JP2013171212A - Light detection device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance accuracy of color detection employing a reference plate having a white layer, and to stabilize color density of an image to be formed.SOLUTION: A light detection device is configured to comprise: irradiation means for irradiating light; light receiving means for receiving the light irradiated from the irradiation means; a reference plate that guides the light irradiated from the irradiation means to the light receiving means; and control means for controlling a light amount of the light irradiated by the irradiation means by using a light reception result of receiving the light from the irradiation means and via the reference plate. In the reference plate, a reflection part reflecting the light passing through the reference plate is lined in a surface opposite to a reference surface to be irradiated with light from the irradiation means.

Description

  The present invention relates to a light detection device that detects image quality using light and an image forming device that detects the image quality of a formed image using the light detection device.

  In recent years, color image forming apparatuses employing an electrophotographic system such as a color printer or a color copying machine, an ink jet system, and the like have been required to improve the output image quality. In particular, the gradation of the density and its stability have a great influence on the judgment of the quality of an image given by a human.

  However, in an electrophotographic image forming apparatus, if there is a change in each part of the apparatus due to environmental changes or long-term use, the density of the obtained image will change. In particular, in the case of an electrophotographic color image forming apparatus, there is a possibility that the color balance may be lost even by a slight change in density, so it is necessary to always maintain a constant gradation-density characteristic.

  Therefore, the toner of each color is configured to have gradation correction means such as several kinds of exposure amounts according to absolute humidity, process conditions such as development bias, and a lookup table (hereinafter referred to as LUT). Then, based on the absolute humidity measured by the temperature / humidity sensor, the process condition at that time and the optimum value for gradation correction are selected.

  In addition, a toner patch for density detection is prepared on the intermediate transfer member or photoconductor drum with each color toner, and the density of the unfixed toner patch is detected by a density detection sensor for unfixed toner, and exposure is performed based on the detection result. Provide feedback on process conditions such as volume and development bias. The concentration is controlled by such a procedure. With this control, a constant gradation-density characteristic can be obtained even when the various parts of the apparatus fluctuate, and a stable image can be printed.

  However, density control using the density detection sensor for unfixed toner forms and detects a patch on an intermediate transfer member, a photosensitive drum, or the like, and subsequently transfers the image to the transfer material and fixes the image by fixing. There is no control over changes in color balance.

  Accordingly, a chromaticity sensor (hereinafter referred to as a color sensor) that detects the color of the toner image on the transfer material after fixing, and a density or chromaticity control color toner patch (hereinafter referred to as a patch) formed on the transfer material. There is something to detect. Thereby, the chromaticity detected by the color sensor is fed back to process conditions such as exposure amount, process condition, and LUT, thereby improving the image quality of the formed image.

And in order to perform color control by detecting the chromaticity of the patch using the color sensor,
(1) Variations in color sensor characteristics and changes over time,
(2) Changes in sensor output due to changes in ambient temperature,
(3) Change in sensor output due to paper dust or toner adhering to the surface,
Need to be corrected. For this reason, generally, the variation factors (1) to (3) are corrected using a white reference plate or the like.

  As the reference plate, a member that does not change color with time and is white and has a diffuse reflection surface is desirable. For example, a block material obtained by roughening the surface of a member made of polytetrafluoroethylene (PTFE) to which a white pigment is added can be used as the reference plate.

  The sheet is made of a matte silver polyethylene terephthalate (PET) resin on which a metal film is deposited, and is formed by adhering the white surface. The white surface is a conventional sheet material containing a PET resin and an acrylic resin. Can be used as a reference plate. This sheet material is configured by adhering a 0.05 mm white surface and a 0.075 mm PTFE resin surface by an adhesive layer of 0.025 mm. This conventional sheet material is generally known by the name “pass peer”.

  On the other hand, when the density or chromaticity of the toner image formed on the transfer material after fixing is detected by the color sensor, a color sensor and a reference plate are installed in the transfer path after fixing, while transferring the transfer material, Alternatively, there is an image forming apparatus that stops conveyance and detects chromaticity (Patent Document 1). This image forming apparatus is configured to improve productivity by detecting an image on a transfer material in parallel with image formation. The conveyance path after fixing is a discharge path or a reversal path that reverses the printing surface of the transfer material for backside printing. A color sensor is installed in the conveyance path of the printer, which is generally a narrow space. To achieve this, it is desirable to reduce the size of the color sensor. The same applies to the reference plate.

  Further, in the configuration in which the color sensor and the reference plate are installed in the conveyance path, there is a concern that paper dust generated due to the passing of the transfer material or discoloration of the reference plate due to toner adhesion. In view of this, a configuration in which the reference plate is retracted from the conveyance path and a mechanical configuration such as a shutter to protect is considered except during sensing. However, it is spatially difficult to incorporate these mechanical configurations into the conveyance path, and the cost increases.

  Therefore, there is a prior application in which the transfer material is held between the reference plate facing the sensing device and the surface of the reference plate is cleaned while being rubbed with the transfer material (Patent Document 2). Dust adhering to the surface of the reference plate facing the sensing device can be removed by rubbing the transfer material.

JP-A-2005-292431 JP 11-216938 A

However, the block material obtained by roughening the surface of the member made of PTFE causes wear due to the sliding of the transfer material in a region where the reference plate is thin (about 3.6 mm or less). And when the thickness change of the reference plate occurs,
(Step 1) A change in the thickness of the reference plate causes a change in the reflectivity of the reference plate.
(Step 2) The change in reflectance of the reference plate causes a colorimetric error (color difference).
These two steps affect the colorimetric accuracy. This will be described in detail with reference to FIGS.

  FIG. 12 is a diagram showing the relationship between the thickness of PTFE and the reflectance in a conventional example. As shown in FIG. 12, the thickness t0 (≈3.6 mm) is a point at which the state of change in reflectance with respect to the thickness changes. With the thickness t0 as a boundary, the region can be divided into a region where the reflectance is stable with respect to the thickness (region A) and a region where the reflectance changes with respect to the thickness (region B).

  FIG. 13 is a diagram for explaining the behavior of light incident on a reference plate in a conventional example. 13A shows a region A where the thickness of the reference plate is larger than t1, and FIG. 13B shows a region B where the thickness of the reference plate is smaller than t1. In FIG. 13B, transmitted light 704a and 705a transmitted to the opposite side of the light source can be confirmed.

  As shown in FIG. 13, the following light enters the reference plate 743 and forms an optical path. That is, an optical path of incident light 701 incident on the reference plate 743, surface reflected light 702, absorbed light 704, internally scattered reflected light 705, transmitted light 704a, and transmitted light 705a is configured.

The reflected light from the reference plate is a combination of the surface reflected light 702 reflected from the reference plate surface and the reflected light 705 internally scattered inside the reference plate. Here, the amount of incident light 701 is the amount of incident light, the amount of reflected light is the amount of reflected light, and the reflectance is
Reflectance = amount of reflected light / amount of incident light (Equation 1)
It is defined as

<Area A>
In the region A (t> t0) where the thickness of the reference plate is greater than t0, the optical loss is only the absorbed light 704 inside the reference plate, and the other components are reflected light. There is no transmission to the surface opposite to the incident surface (hereinafter referred to as the opposite surface), and the amount of reflected light is stable with respect to the thickness change. That is, from Equation 1, even if the thickness of the reference plate is reduced due to durable wear, the reflectance is stable.

<Region B>
In the region B where the thickness of the reference plate is thinner than t0 (t <t0), the absorbed light 704 starts to be transmitted to the opposite surface (transmitted light 704a). Further, the internally scattered light that can become the reflected light 705 in FIG. 13A begins to transmit to the opposite surface (the transmitted light 705a in FIG. 13B), and the transmitted light 705a increases as the thickness decreases.

  As the transmitted light 705a increases, the internally scattered reflected light decreases. Therefore, the total amount of reflected light decreases, and the amount of reflected light decreases as the thickness decreases. That is, from Equation 1, the reflectance decreases as the thickness of the reference plate decreases.

  As described above, in a region where the thickness of the reference plate is t0 (≈3.6 mm) or less, the change in the thickness of the reference plate causes a change in the reflectance of the reference plate.

  Next, the reason why the reflectance change of the reference plate affects the colorimetric accuracy will be described by taking a spectral color sensor as an example.

  Dref (m) is a spectral output actual measurement value of the reference plate in the color sensor, Oref (m) is a theoretical spectral output value, D (m) is a spectral output actual measurement value of the patch in the color sensor, and O (m) is a reference plate. Is the spectral output value of the patch calibrated using. m is the wavelength of the visible light wavelength band, and indicates an arbitrary wavelength in the range of 380 nm to 730 nm.

First, the spectral output measurement value Dref (m) of the reference plate is detected. Next, a correction coefficient (= Oref) is determined by the detected spectral output actual measurement value Dref (m) of the detected reference plate and the spectral reflectance Oref (m) measured and stored in advance by a spectrocolorimeter serving as a master. (M) / Dref (m)). Then, the spectral output measurement value D (m) of the patch is detected, and the above-described correction coefficient (= Oref (m) / Dref (m)) is uniformly multiplied by the patch spectral output measurement value D (m) to obtain a reference plate. Spectral reflectance O (m) corrected using
O (m) = D (m) × Oref (m) / Dref (m) (Formula 2)
Convert to

  If the output value of the spectral reflectance O (m) corrected using the reference plate is obtained, it can be converted into chromaticity in an arbitrary color system such as CIE-XYZ or CIE-Lab in consideration of ambient light. Is possible.

  The relationship between the spectral reflectance Oref (m) and the reflectance is almost equal, and the reflectance characteristic shown in FIG. 12 is the spectral reflectance characteristic. From FIG. 12, when the reference plate having a thickness of 3 mm or less is worn by 100 μm, the spectral output measurement value Dref (m) of the reference plate is reduced by about 0.4%. From Equation 2, a decrease of about 0.4% in the spectral output actual measurement value Dref (m) of the reference plate causes a 0.4% increase in the spectral reflectance O (m) of the object. From the examination result, since the reference plate is worn by about 300 μm in the life of the image forming apparatus, the spectral reflectance O (m) changes by 1.2%. A 1.2% change in the spectral reflectance O (m) results in a color difference variation with a color difference of 0.5 (CIE-ΔE76) in the CIE-Lab color system.

  As described above, a change in reflectance of the reference plate causes a colorimetric error (color difference).

  The measurement error of a general colorimeter has a color difference of about 0.1. In this conventional example, the color difference is 0.5, which greatly exceeds the measurement error of the colorimeter.

  Therefore, in order to avoid this, it is necessary to increase the thickness of the reference plate in advance (3.6 mm or more), resulting in an increase in the size of the device around the conveyance path and an increase in the cost of the reference plate.

  On the other hand, the above-mentioned conventional sheet material that has a thin white layer and actively obtains the amount of reflected light as a whole by actively using the reflected light from the metal deposition surface, and presses it against the transfer material. When the paper is passed through, the reference plate is worn or scratched by the friction between the transfer material and the reference plate. In particular, the conventional sheet material changes its reflection characteristics due to scratches on the surface, and the silver PET resin is exposed as the wear progresses further. Since the reflection characteristics change due to the change in the surface state of the reference plate and the performance as the reference plate is impaired, the conventional sheet material is not suitable as a sliding surface.

  If the color sensor measures the color of the patch with the reflected light amount changed due to scratches or abrasion on the reference plate, the output value of the color sensor will be different from the actual chromaticity of the patch. If chromaticity control is performed using the result, a desired color balance cannot be obtained. In addition, the color balance is reversed and the density-gradation characteristics are deteriorated.

  An object of the present invention is to improve the accuracy of color detection using a reference plate having a white layer and to stabilize the color density of an image to be formed.

A typical configuration of the present invention for achieving the above object is as follows.
Irradiating means for irradiating light;
Receiving means for receiving light emitted from the irradiating means;
A reference plate for guiding the light emitted from the irradiating means to the receiving means;
A control unit that controls the amount of light emitted from the irradiation unit based on a reception result irradiated from the irradiation unit and received through the reference plate,
The reference plate is characterized in that a reflecting portion that reflects light transmitted through the reference plate is lined on a surface facing a reference surface irradiated with light from the irradiation unit.

  With the above configuration, it is possible to improve the accuracy of color detection using a reference plate having a white layer and to stabilize the color density of the formed image.

FIG. 3 is a cross-sectional view illustrating a configuration of an image forming unit in the first embodiment. The figure which shows the structure of the color sensor of the spectroscopy system in 1st Embodiment. 1 is a block diagram of an image forming apparatus according to a first embodiment. FIG. 3 is a diagram illustrating a color sensor unit and a transfer material guide unit according to the first embodiment. The figure showing the relationship between the thickness of PTFE of 1st Embodiment, and a reflectance. The figure showing the relationship between the thickness of PTFE and light quantity of 1st Embodiment. The figure explaining the behavior of the light which injects into the reference | standard board in 1st Embodiment. The figure which shows the change of a reflectance, and color difference when PTFE is worn out in 1st Embodiment. The figure showing the relationship between the thickness of PTFE of 2nd Embodiment, and a reflectance. The figure showing the relationship between the thickness of a 1st resin material, and a reflectance. The figure showing the relationship between the thickness of a 2nd resin material, and a reflectance. The figure showing the relationship between the thickness of PTFE in a prior art example, and a reflectance. The figure explaining the behavior of the light which injects into the reference | standard board in a prior art example.

[First Embodiment]
The feature of this embodiment is that the reference plate for calibrating the output of the image quality detection unit for detecting the image quality is backed by a member having a high reflectance, and the reflection from the backing compensates for the fall of the reflected light. It is to set to a stable thickness region.

  First, a color image forming apparatus 121 equipped with a color sensor 42 (light detection device) as an image quality detection unit will be described with reference to FIG. FIG. 1 is a cross-sectional view showing a configuration of an image forming unit in the first embodiment. The color image forming apparatus 121 is a tandem color image forming apparatus that employs the intermediate transfer member 27.

  First, the operation of the image forming unit will be described. An electrostatic latent image is formed on the image carrier by exposure light that is turned on based on the exposure time converted by the image processing unit 122 described later. The electrostatic latent image is developed to form a single color toner image, and the single color toner image is superimposed on the intermediate transfer member 27 to form a multicolor toner image. The multicolor toner image is transferred to the transfer material 11 and the multicolor toner image on the transfer material 11 is fixed.

  The image forming unit 124 includes a feeding unit 9 and photosensitive drums 1 (image carriers) for each station arranged in parallel for the number of development colors. Further, it includes an injection charger 4 (primary charging means), a toner cartridge 116, a developing sleeve 2 (developing means), an intermediate transfer member 27, a secondary transfer roller 105T, and a fixing unit 30.

  The photosensitive drum 1 is configured by applying an organic optical transmission layer to the outer periphery of an aluminum cylinder, and rotates when a driving force of a driving motor (not shown) is transmitted. The photosensitive drum 1 is rotated counterclockwise by a drive motor in accordance with an image forming operation.

  The plurality of stations described above form toner images of yellow (Y), magenta (M), cyan (C), and black (K) on the photosensitive drum 1, respectively. In the process until the toner image is formed on the photosensitive drum 1, the following process means are arranged at each station.

  There are an injection charger 4 and a developing sleeve 2 as process means for forming an image on the photosensitive drum 1 disposed at each station. The injection charger 4 charges the photosensitive drum 1.

  Exposure light is irradiated from the scanner unit 3 to the photosensitive drum 1 uniformly charged by the injection charger 4. Here, an electrostatic latent image is formed on the photosensitive drum 1 by selectively exposing the surface of the photosensitive drum 1 according to image data.

  In order to visualize the electrostatic latent image, four developing units having yellow (Y), magenta (M), cyan (C), and black (K) toners are provided for each station. Each developing device is provided with a developing sleeve 2. Each color toner is supplied to the photosensitive drum 1 by the developing sleeve 2, and a toner image corresponding to the electrostatic latent image is formed on the photosensitive drum 1.

  The intermediate transfer member 27 is in contact with the four photosensitive drums 1 and rotates clockwise when forming a color image. The intermediate transfer member 27 rotates in accordance with the rotation of the photosensitive drum 1. Here, the monochromatic toner image carried on the photosensitive drum 1 is primarily transferred to the intermediate transfer member 27 by the action of the primary transfer roller 7 disposed through the intermediate transfer member 27 so as to face each station.

  On the other hand, the transfer material 11 fed from the feeding unit 9 and conveyed to a position facing the intermediate transfer member 27 is nipped and conveyed by the intermediate transfer member 27 and the secondary transfer roller 105T. At this time, the multicolor toner image on the intermediate transfer member 27 is transferred to the transfer material 11.

  The fixing unit 30 melts and fixes the transferred multicolor toner image while conveying the transfer material 11. The fixing unit 30 includes a fixing roller 31 that heats the transfer material 11 and a pressure roller 32 that presses the transfer material 11 against the fixing roller 31. The transfer material 11 holding the multicolor toner image is conveyed by the fixing roller 31 and the pressure roller 32 and is applied with heat and pressure. As a result, the toner is fixed on the surface of the transfer material 11.

  The transfer material 11 after the toner image is fixed is discharged to a discharge tray 26 by a discharge roller 25. This completes the image forming operation.

  A color sensor 42 that detects the chromaticity of a predetermined image pattern is disposed downstream of the fixing unit 30 in the transfer material conveyance path. The color sensor 42 is arranged toward the printing surface (surface on which the toner image is formed) of the transfer material 11 and detects the spectral output of the patch after fixing formed on the transfer material 11.

  Next, the configuration of the color sensor 42 using the spectroscopic method will be described with reference to FIG. FIG. 2 is a diagram showing the configuration of the spectral color sensor in the first embodiment.

  The spectroscopic color sensor 42 includes a line sensor 181 that detects the dispersed light dispersed. The light source 53 is a white LED, a halogen lamp, or the like, and has a light emission wavelength distribution over the entire visible light.

  Irradiation light 105 from the light source 53 (irradiation means) is incident on the toner patch surface 104 (reference surface) formed on the transfer material 11 at about 45 °, diffusely reflected by the toner patch surface 104, and spreads upward. The irregularly reflected light 106 is converted into parallel light by the lens 107 and then enters the diffraction grating 108 at an incident angle of 0 ° and is split. The dispersed light separated is incident on the line sensor 181 (light receiving means). Light having a different wavelength range is incident on each pixel of the line sensor 181, and interpolation processing is performed on the output result (light reception result) of each pixel to obtain the spectral output of the object. The converted spectral output of the patch is temporarily stored in a memory 55 of FIG. 3 to be described later, and is converted into absolute chromaticity such as CIE-XYZ or CIE-Lab.

  The processing in the image processing unit and color correction in the color sensor will be described with reference to FIG. FIG. 3 is a block diagram of the image forming apparatus according to the first embodiment.

  The image processing unit 122 and the image forming unit 124 of the image forming apparatus are connected by a video interface (VIF), and the image processing unit 122 is connected to a host computer 123 of an external terminal or a network (not shown). The storage unit of the controller unit stores a color matching table 131, a color separation table 132, and a density correction table 133 used for color conversion.

  In addition, the image forming unit 124 is equipped with a color sensor 42 and a CPU 56 (control unit) that processes image formation processing and measurement results from the color sensor 42. The color sensor 42 is equipped with a memory 55. In the memory 55, an area for temporarily storing the spectral reflectance Oref (m) of the reference plate and the detection values of the reference plate and the patch is secured. In addition, the image forming unit 124 includes a display unit 602, an operation unit 603, and a memory 606.

  Next, processing in the image processing unit 122 will be described with reference to FIG. A color matching table 131 prepared in advance converts an RGB signal representing the color of an image sent from the host computer 123 or the like into a device RGB signal (hereinafter referred to as DevRGB) that matches the color reproduction range of the color image forming apparatus. .

  Next, the DevRGB signal is converted into a CMYK signal that is a color of toner color material of the color image forming apparatus by the color separation table 132. Next, C ′, M ′, Y ′, K obtained by correcting the CMYK signal with the correction of the gradation-density characteristic by the density correction table 133 that corrects the gradation-density characteristic specific to each color image forming apparatus. 'Convert to signal. Thereafter, halftone processing is performed by the halftone table 134 to convert it into a C ″ ″ M ″ ″ ″ ″ K ″ signal. Finally, a PWM (Pulse Width Modulation) table 135 converts the exposure time Tc, Tm, Ty, and Tk of the scanner unit 3 in FIG. 1 corresponding to the C ″ M ″ Y ″ K ″ signal.

  Next, feedback processing of the color separation table by the color sensor will be described.

  In the initial setting, a plurality of CMYK format color patch data is stored in the image processing unit 122 as color patch data, and default CMYK format color patch data is printed.

  The color patch image formed on the transfer material is measured by the color sensor 42, and the chromaticity value (L * a * b *) is read. The read chromaticity value is sent from the memory 55 in the color sensor to the color conversion unit of the image processing unit 122. Further, using a color management system (hereinafter referred to as CMS) (not shown), the chromaticity value is converted into data in CMYK format depending on the image forming apparatus. Then, by comparing the converted CMYK data with the CMYK data of the default color patch data, correction data C ′, M ′, Y ′, K ′ for correcting the difference is generated.

  This is performed on the plurality of patches, and correction data C ′, M ′, Y ′, and K ′ are generated by interpolation for CMYK data that does not exist as patches. These correction data are stored in the image processing unit 122 as a corrected color separation table 132.

  Next, a sandwiching configuration in which the transfer material 11 is sandwiched between the reference plate and the opposing member using the color sensor unit and the transfer material guide portion shown in FIG. 4 will be described. FIG. 4 is a diagram illustrating the color sensor unit and the transfer material guide unit in the first embodiment. FIG. 4A is a cross-sectional view of a state in which the transfer material 11 is not held between the transfer material guide portions in the sheet conveyance. FIG. 4B is a diagram showing a longitudinal state with the angle changed. FIG. 4C is a cross-sectional view showing a state where the transfer material enters and is held by the transfer material guide portion.

  As shown in FIG. 4, the transfer material guide portion includes a lower guide member 54 and an upper guide member 51 that are disposed to face each other across the conveyance path and have substantially the same width as the width of the transfer material 11.

  On the conveyance path side of the lower guide member 54, a pedestal guide member 50 serving as a conveyance guide and a pedestal for a reference plate is disposed via a spring 52. A reference plate 43 is disposed on the pedestal guide member 50. The reference plate 43 is a PTFE resin having a thickness of 2 mm, and a backing member 44 (reflecting portion) that serves as the backing is bonded. The backing member 44 was made of silver PET resin having a thickness of 0.075 mm on which a metal film was formed. The metal film is, for example, an aluminum deposition film, and preferably has a film thickness of at least 0.1 μm in order to prevent light from being transmitted through the backing.

  An opening 51b for allowing incident light from the light source 53 of the color sensor and reflected light from the reference plate or patch is formed in the upper guide member 51 immediately below the color sensor 42.

  On the side of the pedestal guide member 50 and the upper guide member 51 where the transfer material 11 enters, an inclined surface 50a and an inclined surface 51a for introducing the transfer material 11 between the guides are formed. By providing the inclined surfaces 50 a and 51 a, the transfer material 11 can smoothly enter between the base guide member 50 and the upper guide member 51.

Further, a pressure is applied to the pedestal guide member 50 by a spring 52, and the transfer material 11 being conveyed is held between the pedestal guide member 50 and the upper guide member 51, whereby the reference plate 43 is rubbed with the transfer material 11 and becomes dirty. A cleaning effect can be obtained. Further, the pressure is positively applied in order to obtain a good cleaning effect, but the light pressure is sufficiently low to transport a transfer material having low rigidity such as a thin paper having a small basis weight. By examination, it is known that when a thin paper having a basis weight of 60 g is passed under a pressure of 25 g / cm ² , both transportability and cleaning effect can be achieved.

  The behavior of light incident on the reference plate in this embodiment will be described with reference to FIGS.

  FIG. 5 is a diagram illustrating the relationship between the thickness of PTFE and the reflectance according to the first embodiment. In FIG. 5, the solid line is the relationship with the backing. For reference, the relationship between the thickness of PTFE and the reflectance when there is no backing as described in the conventional example is indicated by a broken line.

  FIG. 6 is a diagram illustrating the relationship between the thickness of PTFE and the amount of light according to the first embodiment. In FIG. 6, the relationship between the thickness t of the reference plate provided with the backing member and the amount of reflected light (the amount of light incident on the color sensor) is indicated by a solid line. The relationship between the thickness and the amount of reflected light when there is no backing in the conventional example is indicated by a broken line (fine broken line). The relationship between the amount of reflected light that is a part of the internally scattered light reflected by the backing member 44 and reflected to the incident surface is indicated by a broken line (coarse broken line). The reflected light when the backing member 44 is applied is the sum of the reflected light of the reference plate itself and the reflected light from the backing member 44, and is referred to as the total amount of reflected light.

Here, Equation 1 described in the conventional example is
Reflectivity = total amount of reflected light / amount of incident light (Equation 3)
It becomes.

  FIG. 7 is a diagram for explaining the behavior of light incident on the reference plate in the first embodiment. The reference plate 43 provided with the backing member 44 and the behavior of the incident light 201 on the reference plate will be described with reference to FIG.

  The thicknesses t1 and t2 are points at which the state of the change in reflectance with respect to the thickness changes. t1 is referred to as an upper limit thickness (first thickness), and t2 is referred to as a lower limit thickness (second thickness). As shown in FIGS. 5 and 6, the behavior of light inside the reference plate 43 will be described in detail by dividing the thickness region into two types A and B. FIGS. 7A and 7B correspond to the thickness regions A and B of FIGS.

<Area A>
In the region where the thickness of the reference plate 43 is thicker than t1, the optical loss is only the absorbed light 206 inside the reference plate, and the other components are reflected light (surface reflected light 202 and reflected light 205). There is no transmission to the surface opposite to the incident surface (hereinafter referred to as the opposite surface), and the total amount of reflected light is stable against changes in thickness due to wear. That is, from Equation 3, even when the thickness of the reference plate is reduced due to durable wear, the reflectance is stable.

  When the thickness of the reference plate 43 is near t1, a part of the internally scattered light absorbed inside the reference plate is reflected by the backing member 44. Since the reference plate 43 has a thickness, the reflected light (surface reflected light 202 and reflected light 205) from the backing member 44 is not reflected from the reflecting surface but is absorbed in the reference plate (absorption shown in FIG. 7A). Light 203a). Therefore, the total amount of reflected light is stable with respect to the thickness change.

  That is, from Equation 3, a region A that is a stable region of reflectance as shown by the solid line in FIG. 5 is generated.

<Region B>
In a region where the thickness of the reference plate 43 is smaller than t1 (t <t1), a part of the internally scattered light reflected by the backing member 44 shown by the broken line (coarse broken line) in FIG. Component (reflected light 203b in FIG. 7B) is generated. The thickness at which the ratio of the reflected light 203b to the total reflected light amount is 0.1% is defined as t1. The reflected light 203b increases as the reference plate becomes thinner.

  Next, the region (t <t1) will be further subdivided and described.

<Region B-1>
In a region where the thickness of the reference plate 43 is smaller than t1 and larger than t2 (t2 <t <t1), the total amount of reflected light decreases as the thickness decreases due to wear of the reference plate 43, as shown by the solid line in FIG. ing. However, the amount of change is smaller than when there is no backing member 44 (fine broken line). This is because as the thickness of the reference plate 43 becomes thinner, the reflected light 203b that goes out of the reference plate 43 increases.

  That is, in the region where the thickness is smaller than t1 and larger than t2 (t2 <t <t1), as shown by the solid line in FIG. 5, a region B-1 in which the reflectance decreases as the thickness decreases is generated. However, the amount of change is smaller than when the backing member 44 is not provided.

<Region B-2>
When the thickness of the reference plate 43 is in the vicinity of t2, an inflection point occurs where the amount of change in the amount of reflected light with respect to the thickness is zero. This offsets the decrease in the reflected light (surface reflected light 202 and reflected light 205) from the reference plate 43 itself and the increase in the reflected light 203b from the backing member 44, and the change in the total reflected light amount due to the change in the thickness of the reference plate 43. This is because it disappears.

  That is, a region B-2 having a stable reflectance with respect to the thickness is generated.

<Region B-3>
In a region where the thickness of the reference plate 43 is smaller than t2 (t <t2), the reflectivity increases as the thickness decreases. This is because the reflected light 3b further increases. In this region, the amount of change in reflectance tends to increase as the thickness decreases.

  That is, from Formula 1, a region B-3 in which the reflectance increases as the thickness of the reference plate as shown by the solid line in FIG. 5 is generated.

  As described above, by providing the backing, the thickness of the reference plate is originally reduced, and the component that becomes the transmitted light is reflected by the backing member 44. The upper limit thickness t1 at which reflection at the backing member 44 begins, the decrease in the reflected light of the reference plate itself and the increase in the reflected light from the backing member 44 are offset, and the change in the total amount of reflected light due to the change in the thickness of the reference plate is eliminated. The initial thickness of the reference plate is set between the lower limit thickness t2. With this configuration, it is possible to suppress a change in reflectance with respect to a change in thickness (a decrease in thickness) of the reference plate 43 caused by a transfer material conveyance friction.

In the configuration of the reference plate 43 unique to the present embodiment, when the thickness variation at which the reference plate is worn during the product life is Δtc or less in the holding configuration, the thickness t of the reference plate is
t2 + Δtc <t <t1 (Formula 4)
And The reference plate 43 is used in a thickness region where the change rate of the reflectance by the reflected light 203b from the backing member 44 is stable with respect to the thickness change of the reference plate 43.

  In the case of PTFE resin, t1 is about 3.1 mm and t2 is about 1.9 mm. As a result of the examination, since the wear amount Δtc of the reference plate is about 300 μm throughout the product life, the thickness of the reference plate is set to 2.2 mm or more and 3.1 mm or less.

  FIG. 8 is a diagram showing a change in reflectance and a color difference when PTFE is worn in the first embodiment. FIG. 8 shows a list of changes in reflectance and color differences when PTFE is worn by about 300 μm with or without the backing member 44, that is, with or without the backing. As shown in FIG. 8, in the case with the backing, the change in reflectance is 0.6% and the color difference is 0.2, which is reduced to less than half compared with the case without the backing.

  In the present embodiment, the upper guide member 51 has been described as a counter member, but the present invention is not limited to this. For example, the color sensor 42 itself may be a member facing the reference plate 43 and the transfer material 11 may be sandwiched.

  The thickness t can be arbitrarily set according to the amount of wear Δtc of the reference plate and the reference plate material.

  Further, in the present embodiment, the description has been made on the assumption that the backing member 44 of the silver-colored PET resin on which the metal film is formed. However, the present invention is not limited to this, and a member having high reflectivity is provided on the back of the reference plate 43. Should be installed. For example, the reference plate installation surface of the pedestal guide member 50 may be coated with a highly reflective material, or the pedestal guide member 50 itself may be molded with a highly reflective material.

  Further, although the present embodiment has been described using a spectral color sensor, it may be used for a filter type color sensor using an RGB filter.

  As an effect peculiar to this configuration, by providing the backing, even when the reference plate is worn, the reflectance fluctuation can be suppressed low, and the stable region of the reflectance can be made thinner. By controlling the reflectance variation to a low level, the color measurement accuracy of the color sensor is improved, and the density or chromaticity control is performed using the result, thereby achieving a color balance and obtaining a desired density-gradation characteristic. It will be. In addition, the thickness of the reference plate can be made thinner, and it becomes easier to arrange the color sensor system in a limited narrow space such as in the conveyance path.

  As described above, according to the above-described configuration, even when the reference plate is worn, it is possible to suppress the reflectance fluctuation by compensating the amount of reflected light by the reflection from the backing member 44. As a result, the output value of the color sensor reproduces the actual density or chromaticity of the patch, and the density or chromaticity control is performed using the result, thereby achieving color balance and a desired density-tone characteristic. Can be obtained. Further, by making the thickness t of the reference plate within the range of the above (Equation 4), it is possible to achieve downsizing while maintaining the detection accuracy by the color sensor.

[Second Embodiment]
A second embodiment of the present invention will be described. The initial thickness of the reference plate 43 is set so that the lower limit thickness t2 is included in the region of the initial thickness of the reference plate 43 and the thickness of the reference plate 43 after durability caused by the conveyance friction of the transfer material 11. . This minimizes the color measurement error due to the thickness change of the reference plate 43 caused by the friction of the transfer material 11 and the thickness of the reference plate 43 to be set.

In the configuration of the reference plate unique to the present embodiment, when the thickness variation that the reference plate 43 wears during the product life is Δtc or less, the thickness t of the reference plate 43 is
t−Δtc <t2 <t (Formula 5)
And

  The material of the reference plate used in the description of the present embodiment is a PTFE resin with a backing as in the first embodiment, and t2 is about 1.9 mm.

  FIG. 9 is a diagram illustrating the relationship between the thickness of PTFE and the reflectance according to the second embodiment. FIG. 9 is an enlarged view of region B of FIG.

  When a rough paper with the largest wear of the reference plate 43 is passed through the transfer material included in the product specification while using the upper limit product of the spring 52 (see FIG. 4), the wear amount Δtc during the product life becomes 300 μm. . Here, if the initial thickness of the reference plate 43 is set to 2.05 mm, the thickness after the endurance is 1.75 mm, and t2 = 1.9 mm in the region of the thickness change of the reference plate 43 throughout the product life. Will be included.

  From FIG. 9, the reflectance decreases as the reference plate wears from the initial thickness of 2.05 mm. At time t2, the reflectance fluctuation reaches a maximum value of 0.0007. As the wear further progresses, the reflectance increases, and finally the reflectance becomes equal to the initial value when the thickness is 1.75 mm.

  That is, no color measurement error occurs at the beginning and end of the product life. In addition, the colorimetric error in the case of 0.0007 fluctuation, which is the maximum fluctuation amount of the reflectance during the product lifetime, is 0.03 or less in color difference and is an error level that does not affect the measurement at all.

  As described above, in this embodiment, the initial thickness of the reference plate is included so as to include the thickness t2 in the region between the initial thickness of the reference plate and the thickness of the reference plate 43 after durability caused by the conveyance of the transfer material 11. Set the thickness. Thereby, the thickness of the reference plate 43 can be set thinner than that of the first embodiment.

  Further, based on the thickness t2 at which the decrease in the reflected light of the reference plate 43 itself and the increase in the reflected light from the reflecting portion such as the backing member 44 are offset and the total reflected light amount does not change due to the change in the thickness of the reference plate, An error due to wear of the reference plate 43 is distributed to a region thicker than a base point and a thin region. As a result, the initial thickness of the reference plate 43 can be minimized, and the reflectance fluctuation due to the thickness change can be minimized.

[Other Embodiments]
Since the reference plate 43 generally increases the amount of reflected light, it is preferable to select a white member with little transmission and absorption. Examples of the material of the white reference plate include resins such as PTFE, polyacetal (POM), and polybutylene terephthalate (PBT), and those obtained by mixing a white pigment using these resins as a binder. Further, an elastomer may be used without depending on the resin.

  The backing member 44 uses a highly reflective member in order to increase the amount of reflected light. In the first embodiment, a silver PET resin sheet on which metal is vapor-deposited has been described as the backing member 44. However, not only this but also metal on a block material such as glass may be vapor-deposited. Alternatively, the reflective portion may be formed by directly depositing on the reference plate 43 itself, and this may be used as the backing.

  Hereinafter, two commercially available materials will be described as reference plate materials.

  As the first resin material, PBT is used as a binder resin, and there is a material having excellent weather resistance and wear resistance. FIG. 10 is a diagram showing the relationship between the thickness of the first resin material and the reflectance. A solid line indicates no lining and a broken line indicates lining. From FIG. 10, t1 = 2.2 mm and t2 = 1.8 mm. As the first resin material, for example, “C7015” of “DURANEX” of Nippon Polyplastics is suitable.

  As the second resin material, POM is a binder resin, and the quality is improved in weather resistance and matte. FIG. 11 is a diagram showing the relationship between the thickness of the second resin material and the reflectance. A solid line indicates no lining and a broken line indicates lining. From FIG. 11, t1 = 7.7 mm and t2 = 4.0 mm. As the second resin material, for example, “M90-45” of “DURACON” of Nippon Polyplastics is suitable.

  As mentioned above, although two commercially available materials were demonstrated, the thickness setting according to 1st Embodiment and 2nd Embodiment should just be performed from those thickness t1, t2 also with other materials.

  Generally, when the reference plate is lined, the variation in the amount of reflected light with respect to the thickness change tends to be stable. The thickness t is arbitrarily set within a range where the backing member 44 is not exposed due to the wear of the reference plate, according to the reference plate material, the reference plate wear amount Δtc, and the color measurement accuracy required by the color measurement system. That's fine.

  As an effect peculiar to the present embodiment, it is possible to set an optimum thickness for the resin material that does not deteriorate the colorimetric accuracy.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 9 ... Feeding part 11 ... Transfer material 42 ... Color sensor 43 ... Base plate 44 ... Backing member 53 ... Light source 104 ... Toner patch surface 105 ... Irradiation light 121 ... Color image forming apparatus

Claims (8)

Irradiating means for irradiating light;
A light receiving means for receiving light emitted from the irradiation means;
A reference plate for guiding the light emitted from the irradiation means to the light receiving means;
A control unit that controls the amount of light emitted from the irradiation unit based on a light reception result received from the irradiation unit and received through the reference plate,
The light detection device according to claim 1, wherein a reflection portion that reflects light transmitted through the reference plate is lined on a surface facing the reference surface irradiated with light from the irradiation unit.   The photodetecting device according to claim 1, wherein an initial thickness of the reference plate is set to be thicker than a first thickness at which a reflected light amount from the reference plate is minimized.   The photodetecting device according to claim 2, wherein an initial thickness of the reference plate is made thinner than a second thickness that is thicker than the first thickness at which reflection from the reflecting portion starts. The reference plate is arranged to guide the conveyance of the transfer material to be conveyed by the reference surface being in contact with the transfer material,
3. The guide plate according to claim 2, wherein the reference plate is worn by guiding conveyance of the transfer material, and when the thickness of the reference plate is reduced from the initial thickness, the reference thickness is at least the first thickness. The light detection device according to claim 3. In an image forming apparatus comprising: an image carrier; and an image quality detection unit that is disposed in a conveyance path through which a transfer material to which a toner image formed on the image carrier is transferred is conveyed and detects image quality using light.
The image forming apparatus according to claim 1, wherein the image quality detection unit is the light detection apparatus according to claim 1.   The image forming apparatus according to claim 5, wherein PTFE is used as the reference plate.   6. The image forming apparatus according to claim 5, wherein a PBT is used as the reference plate.   The image forming apparatus according to claim 5, wherein a POM is used as the reference plate.

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