Optical line sensor

Abstract

A plurality of light-receiving lenses 11 are arranged along the main scanning direction. A plurality of light-receiving elements are arranged in a line along the main scanning direction, and receive light which has passed through the plurality of light-receiving lenses 11. The plurality of light-receiving elements form at least two rows of reading lines L. The light-receiving lenses 11 form a telecentric optical system, and the width W1 in the auxiliary scanning direction is smaller than the width W2 in the main scanning direction.

Description

Technical Field

[0001] The present invention mainly relates to an optical line sensor for detecting scratches and defects on the surface of thin inspection objects such as printed matter and films, and scratches and defects inside transparent films.

Background Art

[0002] A contact type optical sensor (hereinafter referred to as CIS) that has been used in inspection machines for discriminating the authenticity of banknotes, flatbed scanners such as office copiers and home printer scanners, etc., has been considered for application to so-called surface inspection machines for inspecting the printing quality of printed matter, surface inspection in the manufacturing process of thin and wide film products, inspection of labels attached to various beverage containers, food containers, cans, etc., and some have been commercialized.

[0003] However, in the CIS that applies SELFOC lenses (「SELFOC」 is a registered trademark, the same applies hereinafter), the working distance (hereinafter referred to as W.D.) is short. In order to avoid contact in the scenes used in the process, a CIS with a long W.D. is desired. In addition, in the inspection of paper materials such as banknotes, although the depth of field can withstand use even if it is relatively shallow, a CIS with a deep depth of field is also strongly desired because the variation of the inspection object in the optical axis direction is large in the manufacturing process of the inspection object.

[0004] As shown in Patent Documents 1 to 5, a telecentric optical system using a mirror optical system is typical for a CIS with a deep depth of field. From the above patent documents, it can be seen that the optical system is very complex. When manufacturing and operating this optical system as a product, it is accompanied by great difficulties. That is, during manufacturing, the process becomes complicated, and manufacturing stability and cost increase become problems. Also, even after commercialization, due to the complex optical system caused by environmental changes and aging changes, the optical axis drifts, and problems such as performance degradation are likely to occur compared to conventional CISs with a simple structure remain.

[0005] Therefore, it is conceivable to improve the W.D. and the depth of field by using a refractive lens made of glass or resin without using the telecentric reflective optical system. Regarding the optical system of the refractive system, certain solutions have been proposed as shown in Patent Document 6 and Patent Document 7. For example, in Patent Document 6, one telecentric refractive optical system is arranged at a distance from a staggered line sensor, and the lenses of the refractive optical system are arranged at a distance and arrayed to realize an optical system with a deep depth of field. In Patent Document 7, a method of preventing crosstalk between lenses by providing a partition plate between the separated lenses is being studied. In Patent Document 6 and Patent Document 7 mentioned above, it is possible to improve the depth of field and prevent crosstalk between lenses, but a normal telecentric refractive optical system is large and it is difficult to make it compact. In addition, in the partition plate shown in Patent Document 7, missing pixels are generated during reading, resulting in incomplete reading. Furthermore, no solution for the shading that one lens inherently has due to the separation of the lenses is shown. The method of suppressing the so-called ripple in the reading line direction is not mentioned either. Moreover, the refractive optical system method has not been realized yet.

[0006] Furthermore, an inspection machine using a camera lens such as a line camera, which is a different method from the above method, is large, and in order to cope with inspection objects with a wide width at the manufacturing site, a large number of units are required. Therefore, the entire device becomes very large, and moreover, its cost is enormous, so it is difficult to deploy it in each process of the factory.

[0007] In order to solve the above problems, a new refractive lens that is small, inexpensive, and can be introduced into each process of the factory, has a long W.D. and a deep depth of field, and uses a new suppression method for the ripple, which is the optical unevenness on the light receiving sensor caused by the shading of each lens, is desired.

Prior Art Documents

Patent Documents

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-019334 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-152713 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-244500 [Patent Document 4] Japanese Patent Application Laid-Open No. 2018-019334 [Patent Document 5] Japanese Patent Application Laid-Open No. 2018-022948 [Patent Document 6] Japanese Patent Application Laid-Open No. 2009-246623 [Patent Document 7] Japanese Patent Application Laid-Open No. 5-14600 [Summary of the Invention] [Problems to be Solved by the Invention]

[0009] Therefore, an object of the present invention is to realize an optical line sensor with a deep depth of field and a compact size. [Means for Solving the Problems]

[0010] The optical line sensor according to the present invention is an optical line sensor that reads an inspection object conveyed in the sub-scanning direction with a reading line extending in the main scanning direction, and includes a plurality of light receiving lenses and a plurality of light receiving elements. The plurality of light receiving lenses are arranged in a plurality along the main scanning direction. The plurality of light receiving elements are arranged in a line along the main scanning direction and receive light transmitted through the plurality of light receiving lenses. The plurality of light receiving elements form at least two or more of the reading lines. The light receiving lens constitutes a telecentric optical system, and the width in the sub-scanning direction is smaller than the width in the main scanning direction. [Effects of the Invention]

[0011] According to the present invention, by using a telecentric optical system, an optical line sensor with a deep depth of field can be realized. Further, since the width of the light receiving lens in the sub-scanning direction is smaller than the width in the main scanning direction, the light receiving lens can be arranged closer in the sub-scanning direction. As a result, the optical line sensor can be made compact. If the light receiving lens is arranged closer in the sub-scanning direction, the light receiving element can also be arranged closer in the sub-scanning direction, so that the processing of the image of the inspection object obtained based on the output signal from the light receiving element (for example, image synthesis processing) can be simplified.

Brief Description of Drawings

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Embodiments for Carrying Out the Invention

[0013] 1. Overall Configuration of Optical Line Sensor A typical CIS is shown in FIG. 1, and a line-shaped illumination optical system for the CIS is similarly shown in FIG. 2. In FIG. 1, a cross-sectional view near the central portion in the longitudinal direction of the CIS is shown. On the other hand, FIG. 2 is an exploded perspective view. The X direction is the main scanning direction, and the Y direction is the sub-scanning direction. The Z direction is orthogonal to the X direction and the Y direction. The line-shaped light source unit 10 is an illumination optical system having an elongated light quantity distribution in the main scanning direction.

[0014] In the CIS shown in FIG. 1, two housings 16 are arranged opposite to each other with the focal plane (inspection surface) 20 interposed therebetween. In each housing 16, a line-shaped light source unit 10 for illuminating an inspection object on the focal plane 20 is provided. In one of the housings 16, a light-receiving lens 11 and a light-receiving unit 12 are provided, and the light from the illuminated inspection object is guided to the light-receiving unit 12 by the light-receiving lens 11. The light-receiving lens 11 forms an image of the light from the inspection object on the light-receiving unit 12. In the CIS shown in FIG. 1, with the focal plane 20 as a reference, one of the two light source units 10 is arranged on the light-receiving unit 12 side, and the other is arranged on the side opposite to the light-receiving unit 12 side.

[0015] The light-receiving unit 12 is mounted on a substrate 13 fixed to one of the housings 16. The light that has passed through the light-receiving lens 11 is received by the light-receiving surface 12A of the light-receiving unit 12, and a signal corresponding to the amount of received light is output from the light-receiving unit 12. As the inspection object is conveyed in one direction Y along the focal plane 20, the light from the inspection object is continuously received by the light-receiving unit 12, and an image (such as a color image or a fluorescence image) of the inspection object is obtained based on the output signal from the light-receiving unit 12. In this way, the inspection object conveyed in the sub-scanning direction (Y direction) is read by a reading line formed by the light-receiving surface 12A of the light-receiving unit 12, which extends in the main scanning direction (X direction).

[0016] The light B3 emitted from one of the light source units 10 passes through the protective glass 14 fixed to the housing 16, is reflected by a reflecting member 17A provided on the inner surface of the protective glass 14A fixed to the other housing 16, and is guided to the focal plane 20. An ultraviolet light blocking filter (UV cut filter) 15 for preventing ultraviolet light from entering the light-receiving unit 12 is provided at an arbitrary position from the focal plane 20 to the light-receiving unit 12. Also, a color filter 18 for passing visible light in a specific wavelength range is provided between the light-receiving unit 12 and the ultraviolet light blocking filter 15. A substrate 5 for fixing a light source 103 (such as an ultraviolet light source or a visible light source) provided in the light source unit 10 is installed at a position facing the bottom surface of the light source unit 10 in one of the housings 16.

[0017] In the example shown in FIGS. 1 and 2, the light source unit 10 includes a transparent light guide 101 extending along the longitudinal direction L, a light source 103 provided near one end surface in the longitudinal direction L, and a cover member 102 for holding each side surface of the light guide 101. The light emitted from the light source 103 enters the light guide 101, is appropriately reflected by the light diffusion pattern P while propagating in the light guide 101, and is emitted in the direction of the arrow from the light emission surface, becoming linear illumination light to illuminate the inspection object. The depth of field of such a CIS is shallow, and when the inspection object has a thickness, it is difficult to inspect the entire thickness direction. Also, since the W.D. is narrow, the inspection object often comes into contact with the inspection object and the inspection itself does not hold.

[0018] In the CIS as described above, for the light-receiving lens 11, for example, a SELFOC (manufactured by Nippon Sheet Glass Co., Ltd.) lens array is used. The SELFOC lens array is an erect and same-magnification lens array. In this lens array, columnar SELFOC lenses are stacked to form a multi-lens. The advantage of the multi-lens is that it can make the so-called brightness of the lens brighter than that of a single lens. That is, the F-number of the multi-lens formed by arranging a plurality of single lenses side by side is smaller than the F-number of a single lens. This is because the effective F-number becomes smaller at the position where the focal position of one lens at an arbitrary position coincides with the focal positions of the lenses around the lens. Conversely, in an erect lens system, it means that the numerical aperture (hereinafter referred to as N.A.) becomes larger when arrayed than that of a single lens. This property is the main reason why the SELFOC lens array is used in the CIS.

[0019] The advantage of the CIS as described above is conversely disadvantageous from the viewpoints of the depth of field and the depth of focus. As is the case with a single-lens, when the numerical aperture increases, the depth of field becomes shallower. For example, in a microscope objective lens, it is well known that as the magnification increases, that is, as the N.A. increases, the depth of field becomes shallower. Also, in a camera lens, the difference in the depth of field between a distant view and a close view is clearly shown, and the aperture is adjusted to ensure the depth of field. That is, the N.A. is changed to obtain a desired depth of field. In addition, an erect multi-lens typified by a SELFOC lens has a structure in which the optical axes of the respective lenses are different and intersect, so that the image is more likely to be blurred when the inspection object changes in the optical axis direction compared with a single-lens. The above is a major drawback of the stacked multi-lens SELFOC lens array. Therefore, as a result of studying how to increase the depth of field of a compact optical line sensor, the obtained embodiments are described below. In the following embodiments, the light-receiving lens 11 constitutes a telecentric optical system.

[0020] 2. Embodiments of the light-receiving system First, the first method is to adopt an array structure that can be regarded as a monocular lens formed by an optical line sensor as shown in FIG. 3. FIG. 3 is a schematic diagram of a light receiving system in which the fields of view of the respective light receiving lenses 11 do not overlap. In FIG. 3, in order to prevent the fields of view of the respective light receiving lenses 11 from overlapping, the respective light receiving lenses 11 are arranged at intervals in the main scanning direction (X direction), and the respective light receiving lenses 11 are also arranged at intervals in the sub-scanning direction (Y direction), whereby the respective light receiving lenses 11 are arranged in a staggered pattern.

[0021] That is, instead of the stacking method, a plurality of light receiving lenses 11 arranged in a plurality along the main scanning direction (X direction) are arranged at intervals from each other. The plurality of light receiving lenses 11 arranged in a plurality along the main scanning direction (X direction) are integrally held by a lens holder 110. At positions facing the respective light receiving lenses 11 in the Z direction, a light receiving element array 120 is arranged which is formed by arranging a plurality of light receiving elements (not shown) in a line along the main scanning direction (X direction). That is, one light receiving element array 120 is formed by arranging a plurality of light receiving elements in an array along the main scanning direction (X direction). Each light receiving element receives the light transmitted through each light receiving lens 11.

[0022] In this example, a light receiving element array 120 is arranged in association with each light receiving lens 11. As a result, each light receiving element array 120 composed of a short sensor is arranged in a staggered pattern alternately along the main scanning direction (X direction). The plurality of light receiving element arrays 120 arranged in a plurality along the main scanning direction (X direction) form one row of reading lines L, and in the example of FIG. 3, two rows of reading lines L are formed. The lens holder 110 is not limited to a configuration provided in association with each reading line L, and may be a configuration in which a single lens holder integrally holds a plurality of light receiving lenses 11 corresponding to each reading line L.

[0023] As shown in FIG. 3, one light-receiving lens 11 may be provided for each light-receiving element array 120, so that a plurality of light-receiving lenses 11 may be arranged in number corresponding to the plurality of light-receiving element arrays 120. The optical axes of the light transmitted through each light-receiving lens 11 and guided to each light-receiving element array 120 may pass through substantially the central portions in the main scanning direction (X direction) of the corresponding light-receiving element arrays 120 on a one-to-one basis. In this method, a plurality of light-receiving element arrays 120 are arranged in a plurality of rows in the sub-scanning direction (Y direction). That is, the plurality of light-receiving element arrays 120 are arranged at intervals in a direction (Y direction) perpendicular to the arrangement direction (X direction) of the light-receiving elements.

[0024] Each light-receiving lens 11 has a width W1 in the sub-scanning direction smaller than the width W2 (lens diameter) in the main scanning direction. That is, each light-receiving lens 11 has an elongated shape along the main scanning direction. The width W1 of each light-receiving lens 11 in the sub-scanning direction corresponds to the field of view of each light-receiving lens 11 in the sub-scanning direction. Also, the width W2 of each light-receiving lens 11 in the main scanning direction corresponds to the field of view of each light-receiving lens 11 in the main scanning direction. It is preferable that the width W1 of each light-receiving lens 11 in the sub-scanning direction is set so that N.A. satisfies 0.001 < N.A. < 0.05. In this example, each light-receiving lens 11 has the same shape and is formed in a rectangular shape when viewed from the direction (Z direction) orthogonal to the main scanning direction and the sub-scanning direction. However, each light-receiving lens 11 is not limited to a rectangle (rectangular shape), and may be an oval or an ellipse, or may have other shapes.

[0025] The plurality of light-receiving lenses 11 are arranged to be spaced apart from each other by a distance equal to or less than the width W2 in the main scanning direction of the light-receiving lens. That is, it is preferable that the plurality of light-receiving lenses 11 are arranged to be spaced apart from each other by a distance equal to or less than the field-of-view dimension (within the field-of-view range) in the main scanning direction of the light-receiving lens 11. As in the example of FIG. 3, the fields of view of the respective light-receiving lenses 11 may be superimposed in the sub-scanning direction. In this case, for the light-receiving elements in the portion where the fields of view of the plurality of light-receiving lenses 11 overlap, the pixel output from the light-receiving element may be subjected to subtraction processing. For example, an image of one light-receiving lens 11 (the amount of light received by the light transmitted through one light-receiving lens 11) may be excluded from the data output from the light-receiving element, or the pixel output from the light-receiving element may be set to an output value approximately half when performing image synthesis. By using a plurality of light-receiving element columns (light-receiving element array 120), the occurrence of pixel dropout can be more reliably prevented than in the case of a single row of light-receiving elements.

[0026] FIG. 4 is a schematic diagram showing another example of a light-receiving system in which a plurality of light-receiving element arrays 120 are arranged. In the example of FIG. 4, each light-receiving lens 11 and each light-receiving element array 120 do not correspond one-to-one, but a plurality (two in this example) of light-receiving lenses 11 arranged in the main scanning direction correspond to one light-receiving element array 120.

[0027] The plurality of light-receiving lenses 11 corresponding to one light-receiving element array 120 are adjacent to each other in the main scanning direction. However, the plurality of light-receiving lenses 11 corresponding to one light-receiving element array 120 may be spaced apart from each other, and in this case, they may be spaced apart from each other by a distance equal to or less than the width W2 in the main scanning direction of the light-receiving lens 11. Also, a light-shielding member may be provided between the respective light-receiving lenses 11.

[0028] FIG. 5 is a schematic diagram showing still another example of the light receiving system in which a plurality of light receiving element arrays 120 are arranged. In FIG. 5, each light receiving element array 120 composed of a long sensor of the same length (the length corresponding to the entire length in the main scanning direction) is arranged in parallel in a plurality (two in this example) side by side in the sub-scanning direction. As shown in this FIG. 5, by associating one light receiving element array 120 with a plurality of light receiving lenses 11 arranged in the main scanning direction (X direction), a plurality of light receiving element arrays 120 may be arranged by the number of columns of the light receiving lenses 11 in the sub-scanning direction (Y direction).

[0029] In any of FIGS. 3 to 5, since the width W1 of the light receiving lens 11 in the sub-scanning direction is smaller than the width W2 in the main scanning direction, the light receiving lenses 11 can be arranged closer to each other in the sub-scanning direction. As a result, the optical line sensor can be made compact. As described above, the short light receiving element arrays 120 may be arranged in a staggered pattern (see FIGS. 3 and 4), or two rows of light receiving element arrays 120 may be arranged spaced apart (see FIG. 5), but not limited thereto, and more light receiving element arrays 120 may be arranged spaced apart in the sub-scanning direction (Y direction).

[0030] 3. Long focal length conversion of the light receiving lens Next, the telecentric focusing of the light-receiving lens will be described. Conventional SELFOC lenses have focused on the miniaturization and cost reduction of CIS, and lenses with a shorter conjugate length have been demanded. However, this trend has contributed to reducing the allowable depth of field. Moreover, the lens diameter has been decreasing. When the light-receiving lens is focused telecentrically, if a conventional light-receiving lens is used, the N.A. becomes extremely small. Therefore, the influence of diffraction increases, and the blur due to the diffraction limit becomes the dominant factor in the degradation of optical resolution rather than the blur due to the geometric optical aberration of the light-receiving lens itself. Since the conventional CIS has a large N.A., it has been able to ignore the blurring of the image due to the diffraction limit. However, in order to increase the W.D., it is necessary to extend the focal length of the light-receiving lens, that is, since the N.A. becomes smaller, with the conventional lens diameter, the influence of diffraction increases as the focal length increases. In this embodiment, a method is proposed in which the W.D. is increased by increasing the lens diameter, and even when the blurring of the image due to the diffraction limit is reduced, the optical resolution is not degraded.

[0031] The Abbe diffraction limit d is inversely proportional to the numerical aperture N.A. Since the optical system is in air, the following formula (1) holds using the wavelength λ in air. d = λ / N.A. (Formula 1) Fig. 6 shows the relationship between the N.A. and the diffraction limit for each wavelength. In the light-receiving lens 11 with the same lens parameters, if the so-called pitch of the light-receiving lens 11 itself is shortened, the focal length increases and the influence of aberration decreases.

[0032] From the above, it can be seen that in order to focus the light-receiving lens 11 telecentrically, it is necessary to increase the lens diameter. If the N.A. is kept the same, the influence of diffraction can be made equivalent to that of the light-receiving lens 11 with a short focal length. However, when the lens diameter is increased, the geometric optical aberration increases. Therefore, it is necessary to examine the minimum confusion circle diameter when the lens diameter is increased in the light-receiving lens 11 with different lens parameters. The wavelength λ was set to λ = 630 nm, which has a large diffraction limit diameter.

[0033] As a result of investigations by the inventor of the present application, it has been found that the relationship between the minimum blur circle for each focal length of a certain light-receiving lens 11 should be considered. For example, the case where the focal length f is f = 50 mm is shown in FIGS. 7A to 7C. Here, when three types of SELFOC lenses (SELFOC lens A, SELFOC lens B, and SELFOC lens C) are used as the light-receiving lens 11, FIG. 7A shows the relationship between the effective diameter and the blur circle diameter of SELFOC lens A, FIG. 7B shows the relationship between the effective diameter and the blur circle diameter of SELFOC lens B, and FIG. 7C shows the relationship between the effective diameter and the blur circle diameter of SELFOC lens C, respectively. In FIGS. 7A to 7C, the solid line indicates the total blur circle, the dashed line indicates the blur circle due to diffraction, and the alternate long and short dash line indicates the geometric-optical blur circle, respectively.

[0034] According to FIGS. 6 and 7A, the relationship between the minimum blur circle and the diffraction limit, that is, the optical resolution at a certain lens diameter and focal length can be understood. Therefore, in the case of the light-receiving lens 11 shown in FIG. 7A, it can be seen that the larger the effective diameter Φ, the smaller the blur circle diameter, and it is sufficient if 1.0 mm ≦ Φ ≦ 3.0 mm.

[0035] On the other hand, according to FIGS. 6 and 7B, the geometric-optical blur circle is large and the dependence on diffraction is small, so the blur circle diameter at Φ = 1.0 mm is the smallest. Moreover, even when Φ = 1.0 mm, the blur circle diameter is nearly twice that of the light-receiving lens 11 shown in FIG. 7A. The light-receiving lens 11 shown in FIG. 7A is a SELFOC lens with less aberration and a larger effective diameter than the light-receiving lens 11 shown in FIG. 7B, and it can be seen that the light-receiving lens 11 in FIG. 7A should be selected. Furthermore, the light-receiving lens 11 in FIG. 7A with the same focal length can have an N.A. at least three times larger than that of the light-receiving lens 11 in FIG. 7B, that is, the received light amount becomes nine times or more, and therefore, the output of the light-receiving element also becomes nine times or more. Accordingly, the shot noise that depends on the received light amount of the light-receiving element is also reduced to 1 / 3, so the light-receiving lens 11 shown in FIG. 7A is preferable from the viewpoint of noise suppression. Also, when the same noise amount is allowed, it can be said that the light-receiving lens 11 in FIG. 7A can improve the scanning speed by nine times compared to the light-receiving lens 11 in FIG. 7B.

[0036] According to FIG. 7C, similar to the SELFOC lens A, the SELFOC lens C also has little aberration and can have a large effective diameter.

[0037] Next, the parameters of the SELFOC lenses A to C shown in FIGS. 7A to 7C are shown in Table 1 below. The most important parameter shown in Table 1 is the refractive index distribution constant. The light-receiving lens 11 with little aberration when the effective diameter is enlarged and the focal length is extended is the SELFOC lens A with the smallest refractive index distribution constant. Next, the light-receiving lens 11 with little aberration is the SELFOC lens C. Needless to say, for high-resolution and high-speed inspection, a light-receiving lens 11 with a large effective diameter, high brightness, and little aberration is preferable.

Table 1

[0038] Furthermore, when four types of plastic rod lenses (plastic refractive index distribution type lenses) are used as the light-receiving lens 11, FIG. 8A shows the relationship between the effective diameter and the confusion circle diameter of the rod lens A, FIG. 8B shows the relationship between the effective diameter and the confusion circle diameter of the rod lens B, FIG. 8C shows the relationship between the effective diameter and the confusion circle diameter of the rod lens C, and FIG. 8D shows the relationship between the effective diameter and the confusion circle diameter of the rod lens D. In FIGS. 8A to 8D, the solid line represents the total confusion circle, the broken line represents the confusion circle due to diffraction, and the one-dot chain line represents the geometric optical confusion circle, respectively. Also, the parameters of the rod lenses A to D shown in FIGS. 8A to 8D are shown in Table 2 below. It can be seen that there is a similar tendency in the plastic rod lens as in the SELFOC lens. Considering the refractive index of the plastic rod lens and the refractive index of the glass lens, the on-axis refractive index is preferably about 1.45 to about 1.65.

Table 2

[0039] From the above, it can be seen that the refractive index distribution constant is the dominant factor of aberration. For an ideal refractive index distribution type lens, the gentler the change in refractive index, the less the aberration. This is the same as in the case of a normal spherical lens, where a rapid angular change is the cause of aberration. A rapid angular change means an increase in the higher-order non-linear effect when Snell's Law is expanded into a polynomial. That is, the aberration increases because the deviation from paraxial optics becomes larger. The inventor of the present application has found that in order to achieve a pixel resolution of 400 dpi or more when the focal length or W.D. is approximately 50 mm or more and the effective diameter Φ is approximately Φ ≧ 1.0 mm, it is preferable to set the refractive index distribution constant to 0.12 or less.

[0040] 4. Modified Example of Light-Receiving Lens The light-receiving lens 11 in the present invention is not limited to a refractive index distribution type lens such as a SELFOC lens or a plastic rod lens. In other lenses, for example, an achromat (color-corrected), an apochromat, etc., considering the cost, a lens with the same aberration due to the non-linear effect in the above-mentioned refractive index distribution type lens, that is, a lens with the same spherical aberration, coma aberration, and astigmatism, or a telecentric refractive optical system can be used in the same arrangement and dimensions (aperture) instead of a refractive index distribution type lens such as a SELFOC lens or a plastic rod lens with the same aberration due to the non-linear effect and diffraction limit. This is also the same for the light-receiving lens 11 that forms an inverted image described later.

[0041] The above-described optical system is centered on an erect lens, but in the case where the fields of view do not overlap, an inverted optical system may be used. That is, the plurality of light-receiving lenses 11 may be configured to form an inverted image. In the case of a two-row lens array, an inverted optical system can also be adopted. In the case of an inverted optical system, since the image is inversion-symmetric about the optical axis, when synthesizing images, the inverted image may be converted into an erect image by image processing. That is, after inverting the inverted images of the plurality of light-receiving lenses 11 and converting them into erect images, image synthesis processing may be performed. Further, in the process of that operation, it is only necessary to determine and correct whether the overlapping portions are necessary or unnecessary from the correction algorithm, and convert them into erect images based on the relationship between the determined pixels. Alternatively, in an inspection where images are not constructed, since it is only necessary to detect scratches or defects, there is no need for image synthesis or image processing, and the detection portions on the inspection surface may overlap. In the case of overlapping, position correction using a correction chart may be performed in advance.

[0042] Furthermore, in the case of an inverted refractive optical system, in the signal processing for each light-receiving element, for example, data obtained from one of two rows of light-receiving element arrays arranged staggeredly so as to be separated in the sub-scanning direction may be acquired for a longer time, and data obtained from the other light-receiving element array may be acquired for a shorter time. After performing an inversion operation of the acquired image into an erect image, image synthesis may be performed. Alternatively, after converting the inverted image data of each light-receiving element into an erect image, a correction coefficient may be multiplied or subtracted from the overlapping portions when synthesizing images.

[0043] Specifically, in an inverted refractive optical system, the plurality of light-receiving element arrays may be light-receiving element arrays shorter than each of the plurality of reading lines respectively arranged in two reading lines. Also, the light-receiving element array arranged in one reading line and the light-receiving element array arranged in the other reading line may be alternately arranged in a staggered manner along the main scanning direction. Since such a configuration is the same as that of the erect refractive optical system described in FIG. 3, detailed description thereof will be omitted.

[0044] In this case, as shown in FIG. 3, a plurality of light receiving elements are arranged in an array of two or more rows to form a plurality of light receiving element arrays 120. Further, each of the plurality of light receiving element arrays 120 is arranged so as to be separated from each other in a direction orthogonal to the reading line L by a width W2 or less in the main scanning direction of the light receiving lens 11. A plurality of light receiving lenses 11 are arranged in a number corresponding to the plurality of light receiving element arrays 120, and the optical axes of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120 pass through substantially the central portion of each light receiving element array 120. However, the optical axis of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120 may pass through a position parallel to the sub-scanning direction and separated from the substantially central portion of each light receiving element array 120.

[0045] 5. Configuration of Illumination Optical System In this embodiment, the focal length f of the light receiving lens 11 is f = 50 mm, the N.A. is N.A. = 0.01, 0.02, 0.025, 0.03, and the refractive index distribution constant √A is √A = 0.077. Regarding the light source 103, since the W.D. is more than 10 times longer than that of the conventional CIS, in the equal magnification system, the inspection surface illuminance requires more than 100 times. Therefore, as the light source 103, for example, a high-brightness white LED array is used. That is, a plurality of light sources 103 may be configured to include white LEDs. When a visible region semiconductor laser is used as the light source 103, the light quantity unevenness during irradiation is reduced by expanding the emitted beam in the main scanning direction and collimating it in the sub-scanning direction.

[0046] An example of an arrangement method when using an RGB-LED or an RGB-LD (laser diode; semiconductor laser) as the light source 103 is shown in FIG. 9A. In this way, the plurality of light sources 103 may be configured to include a red LED (R), a green LED (G), and a blue LED (B), or may be configured to include a laser diode. In FIG. 9A, the plurality of light sources 103 are mounted on a light source substrate 134, and a heat sink 135 is attached to the light source substrate 134. The beams emitted from each light source 103 are collimated by an ellipsoidal condenser lens 104 having different lens powers in the main scanning direction and the sub-scanning direction, and are irradiated onto the object to be inspected. Here, an ellipsoidal condenser lens 104 is shown, but any lens with appropriately different lens powers in the main scanning direction and the sub-scanning direction may be used. Note that the power of a lens is the reciprocal of the focal length and is a measure representing the refractive power of the lens.

[0047] Alternatively, regarding the LD, if an edge-emitting LD whose divergence angle of the emitted beam of the LD itself is different in the horizontal direction and the vertical direction is used, a normal collimator lens may be used. FIG. 9B is a side view showing a specific example of the arrangement method when using the LD as the light source 103. In this case, the LD with the larger divergence angle is arranged parallel to the main scanning direction. The beams emitted from the red LD 131, green LD 132, and blue LD 133 constituting the light source 103 are collimated by the corresponding condenser lenses 104 and then narrowed down to the inspection surface by the cylindrical lens 105. By doing so, each color of RGB is irradiated at substantially the same position in the sub-scanning direction, and it becomes possible to reduce color unevenness with respect to the sub-scanning direction. On the other hand, the light irradiated by the light source 103 such as an LED or an LD and diffusely reflected on the inspection surface is imaged on the light receiving element array by the light receiving lens system. The light receiving element uses an element size of 62 μm corresponding to 400 dpi to 42 μm corresponding to 600 dpi in the same magnification optical system. When using an element size of 600 dpi or more, the power of the illumination light may be increased accordingly. In this way, the plurality of light sources 103 may include light sources 131 to 133 having a plurality of different wavelengths, and a configuration in which the light sources 103 of one unit are arranged in a plurality in the main scanning direction (X direction) with the light sources 131 to 133 as one unit.

[0048] Furthermore, even if the radiance per unit area is the same, if the size of the light-receiving element is different, it is equivalent to the area of the light-emitting part being different. Therefore, the amount of received light decreases in inverse proportion to approximately the square of the light-receiving element area. Considering the above, the illumination light amount is determined. When the element size becomes smaller, with the same accumulation time, the amount of received light decreases in inverse proportion to the element area. This is a physical property of the semiconductor light-receiving element. To maintain the S / N, the illumination light can be increased to increase the power density and make the number of generated electrons generated per unit time the same. As a result, shot noise can be maintained equivalent to that of a light-receiving element with a larger size even when the size of the light-receiving element decreases. Also, the light received by the light-receiving element depends not only on the illuminance of the inspection surface but also on the range that the light-receiving element looks at when receiving light. Needless to say, if the light-receiving solid angle is different and the angle decreases, the amount of received light also decreases. If the inspection surface is a perfect diffusing surface, the amount of received light conforms to the so-called cosθ law. The light diffusely reflected from the inspection surface is captured by the light-receiving lens and condensed onto the light-receiving element, and its output signal is output from the light-receiving element. Also, the output signal from the light-receiving element array is branched from serial to parallel to improve the processing speed and transmitted to the image processing device.

[0049] FIG. 10A is a schematic diagram showing the positional relationship between the light source 103 and the light receiving lens 11, and shows the case where the light receiving element array 120 has two rows. In FIG. 10A, the arrangement of the light receiving lenses 11 arranged in two rows and the light source 103 with respect to the light receiving element array 120 is shown. In this embodiment, the light source 103 is arranged at substantially the center of the two rows of reading lines L. Each light source 103 is arranged side by side in parallel with the reading line L. Further, the optical axis of each light source 103 connects the intersection with the optical axis of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120, and is arranged at an arbitrary position on a virtual plane that intersects the optical axis of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120. In this embodiment, the focal length f of the light receiving lens 11 is f = 50 mm, and the lens diameter Φ is Φ = 4 mm (however, considering the geometric optical aberration, the effective diameter Φ' is Φ' = 2.5 mm using an aperture). In this embodiment, light is irradiated from the light source 103 at an angle of approximately 45 degrees with respect to the inspection surface. Therefore, considering the W.D. of the light receiving lens 11, the distance between the light source 103 and the inspection surface is 70 mm. In this embodiment, an LD is used, but LEDs of each wavelength may also be used.

[0050] The arrangement pitch of the light sources 103 is adjusted according to the lens pitch, and the light sources 103 are arranged at substantially the center between adjacent light receiving lenses 11 and at substantially the center of the two rows of reading lines L at the same time. By doing so, it is possible to further prevent the omission of pixels on the inspection surface, and at the same time, it is possible to further reduce the shading of the light receiving lens 11 and the unevenness of the light quantity of the light source 103. The lens pitch between the light receiving lenses 11 in each row is 7 mm. In this case, the substantial lens pitch is 3.5 mm.

[0051] FIG. 10B is a diagram showing the relationship between the light quantity distribution of the light source 103 (on the inspection surface) in the main scanning direction, the light quantity distribution on the light receiving element surface, and the shading of the light receiving lens 11. In the layout of FIG. 10A, the light quantity distribution on the light receiving element array 120 becomes flat as schematically shown in FIG. 10B, and it becomes possible to effectively use the dynamic range of the light receiving elements.

[0052] 6. Method for suppressing ripples Next, shading caused by each light-receiving lens 11 generates ripples in the direction of the reading line L, which in turn leads to narrowing the dynamic range of the light-receiving element. This suppression method will be described below.

[0053] First, the inspection object is irradiated with illumination light having a negative intensity distribution by the illumination system in advance. For example, in the method of arranging the light source 103 between adjacent light-receiving lenses 11, it does not become a shading suppression method that completely corresponds to various light-receiving lenses 11. That is, there is shading peculiar to each light-receiving lens 11, and if the light-receiving lenses 11 are different, an illumination optical system corresponding thereto must be used. In the present embodiment, a condenser lens 104 having a large power in the main scanning direction is arranged. The light beam transmitted through the condenser lens 104 is then guided to the inspection object by a converging lens such as a cylindrical lens 105, and a light intensity corresponding to the shading of the light-receiving lens 11 is formed on the inspection object. Then, by appropriately changing the position of the condenser lens 104 in the optical axis direction according to the shading of the light-receiving lens 11, for example, if the inspection object is a calibration white reference plate, the light intensity distribution on the light-receiving element can be smoothed. The condenser lens 104 may have power in the sub-scanning direction. In short, it is only necessary to completely suppress the shading of the light-receiving lens 11 and simultaneously realize an effective light intensity distribution considering the focal length of the light-receiving lens 11 with respect to the inspection object. That is, it is preferable that the lens power in the main scanning direction is larger than the lens power in the sub-scanning direction. As the condenser lens 104, for example, a cylindrical lens, a lenticular lens, a Fresnel lens, or a combination of a prism sheet and a spherical lens is preferable. The positional relationship of the light source 103 with respect to the main scanning direction may be arranged at the intermediate position of each light-receiving lens 11, may be arranged on the optical axis of the light-receiving lens 11, or further, the light source 103 may be arranged at the position of the outer periphery of the light-receiving lens 11. Moreover, a lens having a power distribution in the main scanning direction is more preferable.

[0054] In this embodiment, a condenser lens 104 that condenses light beams from a plurality of light sources 103 is provided as a single lens body, and the power of the lens body in the main scanning direction is greater than the power in the sub-scanning direction. However, the condenser lens 104 may be configured to include a first condenser lens and a second condenser lens instead of a single lens body. In this case, the first condenser lens may have a power in the main scanning direction that is greater than the power in the sub-scanning direction, and the second condenser lens may have a power in the sub-scanning direction that is greater than the power in the main scanning direction. Also, the power in the main scanning direction may be adjustable by the first condenser lens and the second condenser lens.

[0055] In the condenser lens 104 provided with the first condenser lens and the second condenser lens as described above, the first condenser lens and the second condenser lens can be configured by a cylindrical lens, a lenticular lens, a Fresnel lens, or a prism array, etc. For example, the first condenser lens may be a lenticular lens or a prism array. Also, the second condenser lens may be a Fresnel lens or a cylindrical lens.

[0056] 7. Parameters of the light-receiving lens A graph of the light-receiving system MTF by lens diameter in this embodiment is shown in FIG. 10C. As a comparative example, FIG. 10D shows the case where the refractive index distribution constant √A = 0.154. The cases where the effective diameter Φ is Φ = 1.0, 1.5, 2.0, 2.5, 3.0 mm are shown in the order of the solid line, short dashed line, long dashed line, and one-dot chain line. Note that the pixel size of the light-receiving element is set to 42.3 μm in both the main scanning direction and the sub-scanning direction to correspond to 600 dpi.

[0057] In this embodiment, at the effective diameter Φ, when the refractive index distribution constant √A satisfies √A = 0.077, if the performance is about 30% at 12 lines / mm equivalent to 600 dpi, the MTF characteristics in the range from Φ1.0 mm to Φ3.0 mm are satisfied. On the other hand, in the comparative example, the MTF characteristics are not satisfied in all ranges of the effective diameter Φ. This indicates that the aberration characteristics are superior when √A = 0.077 than when √A = 0.154. Also, for the case where the focal length f = 50 mm, the MTF of the light-receiving optical system when the refractive index distribution constant √A = 0.1027 is obtained and shown in FIG. 10E. According to FIG. 10E, even when √A = 0.1027, the MTF characteristics are satisfied in the range from Φ1.0 mm to Φ3.0 mm at 12 lines / mm corresponding to a resolution of 600 dpi.

[0058] When the light-receiving lens 11 is a refractive index distribution type lens, the lens is preferably made of glass or resin. In this case, in the lens parameters of the light-receiving lens 11, it is preferable that the on-axis refractive index N0 satisfies 1.45 ≦ N0 ≦ 1.65, the refractive index distribution constant √A satisfies 0.05 ≦ √A ≦ 0.12, and the focal length f satisfies 50 mm ≦ f ≦ 150 mm.

[0059] The light-receiving lens 11 may be an achromat or an apochromat formed by combining a plurality of lenses respectively. In this case, it may be a lens system combining only convex lenses as the plurality of lenses, or a lens system combining convex lenses and concave lenses as the plurality of lenses. Also, it is preferable that the focal length f of the plurality of lenses satisfies 25 mm ≦ f ≦ 250 mm, and further, the aperture Φ of the plurality of lenses satisfies 2 mm ≦ Φ ≦ 50 mm.

[0060] Next, in order to improve the depth of field and resolution, an example is given in which the light-receiving lens system is a reduction optical system. The configuration of the optical system is the same as that in Fig. 10A, and the magnification of the light-receiving lens 11 is changed. That is, the relationship between the lateral magnification of the object point and the image point of the light-receiving lens 11 is changed such as 9:1 or 4:1. By doing so, the depth of field increases to three times that of the equal-magnification system when the lateral magnification is 9:1, and increases to twice that of the equal-magnification system when the lateral magnification is 4:1. When the depth of field is three times, the size of the light-receiving element is set to 1 / 9 of the size of the light-receiving element in the equal-magnification system. Also, when the depth of field is twice, the size of the light-receiving element is set to 1 / 4 of the size of the light-receiving element in the equal-magnification system. In the present embodiment, a light-receiving element with a size of 1 / 4 is used to double the depth of field.

[0061] The MTF characteristics at defocus of the reduction optical system in the present embodiment are shown by the solid line in the graph of Fig. 11. As a comparative example, the MTF characteristics at defocus of the equal-magnification system are shown by the broken line in the graph of Fig. 11. From the comparison between the reduction system and the equal-magnification system in the figure, it can be seen that the depth of field of the reduction optical system is approximately twice as deep as that of the equal-magnification system. Also, if the reduction ratio is S, the N.A. of the light-receiving lens 11 increases by 1 / S, which is the reciprocal. Therefore, even when the lens diameter of the light-receiving lens 11 is small, if the reduction ratio is increased according to the focal length, the effective N.A. can be maintained, so that the blur due to the diffraction effect can also be made constant.

[0062] In the present embodiment, since the focal length is f = 50 mm and the lateral magnification ratio is 1 / 4, in principle, the lens diameter Φ can be used up to Φ = 0.25 mm. Since the same lens as in the case of Fig. 10A is used, the lens diameter Φ is Φ = 4 mm, and the effective diameter Φ' is Φ' = 2.5 mm. The N.A. becomes four times that in the case of Fig. 10A which is an equal-magnification system. Therefore, the received light amount becomes 16 times, and the decrease in the received light amount by 1 / 16 due to downsizing the light-receiving element size to 1 / 4 can be offset.

[0063] 9. Telecentric optical system Next, the telecentric optical system applied to the present embodiment will be described. By using the telecentric optical system, it is possible to achieve a configuration that is easy to assemble and has little change over time. In the telecentric optical system, the light receiving lens 11 is disposed on both sides or one side with the aperture (light transmission portion) interposed therebetween. That is, the telecentric optical system is a bilateral telecentric optical system in which the light receiving lens 11 is disposed on both the inspection object side and the light receiving element array 120 side, or an object side telecentric optical system in which the light receiving lens 11 is disposed only on the inspection object side.

[0064] In the bilateral telecentric optical system, a light beam that is thinly spread parallel to the optical axis from the inspection object becomes a parallel light beam by passing through the front lens, and the parallel light beam that has passed through the aperture inserted behind the front lens passes through the rear lens and is focused on each light receiving element of the light receiving element array 120.

[0065] As shown in FIG. 3 or FIG. 4, when the light receiving element array 120 is arranged in a staggered pattern in the sub-scanning direction, the larger the distance in the sub-scanning direction, the larger the memory capacity needs to be. As the memory capacity increases, the cost increases accordingly. In the present embodiment, by using the telecentric lens optical system, when the N.A. is about 0.03, in the case of a lens with a focal length of 50 mm, a conical light receiving solid angle connecting the main plane of the lens and the object point with Φ = 3 mm is obtained. Therefore, the shortest distance Ls of the light receiving element array 120 arranged in a staggered pattern in the sub-scanning direction is sufficient if Ls > 3 mm. Therefore, if the circular outer periphery of a normal lens is made into a rectangular outer periphery by various processing or molding means and the interval between the light receiving element arrays 120 arranged in a staggered pattern as shown in FIG. 3 or FIG. 4 is narrowed, it is possible to satisfy the light receiving solid angle and make it compact, and at the same time, the memory capacity can be reduced. Note that the N.A. of the light receiving lens 11 is preferably about 0.001 to 0.05 from the viewpoint of the illumination light amount. As described above, the thickness of the light receiving lens 11 in the sub-scanning direction can be shortened in the sub-scanning direction because it is determined by the solid angle defined by the N.A. of the telecentric optical system, and it becomes compact.

[0066] 10. Modification Example of Light Receiving System Next, a modified example of the light receiving system will be described with reference to FIGS. 12A to 12G. In the above embodiment, the configuration in which a plurality of light receiving lenses 11 are arranged in two rows in the sub-scanning direction has been described. However, in FIGS. 12A to 12G, a configuration in which a plurality of light receiving lenses 11 are arranged in a single row along the main scanning direction will be described. Specifically, the layout of a single row of light receiving lenses 11 and the staggered light receiving element array 120 will be described.

[0067] When forming two read lines L by staggering the light receiving element array 120, if the light receiving lenses 11 are also staggered in two rows in the same manner as the light receiving element array 120, in order to satisfy the necessary N.A. of the light receiving lens system, it is necessary to provide an interval in the sub-scanning direction of the light receiving element array 120 that is equal to or greater than the width of the light receiving lens 11 in the sub-scanning direction. Therefore, as shown in FIGS. 12A to 12G, by setting the width of the rectangular lens so that the light receiving lens 11 satisfies the necessary N.A. of the light receiving system and changing from two rows to one row, it becomes possible to narrow the interval in the sub-scanning direction of the light receiving element array 120. That is, the influence of the speed variation in the sub-scanning direction can be reduced, and at the same time, the cost of the light receiving lens 11 can be reduced. Hereinafter, a method of arranging a plurality of light receiving lenses 11 in a single row will be described.

[0068] In FIGS. 12A to 12G, the plurality of light receiving lenses 11 each have the same shape when viewed from a direction perpendicular to the main scanning direction. Specifically, the shape of each light receiving lens 11 when viewed from the Z direction perpendicular to the main scanning direction (X direction) and the sub-scanning direction (Y direction) is the same shape. Note that the "same shape" includes substantially the same shape such as an inverted shape, and slight differences in shape are included in the "same shape".

[0069] In FIG. 12A, the shape of each light-receiving lens 11 as viewed in the Z direction is a parallelogram shape. That is, both end faces of each light-receiving lens 11 in the main scanning direction are inclined with respect to the sub-scanning direction. The inclination angles of both end faces of each light-receiving lens 11 in the main scanning direction are the same. When a plurality of light-receiving lenses 11 are arranged side by side in the main scanning direction as shown in FIG. 12A, the end faces of the adjacent light-receiving lenses 11 face each other at both end faces of each light-receiving lens 11, so that the ends of the light-receiving lenses 11 adjacent to each other in the main scanning direction are arranged in a connected state.

[0070] In FIG. 12B, rectangular notches are formed at both end faces of each light-receiving lens 11 in the main scanning direction as viewed in the Z direction. When a plurality of light-receiving lenses 11 are arranged side by side in the main scanning direction as shown in FIG. 12B, a part of the adjacent light-receiving lens 11 is fitted into the notches formed at both end faces of each light-receiving lens 11, so that the ends of the light-receiving lenses 11 adjacent to each other in the main scanning direction are arranged in a connected state.

[0071] In FIG. 12C, the shape of each light-receiving lens 11 as viewed in the Z direction is a trapezoidal shape. That is, both end faces of each light-receiving lens 11 in the main scanning direction are inclined with respect to the sub-scanning direction. The shape of each light-receiving lens 11 as viewed in the Z direction is an inverted shape with respect to the shape of the adjacent light-receiving lens 11 as viewed in the Z direction, with the main scanning direction as a reference. When a plurality of light-receiving lenses 11 are arranged side by side in the main scanning direction as shown in FIG. 12C, the end faces of the adjacent light-receiving lenses 11 face each other at both end faces of each light-receiving lens 11, so that the ends of the light-receiving lenses 11 adjacent to each other in the main scanning direction are arranged in a connected state. As a result, the plurality of light-receiving lenses 11 are arranged in a state where the adjacent light-receiving lenses 11 are inverted and connected.

[0072] In FIG. 12D, notches having a curved shape (semicircular shape or semi-elliptical shape) are formed at both end faces of each light-receiving lens 11 in the main scanning direction as viewed in the Z direction. When a plurality of light-receiving lenses 11 are arranged side by side in the main scanning direction as shown in FIG. 12D, a part of the adjacent light-receiving lens 11 is fitted into the notches formed at both end faces of each light-receiving lens 11, so that the ends of the light-receiving lenses 11 adjacent to each other in the main scanning direction are arranged in a connected state.

[0073] Next, modifications shown in FIGS. 12E to 12G will be described. FIG. 12E is a modification of FIG. 12C, and it is possible to minimize the occurrence of missing pixels in the light receiving element array 120 described above. In FIG. 12E, each light receiving element array 120 is arranged on the long side of the trapezoidal light receiving lens 11 rather than at the center in the width direction. Further, the length of each light receiving element array 120 in the main scanning direction substantially coincides with the length of each trapezoidal light receiving lens 11 in the main scanning direction at the position where the light receiving element array 120 is arranged. By doing so, the portions indicated by the broken lines in FIG. 12E overlap in the main scanning direction between the adjacent stagger-arranged light receiving element arrays 120, and as will be described later, an output signal missing portion such as that of the stagger-arranged light receiving element array 120 shown in FIG. 12C does not occur.

[0074] The above is not limited to the trapezoidal light receiving lens 11, and any shape that can be connected when each light receiving lens 11 is inverted in the sub-scanning direction to form a light receiving lens array is acceptable. Examples thereof are shown in FIGS. 12F and 12G. FIG. 12F shows a case where a plurality of light receiving lenses 11 having a rectangular notch shape are inverted and connected, and FIG. 12G shows a case where a plurality of light receiving lenses 11 having a circular notch are inverted and connected. As described above, in FIGS. 12E to 12G, the plurality of light receiving lenses 11 are arranged in a state where the adjacent light receiving lenses 11 are inverted and connected. Generally, if the light receiving lens 11 is a line object in the sub-scanning direction, it can be inverted and connected. In FIGS. 12F and 12G as well, the broken line portions overlap in the same manner as the inverted connection of the trapezoidal shape in FIG. 12E, and as will be described later, a signal missing portion does not occur. Note that the light receiving lens 11 in FIG. 12G is provided with an edge portion 112 for ensuring rigidity and avoiding cracking.

[0075] As shown in FIGS. 12A to 12G, in the cross-sectional view in the optical axis direction of the light receiving lens 11, the width in the sub-scanning direction that satisfies the N.A. of the light receiving lens system is set as a cross-sectional shape such as a parallelogram shape, a trapezoidal shape, a rectangular shape, or a notch shape of a curved shape (circle, ellipse) at the lens end, and by connecting them in a row, a lens array extending linearly in the main scanning direction is formed. Further, two rows of light receiving element arrays 120 arranged in a staggered pattern are provided at the central portion in the sub-scanning direction of the lens array. Specifically, a plurality of light receiving element arrays 120 are arranged at the central portions in the main scanning direction of the plurality of light receiving lenses 11, and are arranged alternately in a staggered pattern along the main scanning direction. By doing so, it is possible to deliver the light emitted from the inspection object to the two rows of light receiving element arrays 120 arranged in a staggered pattern with one row of lens array.

[0076] As shown in FIG. 12A, a shielding portion 111 is provided between the ends of the light receiving lenses 11 adjacent to each other in the main scanning direction. The shielding portion 111 is formed in a thin plate shape. The shielding portion 111 extends from between the ends of each light receiving lens 11 toward the light receiving element (light receiving element array 120), and protrudes from the light receiving lens 11 toward the inspection object direction. Further, the shielding portion 111 has a width of at least the width W1 in the sub-scanning direction of the light receiving lens 11. Although the shielding portion 111 is omitted in FIGS. 12B to 12G, the shielding portion 111 may be similarly provided between the ends of each light receiving lens 11. In the embodiments of FIGS. 12F and 12G, the shielding portion 111 is a thin crank-shaped or corrugated shielding plate, respectively. The main point is that light should not leak out to adjacent light receiving systems at the connecting portion.

[0077] As shown in FIGS. 12B to 12D, a plurality of light sources 103 for illuminating the inspection object may be provided so as to correspond one-to-one with the plurality of light receiving element arrays 120. The plurality of light sources 103 may each have an elongated shape extending linearly along the main scanning direction. In this case, as shown in FIGS. 12B to 12D, the plurality of light sources 103 may face the respective light receiving element arrays 120 in the Z direction. Thereby, the plurality of light sources 103 can be arranged in a staggered pattern, and linear light can be efficiently incident on each light receiving element array 120.

[0078] The plurality of light sources 103 have a light intensity distribution of a plurality of lines of illumination light in the sub-scanning direction corresponding to the plurality of light receiving element arrays 120. Although the light sources 103 are omitted in FIGS. 12A, 12E to 12G, the plurality of light sources 103 may be provided so as to correspond one-to-one with the plurality of light receiving element arrays 120 as well. However, even if the plurality of light sources 103 are not arranged in a staggered pattern, line illumination having a light intensity distribution including two intensity peaks in the sub-scanning direction may be used so that the light receiving element arrays 120 of each reading line L have intensity peaks. Also, since the interval in the sub-scanning direction of the staggered light receiving element arrays 120 is narrow, line illumination having one peak may be used.

[0079] FIGS. 12H and 12I are schematic diagrams for explaining the position of the optical axis 113 in the light receiving system. Hereinafter, taking the configuration of FIG. 12E as an example, the position of the optical axis 113 in the light receiving system will be explained using FIGS. 12H and 12I. However, the position of the optical axis 113 can be set in the same manner in other configurations such as FIGS. 12A to 12D, 12F, and 12G.

[0080] In FIG. 12H, the optical axis 113 of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120 passes through a position parallelly separated in the sub-scanning direction (Y direction) from the substantially central portion of each light receiving element array 120. Specifically, the optical axis 113 of each light receiving lens 11 is equidistant from each of the staggeredly arranged light receiving element arrays 120 and passes through a position at approximately half the length of each staggeredly arranged light receiving element array 120 in the main scanning direction. In this example, the optical axes 113 are arranged in a single row along the main scanning direction (X direction), but the configuration is not limited to this.

[0081] In FIG. 12I, the optical axis 113 of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120 passes through substantially the center of each light receiving element array 120 arranged in a staggered pattern. Therefore, each optical axis 113 is arranged in a staggered pattern along two rows of reading lines L, similar to each light receiving element array 120. Thus, by aligning the optical axis 113 of each light receiving lens 11 with each light receiving element array 120, aberration can be reduced.

[0082] FIG. 13 shows the light intensity distribution on the light receiving surface of the light receiving element array 120 when the light intensity distribution of the light source 103 is flat in the case where the lens end is a parallelogram. In FIG. 13, an example of the light intensity distribution on the light receiving surface of each light receiving element array 120 when the configuration of FIG. 12A is adopted is shown. For the sake of explanation, the lens array composed of a plurality of light receiving lenses 11 is assumed to be a lens array composed of three light receiving lenses 11 for convenience.

[0083] The left figure in FIG. 13 shows the light intensity on each light receiving element array 120 of the entire lens array, and the right two figures show enlarged views. Further, FIG. 14 shows the details of the light intensity distribution in the vicinity of the connection part between adjacent light receiving lenses 11. In the present embodiment, in two adjacent light receiving element arrays 120 arranged in a staggered pattern, the signal missing pixels of one light receiving element array 120 are interpolated by the pixels of the other light receiving element array 120. In FIG. 14, the method of interpolating the signal of the signal missing pixels is shown by the arrow marks.

[0084] The portion 121 surrounded by the broken line in FIG. 14 is a light receiving element located at the connection part between adjacent light receiving lenses 11, and a signal missing part is generated because light does not reach the light receiving element. Therefore, in the present embodiment, in the adjacent light receiving element arrays 120 arranged in a staggered pattern, the signal of the signal missing part is supplemented by the output signal of the light receiving element (the portion 122 surrounded by the solid line) facing the light receiving element of the portion 121 in the sub-scanning direction. Thus, a pixel interpolation part is formed along the sub-scanning direction at the connection part between adjacent light receiving lenses 11 (see FIG. 13). The signal missing part may be corrected in advance by a reference medium for inspection. As the reference medium, a white chart for shading correction, a grid pattern, or the like can be used.

[0085] In Fig. 13, the width of the light-receiving lens 11 in the sub-scanning direction is 5 mm. Therefore, when the light-receiving lenses 11 are arranged in a staggered pattern in two rows, the minimum interval of the staggered light-receiving element array 120 needs to be 5 mm or more. However, when using a single-row lens array as described above, the interval is about half (slightly less than 3.0 mm). Also, considering the dynamic range etc. of the light-receiving element array 120 and performing shading correction, it is possible to further narrow the interval. That is, while the interval of the staggered light-receiving element array 120 in the sub-scanning direction is narrowed, the number of light-receiving lenses 11 can be halved. Therefore, there is an advantage that it is less affected by fluctuations in the conveyance speed in the sub-scanning direction and at the same time cost reduction can be achieved.

[0086] In the shielding portion 111 in Fig. 13, a shielding plate with a thickness t = 0.2 mm was arranged. If t = 0.2 mm, there is no problem in terms of strength. Also, the lens system is a double-sided telecentric system. Of course, it goes without saying that it may also be an object-side telecentric system.

[0087] As processing by a specific image processing method or image processing system, regarding the output signals from two light-receiving elements separated in the sub-scanning direction at the same position in the main scanning direction, when the output signal from one light-receiving element (the portion 121 surrounded by the broken line) is lower than the output signal from the other light-receiving element (the portion 122 surrounded by the solid line) and the output signal from one light-receiving element is less than the threshold value, interpolation is performed using the output signal from the other light-receiving element. Also, by synthesizing the interpolated output signal with the output signal from a light-receiving element at another position in the main scanning direction with respect to one light-receiving element, an output signal for one row corresponding to the reading line L is obtained.

[0088] Note that the light-receiving elements in the portion 123 surrounded by the two-dot chain line in Fig. 14 face each other in the sub-scanning direction, but all are shifted from the connection portion between adjacent light-receiving lenses 11 and thus overlap each other. For such overlapping portions, since there is no loss of the output signal from the light-receiving elements, there is no need for interpolation.

[0089] In the example of FIG. 12E, the light intensity of the light-receiving region is shown, and the reason why no signal dropout occurs is schematically shown in FIG. 15. FIG. 15 shows the light intensity distribution at the end of the stagger-arranged light-receiving element array 120, similar to FIG. 14. In FIG. 15, the light-receiving elements in the portion 124 surrounded by the two-dot chain line face each other in the sub-scanning direction, but all are shifted from the connecting portions between adjacent light-receiving lenses 11 and thus overlap each other. As shown in FIG. 15, by arranging the light-receiving element array 120 on the long side in the width direction of the trapezoidal light-receiving lens 11, it becomes possible to obtain the signals necessary for one read line L of the stagger-arranged light-receiving element array 120 except for the signal dropout portions in the light-receiving section.

[0090] As processing by a specific image processing method or image processing system, for the output signals from two light-receiving elements (the portion 124 surrounded by the broken line) spaced apart in the sub-scanning direction at the same position in the main scanning direction, one of the output signals of the overlapping portion of the output signal of one light-receiving element and the output signal of the other light-receiving element is selected, and correction is performed based on the ratio of one of the output signals corrected in advance by a reference medium and the other output signal, and then the two signals are combined to obtain the output signals for one column corresponding to the read line L.

Explanation of Reference Numerals

[0091] 10 Light source unit 11 Light-receiving lens 12 Light-receiving section 20 Focal plane 103 Light source 104 Condensing lens 105 Cylindrical lens 110 Lens holder 111 Shielding section 120 Light-receiving element array 131 Red LD 132 Green LD 133 Blue LD 134 Light source substrate 135 Heat sink

Claims

1. An optical line sensor for reading an object to be inspected conveyed in a sub-scanning direction with a reading line extending in a main scanning direction, comprising: a plurality of light-receiving lenses arranged in a plurality along the main scanning direction; a plurality of light-receiving elements arranged in a line along the main scanning direction and receiving light transmitted through the plurality of light-receiving lenses; the plurality of light-receiving elements form at least two or more rows of the reading lines; the light-receiving lens constitutes a telecentric optical system, and is characterized in that the width in the sub-scanning direction is smaller than the width in the main scanning direction.

2. The optical line sensor according to claim 1, wherein the light-receiving lens is formed in a rectangular shape when viewed from a direction orthogonal to the main scanning direction and the sub-scanning direction, and is arranged at intervals from each other within the width of the light-receiving lens in the main scanning direction.

3. The plurality of light-receiving elements are arranged in an array of two or more rows to constitute a plurality of light-receiving element arrays, the plurality of light-receiving lenses are arranged in a number corresponding to the plurality of light-receiving element arrays, and the optical axis of the light transmitted through each light-receiving lens and guided to each light-receiving element array passes through the central portion of each light-receiving element array, or the plurality of light-receiving lenses are arranged in a number corresponding to the plurality of light-receiving element arrays, and the optical axis of the light transmitted through each light-receiving lens and guided to each light-receiving element array passes through a position parallel to the sub-scanning direction and separated from the central portion of each light-receiving element array. The optical line sensor according to claim 1, characterized in that

4. The plurality of light-receiving element arrays are light-receiving element arrays shorter than each of the plurality of reading lines respectively arranged in two rows of reading lines, and the light-receiving element arrays arranged in one reading line and the light-receiving element arrays arranged in the other reading line are alternately arranged in a staggered manner along the main scanning direction. The optical line sensor according to claim 3, characterized in that

5. further comprising a plurality of light sources for irradiating the object to be inspected with light, the plurality of light sources are arranged side by side in parallel with the reading line, the optical axes of the plurality of light sources connect the intersection points with the optical axes of the light transmitted through the plurality of light-receiving lenses and guided to the plurality of light-receiving elements, and are arranged at an arbitrary position on a virtual plane intersecting the optical axes of the light transmitted through the plurality of light-receiving lenses and guided to the plurality of light-receiving elements, and further, a light source is arranged at the central portion between adjacent light-receiving lenses. The optical line sensor according to claim 1, characterized in that

6. The plurality of light sources include light sources having a plurality of different wavelengths, and taking the light sources having the plurality of different wavelengths as one unit, the optical line sensor according to claim 5, characterized in that a plurality of the units of light sources are arranged in the main scanning direction.

7. The optical line sensor further includes a condenser lens that condenses light beams from the plurality of light sources, the condenser lens includes a first condenser lens whose power in the main scanning direction is greater than the power in the sub-scanning direction and a second condenser lens whose power in the sub-scanning direction is greater than the power in the main scanning direction, or the condenser lens is a single lens body, and the power of the lens body in the main scanning direction is greater than the power in the sub-scanning direction, the optical line sensor according to claim 5.

8. The optical line sensor according to claim 7, characterized in that the power of the condenser lens in the main scanning direction can be adjusted by the first condenser lens and the second condenser lens.

9. The optical line sensor according to claim 5, characterized in that the plurality of light sources include white LEDs, or include red LEDs, green LEDs and blue LEDs, or include laser diodes.

10. The plurality of light receiving lenses are arranged in a row along the main scanning direction, the plurality of light receiving lenses are arranged in a state where the ends of the light receiving lenses adjacent to each other in the main scanning direction are connected, the optical line sensor according to claim 1, characterized in that the plurality of light receiving lenses have the same shape when viewed from a direction perpendicular to the main scanning direction, or the adjacent light receiving lenses are arranged in a state of being inverted and connected.

11. The plurality of light receiving elements are arranged in an array of two or more rows to form a plurality of light receiving element arrays, the plurality of light receiving element arrays are arranged at the central portions of the plurality of light receiving lenses in the main scanning direction and are arranged alternately in a staggered manner along the main scanning direction, the optical axis of the plurality of light receiving lenses is equidistant from each of the light receiving element arrays arranged in a staggered manner and passes through a position of half the length of each of the light receiving element arrays arranged in a staggered manner in the main scanning direction, or the optical axis of the plurality of light receiving lenses passes through the central portion of each of the light receiving element arrays arranged in a staggered manner, the optical line sensor according to claim 10.

12. The plurality of light receiving elements are arranged in an array of two or more rows to form a plurality of light receiving element arrays, The optical line sensor according to claim 10, further comprising a plurality of light sources that illuminate an object to be inspected and correspond one-to-one to the plurality of light-receiving element arrays.

13. The optical line sensor according to claim 12, wherein the plurality of light sources have a light intensity distribution of a plurality of lines of illumination light in a sub-scanning direction corresponding to the plurality of light-receiving element arrays.

14. Further comprising a shielding portion that extends from between ends of the light-receiving lenses adjacent to each other in a main scanning direction toward the plurality of light-receiving elements and has a width of at least the width of the light-receiving lens in the sub-scanning direction, The optical line sensor according to claim 10, wherein the shielding portion protrudes from the light-receiving lens toward the object to be inspected.

15. An image processing method using the optical line sensor according to claim 11, Regarding output signals from two of the light-receiving elements spaced apart in a sub-scanning direction at the same position in the main scanning direction, selecting one of the output signals of a portion where the output signal of one of the light-receiving elements overlaps with the output signal of the other light-receiving element, and correcting by the ratio of one of the output signals corrected in advance by a reference medium and the other output signal to synthesize one signal and the other signal, thereby obtaining a column of output signals corresponding to the read line, or regarding output signals from two of the light-receiving elements spaced apart in a sub-scanning direction at the same position in the main scanning direction, when the output signal from one of the light-receiving elements is lower than the output signal from the other light-receiving element and the output signal from one of the light-receiving elements is less than a threshold value, interpolating with the output signal from the other light-receiving element, and synthesizing the interpolated output signal with the output signal from the light-receiving element at another position in the main scanning direction with respect to the one light-receiving element, thereby obtaining a column of output signals corresponding to the read line.

16. An image processing system using the optical line sensor according to claim 11, Regarding the output signals from two of the light-receiving elements spaced apart in the sub-scanning direction at the same position in the main scanning direction, one of the output signals of the overlapping portion of the output signal of one of the light-receiving elements and the output signal of the other light-receiving element is selected, and by correcting with the ratio of one of the output signals of the output signal pre-corrected by the reference medium and the other output signal and synthesizing one signal and the other signal, an output signal of one column corresponding to the read line is obtained, or regarding the output signals from two of the light-receiving elements spaced apart in the sub-scanning direction at the same position in the main scanning direction, when the output signal from one of the light-receiving elements is lower than the output signal from the other light-receiving element and the output signal from one of the light-receiving elements is less than the threshold value, interpolation is performed with the output signal from the other light-receiving element, and the interpolated output signal is synthesized with the output signal from the light-receiving element at another position in the main scanning direction with respect to the one light-receiving element, thereby obtaining an output signal of one column corresponding to the read line, and an image processing system characterized by this is provided.

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