Image-reading apparatus

Abstract

An image-reading apparatus (100) for reading an image of a reading object (M) and detecting a transparent sheet in contact with the reading object M includes: light-guiding bodies (2A and 2B) for irradiating the reading object M, which is conveyed in a sub-scanning direction orthogonal to a main scanning direction, with light rays extending in the main scanning direction; polarization filters (13) for aligning oscillation directions of the light rays used for irradiation through the light-guiding bodies (2A and 2B); a lens (8) for forming an image of the light rays from the transparent sheet and the reading object M with the light rays in which the oscillation directions have been aligned by the polarization filters (13A and 13B); a UV cut polarization filter (12) for aligning the oscillation directions of the light rays of which the lens (8) forms an image; a sensor chip (11) for converting, into an electrical signal, the light rays of which the lens (8) forms an image and in which the oscillation directions are aligned by the UV cut polarization filter (12), and outputting the electrical signal; and a signal processing device (15) for detecting the transparent sheet on the reading object (M) on the basis of the electrical signal outputted by the sensor chip (11).

Description

Image reading device

[0001] The present disclosure relates to an image reading device.

[0002] Conventionally, there have been signal processing devices that detect foreign objects on paper media, such as banknotes and securities, by irradiating the paper media with light, receiving the reflected light, and converting it into data with multiple different characteristics. Paper media, such as banknotes and securities, typically have fine irregularities on their surfaces, which cause light to scatter. On the other hand, there are sheet-like objects, such as cellophane tape and metallic glossy stickers, that reflect irradiated light in a direction symmetrical to the incident direction. When such sheet-like objects are affixed to a paper medium, if light is irradiated at an angle other than a right angle to the paper medium, the light is reflected in a direction symmetrical to the incident angle, resulting in the same angle of incidence and reflection, similar to specular reflection. Therefore, the characteristics of the data converted from the reflected light vary depending on the surface condition of the paper medium's reading location.

[0003] When a light-transmitting sheet-like object (hereinafter referred to as a transparent sheet) is attached to the surface of a paper medium, a conventional optical reading device reads light that passes through the transparent sheet and is scattered by the underlying paper medium, making it difficult to extract a signal converted from the reflected light from the transparent sheet and detect the transparent sheet. Patent Document 1 presents an image sensor module that can read specularly reflected light from the transparent sheet by positioning a light receiving sensor and optical axis at an incident angle set on the light source side with respect to the object to be read. According to the structure of Patent Document 1, the specularly reflected light specularly reflected by the transparent sheet can be guided to the light receiving sensor. With the structure of Patent Document 1, the amount of light received by the light receiving sensor is greater for the specularly reflected light from the transparent sheet than for the diffusely reflected light, which is light scattered by the underlying paper medium, making it possible to detect the transparent sheet.

[0004] JP 2017-224884 A

[0005] However, when detecting a transparent sheet on an object to be read (paper medium) using the image sensor module described in Patent Document 1, light that passes through the transparent sheet and is diffusely reflected by the object to be read is also imaged onto the light receiving sensor, which poses the problem of making it difficult to accurately distinguish between the transparent sheet and the object to be read.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to improve the detection accuracy of a transparent sheet on an object to be read.

[0007] To achieve the above object, an image reading device according to the present disclosure reads an image of an object to be read and detects a transparent sheet in contact with the object. The image reading device includes an illumination unit, a first polarizing filter, a lens, a second polarizing filter, a light receiving element, and a signal processing device. The illumination unit irradiates the object to be read, which is transported in a sub-scanning direction perpendicular to the main scanning direction, with light extending in the main scanning direction. The first polarizing filter aligns the vibration direction of the light irradiated by the illumination unit. The lens forms an image of the light from the object to be read and the transparent sheet using the light irradiated by the illumination unit and whose vibration direction has been aligned by the first polarizing filter. The second polarizing filter aligns the vibration direction of the light formed by the lens. The light receiving element converts the light whose vibration direction has been aligned by the second polarizing filter and which has been imaged by the lens into an electrical signal and outputs it. The signal processing device detects the transparent sheet on the object to be read based on the electrical signal output by the light receiving element.

[0008] According to the present disclosure, it is possible to improve the detection accuracy of a transparent sheet on an object to be read.

[0009] 1. A cross-sectional view in the sub-scanning direction of an image reading device according to embodiment 1. 2. A developed perspective view of an image reading device according to embodiment 1. 3. A plan view of an image reading device according to embodiment 1, seen from the glass plate side. 4. A cross-sectional view in the main scanning direction passing through a light guide of an image reading device according to embodiment 1. 5. A cross-sectional view in the sub-scanning direction of an image reading device according to embodiment 2.

[0010] An image reading device according to the present embodiment will be described in detail below with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals, and their description will not be repeated in principle. The image reading device reads an image of an object to be read and detects a transparent sheet attached to the object to be read.

[0011] (Embodiment 1) FIG. 1 shows a cross-sectional view of an image reading device 100 according to embodiment 1 in the sub-scanning direction. The configuration of the main parts of the image reading device according to this embodiment will be described using FIG. 1. In the figure, X, Y, and Z indicate coordinate axes. The X axis, Y axis, and Z axis are orthogonal to one another. The main scanning direction of the image reading device 100 is indicated by X, the sub-scanning direction by Y, and the height direction by Z. The main scanning direction is the longitudinal direction of the image reading device 100. The sub-scanning direction is orthogonal to the main scanning direction and is the direction in which the object M to be read is transported. The sub-scanning direction is the width direction of the image reading device 100. In this disclosure, a case will be described in which the object to be read is transported above the image reading device in the height direction. The object M to be read is a paper medium such as a banknote or a check that is printed not only with ink that reflects visible light (wavelength: 400 to 700 nm), but also with invisible ink that reflects infrared light (wavelength: 700 nm) and invisible ink that fluoresces when irradiated with ultraviolet light (wavelength: 200 to 400 nm). The surface of the object M to be read is rough, and the light reflected from the object M is scattered light with a higher intensity than specularly reflected light. The transparent sheet attached to the object M to be read is a sheet-like object that transmits visible light, and the surface of the object M underneath the transparent sheet can be seen through. In other words, the transparent sheet can be said to be in contact with the object M to be read. The surface of the transparent sheet is smooth and glossy, and when light is irradiated at an angle that is not perpendicular to the surface, the intensity of specularly reflected light is higher than that of scattered light.

[0012] The image reading device 100 includes a glass plate 1 on which a read object M is placed, light guides 2A and 2B that emit light toward the read object M, a lens 8 that collects reflected light from the read object M, a frame 9 that has openings on the top and bottom and stores components, a sensor board 10 that is disposed on the bottom of the frame 9, a sensor chip 11 that converts received light into an electrical signal and outputs the electrical signal, a UV-cut polarizing filter 12 that cuts ultraviolet light (UV) and aligns the vibration direction of the light, polarizing filters 13A and 13B that align the vibration direction of the light emitted from the light guides 2A and 2B, and a signal processing device 15 that detects a transparent sheet based on the electrical signal from the sensor chip 11. The sensor chip 11 is an example of a light-receiving element. A polarizing filter is an example of a polarizer, which is an optical device for extracting light with a specific vibration direction from light with no bias in the vibration direction, such as natural light, and may be a polarizing prism such as a Nicol prism or a polarizing plate.

[0013] The light guides 2A and 2B are arranged symmetrically with respect to the optical axis of the lens 8, and light from a light source (not shown) is irradiated at the position where the optical axis of the lens 8 intersects with the surface of the object M facing the glass plate 1. The position where the optical axis of the lens 8 intersects with the surface of the object M facing the glass plate 1 is the reading position 17. The light guides 2A and 2B are formed in a rod shape extending in the main scanning direction. While FIG. 1 shows one light guide 2A and one light guide 2B, this is not limiting and two or more light guides each may be provided, or either one may be provided alone. In this embodiment, the light from the light source includes deep ultraviolet light (wavelength: 200 to 300 nm) having a wavelength that causes the transparent sheet to fluoresce in order to detect the transparent sheet. When multiple light guides are present, some may emit light from a light source including deep ultraviolet light and others may emit light from a light source not including deep ultraviolet light, or the light source including deep ultraviolet light and the light source not including deep ultraviolet light may emit light at different times. The light guides 2A and 2B each have a light scattering section 14A and a light scattering section 14B extending in the main scanning direction. The light scattering sections 14A and 14B each have a light scattering pattern formed by white printing, prisms, or the like. The pattern may be a plurality of patterns arranged in the main scanning direction, or a single pattern extending in the main scanning direction.

[0014] Light incident from a light source on an end face of the light guide 2A is reflected inside the light guide 2A and propagates in the main scanning direction. The propagated light is diffused by the light scattering section 14A extending in the main scanning direction and emitted toward the reading position 17 as linear light extending in the main scanning direction. The light scattering section 14A in the light guide 2A is disposed in a plane parallel to the sub-scanning direction intersecting the main scanning direction, at a position and angle such that the diffused light is emitted in a direction oblique to the normal direction of the object to be read M and illuminates the reading position 17. The angle is preferably between 45° and 90° with respect to the normal direction of the object to be read M. The normal direction of the object to be read M is a direction perpendicular to the plane defined by the main scanning direction and the sub-scanning direction.

[0015] Similarly, light incident on an end face of light guide 2B from a light source is reflected inside light guide 2B and propagates in the main scanning direction. The propagated light is diffused by light scattering section 14B extending in the main scanning direction and emitted toward reading position 17 as linear light extending in the main scanning direction. Light scattering section 14B within light guide 2B is disposed in a plane parallel to the sub-scanning direction intersecting the main scanning direction, such that reflected light is emitted in a direction oblique to the normal direction of object M to be read, and is positioned and angled relative to light guide 2A in the sub-scanning direction to irradiate reading position 17 from the opposite side across lens 8. Light guide 2A and light guide 2B are examples of a first light guide and a second light guide, respectively.

[0016] The linear light emitted from the light guides 2A and 2B toward the reading position 17 passes through the polarizing filters 13A and 13B, respectively, aligning the vibration direction and emitting only light (polarized light) vibrating in a specific direction. Therefore, only light effective for detecting a transparent sheet is irradiated onto the reading position 17. If a transparent sheet is present at the reading position 17, the deep ultraviolet light contained in the light irradiated onto the transparent sheet excites the transparent sheet, causing it to fluoresce. Here, the definition of light effective for detecting a transparent sheet is explained. When natural light (unpolarized light) is specularly reflected by a transparent sheet, the specularly reflected light contains only light vibrating in a direction perpendicular to the surface of the transparent sheet. Therefore, of the light irradiated onto the transparent sheet, the light guided to the sensor chip is polarized light vibrating in a direction perpendicular to the surface of the transparent sheet and unpolarized light diffusely reflected by the surface of the object to be read. In other words, only light vibrating in a direction perpendicular to the surface of the transparent sheet is effective for detecting a transparent sheet.

[0017] Light reflected from the object M to be read at the reading position 17 is incident on the lens 8. If a transparent sheet is present at the reading position 17, fluorescence emitted by the transparent sheet is also incident on the lens 8. The lens 8 forms an image of the light reflected from the object M to be read and the fluorescence emitted by the transparent sheet on the sensor chip 11 arranged on the sensor substrate 10. By providing a UV-cut polarizing filter 12 between the lens 8 and the sensor chip 11, the sensor chip 11 is prevented from receiving ultraviolet light, and the vibration directions of the light reflected from the object M to be read that passes through the lens 8 and the fluorescence emitted by the transparent sheet are aligned, so that only light (polarized light) vibrating in a specific direction is imaged. At this time, the polarization direction of the UV-cut polarizing filter 12 is the same as that of the polarizing filters 13A and 13B. Regularly reflected light that maintains a specific vibration direction is incident on the lens 8 from the transparent sheet, and diffusely reflected light with random vibration directions is incident from the object M to be read. Therefore, the light reflected from the transparent sheet is received in a relatively large amount compared to the light reflected from the object M. The UV-cut polarizing filter 12 may be configured by arranging a UV-cut filter that cuts ultraviolet light and a polarizing filter that aligns the vibration direction of the light that passes through in a predetermined order, or may be configured by combining a UV-cut filter and a polarizing filter into a single filter. The sensor chip 11 converts the optical signal representing the image formed by the light reflected from the object M and the fluorescence emitted by the transparent sheet into an electrical signal and outputs it to the signal processing device 15. The signal processing device 15 performs signal processing to convert the electrical signal from the sensor chip 11 into image data. The signal processing device 15 detects the transparent sheet on the object M based on the image data. The signal processing device 15 may be configured, for example, by performing binarization processing and using a color threshold. The signal processing device 15 may output detection data indicating the detection of the transparent sheet to an external device or system, or may transmit it to a user terminal. Alternatively, the user may be notified of the detection of the transparent sheet by displaying it on a screen or outputting an audio message.

[0018] The component configuration of the image reading device 100 will be described with reference to Fig. 2. Fig. 2 is an exploded perspective view of the image reading device 100 according to the first embodiment. The image reading device 100 includes a glass plate 1, a light guide 2A and a light guide 2B, a light guide support member 3A and a light guide support member 3B that support the light guide 2A and the light guide 2B, respectively, a holder 4 attached to the light guide 2A and the light guide 2B, a light source substrate 5 on which a light source is mounted, a heat conduction sheet 6 that conducts heat from the light source, a heat sink 7 that dissipates heat from the light source, a lens 8, a frame 9, a sensor substrate 10, and a sensor chip 11.

[0019] The frame 9 is a frame body whose longitudinal direction is the main scanning direction and has openings on the top and bottom. The frame 9 is made of a material such as a metal such as aluminum or a resin. A space extending in the main scanning direction is formed inside the frame 9, and the light guides 2A and 2B, the light guide support members 3A and 3B, the holder 4, the light source substrate 5, the heat conduction sheet 6, the heat sink 7, and the lens 8 are housed in the frame 9. The glass plate 1 is disposed on the top surface of the frame 9. The sensor substrate 10 and the sensor chip 11 are disposed on the bottom surface of the frame 9.

[0020] The light guides 2A and 2B are, for example, rod-shaped transparent bodies made of resin. The light guides 2A and 2B extend in the main scanning direction. A light source substrate 5 is provided at the ends of the light guides 2A and 2B in the main scanning direction. A light source (not shown) that emits light is mounted on the light source substrate 5 at a position facing the end faces of the light guides 2A and 2B in the main scanning direction. In order to dissipate heat generated when the light source is turned on, a heat conduction sheet 6 and a heat sink 7 are provided on the surface of the light source substrate 5 opposite the surface on which the light source is mounted.

[0021] The light guides 2A and 2B, the light source substrate 5, the heat conduction sheet 6, and the heat sink 7 are connected by the holder 4. For convenience, in Fig. 2, only the holder 4, the light source substrate 5, the heat conduction sheet 6, and the heat sink 7 provided at one end of the light guides 2A and 2B in the main scanning direction are labeled with reference numerals. However, the holder 4, the light source substrate 5, the heat conduction sheet 6, and the heat sink 7 are also present at the opposite end across the light guides 2A and 2B, and the light guides 2A and 2B, the light source substrate 5, the heat conduction sheet 6, and the heat sink 7 are also connected by the holder 4 at the opposite end.

[0022] A plurality of lenses 8 are arranged in the main scanning direction and are held by, for example, a side plate (not shown). A plurality of lenses 8 arranged in the main scanning direction is also called a lens array. The lens array is supported by a lens body support portion 91 formed on a frame 9. The lenses 8 are, for example, rod lenses or microlenses that form an erect image of incident light at the same magnification.

[0023] A glass plate 1 is placed on the top surface of the frame 9 that houses the various components, covering the opening. The glass plate 1 has a flat plate shape with both the surface facing the frame 9 (inner surface) and the surface opposite the frame 9 (outer surface), both of which are parallel to a plane defined by the main scanning direction and the sub-scanning direction. The outer surface of the glass plate 1 is the surface (reading surface) that reads the image of the object M to be read, and regulates the reading position of the object M in the height direction. The material of the glass plate 1 is, for example, transparent glass or transparent resin.

[0024] A sensor substrate 10, on which a sensor chip 11 is mounted, is disposed on the bottom surface of the frame 9 so as to cover the opening. A plurality of sensor chips 11 are arranged on the sensor substrate 10 in the main scanning direction X. The sensor chips 11 are aligned with the optical axis of the lens 8 and face the lens 8. That is, the optical axis of the lens 8 is aligned so as to pass through the sensor chip 11. An opening larger than the area of ​​the portion of the sensor substrate 10 on which the sensor chip 11 is mounted is formed on the bottom surface of the frame 9. The sensor chip 11 is exposed to the space inside the frame 9 through the opening on the bottom surface. In other words, the sensor chip 11 is sealed by the glass plate 1, the frame 9, and the sensor substrate 10. The frame 9 and the sensor substrate 10 are light-tight. Therefore, the frame 9 and the sensor substrate 10 can block light outside the image reading device 100 except for light incident from the glass plate 1. Furthermore, foreign matter such as dust and dirt can be prevented from entering the interior of the image reading device 100.

[0025] FIG. 3 is a plan view of the image reading device 100 as viewed from the glass plate 1 side. FIG. 4 shows a cross section of the image reading device 100 in the main scanning direction passing through the light guide 2A and a cross section of the image reading device 100 in the main scanning direction passing through the light guide 2B. A light source 31 that emits light is mounted on the surface of the light source substrate 5 of the image reading device 100 facing the end faces of the light guides 2A and 2B in the main scanning direction. The light source 31 is, for example, an LED (light emitting diode) chip. In this embodiment, the light from the light source 31 includes deep ultraviolet light (wavelength: 200 to 300 nm) that excites a transparent sheet to fluoresce in order to detect the transparent sheet. The light emitted by the light source 31 is incident on the end faces of the light guides 2A and 2B. The light from the light source 31 that enters the end faces of the light guides 2A and 2B is reflected inside the light guides 2A and 2B and propagates in the main scanning direction. The propagated light is diffused and emitted toward the glass plate 1 as linear light extending in the main scanning direction. At this time, the light emitted from the light guides 2A and 2B illuminates the reading position 17. The light guides 2A and 2B, the holder 4, the light source substrate 5, the thermal conduction sheet 6, the heat sink 7, and the light source 31 are examples of an illumination unit. The illumination unit irradiates the object to be read, which is transported in the sub-scanning direction, with light extending in the main scanning direction. Irradiating light extending in the main scanning direction means irradiating light with a band of light rays extending in the main scanning direction.

[0026] The image reading device 100 includes a light source 31 that emits light containing deep ultraviolet light that excites the transparent sheet to fluoresce, and polarizing filters 13A and 13B that align the vibration direction of the light from the light source 31 between the light guides 2A and 2B and the reading position 17. A UV-cut polarizing filter 12 is provided between the sensor chip 11 and the lens 8 to align the vibration direction of the light reflected by the object M and the fluorescence emitted by the transparent sheet. By aligning the vibration direction of the light and receiving the fluorescence emitted by the transparent sheet, a clear contrast is achieved between the signal of the object M without a transparent sheet and the signal of the object M with a transparent sheet. This enables the image reading device 100 to detect the transparent sheet attached to the object M with effective and simple signal processing. Therefore, the image reading device 100 can detect the transparent sheet of the detection target with high accuracy. The polarizing filters 13A and 13B are an example of a first polarizing filter, and the UV-cut polarizing filter 12 is an example of a second polarizing filter.

[0027] As described above, according to the first embodiment, by providing polarizing filters 13A, 13B, and UV-cut polarizing filter 12, it is possible to improve detection accuracy and detect a transparent sheet on object M regardless of the transport conditions of object M. Furthermore, by providing light guides 2A and 2B that emit light from both sides of reading position 17, even if object M has a crease, it is possible to prevent the generation of a blind area that is not illuminated by light and becomes a shadow, making it impossible to read.

[0028] (Embodiment 2) In Embodiment 1, the image reading device 100 irradiates the object M to be read with light including deep ultraviolet light that excites the transparent sheet to emit fluorescence, and detects the transparent sheet attached to the object M by utilizing the difference in characteristics between the light reflected by the object M and the fluorescence emitted by the transparent sheet. In contrast, in Embodiment 2, the image reading device 100 guides the light specularly reflected by the object M to the sensor chip 11, and detects the transparent sheet attached to the object M by utilizing the difference in the amount of light received by the sensor chip 11 between the light specularly reflected by the object M and the light specularly reflected by the transparent sheet.

[0029] 5 shows a cross-sectional view in the sub-scanning direction of an image reading device 100 according to embodiment 2. The image reading device 100 includes a glass plate 1 on which an object M to be read is placed, a light guide 2 that emits light to the object M to be read, a lens 8 that collects reflected light from the object M to be read, a frame 9 that has an open top surface and stores components, a sensor board 10 that is disposed on the bottom surface of the frame 9, a sensor chip 11 that converts received light into an electrical signal, a polarizing filter 13 that aligns the vibration direction of the light emitted from the light guide 2, a polarizing filter 16 that aligns the vibration direction of the light received by the sensor chip 11, and a signal processing device 15 that detects a transparent sheet based on the electrical signal from the sensor chip 11.

[0030] The light guide 2 is a light guide that irradiates light onto the object M to be read on the glass plate 1 that is transported in the sub-scanning direction. The light guide 2 irradiates the object M to be read with light from a light source (not shown). The light guide 2 has a light scattering section 14. The light scattering section 14 has a pattern that scatters light, such as by white printing or a prism. Light that is incident on the end surface of the light guide 2 from the light source is reflected inside the light guide 2 and propagates in the main scanning direction. The propagated light is diffused by the light scattering section 14 and emitted toward the reading position 17 as linear light extending in the main scanning direction. The light scattering section 14 in the light guide 2 is positioned and angled so that the reflected light is emitted in a direction oblique to the normal direction of the object M to irradiate the reading position 17.

[0031] The linear light emitted from the light guide 2 toward the reading position 17 passes through the polarizing filter 13, aligning the vibration direction and emitting only light (polarized light) vibrating in a specific direction. Therefore, only light effective for detecting a transparent sheet is irradiated toward the reading position 17. Specularly reflected light from the object M to be read at the reading position 17 is incident on the lens 8. If a transparent sheet is present at the reading position 17, specularly reflected light from the transparent sheet is incident on the lens 8. When light is irradiated at an angle other than a right angle to the object M to be read, the object M reflects light close to diffuse reflection, whereas a transparent sheet reflects light close to specular reflection. Therefore, the amount of specularly reflected light from the transparent sheet that is incident on the lens 8 is greater than the amount of specularly reflected light from the object M to be read. Furthermore, because only light effective for detecting a transparent sheet is irradiated toward the reading position 17, light unnecessary for detecting the transparent sheet is prevented from entering the lens 8, resulting in a striking contrast between the signal from the object M to be read and the signal from the transparent sheet.

[0032] The lens 8 forms an image of the specularly reflected light from the object to be read M and the transparent sheet on the sensor chip 11 disposed on the sensor substrate 10. By providing a polarizing filter 16 between the lens 8 and the sensor chip 11, the vibration directions of the specularly reflected light from the object to be read M and the transparent sheet that passes through the lens 8 are aligned. Here, the specularly reflected light from the transparent sheet is reflected while maintaining the vibration direction of the light incident on the transparent sheet, while the scattered light from the object to be read M is reflected to have a random vibration direction. Therefore, by allowing the sensor chip 11 to receive only light with a specific vibration direction, the contrast between the signal from the object to be read M and the signal from the transparent sheet is enhanced. The sensor chip 11 converts the optical signal of the image formed by the specularly reflected light from the object to be read M and the transparent sheet into an electrical signal and outputs it to the signal processing device 15. The signal processing device 15 performs signal processing to convert the electrical signal from the sensor chip 11 into image data. The signal processing device 15 detects the transparent sheet on the object to be read M based on the image data. The remaining configuration is the same as in the first embodiment. The light guide 2, the holder 4, the light source substrate 5, the heat conduction sheet 6, the heat sink 7, and the light source 31 are an example of an illumination unit.

[0033] The image reading device 100 includes a polarizing filter 13 between the light guide 2 and the reading position 17 for aligning the vibration direction of light from the light source, and a polarizing filter 16 between the sensor chip 11 and the lens 8 for aligning the vibration direction of light specularly reflected from the object M and light specularly reflected from the transparent sheet. This aligns the vibration direction of the light and suppresses scattered light, emphasizing the specularly reflected light component and enhancing the contrast between the object M without a transparent sheet and the object M with a transparent sheet. This enables the image reading device 100 to effectively detect the transparent sheet attached to the object M with simple signal processing. Therefore, the image reading device 100 can detect the transparent sheet of the object M with high accuracy. The polarizing filter 13 is an example of a first polarizing filter, and the polarizing filter 16 is an example of a second polarizing filter.

[0034] As described above, according to embodiment 2, by providing polarizing filters 13 and 16, detection accuracy can be improved, and it becomes possible to detect a transparent sheet on the object to be read M regardless of the transport conditions of the object to be read M.

[0035] In the first and second embodiments described above, the image reading device 100 includes the glass plate 1, but the glass plate 1 is not limited to glass and may be any transparent plate made of a transparent material.

[0036] In the first embodiment described above, the image reading device 100 includes the polarizing filters 13A and 13B. However, if the only purpose is to detect the presence of a transparent sheet on a paper medium, a visible light cut filter may be provided instead of the polarizing filters 13A and 13B. The visible light cut filter cuts out light in the visible range contained in the ultraviolet light source. The transparent sheet emits fluorescence when exposed to ultraviolet light from the ultraviolet light source. This fluorescence is input to the sensor chip, converted into an electrical signal, and output. The signal processing device 15 performs signal processing to convert the electrical signal from the sensor chip 11 into image data. The signal processing device 15 detects the transparent sheet on the paper medium based on the electrical signal from the sensor chip 11.

[0037] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and multiple embodiments can be freely combined, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0038] Various aspects of the present disclosure are summarized below as appendices.

[0039] (Supplementary Note 1) An image reading device that reads an image of an object to be read and detects a transparent sheet in contact with the object to be read, comprising: an illumination unit that irradiates the object to be read, being transported in a sub-scanning direction orthogonal to a main scanning direction, with light extending in the main scanning direction, a first polarizing filter that aligns the vibration direction of the light irradiated by the illumination unit, a lens that forms an image of light from the object to be read and the transparent sheet using the light irradiated by the illumination unit and whose vibration direction has been aligned by the first polarizing filter, a second polarizing filter that aligns the vibration direction of the light imaged by the lens, a light receiving element that converts the light whose vibration direction has been aligned by the second polarizing filter and which has been imaged by the lens into an electrical signal and outputs the electrical signal, and a signal processing device that detects the transparent sheet on the object to be read based on the electrical signal output by the light receiving element. (Supplementary Note 2) The image reading device according to Supplementary Note 1, wherein the vibration direction of light aligned by the first polarizing filter and the vibration direction of light aligned by the second polarizing filter are the same. (Supplementary Note 3) The image reading device according to Supplementary Note 1 or Supplementary Note 2, wherein the light irradiated onto the object to be read by the illumination unit includes deep ultraviolet light having a wavelength that causes the transparent sheet to fluoresce, the lens forms an image of the light reflected from the object to be read and the fluorescence emitted by the transparent sheet using the light irradiated by the illumination unit and whose vibration direction has been aligned by the first polarizing filter, the second polarizing filter includes a UV cut filter that cuts ultraviolet light, the light receiving element converts the light reflected from the object to be read and the fluorescence emitted by the transparent sheet, which have been imaged by the lens and whose vibration direction has been aligned by the second polarizing filter, into an electrical signal and outputs the electrical signal, and the signal processing device detects the transparent sheet on the object to be read based on the electrical signal output by the light receiving element, which is obtained by converting the light reflected from the object to be read and the fluorescence emitted by the transparent sheet.(Supplementary Note 4) An image reading device according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the optical axis of the light irradiated onto the object to be read and the optical axis of the light received by the light receiving element are symmetrical with respect to the normal of the object to be read at the reading position; the lens forms an image of the object to be read and specularly reflected light from the transparent sheet using light irradiated by the illumination unit and whose vibration direction is aligned by the first polarizing filter; the light receiving element converts the specularly reflected light from the object to be read and the transparent sheet, whose vibration direction is aligned by the second polarizing filter and which is imaged by the lens, into an electrical signal and outputs the electrical signal; and the signal processing device detects the transparent sheet on the object to be read based on the electrical signal converted from the specularly reflected light from the object to be read and the transparent sheet output by the light receiving element. (Supplementary Note 5) An image reading device that detects a transparent sheet on a paper medium, comprising: an illumination unit that irradiates the paper medium transported in a sub-scanning direction with light including deep ultraviolet light having a wavelength that causes the transparent sheet to fluoresce; a visible light cut filter that cuts out visible light included in the light irradiated by the illumination unit; a lens that forms an image of light reflected from the paper medium and fluorescence emitted by the transparent sheet using light irradiated by the illumination unit and from which visible light has been cut by the visible light cut filter; a UV cut polarizing filter that cuts out ultraviolet light and aligns the vibration direction of the light imaged by the lens; a light receiving element that converts into electrical signals the reflected light from the paper medium and fluorescence emitted by the transparent sheet imaged by the lens, the ultraviolet light being cut by the UV cut polarizing filter and the vibration direction being aligned; and a signal processing device that detects the transparent sheet based on the electrical signal converted by the light receiving element. (Supplementary Note 6) The image reading device described in any one of Supplementary Note 1 to Supplementary Note 5, wherein the illumination unit comprises: rod-shaped first and second light guides extending in the main scanning direction; and a light source that directs light into the first and second light guides, and the first and second light guides emit light from both sides of an irradiation position in the sub-scanning direction where the light is irradiated onto the object to be read.(Supplementary Note 7) The image reading device according to Supplementary Note 6, wherein at least one of the light sources is provided facing an end face in the main scanning direction of each of the first light guide and the second light guide. (Supplementary Note 8) The image reading device according to any one of Supplementary Notes 1 to 7, wherein the signal processing device converts the electrical signal converted by the light receiving element into image data, and detects the transparent sheet on the reading object based on the image data.

[0040] It should be noted that the present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments are intended to explain the disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and within the meaning of the disclosure equivalent thereto are considered to be within the scope of the present disclosure.

[0041] This application is based on Japanese Patent Application No. 2023-212557, filed on December 15, 2023. The entire specification, claims, and drawings of Japanese Patent Application No. 2023-212557 are incorporated herein by reference.

[0042] 1 Glass plate, 2, 2A, 2B Light guide, 3A, 3B Light guide support member, 4 Holder, 5 Light source substrate, 6 Heat conduction sheet, 7 Heat sink, 8 Lens, 9 Frame, 10 Sensor substrate, 11 Sensor chip, 12 UV cut polarizing filter, 13, 13A, 13B Polarizing filter, 14, 14A, 14B Light scattering unit, 15 Signal processing device, 16 Polarizing filter, 17 Reading position, 31 Light source, 91 Lens body support unit, 100 Image reading device, M Reading object.

Claims

1. An image reading device that reads an image of an object to be read and detects a transparent sheet in contact with the object to be read, comprising: an illumination unit that irradiates the object to be read as it is transported in a sub-scanning direction perpendicular to the main scanning direction with light that extends in the main scanning direction; a first polarizing filter that aligns the vibration direction of the light irradiated by the illumination unit; a lens that forms an image of light from the object to be read and the transparent sheet using the light irradiated by the illumination unit and whose vibration direction has been aligned by the first polarizing filter; a second polarizing filter that aligns the vibration direction of the light imaged by the lens; a light receiving element that converts the light whose vibration direction has been aligned by the second polarizing filter and imaged by the lens into an electrical signal and outputs it; and a signal processing device that detects the transparent sheet on the object to be read based on the electrical signal output by the light receiving element.

2. The image reading device according to claim 1, wherein the vibration direction of light aligned by said first polarizing filter and the vibration direction of light aligned by said second polarizing filter are the same.

3. The image reading device described in claim 1 or 2, wherein the light irradiated by the illumination unit onto the object to be read includes deep ultraviolet light having a wavelength that causes the transparent sheet to fluoresce, the lens forms an image of the reflected light from the object to be read and the fluorescence emitted by the transparent sheet using light irradiated by the illumination unit and whose vibration direction has been aligned by the first polarizing filter, the second polarizing filter includes a UV cut filter that cuts out ultraviolet light, the light receiving element converts the reflected light from the object to be read and the fluorescence emitted by the transparent sheet, which have been imaged by the lens and whose vibration direction has been aligned and ultraviolet light has been cut out by the second polarizing filter, into an electrical signal and outputs it, and the signal processing device detects the transparent sheet on the object to be read based on the electrical signal converted from the reflected light from the object to be read and the fluorescence emitted by the transparent sheet, which are output by the light receiving element.

4. An image reading device as described in any one of claims 1 to 3, wherein the illumination section comprises: rod-shaped first and second light guides extending in the main scanning direction; and a light source that directs light into the first and second light guides, and the first and second light guides emit light from both sides of an irradiation position in the sub-scanning direction at which light is irradiated onto the object to be read.

5. The image reading device according to claim 4, wherein at least one of the light sources is provided facing an end surface in the main scanning direction of each of the first light guide and the second light guide.

6. An image reading device as described in any one of claims 1 to 5, wherein the optical axis of the light irradiated to the object to be read and the optical axis of the light received by the light receiving element are symmetrical with respect to the normal of the object to be read at the reading position, the lens forms an image of specularly reflected light from the object to be read and the transparent sheet using light irradiated by the illumination unit and whose vibration direction is aligned by the first polarizing filter, the light receiving element converts the specularly reflected light from the object to be read and the transparent sheet, whose vibration direction is aligned by the second polarizing filter and which is imaged by the lens, into an electrical signal and outputs it, and the signal processing device detects the transparent sheet on the object to be read based on the electrical signal converted from the specularly reflected light from the object to be read and the transparent sheet output by the light receiving element.

7. An image reading device according to any one of claims 1 to 6, wherein the signal processing device converts the electrical signal converted by the light receiving element into image data, and detects the transparent sheet on the object to be read based on the image data.

8. An image reading device for detecting a transparent sheet on a paper medium, comprising: an illumination unit that irradiates the paper medium transported in a sub-scanning direction with light including deep ultraviolet light having a wavelength that causes the transparent sheet to fluoresce; a visible light cutting filter that cuts visible light contained in the light irradiated by the illumination unit; a lens that forms an image of reflected light from the paper medium and fluorescence emitted by the transparent sheet using light irradiated by the illumination unit and from which visible light has been cut by the visible light cutting filter; a UV-cut polarizing filter that cuts ultraviolet light and aligns the vibration direction of the light imaged by the lens; a light-receiving element that converts the reflected light from the paper medium and fluorescence emitted by the transparent sheet, imaged by the lens and whose vibration direction has been aligned and from which ultraviolet light has been cut by the UV-cut polarizing filter, into an electrical signal; and a signal processing device that detects the transparent sheet based on the electrical signal converted by the light-receiving element.

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