Optical scanner and image forming device

The present invention relates to an optical scanning apparatus and an image forming apparatus.

PROBLEM TO BE SOLVED: To provide an image forming apparatus using an optical scanning apparatus as an optical printer, a digital copying apparatus, a facsimile apparatus, an optical plotter and the like. As the optical scanning apparatus used in these image forming apparatus, in addition to the conventional single beam scanning apparatus, a multi-beam scanning apparatus is being realized, and the image forming apparatus is configured to form a monochrome image. In addition to those, those that form color images and multicolor images are being put into practical use, and among them, those called "tandem type" are being actively developed (see Patent Documents 1 to 6).

[0003] Writing by an optical scanning device is becoming more dense, and it is intended to realize a writing density of 1200 dpi, 1600 dpi, or even higher. In order to realize high-density writing, the stability of the light spot, that is, "the spot diameter of the light spot that is light-scanned on the surface to be scanned does not fluctuate greatly depending on the image height" is indispensable.

[0004] As is well known, one of the causes of the spot diameter fluctuating according to the image height of the light spot is "curvature of field due to the scanning imaging optical system", and in order to improve the stability of the light spot, "image plane". A large number of "scanning imaging optical systems in which curvature is satisfactorily corrected" are known.

[0005] In the multi-beam scanning type optical scanning apparatus, in addition to stabilizing the light spot, the imaging magnification of the scanning imaging optical system that focuses the deflected light beam toward the surface to be scanned is adjusted to the image height of the light spot. It is also important that it is almost constant.

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 11-157128 [Patent Document 2] Japanese Patent Application Laid-Open No. 9-127443 [Patent Document 3] Japanese Patent Application Laid-Open No. 9-54263 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-4948 Japanese Patent Application Laid-Open No. 2001-10107 [Patent Document 6] Japanese Patent Application Laid-Open No. 2001-333720 [0007] [Problems to be Solved by the Invention] This invention has excellent light spot stability and scans. An object of the present invention is to realize an optical scanning apparatus having high stability of imaging magnification of an imaging lens and an image forming apparatus using the optical scanning apparatus.

[Means for Solving the Problems] The optical scanning apparatus of the present invention "deflects a light beam from a light source and guides the light beam deflected by the deflecting means onto a surface to be scanned and is subject to scanning. It is an optical scanning device having a scanning imaging lens that collects light as a light spot on the scanning surface, and has the following features (claim 1).

That is, the scanning imaging lens<u style="single">Two</u>Have scanning lenses and these<u style="single">Two</u>Of the scanning lenses of<u style="single">On the side</u>The "scanning lens" has a "positive refractive power in the main scanning direction" and "a refractive power in the sub-scanning direction is almost zero".<u style="single">Two</u>Of the scanning lenses of<u style="single">On the side</u>The "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 apparatus according to claim 1 is composed of "two scanning lenses".<u style="single">To.</u>In 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 cross section has a convex surface facing the surface to be scanned (claim 2).

[0011] The "main scanning cross section" is a virtual plan cross section including the optical axis of the scanning lens and parallel to the main scanning direction. A virtual plan section orthogonal to the main scanning direction is called a "sub-scanning section".

[0012] The optical scanning apparatus according to claim 1 states that "the distance on the optical axis from the starting point of deflection of the deflecting means to the surface to be scanned: L,<u style="single">Each run</u>It is preferable that the maximum distance of the lens spacing on the optical axis of the inspection lens: a satisfies the condition: (1) 0.3 &lt;| a / L | &lt;0.6 ".

[0013] The scanning imaging lens in the optical scanning apparatus according to claim 1 or 2, "has a function of making the origin of deflection in the deflection means and the surface to be scanned geometrically and optically in a substantially conjugate relationship with respect to the sub-scanning direction. , Horizontal magnification in the sub-scanning direction on the optical axis between the deflection means and the surface to be scanned: β₀, Horizontal magnification in the sub-scanning direction at arbitrary image height: β_hBut the condition: (2) 0.9 &lt;| β_h/ β₀| &lt;Satisfy 1.1 "is preferred (Claim 3).

[0014] The scanning imaging lens in the optical scanning apparatus according to any one of claims 1 to 3 states that "a relationship in which the origin of deflection in the deflecting means and the surface to be scanned are geometrically and optically conjugate with respect to the sub-scanning direction". 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 &lt;| β₀| &lt;Satisfying 0.6 "is preferable (Claim 4).

【0015】<u style="single">light</u>Constituting a scanning imaging lens in a scanning device<u style="single">Two</u>At least one of the scanning lenses can be a plastic lens. In this case, "deflection means<u style="single">Side run</u>The inspection lens can be a "plastic lens"<u style="single">(Claim 1)</u>。

[0016] The optical scanning apparatus according to claim 1 described above is described in "1".<u style="single">Corresponds to each color</u>It has multiple light sources, and the light beam from each light source is deflected by a common deflection means, and by a scanning imaging lens.<u style="single">On different photoconductors</u>It is guided onto the surface to be scanned and focused as a light spot on the corresponding surface to be scanned to form a scanning imaging lens.<u style="single">Two</u>Among the scanning lenses in the above, the scanning lens close to the deflecting means is common to a plurality of light beams directed to different surfaces to be scanned.

【0017】<u style="single">Claims 1-4</u>In the optical scanning apparatus according to any one of the above, "a plurality of light beams directed to different surfaces to be scanned are common to all of them.<u style="single">Side run</u>The inspection lenses can be made to "pass substantially parallel to each other in the sub-scanning direction" (<u style="single">Claim 5</u>)。

【0018】<u style="single">Claims 1-5</u>The optical scanning device according to any one of<u style="single">Corresponds to each color</u>It is a reflective type that has multiple light sources and the deflection means has a deflection reflection surface, and all the light beams deflected by the same deflection reflection surface intersect at approximately one point near the deflection surface in the main scanning direction. " Can be configured as (<u style="single">Claim 6</u>)。

[0019] In the above, "all light beams deflected by the same deflecting reflection surface intersect at approximately one point near the deflection surface in the main scanning direction" means that a plurality of light beams incident on the same deflection reflecting surface are incident on. When viewed from the sub-scanning direction, it means that these light beams intersect at approximately one point near the deflection reflection surface.

[0020] A surface to be scanned that is lightly scanned by an optical scanning device.<u style="single">entity</u>Is the photosensitive surface of a "photosensitive medium" such as a photoconducting photoconductor,<u style="single">Claims 1, 5</u>In addition to the photosensitive surfaces of different photosensitive media, the "different scanned surfaces" in the above description also include "separate optical scanning positions on which different images are written" on the same photosensitive medium.

[0021] Further, the plurality of light beams may lightly scan different surfaces to be scanned, but as in the multi-beam scanning method, a plurality of light beams may lightly scan one surface to be scanned.

[0022] The image forming apparatus of the present invention is an "image forming apparatus that performs image forming by light scanning a photosensitive medium".<u style="single">Claims 1 to 6</u>It has the optical scanning apparatus according to any one of the above (<u style="single">Claim 7</u>). As the photosensitive medium, the above-mentioned photoconducting photoconductor can be used, or a silver salt film can also be used. The latent image formed by optical scanning on the silver halide film can be visualized by a normal silver halide photography development process.

[0023] As described above, the image forming apparatus using the silver salt film as the photosensitive medium can be implemented as an optical plate making machine or an optical drawing apparatus (for forming an image of CT scan).

[0024] The image forming apparatus according to claim 7 states that "a plurality of photoconductive photoconductors are arranged along a transport path of a transfer medium using a plurality of photoconductive photoconductors as photosensitive media, and each photoconductor is subjected to photoscanning to perform electrostatic latency. As an image forming device that forms an image, visualizes each electrostatic latent image as a toner image of a different color, superimposes each color toner image on the same sheet-shaped recording medium, transfers and fixes it, and obtains an image synthetically. Can be configured (<u style="single">Claim 8</u>)。

[0025] The "sheet-shaped recording medium" is a transfer paper, an OHP sheet (plastic sheet for an overhead projector), or the like. The above-mentioned "transfer medium" can be a sheet-shaped 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-shaped recording medium (direct transfer method) or may be transferred via an intermediate transfer medium (intermediate transfer method).

【0026】<u style="single">Claim 8</u>The image forming apparatus described is as an optical scanning apparatus.<u style="single">Claims 5, 6</u>It can be configured as a "tandem type image forming apparatus" by using any one of the above (claim 10). In this case, the number of photoconducting photoconductors is 3 or 4, and a color image can be formed (<u style="single">Claim 10</u>)。

[0027] In the optical scanning apparatus according to claim 1, the scanning imaging lens is used.<u style="single">Two</u>With a scanning lens of<u style="single">Side run</u>The inspection lens has a positive refractive power in the main scanning direction, has almost zero refractive power in the sub-scanning direction, and has a surface to be scanned.<u style="single">Side run</u>The inspection lens has a negative refractive power in the main scanning direction and a positive refractive power in the secondary scanning direction.

[0028] Therefore, the function of realizing the constant velocity characteristic such as the fθ characteristic is described as "deflection means".<u style="single">Side run</u>In addition to allocating to the inspection lens, the imaging function in the sub-scanning direction is mainly performed on the "scanned surface".<u style="single">Side run</u>By allocating to the "inspection lens", it is possible to correct the curvature of field particularly well in the sub-scanning direction. Further, by distributing the imaging function in the sub-scanning direction to the scanning lens close to the surface to be scanned, the imaging magnification in the sub-scanning direction is reduced, a small-diameter light spot can be realized, and the magnification varies depending on the image height. Easy to correct.

[0029] In the optical scanning apparatus according to claim 2, the scanning imaging lens is composed of two scanning lenses, and the scanning lens on the side to be scanned has a shape in the main scanning cross section that is "convex on the surface to be scanned." Since it has a negative meniscus shape, it is easy to keep the optical magnification constant with respect to the image height.

[0030] At least two surfaces in the sub-scanning direction are "a curved center line in which the center of curvature in the sub-scanning cross section is connected in the main scanning direction is a curve different from the non-arc shape in the main scanning direction in the main scanning cross section. As described above, when the radius of curvature in the sub-scanning cross section is changed in the main scanning direction and these two lens surfaces are bent to "adjust the principal point position in the sub-scanning direction", the two surfaces The wider the interval, the larger the amount of change in the principal point position can be taken, and the lateral magnification in the sub-scanning direction can be easily corrected between the image heights.

[0031] From the viewpoint of cost reduction, the optical scanning apparatus according to claim 2 has two scanning imaging lenses, and the scanning lens closest to the deflecting means has a refractive power in the sub-scanning direction of almost zero. For this reason, the two surfaces are the first and second surfaces of the scanning lens on the side to be scanned, and these surfaces should have a "negative meniscus shape with the convex surface facing the surface to be scanned" in the main scanning cross section. As a result, 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 imaging in the sub-scanning direction with respect to the image height of the light spot. The change in magnification can be effectively reduced.

That is, since the optical path length of the peripheral image height is longer than that of the central image height, the principal point position at the peripheral image height is the center in order to keep the lateral magnification in the sub-scanning direction constant regardless of the image height. It is necessary to be on the deflection means side with respect to the image height. In order to realize this, the convex side of the negative meniscus shape is set as the surface to be scanned so that the principal point position at the peripheral image height can be located on the deflection means side with respect to the height of the central image, and further, the most on the surface to be scanned. The first and second surfaces of the close scanning lenses are set so that the curvature center line in which the center of curvature in the sub-scanning cross section is connected in the main scanning direction has a curve different from the non-arc shape in the main scanning direction in the main scanning cross section. In addition, by using "a surface in which the radius of curvature in the sub-scanning cross section is changed in the main scanning direction" and bending the two lens surfaces to "adjust the position of the principal point in the sub-scanning direction", the image height is relative to the image height. The optical magnification can be made substantially constant.

[0033] The condition (2) in claim 3 is a "desirable range" within the effective scanning region of the imaging magnification in the sub-scanning direction of the scanning imaging lens, and if it is out of this range, the spot diameter of the light spot becomes large. The variation within the effective scanning area becomes large, which affects the formed image. By satisfying condition (2), the pitch between multiple scanning lines can be kept constant even when performing optical scanning with a multi-beam scanning method, and it is possible to increase the density and speed by using multi-beams. It will be possible.

[0034] When the lower limit of the condition (3) in claim 4 is exceeded, the lateral magnification in the sub-scanning direction on the optical axis between the deflection means and the surface to be scanned: β with respect to the target spot diameter.₀When is set to a large value, it becomes necessary to set the aperture diameter of the aperture for beam shaping to be small, which tends to cause a problem of insufficient light intensity and deterioration of the spot diameter due to the influence of diffraction in the aperture. When the upper limit of condition (3) is exceeded, the deflection means<u style="single">Side run</u>The distance between the inspection lens and the surface to be scanned becomes large, which tends to lead to an increase in the size of the image forming apparatus.

[0035] For example, in the case of configuring a tandem type image forming apparatus that shares a deflection means,<u style="single">Two</u>Scanning lens<u style="single">Between</u>, A mirror or the like for separating the optical path is arranged on the surface to be scanned corresponding to each color. In such a case, if the lower limit of the condition (1) in claim 1 is exceeded,<u style="single">Two</u>The distance on the optical axis that is the farthest between the scanning lenses becomes too short, and it becomes difficult to arrange a mirror or the like for optical path separation.

Further, when the upper limit value of the condition (1) is exceeded, the scanning lens on the deflection means side approaches the deflection means side, but since this scanning lens has a strong positive refractive power in the main scanning direction, the surface to be scanned The image angle for optical scanning the upper effective scanning area is narrowed, the scanning time is shorter than when the image angle is wide, and the on / off response speed of the LD used as the light source is the writing density. There is a risk that it will not be possible to respond to.

【0037】<u style="single">Claim 1</u>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, the optical characteristics of plastic lenses are liable to change due to temperature changes and the like. In particular, in a rotating multi-sided mirror or the like that is generally used as a deflection means, the ambient temperature tends to rise due to heat generated by a drive motor that rotates the polygon mirror or the like.

【0038】<u style="single">Claim 1</u>If the scanning lens on the deflection means side is a plastic lens as in the optical scanning device described, temperature changes are likely to occur due to the influence of 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 characteristics due 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.<u style="single">Claim 1</u>Deflection means, like the optical scanning device of<u style="single">On the side</u>If the scanning lens (which has the function of correcting the constant velocity characteristic) is "common to multiple light beams directed to different scanning surfaces", the constant velocity fluctuation will occur in the same way for each color, resulting in color shift and hue. The occurrence of change is suppressed.

[Embodiments of the Invention] Hereinafter, embodiments will be described.

[0040] FIG. 1 shows an optical arrangement in one embodiment of an optical scanning device. This optical scanning device guides the deflecting means 5 that deflects the light beam from the light source 1 and the light beam deflected by the deflecting means 5 onto the scanned surface 7, and condenses the light beam as a light spot on the scanned surface 7. An optical scanning apparatus having a scanning imaging lens 6 to be formed, wherein the scanning imaging lens 6 is provided.<u style="single">Two</u>Has scanning lenses 6A, 6B, these<u style="single">Two</u>Of the scanning lenses 6A and 6B, the scanning lens 6A closest to the deflection means 5 has a positive refractive power in the main scanning direction, and the refractive power in the sub-scanning direction is almost zero.<u style="single">Two</u>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 (claim 1).

[0041] More specifically, the light beam emitted from the light source 1 is converted into a parallel luminous flux (which 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 of the aperture 3 to form a beam on the surface to be scanned 7 in order to obtain a desired spot diameter, and then is focused in the sub-scanning direction by the cylindrical lens 4 and passed through the mirror IM. The image is formed as a "long line image in the main scanning direction" in the vicinity of the deflection reflection surface 5A of the deflection means 5, and is deflected at an equal angular velocity by the deflection means 5. The deflection means 5 is a rotating multifaceted mirror.

The light beam deflected by the deflecting means 5 is focused 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 focused at a constant velocity. Optical scan.

[0043] In this optical scanning apparatus, the two scanning lenses 6A and 6B constituting the scanning imaging lens 6 are both plastic lenses. The scanning lens 6A on the deflection means 5 side is provided with a "positive refractive power in the main scanning direction", and this positive refractive power is set so that "constant velocity (fθ characteristic) is satisfactorily corrected". There is. The scanning lens 6B on the side to be scanned 7 has a "negative refractive power in the main scanning direction".

[0044] As described above, by making the refractive power of the scanning lens 6A positive and the refractive power of the scanning lens negative with respect to the main scanning direction, it is caused by environmental changes such as temperature changes and emission wavelength fluctuations in the light source 1. Changes in the optical characteristics of the scanning lenses 6A and 6B are canceled out, and 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 side to be scanned has a "long shape" as shown in the drawing, and when this is configured as a "lens having a positive refractive power in the main scanning direction", the scanning lens 6B is in the longitudinal direction of the lens. The thickness of the peripheral portion is thinner than the thickness of the lens, 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 of "negative in the main scanning direction", a "large wall thickness difference" does not occur in the longitudinal direction, so that shaping processing is easy.

[0047] The scanning lens 6A has a function of correcting the constant velocity property as described above, but since the lens 6A does not have a refractive power in the sub-scanning direction, even if the incident position of the deflected luminous flux deviates in the sub-scanning direction. The constant velocity property of the scanning imaging lens 6 does not deteriorate. In addition, deterioration of imaging performance in the main scanning direction can be suppressed.

[0048] With respect to the sub-scanning direction, the scanning lens 6B has a strong positive refractive power because the refractive power of the scanning lens 6A is substantially zero. Therefore, with respect to the sub-scanning direction, the scanning lens 6B has a function of "condensing the polarized light flux on the surface to be scanned". In this way, since the imaging function in the sub-scanning direction is carried out by the scanning lens 6B close to the surface to be scanned 7, the scanning imaging lens 6 becomes a reduction system in the sub-scanning direction, and the light spot is imaged. The position, spot diameter, etc. are not easily affected by optical component assembly errors, shape errors, etc. Of course, the scanning imaging lens 6 has a "geometrical optic conjugate relationship between the starting point of deflection by the deflection means 5 and the surface to be scanned 7" with respect to the sub-scanning direction. "have.

The plane shape in the main scanning direction of the scanning lens 6A on the deflection means side can be a non-arc shape. The surface shape of the scanning lens 6B on the side to be scanned is "a non-arc shape in the main scanning direction, and the center of curvature in the sub-scanning cross section in which the centers of curvature are connected in the main scanning direction is the main scanning in the main scanning cross section. By using a surface in which the radius of curvature in the sub-scanning cross section is changed in the main scanning direction so that the curve is different from the non-arc shape in the direction, it is possible to satisfactorily correct the image plane curvature in both the main and sub-scan directions. Is.

[0050] In this way, it is possible to achieve stability of the light spot by satisfactorily correcting the curvature of field in the main / sub-scanning directions while maintaining the "constant velocity function" satisfactorily.

[0051] FIG. 2 is a diagram for explaining one embodiment of the optical scanning device of the "tandem type image forming device". This image forming apparatus is an apparatus for forming a color image.

[0052] FIG. 2A shows an explanatory diagram of the optical arrangement as viewed from the sub-scanning direction. In order to simplify the figure, the optical path of the deflected luminous flux is shown in a plane-developed state on the side to be scanned from the deflecting means.

[0053] A color image is formed by synthesizing a "four-color toner image" of yellow, magenta, cyan, and black. In the symbols 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.

As shown in FIG. 2 (a), in the portion from the light source to the deflection means (rotating polymorphic mirror) 5, four light sources 1Y to 1K, four coupling lenses 2Y to 2K, and four coupling lenses Aperture 3Y ~ 3K and 4 cylindrical lenses 4Y ~ 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 the other three couplings when viewed from the sub-scanning direction. The lens light source 2M, 2C, 2K overlaps, the aperture 3Y overlaps with the other three apertures 3M, 3C, 3K when viewed from the sub-scanning direction, and the cylindrical lens 4Y overlaps with the other three cylindrical lenses when viewed from the sub-scanning direction. It overlaps with 4M, 4C, and 4K.

[0055] The light sources 1Y to 1K are semiconductor lasers and 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 luminous flux form suitable for the subsequent optical system, for example, a parallel luminous flux. The beam is shaped by the aperture 3Y (3M, 3C, 3K), and the cylindrical lens 4Y (4M, 4C, 4K) forms an image as a "long line image in the main scanning direction" near the deflection reflection surface 5A of the deflection means, which is common. It is deflected at the same time by the deflection means 5 of.

[0056] The four light beams (main rays) incident on the deflection means from each light source are parallel to each other in the sub-scanning direction.

[0057] Fig. 2 (b) shows a state in which the optical path from the deflection means to the scanned surface 7Y to 7K is linearly developed. The entities of the surfaces 7Y to 7K to be scanned are "photoconducting photoconductors", which are formed in a cylindrical shape and arranged in parallel with each other as shown in FIG. 2 (c). FIG. 2B is drawn so that the scanned surfaces 7Y to 7K are on the same surface.

As shown in FIG. 2 (b), the light beams from the light sources 1Y to 1K are reflected and deflected "parallel to each other" in the direction orthogonal to the rotation axis of the deflection surface by the common deflection means 5. It transmits through the scanning lens L1. The transmissive lens L1 is common to all four light beams.

Each light beam transmitted through the scanning lens L1 is focused by the scanning lenses L2Y to L2K toward the corresponding scanned surfaces 7Y to 7K to form light spots on the scanned surfaces, and the scanned surface is formed. Is lightly scanned.

[0060] The scanning lens L1 and the scanning lens L2Y constitute a "scanning imaging lens that forms an image of a light spot on the scanned surface 7Y", and the scanning lens L1 and the scanning lens L2M (L2C, L2K) form a "scanned surface 7M". A scanning imaging lens that forms an image of a light spot on (7C, 7K) is configured. Each scanning lens L2Y to L2K is the same.

As shown in FIG. 2C, the optical path of the imaged luminous flux formed by each scanning imaging lens is appropriately bent by the optical path bending mirror M and guided to the corresponding photoconductors 7Y to 7K.

[0062] The light spots formed on each of the photoconductors 7Y to 7K lightly scan the photoconductor and write an electrostatic latent image.

[0063] In this embodiment, the lenses constituting the scanning imaging lens are all plastic lenses, and the deflection means 5<u style="single">Side run</u>Of course, the inspection lens L1 is also a plastic lens (<u style="single">Claim 1</u>)。

[0064] Further, the optical scanning device of FIG. 2 is<u style="single">Corresponds to each color</u>It has a plurality of light sources 1Y to 1K, and the light beam from each light source is deflected by the common deflection means 5, and is deflected by the scanning imaging lenses L1 and L2Y to L2K.<u style="single">On different photoconductors</u>It is guided on the surface to be scanned 7Y to 7K and condensed as a light spot on the corresponding surface to be scanned to form a scanning imaging lens.<u style="single">Two</u>Among the scanning lenses of the above, the scanning lens L1 close to the deflection means 5 is common to a plurality of light beams directed to different scanned surfaces 7Y to 7K (claim 1).

Since the scanning lens L1 on the deflection 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 show the scanning lens L1 in FIG. 2 (b). As shown above, they pass substantially parallel to each other in the sub-scanning direction (vertical direction in Fig. 2 (b)).<u style="single">Claim 5</u>). As described above, since the light beams (main rays) transmitted through the scanning lens L1 are parallel to each other and do not approach each other, the optical path dividing mirror M can be easily arranged.

[0066] In the embodiment of FIG. 2, among the lenses constituting the scanning imaging lens, the scanning lens L1 on the deflection means 5 side is used for a plurality of (= 4) light beams directed toward the scanned surface 7Y to 7K. It was standardized. The deflection means 5 is a rotating multi-sided mirror, and the heat generated by the motor unit and the substrate is large, and the temperature inside the optical box rises due to the heat generated by the motor unit. Due to this temperature fluctuation, a temperature distribution is generated in the scanning lens L1 closest to the deflection means 5, and the optical characteristics are changed.

[0067] Since the scanning lens L1 has a function of correcting scanning characteristics (constant velocity function), the constant velocity characteristics change due to the change in the optical characteristics, but such changes in the constant velocity characteristics occur. Even if it occurs, the scanning lens L1 is shared by each light beam that lightly scans the photoconductors 7Y to 7K, so that the change in the constant velocity characteristics is common to each photoconductor 7Y to 7K. There is no "difference in constant velocity characteristics" between the photoconductors. Therefore, even if the environmental fluctuation fluctuates during continuous printing or the like and the constant velocity characteristic of the scanning imaging lens changes, the hue change or color shift of the color image caused by the change in the constant velocity characteristic may occur. Can be suppressed.

[0068] In the embodiment of FIG. 2, the portion from the light source to the cylindrical lens is "arranged so as to be superposed parallel to each other in the sub-scanning direction" for yellow, magenta, cyan, and black. In the layout of the above, it may be folded back appropriately by a folding mirror or the like so that a plurality of light sources, coupling lenses, etc. have a distance in the main scanning direction.

[0069] Further, an optical beam that lightly scans four photoconductors 7Y to 7K is incident on the scanning lens L1 from the deflection means 5 in parallel in the sub-scanning direction. Two scanning lenses corresponding to the scanning lens L1 are arranged on both sides of the deflection means so that the light beams of the book are reflected in opposite directions with respect to the common deflection means, and are distributed to both sides of the deflection means. Each light beam may pass through these two scanning lenses in common.

[0070] Above, an embodiment in the case of lightly scanning a plurality of scanned surfaces by a 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 represented by reference numeral 31 includes two semiconductor lasers and two coupling lenses that couple the light beams emitted from these semiconductor lasers. The two light beams emitted from each semiconductor laser and coupled by the corresponding coupling lenses were "separated in the sub-scanning direction" by the cylindrical lens 32 at the same deflection reflection surface position of the deflection means (rotating polymorphic mirror) 33. The image is formed as a "long line image in the main scanning direction". At this time, the two light fluxes from each semiconductor laser intersect in the main scanning direction at approximately one point at a position near the deflection reflection surface.

Each light beam deflected by the deflecting means 33 passes through the scanning lenses 34A and 34B constituting the scanning imaging lens 35, and the optical path is folded back by the optical path folding mirror 36 to form the substance of the scanned surface. The light is focused toward the conductive photoconductor 37 to form two optical spots separated in the sub-scanning direction, and the surface to be scanned is light-scanned by a multi-beam scanning method.

That is, in this embodiment, the optical scanning device is of a reflection type having a plurality of light sources and the deflection means 33 has a deflection reflection surface, and is deflected by the same deflection reflection surface and has the same subject. All the light beams that lightly scan the scanning surface 37 are configured to intersect at approximately one point near the deflection surface in the main scanning direction (<u style="single">Claim 6</u>)。

[0074] The upper figure of FIG. 3 (b) shows a case where the light is incident on the deflecting reflection surface at different positions. The position of the deflecting reflection surface when the two luminous fluxes (the main rays are shown by the solid line and the broken line) reach the same position P0 on the scanned surface 37 is D for each solid line light beam.₁, Dashed light beam D₂Then, in the case of the above figure in FIG. 3B, the optical paths passing through the scanning lenses 34A and 34B leading to the imaging position P0 are significantly different, and the optical action is also different due to the difference in the optical paths, so that the light paths are formed at the imaging position P0. The spot diameter of the optical 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 of the scanning line pitch on the fluctuation between image heights is large, and the scanning line bending is likely to occur.

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 near the deflected reflection surface, the imaging position on the scanned surface 37 The optical path leading to P0 is substantially the same for each of the solid line and broken line light beams, and the bending of the scanning line 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 side to be scanned from the deflection means 5 is substantially the same for all the light beams, and the amount of the "writing position fluctuation in the main scanning direction" is approximately the same for all the light beams, and the amount of the "writing position fluctuation in the main scanning direction" is approximately the same for all light beams. The writing position shift can be suppressed.

[0076] Further, since all the light beams forming an image at the same imaging position "pass through substantially the same position in the main scanning direction of the scanning optical lens", the influence of the aberration of the scanning lens constituting the scanning imaging lens is affected. It can be kept small, the imaging position in the main scanning direction can be matched accurately for each beam, and even if the delay time is set for all optical beams after synchronization detection, writing starts at the image height. It is possible to suppress the positional deviation in the main scanning direction.

Further, 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 rotating polymorphic mirror can be minimized.

[0078] In the embodiment of FIG. 3, a case where a single surface to be scanned 37 is light-scanned by a multi-beam scanning method has been described, but as in the embodiment of FIG. 2, light directed to different surfaces to be scanned has been described. When the beam is deflected by the same deflection reflection surface of the deflection means, if "each light beam forms an angle with each other in the main scanning direction with respect to the same deflection reflection surface" due to the layout on the light source side, each light beam is polygonal. A similar effect can be obtained by intersecting the mirror 5 in the main scanning direction in the vicinity of the deflecting reflection surface 5A.

[0079] The deviation of the intersection position of each light beam is preferably within 0.5 mm on the deflection reflection surface.

[0080] FIG. 4 shows a laser printer as one embodiment of an image forming apparatus using the optical scanning apparatus shown in FIG. 1.

[0081] The laser printer 100 has a photoconducting photoconductor 111 formed in a cylindrical shape as a photosensitive medium. A charging roller 112, a developing device 113, a transfer roller 114, and a cleaning device 115 as charging means are arranged around the photoconductor 111. A "corona charger" can also be used as the charging means.

[0082] Further, an optical scanning device 117 that performs optical scanning by the laser beam LB is provided, and "exposure by optical writing" is performed between the charging roller 112 and the developing device 113.

In FIG. 4, reference numeral 116 is a fixing device, reference numeral 118 is a cassette, reference numeral 119 is a registration roller pair, reference numeral 120 is a paper feed roller, reference numeral 121 is a transport path, reference numeral 122 is a paper ejection roller pair, and reference numeral 123 is a tray. , Reference numeral P indicates a transfer paper as a sheet-like recording medium.

[0084] When image formation is performed, the photoconducting photoconductor 111 is rotated at a constant speed clockwise, the surface thereof is uniformly charged by the charging roller 112, and the light is written by the laser beam LB of the optical scanning device 117. An electrostatic latent image is formed upon exposure. The formed electrostatic latent image is a so-called "negative latent image", and the image portion is exposed. This electrostatic latent image is inverted and developed by the developing device 113, and a toner image is formed on the image carrier 111.

[0085] The cassette 118 containing the transfer paper P can be attached to and detached from the main body of the image forming apparatus 100, and when the cassette 118 is attached as shown in the figure, the topmost sheet of the stored transfer paper P is the paper feed roller 120. The transfer paper P, which has been fed by, is captured by the resist roller pair 119 at its tip.

[0086] The resist roller pair 119 feeds the transfer paper 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, the toner image is fixed by the fixing device 116, passes through the transport path 121, and is discharged onto the tray 123 by the paper ejection roller pair 122. The surface of the photoconductor 111 after the toner image is transferred is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like.

[0088] As the optical scanning device 117, the one as described with reference to FIG. 1 is used.

[0089] FIG. 5 shows one embodiment of the "tandem type color image forming apparatus" using the optical scanning apparatus as described above with reference to FIG. In the figure, the portion indicated by reference numeral 50 is the optical scanning device portion described in FIG. 2, and reference numerals 5Y, 5M, 5C, and 5K lightly scan the photoconducting photoconductors 7Y, 7M, 7C, and 7K, respectively. It shows a deflected light beam. The explanation of this part is based on the explanation of Fig. 2.

Around the photoconductor 7Y (7M, 7C, 7K), 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 arranged, and the transport belt 2A is arranged so as to come into contact with the photoconductors 7Y, 7M, 7C, 7K.

[0091] The photoconductors 7Y to 7K are uniformly charged by the corresponding charging means YC to KC while rotating to the clock method, are light-scanned by the light beam 5Y to 5K, and the electrostatic latent image is written as a negative latent image. .. These electrostatic latent images are developed by the developing devices YD to KD, and toner images of yellow, magenta, cyan, and black are formed on the photoconductors 7Y, 7M, 7C, and 7K, respectively.

[0092] The transfer paper, which is a sheet-shaped recording medium on which a color image is formed, is fed from the cassette 1A and placed on the transport belt 2A by the resist roller 9. The transport belt 2A is charged by the corona discharge by the charger 18, and the transfer paper is electrostatically adsorbed on the transport belt 2A.

[0093] The transfer paper held on the transfer belt 2A in this way is sequentially conveyed through the transfer portion, from the photoconductor 7K to the "black toner image", from the photoconductor 7C to the "cyan toner image", and from the photoconductor 7M to the "cyan toner image". The "magenta toner image" and the "yellow toner image" from the photoconductor 7Y are sequentially transferred 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 statically eliminated from the static elimination charger 11, separated from the transport belt 2A by the strength of the waist of the transfer paper itself, proceeds to the fixing device 14, and the color image is fixed, and is placed on the tray 15'by the discharge roller 15. Is discharged to. The photoconductors 7Y to 7K after the toner image transfer are cleaned by the cleaning means YL to KL, respectively.

That is, in the image forming apparatus shown in FIG. 5, a plurality of photoconductive photoconductors 7Y to 7K are arranged along the transport path of the transfer medium (transfer paper) as the photosensitive medium, and the photoconductors are arranged on each photoconductor. Optical scanning is performed to form an electrostatic latent image, 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-shaped recording medium, transferred and fixed, and synthetically. Image forming device to obtain an image (<u style="single">Claim 8</u>). In addition, a tandem type image forming device (<u style="single">Claim 9</u>), A tandem type image forming apparatus that forms a color image with 4 photoconductive photoconductors ()<u style="single">Claim 10</u>).

[Examples] Hereinafter, three specific examples of the optical system of the optical scanning apparatus will be given. The optical scanning device shown in FIGS. 1 and 2 is assumed.

Explanation of Symbols The meanings of the symbols are as follows.

RY: Radiation of curvature of the surface in the main scanning direction (including the surface of the aperture) RZ: Radius of curvature of the surface in the sub-scanning direction (including the surface of the aperture) (on the optical axis) N: At the used wavelength (780 nm) Refractive index of the material 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 on the light source side from 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 reflective surface.

[0099] The surface marked with "*" is a "coaxial aspherical surface". Although the numerical value peculiar to the aspherical surface is not shown, it is set so that the wave surface aberration of the "parallel luminous flux" emitted from the coupling lens is satisfactorily corrected. The deflection means is a rotating multifaceted mirror with an inscribed circle diameter of 18 mm and a deflection reflection surface number of 6.

[Optical system after deflection means] β₀(Image magnification on the optical axis in the sub-scanning direction between the deflection 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 reflection 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 ---- ---- Surfaces to be scanned Each surface marked with "*" has a non-arc shape in the main scanning cross section and a straight line in the sub scanning cross section. It has become. This lens surface is represented by the following formula: 1.

That is, X (Y, Z) = Y, where Cm = 1 / RY and Cs (Y) = 1 / RZ.² Cm / [1 + {1- (1 + K) (Y Cm)²}] + A Y⁴+ B Y⁶+ C Y⁸+ D Y¹⁰+ E Y¹² + Cs (Y) Z²/ [1 + {1-(Cs (Y) Z)²}] (Equation: 1).

[0102] Each surface marked with "**" has a non-arc shape in the main scanning direction, and the radius of curvature in the sub-scanning direction continuously changes depending on the lens height (Y) in the main scanning direction. For each surface shape, "Cs (Y)" in the above formula: 1 is changed to Cs (Y) = 1 / RZ + a Y + b Y.²+ c Y³+ d Y⁴+ e Y⁵+ f Y⁶+ g Y⁷ + h Y⁸+ i Y⁹+ j Y¹⁰+ k Y¹¹+ l Y¹² As (Equation: 2), it is expressed by the above equation: 1.

[0103] The aspherical coefficient in Example 1 is as follows.

[0104] 1st surface 2nd surface 3rd surface 4th surface RY 1897.948 -151.350 -4430.699 -4584.974K 8.680E-02 -2.892E-01 -5.249E + 02 -3.313E + 02A -2.362E-08 1.415E -08 7.160E-09 -6.342E-09B -5.964E-14 -1.950E-12 -1.772E-13 1.330E-13C 8.232E-17 -2.372E-16 1.104E-18 -1.838E-18D 1.569E -20 2.083E-20 -1.639E-22 -1.733E-22E 3.315E-24 3.903E-24 -3.107E-29 3.743E-29RZ -88.519 -27.015a ---- ---- 2.440E-07b ---- 1.435E-07 1.197E-07c ---- --1.325E-11d ---- 5.793E-13 -4.423E-12e ---- ---- 3.719E -15f ---- 6.428E-17 -2.276E-16g ---- ---- 1.535E-19h ---- -3.700E-21 5.299E-22i ---- 1.276E-23j ---- -1.126E-25 -4.801E-26k ---- ---- 7.059E-28l ---- -9.704E-30 - 4.770E-30.

[0105] In the above display, for example, "E-30" is "10".^-30This number is related to the previous number.

[0106] In this optical system, a soundproof glass (refractive index: 1.511) having a thickness of 1.9 mm is arranged between the cylindrical lens and the deflection means at an inclination angle of 8 degrees with respect to the sub-scanning direction. There is.

[0107] Example 2 Optical system on the light source side of the deflection means Same as that in Example 1.

[Optical system after deflection means] β₀(Image magnification on the optical axis in the sub-scanning direction between the deflection 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 reflection 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 ---- ---- The surface to be scanned The shape of each surface marked with "* mark, ** mark" is the same as in Example 1, formula: 1 and formula: 2. It is expressed by the formula used: 1.

[0109] The aspherical coefficient in Example 2 is as follows.

[0110] 1st surface 2nd surface 3rd surface 4th surface RY 1898.537 -151.277 -4100.699 -4584.974K 8.080E-00 -2.909E-01 -4.657E + 02 -2.719E + 02A -2.367E-08 1.423E -08 7.146E-09 -6.327E-09B -6.495E-14 -1.942E-12 -1.775E-13 1.333E-13C 8.216E-17 -2.364E-16 1.100E-18 -1.833E-18D 1.586E -20 2.089E-20 -1.639E-22 -1.733E-22E 3.433E-24 3.898E-24 -3.560E-29 3.268E-29RZ -88.511 -27.015a ---- ---- 2.085E-07b ---- -1.439E-07 1.201E-07c ---- --- 1.327E-11d ---- 5.437E-13 -4.400E-12e ---- ---- 3.763E- 15f ---- 6.670E-17 -2.269E-16g ---- 1.516E-19h - --- 3.762E-21 5.862E-22i ---- 1.263E-23j ---- -1.132E-25 -4.732E-26k ---- ---- 7.097E-28l ---- -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 arranged between the cylindrical lens and the deflection means at an inclination angle of 8 degrees with respect to the sub-scanning direction. There is.

[0112] Example 3 Optical system on the light source side of the deflection means Same as that in Example 1.

[0113] Optical system after deflection means β₀(Image magnification on the optical axis in the sub-scanning direction between the deflection 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 reflection 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 ---- ---- The surface to be scanned The shape of each surface marked with "* mark, ** mark" is the same as in Example 1, formula: 1 and formula: 2. It is expressed by the formula used: 1.

[0114] The aspherical coefficient in Example 3 is as follows.

[0115] 1st surface 2nd surface 3rd surface 4th surface RY 1900.703 -151.109 -3500.699 -4584.974K -2.559E + 01 -2.916E-01 -5.852E + 02 -4.187E + 02A -2.362E-08 1.432 E-08 7.071E-09 -6.248E-09B -3.061E-14 -1.965E-12 -1.788E-13 1.347E-13C 8.757E-17 -2.424E-16 1.096E-18 -1.825E-18D 1.526 E-20 2.014E-20 -1.632E-22 -1.739E-22E 2.719E-24 3.969E-24 1.212E-29 -1.262E-30RZ -88.468 -27.016a ---- --- 1.278E-07b ---- -1.447E-07 1.209E-07c ---- --- 1.454E-11d ---- 4.630E-13 -4.339E-12e ---- ---- 4.166E- 15f ---- 7.411E-17 -2.250E-16g ---- 1.256E-19h - ---3.948E-21 7.534E-22i ---- 1.262E-23j ---- -1.104E-25 -4.876E-26k ---- ---- 6.184E-28l ---- 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 arranged between the cylindrical lens and the deflection means at an inclination angle of 8 degrees with respect to the sub-scanning direction. There is.

[0117] FIGS. 6 to 8 show a diagram of curvature of field and constant velocity characteristics (fθ characteristics / linearity) according to Examples 1 to 3. As is clear from these figures, the performance of Examples 1 to 3 is extremely good.

[0118] In each of the scanning imaging lenses in the optical systems of Examples 1 to 3, the deflecting means for deflecting the light beam from the light source and the light beam deflected by the deflecting means are guided onto the surface to be scanned, and the above. It is used in an optical scanning device having a scanning imaging lens that collects light as a light spot on the surface to be scanned. It is composed of two scanning lenses, and the scanning lens on the deflection means side has a positive refractive force in the main scanning direction. The scanning lens on the side to be scanned has a negative refractive force in the main scanning direction and a positive refractive force in the secondary scanning direction (claim 1). 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 cross section has a convex surface facing the surface to be scanned" (claim 2), and is deflected with respect to the sub-scanning direction. It has a function to make the origin of deflection in the means and the surface to be scanned geometrically optically optically coupled, and the lateral magnification in the sub-scanning direction on the optical axis between the deflection means and the surface to be scanned: β.₀, Horizontal magnification in the sub-scanning direction at arbitrary image height: β_hBut the condition: (2) 0.9 &lt;| β_h/ β₀| &lt;Satisfied 1.1 (Claim 3), above horizontal magnification: β₀But the condition: (3) 0.2 &lt;| β₀| &lt;0.6 is satisfied (Claim 4).

[0119] Further, the distance on the optical axis from the starting point of the deflection of the deflection means to the surface to be scanned: L,<u style="single">Each run</u>The maximum distance of the lens spacing on the optical axis of the inspection lens: a satisfies the condition: (1) 0.3 &lt;| a / L | &lt;0.6 (claim 1), and the two lenses constituting the scanning imaging lens. Both scanning lenses are plastic lenses<u style="single">To.</u>[Effects of the Invention] As described above, according to the present invention, a novel optical scanning device and an image forming device can be realized. As described above, the optical scanning apparatus of the present invention can realize a stable light spot by satisfactorily correcting the image plane curvature in the main scanning direction and the sub-scanning direction while maintaining good "constant velocity function such as fθ function". Therefore, an image forming apparatus using this optical scanning can realize good image forming.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an optical arrangement in one embodiment of an optical scanning device.

FIG. 2 is a diagram for explaining an optical scanning apparatus of the present invention and an optical scanning unit of a tandem type image forming apparatus using the optical scanning apparatus.

FIG. 3 is a diagram for explaining one embodiment of a multi-beam scanning optical scanning apparatus using the optical scanning apparatus of the present invention.

FIG. 4 is a diagram showing one embodiment of an image forming apparatus using the optical scanning apparatus of FIG.

5 is a diagram showing one embodiment of a tandem color image forming apparatus using the optical scanning apparatus of FIG. 2. FIG.

FIG. 6 is a diagram showing curvature of field and constant velocity characteristics of Example 1.

FIG. 7 is a diagram showing curvature of field and constant velocity characteristics of Example 2.

FIG. 8 is a diagram showing curvature of field and constant velocity characteristics of Example 3.

[Code description] 1 Light source 2 Coupling lens 4 Cylindrical lens 5 Deflection means 6 Scanning imaging lens