Camera

Abstract

To realize a camera which has a large depth of field and is made more compact.SOLUTION: A camera includes a light reception lens 11 and a light reception element (a light reception array 120) for receiving light which has passed through the light reception lens 11. The camera causes the light reception lens 11 to form light from a target object illuminated in a reading position into an image on the light reception element. When the distance between the light reception lens 11 and the reading position is W and the width of the field of view of the light reception lens 11 is X, the relation of W<X is satisfied, W is larger than 30 mm, and the depth of field is at least 4 mm.SELECTED DRAWING: Figure 16

Description

[Technical field]

[0001] The present invention relates to a camera such as an optical line sensor that detects scratches and defects on the surface of thin objects such as printed matter and films, as well as scratches and defects inside transparent films. [Background technology]

[0002] Contact type optical sensors (hereafter referred to as CIS) that have been used in inspection machines for determining the authenticity of banknotes, etc., and in flatbed scanners such as commercial copy machines and home printer scanners, have been considered for application to so-called surface inspection machines for checking the quality of printed matter, inspecting the surfaces of thin and wide film products in the manufacturing process, and inspecting labels attached to various types of beverage containers, food containers, cans, etc., and some of these have already been commercialized.

[0003] However, the working distance of CIS using SELFOC lenses ("SELFOC" is a registered trademark, hereinafter the same) is still short, and a CIS with a long working distance is desired in order to avoid contact when used in processes. In addition, while a relatively shallow depth of field was sufficient for the inspection of paper sheets such as banknotes, a CIS with a deep depth of field is also strongly desired in the manufacturing process of the above-mentioned objects because of the large fluctuations in the optical axis direction of the objects.

[0004] A typical CIS with a deep depth of field is a telecentric optical system using a mirror optical system, as shown in Patent Documents 1 to 5. From the above patent documents, it can be seen that the optical system is very complicated. It is very difficult to manufacture the optical system and use it as a product. That is, during manufacturing, the process becomes complicated, and manufacturing stability and cost increase become problems. Even after commercialization, there remain problems such as deviation of the optical axis due to the complex optical system caused by environmental changes and changes over time, and the performance is more likely to deteriorate than in conventional CIS with a simple structure.

[0005] Therefore, it is conceivable to improve the working distance and depth of field by using a refractive lens using glass or resin instead of the telecentric reflective optical system. As shown in Patent Document 6 and Patent Document 7, a certain degree of solution has been proposed for the refractive optical system. For example, Patent Document 6 attempts to realize an optical system with a deep depth of field by arranging one telecentric refractive optical system at a distance from a line sensor arranged in a staggered pattern, and arranging the lenses of the refractive optical system at a distance to form an array. In addition, Patent Document 7 considers a method of preventing crosstalk between lenses by providing a partition plate between the separated lenses. In Patent Document 6 and Patent Document 7, the depth of field can be improved and crosstalk between lenses can be prevented, but a normal telecentric refractive optical system is large and it is difficult to make it compact. In addition, the partition plate shown in Patent Document 7 causes missing pixels during reading, resulting in incomplete reading. Furthermore, no solution is shown for the shading that a single lens has in principle when the lenses are spaced apart. There is no mention of a method for suppressing so-called ripples in the reading line direction. Moreover, the refractive optical system has not been realized to date.

[0006] Furthermore, inspection machines using camera lenses, such as line cameras, which are different from the above-mentioned method, are large in size, and many of them are required to handle wide objects at manufacturing sites. As a result, the entire device becomes very large and the cost is enormous, making it difficult to install them at each process in a factory.

[0007] In order to solve the above problems, what is needed is a camera that is small and inexpensive enough to be introduced into each process in a factory, that uses a new refractive lens with a long working distance and a deep depth of field, and that is composed of an illumination system that uses a new method of suppressing ripples, which are optical unevenness on the light-receiving sensor caused by shading of each lens. [Prior art documents] [Patent documents]

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, an object of the present invention is to realize a camera with a deep depth of field and a compact size.

Means for Solving the Problems

[0010] The camera according to the present invention includes a light-receiving lens and a light-receiving element that receives light transmitted through the light-receiving lens, and is a camera that forms an image of light from an object illuminated at a reading position on the light-receiving element by the light-receiving lens. When the distance between the light-receiving lens and the reading position is W and the width of the field of view of the light-receiving lens is X, W < X is satisfied, and W > 30 mm, and the depth of field is 4 mm or more.

Effects of the Invention

[0011] According to the present invention, a camera with a deep depth of field can be realized.

Brief Description of the Drawings

[0012] [Figure 1]FIG. 1 is a cross-sectional view of a typical CIS. [Diagram 2] FIG. 2 is an exploded perspective view of a line-shaped illumination optical system for a CIS. [Diagram 3] FIG. 13 is a schematic diagram of a light receiving system in which the fields of view of the light receiving lenses do not overlap when each light receiving lens is arranged to function as a monocular lens. [Figure 4] 13 is a schematic diagram showing another example of a light receiving system in which a plurality of light receiving element arrays are arranged. FIG. [Diagram 5] FIG. 13 is a schematic diagram showing yet another example of a light receiving system in which a plurality of light receiving element arrays are arranged. [Figure 6] 1 is a graph showing the relationship between NA and the diffraction limit for each wavelength. [Figure 7A] 1 is a graph showing the relationship between the effective diameter of SELFOC lens A and the diameter of the circle of confusion. [Figure 7B] 1 is a graph showing the relationship between the effective diameter of SELFOC lens B and the diameter of the circle of confusion. [Figure 7C] 1 is a graph showing the relationship between the effective diameter of SELFOC lens C and the diameter of the circle of confusion. [Figure 8A] 1 is a graph showing the relationship between the effective diameter of the rod lens A and the diameter of the circle of confusion. [Figure 8B] 13 is a graph showing the relationship between the effective diameter of rod lens B and the diameter of the circle of confusion. [Figure 8C] 1 is a graph showing the relationship between the effective diameter of the rod lens C and the diameter of the circle of confusion. [Figure 8D] 1 is a graph showing the relationship between the effective diameter of a rod lens D and the diameter of the circle of confusion. [Figure 9A] FIG. 1 is a schematic diagram showing an example of an arrangement method when RGB-LEDs or RGB-LDs (laser diodes; semiconductor lasers) are used as light sources. [Figure 9B] 11 is a side view showing a specific example of an arrangement method when an LD is used as a light source. [Figure 10A] FIG. 13 is a schematic diagram showing the positional relationship between a light source and a light-receiving lens when the light-receiving element array has two rows. [Figure 10B]1 is a diagram showing the relationship between the light amount distribution of a light source (on an inspection surface) in the main scanning direction, the light amount distribution on a light receiving element surface, and the shading of a light receiving lens. [Figure 10C] This is a graph of the light receiving system MTF for each lens diameter (√A=0.077). [Figure 10D] This is a graph of the light receiving system MTF for each lens diameter (√A=0.154). [Figure 10E] 13 is a graph showing the MTF of a light receiving optical system having a refractive index distribution constant √A of √A=0.1027. [Figure 11] 11 is a graph showing MTF characteristics when defocused. [Figure 12A] FIG. 13 is a schematic diagram showing a modified example of the light receiving system. [Figure 12B] FIG. 13 is a schematic diagram showing a modified example of the light receiving system. [Figure 12C] FIG. 13 is a schematic diagram showing a modified example of the light receiving system. [Figure 12D] FIG. 13 is a schematic diagram showing a modified example of the light receiving system. [Figure 12E] FIG. 13 is a schematic diagram showing a modified example of the light receiving system. [Figure 12F] FIG. 13 is a schematic diagram showing a modified example of the light receiving system. [Figure 12G] FIG. 13 is a schematic diagram showing a modified example of the light receiving system. [Figure 13] 13 is a diagram showing the light intensity distribution on the light receiving surface of a light receiving element array when the light intensity distribution of the light source is flat when the lens end is a parallelogram. FIG. [Figure 14] 13 is a diagram showing details of the light intensity distribution in the vicinity of a connection portion between adjacent light receiving lenses. FIG. [Figure 15] In the example of FIG. 12E, the light intensity of the light receiving areas is shown, and the reason why no signal dropout occurs is illustrated diagrammatically. [Figure 16] 1 is a schematic diagram for explaining a working distance and an imaging range (field of view) of a light receiving lens. [Figure 17] 1 is a schematic cross-sectional view showing an overall configuration of a reading device according to an embodiment of the present invention. [Figure 18] FIG. 11 is a schematic cross-sectional view showing a first modified example of a reading device. [Figure 19] FIG. 11 is a schematic cross-sectional view showing a second modified example of the reading device. [Figure 20] FIG. 11 is a schematic cross-sectional view showing a third modified example of the reading device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 1. Overall configuration of optical line sensor (camera) A typical CIS is shown in FIG. 1, and a linear illumination optical system for a CIS is similarly shown in FIG. 2. FIG. 1 shows a cross-sectional view of the CIS near the center in the longitudinal direction. Meanwhile, FIG. 2 is an exploded perspective view. The X direction is the main scanning direction, and the Y direction is the sub-scanning direction. The Z direction is perpendicular to the X and Y directions. The linear light source unit 10 is an illumination optical system having a light amount distribution that is elongated in the main scanning direction.

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

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

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

[0017] In the example shown in Fig. 1 and Fig. 2, the light source unit 10 includes a transparent light guide 101 extending along a longitudinal direction L, a light source 103 provided near one end face in the longitudinal direction L, and a cover member 102 for holding each side face of the light guide 101. The light emitted from the light source 103 enters the light guide 101, and while propagating through the light guide 101, is appropriately reflected by the light diffusion pattern P, and is emitted from the light emission surface in the direction of the arrow, becoming a line-shaped illumination light to illuminate the object. The depth of field of such a CIS is shallow, and if the object has thickness, it is difficult to inspect the entire thickness direction, and since the working distance is narrow, the object is often contacted and the inspection itself is not performed.

[0018] In the above-mentioned CIS, for example, a SELFOC (manufactured by Nippon Sheet Glass Co., Ltd.) lens array is used as the light receiving lens 11. The SELFOC lens array is an erect life-size lens array. In this lens array, cylindrical SELFOC lenses are stacked in a bale to form a multi-lens. The advantage of a multi-lens is that it is possible to make the so-called brightness of the lens brighter than that of a single lens. In other words, the F-number of a multi-lens made by arranging multiple single lenses is smaller than the F-number of a single lens. This is because the effective F-number becomes smaller at the point where the focal position of one lens at any position coincides with the focal positions of the lenses around the lens. In other words, in an erect lens system, the numerical aperture (hereinafter referred to as NA) is larger in an array than in a single lens. This property is the main reason why a SELFOC lens array is used in a CIS.

[0019] The advantages of the CIS as described above are disadvantageous in terms of the depth of field and the depth of focus. As with a monocular lens, the larger the numerical aperture, the shallower the depth of field. For example, it is well known that in a microscope objective lens, the greater the magnification, i.e., the larger the NA, the shallower the depth of field. Also, in a camera lens, the difference in the depth of field between a distant view and a close view is clearly shown, and the aperture is adjusted to ensure the depth of field. That is, the NA is changed to obtain the desired depth of field. In addition, an erect multi-lens lens, such as a SELFOC lens, has a structure in which the optical axes of each lens are different and intersect, so that the image is more likely to become blurred when the object changes in the optical axis direction than a monocular lens. The above is a major disadvantage of the multi-lens SELFOC lens array of the bale-stacking method. Therefore, as a result of examining how it is possible to deepen the depth of field of a compact optical line sensor, the obtained examples are described below. In the following embodiment, the light receiving lens 11 constitutes a telecentric optical system.

[0020] 2. Example of light receiving system The first method is to make the optical line sensor into an array structure that can be regarded as a single lens, as shown in Fig. 3. Fig. 3 is a schematic diagram of a light receiving system in which the fields of view of the light receiving lenses 11 do not overlap. In Fig. 3, the light receiving lenses 11 are arranged at intervals in the main scanning direction (X direction) and also at intervals in the sub-scanning direction (Y direction) so that the fields of view of the light receiving lenses 11 do not overlap, so that the light receiving lenses 11 are arranged in a staggered pattern.

[0021] That is, instead of the bale-stacking method, a plurality of light receiving lenses 11 are arranged along the main scanning direction (X direction) at a distance from each other. A plurality of light receiving lenses 11 arranged along the main scanning direction (X direction) are integrally held by a lens holder 110. A light receiving element array 120 is arranged at a position facing each light receiving lens 11 in the Z direction, the light receiving element array 120 being configured by arranging a plurality of light receiving elements (not shown) in a line along the main scanning direction (X direction). That is, a single light receiving element array 120 is configured by arranging a plurality of light receiving elements in an array along the main scanning direction (X direction). Each light receiving element receives light that has passed through each light receiving lens 11.

[0022] In this example, a light receiving element array 120 is arranged in correspondence with each light receiving lens 11. As a result, each light receiving element array 120 made of a short sensor is 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 one reading line L, and in the example of FIG. 3, two reading lines L are formed. The lens holder 110 is not limited to a configuration in which it is provided in correspondence with each reading line L, and may be configured to integrally hold a plurality of light receiving lenses 11 corresponding to each reading line L with one lens holder.

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

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

[0025] The multiple light receiving lenses 11 are arranged at intervals of less than the width W2 of the light receiving lenses in the main scanning direction. That is, it is preferable that the multiple light receiving lenses 11 are arranged at intervals of less than the field of view dimension (within the field of view range) of the light receiving lenses 11 in the main scanning direction. As shown in the example of FIG. 3, the fields of view of the light receiving lenses 11 may be overlapped in the sub-scanning direction. In this case, for the light receiving elements in the overlapping portion of the fields of view of the multiple light receiving lenses 11, the pixel output from the light receiving elements may be subtracted. For example, the image of one light receiving lens 11 (the amount of light received that has passed through one light receiving lens 11) may be excluded from the data output from the light receiving elements, or the pixel output from the light receiving elements may be set to approximately half the output value when the images are synthesized. By using multiple light receiving element rows (light receiving element array 120), the occurrence of pixel missing can be prevented more reliably than in the case of a single line of light receiving element rows.

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

[0027] The multiple light receiving lenses 11 corresponding to one light receiving element array 120 are adjacent to each other in the main scanning direction. However, the multiple light receiving lenses 11 corresponding to one light receiving element array 120 may be spaced apart from each other, in which case they may be spaced apart by less than the width W2 in the main scanning direction of the light receiving lenses 11. A light blocking member may be provided between each of the light receiving lenses 11.

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

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

[0030] 3.Long focal length of receiving lens Next, we will discuss the long focal length of the receiving lens. Conventional SELFOC lenses have placed emphasis on making the CIS compact and reducing costs, and lenses with shorter conjugate lengths have been required. However, this trend has contributed to reducing the allowable depth of field. Moreover, the lens diameter is becoming smaller and smaller. When making the receiving lens longer focal length, the NA becomes extremely small if a conventional receiving lens is used. Therefore, the effect of diffraction becomes greater, and the blur due to the diffraction limit becomes the dominant factor in the deterioration of optical resolution, rather than the blur due to the geometric optical aberration of the receiving lens itself. Conventional CIS has a large NA, so it was possible to ignore the blur of the image due to the diffraction limit. However, in order to increase the working distance, it is necessary to extend the focal length of the receiving lens, which means that the NA becomes smaller. Therefore, with conventional lens diameters, the effect of diffraction increases as the focal length increases. In this embodiment, a method is proposed in which the lens diameter is increased to lengthen the working distance and prevent degradation of the optical resolution even when image blurring due to the diffraction limit is reduced.

[0031] Abbe's diffraction limit d is inversely proportional to the numerical aperture NA. Since the optical system is in air, the following formula 1 holds true using the wavelength λ in air. d=λ / NA (Equation 1) The relationship between the NA and the diffraction limit for each wavelength is shown in Figure 6. For light-receiving lens 11 with the same lens parameters, shortening the so-called pitch of light-receiving lens 11 itself extends the focal length and reduces the effects of aberration.

[0032] From the above, it is clear that in order to make the receiving lens 11 have a long focal length, the lens diameter must be made larger. If the NA is kept the same, the effects of diffraction can be made equivalent to that of a receiving lens 11 with a short focal length. However, increasing the lens diameter increases the geometric optical aberration. Therefore, for receiving lenses 11 with different lens parameters, it is necessary to consider the minimum circle of confusion diameter when the lens diameter is increased. The wavelength λ was set to λ = 630 nm, which is the largest diffraction limit diameter.

[0033] As a result of investigations by the inventors of the present application, it was found that it is sufficient to consider the relationship of the minimum circle of confusion to each focal length of a certain light receiving lens 11. For example, a case where the focal length f is 50 mm is shown in Figs. 7A to 7C. Here, when three types of SELFOC lenses (SELFOC lens A, SELFOC lens B, and SELFOC lens C) are used as the light receiving lens 11, Fig. 7A shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens A, Fig. 7B shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens B, and Fig. 7C shows the relationship between the effective diameter and the circle of confusion diameter of SELFOC lens C. In Figs. 7A to 7C, the solid line shows the total circle of confusion, the dashed line shows the circle of confusion due to diffraction, and the dashed-dotted line shows the circle of confusion due to geometrical optics.

[0034] 6 and 7A show the relationship between the minimum circle of confusion and the diffraction limit, i.e., the optical resolution for a certain lens diameter and focal length. Therefore, in the case of the light receiving lens 11 shown in Fig. 7A, the larger the effective diameter Φ, the smaller the circle of confusion diameter becomes, and it is sufficient for the effective diameter Φ to be 1.0 mm ≦ Φ ≦ 3.0 mm.

[0035] On the other hand, according to Figs. 6 and 7B, the geometrical optical circle of confusion is large and the degree of dependence on diffraction is small, so the circle of confusion diameter is smallest when Φ=1.0 mm. Moreover, even when Φ=1.0 mm, the circle of confusion diameter is nearly twice as large as that of the light receiving lens 11 shown in Fig. 7A. The light receiving lens 11 shown in Fig. 7A is a SELFOC lens with smaller aberration and larger effective diameter than the light receiving lens 11 shown in Fig. 7B, and it is clear that the light receiving lens 11 shown in Fig. 7A should be selected. Furthermore, the light receiving lens 11 in Fig. 7A, which has the same focal length, can have an NA at least three times larger than that of the light receiving lens 11 in Fig. 7B, i.e., the amount of light received is nine times or more, and therefore the output of the light receiving element is also nine times or more. Accordingly, the shot noise dependent on the amount of light received by the light receiving element is also reduced to one-third, so the light receiving lens 11 shown in Fig. 7A is preferable from the viewpoint of noise suppression. In addition, it can also be said that, if the same amount of noise is allowed, the light receiving lens 11 in FIG. 7A can improve the scanning speed by nine times compared to the light receiving lens 11 in FIG. 7B.

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

[0037] Next, the parameters of SELFOC lenses A to C shown in Figures 7A to 7C are shown in Table 1 below. The most important parameter in Table 1 is the refractive index distribution constant. The light-receiving lens 11 with least aberration when the effective diameter is enlarged and the focal length is extended is SELFOC lens A, which has the smallest refractive index distribution constant, and the light-receiving lens 11 with the next least aberration is SELFOC lens C. It goes without saying that to aim for high-resolution, high-speed inspection, a light-receiving lens 11 with a large effective diameter, brightness, and little aberration is preferable. [Table 1]

[0038] Furthermore, when four types of plastic rod lenses (plastic refractive index distribution type lenses) are used as the light receiving lens 11, FIG. 8A shows the relationship between the effective diameter and the diameter of the circle of confusion of rod lens A, FIG. 8B shows the relationship between the effective diameter and the diameter of the circle of confusion of rod lens B, FIG. 8C shows the relationship between the effective diameter and the diameter of the circle of confusion of rod lens C, and FIG. 8D shows the relationship between the effective diameter and the diameter of the circle of confusion of rod lens D. In FIG. 8A to FIG. 8D, the solid line shows the total circle of confusion, the broken line shows the circle of confusion due to diffraction, and the dashed line shows the circle of confusion due to geometrical optics. In addition, the parameters of rod lenses A to D shown in FIG. 8A to FIG. 8D are shown in Table 2 below. It can be seen that the plastic rod lenses 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. [Table 2]

[0039] From the above, it can be seen that the refractive index distribution constant is the dominant factor of aberration. In an ideal refractive index distribution lens, the more gradually the refractive index changes, the less the aberration. This is similar to how a sudden change in angle causes aberration even in a normal spherical lens. A sudden change in angle means an increase in the high-order nonlinear effect when Snell'Law is expanded into a polynomial. In other words, the aberration increases because the deviation from paraxial optics increases. The present inventors have found that in order to achieve a pixel resolution of 400 dpi or more when the focal length or working distance is approximately 50 mm or more and the effective diameter Φ is approximately Φ≧1.0 mm, it is preferable to set the refractive index distribution constant to 0.12 or less.

[0040] 4. Modifications of the light receiving lens The light receiving lens 11 in the present invention is not limited to gradient index lenses such as SELFOC lenses and plastic rod lenses, but may be other lenses, for example, achromats, apochromats, etc., that have the same aberrations due to nonlinear effects as the gradient index lenses, i.e., have the same spherical aberration, coma aberration, and astigmatism, or a telecentric refractive optical system may be used in place of gradient index lenses such as SELFOC lenses and plastic rod lenses that have the same aberrations due to nonlinear effects and diffraction limits as the gradient index lenses, with similar arrangement and dimensions (aperture). This also applies to the light receiving lens 11 that forms an inverted image, which will be described later.

[0041] The optical system described above is a case where the erect lens is the center, but it may be an inverted optical system when the fields of view do not overlap. That is, a configuration in which multiple light receiving lenses 11 form an inverted image may be used. If the lens array is a two-row type, an inverted optical system can also be used. In the case of an inverted optical system, since the image is inverted symmetrical about the optical axis, the inverted image may be converted into an erect image by image processing when synthesizing the images. That is, the inverted images of the multiple light receiving lenses 11 may be inverted and converted into an erect image, and then image synthesis processing may be performed. In addition, during the operation, the necessity or non-necessity of the overlapping parts may be determined and corrected from the correction algorithm, and the image may be converted into an erect image based on the determined relationship between pixels. Alternatively, in an inspection in which an image is not constructed, since it is only necessary to detect scratches or defects, image synthesis and image processing are not necessary, and the detection parts on the inspection surface may overlap. In the case of overlapping, the position is corrected in advance using a correction chart.

[0042] Furthermore, in the case of an inverted refractive optical system, in the signal processing for each light receiving element, for example, data obtained from one of two rows of light receiving element arrays arranged in a staggered manner so as to be spaced apart in the sub-scanning direction may be obtained as a longer data, and data obtained from the other light receiving element array may be obtained as a shorter data, and the obtained images may be inverted to erect images before being combined into images. Alternatively, after converting the inverted image data of each light receiving element into an erect image, a correction coefficient may be multiplied or subtracted from the overlapping parts when combining the images.

[0043] Specifically, in the inverted refractive optical system, the multiple light receiving element arrays may be light receiving element arrays arranged in two reading lines, each of which is shorter than the reading line. Also, the light receiving element array arranged in one reading line and the light receiving element array arranged in the other reading line may be arranged in a staggered pattern alternately along the main scanning direction. This configuration is similar to the erect refractive optical system described in FIG. 3, so a detailed description will be omitted.

[0044] In this case, as shown in Fig. 3, the multiple light receiving elements are arranged in an array of two or more rows to form multiple light receiving element arrays 120. The multiple light receiving element arrays 120 are arranged at intervals of less than the width W2 in the main scanning direction of the light receiving lens 11 in a direction perpendicular to the reading line L. The multiple light receiving lenses 11 are arranged in a number corresponding to the multiple light receiving element arrays 120, and the optical axis of light transmitted through each light receiving lens 11 and guided to each light receiving element array 120 passes through approximately the center of each light receiving element array 120. However, the optical axis of light transmitted through each light receiving lens 11 and guided to each light receiving element array 120 may pass through a position separated from the approximately center of each light receiving element array 120 in parallel with the sub-scanning direction.

[0045] 5. Configuration of the illumination optical system In this 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. As for the light source 103, since the working distance is 10 times longer than that of the conventional CIS, the inspection surface illuminance needs to be 100 times or more in the same magnification system. Therefore, for example, a high-luminance white LED array is used as the light source 103. That is, the multiple light sources 103 may be configured to include white LEDs. When a semiconductor laser in the visible range is used as the light source 103, the emitted beam is expanded in the main scanning direction and collimated in the sub-scanning direction to reduce unevenness in the amount of light during irradiation.

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

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

[0048] Furthermore, even if the radiance per unit area is the same, if the size of the light receiving element is different, it is synonymous with the area of ​​the light emitting part being different, so the amount of light received will decrease inversely proportional to the square of the light receiving element area. The illumination light amount is determined by taking the above into consideration. If the element size becomes smaller, the amount of light received will decrease inversely proportional to the element area for the same accumulation time. This is a physical property of semiconductor light receiving elements, and in order to maintain the S / N ratio, it is sufficient to increase the illumination light, increase the power density, and make the number of electrons generated per unit time the same. This allows the shot noise to be maintained at the same level as that of a larger size light receiving element even if the size of the light receiving element is reduced. In addition, the light received by the light receiving element depends not only on the illuminance of the inspection surface, but also on the range that the light receiving element is looking at when receiving light. Needless to say, if the solid angle of reception is different and the angle decreases, the amount of light received will also decrease, and if the inspection surface is a perfect diffusion surface, the amount of light received will comply with the so-called cosθ law. The light diffused and reflected from the inspection surface is captured by the light receiving lens and collected on the light receiving element, which outputs an output signal. The output signal from the light receiving element array is also split from serial to parallel to increase the processing speed and is transmitted to the image processing device.

[0049] FIG. 10A is a schematic diagram showing the positional relationship between the light source 103 and the light receiving lens 11, in the case where the light receiving element array 120 has two rows. FIG. 10A shows the arrangement of the light source 103 relative to the light receiving lenses 11 and the light receiving element array 120 arranged in two rows. In this embodiment, the light source 103 is arranged in the approximate center of the two rows of reading lines L. The light sources 103 are arranged parallel to the reading lines L. The optical axis of each light source 103 is arranged at an arbitrary position on a virtual plane that intersects with the optical axis of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120, and also intersects with the optical axis of the light transmitted through each light receiving lens 11 and guided to each light receiving element array 120. In this embodiment, the focal length f of the light receiving lens 11 is f=50 mm, and the lens diameter Φ is Φ=4 mm (however, taking into account geometrical optical aberration, the effective diameter Φ' is set to Φ'=2.5 mm using an aperture). In this embodiment, light is irradiated from the light source 103 to the inspection surface at an angle of about 45 degrees. Therefore, the distance between the light source 103 and the inspection surface is set to 70 mm, taking into consideration the working distance of the light receiving lens 11. In this embodiment, an LD is used, but an LED of each wavelength may also be used.

[0050] The arrangement pitch of the light sources 103 is adjusted to the distance between the lenses, and the light sources 103 are arranged at a position that is approximately the center between adjacent light receiving lenses 11 and also approximately the center of two rows of reading lines L. This makes it possible to better prevent missing pixels on the inspection surface, and also to further reduce shading of the light receiving lenses 11 and unevenness in the amount of light from the light sources 103. The lens pitch between the light receiving lenses 11 in each row is set to 7 mm. In this case, the effective lens pitch is 3.5 mm.

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

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

[0053] First, the illumination system irradiates the object with illumination light having a negative intensity distribution in advance. For example, a method of arranging the light source 103 between adjacent light receiving lenses 11 does not provide a shading suppression method that is completely compatible with various light receiving lenses 11. That is, each light receiving lens 11 has its own shading, and if the light receiving lens 11 is different, an illumination optical system corresponding to the individual light receiving lenses 11 must be used. In this embodiment, a condenser lens 104 having a large power in the main scanning direction is arranged. The light beam transmitted through the condenser lens 104 is then guided to the object by a converging lens such as a cylindrical lens 105, and forms a light intensity on the object according to the shading of the light receiving lens 11. Then, by appropriately changing the position of the condenser lens 104 in the optical axis direction according to the shading of the light receiving lens 11, for example, if the 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 have a power in the sub-scanning direction. In short, it is sufficient to completely suppress the shading of the light receiving lens 11 and simultaneously realize an effective light intensity distribution that takes into account the focal length of the light receiving lens 11 with respect to the object. In other words, it is preferable that the lens power in the main scanning direction is greater than the lens power in the sub-scanning direction. As the condenser lens 104, for example, a cylindrical lens, a lenticular lens, a Fresnel lens, or a combination of a prism sheet and a spherical lens, etc. are preferable. The positional relationship of the light source 103 with respect to the main scanning direction may be such that it is disposed at the middle position of each light receiving lens 11, or may be disposed on the optical axis of the light receiving lens 11. Furthermore, the light source 103 may be disposed at the outer periphery of the light receiving lens 11. Furthermore, a lens having a power distribution in the main scanning direction is more preferable.

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

[0055] In the condenser lens 104 having the first condenser lens and the second condenser lens as described above, the first condenser lens and the second condenser lens can be configured by a cylindrical lens, a lenticular lens, a Fresnel lens, or a prism row. For example, the first condenser lens may be a lenticular lens or a prism row. Furthermore, the second condenser lens may be a Fresnel lens or a cylindrical lens.

[0056] 7. Receiver lens parameters A graph of the light receiving system MTF for each lens diameter in this embodiment is shown in Figure 10C. As a comparative example, a case where the refractive index distribution constant √A=0.154 is shown in Figure 10D. The solid line, short dashed line, long dashed line, and dashed dotted line show the cases where the effective diameter Φ is Φ=1.0, 1.5, 2.0, 2.5, and 3.0 mm, respectively. The pixel size of the light receiving element is 42.3 μm in both the main scanning direction and the sub-scanning direction, which is equivalent to 600 dpi.

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

[0058] When the light receiving lens 11 is a gradient index lens, the lens is preferably made of glass or resin. In this case, the lens parameters of the light receiving lens 11 are preferably such that the axial refractive index N0 is 1.45≦N0≦1.65, the refractive index distribution constant √A is 0.05≦√A≦0.12, and the focal length f is 50 mm≦f≦150 mm.

[0059] The light receiving lens 11 may be an achromat or an apochromat that is a combination of multiple lenses. In this case, the multiple lenses may be a lens system that combines only convex lenses, or a lens system that combines convex and concave lenses. It is preferable that the focal length f of the multiple lenses is 25 mm≦f≦250 mm, and that the aperture Φ of the multiple lenses is 2 mm≦Φ≦50 mm.

[0060] Next, an example in which the light receiving lens system is a reduced optical system in order to improve the depth of field and the resolution will be shown. The configuration of the optical system is the same as that of FIG. 10A, and the magnification of the light receiving lens 11 is changed. That is, the relationship between the lateral magnification of the object point and the image point of the light receiving lens 11 is changed to 9:1 or 4:1. By doing so, the depth of field is increased to three times that of the life-size system when the lateral magnification is 9:1, and to twice that of the life-size system when the lateral magnification is 4:1. When the depth of field is tripled, the size of the light receiving element is set to 1 / 9 of the size of the light receiving element of the life-size system. When the depth of field is doubled, the size of the light receiving element is set to 1 / 4 of the size of the light receiving element of the life-size system. In this embodiment, the depth of field is doubled by using a light receiving element of 1 / 4 size.

[0061] The MTF characteristics of the reduction optical system in this embodiment when defocused are shown in the graph of Fig. 11 (solid line). As a comparative example, the MTF characteristics of a life-size system when defocused are shown in the graph of Fig. 11 (dashed line). From the comparison between the reduction system and the life-size system in the figure, it can be seen that the depth of field of the reduction optical system is about twice as deep as that of the life-size system. Furthermore, if the reduction ratio is S, the NA of the light receiving lens 11 increases by 1 / S, which is the reciprocal of the reduction ratio. Therefore, even if the lens diameter of the light receiving lens 11 is small, if the reduction ratio is increased according to the focal length, the effective NA can be maintained, and the blur due to the diffraction effect can also be kept constant.

[0062] In this embodiment, the focal length is f=50 mm and the lateral magnification ratio is 1 / 4, so in principle, the lens diameter Φ can be as small as Φ=0.25 mm. Since the same lens as in FIG. 10A is used, the lens diameter Φ is Φ=4 mm and the effective diameter Φ' is Φ'=2.5 mm. The NA is four times that of the 1x system in 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.

[0063] 8.Telecentric optical system Next, the telecentric optical system applied to this embodiment will be described. By using a telecentric optical system, it is possible to achieve a configuration that is easy to assemble and has little change over time. In a telecentric optical system, a light-receiving lens 11 is arranged on either or both sides of an aperture (light-transmitting portion). In other words, the telecentric optical system is a double-sided telecentric optical system in which a light-receiving lens 11 is arranged on both the object side and the light-receiving element array 120 side, or an object-side telecentric optical system in which a light-receiving lens 11 is arranged only on the object side.

[0064] In a double-telecentric optical system, a thin light beam that spreads out parallel to the optical axis from the object passes through the front lens and becomes a parallel light beam. The parallel light beam passes through an aperture inserted after the front lens and then passes through the rear lens to be focused on each light receiving element of the light receiving element array 120.

[0065] When the light receiving element array 120 is staggered in the sub-scanning direction as shown in FIG. 3 or FIG. 4, the memory capacity needs to be increased as the distance in the sub-scanning direction increases. The larger the memory capacity, the higher the cost. In this embodiment, by using a telecentric lens optical system, if the NA is about 0.03, the lens with a focal length of 50 mm will have a conical light receiving solid angle connecting Φ=3 mm on the main plane of the lens and the object point. Therefore, the shortest distance Ls of the light receiving element array 120 staggered in the sub-scanning direction is sufficient if Ls>3 mm. Therefore, if the circular outer periphery of a normal lens is made into a rectangular outer periphery by various processing or molding means, and the light receiving element array 120 is arranged with a narrower staggered interval as shown in FIG. 3 or FIG. 4, the light receiving solid angle can be satisfied, compactification is possible, and the memory capacity can be reduced at the same time. The NA of the light receiving lens 11 is preferably about 0.001 to 0.05 from the viewpoint of the amount of illumination light. As described above, the thickness of light receiving lens 11 in the sub-scanning direction is determined by the solid angle defined by the NA of the telecentric optical system, and therefore it can be made short in the sub-scanning direction and compact.

[0066] 9. Modifications of the light receiving system Next, modified examples of the light receiving system will be described with reference to Figures 12A to 12G. 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 has been described, but in Figures 12A to 12G, a configuration in which a plurality of light receiving lenses 11 are arranged in one row along the main scanning direction, specifically, a layout of one row of light receiving lenses 11 and a staggered light receiving element array 120 will be described.

[0067] When two rows of reading lines L are formed by staggering the light receiving element array 120, if the light receiving lenses 11 are also staggered in two rows like the light receiving element array 120, it was necessary to provide a spacing in the sub-scanning direction of the light receiving element array 120 that is greater than the width of the light receiving lenses 11 in the sub-scanning direction in order to satisfy the required NA of the light receiving lens system. Therefore, as shown in Figures 12A to 12G, if the width of the rectangular lens of the light receiving lens 11 is set so as to satisfy the NA required for the light receiving system and the number of rows is reduced from two to one, it becomes possible to further narrow the spacing in the sub-scanning direction of the light receiving element array 120. In other words, the effect of speed fluctuation in the sub-scanning direction can be reduced, and at the same time, the cost of the light receiving lenses 11 can be reduced. Below, a method of arranging a plurality of light receiving lenses 11 in one row will be described.

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

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

[0070] 12B, a rectangular notch is formed on both end faces in the main scanning direction of each light receiving lens 11 when viewed in the Z direction. When multiple light receiving lenses 11 are arranged side by side in the main scanning direction as shown in Fig. 12B, parts of adjacent light receiving lenses 11 fit into the notches formed on both end faces of each light receiving lens 11, so that the ends of adjacent light receiving lenses 11 in the main scanning direction are arranged in a connected state.

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

[0072] 12D, a curved (semicircular or semi-elliptical) notch is formed on both end faces in the main scanning direction of each light receiving lens 11 when viewed in the Z direction. When multiple light receiving lenses 11 are arranged side by side in the main scanning direction as in Fig. 12D, parts of adjacent light receiving lenses 11 fit into the notches formed on both end faces of each light receiving lens 11, so that the ends of adjacent light receiving lenses 11 in the main scanning direction are arranged in a connected state.

[0073] Next, modified examples of Fig. 12E to Fig. 12G will be described. Fig. 12E is a modified example of Fig. 12C, which can minimize the occurrence of missing pixels in the above-mentioned light receiving element array 120. In Fig. 12E, each light receiving element array 120 is arranged on the longer side of each trapezoidal light receiving lens 11 from the center in the width direction. In addition, the length of each light receiving element array 120 in the main scanning direction is approximately equal to the length of each trapezoidal light receiving lens 11 in the main scanning direction at the position where the light receiving element array 120 is arranged. By doing so, the portions indicated by the dashed lines in Fig. 12E of the staggered light receiving element arrays 120 adjacent to each other overlap in the main scanning direction, and as described later, no missing portions of the output signal are generated as in the staggered light receiving element array 120 shown in Fig. 12C.

[0074] The above is not limited to the trapezoidal light receiving lens 11, and may be any shape that can be connected when each light receiving lens 11 is inverted in the sub-scanning direction to form a light receiving lens array. Examples are shown in Figs. 12F and 12G. Fig. 12F shows a case where a plurality of light receiving lenses 11 having rectangular cutout shapes are inverted and connected, and Fig. 12G shows a case where a plurality of light receiving lenses 11 having circular cutouts are inverted and connected. Thus, in Figs. 12E to 12G, a plurality of light receiving lenses 11 are arranged in a state where adjacent light receiving lenses 11 are inverted and connected. Generally, inversion connection is possible if the light receiving lenses 11 are line symmetric in the sub-scanning direction. In Figs. 12F and 12G, the dashed line parts overlap as in the trapezoidal inversion connection of Fig. 12E, and as will be described later, no signal missing parts are generated. The light receiving lens 11 in Fig. 12G has an edge part 112 for ensuring rigidity and avoiding cracks.

[0075] As shown in Fig. 12A to Fig. 12G, in a cross-sectional view in the optical axis direction of the light receiving lens 11, the lens end is set to have a cross-sectional shape such as a parallelogram, trapezoid, rectangular, or curved (circle, ellipse) cutout shape in the sub-scanning direction that satisfies the NA of the light receiving lens system, and the lens end is connected in one row to form a lens array extending in a straight line in the main scanning direction. In addition, two rows of staggered light receiving element arrays 120 are provided in the center of the lens array in the sub-scanning direction. Specifically, a plurality of light receiving element arrays 120 are disposed in the center of each of the plurality of light receiving lenses 11 in the main scanning direction, and are alternately disposed in a staggered manner along the main scanning direction. In this way, light emitted from an object can be delivered to the two rows of staggered light receiving element arrays 120 by one row of lens array.

[0076] As shown in FIG. 12A, a shielding portion 111 is provided between the ends of the light receiving lenses 11 adjacent to each other in the main scanning direction. The shielding portion 111 is formed in a thin plate shape. The shielding portion 111 extends from between the ends of each light receiving lens 11 toward the light receiving element (light receiving element array 120) and protrudes from the light receiving lens 11 toward the object. The shielding portion 111 has a width at least equal to or greater than the width W1 of the light receiving lens 11 in the sub-scanning direction. Although the shielding portion 111 is omitted in FIGS. 12B to 12G, the shielding portion 111 may be similarly provided between the ends of each light receiving lens 11. In the embodiment of FIGS. 12F and 12G, the shielding portion 111 is a thin crank-shaped or wave-shaped shielding plate. In short, it is sufficient to prevent light from leaking into the adjacent light receiving systems at the connecting portion.

[0077] 12B to 12D, a plurality of light sources 103 for illuminating an object may be provided in one-to-one correspondence with a plurality of light receiving element arrays 120. Each of the light sources 103 may have an elongated shape extending linearly along the main scanning direction, and in this case, as shown in Fig. 12B to 12D, the light sources 103 may face each of the light receiving element arrays 120 in the Z direction. This allows the light sources 103 to be arranged in a staggered pattern, and allows linear light to be efficiently incident on each of the light receiving element arrays 120.

[0078] The light sources 103 have a light intensity distribution of illumination light of multiple lines in the sub-scanning direction corresponding to the multiple light receiving element arrays 120. Although the light sources 103 are omitted in Fig. 12A and Fig. 12E to Fig. 12G, the multiple light sources 103 may be similarly provided in one-to-one correspondence with the multiple light receiving element arrays 120. However, instead of arranging the multiple light sources 103 in a staggered manner, a 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 array 120 of each reading line L has a light intensity peak. In addition, since the intervals in the sub-scanning direction of the staggered light receiving element arrays 120 are narrow, a line illumination having one peak may be used.

[0079] Fig. 13 shows the light intensity distribution on the light receiving surface of the light receiving element array 120 when the light intensity distribution of the light source 103 is flat when the lens end is a parallelogram. Fig. 13 shows an example of the light intensity distribution on the light receiving surface of each light receiving element array 120 when the configuration of Fig. 12A is adopted. For the sake of explanation, the lens array consisting of multiple light receiving lenses 11 is assumed to be a lens array consisting of three light receiving lenses 11.

[0080] The diagram on the left side of Fig. 13 shows the light intensity on each light receiving element array 120 of the entire lens array, and the two diagrams on the right side show enlarged views. Fig. 14 also shows details of the light intensity distribution near the joint between adjacent light receiving lenses 11. In this embodiment, in two adjacent light receiving element arrays 120 arranged in a staggered pattern, signal missing pixels of one light receiving element array 120 are interpolated with pixels of the other light receiving element array 120. In Fig. 14, the arrow marks indicate a method of interpolating signals of signal missing pixels.

[0081] In FIG. 14, a portion 121 surrounded by a dashed line is a light receiving element located at a connection portion between adjacent light receiving lenses 11, and a signal missing portion occurs when light does not reach the light receiving element. Therefore, in this embodiment, in the adjacent staggered light receiving element array 120, the signal missing portion is supplemented with the output signal of a light receiving element (portion 122 surrounded by a solid line) that faces the light receiving element of the portion 121 in the sub-scanning direction. In this way, a pixel interpolation portion is formed along the sub-scanning direction at the connection portion between adjacent light receiving lenses 11 (see FIG. 13). The signal missing portion may be corrected in advance using a reference medium for inspection. A white chart or a grid pattern for shading correction may be used as the reference medium.

[0082] The width of the light receiving lens 11 in the sub-scanning direction in FIG. 13 is 5 mm. Therefore, when the light receiving lenses 11 are arranged in two staggered rows, the minimum interval of the staggered light receiving element array 120 needs to be 5 mm or more. However, when a single row of lens array is used as described above, the interval becomes about 1 / 2 (just under 3.0 mm). In addition, if shading correction is performed while taking into consideration the dynamic range of the light receiving element array 120, it is possible to further narrow the interval. That is, the interval of the staggered light receiving element array 120 in the sub-scanning direction is narrowed, and at the same time, the number of light receiving lenses 11 can be halved. Therefore, there is an advantage in that it is less susceptible to the influence of fluctuations in the transport speed in the sub-scanning direction and at the same time, costs can be reduced.

[0083] A shielding plate with a thickness t=0.2 mm is placed in the shielding portion 111 in Fig. 13. If t=0.2 mm, there is no problem in terms of strength. The lens system is a double-telecentric system. Of course, it goes without saying that it may be a telecentric system on the object side.

[0084] In a specific image processing method or processing by the image processing system, when an output signal from one light receiving element (part 121 surrounded by a dashed line) is lower than an output signal from the other light receiving element (part 122 surrounded by a solid line) and does not reach a threshold value, the output signal from the other light receiving element is interpolated. The interpolated output signal is then combined with an output signal from a light receiving element at another position in the main scanning direction relative to the one light receiving element to generate an output signal for one row corresponding to the reading line L.

[0085] 14, the light receiving elements in portion 123 surrounded by a two-dot chain line face each other in the sub-scanning direction, but overlap each other because they are shifted from the joints between adjacent light receiving lenses 11. In such overlapping portions, there is no need for interpolation because there is no loss of output signals from the light receiving elements.

[0086] In the example of FIG. 12E, the light intensity of the light receiving region is shown, and the reason why no signal missing portion occurs is shown in FIG. 15. FIG. 15 shows the light intensity distribution at the end of the staggered light receiving element array 120 as in FIG. 14. The light receiving elements in the portion 124 surrounded by the two-dot chain line in FIG. 15 face each other in the sub-scanning direction, but they are all overlapped by being shifted from the connection portion between the adjacent light receiving lenses 11. As shown in FIG. 15, by arranging the light receiving element array 120 on the long side in the width direction of the trapezoidal light receiving lens 11, it is possible to obtain the signal required for one reading line L of the staggered light receiving element array 120, except for the signal missing portion in the light receiving portion.

[0087] As a process by a specific image processing method or an image processing system, for output signals from two light-receiving elements (the portion 124 surrounded by the dashed line) spaced apart in the sub-scanning direction at the same position in the main scanning direction, one of the output signals of the output signals of the overlapping portion of the output signal of one light-receiving element and the output signal of the other light-receiving element is selected, and correction is performed by the ratio of one of the output signals pre-corrected by the reference medium and the other output signal, and then one signal and the other signal are synthesized to obtain an output signal of one column corresponding to the reading line L.

[0088] Here, details of the working distance and imaging range (field of view) regarding the light-receiving lens 11 of the present embodiment will be described. FIG. 16 is a schematic diagram for explaining the working distance and imaging range (field of view) regarding the light-receiving lens 11. Conditions such as the numerical ranges described below are effective for the light-receiving system as shown in FIGS. 12A to 12G, and are particularly effective for a configuration using the trapezoidal light-receiving lens 11 as shown in FIGS. 12C and 12E, but the configuration of the light-receiving system is not limited to these.

[0089] The working distance W is the distance between the light-receiving lens 11 and the reading position of the object. In the present embodiment, the reading position of the object is located on the reading line L along the focal plane 20. On the other hand, the imaging range X is the width of the field of view of the light-receiving lens 11 at the reading position. The working distance W and the imaging range X are determined based on the focal length of the light-receiving lens 11 and the width of the light-receiving element array 120.

[0090] In the present embodiment, the light-receiving lens 11 is designed and the distance between the light-receiving lens 11 and the light-receiving element array 120 is set so that the working distance W and the imaging range X satisfy W < X and W > 30 mm. Further, the depth of field calculated based on the working distance W, the focal length of the light-receiving lens 11, the F value, etc. is 4 mm or more.

[0091] In a conventional CIS, there were problems such that the working distance W was less than 30 mm, which was small, the degree of freedom in arranging the optical system was low, and there was a high risk that the object would come into contact with the CIS. Further, in the conventional CIS, the depth of field was less than 4 mm, which was shallow, and there was also a problem that the image was likely to be blurred according to the thickness of the object.

[0092] In this embodiment, it is possible to provide an optical line sensor (camera) having a large working distance W and a large depth of field that satisfy the above conditions. Further, even under the condition of W < X, the lens aberration is small and the apparatus can be miniaturized. However, it may be a camera configured using other light receiving elements such as an area sensor instead of the light receiving element array 120 in which the light receiving elements are arranged in a line.

[0093] 10. Overall Configuration of Reading Device FIG. 17 is a schematic cross-sectional view showing the overall configuration of a reading device 1 according to an embodiment of the present invention. The reading device 1 according to this embodiment is a device for reading an image of an object 22 irradiated with light, using the above-described optical line sensor (camera 100). In FIG. 17, a cross-section orthogonal to the main scanning direction (X direction) of the reading device 1 is shown.

[0094] The reading device 1 is provided with a camera 100 and a conveyance device 21. The reading device 1 reads an image of the object 22 conveyed along the sub-scanning direction (conveyance direction) by the conveyance device 21 with the camera 100 in a reading line extending in the main scanning direction, and obtains image information of the object 22. Hereinafter, the main scanning direction will be described as the X direction, the sub-scanning direction as the Y direction, and the direction orthogonal to the X direction and the Y direction as the Z direction.

[0095] The conveyance device 21 is constituted by a conveyor or the like and conveys the object 22 in the Y direction at a constant speed. However, the conveyance device 21 is not limited to a configuration that conveys the object 22 at a constant speed, and the conveyance speed of the object 22 may be changed. Further, it is not limited to a configuration that reads while conveying the object 22, and may be a configuration that reads an image of the object 22 in a stationary state.

[0096] The camera 100 includes a light source unit 10, a light receiving unit 12, and a light receiving lens 11. The light source unit 10, the light receiving unit 12, and the light receiving lens 11 are each arranged along the X direction, and are held by a housing 16 so as to extend parallel to each other. In this embodiment, a pair of light source units 10 are provided sandwiching the light receiving lens 11 in the Y direction. However, the number of light source units 10 is not limited to two, and may be one, or three or more. In addition, the light source unit 10 is not limited to being provided in the camera 100, and may be provided separately from the camera 100 as an external light source.

[0097] The light source unit 10 includes, for example, an LED (Light Emitting Diode), and irradiates light onto the object 22. The wavelength of the light irradiated from the light source unit 10 is not particularly limited, but for example, the light source unit 10 irradiates visible light, infrared light, ultraviolet light, or a combination of these.

[0098] When the object 22 is irradiated with light from the light source unit 10, light such as reflected light (including scattered light) or fluorescent light is generated. The light from the object 22 passes through the light receiving lens 11 and enters the light receiving unit 12. The light receiving unit 12 receives the light from the object 22 and performs photoelectric conversion to capture an image of the object 22.

[0099] The configuration of the light receiving lens 11 is as exemplified in the above-mentioned embodiment. As the light receiving lens 11, the configurations exemplified in Fig. 12A to Fig. 12G can be adopted, and for example, the light receiving lens 11 may be a trapezoidal light receiving lens 11 as shown in Fig. 12C or Fig. 12E. The light receiving lens 11 is provided between the object 22 and the light receiving unit 12, and forms an image of the focal position 23 on the light receiving surface of the light receiving unit 12.

[0100] Here, focal position 23 means a position where an image is in focus. In this embodiment, light receiving lens 11 is designed so that the depth of field is deep and the range R of focal position 23 in the Z direction is wide. Therefore, even if there are irregularities on the surface (upper surface) of object 22 as shown in FIG. 17, as long as the height of the irregularities is within the above range R, the surface of object 22 being conveyed can be clearly photographed.

[0101] In this embodiment, by designing the light receiving lens 11 as described above, it is possible to arrange the camera 100 at a distance from the object 22. Specifically, the camera 100 is arranged so that the distance between the focal position 23, which is the reading position, and the lower end face (the face on the object 22 side) of the light receiving lens 11 is 30 mm or more. This makes it possible to photograph a thick object 22. Also, in this embodiment, by transporting the object 22 with the transport device 21, it is possible to photograph the thick object 22 while transporting it.

[0102] 17 shows an example in which focal position 23 is located vertically below light receiving lens 11. That is, in the example of Fig. 17, a straight line connecting focal position 23 and light receiving lens 11 extends in the Z direction perpendicular to the Y direction which is the transport direction of object 22.

[0103] 11. First variant of the reading device Fig. 18 is a schematic cross-sectional view showing a first modified example of reading device 1. Fig. 17 describes a case where the straight line connecting focal position 23 and light receiving lens 11 extends in the Z direction. In contrast, in the example of Fig. 18, the straight line connecting focal position 23 and light receiving lens 11 is inclined with respect to the Z direction. Specifically, the straight line connecting focal position 23 and light receiving lens 11 is inclined with respect to the Z direction at an angle inclined about the X direction.

[0104] 18, the straight line connecting focal position 23 and light receiving lens 11 is inclined toward the upstream side in the conveying direction (Y direction) of object 22. Therefore, it is possible to capture an image of the side surface (the surface on the upstream side in the conveying direction) of object 22, which has a large thickness. In this embodiment, since the distance between focal position 23 and light receiving lens 11 is large, the straight line connecting focal position 23 and light receiving lens 11 can be inclined at a larger angle.

[0105] However, the present invention is not limited to this configuration, and the straight line connecting the focal position 23 and the light receiving lens 11 may be inclined toward the downstream side in the conveying direction (Y direction) of the object 22. Even in this case, it is possible to capture an image of the side surface (the downstream surface in the conveying direction) of the object 22 which has a large thickness.

[0106] 12. Second variant of the reading device Fig. 19 is a schematic cross-sectional view showing a second modified example of the reading device 1. In Fig. 17 and Fig. 18, a case has been described in which the position of the camera 100 is fixed. In contrast, in the example of Fig. 19, the position of the camera 100 can be moved.

[0107] Specifically, a holding member 30 for holding the camera 100 is provided on the reading device 1. In this example, the holding member 30 holds both ends of the camera 100 in the X direction. The holding member 30 is formed with a long hole 31 for slidably holding the camera 100. By sliding the camera 100 along the long hole 31, the camera 100 can be moved to match the shape of the long hole 31.

[0108] The long hole 31 is formed, for example, in an arc shape. In this case, it is preferable that the long hole 31 is formed in an arc shape centered on the focal position 23. This makes it possible to prevent the focal position 23 from shifting as the camera 100 moves. In this example, the camera 100 is movable within a range of about 10 to 45° centered on the X direction.

[0109] However, the range within which camera 100 can move is arbitrary, and may include the angle at which a straight line connecting focal position 23 and light receiving lens 11 extends in the Z direction, as shown in Fig. 17, for example. The shape of slot 31 is not particularly limited, and may be any other shape. Furthermore, holding member 30 may have any other structure as long as it can hold camera 100 movably.

[0110] 19, the angle of the line connecting focal position 23 and light receiving lens 11 can be adjusted by sliding camera 100 relative to holding member 30. Specifically, the angle of the line connecting focal position 23 and light receiving lens 11 can be adjusted around the X direction. Therefore, object 22 with a large thickness can be photographed at a desired angle.

[0111] 13. Third variant of the reading device Fig. 20 is a schematic cross-sectional view showing a third modified example of the reading device 1. In the example of Fig. 20, a photographing assisting device 40 that assists in photographing an image of the object 22 is provided between the focal position 23 and the light receiving lens 11. This allows the photographing assisting device 40 to be provided by utilizing the space between the focal position 23 and the light receiving lens 11.

[0112] The photographing auxiliary tool 40 includes various devices used in the reading device 1. For example, the photographing auxiliary tool 40 may include a lighting device. In this case, various photographs can be taken using the lighting device as the photographing auxiliary tool 40. Specifically, the lighting device may be a lighting device that illuminates the entire surface of the object 22, or a lighting device that illuminates a part of the object 22. The lighting device may also be a lighting device that irradiates the object 22 with light of a different wavelength from that of the light source unit 10. Alternatively, the lighting device may be a lighting device that illuminates the object 22 at an angle different from that of the light source unit 10.

[0113] The photographing auxiliary tool 40 may also include an optical device that transmits or reflects light from the object 22. In this case, various photographs can be taken using the optical device as the photographing auxiliary tool 40. Examples of such optical devices include optical devices used in a reduction optical system, such as a filter, a prism, or a mirror, but the photographing auxiliary tool 40 is not limited to these optical devices, and any other optical device may be included in the photographing auxiliary tool 40.

[0114] Furthermore, the photographing auxiliary tool 40 may include a cleaning device for cleaning. In this case, the inside of the reading device 1 can be cleaned using the cleaning device as the photographing auxiliary tool 40. Examples of such cleaning devices include a brush, a suction device, a blower, and the like, but the cleaning devices are not limited to these, and any other cleaning device may be included in the photographing auxiliary tool 40. The cleaning device may be one that is used manually by the user, or one that performs cleaning automatically.

[0115] 14.Application examples In the reading device 1 of this embodiment, the working distance W is long, at 30 mm or more, so there is a low risk that the imaging system will come into contact with the object 22 and be damaged. In addition, since there is no need to strictly control the position of the object 22, there is an advantage in that the design freedom of the conveying device 21 is high. In addition, in the reading device 1 in which the imaging system is disposed in a position different from the vertical direction with respect to the conveying direction in the modified example, the working distance W is long, so that it is possible to adjust the optimal position and lighting direction for imaging the surface state of the object 22. In another modified example, it is possible to insert a photographing auxiliary tool 40 between the imaging system and the object 22. For example, if a coaxial epi-illumination tool is inserted as the photographing auxiliary tool 40, it is possible to suitably image the glossy object 22. In addition, if a filter that cuts a specific wavelength is inserted, unnecessary light can be cut when imaging the object 22 that emits fluorescence, and the like, and the image can be suitably imaged. In yet another modified example, it is also possible to insert the photographing auxiliary tool 40 between the light receiving lens 11 and the light receiving unit 12.

[0116] Examples of the object 22 include continuously transported objects (sometimes called webs), such as resin films and sheets, rolled paper, fibers and wires, cloth and nonwoven fabric, metal steel sheets and foils, glass and ceramics, and composites thereof such as wallpaper and aluminum-deposited films.In addition, the object is not limited to continuously transported objects, and also includes objects that are intermittently transported in the form of sheets, such as cards, blanks, cardboard boxes, envelopes, lead frames, optical disks, and wafers.

[0117] Other examples of the object 22 include three-dimensional objects with non-flat surfaces, such as mounting boards, screws and nuts, bottles and cans, food, tablets, seeds, and packages that contain them. In an imaging system with a working distance W of less than 30 mm, these objects 22 could not pass under the light receiving lens 11, but the reading device 1 of this embodiment has a long working distance W, so it is possible to image these objects 22. As a result, even when imaging a heat-sealed portion of a pouch packaging bag containing contents, it is possible to image the pouch packaging bag in a bulging state with the contents inside. In the case of imaging the heat-sealed portion of such a pouch packaging bag, the contents may be liquid or gas. Examples of liquids include beverages, seasonings, detergents, oils, blood, medicines, saline, organic solvents, and the like. Examples of gases include industrial gases such as oxygen and helium, as well as steam containing components intended for aroma, deodorization, sterilization, and the like. Furthermore, the reading device 1 of this embodiment can be used not only to detect defects in the appearance of the object 22, but also as a counting device for the object 22. Furthermore, a reading device 1 having an imaging system disposed at a position different from the vertical direction with respect to the conveying direction, which is a modified example, can image the side of a three-dimensional object, making it possible to image a blind spot from the vertical direction. For example, it can be suitably used for solder inspection of relatively large mounted components such as electrolytic capacitors on a mounting board.

[0118] Further examples of the object 22 include food, medicines, medical products, sanitary products, functional films, semiconductor parts, and artworks, which are objects that require strict management in terms of hygiene and quality. The reading device 1 of this embodiment has a long working distance W, which not only reduces the risk of damage and contamination of the object 22, but also allows the insertion of a cleaning device as a modified example, which makes it possible to remove foreign matter attached to the object 22 or the light receiving lens 11, prevent the intrusion of foreign matter, and remove clouding of the light receiving lens 11 or lighting caused by steam or condensation, thereby improving quality control. In particular, in food inspection, the reading device 1 of this embodiment has a great advantage in that it can bring the imaging system close to the food while not coming into contact with it, which can address the problem of contamination by insects, etc., and can also address the problem of steam immediately after cooking and condensation caused by refrigerated or frozen foods.

[0119] In addition, the present invention can be suitably used as a reading device 1 for banknotes, coins, securities, barcodes, labels, printed matter, bankbooks, paintings, sculptures, ceramics, HEPA filters, photocatalyst-supported sheets, honeycomb filters, automobile bodies, tires, paved roads, railway tracks, athletic tracks, artificial turf, tunnel inner walls, concrete structures, electric wires, optical fibers, cables, connectors, plugs, dry batteries, prepregs, punching boards, copper-clad laminates, flexible substrates, electrode sheets, separators, graphite sheets, solar cells, lithium-ion batteries, photomasks, liquid crystal display panels, organic EL panels, LED displays, mini LED displays, micro LED displays, PTP packaging sheets for tablets, pharmaceutical and cosmetic packages, well plates, microfluidic devices, clothing and linen (sheets and towels), nonwoven masks, patches, gel sheets, adhesive tapes, resin pellets, synthetic leather, natural leather, wood, cork, plastic foams, grains, beans, tea leaves, spices, seals, keys, fingerprints, vein patterns, and the like. [Explanation of symbols]

[0120] 1 Reading device 10 Light source section 11 Receiving lens 12 Light receiving part 20 focal plane 22 Object 100 Cameras 103 Light source 104 Condenser Lens 105 Cylindrical Lens 110 Lens Holder 111 Shielding part 120 Photodetector array 131 Red Laser Diode 132 Green Laser Diode 133 Blue Laser Diode 134 Light source board 135 Heatsink

Claims

1. A camera comprising a light receiving lens and a light receiving element that receives light transmitted through the light receiving lens, the light receiving lens forming an image of light from an illuminated object at a reading position on the light receiving element, When the distance between the light receiving lens and the reading position is W and the width of the field of view of the light receiving lens is X, W<X is satisfied and W>30 mm; A camera characterized in that the depth of field is 4 mm or more.

2. a plurality of the light receiving lenses and a plurality of the light receiving elements are arranged in a line along a main scanning direction, 2. The camera according to claim 1, wherein an object transported in a sub-scanning direction is read at a reading position on a reading line extending in a main scanning direction.

3. The plurality of light receiving elements form at least two or more rows of the reading lines, 3. The camera according to claim 2, wherein the light receiving lens constitutes a telecentric optical system, and the width in the sub-scanning direction is smaller than the width in the main scanning direction.

4. 3. The camera according to claim 2, wherein the light receiving lens is formed in a rectangular shape when viewed in a direction perpendicular to the main scanning direction and the sub-scanning direction.

5. 3. The camera according to claim 2, wherein the plurality of light receiving lenses are spaced apart from one another at a distance equal to or smaller than the width of the light receiving lenses in the main scanning direction.

6. 3. The optical lens according to claim 2, wherein the width of the light receiving lens in the sub-scanning direction is set so that the N.A. of the light receiving lens satisfies 0.001<N.A.<0.

05.

7. 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; 3. The camera according to claim 2, wherein 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 light passing through each light-receiving lens and guided to each light-receiving element array passes through approximately the center of each light-receiving element array.

8. 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; 3. The camera according to claim 2, wherein 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 light passing through each light-receiving lens and guided to each light-receiving element array passes through a position spaced parallel to the sub-scanning direction from approximately the center of each light-receiving element array.

9. The camera according to claim 7 or 8, characterized in that the multiple light-receiving element arrays are light-receiving element arrays arranged in multiple rows on each of two reading lines, the light-receiving element array arranged on one reading line and the light-receiving element array arranged on the other reading line are arranged in a staggered pattern alternately along the main scanning direction.

10. 3. The camera according to claim 2, wherein each of the plurality of light receiving lenses includes a gradient index lens that forms an inverted image, an achromat, or an apochromat.

11. 11. The camera according to claim 10, wherein the gradient index lens is made of glass or resin, and the lens parameters of the lens are such that an axial refractive index N0 is 1.45≦N0≦1.65, a refractive index distribution constant √A is 0.05≦√A≦0.12, and a focal length f is 50 mm≦f≦150 mm.

12. 11. The camera according to claim 10, wherein each of the plurality of light receiving lenses is an achromat or an apochromat made up of a combination of a plurality of lenses, the plurality of lenses being a lens system made up of only convex lenses, or the plurality of lenses being a lens system made up of a combination of convex lenses and concave lenses, the focal length f of the plurality of lenses being 25 mm≦f≦250 mm, and the aperture Φ of the plurality of lenses being 2 mm≦Φ≦50 mm.

13. Further comprising a plurality of light sources for irradiating light onto the object; The camera described in claim 2, characterized in that the multiple light sources are arranged in a row parallel to the reading line, the optical axes of the multiple light sources intersect with the optical axis of the light passing through the multiple light receiving lenses and guided to the multiple light receiving elements, and are arranged at any position on an imaginary plane intersecting the optical axis of the light passing through the multiple light receiving lenses and guided to the multiple light receiving elements, and further a light source is arranged in approximately the center between adjacent light receiving lenses.

14. 14. The camera according to claim 13, wherein the plurality of light sources include light sources having a plurality of different wavelengths, each of the light sources having the plurality of different wavelengths being regarded as one unit, and a plurality of such one unit light sources are arranged in the main scanning direction.

15. The camera according to claim 13, further comprising a condenser lens for condensing light beams from the plurality of light sources.

16. 16. The camera according to claim 15, wherein the condenser lens includes a first condenser lens having a power in a main scanning direction greater than its power in a sub-scanning direction, and a second condenser lens having a power in the sub-scanning direction greater than its power in the main scanning direction.

17. 16. The camera according to claim 15, wherein the condenser lens is a single lens body, and the power of the lens body in the main scanning direction is greater than the power in the sub-scanning direction.

18. 17. The camera according to claim 16, wherein the power of the condenser lens in the main scanning direction is adjustable by the first condenser lens and the second condenser lens.

19. 16. The camera according to claim 15, wherein the condenser lens is a cylindrical lens or a Fresnel lens.

20. the first condenser lens is a lenticular lens or a prism array; 17. The camera according to claim 16, wherein the second condenser lens is a Fresnel lens or a cylindrical lens.

21. The camera of claim 13 , wherein the plurality of light sources includes white LEDs.

22. 14. The camera of claim 13, wherein the plurality of light sources includes a red LED, a green LED and a blue LED.

23. 14. The camera of claim 13, wherein the plurality of light sources include laser diodes.

24. a light source substrate on which the plurality of light sources are mounted; The camera of claim 13, further comprising a heat sink attached to the light source substrate.

25. The plurality of light receiving lenses are arranged in a row along the main scanning direction, 3. The camera according to claim 2, wherein the plurality of light receiving lenses are arranged in a state in which ends of the light receiving lenses adjacent to each other in the main scanning direction are connected to each other.

26. 26. The camera according to claim 25, wherein the plurality of light receiving lenses have the same shape when viewed in a direction perpendicular to the main scanning direction.

27. 27. The camera according to claim 26, wherein the plurality of light receiving lenses are arranged in such a manner that adjacent light receiving lenses are inverted and connected to each other.

28. 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; 27. The camera according to claim 25, wherein the plurality of light receiving element arrays are arranged at the center in the main scanning direction of each of the plurality of light receiving lenses, and are alternately arranged in a staggered pattern along the main scanning direction.

29. 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; 27. The camera according to claim 25 or 26, further comprising a plurality of light sources for illuminating an object and in one-to-one correspondence with the plurality of light receiving element arrays.

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

31. The camera according to claim 25 or claim 26, further comprising 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 the width of the light receiving lenses in the sub-scanning direction.

32. 32. The camera according to claim 31, wherein the shielding portion protrudes from the light receiving lens toward the object.

33. A reading device that reads an image of an object illuminated with light, A reading device that reads an image of an object conveyed along a conveying direction by using the camera according to claim 1.

34. 29. An image processing method using the camera according to claim 28, comprising the steps of: an image processing method comprising the steps of: selecting one of the output signals from two light receiving elements spaced apart in the sub-scanning direction at the same position in the main scanning direction where the output signal of one light receiving element overlaps with the output signal of the other light receiving element; correcting the ratio of one output signal to the other output signal, which has been previously corrected using a reference medium, and combining the one signal with the other signal to generate a single row of output signals corresponding to the reading line.

35. 29. An image processing method using the camera according to claim 28, comprising the steps of: an image processing method characterized in that, for output signals from two light-receiving elements spaced apart in the sub-scanning direction at the same position in the main scanning direction, when the output signal from one light-receiving element is lower than the output signal from the other light-receiving element and the output signal from one light-receiving element does not meet a threshold value, the image processing method interpolates the output signal using the output signal from the other light-receiving element and combines the interpolated output signal with an output signal from a light-receiving element located at another position in the main scanning direction relative to the one light-receiving element to generate a row of output signals corresponding to the reading line.

36. An image processing system using the camera according to claim 28, an image processing system characterized in that, for output signals from two light receiving elements spaced apart in the sub-scanning direction at the same position in the main scanning direction, one of the output signals is selected from a portion where the output signal of one of the light receiving elements overlaps with the output signal of the other of the light receiving elements, and the one signal is corrected based on a ratio between the one output signal and the other output signal, which have been previously corrected using a reference medium, and the one signal is combined with the other signal to generate a single row of output signals corresponding to the reading line.

37. An image processing system using the camera according to claim 28, an output signal from one of the light-receiving elements that is located at the same position in the main scanning direction and spaced apart in the sub-scanning direction, the output signal from the other light-receiving element being lower than the output signal from the other light-receiving element and not meeting a threshold value, the output signal from the other light-receiving element being interpolated, and the interpolated output signal being combined with an output signal from a light-receiving element that is located at another position in the main scanning direction relative to the one light-receiving element to generate a row of output signals corresponding to the reading line.

Images