Paper type identification device, paper type identification method, and paper type identification program

Abstract

To reliably discriminate a recycled paper.SOLUTION: A sheet type discrimination device 2 comprises: a first light source unit that irradiates a sheet with light having a first wavelength and light having a second wavelength; a detection unit that detects light from the sheet and acquires a detection value on the basis of the light; and a control unit that derives a determination result of a type of the sheet using the detection value. The first light source unit and the detection unit are located on the same side with respect to the sheet. The detection value includes: a first detection value on the basis of the light from the sheet when the sheet is irradiated with the light having the first wavelength; and a second detection value on the basis of the light from the sheet when the sheet is irradiated with the light having the second wavelength. The control unit discriminates a first type of recycled paper by first processing using the first detection value and discriminates a second type of recycled paper different from the first type of recycled paper by second processing using the second detection value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0006] , , , , ,

[0001] The present disclosure relates to a paper type discrimination device, a paper type discrimination method, and a paper type discrimination program.

Background Art

[0002] Since the fixing conditions of an image forming apparatus vary depending on the paper type, settings according to the paper type are required. Conventionally, the user has input the paper type on the operation panel, but in recent years, a paper type discrimination device that automatically discriminates the paper type using a sensor and changes the settings is known. A paper type discrimination device that automatically discriminates the paper type discriminates the paper type based on the light from the paper when the paper is irradiated with light.

[0003] Japanese Unexamined Patent Application Publication No. 2020-64003 discloses a method for discriminating recycled paper based on the amount of reflected light when the paper is irradiated with light having a certain wavelength.

[0004] Japanese Unexamined Patent Application Publication No. 2005-335869 discloses a method for accurately discriminating the type of the uppermost medium when discriminating the paper type by irradiating light on a laminated thin medium (paper).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The method disclosed in Japanese Patent Publication No. 2020-64003 utilizes the property that recycled paper reflects less light than other types of paper. The reason recycled paper reflects less light than other types of paper is that the recycled pulp contained in the recycled paper absorbs the irradiated light. However, even with the method disclosed in Japanese Patent Publication No. 2020-64003, there were cases where some recycled papers could not be identified as recycled paper.

[0007] One of the objectives of this disclosure is to provide a technology that can reliably identify recycled paper. [Means for solving the problem]

[0008] A paper type discrimination device according to a certain aspect of this disclosure comprises a first light source unit that irradiates paper with light having a first wavelength and light having a second wavelength, a detection unit that detects the light from the paper and acquires a detection value based on the light, and a control unit that uses the detection value to derive a paper type determination result. The first light source unit and the detection unit are located on the same side with respect to the paper. The detection value includes a first detection value based on the light from the paper when the paper is irradiated with light having the first wavelength, and a second detection value based on the light from the paper when the paper is irradiated with light having the second wavelength. The control unit determines a first type of recycled paper by a first process using the first detection value, and determines a second type of recycled paper different from the first type of recycled paper by a second process using the second detection value.

[0009] Preferably, the light having the second wavelength is ultraviolet light. The second type of recycled paper contains more phosphors than the first type of recycled paper. The second process includes distinguishing between coated paper and the second type of recycled paper using the second detection value.

[0010] Preferably, the first light source unit further irradiates the paper with light having a third wavelength. The detected value further includes a third detected value based on the light from the paper when the paper is irradiated with light having a third wavelength. The second process includes calculating the reflectance based on the second detected value, calculating the reflectance based on the third detected value, and distinguishing between coated paper and a second type of recycled paper based on the ratio of the reflectance calculated based on the second detected value to the reflectance calculated based on the third detected value. Preferably, the light having a third wavelength is infrared light.

[0011] Preferably, the light having the second wavelength is ultraviolet light. The second type of recycled paper contains more phosphors than the first type of recycled paper. The second process includes distinguishing between coated paper and the second type of recycled paper using the second detection value and the first detection value.

[0012] Preferably, the first light source unit further irradiates the paper with light having a third wavelength. The detected value further includes a third detected value based on the light from the paper when the paper is irradiated with light having a third wavelength. The second process includes calculating the reflectance based on the first detected value, calculating the reflectance based on the second detected value, calculating the reflectance based on the third detected value, and determining whether the paper is coated paper or a second type of recycled paper based on the ratio of the reflectance calculated based on the first detected value to the reflectance calculated based on the third detected value and the ratio of the reflectance calculated based on the second detected value to the reflectance calculated based on the third detected value. Preferably, the light having a third wavelength is infrared light.

[0013] Preferably, the peak wavelength of the light having the first wavelength is 390 nm or more and less than 550 nm. The first type of recycled paper contains fewer phosphors than the second type of recycled paper. The first process includes identifying the first type of recycled paper using the first detection value.

[0014] Preferably, the first light source unit further irradiates the paper with light having a third wavelength. The detected value further includes a third detected value based on the light from the previous paper when the paper is irradiated with light having a third wavelength. The first process includes calculating the reflectance based on the first detected value, calculating the reflectance based on the third detected value, and determining a first type of recycled paper based on the ratio of the reflectance calculated based on the first detected value to the reflectance calculated based on the third detected value. Preferably, the light having a third wavelength is infrared light.

[0015] Preferably, the peak wavelength of the light having the first wavelength is 390 nm or more and less than 440 nm, and the peak wavelength of the light having the second wavelength is 340 nm or more and less than 390 nm.

[0016] Preferably, the paper type discrimination device further comprises a second light source unit located on the side of the paper opposite to the side where the detection unit is located. The second light source unit further irradiates the paper with light having a fourth wavelength and light having a fifth wavelength. The detected values ​​further include a fourth detected value based on the light from the paper when the paper is irradiated with light having a fourth wavelength, and a fifth detected value based on the light from the paper when the paper is irradiated with light having a fifth wavelength. The control unit further discriminates plain paper by a third process using the fourth and fifth detected values.

[0017] Preferably, the light having the fourth wavelength is infrared light, and the light having the fifth wavelength is blue light.

[0018] A paper type discrimination method according to another aspect of the present disclosure includes irradiating a sheet of paper with light having a first wavelength and light having a second wavelength, detecting light from the sheet of paper, and obtaining a detection value based on the light, and deriving a determination result of the type of the sheet of paper using the detection value. The position where the light having the first wavelength is emitted, the position where the light having the second wavelength is emitted, and the detection position of the light from the sheet of paper are located on the same side with respect to the sheet of paper. The detection value includes a first detection value based on the light from the sheet of paper when the sheet of paper is irradiated with the light having the first wavelength, and a second detection value based on the light from the sheet of paper when the sheet of paper is irradiated with the light having the second wavelength. Deriving the determination result of the type of the sheet of paper includes discriminating a first type of recycled paper by a first process using the first detection value, and discriminating a second type of recycled paper different from the first type of recycled paper by a second process using the second detection value.

[0019] A paper type discrimination program according to another aspect of the present disclosure causes a computer to execute the above paper type discrimination method.

Advantages of the Invention

[0020] According to the present disclosure, recycled paper can be reliably discriminated.

Brief Description of the Drawings

[0021] [Figure 1] It is a diagram showing a schematic configuration of an image forming apparatus in Embodiment 1. [Figure 2] It is a diagram showing a hardware configuration of the image forming apparatus 1. [Figure 3] It is a diagram showing an example of a configuration of the inspection unit 20. [Figure 4] It is a diagram for explaining the light detected by the light receiving element 220 when the light is irradiated from the first light source unit 21X at the timing when the sheet of paper M passes through the inspection unit 20. [Figure 5] It is a diagram for explaining the light detected by the light receiving element 220 when the light is irradiated from the first light source unit 21X at the timing when the sheet of paper M does not pass through the inspection unit 20. [Figure 6]This is a diagram for explaining the light detected by the light receiving element 220 when light is irradiated from the second light source unit 21Y at the timing when the sheet M passes through the inspection unit 20. [Figure 7] This is a diagram for explaining the light detected by the light receiving element 220 when light is irradiated from the second light source unit 21Y at the timing when the sheet M does not pass through the inspection unit 20. [Figure 8] This is a flowchart showing the procedure of the paper type discrimination process in the first embodiment. [Figure 9] This is a diagram for explaining the first process in the first embodiment. [Figure 10] This is a diagram for explaining the second process in the first embodiment. [Figure 11] This is a diagram showing the difference in reflectance between a sheet containing a phosphor and a sheet not containing a phosphor. [Figure 12] This is a flowchart showing the procedure of the determination process in the first embodiment. [Figure 13] This is a diagram for explaining the second process in a modification of the first embodiment. [Figure 14] This is a diagram for explaining the third process in the second embodiment. [Figure 15] This is a flowchart showing the procedure of the determination process in the second embodiment. [Figure 16] This is a diagram for explaining the first process in a modification of the second embodiment. [Figure 17] This is a flowchart showing the procedure of the determination process in a modification of the second embodiment. [Figure 18] This is a diagram for explaining the second process in the third embodiment. [Figure 19] This is a flowchart showing the procedure of the determination process in the third embodiment. [Figure 20] This is a diagram for explaining the second process in a modification of the third embodiment. [Figure 21] This is a flowchart showing the procedure of the determination process in a modification of the third embodiment.

Best Mode for Carrying Out the Invention

[0022] Hereinafter, embodiments and modifications according to the present disclosure will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. Note that the embodiments and modifications described below may be selectively combined as appropriate.

[0023] [Embodiment 1] [A. Configuration of the Image Forming Apparatus]

[0024] Referring to FIGS. 1 and 2, the configuration of the image forming apparatus in Embodiment 1 will be described. FIG. 1 is a diagram showing a schematic configuration of the image forming apparatus in Embodiment 1. FIG. 2 is a diagram showing the hardware configuration of the image forming apparatus 1.

[0025] The image forming apparatus 1 is an MFP (Multifunction Peripheral) that forms an image on paper by an electrophotographic method. The image forming apparatus 1 includes a control unit 10, an inspection unit 20, an image forming unit 30, a fixing unit 40, a scanner 50, an operation panel 60, a communication unit 70, a paper feed tray 81, a conveyance roller 82, a paper discharge tray 83, a conveyance path 27, and a bus 90.

[0026] As shown in FIG. 2, a paper type discrimination device 2 for discriminating the paper type is constituted by the control unit 10 and the inspection unit 20. The control unit 10, the inspection unit 20, the image forming unit 30, the fixing unit 40, the scanner 50, the operation panel 60, and the communication unit 70 are connected by a bus 90.

[0027] The control unit 10 includes a processor 11, memory 12, and storage 13. The processor 11 is composed of, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The memory 12 is composed of, for example, a volatile storage device such as DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory). The storage 13 is composed of, for example, a non-volatile storage device such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or flash memory.

[0028] The storage 13 stores the program 131 and the reference data 132 which will be referenced in the determination process described later. The program 131 includes computer-readable instructions for controlling the image forming apparatus 1. The processor 11 loads the program 131 stored in the storage 13 into the memory 12 and executes it to realize various processes according to this embodiment.

[0029] Program 131 may be provided not as a standalone program, but incorporated as part of any other program. In this case, processing according to this embodiment is realized in cooperation with the other program. Even if a program does not include such a partial module, it does not deviate from the spirit of the image forming apparatus 1 according to this embodiment. Furthermore, some or all of the functions provided by program 131 may be implemented by dedicated hardware.

[0030] Furthermore, the storage 13 stores at least one of the image data received from an external device and the image data generated by the scanner 50.

[0031] The control unit 10 controls each part of the image forming apparatus 1 by having the processor 11 execute the program 131. For example, the processor 11 operates the image forming unit 30, the transport roller 82, and the fixing unit 40 based on the image data stored in the storage 13 to form an image on the paper. Here, the processor 11 changes the operation of each part involved in image formation (for example, the image forming unit 30, the transport roller 82, and the fixing unit 40) according to the paper type determination result by the paper type determination device 2. For example, the transport speed and clamping pressure of the transport roller 82 are changed according to the paper type. Also, the heating temperature and applied pressure of the fixing unit 40 are changed according to the paper type.

[0032] The inspection unit 20 is located along the paper transport path 27, which runs from the paper feed tray 81 to the paper output tray 83, on the upstream side of the image forming unit 30 (between the paper feed tray 81 and the image forming unit 30). However, the position of the inspection unit 20 is not limited to this, and it can be placed at any position along the transport path 27.

[0033] The inspection unit 20 includes a light source unit 21 and a detection unit 22. The light source unit 21 irradiates light toward the transport path 27 according to instructions from the processor 11. The detection unit 22 detects light from the paper.

[0034] The image forming unit 30 applies toner (colorant) to paper supplied from the paper feed tray 81 to form an image. The image forming unit 30 includes an intermediate transfer belt 31, an image forming unit 32, and a transfer roller 33. The intermediate transfer belt 31 is an endless, strip-shaped member that is stretched around a plurality of rollers and moves in a circular motion. The image forming unit 32 is positioned along the intermediate transfer belt 31 and forms toner images of C (cyan), M (magenta), Y (yellow), and K (black) on the intermediate transfer belt 31 based on image data representing the image to be printed. As the paper passes through the nip between the intermediate transfer belt 31 and the transfer roller 33, the toner images are transferred to the paper and an image is formed. In this embodiment, an 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 also be used.

[0035] The fuser unit 40 heats and pressurizes the paper onto which the toner image has been transferred to fix the toner image to the paper. The fuser unit 40 includes a pair of rollers consisting of a heating roller and a pressurizing roller that hold the paper. The paper with the fixed toner image is transported by the transport roller 82 and discharged into the output tray 83. The heating and pressurizing conditions of the fuser unit 40 are controlled by the processor 11 according to the type of paper.

[0036] The scanner 50 includes an optical system such as a light source and a reflector, and an image sensor. It reads an image of paper being transported along a predetermined transport path or placed on a platen glass, and generates bitmap image data for each color: R (red), G (green), and B (blue). The generated image data is stored in the storage 13. By performing image formation by the image forming unit 30 based on this image data, the scanned image can be copied onto another sheet of paper.

[0037] The operation panel 60 includes a display device such as a liquid crystal display and an input device such as a touch panel superimposed on the screen of the display device. The operation panel 60 displays various information such as the operating status and processing results of the image forming apparatus 1 on the display device and converts user input operations to the input device into operation signals and outputs them to the processor 11.

[0038] The communication unit 70 is composed of a network card and the like. The communication unit 70 is connected to a communication network such as a LAN (Local Area Network) and transmits and receives information with external devices on the communication network. The processor 11 communicates with external devices on the communication network via the communication unit 70.

[0039] The paper feed tray 81 stores paper before image formation. The paper feed tray 81 may store multiple types of paper.

[0040] Paper types are characterized by at least one of the following properties: paper material (raw material), surface treatment, presence and amount of phosphors, and color. Therefore, papers with at least one of these properties differing from each other are different types of paper. The types of paper stored in the paper tray 81 include, for example, plain paper, coated paper, a first type of recycled paper, and a second type of recycled paper.

[0041] Plain paper is paper made primarily from wood pulp (i.e., pulp that is not recycled from waste paper, usually chemical pulp). Coated paper is paper with a coating applied to both sides. Recycled paper is paper that contains recycled pulp extracted from waste paper in a specified proportion or higher. Recycled pulp readily absorbs light with a peak wavelength of less than 550 nm (i.e., light with a wavelength shorter than green).

[0042] The first type of recycled paper is recycled paper that contains little phosphor, that is, recycled paper with little phosphor. The second type of recycled paper is recycled paper that contains a lot of phosphor, that is, recycled paper with a lot of phosphor. The second type of recycled paper contains more phosphor than the first type of recycled paper. Also, the second type of recycled paper contains more phosphor than coated paper. Generally, the phosphor contained in the paper absorbs ultraviolet light and emits light (fluorescence) having a wavelength longer than that of ultraviolet light.

[0043] The conveyance roller 82 conveys the sheet of paper along the conveyance path 27 by rotating while sandwiching one sheet of paper. The conveyance timing and conveyance speed by the conveyance roller 82 are controlled by the processor 11 according to the type of paper. The paper discharge tray 83 places the paper on which an image has been formed.

[0044] <B. Configuration of Inspection Unit> Referring to FIG. 3, the configuration of the inspection unit 20 will be described. FIG. 3 is a diagram showing an example of the configuration of the inspection unit 20.

[0045] Arrow A1 shown in FIG. 3 indicates the direction in which the paper M is conveyed (hereinafter referred to as the “conveyance direction”). Arrow A2 indicates the direction perpendicular to the conveyance direction.

[0046] The inspection unit 20 includes a light source unit 21, a detection unit 22, element substrates 23X and 23Y, optical diaphragms 24X and 24Y, a paper passage guide 25, and a reflection unit 26. The paper M is conveyed along a conveyance path 27 provided between the optical diaphragm 24X and the paper passage guide 25. Since the conveyance path 27 has a width in the direction of arrow A2, the passing position of the paper M can vary in the direction of arrow A2 within the range of the width.

[0047] The light source unit 21 includes a first light source unit 21X and a second light source unit 21Y. The first light source unit 21X and the detection unit 22 are located on the same side with respect to the paper M. The first light source unit 21X includes a first light-emitting element 211X, a second light-emitting element 212X, and a third light-emitting element 213X. The first light-emitting element 211X, the second light-emitting element 212X, and the third light-emitting element 213X are, for example, LEDs (Light-Emitting Diodes). The first light-emitting element 211X emits light having a first wavelength, the second light-emitting element 212X emits light having a second wavelength, and the third light-emitting element 213X emits light having a third wavelength.

[0048] The peak wavelength of the light having the first wavelength is 390 nm or more and less than 550 nm. More preferably, the light having the first wavelength is light with a peak wavelength of 390 nm or more and less than 440 nm (i.e., violet light). Wavelengths of 390 nm or more and less than 440 nm are wavelengths in which there is little absorption of light by phosphors contained in the paper, and wavelengths in which there is a lot of absorption of light by recycled paper pulp. As an example, in this embodiment, light with a peak wavelength of 405 nm is used as the light having the first wavelength.

[0049] The light having the second wavelength is ultraviolet light. More preferably, the peak wavelength of the light having the second wavelength is 340 nm or more and less than 390 nm. Wavelengths between 340 nm and less than 390 nm are wavelengths in which light is absorbed greatly by phosphors contained in the paper. As an example, in this embodiment, light with a peak wavelength of 365 nm is used as the light having the second wavelength.

[0050] Light having a third wavelength is infrared light. As an example, in this embodiment, light with a peak wavelength of 850 nm is used as the light having a third wavelength.

[0051] The second light source unit 21Y is located on the side of the paper M opposite to the side where the detection unit 22 is located. That is, the second light source unit 21Y, the transport path 27, and the detection unit 22 are located in this order. The second light source unit 21Y includes a fourth light-emitting element 214Y and a fifth light-emitting element 215Y. The fourth light-emitting element 214Y and the fifth light-emitting element 215Y are LEDs. The fourth light-emitting element 214Y emits light having a fourth wavelength, and the fifth light-emitting element 215Y emits light having a fifth wavelength.

[0052] Light having a fourth wavelength is infrared light. As an example, in this embodiment, light with a peak wavelength of 850 nm is used as the light having a fourth wavelength.

[0053] Light having a fifth wavelength is blue light. As an example, in this embodiment, light with a peak wavelength of 460 nm is used as the light having a fifth wavelength.

[0054] While the paper is passing through the inspection unit 20, the processor 11 causes the first light-emitting element 211X, the second light-emitting element 212X, the third light-emitting element 213X, the fourth light-emitting element 214Y, and the fifth light-emitting element 215Y to emit light in such a way that their emission timings do not overlap. As the first light-emitting element 211X, the second light-emitting element 212X, the third light-emitting element 213X, the fourth light-emitting element 214Y, and the fifth light-emitting element 215Y each emit light, light is shone onto the paper M being transported along the transport path 27.

[0055] The detection unit 22 includes a light-receiving element 220. The light-receiving element 220 is, for example, a photodiode. Photodiodes are better at detecting light with longer wavelengths. The light-receiving element 220 detects incident light and outputs a photocurrent corresponding to the amount of incident light. The detection unit 22 converts the photocurrent output by the light-receiving element 220 into a voltage, converts the voltage into digital data, and outputs it to the processor 11.

[0056] The element substrates 23X and 23Y are provided at positions facing the conveyed paper M. On the surface of the element substrate 23X facing the paper M, a first light-emitting element 211X, a second light-emitting element 212X, a third light-emitting element 213X, and a light-receiving element 220 are provided. On the surface of the element substrate 23Y facing the paper M, a fourth light-emitting element 214Y and a fifth light-emitting element 215Y are provided.

[0057] The optical aperture 24X is located between the paper guide 25 and the element substrate 23X, and the optical aperture 24Y is located between the paper guide 25 and the element substrate 23Y. The optical aperture 24X has an opening 28X in a range including a portion facing the first light-emitting element 211X, the second light-emitting element 212X, the third light-emitting element 213X, and the light-receiving element 220. The optical aperture 24Y has an opening 28Y in a range including a portion facing the fourth light-emitting element 214Y and the fifth light-emitting element 215Y. The irradiation light from the first light source unit 21X enters the paper M through the opening 28X, and the irradiation light from the second light source unit 21Y enters the paper M through the opening 28Y. Since the portion of the optical aperture 24X other than the opening 28X has light-shielding properties and the portion of the optical aperture 24Y other than the opening 28Y has light-shielding properties, light other than the irradiation light is suppressed from entering the paper M.

[0058] The paper guide 25 supports the paper M so that the paper M moves along the conveyance path 27.

[0059] The reflection part 26 is provided at a position facing the first light source unit 21X. The reflection part 26 reflects the light irradiated from the first light source unit 21X. The reflection part 26 is used to evaluate the reflectivity of the paper.

[0060] In the example shown in FIG. 3, the second light source unit 21Y includes the fourth light-emitting element 214Y and the fifth light-emitting element 215Y. However, in the first embodiment, the second light source unit 21Y only needs to include the fourth light-emitting element 214Y and may not include the fifth light-emitting element 215Y.

[0061] <C. Reflected Light and Reflectivity> Refer to Figures 4 and 5 to explain the detection of reflected light and the calculation of reflectance. Reflectance is an index used to evaluate the reflectivity of paper.

[0062] Figure 4 is a diagram illustrating the light detected by the light-receiving element 220 when light is emitted from the first light source unit 21X at the time the paper M passes through the inspection unit 20.

[0063] If a first irradiation light Lx1 having a first wavelength is irradiated from the first light-emitting element 211X at the same time that the paper M is passing through the inspection unit 20, the light-receiving element 220 detects reflected light Lr1 as light from the paper M. The reflected light Lr1 includes the light from the first irradiation light Lx1 that is reflected by the paper M. If the paper M contains a phosphor, the reflected light Lr1 further includes fluorescence emitted by the phosphor that absorbed the first irradiation light Lx1.

[0064] If a second illumination light Lx2 having a second wavelength is irradiated from the second light-emitting element 212X at the same time that the paper M is passing through the inspection unit 20, the light-receiving element 220 detects reflected light Lr2 as light from the paper M. The reflected light Lr2 includes the light from the second illumination light Lx2 that is reflected by the paper M. If the paper M contains a phosphor, the reflected light Lr2 further includes fluorescence emitted by the phosphor that absorbed the second illumination light Lx2.

[0065] If a third irradiation light Lx3 having a third wavelength is irradiated from the third light-emitting element 213X at the same time that the paper M is passing through the inspection unit 20, the light-receiving element 220 detects reflected light Lr3 as light from the paper M. The reflected light Lr3 includes the light from the third irradiation light Lx3 that is reflected by the paper M. If the paper M contains a phosphor, the reflected light Lr3 further includes fluorescence emitted by the phosphor that absorbed the third irradiation light Lx3.

[0066] The detection unit 22 acquires the light intensity of reflected light Lr1, reflected light Lr2, and reflected light Lr3, and outputs the respective light intensity to the processor 11. The amount of reflected light Lr1 acquired by the detection unit 22 is an example of the "first detection value" in this disclosure. The amount of reflected light Lr2 acquired by the detection unit 22 is an example of the "second detection value" in this disclosure. The amount of reflected light Lr3 acquired by the detection unit 22 is an example of the "third detection value" in this disclosure.

[0067] Figure 5 is a diagram illustrating the light detected by the light-receiving element 220 when light is emitted from the first light source unit 21X at a time when the paper M has not yet passed through the inspection unit 20.

[0068] If the first illumination light Lx1 having a first wavelength is emitted from the first light-emitting element 211X at a time when the paper M has not passed through the inspection unit 20, the light-receiving element 220 detects the reflected light sLr1 reflected by the reflecting unit 26.

[0069] If a second illumination light Lx2 having a second wavelength is emitted from the second light-emitting element 212X at a time when the paper M has not passed through the inspection unit 20, the light-receiving element 220 detects the reflected light sLr2 reflected by the reflecting unit 26.

[0070] If a third illumination light Lx3 having a third wavelength is emitted from the third light-emitting element 213X at a time when the paper M has not passed through the inspection unit 20, the light-receiving element 220 detects the reflected light sLr3 reflected by the reflecting unit 26.

[0071] The detection unit 22 acquires the light intensity of reflected light sLr1, reflected light sLr2, and reflected light sLr3, and outputs these light intensity values ​​to the processor 11. The processor 11 stores the light intensity values ​​of reflected light sLr1, reflected light sLr2, and reflected light sLr3 in the storage 13. The light intensity values ​​of reflected light sLr1, reflected light sLr2, and reflected light sLr3 are examples of reference data 132.

[0072] The reflectance in the present disclosure is calculated by the processor 11 using the following Equation 1.

[0073] Reflectance = amount of light Lr / amount of light sLr ··· (Equation 1)

[0074] The amount of light Lr in Equation 1 indicates the amount of light detected by the light receiving element 220 when the paper M is irradiated with light from the first light source unit 21X at the timing when the paper M passes through the inspection unit 20. The amount of light of the reflected light Lr1, the amount of light of the reflected light Lr2, and the amount of light of the reflected light Lr3 are each an example of the amount of light Lr.

[0075] The amount of light sLr in Equation 1 indicates the amount of light detected by the light receiving element 220 when the paper M is irradiated with light from the first light source unit 21X at the timing when the paper M does not pass through the inspection unit 20. The amount of light of the reflected light sLr1, the amount of light of the reflected light sLr2, and the amount of light of the reflected light sLr3 are each an example of the amount of light sLr.

[0076] In the following description, the reflectance Vr of light having the first wavelength, the reflectance UVr of light having the second wavelength, and the reflectance IRr of light having the third wavelength are calculated by the processor 11 using the following Equations 2 to 4.

[0077] Reflectance Vr of light having the first wavelength = (amount of reflected light Lr1) / (amount of reflected light sLr1) ··· (Equation 2)

[0078] Reflectance UVr of light having the second wavelength = (amount of reflected light Lr2) / (amount of reflected light sLr2) ··· (Equation 3)

[0079] Reflectance IRr of light having the third wavelength = (amount of reflected light Lr3) / (amount of reflected light sLr3) ··· (Equation 4)

[0080] <D. Transmitted Light and Transmittance> Referring to FIGS. 6 and 7, the detection of transmitted light and the calculation of transmittance will be described. Transmittance is an index used to evaluate the transparency of paper.

[0081] Figure 6 is a diagram illustrating the light detected by the light-receiving element 220 when light is emitted from the second light source unit 21Y at the same time that the paper M is passing through the inspection unit 20.

[0082] If the fourth light-emitting element 214Y emits a fourth illumination light Ly4 having a fourth wavelength while the paper M is passing through the inspection unit 20, the light-receiving element 220 detects transmitted light Lt4 as light from the paper M. The transmitted light Lt4 includes the light of the fourth illumination light Ly4 that has passed through the paper M. If the paper M contains a phosphor, the transmitted light Lt4 further includes fluorescence emitted by the phosphor that has absorbed the fourth illumination light Ly4.

[0083] If the fifth light-emitting element 215Y emits a fifth illumination light Ly5 having a fifth wavelength at the same time that the paper M is passing through the inspection unit 20, the light-receiving element 220 detects the transmitted light Lt5 as light from the paper M. The transmitted light Lt5 includes the light of the fifth illumination light Ly5 that has passed through the paper M. If the paper M contains a phosphor, the transmitted light Lt5 further includes the fluorescence emitted by the phosphor that has absorbed the fifth illumination light Ly5.

[0084] The detection unit 22 acquires the light intensity of transmitted light Lt4 and transmitted light Lt5, respectively, and outputs the light intensity to the processor 11. The amount of transmitted light Lt4 acquired by the detection unit 22 is an example of the "fourth detection value" in this disclosure. The amount of transmitted light Lt5 acquired by the detection unit 22 is an example of the "fifth detection value" in this disclosure.

[0085] Figure 7 is a diagram illustrating the light detected by the light-receiving element 220 when light is emitted from the second light source unit 21Y at a time when the paper M has not yet passed through the inspection unit 20.

[0086] If the fourth light source 214Y emits a fourth illumination light Ly4 having a fourth wavelength at a time when the paper M has not passed through the inspection unit 20, the photodetector 220 detects the fourth illumination light Ly4.

[0087] If the fifth light source 215Y emits a fifth illumination light Ly5 having a fifth wavelength at a time when the paper M has not passed through the inspection unit 20, the light receiving element 220 detects the fifth illumination light Ly5.

[0088] The detection unit 22 acquires the light intensity of the fourth illumination light Ly4 and the fifth illumination light Ly5, and outputs these light intensity values ​​to the processor 11. The processor 11 stores the light intensity values ​​of the fourth illumination light Ly4 and the fifth illumination light Ly5 in the storage 13. The light intensity values ​​of the fourth illumination light Ly4 and the fifth illumination light Ly5 are examples of reference data 132.

[0089] The transmittance in this disclosure is calculated by the processor 11 using the following formula 5.

[0090] Transmittance=Light amount Lt / Light amount Ly...(Formula 5)

[0091] In Equation 5, the light intensity Lt represents the amount of light detected by the light-receiving element 220 when light is emitted from the second light source unit 21Y at the time the paper M passes through the inspection unit 20. The light intensity of transmitted light Lt4 and the light intensity of transmitted light Lt5 are examples of light intensity Lt.

[0092] In Equation 5, the light intensity Ly represents the amount of light detected by the light-receiving element 220 when light is emitted from the second light source unit 21Y at a time when the paper M has not passed through the inspection unit 20. The light intensity of the fourth illumination light Ly4 and the light intensity of the fifth illumination light Ly5 are examples of light intensity Ly.

[0093] In the following description, the transmittance IRt of light having a fourth wavelength and the transmittance Bt of light having a fifth wavelength are calculated by the processor 11 using the following equations 6 and 7.

[0094] The transmittance of light with a fourth wavelength is IRt = (amount of transmitted light Lt4) / (amount of fourth irradiated light Ly4) ... (Equation 6)

[0095] Transmittance Bt of light having the fifth wavelength = (amount of transmitted light Lt5) / (amount of fifth irradiation light Ly5) ··· (Equation 7)

[0096] <E. Paper type discrimination process> (E1. Paper type discrimination process) Referring to FIG. 8, the paper type discrimination process in Embodiment 1 will be described. FIG. 8 is a flowchart showing the procedure of the paper type discrimination process in Embodiment 1. The paper type discrimination process includes a light amount detection process by the inspection unit 20 and a determination process by the processor 11. The paper type discrimination process is started when the sheet M reaches the inspection unit 20.

[0097] In step S1, the inspection unit 20 performs a light amount detection process. The light amount detection process includes detecting the amount of reflected light Lr1, the amount of reflected light Lr2, the amount of reflected light Lr3, the amount of transmitted light Lt4, and the amount of transmitted light Lt5, and outputting the detected light amounts to the processor 11.

[0098] In step S2, the processor 11 performs a determination process. The determination process includes calculating the reflectance and transmittance based on the light amounts acquired from the inspection unit 20, and discriminating the paper type based on the calculated reflectance and transmittance. After step S2, the paper type discrimination process ends.

[0099] (E2. Determination process) Referring to FIGS. 9 to 12, the determination process (step S2) will be described. The determination process includes a first process of discriminating the paper type based on the reflectance Vr of light having the first wavelength and a second process of discriminating the paper type based on the reflectance UVr of light having the second wavelength.

[0100] Figure 9 is a diagram illustrating the first process in Embodiment 1. Figure 9 shows experimental results obtained using the inspection unit 20 for various brands of recycled paper and coated paper. In the graph of Figure 9, the horizontal axis represents the transmittance IRt of light having the fourth wavelength, and the vertical axis represents the ratio Vr / IRr. The ratio Vr / IRr represents the ratio of the reflectance Vr of light having the first wavelength to the reflectance IRr of light having the third wavelength. The transmittance IRt is calculated using the above formula 6. The ratio Vr / IRr is calculated using the following formula 8.

[0101] Ratio Vr / IRr = (Reflectance Vr of light with the first wavelength) / (Reflectance IRr of light with the third wavelength) ... (Equation 8)

[0102] In the graph in Figure 9, the triangular marks indicate the Vr / IRr ratio for recycled paper, and the square marks indicate the Vr / IRr ratio for coated paper. As shown in Figure 9, for most recycled papers, the Vr / IRr ratio is less than the first threshold TH11, while for coated paper and some recycled papers, the Vr / IRr ratio is greater than or equal to the first threshold TH11.

[0103] The reason for obtaining the experimental results shown in Figure 9 is that the recycled pulp contained in recycled paper readily absorbs light with a peak wavelength of less than 550 nm. Due to the absorption of light by the recycled pulp, recycled paper tends to have a lower reflectance Vr than other types of paper, and for most recycled papers, the ratio Vr / IRr is less than the first threshold TH11. On the other hand, since the amount of light detected by the photodetector 220 increases due to fluorescence, if the recycled paper contains a lot of phosphors, the reflectance Vr will be high even in recycled paper. Therefore, for some recycled papers, the ratio Vr / IRr will be greater than the first threshold TH11.

[0104] Therefore, paper types with a ratio Vr / IRr less than the first threshold TH11 can be determined to be the first type of recycled paper (recycled paper with low phosphor content), and paper types with a ratio Vr / IRr greater than or equal to the first threshold TH11 can be determined to be either coated paper or the second type of recycled paper (recycled paper with high phosphor content). Storage 13 stores the first threshold TH11 predetermined by experiments and is referenced in the first processing. The first threshold TH11 is an example of reference data 132.

[0105] In the first process, the processor 11 calculates the ratio Vr / IRr and the transmittance IRt based on the amount of light acquired from the inspection unit 20, and determines whether the ratio Vr / IRr is equal to or greater than the first threshold TH11.

[0106] More specifically, the processor 11 calculates the reflectance Vr of light having a first wavelength by substituting the amount of reflected light Lr1 obtained from the inspection unit 20 and the amount of reflected light sLr1 stored in the storage unit 13 into Equation 2. The processor 11 calculates the reflectance IRr of light having a third wavelength by substituting the amount of reflected light Lr3 obtained from the inspection unit 20 and the amount of reflected light sLr3 stored in the storage unit 13 into Equation 4. The processor 11 calculates the ratio Vr / IRr by substituting the reflectance Vr and the reflectance IRr into Equation 8. The processor 11 calculates the transmittance IRt of light having a fourth wavelength by substituting the amount of transmitted light Lt4 obtained from the inspection unit 20 and the amount of fourth irradiation light Ly4 stored in the storage unit 13 into Equation 6. The processor 11 obtains the first threshold TH11 corresponding to the transmittance IRt from the storage unit 13.

[0107] If the ratio Vr / IRr is less than the first threshold TH11, the processor 11 determines that the paper type is the first type of recycled paper (recycled paper with low phosphor content). On the other hand, if the ratio Vr / IRr is greater than or equal to the first threshold TH11, the processor 11 performs a second process to determine whether the paper type is coated paper or the second type of recycled paper (recycled paper with high phosphor content).

[0108] Figure 10 is a diagram illustrating the second process in Embodiment 1. Figure 10 shows experimental results obtained using the inspection unit 20 for various brands of recycled paper and coated paper. In the graph of Figure 10, the horizontal axis represents the transmittance IRt of light having the fourth wavelength, and the vertical axis represents the ratio UVr / IRr. The ratio UVr / IRr represents the ratio of the reflectance UVr of light having the second wavelength to the reflectance IRr of light having the third wavelength. The transmittance IRt is calculated using the above equation 6. The ratio UVr / IRr is calculated using the following equation 9.

[0109] The ratio UVr / IRr = (reflectance of light with the second wavelength UVr) / (reflectance of light with the third wavelength IRr) ... (Equation 9)

[0110] In the graph in Figure 10, the triangular marks indicate the UVr / IRr ratio for recycled paper, and the square marks indicate the UVr / IRr ratio for coated paper. As shown in Figure 10, for recycled paper, the UVr / IRr ratio is above the second threshold TH21, while for coated paper, the UVr / IRr ratio is below the second threshold TH21.

[0111] Here, the reason why the experimental results shown in Figure 10 can be obtained will be explained with reference to Figure 11. Figure 11 shows the difference in reflectivity between paper containing a phosphor and paper without a phosphor. In the graph of Figure 11, the horizontal axis represents the wavelength of light irradiated onto the paper, and the vertical axis represents the reflectivity of the light.

[0112] As shown in Figure 11, for paper without phosphors, the reflectance decreases as the wavelength decreases, whereas for paper containing phosphors, the reflectance increases as the wavelength decreases, with a threshold of approximately 400 nm. This is because the phosphors in the paper absorb ultraviolet light (light with a second wavelength) and emit long-wavelength light (fluorescence) that is easily detected by photodiodes, thus seemingly increasing the amount of light detected as reflected light. Since the amount of light detected increases by the amount of fluorescence, the more phosphors the paper contains, the higher the apparent reflectance UVr of light with a second wavelength.

[0113] Referring again to Figure 10, paper types with a ratio UVr / IRr of 1 or higher than the second threshold TH21 can be determined to be paper types containing a lot of phosphor (in Embodiment 1, the second type of recycled paper (recycled paper with a lot of phosphor)), and paper types with a ratio UVr / IRr of 1 or lower than the second threshold TH21 can be determined to be paper types containing little phosphor (in Embodiment 1, coated paper). The second threshold TH21, which has been predetermined by experimentation, is stored in storage 13 and is referenced in the second processing. The second threshold TH21 is an example of reference data 132.

[0114] In the second process, the processor 11 calculates the ratio UVr / IRr based on the amount of light obtained from the inspection unit 20, and determines whether the ratio UVr / IRr is equal to or greater than the second threshold TH21.

[0115] More specifically, the processor 11 calculates the reflectance UVr of light having a second wavelength by substituting the amount of reflected light Lr2 obtained from the inspection unit 20 and the amount of reflected light sLr2 stored in the storage unit 13 into equation 3. The processor 11 calculates the ratio UVr / IRr by substituting the reflectance UVr and the reflectance IRr calculated in the first process into equation 9. The processor 11 obtains the second threshold TH21 corresponding to the transmittance IRt calculated in the first process from the storage unit 13.

[0116] If the ratio UVr / IRr is greater than or equal to the second threshold TH21, the processor 11 determines that the paper type is the second type of recycled paper (recycled paper with a high phosphor content). On the other hand, if the ratio UVr / IRr is less than the second threshold TH21, the processor 11 determines that the paper type is coated paper.

[0117] Figure 12 is a flowchart showing the procedure for the determination process in Embodiment 1. The determination process is performed by the processor 11.

[0118] In step S21, the processor 11 performs a first process. The first process determines whether the ratio Vr / IRr, which is the ratio of the reflectance Vr of light having the first wavelength to the reflectance IRr of light having the third wavelength, is greater than or equal to a first threshold TH11 corresponding to the transmittance IRt. Step S21 identifies a first type of recycled paper (recycled paper with fewer phosphors).

[0119] If the ratio Vr / IRr is greater than or equal to the first threshold TH11 corresponding to the transmittance IRt (YES in step S21), the processor 11 proceeds to step S22. On the other hand, if the ratio Vr / IRr is less than the first threshold TH11 corresponding to the transmittance IRt (NO in step S21), the processor 11 proceeds to step S25.

[0120] In step S22, the processor 11 performs a second process. The second process determines whether the ratio of the reflectance UVr of light having a second wavelength to the reflectance IRr of light having a third wavelength, UVr / IRr, is greater than or equal to a second threshold TH21 corresponding to the transmittance IRt. Step S22 distinguishes between a second type of recycled paper (recycled paper with a high phosphor content) and coated paper.

[0121] If the ratio UVr / IRr is greater than or equal to the second threshold TH21 corresponding to the transmittance IRt (YES in step S22), the processor 11 proceeds to step S23. On the other hand, if the ratio UVr / IRr is less than the second threshold TH21 corresponding to the transmittance IRt (NO in step S22), the processor 11 proceeds to step S24.

[0122] In step S23, the processor 11 determines that the paper type is the second type of recycled paper (recycled paper with a high phosphor content). In step S24, the processor 11 determines that the paper type is coated paper. In step S25, the processor 11 determines that the paper type is the first type of recycled paper (recycled paper with a low phosphor content).

[0123] After step S23, step S24, or step S25, the paper type determination process is completed.

[0124] Thus, the paper type discrimination device 2 in Embodiment 1 distinguishes a first type of recycled paper (recycled paper with few phosphors) by a first process using the amount of light detected as reflected light Lr1 (first detection value), and distinguishes coated paper and a second type of recycled paper (recycled paper with many phosphors) by a second process using the amount of light detected as reflected light Lr2 (second detection value). Therefore, recycled paper can be reliably distinguished.

[0125] Furthermore, in the first process, instead of comparing the reflectance Vr with a threshold, the ratio of reflectance Vr to reflectance IRr is compared with the threshold, thereby suppressing fluctuations in reflectance Vr caused by variations in the position of the paper M. Similarly, in the second process, instead of comparing the reflectance UVr with a threshold, the ratio of reflectance UVr to reflectance IRr is compared with the threshold, thereby suppressing fluctuations in reflectance UVr caused by variations in the position of the paper M. It is known that the reflectance IRr of light having a third wavelength is less affected by the type of paper. Generally, when the position of the paper M is close to the photodetector 220, the amount of light detected by the photodetector 220 increases, and when the position of the paper M is far from the photodetector 220, the amount of light detected by the photodetector 220 decreases, so the reflectance Vr and reflectance UVr may fluctuate depending on the position of the paper M. However, in the first process, since the ratio of reflectance Vr to reflectance IRr is compared with a threshold, fluctuations in reflectance Vr caused by variations in the position of the paper M can be suppressed. Furthermore, in the second process, the ratio of reflectance UVr to reflectance IRr is compared with a threshold value, thereby suppressing fluctuations in reflectance UVr caused by variations in the passage position of the paper M.

[0126] In the first processing step, the processor 11 may determine a first type of recycled paper (recycled paper with fewer phosphors) by comparing the reflectance Vr with a threshold value predetermined by experiment.

[0127] Furthermore, in the second process, the processor 11 may identify a second type of recycled paper (recycled paper with a high phosphor content) by comparing the reflectance UVr with a threshold value predetermined by experiment.

[0128] Furthermore, as mentioned above, the peak wavelength of the light having the first wavelength can be 390 nm or more and less than 550 nm. However, by using light with a peak wavelength of 390 nm or more and less than 440 nm (i.e., violet light) as the light having the first wavelength, the accuracy of paper type discrimination by the first treatment is improved. This is because wavelengths between 390 nm and less than 440 nm are wavelengths at which light is not absorbed much by phosphors contained in the paper, and wavelengths at which light is absorbed a lot by recycled paper pulp. As a result, there is a tendency for a difference in reflectance Vr to occur between recycled paper of the first type (recycled paper with few phosphors) and other types of paper.

[0129] Furthermore, as mentioned above, the light having the second wavelength can be ultraviolet light, but by using light with a peak wavelength of 340 nm or more and less than 390 nm as the light having the second wavelength, the accuracy of paper type discrimination by the second processing is improved. This is because wavelengths of 340 nm or more and less than 390 nm are wavelengths at which a lot of light is absorbed by phosphors contained in the paper, so a difference in reflectance UVr is likely to occur between paper types that contain a lot of phosphors (in Embodiment 1, the second type of recycled paper (recycled paper with a lot of phosphors)) and paper types that do not.

[0130] [Modified example of Embodiment 1] As a second process, the processor 11 may determine between a second type of recycled paper (recycled paper with a high phosphor content) and coated paper based on the difference between the ratio of the reflectance Vr of light having a first wavelength to the reflectance IRr of light having a third wavelength and the ratio of the reflectance UVr of light having a second wavelength to the reflectance IRr of light having a third wavelength.

[0131] Figure 13 is a diagram illustrating a second process in a modified example of Embodiment 1. Figure 13 shows experimental results obtained using the inspection unit 20 for various brands of recycled paper and coated paper. In the graph of Figure 13, the horizontal axis represents the transmittance IRt of light having a fourth wavelength, and the vertical axis represents the ratio difference DR. The ratio difference DR represents the difference between the ratio of the reflectance Vr of light having a first wavelength to the reflectance IRr of light having a third wavelength, and the ratio of the reflectance UVr of light having a second wavelength to the reflectance IRr of light having a third wavelength. The transmittance IRt is calculated using the above equation 6. The ratio difference DR is calculated using the following equation 10.

[0132] Ratio difference DR = (ratio Vr / IRr) - (ratio UVr / IRr) (Formula 10)

[0133] In the graph in Figure 13, the triangular marks indicate the ratio difference DR for recycled paper, and the square marks indicate the ratio difference DR for coated paper. As shown in Figure 13, for coated paper, the ratio difference DR is greater than or equal to the second threshold TH22, while for recycled paper, the ratio difference DR is less than the second threshold TH22.

[0134] The reason for obtaining experimental results like those shown in Figure 13 is that the phosphors contained in the paper absorb ultraviolet light (light with a second wavelength) and emit light with a longer wavelength (fluorescence) that is easily detected by the photodiode, thereby seemingly increasing the amount of light detected as reflected light. Since the amount of detected light increases by the amount of fluorescence, the more phosphors contained in the paper, the higher the apparent reflectance UVr of light with a second wavelength tends to be. Therefore, paper types containing a large amount of phosphors have a ratio difference DR of less than the second threshold TH22.

[0135] Therefore, paper types in which the ratio difference DR is less than the second threshold TH22 can be determined to be paper types containing a large amount of phosphor (in the modified example of Embodiment 1, the second type of recycled paper (recycled paper with a high phosphor content)). The storage 13 stores the second threshold TH22 predetermined by experimentation and is referenced in the second processing. The second threshold TH22 is an example of reference data 132.

[0136] In the second process, the processor 11 calculates the ratio difference DR and determines whether the ratio difference DR is greater than or equal to the second threshold TH22.

[0137] More specifically, the processor 11 calculates the ratio Vr / IRr and the ratio UVr / IRr using the method described above, and then calculates the ratio difference DR by substituting the ratio Vr / IRr and the ratio UVr / IRr into equation 10. The processor 11 obtains the second threshold TH22 corresponding to the transmittance IRt calculated in the first process from the storage 13.

[0138] If the ratio difference DR is greater than or equal to the second threshold TH22, the processor 11 determines that the paper type is coated paper. On the other hand, if the ratio difference DR is less than the second threshold TH22, the processor 11 determines that the paper type is the second type of recycled paper (recycled paper with a high phosphor content).

[0139] Thus, in the second process, the paper type is determined by considering not only the reflectance UVr of light having the second wavelength, but also the reflectance Vr of light having the first wavelength, thereby improving the accuracy of paper type determination.

[0140] Furthermore, instead of comparing the difference between reflectance Vr and reflectance UVr with a threshold, the difference between the ratio of reflectance Vr to reflectance IRr and the ratio of reflectance UVr to reflectance IRr is compared with a threshold. This makes it possible to suppress fluctuations in reflectance Vr and reflectance UVr caused by variations in the passage position of the paper M.

[0141] In the second process, the processor 11 may identify a second type of recycled paper (recycled paper with a high phosphor content) by comparing the difference between the reflectance Vr and the reflectance UVr with a threshold value predetermined by experiment.

[0142] [Embodiment 2] Embodiment 1 described the case of distinguishing between a first type of recycled paper (recycled paper with few phosphors), a second type of recycled paper (recycled paper with many phosphors), and coated paper. Embodiment 2 describes the case of distinguishing between a first type of recycled paper (recycled paper with few phosphors), a second type of recycled paper (recycled paper with many phosphors), coated paper, and plain paper. The image forming apparatus in Embodiment 2 is the same as the image forming apparatus 1 in Embodiment 1, so the same components are denoted by the same reference numerals and the description is not repeated. In Embodiment 1, the second light source unit 21Y did not have to include the fifth light-emitting element 215Y, but in Embodiment 2, the second light source unit 21Y always includes the fifth light-emitting element 215Y.

[0143] The difference between Embodiment 2 and Embodiment 1 lies in the determination process; therefore, this section will describe the determination process in Embodiment 2, and will not repeat the explanation of other processes. The determination process in Embodiment 2 includes the first process and the second process described above, as well as a third process. The third process is a process that determines whether a paper is plain paper based on the transmittance IRt of light having a fourth wavelength and the transmittance Bt of light having a fifth wavelength.

[0144] Figure 14 is a diagram illustrating the third process in Embodiment 2. Figure 14 shows experimental results obtained using the inspection unit 20 for various brands of recycled paper, coated paper, and plain paper. In the graph of Figure 14, the horizontal axis represents the transmittance IRt of light having the fourth wavelength, and the vertical axis represents the transmittance Bt of light having the fifth wavelength. The transmittance IRt and transmittance Bt are calculated using equations 6 and 7 described above, respectively.

[0145] In the graph in Figure 14, the triangular marks indicate the transmittance Bt of recycled paper, the square marks indicate the transmittance Bt of coated paper, and the circular marks indicate the transmittance Bt of plain paper. As shown in Figure 14, for most plain papers, the transmittance Bt is above the third threshold TH31, while for most coated papers and most recycled papers, the transmittance Bt is below the third threshold TH31.

[0146] Therefore, paper types with a transmittance Bt equal to or greater than the third threshold TH31 can be determined to be plain paper, and paper types with a transmittance Bt less than the third threshold TH31 can be determined to be either coated paper or recycled paper. The storage 13 stores the third threshold TH31 predetermined by experimentation and is referenced in the third process. The third threshold TH31 is an example of reference data 132.

[0147] In the third process, the processor 11 calculates the transmittance IRt and the transmittance Bt based on the amount of light obtained from the inspection unit 20, and determines whether the transmittance Bt is equal to or greater than the third threshold TH31.

[0148] More specifically, the processor 11 calculates the transmittance IRt of light having a fourth wavelength by substituting the amount of transmitted light Lt4 obtained from the inspection unit 20 and the amount of the fourth irradiation light Ly4 stored in the storage unit 13 into equation 6. The processor 11 calculates the transmittance Bt of light having a fifth wavelength by substituting the amount of transmitted light Lt5 obtained from the inspection unit 20 and the amount of the fifth irradiation light Ly5 stored in the storage unit 13 into equation 7. The processor 11 obtains the third threshold TH31 corresponding to the transmittance IRt from the storage unit 13.

[0149] If the transmittance Bt is greater than or equal to the third threshold TH31, the processor 11 determines that the paper type is plain paper. On the other hand, if the transmittance Bt is less than the third threshold TH31, the processor 11 performs a further first process to determine whether the paper type is coated paper or recycled paper. If the paper type cannot be determined by the first process, that is, if the ratio Vr / IRr is greater than or equal to the first threshold TH11, the processor 11 performs a further second process to determine whether the paper type is coated paper or a second type of recycled paper (recycled paper with a high phosphor content).

[0150] Figure 15 is a flowchart showing the procedure for the determination process in Embodiment 2. The determination process is executed by the processor 11. In the determination process shown in Figure 15, steps S31 and S32 are added to the determination process shown in Figure 12. In the determination process shown in Figure 15, the same steps as in the determination process shown in Figure 12 are given the same step numbers and the explanation is not repeated.

[0151] In step S31, the processor 11 performs a third process. The third process determines whether the transmittance Bt is greater than or equal to the third threshold TH31 corresponding to the transmittance IRt. Plain paper is identified by step S31.

[0152] If the transmittance Bt is greater than or equal to the third threshold TH31 corresponding to the transmittance IRt (YES in step S31), the processor 11 proceeds to step S32. On the other hand, if the transmittance Bt is less than the third threshold TH31 corresponding to the transmittance IRt (NO in step S31), the processor 11 proceeds to step S21.

[0153] In step S32, the processor 11 determines that the paper type is plain paper. After steps S23, S24, S25, or S32, the paper type determination process ends.

[0154] Thus, the paper type discrimination device 2 in Embodiment 2 distinguishes a first type of recycled paper (recycled paper with few phosphors) by a first process using the amount of light detected as reflected light Lr1 (first detection value), and distinguishes coated paper and a second type of recycled paper (recycled paper with many phosphors) by a second process using the amount of light detected as reflected light Lr2 (second detection value). Therefore, recycled paper can be reliably distinguished.

[0155] Furthermore, the paper type discrimination device 2 in Embodiment 2 can further distinguish plain paper by a third process using the amount of transmitted light Lt4 (fourth detection value) and the amount of transmitted light Lt5 (fifth detection value).

[0156] [Modified version of Embodiment 2] In the judgment process shown in Figure 15, the third process, the first process, and the second process were performed in this order, but the first process, the third process, and the second process may also be performed in this order.

[0157] Figure 16 is a diagram illustrating the first process in a modified example of Embodiment 2. Figure 16 shows experimental results obtained using the inspection unit 20 for various brands of recycled paper, coated paper, and plain paper. In the graph of Figure 16, the horizontal axis represents the transmittance IRt of light having the fourth wavelength, and the vertical axis represents the ratio of the reflectance Vr of light having the first wavelength to the reflectance IRr of light having the third wavelength (ratio Vr / IRr). The transmittance IRt is calculated using the above formula 6. The ratio Vr / IRr is calculated using the above formula 8.

[0158] In the graph in Figure 16, the triangular marks represent the Vr / IRr ratio for recycled paper, the square marks represent the Vr / IRr ratio for coated paper, and the circular marks represent the Vr / IRr ratio for plain paper. As shown in Figure 16, for most recycled papers, the Vr / IRr ratio is less than the first threshold TH12, while for most coated papers, most plain papers, and some recycled papers, the Vr / IRr ratio is greater than or equal to the first threshold TH12.

[0159] The reason for obtaining the experimental results shown in Figure 16 is the same as the reason for obtaining the experimental results shown in Figure 9.

[0160] Therefore, paper types with a ratio Vr / IRr less than the first threshold TH12 can be determined to be the first type of recycled paper (recycled paper with low phosphor content), and paper types with a ratio Vr / IRr greater than or equal to the first threshold TH12 can be determined to be either coated paper, plain paper, or the second type of recycled paper (recycled paper with high phosphor content). The storage 13 stores the first threshold TH12 predetermined by experiments, which is referenced in the first processing. The first threshold TH12 is an example of reference data 132.

[0161] In the first process, the processor 11 calculates the ratio Vr / IRr and transmittance IRt using the method described above, based on the amount of light acquired from the inspection unit 20, and determines whether the ratio Vr / IRr is greater than or equal to the first threshold TH12. More specifically, the processor 11 acquires the first threshold TH12 corresponding to the transmittance IRt from the storage 13, and determines whether the ratio Vr / IRr is greater than or equal to the first threshold TH12.

[0162] If the ratio Vr / IRr is less than the first threshold TH12, the processor 11 determines that the paper type is the first type of recycled paper (recycled paper with low phosphor content). On the other hand, if the ratio Vr / IRr is greater than or equal to the first threshold TH12, the processor 11 performs a third process to determine whether the paper type is coated paper, plain paper, or the second type of recycled paper (recycled paper with high phosphor content). If the paper type cannot be determined by the third process, that is, if the transmittance Bt is less than the third threshold TH31, the processor 11 performs a second process to determine whether the paper type is coated paper or the second type of recycled paper (recycled paper with high phosphor content).

[0163] Figure 17 is a flowchart showing the procedure for the determination process in a modified example of Embodiment 2. The determination process is performed by the processor 11. The determination process shown in Figure 17 differs from the determination process shown in Figure 15 in the order in which the first, second, and third processes are performed. In the determination process shown in Figure 17, the first, third, and second processes are performed in this order. Also, in the determination process shown in Figure 17, step S21A is performed instead of step S21 as the first process. Among the determination processes shown in Figure 17, the same steps as those shown in Figure 15 are given the same step numbers and the explanation is not repeated.

[0164] In step S21A, the processor 11 performs a first process. The first process determines whether the ratio Vr / IRr, which is the ratio of the reflectance Vr of light having the first wavelength to the reflectance IRr of light having the third wavelength, is greater than or equal to a first threshold TH12 corresponding to the transmittance IRt. Step S21A identifies a first type of recycled paper (recycled paper with fewer phosphors).

[0165] If the ratio Vr / IRr is greater than or equal to the first threshold TH12 corresponding to the transmittance IRt (YES in step S21A), the processor 11 proceeds to step S31. On the other hand, if the ratio Vr / IRr is less than the first threshold TH12 corresponding to the transmittance IRt (NO in step S21A), the processor 11 proceeds to step S25.

[0166] After step S23, step S24, step S25, or step S32, the paper type determination process is completed.

[0167] Thus, the paper type discrimination device 2 in the modified embodiment of Embodiment 2 also distinguishes a first type of recycled paper (recycled paper with few phosphors) by the first process, and distinguishes coated paper from a second type of recycled paper (recycled paper with many phosphors) by the second process. Therefore, recycled paper can be reliably distinguished.

[0168] Furthermore, the paper type discrimination device 2 in the modified embodiment of the second embodiment can further distinguish plain paper through a third process.

[0169] [Embodiment 3] Embodiment 2 described the case of distinguishing between a first type of recycled paper (recycled paper with few phosphors), a second type of recycled paper (recycled paper with many phosphors), coated paper, and plain paper. Embodiment 3 describes the case of distinguishing between a first type of recycled paper (recycled paper with few phosphors), a second type of recycled paper (recycled paper with many phosphors), coated paper, plain paper with few phosphors, and plain paper with many phosphors. The image forming apparatus in Embodiment 3 is the same as the image forming apparatus 1 in Embodiment 2, so the same components are denoted by the same reference numerals and the description is not repeated.

[0170] The difference between Embodiment 3 and Embodiment 2 lies in the determination process; therefore, this section will describe the determination process in Embodiment 3, and will not repeat the explanation of the other processes. The determination process in Embodiment 3 also includes a first process, a second process, and a third process, but the order and number of times the first, second, and third processes are performed differ between the determination process in Embodiment 3 and the determination process in Embodiment 2.

[0171] Figure 18 is a diagram illustrating the second process in Embodiment 3. Figure 18 shows experimental results obtained using the inspection unit 20 for various brands of recycled paper, coated paper, and plain paper. In the graph of Figure 18, the horizontal axis represents the transmittance IRt of light having the fourth wavelength, and the vertical axis represents the ratio of the reflectance UVr of light having the second wavelength to the reflectance IRr of light having the third wavelength (ratio UVr / IRr). The transmittance IRt is calculated using equation 6 above. The ratio UVr / IRr is calculated using equation 9 above.

[0172] In the graph in Figure 18, the triangular marks represent the UVr / IRr ratio for recycled paper, the square marks represent the UVr / IRr ratio for coated paper, and the circular marks represent the UVr / IRr ratio for plain paper. As shown in Figure 18, for coated paper, the UVr / IRr ratio is less than the second threshold TH23.

[0173] As described above, the more phosphors a paper contains, the higher the apparent reflectance UVr of light having a second wavelength tends to be. Therefore, paper types with a ratio UVr / IRr of TH23 or higher can be determined to be paper types containing a lot of phosphors (in Embodiment 3, the second type of recycled paper (recycled paper with a lot of phosphors) and plain paper with a lot of phosphors), and paper types with a ratio UVr / IRr of less than TH23 can be determined to be paper types with a little phosphors (in Embodiment 3, coated paper, the first type of recycled paper (recycled paper with a little phosphors), and plain paper with a little phosphors). The second threshold TH23, which has been predetermined by experimentation, is stored in storage 13 and is referenced in the second processing. The second threshold TH23 is an example of reference data 132.

[0174] In the second process, the processor 11 calculates the ratio UVr / IRr using the method described above based on the amount of light acquired from the inspection unit 20, and determines whether the ratio UVr / IRr is greater than or equal to the second threshold TH23. More specifically, the processor 11 acquires the second threshold TH23 corresponding to the transmittance IRt from the storage 13, and determines whether the ratio UVr / IRr is greater than or equal to the second threshold TH23.

[0175] If the ratio UVr / IRr is greater than or equal to the second threshold TH23, the processor 11 determines that the paper type is either the second type of recycled paper (recycled paper with a high phosphor content) or plain paper with a high phosphor content, and further performs a third process to distinguish between the second type of recycled paper (recycled paper with a high phosphor content) and plain paper with a high phosphor content.

[0176] On the other hand, if the ratio UVr / IRr is less than the second threshold TH23, the processor 11 determines that the paper type is one of the first type of recycled paper (recycled paper with low phosphor content), coated paper, or plain paper with low phosphor content, and performs the first process further. If the paper type cannot be determined by the first process, that is, if the ratio Vr / IRr is greater than or equal to the first threshold TH11, the processor 11 performs a third process further to determine whether the paper type is coated paper or plain paper with low phosphor content.

[0177] Figure 19 is a flowchart showing the procedure for the determination process in Embodiment 3. The determination process is performed by the processor 11. The determination process shown in Figure 19 differs from the determination process shown in Figure 15 in the order and number of times the first, second, and third processes are performed. In addition, in the determination process shown in Figure 19, step S22A is performed instead of step S22 as the second process, and steps S31A and S31B are performed instead of step S31 as the third process. Among the determination processes shown in Figure 19, the same steps as those shown in Figure 15 are given the same step numbers and the explanation is not repeated.

[0178] In step S22A, the processor 11 performs a second process. The second process determines whether the ratio of the reflectance UVr of light having a second wavelength to the reflectance IRr of light having a third wavelength, UVr / IRr, is greater than or equal to the second threshold TH23 corresponding to the transmittance IRt. Step S22A distinguishes between paper with a high phosphor content and paper with a low phosphor content.

[0179] If the ratio UVr / IRr is greater than or equal to the second threshold TH23 corresponding to the transmittance IRt (YES in step S22A), the processor 11 proceeds to step S31A. On the other hand, if the ratio UVr / IRr is less than the second threshold TH23 corresponding to the transmittance IRt (NO in step S22A), the processor 11 proceeds to step S21.

[0180] In step S31A, the processor 11 performs a third process. The third process determines whether the transmittance Bt is greater than or equal to the third threshold TH31 corresponding to the transmittance IRt. Step S31A distinguishes between plain paper and paper types other than plain paper.

[0181] If the transmittance Bt is greater than or equal to the third threshold TH31 corresponding to the transmittance IRt (YES in step S31A), the processor 11 proceeds to step S32A. On the other hand, if the transmittance Bt is less than the third threshold TH31 corresponding to the transmittance IRt (NO in step S31A), the processor 11 proceeds to step S23.

[0182] If the ratio Vr / IRr is greater than or equal to the first threshold TH11 corresponding to the transmittance IRt (YES in step S21), the processor 11 proceeds to step S31B.

[0183] In step S31B, the processor 11 performs a third process. The third process determines whether the transmittance Bt is greater than or equal to the third threshold TH31 corresponding to the transmittance IRt. Step S31B distinguishes between plain paper and paper types other than plain paper.

[0184] If the transmittance Bt is greater than or equal to the third threshold TH31 corresponding to the transmittance IRt (YES in step S31B), the processor 11 proceeds to step S32B. On the other hand, if the transmittance Bt is less than the third threshold TH31 corresponding to the transmittance IRt (NO in step S31B), the processor 11 proceeds to step S24.

[0185] In step S32A, the processor 11 determines that the paper type is plain paper with a high phosphor content. In step S32B, the processor 11 determines that the paper type is plain paper with a low phosphor content.

[0186] After step S23, step S24, step S25, step S32A, or step S32B, the paper type determination process is completed.

[0187] Thus, the paper type discrimination device 2 in Embodiment 3 distinguishes between a second type of recycled paper (recycled paper with a high phosphor content) and plain paper with a high phosphor content through the second and third processes. Furthermore, the paper type discrimination device 2 in Embodiment 3 distinguishes between a first type of recycled paper (recycled paper with a low phosphor content) through the second and first processes. In addition, the paper type discrimination device 2 in Embodiment 3 distinguishes between coated paper and plain paper with a low phosphor content through the second, first, and third processes. Therefore, recycled paper can be reliably identified.

[0188] [Modified version of Embodiment 3] As a second process, the processor 11 may determine which paper has a high phosphor content based on the difference between the ratio of the reflectance Vr of light having a first wavelength to the reflectance IRr of light having a third wavelength, and the ratio of the reflectance UVr of light having a second wavelength to the reflectance IRr of light having a third wavelength.

[0189] Figure 20 is a diagram illustrating a second process in a modified example of Embodiment 3. Figure 20 shows experimental results obtained using the inspection unit 20 for various brands of recycled paper, coated paper, and plain paper. In the graph of Figure 20, the horizontal axis represents the transmittance IRt of light having a fourth wavelength, and the vertical axis represents the difference (ratio difference DR) between the ratio of the reflectance Vr of light having a first wavelength to the reflectance IRr of light having a third wavelength, and the ratio of the reflectance UVr of light having a second wavelength to the reflectance IRr of light having a third wavelength. The transmittance IRt is calculated using the above formula 6. The ratio difference DR is calculated using the above formula 10.

[0190] In the graph in Figure 20, the triangular marks indicate the ratio difference DR for recycled paper, the square marks indicate the ratio difference DR for coated paper, and the circular marks indicate the ratio difference DR for plain paper. As shown in Figure 20, for coated paper, the ratio difference DR is greater than or equal to the second threshold TH24.

[0191] As described above, the more phosphors a paper contains, the higher the apparent reflectance UVr of light having a second wavelength tends to be. Therefore, paper types in which the ratio difference DR is less than the second threshold TH24 can be determined to be paper types containing a lot of phosphors (in the modified example of Embodiment 3, the second type of recycled paper (recycled paper with a lot of phosphors) and plain paper with a lot of phosphors), and paper types in which the ratio difference DR is greater than or equal to the second threshold TH24 can be determined to be paper types with little phosphors (in the modified example of Embodiment 3, coated paper, the first type of recycled paper (recycled paper with little phosphors), and plain paper with little phosphors). The second threshold TH24 predetermined by experimentation is stored in storage 13 and is referenced in the second processing. The second threshold TH24 is an example of reference data 132.

[0192] In the second process, the processor 11 calculates the ratio difference DR using the method described above based on the amount of light acquired from the inspection unit 20, and determines whether the ratio difference DR is greater than or equal to the second threshold TH24. More specifically, the processor 11 acquires the second threshold TH24 corresponding to the transmittance IRt from the storage 13, and determines whether the ratio difference DR is greater than or equal to the second threshold TH24.

[0193] If the ratio difference DR is less than the second threshold TH24, the processor 11 determines that the paper type is either the second type of recycled paper (recycled paper with a high phosphor content) or plain paper with a high phosphor content, and further performs the third process to distinguish between the second type of recycled paper (recycled paper with a high phosphor content) and plain paper with a high phosphor content.

[0194] On the other hand, if the ratio difference DR is greater than or equal to the second threshold TH24, the processor 11 determines that the paper type is one of the first type of recycled paper (recycled paper with low phosphor content), coated paper, or plain paper with low phosphor content, and performs the first process further. If the paper type cannot be determined by the first process, that is, if the ratio Vr / IRr is greater than or equal to the first threshold TH11, the processor 11 performs a third process further to determine whether the paper type is coated paper or plain paper with low phosphor content.

[0195] Figure 21 is a flowchart showing the procedure for the determination process in a modified example of Embodiment 3. The determination process is performed by the processor 11. In the determination process shown in Figure 21, step S22B is performed instead of step S22A as the second process. Among the determination processes shown in Figure 21, the same steps as those shown in Figure 19 are given the same step numbers and the explanation is not repeated.

[0196] In step S22B, the processor 11 performs a second process. The second process determines whether the ratio difference DR is greater than or equal to the second threshold TH24, which corresponds to the transmittance IRt. Step S22B distinguishes between paper with a high phosphor content and paper with a low phosphor content.

[0197] If the ratio difference DR is greater than or equal to the second threshold TH24 corresponding to the transmittance IRt (YES in step S22B), the processor 11 proceeds to step S21. On the other hand, if the ratio difference DR is less than the second threshold TH24 corresponding to the transmittance IRt (NO in step S22B), the processor 11 proceeds to step S31A.

[0198] Thus, the paper type discrimination device 2 in the modified embodiment of Embodiment 3 distinguishes between a second type of recycled paper (recycled paper with a high phosphor content) and plain paper with a high phosphor content through the second and third processes. Furthermore, the paper type discrimination device 2 in Embodiment 3 distinguishes between a first type of recycled paper (recycled paper with a low phosphor content) through the second and first processes. In addition, the paper type discrimination device 2 in Embodiment 3 distinguishes between coated paper and plain paper with a low phosphor content through the second, first, and third processes. Therefore, recycled paper can be reliably identified.

[0199] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0200] 1 Image forming apparatus, 2 Paper type discrimination device, 10 Control unit, 11 Processor, 12 Memory, 13 Storage, 20 Inspection unit, 21 Light source unit, 21X First light source unit, 21Y Second light source unit, 22 Detection unit, 23X, 23Y Element substrate, 25 Paper feed guide, 26 Reflector, 27 Transport path, 28X, 28Y Opening, 30 Image forming unit, 31 Intermediate transfer belt, 32 Image forming unit, 33 Transfer roller, 40 Fixing unit, 50 Scanner, 60 Operation panel, 70 Communication unit, 81 Paper feed tray, 82 Transport roller, 83 Paper output tray, 90 Bus, 131 Program, 132 Reference data, 211X First light-emitting element, 212X Second light-emitting element, 213X Third light-emitting element, 214Y Fourth light-emitting element, 215Y Fifth light-emitting element, 220 Photodetector, Bt, IRt transmittance, DR ratio difference, IRr, UVr, Vr reflectance, Lr, Lt, Ly, sLr light intensity, Lr1, Lr2, Lr3, sLr1, sLr2, sLr3 reflected light, Lt4, Lt5 transmitted light, Lx1 first illumination light, Lx2 second illumination light, Lx3 third illumination light, Ly4 fourth illumination light, Ly5 fifth illumination light, M paper, TH11, TH12 first threshold, TH21, TH22, TH23, TH24 second threshold, TH31 third threshold.

Claims

1. A first light source unit that irradiates paper with light having a first wavelength and light having a second wavelength, A detection unit that detects light from the aforementioned paper and acquires a detected value based on that light, The system includes a control unit that uses the detected value to determine the type of paper, The first light source unit and the detection unit are located on the same side with respect to the paper. The detected value includes a first detected value based on the light from the paper when the paper is irradiated with light having the first wavelength, and a second detected value based on the light from the paper when the paper is irradiated with light having the second wavelength. The control unit is The first type of recycled paper is identified by the first processing using the first detected value. A second processing using the second detected value identifies a second type of recycled paper that is different from the first type of recycled paper. The peak wavelength of the light having the first wavelength is 390 nm or more and less than 550 nm. The light having the second wavelength is ultraviolet light, in the paper type identification device.

2. The second type of recycled paper contains more phosphors than the first type of recycled paper, The paper type discrimination device according to claim 1, wherein the second process includes distinguishing between coated paper and the second type of recycled paper using the second detected value.

3. The first light source unit further irradiates the paper with light having a third wavelength, The detected value further includes a third detected value based on light from the paper when the paper is irradiated with light having the third wavelength. The second process described above is: The reflectance is calculated based on the second detected value, The reflectance is calculated based on the third detected value, This includes distinguishing between coated paper and the second type of recycled paper based on the ratio of the reflectance calculated based on the second detection value to the reflectance calculated based on the third detection value, The paper type discrimination device according to claim 2, wherein the light having the third wavelength is infrared light.

4. The second type of recycled paper contains more phosphors than the first type of recycled paper, The paper type discrimination device according to claim 1, wherein the second process includes distinguishing between coated paper and the second type of recycled paper using the second detected value and the first detected value.

5. The first light source unit further irradiates the paper with light having a third wavelength, The detected value further includes a third detected value based on light from the paper when the paper is irradiated with light having the third wavelength. The second process described above is: The reflectance is calculated based on the first detected value, The reflectance is calculated based on the second detected value, The reflectance is calculated based on the third detected value, This includes distinguishing between coated paper and the second type of recycled paper based on the ratio of the reflectance calculated based on the first detection value to the reflectance calculated based on the third detection value, and the ratio of the reflectance calculated based on the second detection value to the reflectance calculated based on the third detection value. The paper type discrimination device according to claim 4, wherein the light having the third wavelength is infrared light.

6. The first type of recycled paper contains less phosphor than the second type of recycled paper, The paper type discrimination device according to claim 1, wherein the first process includes determining the first type of recycled paper using the first detected value.

7. The first light source unit further irradiates the paper with light having a third wavelength, The detected value further includes a third detected value based on light from the paper when the paper is irradiated with light having the third wavelength. The first process is, The reflectance is calculated based on the first detected value, The reflectance is calculated based on the third detected value, This includes determining the first type of recycled paper based on the ratio of the reflectance calculated based on the first detection value to the reflectance calculated based on the third detection value, The paper type discrimination device according to claim 6, wherein the light having the third wavelength is infrared light.

8. The peak wavelength of the light having the first wavelength is 390 nm or more and less than 440 nm. The paper type discrimination device according to any one of claims 1 to 7, wherein the peak wavelength of the light having the second wavelength is 340 nm or more and less than 390 nm.

9. The paper type discrimination device further comprises a second light source unit located on the side of the paper opposite to the side on which the detection unit is located. The second light source unit further irradiates the paper with light having a fourth wavelength and light having a fifth wavelength, The detected value further includes a fourth detected value based on the light from the paper when the paper is irradiated with light having the fourth wavelength, and a fifth detected value based on the light from the paper when the paper is irradiated with light having the fifth wavelength. The control unit further distinguishes plain paper by a third process using the fourth detected value and the fifth detected value, The paper type discrimination device according to claim 1, wherein the light having the fourth wavelength is infrared light, and the light having the fifth wavelength is blue light.

10. A method for identifying paper types, Shining light having a first wavelength and light having a second wavelength toward the paper, The process involves detecting light from the aforementioned paper and obtaining a detected value based on that light. The method includes deriving a determination result for the type of paper using the detected value, The position emitting light having the first wavelength, the position emitting light having the second wavelength, and the position detecting light from the paper are located on the same side with respect to the paper. The detected value includes a first detected value based on the light from the paper when the paper is irradiated with light having the first wavelength, and a second detected value based on the light from the paper when the paper is irradiated with light having the second wavelength. To derive the determination result for the type of paper mentioned above, The first type of recycled paper is determined by a first process using the first detected value, This includes determining a second type of recycled paper different from the first type of recycled paper by a second process using the second detected value, The peak wavelength of the light having the first wavelength is 390 nm or more and less than 550 nm. A method for identifying paper types, wherein the light having the second wavelength is ultraviolet light.

11. A paper type identification program that causes a computer to execute the paper type identification method described in claim 10.

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