Recording medium discrimination device, image forming apparatus, and recording medium discrimination method

Abstract

To provide a recording medium discrimination device, an image forming apparatus, and a recording medium discrimination method that can more appropriately discriminate the type of a recording medium.SOLUTION: A recording medium discrimination device comprises: a light irradiation unit that irradiates a recording medium with inspection light; a light detection unit that detects incident light including at least one of diffused and reflected light of the inspection light with which the recording medium is irradiated and fluorescent light excited by the inspection light on the recording medium; and discrimination means that performs discrimination related to one characteristic of the recording medium based on a result of detection of first incident light according to first inspection light and second incident light according to second inspection light performed by the light detection unit. The first inspection light has an intensity peak wavelength of 750 nm or more and 1100 nm or less, and the second inspection light has an intensity peak wavelength shorter than that of the first inspection light.SELECTED DRAWING: Figure 13

Description

Technical Field

[0001] The present invention relates to a recording medium discrimination device, an image forming apparatus, and a recording medium discrimination method.

Background Art

[0002] Conventionally, in an image forming apparatus that forms an image by applying a coloring material to a recording medium such as paper, a recording medium discrimination device that discriminates the type of the recording medium has been used. By adjusting the conditions related to image formation (for example, conveyance conditions and fixing conditions of the coloring material) according to the discriminated type of the recording medium, an image can be formed with higher quality.

[0003] As the recording medium discrimination device, discrimination related to one characteristic of the recording medium is performed based on the amount of received light of reflected light and / or fluorescence when the recording medium is irradiated with inspection light in a predetermined wavelength range, and the type of the recording medium is discriminated based on this discrimination result (for example, Patent Document 1). Examples of the characteristics of the recording medium to be discriminated include the material, the presence or absence of a fluorescent whitening agent, and the degree of gloss on the surface. In Patent Document 1, the presence or absence of a fluorescent whitening agent is discriminated by irradiating the recording medium with inspection light in the ultraviolet wavelength range and detecting the amount of received fluorescence. Also, the degree of gloss is discriminated by detecting the amount of diffusely reflected light of the inspection light.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the above conventional technique for performing discrimination related to one characteristic of the recording medium using inspection light in one wavelength range, when the amount of received light fluctuates due to factors other than the characteristic to be discriminated, it becomes difficult to accurately discriminate the characteristic related to the recording medium. For example, when the amount of reflected light of the inspection light fluctuates due to differences in basis weight of the recording medium or the like, it is impossible to discriminate whether the fluctuation is due to the characteristic to be discriminated of the recording medium or due to other factors such as basis weight. Thus, in the above conventional technique, there is a problem that it may be difficult to accurately discriminate the characteristic related to the recording medium, and misjudgment related to the type of the recording medium is likely to occur.

[0006] An object of the present invention is to provide a recording medium discrimination device, an image forming apparatus, and a recording medium discrimination method capable of more appropriately discriminating the type of a recording medium.

Means for Solving the Problems

[0007] To achieve the above object, the invention of the recording medium discrimination device according to claim 1 is a light irradiation unit that irradiates inspection light onto a recording medium, a light detection unit that detects incident light including at least one of diffused reflected light of the inspection light irradiated onto the recording medium and fluorescence excited by the inspection light in the recording medium, discrimination means for performing discrimination related to one characteristic of the recording medium based on detection results by the light detection unit of the first incident light corresponding to the first inspection light and the second incident light corresponding to the second inspection light, and the first inspection light has a peak wavelength of intensity of 750 nm or more and 1100 nm or less, the second inspection light has a peak wavelength of intensity shorter than that of the first inspection light < , The light irradiation unit includes: a first light emitting element that emits the first inspection light; a second light emitting element that emits the second inspection light having a certain peak wavelength; a third light emitting element that emits the second inspection light having a peak wavelength different from the certain peak wavelength; and the discrimination means performs discrimination regarding a certain characteristic of the recording medium based on the detection result of the first incident light corresponding to the first inspection light and the detection result of the second incident light corresponding to the second inspection light emitted by the second light emitting element; performs discrimination regarding a characteristic different from the certain characteristic of the recording medium based on the detection result of the first incident light corresponding to the first inspection light and the detection result of the second incident light corresponding to the second inspection light emitted by the third light emitting element 。

[0008] The invention according to claim 2 is the recording medium discrimination device according to claim 1, wherein the discrimination means performs discrimination regarding the characteristic based on a ratio between a first value corresponding to the amount of light received by the light detection unit of the first incident light and a second value corresponding to the amount of light received by the light detection unit of the second incident light.

[0009] The invention according to claim 3 is the recording medium discrimination device according to claim Item 2 wherein the discrimination means performs discrimination regarding the characteristic based on a region among a plurality of predetermined regions in a coordinate plane having the first value and the second value as two axes, in which the coordinates corresponding to the detection result are included.

[0010] The invention according to claim 4 is the recording medium discrimination device according to claim 3, wherein the plurality of regions are divided by a straight line that is non-parallel to the two axes of the coordinate plane.

[0011] The invention according to claim 5 is the recording medium discrimination device according to any one of claims 1 to 4, wherein the second inspection light has a peak wavelength of intensity in the range of 390 nm or more and 440 nm or less.

[0012] The invention according to claim 6 is the recording medium discrimination device according to any one of claims 1 to 4, wherein the second inspection light has a peak wavelength of intensity in the range of 280 nm or more and 400 nm or less.

[0013] The invention according to claim 7 is the recording medium discrimination device according to any one of claims 1 to 6, wherein the first inspection light has a peak wavelength of intensity in the range of 800 nm or more and 900 nm or less.

[0014] The invention according to claim 8 is a recording medium discrimination apparatus according to any one of claims 1 to 7, wherein the light detection unit has a light receiving element for detecting the incident light, the light receiving element is a photodiode or a phototransistor having a detection sensitivity in a wavelength range from the visible wavelength range to the near-infrared wavelength range.

[0015] The invention according to claim 9 is a recording medium discrimination apparatus according to any one of claims 1 to 8, wherein it includes a substrate provided at a position facing the conveyance path of the recording medium, the light irradiation unit has a light emitting element for emitting the inspection light, the light detection unit has a light receiving element for detecting the incident light, the light emitting element and the light receiving element are provided on the substrate.

[0016] The invention according to claim 10 is a recording medium discrimination apparatus according to any one of claims 1 to 9, wherein The first light emitting element, the second light emitting element, and the third light emitting element emit light in order such that their irradiation periods are different from each other. .

[0018] Also, to achieve the above object, the invention of the image forming apparatus according to claim 11 is a recording medium discrimination apparatus according to any one of claims 1 to 10 and an image forming unit that forms an image by applying a coloring material to the recording medium. It includes .

[0019] Also, to achieve the above object, the invention of the recording medium discrimination method according to claim 12 is a recording medium discrimination method using a recording medium discrimination apparatus including a light irradiation unit that irradiates a recording medium with inspection light, and a light detection unit that detects at least one of diffused reflected light of the inspection light irradiated to the recording medium and fluorescence excited by the inspection light in the recording medium. including a step of performing determination regarding one characteristic of the recording medium based on detection results by the light detection unit of the first incident light corresponding to the first inspection light and the second incident light corresponding to the second inspection light; the first inspection light has a peak wavelength of intensity in the range of 750 nm or more and 1100 nm or less; the second inspection light has a peak wavelength of intensity shorter than that of the first inspection light < , The light irradiation unit includes: a first light emitting element that emits the first inspection light; a second light emitting element that emits the second inspection light having a certain peak wavelength; a third light emitting element that emits the second inspection light having a peak wavelength different from the certain peak wavelength; and in the step performs discrimination regarding a certain characteristic of the recording medium based on the detection result of the first incident light corresponding to the first inspection light and the detection result of the second incident light corresponding to the second inspection light emitted by the second light emitting element; performs discrimination regarding a characteristic different from the certain characteristic of the recording medium based on the detection result of the first incident light corresponding to the first inspection light and the detection result of the second incident light corresponding to the second inspection light emitted by the third light emitting element 。

Advantages of the Invention

[0020] According to the present invention, the type of the recording medium can be more appropriately determined.

Brief Description of the Drawings

[0021]

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Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments of a recording medium discrimination apparatus, an image forming apparatus, and a recording medium discrimination method according to the present invention will be described with reference to the drawings.

[0023] (Configuration of Image Forming Apparatus and Recording Medium Discrimination Apparatus) FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram showing a main functional configuration of the image forming apparatus 1. The image forming apparatus 1 is an MFP (Multifunction Peripheral) that forms an image on a recording medium by an electrophotographic method. The image forming apparatus 1 includes a control unit 10, a medium inspection unit 20, an image forming unit 30, a fixing unit 40, a scanner 50, an operation display unit 60, a communication unit 70, a paper feed tray 81, a conveyance roller 82, a paper discharge tray 83, a bus 90, and the like. As shown in FIG. 2, a recording medium discrimination device 2 for discriminating the type of the recording medium is configured by the control unit 10 and the medium inspection unit 20. Each unit of the image forming apparatus 1 is connected by a bus 90.

[0024] The control unit 10 includes a CPU 11 (Central Processing Unit), a RAM 12 (Random Access Memory), and a storage unit 13.

[0025] The CPU 11 reads and executes a program 131 stored in the storage unit 13 and performs various arithmetic processes.

[0026] The RAM 12 provides a working memory space for the CPU 11 and stores temporary data.

[0027] The storage unit 13 is composed of a non-volatile storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), and a flash memory, and stores a program 131 executed by the CPU 11, various data, and the like. Data stored in the storage unit 13 includes image data acquired by the scanner 50, image data input from the outside via the communication unit 70, discrimination reference data 132 referred to in the discrimination operation of the recording medium described later, and the like.

[0028] The control unit 10 functions as a discrimination means by the CPU 11 executing the program 131 stored in the storage unit 13 to perform various processes. The control unit 10 as the discrimination means discriminates based on the data acquired from the medium inspection unit 20 regarding one characteristic of the recording medium, and discriminates the type of the recording medium based on this discrimination result. The discrimination of the type of the recording medium will be described in detail later. Also, the control unit 10 comprehensively controls each part of the image forming apparatus 1 by the CPU 11 executing the program 131. For example, the control unit 10 operates each part of the image forming unit 30, the conveyance roller 82, and the fixing unit 40 based on the image data stored in the storage unit 13 to form an image on the recording medium. Here, the CPU 11 changes the operations related to image formation of each part of the image forming apparatus 1 according to the discrimination result of the recording medium by the recording medium discrimination device 2. For example, according to the type of the recording medium, the conveyance speed and the clamping pressure by the conveyance roller 82 are changed. Also, according to the type of the recording medium, the heating temperature and the applied pressure by the fixing unit 40 are changed.

[0029] The medium inspection unit 20 is provided at a position along the conveyance path on the upstream side of the image forming unit 30 in the conveyance path of the recording medium from the paper feed tray 81 to the paper discharge tray 83. However, the position of the medium inspection unit 20 is not limited to this, and it can be arranged at any position along the conveyance path. As shown in FIG. 2, the medium inspection unit 20 includes a light irradiation unit 21 and a light detection unit 22. The light irradiation unit 21 irradiates inspection light to the recording medium passing through the conveyance path under the control of the control unit 10. The light detection unit 22 detects incident light including at least one of the diffused reflected light of the inspection light irradiated on the recording medium and the fluorescence excited by the inspection light in the recording medium. The configuration and operation of the medium inspection unit 20 will be described in detail later.

[0030] The image forming unit 30 forms an image by applying toner (color material) to a recording medium supplied from the paper feed tray 81. The image forming unit 30 includes an intermediate transfer belt 31, an image forming unit 32, a transfer roller 33, and the like. The intermediate transfer belt 31 is an endless belt-like member that is stretched around a plurality of rollers and moves in a circular motion. The image forming unit 32 is arranged along the intermediate transfer belt 31, and forms toner images of each color of C (cyan), M (magenta), Y (yellow), and K (black) on the intermediate transfer belt 31 based on the image data related to the image to be printed. When the recording medium passes through the nip portion between the intermediate transfer belt 31 and the transfer roller 33, the toner image is transferred to the recording medium to form an image. In addition, in this embodiment, the image forming unit 30 capable of forming a color image is exemplified, but it is not limited to this, and an image forming unit 30 capable of forming a monochrome image may be used.

[0031] The fixing unit 40 heats and presses the recording medium onto which the toner image has been transferred to fix the toner image on the recording medium. The fixing unit 40 includes a pair of rollers including a heating roller and a pressure roller that sandwich the recording medium. The recording medium on which the toner image has been fixed is conveyed by the conveying roller 82 and sent out to the paper discharge tray 83. The heating conditions and pressure conditions by the fixing unit 40 are controlled by the control unit 10 according to the type of the recording medium and the like.

[0032] The scanner 50 includes an optical system such as a light source and a reflecting mirror, and an imaging element, reads an image of a recording medium conveyed through a predetermined conveyance path or a recording medium placed on a platen glass, and generates bitmap format image data for each color of R (red), G (green), and B (blue). The generated image data is stored in the storage unit 13. By performing image formation by the image forming unit 30 based on this image data, the read image can also be copied onto another recording medium.

[0033] The operation display unit 60 includes a display device such as a liquid crystal display, a touch panel arranged to overlap the screen of the display device, and an input device such as operation keys. The operation display unit 60 performs various displays such as the operation status and processing results of the image forming apparatus 1 on the display device, and also converts a user's input operation on the input device into an operation signal and outputs it to the control unit 10.

[0034] The communication unit 70 is constituted by a network card or the like. The communication unit 70 is connected to a communication network such as a LAN (Local Area Network), and transmits and receives information to and from external devices on the communication network. The control unit 10 communicates with external devices on the communication network via the communication unit 70.

[0035] The paper feed tray 81 stores the recording medium before image formation. The paper feed tray 81 may store a plurality of types (kinds) of recording media. Here, the type of the recording medium is characterized by at least one of the characteristics of the material (raw material) of the recording medium, the state of surface treatment, the presence or absence and amount of a fluorescent brightening agent, the presence or absence of bluing, and color. Therefore, recording media with at least one of these characteristics being different from each other are recording media of different types. The recording media stored in the paper feed tray 81 are, for example, plain paper, coated paper, medium paper, and recycled paper, etc., which are an example of recording media of different types. Plain paper is paper produced mainly from pulp made from wood (i.e., pulp not recycled from waste paper, usually chemical pulp). Coated paper is paper with a coating material or the like applied to the surface. Medium paper is, for example, paper produced mainly from mechanical pulp. Recycled paper is paper in which waste paper pulp taken out from waste paper is blended at a blending ratio of a predetermined amount or more. The type of the recording medium stored in the paper feed tray 81 is not limited to the above.

[0036] The conveyance roller 82 conveys the recording medium along the conveyance path by rotating while sandwiching one recording medium. The conveyance timing and conveyance speed by the conveyance roller 82 are controlled by the control unit 10 according to the type of the recording medium and the like.

[0037] The paper discharge tray 83 places the recording medium on which an image has been formed until it is taken out by the user.

[0038] (Configuration of the medium inspection unit) Next, the configuration of the medium inspection unit 20 will be described. FIG. 3 is a diagram showing the configuration of the medium inspection unit 20. FIG. 3(a) is a cross-sectional view of the medium inspection unit 20 as viewed from a direction parallel to the conveyance path (conveyance surface) of the recording medium M. FIG. 3(b) is a plan view of the medium inspection unit 20 as viewed from a direction perpendicular to the conveyance surface (z direction). The medium inspection unit 20 includes an element substrate 23 (substrate) provided at a position facing the conveyance surface of the conveyance path of the recording medium M (in other words, at a position facing the recording medium M passing through the conveyance path), a paper feed guide 25 that supports the recording medium M so that the recording medium M moves along the conveyance path, and an optical aperture 24 provided on the opposite side of the paper feed guide 25 with the recording medium M interposed therebetween.

[0039] The element substrate 23 is arranged perpendicular to the z direction. On the surface of the element substrate 23 facing the recording medium M, a first light emitting element 211 and a second light emitting element 212 of the light irradiation unit 21 and a light receiving element 220 of the light detection unit 22 are provided. The first light emitting element 211 irradiates the recording medium M with a first inspection light L1a. The second light emitting element 212 irradiates the recording medium M with a second inspection light L2a. The light detection unit 22 has one light receiving element 220. The light receiving element 220 outputs a photocurrent corresponding to the incident light amount. The light detection unit 22 converts this photocurrent into a voltage and then into digital data and outputs it to the control unit 10. As shown in FIGS. 3(a) and 3(b), the light receiving element 220 is arranged between the first light emitting element 211 and the second light emitting element 212. It is preferable that the distance from the first light emitting element 211 to the light receiving element 220 is equal to the distance from the second light emitting element 212 to the light receiving element 220.

[0040] The optical aperture 24 is a plate-shaped member arranged perpendicular to the z direction, and has an opening in a range including a portion facing the first light-emitting element 211, the second light-emitting element 212, and the light-receiving element 220. The first inspection light L1a and the second inspection light L2a enter the recording medium M through this opening. Further, the optical aperture 24 has a light-shielding property in portions other than the opening, and suppresses the entry of light other than the inspection light into the recording medium M.

[0041] The recording medium M is conveyed through the gap between the optical aperture 24 and the paper feed guide 25. Since the gap has a width in the z direction, the passing position of the recording medium M can vary in the z direction within the range of the width. In response to the variation in the passing position of the recording medium M, the distances between the first light-emitting element 211, the second light-emitting element 212, and the light-receiving element 220 and the recording medium M also vary. However, since the first light-emitting element 211, the second light-emitting element 212, and the light-receiving element 220 are provided on the same surface of the element substrate 23, the influence of the variation on the inspection result by the medium inspection unit 20 can be minimized.

[0042] FIG. 4 is a diagram for explaining the light to be detected by the medium inspection unit 20. On the surface of the recording medium M, the inspection light LA (the above-described first inspection light L1a or second inspection light L2a) emitted from the light irradiation unit 21 is incident. The reflected light of this inspection light LA on the recording medium M includes the surface diffused reflection light LB1 and the specular reflection light LC. Also, a part of the inspection light LA that has entered the recording medium M is diffusely reflected in a direction having a z-direction component as the internal diffused reflection light LB2. In this specification, the surface diffused reflection light LB1 and the internal diffused reflection light LB2 are collectively referred to as "diffused reflection light". Further, when a fluorescent brightening agent is added to the recording medium M, depending on the wavelength of the inspection light LA, fluorescence LB3 is excited in the recording medium M. The light detection unit 22 (light receiving element 220) of the present embodiment detects the surface diffused reflection light LB1, the internal diffused reflection light LB2, and the fluorescence LB3. Hereinafter, the light incident on the light receiving element 220 of the light detection unit 22 in response to the irradiation of the first inspection light L1a is referred to as "first incident light L1b", and the light incident on the light receiving element 220 of the light detection unit 22 in response to the irradiation of the second inspection light L2a is referred to as "second incident light L2b" (see Fig. 3(a)). The light receiving element 220 is provided at a position where it does not receive the specular reflection light LC of the inspection light LA emitted in the main emission directions (directions in which the emission intensity is the highest) of the first light emitting element 211 and the second light emitting element 212. Note that instead of a configuration in which a single light receiving element 220 is provided, a light receiving element for detecting the first incident light L1b and a light receiving element for detecting the second incident light L2b may be provided separately.

[0043] FIG. 5 is a diagram showing an example of the emission spectra of the first light emitting element 211 and the second light emitting element 212. The first inspection light L1a irradiated from the first light-emitting element 211 has a peak wavelength (center wavelength) of the intensity in the range of 750 nm or more and 1100 nm or less. More preferably, the peak wavelength of the intensity of the first inspection light L1a is in the range of 800 nm or more and 900 nm or less. Further, the second inspection light L2a irradiated from the second light-emitting element 212 has a peak wavelength of the intensity shorter than that of the first inspection light L1a. The peak wavelength of the second inspection light L2a is set according to the purpose of inspection as described later. In FIG. 5, a case where the peak wavelength of the intensity of the first inspection light L1a is 850 nm and the peak wavelength of the intensity of the second inspection light L2a is 400 nm is illustrated. The half-value width of the emission spectra of the first light-emitting element 211 and the second light-emitting element 212 can be, for example, about 20 to 30 nm, but is not limited thereto. As the first light-emitting element 211 and the second light-emitting element 212, for example, an LED (Light Emitting Diode) or an LD (Laser Diode) can be used, but is not limited thereto.

[0044] FIG. 6 is a diagram showing an example of the spectral sensitivity characteristics of the light-receiving element 220. As shown in FIG. 6, the light receiving element 220 of the light detection unit 22 has detection sensitivity (light receiving sensitivity) in a wavelength range from the visible wavelength range to the near-infrared wavelength range. Here, the visible wavelength range is approximately 380 nm or more and 780 nm or less. Also, the near-infrared wavelength range is approximately 780 nm or more and 2500 nm or less. As the light receiving element 220, a photodiode or a phototransistor can be used. In particular, an Si (silicon) photodiode, an Si phototransistor, a Ge (germanium) photodiode, or a Ge phototransistor having detection sensitivity in a wavelength range from the visible wavelength range to the near-infrared wavelength range can be preferably used. These photodiodes and phototransistors have spectral sensitivity characteristics in which the light receiving sensitivity becomes higher toward the longer wavelength side from the visible wavelength range to the near-infrared wavelength range, as shown in FIG. 6. Therefore, since the light receiving sensitivity of fluorescence (blue region in the visible wavelength range) is higher than that of the excitation light of fluorescence (ultraviolet wavelength range), it can be preferably used for discriminating the presence or absence and amount of a fluorescent whitening agent, as described later. In particular, when borosilicate glass or a coating resin is used rather than quartz as the window of the light receiving element 220, the light receiving sensitivity in the ultraviolet wavelength range is lower, so the accuracy of fluorescence discrimination is higher. Note that an element other than a photodiode and a phototransistor may be used as the light receiving element 220.

[0045] Before inspecting the recording medium M, the light emission intensities of the first light emitting element 211 and the second light emitting element 212 are calibrated respectively, so that the reflectance of the recording medium M can be calculated from the amount of light received by the light receiving element 220. That is, first, a predetermined reflecting member for calibration is arranged in the irradiation range of the first inspection light L1a (the second inspection light L2a) from the first light emitting element 211 (the second light emitting element 212), and the amount of light received by the light detection unit 22 of the reflected light from the reflecting member is detected. As the reflecting member for calibration, a standard white plate, a predetermined sheet of paper, or a predetermined sheet can be used. Then, the recording medium M to be inspected is conveyed to the position of the medium inspection unit 20, and the recording medium M is irradiated with the first inspection light L1a (the second inspection light L2a) from the first light emitting element 211 (the second light emitting element 212), and the amount of light received by the light detection unit 22 of the first incident light L1b (the second incident light L2b) is detected. From these detection results, the reflectance R1 (reflectance R2) can be calculated. In this specification, the reflectance is defined as "the amount of light received by the incident light when the recording medium M is irradiated with the inspection light / the amount of light received by the reflected light when the calibration reflecting member is irradiated with the inspection light". Therefore, when fluorescence is excited in the recording medium M, in addition to the amount of light received by the diffused reflected light, the amount of light received by the fluorescence is reflected in the reflectance. The reflectance R1 calculated from the amount of light received by the light detection unit 22 of the first incident light L1b is an aspect of the "first value". Also, the reflectance R2 calculated from the amount of light received by the light detection unit 22 of the second incident light L2b is an aspect of the "second value".

[0046] The first light-emitting element 211 and the second light-emitting element 212 emit light alternately in order under the control of the control unit 10. In other words, the period during which the first light-emitting element 211 irradiates the recording medium M with the first inspection light L1a is different from the period during which the second light-emitting element 212 irradiates the recording medium M with the second inspection light L2a. The light detection unit 22 alternately detects the first incident light L1b corresponding to the irradiation of the first inspection light L1a and the second incident light L2b corresponding to the irradiation of the second inspection light L2a in order. That is, the medium inspection unit 20 of the present embodiment performs time-division measurement. Note that the light emission periods of the first light-emitting element 211 and the second light-emitting element 212 may partially overlap. In this case, the first incident light L1b may be detected during the period when only the first light-emitting element 211 emits light, and the second incident light L2b may be detected during the period when only the second light-emitting element 212 emits light.

[0047] (Operations of the image forming apparatus and the recording medium discrimination apparatus) Next, the operations of the image forming apparatus 1 and the recording medium discrimination apparatus 2 will be described centering on the operations related to the discrimination of the type of the recording medium.

[0048] The optimal conveyance conditions and fixing conditions of the recording medium in the image forming apparatus 1 vary depending on the type of the recording medium. The type of the recording medium to be conveyed may be set according to the user's operation on the operation display unit 60, but setting it every time is troublesome and there is also a problem that incorrect settings may be made. For this reason, in the image forming apparatus 1 of the present embodiment, the recording medium discrimination apparatus 2 can discriminate the type of the recording medium. Specifically, the type of the recording medium can be discriminated based on the discrimination results of the following characteristics (i) to (iv) related to the recording medium. (i) Material of the recording medium (ii) Presence or absence of bluing (iii) Presence and amount of fluorescent whitening agent (iv) Color of the recording medium

[0049] When an inspection light is irradiated onto a recording medium and light is detected at a position where the diffusely reflected light of the inspection light can be received, the influence of the characteristics of the recording medium appears in the reflection spectrum, particularly from the ultraviolet wavelength range to the visible wavelength range. In this specification, the reflection spectrum is defined as the sum of the spectrum of the diffusely reflected light and the spectrum of fluorescence. First, the influence of the above characteristics (i) to (iv) related to the recording medium on the reflection spectrum will be described below.

[0050] (i) Material of the recording medium In the short wavelength side of the near-infrared wavelength range, that is, in the visible wavelength range and the ultraviolet wavelength range, there are many wavelength ranges in which the reflection spectrum is affected by the material (raw material) of the recording medium. For example, in recycled paper containing a large amount of waste paper pulp, light is absorbed by impurities, so as shown in Fig. 7, the reflectance is lower than that of plain paper from the ultraviolet wavelength range to the visible wavelength range. Also, in medium-weight paper containing a large amount of mechanical pulp, light is absorbed by pulp and lignin, so similarly, the reflectance is lower than that of plain paper from the ultraviolet wavelength range to the visible wavelength range. Therefore, by obtaining the reflectance using the inspection light in the wavelength range where the reflectance decreases, it is possible to discriminate the recording medium based on the difference in the material of the recording medium.

[0051] (ii) Presence or absence of blue tint There may be a process called "blue tint" in which a blue dye is added to the recording medium to improve whiteness. In the recording medium with blue tint, as shown in Fig. 8, absorption occurs in the wavelength range from green to red (approximately 500 to 750 nm) due to the dye, and the reflectance in the blue wavelength range relatively increases. Therefore, by obtaining the reflectance using the inspection light in the wavelength range where absorption occurs, it is possible to discriminate the recording medium based on the presence or absence of blue tint.

[0052] (iii) Presence or absence and amount of fluorescent brightening agent There may be a process called "fluorescent whitening" in which a fluorescent brightening agent is added to a recording medium to improve the whiteness of the recording medium. The fluorescent brightening agent mainly absorbs excitation light in the ultraviolet wavelength range and emits fluorescence in the blue wavelength range. FIG. 9 is a diagram showing an example of the relationship between the wavelength that excites fluorescence and the intensity of the excited fluorescence in a recording medium to which a fluorescent brightening agent is added. As shown in FIG. 9, the excitation light in the ultraviolet wavelength range is absorbed, and blue fluorescence with a longer wavelength is generated. As a result, as shown in FIG. 10, the apparent reflectance from the ultraviolet wavelength range to the visible (blue) wavelength range increases due to the fluorescence. Also, the higher the amount of the added fluorescent brightening agent, the greater the increase in the reflectance. Therefore, by obtaining the reflectance using inspection light in the wavelength range where fluorescence occurs, it is possible to discriminate the recording medium based on the presence or absence and amount of the fluorescent brightening agent.

[0053] (iv) Color of the recording medium In the colored paper colored with a dye (coloring material), absorption occurs in a specific wavelength range according to the color of the dye. As a result, as shown in FIG. 11, the reflectance in the wavelength range corresponding to the color of the colored paper becomes relatively large, presenting the desired color. Therefore, by obtaining the reflectance using inspection light in the wavelength range where absorption by the dye occurs, it is possible to discriminate the recording medium based on the difference in color.

[0054] Thus, among the reflection spectra, particularly from the visible wavelength range to the ultraviolet wavelength range, the effects of various characteristics of the recording medium appear. Therefore, by irradiating the recording medium with inspection light in the wavelength range where the effect of the characteristic to be discriminated appears, the characteristics of the recording medium can be discriminated based on the amount of received reflected light or fluorescence, and the type of the recording medium can be specified.

[0055] However, when determining one characteristic of a recording medium using inspection light in one wavelength range, if the amount of received light fluctuates due to factors other than the characteristic to be determined, it becomes difficult to accurately determine the characteristic of the recording medium. For example, as shown in FIG. 12, the amount of reflected light of the inspection light fluctuates according to the basis weight of the recording medium. When the basis weight of the recording medium to be determined is unknown, it is impossible to distinguish between the fluctuation of the reflected light amount caused by this basis weight and the fluctuation of the received light amount caused by the characteristic of the recording medium. For this reason, with the method using inspection light in one wavelength range, it is difficult to accurately determine the characteristic of the recording medium, and misjudgment regarding the type of the recording medium is likely to occur.

[0056] On the other hand, as shown in FIGS. 7, 8, 10, and 11, fluctuations in the reflection spectrum due to the characteristics of the recording medium hardly occur in the near-infrared wavelength range. Therefore, in the recording medium discrimination apparatus 2 of the present embodiment, using the first inspection light in the near-infrared wavelength range with less fluctuation due to the characteristics of the recording medium and the second inspection light in the wavelength range where the influence of the characteristics of the recording medium appears, the discrimination regarding one characteristic of the recording medium is performed considering the wavelength dependence related to two wavelength ranges. That is, based on the amount of received light of the first incident light L1b corresponding to the first inspection light L1a, the fluctuation due to factors other than the characteristics of the recording medium in the amount of received light of the second incident light L2b corresponding to the second inspection light L2a is subtracted (cancelled out).

[0057] As described above, the peak wavelength of the intensity of the first inspection light L1a is set to be 750 nm or more and 1100 nm or less. By setting the upper limit to 1100 nm, the fluctuation of the received light amount due to the water contained in the recording medium can be suppressed. This is because water has unique absorption bands in the vicinity of 1450 nm and 1940 nm, which are derived from the combined vibrations of the stretching and bending vibrations of hydrogen atoms and oxygen atoms. Also, by setting the peak wavelength of the intensity of the first inspection light L1a to be 800 nm or more and 900 nm or less, it is possible to make it less susceptible to the influence of the characteristics of the recording medium.

[0058] As a method for discriminating the characteristics of a recording medium based on the detection results of the first incident light L1b and the second incident light L2b, for example, there is a method of performing discrimination based on the ratio of the reflectance R1 calculated from the amount of received light of the first incident light L1b and the reflectance R2 calculated from the amount of received light of the second incident light L2b (hereinafter referred to as the reflectance ratio R2 / R1). For example, even if the amount of reflected light fluctuates due to differences in basis weight, this fluctuation can be canceled out by taking the reflectance ratio R2 / R1. Therefore, the reflectance ratio R2 / R1 reflects the characteristics of the recording medium excluding the influence of the basis weight. For this reason, by using the reflectance ratio R2 / R1, the characteristics of the recording medium can be appropriately discriminated, and the type of the recording medium can be accurately specified.

[0059] Hereinafter, in the recording medium discrimination apparatus 2, a method for discriminating the above (i) to (iv) characteristics related to the recording medium will be described.

[0060] <Example 1: Discrimination Related to the Material of the Recording Medium> First, as Example 1, a method for discriminating the type (paper quality) of the recording medium based on the absorption of the inspection light by the material of the recording medium will be described.

[0061] In Example 1, as the second inspection light L2a, light having a peak wavelength of intensity in the range of 390 nm or more and 440 nm or less is used. This is because, as shown in FIG. 7, absorption due to the material of the recording medium tends to appear in this wavelength range. Also, by setting the lower limit to 390 nm, the main excitation wavelengths of the fluorescence shown in FIG. 9 can be excluded. Therefore, even when a fluorescent brightener is added to the recording medium, the contribution of fluorescence can be reduced, so that discrimination related to the material can be performed with high accuracy. Further, as shown in FIG. 6, since the light receiving element 220 having a spectral sensitivity characteristic in which the light receiving sensitivity increases toward the longer wavelength side from the visible wavelength range to the near-infrared wavelength range is used, the contribution of fluorescence can be reduced and discrimination related to the material can be performed with high accuracy. Note that the accuracy of discrimination can be further improved by using a light receiving element that does not have sensitivity in the ultraviolet wavelength range.

[0062] Next, the recording medium discrimination process executed by the control unit 10 of the recording medium discrimination device 2 in Example 1 will be described. Here, a case where it is discriminated whether the recording medium is plain paper or coated paper, or recycled paper or medium-quality paper when the recording medium is blank paper will be described as an example. According to this method, for example, when plain paper and medium-quality paper are stored in the paper feed tray 81 of the image forming apparatus 1, it is possible to discriminate whether the recording medium being conveyed is plain paper or medium-quality paper.

[0063] FIG. 13 is a flowchart showing the control procedure of the recording medium discrimination process. When the recording medium discrimination process is started, the control unit 10 starts injecting the first inspection light by the first light emitting element 211 and starts injecting the second inspection light by the second light emitting element 212 (step S101). Here, the control unit 10 causes the first light emitting element 211 and the second light emitting element 212 to emit light such that their light emission periods are different from each other (for example, alternately).

[0064] Based on the output signal from a sensor (not shown), the control unit 10 discriminates whether a recording medium has moved to a position facing the medium inspection unit 20 (step S102). If it is discriminated that the recording medium has not moved ( "NO" in step S102), the process of step S102 is executed again. If it is discriminated that the recording medium has moved to a position facing the medium inspection unit 20 ( "YES" in step S102), the control unit 10 acquires the amount of received light of the first incident light L1b by the light receiving element 220 and calculates the reflectance R1 of the first inspection light L1a. Further, the control unit 10 acquires the amount of received light of the second incident light L2b by the light receiving element 220 and calculates the reflectance R2 of the second inspection light L2a (step S103). Specifically, the control unit 10 calculates the reflectance R1 from the amount of light received by the light receiving element 220 when the recording medium is irradiated with the first inspection light L1a, and calculates the reflectance R2 from the amount of light received by the light receiving element 220 when the recording medium is irradiated with the second inspection light L2a.

[0065] The control unit 10 ends the injection of the first inspection light L1a and the second inspection light L2a (step S104).

[0066] The control unit 10 determines whether the reflectance ratio R2 / R1 is equal to or greater than a reference value V (step S105). The reference value V is set according to the characteristics to be determined and is stored in the storage unit 13 as determination reference data 132. In this embodiment, it is assumed that the reference value V is 0.88.

[0067] When it is determined that the reflectance ratio R2 / R1 is equal to or greater than the reference value V ( "YES" in step S105), the control unit 10 determines that the recording medium is plain paper or coated paper (step S106). When it is determined that the reflectance ratio R2 / R1 is less than the reference value V ( "NO" in step S105), the control unit 10 determines that the recording medium is recycled paper or medium-quality paper (step S107).

[0068] When step S106 or S107 ends, the control unit 10 changes the settings related to image formation according to the determination result of the type of the recording medium (step S108) and ends the recording medium determination process. If another recording medium is to be inspected continuously, the process may return to step S101 after the end of step S108.

[0069] Here, the determination method in steps S103 to S106 will be described in detail. FIG. 14 is a diagram showing an example of the distribution of the reflectance R1 of the first inspection light L1a and the reflectance R2 of the second inspection light L2a for plain paper, coated paper, recycled paper, and medium-quality paper. Specifically, for plain paper, coated paper, recycled paper, and medium-quality paper, the reflectance R1 of the first inspection light L1a with a peak wavelength of 850 nm and the reflectance R2 of the second inspection light L2a with a peak wavelength of 405 nm are obtained and plotted.

[0070] The reference straight line S1 in Fig. 14 is a straight line corresponding to a reflectance ratio R2 / R1 = 0.88. In other words, the reference straight line S1 is a linear function (proportional formula) passing through the origin with a slope of the reference value V. The coordinate plane with the reflectances R1 and R2 as the two axes is divided into two regions Aa and Ab by the reference straight line S1. Region Aa corresponds to a reflectance ratio R2 / R1 ≥ V, and region Ab corresponds to a reflectance ratio R2 / R1 < V. The plots of plain paper and coated paper are distributed in region Aa, and the plots of recycled paper and medium-quality paper are distributed in region Ab. From this, when the detection result of the incident light amount when any recording medium is inspected by the medium inspection unit 20 satisfies the reflectance ratio R2 / R1 ≥ V (when included in region Aa), it can be determined that it is plain paper or coated paper, and when the reflectance ratio R2 / R1 < V is satisfied (when included in region Ab), it can be determined that it is recycled paper or medium-quality paper.

[0071] According to such a method, as described above, even if there are factors that vary the reflectances R1 and R2 other than the characteristics of the recording medium, the influence of such factors can be offset to accurately determine the characteristics of the recording medium. For example, in the data of Fig. 14, the reflectances R1 and R2 vary due to the difference in the basis weight of the recording medium. This can be determined from the fact that the reflectance R1 of the first inspection light L1a, which should have little variation due to the characteristics of the recording medium, varies (the reflectance R1 = 0.46 to 1.15 for plain paper and coated paper, and the reflectance R1 = 0.78 to 1.05 for recycled paper and medium-quality paper). The variation in reflectance due to the difference in basis weight is also reflected in the reflectance R2 of the second inspection light L2a, and the distribution range of the reflectance R2 of plain paper and coated paper (0.48 to 1.1) and the distribution range of the reflectance R2 of recycled paper and medium-quality paper (0.6 to 0.8) partially overlap. For this reason, simply using only the reflectance R2 of the second inspection light L2a cannot accurately determine the paper quality of the recording medium. On the other hand, by using the reflectance ratio R2 / R1 of the first inspection light L1a and the second inspection light L2a as in this embodiment, discrimination considering the wavelength dependence in the two wavelength regions can be performed. That is, in Fig. 14, instead of simply using only the reflectance R2 on the vertical axis, by using the ratio with the reflectance R1 on the horizontal axis, factors other than the material of the recording medium can be offset.

[0072] In FIG. 14, the proportional formula with the slope being the reference value V is used as the reference line S1, but it is not limited to this. The reference line S1 may be any line non-parallel to the two axes on the coordinate plane with the reflectivities R1 and R2 as the two axes. In other words, the reference line S1 may be represented by R2 = a·R1 + b for any constants a and b (where a ≠ 0). In this case, in step S104, if R2 ≥ a·R1 + b is satisfied, it may branch to step S105, and if not satisfied, it may branch to step S106. Further, the constants a and b are preset and stored in the storage unit 13 as discrimination reference data 132.

[0073] Further, the coordinate plane may be divided into three or more regions by two or more reference lines, and based on the region including the coordinates corresponding to the detection result of the incident light amount when the recording medium is inspected by the medium inspection unit 20 among these regions, the recording medium may be discriminated.

[0074] According to the above method, high-quality recycled paper can be preferably discriminated among recycled papers. High-quality recycled paper is paper with a waste paper pulp blending ratio of 70% or more and a whiteness of 75 or less. For paper with a small waste paper pulp blending ratio (for example, about several tens of %), the influence of absorption by impurities in the pulp is small. Also, even for paper marked with a waste paper pulp blending ratio of 100%, when the whiteness is increased using chemicals such as pulp bleaching, fillers, and fluorescent brightening agents, the paper physical properties are close to those of plain paper and high-quality paper.

[0075] <Example 2: Discrimination regarding the presence or absence of blue tint> The presence or absence of blue tint can be discriminated by the same method as in Example 1. In this case, in FIG. 14, the reference line S1 may be set so that the recording medium with blue tint belongs to region Aa and the recording medium without blue tint belongs to region Ab.

[0076] <Example 3: Discrimination regarding the presence or absence and amount of fluorescent brightening agent> Next, as Example 3, a method for discriminating the presence or absence and amount of fluorescent brightening agent will be described.

[0077] In Example 3, as the second inspection light L2a, light with a peak wavelength of 280 nm or more and 400 nm or less in intensity is used. Generally, fluorescent brighteners used in recording media often have molecules with conjugated double bonds and a planar structure, such as stilbene-based, distyryl biphenyl-based, coumarin-based, and oxazole-based ones. These materials absorb ultraviolet light of about 280 nm to about 400 nm and transition to an excited state, and emit blue fluorescence of about 400 nm to about 500 nm when relaxing back to the ground state again. Therefore, in Example 3, the wavelength range of the second inspection light L2a and the wavelength range of the second incident light L2b (mainly fluorescence) corresponding to the second inspection light L2a are different. By using the second inspection light L2a in the above wavelength range, fluorescence can be detected, so the presence and amount of the fluorescent brightener can be accurately discriminated. Also, as shown in FIG. 6, by using a light receiving element 220 having spectral sensitivity characteristics in which the light receiving sensitivity increases toward the longer wavelength side from the visible wavelength range to the near-infrared wavelength range, the contribution of the reflected light of the excitation light (the second inspection light L2a) can be reduced and the fluorescence (the second incident light L2b) can be detected with high accuracy.

[0078] FIG. 15 is a diagram showing an example of the distribution of the reflectance R1 of the first inspection light L1a and the reflectance R2 of the second inspection light L2a in the fluorescent strong paper and the fluorescent weak paper. Here, the fluorescent strong paper is a recording medium to which a predetermined amount or more of a fluorescent brightener is added. Also, the fluorescent weak paper is a recording medium in which no fluorescent brightener is added or the added amount is less than the predetermined amount. FIG. 15 shows the reflectance R1 of the first inspection light L1a with a peak wavelength of 850 nm and the reflectance R2 of the second inspection light L2a with a peak wavelength of 280 nm obtained and plotted for the fluorescent strong paper and the fluorescent weak paper.

[0079] The reference line S2 in Fig. 15 is a line corresponding to a reflectance ratio R2 / R1 = 0.38. In other words, the reference line S2 is a linear function (proportional formula) passing through the origin with a slope of the reference value V (= 0.38). The coordinate plane with the reflectances R1 and R2 as the two axes is divided by the reference line S2 into two regions Ba and Bb. Region Ba corresponds to a reflectance ratio R2 / R1 ≥ V, and region Bb corresponds to a reflectance ratio R2 / R1 < V. The plots of the high-fluorescence papers are distributed in region Ba, and the plots of the low-fluorescence papers are distributed in region Bb. From this, when the detection result of the incident light amount when any recording medium is inspected by the medium inspection unit 20 satisfies the reflectance ratio R2 / R1 ≥ V (when it is included in region Ba), it can be determined that it is a high-fluorescence paper, and when the reflectance ratio R2 / R1 < V is satisfied (when it is included in region Bb), it can be determined that it is a low-fluorescence paper. That is, when discriminating the recording medium in Example 3, in the flowchart of Fig. 13, step S105 may be changed to "discriminate as high-fluorescence paper", and step S105 may be changed to "discriminate as low-fluorescence paper".

[0080] Also in Example 3, by using the reflectance ratio R2 / R1 of the first inspection light L1a and the second inspection light L2a, discrimination considering the wavelength dependence in the two-wavelength region can be performed. That is, instead of simply using only the reflectance R2 on the vertical axis in Fig. 15, by using the ratio with the reflectance R1 on the horizontal axis, factors other than the fluorescent whitening agent can be offset.

[0081] Similar to Examples 1 and 2, the reference line S2 may be expressed as R2 = a·R1 + b for any constants a and b (where a ≠ 0). Also, with two or more reference lines, the coordinate plane may be divided into three or more regions, and the amount of the fluorescent whitening agent may be discriminated based on which region the coordinates corresponding to the detection result of the incident light amount when the recording medium is inspected by the medium inspection unit 20 belong to.

[0082] <Examples 1 + 3: Discrimination related to both the material of the recording medium and fluorescent whitening> Example 1 and Example 3 may be combined. That is, for one recording medium, the discrimination related to the material of Example 1 and the discrimination related to the fluorescent brightener of Example 3 can be performed together.

[0083] FIG. 16 is a diagram showing the configuration of the medium inspection unit 20 when Example 1 and Example 3 are combined. As shown in FIG. 16, when viewed from the Z direction, one first light emitting element 211 and two second light emitting elements 212 (second light emitting elements 2121, 2122) are arranged at equal intervals on a circle centered on the light receiving element 220 of the light detection unit 22. Among these, the second light emitting element 2121 irradiates the recording medium with a second inspection light L2a having a peak wavelength of intensity in the range of 390 nm or more and 440 nm or less, as in Example 1. Further, the second light emitting element 2122 irradiates the recording medium with a second inspection light L2a having a peak wavelength of intensity in the range of 280 nm or more and 400 nm or less, as in Example 3. In the configuration of FIG. 16, the first light emitting element 211 and the two second light emitting elements 2121, 2122 emit light in order such that their irradiation periods are different from each other. From the reflectance R1 of the first inspection light L1a from the first light emitting element 211 and the reflectance R2 of the second inspection light L2a from the second light emitting element 2121, the material of the recording medium can be discriminated. Also, from the reflectance R1 of the first inspection light L1a from the first light emitting element 211 and the reflectance R2 of the second inspection light L2a from the second light emitting element 2122, discrimination related to the fluorescent brightener can be performed. Note that by using the configuration of FIG. 16, Example 2 and Example 3 can also be combined.

[0084] <Example 4: Discrimination Related to the Color of the Recording Medium> Next, as Example 4, a method for discriminating the color of the recording medium will be described.

[0085] In Example 4, as the second inspection light L2a, light having an absorption wavelength of the dye of the color paper is used. Thereby, the recording medium of the corresponding color can be discriminated. For example, by using a second inspection light L2a with a peak wavelength of 600 nm or more and less than 700 nm, it is possible to discriminate between paper having a large absorption in the wavelength range of 600 nm or more and less than 700 nm (for example, blue, red, green, yellow, pink, light green, light yellow, light ivory, orange-based paper) and white paper.

[0086] FIG. 17 is a diagram showing an example of the distribution of the reflectance R1 of the first inspection light L1a and the reflectance R2 of the second inspection light L2a in white paper and colored paper. Specifically, for white paper and colored paper, the reflectance R1 of the first inspection light L1a with a peak wavelength of 850 nm and the reflectance R2 of the second inspection light L2a with a peak wavelength of 670 nm are acquired and plotted.

[0087] The reference line S3 in FIG. 17 is set to distinguish between the plot of white paper and the plot of colored paper. The coordinate plane with the reflectances R1 and R2 as the two axes is divided by the reference line S3 into a region Ca including the plot of white paper and a region Cb including the plot of colored paper. Whether the paper is white paper or colored paper can be discriminated depending on whether the coordinates corresponding to the detection result of the incident light amount when any recording medium is inspected by the medium inspection unit 20 belong to either of the regions Ca and Cb.

[0088] Also, by using a second inspection light L2a with a peak wavelength of 500 nm or more and less than 600 nm, it is possible to discriminate between paper having a large absorption in the wavelength range of 500 nm or more and less than 600 nm (for example, blue, green, yellow, light blue, light yellow, light green-based paper) and white paper.

[0089] FIG. 18 is a diagram showing an example of the distribution of the reflectance R1 of the first inspection light L1a and the reflectance R2 of the second inspection light L2a in white paper and colored paper. Specifically, for white paper and colored paper, the reflectance R1 of the first inspection light L1a with a peak wavelength of 850 nm and the reflectance R2 of the second inspection light L2a with a peak wavelength of 525 nm are acquired and plotted.

[0090] The reference straight line S4 in FIG. 18 is set to distinguish between the plots on white paper and the plots on colored paper. The coordinate plane with the reflectivities R1 and R2 as the two axes is divided by the reference straight line S4 into a region Da including the plots on white paper and a region Db including the plots on colored paper. Whether the paper is white or colored can be determined according to whether the coordinates corresponding to the detection result of the incident light amount when any recording medium is inspected by the medium inspection unit 20 belong to either of the regions Da and Db.

[0091] Similarly, by using the second inspection light L2a with a peak wavelength of 350 nm or more and less than 500 nm, it is possible to distinguish between paper having a large absorption in the wavelength range of 350 nm or more and less than 500 nm (for example, paper of red, green, yellow, pink, light green colors) and white paper. The distribution diagram of the reflectivity in this case is omitted.

[0092] By using the first inspection light L1a and two or more second inspection lights L2a with different wavelength ranges, the color of the recording medium can be discriminated in more detail. For example, when using two second inspection lights L2a with different wavelength ranges, as in FIG. 16, one first light-emitting element 211 and two second light-emitting elements 212 with different emission wavelengths may be used. Also, when using three second inspection lights L2a with different wavelength ranges, a second light-emitting element 212 with a different emission wavelength may be further added.

[0093] Also in Example 4, by using the reflectivity ratio R2 / R1 of the first inspection light L1a and the second inspection light L2a, discrimination considering the wavelength dependence related to the two wavelength ranges can be performed. That is, instead of simply using only the reflectivity R2 on the vertical axis in FIGS. 17 and 18, by using the ratio with the reflectivity R1 on the horizontal axis, factors other than the color of the recording medium can be offset.

[0094] (Modification example) Next, a modification example of the above embodiment will be described. Below, the differences from the above embodiment will be described.

[0095] FIG. 19 is a diagram showing the configuration of the medium inspection unit 20 according to the modified example. FIG. 19(a) is a cross-sectional view of the medium inspection unit 20 viewed from a direction parallel to the conveyance surface. FIG. 19(b) is a plan view of the medium inspection unit 20 viewed from a direction perpendicular to the conveyance surface (z direction).

[0096] The light irradiation unit 21 of this modified example includes one light emitting element 210. The light emitting element 210 irradiates the recording medium M with light including the first inspection light L1a and the second inspection light L2a. As the light emitting element 210, a lamp (for example, halogen, deuterium, tungsten, xenon, etc.) having an emission spectrum in a wavelength range including the first inspection light L1a and the second inspection light L2a (for example, from the ultraviolet wavelength range to the near-infrared wavelength range) can be used.

[0097] The light detection unit 22 has a first light receiving element 221 capable of detecting light in the wavelength range of the first incident light L1b and a second light receiving element 222 capable of detecting light in the wavelength range of the second incident light L2b. For example, as the first light receiving element 221, a filter that selectively transmits light in the wavelength range of the first incident light L1b can be laminated on the light receiving element 220 of the above-described embodiment. Also, as the second light receiving element 222, a filter that selectively transmits light in the wavelength range of the second incident light L2b can be laminated on the light receiving element 220 of the above-described embodiment. With such a configuration, the first light receiving element 221 and the second light receiving element 222 have the spectral sensitivity characteristics shown in FIG. 20. That is, the first light receiving element 221 has a sensitivity peak P1 at a wavelength of, for example, 850 nm. Also, the second light receiving element 222 has a sensitivity peak P2 at a wavelength of, for example, 400 nm. Therefore, as shown in FIG. 19(a), when light including the first incident light L1b and the second incident light L2b is incident on the first light receiving element 221 and the second light receiving element 222, respectively, the first light receiving element 221 can selectively detect the first incident light L1b, and the second light receiving element 222 can selectively detect the second incident light L2b. The peak wavelength of the sensitivity of the second light receiving element 222 is appropriately changed according to the wavelength range of the second inspection light L2a (and thus the wavelength range of the second incident light L2b).

[0098] Thus, since this modification example performs spatial division measurement, it has the advantage that time division measurement becomes unnecessary. That is, during the irradiation period of the light emitting element 210, light can be detected by the first light receiving element 221 and the second light receiving element 222 at an arbitrary timing (for example, simultaneously).

[0099] As described above, the recording medium discrimination device 2 according to the present embodiment includes a light irradiation unit 21 that irradiates a recording medium with inspection light, a light detection unit 22 that detects incident light including at least one of diffused reflected light of the inspection light irradiated on the recording medium and fluorescence excited by the inspection light in the recording medium, and a control unit 10 as discrimination means that performs discrimination related to one characteristic of the recording medium based on detection results by the light detection unit 22 of the first incident light L1b corresponding to the first inspection light L1a and the second incident light L2b corresponding to the second inspection light L2a. The first inspection light L1a has a peak wavelength of intensity in the range of 750 nm or more and 1100 nm or less, and the second inspection light L2a has a peak wavelength of intensity shorter than that of the first inspection light L1a. According to this, by using two-wavelength region inspection light including the first inspection light L1a in the near-infrared wavelength region that is less affected by the characteristics of the recording medium, one characteristic of the recording medium can be appropriately discriminated in consideration of the wavelength dependency related to the two-wavelength region of the diffused reflected light and / or fluorescence of the recording medium. That is, based on the received light amount of the first incident light L1b, fluctuations due to factors other than the characteristics of the recording medium in the received light amount of the second incident light L2b can be subtracted, so that discrimination related to the desired characteristics can be appropriately performed. By using the discrimination result of this characteristic, the type of the recording medium can be discriminated with high accuracy. In addition, since it is not necessary to compare with data obtained for known recording media, discrimination such as paper type can be performed even for unknown recording media.

[0100] Further, the control unit 10 performs discrimination regarding the characteristics of the recording medium (discrimination means) based on the ratio between the reflectance R1 (first value) corresponding to the amount of light received by the light detection unit 22 of the first incident light L1b and the reflectance R2 (second value) corresponding to the amount of light received by the light detection unit 22 of the second incident light L2b. Thereby, it is possible to cancel out the factors causing variations in reflectance other than the characteristics of the discrimination target of the recording medium, and to perform discrimination of characteristics with high accuracy. For example, even when the positional relationship between the light emitting element and the light receiving element and the recording medium is displaced and the reflectance varies, or when the reflectance varies due to differences in the basis weight of the recording medium, the use of the reflectance ratio can cancel out such variations.

[0101] Further, the control unit 10 performs discrimination regarding the characteristics (discrimination means) based on the region that includes the coordinates corresponding to the detection result among a plurality of regions defined in advance in the coordinate plane with the reflectance R1 and the reflectance R2 as two axes. According to this, it is possible to more accurately discriminate the characteristics of the recording medium, and to improve the discrimination system for the type of the recording medium.

[0102] Further, the plurality of regions are divided by a reference straight line that is non-parallel to the two axes of the coordinate plane. According to this, it is possible to perform discrimination of characteristics in consideration of the wavelength dependence of the diffuse reflection light and / or fluorescence of the recording medium.

[0103] Further, in Examples 1 and 2, the second inspection light L2a has a peak wavelength of intensity in the range of 390 nm or more and 440 nm or less. Thereby, it is possible to discriminate characteristics that cause absorption in the purple wavelength range, such as the material of the recording medium and the presence or absence of bluing.

[0104] Further, in Example 3, the second inspection light L2a has a peak wavelength of intensity in the range of 280 nm or more and 400 nm or less. Thereby, it is possible to discriminate the presence or amount of a fluorescent whitening agent.

[0105] Further, the first inspection light L1a has a peak wavelength of intensity in the range of 800 nm or more and 900 nm or less. Thereby, it is possible to further suppress the variation in the reflectance of the first inspection light L1a due to the influence of the characteristics of the recording medium, and to improve the discrimination accuracy of the characteristics.

[0106] In addition, the light detection unit 22 includes a light receiving element 220, and the light receiving element 220 is a photodiode or a phototransistor having detection sensitivity in a wavelength range from the visible wavelength range to the near-infrared wavelength range. Thereby, the influence of the excitation light in the ultraviolet wavelength range can be suppressed, and fluorescence, blue diffuse reflection light and / or fluorescence in the visible wavelength range can be detected with high sensitivity. Therefore, it is possible to accurately determine the material of the recording medium and the presence or amount of a fluorescent whitening agent.

[0107] Further, the recording medium discrimination device 2 includes an element substrate 23 provided at a position facing the conveyance path of the recording medium. The light irradiation unit 21 includes a first light emitting element 211 and a second light emitting element 212, and the light detection unit 22 includes a light receiving element 220. The first light emitting element 211, the second light emitting element 212, and the light receiving element 220 are provided on the element substrate 23. Thereby, even if the distance in the z direction between the element substrate 23 and the recording medium varies, the influence on the discrimination result of the characteristics can be suppressed to a small level.

[0108] In addition, the light irradiation unit 21 includes a first light emitting element 211 that irradiates the recording medium with a first inspection light L1a, and a second light emitting element 212 that irradiates the recording medium with a second inspection light L2a. The light detection unit 22 includes a light receiving element 220 that detects a first incident light L1b and a second incident light L2b. The period during which the first light emitting element 211 irradiates the first inspection light L1a is different from the period during which the second light emitting element 212 irradiates the second inspection light L2a. Thereby, the configuration of the light receiving element 220 and the configuration and processing content related to the processing of the detection result by the light receiving element 220 can be simplified. Also, it is possible to make the light receiving element 220 less susceptible to the influence of changes over time.

[0109] Also, in a modified example, the light irradiation unit 21 has a light emitting element 210 that irradiates a recording medium with light including the first inspection light L1a and the second inspection light L2a, and the light detection unit 22 has a first light receiving element 221 capable of detecting light in the wavelength range of the first incident light L1b and a second light receiving element 221 capable of detecting light in the wavelength range of the second incident light L2b. According to this, since simultaneous detection by the first light receiving element 221 and the second light receiving element 222 is possible, the inspection time can be shortened. In principle, it is also possible to discriminate the type of the recording medium by irradiating the inspection light once and detecting the incident light. Further, it is possible to make the light emitting element 210 less susceptible to the influence of changes over time.

[0110] Also, the image forming apparatus 1 according to the present embodiment includes the above-described recording medium discrimination apparatus 2 and an image forming unit 30 that forms an image by applying a coloring material to the recording medium. Thereby, the type of the recording medium can be appropriately discriminated in the image forming apparatus 1.

[0111] Also, the recording medium discrimination method according to the present embodiment is a recording medium discrimination method by a recording medium discrimination apparatus 2 including a light irradiation unit 21 that irradiates a recording medium with inspection light, and a light detection unit 22 that detects incident light including at least one of diffused reflected light of the inspection light irradiated on the recording medium and fluorescence excited by the inspection light in the recording medium, the method including a step of performing discrimination regarding one characteristic of the recording medium based on detection results by the light detection unit 22 of a first incident light L1b corresponding to the first inspection light L1a and a second incident light L2b corresponding to the second inspection light L2a, the first inspection light L1a having a peak wavelength of intensity of 750 nm or more and 1100 nm or less, and the second inspection light L2a having a peak wavelength of intensity shorter than that of the first inspection light L1a. Thereby, one characteristic of the recording medium can be appropriately discriminated in consideration of the wavelength dependency in two wavelength ranges of the diffused reflected light and / or fluorescence of the recording medium. By using the discrimination result of this characteristic, the type of the recording medium can be discriminated with high accuracy.

[0112] Note that the present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above embodiment, the example in which the recording medium discrimination device 2 is incorporated in the image forming device 1 has been described. However, the present invention is not limited to this, and the recording medium discrimination device 2 may be a device provided separately and independently from the image forming device 1.

[0113] Also, although the reflectance R1 is exemplified as the first value and the reflectance R2 is exemplified as the second value, the present invention is not limited to this. The first value may be any value related to the amount of light received by the light detection unit 22 of the first incident light L1b, and may be, for example, the amount of light received itself. Similarly, the second value may be any value related to the amount of light received by the light detection unit 22 of the second incident light L2b, and may be, for example, the amount of light received itself.

[0114] Further, the characteristics of the recording medium to be discriminated are not limited to those exemplified in the embodiment. Any characteristic that hardly affects the reflectance of the first inspection light L1a in the near-infrared wavelength range and affects the reflectance of the second inspection light L2a in a shorter wavelength range can be the discrimination target.

[0115] Also, although the electrophotographic method is exemplified as the image forming method in the image forming device, the present invention is not limited to this, and the image forming method is arbitrary. For example, an inkjet method in which ink is ejected onto a recording medium to form an image may be used.

[0116] Further, the recording medium is not limited to paper, and may be a resin sheet, cloth, or the like.

[0117] Although some embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, and includes the scope of the invention described in the claims and the equivalent scope thereof.

Description of Reference Numerals

[0118] 1 Image forming device 2 Recording medium discrimination device 10 Control unit (discrimination means) 11 CPU 12 RAM 13 Storage unit 131 Program 132 Discrimination reference data 20 Medium inspection unit 21 Light irradiation unit 210 Light emitting element 211 First light emitting element 212, 2121, 2122 Second light emitting element 22 Light detection unit 220 Light receiving element 221 First light receiving element 222 Second light receiving element 23 Element substrate (substrate) 24 Optical aperture 25 Paper feed guide 30 Image forming unit 40 Fixing unit 50 Scanner 60 Operation display unit 70 Communication unit 81 Paper feed tray 82 Conveyor roller 83 Paper discharge tray 90 Bus L1a First inspection light L1b First incident light L2a Second inspection light L2b Second incident light LA Inspection light LB1 Surface diffused reflection light LB2 Internal diffused reflection light LB3 Fluorescence LC Specular reflection light M Recording medium R1 Reflectance (first value) R2 Reflectance (second value)

Claims

1. A light irradiation unit that irradiates an inspection light onto a recording medium, A light detection unit that detects incident light including at least one of diffused reflected light of the inspection light irradiated on the recording medium and fluorescence excited by the inspection light in the recording medium, Discrimination means for performing discrimination regarding one characteristic of the recording medium based on detection results by the light detection unit of the first incident light corresponding to the first inspection light and the second incident light corresponding to the second inspection light, comprising The first inspection light has a peak wavelength of intensity between 750 nm and 1100 nm, The second inspection light has a peak wavelength of intensity shorter than that of the first inspection light, The light irradiation unit A first light emitting element that emits the first inspection light, A second light emitting element that emits the second inspection light having a certain peak wavelength, A third light emitting element that emits the second inspection light having a peak wavelength different from the certain peak wavelength, having The discrimination means Based on the detection result of the first incident light corresponding to the first inspection light and the detection result of the second incident light corresponding to the second inspection light emitted by the second light emitting element, perform discrimination regarding a certain characteristic of the recording medium, A recording medium discrimination device that performs discrimination regarding a characteristic different from the certain characteristic of the recording medium based on the detection result of the first incident light corresponding to the first inspection light and the detection result of the second incident light corresponding to the second inspection light emitted by the third light emitting element.

2. The discrimination means performs discrimination regarding the characteristic based on a ratio of a first value corresponding to a light reception amount of the first incident light by the light detection unit and a second value corresponding to a light reception amount of the second incident light by the light detection unit. The recording medium discrimination device according to claim 1.

3. The discrimination means performs discrimination regarding the characteristic based on a region among a plurality of predetermined regions in a coordinate plane having the first value and the second value as two axes, in which the coordinates corresponding to the detection result are included. The recording medium discrimination device according to claim 2.

4. The plurality of regions are divided by a straight line non-parallel to the two axes of the coordinate plane. The recording medium discrimination device according to claim 3.

5. The second inspection light has a peak wavelength of intensity in the range of 390 nm or more and 440 nm or less. The recording medium discrimination device according to any one of claims 1 to 4.

6. The second inspection light has a peak wavelength of intensity in the range of 280 nm or more and 400 nm or less. The recording medium discrimination device according to any one of claims 1 to 4.

7. The first inspection light has a peak wavelength of intensity in the range of 800 nm or more and 900 nm or less. The recording medium discrimination device according to any one of claims 1 to 6.

8. The light detection unit has a light receiving element that detects the incident light. The light receiving element is a photodiode or a phototransistor having detection sensitivity in a wavelength range from the visible wavelength region to the near-infrared wavelength region. The recording medium discrimination device according to any one of claims 1 to 7.

9. It includes a substrate provided at a position facing the conveyance path of the recording medium. The light irradiation unit has a light emitting element that emits the inspection light. The light detection unit has a light receiving element that detects the incident light. The light emitting element and the light receiving element are provided on the substrate. The recording medium discrimination device according to any one of claims 1 to 8.

10. The first light emitting element, the second light emitting element, and the third light emitting element emit light in order such that the irradiation periods are different from each other. The recording medium discrimination device according to any one of claims 1 to 9.

11. A recording medium discrimination device according to any one of claims 1 to 10, an image forming unit that applies a coloring material to the recording medium to form an image, and an image forming apparatus comprising the same.

12. A recording medium discrimination method using a recording medium discrimination device including a light irradiation unit that irradiates a recording medium with inspection light, and a light detection unit that detects incident light including at least one of diffused reflected light of the inspection light irradiated on the recording medium and fluorescence excited by the inspection light in the recording medium, the method comprising: performing discrimination regarding one characteristic of the recording medium based on detection results by the light detection unit of first incident light corresponding to the first inspection light and second incident light corresponding to the second inspection light, wherein the first inspection light has a peak wavelength of intensity of 750 nm or more and 1100 nm or less, the second inspection light has a peak wavelength of intensity shorter than that of the first inspection light, the light irradiation unit includes a first light emitting element that emits the first inspection light, a second light emitting element that emits the second inspection light having a certain peak wavelength, and a third light emitting element that emits the second inspection light having a peak wavelength different from the certain peak wavelength, and in the step, performing discrimination regarding a certain characteristic of the recording medium based on the detection result of the first incident light corresponding to the first inspection light and the detection result of the second incident light corresponding to the second inspection light emitted by the second light emitting element; and performing discrimination regarding a characteristic different from the certain characteristic of the recording medium based on the detection result of the first incident light corresponding to the first inspection light and the detection result of the second incident light corresponding to the second inspection light emitted by the third light emitting element. A recording medium discrimination method.

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