Optical line sensor

Abstract

To realize a compact optical line sensor having a large depth of field.SOLUTION: An optical element 200 has a reflection surface 204 disposed on an optical path from light receiving lenses and light receiving elements, and reflects light transmitted through the light receiving lenses by a reflection surface 204 and guides it to the light receiving elements. The multiple light receiving lenses are disposed while being separately mutually at least by a diameter of the light receiving lenses. The multiple light receiving elements form at least a row of reading lines. The light receiving lenses compose a telecentric optical system and the optical element 200 invertedly forms images in a sub-scanning direction on the light receiving elements, or invertedly forms images in a sub-scanning direction or in a main scanning direction on the light receiving elements.SELECTED DRAWING: Figure 18A

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 authenticity of banknotes and the like, flatbed scanners such as office copiers and home printer scanners, has been considered for application to so-called surface inspection machines for checking 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 a SELFOC lens (where "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, due to the large variation in the optical axis direction of the inspection object in the manufacturing process of the inspection object, a CIS with a deep depth of field is also strongly desired.

[0004] A CIS with a deep depth of field is typically a telecentric optical system using a mirror optical system as shown in Patent Documents 1 to 5. From the said patent documents, it can be seen that this optical system is very complex. When manufacturing and operating this optical system as a product, it involves 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 changes over time, the optical axis drifts, and problems remain such as performance deterioration easily occurring compared to conventional CIS with a simple structure.

[0005] Therefore, it is conceivable to improve the working width (WD) and depth of field by using refractive lenses made of glass or resin instead of the aforementioned telecentric reflective optical system. Regarding the aforementioned refractive optical system, some solutions have been proposed as shown in Patent Documents 6 and 7. For example, Patent Document 6 attempts to realize an optical system with a deep depth of field by arranging one telecentric refractive optical system spaced apart in a staggered arrangement of line sensors and arranging the lenses of the refractive optical system spaced apart to form an array. Patent Document 7 also investigates a method to prevent crosstalk between lenses by providing a partition plate between spaced lenses. While Patent Documents 6 and 7 can improve the depth of field and prevent crosstalk between lenses, conventional telecentric refractive optical systems are large and difficult to make compact. Furthermore, the partition plate shown in Patent Document 7 results in missing pixels during reading, leading to incomplete reading. Moreover, no solution is shown for the shading that a single lens inherently has when lenses are spaced apart. There is also no mention of a method for suppressing so-called ripple in the reading line direction. Moreover, the aforementioned refractive optical system has not yet been realized.

[0006] Furthermore, inspection machines using camera lenses, such as line cameras, which are a different method from the aforementioned one, are large, and many units are required to handle the wide range of objects to be inspected in a manufacturing environment. As a result, the entire system becomes very large, and the cost is enormous, making it difficult to deploy them in every process of a factory.

[0007] To solve the above problems, there is a need for an optical line sensor that is small and inexpensive, can be introduced into each process of a factory, uses a new refractive lens with a long working width (WD) and deep depth of field, and employs a new method for suppressing ripple, which is optical unevenness on the light-receiving sensor caused by the shading of individual lenses. Furthermore, although the above invention arranged the optical system on a single straight line, optical systems with a long WD required for production lines have a length in the optical axis direction of several tens of centimeters or more, making it difficult to place them between narrower production equipment. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2018-019334 [Patent Document 2] Japanese Patent Publication No. 2018-152713 [Patent Document 3] Japanese Patent Publication No. 2009-244500 [Patent Document 4] Japanese Patent Publication No. 2018-019334 [Patent Document 5] Japanese Patent Publication No. 2018-022948 [Patent Document 6] Japanese Patent Publication No. 2009-246623 [Patent Document 7] Japanese Patent Application Publication No. 5-14600 [Overview of the project] [Problems that the invention aims to solve]

[0009] Therefore, the present invention aims to realize a compact optical line sensor with a deep depth of field. [Means for solving the problem]

[0010] The optical line sensor according to the present invention is an optical line sensor that reads an object to be inspected being transported in the sub-scanning direction on a reading line extending in the main scanning direction, and comprises a plurality of light-receiving lenses, a plurality of light-receiving elements, and an optical element. 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 that has passed through the plurality of light-receiving lenses. The optical element has a reflective surface arranged on the optical path from the light-receiving lens to the light-receiving element, and guides the light that has passed through the light-receiving lens to the light-receiving element by reflecting it off the reflective surface. The plurality of light-receiving lenses are arranged to be spaced apart from each other by a distance greater than the diameter of the light-receiving lens. Furthermore, the plurality of light-receiving elements form at least one row or more of the reading line. The light-receiving lenses constitute a telecentric optical system, and the optical element inverts and images an image onto the light-receiving element in the sub-scanning direction, or inverts and images an image onto the light-receiving element in both the sub-scanning direction and the main scanning direction. [Effects of the Invention]

[0011] According to the present invention, by reflecting the light transmitted through the light-receiving lens off the reflective surface of the optical element and guiding it to the light-receiving element, it is possible to achieve a compact design while ensuring the optical path length. Furthermore, compared to the conventional stacking method of multiple lenses, when focusing on any light-receiving lens, the optical axes of other light-receiving lenses do not intersect with the optical axis of that light-receiving lens. In addition, by arranging the light-receiving lenses at a distance of approximately the field of view dimension in the direction of the arrangement so that the fields of view do not overlap, or by correcting the output of overlapping areas in image synthesis, the depth of field unique to each light-receiving lens can be ensured. Therefore, an optical line sensor with a deep depth of field can be realized. Moreover, by arranging multiple rows of light-receiving element arrays parallel to the main scanning direction and spaced further apart than the field of view of each light-receiving lens in the sub-scanning direction, the effective diameter of the light-receiving lenses can be appropriately increased, thereby ensuring the amount of received light and making it possible to secure a depth of field that was not possible with conventional methods. Furthermore, if the light-receiving lens system is a reduction optical system, and the reduction optical system is spaced similarly to the field of view of the light-receiving lens, and the pixel size of the light-receiving element is reduced according to the magnification, it becomes possible to increase the depth of field and improve the resolution compared to a 1:1 optical system. In other words, the detection resolution of the object to be inspected is further improved compared to conventional technology. [Brief explanation of the drawing]

[0012] [Figure 1] This is a typical cross-section of a CIS (Central Infrastructure Cross-Section). [Figure 2] This is an exploded perspective view of a linear illumination optical system for CIS. [Figure 3] This is a schematic diagram of a light-receiving system where each light-receiving lens is arranged to function as a monocular lens, and the fields of view of each lens do not overlap significantly. [Figure 4] Figure 3 is a side view showing a part of the light-receiving system. [Figure 5] This is a schematic diagram showing an example of a light-receiving system in which multiple light-receiving element arrays are arranged. [Figure 6A] This is a schematic diagram illustrating another example of a light-receiving system in which multiple light-receiving element arrays are arranged. [Figure 6B] This is a schematic diagram illustrating yet another example of a photodetector system in which multiple photodetector arrays are arranged. [Figure 6C] It is a schematic diagram of a light-receiving system when a single row of light-receiving lenses is arranged between two rows of light-receiving element arrays arranged in a staggered pattern. [Figure 7] It is a graph showing the relationship between N.A. and the diffraction limit for each wavelength. [Figure 8A] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of SELFOC lens A. [Figure 8B] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of SELFOC lens B. [Figure 8C] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of SELFOC lens C. [Figure 9A] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of rod lens A. [Figure 9B] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of rod lens B. [Figure 9C] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of rod lens C. [Figure 9D] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of rod lens D. [Figure 10] It is a schematic diagram when the light-receiving lens is separated by more than the visual field dimension of the light-receiving lens, and each light-receiving element array is separated by more than the visual field dimension of the light-receiving lens in a direction perpendicular to the reading line. [Figure 11] They are graphs respectively showing the relationship between the effective diameter of the reduction lens and the confusion circle shape. [Figure 12A] It is a schematic diagram showing an example of an arrangement method when using an RGB-LED or an RGB-LD (laser diode; semiconductor laser) as a light source. [Figure 12B] It is a side view showing a specific example of an arrangement method when using an LD as a light source. [Figure 13A] It is a side view showing an example of the positional relationship between the light source and the light-receiving system. [Figure 13B] It is a side view showing another example of the positional relationship between the light source and the light-receiving system. [Figure 14A]This is a schematic diagram showing the positional relationship between the light source and the light-receiving lens, assuming a single row of light-receiving element arrays. [Figure 14B] This is a schematic diagram showing the positional relationship between the light source and the light-receiving lens, representing the case where the light-receiving element array has two rows. [Figure 14C] This figure shows the relationship between the light intensity distribution of the light source (on the inspection surface), the light intensity distribution on the photodetector surface, and the shading of the photodetector lens in the main scanning direction. [Figure 14D] This is a graph of the MTF of the light-receiving system for different lens diameters (√A=0.077). [Figure 14E] This is a graph of the MTF of the light-receiving system for different lens diameters (√A=0.154). [Figure 14F] This is a graph of the MTF of a photodetector optical system with a refractive index distribution constant √A = 0.1027. [Figure 15] This graph shows the MTF characteristics during defocus. [Figure 16A] Figure 14A shows a lens holder illustrating a method for preventing crosstalk in a single-row spaced-out lens array system, and is a schematic diagram showing the case where the field of view is restricted by a cylindrical aperture. [Figure 16B] Figure 16A is a detailed view of the cylindrical field-of-view limiting aperture. [Figure 17A] This graph shows the relationship between the effective aperture and the circle of confusion diameter when the focal length f is f = 100 mm (√A = 0.154). [Figure 17B] This graph shows the relationship between the effective aperture and the circle of confusion diameter when the focal length f is f = 100 mm (√A = 0.1027). [Figure 17C] This graph shows the relationship between the effective aperture and the circle of confusion diameter when the focal length f is f = 100 mm (√A = 0.077). [Figure 18A] This diagram shows a bilateral telecentric optical system bent approximately in the center (near the aperture). [Figure 18B] This diagram shows the object-side telecentric optical system bent approximately in the center (near the aperture). [Figure 19]This configuration uses a bilateral telecentric optical system to invert the image only in the sub-scanning direction. [Figure 20] This is a conventional bilateral telecentric optical system. [Figure 21] This figure shows another example of an optical element (a Porro prism). [Figure 22] This diagram conceptually illustrates a configuration using a Porro prism with an aperture, as shown in Figure 21, in a bilateral telecentric optical system. [Modes for carrying out the invention]

[0013] 1. Overall configuration of the optical line sensor A typical CIS is shown in Figure 1, and a similar linear illumination optical system for a CIS is shown in Figure 2. Figure 1 shows a cross-sectional view of the CIS near its longitudinal center. Figure 2, on the other hand, 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 perpendicular to the X and Y directions. The linear light source unit 10 is an illumination optical system with an elongated light intensity distribution in the main scanning direction.

[0014] In the CIS shown in Figure 1, two housings 16 are positioned opposite each other with a focal plane (inspection surface) 20 in between. Each housing 16 is equipped with a linear light source unit 10 for illuminating the object to be inspected on the focal plane 20. One of the housings 16 is equipped with a light-receiving lens 11 and a light-receiving unit 12, and the light from the illuminated object to be inspected 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 object to be inspected on the light-receiving unit 12. In the CIS shown in Figure 1, with respect to the focal plane 20, one of the two light source units 10 is positioned on the side of the light-receiving unit 12, and the other is positioned on the opposite side from the light-receiving unit 12. An optical element 200 is arranged in the optical path from the light-receiving lens 11 to the light-receiving unit 12. The specific configuration of this optical element 200 will be described later. In Figure 1, the light-receiving unit 12 is positioned on the central axis of the light-receiving lens 11. However, depending on the configuration of the optical element 200, the light-receiving unit 12 may not be positioned on the central axis of the light-receiving lens 11.

[0015] The light-receiving unit 12 is mounted on a substrate 13 fixed to one of the housings 16. 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 light received is output from the light-receiving unit 12. As the object to be inspected is transported in one direction Y along the focal plane 20, light from the object to be inspected is continuously received by the light-receiving unit 12, and an image of the object to be inspected (such as a color image or a fluorescent image) is obtained based on the output signal from the light-receiving unit 12. In this way, the object to be inspected transported in the sub-scanning direction (Y direction) is read by the light-receiving unit 12 extending in the main scanning direction (X direction) on a reading line formed by the light-receiving surface 12A of the light-receiving unit 12.

[0016] Light B3 emitted from one light source unit 10 passes through a protective glass 14 fixed to the housing 16, is reflected by a reflective member 17A provided on the inner surface of a protective glass 14A fixed to the other housing 16, and is guided to the focal plane 20. At any position between the focal plane 20 and the light receiving unit 12, an ultraviolet light blocking filter (UV cut filter) 15 is provided to prevent ultraviolet light from entering the light receiving unit 12. In addition, a color filter 18 that allows visible light in a specific wavelength range to pass through is provided between the light receiving unit 12 and the ultraviolet light blocking filter 15. A substrate 5 for fixing the light source 103 (ultraviolet light source, visible light source, etc.) provided in the light source unit 10 is installed at a position opposite the bottom surface of the light source unit 10 inside one housing 16.

[0017] In the example shown in Figures 1 and 2, the light source unit 10 comprises a transparent light guide 101 extending along the longitudinal direction L, a light source 103 provided near one end face in the longitudinal direction L, and a cover member 102 for holding each side of the light guide 101. Light emitted from the light source 103 enters the light guide 101, propagates through the light guide 101, is appropriately reflected by the light diffusion pattern P, and is emitted from the light emission surface in the direction of the arrow, becoming a line-shaped illumination light that illuminates the object to be inspected. The depth of field of such a CIS is shallow, making it difficult to inspect the entire thickness of the object to be inspected if it has thickness, and because the WD is narrow, it often comes into contact with the object to be inspected, making the inspection itself impossible.

[0018] In the CIS described above, for example, a SELFOC lens array (manufactured by Nippon Sheet Glass Co., Ltd.) is used as the light-receiving lens 11. The SELFOC lens array is an erect, 1:1 magnification lens array. In this lens array, cylindrical SELFOC lenses are stacked in a sack-like fashion to form a multi-lens system. The advantage of a multi-lens system is that it is possible to increase the brightness of the lens compared to a single lens. That is, the F-number of a multi-lens system, which consists of multiple single lenses arranged together, is smaller than the F-number of a single lens. This is because the effective F-number becomes smaller at the point where the focal position of one lens at any given position coincides with the focal positions of the surrounding lenses. Conversely, in an erect lens system, this means that the numerical aperture (hereinafter referred to as NA) is larger when the lenses are arrayed than when they are single lenses. This property is a major reason why SELFOC lens arrays are used in CIS systems.

[0019] The advantages of CIS described above are, conversely, disadvantages from the standpoint of depth of field and depth of focus. As is the case with monocular lenses, the greater the numerical aperture, the shallower the depth of field. For example, it is well known that in microscope objective lenses, the depth of field becomes shallower as the magnification increases, i.e., as the numerical aperture increases. Also, in camera lenses, the difference in depth of field between distant and close objects is clearly evident, and the aperture is adjusted to ensure depth of field. That is, the desired depth of field is obtained by changing the numerical aperture. In addition, erect multi-lens arrays, such as SELFOC lenses, have optical axes that are different and intersect, so compared to monocular lenses, the image is more prone to blurring when the object being inspected changes in the direction of the optical axis. The above is a major drawback of the stacked multi-lens SELFOC lens array.Therefore, we investigated how it is possible to deepen the depth of field of a compact optical line sensor, and the resulting embodiment is described below. In the following embodiment, the light-receiving lens 11 constitutes a telecentric optical system.

[0020] 2. Examples of light receiving systems First, the first method is to create an array structure that can be considered as a monocular lens for the optical line sensor, as shown in Figure 3. Figure 3 is a schematic diagram of a light-receiving system in which the fields of view 111 of each light-receiving lens 11 do not overlap. That is, in Figure 3, each light-receiving lens 11 is spaced apart in the main scanning direction (X direction) so that the fields of view 111 of each light-receiving lens 11 do not overlap.

[0021] In other words, instead of a stacking method, multiple light-receiving lenses 11 are arranged along the main scanning direction (X direction) and spaced apart from each other by more than their diameter. This is shown in Figure 4. In Figure 4, a part of the light-receiving system of Figure 3 is shown in a side view, but a plan view of a part of the light-receiving system is also shown for visual clarity. The multiple light-receiving lenses 11 are held together by a lens holder 110. Opposite the multiple light-receiving lenses 11 in the Z direction, a light-receiving element array 120 is arranged, which is composed of multiple light-receiving elements (not shown) arranged in a line along the main scanning direction (X direction). That is, one light-receiving element array 120 is composed of multiple light-receiving elements arranged in a single row array. As a result, the multiple light-receiving elements form a single row of reading lines L. Each light-receiving element receives light that has passed through each light-receiving lens 11. Note that in Figure 4, for the sake of visual clarity, the optical elements 200 arranged along the optical path from the light-receiving lens 11 to the light-receiving element array 120 are omitted from the diagram.

[0022] It is preferable that the multiple light-receiving lenses 11 are spaced apart from each other, with the field of view of each light-receiving lens 11 being less than or equal to the field of view of each lens 11 (within the field of view). In this example, the multiple light-receiving lenses 11 are spaced apart from each other with approximately the same field of view as each of them, but the field of view radii of each light-receiving lens 11 may be superimposed. In this case, for the light-receiving elements in the overlapping fields of view 111 of the multiple light-receiving lenses 11, the pixel output from the light-receiving element can be subtracted. For example, the image of one of the light-receiving lenses 11 (the amount of light received that has passed through one of the light-receiving lenses 11) can be excluded from the data output from the light-receiving element, or the pixel output from the light-receiving element can be set to approximately half the output value when combining images.

[0023] Furthermore, using multiple photodetector arrays (photodetector arrays 120) can more reliably prevent pixel loss than using a single-line photodetector array. When using multiple photodetector arrays 120, the photodetector arrays 120 may be spaced apart in the sub-scanning direction (Y direction). In this case, multiple photodetector arrays 120 are formed by arranging multiple photodetectors in an array of multiple rows (for example, two rows), forming multiple rows of reading lines L. The multiple photodetector arrays 120 may be a multi-line system or a system in which short photodetector arrays are arranged in a staggered pattern.

[0024] Figure 5 is a schematic diagram showing an example of a light-receiving system in which multiple light-receiving element arrays 120 are arranged. In the example in Figure 5, in the main scanning direction (X direction), at least some of the multiple light-receiving lenses 11 are spaced further apart from each other than the field of view of the light-receiving lenses 11, and at least two rows (two rows in this example) of reading lines L are formed by a multi-line system. In the sub-scanning direction (Y direction), it is preferable that the spacing distance of the light-receiving element arrays 120 be greater than the field of view of the light-receiving lenses 11, as shown in Figure 5. However, in the case of an erecting lens system in which multiple light-receiving lenses 11 form an erect image, the fields of view 111 may overlap. In this case, the overlapping positions of the fields of view 111 can be corrected in advance using a correction chart or the like to correct the pixel output from the light-receiving elements. By doing so, the fields of view 111 may overlap, and it becomes possible to make the optical line sensor more compact.

[0025] Figure 6A is a schematic diagram showing another example of a light-receiving system in which multiple light-receiving element arrays 120 are arranged. In Figure 6A, the light-receiving element arrays 120, each consisting of a short sensor, are arranged in a staggered pattern, spaced apart by more than the field of view 111 of the light-receiving lens 11 in the sub-scanning direction (Y direction). As shown in Figure 6A, by associating one light-receiving lens 11 with one light-receiving element array 120, multiple light-receiving lenses 11 may be arranged in a number corresponding to the number of light-receiving element arrays 120. The optical axis of the light that passes through each light-receiving lens 11 and is guided to each light-receiving element array 120 may pass through approximately the center of the main scanning direction (X direction) of each corresponding light-receiving element array 120. In this method, multiple rows of multiple light-receiving element arrays 120 are arranged in the sub-scanning direction (Y direction). That is, multiple rows of light-receiving element arrays 120 are spaced apart in the direction perpendicular to the arrangement direction of the light-receiving elements (X direction) (Y direction).

[0026] Figure 6B is a schematic diagram showing yet another example of a light-receiving system in which multiple light-receiving element arrays 120 are arranged. In Figure 6B, the fields of view 111 or more of the light-receiving lenses 11 are spaced apart in the sub-scanning direction (Y direction), and each light-receiving element array 120, which consists of a long sensor (a length corresponding to the total length in the main scanning direction), is arranged as a line sensor of the same length. As shown in Figure 6B, by associating one light-receiving element array 120 with multiple light-receiving lenses 11 arranged in the main scanning direction (X direction), multiple light-receiving element arrays 120 may be arranged in the same number of rows as the number of light-receiving lenses 11 in the sub-scanning direction (Y direction).

[0027] In both Figure 6A and Figure 6B, each of the multiple photodetector arrays 120 is spaced further apart from each other than the field of view of the photodetector lens 11 in the sub-scanning direction (Y direction) perpendicular to the reading line L. However, the configuration is not limited to this, and each of the multiple photodetector arrays 120 may be spaced further apart from each other than the diameter of the photodetector lens 11 in the sub-scanning direction (Y direction) perpendicular to the reading line L, and also spaced further apart than the field of view of the photodetector lens 11. As described above, short photodetector arrays 120 may be used in a staggered arrangement (see Figure 6A), or two rows of photodetector arrays 120 may be used spaced apart (see Figure 6B), but the configuration is not limited to these, and even more multiple photodetector arrays 120 may be spaced further apart in the sub-scanning direction (Y direction).

[0028] Furthermore, Figure 6C shows the case where a single row of light-receiving lenses 11 is positioned parallel to the light-receiving element array 120, approximately in the center of the staggered arrangement of two rows of light-receiving element arrays 120 in the sub-scanning direction (Y direction). In Figure 6C, a common light-receiving lens 11 is positioned in the sub-scanning direction (Y direction) of the staggered arrangement of light-receiving element arrays 120. In Figure 6C, the multiple light-receiving element arrays 120 positioned on each of the two reading lines L are shorter than each reading line L and spaced apart from each other in the main scanning direction (X direction). Also, the light-receiving element arrays 120 positioned on one reading line L and the light-receiving element arrays 120 positioned on the other reading line L are arranged alternately in a staggered pattern along the main scanning direction (X direction). Between the two rows of reading lines L, multiple light-receiving lenses 11 are arranged in a single row parallel to the multiple light-receiving element arrays 120. The optical axis of the light that passes through each light-receiving lens 11 and is guided to each light-receiving element array 120 passes through approximately the center of the two rows of reading lines L in the sub-scanning direction (Y direction). In this case, even with only one row of light-receiving lenses 11, the light that has passed through each light-receiving lens 11 can be received by the two rows of light-receiving element arrays 120.

[0029] 3. Increased focal length of the light-receiving lens Next, let's discuss the lengthening of the focal length of the light-receiving lens. Conventional SELFOC lenses have prioritized miniaturization and cost reduction of the CIS, resulting in a demand for lenses with shorter conjugate lengths. However, this trend has contributed to a reduction in the allowable depth of field. Moreover, the lens diameter is getting smaller and smaller. When lengthening the focal length of the light-receiving lens, using a conventional light-receiving lens results in an extremely small numerical aperture (NA). Therefore, the effect of diffraction becomes larger, and blurring due to diffraction limits becomes the dominant factor in the deterioration of optical resolution, rather than blurring due to the geometric optical aberrations inherent in the light-receiving lens itself. Conventional CIS systems had a large NA, so the blurring of the image due to diffraction limits could be ignored. However, in order to increase the working width (WD), it is necessary to extend the focal length of the light-receiving lens, which means that the NA becomes smaller. Therefore, with conventional lens diameters, the effect of diffraction increases as the focal length increases. In this embodiment, we propose a method that does not degrade optical resolution even when the working width (WD) is increased by increasing the lens diameter, thereby reducing image blurring due to diffraction limiting.

[0030] Abbe's diffraction limit d is inversely proportional to the numerical aperture NA. Since the optical system is in air, the following equation 1 holds true using the wavelength λ in air. d = λ / NA (Equation 1) Figure 7 shows the relationship between NA and diffraction limit for each wavelength. In a light-receiving lens 11 with the same lens parameters, shortening the so-called pitch of the light-receiving lens 11 itself increases the focal length and reduces the effect of aberrations.

[0031] From the above, it is clear that in order to lengthen the focal length of the light-receiving lens 11, the lens diameter needs to be increased. If the numerical aperture (NA) is kept the same, the diffraction effect can be made equivalent to that of a light-receiving lens 11 with a short focal length. However, increasing the lens diameter increases geometric optical aberrations. Therefore, it is necessary to investigate the minimum circle of confusion diameter when the lens diameter is increased for light-receiving lenses 11 with different lens parameters. The wavelength λ was set to λ = 630 nm, which has a large diffraction limit diameter.

[0032] As a result of the inventor's investigation, it was found that it is sufficient to consider the relationship between the minimum circle of confusion for each focal length of a given light-receiving lens 11. For example, the case where the focal length f = 50 mm is shown in Figures 8A to 8C. 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, Figure 8A shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens A, Figure 8B shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens B, and Figure 8C shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens C. In Figures 8A to 8C, the solid line shows the total circle of confusion, the dashed line shows the circle of confusion due to diffraction, and the dashed line shows the geometrical optical circle of confusion.

[0033] Figures 7 and 8A show the relationship between the minimum circle of confusion and the diffraction limit, that is, the optical resolution at a given lens diameter and focal length. Therefore, in the case of the light-receiving lens 11 shown in Figure 8A, the circle of confusion diameter decreases as the effective diameter Φ increases, and it can be seen that an effective diameter Φ of 1.0 mm ≤ Φ ≤ 3.0 mm is sufficient.

[0034] On the other hand, as shown in Figures 7 and 8B, the geometric optical circle of confusion is large and the dependence on diffraction is small, resulting in the smallest circle of confusion diameter at Φ=1.0 mm. Moreover, even at Φ=1.0 mm, the circle of confusion diameter is nearly twice that of the light-receiving lens 11 shown in Figure 8A. The light-receiving lens 11 shown in Figure 8A is a SELFOC lens with smaller aberrations and a larger effective diameter than the light-receiving lens 11 shown in Figure 8B, indicating that the light-receiving lens 11 in Figure 8A should be selected. Furthermore, the light-receiving lens 11 in Figure 8A, with the same focal length, can achieve a numerical aperture (NA) at least three times larger than the light-receiving lens 11 in Figure 8B, meaning the amount of light received is more than nine times greater, and therefore the output of the light-receiving element is also more than nine times greater. Consequently, the shot noise, which depends on the amount of light received by the light-receiving element, is also reduced to one-third, so the light-receiving lens 11 shown in Figure 8A is preferable from the viewpoint of noise suppression as well. Furthermore, assuming the same amount of noise is acceptable, the light-receiving lens 11 in Figure 8A can improve the scanning speed by nine times compared to the light-receiving lens 11 in Figure 8B.

[0035] According to Figure 8C, SELFOC lens C, like SELFOC lens A, exhibits minimal aberrations and allows for a larger effective aperture.

[0036] Next, the parameters of SELFOC lenses A to C shown in Figures 8A to 8C are shown in Table 1 below. The most important parameter among those shown in Table 1 is the refractive index distribution constant. When the effective diameter is enlarged and the focal length is extended, the light-receiving lens 11 with the least aberration is SELFOC lens A, which has the smallest refractive index distribution constant, and the next light-receiving lens 11 with the least aberration is SELFOC lens C. Needless to say, for high-resolution, high-speed inspection, a light-receiving lens 11 with a large effective diameter, high brightness, and low aberration is preferable. [Table 1]

[0037] Furthermore, when four types of plastic rod lenses (plastic refractive index distribution type lenses) are used as the light-receiving lens 11, Figure 9A shows the relationship between the effective diameter and the circle of confusion diameter of rod lens A, Figure 9B shows the relationship between the effective diameter and the circle of confusion diameter of rod lens B, Figure 9C shows the relationship between the effective diameter and the circle of confusion diameter of rod lens C, and Figure 9D shows the relationship between the effective diameter and the circle of confusion diameter of rod lens D. In Figures 9A to 9D, the solid line shows the total circle of confusion, the dashed line shows the circle of confusion due to diffraction, and the dashed line shows the geometric optical circle of confusion. The parameters of rod lenses A to D shown in Figures 9A to 9D are shown in Table 2 below. It can be seen that the same trend as the SELFOC lens is observed even with plastic rod lenses. Considering the refractive index of the plastic rod lens and the refractive index of the glass lens, the on-axial refractive index is preferably between 1.45 and 1.65. [Table 2]

[0038] From the above, it can be seen that the refractive index distribution constant is the dominant factor in aberration. In an ideal refractive index distribution lens, the more gradually the refractive index changes, the less aberration there is. This is similar to how abrupt angular changes are a cause of aberration even in a normal spherical lens. Abrupt angular changes mean an increase in higher-order nonlinear effects when Snell'Law is expanded into a polynomial. That is, the deviation from paraxial optics increases, leading to increased aberration. The inventors of this application have found that, for a focal length or WD of approximately 50 mm or more and an effective diameter Φ of approximately Φ ≥ 1.0 mm, it is preferable to set the refractive index distribution constant to 0.12 or less in order to achieve a pixel resolution of 400 dpi or more.

[0039] 4. Modified examples of light-receiving lenses Next, a method for further increasing the depth of field is described. Figure 10 is a schematic diagram when the light-receiving lens 11 is replaced with an erect, reduced-magnification multi-lens lens. Figure 10 shows a schematic diagram when the light-receiving lens 11 is spaced further apart than the field of view of the light-receiving lens 11, and each light-receiving element array 120 is arranged in a direction perpendicular to the reading line L, spaced further apart than the field of view of the light-receiving lens 11. In Figure 10, a part of the light-receiving system is shown in a plan view, but a side view of a part of the light-receiving system is also shown for visual clarity. Also, in Figure 10, for visual clarity, the optical elements 200 arranged on the optical path from the light-receiving lens 11 to the light-receiving element array 120 are omitted.

[0040] In this case, the depth of field can be increased by a significant amount compared to the aforementioned erect 1:1 lens. For example, if the horizontal magnification is 4x, the depth of field increases by 2x. If the horizontal magnification is 9x, the depth of field becomes 3x. In this case, the pixel dimensions of the light-receiving element are also made smaller than the pixel dimensions in the 1:1 system, according to the reduction magnification and the desired resolution. However, depending on the resolution, the same pixel dimensions as the 1:1 system may be used.

[0041] Figure 11 shows the relationship between the effective diameter and the circle of confusion diameter of the reduction lens. The reduction ratio of the reduction lens is 1:4, and the wavelength is λ = 630 nm. Comparing Figure 8A and Figure 11, the circle of confusion of the reduction lens is smaller than that of the 1x system. For lens diameters between Φ = 2 mm and Φ = 2.5 mm, the circle of confusion of the 1x system is approximately 40 μm, while that of the reduction system is less than half, at 14 μm to 18 μm. Therefore, it can be seen that depth of field and resolution can be improved.

[0042] Furthermore, the light-receiving lens 11 in the present invention is not limited to refractive index distribution type lenses such as SELFOC lenses or plastic rod lenses, but can also be other lenses, such as achromatic (achromatic) or apochromatic lenses, in which, considering cost, the aberrations due to nonlinear effects in the aforementioned refractive index distribution type lenses are made equivalent, i.e., spherical aberration, coma aberration, and astigmatism are made equivalent, or a telecentric refractive optical system can be used in place of a refractive index distribution type lens such as a SELFOC lens or plastic rod lens, which has equivalent aberrations due to nonlinear effects and diffraction limits, with a similar arrangement and dimensions (aperture). The same applies to the light-receiving lens 11 that forms an inverted image, as described later.

[0043] The optical system described above is the case where an erect lens is at the center, but an inverted optical system may be used when the fields of view 111 do not overlap. That is, a configuration in which multiple light-receiving lenses 11 form an inverted image is also possible. An inverted optical system can be used if a two-row lens array is used. In the case of an inverted optical system, the image is inverted symmetrically about the optical axis, so when combining images, the inverted image can be converted to an erect image by image processing. That is, the inverted images of the multiple light-receiving lenses 11 can be inverted and converted to an erect image, and then the image combining process can be performed. In addition, during this operation, the need or non-necessity of overlapping parts can be determined and corrected using a correction algorithm, and then converted to an erect image based on the relationship between the determined pixels. Alternatively, in inspections where no image is constructed, only scratches or defects need to be detected, so there is no need for image combining or image processing, and the detected parts on the inspection surface can overlap. If there is overlap, the position should be corrected in advance using a correction chart.

[0044] Furthermore, in the case of an inverted refractive optical system, in signal processing for each photodetector, for example, data obtained from one of two rows of photodetector arrays arranged in a staggered pattern so as to be spaced apart in the sub-scanning direction may be acquired for a longer duration, data obtained from the other photodetector array may be acquired for a shorter duration, the acquired images may be inverted to an upright image, and then the images may be combined. Alternatively, the inverted image data from each photodetector may be converted to an upright image, and then a correction coefficient may be applied to or subtracted from the overlapping portion when combining the images.

[0045] Specifically, in an inverted refractive optical system, multiple photodetector arrays may be shorter than each of the two rows of reading lines, with multiple photodetector arrays arranged on each line. Alternatively, the photodetector arrays on one reading line and those on the other reading line may be arranged alternately in a staggered pattern along the main scanning direction. Since this configuration is the same as that of the upright refractive optical system described in Figure 6A, a detailed explanation will be omitted.

[0046] In this case, as shown in Figure 6A, multiple light-receiving elements are arranged in two or more rows to form multiple light-receiving element arrays 120. Furthermore, each of the multiple light-receiving element arrays 120 is spaced further apart from each other than the field of view dimension of the light-receiving lens 11 in a direction perpendicular to the reading line L. Multiple light-receiving lenses 11 are arranged in a number corresponding to the multiple light-receiving element arrays 120, and the optical axis of the light that passes through each light-receiving lens 11 and is guided to each light-receiving element array 120 passes through approximately the center of each light-receiving element array 120.

[0047] 5. Configuration of the illumination optical system In this embodiment, the focal length f of the light-receiving lens 11 is set to f=50mm, the numerical aperture (NA) to NA=0.01, 0.02, 0.025, and 0.03, and the refractive index distribution constant √A to √A=0.077. Regarding the light source 103, since the working width (WD) is more than 10 times longer than that of conventional CIS, the inspection surface illuminance needs to be 100 times greater in a 1x magnification system. For this reason, a high-brightness white LED array is used as the light source 103. That is, a configuration in which multiple light sources 103 include white LEDs is also possible. When a visible-range semiconductor laser is used as the light source 103, the light intensity unevenness during irradiation is reduced by expanding the emitted beam in the main scanning direction and collimating it in the sub-scanning direction.

[0048] Figure 12A shows an example of an arrangement method when using RGB-LEDs or RGB-LDs (laser diodes; semiconductor lasers) as light sources 103. As shown, the multiple light sources 103 may be configured to include red LEDs (R), green LEDs (G), and blue LEDs (B), or they may be configured to include laser diodes. In Figure 12A, the multiple 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 focusing lens 104 with different lens powers for the main scanning direction and the sub-scanning direction, and irradiated onto the object to be inspected. Here, an ellipsoidal focusing lens 104 is shown, but any lens with appropriately different lens powers for the main scanning direction and the sub-scanning direction is acceptable. Note that lens power is the reciprocal of the focal length and is a measure of the refractive power of the lens.

[0049] Alternatively, with respect to LDs, if end-face-emitting LDs are used in which the beam divergence angles of the LD itself differ in the horizontal and vertical directions, a normal collimator lens may be used. Figure 12B is a side view showing a specific example of arrangement when LDs are used as light sources 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 that constitute the light source 103 are collimated by corresponding focusing lenses 104 and then focused onto the inspection surface by a cylindrical lens 105. This ensures that each of the RGB colors is irradiated to approximately the same position in the sub-scanning direction, reducing color unevenness in the sub-scanning direction. Meanwhile, the light irradiated by the light source 103, such as an LED or LD, and diffusely reflected from the inspection surface is imaged onto the photodetector array by the photodetector lens system. In a 1:1 optical system, the photodetector uses an element size ranging from 62 μm equivalent to 400 dpi to 42 μm equivalent to 600 dpi. When using an element size of 600 dpi or higher, the power of the illumination light should be increased accordingly. In this way, the multiple light sources 103 may include multiple light sources 131 to 133 having multiple different wavelengths, and the light sources 131 to 133 may be considered as one unit, with multiple such units of light sources 103 arranged in the main scanning direction (X direction).

[0050] Furthermore, even if the radiance per unit area is the same, if the size of the photodetector is different, it is equivalent to having a different area for the light-emitting part, and therefore the amount of light received decreases inversely proportional to approximately the square of the photodetector area. The illumination light intensity is determined taking the above into consideration. When the element size decreases, the amount of light received decreases inversely proportional to the element area for the same storage time. This is a physical property of semiconductor photodetectors, and in order to maintain the S / N ratio, the illumination light should be increased to increase the power density and the number of generated electrons per unit time should be kept the same. This allows the shot noise to be maintained at the same level as a larger photodetector even when the size of the photodetector decreases. In addition, the light received by the photodetector depends not only on the illuminance of the inspection surface but also on the range that the photodetector is looking at when receiving the light. Needless to say, the solid angle of reception is different, and if that angle decreases, the amount of light received also decreases, and if the inspection surface is a perfectly diffuse surface, the amount of light received will be in accordance with the so-called cosθ law. Light diffusely reflected from the inspection surface is captured by a light-receiving lens and focused by a light-receiving element, and its output signal is output from the light-receiving element. Furthermore, the output signal from the array of light-receiving elements is branched from serial to parallel to improve processing speed and is transmitted to the image processing device.

[0051] In this embodiment, the light-receiving lens system is spaced apart by approximately the field of view. As a result, uneven light intensity due to lens vignetting is likely to occur. Therefore, ingenuity is required in the arrangement of the light source. Figures 13A and 13B show the positional relationship between the light source 103 and the light-receiving system. Figure 13A is a schematic diagram showing one example of the positional relationship between the light source 103 and the light-receiving system, where the two rows of light-receiving element arrays 120 are spaced farther than the field of view 111 of the light-receiving lens 11, and arranged in a staggered pattern for short sensors, or as line sensors of the same length for long sensors (length corresponding to the total length in the main scanning direction). Figure 13B is a schematic diagram showing another example of the positional relationship between the light source 103 and the light-receiving system, showing that the light-receiving lens 11 is arranged in the main scanning direction so that the fields of view 111 of the light-receiving lens 11 do not overlap. Note that in Figures 13A and 13B, the optical elements 200 arranged along the optical path from the light-receiving lens 11 to the light-receiving element array 120 are omitted for visual clarity.

[0052] Figure 14A is a schematic diagram showing the positional relationship between the light source 103 and the light receiving lens 11, where the light receiving element array 120 is in a single row. In the embodiment shown in Figure 14A, the position of the light source 103 is determined such that the minimum value of the unevenness of the illumination light from the light source 103 on the inspection surface is located approximately in the center of the light receiving element array 120. Generally, the position of the light source 103 is determined by considering the absolute irradiance on the inspection surface, at a position on a virtual plane perpendicular to the main scanning direction (X direction), including approximately in the center between adjacent light receiving lenses 11. Each light source 103 is arranged parallel to the reading line L. Furthermore, the optical axis of each light source 103 is positioned at any position on a virtual plane that intersects with the optical axis of the light that passes through each light receiving lens 11 and is guided to each light receiving element array 120, and also intersects with the optical axis of the light that passes through each light receiving lens 11 and is guided to each light receiving element array 120. In Figure 14A, the light source 103 is positioned approximately in the center between adjacent light-receiving lenses 11. 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 geometric optical aberrations, the effective diameter Φ' is set to Φ' = 2.5 mm using an aperture). Therefore, the light sources 103 are spaced approximately 4 mm apart in the main scanning direction (X direction). In this embodiment, light is irradiated from the light source 103 at an angle of approximately 45 degrees to the inspection surface. Therefore, considering the WD of the light-receiving lens 11, the distance between the light source 103 and the inspection surface is set to 70 mm. In this embodiment, an LD was used, but LEDs of various wavelengths may also be used.

[0053] Figure 14B is a schematic diagram showing the positional relationship between the light source 103 and the light-receiving lens 11, where the light-receiving element array 120 has two rows. The lens parameters are the same as in Figure 14A. Figure 14B shows the arrangement of the light source 103 relative to the light-receiving lenses 11 and the light-receiving element array 120 arranged in two rows. In this embodiment, the light source 103 is positioned approximately in the center of the two rows of reading lines L. The difference from Figure 14A is that, since the arrangement pitch of the light-receiving lenses 11 may be wider than the lens diameter and spaced further apart, the arrangement pitch of the light source 103 is also adjusted to match the distance between the lenses, and the light source 103 is positioned approximately in the center between adjacent light-receiving lenses 11 and also approximately in the center of the two rows of reading lines L. This makes it possible to further prevent pixel loss on the inspection surface and to further reduce shading of the light-receiving lenses 11 and light intensity unevenness of the light source 103. The positional relationship between the light source 103 and the inspection surface is the same as in Figure 14A. The lens pitch between the light-receiving lenses 11 in each row was set to 7 mm. In this case, the effective lens pitch is 3.5 mm.

[0054] Figure 14C shows the relationship between the light intensity distribution of the light source 103 (on the inspection surface), the light intensity distribution on the photodetector surface, and the shading of the photodetector lens 11 in the main scanning direction. In the layouts of Figures 14A and 14B, the light intensity distribution on the photodetector array 120 becomes flat, as schematically shown in Figure 14C, making it possible to effectively utilize the dynamic range of the photodetector.

[0055] 6. Methods to suppress ripple Next, we will discuss how shading caused by individual light-receiving lenses 11 generates ripple in the reading line L direction, which in turn narrows the dynamic range of the light-receiving element.

[0056] First, the object to be inspected is pre-illuminated with illumination light having a negative intensity distribution using an illumination system. For example, a method of placing a light source 103 between adjacent light-receiving lenses 11 does not provide a shading suppression method that is perfectly compatible with various types of light-receiving lenses 11. That is, each light-receiving lens 11 has its own unique shading, and if the light-receiving lenses 11 are different, an illumination optical system corresponding to them must be used. In this embodiment, a condensing lens 104 having high power in the main scanning direction is arranged. The light beam that has passed through the condensing lens 104 is then guided to the object to be inspected 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 object to be inspected. Then, by appropriately changing the position of the condensing lens 104 in the optical axis direction according to the shading of the light-receiving lens 11, for example, if the object to be inspected is a white reference plate for calibration, the light intensity distribution on the light-receiving element can be smoothed. The condensing lens 104 may also have power in the sub-scanning direction. In short, the goal is to completely suppress the shading of the light-receiving lens 11 and simultaneously achieve an effective light intensity distribution that takes into account the focal length of the light-receiving lens 11 for the object being inspected. That is, it is preferable that the lens power in the main scanning direction is greater than the lens power in the sub-scanning direction. As the focusing 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 preferred. The positional relationship of the light source 103 with respect to the main scanning direction may be that it is positioned midway between each light-receiving lens 11, or it may be positioned on the optical axis of the light-receiving lens 11. Furthermore, the light source 103 may be positioned on the outer circumference of the light-receiving lens 11. Moreover, it is even more preferable if the lens has a power distribution in the main scanning direction.

[0057] In this embodiment, a focusing lens 104 that focuses light beams from multiple light sources 103 is provided as a single lens body, and the power of this lens body in the main scanning direction is greater than the power in the sub-scanning direction. However, the focusing lens 104 may not be a single lens body, but may include a first focusing lens and a second focusing lens. In this case, the first focusing lens may have a power greater than the power in the sub-scanning direction, and the second focusing lens may have a power greater than the power in the sub-scanning direction. Furthermore, the power in the main scanning direction may be adjustable using the first focusing lens and the second focusing lens.

[0058] In the condensing lens 104 equipped with the first and second condensing lenses described above, the first and second condensing lenses can be composed of cylindrical lenses, lenticular lenses, Fresnel lenses, or prism arrays. For example, the first condensing lens may be a lenticular lens or a prism array. The second condensing lens may be a Fresnel lens or a cylindrical lens.

[0059] 7. Parameters of the light-receiving lens Figure 14D shows graphs of the MTF of the light-receiving system for different lens diameters in this embodiment. As a comparative example, Figure 14E shows the case where the refractive index distribution constant √A = 0.154. The solid line, short dashed line, long dashed line, and dashed line show the cases where the effective diameter Φ is Φ = 1.0, 1.5, 2.0, 2.5, and 3.0 mm, in that order. The pixel dimensions of the light-receiving element are set to 42.3 μm in both the main scanning direction and the sub-scanning direction to match 600 dpi.

[0060] In this embodiment, under the condition that the refractive index distribution constant √A = 0.077 at the effective diameter Φ, the MTF characteristics are satisfied in the range from Φ1.0 mm to Φ3.0 mm if the performance is approximately 30% at 12 lines / mm equivalent to 600 dpi. In contrast, the comparative example does not satisfy the MTF characteristics in the entire range of the effective diameter Φ. This indicates that the aberration characteristics are better when √A = 0.077 than when √A = 0.154. Furthermore, the MTF of the photodetector optical system when the refractive index distribution constant √A = 0.1027 for a focal length f = 50 mm is calculated and shown in Figure 14F. According to Figure 14F, 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 equivalent to a resolution of 600 dpi.

[0061] If the light-receiving lens 11 is a refractive index distribution type lens, it is preferable that the lens be made of glass or resin. In this case, it is preferable that the lens parameters of the light-receiving lens 11 are such that the axial refractive index N0 is 1.45 ≤ N0 ≤ 1.65, the refractive index distribution constant √A is 0.05 ≤ √A ≤ 0.12, and the focal length f is 50 mm ≤ f ≤ 150 mm.

[0062] Each light-receiving lens 11 may be an achromatic or apochromatic lens, each composed of multiple lenses. In this case, the lens system may consist only of convex lenses, or it may consist of a combination of convex and concave lenses. Furthermore, it is preferable that the focal length f of the multiple lenses is 50 mm ≤ f ≤ 250 mm, and the aperture Φ of the multiple lenses is 2 mm ≤ Φ ≤ 20 mm.

[0063] Next, to improve depth of field and resolution, an example of a reduced optical system for the light-receiving lens is presented. The configuration of the optical system is the same as in Figures 14A and 14B, but the magnification of the light-receiving lens 11 is changed. That is, the relationship between the horizontal magnification of the object point and the image point of the light-receiving lens 11 is changed to 9:1 or 4:1. By doing this, the depth of field increases to three times that of the 1x system when the horizontal magnification is 9:1, and to twice that of the 1x system when the horizontal magnification is 4:1. When the depth of field is tripled, the size of the light-receiving element is set to 1 / 9 the size of the light-receiving element of the 1x system. When the depth of field is doubled, the size of the light-receiving element is set to 1 / 4 the size of the light-receiving element of the 1x system. In this embodiment, a light-receiving element of 1 / 4 the size is used to double the depth of field.

[0064] The MTF characteristics of the reduction optical system in this embodiment when defocused are shown in the graph (solid line) of Figure 15. For comparison, the MTF characteristics of the 1:1 system when defocused are shown in the graph (dashed line) of Figure 15. From the comparison of the reduction system and the 1:1 system in the figure, it can be seen that the depth of field of the reduction optical system is about twice as deep as that of the 1:1 system. Also, the NA of the light-receiving lens 11 increases by 1 / S, which is the reciprocal of the reduction ratio, if S is the reduction ratio. Therefore, even when the lens diameter of the light-receiving lens 11 is small, the effective NA can be maintained by increasing the reduction ratio according to the focal length, and thus the blur due to diffraction can be kept constant.

[0065] In this embodiment, since the focal length is f=50mm and the lateral magnification ratio is 1 / 4, the lens diameter Φ can, in principle, be used down to Φ=0.25mm. Since the same lens as in Figures 14A and 14B is used, the lens diameter Φ is Φ=4mm and the effective diameter Φ' is Φ'=2.5mm. The numerical aperture (NA) is four times greater than in the 1:1 system cases of Figures 14A and 14B. Therefore, the amount of light received is 16 times greater, which can offset the 1 / 16 reduction in the amount of light received due to the reduction in the size of the photodetector to 1 / 4.

[0066] 8. Methods to prevent crosstalk In the case of Figure 14A, a method for preventing crosstalk caused by the superposition of the field of view 111 will be explained. In the case of Figure 14A, the lens diameter Φ is Φ = 4 mm and is used by being housed in the lens holder 110. Therefore, Figure 16A shows the configuration of a field of view limiting holder in which the photodetector array 120 side of the lens holder 110 is extended into a cylindrical shape. The effect of this will be explained below.

[0067] A detailed diagram is shown in Figure 16B. Note that in Figures 16A and 16B, for the sake of visual clarity, the optical elements 200 arranged on the optical path from the light-receiving lens 11 to the light-receiving element array 120 are omitted. Multiple light-receiving lenses 11 are inserted into the lens holder 110, and an aperture 112 consisting of a through hole is formed on the light-receiving element array 120 side of each light-receiving lens 11. The outer diameters of the multiple light-receiving lenses 11 are clearance-fit dimensions relative to the inner diameter of the lens holder 110, and clearance fitting is achieved when each light-receiving lens 11 is inserted into the lens holder 110. Each aperture 112 has an inner diameter smaller than the outer diameter of each light-receiving lens 11 and extends along the optical axis of each light-receiving lens 11. In other words, each aperture 112 extends the multiple light-receiving element side (light-receiving element array 120 side) of the lens holder 110 in a cylindrical shape, thereby limiting the field of view 111 of each light-receiving lens 11. The above cylindrical shape refers to a configuration in which the aperture 112 is extended by a cylindrical through hole, but it is not limited to this, and the aperture 112 may be extended in a flat plate shape by a protruding flat plate. The lengths of the multiple light-receiving element side (light-receiving element array 120 side) of the lens holder 110, i.e., the lengths of each aperture 112, may be different for adjacent light-receiving lenses 11.

[0068] The light beams shown by hatching in Figure 16B are within the field of view 111 and are therefore not subject to field of view limitations by the aperture 112, and can be received by the photodetector array 120. However, light beams outside of this area (outside the optical axis of the photodetector lens 11) do not reach the photodetector array 120. In other words, light beams within the field of view 111 of the photodetector lens 11 reach the photodetector facing the photodetector lens 11, but light beams outside the field of view 111 do not reach either the photodetector facing the photodetector lens 11 or any adjacent photodetector. To put it another way, when focusing on any photodetector, light beams outside the field of view 111 of the photodetector lens 11 facing that photodetector do not reach that photodetector, thus preventing crosstalk between adjacent pixels. Moreover, since the aperture 112 is formed in the lens holder 110, a highly accurate crosstalk prevention aperture can be realized.

[0069] In multiple apertures 112, the aperture diameter may be changed individually, and by using a pair of apertures 112 with different diameters, it is possible to prevent the loss of detected pixels on the inspection surface between adjacent pixels. That is, if we focus on an arbitrary aperture, for example in this embodiment, by setting the aperture diameter Φ to Φ = 2.4 mm and the adjacent aperture diameter Φ' to Φ' = 2.6 mm, it is possible to prevent the loss of detected pixels between adjacent pixels. The apertures 112 do not have to be cylindrical. For example, a partition may be provided at an intermediate position between the light-receiving lenses 11 to prevent light received by one light-receiving lens 11 from being received by the other light-receiving lens 11.

[0070] Furthermore, the arrangement of the multiple light-receiving lenses 11 is not limited to a single row. Individual light-receiving lenses 11 may be inserted and fixed into cylindrical holders beforehand, and then the cylindrical holders may be stacked in a bale-like fashion to arrange them in a bale-like configuration. Alternatively, the multiple light-receiving lenses 11 may be positioned using an L-shaped positioning jig, fixed with adhesive, and then placed in a rectangular lens holder.

[0071] Although the aperture 112 described above is provided on the photodetector array 120 side, it may also be provided on the inspection surface side with a length that does not impair the WD. By combining the aperture on the inspection surface side and the aperture on the photodetector side, more effective field of view restriction becomes possible.

[0072] Figures 17A to 17C show the relationship between the effective diameter and the circle of confusion diameter when the focal length f is f = 100 mm. The effective diameter Φ is the same as in Figure 14A. Figure 17A shows the case when √A = 0.154, Figure 17B shows the case when √A = 0.1027, and Figure 17C shows the case when √A = 0.077. In Figures 17A to 17C, the solid line shows the total circle of confusion, the dashed line shows the circle of confusion due to diffraction, and the dashed line shows the geometrical optical circle of confusion. In all of Figures 17A to 17C, N0 is N0 = 1.654. ​​According to Figures 17A to 17C, even when the focal length f is f = 100 mm, the circle of confusion diameter including diffraction is much smaller than the approximately 43 μm required when aiming for a resolution of 600 dpi when the effective diameter Φ is Φ ≥ 1.5 mm.

[0073] 9. Image inversion in telecentric optical systems Next, the telecentric optical system applied to this embodiment will be described. By using a telecentric optical system, a configuration that is easy to assemble and has little change over time can be achieved. In a telecentric optical system, light-receiving lenses 11 are arranged on both sides or on one side of the aperture (light-transmitting part). That is, the telecentric optical system is a double-sided telecentric optical system in which light-receiving lenses 11 are arranged on both the object to be inspected side and the light-receiving element array 120 side, or an object-side telecentric optical system in which light-receiving lenses 11 are arranged only on the object to be inspected side.

[0074] In a bilateral telecentric optical system, a beam of light spreading out in a narrow strip parallel to the optical axis from the object being inspected passes through the front lens to become a parallel beam of light. This parallel beam of light then passes through an aperture inserted behind the front lens, passes through the rear lens, and is focused onto each of the photodetectors in the photodetector array 120.

[0075] In this embodiment, an optical element (image inversion transforming element) 200 is arranged near the aperture. The optical element 200 has a reflective surface positioned on the optical path from the light-receiving lens 11 to the light-receiving element array 120, and guides the light that has passed through the light-receiving lens 11 to the light-receiving element array 120 by reflecting it off the reflective surface. A typical optical element 200 is a Porro prism. This prism is a right-angle prism, a transparent member that has a right-angle triangular shape in plan view, having two surfaces that straddle the right angle and an inclined surface located on the opposite side from the right angle to these two surfaces. When this right-angle prism is used as the optical element 200, the two surfaces that straddle the right angle may be used as reflective surfaces, and the light beam incident from the inclined surface may be totally reflected by the two surfaces that straddle the right angle and emitted from the inclined surface. Alternatively, the inclined surface may be used as the reflecting surface, one of the two surfaces separated by a right angle as the incident surface, and the other surface as the exit surface. The light beam incident from the incident surface may be totally reflected by the inclined surface and exited from the exit surface. In this embodiment, when one right-angle prism is used, the image is inverted in the sub-scanning direction, and when two right-angle prisms are used in combination, the image is inverted (180-degree transformation) in both the sub-scanning direction and the main scanning direction.

[0076] In other words, in a bilateral telecentric optical system, the object point and image point are rotationally symmetric, resulting in an inverted image. However, the Porro prism can convert this inverted image into an upright image.

[0077] Therefore, a bilateral telecentric optical system can achieve an erect image, and subsequent image processing becomes very simple, resulting in improved image processing speed compared to conventional methods.

[0078] Furthermore, the prism allows the image to be inverted in the sub-scanning direction, making the optical system more compact in the optical axis direction. For example, while a bilateral telecentric optical system assembled with a 50mm focal length lens has dimensions of approximately 200mm in the optical axis direction, an optical system with a prism has dimensions of about half that, approximately 100mm in the optical axis direction, increasing the options for introduction into narrow processes.

[0079] Furthermore, when using the inclined surface of a right-angle prism as the reflective surface, apertures (light-transmitting sections) may be provided on each of the two surfaces that straddle the right angle. In this case, since apertures are provided on the incident and exit sides, the diameter of the apertures can be made larger than in conventional methods, improving the positioning accuracy of the apertures and realizing an optical system that also exhibits less change over time.

[0080] Figure 18A shows a double-sided telecentric optical system bent approximately in the center (near the aperture). In the example in Figure 18A, a right-angle prism 201 is used as the optical element 200, and apertures 202 and 203 are provided on the right-angle prism 201. In the case of Figure 18A, the two surfaces that straddle the right angle of a single right-angle prism 201 are the incident surface 211 and the exit surface 212, with aperture 202 provided on the incident surface 211 and aperture 203 provided on the exit surface 212. Apertures 202 and 203 may be approximately circular or may have other shapes.

[0081] Light from the object being inspected, entering from the incident surface 211, is reflected by the reflective surface 204, which is inclined with respect to the incident surface 211. The light reflected by the reflective surface 204 is then emitted from the exit surface 212, which is inclined with respect to the reflective surface 204. In this example, the incident surface 211 is inclined at 45° with respect to the reflective surface 204, and the exit surface 212 is also inclined at 45° with respect to the reflective surface 204. As a result, the light entering from the incident surface 211 is reflected at 90° by the reflective surface 204 and emitted from the exit surface 212. However, the angles of the incident surface 211 and the exit surface 212 with respect to the reflective surface 204 are arbitrary and not limited to the above angles; any angle range that satisfies the total internal reflection condition is acceptable.

[0082] The incident surface 211 is covered by an absorbing surface formed by a mask 205. The absorbing surface is made of a light-absorbing material. An aperture 202 is formed in the mask 205 as a light-transmitting portion. The aperture 202 is formed near the reflective surface 204, but at a distance from the reflective surface 204. As a result, of the light beam incident on the incident surface 211 from the object to be inspected, only the light beam that passes through the aperture 202 is guided to the reflective surface 204, thus limiting the amount of light beam incident on the reflective surface 204.

[0083] The emission surface 212 is covered by an absorption surface formed by a mask 206. The absorption surface is made of a light-absorbing material. An aperture 203, which acts as a light-transmitting portion, is formed in the mask 206. The aperture 203 is formed near the reflection surface 204, but at a distance from the reflection surface 204. As a result, only the light beam that passes through the aperture 203 from the light beam emitted from the reflection surface 204 is guided to the photodetector array 120, thus limiting the light beam emitted from the reflection surface 204.

[0084] Figure 18B shows an object-side telecentric optical system bent approximately in the center (near the aperture). In the example in Figure 18B, a mirror 220 is used as the optical element 200, and an aperture 222 is provided on the reflective surface 221 of the mirror 220. The aperture 222 may be approximately rectangular, oval, or elliptical, or it may have any other shape.

[0085] The reflective surface 221 is covered by an absorbing surface formed by a mask 223. The absorbing surface is made of a light-absorbing material. An aperture 222 is formed in the mask 223 as a light-transmitting portion. The aperture 222 is formed at the position of the reflective surface 221, and of the light beam incident on the reflective surface 221 from the object to be inspected, only the light beam that passes through the aperture 222 is guided to the reflective surface 221. Also, of the light beam emitted from the reflective surface 221, only the light beam that passes through the aperture 222 is guided to the light-receiving element array 120. This makes it possible to limit the light beam incident on the reflective surface 221 and the light beam emitted from the reflective surface 221. Furthermore, as explained in Figure 18A, the angle of incidence on the reflective surface 221 is arbitrary within the range that satisfies the reflection conditions.

[0086] In the examples in Figures 18A and 18B, the image is inverted only in the sub-scanning direction. That is, the image of the object being inspected is inverted in the sub-scanning direction (Y direction) by reflection from the reflective surfaces 204 and 221, and is formed on each of the photodetectors in the photodetector array 120. Here, "inverted in the sub-scanning direction" means that the image is inverted so as to rotate around the X direction (main scanning direction).

[0087] Figure 19 shows a configuration in which the image is inverted only in the sub-scanning direction in a bilateral telecentric optical system, using the right-angle prism 201 shown in Figure 18A as the optical element 200. Figure 19 shows the view along the sub-scanning direction (Y direction), but for visual clarity, a view of the right-angle prism 201 along the main scanning direction (X direction) is also shown.

[0088] The double-sided telecentric optical system includes a first light-receiving lens 11A positioned between the right-angle prism 201 and the object under inspection, and a second light-receiving lens 11B positioned between the right-angle prism 201 and the light-receiving element array 120. However, in the case of an object-side telecentric optical system, the second light-receiving lens 11B may be omitted.

[0089] Each light beam from the object being inspected spreads out as it enters the first light-receiving lens 11A, and becomes a parallel light beam after passing through the first light-receiving lens 11A. The parallel light beam from the first light-receiving lens 11A is reflected by the reflective surface 204 of the right-angle prism 201 and enters the second light-receiving lens 11B. The light beam that passes through the second light-receiving lens 11B is focused onto each light-receiving element of the light-receiving element array 120.

[0090] Figure 20 shows a conventional bilateral telecentric optical system. In a conventional bilateral telecentric optical system, a first light-receiving lens 11A and a second light-receiving lens 11B are provided, but a right-angle prism 201 is not placed between the first light-receiving lens 11A and the second light-receiving lens 11B. An aperture is provided between the first light-receiving lens 11A and the second light-receiving lens 11B, and the parallel light beam from the first light-receiving lens 11A passes through the aperture and enters the second light-receiving lens 11B without reflection.

[0091] As shown in Figure 20, while conventional bilateral telecentric optical systems have a large size in the optical axis direction (Z direction), by bending the light beam at a right angle using the optical element 200 as shown in Figures 18A and 18B, the size in the optical axis direction can be reduced as shown in Figure 19. Therefore, it is possible to make the optical line sensor more compact while ensuring the optical path length of the light beam from the object being inspected.

[0092] Figure 21 shows another example of the optical element 200, in which a Porro prism is used as the optical element 200. A Porro prism is a configuration that includes multiple prisms, and in the example in Figure 21, two right-angle prisms 201 are used. With a configuration using a Porro prism, it is possible to convert an inverted image to an upright image.

[0093] In the example shown in Figure 21, the two surfaces on either side of the right angle of each right-angle prism 201 constitute the reflective surface 204, while the beveled surface functions as the incident surface 211 and the outgoing surface 212. Each beveled surface of the right-angle prism 201 has an aperture 202 that limits the incident light beam and an aperture 203 that limits the outgoing light beam. In other words, each beveled surface of the right-angle prism 201 constitutes a mask equipped with apertures 202 and 203 that act as light-transmitting sections.

[0094] In the example shown in Figure 21, the image is inverted in both the sub-scanning direction and the main scanning direction. That is, the image of the object to be inspected is inverted in the sub-scanning direction (Y direction) by being reflected by the reflective surface 204 of the first right-angle prism 201, and then inverted in the main scanning direction (X direction) by being reflected by the reflective surface 204 of the second right-angle prism 201, before being imaged onto each of the photodetectors in the photodetector array 120. Here, "inverted in the sub-scanning direction" means that the image is inverted so as to rotate around the X direction (main scanning direction), and "inverted in the main scanning direction" means that the image is inverted so as to rotate around the Z direction (a direction perpendicular to both the main scanning direction and the sub-scanning direction).

[0095] Even when using an optical element 200 as shown in Figure 21, the optical line sensor can be made more compact while ensuring the optical path length of the light beam from the object being inspected. However, when using a Porro prism as the optical element 200, the number of right-angle prisms 201 is not limited to two, but may be three or more. Furthermore, each right-angle prism 201 is not limited to having two surfaces that form the reflective surface 204, but may also have a slanted surface that forms the reflective surface 204, as in the example in Figure 18A.

[0096] Figure 22 is a conceptual diagram showing a configuration using the aperture-equipped Porro prisms of Figure 21 in a double-sided telecentric optical system. Each light beam from the object to be inspected spreads out as it enters the first light-receiving lens 11A, and becomes a parallel light beam after passing through the first light-receiving lens 11A. The parallel light beam from the first light-receiving lens 11A enters the optical element 200, which is composed of a pair of Porro prisms (double Porro prisms, or two right-angle prisms 201), and is reflected by the reflective surfaces 204 of each right-angle prism 201, causing the image to be inverted in the sub-scanning direction and the main scanning direction. It is then focused after passing through the second light-receiving lens 11B and formed as an image on each light-receiving element of the light-receiving element array 120.

[0097] Although the optical axis of the aforementioned bent optical system was set to a right angle, for image inversion only in the sub-scanning direction, or for image inversion in both the main and sub-scanning directions, the angle may be set to a right angle if necessary, as long as the total internal reflection condition is satisfied in the reflection of the light beam incident on the prism equipped with an aperture. For example, in the case of optical glass with a refractive index n of n=1.5, total internal reflection occurs when the incident angle θi ≥ 42°, so total internal reflection also occurs at θi=50°. Depending on the structure of the optical system, the angle may be set to satisfy the total internal reflection condition. Alternatively, even if the total internal reflection condition is not satisfied, a reflective surface with high reflectivity may be formed by using a reflective material such as a dielectric multilayer film on the reflective surface.

[0098] Furthermore, by using reflective materials such as the aforementioned dielectric multilayer film, it is possible to use combinations of telecentric optical systems and Porro prisms (pairs) other than the combination of the two-sided telecentric optical system and Porro prism (pair) described above. For example, an object-side telecentric optical system and a Porro prism (pair) may be used. [Explanation of Symbols]

[0099] 10 Light source section 11. Light-receiving lens 11A First light-receiving lens 11B Second light-receiving lens 12 Light receiving part 20 focal plane 103 Light source 104 Focusing lens 105 Cylindrical Lens 110 Lens Holder 111 Field of view 112 Aperture 120 photodetector array 131 Red LD 132 Green LD 133 Blue LD 134 Light source substrate 135 Heatsink 200 optical elements 201 Right-angle prism 202 Aperture 203 Aperture 204 Reflective surface 205 masks 206 masks 211 Incidence plane 212 Ejection surface 220 Mirror 221 Reflective surface 222 Aperture 223 Masks

Claims

1. An optical line sensor that reads an object to be inspected being transported in the sub-scanning direction using a reading line extending in the main scanning direction, Multiple light-receiving lenses arranged along the main scanning direction, Multiple light-receiving elements are arranged in a line along the main scanning direction and receive light that has passed through the multiple light-receiving lenses, The optical element comprises a reflective surface arranged in the optical path from the light-receiving lens to the light-receiving element, and an optical element that reflects light transmitted through the light-receiving lens at the reflective surface to guide it to the light-receiving element, The plurality of light-receiving lenses are arranged so that they are spaced apart from each other at a distance greater than the diameter of the light-receiving lens. The plurality of light-receiving elements form at least one row or more of the reading lines. The aforementioned light-receiving lens constitutes a telecentric optical system. The optical line sensor is characterized in that the optical element inverts and forms an image on the light-receiving element in the sub-scanning direction, or inverts and forms an image on the light-receiving element in both the sub-scanning direction and the main scanning direction.

2. The optical line sensor according to claim 1, characterized in that the optical element has a mask with a light-transmitting portion located at a position away from the reflective surface, which limits at least one of the light beam incident on the reflective surface and the light beam emitted from the reflective surface.

3. The optical line sensor according to claim 1, characterized in that the optical element has a mask at the position of the reflective surface that has a substantially rectangular, oval, or elliptical light-transmitting portion that limits the light beam incident on the reflective surface and the light beam emitted from the reflective surface.

4. The optical line sensor according to claim 1, characterized in that the plurality of light-receiving lenses are spaced apart from each other at a distance greater than the field of view dimension of the light-receiving lenses, and the plurality of light-receiving elements form at least two rows or more of the reading lines.

5. The aforementioned plurality of light-receiving elements are arranged in a single row in an array to form a single light-receiving element array. The optical line sensor according to claim 1, characterized in that the plurality of light-receiving lenses are spaced apart from each other at a distance greater than or equal to the diameter of the light-receiving lens, and spaced apart from each other at a distance less than or equal to the field of view dimension of the light-receiving lens.

6. The plurality of light-receiving elements are arranged in two or more rows to form a plurality of light-receiving element arrays, and each of the plurality of light-receiving element arrays is spaced apart from each other in a direction perpendicular to the reading line, at a distance greater than or equal to the diameter of the light-receiving lens, and at a distance less than or equal to the field of view of the light-receiving lens. The optical line sensor according to claim 1, characterized in that 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 that passes through each light-receiving lens and is guided to each light-receiving element array penetrates approximately the center of each light-receiving element array.

7. The plurality of light-receiving elements are arranged in two or more rows to form a plurality of light-receiving element arrays, and each of the plurality of light-receiving element arrays is spaced apart from each other in a direction perpendicular to the reading line, at a distance greater than the field of view dimension of the light-receiving lens. The optical line sensor according to claim 1, characterized in that 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 that passes through each light-receiving lens and is guided to each light-receiving element array penetrates approximately the center of each light-receiving element array.

8. The optical line sensor according to claim 6 or 7, characterized in that the plurality of light-receiving element arrays are light-receiving element arrays shorter than each of the two reading lines, each of which is arranged in a plurality on each of the two reading lines, and the light-receiving element arrays arranged on one reading line and the light-receiving element arrays arranged on the other reading line are arranged alternately in a staggered pattern along the main scanning direction.

9. The optical line sensor according to claim 8, characterized in that the plurality of light-receiving lenses are arranged in a single row parallel to the plurality of light-receiving element arrays between the two rows of reading lines, and the optical axis of the light that passes through each light-receiving lens and is guided to each light-receiving element array passes through approximately the center in the sub-scanning direction between the two rows of reading lines.

10. The optical line sensor according to claim 1, characterized in that the plurality of light-receiving lenses each include a refractive index distribution lens, an achromatic lens, or an apochromatic lens that forms an inverted image.

11. The optical line sensor according to claim 10, characterized in that the refractive index distribution type lens is made of glass or resin, and in the lens parameters of the lens, the on-axial refractive index N0 is 1.45 ≤ N0 ≤ 1.65, the refractive index distribution constant √A is 0.05 ≤ √A ≤ 0.12, and the focal length f is 50 mm ≤ f ≤ 150 mm.

12. The optical line sensor according to claim 10, characterized in that each of the plurality of light-receiving lenses consists of an achromatic or apochromatic lens, which is a combination of multiple lenses, and the plurality of lenses is a lens system which is a combination of only convex lenses, or a lens system which is a combination of convex and concave lenses, and the focal length f of the plurality of lenses is 50 mm ≤ f ≤ 250 mm, and the aperture Φ of the plurality of lenses is 2 mm ≤ Φ ≤ 20 mm.

13. It is further equipped with multiple light sources that illuminate the object to be inspected, The optical line sensor according to claim 1, characterized in that the plurality of light sources are arranged parallel to the reading line, the optical axes of the plurality of light sources intersect with the optical axes of light that passes through the plurality of light-receiving lenses and is guided to the plurality of light-receiving elements, and are positioned at any position on a virtual plane that intersects with the optical axes of light that passes through the plurality of light-receiving lenses and is guided to the plurality of light-receiving elements, and further, the light sources are positioned approximately in the center between adjacent light-receiving lenses.

14. The optical line sensor according to claim 13, characterized in that the plurality of light sources include light sources having a plurality of different wavelengths, and the plurality of light sources having a plurality of different wavelengths are treated as one unit, with a plurality of such units of light sources arranged in the main scanning direction.

15. The optical line sensor according to claim 13, further comprising a focusing lens for concentrating light beams from the plurality of light sources.

16. The optical line sensor according to claim 15, characterized in that the focusing lens includes a first focusing lens in which the power in the main scanning direction is greater than the power in the sub-scanning direction, and a second focusing lens in which the power in the sub-scanning direction is greater than the power in the main scanning direction.

17. The optical line sensor according to claim 15, characterized in that the condensing 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.

18. The optical line sensor according to claim 16, characterized in that the power in the main scanning direction can be adjusted by the first and second focusing lenses.

19. The optical line sensor according to claim 15, characterized in that the light-gathering lens is a cylindrical lens or a Fresnel lens.

20. The first focusing lens is a lenticular lens or a series of prisms. The optical line sensor according to claim 16, characterized in that the second focusing lens is a Fresnel lens or a cylindrical lens.

21. The optical line sensor according to claim 13, characterized in that the plurality of light sources include white LEDs.

22. The optical line sensor according to claim 13, characterized in that the plurality of light sources include a red LED, a green LED, and a blue LED.

23. The optical line sensor according to claim 13, characterized in that the plurality of light sources include laser diodes.

24. The lens holder further comprises a lens holder for holding the plurality of light-receiving lenses, The optical line sensor according to claim 1, characterized in that the field of view of each light-receiving lens is limited by extending the lens holder on the side of the plurality of light-receiving elements in a cylindrical or flat shape.

25. The lens holder further comprises a lens holder for holding the plurality of light-receiving lenses, The optical line sensor according to claim 1, characterized in that the outer diameters of the plurality of light-receiving lenses are clearance-fit dimensions with respect to the inner diameter of the lens holder, and the plurality of light-receiving lenses are stacked in a slab or arranged in a single row.

26. The optical line sensor according to claim 24, characterized in that, in adjacent light-receiving lenses, the lengths of the lens holder on the side of the plurality of light-receiving elements are different.

27. A light source substrate on which the aforementioned multiple light sources are mounted, The optical line sensor according to claim 13, further comprising a heat sink attached to the light source substrate.

Images