Sheet discrimination apparatus and image forming apparatus

Abstract

To provide a sheet discrimination apparatus and an image forming apparatus that can accurately discriminate the characteristics of a sheet.SOLUTION: A sheet discrimination apparatus 2 comprises: a light emitting device for reflection 211 that causes a light receiving device 220 to receive light reflected on a sheet; a light emitting device for transmission 212 that causes the light receiving device 220 opposite thereto to receive light transmitted through the sheet; and a reflecting member 23 that is opposite to the light emitting device for reflection 211, and reflects light radiated by the light emitting device for reflection 211 when the sheet is not conveyed by a conveying member 24. The light emitting device for reflection 211 includes a first light emitting device for reflection 211a that radiates light with a first wavelength, and a second light emitting device for reflection 211b that radiates light with a second wavelength. The light emitting device for transmission 212 includes a first light emitting device 212a that is opposite to the light emitting device for reflection 211 and radiates light with a third wave length. The reflecting member 23 is provided so that the reflectance of light radiated by the light emitting device for reflection 211 becomes higher than the reflectance of light radiated by the light emitting device for transmission 212 and transmitted through the sheet.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a paper discrimination device and an image forming apparatus. [Background technology]

[0002] Conventionally, there is known a paper discrimination device that automatically discriminates the characteristics of conveyed paper, including the paper type, using a sensor. One known paper discrimination device automatically discriminates the characteristics of paper by using a sensor to receive reflected light or transmitted light irradiated onto the paper from a light source.

[0003] Among such paper discrimination devices, there is known one that is provided with a reflective member for calibrating the amount of light emitted from the light source, as shown in Patent Document 1. In the invention of Patent Document 1, the reflective member is provided to reduce the reflectance of the transmitted light in order to prevent ghost light from being generated when transmitted light hits the reflective member and causing erroneous discrimination of characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-030233 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not describe the reflectance of the reflective member. If the reflective member is provided to reduce the reflectance of the reflected light and the amount of reflected light received by the sensor is reduced, the sensor may be susceptible to electrical noise when calibrating the irradiation amount of the light source, which may reduce the accuracy of determining characteristics. In particular, when multiple reflection wavelengths are used, the transmitted wavelength and the reflected wavelength tend to be close to each other, making it difficult to increase the reflectance of the reflective member.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a paper type discrimination device and an image forming apparatus that can discriminate paper characteristics with high accuracy. [Means for solving the problem]

[0007] In order to solve the above problems, the invention described in claim 1 is: A paper discrimination device including a discrimination unit that discriminates characteristics of a paper sheet conveyed along a predetermined conveying member by receiving light emitted from a light-emitting element and received by a light-receiving element, the light-emitting element includes a reflective light-emitting element that causes the light-receiving element to receive light reflected by the paper, and a transmissive light-emitting element that causes the light-receiving element, which is provided at an opposing position, to receive light that has transmitted through the paper, a reflecting member that is provided at a position facing the reflecting light emitting element, and that reflects light emitted by the reflecting light emitting element when the paper is not being transported by the transport member, and causes the light to be incident on the light receiving element that is provided so as to face the reflecting member; the reflective light-emitting element includes a first reflective light-emitting element that irradiates light of a first wavelength and a second reflective light-emitting element that irradiates light of a second wavelength; the transmissive light emitting element includes a first transmissive light emitting element that is provided at a position facing the reflective light emitting element and that irradiates light of a third wavelength, The reflecting member is provided so that the reflectance of the light emitted by the reflective light emitting element is higher than the reflectance of the light emitted by the transmissive light emitting element and transmitted through the paper.

[0008] The invention described in claim 2 is the paper discrimination device described in claim 1, The first wavelength or the second wavelength is a wavelength in the range of 750 nm to 1100 nm.

[0009] The invention described in claim 3 is the paper discrimination device described in claim 1, the transmissive light emitting element includes a second transmissive light emitting element that irradiates light of a fourth wavelength, the reflective light-emitting element includes a third reflective light-emitting element that irradiates light of a fifth wavelength, The light from the first transmissive light emitting element, the third reflective light emitting element, the second transmissive light emitting element, and the second reflective light emitting element is irradiated in order from the light with the longest wavelength.

[0010] The invention described in claim 4 is the paper discrimination device described in claim 3, The discrimination unit discriminates whether the paper is plain paper, recycled paper, coated paper, or colored paper.

[0011] The invention described in claim 5 is the paper discrimination device described in claim 1, The reflecting member is provided so that the reflectance of light that is irradiated from the transmissive light emitting element onto the paper and scattered thereon is 20% or less.

[0012] The invention described in claim 6 is the paper discrimination device described in claim 1, The reflecting member has a reflectance of 0.07×(d0 / d) for light emitted from the reflecting light emitting element, where d0 is the distance between the light receiving element and the reflecting member, and d is the distance between the light receiving element and the sheet of paper that is the target of paper type discrimination processing. 2 It is set so that the above is true.

[0013] The invention described in claim 7 is the paper discrimination device described in claim 1, The reflecting member is provided on the outside of the transport member.

[0014] The invention described in claim 8 is the paper discrimination device described in claim 1, The reflecting member is provided above the reflective light-emitting element and the transport member in the up-down direction.

[0015] The invention described in claim 9 is the paper discrimination device described in claim 1, the conveying member has an opening in a range including a portion facing the light emitting element and the light receiving element, A transparent protective material having light-transmitting properties is provided so as to cover the opening.

[0016] The invention described in claim 10 is the paper discrimination device described in claim 9, The transparent protective material is provided so as to cover the opening on the light receiving element side and the opening on the reflecting member side.

[0017] The invention described in claim 11 is an image forming apparatus, The paper discrimination device according to any one of claims 1 to 10; and an image forming unit that forms an image on the paper. [Effects of the Invention]

[0018] According to the present invention, the characteristics of paper can be determined with high accuracy. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a schematic cross-sectional side view of the image forming apparatus. [Figure 2] FIG. 1 is a block diagram of an image forming apparatus. [Figure 3] FIG. 2 is a schematic diagram of a paper inspection unit according to the first embodiment. [Figure 4] 6 is a flowchart of a paper type determination process performed by a paper inspection unit according to the first embodiment. [Figure 5] 10A and 10B are diagrams for explaining one aspect of discrimination of recording materials using wavelength dependency of optical characteristics of first to third wavelengths. [Figure 6] FIG. 10 is a schematic diagram of a paper inspection unit according to a second embodiment. [Figure 7] 6 is a flowchart of a paper type determination process performed by a paper inspection unit according to the first embodiment. [Figure 8A] 10A and 10B are diagrams for explaining one aspect of discrimination of recording materials using wavelength dependency of optical characteristics of first, third, and fifth wavelengths. [Figure 8B] 10A and 10B are diagrams for explaining one aspect of discrimination of recording materials using wavelength dependency of optical characteristics of first to third wavelengths. [Figure 8C]10A and 10B are diagrams for explaining one aspect of discrimination of recording materials using the wavelength dependency of optical characteristics of third and fifth wavelengths. [Figure 9A] 1 is a graph showing the relationship between the reflectance of light transmitted through a reflector and the signal-to-noise ratio of the transmitted light. [Figure 9B] 1 is a graph showing the relationship between the reflectance of light transmitted through a reflector and the signal-to-noise ratio of the transmitted light. [Figure 10A] FIG. 10 is a schematic diagram of a paper inspection unit according to a modified example. [Figure 10B] FIG. 10 is a schematic diagram of a paper inspection unit according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, a paper type discrimination device according to an embodiment of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to the illustrated examples. In the following description, components having the same functions and configurations will be given the same reference numerals, and their description may be omitted.

[0021] [Overall configuration of image forming device] 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention, and FIG.

[0022] The image forming apparatus 1 is an MFP (Multifunction Peripheral) that forms an image on paper using an electrophotographic method. The image forming apparatus 1 includes a control unit 10, a paper inspection unit 20, an image forming unit 30, a fixing unit 40, a scanner 50, an operation display unit 60, a communication unit 70, a paper feed tray 81, a transport roller 82, a paper discharge tray 83, and a bus 90.

[0023] 2, a paper discrimination device 2 that discriminates the type of paper is configured by the control unit 10 and the paper inspection section 20. Furthermore, the various sections of the image forming apparatus 1 are connected by a bus 90.

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

[0025] {CPU} The CPU 11 reads and executes a program stored in a program storage area of the storage unit 13 (or a program stored in a storage device outside the image forming apparatus 1), and performs various arithmetic processing.

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

[0027] {Storage section} The storage unit 13 is configured with a non-volatile storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or a flash memory. The storage unit 13 includes a program storage area and a data storage area. The program storage area stores data for various programs. The data storage area stores, for example, image data acquired by the scanner 50, image data input from the outside via the communication unit 70, and / or reference data referenced in the paper type discrimination operation described below.

[0028] The control unit 10 controls each unit of the image forming apparatus 1 by causing the CPU 11 to execute a program. For example, the control unit 10 operates each unit of the image forming unit 30 (particularly the transport roller 82 and the fixing unit 40) based on image data stored in the storage unit 13 to form an image on a sheet. Here, the CPU 11 changes the image formation-related operations of each unit of the image forming apparatus 1 according to the paper type discrimination result by the paper discrimination device 2. For example, the CPU 11 changes the transport speed and clamping pressure of the transport roller 82 according to the type of paper. The CPU 11 also changes the heating temperature and applied pressure of the fixing unit 40 according to the type of paper.

[0029] In addition, the control unit 10 may include a dedicated circuit (such as an ASIC (application specific integrated circuit) or FPGA (field-programmable gate array)) for realizing each function instead of or in addition to the CPU 11.

[0030] (Paper Inspection Department) The paper inspection unit 20 performs a process of determining the paper type of the paper. The paper inspection unit 20 is provided at a position along the paper transport path from the paper feed tray 81 to the paper output tray 83, upstream of the image forming unit 30. However, the position of the paper inspection unit 20 is not limited to this, and the paper inspection unit 20 can be placed at any position along the transport path.

[0031] The detailed configuration of the paper inspection unit 20 (paper discrimination device 2) will be described later.

[0032] (Image forming section) The image forming unit 30 forms an image by applying toner (color material) to paper supplied from the paper feed tray 81. 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 belt-shaped member that is stretched around a plurality of rollers and moves in a circular motion.

[0033] {Image forming unit} The image forming units 32 are arranged along the intermediate transfer belt 31, and form toner images of the colors C (cyan), M (magenta), Y (yellow), and K (black) on the intermediate transfer belt 31 based on image data relating to the image to be printed. When a sheet of paper passes through the nip between the intermediate transfer belt 31 and the transfer roller 33, the toner images are transferred to the sheet of paper to form an image. Note that, although the image forming unit 30 capable of forming a color image has been exemplified in this embodiment, the present invention is not limited to this, and an image forming unit 30 capable of forming a monochrome image may also be used.

[0034] (fixing part) The fixing unit 40 applies heat and pressure to the paper onto which the toner image has been transferred, fixing the toner image to the paper. The fixing unit 40 includes a pair of rollers consisting of a heating roller and a pressure roller that sandwich the paper. The paper with the fixed toner image is transported by transport rollers 82 and sent to a paper output tray 83. The heating and pressure conditions used by the fixing unit 40 are controlled by the control unit 10 according to the type of paper, etc.

[0035] (scanner) The scanner 50 includes an optical system such as a light source and a reflecting mirror, and an imaging element, and reads an image of a sheet of paper being transported along a predetermined transport path or a sheet of paper placed on a platen glass, and generates image data in bitmap format for each of the colors R (red), G (green), and B (blue). The generated image data is stored in the storage unit 13. The scanned image can also be copied onto another sheet of paper by performing image formation by the image forming unit 30 based on this image data.

[0036] (Operation display) The operation display unit 60 includes a display device such as a liquid crystal display, a touch panel overlaid on the screen of the display device, and an input device such as operation keys. The operation display unit 60 displays various information such as the operation status and processing results of the image forming apparatus 1 on the display device, and converts user input operations on the input device into operation signals and outputs them to the control unit 10.

[0037] (Communications Department) The communication unit 70 is configured by a network card or the like. The communication unit 70 is connected to a communication network such as a LAN (Local Area Network) and transmits and receives information to and from external devices on the communication network. The control unit 10 communicates with the external devices on the communication network via the communication unit 70.

[0038] (Paper feed tray) Paper sheets before image formation are stored in the paper feed tray 81. The paper feed tray 81 may store a plurality of types of paper sheets.

[0039] The type of paper is characterized by at least one of the following characteristics: paper material (raw material), surface treatment state, presence and amount of fluorescent whitening agent, presence and color of bluing. Therefore, papers that differ from each other in at least one of these characteristics are different types of paper. Types of paper that can be stored in paper feed tray 81 include, for example, plain paper, colored paper, recycled paper, and coated paper. However, the types of paper that can be stored in paper feed tray 81 are not limited to those mentioned above.

[0040] Plain paper is paper made primarily from wood-based pulp (i.e., pulp that is not recycled from waste paper, usually chemical pulp).

[0041] Colored paper is paper to which a certain percentage or more of dye has been added.

[0042] Recycled paper is paper that contains a specified or higher blending ratio of recycled paper pulp extracted from recycled paper.

[0043] Coated paper is a type of high-quality printing paper that has a coating of 20 to 40 g / m², which is a mixture of white pigments such as kaolin or calcium carbonate and adhesives such as starch. 2 It is a moderately coated paper.

[0044] (Transport roller) The transport rollers 82 rotate while holding a sheet of paper, thereby transporting the sheet along the transport path. The transport timing and transport speed of the transport rollers 82 are controlled by the control unit 10 according to the type of paper, etc.

[0045] (Output tray) The paper discharge tray 83 holds the paper on which the image has been formed until the user removes it.

[0046] [Paper inspection unit configuration] [First embodiment] Next, a detailed configuration of the paper inspection unit 20 according to the first embodiment will be described with reference to Fig. 3. The paper inspection unit 20 includes a light emitting element 21, a sensor 22, a reflecting member 23, and a transport member 24.

[0047] (light-emitting element) The light emitting element 21 emits inspection light of a predetermined wavelength. The light emitting element 21 is, for example, an LED (Light Emitting Diode). The light emitting element 21 includes a reflective light emitting element 211 that causes the sensor 22 to receive light reflected by the paper during the paper type determination process described below. The light emitting element 21 also includes a transmissive light emitting element 212 that causes the sensor 22 to receive light transmitted through the paper.

[0048] 3, the reflective light emitting element 211 is provided on the sensor 22 side. The transmissive light emitting element 212 is provided on the same side as the reflecting member 23. The reflective light emitting element 211 and the sensor 22, and the transmissive light emitting element 212 and the reflecting member 23 are provided at positions facing each other.

[0049] 3, in this embodiment, a first reflective light-emitting element 211a and a second reflective light-emitting element 211b are provided as the reflective light-emitting element 211. In addition, a first transmissive light-emitting element 212a is provided as the transmissive light-emitting element 212.

[0050] {First Reflective Light-Emitting Element} The first reflective light emitting element 211a emits a first inspection light having a first wavelength. In this embodiment, the first wavelength has a peak wavelength of 750 nm or more and 1100 nm or less. That is, the first inspection light is infrared light.

[0051] The reason for selecting wavelengths of 750 nm or more is to suppress the effects of paper bluing. Bluing is the process of adding a blue dye to paper to improve the whiteness of the paper. Bluing paper absorbs visible light of wavelengths outside the blue region, reducing the reflectance of that visible light compared to paper that is not bluing. Therefore, wavelengths of 750 nm or more that are not affected by this bluing are selected.

[0052] The reason for selecting wavelengths below 1100 nm is to suppress the effects of moisture contained in paper. The spectrum of light reflected by paper at wavelengths longer than 1100 nm changes depending on the moisture content of the paper. More specifically, moisture has a unique absorption band at 1450 nm and 1940 nm in the near-infrared region, which originates from the combined vibrations of the stretching and bending vibrations of hydrogen and oxygen atoms, reducing reflectance. For this reason, wavelengths below 1100 nm, which are not affected by the moisture content of paper, are selected.

[0053] In this way, light of the first wavelength, which is a near-infrared wavelength and is less likely to cause fluctuations in reflected light due to the material and raw material of the paper, is used as the first inspection light.

[0054] {Second Reflective Light-Emitting Element} The second reflection-emitting element 211b emits second inspection light of a second wavelength. In this embodiment, the second wavelength has a peak wavelength of 390 nm or more and 440 nm or less. That is, the second inspection light is violet light.

[0055] The wavelength of 390 nm or more and 440 nm or less is selected because it is a wavelength that is less absorbed by the fluorescent material and more absorbed by waste paper pulp, making it possible to distinguish recycled paper containing waste paper pulp by irradiating the second inspection light.

[0056] {First transmissive light-emitting element} In this embodiment, the first transmissive light-emitting element 212a emits third inspection light of a third wavelength. In this embodiment, the third wavelength is 750 nm or more and 1100 nm or less. That is, the third inspection light is infrared light. The reason for selecting the wavelength of 750 nm or more and 1100 nm or less is the same as that for the first reflective light-emitting element 211a.

[0057] The first inspection light and the second inspection light are reflected from the front surface of the paper and enter the sensor 22. The third inspection light is transmitted through the back surface of the paper and enters the sensor 22.

[0058] (sensor) The sensor 22 receives the light emitted by the light-emitting element 21. The sensor 22 includes one light-receiving element 220. The light-receiving element 220 outputs a photocurrent corresponding to the amount of incident light. The sensor 22 converts the photocurrent into a voltage and then into digital data, which are then output to the control unit 10.

[0059] It is preferable that the sensors 22 be provided at positions so that the distances from the respective reflective light emitting elements 211 are equal, but this is not limitative.

[0060] (reflective material) The reflecting member 23 is a plate-like member provided to reflect the inspection light emitted by the light-emitting element 21 and make it incident on the light-receiving element 220 when calibrating the light-emitting element 21 when no paper is passing through.

[0061] The reflecting member 23 is provided so that the reflectance of the third inspection light is lower than the reflectance of the first and second inspection lights. As will be described later, the third inspection light passes through the paper and is received by the sensor 22 during the paper type discrimination process. However, if the reflectance of the first transmitted light by the reflecting member 23 is high, a portion of the first transmitted light reflected by the paper will be reflected by the reflecting member 23 and then received by the sensor 22. This so-called ghost light reduces the accuracy of paper type discrimination.

[0062] Therefore, if the reflectance of the reflective member 23 is set to be low for the third wavelength, the occurrence of ghost light itself can be suppressed, and the accuracy of paper identification can be further improved. The reflectance of the inspection light from the reflective member 23 can be adjusted by, for example, adjusting the color of the reflective member 23.

[0063] As shown in FIG. 3, when the distance between the light receiving surface of the light receiving element 220 and the reflecting member 23 is d0 and the distance between the light receiving surface of the light receiving element 220 and the paper that is the target of the paper type discrimination process described later is d, the reflectance of the first and second inspection lights is 0.07×(d0 / d) 2 By adopting this configuration, it is possible to suppress a decrease in the accuracy of determining the paper type.

[0064] The configuration of the reflecting member 23 will be described in detail later.

[0065] (Transportation member) The transport member 24 is a member that constitutes a transport path along which the paper is transported to be subjected to the paper type determination process by the paper inspection unit 20. The transport member 24 includes an optical diaphragm 241 and a paper passage guide 242.

[0066] The optical diaphragm 241 is a plate-like member that is arranged on the side of the sensor 22 and the reflective light-emitting element 211 so that its main surface is perpendicular to the up-down direction. The optical diaphragm 241 has an opening H in a range that includes the portion facing the light-emitting element 21 and the sensor 22. The inspection light emitted by the light-emitting element 21 is incident on the paper through the opening H. The optical diaphragm 241 has light-blocking properties in the portions other than the opening H, and prevents light other than the inspection light from entering the paper.

[0067] The paper passing guide 242 is a plate-like member that is arranged on the side of the reflecting member 23 and the transmissive light emitting element 212 so as to support the paper as it moves along the conveying member 24. Similar to the optical diaphragm 241, the paper passing guide 242 has an opening H in a range that includes the portions facing the light emitting element 21 and the sensor 22.

[0068] As shown in FIG. 3, the reflecting member 23 is provided outside (below) the paper passing guide 242. If paper dust adheres to the reflecting member 23, the reflection characteristics of the reflecting member 23 change. This may result in an incorrect light intensity being calibrated when the light-emitting element 21 is calibrated, which may reduce the accuracy of the paper type discrimination process described below. On the other hand, as shown in FIG. 3, providing the reflecting member 23 outside the conveying member 24 can prevent paper dust from adhering to the reflecting member 23. Furthermore, with this configuration, the occurrence of ghost light, described below, can be reduced compared to when the reflecting member 23 is provided inside the conveying member 24.

[0069] [Paper type detection process] As described above, the light receiving element 220 of the sensor 22 receives the inspection light emitted by each light emitting element 21, which is reflected by the paper being transported on the transport member 24. At this time, the amount of reflected light received by the light emitting element 213 increases or decreases according to the absorption characteristics of light of each wavelength according to the paper type. Therefore, the control unit 10 can determine the characteristics of the paper, including its paper type, from the reflection amount of the inspection light of each wavelength.

[0070] The paper type discrimination process performed by the paper inspection unit 20 according to the first embodiment will be described in detail with reference to the flowchart in Fig. 4. In this embodiment, the paper is discriminated as being either plain paper or recycled paper. First, the control unit 10 causes each light-emitting element 21 to emit inspection light, thereby calibrating the light intensity of each light-emitting element 21 (step S101).

[0071] Specifically, before the paper passes through the conveying member 24, the control unit 10 causes the first reflective light-emitting element 211a and the second reflective light-emitting element 211b to emit inspection light, which is reflected by the reflecting member 23 and made incident on the light-receiving element 220. The control unit 10 also causes the first transmissive light-emitting element 212a to emit inspection light and make it incident on the light-receiving element 220. The sensor 22 converts each incident inspection light into a voltage and outputs it to the control unit 10. The control unit 10 determines whether the voltage value of each light-emitting element 21 is within a predetermined range, and calibrates the light intensity of any light-emitting element 21 that is outside the predetermined range.

[0072] The control unit 10 stores the voltage values generated at the sensor 22 by the light-emitting elements 21 after the calibration as first to third reference voltages, respectively (step S102).

[0073] Next, the control unit 10 causes each light emitting element 21 to sequentially irradiate various types of inspection light onto the paper being conveyed through the gap between the optical diaphragm 241 and the paper passing guide 242 .

[0074] The first and second inspection lights are reflected by the paper, generating first and second reflected lights, which enter the light receiving element 220. The third inspection light passes through the paper, generating first transmitted light, which enters the light receiving element 220. The sensor 22 converts the incident reflected and transmitted lights into voltages (hereinafter referred to as first to third discrimination voltages) and outputs them to the control unit 10. As described above, the amount of reflected and transmitted light is affected by the paper's absorption characteristics of the inspection light at each wavelength.

[0075] The control unit 10 acquires the reflectance and transmittance of each test light (hereinafter referred to as the first and second reflectances and the first transmittance) using (the first to third discrimination voltages / the first to third reference voltages) (step S103). Then, the control unit 10 distinguishes the paper type from plain paper or recycled paper based on the acquired first and second reflectances and first transmittance (step S104).

[0076] Fig. 5 is a diagram for explaining the determination method. In the graph shown in Fig. 5, the horizontal axis represents the first transmittance, and the vertical axis represents the ratio between the first reflectance and the second reflectance.

[0077] In this way, by using the ratio of reflectance at different wavelengths, it is possible to suppress the effects of changes over time in the light receiving element 220 and changes in the position of the paper. Furthermore, since the amount of change in the amount of received light due to changes in the position of the paper is smaller in transmittance than in reflectance, it is possible to more accurately determine the characteristics of the paper, including its type.

[0078] The graph in FIG. 5 shows values for recycled paper (triangular spots) and plain paper (circular spots). Line L1 shown in FIG. 5 is a line set to distinguish between plain paper and recycled paper. Information specifying line L1 is stored as reference data in memory unit 13. Control unit 10 determines whether a sheet of paper is plain paper or recycled paper depending on whether the coordinates of the sheet of paper are located above line L1 in the graph in FIG. 5. In this way, in the paper discrimination process, control unit 10 functions as a discrimination unit that discriminates characteristics of the sheet of paper, including its type.

[0079] [Second embodiment] Next, a paper inspection unit 20 according to a second embodiment will be described with reference to FIG. 6. Note that the same components as those in the first embodiment are assigned the same reference numerals, and detailed description thereof will be omitted. The paper inspection unit 20 of the second embodiment differs from the first embodiment in that it includes a third reflective light-emitting element 211c and a second transmissive light-emitting element 212b. The paper inspection unit 20 of the second embodiment also differs from the first embodiment in that it distinguishes the paper type from plain paper, recycled paper, coated paper, and colored paper.

[0080] {Second transmissive light-emitting element} The second transmissive light emitting element 212b irradiates a fourth inspection light having a fourth wavelength. In this embodiment, the fourth wavelength has a peak wavelength of 430 nm or more and 490 nm or less. That is, the fourth inspection light is blue light.

[0081] The second transmissive light emitting element 212b is provided on the reflective member 23 side, similar to the first transmissive light emitting element 212a. That is, the sensor 22 receives second transmitted light that is generated by light irradiated from the second transmissive light emitting element 212b and transmitted through the paper. Similar to the first transmissive light emitting element 212a, the second transmissive light emitting element 212b calibrates the light amount by irradiating the sensor 22 with inspection light when the transport member 24 is not transporting the paper.

[0082] {Third Reflective Light-Emitting Element} The third reflection-emitting element 211c emits a fifth inspection light having a fifth wavelength. In this embodiment, the fifth wavelength has a peak wavelength of 620 nm or more and 750 nm or less. That is, the fifth inspection light is red light.

[0083] The third reflection light-emitting element 211c is provided on the sensor 22 side, similar to the other reflection light-emitting elements 211. That is, the sensor 22 receives third reflected light that is emitted from the third reflection light-emitting element 211c and reflected by the paper. Similar to the first reflection light-emitting element 211a and the second reflection light-emitting element 211b, the third reflection light-emitting element 211c calibrates the light intensity by irradiating the reflection member 23 with inspection light when the transport member 24 is not transporting paper.

[0084] [Paper type detection process] The paper discrimination process by the paper inspection unit 20 according to the second embodiment will be described with reference to Fig. 7. Note that steps S201 to S203 are the same as steps S101 to S103, except that the third reflective light-emitting element 211c and the second transmissive light-emitting element 212b calibrate their light intensities before acquiring the third reflectance and second transmittance. Therefore, detailed description thereof will be omitted.

[0085] The control unit 10 determines whether the paper is colored paper or non-colored paper (recycled paper, plain paper, or coated paper) (step S204). FIG. 8A is a diagram for explaining this determination method. In the graph shown in FIG. 8A, the horizontal axis represents the first transmittance, and the vertical axis represents the ratio between the first reflectance and the third reflectance. The graph in FIG. 8A also shows values for non-colored paper (circular spots) and colored paper (triangular spots). The control unit 10 determines whether the paper is colored paper based on the first and third reflectances and the first transmittance.

[0086] If it is determined that the paper is colored paper (step S204; Yes), the control unit 10 ends the paper type determination process. If it is determined that the paper is other than colored paper (step S204; No), the control unit 10 determines whether the paper is recycled paper or other than recycled paper (plain paper or coated paper) (step S205). FIG. 8B is a diagram for explaining this determination method. As in step S104, the control unit 10 determines whether the paper is recycled paper or not based on the first and second reflectivities and the first transmittance.

[0087] If the control unit 10 determines that the paper is recycled paper (step S205; Yes), the control unit 10 ends the paper type discrimination process. If the control unit 10 determines that the paper is not recycled paper (step S205; No), the control unit 10 determines whether the paper is plain paper or coated paper (step S206). FIG. 8C is a diagram for explaining this discrimination method. In the graph shown in FIG. 8C, the horizontal axis represents the first transmittance and the vertical axis represents the second transmittance. The graph in FIG. 8C also shows the values for plain paper (circular spots) and coated paper (square spots). The control unit 10 determines whether the paper is plain paper or coated paper based on the first and second transmittances. When the control unit 10 determines whether the paper is plain paper or coated paper, it ends the paper type discrimination process.

[0088] In the paper type discrimination process according to the second embodiment, if the reflectance of the first and second transmitted light by the reflecting member 23 is high, ghost light will be generated by the first and second transmitted light, reducing the accuracy of paper discrimination. Therefore, it is preferable that the reflecting member 23 be provided so that the reflectance of light of the third and fourth wavelengths is low. More specifically, it is preferable that the reflecting member 23 be provided so that the reflectance of light emitted by the reflective light-emitting element 211 is higher than the reflectance of light emitted by the transmissive light-emitting element 212. This configuration can suppress the generation of ghost light itself, further improving the accuracy of paper discrimination.

[0089] [Detailed structure of reflective material] The relationship between the reflectance of the reflective member 23 and the transmitted light will be described with reference to Figures 9A and 9B. Figures 9A and 9B are graphs showing the relationship between the reflectance of the transmitted light of the reflective member 23 and the ratio of the voltage value of the transmitted light (signal) to the voltage value of the ghost light (noise) of the transmitted light, which corresponds to the reflectance.

[0090] 9A and 9B, the horizontal axis represents the reflectance of transmitted light of the reflective member 23. In FIG. 9A, the vertical axis represents the ratio of transmitted light to ghost light. In FIG. 9B, the vertical axis represents the logarithm of the ratio of transmitted light to ghost light. In addition, in FIGS. 9A and 9B, multiple lines represent transmitted light with different arrangements of the light-emitting element 21, which is the light source. Specifically, level 1 is an arrangement in which the reflective member 23 is most likely to reflect ghost light. In addition, level 3 is an arrangement in which the reflective member 23 is least likely to reflect ghost light.

[0091] 9A and 9B, it can be seen that the signal-to-noise ratio increases sharply, that is, the occurrence of ghost light is suppressed, by setting the reflectance of the reflecting member 23 to 0.2 (20%) or less. Therefore, it is preferable that the reflecting member 23 is provided so that the reflectance of the first transmitted light and the second transmitted light is 20% or less.

[0092] Furthermore, in the paper type discrimination process described above, the reflectance value detected by sensor 22 exceeds 1. As described above, the reflectance is calculated from the ratio of the discrimination voltages of the first, second, and fifth test lights to the reference voltage. That is, the amount of light received by sensor 22 when paper is passing through is greater than the amount of light received by sensor 22 when paper is not passing through.

[0093] If the calibration of the light-emitting element 21 is insufficient, the amount of light received by the sensor 22 when no paper is passing will be low. Therefore, if the reflectance value detected by the sensor 22 is high, the accuracy of paper discrimination will be low. Specifically, the reflectance value detected by the sensor 22 is preferably 10 or less.

[0094] As shown in Figure 3, the distance between the light receiving surface of the light receiving element 220 and the reflecting member 23 is d0, and the distance between the light receiving surface of the light receiving element 220 and the paper that is the target of the paper type discrimination process is d. Also, the reflectance of the reflecting member 23 is R, and the reflectance of the paper is r. Then, the reflectance detected by the sensor 22 is (d0 / d) 2 ×r / R.

[0095] The reflectance r of paper is at least about 70%, so if r = 0.7, then (d0 / d) 2 × 0.7 / R≦10. Solving this equation for R gives (d0 / d) 2 × 0.07≦R. From the above, the reflectance of the inspection light irradiated by the reflective light emitting element 211 is (d0 / d) 2 It is preferable to provide the reflective member 23 so that the reflectance of the inspection light irradiated by the reflective light emitting element 211 is (d0 / d)×0.07 or more. 2 It is more preferable to provide the reflecting member 23 so that the ratio is 0.1 or more. By adopting this configuration, the calibration accuracy of the reflective light emitting element 211 can be improved, and the characteristics of the paper can be determined with high accuracy.

[0096] [Effects of the embodiment] As described above, in the paper discrimination device 2, the reflective member 23 is provided so that the reflectance of the light emitted by the reflective light emitting element 211 is higher than that of the light emitted by the transmissive light emitting element 212. This configuration can suppress the generation of ghost light due to the inspection light emitted by the transmissive light emitting element 212, and can discriminate paper characteristics with high accuracy.

[0097] Furthermore, the first wavelength or the second wavelength is a wavelength within the range of 750 nm to 1100 nm. With this configuration, fluctuations in reflected light due to the material and raw material of the paper are less likely to occur, and the characteristics of the paper can be determined with high accuracy.

[0098] Furthermore, the light emitted by the light emitting element 21 has a first wavelength used as a reference for other reflected wavelengths, as well as a third wavelength, a fifth wavelength, a fourth wavelength, and a second wavelength, in order from longest to longest. In other words, the order is transmission, reflection, transmission, reflection. With this configuration, the paper type can be identified from plain paper, coated paper, recycled paper, and colored paper.

[0099] Furthermore, the reflecting member 23 is provided so that the reflectance of transmitted light is 20% or less. This configuration makes it possible to suppress the occurrence of ghost light and to determine the characteristics of the paper with high accuracy.

[0100] Furthermore, the reflecting member 23 is provided outside the conveying member 24. This configuration makes it difficult for paper dust generated from the paper to adhere to the reflecting member 23, and also suppresses the occurrence of ghost light. Therefore, it is possible to suppress a decrease in the calibration accuracy of the reflective light emitting element 211, and it is possible to determine the characteristics of the paper with high accuracy.

[0101] [Other configurations] Although the present invention has been specifically described above based on the embodiments thereof, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention as defined in the claims and their equivalents.

[0102] 3 and 6, a configuration in which the light-emitting element 21 that generates reflected light is provided above and the reflecting member 23 is provided below is illustrated, but this is not limiting. For example, as shown in FIG. 10A, the reflective light-emitting element 211 and the sensor 22 may be provided below and the transmissive light-emitting element 212 and the reflecting member 23 may be provided above. With this configuration, gravity makes it difficult for paper dust from paper to adhere to the reflecting member 23. Therefore, the effect of paper dust adhering to the reflecting member 23 can be reduced.

[0103] 10B, a transparent protective material W may be provided to cover the opening H, separating the conveying member 24 and the reflecting member 23. The transparent protective material W is a transparent plate-like body that transmits light emitted by the light-emitting element 21. With this configuration, the transparent protective material W can prevent paper dust from adhering to the reflecting member 23. Furthermore, as shown in FIG. 10B, when the transparent protective material W and the conveying member 24 are close to each other, paper dust can be blown away when the paper is conveyed.

[0104] 10B illustrates a configuration in which the transparent protective material W is provided so as to cover both the upper opening H and the lower opening H of the conveying member 24, but the present invention is not limited to this. For example, the transparent protective material W may be provided only on the upper opening H of the conveying member 24. In this configuration, it is possible to prevent paper dust from adhering to the sensor 22.

[0105] Furthermore, although it has been described above that paper dust adheres to the reflecting member 23, paper dust can also adhere to other parts of the sheet, and the inspection light reflected by the paper dust adhered to parts other than the reflecting member 23 may enter the sensor 22, reducing the accuracy of paper type determination. For this reason, the conveying member 24 and the transparent protective material W may also be adjusted to have substantially the same reflective characteristics as the reflecting member 23. With this configuration, the paper type can be determined with higher accuracy.

[0106] Furthermore, in the above example, the paper inspection unit 20 is provided with three or five light emitting elements 21, but it goes without saying that the number may be four or six or more. [Explanation of symbols]

[0107] 1. Image forming device 10 Control unit (discrimination unit) 2 Paper type discrimination device 20 Paper Inspection Department 21 Light-emitting element 211 Reflective light emitting element 211a First reflective light-emitting element 211b Second reflective light-emitting element 212 Transmissive light emitting element 212a First transmissive light-emitting element 212b Second transmissive light-emitting element 220 Photodetector 23 Reflective material 24 Transport member 30 Image forming unit W Transparent protective material H opening

Claims

1. A paper discrimination device including a discrimination unit that discriminates characteristics of a paper sheet conveyed along a predetermined conveying member by receiving light emitted from a light-emitting element and received by a light-receiving element, the light-emitting element includes a reflective light-emitting element that causes the light-receiving element to receive light reflected by the paper, and a transmissive light-emitting element that causes the light-receiving element, which is provided at an opposing position, to receive light that has transmitted through the paper, a reflecting member that is provided at a position facing the reflective light emitting element, and that reflects light emitted by the reflective light emitting element when the paper is not being transported on the transport member, and causes the light to be incident on the light receiving element that is provided so as to face the reflecting member; the reflective light-emitting element includes a first reflective light-emitting element that irradiates light of a first wavelength and a second reflective light-emitting element that irradiates light of a second wavelength; the transmissive light emitting element includes a first transmissive light emitting element that is provided at a position facing the reflective light emitting element and that irradiates light of a third wavelength, The reflecting member is provided so that the reflectance of the light emitted by the reflective light emitting element is higher than the reflectance of the light emitted by the transmissive light emitting element and transmitted through the paper.

2. 2. The paper type discrimination device according to claim 1, wherein the first wavelength or the second wavelength is within a range of 750 nm to 1100 nm.

3. the transmissive light emitting element includes a second transmissive light emitting element that irradiates light of a fourth wavelength, the reflective light-emitting element includes a third reflective light-emitting element that irradiates light of a fifth wavelength, 2. The paper discrimination device according to claim 1, wherein the first transmissive light emitting element, the third reflective light emitting element, the second transmissive light emitting element, and the second reflective light emitting element are irradiated with light in order from longest wavelength to longest wavelength.

4. 4. The paper discrimination device according to claim 3, wherein the discrimination unit discriminates whether the paper is plain paper, recycled paper, coated paper, or colored paper.

5. 2. The paper discrimination device according to claim 1, wherein the reflecting member is provided so that the reflectance of light irradiated from the transmissive light emitting element onto the paper and scattered thereon is 20% or less.

6. The reflecting member is configured such that the distance between the light receiving element and the reflecting member is d ０ When the distance between the light receiving element and the paper to be subjected to the paper type discrimination process is d, the reflectance of the light irradiated from the light emitting element for reflection is 0.07 × (d ０ / d) ２ 2. The paper discrimination device according to claim 1, wherein the paper discrimination device is provided so as to satisfy the above.

7. 2. The paper discrimination device according to claim 1, wherein the reflecting member is provided outside the conveying member.

8. 8. The paper discrimination device according to claim 7, wherein the reflecting member is provided above the reflective light emitting element and the conveying member in the vertical direction.

9. the conveying member has an opening in a range including a portion facing the light emitting element and the light receiving element, 2. The paper discrimination device according to claim 1, further comprising a transparent protective material having light-transmitting properties so as to cover the opening.

10. The paper discrimination device according to claim 9 , further comprising the transparent protective material so as to cover the opening on the light receiving element side and the opening on the reflecting member side.

11. The paper discrimination device according to any one of claims 1 to 10, an image forming unit that forms an image on the paper.

Images