JP3686644B2 - 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 what is called a "tandem type" is being actively developed.
[0003]
  As such a tandem type image forming apparatus, there is known a “system in which a light beam group for optically scanning a plurality of scanned surfaces shares a deflecting means (for example, a rotating polygon mirror)”. Such scanning methods include the “opposing scanning method (see, for example, Patent Documents 1 to 3)” in which the light beam group is deflected so as to be distributed to both sides of the rotary polygon mirror, or one of the rotary polygon mirrors. There is a “one-sided scanning method (see, for example, Patent Documents 4 to 6)” in which deflection is performed on the first side.
[0004]
  In this way, when “a deflecting means is shared by a group of light beams that optically scan a plurality of scanned surfaces”, there is no need to provide a deflecting means for each light beam, and the tandem image forming apparatus can be made compact and low. Cost can be increased.
[0005]
  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.
[0006]
  As is well known, one of the causes of the fluctuation of the spot diameter according to the image height of the light spot is “field curvature in the scanning imaging optical system”. In order to improve the stability of the light spot, the field curvature is improved. Many corrected scanning imaging optical systems are known.
[0007]
  In the multi-beam scanning optical scanning device, in addition to the stability of the light spot, the imaging magnification of the scanning imaging lens that focuses the deflected light beam toward the surface to be scanned is substantially constant regardless of the image height of the light spot. It is also important to do. When the imaging magnification fluctuates depending on the image height, the pitch between a plurality of scanning lines that are simultaneously optically scanned fluctuates, making it difficult to form a good image.
[0008]
[Patent Document 1]
    JP-A-9-58053
[Patent Document 2]
    JP-A-11-157128
[Patent Document 3]
    JP-A-9-127443
[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
[0009]
[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.
[0010]
[Means for Solving the Problems]
  The optical scanning device of the present invention is “emitted from a plurality of light sources.Corresponding to each colorThe light beam group is deflected by a deflecting means common to these light beam groups, and differs depending on the scanning imaging optical system.On the photoreceptorAn optical scanning device that guides and collects one or more light beams on each surface to be scanned, forms one or more light spots on each surface to be scanned, and scans each surface to be scanned with these light spots Is.
[0011]
  Above "Corresponding to each color"Light beam group" is emitted from a plurality of light sources.Corresponding to each colorThe total light beam. Each of the plurality of light sources emits one or more light beams. For example, when optical scanning of each surface to be scanned is performed by a multi-beam scanning method, for example, a semiconductor laser array can be used as each light source. In this case, two or more lights from one light source can be used. A beam will be emitted.
[0012]
  In this case, if the number of scanned surfaces to be optically scanned is n, the number of light sources is n, and the number of light beams for optically scanning one scanned surface is m, the number of light beams is n · m. It is comprised with the light beam of.
[0013]
  On the contrary, a plurality of light beams that optically scan one surface to be scanned may be obtained by “combining light beams emitted from a plurality of light sources”. For example, two light beams emitted from two semiconductor lasers can be combined by a “beam combining prism”, and one surface to be scanned can be optically scanned with two light beams by a multi-beam scanning method.
[0014]
  Thus, considering the case where each of the light sources emits one light beam, the number of scanned surfaces is n, and the number of light beams that are optically scanned on each scanned surface by the multi-beam scanning method is as follows. Assuming m, the light beam group is composed of n · m light beams, and there are n · M light sources.
[0015]
  The “deflecting means” is used in common for the light beam group, and deflects each light beam constituting the light beam group. As the deflecting means, a rotating polygon mirror can be preferably used. However, the present invention is not limited to this, and an oscillating mirror such as a galvano mirror can be used, and a rotating single mirror or a rotating dihedral mirror can also be used. it can.
[0016]
  The “scanning imaging optical system” is an optical system in which each light beam deflected by the deflecting means is guided to a corresponding scanned surface and condensed to form one or more light spots on each scanned surface. This system is composed of a plurality of lenses.
[0017]
  The optical scanning device according to claim 1 has the following characteristics.
  That is, the scanning imaging optical system has a “scanning imaging lens corresponding to each surface to be scanned”.
  A “scanning imaging lens” exists for each surface to be scanned. For example, when an arbitrary scanned surface A is considered among a plurality of scanned surfaces, a scanning imaging lens A corresponding to the scanned surface A exists, and the scanning imaging lens A is a deflected light beam group. Among them, a light beam to be scanned on the scanned surface A is guided to the scanned surface A and condensed to form a light spot.
[0018]
  Each scanning imaging lens isTwoIt is comprised by a scanning lens.
  theseTwoA deflection hand out of the scanning lensStep side runningThe inspection lens has a positive refractive power in the main scanning direction and a refractive power in the sub-scanning direction of almost zero.Surface side runningThe review lens has “positive refractive power in both main and sub scanning directions”.
[0019]
  Furthermore, in the scanning imaging optical system,Step side runningAt least one of the reviewers is differentOn the photoreceptorCommon to the light beam directed to the surface to be scanned.
[0020]
  For example, when considering the above-described one-side scanning system as a color image forming optical scanning device having four scanning surfaces, the light beam group is deflected on one side of a rotary polygon mirror as a deflecting unit. Therefore, each of the scanning imaging lenses constituting the scanning imaging optical system for forming the light spot on the four scanned surfaces is composed of two scanning lenses, and one scanning lens is individually provided on the scanned surface side. The other scanning lens is disposed on the rotary polygon mirror side, and this scanning lens isCorresponding to each colorCommon to the entire light beam group.
[0021]
  In this case, the scanning imaging optical system has “four sets of scanning imaging lenses”. However, since the scanning lens on the rotary polygon mirror side is shared by all the light beams, the scanning imaging optical system is totally used. It is composed of five scanning lenses.
[0022]
  In the optical scanning device according to claim 1, "different"On the photoreceptorThe scanning lens shared by the light beam traveling toward the surface to be scanned can be configured so that the light beams pass substantially parallel to each other in the sub-scanning direction.
[0023]
  3. The optical scanning device according to claim 1, wherein when a “reflective type having a deflecting reflecting surface (for example, a rotating polygon mirror)” is used as a deflecting unit, all light beams incident on the same deflecting reflecting surface are used. Is preferably set so that “at approximately one point in the vicinity of the same deflecting and reflecting surface intersects the main scanning direction”.
[0024]
  In the above, “all light beams deflected by the same deflecting / reflecting surface intersect at approximately one point near the deflecting / reflecting surface in the main scanning direction” means that a plurality of light beams incident on the same deflecting / reflecting surface are sub-directed. When viewed from the scanning direction, it means that these light beams intersect at approximately one point in the vicinity of the deflecting reflecting surface.
[0025]
  The optical scanning device according to any one of claims 1 to 3, wherein each scanned objectFace sideIt is preferable that the scanning lens “a shape in the main scanning section is a positive meniscus shape with a convex surface facing the scanned surface”.
  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”.
[0026]
  The optical scanning device according to any one of claims 1 to 3, wherein each scanning imaging lens is configured such that a deflected light beam, which is a parallel light beam, is incident and condensed on each surface to be scanned. It can be configured to form a light spot.
[0027]
  When the deflecting means is a “reflective material having a deflecting reflecting surface” such as a rotating polygon mirror, each light beam from the light source side is connected as a “line image long in the main scanning direction” near the deflecting reflecting surface. So that the so-called “surface tilt” is corrected by configuring the scanning imaging lens so that the deflection reflection surface position and each scanning surface position have a geometrically optically conjugate relationship. it can.
[0028]
  Claims 5-6In the optical scanning device according to any one of the above, it is premised that the scanning imaging lens has a function of “making the deflecting reflection surface position and each scanning surface position substantially geometrically conjugate to each other”.
[0029]
  Claim 1The optical scanning device described isTo place multiple separation mirrors,Deflection meansThe distance on the optical axis from the deflection starting point to the surface to be scanned: L, the maximum scanning lens interval within the same scanning imaging lens: a, the condition:
  (1)0.3 <| A / L | < 0.6
Preferably to satisfyYes.
[0030]
  Claims 1-4The optical scanning device according to any one of 1), the lateral magnification in the sub-scanning direction on the optical axis between the deflecting means and the surface to be scanned: β₀,Horizontal magnification in the sub-scanning direction at an arbitrary image height: β _h But,conditions:
  (2)0.9 <| Β _h /β₀ ｜ < 1.1
Is preferably satisfied (Claim 5).
[0031]
  Claims 1-5The optical scanning device according to any one of 1 to 4, wherein the deflecting meansMagnification in the sub-scanning direction on the optical axis between the scanning surface and the surface to be scanned: β ₀ But,conditions:
  (3)0.2 <| Β ₀ ｜ < 0.6
Is preferably satisfied (claim 6).
[0032]
  lightIn a scanning device, one or more of the scanning lenses included in the scanning imaging lens can be a “plastic lens”.TheIn this case, the deflection meansSideThe scanning lens can be a “plastic lens”The ( Claim 1 )
[0033]
  The image forming apparatus of the present invention is “an image forming apparatus that individually scans three or four photosensitive media, writes each color component of a color image, and forms a color image by synthesizing each color component image”.
[0034]
  Claim 8The described image forming apparatus has the following characteristics.
  That is, as an optical scanning device that optically scans three or four photosensitive mediaClaims 1-7And the deflecting means deflects the entire light beam “on the same side with respect to the deflecting means”. That is, this image forming apparatus is of the “one-side scanning method” described above.
[0035]
  Claim 9The described image forming apparatus has the following characteristics.
  That is, as an optical scanning device that optically scans three or four photosensitive media,Claims 1-7The deflecting unit deflects the entire light beam by “distributing it to both sides of the deflecting unit”. In other words, this image forming apparatus is the “opposite scanning type” described above.
[0036]
  The “photosensitive medium” is the “substance of the scanned surface” in the above description.
“Optical scanning is performed as a surface to be scanned”.
[0037]
  Of the scanning surface optically scanned by the optical scanning device.entityIs the photosensitive surface of a “photosensitive medium” such as a photoconductive photoreceptor as described above.Claims 1-7The “scanning surfaces different from each other” in the description of FIG. 5 includes “different images written on the same photosensitive medium as described in FIG. 1 of Patent Document 1, for example, in addition to the photosensitive surfaces of different photosensitive media. Separate optical scanning positions ".
[0038]
  Claims 1-9In the described invention, the plurality of light beams may individually “light scan different scanning surfaces”. However, as described above, as in the multi-beam scanning method, “one scanning surface has a plurality of light beams. In some cases, optical scanning is performed.
[0039]
  As the “photosensitive medium”, the above-mentioned photoconductive photosensitive member can be used, and “coloring sheet” that develops a different color depending on the amount of exposure energy can also be used. In such a case, the image forming apparatus can be implemented as an optical drawing apparatus (forming a CT scan image).
[0040]
  When a “photoconductive photoconductor” is used as the photosensitive medium, three or four photoconductive photoconductors are arranged along the transfer medium conveyance path, and optical scanning is performed on each photoconductor. Forming an electrostatic latent image, visualizing each electrostatic latent image as a toner image of a different color, superimposing and transferring and fixing each color toner image on the same sheet-like recording medium, A color image can be obtained.
[0041]
  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).
[0042]
  The optical scanning device according to claim 1 is a deflection hand among the scanning lenses constituting the scanning imaging lens.Stage-side scanning lensIs given a “positive refractive power in the main scanning direction”. In addition, the scannedFront side scanThe lens is also given a positive refractive power in the main scanning direction.
[0043]
  deflectionVessel side running"Different among the review lenses"On the photoreceptorIn the case where a plurality of light beams traveling toward the scanning surface pass, the lens height (thickness) in the sub-scanning direction is increased. In such a case, it is desirable to “reduce the thickness of the scanning lens in the optical axis direction” in order to reduce the cost of manufacturing the lens. When the scanning lens is molded with a plastic material, the lens volume is preferably small in order to improve molding accuracy and shorten molding time.
[0044]
  The optical scanning device according to claim 1, wherein the surface to be scanned isSideThe scanning lens also has a positive refractive power in the main scanning direction to deflect itVessel side runningAs a plastic lens, the inspection lens is prevented from becoming “thick in the optical axis direction due to an excessive positive refractive index”, so that the thickness in the vicinity of the optical axis and in the main scanning direction is not excessively increased. Deformation due to “sink” or the like in shaping is difficult to occur.
[0045]
  In this way, both the scanning lens on the deflecting means side and the scanning lens on the scanned surface side are given a “positive refractive power in the main scanning direction”, and each lens has an aberration correction function, a constant velocity correction function such as an fθ characteristic, etc. Can be obtained in a well-balanced manner to obtain good optical performance.
[0046]
  Deflection handStep side runningSince the sub-lens has “sub-scanning refracting power of approximately 0”, the shape in the sub-scanning cross-section is linear and has no refracting power in the sub-scanning direction. Even when the direction is deviated, the optical characteristics are not changed. Degradation of the imaging performance in the main scanning direction can also be suppressed.
[0047]
  Further, as in the optical scanning device according to claim 2, when a plurality of light beams pass “parallel to each other in the sub-scanning direction” through this scanning lens, depending on a change in the passing position in the sub-scanning direction, the transmitted light beam is optically changed. There is no change in characteristics.
[0048]
  Deflection handStep side runningThe scanning lens does not have refractive power in the sub-scanning direction, so it is scannedSurface side runningThe inspection lens has a strong positive refractive index in the sub-scanning direction, the imaging magnification in the sub-scanning direction of the scanning imaging lens is reduced, and performance degradation due to component assembly errors and shape errors can be suppressed. Therefore, it is possible to realize a light spot with a small diameter, and to easily correct a variation in magnification due to an image height.
[0049]
  Furthermore, the deflection handStep side runningThe shape of the inspection lens in the main scanning section is a non-arc shape, the surface shape of the other scanning lens is a non-arc shape in the main scanning section, and “the center of curvature in the sub-scanning section is connected in the main scanning direction. By using a surface in which the radius of curvature in the sub-scanning section is changed in the main scanning direction so that the center line of curvature becomes a curve different from the non-arc shape in the main scanning direction in the main scanning section, -It is possible to correct field curvature well in both the sub-scanning direction, and it is possible to realize a stable light spot by properly correcting field curvature in the main and sub-scanning directions while maintaining a uniform speed function. .
[0050]
  5. The optical scanning device according to claim 4, wherein the shape of the scanning lens on the scanning surface side in the main scanning section is “a positive meniscus shape with a convex surface facing the scanning surface”, and therefore the optical magnification with respect to the image height. Is easy to keep constant.
[0051]
  That is, scannedSurface side runningBy making the shape of the scanning lens in the main scanning section a meniscus shape, it becomes possible to adjust the “principal point position in imaging in the sub-scanning direction” of the scanning lens according to the image height. Since the optical path length of the peripheral image height is longer than the central image height, in order to make the imaging magnification in the sub-scanning direction constant regardless of the image height, the main point position in the sub-scanning direction is set to “peripheral image height”. As it goes, it is necessary to be on the deflection means side with respect to the center image height.
[0052]
  ScannedSurface side runningSince the shape in the main scanning section of the review lens is “a meniscus shape with a convex surface facing the scanned surface”, the position of the principal point of the lens in image formation in the sub-scanning direction is the highest in the center image height. It is easy to locate the principal point position on the deflection means side as it goes closer to the scanning plane and goes to the periphery.
[0053]
  The shape of the entrance surface and exit surface of the scanning lens is “a curvature center line obtained by connecting the center of curvature in the sub-scan section in the main scan direction is a curve different from the non-arc shape in the main scan section. "Surface whose curvature radius in the scanning cross section is changed in the main scanning direction" and these two lens surfaces are bent to "adjust the main point position in the sub-scanning direction" to make it optical with respect to the image height. It becomes possible to make the magnification constant with high accuracy.
[0054]
  In addition, since the positive meniscus convex surface faces the surface to be scanned, the deflecting means side is concave, and the incident angle of the light beam deflected by the deflecting means becomes small, thereby suppressing the occurrence of various aberrations. It becomes possible.
[0055]
  In claim 5Condition (2)Is the “desirable range” within the effective scanning area of the imaging magnification in the sub-scanning direction of the scanning imaging lens, and if it is outside this range, the spot diameter variation in the effective scanning area increases, and the formed image Will be affected.
[0056]
  Satisfying condition (2) allows the beam pitch between multiple beams to be kept constant even when performing multi-beam scanning optical scanning. It becomes possible.
[0057]
  Claim 6If the lower limit of the condition (3) is exceeded, the lateral magnification in the sub-scanning direction on the optical axis between the deflecting means and the scanned surface 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. When the upper limit value of the condition (3) is exceeded, the distance between the scanning lens closest to the deflecting means and the surface to be scanned becomes large, and the size of the image forming apparatus tends to increase.
[0058]
  When configuring a tandem image forming apparatus that shares a deflecting means,TwoScanning lensBetween,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 value of the condition (1) in claim 1 is exceeded,RunBetween the lensSeparation atThe interval on the optical axis is too short, and it becomes difficult to dispose an optical path separating mirror or the like.
[0059]
  When the upper limit of condition (1) is exceeded, the scanning lens on the deflecting means side approaches the deflecting means side, but this scanning lens acts on the surface to be scanned by the action of “positive refractive power in the main scanning direction”. The field angle for optical scanning of the effective scanning area is narrow, 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 can cope with the writing density. There is a risk of disappearing.
[0060]
  Claims 1 and 7When a plastic lens is used for the scanning lens as in the optical scanning device described, 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, a rotating polygon mirror or the like is used as the deflecting means, but the ambient temperature is likely to rise due to heat generated by a drive motor that rotates the polygon mirror.
[0061]
  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. The tandem type uses a separate scanning imaging lens for each surface to be scanned. In the “color image forming apparatus”, the “change in constant velocity characteristic 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. As in the present invention, the deflection meansSide runningReviewers `` differentOn the photoreceptorWhen “shared by a plurality of light beams directed toward the surface to be scanned” is performed, fluctuations in isokineticity occur in the same way for each color, and the occurrence of color shift and hue change is suppressed.
[0062]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments will be described.
[0063]
  FIG. 1 is a diagram for explaining one embodiment of an optical scanning device in a “tandem image forming apparatus”. This image forming apparatus is an apparatus for forming a color image.
[0064]
  FIG. 1A is an explanatory view showing the optical arrangement 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.
[0065]
  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.
[0066]
  As shown in FIG. 1A, in the portion from the light source to the deflecting means (rotating polygonal 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.
[0067]
  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 “line image long in the main scanning direction” by the cylindrical lens 4Y (4M, 4C, 4K) in the vicinity of the deflection reflection surface 4A of the deflecting unit. Are simultaneously deflected by the deflection means 5.
[0068]
  The four light beams (principal rays) incident on the deflecting means 5 from the light sources 1Y to 1K are parallel to each other in the sub-scanning direction.
[0069]
  FIG. 1B shows a state in which the optical path from the deflecting means 5 to the scanned surfaces 7Y to 7K is linearly developed. The entities of the scanned surfaces 7Y to 7K are “photoconductive photoreceptors”, and are formed in a cylindrical shape and arranged in parallel to each other as shown in FIG. FIG. 1B illustrates the scanned surfaces 7Y to 7K so that they are the same surface.
[0070]
  As shown in FIG. 1B, the light beams from the light sources 1Y to 1K are reflected and deflected "parallel to each other" in the direction perpendicular to the rotation axis of the deflection surface by the common deflecting means 5, and the scanning lens L1. Are transmitted in parallel to each other.scanningThe lens L1 is common to the four light beams.
[0071]
  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.
[0072]
  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.
[0073]
  As shown in FIG. 1C, the optical path of the imaging light flux by each scanning imaging lens is appropriately bent by the optical path bending mirror M and guided to the corresponding photoconductors 7Y to 7K.
[0074]
  The light spots formed on the photoconductors 7Y to 7K optically scan the photoconductor to write an electrostatic latent image.
[0075]
  In this embodiment, the lenses constituting the scanning imaging lens are all plastic lenses (Claim 7), and the deflection means 5SideOf course, the scanning lens L1 is also a plastic lens.(Claim 1).
[0076]
  As described above, in the four sets of scanning imaging lenses for guiding the light beams to the four scanned surfaces, the deflection means 5SideThe scanning lens L1 is shared by the four light beams. This scanning lens L1 has a positive refractive power in the main scanning direction, and has substantially no refractive power in the sub-scanning direction. The scanning lenses L2Y to L2K individualized for each scanned surface are closest to each scanned surface and have “positive refractive power in both main and sub-scanning directions”.
[0077]
  That is, the optical scanning device shown in FIG. 1 emits light from a plurality of light sources 1Y to 1K.Corresponding to each colorThe light beam group is deflected by the deflecting means 5 common to these light beam groups, and differs depending on the scanning imaging optical system.On the photoreceptorOne or more light beams are guided and condensed on the scanned surfaces 7Y to 7K, respectively, and one or more light spots are formed on each scanned surface, and each scanned surface is optically scanned with these light spots. In the optical scanning device, the scanning imaging optical system has a scanning imaging lens corresponding to each surface to be scanned.TwoThe scanning lenses L1, L2Y to L2KTwoAmong the scanning lenses, deflection means 5SideThe scanning lens L1 has a positive refractive power in the main scanning direction, a refractive power in the sub-scanning direction is substantially zero, and the scanned surfaces 7Y to 7K.SideThe scanning lenses L2Y to L2K have a positive refractive power in both the main and sub-scanning directions.SideThe scanning lens L1 is differentOn the photoreceptorCommon to the light beam directed to the surface to be scanned ”(Claim 1).
[0078]
  The scanning lens L1 on the deflecting means 5 side is different because it has no refractive power in the sub-scanning direction.On the photoreceptorThe plurality of light beams directed to the scanned surfaces 7Y to 7K pass through the scanning lens L1 substantially in parallel with each other in the sub-scanning direction (vertical direction in FIG. 1B) as shown in FIG. (Claim 2). 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.
[0079]
  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, the deflection means 5SideA temperature distribution is generated in the scanning lens L1, the optical characteristics are changed, and the position of the light spot on each scanning surface is changed in the main scanning direction.
[0080]
  However, since each deflected light beam is transmitted through the scanning lens L1 in common, even if the optical characteristics of the scanning lens L1 vary, the influence is common to all the light beams, and the main light beam on each scanned surface is affected. Variations in the position in the scanning direction are effectively suppressed. For this reason, even if the environmental fluctuation fluctuates during continuous printing, etc., and the optical characteristics of the scanning imaging lens fluctuate, the occurrence of "color shift and hue change" of the color image due to this "fluctuation in optical characteristics" Is effectively suppressed.
[0081]
  In the embodiment of FIG. 1, the portion from the light source to the cylindrical lens is “arranged so as to overlap each other in parallel 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.
[0082]
  In the embodiment of FIG. 1 described above, the optical scanning is the “one-side scanning method”, but the optical scanning device of the present invention can also be the “opposing scanning method”. An embodiment in this case is shown in FIG. In order to avoid complications, the same reference numerals as in FIG. 1 are used for those that are not likely to be confused.
[0083]
  In the embodiment of FIG. 2, on one side (right side in the figure) of the deflecting means 51, the three light beams that optically scan the photoconductors 7M, 7C, and 7K are deflected, and the other side (see FIG. The left side of FIG. 3 deflects the light beam that optically scans the photoconductor 7Y.
[0084]
  The scanning imaging lens has a configuration in which the scanning lens L10 is combined with the scanning lenses L2M, L2C, and L2K with respect to the photoreceptors 7M, 7C, and 7K, and the scanning lens L11 and the scanning lens L2Y with respect to the photoreceptor 7Y. It consists of a combination.
[0085]
  The light beams that optically scan the photoconductors 7M, 7C, and 7K are transmitted through the scanning lens L10 "parallel to each other in the sub-scanning direction". The scanning lens L10 and the scanning lens L11 have the same optical function. These have positive refractive power in the main scanning direction and substantially no refractive power in the sub-scanning direction.
[0086]
  In this way, the four light beams are distributed to one side and three sides on both sides of the deflecting means 5 and deflected, so that the sub-scanning of the scanning lens L10 is performed as compared with the optical scanning device (one-side scanning method) of FIG. The width in the direction and the width in the sub-scanning direction of the deflection scanning surface of the deflecting means can be reduced, and the cost can be reduced and the power consumption for rotating the deflecting means can be reduced. In addition, the scanning lenses L10 and L11 have improved processability (moldability) when they are made of plastic lenses, and can achieve a highly accurate surface shape.
[0087]
  In the optical scanning device of FIG. 2, since the photoconductors 7M, 7C, and 7K are made common to the light beams for optical scanning, color shift and hue change between magenta, cyan, and black color component images are effectively reduced. However, a color shift of the yellow color component image occurs. However, since the color shift of the yellow component image is "not noticeable on the image", an image forming apparatus that balances the workability of the scanning imaging optical system and deflector and the image (for environment, cost, etc.) is realized. it can.
[0088]
  That is, the color image forming apparatus configured by using the optical scanning device in FIG. 2 “scans the four photosensitive media 7Y to 7K separately, writes each color component of the color image, and synthesizes each color component image. In the image forming apparatus for forming a color image by using the above-described optical scanning apparatus for optically scanning four photosensitive media, the one described in claim 1 is used, and the deflecting unit 51 converts the entire light beam into the deflecting unit. Opposing scanning type that distributes to both sides and deflects(Claim 9)It is.
[0089]
  In the embodiment shown in FIG. 2, the light beam for optically scanning the three photoconductors 7M to 7K is “incident in parallel in the sub-scanning direction” from the deflecting unit 51 to the scanning lens L10. As a configuration, for example, four light beams are reflected and deflected in opposite directions by two on both sides of the deflecting means by a common deflecting means, and two scanning lenses common to the two light beams are deflected by the deflecting means. Two light beams arranged symmetrically to each other and distributed to both sides of the deflecting means may be transmitted through these two scanning lenses in common.
[0090]
  FIG. 3 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, reference numeral 50 denotes the “optical scanning device” described in FIG. 1, and reference numerals 5Y, 5M, 5C, and 5K optically scan the photoconductive photoreceptors 7Y, 7M, 7C, and 7K, respectively. A deflected light beam is shown. For the description of this part, the description related to FIG.
[0091]
  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.
[0092]
  The photoconductors 7Y to 7K are uniformly charged by the corresponding charging means YC to KC while being rotated clockwise, and are optically scanned by the light beams 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 yellow, magenta, cyan, and black toner images are formed on the photoreceptors 7Y, 7M, 7C, and 7K, respectively.
[0093]
  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. The transfer paper held on the transport belt 2A is sequentially transported through the transfer section, while the “black toner image” from the photoconductor 7K, the “cyan toner image” from the photoconductor 7C, the “magenta toner image” from the photoconductor 7M, and the photoconductor. The “yellow toner image” is sequentially transferred from 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 transport belt 2A by the stiffness of the transfer paper itself, and proceeds to the fixing device 14, where the color image is fixed,Discharge roller 16Is discharged onto the tray 15 '. 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. 3 is an image forming apparatus that separately scans the four photosensitive media 7Y to 7K, writes each color component of the color image, and forms a color image by combining the color component images. A one-side scanning type optical scanning device that scans the four photosensitive media 7Y to 7K using the one described in claim 1 and the like, and the deflecting means deflects the entire light beam on the same side with respect to the deflecting means. thing(Claim 8)It is.
[0096]
  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.
[0097]
  4A, the light source device denoted by reference numeral 31 includes two semiconductor lasers and two coupling lenses that couple 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.
[0098]
  Each light beam deflected by the deflecting means 5 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 substance of the scanned 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.
[0099]
  The upper part of FIG. 4B 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.₁D for the broken light beam₂Then, in the case of the upper diagram in FIG. 4B, the optical path passing through the scanning lenses 34A and 34B to the imaging position P0 is greatly different, and the optical action is also different depending on the optical path difference, so that it is formed at the imaging position P0. The spot diameter, magnification, and the like of the light spot 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.
[0100]
  On the other hand, as shown in FIG. 4A, 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 formation 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 part on the scanning surface side from the deflecting unit 33 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.
[0101]
  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.
[0102]
  Further, if the plurality of light beams intersect with each other in the main scanning direction at approximately one point in the vicinity of the deflecting / reflecting surface, the size of the deflecting / reflecting surface can be minimized, and the inscribed circle radius of the rotary polygon mirror can be minimized.
[0103]
  In FIG. 4, the case where the single scanning surface 37 is optically scanned by the multi-beam scanning method has been described. However, as in the embodiment shown in FIG. In the case of “deflecting with the same deflecting / reflecting surface”, when the light beams are arranged at angles with respect to the same deflecting / reflecting surface with respect to the same deflecting / reflecting surface, the light beams are reflected by the deflecting means 33. The effect similar to the above can be obtained by “intersecting in the main scanning direction” at approximately one point in the vicinity of the surface. The deviation of the crossing position of each light beam is preferably within 0.5 mm on the deflecting / reflecting surface.
[0104]
【Example】
  Hereinafter, three specific examples of the optical system of the optical scanning device will be given. The optical scanning apparatus shown in FIG. 1 is assumed.
[0105]
  Explanation of symbols
  The meanings of the symbols are as follows.
[0106]
  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
  "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 stop
6 ∞ 48.0 3.0 1.511 Cylindrical lens
7 ∞ ∞ 93.57--
8----Deflection reflecting surface
  Surfaces marked with “*” are “coaxial aspheric surfaces”. Although the numerical value specific to the aspherical surface is not shown, it is set so that the wavefront aberration of the “parallel light beam” emitted from the coupling lens is satisfactorily corrected. The deflecting means is a rotating polygon mirror having an inscribed circle diameter of 18 mm and a number of deflecting reflecting surfaces of 6.
[0107]
  "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
Deflection surface ∞ ∞ 67.9-Deflection surface
1 * 1887.585 ∞ 31.4 1.524 Scanning lens
2 * -151.472 ∞ 162.1--
3 ** -4430.699 -88.519 8.2 1.524 Scanning lens
4 ** -4084.974 -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.
[0108]
  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).
[0109]
  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.
[0110]
  The aspheric coefficients in Example 1 are as follows.
[0111]
            1st surface 2nd surface 3rd surface 4th surface
RY 1887.585 -151.472 -4430.699 -4084.974
K -7.129 -2.866E-01 -4.260E + 02 -4.470E + 02
A -2.360E-08 1.398E-08 7.278E-09 -6.469E-09
B -7.646E-14 -1.940E-12 -1.758E-13 1.313E-13
C 8.043E-17 -2.345E-16 1.103E-18 -1.843E-18
D 1.622E-20 2.102E-20 -1.652E-22 -1.722E-22
E 3.854E-24 3.780E-24 -1.129E-28 1.119E-28
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
  In the above display, for example, “E-30” is “10^-30This number is the one immediately preceding the number.
[0112]
  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.
[0113]
  Example 2
  "Optical system on the light source side from the deflection means"
  The same as in the first embodiment.
[0114]
  "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
Deflection surface ∞ ∞ 67.9-Deflection surface
1 * 2935.904 ∞ 31.3 1.524 Scanning lens
2 * -147.472 ∞ 162.0--
3 ** -2800.436 -88.759 8.4 1.524 Scanning lens
4 ** -2139.643 -27.048 100.0--
5----Surface to be scanned
  The shape of each surface marked with “*” and “**” is the same as that in Example 1, with the formula: 1 and
Formula: 1 using Formula: 2.
[0115]
  The aspheric coefficients in Example 2 are as follows.
[0116]
            1st surface 2nd surface 3rd surface 4th surface
RY 2935.904 -147.472 -2800.436 -2139.643
K 3.469E + 02 -2.754E-01 -9.349E + 02 -5.131E + 02
A -2.346E-08 1.344E-08 7.939E-09 -7.041E-09
B -7.787E-14 -1.951E-12 -1.827E-13 1.420E-13
C 7.756E-17 -2.321E-16 1.062E-18 -1.654E-18
D 1.487E-20 2.206E-20 -1.612E-22 -1.735E-22
E 3.885E-24 4.061E-24 1.904E-28 -6.991E-29
RZ ∞ ∞ -88.759 -27.048
a----1.133E-07
b---1.464E-07 1.106E-07
c---1.322E-11
d--4.982E-14 -5.250E-12
e----4.288E-15
f---1.627E-16 -2.910E-16
g---1.279E-19
h---3.680E-21 8.867E-22
i---1.277E-23
j---9.668E-26 -4.793E-26
k----5.904E-28
l---6.550E-30 -5.920E-30
  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]
  Example 3
  "Optical system on the light source side from the deflection means"
  The same as in the first embodiment.
[0118]
  "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
Deflection surface ∞ ∞ 67.8-Deflection surface
1 * 1889.776 ∞ 31.4 1.524 Scanning lens
2 * -151.493 ∞ 162.0--
3 ** -4016.530 -88.498 8.4 1.524 Scanning lens
4 ** -3342.445 -27.018 100.0--
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.
[0119]
  The aspheric coefficients in Example 3 are as follows.
[0120]
          1st surface 2nd surface 3rd surface 4th surface
RY 1889.776 -151.493 -4016.530 -3342.445
K -6.233E + 00 -2.859E-01 -4.298E + 02 -3.738E + 02
A -2.359E-08 1.393E-08 7.329E-09 -6.508E-09
B -7.764E-14 -1.941E-12 -1.751E-13 1.308E-13
C 8.018E-17 -2.341E-16 1.108E-18 -1.844E-18
D 1.634E-20 2.112E-20 -1.656E-22 -1.719E-22
E 3.946E-24 3.790E-24 -1.410E-28 1.400E-28
RZ ∞ ∞ -88.498 -27.018
a----2.322E-07
b---1.435E-07 1.196E-07
c---1.407E-11
d--5.795E-13 -4.444E-12
e----3.696E-15
f---6.469E-17 -2.292E-16
g---1.531E-19
h---3.640E-21 4.860E-22
i---1.265E-23
j---1.094E-25 -5.044E-26
k----7.167E-28
l---9.525E-30 -4.891E-30
  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.
[0121]
  5 to 7 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.
[0122]
  The optical systems of Examples 1 to 3 are each scanned surfaceSideThe scanning lens has a positive meniscus shape with a convex surface facing the surface to be scanned in the main scanning section (Claim 4), and the sub-scanning direction on the optical axis between the deflecting means and the surface to be scanned. Horizontal magnification: 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 5), the lateral magnification in the sub-scanning direction on the optical axis between the deflecting means and the surface to be scanned: β₀But the condition:
  (3) 0.2 <| β₀｜ <0.6
(Claim 6).
[0123]
  Further, the distance on the optical axis from the starting point of deflection by the deflection means to the surface to be scanned: L, the maximum scanning lens interval within the same scanning imaging lens: a, the condition:
  (1) 0.3 <| a / L | <0.6
Satisfy(Claim 1). Furthermore, the scanning lenses included in the scanning imaging lens are all plastic lenses.(Claims 1 and 7).
[0124]
  Note that “consisting of two or more scanning lenses and deflecting means”SideThe scanning lens has a positive refractive power in the main scanning direction, and the refractive power in the sub-scanning direction is substantially zero.SideA scanning imaging lens in which the scanning lens has a positive refractive power in both the main and sub-scanning directions itself is a normal optical scanning device (scans a single surface to be scanned by a single beam or multi-beam scanning method). The first to third embodiments are also examples of such a scanning imaging lens.
[0125]
【The invention's effect】
  As described above, according to the present invention, a novel optical scanning device and image forming apparatus can be realized. The optical scanning device of the present invention can realize a stable light spot by properly correcting the curvature of field in the main and sub-scanning directions on a plurality of scanned surfaces. Therefore, an image forming apparatus using this optical scanning is excellent. Color image formation and multicolor images can be formed.
[Brief description of the drawings]
FIG. 1 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. 2 is a diagram for explaining one embodiment of a multi-beam scanning type optical scanning device using the optical scanning device of the present invention;
3 is a diagram showing an embodiment of a tandem color image forming apparatus using the optical scanning device of FIG. 1. FIG.
FIG. 4 is a view for explaining the invention according to claim 3;
5 is a diagram showing field curvature and constant velocity characteristics of Example 1. FIG.
6 is a diagram showing field curvature and constant velocity characteristics of Example 2. FIG.
7 is a diagram showing field curvature and constant velocity characteristics of Example 3. FIG.
[Explanation of symbols]
  1Y ~ 1K light source
  2Y ~ 2K coupling lens
  4Y-4K cylindrical lens
  5 Deflection means
  L1 scanning lens
  L2Y-L2K scanning lens
  7Y-7K surface to be scanned

Claims (9)

A light beam group corresponding to each color emitted from a plurality of light sources is deflected on one side of the deflecting means by a deflecting means common to the light beam groups, and is applied to a scanned surface on a different photosensitive member by a scanning imaging optical system. In an optical scanning apparatus that guides and collects one or more light beams to form one or more light spots on each scanned surface, and performs optical scanning of each scanned surface with these light spots,
The scanning imaging optical system has a scanning imaging lens corresponding to each scanned surface,
The scanning imaging lens is constituted by two scanning lenses, of these two scanning lenses, deflecting means side of the run査lens has a positive refractive power in the main scanning direction, the refractive power in the sub-scanning direction is substantially is zero, run査lens surface to be scanned side has a main sub-scanning direction are positive refractive power,
In the scanning image forming optical system, the deflecting means side of the run査lenses are common to the light beam towards the surface to be scanned on different photoreceptor,
It said deflecting means side of the scanning lens is a plastic lens,
Between the two scanning lenses, separation mirror for separating the optical path is arranged to the surface to be scanned,
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,
An optical scanning device characterized in that light beams pass through a scanning lens shared by light beams directed to scanning surfaces on different photoconductors substantially parallel to each other in the sub-scanning direction. The optical scanning device according to claim 1 or 2,
The deflecting means is of a reflective type having a deflecting reflecting surface, and all light beams incident on the same deflecting reflecting surface intersect the main scanning direction at substantially one point in the vicinity of the same deflecting reflecting surface. An optical scanning device. The optical scanning device according to any one of claims 1 to 3,
Each scanned surface side of the run査lens, the shape of the main scanning cross section, an optical scanning device which is a positive meniscus shape with a convex surface directed to the surface to be scanned side. The optical scanning device according to any one of claims 1 to 4,
The lateral magnification in the sub-scanning direction on the optical axis between the deflecting means and the surface to be scanned: β ₀ , the lateral magnification in the sub-scanning direction at an arbitrary image height: β _h , conditions:
(2) 0.9 <| β _h / β ₀ | <1.1
An optical scanning device characterized by satisfying In the optical scanning device according to any one of claims 1 to 5,
The lateral magnification in the sub-scanning direction on the optical axis between the deflecting means 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 The optical scanning device according to any one of claims 1 to 6,
Optical scanning apparatus, wherein the scanning lens surface to be scanned side is a plastic lens. In an image forming apparatus that separately scans three or four photosensitive media, writes each color component of a color image, and forms a color image by combining the color component images.
The photosensitive medium 3 or 4 sides as the optical scanning device for optical scanning, using those described in any one of claims 1 to 7, and, deflecting deflection means a total light beam, in the same side with respect to the deflecting means One-side scanning type image forming apparatus. In an image forming apparatus that separately scans three or four photosensitive media, writes each color component of a color image, and forms a color image by combining the color component images.
The photosensitive medium 3 or 4 sides as the optical scanning device for optical scanning, using those described in any one of claims 1 to 7, and the deflection means a total light beam, are distributed on both sides of the deflecting means A counter-scanning image forming apparatus characterized by deflecting.

Images