Paper type discrimination device, image forming device, paper type discrimination method, and program

Abstract

To provide a technique to improve the accuracy of discriminating a sheet.SOLUTION: In an image forming apparatus 1, a control unit 10 derives a result of determination of the type of a sheet. More specifically, the control unit 10 derives the result of determination of the type of the sheet by using a first detection value based on absorption of light with a first wavelength on the sheet and a second detection value based on absorption of light with a second wavelength on the sheet. The first wavelength is a wavelength within a range of 750 nm to 1100 nm. The second wavelength is a wavelength within a range of 400 nm to 500 nm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to discrimination of paper used in an image forming apparatus. [Background technology]

[0002] Various studies have been conducted on the discrimination of paper used in image forming devices such as MFPs (Multi-Functional Peripherals) (Patent Documents 1 to 7). In particular, Patent Documents 4 to 7 disclose techniques for deriving the basis weight of a recording material by using the amount of transmitted light of two different wavelengths of light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-167082 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-315856 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-016166 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-107269 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-145760 [Patent Document 6] Japanese Patent Application Laid-Open No. 2015-221509 [Patent Document 7] Japanese Patent Publication No. 2020-064003 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for a technique to improve the accuracy of the above-described paper type discrimination. The present disclosure has been devised in view of the above circumstances, and its purpose is to provide a technique for improving the accuracy of paper type discrimination. [Means for solving the problem]

[0005] According to one aspect of the present disclosure, there is provided a paper discrimination device including: a light source unit that irradiates light of two or more wavelengths toward paper; and a detection unit that obtains detection results based on the absorption of each of the light of the two or more wavelengths by the paper, wherein the light of the two or more wavelengths includes light having a first wavelength and light having a second wavelength, and the detection results include a first detection value based on the absorption of light of the first wavelength by the paper and a second detection value based on the absorption of light of the second wavelength by the paper, and the paper discrimination device further includes a control unit that derives a paper type determination result using the first detection value and the second detection value, wherein the first wavelength is a wavelength within a range of 750 nm to 1100 nm, and the second wavelength is a wavelength within a range of 400 nm to 500 nm.

[0006] Preferably, the first detection value includes an amount of light of the first wavelength transmitted through the paper, and the second detection value includes an amount of light of the second wavelength transmitted through the paper.

[0007] Preferably, using the first detection value and the second detection value includes calculating a first transmittance, which is the transmittance of light of a first wavelength through the paper, from the first detection value, calculating a second transmittance, which is the transmittance of light of a second wavelength through the paper, from the second detection value, and calculating at least one of the ratio and the difference between the first transmittance and the second transmittance.

[0008] Preferably, using the first detection value and the second detection value includes calculating a first transmittance, which is the transmittance of light of a first wavelength through the paper, from the first detection value, calculating a second transmittance, which is the transmittance of light of a second wavelength through the paper, from the second detection value, and deriving a result of a given calculation using the first transmittance and the second transmittance.

[0009] Preferably, deriving the paper type determination result includes identifying a range to which coordinates defined by values ​​based on the first detection value and values ​​based on the second detection value belong, out of two or more ranges in a figure having a vertical axis to which values ​​based on the first detection value correspond and a horizontal axis to which values ​​based on the second detection value correspond.

[0010] More preferably, in the diagram, the two or more ranges are distinguished from one another by straight lines according to a linear function.

[0011] Preferably, the first wavelength is in the range of 800 nm to 900 nm. Preferably, the second wavelength is in the range of 420 nm to 480 nm.

[0012] According to another aspect of the present disclosure, there is provided a paper discrimination device including: a light source unit that irradiates light of two or more wavelengths onto paper; a detection unit that obtains detection results based on the absorption of each of the light of the two or more wavelengths by the paper; and a control unit that derives a paper type determination result based on whether the detection results conform to two or more conditions.

[0013] Preferably, the light having two or more wavelengths includes light having a wavelength of 390 to 420 nm, light having a wavelength of 400 to 500 nm, light having a wavelength of 600 to 700 nm, and light having a wavelength of 750 to 1100 nm.

[0014] Preferably, the light having two or more wavelengths further includes light having a wavelength of 500 to 600 nm. Preferably, the detection unit includes a photodiode or phototransistor having a light-receiving sensitivity equal to or greater than a given threshold for all of light of two or more wavelengths.

[0015] Preferably, the light receiving element of the detection unit is disposed on the substrate on which the light source of the light source unit is disposed.

[0016] Preferably, the detection unit includes a single light receiving element that obtains detection results based on the absorption of each of the two or more wavelengths of light at timings corresponding to the respective light of the two or more wavelengths irradiated from the light source unit.

[0017] Preferably, the detection unit includes two or more filters having different transmission characteristics for light of two or more wavelengths, and two or more light-receiving elements each equipped with one of the two or more filters.

[0018] Preferably, the light source unit is configured to irradiate light of two or more wavelengths onto a transport path along which paper is transported within the paper discrimination device.

[0019] Preferably, the paper type determination result distinguishes between plain paper and recycled paper or medium-weight paper.

[0020] According to yet another aspect of the present disclosure, there is provided an image forming apparatus including the above-described paper discrimination device and an image forming unit that forms an image on paper.

[0021] According to one aspect of the present disclosure, there is provided a paper discrimination method comprising the steps of irradiating light of two or more wavelengths onto paper and obtaining detection results based on the absorption of each of the light of the two or more wavelengths in the paper, wherein the light of the two or more wavelengths includes light having a first wavelength and light having a second wavelength, and the detection results include a first detection value based on the absorption of light of the first wavelength in the paper and a second detection value based on the absorption of light of the second wavelength in the paper, and further comprising the step of deriving a paper type determination result using the first detection value and the second detection value, wherein the first wavelength is a wavelength in the range of 750 nm to 1100 nm and the second wavelength is a wavelength in the range of 400 nm to 500 nm.

[0022] According to another aspect of the present disclosure, there is provided a paper discrimination method comprising the steps of irradiating light of two or more wavelengths onto paper, obtaining detection results based on the absorption of each of the light of the two or more wavelengths by the paper, and deriving a paper type determination result based on whether the detection results meet two or more conditions.

[0023] According to another aspect of the present disclosure, there is provided a program that, when executed by a computer, causes the computer to implement the above-described paper type discrimination method. [Effects of the Invention]

[0024] According to one aspect of the present disclosure, the wavelength ranges of the first wavelength and the second wavelength used to derive the paper type determination result are appropriately selected, thereby improving the accuracy of paper type determination.

[0025] According to another aspect of the present disclosure, two or more conditions are used to derive a paper type determination result, thereby improving the accuracy of paper type determination. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention. [Figure 2] FIG. 1 is a block diagram of an image forming apparatus 1. [Figure 3] FIG. 2 is a diagram showing the configuration of a medium inspection unit 20. [Figure 4] 10 is a diagram for explaining a manner in which reflected light is detected in the image forming apparatus 1. FIG. [Figure 5] 2 is a diagram for explaining a detection mode of transmitted light in the image forming apparatus 1. FIG. [Figure 6] FIG. 10 is a diagram showing an example of changes in absorption coefficient with respect to wavelength for two types of recording material M. [Figure 7] 10A and 10B are diagrams for explaining the influence of bluing on the optical characteristics of a recording material. [Figure 8] 10A and 10B are diagrams for explaining the influence of a fluorescent whitening agent on the optical properties of a recording material. [Figure 9] 10A and 10B are diagrams for explaining one aspect of discrimination of recording materials using wavelength dependency of optical characteristics of a first wavelength and a second wavelength. [Figure 10] 10 is a flowchart of a process for acquiring a reference light amount used to derive the transmittance of a first wavelength and a second wavelength. [Figure 11] 10 is a flowchart of a process for determining the type of recording material. [Figure 12] 10A and 10B are diagrams for explaining another aspect of discrimination of the recording material. [Figure 13] FIG. 13 is a diagram showing the relationship between the discrimination index and the determination result in the processing of FIG. [Figure 14] FIG. 10 is a diagram showing the relationship between the reflectances of two types of recording material. [Figure 15] FIG. 10 is a diagram showing the reflectance of some plain paper sheets. [Figure 16] 10 is a flowchart illustrating an example of a process for determining the type of recording material M. [Figure 17] FIG. 17 is a diagram showing the relationship between the discrimination index and the determination result in the processing of FIG. [Figure 18] FIG. 18 is a diagram for explaining the content (step SA10) corresponding to the discrimination index A in FIG. [Figure 19] FIG. 18 is a diagram for explaining the content (step SA12) corresponding to discrimination index B in FIG. [Figure 20] FIG. 18 is a diagram for explaining the content (step SA14) corresponding to the discrimination index C in FIG. [Figure 21] 10 is a flowchart of another example of the process of the method for determining the type of recording material M. [Figure 22] FIG. 22 is a diagram showing the relationship between the discrimination index and the determination result in the processing of FIG. 21. [Figure 23] FIG. 10 is a diagram for explaining step SA01. [Figure 24] FIG. 10 is a diagram for explaining step SA02. [Figure 25] 10 is a diagram showing the change in light receiving sensitivity of the light receiving element 220 with respect to wavelength. FIG. [Figure 26] 10 is a diagram showing the configuration of a modified example of the light detection unit 22. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of 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, the description thereof will not be repeated.

[0028] [1. 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.

[0029] The image forming apparatus 1 is an MFP (Multifunction Peripheral) that forms an image on a recording material by electrophotography. The image forming apparatus 1 includes a control unit 10, a medium inspection unit 20, an image forming unit 30, a fixing unit 40, a scanner 50, an operation display unit 60, a communication unit 70, a paper feed tray 81, a transport roller 82, a paper discharge tray 83, and a bus 90.

[0030] 2, a recording material discrimination device 2 that discriminates recording materials is configured by a control unit 10 and a medium inspection unit 20. The various components of the image forming apparatus 1 are connected to each other by a bus 90.

[0031] The control unit 10 includes a CPU 11 (Central Processing Unit), a RAM 12 (Random Access Memory), and a storage unit 13.

[0032] 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 131 and a data storage area 132. The program storage area 131 stores data for various programs. The data storage area 132 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 recording material discrimination operation described below.

[0033] The CPU 11 reads and executes a program stored in a program storage area 131 of the storage unit 13 (or a program stored in a storage device outside the image forming apparatus 1), and performs various arithmetic processing.

[0034] The RAM 12 provides a working memory space for the CPU 11 and temporarily stores data.

[0035] The control unit 10 controls each part of the image forming apparatus 1 by the CPU 11 executing a program. For example, the control unit 10 operates each part of the image forming section 30, the transport roller 82, and the fixing section 40 based on image data stored in the storage section 13 to form an image on the recording material. Here, the CPU 11 changes the image formation-related operations of each part of the image forming apparatus 1 according to the recording material discrimination result by the recording material 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 recording material. The CPU 11 also changes the heating temperature and applied pressure of the fixing section 40 according to the type of recording material.

[0036] In addition, the control unit 10 may include dedicated circuits (such as ASICs (application specific integrated circuits), FPGAs (field-programmable gate arrays), etc.) for realizing each function, instead of or in addition to the CPU 11.

[0037] The medium inspection unit 20 is provided at a position along the conveyance path of the recording material, upstream of the image forming unit 30, from the paper feed tray 81 to the paper discharge tray 83. However, the position of the medium inspection unit 20 is not limited to this, and the medium inspection unit 20 can be placed at any position along the conveyance path.

[0038] The medium inspection section 20 includes a light irradiation unit 21X, a light irradiation unit 21Y, and a light detection unit 22.

[0039] Each of the light irradiation unit 21X and the light irradiation unit 21Y, under the control of the control unit 10, irradiates an inspection light beam toward the transport path.

[0040] The light detection unit 22 detects the inspection light directed toward the transport path, and the detected light includes reflected light and transmitted light from the recording material.

[0041] The image forming unit 30 applies toner (color material) to the recording material supplied from the paper feed tray 81 to form an image. The image forming unit 30 includes an intermediate transfer belt 31, image forming units 32, and transfer rollers 33. The intermediate transfer belt 31 is an endless belt-shaped member that is stretched around multiple rollers and moves around. The image forming units 32 are arranged along the intermediate transfer belt 31 and form toner images of the respective 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 the recording material passes through the nip portion between the intermediate transfer belt 31 and the transfer rollers 33, the toner images are transferred to the recording material to form an image. Note that, although the present embodiment illustrates an image forming unit 30 capable of forming color images, the present invention is not limited to this, and an image forming unit 30 capable of forming monochrome images may also be used.

[0042] The fixing unit 40 applies heat and pressure to the recording material onto which the toner image has been transferred, thereby fixing the toner image to the recording material. The fixing unit 40 includes a pair of rollers consisting of a heating roller and a pressure roller that sandwich the recording material. The recording material 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 recording material, etc.

[0043] The scanner 50 includes an optical system such as a light source and a reflecting mirror, and an image sensor, and reads an image on a recording material being transported along a predetermined transport path or placed on a platen glass, and generates bitmap image data 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 recording material by performing image formation by the image forming unit 30 based on this image data.

[0044] 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.

[0045] 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.

[0046] Recording materials before image formation are stored in the paper feed tray 81. The paper feed tray 81 may store a plurality of types of recording materials.

[0047] The type of recording material is characterized by at least one of the following characteristics: the material (raw material), the state of surface treatment, the presence and amount of fluorescent whitening agent, the presence or absence of bluing, and color. Therefore, recording materials that differ from each other in at least one of these characteristics are different types of recording materials. The types of recording materials that can be stored in the paper feed tray 81 include, for example, plain paper, medium-grade paper, and recycled paper. However, the types of recording materials that can be stored in the paper feed tray 81 are not limited to those mentioned above.

[0048] Plain paper is paper made primarily from wood-based pulp (i.e., pulp that is not recycled from waste paper, usually chemical pulp).

[0049] Wood-based paper is paper made primarily from mechanical pulp, for example. Plain paper and wood-based paper are sometimes distinguished from each other by the fact that plain paper is bleached, while wood-based paper is unbleached.

[0050] Recycled paper is paper that contains a specified or higher blending ratio of recycled paper pulp extracted from recycled paper.

[0051] The conveying rollers 82 rotate while sandwiching a sheet of recording material, thereby conveying the recording material along the conveying path. The conveying timing and conveying speed of the conveying rollers 82 are controlled by the control unit 10 according to the type of recording material, etc.

[0052] The paper discharge tray 83 holds the recording material on which the image has been formed until it is removed by the user.

[0053] [2. Media Inspection Unit Configuration] Next, the configuration of the medium inspection unit 20 will be described with reference to Fig. 3. Fig. 3 is a diagram showing the configuration of the medium inspection unit 20.

[0054] 3, the recording material is indicated as "recording material M." Arrow A1 indicates the direction in which recording material M is conveyed on the conveyance path. Arrow A2 indicates the direction perpendicular to the conveyance surface of recording material M.

[0055] The media inspection unit 20 includes element substrates 23X and 23Y arranged at a position opposite the conveying surface of the conveying path of the recording material M (in other words, at a position opposite the recording material M passing through the conveying path), a paper passing guide 25 that supports the recording material M so that the recording material M moves along the conveying path, and optical apertures 24X and 24Y located between the recording material M and the element substrates 23X and 23Y, respectively.

[0056] Each of the element substrates 23X and 23Y is disposed so that its main surface is positioned perpendicular to the z direction.

[0057] A first light-emitting element 211X, a second light-emitting element 212X, and a light-receiving element 220 are provided on the surface of the element substrate 23X facing the recording material M. The first light-emitting element 211X and the second light-emitting element 212X are components of the light irradiation unit 21X. The first light-emitting element 211X irradiates light of a first wavelength, and the second light-emitting element 212X irradiates light of a second wavelength.

[0058] The light receiving element 220 is a component of the light detection unit 22. The light detection unit 22 has one light receiving element 220. The light receiving element 220 outputs a photocurrent according to the amount of incident light. The light detection unit 22 converts this photocurrent into a voltage, then converts it into digital data and outputs it to the control unit 10.

[0059] A first light-emitting element 211Y and a second light-emitting element 212Y are provided on the surface of the element substrate 23Y facing the recording material M. The first light-emitting element 211Y and the second light-emitting element 212Y are components of the light irradiation unit 21Y. The first light-emitting element 211Y irradiates light of a first wavelength, and the second light-emitting element 212Y irradiates light of a second wavelength.

[0060] The optical diaphragms 24X and 24Y are plate-like members arranged so that their respective principal surfaces are perpendicular to the direction of the arrow A2z.

[0061] The light receiving element 220 is disposed between the first light emitting element 211X and the second light emitting element 212X. It is preferable that the distance from the first light emitting element 211X to the light receiving element 220 is equal to the distance from the second light emitting element 212X to the light receiving element 220.

[0062] The recording material M is transported through the gap between the optical diaphragm 24X and the paper passing guide 25. Because this gap has a width in the direction of arrow A2, the passing position of the recording material M can fluctuate in the direction of arrow A2 within the range of this width. In response to this fluctuation in the passing position of the recording material M, the distances between the first light-emitting element 211X, the second light-emitting element 212X, and the light-receiving element 220 and the recording material M can also fluctuate. However, because the first light-emitting element 211X, the second light-emitting element 212X, and the light-receiving element 220 are provided on the same surface of the element substrate 23X, the effect of this fluctuation on the inspection results based on reflected light by the medium inspection unit 20 can be minimized.

[0063] 4 is a diagram for explaining the manner in which reflected light is detected in the image forming apparatus 1. The first light-emitting element 211X irradiates the recording material M with a first inspection light Lx1. The second light-emitting element 212X irradiates the recording material M with a second inspection light Lx2.

[0064] The optical diaphragm 24X has an opening in a range that includes the first light-emitting element 211X, the second light-emitting element 212X, and the portion facing the light-receiving element 220. The first inspection light Lx1 and the second inspection light Lx2 pass through this opening and are incident on the recording material M. The optical diaphragm 24X has a light-blocking property in the portion other than the opening, and prevents light other than the inspection light from being incident on the recording material M.

[0065] The light receiving element 220 receives reflected light Lr1 and reflected light Lr2, which are generated when the first inspection light Lx1 and the second inspection light Lx2 are reflected by the recording material M. The light receiving element 220 detects the amount of reflected light Lr1 and reflected light Lr2. The amount of reflected light Lr1 is affected by the absorption characteristics of the recording material M for light of a first wavelength. The amount of reflected light Lr2 is affected by the absorption characteristics of the recording material M for light of a second wavelength. Therefore, the amount of reflected light Lr1 is an example of a first detection value based on the absorption of light of the first wavelength in the recording material. The amount of reflected light Lr2 is an example of a second detection value based on the absorption of light of the second wavelength in the recording material.

[0066] 5 is a diagram for explaining the detection mode of transmitted light in the image forming apparatus 1. The first light-emitting element 211Y irradiates the recording material M with a first inspection light Ly1. The second light-emitting element 212Y irradiates the recording material M with a second inspection light Ly2.

[0067] The optical diaphragm 24Y has an opening in a range including the portion facing the first light-emitting element 211Y and the second light-emitting element 212Y. The first inspection light Ly1 and the second inspection light Ly2 pass through this opening and are incident on the recording material M. The optical diaphragm 24Y has a light-blocking property in the portion other than the opening, and prevents light other than the inspection light from being incident on the recording material M.

[0068] The light receiving element 220 receives transmitted light Lt1 and transmitted light Lt2, which are generated when the first inspection light Ly1 and the second inspection light Ly2, respectively, pass through the recording material M. The light receiving element 220 detects the amount of transmitted light Lt1 and transmitted light Lt2. The amount of transmitted light Lt1 is affected by the absorption characteristics of the recording material M for light of a first wavelength. The amount of transmitted light Lt2 is affected by the absorption characteristics of the recording material M for light of a second wavelength. Therefore, the amount of transmitted light Lt1 is an example of a first detection value based on the absorption of light of the first wavelength in the recording material. The amount of transmitted light Lt2 is an example of a second detection value based on the absorption of light of the second wavelength in the recording material.

[0069] [3. Examples of light wavelengths used to distinguish recording materials] FIG. 6 shows an example of the change in absorption coefficient with respect to wavelength for two types of recording material M. Line L11 shows the change for plain paper. Line L12 shows the change for recycled paper and medium-weight paper (a combination of the changes for recycled paper and medium-weight paper).

[0070] As shown by line L12, there is a relatively large difference in absorption coefficient between near 460 nm and near 850 nm for recycled paper and medium-weight paper. On the other hand, as shown by line L11, there is no particular difference in absorption coefficient between near 460 nm and near 850 nm for plain paper. In other words, while the change in recycled paper and medium-weight paper is wavelength-dependent in the difference in absorption coefficient between near 460 nm and near 850 nm, the change in plain paper is not particularly wavelength-dependent in the difference in absorption coefficient between near 460 nm and near 850 nm.

[0071] In order to distinguish the recording material by utilizing the presence or absence of wavelength dependency depending on the type of recording material, in one implementation example, of the two wavelengths mentioned above, near-infrared light, which is light in the range including 850 nm, is used as the first wavelength light, and blue light, which is light in the range including 460 nm, is used as the second wavelength light.

[0072] <1st wavelength> As the light of the first wavelength, for example, light within the range of 750 nm to 1100 nm is set.

[0073] The reason why it is preferable to select a wavelength of 750 nm or more is that, for example, light with a wavelength shorter than 750 nm may be affected by bluing the recording material M during the papermaking process. Bluing is mainly performed when paper is used as the recording material M. In bluing, a dye that gives the paper a blue color is added to the paper to improve the whiteness of the paper. This reduces the reflectance of wavelengths outside the blue region of the paper through absorption, and relatively improves the reflectance of wavelengths in the blue region of the paper.

[0074] Fig. 7 is a diagram illustrating the effect of bluing on the optical properties of recording materials. Fig. 7 shows the transmittance of paper from 250 nm to 900 nm. Line L21 shows the transmittance of bluing-tinted paper, and line L22 shows the transmittance of non-bluing-tinted paper.

[0075] In the example shown in Figure 7, the value of line L21 is significantly lower than the value of line L22 from 500 nm to 750 nm. A low transmittance of the medium corresponds to a decrease in reflectance due to absorption by the medium. In other words, Figure 7 also shows that the bluing reduces the reflectance of the recording material in the green to red wavelength range.

[0076] For these reasons, in order to ensure the above-mentioned wavelength dependency, it is preferable to select a wavelength of 750 nm or more as the first wavelength, and more preferably a wavelength of 800 nm or more as the first wavelength.

[0077] The reason why wavelengths of 1100 nm or less are preferably selected is, for example, the influence of moisture contained in the recording material. That is, at wavelengths longer than 1100 nm, the spectrum of reflected light from the recording material (paper) changes depending on the moisture content of the recording material. More specifically, moisture has a specific absorption band at 1450 nm and 1940 nm in the near-infrared region, which is derived from the combined vibration of the stretching and bending vibration of hydrogen and oxygen atoms, and therefore the reflection characteristics of the recording material can change depending on the moisture content of the recording material.

[0078] For the above reasons, in order to ensure the above-mentioned wavelength dependency, it is preferable to select a wavelength of 1100 nm or less as the first wavelength, and more preferably a wavelength of 900 nm or less as the first wavelength.

[0079] <Second wavelength> As the light of the second wavelength, for example, light within the range of 400 nm to 500 nm is set.

[0080] The reason why it is preferable to select a wavelength of 400 nm or more is that this is the wavelength range of fluorescent light emitted by a fluorescent brightening agent contained in the recording material (paper), for example.

[0081] Fig. 8 is a diagram illustrating the influence of a fluorescent brightening agent on the optical properties of a recording material. Fig. 8 shows the transmittance of paper from 250 nm to 900 nm. Line L31 shows the transmittance of paper containing a fluorescent brightening agent, and line L32 shows the transmittance of paper without a fluorescent brightening agent.

[0082] In the example shown in Figure 8, the value of line L31 is significantly lower than the value of line L32 at wavelengths shorter than 400 nm. The cause of this difference in values ​​is thought to be the fluorescent emission of the fluorescent brightener at wavelengths shorter than 400 nm.

[0083] That is, in the wavelength range shorter than 400 nm, the fluorescent light emitted by the fluorescent whitening agent is included in the light transmitted through the recording material itself.

[0084] For the above reasons, in order to ensure the above-mentioned wavelength dependency, it is preferable to select a wavelength of 400 nm or more as the second wavelength, and more preferably a wavelength of 420 nm or more as the second wavelength.

[0085] The reason why wavelengths of 500 nm or less are preferably selected is, for example, the bluing of the recording material. As shown in Figure 7, the value of line L21 is lower than the value of line L22 in the wavelength range longer than 500 nm. In other words, in the wavelength range longer than 500 nm, the bluing reduces the reflectance of the recording material in the green to red wavelength range.

[0086] For these reasons, in order to ensure the above-mentioned wavelength dependency, it is preferable to select a wavelength of 500 nm or less as the second wavelength, and more preferably a wavelength of 480 nm or less as the second wavelength.

[0087] [5. Recording material discrimination mode (1)] FIG. 9 is a diagram for explaining one aspect of discrimination of recording materials using the wavelength dependency of the optical characteristics of the first wavelength and the second wavelength.

[0088] Fig. 9 shows the transmittance of each of a plurality of recording materials at the first wavelength and the second wavelength. More specifically, in the graph of Fig. 9, the vertical axis represents the transmittance of the second wavelength, and the horizontal axis represents the transmittance of the first wavelength.

[0089] In the graph of Fig. 9, the circular spots represent values ​​for recording materials classified as plain paper, and the triangular spots represent values ​​for recording materials classified as recycled paper or medium-weight paper. In the example of Fig. 9, the values ​​for plain paper and the values ​​for recycled paper or medium-weight paper can be separated by line L41. More specifically, the values ​​for recording materials classified as plain paper are located above line L41, and the values ​​for recording materials classified as recycled paper or medium-weight paper are located below line L41.

[0090] Therefore, the image forming apparatus 1 stores information identifying the line L41 as reference data, detects the transmittance of the first wavelength and the transmittance of the second wavelength of the recording material M, arranges coordinates representing these transmittances on a graph such as that shown in Figure 9, and identifies the position of the coordinates relative to the line L41, thereby being able to derive a determination result for the type of the recording material M.

[0091] More specifically, if the coordinates are located above line L41, "plain paper" is derived as the determination result for the type of recording material M. On the other hand, if the coordinates are located below line L41, "recycled paper or medium-quality paper" is derived as the determination result for the type of recording material M. By deriving the determination result for the type of recording material M in this way, the image forming apparatus 1 distinguishes the recording material M.

[0092] The transmittance of the recording material M can be detected as the ratio of the amount of light transmitted through the recording material M to the amount of light not transmitted through the recording material M, as will be described later with reference to FIGS.

[0093] The determination based on the positional relationship with the line L41 in the graph, described with reference to Figure 9, is an example of determination based on identifying the range to which the coordinates defined by the first and second detection values ​​of the recording material M belong, among two or more ranges in the figure. In this example, the two or more ranges are separated by the line L41. The line L41 is an example of a straight line according to a linear function formula for separating the figure into two ranges.

[0094] In the determination, the graph may be divided into two or more ranges by one or more curves. In this case, information specifying the one or more curves is stored as reference data in the data storage area 132. Each of the two or more ranges is associated with one or more types. The range to which the coordinates of the recording material M belong is identified among the two or more ranges, and the type associated with the identified range is derived as the determination result for the type of recording material M.

[0095] Furthermore, the recording material may be identified based on at least one of the ratio or difference between the transmittance of the first wavelength and the transmittance of the second wavelength.

[0096] In one implementation example, a ratio range corresponding to plain paper and a ratio range corresponding to recycled paper or medium-weight paper are stored as reference data in the data storage area 132. The image forming apparatus 1 calculates the ratio between the transmittance of the first wavelength and the transmittance of the second wavelength of the recording material M, and derives the type corresponding to the range to which the calculated ratio belongs (plain paper, or recycled paper or medium-weight paper) as the determination result of the type of the recording material M.

[0097] In another implementation example, a difference range corresponding to plain paper and a difference range corresponding to recycled paper or medium-weight paper are stored as reference data in the data storage area 132. The image forming apparatus 1 calculates the difference between the transmittance of the recording material M at the first wavelength and the transmittance of the recording material M at the second wavelength, and derives the type corresponding to the range to which the calculated difference belongs (plain paper, or recycled paper or medium-weight paper) as the determination result of the type of recording material M.

[0098] Furthermore, the recording material may be identified based on the result of a given calculation using the transmittance of the first wavelength and the transmittance of the second wavelength. An example of the given calculation is as follows:

[0099] ax+by=c …(1) In formula (1), x represents the transmittance of the first wavelength, y represents the transmittance of the second wavelength, a and b represent predetermined constants, and c represents the result of the calculation.

[0100] In one implementation example, a range of calculation results corresponding to plain paper and a range of calculation results corresponding to recycled paper or medium-weight paper are stored as reference data in the data storage area 132. The image forming apparatus 1 calculates the calculation result of equation (1) for the recording material M using the transmittance of the recording material M at the first wavelength and the transmittance of the recording material M at the second wavelength, and derives the type (plain paper, or recycled paper or medium-weight paper) corresponding to the range to which the calculated calculation result belongs as the determination result of the type of the recording material M.

[0101] Other examples of given operations follow equations (2) and (3). px+qy=c …(2) (Tx <x) mx+ny=c …(3) (x≦Tx) In equations (2) and (3), x represents the transmittance of the first wavelength, and y represents the transmittance of the second wavelength, as in equation (1). p, q, m, and n each represent a predetermined constant. Equation (2) is used when the value of x exceeds a given threshold (Tx), and equation (3) is used when the value of x is equal to or less than the threshold. That is, in an example that follows equations (2) and (3), the equation used to derive the calculation result is selected according to the value of the transmittance of the first wavelength.

[0102] In addition to this example, when deriving the result of the calculation, the formula used to derive the result may be selected according to the value of y, or the formula used to derive the result may be selected according to both the value of x and the value of y.

[0103] Like transmittance, reflectance is a value that can change depending on the light absorption characteristics of the recording material. Therefore, reflectance may be used instead of or in addition to transmittance to distinguish recording materials.

[0104] In one implementation, the image forming apparatus 1 defines a graph in which the horizontal axis represents the reflectance at a first wavelength and the vertical axis represents the reflectance at a second wavelength, similar to line L1 in FIG. 9, and stores, as reference data, information identifying a figure (corresponding to line L41 in FIG. 9) that separates multiple types of recording material on the graph. The image forming apparatus 1 also detects the reflectance at the first wavelength and the reflectance at the second wavelength for the recording material M. The reflectance is identified, for example, as the ratio of the amount of light reflected by the recording material to the amount of light output. The image forming apparatus 1 then derives a determination result for the type of recording material M based on the positional relationship between the coordinates in the graph identified by the reflectance at the first wavelength and the second wavelength of the recording material M and the figure.

[0105] [6. Processing flow] As an example of the process for determining the type of recording material, the process for determining the type of recording material using the transmittance of the first wavelength and the second wavelength, as described with reference to FIG. 9, will be described.

[0106] <Acquisition of reference light intensity> 10 is a flowchart of a process for acquiring a reference light amount used to derive the transmittance of the first wavelength and the second wavelength. In one implementation example, in the image forming apparatus 1, the process of FIG. 10 is performed by the CPU 11 executing a given program.

[0107] The process of FIG. 10 may be started every time a certain time period has elapsed, may be started when the image forming apparatus 1 is started, or may be started in response to an instruction from the user.

[0108] In step S1110, the image forming apparatus 1 outputs an instruction signal to the light irradiation unit 21Y to irradiate irradiation light having a first wavelength. In response to this, the first light emitting element 211Y outputs light. The amount of light to be detected by the light receiving element 220 at this time is also referred to as a first reference light amount.

[0109] In step S1115, the image forming apparatus 1 determines whether or not the first reference light amount has been acquired from the light detection unit 22. This determination is made based on information received from the light detection unit 22. The light detection unit 22 outputs the light amount detected by the light receiving element 220 to the CPU 11. If the image forming apparatus 1 determines that the first reference light amount has been acquired from the light detection unit 22 (YES in step S1115), the image forming apparatus 1 proceeds to control step S1120. If not (NO in step S1115), the image forming apparatus 1 switches control to step S1125.

[0110] In step S1115, the light detection unit 22 from It may be determined whether the received information includes a detection value within a range that is predetermined to be valid as the first reference light amount. If the received information includes a detection value within the range, it is determined that the first reference light amount has been detected, and if the received information does not include a detection value within the range, it is determined that the first reference light amount has not been detected.

[0111] In step S1125, image forming apparatus 1 uses a timer (not shown) to measure the elapsed time since the initial determination was started in step S1115, and determines whether a timeout has occurred based on the elapsed time. In one implementation example, when the elapsed time reaches a predetermined period (e.g., one minute), it determines that a timeout has occurred. If image forming apparatus 1 determines that a timeout has occurred (YES in step S1125), it ends the processing of FIG. 10. If not (NO in step S1125), image forming apparatus 1 returns control to step S1115.

[0112] In step S1120, the image forming apparatus 1 outputs an instruction signal to the light irradiation unit 21Y to irradiate irradiation light having the second wavelength. In response to this, the second light emitting element 212Y outputs light. The amount of light to be detected by the light receiving element 220 at this time is also referred to as a second reference light amount.

[0113] In step S1130, the image forming apparatus 1 determines whether or not the second reference light amount has been acquired from the light detection unit 22. This determination is made based on information received from the light detection unit 22. The light detection unit 22 outputs the light amount detected by the light receiving element 220 to the CPU 11. If the image forming apparatus 1 determines that the second reference light amount has been acquired from the light detection unit 22 (YES in step S1130), the image forming apparatus 1 proceeds to control step S1135. If not (NO in step S1130), the image forming apparatus 1 switches control to step S1140.

[0114] In step S1130, the light detection unit 22 from It may be determined whether the received information includes a detection value within a range that is predetermined to be valid as the second reference light amount. If the received information includes a detection value within the range, it is determined that the second reference light amount has been acquired, and if the received information does not include a detection value within the range, it is determined that the second reference light amount has not been acquired.

[0115] In step S1140, image forming apparatus 1 uses a timer (not shown) to measure the elapsed time since the initial determination was started in step S1130, and determines whether a timeout has occurred based on the elapsed time. In one implementation example, when the elapsed time reaches a predetermined period (e.g., one minute), it determines that a timeout has occurred. If image forming apparatus 1 determines that a timeout has occurred (YES in step S1140), it ends the processing of FIG. 10. If not (NO in step S1140), image forming apparatus 1 returns control to step S1130.

[0116] In step S1135, the image forming apparatus 1 stores the first and second reference light amounts in the data storage area 132. After that, the image forming apparatus 1 ends the processing of FIG.

[0117] <Determining the type of recording material> 11 is a flowchart of a process for determining the type of recording material. In one implementation example, the process of FIG.

[0118] The processing of FIG. 11 may be initiated in response to the acquisition of an instruction to start a job that includes image formation, such as a print job, or in response to a user instruction (which may be input independently of the job that includes image formation).

[0119] 11, in step S1210, the image forming apparatus 1 determines whether or not a detection signal indicating that the recording material M has been detected has been acquired from a timing sensor (not shown). The timing sensor is disposed, for example, upstream of the element substrate 23X on the conveyance path, and detects the passage of the recording material M.

[0120] If image forming apparatus 1 determines that it has acquired a detection signal from the timing sensor (YES in step S1210), it switches control to step S1215, and if not (NO in step S1210), it switches control to step S1220.

[0121] In step S1220, image forming apparatus 1 determines whether a timeout has occurred in obtaining a detection signal from the timing sensor. A timeout in obtaining a detection signal from the timing sensor occurs when a given time has elapsed since the image forming apparatus 1 first started determining in step S1210 whether a detection signal has been obtained from the timing sensor.

[0122] If image forming apparatus 1 determines that a timeout has occurred (YES in step S1220), it ends the process of FIG. 11, and if not (NO in step S1220), it switches control to step S1210.

[0123] In step S1215, the image forming apparatus 1 outputs an instruction signal to the light irradiation unit 21Y to irradiate irradiation light having the first wavelength. In response to this, the first light emitting element 211Y outputs light. The amount of light to be detected by the light receiving element 220 at this time is also referred to as the first detected light amount.

[0124] In step S1225, the image forming apparatus 1 determines whether or not the first detected light amount has been acquired from the light detection unit 22. This determination is made based on information received from the light detection unit 22. The light detection unit 22 outputs the light amount detected by the light receiving element 220 to the CPU 11. If the image forming apparatus 1 determines that the first detected light amount has been acquired from the light detection unit 22 (YES in step S1225), the image forming apparatus 1 proceeds to control step S1230. If not (NO in step S1225), the image forming apparatus 1 switches control to step S1235.

[0125] In step S1225, the light detection unit 22 from It may be determined whether the received information includes a detection value within a predetermined range that is valid as the first detected light amount. If the received information includes a detection value within the range, it is determined that the first detected light amount has been detected, and if the received information does not include a detection value within the range, it is determined that the first detected light amount has not been detected.

[0126] In step S1235, image forming apparatus 1 determines whether a timeout has occurred in obtaining the first detected light amount. This timeout occurs, for example, when a given time has elapsed since the output of the instruction signal in step S1215. If image forming apparatus 1 determines that a timeout has occurred (YES in step S1235), it ends the processing in FIG. 11. If not (NO in step S1235), image forming apparatus 1 returns control to step S1225.

[0127] In step S1230, the image forming apparatus 1 outputs an instruction signal to the light irradiation unit 21Y to irradiate irradiation light having the second wavelength. In response to this, the second light emitting element 212Y outputs light. The amount of light to be detected by the light receiving element 220 at this time is also referred to as the second detected light amount.

[0128] In step S1240, the image forming apparatus 1 determines whether or not the second detected light amount has been acquired from the light detection unit 22. This determination is made based on information received from the light detection unit 22. The light detection unit 22 outputs the light amount detected by the light receiving element 220 to the CPU 11. If the image forming apparatus 1 determines that the second detected light amount has been acquired from the light detection unit 22 (YES in step S1240), the image forming apparatus 1 proceeds to control step S1245. If not (NO in step S1240), the image forming apparatus 1 switches control to step S1250.

[0129] In step S1250, image forming apparatus 1 determines whether a timeout has occurred in obtaining the second detected light amount. This timeout occurs, for example, when a given time has elapsed since the output of the instruction signal in step S1230. If image forming apparatus 1 determines that a timeout has occurred (YES in step S1250), it ends the processing in FIG. 11. If not (NO in step S1250), image forming apparatus 1 returns control to step S1240.

[0130] In step S1245, the image forming apparatus 1 derives a determination result of the type of the recording material M. More specifically, the image forming apparatus 1 derives the transmittance of the first wavelength from the first reference light amount and the first detected light amount, derives the transmittance of the second wavelength from the second reference light amount and the second detected light amount, determines whether coordinates specified from the transmittance of the first wavelength and the transmittance of the second wavelength are located above or below line L41 in FIG. 9, and derives the type corresponding to the determination result as the type of the recording material M. If the coordinates are located above line L41, the type corresponding to the determination result is "plain paper." If the coordinates are located below line L41, the type corresponding to the determination result is "recycled paper or medium-quality paper."

[0131] 10 and 11, the type of recording material M2 is derived using the detection results based on the absorption of the two wavelengths of recording material M. In one implementation example, the paper type determination result according to aspect (1) distinguishes between plain paper and recycled paper or medium-weight paper.

[0132] [7. Recording material discrimination mode (2)] Fig. 12 is a diagram for explaining another aspect of discrimination of recording materials. Fig. 12 shows a modified example of the method for determining the type of recording material M in step S1245 of Fig. 11. The flowchart shown in Fig. 12 is an example of a subroutine of step S1245, and shows processing for deriving a determination result of the type of recording material M based on whether the detection result based on the light absorption of the recording material M satisfies two or more conditions. Fig. 12 schematically shows three discrimination indices corresponding to three conditions, respectively, as discrimination indices A to C.

[0133] More specifically, in step SA10, the image forming apparatus 1 determines whether the detection result satisfies the discrimination index A, and if it determines that it does (YES in step SA10), it proceeds to step SA12, and if it determines that it does not (NO in step SA10), it proceeds to step SA14.

[0134] In step SA12, the image forming apparatus 1 determines whether the detection result satisfies the discrimination index B, and if it determines that it does (YES in step SA12), it proceeds to step SA16, and if it determines that it does not (NO in step SA12), it proceeds to step SA18.

[0135] In step SA14, the image forming apparatus 1 determines whether the detection result satisfies the discrimination index C, and if it determines that it does (YES in step SA14), it proceeds to step SA20, and if it determines that it does not (NO in step SA14), it proceeds to step SA22.

[0136] In step SA16, the image forming apparatus 1 derives paper type A as the type of recording material M, and returns control to Fig. 11. In steps SA18 and SA22, the image forming apparatus 1 derives paper type B as the type of recording material M, and returns control to Fig. 11. In step SA20, the image forming apparatus 1 derives paper type C as the type of recording material M, and returns control to Fig. 11.

[0137] Fig. 13 is a diagram showing the relationship between the discrimination index and the determination result in the process of Fig. 12. Fig. 13 shows the determination results (YES or NO) for each of the discrimination indexes A to C, which are required to derive three types of determination results (paper types A to C) as the type of recording material M. In Fig. 13, for example, the conditions for deriving "paper type A" are confirmed.

[0138] As described with reference to FIG. 12, in order to derive "paper type A," a judgment of "YES" is required for both discrimination index A and discrimination index B. Note that, in order to derive "paper type A," a judgment of "YES" is required for discrimination index A, and therefore, when "paper type A" is derived, a judgment in step SA14 is not required. Therefore, for "paper type A," discrimination index C may be either "YES" or "NO." This corresponds to the top two rows of the eight rows of results shown in FIG. 13. In other words, if the judgment results for both discrimination index A and discrimination index B are "YES," "paper type A" is derived regardless of whether the judgment result for discrimination index C is "YES" (first row) or "NO" (second row).

[0139] 12 and 13, at least two conditions are required to derive a determination result for each of paper types A to C. For example, one example of two conditions for paper type A is (1) a determination of "YES" is made for discrimination indicator A, and (2) a determination of "YES" is made for discrimination indicator B.

[0140] An example of two conditions for paper type B is (1) a determination of "YES" is made for discrimination indicator A, and (2) a determination of "NO" is made for discrimination indicator B.

[0141] Another example of two conditions for paper type B is (1) a determination of "NO" is made for discriminant indicator A, and (2) a determination of "NO" is made for discriminant indicator C.

[0142] An example of two conditions for paper type C is (1) a determination of "NO" is made for discrimination indicator A, and (2) a determination of "YES" is made for discrimination indicator C.

[0143] <Effects of mode (2)> The effect of using two or more conditions to derive a determination result for one type of recording material will be described with reference to Figures 14 and 15. Figure 14 is a diagram showing the relationship between the reflectance of two types of recording material. In the graph of Figure 14, the vertical axis [Reflectance (purple)] represents the reflectance of purple light (center wavelength: 390 to 420 nm). The horizontal axis [Reflectance (near-infrared)] represents the reflectance of near-infrared light (center wavelength: 750 to 1100 nm).

[0144] In FIG. 14, the values ​​for plain paper are represented by circular spots, and the values ​​for recycled paper or medium-weight paper are represented by triangular spots. In the graph of FIG. 14, it is possible to roughly distinguish between "plain paper" and "recycled paper or medium-weight paper" by line L51. However, while most of the values ​​for plain paper are located above line L51, some are located below line L51, as shown in frame A51. Therefore, in the example of FIG. 14, it is not possible to completely separate the values ​​for "plain paper" from the values ​​for "recycled paper or medium-weight paper" by line L51.

[0145] That is, in the example of Figure 14, it is not possible to determine whether the type of recording material in question is "plain paper" or "recycled paper or medium-quality paper" based on a single condition. One reason for this is the pigments added to some plain paper. This point will be explained with reference to Figure 15.

[0146] 15 is a graph showing the reflectance of some plain paper. In one embodiment, the plain paper is ivory-colored paper. In the graph of FIG. 15, the vertical axis represents reflectance and the horizontal axis represents wavelength.

[0147] Some plain paper is added with an ivory-colored pigment to impart a design element. This pigment absorbs a large amount of light near 400 nm, as shown by line L61 in Figure 15. That is, the reflectance of plain paper with the pigment added near 400 nm tends to be lower than that of plain paper without the pigment added. Therefore, the reflectance of purple light of plain paper containing the pigment decreases due to the influence of the pigment, and as a result, the purple light reflection behavior of plain paper containing the pigment becomes closer to the purple light reflection behavior of recycled paper or medium-weight paper.

[0148] On the other hand, in aspect (2), the type of the target recording material is derived when the detection result satisfies two or more conditions, thereby allowing the type of recording material to be accurately derived even if various factors such as the above-mentioned dye affect the light absorption behavior of the recording material.

[0149] In embodiment (2), light with a wider wavelength range than embodiment (1) can be used. More specifically, five types of light with two or more wavelengths can be used: violet light with a wavelength of 390 to 420 nm, blue light with a wavelength of 420 to 500 nm, green light with a wavelength of 500 to 600 nm, red light with a wavelength of 600 to 700 nm, and near-infrared light with a wavelength of 750 to 1100 nm. Note that in each graph from FIG. 18 onward, light with a wavelength of 405 nm is used as violet light, light with a wavelength of 460 nm as blue light, light with a wavelength of 530 nm as green light, light with a wavelength of 670 nm as red light, and light with a wavelength of 940 nm as near-infrared light are used as examples of light of each color.

[0150] <First specific example of aspect (2)> FIG. 16 is a flowchart of an example of a method for determining the type of recording material M. The process in FIG. 16 corresponds to a specific example of the method for determining the type of recording material M in step S1245 in FIG. 11. However, while the process shown in FIG. 11 uses the transmittance of each of two wavelengths for the recording material M to be identified, the number of target wavelengths is not limited to two in the process shown in FIG. 16. In the process shown in FIG. 16, the type of value calculated using the "detection value based on the absorption of light in the recording material" may be transmittance, reflectance, or both transmittance and reflectance.

[0151] The process shown in Fig. 16 corresponds to a specific example of the process shown in Fig. 12. In the process shown in Fig. 16, the discrimination indicators A to C shown in Fig. 12 correspond to the following: Coordinates refer to coordinates arranged on each graph using values ​​acquired for the recording material M to be discriminated.

[0152] Discrimination index A (step SA10): The coordinates in [reflectance V-IR] are below the first threshold. Discrimination index B (step SA12): transparent Coordinates in the [IR-B] are below the second threshold Discrimination index C (step SA14): transparent Coordinates in the [IR-B] are below the third threshold In the process shown in FIG. 16, the paper types A to C shown in FIG. 12 correspond to the following contents.

[0153] Paper type A: Recycled paper or medium-quality paper Paper type B: Plain paper Paper type C: Coated paper Coated paper is a type of coated paper for printing, and is, for example, a type of high-quality printing paper that has a coating of 20 to 40 g / m2 of white pigment such as kaolin or calcium carbonate mixed with an adhesive such as starch applied to its surface. 2 It is coated to a certain extent.

[0154] Fig. 17 is a diagram showing the relationship between the discrimination indexes and the determination results in the processing of Fig. 16. Like the flowchart of Fig. 16, Fig. 17 lists specific examples of the discrimination indexes A to C and the paper types A to C in Fig. 13.

[0155] Fig. 18 is a diagram for explaining the content (step SA10) corresponding to discrimination index A in Fig. 17. The graph shown in Fig. 18 is a graph of [reflectance V-IR] mentioned in discrimination index A.

[0156] In the graph of Fig. 18, the vertical axis [Reflectance (Purple)] represents the reflectance of the recording material for purple light. The horizontal axis [Reflectance (Near Infrared)] represents the reflectance of the recording material for near-infrared light. The graph of Fig. 18 shows values ​​for three types of recording material: plain paper (circular spots), coated paper (diamond spots), and recycled paper or medium-quality paper (triangular spots).

[0157] Line L81 shown in FIG. 18 is a straight line set in advance to separate coated paper from other types. Information specifying line L81 is stored as reference data in data storage area 132. Line L81 constitutes a collection of first threshold values. That is, the determination in step SA10 of whether the coordinates of the recording material M to be identified are below the first threshold value is a determination of whether the coordinates of the recording material M to be identified are located below line L81 in the graph shown in FIG. 18. Being located below line L81 means that the [reflectance (purple)] value is smaller than the first threshold value.

[0158] Fig. 19 is a diagram for explaining the content (step SA12) corresponding to discrimination index B in Fig. 17. The graph shown in Fig. 19 is a graph of [transmittance IR-B] mentioned in discrimination index B.

[0159] In the graph of Figure 19, the vertical axis [Transmittance (Blue)] represents the transmittance of blue light through the recording material. The horizontal axis [Transmittance (Near Infrared)] represents the transmittance of near infrared light through the recording material. The graph of Figure 19 shows values ​​for two types of recording material: plain paper (circular spots) and recycled paper or medium-quality paper (triangular spots).

[0160] Line L82 shown in FIG. 19 is a straight line set in advance to distinguish between plain paper and recycled paper or medium-quality paper. Information specifying line L82 is stored as reference data in data storage area 132. Line L82 constitutes a collection of second threshold values. That is, the determination in step SA12 of whether the coordinates of the recording material M to be discriminated are below the second threshold value is a determination of whether the coordinates of the recording material M to be discriminated are located below line L82 in the graph shown in FIG. 19. Being located below line L82 means that the [transmittance (blue)] value is smaller than the second threshold value.

[0161] Fig. 20 is a diagram for explaining the content (step SA14) corresponding to discrimination index C in Fig. 17. The graph shown in Fig. 20 is a graph of [transmittance IR-B] mentioned in discrimination index C.

[0162] In the graph of Fig. 20, the vertical axis [Transmittance (Blue)] represents the transmittance of blue light through the recording material. The horizontal axis [Transmittance (Near Infrared)] represents the transmittance of near-infrared light through the recording material. The graph of Fig. 20 shows values ​​for two types of recording material: plain paper (circular spots) and coated paper (diamond-shaped spots).

[0163] Line L83 shown in FIG. 20 is a straight line set in advance to distinguish between plain paper and coated paper. Information specifying line L83 is stored as reference data in data storage area 132. Line L83 constitutes a collection of third threshold values. That is, the determination in step SA14 of whether the coordinates of the recording material M to be distinguished are below the third threshold value is a determination of whether the coordinates of the recording material M to be distinguished are located below line L83 in the graph shown in FIG. 20. Being located below line L83 means that the [transmittance (blue)] value is smaller than the third threshold value. The paper type determination result according to the specific example of mode (2) described above distinguishes at least between plain paper and recycled paper or medium-weight paper.

[0164] <Second Specific Example of Aspect (2)> FIG. 21 is a flowchart of another example of the process of determining the type of recording material M. In the process shown in FIG. 21, the control of steps SA01 to SA04 is added before the process shown in FIG. 16. The process shown in FIG. 21 further includes "colored paper" as a recording material that can be derived as a determination result. "Colored paper" means, for example, paper to which a given proportion or more of dye has been added.

[0165] In step SA01, the image forming apparatus 1 determines whether the coordinates determined from the detection results of the recording material M to be discriminated in the graph [Reflectance R-IR] are below the fourth threshold value, and if it determines that this is the case (YES in step SA01), it proceeds to step SA03, and if it determines that this is not the case (NO in step SA01), it proceeds to step SA02.

[0166] In step SA02, the image forming apparatus 1 determines whether the coordinates determined from the detection results of the recording material M to be discriminated in the graph [Reflectance G-IR] are below the fifth threshold value, and if it determines that this is the case (YES in step SA02), it proceeds to step SA04, and if it determines that this is not the case (NO in step SA02), it proceeds to step SA10.

[0167] In both steps SA03 and SA04, the image forming apparatus 1 derives "colored paper" as the determination result of the type of recording material M, and returns the control to FIG.

[0168] FIG. 22 is a diagram showing the relationship between the discrimination index and the determination result in the process of FIG. 2 In the above, "-" means that it does not matter whether the result of the judgment using the corresponding discriminant index is YES or NO.

[0169] For example, according to the first line of Figure 22, if the result of the judgment in step SA01 is YES, then "colored paper" is derived as the judgment result regardless of whether the results of the remaining four judgments (the judgments in steps SA02, SA10, SA20, and SA30) are YES or NO.

[0170] Also, according to the second line of Figure 22, if the result of the judgment in step SA01 is NO and the result of the judgment in step SA02 is YES, then "colored paper" is derived as the judgment result regardless of whether the results of the remaining three judgments (the judgments in steps SA10, SA20, and SA30) are YES or NO.

[0171] Fig. 23 is a diagram for explaining step SA01. The graph shown in Fig. 23 is a graph of [reflectance R-IR].

[0172] In the graph of FIG. 23, the vertical axis [Reflectance (Red)] represents the reflectance of the recording material to red light. The horizontal axis [Reflectance (Near Infrared)] represents the reflectance of the recording material to near infrared light. The graph of FIG. 23 shows values ​​for two types of recording material: white paper (circular spots) and colored paper (triangular spots). "White paper" refers to plain paper with less than a given percentage of dye added.

[0173] Line L84 shown in FIG. 23 is a straight line set in advance to distinguish between white paper and colored paper. Information specifying line L84 is stored as reference data in data storage area 132. Line L84 constitutes a collection of fourth threshold values. That is, the determination in step SA01 of whether the coordinates of the recording material M to be discriminated are below the fourth threshold value is a determination of whether the coordinates of the recording material M to be discriminated are located below line L84 in a graph such as that shown in FIG. 23. Being located below line L84 means that the [reflectance (red)] value is smaller than the fourth threshold value.

[0174] Fig. 24 is a diagram for explaining step SA02. The graph shown in Fig. 24 is a graph of [reflectance G-IR].

[0175] In the graph of FIG. 24, the vertical axis [Reflectance (Green)] represents the reflectance of the recording material for green light. The horizontal axis [Reflectance (Near Infrared)] represents the reflectance of the recording material for near-infrared light. The graph of FIG. 24 shows values ​​for two types of recording material: white paper (circular spots) and colored paper (triangular spots). "White paper" refers to plain paper with less than a given percentage of dye added.

[0176] Line L85 shown in FIG. 24 is a straight line set in advance to distinguish between white paper and colored paper. Information specifying line L85 is stored as reference data in data storage area 132. Line L85 constitutes a collection of fifth thresholds. That is, the determination in step SA02 of whether the coordinates of the recording material M to be discriminated are below the fifth threshold is a determination of whether the coordinates of the recording material M to be discriminated are located below line L85 in a graph such as that shown in FIG. 24. Being located below line L85 means that the [reflectance (green)] value is smaller than the fifth threshold.

[0177] [8. Light receiving element] Fig. 25 is a diagram showing the change in the light sensitivity of the light receiving element 220 with respect to wavelength. In Fig. 25, the line Ls represents the light sensitivity of the light receiving element 220 at each wavelength.

[0178] 25, the light receiving sensitivity of the light receiving element 220 reaches a given value (SE(A / W)) at 390 nm and increases as the wavelength becomes longer. The given value is preset as the sensitivity required to distinguish the recording material.

[0179] As described above, in embodiment (1), the detection results for wavelengths of 400 to 500 nm and 750 to 1100 nm are used. In embodiment (2), the detection results for wavelengths of 390 to 1100 nm are used. Therefore, when embodiment (1) is used for recording materials, a photodiode or phototransistor having a detection sensitivity equal to or greater than the given value in the ranges of 400 to 500 nm and 750 to 1100 nm may be employed as the light receiving element 220. When embodiment (2) is used for recording materials, a photodiode or phototransistor having a detection sensitivity equal to or greater than the given value in the ranges of 390 to 1100 nm may be employed as the light receiving element 220.

[0180] [9. Obtaining detection results for multiple wavelengths of light] 10 and 11, the light receiving element 220 acquires the amount of light of each of the plurality of wavelengths at different timings. For example, in the process of FIG. 11, the light receiving element 220 acquires the amount of light of the first wavelength in step S1225 and the amount of light of the second wavelength in step S1240. In other words, the light receiving element 220 is an example of a single light receiving element that acquires detection results based on the absorption of each of the two or more wavelengths of light irradiated from the light source unit at timings corresponding to the respective light of the two or more wavelengths.

[0181] 26 is a diagram showing a modified example of the configuration of the light detection unit 22. The light detection unit 22 may be configured so as to simultaneously acquire the light intensities of light of a plurality of wavelengths.

[0182] 26, the light detection unit 22 includes a first light receiving element 220A and a second light receiving element 220B. A first filter 221A is attached to the first light receiving element 220A. A second filter 221B is attached to the second light receiving element 220B.

[0183] First filter 221A and second filter 221B have different transmission characteristics. More specifically, first filter 221A has a higher transmittance for a first wavelength than for other wavelength regions. Second filter 221B has a higher transmittance for a second wavelength than for other wavelength regions.

[0184] 26, the light detection unit 22 can acquire, at a certain timing, transmitted light (or reflected light) of a first wavelength using the first light receiving element 220A based on light transmitted through (or reflected from) the recording material M, and can acquire transmitted light (or reflected light) of a second wavelength using the second light receiving element 220B. This can reduce the time required to identify the recording material.

[0185] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. Furthermore, the inventions described in the embodiments and modifications are intended to be practiced, as far as possible, either alone or in combination. [Explanation of symbols]

[0186] 1 image forming apparatus, 2 recording material discrimination device, 10 control unit, 11 CPU, 12 RAM, 13 storage unit, 20 medium inspection unit, 21X, 21Y light irradiation unit, 22 light detection unit, 23X, 23Y element substrate, 24X, 24Y optical aperture, 25 paper passing guide, 30 image forming unit, 32 image forming unit, 31 intermediate transfer belt, 33 transfer roller, 40 fixing unit, 50 scanner, 60 operation display unit, 70 communication unit, 81 paper feed tray, 82 transport roller, 83 paper output tray, 90 bus, 131 program storage area, 132 data storage area, 211X, 211Y first light emitting element, 212X, 212Y second light emitting element, 220 light receiving element, 220A first light receiving element, 220B second light receiving element, 221A First filter, 221B second filter, Lr1, Lr2 reflected light, Lt1, Lt2 transmitted light, Lx1, Ly1 first inspection light, Lx2, Ly2 second inspection light, M recording material.

Claims

1. A paper discrimination device, a light source unit that irradiates light of two or more wavelengths onto the paper; a detection unit that acquires a detection result based on the absorption of each of the light beams of the two or more wavelengths in the paper; the light having two or more wavelengths includes light having a first wavelength and light having a second wavelength, the detection result includes a first detection value based on absorption of light of the first wavelength in the paper and a second detection value based on absorption of light of the second wavelength in the paper, The paper discrimination device a control unit that uses the first detection value and the second detection value to determine the type of the paper; the first wavelength is a wavelength in the range of 750 nm to 1100 nm; the second wavelength is a wavelength in the range of 400 nm to 500 nm; Using the first detection value and the second detection value calculating a first transmittance, which is the transmittance of light of the first wavelength through the paper, from the first detected value; calculating a second transmittance, which is the transmittance of light of the second wavelength through the paper, from the second detected value; and and deriving the type of the paper corresponding to a range to which the ratio or difference between the first transmittance and the second transmittance belongs.

2. A paper discrimination device, a light source unit that irradiates light of two or more wavelengths onto the paper; a detection unit that acquires a detection result based on the absorption of each of the light beams of the two or more wavelengths in the paper; the light having two or more wavelengths includes light having a first wavelength and light having a second wavelength, the detection result includes a first detection value based on absorption of light of the first wavelength in the paper and a second detection value based on absorption of light of the second wavelength in the paper, The paper discrimination device a control unit that uses the first detection value and the second detection value to determine the type of the paper; the first wavelength is a wavelength in the range of 750 nm to 1100 nm; the second wavelength is a wavelength in the range of 400 nm to 500 nm; A paper discrimination device in which deriving the paper type determination result includes identifying a range to which coordinates defined by values ​​based on the first detection value and values ​​based on the second detection value belong, out of two or more ranges in a figure having a vertical axis corresponding to values ​​based on the first detection value and a horizontal axis corresponding to values ​​based on the second detection value.

3. 3. The paper type discrimination device according to claim 2, wherein the two or more ranges in the graphic are distinguished from one another by straight lines that conform to a linear function.

4. Using the first detection value and the second detection value calculating a first transmittance, which is the transmittance of light of the first wavelength through the paper, from the first detected value; calculating a second transmittance, which is the transmittance of the light of the second wavelength through the paper, from the second detected value; and 4. The paper type discrimination device according to claim 2, further comprising: deriving a result of a given calculation using the first transmittance and the second transmittance.

5. the first detection value includes a light amount of light of the first wavelength transmitted through the paper; 5. The paper discrimination device according to claim 1, wherein the second detection value includes a light amount of the light of the second wavelength that has passed through the paper.

6. A paper discrimination device, a light source unit that irradiates light of two or more wavelengths onto the paper; a detection unit that acquires a detection result based on the absorption of each of the light beams of the two or more wavelengths in the paper; the light having two or more wavelengths includes light having a first wavelength and light having a second wavelength, the detection result includes a first detection value based on absorption of light of the first wavelength in the paper and a second detection value based on absorption of light of the second wavelength in the paper, The paper discrimination device a control unit that uses the first detection value and the second detection value to determine the type of the paper; the first detection value includes a light amount of light of the first wavelength transmitted through the paper; the second detection value includes a light amount of the light of the second wavelength transmitted through the paper; the first wavelength is a wavelength in the range of 750 nm to 1100 nm; the second wavelength is a wavelength in the range of 400 nm to 500 nm; A paper discrimination device that discriminates between plain paper and recycled paper based on the result of the paper type determination.

7. 7. The paper discrimination device according to claim 1, wherein the first wavelength is a wavelength in the range of 800 nm to 900 nm.

8. 8. The paper discrimination device according to claim 1, wherein the second wavelength is within a range of 420 nm to 480 nm.

9. A paper discrimination device, a light source unit that irradiates light of two or more wavelengths onto the paper; a detection unit for obtaining a detection result based on absorption of each of the light beams having the two or more wavelengths by the paper; a control unit that determines the type of paper based on whether the detection result satisfies two or more conditions, The light of two or more wavelengths includes light of wavelengths of 390 to 420 nm, light of wavelengths of 420 to 500 nm, light of wavelengths of 600 to 700 nm, and light of wavelengths of 750 to 1100 nm.

10. 10. The paper discrimination device according to claim 9, wherein the light of two or more wavelengths further includes light of a wavelength of 500 to 600 nm.

11. 11. The paper discrimination device according to claim 1, wherein the detection unit includes a photodiode or a phototransistor having a light receiving sensitivity equal to or greater than a given threshold value for all of the light of the two or more wavelengths.

12. 12. The paper discrimination device according to claim 1, wherein the light receiving element of the detection unit is disposed on a substrate on which the light source of the light source unit is disposed.

13. The paper discrimination device according to any one of claims 1 to 12, wherein the detection unit includes a single light receiving element that acquires a detection result based on absorption of each of the two or more wavelengths of light at a timing corresponding to each of the two or more wavelengths.

14. The detection unit two or more filters having different transmission characteristics for the two or more wavelengths of light; 13. The paper discrimination device according to claim 1, further comprising two or more light receiving elements to which the two or more filters are respectively attached.

15. The paper discrimination device according to any one of claims 1 to 14, wherein the light source unit is configured to irradiate light of two or more wavelengths toward a transport path for transporting paper within the paper discrimination device.

16. The paper discrimination device according to any one of claims 1 to 15, an image forming unit that forms an image on the paper.

17. irradiating light of two or more wavelengths onto a sheet of paper; and acquiring a detection result based on absorption of each of the two or more wavelengths of light in the paper, the light having two or more wavelengths includes light having a first wavelength and light having a second wavelength, the detection result includes a first detection value based on absorption of light of the first wavelength in the paper and a second detection value based on absorption of light of the second wavelength in the paper, deriving a determination result of the type of the paper using the first detection value and the second detection value, the first wavelength is a wavelength in the range of 750 nm to 1100 nm; the second wavelength is a wavelength in the range of 400 nm to 500 nm; Using the first detection value and the second detection value calculating a first transmittance, which is the transmittance of light of the first wavelength through the paper, from the first detected value; calculating a second transmittance, which is the transmittance of light of the second wavelength through the paper, from the second detected value; and A paper discrimination method comprising: deriving the type of the paper corresponding to a range to which a ratio or difference between the first transmittance and the second transmittance belongs.

18. irradiating light of two or more wavelengths onto a sheet of paper; and acquiring a detection result based on absorption of each of the two or more wavelengths of light in the paper, the light having two or more wavelengths includes light having a first wavelength and light having a second wavelength, the detection result includes a first detection value based on absorption of light of the first wavelength in the paper and a second detection value based on absorption of light of the second wavelength in the paper, deriving a determination result of the type of the paper using the first detection value and the second detection value, the first wavelength is a wavelength in the range of 750 nm to 1100 nm; the second wavelength is a wavelength in the range of 400 nm to 500 nm; A paper discrimination method in which deriving a paper type determination result includes identifying a range to which coordinates defined by values ​​based on the first detection value and values ​​based on the second detection value belong, out of two or more ranges in a figure having a vertical axis to which values ​​based on the first detection value correspond and a horizontal axis to which values ​​based on the second detection value correspond.

19. irradiating light of two or more wavelengths onto a sheet of paper; obtaining a detection result based on absorption of each of the two or more wavelengths of light in the paper; and deriving a determination result of the paper type based on whether the detection result satisfies two or more conditions, The light having two or more wavelengths includes light having a wavelength of 390 to 420 nm, light having a wavelength of 420 to 500 nm, light having a wavelength of 600 to 700 nm, and light having a wavelength of 750 to 1100 nm.

20. A program that, when executed by a computer, causes the computer to implement the paper discrimination method according to any one of claims 17 to 19.

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