JP2010002866A - Optical scanner, image forming apparatus and method of adjusting light quantity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner, which scans a face to be scanned with light emitted from a light source, furnished with a light quantity adjustment element which adjusts the efficiency of light utility for each optical scanner and reduces the intensity of ghost light, to provide an image forming apparatus having the optical scanner, such as a copying machine, a facsimile, a printer and an optical plotter, and to provide a method of adjusting light quantity using a light quantity element in the optical scanner. <P>SOLUTION: Optical systems 112K, 113K, 114K, 116, 117a, 118K and 119K are used to guide light emitted from a light source 111K onto a face to be scanned 20K, and a light quantity adjustment element 114K which is disposed in the optical path of the light emitted from the light source is used in which the light transmittance thereof is selected so that a first ratio fits into a first range corresponding to a second ratio of the intensity of emitted light to the intensity of light which passes through the optical systems and scans the face to be scanned, when the second ratio fits into a second range, and the light quantity adjustment element has different light transmittances on the incident surface and emitting surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is an optical scanning device that scans a surface to be scanned with light emitted from a light source, and includes a light amount adjusting element that adjusts a ratio between the intensity of the light and the intensity of light that scans the surface to be scanned. The present invention relates to an optical scanning device, an image forming apparatus such as a copying machine, a facsimile, a printer, and an optical plotter having the optical scanning device, and a light amount adjustment method using the light amount adjustment element in the optical scanning device.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines, facsimile machines, printers, and optical plotters emit light from a light source based on information corresponding to an image to be formed, and the object on the image carrier is emitted by the emitted light. Optical scanning devices that scan a scanning surface are known (see, for example, [Patent Document 1] to [Patent Document 4]). Such an optical scanning device includes an optical system that guides light emitted from a light source to a surface to be scanned.

  This optical system is composed of various optical elements such as a deflector such as a polygon mirror, a cylindrical lens, and a scanning lens. However, each optical element has variations in optical characteristics such as light transmittance and reflectance. In addition, the optical characteristics change depending on the incident angle of light to each optical element, and it is difficult to make the installation position of each optical element completely the same between the optical scanning devices. Even in the configuration of the optical scanning device, the ratio of the scanning light amount of the surface to be scanned to the light emission amount of the light source, in other words, the light utilization efficiency varies.

  Variations in the light utilization efficiency can cause variations in the amount of scanning light, as well as variations in image quality, which is contrary to the requirement for high-quality image formation. Therefore, in order to reduce the variation in the amount of scanning light, a technique has been proposed in which the amount of light emitted from the light source has a certain width and the amount of light emitted is adjusted to make the amount of scanning light uniform.

  However, when such a technique is used, the amount of emitted light is reduced in a device with high light utilization efficiency. However, if the amount of emitted light is reduced, the drooping characteristics are deteriorated and the emission characteristics of the light source become unstable. There is. If the light emission characteristics of the light source become unstable, unevenness in the amount of emitted light, deterioration of the beam spot system, and the like occur, thereby affecting the output image.

  On the other hand, there is known a technique capable of reducing variation in light utilization efficiency itself (see, for example, [Patent Document 1] to [Patent Document 3]). As one of them, for example, an optical element such as a cylindrical lens is used. There is a technique for reducing variation in light utilization efficiency by reducing light transmittance (see, for example, [Patent Document 1]). If the variation in the light utilization efficiency itself is suppressed, it may not be necessary to reduce the light emission amount of the light source to such an extent that the light emission characteristics of the light source become unstable, so that it is expected to reduce the influence on the output image, It is also expected to suppress variations in the amount of scanning light.

JP 2008-033062 A JP 2001-305460 A Japanese Patent No. 2533456 JP 2006-235213 A

  However, the above-described technique for reducing the variation in light utilization efficiency by reducing the light transmittance of the optical element lowers the light transmittance of the optical element originally provided in the optical system. Since the target value of the ratio for reducing the transmittance is uniformly set, the variation range of the light utilization efficiency is reduced, but the light utilization efficiency is adjusted according to the actual value of the light utilization efficiency in each optical scanning device. There is a problem that the amount of scanning light cannot be adjusted sufficiently.

  For example, in an image forming apparatus that includes a plurality of image carriers and forms a color image as a composite image of each color image formed on each image carrier, the quality of the image obtained as a composite image is improved. It is necessary to form an image of each color, and for this purpose, it is necessary to scan each image carrier with a scanning light amount suitable for obtaining such an image of each color. However, if the target value of the ratio for reducing the light transmittance is uniform, it is difficult to scan each image carrier with a scanning light amount suitable for obtaining an image of each color, and an image obtained as a composite image The quality of the can be reduced.

  On the other hand, as a method of adjusting the light transmittance, there is a method of adjusting the light reflectance on the light incident side and the light emitting side in the optical element. When adjusting the reflectance of light on the incident side and the exit side, the light utilization efficiency is determined by the product of the respective reflectances. It was found that the intensity of so-called ghost light changes depending on the correlation between the reflectance on the side and the exit side. Ghost light is generated when the reflected light generated in the optical element is tilted with respect to the optical axis of the incident light, and the image carrier is scanned at a position different from the original scanning position. It is necessary to avoid as much as possible. However, the ghost light is generated not only when the light incident surface and the light exit surface of the optical element are curved surfaces or when these are intentionally tilted with respect to the optical axis of the incident light, but also due to an installation error of the optical element. Therefore, it is difficult to eliminate completely, and it is desirable to reduce the strength as much as possible. However, using, for example, a cylindrical lens and simply trying to reduce the variation in light utilization efficiency by reflecting the incident surface and the reflecting surface, not only the above-mentioned problem, but also the intensity of the ghost light is increased. It is not preferable.

  The present invention is an optical scanning device that scans a surface to be scanned with light emitted from a light source, and includes a light amount adjusting element that adjusts light use efficiency and reduces the intensity of ghost light for each optical scanning device. It is an object of the present invention to provide a scanning device, an image forming apparatus such as a copying machine, a facsimile, a printer, and an optical plotter having the scanning device, and a light amount adjusting method using the light amount adjusting element in the optical scanning device.

  In order to achieve the above object, an invention according to claim 1 is directed to an optical system that guides light emitted from the light source to the scanned surface in order to scan the scanned surface with light emitted from the light source, and the light source. A light amount adjusting element for adjusting a first ratio of the intensity of light emitted from the light source and the intensity of scanning light for scanning the surface to be scanned to a first range, When the second ratio between the intensity and the intensity of the light that scans the scanned surface through the optical system is in the second range, the first ratio is in the first range according to the second ratio. A light amount adjusting element disposed on the optical path of the light emitted from the light source, the light amount adjusting element being arranged so as to be contained, and the light amount adjusting element includes the light transmittance T1 of the incident surface and the emitting surface. The optical scanning devices have different light transmittances T2.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, T1> T2.

  According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the light amount adjusting element has a virtual surface in which at least one of the incident surface and the light exit surface is perpendicular to the optical axis of light entering the surface. Inclined with respect to the surface.

  According to a fourth aspect of the invention, in the optical scanning device according to any one of the first to third aspects, (1-T1) · (1-T2) <0.04 and T1 · T2 <0.64 are satisfied. It is characterized by satisfying.

  According to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, the light amount adjusting element is provided in the optical system in an optical path of light emitted from the light source. It is characterized in that it is arranged closer to the light source than the deflecting means for deflecting the light emitted from the light source.

  A sixth aspect of the present invention is the optical scanning device according to any one of the first to fourth aspects, further comprising a dustproof member for preventing dust from entering the optical scanning device. The light quantity adjusting element is used.

  A seventh aspect of the present invention is the optical scanning device according to any one of the first to sixth aspects, wherein the light quantity adjusting element is formed from the light source. The second ratio of the intensity of the emitted light and the intensity of the light that scans the surface to be scanned through the optical system corresponds to the surface to be scanned that is in the second range, according to the second ratio. The light transmittance is selected so that the first ratio falls within the first range, and the light ratio is disposed on the optical path of the light emitted from the light source.

  According to an eighth aspect of the present invention, in the optical scanning device according to any one of the first to seventh aspects, the light amount adjusting element has a plane of incidence and a plane of emission.

  According to a ninth aspect of the present invention, there is provided the optical scanning device according to any one of the first to eighth aspects, wherein the light intensity detecting means for detecting the intensity of the light emitted from the light source, and the light intensity detection. And a light intensity control means for controlling the intensity of light emitted from the light source based on the light intensity detected by the means.

  According to a tenth aspect of the present invention, in the optical scanning device according to any one of the first to ninth aspects, the light source is a surface emitting laser.

  An eleventh aspect of the invention is an image having the optical scanning device according to any one of the first to tenth aspects and an image carrier that forms the scanned surface and forms a latent image by the scanning light. In the forming device.

  According to a twelfth aspect of the present invention, the image forming apparatus according to the eleventh aspect includes a plurality of the optical scanning devices.

  According to a thirteenth aspect of the present invention, there is provided an optical scanning device including an optical system that guides the light to the scanned surface in order to scan the scanned surface with light emitted from a light source. A light amount adjustment method for adjusting a first ratio with the intensity of scanning light that scans the light to a first range, the intensity of light and the intensity of light that scans the surface to be scanned through the optical system When the second ratio is within the second range, the light transmittance is selected according to the second ratio so that the first ratio falls within the first range, and the light ratio is arranged on the optical path of the light. The light amount adjusting element is a light amount adjusting method using a light adjusting element which is different from each other in light transmittance T1 on the incident surface and light transmittance T2 on the exit surface.

  The present invention provides an optical system that guides the light emitted from the light source to the scanned surface in order to scan the scanned surface with the light emitted from the light source, the intensity of the light emitted from the light source, and the scanned object. A light amount adjusting element for adjusting a first ratio with the intensity of scanning light for scanning a surface to a first range, wherein the surface to be scanned passes through the intensity of light emitted from the light source and the optical system. When the second ratio to the intensity of the light that scans is within the second range, the light transmittance is selected according to the second ratio so that the first ratio falls within the first range. A light amount adjusting element disposed on the optical path of the light emitted from the light source, and the light amount adjusting element has light having different light transmittance T1 on the incident surface and light transmittance T2 on the emitting surface. Because it is in the scanning device, the light utilization efficiency can be adjusted, and the deterioration of the light source characteristics can be reduced. , It is possible to provide a contribution capable optical scanning apparatus excellent image formation by reducing the intensity of the ghost light.

  If T1> T2, it is possible to adjust the light use efficiency and reduce the deterioration of the characteristics of the light source, and contribute to better image formation by reducing the intensity of the ghost light to a higher degree. An optical scanning device can be provided.

  The light amount adjusting element adjusts the light use efficiency if at least one of the incident surface and the exit surface is inclined with respect to a virtual plane perpendicular to the optical axis of the light entering the surface. Therefore, it is possible to provide an optical scanning device that can reduce deterioration in characteristics of a light source and contribute to better image formation by reducing the intensity of ghost light to a higher degree.

  If (1−T1) · (1−T2) <0.04 and T1 · T2 <0.64 are satisfied, the light use efficiency can be adjusted, and the deterioration of the characteristics of the light source can be reduced. An optical scanning device that can contribute to better image formation by reducing the intensity of ghost light can be provided.

  If the light amount adjusting element is disposed on the light source side with respect to the deflecting means for deflecting the light emitted from the light source provided in the optical system in the optical path of the light emitted from the light source, the comparison is made. Light that can adjust the light utilization efficiency while controlling costs with a small-sized light amount adjustment element, and can reduce the deterioration of the characteristics of the light source, and can contribute to good image formation by reducing the intensity of ghost light A scanning device can be provided.

  Provided with a dustproof member for preventing dust from entering the optical scanning device, and using the dustproof member as the light quantity adjusting element, the light utilization efficiency while suppressing the cost without increasing the number of parts It is possible to adjust the optical characteristics of the entire optical system by adjusting the intensity of the light after passing through the optical system. It is possible to provide an optical scanning device that can contribute to good image formation by reducing the image quality.

  An optical scanning device that scans a plurality of scanned surfaces, wherein the light amount adjusting element is a second of an intensity of light emitted from the light source and an intensity of light that scans the scanned surface through the optical system. The light transmittance is selected so that the first ratio falls within the first range according to the second ratio corresponding to the surface to be scanned in the second range, and is emitted from the light source. If it is arranged on the optical path of light, the light utilization efficiency of each light scanning device can be adjusted so as to suppress the variation in light utilization efficiency among the light scanning devices, and the deterioration of the characteristics of the light source can be reduced. It is possible to provide an optical scanning device that can contribute to good image formation by reducing the intensity of ghost light.

  Assuming that the light intensity adjusting element is flat on the incident surface and the light exiting surface, the change in optical characteristics is suppressed, and the light use efficiency is adjusted while minimizing the positional deviation of the optical path due to the presence or absence of the light amount adjusting element. Thus, it is possible to provide an optical scanning device that can reduce deterioration of the characteristics of the light source and contribute to good image formation by reducing the intensity of the ghost light.

  Light intensity detection means for detecting the intensity of light emitted from the light source, and light intensity for controlling the intensity of light emitted from the light source based on the intensity of light detected by the light intensity detection means Control means, the intensity of light emitted from the light source and the light utilization efficiency can be adjusted, and the deterioration of the characteristics of the light source can be reduced and the intensity of the scanning light for scanning the surface to be scanned is high. Therefore, it is possible to provide an optical scanning device that can be adjusted and can contribute to good image formation by reducing the intensity of ghost light.

  If the light source is a surface emitting laser, it is possible to adjust the light use efficiency and reduce the deterioration of the characteristics of the light source, as well as to achieve good image formation and high speed by reducing the intensity of the ghost light. An optical scanning device that can contribute to image formation with high image quality can be provided.

  The present invention resides in an image forming apparatus having such an optical scanning device and an image carrier that forms the surface to be scanned and forms a latent image by the scanning light. It is possible to provide an image forming apparatus capable of reducing the deterioration of the characteristics and capable of forming a good image by reducing the intensity of the ghost light.

  If there are a plurality of the optical scanning devices, it is possible to adjust the light usage efficiency of each optical scanning device so as to suppress the variation in the light usage efficiency among the respective optical scanning devices, and to reduce the deterioration of the characteristics of the light source. In addition, an image forming apparatus capable of forming a good image by reducing the intensity of ghost light can be provided.

  The present invention provides an optical scanning device including an optical system that guides the light to the scanned surface in order to scan the scanned surface with light emitted from a light source, and scans the intensity of the light and the scanned surface. A light amount adjustment method for adjusting a first ratio of light intensity to a first range, wherein the light intensity and second intensity of light that scans the surface to be scanned through the optical system. When the ratio is within the second range, the light transmittance is selected so that the first ratio falls within the first range according to the second ratio, and the amount of light disposed on the optical path of the light Since there is a light amount adjustment method using light adjusting elements that are different from each other in the light transmittance T1 of the light incident surface and the light transmittance T2 of the light exit surface, the light use efficiency can be adjusted. A good image by reducing the intensity of ghost light while reducing the degradation of characteristics Light amount adjusting method capable contribute to formed can be provided.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 100 is a multifunction peripheral of a copying machine, a printer, and a facsimile machine, and can perform full color image formation. When the image forming apparatus 100 is used as a printer or a facsimile, the image forming apparatus 100 performs an image forming process based on an image signal corresponding to image information received from the outside.

  The image forming apparatus 100 is used as a sheet-like recording medium as a transfer sheet, which is a recording sheet, in addition to plain paper generally used for copying, etc., OHP sheets, cardboard, cardboard, cardboard, etc. It is possible to perform image formation.

  The image forming apparatus 100 includes a main body 99 that occupies a center position in the vertical direction, a reading device 21 that is positioned above the main body 99 and that reads a document, and is positioned on the upper side of the reading device 21 and loaded with a document. An automatic document feeder 22 called ADF that feeds the document toward the reading device 21 and the photosensitive drums 20Y, 20M, 20C, and 20K positioned below the main body 99 and conveyed between the intermediate transfer belt 11 A sheet feeding device 23 serving as a sheet feeding table on which the transfer sheet S as a transfer medium as a recording medium is loaded.

  The image forming apparatus 100 is a cylindrical light that is a latent image carrier as a plurality of image carriers capable of forming images as images corresponding to colors separated into yellow, magenta, cyan, and black. This is a tandem structure adopting a tandem structure in which photosensitive drums 20Y, 20M, 20C, and 20K, which are conductive photosensitive bodies, are arranged side by side, in other words, a tandem type, that is, a tandem type image forming apparatus.

  The photoconductor drums 20Y, 20M, 20C, and 20K have the same diameter, and the outer peripheral surface of the transfer belt 11 as an intermediate transfer belt that is an endless belt disposed almost in the center of the main body 99 of the image forming apparatus 100. They are arranged at equal intervals on the side, that is, on the image forming surface side.

  The photosensitive drums 20Y, 20M, 20C, and 20K are arranged in this order from the upstream side in the A1 direction. Each of the photosensitive drums 20Y, 20M, 20C, and 20K has image stations 60Y, 60M, 60C, and 60K as image forming units as image forming units for forming yellow, magenta, cyan, and black images, respectively. Is provided.

  The transfer belt 11 is movable in the direction of the arrow A1 while facing the photosensitive drums 20Y, 20M, 20C, and 20K. The visible image, that is, the toner image formed on each of the photoconductive drums 20Y, 20M, 20C, and 20K is superimposed and transferred to the transfer belt 11 that moves in the direction of the arrow A1, and then transferred onto the transfer sheet S in a lump. It has become.

  In the superimposing transfer to the transfer belt 11, the toner images formed on the photosensitive drums 20Y, 20M, 20C, and 20K are transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A1 direction. As described above, voltage is applied by primary transfer rollers 12Y, 12M, 12C, and 12K as transfer chargers disposed at positions facing the respective photosensitive drums 20Y, 20M, 20C, and 20K with the transfer belt 11 interposed therebetween. , The timing is shifted from the upstream side toward the downstream side in the A1 direction, and the transfer is performed at the transfer position opposite to the photosensitive drums 20Y, 20M, 20C, and 20K and the transfer belt 11.

  The transfer belt 11 is an elastic belt whose entire layer is formed using an elastic member such as a rubber agent. The transfer belt 11 may be a single-layer elastic belt, may be an elastic belt using a part of the elastic belt, or a conventionally used fluorine-based resin, polycarbonate resin, or polyimide resin. Or an inelastic belt may be used.

  The image forming apparatus 100 is an intermediate transfer apparatus that includes four image stations 60Y, 60M, 60C, and 60K, and is disposed below the photosensitive drums 20Y, 20M, 20C, and 20K, and includes a transfer belt 11. A transfer belt unit 10 as a certain belt unit, and a transfer member that is disposed opposite to the transfer belt 11 and contacts the transfer belt 11 and rotates in the same direction as the transfer belt 11 at the contact position with the transfer belt 11. And a secondary transfer roller 5 as a transfer device which is a paper transfer belt.

  The image forming apparatus 100 also includes a cleaning device (not shown) as an intermediate transfer belt cleaning device that is disposed opposite to the transfer belt 11 and includes an intermediate transfer cleaning blade that cleans the transfer belt 11, and image stations 60Y, 60M, And an optical scanning device 8 as a writing device as an optical writing device, which is writing means arranged to face above 60C and 60K.

  The image forming apparatus 100 also transfers the recording sheet S conveyed from the sheet feeding apparatus 23 at a predetermined timing in accordance with the toner image formation timing by the image stations 60Y, 60M, 60C, and 60K. A registration roller pair 13 that is fed toward the transfer portion between the next transfer rollers 5 and a sensor (not shown) that detects that the leading edge of the transfer sheet S has reached the registration roller pair 13 are provided.

  The image forming apparatus 100 also includes a fixing device 6 as a roller fixing type fixing unit for fixing the toner image onto the transfer sheet S that has entered the toner image transferred and conveyed in the direction of arrow C1, and fixing. A sheet discharge roller 7 for discharging the transfer sheet S passed through the apparatus 6 to the outside of the main body 99 and a sheet discharge for stacking the transfer sheet S disposed on the upper portion of the main body 99 and discharged to the outside of the main body 99 by the sheet discharge roller 7. And a paper discharge tray 17 as a unit.

  The image forming apparatus 100 also includes a CPU, a memory, and the like (not shown). The control unit 40 controls the overall operation of the image forming apparatus 100 such as drive control of the optical scanning device 8 and controls the overall operation of the image forming apparatus 100. A communication control device 41 for controlling bidirectional communication with a host device such as a personal computer connected to the network 42, and a toner bottle (not shown) filled with yellow, magenta, cyan, and black toners. is doing.

  The image forming apparatus 100 is an in-body discharge type image forming apparatus in which the discharge tray 17 is positioned above the main body 99 and below the reading device 21. The transfer paper S stacked on the paper discharge tray 17 is taken out downstream in the direction D1 corresponding to the left side in FIG.

  In addition to the transfer belt 11, the transfer belt unit 10 includes primary transfer rollers 12Y, 12M, 12C, and 12K, and a transfer roller as a secondary transfer counter roller that is wound around an intermediate transfer belt 11. 73 and a tension roller 74 which is a driven roller. The drive roller 72 is rotationally driven by driving a motor as a drive source (not shown), and thereby the transfer belt 11 is rotationally driven in the A1 direction.

  The fixing device 6 includes a fixing roller 62 having a heat source therein, and a pressure roller 63 pressed against the fixing roller 62. The fixing sheet 62 carrying the toner image is transferred to the fixing roller 62 and the pressure roller 63. By passing through a fixing portion that is a pressure contact portion, the carried toner image is fixed on the surface of the transfer paper S by the action of heat and pressure.

  The optical scanning device 8 scans and exposes the surfaces to be scanned formed by the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20K, and forms a latent image as a laser beam based on an image signal. Emits beams LY, LM, LC, and LK, which are laser beams. The beams LY, LM, LC, and LK are obtained by converting electronic information corresponding to an image to be formed into optical information, and the optical scanning device 8 converts the optical information into the photosensitive drums 20Y, 20M, 20C, and 20K. It is fixed as a latent image on the top.

  The optical scanning device 8 is detachable with respect to the main body 99. When the optical scanning device 8 is detached, process cartridges (described later) provided in the image stations 60Y, 60M, 60C, and 60K can be independently taken out from the main body 99, respectively. It has become.

  The sheet feeding device 23 includes a paper feed tray 15 on which the transfer paper S is stacked, and a paper feed roller 16 that sends out the transfer paper S stacked on the paper feed tray 15.

  The reading device 21 is positioned above the main body 99, and is pivotally integrated with the main body 99 by a shaft 24 disposed at the upstream end of the image forming apparatus 100 in the D1 direction, and can be opened and closed with respect to the main body 99. It has become.

  The reading device 21 has a gripping portion 25 for gripping when the reading device 21 is opened with respect to the main body 99 at the downstream end portion in the D1 direction. The reading device 21 is rotatable about a shaft 24 and opens with respect to the main body 99 by gripping the grip portion 25 and rotating it upward. The opening angle of the reading device 21 with respect to the main body 99 is approximately 90 degrees, and access to the inside of the main body 99, work for closing the reading device 21, and the like are facilitated.

  The reading device 21 includes a contact glass 21a on which a document is placed, a light source (not shown) that irradiates light on the document placed on the contact glass 21a, and a first light source (not shown) that reflects light reflected from the light source. A first traveling body 21b that includes a reflector and travels in the left-right direction in FIG. 1; a second traveling body 21c that includes a second reflector (not shown) that reflects light reflected by the reflector of the first traveling body 21b; An image forming lens 21d for forming an image of light from the second traveling body 21c, a reading sensor 21e for receiving the light passing through the image forming lens 21d and reading the contents of the document are provided.

  The automatic document feeder 22 is positioned above the reading device 21, and is integrated with the reading device 21 by a shaft 26 disposed at the upstream end of the image forming apparatus 100 in the D1 direction. Can be opened and closed.

  The automatic document feeder 22 has a grip portion 27 for gripping the automatic document feeder 22 when the automatic document feeder 22 is opened with respect to the reading device 21 at the downstream end of the D1 direction. The automatic document feeder 22 is rotatable about a shaft 26. The automatic document feeder 22 is opened with respect to the reading device 21 by gripping the gripping portion 27 and rotating upward to expose the contact glass 21a.

  The automatic document feeder 22 includes a document table 22a on which a document is placed, and a drive unit including a motor (not shown) that feeds the document placed on the document table 22a. When copying using the image forming apparatus 100, the document is set on the document table 22a of the automatic document feeder 22, or the automatic document feeder 22 is turned upward to manually move the document onto the contact glass 21a. After the document is placed on the automatic document feeder 22, the automatic document feeder 22 is closed and the document is pressed against the contact glass 21a. The opening angle of the automatic document feeder 22 with respect to the reading device 21 is approximately 90 degrees, and the work of placing a document on the contact glass 21a, the maintenance work of the contact glass 21a, and the like are easy.

  With reference to FIG. 1, the configuration of one of the image stations 60Y, 60M, 60C, and 60K will be described on behalf of the configuration of the image station 60Y including the photosensitive drum 20Y. Since the configuration of the other image station is substantially the same, in the following description, for the sake of convenience, a reference numeral corresponding to the reference symbol assigned to the configuration of the image station 60Y is attached to the configuration of the other image station. Further, detailed description will be omitted as appropriate, and those with Y, M, C, and K at the end of the reference numerals are configurations for forming yellow, magenta, cyan, and black images, respectively. Will be shown.

  The image station 60Y provided with the photoconductive drum 20Y is for cleaning the primary transfer roller 12Y and the photoconductive drum 20Y around the photoconductive drum 20Y along its rotation direction B1, which is the clockwise direction in the drawing. A cleaning device 70Y as a cleaning device, a charging device 30Y as a charging device as a charging device for charging the photosensitive drum 20Y to a high voltage, and a developing device as a developing device for developing the photosensitive drum 20Y A developing device 50Y. The developing device 50Y has a developing roller 51Y disposed at a position facing the photosensitive drum 20Y.

  The photosensitive drum 20Y, the cleaning device 70Y, the charging device 30Y, and the developing device 50Y are integrated to form a process cartridge. The process cartridge is detachable from the main body 99. Making a process cartridge in this way is very preferable because it can be handled as a replacement part, so that the maintainability is remarkably improved.

  With the configuration described above, the surface of the photosensitive drum 20Y is uniformly charged by the charging device 30Y as it rotates in the B1 direction, and corresponds to the yellow color by the exposure scanning of the beam LY from the optical scanning device 8. An electrostatic latent image is formed. The electrostatic latent image is formed by scanning the beam LY in the main scanning direction, which is a direction perpendicular to the paper surface, and performing sub scanning in the circumferential direction of the photosensitive drum 20Y by rotating the photosensitive drum 20Y in the B1 direction. This is done by scanning in the direction as well.

  To the electrostatic latent image formed in this manner, charged yellow toner supplied by the developing device 50Y adheres, and is developed into a yellow color to be visualized. The toner image, which is a visible image, is primarily transferred to the transfer belt 11 moving in the A1 direction by the primary transfer roller 12Y, and foreign matters such as toner remaining after the transfer are scraped off and stored by the cleaning device 70Y. The drum 20Y is subjected to the next charging by the charging device 30Y.

  Similarly, toner images of the respective colors are formed on the other photosensitive drums 20C, 20M, and 20K, and the formed toner images of the respective colors are transferred in the A1 direction by the primary transfer rollers 12C, 12M, and 12K. 11 is sequentially transferred to the same position on the head. As will be described later, the toner image of each color has a good toner density, and there is no density unevenness, and a ghost image is prevented or suppressed.

  The toner image superimposed on the transfer belt 11 moves to the transfer portion that is the secondary transfer portion that is the position facing the secondary transfer roller 5 as the transfer belt 11 rotates in the A1 direction. Secondary transfer is performed on the transfer paper S.

  The transfer sheet S conveyed between the transfer belt 11 and the secondary transfer roller 5 is fed out from the sheet feeding device 23 and is transferred onto the transfer belt 11 by the registration roller pair 13 based on the detection signal from the sensor. The toner image is sent out at the timing when the leading end of the toner image faces the secondary transfer roller 5.

  When the toner images of all colors are collectively transferred and carried on the transfer paper S, the transfer paper S is transported in the C1 direction and enters the fixing device 6 and passes through the fixing portion between the fixing roller 62 and the pressure roller 63. The carried toner image is fixed by the action of heat and pressure, and a color image which is a composite color image is formed on the transfer paper S by this fixing process. This color image is of high quality because the toner density of each color toner image is good.

  The fixed transfer paper S that has passed through the fixing device 6 passes through the paper discharge roller 7 and is stacked on the paper discharge tray 17. On the other hand, the transfer belt 11 that has finished the secondary transfer is cleaned by a cleaning device to prepare for the next primary transfer.

  Since the image forming apparatus 100 performs high-speed image formation, writing of latent images on the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20K by the optical scanning device 8 is performed at high speed. For this reason, the optical scanning device 8 employs a structure in which a plurality of rotary polygon mirrors are provided, and a technique described below, such as a high speed rotation of the rotary polygon mirror, is employed.

  The optical scanning device 8 will be described in detail below. As the writing speed of the optical scanning device 8 is increased, the photosensitive drums 20Y, 20M, 20C, and 20K, the rotational speed of the transfer belt 11, the transfer speed of the transfer paper S, and the like are also increased.

  FIG. 2 schematically shows the optical scanning device 8 as viewed from the same direction as shown in FIG. The optical scanning device 8 has an optical deflector 117 as a deflecting means at the center in the left-right direction in the figure, and has a symmetrical structure in the left-right direction in the figure with the optical deflector 117 at the center. .

  FIG. 3 shows the structure of the optical scanning device 8 on the left side from the optical deflector 117 in the left-right direction in FIGS. As described above, the optical scanning device 8 has a symmetrical structure in the horizontal direction in FIGS. 1 and 2 with the optical deflector 117 as the center, and therefore the structure of the optical scanning device 8 will be described with reference to FIG. 1 and FIG. 2 with respect to the structure on the right side of the optical deflector 117 in the left-right direction, the corresponding reference numerals are attached to FIG.

  In FIG. 3, reference numerals 111K and 111C denote semiconductor lasers. Each of the semiconductor lasers 111K and 111C constitutes one light source, and emits one light beam for scanning the photosensitive drums 20K and 20C. As shown in FIG. 4, the semiconductor lasers 111K and 111C have the same intensity or the same intensity as that of the light beam, as shown in FIG. 4, separately from the light beam for scanning the photosensitive drums 20K and 20C. A light beam having a predetermined ratio with respect to the intensity of the light beam is also emitted, and this is detected by the light intensity detecting means 122K and 122C described later with reference to FIG. The semiconductor lasers 111K and 111C can modulate or adjust the intensity of the emitted light beam, that is, the light intensity, and both are held by a holder (not shown).

  As shown in FIG. 3, each light beam emitted from the semiconductor lasers 111K and 111C is converted into a parallel light beam which is a light beam form suitable for the subsequent optical system by the coupling lenses 112K and 112C, respectively. The coupling lenses 112K and 112C may convert the light beams emitted from the semiconductor lasers 111K and 111C into weakly divergent or weakly convergent light beams, respectively, according to the subsequent optical system. .

  The respective light beams that have passed through the coupling lenses 112K and 112C to become parallel light beams having a desired light beam shape pass through the openings of the apertures 113K and 113C, which are aperture stops that regulate the light beam width, and are shaped. After the beam diameter is stabilized, only the light beam that has passed through the aperture 113K passes through the light amount adjusting element 114K. The light quantity adjusting element 114K will be described in detail later.

  Each light beam is incident on the cylindrical lenses 115K and 115C, is condensed in the sub-scanning direction by the action of the cylindrical lenses 115K and 115C, is reflected by the incident mirror 116, and then is mainly near the deflection reflection surface of the optical deflector 117. An image is formed as a long line image in the scanning direction.

  The coupling lens 112K, the aperture 113K, the cylindrical lens 115K, and the incident mirror 116 constitute a pair of pre-deflector optical systems that guide the light beam emitted from the semiconductor laser 111K, which is a light source, to the optical deflector 117. The lens 112C, the aperture 113C, the cylindrical lens 115C, and the incident mirror 116 constitute a set of pre-deflector optical systems that guide the light beam emitted from the semiconductor laser 111C, which is a light source, to the optical deflector 117.

  In the figure, reference numeral 121 denotes a soundproof glass provided on a window of a soundproof housing (not shown) of the optical deflector 117. The light beam reflected by the incident mirror 116 enters the optical deflector 117, is deflected by the optical deflector 117, and exits to the scanning imaging optical system side through the soundproof glass 121. The optical deflector 117 includes a rotating polygon mirror 117a as an upper polygon mirror and a rotating polygon mirror 117b as a lower polygon mirror in a state of being stacked and integrated in two upper and lower stages in the direction of the rotation axis. In this example, the mirrors 117a and 117b have the same shape with four deflecting and reflecting surfaces.

  In the figure, reference numerals 118K and 118C denote scanning lenses, reference numerals 119K and 119C denote optical path folding mirrors, and reference numerals 120K and 120C denote dustproof glasses, respectively. The dust-proof glasses 120K and 120C are dust-proof members arranged to prevent dust from entering the optical scanning device 8.

  The scanning lens 118K and the optical path bending mirror 119K are a photosensitive drum that is a corresponding light scanning position of the light beam deflected by the rotating polygon mirror 117a of the optical deflector 117, that is, the light beam emitted from the semiconductor laser 111K. A set of scanning imaging optical systems that guide light onto 20K to form a light spot are configured. The scanning lens 118 </ b> C and the optical path bending mirror 119 </ b> C are a photosensitive drum that corresponds to a light beam deflected by the rotary polygon mirror 117 b of the optical deflector 117, that is, a light beam emitted from the semiconductor laser 111 </ b> C. A set of scanning imaging optical systems that guide light onto 20C and form a light spot are configured. The dustproof glasses 120K and 120C are not included in the scanning imaging optical system because the light beam incident / exit surfaces are parallel flat plates having no curvature and are non-powered with respect to the incident / exiting light beam.

  In this way, the light beam deflected by the rotary polygon mirror 117a of the optical deflector 117 reaches the photosensitive drum 20K through the scanning imaging optical system including the scanning lens 118K and the dustproof glass 120K, whereby the photosensitive member. Light that is scanned by the drum 20K and deflected by the rotary polygon mirror 117b of the optical deflector 117 reaches the photosensitive drum 20K through the scanning imaging optical system including the scanning lens 118C and the dustproof glass 120C, and is exposed to light. The body drum 20C is scanned.

  The pre-deflector optical system including the coupling lens 112K, the optical deflector 117, and the scanning imaging optical system including the scanning lens 118K are light applied to scan the photosensitive drum 20K with the light beam emitted from the semiconductor laser 111K. A pair of optical systems for guiding the beam to the photosensitive drum 20K is configured, and the pre-deflector optical system including the coupling lens 112C, the optical deflector 117, and the scanning imaging optical system including the scanning lens 118C are semiconductor lasers. In order to scan the photosensitive drum 20C with the light beam emitted from 111C, a set of optical systems for guiding the light beam to the photosensitive drum 20C is configured.

  As shown in FIG. 4, the optical scanning device 8 includes light intensity detection means 122K and 122C for detecting the amount of light emitted from the semiconductor lasers 111K and 111C backward, in other words, intensity, and light intensity detection means 122K. In order to maintain the intensity of the light beam that scans the photosensitive drums 20K and 20C within a predetermined range based on the light amount, that is, the intensity of the light detected by 122C, the semiconductor lasers 111K and 111C change to the photosensitive drums 20K and 20C. The light intensity control device 124 includes a light intensity control unit 123 that is realized as a part of the function of the control unit 40 that controls the light amount of the light beam emitted toward the other side, in other words, the intensity.

  The light intensity detectors 122K and 122C detect the emitted light emitted backward from the semiconductor lasers 111K and 111C. The light intensity control means 123 controls the drive current of the semiconductor lasers 111K and 111C based on the light intensity detected by the light intensity detection means 122K and 122C so that it takes a predetermined value. Control), which is referred to as “Control”, is performed.

  However, actually, the light intensity detection means 122K and 122C are generated when passing through at least a part of the optical system such as the coupling lenses 112K and 112C in addition to the emitted light emitted backward from the semiconductor lasers 111K and 111C. In order to detect scattered light, the intensity of the combined light is detected. In addition to at least a part of the optical system, the light intensity detectors 122K and 122C can also detect scattered light that has passed through a light amount adjusting element such as the light amount adjusting element 114K and other light amount adjusting elements 114C, 120K, and 120C described later. However, the light intensity detection means 122K and 122C do not detect all of the scattered light generated when passing through the optical system and the light amount adjustment element.

  Therefore, when the light intensity control unit 123 performs feedback control, the light intensity detection units 122K and 122C detect part of the scattered light generated when passing through the optical system and the light amount adjustment element. As described above, since the light beam is attenuated in an indefinite amount due to the generation of scattered light due to various factors when passing through the optical system and the light amount adjusting element, the photosensitive drum is controlled by the feedback control. It is difficult to control the intensity of the light beam that scans 20K and 20C to be constant, and the light intensity control means 123 substantially sets the intensity of the light beam that scans the photosensitive drums 20K and 20C within a predetermined range. It is meant to be maintained.

  The light amount adjustment element 114K is provided to adjust the intensity of scanning light for scanning the photosensitive drum 20K. The light amount adjusting element 114K will be described as follows.

  In the optical scanning device 8 with all components except the light amount adjusting element 114K attached, the scanning light that reaches the photosensitive drum 20K and scans the photosensitive drum 20K with respect to the light amount of the light beam emitted from the semiconductor laser 111K. When the ratio of the amount of light of a certain light beam was measured, it was 5%. That is, the light utilization efficiency when passing through the optical system including the coupling lens 112K was 5%. On the other hand, the light utilization efficiency when passing through the optical system including the coupling lens 112C was 3%. Therefore, when the light beams emitted from the semiconductor lasers 111K and 111C have the same light amount, a difference occurs in the light amount of the scanning light that scans the photosensitive drums 20K and 20C, and a difference also occurs in the formed images. Therefore, by selecting a light amount adjusting element 111K having a light transmittance of 60% and disposing it in the optical scanning device 8, the light amounts of the scanning light are made equal to each other. Note that the difference in light utilization efficiency occurs even if the same member is used for the optical system including the coupling lens 112K and the optical system including the coupling lens 112C. The reason is that there is a slight difference in the optical characteristics in the manufacturing process and the like, and it is difficult to completely eliminate the mounting error.

  As described above, when an element that reduces the light utilization efficiency, such as the light amount adjustment element 114K, is provided, it is possible to suppress variations in the light utilization efficiency. In order to set the light transmittance to 60%, the light amount adjusting element 114K in the case shown in FIG. 3 is provided with a light reducing coating on the incident surface to decrease and increase the transmittance. “T1”) is 64.81%, and the light exit surface is provided with a low reflection coating, and the light transmittance of the light exit surface (hereinafter referred to as “T2”) is 92.58%.

  The light amount adjusting element 114K is a parallel plate having a light beam incident / exit surface having no curvature, and is non-powered with respect to the incident / exiting light beam. That is, the light amount adjusting element 114K is literally provided only for adjusting the transmitted light amount. This is the same in all the light amount adjusting elements such as the light amount adjusting elements 114C, 120K, and 120C described below. Thereby, the exposure position shift by arrange | positioning the light quantity adjustment element is suppressed.

  The light amount adjusting elements such as the light amount adjusting element 114K are arranged as necessary so as to match the light amounts of the respective scanning lights, and are appropriately arranged in the manner shown in FIGS.

  In the optical scanning device 8 shown in FIG. 5, the light amount adjusting elements 114K and 114C are provided. In the optical scanning device 8 shown in the figure, in a state where all the components except the light amount adjusting elements 114K and 114C are attached, the light use efficiency with respect to the light beam emitted from the semiconductor laser 111K is 5%, and the semiconductor laser 111C The light utilization efficiency for the light beam emitted from was 4%. For this reason, the light amount adjusting element 111K having a light transmittance of 50% (T1 = 52.44%, T2 = 95.35%) is selected, and the light amount adjusting element 111C has a light transmittance of 62.5%. (T1 = 68.47%, T2 = 91.29%) is selected and disposed in the optical scanning device 8 so that the light utilization efficiency of each station is 2.5%, and the photosensitive drum 20K, The amounts of 20C scanning light are the same.

  In the optical scanning device 8 shown in FIG. 6, the dust-proof glasses 120K and 120C are used as the light amount adjusting elements. In the optical scanning device 8 shown in the figure, in the state where all the components except the dustproof glasses 120K and 120C are attached, the light utilization efficiency with respect to the light beam emitted from the semiconductor laser 111K is 5%. The light utilization efficiency for the emitted light beam was 4%. Therefore, as the dustproof glass 120K, one having a light transmittance of 50% (T1 = 52.44%, T2 = 95.35%) is selected and the dustproof glass 120C has a light transmittance of 62.5% ( T1 = 68.47% and T2 = 91.29%) are selected and disposed in the optical scanning device 8 as a light quantity adjusting element, so that the light utilization efficiency of each station is 2.5%, and the photosensitive The amounts of scanning light from the body drums 20K and 20C are the same.

  In the example shown in FIG. 3, the light amount adjusting element 114K, and in the example shown in FIG. 5, the light amount adjusting elements 114K and 114C, the photosensitive drum 20K of the light beam emitted from the semiconductor lasers 111K and 111C, respectively. In the optical path up to 20C, the optical deflector 117 is disposed closer to the semiconductor lasers 111K and 111C. If the light amount adjusting element is disposed on the photosensitive drums 20K and 20C side of the light deflector 117 in the optical path, the light amount adjusting element is disposed in the passage region of the light beam scanned by the light deflector 117. Therefore, the light quantity adjustment element must be long in the main scanning direction. Since the cost of the optical element is substantially proportional to the size, it is disadvantageous in terms of cost to make the light amount adjusting element long in the main scanning direction. However, as in the example shown in FIGS. 3 and 5, if the light amount adjusting element is disposed on the side of the semiconductor lasers 111 </ b> K and 111 </ b> C with respect to the optical deflector 117 in the optical path, the size of the light amount adjusting element is reduced. Can be small, which is advantageous in terms of cost.

  In the example shown in FIG. 3 and the example shown in FIG. 5, the latter is disadvantageous in terms of cost in that the number of light adjustment elements increases and the number of work processes increases. As shown in the example, if you try to match the light utilization efficiency with a small number of light adjustment elements, it is disadvantageous in terms of cost because it is necessary to arrange various light adjustment elements with respect to light transmittance, so either one is adopted It is selected by these comparisons. In consideration of this, in the entire optical scanning device 8, for example, the light transmittance of the light amount adjusting element is 70% for the beam LY in the image station 60Y, 50% for the beam LM in the image station 60M, and 60C for the image station 60C. It is possible to use a combination such that the beam LC at 60% is 60% and the light amount adjusting element is not provided for the beam LK at the image station 60K.

  In the example shown in FIGS. 3 and 5 and the example shown in FIG. 6, as described above, the latter needs to have a larger light amount adjustment element, but the latter is originally required for the optical scanning device 8. As the light-adjusting element is made of dust-proof glass, the increase in cost due to an increase in the number of parts and assembly man-hours is suppressed, and the ease of assembly adjustment and improvement of assembly adjustment accuracy are expected. The change in the optical path length and the change in the optical characteristics due to the presence or absence of light are suppressed. Furthermore, since the light beam that has passed through the optical system is transmitted, it is possible to adjust so as to absorb variations in transmittance and reflectance in all of the optical elements included in the optical system.

  Regarding the creation of the light quantity adjustment element, the light quantity adjustment element is produced by selectively applying a light-reducing coating and a low reflection coating on both the incident surface and the exit surface as appropriate. In addition, the light amount adjusting element 114K and / or the light amount adjusting element 114C are provided according to the accuracy of the light amount adjustment by each light amount adjusting element, the restriction of the arrangement position of the light amount adjusting elements 114K and 114C, and the dustproof glass 120K and / or Or it is good also as a structure which uses the dust-proof glass 120C as a light quantity adjustment element.

  In general, the light utilization efficiency is determined by the optical characteristics of the optical elements that make up the optical system, such as the divergence angle of the light emitted from the light source, the transmittance of each lens, and the reflectance of the polygon mirror and the folding mirror. Therefore, the light flux reaching the image surface of the photosensitive member is in a state including all variations, and thus the light utilization efficiency is wide. For example, when the divergence angle of light emitted from the light source varies, the ratio of light passing through the aperture varies, so that the light utilization efficiency also varies.

  FIG. 7 shows a conceptual diagram regarding the distribution of light utilization efficiency. This figure shows the variation in light utilization efficiency for each optical scanning device, where the horizontal axis represents the light utilization efficiency and the vertical axis represents the number of samples. If it is considered that the light utilization efficiency of each optical component can be represented by a substantially normal distribution, the light utilization efficiency of the entire optical scanning device is also represented by a substantially normal distribution as shown in FIG. In the figure, the distribution is a Gaussian distribution with 0.04 as the center value, but the center value is not limited to this.

  In the distribution shown in the figure, when a light amount adjusting element such as the light amount adjusting elements 114K, 114C, 120K, and 120C is not used, if the variation is defined by 3σ with respect to the center value in the normal distribution, the light use efficiency is 0.025 to 0. There is variation in the range of 055. With this variation, the ratio of the light utilization efficiency of the light scanning device with the highest light utilization efficiency to the light scanning device with the lowest light utilization efficiency reaches 2.5 times. The amount of light required for exposure of the photoconductor is determined regardless of the light utilization efficiency of the optical scanning device. Become wider.

  For example, when the required light amount of the light source is 4 to 8 mW with respect to an optical scanning device having a light utilization efficiency center value of 0.04 without a light amount adjustment element, the light utilization efficiency is 0.025. The necessary amount of light is 6.4 mW to 12.8 mW, and the amount of light necessary for an apparatus having a light use efficiency of 0.055 is 2.9 mW to 5.8 mW. And the minimum value is 2.9 mW to 12.8 mW. When the light quantity of the light source is set to the minimum light quantity and the emitted light quantity is reduced, if the emitted light quantity is too small, the droop characteristic is deteriorated, leading to deterioration of image quality such as density unevenness.

  Therefore, it is considered to increase the minimum required light amount of the light source and stabilize the light emission of the light source by installing a light amount adjusting element that reduces the light utilization efficiency for an optical scanning device with high light utilization efficiency. For example, in the distribution shown in FIG. 7, if a light amount adjusting element having a transmittance of 62.5% is installed in an optical scanning device having a light utilization efficiency of 0.04 or more, the light utilization efficiency shown in FIG. Distribution is obtained. In the example shown in the figure, by installing a light amount adjusting element in an optical scanning device with high light utilization efficiency, variation in light utilization efficiency is mainly suppressed between 0.025 and 0.04. Yes. Therefore, when the appropriate value of the light amount range emitted by the light source to be used is 4 mW to 13 mW, the light amount adjusting element is used to obtain the distribution of light utilization efficiency as shown in FIG. If it is .8 mW, deterioration of the droop characteristic and the like are suppressed or prevented, and a high-quality image without density unevenness can be obtained.

  Therefore, the light quantity adjusting elements 114K, 114C, 120K, and 120C have a high image quality that does not cause unevenness in the light utilization efficiency and the minimum light quantity of the emitted light from the semiconductor lasers 111K and 111C as light sources does not cause a problem of droop characteristics. If necessary, it is arranged so as to be within the first range where a clear image can be obtained. That is, the light amount adjusting elements 114K, 114C, 120K, and 120C have light utilization efficiencies when they are not disposed in the second range outside the first range, depending on the light utilization efficiency. The light transmittance is selected and disposed in the above-described optical path so that the light utilization efficiency in the state where the light is disposed is within the first range.

  The first range is the light utilization efficiency when the light amount adjusting elements 114K, 114C, 120K, and 120C are arranged as necessary, that is, the intensity of the light beam emitted from the semiconductor lasers 111K and 111C, and the light beam is optical. A value defined in the first ratio with the intensity of the light beam as scanning light that scans the photosensitive drums 20K and 20C via the system and the light quantity adjusting elements 114K, 114C, 120K, and 120C provided as necessary. For example, the second range is emitted from the semiconductor lasers 111K and 111C when the light amount adjusting elements 114K, 114C, 120K, and 120C are not disposed. The intensity of the light beam and the optical beam as scanning light that scans the photosensitive drums 20K and 20C through the optical system only. A second range of values defined in the ratio of the intensity of the beam, for example, in the range of 0.04 or more.

  Therefore, by arranging the light quantity adjusting elements 114K, 114C, 120K, and 120C based on such conditions, the minimum light quantity of the emitted light from the semiconductor lasers 111K and 111C is deteriorated in the droop characteristic in the single image of each color. Thus, a high-quality image without density unevenness is obtained. Further, as described above, the light transmittance of the light amount adjusting elements 114K, 114C, 120K, and 120C is selected so as to equalize the light use efficiency in each station. The image quality in the image is improved.

  Here, the light beams emitted from the semiconductor lasers 111K and 111C are scattered due to optical characteristics or attachment errors of optical elements constituting the optical system in the course of passing through the optical system. Such light beam scattering is also caused by tilting the light amount adjusting elements 114K, 114C, 120K, and 120C with respect to the optical axis of the entering light beam, as will be described later. The scattered light passes through the optical system and the light amount adjusting elements 114K, 114C, 120K, 120C, and scans the photosensitive drums 20K, 20C as so-called ghost light at a position different from the original scanning position. This is a direct cause of disturbing the image and must be avoided as much as possible. Scattered light should be avoided as much as possible because it causes disturbance when feedback control is performed on the intensity of the light beam emitted from the semiconductor lasers 111K and 111C and because it causes an indefinite decrease in light utilization efficiency. There is.

  Therefore, the light amount adjusting elements 114K, 114C, 120K, and 120C are adjusted in the light reduction coating and the low reflection coating so that the light transmittance T1 on the incident surface is different from the light transmittance T2 on the light emission surface. . The reason why T1 ≠ T2 will be described below.

  FIG. 9 shows the relationship between the light transmittance ratio between the incident surface and the exit surface and the deterioration rate of the incident light amount in the light amount adjusting elements such as the light amount adjusting elements 114K, 114C, 120K, and 120C. Shown for each transmittance. Here, in the light amount adjusting element, the entrance surface and the exit surface are parallel to a virtual plane perpendicular to the incident light. The transmittance ratio is a value obtained by dividing the light transmission amount of one surface of the incident surface and the exit surface, the light transmittance of which is equal to or higher than the other surface, by the light transmittance of the other surface. The deterioration rate of the incident light amount is a ratio of the total amount of light reflected from the incident surface and the exit surface of the light amount adjusting element out of the light amount incident on the incident surface of the light amount adjusting element.

  From the figure, it can be seen that when the transmittance ratio is 1, that is, when T1 = T2, the deterioration rate is the highest. Specifically, when T1 = T2 (= 0.708) in the light amount adjustment element having an overall light transmittance of 50%, the deterioration rate takes a maximum value of 8.5% outside the figure.

  As will be described later, it is desirable to suppress the ghost light to 4% or less of the amount of incident light. Therefore, the light amount adjusting element having the same light transmittance of 50% satisfies this (1-T1) · (1-T2) <0.04, The values of T1 and T2 are obtained from the conditions of T1 · T2 = 0.05 and T1 ≠ T2.

  Here, using the reflectance R1 (= 1−T1) of the light on the incident surface and the reflectance R2 (= 1−T2) of the light on the exit surface, the values of T1 and T2 satisfy such a condition, for example. Since R1 = 0.525 and R2 = 0.953, and R1 · R2 = (1-T1) · (1-T2) = 0.022 at this time, the ghost light has an incident light quantity of 2. The value is less than 2%.

On the other hand, in the case shown in the figure, when T1 = T2, the ratio of the ghost light (1-T1) · (1-T2) becomes the limit value of 0.04 because the total light transmittance (= T1 · T2) is a light amount adjusting element having 64%. Therefore, when the limit value of the ratio of ghost light is 0.04,
(1-T1) · (1-T2) <0.04 (1)
T1 · T2 <0.64 (2)
If it is, the light quantity adjustment element which suppresses ghost light is obtained, and, thereby, a density nonuniformity, a streak image, etc. are fully suppressed, and a favorable image is obtained.

  Here, the limit value of the ratio of the ghost light, in other words, the reason why the upper limit value is set to 0.04 will be described. Conventionally, in an optical element such as a soundproof glass and a scanning lens that should be non-powered, ghost light due to a single reflection on an optical surface that should be transmitted has been a problem (see, for example, the above-mentioned [Patent Document 4]). However, although the amount of the ghost light slightly increases or decreases depending on the light incident angle or the polarization state of the light, when the refractive index of the medium of the optical element is 1.5, it is about 4% of the incident light amount. Therefore, the upper limit is set to 0.04.

  In order to further suppress image disturbance due to ghost light, the light amount adjusting elements 114K, 114C, 120K, and 120C are light beams of at least one of the light beam incident surface and the light exit surface that enter the surface. It is desirable to incline with respect to a virtual plane perpendicular to the axis.

  The reason for this will be described with reference to FIG. In the figure, reference numeral 125 indicates a light amount adjusting element corresponding to the light amount adjusting elements 114K, 114C, 120K, and 120C, and reference numeral 126 indicates such a virtual plane. Reference symbol L1 indicates reflected light on the incident surface of the light amount adjusting element 125 and returns light to the light source side, and reference symbol L2 indicates a light source that has passed through the incident surface of the reflected light on the exit surface of the light amount adjusting element 125. The reference light L3 indicates the light reflected further from the incident surface and transmitted through the exit surface toward the image carrier among the reflected light from the exit surface of the light amount adjusting element 125. In the example shown in the figure, the incident surface and the exit surface of the light beam are inclined at an angle of θ with respect to the virtual surface 126 perpendicular to the optical axis of the light beam entering these surfaces. Although scattered light may be generated in addition to the light L1 to L3, only typical light L1 to L3 that can affect the image is shown in the figure, and only these will be described.

  The light L3 acts as ghost light when entering the image carrier. Therefore, if the light quantity adjusting element 125 is installed by adjusting the angle θ so that the light L3 does not enter the image carrier, the disturbance of the image due to the light L3 can be prevented. In the light amount adjusting elements 114K, 114C, 120K, and 120C shown in FIG. 3, FIG. 6, or FIG. 7, θ is set to 10 degrees, for example. For example, the light amount adjusting element 114K shown in FIG. 3 has T1 of 64.81% and T2 of 92.58% as described above, and the light L3 is suppressed to 2.6% of the incident light amount. Since the angle θ is 10 deg, the light L3 is prevented from becoming ghost light.

  In addition, since the position of the light beam emitted from the light amount adjusting element 125 is shifted with respect to the light beam incident on the light amount adjusting element 125 due to the inclination of the angle θ, the position of the light source is slightly shifted so as to cancel this, A parallel plate with high transmittance that can be ignored by the adjustment function is placed in place.

  Further, the light amount adjusting element 125 may be configured such that at least one of the incident surface and the emitting surface of the light beam is inclined with respect to the virtual surface 126 so that the light L3 does not become ghost light. When the position of the light beam emitted from the light amount adjustment element 125 is shifted or inclined with respect to the light beam incident on the light beam 125, the position of the light source is slightly shifted so as to cancel this, or the light amount adjustment function is ignored. Place parallel plates with high transmittance and so on in place.

  In order to further suppress image disturbance due to ghost light, the light amount adjusting elements 114K, 114C, 120K, and 120C satisfy T1> T2. The reason for this will be described below.

  As a light quantity adjusting element satisfying the above formulas (1) and (2), as shown in Table 1, T1 and T2 are in an inverse relationship to each other (T1 = 0.9, T2 = 0.7). In the adjustment element A and the light amount adjustment element B of (T1 = 0.7, T2 = 0.9), the ratio of the light amounts of the light L1, L2, and L3 to the incident light amount is as shown in the table.

  As can be seen from the table, in the light amount adjusting element A in which the light amounts of the light L3 are the same, but the light amounts of the lights L1 and L2 are greatly different and T1> T2 are satisfied, T1 <T2. The light L1 is smaller than B. On the other hand, the light L2 has an opposite relationship. The light L1, L2, and L3 values do not take into account light absorption in the light amount adjusting elements A and B.

The light L1 and the light L2 can both be disturbances when the light intensity control device 124 controls the amount of light emitted from the semiconductor lasers 111K and 111C. It is easy to enter 122C, and the influence as a disturbance is great. This is because the light path of the light L <b> 2 is shifted due to refraction inside the light amount adjusting element 125. For example, when light absorption in the light amount adjusting element 125 is taken into consideration, the intensity of the light L2 in the light amount adjusting element A is further lowered than the intensity of the light L1 in the light amount adjusting element B.
Therefore, in the light quantity adjustment element A satisfying T1> T2, the emission light quantity control accuracy of the semiconductor lasers 111K and 111C is higher than that of the light quantity adjustment element B in which T1 <T2.

  The semiconductor lasers 111K and 111C are preferably surface emitting lasers from the viewpoint of obtaining high-quality images at high speed. As the surface emitting laser, it is preferable to use a vertical cavity surface emitting laser called VCSEL that can easily form many light emitting points for generating a light beam on one element. As a result, it becomes possible to write on one image carrier simultaneously with a large number of light beams, and when writing simultaneously with n light beams, writing with a light source that emits one light beam; In comparison, the latent image forming area is n times, and the time required for image formation is 1 / n. It is also possible to increase the writing density while maintaining or improving the writing speed. Therefore, high-speed and high-quality images can be obtained by using a VCSEL as a light source.

  The VCSEL has a disadvantageous characteristic with respect to a general laser diode, but such a characteristic is eliminated by the above-described light amount adjusting element. That is, in a general laser diode used for an optical scanning device such as the optical scanning device 8, an output range suitable for writing is about 4 to 15 mW, whereas a VCSEL is about 0.5 to 1.2 mW. Higher output and wider output range are issues. Although it is possible to cope with a small output by increasing the sensitivity of the photoconductor, there is a case where light on the lower output side is necessary. In this case, if the VCSEL is used at a low output, the light divergence angle is not good. It becomes stable and the influence of density unevenness on the image comes out. Further, it is difficult to expand the output range of the VCSEL due to the structure of the element. However, if the above-described light amount adjusting element is used, the effective light amount can be reduced while using the VCSEL with high output. For example, when a light amount of 0.3 mw is required, even if the VCSEL emits light so as to obtain a light amount of 0.3 mW, the VCSEL emits light so as to obtain a light amount of 0.5 mW that does not deteriorate the characteristic. If a light amount adjusting element having a transmittance of 0.6 is used, a light amount of 0.3 mW can be obtained as a result, and a stable image can be obtained.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, in the above-described embodiment, one light amount adjusting element is provided in each optical path. However, two or more light amount adjusting elements are provided in each optical path in order to optimize variation suppression of light utilization efficiency. In this case, the light transmittance of these light quantity adjusting elements may be different.

  In the above-described embodiment, one optical scanning device is provided for all image carriers, and only one image forming apparatus is provided. However, the optical scanning device may be one image carrier or a plurality of image carriers. For example, a plurality of image forming apparatuses may be provided. In this case as well, it is possible to arrange a light amount adjusting element in the optical scanning device as necessary in accordance with the output characteristics of the light source. In addition, when there are a plurality of light sources and image carriers, a light amount adjusting element can be provided in the optical scanning device as necessary so as to make the light amount between the scanning lights uniform, thereby preventing density unevenness. In addition, a suppressed high-quality image can be formed.

  The image forming apparatus is not a so-called tandem type image forming apparatus, but a so-called one-drum type image forming apparatus in which each color toner image is sequentially formed on one photosensitive drum and the respective color toner images are sequentially superimposed to obtain a color image. The same applies to the device. The image forming apparatus may be capable of forming only a monocolor image.

  In any type of image forming apparatus, the toner image of each color may be directly transferred onto a sheet such as the transfer sheet S without using an intermediate transfer member. In this case, the toner images on the plurality of image carriers are directly transferred to the same sheet in the process of being conveyed by the conveyance belt, for example.

  The image forming apparatus may not be a copier, a printer, and a facsimile machine, but may be a single unit thereof, or may be a multi-function machine of another combination such as a copier and printer. .

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic front view of a part of an optical scanning device provided in the image forming apparatus shown in FIG. 1. FIG. 5 is a schematic perspective view of another part of the optical scanning device provided in the image forming apparatus shown in FIG. 1. FIG. 10 is a schematic control block diagram of still another part of the optical scanning device provided in the image forming apparatus shown in FIG. 1. It is a schematic perspective view which shows the other structural example of a part of optical scanning apparatus shown in FIG. FIG. 4 is a schematic perspective view showing still another configuration example of a part of the optical scanning device shown in FIG. 3. It is the graph which showed the example of the dispersion | variation in the light utilization efficiency of a general optical scanning device. It is the graph which showed the example of the dispersion | variation in the light utilization efficiency of the optical scanning device when a light quantity adjustment element is applied. It is a correlation diagram between the ratio of the light transmittance of the light incident / exit surface of the light amount adjusting element and the deterioration amount of the light incident on the light amount adjusting element. It is a conceptual diagram explaining the aspect in which the light which injected into the light quantity adjustment element deteriorates.

Explanation of symbols

8 Optical scanning device 20C, 20K, 20M, 20Y Scanned surface, image carrier 100 Image forming device 112C, 113C, 114C, 116, 117b, 118C, 119C Optical system 112K, 113K, 114K, 116, 117a, 118K, 119K Optical system 114C, 114K, 120C, 120K, 125 Light quantity adjusting element 117, 117a, 117b Polarizing means 117a, 118Y, 119Y Optical system 117b, 118M, 119M Optical system 111C, 111K Light source 120C, 120K Dustproof member 122C, 122K Light intensity detection Means 123 Light intensity control means 126 Virtual plane

Claims (13)

An optical system for guiding the light emitted from the light source to the scanned surface in order to scan the scanned surface with the light emitted from the light source;
A light amount adjusting element for adjusting a first ratio between the intensity of light emitted from the light source and the intensity of scanning light for scanning the surface to be scanned to a first range, which is emitted from the light source When the second ratio between the intensity of light and the intensity of light that scans the surface to be scanned through the optical system is in the second range, the first ratio is the first ratio according to the second ratio. A light amount adjusting element disposed on an optical path of light emitted from the light source, the light transmittance of which is selected so as to fall within a range;
The light quantity adjusting element is an optical scanning device in which the light transmittance T1 on the incident surface is different from the light transmittance T2 on the light emission surface.   2. The optical scanning device according to claim 1, wherein T1> T2. The optical scanning device according to claim 1 or 2,
The light scanning device according to claim 1, wherein at least one of the light incident surface and the light exit surface is inclined with respect to a virtual surface perpendicular to an optical axis of light entering the surface. In the optical scanning device according to any one of claims 1 to 3,
(1-T1). (1-T2) <0.04
And T1 / T2 <0.64
An optical scanning device characterized by satisfying the above. In the optical scanning device according to any one of claims 1 to 4,
The light quantity adjusting element is disposed on the light source side with respect to a deflecting means provided in the optical system for deflecting the light emitted from the light source in the optical path of the light emitted from the light source. Scanning device. In the optical scanning device according to any one of claims 1 to 4,
A dustproof member for preventing dust from entering the optical scanning device,
An optical scanning device characterized in that the dustproof member is the light quantity adjusting element. In the optical scanning device according to any one of claims 1 to 6,
An optical scanning device that scans a plurality of scanned surfaces,
The light amount adjusting element corresponds to a surface to be scanned in which a second ratio between the intensity of light emitted from the light source and the intensity of light that scans the surface to be scanned through the optical system is in a second range. The light transmittance is selected so that the first ratio falls within the first range according to the second ratio, and the light is disposed on the optical path of the light emitted from the light source. Scanning device. In the optical scanning device according to any one of claims 1 to 7,
The light amount adjusting element has an incident surface and an output surface that are flat. In the optical scanning device according to any one of claims 1 to 8,
Light intensity detection means for detecting the intensity of light emitted from the light source, and light intensity for controlling the intensity of light emitted from the light source based on the intensity of light detected by the light intensity detection means And an optical scanning device. In the optical scanning device according to any one of claims 1 to 9,
An optical scanning device, wherein the light source is a surface emitting laser.   11. An image forming apparatus comprising: the optical scanning device according to claim 1; and an image carrier that constitutes the surface to be scanned and forms a latent image by the scanning light.   12. The image forming apparatus according to claim 11, comprising a plurality of the optical scanning devices. In an optical scanning apparatus having an optical system for guiding the light to the scanned surface in order to scan the scanned surface with light emitted from a light source, the intensity of the light and the intensity of scanning light for scanning the scanned surface A light amount adjustment method for adjusting the first ratio of the first ratio to the first range,
When the second ratio between the intensity of the light and the intensity of the light that scans the surface to be scanned through the optical system is in the second range, the first ratio is the first according to the second ratio. The light transmittance is selected so that the light transmittance falls within the range, and is arranged on the light path. The light transmittance T1 on the incident surface and the light transmittance T2 on the light exit surface are mutually equal. A light amount adjustment method using different light adjustment elements.

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