JP2017021300A - Imaging optical system, image forming apparatus, and image reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system that can achieve both imaging performance and efficiency in light utilization, while reducing an influence due to dust adhered to a light source and a sensor and defects in elements in an image forming apparatus and an image reading device.SOLUTION: There is provided an imaging optical system 100 used for an image forming apparatus, and comprising a plurality of imaging parts 105 arranged in a first direction, wherein the plurality of imaging parts 105 each form an object 101 into an erect image at a unity magnification in a first cross section including the first direction and optical axis direction, and form the object 101 into an inverted image at a reduced magnification in a second cross section perpendicular to the first direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging optical system used in an image forming apparatus such as a printer or a copying machine, an image reading apparatus, or the like.

  In recent years, an image forming apparatus and an image reading apparatus having an imaging optical system having a microlens array (MLA) in which a plurality of lenses are arranged at equal intervals have been developed. For example, an image forming apparatus and an image reading apparatus are known that include an optical device in which an MLA is held by a housing together with an array light source, a line sensor, and the like. According to this configuration, the number of parts can be reduced compared to a configuration in which a photoconductor is optically scanned by a polygon mirror, or a configuration in which an image is read through a plurality of mirrors. Cost reduction can be realized.

  Patent Document 1 discloses a lens array in which a plurality of lenses are arranged in one direction (first direction). Each of the plurality of lenses forms an erecting equal-magnification image of an object in a cross section including the first direction and the optical axis direction (first cross section), and is a cross section perpendicular to the first direction (second cross section). In (), an object is imaged upside down at an equal magnification. In this configuration, the power of the lens in the second cross section can be reduced as compared with an optical system that forms an erecting equal magnification in the second cross section. It is advantageous for coexistence.

JP 2012-247565 A

  However, since the lens array disclosed in Patent Document 1 forms an object at the same magnification in the second cross section, when this is applied to an image forming apparatus or an image reading apparatus, the required resolution is obtained. A light source or sensor of a corresponding size is required. Therefore, the size of the light source or sensor cannot be increased sufficiently, and there is a possibility that good image quality of the formed image and the read image cannot be realized when dust adheres or the element is defective. is there.

  An object of the present invention is an image forming optical system capable of satisfying both image forming performance and light use efficiency while reducing the influence of dust adhering to a light source or a sensor or an element defect in an image forming apparatus or an image reading apparatus. Is to provide.

  In order to achieve the above object, an imaging optical system according to one aspect of the present invention is an imaging optical system used in an image forming apparatus, and has a plurality of imaging units arranged in a first direction. Each of the plurality of image forming units forms an object at an erecting equal magnification within a first cross section including the first direction and the optical axis direction, and a second perpendicular to the first direction. In the cross-section, the object is inverted and reduced-imaged.

  The imaging optical system as another aspect is an imaging optical system used in an image reading apparatus, and has a plurality of imaging units arranged in a first direction, and the plurality of imaging units In each of the above, an object is imaged upright at an equal magnification in a first cross section including the first direction and the optical axis direction, and the object is inverted and enlarged in a second cross section perpendicular to the first direction. It forms an image.

  According to the present invention, in an image forming apparatus or an image reading apparatus, an imaging optical system capable of satisfying both imaging performance and light utilization efficiency while reducing the influence of dust adhering to a light source or a sensor or a defect of an element. Can be provided.

1 is a schematic diagram of a main part of an imaging optical system according to an embodiment of the present invention. 1 is a schematic diagram of a main part of an optical device according to Embodiment 1 of the present invention. FIG. 6 is a schematic diagram of a main part of an optical device according to a comparative example. The schematic diagram of the optical path which concerns on Example 1 and a comparative example of this invention. The figure which shows the relationship between the magnification in a 2nd cross section, a light source size, and a breadth half angle. The figure which shows the effective diameter of each lens surface which concerns on Example 1 and a comparative example of this invention. The figure for demonstrating the relationship between arrangement | positioning of each lens part, and an aberration. FIG. 6 is a schematic diagram of a main part of an optical device according to Embodiment 2 of the present invention. 1 is a schematic view of a main part of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic view of a main part of an image reading apparatus according to an embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Each drawing may be drawn on a different scale for convenience. Moreover, in each drawing, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

  1A and 1B are schematic views of a main part of an imaging optical system (lens array optical system) according to the present embodiment. FIG. 1A is an XY sectional view, FIG. 1B is a ZX sectional view, and FIG. ) Shows a YZ sectional view, respectively. The imaging optical system 100 includes a plurality of imaging units 105 arranged in a first direction (Y direction), and each of the plurality of imaging units 105 is arranged in an optical axis direction (X direction). The plurality of lens units 102 and 104 are provided.

  In addition, each of the plurality of imaging units 105 forms an erect image of the object placed on the object plane 101 at an equal magnification within the first cross section (within the XY cross section) including the first direction and the optical axis direction. This is a system (an erecting equal-magnification imaging system) that performs (erecting an object at an equal magnification). Note that the “same size” here is not limited to the exact same size but also includes a magnification slightly deviated from the same size within a range where image formation and image reading are possible. On the other hand, in the second cross section (ZX cross section) perpendicular to the first direction, this is a system (inverted non-magnification imaging system) that forms an inverted image of an object at a magnification different from the same magnification.

  Specifically, when the imaging optical system 100 is applied to an optical apparatus used for an image forming apparatus, each of the plurality of imaging units 105 is a system (inverted) that forms an inverted and reduced image of an object in the second cross section. Reduction imaging system). In other words, in the optical device provided in the image forming apparatus, when the magnification in the ZX cross section of the imaging optical system 100 is βs, the condition of −1 <βs <0 is satisfied. Further, when the imaging optical system 100 is applied to an optical device used for an image reading apparatus, each of the plurality of imaging units 105 is a system (inverted enlarged imaging) that forms an object in an inverted enlarged image in the second cross section. System). That is, in the optical device provided in the image reading apparatus, the condition of βs <−1 is satisfied.

  As described above, since the imaging optical system 100 according to the present embodiment is an inverted imaging system in the second cross section, each imaging unit in the second cross section is compared with the erect imaging system. Since the power of 105 can be reduced, both imaging performance and light utilization efficiency are realized. Further, the imaging optical system 100 becomes an inverted reduction imaging system or an inverted enlargement imaging system when applied to an image forming apparatus or an image reading apparatus. The size of the part (sensor) can be made sufficiently large. As a result, it is possible to suppress the deterioration of the image quality of the formed image and the read image due to the adhesion of dust to the light source and the light receiving part, the defect of the light emitting element and the light receiving element, and the like. Can be secured).

[Example 1]
Hereinafter, the imaging optical system according to Example 1 of the present invention will be described in detail. In the present embodiment, description will be made on the assumption that an imaging optical system is disposed in an optical device (exposure unit) provided in the image forming apparatus. 2A and 2B are schematic views of a main part of the optical device 10 according to the present embodiment, in which FIG. 2A is an XY sectional view, FIG. 2B is a ZX sectional view, and FIG. 2C is a YZ sectional view. Respectively. In FIG. 2, only a part of the plurality of image forming units 105 included in the image forming optical system 100 is illustrated, and only characteristic light rays among the infinite number of light rays are illustrated.

  The optical device 10 includes a light source 101, an imaging optical system 100, a housing 110, a first change unit 107, and a second change unit 108. The light source 101 has a plurality of light emitting elements (light emitting points) arranged at equal intervals in the Y direction, and an LED, an organic EL element (organic light emitting element), a laser, or the like can be used as the light emitting element. . In the image forming apparatus, a light source 101 is disposed on the object plane of the imaging optical system 100, and a light receiving surface (photosensitive surface) 106 is disposed on the image plane of the imaging optical system 100.

  Each of the plurality of imaging units 105 included in the imaging optical system 100 includes a first lens unit 102 and a second lens unit 104 arranged symmetrically with respect to the YZ plane. In the present embodiment, each of the first lens unit 102 and the second lens unit 104 is constituted by one optical element (lens). As shown in FIG. 2B, the shape of the first lens portion 102 and the shape of the second lens portion 104 are different from each other in the ZX cross section. It is an image system. Here, the lens surfaces (optical surfaces) 102a and 102b of the first lens unit 102 and the lens surfaces 104a and 104b of the second lens unit 104 are anamorphic aspheric surfaces.

  The imaging optical system 100 according to the present embodiment is disposed between the first lens unit 102 and the second lens unit 104, and is a light shield provided with a plurality of rectangular openings corresponding to the imaging units 105. Part 103 is provided. The center of each opening in the light shielding unit 103 is located on the optical axis of each image forming unit 105, and the light shielding wall between adjacent openings is located at the boundary between the adjacent image forming units 105 in the Y direction. ing. According to the light shielding unit 103, among the light beams that pass through the first lens unit 102 related to each image forming unit 105, only the image forming light beam that participates in the image formation is allowed to pass, and the stray light beam that does not contribute to the image formation (others). Light beam incident on the second lens unit 104 of the image forming unit 105) can be shielded.

  The housing 110 accommodates members such as the light source 101, the imaging optical system 100, the first changing unit 107, the second changing unit 108, and the like. The first changing unit 107 and the second changing unit 108 are members made of screws, pins, or the like, and are in contact with the reference unit 109 of the first lens unit 102 and the housing 110, respectively. According to the first changing unit 107, the focal position in the XY section and the ZX section are changed by changing the interval (first interval) between the light source 101 and the first lens unit 102 in the X direction. The astigmatic difference (as), which is the difference from the focal position, can be adjusted. In addition, according to the second changing unit 108, the distance between the housing 110 and the light receiving surface 106 (second interval) in the X direction is changed, which is caused by the adjustment of the ass by the first changing unit 107. The focus shift can be adjusted.

  As shown in FIG. 2A, the light beam emitted from the light source 101 is condensed on the intermediate imaging plane A by the first lens unit 102 in the XY cross section. Here, the intermediate image formation surface A is a virtual surface on which the first lens unit 102 forms an intermediate image of the light source 101 (intermediate image formation on the object surface). Then, the light beam once condensed on the intermediate imaging surface A is condensed on the light receiving surface 106 by the second lens unit 104. As a result, an intermediate image of the light source 101 is formed in the vicinity of the light receiving surface 106 (the intermediate image is re-imaged in the vicinity of the light receiving surface 106). That is, the imaging optical system 100 is an erecting equal-magnification imaging system that forms an erecting equal-magnification image of the light source 101 in the vicinity of the light receiving surface 106 in the XY cross section.

  On the other hand, as shown in FIG. 2B, in the ZX cross section, the light beam emitted from the light source 101 is focused on the vicinity of the light receiving surface 106 without being focused on the intermediate imaging plane A. At this time, the light source 101 is reduced and imaged near the light receiving surface 106 by the first lens unit 102 and the second lens unit 104. That is, the imaging optical system 100 is an inverted reduction imaging system that forms an inverted reduced image of the light source 101 in the vicinity of the light receiving surface 106 in the ZX cross section.

  Various characteristics of the optical device 10 according to this example are shown in Table 1 below.

  As shown in Table 1, the magnification in the ZX section of the imaging optical system 100 according to this example is βs = −0.769, and the size of each light emitting element included in the light source 101 is 42.30 μm × 54.99 μm. It is. That is, when the resolution of the image forming apparatus is 600 dpi, the size of each light emitting element in the second direction is 1.3 (= 1/0) with respect to the size of dots to be printed (42.30 μm × 42.30 μm). .769) times the size (42.3 μm × 1.3 = 54.99 μm).

  The intersection of each lens surface of the imaging optical system 100 and the optical axis (X axis) is the origin, the axis orthogonal to the optical axis in the first direction is the Y axis, and the optical axis is orthogonal to the second direction. When the axis is the Z-axis, the aspherical shape is represented by the following aspherical expression (1). Where R is a radius of curvature, k is a conic constant, and Aij (i = 0, 1, 2, 3..., J = 0, 1, 2, 3...) Is an aspheric coefficient.

(Comparative example)
Hereinafter, effects of the imaging optical system 100 according to the present embodiment will be described using comparative examples. The imaging optical system 300 according to the comparative example is an imaging optical system 100 according to the present embodiment in that the imaging optical system 300 according to the comparative example is a system (inverted equal magnification imaging system) for imaging an object in the ZX cross section. Is different.

  FIG. 3 is a schematic diagram of a main part of an optical device 30 according to a comparative example. As shown in FIG. 3, the configuration of the optical device 30 according to the comparative example is the same as the configuration of the optical device 10 according to the present embodiment except for the imaging optical system 300. Specifically, as shown in FIG. 3B, in the ZX cross section, the first lens unit 302 and the second lens unit 304 have the same shape, and with respect to the YZ plane. They are arranged symmetrically. With this configuration, the imaging unit 305 forms an inverted equal magnification imaging system in the ZX cross section.

  Various characteristics of the optical device 30 according to the comparative example are shown in Table 2 below.

  As shown in Table 2, since the magnification in the ZX section of the imaging optical system 300 according to the comparative example is βs = −1, when the resolution of the image forming apparatus is 600 dpi, the size equivalent to the dot to be printed ( 42.30 μm × 42.30 μm) light emitting element is required.

  When dust adheres to the light emitting element or when a defect of the light emitting element occurs, the amount of light reduction on the image plane is proportional to the ratio of the area of the dust or defective element to the total area of the light emitting element in the light source. In this embodiment, the imaging optical system 100 is an inverted reduction imaging system, so that the size of the light emitting element can be increased compared to the comparative example, and when dust or element defects of the same size occur, The area ratio can be made smaller than in the comparative example. In other words, it is possible to secure sufficient dust resistance and to reduce the amount of light reduction.

  Furthermore, according to the imaging optical system 100 according to the present embodiment, the second light of the lens surface of the first lens unit is maintained while maintaining the total light utilization efficiency (the area of the object plane × the light utilization efficiency of the imaging unit). The effective diameter in the cross section (the diameter of the effective surface through which the effective light beam contributing to the imaging passes) can be reduced. This will be described in detail with reference to FIG. FIG. 4 is a diagram schematically showing the optical path of the imaging optical system in the ZX section and the optical path of the marginal ray from the light source 101 passing therethrough, and FIG. 4A is an imaging optical system 300 according to the comparative example. FIG. 4B shows the imaging optical system 100 according to the present embodiment. In FIG. 4, the first and second lens portions (main planes) are indicated by arrows.

When the size in the ZX section of the light emitting element of the light source 101 is Do, the size in the ZX section of the image 106 is Di, and the magnification in the ZX section of the imaging optical system is βs, the following equation (2) is established.
Do = Di / βs (2)

Further, assuming that the spread half angle (half value of the opening angle) of the marginal ray on the light source side (object side) is θo and the spread half angle of the marginal ray on the image side is θi, the following formula ( 3) holds.
Do × tan θo = Di × tan θi (3)

Therefore, the following formula (4) is obtained from the formulas (2) and (3).
tan θo = Di × tan θi / Do = | βs | × tan θi (4)

When it is assumed that the light source 101 emits isotropically, the light amount V (proportional to the total light utilization efficiency) of the image 106 is approximately expressed by the following equation (5).
V∝Do × tan θo = Di × tan θi (5)

  In the comparative example, βs = −1, Do = Di = 42.30 μm, and θo = θi = 21.2 °.

  Here, in the configuration according to the comparative example, when the magnification βs is changed without changing the size Di and the light amount V of the image 106, the size Do of the light emitting element of the light source 101, the object-side spreading half angle θo, and the image side Each of the spread half angle θi is shown in FIG. FIG. 5 shows that when the imaging optical system is an inverted imaging system in the ZX cross section, the object-side spreading half angle θo decreases as the magnification βs increases, that is, as the reduction ratio increases. At this time, the image-side spread half angle θi is also reduced, but the amount of change relative to before the magnification βs is changed (when βs = −1) is very small. The size Do of the light emitting element increases as the absolute value of the magnification βs decreases.

  Therefore, the imaging optical system is an inverted reduction imaging system (-1 <βs <0) in the ZX cross section, and the size Do and the light amount V of the image 106 are set by making the size Do of the light emitting element larger than that of the comparative example. Without changing, it is possible to reduce the object-side spreading half angle θo. At this time, as described above, the image-side spread half angle θi is substantially unchanged.

  In the present embodiment, the magnification Di in the ZX section of the imaging optical system 100 is set to βs = −0.769 (= −1 / 1.3), so that the size Di and the light amount of the image 106 are compared with the comparative example. Without changing V, the size Do of the light emitting element is 1.3 times. At this time, it can be seen from FIG. 5 that θo = 16.3 ° and θi = 20.8 °, and the spread half angle is smaller than that of the comparative example.

  Therefore, as shown in FIG. 4B, the light flux width (interval between marginal rays) L1 passing through the first lens unit 102 in the ZX cross section is the light flux width according to the comparative example shown in FIG. Since it becomes smaller than L1, the effective diameter of the 1st lens part 102 can be made small. By reducing the effective diameter of the lens unit, it is possible to reduce the size of the entire imaging optical system, shorten the processing time of the lens mold, reduce the effective surface shape error, etc. become. Note that it is not always necessary to reduce the entire optical surface as a mirror surface (mirror-finished surface) in the lens portion, and the effect of the present invention can be obtained by reducing at least the effective surface portion of the optical surface.

  FIG. 6 is a diagram illustrating an effective diameter in the ZX cross section of each lens surface according to Example 1 and the comparative example. Here, in the object height on the optical axis (on-axis object height), the range surrounded by the passing positions of the marginal rays of the effective light beam among the lens surfaces is defined as the effective surface, and the diameter is set as the effective diameter. 6 that the effective diameters of the lens surface 102a (incident surface) and the lens surface 102b (exit surface) of the first lens unit 102 according to the present embodiment are significantly smaller than those of the comparative example. . On the other hand, the effective diameters of the lens surface 104b (incident surface) and the lens surface 104a (exit surface) of the second lens unit 104 are approximately the same in this embodiment and the comparative example.

  Table 3 below shows the ratio of the effective diameters of the lens surfaces according to the present example when the effective diameter of the lens surfaces according to the comparative example is 100%. From Table 3, it can be seen that the effective diameters of the lens surface 102a and the lens surface 102b according to the present example are about 20 to 30% smaller than the comparative example.

In this embodiment, the magnification in the second cross section of the imaging optical system 100 is set to βs = −0.769. However, the present invention is not limited to this. However, in the image forming apparatus, in order to ensure sufficient dust resistance, it is required to increase the size of the light emitting element of the light source 101 as much as possible. For this reason, at least the size of the light source 101 in the second direction is desirably about 5% larger than the dot size for printing. That is, each of the plurality of light emitting elements included in the light source 101 is configured to satisfy the following conditional expression (6), where α is the ratio of the length in the second direction to the length in the first direction. It is preferable to do.
α ≧ 1.05 (6)

As shown in Table 1, in this example, α = 54.99 / 42.30 = 1.300, which satisfies the conditional expression (6). Therefore, it is more desirable that the magnification βs in the second cross section of the imaging optical system 100 (imaging unit 105) satisfies the following conditional expression (7).
0> βs ≧ −0.95 (7)

  In this embodiment, as shown in Table 1, the distance from the light source 101 (object plane) to the intermediate imaging plane A is Lo = 2.62 mm + 1.27 mm + 1.08 mm = 4.97 mm. Further, since the distance from the intermediate image plane A to the light receiving surface 106 (image plane) is Li = 1.08 mm + 1.27 mm + 2.62 mm = 4.97 mm, the relationship Lo = Li is satisfied.

  The effect obtained by satisfying the relationship Lo = Li will be described with reference to FIG. In FIG. 7, each of the lens portions (main planes) of the imaging optical system is indicated by arrows, and only characteristic light rays that pass through each lens portion are shown. In the XY cross section, the object height (intermediate position) between the light emitting point 101a located at the object height on the optical axis of the imaging unit (on-axis object height) and the optical axes of two adjacent imaging units. The light rays emitted from each of the light emitting points 101b located at the (object height) are shown.

  In FIG. 7A, similarly to the imaging optical system 100 according to the present embodiment, the magnification in the XY section is βm = 1, the magnification in the ZX section is −1 <βs <0, and Lo = It is the figure which showed typically the optical system used as Li. As can be seen from the optical path in the ZX cross section, the second lens unit disposed between the intermediate image plane A and the image plane 106 is located between the object plane 101 and the intermediate image plane A. The power in the ZX cross section is larger than that of the first lens unit to be arranged. Therefore, the aberration related to the second lens portion tends to increase in the ZX cross section. On the other hand, in the XY cross section, since the power is distributed substantially equally between the first lens portion and the second lens portion, the aberration associated with each lens portion is unlikely to increase.

  FIG. 7B is a diagram schematically showing an optical system in which the magnification in the XY section is βm = 1 and the magnification in the ZX section is −1 <βs <0, but Lo> Li. . As can be seen from the optical path in the ZX cross section, since the power is distributed approximately equally between the first lens portion and the second lens portion, the aberration associated with each lens portion is unlikely to increase. On the other hand, in the XY cross section, since the intermediate image plane A is closer to the image plane 106 than in FIG. 7A, the power of the second lens unit is increased. Furthermore, it can be seen that the incident angle (aperture angle) of the light beam emitted from the second lens portion with respect to the image plane 106 is larger than that in FIG. Therefore, the aberration related to the second lens portion tends to increase in the XY cross section.

Thus, in an optical system in which the object plane is imaged upright at the same magnification in the XY section and the object surface is inverted and reduced in the ZX section, the absolute values of the magnifications in each section are different from each other. In the cross section, it is difficult to evenly distribute the power to the lens portions. That is, the aberration of the light flux is likely to be larger in one cross section than in the other cross section. At this time, in the XY cross section, the power required by each lens unit is large, and in the configuration in which Lo> Li, it is difficult to reduce the aberration of the luminous flux. Therefore, the configuration in which Lo = Li is more preferable. However, as long as the following conditional expression (8) is satisfied, an increase in the aberration of the light beam in each cross section can be suppressed.
0.8 ≦ Lo / Li ≦ 1.2 (8)

  The above description is based on the premise that the number of lenses constituting the optical system is as small as four or less, and the position of the lens portion (main plane) in the XY section and the ZX section cannot be changed greatly. In particular, in the imaging optical system in which the imaging unit is composed of only two lenses as in the present embodiment, it is difficult to greatly change the position of the main plane in each cross section, so conditional expression (8) The effect by satisfying is increased.

  In this embodiment, the case where the imaging optical system 100 is applied to an image forming apparatus has been described. However, the present invention is not limited to this, and the imaging optical system 100 may be applied to an image reading apparatus, for example. . When the imaging optical system 100 is applied to an image reading apparatus, a document (document table) extending in the first direction is arranged on the object surface, and a light receiving element such as a CMOS sensor is arranged on the image surface. A light receiving unit is arranged.

  At this time, since the imaging optical system 100 is an inverted magnification imaging system in the ZX cross section, the size of the light receiving element can be increased. The dust resistance performance of the element can be improved. Furthermore, it is possible to reduce the effective diameter of each lens unit without changing the size of the reading area and the reading efficiency (total light utilization efficiency).

Similar to the image forming apparatus, in the image reading apparatus, the ratio α of the length in the second direction to the length in the first direction for each of the plurality of light receiving elements satisfies the conditional expression (6). It is preferable to configure. Therefore, it is more preferable that the magnification βs in the second cross section of the imaging optical system 100 (imaging unit 105) satisfies the following conditional expression (9).
βs ≦ −1.05 (9)

  In order to sufficiently secure dust resistance, the power ratio in the ZX cross section between the first lens unit and the second lens unit in each imaging unit 105 should be 1.05 or more. desirable. At this time, in the image reading apparatus, the first lens unit has a higher power in the ZX cross section than the second lens unit. In consideration of the imaging performance of the imaging unit 105, the magnification βs is set to −0.7 or less in the image forming apparatus, and the magnification βs is set to −1 / 0.7 = −1. It is preferable to set it to 43 or more.

  As described above, according to the imaging optical system according to the present embodiment, in the image forming apparatus and the image reading apparatus, both the imaging performance and the light utilization efficiency can be achieved while sufficiently securing the dust resistance performance of the light source and the light receiving unit. Is possible. Furthermore, according to the imaging optical system according to the present embodiment, it is possible to reduce the effective diameter in the second cross section of each lens unit.

[Example 2]
Hereinafter, the imaging optical system according to Example 2 of the present invention will be described in detail. FIG. 8 is a schematic diagram of a main part of the optical device 80 according to the present embodiment. As shown in FIG. 8, the configuration of the optical device 80 according to the present embodiment is the same as that of the first embodiment except for the imaging optical system 800. This is the same as the configuration of the optical device 10 according to the above. Specifically, in the imaging optical system 800 according to the present embodiment, the imaging optical system 100 according to the first embodiment is vertically divided into two, and one of them is half of the arrangement period of each lens unit (half pitch). Only a configuration shifted in the Y direction (stage shift structure) is employed.

  That is, the imaging optical system 800 according to the present embodiment has a configuration in which a plurality of imaging units 805 are arranged not only in the first direction but also in the second direction perpendicular thereto. Similarly to the first embodiment, the lens surfaces 802a, 802b, 802c, and 802d of the upper and lower first lens portions 802 and the lens surfaces 804a, 804b, 804c, and 804d of the upper and lower second lens portions 804, respectively. Is an anamorphic aspherical surface. In addition, the aspheric shape of each lens surface is represented by the above-described aspheric expression (1).

  Various characteristics of the optical device 80 according to this example are shown in Table 4 below.

  Since the magnification in the second cross section of the imaging optical system 800 according to the present example is βs = −0.769 as in the first example, the above conditional expression (7) is satisfied, which is carried out. The same effect as in Example 1 can be obtained. Furthermore, in this embodiment, the number of lens portions through which a light beam emitted from one light emitting point passes can be increased as compared with the first embodiment by adopting the step shifting structure as described above. Thereby, the optical performance with respect to each light beam is averaged, and it is possible to significantly reduce the unevenness of the imaging performance (MTF and light utilization efficiency) in the first direction.

  However, when adopting a staggered structure as in this example, it becomes more complex than the configuration according to Example 1, so in the manufacturing process such as when the mold is processed or released from the mold, A shape error of each lens surface is likely to occur. However, since the effective diameter of each lens unit according to this example is the same as that of Example 1, the effective diameter of each lens unit is compared with that of Example 1 while ensuring the size and the amount of light of the image 106 as in Example 1. Can be made smaller. That is, by forming the imaging optical system 800 as an inverted reduction imaging system in the second cross section, it is possible to suppress the occurrence of shape errors of the lens surfaces even when a step-shifting structure is employed. .

  Here, the description has been made on the assumption that each lens part is manufactured by molding. However, the present invention is not limited to this. For example, even when each lens part is manufactured by cutting, the present invention reduces the shape error of each lens surface. A reduction effect can be obtained.

[Image forming apparatus]
FIG. 9 is a schematic diagram (ZX sectional view) of a main part of the image forming apparatus 33 according to the embodiment of the present invention. The image forming apparatus 33 includes four optical devices (exposure units) each having the imaging optical system according to any of the above-described embodiments, and each of them receives a light receiving surface (photosensitive surface) of a photosensitive drum (photosensitive member) in parallel. Is a tandem type color image forming apparatus.

  The image forming apparatus 33 includes a printer controller 36, exposure units 17, 18, 19, and 20, photosensitive drums 21, 22, 23, and 24 as image carriers, developing devices 25, 26, 27, and 28, and conveyance A belt 34 and a fixing device 37 are provided. Here, each of the exposure units 17 to 20 is arranged such that the second direction of the imaging optical system coincides with the Z direction that is the rotation direction of the photosensitive drums 21 to 24.

  As shown in FIG. 9, R (red), G (green), and B (blue) color signals are output from an external device 35 such as a personal computer. Each color signal is converted into image signals (dot data) of Y (yellow), M (magenta), C (cyan), and K (black) by the printer controller 36, and input to the corresponding exposure units 17-20. . The printer controller 36 controls not only the signal conversion described above but also each part of the image forming apparatus 33 such as a motor described later.

  Each of the exposure units 17 to 20 has a photosensitive surface of each of the photosensitive drums 21 to 24 that is charged by a charging roller (not shown) by each of the exposure light 29, 30, 31, and 32 modulated according to each image signal. Are exposed to form an electrostatic latent image. Each of the photosensitive drums 21 to 24 is rotated in the ZX section by a motor (not shown), and the photosensitive surface of each photosensitive drum is moved in the Z direction along with the rotation. Thereafter, the electrostatic latent images of the respective colors formed on the respective photosensitive surfaces are developed as toner images of the respective colors by the developing devices 25 to 28, respectively. The toner images of the respective colors are multiplexed and transferred onto a transfer material (recording medium) conveyed by the conveyance belt 34 by a transfer device (not shown), and then fixed on the transfer material by a fixing device 37. One full color image is formed by the above process.

[Image reading device]
FIG. 10 is a schematic diagram (ZX cross-sectional view) of a main part of the image reading device 44 according to the present embodiment. The image reading device 44 includes a document table 43 made of a transmissive member, and an optical device (reading unit) 41 having an imaging optical system according to any of the above-described embodiments, and is placed on the upper surface of the document table 43. This is a device for reading a placed document 40 by a reading unit 41. The document table 43 is supported by a frame 42, and the upper surface of the document table 43 coincides with the document surface of the document 40.

  Here, the reading unit 41 includes an illumination unit that illuminates the document 40 via the document table 43, the imaging optical system according to any of the above-described embodiments, and the document 40 condensed by the imaging optical system. A light receiving portion that receives reflected light from the light source, and a housing (housing) that holds each member. Since the reading unit 41 is configured to be movable in the X direction by a drive unit (not shown), the relative position between the document table 43 (document 40) and the imaging optical system is changed to the X direction (second direction). be able to. With this configuration, the reading unit 41 can sequentially read the document surface of the document 40 in the sub-scanning direction, and can acquire image data of the entire document surface of the document 40.

  At this time, the upper surface of the document table 43, that is, the document surface of the document 40 is disposed on the object surface of the imaging optical system, and the light receiving surface (sensor surface) of the light receiving unit is disposed on the image surface of the imaging optical system. Has been. The imaging optical system is arranged so that the second direction coincides with the sub-scanning direction. As the light receiving unit, for example, a line sensor constituted by a CCD sensor, a CMOS sensor, or the like can be used. Note that the image reading device 44 may have a configuration in which transmitted light from the document 40 illuminated by the illumination unit is received by the light receiving unit. Further, the illumination unit is not limited to the one including the light source, and a configuration in which light from the outside is guided to the document 40 may be adopted.

[Modification]
The preferred embodiments and examples of the present invention have been described above, but the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes can be made within the scope of the gist.

  For example, each lens surface of the imaging unit in each of the above-described embodiments is an anamorphic aspherical surface expressed by Expression (1), but is not limited thereto, and is an aspherical surface expressed by another expression. May be. In addition, the image forming unit according to each embodiment has a configuration including two lenses having different shapes arranged in the optical axis direction, but two lenses having the same shape may be employed. However, in order to correct aberrations satisfactorily, it is preferable to employ different lenses. Further, the number of lenses is not limited to two, and a configuration having three or more lenses may be employed, and a configuration in which lenses are arranged on an intermediate image plane may be employed. In this case, the optical system from the object plane to the intermediate image plane is the first lens unit, and the optical system from the intermediate image plane to the image plane is the second lens unit. In the second embodiment, the configuration in which two image forming units are arranged in the second direction is adopted. However, the configuration is not limited to this, and the configuration in which three or more image forming units are arranged in the second direction is used. It is good.

  In the imaging optical system according to each embodiment, the opening of the light shielding portion is an opening surface. However, the present invention is not limited to this, and the lens surface may be an opening surface. In addition, the shape of the opening of the light-shielding portion according to each embodiment is a rectangle, but the rectangle here indicates a substantially rectangular shape, and the sides constituting the rectangle are curved and each vertex is eliminated. In a substantially circular shape or a substantially elliptical shape. Note that the aperture shape is not limited to a rectangle, but by using a rectangle corresponding to the shape of the light emitting element or the print dot, the light utilization efficiency is improved compared to the case where the aperture shape is a circle or an ellipse. Can be improved. In the second cross section, the shape of the upper and lower ends of the opening may be inclined along the locus of the effective light beam.

  In each embodiment, since it is assumed that 600 dpi dots are printed in both the Y direction and the Z direction, the dot shape is square, but the present invention is not limited to this. Similarly, the shape of the light emitting element (light emitting surface) included in the light source is not limited to a rectangle, and may be, for example, a rhombus, an ellipse, a parallelogram, or the like according to the shape of a print dot. Furthermore, as the light source, a configuration in which a plurality of light emitting elements are arranged not only in the first direction but also in the second direction may be employed.

  The recording density in the image forming apparatus and the image reading apparatus described above is not limited. However, considering that the higher the recording density is, the higher the image quality is required, the optical device according to each of the above-described embodiments exhibits a higher effect in an image forming apparatus of 600 dpi or more. Further, a color digital copying machine may be configured by connecting the above-described image reading apparatus as an external device to the image forming apparatus. Of course, the imaging optical system according to each embodiment may be applied to a monochrome image forming apparatus.

100 Imaging optical system 101 Light source (object plane)
105 Imaging unit

Claims (24)

An imaging optical system used in an image forming apparatus,
A plurality of imaging portions arranged in a first direction;
Each of the plurality of imaging units forms an erecting image at an equal magnification in a first cross section including the first direction and the optical axis direction, and in a second cross section perpendicular to the first direction. Then, an imaging optical system characterized in that the object is imaged in an inverted manner. When the magnification of each of the plurality of imaging portions in the second cross section is βs,
βs ≧ −0.95
The imaging optical system according to claim 1, wherein the following condition is satisfied.   Each of the plurality of image forming units includes a first lens unit that forms an intermediate image of the object in the first cross section and a second lens unit that re-images the intermediate image. The imaging optical system according to claim 1 or 2.   4. The imaging optical system according to claim 3, wherein a power of the second lens unit is larger than a power of the first lens unit in the second cross section. 5. In the first cross section, when the distance from the object plane to the intermediate imaging plane is Lo and the distance from the intermediate imaging plane to the image plane is Li, respectively, for each of the plurality of imaging sections,
0.8 ≦ Lo / Li ≦ 1.2
The imaging optical system according to claim 3 or 4, wherein the following condition is satisfied.   6. The apparatus according to claim 1, further comprising: a plurality of image forming units arranged in the first direction and a second direction perpendicular to the first direction and the optical axis direction. The imaging optical system according to claim 1.   7. The imaging optical system according to claim 1, wherein each of the plurality of imaging units has a rectangular opening surface.   The imaging optical system according to claim 1, wherein each of the plurality of imaging units includes four or less lenses.   An optical apparatus comprising: a light source; and the imaging optical system according to claim 1 that forms an image of the light source. The light source includes a plurality of light emitting elements arranged in the first direction, and each of the plurality of light emitting elements is in the first direction and the optical axis direction with respect to the length in the first direction. When the ratio of lengths in the vertical second direction is α,
α ≧ 1.05
The optical device according to claim 9, wherein the following condition is satisfied.   11. The optical device according to claim 9 or 10, a developing device that develops an electrostatic latent image formed on a photosensitive surface of a photoreceptor by the optical device as a toner image, and the developed toner image on a recording medium. An image forming apparatus comprising: a transfer device for transferring; and a fixing device for fixing the transferred toner image to the recording medium.   The image forming apparatus according to claim 11, wherein the photoconductor rotates within the second cross section. An imaging optical system used in an image reading apparatus,
A plurality of imaging portions arranged in a first direction;
Each of the plurality of imaging units forms an erecting image at an equal magnification in a first cross section including the first direction and the optical axis direction, and in a second cross section perpendicular to the first direction. Then, an imaging optical system characterized in that the object is inverted and enlarged. When the magnification of each of the plurality of imaging portions in the second cross section is βs,
βs ≦ −1.05
The imaging optical system according to claim 13, wherein the following condition is satisfied.   Each of the plurality of image forming units includes a first lens unit that forms an intermediate image of the object in the first cross section and a second lens unit that re-images the intermediate image. The imaging optical system according to claim 13 or 14.   The imaging optical system according to claim 15, wherein in the second cross section, the power of the first lens unit is larger than the power of the second lens unit. In the first cross section, when the distance from the object plane to the intermediate imaging plane is Lo and the distance from the intermediate imaging plane to the image plane is Li, respectively, for each of the plurality of imaging sections,
0.8 ≦ Lo / Li ≦ 1.2
The imaging optical system according to claim 15 or 16, wherein the following condition is satisfied.   18. The image forming apparatus according to claim 13, further comprising: a plurality of image forming units arranged in the first direction and a second direction perpendicular to the first direction and the optical axis direction. The imaging optical system according to claim 1.   The imaging optical system according to claim 13, wherein each of the plurality of imaging units has a rectangular opening surface.   20. The imaging optical system according to claim 13, wherein each of the plurality of imaging units includes four or less lenses.   21. An optical apparatus comprising: the imaging optical system according to claim 13 that forms an image of a document; and a light receiving unit that receives light from the imaging optical system. The light receiving unit includes a plurality of light receiving elements arranged in the first direction, and for each of the plurality of light receiving elements, the first direction and the optical axis direction with respect to the length in the first direction When the ratio of lengths in the second direction perpendicular to is α,
α ≧ 1.05
The optical device according to claim 21, wherein the following condition is satisfied.   23. An image reading apparatus comprising: the optical device according to claim 21; and a document table on which the document is placed.   And a driving unit configured to change a relative position between the document table, the imaging optical system, and the light receiving unit in a second direction perpendicular to the first direction and the optical axis direction. Item 24. The image reading apparatus according to Item 23.

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