JP4125910B2 - Lens array unit and optical apparatus having the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical device such as an image reading device, and a lens array unit suitable for use in forming a desired object image by being incorporated in the optical device.
[0002]
[Prior art]
As an image reading apparatus incorporated in a facsimile apparatus or a scanner apparatus, a document image is read by forming an erecting equal-magnification image of an original image on a plurality of light receiving elements for image reading using a lens array. There is something that has been made to do. As an example of a conventional traditional lens array used for such an application, there is one in which a plurality of rod lenses capable of forming an erecting equal-magnification image are held by a synthetic resin holder. However, in the lens array having such a structure, the manufacturing of the plurality of rod lenses is complicated, and the operation of incorporating the plurality of rod lenses into the synthetic resin holder is also complicated, and the manufacturing cost is expensive. It was.
[0003]
Therefore, the inventors of the present application have previously proposed a lens array unit described in Japanese Patent Application Laid-Open No. 2001-352429. The lens array unit described in the publication has first and second lens arrays 8A and 8B and a light shielding mask 9, as shown in FIG. In the first and second lens arrays 8A and 8B, a plurality of convex lenses 81A and 81B and holder portions 80A and 80B for holding them are integrally formed of a transparent synthetic resin, and these are laminated in the thickness direction. Has been. The light shielding mask 9 is arranged in front of the first lens array 8A, and has a plurality of through holes 90 positioned in front of each convex lens 81A.
[0004]
According to the lens array unit having the above configuration, the light traveling from the object (a → b → c) at the starting point S passes through the convex lenses 81A and 81B of the first and second lens arrays 8A and 8B. An erecting equal-magnification image (a ′ → b ′ → c ′) of the object can be formed on the imaging point R. Such an effect is obtained by forming a reduced inverted image of the object at the intermediate point between the start point S and the imaging point R by the convex lens 81A, and then inverting the reduced inverted image while enlarging it by the convex lens 81B. It is done. Since the first and second lens arrays 8A and 8B are formed by integrally forming the convex lenses 81A and 81B and the holder portions 80A and 80B with a synthetic resin, they can be easily manufactured using a mold. It is possible to reduce the manufacturing cost of the entire unit. On the other hand, the light-shielding mask 9 serves to prevent light from entering the holder portion 80A of the first lens array 8A and to prevent a problem that the light transmitted through the holder portion 80A reaches the imaging point R. At the same time, the light traveling at a large inclination angle with respect to the axis C of the convex lenses 81A and 81B is prevented from traveling into the convex lenses 81A and 81B. Therefore, an erecting equal-magnification image (a ′ → b ′ → c ′) can be made clear.
[0005]
[Problems to be solved by the invention]
The inventors of the present application manufactured the lens array unit having the structure described above, and provided it for testing and actual use. For example, it was confirmed that sufficient optical performance was obtained for use in a general facsimile machine. Although it was possible, it was found that when the formed image actually obtained was compared with the theoretical value obtained by simulation, the sharpness was inferior. The inventors of the present application have sought to investigate the cause, and as a result, have found that light diffraction is the cause. That is, when light travels in the through hole 90 of the light shielding mask 9, light passing through the vicinity of the opening periphery of the through hole 90 is diffracted and changes in the traveling direction. As a result of such diffracted light subsequently passing through the lenses of the first and second lens arrays 8A and 8B and reaching the image forming point R, the sharpness of the formed image was lowered. Depending on the application of the lens array, the optical performance may have to be further improved. In the past, there has been room for improvement in order to meet such a demand.
[0006]
The invention of the present application has been conceived under such circumstances, and has a superior optical performance capable of reducing the influence of light diffraction and improving the sharpness of an image formed as compared with the prior art. The problem is to provide an array unit.
[0007]
DISCLOSURE OF THE INVENTION
In order to solve the above problems, the present invention takes the following technical means.
[0008]
The lens array unit provided by the first aspect of the present invention includes a plurality of lenses arranged in a line, a plurality of first lens surfaces for light incidence, and a plurality of second lens surfaces for light emission. At least one lens array having a plurality of through holes penetrating in the axial length direction of each of the lenses, and the plurality of through holes being positioned in front of the first lens surfaces. A first light-shielding mask that covers the front surface of the lens array, the lens array unit having a plurality of through-holes penetrating in the axial direction of the lenses, and the plurality of the plurality of through-holes. The apparatus further includes a second light shielding mask disposed behind the lens array so that a through hole is located behind each second lens surface, and the first light shielding mask includes the second light shielding mask. From shading mask It is characterized in that the axial length direction of the thickness of each lens is small.
[0010]
In a preferred embodiment of the present invention, the first and second light shielding masks are such that at least the inner wall surface of each through hole is black or a dark color close thereto.
[0011]
In a preferred embodiment of the present invention, the lens array is formed by integrally forming the lenses and a holder portion for holding the lenses with a synthetic resin having translucency.
[0012]
In a preferred embodiment of the present invention, each of the lenses of the lens array is capable of forming an erecting equal-magnification image of the object when receiving light from the object. Is a convex curved surface.
[0013]
In a preferred embodiment of the present invention, the lens array includes a first lens array and a second lens array stacked such that the axes of the lenses are aligned, and the first and second lens arrays. Is configured such that an erecting equal-magnification image of the object can be formed by transmitting light from the object through the respective lenses of the first and second lens arrays.
[0014]
In a preferred embodiment of the present invention, the first and second lens surfaces are convex curved surfaces having a larger diameter than one end opening of each through hole of the first and second light shielding masks, And it has partially entered these through holes.
[0015]
The optical device provided by the second aspect of the present invention includes the lens array unit provided by the first aspect of the present invention.
[0016]
Other features and advantages of the present invention will become more apparent from the following description of embodiments of the invention.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be specifically described with reference to the drawings.
[0018]
1 to 3 show an example of a lens array unit according to the present invention. The lens array unit U1 of this embodiment includes a lens array 1 and first and second light shielding masks 2A and 2B.
[0019]
The lens array 1 has a substantially block shape extending in a fixed direction, and a plurality of convex lenses 11 arranged in two rows in the longitudinal direction of the lens array 1 and a holder portion 10 connected to the plurality of convex lenses 11 and holding them. And have. Each convex lens 11 and the holder portion 10 are integrally formed of a synthetic resin having translucency. The specific material is, for example, PMMA (polymethyl methacrylate (methacrylic resin)) or PC (polycarbonate).
[0020]
The convex lens 11 is a biconvex lens having first and second lens surfaces 11 a and 11 b as convex curved surfaces spaced in the thickness direction of the lens array 1. Unlike the prior art shown in FIG. 11, the lens array 1 is configured so that an erecting equal-magnification image of an object can be formed only by the lens array 1. If the structure of the convex lens 11 is shown typically, it has a structure as shown in FIG. In the figure, when the first lens surface 11a receives light from an object (a → b) existing at the start point S in front of the first lens surface 11a, the first lens surface 11a focuses the light to focus the object. This is a convex curved surface that forms an inverted reduced image (a ″ → b ″) inside the convex lens 11. The second lens surface 11b is a convex curved surface that inverts and enlarges the inverted reduced image (a "→ b") when receiving light transmitted through the first lens surface 11a. Thus, an erecting equal-magnification image (a ′ → b ′) of the object (a → b) can be formed at the imaging point R behind the second lens surface 11b.
[0021]
The plurality of convex lenses 11 are arranged in a staggered pattern. Although the size of the first and second lens surfaces 11a and 11b is not particularly limited, the diameter D2 of the second lens surface 11b may be larger than the diameter D1 of the first lens surface 11a.
[0022]
The first and second light shielding masks 2A and 2B are both made of, for example, black synthetic resin having light shielding properties. These are substantially plate-shaped or substantially block-shaped extending in a certain direction, and have a plurality of through holes 20A, 20B corresponding to the arrangement of the plurality of convex lenses 11 of the lens array 1. The inner wall surfaces of these through holes 20A and 20B are also black. Both the first and second light shielding masks 2A and 2B can be manufactured by resin molding using a mold, and the through holes 20A and 20B can be formed at the time of the resin molding. However, the through holes 20A and 20B may be formed by machining or the like.
[0023]
The first light shielding mask 2A is assembled to the lens array 1 so as to be superimposed on the front surface (upper side in the drawing) of the lens array 1. This assembly is performed, for example, by fitting a pair of convex portions 13a at both ends in the longitudinal direction of the lens array 1 to a pair of concave portions 23a at both ends in the longitudinal direction of the first light shielding mask 2A. By these fittings, each through hole 20A is positioned so as to open in front of each first lens surface 11a. The diameter D1 of the first lens surface 11a is larger than the lower opening diameter Da of the through hole 20A, and a part of the first lens surface 11a enters the lower opening of the through hole 20A.
[0024]
The second light shielding mask 2B is assembled to the lens array 1 so as to be superimposed on the back of the lens array 1. Also in this assembly, for example, like the first light shielding mask 2A, the pair of convex portions 13b at both ends in the longitudinal direction of the lens array 1 are fitted into the pair of concave portions 23b at both ends in the longitudinal direction of the second light shielding mask 2B. Each through hole 20B is positioned so as to open behind each second lens surface 11b. The diameter D2 of the second lens surface 11b is larger than the upper opening diameter Db of the through hole 20B, and a part of the second lens surface 11b enters the upper opening of the through hole 20B.
[0025]
The thickness ta of the first light shielding mask 2A is, for example, about 1 mm, and is relatively thin. On the other hand, the thickness tb of the second light shielding mask 2B is, for example, about 3 mm, which is larger than that of the first light shielding mask 2A.
[0026]
Next, the operation of the lens array unit U1 will be described.
[0027]
The lens array unit U1 constitutes an optical system as shown in FIG. 5, for example. In this optical system, when light starting from the starting point S in front of the first light shielding mask 2A passes through each through-hole 20A of the first light shielding mask 2A, this light is then transmitted to each convex lens 11 and the second light shielding. After passing through each through-hole 20B of the mask 2B, it reaches the imaging point R behind them. The operation of each convex lens 11 is as described with reference to FIG. Accordingly, an erecting equal-magnification image (a ′ → b ′ → c ′) of the object (a → b → c) at the starting point S shown in FIG. Since the front surface of the holder portion 10 of the lens array 1 is covered with the first light shielding mask 2A, the light traveling from the starting point S does not pass through the holder portion 10 and reach the imaging point R.
[0028]
When light travels in each through-hole 20A of the first light shielding mask 2A, light passing through the vicinity of the opening of each through-hole 20A is diffracted (in FIG. 5, diffracted light is shown) as in the case of the prior art. Not) However, in the lens array unit U1, the influence of the diffraction on the imaging at the imaging point R can be reduced by the following.
[0029]
First, since the thickness of the first light-shielding mask 2A is reduced, the distance from the surface (upper surface) of the first light-shielding mask 2A to the imaging point R is shortened accordingly. More specifically, when a case where the thickness ta of the first light-shielding mask 2A is small as shown in FIG. 7A and a case where the thickness ta ′ is large as shown in FIG. The distances L1 and L2 from the surface of the first light shielding mask 2A to the imaging point R are L1 <L2, and the distance becomes shorter as the thickness of the first light shielding mask 2A is smaller. Assuming that light is diffracted by a predetermined angle θ at the upper opening of each through-hole 20A and this diffracted light travels straight thereafter, the longer the travel distance, the longer the travel distance of the diffracted light from the original optical path indicated by the thin line in FIG. The amount of deviation increases. Accordingly, the diffracted light shift amounts s1 and s2 at the image forming points R in FIGS. 4A and 4B are s1 <s2, and the smaller the thickness of the first light shielding mask 2A, the larger the thickness. The amount of light shift at the image point R is smaller than in the case. In the lens array unit U1, since the thickness of the first light-shielding mask 2A is reduced, the degree of the diffracted light as described above blurring the formed image at the image forming point R according to the principle described above. It can be made smaller. The reason why the thickness of the first light shielding mask 2A can be reduced is that the second light shielding mask 2B is provided, which will be described later.
[0030]
In FIG. 5, the thickness of the second light shielding mask 2B is larger than that of the first light shielding mask 2A, and the depth of each through hole 20B is deeper. For this reason, of the light emitted from the second lens surface 11b, the light traveling at a relatively large inclination angle with respect to the axis C of the convex lens 11 reaches the inner wall surface of each through-hole 20B. Since the inner wall surface is black, the light that reaches the inner wall surface is absorbed and does not travel to the imaging point R. The light blocked by the second light shielding mask 2B in this way includes light diffracted at a large angle when entering the through holes 20A of the first light shielding mask 2A. Therefore, this also makes it difficult for the formed image to be affected by the diffracted light, and makes the formed image clear.
[0031]
In order to make the formed image clear, it is desired that the light traveling at a relatively large inclination angle with respect to the axis C of the convex lens 11 does not reach the image forming point R as much as possible. Here, unlike the present embodiment, when only the first light shielding mask 2A is used without using the second light shielding mask 2B, the thickness of the first light shielding mask 2A must be increased. . On the other hand, in the present embodiment, since the light with a large inclination angle can be blocked by the second light shielding mask 2B, the thickness of the first light shielding mask 2A can be reduced. The effects described with reference to FIGS. 7A and 7B can be preferably obtained.
[0032]
The diffraction of light is not limited to the case where light passes through the upper opening of each through hole 20A, but also passes through the lower opening of each through hole 20A, and the upper and lower openings of each through hole 20B. It can also happen if you do. However, among these diffractions of light, the largest effect on the imaged image is the diffraction that occurs at the upper opening of each through-hole 20A that first receives light and is farthest from the imaging point R. is there. As described above, in the present embodiment, since the influence of the diffraction of light generated in that portion on the formed image can be reduced, the sharpness of the formed image is effectively increased.
[0033]
Next, considering the optical action in the width direction of the lens array unit U1, in FIG. 6, the light from the point P of the starting point S passes through each of the two convex lenses 11 arranged in the width direction of the lens array 1. To reach the same point of the image forming point R to form an image P ′. In this way, if the same image is formed using the light passing through the two convex lenses 11, the amount of light reaching the imaging point is larger than the case where only one convex lens is used. A bright image is obtained. Since the plurality of convex lenses 11 are arranged in a staggered manner, the pitch of the lenses in the width direction of the lens array 1 can be reduced to appropriately achieve the above. In addition, since each convex lens 11 has a larger diameter on the second lens surface 11b than on the first lens surface 11a, most of the light incident on the first lens surface 11a is supplied to the second lens surface 11a. The light can be effectively emitted from the surface 11b. Therefore, the image at the image point R can be brightened also by such a thing.
[0034]
As shown in FIG. 1, the first and second light shielding masks 20A and 20B are assembled to the lens array 1 by fitting a pair of convex portions 13a and 13b and a pair of concave portions 23a and 23b. For this reason, the lens array 1 is not easily displaced. Since a part of the first and second lens surfaces 11a and 11b are fitted into the through holes 20A and 20B of the first and second light shielding masks 2A and 2B, the above-described positional deviation is more reliably prevented. The In addition, since each of the first and second lens surfaces 11a and 11b has a larger diameter than the one end openings of the through holes 20A and 20B, the through holes 20A and 20B and the first and second lenses are temporarily assumed. Even if a misalignment occurs between the surfaces 11a and 11b, the through holes 20A and 20B are appropriately placed in front of or behind the first and second lens surfaces 11a and 11b if the deviation is within the radius difference between them. Can also be placed. For example, if the through-hole 20A and the first lens surface 11a have the same diameter, a part of the through-hole 20A is detached from the front surface of the first lens surface 11a even if their centers are slightly shifted. Such a situation can also be avoided in the present embodiment.
[0035]
FIG. 8 shows an example of an optical device according to the present invention.
[0036]
The optical device A shown in FIG. 1 includes a transparent plate 70, a synthetic resin case 71 on which the transparent plate 70 is mounted, and a substrate 72 assembled to the bottom surface of the case 71. . On the surface of the substrate 72, a plurality of dot light sources 73 arranged in a row at intervals in the main scanning direction (direction orthogonal to the paper surface), and the plurality of light sources 73 are arranged in the same direction. A plurality of light receiving elements 74 are mounted. Each light source 73 is configured using, for example, a light emitting diode. Each light receiving element 74 has a photoelectric conversion function, and when receiving light, outputs a signal (image signal) of an output level corresponding to the amount of received light.
[0037]
Between the transparent plate 70 and each light receiving element 74, the above-described lens array unit U1 is disposed. Since the lens array unit U1 is fitted in a concave groove 75 provided in the case 71, a plurality of rows of convex lenses 11 are incorporated so as to extend in the main scanning direction. Of the surface portion of the transparent plate 70, the portion facing the lens array unit U1 is a line-shaped image reading region La. The image reading area La can be irradiated with light from each light source 73.
[0038]
In the optical apparatus A, when the original G guided onto the surface of the transparent plate 70 is irradiated with light from each light source 73, the reflected light travels toward the lens array unit U1. Then, an image for one line of the original G in the image reading area La is formed on the plurality of light receiving elements 74 at an equal magnification by the action of the lens array unit U1 described above. Therefore, an image signal for one line corresponding to the image of the document G is output from the plurality of light receiving elements 74. Such a reading process is repeatedly executed a plurality of times in the process in which the original G is conveyed in the sub-scanning direction by the platen roller 77, for example.
[0039]
In this optical apparatus A, since the lens array unit U1 forms a clear image of the original image on the plurality of light receiving elements 74, a high-quality read image can be obtained. Further, each member constituting the lens array unit U1 can be manufactured by resin molding using a mold, and the cost thereof can be reduced. Therefore, the entire manufacturing cost of the optical device A is also low. Become.
[0040]
9 and 10 show another embodiment of the present invention. In these drawings, the same or similar elements as those in the above embodiment are denoted by the same reference numerals as those in the above embodiment.
[0041]
The lens array unit U2 shown in FIG. 9 is configured to include the first and second lens arrays 1A and 1B, as in the prior art. Each convex lens 14A of the first lens array 1A has lens surfaces 14a and 14a ', and each convex lens 14B of the second lens array 1B has lens surfaces 14b and 14b'. The lens surfaces 14a 'and 14b' face each other. In the present embodiment, the lens surfaces 14a and 14b correspond to the first and second lens surfaces in the present invention. When an erecting equal-magnification image of an object is formed using the first and second lens arrays 1A and 1B as in the present embodiment, light from a total of four lens surfaces 14a, 14a ′, 14b, and 14b ′ Therefore, the curvature of each lens surface can be made gentler than that of the lens array unit U1. This is suitable for reducing defocus when there is distortion on each lens surface. On the other hand, according to the lens array unit U1, the number of parts can be reduced as compared with the lens array unit U2, the cost can be reduced more thoroughly, the overall thickness can be reduced, and the space can be reduced. It will be suitable for mounting use.
[0042]
The lens array 1C of the lens array unit U3 shown in FIG. 10 has a substantially rectangular plate shape, and is configured as a planar lens array in which a plurality of convex lenses 11 are arranged in a matrix. The first and second light shielding masks 2C and 2D are also substantially rectangular plate shapes corresponding to the lens array 1C, and have a configuration in which a plurality of through holes 20C and 20D are arranged in a matrix. According to such a lens array unit U3, it is possible to form an image of a planar region having a certain area at an erecting equal magnification. Therefore, for example, it is suitable for an application in which an image displayed on the screen of a liquid crystal display or other display device is imaged at a predetermined position at an equal magnification.
[0043]
As understood from these embodiments, the specific arrangement of the plurality of lenses is not particularly limited in the lens array unit according to the present invention. It can also be set as the structure which provided the several lens only in 1 row. Further, the lens array unit is not limited to one that forms an erecting equal-magnification image. Depending on the optical device, for example, it may be desired to form an inverted reduced image of an object using a lens array. In the present invention, it may be configured as a lens array unit used for such an application. Each lens of the lens array is not limited to a biconvex lens, and may be a single convex lens or a concave lens.
[0044]
The present invention is not limited to the contents of the above-described embodiment, and the specific configuration of each part can be varied in design in various ways.
[0045]
For example, the first and second light shielding masks referred to in the present invention do not have to be made of black synthetic resin, and can be configured to have a dark color close to black or a color different from them. However, at least the inner wall surface of each through hole is preferably black or a dark color close to it from the viewpoint of preventing unnecessary reflection of light. The light-shielding mask does not need to be manufactured by a resin molding process, and its specific manufacturing method does not matter. As a means for forming the first light-shielding mask thinly, for example, a portion of the lens array excluding the lens surface may be painted black, and this coating film may be used as the first light-shielding mask.
[0046]
The lens array unit according to the present invention does not require the first and second light shielding masks to be directly attached to the lens array. The first and second light shielding masks may be configured to cover the lens array by being attached to a member different from the lens array.
[0047]
The optical device according to the present invention is not limited to an image reading device for reading various images. The present invention can also be applied to an optical device having a configuration in which, for example, light emitted from a light source is condensed to perform exposure processing at a predetermined location.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a lens array unit according to the present invention.
FIG. 2 is a cross-sectional view taken along the line II-II in FIG.
3 is an exploded perspective view of the lens array unit shown in FIG. 1. FIG.
FIG. 4 is an explanatory diagram showing the operation of a convex lens.
FIG. 5 is an operation explanatory diagram of the lens array unit shown in FIG. 1;
6 is an operation explanatory diagram of the lens array unit shown in FIG. 1. FIG.
FIGS. 7A and 7B are explanatory diagrams for understanding the operation of the present invention. FIG.
FIG. 8 is a cross-sectional view showing an example of an optical device according to the present invention.
FIG. 9 is a cross-sectional view showing another example of a lens array unit according to the present invention.
FIG. 10 is an exploded perspective view showing another example of a lens array unit according to the present invention.
FIG. 11 is a cross-sectional view showing an example of a conventional technique.
[Explanation of symbols]
U1 to U3 Lens array unit A Optical device 1, 1C Lens array 1A First lens array 1B Second lens array 2A, 2C First light shielding mask 2B, 2D Second light shielding mask 10 Holder portion 11 Convex lens 11a First Lens surface 11b Second lens surface 14A, 14B Convex lens 20A, 20B Through-hole

Claims (7)

A plurality of lenses arranged in a line, and at least one lens array having a plurality of first lens surfaces for light incidence and a plurality of second lens surfaces for light emission;
A plurality of through holes penetrating in the axial length direction of the respective lenses, and the plurality of through holes covering the front of the lens array so as to be positioned in front of the first lens surfaces; 1 shading mask;
A lens array unit comprising:
Each lens has a plurality of through holes penetrating in the axial length direction, and the plurality of through holes are arranged behind the lens array so as to be located behind the second lens surfaces. A second shading mask , and
The lens array unit according to claim 1, wherein the first light-shielding mask has a smaller axial thickness of each lens than the second light-shielding mask . 2. The lens array unit according to claim 1, wherein the first and second light shielding masks have at least an inner wall surface of each of the through holes being black or a dark color close thereto. 3. The lens array unit according to claim 1, wherein the lens array is formed by integrally forming the lenses and a holder portion for holding the lenses with a synthetic resin having translucency. Each lens of the lens array has a convex curved surface on each of the first and second lens surfaces so that an erecting equal-magnification image of the object can be formed when receiving light from the object. , the lens array unit according to any one of claims 1 to 3. The lens array includes a first lens array and a second lens array which are stacked so that the axes of the lenses are aligned, and the first and second lens arrays are configured so that light from an object is the first one. and by passing through the respective lenses of the second lens array and is configured to be imaged the erect image of the object, the lens array unit according to any one of claims 1 to 3. The first and second lens surfaces are convex curved surfaces having a diameter larger than that of one end openings of the through holes of the first and second light shielding masks, and partly enter the through holes. The lens array unit according to any one of claims 1 to 5 . Characterized in that it comprises a lens array unit according to any one of claims 1 to 6, the optical device.

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