JP2012078834A - Lens array unit and image forming device - Google Patents

Abstract

Provided is a lens array device capable of improving the original performance of a lens with good light condensing characteristics and high optical efficiency and reducing stray light.
In a lens array device according to an embodiment, a plurality of first and second microlenses each having a biconvex incident surface and an output surface are arranged, and a long side direction corresponds to a main scanning direction. A first lens array and a second lens array having a rectangular shape whose side direction corresponds to the sub-scanning direction, wherein the plurality of first and second microlenses are arranged at corresponding positions, and the second lens array Are arranged in parallel to the emission side of the first lens array, the plurality of first and second microlenses are arranged in a hexagonal close-packed manner, and arranged in a straight line in the main scanning direction. The second microlenses are arranged such that the intervals between the second microlenses are larger than the intervals between the first and second microlenses arranged linearly in the sub-scanning direction.
[Selection] Figure 4

Description

  Embodiments described herein relate generally to a lens array device and an image forming apparatus.

  A lens array device is used as an erecting equal-magnification imaging optical system in an original reading portion of an image reading device such as a scanner or an exposure portion of an image forming device that forms an electrostatic latent image on a photosensitive drum using an LED. There is.

  Further, as a lens array device, there is a type in which a plurality of minute convex lenses are regularly arranged in a surface array to form a lens array plate, and a plurality of (for example, two) lens array plates are stacked. Known (for example, Patent Document 1).

JP 2005-37891 A

  As performance required for a lens, good light condensing characteristics and high optical efficiency are required. The same applies to the lens array device described above, and further efforts have been made to improve these performances, but further improvements are desired.

  On the other hand, when a lens array device is configured with a lens array plate in which micro convex lenses are regularly arranged, a phenomenon called stray light may occur in which light incident on the lens array plate reaches an area other than the original image formation point. When stray light is generated, an unnecessary ghost image is generated on the image plane. Therefore, conventionally, a device for reducing stray light has been studied.

  However, it is not so easy to achieve both the improvement in the original performance of the lens that realizes good condensing characteristics and high optical efficiency and the desire to reduce stray light at a low cost.

  The present invention has been made in view of such circumstances, and provides a lens array device and an image forming apparatus that can improve the original performance of a lens with good light collection characteristics and high optical efficiency and reduce stray light. The purpose is to provide.

  In the lens array device according to the embodiment, a plurality of first microlenses having a biconvex incident surface and an output surface are arranged in a direction orthogonal to the optical axis, and the long side direction corresponds to the main scanning direction, and the short side direction Is a first lens array having a rectangular shape corresponding to the sub-scanning direction, and a second lens array in which a plurality of second microlenses having biconvex incident and emission surfaces are arranged in a direction perpendicular to the optical axis The plurality of second microlenses are arranged corresponding to the arrangement positions of the plurality of first microlenses, and are parallel to the first lens array on the emission side of the first lens array. And a second lens array having a rectangular shape in which the long side direction corresponds to the main scanning direction and the short side direction corresponds to the sub-scanning direction, and the plurality of first and second microlenses are Hexagon densely arranged, and The distance between the first and second microlenses arranged linearly in the main scanning direction is the distance between the first and second microlenses arranged linearly in the sub-scanning direction. It arrange | positions so that it may become larger, It is characterized by the above-mentioned.

1 is a perspective view illustrating an example of an appearance of an image forming apparatus according to an embodiment. FIG. 3 is a cross-sectional view showing an internal configuration example of the image forming apparatus according to the embodiment, and a cross-sectional view showing an arrangement example of the lens array device in the optical reading apparatus. The disassembled perspective view which shows the structural example of a lens array apparatus. The figure which shows the example of arrangement | positioning of the opening of the micro lens and aperture in a lens array. The figure which shows the cross-sectional structure example of the main scanning direction in 1st Example. The figure which shows the basic concept of the manufacturing method of a lens array apparatus. The figure which shows an example of the aspherical shape of the micro lens in a 1st Example. The figure which shows the positional relationship of the optical axis direction of the micro lens and aperture in a 1st Example. The figure which illustrates the path | route of the main scanning direction of the light ray from the object surface in the 1st Example to an image surface. FIG. 5 is a diagram illustrating an example of MTF characteristics of the lens array device according to the first embodiment. The figure which shows the cross-section structural example of the subscanning direction in 1st Example. The figure which shows the example of the arrangement | positioning of the path | route of the subscanning direction of the light ray from the object surface in the 1st Example to an image surface, and a light shielding plate. The figure which shows the hexagonal close-packed arrangement | positioning of the microlens of this embodiment, and the other hexagonal close-packed arrangement as a comparative example. The figure which shows the positional relationship of the optical axis direction of the microlens and aperture in a 2nd Example. The figure which shows the cross-section of the main scanning direction in a 2nd Example. The figure which shows an example of the aspherical surface shape of the micro lens in a 2nd Example. The figure which illustrates the path | route of the main scanning direction of the light ray from the object surface in the 2nd Example to an image surface. The figure which shows an example of the MTF characteristic of the lens array apparatus in a 2nd Example. The figure which shows the cross-section structural example of the subscanning direction in 2nd Example. The figure which shows the example of the arrangement | positioning of the path | route of the subscanning direction of the light ray from the object surface in the 2nd Example to an image surface, and a light-shielding plate. 1 is a diagram illustrating a configuration example of an image forming apparatus in which a lens array device is incorporated as an exposure device.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(1) Image Forming Apparatus FIG. 1 is a diagram illustrating an external appearance example of a copying machine (or MFP: Multi-Function Peripheral) as a typical example of an image forming apparatus 1 including a lens array device 100 according to the present embodiment. .

  The image forming apparatus 1 includes an image reading device 2, an image forming unit 3, a paper feeding unit 4, an operation unit 5, and the like.

  The image reading device 2 optically reads a document placed on a document table or a document input to an ADF 6 (Auto Document Feeder) to generate image data.

  The image forming unit 3 prints image data on a sheet supplied from the sheet feeding unit 4 using an electrophotographic method. The printed sheets are discharged and stacked on the discharge tray 7.

  The operation unit 5 is provided with a display unit as a user interface and various operation buttons.

  FIG. 2B is a schematic cross-sectional view illustrating an internal configuration example of the image forming apparatus 1. The image forming apparatus 1 has a configuration capable of color printing by, for example, a tandem electrophotographic method.

  FIG. 2A is a schematic cross-sectional view showing an example of an internal configuration of the optical reading device 20 built in the image reading device 2 of the image forming apparatus 1 in an enlarged manner. The optical reading device 20 is configured as a so-called contact optical system (CIS method: Contact Image Sensor method), and light sources 21a and 21b for irradiating a document and an optical sensor 22 composed of a CCD or the like are close to the document. Is provided. Between the document and the optical sensor 22, a lens array device 100 for forming an incident light from the document as an object surface on the optical sensor 22 is disposed. The lens array apparatus 100 forms an image of an object (in this case, a document) on the optical sensor 22 as an erecting equal-magnification image. That is, the light that has passed through the lens array device 100 is received on the optical sensor 22. A more specific configuration and structure of the lens array device 100 will be described later.

  On the other hand, the image forming unit 3 of the image forming apparatus 1 corresponds to four colors of yellow (Y), magenta (M), cyan (C), and black (K) as shown in FIG. Four photosensitive drums 10 a to 10 d are arranged in parallel along the conveyance direction of the transfer belt 30. Around each photosensitive drum 10, charging devices 11a to 11d, developing devices 12a to 12d, transfer rollers 13a to 13d, cleaners 14a to 14d, and the like are sequentially arranged from the upstream to the downstream of the rotation. Here, the letters a, b, c, and d attached to the reference numbers of the components correspond to the print colors Y, M, C, and K, respectively.

  The surfaces of the photosensitive drums 10a to 10d are uniformly charged to a predetermined potential by the charging devices 11a to 11d. Thereafter, the surface of the photosensitive drums 10a to 10d for each color is irradiated with laser light that is pulse width modulated in accordance with the level of the image data of each color of Y, M, C, and K. The image data used here is obtained by performing various types of image processing and color conversion processing on image data such as R, G, and B read by the optical reading device 20. When each laser beam is irradiated, the potential of the portion is lowered, and electrostatic latent images are formed on the surfaces of the photosensitive drums 10a to 10d.

  The developing devices 12a to 12d develop electrostatic latent images on the respective photosensitive drums 10a to 10d with toners corresponding to the respective colors. By this development, toner images of each color of Y, M, C, and K are formed on the photosensitive drums 10a to 10d.

  On the other hand, the transfer belt 30 is looped around a drive roller 31 and a secondary transfer counter roller 32 and is continuously rotated in the direction of the arrow shown by the drive roller 31.

  While the transfer belt 30 passes through each nip formed by the photosensitive drums 10a to 10d and the transfer rollers 13a to 13d, toner images of Y, M, C, and K colors are sequentially formed on the outer peripheral surface of the transfer belt 30. It will be transcribed.

  First, a Y toner image is transferred from the photosensitive drum 10a to the transfer belt 30 at a position where the Y photosensitive drum 10a and the Y transfer roller 13a face each other (Y transfer position).

  Next, the M toner image is transferred from the photosensitive drum 10b to the transfer belt 30 at a position where the M photosensitive drum 10b and the M transfer roller 13b face each other (M transfer position). At this time, the M toner image is transferred so that the position overlaps with the Y toner image already transferred to the outer peripheral surface of the transfer belt 30.

  Thereafter, similarly, the C toner image and the K toner image are sequentially superimposed on the outer peripheral surface of the transfer belt 30 and transferred, and a full-color toner image is formed on the transfer belt 30. The full-color toner image reaches the nip (secondary transfer position) formed by the secondary transfer roller 33 and the secondary transfer counter roller 32 as the transfer belt 30 moves.

  On the other hand, the paper picked up from one of the paper feed cassettes 4A, 4B, 4C of the paper feed unit 4 is conveyed to the secondary transfer position. Then, at this secondary transfer position, the full-color toner image on the transfer belt 30 is transferred to the paper. The full-color toner image is heated and pressurized by the fixing device 40 and fixed on the paper. Thereafter, the paper is discharged onto the paper discharge tray 7 by the paper discharge roller 34.

  In each of the photoconductive drums 10a to 10d after the transfer to the transfer belt 30, the toner remaining on the surface is removed by the cleaners 14a to 14d to prepare for the printing of the next sheet. By repeating the above processing, continuous full color printing can be performed.

  On the other hand, when performing monochrome printing, the K toner image is transferred to the transfer belt 30 only by the K photoconductor drum 10d and the transfer roller 13d, and the Y, M, and C photoconductor drums 10a to 10c and the transfer roller 30d are transferred. The rollers 13a to 13c are not used.

(2) Lens array device (first embodiment)
3A is a cross-sectional view of the same optical reading device 20 as FIG. 2A, and FIG. 3B is an exploded perspective view schematically showing the configuration of the lens array device 100 according to the present embodiment. is there.

  As shown in FIG. 3B, the lens array device 100 includes a first aperture 201, a first lens array 101, a first inner aperture 301, a second inner aperture 302, and a second lens array along the light beam traveling direction. 102 and the second aperture 201 are sequentially stacked.

  Each of the apertures 201, 202, 301, 302 and the lens arrays 101, 102 has a rectangular shape that is long in the main scanning direction and short in the sub scanning direction. Here, the main scanning direction refers to the front / rear direction (the depth of the paper surface in FIG. 2B) when the side on which the operation unit 5 is arranged in FIG. 1 is the front side and the opposite side is the rear side. The sub-scanning direction is a document reading direction (left-right direction in FIG. 2B) orthogonal to the main scanning direction.

  The first lens array 101 includes a large number of minute microlenses (first macrolens 111) having biconvex entrance and exit surfaces in a direction perpendicular to the optical axis of each microlens (that is, on the array plane). It is configured by arranging. Similarly, in the second lens array 102, a minute microlens (second macrolens 112) having a biconvex entrance surface and an exit surface is arranged in a direction perpendicular to the optical axis of each microlens (that is, on the array plane). B) a large number of arrays. The first lens array 101 and the second lens array 102 are arranged in parallel to each other, and the positions of the second microlenses 112 correspond to the arrangement positions of the first microlenses 111.

  The first aperture 201 is a thin plate-like member in which a plurality of minute openings 211 are formed corresponding to the positions of the plurality of first microlenses 111, and the first aperture 201 is arranged on the incident surface side of the first lens array 101. The lens 111 is disposed orthogonal to the optical axis. Each opening 211 allows light to pass through, but the region other than each opening 211 of the thin plate member blocks incident light.

  Similarly, the second aperture 202 is a thin plate-like member in which a plurality of openings 212 are formed corresponding to the positions of the plurality of second microlenses 112, and on the emission surface side of the second lens array 102, The micro lens 112 is disposed perpendicular to the optical axis. Each opening 212 allows light to pass through, but a region other than each opening 212 of the thin plate member blocks light emitted from the second lens array 102.

  Further, first and second inner apertures 301 and 302 are disposed between the first lens array 101 and the second lens array 102, respectively. The first inner aperture 301 is a thin plate member in which a plurality of openings 311 are formed corresponding to the positions of the plurality of first microlenses 111, and is close to the exit surface side of the first lens array 101. Arranged. The second inner aperture 302 is a thin plate member in which a plurality of openings 312 are formed corresponding to the positions of the plurality of second microlenses 112, and is close to the incident surface side of the second lens array 102. Arranged.

  The respective apertures 211, 212, 311 and 312 of the respective apertures 201, 202, 301 and 302 have the same diameter, and are arranged without being eccentric with respect to the light beam traveling direction. The opening 211 and the opening 212 may have the same diameter, the opening 311 and the opening 312 may have the same diameter, and the respective diameters may be different. Each of the microlenses 111 and 112 in the first and second lens arrays 101 and 102 has a lens effective diameter that is substantially the same as or larger than the aperture diameter of each aperture. And the center positions of the apertures 211, 212, 311, 312 of each aperture are arranged at the same position.

  Therefore, the arrangement pattern seen from the optical axis direction of the respective apertures 211, 212, 311 and 312 in each aperture 201, 202, 301 and 302, and the respective microlenses 111 in the first and second lens arrays 101 and 102, The arrangement pattern viewed from the optical axis direction 112 is the same. Therefore, in the following description, when the arrangement pattern viewed from the optical axis direction is described, it is simply described as the arrangement of the microlenses 111 and the like.

  4A and 4B are diagrams illustrating an example of the arrangement of the microlenses 111 and the like according to the present embodiment. FIG. 4B is a diagram showing the entire array (however, a part in the main scanning direction is omitted), and FIG. 4A is an enlarged view of a part of the array.

For the microlenses 111 and the like, an array in which nine microlenses 111 and the like are arranged in a straight line in the sub-scanning direction and an array in which eight microlenses 111 are arranged in a straight line are alternately repeated in the main scanning direction. Pitch () _{D X} of the centers of such microlenses 111 in the sub-scanning direction, in this example, a 0.4mm as shown in Figure 4 (a). Therefore, the width of the first and second lens arrays 101 and 102 and the apertures 201, 201, 301, and 302 in the sub-scanning direction is approximately 0.4 mm × 8 = 3.2 mm. The number of arrays in the sub-scanning direction is not limited to the above nine and eight, and may be eight and seven, for example.

On the other hand, the main arranged in a row in the scanning direction spacing of the centers of such each microlens 111 (pitch) _{D Y} is, in this example, is 0.694Mm. The microlenses 111 and the like are arranged in 447 columns (the number of columns whose centers coincide with the main scanning direction) in the main scanning direction, and the first and second lens arrays 101 and 102, each aperture 201, The length of 201, 301, 302 in the main scanning direction is approximately 0.694 mm × 447 = 310 mm.

Is like a microlens 111, FIG. 4 (a), the has a hexagonal close-packed arrangement (b), the better the pitch D _Y in the main scanning direction, is larger than the pitch D _X in the sub-scanning direction Yes.

First, the lens effective diameter of the second microlenses 111, 112 are 0.4 mm, the same as the pitch _{D X} in the sub-scanning direction. On the other hand, the diameters of the apertures 211, 212, 311 and 312 of each aperture are 0.35 mm (radius 0.175 mm), which is set slightly smaller than the pitch D _X (0.4 mm) in the sub-scanning direction. .

  Therefore, on the line in the sub-scanning direction connecting the centers of the openings (211, 212, 311, 312) (on the line XX ′ in FIG. 4A), there is a light-shielding region of 0.05 mm between adjacent openings. Exists.

  On the other hand, on the line in the main scanning direction connecting the centers of the openings (211, 212, 311, 312) (on the YY ′ line in FIG. 4A), 0.344 mm (0.694 mm) between adjacent openings. -0.35 mm) light-shielding area exists.

  Next, the arrangement and structure of the lens array device 100 (first embodiment) in the thickness direction (that is, the optical axis direction) will be described.

FIG. 5A is a diagram showing a cross section in the optical axis direction in the main scanning direction, and is a YY ′ cross sectional view in FIG. FIG. 5B is an enlarged view of a part of FIG. In FIG. 5B, the microlenses 111 and 112 indicated by solid lines are the microlenses centered on the YY ′ line in FIG. 4A, and the microlens indicated by the broken line is halfway from the YY ′ line. This is a microlens centered at a position separated in the sub-scanning direction by a pitch (D _X / 2).

  In the lens array device 100 according to the present embodiment, unlike the incident surface shape S1 and the exit surface shape S2 of the first microlens 111 of the first lens array 101 disposed on the incident side, the second array disposed on the exit side. The second microlens 112 of the lens array 102 also has a first feature that the incident surface shape S2 and the output surface shape S1 are different. On the other hand, the incident surface shape S1 of the first microlens 111 and the exit surface shape S1 of the second microlens 112 are the first spherical surface S1 or the same aspherical surface, and the first microlens 111 is the first microlens. There is also a second feature that the exit surface shape S2 of 111 and the incident surface shape S2 of the second microlens 112 are the second shape S2 having the same spherical surface or the same aspherical surface.

  The first feature and the second feature described above are closely related to the condensing characteristic (a characteristic for reducing aberration) of the lens array device 100 and the manufacturing direction of the lens array device 100, which will be described below.

  In general, when a plurality of lens arrays (for example, two as in the present embodiment) are overlapped to form an erecting equal-magnification lens array device, if microlenses at corresponding positions are eccentric, The light condensing performance deteriorates rapidly. When a lens array is manufactured by molding a resin with a mold, if each lens array that forms a set with different molds or different cavities is molded separately, individual differences between the molds and the cavities themselves and temperature in the molds are reduced. Due to the uniformity, there is a shift in the shape of the microlens and the center position of the microlens between the generated lens arrays, and the positions of all the microlenses are completely changed between the paired lens arrays. It will be difficult to match. In particular, in the longitudinal direction of the lens array, the absolute amount of contraction during cooling and the change in position of the microlens due to the environment during use increases, and the eccentricity of the microlenses at the corresponding positions increases.

  Therefore, in the lens array device 100 according to the present embodiment, two lens arrays (first and second lens arrays) are formed using the same mold and the same cavity as shown in FIG. It is produced by resin molding. By this manufacturing method, shrinkage during formation and eccentricity between microlenses located at corresponding positions with the same internal residual stress can be reduced.

  On the other hand, it is known that spherical aberration and coma aberration can be simultaneously reduced by making the entrance surface and exit surface of the lens different from each other. For example, when each shape of the biconvex lens is a spherical surface, by setting the curvature of the entrance surface and the curvature of the exit surface to different values, the lens of spherical aberration and coma aberration that are smaller than those of the same curvature on both sides Is obtained.

  On the other hand, when combining two lenses, the shape of the lens on the incident side and the lens on the output side should be symmetrical with respect to the center plane (surface perpendicular to the optical axis) sandwiched between the two lenses. Thus, it is also known that distortion can be reduced. This is because the distortion occurring in the incident side lens and the distortion occurring in the exit side lens are canceled out, so that the shape of the entrance side lens and the exit side lens is completely the center of the two lenses. In the case of a symmetrical shape, the distortion aberration can theoretically be zero.

  Therefore, in the lens array device 100 according to the present embodiment, two lens arrays having different shapes (S1 and S2) of the entrance surface and the exit surface of the microlens are formed using the same mold and the same cavity. By using and molding by resin molding, two lens arrays having small spherical aberration and coma aberration and small eccentricity between corresponding microlenses are generated. Then, when the two lens arrays are overlapped, as shown in the lower right of FIG. 6, one of the two lens arrays is overlapped after being inverted in the lateral direction (sub-scanning direction) of the lens array. I have to. By reversing one lens array, the surfaces of the same shape (S2 in the example of FIG. 6) face each other with respect to the center of the lens array, and the first lens array 101 and the second lens array 102 Is symmetrical with respect to. As a result, distortion can be reduced as described above.

  Note that when one lens array is inverted, it may be inverted in the longitudinal direction of the lens array. However, even if two lens arrays are molded with the same mold and the same cavity, the microlens in the longitudinal direction is caused by the non-uniformity of the temperature distribution in the cavity and the environment during use. The magnitude of the displacement is inevitably larger than the displacement in the short direction. Therefore, when reversing one lens array, the direction of the two lens arrays when molded in the cavity is matched in the longitudinal direction and the short direction is reversed, so that the eccentricity of the corresponding micro lens is minimized. Can be suppressed.

  In the above description, the spherical aberration and the coma aberration can be reduced by making the entrance surface and the exit surface of the microlens different shapes, but the entrance surface and the exit surface are made aspherical (No. 1). (3), spherical aberration and coma aberration can be further reduced.

  FIGS. 7A and 7B are diagrams showing an example of the aspherical shape of the microlens of the present embodiment. As shown in FIG. 7A, the entrance surface shape S1 of the first microlens 111 and the exit surface shape S1 of the second microlens 112 have the largest absolute value of curvature at the center of the lens, and go to the outside of the lens. As the absolute value of curvature gradually decreases, the aspherical shape is reduced. Further, as shown in FIG. 7B, the exit surface shape S2 of the first microlens 111 and the entrance surface shape S2 of the second microlens 112 have an absolute curvature in the vicinity of the center of the lens as the distance from the optical axis of the lens increases. Although the value is small, it has an aspherical shape in which the absolute value of the curvature increases as the distance from the optical axis increases.

  In the case of a spherical lens with a uniform curvature, a certain amount of spherical aberration occurs due to the converging position approaching the lens side as the incident position of the parallel rays moves away from the optical axis of the lens. By making the absolute value smaller as it moves away from the optical axis (increase the absolute value when the power is negative), it is possible to concentrate the condensing position at one point regardless of the incident position of the parallel rays. And can improve the light condensing characteristics.

  FIG. 8 is a diagram for explaining a fourth feature of the lens array device 100 according to the present embodiment. The fourth feature is that the position of the first aperture 201 in the optical axis direction is arranged in the vicinity of the front focal position of the first microlens 111 of the first lens array 101, and the optical aperture direction of the second aperture 202 is set. The position is arranged in the vicinity of the rear focal position of the second microlens 112 of the second lens array 102.

  As described above, the shapes of the first lens array 101 and the first lens array 102 are symmetric with respect to the center plane CP shown in FIG. In this embodiment, the distance on the optical axis from the vertex of the incident surface of the first microlens 111 to the first aperture 201 and the optical axis from the vertex of the emission surface of the second microlens 112 to the second aperture 201 are also shown. Further, the distance from the object plane to the first aperture 201 and the distance from the second aperture 201 to the image plane are set to be equal. That is, in the lens array device 100 of the present embodiment, the lens array apparatus 100 is symmetric with respect to the center plane CP including the object plane to the image plane.

  Therefore, the positional relationship between the second aperture 202 and the second lens array 102 shown in FIG. 8 corresponds to the positional relationship between the first aperture 201 and the first lens array 101 as it is.

  FIG. 8 shows the result of calculating where the parallel light is incident on the incident surface S2 of the second microlens 112 and where the light emitted from the exit surface S1 is collected. Then, an opening 212 of the second aperture 202 is disposed in the vicinity of the condensing position when parallel light is incident on the incident surface S2 of the second microlens 112, that is, in the vicinity of the rear focal position of the second microlens 112. Yes. With such an arrangement, light from the object plane can be transmitted to the image plane with high optical efficiency.

  When the sum of the amounts of light output from the point light source on the object plane toward the hemisphere in the image plane direction is defined as P0, the received light amount on the image plane is defined as PI, and the optical efficiency η is defined as η = PI / P0, the lens When the reflection on the surface is not taken into consideration, the calculated value of the optical efficiency η is 7.37%, which is a considerably high value.

  FIG. 9 is a diagram illustrating a result of calculating the path in the main scanning direction of the light beam emitted from the object points a and b on the object plane to the image plane. The object points a and b on the object plane are imaged as image points a 'and b' on the image plane at the same intervals and in the same direction, and an erect life-size image is obtained.

  On the other hand, an inverted image of the object is formed at the position of the center plane between the first and second lens arrays 101 and 102, as can be seen from FIG.

  The fifth feature of the lens array device 100 according to the present embodiment is that the first and second inner apertures 301 and 302 are arranged at a position other than the position where the inverted image is formed. That is, the first inner aperture 301 is disposed closer to the exit surface side of the first lens array 101 than the position where the inverted image is formed, and the second inner aperture 302 is second than the position where the inverted image is formed. The lens array 102 is disposed close to the incident surface side. If the first and second inner apertures 301 and 302 are present at the position where the inverted image is formed, the aperture of each aperture may be slightly decentered or the aperture diameter may not be as designed. As a result, many of the light rays that should not be shielded may be shielded, and conversely, many of the light rays that should be shielded may not be shielded. In the present embodiment, such a situation is avoided by arranging the first and second inner apertures 301 and 302 at a position other than the position where the inverted image is formed.

  One of the indexes representing the light collection characteristics or resolution of the lens system is MTF (Modulation Transfer Function). MTF is the ratio of the degree of modulation on the lens output side to the degree of modulation on the input side when the object light source having a predetermined spatial frequency (cycle / mm) is input to the lens system. is there.

  FIG. 10 is a graph in which the MTF (vertical axis) at 6 cycle / mm is plotted with the horizontal axis as the defocus position. In the graph of FIG. 10, a plurality of curves are displayed in an overlapping manner. Each curve has a case where an object point is placed at the center of the optical axis on the object plane and a plurality of Field Points apart from the center of the optical axis. The MTF in the case where an object point is placed on is shown. Further, T and S shown in the upper left of FIG. 10 correspond to the tangential direction (horizontal direction) and the sagittal direction (vertical direction), respectively. As can be seen from FIG. 10, at each field point, the MTF is approximately 55% or more in the range of the focal position ± 0.1 mm, and the MTF characteristics are good.

  Up to this point, the cross-sectional configuration and light beam path in the main scanning direction have been described. Next, the cross-sectional structure and light beam path in the sub-scanning direction will be described.

FIG. 11A is a diagram illustrating a cross section in the sub-scanning direction, and is a cross-sectional view taken along the line XX ′ in FIG. Moreover, FIG.11 (b) is the figure which expanded a part of Fig.11 (a). In FIG. 11B, the microlenses 111 and 112 indicated by solid lines are microlenses centered on the line XX ′ in FIG. 4A, and the microlens indicated by the broken line is halfway from the line XX ′. This is a microlens centered at a position separated in the sub-scanning direction by a pitch (D _Y / 2).

As described above, the microlenses 111 and the like in the lens array device 100 of the present embodiment are arranged in a hexagonal close-packed arrangement as shown in FIGS. 4 (a) and 4 (b). The hexagonal close-packed arrangement is a method for arranging circles having the same diameter at the highest density. Further, the characteristic arrangement method in this embodiment, towards the pitch D _Y in the main scanning direction is in a point that is larger than the pitch D _X in the sub-scanning direction. Hereinafter, this feature will be described.

  FIG. 12 is a diagram illustrating a result of calculation of a path in the sub-scanning direction of light beams emitted from the object points a and b on the object plane to the image plane, and is a diagram corresponding to FIG. 9 illustrating a light beam path in the main scanning direction. is there. It should be noted here that stray light is generated in the light path in the sub-scanning direction shown in FIG. 12, whereas stray light is not generated in the light path in the main scanning direction shown in FIG. . The stray light is light that a light beam emitted from an object point on the object plane reaches other than the corresponding image point on the image plane.

  If stray light is generated in the main scanning direction, the stray light enters an optical sensor that is long in the main scanning direction. If a light-shielding plate is inserted in front of the optical sensor in order to block this stray light, even regular light from the object point is blocked, so regular light and stray light cannot be spatially separated.

  On the other hand, even if stray light occurs in the sub-scanning direction, since the width of the optical sensor in the sub-main scanning direction is small, a light shielding plate is provided between the optical sensor (image plane) and the lens array device 100 as shown in FIG. Even if 500a and 500b are arranged, regular light is not blocked from an object point. The light-shielding plates 500a and 500b are, for example, two rectangular plate-like members that are long in the main scanning direction (the depth direction of the paper surface in FIG. 12) and short in the sub-scanning direction, and do not hinder the passage of regular light rays from the object point. , And at a position that sufficiently blocks stray light. A part having a slit-like opening having a rectangular hole in the center may be used.

In the present embodiment, the length of the light shielding region of the microlens 111 or the like while still a hexagonal close-packed arrangement, the pitch D _Y in the main scanning direction larger than the pitch D _X in the sub-scanning direction, between the opening of each aperture In order to suppress the generation of stray light in the main scanning direction. On the other hand, although the sub-scanning direction of the stray light for the smaller pitch D _X in the sub-scanning direction tends to occur, for this stray light, the configuration of providing the light shielding plate between the lens array unit 100 and the image point This eliminates adverse effects of stray light on the optical sensor.

  FIG. 13 is a diagram showing another arrangement for obtaining hexagonal denseness as a comparative example with respect to the arrangement of microlenses and the like (FIG. 13C) in this embodiment.

Comparative Example 1 shown in FIG. 13A is an arrangement that has been used relatively frequently. Arrangement of Comparative Example 1 is an arrangement pitch D _Y in the main scanning direction is smaller than the pitch D _X in the sub-scanning direction, the stray light is likely to occur in the main scanning direction.

  On the other hand, Comparative Example 2 shown in FIG. 13B is disclosed in Patent Document 1 as an arrangement for reducing stray light, and the main arrangement direction of the lenses is inclined with respect to the main scanning direction. In the case of this arrangement, the difference between the shortest part and the longest part in the sub-scanning direction is 0.776P (P is a pitch) on one side and 1.452P on both sides. On the other hand, the difference between the shortest portion and the longest portion in the sub-scanning direction in this embodiment is 0.5P on one side (1.0P on both sides), and the arrangement of Comparative Example 2 is compared with the arrangement of this embodiment. The utilization efficiency of the end region in the sub-scanning direction is low.

  Further, the arrangement of Comparative Example 2 is an asymmetric arrangement in the vertical direction with respect to the center in the sub-scanning direction. For this reason, the configuration of this embodiment (see the lower right in FIG. 6) in which one of the two lens arrays is reversed and overlapped in the sub-scanning direction cannot be taken. Therefore, the technical effect peculiar to the present embodiment that distortion can be reduced by making the shape of the lens on the entrance side and the lens on the exit side symmetrical with respect to the center plane of the space sandwiched between the two lenses. Cannot be obtained with the configuration of Comparative Example 2.

  In contrast to these comparative examples, the arrangement of the present embodiment can eliminate the influence of stray light, and the lens array device 100 with high utilization efficiency of the end region in the sub-scanning direction and low distortion. realizable.

(3) Lens array device (second embodiment)
FIG. 14 is a diagram illustrating differences between the lens array device 100 according to the first embodiment and the lens array device 100 according to the second embodiment. As can be seen from comparison with FIG. 8 showing the first embodiment, in the second embodiment, the region in which the second aperture 202 is substantially coincident with the vertex position of the emission surface S1 of the second microlens 112 is Only near the optical axis. Further, although not shown in FIG. 14, the region where the first aperture 201 is substantially coincident with the apex position of the incident surface S <b> 1 of the first microlens 111 is only in the vicinity of the optical axis. This arrangement has been found that the collimated light collection position is slightly outside the thickness of the aperture, but the optical efficiency itself is not significantly reduced. As a result of performing the calculation equivalent to that of the first example, the calculated value of the optical efficiency η is 6.77%, which is a value comparable to 7.37% of the first example. ing.

  The main differences between the second embodiment and the first embodiment are as described above, and other structures and features are common to the second embodiment and the first embodiment. Hereinafter, the correspondence between the explanatory diagram of the first embodiment and the explanatory diagram of the second embodiment will be shown.

  FIG. 15 is a diagram showing a cross-sectional configuration in the main scanning direction in the second embodiment, and corresponds to FIG. FIG. 16 is a diagram illustrating the curvatures of the aspherical shapes S1 and S2 of the microlens in the second embodiment, and corresponds to FIG. FIG. 17 is a diagram illustrating an example of a result of calculating a path in the main scanning direction of a light ray from the object point on the object plane to the image plane in the second embodiment, and corresponds to FIG. In the second embodiment as well, no stray light is generated in the main scanning direction. FIG. 18 is a diagram illustrating an example of the MTF calculation result in the second embodiment, and corresponds to FIG. Also in the second embodiment, at each field point, the MTF is approximately 55% or more in the range of the focal position ± 0.1 mm, and the MTF characteristics are good.

  FIG. 19 is a diagram showing a cross-sectional configuration in the sub-scanning direction in the second embodiment, and corresponds to FIG. FIG. 20 is a diagram illustrating an example of a result of calculating a path in the sub-scanning direction of a light beam from the object point on the object plane to the image plane in the second embodiment, and corresponds to FIG. Also in the second embodiment, stray light is generated in the sub-scanning direction, and this stray light can be blocked by the light shielding plate.

(4) Application of lens array apparatus to exposure apparatus So far, the embodiment in which the lens array apparatus 100 is incorporated in the optical reading apparatus 20 that reads a document has been described. However, the application of the lens array apparatus 100 according to the present embodiment has been described. It is not limited to the optical reader 20. For example, as shown in FIG. 21, the image forming apparatus 1 can be incorporated in the exposure apparatus 200. In this embodiment, an arrayed LED light source that is long in the main scanning direction is disposed at a position corresponding to the object plane, and the photosensitive drum 10 is disposed at a position corresponding to the image plane. That is, the light that has passed through the lens array device 100 is irradiated onto the photosensitive drum 10. Even in this configuration, the lens array device 100 of the present embodiment having good light collection characteristics and high optical efficiency functions effectively.

  As described above, according to the lens array device 100 of the present embodiment, it is possible to improve the original performance of the lens, such as good condensing characteristics and high optical efficiency, and reduce stray light.

In the present exemplary embodiment, the image forming apparatus 1 is defined as including the image reading apparatus 2 and the image forming unit 3. However, the image forming apparatus is not limited to these embodiments, and only the image reading apparatus 2 shown in FIG. 1 may be defined as an image forming apparatus.

  Although several 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 embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image reading apparatus 100 Lens array apparatus 101 1st lens array 102 2nd lens array 111 1st micro lens 112 2nd micro lens 201 1st aperture 201 2nd aperture 301 1st inside aperture 302 2nd inside aperture

Claims (11)

A plurality of first microlenses having a biconvex incident surface and an output surface are arranged in a direction orthogonal to the optical axis, the long side direction corresponds to the main scanning direction, and the short side direction corresponds to the sub scanning direction. A first lens array comprising:
A plurality of second microlenses whose incident surfaces and output surfaces are biconvex are arranged in a direction perpendicular to the optical axis, wherein the plurality of second microlenses are the plurality of second microlenses. Are arranged corresponding to the arrangement position of one microlens, arranged parallel to the first lens array on the emission side of the first lens array, the long side direction corresponds to the main scanning direction, and the short side A second lens array whose direction is a rectangle corresponding to the sub-scanning direction;
With
The plurality of first and second microlenses are arranged in a hexagonal close-packed manner, and a distance between each of the first and second microlenses arranged linearly in the main scanning direction is the sub-scanning direction. Arranged so as to be larger than the interval between the first and second microlenses arranged in a straight line.
A lens array device. In the first and second microlenses, an odd number array and an even number array arranged in a straight line in the sub-scanning direction are arranged in parallel, and the odd number array and the even number array are arranged in parallel. The pairs are arranged to repeat in the main scanning direction;
The lens array device according to claim 1. A light shielding member that is disposed between the second lens array and the image plane and shields stray light in the sub-scanning direction;
The lens array device according to claim 1, further comprising: The light shielding members are two rectangular plate-like members that are long in the main scanning direction and short in the sub-scanning direction, and each of the two plate-like members is incident from an object point toward the first lens array. The regular light beam that is imaged on the image plane is sandwiched from the opposite direction so as not to obstruct the path, and the stray light that takes a path other than the normal light path is disposed at a position that blocks the stray light.
The lens array device according to claim 3. A thin plate-like member in which a plurality of openings are formed corresponding to the respective positions of the plurality of first microlenses, and is disposed on the incident surface side of the first lens array and orthogonal to the optical axis. A first aperture to be
A thin plate-like member in which a plurality of openings are formed corresponding to the respective positions of the plurality of second microlenses, and is disposed on the exit surface side of the second lens array so as to be orthogonal to the optical axis. A second aperture to be
The lens array device according to claim 1, further comprising: Unlike the entrance surface shape and the exit surface shape of the first microlens, the second microlens also differs from the entrance surface shape and the exit surface shape, while the entrance surface shape of the first microlens is different from the entrance surface shape of the first microlens. The exit surface shape of the second microlens is a first shape having the same spherical surface or the same aspheric surface, and the exit surface shape of the first microlens and the entrance surface shape of the second microlens Are second shapes forming the same spherical surface or the same aspherical surface,
The lens array device according to claim 1, wherein The first lens array and the second lens array are obtained by arranging two lens arrays formed using the same cavity of the same mold.
The lens array device according to claim 1, wherein The first lens array and the second lens array have a short direction of one of the two rectangular resinous lens arrays formed using the same cavity of the same mold. It is a reversed arrangement,
The lens array device according to claim 1, wherein A lens array device according to claim 1;
An optical sensor that receives light that has passed through the lens array device;
An image forming apparatus comprising: A lens array device according to claim 1;
A photosensitive drum irradiated with light that has passed through the lens array device;
An image forming apparatus comprising: In the first and second microlenses, an odd number array and an even number array arranged in a straight line in the sub-scanning direction are arranged in parallel, and the odd number array and the even number array are arranged in parallel. The pairs are arranged to repeat in the main scanning direction;
The image forming apparatus according to claim 10.