Optical line sensor

Abstract

This optical line sensor enables even illumination of multiple photodetector arrays arranged in two rows of reading lines, even when the inspection surface is not flat, and also improves image quality. [Solution] The light-receiving lens 11 constitutes a telecentric optical system, and its width in the sub-scanning direction is smaller than its width in the main scanning direction. Multiple light-receiving elements constitute a plurality of light-receiving element arrays 120 arranged in two rows of reading lines. The straight lines connecting each pixel of the plurality of light-receiving elements to each pixel on the object being inspected that corresponds one-to-one with the light-receiving element arrays 120 arranged in two rows of reading lines are tilted symmetrically across the optical axis of the telecentric optical system so that the light transmitted through the plurality of light-receiving lenses 11 is incident equally on the plurality of light-receiving element arrays 120 arranged in two rows of reading lines.

Description

Technical Field

[0005]

[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, flatbed scanners such as office copiers and home printer scanners, etc. has been considered for application to so-called surface inspection machines for inspecting 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. Some of them have been commercialized.

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

[0004] As shown in Patent Documents 1 to 5, a telecentric optical system using a mirror optical system is typical for a CIS with a deep depth of field. It can be seen from the above patent documents that the optical system is very complicated. 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 complicated optical system caused by environmental changes and aging changes, the optical axis drifts, and problems such as easy performance degradation compared to conventional CIS with a simple structure remain.

[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, inexpensive, and can be introduced into each process of a factory, using a new refractive lens with a long working distance (WD) and deep depth of field, and employing a new illumination system that suppresses ripple, which is optical unevenness on the light-receiving sensor caused by the shading of individual lenses.

[0008] Therefore, the inventors of the present invention proposed one solution to the aforementioned problems in Patent Document 8 below. The optical line sensor disclosed in Patent Document 8 is an optical line sensor that reads an object to be inspected being transported in the sub-scanning direction with a reading line extending in the main scanning direction, and comprises a plurality of light-receiving lenses and a plurality of light-receiving elements. The plurality of light-receiving lenses are arranged in a plurality along the main scanning direction. The plurality of light-receiving elements are arranged in a line along the main scanning direction and receive light that has passed through the plurality of light-receiving lenses. The plurality of light-receiving elements form at least two rows or more of the reading line. The light-receiving lenses constitute a telecentric optical system, and their width in the sub-scanning direction is smaller than their width in the main scanning direction. [Prior art documents] [Patent Documents]

[0009] [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 [Patent Document 8] International Publication No. 2023 / 238480 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, a new problem has emerged with the optical line sensor disclosed in Patent Document 8. Specifically, when a light-receiving element array is constructed using multiple light-receiving elements and multiple light-receiving element arrays are arranged in a staggered pattern on two rows of reading lines, it can be difficult to ensure that light transmitted through multiple light-receiving lenses is evenly incident on each light-receiving element array and to obtain good light-receiving efficiency.

[0011] First, if the optical axis of light passing through multiple light-receiving lenses is aligned with the optical axis of a light-receiving element array arranged on one reading line, the amount of light received by the light-receiving element array arranged on the other reading line decreases, making it impossible to evenly incident light on each light-receiving element array. Therefore, if the optical axis of light passing through multiple light-receiving lenses is positioned in the center of the sub-scanning direction for multiple light-receiving element arrays arranged in a staggered pattern, as disclosed in Patent Document 8, it is possible to evenly incident light on each light-receiving element array, but the amount of light received by each light-receiving element array decreases overall, making it impossible to obtain good light-receiving efficiency, and thus the image quality deteriorates.

[0012] Furthermore, if the inspection surface of the object being inspected is not flat, it becomes difficult to evenly illuminate each light-receiving element array. Specifically, as in the optical line sensor disclosed in Patent Document 8, when the optical axis of light passing through multiple light-receiving lenses is positioned in the center of the sub-scanning direction for multiple light-receiving element arrays arranged in a staggered pattern, the optical axes of each light-receiving element array are parallel to each other. In this case, if the inspection surface is arc-shaped, such as the surface of a rotating body, and the arc-shaped inspection surface is aligned with the optical axis of a light-receiving element array on one reading line, the specularly reflected light will be reflected in a different direction from the light-receiving element array on the other reading line. With diffusely reflected light, each light-receiving element array can receive light to some extent even if the optical axis is misaligned, but with specularly reflected light, the reflection angle differs when the optical axis of each light-receiving element array reflects off the arc-shaped inspection surface. Therefore, if the reflection angle is aligned with the optical axis of a light-receiving element array on one reading line, the optical axis will not coincide with the light-receiving element array on the other reading line, and it will not be possible to evenly illuminate each light-receiving element array.

[0013] Therefore, the present invention aims to provide an optical line sensor that can evenly illuminate multiple light-receiving element arrays arranged in two rows of reading lines, even when the inspection surface is not flat, and that can improve image quality. [Means for solving the problem]

[0014] The first 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 light source, a plurality of light-receiving lenses, and a plurality of light-receiving elements. The light source is arranged in a line along the main scanning direction and illuminates the object to be inspected. The plurality of light-receiving lenses are arranged in a line along the main scanning direction and transmit light from the object to be inspected illuminated by the light source. The plurality of light-receiving elements are arranged in a line along the main scanning direction and receive light that has been transmitted through the plurality of light-receiving lenses. The light-receiving lenses constitute a telecentric optical system, and their width in the sub-scanning direction is smaller than their width in the main scanning direction. The plurality of light-receiving elements constitute a plurality of light-receiving element arrays arranged in two rows of the reading line. The straight lines connecting each pixel of the plurality of light-receiving elements to each pixel on the object being inspected, which correspond one-to-one with the respective pixels of the plurality of light-receiving elements, are tilted symmetrically across the optical axis of the telecentric optical system, so that the light transmitted through the plurality of light-receiving lenses is evenly incident on the plurality of light-receiving element arrays arranged in two rows of the reading lines.

[0015] A second 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 light source, a plurality of light-receiving lenses, and a plurality of light-receiving elements. The light source is arranged in a line along the main scanning direction and illuminates the object to be inspected. The plurality of light-receiving lenses are arranged in a line along the main scanning direction and transmit light from the object to be inspected illuminated by the light source. The plurality of light-receiving elements are arranged in a line along the main scanning direction and receive light that has been transmitted through the plurality of light-receiving lenses. The light-receiving lenses constitute a telecentric optical system, and their width in the sub-scanning direction is smaller than their width in the main scanning direction. The plurality of light-receiving elements constitute a plurality of light-receiving element arrays arranged in two rows of the reading lines. The optical line sensor further comprises an optical branching element that branches the light so that the light transmitted through the plurality of light-receiving lenses is evenly incident on the plurality of light-receiving element arrays arranged in two rows of the reading lines and guides the light to the plurality of light-receiving element arrays.

[0016] A third 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 light source, a plurality of light-receiving lenses, and a plurality of light-receiving elements. The light source is arranged in a line along the main scanning direction and illuminates the object to be inspected. The plurality of light-receiving lenses are arranged in a line along the main scanning direction and transmit light from the object to be inspected illuminated by the light source. The plurality of light-receiving elements are arranged in a line along the main scanning direction and receive light that has been transmitted through the plurality of light-receiving lenses. The plurality of light-receiving elements constitute a plurality of light-receiving element arrays arranged in two rows of the reading line. The optical line sensor further comprises an optical branching element that branches the light so that the light transmitted through the plurality of light-receiving lenses is evenly incident on the plurality of light-receiving element arrays arranged in two rows of the reading line, and guides the light to the plurality of light-receiving element arrays. [Effects of the Invention]

[0017] According to the present invention, even when the inspection surface is not flat, it is possible to evenly irradiate light onto a plurality of light receiving element arrays arranged in two rows, and the image quality can be improved.

Brief Description of the Drawings

[0018] [Figure 1] It is a cross-sectional view of a typical CIS. [Figure 2] It is an exploded perspective view of a line-shaped illumination optical system for CIS. [Figure 3] It is a schematic diagram of a light receiving system in which the visual fields of each light receiving lens do not overlap when each light receiving lens is arranged to act as a monocular lens. [Figure 4] It is a schematic diagram showing another example of a light receiving system in which a plurality of light receiving element arrays are arranged. [Figure 5] It is a schematic diagram showing still another example of a light receiving system in which a plurality of light receiving element arrays are arranged. [Figure 6] It is a graph showing the relationship between N.A. and diffraction limit for each wavelength. [Figure 7A] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of SELFOC lens A. [Figure 7B] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of SELFOC lens B. [Figure 7C] It is a graph showing the relationship between the effective diameter and the confusion circle diameter of SELFOC lens C. [[ID=​​​​​​​​​​​​​​ [Figure 9B] This is a side view showing a specific example of an arrangement method when using an LD as a light source. [Figure 10A] 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 10B] 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 10C] This is a graph of the MTF of the light-receiving system for different lens diameters (√A=0.077). [Figure 10D] This is a graph of the MTF of the light-receiving system for different lens diameters (√A=0.154). [Figure 10E] This is a graph of the MTF of a photodetector optical system with a refractive index distribution constant √A = 0.1027. [Figure 11] This graph shows the MTF characteristics during defocusing. [Figure 12A] This is a schematic diagram showing a modified light-receiving system. [Figure 12B] This is a schematic diagram showing a modified light-receiving system. [Figure 12C] This is a schematic diagram showing a modified light-receiving system. [Figure 12D] This is a schematic diagram showing a modified light-receiving system. [Figure 12E] This is a schematic diagram showing a modified light-receiving system. [Figure 12F] This is a schematic diagram showing a modified light-receiving system. [Figure 12G] This is a schematic diagram showing a modified light-receiving system. [Figure 13] This figure shows the light intensity distribution on the light-receiving surface of a photodetector array when the light intensity distribution of the light source is flat, with the lens edges being parallelogram-shaped. [Figure 14] This diagram shows the detailed light intensity distribution near the connection point between adjacent light-receiving lenses. [Figure 15] In the example shown in Figure 12E, the light intensity of the light-receiving region is shown, illustrating in general terms why no signal loss occurs. [Figure 16]This diagram illustrates the factors that cause a decrease in light reception efficiency when the optical axis of one of two photodetector arrays arranged in two reading lines is aligned with the optical axis of the other array. [Figure 17] This diagram shows the optical axis of the light-receiving lens aligned between two rows of light-receiving element arrays arranged on the reading lines, and the optical axes of each light-receiving element array intersecting near the inspection surface. [Figure 18] This diagram illustrates how the diffuse solid angles of light beams partially diffused on the inspection surface overlap, centered on the optical axes that intersect each photodetector array on the inspection surface. (This is an example where the spacing in the sub-scanning direction of a staggered arrangement of photodetector arrays is 2 mm.) [Figure 19A] This figure demonstrates that the same light-receiving lens can be used even if the position of the light beam incident on the light-receiving lens relative to the optical axis of specularly reflected light is offset from the optical axis of the light-receiving lens. (This is the case when the spacing of the staggered-arranged light-receiving element array is close to the optical axis.) [Figure 19B] This figure demonstrates that the same light-receiving lens can be used even when the position of the light beam incident on the light-receiving lens relative to the optical axis of specularly reflected light is offset from the optical axis of the light-receiving lens. (When the spacing of the light-receiving element array is far from the optical axis) [Figure 19C] This figure shows that the aperture of a telecentric optical system can be positioned by shifting its location parallel to the optical axis of the original light-receiving lens in the sub-scanning direction, so that it connects the intersection points of the optical axes of each light-receiving element array on the inspection surface. (When the spacing of the staggered-arranged light-receiving element arrays in the sub-scanning direction is narrow.) [Figure 19D] This figure shows that the aperture of a telecentric optical system can be positioned by shifting its location parallel to the optical axis of the original light-receiving lens in the sub-scanning direction, so that it intersects with the optical axes of each light-receiving element array on the inspection surface. (This applies when the spacing between the staggered-arranged light-receiving element arrays in the sub-scanning direction is wide.) [Figure 19E]This figure shows that the aperture of a telecentric optical system can be positioned by shifting its location parallel to the optical axis of the original light-receiving lens in the sub-scanning direction, so that it intersects with the optical axes of each light-receiving element array on the inspection surface. (This applies when the spacing between the staggered light-receiving element arrays in the sub-scanning direction is wide, and the outline of the light-receiving lens viewed from the optical axis direction is trapezoidal.) [Figure 20A] This is a schematic diagram illustrating the reception of light scattered from a single point on the same plane in the sub-scanning direction of the object being inspected. (The optical axes connecting the aperture and the photodetector array intersect on the inspection surface.) [Figure 20B] This is a schematic diagram illustrating the reception of light scattered from a single point on the same plane in the sub-scanning direction of the object being inspected. (It shows that even when an oval aperture is used in the sub-scanning direction, light passing through the center of the oval does not reach the photodetector array.) [Figure 21A] This is a schematic diagram showing the optical system in Figure 20A with an angle adjustment element added. [Figure 21B] Figure 21A shows how the angle adjustment element of the optical system is positioned near the aperture on the inspection surface side, allowing a light beam parallel to the optical axis, emitted from the inspection surface near the optical axis, to be received by a staggered array of photodetectors. Alternatively, it is possible to receive light reflected from a position on the same inspection surface by intersecting the beams at an extremely small angle (represented by the dotted line). [Figure 21C] This diagram illustrates a method of splitting specularly reflected light into two using a prism and a half-mirror (the light intensity is halved, but specularly reflected light can be reliably received), and shows that the receiving lens can be of various shapes, such as notched, trapezoidal, or parallelogram, when viewed in cross-sectional view in the main scanning direction. Furthermore, an aperture for creating a telecentric optical system is positioned at the rear focal point of the lens. [Figure 21D] Figure 21C shows the optical axis bifurcating element positioned behind the light-receiving lens (on the light-receiving element array side). (This is particularly effective for multi-lens arrays.) [Figure 22A] This diagram shows another configuration using a prism as an optical branching element. [Figure 22B]This diagram shows yet another configuration using a prism as an optical branching element. [Figure 23A] This figure shows a case where a prism is used as the light splitting element and a multi-lens system is used as the light receiving lens. [Figure 23B] This diagram shows the joints of a wedge prism in particular, when a prism is used as an optical branching element and a multi-lens is used as a light-receiving lens. [Figure 23C] This figure shows a side view, particularly in the direction of the main scanning, when a prism is used as the optical branching element and a multi-lens is used as the light-receiving lens. [Modes for carrying out the invention]

[0019] 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.

[0020] In the CIS shown in Figure 1, two housings 16 are positioned opposite each other with the focal plane (inspection surface) 20 in between. Each housing 16 is equipped with a light source unit 10 for illuminating the object to be inspected on the focal plane 20. The light source units 10 are arranged in a line along the main scanning direction (X direction). 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] In the CIS described above, a refractive index distribution lens array, such as a SELFOC (manufactured by Nippon Sheet Glass Co., Ltd.) lens array, may be used as the light-receiving lens 11. This type of refractive index distribution lens array is an erect, 1x magnification lens array. Cylindrical refractive index distribution lenses may be stacked 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, is smaller than that of a single lens. This is because the effective F-number decreases 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 refractive index distribution lens arrays are used in CIS systems.

[0025] 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 depth of field becomes shallower as the numerical aperture increases. 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 those represented by refractive index distribution lenses, have a structure in which the image is more prone to blurring when the object being inspected changes in the direction of the optical axis, compared to monocular lenses, because the optical axes of each lens are different and intersect. The above is a major drawback of the stacked multi-lens refractive index distribution 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.

[0026] 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 of each light-receiving lens 11 do not overlap. In Figure 3, each light-receiving lens 11 is spaced apart in the main scanning direction (X direction) and also spaced apart in the sub-scanning direction (Y direction) so that the fields of view of each light-receiving lens 11 do not overlap, so that each light-receiving lens 11 is arranged in a staggered pattern.

[0027] In other words, instead of a stacking method, multiple light-receiving lenses 11 are arranged in a line along the main scanning direction (X direction) and spaced apart from each other. The multiple light-receiving lenses 11 arranged in a line along the main scanning direction (X direction) are integrally held by a lens holder 110. Opposite each light-receiving lens 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 an array along the main scanning direction (X direction). Each light-receiving lens 11 transmits light from the object to be inspected illuminated by the light source unit 10, and each light-receiving element receives the light that has passed through each light-receiving lens 11.

[0028] In this example, the photodetector array 120 is arranged in correspondence with each photodetector lens 11. As a result, each photodetector array 120, which consists of short sensors, is arranged alternately in a staggered pattern along the main scanning direction (X direction). Multiple photodetector arrays 120 arranged along the main scanning direction (X direction) form one row of reading lines L, and in the example of Figure 3, two rows of reading lines L are formed. The lens holder 110 is not limited to a configuration in which it is provided in correspondence with each reading line L, but may also be configured to integrally hold multiple photodetector lenses 11 corresponding to each reading line L with a single lens holder.

[0029] As shown in FIG. 3, one light-receiving lens 11 may be provided for each light-receiving element array 120, so that a plurality of light-receiving lenses 11 may be arranged in number corresponding to the plurality of light-receiving element arrays 120. The optical axes of the light transmitted through each light-receiving lens 11 and guided to each light-receiving element array 120 may pass through substantially the central portions in the main scanning direction (X direction) of the corresponding light-receiving element arrays 120 on a one-to-one basis. In this method, a plurality of light-receiving element arrays 120 are arranged in a plurality of rows in the sub-scanning direction (Y direction). That is, the plurality of light-receiving element arrays 120 are arranged at intervals in the direction (Y direction) perpendicular to the arrangement direction (X direction) of the light-receiving elements.

[0030] The width W1 of each light-receiving lens 11 in the sub-scanning direction is smaller than the width W2 (lens diameter) in the main scanning direction. That is, each light-receiving lens 11 has an elongated shape along the main scanning direction. The width W1 of each light-receiving lens 11 in the sub-scanning direction corresponds to the field of view of each light-receiving lens 11 in the sub-scanning direction. Also, the width W2 of each light-receiving lens 11 in the main scanning direction corresponds to the field of view of each light-receiving lens 11 in the main scanning direction. It is preferable that the width W1 of each light-receiving lens 11 in the sub-scanning direction is set so that 0.001 < N.A. < 0.05 is satisfied. In this example, each light-receiving lens 11 has the same shape and is formed in a rectangular shape when viewed from the direction (Z direction) orthogonal to both the main scanning direction and the sub-scanning direction. However, each light-receiving lens 11 is not limited to a rectangle (a rectangular shape), and may be an oval or an ellipse, or may have other shapes.

[0031] Multiple light-receiving lenses 11 are arranged spaced apart from each other, with a width W2 or less in the main scanning direction of each light-receiving lens 11. That is, it is preferable that the multiple light-receiving lenses 11 are spaced apart from each other within a field of view dimension (within the field of view) in the main scanning direction of each light-receiving lens 11. As shown in the example in Figure 3, the fields of view of each light-receiving lens 11 may be superimposed in the sub-scanning direction. In this case, for the light-receiving elements in the overlapping portion of the fields of view of the multiple light-receiving lenses 11, the pixel output from the light-receiving element should be subtracted. For example, the image of one light-receiving lens 11 (the amount of light received that passed through one light-receiving lens 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. By using multiple light-receiving element arrays (light-receiving element array 120), the occurrence of pixel loss can be prevented more reliably than with a single line of light-receiving elements.

[0032] Figure 4 is a schematic diagram showing another example of a photodetector system in which multiple photodetector arrays 120 are arranged. In the example in Figure 4, there is no one-to-one correspondence between each photodetector lens 11 and each photodetector array 120; rather, multiple (two in this example) photodetector lenses 11 arranged in the main scanning direction correspond to one photodetector array 120.

[0033] Multiple light-receiving lenses 11 corresponding to one light-receiving element array 120 are adjacent to each other in the main scanning direction. However, the multiple light-receiving lenses 11 corresponding to one light-receiving element array 120 may be spaced apart from each other, in which case the spacing between them may be less than or equal to the width W2 of the light-receiving lenses 11 in the main scanning direction. In addition, light-shielding members may be provided between each light-receiving lens 11.

[0034] Figure 5 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 5, multiple (two in this example) light-receiving element arrays 120, each consisting of a long sensor of the same length (corresponding to the total length in the main scanning direction), are arranged in parallel in the sub-scanning direction. As shown in Figure 5, 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).

[0035] In all of Figures 3 to 5, the width W1 of the light-receiving lens 11 in the sub-scanning direction is smaller than the width W2 in the main scanning direction. As a result, the light-receiving lens 11 can be positioned closer to the sub-scanning direction, and the optical line sensor can be made more compact. As described above, short light-receiving element arrays 120 may be used in a staggered arrangement (see Figures 3 and 4), or two rows of light-receiving element arrays 120 may be used spaced apart (see Figure 5). However, the system is not limited to these arrangements, and even more light-receiving element arrays 120 may be spaced apart in the sub-scanning direction (Y direction).

[0036] 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 distributed refractive index lenses have prioritized miniaturization and cost reduction of 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 becoming smaller and smaller. When lengthening the focal length of the light-receiving lens, using conventional light-receiving lenses 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 proportionally 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.

[0037] 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 6 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.

[0038] 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.

[0039] 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 7A to 7C. Here, when three types of refractive index distribution lenses (SELFOC lens A, SELFOC lens B, and SELFOC lens C) are used as the light-receiving lens 11, Figure 7A shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens A, Figure 7B shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens B, and Figure 7C shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens C. In Figures 7A to 7C, 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.

[0040] Figures 6 and 7A 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 7A, 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.

[0041] On the other hand, as shown in Figures 6 and 7B, 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 7A. The light-receiving lens 11 shown in Figure 7A is a refractive index distribution type lens with smaller aberrations and a larger effective diameter than the light-receiving lens 11 shown in Figure 7B, indicating that the light-receiving lens 11 in Figure 7A should be selected. Furthermore, the light-receiving lens 11 in Figure 7A, with the same focal length, can achieve a numerical aperture (NA) at least three times larger than the light-receiving lens 11 in Figure 7B, 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 7A 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 7A can improve the scanning speed by nine times compared to the light-receiving lens 11 in Figure 7B.

[0042] According to Figure 7C, SELFOC lens C, like SELFOC lens A, exhibits minimal aberrations and allows for a larger effective aperture.

[0043] Next, the parameters of SELFOC lenses A to C shown in Figures 7A to 7C 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]

[0044] Furthermore, when four types of plastic rod lenses (plastic refractive index distribution type lenses) are used as the light-receiving lens 11, Figure 8A shows the relationship between the effective diameter and the circle of confusion diameter of rod lens A, Figure 8B shows the relationship between the effective diameter and the circle of confusion diameter of rod lens B, Figure 8C shows the relationship between the effective diameter and the circle of confusion diameter of rod lens C, and Figure 8D shows the relationship between the effective diameter and the circle of confusion diameter of rod lens D. In Figures 8A to 8D, 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 8A to 8D are shown in Table 2 below. It can be seen that the same trend as the refractive index distribution type lenses 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]

[0045] 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's Law is expanded into a polynomial. In other words, 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.

[0046] 4. Modified examples of light-receiving lenses The light-receiving lens 11 in the present invention is not limited to refractive index distribution lenses such as refractive index distribution lenses or plastic rod lenses, but can also be other lenses, such as achromatic (achromatic) or apochromatic lenses, which, considering cost, have the same aberrations due to nonlinear effects as the aforementioned refractive index distribution lenses, i.e., lenses with the same spherical aberration, coma aberration, and astigmatism. Alternatively, a telecentric refractive optical system can be used in place of refractive index distribution lenses such as refractive index distribution lenses or plastic rod lenses, with the same arrangement and dimensions (aperture), but with the same aberrations due to nonlinear effects and diffraction limits as the aforementioned refractive index distribution lenses. The same applies to the light-receiving lens 11 that forms an inverted image, as described later.

[0047] 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 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 determined relationship between 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.

[0048] 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.

[0049] Specifically, in an inverted refractive optical system, multiple photodetector arrays may be shorter than each of the two reading lines, with multiple photodetector arrays arranged on each reading 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 3, a detailed explanation will be omitted.

[0050] In this case, as shown in Figure 3, multiple photodetectors are arranged in two or more rows to form multiple photodetector arrays 120. Each of the multiple photodetector arrays 120 is spaced apart from the others in a direction perpendicular to the reading line L, with a width W2 or less in the main scanning direction of the photodetector lens 11. Multiple photodetectors 11 are arranged in a number corresponding to the multiple photodetector arrays 120, and the optical axis of the light that passes through each photodetector lens 11 and is guided to each photodetector array 120 passes through approximately the center of each photodetector array 120. However, the optical axis of the light that passes through each photodetector lens 11 and is guided to each photodetector array 120 may pass through a position parallel to the sub-scanning direction from approximately the center of each photodetector array 120.

[0051] 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.

[0052] Figure 9A 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 9A, 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.

[0053] 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 9B 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 LEDs or LDs, 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).

[0054] 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.

[0055] Figure 10A 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 arranged in two rows. Figure 10A shows the arrangement of the light source 103 relative to the light-receiving lenses 11 and the light-receiving element array 120, which are 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. Each light source 103 is arranged parallel to the reading line L. Furthermore, the optical axis of each light source 103 is positioned at an arbitrary 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 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). 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 working width (WD) of the light receiving lens 11, the distance between the light source 103 and the inspection surface was set to 70 mm. In this embodiment, an LD was used, but LEDs of various wavelengths may also be used.

[0056] The array pitch of the light sources 103 is matched to the distance between the lenses, and the light sources 103 are 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 prevents pixel loss on the inspection surface and reduces shading of the light-receiving lenses 11 and unevenness in the light intensity of the light sources 103. The lens pitch between the light-receiving lenses 11 in each row is set to 7 mm. In this case, the effective lens pitch is 3.5 mm.

[0057] Figure 10B 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 layout of Figure 10A, the light intensity distribution on the photodetector array 120 becomes flat, as schematically shown in Figure 10B, making it possible to effectively utilize the dynamic range of the photodetector.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 7. Parameters of the light-receiving lens Figure 10C shows graphs of the MTF of the light-receiving system for different lens diameters in this embodiment. As a comparative example, Figure 10D 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.

[0063] 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 10E. According to Figure 10E, even when √A = 0.1027, the MTF characteristics are satisfied in the range from Φ1.0 mm to Φ3.0 mm at 12 lines / mm equivalent to a resolution of 600 dpi.

[0064] 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.

[0065] 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 25mm ≤ f ≤ 250mm, and the aperture Φ of the multiple lenses is 2mm ≤ Φ ≤ 50mm.

[0066] 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 Figure 10A, with the magnification of the light-receiving lens 11 being changed. 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 in 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 in the 1x system. In this embodiment, a light-receiving element of 1 / 4 the size is used to double the depth of field.

[0067] The MTF characteristics of the reduction optical system in this embodiment when defocused are shown in the graph (solid line) of Figure 11. For comparison, the MTF characteristics of the 1:1 system when defocused are shown in the graph (dashed line) of Figure 11. 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.

[0068] In this embodiment, since the focal length is f=50mm and the lateral magnification ratio is 1 / 4, the lens diameter Φ can theoretically be used down to Φ=0.25mm. Since the same lens as in Figure 10A 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 case of Figure 10A, which is a 1:1 magnification system. 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.

[0069] 9. Telecentric Optics 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.

[0070] 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.

[0071] As shown in Figure 3 or Figure 4, if the photodetector array 120 is arranged in a staggered pattern in the sub-scanning direction, the memory capacity needs to be increased as the distance in the sub-scanning direction increases. However, increased memory capacity leads to increased costs. In this embodiment, by using a telecentric lens optical system, if the NA is set to about 0.03, a lens with a focal length of 50 mm will have a conical solid angle of light reception connecting Φ=3 mm to the object point on the main plane of the lens. Therefore, the shortest distance Ls of the staggered photodetector array 120 in the sub-scanning direction only needs to be Ls > 3 mm. Accordingly, by changing the circular outer periphery of a normal lens to a rectangular outer periphery using various processing or molding means, and by narrowing the spacing of the staggered arrangement of the photodetector array 120 as shown in Figure 3 or Figure 4, the solid angle of light reception can be satisfied, miniaturization is possible, and the memory capacity can be reduced. Furthermore, the NA of the photodetector lens 11 is preferably about 0.001 to 0.05 from the viewpoint of illumination light intensity. As explained above, the thickness of the light-receiving lens 11 in the sub-scanning direction is determined by the solid angle defined by the NA of the telecentric optical system, so it can be shortened in the sub-scanning direction, resulting in a more compact design.

[0072] 10. Variations of the light-receiving system Next, a modified example of the light-receiving system will be described using Figures 12A to 12G. In the above embodiment, a configuration in which multiple light-receiving lenses 11 are arranged in two rows in the sub-scanning direction was described, but Figures 12A to 12G describe a configuration in which multiple light-receiving lenses 11 are arranged in one row along the main scanning direction, specifically, a layout of one row of light-receiving lenses 11 and a staggered arrangement of light-receiving element arrays 120.

[0073] When two reading lines L are formed by arranging the photodetector array 120 in a staggered pattern, if the photodetector lenses 11 are also arranged in two staggered patterns similar to the photodetector array 120, it was necessary to ensure that the spacing of the photodetector array 120 in the sub-scanning direction was greater than the width of the photodetector lenses 11 in the sub-scanning direction in order to satisfy the required numerical aperture (NA) of the photodetector lens system. Therefore, as shown in Figures 12A to 12G, by setting the width of the rectangular lens of the photodetector lens 11 to satisfy the required NA of the photodetector system and reducing the number of rows from two to one, it becomes possible to further narrow the spacing of the photodetector array 120 in the sub-scanning direction. In other words, the effect of speed fluctuations in the sub-scanning direction can be reduced, and at the same time, the cost of the photodetector lenses 11 can be reduced. The following describes a method for arranging multiple photodetector lenses 11 in a single row.

[0074] In Figures 12A to 12G, the multiple light-receiving lenses 11 each have the same shape when viewed from a direction perpendicular to the main scanning direction. Specifically, the shape of each light-receiving lens 11 is the same when viewed from the Z direction, which is perpendicular to the main scanning direction (X direction) and the sub-scanning direction (Y direction). Note that "same shape" includes substantially identical shapes such as inverted shapes, and slight differences in shape are included in "same shape".

[0075] In Figure 12A, the shape of each light-receiving lens 11 as viewed in the Z direction is a parallelogram. That is, both end faces of each light-receiving lens 11 in the main scanning direction are inclined with respect to the sub-scanning direction. The inclination angles of both end faces of each light-receiving lens 11 in the main scanning direction are the same. When multiple light-receiving lenses 11 are arranged side by side in the main scanning direction as shown in Figure 12A, the end faces of adjacent light-receiving lenses 11 face each other, so that the ends of adjacent light-receiving lenses 11 are connected in the main scanning direction.

[0076] In Figure 12B, rectangular notches are formed on both end faces of each light-receiving lens 11 in the main scanning direction when viewed in the Z direction. When multiple light-receiving lenses 11 are arranged side by side in the main scanning direction as shown in Figure 12B, a portion of the adjacent light-receiving lens 11 is fitted into the notches formed on both end faces of each light-receiving lens 11, so that the ends of adjacent light-receiving lenses 11 in the main scanning direction are connected.

[0077] In Figure 12C, the shape of each light-receiving lens 11 as viewed in the Z direction is trapezoidal. That is, both end faces of each light-receiving lens 11 in the main scanning direction are inclined with respect to the sub-scanning direction. The shape of each light-receiving lens 11 as viewed in the Z direction is an inverted shape with respect to the main scanning direction compared to the shape of adjacent light-receiving lenses 11 as viewed in the Z direction. When multiple light-receiving lenses 11 are arranged side by side in the main scanning direction as shown in Figure 12C, the end faces of adjacent light-receiving lenses 11 face each other, so that the ends of adjacent light-receiving lenses 11 in the main scanning direction are connected. As a result, multiple light-receiving lenses 11 are arranged in a state where adjacent light-receiving lenses 11 are inverted and connected.

[0078] In Figure 12D, curved (semicircular or semielliptical) notches are formed on both end faces of each light-receiving lens 11 in the main scanning direction when viewed in the Z direction. When multiple light-receiving lenses 11 are arranged side by side in the main scanning direction as shown in Figure 12D, a portion of the adjacent light-receiving lens 11 is fitted into the notches formed on both end faces of each light-receiving lens 11, so that the ends of adjacent light-receiving lenses 11 are connected in the main scanning direction.

[0079] Next, we will describe the modified versions shown in Figures 12E to 12G. Figure 12E is a modified version of Figure 12C, which minimizes the occurrence of missing pixels in the aforementioned photodetector array 120. In Figure 12E, each photodetector array 120 is positioned on the longer side of the trapezoidal photodetector lens 11, rather than the center in the width direction. Furthermore, the length of each photodetector array 120 in the main scanning direction is approximately equal to the length of each trapezoidal photodetector lens 11 in the main scanning direction at the position where the photodetector array 120 is positioned. By doing this, the adjacent staggered photodetector arrays 120 shown by the dashed lines in Figure 12E overlap in the sub-scanning direction, and, as will be described later, this prevents the occurrence of missing parts in the output signal, as seen in the staggered photodetector array 120 shown in Figure 12C.

[0080] The above applies not only to trapezoidal light-receiving lenses 11, but also to any shape that can be connected when each light-receiving lens 11 is inverted in the sub-scanning direction to form a light-receiving lens array. Examples are shown in Figures 12F and 12G. Figure 12F shows a case where multiple light-receiving lenses 11 with rectangular cutouts are inverted and connected, and Figure 12G shows a case where multiple light-receiving lenses 11 with circular cutouts are inverted and connected. Thus, in Figures 12E to 12G, the multiple light-receiving lenses 11 are arranged in a state where adjacent light-receiving lenses 11 are inverted and connected. Generally, if the light-receiving lenses 11 are symmetrical in the sub-scanning direction, they can be inverted and connected. In Figures 12F and 12G, the dashed lines overlap, similar to the trapezoidal inverted connection in Figure 12E, and as will be described later, no signal loss occurs. Note that the light-receiving lens 11 in Figure 12G is equipped with an edge portion 112 to ensure rigidity and prevent cracking.

[0081] As shown in Figures 12A to 12G, in a cross-sectional view along the optical axis of the light-receiving lens 11, the lens ends are given a cross-sectional shape such as a parallelogram, trapezoid, rectangle, or curved shape (circle, ellipse) notch, and the width in the sub-scanning direction that satisfies the NA of the light-receiving lens system is set, and by connecting them in a row, a lens array extending in a straight line in the main scanning direction is formed. In addition, two rows of staggered light-receiving element arrays 120 are provided in the center of the sub-scanning direction of the lens array. Specifically, multiple light-receiving element arrays 120 are placed in the center of the main scanning direction of each of the multiple light-receiving lenses 11, and are arranged alternately in a staggered pattern along the main scanning direction. In this way, a single row of lens arrays can deliver light emitted from the object to be inspected to two rows of staggered light-receiving element arrays 120.

[0082] As shown in Figure 12A, a shielding portion 111 is provided between the ends of adjacent light-receiving lenses 11 in the main scanning direction. The shielding portion 111 is formed in the shape of a thin plate. The shielding portion 111 extends from between the ends of each light-receiving lens 11 toward the light-receiving element (light-receiving element array 120) and protrudes from the light-receiving lens 11 toward the object to be inspected. The shielding portion 111 also has a width of at least the width W1 in the sub-scanning direction of the light-receiving lens 11. In Figures 12B to 12G, the shielding portion 111 is omitted, but it may similarly be provided between the ends of each light-receiving lens 11. In the embodiments of Figures 12F and 12G, the shielding portion 111 is a thin crank-shaped and wave-shaped shielding plate, respectively. The main point is to prevent light from leaking into adjacent light-receiving systems at the connecting portion.

[0083] As shown in Figures 12B to 12D, multiple light sources 103 for illuminating the object to be inspected may be provided in a one-to-one correspondence with multiple photodetector arrays 120. Each of the multiple light sources 103 may have an elongated shape extending in a straight line along the main scanning direction. In this case, as shown in Figures 12B to 12D, the multiple light sources 103 may face each photodetector array 120 in the Z direction. This allows the multiple light sources 103 to be arranged in a staggered pattern, enabling efficient incidence of linear light segments onto each photodetector array 120.

[0084] Multiple light sources 103 have multiple line intensity distributions of illumination light in the sub-scanning direction, corresponding to multiple photodetector arrays 120. In Figures 12A, 12E to 12G, the light sources 103 are omitted, but similarly, multiple light sources 103 may be provided so that they correspond one-to-one with multiple photodetector arrays 120. However, even without arranging the multiple light sources 103 in a staggered pattern, line illumination with an intensity distribution that includes two intensity peaks in the sub-scanning direction may be used so that each photodetector array 120 of each reading line L has a peak in light intensity. Also, because the spacing of the staggered photodetector arrays 120 in the sub-scanning direction is narrow, line illumination with one peak may also be used.

[0085] Figure 13 shows the light intensity distribution on the light-receiving surface of the photodetector array 120 when the light intensity distribution of the light source 103 is flat, with the lens ends being parallelogram-shaped. Figure 13 shows an example of the light intensity distribution on the light-receiving surface of each photodetector array 120 when the configuration shown in Figure 12A is adopted. For the sake of explanation, the lens array consisting of multiple light-receiving lenses 11 is shown as a lens array consisting of three light-receiving lenses 11.

[0086] The left-hand diagram of Figure 13 shows the light intensity on each photodetector array 120 of the entire lens array, while the two diagrams on the right show magnified views. Figure 14 also shows details of the light intensity distribution near the connection between adjacent photodetector lenses 11. In this embodiment, in two adjacent photodetector arrays 120 arranged in a staggered pattern, a pixel with a signal loss in one photodetector array 120 is interpolated with a pixel in the other photodetector array 120. In Figure 14, the method of interpolating the signal of a pixel with a signal loss is shown by arrow marks.

[0087] In Figure 14, the portion 121 enclosed by the dashed line is a light-receiving element located at the connection point between adjacent light-receiving lenses 11. When light does not reach this light-receiving element, a signal loss occurs. Therefore, in this embodiment, in the staggered array of adjacent light-receiving elements 120, the signal of the signal loss is compensated for by the output signal of the light-receiving element in portion 121 (the portion 122 enclosed by the solid line) that is opposite to the light-receiving element in the sub-scanning direction. In this way, a pixel interpolation section is formed along the sub-scanning direction at the connection point between adjacent light-receiving lenses 11 (see Figure 13). The signal loss can be corrected in advance using a reference medium for inspection. A white chart or grid pattern for shading correction can be used as the reference medium.

[0088] In Figure 13, the width of the light-receiving lens 11 in the sub-scanning direction is 5 mm. Therefore, if the light-receiving lenses 11 are arranged in a staggered pattern in two rows, the minimum spacing between the staggered light-receiving element array 120 must be 5 mm or more. However, as described above, using a single-row lens array reduces the spacing to approximately half (slightly less than 3.0 mm). Furthermore, by applying shading correction while considering the dynamic range of the light-receiving element array 120, it is possible to further narrow the spacing. In other words, as the spacing of the staggered light-receiving element array 120 in the sub-scanning direction narrows, it becomes possible to halve the number of light-receiving lenses 11. Therefore, it becomes less susceptible to fluctuations in the transport speed in the sub-scanning direction, and at the same time, cost reduction is achieved.

[0089] In Figure 13, a shielding plate with a thickness of t=0.2 mm was placed in the shielding section 111. A thickness of t=0.2 mm is sufficient in terms of strength. Furthermore, the lens system is a double-sided telecentric system. Of course, it goes without saying that an object-side telecentric system would also be acceptable.

[0090] In terms of specific image processing methods or image processing systems, for two photodetectors located at the same position in the main scanning direction but separated in the sub-scanning direction, if the output signal from one photodetector (part 121 enclosed by a dashed line) is lower than the output signal from the other photodetector (part 122 enclosed by a solid line), and the output signal from one photodetector falls below a threshold, the output signal from the other photodetector is used for interpolation. Furthermore, the interpolated output signal is combined with the output signals from photodetectors at other positions in the main scanning direction relative to the first photodetector to obtain a single line of output signals corresponding to the reading line L.

[0091] In Figure 14, the photodetectors in the area 123 enclosed by the dashed line face each other in the sub-scanning direction, but they overlap each other due to being offset from the connecting portion between adjacent photodetectors 11. Since no loss of output signal occurs from the photodetectors in such overlapping areas, interpolation is not necessary.

[0092] In the example shown in Figure 12E, the light intensity of the light-receiving region is shown, and the reason why no signal loss occurs is schematically illustrated in Figure 15. Figure 15, like Figure 14, shows the light intensity distribution at the edges of the staggered arrangement of photodetector arrays 120. In Figure 15, the photodetectors in the portion 124 enclosed by the dashed line face each other in the sub-scanning direction, but they overlap each other because they are offset from the connecting portions of adjacent photodetectors 11. As shown in Figure 15, by arranging the photodetector array 120 on the longer side in the width direction of the trapezoidal photodetector lens 11, it becomes possible to obtain the signal necessary for one row of reading lines L of the staggered arrangement of photodetector arrays 120, excluding the signal loss portion in the light-receiving section.

[0093] As a specific image processing method or image processing system, for the output signals from two photodetectors (areas enclosed by dashed lines 124) that are spaced apart in the sub-scanning direction at the same position in the main scanning direction, one of the output signals from one photodetector overlaps with the output signal from the other photodetector. This is then corrected using a reference medium, and the two signals are combined to form a single output signal corresponding to the reading line L.

[0094] 11. Setting the optical axis of the light-receiving lens Figure 16 illustrates the factors that cause the optical axis of one of the two photodetector arrays 120 arranged in two reading lines L to be misaligned, resulting in a deterioration of light reception efficiency. When illumination light is incident on a cylindrical inspection surface (cylindrical surface), the angle of incidence on the cylindrical surface changes depending on the position of the point of incidence, and the angle of reflection on the cylindrical surface also changes. An example of an inspection surface being composed of a cylindrical surface is when an object to be inspected is wrapped around a cylindrical roller for inspection.

[0095] One example of a configuration in which the photodetector array 120 is arranged on two rows of reading lines L is one in which the photodetector array 120 on one reading line L and the photodetector array 120 on the other reading line L are arranged alternately in a staggered pattern along the main scanning direction. However, as shown in the example in Figure 5, it is also possible to have a configuration in which two photodetector arrays 120 are arranged parallel to each other along the two rows of reading lines L in the sub-scanning direction.

[0096] When the surface of the object to be inspected (inspection surface) is cylindrical, the reflection angle changes depending on the position. Therefore, if the optical axis of the light receiving system is aligned with one of the two light receiving element arrays 120 arranged in two rows L, it will not coincide with the optical axis of the other light receiving element array 120, as shown in Figure 16, resulting in a decrease in the amount of light received. To address this, the optical axes of the multiple light receiving elements (light receiving element arrays 120) are arranged non-parallel to the optical axes of the light incident on the multiple light receiving lenses 11, so that the light transmitted through the multiple light receiving lenses 11 is incident equally on the two light receiving element arrays 120 arranged in two rows L.

[0097] Specifically, the optical axis of the specularly reflected light is set to the center of the sub-scanning direction of the photodetector array 120 arranged in two rows of reading lines L, the optical axis of the specularly reflected light is included within the solid angle (NA) of light reception as seen from each photodetector array 120, and the optical axes of each photodetector array 120 intersect near the inspection surface. The vicinity of the inspection surface is not limited to the inspection surface itself, but may be a position closer to the inspection surface between the inspection surface and the photodetector lens 11, or a position close to the inspection surface on the opposite side of the inspection surface from the photodetector lens 11. Figure 17 shows the optical axis of the photodetector lens 11 aligned between the photodetector arrays 120 arranged in two rows of reading lines L, and the optical axes of each photodetector array 120 intersecting near the inspection surface.

[0098] In the example shown in Figure 17, the optical axes of each photodetector array 120 are tilted by a small angle in the sub-scanning direction and intersect on the inspection surface. As a result, the lines connecting each pixel of the multiple photodetectors to each corresponding pixel on the object under inspection are tilted symmetrically across the optical axis of the telecentric optical system (the optical axis of light incident on the photodetector lens 11). Each pixel of the multiple photodetectors may be composed of one photodetector or two or more photodetectors. Each pixel on the object under inspection is each pixel on the inspection surface, and is a region on the inspection surface projected onto each pixel of the multiple photodetectors that correspond one-to-one.

[0099] In other words, the back projection image of the reading lines formed on the inspection surface by the photodetector array 120, which has two rows of reading lines, forms a single row. To put it another way, if an isosceles triangle is formed by using a line segment parallel to the sub-scanning direction, formed by connecting the two rows of photodetector arrays 120, as the base, and connecting one point on the reading line on the inspection surface with the endpoint of the line segment parallel to the optical axis, an isosceles triangle is formed. In this case, the angle of inclination of the straight line connecting each pixel of the multiple photodetectors (photodetector array 120) to each pixel on the inspection object side that corresponds one-to-one with it, with respect to the optical axis of the telecentric optical system, is minute, so a deep depth of field can be secured. Furthermore, the spacing of the photodetector arrays 120 arranged in the two rows of reading lines L in the sub-scanning direction may be adjusted according to the inclination angle and the lateral magnification of the photodetector optical system.

[0100] For example, in the case of a 1:1 magnification system, if the distance from the inspection surface to the light-receiving lens 11 and from the light-receiving lens 11 to the light-receiving element array 120 are both 50 mm, and the spacing of the light-receiving element arrays 120 arranged in two rows L in the sub-scanning direction is 2 mm, then the tilt angle θt of the optical axis of each light-receiving element array 120 with respect to the optical axis of the specularly reflected light is θt = 1 mm / 100 mm ≈ 10 mrad, and the total angle is θt = 20 mrad. On the other hand, in the case of a telecentric optical system, if the aperture diameter Φtelea = 2 mm, the solid angle θr is approximately 1 mm / 50 mm = 10 mrad, and the overlap angle θo of each light-receiving element array 120 can be secured with θo = 10 mrad on either side of the optical axis of the specularly reflected light. Therefore, specularly reflected light can be received without bias towards one of the light-receiving element arrays 120. Figure 18 shows how the extended solid angles overlap.

[0101] The light-receiving lens 11 in Figure 18 constitutes a telecentric optical system and is a rectangular lens array with a notch, where the width in the sub-scanning direction is smaller than the width in the main scanning direction. Compared to other rectangular lenses, such a light-receiving lens 11 is advantageous because even if the distance of the light-receiving element array 120 in the sub-scanning direction relative to the optical axis of specular reflection changes when the spacing of the light-receiving element array 120 arranged in two rows L in the sub-scanning direction is changed, or when the focal length of the light-receiving lens 11 is changed, the length of the light-receiving lens 11 in the main scanning direction does not change. Therefore, the same light-receiving lens 11 can be used even if the inclination angle of the light-receiving lens 11 relative to the optical axis of specular reflection is changed so that each light-receiving element array 120 can receive light well.

[0102] As shown by solid and dashed lines in Figure 18, the light-receiving lens 11 corresponding to one of the two light-receiving element arrays 120 arranged in the two reading lines L may be tilted at different angles. That is, the optical axes of the multiple light-receiving lenses 11 may be arranged non-parallel to the optical axes of the light incident on the multiple light-receiving lenses 11 so that the light transmitted through each light-receiving lens 11 is incident on the multiple light-receiving element arrays 120 arranged in the two reading lines L.

[0103] Figures 19A and 19B illustrate that the same light-receiving lens 11 can be used even if the position of the light beam incident on the light-receiving lens 11 is separated from the optical axis of the light-receiving lens 11 relative to the optical axis of specular reflection. Figure 19A shows the case where the spacing of the light-receiving element array 120 arranged in two rows of reading lines L is narrow in the sub-scanning direction. On the other hand, Figure 19B shows the case where the spacing of the light-receiving element array 120 arranged in two rows of reading lines L is wide in the sub-scanning direction.

[0104] As shown by the dashed lines in Figures 19A and 19B, in the portion where the photodetector array 120 overlaps in the sub-scanning direction, even if the spacing of the photodetector array 120 arranged in the two rows of reading lines L is changed, it is not necessary to change the length of the photodetector lens 11 in the main scanning direction in the overlapping portion. Therefore, even if the spacing of the photodetector array 120 arranged in the two rows of reading lines L is changed, the same photodetector lens 11 can be used.

[0105] Figures 19C and 19D correspond to the configurations shown in Figures 19A and 19B, respectively, and show a configuration with an aperture 130. The aperture 130 constitutes a telecentric optical system and is positioned between each photodetector array 120 and each photodetector lens 11, corresponding to each photodetector array 120. The shape of the aperture 130 is not particularly limited, but in this example it is circular.

[0106] Each aperture 130 is positioned at a distance from a straight line extending perpendicular to the main scanning direction and the sub-scanning direction from the starting point of specularly reflected light on the object under inspection (inspection surface). That is, the optical axis of the light incident on each light-receiving lens 11 (light that passes through each light-receiving lens 11 and is guided to each light-receiving element array 120) extends perpendicular to the main scanning direction and the sub-scanning direction, and each aperture 130 is positioned at a distance from this optical axis.

[0107] More specifically, each aperture 130 is positioned at a location that includes the optical axis of the specularly reflected light and is spaced apart from a plane parallel to the main scanning direction of each photodetector array 120. Each aperture 130 is positioned on a straight line connecting the point where the optical axis of the specularly reflected light intersects with the optical axis of each photodetector array 120 and each photodetector array 120, in a position that satisfies the requirements for a telecentric optical system. In this example, each aperture 130 is positioned at a location spaced apart in the sub-scanning direction from the center of each photodetector array 120 in the main scanning direction.

[0108] Figure 19E shows the case where a light-receiving lens 11 with a different shape than those shown in Figures 19A to 19D is used. Figure 19E shows the case where a trapezoidal light-receiving lens 11 is used, but the shape of the light-receiving lens 11 is arbitrary, and other shapes such as a parallelogram may be used.

[0109] In the example shown in Figure 19E, as indicated by the dashed line, even if the spacing between the photodetector arrays 120 arranged in the two reading lines L is changed in the sub-scanning direction, it is not necessary to change the length of the photodetector lens 11 in the main scanning direction in the overlapping portion. Therefore, even if the spacing between the photodetector arrays 120 arranged in the two reading lines L is changed in the sub-scanning direction, the same photodetector lens 11 can be used.

[0110] Furthermore, similar to the configurations in Figures 19C and 19D, apertures 130 constituting a telecentric optical system are positioned between each photodetector array 120 and each photodetector lens 11, corresponding to each photodetector array 120. As shown by the arrows in Figure 19E, the position of the apertures 130 may be finely adjusted in the sub-scanning direction. In this case, a mechanism for moving each aperture 130 manually or electrically may be provided as a position adjustment mechanism for finely adjusting the position of each aperture 130. Note that the position adjustment mechanism for each aperture 130 is not limited to the configuration in Figure 19E, but can be used in configurations using photodetector lenses 11 of any shape.

[0111] 12. Installation of optical branching element Next, as a method for splitting light into two, we will describe a configuration in which a common light transmitted through the light-receiving lens 11 is split into two by an optical splitting element, and each can be received by a light-receiving element array 120 arranged in two rows of reading lines L. Figure 20A is a schematic diagram of the case in which light scattered from a point on the same plane in the sub-scanning direction of the object to be inspected is received. In this example, we will describe a configuration in which the optical splitting element 140 is equipped with an aperture 130. Also, although Figure 20A shows a bilateral telecentric optical system in which light-receiving lenses 11 are provided on both sides in the optical axis direction with the aperture 130 in between, it is not limited to this and may also be a unilateral telecentric optical system.

[0112] The photodetector arrays 120 arranged in two reading lines L have separate optical axes and are positioned offset from each other in the sub-scanning direction. Therefore, if the aperture 130 of the telecentric optical system is aligned with the optical axis of one photodetector array 120, the light scattered from one point on the object being inspected will not enter the other photodetector array 120, making it impossible to evenly incident light on each photodetector array 120. To solve this, the two apertures 130 are positioned symmetrically in the sub-scanning direction with respect to the optical axis containing the origin of the scattered light on the object being inspected (inspection surface), so that scattered light from the object being inspected is received evenly by each photodetector array 120 regardless of the divergence angle of the scattered light.

[0113] In other words, as shown in the front view of the optical branching element 140 shown alongside the side view of the optical branching element 140 in Figure 20A, the optical branching element 140 has two apertures 130 arranged side by side in the sub-scanning direction. By setting the optical axis of the light that has passed through the light-receiving lens 11 in the center between these apertures 130, the light can be passed through each aperture 130 equally, and the light can be received equally by each light-receiving element array 120 corresponding to each aperture. Thus, with the optical branching element 140 shown in Figure 20A, the light that has passed through the multiple light-receiving lenses 11 can be branched non-parallel to the optical axis of the telecentric optical system and guided to the multiple light-receiving element arrays 120 so that the light is incident equally on the multiple light-receiving element arrays 120 arranged in two rows of reading lines L.

[0114] Furthermore, in the example shown in Figure 20A, a straight line connecting each pixel of the multiple photodetectors to each corresponding pixel on the object being inspected passes through the center of the aperture 130. The position of each aperture 130 of the optical branching element 140 may be adjustable in the sub-scanning direction. In this case, a position adjustment mechanism for adjusting the position of each aperture 130 may be provided, which moves each aperture 130 manually or electrically.

[0115] As a modified example, as shown in Figure 20B, an aperture 130 having an elongated shape in the sub-scanning direction with respect to the optical axis containing the origin of scattered light on the object to be inspected (inspection surface) may be arranged. Examples of the elongated aperture 130 include oval, elliptical, or rectangular shapes. In this case, as shown in Figure 20B, scattered light on the optical axis containing the origin of scattered light does not enter the photodetector array 120.

[0116] In other words, in the example shown in Figure 20B, the aperture 130 is formed in an oval, elliptical, or rectangular shape extending in the sub-scanning direction, on a straight line extending from the starting point of scattered light on the object to be inspected (inspection surface) in a direction perpendicular to the main scanning direction and the sub-scanning direction. By setting the optical axis of the light transmitted through the light-receiving lens 11 to the center of the sub-scanning direction in this aperture 130, the light can be received uniformly by each light-receiving element array 120. Thus, with the optical branching element 140 shown in Figure 20B, the light transmitted through the multiple light-receiving lenses 11 can be branched non-parallel to the optical axis of the telecentric optical system and guided to the multiple light-receiving element arrays 120 so that the light is incident uniformly on the multiple light-receiving element arrays 120 arranged in two rows of reading lines L.

[0117] Furthermore, in the example shown in Figure 20B, the optical axis of the telecentric optical system passes through the center of the aperture 130, and a straight line that is symmetrical with respect to the optical axis (a straight line connecting each pixel of the multiple photodetectors to each pixel on the object being inspected that corresponds one-to-one) also passes through the aperture 130. The longitudinal length of the aperture 130 of the optical branching element 140 may be adjustable. In this case, a length adjustment mechanism for adjusting the length of the aperture 130 may be provided, which can be manually or electrically modified. Additionally, the position of the aperture 130 of the optical branching element 140 may be adjustable.

[0118] As another variation, Figure 21A shows a configuration in which an angle adjustment element 150 is added to the optical system of Figure 20A. In this example, the angle adjustment element 150 is positioned to adjust the angle of the optical axis so that scattered light is incident on each photodetector array 120 at a position that satisfies the scattering angle of the scattered light, rather than receiving light from the optical axis that includes the origin of the scattered light.

[0119] Each angle adjustment element 150, associated with each light-receiving element array 120, changes the angle of the light that has passed through each aperture 130 by reflecting (not shown) or refracting it, and directs it into each light-receiving element array 120. In the case of Figure 21A, each angle adjustment element 150, made of a parallel planar substrate, is placed on the optical axis of the light that has passed through each aperture 130, and each angle adjustment element 150 is rotated with respect to the optical axis so that the light is incident into each light-receiving element array 120. Instead of parallel planar substrates, other optical elements such as wedge prisms may be used as angle adjustment elements 150.

[0120] Figure 21B shows a configuration in which each angle adjustment element 150 is placed on the inspection object side of each aperture 130, so that the optical axis from each aperture 130 to each photodetector array 120 is parallel to the optical axis of the original telecentric optical system. As a result, the spacing of each photodetector array 120 in the sub-scanning direction remains the same, and reflected light parallel to the optical axis near the optical axis on the inspection surface of the telecentric optical system can be received almost uniformly by each photodetector array 120. Furthermore, by fine-tuning each angle adjustment element 150, reflected light with a narrow intersection angle shown by the dotted line can also be received uniformly by each photodetector array 120.

[0121] Each angle adjustment element 150 consists of a parallel-plane substrate or a transparent block such as a wedge prism, and is composed of parallel planes with the incident and exit surfaces parallel to each other. By rotating each angle adjustment element 150, the light beam can be translated in the sub-scanning direction. As for each light-receiving lens 11 corresponding to each light-receiving element array 120, various shapes of light-receiving lenses 11 can be used, such as notched, trapezoidal, and parallelogram shapes in a cross-sectional view in the main scanning direction, as illustrated in Figures 19A to 19E. This type of light-receiving lens 11 has a long portion and a short portion in the main scanning direction, and Figure 21B shows the long portion of each light-receiving lens 11 in the main scanning direction.

[0122] Thus, the optical branching element 140 shown in Figure 21B allows light that has passed through multiple light-receiving lenses 11 to be branched parallel to the optical axis of the telecentric optical system and guided to multiple light-receiving element arrays 120 arranged in two rows of reading lines L, so that the light is incident on each array equally. Similarly, examples of optical branching elements 140 that branch light parallel to the optical axis of the telecentric optical system are shown in Figures 21C and 21D.

[0123] Figure 21C shows a method of splitting specularly reflected light into two using a prism 145 and a half mirror 146. The prism 145 and the half mirror 146 constitute an optical splitting element 140. In this example of Figure 21C, as in Figure 21B, various shapes of light-receiving lenses 11 such as notched, trapezoidal, and parallelogram shapes can be used in a cross-sectional view in the main scanning direction, and Figure 21C shows the longer portion of each light-receiving lens 11 in the main scanning direction.

[0124] The prism 145 is composed of a long prism that is longer in the main scanning direction. The prism 145 has a pair of parallel inclined surfaces that are tilted at 45° with respect to the incident specularly reflected light, and a half mirror 146 is provided on one of the inclined surfaces. As a result, light incident on the prism 145 from an incident surface perpendicular to the specularly reflected light partially passes through the half mirror 146 on one of the inclined surfaces, and the remaining light is reflected by the half mirror 146 and reflected again on the other inclined surface.

[0125] Light passing through the half-mirror 146 passes through one of the light-receiving lenses 11, then through the aperture 130, and enters the light-receiving element array 120 corresponding to that light-receiving lens 11. Light reflected by the half-mirror 146 and then reflected again by the other inclined surface passes through the other light-receiving lens 11, then through the aperture 130, and enters the light-receiving element array 120 corresponding to that light-receiving lens 11. The optical axes of the light incident on each light-receiving element array 120 are parallel to each other.

[0126] In the example shown in Figure 21C, in the telecentric optical system, the optical branching element 140 is positioned on the side of the object to be inspected in the optical axis direction relative to the light-receiving lens 11, and is also close to the light-receiving lens 11. The optical branching element 140 may be in contact with the light-receiving lens 11, or it may be separated by a small gap. When the half-mirror 146 is used in this way, the amount of light is halved, but the specularly reflected light can be reliably received by each light-receiving element array 120.

[0127] To further explain the configuration of Figure 21C, Figure 21C shows a system in which light is split by an optical branching element 140 from the first optical axis connecting one photodetector array 120 and the reading line on the inspection surface, and aligned with the second optical axis of the other photodetector array 120. The optical branching element 140 is positioned on the object to be inspected side in front of the photodetector lens 11 and has a parallelogram cross-section with a hypotenuse of 45° in a cross-sectional view perpendicular to the main scanning direction. The optical branching element 140 is long in the main scanning direction and has approximately the same length as the photodetector lens array. In addition to a parallelogram, the hypotenuses of right-angle prisms may be arranged parallel to each other and spaced apart. Half mirrors 146 are deposited on the hypotenuses of the optical branching element 140 to evenly split the light into two. As for the type of half mirror 146, metals such as aluminum or silver, or dielectric multilayer films can be used. Note that Figure 21C represents the object-side telecentric optical system, and an aperture 130 is positioned at the rear focal position of the photodetector lens 11.

[0128] In the example shown in Figure 21C, the same location on the inspection surface can be viewed at the same time. As a result, when each light-receiving element array 120 receives specularly reflected light, a common reading line can be used even if each light-receiving element array 120 is arranged in a staggered pattern. Therefore, each staggered light-receiving element array 120 can receive reflected light evenly.

[0129] Figure 21D shows the optical branching element 140 from Figure 21C positioned behind the light-receiving lens 11 (on the light-receiving element array 120 side). In this example, a rod lens (refractive index distributed lens) is used as the light-receiving lens 11. The rod lenses used as the light-receiving lens 11 are arranged in a line in the main scanning direction to form a multi-lens array. The prism 145 and half-mirror 146 that constitute the optical branching element 140 have the same configuration as in Figure 21C, so a detailed explanation is omitted.

[0130] Light entering the light-receiving lens 11 from the inspection surface passes through the light-receiving lens 11 and enters the prism 145. The light entering the prism 145 partially passes through the half mirror 146 provided on one of the inclined surfaces, and the remaining light is reflected by the half mirror 146 and reflected again on the other inclined surface. The light that has passed through the half mirror 146 enters one of the light-receiving element arrays 120. The light that has been reflected by the half mirror 146 and reflected again on the other inclined surface enters the other light-receiving element array 120. The optical axes of the light entering each light-receiving element array 120 are parallel to each other.

[0131] The optical branching element 140 may be in contact with the light-receiving lens 11 or separated by a small gap, but it is easier to secure a field of view if it is positioned in contact with the light-receiving lens 11. Also, if the optical branching element 140 is positioned behind the light-receiving lens 11 as shown in Figure 21D, it is easier to secure the working distance WD.

[0132] 13. Other installation examples of prisms Next, Figure 22A shows another configuration using a prism as the optical branching element 140. In the example in Figure 22A, the wedge prism 141 constituting the optical branching element 140 is positioned close to the object to be inspected in the optical axis direction relative to the light receiving lens 11. The wedge prism 141 transmits light incident from the incident surface 142 and emits it from the exit surface 143. The incident surface 142 is inclined with respect to the exit surface 143, and the optical axis of the light incident from the incident surface 142 intersects with the optical axis of the light emitted from the exit surface 143.

[0133] Specifically, the wedge prism 141 is placed only on one side of the sub-scanning direction relative to the optical axis of the specularly reflected light, so that on that side of the sub-scanning direction, the light transmitted through the wedge prism 141 is incident on the light-receiving lens 11. In this case, since the wedge prism 141 is not placed on the other side of the sub-scanning direction, light is directly incident on the light-receiving lens 11 on that side. The incident surface 142 of the wedge prism 141 is inclined so that it approaches the light-receiving lens 11 as it moves away from the optical axis of the specularly reflected light. On the other hand, the exit surface 143 of the wedge prism 141 is parallel to the incident surface of the light-receiving lens 11.

[0134] In this case, only one beam of light on one side of the sub-scanning direction can be tilted by the wedge prism 141 and branched to one of the photodetector arrays 120. By arranging the wedge prism 141, it is relatively easy to partially tilt one beam of light (specular reflected light) and partially branch it into two beams of light. As a result, the beam of light from the object being inspected is partially divided into two beams and imaged at each photodetector array 120 at the focal position of the photodetector lens 11. At that time, the imaging position of each branched beam of light must be precisely at the position of each photodetector array 120.

[0135] The relationship between the apex angle θw and the deflection angle δc of the wedge prism 141 is given by δc = θw·(n-1), where n is the refractive index of the wedge prism 141. Therefore, for example, if the distance between the emission surface of the light-receiving lens 11 and each light-receiving element array 120 is 50 mm, and the spacing between each light-receiving element array 120 in the sub-scanning direction is 2 mm, then the distance of each light-receiving element array 120 with respect to the optical axis of the specularly reflected light becomes 1 mm, and thus the angle between the light beam and the optical axis of the light-receiving lens 11, i.e., the intersection angle θc (=δc), becomes θc ≈ 20 mrad ≈ 1.15°. Thus, the apex angle θw of the wedge prism 141 is θw ≈ 2.3°.

[0136] Figure 22B shows yet another configuration in which a prism is used as the optical branching element 140. In the example of Figure 22B, wedge prisms 141 constituting the optical branching element 140 are arranged in correspondence with each light-receiving element array 120. One wedge prism 141 is positioned on one side in the sub-scanning direction, and light that passes through this wedge prism 141 passes through the light-receiving lens 11 and is incident on one of the light-receiving element arrays 120. The other wedge prism 141 is positioned on the other side in the sub-scanning direction, and light that passes through this wedge prism 141 passes through the light-receiving lens 11 and is incident on the other light-receiving element array 120.

[0137] The incident surface 142 of one wedge prism 141 is tilted so that it moves away from the light-receiving lens 11 as it moves away from the optical axis of the specularly reflected light. Similarly, the incident surface 142 of the other wedge prism 141 is also tilted so that it moves away from the light-receiving lens 11 as it moves away from the optical axis of the specularly reflected light.

[0138] In the examples shown in Figures 22A and 22B, a configuration was described in which the wedge prism 141 is positioned close to the object to be inspected in the optical axis direction relative to the light-receiving lens 11. However, the configuration is not limited to this, and the wedge prism 141 may be positioned close to the light-receiving element array 120 in the optical axis direction relative to the light-receiving lens 11, or it may be positioned at a distance from the light-receiving lens 11.

[0139] Figures 23A to 23C show the case where a prism is used as the optical branching element 140 and a multi-lens system is used as the light-receiving lens 11. The light-receiving lens 11 is composed of a multi-lens array 160 made up of multiple refractive index distribution lenses stacked together. In other words, unlike the telecentric optical system described above, a refractive index distribution lens (rod lens) is used to split one specularly reflected light into two, thereby evenly distributing the amount of light received by each light-receiving element array 120.

[0140] Figure 23A shows the light-receiving optical system as viewed along the optical axis of specularly reflected light. Figure 23B shows the light-receiving lens 11 and the optical branching element 140 as viewed along the sub-scanning direction. Figure 23C shows the light-receiving optical system as viewed along the main scanning direction. In this example, the wedge prism 141 constituting the optical branching element 140 is positioned close to the object to be inspected in the optical axis direction relative to the multi-lens array 160. The wedge prism 141 transmits light incident from the incident surface 142 and emits it from the exit surface 143. The incident surface 142 is inclined with respect to the exit surface 143, and the optical axis of the light incident from the incident surface 142 intersects with the optical axis of the light emitted from the exit surface 143.

[0141] The wedge prisms 141 constituting the optical branching element 140 are arranged in correspondence with each photodetector array 120. The width of each wedge prism 141 in the main scanning direction is approximately the same as the width of the corresponding photodetector array 120. In addition, the width of each wedge prism 141 in the sub-scanning direction is approximately the same as the width of the multi-lens array 160.

[0142] As shown in Figure 23C, the wedge prism 141 corresponding to the photodetector array 120 on one reading line L and the wedge prism 141 corresponding to the photodetector array 120 on the other reading line L have different inclination directions of the incident surface 142. Specifically, the incident surface 142 of the wedge prism 141 corresponding to the photodetector array 120 on one reading line L and the wedge prism 141 corresponding to the photodetector array 120 on the other reading line L are arranged symmetrically with respect to the optical axis of the specularly reflected light incident on each incident surface 142.

[0143] As a result, light that passes through the wedge prism 141 corresponding to the light-receiving element array 120 provided on one reading line L passes through the light-receiving lens 11 and enters the light-receiving element array 120 provided on one reading line L, and light that passes through the wedge prism 141 corresponding to the light-receiving element array 120 provided on the other reading line L passes through the light-receiving lens 11 and enters the light-receiving element array 120 provided on the other reading line L.

[0144] In the examples shown in Figures 23A to 23C, a configuration was described in which the wedge prism 141 is positioned close to the object to be inspected in the optical axis direction relative to the multi-lens array 160. However, the configuration is not limited to this, and the wedge prism 141 may be positioned close to the photodetector array 120 in the optical axis direction relative to the multi-lens array 160, or it may be positioned at a distance from the multi-lens array 160.

[0145] It is preferable that the seams 144 between adjacent wedge prisms 141 be located in the overlapping portion (dashed line in the figure) between the corresponding photodetector arrays 120. When the overlapping portion of the photodetector array 120 is aligned with the seams 144 of the wedge prisms 141 in this way, specularly reflected light incident on the seam 144 cannot pass through the photodetector lens 11 directly in front of it. However, the effect of erect, 1:1 imaging by the photodetector lenses 11 located in the periphery can compensate to some extent for the light lost at the seam 144, and therefore no pixels with no output occur. Furthermore, if the output is small for pixels other than those at the seam 144, the pixel outputs of the overlapping portion may be added together.

[0146] Furthermore, the optical branching element 140 is not limited to the wedge prism 141; if there is sufficient light intensity, it may be composed of other prisms such as Fresnel biprisms, or of optical elements other than prisms. Also, only the wedge prism 141 corresponding to the light-receiving element array 120 provided on one reading line L may be provided, and the wedge prism 141 corresponding to the light-receiving element array 120 provided on the other reading line L may be omitted. [Explanation of Symbols]

[0147] 10 Light source section 11. Light-receiving lens 12 Light receiving section 20 focal plane 103 Light source 104 Focusing lens 105 Cylindrical Lens 110 Lens Holder 111 Shielding part 120 photodetector array 130 Aperture 140 Optical Splitter 150 Angle adjustment element 160 Multi-lens Array

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, Arranged in a line along the main scanning direction, the light source illuminates the object being inspected, Multiple light-receiving lenses are arranged in a line along the main scanning direction and transmit light from the object to be inspected illuminated by the light source, It comprises a plurality of light-receiving elements arranged in a line along the main scanning direction, which receive light that has passed through the plurality of light-receiving lenses, The light-receiving lens constitutes a telecentric optical system, and its width in the sub-scanning direction is smaller than its width in the main scanning direction. The aforementioned plurality of light-receiving elements constitute a plurality of light-receiving element arrays arranged in two rows of the reading line, An optical line sensor characterized in that the straight lines connecting each pixel of the plurality of light-receiving elements to each pixel on the object to be inspected that corresponds one-to-one with each pixel of the plurality of light-receiving elements, arranged in two rows of the reading line, are inclined symmetrically across the optical axis of the telecentric optical system, such that light transmitted through the plurality of light-receiving lenses is evenly incident on the plurality of light-receiving element arrays arranged in two rows of the reading line.

2. 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, Arranged in a line along the main scanning direction, the light source illuminates the object being inspected, Multiple light-receiving lenses are arranged in a line along the main scanning direction and transmit light from the object to be inspected illuminated by the light source, It comprises a plurality of light-receiving elements arranged in a line along the main scanning direction, which receive light that has passed through the plurality of light-receiving lenses, The light-receiving lens constitutes a telecentric optical system, and its width in the sub-scanning direction is smaller than its width in the main scanning direction. The aforementioned plurality of light-receiving elements constitute a plurality of light-receiving element arrays arranged in two rows of the reading line, An optical line sensor further comprising an optical branching element that branches the light, either non-parallel to or parallel to the optical axis of the telecentric optical system, and guides it to the array of light-receiving elements such that the light transmitted through the array of light-receiving lenses is evenly incident on the array of light-receiving elements arranged in two rows of the reading line.

3. 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, Arranged in a line along the main scanning direction, the light source illuminates the object being inspected, Multiple light-receiving lenses are arranged in a line along the main scanning direction and transmit light from the object to be inspected illuminated by the light source, It comprises a plurality of light-receiving elements arranged in a line along the main scanning direction, which receive light that has passed through the plurality of light-receiving lenses, The aforementioned plurality of light-receiving elements constitute a plurality of light-receiving element arrays arranged in two rows of the reading line, An optical line sensor further comprising an optical branching element that branches the light transmitted through the plurality of light-receiving lenses and guides it to the plurality of light-receiving element arrays arranged in two rows of the reading line so that the light is evenly incident on the plurality of light-receiving element arrays.

4. The optical line sensor according to any one of claims 1 to 3, characterized in that the light-receiving element array arranged on one reading line and the light-receiving element array arranged on the other reading line are arranged alternately in a staggered pattern along the main scanning direction.

5. The aforementioned telecentric optical system further comprises an aperture, The optical line sensor according to claim 1, characterized in that a straight line connecting each pixel of the plurality of light-receiving elements to each pixel on the object to be inspected that corresponds one-to-one with the others passes through the center of the aperture, or the optical axis of the telecentric optical system passes through the center of the aperture, and the straight line which is symmetric with respect to the optical axis also passes through the aperture.

6. The optical line sensor according to claim 2, characterized in that the optical branching element is positioned on the side of the object to be inspected that is closer to the light-receiving lens in the optical axis direction, and is in close proximity to the light-receiving lens.

7. The optical line sensor according to claim 3, characterized in that the plurality of light-receiving lenses constitute a multi-lens array, and the optical branching element is positioned close to the object to be inspected in the optical axis direction with respect to the multi-lens array, or close to the light-receiving element array.

8. The optical line sensor according to claim 1 or 2, characterized in that the plurality of light-receiving lenses are spaced apart from each other so as to be less than or equal to the width of the light-receiving lens in the main scanning direction.

9. The aforementioned telecentric optical system further comprises an aperture, The optical licensor according to claim 1 or 2, characterized in that the aperture is positioned at a distance from a straight line extending from the starting point of the object to be inspected in a direction perpendicular to the main scanning direction and the sub-scanning direction.

10. The optical line sensor according to claim 1 or 2, 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.

11. The optical line sensor according to claim 1 or 2, 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 a position parallel to the sub-scanning direction from approximately the center of each light-receiving element array.

12. The optical line sensor according to claim 9, characterized in that the position of the aperture, which is positioned at a distance from a straight line extending from the starting point of the object to be inspected in a direction perpendicular to the main scanning direction and the sub-scanning direction, is adjustable.

13. The aforementioned telecentric optical system further comprises an aperture, The optical licensor according to claim 1 or 2, characterized in that the aperture is formed in the shape of an oval, ellipse, or rectangle extending in the sub-scanning direction on a straight line extending from the starting point of the object to be inspected in a direction perpendicular to the main scanning direction and the sub-scanning direction.

14. The optical licensor according to claim 13, characterized in that the longitudinal length of the aperture is adjustable.

15. The light source comprises multiple such light sources, The optical line sensor according to claim 1 or 2, 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 plurality of light sources are positioned approximately in the center between adjacent light-receiving lenses.

16. The optical line sensor according to claim 15, 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 a single unit, with a plurality of such single units of light sources arranged in the main scanning direction.

17. The optical line sensor according to claim 1 or 2, characterized in that the plurality of light-receiving lenses are arranged in a row along the main scanning direction, the ends of adjacent light-receiving lenses in the main scanning direction are connected, and they have the same shape when viewed from a direction perpendicular to the main scanning direction.

18. The optical line sensor according to claim 17, characterized in that the plurality of light-receiving lenses are arranged in a state in which adjacent light-receiving lenses in the main scanning direction are inverted and connected.

19. The optical line sensor according to claim 1 or 2, characterized in that the array of multiple light-receiving elements is arranged in the center of each of the multiple light-receiving lenses in the main scanning direction.

Images