JP3686643B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an optical scanning device and an image forming apparatus.
[0002]
[Prior art]
  2. Description of the Related Art Image forming apparatuses using an optical scanning device are widely used as optical printers, digital copying apparatuses, facsimile apparatuses, optical plotters, and the like. As the optical scanning device used in these image forming apparatuses, in addition to the conventional single beam scanning type, a multi-beam scanning type is also being realized. As the configuration of the image forming apparatus, monochrome image formation is performed. In addition to those, those that form color images and multicolor images are being put into practical use, and among them, what is called a “tandem type” is being actively developed (see Patent Documents 1 to 6).
[0003]
  The writing by the optical scanning device is increasing in density, and it is intended to realize a writing density of 1200 dpi, 1600 dpi, and higher. In order to realize high-density writing, the stability of the light spot, that is, “the spot diameter of the light spot that optically scans the surface to be scanned does not vary greatly with the image height” is indispensable.
[0004]
  As is well known, one of the causes of the spot diameter fluctuation depending on the image height of the light spot is “field curvature by the scanning imaging optical system”. In order to improve the stability of the light spot, A large number of "scanning imaging optical systems corrected to" are known.
[0005]
  In a multi-beam scanning optical scanning device, in addition to the stability of the light spot, the imaging magnification of the scanning imaging optical system that condenses the deflected light beam toward the surface to be scanned is substantially independent of the image height of the light spot. It is also important that it is constant.
[0006]
[Patent Document 1]
    JP-A-11-157128
[Patent Document 2]
    JP-A-9-127443
[Patent Document 3]
    JP-A-9-54263
[Patent Document 4]
    Japanese Patent Laid-Open No. 2001-4948
[Patent Document 5]
    Japanese Patent Laid-Open No. 2001-10107
[Patent Document 6]
    JP 2001-33720 A
[0007]
[Problems to be solved by the invention]
  An object of the present invention is to realize an optical scanning device that is excellent in the stability of a light spot and has a high imaging magnification of a scanning imaging lens, and an image forming apparatus using the same.
[0008]
[Means for Solving the Problems]
  The optical scanning device according to the present invention includes: “a deflection unit that deflects a light beam from a light source; and a scanning link that guides the light beam deflected by the deflection unit onto a surface to be scanned and collects the light beam on the surface to be scanned as a light spot. An optical scanning device having an image lens ”has the following characteristics (claim 1).
[0009]
  That is, the scanning imaging lensTwoThese have a scanning lensTwo"Scanning lens"SideThe “scanning lens” has “positive refractive power in the main scanning direction” and “refractive power in the sub-scanning direction is substantially zero”.Two"Scanned surface"SideThe “scanning lens” has “a negative refractive power in the main scanning direction and a positive refractive power in the sub-scanning direction”.
[0010]
  The scanning imaging lens in the optical scanning device according to claim 1 is composed of “two scanning lenses”.TheIn this case, it is preferable that the scanning lens on the scanning surface side has a “negative meniscus shape in which the shape in the main scanning section faces the surface to be scanned” (claim 2).
[0011]
  The “main scanning section” is a virtual flat section including the optical axis of the scanning lens and parallel to the main scanning direction. A virtual flat section perpendicular to the main scanning direction is referred to as a “sub-scanning section”.
[0012]
  The optical scanning device according to claim 1, wherein the distance on the optical axis from the deflection starting point of the deflecting means to the surface to be scanned: L,Each runMaximum distance of the lens interval on the optical axis in the review lens: a is the condition:
  (1) 0.3 <| a / L | <0.6
It is preferable to satisfy “.
[0013]
  3. The scanning imaging lens in the optical scanning device according to claim 1, wherein the scanning imaging lens has the function of having a geometrically optically conjugate relationship between the deflection starting point of the deflection means and the surface to be scanned in the sub-scanning direction. Magnification in the sub-scanning direction on the optical axis between the scanning surface and the surface to be scanned: β₀Lateral magnification in the sub-scanning direction at an arbitrary image height: β_hBut the condition:
  (2) 0.9 <| β_h/ β₀｜ <1.1
It is preferable to satisfy (Claim 3).
[0014]
  The scanning imaging lens in the optical scanning device according to any one of claims 1 to 3, wherein “the function of causing the deflection start point of the deflecting means and the surface to be scanned to be substantially conjugate with respect to the sub-scanning direction is geometrically optically conjugate. Horizontal magnification in the sub-scanning direction on the optical axis between the deflection surface and the surface to be scanned: β₀But the condition:
  (3) 0.2 <| β₀｜ <0.6
It is preferable to satisfy (Claim 4).
[0015]
  lightConfiguring a scanning imaging lens in a scanning deviceTwoAt least one of the scanning lenses can be a plastic lens. In this case, “deflection means”Side runningThe review lens can be a plastic lens.(Claim 1).
[0016]
  The optical scanning device according to claim 1 described above is “Corresponding to each colorIt has a plurality of light sources, the light beam from each light source is deflected by a common deflecting means, and by a scanning imaging lensOn different photoreceptorsAre formed as light spots on the corresponding scanned surface to form a scanning imaging lens.TwoAmong the scanning lenses, the scanning lens close to the deflecting unit is shared by a plurality of light beams directed to different scanning surfaces ”.
[0017]
  Claims 1-4In the optical scanning device according to any one of the above, “a plurality of light beams directed to different scanning surfaces are common to these deflecting means”Side running(The crossing lenses pass substantially parallel to each other in the sub-scanning direction.)Claim 5).
[0018]
  Claims 1-5The optical scanning device according to any one of the above "Corresponding to each colorIt is a reflection type having a plurality of light sources and the deflecting means having a deflecting reflecting surface, and all light beams deflected by the same deflecting reflecting surface intersect at substantially one point near the deflecting surface in the main scanning direction. '' Can be configured as (Claim 6).
[0019]
  In the above, “all light beams deflected by the same deflecting / reflecting surface intersect at approximately one point near the deflecting surface in the main scanning direction” means that a plurality of light beams incident on the same deflecting / reflecting surface are sub-scanned. When viewed from the direction, it means that these light beams intersect at approximately one point near the deflecting reflecting surface.
[0020]
  Of the scanning surface optically scanned by the optical scanning device.entityIs the photosensitive surface of a “photosensitive medium” such as a photoconductive photoreceptor.Claims 1 and 5In addition to the photosensitive surfaces of different photosensitive media, “different scanning surfaces” on the same photosensitive medium also include “separate optical scanning positions at which different images are written”.
[0021]
  In addition, a plurality of light beams may be optically scanned on different scanned surfaces, but a plurality of light beams may be optically scanned on one scanned surface as in the multi-beam scanning method.
[0022]
  The image forming apparatus according to the present invention is an “image forming apparatus that forms an image by performing optical scanning on a photosensitive medium”,Claims 1-6The optical scanning device according to any one of (1) is included (Claim 7). As the photosensitive medium, the above-described photoconductive photoreceptor can be used, and a silver salt film can also be used. The latent image formed on the silver salt film by optical scanning can be visualized by a normal silver salt photographic development process.
[0023]
  As described above, an image forming apparatus using a silver salt film as a photosensitive medium can be implemented as an optical plate making machine or an optical drawing apparatus (forming a CT scan image).
[0024]
  The image forming apparatus according to claim 7, wherein a plurality of photoconductive photosensitive members are arranged as photosensitive media along a transfer medium conveyance path, and an electrostatic latent image is formed by performing optical scanning on each photosensitive member. In addition, each electrostatic latent image is visualized as a toner image of a different color, and each color toner image is superimposed on the same sheet-like recording medium, transferred and fixed, and configured as an image forming apparatus that obtains an image synthetically ” (Claim 8).
[0025]
  The “sheet-like recording medium” is a transfer paper, an OHP sheet (plastic sheet for an overhead projector), or the like.
  The “transfer medium” can be a sheet-like recording medium itself, but can also be an intermediate transfer medium such as an intermediate transfer belt. That is, the toner image formed on each photoconductor may be directly transferred to a sheet-like recording medium (direct transfer method) or may be transferred via an intermediate transfer medium (intermediate transfer method).
[0026]
  Claim 8The image forming apparatus described is an optical scanning apparatus.Claims 5 and 61 can be used to constitute a “tandem-type image forming apparatus”. In this case, the number of photoconductive photoconductors is 3 or 4, and a color image can be formed (Claim 10).
[0027]
  The optical scanning device according to claim 1, wherein the scanning imaging lens isTwoScanning lens and deflecting meansSide runningThe review lens has a positive refractive power in the main scanning direction and a refractive power in the sub-scanning direction is substantially zero.Side runningThe review lens has a negative refractive power in the main scanning direction and a positive refractive power in the sub-scanning direction.
[0028]
  Therefore, the function for realizing constant velocity characteristics such as the fθ characteristic is referred to as “deflecting means”.Side runningIn addition to allocating to the “lens”, the imaging function in the sub-scanning direction is mainly used for the “scanned surface”.Side runningBy allocating to the “lens”, it is possible to correct the curvature of field particularly in the sub-scanning direction. In addition, since the imaging function in the sub-scanning direction is distributed to the scanning lens close to the surface to be scanned, the imaging magnification in the sub-scanning direction can be reduced, a small-diameter light spot can be realized, and the variation in magnification due to the image height can also be achieved. Easy to correct.
[0029]
  In the optical scanning device according to claim 2, the scanning imaging lens is composed of two scanning lenses, and the scanning lens on the scanning surface side has a shape in the main scanning section of “a negative surface with a convex surface facing the scanning surface”. Because of the “meniscus shape”, it is easy to make the optical magnification constant with respect to the image height.
[0030]
  At least two surfaces in the sub-scanning direction are expressed as “a curvature center line obtained by connecting the center of curvature in the sub-scanning section in the main scanning direction is a curve different from the non-arc shape in the main scanning direction in the main scanning section. When the curvature radius in the sub-scan section is changed in the main scanning direction and the two lens surfaces are bent to adjust the main point position in the sub-scanning direction, the distance between the two surfaces is wide. As the amount of change in the principal point position increases, the lateral magnification in the sub-scanning direction can be easily corrected between image heights.
[0031]
  In the optical scanning device according to the second aspect, from the viewpoint of cost reduction, the number of scanning imaging lenses is two, and the scanning lens closest to the deflecting unit has almost no refractive power in the sub-scanning direction. For this reason, the two surfaces become the first and second surfaces of the scanning lens on the scanning surface side, and these surfaces are set to “negative meniscus shape with the convex surface facing the scanning surface” in the main scanning section. Thus, the distance between the two surfaces increases as the distance from the optical axis increases, facilitating “adjustment of the principal point position in the sub-scanning direction on the peripheral side”, and image formation in the sub-scanning direction with respect to the image height of the light spot. The change in magnification can be effectively reduced.
[0032]
  In other words, since the optical path length of the peripheral image height is longer than the central image height, in order to keep the lateral magnification in the sub-scanning direction constant regardless of the image height, the principal point position at the peripheral image height is set to the central image height. On the other hand, there is a point on the deflection means side. In order to realize this, the negative meniscus convex side is set as the scanned surface side so that the principal point position at the peripheral image height can be positioned on the deflection means side with respect to the central image height, The first and second surfaces of the near scanning lens are “the curvature center line obtained by connecting the center of curvature in the sub-scanning section in the main scanning direction is a curve different from the non-arc shape in the main scanning direction in the main scanning section. In addition, using a surface whose curvature radius in the sub-scanning section is changed in the main scanning direction, and bending the two lens surfaces to adjust the main point position in the sub-scanning direction, The optical magnification can be made substantially constant.
[0033]
  The condition (2) in claim 3 is a “desired range” within the effective scanning region of the imaging magnification in the sub-scanning direction of the scanning imaging lens, and if outside this range, the effective scanning region of the spot diameter of the light spot Variation in the image becomes larger, and the formed image is affected. Satisfying condition (2) allows the pitch between multiple scanning lines to be kept constant even when performing multi-beam scanning optical scanning. It becomes possible.
[0034]
  If the lower limit of condition (3) in claim 4 is exceeded, the lateral magnification in the sub-scanning direction on the optical axis between the deflecting means and the surface to be scanned with respect to the target spot diameter: β₀Is set large, the aperture diameter in the beam shaping aperture needs to be set small, and the problem of insufficient light quantity and the deterioration of the spot diameter due to the influence of diffraction in the aperture are likely to occur. Deflection means when the upper limit of condition (3) is exceededSide runningThe distance between the scanning lens and the surface to be scanned is increased, which tends to increase the size of the image forming apparatus.
[0035]
  For example, in the case of configuring a tandem image forming apparatus that shares a deflecting unit,TwoScanning lensBetweenIn this case, when the lower limit of the condition (1) in claim 1 is exceeded, a mirror for separating the optical path is arranged on the surface to be scanned corresponding to each color.TwoThe distance on the optical axis that is farthest between the scanning lenses becomes too short, making it difficult to dispose an optical path separation mirror or the like.
[0036]
  If the upper limit of condition (1) is exceeded, the scanning lens on the deflection means side approaches the deflection means side, but this scanning lens has a strong positive refractive power in the main scanning direction, so that it is effective on the surface to be scanned. The field angle for optical scanning of the scanning area is narrowed, the scanning time is shorter than when the field angle is wide, and the on / off response speed of the LD used for the light source corresponds to the writing density There is a risk that it will not be possible.
[0037]
  Claim 1As described above, when a plastic lens is used as the scanning lens, it can be manufactured at low cost, and a complicated surface shape such as an aspherical surface can be easily formed. On the other hand, a plastic lens is likely to change its optical characteristics due to temperature changes. In particular, in a rotary polygon mirror or the like that is a general deflecting means, the ambient temperature tends to rise due to heat generated by a drive motor that rotates a polygon mirror or the like.
[0038]
  Claim 1If the scanning lens on the deflecting means side is a plastic lens as in the optical scanning device described, the temperature is likely to change due to the heat generated by the drive motor, and a tandem color that uses a separate scanning imaging lens for each photoconductor. In the image forming apparatus, the “change in constant velocity attributed to temperature change” of the scanning imaging lens is divided for each scanning imaging lens, and color shift and hue change are likely to occur in the composite color image.Claim 1Deflection means, such as an optical scanning deviceSideIf the scanning lens (having the function of correcting the constant velocity characteristics) is “shared by multiple light beams directed to different scanning surfaces”, the constant velocity variation will occur in the same way for each color, and the color shift and hue The occurrence of changes is suppressed.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments will be described.
[0040]
  FIG. 1 shows an optical arrangement in an embodiment of an optical scanning device.
  The optical scanning device deflects the light beam from the light source 1 and guides the light beam deflected by the deflecting means 5 onto the surface to be scanned 7 and collects it as a light spot on the surface to be scanned 7. And an optical scanning device having a scanning imaging lens 6.TwoScanning lenses 6A, 6BTwoOf the scanning lenses 6A and 6B, the scanning lens 6A closest to the deflecting means 5 has a positive refractive power in the main scanning direction and a refractive power in the sub-scanning direction of substantially zero.TwoOf these scanning lenses, the scanning lens 6B closest to the scanned surface 7 has a negative refractive power in the main scanning direction and a positive refractive power in the sub-scanning direction.
[0041]
  More specifically, the light beam emitted from the light source 1 is converted into a parallel light beam (may be weakly convergent or weakly divergent) by the coupling lens 2 and coupled to the subsequent optical system. The coupled light beam passes through the aperture 3 of the aperture 3 to obtain a desired spot diameter on the surface 7 to be scanned, and then is shaped in the sub-scanning direction by the cylindrical lens 4 and passes through the mirror IM. Thus, an image is formed as a “line image long in the main scanning direction” in the vicinity of the deflection reflection surface 5 A of the deflecting means 5, and is deflected by the deflecting means 5 at an equal angular velocity. The deflection means 5 is a rotary polygon mirror.
[0042]
  The light beam deflected by the deflecting means 5 is condensed as a light spot on the scanned surface 7 by the scanning lenses 6A and 6B constituting the scanning imaging lens 6, and the scanned surface 7 is optically scanned at a constant speed. .
[0043]
  In this optical scanning device, the two scanning lenses 6A and 6B constituting the scanning imaging lens 6 are both plastic lenses. The scanning lens 6A on the deflecting means 5 side is given a "positive refractive power in the main scanning direction", and this positive refractive power is set so that "constant velocity (fθ characteristic) is well corrected". Yes. The scanning lens 6B on the scanned surface 7 side has “negative refractive power in the main scanning direction”.
[0044]
  In this way, with respect to the main scanning direction, by making the refractive power of the scanning lens 6A positive and the refractive power of the scanning lens negative, each scanning lens caused by environmental fluctuations such as temperature changes and emission wavelength fluctuations in the light source 1 is obtained. The change in the optical characteristics of 6A and 6B is canceled out, and the deterioration of the optical characteristics of the scanning imaging lens 6 due to environmental fluctuations and wavelength fluctuations is reduced.
[0045]
  The scanning lens 6B on the scanning surface side has a “long shape” as shown in the figure. When this is configured as “a lens having a positive refractive power in the main scanning direction”, the lens thickness in the lens longitudinal direction is set. On the other hand, the thickness of the peripheral portion becomes thinner, and the thickness of the central portion and the peripheral portion in the longitudinal direction tends to cause deformation of the lens shape due to “shrinkage” or the like during shaping.
[0046]
  However, since the scanning lens 6B has a refractive index “negative in the main scanning direction”, a “large thickness difference” does not occur in the longitudinal direction, and thus shaping is easy.
[0047]
  Although the scanning lens 6A has the function of correcting the constant velocity as described above, since the lens 6A has no refractive power in the sub-scanning direction, scanning imaging is performed even if the incident position of the deflected light beam is shifted in the sub-scanning direction. The constant velocity as the lens 6 does not deteriorate. In addition, it is possible to suppress deterioration of the imaging performance in the main scanning direction.
[0048]
  Regarding the sub-scanning direction, since the refractive power of the scanning lens 6A is substantially 0, the scanning lens 6B has a strong positive refractive power. Therefore, in the sub-scanning direction, the scanning lens 6B has a function of “condensing the deflected light beam on the surface to be scanned”. In this way, since the imaging function in the sub-scanning direction is borne by the scanning lens 6B close to the scanned surface 7, the scanning imaging lens 6 becomes a “reduction system” in the sub-scanning direction and forms an image of the light spot. The position, spot diameter, etc. are not easily affected by assembly errors or shape errors of optical components. Of course, the scanning imaging lens 6 has a “geometrical conjugate relationship between the starting point of deflection by the deflecting means 5 and the surface to be scanned 7” in the sub-scanning direction. "have.
[0049]
  The “surface shape in the main scanning direction” of the scanning lens 6A on the deflection means side can be a non-arc shape. Further, the surface shape of the scanning lens 6B on the scanned surface side is “a non-arc shape in the main scanning direction, and the center of curvature connecting the center of curvature in the sub-scan section in the main scan direction is the main scan in the main scan section. The field curvature in both the main and sub-scan directions can be corrected satisfactorily by using a surface whose curvature radius in the sub-scan section is changed in the main scan direction so that it has a different curve from the non-arc shape in the direction. It is.
[0050]
  In this way, it is possible to satisfactorily correct the curvature of field in the main and sub-scanning directions and achieve the stability of the light spot while maintaining the “constant velocity function” satisfactorily.
[0051]
  FIG. 2 is a diagram for explaining one embodiment of an optical scanning device of a “tandem type image forming apparatus”. This image forming apparatus is an apparatus for forming a color image.
[0052]
  FIG. 2A is a diagram illustrating the optical arrangement as viewed from the sub-scanning direction. In order to simplify the drawing, the optical path of the deflected light beam is shown in a flat state on the scanning surface side from the deflecting means.
[0053]
  The color image is formed by combining “four color toner images” of yellow, magenta, cyan, and black. In the following description, “Y” is related to yellow, “M” is related to magenta, “C” is related to cyan, and “K” is related to black.
[0054]
  As shown in FIG. 2A, in the portion from the light source to the deflecting means (rotating polygon mirror) 5, four light sources 1Y to 1K, four coupling lenses 2Y to 2K, and four apertures 3Y to 3Y. 3K and four cylindrical lenses 4Y to 4K are arranged. That is, the light source 1Y overlaps with the other three light sources 1M, 1C, and 1K when viewed from the sub-scanning direction (direction orthogonal to the drawing), and the coupling lens 2Y is viewed from the sub-scanning direction and the other three couplings. The lens light sources 2M, 2C, and 2K overlap, the aperture 3Y is seen from the sub-scanning direction, the other three apertures 3M, 3C, and 3K overlap, and the cylindrical lens 4Y is seen from the sub-scanning direction, and the other three cylindrical lenses It overlaps with 4M, 4C, 4K.
[0055]
  The light sources 1Y to 1K are semiconductor lasers or the like. The light beam emitted from the light source 1Y (1M, 1C, 1K) is coupled by the coupling lens 2Y (2M, 2C, 2K) and converted into a light beam form suitable for the subsequent optical system, for example, a parallel light beam, The beam is shaped by the aperture 3Y (3M, 3C, 3K), and is formed as a "long line image in the main scanning direction" by the cylindrical lens 4Y (4M, 4C, 4K) in the vicinity of the deflection reflection surface 5A of the deflecting means. Are simultaneously deflected by the deflection means 5.
[0056]
  The four light beams (principal rays) incident on the deflecting means from each light source are parallel to each other in the sub-scanning direction.
[0057]
  FIG. 2B shows a state in which the optical path from the deflecting means to the scanned surfaces 7Y to 7K is linearly developed. The bodies of the scanned surfaces 7Y to 7K are “photoconductive photoreceptors”, and are formed in a cylindrical shape and arranged in parallel with each other as shown in FIG. FIG. 2B illustrates the scanned surfaces 7Y to 7K so that they are the same surface.
[0058]
  As shown in FIG. 2B, the light beams from the light sources 1Y to 1K are reflected and deflected in a direction perpendicular to the rotation axis of the deflecting surface by the common deflecting means 5, and are deflected, thereby scanning the lens L1. Transparent. The transmission lens L1 is common to the four light beams.
[0059]
  Each light beam transmitted through the scanning lens L1 is condensed toward the corresponding scanned surfaces 7Y to 7K by the scanning lenses L2Y to L2K, forms a light spot on each scanned surface, and optically scans the scanned surface. To do.
[0060]
  The scanning lens L1 and the scanning lens L2Y constitute a “scanning imaging lens for forming a light spot on the scanned surface 7Y”, and the scanning lens L1 and the scanning lenses L2M (L2C, L2K) are “scanned surface 7M (7C, 7K) constitutes a “scanning imaging lens” for imaging a light spot. The scanning lenses L2Y to L2K are the same.
[0061]
  As shown in FIG. 2C, the optical path of the imaging light beam by each scanning imaging lens is appropriately bent by the optical path bending mirror M and guided to the corresponding photoreceptors 7Y to 7K.
[0062]
  The light spots formed on the photoconductors 7Y to 7K optically scan the photoconductor to write an electrostatic latent image.
[0063]
  In this embodiment, the lenses constituting the scanning imaging lens are all plastic lenses, and the deflection means 5Side runningThe lens L1 is of course also a plastic lens (Claim 1).
[0064]
  The optical scanning device in FIG.Corresponding to each colorA plurality of light sources 1Y to 1K are provided, and light beams from the respective light sources are deflected by a common deflecting means 5, and are scanned and formed by scanning imaging lenses L1 and L2Y to L2K.On different photoreceptorsAre scanned as light spots on the corresponding scanned surfaces to form a scanning imaging lens.TwoAmong these scanning lenses, the scanning lens L1 close to the deflecting means 5 is shared by a plurality of light beams directed to different scanned surfaces 7Y to 7K.
[0065]
  Since the scanning lens L1 on the deflecting means 5 side does not have a refractive power in the sub-scanning direction, a plurality of light beams directed to different scanned surfaces 7Y to 7K cause the scanning lens L1 to pass through the sub-lens as shown in FIG. In the scanning direction (vertical direction in FIG. 2B), they pass substantially parallel to each other (Claim 5). In this way, the light beams (principal rays) transmitted through the scanning lens L1 are parallel to each other and do not approach each other, so that the optical path dividing mirror M can be easily disposed.
[0066]
  In the embodiment of FIG. 2, among the lenses forming the scanning imaging lens, the scanning lens L1 on the deflection means 5 side is shared by a plurality (= 4) of light beams directed to the scanned surfaces 7Y to 7K. did. The deflecting means 5 is a rotary polygon mirror, and heat generated by the motor unit and the base is large, and the temperature in the optical box rises due to heat generated by the motor unit. Due to this temperature variation, a temperature distribution is generated in the scanning lens L1 closest to the deflecting means 5, and the optical characteristics are changed.
[0067]
  Since the scanning lens L1 has a function of correcting the scanning characteristic (constant speed function), the change in the constant speed characteristic occurs due to the change in the optical characteristic, but even if such a change in the constant speed characteristic occurs. Since the scanning lens L1 is shared by the respective light beams for optically scanning the photoconductors 7Y to 7K, the change in constant velocity characteristics is made common to the photoconductors 7Y to 7K. No “difference in constant velocity characteristics” occurs. Therefore, even if the environmental fluctuations fluctuate during continuous printing, etc., and the constant velocity characteristics of the scanning imaging lens change, the hue change or color shift of the color image caused by this `` change in constant velocity characteristics '' occurs. Can be suppressed.
[0068]
  In the embodiment of FIG. 2, the portion from the light source to the cylindrical lens is “arranged in parallel with each other in the sub-scanning direction” for yellow, magenta, cyan, and black. Alternatively, a plurality of light sources, coupling lenses, and the like may be arranged so as to have a distance in the main scanning direction by appropriately folding back with a folding mirror or the like.
[0069]
  Further, the light beam for optically scanning the four photoconductors 7Y to 7K is incident in parallel in the sub-scanning direction from the deflecting unit 5 to the scanning lens L1, but as another configuration, for example, four light beams The beams are reflected in opposite directions with respect to the common deflecting means, one scanning lens corresponding to the scanning lens L1 is arranged on each side of the deflecting means, and two light beams distributed on both sides of the deflecting means. The beam may be transmitted through these two scanning lenses in common.
[0070]
  In the above, the embodiment in the case where the plurality of scanned surfaces are optically scanned by the single beam scanning method has been described. As described above, the optical scanning of the surface to be scanned may be performed by a multi-beam scanning method. An embodiment in this case will be described with reference to FIG.
[0071]
  In FIG. 3A, the light source device denoted by reference numeral 31 has two semiconductor lasers and two coupling lenses for coupling light beams emitted from these semiconductor lasers. The two light beams emitted from the respective semiconductor lasers and coupled by the corresponding coupling lens are separated by the cylindrical lens 32 into the same deflection reflection surface position of the deflection means (rotating polygon mirror) 33 in the sub-scanning direction. An image is formed as a “line image long in the main scanning direction”. At this time, the two light beams from the respective semiconductor lasers cross in the main scanning direction at substantially one point near the deflection reflecting surface.
[0072]
  Each light beam deflected by the deflecting means 33 is transmitted through the scanning lenses 34A and 34B constituting the scanning imaging lens 35, and the optical path is folded by the optical path folding mirror 36 to form the photoconductive surface. Two light spots that are condensed toward the photosensitive member 37 and separated in the sub-scanning direction are formed, and the surface to be scanned is optically scanned by the multi-beam scanning method.
[0073]
  In other words, in this embodiment, the optical scanning device has a plurality of light sources, and the deflecting means 33 is a reflection type having a deflecting reflecting surface, and is deflected by the same deflecting reflecting surface and the same scanned surface 37. Are configured such that all light beams that optically scan are intersected at approximately one point near the deflection surface in the main scanning direction (Claim 6).
[0074]
  The upper diagram of FIG. 3B shows a case where the light is incident on the deflecting / reflecting surface at different positions. The position of the deflection reflection surface when two light beams (the principal rays are indicated by solid lines and broken lines) reach the same position P0 of the surface to be scanned 37 is represented by D for the solid light beam.₁D₂In the case of FIG. 3B, the optical path passing through the scanning lenses 34A and 34B leading to the imaging position P0 is greatly different, and the optical action is also different depending on the optical path, so that the optical path is formed at the imaging position P0. The spot diameter of the light spot, the imaging magnification, and the like are likely to be different between the solid line and the broken line light beam, and in particular, the influence on the fluctuation of the scanning line pitch between the image heights is large, and the scanning line is likely to be bent.
[0075]
  On the other hand, as shown in FIG. 3A, when the two light beams from the light source side intersect in the main scanning direction in the vicinity of the deflecting reflection surface, the image forming position P0 on the scanned surface 37 is reached. The optical path is substantially the same for each of the solid and broken light beams, and the scanning line bending can be effectively reduced. Further, the “writing position fluctuation in the main scanning direction” between the light beams due to the variation of each component on the scanning surface side from the deflecting unit 5 is substantially the same for all the light beams, and the main scanning direction between the light beams is the same. Writing position shift can be suppressed.
[0076]
  Furthermore, all the light beams that are imaged at the same imaging position “pass through substantially the same position in the main scanning direction of the scanning optical lens”, thereby minimizing the influence of the aberration of the scanning lens constituting the scanning imaging lens. The image forming position in the main scanning direction can be matched with each beam with high accuracy, and the main scanning direction at the writing start image height can be set even if the delay time is set for all the light beams after synchronization detection. Can be suppressed.
[0077]
  In addition, when a plurality of light beams intersect in the main scanning direction in the vicinity of the deflection reflection surface, the size of the deflection reflection surface can be minimized, and the inscribed circle radius of the rotary polygon mirror can be minimized.
[0078]
  In the embodiment of FIG. 3, the case where the single scanned surface 37 is optically scanned by the multi-beam scanning method has been described. However, as in the embodiment of FIG. 2, the light beams directed to different scanned surfaces are deflected. When the light is deflected by the same deflecting / reflecting surface of the means, according to the layout on the light source side, “when each light beam forms an angle in the main scanning direction with respect to the same deflecting / reflecting surface”, each light beam is reflected on the polygon mirror 5. A similar effect can be obtained by intersecting in the main scanning direction in the vicinity of the deflecting and reflecting surface 5A.
[0079]
  The deviation of the crossing position of each light beam is preferably within 0.5 mm on the deflecting / reflecting surface.
[0080]
  FIG. 4 shows a “laser printer” as an embodiment of an image forming apparatus using the optical scanning device shown in FIG.
[0081]
  The laser printer 100 includes a photoconductive photosensitive member 111 formed in a cylindrical shape as a “photosensitive medium”. Around the photoconductor 111, a charging roller 112, a developing device 113, a transfer roller 114, and a cleaning device 115 are provided as charging means. A “corona charger” can also be used as the charging means.
[0082]
  Further, an optical scanning device 117 that performs optical scanning with the laser beam LB is provided, and “exposure by optical writing” is performed between the charging roller 112 and the developing device 113.
[0083]
  In FIG. 4, reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a registration roller pair, reference numeral 120 denotes a paper feed roller, reference numeral 121 denotes a conveyance path, reference numeral 122 denotes a discharge roller pair, reference numeral 123 denotes a tray, reference numeral P Indicates a transfer sheet as a “sheet-like recording medium”.
[0084]
  When performing image formation, the photoconductive photosensitive member 111 is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 112, and is subjected to exposure by optical writing of the laser beam LB of the optical scanning device 117. As a result, an electrostatic latent image is formed. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. This electrostatic latent image is reversed and developed by the developing device 113, and a toner image is formed on the image carrier 111.
[0085]
  The cassette 118 storing the transfer paper P is detachable from the main body of the image forming apparatus 100. When the transfer paper P is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper P is fed by the paper supply roller 120. The leading edge of the fed transfer paper P is caught by the registration roller pair 119.
[0086]
  The registration roller pair 119 feeds the transfer sheet P to the transfer unit at the timing when the toner image on the photoconductor 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114.
[0087]
  The transfer paper P to which the toner image is transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the discharge roller pair 122. The surface of the photoreceptor 111 after the toner image is transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like.
[0088]
  As the optical scanning device 117, the one described with reference to FIG. 1 is used.
[0089]
  FIG. 5 shows an embodiment of a “tandem type color image forming apparatus” using the optical scanning device as described above with reference to FIG. In the figure, the part denoted by reference numeral 50 is a figure.
The reference numerals 5Y, 5M, 5C, and 5K denote deflected light beams that optically scan the photoconductive photoreceptors 7Y, 7M, 7C, and 7K, respectively. For the description of this part, the description related to FIG. 2 is used.
[0090]
  Around the photoreceptor 7Y (7M, 7C, 7K), there are charging means YC (MC, CC, KC), developing means YD (MD, CD, KD), transfer means YT (MT, CT, KT), cleaning means. YL (ML, CL, KL) is disposed, and a conveyor belt 2A is disposed so as to contact the photoreceptors 7Y, 7M, 7C, 7K.
[0091]
  The photoconductors 7Y to 7K are uniformly charged by the corresponding charging means YC to KC while rotating clockwise, and are optically scanned by the light beams 5Y to 5K to write the electrostatic latent image as a negative latent image. These electrostatic latent images are developed by the developing devices YD to KD, and yellow, magenta, cyan, and black toner images are formed on the photoreceptors 7Y, 7M, 7C, and 7K, respectively.
[0092]
  A transfer sheet, which is a sheet-like recording medium on which a color image is formed, is fed from the cassette 1A and is placed on the transport belt 2A by a registration roller 9. The conveying belt 2A is charged by corona discharge by the charger 18, and the transfer paper is electrostatically adsorbed on the conveying belt 2A.
[0093]
  The transfer paper held in this manner on the conveyor belt 2A is sequentially conveyed through the transfer portion, and is “black toner image” from the photoconductor 7K, “cyan toner image” from the photoconductor 7C, and “magenta toner image” from the photoconductor 7M. "The yellow toner image" is sequentially transferred from the photoreceptor 7Y by the action of the transfer means KT to YT.
[0094]
  In this way, a color image is synthetically formed on the transfer paper. The transfer paper carrying the color image is neutralized by the static elimination charger 11, separated from the conveying belt 2 </ b> A by the stiffness of the transfer paper itself, proceeds to the fixing device 14, the color image is fixed, and is discharged onto the tray 15 ′ by the discharge roller 15. To be discharged. The photoreceptors 7Y to 7K after the toner image transfer are cleaned by the cleaning units YL to KL, respectively.
[0095]
  That is, the image forming apparatus shown in FIG. 5 arranges a plurality of photoconductive photoconductors 7Y to 7K as photosensitive media along a transfer medium (transfer paper) conveyance path, and performs optical scanning on each photoconductor. To form an electrostatic latent image, visualize each electrostatic latent image as a toner image of a different color, superimpose and transfer and fix each color toner image on the same sheet-like recording medium, and obtain an image synthetically Image forming device (Claim 8). In addition, a tandem type image forming apparatus (Claim 9), And a tandem type image forming apparatus that forms a color image with four photoconductive photoconductors (Claim 10).
[0096]
【Example】
  Hereinafter, three specific examples of the optical system of the optical scanning device will be given. The optical scanning device shown in FIGS. 1 and 2 is assumed.
[0097]
  Explanation of symbols
  The meanings of the symbols are as follows.
[0098]
  RY: Curvature radius of the surface in the main scanning direction (including the aperture surface)
  RZ: radius of curvature (on the optical axis) of the surface in the sub-scanning direction (including the aperture surface)
  N: Refractive index of the material at the wavelength used (780nm)
  X: Distance in the optical axis direction
  Y: distance in the main scanning direction from the optical axis
  Z: distance in the sub-scanning direction from the optical axis
  Example 1
  "Optical system closer to the light source than the deflection means"
Surface number RY (mm) RZ (mm) X (mm) N Remarks
Light source--0.51-Semiconductor laser array
1 ∞ ∞ 0.3 1.511 Cover glass
2 ∞ ∞ 12.0--
3 * 52.59 52.59 3.8 1.512 coupling lens
4 * -8.71 -8.71 15.0--
5 ∞ ∞ 138.85-Aperture
6 ∞ 48.0 3.0 1.511 Cylindrical lens
7 ∞ ∞ 93.57--
8----Deflection reflecting surface.
[0099]
  Surfaces marked with “*” are “coaxial aspheric surfaces”. Although the numerical value specific to the aspherical surface is not shown, the wavefront aberration of the “parallel light beam” emitted from the coupling lens is well corrected.
Is set to The deflecting means is a rotary polygon mirror having an inscribed circle diameter of 18 mm and a number of deflecting reflecting surfaces of 6.
[0100]
  "Optical system after deflection means"
  β₀(Image forming magnification on the optical axis in the sub-scanning direction between the deflecting means and the surface to be scanned): 0.38
  ｜ β_h/ β₀Maximum value of |: 0.99.
Surface number RY (mm) RZ (mm) X (mm) N Remarks
0 ∞ ∞ 68.0-Deflection reflecting surface
1 * 1897.948 ∞ 31.4 1.524 Scanning lens
2 * -151.350 ∞ 162.0--
3 ** -4430.699 -88.519 8.2 1.524 Scanning lens
4 ** -4584.974 -27.015 100.0--
5----Surface to be scanned
  Each surface marked with “*” has a non-arc shape in the main scanning section and a straight line in the sub-scanning section. This lens surface is represented by the following formula: 1.
[0101]
  That is, Cm = 1 / RY, Cs (Y) = 1 / RZ,
  X (Y, Z) = Y²・ Cm / [1 + √ {1- (1 + K) ・ (Y ・ Cm)²}]
          + A ・ Y^Four+ B ・ Y⁶+ C ・ Y⁸+ D ・ Y^Ten+ E ・ Y¹²
          + Cs (Y) ・ Z²/ [1 + √ {1- (Cs (Y) ・ Z)²}] (Formula: 1).
[0102]
  Each surface marked with “**” is a surface in which the shape in the main scanning direction is a non-arc shape, and the radius of curvature in the sub-scanning direction continuously changes depending on the lens height (Y) in the main scanning direction, Each surface shape is “Cs (Y)” in the above formula:
  Cs (Y) = 1 / RZ + a ・ Y + b ・ Y²+ c ・ Y^Three+ d ・ Y^Four+ e ・ Y^Five+ f ・ Y⁶+ g ・ Y⁷
             + h ・ Y⁸+ i ・ Y⁹+ j ・ Y^Ten+ k ・ Y¹¹+ l ・ Y¹²           (Formula: 2)
Is represented by the above formula: 1.
[0103]
  The aspheric coefficients in Example 1 are as follows.
[0104]
            1st surface 2nd surface 3rd surface 4th surface
RY 1897.948 -151.350 -4430.699 -4584.974
K 8.680E-02 -2.892E-01 -5.249E + 02 -3.313E + 02
A -2.362E-08 1.415E-08 7.160E-09 -6.342E-09
B -5.964E-14 -1.950E-12 -1.772E-13 1.330E-13
C 8.232E-17 -2.372E-16 1.104E-18 -1.838E-18
D 1.569E-20 2.083E-20 -1.639E-22 -1.733E-22
E 3.315E-24 3.903E-24 -3.107E-29 3.743E-29
RZ ∞ ∞ -88.519 -27.015
a----2.440E-07
b---1.435E-07 1.197E-07
c---1.325E-11
d--5.793E-13 -4.423E-12
e----3.719E-15
f---6.428E-17 -2.276E-16
g---1.535E-19
h---3.700E-21 5.299E-22
i---1.276E-23
j---1.126E-25 -4.801E-26
k----7.059E-28
l---9.704E-30 -4.770E-30.
[0105]
  In the above display, for example, “E-30” is “10^-30This number is the one immediately preceding the number.
[0106]
  In this optical system, a soundproof glass (refractive index: 1.511) having a thickness of 1.9 mm is disposed between the cylindrical lens and the deflecting means at an inclination angle of 8 degrees with respect to the sub-scanning direction. Yes.
[0107]
  Example 2
  "Optical system on the light source side from the deflection means"
  The same as in the first embodiment.
[0108]
  "Optical system after deflection means"
  β₀(Image forming magnification on the optical axis in the sub-scanning direction between the deflecting means and the surface to be scanned): 0.38
  ｜ β_h/ β₀Maximum value of |: 0.99.
Surface number RY (mm) RZ (mm) X (mm) N Remarks
0 ∞ ∞ 68.0-Deflection reflecting surface
1 * 1898.537 ∞ 31.4 1.524 Scanning lens
2 * -151.277 ∞ 162.0--
3 ** -4100.699 -88.511 8.2 1.524 Scanning lens
4 ** -4584.974 -27.015 100.0--
5----Surface to be scanned
  The shape of each surface marked with “* mark, ** mark” is expressed by Formula: 1 using Formula: 1 and Formula: 2, as in Example 1.
[0109]
  The aspheric coefficients in Example 2 are as follows.
[0110]
            1st surface 2nd surface 3rd surface 4th surface
RY 1898.537 -151.277 -4100.699 -4584.974
K 8.080E-00 -2.909E-01 -4.657E + 02 -2.719E + 02
A -2.367E-08 1.423E-08 7.146E-09 -6.327E-09
B -6.495E-14 -1.942E-12 -1.775E-13 1.333E-13
C 8.216E-17 -2.364E-16 1.100E-18 -1.833E-18
D 1.586E-20 2.089E-20 -1.639E-22 -1.733E-22
E 3.433E-24 3.898E-24 -3.560E-29 3.268E-29
RZ ∞ ∞ -88.511 -27.015
a----2.085E-07
b---1.439E-07 1.201E-07
c---1.327E-11
d--5.437E-13 -4.400E-12
e----3.763E-15
f---6.670E-17 -2.269E-16
g---1.516E-19
h---3.762E-21 5.862E-22
i---1.263E-23
j---1.132E-25 -4.732E-26
k----7.097E-28
l---9.544E-30 -4.880E-30.
[0111]
  Also in this optical system, a soundproof glass (refractive index: 1.511) having a thickness of 1.9 mm is disposed between the cylindrical lens and the deflecting means at an inclination angle of 8 degrees with respect to the sub-scanning direction. Yes.
[0112]
  Example 3
  "Optical system on the light source side from the deflection means"
  The same as in the first embodiment.
[0113]
  "Optical system after deflection means"
  β₀(Image forming magnification on the optical axis in the sub-scanning direction between the deflecting means and the surface to be scanned): 0.38
  ｜ β_h/ β₀Maximum value of |: 0.99.
Surface number RY (mm) RZ (mm) X (mm) N Remarks
0 ∞ ∞ 68.0-Deflection reflecting surface
1 * 1900.703 ∞ 31.4 1.524 Scanning lens
2 * -151.109 ∞ 162.0--
3 ** -3500.699 -88.468 8.2 1.524 Scanning lens
4 ** -4584.974 -27.016 100.0--
5----Surface to be scanned
  The shape of each surface marked with “* mark, ** mark” is expressed by Formula: 1 using Formula: 1 and Formula: 2, as in Example 1.
[0114]
  The aspheric coefficients in Example 3 are as follows.
[0115]
            1st surface 2nd surface 3rd surface 4th surface
RY 1900.703 -151.109 -3500.699 -4584.974
K -2.559E + 01 -2.916E-01 -5.852E + 02 -4.187E + 02
A -2.362E-08 1.432E-08 7.071E-09 -6.248E-09
B -3.061E-14 -1.965E-12 -1.788E-13 1.347E-13
C 8.757E-17 -2.424E-16 1.096E-18 -1.825E-18
D 1.526E-20 2.014E-20 -1.632E-22 -1.739E-22
E 2.719E-24 3.969E-24 1.212E-29 -1.262E-30
RZ ∞ ∞ -88.468 -27.016
a----1.278E-07
b---1.447E-07 1.209E-07
c---1.454E-11
d--4.630E-13 -4.339E-12
e----4.166E-15
f---7.411E-17 -2.250E-16
g---1.256E-19
h---3.948E-21 7.534E-22
i---1.262E-23
j---1.104E-25 -4.876E-26
k----6.184E-28
l---8.419E-30 -5.695E-30.
[0116]
  Also in this optical system, a soundproof glass (refractive index: 1.511) having a thickness of 1.9 mm is disposed between the cylindrical lens and the deflecting means at an inclination angle of 8 degrees with respect to the sub-scanning direction. Yes.
[0117]
  FIG. 6 to FIG. 8 are diagrams of field curvature and constant velocity characteristics (fθ characteristics / linearity) regarding Examples 1 to 3. FIG. As is clear from these figures, the performances of Examples 1 to 3 are extremely good.
[0118]
  Each of the scanning imaging lenses in the optical systems of Embodiments 1 to 3 deflects the light beam from the light source and guides the light beam deflected by the deflecting means onto the surface to be scanned. It is used in an optical scanning device having a scanning imaging lens for focusing as a light spot, and is composed of two scanning lenses, the scanning lens on the deflection means side has a positive refractive power in the main scanning direction, The refractive power in the sub-scanning direction is zero, and the scanning lens on the scanning surface side has a negative refractive power in the main scanning direction and a positive refractive power in the sub-scanning direction. In addition, of the two scanning lenses, the scanning lens on the scanning surface side has a “negative meniscus shape in which the shape in the main scanning section has a convex surface facing the surface to be scanned” (Claim 2), and is deflected in the sub-scanning direction. The function of making the deflection starting point of the means and the surface to be scanned have a geometrically optically conjugate relationship, and the lateral magnification in the sub-scanning direction on the optical axis between the deflecting means and the surface to be scanned: β₀Lateral magnification in the sub-scanning direction at an arbitrary image height: β_hBut the condition:
(2) 0.9 <| β_h/ β₀｜ <1.1
(Claim 3) and the lateral magnification: β₀But the condition:
(3) 0.2 <| β₀｜ <0.6
Is satisfied (claim 4).
[0119]
  Further, the distance on the optical axis from the deflection starting point of the deflecting means to the surface to be scanned: L,Each runMaximum distance of the lens interval on the optical axis in the review lens: a is the condition:
  (1) 0.3 <| a / L | <0.6
(Claim 1), and the two scanning lenses constituting the scanning imaging lens are both plastic lenses.The
[0120]
【The invention's effect】
  As described above, according to the present invention, a novel optical scanning device and image forming apparatus can be realized. As described above, the optical scanning device of the present invention can achieve a stable light spot by properly correcting the curvature of field in the main scanning direction and the sub-scanning direction while maintaining the “constant speed function such as the fθ function”. Therefore, the image forming apparatus using this optical scanning can realize good image formation.
[Brief description of the drawings]
FIG. 1 is a diagram showing an optical arrangement in an embodiment of an optical scanning device.
FIG. 2 is a diagram for explaining an optical scanning device of the present invention and an optical scanning unit of a tandem type image forming apparatus using the same.
FIG. 3 is a diagram for explaining an embodiment of a multi-beam scanning type optical scanning device using the optical scanning device of the present invention;
4 is a diagram showing an embodiment of an image forming apparatus using the optical scanning device of FIG. 1. FIG.
5 is a diagram showing an embodiment of a tandem type color image forming apparatus using the optical scanning device of FIG. 2. FIG.
6 is a diagram showing field curvature and constant velocity characteristics of Example 1. FIG.
7 is a diagram showing field curvature and constant velocity characteristics in Example 2. FIG.
FIG. 8 is a diagram showing field curvature and constant velocity characteristics of Example 3.
[Explanation of symbols]
  1 Light source
  2 Coupling lens
  4 Cylindrical lens
  5 Deflection means
  6 Scanning imaging lens

Claims (10)

It has a plurality of light sources corresponding to each color ,
The light beam from each light source is deflected on one side of the deflecting means by a common deflecting means, guided to a scanned surface on a different photosensitive member by a scanning imaging lens, and a light spot on the corresponding scanned surface. In the optical scanning device focused as
The scanning imaging lens is composed of two scanning lenses,
The two of said deflecting means side of the run査lens of the scan lens has a positive refractive power in the main scanning direction, the refractive power in the sub-scanning direction is approximately zero, a plurality toward different scan surfaces light beam Is shared with
Of the two scanning lenses , the scanning lens on the scanned surface side has a negative refractive power in the main scanning direction and a positive refractive power in the sub-scanning direction.
The scanning lens on the deflection means side is a plastic lens,
A separation mirror for separating the optical path to each scanned surface is disposed between the two scanning lenses ,
In order to arrange a plurality of the separation mirrors, the distance on the optical axis from the deflection starting point of the deflecting means to the surface to be scanned: L, the maximum distance of the lens interval on the optical axis of each scanning lens: a, conditions:
(1) 0.3 <| a / L | <0.6
An optical scanning device characterized by satisfying The optical scanning device according to claim 1,
Of the two scanning lenses, the surface to be scanned side of the scanning lens includes an optical scanning apparatus, wherein the shape of the main scanning cross section is a negative meniscus shape with a convex surface directed to the surface to be scanned. The optical scanning device according to claim 1 or 2,
The scanning imaging lens has a function of making the deflection starting point of the deflecting means and the surface to be scanned substantially geometrically conjugate with respect to the sub-scanning direction,
The lateral magnification in the sub-scanning direction on the optical axis between the deflecting means and the surface to be scanned: β ₀ , and the lateral magnification in the sub-scanning direction at an arbitrary image height: β _h are:
(2) 0.9 <| β _h / β ₀ | <1.1
An optical scanning device characterized by satisfying The optical scanning device according to any one of claims 1 to 3,
The scanning imaging lens has a function of making the deflection starting point of the deflecting means and the surface to be scanned substantially geometrically conjugate with respect to the sub-scanning direction,
Transverse magnification in the sub-scanning direction on the optical axis between the deflecting surface and the surface to be scanned: β ₀ is the condition:
(3) 0.2 <| β ₀ | <0.6
An optical scanning device characterized by satisfying In the optical scanning device according to any one of claims 1 to 4,
A plurality of light beams directed to different scan plane, common to these, the run査lens deflection means side, the optical scanning device which is characterized substantially by parallel pass each other at the sub-scanning direction. In the optical scanning device according to any one of claims 1 to 5,
It has a plurality of light sources corresponding to each color ,
The deflecting means is of a reflective type having a deflecting reflecting surface, and is constructed such that all light beams deflected by the same deflecting reflecting surface intersect at approximately one point near the deflecting surface in the main scanning direction. An optical scanning device characterized by the above. In an image forming apparatus that forms an image by performing optical scanning on a photosensitive medium,
An image forming apparatus comprising the optical scanning device according to claim 1. The image forming apparatus according to claim 7.
A plurality of photoconductive photoconductors are arranged as photosensitive media along the transfer medium conveyance path, and each photoconductor is scanned with light to form an electrostatic latent image. An image forming apparatus that visualizes each toner image and superimposes, transfers, and fixes each color toner image on the same sheet-like recording medium to obtain an image synthetically. The image forming apparatus according to claim 8.
A tandem type image forming apparatus using the optical scanning apparatus according to any one of claims 8 to 9. The tandem type image forming apparatus according to claim 9.
A tandem type image forming apparatus, wherein the number of photoconductive photoconductors is 3 or 4, and a color image is formed.

Images