JP2005091757A - Optical scanner and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner having a deflection means which deflects a light beam emitted from a light source and a scanning and imaging lens which guides the light beam deflected with the deflection means to a plane to be scanned, in which scanning and imaging lens the curvature of an image plane in a main scanning direction and subscanning direction is excellently corrected and the stability of a light spot is realized while excellently keeping the conjugating function and the constant-speeding function, further, the optical magnification is kept constant with respect to the image height of the light spot, and to provide an image forming device furnished with the optical scanner. <P>SOLUTION: The scanning and imaging lens of the optical scanner is composed of at least two scanning and imaging lenses, the scanning and imaging lens L1, which is located at a position nearest an optical deflection device 403 which is the deflection means, has a positive refractive power in the main scanning direction, the refracting power in the subscanning direction is zero or approximately zero, the scanning and imaging lens L2, which is located at a position nearest to a plane to be scanned 407, has a negative refractive power in the main scanning direction and a positive refractive power in the subscanning direction, and the incident side plane in the subscanning direction of the scanning and imaging lens L2 nearest the plane to be scanned 407 is formed in a convex plane toward the plane to be scanned 407. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning device such as a digital copying machine, a laser printer, and a laser facsimile, and an image forming apparatus using the same.

  In general, an optical scanning device widely known in connection with a laser printer or the like generally deflects a light beam from a light source side by an optical deflector and condenses it toward a surface to be scanned by a scanning imaging optical system such as an fθ lens. Thus, a light spot is formed on the surface to be scanned, and the surface to be scanned is optically scanned (main scan) with this light spot. What constitutes the surface to be scanned is a photosensitive surface of a photosensitive medium such as a photoconductive photosensitive member.

  The writing density of the optical scanning device is steadily increasing, and it is intended to realize a writing density of 1200 dpi, 1600 dpi, or higher. In order to realize such high-density writing, the stability of the light spot is indispensable. The stability of the light spot means that the “change due to the image height of the light spot diameter on the surface to be scanned” is small. To achieve this, the light beam deflected by the optical deflector is placed on the surface to be scanned. The scanning imaging optical system that forms an image as a light spot needs to have high performance.

  As well known, a factor causing the light spot diameter to fluctuate is “field curvature by a scanning optical system”, and many scanning imaging optical systems that have corrected the field curvature well have been proposed. Further, it is important that the optical magnification of the scanning image-forming optical system is constant regardless of the image height in order to stabilize the light spot and cope with multi-beams to cope with a high writing density.

  As an example of the optical scanning device, four photoconductors are arranged in the conveyance direction of the recording paper, and light beams emitted from a plurality of light source devices corresponding to the photoconductors are converted into one deflecting unit (optical deflector). ), And a plurality of scanning imaging optical systems corresponding to the respective photoconductors are simultaneously exposed to the respective photoconductors to form latent images, and these latent images are produced in different colors such as yellow, magenta, cyan, and black. A visible image is developed with a developing device using the above developer, and these visible images are sequentially superimposed and transferred and fixed on the same recording paper, whereby a color image can be obtained.

  As described above, an image forming apparatus that obtains a two-color image, a multicolor image, a color image, or the like by using two or more combinations of optical scanning devices and photoreceptors is known as a “tandem image forming apparatus”. Yes.

As such a tandem type image forming apparatus, a system in which a plurality of photosensitive media share a single optical deflector is disclosed. As the prior art related to the present invention, there are the following patent documents.
JP-A-11-157128 JP-A-9-127443 JP-A-9-54263 JP 2001-4948 A Japanese Patent Laid-Open No. 2001-10107 JP 2001-33720 A JP 2001-350110 A Japanese Patent Laid-Open No. 9-58053

  In Patent Document 1 and Patent Document 2, a counter scanning method is adopted in which light beams are incident from both sides of the optical deflector and the light beams are distributed and scanned. In Patent Document 3, a plurality of light beams that are substantially parallel and separated in the sub-scanning direction are incident on an optical deflector, and a plurality of scanning optical elements corresponding to the plurality of light beams are arranged in the sub-scanning direction for scanning. Adopted.

  In Patent Documents 4, 5, and 6, a light beam is incident from one side of the optical deflector, and the first and second scanning imaging lenses L1 and L2 are different in a three-scanning scanning optical system of scanning imaging lenses. A plurality of light beams traveling toward the scanned surface pass, and the third scanning imaging lens L3 is provided for each scanned surface.

  As described above, when the optical deflectors are shared by a plurality of scanned surfaces, it is possible to reduce the number of optical deflectors, thereby reducing the size and cost of the image forming apparatus.

  In Patent Document 7, an optical scanning device corresponding to a tandem method is disclosed.

  However, in the conventional technology, in the scanning imaging lens, while maintaining the “conjugate function” and “constant speed function” in good condition, the field curvature in the main scanning direction and the sub-scanning direction is corrected well, and the light spot of the light spot is corrected. It has not been achieved that stability is achieved and that the optical magnification is constant with respect to the image height of the light spot.

  In recent years, a special surface represented by an aspherical surface has been widely used as an optical element of an optical scanning device for the purpose of improving scanning characteristics. Such a special surface can be easily formed, and the cost can be reduced. However, inexpensive “resin-made optical elements” are frequently used. In particular, in the conventional tandem image forming apparatus, since the number of optical elements used is large, the cost reduction effect by using the resin optical elements is very large.

  As described above, when a resin optical element is used in the optical scanning device, a change in temperature causes a large change in shape because the coefficient of thermal expansion is larger than that of glass, and the optical characteristics of the resin optical element change.

  When the temperature in the optical box rises due to deflection means (optical deflector) such as a polygon mirror that generates a large amount of heat, the heat is uniformly transferred due to the airflow generated by the rotation of the polygon mirror and the difference in the shape of the optical box. The temperature inside the optical box has a temperature distribution. Also in the scanning imaging lens, there is no uniform temperature change due to differences in heat transmission, lens shapes (difference in installation area to the optical box), etc., and temperature differences depending on the location of the scanning imaging lens Occurs.

  In a conventional tandem type image forming apparatus, the light fluxes directed to each photoconductor pass through different scanning imaging lenses, and the temperature distribution varies among the scanning imaging lenses due to the temperature distribution in the optical box holding the scanning imaging lens. Therefore, the change in the shape of the scanning imaging lens, the change in the refractive index, and the like are not uniform, and the amount of change in the scanning length and the change in the constant velocity of each photoconductor are different. These latent images are visualized with a developing device using different color developers such as yellow, magenta, cyan, and black, and then these visible images are sequentially superimposed and transferred onto the same recording paper. When a color image is obtained by fixing, so-called “color shift” occurs. In particular, when the scanning imaging lens closest to the deflecting means such as a polygon mirror that generates a large amount of heat in the optical box is made of resin, the change in optical characteristics becomes large.

  Further, in the case of continuous output, particularly when the number of continuous outputs is large, the internal temperature (temperature in the optical box) rises due to heat generated by the deflection means. For this reason, the temperature distribution of each scanning imaging lens changes, color shift occurs as described above, and the amount of change also changes. As a result, there is a problem that the color changes between the first output image and the last output image due to color misregistration.

  As a method of coping with the above-mentioned problem of “change in scanning length”, light receiving means are arranged on the writing start side and writing end side, and the image frequency of each light beam is determined based on the light receiving time difference of each light receiving means. (See Patent Document 8), if this method is adopted in the above-described tandem image forming apparatus that “shared a plurality of scanned surfaces with an optical deflector”, a light receiving means is provided on the writing end side. Since an arrangement space is required, it becomes more difficult to secure an effective write width.

  Further, in the method of arranging the light receiving means on the writing start side and the writing end side and adjusting the image frequency of each light beam based on the light receiving time difference of each light receiving means, the length of the scanning line on each photoconductor However, it is impossible to correct the change in isokineticity due to the temperature distribution of each scanning imaging lens. For this reason, for example, even if the dot positions in the main scanning direction at the start and end of writing are corrected by each photoconductor, the dot positions in the main scanning direction in the middle do not match, and color misregistration occurs. .

  In tandem optical scanning devices, in order to solve the above problem, there are many examples in which the material of the scanning imaging lens closest to the deflecting means such as a polygon mirror that generates a large amount of heat is made of glass. There is a problem that the cost is significantly increased as compared with the image lens.

  Further, the conventional tandem image forming apparatus has the following problems. Only Patent Documents 1 and 2 can scan only two different surfaces to be scanned, and cannot cope with four-color writing. In addition, since beams directed toward the scanning surfaces pass through different scanning optical elements, the beam positions are relatively shifted on the scanning surfaces, and the above-described “color shift” is likely to occur.

  Moreover, in the technique of Patent Document 3, the size of the apparatus is increased, for example, the optical deflector is increased. Further, there are problems of noise, power consumption, and durability deterioration. In addition, the number of optical elements increases, leading to an increase in cost. Since beams directed to each scanning surface pass through different scanning optical elements, the beam position is relatively shifted on each scanning surface, and the above-mentioned “color shift” is likely to occur.

  In the techniques of Patent Documents 4, 5, and 6, the first scanning imaging lens L1 has a positive power in the sub-scanning direction, and the light flux directed to each scanned surface is converged and applied to each scanned surface. Separation becomes difficult.

  The present invention has been made in view of the above problems, and includes a deflecting unit that deflects a light beam from a light source, and a scanning imaging lens that guides the light beam deflected by the deflecting unit onto a surface to be scanned. In an optical scanning device, the scanning imaging lens maintains good "conjugation function" and "constant speed function", and corrects the field curvature in the main scanning direction and sub-scanning direction to stabilize the light spot. Further, an object of the present invention is to provide an optical scanning device in which the optical magnification is constant and the optical magnification is constant with respect to the image height of the light spot, and an image forming apparatus including the optical scanning device.

  In order to achieve the above object, the invention described in claim 1 includes a deflecting unit that deflects a light beam from a light source, and a scanning imaging lens that guides the light beam deflected by the deflecting unit onto a surface to be scanned. The scanning imaging lens includes at least two scanning imaging lenses, and the scanning imaging lens closest to the deflection unit has a positive refractive power in the main scanning direction and is refracted in the sub-scanning direction. The scanning imaging lens whose force is zero or close to zero and closest to the surface to be scanned has negative refractive power in the main scanning direction and positive refractive power in the sub-scanning direction. The incident-side surface in the direction is a surface convex toward the scanned surface side.

  According to a second aspect of the present invention, in the first aspect of the present invention, there are a plurality of light sources, and a light beam from each light source of the plurality of light sources is deflected by a single deflecting unit and varies depending on the scanning imaging lens. A plurality of light beams directed to different scanning surfaces pass through a scanning imaging lens that is guided onto the scanning surface and is closest to the deflection unit among the scanning imaging lenses.

  According to a third aspect of the present invention, in the second aspect of the present invention, the plurality of light beams directed to different scanning surfaces pass through the scanning imaging lens closest to the deflecting unit substantially parallel to the sub-scanning direction. And

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, all the light beams deflected by the same deflecting reflection surface of the deflecting unit are mainly adjacent to the deflecting surface of the deflecting unit. The scanning section is configured to intersect at substantially one point.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the scanning imaging lens is composed of two lenses, and the main shape of the scanning imaging lens on the scanned surface side is the scanned image. It is a negative meniscus lens having a convex surface facing the surface.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the lateral magnification in the sub-scanning direction on the optical axis between the deflection surface and the surface to be scanned is β0, and the arbitrary image height is set. When the horizontal magnification in the sub-scanning direction is βh, “0.9 <| βh / β0 | <1.1” is satisfied.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the lateral magnification in the sub-scanning direction on the optical axis between the deflection surface and the surface to be scanned is β0. 0.2 <| β0 | <0.6 ”is satisfied.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the distance from the base point of the deflecting means on the optical axis to the surface to be scanned is L, and a plurality of scanning imaging lens intervals. When the distance on the optical axis that is farthest away is a, “0.3 <| a / L | <0.6” is satisfied.

  The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein at least one material of the scanning imaging lens is plastic.

  According to a tenth aspect of the invention, in the ninth aspect of the invention, the material of the scanning imaging lens closest to the deflecting means is plastic.

  An eleventh aspect of the present invention is an image forming apparatus including the optical scanning device according to any one of the first to tenth aspects.

  A twelfth aspect of the present invention is a full-color tandem type image forming apparatus including the optical scanning device according to any one of the first to tenth aspects.

  In an optical scanning device having a deflecting unit for deflecting a light beam from a light source and a scanning imaging lens for guiding the light beam deflected by the deflecting unit onto a surface to be scanned, the scanning imaging lens has at least two scanning imagings. The scanning imaging lens that is composed of a lens and is closest to the deflecting means has a positive refractive power in the main scanning direction, the refractive power in the sub-scanning direction is zero or close to zero, and the scanning imaging lens that is closest to the surface to be scanned is By making the surface on the incident side in the sub-scanning direction of the scanning imaging lens closest to the surface to be scanned convex to the surface to be scanned has a negative refractive power in the main scanning direction and a positive refractive power in the sub-scanning direction. In the scanning imaging lens, the light that achieves the stability of the light spot by properly correcting the curvature of field in the main scanning direction and the sub-scanning direction while maintaining the “conjugate function” and “constant speed function” in good condition A scanning device can be provided. Furthermore, by using the optical scanning device of the present invention, it is possible to realize an image forming apparatus capable of ensuring high-quality image reproducibility, and to suppress the occurrence of color misregistration and color change in a color machine. Thus, an image forming apparatus with small color misregistration can be realized.

  Embodiments of the present invention will be described in detail with reference to the drawings.

  In the optical scanning device of the present invention, the scanning imaging lens is composed of at least two scanning imaging lenses, and the scanning imaging lens closest to the deflecting means (optical deflector) has a positive refractive power in the main scanning direction. The refractive power in the sub-scanning direction is zero or close to zero, and the scanning imaging lens closest to the scanned surface has a negative refractive power in the main scanning direction and a positive refractive power in the sub-scanning direction.

  FIG. 1 is a sectional view showing the configuration of two scanning imaging lenses in the first embodiment of the optical scanning device of the present invention.

  The light beams emitted from the light source device 100 are respectively coupled to parallel light beams (which may be weakly convergent or divergent light beams) by the first optical system. The light beam of the coupled light beam passes through the second optical system after passing through an aperture stop for obtaining a desired beam spot diameter on the surface to be scanned 407, and mainly in the vicinity of the optical deflector 403 serving as a deflecting unit. A long line image is formed in the scanning direction. The light beam scanned by the optical deflector 403 passes through the scanning imaging lenses L1 and L2 of the third optical system, scans the corresponding scanned surface 407 at a substantially constant speed, and collects in the vicinity of the scanned surface 407. Shine.

  In the optical scanning device of the present invention, the scanning imaging lens L1 closest to the optical deflector 403 in the main scanning direction has a positive refractive power and corrects the constant velocity well. Further, the scanning imaging lens L2 closest to the scanned surface 407 has a negative refractive power, thereby canceling the deterioration of the optical characteristics when the environment changes and when the wavelength changes. Furthermore, since the scanning imaging lens L2 closest to the scanned surface 407 has a long shape, there is a great problem in workability. However, the scanning imaging lens L2 has a negative refracting power, and it is easy to make the lens thickness uniform in the main scanning direction, which is advantageous in processing.

  With respect to the sub-scanning direction, the refractive power of the scanning imaging lens L1 closest to the optical deflector 403 is zero or close to zero. As described above, the scanning imaging lens L1 has a strong positive refractive power in the main scanning direction and corrects the constant velocity well. Since the scanning imaging lens L1 has almost no refractive power in the sub scanning, the main scanning sectional shape does not change in the sub scanning direction. For this reason, even when the incident light beam is deviated in the sub-scanning direction, the constant velocity does not deteriorate. In addition, it is possible to suppress deterioration of the imaging performance in the main scanning direction.

  Further, since the sub-scanning refractive power of the scanning imaging lens L1 closest to the optical deflector 403 is substantially zero, the scanning imaging lens L2 closest to the scanned surface 407 has a strong positive refractive index in the sub-scanning direction. Have. As a result, the sub-scanning magnification of the scanning imaging optical system becomes a reduction system, and performance degradation due to component assembly errors, component shape errors, and the like can be suppressed. In the sub-scanning direction, it is needless to say that the base point of the optical deflector 403 and the surface to be scanned 407 have a conjugate relationship, and the optical deflector 403 has a surface tilt correction function.

  Further, the surface on the incident surface side in the sub-scanning direction of the scanning imaging lens L2 closest to the scanned surface 407 has a convex shape toward the scanned surface 407, so that the lens shape in the sub-scanning direction is on the scanned surface side. It has a convex meniscus shape, and the principal point position can be behind (to be scanned 407 side). As a result, it is possible to realize a reduction system with the same lens arrangement, suppress performance degradation due to component assembly errors, component shape errors, and the like, and maintain stable imaging performance. Furthermore, since the principal point position can be on the scanned surface 407 side, the lens is closer to the optical deflector 403 side than the other shapes (for example, a meniscus shape convex to the optical deflector side) at the same reduction ratio. Can be arranged. As a result, the length of the lens in the main scanning direction can be shortened, the shape accuracy of the lens surface during lens molding can be improved, and a low-cost scanning imaging lens can be realized by shortening the length.

  Further, for example, the surface shape in the main scanning direction of the scanning imaging lens L1 closest to the optical deflector 403 that is a deflecting unit is a non-arc shape, or the surface shapes of other scanning imaging lenses are non-arc shapes in the main scanning direction. And the curvature in the sub-scanning section is such that the center line of curvature connecting the centers of curvature in the sub-scanning section in the main scanning direction is a different curve from the non-arc shape in the main scanning direction in the main scanning section. By using a surface whose radius is changed in the main scanning direction, it is possible to satisfactorily correct field curvature in both the main scanning direction and the sub-scanning direction.

  As described above, according to the first embodiment of the present invention, the scanning imaging lens closest to the deflecting unit has positive refractive power in the main scanning direction and zero or zero refractive power in the sub-scanning direction. The scanning imaging lens closest to the surface to be scanned has a negative refractive power in the main scanning direction and a positive refractive power in the sub scanning direction, and is closer to the incident side in the sub scanning direction of the scanning imaging lens closest to the surface to be scanned. By making the surface convex toward the surface to be scanned, in the scanning imaging lens, the curvature of field in the main scanning direction and the sub-scanning direction is maintained while maintaining a good “conjugate function” and “constant speed function”. Thus, it is possible to provide an optical scanning device that corrects the above and realizes the stability of the light spot.

  A second embodiment of the optical scanning device of the present invention will be described with reference to the drawings. In the second embodiment, as an example of the case where the optical scanning device described in the first embodiment is developed on a color machine, for example, four light source devices corresponding to four photoreceptors of cyan, magenta, yellow, and black are provided. The optical scanning device to be described will be described with reference to FIGS. 2 (a) and 2 (b). The light beam from each light source is deflected by a single deflecting means and guided to a different scanning surface by a scanning imaging lens, and the scanning imaging lens of the scanning imaging lens closest to the deflection means has a different scanning target. A plurality of light beams traveling toward the surface are configured to pass.

  FIG. 2 is a development view of the optical system in the second embodiment of the optical scanning device of the present invention. In FIG. 2A, the main scanning section is shown, and for the sake of convenience, all the folding mirrors are omitted, and these are shown in an unfolded state in which the optical path of the scanning beam is not changed. In the upper part of FIG. 2B, a sub-scanning section is shown, and the optical path from the optical deflector to the surface to be scanned is shown including the folding mirror. In the lower part of FIG. 2B, the connection between the photoconductor for the color image and the scanning imaging lens is shown.

  As shown in FIG. 2A, the light beams emitted from the light source devices corresponding to the respective colors (arranged in parallel in the sub-scanning direction) are parallel light beams (even weakly convergent or divergent light beams) by the first optical system. Are coupled to each other. At this time, the beam form of each light beam coupled by the first optical system is the “same beam form”. This beam form can be a “parallel beam” or a “convergent or divergent beam”. The light beam of each light beam passes through the aperture stop for obtaining a desired beam spot diameter on the surface to be scanned, then passes through the second optical system, and forms a long line image in the main scanning direction in the vicinity of the optical deflector. To do.

  In this description, the light source devices are arranged in parallel in the sub-scanning direction. However, on the layout of the optical scanning device, the light source devices may be folded back by a folding mirror or the like, and a plurality of light source devices may be arranged at a distance in the main scanning direction.

  Further, as shown in FIGS. 2A and 2B, the light beam scanned by the optical deflector passes through the scanning imaging lenses L1 and L2 of the third optical system, and substantially corresponds to the surface to be scanned. Scanning at a constant speed and condensing near the surface to be scanned. At this time, as shown in FIG. 2B, the scanning imaging lens L1 of the third optical system passes the light beams of the light beams emitted from all the light sources side by side in the sub-scanning direction. The surface to be scanned is essentially the photosensitive surface of the photosensitive medium. In this embodiment, “the photosensitive surface of the photoconductive photosensitive member is optically scanned in the vertical direction of FIG. The vertical direction in FIG. 2A is the main scanning direction (the direction of the main scanning line).

  Since the scanning imaging lens L1 closest to the deflecting means (optical deflector) is configured to pass a plurality of light beams directed to different scanned surfaces, the main scanning direction between different scanned surfaces, that is, between the respective colors. Beam spot position deviation can be reduced, and image degradation due to color deviation and color can be suppressed.

  In addition, the scanning imaging lens L1 closest to the deflecting unit has a strong positive refractive power in the main scanning direction and corrects constant velocity. By passing a plurality of light beams directed to different scanned surfaces through this lens, the beam spot position deviation in the main scanning direction due to processing variations of the scanning imaging lens becomes the same on different scanned surfaces, and color misregistration occurs. Can be suppressed.

  Furthermore, the rotary polygon mirror as the deflecting means (optical deflector) generates a large amount of heat by the motor unit and the base. With respect to the substrate, it is possible to reduce the temperature fluctuation in the optical box by taking it out of the optical box, but the temperature rises due to the heat generated by the motor unit. The heat due to the temperature fluctuation propagates through the optical box and causes a temperature distribution in the scanning imaging lens, particularly the scanning imaging lens closest to the rotary polygon mirror. This temperature distribution is generated because a uniform temperature change does not occur in the scanning imaging lens due to the airflow in the optical box by the rotary polygon mirror, the shape of the scanning imaging lens, and the like. As a result, in a tandem color machine of an opposite scanning type in which beams directed to each scanned surface pass through different scanning optical elements, the relative beam spot position in the main scanning direction on each scanned surface during continuous printing is obtained. It fluctuates and the color changes.

  However, in the optical scanning device of the present invention, since the scanning imaging lens L1 closest to the deflecting unit passes a plurality of light beams directed to different scanning surfaces, the scanning imaging lens L1 has a temperature distribution in the main scanning direction. Even in the case of having, the beam spot position deviation in the main scanning direction is the same on different scanned surfaces, and it is possible to suppress changes in color and occurrence of color deviation during continuous printing.

  Further, a plurality of light beams traveling toward different scanning surfaces are allowed to pass through the scanning imaging lens L1 closest to the deflecting means substantially parallel to the sub-scanning direction, so that the incident light flux is shifted in the sub-scanning direction. The constant velocity does not deteriorate. In addition, it is possible to suppress deterioration of the imaging performance in the main scanning direction. In addition, the occurrence of bending of the scanning line can be suppressed.

  Here, an example has been described in which the scanning imaging lens L1 passes the light beams of the light beams corresponding to the four photosensitive members side by side in the sub-scanning direction from the rotary polygon mirror (optical deflector) which is the deflection means. Similarly, the first scanning imaging lens L1 from the optical deflector passes the light beams of the light beams directed to two different scanned surfaces side by side in the sub-scanning direction, and is a rotating polygon mirror (optical deflector) that is a deflecting unit. ), The surface to be scanned is arranged on both sides thereof, and the photoconductor may be four surfaces to be scanned.

  As described above, in the second embodiment of the present invention, a plurality of light sources are provided, and a light beam from each light source is deflected by a single deflecting means (light deflector) and is scanned by a scanning imaging lens. The scanning imaging lens that is guided on different scanning surfaces and is closest to the deflecting means of the scanning imaging lens allows a plurality of light beams to pass through different scanning surfaces to pass through the “conjugation function” and “etc.” Optical scanning that corrects the curvature of field in the main scanning direction and sub-scanning direction to achieve the stability of the light spot while keeping the speeding function good, and also suppresses the occurrence of color shift and color change. An apparatus can be provided.

  Next, a third embodiment of the optical scanning device of the present invention will be described. FIG. 3 is a block diagram showing the configuration of the third embodiment of the optical scanning device of the present invention. In FIG. 3, (a) is a perspective view, and (b) and (c) are ray diagrams to the surface to be scanned. 2B and 2C also use two scanning imaging lenses, and the scanning imaging lens L1 has a two-lens configuration.

3B and 3C, it is preferable that all light beams emitted from the semiconductor laser 101 intersect each other in the main scanning direction in the vicinity of the reflection surface of a polygon mirror (optical deflector) 403 which is a deflecting unit. D ₁ represents the reflection surface of the polygon mirror (light deflector) 403 when the light beam emitted from the semiconductor laser 101 reaches a certain image height on the scanned surface 407, and D ₂ is emitted from the semiconductor laser 102. The reflection surface of the polygon mirror 403 when the light beam reaches the same image height on the surface to be scanned 407 is shown.

Each light beam is separated by an angle Δα when entering the polygon mirror 403. Therefore, a time delay (such as D ₁ and D ₂ ) occurs on the reflecting surface for reaching the same image height by this angular difference.

  In the case of FIG. 3 (b), the two light beams pass through quite different optical paths, and in the case of FIG. 3 (c), they pass through the exact same optical path. When the light beam passes through a different position of each optical element, it naturally undergoes different optical action. Therefore, the optical characteristics such as aberration of the two light beams that reach the same image height in the main scanning direction on the scanned surface 407 are as follows. In particular, the influence on the fluctuation of the scanning line pitch between the image heights is very large.

  Therefore, as shown in FIG. 3C, when the two light beams intersect each other in the vicinity of the reflection surface of the polygon mirror 403, when the same image height in the main scanning direction on the surface to be scanned is reached, the main scanning of the optical element is performed. The optical paths that pass through substantially the same direction can be effectively reduced, and the bending of the scanning line can be effectively reduced. Further, the fluctuation in the main scanning direction writing position between the respective light beams due to the variation of each part on the image plane side from the polygon mirror 403 is substantially the same for all the light beams, and the main scanning direction writing position shift between the respective beams. Is suppressed. Furthermore, by passing all the light beams formed at the same image height through substantially the same position in the main scanning direction of the scanning optical system, the influence of the aberration of the lenses constituting the scanning optical system can be suppressed and The imaging position in the scanning direction can be accurately matched to each beam, and even if a delay time is set for all the light beams after synchronous detection, the positional deviation in the main scanning direction at the initial image height can be suppressed. Is possible. Further, by making it as shown in FIG. 3C, the inscribed circle radius of the polygon mirror 403 can be minimized.

  In the third embodiment, an example of a multi-beam light source has been described. However, when a light beam traveling toward a different surface to be scanned is deflected by the same reflecting surface of the polygon mirror 403, each light beam is reflected by the reflecting surface of the polygon mirror 403. A similar effect can be obtained by intersecting in the main scanning direction in the vicinity. Further, it is desirable that the deviation of the crossing position in each beam main scanning section is within 0.5 mm on the reflection surface of the polygon mirror 403.

  As described above, in the third embodiment of the present invention, a plurality of light beams traveling toward different scanning surfaces are arranged so that the scanning imaging lens closest to the deflecting means (optical deflector) is substantially parallel to the sub-scanning direction. By letting it pass, while maintaining the `` conjugation function '' and `` constant speed function '' well, the field curvature in the main scanning direction and the sub-scanning direction is corrected well, and the stability of the light spot is realized, It is possible to provide an optical scanning device in which the optical magnification is constant with respect to the image height of the light spot, and further, the occurrence of color shift and color change is suppressed, and the occurrence of scanning line bending is suppressed.

  Also, all the light beams deflected by the same deflecting and reflecting surface of the deflecting means are configured to intersect at one point near the deflecting surface of the deflecting means, thereby ensuring good beam position accuracy even when the environment changes. However, good optical performance can be obtained. In addition, the polygon mirror that is an optical deflector can be made smaller, and an optical scanning device with reduced noise can be provided.

  Next, a fourth embodiment of the optical scanning device of the present invention will be described. In the above-described embodiment, the scanning imaging lens is composed of two lenses, and the main shape of the scanning imaging lens on the scanned surface side is a negative meniscus lens having a convex surface facing the scanned surface, so that the image height is reduced. The optical magnification can be made constant.

  The curvature center line obtained by connecting at least two surfaces in the sub-scanning direction with the center of curvature in the sub-scanning section in the main scanning direction is a curve different from the non-arc shape in the main scanning direction in the main scanning section. When using a surface in which the radius of curvature in the sub-scanning section is changed in the main scanning direction and bending the two lens surfaces to “adjust the main point position in the sub-scanning direction”, the distance between these two surfaces is wider. However, a large change amount of the principal point position can be taken. That is, the horizontal magnification of sub-scanning can be corrected between image heights.

  However, in the present invention, a two-lens configuration is used aiming at low cost, and the sub-scanning of the scanning imaging lens closest to the deflecting means makes the refractive power almost zero. Therefore, these two surfaces are the first surface and the second surface of the scanning imaging lens closest to the surface to be scanned. In this case, it is difficult to satisfactorily correct the lateral magnification of sub-scanning between image heights.

  In the optical scanning device of the present invention, the main shape of the scanning imaging lens on the scanning surface side is a negative meniscus lens having a convex surface facing the scanning surface, so that the optical magnification is constant with respect to the image height. .

  As a result, the optical path length of the peripheral image height is longer than the central image height, so in order to keep the central image height and the sub-scanning lateral magnification constant, the principal point position at the peripheral image height is relative to the central image height. It is necessary to be on the deflection means side. Therefore, the main shape of the scanning imaging lens on the scanning surface side is a shape in which the convex surface is directed to the scanning surface, the principal point position at the peripheral image height is the deflection means side with respect to the central image height, and the scanning surface The curvature center line connecting the curvature centers in the sub-scanning section of the first and second surfaces of the scanning imaging lens closest to the main scanning direction is different from the non-arc shape in the main scanning direction in the main scanning section. By using a surface in which the radius of curvature in the sub-scan section is changed in the main scanning direction so as to form a curve, the two lens surfaces are bent to adjust the main point position in the sub-scanning direction. In contrast, the optical magnification can be made constant.

  Further, when the horizontal magnification in the sub-scanning direction on the optical axis between the deflection surface and the surface to be scanned is β0 and the horizontal magnification in the sub-scanning direction at an arbitrary image height is βh, “0.9 <| βh / β0 | <1.1 ”is preferable. Furthermore, by making the optical magnification constant with respect to the image height, when the surface to be scanned is scanned simultaneously with multiple light beams by using multiple beams, the beam pitch in the sub-scanning direction between the multiple beams is kept constant. In addition, it is possible to provide an optical scanning device that can cope with higher density and higher speed by using multi-beams.

  As described above, in the fourth embodiment, the scanning imaging lens is composed of two lenses, and the main shape of the scanning imaging lens on the scanned surface side is a negative meniscus lens having a convex surface facing the scanned surface. Therefore, in the scanning imaging lens, while maintaining the “conjugate function” and “constant speed function” in good condition, the field curvature in the main scanning direction and sub-scanning direction is corrected well, and the light spot stability is realized. Furthermore, it is possible to provide an optical scanning device in which the optical magnification is constant with respect to the image height of the light spot.

  Further, when the lateral magnification in the sub-scanning direction on the optical axis between the deflection surface and the surface to be scanned is β0 and the lateral magnification in the sub-scanning direction at an arbitrary image height is βh, by satisfying the conditional expression, It is possible to provide an optical scanning device that can cope with a higher density and a higher speed by using a multi-beam for the image height of the light spot.

  Next, a fifth embodiment of the optical scanning device of the present invention will be described. In the fifth embodiment, when the lateral magnification in the sub-scanning direction on the optical axis between the deflection surface and the surface to be scanned is β0, “0.2 <| β0 | <0.6” is satisfied. Yes.

  If the lower limit of the conditional expression is exceeded, the aperture (aperture stop) diameter will be smaller than the target beam spot system when the lateral magnification in the sub-scanning direction on the optical axis between the deflection surface and the scanned surface is set large. It is necessary to set a small value. As a result, a problem of insufficient light quantity and a problem of deterioration of the beam spot diameter due to the influence of diffraction at the aperture occur. The influence of diffraction is described in JP-A-7-110451.

  If the upper limit of the conditional expression is exceeded, after passing through the scanning imaging lens closest to the deflecting means, if a mirror or the like for separating the optical path is arranged on the scanned surface corresponding to each color, the entire optical path length needs to be increased. The layout in the optical scanning device becomes difficult, for example, the size of the device increases.

  As described above, in the fifth embodiment of the present invention, when the lateral magnification in the sub-scanning direction on the optical axis between the deflection surface and the surface to be scanned is β0, scanning is performed by satisfying the conditional expression. In the imaging lens, while maintaining the “conjugation function” and “constant speed function” in good condition, the field curvature in the main scanning direction and sub-scanning direction is corrected well to realize the stability of the light spot, It is possible to provide an optical scanning device capable of separating a light beam directed to each surface to be scanned and obtaining a sufficient amount of light while making the optical magnification constant with respect to the image height of the light spot.

  Next, a sixth embodiment of the optical scanning device of the present invention will be described. In the sixth embodiment, when the distance from the base point of the optical deflector on the optical axis to the surface to be scanned is L, and the distance on the optical axis that is the farthest among the plurality of scanning imaging lenses is a, “0.3 <| a / L | <0.6” is satisfied.

  Usually, a mirror or the like for separating an optical path to a scanned surface corresponding to each color is disposed within a distance on the optical axis that is farthest between a plurality of scanning imaging lenses. At this time, if the lower limit of the conditional expression is exceeded, the distance on the optical axis that is the farthest between the plurality of scanning imaging lenses becomes too short, such as a mirror for separating the optical path to the scanned surface corresponding to each color. Placement becomes difficult.

  On the other hand, if the upper limit of the conditional expression is exceeded, the scanning imaging lens that has a strong refractive power at least in the main scanning direction and corrects the constant velocity with respect to the scanning imaging lens on the scanned surface side is Get closer to. As a result, the angle of view for scanning the image area on the surface to be scanned is narrowed, and the scanning time for the image area is shorter than when the angle of view is wide. Since the scanning time of the image area is shortened, there arises a problem that ON / OFF of a light source such as an LD cannot cope with the writing density (response speed is not in time).

  As described above, in the sixth embodiment of the present invention, the distance from the base point of the optical deflector on the optical axis to the surface to be scanned is L, on the optical axis that is farthest among the plurality of scanning imaging lenses. When the distance of a is set to a, by satisfying the conditional expression, the image plane in the main scanning direction and the sub-scanning direction can be maintained while maintaining good “conjugation function” and “constant speed function” in the scanning imaging lens. An optical scanning device capable of correcting the curvature well to realize the stability of the light spot, and further separating the light beam directed to each scanned surface while keeping the optical magnification constant with respect to the image height of the light spot. Can be provided.

  Next, a seventh embodiment of the optical scanning device of the invention will be described. In the seventh embodiment, since the scanning imaging lens is made of plastic, a special surface typified by an aspheric surface can be easily formed on the optical element of the optical scanning device with the aim of improving scanning characteristics, and the cost is also reduced. It can be made cheap.

  In particular, in the case of a tandem type image forming apparatus using the optical scanning device of the present invention, since the number of optical elements used is large, the cost reduction effect by using resin optical elements is very large.

  Conventionally, when a resin optical element is used in an optical scanning device, the temperature in the optical box rises due to deflection means such as a polygon mirror that generates a large amount of heat. Due to differences, heat is not transmitted uniformly, and the temperature inside the optical box has a temperature distribution, so that the thermal expansion coefficient is larger than that of glass, resulting in a large shape change, and the optical characteristics of the resin optical element change. There was a problem. Also in the scanning imaging lens, there is no uniform temperature change due to differences in heat transmission, lens shapes (difference in installation area to the optical box), etc., and temperature differences depending on the location of the scanning imaging lens However, the occurrence of color misregistration has occurred due to the difference in optical performance, in particular the constant velocity of each color.

  However, according to the present invention, the scanning imaging lens closest to the deflecting means passes through a plurality of light beams directed to different scanning surfaces, so that the change in isokineticity occurs in the same way for each color and the color shift. The occurrence of is suppressed. For this reason, even when the scanning imaging lens closest to the deflecting means is included and the materials of all the scanning imaging lenses are made of plastic, the “conjugation function” and “constant speed function” are maintained well while maintaining the main function. It is possible to provide an optical scanning device that satisfactorily corrects the curvature of field in the scanning direction and the sub-scanning direction, realizes the stability of the light spot, and further suppresses the occurrence of color shift and color change.

  As described above, in the seventh embodiment of the present invention, at least one material of the scanning imaging lens is made of plastic, so that “conjugation function” and “constant speed function” are kept good. A low-cost optical scanning device that corrects the field curvature in the main scanning direction and sub-scanning direction, achieves the stability of the light spot, and has a constant optical magnification with respect to the image height of the light spot. Can be provided.

  Furthermore, in the seventh embodiment of the present invention, the material of the scanning imaging lens closest to the deflecting means is plastic, so that the “conjugation function” and “constant speed function” are kept good, while maintaining the main scanning direction. Further, the optical surface curvature in the sub-scanning direction is satisfactorily corrected to realize the stability of the light spot, and the optical scanning device in which the optical magnification is constant with respect to the image height of the light spot is provided at a low cost. be able to.

  Next, an eighth embodiment of the present invention will be described. In the eighth embodiment, an image forming apparatus using the optical scanning device of the present invention will be described. FIG. 4 is a cross-sectional view of an image forming apparatus using the optical scanning device of the present invention. As an example of the image forming apparatus, a laser printer is used in FIG.

  The laser printer 150 includes a “photoconductive photosensitive member formed in a cylindrical shape” as the latent image carrier 111. Around the latent image carrier 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are provided. A “corona charger” can also be used as the charging means. Further, an optical scanning device 117 that performs optical scanning with the laser beam LB is provided, and “exposure by optical writing” is performed between the charging roller 112 and the developing device 113.

  In FIG. 4, reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a registration roller pair, reference numeral 120 denotes a paper feed roller, reference numeral 121 denotes a conveyance path, reference numeral 122 denotes a discharge roller pair, reference numeral 123 denotes a tray, reference numeral P Indicates transfer paper as a recording medium.

  When image formation is performed, the latent image carrier 111, which is a photoconductive photosensitive member, is rotated at a constant speed in the clockwise direction, and the surface thereof is uniformly charged by the charging roller 112, and the light of the laser beam LB of the optical scanning device 117 is obtained. An electrostatic latent image is formed upon exposure by writing. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

  This electrostatic latent image is reversed and developed by the developing device 113, and a toner image is formed on the latent image carrier 111. The cassette 118 storing the transfer paper P is detachable from the main body of the image forming apparatus. When the transfer paper P is mounted as shown in FIG. The fed transfer paper P is fed by the registration roller pair 119 at its leading end. The registration roller pair 119 feeds the transfer paper P to the transfer unit at the timing when the toner image on the latent image carrier 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. The transfer paper P to which the toner image is transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the discharge roller pair 122.

  The surface of the latent image carrier 111 after the toner image is transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like. Third Embodiment As an optical scanning device that optically scans the latent image carrier 111 in an image forming apparatus that forms a latent image on the latent image carrier 111 by optical scanning and visualizes the latent image to obtain a desired recorded image. The latent image carrier 111 is a photoconductive photosensitive member, and an electrostatic latent image is formed by uniform charging and optical scanning, and the formed electrostatic latent image is used. The image is visualized as a toner image.

  As described above, according to the eighth embodiment of the present invention, it is possible to provide an image forming apparatus that can ensure high-quality image reproducibility using the optical scanning device of the present invention.

  Next, a ninth embodiment of the present invention will be described. In the ninth embodiment, a tandem type full-color laser printer using the optical scanning device of the present invention will be described. FIG. 5 is a cross-sectional view of a tandem type full-color laser printer using the optical scanning device of the present invention.

  With reference to FIG. 5, an application example of the optical scanning device of the present invention to a tandem type full color laser printer will be described.

  First, on the lower side in the apparatus, a conveying belt 2 is provided that conveys transfer paper (not shown) that is disposed in the horizontal direction and is fed from the sheet feeding cassette 1. On the conveying belt 2, a photosensitive body 3Y for yellow Y, a photosensitive body 3M for magenta M, a photosensitive body 3C for cyan C, and a photosensitive body 3K for black K are sequentially arranged at equal intervals from the upstream side. Yes. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction.

  These photoreceptors 3Y, 3M, 3C, and 3K are all formed to have the same diameter, and process members are sequentially disposed around the photoreceptors in accordance with an electrophotographic process. Taking the photoconductor 3Y as an example, a charging charger 4Y, an optical scanning optical system 5Y, a developing device 6Y, a transfer charger 7Y, a cleaning device 8Y, and the like are sequentially arranged. The same applies to the other photoconductors 3M, 3C, and 3K. That is, in this embodiment, the photosensitive members 3Y, 3M, 3C, and 3K are irradiated surfaces set for the respective colors, and the optical scanning optical systems 5Y, 5M, 5C, and 5K are 1 for each. They are provided in a one-to-one correspondence. However, the scanning imaging lens is commonly used for M and Y, and commonly used for K and C.

  In addition, a registration roller 9 and a belt charging charger 10 are provided around the transport belt 2 on the upstream side of the photoconductor 5Y, and a belt separation charger 11 is provided on the downstream side of the photoconductor 5K. A static elimination charger 12, a cleaning device 13, and the like are provided in this order. Further, a fixing device 14 is provided on the downstream side of the belt separating charger 11 in the transport direction, and is connected to a paper discharge tray 15 by a paper discharge roller 16.

  In such a schematic configuration, for example, in the full color mode (multiple color mode), each of the photoconductors 3Y, 3M, 3C, and 3K is based on image signals of colors Y, M, C, and K, respectively. An electrostatic latent image is formed by optical scanning of the light beam by the optical scanning devices 5Y, 5M, 5C, and 5K. These electrostatic latent images are developed with the corresponding color toners to form toner images, which are superposed by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transport belt 2 and transported. After being fixed as an image, it is discharged.

By applying the optical scanning device of the present invention to the optical scanning optical systems 5Y, 5M, 5C, and 5K of a tandem type full-color laser printer that is an image forming device, there is no color misregistration and high-quality image reproducibility can be ensured. An image forming apparatus can be realized.

  As described above, according to the ninth embodiment of the present invention, high-quality image reproducibility can be ensured by using the optical scanning device of the present invention, and color misregistration and color change can be achieved in a color machine. Therefore, it is possible to provide an image forming apparatus that suppresses the occurrence of color misregistration and has a small color shift.

  Next, numerical examples of the optical scanning device according to the embodiment of the present invention will be described. First, Numerical Example 1 of the optical scanning device according to the embodiment of the present invention will be described.

表１は、光源装置から光偏向器に到る光路上の光学系の数値実施例１を示している。すなわち、光偏向器前の光学系における数値実施例である。
ここで、ＲＹ：主走査方向曲率半径、ＲＺ：副走査方向曲率半径（レンズ中心）、
Ｎ：使用波長(６５５ｎｍ)での屈折率、Ｘ：光軸方向の距離、を示す。
また、*の面は共軸非球面である。数値は示さないが、カップリングレンズを射出した波面収差は良 好に補正されている。また、光偏向器は、Ａ寸１８ｍｍ（回転中心と反射面の距離：内接円半径）で６面のポリゴンミラーとする。

Table 1 shows a numerical example 1 of the optical system on the optical path from the light source device to the optical deflector. That is, it is a numerical example in the optical system before the optical deflector.
Where RY: radius of curvature in the main scanning direction, RZ: radius of curvature in the sub-scanning direction (lens center),
N: Refractive index at the wavelength used (655 nm), X: Distance in the optical axis direction.
The * surface is a coaxial aspherical surface. Although no numerical value is shown, the wavefront aberration emitted from the coupling lens is well corrected. The optical deflector is a 6-sided polygon mirror with an A dimension of 18 mm (distance between rotation center and reflecting surface: inscribed circle radius).

表２は、光偏向器後の光学系の数値実施例１を示している。
ここで、β(光偏向器と被走査面間の副走査倍率)：０．５、βｈ/β０：０．９７（中央像高との倍率差の最も大きい像高での値）である。*の各面は、主走査方向の形状が非円弧形状であり、副走査方向は平面となっている。

Table 2 shows a numerical example 1 of the optical system after the optical deflector.
Here, β (sub-scanning magnification between the optical deflector and the scanning surface): 0.5, βh / β0: 0.97 (value at the image height having the largest magnification difference from the central image height). Each surface of * has a non-arc shape in the main scanning direction, and is a flat surface in the sub-scanning direction.

The lens surface shape is given by equation (1).
X (Y, Z) ＝ Y ^ 2 ・ Cm / 1 + √ [1- (1 + K) ・ (Y ・ Cm) ^ 2] + A ・ Y ^ 4 + B ・ Y ^ 6 + C ・ Y ^ 8 + D ・ Y ^ 10 + E ・ Y ^ 12 + F ・ Y ^ 14 + Cs (Y) ・ Z ^ 2/1 + √ [1- (Cs (Y) ・ Z) ^ 2] （１）
However, Cm = 1 / RY and Cs (Y) = 1 / RZ.
Each surface of ** has a non-arc shape in the main scanning direction, and the curvature radius in the sub-scanning direction continuously changes depending on the lens height. Each surface shape is given by the above formula. However, Cs (Y) is given by Equation (2).
Cs (Y) = 1 / RZ + aY + bY ^ 2 + cY ^ 3 + dY ^ 4 + eY ^ 5 + fY ^ 6 + gY ^ 7 + hY8 + iY ^ 9 + jY ^ 10 + kY ^ 11 + lY ^ 12 (2)

表３は、数値実施例１における非球面係数であり、以下のように定めた。なお、本光学系において、厚さ１．９ｍｍの防音ガラス（屈折率１．５１４３７）を挿入し、防音ガラスは８度偏向面内で傾けて配置している。

Table 3 shows the aspheric coefficients in Numerical Example 1 and was determined as follows. In this optical system, a soundproof glass (refractive index of 1.51437) having a thickness of 1.9 mm is inserted, and the soundproof glass is disposed so as to be inclined within the deflection plane of 8 degrees.

  FIG. 6 is an optical characteristic diagram on the surface to be scanned based on Numerical Example 1 of the present invention. In FIG. 6, the left part shows field curvature, and the right part shows constant velocity characteristics. As shown in FIG. 6, both the field curvature and the constant velocity characteristic are corrected well.

  Next, Numerical Example 2 of the optical scanning device according to the embodiment of the present invention will be described. Here, the pre-deflection optical system is the same as in Numerical Example 1.

表４は、数値実施例２における光偏向器後の光学系の数値を示している。
ここで、β(光偏向器と被走査面間の副走査倍率)：０．３４、βｈ/β０：０．９８（中央像高との倍率差の最も大きい像高での値）である。*、**の各面形状は、数値実施例１と同じ数式で与えられる。

Table 4 shows the numerical values of the optical system after the optical deflector in Numerical Example 2.
Here, β (sub-scanning magnification between the optical deflector and the surface to be scanned): 0.34, βh / β0: 0.98 (value at the image height having the largest magnification difference from the central image height). Each surface shape of * and ** is given by the same formula as in Numerical Example 1.

表５は、数値実施例２における非球面係数であり、以下のように定めた。なお、本光学系において、厚さ１．９ｍｍの防音ガラス（屈折率１．５１４３７）を挿入し、防音ガラスは８度偏向面内で傾けて配置している。

Table 5 shows the aspheric coefficients in Numerical Example 2, and was determined as follows. In this optical system, a soundproof glass (refractive index of 1.51437) having a thickness of 1.9 mm is inserted, and the soundproof glass is disposed so as to be inclined within the deflection plane of 8 degrees.

  FIG. 7 is an optical characteristic diagram on the surface to be scanned based on Numerical Example 2 of the present invention. In FIG. 7, the left part shows field curvature, and the right part shows constant velocity characteristics. As shown in FIG. 7, both the field curvature and the constant velocity characteristic are corrected well.

  Next, Numerical Example 3 of the optical scanning device according to the embodiment of the present invention will be described. Here, the pre-deflection optical system is the same as in Numerical Example 1.

表６は、数値実施例３における光偏向器後の光学系の数値を示している。
ここで、β(光偏向器と被走査面間の副走査倍率)：０．３８、βｈ/β０：０．９９（中央像高との倍率差の最も大きい像高での値）である。*、**の各面形状は、数値実施例１と同じ数式で与えられる。

Table 6 shows the numerical values of the optical system after the optical deflector in Numerical Example 3.
Here, β (sub-scanning magnification between the optical deflector and the surface to be scanned): 0.38, βh / β0: 0.99 (value at the image height having the largest magnification difference from the central image height). Each surface shape of * and ** is given by the same formula as in Numerical Example 1.

表７は、数値実施例３における非球面係数であり、以下のように定めた。なお、本光学系において、厚さ１．９ｍｍの防音ガラス（屈折率１．５１４３７）を挿入し、防音ガラスは８度偏向面内で傾けて配置している。

Table 7 shows the aspheric coefficients in Numerical Example 3, and was determined as follows. In this optical system, a soundproof glass (refractive index of 1.51437) having a thickness of 1.9 mm is inserted, and the soundproof glass is disposed so as to be inclined within the deflection plane of 8 degrees.

  FIG. 8 is an optical characteristic diagram on the surface to be scanned based on Numerical Example 3 of the present invention. In FIG. 8, the left part shows field curvature, and the right part shows constant velocity characteristics. As shown in FIG. 8, both the field curvature and the constant velocity characteristic are corrected well.

  In the embodiments described above, the plurality of light beams are light beams directed to different scanned surfaces, and the light beams directed to the respective scanned surfaces are described as one light beam. However, the light beams directed to the respective scanned surfaces are described. There may be a plurality of light beams. Further, the present invention can be applied to a case where different scanned surfaces are greatly different on the same photoconductor.

  Although the embodiment of the present invention has been described in detail as described above, the above-described embodiment is a preferred embodiment of the present invention, and is not limited thereto, and does not depart from the gist of the present invention. Various modifications can be made within the range.

2 is a cross-sectional view showing a configuration of two scanning imaging lenses in the first embodiment of the optical scanning device of the present invention. FIG. It is an expanded view of the optical system in 2nd Embodiment of the optical scanning device of this invention. It is a block diagram which shows the structure of 3rd Embodiment of the optical scanning device of this invention. 1 is a cross-sectional view of an image forming apparatus using an optical scanning device of the present invention. 1 is a cross-sectional view of a tandem type full color laser printer using an optical scanning device of the present invention. It is an optical characteristic figure on the to-be-scanned surface based on Numerical Example 1 of this invention. It is an optical characteristic figure on the to-be-scanned surface based on Numerical Example 2 of this invention. It is an optical characteristic figure on the to-be-scanned surface based on Numerical Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Light source device 403 Optical deflector 407 Scan surface L1, L2 Scan imaging lens

Claims (12)

Deflecting means for deflecting the light beam from the light source;
A scanning imaging lens that guides the light beam deflected by the deflecting means onto a surface to be scanned,
The scanning imaging lens comprises at least two scanning imaging lenses;
The scanning imaging lens closest to the deflecting unit has a positive refractive power in the main scanning direction, and a refractive power in the sub-scanning direction is zero or close to zero.
The scanning imaging lens closest to the scanned surface has a negative refractive power in the main scanning direction and a positive refractive power in the sub-scanning direction,
An optical scanning device characterized in that the surface on the incident side in the sub-scanning direction of the scanning imaging lens closest to the scanned surface is a convex surface on the scanned surface side. The light source is plural,
A light beam from each light source of the plurality of light sources is deflected by a single deflecting unit and guided onto a different surface to be scanned by the scanning imaging lens,
2. The optical scanning device according to claim 1, wherein, among the scanning imaging lenses, the plurality of light beams directed to different scanning surfaces pass through the scanning imaging lens closest to the deflecting unit. .   3. The optical scanning device according to claim 2, wherein the plurality of light beams directed toward different scanning surfaces pass through the scanning imaging lens closest to the deflecting unit substantially parallel to the sub-scanning direction.   2. All the light beams deflected by the same deflecting reflection surface of the deflecting unit are configured to intersect at substantially one point in the main scanning section in the vicinity of the deflecting surface of the deflecting unit. 4. The optical scanning device according to any one of items 3.   5. The scanning imaging lens is composed of two lenses, and the main shape of the scanning imaging lens on the scanned surface side is a negative meniscus lens having a convex surface facing the scanned surface. The optical scanning device according to claim 1.   When the lateral magnification in the sub-scanning direction on the optical axis between the deflection surface and the surface to be scanned is β0, and the lateral magnification in the sub-scanning direction at an arbitrary image height is βh, 0.9 <| βh / The optical scanning device according to claim 1, wherein β0 | <1.1 is satisfied.   2. When the lateral magnification in the sub-scanning direction on the optical axis between the deflection surface and the scanned surface is β0, 0.2 <| β0 | <0.6 is satisfied. 7. The optical scanning device according to any one of items 1 to 6.   When the distance from the base point of the deflecting means on the optical axis to the scanned surface is L, and the distance on the optical axis that is the farthest among the plurality of scanning imaging lens intervals is a, 0.3 <| a /L|<0.6 is satisfied, The optical scanning device of any one of Claim 1 to 7 characterized by the above-mentioned.   9. The optical scanning device according to claim 1, wherein at least one material of the scanning imaging lens is plastic.   10. The optical scanning device according to claim 9, wherein a material of the scanning imaging lens closest to the deflecting unit is plastic.   An image forming apparatus comprising the optical scanning device according to claim 1.   A full-color tandem type image forming apparatus comprising the optical scanning device according to claim 1.

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