JP7082319B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus having an optical writing unit, and more particularly to an image forming apparatus including an imaging optical system for forming an image of a light emitting point cloud on a light receiving surface.

Conventionally, an optical book including a light emitting substrate in which a plurality of light emitting point clouds composed of a plurality of light emitting points are arranged in a main direction and a plurality of sub directions, and a lens array in which an imaging lens is arranged so as to face each other in a one-to-one manner with respect to each light emitting point cloud. An image forming apparatus having a recess is known. In the optical writing unit of such an image forming apparatus, the light emitted from the light emitting point is made into a desired beam spot at a desired position on the photoconductor by interposing an imaging lens.

In each element optical system arranged in the order of the light source, the front lens array, the aperture, the rear lens array, and the image plane from the light source side along the optical axis, the incident light rays have different rows or apertures of the element optical system. It is desirable to arrange a light-shielding body on the light source side of the front lens array in order to prevent it from passing through and becoming stray light. However, this light-shielding body alone cannot completely block the light passing through the peripheral portion of the light-shielding body and advancing to the apertures of different rows, and there is a possibility that stray light may occur.

Further, like the optical system of the lens array mounted on the image forming apparatus of Patent Document 1, two transparent plates are provided between the two lens arrays, and a light-shielding portion having a light-shielding pattern formed on each surface of the transparent plates is provided. There is something provided. In Patent Document 1, there are three openings corresponding to each light-shielding pattern along the optical axis, and in order to block light rays that reduce the contrast of the imaged image of the light emitting portion, the central portion formed between the two transparent plates is formed. The diameter of the opening provided in the light-shielding pattern is minimized. However, in the image forming apparatus of Patent Document 1, when the light emitting points are not on the same plane, the optical system cannot completely block the light traveling to the light blocking pattern of different rows, and it is not possible to efficiently prevent the stray light. Have difficulty.

Japanese Unexamined Patent Publication No. 2008-0887185

The present invention has been made in view of the above background technique, and an object of the present invention is to provide an image forming apparatus provided with an optical writing unit that efficiently prevents stray light when the light emitting point cloud is not on the same plane. ..

In order to solve the above problems, the image forming apparatus according to the present invention has a photoconductor having a surface conveyed in a subdirection substantially orthogonal to the main direction, and a light emitting substrate having a plurality of light emitting point groups arranged in two dimensions. And a plurality of imaging optics for forming an image of light from a plurality of emission point groups at different positions on the photoconductor, the optical axes of the plurality of imaging optics are parallel to each other, and a plurality of imaging is performed. The imaging magnification of the optical system is substantially equal for each emission point group, and the plurality of imaging optical systems are a first lens array having a plurality of imaging lenses arranged facing the emission point group and a first lens array. A second lens array having a plurality of imaging lenses arranged opposite to each of the plurality of imaging lenses constituting the above, and arranged so as to face the plurality of imaging lenses between the first and second lens arrays. The center point of the light emitting point group is located on the first plane which is substantially the same plane, and the center points of the plurality of imaging lenses constituting the first lens array are substantially the same plane. It exists in a second plane, the first plane has a predetermined non-zero angle with respect to the plane perpendicular to the optical axis, and the second plane has a predetermined non-zero angle with respect to the plane perpendicular to the optical axis. None, the plurality of light beam control plates are substantially parallel to the second plane, and the light beam control plate has a plurality of openings through which light passes and a plurality of light shielding portions surrounding the openings to block light. The opening having the smallest diameter along the optical axis is the minimum opening, and the minimum opening is arranged on different surfaces of a plurality of light beam control plates for an imaging lens array having different arrangements in the subdirection. The lens.

According to the image forming apparatus, the first lens array and the light flux regulating plate are substantially parallel to each other, and the minimum opening is provided on different surfaces of the plurality of light flux regulating plates in order to prevent stray light from the first lens array. It is possible to form an image with substantially the same magnification for each light emitting point group while achieving high light-shielding performance by arranging the light flux regulating plate which is a member of the above in close proximity. As a result, even if the positions of the light emitting point clouds in the optical axis direction are different, it is possible to suppress variations in the magnification of each imaging lens and achieve a highly manufacturable stray light prevention function.

In one specific aspect of the present invention, in the image forming apparatus, the diameter of the opening closest to the first lens array along the optical axis among the plurality of openings is larger than the minimum opening. In this case, the luminous flux control plate closest to the first lens array has a stray light prevention function.

In another aspect of the present invention, as a plurality of luminous flux control plates, a light-shielding plate arranged closest to the first lens array and a plurality of diaphragm plates arranged between the light-shielding plate and the second lens array are provided. Have.

In yet another aspect of the present invention, the luminous flux control plate has a light-shielding layer constituting a light-shielding portion on at least one surface of a flat plate having light transmission. In this case, since the diaphragm position and the diaphragm shape can be formed more accurately, the telecentricity on both sides can be further enhanced.

In yet another aspect of the present invention, a light shielding body is provided between the light emitting point cloud and the first lens array. In this case, stray light can be prevented more.

In yet another aspect of the invention, the plurality of luminous flux control plates have the same thickness. In this case, since the same manufacturing apparatus and the same material can be used, the manufacturability can be improved.

In yet another aspect of the present invention, the center points of the plurality of imaging lenses constituting the second lens array are located in a third plane which is substantially the same plane, and the first plane and the plane perpendicular to the optical axis direction. The angle formed is θa, the angle formed by the second plane and the plane perpendicular to the optical axis direction is θb, and the angle formed by the plane connecting the center points of the plurality of minimum openings and the plane perpendicular to the optical axis direction is defined as the angle formed. When θc is set and the angle formed by the third plane and the plane perpendicular to the optical axis direction is θd, the following relationship θa>θb>θc> θd
Meet. When the positions of the light emitting point clouds in the optical axis direction are different, the variation in magnification can be suppressed by satisfying the above relationship.

It is a partial cross-sectional view which shows the schematic structure of the image forming apparatus of 1st Embodiment. It is a conceptual diagram of the side surface side explaining the structure of an optical print head which constitutes an image formation unit. (A) is a conceptual perspective view for explaining the structure of a light emitting element, (B) is a diagram for explaining a light emitting point cloud provided in the light emitting element, and (C) is a light emitting point cloud and a lens. It is a figure explaining the arrangement of. (A) and (B) are conceptual diagrams illustrating a specific optical system of an optical print head. It is a figure explaining the modification of the optical print head of FIG. (A) and (B) are conceptual diagrams illustrating a specific optical system of an optical print head mounted on the image forming apparatus of the second embodiment. It is a conceptual diagram explaining the specific optical system of the optical print head mounted on the image forming apparatus of 3rd Embodiment.

[First Embodiment]
As shown in FIG. 1, the image forming apparatus 100 of the embodiment is used as, for example, a digital copier, and has an image reading unit 10 for reading a color image formed on a document D and an image corresponding to the document D on paper P. The image forming unit 20 formed in the image forming unit 20, the feeding unit 40 for feeding the paper P to the image forming unit 20, the conveying unit 50 for conveying the paper P, and the control unit 90 for comprehensively controlling the operation of the entire apparatus. including.

The image forming unit 20 includes an image forming unit 70Y, 70M, 70C, 70K provided for each of the cyan, magenta, yellow, and black colors, an intermediate transfer unit 81 on which a toner image obtained by synthesizing each color is formed, and a toner. It is provided with a fixing portion 82 for fixing an image.

Of the image forming units 20, the image forming unit 70Y is a portion that forms a Y (yellow) color image, and includes a photosensitive drum 71, a charging unit 72, an optical print head (optical writing device) 73, a developing unit 74, and the like. It is equipped with. The photosensitive drum 71 forms a Y-color toner image, the charging portion 72 is arranged around the photosensitive drum 71, and the surface of the photosensitive drum 71 is charged as a photosensitive member by corona discharge, and the optical print head 73 is photosensitive. The drum 71 is irradiated with light corresponding to the image of the Y color component, and the developing unit 74 forms a toner image from the electrostatic latent image by adhering the toner of the Y color component to the surface of the photosensitive drum 71. The photosensitive drum 71 has a cylindrical shape and rotates around the rotation axis RX. The cylindrical surface of the photosensitive drum 71 is a light receiving surface 71a for forming an image by the optical print head 73.

Since the other image forming units 70M, 70C, and 70K have the same structure and function as the image forming unit 70Y for Y color except that the colors of the images to be formed are different, the description of these structures and the like will be omitted. The image forming unit 70 means any unit among the four color image forming units 70Y, 70M, 70C, and 70K, and as elements adapted to each color, the photosensitive drum 71, the charging unit 72, and the optical print are used. It includes a head 73 and a developing unit 74.

FIG. 2 is a side view of the optical print head 73. The optical print head 73 is exposed to light from a light emitting element 73a having light emitting areas 3a, 3b, 3c forming a two-dimensionally arranged light emitting point group DG, and light from the light emitting point group DG of the light emitting points 3a, 3b, 3c. An optical system 73b having an imaging optical system 2a, 2b, 2c for forming an image on the light receiving surface 71a of the drum (photoreceptor) 71 is provided. The optical print head 73 further includes a light-shielding body 6 between the light emitting point cloud group DG and the optical system 73b (specifically, the first lens array A1 described later). By providing the light-shielding body 6, stray light can be further prevented.

The imaging optical systems 2a, 2b, and 2c are arranged at equal intervals in the directions of the upper and lower ± X axes. The imaging optical systems 2a, 2b, and 2c are telecentric on both sides and have the same imaging magnification, but do not have exactly the same shape, but have slightly different sizes in the directions of the left and right ± Z axes. ing. Here, the Y-axis parallel to the rotation axis RX of the photosensitive drum 71 corresponds to the main scanning direction or the main direction, is orthogonal to the rotation axis RX of the photosensitive drum 71, and the X-axis extending perpendicular to the optical axis AX is. Corresponds to the sub-scanning direction or the sub-direction. That is, in the optical print head 73, light emitting regions 3a, 3b, and 3c are provided at three locations in the vertical sub-scanning direction, and imaging optical systems 2a, 2b, and 2c are provided corresponding to the light emitting regions 3a, 3b, and 3c. The imaging optical systems 2a, 2b, and 2c are positioned and fixed to the light emitting element 73a in a state of being mutually positioned by a holder (not shown).

As shown in FIG. 3A, the light emitting element 73a has a three-layer structure, and three light emitting substrates 76a, 76b, 76c are laminated in the Z-axis direction parallel to the optical axis AX. On each light emitting substrate 76a, light emitting regions 3a, 3b, 3c are formed at predetermined intervals along reference lines SXa, SXb, and SXc extending in the Y direction. That is, the light emitting regions 3a, 3b, and 3c are arranged two-dimensionally. The light emitting region 3b on the upper layer side (that is, the upper side in FIG. 2) is arranged so as to be shifted in the + Z side toward the photosensitive drum 71 with respect to the intermediate light emitting region 3a, and is arranged on the lower layer side (that is, the lower side in FIG. 2). The light emitting region 3c on the side) is arranged so as to be shifted in the direction away from the photosensitive drum 71 on the −Z side with respect to the intermediate light emitting region 3a. As will be described in detail later, the centers of the light emitting regions 3a, 3b, and 3c are arranged on the same plane.

FIG. 3B is a partially enlarged view from behind explaining the arrangement of the light emitting point cloud group DG or the light emitting point ED formed in the single light emitting region 3a. The vertical direction of the drawing is the sub-scanning direction (secondary direction), and the horizontal direction of the drawing is the main scanning direction (main direction). The light emitting point EDs constituting the light emitting point cloud DG are arranged at equal intervals in the Y direction corresponding to the main scanning direction, and are also arranged at equal intervals in the direction inclined with respect to the X direction corresponding to the sub scanning direction. .. The diameter of one light emitting point ED is, for example, 30 μm, and the main direction is arranged at a pitch of 10.6 μm corresponding to one dot of 2400 dpi. Although not shown, there are 32 light emitting point EDs per row, and a total of 128 light emitting point EDs are arranged in a parallelogram matrix in 4 rows as a whole.

As shown in FIG. 3C, in the light emitting element 73a, the light emitting set SCn (n = 1, 2, 3, ...) Containing three adjacent light emitting regions 3a, 3b, 3c as a set repeats in the Y direction. They are evenly spaced. Note that FIG. 2 corresponds to the AA cross section of FIG. 3 (C). The light emitting regions 3a, 3b, and 3c constituting the light emitting group SCn are arranged at different positions in the main scanning direction or the Y direction, and are arranged at different positions in the sub scanning direction or the X direction. Similarly, in the optical system 73b, the imaging set LCn (n = 1, 2, 3, ...) Consisting of three adjacent imaging optical systems 2a, 2b, 2c are repeatedly arranged at equal intervals in the Y direction. Has been done. The imaging optical systems 2a, 2b, and 2c constituting the imaging set LCn are arranged at different positions in the main scanning direction or the Y direction, and are arranged at different positions in the sub-scanning direction or the X direction. In a specific example, about 100 imaging optical systems 2a, 2b, 2c are provided per row extending in the Y direction, and a total of 287 imaging optical systems 2a, 2b, 2c or light emitting regions 3a are provided as a whole. , 3b, 3c are arranged in a parallelogram matrix.

Returning to FIG. 2, in the optical system 73b, each imaging optical system 2a, 2b, 2c has a first imaging lens 5d, a plurality of diaphragms 5e, and a second imaging lens 5f, respectively. The first imaging lens 5d collimates the light rays LB from the light emitting regions 3a, 3b, and 3c. The second imaging lens 5f collects the light beam LB from the first imaging lens 5d and projects the images of the light emitting regions 3a, 3b, and 3c on the light receiving surface 71a of the photosensitive drum 71. As a result, projections having the same pattern as the light emitting point cloud group DG of the two-dimensional array formed in the light emitting regions 3a, 3b, 3c but having the same or different magnifications on the light receiving regions 4a, 4b, 4c on the light receiving surface 71a. An image group PG is formed. As will be described in detail later, the plurality of first imaging lenses 5d constituting the optical system 73b are arranged two-dimensionally, and their centers are arranged on the same plane. The plurality of second imaging lenses 5f constituting the optical system 73b are two-dimensionally arranged, and their centers are arranged on the same plane. Further, the plurality of diaphragms 5e constituting the optical system 73b are arranged two-dimensionally.

As shown in FIGS. 4A and 4B, the first imaging lens 5d is a convex lens, and more specifically, the lens shape of the first imaging lens 5d is biconvex in the vicinity of the optical axis. be. In the illustrated example, the first imaging lens 5d has resin lens portions 5i and 5j formed on both sides of a common lens substrate 5h made of glass or the like. That is, the lens surface of the lens portions 5i and 5j is formed of resin. The first imaging lens 5d arranged at three different positions with respect to the sub-scanning direction constitutes the first lens array A1. The second imaging lens 5f is a convex lens, and more specifically, the lens shape of the second imaging lens 5f is biconvex in the vicinity of the optical axis. In the illustrated example, the second imaging lens 5f has resin lens portions 5m and 5n formed on both sides of a common lens substrate 5k made of glass or the like. That is, the lens surfaces of the lens portions 5m and 5n are formed of resin. The second imaging lens 5f arranged at three different positions with respect to the sub-scanning direction constitutes the second lens array A2. The optical axes AX of the respective imaging optical systems 2a, 2b, and 2c are parallel to each other, and the light emitting point cloud group DG of the light emitting regions 3a, 3b, and 3c is also with respect to the light receiving surface 71a of the photosensitive drum (photoreceptor) 71. Is also vertical. The optical axis AX referred to here means an optical axis not in the medium, for example, an optical axis in the optical path in the front stage of the first lens array A1.

The diaphragm 5e is composed of a plurality of luminous flux control plates 60. The luminous flux control plate 60 (aperture 5e) is arranged between the first and second lens arrays A1 and A2 so as to face a plurality of imaging lenses 5d and 5f. The optical system 73b has a light-shielding plate 61 and a plurality of diaphragm plates 62 as a plurality of luminous flux control plates 60. The light-shielding plate 61 of the luminous flux control plate 60 is provided on the side closest to the first lens array A1. Further, the diaphragm plate 62 is provided between the light-shielding plate 61 and the second lens array A2 at a predetermined distance from the light-shielding plate 61. For example, a spacer may be provided between the light-shielding plate 61 and the diaphragm plate 62. In the present embodiment, the luminous flux control plate 60 has a layered light-shielding layer 60c formed on at least one surface of a diaphragm substrate 5p, which is a flat plate having light transmission and is made of glass. The plurality of diaphragm substrates 5p and the light-shielding layer 60c constituting the luminous flux control plate 60 (light-shielding plate 61 and diaphragm plate 62) have the same thickness. As a result, the same manufacturing apparatus and the same material can be used, so that the manufacturability can be improved. The diaphragm substrate 5p is a transparent body and transmits cyan, magenta, yellow, and black colors.

The luminous flux control plate 60 has a plurality of openings 60a through which light passes, and a light-shielding portion 60b that blocks light around the openings 60a. Of the plurality of openings 60a, the opening having the smallest diameter along the optical axis AX is referred to as the minimum opening 65, and the details will be described later. It is arranged on different surfaces (specifically, one surface of a plurality of aperture plates 62) of the light flux regulating plate 60 of the above. The arrangement of the minimum openings 65 is different for any combination of the plurality of luminous flux control plates 60. Further, the diameter of the opening 60a closest to the first lens array A1 along the optical axis AX among the plurality of openings 60a is larger than that of the minimum opening 65. That is, the opening 60a formed in the light-shielding plate 61 is larger than the minimum opening 65 formed in the diaphragm plate 62. As a result, the light-shielding layer 60c of the light flux regulating plate 60 closest to the first lens array A1 has a stray light prevention function. The light-shielding portion 60b corresponds to a portion where the light-shielding layer 60c is formed on the surface of the diaphragm substrate 5p. By forming the light-shielding portion 60b with the light-shielding layer 60c, the diaphragm position and the diaphragm shape can be formed more accurately, so that the telecentricity on both sides can be further enhanced.

The diaphragm plate 62 is formed by laminating a plurality of diaphragm substrates 5p in the optical axis AX direction. In the present embodiment, the diaphragm plate 62 is composed of three diaphragm substrates 5p. The diaphragm plate 62 has a first diaphragm plate 62a, a second diaphragm plate 62b, and a third diaphragm plate 62c in this order from the first lens array A1 side. The first to third drawing plates 62a to 62c are integrated by using, for example, an adhesive or the like. The first to third diaphragm plates 62a to 62c have a minimum aperture 65 as an aperture diaphragm at positions corresponding to the first imaging optical systems 2a, 2b, 2c of the first lens array A1. The first diaphragm plate 62a has a minimum aperture 65 that regulates the light beam of the first imaging lens 5d on the upper side of the first lens array A1, and the second diaphragm plate 62b has a central first imaging lens 5d. The third aperture plate 62c has a minimum aperture 65 that regulates the light beam of the lower first imaging lens 5d.

Each light emitting substrate 76a, 76b, 76c constituting the light emitting element 73a is a bottom emission type organic EL element in which light emitting point EDs are two-dimensionally arranged on a glass plate 73q. Each light emitting point group DG constituting the light emitting element 73a is projected as a projected image group PG on the light receiving surface 71a, and the projected image group PG includes a large number of projected image PDs corresponding to a large number of light emitting point EDs.

In the light emitting element 73a, the centers of the binary arranged light emitting regions 3a, 3b, 3c are arranged on a common first plane PLa. That is, the center point of the light emitting point cloud DG exists in the first plane PLa which is substantially the same plane. The first plane PLa forms a predetermined non-zero angle, that is, an angle θ _a with respect to the YX plane (a plane perpendicular to the optical axis AX direction) substantially parallel to the facing region of the light receiving surface 71a of the photosensitive drum 71. In the optical system 73b, the center of the first imaging lens 5d of the imaging optical systems 2a, 2b, and 2c is arranged on a common second plane PLb. That is, the center points of the plurality of imaging lenses 5d constituting the first lens array A1 exist in the second plane PLb which is substantially the same plane. Here, the center point of the imaging lens 5d means the center between the pair of optical surfaces of the imaging lens 5d on the optical axis AX. The second plane PLb forms a non-zero predetermined angle, that is, an angle θ _b with respect to the YX plane. The plurality of luminous flux control plates 60 are substantially parallel to the second plane PLb. Of the imaging optical systems 2a, 2b, and 2c, the center of the second imaging lens 5f is arranged on a common third plane PLd. That is, the center points of the plurality of imaging lenses 5f constituting the second lens array A2 exist in the third plane PLd which is substantially the same plane. Here, the center point of the imaging lens 5f means the center between the pair of optical surfaces of the imaging lens 5f on the optical axis AX. The third plane PLd forms an angle θ _d with respect to the YX plane. The first plane PLa, the second plane PLb, and the third plane PLd are inclined with respect to the sub-direction or the sub-scanning direction with respect to the YX plane perpendicular to the optical axis AX direction, but with respect to the main direction or the main scanning direction. It does not have a tilt component. That is, the planes PLa, PLb, and PLd are inclined along the YX plane.

As is clear from the figure, the angle between the first plane PLa and the plane perpendicular to the optical axis AX direction is θa, and the angle between the second plane PLb and the plane perpendicular to the optical axis AX direction is θb. Let θc be the angle between the fourth plane PLc connecting the center points of the plurality of minimum openings 65 and the plane perpendicular to the optical axis AX direction, and the angle between the third plane PLd and the plane perpendicular to the optical axis AX direction. When θd is, the following relationship θa>θb>θc> θd ... (1)
Meet. When the positions of the light emitting point cloud groups DG in the optical axis AX direction are different, the variation in magnification can be suppressed by satisfying the above relationship. More specifically, the angles θ _a to θ d formed by the first, second, fourth, and third planes PLa, PLb, PLc, and PLd with respect to the YX plane are the angles θ _d with the angle θ _a as the maximum value _. Is the minimum value, and the value gradually decreases from the angle θ _a to the angle θ _d .

式が得られ、発光素子７３ａに設定された第１平面ＰＬａの傾斜角である角度θ_ａに対する角度θ_ｂ、θ_ｃ、及びθ_ｄの最適値が定まる。関係式（３）～（５）を満たす最適な角度に対して±１０％の範囲程度となるように第２、第４、及び第３平面ＰＬｂ，ＰＬｃ，ＰＬｄを傾けること、つまり第１レンズアレイＡ１、光束規制板６０、及び第２レンズアレイＡ２を傾けることで、両側テレセントリック及び倍率均一性の確保に関して実用上十分な効果が得られる。つまり、角度θａ～θｄの関係は、関係式（３）～（５）のように厳密でなくてもよく、関係式（１）を満たしていればよい。 The imaging optical systems 2a, 2b, and 2c realize bilateral telecentricity and magnification uniformity. In this way, in order to realize bilateral telecentricity and to make the magnification substantially equal in each imaging optical system, for example, regarding the imaging optical system 2a, the first imaging lens 5d constituting the first lens array A1 is used. The distance from the center of the light emitting region 3a of the light emitting substrate 76a to the center of the first imaging lens 5d and the first imaging are defined by β as the magnification obtained by combining the second imaging lens 5f constituting the second lens array A2. The distance from the center of the lens 5d to the center of the aperture 5e (specifically, the center of the minimum opening 65) and from the center of the aperture 5e (the center of the minimum opening 65) to the center of the second imaging lens 5f. The distance between the center of the second imaging lens 5f and the center of the light receiving region 4a of the light receiving surface 71a has a 1: 1: β: β relationship. Such a relationship holds not only for the imaging optical system 2a but also for the imaging optical systems 2b and 2c, and the light receiving surface 71a can be approximately treated as a flat surface. Therefore, the light emitting regions 3a to 3c of the light emitting substrates 76a to 76c, the light emitting point group DG, the first imaging lens 5d of the first lens array A1, and the aperture 5e (specifically, the light flux regulation provided with the minimum opening 65). Ideally, the ratio of the distances of the plate 60), the second imaging lens 5f of the second lens array A2, and the light receiving regions 4a to 4c of the light receiving surface 71a with respect to the optical axis AX direction is as follows by using the magnification β. It can be determined as follows.
θ _a : θ _b : θ _c : θ _d
= 2 + 2β: 1 + 2β: 2β: β ... (2)
Here, 2 + 2β is a relative value corresponding to the distance from the light emitting region 3a to 3c to the light receiving region 4a to 4c, and 1 + 2β is the distance from the center of the first imaging lens 5d to the light receiving region 4a to 4c. 2β is a relative value corresponding to the distance from the center of the aperture 5e (the center of the minimum aperture 65) to the light receiving regions 4a to 4c, and β is the second imaging lens 5f. It is a relative value corresponding to the distance from the center of the light receiving region 4a to 4c. From equation (2) to the following relational equations (3) to (5)

The equation is obtained, and the optimum values of the angles θ _b , θ _c , and θ _d with respect to the angle θ _a which is the inclination angle of the first plane PLa set in the light emitting element 73 a are determined. Tilt the second, fourth, and third planes PLb, PLc, PLd so that they are in the range of ± 10% with respect to the optimum angle satisfying the relational expressions (3) to (5), that is, the first lens. By tilting the array A1, the luminous flux control plate 60, and the second lens array A2, a practically sufficient effect can be obtained in terms of ensuring bilateral telecentricity and magnification uniformity. That is, the relationship between the angles θa to θd does not have to be as strict as the relational expressions (3) to (5), and may satisfy the relational expression (1).

According to the image forming apparatus described above, the first lens array A1 and the light flux regulating plate 60 are substantially parallel to each other, and the minimum aperture 65 is provided on different surfaces of the plurality of light flux regulating plates 60, whereby the first lens array is arranged. The A1 and the luminous flux control plate 60, which is a member for preventing stray light, are arranged close to each other, and an image can be formed at substantially the same magnification for each light emitting point group DG while achieving high light-shielding performance. As a result, even if the positions of the light emitting point cloud DGs in the optical axis AX direction are different, it is possible to suppress the variation in the magnification of each of the imaging lenses 5d and 5f, and it is possible to achieve a highly manufacturable stray light prevention function.

On the other hand, under the condition that the light emitting point cloud is not on the same plane, it is necessary to arrange at least the first lens array and the light-shielding plate among the luminous flux control plates substantially in parallel in order to improve the light-shielding property. When the optical system is arranged in this way, plates (light-shielding plate and diaphragm plate) having different arrangement angles of the luminous flux control plate are present in close proximity to each other in the vicinity of the holding portion, which complicates the configuration of the holding member of the plate and makes manufacturing difficult. It becomes.

〔Example〕
Hereinafter, specific examples of the optical system 73b incorporated in the image forming apparatus 100 will be described.

［表２］

［表３］

[Example 1]
The optical system 73b of the first embodiment is the same as that shown in FIGS. 4 (A) and 4 (B). The following Tables 1 to 3 summarize the basic specifications of the optical system 73b of the first embodiment. In the following tables, the upper imaging optical system means the imaging optical system 2b as shown in FIG. 4 (A), and the central imaging optical system refers to the imaging optical system 2a as shown in FIG. 4 (A). The lower imaging optical system means the imaging optical system 2c as shown in FIG. 4 (A).
[Table 1]

[Table 2]

[Table 3]

中央の結像光学系２ａの自由曲面形状について表５にまとめた。記載した自由曲面の形状式は、Ｘ、Ｙ、Ｚに対応するローカル座標をｘ、ｙ、ｚとして

である。なお、表に無い非球面係数はすべて０である。これらの点は以下でも同様である。
［表５］

[1-a: Central imaging optical system]
Hereinafter, the data of the central imaging optical system 2a will be described. Table 4 shows the optics of the imaging lens (first imaging lens) 5d, the luminous flux control plate 60 (aperture 5e), and the imaging lens (second imaging lens) 5f constituting the central imaging optical system 2a. It is a summary of the coordinates of the surface optics of the surface. In Table 4, the first to third lens diaphragm surfaces are the surfaces of the first to second diaphragm plates 62a to 62c on which the opening 60a is formed (in this embodiment, the surface on which the light shielding layer 60c is formed). handle. The unit of distance is mm and the unit of angle is degrees. The refractive index of the lens substrate is 1.5145 for light having a wavelength of 650 nm, and the refractive index of the resin lens portion provided between the lens surface and the glass substrate is 1.5285. The imaging magnification β is -1 in all optical systems. The above is the same not only for the central imaging optical system but also for the upper and lower imaging optical systems. Moreover, these points are the same in other examples.
[Table 4]

Table 5 summarizes the free-form surface shape of the central imaging optical system 2a. In the described free-form surface shape formula, the local coordinates corresponding to X, Y, Z are set as x, y, z.

Is. The aspherical coefficients not shown in the table are all 0. These points are the same in the following.
[Table 5]

上側の結像光学系２ｂの自由曲面形状について表７にまとめた。
［表７］

[1-b: Upper imaging optical system]
Hereinafter, the data of the upper imaging optical system 2b will be described. Table 6 shows the optics of the imaging lens (first imaging lens) 5d, the luminous flux control plate 60 (aperture 5e), and the imaging lens (second imaging lens) 5f constituting the upper imaging optical system 2b. It is a summary of the coordinates of the surface optics of the surface.
[Table 6]

Table 7 summarizes the free-form surface shape of the upper imaging optical system 2b.
[Table 7]

下側の結像光学系２ｃの自由曲面形状について表９にまとめた。
［表９］

[1-c: Lower imaging optical system]
Hereinafter, the data of the lower imaging optical system 2c will be described. Table 8 shows the imaging lens (first imaging lens) 5d, the luminous flux control plate 60 (aperture 5e), and the imaging lens (second imaging lens) 5f constituting the lower imaging optical system 2c. It is a summary of the coordinates of the surface apex of the optical surface.
[Table 8]

Table 9 summarizes the free-form surface shape of the lower imaging optical system 2c.
[Table 9]

In the present embodiment, the diaphragm substrate 5p, which is a glass plate constituting the diaphragm plate 62, is composed of three pieces, but as shown in FIG. 5, the diaphragm substrate 5p may be two pieces. In this case, a minimum aperture 65 that regulates the light beam of, for example, the upper first imaging lens 5d is formed on the surface of the first diaphragm plate 62a on the first lens array A1 side, and the first and second diaphragm plates 62a, 62b are formed. For example, a minimum aperture 65 that regulates the light beam of the central first imaging lens 5d is formed on the surface between them, and for example, the lower first imaging lens is formed on the surface of the second diaphragm plate 62b on the second lens array A2 side. The minimum opening 65 that regulates the light beam of 5d is formed. By forming the drawing plate 62 with two drawing substrates 5p, the number of drawing plates 62 can be reduced and the production cost can be reduced.

[Second Embodiment]
Hereinafter, the image forming apparatus according to the second embodiment will be described. The image forming apparatus of the second embodiment is a modification of the image forming apparatus of the first embodiment, and the matters not particularly described are the same as those of the first embodiment and the like.

As shown in FIGS. 6A and 6B, in the optical system 73b of the present embodiment, the diaphragm substrate 5p of the light-shielding plate 61 of the luminous flux control plate 60 is thickened and integrated with the diaphragm plate 62. .. That is, the light-shielding plate 61 and the diaphragm plate 62 constituting the luminous flux control plate 60 are integrally laminated. By integrating the light-shielding plate 61 and the diaphragm plate 62, the relative position accuracy can be improved, the stray light prevention function of the luminous flux control plate 60 can be further enhanced, and the relative position between the light-shielding plate 61 and the diaphragm plate 62 can be improved. It is possible to prevent vignetting on the light-shielding plate 61 due to misalignment. In this embodiment, the plurality of diaphragm substrates 5p and the light-shielding layer 60c constituting the diaphragm plate 62 have the same thickness.

［表１１］

[Example 2]
The optical system 73b of the second embodiment is the same as that shown in FIGS. 6 (A) and 6 (B). Tables 10 and 11 below summarize the basic specifications of the optical system 73b of the second embodiment.
[Table 10]

[Table 11]

中央の結像光学系２ａの自由曲面形状について表１３にまとめた。
［表１３］

[2-a: Central imaging optical system]
Hereinafter, the data of the central imaging optical system 2a will be described. Table 12 shows the optics of the imaging lens (first imaging lens) 5d, the luminous flux control plate 60 (aperture 5e), and the imaging lens (second imaging lens) 5f constituting the central imaging optical system 2a. It is a summary of the coordinates of the surface optics of the surface.
[Table 12]

Table 13 summarizes the free-form surface shape of the central imaging optical system 2a.
[Table 13]

上側の結像光学系２ｂの自由曲面形状について表１５にまとめた。
［表１５］

[2-b: Upper imaging optical system]
Hereinafter, the data of the upper imaging optical system 2b will be described. Table 14 shows the optics of the imaging lens (first imaging lens) 5d, the luminous flux control plate 60 (aperture 5e), and the imaging lens (second imaging lens) 5f constituting the upper imaging optical system 2b. It is a summary of the coordinates of the surface optics of the surface.
[Table 14]

Table 15 summarizes the free-form surface shape of the upper imaging optical system 2b.
[Table 15]

下側の結像光学系２ｃの自由曲面形状について表１７にまとめた。
［表１７］

[2-c: Lower imaging optical system]
Hereinafter, the data of the lower imaging optical system 2c will be described. Table 16 shows the imaging lens (first imaging lens) 5d, the luminous flux control plate 60 (aperture 5e), and the imaging lens (second imaging lens) 5f constituting the lower imaging optical system 2c. It is a summary of the coordinates of the surface apex of the optical surface.
[Table 16]

Table 17 summarizes the free-form surface shape of the lower imaging optical system 2c.
[Table 17]

[Third Embodiment]
Hereinafter, the image forming apparatus according to the third embodiment will be described. The image forming apparatus of the third embodiment is a modification of the image forming apparatus of the first embodiment, and the matters not particularly described are the same as those of the first embodiment and the like.

As shown in FIG. 7, in the optical system 73b of the present embodiment, in the luminous flux control plate 60 (light-shielding plate 61 and diaphragm plate 62), a hole corresponding to the opening 60a is formed instead of the diaphragm substrate and the light-shielding layer. A light-shielding flat plate 5r is used. The light-shielding flat plate 5r is formed of, for example, a plate-shaped member having a light-shielding property. By using the light-shielding flat plate 5r, surface reflection can be reduced as compared with the case of using a diaphragm substrate which is a glass plate, and the efficiency of the optical system 73b can be increased.

Although the image forming apparatus as a specific embodiment has been described above, the image forming apparatus according to the present invention is not limited to the above. For example, in the above embodiment, the imaging optical system constituting the optical system 73b is not limited to three, but may be two or four or more.

In the above embodiment, the image magnification β of the optical system 73b is set to -1, but the image magnification β of the optical system 73b can be enlarged with an absolute value larger than 1, and reduced with an absolute value smaller than 1. Can be. The imaging magnifications β of the imaging optical systems 2a to 2c constituting the optical system 73b do not have to be exactly equal, and in that case, the arrangement of the emission point ED constituting the emission point cloud group DG and other factors may be changed. It is possible to compensate for the difference in magnification.

In the above embodiment, although not shown, transparent flat glass may be arranged between the light receiving surface 71a of the photosensitive drum 71 and the second lens array A2. By covering the optical system 73b with flat glass, it is possible to prevent dust from adhering to the second imaging lens 5f and the like.

In the above embodiment, the specific examples regarding the number and arrangement of the light emitting point EDs constituting the light emitting point cloud group DG are merely examples, and the number and arrangement of the light emitting point EDs can be changed according to the intended use and purpose.

In the above embodiment, the intervals in the sub-scanning direction or the X direction of the imaging optical systems 2a to 2c do not have to be equal, and for example, three first image formations having different positions with respect to the sub-scanning direction of the imaging optical systems 2a to 2c. The centers of the lens 5d do not have to be exactly aligned on the second plane PLb. Similarly, the centers of the three second imaging lenses 5f, which are located at different positions with respect to the sub-scanning directions of the imaging optical systems 2a to 2c, do not have to be strictly arranged on the third plane PLd.

In the above embodiment, the center points of the plurality of imaging lenses 5d and 5f constituting the first and second lens arrays A1 and A2 are set as a common coplanar reference, but the lens substrate 5h of the lens arrays A1 and A2, The intersection of the surface of 5k and the optical axis AX may be used as a center point, and this center point may be used as a reference for the same plane.

A1 ... 1st lens array, A2 ... 2nd lens array, AX ... optical axis, DG ... emission point group, ED ... emission point, LB ... ray, PG ... projection image group, PLa, PLb, PLc, PLd ... plane, RX ... rotation axis, SXa to SXc ... reference line, 2a to 2c ... imaging optical system, 3a to 3c ... light emitting region, 4a to 4c ... light receiving region, 76a to 76c ... light emitting substrate, 5d, 5f ... imaging lens, 5e ... aperture, 5p ... aperture substrate, 5r ... light-shielding flat plate, 6 ... light-shielding body, 10 ... image reading unit, 20 ... image forming unit, 40 ... paper feed unit, 50 ... transport unit, 60 ... light beam control plate, 60a ... Opening, 60b ... light-shielding part, 60c ... light-shielding layer, 61 ... light-shielding plate, 62, 62a, 62b, 62c ... drawing plate, 65 ... minimum opening, 70 ... image forming unit, 70M, 70C, 70K ... image forming unit , 71 ... Photosensitive drum, 71a ... Light receiving surface, 100 ... Image forming apparatus

Claims (7)

A photoconductor having a surface transported in a sub-direction substantially orthogonal to the main direction,
A light emitting board having a plurality of light emitting point groups arranged in two dimensions,
A plurality of imaging optical systems for forming an image of light from the plurality of light emitting point groups at different positions on the photoconductor, and a plurality of imaging optical systems.
Equipped with
The optical axes of the plurality of imaging optical systems are parallel to each other, and the optical axes are parallel to each other.
The imaging magnifications of the plurality of imaging optical systems are substantially equal for each emission point cloud.
The plurality of imaging optical systems face each of a first lens array having a plurality of imaging lenses arranged to face the light emitting point group and the plurality of imaging lenses constituting the first lens array. It is composed of a second lens array having a plurality of imaging lenses arranged in a row, and a plurality of light beam control plates arranged between the first and second lens arrays so as to face the plurality of imaging lenses. Being done
The center point of the light emitting point group exists in the first plane which is substantially the same plane, and
The center points of the plurality of imaging lenses constituting the first lens array exist in a second plane which is substantially the same plane.
The first plane forms a non-zero predetermined angle with respect to the plane perpendicular to the optical axis direction.
The second plane forms a non-zero predetermined angle with respect to the plane perpendicular to the optical axis direction.
The plurality of luminous flux control plates are substantially parallel to the second plane.
The luminous flux control plate has a plurality of openings through which light passes, and a light-shielding portion that blocks light around the openings.
Of the plurality of openings, the opening having the smallest diameter along the optical axis is defined as the minimum opening.
The image forming apparatus, wherein the minimum opening is arranged on different surfaces of the plurality of light flux restricting plates with respect to an imaging lens array having different arrangements in the sub-direction. The image forming apparatus according to claim 1, wherein the diameter of the opening closest to the first lens array along the optical axis of the plurality of openings is larger than the minimum opening. The plurality of luminous flux control plates are characterized by having a light-shielding plate arranged closest to the first lens array and a plurality of diaphragm plates arranged between the light-shielding plate and the second lens array. The image forming apparatus according to any one of claims 1 and 2. The image forming apparatus according to any one of claims 1 to 3, wherein the luminous flux control plate has a light-shielding layer constituting the light-shielding portion on at least one surface of a flat plate having light transmission. The image forming apparatus according to any one of claims 1 to 4, wherein a light-shielding body is provided between the light emitting point cloud and the first lens array. The image forming apparatus according to any one of claims 1 to 5, wherein the plurality of luminous flux control plates have the same thickness. The center points of the plurality of imaging lenses constituting the second lens array exist in a third plane which is substantially the same plane.
The angle between the first plane and the plane perpendicular to the optical axis direction is θa, the angle between the second plane and the plane perpendicular to the optical axis direction is θb, and the center of the plurality of minimum openings. When the angle between the plane connecting the points and the plane perpendicular to the optical axis direction is θc and the angle between the third plane and the plane perpendicular to the optical axis direction is θd, the following relationship θa>θb>θc> θd
The image forming apparatus according to any one of claims 1 to 6, wherein the image forming apparatus satisfies the above conditions.

Images