JP2017102046A - Image forming apparatus and recording medium thickness determination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that, in determination of the thickness of a recording medium including paper, is not easily affected by a change or variation in the amount of received light by using optical means and can accurately determine the thickness of the recording medium.SOLUTION: An image forming apparatus comprises: light source parts 3 (light source 31 and light source 32) that irradiate a recording medium 2 with rays of irradiation light having different wavelengths or wavelength ranges; and light receiving means 4 (light receiving part 41 and light receiving part 42) that receive the irradiation light that has transmitted through the recording medium 2, and determines the thickness of the recording medium 2 on the basis of a difference in the amount of received rays of light having different wavelengths or wavelength ranges.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for determining the thickness of a recording medium such as paper.

For recording media (paper, etc.) used in image forming apparatuses (printers, copiers, etc.), conventionally, information on recording media used by the user from the operation panel of the image forming apparatus (paper type, thickness, etc.) ) And appropriate control conditions such as fixing conditions, transfer conditions, and transport conditions are derived based on the information. In addition, there is an apparatus that automatically determines information about a recording medium by using an optical sensor or the like and derives control conditions such as an appropriate fixing condition, transfer condition, and conveying condition based on the information.
In this regard, Patent Document 1 discloses a technique for determining the thickness of a recording medium using an optical sensor.

JP 2014-145761 A

The technique disclosed in Patent Document 1 is that “amount of light in a high reflection state” obtained with the reference reflector closed and “amount of light in a low reflection state” obtained with the reference reflector opened. The thickness of the recording medium is obtained by the ratio. However, in this method, it is essential to provide a mechanism for opening and closing the reference reflector. The addition of a mechanism having a movable part leads to an increase in cost and increases the cause of problems such as failure.
In the case of a method of using a photosensor to receive light that has been transmitted or reflected through a recording medium and determining the thickness of the recording medium based on the amount of received light (absolute amount), such as sensor aging, dirt, etc. When the amount of received light is affected by an external factor, there is a problem in that the received light amount value changes or varies, and the discrimination accuracy decreases.

  In view of the above-mentioned points, the present invention suppresses the influence of change or variation in the amount of received light while using optical means in the determination of the thickness of a recording medium such as paper. An object of the present invention is to provide an image forming apparatus capable of determining the thickness.

(Configuration 1)
A recording medium transporting unit, a light source unit, and a light receiving unit, wherein the light source unit irradiates the recording medium being transported by the recording medium transporting unit with irradiation light having a different wavelength or wavelength region; The transmitted light transmitted through the recording medium being conveyed is transmitted light, the received light amount for each transmitted light corresponding to the irradiated light of the different wavelength or wavelength region is obtained, and the received light amount difference for each transmitted light To determine the thickness of the recording medium.

(Configuration 2)
The ratio of the received light amount for each transmitted light is calculated, and the thickness of the recording medium is determined by comparing the calculated ratio of the received light amount with a preset threshold value for each thickness of the recording medium. The image forming apparatus according to Configuration 1, wherein:

(Configuration 3)
The image formation according to Configuration 1 or Configuration 2, wherein the received light amount of the transmitted light is normalized by using the received light amount when the irradiation light from the light source unit is received without passing through the recording medium. apparatus.

(Configuration 4)
4. The image forming apparatus according to any one of Configurations 1 to 3, wherein the irradiation light of the different wavelength or wavelength region is irradiation light of three or more different wavelengths or wavelength regions.

(Configuration 5)
The image according to any one of Configurations 1 to 4, wherein the irradiation light having the different wavelength or wavelength region includes light having a wavelength or wavelength region of less than 760 nm and light having a wavelength or wavelength region of 760 nm or more. Forming equipment.

(Configuration 6)
6. The image forming apparatus according to Configuration 5, wherein the wavelength region of less than 760 nm is 400 to 500 nm, and the wavelength region of 760 nm or more is 800 to 900 nm.

(Configuration 7)
The image forming apparatus according to any one of Configurations 1 to 6, wherein the irradiation light having the different wavelength or wavelength region includes light outside the visible region.

(Configuration 8)
The light source unit has a plurality of light sources that irradiate irradiation light of the different wavelengths or wavelength regions, and the light receiving unit obtains an amount of received light for each transmitted light corresponding to the irradiation light of the different wavelengths or wavelength regions. The image forming apparatus according to any one of Configurations 1 to 7, further comprising: a plurality of light receiving units.

(Configuration 9)
The light source unit includes one light source that emits light including irradiation light of the different wavelength or wavelength region, and the light receiving unit receives light for each transmitted light corresponding to the irradiation light of the different wavelength or wavelength region. The image forming apparatus according to any one of Configurations 1 to 7, further comprising a plurality of light receiving units that acquire the amount.

(Configuration 10)
The light source unit includes a plurality of light sources that irradiate irradiation light for the different wavelengths or wavelength regions, and the light receiving unit acquires a received light amount of transmitted light corresponding to the irradiation light of the different wavelengths or wavelength regions. The structure 1 to the structure 7 having one light receiving unit, lighting the plurality of light sources in a time-sharing manner, and obtaining a received light amount for each transmitted light corresponding to the irradiation light of the different wavelength or wavelength region The image forming apparatus according to any one of the above.

(Configuration 11)
A method for optically detecting a thickness of a recording medium in an image forming apparatus, wherein the thickness of the recording medium is determined based on a component ratio of a transmitted light spectrum transmitted through the recording medium. Recording medium thickness discrimination method.

(Configuration 12)
The component ratio of the transmitted light spectrum is normalized by the component ratio of the received light spectrum when light is received without passing through the recording medium, and the thickness of the recording medium is determined based on the normalized value. The recording medium thickness determination method according to Configuration 11.

(Configuration 13)
The recording medium thickness discrimination method according to Configuration 11 or Configuration 12, wherein light having three or more different wavelengths or wavelength regions is irradiated as a light source for obtaining the transmitted light.

(Configuration 14)
The light source for obtaining the transmitted light is irradiated with light having a wavelength or wavelength region of less than 760 nm and light having a longer wavelength or wavelength region of 760 or more. Recording medium thickness discrimination method.

(Configuration 15)
The recording medium thickness determination method according to Configuration 14, wherein the wavelength region of less than 760 nm is 400 to 500 nm, and the wavelength region of 760 nm or more is 800 to 900 nm.

(Configuration 16)
16. The recording medium thickness determination method according to any one of Configurations 11 to 15, wherein light outside the visible range is irradiated as a light source for obtaining the transmitted light.

  The image forming apparatus and the recording medium thickness determination method of the present invention determine the thickness of a recording medium based on the difference in the amount of light received at different wavelengths or wavelength regions, and absolutely use the light amount value. Rather than discriminating, the detected light amount is relatively used. Therefore, even when the variation in the light amount value occurs, there is an effect of canceling this, and it is possible to suppress a decrease in the discrimination accuracy due to the variation in the received light amount value even though it is optical.

1 is a block diagram showing an outline of a part related to the present invention of an image forming apparatus according to a first embodiment; Schematic flowchart relating to the present invention of the image forming apparatus of Embodiment 1 Emission spectrum of light source unit of image forming apparatus of embodiment 1 A graph comparing the emission spectrum of a light source and the spectrum of transmitted light for each paper thickness (70 μm, 200 μm, 400 μm) by the same light source A graph showing the relationship between the component ratio of the transmitted light spectrum (ratio of transmitted light received amount of 400-500 nm and transmitted light received amount of 800-900 nm) and paper thickness Schematic block diagram showing another example of the image forming apparatus according to the present invention. Graph showing the relationship with the paper thickness when the component ratio of the transmitted light spectrum is normalized by the component ratio of the received light spectrum when light is received without passing through paper FIG. 3 is a block diagram showing an outline of a part related to the present invention of an image forming apparatus according to a second embodiment. Schematic flowchart relating to the present invention of the image forming apparatus of Embodiment 2.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In addition, the following embodiment is one form at the time of actualizing this invention, Comprising: This invention is not limited within the range.

<Embodiment 1>
FIG. 1 is a block diagram showing an outline of a part related to the present invention of the image forming apparatus of the present embodiment.
The image forming apparatus 1 according to the present embodiment discriminates the thickness of a recording medium 2 (paper or the like) by optical means. As shown in FIG. 1, a light source unit 3 that irradiates light onto the recording medium 2 and , A light receiving unit 4 that receives the transmitted light transmitted through the recording medium 2 by the light emitted from the light source unit 3, a transmitted light processing unit 5 that processes a signal from the light receiving unit 4, and an output of the transmitted light processing unit 5 A comparison discriminator 6 for discriminating the thickness of the recording medium 2 by comparing the result with a threshold is provided. Although not particularly illustrated, the image forming apparatus 1 includes a transport unit that transports the recording medium 2.

The light source unit 3 is a light source that irradiates the recording medium 2 with irradiation light having different wavelengths or wavelength regions. In the present embodiment, the light source unit 3 includes a light source 31 and a light source 32 that irradiate light in different wavelength regions.
In the present embodiment, as shown in FIG. 3, the light source 31 has an emission spectrum in the wavelength region of the blue region (400 to 500 nm), and the light source 32 has an emission spectrum in the red and infrared regions (800 to 900 nm). Have.

  The light receiving means 4 is a transmitted light based on the irradiation light of different wavelengths or wavelength regions, and detects the received light amount for each transmitted light corresponding to the irradiation light of the different wavelengths or wavelength regions. In the present embodiment, the light receiving unit 41 having light receiving sensitivity in the blue region (400 to 500 nm) and the light receiving unit 42 having light receiving sensitivity in the red and infrared regions (800 to 900 nm) are configured.

The transmitted light processing unit 5 performs A / D conversion of a signal (sensor voltage) from the light receiving unit 4 and calculates a wavelength component ratio that is a ratio between the amount of light received by the light receiving unit 41 and the amount of light received by the light receiving unit 42 (transmitted light). Processing for calculating a spectral component ratio is performed.
The comparison discriminating unit 6 compares the wavelength component ratio of the transmitted light derived by the transmitted light processing unit 5 with a predetermined threshold value and discriminates the thickness of the recording medium.
The transmitted light processing unit 5 and the comparison / discrimination unit 6 may be configured by dedicated circuits, or may be realized by a program on a general-purpose microcomputer. (An A / D converter may be provided between the light receiving means 4 and the microcomputer)

Here, the basic principle of the present invention will be described.
The light has a property that the transmittance with respect to the recording medium differs depending on the wavelength, and the longer wavelength light has a higher transmittance than the shorter wavelength light. The present invention utilizes this property to determine the thickness of a recording medium.
FIG. 4 shows the emission spectrum of the light source itself and the transmitted light spectrum for each thickness of the recording medium (so-called plain paper). FIG. 4A shows the emission spectrum of the light source itself and the spectrum of transmitted light for each paper thickness (70 μm, 200 μm, 400 μm), with the horizontal axis representing the wavelength component and the vertical axis representing the emission intensity (≈the amount of received light). Is. FIG. 4B shows a spectrum normalized with the maximum value of the amount of transmitted light of each thickness of the recording medium in FIG. 4A (the vertical axis is dimensionless). Note that the thicknesses of 70 μm, 200 μm, and 400 μm of the recording medium correspond to thicknesses called thin paper, medium thick paper, and thick paper in the electrophotographic apparatus field.
As shown in FIGS. 4A and 4B, the transmitted light transmitted through the recording medium has a wavelength component that changes in correlation with the thickness of the recording medium. As the recording medium becomes thicker, the transmitted light has a longer wavelength component with respect to a shorter wavelength component. That is, it can be seen that the wavelength component ratio of 70 um (thin paper) is equivalent to that of the light source, but the wavelength component ratio changes as the recording medium becomes thicker.
As shown in FIG. 4B, the wavelength component ratio is decreased corresponding to the thickness of the recording medium on the short wavelength side with 760 nm as a boundary. On the other hand, the wavelength component ratio increases on the long wavelength side (although there is almost no change in the spectrum after normalization, the wavelength component ratio increases because the short wavelength side decreases).
Based on this, this embodiment irradiates light of a wavelength or wavelength region (blue region) of less than 760 nm and light of a wavelength or wavelength region (red and infrared region) of 760 nm or more, and the wavelength component of the transmitted light. The thickness of the recording medium is detected by the ratio. Although it is preferable to use the wavelength component ratio between the short wavelength and the long wavelength at the boundary of 760 nm, as is understood from FIG. 4, the wavelength component ratio between the short wavelength and the long wavelength at the boundary of 760 nm is not necessarily used. Even if this is not the case, there are combinations in which the wavelength component ratio changes depending on the thickness of the recording medium. Therefore, for example, a thickness detection using these wavelength component ratios based on two wavelength regions (or wavelengths) of less than 760 nm may be used.

Next, the operation of the image forming apparatus 1 of the present embodiment will be described.
FIG. 2 is a flowchart showing an outline of processing relating to the present invention of the image forming apparatus.
In the image forming apparatus 1, the recording medium 2 is picked up from the paper feed tray in accordance with a print instruction or the like, and is transported along the transport path by a recording medium transport unit for printing on a print processing unit (photosensitive drum or the like). An optical sensor unit for detecting the type and thickness of the recording medium is provided on the conveyance path (before the print processing unit), and the light source unit 3 and the light receiving unit 4 constitute the optical sensor unit. It is.
In step 201 of the flowchart of FIG. 2, irradiation light is irradiated from the light source unit 3 to the recording medium 2 on the conveyance path. In the present embodiment, the light source 31 and the light source 32 emit light at the same time, and the light receiving amount is detected by the light receiving unit 41 and the light receiving unit 42. That is, the light in the blue region (400 to 500 nm) and the light in the red and infrared regions (800 to 900 nm) are simultaneously irradiated to detect the amount of received transmitted light.

In the subsequent step 203, the transmitted light processing unit 5 receives the amount of transmitted light in the blue region (400 to 500 nm) obtained by the light receiving unit 41 and the light receiving unit 42 (integration of 400 to 500 nm in the graph of FIG. 4A). The wavelength component ratio is calculated (transmitted light) between the received light amount of the transmitted light in the red and infrared regions (800 to 900 nm) (synonymous with the integrated value of 800 to 900 nm in the graph of FIG. 4A). Processing for calculating a spectral component ratio is performed.
Then, the wavelength component ratio of the transmitted light obtained in this way is compared with a threshold value in the comparison discriminating unit 6 to discriminate the thickness of the recording medium 2.

The “threshold value” here is a value set for each thickness to be discriminated with respect to the above-described wavelength component ratio that changes according to the thickness of the recording medium, and is a value obtained by a prior experiment or the like. Is set in the image forming apparatus 1 as a threshold value.
FIG. 5 shows the relationship between the component ratio of the transmitted light spectrum (the ratio of the amount of transmitted light received from 400 to 500 nm and the amount of received light received from 800 to 900 nm) and the threshold corresponding to the thickness of the recording medium. . P1 in P2 / P1 on the vertical axis is the amount of transmitted light received from 400 to 500 nm, and P2 is the amount of received light received from 800 to 900 nm. That is, P2 / P1 is the wavelength component ratio.
As shown in the figure, A (4.6 <A <6.0) is used as a threshold for discriminating the recording medium thickness of 70 μm (thin paper) and 200 μm (medium thick paper), and the recording medium thickness is 200 μm and 400 μm. By setting B (6.0 <B <8.4) as a threshold for determining (thick paper), it is possible to determine thin paper, medium thick paper, and thick paper. (This is an example, and a threshold may be set as appropriate according to the thickness to be determined.)

As described above, according to the image forming apparatus 1 of the present embodiment,
It is not a discrimination technique that absolutely uses a light quantity value as in the prior art, but a discrimination technique that relatively uses this based on the difference in the quantity of light detected at different wavelengths. Therefore, the variation in the light quantity value is canceled, and the thickness can be detected with high accuracy without requiring a light quantity correction process or a special mechanism.

In the present embodiment, an example of a light source unit including two light sources 31 and 32 and two light receiving units corresponding to the light sources 31 and 42 (light receiving units 41 and 42) has been described. It is also possible to irradiate the region with irradiation light and receive it respectively.
For example, in the case of a recording medium having reflection characteristics for a specific wavelength region such as colored paper, it may be difficult to obtain transmitted light in that wavelength region. On the other hand, by using irradiated light in three or more wavelength regions so that transmitted light can be obtained in any two or more wavelength regions, it is highly accurate even in the case of colored paper or the like. Thickness detection can be performed. (When three or more wavelength regions are used, a thickness can be detected for any combination of received wavelength regions by providing a threshold value for each combination of wavelength regions. .)
For the same reason, a light source that emits light outside the visible range may be used as the light source. Thereby, even in the case of colored paper or the like, the thickness can be detected with high accuracy. The “visible region” is a wavelength region of 360 nm to 830 nm, and “light outside the visible region” is light having a wavelength outside this range.

In the present embodiment, the light source (light source 31, 32) is provided for each wavelength region, but one light source having a broader spectrum may be provided (for example, a white light source). .
FIG. 6 shows an example of such a thing (the same reference numerals are used for the same components as in FIG. 1).
As shown in FIG. 6A, for example, one light source 33 that emits white light is provided, the light receiving unit 41 has a shorter wavelength side (wavelength shorter than 760 nm), and the light receiving unit 42 has a longer wavelength side (wavelength longer than 760 nm). ) May be received. (That is, the light source 33 may be any light source that includes at least a wavelength shorter than 760 nm and a wavelength longer than 760 nm.)
Further, as shown in FIG. 6B, for each light receiving part having light receiving sensitivity for each wavelength region, the same element (light receiving part 43) having a broad light receiving sensitivity is used as the element, May be provided (the optical filter 71 and the light receiving unit 43, and the optical filter 72 and the light receiving unit 43 are synonymous with the light receiving units 41 and 42, respectively).
In either case, the operation is the same as described above.

  In this embodiment, the irradiation light having a predetermined wavelength region is described as being used. However, light having a single wavelength may be used. That is, two or more different single-wavelength irradiation lights may be used, and the thickness may be determined based on the component ratio of the amount of transmitted light received.

In the present embodiment, the wavelength component ratio of the transmitted light has been described as an example obtained from the amount of light received in each wavelength region and used as it is. However, the light reception when the irradiation light from the light source unit is received without going through the recording medium. The amount of transmitted light received may be normalized using the amount (the light emission intensity of the light source).
FIG. 7 is a graph showing the relationship with the paper thickness when the wavelength component ratio of transmitted light is normalized by the component ratio of the received light spectrum when light is received without passing through the recording medium.
Α in the figure is a value obtained by dividing the received light amount of 800 to 900 nm in the absence of the recording medium (that is, the direct light reception) by the received light amount of 400 to 500 nm in the same state of the recording medium. Which is normalized by multiplying this α by P2 / P1, which is the wavelength component ratio of transmitted light. (Naturally, the threshold value is also a value based on FIG. 7.)
In this way, by using a value normalized by the light emission intensity (including the light receiving performance of the light receiving means 4) of the light source unit 3 itself, individual differences of the light source unit 3 and the light receiving unit 4, aging of each element, Since it is possible to cancel (calibrate) a characteristic change based on the temperature characteristic of the element, it is more preferable.

<Embodiment 2>
FIG. 8 is a block diagram showing an outline of a part related to the present invention of the image forming apparatus according to the second embodiment. Constituent elements similar to those in the first embodiment (FIG. 1) are denoted by the same reference numerals, and description thereof is omitted or simplified.
As shown in FIG. 8, the image forming apparatus 1 according to the present embodiment is different from the first embodiment in that the light receiving unit 4 includes one light receiving unit 43.
The light receiving unit 43 is the same as the light receiving unit 43 shown in FIG. 6B, and is an element having a broad light receiving sensitivity. That is, in the block diagram of FIG. 8, the light receiving unit 43 has a light receiving sensitivity including a blue region (400 to 500 nm) emitted from the light source 31 and a red and infrared region (800 to 900 nm) emitted from the light source 32. Is.
Here, for the sake of simplicity of explanation, the light source unit 3 is a block diagram having the same configuration as that of the first embodiment. However, the light source unit 3 may be irradiated with light in three or more wavelength regions, or is irradiated with light outside the visible region. The points that may be performed are as described in the first embodiment.

Next, the operation of the image forming apparatus 1 of the present embodiment will be described.
FIG. 9 is a flowchart illustrating an outline of processing related to the present invention of the image forming apparatus according to the second embodiment. Here, an example will be described in which there are three or more light sources and a threshold for determining the thickness of the recording medium is set for each combination of wavelengths or wavelength regions (wavelength components).

  Step 901 is an initialization process, in which 1 is substituted for i and the number of light sources is substituted for n. Note that n is used as a variable for explanation of “three or more light sources”, and the number of light sources (the number of wavelengths or wavelength regions for obtaining the wavelength component ratio) is determined in an actual apparatus. Therefore, the following processing is performed with constants.

  First, similarly to the first embodiment, the recording medium 2 conveyed on the conveyance path based on a print instruction or the like is irradiated with irradiation light only by the i-th light source (step 902). In the subsequent step 903, the transmitted light is received by the light receiving unit 43, and the received light amount is stored as the transmitted light amount of the i-th light source.

  In steps 904 and 905, i is incremented, and it is determined whether or not i exceeds n. If not, the process returns to step 902 to repeat the process, and if it exceeds, the process proceeds to step 906. . That is, the processing of steps 902 to 905 is repeated until each of “three or more light sources” is subjected to light emission and transmission light reception processing (each light source is turned on in a time-sharing manner), and light emission and transmission light reception is performed for all light sources. When the processing is completed, the process proceeds to step 906.

In step 906, among the data of the amount of light received by each light source stored in step 903, among the light sources that emit light having a wavelength of less than 760 nm, the maximum transmitted light amount is 760 nm or more. Are determined and selected, and the ratio of these wavelength components is calculated.
In addition, regarding “the one that emits light having a wavelength of less than 760 nm (or more)”, the amount of light actually transmitted is normalized by the amount of light directly received by the light source of the corresponding wavelength, Based on this value, the size is compared. For example, when the transmitted light amount at 500 nm is X, X is normalized using a received light amount of 500 nm (approximately 500 nm emission intensity) Y received without passing through the recording medium, and based on these normalized values. Compare the size.

  In step 907, the calculated wavelength component ratio of the transmitted light is compared with threshold values corresponding to the two selected wavelengths or wavelength regions (wavelength components) to determine the thickness of the recording medium.

As described above, according to the present embodiment, as in the first embodiment, since the relative use is performed based on the difference in the amount of light detected at different wavelengths, the variation in the light amount value is canceled, and the light amount value correction process is performed. In addition, the thickness can be detected with high accuracy without requiring a special mechanism or the like.
In addition, the number of wavelengths or wavelength regions for obtaining the wavelength component ratio is set to 3 or more, and the wavelength with the highest received light level (value after normalization) is selected from these, and the wavelength for thickness discrimination Since the component ratio is obtained, the thickness can be detected with high accuracy.

In the present embodiment, a single light receiving unit 43 having broad light receiving sensitivity is provided, and each light source is turned on in a time-sharing manner, thereby obtaining “amount of received light for each transmitted light corresponding to irradiation light of different wavelengths or wavelength regions”. Like to do. That is, not only the light receiving unit 43 but also a control unit (such as a microcomputer not shown) that lights each light source in a time-sharing manner and the transmitted light processing unit 5, for each transmitted light corresponding to irradiation light of different wavelengths or wavelength regions. The light receiving means for acquiring the amount of received light is configured.
In this way, by irradiating irradiation light of each wavelength in a time-sharing manner, one light receiving unit can be provided, which is advantageous for downsizing and cost reduction of the apparatus.

In the present embodiment, the selection of the wavelength component of less than 760 nm and the wavelength component of 760 nm or more for obtaining the wavelength component ratio is exemplified by selecting the one with the largest normalized light reception amount. The method may be other methods (for example, a method in which a priority order is set in advance and the one with the highest priority order is selected from among those that have obtained a received light amount of a predetermined level or higher).
In the present embodiment, the wavelength component of less than 760 nm and the wavelength component of 760 nm or more are selected one by one and the thickness is determined by determining one wavelength component ratio. However, a combination of a plurality of wavelength components is used. For a plurality of wavelength component ratios, the thickness determination results obtained for each may be used to determine the final thickness (for example, among the plurality of thickness determination results obtained, For example, the most frequent result is determined as the final thickness).

The “transmitted light” in the present invention is a concept including diffuse reflected light. Diffuse reflected light is light diffused inside the recording medium, that is, obtained as a result of passing through the inside of the recording medium, and includes information based on the thickness of the recording medium.
Therefore, the concept of “transmitted light” in the present invention includes diffusely reflected light, and also includes a light receiving means provided on the same side as the light source unit with respect to the recording medium in order to receive diffusely reflected light.

  In the present invention, the recording medium for determining the thickness is preferably a paper using pulp (so-called plain paper), but is not limited to this, and the transmitted light spectrum changes depending on the thickness. If it does, it can apply with respect to various recording media.

1. . . 1. Image forming apparatus . . 2. Recording medium . . Light source unit 31, 32. . . Light source 4. . . Light receiving means 41, 42. . . Light receiving part 5. . . Transmitted light processing unit 6. . . Comparison discriminator

Claims (16)

A recording medium conveying means, a light source unit, and a light receiving means;
The light source unit irradiates the recording medium being conveyed by the recording medium conveying means with irradiation light of different wavelengths or wavelength regions,
The light receiving means is a transmitted light through which the irradiation light has transmitted through the recording medium being conveyed, and obtains a received light amount for each transmitted light corresponding to the irradiation light of the different wavelength or wavelength region,
An image forming apparatus, wherein the thickness of the recording medium is determined based on a difference in received light amount for each transmitted light.   The ratio of the received light amount for each transmitted light is calculated, and the thickness of the recording medium is determined by comparing the calculated ratio of the received light amount with a preset threshold value for each thickness of the recording medium. The image forming apparatus according to claim 1.   The received light amount of the transmitted light is normalized by using the received light amount when the irradiation light from the light source unit is received without passing through the recording medium. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the irradiation light having the different wavelength or wavelength region is irradiation light having three or more different wavelengths or wavelength regions.   The irradiation light having the different wavelength or wavelength region includes light having a wavelength or wavelength region of less than 760 nm and light having a wavelength or wavelength region of 760 nm or more. Image forming apparatus.   6. The image forming apparatus according to claim 5, wherein the wavelength region of less than 760 nm is 400 to 500 nm, and the wavelength region of 760 nm or more is 800 to 900 nm.   The image forming apparatus according to claim 1, wherein the irradiation light having the different wavelength or wavelength region includes light outside the visible region. The light source unit has a plurality of light sources that irradiate irradiation light for the different wavelengths or wavelength regions,
The said light-receiving means has a some light-receiving part which acquires the light reception amount for every transmitted light corresponding to the irradiation light of the said different wavelength or wavelength range, The any one of Claims 1-7 characterized by the above-mentioned. Image forming apparatus. The light source unit has one light source that emits light including irradiation light of the different wavelength or wavelength region,
The said light-receiving means has a some light-receiving part which acquires the light reception amount for every transmitted light corresponding to the irradiation light of the said different wavelength or wavelength range, The any one of Claims 1-7 characterized by the above-mentioned. Image forming apparatus. The light source unit has a plurality of light sources that irradiate irradiation light for the different wavelengths or wavelength regions,
The light receiving means has one light receiving unit for acquiring a received light amount of transmitted light corresponding to irradiation light of the different wavelength or wavelength region;
8. The image according to claim 1, wherein the plurality of light sources are turned on in a time-sharing manner, and the received light amount for each transmitted light corresponding to the irradiation light of the different wavelength or wavelength region is acquired. Forming equipment.   A method for optically detecting a thickness of a recording medium in an image forming apparatus, wherein the thickness of the recording medium is determined based on a component ratio of a transmitted light spectrum transmitted through the recording medium. Recording medium thickness discrimination method.   The component ratio of the transmitted light spectrum is normalized by the component ratio of the received light spectrum when light is received without passing through the recording medium, and the thickness of the recording medium is determined based on the normalized value. The recording medium thickness determination method according to claim 11.   13. The recording medium thickness determination method according to claim 11, wherein light having three or more different wavelengths or wavelength regions is irradiated as a light source for obtaining the transmitted light.   The light source for obtaining the transmitted light is irradiated with light having a wavelength or wavelength region of less than 760 nm and light having a wavelength or wavelength region of 760 nm or more. Recording medium thickness determination method.   The recording medium thickness determination method according to claim 14, wherein the wavelength region of less than 760 nm is 400 to 500 nm, and the wavelength region of 760 nm or more is 800 to 900 nm.   The recording medium thickness determination method according to claim 11, wherein light outside the visible range is irradiated as a light source for obtaining the transmitted light.

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