Lens mirror array

Abstract

To provide a lens mirror array capable of providing a large depth of field.SOLUTION: A lens mirror array according to an embodiment comprises multiple optical elements arranged in a main scanning direction. Each optical element has an incident lens surface for transmitting and converging incident light, an upstream mirror surface for reflecting the light entering via the incident lens surface, a downstream mirror surface for reflecting the light reflected by the upstream mirror surface, and an exit lens surface for transmitting and converging the light reflected by the downstream mirror surface. A distance from an object surface to the incident lens surface is longer than a distance from the exit lens surface to the image plane.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] Embodiments of the present invention relate to a lens mirror array used, for example, in a scanner of an image forming apparatus installed in a workplace.

Background Art

[0002] For example, a scanner of a copying machine has a lens and mirror integrated array (hereinafter referred to as a lens mirror array) for refracting and reflecting light reflected from an original surface and condensing it onto a CCD sensor or the like. The lens mirror array has, for example, a plurality of optical elements arranged in the main scanning direction. Each optical element has an incident-side lens surface that transmits and converges incident light, an upstream-side mirror surface that reflects light incident through the incident-side lens surface, a downstream-side mirror surface that reflects light reflected by the upstream-side mirror surface, and an exit-side lens surface that transmits and converges light reflected by the downstream-side mirror surface.

[0003] Hitherto, in such a lens mirror array, the optical path length from the incident-side lens surface to the downstream-side mirror surface and the optical path length from the downstream-side mirror surface to the exit-side lens surface have been set to be substantially the same. Also, the distance from the object surface to the incident-side lens surface and the distance from the exit-side lens surface to the image surface have been set to be substantially the same. Further, the optical power in the main scanning direction at the exit-side lens surface and the optical power in the main scanning direction at the incident-side lens surface have been set to be substantially the same.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, with such a lens mirror array, it is difficult to increase the depth of field to a certain extent or more.

[0006] The problem to be solved by the present invention is to provide a lens mirror array capable of increasing the depth of field.

Means for Solving the Problem

[0007] The lens mirror array according to the embodiment has a plurality of optical elements arranged in the main scanning direction. Each optical element has an incident-side lens surface that transmits and converges incident light, an upstream-side mirror surface that reflects the light incident through the incident-side lens surface, a downstream-side mirror surface that reflects the light reflected by the upstream-side mirror surface, and an exit-side lens surface that transmits and converges the light reflected by the downstream-side mirror surface. The distance from the object surface to the incident-side lens surface is longer than the distance from the exit-side lens surface to the image surface.

Brief Description of the Drawings

[0008]

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DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings. Note that the scales of the respective parts in the following drawings may be appropriately changed. Also, in the following drawings used for the description of the embodiments, a part of the configuration may be omitted for easy understanding of the description. Further, each element shown in the drawings conceptually shows the configuration, and the ratios of the respective parts are not necessarily strictly accurate, nor do they limit the invention.

[0010] Also, in each figure, the XYZ coordinate system is set as follows. The vertical direction is the Z direction. The moving direction of the reading module 70 of the scanner 20, which will be described later, is the Y direction. The direction perpendicular to the Y direction and the Z direction is the X direction. The X direction is the main scanning direction. The Y direction is the sub-scanning direction.

[0011] (Image forming apparatus) First, with reference to FIG. 1, the image forming apparatus 100 will be described. The image forming apparatus 100 specifically has a scanner 20 having a reading module 70 with a lens mirror array 90 (see FIG. 3). FIG. 1 is a schematic diagram showing the image forming apparatus 100.

[0012] The image forming apparatus 100 is, for example, an MFP (multifunction peripheral). The image forming apparatus 100 has functions such as a printing function, a scanning function, and a copying function. The printing function is a function of forming a toner image on the paper P. The scanning function is a function of reading an image from a document or the like on which an image is formed. The copying function is, for example, a function of printing an image read from a document or the like using the scanning function on the paper P using the printing function.

[0013] The image forming apparatus 100 includes a printer 10, a scanner 20, and an operation panel 30.

[0014] The printer 10 includes a plurality of paper feed cassettes 11, a manual feed tray 12, and a plurality of paper feed rollers 13. The paper feed cassette 11 stores the paper P used for printing. The manual feed tray 12 is for manually inserting the paper P. The paper feed roller 13 selectively takes out the paper P from either the paper feed cassette 11 or the manual feed tray 12 by rotating.

[0015] The printer 10 includes four toner cartridges 141, 142, 143, 144, four image forming units 151, 152, 153, 154, an optical scanning device 16, a transfer belt 17, a secondary transfer roller 18, and a fixing unit 19.

[0016] The toner cartridges 141 to 144 each contain toner to be supplied to the image forming units 151 to 154. The toner cartridge 141 contains yellow (Y) toner. The toner cartridge 142 contains magenta (M) toner. The toner cartridge 143 contains cyan (C) toner. The toner cartridge 144 contains black (K) toner. The combination of toner colors is not limited to YMCK and may be other color combinations.

[0017] The image forming units 151 to 154 each receive toner supply from the toner cartridges 141 to 144 and form toner images of different colors. The image forming unit 151 forms a yellow (Y) toner image. The image forming unit 152 forms a magenta (M) toner image. The image forming unit 153 forms a cyan (C) toner image. The image forming unit 154 forms a black (K) toner image.

[0018] (Image forming unit) The image forming units 151 to 154 have the same configuration except for the difference in toner. Therefore, here, with reference to FIG. 2, the image forming unit 151 for yellow will be described as a representative, and the description of the image forming units 152 to 154 for other colors will be omitted. FIG. 2 is a schematic diagram showing the image forming unit 151 of the image forming apparatus 100.

[0019] The image forming unit 151 for yellow includes a photosensitive drum 41, a charging device 42, a developing device 43, a primary transfer roller 44, a cleaner 45, and a charge elimination lamp 46.

[0020] The photosensitive drum 41 has a surface that receives the light beam BY irradiated from the optical scanning device 16. The optical scanning device 16 forms an electrostatic latent image on the surface of the photosensitive drum 41. The charging device 42 charges the surface of the photosensitive drum 41 with positive charges. The developing device 43 develops the electrostatic latent image on the surface of the photosensitive drum 41 using the yellow toner D supplied from the toner cartridge 141. That is, the developing device 43 forms a yellow toner image on the surface of the photosensitive drum 41.

[0021] Further, the image forming unit 151 includes a primary transfer roller 44 at a position facing the photosensitive drum 41 with the transfer belt 17 interposed therebetween. The primary transfer roller 44 generates a transfer voltage between itself and the photosensitive drum 41. Thereby, the primary transfer roller 44 transfers (primary transfer) the yellow toner image on the surface of the photosensitive drum 41 to the surface of the transfer belt 17 that is in contact with the photosensitive drum 41.

[0022] The cleaner 45 removes the toner remaining on the surface of the photosensitive drum 41. The charge elimination lamp 46 removes the charges remaining on the surface of the photosensitive drum 41.

[0023] The optical scanning device 16 irradiates the surfaces of the photosensitive drums 41 of the image forming units 151, 152, 153, 154 with light beams BY, BM, BC, BK, respectively, according to the input image data. The light beams BY, BM, BC, BK are respectively based on the image data of each color obtained by color-separating the image data into Y, M, C, K colors.

[0024] The optical scanning device 16 emits the light beam BY according to the Y-component image data to form a yellow electrostatic latent image on the surface of the photosensitive drum 41 of the image forming unit 151. Similarly, the optical scanning device 16 emits the light beams BM, BC, BK according to the M, C, K-component image data to form electrostatic latent images for each color on the surfaces of the photosensitive drums 41 of the image forming units 152, 153, 154.

[0025] Note that the image data input to the optical scanning device 16 is, for example, image data read from a document or the like by the scanner 20. Or, the image data input to the optical scanning device 16 is image data transmitted from a device different from the image forming device 100 to the image forming device 100.

[0026] The transfer belt 17 is stretched in an endless shape and rotates by rotating the drive roller 171 around which the transfer belt 17 is wound. By rotating, the transfer belt 17 conveys the toner images of various colors formed on the surface of the transfer belt 17 by the image forming units 151 to 154 to the transfer area facing the secondary transfer roller 18.

[0027] The secondary transfer roller 18 faces the drive roller 171 with the transfer belt 17 interposed therebetween. The secondary transfer roller 18 transfers (secondary transfer) the toner image formed on the transfer belt 17 onto the paper P passing between the secondary transfer roller 18 and itself.

[0028] The fixing unit 19 heats and presses the paper P. The fixing unit 19 includes a heating roller 191 and a pressure roller 192 that face each other with the conveyance path of the paper P interposed therebetween. The heating roller 191 includes a heat source such as a heater. The heating roller 191 heated by the heat source heats the paper P. The pressure roller 192 presses the paper P passing between the pressure roller 192 and the heating roller 191. Therefore, the fixing unit 19 fixes the toner image transferred onto the paper P.

[0029] In addition, the printer 10 includes a duplex unit 50 and a paper output tray 60. The duplex unit 50 makes the paper P printable on the back side. The duplex unit 50 reverses the front and back of the paper P by switching it back and feeds it into the transfer area between the transfer belt 17 and the secondary transfer roller 18. The paper output tray 60 receives the paper P discharged after printing.

[0030] The scanner 20 reads an image from a document or the like. The scanner 20 includes a reading module 70 and a document feeder 80.

[0031] The reading module 70 irradiates illumination light onto the surface of the document having the image to be read (hereinafter referred to as the document surface), and receives the reflected light with an image sensor 76 (see FIG. 3) and converts it into a digital signal. Thereby, the reading module 70 reads an image from the document surface. The reading module 70 includes a lens mirror array 90 (see FIG. 3) that guides the reflected light from the document to the image sensor 76.

[0032] The document feeder 80 is, for example, an ADF (auto document feeder) or the like. The document feeder 80 sequentially conveys the documents placed on the document tray 81 through the document glass 82. The reading module 70 reads an image from the document conveyed to the document glass 82. The document feeder 80 may be provided with another reading module for reading an image from the back surface of the document.

[0033] The operation panel 30 is a man-machine interface that performs input and output between the image forming apparatus 100 and the operator of the image forming apparatus 100. The operation panel 30 includes, for example, a touch panel 31 and an input device 32.

[0034] The touch panel 31 is, for example, a laminate of a display such as a liquid crystal display or an organic EL display and a pointing device by touch input. The display of the touch panel 31 displays a screen for notifying various information to the operator of the image forming apparatus 100. Further, the touch panel 31 receives a touch operation by the operator.

[0035] The input device 32 receives an operation by the operator of the image forming apparatus 100. The input device 32 is, for example, a keyboard, a keypad, or a touch pad.

[0036] (Reading Module) Next, with reference to FIG. 3, the reading module 70 of the scanner 20 of the image forming apparatus 100 will be described. FIG. 3 is a cross-sectional view showing the reading module 70 of the scanner 20 of the image forming apparatus 100.

[0037] As shown in FIG. 3, the reading module 70 includes a lens mirror array 90, two reflectors 72, two light guides 74, an image sensor 76, and a holder 78. The holder 78 positions and holds the lens mirror array 90, the reflectors 72, the light guides 74, and the image sensor 76 (substrate 75 on which the image sensor 76 is mounted).

[0038] The lens mirror array 90 forms an erect image of the image on the document surface on the image sensor 76. Therefore, by moving the reading module 70 along the document glass 82 in the sub-scanning direction (Y direction), the entire image on the document surface can be read by the image sensor 76.

[0039] The image sensor 76 has a long structure extending in the main scanning direction. The image sensor 76 is a line sensor in which a plurality of imaging elements that convert light into electrical signals are arranged in a line in the main scanning direction. The image sensor 76 is one or more line sensors. The image sensor 76 can be composed of, for example, a Charge Coupled Device (CCD), a Complimentary Metal Oxide Semiconductor (CMOS), or other imaging elements.

[0040] The holder 78 has a long structure extending in the main scanning direction. The holder 78 can be formed by integrally molding resin using a mold. The holder 78 has a pair of side walls 781 arranged along the main scanning direction, a pair of end walls 782 arranged at both longitudinal ends of the side walls 781 (only the back side is shown in FIG. 3), and a partition wall 783 connecting the inner surfaces of the middle portions in the vertical direction of the pair of side walls 781 and the inner surfaces of the middle portions in the vertical direction of the pair of end walls 782. There is a bulging portion 784 bulging upward in the middle portion in the sub-scanning direction (Y direction) of the partition wall 783. The bulging portion 784 has a long structure extending in the main scanning direction.

[0041] The bulging portion 784 of the holder 78 has a rectangular slit-shaped aperture 785 extending in the main scanning direction at approximately the center in the sub-scanning direction. The aperture 785 allows the reflected light from the original document surface to pass through, narrows the width of the reflected light in the sub-scanning direction, and guides it to the lens mirror array 90. The holder 78 holds the lens mirror array 90 inside the bulging portion 784, that is, below the aperture 785 in the drawing. The width of the aperture 785 in the sub-scanning direction is smaller than the width at which the reflected light from the original document passing through the aperture 785 is incident on the plurality of incident-side lens surfaces 92 (see FIG. 4) of the lens mirror array 90. The lens mirror array 90 is positioned such that the optical axis in the sub-scanning direction of the incident-side lens surface 92 passes through the center in the sub-scanning direction of the aperture 785.

[0042] The holder 78 holds the reflector 72 and the light guide 74 inside the two side walls 781 and above the partition wall 783 on both sides sandwiching the bulging portion 784 along the sub-scanning direction. The reflector 72 and the light guide 74 are held by an existing holding structure (not shown). Details of the holding structure of the reflector 72 and the light guide 74 are omitted.

[0043] The reflector 72 is, for example, a long rectangular plate extending in the main scanning direction. The reflector 72 has a reflecting surface facing a light diffusing portion (not shown) of the light guide 74. The light diffusing portion of the light guide 74 has, for example, unevenness on its surface. Alternatively, the light diffusing portion of the light guide 74 has white ink applied to its surface. The reflector 72 has, for example, white ink applied to its reflecting surface. Alternatively, the reflector 72 has a white resin formed in a rectangular plate shape on its reflecting surface. The reflector 72 has a function of reflecting the light leaking from the light diffusing portion of the light guide 74 back to the light guide 74.

[0044] The light guide 74 is, for example, a substantially columnar transparent resin long in the main scanning direction, and has the above-described light diffusing portion along the longitudinal direction on a part of its surface. The light guide 74 guides the light emitted from an LED light source (not shown) arranged at one end in its longitudinal direction. The reflector 72 reflects the light leaking from the light diffusing portion of the light guide 74 and returns it to the light guide 74.

[0045] Since there is a bulging portion 784 of the partition wall 783 of the holder 78 between the two light guides 74, it is necessary to arrange them at a certain distance from each other in the sub-scanning direction so that the bulging portion 784 does not create a shadow of the illumination light. On the other hand, if the two light guides 74 are separated in the sub-scanning direction, the angle of the illumination light hitting the image reading area on the document surface becomes large, and the change in illuminance when the distance between the document glass 82 and the document surface changes becomes large. Therefore, it is desirable to arrange the two light guides 74 as close to each other as possible in the sub-scanning direction.

[0046] The holder 78 has a plurality of bosses 786 protruding downward from the lower surface (as shown in the figure) of the partition wall 783. The bosses 786 are provided, for example, at three locations on both ends and the center of the partition wall 783 in the main scanning direction, on both sides of the bulging portion 784 in the sub-scanning direction. These six bosses 786 are each for fixing the substrate 75 to the holder 78 using screws 787. Note that the holder 78 includes a plurality of bosses 788 for positioning the substrate 75 on the holder 78.

[0047] (Lens mirror array) Next, with reference to FIGS. 4 to 6, the details of the lens mirror array 90 incorporated in the reading module 70 will be described. FIG. 4 is a view of the lens mirror array 90 incorporated in the reading module 70 as seen from the main scanning direction. FIG. 5 is a perspective view of the lens mirror array 90 as seen from the side of the downstream mirror. FIG. 6 is a perspective view of the lens mirror array 90 as seen from the side of the emitting side lens.

[0048] As shown in FIGS. 4 to 6, the lens mirror array 90 has an elongated structure extending in its longitudinal direction (only a part is shown in FIGS. 5 and 6). The lens mirror array 90 has a plurality of transparent optical elements 91 arranged integrally in its longitudinal direction.

[0049] Here, the longitudinal direction of the lens mirror array 90 coincides with the main scanning direction (X direction) in the state of being incorporated in the reading module 70. Hereinafter, the lens mirror array 90 is assumed to be incorporated in the reading module 70, and its longitudinal direction is also referred to as the main scanning direction or the X direction.

[0050] The plurality of optical elements 91 have the same shape. The shape of each optical element 91 is symmetric with respect to an imaginary central plane passing through the longitudinal center of the optical element 91 and perpendicular to the longitudinal direction.

[0051] In addition to the plurality of optical elements 91, the lens mirror array 90 has extension portions 97 (only one is shown in FIG. 6) at both ends in its longitudinal direction for an operator to grip the lens mirror array 90. When the operator holds the lens mirror array 90 by hand, it is desirable to hold this extension portion 97 so as not to touch the surface that guides the reflected light from the original document.

[0052] For example, the lens mirror array 90 can be formed by integrally molding a transparent resin using a mold. The lens mirror array 90 can also be formed from transparent glass.

[0053] Each optical element 91 of the lens mirror array 90 guides light so as to form an image of diffused light from an object point at an image point on the image plane. One optical element 91 forms an image of light from a plurality of object points arranged in the main scanning direction on the image plane. For example, one optical element 91 forms an image of light from object points arranged within a width that is two to five times the pitch in the main scanning direction of the optical element 91 on the image plane. Each optical element 91 of the lens mirror array 90 reflects the incident light twice and then emits it, forming an upright image of the object point on the image plane.

[0054] Each optical element 91 of the lens mirror array 90 has, on its surface, an incident-side lens surface 92, an upstream-side mirror surface 93, a downstream-side mirror surface 94, and an exit-side lens surface 95. The incident-side lens surface 92, the downstream-side mirror surface 94, and the exit-side lens surface 95 are all free-form surfaces convex outward. The upstream-side mirror surface 93 is a plane. The other surfaces of the plurality of optical elements 91 each constitute one flat surface that extends in the main scanning direction over the entire length of the lens mirror array 90.

[0055] The incident-side lens surface 92 of the optical element 91 faces the aperture opening 785 in the bulging portion 784 of the holder 78. In other words, the lens mirror array 90 is fixed to the bulging portion 784 in the state shown in FIG. 3 where the incident-side lens surfaces 92 of the plurality of optical elements 91 face the aperture opening 785. The incident-side lens surface 92 has a positive optical power for making incident the light reflected by the original surface and passing through the aperture opening 785, and refracting and converging this incident light. That is, the incident-side lens surface 92 transmits and converges the incident light.

[0056] The upstream-side mirror surface 93 is adjacent to the incident-side lens surface 92 on the opposite side of the protruding portion 901. That is, the upstream-side mirror surface 93 is located on the optical path of the incident light incident through the incident-side lens surface 92. The upstream-side mirror surface 93 totally reflects or Fresnel-reflects the incident light incident through the incident-side lens surface 92 toward the downstream-side mirror surface 94.

[0057] Each optical element 91 has a protrusion 931 with a part protruding outward. The protrusion 931 has the upstream-side mirror surface 93 at its top. The plurality of protrusions 931 of the plurality of optical elements 91 are spaced apart from each other in the longitudinal direction. Each protrusion 931 has a light-shielding film 932 on its side surface. The light-shielding film 932 of each protrusion 931 prevents light from traveling through the side surface of each protrusion 931.

[0058] The downstream mirror surface 94 is continuous with the opposite side of the protruding portion 902 with respect to the incident-side lens surface 92. That is, the downstream mirror surface 94 is located on the optical path of the reflected light reflected by the upstream mirror surface 93. The downstream mirror surface 94 totally reflects or Fresnel-reflects the reflected light reflected by the upstream mirror surface 93 toward the exit-side lens surface 95. The downstream mirror surface 94 is a free-form surface having a positive optical power that reflects and converges light. For example, the downstream mirror surface 94 has a positive optical power in the sub-scanning direction. That is, the downstream mirror surface 94 converges the reflected light reflected by the upstream mirror surface 93 in the sub-scanning direction and totally reflects or Fresnel-reflects it toward the exit-side lens surface 95. The width of the downstream mirror surface 94 in the main scanning direction is narrower than the width of the optical element 91.

[0059] The exit-side lens surface 95 is continuous with the opposite side of the protruding portion 903 with respect to the downstream mirror surface 94. That is, the exit-side lens surface 95 is located on the optical path of the reflected light reflected by the downstream mirror surface 94. The exit-side lens surface 95 is a free-form surface having a positive optical power that transmits and converges the reflected light reflected by the downstream mirror surface 94. That is, the exit-side lens surface 95 transmits the reflected light reflected by the downstream mirror surface 94 and converges it onto the image sensor 76. The lens mirror array 90 has a propagation blocking portion 96 that blocks the propagation of light between the two downstream mirror surfaces 94 of two adjacent optical elements 91 in the main scanning direction. For example, the width of the propagation blocking portion 96 in the main scanning direction is narrower than the width of the downstream mirror surface 94 in the main scanning direction. For example, the propagation blocking portion 96 blocks the incident light. Therefore, the propagation blocking portion 96 has a light-shielding film. Instead of blocking the light, the propagation blocking portion 96 may direct the light toward the image sensor 76 in another direction.

[0060] (Optical System of the Reading Module) Next, with reference to FIGS. 7 and 8, the optical system of the reading module 70 having the lens mirror array 90 will be described. FIG. 7 is a diagram schematically showing the optical system in the sub-scanning direction in the reading module 70 of FIG. 3. FIG. 8 is a diagram schematically showing the optical system in the main scanning direction in the reading module 70 of FIG. 3.

[0061] In the optical system of the reading module 70, the light incident on the incident-side lens surface 92 from the object surface Pobj becomes convergent light by passing through the incident-side lens surface 92 and is reflected by the upstream-side mirror surface 93. The light reflected by the upstream-side mirror surface 93 is subsequently reflected by the downstream-side mirror surface 94 and then enters the exit-side lens surface 95. The light incident on the exit-side lens surface 95 becomes convergent light by passing through the exit-side lens surface 95 and forms an erect and same-magnification image on the image surface Pimg.

[0062] The inventor optimized from the initial values combined with various parameters of the optical system of such a reading module 70 and found several conditions that can increase the depth of field while satisfying the imaging characteristics. These conditions are as follows. ·(Distance from the object surface Pobj to the incident-side lens surface 92) / (Distance from the exit-side lens surface 95 to the image surface Pimg)>1.3 ·(Optical path length from the incident-side lens surface 92 to the downstream-side mirror surface 94) / (Optical path length from the downstream-side mirror surface 94 to the exit-side lens surface 95)>1.8 ·(Optical power in the main scanning direction at the exit-side lens surface 95) / (Optical power in the main scanning direction at the incident-side lens surface 92)>2 It has been found that when at least one of these three conditions is satisfied, preferably when two conditions are satisfied, and more preferably when all conditions are satisfied, the depth of field can be increased.

[0063] Table 1 shows the parameters in the optical system of the reading module 70 having the lens mirror array 90 according to Example 1, Example 2, and Example 3 that satisfy the above conditions, and the parameters in the optical system of the reading module 70 having the lens mirror array 90 according to the conventional Example 1 as before.

[0064]

Table 1

[0065] For the optical system of the reading module 70 shown in FIGS. 7 and 8, the parameters are defined as follows. Herein, the effective width is the width of the range through which the light rays emitted from the object surface pass. The influence of dimensional variations during manufacturing is also taken into account. ·Pa = Distance from the object surface Pobj to the incident-side lens surface 92 (mm) ·Pb = Distance from the exit-side lens surface 95 to the image surface Pimg (mm) ·Pc = Optical path length from the incident-side lens surface 92 to the downstream-side reflecting surface 94 (mm) ·Pca = Optical path length from the incident-side lens surface 92 to the upstream-side reflecting surface 93 (mm) ·Pcb = Optical path length from the upstream-side reflecting surface 93 to the downstream-side reflecting surface 94 (mm) ·Pd = Optical path length from the downstream-side reflecting surface 94 to the exit-side lens surface 95 (mm) ·Pe = Optical power in the main scanning direction at the incident-side lens surface 92 ·Pf = Optical power in the main scanning direction at the downstream-side reflecting surface 94 ·Pg = Optical power in the main scanning direction at the exit-side lens surface 95 ·Ph = Optical power in the sub-scanning direction at the incident-side lens surface 92 ·Pi = Optical power in the sub-scanning direction at the downstream-side reflecting surface 94 ·Pj = Optical power in the sub-scanning direction at the exit-side lens surface 95 ·Pk = Width in the sub-scanning direction of the aperture opening 785 (mm) ·Pl = Effective width in the sub-scanning direction at the upstream-side mirror surface (mm) ·Pm = Effective width in the sub-scanning direction at the downstream-side mirror surface (mm) ·Pn = Effective width in the sub-scanning direction at the incident-side lens surface 92 (mm) ·Po = Effective width in the sub-scanning direction at the exit-side lens surface 95 (mm) Pc = The optical path length from the incident-side lens surface 92 to the downstream-side reflecting surface 94 (mm) is ·Pca = Optical path length from the incident-side lens surface 92 to the upstream-side reflecting surface 93 (mm) ·Pcb = Optical path length from the upstream-side reflecting surface 93 to the downstream-side reflecting surface 94 (mm) If defined in this way, Pc = Pca + Pcb.

[0066] In the optical system of the reading module 70 according to Conventional Example 1, (distance from the object plane Pobj to the incident-side lens surface 92) / (distance from the exit-side lens surface 95 to the image plane Pimg) = Pa / Pb, and (optical path length from the incident-side lens surface 92 to the downstream mirror surface) / (optical path length from the downstream mirror surface to the exit-side lens surface 95) = Pc / Pd are both 1.00 as before. Also, (optical power in the main scanning direction at the exit-side lens surface 95) / (optical power in the main scanning direction at the incident-side lens surface 92) = Pg / Pe = 0.98.

[0067] On the other hand, in any of the optical systems of the reading module 70 according to Example 1, Example 2, and Example 3, (distance from the object plane Pobj to the incident-side lens surface 92) / (distance from the exit-side lens surface 95 to the image plane Pimg) = Pa / Pb > 1.3, (optical path length from the incident-side lens surface 92 to the downstream mirror surface) / (optical path length from the downstream mirror surface to the exit-side lens surface 95) = Pc / Pd > 1.8, and (optical power in the main scanning direction at the exit-side lens surface 95) / (optical power in the main scanning direction at the incident-side lens surface 92) = Pg / Pe > 2 are satisfied.

[0068] As a result, in the optical system of the reading module 70 according to Conventional Example 1, the depth of field is 1.9 mm, while in the optical system of the reading module 70 according to Example 1, the depth of field is 4.2 mm, in the optical system of the reading module 70 according to Example 2, the depth of field is 6.5 mm, and in the optical system of the reading module 70 according to Example 3, the depth of field is 5.4 mm.

[0069] That is, in any of Example 1, Example 2, and Example 3, the depth of field can be increased.

[0070] Also, in the optical system of the reading module 70 according to the conventional example 1, (the effective width (mm) in the sub-scanning direction at the incident-side lens surface 92) = (Po = the effective width (mm) in the sub-scanning direction at the exit-side lens surface 95), that is, Pn = Po. In contrast, in any of the first embodiment, the second embodiment, and the third embodiment, (the effective width (mm) in the sub-scanning direction at the incident-side lens surface 92) > (Po = the effective width (mm) in the sub-scanning direction at the exit-side lens surface 95), that is, Pn > Po.

[0071] Also, in the optical system of the reading module 70 according to the conventional example 1, (the effective width (mm) in the sub-scanning direction at the upstream-side mirror surface 93) = (the effective width (mm) in the sub-scanning direction at the downstream-side mirror surface 94), that is, Pl = Pm. In contrast, in any of the first embodiment, the second embodiment, and the third embodiment, (the effective width (mm) in the sub-scanning direction at the upstream-side mirror surface 93) > (the effective width (mm) in the sub-scanning direction at the downstream-side mirror surface 94), that is, Pl > Pm.

[0072] This is due to the following reason. The incident-side lens surface 92, the exit-side lens surface 95, and the downstream-side mirror surface 94 are all free-form surfaces represented by polynomials. It has been found that in the downstream-side mirror surface 94, the higher-order terms of the polynomial affect the optical characteristics when the position of the original document surface changes significantly. If the higher-order terms of the polynomial are increased while the width in the sub-scanning direction of the downstream-side mirror surface 94 remains large, the curvature at the end becomes large and the processing becomes difficult. To avoid this, the effective width in the sub-scanning direction of the downstream-side mirror surface 94 is reduced.

[0073] Figures 9 to 12 are diagrams plotting the MTF (Modulation Transfer Function) against the amount of original document lift in an image forming apparatus 100 having a reading module 70 with a lens mirror array 90 according to Examples 1 to 3 and Conventional Example 1 described in Table 1. The original document lift direction is the +Z direction in FIG. 3. The original document lift amount = 0 indicates a state where the original document is in contact with the original document glass 82 without any gap. Also, when the original document lift amount is "-", it means that when a heavy book or the like is placed on the original document glass 82, or when the weight is placed on it and the original document such as a book is pressed from above, the original document glass 82 is bent and the original document surface approaches the side of the reading module 70. mainR, mainG, and mainB are the values for the wavelengths of Red, Green, and Blue, respectively, in the main scanning direction. Also, subR, subG, and subB are the values for the wavelengths of Red, Green, and Blue, respectively, in the sub-scanning direction.

[0074] FIG. 9 shows the MTF against the amount of original document lift in Example 1. In Example 1, a wide region with good MTF is obtained at all wavelengths of RGB. The wide region with good MTF in Example 1 is more than twice that of the wide region with good MTF in Conventional Example 1 (see FIG. 12) where the aforementioned parameter ratios (Pa / Pb, Pc / Pd, Pg / Pe) are close to 1.

[0075] FIG. 10 shows the MTF against the amount of original document lift in Example 2. In Example 2, a wide region with good MTF is obtained at all wavelengths of RGB. The wide region with good MTF in Example 2 is more than three times that of the wide region with good MTF in Conventional Example 1 (see FIG. 12).

[0076] FIG. 11 shows the MTF with respect to the original floating amount in Example 3. In Example 3, a wide region with good MTF is obtained at all wavelengths of RGB. The wide region with good MTF in Example 3 is more than 2.5 times that of the wide region with good MTF in Conventional Example 1 (see FIG. 12).

[0077] Table 2 shows the parameters in the optical system of the reading module 70 having the lens mirror array 90 according to other embodiments and other conventional examples.

[0078] [Table 2]

[0079] FIG. 13 is a graph in which the parameter ratio (Pa / Pb) is taken on the horizontal axis and the depth of field is taken on the vertical axis for the examples and conventional examples described in Table 1, and other examples and other conventional examples described in Table 2. FIG. 14 is a graph in which the parameter ratio (Pc / Pd) is taken on the horizontal axis and the depth of field is taken on the vertical axis for the examples and conventional examples described in Table 1, and other examples and other conventional examples described in Table 2. FIG. 15 is a graph in which the parameter ratio (Pg / Pe) is taken on the horizontal axis and the depth of field is taken on the vertical axis for the examples and conventional examples described in Table 1, and other examples and other conventional examples described in Table 2.

[0080] From these FIGS. 13 to 15, it can also be seen that a large depth of field is obtained in both the examples and other examples as compared with the conventional examples and other conventional examples in which the parameter ratios (Pa / Pb, Pc / Pd, Pg / Pe) are close to 1.

[0081] (Effect) As can be seen from the above description, according to the embodiment, a lens mirror array capable of increasing the depth of field is provided.

[0082] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

[0083] The embodiments disclose the invention described below.

[0084] [1] Having a plurality of optical elements arranged in the main scanning direction, The optical element, An incident-side lens surface that transmits and converges incident light, An upstream-side mirror surface that reflects light incident through the incident-side lens surface, A downstream-side mirror surface that reflects light reflected by the upstream-side mirror surface, And an exit-side lens surface that transmits and converges light reflected by the downstream-side mirror surface, The distance from the object surface to the incident-side lens surface is longer than the distance from the exit-side lens surface to the image surface, Lens mirror array.

[0085] [2] (Optical path length from the incident-side lens surface to the downstream-side mirror surface) / (Optical path length from the downstream-side mirror surface to the exit-side lens surface) > 1.8, The lens mirror array according to [1].

[0086] [3] (Optical power in the main scanning direction at the exit-side lens surface) / (Optical power in the main scanning direction at the incident-side lens surface) > 2, The lens mirror array according to [1].

[0087] [4] The upstream-side mirror surface is a plane, The lens mirror array according to [1].

[0088] [5] The downstream mirror surface is a curved surface and has a positive optical power. The lens mirror array according to [1].

[0089] [6] Between the two downstream mirror surfaces of the two optical elements adjacent in the main scanning direction, there is a propagation blocking portion that blocks the propagation of light. The lens mirror array according to [1].

Explanation of Reference Numerals

[0090] 10… Printer, 11… Paper feed cassette, 12… Manual feed tray, 13… Paper feed roller, 141~144… Toner cartridge, 151~154… Image forming unit, 16… Optical scanning device, 17… Transfer belt, 171… Driving roller, 18… Secondary transfer roller, 19… Fixing unit, 191… Heating roller, 192… Pressing roller, 20… Scanner, 30… Operation panel, 31… Touch panel, 32… Input device, 41… Photoconductor drum, 42… Charging device, 43… Developing device, 44… Secondary transfer roller, 45… Cleaner, 46… Discharge lamp, 50… Duplex unit, 60… Paper discharge tray, 70… Reading module, 72… Reflector, 74… Light guide, 75… Substrate, 76… Image sensor, 78… Holder, 781… Side wall, 782… End wall, 783… Partition wall, 784… Bulging portion, 785… Aperture opening, 786… Boss, 787… Screw, 788… Boss, 80… Original document feeder, 81… Original document tray, 82… Original document glass, 90… Lens mirror array, 901… Protruding portion, 902… Protruding portion, 903… Protruding portion, 91… Optical element, 92… Incident side lens surface, 93… Upstream mirror surface, 931… Protrusion, 932… Light shielding film, 94… Downstream mirror surface, 95… Exit side lens surface, 96… Propagation blocking portion, 97… Extended portion, 97… Extension portion, 100… Image forming apparatus.

Claims

1. having a plurality of optical elements arranged in the main scanning direction, wherein the optical element has an incident-side lens surface that transmits and converges incident light, an upstream-side mirror surface that reflects light incident through the incident-side lens surface, a downstream-side mirror surface that reflects light reflected by the upstream-side mirror surface, and an exit-side lens surface that transmits and converges light reflected by the downstream-side mirror surface, wherein the distance from the object surface to the incident-side lens surface is longer than the distance from the exit-side lens surface to the image surface, a lens mirror array.

2. (distance from the object surface to the incident-side lens surface) / (distance from the exit-side lens surface to the image surface) > 1.3, the lens mirror array according to Claim 1.

3. wherein the effective width in the sub-scanning direction of the upstream-side mirror surface is larger than the effective width in the sub-scanning direction of the downstream-side mirror surface, the lens mirror array according to Claim 1.

4. wherein the effective width in the sub-scanning direction of the incident-side lens surface is larger than the effective width in the sub-scanning direction of the exit-side lens surface, the lens mirror array according to Claim 1.

5. wherein the optical element has a protrusion having the upstream-side mirror surface at its top, and the protrusion has a light-shielding film on its side surface that blocks light from traveling through the side surface, the lens mirror array according to Claim 1.

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