JP5593858B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly, to an optical scanning apparatus that scans a surface to be scanned with a light beam, and an image forming apparatus including the optical scanning apparatus.

  Optical scanning devices are widely known in connection with laser printers and the like. In general, in an optical scanning device, a light beam emitted from a light source is deflected by an optical deflector and condensed toward a scanned surface by a scanning optical system such as an fθ lens to form a light spot on the scanned surface. ing. This light spot moves in the main scanning direction on the surface to be scanned as the optical deflector rotates. At this time, what constitutes the substance of the scanned surface is the photosensitive surface of the photoconductive photoconductor.

  In addition, a color image forming apparatus having a plurality of photoconductors arranged along the conveyance direction of the recording paper, a plurality of light sources corresponding to the photoconductors, and a plurality of scanning optical systems corresponding to the photoconductors is known. It has been. In this image forming apparatus, each light beam emitted from a plurality of light sources is deflected by one optical deflector, and a latent image is formed on a photosensitive surface of a corresponding photosensitive member via a corresponding scanning optical system. These latent images are visualized using different color developers such as yellow, magenta, cyan, and black, and then sequentially superimposed and transferred and fixed on the same recording paper.

  As described above, an image forming apparatus that uses two or more combinations of an optical system and a photoreceptor to obtain a two-color image, a multicolor image, a color image, or the like is known as a “tandem color image forming apparatus”. Yes.

  More recently, in order to reduce the cost of a color image forming apparatus, a surface perpendicular to the rotation axis of the optical deflector is used as a pre-deflector optical system that guides the light beam emitted from the light source to the deflecting reflective surface of the optical deflector. An optical scanning device having an oblique incidence optical system that makes a light beam incident from a direction inclined with respect to the angle has been devised (see, for example, Patent Document 1).

  In this optical scanning device, each light beam emitted from a plurality of light sources and passing through a corresponding oblique incident optical system is deflected and reflected by the same deflecting and reflecting surface, and then separated by a folding mirror or the like, and corresponding photosensitive Guided to the body.

  At this time, the incident angle of each light beam with respect to the deflecting reflection surface (hereinafter also referred to as “oblique incident angle”) is set to an angle that can be separated by a folding mirror or the like.

  By using this oblique incidence optical system, the interval between adjacent light beams at a predetermined position of a plurality of light beams via the light deflector without increasing the size of the deflection reflection surface in the rotation axis direction of the light deflector. Can be separated by a folding mirror or the like. That is, it is possible to reduce the size of the optical deflector.

  Therefore, for example, when a polygon mirror is used as the optical deflector, large energy is not required for high-speed rotation, and “wind noise” when rotating at high speed can be reduced.

  However, when the oblique incidence optical system is used, particularly when entering the scanning lens, the light beam entering the position away from the optical axis of the scanning lens in the main scanning direction is incident on the scanning lens in a twisted state. Thus, wavefront aberration increases. For this reason, the spot diameter of the light spot formed on the surface of the photosensitive member is increased, which hinders the improvement of the image quality.

  Further, when the oblique incidence optical system is used, the scanning line bending becomes large. Since the degree of scanning line bending at this time varies depending on the oblique incident angle, a color shift occurs in the output image.

  Therefore, the present applicant has proposed an optical scanning apparatus and an image forming apparatus that can effectively correct scanning line bending and wavefront aberration degradation in an oblique incidence type optical scanning apparatus (see Patent Document 2).

  However, the optical scanning device disclosed in Patent Document 2 requires a two-lens scanning lens. And since the scanning lens arranged on the scanning surface side is long and is provided for each color individually, when laying out the optical path from the optical deflector to the scanning surface, the degree of freedom of design is reduced. It was. In particular, in an image forming apparatus aiming at miniaturization, the optical scanning device to be mounted is strongly required to be miniaturized, and therefore, the arrangement of the scanning lens on the scanning surface side has been an adverse effect of miniaturization.

  The present invention has been made under such circumstances, and a first object of the present invention is to provide an optical scanning device that can be reduced in cost and size without degrading scanning accuracy.

  A second object of the present invention is to provide an image forming apparatus capable of reducing cost and size while maintaining high image quality.

According to a first aspect of the present invention, there is provided an optical scanning device that scans a plurality of scanned surfaces in the main scanning direction with a light beam, and a plurality of light sources corresponding to the plurality of scanned surfaces; An optical deflector that rotates a plurality of deflecting reflecting surfaces around an axis parallel to a sub-scanning direction orthogonal to the direction and deflects a light beam from the plurality of light sources; and includes at least one scanning lens; A scanning optical system for condensing the plurality of light beams deflected by the deflectors on the corresponding scanned surfaces, respectively, and the plurality of light beams are all on a surface orthogonal to the rotation axis of the light deflector. The scanning lens is incident on the deflecting / reflecting surface of the optical deflector from an inclined direction, and the scanning lens has a plurality of optical surfaces respectively corresponding to the plurality of light beams on an incident side and an exit side of the light beam, each of the plurality of optical surfaces on the incident side and Intersection line between a virtual plane perpendicular to the main scanning direction at any position in the main scanning direction, Ri straight der which is inclined with respect to the sub-scanning direction, and a plurality of optical surfaces of said incident side subscanning The optical scanning device is characterized in that a line of intersection with a virtual plane orthogonal to the sub-scanning direction at an arbitrary position in the direction is a curve .

  According to this, cost reduction and size reduction can be achieved without reducing scanning accuracy.

  According to a second aspect of the present invention, there are provided a plurality of image carriers; and the optical scanning device of the present invention that scans the plurality of image carriers with a light beam modulated according to corresponding image information. An image forming apparatus provided.

  According to this, since the optical scanning device of the present invention is provided, as a result, it is possible to achieve cost reduction and size reduction while maintaining high image quality.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. It is FIG. (1) for demonstrating schematic structure of an optical scanning device. FIG. 3 is a second diagram for explaining a schematic configuration of the optical scanning device; FIG. 3 is a third diagram for explaining a schematic configuration of the optical scanning device; FIG. 4 is a diagram (part 4) for explaining a schematic configuration of the optical scanning device; It is FIG. (1) for demonstrating two light beams reflected by the deflection | deviation reflective surface. It is FIG. (2) for demonstrating two light beams reflected by the deflection | deviation reflective surface. It is a figure for demonstrating the thickness of a deflection | deviation reflective surface, and the reflective position of two light beams in a deflection | deviation reflective surface. It is a figure for demonstrating an example of a design value. It is a figure for demonstrating scanning lens 2105A in this embodiment. It is a figure for demonstrating the scanning lens 2105B in this embodiment. 12A and 12B are diagrams for explaining the origin on the incident-side surface of the scanning lens. It is a figure for demonstrating the shape of the 2nd incident optical surface of the scanning lens 2105B, and each output optical surface. FIGS. 14A and 14B are diagrams for explaining the origin on the first exit optical surface of the scanning lens. FIG. 15A and FIG. 15B are diagrams for explaining the origin on the second exit optical surface of the scanning lens. It is a figure for demonstrating the thickness of a scanning lens. It is a figure for demonstrating the attitude | position of the dust-proof glass with respect to incident light. It is a figure for demonstrating the shape of the surface of the entrance side of a dustproof glass, and the surface of an injection | emission side. It is a figure for demonstrating the change of the reflective position in a deflection | deviation reflective surface by the dispersion | variation in the distance from a rotation center to each deflection | deviation reflective surface. It is a figure for demonstrating the relationship between an oblique incident angle and a folding mirror position. It is a figure for demonstrating the relationship between the incident position and incident angle of the light beam in the scanning lens regarding a main scanning corresponding | compatible direction. It is FIG. (1) for demonstrating the effect | action of the scanning lens in this embodiment. It is FIG. (2) for demonstrating the effect | action of the scanning lens in this embodiment. It is a figure for demonstrating the case where the incident side surface of a scanning lens has a curvature regarding a subscanning corresponding | compatible direction. It is a figure for demonstrating the case where the incident side surface of a scanning lens is planar shape. It is a figure for demonstrating the metal mold components used when shape | molding the scanning lens in this embodiment. It is a figure for demonstrating the case where the surface of the emission side of a scanning lens is comprised by 1 surface. It is a figure for demonstrating the case where the surface of the injection | emission side of a scanning lens is comprised by 2 surfaces arranged along a subscanning corresponding direction. It is a figure for demonstrating the effect that the reflection position of two light beams in a deflection | deviation reflective surface differs regarding the subscanning corresponding | compatible direction. It is a figure for demonstrating the effect that two light beams which inject into the same deflection | deviation reflective surface cross | intersect when seeing from the main scanning corresponding | compatible direction before incidence.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a color printer 2000 according to an embodiment.

  The color printer 2000 is a tandem color printer that superimposes four colors (black, cyan, magenta, and yellow) to form a multicolor image, and includes four photosensitive drums (K1, C1, M1, and Y1). ) Four drum charging devices (K2, C2, M2, Y2), four developing devices (K4, C4, M4, Y4), four drum cleaning devices (K5, C5, M5, Y5), four transfer devices (K6, C6, M6, Y6), optical scanning device 2010, belt charging device 2030, belt separation device 2031, belt neutralization device 2032, conveyor belt 2040, belt cleaning device 2042, fixing device 2050, paper feed roller 2054, registration roller A pair 2056, a paper discharge roller 2058, a paper feed tray 2060, a communication control device 2080, and the above-described units. A printer control device 2090 for Batch controlled.

  In this specification, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is described as the Y-axis direction, and the direction along the arrangement direction of the four photosensitive drums is described as the X-axis direction.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The printer control device 2090 notifies the optical scanning device 2010 of multi-color image information (black image information, cyan image information, magenta image information, yellow image information) received from the host device via the communication control device 2080.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

  The photosensitive drum K1, the drum charging device K2, the developing device K4, the drum cleaning device K5, and the transfer device K6 are used as a set and form an image forming station for forming a black image (hereinafter also referred to as “K station” for convenience). ).

  The photosensitive drum C1, the drum charging device C2, the developing device C4, the drum cleaning device C5, and the transfer device C6 are used as a set and form an image forming station for forming a cyan image (hereinafter also referred to as “C station” for convenience). ).

  The photosensitive drum M1, the drum charging device M2, the developing device M4, the drum cleaning device M5, and the transfer device M6 are used as a set and form an image forming station (hereinafter also referred to as “M station” for convenience). ).

  The photosensitive drum Y1, the drum charging device Y2, the developing device Y4, the drum cleaning device Y5, and the transfer device Y6 are used as a set and form an yellow image forming station (hereinafter also referred to as “Y station” for convenience). ).

  Each drum charging device uniformly charges the surface of the corresponding photosensitive drum.

  The optical scanning device 2010 corresponds to the light beam modulated for each color based on multi-color image information (black image information, magenta image information, cyan image information, yellow image information) from the printer control device 2090. Irradiate each surface of the charged photosensitive drum. As a result, on the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing device as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

  The developing device K4 causes a black toner to adhere to the latent image formed on the surface of the photosensitive drum K1 to make it visible.

  The developing device C4 causes cyan toner to adhere to the latent image formed on the surface of the photosensitive drum C1 to make it visible.

  The developing device M4 causes a magenta toner to adhere to the latent image formed on the surface of the photosensitive drum M1 to make a visible image.

  The developing device Y4 causes yellow toner to adhere to the latent image formed on the surface of the photosensitive drum Y1 to make it visible.

  An image to which toner is attached by each developing device (hereinafter referred to as “toner image” for convenience) moves in the direction of the corresponding transfer device as the photosensitive drum rotates.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 2056. The registration roller pair 2056 sends the recording paper toward the conveyance belt 2040 at a predetermined timing.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto a recording sheet on the conveying belt 2040 by a corresponding transfer device at a predetermined timing, and are superimposed to form a color image. The recording paper on which each toner image is transferred is sent to the fixing device 2050.

  In the fixing device 2050, heat and pressure are applied to the recording paper, whereby each toner image is fixed on the recording paper. The recording paper is sent to a paper discharge tray via a paper discharge roller 2058 and is sequentially stacked on the paper discharge tray.

  Each drum cleaning device removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The surface of the photosensitive drum from which the residual toner has been removed returns to the position facing the corresponding charging device again.

  The belt charging device 2030 charges the surface of the conveyance belt 2040. As a result, the recording paper is electrostatically attracted to the surface of the conveyance belt 2040.

  The belt separation device 2031 releases the adsorption of the recording paper that is electrostatically adsorbed on the conveyance belt 2040.

  The belt neutralizer 2032 neutralizes the surface of the conveyor belt 2040.

  The belt cleaning device 2042 removes foreign matters adhering to the surface of the conveyance belt 2040.

  Next, the configuration of the optical scanning device 2010 will be described.

  2 to 5 as an example, the optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four coupling lenses (2201a, 2201b, 2201c, 2201d), four openings. Plate (2202a, 2202b, 2202c, 2202d), two cylindrical lenses (2204A, 2204B), polygon mirror 2104, two scanning lenses (2105A, 2105B), six folding mirrors (2106a, 2106b, 2106c, 2106d, 2108b) 2108c), four dust-proof glasses (2109a, 2109b, 2109c, 2109d), a scanning control device (not shown), and the like. These are assembled at predetermined positions of the optical housing 2300 (not shown in FIGS. 2 to 4, see FIG. 5).

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  Here, when viewed from the Z-axis direction, the light source 2200b and the light source 2200c are arranged at positions separated from each other in the X-axis direction. The light source 2200a is disposed on the −Z side of the light source 2200b. The light source 2200d is arranged on the −Z side of the light source 2200c.

  The optical axis direction of the cylindrical lens 2204A is defined as “w1 direction”, and the optical axis direction of the cylindrical lens 2204B is defined as “w2 direction”. Further, the main scanning corresponding direction in the light source 2200a and the light source 2200b is “m1 direction”, and the main scanning corresponding direction in the light source 2200c and the light source 2200d is “m2 direction”.

  The coupling lens 2201a is disposed on the optical path of a light beam emitted from the light source 2200a (hereinafter also referred to as “light beam LBa”), and the light beam is a substantially parallel light beam.

  The coupling lens 2201b is disposed on the optical path of a light beam emitted from the light source 2200b (hereinafter also referred to as “light beam LBb”), and the light beam is a substantially parallel light beam.

  The coupling lens 2201c is disposed on the optical path of a light beam emitted from the light source 2200c (hereinafter also referred to as “light beam LBc”), and the light beam is a substantially parallel light beam.

  The coupling lens 2201d is disposed on the optical path of a light beam emitted from the light source 2200d (hereinafter also referred to as “light beam LBd”), and the light beam is a substantially parallel light beam.

  The aperture plate 2202a has an aperture and shapes the light beam that has passed through the coupling lens 2201a.

  The aperture plate 2202b has an aperture, and shapes the light beam that has passed through the coupling lens 2201b.

  The aperture plate 2202c has an aperture and shapes the light beam that has passed through the coupling lens 2201c.

  The aperture plate 2202d has an aperture and shapes the light beam that has passed through the coupling lens 2201d.

  The cylindrical lens 2204A forms an image of the light beam that has passed through the aperture of the aperture plate 2202a and the light beam that has passed through the aperture of the aperture plate 2202b in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204B forms an image of the light beam that has passed through the aperture of the aperture plate 2202c and the light beam that has passed through the aperture of the aperture plate 2202d in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  Each cylindrical lens is provided with a diffractive surface having a function of correcting a change in the image forming position in the Z-axis direction due to temperature fluctuations. In this case, even if the magnification of the scanning lens in the sub-scanning corresponding direction is high, the temperature fluctuation can be corrected and stable optical performance can be obtained.

  An optical system including the coupling lens 2201a, the aperture plate 2202a, and the cylindrical lens 2204A is a pre-deflector optical system of the light source 2200a (hereinafter referred to as “pre-deflector optical system A”).

  An optical system including the coupling lens 2201b, the aperture plate 2202b, and the cylindrical lens 2204A is a pre-deflector optical system (hereinafter referred to as “pre-deflector optical system B”) of the light source 2200b.

  That is, the cylindrical lens 2204A is shared by the two pre-deflector optical systems.

  An optical system including the coupling lens 2201c, the aperture plate 2202c, and the cylindrical lens 2204B is a pre-deflector optical system (hereinafter referred to as “pre-deflector optical system C”) of the light source 2200c.

  An optical system including the coupling lens 2201d, the aperture plate 2202d, and the cylindrical lens 2204B is a pre-deflector optical system (hereinafter referred to as “pre-deflector optical system D”) of the light source 2200d.

  That is, the cylindrical lens 2204B is shared by the two pre-deflector optical systems.

  The polygon mirror 2104 has a four-sided mirror that rotates around an axis parallel to the Z-axis, and each mirror serves as a deflecting / reflecting surface. That is, the polygon mirror 2104 has four deflection reflection surfaces.

  Here, the light beam LBa and the light beam LBb from the cylindrical lens 2204 </ b> A are incident on the same deflecting / reflecting surface located on the −X side of the polygon mirror 2104.

  On the other hand, the light beam LBc and the light beam LBd from the cylindrical lens 2204B are incident on the same deflecting / reflecting surface located on the + X side of the polygon mirror 2104.

  Here, the light source 2200a and the pre-deflector optical system A are arranged so that the light beam LBa is incident on the deflecting / reflecting surface from a direction inclined by an angle θa on the −Z side with respect to the w1 direction. In addition, the light source 2200b and the pre-deflector optical system B are arranged so that the light beam LBb is incident on the deflecting / reflecting surface from a direction inclined by an angle θb on the + Z side with respect to the w1 direction. That is, the pre-deflector optical system A is an oblique incident optical system with an oblique incident angle of −θa, and the pre-deflector optical system B is an oblique incident optical system with an oblique incident angle of θb.

  Further, the light source 2200c and the pre-deflector optical system C are arranged so that the light beam LBc is incident on the deflecting / reflecting surface from a direction inclined by an angle θc to the + Z side with respect to the w2 direction. Further, the light source 2200d and the pre-deflector optical system D are arranged so that the light beam LBd is incident on the deflecting / reflecting surface from the direction inclined by the angle θd on the −Z side with respect to the w2 direction. That is, the pre-deflector optical system C is an oblique incidence optical system having an oblique incident angle of θc, and the pre-deflector optical system D is an oblique incident optical system having an oblique incident angle of −θd.

  Hereinafter, when the light beam is incident on the deflecting / reflecting surface, it is referred to as “oblique incidence” to be incident from a direction inclined with respect to a surface orthogonal to the sub-scanning corresponding direction (here, the Z-axis direction). The incident from a direction parallel to the plane orthogonal to the sub-scanning corresponding direction is called “horizontal incidence”.

  Then, the light beam LBa and the light beam LBb from the cylindrical lens 2204A are deflected to the −X side of the polygon mirror 2104. On the other hand, the light beam LBc and the light beam LBd from the cylindrical lens 2204B are deflected to the + X side of the polygon mirror 2104.

  As an example, as shown in FIG. 6, the light beam LBa incident on the deflecting / reflecting surface is reflected in a direction inclined by an angle θa on the + Z side with respect to the surface orthogonal to the sub-scanning corresponding direction. As an example, as shown in FIG. 6, the light beam LBb incident on the deflecting / reflecting surface is reflected in a direction inclined by an angle θb on the −Z side with respect to a surface orthogonal to the sub-scanning corresponding direction.

  As an example, as shown in FIG. 7, the light beam LBc incident on the deflecting / reflecting surface is reflected in a direction inclined by an angle θc on the −Z side with respect to a surface orthogonal to the sub-scanning corresponding direction. As an example, as shown in FIG. 7, the light beam LBd incident on the deflecting / reflecting surface is reflected in a direction inclined by an angle θd on the + Z side with respect to a surface orthogonal to the sub-scanning corresponding direction.

  The scanning lens 2105A is disposed on the −X side of the polygon mirror 2104, and the scanning lens 2105B is disposed on the + X side of the polygon mirror 2104.

  The light beam LBa deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum K1 through the scanning lens 2105A, the folding mirror 2106a, and the dust-proof glass 2109a to form a light spot. This light spot moves in the longitudinal direction of the photosensitive drum K1 as the polygon mirror 2104 rotates. That is, the photosensitive drum K1 is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum K1, and the rotational direction of the photosensitive drum K1 is the “sub-scanning direction” on the photosensitive drum K1.

  The light beam LBb deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum C1 through the scanning lens 2105A, the folding mirror 2106b, the folding mirror 2108b, and the dust-proof glass 2109b to form a light spot. This light spot moves in the longitudinal direction of the photosensitive drum C1 as the polygon mirror 2104 rotates. That is, the photosensitive drum C1 is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum C1, and the rotational direction of the photosensitive drum C1 is the “sub-scanning direction” on the photosensitive drum C1.

  The light beam LBc deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum M1 through the scanning lens 2105B, the folding mirror 2106c, the folding mirror 2108c, and the dust-proof glass 2109c, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum M1 as the polygon mirror 2104 rotates. That is, the photosensitive drum M1 is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum M1, and the rotational direction of the photosensitive drum M1 is the “sub-scanning direction” on the photosensitive drum M1.

  The light beam LBd deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum Y1 through the scanning lens 2105B, the folding mirror 2106d, and the dust-proof glass 2109d, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum Y1 as the polygon mirror 2104 rotates. That is, the photosensitive drum Y1 is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum Y1, and the rotational direction of the photosensitive drum Y1 is the “sub-scanning direction” on the photosensitive drum Y1.

  An optical system disposed on the optical path between the polygon mirror 2104 and each photosensitive drum is also called a scanning optical system.

  In the present embodiment, the scanning optical system of the K station is configured by the scanning lens 2105A, the folding mirror 2106a, and the dust-proof glass 2109a.

  The scanning optical system of the C station is constituted by the scanning lens 2105A, the two folding mirrors (2106b, 2108b), and the dust-proof glass 2109b.

  That is, the scanning lens 2105A is shared by the two scanning optical systems.

  Further, the scanning optical system of the M station is configured by the scanning lens 2105B, the two folding mirrors (2106c, 2108c), and the dust-proof glass 2109c.

  The scanning optical system of the Y station is composed of the scanning lens 2105B, the folding mirror 2106d, and the dust-proof glass 2109d.

  That is, the scanning lens 2105B is shared by the two scanning optical systems.

  Here, an example of specific design values will be described.

  The wavelength of the light beam emitted from each light source is 659 nm.

  Each coupling lens is made of glass having a refractive index of 1.6894 for light having a wavelength of 659 nm. The focal length of each coupling lens is about 27 mm.

  The opening of each aperture plate has a width in the Y-axis direction of about 2.3 mm and a width in the X-axis direction of about 2.1 mm.

  Each cylindrical lens has optical power only in the sub-scanning corresponding direction and is made of a resin having a refractive index of 1.5271 for light having a wavelength of 659 nm.

  The oblique incident angle of each light beam is | θa | = | θb | = | θc | = | θd | = 1 °.

The magnitude (absolute value) of the inclination angle θ _{A in} the w1 direction with respect to the X-axis direction and the inclination angle θ _B (see FIG. 2) in the w2 direction with respect to the X-axis direction are both about 68 °.

  The radius of the inscribed circle of the polygon mirror 2104 is about 7 mm.

  The length of the deflection reflection surface of the polygon mirror 2104 in the sub-scanning corresponding direction (Dp in FIG. 8, hereinafter, also referred to as “deflection reflection surface thickness”) is about 4 mm. Further, the incident positions of the two light beams incident on the same deflecting / reflecting surface on the deflecting / reflecting surface are separated by about 2.5 mm (Db in FIG. 8) with respect to the sub-scanning corresponding direction.

  The distance from the rotation center of the polygon mirror 2104 to the center of the incident-side surface of each scanning lens is about 40.9 mm (see FIG. 9). The distance from the rotation center of the polygon mirror 2104 to each scanned surface is about 210 mm (see FIG. 9). FIG. 9 is a diagram in which each light beam is developed on the XZ plane so that each light beam becomes one straight line.

  Each scanning lens is made of a resin having a refractive index of 1.5271 with respect to light having a wavelength of 659 nm.

  Each scanning lens has two optical surfaces arranged in the sub-scanning corresponding direction on both the incident side and the exit side (see FIGS. 10 and 11).

  Of the two incident-side optical surfaces, the + Z-side optical surface is referred to as a first incident optical surface, and the −Z-side optical surface is referred to as a second incident optical surface. Of the two optical surfaces on the exit side, the + Z side optical surface is referred to as a first exit optical surface, and the −Z side optical surface is referred to as a second exit optical surface.

  In the scanning lens 2105A, the first incident optical surface and the first emission optical surface are optical surfaces corresponding to the light beam LBa, and the second incident optical surface and the second emission optical surface are optical surfaces corresponding to the light beam LBb. is there.

  Further, the first incident optical surface and the first emission optical surface in the scanning lens 2105B are optical surfaces corresponding to the light beam LBd, and the second incident optical surface and the second emission optical surface are optics corresponding to the light beam LBc. Surface.

  The reference axis of the first incident optical surface and the reference axis of the second incident optical surface in each scanning lens coincide with each other. Hereinafter, the reference axis of the first incident optical surface and the reference axis of the second incident optical surface are collectively referred to as “incident side reference axis”. The incident side reference axis is orthogonal to both the main scanning corresponding direction and the sub scanning corresponding direction, and passes through the contact point between the first incident optical surface and the second incident optical surface in the sub scanning corresponding direction. Further, the incident side reference axis is deviated by about 3.8 mm toward the light source side (here, + Y side) with respect to the rotation center of the polygon mirror 2104 with respect to the scanning corresponding direction.

  In this way, by making the reference axis of the first incident optical surface coincide with the reference axis of the second incident optical surface, the first incident optical surface is produced when a mold used for molding each scanning lens is manufactured. In addition, two surfaces corresponding to the second incident optical surface can be processed at the same time, and the processing accuracy can be improved.

  The absolute value of the inclination angle of each incident optical surface on the incident side reference axis with respect to the sub-scanning corresponding direction is about 0.5 °.

  The reference axis of the first emission optical surface in each scanning lens is orthogonal to both the main scanning corresponding direction and the sub scanning corresponding direction, and passes through the center of the first emission optical surface with respect to the sub scanning corresponding direction. Further, the reference axis of the second emission optical surface in each scanning lens is orthogonal to both the main scanning corresponding direction and the sub scanning corresponding direction, and passes through the center of the second emission optical surface with respect to the sub scanning corresponding direction. The reference axis of the first exit optical surface and the reference axis of the second exit optical surface are parallel, and the main scanning correspondence direction is at the same position as the incident side reference axis. Regarding the sub-scanning corresponding direction, the reference axis of the first exit optical surface is located approximately 2.06 mm away on the + Z side with respect to the entrance side reference axis, and the reference axis of the second exit optical surface is the entrance. The position is about 2.06 mm away from the side reference axis on the -Z side.

  Each incident optical surface of each scanning lens is a special surface expressed by the following equation (1).

  In the above equation (1), the distance from the incident side reference axis in the main scanning corresponding direction is y, and the distance from the incident side reference axis in the sub scanning corresponding direction is z (FIGS. 12A and 12B). )reference). That is, with respect to the main scanning corresponding direction and the sub-scanning corresponding direction, the position of the incident side reference axis is set as the origin. The paraxial curvature radius in the “main scanning section” that includes the incident-side reference axis and is parallel to the main scanning-corresponding direction is Ry, includes the incident-side reference axis, and is orthogonal to the main scanning section. The paraxial radius of curvature in "" is Rz. Further, the higher-order coefficients are A, B, C, D. Furthermore, Cm = 1 / Ry and Cs (y) = 1 / Rz.

By the way, (F0 + F1 · y + F2 · y ² + F3 · y ³ + F4 · y ⁴ +...) Z in the above equation (1) is an inclination amount with respect to the sub-scanning corresponding direction (hereinafter also referred to as “tilt amount”). It is a part showing. This tilt amount differs depending on the position in the main scanning corresponding direction. When there is no tilt amount, F0, F1, F2,.

  A specific example of Ry, Rz, and each coefficient in the above equation (1) of the second incident optical surface in the scanning lens 2105B is shown in FIG.

  That is, each incident optical surface of each scanning lens is a plane whose inclination with respect to the sub-scanning corresponding direction differs depending on the position in the main scanning corresponding direction. It is also possible to specify the same surface shape using an expression different from the above expression (1). Further, the origin in the above equation (1) may be set individually for the two incident optical surfaces.

  Each exit optical surface of each scanning lens is an aspherical surface expressed by the following equation (2).

For the first exit optical surface, in the above equation (2), the distance from the reference axis of the first exit optical surface in the main scanning correspondence direction is y, and the distance from the reference axis of the first exit optical surface in the sub scan correspondence direction is y. The distance is z (see FIGS. 14A and 14B). That is, with respect to the main scanning corresponding direction and the sub-scanning corresponding direction, the position of the reference axis of the first emission optical surface is the origin. The paraxial radius of curvature in the “main scanning section”, which is a section parallel to the main scanning corresponding direction, including the reference axis of the first emission optical surface, includes the reference axis of the first emission optical surface, and includes main scanning. The paraxial radius of curvature in the “sub-scanning cross section” orthogonal to the cross section is Rz. Further, the higher-order coefficients are A, B, C, D. Furthermore, Cm = 1 / Ry, Cs (y) = 1 / Rz + ay + by ² + cy ³ + dy ⁴ + ey ⁵ + fy ⁶ + hy ⁷ + hy ⁸ + y ⁹ + ji ¹⁰ .

  For the second exit optical surface, in the above equation (2), the distance from the reference axis of the second exit optical surface in the main scanning correspondence direction is y, and the distance from the reference axis of the second exit optical surface in the sub scan correspondence direction is y. The distance is z (see FIGS. 15A and 15B). That is, with respect to the main scanning corresponding direction and the sub-scanning corresponding direction, the position of the reference axis of the second emission optical surface is set as the origin. The paraxial radius of curvature in the “main scanning section”, which is a section parallel to the main scanning corresponding direction, including the reference axis of the second exit optical surface, includes the reference axis of the second exit optical surface, and includes main scanning. The paraxial radius of curvature in the “sub-scanning cross section” orthogonal to the cross section is Rz.

  Specific examples of Ry, Rz, and each coefficient in the above equation (2) are shown in FIG. That is, each exit optical surface is a surface having strong optical power in the sub-scanning corresponding direction.

  The thickness of the scanning lens is the distance from the origin of the above equation (1) to the origin of the above equation (2) in the optical axis direction (see FIG. 16). Here, the thickness of each scanning lens is about 14 mm.

  Each dustproof glass has no optical power in either the main scanning corresponding direction or the sub-scanning corresponding direction. The thickness of each dustproof glass is about 1.9 mm. The distance from each dustproof glass to the corresponding photosensitive drum surface (scanned surface) is about 90 mm (see FIG. 9).

  The surface of each dustproof glass is inclined by 14 ° with respect to the sub-scanning corresponding direction (see FIG. 17). FIG. 17 is a diagram developed on the XZ plane so that each light beam becomes one straight line.

  Each dust-proof glass is a special surface whose one surface is expressed by the above formula (1). Specific examples of Ry, Rz, and coefficients in the above equation (1) of each dustproof glass are shown in FIG.

  The spot diameter of the light spot formed on each photosensitive drum surface (surface to be scanned) was about 65 μm in the main scanning direction and about 70 μm in the sub scanning direction.

  As an example, as shown in FIG. 19, when there is a variation in the distance from the center of rotation of the polygon mirror 2104 to each deflecting / reflecting surface (Δd in FIG. 19), the light beam is obliquely incident on the deflecting / reflecting surface. The reflection position on the deflecting reflection surface changes (ΔS in FIG. 19) with respect to the sub-scanning corresponding direction (here, the Z-axis direction). When the reflection position on the deflection reflection surface changes in the sub-scanning corresponding direction, the imaging position also changes in the sub-scanning corresponding direction on the surface to be scanned. This leads to fluctuations in the scanning line pitch on the surface to be scanned.

  Therefore, when there is the above-described variation, the polygon mirror having four deflecting and reflecting surfaces causes the pitch variation of the scanning lines at a cycle of four lines.

  The pitch variation of the scanning line is ΔS × β, where β is the magnification of the scanning lens in the sub-scanning corresponding direction. When this value is 5 μm or more, the density becomes uneven on the output image, and the image quality is greatly deteriorated.

  When the light beam is incident horizontally on the deflecting / reflecting surface, the reflection position does not change in the sub-scanning corresponding direction even if there is the above-described variation, so that the imaging position on the surface to be scanned does not change.

  As a first method for suppressing the deterioration of the image quality, it is conceivable to increase the distance β between the scanning lens and the polygon mirror to reduce the magnification β. In this case, it is necessary to lengthen the length of the scanning lens in the main scanning correspondence direction, which increases the cost of the scanning lens and increases the size of the optical scanning device. Further, in order to keep the angle of view constant and reduce the magnification β, it is necessary to increase the optical path length between the polygon mirror and the photosensitive drum, which leads to an increase in the size of the image forming apparatus.

  As a second method for suppressing the deterioration of the image quality, it is conceivable to reduce the oblique incident angle of the light beam. When the oblique incident angle is small, the reflection position shift ΔS on the deflecting reflecting surface in the sub-scanning corresponding direction is small.

  However, when the oblique incidence angle of the light beam is small, the angle formed by the two light beams reflected by the same deflecting reflection surface is also small, and as shown in FIG. 20 as an example, the two light beams are separated. The distance between the folding mirror and the deflecting reflecting surface becomes longer. That is, the optical scanning device is increased in size.

  Further, when the light beam is obliquely incident, the wavefront aberration increases. When viewed from the sub-scanning corresponding direction, unless the shape of the surface on the incident side of the scanning lens is an arc shape centered on the reflection position on the deflection reflection surface, from the reflection position on the deflection reflection surface to the incidence position on the scanning lens The optical path length differs depending on the position in the main scanning corresponding direction.

  It is difficult to keep the shape of the surface on the incident side of the scanning lens in the arc shape in order to maintain optical performance. Therefore, normally, the light beam deflected by the polygon mirror and incident on the scanning lens does not enter perpendicularly to the optical surface at a position other than the optical axis when viewed from the direction corresponding to the main scanning, and other than 0 °. Incident at an incident angle (see FIG. 21).

  In addition, the light beam reflected by the polygon mirror has a certain width in the main scanning direction, and the light beams at both ends in the main scanning direction in the light beam travel from the deflection reflection surface to the incident position of the scanning lens. The optical path lengths are different and are inclined with respect to the sub-scanning corresponding direction. Therefore, the light beam is incident on the scanning lens in a twisted state.

  When this twisted light beam is incident on a scanning lens having strong optical power in the sub-scanning corresponding direction, the wavefront aberration is increased. That is, when a light beam having a skew characteristic is incident on a surface having strong optical power in the sub-scanning corresponding direction, the refraction angles of the light beams at both ends in the main scanning corresponding direction in the light beam are different. In the above, each light beam is not collected at one point, and the light spot becomes fat.

  In addition, the difference in the incident position of the light beam at both ends of the incident light beam in the main scanning corresponding direction to the scanning lens in the sub scanning corresponding direction is that the incident position of the light beam in the main scanning corresponding direction is light. The larger the distance from the axis, the larger. That is, the farther the incident position of the light beam in the direction corresponding to the main scanning is away from the optical axis, the greater the twist of the light beam, and the light spot on the scanned surface becomes thicker due to the deterioration of wavefront aberration.

  In each scanning lens in the present embodiment, as shown in FIG. 22 as an example, since the incident side surface is inclined with respect to the sub-scanning corresponding direction, it is formed by two light beams transmitted through the incident side surface. The angle (θout) can be made larger than the incident angle (θin).

  Therefore, as shown in FIG. 23 as an example, even if the oblique incident angles of the two light beams are small, the distance between the folding mirror for separating the two light beams and the deflecting reflection surface can be shortened.

  As a result, since the oblique incident angle of the two light beams can be reduced, the deviation ΔS of the reflection position on the deflecting reflection surface is reduced, so that the magnification β is not reduced. The pitch variation of the scanning line can be reduced without being away from the scanning line.

  Next, the reason why the shape of the special surface of each scanning lens in the present embodiment is a planar shape will be described.

  If the special surface has a curvature in the sub-scanning corresponding direction, the shape in the main-scanning corresponding direction is greatly different for each position in the sub-scanning corresponding direction. At this time, if the incident position of the light beam in the sub-scanning corresponding direction is shifted due to temperature variation or an optical element assembly error, a large magnification error occurs. In a multicolor image forming apparatus, the position of the light spot on the surface to be scanned between the colors is shifted, and as a result, the output image has a color shift.

  On the other hand, when the shape of the special surface is a planar shape, the change in shape in the main scanning correspondence direction due to the position in the sub scanning correspondence direction can be reduced, and even if the incident position of the light beam in the sub scanning correspondence direction is deviated, the magnification error does not occur. It will never grow.

  Note that the special surface of each scanning lens in the present embodiment has a different shape in the main scanning corresponding direction depending on the position in the sub scanning corresponding direction, but the main scanning corresponding direction as compared with the case of having a curvature in the sub scanning corresponding direction. The shape change for is very small.

  Also, if the special surface has a curvature in the sub-scanning corresponding direction, the traveling direction of the light transmitted through the incident-side surface changes when the incident light is shifted in the sub-scanning corresponding direction (see FIG. 24). . In this case, a large scanning line curve occurs on the surface to be scanned. In addition, light beam skew occurs, which increases wavefront aberration and increases the spot diameter of the light spot.

  On the other hand, when the shape of the special surface is a planar shape, even if the incident light beam is shifted in the sub-scanning corresponding direction, the traveling direction of the light beam transmitted through the incident side surface is only shifted, and the change is small (see FIG. 25).

  For the above reasons, the special surface of each scanning lens in the present embodiment has a planar shape.

  By the way, in order to correct the wavefront aberration, it is necessary to correct the incident position on the optical surface having a strong optical power in the sub-scanning corresponding direction so that the light is condensed at one point on the surface to be scanned. In the single-lens scanning lens, the optical surface having strong optical power in the sub-scanning corresponding direction is the exit-side optical surface.

  In each scanning lens according to the present embodiment, an emission optical surface having strong optical power in the sub-scanning corresponding direction is obtained by varying the inclination angle of the incident optical surface with respect to the sub-scanning corresponding direction according to the position in the main scanning corresponding direction. The wavefront aberration is corrected by adjusting the incident position of the light beam. That is, the increase in wavefront aberration due to the use of the oblique incidence optical system is corrected.

  In each scanning lens according to the present embodiment, the incident optical surface is inclined with respect to the sub-scanning corresponding direction even in the vicinity of the incident-side reference axis. Compared with the vicinity of the end of the scanning lens in FIG. 4, the skew of the light beam is extremely small, so there is no problem.

  In addition, the surface on the incident side of each scanning lens in this embodiment is inclined with respect to the sub-scanning corresponding direction in the entire region in the main scanning corresponding direction through which the light beam is transmitted.

  The surface on the incident side of the scanning lens is shaped so that the distance between the two light beams emitted from each optical surface is widened in the sub-scanning corresponding direction, thereby forming the surface on the incident side of the scanning lens. As shown in FIG. 26, the shape of the mold part used can be a mountain shape (a valley shape as an optical surface) in the entire main scanning direction. When the shape on the mold part side is a valley shape, it is difficult to process the ridge line portion in the sub-scanning corresponding direction of each surface. Specifically, since a clearance portion for the cutting tool is required at the time of processing, it is necessary to widen the distance between the lens surfaces arranged in the sub-scanning corresponding direction, and the scanning lens becomes large. When the interval between the lens surfaces arranged in the sub-scanning corresponding direction is widened, there arises a disadvantage that the oblique incident angle needs to be increased.

  By the way, if there is only one exit optical surface in the scanning lens, as shown in FIG. 27 as an example, the light beam passes off-axis in the sub-scanning corresponding direction, so that it is emitted from the scanning lens 2. The intervals between the two light beams are gradually narrowed in the sub-scanning corresponding direction. In this case, it is difficult to set the arrangement position of the folding mirror for separating the two light beams.

  On the other hand, in each scanning lens according to the present embodiment, as shown in FIG. 28 as an example, the two light beams pass through the vicinity of the reference axis of each exit optical surface, so that they are refracted in the sub-scanning corresponding direction. Can be suppressed. That is, the surface on the exit side of each scanning lens in the present embodiment can maintain the angle formed by the two light beams while having an imaging function.

  In the present embodiment, two light beams incident on the same deflecting / reflecting surface intersect when viewed from the sub-scanning corresponding direction before entering the deflecting / reflecting surface. A cylindrical lens is disposed in the vicinity of the intersection position. The intersection here does not necessarily need to collide with the two light beams, but it may simply appear as if they intersect when viewed from the sub-scanning corresponding direction.

  Thereby, as shown in FIG. 29 and FIG. 30 as an example, the oblique incidence angle can be reduced without increasing the distance between the polygon mirror and the scanning lens.

  In this case, since the two light beams are incident on different positions of the same deflecting / reflecting surface with respect to the sub-scanning corresponding direction, the thickness of the deflecting / reflecting surface is made thicker than when the conventional oblique incidence optical system is used. There is a need. However, in this embodiment, since the thickness of the deflecting reflection surface is suppressed to about 4 mm, there is almost no increase in cost, increase in power consumption, and increase in noise. When the two light beams are horizontally incident and the two scanning lenses are arranged so as to overlap each other in the sub-scanning corresponding direction, the thickness of the deflection reflection surface is often about 8 to 10 mm.

  In addition, when a conventional oblique incidence optical system is used, the oblique incidence angle is often set to about 3 to 5 °, but in this embodiment, the oblique incidence angle can be set to about 1 °. .

  In this embodiment, the cylindrical lens is shared by two light beams directed to the same deflection reflection surface, and when viewed from the sub-scanning corresponding direction before the two light beams enter the deflection reflection surface. It is arranged at the crossing position. In this case, the number of parts can be reduced.

  The special surfaces of each dustproof glass have different inclination angles with respect to the sub-scanning corresponding direction depending on the position in the main-scanning corresponding direction. Therefore, the optical path of the light beam incident on each dustproof glass is bent in the sub-scanning corresponding direction according to the incident position of the light beam in the main scanning corresponding direction. Here, this corrects the scanning line curve on the surface of the photosensitive drum. In this embodiment, the scanning line bending can be set to 20 μm or less. The scanning line bending is a PV (Peak to Valley) value at a position in the sub-scanning direction of a light spot formed on the surface of the photosensitive drum.

  By the way, if a special surface for correcting the scanning line curvature is arranged at a place where the light beam is not particularly focused in the main scanning correspondence direction, the light beam may be twisted to increase the wavefront aberration. Therefore, in the present embodiment, a special surface for correcting the scanning line curve is arranged at a position where the light beam is focused in the main scanning direction, that is, at a position close to the photosensitive drum. Thereby, it is possible to correct the scanning line bending without increasing the wavefront aberration.

  Further, at a position close to the photosensitive drum, the light beams directed to the respective positions of the photosensitive drum are further separated in the main scanning direction, and the overlapping of adjacent light beams is small. For this reason, the inclination amount in the special surface of each dustproof glass can be set finely.

  In addition, each dustproof glass has no optical power in both the main scanning corresponding direction and the sub-scanning corresponding direction. In this case, each dustproof glass can be made into a substantially parallel flat plate shape, and has a substantially uniform thickness. Further, when the material is resin, molding is easy and shape accuracy is improved. Actually, since it has a special surface, it does not have a completely uniform thickness, but the tilt amount with respect to the sub-scanning corresponding direction on the special surface is small, and can be regarded as a parallel plate for molding. .

  Furthermore, since each dustproof glass has a function of preventing toner and dust from entering the optical scanning device, an optical scanning device having good optical performance can be provided without increasing the number of components. Can do.

  The dust-proof glass 2109a and the dust-proof glass 2109b include the incident-side reference axis of the scanning lens 2105A and are arranged on the XY plane when the light beam LBa and the light beam LBb are spread on the XZ plane so as to be one straight line. The arrangement position and the surface shape are symmetric with respect to the parallel surface.

  Similarly, the dust-proof glass 2109c and the dust-proof glass 2109d include the incident-side reference axis of the scanning lens 2105B when the light beam LBc and the light beam LBd are spread on the XZ plane so as to be one straight line, and the XY plane. Both the arrangement position and the surface shape are symmetric with respect to the plane parallel to.

  As described above, according to the optical scanning device 2010 according to the present embodiment, four light sources (2200a to 2200e), a plurality of deflection reflection surfaces, and light beams (LBa to LBd) emitted from the respective light sources are used. A deflecting polygon mirror 2104, a scanning lens 2105A on which two light beams (LBa and LBb) deflected by the polygon mirror 2104 are incident, and two light beams (LBc and LBd) deflected by the polygon mirror 2104 are incident. A scanning lens 2105B, a plurality of folding mirrors that guide the light beams that have passed through the scanning lenses to the corresponding photosensitive drums, and four dust-proof glasses through which the light beams that pass through the folding mirrors pass.

  All the light beams (LBa to LBd) emitted from the respective light sources are obliquely incident on the polygon mirror 2104.

  The scanning lens 2105A has a first incident optical surface and a first emission optical surface corresponding to the light beam LBa, and a second incidence optical surface and a second emission optical surface corresponding to the light beam LBb.

  Further, the scanning lens 2105B has a first incident optical surface and a first emission optical surface corresponding to the light beam LBd, and a second incident optical surface and a second emission optical surface corresponding to the light beam LBc.

  Each incident optical surface of each scanning lens is a flat surface whose inclination with respect to the sub-scanning corresponding direction differs depending on the position in the main scanning corresponding direction. Each exit optical surface of each scanning lens is a surface having strong optical power in the sub-scanning corresponding direction.

  This shortens the distance between the folding mirror for separating two light beams deflected by the same deflecting reflection surface and the deflecting reflecting surface, and oblique incidence of the two light beams incident on the same deflecting reflecting surface. The corner can be reduced. In addition, wavefront aberration due to oblique incidence can be reduced. Furthermore, it is possible to easily and accurately produce a mold part used when molding each scanning lens.

  Further, when viewed from the main scanning corresponding direction, the two light beams incident on the same deflecting / reflecting surface enter the deflecting / reflecting surface after intersecting each other. In this case, the distance between the polygon mirror 2104 and each scanning lens can be shortened without reducing the oblique incident angle.

  In addition, each dustproof glass has no optical power in either the main scanning corresponding direction or the sub scanning corresponding direction, and at least one surface has a special inclination angle with respect to the sub scanning corresponding direction depending on the position in the main scanning corresponding direction. Has a surface. In this case, the scanning line curve on the surface of the photosensitive drum can be reduced, and color misregistration when a plurality of toner images are superimposed can be reduced.

  Thus, cost reduction and size reduction can be achieved without reducing the scanning accuracy.

  Further, since the light beam incident on the deflecting / reflecting surface is obliquely incident, the thickness of the polygon mirror having a high cost ratio among the components constituting the optical scanning device can be made smaller than that in the case where it is incident horizontally. . That is, the polygon mirror can be reduced in size. With this miniaturization, it is possible to provide an optical scanning device that not only lowers the cost but also reduces power consumption and noise and considers the environment.

  In addition, since one scanning lens is shared by two image forming stations, the number of parts can be reduced and the cost can be reduced.

  In addition, each scanning lens allows two optical surfaces arranged along the sub-scanning corresponding direction to be close to each other, as compared with the case where two scanning lenses are arranged in the sub-scanning corresponding direction as in the prior art. The oblique incident angle can be reduced, and the scanning lens can be reduced in size.

  Further, the degree of freedom in optical layout from the polygon mirror 2104 to the photosensitive drum is high. In particular, since each scanning lens can be arranged near the polygon mirror 2104, the optical scanning device can be downsized (thinned) in the sub-scanning corresponding direction.

  Further, since the color printer 2000 according to the present embodiment includes the optical scanning device 2010, as a result, it is possible to achieve cost reduction and size reduction while maintaining high image quality.

  In the above-described embodiment, the light source and the pre-deflector optical system are inclined with respect to the XY plane in order to make the light beam obliquely incident on the deflecting / reflecting surface. However, the present invention is not limited thereto. It is not a thing. For example, a mirror may be added to the pre-deflector optical system, and the light beam may be tilted by the mirror.

  Moreover, in the said embodiment, each light source may each have a some light emission part. In this case, the surface to be scanned can be scanned simultaneously with a plurality of light beams, so that the image formation speed can be increased and the image density can be increased.

  In the above-described embodiment, two light sources that emit two light beams incident on the same deflecting / reflecting surface may be separated in the main scanning corresponding direction, and two cylindrical lenses may be provided corresponding to the respective light sources. In this case, it is possible to obtain good optical characteristics by making the shapes of the two optical surfaces arranged along the sub-scanning corresponding direction of the scanning lens different from each other.

  In the above embodiment, in order to avoid the interference of the coupling lens while sharing the cylindrical lens with respect to the two light beams incident on the same deflecting / reflecting surface, the two light sources for emitting the two light beams are used. They may be separated in the main scanning corresponding direction. In this case, it is desirable that the two light beams intersect in the vicinity of the deflecting reflection surface when viewed from the sub-scanning corresponding direction. Further, when the separation distance between the two light sources in the main scanning correspondence direction is small, the shapes of the two optical surfaces arranged along the sub scanning correspondence direction of the scanning lens may be the same.

  In the above embodiment, the case where the image forming apparatus has four photosensitive drums has been described. However, the present invention is not limited to this. For example, the image forming apparatus may have five photosensitive drums. good.

  In the above embodiment, the case where the special surface for correcting the scanning line curvature is provided on the dustproof glass is not limited to this, and the special surface for correcting the scanning line curvature is separate from the dustproof glass. An optical element having a surface may be provided.

  In the above embodiment, the case where the optical scanning device 2010 is used in a printer has been described. However, the present invention is also suitable for an image forming apparatus other than a printer, for example, a copier, a facsimile, or a multifunction machine in which these are integrated. .

  As described above, the optical scanning device of the present invention is suitable for cost reduction and size reduction without reducing the scanning accuracy. The image forming apparatus according to the present invention is suitable for cost reduction and size reduction while maintaining high image quality.

  2000 ... color printer (image forming apparatus), 2010 ... optical scanning device, K1, C1, M1, Y1 ... photosensitive drum (image carrier), 2104 ... polygon mirror (optical deflector), 2105A ... scanning lens, 2105B ... Scanning lens, 2109a to 2109d ... dustproof glass (optical element), 2200a to 2200d ... light source, 2204A ... cylindrical lens, 2204B ... cylindrical lens.

JP 2003-5114 A JP 2006-72288 A

Claims (9)

An optical scanning device that scans a plurality of scanned surfaces with a light beam in the main scanning direction,
A plurality of light sources corresponding to the plurality of scanned surfaces;
An optical deflector that rotates a plurality of deflection reflecting surfaces around an axis parallel to a sub-scanning direction orthogonal to the main scanning direction to deflect light beams from the plurality of light sources;
A scanning optical system including at least one scanning lens, and condensing a plurality of light beams deflected by the optical deflector on a corresponding scanned surface, respectively.
The plurality of light beams are incident on the deflection reflection surface of the optical deflector from a direction inclined with respect to a plane orthogonal to the rotation axis of the optical deflector,
The scanning lens has a plurality of optical surfaces respectively corresponding to the plurality of light beams on an incident side and an exit side of the light beam,
The line of intersection of a plurality of optical surfaces on the incident side respectively, a virtual plane perpendicular to the main scanning direction at any position in the main scanning direction, Ri straight der which is inclined with respect to the sub-scanning direction,
An optical scanning device characterized in that an intersection line between each of the plurality of incident-side optical surfaces and a virtual plane orthogonal to the sub-scanning direction at an arbitrary position in the sub-scanning direction is a curve .   2. The optical scanning device according to claim 1, wherein the plurality of incident-side optical surfaces have different inclination angles with respect to the sub-scanning direction according to positions in the main scanning direction.   The optical scanning device according to claim 1, wherein the at least one scanning lens is a single scanning lens. The plurality of light beams are two light beams;
An inclination angle of each optical surface on the incident side with respect to the sub-scanning direction is set such that an interval between two light beams emitted from the respective optical surfaces on the incident side is widened in the sub-scanning direction. The optical scanning device according to claim 1.   5. The optical scanning device according to claim 1, wherein the light beams from the plurality of light sources intersect with each other in the sub-scanning direction and are incident on the deflecting reflection surface.   The optical scanning device according to claim 5, further comprising a pre-deflector optical element disposed at the intersecting position. An optical element disposed between the scanning lens and the surface to be scanned;
The optical element has no optical power in any of the main scanning direction and the sub-scanning direction, and one surface has an inclination angle with respect to the sub-scanning direction depending on a position in the main scanning direction. Item 7. The optical scanning device according to any one of Items 1 to 6.   The light deflector deflects a light beam from a part of the plurality of light sources to one side and deflects a light beam from the remaining light sources to the other side. The optical scanning device according to any one of the above. A plurality of image carriers;
An image forming apparatus comprising: the optical scanning device according to claim 1, wherein each of the plurality of image carriers is scanned with a light beam modulated according to corresponding image information.

Images