JP7694146B2 - Recording medium discrimination device, image forming apparatus, and recording medium discrimination method - Google Patents

Description

The present invention relates to a recording medium discrimination device, an image forming device, and a recording medium discrimination method.

Conventionally, in image forming devices that apply color materials to recording media such as paper to form images, a recording medium discrimination device that discriminates the type of recording medium is used. By adjusting the conditions related to image formation (e.g., transport conditions and color material fixing conditions) according to the type of recording medium that has been discriminated, it is possible to form images with higher quality.

A recording medium discrimination device is known that discriminates one characteristic of a recording medium based on the amount of reflected light and/or fluorescent light received when the recording medium is irradiated with inspection light in a specified wavelength range, and discriminates the type of recording medium based on the discrimination result (for example, Patent Document 1). The characteristics of the recording medium to be discriminated include the material, the presence or absence of fluorescent whitening agent, and the degree of gloss of the surface. In Patent Document 1, the presence or absence of fluorescent whitening agent is discriminated by irradiating the recording medium with inspection light in the ultraviolet wavelength range and detecting the amount of fluorescent light received. In addition, the degree of gloss is discriminated by detecting the amount of diffusely reflected light of the inspection light.

JP 2006-16166 A

However, in the above-mentioned conventional technology in which one characteristic of a recording medium is identified using an inspection light of one wavelength range, if the amount of received light varies due to factors other than the characteristic to be identified, it becomes difficult to accurately identify the characteristic of the recording medium. For example, if the amount of reflected light of the inspection light varies due to differences in the basis weight of the recording medium, it is not possible to determine whether the variation is due to the characteristic to be identified of the recording medium or due to other factors such as basis weight.
As described above, in the conventional technology, it may be difficult to accurately determine the characteristics of a recording medium, and there is a problem in that erroneous determination of the type of recording medium may occur.

The object of this invention is to provide a recording medium discrimination device, an image forming device, and a recording medium discrimination method that can more appropriately discriminate the type of recording medium.

In order to achieve the above object, the present invention provides a recording medium discrimination device, comprising:
a light irradiation unit that irradiates the recording medium with inspection light;
a light detection unit that detects incident light including at least one of diffuse reflected light of the inspection light irradiated onto the recording medium and fluorescence excited by the inspection light in the recording medium;
a discrimination unit that discriminates a characteristic of the recording medium based on a detection result of the first incident light corresponding to the first inspection light and the second incident light corresponding to the second inspection light by the light detection unit;
Equipped with
the first inspection light has a peak intensity wavelength of 750 nm or more and 1100 nm or less;
the second inspection light has a peak intensity wavelength shorter than that of the first inspection light;
The light irradiation unit includes:
a first light emitting element that emits the first inspection light;
a second light emitting element that emits the second inspection light having a certain peak wavelength;
a third light emitting element that emits the second inspection light having a peak wavelength different from the certain peak wavelength;
having
The discrimination means is
determining a certain characteristic of the recording medium based on a detection result of the first incident light corresponding to the first inspection light and a detection result of the second incident light corresponding to the second inspection light emitted by the second light-emitting element;
Based on a detection result of the first incident light corresponding to the first inspection light and a detection result of the second incident light corresponding to the second inspection light emitted by the third light-emitting element, a determination is made regarding a characteristic of the recording medium that is different from the certain characteristic .

The present invention relates to a recording medium discrimination device, comprising:
The discrimination means discriminates the characteristic based on a ratio between a first value corresponding to the amount of light received by the light detection unit of the first incident light and a second value corresponding to the amount of light received by the light detection unit of the second incident light.

The present invention relates to a recording medium discrimination device, comprising :
The discrimination means discriminates the characteristic based on a region that includes coordinates corresponding to the detection result among a plurality of predetermined regions on a coordinate plane having two axes defined by the first value and the second value.

According to a fourth aspect of the present invention, in the recording medium discrimination device according to the third aspect,
The multiple regions are divided by straight lines that are non-parallel to the two axes of the coordinate plane.

The invention described in claim 5 is the recording medium discrimination device described in any one of claims 1 to 4,
The second inspection light has a peak intensity wavelength of 390 nm or more and 440 nm or less.

The present invention relates to a recording medium discrimination device, comprising:
The second inspection light has a peak intensity wavelength of 280 nm or more and 400 nm or less.

The invention described in claim 7 is the recording medium discrimination device described in any one of claims 1 to 6,
The first inspection light has a peak intensity wavelength of 800 nm or more and 900 nm or less.

The invention described in claim 8 is the recording medium discrimination device described in any one of claims 1 to 7,
the light detection unit has a light receiving element that detects the incident light,
The light receiving element is a photodiode or a phototransistor having detection sensitivity in a wavelength range from the visible wavelength range to the near infrared wavelength range.

The present invention relates to a recording medium discrimination device, comprising:
a substrate provided at a position facing a transport path of the recording medium;
the light irradiation unit has a light emitting element that emits the inspection light,
the light detection unit has a light receiving element that detects the incident light,
The light emitting element and the light receiving element are provided on the substrate.

The present invention relates to a recording medium discrimination device, comprising:
The first light-emitting element, the second light-emitting element, and the third light-emitting element emit light in sequence such that their irradiation periods are different from one another .

In order to achieve the above object, the present invention provides an image forming apparatus comprising:
A recording medium discrimination device according to any one of claims 1 to 10 ,
an image forming unit that applies a coloring material to the recording medium to form an image;
Equipped with.

In order to achieve the above object, the present invention provides a recording medium discrimination method, comprising:
A recording medium discrimination method using a recording medium discrimination device including a light irradiation unit that irradiates an inspection light onto a recording medium, and a light detection unit that detects incident light including at least one of diffuse reflected light of the inspection light irradiated onto the recording medium and fluorescence excited by the inspection light in the recording medium, the method comprising:
determining a characteristic of the recording medium based on a detection result by the light detection unit of the first incident light corresponding to the first inspection light and the second incident light corresponding to the second inspection light;
the first inspection light has a peak intensity wavelength of 750 nm or more and 1100 nm or less;
the second inspection light has a peak intensity wavelength shorter than that of the first inspection light;
The light irradiation unit includes:
a first light emitting element that emits the first inspection light;
a second light emitting element that emits the second inspection light having a certain peak wavelength;
a third light emitting element that emits the second inspection light having a peak wavelength different from the certain peak wavelength;
having
In the above step,
determining a certain characteristic of the recording medium based on a detection result of the first incident light corresponding to the first inspection light and a detection result of the second incident light corresponding to the second inspection light emitted by the second light-emitting element;
Based on a detection result of the first incident light corresponding to the first inspection light and a detection result of the second incident light corresponding to the second inspection light emitted by the third light-emitting element, a determination is made regarding a characteristic of the recording medium that is different from the certain characteristic .

The present invention makes it possible to more appropriately determine the type of recording medium.

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus. 1 is a block diagram showing a main functional configuration of an image forming apparatus; FIG. 2 is a diagram illustrating a configuration of a media inspection unit. 11A and 11B are diagrams illustrating light to be detected by a medium inspection unit. 5A and 5B are diagrams illustrating examples of emission spectra of a first light-emitting element and a second light-emitting element. FIG. 4 is a diagram illustrating an example of the spectral sensitivity characteristics of a light receiving element. FIG. 1 is a diagram showing examples of reflectance spectra of plain paper and recycled paper. FIG. 13 is a diagram showing an example of the difference in reflectance spectrum depending on whether or not a bluing is applied. 1 is a diagram showing an example of the relationship between the wavelength that excites fluorescence in a recording medium to which a fluorescent whitening agent has been added and the intensity of the excited fluorescence. FIG. 1 is a diagram showing an example of differences in reflectance spectrum depending on the amount of fluorescent whitening agent added. FIG. 13 is a diagram showing an example of differences in reflectance spectrum depending on the color of colored paper. FIG. 11 is a diagram showing an example of the amount of reflected light depending on the basis weight. 10 is a flowchart showing a control procedure for a recording medium discrimination process. 13 is a diagram showing an example distribution of the reflectance R1 of the first inspection light and the reflectance R2 of the second inspection light for plain paper, coated paper, recycled paper, and medium-quality paper. FIG. 13A and 13B are diagrams illustrating an example of distribution of the reflectance R1 of the first inspection light and the reflectance R2 of the second inspection light for strong fluorescence paper and weak fluorescence paper. FIG. 13 is a diagram showing the configuration of a media inspection unit when the first and third embodiments are combined. 13 is a diagram showing an example distribution of the reflectance R1 of the first inspection light and the reflectance R2 of the second inspection light on white paper and colored paper; FIG. 13 is a diagram showing an example distribution of the reflectance R1 of the first inspection light and the reflectance R2 of the second inspection light on white paper and colored paper; FIG. 13 is a diagram showing the configuration of a medium inspection unit according to a modified example. 5 is a diagram showing an example of the spectral sensitivity characteristics of a first light receiving element and a second light receiving element; FIG.

The following describes embodiments of the recording medium discrimination device, image forming device, and recording medium discrimination method of the present invention with reference to the drawings.

(Configuration of image forming apparatus and recording medium discrimination device)
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention.
FIG. 2 is a block diagram showing the main functional configuration of the image forming apparatus 1. As shown in FIG.
The image forming apparatus 1 is an MFP (Multifunction Peripheral) that forms an image on a recording medium by an electrophotographic method. The image forming apparatus 1 includes a control unit 10, a medium inspection unit 20, an image forming unit 30, a fixing unit 40, a scanner 50, an operation display unit 60, a communication unit 70, a paper feed tray 81, a transport roller 82, a paper discharge tray 83, and a bus 90. As shown in FIG. 2, the control unit 10 and the medium inspection unit 20 constitute a recording medium discrimination device 2 that discriminates the type of recording medium. The various units of the image forming apparatus 1 are connected to each other by the bus 90.

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

The CPU 11 reads and executes the program 131 stored in the memory unit 13 to perform various calculation processes.

RAM 12 provides working memory space for CPU 11 and stores temporary data.

The storage unit 13 is composed of a non-volatile storage device such as a hard disk drive (HDD), a solid state drive (SSD), and a flash memory, and stores a program 131 executed by the CPU 11, various data, etc. The data stored in the storage unit 13 includes image data acquired by the scanner 50, image data input from the outside via the communication unit 70, and discrimination reference data 132 referenced in the discrimination operation of the recording medium described below.

The control unit 10 functions as a discrimination means by the CPU 11 executing various processes by executing the program 131 stored in the storage unit 13. The control unit 10 as a discrimination means discriminates one characteristic of the recording medium based on the data acquired from the media inspection unit 20, and discriminates the type of the recording medium based on the discrimination result. The discrimination of the type of the recording medium will be described in detail later.
Furthermore, the control unit 10 performs overall control of each unit of the image forming apparatus 1 by the CPU 11 executing the program 131. For example, the control unit 10 operates each unit of the image forming unit 30, the transport roller 82, and the fixing unit 40 based on image data stored in the storage unit 13 to form an image on the recording medium. Here, the CPU 11 changes the operation related to image formation of each unit of the image forming apparatus 1 according to the discrimination result of the recording medium by the recording medium discrimination device 2. As an example, the CPU 11 changes the transport speed and clamping pressure of the transport roller 82 according to the type of recording medium. Also, the CPU 11 changes the heating temperature and applied pressure of the fixing unit 40 according to the type of recording medium.

The media inspection unit 20 is provided along the transport path of the recording medium from the feed tray 81 to the discharge tray 83, upstream of the image forming unit 30. However, the location of the media inspection unit 20 is not limited thereto, and the media inspection unit 20 can be located at any position along the transport path. As shown in FIG. 2, the media inspection unit 20 includes a light irradiation unit 21 and a light detection unit 22. The light irradiation unit 21 irradiates the recording medium passing through the transport path with inspection light under the control of the control unit 10. The light detection unit 22 detects incident light including at least one of the diffuse reflection light of the inspection light irradiated to the recording medium and the fluorescence excited by the inspection light in the recording medium. The configuration and operation of the media inspection unit 20 will be described in detail later.

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

The fixing unit 40 heats and pressurizes the recording medium onto which the toner image has been transferred, fixing the toner image to the recording medium. The fixing unit 40 has a pair of rollers consisting of a heating roller and a pressure roller that sandwich the recording medium. The recording medium onto which the toner image has been fixed is transported by transport rollers 82 and sent to a paper output tray 83. The heating and pressure conditions used by the fixing unit 40 are controlled by the control unit 10 according to the type of recording medium, etc.

The scanner 50 is equipped with an optical system including a light source and a reflecting mirror, and an image sensor, and reads an image of a recording medium transported along a predetermined transport path or a recording medium placed on a platen glass, and generates image data in a bitmap format for each of the colors R (red), G (green), and B (blue). The generated image data is stored in the memory unit 13. The scanned image can also be copied onto another recording medium by performing image formation by the image forming unit 30 based on this image data.

The operation display unit 60 includes a display device such as a liquid crystal display, a touch panel arranged over the screen of the display device, and an input device such as operation keys. The operation display unit 60 displays various types of information such as the operation status and processing results of the image forming device 1 on the display device, and also converts user input operations on the input device into operation signals and outputs them to the control unit 10.

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

The paper feed tray 81 stores recording media before image formation. The paper feed tray 81 may store multiple types (varieties) of recording media. Here, the type of recording media is characterized by at least one of the following characteristics: the material (raw material) of the recording media, the state of the surface treatment, the presence or absence and amount of fluorescent whitening agent, the presence or absence of bluing, and color. Therefore, recording media that differ from each other in at least one of these characteristics are recording media of different types. The recording media stored in the paper feed tray 81 are, for example, plain paper, coated paper, medium-weight paper, and recycled paper, which are examples of recording media of different types. Plain paper is paper made mainly from wood-based pulp (i.e., pulp that is not recycled from waste paper, usually chemical pulp). Coated paper is paper with a coating material or the like applied to the surface. Medium-weight paper is paper made mainly from mechanical pulp, for example. Recycled paper is paper in which waste paper pulp extracted from waste paper is mixed at a predetermined or higher mixing ratio. The types of recording media stored in the paper feed tray 81 are not limited to those described above.

The transport roller 82 rotates while holding a sheet of recording medium, thereby transporting the recording medium along the transport path. The transport timing and transport speed of the transport roller 82 are controlled by the control unit 10 according to the type of recording medium, etc.

The output tray 83 holds the recording medium on which an image has been formed until it is removed by the user.

(Configuration of the Media Inspection Section)
Next, the configuration of the media inspection unit 20 will be described.
FIG. 3 is a diagram showing the configuration of the media inspection unit 20. As shown in FIG.
Fig. 3A is a cross-sectional view of the media inspection unit 20 as viewed from a direction parallel to the transport path (transport surface) of the recording medium M. Fig. 3B is a plan view of the media inspection unit 20 as viewed from a direction perpendicular to the transport surface (z direction). The media inspection unit 20 includes an element substrate 23 (substrate) provided at a position facing the transport surface of the transport path of the recording medium M (in other words, at a position facing the recording medium M passing through the transport path), a paper passing guide 25 that supports the recording medium M so that the recording medium M moves along the transport path, and an optical aperture 24 provided on the opposite side of the paper passing guide 25 with the recording medium M in between.

The element substrate 23 is disposed perpendicular to the z direction. On the surface of the element substrate 23 facing the recording medium M, the first light-emitting element 211 and the second light-emitting element 212 of the light irradiation unit 21 and the light-receiving element 220 of the light detection unit 22 are provided. The first light-emitting element 211 irradiates the recording medium M with the first inspection light L1a. The second light-emitting element 212 irradiates the recording medium M with the second inspection light L2a. The light detection unit 22 has one light-receiving element 220. The light-receiving element 220 outputs a photocurrent according to the amount of incident light. The light detection unit 22 converts this photocurrent into a voltage, then converts it into digital data and outputs it to the control unit 10. As shown in Figures 3(a) and 3(b), the light-receiving element 220 is disposed between the first light-emitting element 211 and the second light-emitting element 212. It is preferable that the distance from the first light-emitting element 211 to the light-receiving element 220 is equal to the distance from the second light-emitting element 212 to the light-receiving element 220.

The optical aperture 24 is a plate-like member arranged perpendicular to the z direction, and has an opening in a range including the portions facing the first light-emitting element 211, the second light-emitting element 212, and the light-receiving element 220. The first inspection light L1a and the second inspection light L2a pass through this opening and enter the recording medium M. In addition, the optical aperture 24 has light-blocking properties in the portions other than the opening, preventing light other than the inspection light from entering the recording medium M.

The recording medium M is transported through the gap between the optical aperture 24 and the paper guide 25. Since this gap has a width in the z direction, the passing position of the recording medium M can vary in the z direction within the range of this width. In response to this variation in the passing position of the recording medium M, the distance between the first light-emitting element 211, the second light-emitting element 212, and the light-receiving element 220 and the recording medium M also varies. However, since the first light-emitting element 211, the second light-emitting element 212, and the light-receiving element 220 are provided on the same surface of the element substrate 23, the effect of this variation on the inspection results by the media inspection unit 20 can be minimized.

FIG. 4 is a diagram for explaining the light to be detected by the medium inspection unit 20. As shown in FIG.
The inspection light LA (the above-mentioned first inspection light L1a or second inspection light L2a) emitted from the light irradiation unit 21 is incident on the surface of the recording medium M. The reflected light of this inspection light LA on the recording medium M includes surface diffuse reflected light LB1 and regular reflected light LC. In addition, a part of the inspection light LA that enters the inside of the recording medium M is diffusely reflected in a direction having a z-direction component as internal diffuse reflected light LB2. In this specification, the surface diffuse reflected light LB1 and the internal diffuse reflected light LB2 are collectively referred to as "diffuse reflected light". In addition, when a fluorescent whitening agent is added to the recording medium M, depending on the wavelength of the inspection light LA, fluorescence LB3 is excited in the recording medium M. The light detection unit 22 (light receiving element 220) of this embodiment detects the surface diffuse reflected light LB1, the internal diffuse reflected light LB2, and the fluorescence LB3. Hereinafter, the light incident on the light receiving element 220 of the light detection unit 22 in response to the irradiation of the first inspection light L1a will be referred to as the "first incident light L1b", and the light incident on the light receiving element 220 of the light detection unit 22 in response to the irradiation of the second inspection light L2a will be referred to as the "second incident light L2b" (see FIG. 3A). The light receiving element 220 is provided at a position where it does not receive the regular reflection light LC of the inspection light LA emitted in the main light emission direction (the direction in which the light emission intensity is the highest) of the first light emitting element 211 and the second light emitting element 212. Note that instead of the configuration in which a single light receiving element 220 is provided, a light receiving element that detects the first incident light L1b and a light receiving element that detects the second incident light L2b may be provided separately.

FIG. 5 is a diagram showing an example of the emission spectrum of the first light-emitting element 211 and the second light-emitting element 212. In FIG.
The first inspection light L1a emitted from the first light-emitting element 211 has a peak intensity wavelength (center wavelength) of 750 nm or more and 1100 nm or less. More preferably, the peak intensity wavelength of the first inspection light L1a is 800 nm or more and 900 nm or less. The second inspection light L2a emitted from the second light-emitting element 212 has a peak intensity wavelength shorter than that of the first inspection light L1a. The peak wavelength of the second inspection light L2a is set according to the purpose of the inspection, as described later. FIG. 5 illustrates a case where the peak intensity wavelength of the first inspection light L1a is 850 nm and the peak intensity wavelength of the second inspection light L2a is 400 nm. The half-width of the emission spectrum of the first light-emitting element 211 and the second light-emitting element 212 can be, for example, about 20 to 30 nm, but is not limited thereto. The first light emitting element 211 and the second light emitting element 212 may be, for example, a light emitting diode (LED) or a laser diode (LD), but are not limited thereto.

FIG. 6 is a diagram showing an example of the spectral sensitivity characteristic of the light receiving element 220. As shown in FIG.
As shown in FIG. 6, the light receiving element 220 of the light detection unit 22 has detection sensitivity (light receiving sensitivity) in a wavelength range from the visible wavelength range to the near infrared wavelength range. Here, the visible wavelength range is approximately 380 nm or more and 780 nm or less. The near infrared wavelength range is approximately 780 nm or more and 2500 nm or less. As the light receiving element 220, a photodiode or a phototransistor can be used. In particular, a Si (silicon) photodiode, a Si phototransistor, a Ge (germanium) photodiode, or a Ge phototransistor having detection sensitivity in a wavelength range from the visible wavelength range to the near infrared wavelength range can be preferably used. As shown in FIG. 6, these photodiodes and phototransistors have a spectral sensitivity characteristic in which the light receiving sensitivity increases toward the longer wavelength side from the visible wavelength range to the near infrared wavelength range. Therefore, since the light receiving sensitivity of the fluorescence (blue region of the visible wavelength range) is higher than that of the excitation light of the fluorescence (ultraviolet wavelength range), it can be preferably used to determine the presence or absence and amount of a fluorescent whitening agent, as described later. In particular, the accuracy of fluorescence discrimination is higher when borosilicate glass or coating resin is used than when quartz is used as the window of the light receiving element 220, since the light receiving sensitivity in the ultraviolet wavelength range is lower. Note that elements other than photodiodes and phototransistors may be used as the light receiving element 220.

Before inspecting the recording medium M, the light emission intensity of each of the first light-emitting element 211 and the second light-emitting element 212 is calibrated, so that the reflectance of the recording medium M can be calculated from the amount of light received by the light-receiving element 220. That is, first, a predetermined reflective member for calibration is placed in the irradiation range of the first inspection light L1a (second inspection light L2a) from the first light-emitting element 211 (second light-emitting element 212), and the amount of light received by the light detection unit 22 of the reflected light from the reflective member is detected. As the reflective member for calibration, a standard white board, a predetermined paper, a predetermined sheet, or the like can be used. Thereafter, the recording medium M to be inspected is transported to the position of the media inspection unit 20, and the first inspection light L1a (second inspection light L2a) is irradiated from the first light-emitting element 211 (second light-emitting element 212) to the recording medium M, and the amount of light received by the light detection unit 22 of the first incident light L1b (second incident light L2b) is detected. From these detection results, the reflectance R1 (reflectance R2) can be calculated. In this specification, the reflectance is defined as "amount of incident light received when the recording medium M is irradiated with the inspection light/amount of reflected light received when the inspection light is irradiated with the calibration reflecting member." Therefore, when fluorescence is excited in the recording medium M, the amount of fluorescent light received is reflected in the reflectance in addition to the amount of diffuse reflected light received. The reflectance R1 calculated from the amount of light received by the light detection unit 22 of the first incident light L1b is one aspect of the "first value." Also, the reflectance R2 calculated from the amount of light received by the light detection unit 22 of the second incident light L2b is one aspect of the "second value."

The first light-emitting element 211 and the second light-emitting element 212 emit light alternately under the control of the control unit 10. In other words, the period during which the first light-emitting element 211 irradiates the recording medium M with the first inspection light L1a is different from the period during which the second light-emitting element 212 irradiates the recording medium M with the second inspection light L2a. The light detection unit 22 detects the first incident light L1b corresponding to the irradiation of the first inspection light L1a and the second incident light L2b corresponding to the irradiation of the second inspection light L2a alternately in sequence. That is, the medium inspection unit 20 of this embodiment performs time-division measurement. Note that the light-emitting periods of the first light-emitting element 211 and the second light-emitting element 212 may overlap in part. In this case, the first incident light L1b may be detected during a period during which only the first light-emitting element 211 is emitting light, and the second incident light L2b may be detected during a period during which only the second light-emitting element 212 is emitting light.

(Operations of the image forming apparatus and the recording medium discrimination device)
Next, the operations of the image forming apparatus 1 and the recording medium discrimination device 2 will be described, focusing on the operations related to discrimination of the type of recording medium.

The optimal transport conditions and fixing conditions for the recording medium in the image forming apparatus 1 differ depending on the type of recording medium. The type of recording medium to be transported may be set according to the user's operation on the operation display unit 60, but setting it every time is troublesome and may result in incorrect settings. For this reason, in the image forming apparatus 1 of this embodiment, it is possible to determine the type of recording medium by the recording medium discrimination device 2. Specifically, the type of recording medium can be determined based on the discrimination results of the following characteristics (i) to (iv) related to the recording medium.
(i) The material of the recording medium; (ii) Whether or not there is a bluing agent; (iii) The presence or absence and amount of fluorescent whitening agent; and (iv) The color of the recording medium.

When inspection light is irradiated onto a recording medium and the light is detected at a position where the diffuse reflected light of the inspection light can be received, the reflection spectrum is affected by the characteristics of the recording medium, particularly from the ultraviolet wavelength range to the visible wavelength range. In this specification, the reflection spectrum is defined as the sum of the spectrum of the diffuse reflected light and the spectrum of the fluorescent light. Below, we will first explain the effects that the above characteristics (i) to (iv) of the recording medium have on the reflection spectrum.

(i) Material of the recording medium In the shorter wavelength side than the near-infrared wavelength range, i.e., in the visible and ultraviolet wavelength ranges, there are many wavelength ranges in which the reflectance spectrum is affected by the material (raw material) of the recording medium. For example, in recycled paper containing a large amount of waste paper pulp, light is absorbed by impurities, so that the reflectance is lower than that of plain paper from the ultraviolet wavelength range to the visible wavelength range, as shown in FIG. 7. In addition, in medium-weight paper containing a large amount of mechanical pulp, light is absorbed by pulp and lignin, so that the reflectance is similarly lower than that of plain paper from the ultraviolet wavelength range to the visible wavelength range. For this reason, by acquiring the reflectance using inspection light in a wavelength range where the reflectance is lower, it is possible to distinguish the recording medium based on the difference in the material of the recording medium.

(ii) Presence or absence of bluing In some cases, a process called "bluing" is carried out in which a blue dye is added to a recording medium to improve the whiteness. In a recording medium that has been bluing-tinted, the dye causes absorption in the green to red wavelength range (approximately 500 to 750 nm), as shown in FIG. 8, and the reflectance in the blue wavelength range is relatively high. Therefore, by obtaining the reflectance using an inspection light in the wavelength range where absorption occurs, it is possible to distinguish the recording medium based on the presence or absence of bluing.

(iii) Presence or absence and amount of fluorescent brightener In some cases, a process called "fluorescent brightening" is carried out to improve the whiteness of a recording medium by adding a fluorescent brightener to the recording medium. The fluorescent brightener mainly absorbs excitation light in the ultraviolet wavelength range and emits fluorescence in the blue wavelength range. FIG. 9 is a diagram showing an example of the relationship between the wavelength that excites fluorescence in a recording medium to which a fluorescent brightener has been added and the intensity of the excited fluorescence. As shown in FIG. 9, the excitation light in the ultraviolet wavelength range is absorbed, and blue fluorescence on the longer wavelength side is generated. As a result, as shown in FIG. 10, the apparent reflectance from the ultraviolet wavelength range to the visible (blue) wavelength range is increased by the fluorescence. Also, the reflectance increases more as the amount of the fluorescent brightener added increases. Therefore, by acquiring the reflectance using inspection light in the wavelength range in which fluorescence is generated, it is possible to distinguish the recording medium based on the presence or absence and amount of the fluorescent brightener.

(iv) Color of the Recording Medium Colored paper colored with dye (coloring material) absorbs light in a specific wavelength range according to the color of the dye. As a result, as shown in Fig. 11, the reflectance in the wavelength range corresponding to the color of the colored paper becomes relatively large, and the desired color is exhibited. Therefore, by acquiring the reflectance using inspection light in a wavelength range where absorption occurs due to the dye, it is possible to distinguish the recording medium based on the difference in color.

In this way, the influence of various characteristics of the recording medium appears in the reflection spectrum, particularly from the visible wavelength range to the ultraviolet wavelength range. Therefore, by irradiating the recording medium with inspection light in a wavelength range in which the influence of the characteristic to be identified appears, it is possible to determine the characteristics of the recording medium based on the amount of reflected light and fluorescent light received, and identify the type of recording medium.

However, when one characteristic of a recording medium is identified using inspection light in one wavelength range, if the amount of received light varies due to factors other than the characteristic being identified, it becomes difficult to accurately identify the characteristics of the recording medium. For example, as shown in FIG. 12, the amount of reflected light of the inspection light varies depending on the basis weight of the recording medium. If the basis weight of the recording medium to be identified is unknown, it is not possible to distinguish between the variation in the amount of reflected light caused by the basis weight and the variation in the amount of received light caused by the characteristics of the recording medium. For this reason, with a method using inspection light in one wavelength range, it is difficult to accurately identify the characteristics of the recording medium, and erroneous determination of the type of recording medium is likely to occur.

On the other hand, as shown in FIGS. 7, 8, 10 and 11, the fluctuation in the reflection spectrum caused by the characteristics of the recording medium hardly occurs in the near-infrared wavelength range.
Therefore, in the recording medium discrimination device 2 of this embodiment, a first inspection light in a near-infrared wavelength range with little fluctuation due to the characteristics of the recording medium and a second inspection light in a wavelength range where the influence of the characteristics of the recording medium appears are used to discriminate one characteristic of the recording medium while taking into consideration the wavelength dependency in the two wavelength ranges. That is, based on the amount of received first incident light L1b corresponding to the first inspection light L1a, the fluctuation due to factors other than the characteristics of the recording medium in the amount of received second incident light L2b corresponding to the second inspection light L2a is subtracted (cancelled).

As described above, the peak wavelength of the intensity of the first inspection light L1a is set to 750 nm or more and 1100 nm or less. By setting the upper limit at 1100 nm, it is possible to suppress fluctuations in the amount of received light caused by water contained in the recording medium. This is because water has a unique absorption band in the range of 1450 nm and 1940 nm, which is derived from the bond vibration of the stretching motion and bending vibration of hydrogen atoms and oxygen atoms. In addition, by setting the peak wavelength of the intensity of the first inspection light L1a to 800 nm or more and 900 nm or less, it is possible to make it less susceptible to the effects of the characteristics of the recording medium.

As a method of determining the characteristics of a recording medium based on the detection results of the first incident light L1b and the second incident light L2b, for example, there is a method of determining based on the ratio of the reflectance R1 calculated from the amount of received first incident light L1b to the reflectance R2 calculated from the amount of received second incident light L2b (hereinafter referred to as the reflectance ratio R2/R1). For example, even if the amount of reflected light varies due to differences in basis weight, this variation can be offset by taking the reflectance ratio R2/R1. Therefore, the reflectance ratio R2/R1 reflects the influence of the characteristics of the recording medium excluding the influence of basis weight. Therefore, by using the reflectance ratio R2/R1, the characteristics of the recording medium can be appropriately determined and the type of recording medium can be accurately identified.

The following describes how the recording medium discrimination device 2 discriminates the above characteristics (i) to (iv) related to a recording medium.

Example 1: Determination of the material of a recording medium
First, as a first embodiment, a method for determining the type (paper quality) of a recording medium based on the absorption of inspection light by the material of the recording medium will be described.

In the first embodiment, the second inspection light L2a has a peak wavelength of 390 nm or more and 440 nm or less. This is because, as shown in FIG. 7, in this wavelength range, absorption due to the material of the recording medium is likely to occur. In addition, by setting the lower limit at 390 nm, the main excitation wavelength of the fluorescence shown in FIG. 9 can be excluded. Therefore, even if a fluorescent whitening agent is added to the recording medium, the contribution of the fluorescence can be reduced, so that the material can be identified with high accuracy. In addition, as shown in FIG. 6, the light receiving element 220 is used, which has a spectral sensitivity characteristic in which the light receiving sensitivity increases toward the long wavelength side from the visible wavelength range to the near-infrared wavelength range, so that the contribution of the fluorescence can be reduced and the material can be identified with high accuracy. In addition, the accuracy of the identification can be further improved by using a light receiving element that does not have sensitivity in the ultraviolet wavelength range.

Next, the recording medium discrimination process executed by the control unit 10 of the recording medium discrimination device 2 in the first embodiment will be described. Here, an example will be described in which, when the recording medium is blank, it is determined whether the recording medium is plain paper or coated paper, or recycled paper or medium-weight paper. According to this method, for example, when plain paper and medium-weight paper are stored in the paper feed tray 81 of the image forming device 1, it is possible to determine whether the recording medium being conveyed is plain paper or medium-weight paper.

FIG. 13 is a flowchart showing a control procedure for the recording medium discrimination process.
When the recording medium discrimination process is started, the control unit 10 causes the first light-emitting element 211 to start emitting the first inspection light, and causes the second light-emitting element 212 to start emitting the second inspection light (step S101). Here, the control unit 10 causes the first light-emitting element 211 and the second light-emitting element 212 to emit light so that their light-emitting periods are different from each other (for example, alternately).

Based on the output signal from a sensor (not shown), the control unit 10 determines whether the recording medium has moved to a position opposite the media inspection unit 20 (step S102). If it is determined that the recording medium has not moved ("NO" in step S102), the control unit 10 executes the process of step S102 again. If it is determined that the recording medium has moved to a position opposite the media inspection unit 20 ("YES" in step S102), the control unit 10 acquires the amount of the first incident light L1b received by the light receiving element 220 and calculates the reflectance R1 of the first inspection light L1a. The control unit 10 also acquires the amount of the second incident light L2b received by the light receiving element 220 and calculates the reflectance R2 of the second inspection light L2a (step S103). In detail, the control unit 10 calculates the reflectance R1 from the amount of light received by the light receiving element 220 when the first inspection light L1a is irradiated onto the recording medium, and calculates the reflectance R2 from the amount of light received by the light receiving element 220 when the second inspection light L2a is irradiated onto the recording medium.

The control unit 10 terminates the emission of the first inspection light L1a and the second inspection light L2a (step S104).

The control unit 10 determines whether the reflectance ratio R2/R1 is equal to or greater than a reference value V (step S105). The reference value V is set according to the characteristics of the object to be determined, and is stored in the storage unit 13 as determination reference data 132. In this embodiment, the reference value V is set to 0.88.

If it is determined that the reflectance ratio R2/R1 is equal to or greater than the reference value V ("YES" in step S105), the control unit 10 determines that the recording medium is plain paper or coated paper (step S106). If it is determined that the reflectance ratio R2/R1 is less than the reference value V ("NO" in step S105), the control unit 10 determines that the recording medium is recycled paper or medium-weight paper (step S107).

When step S106 or S107 is completed, the control unit 10 changes the settings related to image formation in accordance with the result of the determination of the type of recording medium (step S108), and ends the recording medium determination process. Note that, if another recording medium is to be subsequently inspected, the process may be returned to step S101 after step S108 is completed.

Here, the determination method in steps S103 to S106 will be described in detail.
14 is a diagram showing an example of distribution of the reflectance R1 of the first inspection light L1a and the reflectance R2 of the second inspection light L2a for plain paper, coated paper, recycled paper, and medium-weight paper. In detail, the reflectance R1 of the first inspection light L1a with a peak wavelength of 850 nm and the reflectance R2 of the second inspection light L2a with a peak wavelength of 405 nm are acquired and plotted for plain paper, coated paper, recycled paper, and medium-weight paper.

The reference line S1 in FIG. 14 is a line corresponding to the reflectance ratio R2/R1=0.88. In other words, the reference line S1 passes through the origin and is a linear function (proportional equation) whose slope is the reference value V. The coordinate plane with the reflectances R1 and R2 as two axes is divided into two regions Aa and Ab by the reference line S1. The region Aa corresponds to the reflectance ratio R2/R1≧V, and the region Ab corresponds to the reflectance ratio R2/R1<V. The plots of plain paper and coated paper are distributed in the region Aa, and the plots of recycled paper and medium-weight paper are distributed in the region Ab. From this, when the detection result of the amount of incident light when an arbitrary recording medium is inspected by the media inspection unit 20 satisfies the reflectance ratio R2/R1≧V (when included in the region Aa), it can be determined that it is plain paper or coated paper, and when the reflectance ratio R2/R1<V is satisfied (when included in the region Ab), it can be determined that it is recycled paper or medium-weight paper.

According to this method, as described above, even if there are factors other than the characteristics of the recording medium that cause the reflectances R1 and R2 to vary, the effects of these factors can be offset and the characteristics of the recording medium can be accurately determined. For example, in the data in FIG. 14, the reflectances R1 and R2 vary due to differences in the basis weight of the recording medium. This can be determined from the fact that the reflectance R1 of the first inspection light L1a, which should have little variation due to the characteristics of the recording medium, varies (reflectance R1 = 0.46 to 1.15 for plain paper and coated paper, and reflectance R1 = 0.78 to 1.05 for recycled paper and medium-weight paper). Due to the effect that the variation in reflectance due to differences in basis weight is also reflected in the reflectance R2 of the second inspection light L2a, the distribution range of the reflectance R2 of plain paper and coated paper (0.48 to 1.1) partially overlaps with the distribution range of the reflectance R2 of recycled paper and medium-weight paper (0.6 to 0.8). For this reason, if only the reflectance R2 of the second inspection light L2a is used, the paper quality of the recording medium cannot be accurately determined. In contrast, by using the reflectance ratio R2/R1 of the first inspection light L1a and the second inspection light L2a as in this embodiment, it is possible to perform a determination that takes into account the wavelength dependency related to the two wavelength ranges. In other words, by using the ratio with the reflectance R1 on the horizontal axis instead of simply using the reflectance R2 on the vertical axis in Figure 14, factors other than the material of the recording medium can be offset.

In FIG. 14, the reference line S1 is a proportional equation whose slope is the reference value V, but is not limited to this. The reference line S1 may be any line that is not parallel to the two axes on a coordinate plane with the reflectances R1 and R2 as the two axes. In other words, the reference line S1 may be expressed as R2=a·R1+b for any constants a and b (where a≠0). In this case, in step S104, if R2≧a·R1+b is satisfied, the process branches to step S105, and if not, the process branches to step S106. The constants a and b are preset and stored in the storage unit 13 as discrimination criterion data 132.

In addition, the coordinate plane may be divided into three or more regions using two or more reference lines, and the recording medium may be identified based on the region among these regions that contains the coordinates corresponding to the detection result of the amount of incident light when the recording medium is inspected by the media inspection unit 20.

The above method can be used to effectively distinguish recycled wood-free paper from among recycled papers. Recycled wood-free paper is paper with a recycled paper pulp content of 70% or more and a whiteness of 75 or less. Paper with a low recycled paper pulp content (for example, a few tens of percent) is less susceptible to absorption by impurities in the pulp, and even if a paper is labeled as having a 100% recycled paper pulp content, if the whiteness has been increased using chemicals such as pulp bleaching, fillers, or fluorescent whitening agents, the paper's physical properties are similar to those of regular paper and wood-free paper.

Example 2: Determination of the Presence or Absence of Blue Tint
The presence or absence of bluing can be determined by the same method as in Example 1. In this case, the reference line S1 may be set so that recording media that have been bluing belong to the area Aa and recording media that have not been bluing belong to the area Ab in Fig. 14 .

Example 3: Determination of the presence and amount of fluorescent whitening agent
Next, as a third embodiment, a method for determining the presence and amount of a fluorescent whitening agent will be described.

In Example 3, the second inspection light L2a is a light having a peak intensity wavelength of 280 nm or more and 400 nm or less. Many fluorescent brighteners generally used in recording media have conjugated double bonds and planar structures, such as stilbenes, distyrylbiphenyls, coumarins, and oxazoles. These materials absorb ultraviolet light of about 280 nm to about 400 nm, transition to an excited state, and emit blue fluorescence of about 400 nm to about 500 nm when relaxing back to the ground state. Therefore, in Example 3, the wavelength range of the second inspection light L2a is different from the wavelength range of the second incident light L2b (mainly fluorescence) corresponding to the second inspection light L2a. By using the second inspection light L2a in the above wavelength range, fluorescence can be detected, so that the presence and amount of the fluorescent brightener can be accurately determined. In addition, as shown in FIG. 6, by using a light receiving element 220 having a spectral sensitivity characteristic in which the light receiving sensitivity increases toward the longer wavelength side from the visible wavelength range to the near-infrared wavelength range, the contribution of reflected light of the excitation light (second inspection light L2a) can be reduced, and the detection of the fluorescence (second incident light L2b) can be performed with high accuracy.

Figure 15 shows an example distribution of the reflectance R1 of the first inspection light L1a and the reflectance R2 of the second inspection light L2a for strong fluorescent paper and weak fluorescent paper. Here, strong fluorescent paper is a recording medium to which a predetermined amount or more of fluorescent brightener has been added. Weak fluorescent paper is a recording medium to which no fluorescent brightener has been added or to which the amount added is less than a predetermined amount. Figure 15 shows the reflectance R1 of the first inspection light L1a with a peak wavelength of 850 nm and the reflectance R2 of the second inspection light L2a with a peak wavelength of 280 nm, which have been acquired and plotted for strong fluorescent paper and weak fluorescent paper.

The reference line S2 in FIG. 15 is a line corresponding to the reflectance ratio R2/R1=0.38. In other words, the reference line S2 is a linear function (proportional equation) that passes through the origin and has a slope of the reference value V (=0.38). The coordinate plane with the reflectances R1 and R2 as two axes is divided into two regions Ba and Bb by the reference line S2. Region Ba corresponds to the reflectance ratio R2/R1≧V, and region Bb corresponds to the reflectance ratio R2/R1<V. The plots of strong fluorescent paper are distributed in region Ba, and the plots of weak fluorescent paper are distributed in region Bb. From this, if the detection result of the amount of incident light when inspecting an arbitrary recording medium with the media inspection unit 20 satisfies the reflectance ratio R2/R1≧V (if included in region Ba), it can be determined that the recording medium is strong fluorescent paper, and if the detection result satisfies the reflectance ratio R2/R1<V (if included in region Bb), it can be determined that the recording medium is strong fluorescent paper. That is, when identifying the recording medium in the third embodiment, step S105 in the flowchart in FIG. 13 should be changed to "identify as strong fluorescent paper" and step S105 should be changed to "identify as weak fluorescent paper."

In Example 3, by using the reflectance ratio R2/R1 of the first inspection light L1a and the second inspection light L2a, it is possible to perform discrimination taking into account the wavelength dependency in the two wavelength ranges. In other words, by using the ratio with the reflectance R1 on the horizontal axis instead of simply using the reflectance R2 on the vertical axis in FIG. 15, it is possible to offset factors other than the fluorescent whitening agent.

As in the first and second embodiments, the reference line S2 may be expressed as R2 = a·R1 + b for any constants a and b (where a ≠ 0). In addition, the coordinate plane may be divided into three or more regions using two or more reference lines, and the amount of fluorescent whitening agent may be determined based on which region the coordinates corresponding to the detection results of the amount of incident light when the recording medium is inspected by the media inspection unit 20 belong to.

<Example 1 + Example 3: Discrimination of both the material of the recording medium and fluorescent whitening>
It is also possible to combine Example 1 and Example 3. That is, for one recording medium, the discrimination related to the material in Example 1 and the discrimination related to the fluorescent whitening agent in Example 3 can be performed in combination.

FIG. 16 is a diagram showing the configuration of the media inspection unit 20 when the first and third embodiments are combined.
As shown in Fig. 16, when viewed from the Z direction, one first light-emitting element 211 and two second light-emitting elements 212 (second light-emitting elements 2121, 2122) are arranged at equal intervals on a circle centered on the light-receiving element 220 of the light detection unit 22. Of these, the second light-emitting element 2121 irradiates the recording medium with the second inspection light L2a having an intensity peak wavelength of 390 nm or more and 440 nm or less, as in Example 1. Also, the second light-emitting element 2122 irradiates the recording medium with the second inspection light L2a having an intensity peak wavelength of 280 nm or more and 400 nm or less, as in Example 3. In the configuration of Fig. 16, the first light-emitting element 211 and the two second light-emitting elements 2121, 2122 emit light in sequence so that their irradiation periods are different from each other. The material of the recording medium can be determined from the reflectance R1 of the first inspection light L1a from the first light-emitting element 211 and the reflectance R2 of the second inspection light L2a from the second light-emitting element 2121. In addition, the fluorescent whitening agent can be determined from the reflectance R1 of the first inspection light L1a from the first light-emitting element 211 and the reflectance R2 of the second inspection light L2a from the second light-emitting element 2122.
It should be noted that by using the configuration of FIG. 16, the second and third embodiments can be combined.

<Example 4: Determination of Color of Recording Medium>
Next, a method for determining the color of a recording medium will be described as a fourth embodiment.

In the fourth embodiment, the second inspection light L2a is light having an absorption wavelength of the dye of the color paper, which makes it possible to distinguish the recording medium of the corresponding color.
For example, by using the second inspection light L2a having a peak wavelength of 600 nm or more and less than 700 nm, it is possible to distinguish between paper that has high absorption in the wavelength range of 600 nm or more and less than 700 nm (e.g., blue, red, green, yellow, pink, light green, light yellow, light ivory, and orange paper) and blank paper.

Figure 17 shows an example distribution of the reflectance R1 of the first inspection light L1a and the reflectance R2 of the second inspection light L2a for white paper and colored paper. In more detail, the reflectance R1 of the first inspection light L1a with a peak wavelength of 850 nm and the reflectance R2 of the second inspection light L2a with a peak wavelength of 670 nm are acquired and plotted for white paper and colored paper.

The reference line S3 in FIG. 17 is set to separate the blank paper plot from the colored paper plot. The coordinate plane with the reflectances R1 and R2 as its two axes is divided by the reference line S3 into an area Ca including the blank paper plot and an area Cb including the colored paper plot. Whether the recording medium is blank or colored paper can be determined depending on whether the coordinates corresponding to the detection results of the amount of incident light when inspected by the media inspection unit 20 belong to area Ca or Cb.

In addition, by using the second inspection light L2a with a peak wavelength of 500 nm or more and less than 600 nm, it is possible to distinguish between paper that has a high absorption in the wavelength range of 500 nm or more and less than 600 nm (e.g., blue, green, yellow, light blue, light yellow, and light green paper) and blank paper.

Figure 18 shows an example distribution of the reflectance R1 of the first inspection light L1a and the reflectance R2 of the second inspection light L2a for white paper and colored paper. In more detail, the reflectance R1 of the first inspection light L1a with a peak wavelength of 850 nm and the reflectance R2 of the second inspection light L2a with a peak wavelength of 525 nm are acquired and plotted for white paper and colored paper.

The reference line S4 in FIG. 18 is set to separate the blank paper plot from the colored paper plot. The coordinate plane with the reflectances R1 and R2 as its two axes is divided by the reference line S4 into an area Da including the blank paper plot and an area Db including the colored paper plot. Whether the recording medium is blank or colored can be determined depending on whether the coordinates corresponding to the detection result of the amount of incident light when inspected by the media inspection unit 20 belong to area Da or Db.

Similarly, by using the second inspection light L2a with a peak wavelength of 350 nm or more and less than 500 nm, it is possible to distinguish between paper that has a large absorption in the wavelength range of 350 nm or more and less than 500 nm (e.g., red, green, yellow, pink, and light green paper) and blank paper. The reflectance distribution diagram in this case is omitted.

By using the first inspection light L1a and two or more second inspection lights L2a with different wavelength ranges, the color of the recording medium can be determined in more detail. For example, when using two second inspection lights L2a with different wavelength ranges, one first light-emitting element 211 and two second light-emitting elements 212 with different emission wavelengths can be used as in FIG. 16. When using three second inspection lights L2a with different wavelength ranges, an additional second light-emitting element 212 with a different emission wavelength can be added.

In Example 4, by using the reflectance ratio R2/R1 of the first inspection light L1a and the second inspection light L2a, it is possible to perform discrimination taking into account the wavelength dependency in the two wavelength ranges. In other words, by using the ratio with the reflectance R1 on the horizontal axis instead of simply using the reflectance R2 on the vertical axis in Figures 17 and 18, it is possible to offset factors other than the color of the recording medium.

(Modification)
Next, a modification of the above embodiment will be described, focusing on the differences from the above embodiment.

Figure 19 is a diagram showing the configuration of a media inspection unit 20 according to a modified example. Figure 19(a) is a cross-sectional view of the media inspection unit 20 as viewed from a direction parallel to the conveying surface. Figure 19(b) is a plan view of the media inspection unit 20 as viewed from a direction perpendicular to the conveying surface (z direction).

The light irradiation unit 21 of this modified example includes one light emitting element 210. The light emitting element 210 irradiates the recording medium M with light including the first inspection light L1a and the second inspection light L2a. As the light emitting element 210, a lamp (e.g., halogen, deuterium, tungsten, xenon, etc.) having an emission spectrum in a wavelength range (e.g., from the ultraviolet wavelength range to the near-infrared wavelength range) including the first inspection light L1a and the second inspection light L2a can be used.

The light detection unit 22 has a first light receiving element 221 capable of detecting light in the wavelength range of the first incident light L1b, and a second light receiving element 222 capable of detecting light in the wavelength range of the second incident light L2b. For example, the first light receiving element 221 can be a light receiving element 220 of the above embodiment with a filter that selectively transmits light in the wavelength range of the first incident light L1b laminated thereon. Also, the second light receiving element 222 can be a light receiving element 220 of the above embodiment with a filter that selectively transmits light in the wavelength range of the second incident light L2b laminated thereon. With this configuration, the first light receiving element 221 and the second light receiving element 222 have the spectral sensitivity characteristics shown in FIG. 20. That is, the first light receiving element 221 has a sensitivity peak P1 at a wavelength of, for example, 850 nm. Also, the second light receiving element 222 has a sensitivity peak P2 at a wavelength of, for example, 400 nm. Therefore, as shown in FIG. 19(a), light including the first incident light L1b and the second incident light L2b is incident on the first light receiving element 221 and the second light receiving element 222, respectively, and the first light receiving element 221 can selectively detect the first incident light L1b, and the second light receiving element 222 can selectively detect the second incident light L2b. The peak wavelength of sensitivity of the second light receiving element 222 is appropriately changed to match the wavelength range of the second inspection light L2a (and therefore the wavelength range of the second incident light L2b).

In this way, this modified example has the advantage that time-division measurement is not required because it performs space-division measurement. In other words, during the irradiation period of the light-emitting element 210, light can be detected by the first light-receiving element 221 and the second light-receiving element 222 at any timing (for example, simultaneously).

As described above, the recording medium discrimination device 2 according to the present embodiment includes a light irradiation unit 21 that irradiates the recording medium with an inspection light, a light detection unit 22 that detects incident light including at least one of the diffuse reflection light of the inspection light irradiated on the recording medium and the fluorescence excited by the inspection light in the recording medium, and a control unit 10 as a discrimination means that discriminates one characteristic of the recording medium based on the detection results by the light detection unit 22 of the first incident light L1b corresponding to the first inspection light L1a and the second incident light L2b corresponding to the second inspection light L2a, and the first inspection light L1a has a peak intensity wavelength of 750 nm or more and 1100 nm or less, and the second inspection light L2a has a peak intensity wavelength shorter than that of the first inspection light L1a. According to this, by using inspection light of two wavelength ranges including the first inspection light L1a in the near-infrared wavelength range that is less susceptible to the influence of the characteristics of the recording medium, one characteristic of the recording medium can be appropriately discriminated in consideration of the wavelength dependency of the two wavelength ranges of the diffuse reflection light and/or fluorescence of the recording medium. That is, based on the amount of received first incident light L1b, it is possible to subtract the fluctuation in the amount of received second incident light L2b due to factors other than the characteristics of the recording medium, so that it is possible to appropriately determine the desired characteristics. By using the results of this characteristic determination, it is possible to determine the type of recording medium with high accuracy. In addition, since there is no need to compare with data obtained for known recording media, it is possible to determine the paper type, etc., of unknown recording media.

The control unit 10 also performs discrimination regarding the characteristics of the recording medium based on the ratio between the reflectance R1 (first value) corresponding to the amount of light received by the light detection unit 22 of the first incident light L1b and the reflectance R2 (second value) corresponding to the amount of light received by the light detection unit 22 of the second incident light L2b (discrimination means). This allows for highly accurate discrimination of the characteristics by offsetting factors that cause fluctuations in the reflectance other than the characteristics of the recording medium to be discriminated. For example, even if the reflectance fluctuates due to a misalignment of the positional relationship between the light-emitting element and the light-receiving element and the recording medium, or the reflectance fluctuates due to differences in the basis weight of the recording medium, the fluctuations can be offset by using the reflectance ratio.

The control unit 10 also performs a characteristic determination based on an area that includes coordinates corresponding to the detection result among multiple predetermined areas on a coordinate plane with reflectance R1 and reflectance R2 as two axes (determination means). This makes it possible to more accurately determine the characteristics of the recording medium, and improves the accuracy of determining the type of recording medium.

The multiple regions are also divided by reference lines that are non-parallel to the two axes of the coordinate plane. This makes it possible to determine characteristics that take into account the wavelength dependency of the diffuse reflected light and/or fluorescence from the recording medium.

In addition, in Examples 1 and 2, the second inspection light L2a has a peak intensity wavelength of 390 nm or more and 440 nm or less. This makes it possible to determine characteristics that cause absorption in the purple wavelength range, such as the material of the recording medium and the presence or absence of a bluing.

In addition, in Example 3, the second inspection light L2a has a peak intensity wavelength of 280 nm or more and 400 nm or less. This makes it possible to determine the presence or absence and amount of fluorescent whitening agent.

The first inspection light L1a has a peak intensity wavelength of 800 nm or more and 900 nm or less. This makes it possible to further reduce the fluctuation in reflectance of the first inspection light L1a caused by the characteristics of the recording medium, thereby improving the accuracy of identifying the characteristics.

The light detection unit 22 also has a light receiving element 220, which is a photodiode or phototransistor with detection sensitivity in a wavelength range from the visible wavelength range to the near-infrared wavelength range. This makes it possible to suppress the influence of excitation light in the ultraviolet wavelength range and detect fluorescent light and/or blue diffuse reflected light in the visible wavelength range with high sensitivity. This makes it possible to determine the material of the recording medium and the presence and amount of fluorescent whitening agent with high accuracy.

The recording medium discrimination device 2 also includes an element substrate 23 disposed at a position facing the recording medium transport path, the light irradiation unit 21 having a first light-emitting element 211 and a second light-emitting element 212, the light detection unit 22 having a light-receiving element 220, and the first light-emitting element 211, the second light-emitting element 212, and the light-receiving element 220 being disposed on the element substrate 23. This makes it possible to minimize the effect on the characteristic discrimination results even if the distance between the element substrate 23 and the recording medium in the z direction fluctuates.

The light irradiation unit 21 has a first light-emitting element 211 that irradiates the recording medium with the first inspection light L1a, and a second light-emitting element 212 that irradiates the recording medium with the second inspection light L2a, and the light detection unit 22 has a light-receiving element 220 that detects the first incident light L1b and the second incident light L2b, and the period during which the first light-emitting element 211 irradiates the first inspection light L1a is different from the period during which the second light-emitting element 212 irradiates the second inspection light L2a. This simplifies the configuration of the light-receiving element 220 and the configuration and processing content related to the processing of the detection result by the light-receiving element 220. It can also be made less susceptible to the effects of changes over time in the light-receiving element 220.

In a modified example, the light irradiating unit 21 has a light emitting element 210 that irradiates the recording medium with light including the first inspection light L1a and the second inspection light L2a, and the light detecting unit 22 has a first light receiving element 221 capable of detecting light in the wavelength range of the first incident light L1b, and a second light receiving element 221 capable of detecting light in the wavelength range of the second incident light L2b. This allows simultaneous detection by the first light receiving element 221 and the second light receiving element 222, thereby shortening the inspection time. In principle, it is also possible to determine the type of recording medium by irradiating the inspection light once and detecting the incident light. In addition, it is possible to make the light emitting element 210 less susceptible to the effects of changes over time.

The image forming device 1 according to this embodiment also includes the recording medium discrimination device 2 and an image forming unit 30 that applies color material to a recording medium to form an image. This allows the image forming device 1 to appropriately discriminate the type of recording medium.

The recording medium discrimination method according to the present embodiment is a recording medium discrimination method using a recording medium discrimination device 2 including a light irradiation unit 21 that irradiates an inspection light onto the recording medium, and a light detection unit 22 that detects incident light including at least one of the diffuse reflection light of the inspection light irradiated onto the recording medium and the fluorescence excited by the inspection light in the recording medium, and includes a step of discriminating one characteristic of the recording medium based on the detection results by the light detection unit 22 of the first incident light L1b corresponding to the first inspection light L1a and the second incident light L2b corresponding to the second inspection light L2a, in which the first inspection light L1a has a peak intensity wavelength of 750 nm or more and 1100 nm or less, and the second inspection light L2a has a peak intensity wavelength shorter than that of the first inspection light L1a. This makes it possible to appropriately discriminate one characteristic of the recording medium in consideration of the wavelength dependency of the diffuse reflection light and/or the fluorescence of the recording medium in two wavelength ranges. By using the discrimination result of this characteristic, it is possible to discriminate the type of the recording medium with high accuracy.

The present invention is not limited to the above-described embodiment, and various modifications are possible.
For example, in the above embodiment, an example was described in which the recording medium discrimination device 2 is incorporated into the image forming device 1, but this is not limited to this, and the recording medium discrimination device 2 may be a device that is provided separately and independently from the image forming device 1.

In addition, reflectance R1 has been exemplified as the first value, and reflectance R2 has been exemplified as the second value, but this is not limited to the above. The first value may be any value related to the amount of light received by the light detection unit 22 of the first incident light L1b, and may be, for example, the amount of light received itself. Similarly, the second value may be any value related to the amount of light received by the light detection unit 22 of the second incident light L2b, and may be, for example, the amount of light received itself.

The characteristics of the recording medium to be identified are not limited to those exemplified in the embodiment. Any characteristic that is unlikely to affect the reflectance of the first inspection light L1a in the near-infrared wavelength range, but that affects the reflectance of the second inspection light L2a in a shorter wavelength range, can be identified.

In addition, although an electrophotographic method has been exemplified as an image forming method in an image forming device, the present invention is not limited to this, and any image forming method may be used. For example, an inkjet method may be used in which an image is formed by ejecting ink onto a recording medium.

The recording medium is not limited to paper, but may be a resin sheet, fabric, etc.

Although several embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents.

1 Image forming apparatus 2 Recording medium discrimination device 10 Control unit (discrimination means)
11 CPU
12 RAM
13 Storage unit 131 Program 132 Discrimination reference data 20 Medium inspection unit 21 Light irradiation unit 210 Light emitting element 211 First light emitting element 212, 2121, 2122 Second light emitting element 22 Light detection unit 220 Light receiving element 221 First light receiving element 222 Second light receiving element 23 Element substrate (substrate)
24 Optical aperture 25 Paper passing guide 30 Image forming section 40 Fixing section 50 Scanner 60 Operation display section 70 Communication section 81 Paper feed tray 82 Transport roller 83 Paper discharge tray 90 Bus L1a First inspection light L1b First incident light L2a Second inspection light L2b Second incident light LA Inspection light LB1 Surface diffuse reflected light LB2 Internal diffuse reflected light LB3 Fluorescence LC Regularly reflected light M Recording medium R1 Reflectance (first value)
R2 reflectance (second value)

Claims (12)

a light irradiation unit that irradiates the recording medium with inspection light;
a light detection unit that detects incident light including at least one of diffuse reflected light of the inspection light irradiated onto the recording medium and fluorescence excited by the inspection light in the recording medium;
a discrimination unit that discriminates a characteristic of the recording medium based on a detection result of the first incident light corresponding to the first inspection light and the second incident light corresponding to the second inspection light by the light detection unit;
Equipped with
the first inspection light has a peak intensity wavelength of 750 nm or more and 1100 nm or less;
the second inspection light has a peak intensity wavelength shorter than that of the first inspection light;
The light irradiation unit includes:
a first light emitting element that emits the first inspection light;
a second light emitting element that emits the second inspection light having a certain peak wavelength;
a third light emitting element that emits the second inspection light having a peak wavelength different from the certain peak wavelength;
having
The discrimination means is
determining a certain characteristic of the recording medium based on a detection result of the first incident light corresponding to the first inspection light and a detection result of the second incident light corresponding to the second inspection light emitted by the second light-emitting element;
a recording medium discrimination device that discriminates a characteristic of the recording medium that is different from the certain characteristic based on a detection result of the first incident light corresponding to the first inspection light and a detection result of the second incident light corresponding to the second inspection light emitted by the third light-emitting element . The recording medium discrimination device according to claim 1, wherein the discrimination means discriminates the characteristics based on a ratio between a first value corresponding to the amount of light received by the light detection unit of the first incident light and a second value corresponding to the amount of light received by the light detection unit of the second incident light. 3. The recording medium discrimination device according to claim 2, wherein the discrimination means performs discrimination related to the characteristic based on an area including coordinates corresponding to the detection result among a plurality of predetermined areas on a coordinate plane having two axes of the first value and the second value . The recording medium discrimination device according to claim 3, wherein the plurality of regions are divided by straight lines that are not parallel to the two axes of the coordinate plane. The recording medium discrimination device according to any one of claims 1 to 4, wherein the second inspection light has a peak intensity wavelength of 390 nm or more and 440 nm or less. The recording medium discrimination device according to any one of claims 1 to 4, wherein the second inspection light has a peak intensity wavelength of 280 nm or more and 400 nm or less. The recording medium discrimination device according to any one of claims 1 to 6, wherein the first inspection light has a peak intensity wavelength of 800 nm or more and 900 nm or less. the light detection unit has a light receiving element that detects the incident light,
8. The recording medium discrimination device according to claim 1, wherein the light receiving element is a photodiode or a phototransistor having detection sensitivity in a wavelength range from the visible wavelength range to the near infrared wavelength range. a substrate provided at a position facing a transport path of the recording medium;
the light irradiation unit has a light emitting element that emits the inspection light,
the light detection unit has a light receiving element that detects the incident light,
9. The recording medium discrimination device according to claim 1, wherein the light emitting element and the light receiving element are provided on the substrate. 10. The recording medium discrimination device according to claim 1 , wherein the first light-emitting element, the second light-emitting element, and the third light-emitting element emit light in sequence so that their irradiation periods are different from each other . A recording medium discrimination device according to any one of claims 1 to 10 ,
an image forming unit that applies a coloring material to the recording medium to form an image;
An image forming apparatus comprising: A recording medium discrimination method using a recording medium discrimination device including a light irradiation unit that irradiates an inspection light onto a recording medium, and a light detection unit that detects incident light including at least one of diffuse reflected light of the inspection light irradiated onto the recording medium and fluorescence excited by the inspection light in the recording medium, the method comprising:
a step of determining a characteristic of the recording medium based on a detection result by the light detection unit of the first incident light corresponding to the first inspection light and the second incident light corresponding to the second inspection light,
the first inspection light has a peak intensity wavelength of 750 nm or more and 1100 nm or less;
the second inspection light has a peak intensity wavelength shorter than that of the first inspection light;
The light irradiation unit includes:
a first light emitting element that emits the first inspection light;
a second light emitting element that emits the second inspection light having a certain peak wavelength;
a third light emitting element that emits the second inspection light having a peak wavelength different from the certain peak wavelength;
having
In the above step,
determining a certain characteristic of the recording medium based on a detection result of the first incident light corresponding to the first inspection light and a detection result of the second incident light corresponding to the second inspection light emitted by the second light-emitting element;
A recording medium discrimination method, comprising: discriminating a characteristic of the recording medium that is different from the certain characteristic based on a detection result of the first incident light corresponding to the first inspection light and a detection result of the second incident light corresponding to the second inspection light emitted by the third light-emitting element .

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