SHEET DISCRIMINATING APPARATUS AND IMAGE FORMING APPARATUS

Abstract

A sheet discriminating apparatus includes a hardware processor that discriminates characteristics of a sheet. The light emitting element includes a reflective light emitting element and a transmission light emitting element. The sheet discriminating apparatus further includes a reflector that reflects the light when the sheet is not conveyed so that the reflected light enters the light receiving element. The reflective light emitting element includes a first reflective light emitting element that emits light with a first wavelength and a second reflective light emitting element that emits light with a second wavelength. The transmission light emitting element includes a first transmission light emitting element that emits the light with a third wavelength. The reflector is provided in a position that a reflectance of the light emitted by the reflective light emitting element is higher than the reflectance of the light emitted by the transmission light emitting element.

Claims

1. A sheet discriminating apparatus comprising: a hardware processor that discriminates characteristics of a sheet by receiving light emitted from a light emitting element to the sheet conveyed along a predetermined conveyor by a light receiving element, wherein, the light emitting element includes a reflective light emitting element that causes the light receiving element to receive light reflected off the sheet and a transmission light emitting element that causes the light receiving element provided at an opposing position to receive the light transmitted through the sheet, the sheet discriminating apparatus further includes a reflector that is provided at a position facing the reflective light emitting element and that reflects the light emitted by the reflective light emitting element when the sheet is not conveyed by the conveyor so that the reflected light enters the light receiving element provided so as to face the reflector, the reflective light emitting element includes a first reflective light emitting element that emits light with a first wavelength and a second reflective light emitting element that emits light with a second wavelength, the transmission light emitting element includes a first transmission light emitting element that is provided at a position facing the reflective light emitting element and that emits the light with a third wavelength, and the reflector is provided in a position that a reflectance of the light emitted by the reflective light emitting element is higher than the reflectance of the light emitted by the transmission light emitting element and transmitted through the sheet.

2. The sheet discriminating apparatus according to claim 1, wherein the first wavelength or the second wavelength is a wavelength within a range from 750 nm to 1100 nm.

3. The sheet discriminating apparatus according to claim 1, wherein, the transmission light emitting element includes a second transmission light emitting element that emits the light with a fourth wavelength, the reflective light emitting element includes a third reflective light emitting element that emits light with a fifth wavelength, and the first transmission light emitting element, the third reflective light emitting element, the second transmission light emitting element, and the second reflective light emitting element are sequentially irradiated with light from a light having a long wavelength.

4. The sheet discriminating apparatus according to claim 3, wherein the hardware processor discriminates whether the sheet is any one of a plain sheet, a recycled sheet, a coated sheet, and a color sheet.

5. The sheet discriminating apparatus according to claim 1, wherein the reflector is provided in a position that the reflectance of the light emitted from the transmission light emitting element to the sheet and scattered is 20% or less.

6. The sheet discriminating apparatus according to claim 1, wherein the reflector is provided so that the reflectance of the light emitted from the reflective light emitting element is 0.07(d.sub.0/d).sup.2 or more, where d.sub.0 is a distance between the light receiving element and the reflector, and d is a distance between the light receiving element and the sheet as a target to be subjected to a sheet type discrimination processing.

7. The sheet discriminating apparatus according to claim 1, wherein the reflector is provided outside the conveyor.

8. The sheet discriminating apparatus according to claim 7, wherein the reflective member is provided above the reflective light emitting element and the conveyor in an up-down direction.

9. The sheet discriminating apparatus according to claim 1, wherein, the conveyance member includes an opening in a range including a portion facing the light emitting element and the light receiving element, and the sheet discriminating apparatus further includes a transparent protective material that includes translucency in a manner that covers the opening.

10. The sheet discriminating apparatus according to claim 9, wherein the transparent protective material is provided in a manner that covers the opening on the light receiving element side and the reflector side.

11. An image forming apparatus comprising: the sheet discriminating apparatus according to claim 1; and an image former that forms an image on the sheet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinafter and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein:

[0010] FIG. 1 is a schematic side cross-sectional view of an image forming apparatus;

[0011] FIG. 2 is a block diagram of the image forming apparatus;

[0012] FIG. 3 is a schematic diagram of a sheet inspection section according to the first embodiment;

[0013] FIG. 4 is a flowchart of sheet type discrimination processing by the sheet inspection section according to the first embodiment;

[0014] FIG. 5 is a view for explaining an aspect of discrimination of recording material using a wavelength dependency of optical characteristics of first to third wavelengths;

[0015] FIG. 6 is a schematic diagram of a sheet inspection section according to a second embodiment;

[0016] FIG. 7 is a flowchart of sheet type discrimination processing by the sheet inspection section according to the first embodiment;

[0017] FIG. 8A is a view illustrating an aspect of discrimination of a recording material utilizing first, third, and fifth wavelength dependencies of optical characteristics of wavelengths;

[0018] FIG. 8B is a view for explaining an aspect of discrimination of the recording material utilizing wavelength dependencies of optical characteristics of first to third wavelengths;

[0019] FIG. 8C is a view illustrating an aspect of discrimination of the recording material utilizing wavelength-dependencies of optical characteristics of third and fifth wavelengths;

[0020] FIG. 9A is a graph illustrating a relationship between a reflectance of transmitted light of a reflector plate and an SN ratio of the transmitted light;

[0021] FIG. 9B is a graph illustrating the relationship between the reflectance of the transmitted light through the reflector plate and the SN ratio of the transmitted light;

[0022] FIG. 10A is a schematic diagram of a sheet inspection section according to a modification example; and

[0023] FIG. 10B is a schematic diagram of a sheet inspection section according to the modification example.

DETAILED DESCRIPTION

[0024] Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments.

[0025] Hereinafter, a sheet discriminating apparatus 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 disclosed embodiments. In the following description, components having the same functions and configurations are denoted by the same reference numerals, and a description thereof may be omitted.

[Overall Configuration of Image Forming Apparatus]

[0026] FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram of the image forming apparatus 1.

[0027] The image forming apparatus 1 is a multifunction peripheral (MFP) that forms an image on a sheet by an electrophotographic method. The image forming apparatus 1 includes a controller 10 (hardware processor), a sheet inspection section 20, an image forming section (image former) 30, a fixing section 40, a scanner 50, an operation/display part 60, a communicator 70, a sheet feed tray 81, a conveyance roller 82, a sheet ejection tray 83, and a bus 90.

[0028] Note that as illustrated in FIG. 2, the control unit 10 and the sheet inspection section 20 constitute a sheet discriminating apparatus 2 that discriminates a sheet. In addition, each unit of the image forming apparatus 1 is connected by a bus 90.

(Controller)

[0029] The controller 10 includes a central processing unit (CPU 11), a random access memory (RAM 12), and a storage section 13.

{CPU}

[0030] The CPU 11 reads and executes a program stored in a program storage area of the storage section 13 (or a program stored in a storage device outside the image forming apparatus 1) to perform various kinds of arithmetic processing.

{RAM}

[0031] The RAM 12 provides a working memory space for the CPU 11 and temporarily stores data.

{Storage}

[0032] The storage section 13 may be a hard disk drive (HDD), a solid state drive (SSD), or a nonvolatile storage device such as a flash memory.

[0033] The storage section 13 includes a program storage area and a data storage area. Data of various programs is stored in the program storage area. The data storage area stores, for example, image data acquired by the scanner 50, image data externally input via the communicator 70, and/or reference data to be referred to in a sheet discrimination operation described later.

[0034] The controller 10 comprehensively controls each part of the image forming apparatus 1 by the CPU 11 executing a program. For example, the controller 10 operates the components (in particular, the conveyance roller 82 and the fixing section 40) of the image forming section 30 on the basis of the image data stored in the storage section 13 to form an image on the sheet. Here, the CPU 11 changes the operation related to image formation of each section of the image forming apparatus 1 according to a discrimination result of the sheet by the sheet discriminating apparatus 2. In one example, conveyance speed and pinching pressure of the conveyance roller 82 are changed according to the type of sheet. Furthermore, heating temperature and applied pressure by the fixing section 40 are changed according to the type of the sheet.

[0035] The control unit 10 may include a dedicated circuit (application specific integrated circuit (ASIC), field-programmable gate array (FPGA), or the like) for realizing each function instead of the CPU 11 or in addition to the CPU 11.

(Sheet Inspection Section)

[0036] The sheet inspection section 20 performs processing for discriminating the sheet type of the sheet. The sheet inspection section 20 is provided at a position along a conveyance path on the upstream side of the image forming section 30 in the conveyance path of the sheet from the sheet feed tray 81 to the sheet ejection tray 83. However, the position of the sheet inspection section 20 is not limited to this, and the sheet inspection section 20 can be disposed at any position along the conveyance path.

[0037] The detailed configuration of the sheet inspection section 20 (sheet discriminating apparatus 2) will be described later.

(Image Forming Section)

[0038] The image forming section 30 applies toner (color material) to the sheet supplied from the sheet feed tray 81 to form the image. The image forming section 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 band-like member that is looped around a plurality of rollers and circulates.

{Image Forming Unit}

[0039] The image forming unit 32 is arranged along the intermediate transfer belt 31 and forms a toner image of respective colors of C (cyan), M (magenta), Y (yellow), and K (black) on the intermediate transfer belt 31 based on image data related to an image to be printed. When the sheet passes through a nip portion between the intermediate transfer belt 31 and the transfer roller 33, the toner image is transferred onto the sheet to form the image. In the present embodiment, the image forming section 30 capable of forming a color image is exemplified, but the present invention is not limited thereto, and the image forming section 30 capable of forming a monochrome image may be used.

(Fixing Section)

[0040] The fixing section 40 applies heat and pressure to the sheet to which the toner image is transferred, to fix the toner image to the sheet. The fixing section 40 includes a pair of rollers, which are a heating roller and a pressure roller, to sandwich the sheet. The sheet on which the toner image is fixed is conveyed by the conveyance roller 82 and delivered to the sheet ejection tray 83. Heating conditions and pressurization conditions by the fixing section 40 are controlled by the control unit 10 in accordance with the type of sheet and the like.

(Scanner)

[0041] The scanner 50 includes an optical system such as a light source and a mirror reflector, and an imaging element, reads the image of the sheet conveyed through the predetermined conveyance path or the sheet placed on a platen glass, and generates the image data in a bitmap format for each color of red (R), green (G), and blue (B). The generated image data is stored in the storage section 13. The read image can also be copied onto another sheet by performing image formation by the image forming section 30 based on this image data.

(Operation/Display Part)

[0042] The operation/display part 60 includes a display device, such as a liquid crystal display, and input devices, such as a touch screen and operation keys, overlaid on a screen of the display device. The operation/display part 60 performs various displays such as an operation status and a processing result of the image forming apparatus 1 in the display device and converts a user's input operation to the input device into an operation signal and outputs the operation signal to the control unit 10.

(Communicator)

[0043] The communicator 70 includes a network card or the like. The communicator 70 is connected to a communication network such as a local area network (LAN) so as to transmit information to and receive information from an external device on the communication network. The control unit 10 communicates with the external device on the communication network via the communicator 70.

(Sheet Feed Tray)

[0044] In the sheet feed tray 81, the sheet before image formation is stored. The sheet feed tray 81 may store a plurality of types of sheets.

[0045] The sheet type is characterized by at least one of the following characteristics: material (raw material) of the sheet, a state of surface treatment, presence or absence and amount of a fluorescent brightener, presence or absence of bluing, and the color. Therefore, sheets different from each other in at least one of these characteristics are different types of sheets. The types of sheets stored in the sheet feed tray 81 include, for example, plain sheet, colored sheet, recycled sheet, and coated sheet. Note that the type of sheet stored in the sheet feed tray 81 is not limited to the above.

[0046] The plain sheet is the sheet produced from wood-based pulp (i.e., pulp not recycled from waste sheet, usually chemical pulp) as a main raw material.

[0047] The colored sheet is the sheet to which a given proportion or more of dye is added.

[0048] The recycled sheet is the sheet in which waste sheet pulp extracted from waste sheet is blended at a predetermined blending ratio or more.

[0049] The coated sheet is, for example, the sheet obtained by coating about 20 to 40 g/m 2 of a coating material in which white pigments such as kaolin and calcium carbonate and an adhesive such as starch are mixed on the surfaces of high-grade printing sheet.

(Conveyance Roller)

[0050] The conveyance roller 82 rotates while pinching one sheet to convey the sheet along the conveyance path. The conveyance timing and the conveyance speed of the conveyance roller 82 is controlled by the control unit 10 in accordance with the type of sheet and the like.

(Sheet Ejection Tray)

[0051] The sheet ejection tray 83 holds the sheet on which the image has been formed until a user takes out the sheet.

[Configuration of Sheet Inspection Section]

First Embodiment

[0052] Next, a detailed configuration of the sheet inspection section 20 according to the first embodiment will be described with reference to FIG. 3.

[0053] The sheet inspection section 20 includes a light emitting element 21, a sensor 22, a reflective member (reflector) 23, and a conveyance member (conveyor) 24.

(Light Emitting Element)

[0054] The light emitting element 21 emits inspection light having a predetermined wavelength. The light emitting element 21 is, for example, a light emitting diode (LED). The light emitting element 21 includes a reflective light emitting element 211 that causes the sensor 22 to receive reflected light reflected off a sheet in sheet type discrimination processing described later. In addition, the light emitting element 21 includes a transmission light emitting element 212 that causes the sensor 22 to receive transmitted light transmitted through the sheet.

[0055] As illustrated in FIG. 3, the reflective light emitting element 211 is provided on the sensor 22 side. The transmission light emitting element 212 is provided on the same side as the reflective member 23. In addition, the reflective light emitting element 211 and the sensor 22, and the transmission light emitting element 212 and the reflective member 23 are provided at positions facing each other.

[0056] In the present embodiment, as illustrated in FIG. 3, a first reflective light emitting element 211a and a second reflective light emitting element 211b are provided as the reflective light emitting elements 211. In addition, a first transmission light emitting elements 212a is provided as the transmission light emitting element 212.

{First Reflective Light Emitting Element}

[0057] The first reflective light emitting element 211a emits first inspection light having a first wavelength. In the present embodiment, a peak wavelength of the first wavelength is 750 nm or more and 1100 nm or less. That is, the first inspection light is infrared light.

[0058] The reason why the wavelength being 750 nm or more is selected is to suppress the influence of bluing of the sheet. Bluing is adding a dye that exhibits a blue color to the sheet in order to improve the whiteness of the sheet. The blue-tinted sheet absorbs visible light having a wavelength other than the blue region, and reduces the reflectance of the visible light as compared with non-, blue-tinted sheet. Therefore, the wavelength that is 750 nm or more is selected because such wavelength is not affected by such bluing.

[0059] The reason why the wavelength being 1100 nm or less is selected is to suppress the influence of moisture contained in the sheet. The spectrum of the reflected light of the sheet with respect to the light having the wavelength longer than 1100 nm changes according to the moisture content of the sheet. To be more specific, a unique absorption band derived from a combined vibration of stretching motion and bending vibration of hydrogen atoms and oxygen atoms are present in 1450 nm and 1940 nm of moisture in the near infrared region, and this reduces the reflectance. Therefore, wavelengths equal to or shorter than 1100 nm, which are not affected by the moisture content of the sheet, are selected.

[0060] In this way, as the first inspection light, light having the first wavelength which is a near-infrared wavelength and in which a change in reflected light due to the material and raw material of the sheet is unlikely to occur is used.

{Second Reflective Light Emitting Element}

[0061] The second reflective light emitting element 211b emits second inspection light having a second wavelength. In the present embodiment, the peak wavelength of the second wavelength is 390 nm or more and 440 nm or less. That is, the second inspection light is violet light.

[0062] The reason why the wavelength being 390 nm or more and 440 nm or less is selected is that this is the wavelength at which the amount of absorption by the phosphor is small and the amount of absorption by the waste sheet pulp is large. That is, this is because the recycled sheet including waste sheet pulp can be discriminated by the irradiation with the second inspection light.

{First Transmission Light Emitting Element}

[0063] In the present embodiment, the first transmission light emitting element 212a emits third inspection light having a third wavelength. In the present embodiment, the third wavelength is 750 nm or more and 1100 nm or less. That is, the third inspection light is infrared light. Note that the reason why the wavelength being 750 nm or more and 1100 nm or less is selected is the same as that for the first reflective light emitting element 211a.

[0064] The first inspection light and the second inspection light are reflected off the surface of the sheet and enter the sensor 22. The third inspection light is transmitted through the back surface of the sheet and enters the sensor 22.

(Sensor)

[0065] 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 digital data, and outputs the voltage and the digital data to the controller 10.

[0066] Note that the sensor 22 is preferably provided at a position such that distances from the respective reflective light emitting elements 211 are equal but is not limited thereto.

(Reflective Member)

[0067] The reflective member 23 is a plate-shaped member provided to reflect the inspection light emitted from the light emitting element 21 and to make the inspection light incident on the light receiving element 220 when the light emitting element 21 is calibrated when the sheet does not pass.

[0068] The reflective member 23 is provided such that the reflectance of the third inspection light is lower than the reflectances of the first and second inspection light. As will be described later, the third inspection light passes through the sheet and is received by the sensor 22 in the sheet type discrimination process. However, when the reflectance of the first transmitted light by the reflective member 23 is high, part of the first transmitted light reflected off the sheet is received by the sensor 22 after being reflected off the reflective member 23. Such so-called ghost light reduces accuracy in discrimination of the sheet.

[0069] Therefore, when the reflective member 23 is provided so that the reflectance of the third wavelength is low, the generation of the ghost light itself can be suppressed, and the discrimination accuracy of the sheet can be further improved. Note that the reflectance of the inspection light in the reflective member 23 can be adjusted by, for example, adjusting the color of the reflective member 23.

[0070] As shown in FIG. 3, the reflective member 23 is preferably provided such that the reflectances of the first and second inspection light are 0.07(d.sub.0/d).sup.2 or more, where d.sub.0 is the distance between the light receiving surface of the light receiving element 220 and the reflective member 23, and d is the distance between the light receiving surface of the light receiving element 220 and the sheet to be subjected to the sheet type discrimination processing described later. With such a configuration, it is possible to suppress a decrease in the accuracy of discriminating the sheet type of the sheet.

[0071] The detailed description of the configuration of the above-described reflective member 23 will be described later.

(Conveyance Member)

[0072] The conveyance member 24 is a member that forms a conveyance path along which a sheet to be subjected to sheet type discrimination processing by the sheet inspection section 20 is conveyed. The conveyance member 24 includes an optical diaphragm 241 and a sheet passing guide 242.

[0073] The optical diaphragm 241 is a plate-shaped member disposed on the side of the sensor 22 and the reflective light emitting element 211 so that a principal surface thereof is perpendicular to the up-down direction. The optical diaphragm 241 includes an opening H in a range including a portion facing the light emitting element 21 and the sensor 22. The inspection light emitted by the light emitting element 21 enters the sheet through the opening H. The optical diaphragm 241 includes a light shielding property in a portion other than the opening H and suppresses light other than the inspection light from being incident on the sheet.

[0074] The sheet passing guide 242 is a plate-shaped member arranged on the side of the reflective member 23 and the transmission light emitting element 212 to support the sheet so that the sheet moves along the conveyance member 24.

[0075] Similarly to the optical diaphragm 241, the sheet passing guide 242 includes an opening H in a range including a portion facing the light emitting element 21 and the sensor 22.

[0076] As illustrated in FIG. 3, the reflective member 23 is provided outside (below) the sheet passing guide 242. When sheet dust of the sheet adheres to the reflective member 23, the reflection characteristic of the reflective member 23 changes. In this case, the light amount of the light emitting element 21 may be corrected to an incorrect light amount, and the discrimination accuracy of the sheet type discrimination process, which will be described later, may decrease. On the other hand, as illustrated in FIG. 3, when the reflective member 23 is provided outside the conveyance member 24, it is possible to prevent sheet dust of the sheet from adhering to the reflective member 23. In addition, with the above-described configuration, compared to a case where the reflective member 23 is provided on the inner side of the conveyance member 24, it is possible to suppress the generation of ghost light which will be described later.

[Sheet Type Discrimination Processing]

[0077] As described above, the light receiving element 220 of the sensor 22 receives the reflected light which is the inspection light emitted from each of the light emitting elements 21 and reflected by the sheet conveyed on the conveyance member 24. At this time, the light amount of the reflected light received by the light emitting element 213 increases or decreases according to absorption characteristics of light of each wavelength according to the sheet type of the sheet. Therefore, the controller 10 can discriminate the characteristics including the sheet type of the sheet from the reflection amount of the inspection light having each wavelength.

[0078] The sheet type discrimination processing by the sheet inspection section 20 according to the first embodiment will be described in detail with reference to the flowchart of FIG. 4. In the present embodiment, it is discriminated whether the sheet is the plain sheet or the recycled sheet. First, the controller 10 causes each of the light emitting elements 21 to emit the inspection light and calibrates the light amount of each of the light emitting elements 21 (step S101).

[0079] To be specific, before the sheet passes through the conveyance member 24, the controller 10 causes the first reflective light emitting element 211a and the second reflective light emitting element 211b to emit inspection light, causes the inspection light to be reflected off the reflective member 23, and causes the inspection light to be incident on the light receiving element 220. The controller 10 also causes the first transmission light emitting element 212a to emit inspection light, which is incident on the light receiving element 220. The sensor 22 converts each incident inspection light into a voltage, and outputs the voltage to the controller 10. The controller 10 determines whether the voltage value of each of the light emitting elements 21 is within a predetermined range and calibrates the light amount of the light emitting element 21 whose voltage value is outside the predetermined range.

[0080] The controller 10 stores, as the first to third reference voltages, the respective voltage values generated in the sensor 22 by the calibrated light emitting elements 21 (step S102).

[0081] Next, the controller 10 causes each of the light emitting elements 21 to sequentially irradiate the sheet conveyed in the gap between the optical diaphragm 241 and the sheet passing guide 242 with various kinds of inspection light.

[0082] The first inspection light and the second inspection light are reflected off the sheet, and thus first reflected light and second reflected light are generated and enter the light receiving element 220. Furthermore, when the third inspection light passes through the sheet, the first transmitted light is generated and enters the light receiving element 220. The sensor 22 converts the incident reflected light and transmitted light into voltages (hereinafter referred to as first to third discrimination voltages), and outputs the voltages to the controller 10. As described above, at this time, the light amounts of the reflected light and the transmitted light are influenced by the absorption characteristics of the inspection light having each wavelength in the sheet.

[0083] The controller 10 acquires the reflectance and the transmittance (hereinafter referred to as first and second reflectance and first transmittance) of each inspection light by (first to third discrimination voltage/first to third reference voltage) (step S103). Next, based on the acquired first and second reflectances and the first transmittance, the controller 10 discriminates the sheet type of the sheet as the plain sheet or the recycled sheet (step S104).

[0084] FIG. 5 is a diagram for explaining the discrimination method. In the graph illustrated 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.

[0085] In this way, by using the ratio of the reflectances of different wavelengths, it is possible to suppress the influence of the temporal change of the light receiving element 220 and the position fluctuation of the sheet. Further, since the transmittance has a smaller amount of change in the amount of received light due to a change in the position of the sheet than the reflectance, the characteristics including the sheet type of the sheet can be discriminated with higher accuracy.

[0086] The graph of FIG. 5 shows the respective values for the recycled sheet (triangular spot) and the plain sheet (circular spot). Furthermore, a line L1 illustrated in FIG. 5 is a line set to distinguish between the plain sheet and the recycled sheet. Information identifying the line L1 is stored in the storage section 13 as reference data. The controller 10 discriminates whether the sheet is the plain sheet or the recycled sheet according to whether the coordinates of the sheet are located above the line L1 in the graph of FIG. 5. In this way, in the sheet discrimination process, the controller 10 functions as a discrimination section that discriminates the characteristics including the sheet type of the sheet.

Second Embodiment

[0087] Next, the sheet inspection section 20 according to a second embodiment will be described with reference to FIG. 6. Note that contents that are the same as those of the first embodiment are denoted by the same reference signs, and a detailed description thereof will be omitted. The sheet inspection section 20 of the second embodiment is different from the first embodiment in that the sheet inspection section 20 of the second embodiment includes a third reflective light emitting element 211c and a second transmission light emitting element 212b. Furthermore, the sheet inspection section 20 according to the second embodiment is different from that according to the first embodiment in that the sheet inspection section 20 discriminates the sheet type of the sheet from the plain sheet, the recycled sheet, the coated sheet, and the colored sheet.

{Second Transmission Light Emitting Element}

[0088] The second transmission light emitting element 212b emits fourth inspection light having a fourth wavelength. In the present embodiment, the peak wavelength of the fourth wavelength is 430 nm or more and 490 nm or less. That is, the fourth inspection light is blue light.

[0089] The second transmission light emitting element 212b is provided on the reflective member 23 side in the same manner as the first transmission light emitting element 212a. That is, the sensor 22 receives the second transmitted light generated by being irradiated from the second transmission light emitting element 212 and transmitted through the sheet. Similarly to the first transmission light emitting element 212a, the second transmission light emitting element 212b calibrates the light amount by irradiating the sensor 22 with the inspection light when the conveyance member 24 is not conveying the sheet.

{Third Reflective Light Emitting Element}

[0090] The third reflective light emitting element 211c emits fifth inspection light having a fifth wavelength. In the present embodiment, the peak wavelength of the fifth wavelength is 620 nm or more and 750 nm or less. That is, the fifth inspection light is red light.

[0091] The third reflective light emitting element 211c is provided on the sensor 22 side similarly to the other reflective light emitting element 211. That is, the sensor 22 receives a third reflected light which is emitted from the third reflective light emitting element 211c and is reflected off the sheet. Similarly to the first reflective light emitting element 211a and the second reflective light emitting element 211b, the third reflective light emitting element 211c corrects the amount of light by irradiating the reflective member 23 with the inspection light when the conveyance member 24 is not conveying the sheet.

[Sheet Type Discrimination Processing]

[0092] The sheet discrimination processing performed by the sheet inspection section 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 transmission light emitting element 212b acquire the third reflectance and the second transmittance after calibrating the light amounts. Therefore, detailed description will be omitted.

[0093] The controller 10 discriminates whether the sheet is the colored sheet or the sheet other than colored sheet (the recycled sheet, the plain sheet, or the coated sheet) (step S204). FIG. 8A is a diagram for explaining the discrimination method. In the graph illustrated 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. Furthermore, the graph of FIG. 8A shows respective values for the colored sheet (triangular spot) and for the sheet other than colored sheet (circular spot). The controller 10 discriminates, based on the first and third reflectances and the first transmittance, whether the sheet is the colored sheet.

[0094] In a case where it is determined that the sheet is the colored sheet (step S204; Yes), the controller 10 ends the sheet type discrimination process. In a case where it is determined that the sheet is other than the colored sheet (step S204; No), the controller 10 discriminates whether the sheet is the recycled sheet or the sheet other than recycled sheet (the plain sheet or the coated sheet) (step S205). FIG. 8B is a diagram for explaining the discrimination method. As in step S104, the controller 10 discriminates, based on the first and second reflectances and the first transmittance, whether the sheet is the recycled sheet.

[0095] In a case where it is determined that the sheet is the recycled sheet (step S205; Yes), the controller 10 ends the sheet type discrimination process. In a case where it is determined that the sheet is the sheet other than the recycled sheet (step S205; No), the controller 10 discriminates whether the sheet is the plain sheet or the coated sheet (step S206). FIG. 8C is a diagram for explaining the discrimination method. In the graph illustrated in FIG. 8C, the horizontal axis represents the first transmittance, and the vertical axis represents the second transmittance. Furthermore, the graph of FIG. 8C shows respective values for the plain sheet (circular spot) and the coated sheet (rectangular spot). The controller 10 discriminates, based on the first and second transmittances, whether the sheet is the plain sheet or the coated sheet. Upon discriminating whether the sheet is the plain sheet or the coated sheet, the controller 10 ends the sheet type discrimination processing.

[0096] Note that in the sheet type discrimination processing according to the second embodiment, if the reflectances of the first and second transmitted light by the reflective member 23 are high, the ghost light is generated by the first and second transmitted light, thus degrading the accuracy of the sheet discrimination. Therefore, the reflective member 23 is preferably provided so that the reflectance of light having the third and fourth wavelengths is low. More specifically, the reflective member 23 is preferably provided such that the reflectance of the light emitted by the reflective light emitting element 211 is higher than the reflectance of the light emitted by the transmission light emitting element 212. With this configuration, the generation of the ghost light itself can be suppressed, and the accuracy in sheet discrimination can be further increased.

[Detailed Configuration of Reflective Member]

[0097] The relation between the reflective member 23 and the reflectance of the transmitted light will be described with reference to FIG. 9A and FIG. 9B. FIG. 9A and FIG. 9B are graphs each illustrating a relation between a reflectance of transmitted light of the reflective member 23 and a ratio of a voltage value of the transmitted light (signal) in accordance with the reflectance to a voltage value of the ghost light (noise) of the transmitted light.

[0098] In FIG. 9A and FIG. 9B, the horizontal axis represents the reflectance of the transmitted light of the reflective member 23. In FIG. 9A, the vertical axis represents the ratio of the transmitted light to the ghost light. In FIG. 9B, the vertical axis represents a logarithm of the ratio between the transmitted light and the ghost light. In addition, in FIG. 9A and FIG. 9B, a plurality of lines indicate the transmitted light in which the positions of the light emitting elements 21 as the light source being different from each other. Specifically, level 1 is an arrangement where the reflective member 23 is most likely to reflect the ghost light. Level 3 is an arrangement in which the reflective member 23 is least likely to reflect the ghost light.

[0099] As illustrated in FIG. 9A and FIG. 9B, it is found that setting the reflectance of the reflective member 23 to 0.2 (20%) or less drastically increases the SN ratio, that is, suppresses the occurrence of the ghost light. Therefore, the reflective member 23 is preferably provided such that the reflectance of the first transmitted light and the second transmitted light is 20% or less.

[0100] Furthermore, in the above-described sheet type discrimination processing, the value of the reflectance detected by the sensor 22 exceeds 1. As described above, the reflectance is calculated from the ratio between the discrimination voltage of the first, second, and fifth inspection light and the reference voltage. That is, the amount of light received by the sensor 22 during sheet passing is larger than the amount of light received by the sensor 22 during non-sheet passing.

[0101] In a case where the calibration of the light emitting element 21 is insufficient, the amount of light received by the sensor 22 during non-sheet passing decreases. Therefore, in a case where the value of the reflectance detected by the sensor 22 is large, the accuracy of sheet discrimination is low. Specifically, the value of the reflectance detected by the sensor 22 is preferably 10 or less.

[0102] As illustrated in FIG. 3, it is assumed that a distance between the light receiving surface of the light receiving element 220 and the reflective member 23 is d.sub.0 and a distance between the light receiving surface of the light receiving element 220 and the sheet as the target of the sheet type discrimination process is d. R is to be the reflectance of the reflective member 23, and r is to be the reflectance of the sheet. Then, the reflectance detected by the sensor 22 is obtained by (d.sub.0/d).sup.2r/R.

[0103] Since the reflectance r of the sheet is as low as about 70%, assuming r=0.7, it is sufficient that: (d.sub.0/d).sup.20.7/R10. Solving the above equation for R gives: (d.sub.0/d).sup.20.07R. From the above, it is preferable that the reflective member 23 is provided so that the reflectance of the inspection light emitted by the reflective light emitting element 211 is (d.sub.0/d).sup.20.07 or more. In particular, it is more preferable to set r=1 and provide the reflective member 23 such that the reflectance of the inspection light emitted by the reflective light emitting element 211 is (d.sub.0/d).sup.20.1 or more. With the above configuration, the calibration accuracy of the reflective light emitting element 211 can be increased, and the characteristics of the sheet can be discriminated with high accuracy.

[Effects of Embodiment]

[0104] As described above, in the sheet discriminating apparatus 2, the reflective member 23 is provided such that the reflectance of the light emitted by the reflective light emitting element 211 is higher than the reflectance of the light emitted by the transmission light emitting element 212. According to the configuration, it is possible to suppress the generation of the ghost light due to the inspection light emitted by the transmission light emitting element 212, and to discriminate the characteristics of the sheet with high accuracy.

[0105] Furthermore, the first wavelength or the second wavelength is the wavelength within a range from 750 nm to 1100 nm. According to the configuration, fluctuation of the reflected light caused by the material and raw material of the sheet is unlikely to occur, and the characteristics of the sheet can be discriminated with high accuracy.

[0106] In addition, the light emitted from the light emitting element 21 includes, in addition to the first wavelength used as a reference for other reflected wavelengths, the third wavelength, the fifth wavelength, the fourth wavelength, and the second wavelength in order from the longest wavelength. That is, the order is transmission, reflection, transmission, and reflection. With this structure, the sheet type of the sheet can be discriminated from the plain sheet, the coated sheet, the recycled sheet, and the colored sheet.

[0107] The reflective member 23 is provided so that the reflectance of the transmitted light is 20% or less. According to the above configuration, the generation of the ghost light can be suppressed, and the characteristic of the sheet can be discriminated with high accuracy.

[0108] Further, the reflective member 23 is provided outside the conveyance member 24. According to the above configuration, the sheet dust generated from the sheet is less likely to adhere to the reflective member 23, and the generation of the ghost light can also be suppressed. Therefore, the decrease in the calibration accuracy of the reflective light emitting element 211 can be suppressed, and the characteristics of the sheet can be discriminated with high accuracy.

[Other Configurations]

[0109] Although the present invention has been described in detail based on the embodiment, the present invention is not limited to the above-described embodiment. Of course, various modifications are possible within the scope of the invention described in the claims and their equivalents.

[0110] In the above description, in FIG. 3 and FIG. 6, a configuration in which the light emitting element 21 that generates reflected light is provided on the upper side and the reflective member 23 is provided on the lower side has been exemplified, but the invention is not limited thereto. For example, as illustrated in FIG. 10A, the reflective light emitting element 211 and the sensor 22 may be provided on the lower side, and the transmission light emitting element 212 and the reflective member 23 may be provided on the upper side. With the above-described configuration, sheet dust of the sheet is less likely to adhere to the reflective member 23 due to gravity. Therefore, the influence of the sheet dust adhering to the reflective member 23 can be reduced.

[0111] In addition, as illustrated in FIG. 10B, a transparent protective material W may be provided in a manner covering the opening H, which isolates the conveyance member 24 and the reflective member 23 from each other. The transparent protective material W is a transparent plate-shaped body that transmits light emitted by the light emitting element 21. With this configuration, the transparent protective material W can suppress adhesion of the sheet dust of the sheet to the reflective member 23. Furthermore, as illustrated in FIG. 10B, when the transparent protective material W and the conveyance member 24 are close to each other, the sheet dust can be blown off at the time of conveying the sheet.

[0112] Note that, although the transparent protective material W is provided so as to cover both the upper opening H and the lower opening H of the conveyance member 24 in FIG. 10B, it is not limited thereto. For example, the transparent protective material W may be provided only in the opening H above the conveyance member 24. In the above-described configuration, it is possible to prevent sheet dust from adhering to the sensor 22.

[0113] Furthermore, in the above description, it is assumed that the sheet dust adheres to the reflective member 23, but the sheet dust may also adhere to a part other than the reflective member 23, and the inspection light reflected off the sheet dust adhering to the part other than the reflective member 23 may enter the sensor 22, resulting in a decrease in the accuracy of discriminating the sheet type. Therefore, the conveyance member 24 and the transparent protective material W may also be adjusted to includes substantially the same reflection characteristics as the reflective member 23, and with the above-described configuration, the sheet type can be discriminated with higher accuracy.

[0114] In addition, in the above description, the sheet inspection section 20 including three or five light emitting elements 21 is exemplified, but the number of light emitting elements may be four or six or more.

[0115] Although embodiments of the present invention have been described and shown in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.