Discrimination device, image forming apparatus, discrimination method, and program

Abstract

To enable a type of a sheet to be discriminated with higher accuracy.SOLUTION: A media sensor 20 includes: a plurality of light sources, a light-receiving sensor that acquires, for each of the plurality of light sources, a light-receiving amount indicating an amount of reflected light or transmitted light of light irradiated on a sheet by the plurality of light sources; and a discrimination unit that discriminates a type of the sheet on the basis of the light-receiving amount acquired for each of the plurality of light sources. The plurality of light sources are arranged along a conveyance direction of the sheet. Light is emitted sequentially from the light source having a peak of irradiance on an upstream side in a conveyance direction of the plurality of light sources.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a discrimination device for determining the type of sheet. [Background technology]

[0002] In image forming apparatuses, fixing conditions and other settings differ depending on the type of sheet (recording material), so settings must be adjusted according to the sheet type. Traditionally, users would input the sheet type from the control panel. In recent years, image forming apparatuses that use sensors to identify the sheet type and change the settings have become known. One known sensor for identifying the sheet type has multiple light sources, and by sequentially emitting light from these multiple light sources, it irradiates the sheet with light and identifies the sheet type and basis weight.

[0003] Japanese Patent Publication No. 2018-189741 discloses a method for determining the type of sheet based on the intensity of light reflected by the sheet and the intensity of light transmitted through the sheet, by sequentially emitting light from multiple light sources. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-189741 [Overview of the project] [Problems that the invention aims to solve]

[0005] The characteristics of a sheet (e.g., sheet thickness, composition, and surface properties) vary within the plane of the sheet. However, the image forming apparatus disclosed in Japanese Patent Application Publication No. 2018-189741 did not take this into consideration, and as a result, it was sometimes impossible to correctly identify the type of sheet due to the influence of in-plane variations in sheet characteristics.

[0006] One of the purposes of this disclosure is to determine the type of sheet with greater accuracy. [Means for solving the problem]

[0007] A discrimination device according to a certain aspect of this disclosure comprises a plurality of light sources, a light receiving sensor that acquires a light receiving amount indicating the amount of reflected or transmitted light from the light source to the sheet for each of the plurality of light sources, and a discrimination unit that determines the type of sheet based on the light receiving amounts acquired for each of the plurality of light sources. The plurality of light sources are arranged along the sheet transport direction. The light sources emit light in order from the light source with the peak of irradiance on the upstream side in the transport direction.

[0008] Preferably, the sheet type includes at least one of plain paper, recycled paper, and coated paper.

[0009] Preferably, the multiple light sources are arranged in concentric circles centered around the light receiving sensor.

[0010] Preferably, the illumination areas of the sheet that are irradiated by light overlap by 50% or more between multiple light sources.

[0011] Preferably, the multiple light sources have Lambertshan characteristics.

[0012] Preferably, when the sheet transport speed is v, the emission interval of the multiple light sources is t, the distance between each light-emitting point of the multiple light sources and the center of the light-receiving surface of the light-receiving sensor along a plane parallel to the sheet is r, the distance between each light-emitting point of the multiple light sources and the sheet is d, and the maximum distance between the multiple light sources is D, then the arrangement conditions for each of the multiple light sources are: |(D-vt) / (d 2 +r 2 / 4) 1 / 2 |<0.71 The relationship satisfies the given equation.

[0013] Preferably, the discrimination device further comprises a substrate on which multiple light sources are arranged. The multiple light sources are arranged on the same substrate surface of the substrate.

[0014] Preferably, the multiple light sources include a reference light source and one or more other light sources different from the reference light source. The discrimination unit determines the type of sheet based on the relative relationship between the amount of light received by the reference light source and the amount of light received by each of the one or more other light sources.

[0015] Preferably, when the number of light sources is 2N-1 and N is an integer of 2 or more, the reference light source is the Nth light source from the upstream side in the transport direction where the position of peak irradiance among the multiple light sources is. When the number of light sources is 2N and N is an integer of 2 or more, the reference light source is the Nth or N+1th light source from the upstream side in the transport direction where the position of peak irradiance among the multiple light sources is.

[0016] Preferably, the discrimination device further includes a light emission control unit that controls the emission of multiple light sources. The light emission control unit performs control on the sheet multiple times, causing the multiple light sources to emit light sequentially. The discrimination unit calculates the relative relationship for each of the multiple times and determines the type of sheet based on the average relative relationship obtained from the relative relationships of the multiple times.

[0017] Preferably, the light emitted by the reference light source is infrared light.

[0018] Preferably, the multiple light sources include three or more light sources. When the number of multiple light sources is 2N-1 and N is an integer of 2 or more, the reference light source is positioned at the Nth position in the sequence of multiple light sources. When the number of multiple light sources is 2N and N is an integer of 2 or more, the reference light source is positioned at the Nth or N+1th position in the sequence of multiple light sources.

[0019] Preferably, the design is such that as the distance between each light-emitting point of the multiple light sources and the substrate surface on which the multiple light sources are arranged increases, the distance between each light-emitting point of the multiple light sources and the center of the light-receiving surface of the light-receiving sensor, along a plane parallel to the sheet, decreases.

[0020] Preferably, the reference light source is not the light source among the plurality of light sources with the longest distance between the light emitting point and the substrate surface on which the plurality of light sources are arranged, and the reference light source is not the light source among the plurality of light sources with the shortest distance between the light emitting point and the substrate surface.

[0021] Preferably, the substrate is arranged such that the substrate surface and the sheet are parallel.

Advantages of the Invention

[0022] According to the present disclosure, the type of the sheet can be discriminated with higher accuracy.

Brief Description of the Drawings

[0023] [Figure 1] It is a diagram showing an example of an image forming apparatus in Embodiment 1. [Figure 2] It is a diagram showing an example of the hardware configuration of the image forming apparatus in Embodiment 1. [Figure 3] It is a diagram showing an example of the hardware configuration of the media sensor in Embodiment 1. [Figure 4] It is a first diagram showing the positional relationship between the light receiving sensor and the plurality of light sources in Embodiment 1. [Figure 5] It is a second diagram showing the positional relationship between the light receiving sensor and the plurality of light sources in Embodiment 1. [Figure 6] It is a diagram showing an overview of the discrimination process of the media sensor in Embodiment 1. [Figure 7] It is a diagram showing an example of the irradiation area in Embodiment 1. [Figure 8] It is a diagram showing another example of the irradiation area in Embodiment 1. [Figure 9] It is a diagram showing the irradiation area in Reference Embodiment 1. [Figure 10] It is a diagram showing the irradiation area in Reference Embodiment 2. <00​​​​It is a first diagram showing the positional relationship between the light-receiving sensor and a plurality of light sources in Embodiment 3. [Figure 13] It is a second diagram showing the positional relationship between the light-receiving sensor and a plurality of light sources in Embodiment 3. [Figure 14] It is a first diagram showing the positional relationship between the light-receiving sensor and a plurality of light sources in Embodiment 4. [Figure 15] It is a second diagram showing the positional relationship between the light-receiving sensor and a plurality of light sources in Embodiment 4. [Figure 16] It is a graph showing the ideal arrangement conditions of the light source 1 and the light source 2, in which the ratio of the light reception amount of the light source 1 and the light reception amount of the light source 2 obtained by the light-receiving sensor 22 does not change even if the position of the sheet P fluctuates.

Embodiments for Carrying out the Invention

[0024] Hereinafter, embodiments and modification examples according to the present disclosure will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. Note that the embodiments and modification examples described below may be selectively combined as appropriate.

[0025] In the following description, the arrow x shown in the figure indicates the conveyance direction of the sheet P. The conveyance direction of the sheet P is a direction along the surface of the sheet P. In the following description, the arrow y shown in the figure indicates the width direction of the sheet P. In the following description, the arrow z shown in the figure indicates the normal direction of the surface of the sheet P. In other words, the arrow z indicates the thickness direction of the sheet P. The direction indicated by the arrow z is perpendicular to the surface of the sheet P. The direction indicated by the arrow z is perpendicular to the conveyance direction of the sheet P. The direction indicated by the arrow z is hereinafter referred to as the "normal direction" perpendicular to the surface of the sheet P.

[0026] [Embodiment 1] <A. Configuration of the Image Forming Apparatus> The configuration of the image forming apparatus in Embodiment 1 will be described with reference to Figures 1 and 2. Figure 1 is a diagram showing an example of the image forming apparatus in Embodiment 1. Figure 2 is a diagram showing an example of the hardware configuration of the image forming apparatus in Embodiment 1.

[0027] Referring to Figures 1 and 2, the image forming apparatus 100 forms an image on a sheet P. The sheet P is, for example, a sheet of paper.

[0028] The image forming apparatus 100 comprises a control device 10, a paper feeding unit 15, a media sensor 20, an image forming unit 30, a fixing unit 40, an operation panel 50, and a communication interface 60. The control device 10, the paper feeding unit 15, the media sensor 20, the image forming unit 30, the fixing unit 40, the operation panel 50, and the communication interface 60 are connected by a bus 99.

[0029] The control device 10 includes a processor 11, memory 12, and storage 13. The processor 11 is composed of, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The memory 12 is composed of, for example, a volatile storage device such as DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory). The storage 13 is composed of, for example, a non-volatile storage device such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or flash memory.

[0030] The storage 13 stores the program 131. The program 131 includes computer-readable instructions for controlling the image forming apparatus 100. The processor 11 executes the program 131 to control various parts of the image forming apparatus 100 and to realize various processes according to this embodiment.

[0031] Program 131 may be provided not as a standalone program, but incorporated as part of any other program. In this case, processing according to this embodiment is realized in cooperation with the other program. Even if a program does not include such a partial module, it does not deviate from the spirit of the image forming apparatus 100 according to this embodiment. Furthermore, some or all of the functions provided by Program 131 may be implemented by dedicated hardware.

[0032] The paper feeding unit 15 holds multiple sheets P. The paper feeding unit 15 feeds the sheets P one by one onto the transport path R and supplies the sheets P to the image forming unit 30.

[0033] The media sensor 20 is an example of a “discrimination device” in this disclosure. The media sensor 20 irradiates light onto the sheet P to determine the type of sheet P. The type of sheet P includes at least one of plain paper, recycled paper, and coated paper.

[0034] The image forming unit 30 uses toner to form an image on the sheet P based on image data. 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 stretched around a plurality of rollers and travels in the direction of arrow 35. The image forming unit 32 is arranged in series along the direction of travel of the intermediate transfer belt 31. Based on the image data, the image forming unit 32 forms toner images of each color, Y (yellow), M (magenta), C (cyan), and K (black), on the intermediate transfer belt 31. As the sheet P passes through the nip portion 34 formed between the intermediate transfer belt 31 and the transfer roller 33, the toner image is transferred to the sheet P and an image is formed on the sheet P.

[0035] The fuser unit 40 heats and pressurizes the sheet P on which the toner image has been transferred to fix the toner image to the sheet P. The processor 11 changes the heating and pressurizing conditions of the fuser unit 40 according to the type of sheet P determined by the media sensor 20. The sheet P on which the toner image has been fixed is discharged into the tray 83.

[0036] The operation panel 50 includes an input unit 51 and a display unit 52. The input unit 51 receives the user's operation, converts the operation into an operation signal, and outputs it to the processor 11. The input unit 51 is, for example, a touch pad. The display unit 52 displays various information such as the operation status and processing results of the image forming apparatus 100. The display unit 52 is, for example, a liquid crystal display. In the operation panel 50, the input unit 51 is disposed so as to overlap the display unit 52.

[0037] The communication interface 60 transmits and receives information to and from an external device 500. As an example, the processor 11 receives image data from the external device 500 via the communication interface 60.

[0038] <B. Configuration of Media Sensor Referring to FIGS. 3 to 5, the configuration of the media sensor 20 in Embodiment 1 will be described.

[0039] FIG. 3 is a diagram showing an example of the hardware configuration of the media sensor in Embodiment 1. The media sensor 20 includes a control device 210, a plurality of light sources, and a light receiving sensor 22. The control device 210, the plurality of light sources, and the light receiving sensor 22 are connected by a bus 299.

[0040] The control device 210 includes a processor 211, a memory 212, and a storage 213. The processor 211 is composed of, for example, a CPU or an MPU. The memory 212 is composed of a volatile storage device such as a DRAM or an SRAM. The storage 213 is composed of a non-volatile storage device such as an HDD, an SSD, or a flash memory.

[0041] The storage 213 stores the program 214. The program 214 includes computer-readable instructions for controlling the media sensor 20. The processor 211 executes the program 214 to control the various parts of the media sensor 20 and realize various processes according to this embodiment.

[0042] Program 214 may be provided not as a standalone program, but incorporated as part of any other program. In this case, processing according to this embodiment is realized in cooperation with the other program. Even if a program does not include such a partial module, it does not deviate from the spirit of the media sensor 20 according to this embodiment. Furthermore, some or all of the functions provided by program 214 may be implemented by dedicated hardware.

[0043] The multiple light sources include light source 1, light source 2, and light source 3. Light sources 1, 2, and 3 are reflective light sources. The light receiving sensor 22 acquires a light receiving amount for each of light sources 1, 2, and 3, which indicates the amount of reflected light from the light source irradiated onto sheet P.

[0044] Figure 4 is a first diagram showing the positional relationship between the light receiving sensor and the multiple light sources in Embodiment 1. Figure 5 is a second diagram showing the positional relationship between the light receiving sensor and the multiple light sources in Embodiment 1.

[0045] Referring to Figures 4 and 5, the media sensor 20 includes a light source 1, a light source 2, a light source 3, a light receiving sensor 22, substrates 23 and 24, and a reflector 25.

[0046] In Embodiment 1, three reflective light sources are provided for one light receiving sensor 22. The three reflective light sources include light source 1, light source 2, and light source 3. Light sources 1, 2, and 3 emit light in a wavelength range that is reflected by the surface of the sheet P. Light sources 1, 2, and 3 are, for example, LEDs (Light-Emitting Diodes).

[0047] Light sources 1, 2, and 3 are arranged along the transport direction of sheet P. Light sources 1, 2, and 3 are placed on the substrate surface 231 of substrate 23. The light receiving sensor 22 is also placed on the substrate surface 231.

[0048] The substrate 23 is positioned so that the substrate surface 231 and the sheet P are parallel. The distance dr between the light-emitting point LP of the reflective light source and the sheet P is the same for all three reflective light sources. That is, the distance d1 between the light-emitting point LP1 of light source 1 and the sheet P, the distance d2 between the light-emitting point LP2 of light source 2 and the sheet P, and the distance d3 between the light-emitting point LP3 of light source 3 and the sheet P are all the same. If the light-emitting area of ​​a reflective light source is extended, the light-emitting point LP of the reflective light source is considered to be at the center of the light-emitting area.

[0049] The distance hr (hereinafter also referred to as "height hr of the light-emitting point") between the substrate surface 231 and the light-emitting point LP of the reflective light source is the same for all three reflective light sources. That is, the distance h1 between the substrate surface 231 and the light-emitting point LP1 of light source 1, the distance h2 between the substrate surface 231 and the light-emitting point LP2 of light source 2, and the distance h3 between the substrate surface 231 and the light-emitting point LP3 of light source 3 are all the same.

[0050] The three reflective light sources are arranged in close proximity to each other and side by side. In Embodiment 1, light source 2, which is positioned in the center of the arrangement of the three reflective light sources, is designated as the "reference light source," and light sources 1 and 3 are designated as "one or more other light sources." The reference light source is the reference light source among the multiple light sources.

[0051] Light sources 1, 2, and 3 emit light of different wavelengths. The light emitted by light source 2, which is the reference light source, is infrared light that is less affected by the characteristics of sheet P (e.g., sheet thickness, composition, and surface properties).

[0052] The light-receiving sensor 22 is, for example, a photodiode. The light-receiving sensor 22 has a light-receiving surface 22a. The light-receiving sensor 22 is positioned in the optical path of light emitted from each of the three reflective light sources and reflected from the surface of the sheet P. In the following description, the light emitted from the reflective light sources and reflected from the surface of the sheet P is referred to as "reflected light". The aperture 26 that regulates the amount of reflected light is designed to be sufficiently large.

[0053] Light sources 1, 2, and 3 are arranged on concentric circles centered on the light receiving sensor 22. Therefore, the distance rr between the light emission point LP of the reflective light source and the light receiving point RP of the light receiving sensor 22, along a plane parallel to the sheet P, is the same for all three reflective light sources. The light receiving point RP is the center of the light receiving surface 22a of the light receiving sensor 22. That is, the distance r1 between the light emission point LP1 of light source 1 and the light receiving point RP of the light receiving sensor 22, along a plane parallel to the sheet P, the distance r2 between the light emission point LP2 of light source 2 and the light receiving point RP of the light receiving sensor 22, along a plane parallel to the sheet P, and the distance r3 between the light emission point LP3 of light source 3 and the light receiving point RP of the light receiving sensor 22, along a plane parallel to the sheet P, are all the same.

[0054] Light sources 1, 2, and 3 have different positions where their irradiance peaks relative to sheet P. The position where light source 2, which is designated as the reference light source, peaks in irradiance is between the position where light source 1 peaks in irradiance and the position where light source 3 peaks in irradiance, along the conveying direction of sheet P. Light sources 1, 2, and 3 emit light for predetermined periods of time relative to sheet P as it passes through the conveying path R. More specifically, among light sources 1, 2, and 3, the light source with the peak irradiance on the upstream side in the conveying direction of sheet P emits light in order.

[0055] Light emitted from the light source is diffusely reflected off the surface of the sheet P, and the reflected light (diffuse light) is incident on the light receiving sensor 22. The light receiving sensor 22 acquires a light receiving amount indicating the amount of reflected light for each of the light sources 1, 2, and 3. The processor 211 determines the type of sheet P based on the light receiving amounts acquired for each of the light sources 1, 2, and 3.

[0056] The reflection unit 25 is provided to calibrate the emission powers of the three light sources for reflection. The reflection unit 25 reflects the light from the light sources for reflection. The reflection unit 25 is disposed on the substrate surface 241 of the substrate 24. The substrate 24 is disposed such that the substrate surface 241 and the sheet P are parallel. Using the reflection unit 25, the emission powers of the three light sources for reflection are calibrated so that the received light amounts obtained by the light-receiving sensor 22 are the same for the three light sources for reflection when the three light sources for reflection are caused to emit light in order in a state where the sheet P has not passed through. Thereby, the reflectivity of the sheet P can be evaluated from the received light amount of the light-receiving sensor 22.

[0057] <C. Discrimination Process of Media Sensor> Referring to FIG. 6, the discrimination process of the media sensor 20 in Embodiment 1 will be described. FIG. 6 is a diagram showing an outline of the discrimination process of the media sensor in Embodiment 1. The discrimination process is a process for discriminating the type of the sheet P.

[0058] Referring to FIG. 6, the media sensor 20 includes a light emission control unit 251, a light source 1, a light source 2, a light source 3, a light-receiving sensor 22, and a discrimination unit 252. The light emission control unit 251 and the discrimination unit 252 are realized by the processor 211 executing the program 214.

[0059] The light emission control unit 251 controls the emission of the three light sources for reflection. The light emission control unit 251 executes once a control for causing the three light sources for reflection to emit light in order with respect to the sheet P. More specifically, during the passage of the sheet P, the light emission control unit 251 causes the light sources having peaks of irradiance in the upstream side in the conveyance direction of the sheet P among the three light sources for reflection to emit light in order.

[0060] The light-receiving sensor 22 acquires a received light amount indicating the amount of reflected light for each of the three light sources for reflection.

[0061] The discrimination unit 252 determines the type of sheet P based on the reflectivity of the sheet P. More specifically, the discrimination unit 252 determines the type of sheet P based on the amount of light received acquired for each of the three reflective light sources. The emission power of the three reflective light sources is calibrated so that the amount of light received by the light receiving sensor 22 is the same for all three reflective light sources when the three reflective light sources are emitted sequentially without sheet P passing through them. Therefore, the amount of light received acquired for each of the three reflective light sources is an indicator of the reflectivity of sheet P.

[0062] The discrimination unit 252 determines the type of sheet P based on the relative relationship between the amount of light received from the reference light source and the amount of light received from each of the one or more other light sources. More specifically, the discrimination unit 252 calculates the ratio of the amount of light received from each of the one or more other light sources to the amount of light received from the reference light source using the following formula 1.

[0063] Rw = Wk / Ws ... Equation 1

[0064] In Equation 1, "Rw" represents the ratio of the amount of light received from each of the one or more other light sources to the amount of light received from the reference light source. In Equation 1, "Wk" represents the amount of light received from each of the one or more other light sources. In Equation 1, "Ws" represents the amount of light received from the reference light source.

[0065] More specifically, the discrimination unit 252 calculates the ratio of the amount of light received by light source 1 to the amount of light received by light source 2, which is designated as a reference light source (hereinafter referred to as "ratio Rw1"), and the ratio of the amount of light received by light source 3 to the amount of light received by light source 2, which is designated as a reference light source (hereinafter referred to as "ratio Rw3").

[0066] Finally, the discrimination unit 252 determines the type of sheet P based on the ratios Rw1 and Rw3. The discrimination unit 252 transmits the type of sheet P to the control device 10. The control device 10 changes the heating and pressurizing conditions of the fixing unit 40 according to the type of sheet P.

[0067] The relative relationship between the amount of light received for the reference light source and the amount of light received for each of one or more other light sources may be the difference between the amount of light received for the reference light source and the amount of light received for each of one or more other light sources.

[0068] <Effects Obtained by the Media Sensor> Referring to FIGS. 7 to 10, the effects obtained by the media sensor 20 in Embodiment 1 will be described.

[0069] (D1: Irradiation Region in Embodiment 1) FIG. 7 is a diagram showing an example of the irradiation region in Embodiment 1. The irradiation region indicates the region of the sheet P irradiated with light. The irradiation region is a region where the irradiance is 1 / 10 or more of the peak. In the example shown in FIG. 7, the light source 1 has a peak of irradiance on the most upstream side in the conveyance direction of the sheet P among the plurality of light sources. In the example shown in FIG. 7, the light source 2 has a peak of irradiance on the upstream side next to the light source 1 in the conveyance direction of the sheet P among the plurality of light sources. In the example shown in FIG. 7, the light source 3 has a peak of irradiance on the most downstream side in the conveyance direction of the sheet P among the plurality of light sources.

[0070] The light emission control unit 251 causes the light sources having peaks of irradiance on the upstream side in the conveyance direction of the sheet P among the plurality of light sources to emit light in order while the sheet P is passing. Therefore, in the example shown in FIG. 7, the light emission control unit 251 causes the light source 1, the light source 2, and the light source 3 to emit light in this order. As a result, the light source 1, the light source 2, and the light source 3 emit light in this order.

[0071] As shown in FIG. 7, by such light emission control, the irradiation region AR1 when the light source 1 emits light, the irradiation region AR2 when the light source 2 emits light, and the irradiation region AR3 when the light source 3 emits light overlap each other.

[0072] Figure 8 shows another example of the irradiation area in Embodiment 1. In the example shown in Figure 8, light source 3 has its irradiance peak furthest upstream in the conveying direction of sheet P among the multiple light sources. In the example shown in Figure 8, light source 2 has its irradiance peak furthest upstream of light source 3 in the conveying direction of sheet P among the multiple light sources. In the example shown in Figure 8, light source 1 has its irradiance peak furthest downstream in the conveying direction of sheet P among the multiple light sources.

[0073] The light emission control unit 251 causes the multiple light sources to emit light sequentially, starting with the light source whose irradiance peak is on the upstream side in the conveying direction of the sheet P, as the sheet P passes through. Therefore, in the example shown in Figure 8, the light emission control unit 251 causes light sources 3, 2, and 1 to emit light in this order. As a result, light sources 3, 2, and 1 emit light in this order.

[0074] As shown in Figure 8, with this type of light emission control, the illumination area AR1 when light source 1 is emitted, the illumination area AR2 when light source 2 is emitted, and the illumination area AR3 when light source 3 is emitted overlap with each other.

[0075] As can be seen from Figures 7 and 8, in the media sensor 20 of Embodiment 1, the light sources with the peak irradiance on the upstream side in the transport direction of the sheet P are emitted in order, so that the irradiation areas of the multiple light sources overlap. Therefore, the area for measuring the characteristics of the sheet P (hereinafter simply referred to as the "measurement area") is the same or close to the same area among the multiple light sources. Generally, the characteristics of the sheet P vary within the plane of the sheet P, so if the measurement areas differ significantly among the multiple light sources, it may not be possible to correctly identify the type of sheet P. However, in the media sensor 20 of Embodiment 1, the measurement area is the same or close to the same area among the multiple light sources, so the effect of in-plane variation in sheet characteristics can be suppressed. Therefore, the media sensor 20 of Embodiment 1 can identify the type of sheet P with higher accuracy.

[0076] (D2: Irradiation area in the reference configuration) Figure 9 shows the irradiation area in Reference Embodiment 1. Reference Embodiment 1 differs from Embodiment 1 in the control of emission from multiple light sources. More specifically, in Reference Embodiment 1, the light sources with the peak irradiance on the downstream side in the transport direction of the sheet P are emitted in order.

[0077] In the example shown in Figure 9, light source 1 has its irradiance peak furthest upstream in the direction of sheet P's transport among the multiple light sources. In the example shown in Figure 9, light source 2 has its irradiance peak furthest upstream of light source 1 in the direction of sheet P's transport among the multiple light sources. In the example shown in Figure 9, light source 3 has its irradiance peak furthest downstream in the direction of sheet P's transport among the multiple light sources. Therefore, in reference embodiment 1 shown in Figure 9, light source 3, light source 2, and light source 1 emit light in this order.

[0078] As can be seen from Figure 9, when multiple light sources are emitted sequentially, starting with the light source whose irradiance peak is downstream in the conveying direction of sheet P, the irradiation area AR1 when light source 1 is emitted, the irradiation area AR2 when light source 2 is emitted, and the irradiation area AR3 when light source 3 is emitted do not overlap with each other.

[0079] Figure 10 shows the irradiation area in Reference Embodiment 2. In Reference Embodiment 2, the position where the irradiance of the multiple light sources peaks is different from that of Embodiment 1. More specifically, in Reference Embodiment 2, the position where the irradiance peaks is the same for light source 1, light source 2, and light source 3.

[0080] In Reference Form 2, when light sources 1, 2, and 3 are emitted in this order, as shown in Figure 10, the illumination area AR1 when light source 1 is emitted, the illumination area AR2 when light source 2 is emitted, and the illumination area AR3 when light source 3 is emitted do not overlap with each other.

[0081] Figure 10 shows an example where light source 1, light source 2, and light source 3 emit light in this order. However, if the position where the irradiance peaks is the same for all light sources, the irradiation areas will not overlap, or if they do overlap, the overlapping area will be smaller than in Embodiment 1, regardless of the order in which the light sources emit light.

[0082] As can be seen from FIGS. 9 and 10, in the reference embodiment, the irradiation regions do not overlap between the plurality of light sources, or even if they overlap, the overlapping region is smaller than that in the first embodiment. Therefore, in the reference embodiment, most of the measurement region becomes different regions between the plurality of light sources, so there is a possibility that the type of the sheet P cannot be correctly discriminated due to the influence of the in-plane variation of the sheet characteristics.

[0083] <E. Ideal Arrangement Conditions of Light Sources> As described above, in the media sensor 20 in the first embodiment, since the light sources emit light in order from the light source having the peak of the irradiance on the upstream side in the conveyance direction of the sheet P among the plurality of light sources, the irradiation regions overlap with each other between the plurality of light sources.

[0084] It is preferable that the irradiation regions overlap by 50% or more between the plurality of light sources. When the plurality of light sources have a Lambertian characteristic (when having a substantially Lambertian orientation distribution), the arrangement conditions of each light source for the irradiation regions to overlap by 50% or more between the plurality of light sources are shown by the following formula 2.

[0085] |(D - vt) / (d 2 + r 2 / 4) 1 / 2 |<0.71 ··· Formula 2

[0086] “D” in formula 2 indicates the maximum distance between the plurality of light sources. The maximum distance between the plurality of light sources is the distance between the light emission point of the light source located at one end of the arrangement of the plurality of light sources and the light emission point of the light source located at the other end of the arrangement of the plurality of light sources along the conveyance direction of the sheet P. In the first embodiment, the maximum distance between the plurality of light sources is the distance Dr (see FIG. 4) between the light emission point LP1 of the light source 1 and the light emission point LP3 of the light source 3.

[0087] “v” in formula 2 indicates the conveyance speed of the sheet P. “t” in formula 2 indicates the light emission interval of the plurality of light sources.

[0088] In Equation 2, "d" represents the distance between the emission point LP of each of the plurality of light sources and the sheet P. In Embodiment 1, the distance between the emission point LP of each of the plurality of light sources and the sheet P is the distance dr (see FIG. 4).

[0089] In Equation 2, "r" represents the distance between the emission point LP of each of the plurality of light sources and the center (light reception point RP) of the light reception surface 22a of the light reception sensor 22 along a plane parallel to the sheet P. In Embodiment 1, the distance between the emission point LP of each of the plurality of light sources and the center (light reception point RP) of the light reception surface 22a of the light reception sensor 22 along a plane parallel to the sheet P is the distance rr (see FIG. 5).

[0090] The Lambertian distribution means a distribution in which when the angle with respect to the front direction of the light source (in FIG. 4, the vertical direction in the figure) is θ, the intensity of the light emitted in the direction of the angle θ is cos θ times the intensity of the light emitted in the front direction. Since the light source has Lambertian characteristics, a lens is not required for the light source, and a light source with a simple configuration can be realized.

[0091] When the plurality of light sources have Lambertian characteristics, each of the plurality of light sources satisfies the arrangement conditions represented by Equation 2, and by emitting light in order from the light source having a peak in irradiance on the upstream side in the conveyance direction of the sheet P among the plurality of light sources, the irradiation regions overlap by 50% or more between the plurality of light sources.

[0092] It is more preferable that the irradiation regions overlap by 80% or more between the plurality of light sources. When the plurality of light sources have Lambertian characteristics, each of the plurality of light sources satisfies the arrangement conditions represented by the following Equation 3, and by emitting light in order from the light source having a peak in irradiance on the upstream side in the conveyance direction of the sheet P among the plurality of light sources, the irradiation regions overlap by 80% or more between the plurality of light sources.

[0093] |(D - vt) / (d 2 + r 2 / 4) 1 / 2 |< 0.28 ··· Equation 3

[0094] In Equation 3, "D", "v", "t", "d", and "r" are the same as "D", "v", "t", "d", and "r" in Equation 2.

[0095] Thus, in the media sensor 20 of Embodiment 1, the light sources with the peak irradiance on the upstream side in the transport direction of the sheet P are emitted in order, so the irradiation areas overlap among the multiple light sources. Therefore, in the media sensor 20 of Embodiment 1, the measurement area is the same or close to the same area among the multiple light sources, so the influence of in-plane variation in sheet characteristics can be suppressed. Consequently, the media sensor 20 of Embodiment 1 can determine the type of sheet P with higher accuracy.

[0096] In Embodiment 1, the multiple light sources are arranged in concentric circles centered on the light receiving sensor 22. As a result, even if the position of the sheet P changes in the normal direction, the relative values ​​of the amount of light received by the light receiving sensor 22 among the multiple light sources do not change. Therefore, the influence of positional changes of the sheet P in the normal direction can be suppressed, and the type of sheet P can be determined with high accuracy.

[0097] In Embodiment 1, multiple light sources are arranged on the same substrate surface 231. This allows the height hr of the light-emitting point LP of the light sources to be precisely positioned at a desired location. Furthermore, the distance dr between the light-emitting point LP of the light sources and the sheet P can be precisely positioned at a desired location.

[0098] In Embodiment 1, the discrimination unit 252 determines the type of sheet P based on the relative relationship between the amount of light received from a reference light source and the amount of light received from each of the one or more other light sources. As a result, even if the position of sheet P changes in the normal direction, the relative value of the amount of light received by the light receiving sensor 22 among the multiple light sources does not change. Therefore, the influence of positional changes of sheet P in the normal direction can be suppressed, and the type of sheet P can be determined with high accuracy.

[0099] In Embodiment 1, the light emitted by the light source 2, which is used as the reference light source, is infrared light that is less affected by the characteristics of the sheet P. Therefore, the type of sheet P can be determined with high accuracy.

[0100] In Embodiment 1, the reference light source 2 is positioned in the center of a row of multiple light sources. This ensures that the reference light source and each of the other one or more light sources are positioned in close proximity. Therefore, the influence of changes in the orientation of the sheet P during transport can be suppressed, enabling high-precision identification of the sheet P type.

[0101] In Embodiment 1, the position where the irradiance of light source 2, which is designated as the reference light source, peaks is between the position where the irradiance of light source 1 peaks and the position where the irradiance of light source 3 peaks, along the conveying direction of the sheet P. Therefore, by emitting light sequentially from the light sources with irradiance peaks on the upstream side of the conveying direction of the sheet P, light source 2, which is designated as the reference light source, emits light at an intermediate timing among the multiple light sources. This makes it possible to minimize the difference in emission timing between the reference light source and one or more other light sources. As a result, the influence of changes in the orientation of the sheet P during conveying can be suppressed, and the type of sheet P can be determined with high accuracy.

[0102] [Embodiment 2] In Embodiment 1, the light emission control unit 251 performs a control to sequentially emit multiple light sources onto the sheet P only once, and the discrimination unit 252 determines the type of sheet P based on the measurement result of that one measurement. In contrast, in Embodiment 2, the light emission control unit 251 performs a control to sequentially emit multiple light sources onto the sheet P multiple times, and the discrimination unit 252 determines the type of sheet P based on the measurement results of multiple measurements. Note that the media sensor in Embodiment 2 has the same configuration as the media sensor 20 in Embodiment 1, so the same reference numerals are used and the description will not be repeated. Embodiment 2 will mainly describe the differences from Embodiment 1.

[0103] Figure 11 is a diagram illustrating the light emission control and sheet type determination method in Embodiment 2. In the example shown in Figure 11, the light emission control unit 251 performs control to sequentially emit light from multiple light sources to the sheet P four times. In the example shown in Figure 11, light source 1 has its irradiance peak furthest upstream of the multiple light sources in the transport direction of the sheet P. In the example shown in Figure 11, light source 2 has its irradiance peak furthest upstream of the multiple light sources, after light source 1 in the transport direction of the sheet P. In the example shown in Figure 11, light source 3 has its irradiance peak furthest downstream of the multiple light sources in the transport direction of the sheet P.

[0104] The light emission control unit 251, in each cycle, causes the light sources to emit light sequentially, starting with the light source whose irradiance peak is on the upstream side in the transport direction of the sheet P. Therefore, in the example shown in Figure 11, the light emission control unit 251 performs the control of causing light source 1, light source 2, and light source 3 to emit light in this order four times. Irradiation area group F1 shown in Figure 11 indicates the area irradiated by the first light emission control. Irradiation area group F2 shown in Figure 11 indicates the area irradiated by the second light emission control. Irradiation area group F3 shown in Figure 11 indicates the area irradiated by the third light emission control. Irradiation area group F4 shown in Figure 11 indicates the area irradiated by the fourth light emission control. Figure 11 shows the state in which light source 3 is emitting light during the fourth light emission control.

[0105] With this type of light emission control, in each cycle, the illumination area AR1 when light source 1 is emitted, the illumination area AR2 when light source 2 is emitted, and the illumination area AR3 when light source 3 is emitted overlap with each other.

[0106] The discrimination unit 252 calculates the relative relationship between the amount of light received from the reference light source and the amount of light received from each of the one or more other light sources for each of the multiple measurements. The discrimination unit 252 determines the type of sheet P based on the average relative relationship obtained from the relative relationships of the multiple measurements.

[0107] More specifically, first, the discrimination unit 252 calculates the average value of the ratio Rw1 over four trials (hereinafter referred to as "average value Rwave1"). Next, the discrimination unit 252 calculates the average value of the ratio Rw3 over four trials (hereinafter referred to as "average value Rwave3"). Finally, the discrimination unit 252 determines the type of sheet P based on average value Rwave1 and average value Rwave3.

[0108] Thus, in the media sensor 20 of Embodiment 2, the type of sheet P is determined based on the average relative relationship obtained from multiple relative relationships. Therefore, the influence of in-plane variation in sheet characteristics can be further suppressed. Consequently, the media sensor 20 of Embodiment 2 can determine the type of sheet P with higher accuracy.

[0109] [Embodiment 3] In Embodiment 1, the media sensor 20 had three reflective light sources for one light-receiving sensor 22. In Embodiment 3, the media sensor has three reflective light sources and two transmissive light sources for one light-receiving sensor 22. Embodiment 3 mainly differs from Embodiment 1 in the points described below.

[0110] The media sensor in Embodiment 3 will be described with reference to Figures 12 and 13. Figure 12 is the first diagram showing the positional relationship between the light receiving sensor and the multiple light sources in Embodiment 3. Figure 13 is the second diagram showing the positional relationship between the light receiving sensor and the multiple light sources in Embodiment 3.

[0111] In Embodiment 3, the media sensor 20A is provided with three reflective light sources and two transmissive light sources for one light receiving sensor 22. The three reflective light sources include light source 1, light source 2, and light source 3. The two transmissive light sources include light source 4 and light source 5. The three reflective light sources and two transmissive light sources are an example of "multiple light sources".

[0112] Since light sources 1, 2, and 3 in Embodiment 3 are the same as those in Embodiment 1, the description will not be repeated. Light sources 4 and 5 emit light in a wavelength range that passes through sheet P. Light sources 4 and 5 are, for example, LEDs.

[0113] Light sources 4 and 5 are arranged along the transport direction of sheet P. Light sources 4 and 5 are placed on the substrate surface 241 of substrate 24. The light receiving sensor 22 is placed on the substrate surface 231.

[0114] The substrate 24 is positioned so that the substrate surface 241 and the sheet P are parallel. The distance dt between the light-emitting point LP of the light-transmitting light source and the sheet P is the same for both light-transmitting light sources. That is, the distance d4 between the light-emitting point LP4 of light source 4 and the sheet P is the same as the distance d5 between the light-emitting point LP5 of light source 5 and the sheet P. If the light-emitting region of the light-transmitting light source is extended, the light-emitting point LP of the light-transmitting light source is considered to be at the center of the light-emitting region.

[0115] The distance ht between the substrate surface 241 and the light-emitting point LP of the light-transmitting light source (hereinafter also referred to as "height of the light-emitting point ht") is the same for both light-transmitting light sources. That is, the distance h4 between the substrate surface 241 and the light-emitting point LP4 of light source 4 and the distance h5 between the substrate surface 241 and the light-emitting point LP5 of light source 5 are the same.

[0116] The two transmission light sources are positioned close to each other and side by side. Light sources 4 and 5 emit light of different wavelengths. In Embodiment 3, there is one reference light source each for the reflection light source and the transmission light source. In the three reflection light sources, the reference light source is light source 2, and light sources 1 and 3 are "one or more other light sources" in the three reflection light sources. In the two transmission light sources, the reference light source is light source 5, and light source 4 is "one or more other light sources" in the two transmission light sources. The light emitted by light source 5, which is the reference light source in the two transmission light sources, is infrared light that is less affected by the characteristics of sheet P.

[0117] The light receiving sensor 22 is positioned on the optical path of the light emitted from each of the three reflective light sources and reflected from the surface of the sheet P, and on the optical path of the light emitted from each of the two transmissive light sources and transmitted through the sheet P. In the following description, the light emitted from the transmissive light sources and transmitted through the sheet P will be referred to as "transmitted light". The aperture 26 that regulates the amount of transmitted light is designed to be sufficiently large.

[0118] Light sources 4 and 5 are arranged on concentric circles centered on the light receiving sensor 22. Therefore, the distance rt between the light emission point LP of the light transmission light source and the light receiving point RP of the light receiving sensor 22, along a plane parallel to the sheet P, is the same for both light transmission light sources. That is, the distance r4 between the light emission point LP4 of light source 4 and the light receiving point RP of the light receiving sensor 22, along a plane parallel to the sheet P, and the distance r5 between the light emission point LP5 of light source 5 and the light receiving point RP of the light receiving sensor 22, along a plane parallel to the sheet P, are the same.

[0119] Light sources 1, 2, 3, 4, and 5 have different positions where their irradiance peaks. Preferably, the position where the irradiance of light source 2, which is designated as the reference light source among the three reflective light sources, peaks is between the position where the irradiance of light source 1 peaks and the position where the irradiance of light source 3 peaks, along the conveying direction of the sheet P.

[0120] The light emission control unit 251 controls the light emission of light sources 1, 2, 3, 4, and 5. As a result, light sources 1, 2, 3, 4, and 5 emit light for a predetermined amount of time at a predetermined time in a predetermined order relative to the sheet P passing through the transport path R. More specifically, the light emission control unit 251 causes light sources 1, 2, 3, 4, and 5 to emit light in order from the light source with the peak irradiance on the upstream side in the transport direction of the sheet P. As a result, light sources 1, 2, 3, 4, and 5 emit light in order from the light source with the peak irradiance on the upstream side in the transport direction of the sheet P.

[0121] Light emitted from each of the three reflective light sources is diffusely reflected off the surface of sheet P, and the reflected light (diffuse light) is incident on the light receiving sensor 22. Light emitted from each of the two transmissive light sources that passes through sheet P is also incident on the light receiving sensor 22. The light receiving sensor 22 acquires a light intensity indicating the amount of reflected light for each of the three reflective light sources, and a light intensity indicating the amount of transmitted light for each of the two transmissive light sources. The emission power of the two transmissive light sources is calibrated so that the light intensity acquired by the light receiving sensor 22 is the same for both transmissive light sources when the two transmissive light sources are emitted sequentially without sheet P passing through them. This allows the light transmittance of sheet P to be evaluated from the light intensity received by the light receiving sensor 22. The discrimination unit 252 determines the type of sheet P based on the reflectivity and transmittance of sheet P.

[0122] More specifically, first, the discrimination unit 252 calculates the ratio Rw1 and the ratio Rw3 using the above-mentioned formula 1. Next, with respect to the light source used for transmission, the discrimination unit 252 calculates the relative relationship between the amount of light received by the reference light source and the amount of light received by each of the one or more other light sources. More specifically, with respect to the light source used for transmission, the discrimination unit 252 calculates the ratio of the amount of light received by each of the one or more other light sources to the amount of light received by the reference light source using the above-mentioned formula 1.

[0123] More specifically, the discrimination unit 252 calculates the ratio of the amount of light received by light source 4 to the amount of light received by light source 5, which is designated as the reference light source for the transmitted light source (hereinafter referred to as "ratio Rw4").

[0124] Next, the discrimination unit 252 determines the type of sheet P based on ratios Rw1, Rw3, and Rw4. The discrimination unit 252 transmits the type of sheet P to the control device 10. The control device 10 changes the heating and pressurizing conditions of the fixing unit 40 according to the type of sheet P.

[0125] Furthermore, the relative relationship between the amount of light received by the reference light source and the amount of light received by each of the one or more other light sources for a light source used for transmission may also be expressed as the difference between the amount of light received by the reference light source and the amount of light received by each of the one or more other light sources.

[0126] Furthermore, although the reflective portion 25 is omitted from Figure 12 for the sake of readability, the media sensor 20A also includes the reflective portion 25.

[0127] As described above, in the media sensor 20A of Embodiment 3, the light sources with the peak irradiance on the upstream side in the transport direction of the sheet P are emitted in order. Therefore, the irradiation areas of the multiple light sources overlap with each other.

[0128] It is preferable that the irradiation areas overlap by 50% or more among the multiple light sources. If the multiple light sources have lumbershan characteristics, each of the multiple light sources satisfies the arrangement conditions shown by Equation 2 above, and by emitting light sequentially from the light source with the peak of irradiance on the upstream side in the transport direction of the sheet P, the irradiation areas overlap by 50% or more among the multiple light sources.

[0129] It is more preferable that the irradiation areas overlap by 80% or more among the multiple light sources. When the multiple light sources have lumbershan characteristics, each of the multiple light sources satisfies the arrangement conditions shown by Equation 3 above, and by emitting light sequentially from the light source with the peak of irradiance on the upstream side in the transport direction of the sheet P, the irradiation areas overlap by 80% or more among the multiple light sources.

[0130] The maximum distance between multiple light sources (represented by "D" in Equations 2 and 3) is, for three reflective light sources, the distance Dr between the light emission point LP1 of light source 1 and the light emission point LP3 of light source 3, and for two transmissive light sources, the distance Dt between the light emission point LP4 of light source 4 and the light emission point LP5 of light source 5.

[0131] The distance between each light-emitting point LP of the multiple light sources and the sheet P (represented by "d" in Equations 2 and 3) is dr for reflective light sources and dt for transmissive light sources.

[0132] The distance (r in equations 2 and 3) between the light-emitting point LP of each of the multiple light sources along a plane parallel to sheet P and the center of the light-receiving surface 22a of the light-receiving sensor 22 (light-receiving point RP) is rr for the reflective light source (see Figure 5) and rt for the transmissive light source.

[0133] The characteristics of sheet P measured by reflected light and transmitted light are different. Therefore, distances Dr and Dt may be the same, or they may be different. Also, distances dr and dt may be the same, or they may be different. Furthermore, distances rr and rt may be the same, or they may be different.

[0134] Furthermore, when multiple light sources have Lambertshan characteristics, it is preferable that at least one of Equations 2 and 3 is satisfied for both the reflective light source and the transmissive light source, but it is also acceptable for only one of the reflective light source or the transmissive light source to satisfy at least one of Equations 2 and 3.

[0135] Thus, in the media sensor 20A of Embodiment 3, the light sources with the peak irradiance on the upstream side in the transport direction of the sheet P are emitted in order, so that the irradiation areas overlap among the multiple light sources. Therefore, in the media sensor 20A of Embodiment 3, the measurement area is the same or close to the same area among the multiple light sources, so the influence of in-plane variation in sheet characteristics can be suppressed. Consequently, the media sensor 20A of Embodiment 3 can determine the type of sheet P with higher accuracy.

[0136] In Embodiment 3, the three reflective light sources and the two transmissive light sources are arranged on concentric circles centered on the light receiving sensor 22. As a result, even if the position of the sheet P changes in the normal direction, the relative values ​​of the amount of light received by the light receiving sensor 22 among the multiple reflective light sources (or multiple transmissive light sources) do not change. Therefore, the influence of positional changes of the sheet P in the normal direction can be suppressed, and the type of sheet P can be determined with high accuracy.

[0137] In Embodiment 3, three reflective light sources are arranged on the same substrate surface 231, and two transmissive light sources are arranged on the same substrate surface 241. This allows the heights hr and ht of the light-emitting points LP to be precisely positioned at desired locations. Furthermore, the distances dr and dt between the light-emitting points LP and the sheet P can be precisely positioned at desired locations.

[0138] In Embodiment 3, the discrimination unit 252 determines the type of sheet P based on the relative relationship between the amount of light received from a reference light source and the amount of light received from each of the one or more other light sources. As a result, even if the position of sheet P changes in the normal direction, the relative value of the amount of light received acquired by the light receiving sensor 22 among the multiple reflective light sources (or multiple transmissive light sources) does not change. In other words, the influence of positional changes of sheet P in the normal direction can be suppressed. Therefore, the type of sheet P can be determined with high accuracy.

[0139] In Embodiment 3, the light emitted by light sources 2 and 5, which are used as reference light sources, is infrared light that is less affected by the characteristics of sheet P. Therefore, the type of sheet P can be determined with high accuracy.

[0140] In Embodiment 3, the reference light source 2 in the three reflective light sources is positioned in the center of the arrangement of the three reflective light sources. As a result, in the multiple reflective light sources, the reference light source and each of the one or more other light sources are positioned in close proximity. Also, the reference light source 5 in the two transmissive light sources is positioned in close proximity to light source 4. Therefore, the influence of changes in the orientation of the sheet P during transport can be suppressed, and the type of sheet P can be determined with high accuracy.

[0141] In Embodiment 3, the position where the irradiance of light source 2, which is designated as the reference light source among the three reflective light sources, peaks was between the position where the irradiance of light source 1 peaks and the position where the irradiance of light source 3 peaks, along the conveying direction of the sheet P. Therefore, by emitting light sequentially from the light source with the irradiance peak on the upstream side in the conveying direction of the sheet P, light source 2, which is designated as the reference light source among the three reflective light sources, emits light at an intermediate timing among the three reflective light sources. This makes it possible to minimize the difference in emission timing between the reference light source and one or more other light sources among the three reflective light sources. As a result, the influence of changes in the orientation of the sheet P during conveying can be suppressed, and the type of sheet P can be determined with high accuracy.

[0142] [Embodiment 4] In Embodiment 1, the media sensor 20 had the same light-emitting point height across multiple light sources. In Embodiment 4, the media sensor has different light-emitting point heights across multiple light sources. Embodiment 4 mainly differs from Embodiment 1 in the following points.

[0143] Figure 14 is a first diagram showing the positional relationship between the light receiving sensor and the multiple light sources in Embodiment 4. Figure 15 is a second diagram showing the positional relationship between the light receiving sensor and the multiple light sources in Embodiment 4.

[0144] In the media sensor 20B of Embodiment 4, similar to Embodiment 1, three reflective light sources are provided for one light-receiving sensor 22. The three reflective light sources include light source 1, light source 2, and light source 3. Except that the heights of the light-emitting points of light source 1, light source 2, and light source 3 are different from each other, and that light source 1, not light source 2, emits infrared light, light sources 1, light source 2, and light source 3 in Embodiment 4 are the same as light sources 1, light source 2, and light source 3 in Embodiment 1.

[0145] Light sources 1, 2, and 3 are arranged along the transport direction of sheet P. Light sources 1, 2, and 3 are arranged in close proximity to each other on the substrate surface 231 of substrate 23. The light receiving sensor 22 is also arranged on the substrate surface 231.

[0146] The height hr of the light-emitting point LP differs for light source 1, light source 2, and light source 3. As mentioned above, the height hr is the distance between the substrate surface 231 and the light-emitting point LP of the reflective light source. More specifically, the height h1 of the light-emitting point LP1 of light source 1, the height h2 of the light-emitting point LP2 of light source 2, and the height h3 of the light-emitting point LP3 of light source 3 are all different.

[0147] Of the heights h1, h2, and h3, height h2 is the lowest and height h3 is the highest. Of the heights h1, h2, and h3, height h1 is the intermediate height. In Embodiment 4, among the three reflective light sources, light source 1, whose light emission point LP height hr is the intermediate height, is designated as the "reference light source," and light sources 2 and 3 are designated as "one or more other light sources." That is, in Embodiment 4, the reference light source is neither the light source with the longest distance between the light emission point LP and the substrate surface 231 on which the multiple light sources are arranged, nor the light source with the shortest distance between the light emission point LP and the substrate surface 231. Light source 1, which is designated as the reference light source, is positioned in the center of the arrangement of the three reflective light sources.

[0148] Light sources 1, 2, and 3 emit light of different wavelengths. The light emitted by light source 1, which is the reference light source, is infrared light that is less affected by the characteristics of sheet P.

[0149] If the heights hr of the light-emitting points LP differ among the three reflective light sources, the relative values ​​of the light received by the light-receiving sensor 22 will change due to changes in the orientation of the sheet P. Therefore, it is better to shift the arrangement of the three reflective light sources away from a concentric arrangement centered on the light-receiving sensor 22.

[0150] Therefore, in Embodiment 4, the arrangement of light sources 1, 2, and 3 is deviated from a concentric arrangement centered on the light receiving sensor 22. As a result, in Embodiment 4, the distance rr between the light emission point LP of the reflective light source and the light receiving point RP of the light receiving sensor 22 along a plane parallel to the sheet P is different for each of the three reflective light sources. That is, the distance r1 between the light emission point LP1 of light source 1 and the light receiving point RP of the light receiving sensor 22 along a plane parallel to the sheet P, the distance r2 between the light emission point LP2 of light source 2 and the light receiving point RP of the light receiving sensor 22 along a plane parallel to the sheet P, and the distance r3 between the light emission point LP3 of light source 3 and the light receiving point RP of the light receiving sensor 22 along a plane parallel to the sheet P are all different.

[0151] The distance dr between the light-emitting point LP of the reflective light source and the sheet P is also different for each of the three reflective light sources. That is, the distance d1 between the light-emitting point LP1 of light source 1 and the sheet P, the distance d2 between the light-emitting point LP2 of light source 2 and the sheet P, and the distance d3 between the light-emitting point LP3 of light source 3 and the sheet P are all different.

[0152] The distance d0 shown in Figure 14 represents the distance between the light receiving point RP of the light receiving sensor 22 and the sheet P.

[0153] Light sources 1, 2, and 3 have different positions where their irradiance peaks. The position where the irradiance of light source 1, which is designated as the reference light source, peaks is between the position where the irradiance of light source 2 peaks and the position where the irradiance of light source 3 peaks, along the conveying direction of the sheet P. Light sources 1, 2, and 3 emit light for predetermined periods of time in a predetermined order to the sheet P as it passes through the conveying path R. More specifically, among light sources 1, 2, and 3, the light source with the irradiance peak on the upstream side in the conveying direction of the sheet P emits light in order. As described in Embodiment 1, the discrimination unit 252 determines the type of sheet P based on the relative relationship between the amount of light received by the reference light source and the amount of light received by each of the one or more other light sources.

[0154] Figure 16 is a graph showing the ideal arrangement conditions for light sources 1 and 2, in which the ratio of the amount of light received by light source 1 and the amount of light received by light source 2, as acquired by the light receiving sensor 22, does not change even when the position of sheet P changes. The horizontal axis B in Figure 16 is expressed by the following equation 4, using the distances d0, d1, and r1 shown in Figure 14.

[0155] B=2r1 / (d0+d1)...Equation 4

[0156] The vertical axis A in Figure 16 can be expressed by the following equation 5, using the distances r1, r2, h1, and h2 shown in Figure 14.

[0157] A=(r2-r1) / (h2-h1)...Equation 5

[0158] Figure 16 shows the results obtained from a ray simulation of the ideal arrangement conditions for light sources 1 and 2, in which, when the position of sheet P in the normal direction changes and distances d0, d1, and d2 change, the amount of light emitted from light source 1, reflected by sheet P and received by the light receiving sensor 22, and the amount of light emitted from light source 2, reflected by sheet P and received by the light receiving sensor 22, do not change relatively, that is, the ratio of the two amounts of light remains unchanged.

[0159] The simulation will follow the following conditions: The light source follows a Lambertian distribution. • The light-emitting area is sufficiently small. Sheet P is perfectly diffused. The aperture 26 (see Figure 4) that regulates the amount of reflected light is sufficiently large. The magnitudes of distances d0, d1, and d2 are close to each other. The variation in the position of sheet P in the normal direction is within the range of +10% to -10% of (d0+d1) / 2.

[0160] The graph shown in Figure 16 is obtained by averaging the results of simulations of the variation in the position of sheet P on the side where distances d0, d1, and d2 are increased, and the results of simulations of the variation in the position of sheet P on the side where distances d0, d1, and d2 are decreased.

[0161] By arranging light sources 1 and 2 to satisfy the arrangement conditions shown in Figure 16, the amount of light emitted from light source 1, reflected by sheet P and received by the light receiving sensor 22, and the amount of light emitted from light source 2, reflected by sheet P and received by the light receiving sensor 22, do not change relatively when the position of sheet P in the normal direction changes. Therefore, the type of sheet P can be determined with high accuracy.

[0162] When B on the horizontal axis, as shown in Figure 16, is 0.84 or higher, in order for light source 1 and light source 2 to satisfy the ideal arrangement conditions, light source 1 and light source 2 should be arranged so that A on the vertical axis is negative.

[0163] More specifically, according to Equation 5, in the case where the height h1 of the light-emitting point LP1 of light source 1 is higher than the height h2 of the light-emitting point LP2 of light source 2 (h2-h1<0), in order for A<0, we must set r2-r1>0. That is, the distance r1 between the light-emitting point LP1 of light source 1 and the light-receiving point RP along a plane parallel to sheet P is shorter than the distance r2 between the light-emitting point LP2 of light source 2 and the light-receiving point RP along a plane parallel to sheet P.

[0164] From Equation 5, if the height h2 of the light-emitting point LP2 of light source 2 is higher than the height h1 of the light-emitting point LP1 of light source 1 (h2-h1>0), then in order for A<0, we must set r2-r1<0. That is, the distance r2 between the light-emitting point LP2 of light source 2 and the light-receiving point RP along a plane parallel to sheet P must be shorter than the distance r1 between the light-emitting point LP1 of light source 1 and the light-receiving point RP along a plane parallel to sheet P.

[0165] The arrangement conditions for light source 1 and light source 2 when B on the horizontal axis shown in Figure 16 is 0.84 or higher also apply to light source 1 and light source 3. That is, when B on the horizontal axis shown in Figure 16 is 0.84 or higher, the higher the height hr of the light source's light emission point LP, the shorter the distance rr between the light emission point LP and the light receiving point RP of the light source along the plane parallel to sheet P.

[0166] When B on the horizontal axis, as shown in Figure 16, is less than 0.84, in order for light source 1 and light source 2 to satisfy the ideal arrangement conditions, light source 1 and light source 2 should be arranged so that A on the vertical axis is positive.

[0167] More specifically, according to Equation 5, when the height h1 of the light-emitting point LP1 of light source 1 is higher than the height h2 of the light-emitting point LP2 of light source 2 (h2-h1<0), in order for A>0, we must set r2-r1<0. That is, the distance r1 between the light-emitting point LP1 of light source 1 and the light-receiving point RP along a plane parallel to sheet P is made longer than the distance r2 between the light-emitting point LP2 of light source 2 and the light-receiving point RP along a plane parallel to sheet P.

[0168] From Equation 5, if the height h2 of the light-emitting point LP2 of light source 2 is higher than the height h1 of the light-emitting point LP1 of light source 1 (h2-h1>0), then in order for A>0, we must set r2-r1>0. That is, the distance r2 between the light-emitting point LP2 of light source 2 and the light-receiving point RP along a plane parallel to sheet P must be longer than the distance r1 between the light-emitting point LP1 of light source 1 and the light-receiving point RP along a plane parallel to sheet P.

[0169] The arrangement conditions for light source 1 and light source 2 when B on the horizontal axis shown in Figure 16 is less than 0.84 also apply to light source 1 and light source 3. That is, when B on the horizontal axis shown in Figure 16 is less than 0.84, the higher the height hr of the light source's light emission point LP, the longer the distance rr between the light emission point of the light source and the light receiving point RP of the light receiving sensor 22, along the plane parallel to sheet P.

[0170] When the light source is positioned such that the horizontal axis B is 0.84 or greater and the vertical axis A is negative, the ideal light source positioning conditions shown in Figure 16 are represented by an almost straight line. On the other hand, in order to satisfy the ideal light source positioning conditions when the horizontal axis B is less than 0.84, the light source must be positioned so that the vertical axis A is positive. In the range where the vertical axis A is positive, as shown in Figure 16, the value of the vertical axis A increases rapidly as the horizontal axis B decreases. In the range where the vertical axis A is positive, errors in light source positioning make it easier for the light source positioning conditions to deviate from the ideal positioning conditions.

[0171] Therefore, it is preferable that the multiple light sources be arranged such that A is negative (B is 0.84 or greater) among the arrangement conditions shown by the curve in Figure 16. In other words, it is preferable that the arrangement is designed so that the longer the distance between each light-emitting point LP of the multiple light sources and the substrate surface on which the multiple light sources are arranged, the shorter the distance between each light-emitting point LP of the multiple light sources and the center of the light-receiving surface 22a of the light-receiving sensor (light-receiving point RP) along the plane parallel to the sheet P.

[0172] Thus, in the media sensor 20B of Embodiment 4, the light sources with the peak irradiance on the upstream side in the transport direction of the sheet P are emitted in order, so the irradiation areas overlap among the multiple light sources. Therefore, in the media sensor 20B of Embodiment 4, the measurement area is the same or close to the measurement area among the multiple light sources, so the influence of in-plane variation in sheet characteristics can be suppressed. Consequently, the media sensor 20B of Embodiment 4 can determine the type of sheet P with higher accuracy.

[0173] In Embodiment 4, the height h1 of the light-emitting point LP1 of the reference light source 1 is the midpoint among the heights of the light-emitting points of the multiple light sources. This reduces the difference between the height h1 of the light-emitting point LP1 of light source 1 and the height h2 of the light-emitting point LP2 of light source 2, and also reduces the difference between the height h1 of the light-emitting point LP1 of light source 1 and the height h3 of the light-emitting point LP3 of light source 3. Therefore, when the height hr of the light-emitting point LP of each light source, and / or the distance rr between the light-emitting point LP and the light-receiving point RP of the light-receiving sensor 22 along a plane parallel to the sheet P, deviates from the ideal arrangement conditions (see Figure 16), the influence of positional fluctuations of the sheet P in the normal direction can be suppressed. Thus, the type of sheet P can be determined with high accuracy.

[0174] In Embodiment 4, the multiple light sources included multiple reflective light sources. However, when the multiple light sources include multiple transmissive light sources, it is preferable that the multiple transmissive light sources also satisfy the ideal arrangement conditions shown in Figure 16.

[0175] [Differentiation] Modifications of Embodiments 1 to 4 will be described below.

[0176] (Variation 1) In embodiments 1 to 4, the multiple reflective light sources do not have to be arranged on the same substrate surface 231. In embodiment 3, the multiple transmissive light sources do not have to be arranged on the same substrate surface 241.

[0177] (Modification 2) In embodiments 1 to 4, the discrimination unit 252 may determine the type of sheet P based on the amount of light received from each of the one or more other light sources, without calculating the relative relationship between the amount of light received from the reference light source and the amount of light received from each of the one or more other light sources.

[0178] (Variation 3) In embodiments 1 to 4, the multiple light sources may or may not have lumbershan characteristics. When the multiple light sources have lumbershan characteristics, lenses are not required for the light sources, and a light source with a simple configuration can be realized.

[0179] (Modification 4) In Embodiments 1 to 4, the number of multiple reflective light sources is not limited to 3. In Embodiments 1 to 4, when the number of multiple reflective light sources is 2N-1 and N is an integer of 2 or more, it is preferable that the reference light source in the multiple reflective light sources is positioned at the Nth position in the sequence of multiple reflective light sources. In Embodiments 1 to 4, when the number of multiple reflective light sources is 2N and N is an integer of 2 or more, it is preferable that the reference light source in the multiple reflective light sources is positioned at the Nth or N+1th position in the sequence of multiple reflective light sources.

[0180] As a result, the reference light source in a multi-reflector system is positioned approximately in the center of the arrangement of the multi-reflector system. This ensures that the reference light source and each of the one or more other light sources are positioned in close proximity. Therefore, the effects of changes in the orientation of the sheet P during transport can be minimized, enabling highly accurate identification of the sheet P type.

[0181] In Embodiment 3, the number of multiple light sources for transmission is not limited to 2. In Embodiment 3, if the number of multiple light sources for transmission is 2N-1 and N is an integer of 2 or more, it is preferable that the reference light source in the multiple light sources is positioned at the Nth position in the sequence of the multiple light sources. In Embodiment 3, if the number of multiple light sources for transmission is 2N and N is an integer of 2 or more, it is preferable that the reference light source in the multiple light sources is positioned at the Nth or N+1th position in the sequence of the multiple light sources.

[0182] As a result, the reference light source in a group of transmissive light sources is positioned approximately in the center of the arrangement of the multiple transmissive light sources. This ensures that in a group of transmissive light sources, the reference light source and each of the one or more other light sources are positioned in close proximity. Therefore, the effects of changes in the orientation of the sheet P during transport can be suppressed, allowing for highly accurate identification of the type of sheet P.

[0183] (Variation 5) In Embodiments 1 to 4, the number of multiple reflective light sources is not limited to 3. In Embodiments 1 to 4, when the number of multiple reflective light sources is 2N-1 and N is an integer of 2 or more, it is preferable that the reference light source among the multiple reflective light sources is the Nth light source from the upstream side in the conveying direction of the sheet P, where the position where the irradiance of the multiple reflective light sources is at its peak. In Embodiments 1 to 4, when the number of multiple reflective light sources is 2N and N is an integer of 2 or more, it is preferable that the reference light source among the multiple reflective light sources is the Nth or N+1th light source from the upstream side in the conveying direction of the sheet P, where the position where the irradiance of the multiple reflective light sources is at its peak.

[0184] As a result, the reference light source among the multiple reflective light sources emits light at approximately the midpoint of the timing of the other reflective light sources. This minimizes the difference in emission timing between the reference light source and one or more other light sources among the multiple reflective light sources. Therefore, the influence of changes in the orientation of the sheet P during transport can be suppressed, allowing for highly accurate identification of the type of sheet P.

[0185] In Embodiment 3, the number of multiple transmission light sources is not limited to 2. In Embodiment 3, when the number of multiple transmission light sources is 2N-1 and N is an integer of 2 or more, it is preferable that the reference light source among the multiple transmission light sources is the Nth light source from the upstream side in the conveying direction of the sheet P, where the position where the irradiance of the multiple transmission light sources is at its peak. In Embodiment 3, when the number of multiple transmission light sources is 2N and N is an integer of 2 or more, it is preferable that the reference light source among the multiple transmission light sources is the Nth or N+1th light source from the upstream side in the conveying direction of the sheet P, where the position where the irradiance of the multiple transmission light sources is at its peak.

[0186] As a result, the reference light source in the multiple light sources emits light at approximately the midpoint of the timing of the other light sources. This minimizes the difference in emission timing between the reference light source and one or more other light sources in the multiple light sources. Therefore, the influence of changes in the orientation of the sheet P during transport can be suppressed, allowing for highly accurate identification of the type of sheet P.

[0187] (Experimental variation 6) Embodiment 3 and Embodiment 2 may be combined. Embodiment 4 and Embodiment 2 may also be combined.

[0188] [Note] The embodiments and variations described above include the following technical concepts.

[0189] [Configuration 1] Multiple light sources, For each of the aforementioned multiple light sources, a light receiving sensor is provided to acquire a light receiving amount indicating the amount of reflected or transmitted light from the light source irradiated onto the sheet, The system includes a discrimination unit that determines the type of sheet based on the amount of light received obtained for each of the plurality of light sources, The aforementioned plurality of light sources are arranged along the conveying direction of the sheet, A discrimination device that emits light sequentially from the light source having the peak of irradiance on the upstream side in the transport direction among the plurality of light sources.

[0190] [Configuration 2] The discriminant device according to configuration 1, wherein the type of sheet includes at least one of plain paper, recycled paper, and coated paper.

[0191] [Configuration 3] The discrimination device according to configuration 1 or 2, wherein the plurality of light sources are arranged in concentric circles centered on the light receiving sensor.

[0192] [Structure 4] A discrimination device according to any one of configurations 1 to 3, wherein the irradiation area of ​​the sheet irradiated by the light overlaps by 50% or more among the multiple light sources.

[0193] [Composition 5] The discrimination device according to configuration 4, wherein the plurality of light sources have Lambertshan characteristics.

[0194] [Composition 6] If the conveying speed of the sheet is v, the emission interval of the plurality of light sources is t, the distance between each light-emitting point of the plurality of light sources and the center of the light-receiving surface of the light-receiving sensor along a plane parallel to the sheet is r, the distance between each light-emitting point of the plurality of light sources and the sheet is d, and the maximum distance between the plurality of light sources is D, then the arrangement conditions for each of the plurality of light sources are: |(D-vt) / (d 2 +r 2 / 4) 1 / 2 |<0.71 A discrimination device according to configuration 5 that satisfies the relationship.

[0195] [Composition 7] The discrimination device further comprises a substrate on which the plurality of light sources are arranged, The discrimination device according to any one of configurations 1 to 6, wherein the plurality of light sources are arranged on the same substrate surface of the substrate.

[0196] [Structure 8] The plurality of light sources include a reference light source and one or more other light sources different from the reference light source. The discrimination device according to any one of configurations 1 to 7, wherein the discrimination unit determines the type of the sheet based on the relative relationship between the amount of light received for the reference light source and the amount of light received for each of the one or more other light sources.

[0197] [Composition 9] When the number of the multiple light sources is 2N-1 and N is an integer of 2 or more, the reference light source is the Nth light source from the upstream side in the transport direction, where the position where the irradiance peaks among the multiple light sources is. The discrimination device according to configuration 8, wherein when the number of the plurality of light sources is 2N and N is an integer of 2 or more, the reference light source is the Nth or N+1th light source from the upstream side in the transport direction among the plurality of light sources, where the position where the irradiance peaks is located.

[0198] [Configuration 10] The discrimination device further comprises a light emission control unit that controls the emission of light from the plurality of light sources, The light emission control unit performs a control multiple times to cause the sheet to emit light from the multiple light sources in sequence. The discrimination device according to configuration 8 or 9, wherein the discrimination unit calculates the relative relationship for each of the multiple times and determines the type of sheet based on the average relative relationship obtained from the relative relationships of the multiple times.

[0199] [Composition 11] The discriminant device according to any one of configurations 8 to 10, wherein the light emitted by the reference light source is infrared light.

[0200] [Composition 12] The aforementioned multiple light sources include three or more light sources, When the number of the multiple light sources is 2N-1 and N is an integer of 2 or more, the reference light source is positioned at the Nth position in the arrangement of the multiple light sources. The discrimination device according to any one of configurations 8 to 11, wherein, when the number of the plurality of light sources is 2N and N is an integer of 2 or more, the reference light source is positioned as the Nth or N+1th in the arrangement of the plurality of light sources.

[0201] [Composition 13] The discrimination device according to configuration 5, wherein the distance between each light-emitting point of the plurality of light sources and the substrate surface on which the plurality of light sources are arranged increases, and the distance between each light-emitting point of the plurality of light sources and the center of the light-receiving surface of the light-receiving sensor along a plane parallel to the sheet decreases.

[0202] [Composition 14] The aforementioned reference light source is not the light source among the plurality of light sources that has the longest distance between its light-emitting point and the substrate surface on which the plurality of light sources are arranged, The discrimination device according to configuration 8, wherein the reference light source is not the light source among the plurality of light sources that has the shortest distance between its light-emitting point and the substrate surface.

[0203] [Composition 15] The discrimination device according to configuration 7, wherein the substrate is arranged so that the substrate surface and the sheet are parallel.

[0204] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0205] 1,2,3,4,5 Light source, 10,210 Control device, 11,211 Processor, 12,212 Memory, 13,213 Storage, 15 Paper feed unit, 20,20A,20B Media sensor, 22 Light receiving sensor, 22a Light receiving surface, 23,24 Substrate, 25 Reflecting part, 26 Aperture, 30 Image forming unit, 31 Intermediate transfer belt, 32 Image forming unit, 33 Transfer roller, 34 Nip part, 35 x,y,z arrows, 40 Fixing unit, 50 Operation panel, 51 Input unit, 52 Display unit, 60 Communication interface, 83 Tray, 99,299 Bus, 100 Image forming apparatus, 131,214 Program, 231,241 Substrate surface, 251 Light emission control unit, 252 Discrimination unit, 500 External device, A Vertical axis: AR1, AR2, AR3 Irradiation area, B Horizontal axis: Dr, Dt, d0, d1, d2, d3, d4, d5, dr, dt, h1, h2, h3, h4, h5, hr, ht, r1, r2, r3, r4, r5, rr, rt Distance, F1, F2, F3, F4 Irradiation area group, LP, LP1, LP2, LP3, LP4, LP5 Light emission point, P Sheet, R Transport path, RP Light receiving point, Rw1, Rw3, Rw4 Ratio, Rwave1, Rwave3 Average value.

Claims

1. Multiple light sources, For each of the aforementioned multiple light sources, a light receiving sensor is provided to acquire a light receiving amount indicating the amount of reflected or transmitted light from the light source irradiated onto the sheet, The system includes a discrimination unit that determines the type of sheet based on the amount of light received obtained for each of the plurality of light sources, The plurality of light sources are arranged along the conveying direction of the sheet and are arranged in concentric circles centered on the light receiving sensor. Of the plurality of light sources, the light sources having the peak of irradiance on the upstream side in the transport direction are emitted in order. A discrimination device in which at least a portion of the illumination area of ​​the sheet, which is irradiated by light from each of the plurality of light sources, overlaps with each other.

2. The discrimination device according to claim 1, wherein the type of sheet includes at least one of plain paper, recycled paper, and coated paper.

3. The discrimination device according to claim 1 or 2, wherein the irradiation area overlaps by 50% or more between the multiple light sources.

4. The discrimination device according to claim 3, wherein the plurality of light sources have Lambertshan characteristics.

5. If the conveying speed of the sheet is v, the emission interval of the plurality of light sources is t, the distance between each light-emitting point of the plurality of light sources and the center of the light-receiving surface of the light-receiving sensor along a plane parallel to the sheet is r, the distance between each light-emitting point of the plurality of light sources and the sheet is d, and the maximum distance between the plurality of light sources is D, then the arrangement conditions for each of the plurality of light sources are: |(D-vt) / (d ２ +r ２ / 4) １／２ |<0.71 The discrimination device according to claim 4, which satisfies the relationship.

6. The discrimination device further comprises a substrate on which the plurality of light sources are arranged, The discrimination device according to claim 1 or 2, wherein the plurality of light sources are arranged on the same substrate surface of the substrate.

7. The plurality of light sources include a reference light source and one or more other light sources different from the reference light source. The discrimination device according to claim 1 or 2, wherein the discrimination unit determines the type of the sheet based on the relative relationship between the amount of light received for the reference light source and the amount of light received for each of the one or more other light sources.

8. When the number of the plurality of light sources is 2N-1 and N is an integer of 2 or more, the reference light source is the Nth light source from the upstream side in the transport direction, where the position where the irradiance peaks among the plurality of light sources is. The discrimination device according to claim 7, wherein, when the number of the plurality of light sources is 2N and N is an integer of 2 or more, the reference light source is the Nth or N+1th light source from the upstream side in the transport direction among the plurality of light sources, where the position where the irradiance peaks is located.

9. The discrimination device further comprises a light emission control unit that controls the emission of light from the plurality of light sources, The light emission control unit performs a control multiple times to cause the sheet to emit light from the multiple light sources in sequence. The discrimination device according to claim 7, wherein the discrimination unit calculates the relative relationship for each of the multiple times and determines the type of sheet based on the average relative relationship obtained from the relative relationships of the multiple times.

10. The discrimination device according to claim 7, wherein the light emitted by the reference light source is infrared light.

11. The aforementioned multiple light sources include three or more light sources, When the number of the multiple light sources is 2N-1 and N is an integer of 2 or more, the reference light source is positioned at the Nth position in the arrangement of the multiple light sources. The discrimination device according to claim 7, wherein, when the number of the plurality of light sources is 2N and N is an integer of 2 or more, the reference light source is positioned as the Nth or N+1th in the arrangement of the plurality of light sources.

12. The aforementioned reference light source is not the light source among the plurality of light sources that has the longest distance between its light-emitting point and the substrate surface on which the plurality of light sources are arranged, The discrimination device according to claim 7, wherein the reference light source is not the light source among the plurality of light sources that has the shortest distance between its light-emitting point and the substrate surface.

13. The discrimination device according to claim 6, wherein the substrate is arranged so that the substrate surface and the sheet are parallel.

14. An image forming apparatus comprising the discrimination device described in Claim 1.

15. A method for determining the type of sheet, The process includes irradiating the sheet with light from each of the multiple light sources such that at least a portion of the irradiation area of ​​the sheet irradiated by light from each of the multiple light sources overlaps with each other. The plurality of light sources are arranged along the conveying direction of the sheet and are arranged in concentric circles centered on the light receiving sensor. The aforementioned determination method is, Among the plurality of light sources, the light sources having the peak of irradiance on the upstream side in the transport direction are to be emitted in order, For each of the aforementioned multiple light sources, the amount of light received, which indicates the amount of reflected or transmitted light from the light source irradiated onto the sheet, is obtained from the light receiving sensor. A method for determining the type of sheet, further comprising determining the type of sheet based on the amount of light received obtained for each of the plurality of light sources.

16. A program that causes a computer to execute a method for determining the type of sheet, The determination method includes irradiating the sheet with light from each of the multiple light sources such that at least a portion of the irradiation area of ​​the sheet irradiated with light by each of the multiple light sources overlaps with each other. The plurality of light sources are arranged along the conveying direction of the sheet and are arranged in concentric circles centered on the light receiving sensor. The aforementioned determination method is, Among the plurality of light sources, the light sources having the peak of irradiance on the upstream side in the transport direction are to be emitted in order, For each of the aforementioned multiple light sources, the amount of light received, which indicates the amount of reflected or transmitted light from the light source irradiated onto the sheet, is obtained from the light receiving sensor. A program further comprising determining the type of sheet based on the amount of light received obtained for each of the plurality of light sources.

Images