JP4508817B2 - Exposure head and image forming apparatus using the same - Google Patents

Description

The present invention relates to an exposure head that exposes light emitted from an organic EL light emitting element array onto a photosensitive member by an imaging optical system, and an image forming apparatus using the exposure head .

Conventionally, in an image forming apparatus such as a copying machine, a printer, and a fax machine using electrophotography, a laser beam emitted from a laser light source is scanned as a writing unit by using a rotating polygon mirror (photosensitive mirror), and photosensitive. An image forming apparatus that forms an electrostatic latent image on a body and an image forming apparatus that forms an electrostatic latent image on a photosensitive member using an LED array in which a plurality of LED elements are linearly arranged are known. An image forming apparatus in which organic EL light emitting elements are linearly arranged is also known.
JP-A-2-273258 JP 11-198433 A Japanese Patent Laid-Open No. 2000-50816 JP 2000-103114 A

  However, in the case of the exposure method using a laser beam, optical parts such as a polygon mirror and a lens are required, and there is a problem that it is difficult to reduce the size of the apparatus and it is difficult to increase the speed. Further, in a color image forming apparatus having a tandem arrangement, it is difficult to improve the scanning position accuracy of the four scanning beams, causing a problem of color misregistration and deterioration of image quality.

  In the case of an exposure method using an LED array in which a large number of minute LED elements are arranged in a straight line, the LED element can generally obtain high brightness, but the LED element is basically manufactured using a semiconductor process. The substrate is expensive and cannot be made long because of the manufacturing yield, and it is necessary to arrange a large number of chips in a row. At this time, there is a problem that the difference in level difference between the chips and the gap causes variation in luminance, and density unevenness appears remarkably in the image.

An organic EL light emitting device using an organic material for the light emitting layer is easier to manufacture than other light emitting devices and has a small amount of heat generation. It can be thin and lightweight. However, since the emission wavelength of the organic EL light emitting element has a wide half-value width of about 100 nm, the effective wavelength distribution (the emission wavelength distribution viewed from the photoreceptor) also has a wide half-value width of about 100 nm. FIG. 8 shows an imaging state of the writing light from the light emitting portion 8 of the organic EL light emitting element on the photosensitive member 2 through the rod lens 3. Since the organic EL light emitting element has a wide emission wavelength distribution, a long wavelength light beam indicated by a dotted line forms an image with a large spot diameter on the photosensitive member 2 due to the chromatic aberration of the rod lens 3. FIG. 9 is a diagram comparing the emission intensity and the spot diameter of a single wavelength with writing light having a wide wavelength distribution such as an organic EL light emitting device. There is a problem that the spot diameter (dotted line) of the writing light of the organic EL light emitting device having a wide wavelength distribution is larger than the spot diameter (solid line) of the writing light having a single wavelength, and it is difficult to form a clear image. appear. When the spot diameter increases, the outline of the image becomes unclear and affects the image quality.
As disclosed in Japanese Patent Laid-Open Nos. 2000-50816 and 2000-103114, a plurality of lines in which a plurality of organic EL light emitting elements are arranged in the main scanning direction of the photosensitive member are arranged in a plurality of rows in the sub-scanning direction of the photosensitive member. In the case of an image forming apparatus that performs multiple exposure of the same pixel on the photoconductor with a plurality of lines in the sub-scanning direction, when expressing gradation by PWM (pulse width modulation) control, a plurality of columns of organic EL light emission Since the spot of the element is exposed on the same pixel on the photoconductor, the accuracy of the shape of the spot of the photoconductor greatly affects the image quality.

The present invention solves the above-mentioned problems of the prior art, prevents the increase of the spot diameter caused by the wavelength distribution of the organic EL light emitting element, and has an exposure head composed of an organic EL light emitting element line head with good image quality. An object is to provide an image forming apparatus using the same .

In order to solve the above-described problems, an exposure head according to the present invention includes a light-emitting element composed of an organic EL light- emitting element, a rod lens array including a plurality of gradient index rod lenses, and a pair of the gradient index rod lenses. A plurality of chromatic aberration correction lenses corresponding to each other , wherein the chromatic aberration correction lenses are arranged in a line on a substrate, and the image forming apparatus of the present invention includes a photosensitive member, a charging unit, and a charging unit. Means, a light emitting element composed of an organic EL light emitting element, a rod lens array in which a plurality of gradient index rod lenses are arranged, and a linear pattern on the substrate so as to correspond to the gradient index rod lens on a one-to-one basis. The image forming apparatus of the present invention is configured by arranging a plurality of the light emitting elements in a straight line. The exposure head includes a plurality of chromatic aberration correction lenses, and a developing device. A plurality of lines are arranged in the sub-scanning direction of the photoconductor, and in the image forming apparatus of the present invention , the rod lens array is arranged in the plurality of rows arranged in the sub-scanning direction of the photoconductor. One is arranged for each line.
more than

An imaging optical system in which a plurality of organic EL light emitting elements are arranged in a line on a substrate, and the light emitted from the organic EL light emitting elements is arranged in a line so as to correspond to the lines of the organic EL light emitting elements. In the image forming apparatus that exposes the photosensitive member through the image forming apparatus, the chromatic aberration correcting lens is formed separately and arranged to correspond to the image forming optical system on a one-to-one basis, thereby forming the image forming optical by the wavelength distribution of the organic EL light emitting element. An increase in the spot diameter can be prevented by the chromatic aberration of the system, an image with good image quality can be obtained, and the chromatic aberration correction lens is arranged so as to correspond to the imaging optical system on a one-to-one basis. improves. In addition, since the chromatic aberration correction lens is arranged separately from the optical system of the image forming apparatus, the chromatic aberration correction lens can be easily manufactured and can be easily arranged.
A plurality of chromatic aberration correction lenses are arranged in a line on a long substrate and are integrally formed, and each chromatic aberration correction lens formed on the long substrate has a one-to-one correspondence with the imaging optical system arranged in a line. With such a configuration, the chromatic aberration correction lens can be easily manufactured and can be easily positioned and arranged in the optical system.
By measuring the center position of the chromatic aberration correction lens and the center position of the imaging optical system with an optical device and calculating the amount of positional deviation between them, the positioning of the chromatic aberration correction lens with respect to the imaging optical system can be performed with high accuracy. This makes it possible to correct chromatic aberration.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of an exposure means 1 on a photoreceptor 2 using an organic EL light emitting device 6 of the present invention. The exposure unit 1 includes an opaque housing 4 in which a gradient index rod lens 3 is stacked and attached so as to face the photoreceptor 2 and communicate with the inside and outside. The gradient index rod lens 3 is formed as a cylindrical transparent body whose refractive index is continuously distributed from the center toward the periphery. The plurality of rod lenses 3 constitutes a rod lens array 3 ′ arranged linearly. The rod lens array 3 ′ is arranged in at least one row in the sub-scanning direction of the photoreceptor 2. An organic EL light emitting element 6 formed on a substrate 5 mounted facing the rear surface of the gradient index rod lens array 3 ′ in the opaque housing 4 is disposed. A plurality of organic EL light emitting elements 6 are linearly arranged to constitute an organic EL light emitting element array 6 '. A plurality of organic EL light emitting element arrays 6 ′ are arranged in the sub-scanning direction of the photoreceptor 2. The rod lens array 3 'and the organic EL light emitting element array 6' are positioned so as to correspond to each other. Between the organic EL light emitting element array 6 ′ and the rod lens array 3 ′, a chromatic aberration correction lens 25 for correcting chromatic aberration is arranged so as to correspond to each rod lens 3 of the rod lens array 3 ′ on a one-to-one basis. The chromatic aberration correction lens 25 is formed separately as a long body extending in the direction in which the rod lens array 3 'extends. The opaque cover 7 shields the organic EL light emitting element array 6 ′ from the back of the opaque housing 4, and the housing 4 is pressed by pressing the opaque cover 7 against the back of the housing 4 by a fixed plate spring 24. It is designed to seal light tightly.

    FIG. 2 is an enlarged view of the chromatic aberration correcting lens 25 of the present invention. The chromatic aberration correction lens 25 is formed on the long substrate 30 by means such as an ink jet method. On the long substrate 30, a plurality of chromatic aberration correction lenses 25 are arranged in a line in at least one row. The chromatic aberration correction lens 25 on the long substrate 30 is arranged so as to correspond to the rod lens 3 arranged in a line on a one-to-one basis. FIG. 3 shows a chromatic aberration correction lens 25 arranged in a line on a long substrate 30 and a rod lens array 3 ′ arranged in a line on a plurality of rod lenses 3, and each chromatic aberration correction lens 25 and each rod lens 3. Are arranged so as to correspond one-to-one.

  FIG. 4 shows a configuration for positioning the chromatic aberration correction lens 25 with respect to the rod lens 3 which is an imaging optical system. As shown in FIG. 4, a deviation amount between the center position 28 of the rod lens 3 and the center position 29 of the chromatic aberration correction lens 25 is detected by an optical device 30 such as a camera, and the chromatic aberration correction lens 25 is changed to the rod lens 3. Place it in the correct position.

  FIG. 5 shows a cross-sectional view of an example near the light emitting portion 8 of the organic EL light emitting element 6 of the exposure means 1. In the organic EL light emitting element 6, for example, a TFT 9 made of polysilicon having a thickness of 50 nm for controlling the light emission of the light emitting unit 8 is provided on the substrate 5 having a thickness of 0.5 mm corresponding to the light emitting unit 8. An insulating film 10 made of SiO 2 having a thickness of about 100 nm is formed on the substrate 5 except for the contact hole on the TFT 9. An anode 11 made of ITO having a thickness of 150 nm is formed in one of the light emitting portions 8 so as to be connected to the TFT 9 through the contact hole. In a portion corresponding to a position other than the light emitting portion 8, another insulating film 12 made of SiO2 having a thickness of about 120 nm is formed. A bank 14 made of polyimide having a thickness of 2 μm and having a hole 13 corresponding to the light emitting portion 8 is provided on the insulating film 12. A hole injection layer 15 having a thickness of 50 nm and a light emitting layer 16 having a thickness of 50 nm are formed in this order from the anode 11 in the hole 13 of the bank 14. A cathode first layer 17 made of Ca having a thickness of 100 nm and a cathode second layer 18 made of Al having a thickness of 200 nm are sequentially formed so as to cover the upper surface of the light emitting layer 16, the inner surface of the hole 13, and the outer surface of the bank 14. The light emitting portion 8 of the organic EL light emitting element 6 is formed by being covered with a cover glass 20 having a thickness of about 1 mm via an inert gas 19 such as nitrogen gas. Light emission from the light emitting unit 8 is performed on the substrate 5 side.

    FIG. 6 is a perspective view showing the exposure means 1 positioned and arranged with respect to the photoconductor 2 attached to the photoconductor unit. A plurality of lines in which a plurality of organic EL light emitting elements 6 are arranged in a straight line are arranged in the sub-scanning direction of the photosensitive member 2, and the pixels on the photosensitive member 2 are exposed by one line of the organic EL light emitting element array 6 ′. Then, an image apparatus is shown in which the photosensitive member 2 is moved, and multiple exposure is performed by superimposing the pixel on the organic EL light emitting element array 6 'in the next line. The rod lens array 3 ′ is arranged in a plurality of rows so as to correspond to the organic EL light emitting element array 6 ′ arranged in a plurality of rows. Further, one rod lens array 3 ′ corresponds to one-to-N (N: integer greater than or equal to 2), such as one for a plurality of organic EL light emitting element arrays 6 ′ arranged in the sub-scanning direction. You may arrange. A chromatic aberration correction lens 25 formed separately is disposed between the light emitting portion 8 of the organic EL light emitting element array 6 ′ and the photosensitive member 2 so as to correspond to the rod lens 3 on a one-to-one basis. That is, if the separately formed chromatic aberration correction lens 25 is positioned and arranged so as to correspond to the rod lens 3 on a one-to-one basis, the rod lens can be arranged between the light emitting unit 8 and the rod lens 3. 3 and the photosensitive member 2 may be disposed. The exposure means 1 is held in a long opaque housing 4. The positioning pins 21 provided at both ends of the long opaque housing 4 are fitted into the opposing positioning holes of the case of the photosensitive unit, and the fixing screws are passed through the fixing screw holes 22 provided at both ends of the long opaque housing 4. Is fixed by screwing it into the screw hole of the case, and the exposure means 1 is fixed at a predetermined position. Reference numeral 23 denotes a drive circuit.

    In the present invention, the exposure means 1 using the organic EL array of the present invention as described above is used for an exposure head of an electrophotographic color image forming apparatus, for example. FIG. 7 shows tandem color image formation in which four organic EL array exposure heads 1K, 1C, 1M, and 1Y are arranged at the exposure positions of corresponding four photosensitive drums 41K, 41C, 41M, and 41Y, respectively. It is a front view which shows the schematic structure of the whole example of an apparatus. As shown in FIG. 7, this image forming apparatus is tensioned by a driving roller 51, a driven roller 52, and a tension roller 53, and is intermediately transferred by being circulated in the direction indicated by the arrow (counterclockwise). Photoconductors 41K, 41C, 41M, and 41Y having a belt 50 and having photosensitive layers on the outer peripheral surfaces as four photoconductors arranged at a predetermined interval with respect to the intermediate transfer belt 50 are arranged. “K”, “C”, “M”, and “Y” added after the symbols mean black, cyan, magenta, and yellow, respectively, and indicate that the photoconductors are for black, cyan, magenta, and yellow, respectively. The same applies to other members. The photoconductors 41K, 41C, 41M, and 41Y are driven to rotate in the direction indicated by the arrow (clockwise) in synchronization with the driving of the intermediate transfer belt 50, but around each photoconductor 41 (K, C, M, Y). Are respectively charging means (corona charger) 42 (K, C, M, Y) for uniformly charging the outer peripheral surface of the photoconductor 41 (K, C, M, Y) and this charging means 42 (K, The organic EL array exposure as described above according to the present invention, in which the outer peripheral surface uniformly charged by C, M, Y) is sequentially scanned in line in synchronization with the rotation of the photoconductor 41 (K, C, M, Y). A toner as a developer is applied to the electrostatic latent image formed by the head 1 (K, C, M, Y) and the organic EL array exposure head 1 (K, C, M, Y) to form a visible image. Developing with the developing device 44 (K, C, M, Y) as a (toner image) and the developing device 44 (K, C, M, Y) A primary transfer roller 45 (K, C, M, Y) as transfer means for sequentially transferring the toner image to the intermediate transfer belt 50 as a primary transfer target, and a photoreceptor 41 (K, C, M, And a cleaning device 46 (K, C, M, Y) as a cleaning means for removing the toner remaining on the surface of Y).

  The organic EL array exposure head 1 (K, C, M, Y) used in FIG. 7 corrects the chromatic aberration formed separately so as to correspond to each rod lens array 3 ′, as shown in FIG. A chromatic aberration correction lens 25 is disposed between the organic EL light emitting element exposure head 1 (K, C, M, Y) and the photoreceptor 2 so as to correspond to the rod lens 3 on a one-to-one basis. That is, the arrangement of the chromatic aberration correction lens 25 formed separately may be arranged between the organic EL array exposure head 1 (K, C, M, Y) and the rod lens array 3 ′, or the rod lens array 3. 'And the photosensitive member 41 (K, C, M, Y).

  The developing device 44 (K, C, M, Y) uses, for example, a non-magnetic one-component toner as a developer, and the one-component developer is conveyed to the developing roller by a supply roller, for example, and adheres to the surface of the developing roller. The film thickness of the developed developer is regulated by a regulation blade, and the potential of the photoreceptor 41 (K, C, M, Y) is adjusted by bringing the developing roller into contact with or pushing the photoreceptor 41 (K, C, M, Y). The toner image is developed by attaching a developer according to the level.

  The black, cyan, magenta, and yellow toner images formed by the four-color single-color toner image forming station are intermediated by the primary transfer bias applied to the primary transfer roller 45 (K, C, M, Y). The toner image, which is sequentially primary transferred onto the transfer belt 50 and sequentially superposed on the intermediate transfer belt 50 to become a full color, is secondarily transferred to a recording medium P such as paper by a secondary transfer roller 66, and serves as a fixing unit. The toner is fixed on the recording medium P by passing through the fixing roller pair 61, and is discharged onto a paper discharge tray 68 formed in the upper part of the apparatus by a paper discharge roller pair 62.

  In FIG. 7, reference numeral 63 denotes a paper feed cassette in which a large number of recording media P are stacked and held, 64 denotes a pickup roller for feeding the recording media P one by one from the paper feed cassette 63, and 65 denotes a secondary transfer roller. A pair of gate rollers for defining the supply timing of the recording medium P to the secondary transfer portion 66, a secondary transfer roller 66 as a secondary transfer means for forming a secondary transfer portion with the intermediate transfer belt 50, 67 Is a cleaning blade as a cleaning means for removing the toner remaining on the surface of the intermediate transfer belt 50 after the secondary transfer.

Is a diagram showing an embodiment of an exposure head of the present invention. Is a diagram showing an embodiment of an exposure head of the present invention. Is a diagram showing an embodiment of an exposure head of the present invention. Is a diagram showing an embodiment of an exposure head of the present invention. Is a diagram showing an embodiment of an exposure head of the present invention. Is a diagram showing an embodiment of an exposure head of the present invention. 1 is a diagram showing an embodiment of an image forming apparatus of the present invention. It is a figure which shows a prior art. It is a figure which shows a prior art.

Explanation of symbols

1: Exposure means 1 (K, C, M, Y): Organic EL array exposure head 2: Photoconductor 3: Rod lens 3 ′: Rod lens array 4: Housing 5: Substrate 6: Organic EL light emitting element 6 ′: Organic EL light emitting element array 7: Opaque cover 8: Light emitting part 9: TFT
10: Insulating film 11: Anode 12: Insulating film 13: Hole 14: Bank 15: Hole injection layer 16: Light emitting layer 17: First cathode layer 18: Second cathode layer 19: Inert gas 20: Cover glass 21: Positioning pin 22: Fixing screw hole 23: Drive circuit 24: Fixing plate spring 25: Chromatic aberration correction lens 26: First lens of chromatic aberration correction lens 27: Second lens of chromatic aberration correction lens 28: Center position of rod lens 29: Correction of chromatic aberration Lens center position 30: Long substrate 42 (K, C, M, Y): Photosensitive drum 44 (K, C, M, Y): Charging means (corona charger)
45 (K, C, M, Y): Developer 46 (K, C, M, Y): Primary transfer roller 50: Cleaning device 51: Intermediate transfer belt 52: Drive roller 53: Drive roller 61: Tension roller 62: Fixing roller pair 63: Paper discharge roller pair 64: Paper feed cassette 65: Pickup roller 66: Gate roller pair 67: Secondary transfer roller 68: Cleaning blade S: Paper discharge tray P: Recording medium

Claims (4)

A light emitting device comprising an organic EL light emitting device;
A rod lens array in which a plurality of gradient index rod lenses are arranged;
A plurality of chromatic aberration correction lenses corresponding one-to-one with the gradient index rod lens;
Have
The exposure head according to claim 1, wherein the chromatic aberration correction lens is arranged in a line on a substrate. A photoreceptor,
Charging means;
A light emitting element composed of an organic EL light emitting element, a rod lens array in which a plurality of gradient index rod lenses are arranged, and a linear arrangement on the substrate so as to correspond one-to-one with the gradient index rod lens. An exposure head having a plurality of chromatic aberration correction lenses;
A developing device;
An image forming apparatus comprising: The image forming apparatus according to claim 2 , wherein a plurality of lines each including a plurality of light emitting elements arranged in a straight line are arranged in a sub-scanning direction of the photoconductor. The image forming apparatus according to claim 3 , wherein one rod lens array is arranged for the plurality of lines arranged in the sub-scanning direction of the photoconductor.

Images