodiment FIG. 1(a) shows an outline of an embodiment of an image forming apparatus to which the present invention is applied. In the figure, an image forming apparatus 10 includes an optical writing device 11 and an image holding means 12 that is disposed opposite the optical writing device 11 and holds an image written by the optical writing device 11 using light. Here, the optical writing device 11 comprises a light-emitting component 1 and an imaging means 6 that focuses the light emitted from each light-emitting element 4 of the light-emitting component 1 onto an image holding means 12 capable of holding an image formed by light, and writes an image formed by light onto the image holding means 12. The image holding means 12 referred to here is not limited to a photoreceptor but also includes dielectric materials, and its form may be appropriately selected from a drum type, a belt type, etc. In addition, the image formed by light may be, for example, an electrostatic latent image formed by discharging a predetermined level of electricity with light according to an image pattern, with a potential difference. Furthermore, the imaging means 6 may be a lens that refracts light on its surface (e.g., a cylindrical lens) or a lens that refracts light internally (e.g., a gradient index lens), etc., as long as it images the light emitted from each light-emitting element 4 of the light-emitting component 1 onto the image-holding means 12.

[0013] As shown in Fig. 1(b), the light-emitting component 1 comprises a first light-emitting element row 2 consisting of light-emitting elements 4 arranged in the main scanning direction, and a second light-emitting element row 3 arranged in the main scanning direction so as to be biased in the sub-scanning direction with respect to the first light-emitting element row 2 and to be located between each light-emitting element 4 of the first light-emitting element row 2. As shown in Fig. 1(c), a light-emitting point area WA1, which is an area where each light-emitting element 4 of the first light-emitting element row 2 emits light, and a light-emitting point area WA2, which is an area where each light-emitting element 4 of the second light-emitting element row 3 emits light, are arranged to overlap with each other in the main scanning direction. Here, the light emitting element 4 may be, for example, a light emitting diode (LED). In this case, the specific configuration of the light emitting element 4 is a laminate of a p-anode layer, a light emitting layer, and an n-cathode layer constituting the light emitting diode LED, and grooves are formed in the laminated layers so that the light emitting element 4 has separate light emitting points. In this example, the light emitting point areas WA1 and WA2 are the same as the width of the cathode layer of the light emitting diode LED, but this is not limited thereto, and it is also possible to configure the light emitting element 4 to emit light in a narrower area by using a current constriction layer provided in the p-anode layer. The light emitting element 4 is not limited to an LED, but may be a VCSEL (Vertical Cavity Surface Emitting LASER) or the like.

[0014] In this technical means, since it cannot be realized by simply arranging the light-emitting elements 4 in a row in the main scanning direction, the present invention is premised on an embodiment including a first light-emitting element row 2 and a second light-emitting element row 3. However, the present invention is not limited to an embodiment in which the first light-emitting element row 2 and the second light-emitting element row 3 are arranged in a staggered pattern, and further includes an embodiment including a third light-emitting element row (not shown). In this example, when the light emitting component 1 of the optical writing device 11 divides an image into a plurality of lines and writes it, the movement in the line direction is called main scanning, and the movement in the next line direction is called sub-scanning. In addition, the arrangement of the first and second light-emitting element rows 2, 3 is typically arranged in a straight line along the main scanning direction, but also includes arrangements in which they are not arranged in a straight line. For example, in an arrangement in which a light-emitting element array including the first light-emitting element row 2 and the second light-emitting element row 3 is made up of a plurality of light-emitting element chips and the plurality of light-emitting element chips are arranged in a staggered pattern, the first and second light-emitting element rows 2, 3 are not arranged in a straight line between odd-numbered light-emitting element chips and even-numbered light-emitting element chips, but these arrangements are also included.

[0015] Furthermore, when a linear image is created using the first light-emitting element row 2 and the second light-emitting element row 3 of the light-emitting component 1, a delay circuit may be used or the image writing timing may be appropriately shifted to perform drawing, taking into consideration, for example, the moving speed of the image holding means 12 in the sub-scanning direction and the arrangement pitch in the sub-scanning direction of the first light-emitting element row 2 and the second light-emitting element row 3. In an embodiment employing a plurality of light-emitting element chips, it is necessary to further take into consideration the arrangement pitch in the sub-scanning direction of the light-emitting element chips and adjust the image writing timing of the odd-numbered light-emitting element row and the even-numbered light-emitting element row.

[0016] 1(c), in this embodiment, an electrode 5 that does not transmit light is disposed on the surface of each light-emitting element 4 of the first and second light-emitting element rows 2 and 3. Therefore, in this example, the region inside the electrode 5 is the light-emitting beam region in which light is emitted from the light-emitting element 4 and emitted toward the target object. The light-emitting beam region w1 of each light-emitting element 4 of the first light-emitting element row 2 and the light-emitting beam region w2 of each light-emitting element 4 of the second light-emitting element row 3 are disposed so as to have no gap in the main scanning direction. In addition, the light emitting point region and the light emitting beam region are determined by the size secured as an opening capable of emitting light, minus the width dimension for separating the light emitting island from the multilayer structure of the light emitting element 4, the width dimension for the etching process, and the electrode width. In this way, by devising the arrangement of the light-emitting elements 4 of the light-emitting component 1 in the main scanning direction, the image formed by the imaging means 6 on the image holding means 12 becomes an image of a beam corresponding to the light-emitting point of each light-emitting element 4 of the light-emitting component 1.

[0017] Next, a representative or preferred embodiment of the light emitting component according to the present embodiment will be described. First, a typical method for selecting the arrangement pitch of the light-emitting points of the first and second light-emitting element rows 2 and 3 is that the arrangement pitch hp along the main scanning direction between the light-emitting points of each light-emitting element 4 of the first light-emitting element row 2 and the light-emitting points of each light-emitting element 4 of the second light-emitting element row 3 is less than or equal to half the arrangement pitch in the main scanning direction between the light-emitting points of each light-emitting element 4 of the first and second light-emitting element rows 2 and 3. Here, in an embodiment in which the light-emitting component 1 has only the first and second light-emitting element rows 2 and 3, the arrangement pitch is a maximum of 1 / 2. However, in an embodiment in which, for example, a third light-emitting element row (not shown) is added in addition to the first and second light-emitting element rows 2 and 3, the arrangement pitch can be less than 1 / 2.

[0018] As a preferred arrangement of the light-emitting points in the main scanning direction, the light-emitting point areas of the adjacent light-emitting elements 4 between the first and second light-emitting element rows 2 and 3 overlap in the main scanning direction by 30 to 70%. This is because if the overlap is too great, the effect of the resolution improvement is small even if the resolution is increased by shifting in the sub-scanning direction, and when the assumption of configuring in two rows in the sub-scanning direction is added, the wiring and the space between the light-emitting elements cannot be sufficiently secured, resulting in an unstable current state, and when three or more rows are used, the light-emitting device becomes large in the sub-scanning direction. Simulation results show that such problems begin to occur when the overlap exceeds 65%, while if the overlap is too small, a sufficient light-emitting point area cannot be secured, resulting in insufficient light intensity, which occurs when the overlap is less than 30%. In the example of Fig. 1(c), the light emitting elements are arranged at 2400 dpi, so that the light emitting elements 4 in the first light emitting element row 2 and the light emitting elements 4 in the second light emitting element row 3 are spaced 10.5 µm apart. Since the width of the cathode layer of the light emitting element is set to 15.4 µm, one light emitting element 4 in the first row overlaps with two adjacent light emitting elements 4 in the second row, so the overlapping area is set to 63.6%. Note that this is not the median of the appropriate values, and the reason for setting the overlapping area to the larger side is also related to the fact that in this embodiment, the electrodes are arranged to cover the light emitted in the light emitting point area. Also, as shown in FIG. 1(c), the inner dimension of the electrode 5 when it is arranged is 10.6 μm, which is almost equal to the pitch of 2400 dpi. Although the entire light-emitting area of ​​the light-emitting element 4 emits light, the light intensity near the sides is weak and the light intensity in the center is strong. The light-emitting area is designed to have a large overlap and to be wide relative to the pitch, so that the electrode 5 is in a state of extracting a portion where a stable light intensity can be obtained. However, if it is made smaller than the pitch, especially when the interval is narrow such as 2400 dpi or more, there is a high possibility that the light intensity will be insufficient, so it is better to have a slight overlap rather than zero overlap with no gap. However, from the viewpoint of resolution, it is better to keep it within 10%. Furthermore, as a preferred arrangement mode of the light-emitting points in the sub-scanning direction, the arrangement pitch in the sub-scanning direction between the light-emitting points of each light-emitting element 4 in the first light-emitting element row 2 and the light-emitting points of each light-emitting element 4 in the second light-emitting element row 3 is an integer N times the imaging line interval. According to this example, if an integer N times the imaging line interval is selected, it is possible to write images of the same line by the first and second light-emitting element rows 2 and 3 by shifting the writing timing by N lines.

[0019] As a preferred embodiment of the imaging means 6 of the optical writing device 11, Each light emitting element 4 and the second light emitting element row 3 Each light emitting element 4 In this example, a gradient index lens is used as the imaging means 6, and light from each of the light-emitting elements 4 in the first light-emitting element row 2 and the second light-emitting element row 3 is made incident on the same gradient index lens. Here, in a case where a gradient index lens is used as the imaging means 6, the first light-emitting element row 2 and the second light-emitting element row 3 are arranged so that the emitted light is incident on the gradient index lens at different positions in the sub-scanning direction. In addition, there are a plurality of light-emitting element chips (not shown) including the first light-emitting element row 2 and the second light-emitting element row 3, and the plurality of light-emitting element chips are arranged in a biased manner in the sub-scanning direction and the main scanning direction, and the imaging means 6 is a plurality of rows of gradient index lenses arranged adjacent to each other in the main scanning direction, and light from each light-emitting element 4 of the same light-emitting element chip is incident on the gradient index lenses arranged in the same row in the main scanning direction, and light from each light-emitting element 4 of adjacent light-emitting element chips is incident on the gradient index lenses in different rows. This example is an embodiment in which a plurality of light-emitting element chips are arranged in a biased manner and a plurality of rows of gradient index lenses are used, and a plurality of rows of gradient index lenses are assigned to the light paths from the biased light-emitting element chips. When light emitted from both light-emitting element chips is incident on the gradient index lenses in the same row, the difference in the light path lengths from both light-emitting element chips becomes large, and the imaging characteristics are easily varied accordingly, whereas this embodiment is preferable in that such an effect is suppressed.

[0020] The present invention will now be described in more detail with reference to the embodiments shown in the accompanying drawings. First embodiment <Overall configuration of image forming apparatus> FIG. 2 shows the overall configuration of the image forming apparatus according to the first embodiment. In the figure, the image forming apparatus 20 is generally called a tandem type image forming apparatus. The image forming apparatus 20 includes an image forming process unit 21 that forms an image corresponding to image data of each color, an image output control unit 40 that controls the image forming process unit 21, and an image processing unit 50 that is connected to, for example, a personal computer (PC) 61 or an image reading device 62 and performs predetermined image processing on image data received from these devices.

[0021] The image forming process unit 21 includes image forming units 22 arranged in parallel at regular intervals. The image forming units 22 are configured with four image creating engines 23 (23a to 23d) which are an example of a toner image forming means for forming toner images of four colors (yellow (Y), magenta (M), cyan (C), and black (K) in this example). Each of the image creating engines 23 (23a to 23d) includes, for example, a drum-shaped photoconductor 24 as an example of an image holding means for forming an electrostatic latent image and holding the toner image, a charger 25 for uniformly charging the surface of the photoconductor 24 with a predetermined potential, an optical writing device 26 for exposing the photoconductor 24 charged by the charger 25 to light to form an electrostatic latent image, and a developer 27 for developing the electrostatic latent image formed by the optical writing device 26. The image forming engines 23 (23a to 23d) form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In addition, the image forming process unit 21 is equipped with a paper transport belt 30 that transports the recording paper, a transfer device (in this example, a transfer roll is used) 31 that transfers the toner image of the photoconductor 24 onto the recording paper, and a fixing device 32 that fixes the toner image to the recording paper, in order to transfer the toner images of each color formed on the photoconductor 24 of each image creating engine 23 (23a to 23d) in a multiplex manner onto the recording paper 29 as an example of a recording medium.

[0022] In this image forming apparatus 20, the image forming process unit 21 performs an image forming operation based on various control signals supplied from the image output control unit 40. Under the control of the image output control unit 40, image data received from a personal computer (PC) 61 or an image reading device 62 is subjected to image processing by the image processing unit 50 and supplied to the image creation engine 23. For example, in the image creation engine 23d for black (K), the photoconductor 24 is charged to a predetermined potential by the charger 25 while rotating in the direction of the arrow, and is exposed by the optical writing device 26 that emits light based on the image data supplied from the image processing unit 50. As a result, an electrostatic latent image for a black (K) image is formed on the photoconductor 24. The electrostatic latent image formed on the photoconductor 24 is developed by the developer 27, and a black (K) toner image is formed on the photoconductor 24. Similarly, in each of the image creation engines 23 (23a to 23c), a toner image of each color, yellow (Y), magenta (M), and cyan (C), is formed.

[0023] The toner images of each color formed on the photoconductor 24 by each image forming engine 23 (23a to 23d) are conveyed to a paper conveying belt moving in the direction of the arrow. 30 The transfer machine transfers the recording paper 29 supplied with the 31 The toners are electrostatically transferred in sequence by a transfer electric field applied to the transfer roll, and a composite toner image is formed on the recording paper 29 in which the toners of the respective colors are superimposed. Thereafter, the recording paper 29 onto which the composite toner image has been electrostatically transferred is transported to the fixing device 32. The composite toner image on the recording paper 29 transported to the fixing device 32 is fixed onto the recording paper 29 by a fixing process using heat and pressure by the fixing device 32, and the recording paper 29 is discharged from the image forming apparatus 20.

[0024] <Configuration example of optical writing device> FIG. 3 shows an example of the configuration of an optical writing device 26 to which this embodiment is applied, and FIG. 4 shows a perspective explanatory view thereof. In the same figure, the optical writing device 26 comprises a device housing 71, a light-emitting element array 72 held in the device housing 71 and having a plurality of LEDs as light-emitting elements, and an imaging lens 73 as an example of an imaging means held in the device housing 71 for imaging the optical output emitted from the light-emitting elements of the light-emitting element array 72 to expose the photosensitive member 24 and form an electrostatic latent image. In this example, the device housing 71 is formed of, for example, metal, holds the light-emitting element array 72 and the imaging lens 73, and is configured to align the light-emitting point L of the light-emitting element 80 of the light-emitting element array 72 with the focal plane of the imaging lens 73. The imaging lens 73 is disposed along the axial direction of the photoconductor 24 (corresponding to the main scanning direction). The light emitting element array 72 is connected via a flexible substrate 74 to a control substrate 75 on which a signal generating circuit 76 (see FIG. 9(a)) is mounted.

[0025] <Configuration example of light-emitting element array> FIG. 5( a ) shows an example of the configuration of the light emitting element array 72 . In the same figure, the light-emitting element array 72 has multiple light-emitting element chips C (C1 to Cn) arranged in a staggered pattern on a circuit board 90, facing each other in two rows in the main scanning direction, and each light-emitting element chip C (C1 to Cn) has light-emitting elements 80 arranged in the main scanning direction.Furthermore, a signal generating circuit 76 mounted on a control board 75 is directly connected to each light-emitting element 80 of the multiple light-emitting element chips C, so that the light emission of each light-emitting element 80 is individually controlled by the signal generating circuit 76. In this example, the light-emitting element chips C are arranged in a staggered pattern to avoid the problem of not being able to maintain uniform spacing between the light-emitting elements 80 at the ends of the light-emitting element chips C when multiple light-emitting element chips C are arranged in one direction.

[0026] -Light emitting element chip- FIG. 5(b) shows a configuration example of the light-emitting element chips C (Ci to Ci+2). In the same figure, among the light-emitting element chips C mounted on the light-emitting element array 72, the odd-numbered light-emitting element chips C (in this example, Ci, Ci+2:i are odd numbers) have a first light-emitting element row 82 of light-emitting elements 80 arranged in the main scanning direction in an area closer to the even-numbered light-emitting element chip C (in this example, Ci+1:i is odd numbers) on the chip substrate 81, and a second light-emitting element row 83 arranged in the main scanning direction so as to be biased in the sub-scanning direction relative to the first light-emitting element row 82 and positioned between each light-emitting element 80 in the first light-emitting element row 82. On the other hand, the even-numbered light-emitting element chip C (in this example, Ci+1:i is odd) has a first light-emitting element row 82 of light-emitting elements 80 arranged in the main scanning direction in an area closer to the odd-numbered light-emitting element chip C (in this example, Ci, Ci+2:i are odd numbers) on the chip substrate 81, and a second light-emitting element row 83 arranged in the main scanning direction so as to be biased in the sub-scanning direction relative to the first light-emitting element row 82 and positioned between each light-emitting element 80 in the first light-emitting element row 82.

[0027] In this example, if the arrangement pitch in the main scanning direction of each light-emitting element 80 in the first light-emitting element row 82 and the second light-emitting element row 83 (corresponding to the distance between the main-scanning direction center lines of adjacent light-emitting elements 80) is P, the arrangement pitch along the main scanning direction between the light-emitting element 80 in the first light-emitting element row 82 and the light-emitting element 80 in the adjacent second light-emitting element row 83 is P / 2. Furthermore, in this example, the distance xc between the main scanning direction center line position of the light emitting element 80 located at the rear end (right end in the figure) of the odd-numbered light emitting element chip C (e.g. Ci) and the main scanning direction center line position of the light emitting element 80 located at the beginning (left end in the figure) of the adjacent even-numbered light emitting element chip C (e.g. Ci+1) is selected to match the arrangement pitch P / 2. Also, the distance xc between the main scanning direction center line position of the light emitting element 80 located at the beginning of the odd-numbered light emitting element chip C (e.g. Ci+2) and the main scanning direction center line position of the light emitting element 80 located at the rear end of the adjacent even-numbered light emitting element chip C (e.g. Ci+1) is also selected to match the arrangement pitch P / 2. In addition, if the center position of the light-emitting point L connecting the center positions in the sub-scanning direction between the first light-emitting element row 82 and the second light-emitting element row 83 of the odd-numbered light-emitting element chip C (Ci, Ci+2) is m1, and the center position of the light-emitting point L connecting the center positions in the sub-scanning direction between the first light-emitting element row 82 and the second light-emitting element row 83 of the even-numbered light-emitting element chip C (Ci+1) is m2, the offset distance yc in the sub-scanning direction between adjacent light-emitting element chips C is selected to be |m1-m2|.

[0028] <Example of arrangement of light emitting elements in the first and second light emitting element rows> In describing an example of the arrangement of the light-emitting elements 80 in the first and second light-emitting element rows 82 and 83, a case in which the arrangement pitch of the light-emitting elements in the light-emitting element array according to the first comparative example is narrowed will first be described. Comparison form 1 In the light-emitting element array 72' of comparative form 1, for example, even if the light-emitting element chips are arranged in a staggered pattern, each light-emitting element chip is arranged in a row of light-emitting elements 80 with an arrangement pitch P in the main scanning direction, as shown in Figure 6(a). At this time, the light emitting points L of the light emitting elements 80 are arranged in the main scanning direction x at an equal arrangement pitch P. Here, a width 2a is required to separate the light emitting islands 91 corresponding to the light emitting point regions of the adjacent light emitting elements 80, and when the light emitting elements 80 are separated by wet etching, if the etching depth is e, it is necessary that a>e. Furthermore, in this example, an electrode 92 that does not transmit light is arranged on the surface of the light emitting element 80. Since the light emitted under the electrode 92 cannot be extracted, it is necessary to secure a width 2b of the electrode 92 as a non-light emitting region. For this reason, it is understood that the region W that can actually emit light (corresponding to the light emitting beam region) among the regions of the light emitting islands 91 of the light emitting element 80 is P-2a-2b. Now, at 1200 dpi (dots per inch), if P = 21-2 μm, a = 2 μm, and b = 2.5 μm, then W = 21.2-4-5 = 12.2 μm.

[0029] Next, in the light-emitting element array 72' according to the comparative embodiment 1, assuming that the arrangement pitch between the light-emitting elements 80 is P / 2 (corresponding to 2400 dpi), as shown in FIG. 6(b), P / 2=10.6 μm, and therefore, when the width 2a for separating the light-emitting islands 91 and the width 2b of the electrodes 92 are subtracted, the width dimension of the area (light-emitting beam area) W of the light-emitting point L that can actually emit light becomes 10.6-4-5=1.6 μm. In this way, the width dimension of the area W of the light-emitting point L that can actually emit light becomes 1.6 / 12.2=1 / 7.6 smaller than the case shown in FIG. 6(a). In this case, the proportion of the light-emitting islands 91 that are hidden by the electrodes 92 also increases, and the light-emitting efficiency decreases. For this reason, the current increases by the amount of the decrease in the light-emitting efficiency, and the light-emitting area decreases, resulting in an increase in current density, which leads to factors that promote deterioration of the light-emitting elements 80, and the reliability of the light-emitting elements 80 decreases.

[0030] In contrast, in the embodiment, each light-emitting element chip C has a first light-emitting element row 82 and a second light-emitting element row 83, as shown in Figure 7(a), and the arrangement pitch of each light-emitting element 80 in the first and second light-emitting element rows 82, 83 along the main scanning direction is P. The arrangement pitch in the main scanning direction between the light-emitting elements 80 in the first light-emitting element row 82 and the light-emitting elements 80 in the adjacent second light-emitting element row 83 is P / 2, and the distance p between them in the sub-scanning direction (in this example, the distance between the sub-scanning direction center line positions of each light-emitting element 80) is selected as an integer N times the line spacing. Furthermore, in this example, among the light-emitting points L (L1, L2) of each light-emitting element 80 in the first and second light-emitting element rows 82, 83, the areas that can actually emit light are all ensured to be approximately the same as those of the light-emitting element array 72' used in comparative embodiment 1. In other words, among the light-emitting points L (L1, L2), the area inside the electrode 92 is the light-emitting beam area W in this example (specifically, W1, W2: in this example, W1=W2). In this example, the light emitting beam area W1 formed by each light emitting element 80 in the first light emitting element row 82 and the light emitting beam area W2 formed by each light emitting element 80 in the second light emitting element row 83 are arranged so that there is no gap in the main scanning direction. Furthermore, the light emission beam area W1 of the light emitting point L (L1) of the light emitting element 80 of the first light emitting element row 82 is selected to overlap with the light emission beam area W2 of the light emitting point L of the light emitting element 80 of the second light emitting element row 83 by ΔW in the main scanning direction. In this example, ΔW is selected to be, for example, 0.05% of the light emission beam area W (W1, W2) of the light emitting point L. Here, if ΔW is a negative value smaller than 0, the overlap in the main scanning direction of the adjacent light emitting points L between the first light emitting element row 82 and the second light emitting element row 83 is likely to become unstable, and if ΔW exceeds 10% of W, there is a concern that the light emitted from the light emitting points L will overlap too much, which may affect the resolution of each light emitting point L. Therefore, in this example, the beam diameter d (specifically, d1, d2), which is diagrammatically represented by a circle, of the light emitted from adjacent light-emitting points L between the first light-emitting element row 82 and the second light-emitting element row 83 overlaps by only an area OL that roughly corresponds to the overlap ΔW of the light-emitting points L in the main scanning direction. Since adjacent light-emitting elements 80 between the first light-emitting element row 82 and the second light-emitting element row 83 are spaced apart by p in the sub-scanning direction, in order to create an image that is lined up in a straight line on the photosensitive member 24, the image can be drawn using an image creation timing or delay circuit that is shifted by N lines.

[0031] - Example of cross-sectional structure of light-emitting element chip - In this example, the light-emitting element chip C uses a self-scanning light-emitting element (SLED: self scanning light emitting diode), and a p-anode layer 101, a light-emitting layer 102, and an n-cathode layer 103 constituting a light-emitting diode LED are laminated on a p-type substrate 100. Grooves are formed in the laminated layers so that the light-emitting element 80 becomes a separate light-emitting point, and a p-anode layer 105, an n-gate layer 106, a p-gate layer 107, and an n-cathode layer 108 constituting a setting thyristor S are laminated via a tunnel junction layer 104. The setting thyristor S has an n-ohmic electrode 111 provided on the n-cathode layer 108 as a cathode electrode, and a p-type ohmic electrode 112 provided on the p-gate layer 107 exposed by removing the n-cathode layer as a gate electrode. The p-anode layer 101 is composed of a lower p-anode layer 101a, a current confinement layer 101b, and an upper p-anode layer 101c. In this example, the light-emitting point regions WA1 and WA2 are the same as the width of the n-cathode layer 103 of the light-emitting diode LED. In other words, the entire width of the n-cathode layer 103, which corresponds to the outer periphery of each light-emitting element 80, is configured to emit light, and the width of the n-cathode layer 103 is considered to be the light-emitting point regions WA1 and WA2, but this is not limiting, and for example, the light-emitting point regions WA1 and WA2 may be made smaller by making the region narrower with the current confinement layer 101b, so that only the central portion of the light-emitting element 80 emits light. Furthermore, the light emitting diode LED emits light in a direction perpendicular to the substrate 100, as indicated by the arrow. Therefore, it can be used when utilizing light emitted in a direction perpendicular to the substrate 100. Since the n-ohmic electrode 111 has an opening in the center, the light passes through the tunnel junction layer 104 and is emitted. Incidentally, a current confinement layer may be provided in the p anode layer 105 of the setting thyristor S, and a current confinement layer may be provided in the n cathode layer 103 of the light emitting diode LED and the n cathode layer 108 of the setting thyristor S. Thus, in this example, the emitted light beam region W (W1, W2) of the light emitting point L of the light emitting element 80 is determined by the width dimension of the current confinement layer 101b and the diameter of the opening of the n-ohmic electrode 111 in the light emission direction.

[0032] -Wiring structure for light-emitting elements- In this example, a gate electrode 120 for applying a light emission start signal from the signal generating circuit 76 is connected to the light emitting points L (specifically, L1, L2) of each light emitting element 80 in the first and second light emitting element rows 82, 83, respectively, as shown in Figure 9(a). Here, the light emitting points L (specifically, L1) of the light emitting elements 80 in the first light emitting element row 82 are connected via the gate electrode 120 on the gate semiconductor layer 121. Furthermore, the light-emitting point L (specifically L2) of the light-emitting element 80 in the second light-emitting element column 83 requires a gate electrode to be wired so as to pass through the area between the light-emitting elements 80 in the first light-emitting element column 82. However, as with the first light-emitting element column 82, if one attempts to wire a gate electrode between each light-emitting element 80, there is a concern that the gate electrode may come into contact with the light-emitting element 80 in the first light-emitting element column 82. Therefore, in this example, as shown in Figures 9(b) and (c), each light-emitting element 80 in the first light-emitting element row 82 and the area between each light-emitting element 80 are covered with a transparent insulating film 122 (e.g., silicon), and an electrode terminal 123 connected to the light-emitting point L (specifically, L2) of each light-emitting element 80 in the second light-emitting element row 83 is provided below this insulating film 122, and a divided gate electrode 124 is installed in the insulating film 122 in the area between the light-emitting elements 80 in the first light-emitting element row 82, and contact holes 125, 126 are opened at the ends of the electrode terminal 123 and the divided gate electrode 124 on the light-emitting element 80 side, respectively. A metal wiring 127 is laid between the contact holes 125, 126 on the insulating film 122, and the metal wiring 127 is connected to the electrode terminal 123 and the divided gate electrode 124 through the contact holes 125, 126. In this example, it is possible to provide a wiring structure for each light-emitting element 80 in the second light-emitting element row 83 without narrowing the width dimension of the light-emitting point area of ​​the light-emitting point L (L1, L2) of each light-emitting element 80 in the first and second light-emitting element rows 82, 83.

[0033] <Drive control of light-emitting element array> FIG. 10 shows a flow chart for controlling the driving of the light-emitting element array in this embodiment. First, image data DT of the main scan line j is read into the signal generating circuit 76 of the control board 75. This image data DT is given to each light-emitting element 80 of each light-emitting element chip C of the light-emitting element array 72 and serves as a signal start signal. First, it is determined whether the light-emitting element chip C is in an odd-numbered row, and then it is determined whether the light-emitting point L of each light-emitting element 80 is in the first row (first light-emitting element row 82). As a result, the image data DT from the signal generating circuit 76 is supplied to the light-emitting elements 80 divided into the following four groups. (1) Light-emitting element chip C is in an odd-numbered row, and the first row of light-emitting points (2) Light-emitting element chip C is in an odd-numbered row, and the light-emitting points are in the second row. (3) Light-emitting element chip C is in an even-numbered row, and the first row of light-emitting points (4) Light-emitting element chip C is in an even-numbered row, and the light-emitting points are in the second row. Here, in the case of (1), as shown in FIG. 5(b), the light-emitting points L1 of the light-emitting elements 80 in the first row of the odd-numbered light-emitting element chips C are driven as targets, and the light-emitting timing is set to A. 5(b), in the case of (2), the light emitting points L2 of the light emitting elements 80 in the second row of the odd-numbered light emitting element chips C are driven as targets, and the light emission timing is set to B. Setting B in this example is such that, compared to setting A, the light emission timing is adjusted taking into consideration the distance p (an integer N times the line distance) in the sub-scanning direction of the light emitting elements 80 between the first and second light emitting element rows 82, 83. Furthermore, in the case of (3), as shown in Fig. 5(b), the light-emitting points L1 of the light-emitting elements 80 in the first row of the even-numbered light-emitting element chips C are driven as targets, and the light-emitting timing is set to C. The C setting in this example is such that, compared to the A setting, the light-emitting timing is adjusted taking into consideration the distance g (corresponding to yc in Fig. 5(b)) in the sub-scanning direction between the light-emitting elements 80 in the first row of the odd-numbered light-emitting element chips C and the light-emitting elements 80 in the first row of the even-numbered light-emitting element chips C. 5(b), in the case of (4), the light-emitting points L2 of the light-emitting elements 80 in the second row of the even-numbered light-emitting element chips C are driven as targets, and the light-emitting timing is set to D. In the case of setting D in this example, the light-emitting timing is adjusted in consideration of the distance h in the sub-scanning direction between the light-emitting elements 80 in the first row of the odd-numbered light-emitting element chips C and the light-emitting elements 80 in the second row of the even-numbered light-emitting element chips C, as compared to setting A.

[0034] <Imaging lens> In this embodiment, as shown in Fig. 3, Fig. 4 and Fig. 11(a)(b), the imaging lens 73 is configured by a lens holder 130 including a pair of side plates 131 extending along the axial direction of the photoconductor 24 and a backing plate 132 closing both ends between the side plates 131, and in the space of the lens holder 130, cylindrical gradient index lenses 135 extending between the light emitting element array 72 and the photoconductor 24 are arranged adjacent to each other in two rows along the axial direction (corresponding to the main scanning direction) of the photoconductor 24 to configure an array. The peripheral wall of the gradient index lenses 135 is covered with a protective layer such as resin. The number of rows of the gradient index lenses 135 is not limited to two rows, and may be three or more rows, or may be one example. In this example, the gradient index lens 135 has a conjugate length TC between the light-emitting point L (corresponding to an object point) of the light-emitting element array 72 and the image point on the photosensitive body 24, and receives the light emitted from the light-emitting point L, passes through the inside of the lens due to the refractive index distribution, and exits to converge on the image point. In this example, the gradient index lens 135 has a length Z0, a distance to the light-emitting point L is L0, and a distance to the image point is Li. The lens diameter D is selected to be four or more times larger (e.g., 40 to 45 μm) than the beam diameter d at the light-emitting point L (e.g., 10 μm). The imaging lens 73 has a lens array in which the gradient index lenses 135 are arranged in two rows and has a total width Wt, which is selected to be equal to or larger than the effective image width Wi.

[0035] <Relationship between light emitting point and image point> In this example, the light-emitting points L (specifically, L1, L2) of each light-emitting element 80 in the light-emitting element array 72 emit light at an arrangement pitch P / 2 along the main scanning direction of adjacent light-emitting elements 80 between the first and second light-emitting element rows 82, 83, as shown in Figure 12. In this state, the light emitted from the light emitting point L is imaged on the photoconductor 24 via the imaging lens 73 . At this time, if the light-emitting element array 72 draws an image (linear image) by linear light extending in the main scanning direction, the image G on the photoconductor 24 is formed as dots at an arrangement pitch of P / 2 as shown in Fig. 12, but the dot-shaped image G overlaps with each other at adjacent locations. In this state, the dot-shaped image G is drawn with overlapping to the same extent as the overlapping of the beam diameter d in the main scanning direction of the light-emitting points L of the light-emitting element array 72, and the overlapping of the dot-shaped image G increases the light amount distribution of the dot-shaped image G. In this example, P is, for example, 1200 dpi, and P / 2 is 2400 dpi.

[0036] <Image quality> -Embodiment 1- In the first embodiment, the light emitted from adjacent light-emitting points L (L1, L2) is imaged on the photoconductor 24 via the imaging lens 73. At this time, adjacent dot-shaped imaging images G corresponding to adjacent light-emitting points L (L1, L2) are drawn with their imaging beam areas partially overlapping, as shown in Figure 13(a), and the light quantity distribution of the dot-shaped imaging images G increases, resulting in a normal density image. Now, assuming that the light-emitting characteristics of some of the light-emitting points L vary, as shown in Figure 13(a), the variation in the light-emitting characteristics of one of the light-emitting points L increases the amount of light due to the overlap of the image G formed by the adjacent light-emitting points L with normal light-emitting characteristics, and therefore the quality of the image G corresponding to the light-emitting points L with varying light-emitting characteristics is corrected to a certain extent. -Comparative form 1- In contrast, when the light-emitting element array according to the comparative embodiment 1 (see FIG. 6) is used, the beam diameters of the light-emitting points L adjacent to each other in the main scanning direction do not overlap, and therefore the image G corresponding to the light-emitting point L depends directly on the light-emitting characteristics of the light-emitting point. In other words, when the light-emitting characteristics of the light-emitting point L are normal, the dot-shaped image G will depict a normal density image as shown in FIG. 13(b), but when the light-emitting characteristics of the light-emitting points L vary, the light amount distribution of the dot-shaped image G will be insufficient as shown in FIG. 13(b), and there is a concern that, for example, sufficient image density cannot be obtained.

[0037] -Effects of imaging lens layout- Now, assuming that the imaging lens 73 is installed in an ideal position, in both embodiment 1 and comparative embodiment 1, when the light-emitting element array 72 draws a linear image extending in the main scanning direction, the light emitted from the light-emitting point L of the light-emitting element array 72 is incident along the center position in the arrangement direction of the refractive index distribution lens 135 that constitutes the imaging lens 73. At this time, in embodiment 1, the light-emitting element array 72 writes an optical image using light-emitting points L arranged at an arrangement pitch P in the first light-emitting element row 82 and the second light-emitting element row 83, and draws at an arrangement pitch of P / 2 in the main scanning direction. Therefore, as shown in Figure 14(a), it is possible to form an optical image with a large amount of light on the photosensitive body 24 side while ensuring a large light-emitting area of ​​the light-emitting points L and by partially overlapping the beam diameters emitted from the light-emitting points L. In the light-emitting element array of comparative embodiment 1, when the light-emitting points L are arranged at an arrangement pitch of P / 2, as shown in Figure 6(b), the light-emitting area of ​​the light-emitting points L is small and the amount of light emitted from the light-emitting points L is also small. -Tilt and misalignment of imaging lens- Furthermore, when installing the imaging lens 73, the imaging lens 73 may be tilted or oar-set. In such a case, the light emitted from the light emitting point L of the light emitting element array 72 is incident on a position offset from the center line of the gradient index lens 135 in the arrangement direction, as shown in FIG. 14(b). At this time, in the light-emitting element array 72 of embodiment 1, it is possible to form an optical image with a large amount of light on the photosensitive body 24 side while ensuring a large light-emitting area of ​​the light-emitting point L and by partially overlapping the beam diameters emitted from the light-emitting point L, so even if the amount of light that can be picked up is slightly reduced due to the inclination θ or offset of the imaging lens 73, this is compensated for by the increase in the amount of light due to the overlap of the beam diameters, and the reduction in the amount of light of the optical image is mitigated. In this regard, in the light-emitting element array of comparative embodiment 1, since there is no light quantity compensation as in embodiment 1, if the amount of light that can be picked up decreases due to the inclination or offset of the imaging lens 73, there is a concern that this will directly affect the quality of the image formed.

[0038] -How light-emitting element chips are incident on the imaging lens due to their staggered arrangement- In this embodiment, the light-emitting element array 72 has multiple light-emitting element chips C arranged in a staggered pattern, and each light-emitting element chip C has first and second light-emitting element rows 82, 83 arranged in the main scanning direction at an arrangement pitch P. Furthermore, the light-emitting points L of adjacent light-emitting elements 80 between the first light-emitting element row 82 and the second light-emitting element row 83 are arranged in the main scanning direction at an arrangement pitch of P / 2, and the beam diameters emitted from the light-emitting points L are partially overlapped. Therefore, in this embodiment, as shown in Figure 15(a), light Bm1 emitted from the light-emitting point L of the light-emitting element chip C located at an odd-numbered position among the light-emitting element chips C passes through the refractive index distribution lens 135 in the first row, while light Bm2 emitted from the light-emitting point L of the light-emitting element chip C located at an even-numbered position passes through the refractive index distribution lens 135 in the second row. In this way, the light emitted from the staggered light-emitting element chips C is distributed to and incident on the first and second rows of gradient index lenses 135. The amount of incident light at this time is greater than that in the light-emitting element array according to comparative embodiment 1 (see FIG. 15(b)) since the beam diameters from the light-emitting points L partially overlap. Furthermore, even if the imaging lens 73 is tilted or offset, the lens diameter D of the refractive index distribution lens 135 is sufficiently larger than the beam diameter, so that the light emitted from the staggered light-emitting element chips C is distributed and incident on the first and second rows of refractive index distribution lenses 135, making it possible to obtain the imaging characteristics of the imaging lens 73.

[0039] ◎Transformation form 1 FIG. 16 shows a main part of a light-emitting element array according to the first modified embodiment. In the same figure, the light-emitting element array 72 has a plurality of light-emitting element chips C arranged in a staggered pattern, as in embodiment 1, but unlike embodiment 1, each light-emitting element chip C has first, second and third light-emitting element rows 82, 83 and 84. In this example, the odd-numbered light-emitting element chip C (Ci, Ci+2:i = odd number) has a first light-emitting element row 82, a second light-emitting element row 83, and a third light-emitting element row 84, arranged from a position away from the even-numbered light-emitting element chip C (Ci+1:i = odd number) toward a position approaching it. In this example, the first to third light emitting element rows 82, 83, and 84 are each formed by arranging the light emitting elements 80 at an arrangement pitch P along the main scanning direction. The light-emitting elements 80 in the first light-emitting element row 82 and the light-emitting elements 80 in the second light-emitting element row 83 are arranged at an arrangement pitch of P / 3 in the main scanning direction, and the light-emitting elements 80 in the second light-emitting element row 83 and the light-emitting elements 80 in the third light-emitting element row 84 are arranged at an arrangement pitch of P / 3 in the main scanning direction.

[0040] In addition, the light-emitting point L (specifically, L1) of the light-emitting element 80 in the first light-emitting element row 82 and the light-emitting point L (specifically, L2) of the light-emitting element 80 in the second light-emitting element row 83 are arranged so as to overlap partially in the main scanning direction, and the light-emitting point L (specifically, L2) of the light-emitting element 80 in the second light-emitting element row 83 and the light-emitting point L (specifically, L3) of the light-emitting element 80 in the third light-emitting element row 84 are arranged so as to overlap partially in the main scanning direction. The first to third light emitting element rows 82, 83, and 84 are arranged at intervals of an integer N times the line interval in the sub-scanning direction. In addition, the even-numbered light-emitting element chip C (Ci+1:i = odd number) has a first light-emitting element row 82, a second light-emitting element row 83, and a third light-emitting element row 84, arranged from a position close to the odd-numbered light-emitting element chip C (Ci, Ci+2:i = odd number) toward a position away from the odd-numbered light-emitting element chip C (Ci, Ci+2:i = odd number). Here, the configurations of the first to third light-emitting element rows 82, 83, and 84 are substantially the same as those of the odd-numbered light-emitting element chips C. In addition, in Figure 16, xc indicates the distance between the main scanning direction center line position of the first light-emitting element 80 of an odd-numbered light-emitting element chip C (e.g., Ci+2) and the main scanning direction center line position of the last light-emitting element 80 of an adjacent even-numbered light-emitting element chip C (e.g., Ci+1), and in this example is selected to match the array pitch P / 3. In addition, if the center position of the light-emitting point L connecting the center positions of the second light-emitting element rows 83 of the odd-numbered light-emitting element chips C (Ci, Ci+2) in the sub-scanning direction is m1, and the center position of the light-emitting point L connecting the center positions of the second light-emitting element rows 83 of the even-numbered light-emitting element chips C (Ci+1) in the sub-scanning direction is m2, the offset distance yc in the sub-scanning direction of adjacent light-emitting element chips C is selected to be |m1-m2|.

[0041] According to this embodiment, each light-emitting element chip C of the light-emitting element array 72 is provided with three light-emitting element rows 82 to 84, with the first light-emitting element row 82 being assigned to light-emitting points L of 1, 4, 7... (specifically, L1), the second light-emitting element row 83 being assigned to light-emitting points L of 2, 5, 8... (specifically, L2), and the third light-emitting element row 84 being assigned to light-emitting points L of 3, 6, 9... (specifically, L3). Therefore, in this example, in each light-emitting element chip C, an image may be formed on the photoconductor 21 by adjusting the light-emitting timing of the light-emitting points L of the three light-emitting element rows 82 to 84. In particular, in this example, if P is 800 dpi, then P / 3=2400 dpi, and therefore, like the first embodiment, an image of 2400 dpi can be formed. In this embodiment, the light-emitting element chip C is provided with three light-emitting element rows 82 to 84, but the present invention is not limited to this, and it is also possible to use, for example, four or more light-emitting element rows. EXAMPLES

[0042] Example 1 In this example, an image forming apparatus according to the first embodiment is embodied, and a light amount profile of the light emitting element array of the optical writing device and a print sample are obtained. FIG. 17(a) shows the light amount distribution of the light emitting element array of the optical writing device according to the first embodiment (denoted by LPH in the drawing). In the figure, the luminance of the beam emitted from the light emitting point of the light emitting element of the light emitting element array is shown. For comparison, a light quantity profile using a surface emitting laser (denoted by ROS in the figure) was compared, and it was confirmed that the light quantity distribution of the light emitting element array according to the embodiment was large. Although the light amount distribution in FIG. 17(a) is shown in the sub-scanning direction, a similar tendency was observed in the main scanning direction. Also, as shown in Fig. 17(b), when a print sample of 2400 dpi characters was taken, high-definition image reproduction was confirmed. The evaluation conditions were: best focus, ladder 600 dpi / 2on2off, and characters 4pt Mincho. For comparison, when a print sample was taken using a surface-emitting laser, the print sample according to the embodiment was finer. [Explanation of symbols]

[0043] 1...light emitting component, 2...first light emitting element row, 3...second light emitting element row, 4...light emitting element, 5...electrode, 6...imaging means, 10...image forming device, 11...optical writing device, 12...image holding means, WA1, WA2...light emitting point area, W1, W2...light emitting beam area

Claims

1. a first light emitting element row including light emitting elements arranged in a main scanning direction; a second light-emitting element row arranged in the main scanning direction so as to be offset from the first light-emitting element row in the sub-scanning direction and positioned between each light-emitting element in the first light-emitting element row, an arrangement pitch in a main scanning direction between a light emitting point of each light emitting element of the first light emitting element row and a light emitting point of each light emitting element of the second light emitting element row is equal to or smaller than ½ of an arrangement pitch in the main scanning direction between the light emitting points of each light emitting element of the first and second light emitting element rows; a light-emitting point region, which is a region where each light-emitting element of the first light-emitting element row emits light, and a light-emitting point region, which is a region where each light-emitting element of the second light-emitting element row emits light, are arranged so as to overlap with each other in a main scanning direction; the light-emitting point regions of adjacent light-emitting elements between the first and second light-emitting element rows overlap in a range of 30 to 70% in the main scanning direction; an emission beam region in which light is emitted toward an object from a portion of an emission point region, which is a region in which each light-emitting element of the first light-emitting element row emits light, other than the non-transparent electrodes arranged around the region, and an emission beam region in which light is emitted toward an object from a portion of an emission point region, which is a region in which each light-emitting element of the second light-emitting element row emits light, other than the non-transparent electrodes arranged around the region, are arranged so as to have no gaps in the main scanning direction; The light emitting component is characterized in that the light emitting beam areas of adjacent light emitting elements between the first and second light emitting element rows overlap each other in the main scanning direction within a range of 0 to 10%.

2. 2. The light emitting component according to claim 1, A light-emitting component characterized in that an arrangement pitch along the sub-scanning direction between light-emitting points caused by each light-emitting element of the first light-emitting element row and light-emitting points caused by each light-emitting element of the second light-emitting element row is an integer N times the spacing between image-forming lines.

3. A light emitting component according to claim 1 or 2; an image forming means for forming an image of the light emitted from each light-emitting element of the light-emitting component on an image holding means capable of holding an image formed by light, and an optical writing device characterized in that the optical image is written onto the image holding means.

4. 4. The optical writing device according to claim 3, The optical writing device is characterized in that the imaging means is a refractive index distribution lens arranged in the main scanning direction, the diameter of which is larger than the difference in the sub-scanning direction between each light-emitting element of the first light-emitting element row and each light-emitting element of the second light-emitting element row.

5. 5. The optical writing device according to claim 4, The optical writing device according to claim 1, wherein the first light emitting element row and the second light emitting element row emit light beams incident on the refractive index distribution lens at different positions in the sub-scanning direction.

6. 6. The optical writing device according to claim 5, a plurality of light-emitting element chips each including the first light-emitting element row and the second light-emitting element row; The plurality of light-emitting element chips are arranged to be biased in a sub-scanning direction and a main scanning direction, the imaging means has the gradient index lenses arranged adjacent to each other in a plurality of rows in the main scanning direction, An optical writing device characterized in that light from each light-emitting element of the same light-emitting element chip is incident on the same row of refractive index distribution lenses aligned in the main scanning direction, and light from each light-emitting element of adjacent light-emitting element chips is incident on refractive index distribution lenses in different rows.

7. An optical writing device according to any one of claims 3 to 6, an image holding unit provided opposite the optical writing device, for holding an image formed by light written by the optical writing device;

8. 8. The image forming apparatus according to claim 7, The image forming apparatus is characterized in that, when a linear image along the main scanning direction is written onto the image holding means using light emitted from each light-emitting element of the first light-emitting element row and the second light-emitting element row, the imaging beam areas corresponding to adjacent light-emitting points in the main scanning direction are arranged to overlap.

Images