JP5921318B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer, and to a colorimetric method for an image output by the image forming apparatus.

  In recent years, color image forming apparatuses such as color printers and color copying machines have been required to improve the output image quality. In particular, the stability of the image gradation and the image color greatly affects the image quality. Generally, the color stability required for printed matter is said to be 3 or less in terms of CIE-ΔE. In the image forming apparatus, the following adjustment is performed so as to obtain the minimum necessary color difference required for such printed matter. That is, a patch of toner mixed with each color is printed as a test chart, the chromaticity of the toner patch is detected by a color sensor, and a look-up table (hereinafter referred to as LUT), exposure amount, development bias, etc. are set to a desired value. Give feedback on image forming conditions.

  The color reproducibility, which is the output color variation characteristic of the image forming apparatus, is determined by (1) printer engine output variation, (2) color sensor detection variation, and (3) color matching algorithm variation. . The output variation of a general electrophotographic printer engine is about ΔE = 2.0, and the algorithm for feeding back the LUT also has a variation of about ΔE = 0.3. FIG. 6A shows a detection result of the color sensor in this case and a simulation result of color reproducibility as the image forming apparatus system. As shown in FIG. 6A, in order to keep the color reproducibility of the image forming apparatus system at ΔE of 3.0 or less, it is necessary to suppress the detection variation of the color sensor to 2.2 or less at ΔE.

  As a factor that increases the detection variation of the color sensor, there is stray light that is incident on the line sensor without passing through a measurement object such as a toner patch. The amount of stray light is determined by the optical configuration of the color sensor, and stray light is included in many sensors using most optical systems. In the case of a spectroscopic color sensor, it is desirable to suppress the amount of stray light because it is a determining factor of the colorimetric range as the upper limit of the high density region that can be detected. In addition, the stray light includes reflected light from impurities such as dust and dirt attached to the dust-proof glass to prevent the intrusion of dust into the color sensor, which is distinguished from stray light that the color sensor has in advance. Therefore, it is defined as stray light of external factors. For example, in an image forming apparatus configured to read a toner patch on a transfer material being transported by a color sensor mounted in the transport path of the transfer material (flow-reading), the transfer material may be applied to a dust-proof glass surface at the time of reading. Paper dust accompanying conveyance (also called paper passing) may adhere. Reflected light from the paper dust adhering to the dust-proof glass surface is taken into the sensor as stray light, increasing the detection variation of the color sensor. Particularly in high-concentration patches, the amount of reflected light from the patch is small, so even a small amount of stray light due to light paper dust stains reduces the SN ratio, and two or three paper powders adhering to the dust-proof glass (to 2% stray light) Equivalent), but a color difference of about 4 is generated by ΔE.

  If the amount of stray light changes due to an external factor, detection variations of the color sensor occur. When stray light having white noise characteristics as an external factor increases in a spectroscopic color sensor having 0.5% stray light in advance, the result of simulating the relationship between stray light quantity and color difference as an external factor is shown in FIG. b). FIG. 6B is a graph in which the horizontal axis is stray light (%) and the vertical axis is the color difference ΔE. The patches used for the simulation are cyan (C), magenta (M), yellow (Y), and black (K) solid toner patches, and the colorimetric values of each patch in the absence of stray light due to external factors. To find the color difference. According to this, the color difference increases as stray light increases. Further, even with the same stray light amount, the color difference ΔE differs depending on the color. Among the four colors, the color difference of the K color is the largest, and in order to satisfy the color difference ΔE of 2.2 or less with the K color, the stray light as an external factor must be suppressed to less than about 1%. There is. Therefore, a paper dust removing method using a cleaning effect of a dust-proof glass surface by paper is carried out by sandwiching and transporting paper between a color sensor and a facing member. During normal printing, the color sensor is in the retracted position, suppresses the adhesion of paper dust, contacts when reading a test chart, and removes paper dust with paper while reading a toner patch (for example, see Patent Document 1).

JP-A-11-216938

  However, in the prior art, the pressing pressure against the transfer material is light considering the transportability and damage to the test chart, and the cleaning effect is limited. Therefore, in order to prevent paper dust from adhering to the glass surface, it is necessary to suppress the generation of paper dust itself. Paper dust is generated from normal printing and test chart printing, but the amount of paper dust generated per sheet is higher in test chart printing that is nipped and conveyed while rubbing paper than in normal printing. . For this reason, if there are many opportunities (calibration) to print a test chart, a lot of paper dust will be generated. Therefore, it is more effective to suppress the generation of paper dust, particularly when transporting paper while pinching the test chart.

  The present invention has been made under such circumstances, and an object thereof is to suppress the generation of paper dust from the transfer material when the detection is performed by the sensor while the transfer material is held.

  In order to solve the above-described problems, the present invention has the following configuration.

  (1) Detection means for detecting a first image after fixing formed on a transfer material, control means for correcting image forming conditions based on a result of detecting the first image by the detection means, and the image An image forming apparatus comprising: an image forming unit that forms an image on a transfer material based on a forming condition, wherein the control unit makes contact between the detection unit and the transfer material in a direction orthogonal to a transfer material transport direction. An image forming apparatus, wherein a second image having a width including at least a part of a region to be formed is formed on a transfer material together with the first image by the image forming unit.

  (2) Image forming conditions based on detection means for detecting the first image after fixing formed on the transfer material, conveyance means for conveying the transfer material, and results of detection of the first image by the detection means An image forming apparatus comprising: a control unit that corrects image forming; and an image forming unit that forms an image on a transfer material based on the image forming condition, wherein the control unit is arranged in a direction orthogonal to the transfer direction of the transfer material. An image forming apparatus, wherein a second image having a width including at least a part of a region where the conveying unit and the transfer material contact is formed on the transfer material together with the first image by the image forming unit.

  According to the present invention, it is possible to suppress the generation of paper dust from the transfer material when performing detection by the sensor while sandwiching the transfer material.

Sectional drawing which shows the whole structure of the image forming apparatus of Examples 1-3, and the schematic diagram of a color sensor Schematic illustrating the image processing unit of Examples 1 to 3, a diagram showing the periphery of the color sensor The figure which shows the test chart of Example 1 FIG. 3 is a graph showing a relationship between the printing rate of the toner patch of Example 1 and stray light, and a diagram showing a test chart of Example 2. FIG. Graph showing the spectral characteristics of the toner patch of Example 3, and graph showing simulation results of stray light and color difference of external factors Graph showing the simulation results of the conventional example

  The mode for carrying out the present invention will be described in detail below with reference to examples.

[Configuration of Image Forming Apparatus]
A color image forming apparatus in which the color sensor 42 (detecting means) is mounted will be described with reference to FIG. FIG. 1A is a cross-sectional view showing the configuration of the image forming apparatus. This apparatus is a tandem color image forming apparatus that employs an intermediate transfer belt 27. The image forming apparatus of the present embodiment is, for example, a four-color image forming apparatus of yellow (Y), magenta (M), cyan (C), and black (K). FIG. Although the code | symbol which shows a color is described, the code | symbols Y-K showing a color are abbreviate | omitted except the case where it is required below. The color image forming apparatus is not limited to a four-color image forming apparatus, and may be a single color or, for example, a six-color image forming apparatus.

  The photosensitive drum 1 is configured by applying an organic optical transmission layer to the outer periphery of an aluminum cylinder, and rotates by receiving a driving force of a driving motor (not shown). The driving motor drives the photosensitive drum 1 in accordance with an image forming operation. Rotate counterclockwise. The injection charger 4 (charging means) charges the Y, M, C, and K photosensitive drums 1 for each station. The scanner unit 3 may, for example, use laser light based on the exposure time (Tc, Tm, Ty, Tk, which will be described later with reference to FIG. 2A) converted by the image processing unit 122 (control means) illustrated in FIG. An electrostatic latent image is formed on the photosensitive drum 1 by the exposure light that is turned on. In order to visualize the electrostatic latent image formed on the surface of the photosensitive drum 1, the developing device develops the toner of each color in the toner cartridge 116 at each station, and a single-color toner image on each photosensitive drum 1. Is formed. Each developing device is provided with a developing roller 2.

  The intermediate transfer belt 27 is in contact with the photosensitive drum 1, rotates clockwise when forming a color image, and rotates with the rotation of the photosensitive drum 1. The single-color toner images formed on the respective photosensitive drums 1 are sequentially superimposed and transferred onto the intermediate transfer belt 27 by the primary transfer roller 7 at the timing of each nip portion T1. A toner image is formed. The transfer material 11 placed on the paper feeding unit 9 is conveyed to the secondary transfer roller 105T at a timing so that the multicolor toner image on the intermediate transfer belt 27 is transferred to a desired position on the transfer material 11. Is done. The secondary transfer roller 105T comes into contact with the intermediate transfer belt 27, the transfer material 11 is nipped and conveyed, and the multicolor toner image on the intermediate transfer belt 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 heats the transfer material 11 and presses the transfer material 11 against the fixing roller 31. A pressure roller 32 is provided. The transfer material 11 on which the multicolor toner image has been transferred is conveyed by a fixing roller 31 and a pressure roller 32, and heat and pressure are applied to fix the toner on the surface of the transfer material 11. The image forming unit 121 (image forming unit) includes the paper feeding unit 9, the photosensitive drum 1, the injection charger 4, the toner cartridge 116, the developing unit, the intermediate transfer belt 27, the secondary transfer roller 105T, and the fixing unit 30. Has been. After the toner image is fixed, the transfer material 11 is then transported by the transport roller pair 75a and 75b, and is discharged to the paper discharge tray 26 by the discharge roller 25, thereby completing the image forming operation.

  A color sensor 42 that detects the chromaticity of a predetermined image pattern is arranged toward the printing surface downstream of the fixing unit 30 in the transfer material conveyance path, and the chromaticity of the patch after fixing formed on the transfer material 11 ( This is an optical sensor for detecting (spectral output). The facing member 50 will be described later.

[Configuration of color sensor]
The color sensor will be described by taking a spectrophotometric color sensor as an example. The spectroscopic color sensor irradiates the toner patch with white light, disperses the reflected light using a diffraction grating or a prism, detects the intensity of the dispersed light for each wavelength with a line sensor, and uses the light from the light source. The spectral reflectance of the toner patch is obtained by correcting the wavelength distribution and the spectral sensitivity of the sensor.

  The configuration of the color sensor 42 using the spectroscopic method will be described in detail with reference to FIG. The spectroscopic color sensor 42 includes a line sensor 101 that detects dispersed dispersed light. The light source 102 is a white LED, a halogen lamp, or the like, and has a light emission wavelength distribution over the entire visible light. In addition, as a dust-proof mechanism inside the color sensor 42, a dust-proof glass 110 is provided in the opening 99 (see FIG. 3).

  Light 105 from the light source 102 is incident on a toner patch surface (hereinafter referred to as toner surface) 104 formed on the transfer material 11 at about 45 °, diffusely reflected by the toner 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 and is split. The dispersed light separated is incident on the line sensor 101. Light having different wavelength ranges is incident on each pixel of the line sensor 101, and a CPU 53 described later performs an interpolation process on the output result of each pixel to obtain a spectral output of the object. The CPU 53 temporarily stores the converted spectral output of the toner patch in the memory 55 of FIG. 2A, and further converts it into absolute chromaticity such as CIE-XYZ or CIE-Lab. As described above, the CPU 53 of the color sensor 42 calculates the absolute chromaticity of the toner patch, and outputs information on the calculated absolute chromaticity to, for example, a CPU 56 described later.

[Image processing unit]
Processing in the image processing unit and color correction in the color sensor 42 will be described with reference to a schematic diagram illustrating the image processing unit in FIG. The image processing unit 122 and the image forming unit 121 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). A color matching table 131, a color separation table 132, a density correction table 133, a halftone table 134, and a PWM table 135 used for color conversion are stored in, for example, a memory that is a storage unit of the image processing unit 122. In addition, the image forming unit 121 includes a color sensor 42 and a CPU 56 that processes image forming processing and measurement results from the color sensor 42. Furthermore, the image forming unit 121 includes a memory 606 that temporarily stores various programs executed by the CPU 56 and results of processes executed by the CPU 56. The color sensor 42 includes a CPU 53 and a memory 55, and an area for temporarily storing the spectral output of the patch converted by the CPU 53, which is a patch detection value, is secured in the memory 55.

  Next, the processing in the image processing unit 122 in FIG. When an RGB signal representing the color of an image is input from the host computer 123 or the like, the image processing unit 122 performs the following processing. That is, the image processing unit 122 converts the RGB signal into a device RGB signal (hereinafter referred to as DevRGB signal) that matches the color gamut of the color image forming apparatus using a color matching table 131 prepared in advance. Next, the image processing unit 122 converts the DevRGB signal into a CMYK signal that is a toner color material color of the color image forming apparatus using the color separation table 132. Next, the image processing unit 122 performs C′M′Y′K on which the CMYK signal is corrected for 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. After that, the image processing unit 122 performs halftone processing using the halftone table 134 and converts the signal into a C ″ ″ M ″ Y ″ ″ ″ signal. Finally, a PWM (Pulse Width Modulation) table 135 converts the exposure time Tc, Tm, Ty, and Tk of the scanner unit 3 corresponding to the C ″ M ″ Y ″ K ″ signal.

[Correction of color separation table based on detection result of color sensor]
Next, feedback processing of the color separation table 132 by the color sensor 42 will be described. A plurality of color patch data in CMYK format is stored in advance as color patch data in a memory (not shown) of the image processing unit 122, and default color patch data in CMYK format is printed. The color patch data here is formed for the purpose of correcting the color separation table, and is a test chart described in the background art, for example, known color patch data.

  The color patch image formed on the transfer material by the image forming unit 121 based on the color patch data transmitted from the image processing unit 122 is measured by the color sensor 42 after being fixed by the fixing unit 30, and the chromaticity value is determined by the CPU 53. Is calculated, that is, the chromaticity value is read. Thus, the chromaticity value read by the color sensor 42 is sent from the memory 55 in the color sensor 42 by the CPU 53 to the color conversion unit of the image processing unit 122 via the CPU 56. The color conversion unit of the image processing unit 122 converts a chromaticity value read by the color sensor 42 into CMYK format data depending on the image forming apparatus, using a color management system (hereinafter referred to as CMS) (not shown). To do. Then, the image processing unit 122 compares the CMYK data converted by the color conversion unit with the CMYK data of the default color patch data to correct the difference ΔC, ΔM, ΔY, ΔK. Is generated.

  The image processing unit 122 performs the above-described processing for a plurality of patches, and for the CMYK data that does not exist as patches, for example, correction data ΔC, ΔM, ΔY, ΔK is generated by interpolation processing. These correction data are stored as a corrected color separation table 132 in a memory (not shown) of the image processing unit 122.

  The detection result by the color sensor 42 may be used to correct not only the color separation table 132 described above but also other table, image forming conditions such as exposure amount and developing bias.

[Transfer material sandwiched by color sensor and opposing member]
Next, the color sensor 42 shown in FIGS. 2B and 2C, and the color sensor 42 (first member) and the opposing member 50 (second member) disposed opposite to each other across the conveyance path, are used. A sandwiching configuration in which the transfer material is sandwiched between the sensor 42 and the opposing member 50 will be described. FIG. 2B is a cross-sectional view showing a state where the transfer material is not sandwiched between the sheet guide portion including the color sensor 42 and the facing member 50. Moreover, FIG.2 (c) is a figure which shows the mode of the longitudinal direction which changed the angle of FIG.2 (b). The longitudinal direction is a direction orthogonal to the transfer material conveyance direction (paper feeding direction in FIG. 3).

  The facing member 50 is disposed to face the color sensor 42 across the conveyance path, and includes a lower guide member 54 having a width equal to or larger than that of the transfer material, and an upper guide member (not shown) on the color sensor 42 side. The facing member 50 is fixed to the lower guide member 54 via a spring 52.

  The transfer material 11 smoothly enters between an upper guide member (not shown) and a lower guide member 54 and enters between the color sensor 42 and the opposing member 50. The color sensor 42 moves up and down at a predetermined timing and retracts to the upper side of the drawing during normal printing. However, when the color patch as a test chart is measured, the color sensor 42 is moved downward in FIGS. 2 (b) and 2 (c). Moves to the side and contacts the opposing member 50. The opposing member 50 applies a pressure to the color sensor 42 with a spring 52, and the transfer material being conveyed enters between the color sensor 42 and the opposing member 50 to sandwich and convey the transfer material 11, thereby causing the transfer material 11 to flutter. Measure color while suppressing. Reference numeral 100 will be described later.

  In FIGS. 2B and 2C, the color sensor 42 is disposed on the upper side in the vertical direction and the opposing member 50 is disposed on the lower side in the vertical direction. However, as shown in FIG. 2 (b) and FIG. 2 (c) may be arranged in a state rotated 90 degrees. That is, FIG. 2B and FIG. 2C may be rotated 90 degrees, and for example, the opposing member 50 may be disposed on the left side, for example, the color sensor 42 on the right side, as shown in FIG. May be.

The material of the facing member 50 is preferably a resin having good slidability, and is made of, for example, PTFE, polyacetal, polybutylene terephthalate, or the like. Further, the pressure is positively applied in order to obtain the effect of removing the paper dust from the surface of the dustproof glass 110, but in order to convey a transfer material having low rigidity such as a thin paper having a small basis weight (g / m ² ), a light pressure is used. There is a need. For example, when thin paper having a basis weight of 60 g / m ² is passed under a pressure of 25 g / cm ² , both transportability and a certain amount of paper dust removal effect can be achieved. However, as described above, it is not sufficient to completely remove the paper dust.

  Here, a plate-like member has been described as an example of the facing member 50. However, the present invention is not limited to this. For example, a cylindrical member such as a conveyance roller may be used as a holding structure for holding the transfer material. .

[Test chart of this example]
Next, a test chart specific to this embodiment will be described with reference to FIG. A measurement patch 98 (first image) is arranged in the transport direction so as to pass through the opening 99 of the color sensor 42 arranged in the center in the longitudinal direction. Here, the measurement patch 98 refers to a color patch formed, for example, for correcting the color separation table 132 based on the detection result of the color sensor 42, and corresponds to a conventional test chart. A known patch pattern of each color is formed in circles 1 to 12 of the measurement patch 98. A region indicated by an arrow 100 between the two lines indicated by a broken line in the drawing (hereinafter referred to as a sandwiching region 100) is a range in which the transfer material 11 is sandwiched between the color sensor 42 and the opposing member 50, and the measurement patch 98 is shown. A toner patch 97 (second image) is printed so as to cover this region from each end of the image. The toner patch 97 covers the surface of the transfer material with a toner layer, and prevents contact between the surface of the transfer material and the color sensor 42. This suppresses the generation of paper dust due to the rubbing between the color sensor 42 and the transfer material 11. That is, the toner patch 97 is a patch formed to suppress paper dust generated from the transfer material 11, and is formed for a purpose different from the measurement patch 98. Note that the length of the toner patch 97 in the transport direction is, for example, the same as that of the measurement patch 98, so that generation of paper dust when the measurement patch 98 is detected by the color sensor 42 can be suppressed. Note that the effect of covering the surface of the transfer material with the toner layer becomes greater when the printing rate of the toner patch 97 is 100%, but even if the printing rate is less than 100%, there is an effect of suppressing paper dust.

[Relationship between Toner Patch 97 Printing Rate and Stray Light]
FIG. 4A shows the relationship between the printing rate of the toner patch 97 and stray light. The stray light amount is a ratio to the irradiation light amount from the light source. FIG. 4A is a graph showing the relationship between the printing rate (%) of the toner patch 97 and stray light (%). This graph was obtained by holding two sheets of plain paper with a basis weight of 80 g / m ² (broken line) and a basis weight of 75 g / m ² (solid line) between the color sensor 42 and the opposing member 50 and passing 200 sheets. It is. Here, the reason why the relationship between the printing rate and stray light was obtained for the two types of transfer materials is to compare papers having different easiness of paper dust generation. Here, 200 sheets of paper are assumed to be printed once and one test chart is printed by one calibration. Thus, for example, when calibration is performed every 1000 prints, it is possible to assume that 200,000 sheets are passed and that the stray light due to paper dust adhesion is in a stable equilibrium state.

FIG. 4A shows that stray light is reduced due to the paper dust suppressing effect by increasing the printing rate of the toner patch 97. It can also be seen that the relationship between the printing rate and stray light varies depending on the paper type such as basis weight. The reason why the relationship between the printing rate and stray light differs according to the paper type such as the basis weight is because the amount of paper dust generated varies depending on the transfer material. As described with reference to FIG. 6B, stray light needs to be suppressed to 1% or less in order to suppress the colorimetric accuracy of the K toner patch to 2.2 or less in ΔE. For this purpose, the transfer rate of the toner patch 97 may be set to 50% or more when a transfer material having a basis weight of 80 g / m ² is used, and 30% when a transfer material having a basis weight of 75 g / m ² is used. What is necessary is just to set it above.

  For example, information indicating the relationship between the printing rate and stray light corresponding to the paper type (basis weight) as shown in FIG. Then, the image processing unit 122 changes the printing rate of the toner patch 97 in order to suppress stray light to 1% or less based on the information stored in the memory and the paper type information. Here, the printing rate is, for example, CMYK data, and is processed by the halftone table 134 of the image processing unit 122, for example. When the image processing unit 122 sets the printing rate of the toner patch 97 to 30% or 50%, the halftone toner patch 97 having a desired printing rate is formed in the image forming unit 121 via the CPU 56. Control. That is, the printing rate of the toner patch 97 may be selected in consideration of colorimetric accuracy, transfer material, and toner consumption. Alternatively, the toner patches 97 may be formed with a printing rate of 100% or more by overlapping toners of different colors.

  Here, the paper type (basis weight, etc.) of the transfer material is a result of detection by a user using information input from an operation unit (not shown) of the image forming apparatus or a known paper type detection sensor (transfer material detection means). It can be judged using. In addition, for example, the CPU 56 may manage the toner consumption amount by, for example, a known method for detecting the toner amount. Furthermore, in the present embodiment, it has been described that the toner patch 97 is printed so as to include the sandwiching area 100 with respect to the width in the longitudinal direction of the toner patch 97. However, even if printing is performed so that the longitudinal width of the toner patch 97 becomes a part of the sandwiching area 100, the effect of suppressing paper dust can be obtained.

  When the transfer material 11 is nipped and conveyed by the color sensor 42, paper powder such as fibers and additives from the transfer material printing surface is scraped off and separated from the transfer material. This adheres to the opening 99 of the color sensor 42. In this embodiment, for example, a toner patch 97 as shown in FIG. 3 is formed in the holding portion of the transfer material 11, and the transfer material 11 is conveyed, whereby the paper from the transfer material is formed by the toner layer formed on the transfer material. By suppressing the separation of the powder, the paper dust is prevented from adhering to the dust-proof glass 110. The color of each color measurement patch can be detected with high accuracy, and an image forming apparatus with good color reproducibility can be provided at low cost by feedback control to the LUT and process conditions. In this way, by suppressing the generation of paper dust, stray light caused by paper dust can be suppressed, stable colorimetry with little detection variation can be realized, and an image forming apparatus with high color reproducibility can be realized.

  As described above, according to the present embodiment, it is possible to suppress the generation of paper dust from the transfer material when the sensor performs detection while sandwiching the transfer material.

  In the second embodiment, when a conveyance member located in the vicinity of the color sensor 42 installed in the conveyance path nipping and conveying the transfer material, a toner patch is printed on the transfer material so as to cover the nipping range, and the paper dust Generation is suppressed. The place where the paper dust is generated is not limited to the clamping portion of the color sensor 42. For example, paper dust is also generated by a pair of conveying rollers 75a (first member and second member) positioned upstream of the color sensor 42 in FIG. 1A, and the generated paper dust is conveyed to the color sensor 42 together with the transfer material. The In addition, paper dust is also generated in the conveyance roller pair 75b (first member and second member) positioned downstream of the color sensor 42 in FIG. 1A, and the generated paper dust is caused by gravity, in-machine airflow, or the like. Carried to 42. As described above, paper dust is also generated from the transport guide, the transport roller pair 75a and 75b, the transport roller, and the like. In particular, the paper dust generated by the transport member arranged around the color sensor 42 reaches the color sensor 42 and adheres thereto. It's easy to do.

[Test chart of this example]
FIG. 4B includes a range 96 (hereinafter referred to as a nipping region 96) in which each of a pair of conveying rollers 75a and 75b (simply indicated as 75 in the figure) that is a conveying member around the color sensor 42 holds the transfer material. Thus, the toner patch 95 (second image) is printed. If toner patches are printed on the portions where the transfer material 11 contacts these conveying members, the generation of paper dust can be suppressed by the same effect as in the first embodiment. As in the first embodiment, even if printing is performed such that the width in the longitudinal direction of the toner patch 95 is a part of the sandwiching region 96, the effect of suppressing paper dust can be obtained. Although not shown in FIG. 4B, the toner patch 97 according to the first embodiment including the clamping region 100 formed by the color sensor 42 and the facing member 50 as in the first embodiment is used. You may form together with the toner patch 95 of an Example. Further, the relationship between the printing rate of the toner patch 95 and the paper type (basis weight, etc.) is the same as that in the first embodiment, and a description thereof will be omitted.

  As described above, as an effect unique to the present embodiment, it is possible to detect the color of the measurement patch with high accuracy by suppressing the generation of paper dust due to the friction between the transfer member disposed around the color sensor and the transfer material. .

  As described above, according to the present embodiment, it is possible to suppress the generation of paper dust from the transfer material when the sensor performs detection while sandwiching the transfer material.

  In the third embodiment, the toner patches 97 and 95 of the first and second embodiments are formed of K (black) toner, thereby reducing the stray light from the toner due to the adhesion of the toner to the dust-proof glass surface, and the color caused by the stray light. The detection variation of the sensor is reduced.

[Effect of toner color on dust-proof glass]
FIG. 5A shows the spectral characteristics of each toner color, and FIGS. 5B and 5C show simulation results of stray light from the toner adhering to the dust-proof glass 110 and color difference. The occurrence of paper dust at the clamping unit described in the first and second embodiments is suppressed by printing the toner patches 97 and 95. However, the toner patches 97 and 95 may peel from the transfer material 11 and adhere to the surface of the dust-proof glass 110. The toner adhering to the surface of the dust-proof glass 110 causes stray light.

  FIG. 5B is a graph showing the relationship between stray light (%) and color difference ΔE when each color patch is read by the color sensor 42 with the Y color toner attached to the surface of the dust-proof glass 110. Specifically, in FIG. 5B, Y-color toner adheres to the surface of the dust-proof glass 110, and the Y-color toner reflects stray light with a certain ratio [%] with respect to the light source light amount, and is spectrally separated by the diffraction grating 108 and applied to the line sensor 101. It is the result of simulating the relationship between stray light and color difference when incident. FIG. 5C is a graph showing the relationship between the stray light (%) and the color difference ΔE when each color patch is read by the color sensor 42 with the K-color toner attached to the surface of the dust-proof glass 110. . That is, FIG. 5C shows the same simulation result when the K-color toner adheres to the glass surface of the dust-proof glass 110. In both FIG. 5B and FIG. 5C, the horizontal axis represents stray light (%) and the vertical axis represents the color difference ΔE. Stray light [%] on the horizontal axis of FIGS. 5B and 5C is proportional to the amount of toner adhering to the glass surface of the dust-proof glass 110, and the same amount if the stray light amount is the same. It can be considered that the toner is attached.

  Here, in FIG. 5A, the horizontal axis represents the wavelength (nm), the vertical axis represents the spectral reflection characteristics, the long-pitch broken line is Y-color toner, the alternate long and short dash line is M-color toner, and the short-pitch broken line is C-color. The toner and the solid line indicate the spectral reflection characteristics of the K color toner. For example, the K color toner has a low reflectance over a wavelength range of 350 nm to 750 nm. In addition, for example, the Y color toner has a low reflectance in a wavelength region shorter than a wavelength of 500 nm and a high reflectance in a wavelength region longer than a wavelength of 500 nm. Thus, the spectral reflection characteristics differ depending on the color of the toner.

  As shown in FIG. 5C, even if the K color toner adheres to the dust-proof glass 110, the absolute light quantity of the reflected light from the attached toner becomes small. As described above, this is because the K-color toner has a low spectral reflectance characteristic in the visible light region (400 to 700 nm). On the other hand, as described above, the Y-color spectral reflection characteristic tends to have a low reflectance on the low wavelength side in the visible light region and a high reflectance on the long wavelength side. This also applies to the spectral characteristics of stray light reflected from the Y color toner adhering to the glass surface of the dust-proof glass 110. That is, it can be said that when Y toner adheres to the dust-proof glass 110, the amount of reflected light from the adhered Y toner increases in the long wavelength region. From the above, since the reflectance on the long wavelength side is high, the influence of stray light is greater in the Y color toner shown in FIG. 5B than in the case where the K color toner shown in FIG. When attached, it becomes larger.

[Relationship between toner color and stray light]
In order to specifically describe the color difference ΔE that occurs, a case where 1% of stray light is generated due to toner adhering to the glass surface of the dust-proof glass 110 will be described. Further, the influence on the color difference has the largest influence on the K color patch among the four single color patches formed on the transfer material. Therefore, the measurement patch for K color will be described as an example.

  For example, when the toner patch (97 or 95) printed on the nipping portion is set to Y color in order to reduce the generation of paper dust, the Y color toner adheres to the glass surface of the dustproof glass 110 and 1% stray light is generated. It becomes as follows. That is, as shown in FIG. 5B, the color difference of the K color test patch (the K color patch in the measurement patch 98) is 3 in ΔE. In addition, when the toner patch (97 or 95) printed on the nipping part is set to K color to reduce the generation of paper dust, and the K color toner adheres to the glass surface of the dustproof glass 110, 1% stray light is generated. It becomes as follows. That is, as shown in FIG. 5C, the color difference of the K color test patch is 0.13 in ΔE. Thus, even when the same stray light is generated, it can be seen that the color difference varies depending on the color of the toner attached to the surface of the dust-proof glass 110 that has caused the stray light. Therefore, by changing the toner patch (97 or 95) to be printed on the nipping portion from Y color to K color in order to reduce the generation of paper dust, the color difference generated with respect to the measurement patch 98 can be 3 to 0.00 in ΔE. It can be greatly improved to 13.

  As described above, according to the present embodiment, the toner patch (97 or 95) that is printed on the clamping portion of the test chart described in the first and second embodiments is set to K color. Thereby, even when the toner adheres to the dust-proof glass surface, it is possible to reduce the absolute light quantity of the reflected light from the adhered toner and reduce the color difference. The effect peculiar to the present embodiment is that detection of a color sensor caused by stray light due to adhesion of toner to the glass surface by making the toner patch K color, although the generation of paper dust at the transfer material clamping portion can be suppressed by the toner patch. Variations can be reduced.

  As described above, according to the present embodiment, it is possible to suppress the generation of paper dust from the transfer material when the sensor performs detection while sandwiching the transfer material.

[Other Examples]
In an image forming apparatus in which toner peeling from the transfer material is a concern, K-color toner may be used as described in the third embodiment. Further, in an image forming apparatus in which there is no concern about toner peeling, in order to reduce the bias of the consumed toner, color toners other than the K color toner (for example, Y color, M color, and C color toners) are included. It is suitable to use with K color. That is, the color of the toner used for the toner patches 97 and 95 may be selected according to the characteristics of the image forming apparatus.
The toner patches 97 and 95 do not need to be printed on a transfer material that does not generate paper dust, such as a resin sheet (a predetermined type of transfer material) used for water-resistant printed matter. When a resin sheet is detected by printing the toner patches 97 and 95 and avoiding the risk of adhesion of the toner to the glass surface by specifying the print mode or by a transfer material detection means (for example, a paper type detection sensor). Does not print toner patches 97 and 95. Thereby, adhesion of the toner to the glass surface can be avoided and toner consumption can be suppressed.
In the first to third embodiments, the spectral color sensor has been described. However, the present invention is applicable to any optical sensor that detects the optical characteristics of the toner image fixed on the surface of the transfer material or the transfer material, such as a color sensor, a density sensor, and a gloss sensor as detection means arranged in the conveyance path after fixing. The effect of improving the accuracy of detection results can be expected. For example, a filter type color sensor using RGB light receiving elements has the same effect, and the present invention can be applied. In other words, any sensor can be used as long as the detection accuracy of the sensor is reduced by paper dust or the like generated from the transferred transfer material.
In the first to third embodiments, the image forming apparatus as illustrated in FIG. 1 has been described as an example. However, the present invention can be applied to any image forming apparatus provided that the sensor includes a sensor whose detection accuracy is lowered due to paper dust generated from the conveyed transfer material.
As described above, also in other embodiments, it is possible to suppress the generation of paper dust from the transfer material when performing detection by the sensor while sandwiching the transfer material.

11 Transfer material 42 Color sensor 50 Opposing member 97 Toner patch 98 Measurement patch 100 Holding region

Claims (16)

Detecting means for detecting the first image after fixing formed on the transfer material;
Control means for correcting image forming conditions based on the result of detecting the first image by the detection means;
Image forming means for forming an image on a transfer material based on the image forming conditions;
An image forming apparatus comprising:
The control means, together with the first image, forms a second image having a width including at least a part of a region where the detection means and the transfer material are in contact with each other in a direction orthogonal to the transfer material conveyance direction. An image forming apparatus formed on a transfer material. Provided at a position facing the detection means, and provided with a facing member for sandwiching a transfer material together with the detection means,
The image forming apparatus according to claim 1, wherein the region where the detection unit and the transfer material are in contact is a region where the transfer material is sandwiched between the detection unit and the opposing member.   The image forming apparatus according to claim 1, wherein the image forming unit forms the first image on the second image.   The image forming apparatus according to claim 1, wherein the image forming unit forms the second image in an area where the first image is not formed.   The image forming apparatus according to claim 1, wherein the control unit forms the second image with a black color.   The image forming apparatus according to claim 1, wherein the control unit sets the printing rate of the second image to 100%.   The image forming apparatus according to claim 1, wherein the control unit changes a printing rate of the second image according to a type of the transfer material.   The image forming apparatus according to any one of claims 1 to 7, wherein the control unit prevents the second image from being formed when the transfer material is a predetermined type of transfer material. apparatus. Provided with a transfer material detection means for detecting the type of transfer material,
The image forming apparatus according to claim 7, wherein the control unit determines the type of transfer material based on a detection result of the transfer material detection unit. Detecting means for detecting the first image after fixing formed on the transfer material;
Conveying means for conveying the transfer material;
Control means for correcting image forming conditions based on the result of detecting the first image by the detection means;
Image forming means for forming an image on a transfer material based on the image forming conditions;
An image forming apparatus comprising:
The control means, together with the first image, forms a second image having a width including at least a part of a region where the conveying means and the transfer material are in contact with each other in a direction orthogonal to the conveying direction of the transfer material. An image forming apparatus formed on a transfer material.   The image forming apparatus according to claim 10, wherein the image forming unit forms the second image in an area where the first image is not formed.   The image forming apparatus according to claim 10, wherein the control unit forms the second image with a black color.   The image forming apparatus according to claim 10, wherein the control unit sets the printing rate of the second image to 100%.   The image forming apparatus according to claim 10, wherein the control unit changes a printing rate of the second image according to a type of the transfer material.   15. The image formation according to claim 10, wherein the control unit prevents the second image from being formed when the transfer material is a predetermined type of transfer material. apparatus. Provided with a transfer material detection means for detecting the type of transfer material,
16. The image forming apparatus according to claim 14, wherein the control unit determines the type of transfer material based on a detection result of the transfer material detection unit.

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