JP2024070594A - Paper type discrimination device and image forming device - Google Patents

Abstract

[Problem] To improve the accuracy of identifying paper types. [Solution] A light-emitting element that emits light and a light-receiving element that receives reflected or transmitted light irradiated from the light-emitting element onto paper on a light-receiving surface are provided with a plurality of the other element for each of the light-emitting elements and the light-receiving elements. The substrate has a support surface that supports the other of the plurality of light-emitting elements and the light-receiving elements. In a surface direction along the surface of the paper, the distance between the first light-emitting and receiving point and the second light-emitting and receiving point is r1, and the distance between the first light-emitting and receiving point and the third light-emitting and receiving point is r2. In a normal direction to the surface of the paper, the distance between the support surface and the second light-emitting and receiving point is h1, the distance between the support surface and the third light-emitting and receiving point is h2, the distance between the first light-emitting and receiving point and the paper is z0, and the distance between the second light-emitting and receiving point and the paper is z1. If A = (r2-r1)/(h2-h1) and x = 2r1/(z0+z1), then A and x satisfy k1/x+a1.x+b1≦A≦k2/x+a2.x+b2. [Selected figure] Figure 15

Description

This disclosure relates to a paper type discrimination device and an image forming device.

The fixing conditions of an image forming device vary depending on the paper type, so settings according to the paper type are necessary. Conventionally, the user would input the paper type into an operation panel, but in recent years, paper type discrimination devices have become known that use sensors to automatically determine the paper type and change the settings. Some paper type discrimination devices that automatically determine the paper type determine the paper type based on the amount of reflected light and transmitted light when light is irradiated onto the paper.

International Publication No. WO 2018/029884 (Patent Document 1) describes a method of irradiating paper with light from multiple light sources with different wavelengths and using the reflected light to identify the paper type. Japanese Patent Application Laid-Open No. 2019-056613 (Patent Document 2) describes a method of receiving reflected light from a light source with multiple sensors to identify the paper type.

International Publication No. 2018/029884 JP 2019-056613 A

If the position of the paper being identified changes, the amount of light received by the multiple sensors that receive the reflected light changes relatively, which can reduce the accuracy of identifying the paper type.

This disclosure proposes technology that can improve the accuracy of identifying paper types.

In the present disclosure, the following paper type discrimination device is proposed.
(1) The paper type discrimination device includes a light-emitting element and a light-receiving element. The light-emitting element irradiates light toward the paper. The light-receiving element has a light-receiving surface that receives light, and detects reflected or transmitted light of the light irradiated from the light-emitting element to the paper. For each of the light-emitting element and the light-receiving element, a plurality of the other of the light-emitting element and the light-receiving element are provided. Either the light-emitting element or the light-receiving element has a first light-emitting and receiving point. The other of the light-emitting element and the light-receiving element has a second light-emitting and receiving point and a third light-emitting and receiving point. The light-emitting and receiving point is the position of a virtual image point of a light ray emitted from the light-emitting element, or a virtual image point on the light-receiving surface of the light-receiving element. The paper type discrimination device further includes a substrate. The substrate has a support surface that supports the other of the plurality of light-emitting elements and the plurality of light-receiving elements. The distance between the first light-emitting and receiving point and the second light-emitting and receiving point in the surface direction along the surface of the paper is defined as r1. The distance between the first light-emitting and receiving point and the third light-emitting and receiving point in the surface direction is r2. The distance between the support surface and the second light-emitting and receiving point in the normal direction of the paper surface is h1. The distance between the support surface and the third light-emitting and receiving point in the normal direction is h2. The distance between the first light-emitting and receiving point and the paper in the normal direction is z0. The distance between the second light-emitting and receiving point and the paper in the normal direction is z1. A=(r2-r1)/(h2-h1). x=2r1/(z0+z1). A and x satisfy the relational expression k1/x+a1.x+b1≦A≦k2/x+a2.x+b2. However, k1=0.059, a1=-1.050, b1=0.304, k2=0.714, a2=-0.467, b2=0.0666.

(2) In the paper type discrimination device described in 1, the distance between the light emitting element and the light receiving element in the surface direction may be reduced as the distance between the support surface and the light receiving point in the normal direction increases.

(3) In the paper type discrimination device described in 1 or 2, x may satisfy the relational expression x ≧ 0.84.

(4) In the paper type discrimination device described in any one of paragraphs 1 to 3, the light-emitting element may have Lambertian characteristics.

(5) In the paper type discrimination device described in any one of paragraphs 1 to 4, the support surface may be flat, and either the light-emitting element or the light-receiving element may be disposed on the support surface.

(6) In the paper type discrimination device described in any one of paragraphs 1 to 5, the paper type may be discriminated using the ratio of the amount of light emitted by the other of the multiple light-emitting elements and the multiple light-receiving elements and received by either the light-emitting element or the light-receiving element, i.e., the ratio of the amount of light emitted by each of the multiple light-emitting elements and received by the light-receiving element. Alternatively, the paper type may be discriminated using the ratio of the amount of light received by the other of the multiple light-emitting elements and the multiple light-receiving elements, i.e., the ratio of the amount of light received by each of the multiple light-receiving elements.

(7) In the paper type discrimination device described in any one of paragraphs 1 to 6, multiple light-emitting elements may be provided for each light-receiving element.

(8) In the paper type discrimination device described in 7, three or more light emitting elements may be provided for each light receiving element.

(9) In the paper type discrimination device described in 8, a light-emitting element in which the distance between the support surface and the virtual image point of the light-emitting element in the normal direction is neither maximum nor minimum may be used as a reference light-emitting element having a second light-receiving point.

(10) In the paper type discrimination device described in paragraph 8 or 9, three or more light-emitting elements may be arranged in close proximity, and a light-emitting element that is not arranged at the end of the row of light-emitting elements may be used as a reference light-emitting element having a second light-receiving point.

(11) In the paper type discrimination device described in any one of paragraphs 7 to 10, the multiple light-emitting elements include a reference light-emitting element having a second light-receiving point and another light-emitting element different from the reference light-emitting element, the other light-emitting element is arranged with the light-receiving element sandwiched between it and the reference light-emitting element, the angle between a straight line passing through the virtual image point of the reference light-emitting element and the virtual image point on the light-receiving surface of the light-receiving element and a straight line passing through the virtual image point of the other light-emitting element and the virtual image point on the light-receiving surface of the light-receiving element is 150° or more and 210° or less, and x may satisfy the relational expression 1.41≦x≦1.89.

(12) In the paper type discrimination device described in 11, x may satisfy the relational expression 1.67≦x≦1.82.

(13) In the paper type discrimination device described in any one of paragraphs 1 to 12, the light-emitting element has a light-emitting surface from which light is emitted, and the light-emitting surface may be a plane parallel to the surface direction.

(14) In the paper type discrimination device described in any one of paragraphs 1 to 13, the paper type of the paper may be discriminated while the paper is being transported.

(15) In the paper type discrimination device described in any one of paragraphs 1 to 6, paragraph 13 not citing any one of paragraphs 7 to 12, or paragraph 14 not citing any one of paragraphs 7 to 12, multiple light receiving elements may be provided for each light emitting element.

The present disclosure proposes the following image forming apparatus.
(Item 16) An image forming apparatus includes the paper type discrimination device according to any one of items 1 to 15 above, and an image forming unit that forms an image on paper.

This disclosure makes it possible to improve the accuracy of identifying paper types.

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus. FIG. 2 is a diagram illustrating a hardware configuration of an image forming apparatus. FIG. 2 is a diagram illustrating an example of a configuration of an inspection unit. 11A and 11B are diagrams illustrating a state in which reflected light is detected when a sheet passes through an inspection unit. 13A and 13B are diagrams illustrating a state in which reflected light is detected when a sheet of paper does not pass through an inspection unit. 13A and 13B are diagrams illustrating a detection state of transmitted light when a sheet of paper passes through an inspection unit. 13A and 13B are diagrams illustrating a detection state of transmitted light when a sheet of paper does not pass through an inspection unit. FIG. 2 is a diagram illustrating a first example of the configuration of a reflective light-emitting element. FIG. 13 is a diagram illustrating a second example of the configuration of the reflective light-emitting element. FIG. 13 is a diagram illustrating a third example of the configuration of a reflective light-emitting element. FIG. 13 is a diagram illustrating a fourth example of the configuration of a reflective light-emitting element. FIG. 2 is a first diagram showing a first example of a positional relationship between a light-emitting element and a light-receiving element; FIG. 2 is a second diagram showing a first example of the positional relationship between a light-emitting element and a light-receiving element. 11 is a graph showing ideal arrangement conditions of optical elements that maintain the ratio of the amount of light received by the light receiving elements even when the paper position fluctuates. 1 is a graph showing deviations from ideal arrangement conditions of optical elements. FIG. 11 is a first diagram showing a second example of the positional relationship between a light-emitting element and a light-receiving element. FIG. 11 is a second diagram showing a second example of the positional relationship between the light-emitting element and the light-receiving element. 11 is a diagram showing angles formed between a plurality of light-emitting elements and a light-receiving element. FIG. 10 is a first diagram showing the effect of the arrangement of optical elements on the ratio of the amount of light received by light receiving elements when the position of the paper changes; FIG. 13 is a second diagram showing the effect of the arrangement of the optical elements on the ratio of the amount of light received by the light receiving elements when the position of the paper changes. FIG. 13 is a diagram showing a third example of the positional relationship between a light-emitting element and a light-receiving element; FIG. 13 is a diagram showing a fourth example of the positional relationship between a light-emitting element and a light-receiving element. FIG. FIG. 11 is a first diagram showing a fifth example of the positional relationship between a light-emitting element and a light-receiving element. FIG. 13 is a second diagram showing a fifth example of the positional relationship between a light-emitting element and a light-receiving element. FIG. 13 is a diagram showing a sixth example of the positional relationship between a light-emitting element and a light-receiving element. 11 is a table showing the effect of the arrangement of optical elements on the ratio of the amount of light received by the light receiving elements in the example.

The following describes the embodiments with reference to the drawings. In the following description, identical parts and components are given the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of these will not be repeated. It is also intended from the outset that any configuration may be extracted from the embodiments and that they may be combined in any manner.

<Configuration of Image Forming Apparatus 1>
First, a configuration of an image forming apparatus to which a paper type discrimination device according to an embodiment is applied will be described. Fig. 1 is a diagram showing a schematic configuration of the image forming apparatus 1. Fig. 2 is a diagram showing a hardware configuration of the image forming apparatus 1.

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

As shown in FIG. 2, the control unit 10 and the inspection unit 20 constitute a paper type discrimination device 2 that discriminates the paper type. The control unit 10, the inspection unit 20, the image forming unit 30, the fixing unit 40, the scanner 50, the operation panel 60, and the communication unit 70 are connected by a bus 90.

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

Storage 13 stores program 131 and reference data 132 referenced in the paper type discrimination process. Program 131 includes computer-readable instructions for controlling image forming device 1. Processor 11 performs various types of arithmetic processing by expanding program 131 stored in storage 13 into memory 12 and executing it.

Program 131 may be provided not as a standalone program, but as part of an arbitrary program. In this case, the processing according to this embodiment is executed in cooperation with the arbitrary program. Even if the program does not include some of these modules, this does not deviate from the spirit of the image forming device 1 according to this embodiment. Some or all of the functions provided by program 131 may be executed by dedicated hardware.

The storage 13 also stores at least one of image data received from an external device and image data generated by the scanner 50.

The control unit 10 controls each part of the image forming device 1 by the processor 11 executing the program 131. For example, the processor 11 operates the image forming section 30, the transport roller 82, and the fixing section 40 based on the image data stored in the storage 13 to form an image on paper. Here, the processor 11 changes the operation of each part involved in image formation (for example, the image forming section 30, the transport roller 82, and the fixing section 40) according to the paper type discrimination result by the paper type discrimination device 2. As one example, the processor 11 changes the transport speed and clamping pressure of the transport roller 82 according to the paper type. In addition, the processor 11 changes the heating temperature and applied pressure of the fixing section 40 according to the paper type.

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

The inspection section 20 includes a light source unit 21 and a detection unit 22. The light source unit 21 irradiates light toward the transport path 27 in accordance with instructions from the processor 11. The detection unit 22 detects the light from the paper.

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

The fixing unit 40 applies heat and pressure to the paper onto which the toner image has been transferred, fixing the toner image to the paper. The fixing unit 40 includes a pair of rollers consisting of a heating roller and a pressure roller that hold the paper. The paper onto which the toner image has been fixed is transported by transport rollers 82 and discharged onto the paper output tray 83. The heating and pressure conditions used by the fixing unit 40 are controlled by the processor 11 according to the type of paper.

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

The operation panel 60 includes a display device such as a liquid crystal display, and an input device such as a touch panel that is arranged over the screen of the display device. The operation panel 60 displays various information such as the operational status and processing results of the image forming device 1 on the display device, and converts user input operations on the input device into operation signals and outputs them to the processor 11.

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

The paper feed tray 81 holds paper before image formation. The paper feed tray 81 may hold multiple types of paper.

The transport rollers 82 rotate while holding a sheet of paper, transporting the sheet along the transport path 27. The transport timing and transport speed of the transport rollers 82 are controlled by the processor 11 according to the type of paper. The paper output tray 83 holds the paper on which an image has been formed.

The image forming device 1 is not limited to an MFP and may be, for example, a production print machine.

<Configuration of Inspection Unit 20>
The configuration of the inspection unit 20 will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of the configuration of the inspection unit 20.

Arrow A1 in FIG. 3 indicates the direction in which paper M is transported (hereinafter referred to as the "transport direction"). The transport direction is a direction along the surface of paper M. Arrow A2 indicates the normal direction to the surface of paper M. Arrow A2 indicates the thickness direction of paper M. The direction indicated by arrow A2 is perpendicular to the surface of paper M. The direction indicated by arrow A2 is perpendicular to the transport direction of paper M. Hereinafter, the direction indicated by arrow A2 will be referred to as the "normal direction" perpendicular to the surface of the paper. In FIG. 3, the transport direction is the left-right direction in the figure, and the normal direction is the up-down direction in the figure.

The inspection unit 20 includes a light source unit 21, a detection unit 22, element substrates 23X and 23Y, optical apertures 24X and 24Y, a paper guide 25, and a reflecting unit 26. The paper M is transported along a transport path 27 provided between the optical aperture 24X and the paper guide 25.

The light source unit 21 includes a reflected light emitting element 21X and a transmitted light emitting element 21Y. The reflected light emitting element 21X and the detection unit 22 are located on the same side of the paper M. The reflected light emitting element 21X includes a first reflected light emitting element 211X and a second reflected light emitting element 212X. The first reflected light emitting element 211X and the second reflected light emitting element 212X are, for example, LEDs (Light-Emitting Diodes).

The transmitted light emitting element 21Y is located on the opposite side of the paper M from the side on which the detection unit 22 is located. That is, in the normal direction, the transmitted light emitting element 21Y, the transport path 27, and the detection unit 22 are located in this order. The transport path 27 is located between the transmitted light emitting element 21Y and the detection unit 22. The transmitted light emitting element 21Y is, for example, an LED.

While the paper passes through the inspection section 20, the processor 11 causes the first reflected light emitting element 211X, the second reflected light emitting element 212X, and the transmitted light emitting element 21Y to emit light so that their emission timing does not overlap. The first reflected light emitting element 211X, the second reflected light emitting element 212X, and the transmitted light emitting element 21Y each emit light and emit light, which is irradiated toward the paper M being transported along the transport path 27.

The detection unit 22 includes a light receiving element 220. The light receiving element 220 is, for example, a photodiode. A photodiode can detect light with a longer wavelength more easily. The light receiving element 220 detects the incident light and outputs a photocurrent according to the amount of incident light. The detection unit 22 converts the photocurrent output by the light receiving element 220 into a voltage, converts the voltage into digital data, and outputs it to the processor 11.

The element substrates 23X and 23Y are provided at positions facing the paper M being transported along the transport path 27. The surface of the element substrate 23X facing the paper M is perpendicular to the normal direction, and a first reflected light emitting element 211X, a second reflected light emitting element 212X, and a light receiving element 220 are provided on this surface. The surface of the element substrate 23Y facing the paper M is perpendicular to the normal direction, and a transmitted light emitting element 21Y is provided on this surface.

The optical aperture 24X is located between the paper guide 25 and the element substrate 23X. The optical aperture 24Y is located between the paper guide 25 and the element substrate 23Y. The optical aperture 24X has an opening 28X in a range including the portion facing the first reflected light emitting element 211X, the second reflected light emitting element 212X, and the light receiving element 220. The optical aperture 24Y has an opening 28Y in a range including the portion facing the transmitted light emitting element 21Y.

The light emitted from the reflected light emitting element 21X passes through the opening 28X and is irradiated onto the paper M. The light emitted from the transmitted light emitting element 21Y passes through the opening 28Y and is irradiated onto the paper M. The optical aperture 24X has a light blocking property other than the opening 28X, and the optical aperture 24Y has a light blocking property other than the opening 28Y, so that light other than the irradiation light emitted by the light source unit 21 is prevented from being irradiated onto the paper M.

The paper guide 25 supports the paper M so that the paper M moves along the transport path 27 .
The reflecting section 26 is provided at a position facing the reflected light emitting element 21X. The reflecting section 26 reflects the light emitted from the reflected light emitting element 21X. The reflecting section 26 is used to evaluate the reflectivity of the paper.

<Reflected light and reflectance>
The detection of reflected light and the calculation of reflectance will be described with reference to Figures 4 and 5. Reflectance is an index used to evaluate the reflectivity of paper.

Figure 4 is a diagram showing the detection state of reflected light when paper M passes through the inspection section 20. When the first irradiation light Lx1 is irradiated onto paper M from the first reflected light emitting element 211X at the timing when paper M passes through the inspection section 20, the light receiving element 220 detects reflected light Lr1 as light from paper M. The reflected light Lr1 includes light of the first irradiation light Lx1 that is reflected by paper M. When paper M includes a phosphor, the reflected light Lr1 further includes fluorescence emitted by the phosphor that absorbs the first irradiation light Lx1.

When the second irradiation light Lx2 is irradiated onto the paper M from the second reflected light emitting element 212X at the timing when the paper M passes through the inspection section 20, the light receiving element 220 detects the reflected light Lr2 as light from the paper M. The reflected light Lr2 includes the light of the second irradiation light Lx2 that is reflected by the paper M. When the paper M includes a phosphor, the reflected light Lr2 further includes the fluorescence emitted by the phosphor that absorbs the second irradiation light Lx2.

The detection unit 22 acquires the light intensity of each of the reflected lights Lr1 and Lr2, and outputs the light intensity to the processor 11.

Figure 5 shows the detection state of reflected light when paper M has not passed through the inspection section 20.

When the first reflected light emitting element 211X emits the first irradiation light Lx1 at a timing when the paper M has not passed through the inspection section 20, the light receiving element 220 detects the reflected light sLr1 reflected by the reflecting section 26.

When the second reflected light emitting element 212X emits the second irradiation light Lx2 at a timing when the paper M has not passed through the inspection section 20, the light receiving element 220 detects the reflected light sLr2 reflected by the reflecting section 26.

The detection unit 22 acquires the light amount of each of the reflected lights sLr1 and sLr2, and outputs the light amount to the processor 11. The processor 11 stores the light amount of each of the reflected lights sLr1 and sLr2 in the storage 13.

In this disclosure, reflectance is calculated by processor 11 using Equation 1 below.
Reflectance=light amount Lr/light amount sLr (Equation 1)
The light amount Lr in Equation 1 indicates the amount of light detected by the light receiving element 220 when light is emitted from the reflected light emitting element 21X and reflected by the paper M at the timing when the paper M passes through the inspection unit 20. Each of the light amounts of the reflected light Lr1 and the reflected light Lr2 is an example of the light amount Lr.

The light amount sLr in Equation 1 indicates the amount of light reflected by the reflecting section 26 and detected by the light receiving element 220 when light is emitted from the reflected light emitting element 21X at a timing when the paper M has not passed through the inspection section 20. Each of the light amount of the reflected light sLr1 and the light amount of the reflected light sLr2 is an example of the light amount sLr.

<Transmitted light and transmittance>
Detection of transmitted light and calculation of transmittance will be described with reference to Figures 6 and 7. Transmittance is an index used to evaluate the transparency of paper.

Figure 6 is a diagram showing the detection state of transmitted light when paper M passes through the inspection section 20. When irradiation light Ly is irradiated from the transmitted light emitting element 21Y at the timing when paper M passes through the inspection section 20, the light receiving element 220 detects transmitted light Lt as light from the paper M. The transmitted light Lt includes light of the irradiated light Ly that has passed through the paper M. When the paper M includes a phosphor, the transmitted light Lt further includes fluorescence emitted by the phosphor that absorbs the irradiated light Ly.

The detection unit 22 acquires the amount of transmitted light Lt and outputs the amount of light to the processor 11.

Figure 7 is a diagram showing the detection state of transmitted light when the paper M has not passed through the inspection section 20. When the transmitted light emitting element 21Y irradiates the irradiated light Ly at a timing when the paper M has not passed through the inspection section 20, the light receiving element 220 detects the irradiated light Ly.

The detection unit 22 acquires the amount of light of the irradiated light Ly and outputs the amount of light to the processor 11. The processor 11 stores the amount of light of the irradiated light Ly in the storage 13.

In this disclosure, the transmittance is calculated by the processor 11 using Equation 2 below.
Transmittance=light amount Lt/light amount Ly (Equation 2)
The light amount Lt in Equation 2 indicates the amount of light detected by the light receiving element 220 when light is emitted from the transmitted light emitting element 21Y at the timing when the paper M passes through the inspection unit 20. The light amount of the transmitted light Lt is an example of the light amount Lt.

The light quantity Ly in Equation 2 indicates the amount of light detected by the light receiving element 220 when light is emitted from the transmitted light emitting element 21Y at a timing when the paper M has not passed through the inspection unit 20. The light quantity of the irradiated light Ly is an example of the light quantity Ly.

<Example of paper type discrimination process>
The paper stored in the paper feed tray 81 (FIG. 1) is characterized by at least one of the following characteristics: the paper material (raw material), the state of the surface treatment, the presence or absence of phosphor, the amount of phosphor, and the color of the paper. Therefore, papers that differ from each other in at least one of these characteristics are different types of paper. The types of paper stored in the paper feed tray 81 include, for example, plain paper, coated paper, a first type of recycled paper, and a second type of recycled paper.

Plain paper is paper made primarily from wood-based pulp (i.e., pulp that is not recycled from waste paper, usually chemical pulp). Coated paper is paper that has a coating applied to both sides. Recycled paper is paper that contains a certain or higher percentage of waste paper pulp extracted from waste paper. Waste paper pulp is prone to absorbing light with a peak wavelength of less than 550 nm (i.e., light with a wavelength shorter than green).

The first type of recycled paper is recycled paper that does not contain much phosphor, i.e., recycled paper with little phosphor. The second type of recycled paper is recycled paper that contains a lot of phosphor, i.e., recycled paper with a high phosphor content. The second type of recycled paper contains more phosphor than the first type of recycled paper. Also, the second type of recycled paper contains more phosphor than coated paper. Generally, phosphors contained in paper absorb ultraviolet light and emit light (fluorescence) that has a longer wavelength than ultraviolet light.

The process of optically determining the paper type by the paper type determination device 2 of the embodiment is started when the paper M reaches the inspection unit 20. The paper type determination process includes a light amount detection process by the inspection unit 20 and a determination process by the processor 11.

The light amount detection process by the inspection unit 20 includes detecting the amount of reflected light Lr1, the amount of reflected light Lr2, and the amount of transmitted light Lt, and outputting the detected light amounts to the processor 11. The determination process by the processor 11 includes calculating the reflectance and transmittance based on the amount of light obtained from the inspection unit 20, and determining the paper type based on the calculated reflectance and transmittance.

For example, recycled paper has a lower light reflectance than other paper types due to light absorption by waste paper pulp. On the other hand, if the recycled paper contains a large amount of fluorescent material, the amount of light detected by the light receiving element 220 increases by the amount of fluorescence, so that the light reflectance of the recycled paper is high. Therefore, a first threshold value and a second threshold value greater than the first threshold value can be set for the light reflectance.

For example, if the transmittance of infrared wavelengths of the same paper is used as a standard, the transmittance of short wavelengths is higher for plain paper than for recycled paper and coated paper. Therefore, a third threshold value can be set for the light transmittance.

The first threshold, the second threshold, and the third threshold constitute the reference data 132 (Figure 2) and are stored in the storage 13.

The processor 11 can determine that a paper type whose light transmittance is equal to or greater than a third threshold is plain paper, and can determine that a paper type whose light transmittance is less than the third threshold is coated paper or recycled paper. For paper types whose light transmittance is less than the third threshold, the processor 11 can determine that the paper type is recycled paper with less phosphor if the light reflectance is less than a first threshold, can determine that the paper type is coated paper if the light reflectance is equal to or greater than the first threshold and less than a second threshold, and can determine that the paper type is recycled paper with more phosphor if the light reflectance is equal to or greater than the second threshold.

To improve the accuracy of identifying the paper M, the wavelength range of the light irradiated onto the paper M may be appropriately selected.

<Configuration of Reflected Light Emitting Element 21X and Light Emitting Point Height>
Next, the configuration of the reflected light emitting element 21X and the light emitting point height of the reflected light emitting element 21X will be described.

Figure 8 is a diagram showing a first example of the configuration of the reflected light emitting element 21X. The element substrate 23X has a support surface 23X1 that supports the reflected light emitting element 21X (and the detection unit 22). The support surface 23X1 is the surface of the element substrate 23X that faces the paper M. The support surface 23X1 has a flat shape. The support surface 23X1 is a plane perpendicular to the normal direction. The support surface 23X1 is a plane parallel to the transport direction of the paper M and parallel to the width direction of the paper M. The reflected light emitting element 21X is disposed on the support surface 23X1.

The reflected light emitting element 21X shown in FIG. 8 has a base 21X1 and a light source 21X2. The base 21X1 is mounted on a support surface 23X1. The light source 21X2 is mounted on the upper surface of the base 21X1. The light source 21X2 emits light. The light source 21X2 is, for example, an LED chip. The light source 21X2 has a light emitting surface 21X4. The light emitting surface 21X4 is a surface from which light is emitted from the reflected light emitting element 21X. In FIG. 8, the light emitting surface 21X4 is a flat surface. In FIG. 8, the light emitting surface 21X4 is a flat surface parallel to the transport direction of the paper M and parallel to the width direction of the paper M.

In the reflected light emitting element 21X shown in FIG. 8, the light source 21X2 is not sealed with resin and is exposed to the atmosphere. In this case, as shown in FIG. 8, the distance between the support surface 23X1 of the element substrate 23X and the light emitting surface 21X4 in the direction perpendicular to the support surface 23X1 is defined as the light emitting point height.

Figure 9 is a diagram showing a second example of the configuration of the reflected light emitting element 21X. In the reflected light emitting element 21X shown in Figure 9, a recess is formed on the upper surface of the base 21X1 (the surface facing away from the element substrate 23X), with a portion of the upper surface being recessed. The light source 21X2 is mounted on the bottom surface of the recess. The reflected light emitting element 21X has a sealing resin 21X3 that is filled in the recess of the base 21X1. The light source 21X2 is sealed with the sealing resin 21X3. The surface of the sealing resin 21X3 and the upper surface of the base 21X1 are on the same plane. The surface of the sealing resin 21X3 is flat.

Light emitted from light source 21X2 is refracted at the surface of sealing resin 21X3 and emitted from reflected light emitting element 21X. The surface of sealing resin 21X3 is light emitting surface 21X4. In FIG. 9, light emitting surface 21X4 is a flat surface. In FIG. 9, light emitting surface 21X4 is a flat surface parallel to the transport direction of paper M and parallel to the width direction of paper M. Irradiation light Lx shown in FIG. 9 corresponds to irradiation light Lx1 and Lx2 shown in FIGS. 4 and 5.

The dashed lines in FIG. 9 indicate lines extending in the opposite direction of the irradiation light Lx emitted from the reflected light emitting element 21X. A point where multiple dashed lines intersect is the virtual image point. In the reflected light emitting element 21X shown in FIG. 9, the position of the virtual image point is the light emitting point LP. The light emitting point height is the distance between the support surface 23X1 and the light emitting point LP in the direction perpendicular to the support surface 23X1 of the element substrate 23X.

The reflected light emitting element 21X shown in Figures 8 and 9 generally has a substantially Lambertian orientation distribution. A Lambertian distribution is a distribution in which, when the angle with respect to the front direction of the reflected light emitting element 21X (in Figures 8 and 9, the up and down direction in the figures) is θ, the intensity of the light emitted in the direction of angle θ is cosθ times the intensity of the light emitted in the front direction. Because the reflected light emitting element 21X has Lambertian characteristics, no lens is required for the reflected light emitting element 21X, and a light emitting element with a simple configuration can be realized.

Figure 10 is a diagram showing a third example of the configuration of the reflected light emitting element 21X. The reflected light emitting element 21X shown in Figure 10 has a base 21X1, a light source 21X2, and a sealing resin 21X3, similar to Figure 9. The light emitting surface 21X4 on the surface of the sealing resin 21X3 has a curved shape. Typically, the light emitting surface 21X4 has a spherical shape. In the reflected light emitting element 21X shown in Figure 10, an LED package with an attached lens is realized due to the curved shape of the surface of the sealing resin 21X3.

The light emitted from the light source 21X2 is refracted at the light emitting surface 21X4 and emitted from the reflected light emitting element 21X. The position of the virtual image point of the light ray emitted from the reflected light emitting element 21X is the light emitting point LP of the reflected light emitting element 21X shown in FIG. 10. The light emitting point height is the distance between the support surface 23X1 and the light emitting point LP in the direction perpendicular to the support surface 23X1 of the element substrate 23X.

Figure 11 is a diagram showing a fourth example of the configuration of the reflected light emitting element 21X. The reflected light emitting element 21X shown in Figure 11 has a base 21X1, a light source 21X2, and a sealing resin 21X3, similar to Figure 9. The shapes of the base 21X1 and the sealing resin 21X3 are the same as those in Figure 9, and the surface of the sealing resin 21X3 is flat.

The reflected light emitting element 21X further includes a lens 21X5. The lens 21X5 has a planar light incident surface and a curved light exit surface. The light incident surface of the lens 21X5 faces the surface of the sealing resin 21X3 with a gap therebetween and is disposed parallel to the surface of the sealing resin 21X3. The light exit surface of the lens 21X5 typically has a spherical shape. The light exit surface of the lens 21X5 is the light emitting surface 21X4 from which light is emitted from the reflected light emitting element 21X. In the reflected light emitting element 21X shown in FIG. 11, an optical system (lens 21X5) is attached outside the LED package.

The light emitted from the light source 21X2 is refracted at the surface of the sealing resin 21X3, refracted at the light entrance surface of the lens 21X5, and refracted at the light exit surface (light emitting surface 21X4) of the lens 21X5, and is emitted from the reflected light emitting element 21X. The position of the virtual image point of the light ray emitted from the reflected light emitting element 21X is the light emitting point LP of the reflected light emitting element 21X shown in Figure 11. The light emitting point height is the distance between the support surface 23X1 and the light emitting point LP in the direction perpendicular to the support surface 23X1 of the element substrate 23X.

<Arrangement of Light Emitting Element and Light Receiving Element>
3 to 7 has a width in the normal direction indicated by arrow A2. Therefore, the position of the paper M passing through the inspection unit 20 in the normal direction may vary within the range of this width. In response to such variation in the position of the paper M, the distance between the first reflected light emitting element 211X, the second reflected light emitting element 212X, and the light receiving element 220 and the paper M may also vary. The arrangement of the light emitting elements and the light receiving elements to enable the paper type to be determined with sufficient accuracy even if this variation in distance occurs will be described below.

12 is a first diagram showing a first example of the positional relationship between the light-emitting element and the light-receiving element. FIG. 13 is a second diagram showing a first example of the positional relationship between the light-emitting element and the light-receiving element. Arrow A3 shown in FIG. 12 indicates the width direction of the paper M transported through the inspection unit 20. The direction indicated by arrow A3 is a direction along the surface of the paper M. Arrow A3 is perpendicular to the transport direction indicated by arrow A1 and perpendicular to the normal direction indicated by arrow A2. In FIG. 12, the transport direction of the paper M is the left-right direction in the figure, and the width direction of the paper M is the up-down direction in the figure. The direction along the surface of the paper M (hereinafter referred to as the "surface direction") is a direction along the paper surface in FIG. 12. The surface direction includes the transport direction indicated by arrow A1, the width direction of the paper M indicated by arrow A3, and any direction on a plane including the transport direction and width direction of the paper M. The normal direction indicated by arrow A2 is a direction perpendicular to the surface direction.

12 and 13, a plurality of reflected light emitting elements 21X are provided for one light receiving element 220. Specifically, the reflected light emitting element 21X includes a first reflected light emitting element 211X and a second reflected light emitting element 212X. The two reflected light emitting elements 211X and 212X are supported on the support surface 23X1 of the element substrate 23X. The light receiving element 220 is also disposed on the support surface 23X1. The support surface 23X1 is a flat surface. The support surface 23X1 extends parallel to the conveying direction of the paper M indicated by the arrow A1 and parallel to the width direction of the paper M indicated by the arrow A3. The support surface 23X1 extends in the planar direction. FIG. 12 corresponds to a view of a part of the support surface 23X1 on which the reflected light emitting elements 211X and 212X and the light receiving element 220 are mounted, viewed from a direction perpendicular to the support surface 23X1.

The first reflected light emitting element 211X and the second reflected light emitting element 212X may have any of the configurations shown in FIG. 8 to FIG. 11. For example, the first reflected light emitting element 211X and the second reflected light emitting element 212X may have the configuration shown in FIG. 9. The first reflected light emitting element 211X has a light emitting point LP1. The second reflected light emitting element 212X has a light emitting point LP2. As shown in FIG. 9, the light emitting points LP1 and LP2 are disposed inside the sealing resin 21X3 and are disposed at positions outside the light emitting surface 21X4 of the reflected light emitting element 21X, but in FIG. 13, the light emitting point LP1 is shown to be disposed on the surface of the first reflected light emitting element 211X and the light emitting point LP2 is shown to be disposed on the surface of the second reflected light emitting element 212X.

The light emitting point LP1 is disposed at the center of the first reflected light emitting element 211X in the transport direction. The light emitting point LP2 is disposed at the center of the second reflected light emitting element 212X in the transport direction. The light receiving element 220 has a light receiving surface 221 that receives light. The light receiving point RP shown in FIG. 13 is the center of the light receiving surface 221. The light receiving surface 221 is, for example, a semiconductor light receiving surface of a photodiode. When the light receiving surface is sealed, the position of the virtual image point of the light receiving surface created by the sealing resin is set as the light receiving point RP, as in the case of the light emitting element. In FIG. 13, the light receiving point RP is diagrammatically illustrated as being disposed on the surface of the light receiving element 220. The light receiving point RP is an example of a "first light receiving and emitting point" in this example. The light emitting point LP1 is an example of a "second light receiving and emitting point" in this example. The light emitting point LP2 is an example of a "third light receiving and emitting point" in this example.

The height h1 shown in FIG. 13 is the distance between the support surface 23X1 of the element substrate 23X and the light-emitting point LP1 of the first reflected light-emitting element 211X in the normal direction indicated by the arrow A2 (i.e., the light-emitting point height shown in FIGS. 8 to 11). The height h2 is the distance between the support surface 23X1 and the light-emitting point LP2 of the second reflected light-emitting element 212X in the normal direction (i.e., the light-emitting point height shown in FIGS. 8 to 11).

The distance z0 shown in FIG. 13 is the distance in the normal direction from the light receiving point RP of the light receiving element 220 to the paper M. The distance z1 is the distance in the normal direction from the light emitting point LP1 of the first reflected light emitting element 211X to the paper M. The distance z2 is the distance in the normal direction from the light emitting point LP2 of the second reflected light emitting element 212X to the paper M.

The distance r1 shown in FIG. 13 is the distance in the surface direction (transport direction) between the light receiving point RP of the light receiving element 220 and the light emitting point LP1 of the first reflected light emitting element 211X. The distance r2 is the distance in the surface direction (transport direction) between the light receiving point RP of the light receiving element 220 and the light emitting point LP2 of the second reflected light emitting element 212X.

In this example, the light-emitting point height of the first reflected light-emitting element 211X is different from the light-emitting point height of the second reflected light-emitting element 212X. Specifically, the height h1 is greater than the height h2. The height h1 of the light-emitting point LP1 relative to the support surface 23X1 of the element substrate 23X is greater than the height h2 of the light-emitting point LP2 relative to the support surface 23X1.

In this example, the distances from the light receiving point RP of the light receiving element 220 to the light emitting points LP1 and LP2 of the reflected light emitting element 21X are different from each other. Specifically, the distance r2 is greater than the distance r1. The distance r1 between the first reflected light emitting element 211X, which has a larger light emitting point height, and the light receiving element 220 is smaller than the distance r2 between the second reflected light emitting element 212X, which has a smaller light emitting point height, and the light receiving element 220. The distance from the light receiving element 220 to the reflected light emitting element 21X is changed depending on the height of the light emitting points LP1 and LP2 from the support surface 23X1 of the element substrate 23X. The greater the distance between the support surface 23X1 and the light emitting points LP1 and LP2 in the normal direction, the smaller the distance between the reflected light emitting element 21X and the light receiving element 220 in the surface direction.

Figure 14 is a graph showing the ideal arrangement conditions of the optical elements where the ratio of the amount of light received by the light receiving element 220 does not change even if the position of the paper M changes. The horizontal axis x in Figure 14 is expressed by the following formula 3 using the distances z0, z1, and r1 shown in Figure 13.

x = 2r1 / (z0 + z1) (Equation 3)
The vertical axis A in FIG. 14 is expressed by the following equation 4 using the distance r1, the distance r2, the height h1, and the height h2 shown in FIG.

A = (r2 - r1) / (h2 - h1) ... (Equation 4)
Figure 14 shows the results of light ray simulation to determine the ideal arrangement conditions of the optical elements under which, when the position of the paper M in the normal direction changes and the distance from the light emitting point of the reflected light emitting element 21X and the light receiving point of the light receiving element 220 in the normal direction to the paper M changes, the amount of light emitted from the first reflected light emitting element 211X, reflected by the paper M, and received by the light receiving element 220 and the amount of light emitted from the second reflected light emitting element 212X, reflected by the paper M, and received by the light receiving element 220 do not change relatively, i.e., the ratio between the two amounts of received light does not change.

The simulation was performed under the following conditions: the light source has a Lambertian distribution and a sufficiently small light-emitting area, the paper M is completely diffuse, the opening 28X (Figure 3) of the optical diaphragm 24X that regulates the amount of reflected light is sufficiently large, the distances z0, z1 and z2 are close to each other, and the amount of variation in the position of the paper M in the normal direction is in the range of plus 10% to minus 10% of (z0 + z1)/2, and the average is taken between the variation in the position of the paper M on the side where the distances z0, z1 and z2 are increased and the variation in the position of the paper M on the side where the distances z0, z1 and z2 are decreased.

By arranging the light receiving element 220 and the first and second reflected light emitting elements 211X and 212X so that x and A satisfy the arrangement conditions of the curve shown in FIG. 14, when the position of the paper M changes in the normal direction, the amount of light received by the light receiving element 220 after being emitted from the first reflected light emitting element 211X and reflected by the paper M, and the amount of light received by the light receiving element 220 after being emitted from the second reflected light emitting element 212X and reflected by the paper M, do not change relatively. Therefore, the paper type can be determined with high accuracy.

When x on the horizontal axis shown in FIG. 14 is 0.84 or more, in order to satisfy the ideal arrangement condition of the optical elements, the optical elements are arranged so that A on the vertical axis is negative. According to formula 4, if the light-emitting point height (height h1) of the first reflected light-emitting element 211X is greater than the light-emitting point height (height h2) of the second reflected light-emitting element 212X, then h2-h1<0, and therefore, to make A<0, r2-r1> is used. In other words, the distance r2 between the light-emitting point LP2 and the light-receiving point RP of the second reflected light-emitting element 212X is made greater than the distance r1 between the light-emitting point LP1 of the first reflected light-emitting element 211X and the light-receiving point RP of the light-receiving element 220.

When optical elements are arranged so that x on the horizontal axis is 0.84 or more and A on the vertical axis is negative, the ideal arrangement condition of optical elements shown in FIG. 14 is represented by an almost straight line. On the other hand, when x on the horizontal axis is less than 0.84, in order to satisfy the ideal arrangement condition of optical elements, the optical elements are arranged so that A on the vertical axis is positive. In the range where A on the vertical axis is positive, as shown in FIG. 14, the value of A on the vertical axis increases rapidly as x on the horizontal axis becomes smaller. In the range where A on the vertical axis is positive, errors in the arrangement of optical elements can easily cause deviation from the ideal arrangement condition. Therefore, it is desirable to make A negative by setting x ≧ 0.84.

Figure 15 is a graph showing the error from the ideal arrangement conditions of the optical elements. The horizontal axis x and vertical axis A in Figure 15 are the same as those in Figure 14.

Figure 15 shows a curve where the change in the ratio between the amount of light received by the first reflected light emitting element 211X, reflected by the paper M, and received by the light receiving element 220 and the amount of light received by the second reflected light emitting element 212X, reflected by the paper M, and received by the light receiving element 220 is 0.5% when the position of the paper M in the normal direction is changed. Below the curve showing the ideal arrangement conditions also shown in Figure 14, a curve showing the condition where the change in the ratio of the amount of light received is minus 0.5% is shown by a dashed line. Above the curve showing the ideal arrangement conditions, a curve showing the condition where the change in the ratio of the amount of light received is plus 0.5% is shown by a dashed line.

If the optical element placement conditions are in a range between two curves, one above and one below the curve that indicates the ideal placement conditions, the change in the ratio of the amount of received light due to fluctuations in the position of the paper M is 0.5% or less, which is desirable. When x on the horizontal axis and A on the vertical axis satisfy the following formula 5, the optical element placement conditions are in a range between two curves, one above and one below, when x on the horizontal axis is in the range of 0.15 to 2.

k1/x+a1.x+b1≦A≦k2/x+a2.x+b2 (Equation 5)
where k1 = 0.059, a1 = -1.050, b1 = 0.304, k2 = 0.714, a2 = -0.467, and b2 = 0.0666.

By arranging the light receiving element 220 and the first reflected light emitting element 211X and the second reflected light emitting element 212X so that x and A are in the range between the two upper and lower curves shown in FIG. 15, when the position of the paper M changes in the normal direction, the relative change in the amount of light emitted from the first reflected light emitting element 211X, reflected by the paper M, and received by the light receiving element 220, and the amount of light emitted from the second reflected light emitting element 212X, reflected by the paper M, and received by the light receiving element 220, can be kept sufficiently small. Therefore, the effect of the change in the position of the paper M can be reduced, and the paper type can be determined with high accuracy.

The value A in equation 4 can be made negative by decreasing the distance between the reflected light emitting element 21X and the light receiving element 220 as the light emitting point height of the reflected light emitting element 21X increases. As shown in FIG. 14, the value x in this case satisfies x≧0.84. In this way, even if the arrangement of the optical elements deviates from the ideal arrangement, the amount of deviation from the ideal line shown in FIG. 14 can be reduced, making it easier to keep the range between the two upper and lower curves shown in FIG. 15.

The first reflected light emitting element 211X, the second reflected light emitting element 212X, and the light receiving element 220 are all arranged on the support surface 23X1 of the element substrate 23X and are provided on the same plane. This allows the light emitting points LP1, LP2 of the reflected light emitting element 21X and the light receiving surface 221 of the light receiving element 220 to be accurately positioned at the desired height. This ensures that the effect of fluctuations in the position of the paper M in the normal direction on the paper type discrimination results can be reduced.

If the paper type of paper M is determined using the ratio between the amount of light emitted by the first reflected light emitting element 211X and received by the light receiving element 220 and the amount of light emitted by the second reflected light emitting element 212X and received by the light receiving element 220, the effects of positional fluctuations of the paper M in the normal direction can be eliminated, and the robustness of the paper type determination device 2 can be increased, which is desirable.

By providing multiple reflected light emitting elements 21X per light receiving element 220, the wavelength of the irradiation light Lx1 emitted from the first reflected light emitting element 211X and the wavelength of the irradiation light Lx2 emitted from the second reflected light emitting element 212X can be made different. By using information from the irradiation light Lx of multiple wavelengths to determine the paper type, the accuracy of the determination can be improved.

By applying the configuration shown in FIG. 9 to the reflected light emitting element 21X and making the light emitting surface 21X4 a plane parallel to the transport direction and width direction of the paper M, it is possible to easily realize a reflected light emitting element 21X having Lambertian characteristics. By eliminating the need for a lens in the reflected light emitting element 21X, it is possible to simplify the configuration of the reflected light emitting element 21X.

The position of the paper M is likely to fluctuate while the paper M is being transported. By applying the paper type discrimination device 2 of this embodiment, the effects of fluctuations in the position of the paper M can be reduced, making it possible to discriminate the paper type with high accuracy while the paper M is being transported.

<Second Example of Arrangement of Light Emitting Element and Light Receiving Element>
FIG. 16 is a first diagram showing a second example of the positional relationship between the light-emitting element and the light-receiving element. FIG. 17 is a second diagram showing a second example of the positional relationship between the light-emitting element and the light-receiving element. In the example shown in FIGS. 16 and 17, three reflected light-emitting elements 21X are provided for one light-receiving element 220. The reflected light-emitting element 21X includes a first reflected light-emitting element 211X, a second reflected light-emitting element 212X, and a third reflected light-emitting element 213X. The three reflected light-emitting elements 21X are supported on the support surface 23X1 of the element substrate 23X. The light-receiving element 220 is also disposed on the support surface 23X1. The support surface 23X1 is a plane extending parallel to the conveying direction of the paper M and the width direction of the paper M. In FIGS. 16 and 17, the left-right direction in the figures is the conveying direction of the paper M. The normal direction is a direction perpendicular to the paper surface in FIG. 16, and is a vertical direction in FIG. 17.

The first reflected light emitting element 211X has a light emitting point LP1. The second reflected light emitting element 212X has a light emitting point LP2. The third reflected light emitting element 213X has a light emitting point LP3. In FIG. 17, the light emitting point LP1 is shown to be located on the surface of the first reflected light emitting element 211X, the light emitting point LP2 is shown to be located on the surface of the second reflected light emitting element 212X, and the light emitting point LP3 is shown to be located on the surface of the third reflected light emitting element 213X. In FIG. 17, the light receiving point RP is shown to be located on the surface of the light receiving element 220.

The height h3 shown in FIG. 17 is the distance between the support surface 23X1 of the element substrate 23X and the light emitting point LP3 of the third reflected light emitting element 213X in the normal direction (i.e., the light emitting point height). The distance z3 shown in FIG. 17 is the distance from the light emitting point LP3 of the third reflected light emitting element 213X to the paper M in the normal direction. The distance r2 shown in FIG. 16 and FIG. 17 is the distance between the light receiving point RP and the light emitting point LP2 of the second reflected light emitting element 212X in the surface direction. The distance r3 shown in FIG. 16 and FIG. 17 is the distance between the light receiving point RP and the light emitting point LP3 of the third reflected light emitting element 213X in the surface direction. In this example, the light receiving point RP and the light emitting point LP1 are aligned in the transport direction. The light receiving point RP and the light emitting point LP2, and the light receiving point RP and the light emitting point LP3 are aligned in a direction that is included in the surface direction and is different from the transport direction.

In this example, the light emitting point height of the first reflected light emitting element 211X, the light emitting point height of the second reflected light emitting element 212X, and the light emitting point height of the third reflected light emitting element 213X are different. Specifically, the height h1 of the light emitting point LP1 relative to the support surface 23X1 of the element substrate 23X is greater than the height h2 of the light emitting point LP2 relative to the support surface 23X1. The height h1 of the light emitting point LP1 relative to the support surface 23X1 is smaller than the height h3 of the light emitting point LP3 relative to the support surface 23X1.

In addition, in this example, the distances from the light receiving point RP of the light receiving element 220 to the light emitting points LP1, LP2, and LP3 of the reflected light emitting element 21X are different from one another. Specifically, distance r2 is greater than distance r1, and distance r3 is less than distance r1. The distance from the light receiving element 220 to the reflected light emitting element 21X is changed depending on the height of the light emitting points LP1, LP2, and LP3 from the support surface 23X1. The greater the distance between the support surface 23X1 and the light emitting points LP1, LP2, and LP3 in the normal direction, the smaller the distance between the reflected light emitting element 21X and the light receiving element 220 in the surface direction.

The virtual circle C shown in FIG. 16 is a virtual circle drawn on the support surface 23X1, with the light receiving point RP as the center and the distance r1 as the radius. The first reflected light emitting element 211X is arranged on the virtual circle C. The second reflected light emitting element 212X is arranged inside the virtual circle C, i.e., closer to the light receiving point RP than the virtual circle C. The third reflected light emitting element 213X is arranged outside the virtual circle C, i.e., farther from the light receiving point RP than the virtual circle C.

Of the three reflected light emitting elements 21X, the second reflected light emitting element 212X has the smallest light emitting point height, and the third reflected light emitting element 213X has the largest light emitting point height. Of the three reflected light emitting elements 21X, the first reflected light emitting element 211X, whose light emitting point height is neither the largest nor the smallest, is set as the reference light emitting element. The light receiving point RP is an example of a "first light receiving and emitting point" in this example. The light emitting point LP1 is an example of a "second light receiving and emitting point" in this example. The light emitting points LP2 and LP3 are examples of a "third light receiving and emitting point" in this example.

The three reflected light emitting elements 21X are arranged in close proximity to each other and in a line. The second reflected light emitting element 212X is arranged at one end of the line of the three reflected light emitting elements 21X, and the third reflected light emitting element 213X is arranged at the other end of the line of the three reflected light emitting elements 21X. The first reflected light emitting element 211X, which is the reference light emitting element, is not arranged at the end of the line of the three reflected light emitting elements 21X. The first reflected light emitting element 211X is arranged in the center of the line of the three reflected light emitting elements 21X, and the second reflected light emitting element 212X and the third reflected light emitting element 213X are arranged close to the first reflected light emitting element 211X on both sides of the first reflected light emitting element 211X.

By setting the light emitting point height of the first reflected light emitting element 211X, which is the reference light emitting element, to the intermediate value of the light emitting point heights of the three reflected light emitting elements 21X, the difference between the light emitting point height of the first reflected light emitting element 211X and the light emitting point height of the second reflected light emitting element 212X can be reduced, and the difference between the light emitting point height of the first reflected light emitting element 211X and the light emitting point height of the third reflected light emitting element 213X can be reduced. When the light emitting point height of each reflected light emitting element 21X and/or the distance from the light receiving element 220 deviates from the ideal condition shown in FIG. 14, the effect of error can be reduced, and the effect of fluctuations in the position of the paper M can be reduced.

By arranging the three reflected light emitting elements 21X closely together and not arranging the first reflected light emitting element 211X, which is the reference light emitting element, at the end of the row of reflected light emitting elements 21X, the distance between the first reflected light emitting element 211X and the second and third reflected light emitting elements 212X and 213X can be reduced, making it less susceptible to the effects of fluctuations in the position of the paper M.

By providing three or more reflected light emitting elements 21X per light receiving element 220, it is possible to use irradiation light Lx of three or more wavelengths, thereby further improving the discrimination accuracy.

<Third Example of Arrangement of Light Emitting Element and Light Receiving Element>
Fig. 18 is a diagram showing angles formed between a plurality of light-emitting elements and a light-receiving element. Fig. 18 shows a light-receiving element 220, a first reflected light-emitting element 211X, and a second reflected light-emitting element 212X. The angle θ shown in Fig. 18 is an angle formed between a straight line passing through a light-emitting point LP1 of the first reflected light-emitting element 211X and a light-receiving point RP of the light-receiving element 220, and a straight line passing through a light-emitting point LP2 of the second reflected light-emitting element 212X and a light-receiving point RP of the light-receiving element 220.

Figure 19 is a first diagram showing the effect of the arrangement of optical elements on the ratio of the amount of light received by the light receiving element when the position of the paper M changes. Figure 20 is a second diagram showing the effect of the arrangement of optical elements on the ratio of the amount of light received by the light receiving element when the position of the paper M changes. The horizontal axis of Figures 19 and 20 is the angle θ shown in Figure 18. The "relative value change of 2 LEDs" on the vertical axis of Figures 19 and 20 indicates the ratio of the amount of light between the reflected light Lr1 and the reflected light Lr2 (Figure 4) received by the light receiving element 220 when the first reflected light emitting element 211X and the second reflected light emitting element 212X are arranged under the ideal conditions shown in Figure 14.

Figure 19 shows the results of a simulation in which paper M is rotated 2° relative to the transport direction of paper M indicated by arrow A1. Figure 20 shows the results of a simulation in which paper M is rotated 2° relative to the width direction of paper M indicated by arrow A3. The value x shown as a legend in Figures 19 and 20 is a function value for the arrangement of optical elements, expressed by Equation 3 above. Figures 19 and 20 show the change in the ratio of the light intensity of reflected light Lr1, Lr2 when the angle θ is changed for multiple values of x.

As shown in FIG. 19, when the position of the paper M relative to the element substrate 23X fluctuates and the paper M rotates around the transport direction, if the first reflected light emitting element 211X and the second reflected light emitting element 212X are arranged at an angle θ of approximately 0° or approximately θ of 180°, the fluctuation in the ratio of the light intensities of the reflected lights Lr1 and Lr2 is small. When the two reflected light emitting elements 21X are arranged in positions facing each other across the light receiving element 220, the angle θ is set in the range of 180°±30°, that is, the angle θ is set to 150° or more and 210° or less, and the value x is set to 1.41≦x≦1.89. By setting in this way, the relative change in the ratio of the light intensities of the reflected lights Lr1 and Lr2 can be sufficiently reduced to 0.5% or less.

20, when the position of the paper M relative to the element substrate 23X fluctuates and the paper M rotates around the width direction, if the first reflected light emitting element 211X and the second reflected light emitting element 212X are arranged at an angle θ of approximately 0°, the fluctuation in the ratio of the light intensities of the reflected lights Lr1 and Lr2 is small. When the two reflected light emitting elements 21X are arranged at positions facing each other across the light receiving element 220, the relative change in the ratio of the light intensities of the reflected lights Lr1 and Lr2 can be sufficiently reduced to 0.5% or less by setting the value x to 1.67≦x≦1.82. When the value x satisfies the relational expression of 1.67≦x≦1.82, the relative change in the ratio of the light intensities of the reflected lights Lr1 and Lr2 can be suppressed to 0.5% or less, regardless of the angle θ, even when the paper M rotates in the transport direction.

Figure 21 is a diagram showing a third example of the positional relationship between the light-emitting element and the light-receiving element. In the example shown in Figure 21, four reflected light-emitting elements 21X are provided for one light-receiving element 220. The reflected light-emitting element 21X includes a fourth reflected light-emitting element 214X in addition to the first to third reflected light-emitting elements 211X, 212X, and 213X. The fourth reflected light-emitting element 214X is supported by the support surface 23X1 of the element substrate 23X.

The light receiving element 220 and the first to third reflected light emitting elements 211X, 212X, and 213X are arranged in the same positions as in Figures 16 and 17. The light emitting point LP1 of the first reflected light emitting element 211X is an example of a "second light receiving and emitting point" in this example. The second reflected light emitting element 212X and the third reflected light emitting element 213X are arranged so that the angle θ they form with the first reflected light emitting element 211X, which is the reference light emitting element, is θ≦30°.

In this example, the first reflected light emitting element 211X is an example of a "reference light emitting element" having a "second light receiving and emitting point", and the fourth reflected light emitting element 214X is an example of an "another light emitting element" different from the reference light emitting element. The fourth reflected light emitting element 214X is arranged with the light receiving element 220 sandwiched between it and the first reflected light emitting element 211X. The transport direction of the paper M is the left-right direction in FIG. 21. In the transport direction of the paper M, the first reflected light emitting element 211X, the light receiving element 220, and the fourth reflected light emitting element 214X are arranged in this order.

When four reflected light emitting elements 21X are provided for one light receiving element 220, the reflected light emitting elements 21X can be arranged in close proximity to the light receiving element 220 in one direction, as in the first to third reflected light emitting elements 211X to 213X, and the fourth reflected light emitting element 214X can be arranged in a position facing the light receiving element 220 on either side. The fourth reflected light emitting element 214X can reduce the influence of fluctuations in the position of the paper M by setting the angle θ between the first reflected light emitting element 211X to 150° or more and 210° or less, and setting the value x to 1.41≦x≦1.89. Setting the value x to 1.67≦x≦1.82 can reduce the influence of fluctuations in the position of the paper M regardless of the angle θ.

<Fourth Example of Arrangement of Light Emitting Element and Light Receiving Element>
Fig. 22 is a diagram showing a fourth example of the positional relationship between the light-emitting element and the light-receiving element. In the example shown in Fig. 22, five reflected light-emitting elements 21X are provided for one light-receiving element 220. The reflected light-emitting element 21X includes a fifth reflected light-emitting element 215X in addition to the first to fourth reflected light-emitting elements 211X to 214X. The fifth reflected light-emitting element 215X is supported by a support surface 23X1 of the element substrate 23X.

The light receiving element 220 and the first to third reflected light emitting elements 211X, 212X, and 213X are arranged in the same positions as in Figures 16 and 17. The light emitting point LP1 of the first reflected light emitting element 211X is an example of a "second light receiving and emitting point" in this example. In this example, the first reflected light emitting element 211X is an example of a "reference light emitting element" having a "second light receiving and emitting point", and the fourth reflected light emitting element 214X and the fifth reflected light emitting element 215X are examples of "another light emitting element" different from the reference light emitting element. The fourth reflected light emitting element 214X and the fifth reflected light emitting element 215X are arranged with the light receiving element 220 sandwiched between them and the first reflected light emitting element 211X.

When five reflected light emitting elements 21X are provided for one light receiving element 220, the reflected light emitting elements 21X can be arranged in close proximity to the light receiving element 220 in one direction, such as the first to third reflected light emitting elements 211X to 213X, and the fourth and fifth reflected light emitting elements 214X and 215X can be arranged in opposing positions across the light receiving element 220. The fourth reflected light emitting element 214X and the fifth reflected light emitting element 215X can reduce the influence of fluctuations in the position of the paper M by setting the angle θ between the first reflected light emitting element 211X to 150° or more and 210° or less, and setting the value x to 1.41≦x≦1.89. By setting the value x to 1.67≦x≦1.82, the influence of fluctuations in the position of the paper M can be reduced regardless of the angle θ.

<Fifth Example of Arrangement of Light Emitting Element and Light Receiving Element>
Fig. 23 is a first diagram showing a fifth example of the positional relationship between the light-emitting element and the light-receiving element. Fig. 24 is a second diagram showing a fifth example of the positional relationship between the light-emitting element and the light-receiving element. In the examples described so far, a plurality of reflected light-emitting elements 21X are provided for one light-receiving element 220, but this is not limited thereto, and a plurality of light-receiving elements 220 may be provided for one reflected light-emitting element 21X.

23 and 24, two light receiving elements 220 are provided for one reflected light emitting element 21X. The light receiving element 220 includes a first light receiving element 222 and a second light receiving element 223. The first light receiving element 222 and the second light receiving element 223 are supported on the support surface 23X1 of the element substrate 23X. The reflected light emitting element 21X is also disposed on the support surface 23X1.

The reflected light emitting element 21X has a light emitting point LP. The first light receiving element 222 has a light receiving point RP1. The light receiving point RP1 is a point at the center of the light receiving surface 221 of the first light receiving element 222. The second light receiving element 223 has a light receiving point RP2. The light receiving point RP2 is a point at the center of the light receiving surface 221 of the second light receiving element 223. If the light receiving surface is sealed, the positions of the virtual image points of the light receiving surface created by the sealing resin are the light receiving points RP1 and RP2. The light emitting point LP is an example of the "first light receiving/emitting point" in this example. The light receiving point RP1 is an example of the "second light receiving/emitting point" in this example. The light receiving point RP2 is an example of the "third light receiving/emitting point" in this example.

23 and 24, the left-right direction in the figure is the transport direction of the paper M. The normal direction is perpendicular to the paper surface in FIG. 23, and is up-down in FIG. 24. Height h1 shown in FIG. 24 is the distance in the normal direction between the support surface 23X1 of the element substrate 23X and the light receiving point RP1 of the first light receiving element 222. Height h2 is the distance in the normal direction between the support surface 23X1 and the light receiving point RP2 of the second light receiving element 223. Height h1 is greater than height h2. Height h1 of light receiving point RP1 relative to support surface 23X1 of element substrate 23X is greater than height h2 of light receiving point RP2 relative to support surface 23X1.

The distance z0 shown in FIG. 24 is the distance in the normal direction from the light emitting point LP of the reflected light emitting element 21X to the paper M. The distance z1 is the distance in the normal direction from the light receiving point RP1 of the first light receiving element 222 to the paper M. The distance z2 is the distance in the normal direction from the light receiving point RP2 of the second light receiving element 223 to the paper M. The distance r1 is the distance in the surface direction (transport direction) between the light emitting point LP of the reflected light emitting element 21X and the light receiving point RP1 of the first light receiving element 222. The distance r2 is the distance in the surface direction (transport direction) between the light emitting point LP of the reflected light emitting element 21X and the light receiving point RP2 of the second light receiving element 223.

The distances from the light emitting point LP of the reflected light emitting element 21X to the light receiving points RP1 and RP2 of the light receiving element 220 in the surface direction are different from each other. Specifically, the distance r2 is greater than the distance r1. The distance r1 between the first light receiving element 222, which has a larger height h1 of the light receiving point RP1 relative to the support surface 23X1, and the reflected light emitting element 21X is smaller than the distance r2 between the second light receiving element 223, which has a smaller height h2 of the light receiving point RP2 relative to the support surface 23X1, and the reflected light emitting element 21X. The distance from the reflected light emitting element 21X to the light receiving element 220 is changed depending on the height of the light receiving point from the support surface 23X1 of the element substrate 23X. The greater the distance between the support surface 23X1 and the light receiving points RP1 and RP2 in the normal direction, the smaller the distance between the light receiving element 220 and the reflected light emitting element 21X in the surface direction.

In this configuration, the reflected light emitting element 21X and the first and second light receiving elements 222 and 223 can be arranged so that the value x shown in the above-mentioned formula 3 and the value A shown in the above-mentioned formula 4 are in the range between the two upper and lower curves shown in FIG. 15, ideally satisfying the arrangement conditions of the curves shown in FIG. 14. In this way, when the position of the paper M changes in the normal direction, the relative change in the amount of light emitted from the reflected light emitting element 21X, reflected by the paper M, and received by the first light receiving element 222 and the amount of light emitted from the reflected light emitting element 21X, reflected by the paper M, and received by the second light receiving element 223 can be kept sufficiently small. Therefore, the influence of the change in the position of the paper M can be reduced, and the paper type can be determined with high accuracy.

<Sixth Example of Arrangement of Light Emitting Element and Light Receiving Element>
Fig. 25 is a diagram showing a sixth example of the positional relationship between the light emitting element and the light receiving element. In the example shown in Fig. 25, three light receiving elements 220 are provided for one reflected light emitting element 21X. The light receiving element 220 includes a first light receiving element 222, a second light receiving element 223, and a third light receiving element 224. The three light receiving elements 220 are supported by a support surface 23X1 of the element substrate 23X. The reflected light emitting element 21X is also disposed on the support surface 23X1.

The third light receiving element 224 has a light receiving point which is the center point of the light receiving surface 221. When the light receiving surface is sealed, the position of the virtual image point of the light receiving surface created by the sealing resin is the light receiving point. In this example, the reflected light emitting element 21X and the first light receiving element 222 are aligned in the conveying direction. The reflected light emitting element 21X and the second light receiving element 223, and the reflected light emitting element 21X and the third light receiving element 224 are aligned in a direction that is included in the surface direction and is different from the conveying direction. The distance r2 shown in FIG. 25 is the distance between the light emitting point of the reflected light emitting element 21X and the light receiving point of the second light receiving element 223 in the surface direction. The distance r3 shown in FIG. 25 is the distance between the light emitting point of the reflected light emitting element 21X and the light receiving point of the third light receiving element 224 in the surface direction. The distance r3 is smaller than the distance r1. In addition, the distance in the normal direction between the support surface 23X1 and the light receiving point of the third light receiving element 224 is greater than the height h1 shown in FIG. 24. The greater the distance in the normal direction between the support surface 23X1 and the light receiving point, the smaller the distance in the surface direction between the light receiving element 220 and the reflected light emitting element 21X.

Of the three light receiving elements 220 arranged close to each other in a row, the first light receiving element 222 that is not arranged at the end of the row is set as the reference light receiving element, and the height of the light receiving point RP1 of the first light receiving element 222 from the support surface 23X1 is set to the intermediate value of the heights of the light receiving points of the three light receiving elements 220. This makes it possible to reduce the influence of fluctuations in the position of the paper M when the height of the light receiving point of each light receiving element 220 and/or the distance from the reflected light emitting element 21X deviates from the ideal condition shown in FIG. 14. By reducing the distance between the first light receiving element 222, which is set as the reference light receiving element, and the second light receiving element 223 and the third light receiving element 224, it is possible to reduce the influence of fluctuations in the position of the paper M.

In the above explanation, the arrangement of the reflected light emitting element 21X and the light receiving element 220 that detects the reflected light of the light irradiated from the reflected light emitting element 21X to the paper M has been described. The reflected light from the paper M is desirable because it is highly sensitive to the change in the distance from the element to the paper M, but is not limited to this example. When multiple of either the transmitted light emitting element 21Y or the light receiving element 220 that receives the transmitted light of the light irradiated from the transmitted light emitting element 21Y to the paper M are provided for each other, the positional relationship of any of the above examples may be applied to the arrangement of the transmitted light emitting element 21Y and the light receiving element 220.

The following describes an example. In the example shown in Figures 12 and 13, where two reflected light emitting elements 21X are provided for one light receiving element 220, the value A shown in formula 4 is changed by changing the setting of the distance r2 between the light receiving point RP of the light receiving element 220 and the light emitting point LP2 of the second reflected light emitting element 212X, and the change in the amount of light reflected by the light receiving element 220 Lr1 and Lr2 when the position of the paper M is changed under each condition is confirmed by simulation.

The height of the light receiving surface 221 of the light receiving element 220 from the support surface 23X1 was set to 1.0 mm. The light emitting point height h1 of the first reflected light emitting element 211X was set to 1.4 mm. The light emitting point height h2 of the second reflected light emitting element 212X was set to 0.8 mm. The distance z0 from the light receiving point RP of the light receiving element 220 to the paper M was set to 10.4 mm. The distance z1 from the light emitting point LP1 of the first reflected light emitting element 211X to the paper M was set to 10.0 mm. The distance r1 between the light receiving point RP of the light receiving element 220 and the light emitting point LP1 of the first reflected light emitting element 211X was set to 19.0 mm.

Figure 26 is a table showing the effect of the arrangement of optical elements on the ratio of the amount of light received by the light receiving elements in the embodiment. "Change due to z shift" in Figure 26 is the amount of change in the amount of light reflected by the light receiving element 220, Lr1, Lr2, when the position of the paper M in the normal direction is changed within the range of plus 10% to minus 10% of (z0 + z1)/2.

In the case of the normal arrangement (condition 1), where distance r2 is 19.00 mm, equal to distance r1, the change in the amount of reflected light was large at 0.85%. In condition 2, where distance r2 is 19.20 mm, larger than in condition 1, and value A is a negative value, the change in the amount of reflected light was 0.58%, which was less than condition 1, but still exceeded 0.5%. Therefore, conditions 1 and 2 were judged to be "unacceptable."

In condition 3, where distance r2 is set to 19.40 mm, even larger than in condition 2, the change in the amount of reflected light could be suppressed to 0.30%, less than 0.5%, and was judged as "passable." Condition 4 is the optimal arrangement that satisfies the ideal arrangement conditions shown in Figure 14, and the change in the amount of reflected light was sufficiently small at 0.01%, so it was judged as "good."

In this way, by setting the placement conditions of the optical elements to a range sufficiently close to the ideal conditions, even if the position of the paper M changes and the distance from the elements to the paper M changes, the change in the light intensity of the reflected lights Lr1 and Lr2 can be kept small, and therefore it has been shown that paper type can be identified with high accuracy.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 Image forming apparatus, 2 Paper type discrimination device, 10 Control unit, 20 Inspection unit, 21 Light source unit, 21X Reflected light emitting element, 21X1 Base, 21X2 Light source, 21X3 Sealing resin, 21X4 Light emitting surface, 21X5 Lens, 21Y Transmitted light emitting element, 22 Detection unit, 23X, 23Y Element substrate, 23X1 Support surface, 24X, 24Y Optical aperture, 25 Paper passing guide, 26 Reflection unit, 27 Transport path, 28X, 28Y Opening, 30 Image forming unit, 40 Fixing unit, 50 Scanner, 60 Operation panel, 70 Communication unit, 81 Paper feed tray, 211X First reflected light emitting element, 212X Second reflected light emitting element, 213X Third reflected light emitting element, 214X Fourth reflected light emitting element, 215X Fifth reflected light emitting element, 220 Light receiving element, 221 light receiving surface, 222 first light receiving element, 223 second light receiving element, 224 third light receiving element, C virtual circle, LP, LP1, LP2, LP3 light emitting point, Lr1, Lr2, sLr1, sLr2 reflected light, Lt transmitted light, Lx, Lx1, Lx2, Ly emitted light, M paper, RP, RP1, RP2 light receiving point, h1, h2, h3 height, r1, r2, r3, z0, z1, z2, z3 distance.

Claims (16)

A light emitting element that irradiates light toward the paper;
a light receiving element having a light receiving surface for receiving light and configured to detect reflected light or transmitted light of the light irradiated from the light emitting element to the paper;
a plurality of the other of the light emitting element and the light receiving element are provided for each of the light emitting element and the light receiving element;
one of the light-emitting element and the light-receiving element has a first light-emitting and receiving point, and the other of the light-emitting element and the light-receiving element has a second light-emitting and receiving point and a third light-emitting and receiving point, the light-emitting and receiving points being positions of virtual image points of light rays emitted from the light-emitting element or virtual image points of the light-receiving surface,
a substrate having a support surface for supporting the other of the plurality of light emitting elements and the plurality of light receiving elements;
a distance between the first light receiving and emitting point and the second light receiving and emitting point in a surface direction along the surface of the paper is r1, a distance between the first light receiving and emitting point and the third light receiving and emitting point in the surface direction is r2, a distance between the support surface and the second light receiving and emitting point in a normal direction to the surface of the paper is h1, a distance between the support surface and the third light receiving and emitting point in the normal direction is h2, a distance between the first light receiving and emitting point and the paper in the normal direction is z0, and a distance between the second light receiving and emitting point and the paper in the normal direction is z1,
A = (r2 - r1) / (h2 - h1)
x = 2r1 / (z0 + z1)
Then, A and x are
k1/x+a1.x+b1≦A≦k2/x+a2.x+b2
where k1=0.059, a1=-1.050, b1=0.304, k2=0.714, a2=-0.467, and b2=0.0666. The paper type discrimination device according to claim 1, wherein the greater the distance between the support surface and the light receiving point in the normal direction, the smaller the distance between the light emitting element and the light receiving element in the surface direction. The paper type discrimination device according to claim 1 or claim 2, wherein x satisfies the relational expression x ≧ 0.84. The paper type discrimination device according to claim 1 or 2, wherein the light-emitting element has a Lambertian characteristic. the support surface is a plane;
3. The paper type discriminating device according to claim 1, wherein either the light emitting element or the light receiving element is disposed on the support surface. The paper type discrimination device according to claim 1 or 2, which discriminates the paper type using the ratio of the amount of light emitted by either the light-emitting element or the light-receiving element and received by either the light-emitting element or the light-receiving element, or the ratio of the amount of light received by either the light-emitting element or the light-receiving element. The paper type discrimination device according to claim 1 or claim 2, in which a plurality of the light emitting elements are provided for each of the light receiving elements. The paper type discrimination device according to claim 7, wherein three or more of the light emitting elements are provided for each of the light receiving elements. The paper type discrimination device according to claim 8, wherein the light-emitting element having the second light-receiving point is a reference light-emitting element having a distance that is neither maximum nor minimum between the support surface and the virtual image point of the light-emitting element in the normal direction. The paper type discrimination device according to claim 8, wherein three or more of the light-emitting elements are arranged in close proximity to each other, and the light-emitting element that is not arranged at the end of the row of the light-emitting elements is set as a reference light-emitting element having the second light-receiving point. the plurality of light-emitting elements include a reference light-emitting element having the second light-emitting point and another light-emitting element different from the reference light-emitting element,
the other light-emitting element is disposed between the reference light-emitting element and the light-receiving element,
an angle between a straight line passing through the virtual image point of the reference light-emitting element and the virtual image point of the light receiving surface and a straight line passing through the virtual image point of the other light-emitting element and the virtual image point of the light receiving surface is 150° or more and 210° or less;
8. The paper type discrimination device according to claim 7, wherein the x satisfies a relational expression of 1.41≦x≦1.89. The paper type discrimination device according to claim 11, wherein x satisfies the relational expression 1.67≦x≦1.82. The light-emitting element has a light-emitting surface through which light is emitted from the light-emitting element,
The paper type discrimination device according to claim 1 , wherein the light emitting surface is a flat surface parallel to the surface direction. The paper type discrimination device according to claim 1 or claim 2, which discriminates the paper type of the paper while the paper is being transported. The paper type discrimination device according to claim 1 or claim 2, in which multiple light receiving elements are provided for each light emitting element. The paper type discrimination device according to claim 1 or 2,
an image forming unit that forms an image on the paper.

Images