JP5493433B2 - Optical scanning apparatus, image forming apparatus, and optical scanning method - Google Patents

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 an optical scanning device that includes a surface emitting laser array as a light source, a copier, a facsimile, a printer, an optical plotter, and the like. And an optical scanning method using such a surface emitting laser array.

  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 3]). 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 that can reduce the variation in light utilization efficiency itself, and one of the techniques is to reduce the variation in light utilization efficiency by reducing the light transmittance of an optical element such as a cylindrical lens. (For example, refer to [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.

  On the other hand, in such an image forming apparatus, a technique is known in which the moving speed of an image carrier such as a photoconductor is positively changed to change the image forming speed called process speed. That is, for example, in such an image forming apparatus, when an image is formed on an OHP sheet or a thick paper, a technique for reducing the image forming speed is known as compared with a case where an image is formed on plain paper (for example, [Patent Documents] 2] and [Patent Document 3]). Such a technique has an advantage that, for example, when an image is formed on an OHP sheet, a vivid image is obtained and the glossiness is improved. In particular, it is formed by different colors such as yellow, magenta, cyan, and black. When forming a color image by superimposing the formed toner images, the image formation speed is reduced to sufficiently dissolve the toner of each color so that reflection of the toner boundary surface does not occur, thereby preventing color turbidity. Suitable for obtaining vivid images.

  As described above, in the technique of changing the moving speed of the image carrier in order to change the image forming speed, it is possible to adjust the exposure amount of the image carrier in accordance with the change of the moving speed. It is important for prevention of deterioration. For example, when the rotational speed of the image carrier is reduced to 1/2 or 1/3, the total light emission amount may be increased by a factor of 1/2 or 1/3 by reducing the light emission amount and the light emission time of the light source. Desired. Therefore, in order to adjust the exposure amount, in the optical scanning device, a technique for adjusting the amount of light emitted from the light source (see, for example, [Patent Document 2]) and a technique for intermittently using a polygon mirror (for example, [Patent Document 3]). Have been proposed).

  However, in these techniques, for example, the droop characteristic may be deteriorated in the former technique as in the above technique, and in the latter technique, the polygon mirror is intermittently used depending on the degree of change in the moving speed of the image carrier. Since it may not be possible to cope with changes in the moving speed of the image carrier, such as in some cases, it has been required to develop further technology.

In particular, when a surface emitting laser array in which a plurality of surface emitting laser elements are arranged as a light source is used, such a problem is likely to occur because the light output range is narrow.
Further, when a surface emitting laser array is used as a light source, the following problem arises because the light output range is narrow. That is, there are a problem in correcting shading characteristics, a problem in dealing with deterioration of the image carrier over time, and environmental changes.
The shading characteristics are non-uniform exposure intensities at the center and the end in the main scanning direction due to the optical characteristics of the polygon mirror and the optical element. This non-uniformity is relatively large because it is caused by the product of such optical characteristics and the above-described light utilization efficiency. To correct the shading characteristics, it is necessary to change the output of the light source so as to cancel out such a relatively large non-uniformity, but if the light output range is narrow, an output sufficient to sufficiently cancel out the non-uniformity can be obtained. Absent.
Explaining the deterioration over time and the environmental change of the image carrier, the output of the light source is determined in consideration of the light utilization efficiency etc. after the assembly of the apparatus. Therefore, it is necessary to make adjustments in consideration of deterioration with time of the image carrier and environmental changes. Such adjustment is performed by so-called process control, for example. However, when the light output range is narrow, such adjustment is not sufficiently performed.

In addition, the present inventors diligently researched and used a plurality of light amount adjusting elements called ND filters having different light transmittances, and adjusted the light amount of suitable light transmittance according to the change in the moving speed of the image carrier. If the exposure amount is adjusted by selecting the element and making the selected light amount adjustment element enter the optical path from the light source to the image carrier, the following problems will occur, but the movement speed of the image carrier will change. It has been found that this technique can be used (in a field different from that of the optical scanning device, a technique for selectively using a light amount adjusting element having a different light transmittance is known (for example, see [Patent Document 4]).
That is, when the light amount adjusting element is simply disposed in the optical path, reflected light generated by the light amount adjusting element disposed in the optical path may affect image formation. In the optical scanning device, a technique for controlling the light emission amount of the light source by detecting the intensity of the light emitted from the light source may be used. When such a technique is used, the reflection caused by the light amount adjusting element is used. If the light is detected together with the light emitted from the light source, the control accuracy of the light emission amount is lowered, and image unevenness or the like occurs to affect the image quality, which is a problem. Further, when such reflected light is incident on the image carrier, a so-called ghost image is formed, which affects the image quality, which is a problem. Such a problem can also be caused by the reflected light from the optical element in the above-described technique for reducing the light transmittance of the optical element such as a cylindrical lens.
Therefore, it is desirable to consider such a problem when selectively using light amount adjusting elements having different light transmittances.

  The present invention is an optical scanning device that uses a surface-emitting laser array as a light source and scans a surface to be scanned with light emitted from the light source, and an optical scanning device corresponding to a narrow light output range. In addition, when a plurality of light amount adjusting elements are selectively used, an optical scanning device that takes into consideration the influence of the reflected light from the light amount adjusting elements on the image quality due to disturbance, such as a copying machine, a facsimile, a printer, an optical plotter, etc. An object of the present invention is to provide an image forming apparatus and an optical scanning method using such a surface emitting laser array.

In order to achieve the above object, a first aspect of the present invention provides a surface emitting laser array in which a plurality of surface emitting laser elements are arranged, and scanning a surface to be scanned with light emitted from the surface emitting laser array. An optical system having a plurality of optical elements that guide light emitted from the same surface emitting laser array to the surface to be scanned, a plurality of light amount adjusting elements having different light transmittances, and one of the plurality of light amount adjusting elements And a light amount adjusting element switching means for disposing one at a predetermined position in the optical path of the light emitted from the surface emitting laser array, wherein the plurality of optical elements cup the light emitted from the surface emitting laser array. A coupling lens that rings, and a cylindrical lens that transmits light emitted from the surface-emitting laser array and having passed through the light amount adjusting element disposed at the predetermined position. Of the plurality of light amount adjustment elements, at least an incident surface of the incident surface and the emission surface of the light amount adjustment element arranged at the predetermined position by the light amount adjustment element switching unit is light emitted from the surface emitting laser array. Is inclined at a predetermined angle θ (≠ 0) with respect to a plane perpendicular to the light passing through the predetermined position along the optical axis of the coupling lens, and the angle of the same light amount adjusting element with respect to the vertical plane is The diameter of the cylindrical lens on the plane perpendicular to the plane θ is a, and the light passing through the light quantity adjusting element arranged at the predetermined position is light along the optical axis of the coupling lens. A distance from the same light amount adjusting element to the cylindrical lens is b, and the light passing through the light amount adjusting element disposed at the predetermined position is along the optical axis of the coupling lens. Is incident on the cylindrical lens so that the amount of deviation from the position of the optical surface of the cylindrical lens that intersects the surface on the same light amount adjusting element side to the center of the same surface is Δ. In the direction perpendicular to the rotation axis direction of the optical deflector and the optical axis direction of the coupling lens, they are arranged so as to be shifted toward the side where the distance between the center and the same light amount adjustment element approaches, and θ is (a / 2− The optical scanning device satisfies (Δ) / b ≦ tan (2θ) .

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the light amount adjusting element switching means has the same moving speed according to the moving speed of the surface to be scanned among the plurality of light amount adjusting elements. One corresponding light quantity adjusting element is arranged at the predetermined position .

  According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, at least one of the incident surface and the output surface of the light amount adjusting element is provided with a metal coating for adjusting light transmittance. It is characterized by being.

The invention of claim 4, wherein, in have your optical scanning apparatus according to claim 3, wherein the metal coating is characterized by being subjected to the predetermined angle θ inclined and face.

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 a wedge-type prism.

According to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to fifth aspects, the plurality of optical elements limit a thickness of light emitted from the surface emitting laser array. Including a first aperture having an aperture for limiting the thickness of the light, and the predetermined position is adjacent to the first aperture and passed through the first aperture. The position where light enters, and the diameter of the opening on the plane with the angle of the same light amount adjustment element with respect to the vertical plane being θ is φ, and the diameter of the opening on the plane is φ Θ is φ / d, where d is the shortest distance along the optical path of the light emitted from the surface emitting laser array from the edge to the light amount adjusting element occupying the predetermined position. ≦ tan (2θ) is satisfied Features.

  According to a seventh aspect of the invention, in the optical scanning device according to the sixth aspect, the first aperture is subjected to black painting and / or roughening.

  According to an eighth aspect of the present invention, in the optical scanning device according to the sixth or seventh aspect, the first aperture is inclined to the −θ side with respect to the vertical plane on the plane. To do.

Invention of claim 9, of the light-scanning apparatus odor according to any one of claims 1 to 8, wherein the predetermined position is adjacent to the cylindrical lens, the light quantity adjusting device which is arranged in the same predetermined position It is a position where the passed light enters the cylindrical lens.

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 plurality of optical elements scan the surface to be scanned with the light emitted from the surface emitting laser array. Therefore, the deflecting optical element includes a rotating polygon mirror having a plurality of reflecting surfaces, or a vibrating element in which the reflecting surface vibrates, and the moving speed of the scanned surface is increased. Accordingly, the reflection period of the light emitted from the surface emitting laser array by the deflecting optical element is varied .

The invention according to claim 11 is the optical scanning device according to any one of claims 1 to 10 , wherein an incident surface and / or an exit surface of the cylindrical lens is provided with an antireflection coating. To do.

According to a twelfth aspect of the present invention, in the optical scanning device according to any one of the first to eleventh aspects, a portion outside the effective area of the entrance surface and / or the exit surface of the cylindrical lens is roughened and / or Or it is characterized by having a discontinuous uneven shape.

  In a thirteenth aspect of the present invention, in the optical scanning device according to any one of the first to twelfth aspects, the plurality of optical elements are light reflected by the light amount adjusting element disposed at the predetermined position. A second aperture is included, which blocks light traveling toward the scanned surface side so that the light is guided outside the scanned surface.

  According to a fourteenth aspect of the present invention, in the optical scanning device according to any one of the first to thirteenth aspects, the plurality of optical elements scan a surface to be scanned with light emitted from the surface emitting laser array. For this purpose, an optical element that utilizes light transmittance and includes an optical element whose incident surface or reflection surface is a flat surface, and at least one of the flat surfaces is provided with an antireflection coating.

  According to a fifteenth aspect of the present invention, in the optical scanning device according to any one of the first to fourteenth aspects, at least one of the plurality of light amount adjusting elements is formed of a glass material or a plastic material with an increased reflection coating. It is characterized by being an applied element, a light absorbing element, a glass material or a plastic material.

  A sixteenth aspect of the present invention is the optical scanning device according to any one of the first to fifteenth aspects, wherein the plurality of light amount adjusting elements have a plane of incidence and a plane of emission.

  According to a seventeenth aspect of the present invention, in the optical scanning device according to any one of the first to sixteenth aspects, the light amount adjusting element switching unit includes a holding member that holds the plurality of light amount adjusting elements, and the holding member. And driving means for arranging one of the plurality of light quantity adjusting elements at the predetermined position by rotational driving or parallel driving.

According to an eighteenth aspect of the present invention, there is provided an image having the optical scanning device according to any one of the first to seventeenth aspects and an image carrier that forms the surface to be scanned and forms a latent image by the scanning light. In the forming device.

According to a nineteenth aspect of the present invention, in the image forming apparatus according to the eighteenth aspect , a plurality of the optical scanning devices are provided.

The invention according to claim 20 is a surface emitting laser array in which a plurality of surface emitting laser elements are arranged, and is emitted from the surface emitting laser array for scanning the surface to be scanned by light emitted from the surface emitting laser array. An optical system having a plurality of optical elements for guiding the emitted light to the surface to be scanned, a plurality of light amount adjusting elements having different light transmittances, and one of the plurality of light amount adjusting elements as the surface emitting laser array A light amount adjusting element switching means arranged at a predetermined position in the optical path of the light emitted from the plurality of optical elements, a coupling lens for coupling the light emitted from the surface emitting laser array; A cylindrical lens that transmits the light emitted from the surface emitting laser array and passed through the light amount adjusting element disposed at the predetermined position, and the plurality of light amount adjusting elements. Among the light emitted from the surface emitting laser array, at least the incident surface of the incident surface and the emitting surface of the light amount adjusting element disposed at the predetermined position by the light amount adjusting element switching unit is the coupling lens. Is inclined at a predetermined angle θ (≠ 0) with respect to a plane perpendicular to the light passing through the predetermined position along the optical axis, and on the plane where the angle of the same light amount adjusting element with respect to the vertical plane is θ. The same light amount adjusting element along the light along the optical axis of the coupling lens out of the light passing through the light amount adjusting element arranged at the predetermined position, where a is the diameter of the cylindrical lens on the same vertical surface The distance from the cylindrical lens to the cylindrical lens is b, and the light along the optical axis of the coupling lens among the light that has passed through the light amount adjusting element disposed at the predetermined position is the cylindrical lens. Optical deflector on which the light passing through the cylindrical lens is incident so that the amount of deviation from the position of the optical surface of the lens that intersects the surface on the same light amount adjustment element side to the center of the surface is Δ In a direction perpendicular to the rotation axis direction of the coupling lens and the optical axis direction of the coupling lens, the distance between the center and the same light amount adjustment element is shifted toward the closer side, and θ is (a / 2−Δ) / The optical scanning method satisfies b ≦ tan (2θ) .

The present invention relates to a surface-emitting laser array in which a plurality of surface-emitting laser elements are arranged, and light emitted from the surface-emitting laser array for scanning a surface to be scanned by light emitted from the surface-emitting laser array. An optical system having a plurality of optical elements guided to the surface to be scanned, a plurality of light amount adjusting elements having different light transmittances, and one of the plurality of light amount adjusting elements emitted from the surface emitting laser array A light amount adjusting element switching unit disposed at a predetermined position in the optical path of the light, wherein the plurality of optical elements include a coupling lens for coupling light emitted from the surface emitting laser array, and the surface emitting laser. A cylindrical lens that transmits light emitted from the array and passed through the light amount adjusting element disposed at the predetermined position, and the light among the plurality of light amount adjusting elements. At least the incident surface of the incident surface and the emitting surface of the light amount adjusting element arranged at the predetermined position by the adjusting element switching unit is on the optical axis of the coupling lens among the light emitted from the surface emitting laser array. The cylindrical lens on a plane that is inclined by a predetermined angle θ (≠ 0) with respect to a plane perpendicular to the light passing through the same predetermined position and having an angle of the same light amount adjusting element with respect to the vertical plane as θ. The cylindrical lens from the same light amount adjusting element along the light along the optical axis of the coupling lens among the light passing through the light amount adjusting element disposed at the predetermined position, where a is a diameter on the same vertical surface The light along the optical axis of the coupling lens is the optical surface of the cylindrical lens among the light that has passed through the light amount adjusting element disposed at the predetermined position. The cylindrical lens is arranged so that the amount of deviation from the position where it intersects the surface on the same light quantity adjusting element side to the center of the same surface is Δ and the rotation axis direction of the optical deflector on which the light passing through the cylindrical lens is incident. In the direction perpendicular to the optical axis direction of the coupling lens, the center and the same light amount adjustment element are shifted to the closer side, and θ is (a / 2-Δ) / b ≦ tan (2θ ) since the optical scanning device satisfying, even with a small angle theta, the reflected light of the light amount adjusting device which is disposed at a predetermined position is incident on the surface to be scanned through a cylindrical lens, giving the disturbance and makes quality as ghost light, etc. effect suppresses or prevents, in response to this change even when the moving speed of the scanning surface changes adjustable exposure amount of the surface to be scanned, better using the surface emitting laser array as a light source Can contribute to the image formation, it is possible to provide an optical system, high optical scanning apparatus freedom of layout of such light quantity adjusting element.

If the light quantity adjustment element switching means arranges one light quantity adjustment element corresponding to the movement speed among the plurality of light quantity adjustment elements at the predetermined position according to the movement speed of the scanned surface. by arranged quantity adjusting element in position, contributes to the good image formation using in response to changes in the moving speed of the surface to be scanned by adjusting the exposure amount of the scanned surface, a surface-emitting laser array as a light source It is possible to provide an optical scanning device capable of performing the above.

  If at least one of the entrance surface and the exit surface of the light amount adjusting element is provided with a metal coating for adjusting the light transmittance, the light amount can be reduced by the metal coating disposed at a predetermined position. A well-adjustable light amount adjustment element can adjust the exposure amount of the scanned surface in response to this change even when the moving speed of the scanned surface changes, and it is good to use a surface emitting laser array as the light source It is possible to provide an optical scanning device that can contribute to stable image formation.

  If the metal coating is applied to the surface inclined at the predetermined angle θ, the reflected light is disturbed by a light amount adjusting element arranged at a predetermined position and capable of adjusting the light amount well by the metal coating. In addition to suppressing or preventing the influence on the image quality, the amount of exposure on the scanned surface can be adjusted in response to the change in the moving speed of the scanned surface, and a surface emitting laser array is used as the light source. Therefore, it is possible to provide an optical scanning device that can contribute to good image formation.

  If the light quantity adjusting element is a wedge-type prism, color blur can be highly suppressed by the light quantity adjusting element arranged at a predetermined position, and also when the moving speed of the scanned surface changes. It is possible to provide an optical scanning device that can adjust the exposure amount of the surface to be scanned in response to this change and can contribute to good image formation using a surface emitting laser array as a light source.

The plurality of optical elements have a first aperture for limiting the thickness of the light for limiting the thickness of the light emitted from the surface emitting laser array and then entering the scanning means for scanning the light. includes one aperture, the predetermined position is adjacent to the first aperture, a position der light passed through the first aperture enters is, on a plane the angle of the light amount adjusting device with respect to the plane perpendicular with θ The diameter of the aperture of the aperture in the vertical plane is φ, and the light emitted from the surface emitting laser array from the edge of the aperture to the light amount adjusting element occupying the predetermined position on the plane is Of these, when d is the shortest distance along the optical path of the light passing through the aperture, if θ satisfies φ / d ≦ tan (2θ), the reflected light from the light quantity adjusting element disposed at a predetermined position The opening of the first aperture? In addition to suppressing or preventing the influence on the image quality due to disturbance by returning to the light source side, the exposure amount of the scanned surface can be adjusted in response to this change even when the moving speed of the scanned surface changes, By using a surface emitting laser array as a light source, an optical scanning device that can contribute to good image formation can be provided.

  If the first aperture is black painted and / or roughened, the light reflected by the light amount adjusting element arranged at a predetermined position may return to the light source side from the opening of the first aperture. Reflecting with one aperture can suppress or prevent the influence on the image quality due to disturbance and adjust the exposure amount of the scanned surface in response to the change in the moving speed of the scanned surface. Therefore, it is possible to provide an optical scanning device that can contribute to good image formation using a surface emitting laser array as a light source.

  On the plane, if the first aperture is inclined to the −θ side with respect to the vertical plane, the light reflected by the light amount adjusting element arranged at a predetermined position is the opening of the first aperture. It is difficult to return to the light source side, and this reflected light is disturbed to suppress or prevent the influence on the image quality, and also when the moving speed of the scanned surface changes, the exposure amount of the scanned surface can be adjusted in response to this change. An optical scanning device that can be adjusted and can contribute to good image formation using a surface emitting laser array as a light source can be provided.

The plurality of optical elements include a cylindrical lens that transmits light emitted from the surface emitting laser array and passed through the light amount adjusting element disposed at the predetermined position, and the predetermined position includes the cylindrical lens. next, Ri position der light passing through the light quantity adjusting device which is arranged in the same predetermined position enters the same cylindrical lens, on the plane to the angle of the light amount adjusting device with respect to the plane perpendicular theta, the cylindrical The diameter of the lens on the vertical plane is a, and out of the light passing through the light amount adjusting element disposed at the predetermined position, the cylindrical light source from the same light amount adjusting element along the light along the optical axis of the coupling lens. Assuming that the distance to the lens is b, if θ satisfies (a / 2) / b ≦ tan (2θ), the amount of light arranged at a predetermined position Reflected light from the rectifying element enters the surface to be scanned through a cylindrical lens and suppresses / prevents the influence on the image quality due to disturbance as ghost light, etc., and responds to this change even when the moving speed of the surface to be scanned changes Thus, it is possible to provide an optical scanning device capable of adjusting the exposure amount of the surface to be scanned and contributing to good image formation using a surface emitting laser array as a light source.

The plurality of optical elements include a deflecting optical element that deflects the light to scan the surface to be scanned with light emitted from the surface emitting laser array, and the deflecting optical element includes a plurality of reflecting surfaces. A rotary polygon mirror or a vibrating element whose reflecting surface vibrates, and changes a reflection period of light emitted from the surface emitting laser array by the deflecting optical element according to a moving speed of the scanning surface. If so, even with a small amount of light amount adjustment elements, the amount of exposure on the surface to be scanned can be adjusted in response to this change even when the movement speed of the surface to be scanned changes with the light amount adjustment element arranged at a predetermined position. in it, it is possible to provide an optical run査device as possible out to contribute to good image formation using a surface emitting laser array as a light source.

  If the incident surface and / or the exit surface of the cylindrical lens are provided with an antireflection coating, the reflected light from the light amount adjusting element arranged at a predetermined position enters the scanned surface through the cylindrical lens, and is ghosted. The anti-reflection coating suppresses or prevents the effects of disturbance as light and other factors on the image quality, and also adjusts the exposure amount of the scanned surface in response to changes in the scanning surface movement speed. Therefore, it is possible to provide an optical scanning device that can contribute to good image formation.

  If a portion outside the effective area of the entrance surface and / or the exit surface of the cylindrical lens is roughened and / or has a discontinuous irregular shape, the light amount adjusting element disposed at a predetermined position is used. When reflected light is incident on the surface to be scanned through a cylindrical lens and becomes disturbed as ghost light, etc., and the influence on the image quality is reduced or prevented more highly by processing and uneven shapes, and the moving speed of the surface to be scanned changes In addition, it is possible to provide an optical scanning device that can adjust the exposure amount of the surface to be scanned in response to this change and can contribute to good image formation using a surface emitting laser array as a light source.

  The plurality of optical elements block light that is reflected by the light amount adjusting element disposed at the predetermined position and that travels toward the scanned surface, thereby guiding the light to the outside of the scanned surface. If the second aperture to be included is included, the reflected light from the light amount adjusting element arranged at a predetermined position is incident on the surface to be scanned and becomes a disturbance as ghost light or the like, and the influence on the image quality is caused by the second aperture. In addition to suppressing or preventing, the exposure amount of the surface to be scanned can be adjusted in response to the change in the moving speed of the surface to be scanned, and good image formation can be achieved by using a surface emitting laser array as a light source. An optical scanning device that can contribute can be provided.

  The plurality of optical elements are optical elements that utilize light transmittance to scan a surface to be scanned with light emitted from the surface emitting laser array, and an optical element having a flat incident surface or reflecting surface. In addition, if at least one of the planes is provided with an antireflection coating, the light reflected by the light amount adjusting element arranged at a predetermined position is disturbed and has an effect on the image quality on the plane of the optical element. In addition to being suppressed or prevented by antireflection coating, it is possible to adjust the exposure amount of the scanned surface corresponding to this change even when the moving speed of the scanned surface changes, and it is good to use a surface emitting laser array as the light source It is possible to provide an optical scanning device that can contribute to stable image formation.

  If at least one of the plurality of light quantity adjusting elements is a glass material or a plastic material with an increased reflection coating, or a light absorption type element, or a glass material or a plastic material. Using a light amount adjusting element whose light transmittance is adjusted by various configurations, the reflected light from the light amount adjusting element arranged at a predetermined position is disturbed to suppress or prevent the influence on the image quality, and the moving speed of the scanned surface To provide an optical scanning device capable of adjusting the exposure amount of the surface to be scanned in response to the change, and contributing to good image formation by using a surface emitting laser array as a light source. Can do.

  If the incident surface and the exit surface are flat, the plurality of light amount adjustment elements suppress changes in optical characteristics due to the arrangement of the light amount adjustment elements arranged at predetermined positions, and the moving speed of the surface to be scanned is It is possible to provide an optical scanning device that can adjust the exposure amount of the surface to be scanned in response to this change even when it changes, and can contribute to good image formation by using a surface emitting laser array as a light source. it can.

  The light quantity adjusting element switching means includes a holding member holding the plurality of light quantity adjusting elements and one of the plurality of light quantity adjusting elements by rotating or holding the holding member in parallel. Drive means for disposing one at the predetermined position, the moving speed of the surface to be scanned is changed by the light amount adjusting element disposed at the predetermined position by the light amount adjusting element switching means having a relatively simple configuration. Even in this case, the exposure amount of the surface to be scanned can be adjusted in accordance with this change, and an optical scanning device that can contribute to good image formation by using a surface emitting laser array as a light source 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 scanned surface and forms a latent image by the scanned light, so that the moving speed of the scanned surface changes. In addition, it is possible to provide an image forming apparatus capable of adjusting the exposure amount of the surface to be scanned in response to this change and capable of forming a good image using a surface emitting laser array as a light source.

  If each of the optical scanning devices has a plurality of the optical scanning devices, the exposure amount of the scanned surface can be adjusted in response to the change even when the moving speed of the scanned surface changes. An image forming apparatus capable of performing good image formation using a surface emitting laser array can be provided.

The present invention relates to a surface-emitting laser array in which a plurality of surface-emitting laser elements are arranged, and light emitted from the surface-emitting laser array for scanning a surface to be scanned by light emitted from the surface-emitting laser array. An optical system having a plurality of optical elements guided to the surface to be scanned, a plurality of light amount adjusting elements having different light transmittances, and one of the plurality of light amount adjusting elements emitted from the surface emitting laser array A light amount adjusting element switching means arranged at a predetermined position in the optical path of the light, wherein the plurality of optical elements are a coupling lens for coupling light emitted from the surface emitting laser array, and the surface emitting laser array. A cylindrical lens that transmits the light emitted from the light passing through the light amount adjusting element disposed at the predetermined position, and the light among the plurality of light amount adjusting elements At least the incident surface of the incident surface and the emitting surface of the light amount adjusting element arranged at the predetermined position by the adjusting element switching unit is on the optical axis of the coupling lens among the light emitted from the surface emitting laser array. The cylindrical lens on a plane that is inclined by a predetermined angle θ (≠ 0) with respect to a plane perpendicular to the light passing through the same predetermined position and having an angle of the same light amount adjusting element with respect to the vertical plane as θ. The cylindrical lens from the same light amount adjusting element along the light along the optical axis of the coupling lens among the light passing through the light amount adjusting element disposed at the predetermined position, where a is a diameter on the same vertical surface The light along the optical axis of the coupling lens is the optical surface of the cylindrical lens among the light that has passed through the light amount adjusting element disposed at the predetermined position. The cylindrical lens is arranged so that the amount of deviation from the position where it intersects the surface on the same light quantity adjusting element side to the center of the same surface is Δ and the rotation axis direction of the optical deflector on which the light passing through the cylindrical lens is incident. In the direction perpendicular to the optical axis direction of the coupling lens, the center and the same light amount adjustment element are shifted to the closer side, and θ is (a / 2-Δ) / b ≦ tan (2θ ) since the optical scanning method satisfying, even with a small angle theta, the reflected light of the light amount adjusting device which is disposed at a predetermined position is incident on the surface to be scanned through a cylindrical lens, giving the disturbance and makes quality as ghost light, etc. effect suppresses or prevents, in response to this change even when the moving speed of the scanning surface changes adjustable exposure amount of the surface to be scanned, better using the surface emitting laser array as a light source Can contribute to the image formation, it is possible to provide an optical system, a high degree of freedom optical scanning method of the layout of such light quantity adjusting element.

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. FIG. 6 is a schematic plan view of still another part of the optical scanning device provided in the image forming apparatus shown in FIG. 1. FIG. 2 is a schematic plan view illustrating a configuration example of a light amount adjustment element of a light amount adjustment element switching unit provided in the optical scanning device illustrated in FIG. 1 and a holding member that holds the light amount adjustment element. It is a schematic plan view which shows the other example of a structure of the light quantity adjustment element of the light quantity adjustment element switching means with which the optical scanning apparatus shown in FIG. 1 was equipped, and the holding member holding this. It is a conceptual diagram explaining the generation | occurrence | production aspect of the reflected light by a light quantity adjustment element. It is a conceptual diagram for demonstrating arrangement | positioning conditions of the light quantity adjustment element by the light quantity adjustment element switching means shown in FIG. It is a front view which shows the outline of a structure of the 1st, 2nd aperture and cylindrical lens with which the optical scanning apparatus shown in FIG. 1 was equipped. It is a conceptual diagram which shows the other structural example of the light source shown in FIG. It is a conceptual diagram which shows the other arrangement | positioning aspect of the aperture shown in FIG. It is a conceptual diagram for demonstrating the other arrangement | positioning conditions of the light quantity adjustment element by the light quantity adjustment element switching means shown in FIG. It is a conceptual diagram for demonstrating other arrangement conditions of the light quantity adjustment element by the light quantity adjustment element switching means shown in FIG. FIG. 14 is a schematic perspective view illustrating a configuration example in which a second aperture is added to the configuration example of the optical scanning device illustrated in FIG. 13. It is the conceptual diagram which showed another example of the setting direction of angle (theta). It is the schematic plan view which showed another structural example of the light quantity adjustment element.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 100 is a digital multi-function machine such as 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 is conveyed below the main body 99 and between the photosensitive drums 20 </ b> Y, 20 </ b> M, 20 </ b> C, 20 </ b> K and 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. 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.

  The control means 40 includes a CPU as information calculation means, a memory as storage means, and the like. The control means 40 appropriately adjusts the density and the like of the toner images formed in the image stations 60Y, 60M, 60C, and 60K in accordance with the time-dependent characteristic change, environment change, etc. of the photosensitive drums 20Y, 20M, 20C, and 20K. Do so-called process control to keep. The control means 40 also corrects the shading characteristics in the main scanning direction of the photosensitive drums 20Y, 20M, 20C, and 20K.

  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.

  As described above, the image forming apparatus 100 can use not only plain paper but also OHP sheets, thick paper such as cards and postcards as transfer paper S for image formation. Since the OHP sheet and the thick paper have a larger amount of heat absorption at the time of fixing than the plain paper, it is desirable to slow down the conveying speed in the fixing device 6 in order to perform good fixing and form a high-quality image. In particular, when an image is formed on an OHP sheet, if the amount of heat applied by slowing the fixing speed is increased, a vivid image can be obtained and the glossiness is improved. In particular, yellow, magenta, cyan, black In the case of forming a color image by superimposing toner images formed with different colors, the toner of each color is sufficiently dissolved so that reflection of the toner boundary surface does not occur due to a decrease in fixing speed. Color turbidity is prevented or suppressed, and a vivid image can be obtained.

  Therefore, in the image forming apparatus 100, the fixing speed is changed according to the type of the transfer sheet S. However, if only the fixing speed is decreased in each step of image formation, it is difficult to perform image formation continuously. Therefore, in the image forming apparatus 100, the fixing speed is changed according to the type of the transfer paper S, and the moving speeds of the transfer belt 11, the photosensitive drums 20C, 20M, 20K, and the like are also changed accordingly. ing. In other words, the image forming apparatus 100 changes the image forming speed, in other words, the process speed, in accordance with the type of the transfer sheet S.

  On the other hand, in recent years, speeding up of image formation has been demanded, and there is a strong demand for speeding up, especially when forming a monochromatic image with only black. Therefore, the image forming apparatus 100 is configured to perform monochromatic image formation at a high speed when the transfer paper S is plain paper.

  For these reasons, the image forming apparatus 100 has four modes, specifically, a mode for forming a monocolor image on plain paper, a mode for forming a color image on plain paper, and a mode for forming an image on an OHP sheet. , A mode for performing image formation on cardboard is provided, and in accordance with these modes, the image formation speeds in the order of these modes are V1 (= 100 mm / sec), V2 (= 50 mm / sec), and V3 (= 40 mm / sec) and V4 (= 33 mm / sec).

  Therefore, in accordance with these modes, the moving speeds of the photosensitive drums 20Y, 20M, 20C, 20K, the transfer belt 11, and the other developing rollers 51Y, 51M, 51C, 51K, etc., in other words, the rotational speeds are V1, V2, V3, The fixing speed is V1, V2, V3, and V4. The control unit 40 recognizes in which mode image formation is performed, and the control unit 40 also switches the speed.

  As described above, when the moving speed of the photosensitive drums 20Y, 20M, 20C, and 20K is changed in order to change the image forming speed, the photosensitive drums 20Y, 20M, 20C, and 20K are changed according to the change in the moving speed. Since adjusting the exposure amount is important for preventing deterioration in image quality, the writing of latent images on the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20K by the optical scanning device 8 depends on the mode. Therefore, it is performed by changing the amount of light. For this reason, the following technique is employed in the optical scanning device 8.

The optical scanning device 8 will be described in detail below.
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 that is a deflecting means as a scanning means at the center in the left-right direction in the figure, and is symmetrical in the left-right direction in the figure with the optical deflector 117 at the center. It has become.

  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. 2 shows a part of the configuration shown in FIG.

In FIG. 3, reference numerals 111K and 111C denote semiconductor lasers using a surface emitting laser array in which a plurality of surface emitting laser elements (not shown) are arranged.
The surface emitting laser array has an advantage that a high-quality image can be obtained at high speed. As the surface emitting laser array, 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 VCSEL as the light source.

  The VCSEL has a disadvantageous characteristic in the output range and the like compared with a general laser diode, but such a characteristic is eliminated by a light amount adjusting element described later. 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 a light amount adjusting element described later is used, the effective light amount can be reduced while using the VCSEL at a 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 0.6 mW that does not deteriorate the characteristic even if the characteristics deteriorate. If a light amount adjusting element having a transmittance of 0.5 is used, a light amount of 0.3 mW can be obtained as a result, and a stable image can be obtained.

  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 detected by light intensity detecting means 122K and 122C, which will be 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, the light beams emitted from the semiconductor lasers 111K and 111C are respectively coupled by coupling lenses 112K and 112C configured by collimating lenses, and have a light beam form suitable for the subsequent optical system. It is converted into a parallel light beam. 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. .

  Each of the light beams that have passed through the coupling lenses 112K and 112C to become a parallel light beam having a desired light beam shape regulates the light beam width, in other words, an aperture 113K that is an aperture stop that restricts the thickness of the light beam. After passing through 113C, the beam is shaped and the beam diameter is stabilized, and then enters a cylindrical lens 115K, 115C through a light amount adjusting element occupying a predetermined position by a light amount adjusting element switching means 114K, 114C, as will be described later. These cylindrical lenses 115K and 115C are condensed in the sub-scanning direction and formed as a long line image in the main scanning direction in the vicinity of the deflection reflection surface of the optical deflector 117.

  The coupling lens 112K, the aperture 113K, and the cylindrical lens 115K constitute a set 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 coupling lens 112C, the aperture The 113C and the cylindrical lens 115C 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 addition, the coupling lens 112K and the coupling lens 112C constitute a first optical system for coupling a light beam, that is, a light beam from the semiconductor laser 111K and the semiconductor laser 111C, respectively, and the cylindrical lens 115K and the cylindrical lens 115C respectively A second optical system that condenses light beams from the coupling lens 112 </ b> K and the coupling lens 112 </ b> C that are one optical system, that is, a light beam, is long in the main scanning direction and substantially linear.

  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 are configured as deflecting optical elements each having six deflecting reflecting surfaces, and have the same shape.

  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. The light scanned by the drum 20K and deflected by the rotary polygon mirror 117b of the optical deflector 117 reaches the photosensitive drum 20C through the scanning imaging optical system including the scanning lens 118C and the dust-proof glass 120C, and thereby the photosensitive member. The drum 20C is scanned. The scanning lens 118K and the scanning lens 118C constitute a third optical system that condenses the light beams deflected by the rotating polygon mirror 117a and the rotating polygon mirror 117b on the photosensitive drum 20K and the photosensitive drum 20C, respectively.

  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. In addition, since the structure of these optical systems is comprised similarly, only one is demonstrated below suitably and the description of the other is abbreviate | omitted below.

  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. The light intensity detectors 122K and 122C can also detect scattered light generated in the light amount adjusting element switching units 114K and 114C in addition to at least a part of the optical system. 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 quantity adjustment element switching means 114K and 114C, and as will be described later, the light quantity adjustment element switching. Detection of scattered light generated when passing through the means 114K and 114C by the light intensity detection means 122K and 122C is suppressed to a level that can be prevented or ignored.

  The light quantity adjustment element switching means 114K and 114C are provided for adjusting the exposure amounts of the photosensitive drums 20K and 20C in accordance with the above four modes. Since the structures of the light quantity adjustment element switching means 114K and 114C are the same, a specific configuration will be described below as a representative of the structure of the light quantity adjustment element switching means 114K.

  As shown in FIG. 5 and FIG. 6, the light quantity adjustment element switching means 114K includes glass plates 130K and ND as a plurality of light quantity adjustment elements whose light beam transmittances are 100%, 50%, 40%, and 33%, respectively. The holding member 127K holding the filters (Neutral Density Filters) 131K, 132K, and 133K, and the holding member 127K are driven, so that only one of the glass plate 130K and the ND filters 131K, 132K, and 133K is an optical path of the light beam. And driving means 128K for entering the inside. In FIG. 5, the black member of the configuration shown in FIG. 3 is illustrated, and the optical path bending mirror 119 </ b> K, the dustproof glass 120 </ b> K, and the soundproof glass 121 are omitted.

  The glass plate 130K is made of a glass material in which both the incident surface and the exit surface of the light beam are flat and parallel to each other. The ND filters 131K, 132K, and 133K use the same material and shape as the glass plate 130K, and the light transmittance is adjusted as described above by applying an increased reflection coating to the incident surface of the light beam. ing. The increased reflection coating may be provided on the exit surface in place of the incident surface of the light beam or together with the incident surface. When the increased reflection coating is formed by a metal coating, there are advantages in uniforming and improving the light transmittance and facilitating production. Thus, the glass plate 130K and the ND filters 131K, 132K, and 133K have different light transmittances.

  In the example shown in FIG. 6A, the holding member 127K has a disc shape, and holds the glass plate 130K and the ND filters 131K, 132K, and 133K radially from the center at equal intervals. The holding member 127K has a rectangular shape in the example shown in FIG. 6B, and holds the glass plate 130K and the ND filters 131K, 132K, and 133K in a line at equal intervals. As described above, the holding member 127K is a support plate that supports the light quantity adjustment element group including the glass plate 130K and the ND filters 131K, 132K, and 133K. The holding member 127K is colored black so that the transmittance of the light beam is 0% except for the portion holding the glass plate 130K and the ND filters 131K, 132K, and 133K. The holding member 127K is actually composed of a single glass material integrally including a glass plate 130K and ND filters 131K, 132K, and 133K. The glass plate 130K and the ND filters 131K and 132K are obtained by surface processing of the glass material. 133K is formed.

  The driving means 128K has a stepping motor (not shown) driven by the control means 40. By driving the holding member 127K, when the rotational speed of the photosensitive drum 20K is V1, the glass plate 130K and the photosensitive drum When the rotational speed of 20K is V2, the ND filter 131K, when the rotational speed of the photosensitive drum 20K is V3, the ND filter 132K, when the rotational speed of the photosensitive drum 20K is V4, the ND filter 133K, and the pre-deflector optics In the optical path of the light beam formed by the system, specifically, it is disposed at a fixed position between the aperture 113K and the cylindrical lens 115K.

  When the holding member 127K has the shape shown in FIG. 6A, the driving means 128K supports the rotation center of the holding member 127K on the output shaft of the stepping motor, and rotates the holding member 127K by energizing the stepping motor. To do. The drive means 128K manages the phase of the holding member 127K by the number of energization pulses to the stepping motor, and as shown in the following Table 1, the glass plate 130K, the ND filter, according to the rotational speed of the photosensitive drum 20K. A corresponding light quantity adjusting element among 131K, 132K, and 133K is disposed at a fixed position between the aperture 113K and the cylindrical lens 115K. At this time, as shown in the table, skipping the surface, that is, intermittently scanning the light beam by skipping any one of the six deflection reflecting surfaces constituting the rotary polygon mirror 117a. However, the control of changing the reflection period of the light beam is not performed.

  When the holding member 127K has the shape shown in FIG. 6B, the driving means 128K supports the holding member 127K with a rack and pinion mechanism coupled to the output shaft of the stepping motor, and the holding member 127K is energized with the stepping motor. 127K is driven in parallel in the direction in which the glass plate 130K and the ND filters 131K, 132K, and 133K are arranged, in other words, the direction across the glass plate 130K and the ND filters 131K, 132K, and 133K. The drive unit 128K manages the position of the holding member 127K by the number of energization pulses to the stepping motor, and as shown in the table, according to the rotational speed of the photosensitive drum 20K, the glass plate 130K, the ND filter 131K, The corresponding light quantity adjustment element of 132K and 133K is disposed at a fixed position between the aperture 113K and the cylindrical lens 115K. At this time, skipping is not performed.

  In this manner, the exposure amount of the photosensitive drum 20K is adjusted in accordance with the rotational speed of the photosensitive drum 20K, and the exposure amount of the photosensitive drum 20K is always substantially constant regardless of the rotational speed of the photosensitive drum 20K. To be kept.

  FIG. 7 shows another example of the configuration of the holding member 127K. The holding member 127K shown in the figure has a disk shape like the holding member 127K shown in FIG. 6A, but the holding member 127K shown in FIG. Only two glass plates 130K and ND filters 134K having light beam transmittances of 100% and 80%, respectively, are held as elements. The rest of the configuration and the light transmittance adjustment method are the same as those of the light amount adjustment element switching means 114K described with reference to FIG.

  However, in the light quantity adjusting element switching means 114K having the holding member 127K shown in FIG. 7, in order to adjust the exposure amount of the photosensitive drum 20K in the optical scanning device 8, as shown in Table 2, the glass plate 130K is used. In addition to disposing any one of the ND filters 134K at the above-mentioned fixed position, the surface of the six deflecting reflecting surfaces constituting the rotary polygon mirror 117a is skipped to intermittently scan the light beam, By performing control such as changing the reflection period of the light beam, the exposure amount of the photosensitive drum 20K is adjusted in accordance with the rotational speed of the photosensitive drum 20K, as in the case shown in FIG. Regardless of the rotational speed of the drum 20K, the exposure amount of the photosensitive drum 20K is always kept substantially constant. As described above, the combination with the surface skip has an advantage that the number of kinds of light amount adjusting elements can be reduced.

  The holding mode of the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K by the holding member 127K and the configuration mode, driving mode, and surface skipping mode of the driving means 128K associated therewith are shown in FIGS. These are not limited to those described above with reference to Table 2. Further, when the distance between the light path of the black light beam and the light path of the cyan light beam is small, the light for cyan together with the light beam for black is applied to the glass plate 130K, the ND filters 131K, 132K, 133K, and 134K. The beam may be transmitted. In this case, the light amount adjustment element switching unit 114K has a configuration common to the light amount adjustment element switching unit 114C. As described above, the light amounts of a plurality of light beams having different target scan surfaces may be adjusted by one light amount adjustment element switching unit.

  As described above, if the light amount adjusting element switching unit 114K is used, the exposure amount of the photosensitive drum 20K can be kept constant regardless of the rotational speed of the photosensitive drum 20K. If only 131K, 132K, 133K, and 134K are selectively disposed in the optical path, reflected light generated by the light amount adjusting element disposed in the optical path may be disturbed and affect image formation.

  For example, when the reflected light generated by the light beam that has passed through the aperture 113K and reflected by one of the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K is detected by the light intensity detector 122K, As the output of the semiconductor laser 111K varies, the control accuracy of the light emission amount of the semiconductor laser 111K decreases, and image unevenness or the like occurs, affecting the image quality. Further, the light beam transmitted through any one of the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K is reflected by the cylindrical lens 115K, and is further reflected by the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K. When the reflected light generated by the reflection enters the photosensitive drum 20K, a so-called ghost image is formed, which affects the image quality, which is a problem.

Therefore, as shown in FIG. 8, the light amount adjustment element switching means 114K is configured to place the light amount adjustment element 125 corresponding to the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K disposed at the above-described fixed positions. Among the light beams passing through the optical axis 126 perpendicular to the light beam along the optical axis of the coupling lens 112K (hereinafter, the axis line coinciding with the light beam is referred to as “optical axis S”). ), The reflected lights L1 to L3 from the light amount adjusting element 125 are guided to the outside of the area where the disturbance occurs. Incidentally, with respect to the optical axis S, and "along the optical axis of the coupling lens 112K", but refers to match the optical axis of the coupling lens 112K, light having passed through the coupling lens 112K refraction, reflection In this case, it is assumed that the direction of the optical axis S also changes according to the refraction direction and the reflection direction.

  Note that the reflected light L1 is reflected light on the incident surface of the light amount adjusting element 125 and is returned to the light source side, and the reflected light L2 is transmitted through the incident surface of the reflected light on the exit surface of the light amount adjusting element 125. The return light to the light source side is shown, and the reflected light L3 is the light reflected from the exit surface of the light amount adjusting element 125 and further reflected by the entrance surface and transmitted through the exit surface toward the image carrier. Although scattered light can be generated in addition to the light L1 to L3, only representative reflected lights L1 to L3 that can affect the image as disturbances are shown in FIG.

  Further, regarding the reflected light L1, the light transmittance in the ND filters 131K, 132K, 133K, and 134K as the light amount adjusting element 125 is adjusted due to the increase in reflection coating on the incident surface as described above. The lower the rate, the greater the intensity of the reflected light L1. In this regard, the configuration example shown in FIG. 7 has a higher light transmittance than the configuration example shown in FIG. 6, so that the reflected light L <b> 1 is less likely to be generated and disturbance to the control in the light intensity control device 124 is less likely to occur. There are advantages.

In the light amount adjusting element switching means 114K, the angle θ is further indicated by φ as the diameter of the opening 113′K of the aperture 113K as shown in FIG. 9, and from the edge of the opening 113′K as the holding member 127K in the same figure. When the shortest distance to the light quantity adjustment element 125 is d
φ / d ≦ tan (2θ) (1)
It comes to satisfy.

  Here, the opening 113′K restricts the thickness of the black light beam, and its diameter φ is a plane parallel to the paper surface of FIG. 9, that is, the optical axis S at the above-mentioned fixed position. Means a diameter in a direction parallel to the virtual surface 126 in a plane in which the angle of the light amount adjusting element 125 with respect to the virtual surface 126 is θ. Further, the shortest distance d is the shortest distance along the optical path of the light beam passing through the opening 113'K from the edge of the opening 113'K to the light amount adjusting element 125 occupying the fixed position on the plane.

  As shown in FIG. 9, the reflected light from the light amount adjusting element 125 indicated by the one-dot chain line arrow forms an angle 2θ with respect to the optical axis S on the plane, and thus satisfies the above formula (1). Almost all of the reflected lights L1 and L2 are guided to the main body of the aperture 113K, and the reflected lights L1 and L2 are guided outside the region where the disturbance occurs. Therefore, the reflected lights L1 and L2 do not become disturbances to the control in the light intensity control device 124, the control accuracy of the light emission amount of the semiconductor laser 111K is maintained, image unevenness or the like occurs, and the image quality is affected. Prevented or suppressed. The same applies to the case where the light beam emitted from the semiconductor laser 111K is converted into a weakly divergent or weakly convergent light beam by the coupling lens 112K.

  Note that the surface of the aperture 113K main body on the light amount adjustment element 125 side is painted black so that the entire light beam is absorbed. However, as shown in FIG. A shape may be applied, or instead of or along with this, a roughening process may be applied so that the incident light beam is not scattered and disturbed.

  As shown in FIG. 12, the aperture 113K is preferably inclined to the −θ side with respect to the virtual plane 126 shown in FIG. This is because the direction of the aperture 113K becomes nearly parallel to the reflected lights L1 and L2, and the reflected lights L1 and L2 are less likely to be detected by the light intensity detector 122K through the opening 113'K. This configuration is also applicable to various configuration examples described below.

  As described above, the angle θ is set to θ ≠ 0, and in addition to this, the formula (1) is set so that the reflected lights L1 and L2 from the light amount adjusting element 125 are controlled by the light intensity control device 124. Therefore, the control accuracy of the light emission amount of the semiconductor laser 111K is maintained, and it is possible to prevent or suppress the occurrence of image unevenness and the like to affect the image quality, and to reduce or suppress or prevent the ghost image. Is done. The ghost image is reflected by the cylindrical lens 115K out of the reflected light L3 and the light beam transmitted through the light amount adjusting element 125 occupying the above-mentioned fixed position, and is further reflected by the same light amount adjusting element 125. The reflected light corresponding to the reflected light L1 enters the photosensitive drum 20K and is disturbed as ghost light. However, by setting the angle θ to θ ≠ 0, it is mitigated, suppressed, or prevented. Therefore, the degree of relaxation or the like is improved by setting so as to satisfy the formula (1).

  However, for example, the surface of the cylindrical lens 115K on the light amount adjusting element 125 side is a plane perpendicular to the optical axis S, and the same surface is not subjected to low reflection processing, and the refractive index with respect to incident light is 1.5. In some cases, the reflectance on the same surface is 4%, and if the reflected light on the same surface enters the light amount adjusting element 125 having a light transmittance of 50%, the reflected light has an intensity of 2% and the cylindrical lens 115K. The light is condensed on the photosensitive drum 20K through the following optical elements, which may reach a problem level as ghost light.

Therefore, in order to further suppress or prevent such reflected light from affecting the image quality as a cause of the ghost image, in the light amount adjustment element switching unit 114K, the angle θ is equal to or in addition to the expression (1). Instead, as shown in FIG. 13, when the diameter of the cylindrical lens 115K is a, and the distance to the light amount adjustment element 125 shown as the holding member 127K in FIG.
(A / 2) / b ≦ tan (2θ) (2)
It comes to satisfy.

  Here, the diameter a of the cylindrical lens 115K is a plane parallel to the paper surface of FIG. 13, that is, a plane through which the optical axis S at the fixed position passes, and the angle of the light amount adjusting element 125 with respect to the virtual plane 126 is θ. This means the size of the diameter in the direction parallel to the virtual surface 126 in the plane. The distance d is a distance from the light amount adjusting element 125 to the cylindrical lens 115K along the optical axis S through the light amount adjusting element 125 occupying the fixed position.

  As shown in FIG. 13, the reflected light from the light amount adjusting element 125 indicated by the one-dot chain line arrow forms an angle 2θ with respect to the optical axis S on the plane, and thus satisfies the above formula (2). More than half of the reflected light is guided out of the area outside the cylindrical lens 115K, that is, outside the disturbance area, and more than half of the energy as ghost light is removed. The reflected light L3 is low in intensity and is at a level that is not so problematic as ghost light. Further, the reflected light from the cylindrical lens 115K is also at a level with no problem if the reflectance is small. Further, when the intensity of the reflected light by the light amount adjusting element 125 is small as shown in FIG. 7, it is at a level where there is no problem even if the angle θ is set at or near the boundary of the equation (2). Therefore, the reflected light does not become a disturbance to the latent image writing on the photosensitive drum 20K, and the occurrence of a ghost image and the influence on the image quality is prevented or suppressed. The same applies to the case where the light beam emitted from the semiconductor laser 111K is converted into a weakly divergent or weakly convergent light beam by the coupling lens 112K.

In the configuration example shown in FIG. 14, in the light amount adjustment element switching unit 114 </ b> K, the angle θ is set to the same as the diameter of the cylindrical lens 115 </ b> K together with or instead of the expression (1), and in FIG. When the distance to the light amount adjustment element 125 shown as 127K is b as described above, and the deviation amount of the cylindrical lens 115K is Δ,
(A / 2-Δ) / b ≦ tan (2θ) (3)
It comes to satisfy. Also in this figure, the light amount adjusting element 125 is shown as a holding member 127K.

  Here, the deviation amount Δ is a plane parallel to the paper surface of FIG. 14, that is, a plane through which the optical axis S at the fixed position passes, and a plane in which the angle of the light amount adjusting element 125 with respect to the virtual plane 126 is θ. This means the shift amount of the cylindrical lens 115K in the direction parallel to the virtual surface 126. The amount of the deviation Δ is such that the center of the same surface from the position where the optical axis S that has passed through the light amount adjusting element 125 arranged at the fixed position intersects the surface on the light amount adjusting element 125 side of the optical surface of the cylindrical lens 115K. This is the distance to S ′, and in other words, the direction of shift is the −θ side on the plane.

  As shown in FIG. 14, the light reflected by the light amount adjustment element 125 indicated by the dashed-dotted arrow has an angle 2θ with respect to the optical axis S on such a plane, but the cylindrical lens 115K is shifted in this direction. By arranging, the value of the angle θ may be small, and the degree of freedom of layout such as the arrangement position of each optical element and the light amount adjusting element 125 is improved.

  In addition to setting the angle θ to θ ≠ 0, or in addition to each of the combinations related to the above formulas (1) to (3), the cylindrical lens 115K is connected to the cylindrical lens 115K on the side opposite to the light amount adjusting element 125. A second aperture is arranged at an adjacent position, and light that passes through the cylindrical lens 115K and is directed toward the photosensitive drum 20K among the light reflected by the light amount adjusting element 125 is blocked by the second aperture. It is possible to prevent the occurrence of a ghost image.

  FIG. 15 shows a configuration example in which an aperture 116 </ b> K having an opening 116 ′ K is arranged as a second aperture in combination with an angle θ (≠ 0), Formula (1), and Formula (2). Also in this figure, the light amount adjusting element 125 is shown as a holding member 127K. The aperture 116K may be disposed so as to block the reflected light from the light amount adjusting element 125 when it passes through the cylindrical lens 115K. However, when the position of the aperture 116K is determined first, the angle θ is set to θ ≠ 0. In addition to 1. distance from the light amount adjusting element 125 to the aperture; 2. Refractive index of cylindrical lens 115K. It is clearly determined from the thickness of the cylindrical lens 115K.

  The surface of the aperture 116K body on the side of the cylindrical lens 115K is painted black so that the entire light beam is absorbed. However, as shown in FIG. Alternatively, or instead of this, a roughening process may be performed so that the incident light beam is not scattered and disturbed.

  Further, in order to prevent the cylindrical lens 115K from generating reflected light in a portion outside the effective region and not generating a ghost image due to light transmission in the portion outside the effective region, as shown in FIG. A discontinuous and fine uneven shape may be applied to a portion outside the effective region 115′K, or a roughening process may be applied instead of or together with this. Instead of or together with this, for the same purpose, either one of the entrance surface and exit surface of the cylindrical lens 115K may be provided with an antireflection coating.

  Here, the effective area is a portion also referred to as an effective diameter, and usually refers to a range in which normal light used for latent image formation, that is, optical writing is expected to pass. Therefore, the optical surface within the effective diameter is formed with high accuracy, but the cylinder surface continues outside the effective diameter, and the surface accuracy is inferior to that within the effective diameter, but it has a converging effect on the light flux. No. Therefore, for example, when the inclination θ of the light amount adjusting element 125 is not set appropriately, the light flux that has passed outside the effective diameter of each of the incident side and emission side surfaces of the cylinder lens 115K is condensed on the photosensitive drum 20K to form a ghost image. It can happen. However, even in such a case, the ghost image is prevented or suppressed by performing the processing on the incident side surface of the cylinder lens 115K.

  For the same purpose and in addition to this, for the purpose of preventing disturbance to the control in the light intensity control device 124, a plurality of optical elements included in the optical system, such as the cylinder lens 115K in the set of optical systems described above. In the optical element using light transmittance among them, when the incident surface or the reflection surface is a flat surface, it is preferable that at least one of the flat surfaces is provided with an antireflection coating.

  As described above, the angle θ is set to θ ≠ 0, and various configurations other than the formulas (1), (2), and (3) are added to the positioning of the holding member 127K by the light amount adjusting element switching unit 114K. There is also a reason that the error that occurs in cannot be completely eliminated. However, if the angle θ is θ ≠ 0 and various configurations are added in addition to the formulas (1), (2), and (3), an error occurs in the positioning of the holding member 127K, and it is arranged at the fixed position. Even if an error occurs in the angle θ related to the light amount adjusting element 125, the intended purpose of tilting the light amount adjusting element 125 by the angle θ is achieved.

  In each configuration example described above, the angle θ is configured by an angle inclined in the scanning plane as is apparent from FIG. 5, but the angle θ includes the optical axis S as shown in FIG. You may comprise by the angle inclined in the surface perpendicular | vertical to a surface, and you may comprise by the inclination which combined these. In the drawing, in addition to the scanning lens 118K, a second scanning lens 118 'is provided. Such a configuration is applicable to other configuration examples.

  Further, the light amount adjusting element 125, that is, the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K are parallel flat plates having no curvature on the light incident / exit surface, and have no power with respect to the incident / exiting light beam. ing. That is, the light amount adjusting element 125K is literally provided only for adjusting the transmitted light amount. Thereby, the exposure position shift by arrange | positioning the light quantity adjustment element is suppressed.

  However, since the position of the light beam emitted from the light amount adjustment element 125 is shifted with respect to the light beam incident on the light amount adjustment element 125 due to the inclination of the angle θ, the position of the light source is slightly shifted to cancel this, It is also possible to arrange parallel plates with high transmittance that can be ignored by the adjustment function in place.

  Further, although the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K have been described as glass materials or elements with an increased reflection coating applied thereto in the above-described example, a plastic material or an increased reflection coating is applied to this. It may be an element, a light absorption element, or a combination thereof. Further, a combination of original coating and low reflection coating may be used as appropriate.

  The glass plate 130K and the ND filters 131K, 132K, 133K, and 134K are used to adjust the exposure amount according to the image forming speed, and together with this, the photosensitive drums 20Y, 20M, 20C, and 20K are scanned. You may use in order to equalize the intensity of scanning light. In this way, in the optical system corresponding to each color, there is a slight difference in the optical characteristics of each optical element in the manufacturing process or the like, and it is difficult to completely eliminate the mounting error. As described above, even if the light use efficiencies are different from each other, the variation in the light use efficiencies is suppressed, and the toner images of the respective colors are favorably formed at a density that makes the synthesized color image good. It is also effective in reducing the deterioration of droop characteristics.

  In each of the configuration examples described above, the light amount adjusting element is a member in which the incident surface and the emitting surface of the light beam are parallel to each other like the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K. As shown in FIG. 17, the element may be a prism-like member in which the light beam entrance surface and the light exit surface form the angle θ described above. These light quantity adjusting elements corresponding to the glass plate 130K and the ND filters 131K, 132K, 133K, and 134K described above are indicated by the same reference numerals with “′”. These members are hereinafter referred to as prisms 130K ', 131K', 132K ', 133K', and 134K ', respectively.

  In the configuration example shown in the figure, the incident surfaces of the light beams in the prisms 130K ′, 131K ′, 132K ′, 133K ′, and 134K ′ form an angle θ with respect to the optical axis S, and the holding member 127K 130K ', 131K', 132K ', 133K', and 134K 'are perpendicular to the optical axis S on the incident surface side, and the exit surface sides of the prisms 130K', 131K ', 132K', 133K ', and 134K' are different from each other at appropriate positions. I support it.

  The holding member 127K may support the incident surface side of the prisms 130K ′, 131K ′, 132K ′, 133K ′, and 134K ′. In this case, the prisms 130K ′, 131K ′, 132K ′, 133K ′, and 134K ′ are supported. Are arranged so as to form an angle θ with respect to the optical axis S on the exit surface side.

  In any case, the optical axis S on the exit surface side of the prisms 130K ′, 131K ′, 132K ′, 133K ′, and 134K ′ is the light on the incident surface side of the prisms 130K ′, 131K ′, 132K ′, 133K ′, and 134K ′. In order to make an angle θ with respect to the axis S, the members such as the cylindrical lens 115K and the aperture 116K through which the light beams that have passed through the prisms 130K ′, 131K ′, 132K ′, 133K ′, and 134K ′ pass are placed in the optical path of the light beam. Arrange along. In this case, if each member such as the cylindrical lens 115K and the aperture 116K is appropriately arranged so as to satisfy each condition in each of the above-described configuration examples, each advantage can be obtained.

  Each of the prisms 130K ', 131K', 132K ', 133K', and 134K 'is a wedge side prism, and color blur is highly suppressed. In addition, the metal coating forming the enhanced reflection coating is composed of the prisms 130K ′, 131K ′, 132K ′, 133K ′, and 134K ′ among the incident surfaces and the exit surfaces of the prisms 130K ′, 131K ′, 132K ′, 133K ′, and 134K ′. Is provided on the surface on the side that forms an angle θ with respect to the optical axis S incident on the light, and exhibits its function well.

  In the image forming apparatus 100 described above, the exposure amount for the photosensitive drums 20Y, 20M, 20C, and 20K by the light source such as the semiconductor lasers 111K and 111C is adjusted even when the shading characteristics are corrected and the process control is performed. . At this time, even if the output characteristics of the light source have the disadvantages as described above, the light source performance can be improved by selectively using the light amount adjusting elements such as the glass plate 130K, the ND filters 131K, 132K, 133K, and 134K. Is good and the exposure is good. This is because, when a light amount adjusting element having a low light transmittance is used, the light source can be operated in a range where the output of the light source is good due to flattening of shading characteristics.

  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 disposed in each optical path. However, two or more light amount adjusting elements are disposed in each optical path in order to optimize the image forming speed. At this time, the light transmittance of these light quantity adjusting elements may be different.

  Further, in the above-described embodiment, the light amount adjustment element is disposed from the light source to the scanning unit, particularly between the aperture and the cylindrical lens. However, if possible, the arrangement position of the light amount adjustment element is not limited to this. It may be arranged at another position in the optical path to the scanning means, or may be arranged at any position in the optical path from the scanning means to the surface to be scanned. However, if it is arranged in the optical path from the scanning means to the surface to be scanned, the light quantity adjustment element is arranged for the light beam after scanning, and the light quantity adjustment element and the light quantity adjustment element switching means are enlarged. It is desirable to arrange in the optical path to the scanning means.

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. Also in this case, the light amount adjusting element is selected in each optical scanning device in accordance with the image forming speed, and the angle θ is determined as described above.
The deflecting unit may be a vibrating element whose reflecting surface vibrates instead of a rotating polygonal mirror such as a polygon mirror.

  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.

8 Optical scanning device 20C, 20K, 20M, 20Y Scanned surface, image carrier 100 Image forming device 111C, 111K Surface emitting laser array 112C, 112K Coupling lens 112C, 113C, 115C, 117b, 118C, 119C Multiple optical elements , Optical system 112K, 113K, 115K, 116K, 117a, 118K, 118′K, 119K multiple optical elements, optical system 113C, 113K first aperture 113′K aperture 114K light quantity adjusting element switching means 115C, 115K cylindrical lens 116C 116K Second aperture 117 Scanning means 117a, 117b Deflection optical element, rotary polygon mirror 117a, 118Y, 119Y Multiple optical elements, optical systems 117b, 118M, 119M Multiple optical elements, optical systems 125, 13 0K, 131K, 132K, 133K, 134K Light quantity adjusting element 130K ′, 131K ′, 132K ′, 133K ′, 134K ′ Light quantity adjusting element, wedge-shaped prism 126 Surface perpendicular to optical axis 127K Holding member 128K Driving means S Optical axis

JP 2008-033062 A JP 2002-341699 A JP 2003-260813 A JP 2000-241867 A

Claims (20)

A surface emitting laser array in which a plurality of surface emitting laser elements are arranged;
An optical system having a plurality of optical elements for guiding the light emitted from the surface emitting laser array to the scanned surface in order to scan the scanned surface with the light emitted from the surface emitting laser array;
A plurality of light amount adjusting elements having different light transmittances;
A light amount adjusting element switching means for disposing one of the plurality of light amount adjusting elements at a predetermined position in the optical path of the light emitted from the surface emitting laser array;
The plurality of optical elements include a coupling lens that couples light emitted from the surface emitting laser array, and the light amount adjusting element that is light emitted from the surface emitting laser array and disposed at the predetermined position. Including a cylindrical lens that transmits light having passed through
Of the plurality of light amount adjustment elements, at least an incident surface of the incident surface and the emission surface of the light amount adjustment element arranged at the predetermined position by the light amount adjustment element switching unit is light emitted from the surface emitting laser array. Is inclined at a predetermined angle θ (≠ 0) with respect to a plane perpendicular to light passing through the predetermined position along the optical axis of the coupling lens,
The diameter of the cylindrical lens on the plane with the angle of the same light amount adjustment element with respect to the vertical plane as θ is a,
The distance from the same light amount adjusting element along the light along the optical axis of the coupling lens out of the light passing through the light amount adjusting element disposed at the predetermined position to the cylindrical lens is b,
From the position where the light along the optical axis of the coupling lens among the light that has passed through the light amount adjusting element disposed at the predetermined position intersects the surface on the same light amount adjusting element side of the optical surface of the cylindrical lens, The cylindrical lens is placed in a direction perpendicular to the rotation axis direction of the optical deflector on which the light passing through the cylindrical lens is incident and the optical axis direction of the coupling lens so that the deviation amount to the center is Δ. Shift the distance between the center and the same light intensity adjustment element closer to the side,
θ is an optical scanning device that satisfies (a / 2−Δ) / b ≦ tan (2θ) . The optical scanning device according to claim 1,
The light quantity adjusting element switching means is characterized in that, among the plurality of light quantity adjusting elements, one light quantity adjusting element corresponding to the moving speed is arranged at the predetermined position according to the moving speed of the scanned surface. Optical scanning device. The optical scanning device according to claim 1 or 2,
At least one of the entrance surface and the exit surface of the light amount adjusting element is provided with a metal coating for adjusting light transmittance. And has it the optical scanning apparatus according to claim 3,
The optical scanning device according to claim 1, wherein the metal coating is applied to a surface inclined at the predetermined angle θ. In the optical scanning device according to any one of claims 1 to 4,
The light scanning device according to claim 1, wherein the light amount adjusting element is a wedge-type prism. In the optical scanning device according to any one of claims 1 to 5 ,
The plurality of optical elements have a first aperture for limiting the thickness of the light for limiting the thickness of the light emitted from the surface emitting laser array and then entering the scanning means for scanning the light. Including one aperture,
The predetermined position is a position adjacent to the first aperture, where light having passed through the first aperture enters,
On the plane where the angle of the same light amount adjustment element with respect to the vertical plane is θ, the diameter of the opening on the vertical plane is φ,
The shortest distance along the optical path of the light emitted from the surface emitting laser array from the edge of the opening to the light amount adjusting element occupying the predetermined position on the plane is defined as d. When
θ satisfies the following condition: φ / d ≦ tan (2θ). The optical scanning device according to claim 6.
An optical scanning device, wherein the first aperture is subjected to black painting and / or roughening. The optical scanning device according to claim 6 or 7,
On the plane, the first aperture is inclined to the -θ side with respect to the vertical plane. Of the light-scanning apparatus odor according to any one of claims 1 to 8,
Wherein the predetermined position includes an optical scanning device, characterized in that the next to the cylindrical lens, the light passing through the light quantity adjusting device which is arranged in the same predetermined position is a position which enters to the cylindrical lens. In the optical scanning device according to any one of claims 1 to 9 ,
The plurality of optical elements include a deflection optical element that deflects the light to scan the surface to be scanned with the light emitted from the surface emitting laser array,
This deflection optical element is a rotary polygon mirror having a plurality of reflection surfaces, or a vibration element in which the reflection surfaces vibrate,
An optical scanning device characterized in that a reflection period of light emitted from the surface emitting laser array by the deflecting optical element is changed in accordance with a moving speed of the surface to be scanned . In the optical scanning device according to any one of claims 1 to 10 ,
An optical scanning device characterized in that an entrance surface and / or an exit surface of the cylindrical lens is provided with an antireflection coating. The optical scanning device according to any one of claims 1 to 11 ,
An optical scanning device characterized in that a portion outside the effective region of the incident surface and / or the exit surface of the cylindrical lens is subjected to a roughening process and / or a discontinuous uneven shape. In the optical scanning device according to any one of claims 1 to 12,
The plurality of optical elements block light that is reflected by the light amount adjusting element disposed at the predetermined position and that travels toward the scanned surface, thereby guiding the light to the outside of the scanned surface. An optical scanning device comprising a second aperture to be made. In the optical scanning device according to any one of claims 1 to 13,
The plurality of optical elements are optical elements that utilize light transmittance to scan a surface to be scanned with light emitted from the surface emitting laser array, and an optical element having a flat incident surface or reflecting surface. Including
At least one of the planes is provided with an antireflection coating. In the optical scanning device according to any one of claims 1 to 14,
At least one of the plurality of light amount adjusting elements is an element in which a glass or plastic material is coated with an increased reflection coating, a light absorption element, a glass material or a plastic material, Optical scanning device. In the optical scanning device according to any one of claims 1 to 15,
The light scanning device according to claim 1, wherein the plurality of light amount adjustment elements have a plane of incidence and a plane of emission. The optical scanning device according to any one of claims 1 to 16,
The light quantity adjusting element switching means includes a holding member holding the plurality of light quantity adjusting elements and one of the plurality of light quantity adjusting elements by rotating or holding the holding member in parallel. And an optical scanning device characterized in that the optical scanning device has a driving means for disposing one at the predetermined position. An image forming apparatus comprising: the optical scanning device according to claim 1 ; and an image carrier that forms the surface to be scanned and forms a latent image by the scanning light . The image forming apparatus according to claim 18, comprising a plurality of the optical scanning devices. A surface emitting laser array in which a plurality of surface emitting laser elements are arranged;
An optical system having a plurality of optical elements for guiding the light emitted from the surface emitting laser array to the scanned surface in order to scan the scanned surface with the light emitted from the surface emitting laser array;
A plurality of light amount adjusting elements having different light transmittances;
A light amount adjusting element switching means for disposing one of the plurality of light amount adjusting elements at a predetermined position in the optical path of the light emitted from the surface emitting laser array;
The plurality of optical elements include a coupling lens that couples light emitted from the surface emitting laser array, and the light amount adjusting element that is light emitted from the surface emitting laser array and disposed at the predetermined position. Including a cylindrical lens that transmits light having passed through
Of the plurality of light amount adjustment elements, at least an incident surface of the incident surface and the emission surface of the light amount adjustment element arranged at the predetermined position by the light amount adjustment element switching unit is light emitted from the surface emitting laser array. Is inclined at a predetermined angle θ (≠ 0) with respect to a plane perpendicular to light passing through the predetermined position along the optical axis of the coupling lens,
The diameter of the cylindrical lens on the plane with the angle of the same light amount adjustment element with respect to the vertical plane as θ is a,
The distance from the same light amount adjusting element along the light along the optical axis of the coupling lens out of the light passing through the light amount adjusting element disposed at the predetermined position to the cylindrical lens is b,
From the position where the light along the optical axis of the coupling lens among the light that has passed through the light amount adjusting element disposed at the predetermined position intersects the surface on the same light amount adjusting element side of the optical surface of the cylindrical lens, The cylindrical lens is placed in a direction perpendicular to the rotation axis direction of the optical deflector on which the light passing through the cylindrical lens is incident and the optical axis direction of the coupling lens so that the deviation amount to the center is Δ. Shift the distance between the center and the same light intensity adjustment element closer to the side,
θ is an optical scanning method that satisfies (a / 2−Δ) / b ≦ tan (2θ) .

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