JP2008298854A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize an image color by performing inexpensive and accurate sensor calibration in an image forming apparatus using an optical sensor. <P>SOLUTION: The image forming apparatus has a means for detecting optical density that is the light reflection characteristic of a toner image for detection formed on transfer material or an intermediate transfer body or a transfer material carrier by the optical sensor. In the image forming apparatus, a cartridge container for printing white color material is changed to a cartridge container printing chromatic (cyan (C), magenta (M), yellow (Y) or black (K)) color material attached to a station, and a reference image pattern composed of the white color material is formed on the transfer material or the intermediate transfer body or the transfer material carrier, and the optical sensor is corrected by using the reference image pattern, whereby a white reference plate for calibration is not required, the color detecting accuracy of the sensor is improved, and excellent image density control is made. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic or inkjet printer and a copying machine.

  In recent years, color image forming apparatuses such as color printers and color copiers are required to improve the output image quality. In particular, the stability of the image gradation and the image color greatly affects the image quality.

  However, in the color image forming apparatus, when there is a change in each part of the apparatus due to a change in environment or long-term use, the color of the obtained image changes. In particular, in the case of an electrophotographic color image forming apparatus, even slight environmental fluctuations may cause color fluctuations, which may cause the color balance to be lost. Therefore, there is a means for stably reproducing colors and color gradations. is doing.

  As a means therefor, there is a means using a density detection sensor (hereinafter referred to as a density detection sensor) disclosed in Japanese Patent Application Laid-Open No. 2003-107835. For example, a density detection toner patch is formed on an image carrier, a photoconductor, etc. with a single color toner so that a constant color and gradation of color can be obtained even if each part of the apparatus fluctuates. The density of the unfixed single-color toner patch is detected by a density detection sensor for unfixed toner (hereinafter referred to as a darkness sensor), and the detection result is fed back to process conditions such as exposure amount and development bias, and tone correction means such as LUT. By performing the density control over the above, it is configured to obtain stable color and color gradation.

As another method, cyan (C), magenta (M), yellow (Y), and black (K) single-color gradation patches or C, M, and Y mixed color patches are formed on the recording medium and fixed. There is also a color image forming apparatus in which a sensor (hereinafter referred to as a color sensor) for detecting the density or chromaticity of a patch on a recording medium is installed (Japanese Patent Laid-Open No. 2005-14344, etc.). In this color image forming apparatus, the final output image formed on the recording medium is fed back to the calibration table for correcting the exposure amount, process conditions, and density-tone characteristics of the image forming unit. Density or chromaticity can be controlled. Although it is possible to detect the output image of the color image forming apparatus with an external image reading device or a densitometer / chromaticity meter and perform the same control, this method completes the control within the color image forming apparatus. Is excellent. In this color sensor, for example, three or more light sources having different emission spectra such as red (R), green (G), and blue (B) are used as the light emitting elements, or the light emitting elements emit light of white (W). And three or more types of filters having different spectral transmittances such as red (R), green (G), and blue (B) are formed on the light receiving element. As a result, three or more different outputs such as RGB output can be obtained. If the obtained RGB output value is converted into chromaticity data using an RGB-Lab conversion table or the like, the chromaticity value of the density detection image can be obtained. If the RGB output value is converted into density data using an RGB-density conversion table or the like, the density value of the density detection image can be obtained. By performing image density control based on the chromaticity value and density value thus obtained, the color image forming apparatus can stably output a desired color.
JP 2003-107835 A JP-A-2005-14344

  The conventional example has the following problems.

  The light emitting element and the light receiving element constituting the optical sensor have a difference in spectral characteristics for each element. In order to absorb the difference due to the temporal change of the optical sensor or the like, it is necessary to calibrate the dispersion of the spectral characteristics using the reference reflector. However, when a white reference plate for calibration is provided for the purpose of correcting deviation, if the reference plate is expensive, the cost of the apparatus is increased.

  In the image forming apparatus, the white surface of the calibration white reference plate is provided on the opposite surface of the optical sensor. Therefore, when reading paper dust from paper being transported, toner adhesion, or color patches on paper after fixing, the opposite or white surface comes into contact with the paper being transported and rubs, causing dirt or scratches on the surface. Discoloration or the like may occur, and an error may occur in chromaticity adjustment or absolute chromaticity adjustment. Furthermore, since the optical sensor has different density or chromaticity depending on the distance to the measurement surface, the distance from the optical sensor is the white reference plate for calibration, the transfer material or the intermediate transfer member, and the transfer material carrier. If they are not equal, high-precision sensor calibration cannot be performed. Further, if the mounting accuracy is poor, an error may occur as well.

  To prevent dirt and scratches, a shutter that covers the reference plate or a mechanism for retracting the reference plate is required. To prevent errors due to the measurement distance, the position of the reference plate is moved and further corrected. Since a mechanism to perform this is required, the cost is further increased.

  The present invention has been made under such circumstances, and aims to stabilize image colors by performing low-cost and high-precision sensor calibration in an image forming apparatus using an optical sensor. To do.

  In order to achieve the above object, in the present invention, an image forming apparatus is configured as follows.

  (1) means for detecting light reflection characteristics of a detection image formed on a transfer material by an optical sensor, control means for controlling image forming conditions in accordance with a detection output value of the optical sensor, and transfer Means for forming a reference image pattern made of a color material on the material, and means for correcting the optical sensor in accordance with the detection result of the reference image pattern, wherein the reference image pattern is a white color material. An image forming apparatus having the image pattern used.

  (2) means for detecting light reflection characteristics of the detection image formed on the intermediate transfer member by an optical sensor, control means for controlling image forming conditions in accordance with the detection output value of the optical sensor, Means for forming a reference image pattern made of a color material on an intermediate transfer member; and means for correcting the optical sensor in accordance with a detection result of the reference image pattern, wherein the reference image pattern is a white color An image forming apparatus comprising an image pattern using a material.

  (3) means for detecting light reflection characteristics of the detection image formed on the transfer material carrier with an optical sensor, and control means for controlling image forming conditions in accordance with the detection output value of the optical sensor; And a means for forming a reference image pattern made of a color material on a transfer material carrier, and a means for correcting the optical sensor in accordance with the detection result of the reference image pattern, wherein the reference image pattern is white An image forming apparatus using an image pattern using any of the above color materials.

  (4) The image forming apparatus according to any one of claims 1, 2, and 3, wherein the reference image pattern is a solid pattern.

  (5) A cartridge container capable of printing white color material is a cartridge capable of printing colored (cyan (C), magenta (M), yellow (Y), black (K)) color materials mounted on the station. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to be replaceable with a container.

  As described above, according to the present invention, the optical density, which is the light reflection characteristic of the detection toner image formed on the transfer material, the intermediate transfer member, or the transfer material carrier, is detected by the optical sensor. In the image forming apparatus having the means, a cartridge container capable of printing a white color material is colored (cyan (C), magenta (M), yellow (Y), black (K)) mounted on the station. Replace the color material with a printable cartridge container, and form a reference image pattern of white color material on the transfer material, intermediate transfer body, or transfer material carrier, and use the reference image pattern to change the optical sensor. The correction eliminates the need for a calibration white reference plate, improves the color detection accuracy of the sensor, and enables good image density control.

Example 1
In this embodiment, in an image forming apparatus having a means for detecting, by a color sensor, an optical density that is a light reflection characteristic of a detection toner image formed on a transfer material, a white color material is used on the transfer material. A method for improving the color detection accuracy of the sensor by forming a reference image pattern and correcting the color sensor using the reference image pattern and performing good image density control will be described.

  FIG. 1 is a cross-sectional view illustrating the overall configuration of the color image forming apparatus according to the first embodiment. As shown in the figure, this apparatus is a tandem color image forming apparatus that employs an intermediate transfer member 27 that is an example of an electrophotographic color image forming apparatus. The color image forming apparatus includes an image forming unit shown in FIG. 1 and an image processing unit (not shown).

  Hereinafter, the operation of the image forming unit in the electrophotographic color image forming apparatus will be described with reference to FIG.

  The image forming unit forms an electrostatic latent image with exposure light that is turned on based on the exposure time converted by the image processing unit, develops the electrostatic latent image to form a single color toner image, and converts the single color toner image A multi-color toner image is formed by superimposing, and the multi-color toner image is transferred to the transfer material 11 and the multi-color toner image on the transfer material 11 is fixed. Photoconductors (22Y, 22M, 22C, 22K) for each station, injection charging means (23Y, 23M, 23C, 23K) as primary charging means, toner cartridges (25Y, 25M, 25C, 25K), developing means (26Y, 26M, 26C, and 26K), an intermediate transfer member 27, a transfer roller 28, a cleaning unit 29, a fixing unit 30, and a color sensor 42.

  The photosensitive drums (photoconductors) 22Y, 22M, 22C, and 22K are configured by applying an organic optical conductive layer to the outer periphery of an aluminum cylinder, and are rotated by the driving force of a driving motor (not shown) being transmitted. Rotates the photosensitive drums 22Y, 22M, 22C, and 22K in the counterclockwise direction in accordance with the image forming operation.

  As the primary charging means, four injection chargers 23Y, 23M, 23C, and 23K for charging the yellow (Y), magenta (M), cyan (C), and black (K) photoreceptors are provided for each station. In configuration, each injection charger is provided with a sleeve 23YS, 23MS, 23CS, 23KS.

  Exposure light to the photosensitive drums 22Y, 22M, 22C, and 22K is sent from the scanner units 24Y, 24M, 24C, and 24K, and the electrostatic latent images are selectively exposed by exposing the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K. An image is formed.

  As developing means, in order to visualize the electrostatic latent image, four developing devices 26Y, 26M for developing yellow (Y), magenta (M), cyan (C), and black (K) for each station, Each developing device is provided with a sleeve 26YS, 26MS, 26CS, and 26KS. Each developing device is detachably attached.

  The intermediate transfer member 27 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, and rotates clockwise when forming a color image. The intermediate transfer member 27 rotates in accordance with the rotation of the photosensitive drums 22Y, 22M, 22C, and 22K. The toner image is transferred. Thereafter, a transfer roller 28 to be described later comes into contact with the intermediate transfer member 27 to sandwich and convey the transfer material 11, and the multicolor toner image on the intermediate transfer member 27 is transferred to the transfer material 11.

  The transfer roller 28 contacts the transfer material 11 at the position 28a while the multicolor toner image is transferred onto the transfer material 11, and is separated to the position 28b after the printing process.

  The fixing unit 30 melts and fixes the transferred multi-color toner image while conveying the transfer material 11, and as shown in FIG. 1, the fixing roller 31 for heating the transfer material 11 and the transfer material 11 are fixed to the fixing roller. A pressure roller 32 is provided for pressure contact with 31. The fixing roller 31 and the pressure roller 32 are formed in a hollow shape, and heaters 33 and 34 are incorporated therein, respectively. That is, the transfer material 11 holding the multicolor toner image is conveyed by the fixing roller 31 and the pressure roller 32, and heat and pressure are applied to fix the toner on the surface.

  After the toner image is fixed, the transfer material 11 is discharged to a discharge tray (not shown) by a discharge roller (not shown) and the image forming operation is finished.

  The cleaning unit 29 cleans the toner remaining on the intermediate transfer member 27. The waste toner after the four-color multicolor toner image formed on the intermediate transfer member 27 is transferred to the transfer material 11 is: Stored in a cleaner container.

  The color sensor 42 is disposed toward the image forming surface of the transfer material 11 downstream from the fixing unit 30 in the transfer material conveyance path in the color image forming apparatus of FIG. 1, and after the fixing formed on the transfer material 11. The toner image density value is detected.

  Next, the color sensor will be described. FIG. 2 is a schematic configuration diagram of an example of a color sensor. The color sensor 42 includes a white LED 53 and a charge storage sensor 54a with an RGB on-chip filter. The white LED 53 is incident at an angle of 45 degrees with respect to the transfer material 11 on which the patch after fixing is formed, and the intensity of irregularly reflected light in the 0 degree direction is detected by the charge storage sensor 54a with an RGB on-chip filter. The light receiving portion of the charge storage type sensor 54a with RGB on-chip filter is a pixel independent of RGB like 54b. The charge storage sensor of the RGB on-chip filter charge storage sensor 54 may be a photodiode. A plurality of RGB three-pixel sets may be arranged. Further, a configuration in which the incident angle is 0 degree and the reflection angle is 45 degrees may be employed. Furthermore, you may comprise by LED which emits RGB three colors, and a sensor without a filter.

  Hereinafter, calibration of a color sensor using a white reference image, which is a feature of the present invention, will be described.

  First, the characteristics of the white toner used in the present invention will be described. A white toner is a toner used in electrophotography, which has a color material component and a binder resin component as main components. The color material component of this toner is only a white pigment, and other than a white single color such as a colored pigment or a colored dye. It is characterized in that it does not contain any colored coloring material component.

  In the embodiment of the present invention, a white toner using titanium dioxide as a white pigment and polyester as a binder resin component is examined.

  As the white pigment, natural products and / or synthetic products listed below can also be used. For example, titanium dioxide (anatase and rutile), zinc oxide, zinc sulfide, lithopone, lead pigment (lead carbonate, basic lead sulfate, basic lead silicate, basic silicosulfate, dibasic lead phosphite, etc.) , Antimony oxide, zirconium oxide, zircon, kaolin, clay, calcium carbonate, barium sulfate, silicate (eg talc obtained from steatite, asbestine, etc.), mica, hydrated alumina, pumice, asbestos, calcium sulfate, aluminosilicate Examples thereof include sodium and sodium potassium aluminosilicate. Two or more of these may be mixed and used.

  As the binder resin component, the following natural and / or synthetic polymers which have been used as binder resin components of conventional toners can also be used. For example, polyester, polyethylene, polystyrene, styrene copolymer (eg, styrene-acrylic resin, styrene-butadiene resin), acrylate and methacrylate resin, polyvinyl chloride resin, vinyl acetate resin, vinyl chloride / vinyl acetate copolymer resin, chloride Examples thereof include vinyl / vinyl acetate / maleic acid copolymer resins, vinyl butyral resins, polyvinyl alcohol resins, polyurethane resins, polyimide resins, polyamide resins, polyether resins, and epoxy resins. Two or more of these may be mixed and used.

  The kind and molecular weight of the binder resin component in the white toner of the present invention and the content of the binder resin component and white pigment in the white toner of the present invention are optimally prepared by adjusting to the electrophotographic system to be used. There is no particular limitation.

  In the present invention, when the optical sensor is calibrated, a cartridge container capable of printing a white color material is set to a color (cyan (C), magenta (M), yellow (Y), black ( K)) is replaced with a printable cartridge container. This is because it is not preferable to increase the size of the image forming apparatus by providing a station for the white toner cartridge. However, if it is desired to frequently calibrate the sensor or replace the cartridge is troublesome. A method of installing a second station is also an object of adoption. In the first embodiment, a cartridge container capable of printing a black (K) color material and a cartridge container capable of printing a white color material are exchanged to perform sensor calibration.

  A sensor calibration control procedure and an image density control procedure in this embodiment will be described with reference to the flowchart of FIG.

  First, the sensor calibration control procedure will be described in STEPs 1 to 3.

STEP1
A cartridge container capable of printing white toner is inserted into a black (K) station, which is a colored cartridge container, and a patch pattern of a white image for sensor calibration is formed on the transfer material.

  FIG. 4 is a diagram illustrating a calibration patch pattern formed on the transfer material 11 in the first embodiment (A3 size longitudinal feed of 297 mm × 420 mm in this example). In the portion where the color sensor 42 is disposed. One 8 mm square patch is formed. The patch printing rate is set to 100% (solid pattern).

STEP2
Reflected light from the white toner patch fixed on the transfer material is detected by the color sensor 42.

  As for the detection output value of the color sensor, the detection output of the R light receiving element is R1, the detection output of the G light receiving element is G1, and the detection output of the B light receiving element is B1. Note that there is one sensor output value used for each toner of C, M, Y, and K, R output for C toner, G output for M toner, and Y toner. Uses B output, and K output uses G output.

STEP3
The output value of the color sensor is converted into density. At that time, the correction coefficient of the sensor is calculated.

  FIG. 5 shows an average spectral characteristic of the light emission source (white LED) of the color sensor, which is normalized with the maximum value being 1. The spectral characteristics of the light-emitting element have a certain degree of variation around this characteristic.

  FIG. 6 shows average spectral characteristics of the light receiving elements of the color sensor. Here, the maximum value of the R element is set to 1, and the spectral characteristics of the R element, the G element, and the B element are normalized.

  When the spectral reflectance of a white solid image is normalized to 1, the sensor output value when the average color sensor (the sensor whose light emission and light receiving element spectral characteristics are average values) detects a white solid patch is as follows: become that way.

Output value of R element = Σ (spectral reflectance of white toner x spectral characteristic of light emitting element x spectral characteristic of R element)
Output value of G element = Σ (spectral reflectance of white toner x spectral characteristic of light emitting element x spectral characteristic of G element)
Output value of B element = Σ (spectral reflectance of white toner x spectral characteristic of light emitting element x spectral characteristic of B element)
* Σ (A): A is calculated for each wavelength of 400 to 700 nm, and integration is performed. When multiplied by the above-mentioned spectral characteristics (Figures 5 and 6), the output characteristics of the element are as shown in Figure 7. When integration is performed in the range of 400 to 700 nm,
Output value of R element: Output value of G element: Output value of B element = 5.53: 5.05: 3.13.

  In this embodiment, when white toner is detected, the output average values of the light receiving elements are set to R = 5.53V, G = 5.05V, and B = 3.13V, respectively. This value is taken as the standard output value of the sensor.

  Naturally, when the spectral characteristics of the light emitting element and light receiving element of the sensor deviate from the average value (due to initial characteristic variation and durability deterioration), the output value of the sensor does not become the same value as the standard output value described above. .

  Calibration of the sensor output is performed as follows.

  First, the output value of the reference toner image (white solid image) is detected by the color sensor.

  The output values at this time are R0, G0, and B0.

  Next, an output correction coefficient of the color sensor is calculated. The calculation method is calculated by comparing the output values R0, G0, and B0 of the reference toner image with the standard output values R = 5.53V, G = 5.05V, and B = 3.13V of the sensor. The output correction coefficients are determined for the R, G, and B output values of the color sensor, and the correction coefficients are αR, αG, and αB, respectively.

  The formula for calculating the output correction coefficient is shown below.

αR = R0 ÷ 5.53
αG = G0 ÷ 5.05
αB = B0 ÷ 3.13
Sensor calibration (output correction) is performed using the correction coefficient calculated as described above. If the corrected R, G and B output values are R ', G' and B ', respectively,
R ′ ＝ R1 ÷ αR
G ′ ＝ G1 ÷ αG
B ′ ＝ B1 ÷ αB
It becomes. The above is the description of the sensor calibration control procedure. The actual output correction is performed at the time of image density control.

  Next, the image density control procedure will be described in STEPs 4 to 5.

STEP4
A patch pattern for correcting the gradation characteristic γ is formed.

  FIG. 8 is a diagram showing a patch pattern formed on the transfer material 11 (in this example, 297 mm × 420 mm A3 size longitudinal feed), and an 8 mm square patch is 10 mm on the portion where the color sensor 42 is arranged. At intervals, the image printing rate (density gradation degree) is changed in 8 steps for each of Y, M, C, and K (8 patches for each color), and a total of 32 images are formed. The correspondence between each patch and the printing rate (gradation) is Y1, M1, C1, K1 = 12.5%, Y2, M2, C2, K2 = 25%, Y3, M3, C3, K3 = 37.5%, Y4, M4 , C4, K4 = 50%, Y5, M5, C5, K5 = 62.5%, Y6, M6, C6, K6 = 75%, Y7, M7, C7, K7 = 87.5%, Y8, M8, C8, K8 = 100 %, Is set to.

STEP5
Perform image gradation control (gradation correction).

  Image gradation control (gradation correction) will be described with reference to FIG. The method of converting the correction output value of the color sensor into a density is a system using a conventionally known detection signal-to-density conversion table (density conversion table). Here, only cyan tone correction will be described, but magenta, yellow, and black are also corrected in the same manner.

  In FIG. 9, the horizontal axis represents image data. The vertical axis represents the density detection value of the color sensor 42. In the figure, ◯ represents the output density value of the color sensor for each patch of C1, C2, C3, C4, C5, C6, C7, and C8. Next, a straight line T represents a target density gradation characteristic for image density control. In this embodiment, the target density gradation characteristic T is determined so that the relationship between image data and density is proportional. A curve γ represents a density gradation characteristic in a state where density control (tone correction control) is not performed. It should be noted that the density of gradations not forming a patch is calculated by performing spline interpolation through the origin and C1, C2, C3, C4, C5, C6, C7, and C8.

  A curve D represents a gradation correction table calculated by this control, and is calculated by obtaining a symmetric point with respect to the target gradation characteristic T of the gradation characteristic γ before correction. The calculation of the gradation correction table D is executed by a main body CPU (not shown), and the calculated gradation correction table D is stored in a main body memory (not shown) (a non-volatile memory is used in this embodiment). Is done.

  When the print image is formed, the target gradation characteristics can be obtained by correcting the image data with the gradation correction table D.

  In this embodiment, as sensor calibration and image density control timing, sensor calibration is performed when 10,000 sheets of A3 size paper are fed vertically, and image density control is performed when 200 sheets are passed. However, the timing for performing sensor calibration and image density control may be determined flexibly according to the usage status of the color image forming apparatus and the density of the output image, and sensor calibration is performed each time image density control is performed. The number of sheets to be passed may not be specified.

  In the present embodiment, a solid image made of a white color material was used as a reference image for calibration of the color sensor. The reason is as follows. If the density of the reference image pattern is too light, it may be affected by the density fluctuation of the reference image or the spectral reflection characteristics of the transfer material. Therefore, even if the same patch is formed, if it is formed on a different transfer material, the chromaticity will be different. That is, the color sensor output is different. Therefore, a solid image made of a white color material was used to make it less susceptible to the influence of the transfer material. When the transfer material is white, the sensor correction effect can be obtained even if the reference image pattern is not a solid image but the density is light.

  As described above, in this embodiment, in the image forming apparatus having a means for detecting the optical density, which is the light reflection characteristic of the detection toner image formed on the transfer material, by the color sensor, a white color is formed on the transfer material. A method has been described in which a reference image pattern made of a material is formed and a color sensor is corrected using the reference image pattern, thereby improving the color detection accuracy of the sensor and performing good image density control.

(Example 2)
In this embodiment, in an image forming apparatus having means for detecting an optical density, which is a light reflection characteristic of a detection toner image formed on an intermediate transfer body, by a darkness sensor, a white color is formed on the intermediate transfer body. A method for improving the color detection accuracy of a sensor by forming a reference image pattern made of a color material and correcting the darkness detection sensor using the reference image pattern to perform good image density control will be described.

  As described above, the light-emitting elements and light-receiving elements constituting the dark detection sensor have variations in their spectral characteristics for each element. In addition, since the spectral characteristics of the light emitting element and the light receiving element change due to dirt or aging due to the use of the image forming apparatus, highly accurate sensor calibration is required before image density control.

  FIG. 10 is a cross-sectional view illustrating the overall configuration of the color image forming apparatus according to the second embodiment. Similar to the first embodiment, this apparatus is a tandem color image forming apparatus that employs an intermediate transfer member 27 that is an example of an electrophotographic color image forming apparatus. The color image forming apparatus includes an image forming unit shown in FIG. 10 and an image processing unit (not shown). The operation of the image forming unit in the color image forming apparatus used in the present embodiment is the same as that of the image forming apparatus described in the first embodiment, and a description thereof is omitted.

  The second embodiment differs from the first embodiment in that the dark sensor 41 detects the reflected light from the white toner patch formed on the intermediate transfer member 27.

  Next, the dark detection sensor will be described. FIG. 11 is a schematic configuration diagram of an example of the dark detection sensor. The dark detection sensor 41 includes a white LED 51 as a light source and a charge accumulation sensor 52b as a light receiving element. The white LED 51 is made incident on the intermediate transfer body 27 on which the patch after fixing is formed at an angle of 45 degrees, and the intensity of irregularly reflected light in the 0 degree direction is detected by the charge storage sensor 52b. The charge storage type sensor 52b only needs to have sensitivity in the visible range of wavelength 400 to 700 nm, and a photodiode may be used. Further, a configuration in which the incident angle is 0 degree and the reflection angle is 45 degrees may be employed. By combining a white light source and a light receiving element having sensitivity in the visible range, it is possible to measure the optical density of each color of YMCK.

  A specific sensor calibration procedure and image density correction method will be described below.

  First, the sensor calibration control procedure will be described in STEPs 1 to 3.

STEP1
A cartridge container capable of printing white toner is inserted into a black (K) station which is a colored cartridge container.

STEP2
A patch pattern of a white image for sensor calibration is formed on the intermediate transfer member 27.

  FIG. 12 is a diagram showing a calibration patch pattern formed on the intermediate transfer member 27 in the second embodiment, and one 8 mm square white patch is formed in the portion where the density sensor 41 is arranged. The patch printing rate is set to 100% (solid pattern).

STEP3
The reflected light from the white toner patch on the intermediate transfer member 27 is detected by the darkness sensor 41.

  The density sensor 41 detects the density of the correction patch on the intermediate transfer member 27. Next, the output correction of the density sensor 41 will be described with reference to FIG. In FIG. 12, the horizontal axis represents the patch density, and the vertical axis represents the sensor output of the dark detection sensor 41. Here, the standard output value of the reference toner image (white solid image) is T0 (white circle), and the curve δ is calculated by interpolating the sensor output between the origin and the white circle. Further, the output value of the reference toner image (white solid image) before the sensor output correction is performed is T1 (black circle), and the curve ζ is calculated by interpolating the sensor output between the origin and the black circle. .

  Next, the output correction coefficient of the dark detection sensor is calculated. The calculation method is calculated by comparing the standard output value T0 of the reference toner image with the output value T1 of the sensor. The formula for calculating the output correction coefficient β is shown below.

β ＝ T1 ÷ T0
Sensor calibration (output correction) is performed using the correction coefficient β calculated as described above. If the output value after sensor correction is T1 ',
T1 '＝ T1 ÷ β
It becomes. The sensor output value having a lighter patch density than the reference toner image (white solid image) is similarly corrected using the correction coefficient β. The above is the description of the sensor calibration control procedure. The actual output correction is performed at the time of image density control using the darkness sensor.

  Next, the image density control procedure will be described in STEPs 4 to 5.

STEP4
A patch pattern for correcting the gradation characteristic γ is formed.

  FIG. 14 is a diagram showing a patch pattern formed on the intermediate transfer member 27. In the portion where the darkness detection sensor 41 is arranged, 8 mm square patches are provided at intervals of 10 mm for each of Y, M, C, and K. A total of 32 images are formed by changing the image printing rate (density gradation degree) in 8 steps (8 patches for each color). The correspondence between each patch and the printing rate (gradation) is Y1, M1, C1, K1 = 12.5%, Y2, M2, C2, K2 = 25%, Y3, M3, C3, K3 = 37.5%, Y4, M4 , C4, K4 = 50%, Y5, M5, C5, K5 = 62.5%, Y6, M6, C6, K6 = 75%, Y7, M7, C7, K7 = 87.5%, Y8, M8, C8, K8 = 100 %, Is set to.

STEP5
Perform image gradation control (gradation correction).

  The image density correction patch is formed on the transfer material and the intermediate transfer member, and the color detection and the density detection sensor are used for density detection. 1 and is not described here.

  As described above, in this embodiment, in an image forming apparatus having means for detecting the optical density, which is the light reflection characteristic of the detection toner image formed on the intermediate transfer body, by the darkness detection sensor, on the intermediate transfer body. A method has been described in which a reference image pattern made of a white color material is formed and the darkness detection sensor is corrected using the reference image pattern, thereby improving the color detection accuracy of the sensor and performing good image density control.

(Example 3)
In this embodiment, in an image forming apparatus having a means for detecting, by a color sensor, an optical density that is a light reflection characteristic of a detection toner image formed on a transfer material, a white color material is used on the transfer material. A method for improving the color detection accuracy of the sensor by forming a reference image pattern and correcting the color sensor using the reference image pattern and performing good image density control will be described.

  The embodiment 3 differs from the embodiment 1 in that an electrophotographic image forming apparatus uses a transport belt as a transfer material transport member.

  FIG. 15 is a cross-sectional view illustrating the overall configuration of the color image forming apparatus according to the third embodiment. As shown in the figure, this apparatus is an electrophotographic image forming apparatus using a conveying belt as a transfer material conveying member, which is an example of an electrophotographic color image forming apparatus. The image forming apparatus shown in the figure has a rotatable drum-shaped electrophotographic photosensitive member as a transfer material carrier, that is, photosensitive drums 1a, 1b, 1c, and 1d having a photosensitive layer on a conductive substrate. . The surfaces of the photosensitive drums 1a, 1b, 1c, and 1d are uniformly charged by charging rollers (charging devices) 2a, 2b, 2c, and 2d, and then exposed to exposure devices 3a, 3b, 3c, and the like such as LEDs and laser scanners. The exposure according to the image information is performed by 3d, whereby an electrostatic latent image is formed. Thereafter, the electrostatic latent image is developed as a toner image by electrostatically attaching toner to the developing devices 4a, 4b, 4c, and 4d. The toner images on the photosensitive drums are transferred onto transfer materials (transfer devices) 12a, 12b, and transfer materials P, which have been conveyed by the transfer material carrier 50 to a transfer position facing the photosensitive drums 1a, 1b, 1c, 1d. Electrostatically transferred by 12c and 12d.

  The unfixed toner image thus transferred onto the transfer material P is fixed onto the transfer material P by being heated and pressed by the fixing device 20. Thereby, a permanent image is formed.

  On the other hand, the toner remaining on the surfaces of the photosensitive drums 1a, 1b, 1c, and 1d after the toner image transfer is removed by cleaning blades (photoconductor cleaning devices) 6a, 6b, 6c, and 6d and collected in a waste toner container. The The photosensitive drums 1a, 1b, 1c and 1d whose surfaces have been cleaned in this way are repeatedly used for image formation.

  A specific sensor calibration procedure and image density correction method will be described below.

  First, the sensor calibration control procedure will be described in STEPs 1 to 3.

STEP1
A cartridge container capable of printing white toner is inserted into a black (K) station which is a colored cartridge container.

STEP2
A patch pattern of a white image for sensor calibration is formed on the transfer material P.

  FIG. 16 is a diagram showing a calibration patch pattern formed on the transfer material P in the third embodiment (A3 size longitudinal feed of 297 mm × 420 mm in this example). In the portion where the color sensor 42 is arranged, FIG. One 8 mm square patch is formed. The patch printing rate is set to 100% (solid pattern).

STEP3
Reflected light from the white toner patch fixed on the transfer material P is detected by the color sensor 42.

  The correction of the sensor output is the same as that in the first embodiment, and a description thereof will be omitted.

  Next, the image density control procedure will be described in STEPs 4 to 5.

STEP4
A patch pattern for correcting the gradation characteristic γ is formed.

  The formation of the patch pattern is the same as that of the first embodiment, and the description thereof is omitted.

STEP5
Perform image gradation control (gradation correction).

  The image density control method is the same as that in the first embodiment, and a description thereof will be omitted.

  As described above, in this embodiment, in the image forming apparatus having a means for detecting the optical density, which is the light reflection characteristic of the detection toner image formed on the transfer material, by the color sensor, a white color is formed on the transfer material. A method has been described in which a reference image pattern made of a material is formed and a color sensor is corrected using the reference image pattern, thereby improving the color detection accuracy of the sensor and performing good image density control.

Example 4
In this embodiment, in an image forming apparatus having means for detecting an optical density, which is a light reflection characteristic of a detection toner image formed on a transfer material carrier, by a darkness sensor, the image is formed on the transfer material carrier. A method of improving the color detection accuracy of the sensor by forming a reference image pattern made of a white color material and correcting the darkness detection sensor using the reference image pattern to perform good image density control will be described.

  FIG. 17 is a cross-sectional view illustrating the overall configuration of the color image forming apparatus according to the fourth embodiment. Similar to the third embodiment, this apparatus is an electrophotographic image forming apparatus that uses a conveying belt as a transfer material conveying member, which is an example of an electrophotographic color image forming apparatus. The operation of the image forming unit in the color image forming apparatus used in the present embodiment is the same as that of the image forming apparatus described in the third embodiment, and a description thereof is omitted.

  The embodiment 4 differs from the embodiment 3 in that the reflected light from the white toner patch formed on the transfer material carrier 50 is detected by the darkness sensor 41.

  A specific sensor calibration procedure and image density correction method will be described below.

  First, the sensor calibration control procedure will be described in STEPs 1 to 3.

STEP1
A cartridge container capable of printing white toner is inserted into a black (K) station which is a colored cartridge container.

STEP2
A patch pattern of a white image for sensor calibration is formed on the transfer material carrier 50.

  FIG. 18 is a diagram showing a calibration patch pattern formed on the transfer material carrier 50 according to the fourth embodiment. One white patch of 8 mm square is formed on the portion where the darkness sensor 41 is arranged. Yes. The patch printing rate is set to 100% (solid pattern).

STEP3
The reflected light from the white toner patch on the transfer material carrier is detected by the darkness sensor 41.

  Although there is a difference between the formation position of the white toner patch on the intermediate transfer member and the transfer material carrier, the sensor output correction method is the same as that of the second embodiment, and the description is omitted.

  Next, the image density control procedure will be described in STEPs 4 to 5.

STEP4
A patch pattern for correcting the gradation characteristic γ is formed.

  Although the patch pattern is formed on the intermediate transfer member and the transfer material carrier, the patch pattern is the same as that of the second embodiment, and the description thereof is omitted.

STEP5
Perform image gradation control (gradation correction).

  The difference between the image tone correction patch formation location on the transfer material and the transfer material carrier, and the difference between the color sensor and the darkness sensor used for density detection is the method of image density control. It is the same as that of Example 1, and description is abbreviate | omitted.

  As described above, in this embodiment, in an image forming apparatus having means for detecting the optical density, which is the light reflection characteristic of the detection toner image formed on the transfer material carrier, by the darkness detection sensor, the transfer material carrier. A method for improving the color detection accuracy of a sensor by forming a reference image pattern made of a white color material on the top and correcting the darkness detection sensor using the reference image pattern to perform good image density control has been described. .

Sectional drawing which shows the whole structure of the image forming apparatus in Example 1. FIG. The figure which shows the structure of the color sensor 42 Flow chart explaining the image density procedure Arrangement diagram of patch pattern on transfer material in embodiment 1 Diagram showing spectral characteristics of light-emitting elements Diagram showing spectral characteristics of light receiving element Diagram showing the output characteristics of the element Arrangement diagram of patch pattern for image density control in embodiment 1 The figure explaining the image gradation control method Sectional drawing which shows the whole structure of the image forming apparatus in Example 2. FIG. The figure which shows the structure of the dark detection sensor 41 Arrangement diagram of patch pattern on intermediate transfer material in embodiment 2 FIG. 6 is a diagram for explaining dark sensor output calibration in the second embodiment. Arrangement diagram of image density control patch pattern in embodiment 2 Sectional drawing which shows the whole structure of the image forming apparatus in Example 3. Arrangement diagram of patch pattern on transfer material carrier in embodiment 3 Sectional drawing which shows the whole structure of the image forming apparatus in Example 4. FIG. Arrangement diagram of patch pattern on transfer material carrier in embodiment 4

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Transfer material 22 Photoconductor, photosensitive drum 26 Developing means 27 Intermediate transfer body 30 Fixing device 41 Dark detection sensor 42 Color sensor 1, 1a, 1b, 1c, 1d Photoconductor (photosensitive drum)
2, 2a, 2b, 2c, 2d Charging device 3, 3a, 3b, 3c, 3d Exposure device 4, 4a, 4b, 4c, 4d Developing device 6, 6a, 6b, 6c, 6d Photoconductor cleaning device 7, 7a, 7b, 7c, 7d Process cartridge 9, 9a, 9b, 9c, 9d Polygon mirror 10, 10a, 10b, 10c, 10d Imaging lens 50 Transfer material carrier 12a, 12b, 12c, 12d Transfer device (transfer roller)
14c Conveyor belt cleaning device 18 Paper feed roller 51 Adsorption roller 52 Fixing roller 53 Pressure roller 54 Paper discharge roller pair 55 Paper output tray 30 Electromagnetic solenoid 31 Actuation rod 32 Adsorption roller support member 33 Pressure spring 34 Used for transfer of toner image Area 35 phase detection member 36 light emitting diode 37 light receiving element 100 image forming apparatus main body 200 suction contact / separation mechanism P transfer material Sa, Sb, Sc, Sd image forming station

Claims (5)

  In an image forming apparatus, comprising: means for detecting a light reflection characteristic of a detection image formed on a transfer material by an optical sensor; and a control means for controlling an image forming condition in accordance with a detection output value of the optical sensor. And a means for forming a reference image pattern made of a color material on a transfer material, and a means for correcting the optical sensor in accordance with a detection result of the reference image pattern, wherein the reference image pattern is a white color An image forming apparatus comprising an image pattern using a material.   An image forming apparatus comprising: means for detecting light reflection characteristics of a detection image formed on the intermediate transfer member by an optical sensor; and control means for controlling image forming conditions in accordance with a detection output value of the optical sensor. And a means for correcting the optical sensor in accordance with a detection result of the reference image pattern, wherein the reference image pattern is white. An image forming apparatus using an image pattern using any of the above color materials.   Image forming apparatus comprising: means for detecting light reflection characteristics of the detection image formed on the transfer material carrier with an optical sensor; and control means for controlling image forming conditions in accordance with a detection output value of the optical sensor. In the apparatus, the image forming apparatus includes means for forming a reference image pattern made of a color material on a transfer material carrier, and means for correcting the optical sensor according to a detection result of the reference image pattern. An image forming apparatus characterized by being an image pattern using a white color material.   The image forming apparatus according to claim 1, wherein the reference image pattern is a solid image pattern.   Replace the cartridge container that can print the white color material with the cartridge container that can print the colored (cyan (C), magenta (M), yellow (Y), black (K)) color material installed in the station. The image forming apparatus according to claim 1, wherein the image forming apparatus has a possible configuration.

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