Optical line sensor

Abstract

A plurality of light receiving lenses (11) are arranged along the main scanning direction. The plurality of light-receiving elements are arranged linearly along the main scanning direction, and receive light transmitted through the plurality of light-receiving lenses (11). The plurality of light-receiving elements form at least two or more rows of read lines L. The light receiving lens 11 constitutes a telecentric optical system, and the width W1 in the sub-scanning direction is smaller than the width W2 in the main scanning direction.

Description

Technical Field

[0001] The present invention mainly relates to an optical line sensor for detecting scratches and defects on the surface of a thin inspection object such as a printed material or a film, and scratches and defects inside a transparent film. Background Art

[0002] Research is underway to apply contact optical sensors (hereinafter referred to as CIS) used in inspection machines for determining the authenticity of banknotes, commercial copiers, flatbed scanners such as home printer scanners, etc. to so-called surface inspection machines that inspect the printing effects of printed materials, surface inspection in the manufacturing process of thin and wide film products, inspection of labels attached to various beverage containers, food containers, cans, etc., and some of these machines have already been commercialized.

[0003] However, in CIS that still uses SELFOC lens ("SELFOC" is a registered trademark, the same applies below), the working distance (hereinafter referred to as WD) is short, and in order to avoid contact when used in the process, a CIS with a long WD is desired. On this basis, in the inspection of paper materials such as banknotes, even if the depth of field is relatively shallow, it can withstand use, but because the inspection object changes greatly in the optical axis direction during the manufacturing process of the inspection object, a CIS with a deep field is also strongly desired.

[0004] As shown in Patent Documents 1 to 5, a representative CIS with a depth of field is a telecentric optical system using a mirror optical system. As can be seen from the patent documents, the optical system is very complex. There are great difficulties in manufacturing the optical system and using it as a commercial product. That is, during manufacturing, the process is complicated, and manufacturing stability and cost increase become problems. In addition, after commercialization, there will be deviations in the optical axis caused by the complex optical system due to changes in the environment and changes over time. Compared with the previous CIS with a simple structure, there are problems such as easy performance degradation.

[0005] Therefore, it is considered that instead of using the telecentric reflective optical system, a lens of a refractive system using glass or resin is used to improve WD and depth of field. Regarding the optical system of the refractive system, a certain degree of solution has been proposed, as shown in Patent Documents 6 and 7. For example, in Patent Document 6, a telecentric refractive optical system is separately configured on a staggered line sensor, and the lenses of the refractive optical system are separately configured and arrayed, thereby realizing an optical system with a deep field. In addition, in Patent Document 7, a method of preventing crosstalk between lenses by setting a partition plate between separated lenses is studied. In Patent Documents 6 and 7, although the depth of field can be improved and crosstalk between lenses can be prevented, the conventional telecentric refractive optical system is large and difficult to be compact. In addition, in the partition plate shown in Patent Document 7, missing pixels are generated during reading, and the reading is incomplete. In addition, there is no solution to the vignetting effect that a lens has in principle due to lens separation. There is also no mention of a method for suppressing the so-called fluctuation in the reading line direction. Moreover, the refractive optical system method has not been implemented so far.

[0006] In addition, inspection machines using camera lenses such as line cameras, which are different from the above methods, are large in size and require a large number of them to cope with the wide range of inspection objects at the manufacturing site. Therefore, the entire device becomes very large and its cost becomes huge, making it difficult to equip it in each process of the factory.

[0007] In order to solve the above-mentioned problems, an optical line sensor is desired, which is composed of a lighting system that uses a new refractive system lens that is small and inexpensive and has a long WD and a deep depth of field and can be introduced into each process of the factory, and uses a new suppression method for optical unevenness or fluctuation on the light receiving sensor caused by the vignetting effect of each lens.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2018-019334

[0011] Patent Document 2: Japanese Patent Application Publication No. 2018-152713

[0012] Patent Document 3: Japanese Patent Application Publication No. 2009-244500

[0013] Patent Document 4: Japanese Patent Application Publication No. 2018-019334

[0014] Patent Document 5: Japanese Patent Application Publication No. 2018-022948

[0015] Patent Document 6: Japanese Patent Application Publication No. 2009-246623

[0016] Patent Document 7: Japanese Patent Application Laid-Open No. 5-14600 Summary of the invention

[0017] Problems to be solved by the invention

[0018] Therefore, an object of the present invention is to realize a compact optical line sensor with a large depth of field.

[0019] Means used to solve problems

[0020] The optical line sensor involved in the invention of the present application reads the inspection object conveyed along the sub-scanning direction at the reading line extending along the main scanning direction, wherein the optical line sensor has 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 linear shape along the main scanning direction to receive light passing through the plurality of light-receiving lenses. The plurality of light-receiving elements form at least two columns of the reading line. The light-receiving lenses constitute a telecentric optical system, and the width in the sub-scanning direction is smaller than the width in the main scanning direction.

[0021] Effects of the Invention

[0022] According to the invention of the present application, an optical line sensor with a depth of field can be realized by using a telecentric optical system. In addition, the width of the light receiving lens in the sub-scanning direction is smaller than the width in the main scanning direction, so the light receiving lenses can be arranged close to each other in the sub-scanning direction, and as a result, the optical line sensor can be made compact. If the light receiving lenses are arranged close to each other in the sub-scanning direction, the light receiving elements can also be arranged close to each other in the sub-scanning direction, so that the processing of the image of the inspection object obtained based on the output signal from the light receiving element (for example, image synthesis processing) can be simplified. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a cross-sectional view of a typical CIS.

[0024] Figure 2 This is an exploded perspective view of the linear illumination optical system for CIS.

[0025] Figure 3 This is a schematic diagram of a light receiving system in which the fields of view of each light receiving lens do not overlap when each light receiving lens is arranged so as to function as a single-eye lens.

[0026] Figure 4 This is a schematic diagram showing another example of a light receiving system in which a plurality of light receiving element arrays are arranged.

[0027] Figure 5 This is a schematic diagram showing another example of a light receiving system in which a plurality of light receiving element arrays are arranged.

[0028] Figure 6 It is a graph showing the relationship between NA and diffraction limit for each wavelength.

[0029] Fig. 7A Graph showing the relationship between the effective diameter of the SELFOC lens A and the diameter of the circle of confusion.

[0030] Figure 7B Graph showing the relationship between the effective diameter of the SELFOC lens B and the diameter of the circle of confusion.

[0031] Figure 7C Graph showing the relationship between the effective diameter of the SELFOC lens C and the diameter of the circle of confusion.

[0032] Fig. 8A It is a graph showing the relationship between the effective diameter of the rod lens A and the diameter of the circle of confusion.

[0033] Figure 8B Graph showing the relationship between the effective diameter of the rod lens B and the diameter of the circle of confusion.

[0034] Figure 8C Graph showing the relationship between the effective diameter of the rod lens C and the diameter of the circle of confusion.

[0035] Fig.8D : is a graph showing the relationship between the effective diameter of the rod lens D and the diameter of the circle of confusion.

[0036] Fig.9A This is a schematic diagram showing an example of an arrangement method when RGB-LED or RGB-LD (laser diode; semiconductor laser) is used as a light source.

[0037] Fig. 9B It is a side view showing a specific example of the arrangement method when using LD as a light source.

[0038] Fig. 10A This is a schematic diagram showing the positional relationship between the light source and the light receiving lens, and is a case where the light receiving element array is two rows.

[0039] Fig. 10B This is a diagram showing the relationship between the light intensity distribution of the light source (on the inspection surface) in the main scanning direction, the light intensity distribution on the light receiving element surface, and the vignetting effect of the light receiving lens.

[0040] Fig. 10C This is a graph of the MTF of the light receiving system for different lens diameters (√A=0.077).

[0041] Fig. 10D This is a graph of the MTF of the light receiving system for different lens diameters (√A=0.154).

[0042] Fig. 10E This is a graph of the MTF of a light-receiving optical system whose refractive index distribution constant √A is √A=0.1027.

[0043] Fig.11 This is a diagram showing the MTF characteristics when the image is defocused.

[0044] Fig. 12A It is a schematic diagram showing a modified example of the light receiving system.

[0045] Fig. 12B It is a schematic diagram showing a modified example of the light receiving system.

[0046] Fig. 12C It is a schematic diagram showing a modified example of the light receiving system.

[0047] Fig.12D It is a schematic diagram showing a modified example of the light receiving system.

[0048] Fig.12E It is a schematic diagram showing a modified example of the light receiving system.

[0049] Fig.12F It is a schematic diagram showing a modified example of the light receiving system.

[0050] Figure 12G It is a schematic diagram showing a modified example of the light receiving system.

[0051] Fig.12H This is a schematic diagram for explaining the position of the optical axis in the light receiving system.

[0052] Fig.12I This is a schematic diagram for explaining the position of the optical axis in the light receiving system.

[0053] Fig.13 This is a diagram showing the light intensity distribution on the light receiving surface of the light receiving element array when the light intensity distribution of the light source is flat when the lens end is a parallelogram.

[0054] Fig.14 It is a diagram showing the details of the light intensity distribution near the connection portion between adjacent light receiving lenses.

[0055] Fig.15 express Fig.12E The light intensity of the light receiving area in the example of FIG. 1 is used to schematically illustrate the reason why no signal missing portion is generated. DETAILED DESCRIPTION

[0056] 1. Overall structure of optical line sensor

[0057] A typical CIS is shown in Figure 1 Similarly, the CIS linear illumination optical system is shown in Figure 2 .exist Figure 1 , a cross-sectional view of the vicinity of the center portion in the longitudinal direction of the CIS is shown. Figure 2 1 is an exploded perspective view. The X direction is the main scanning direction, and the Y direction is the sub-scanning direction. The Z direction is orthogonal to the X direction and the Y direction. The linear light source unit 10 is an illumination optical system having a light quantity distribution that is elongated in the main scanning direction.

[0058] exist Figure 1 In the CIS shown, two frames 16 are arranged opposite to each other with a focal plane (inspection plane) 20 in between. A linear light source unit 10 is provided in each frame 16 for illuminating an inspection object located on the focal plane 20. A light receiving lens 11 and a light receiving unit 12 are provided in one frame 16, and light from the illuminated inspection object is guided to the light receiving unit 12 through the light receiving lens 11. The light receiving lens 11 forms an image of the light from the inspection object on the light receiving unit 12. Figure 1 In the illustrated CIS, one of the two light source units 10 is arranged on the light receiving unit 12 side, and the other is arranged on the side opposite to the light receiving unit 12 side, with reference to the focal plane 20 .

[0059] The light receiving unit 12 is mounted on a substrate 13 of a frame 16 fixed to one side. The light passing 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. By transporting the inspection object in a direction Y along the focal plane 20, the light from the inspection object is continuously received by the light receiving unit 12, and an image (color image, fluorescent image, etc.) of the inspection object is obtained based on the output signal from the light receiving unit 12. In this way, the inspection object transported in the sub-scanning direction (Y direction) is read by the light receiving unit 12 extending in the main scanning direction (X direction) through the reading line formed by the light receiving surface 12A of the light receiving unit 12.

[0060] The light B3 emitted from the light source unit 10 on one side passes through the protective glass 14 fixed to the frame 16, is reflected by the reflective member 17A provided on the inner surface of the protective glass 14A fixed to the frame 16 on the other side, and is guided to the focal plane 20. An ultraviolet light cut filter (UV cut filter) 15 that prevents ultraviolet light from entering the light receiving unit 12 is provided at any position from the focal plane 20 to the light receiving unit 12. In addition, a color filter 18 that allows visible light in a specific wavelength range to pass is provided between the light receiving unit 12 and the ultraviolet light cut 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 provided at a position opposite to the bottom surface of the light source unit 10 in the frame 16 on one side.

[0061] exist Figure 1 as well as Figure 2 In the example shown, the light source unit 10 includes a transparent light guide 101 extending along the longitudinal direction L, a light source 103 provided near one end surface in the longitudinal direction L, and a cover member 102 for holding each side surface of the light guide 101. Light emitted from the light source 103 enters the light guide 101, is appropriately reflected by the light diffusion pattern P while propagating in the light guide 101, and is emitted from the light emission surface in the direction of the arrow to form a linear illumination light to illuminate the inspection object. Such a CIS has a shallow depth of field. When the inspection object has thickness, it is difficult to inspect the entire thickness direction. In addition, since the WD is narrow, there are many cases where the inspection object is contacted and the inspection itself is not established.

[0062] In the CIS as described above, as the light receiving lens 11, for example, a SELFOC (manufactured by Nippon Sheet Glass Co., Ltd.) lens array is used. The SELFOC lens array is an upright lens array of equal magnification. In this lens array, cylindrical SELFOC lenses are stacked to form a multi-eye lens. The advantage of a multi-eye lens is that the brightness of the so-called lens can be brighter than that of a single lens. That is, compared with the F value of a single lens, the F value of a multi-eye lens formed by arranging multiple single lenses is smaller. This is because the effective F value becomes smaller at a location where the focal position of a lens located at an arbitrary position coincides with the focal position of the lenses around the lens. In other words, it means that in an upright lens system, the numerical aperture (hereinafter referred to as NA) is larger in the arrayed state than in the single lens. This property is the main reason for using a SELFOC lens array in a CIS.

[0063] From the perspective of depth of field and depth of focus, the advantages of the CIS described above have become disadvantages. As with a single-eye lens, if the numerical aperture increases, the depth of field becomes shallower. For example, it is well known that in a microscope objective, as the magnification increases, that is, the NA increases, the depth of field becomes shallower. In addition, in a camera lens, the length of the depth of field is also faithfully represented in the distant view and the near view, and the aperture is adjusted to ensure the depth of field. That is, the NA is changed to obtain the desired depth of field. On this basis, the upright multi-eye lens represented by the SELFOC lens crosses because the optical axes of each lens are different. Therefore, compared with the single-eye lens, it is formed into a structure that the image is easily blurred when the inspection object changes in the optical axis direction. The above is a major disadvantage of the stacking method of multi-eye SELFOC lens array. Therefore, it was studied how to deepen the depth of field of a compact optical line sensor, and as a result, the obtained embodiment is recorded as follows. In the following embodiment, the light-receiving lens 11 constitutes a telecentric optical system.

[0064] 2. Embodiment of light receiving system

[0065] First, the first method is Figure 3 As shown, the optical line sensor is regarded as an array structure in which a single lens is formed. Figure 3 Schematic diagram of a light receiving system in which the fields of view of the light receiving lenses 11 do not overlap. Figure 3 In the embodiment, each light receiving lens 11 is separately arranged in the main scanning direction (X direction) so that the fields of view of each light receiving lens 11 do not overlap, and each light receiving lens 11 is also separated in the sub-scanning direction (Y direction), thereby each light receiving lens 11 is arranged in a staggered manner.

[0066] That is, the plurality of light receiving lenses 11 arranged along the main scanning direction (X direction) are arranged separately from each other, not in a stacking manner. The plurality of light receiving lenses 11 arranged along the main scanning direction (X direction) are held integrally by a lens holder 110. At a position opposite to each light receiving lens 11 in the Z direction, a light receiving element array 120 is arranged, which is formed by arranging a plurality of light receiving elements (not shown) in a linear shape along the main scanning direction (X direction). That is, a plurality of light receiving elements are arranged in an array shape along the main scanning direction (X direction), thereby forming a light receiving element array 120. Each light receiving element receives light transmitted through each light receiving lens 11.

[0067] In this example, a light receiving element array 120 is arranged corresponding to each light receiving lens 11. Thus, each light receiving element array 120 composed of short sensors is alternately arranged in a staggered manner along the main scanning direction (X direction). A plurality of light receiving element arrays 120 arranged along the main scanning direction (X direction) form a column of reading lines L. Figure 3In the example of , two columns of reading lines L are formed. The lens holder 110 is not limited to the configuration provided corresponding to each reading line L, and a plurality of light receiving lenses 11 corresponding to each reading line L may be integrally held by one lens holder.

[0068] If the Figure 3 As shown, a plurality of light receiving lenses 11 corresponding to a plurality of light receiving element arrays 120 may be arranged by making one light receiving lens 11 correspond to one light receiving element array 120. The optical axis of the light guided to each light receiving element array 120 through each light receiving lens 11 may also pass through the approximate center of the main scanning direction (X direction) of each light receiving element array 120 corresponding one to one. In this method, a plurality of light receiving element arrays 120 are arranged in a plurality of columns in the sub-scanning direction (Y direction). That is, a plurality of columns of light receiving element arrays 120 are separately arranged in a direction (Y direction) perpendicular to the arrangement direction (X direction) of the light receiving elements.

[0069] 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 a shape that is elongated 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. In addition, 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 preferred that the width W1 of each light receiving lens 11 in the sub-scanning direction is set in such a manner that NA satisfies 0.001<NA<0.05. In this example, each light receiving lens 11 has the same shape, and is formed to be rectangular when viewed from a direction (Z direction) orthogonal to the main scanning direction and the sub-scanning direction. However, each light receiving lens 11 is not limited to a rectangle (rectangular), and may also be an oblong or elliptical shape, or may be other shapes.

[0070] The plurality of light receiving lenses 11 are arranged to be separated from each other by a width W2 or less in the main scanning direction of the light receiving lens. That is, the plurality of light receiving lenses 11 are preferably arranged to be separated from each other by a width W2 or less in the main scanning direction of the light receiving lens 11 (within the field of view). Figure 3, the fields of view of each light receiving lens 11 are overlapped in the sub-scanning direction. In this case, for the light receiving elements in the portion where the fields of view of the multiple light receiving lenses 11 overlap, the pixel output from the light receiving element can be subtracted. For example, the image of one of the light receiving lenses 11 (the amount of light received by one of the light receiving lenses 11) can be excluded from the data output by the light receiving element, or the pixel output from the light receiving element can be set to approximately half of the output value when performing image synthesis. If multiple light receiving element columns (light receiving element array 120) are used, pixel loss can be more reliably prevented than in the case of a single line of light receiving element columns.

[0071] Figure 4 1 is a schematic diagram showing another example of a light receiving system including a plurality of light receiving element arrays 120. Figure 4 In the example, each light receiving lens 11 does not correspond one-to-one to each light receiving element array 120 , but a plurality of (two in this example) light receiving lenses 11 arranged in the main scanning direction correspond to one light receiving element array 120 .

[0072] The plurality of light receiving lenses 11 corresponding to one light receiving element array 120 are adjacent to each other in the main scanning direction. However, the plurality of light receiving lenses 11 corresponding to one light receiving element array 120 may be separated from each other. In this case, the plurality of light receiving lenses 11 may be separated from each other by a width W2 or less in the main scanning direction of the light receiving lenses 11. In addition, a light shielding member may be provided between each light receiving lens 11.

[0073] Figure 5 1 is a schematic diagram showing another example of a light receiving system in which a plurality of light receiving element arrays 120 are arranged. Figure 5 In the embodiment, a plurality of light receiving element arrays 120 (two in this example) composed of strip sensors of the same length (length corresponding to the full length in the main scanning direction) are arranged in parallel in the sub-scanning direction. Figure 5 As shown, a plurality of light receiving element arrays 120 corresponding to the number of columns of the light receiving lenses 11 in the sub scanning direction (Y direction) may be arranged by making one light receiving element array 120 correspond to a plurality of light receiving lenses 11 arranged in the main scanning direction (X direction).

[0074] exist Figure 3 to Figure 5 In any of the above, 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, so the light receiving lenses 11 can be arranged close to each other in the sub-scanning direction, resulting in the optical line sensor being compact. As described above, the short light receiving element arrays 120 can be arranged in a staggered manner for use (see Figure 3 as well as Figure 4), or two rows of light receiving element arrays 120 may be configured separately for use (refer to Figure 5 ), but not limited to this, more multiple light receiving element arrays 120 can also be configured separately in the sub-scanning direction (Y direction).

[0075] 3. Long focal length of the light receiving lens

[0076] Next, the telephoto of the light-receiving lens is described. In the past, SELFOC lenses focused on the compactness and cost reduction of CIS, and lenses with shorter conjugate lengths were required. However, this trend has become a major reason for the reduction in the allowable depth of field. In addition, the lens diameter is getting smaller and smaller. In the case of telephotoizing the light-receiving lens, if the previous light-receiving lens is used, the NA becomes extremely small. Therefore, the influence of diffraction becomes larger, and the blur caused by the diffraction limit becomes the dominant factor in the degradation of optical resolution compared to the blur caused by the geometric optical aberration of the light-receiving lens itself. Since the NA of the existing CIS is large, the blur of the image caused by the diffraction limit can be ignored. However, in order to increase the WD, it is necessary to extend the focal length of the light-receiving lens, that is, the NA becomes smaller. Therefore, in the previous lens diameter, the larger the focal length, the greater the influence of diffraction. In this embodiment, a method is proposed that does not degrade the optical resolution even when the WD is increased by increasing the lens diameter and the blur of the image caused by the diffraction limit is reduced.

[0077] Abbe's diffraction limit d is inversely proportional to the numerical aperture NA. Since the optical system is located in the air, the following equation 1 is established using the wavelength λ in the air.

[0078] d = λ / NA (Formula 1)

[0079] Figure 6 The relationship between the NA and the diffraction limit for each wavelength is shown. In the light receiving lens 11 with the same lens parameters, if the so-called pitch of the light receiving lens 11 itself is shortened, the focal length is extended and the influence of aberration is reduced.

[0080] Based on the above, it can be seen that in order to make the light receiving lens 11 telephoto, the lens diameter needs to be further increased. If the NA is kept the same, the effect of diffraction can be made equal to that of the short-focus light receiving lens 11. However, if the lens diameter is increased, the geometric optical aberration increases. Therefore, in the light receiving lens 11 with different lens parameters, it is necessary to study the minimum circle of confusion diameter when the lens diameter is increased. The wavelength λ is λ=630nm, which is the largest diffraction limit diameter.

[0081] The inventors of the present application have found out from their research that it is sufficient to consider the relationship between the minimum circle of confusion and the focal length of each light receiving lens 11. For example, Figure 7A to Figure 7C, where the focal length f is f=50 mm. Here, when three types of SELFOC lenses (SELFOC lens A, SELFOC lens B, and SELFOC lens C) are used as the light receiving lens 11, Fig. 7A The relationship between the effective diameter of the SELFOC lens A and the diameter of the confusion circle is shown. Figure 7B The relationship between the effective diameter of the SELFOC lens B and the diameter of the confusion circle is shown. Figure 7C The relationship between the effective diameter of the SELFOC lens C and the diameter of the confusion circle is shown. Figure 7A to Figure 7C In the figure, the solid line represents the total confusion circle, the dashed line represents the confusion circle based on diffraction, and the dashed-dotted line represents the geometrical optics confusion circle.

[0082] according to Figure 6 and Fig. 7A It can be seen that the relationship between the minimum circle of confusion and the diffraction limit is the optical resolution under a certain lens diameter and focal length. Fig. 7A In the case of the light receiving lens 11 shown, the larger the effective diameter Φ is, the smaller the diameter of the circle of confusion is. The effective diameter Φ may be 1.0 mm ≤ Φ ≤ 3.0 mm.

[0083] On the other hand, according to Figure 6 and Figure 7B , the geometric optical circle of confusion is large, and the diffraction dependence becomes small, so the diameter of the circle of confusion is the smallest when Φ = 1.0 mm. Moreover, even when Φ = 1.0 mm, it becomes Fig. 7A The diameter of the circle of confusion is nearly double that of the light receiving lens 11 shown. Fig. 7A The light receiving lens 11 shown is Figure 7B Compared with the SELFOC lens, which has a smaller aberration and a larger effective diameter, the light receiving lens 11 shown in FIG. Fig. 7A The light receiving lens 11 of the same focal length Fig. 7A The light receiving lens 11 and Figure 7B Compared with the light receiving lens 11, the NA can be increased by at least 3 times, that is, the amount of light received is 9 times or more, so the output of the light receiving element is also 9 times or more. Along with this, the shot noise depending on the amount of light received by the light receiving element is also reduced to 1 / 3, so from the perspective of suppressing noise, it is also preferred Fig. 7A The light receiving lens 11 shown. In addition, if the same amount of noise is allowed, it can also be said that Fig. 7A The light receiving lens 11 and Figure 7B Compared with the light receiving lens 11, the scanning speed can be increased to 9 times.

[0084] according to Figure 7C , SELFOC lens C also has small aberrations like SELFOC lens A and can increase the effective diameter.

[0085] Next, Figure 7A to Figure 7C The parameters of SELFOC lens A to SELFOC lens C are shown in Table 1 below. The most important parameter among the parameters 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 smallest aberration is SELFOC lens A with the smallest refractive index distribution constant, and the light receiving lens 11 with the second smallest aberration is SELFOC lens C. In order to perform high-speed inspection with high resolution, it is of course preferred to have a light receiving lens 11 with a large effective diameter, a bright light, and small aberration.

[0086] Table 1

[0087]

[0088] In addition, when four types of plastic rod lenses (plastic refractive index distribution type lenses) are used as the light receiving lens 11, Fig. 8A It represents the relationship between the effective diameter of the rod lens A and the diameter of the circle of confusion, Figure 8B It represents the relationship between the effective diameter of the rod lens B and the diameter of the circle of confusion, Figure 8C It represents the relationship between the effective diameter of the rod lens C and the diameter of the circle of confusion, Fig.8D It represents the relationship between the effective diameter of the rod lens D and the diameter of the circle of confusion. Figures 8A to 8D In the figure, the solid line represents the total confusion circle, the dotted line represents the confusion circle based on diffraction, and the single-point dashed line represents the geometrical optical confusion circle. Figures 8A to 8D Parameters of rod lenses A to D are shown. It can be seen that the plastic rod lenses also have the same tendency as the SELFOC lens. Considering the refractive index of the plastic rod lens and the refractive index of the glass lens, the on-axis refractive index is preferably about 1.45 to about 1.65.

[0089] Table 2

[0090]

[0091] From the above, we can know that the refractive index distribution constant is the dominant factor of aberration. If it is an ideal refractive index distribution lens, the more gradually the refractive index changes, the smaller the aberration. This is the same as the situation that even for ordinary spherical lenses, abrupt angle changes are also the cause of aberration. Abrupt angle changes mean that the Snell'La w The increase of the higher-order nonlinear effect when performing polynomial expansion. That is, the aberration becomes larger because the deviation from the paraxial optics becomes larger. The inventors of the present application have found that when the focal length or WD is approximately 50 mm or more and the effective diameter Φ is approximately Φ ≥ 1.0 mm, in order to achieve a pixel resolution of 400 dpi or more, it is preferred to make the refractive index distribution constant below 0.12.

[0092] 4. Modification of the light receiving lens

[0093] The light receiving lens 11 in the present invention is not limited to SELFOC lens, plastic rod lens and other refractive index distribution type lenses. In other lenses, such as achromatic lens, apochromatic lens, etc., considering the cost, SELFOC lens, plastic rod lens and other refractive index distribution type lenses with the same aberration caused by the nonlinear effect and diffraction limit as the above-mentioned refractive index distribution type lenses can be replaced by lenses with the same aberration caused by the nonlinear effect as the above-mentioned refractive index distribution type lenses, i.e., spherical aberration, coma, and astigmatism, or telecentric refractive optical systems with the same configuration and size (aperture). This is also the case with the light receiving lens 11 that forms an inverted image described later.

[0094] The above optical system is centered on an upright lens, but it can also be an inverted optical system when the fields of view do not overlap. That is, it can also be a structure in which multiple light-receiving lenses 11 form an inverted image. As long as it is a two-row lens array, an inverted optical system can also be used. In the case of an inverted optical system, the image is flipped symmetrically around the optical axis, so the inverted image can be converted into an upright image by image processing during image synthesis. That is, the flipped images of multiple light-receiving lenses 11 are flipped, converted into upright images, and then image synthesis processing is performed. In addition, during this operation, the parts to be overlapped or not are determined according to the correction algorithm and corrected, and converted into upright images according to the determined relationship between pixels. Alternatively, in the inspection without constructing an image, only flaws or defects are detected, so image synthesis and image processing are not required, and the detection parts in the inspection surface can also overlap. In the case of overlap, correction based on the position of the correction diagram is performed in advance.

[0095] In addition, in the case of an inverted refractive optical system, in the signal processing for each light receiving element, for example, data obtained from one of the two light receiving element arrays arranged separately and staggered in the sub-scanning direction may be obtained at a longer time, and data obtained from the other light receiving element array may be obtained at a shorter time, and after performing a flip operation of flipping the acquired image into an erect image, image synthesis may be performed. Alternatively, after converting the inverted image data of each light receiving element into an erect image, the overlapped portion may be multiplied by a correction coefficient or subtracted when synthesizing the image.

[0096] Specifically, in the inverted refractive optical system, the plurality of light receiving element arrays may be shorter than the light receiving element arrays of each of the two columns of reading lines. In addition, the light receiving element arrays arranged on one reading line and the light receiving element arrays arranged on the other reading line may be arranged alternately in a staggered manner along the main scanning direction. Such a configuration is similar to Figure 3This is the same as the case of the upright refractive optical system described in , so the detailed description is omitted.

[0097] In this case, if Figure 3 As shown, a plurality of light receiving elements are arranged in an array shape of two or more rows to form a plurality of light receiving element arrays 120. In addition, the plurality of light receiving element arrays 120 are respectively arranged to be separated from each other by less than the width W2 in the main scanning direction of the light receiving lens 11 in a direction orthogonal to the reading line L. The plurality of light receiving lenses 11 are arranged in a number corresponding to the plurality of light receiving element arrays 120, and the optical axis of the light guided to each light receiving element array 120 through each light receiving lens 11 passes through the approximate center of each light receiving element array 120. However, the optical axis of the light guided to each light receiving element array 120 through each light receiving lens 11 may also pass through a position away from the approximate center of each light receiving element array 120 in parallel with the sub-scanning direction.

[0098] 5. Composition of the illumination optical system

[0099] In the present embodiment, the focal length f of the light receiving lens 11 is f=50 mm, the NA is NA=0.01, 0.02, 0.025, 0.03, and the refractive index distribution constant √A is √A=0.077. Regarding the light source 103, the WD is more than 10 times longer than that of the previous CIS, so in an equal magnification system, the inspection surface illumination needs to be more than 100 times. Therefore, as the light source 103, for example, a high-brightness white LED array is used. That is, it is also possible to have a configuration in which multiple light sources 103 include white LEDs. When a semiconductor laser in the visible region is used as the light source 103, the unevenness of the amount of light during irradiation is reduced by amplifying the emitted light beam in the main scanning direction and collimating it in the sub-scanning direction.

[0100] exist Fig.9A An example of a configuration method when using RGB-LED or RGB-LD (laser diode; semiconductor laser) as the light source 103 is shown in FIG. In this way, the plurality of light sources 103 may be composed of a red LED (R), a green LED (G), and a blue LED (B), or may be composed of a laser diode. Fig.9A In the embodiment, a plurality of light sources 103 are mounted on a light source substrate 134, and a heat sink 135 is mounted on the light source substrate 134. The light beams emitted from each light source 103 are collimated by an ellipsoidal condenser lens 104 having different lens focal powers in the main scanning direction and the sub-scanning direction, and irradiated onto the inspection object. Here, an ellipsoidal condenser lens 104 is shown, but any lens having appropriately different lens focal powers in the main scanning direction and the sub-scanning direction may be used. It should be noted that the focal power of a lens is the reciprocal of the focal length and is a measure of the refractive power of the lens.

[0101] Alternatively, regarding the LD, if an end-emitting LD in which the divergence angle of the light beam emitted from the LD itself is different in the horizontal direction and the vertical direction is used, a normal collimator lens may be used. Fig. 9B It is a side view showing a specific example of a configuration method when LD is used as the light source 103. In this case, the LD with a large expansion angle is configured parallel to the main scanning direction. The light beams emitted from the red LD 131, the green LD 132 and the blue LD 133 constituting the light source 103 are collimated by the corresponding focusing lenses 104, and then converged to the inspection surface by the cylindrical lens 105. As a result, each color of RGB is irradiated to approximately the same position in the sub-scanning direction, which can reduce color unevenness relative to the sub-scanning direction. On the other hand, the light irradiated by the light source 103 such as LED and LD and diffusely reflected on the inspection surface is imaged on the light receiving element array through the light receiving lens system. In the equal magnification optical system, the light receiving element uses an element size of 62μm equivalent to 400dpi to an element size of 42μm equivalent to 600dpi. When using an element size of 600dpi or more, the power of the illumination light can be increased accordingly. Thus, the plurality of light sources 103 may include light sources 131 to 133 having a plurality of different wavelengths, and the light sources 131 to 133 may be considered as a unit, and a plurality of light sources 103 of the unit may be arranged in the main scanning direction (X direction).

[0102] In addition, even if the radiant brightness per unit area is the same, if the size of the light receiving element is different, it is equivalent to the case where the area of ​​the light emitting portion is different, so the amount of light received decreases inversely proportional to the square of the area of ​​the light receiving element. Considering the above situation, the amount of illumination light is determined. When the element size becomes smaller, the amount of light received decreases inversely proportional to the element area in the same accumulation time. This is a physical property of semiconductor light receiving elements. In order to maintain S / N, the illumination light is increased, the power density is increased, and the number of generated electrons generated per unit time is the same. Therefore, even if the size of the light receiving element is reduced, the shot noise can be maintained at the same level as that of a large-sized light receiving element. In addition, the light received by the light receiving element depends not only on the illumination of the inspection surface, but also on the range observed by the light receiving element when receiving light. Of course, the solid angle of light reception is different. If the angle is reduced, the amount of light received also decreases. If the inspection surface is a completely diffuse surface, it becomes the amount of light received corresponding to the so-called cosθ law. The light diffusely reflected from the inspection surface is captured by the light receiving lens and focused on the light receiving element, and its output signal is output from the light receiving element. In addition, the output signals from the light receiving element array are branched from serial to parallel to increase the processing speed, and are transmitted to the image processing device.

[0103] Fig. 10A 1 is a schematic diagram showing the positional relationship between the light source 103 and the light receiving lens 11, and is a case where the light receiving element array 120 is two rows. Fig. 10A, the arrangement of the light receiving lenses 11 and the light source 103 arranged in two rows relative to the light receiving element array 120 is shown. In the present embodiment, the light source 103 is arranged at the approximate center of the two rows of reading lines L. Each light source 103 is arranged parallel to the reading line L. In addition, the optical axis of each light source 103 is arranged at an arbitrary position of a virtual plane that connects the intersection point with the optical axis of the light guided to each light receiving element array 120 through each light receiving lens 11 and intersects with the optical axis of the light guided to each light receiving element array 120 through each light receiving lens 11. In the present embodiment, the focal length f of the light receiving lens 11 is f=50 mm, and the lens diameter Φ is Φ=4 mm (wherein, considering geometric optical aberration, an aperture is used and the effective diameter Φ' is set to Φ'=2.5 mm). In the present embodiment, light is irradiated from the light source 103 at an angle of about 45 degrees relative to the inspection surface. Therefore, considering the WD of the light receiving lens 11, the distance between the light source 103 and the inspection surface is set to 70 mm. In this embodiment, LD is used, but LEDs of various wavelengths may also be used.

[0104] The arrangement pitch of the light source 103 is consistent with the distance between the lenses, and the light source 103 is arranged at the approximate center between the adjacent light receiving lenses 11 and at the approximate center of the two columns of reading lines L. This can further prevent the loss of pixels on the inspection surface, and at the same time further reduce the vignetting effect of the light receiving lens 11 and the uneven light amount of the light source 103. The lens pitch between the light receiving lenses 11 of each column is set to 7 mm. In this case, the actual lens pitch is 3.5 mm.

[0105] Fig. 10B 1 is a diagram showing the relationship between the light quantity distribution of the light source 103 (on the inspection surface) in the main scanning direction, the light quantity distribution on the light receiving element surface, and the vignetting effect of the light receiving lens 11. Fig. 10A In the layout, such as Fig. 10B As schematically shown, the light intensity distribution on the light receiving element array 120 is flat, and the dynamic range of the light receiving elements can be effectively utilized.

[0106] 6. Fluctuation suppression methods

[0107] Next, a method for suppressing the vignetting effect caused by each light-receiving lens 11, which produces fluctuations in the direction of the readout line L and causes the dynamic range of the light-receiving element to be narrowed, will be described.

[0108] First, the inspection object is irradiated with illumination light having a negative intensity distribution in advance by the illumination system. For example, the method of disposing the light source 103 between adjacent light-receiving lenses 11 is not a method for suppressing the vignetting effect completely corresponding to various light-receiving lenses 11. That is, if each light-receiving lens 11 has a unique vignetting effect and the light-receiving lenses 11 are different, an illumination optical system corresponding thereto must be used. In this embodiment, a condenser lens 104 having a large optical focal length is disposed in the main scanning direction. The light beam passing through the condenser lens 104 is then guided to the inspection object by a converging lens such as a cylindrical lens 105, and a light intensity corresponding to the vignetting effect of the light-receiving lens 11 is formed on the inspection object. Moreover, by appropriately changing the position of the condenser lens 104 in the optical axis direction according to the vignetting effect of the light-receiving lens 11, for example, if the inspection object is a white reference plate for calibration, the light intensity distribution on the light-receiving element can be smoothed. The condenser lens 104 may also have an optical focal length in the sub-scanning direction. In short, as long as the vignetting effect of the light-receiving lens 11 can be completely suppressed and an effective light intensity distribution that takes into account the focal length of the light-receiving lens 11 for the inspection object can be achieved at the same time. That is, it is preferred that the lens optical focal length in the main scanning direction is greater than the lens optical focal length in the sub-scanning direction. As the focusing lens 104, for example, a cylindrical lens, a cylindrical lens, a Fresnel lens, or a combination of a prism lens and a spherical lens is preferred. Regarding the positional relationship of the light source 103 with respect to the main scanning direction, it can be arranged in the middle position of each light-receiving lens 11, or it can be arranged on the optical axis of the light-receiving lens 11. In addition, the light source 103 can also be arranged at a position on the periphery of the light-receiving lens 11. In addition, a lens having an optical focal length distribution in the main scanning direction is more preferred.

[0109] In the present embodiment, the focusing lens 104 for focusing the light beams from the plurality of light sources 103 is configured as a lens body, and the focal length of the lens body in the main scanning direction is greater than the focal length of the sub-scanning direction. However, the focusing lens 104 may not be a lens body, and may be a structure including a first focusing lens and a second focusing lens. In this case, the focal length of the first focusing lens in the main scanning direction may be greater than the focal length of the sub-scanning direction, and the focal length of the second focusing lens in the sub-scanning direction may be greater than the focal length of the main scanning direction. In addition, the focal length of the main scanning direction may be adjusted by the first focusing lens and the second focusing lens.

[0110] In the condenser lens 104 having the first condenser lens and the second condenser lens as described above, the first condenser lens and the second condenser lens can be composed of a cylindrical lens, a columnar lens, a Fresnel lens, or a prism array, etc. For example, the first condenser lens can also be a columnar lens or a prism array. In addition, the second condenser lens can also be a Fresnel lens or a cylindrical lens.

[0111] 7. Parameters of the light receiving lens

[0112] exist Fig. 10C FIG. 2 shows a graph of the MTF of the light receiving system according to the lens diameter in this embodiment. Fig. 10D The case where the refractive index distribution constant √A = 0.154 is shown in FIG. The case where the effective diameter Φ is Φ = 1.0, 1.5, 2.0, 2.5, and 3.0 mm is shown in the order of solid line, short dash line, long dash line, and single dot dash line. It should be noted that the pixel size of the light receiving element is set to 42.3 μm in both the main scanning direction and the sub-scanning direction to match the case of 600 dpi.

[0113] In the present embodiment, in the effective diameter Φ, under the condition that the refractive index distribution constant √A is √A=0.077, if it is 12 lines / mm equivalent to 600dpi and the performance is about 30%, the MTF characteristics in the range from Φ1.0mm to Φ3.0mm are satisfied. In contrast, the effective diameter Φ of the comparative example does not satisfy the MTF characteristics in the entire range. This means that the aberration characteristics are better when √A is √A=0.077 than when √A=0.154. In addition, for the case of focal length f=50mm, the MTF of the light-receiving optical system is obtained when the refractive index distribution constant √A is √A=0.1027, as shown in FIG. Fig. 10E As shown. Fig. 10E Even when √A is √A=0.1027, the MTF characteristic is satisfied within the range of 12 lines / mm and Φ1.0 mm to Φ3.0 mm, which is equivalent to a resolution of 600 dpi.

[0114] When the light receiving lens 11 is a refractive index distribution type lens, the lens is preferably made of glass or resin. In this case, among the lens parameters of the light receiving lens 11, it is preferred that the on-axis 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 50mm≤f≤150mm.

[0115] The light receiving lens 11 may also be an achromatic lens or an apochromatic lens formed by combining multiple lenses. In this case, it may be a lens system in which only convex lenses are combined as multiple lenses, or a lens system in which convex lenses and concave lenses are combined as multiple lenses. In addition, it is preferred that the focal length f of the multiple lenses is 25 mm ≤ f ≤ 250 mm, and it is more preferred that the aperture Φ of the multiple lenses is 2 mm ≤ Φ ≤ 50 mm.

[0116] Next, an example is given of a case where the light receiving lens system is set as a reduction optical system in order to improve the depth of field and resolution. Fig. 10ASimilarly, the magnification of the light receiving lens 11 is changed. That is, the relationship between the lateral magnification of the object point and the image point of the light receiving lens 11 is changed to 9:1 and 4:1. As a result, the depth of field increases to 3 times of that of the equal magnification system when the lateral magnification is 9:1, and increases to 2 times of that of the equal magnification system when the lateral magnification is 4:1. When the depth of field is set to 3 times, the size of the light receiving element is set to 1 / 9 of the size of the light receiving element of the equal magnification system. In addition, when the depth of field is set to 2 times, the size of the light receiving element is set to 1 / 4 of the size of the light receiving element of the equal magnification system. In the present embodiment, a 1 / 4-sized light receiving element is used to set the depth of field to 2 times.

[0117] exist Fig.11 The MTF characteristics of the reduction optical system of this embodiment when defocused are shown in the graph (solid line). Fig.11 The MTF characteristics of the equal-magnification system when defocused are shown in the graph (dashed line). According to the comparison between the reduction system and the equal-magnification system in the figure, the depth of field of the reduction optical system is about twice that of the equal-magnification system. In addition, if the reduction ratio is set to S, the NA of the light-receiving lens 11 increases as its reciprocal 1 / S. Therefore, even in the case where the lens diameter of the light-receiving lens 11 is small, as long as the reduction ratio is increased according to the focal length, the actual effective NA can be maintained, and therefore the blur based on the diffraction effect can be made constant.

[0118] In this embodiment, the focal length is set to f = 50 mm and the lateral magnification ratio is set to 1 / 4, so the lens diameter Φ can be used to be Φ = 0.25 mm in principle. Fig. 10A The lens with the same situation, so the lens diameter Φ is Φ = 4mm, the effective diameter Φ' is Φ' = 2.5mm. Fig. 10A Therefore, the amount of received light is 16 times, which can offset the 1 / 16 reduction in the amount of received light caused by reducing the size of the light receiving element to 1 / 4.

[0119] 9. Telecentric optical system

[0120] Next, the telecentric optical system applied to the present embodiment is described. By using the telecentric optical system, it is possible to achieve a structure that is easy to assemble and has little change over time. In the telecentric optical system, the light-receiving lens 11 is arranged on both sides or on one side through a gap (translucent portion). That is, the telecentric optical system is a two-side telecentric optical system in which the light-receiving lens 11 is arranged on both sides of the inspection object side and the light-receiving element array 120 side, or an object-side telecentric optical system in which the light-receiving lens 11 is arranged only on the inspection object side.

[0121] In the bilateral telecentric optical system, a light beam that is diffused thinly from the inspection object parallel to the optical axis passes through the front lens to form a parallel light beam, and a parallel light beam that passes through the aperture inserted behind the front lens passes through the rear lens to converge on each light receiving element of the light receiving element array 120.

[0122] like Figure 3 or Figure 4 As shown, in the case where the light receiving element array 120 is staggered in the sub-scanning direction, the greater the distance in the sub-scanning direction, the greater the memory capacity needs to be. If the memory capacity becomes larger, the cost will increase accordingly. In the present embodiment, by using a telecentric lens optical system, if the NA is set to about 0.03, then in the case of a lens with a focal length of 50mm, a conical light receiving solid angle connecting Φ=3mm and the object point on the principal plane of the lens is formed. Therefore, the shortest distance Ls of the light receiving element array 120 staggered in the sub-scanning direction only needs to be Ls>3mm. Therefore, if the circular outer periphery of a conventional lens is formed into a rectangular outer periphery by various processing or molding means, and as shown Figure 3 or Figure 4 By configuring the staggered arrangement of the light receiving element array 120 at a narrower interval, the light receiving solid angle can be satisfied and compactness can be achieved, and the memory capacity can be reduced. It should be noted that from the perspective of the amount of illumination light, the NA of the light receiving lens 11 is preferably about 0.001 to 0.05. Based on the above, the thickness of the light receiving lens 11 in the sub-scanning direction is determined by the solid angle specified by the NA of the telecentric optical system, so it can be shortened in the sub-scanning direction and become compact.

[0123] 10. Modification of the light receiving system

[0124] Next, use Figures 12A to 12G A modified example of the light receiving system is described. In the above embodiment, a configuration in which a plurality of light receiving lenses 11 are arranged in two rows in the sub-scanning direction is described. Figures 12A to 12G In the following, a configuration in which a plurality of light receiving lenses 11 are arranged in a row along the main scanning direction, specifically, a layout of a row of light receiving lenses 11 and a staggered arrangement of light receiving element arrays 120 will be described.

[0125] When two columns of reading lines L are formed by staggering the light receiving element array 120, when the light receiving lenses 11 are also staggered into two columns like the light receiving element array 120, in order to satisfy the NA required by the light receiving lens system, the interval in the sub-scanning direction of the light receiving element array 120 needs to be set to be larger than the width in the sub-scanning direction of the light receiving lens 11. Figures 12A to 12GAs shown in the figure, the width of the rectangular lens is set so that the light receiving lens 11 satisfies the NA required by the light receiving system. If the width of the rectangular lens is changed from two rows to one row, the interval in the sub-scanning direction of the light receiving element array 120 can be further reduced. That is, the influence of the speed variation in the sub-scanning direction can be further reduced, and the cost of the light receiving lens 11 can be reduced. The following describes a method of arranging a plurality of light receiving lenses 11 in one row.

[0126] exist Figures 12A to 12G In the embodiment, the plurality of light receiving lenses 11 have the same shape when observed from a direction perpendicular to the main scanning direction. Specifically, the shapes of the light receiving lenses 11 when observed from a Z direction perpendicular to the main scanning direction (X direction) and the sub-scanning direction (Y direction) are the same. It should be noted that "the same shape" includes substantially the same shape such as a reverse shape, and some differences in shape are included in "the same shape".

[0127] exist Fig. 12A In the embodiment, the shape of each light receiving lens 11 observed along the Z direction is a parallelogram. That is, the two end faces of each light receiving lens 11 in the main scanning direction are inclined relative to the sub-scanning direction. The inclination angles of the two end faces of each light receiving lens 11 in the main scanning direction are the same. Fig. 12A When a plurality of light receiving lenses 11 are arranged in the main scanning direction, the end faces of adjacent light receiving lenses 11 face both end faces of each light receiving lens 11, so that the ends of the adjacent light receiving lenses 11 in the main scanning direction are connected to each other.

[0128] exist Fig. 12B In the embodiment, rectangular cutouts are formed on both end faces of each light receiving lens 11 in the main scanning direction when viewed along the Z direction. Fig. 12B When a plurality of light receiving lenses 11 are arranged in the main scanning direction, a portion of the adjacent light receiving lenses 11 is fitted into the cutouts formed on the two end faces of each light receiving lens 11, thereby configuring the light receiving lenses 11 so that the ends of the adjacent light receiving lenses 11 in the main scanning direction are connected to each other.

[0129] exist Fig. 12C In the embodiment, the shape of each light receiving lens 11 observed along the Z direction is a trapezoidal shape. That is, the two end faces of each light receiving lens 11 in the main scanning direction are inclined relative to the sub-scanning direction. The shape of each light receiving lens 11 when observed along the Z direction is a reverse shape with respect to the shape of the light receiving lens 11 adjacent in the main scanning direction when observed along the Z direction, with the main scanning direction as the reference. Fig. 12CWhen a plurality of light receiving lenses 11 are arranged in the main scanning direction, the end faces of the adjacent light receiving lenses 11 are opposite to the two end faces of each light receiving lens 11, and the ends of the light receiving lenses 11 adjacent to each other in the main scanning direction are arranged in a state of being connected to each other. Thus, the plurality of light receiving lenses 11 are arranged in a state in which the adjacent light receiving lenses 11 are turned over and connected.

[0130] exist Fig.12D In the embodiment, curved (semicircular or semi-elliptical) cutouts are formed on both end faces of each light receiving lens 11 in the main scanning direction when viewed along the Z direction. Fig.12D When a plurality of light receiving lenses 11 are arranged in the main scanning direction, a portion of the adjacent light receiving lenses 11 is fitted into the cutouts formed on the two end faces of each light receiving lens 11, thereby configuring the light receiving lenses 11 so that the ends of the adjacent light receiving lenses 11 in the main scanning direction are connected to each other.

[0131] Next, Figure 12E to Figure 12G A modified example of is described below. Fig.12E yes Fig. 12C The modified example can minimize the occurrence of missing pixels in the aforementioned light receiving element array 120. Fig.12E In the embodiment, each light receiving element array 120 is arranged at a position closer to the long side than the center of the width direction of each light receiving lens 11 of the trapezoid. In addition, the length of each light receiving element array 120 in the main scanning direction is substantially the same as the length of each light receiving lens 11 in the trapezoid in the main scanning direction at the position where the light receiving element array 120 is arranged. Fig.12E The adjacent staggered light receiving element arrays 120 shown by the dotted lines overlap each other in the main scanning direction, and as described later, no Fig. 12C The missing portion of the output signal is shown in the staggered arrangement of the light receiving element array 120.

[0132] The above-mentioned light receiving lenses 11 are not limited to trapezoidal shapes, and any shape may be used as long as the light receiving lenses 11 are connected when they are reversed in the sub-scanning direction to form a light receiving lens array. Fig.12F as well as Figure 12G This example is shown in FIG. Fig.12F This is a case where a plurality of light receiving lenses 11 formed of rectangular cutout shapes are reversed and connected. Figure 12G This is a case where a plurality of light receiving lenses 11 having circular cutouts are reversed and connected. Figure 12E to Figure 12G In the embodiment, the plurality of light receiving lenses 11 are arranged in a state where the adjacent light receiving lenses 11 are reversed and connected. Generally, if the light receiving lenses 11 are arranged in a line in the sub-scanning direction, they can be reversed and connected. Fig.12F as well as Figure 12G also with Fig.12EThe trapezoidal shape of the reverse connection is similarly overlapped by the dotted line portion, and as described later, no signal missing portion is generated. It should be noted that, Figure 12G The light receiving lens 11 includes an edge portion 112 for ensuring rigidity and avoiding cracking.

[0133] like Figures 12A to 12G As shown, in the cross-sectional view in the optical axis direction of the light-receiving lens 11, the end of the lens is set to a cross-sectional shape such as a parallelogram shape, a trapezoidal shape, a rectangular shape or a curved shape (circle, ellipse) cutout shape, and the width in the sub-scanning direction that satisfies the NA of the light-receiving lens system is set, and connected in a row, thereby forming a lens array extending in a straight line in the main scanning direction. In addition, two rows of light-receiving element arrays 120 arranged in a staggered manner are set in the central part of the sub-scanning direction of the lens array. Specifically, a plurality of light-receiving element arrays 120 are arranged in the central part of the main scanning direction of each of the plurality of light-receiving lenses 11, and are alternately arranged in a staggered manner along the main scanning direction. Thus, a row of lens arrays can be used to allow light emitted from the inspection object to reach the two rows of staggered light-receiving element arrays 120.

[0134] like Fig. 12A As shown, a shielding portion 111 is provided between the ends of the light receiving lenses 11 adjacent to each other in the main scanning direction. The shielding portion 111 is formed in a thin plate shape. The shielding portion 111 extends from between the ends of each light receiving lens 11 toward the light receiving element (light receiving element array 120), and protrudes from the light receiving lens 11 toward the inspection object. In addition, the shielding portion 111 has a width that is at least greater than the width W1 of the light receiving lens 11 in the sub-scanning direction. Figure 12B to Figure 12G Although the shielding portion 111 is omitted in the figure, the shielding portion 111 may also be provided between the ends of each light receiving lens 11. Fig.12F and Figure 12G In the embodiment of the present invention, the shielding part 111 is a thin crank-shaped shielding plate or a corrugated shielding plate. In short, in the connecting part, it is sufficient to prevent light from leaking to the adjacent light receiving system.

[0135] like FIG. 12B to FIG. 12D As shown in FIG. 1 , a plurality of light sources 103 for illuminating the inspection object may be provided in a one-to-one correspondence with the plurality of light receiving element arrays 120. The plurality of light sources 103 may also be elongated shapes extending in a straight line along the main scanning direction. In this case, as shown in FIG. FIG. 12B to FIG. 12D As shown, the plurality of light sources 103 may be opposed to each light receiving element array 120 in the Z direction. Thus, the plurality of light sources 103 can be arranged in a staggered pattern, so that line-shaped light can be incident on each light receiving element array 120 efficiently.

[0136] The plurality of light sources 103 and the plurality of light receiving element arrays 120 have a plurality of lines of light intensity distribution of illumination light in the sub-scanning direction. Fig. 12A , Figure 12E to Figure 12G Although the light source 103 is omitted in the figure, a plurality of light sources 103 may be provided in a one-to-one correspondence with a plurality of light receiving element arrays 120. However, instead of arranging the plurality of light sources 103 in a staggered manner, line illumination having a light intensity distribution including two intensity peaks in the sub-scanning direction may be used so that the light receiving element arrays 120 of each reading line L have a peak of light intensity. In addition, since the intervals in the sub-scanning direction of the staggered light receiving element arrays 120 are narrow, line illumination having a single peak may also be used.

[0137] Fig.12H as well as Fig.12I is a schematic diagram for explaining the position of the optical axis 113 in the light receiving system. Fig.12E As an example, using Fig.12H as well as Fig.12I The position of the optical axis 113 in the light receiving system will be described. FIG. 12A to FIG. 12D , Fig.12F , Figure 12G In other structures, the position of the optical axis 113 can be set similarly.

[0138] exist Fig.12H In the embodiment, the optical axis 113 of the light guided to each light receiving element array 120 through each light receiving lens 11 passes through a position parallel to the sub scanning direction (Y direction) and away from the approximate center of each light receiving element array 120. Specifically, the optical axis 113 of each light receiving lens 11 passes through a position that is approximately equidistant from each light receiving element array 120 arranged in a staggered shape and approximately 1 / 2 of the length in the main scanning direction of each light receiving element array 120 arranged in a staggered shape. In this example, each optical axis 113 is arranged in a row along the main scanning direction (X direction), but the configuration is not limited to this.

[0139] exist Fig.12I In the embodiment, the optical axis 113 of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120 passes through the substantially central portion of each light receiving element array 120 arranged in a staggered manner. Therefore, each optical axis 113 is arranged along two columns of readout lines L, similarly to each light receiving element array 120, in a staggered manner. In this way, by making the optical axis 113 of each light receiving lens 11 consistent with each light receiving element array 120, aberration can be reduced.

[0140] Fig.13 The light intensity distribution on the light receiving surface of the light receiving element array 120 when the lens end is a parallelogram and the light intensity distribution of the light source 103 is flat is shown. Fig.13 It shows that in the Fig. 12AAn example of light intensity distribution on the light receiving surface of each light receiving element array 120 in the case of the configuration of . For convenience of explanation, the lens array composed of a plurality of light receiving lenses 11 is a lens array composed of three light receiving lenses 11 .

[0141] exist Fig.13 The left figure shows the light intensity on each light receiving element array 120 of the entire lens array, and the two figures on the right show enlarged views. Fig.14 The details of the light intensity distribution near the connecting portion between adjacent light receiving lenses 11 are shown in FIG. In this embodiment, in two adjacent light receiving element arrays 120 arranged in a staggered manner, the signal missing pixels of one light receiving element array 120 are interpolated with the pixels of the other light receiving element array 120. Fig.14 In FIG. 1 , a method of interpolating the signal of a pixel with missing signal is shown by arrow marks.

[0142] exist Fig.14 The portion 121 surrounded by the dotted line in the figure is a light-receiving element located at the connection portion between the adjacent light-receiving lenses 11. Since light cannot reach the light-receiving element, a signal missing portion is generated. Therefore, in the present embodiment, in the adjacent light-receiving element array 120 arranged in a staggered manner, the output signal of the light-receiving element (the portion 122 surrounded by the solid line) that is opposite to the light-receiving element of the portion 121 in the sub-scanning direction is used to compensate for the signal missing portion. In this way, a pixel interpolation portion (refer to FIG. 1 ) is formed along the sub-scanning direction at the connection portion between the adjacent light-receiving lenses 11. Fig.13 ). The signal missing part may be corrected in advance using a reference medium for inspection. The reference medium may be a white image or a grid pattern for vignetting correction.

[0143] Fig.13 The width of the light receiving lens 11 in the sub-scanning direction is 5 mm. Therefore, when the light receiving lens 11 is set to be staggered in two rows, the minimum spacing of the staggered light receiving element array 120 needs to be more than 5 mm. However, if a single row of lens arrays is used as described above, the spacing becomes about 1 / 2 (less than 3.0 mm). In addition, if the vignetting effect correction is performed while taking into account the dynamic range of the light receiving element array 120, the spacing can be further reduced. That is, while the spacing in the sub-scanning direction of the staggered light receiving element array 120 is narrowed, the number of light receiving lenses 11 can be halved. Therefore, it is not easily affected by the change of the conveying speed in the sub-scanning direction, and the advantage of cost reduction is achieved.

[0144] exist Fig.13The shielding portion 111 in the image is provided with a shielding plate with a thickness of t=0.2 mm. If t=0.2 mm, there is no problem in terms of strength. In addition, the lens system is a bilateral telecentric system. Of course, it can also be an object-side telecentric system.

[0145] As a specific image processing method or processing of the image processing system, for output signals from two light receiving elements separated in the sub-scanning direction at the same position in the main scanning direction, when the output signal from one light receiving element (a portion 121 surrounded by a dotted line) is lower than the output signal from the other light receiving element (a portion 122 surrounded by a solid line) and the output signal from one light receiving element does not reach a threshold value, the output signal from the other light receiving element is interpolated. In addition, the interpolated output signal is synthesized with the output signal from the light receiving element at another position in the main scanning direction relative to the one light receiving element to obtain an output signal of one column corresponding to the read line L.

[0146] It should be noted that in Fig.14 The light receiving elements of the portion 123 surrounded by the double-dashed line in the figure are opposite to each other in the sub-scanning direction, but are offset from the connecting portion between the adjacent light receiving lenses 11, so that they overlap each other. For such overlapping portions, since there is no loss of output signals from the light receiving elements, interpolation is not required.

[0147] exist Fig.12E The example shows the light intensity of the light receiving area. Fig.15 The reason why no signal missing portion is generated is briefly shown in FIG. Fig.15 Shown with Fig.14 Similarly, the light intensity distribution at the end of the staggered arrangement of the light receiving element array 120. Fig.15 The light receiving elements of the portion 124 surrounded by the double-dashed line in FIG. 1 are opposed to each other in the sub-scanning direction, but are offset from the connecting portion between the adjacent light receiving lenses 11, so that they overlap each other. Fig.15 As shown, by arranging the light receiving element array 120 on the long side in the width direction of the trapezoidal light receiving lens 11, the required signal of one column of readout lines L of the staggered light receiving element array 120 can be obtained except for the signal missing portion in the light receiving part.

[0148] As a specific image processing method or processing of an image processing system, with respect to output signals from two light receiving elements (portion 124 surrounded by a dotted line) separated in a sub-scanning direction at the same position in a main scanning direction, one of the output signals of the portion where the output signal of one light receiving element overlaps with the output signal of the other light receiving element is selected, and correction is performed based on the ratio of the output signal of one side that has been pre-corrected using a reference medium to the output signal of the other side, and the signal of one side is synthesized with the signal of the other side, thereby obtaining an output signal of a column corresponding to the reading line L.

[0149] Description of Reference Numerals

[0150] 10: Light source;

[0151] 11: light receiving lens;

[0152] 12: light receiving part;

[0153] 20: focal plane;

[0154] 103: light source;

[0155] 104: focusing lens;

[0156] 105: cylindrical lens;

[0157] 110: lens holder;

[0158] 111: shielding part;

[0159] 120: light receiving element array;

[0160] 131: red LD;

[0161] 132: green LD;

[0162] 133: blue LD;

[0163] 134: Light source substrate;

[0164] 135: Radiator.

Claims

1. An optical line sensor that reads an inspection object conveyed in a sub-scanning direction at a reading line extending in a main scanning direction, characterized in that: The optical line sensor comprises: a plurality of light receiving lenses, which are arranged in plurality along the main scanning direction; and A plurality of light receiving elements are arranged in a line along the main scanning direction to receive the light transmitted through the plurality of light receiving lenses. The plurality of light receiving elements form at least two columns of the reading lines, The light receiving lens forms a telecentric optical system, and the width in the sub-scanning direction is smaller than the width in the main scanning direction.

2. The optical line sensor according to claim 1, characterized in that The light receiving lens is formed in a rectangular shape when viewed from a direction perpendicular to the main scanning direction and the sub-scanning direction.

3. The optical line sensor according to claim 1, characterized in that The plurality of light receiving lenses are arranged to be separated from each other by a distance equal to or smaller than a width of the light receiving lens in the main scanning direction.

4. The optical line sensor according to claim 1, characterized in that The width of the light receiving lens in the sub scanning direction is set so that the NA of the light receiving lens satisfies 0.001<NA<0.

05.

5. The optical line sensor according to claim 1, characterized in that The plurality of light receiving elements are arranged in an array of two or more rows to form a plurality of light receiving element arrays. The plurality of light receiving lenses are arranged in a number corresponding to the plurality of light receiving element arrays, and the optical axis of the light transmitted through each light receiving lens and guided to each light receiving element array passes through a substantially central portion of each light receiving element array.

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

7. The optical line sensor according to claim 5 or 6, characterized in that The plurality of light receiving element arrays are shorter than the plurality of reading lines respectively arranged on the two columns of reading lines, and the light receiving element array arranged on one reading line and the light receiving element array arranged on the other reading line are alternately arranged in a staggered manner along the main scanning direction.

8. The optical line sensor according to claim 1, characterized in that Each of the plurality of light receiving lenses includes a distributed index lens that forms an inverted image, an achromatic lens, or an apochromatic lens.

9. The optical line sensor according to claim 8, characterized in that The refractive index distribution lens is made of glass or resin. Among the lens parameters of the lens, the on-axis 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 50mm≤f≤150mm.

10. The optical line sensor according to claim 8, characterized in that The multiple light-receiving lenses are respectively composed of achromatic lenses or apochromatic lenses combined with multiple lenses, and are a lens system in which only convex lenses are combined as the multiple lenses, or a lens system in which convex lenses and concave lenses are combined as the multiple lenses. In addition, the focal length f of the multiple lenses is 25mm≤f≤250mm, and the aperture Φ of the multiple lenses is 2mm≤Φ≤50mm.

11. The optical line sensor according to claim 1, characterized in that The optical line sensor further includes a plurality of light sources for irradiating light to the inspection object. The multiple light sources are arranged parallel to the reading line, and the optical axes of the multiple light sources are arranged at any position of an imaginary plane that connects the intersection of the optical axes of the light guided to the multiple light receiving elements through the multiple light receiving lenses and intersects with the optical axes of the light guided to the multiple light receiving elements through the multiple light receiving lenses. In addition, a light source is arranged in the approximate center between adjacent light receiving lenses.

12. The optical line sensor according to claim 11, characterized in that The plurality of light sources include light sources with a plurality of different wavelengths. The light sources with the plurality of different wavelengths are regarded as a unit, and a plurality of the light sources of the unit are arranged in a main scanning direction.

13. The optical line sensor according to claim 11, characterized in that The optical line sensor further includes a condenser lens for condensing the light beams from the plurality of light sources.

14. The optical line sensor according to claim 13, characterized in that The condenser lens includes a first condenser lens whose optical power in the main scanning direction is greater than that in the sub-scanning direction and a second condenser lens whose optical power in the sub-scanning direction is greater than that in the main scanning direction.

15. The optical line sensor according to claim 13, characterized in that The condenser lens is a lens body, and the optical focal length of the lens body in the main scanning direction is greater than the optical focal length in the sub-scanning direction.

16. The optical line sensor according to claim 14, characterized in that The condenser lens can adjust the optical power in the main scanning direction through the first condenser lens and the second condenser lens.

17. The optical line sensor according to claim 13, characterized in that The condenser lens is a cylindrical lens or a Fresnel lens.

18. The optical line sensor according to claim 14, characterized in that The first focusing lens is a cylindrical lens or a prism array, The second condensing lens is a Fresnel lens or a cylindrical lens.

19. The optical line sensor according to claim 11, characterized in that The plurality of light sources include white LEDs.

20. The optical line sensor according to claim 11, characterized in that The plurality of light sources include a red LED, a green LED, and a blue LED.

21. The optical line sensor according to claim 11, characterized in that The plurality of light sources include laser diodes.

22. The optical line sensor according to claim 11, characterized in that The optical line sensor further comprises: a light source substrate on which the plurality of light sources are mounted; and A heat sink is mounted on the light source substrate.

23. The optical line sensor according to claim 1, characterized in that The plurality of light receiving lenses are arranged in a row along the main scanning direction. The plurality of light receiving lenses are arranged in a state where end portions of the light receiving lenses adjacent to each other in the main scanning direction are connected to each other.

24. The optical line sensor according to claim 23, characterized in that The plurality of light receiving lenses have the same shape when viewed from a direction perpendicular to the main scanning direction.

25. The optical line sensor according to claim 24, characterized in that The plurality of light receiving lenses are arranged in a state where adjacent light receiving lenses are reversed and connected.

26. The optical line sensor according to claim 23 or 24, characterized in that The plurality of light receiving elements are arranged in an array of two or more rows to form a plurality of light receiving element arrays. The plurality of light receiving element arrays are arranged at the center of each of the plurality of light receiving lenses in the main scanning direction, and are alternately arranged in a staggered pattern along the main scanning direction.

27. The optical line sensor according to claim 26, characterized in that The optical axes of the plurality of light receiving lenses extend through positions which are substantially equidistant from the light receiving element arrays arranged in a staggered pattern and which extend through positions which are substantially 1 / 2 of the length of the light receiving element arrays arranged in a staggered pattern in the main scanning direction.

28. The optical line sensor according to claim 26, characterized in that The optical axes of the plurality of light receiving lenses penetrate substantially the center of each light receiving element array arranged in a staggered manner.

29. The optical line sensor according to claim 23 or 24, characterized in that The plurality of light receiving elements are arranged in an array of two or more rows to form a plurality of light receiving element arrays. The optical line sensor further includes a plurality of light sources that illuminate the inspection object and correspond one-to-one to the plurality of light receiving element arrays.

30. The optical line sensor according to claim 29, characterized in that The plurality of light sources have a plurality of lines of light intensity distribution of illumination light in the sub-scanning direction corresponding to the plurality of light receiving element arrays.

31. The optical line sensor according to claim 23 or 24, characterized in that The optical line sensor further includes a shielding portion extending from between ends of the light receiving lenses adjacent to each other in the main scanning direction toward the plurality of light receiving elements and having a width at least equal to or greater than a width of the light receiving lenses in the sub scanning direction.

32. The optical line sensor according to claim 31, characterized in that The shielding portion protrudes from the light receiving lens toward the inspection object.

33. An image processing method using the optical line sensor according to claim 26, wherein: For output signals from two light receiving elements separated in the sub-scanning direction at the same position in the main scanning direction, one of the output signals of the part where the output signal of one of the light receiving elements overlaps with the output signal of the other light receiving element is selected, and correction is performed based on the ratio of the signal of one of the output signals pre-corrected by a reference medium to the output signal of the other, and the signal of one of the output signals is synthesized with the signal of the other to thereby serve as a column of output signals corresponding to the reading line.

34. An image processing method using the optical line sensor according to claim 26, wherein: For output signals from two light receiving elements separated in the sub-scanning direction at the same position in the main scanning direction, when the output signal from one of the light receiving elements is lower than the output signal from the other light receiving element and the output signal from one of the light receiving elements does not reach a threshold value, the output signal from the other light receiving element is interpolated, and the interpolated output signal is synthesized with the output signal from the light receiving element at other positions in the main scanning direction relative to the one light receiving element, thereby serving as a column of output signals corresponding to the read line.

35. An image processing system using the optical line sensor according to claim 26, wherein: For output signals from two light receiving elements separated in the sub-scanning direction at the same position in the main scanning direction, one of the output signals of the part where the output signal of one of the light receiving elements overlaps with the output signal of the other light receiving element is selected, and correction is performed based on the ratio of the signal of one of the output signals pre-corrected by a reference medium to the output signal of the other, and the signal of one of the output signals is synthesized with the signal of the other to thereby serve as a column of output signals corresponding to the reading line.

36. An image processing system using the optical line sensor according to claim 26, wherein: For output signals from two light receiving elements separated in the sub-scanning direction at the same position in the main scanning direction, when the output signal from one of the light receiving elements is lower than the output signal from the other light receiving element and the output signal from one of the light receiving elements does not reach a threshold value, the output signal from the other light receiving element is interpolated, and the interpolated output signal is synthesized with the output signal from the light receiving element at other positions in the main scanning direction relative to the one light receiving element, thereby serving as a column of output signals corresponding to the read line.

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