JP2005250359A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which performs excellent color correction even when analyzing colors by using light containing no UV ray. <P>SOLUTION: The fluorescence measuring section 5 stores in the memory 53 the threshold V<SB>th</SB>matching the voltage the photo detector 52 outputs when it is receiving light and measures the fluorescence of the paper based on this threshold V<SB>th</SB>, then outputs the measured result to the color correction section 6. The color correction section 6 corrects the color inputted from the color measuring section 4 based on this result to output to the image controller 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for correcting image forming conditions using a color calibration patch.

  2. Description of the Related Art An image forming apparatus that performs so-called calibration that includes a color measuring unit that measures a color calibration patch formed on a sheet and corrects an image forming condition according to the color measurement result is widely known. In particular, in an electrophotographic image forming apparatus, it is common to perform calibration by using an external device such as a colorimeter as a colorimetric means and causing the colorimetric means to manually read a color calibration patch. It is. However, such a method requires labor and time, and is inconvenient for the user.

Therefore, a method in which the image forming apparatus itself has a built-in color measuring means, and color calibration patches formed on a sheet or an intermediate transfer belt inside the apparatus are read at the same speed as the image forming process and calibrated. Is desirable. In order to realize this, the colorimetric means is required to have a high-speed response, a long life, a low cost, and a small size.
However, a light source used in a conventional colorimeter or the like is generally a light source having high color rendering properties such as a tungsten lamp or a halogen lamp (hereinafter referred to as “standard light source”). Such a standard light source is expensive and has a short life because it is difficult to maintain color rendering for a long period of time.

  As a method for solving this problem, a method of using R (Red), G (Green), and B (Blue) three-color LEDs (light emitting diodes) as a light source can be considered. LEDs have various advantages over standard light sources, such as high-speed response, long life, low cost, and small size. However, on the other hand, when R, G, B3 LEDs are used as the light source as described above, unlike the standard light source, no component in the ultraviolet region is included in the spectrum. For this reason, when an LED is used as the light source, there is the following problem when a paper containing a fluorescent material (hereinafter referred to as “fluorescent paper”) is used for image formation in order to increase whiteness. .

  When measuring an image formed on fluorescent paper, the reflection spectrum differs between when the light source includes an ultraviolet component and when it does not. This is because the fluorescent material is excited by absorbing the ultraviolet component of light and emits light having a longer wavelength than the absorbed light when returning to the ground state (fluorescence). As a result, ultraviolet light from a standard light source or the like is emitted. The specific wavelength of the reflected light when the colorimetry is performed with the light source including the light source and when the colorimetry is performed with the light source not including the ultraviolet light (in the case of a fluorescent material generally included in the paper, the wavelength is approximately 440 nm). Will be different from each other (see, for example, Patent Document 1 and FIG. 5). In normal calibration, the image forming conditions are determined based on the colorimetric values when the color calibration patch is irradiated with a standard light source. Therefore, if a light source that does not contain ultraviolet light is used as the colorimetric means, a colorimetric error will occur. As a result, the image forming conditions cannot be properly corrected.

Japanese Patent Laid-Open No. 10-108032

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image forming apparatus capable of performing good color correction even when color measurement is performed using light that does not include ultraviolet light. Is to provide.

In order to solve the above-described problems, the present invention irradiates light to a fluorescence determination unit that determines the fluorescence of a recording material on which an image is to be formed, and a color calibration patch formed on the recording material. A colorimetric means for measuring the color of the patch and obtaining the colorimetric value, and a colorimetric value correction for correcting the colorimetric value obtained by the colorimetric means based on the fluorescence determined by the fluorescence determination means An image control unit that corrects an image forming condition based on the colorimetric value corrected by the colorimetric value correcting unit, and an image is formed on the recording material according to the image forming condition corrected by the image control unit. An image forming apparatus is provided.
According to such an image forming apparatus, since the colorimetric value can be corrected according to the fluorescence of the recording material determined by the fluorescence determination unit, color measurement is performed using light that does not include ultraviolet light. Even in this case, good color correction can be performed.

In a more preferred aspect of the image forming apparatus of the present invention, the fluorescence determination unit includes a light source that emits ultraviolet light and a light receiving element that receives visible light, and the light source irradiates the recording material. The fluorescence of the recording material is determined based on the amount of light emitted when the light receiving element receives at least one of reflected light from the recording material and fluorescence.
In a further preferred aspect, the light source is a light emitting diode that emits ultraviolet light.
Thereby, the determination of the fluorescence by the fluorescence determination means can be performed at high speed, and a reduction in size and cost can be realized.

In a more preferred aspect of the image forming apparatus of the present invention, the colorimetric means performs colorimetry using light emitting diodes of three colors of red, green, and blue.
Thereby, color measurement by the color measurement means can be performed at high speed, and miniaturization and cost reduction can be realized.

(1) Configuration Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
In the embodiment described below, the CIE 1976 (L * a * b *) color system defined by the CIE (Commission Internationale de l'Eclairage) is used as the color system. A color value in a color space represented by color coordinate values (L *, a *, b *) using a color system is referred to as an “L * a * b * value”.

  FIG. 1 is a diagram showing a configuration of an image forming apparatus 100 according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 100 includes an image forming unit 1, a paper feeding unit 2, a paper conveyance path 3, a fixing unit 8, a color measuring unit 4, and a fluorescence determination unit 5. A colorimetric value correction unit 6 and an image control unit 7.

  The image forming unit 1 forms photoreceptor images 10Y and 10M that form toner images while rotating in the direction of arrow a in the drawing for each color of yellow (Y), magenta (M), cyan (C), and black (K). , 10C, 10K, chargers 11Y, 11M, 11C, 11K for uniformly charging the photoconductors, and the photoconductors 10Y, 10M, 10C charged with exposure light modulated based on the image data of each color of YMCK. , 10K, and developing the electrostatic latent images formed on the photoconductors 10Y, 10M, 10C, and 10K using toners, and the exposure units 12Y, 12M, 12C, and 12K that form electrostatic latent images of each color of YMCK. As a result, the developing devices 13Y, 13M, 13C, and 13K that form toner images on the photoconductors 10Y, 10M, 10C, and 10K, and the developing devices 13Y, 13M, 13C, and 13K, each color toner. Supplying toner box 14Y, it includes 14M, 14C, and 14K.

  Further, the image forming unit 1 is laid over a drive roll 19 and a counter roll 18 and is circulated and moved in the direction of arrow b in the figure while being in contact with the photoreceptors 10Y, 10M, 10C, and 10K, and an intermediate transfer belt 15 A nip region is formed with the photoconductors 10Y, 10M, 10C, and 10K across the transfer belt 15, and a toner image on the circumferential surface of the photoconductors 10Y, 10M, 10C, and 10K is transferred to the intermediate transfer belt 15 in the nip region. A transfer roll 16Y, 16M, 16C, and 16K, and a secondary transfer roll 17 that forms a nip region with the opposing roll 18 across the intermediate transfer belt 15 and secondarily transfers the toner image on the intermediate transfer belt 15 to a sheet. I have. The nip area formed by the secondary transfer roll 17 and the counter roll 18 is hereinafter referred to as “secondary transfer position”.

The paper feed unit 2 stores papers of various sizes in a plurality of paper trays 21 and supplies papers according to the size of the image to be formed. In the present embodiment, the types of paper accommodated in the paper tray 21 include fluorescent paper containing a fluorescent material and plain paper containing no fluorescent material.
The sheet conveyance path 3 includes a plurality of conveyance rolls 31 (some of which are not shown), conveys the sheet supplied from the sheet feeding unit 2 to the image forming unit 1, and discharges the sheet on which the image is formed.
The fixing unit 8 includes a fixing roll 81 having a heat source therein and a pressure roll 82, and a sheet on which the toner image is transferred by the image forming unit 1 in a nip region where the fixing roll 81 and the pressure roll 82 face each other. By heating and pressurizing, the toner is melted and fixed on the paper.

  With this configuration, the image forming unit 1 forms toner images of Y, M, C, and K colors based on image data input from a scanner, personal computer, or the like (not shown), and supplies the toner images to the paper feeding unit 2. Then, the image is formed on the sheet conveyed by the sheet conveyance path 3 and fixed by the fixing unit 8. In the calibration, the image forming unit 1 forms a toner patch image with toners of Y, M, C, and K colors, and transfers the toner patch image onto the paper so that the color calibration patch is placed on the paper. Form.

  The color measuring unit 4 is provided along the paper transport path 3 at a position downstream in the paper transport direction as viewed from the secondary transfer position, and is formed on the paper transported through the paper transport path 3. Measure the color calibration patch. The fluorescence determination unit 5 is provided at an arbitrary position along the sheet conveyance path 3 and determines the fluorescence of the sheet conveyed through the sheet conveyance path 3.

Here, FIG. 2 is a block diagram showing a functional configuration of the image forming apparatus 100.
The color measurement unit 4 includes a light source 41 and a light receiving element 42, and outputs a color measurement value (L * a * b * value) of a color calibration patch to the color measurement value correction unit 6. The light source 41 includes LEDs of R, G, and B colors. These LEDs do not emit ultraviolet light. The light receiving element 42 is, for example, a photodiode having sensitivity in almost the entire visible region, and receives reflected light emitted from the light source 41 and reflected by a toner image (color calibration patch) on the paper.

FIG. 3 is a diagram showing a color calibration patch in the present embodiment. In the present embodiment, the color calibration patch is a generic name for a plurality of patches P of different colors P _{1 to} P _n formed on a sheet. The number n of patches P is arbitrary, and is determined according to the processing speed and correction accuracy required for calibration. If the number n is increased, highly accurate calibration can be performed, but the number of sheets to be used increases because the number of measurements increases. In addition, the color of the patch P can be arbitrarily selected, and a color that can be optimally calibrated with the determined number n of patches P may be selected as appropriate.
When such a color calibration patch is colorimetrically measured, the colorimetric value is represented by the matrix A as shown in Equation 1. In Equation 1, L * (P _n ), a * (P _n ), and b * (P _n ) are the L * value, a * value, and b * value of the patch P _n , respectively.

  The fluorescence determination unit 5 includes a light source 51, a light receiving element 52, and a memory 53. The light source 51 includes an ultraviolet LED that emits ultraviolet light. The light receiving element 52 is a photodiode having sensitivity in a specific visible region, for example, around 440 nm, and receives reflected light emitted from the light source 51 and reflected by the paper. The fluorescence determination unit 5 determines the fluorescence based on the amount of the received light.

Here, the fluorescence is a value indicating the degree of fluorescence emitted by the fluorescent material contained in the paper. In this embodiment, the fluorescence is either “1 (fluorescent paper)” or “0 (plain paper)”. Suppose that For example, it is obtained by experiment or calculation that the output voltage at the time of light reception by the light receiving element 52 is about V ₀ for reflected light of plain paper and about V ₁ (V ₀ <V ₁ ) for reflected light of fluorescent paper. In other words, a threshold value V _th that satisfies V ₀ <V _th <V ₁ is stored in the memory 53 of the fluorescence determination unit 5 in advance. Then, the fluorescence determination unit 5, if the output voltage of the light receiving element 52 is "V _0" to "0", and the data indicating "1" if it is "V _1" to the colorimetric value correction unit 6 Output.

The colorimetric value correction unit 6 includes a memory 61 in which a correction coefficient group C corresponding to the color calibration patch is stored.
FIG. 4 is a diagram for explaining the correction coefficient group C. FIG. The correction coefficient group C has three types of correction coefficients C _L , C _a , and C _b corresponding to the L * a * b * values, and these three types of correction coefficients C _L , C _a , and C _b are patch P _1. It is defined for each of ~ _Pn . These correction coefficient groups C are measured in advance by using a standard light source and a light source 41 for patches P _{1 to} P _n experimentally formed by the image forming apparatus 100 in an ideal state in which color reproducibility is well maintained. It is determined based on the L * a * b * value when colored. For example, the correction coefficient C _L1 of the patch P ₁ is, in the case where the patch P ₁ from the L * value in the case of colorimetry in a standard light source "L * (A1)" colorimetry patch P ₁ in the light source 41 L * value A value obtained by subtracting “L * (B1)”, that is, “L * (A1) −L * (B1)”. Similarly, the correction coefficients C _a1 and C _b1 of the patch P ₁ are “a * (A1) −a * (B1)” and “b * (A1) −b * (B1)”, respectively. _{2 to Pn} are defined in the same manner. That is, when the correction coefficient group C is represented by a matrix, it is as shown in Equation 2.

The memory 61 stores such a correction coefficient group C for each of the case where the color calibration patch is formed on plain paper and the case where it is formed on fluorescent paper. That is, the correction coefficient group C includes a correction coefficient group (hereinafter referred to as a correction coefficient group C1) corresponding to the fluorescence value “1” (that is, fluorescent paper) output by the fluorescence determination unit 5 and the fluorescence value. There is a correction coefficient group (hereinafter referred to as a correction coefficient group C0) corresponding to the value “0” (that is, plain paper).
The colorimetric value correction unit 6 selects correction coefficient groups C1 to C0 corresponding to the fluorescence input from the fluorescence determination unit 5, and adds the selected correction coefficient group to the colorimetric values input from the colorimetry unit 4. Then, the colorimetric values corrected in this way are output to the image control unit 7.

  The image control unit 7 corrects the image forming conditions based on the colorimetric values input from the colorimetric value correction unit 6. Specifically, the image control unit 7 measures the colorimetric values (hereinafter referred to as “color measurement values” of color correction patches experimentally formed by the image forming apparatus 100 in an ideal state in which color reproducibility is well maintained. Is referred to as a “reference colorimetric value”) and the colorimetric value input from the colorimetric value correction unit 6 described above, and if there is a difference, the image forming unit 1 uses the color calibration patch as a reference colorimetry. The charging potential in the chargers 11Y, 11M, 11C, and 11K, the exposure amount in the exposure devices 12Y, 12M, 12C, and 12K, the developing bias potential in the developing devices 13Y, 13M, 13C, and 13K, Alternatively, correction data for adjusting at least one of the toner supply amounts in the toner boxes 14Y, 14M, 14C, and 14K is output to the image forming unit 1.

(2) Operation Based on the configuration described above, the image forming apparatus 100 forms an image on a sheet. Then, calibration is executed based on a calibration execution instruction from the user or a predetermined timing set in the image forming apparatus 100, and the image forming conditions are corrected to maintain a good color reproducibility.

FIG. 5 is a flowchart showing the calibration operation in the present embodiment. The following description is based on this flowchart.
When calibration is executed as described above, first, the paper supply unit 2 supplies paper, and the fluorescence determination unit 5 detects this paper and determines the fluorescence (step S1). Then, the fluorescence determination unit 5 outputs data indicating the fluorescence of “1” or “0” to the colorimetric value correction unit 6. The colorimetric value correction unit 6 selects either “C1” or “C0” as a correction coefficient group C to be used in the present operation based on the input fluorescence (step S2). In the present embodiment, “C1” is selected if the paper is fluorescent paper, and “C0” is selected if the paper is plain paper.

Subsequently, the image forming unit 1 forms a color calibration patch on the above-described sheet, and the color measurement unit 4 measures the color calibration patch (step S3). The color measurement unit 4 outputs the color measurement value of the color calibration patch to the color measurement value correction unit 6.
Here, the colorimetric value correction unit 6 adds the correction coefficient group C selected in step S2 to the colorimetric values input from the colorimetry unit 4 (step S4). That is, when the colorimetric values corrected by the colorimetric value correction unit 6 are represented by the matrix A ′, the following equation 3 is obtained.

The colorimetric value correction unit 6 outputs the corrected colorimetric values represented by the matrix A ′ to the image control unit 7, and the image control unit 7 corrects the image forming conditions according to the colorimetric values. Correction data is output to the image forming unit 1 (step S5). The image forming unit 1 adjusts the charging potential, the exposure amount, the developing bias potential, or the toner supply amount in the image forming unit 1 based on the correction data.
By executing such calibration, the image forming apparatus 100 of the present embodiment can perform good color correction even when a light source that does not include ultraviolet light is used.

(3) Modifications Note that the image forming apparatus according to the present invention is not limited to the above-described aspect of the image forming apparatus 100, and various modifications as described below are possible.
First, in the above-described embodiment, the image forming apparatus 100 is shown in a so-called tandem system including the intermediate transfer belt 15, but the present invention is not limited to the above-described configuration, and for example, a so-called cycle-type image forming apparatus. In addition, the present invention can be applied to an image forming apparatus including a sheet conveying belt instead of the intermediate transfer belt.
Further, the toner used in the image forming apparatus is not limited to the four colors Y, M, C, and K. Other colors can be used and the number of colors can be increased or decreased.

Further, the colorimetric unit 4 in the above-described embodiment is not limited to the position shown in FIG. Since the color measuring unit 4 measures the color calibration patch formed by the image forming unit 1, the color measuring unit 4 is behind the above-described fixing position on the paper conveyance path 3 and can shield external light. It may be provided anywhere as long as it is a position.
Furthermore, the fluorescence determination unit 5 is not limited to the position shown in FIG. 1, and can be provided on the sheet conveyance path 3 or at an arbitrary position on the sheet feeding unit 2.

Further, in the above-described embodiment, the light source 41 of the color measuring unit 4 is not limited to the LED, but it is a light source having a performance equivalent to or higher than that of the LED in terms of responsiveness and cost. Is desirable. In the above-described embodiment, it is described that the colorimetric unit 4 outputs L * a * b * values as colorimetric values, but of course the invention is not limited to L * a * b * values. For example, tristimulus Values X, Y, Z, etc. may be used.
In the above-described embodiment, it is described that the light source 41 of the color measurement unit 4 does not emit ultraviolet light. However, even a light emitting element that emits a small amount of ultraviolet light can be used as the light source 41. It is. Even in such a light emitting element, if the spectrum of the ultraviolet region of the light emitting element is different from the spectrum of the ultraviolet region of the standard light source, the intensity of emitted fluorescence will be different. Needless to say, it can be done.
Furthermore, when implementing the present invention, the color measuring unit 4 does not necessarily have to be built in, and may be a color measuring device in which the color measuring unit is an external device.

  Further, in the above-described embodiment, only two levels of fluorescence including or not including a fluorescent substance are set. Of course, even if a plurality of fluorescence levels of three or more levels according to the degree of fluorescence are set. Good. In this case, needless to say, it is necessary to store the correction coefficient group C corresponding to each fluorescence.

  Further, in the above-described embodiment, the paper on which the fluorescence is determined and the paper on which the color calibration patch is formed are the same. However, if, for example, a plurality of sheets of plain paper or fluorescent paper are used in succession, the paper on which the fluorescence is determined and the paper on which the color calibration patch is formed need not be the same. There is no problem even if a color calibration patch is formed on several sheets after the sheet whose fluorescence has been determined.

Although the above-described embodiment has been described with reference to an electrophotographic image forming apparatus, the application of the present invention is not limited to an electrophotographic image forming apparatus, and various image forming apparatuses such as an inkjet method and a thermal transfer method can be used. It is possible to apply to.
In the above-described embodiment, the case where paper is used as the recording material is described. However, the recording material of the present invention is not limited to paper, and various recording materials such as cloth and resin may be used. Is possible.

1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a functional configuration of each unit of the image forming apparatus according to the embodiment. It is the figure which showed the patch for color calibration in the same embodiment. It is a figure for demonstrating the correction coefficient group C in the embodiment. It is the flowchart which showed the operation | movement of the calibration in this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 1 ... Image forming part, 10Y, 10M, 10C, 10K ... Photoconductor, 11Y, 11M, 11C, 11K ... Charger, 12Y, 12M, 12C, 12K ... Exposure device, 13Y, 13M, 13C , 13K ... developer, 14Y, 14M, 14C, 14K ... toner box, 15 ... intermediate transfer belt, 16Y, 16M, 16C, 16K ... primary transfer roll, 17 ... secondary transfer roll, 18 ... opposite roll, 19 ... Drive roll, 2 ... paper feed unit, 21 ... paper tray, 3 ... paper transport path, 31 ... transport roll, 4 ... colorimetry unit, 41 ... light source, 42 ... light receiving element, 5 ... fluorescence determination unit, 51 ... light source 52. Light receiving element 6. Colorimetric value correction unit 61 61 Memory 7 Image control unit

Claims (4)

Fluorescence determination means for determining the fluorescence of the recording material on which an image is to be formed;
Colorimetric means for irradiating light to a color calibration patch formed on the recording material to measure the color of the patch and obtaining a colorimetric value;
A colorimetric value correcting unit for correcting the colorimetric value obtained by the colorimetric unit based on the fluorescence determined by the fluorescence determining unit;
Image control means for correcting image forming conditions based on the colorimetric values corrected by the colorimetric value correction means;
An image forming apparatus comprising: an image forming unit that forms an image on the recording material in accordance with the image forming condition corrected by the image control unit. The fluorescence determination means includes
A light source that emits ultraviolet light;
A light receiving element for receiving visible light,
The fluorescence of the recording material is determined based on the amount of light when the light receiving element receives at least one of reflected light and fluorescence emitted from the light source by irradiating the recording material. The image forming apparatus according to 1. The image forming apparatus according to claim 2, wherein the light source is a light emitting diode that emits ultraviolet light. The image forming apparatus according to claim 1, wherein the color measurement unit performs color measurement using light emitting diodes of three colors of red, green, and blue.

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