JP2005274771A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which realizes excellent color reproducibility and is capable of outputting images of high quality having less difference of color reproducibility between image forming apparatus and less color variance with time, for a long period of time. <P>SOLUTION: An image processing part 400 for forming an image on a recording material on the basis of an image forming condition forms a color pattern image using one colorant independently and a color pattern image using combination of two or more colorants, by using a plurality of colorants for forming the image, and a color sensor 71 for detecting the image has a plurality of LEDs 201 to 208 which emit detection light in a wavelength region where the light absorption amount is changed at a prescribed rate in accordance with the pattern images, and a light reception part 210 which receives reflected light from the pattern images of the detection light and outputs a detection result. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer that forms an image on a recording material, and an image forming method thereof.

Conventionally, in this type of image forming apparatus, a patch of each color material of cyan (C), magenta (M), yellow (Y), and black (B) is formed, and a change in the amount of reflected light from the patch is detected by a sensor. By measuring, patch density is detected, and maximum density and gradation characteristics are corrected from the detected density information (for example, refer to Patent Document 1).
JP-A-4-193576

  However, in a conventional image forming apparatus, the degree of color misregistration caused by the misregistration of the image forming positions between the color materials and the transferability at the time of superposition when forming color images by overlaying the color materials are different for each color. Due to the difference in materials, density and gradation correction alone is not sufficient to suppress differences in color reproducibility between image forming apparatuses and temporal color reproducibility degradation.

  Furthermore, when performing the above correction, it is necessary to read an image that has been printed once by an image reading device such as a scanner, which requires a lot of trouble.

  Therefore, the present invention has been made in view of the above-described problems of the prior art, and can realize excellent color reproducibility, color reproducibility between image forming apparatuses, An object of the present invention is to provide an image forming apparatus and an image forming method capable of outputting a high-quality image with little color variation over a long period of time.

  In order to achieve the above object, the present invention provides an image forming apparatus for correcting an image forming condition in accordance with a detection result of an output image, and forming the image on a recording material based on the image forming condition. Detecting means for detecting the image and outputting the detection result, a conveying means for conveying the recording material from the image forming means to the detecting means, and the image forming condition according to the detection result of the detecting means The image forming means combines a color pattern image using a single color material alone with a plurality of color materials forming the image and two or more color materials. A color pattern image, and the detection means emits detection light in a wavelength region in which the amount of light absorption changes at a predetermined rate according to the pattern image, and the pattern image of the detection light To provide an image forming apparatus; and a light receiving unit which outputs the detection result by receiving the reflected light et.

  In order to achieve the above object, the present invention provides an image forming method for correcting an image forming condition in accordance with a detection result of an output image, and forming an image on a recording material based on the image forming condition. A forming step, a detecting step for detecting the image and outputting the detection result, a conveying step for conveying the recording material from the image forming step to the detecting step, and the image according to the detection result in the detecting step. A correction process for correcting the forming conditions, wherein the image forming process includes a color pattern image using one color material alone using a plurality of color materials forming the image, and two or more color materials. Forming a combined color pattern image, wherein the detection step includes a plurality of light sources that emit detection light in a wavelength region in which light absorption changes at a predetermined rate according to the pattern image, and the pattern of the detection light. To provide an image forming method characterized by detecting with a light receiving unit which outputs the detection result by receiving the reflected light from the image.

  According to the present invention, excellent color reproducibility can be realized, and a high-quality image with little difference in color reproducibility between image forming apparatuses and little color variation with time can be output over a long period of time.

  Embodiments of an image forming apparatus and an image forming method of the present invention will be described below with reference to the drawings.

[First Embodiment]
First, a first embodiment will be described with reference to FIGS.

  FIG. 1 is a cross-sectional view showing a schematic configuration of the image forming apparatus according to the present embodiment.

  In FIG. 1, reference numeral 1 denotes an image forming apparatus, which is provided with four image forming stations for forming images of respective colors of magenta (M), cyan (c), yellow (Y), and black (B). As shown in FIG. 1, each image forming station is provided with a charger, a cleaner 4a, an electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1a, 1b, 1c, and 1d as an image holder. 4b, 4c, 4d and developing devices 2a, 2b, 2c, 2d. The photosensitive drums 1a, 1b, 1c, and 1d are supported so as to be rotatable in the arrow direction (clockwise direction) in the drawing.

  A transfer unit 3 is disposed below the photosensitive drums 1a, 1b, 1c, and 1d between the developing units 2a, 2b, 2c, and 2d and the cleaners 4a, 4b, 4c, and 4d. The transfer unit 3 includes a transfer belt 31 serving as a recording paper conveying unit common to the image forming stations and transfer chargers 3a, 3b, 3c, and 3d. The transfer belt 31 sequentially conveys recording paper as a recording medium to each of the photosensitive drums 1a, 1b, 1c, and 1d. In each image forming station, the images formed on the photosensitive drums 1a, 1b, 1c, and 1d are transferred to a recording sheet on the transfer belt 31.

  Further, the image forming apparatus 1 is provided with a plurality of supply means, that is, a paper feed cassette 61 and a manual paper feed tray 61a that can be pulled out in the direction of arrow R in the figure. One of high, medium and low gloss recording paper is loaded. The toner images of the respective colors formed on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred onto the recording paper in the process of being supported on the transfer belt 31 and passing through the image forming stations. When this transfer process is completed, the recording sheet is separated from the transfer belt 31 and conveyed to the fixing unit 5 by the conveying belt 62 serving as a recording sheet guiding unit.

  The fixing unit 5 includes a fixing roller 51 that is rotatably supported, a pressure roller 52 that rotates while being in pressure contact with the fixing roller 51, a release agent supply and application unit 53, and a roller cleaning unit. is there. Inside the fixing roller 51 and the pressure roller 52, heaters such as halogen lamps are disposed. A thermistor or the like (not shown) is in contact with the fixing roller 51 and the pressure roller 52, respectively. By controlling the voltage applied to the heater via the temperature adjusting means 60, the fixing roller 51 and the pressure roller 52 are controlled. The surface temperature is adjusted.

  The fixing roller 51 is in contact with a release agent supply and application means 53 for applying silicone oil as a release agent to the surface of the fixing roller 51. The release agent supply and application means 53 applies silicone oil as a release agent to the fixing roller 51, whereby the recording paper is conveyed by the conveyance belt 62 and between the fixing roller 51 and the pressure roller 52. The toner is prevented from adhering to the surface of the fixing roller 51 when passing through the fixing roller 51. Further, an application amount control unit 63 is connected to the release agent supply application unit 53. The application amount of silicon oil applied to the surface of the fixing roller 51 can be controlled by the application amount control means 63.

  A driving motor (not shown) that drives the fixing roller 51 and the pressure roller 52 includes a conveyance speed of the recording paper, that is, rotation of the fixing roller 51 and the pressure roller 52 that press / heat both the front and back surfaces of the recording paper. A speed control means 64 for controlling the speed is connected. As a result, the unfixed toner image on the surface of the recording paper is melted and fixed, and a full-color image is formed on the recording paper. The recording paper on which the full-color image is fixed is separated from the pressure roller 52 by a separation claw (not shown).

  The recording paper separated from the pressure roller 52 fixes the full-color image, and then, as necessary, the chromaticity and density are measured by a color sensor 71 arranged in front of the paper discharge tray.

  A color conversion profile is created based on the chromaticity value measured by the color sensor 71, and internal conversion color processing is performed using the profile. EFI that maintains the Color Rendering Dictionary (CRD) adopted from the Post Script level (2) proposed by Adobe as a profile that realizes excellent color reproducibility, the color separation table in Photoshop, and the black plate information There are CMYK simulations in Color Wise, etc. Here, an ICC (International Color Consortium) profile that has been accepted in the market in recent years is used. This ICC profile will be described later.

  FIG. 2 is a diagram showing a detailed configuration around the color sensor 71.

  In FIG. 2, 201 to 208 are LEDs (light emitting diodes), 209 is an imaging lens, 210 is a light receiving unit, 211 is a measurement opening, 211n is a normal line of the measurement opening 211, and 212 is a patch (including an image). ) 213 is a white plate.

  The LEDs 201 to 208 are each arranged at an angle inclined by 45 ° with respect to the normal line 211n of the measurement opening 211, and irradiate the patch 212 formed on the recording paper conveyed to the measurement opening 211. Thus, they are arranged at equal intervals on a circumference centered on the normal line 211n.

  The light emission peak wavelengths of the LEDs 201 to 208 have values different from each other within a range of 400 nm to 700 nm, for example, and correspond to the LEDs 201 to 208, respectively. 308.

  FIG. 3 is a diagram illustrating the relationship between the wavelength and sensitivity of the LEDs 201 to 208 in the image forming apparatus 1 according to the present embodiment, in which the vertical axis indicates sensitivity and the horizontal axis indicates wavelength.

  In FIG. 2, the imaging lens 209 and the light receiving unit 210 are arranged on the normal line 211 n of the measurement opening 211, and the normal line out of the reflected light from the patch 212 on the recording paper irradiated by the LEDs 201 to 208. The component in the 211n direction is imaged on the light receiving surface of the light receiving unit 210 by the imaging lens 209. The light receiving unit 210 is configured by arranging one or a plurality of photoelectric conversion elements such as photodiodes.

  A recording surface glass, which is a measurement opening 211, is installed between the color sensor 71 and the recording paper, and the recording paper is conveyed in close contact with the recording surface glass 211, so that the optical path length with the recording paper is always set. Measure while keeping constant. The white plate 213 is for performing white correction of the color sensor 71 and is disposed at a position where the color sensor 71 faces the recording surface glass 211.

  FIG. 4 is a block diagram illustrating a configuration of the image forming apparatus 1 according to the present embodiment.

  In FIG. 4, an image processing unit 400 includes an external input I / F (interface) 401, an input ICC profile storage unit 402, a CMM (color management module) 403, an output ICC profile storage unit 404, a spatial filter 405, and an image memory 406. , LUT (look-up table) 407, color sensor input ICC profile storage unit 408, profile creation unit 409, pattern generator 410, optical density conversion unit 411, contrast potential control unit 412, and LUT creation unit 413.

  4, 414 is an A (analog) / D (digital) conversion unit, 415 is a sensor control unit, 416 is a CPU (central processing unit), 417 is an operation unit, 418 is a printer unit, 71 is a color sensor, Reference numerals 201 to 208 denote LEDs, and 210 denotes a light receiving unit.

  4, 419 and 419a are light reception signals, 420 is image data, 421 is a CMYK (Cyan Magenta Yellow Black) signal (data), 422 is an RGB signal (data), 423 is an L * a * b * signal ( (Data), 424 is a CMYK signal (data), 425, 426, and 427 are L * a * b * signals (data), 428 is an image signal, 429 is image data, and 430 is a CMYK signal (data).

  In the following, color conversion processing using a color conversion profile of image data input from the external input I / F 401 and multidimensional calibration for creating a color conversion profile based on chromaticity values measured by the color sensor 71 ( Multi-dimensional CAL) and density / gradation calibration (density / gradation CAL) for correcting gradation characteristics based on density values measured by the color sensor 71 will be described.

  First, color conversion processing of image data input from the external input I / F 401 will be described with reference to FIG.

  In the color conversion when outputting the image data 420 input from the scanner unit of the image forming apparatus 1 according to the present embodiment, the RGB signal 422 input from the scanner unit via the external input I / F 401 is input. It is sent to the ICC profile storage unit 402. In the input ICC profile storage unit 402 in which the profile of the scanner unit is stored in advance, RGB → L * a * b * conversion processing is performed. That is, the input ICC profile is used to convert RGB data dependent on the input device into CIE (International Lighting Commission) L * a * b * independent of the input device.

  The ICC profile is composed of a one-dimensional LUT (lookup table) for controlling the gamma of the input signal, a multi-order color LUT called direct mapping, and a one-dimensional LUT for controlling the gamma of the generated conversion data. The RGB data 422 is converted into L * a * b * data 425 using a lookup table.

  The image signal converted into the L * a * b * data 425 is input to the CMM 403. Here, GUMAT conversion for mapping a mismatch between a reading color space of the scanner unit as an input device and an output color reproduction range of the printer unit 418 as an output device, or a case of observing a light source type and an output product at the time of input Color conversion for adjusting a mismatch with the light source type (also referred to as color temperature setting mismatch), black character determination, and the like are performed and converted to L * a * b * data 426. The image signal converted into the L * a * b * data 426 is input to the output ICC profile storage unit 404, converted into a CMYK signal 421 depending on the output device, and supplied to the spatial filter unit (output filter unit) 405. Is output.

  The spatial filter unit 405 performs edge enhancement processing or smoothing processing. Further, the image memory unit 406 temporarily stores the image signal 428 processed by the spatial filter unit 405, and outputs image data 429 to the LUT 407 in synchronization with image formation of the printer unit 418. The CMYK image data 430 subjected to gradation measurement by the LUT 407 is sequentially sent to the printer unit 418. The printer unit 418 performs pulse width modulation (PWM) on the input image data 430, drives the laser in accordance with the image data pulse-width modulated by the laser driver, and outputs a desired image.

  In addition to the image data from the scanner unit, image data 420 from an externally connected device is input to the image processing unit 400 via the external input I / F 401. The image data 420 in this case includes CMYK other than RGB data, and L * a * b * data types. When L * a * b * data 423 is input, color conversion is performed via the CMM 403. In addition, when the CMYK data 424 is input, it is highly likely that the user has arbitrarily performed color conversion. Therefore, the image processing unit 400 does not perform new color conversion and outputs the CMYK data 421 to the printer unit 418. Send a signal.

  Furthermore, when connecting to an external scanner, an input ICC profile attached to the external scanner may be downloaded.

  By processing in this way, the user can create a profile by the image forming apparatus 1 according to the present embodiment and establish a multi-order color CAL without purchasing expensive software and a colorimeter. Can do.

  Therefore, it is possible to easily perform a color conversion simulation, and it is possible to provide the image forming apparatus 1 with high usability.

  Next, the profile creation process using the multi-order color CAL will be described with reference to FIGS.

  FIG. 5 is a flowchart showing the flow of the profile creation processing operation by the multi-order color CAL in the image forming apparatus 1 according to the present embodiment.

  When replacing service parts, before the JOB where color matching accuracy is required, or when the user wants to know the color of the final output at the design concept stage, etc., the user operates the operation unit 417. By setting the color CAL mode, a profile creation process is performed.

  The profile creation process is performed in the image processing unit 400.

  First, the instruction of the multi-dimensional CAL mode set by the operation unit 417 is input to the CPU 416 that comprehensively controls the image forming apparatus 1 according to this embodiment including the image processing unit 400 and the printer unit 418. When there is an instruction for the multi-dimensional CAL mode, the CPU 416 transmits the color chart for colorimetry to the pattern generator unit 410 and the printer unit 418 so as to output without passing through the profile, and at the same time, via the sensor control unit 415. A color measurement instruction signal is output to the color sensor 71.

  The pattern generator unit 410 stores patch data of an ISO12642 test image as a CMYK (Cyan Magenta Yellow Black) test pattern 601 as shown in FIG. 6 that is measured by the color sensor 71, and is stored in the LUT 407 according to an instruction from the CPU 416. Outputs patch data.

  FIG. 6 is a diagram showing an example of a test pattern on a test print measured by the color sensor 71. In FIG. 6, 600 is a test print, and 601 is a test pattern. The test pattern 601 includes CMYK (Cyan Magenta Yellow Black) having a predetermined gradation formed in the sub-scanning direction, a patch combining a secondary color and a tertiary color, a gray patch, a 4-color patch, and the like. It is a patch pattern of the ISO12642 test image. The patch 212 is conveyed to the color sensor 71 and is sequentially read by the color sensor 71.

  When the patch data is input, the LUT 407 performs gamma conversion processing so that an ideal gradation can be obtained by the printer unit 418, and outputs CMYK image data 430 to the printer unit 418, which has been described with reference to FIG. Through such charging, exposure, development, transfer, and fixing processes, a test pattern 601 for color measurement as shown in FIG. 6 is output (step S501 in FIG. 5).

  When the sensor control unit 415 receives a reading instruction signal of the patch 212 from the CPU 416, the sensor control unit 415 starts the reading operation of the patch 212 described below.

  The sensor control unit 415 has a selector used for driving the LEDs 201 to 208 and adjusts the light intensity of the LEDs 201 to 208 after white correction using the white plate 213 and the function of causing the LEDs 201 to 208 to emit light independently. And a light amount adjustment function.

  The light emission operation of the LEDs 201 to 208 in the multi-dimensional CAL mode will be described in an actual operation. When a colorimetry command is input from the CPU 416, the LED 201 first emits light at a predetermined timing, and the reflected light from the patch 212 is received. The light is received by the unit 210. A light reception signal 419 corresponding to the received light intensity is sent from the light receiving unit 210 to the A / D conversion unit 414, and the A / D conversion unit 414 converts analog data into digital data. The light reception signal 419a converted into digital data is input to the color sensor input ICC profile storage unit 408. The light reception signal 419 at this time substantially matches the spectral intensity of the LED 201. However, strictly speaking, it is necessary to consider the optical system such as the imaging lens 209 and the spectral sensitivity of the light receiving unit 210 (step S502 in FIG. 5).

  Next, the LED 202 emits light in the same manner as the LED 201, and the received light signal 419 is input to the color sensor input ICC profile storage unit 408 via the A / D conversion unit 414. Repeat until. In this manner, eight received light signals 419a that match the spectral intensities of the LEDs 201 to 208 are input to the color sensor input ICC profile storage unit 408 (steps S503 to S509 in FIG. 5).

  The above patch 212 reading operation is performed until all the patches 212 on the test print 600 shown in FIG. 6 are read (step S510 in FIG. 5).

  The color sensor input ICC profile storage unit 408 first converts the received light reception signal 419a into XYZ data as chromaticity values using the color matching function of the XYZ color system of the CIE (International Commission on Illumination). The data is converted into L * a * b * 427 data that is generally used as a color space signal of the image output device by the CIELAB calculation formula. This color sensor input ICC profile generates CIEL * a * b * data independent of the device.

  The profile creation unit 409 inputs the output CMYK signal of the ISO 12642 test form and the L * a * b * data converted by the color sensor input ICC profile storage unit 408, and creates a conversion table of CYMK → Lab. Then, based on these pieces of information, an inverse conversion table is created (output ICC profile creation).

  Then, the created output ICC profile is replaced with the profile stored in the output ICC profile storage unit 404 (step S511 in FIG. 5). Thereafter, this processing operation is terminated.

  Here, the eight LEDs 201 to 208 are used as the light source of the sensor when detecting the chromaticity and density of the patch 212, but the present invention is not limited to this, for example, 400 to 500 nm. , RGB received light signals 419a detected using three LEDs having peak wavelengths in the respective bands of 500 to 600 nm and 600 to 700 nm are input in the color sensor input ICC profile storage unit 408, and the RGB data → L * You may make it convert into a * b * 427 data.

  As described above, since the internal color conversion of the image forming apparatus 1 according to the present embodiment is performed using the ICC profile created by performing multidimensional CAL, the color reproducibility is excellent without depending on changes with time. The image forming apparatus 1 can be provided.

  Below, the density of the test pattern formed on the recording material is read in order to correct fluctuations in image density and gradation reproducibility caused by various factors such as short-term, long-term, etc. Density / gradation calibration (hereinafter, density / gradation CAL) for controlling the image forming conditions based on the characteristics will be described with reference to FIGS.

  7 and 8 are flowcharts showing the flow of the density / gradation CAL operation in the image forming apparatus 1 according to the present embodiment.

  The optical density conversion unit 411 converts the received light signal 419a read by the color sensor 71 into an optical density of CMYK using a conversion LUT. The contrast potential control unit 412 inputs the obtained density data 431 to calculate the contrast potential, and sets data for setting the grid potential, the developing bias potential, and the like so as to obtain the calculated contrast potential. Output to 418. The LUT creation unit 413 creates and sets the contents of the LUT 407 for obtaining linear gradation characteristics from the input density data 431 according to an instruction from the CPU 416.

  Hereinafter, the density / gradation CAL control operation will be described with reference to the flowcharts of FIGS.

  When a density / gradation CAL control instruction is input from the operation unit 417 to the CPU 416, the pattern generator 410 outputs density / gradation CAL test pattern data to the printer unit 418, and the density measurement test print is described above. The image is output in accordance with the image forming process (step S701 in FIG. 7). The contrast potential (described later) at the time of image formation of the density measurement test print is registered as an initial value in a standard state corresponding to the environment, and this is used.

  As shown in FIG. 9, the test pattern 903 includes a pattern 901 composed of intermediate gradation densities for four colors Y, M, C, and K, and a maximum density patch (density signal for each color of Y, M, C, and K). And a patch pattern 902 consisting of 255 levels).

  The test pattern 903 on the density measurement test print is read by the color sensor 71 arranged in front of the paper discharge port.

  The sensor control unit 415 has a selector used to drive the LEDs 201 to 208, has a function of causing the LEDs 201 to 208 to emit light independently, and has the Y, M, C, and K colors of the test pattern 903 in FIG. The LEDs 201 to 208 having peaks in the wavelength ranges of 400 to 500 nm (B), 500 to 600 nm (G), and 600 to 700 nm (R) shown in FIG. For example, in the case of the Y patch, the LED 202 (or LED 201) having a peak in the B wavelength range is emitted, and in the case of the M patch, the LED 204 (or LEDs 203 and 205) having a peak in the G wavelength range is used. In the case of the C patch, the LED 207 (or LED 206) having a peak in the R wavelength region emits light. Here, in the case of the patch B, it is not necessary to limit the sensitivity because it has sensitivity in the entire visible light region, but here, the LED 204 (or the LEDs 203 and 205) having a peak in the G wavelength region is used.

  The light emission of the LEDs 201 to 208 corresponding to each color patch is not limited to one LED. In the above case, when reading the Y patch, the LED 201 and the LED 202 emit light at the same time. Sensor sensitivity can be increased by simultaneously emitting LED 204 and LED 205 for the M patch, LED 206 and LED 207 for the C patch, and LED 203 and LED 204 for the B patch.

  The light emission operation of the LEDs 201 to 208 in the density / gradation CAL mode will be described in an actual operation. When the reading instruction signal for the test pattern 903 is input from the CPU 416, the LED 201 has a predetermined timing according to the color of the test pattern 903. -208 emits light. Then, the reflected light from the test pattern 903 is received by the light receiving unit 210. A light reception signal 419 corresponding to the received light intensity is sent from the light receiving unit 210 to the A / D conversion unit 414, and the A / D conversion unit 414 converts the analog data into digital data. The received light signal 419a converted into digital data is input to the optical density converter 411 (steps S702 to S709 in FIG. 7).

  The above-described reading operation corresponding to each color patch is performed until all the test patterns 903 on the test print are read (step S710 in FIG. 7).

  The optical density conversion unit 411 receives the light reception signal 419a and converts it into an optical density using a conversion LUT. In the LUT, a coefficient calculated using the following formula (1) is set in advance. The correction coefficient (k) is adjusted so as to obtain an optical density.

C = −kc × log 10 (R / 255)
M = −km × log 10 (G / 225) (1)
Y = −ky × log 10 (B / 225)
Bk = −kbk × log10 (G / 225)
Next, a method for correcting the maximum density from the density information of the obtained density data 431 will be described.

  FIG. 10 is a diagram showing the relationship between the surface potential of the relative photosensitive drum and the image density obtained by the above calculation.

  The difference between the surface potentials of the photosensitive drums 1a to 1d when the maximum level of the semiconductor laser of each color of the printer unit 418 is emitted after the contrast potential used at that time, that is, the primary charging from the developing bias potential is a. In the case of the maximum density Da obtained by the setting, the image density almost corresponds to the linear as shown by the solid line L with respect to the surface potential of the relative photosensitive drum in the density region of the maximum density. However, in the two-component development system, when the toner density in the developing device fluctuates and falls, there may be nonlinear characteristics in the density region of the maximum density as indicated by the broken line N.

  Therefore, here, the final target value for the maximum density is set to 1.6, but in consideration of a margin of 0.1, 1.7 is set as the target value for the control to match the maximum density. The control amount was determined.

  The contrast potential b here is obtained using the following formula (2).

b = (a + ka) × 1.7 / Da (2)
Here, ka is a correction coefficient, and it is preferable to optimize the value depending on the type of development method (step S711 in FIG. 7).

  Next, a method for obtaining the grid potential and the developing bias potential from the contrast potential will be briefly described.

  FIG. 11 is a diagram showing the relationship between the grid potential and the surface potential of the photosensitive drum.

  The surface potential Vd when scanning is performed with the grid potential set to -300 V and the emission pulse level of the semiconductor laser is minimized, and the surface potential Vl when the emission pulse level of the semiconductor laser is maximized. It is measured by each surface electrometer (not shown) provided on the drum. Similarly, Vd and Vl when the grid potential is set to −700 V are measured by the surface potentiometers 101 to 104. By interpolating and extrapolating -300V data and -700V data, the relationship between the grid potential and the surface potential of the photosensitive drum can be obtained. Control for obtaining this potential data is referred to as potential measurement control.

  The development bias Vdc is set by providing a difference between the surface potential Vd when scanning is performed with the emission pulse level of the semiconductor laser being minimized and Vback (here, set to 150 V) set so that fog toner does not adhere to the image. . The contrast potential Vcont is a differential voltage between the development biases Vdc and Vl. As described above, the maximum density can be increased as the Vcont increases.

  In order to obtain the calculated contrast potential b, it is possible to calculate how many volts of grid potential and how many development bias potentials are necessary from the relationship shown in FIG.

  Here, the contrast potential is obtained so that the maximum density is 0.1 higher than the final target value, and the grid potential and the development bias potential are set so that the contrast potential can be obtained (step S712 in FIG. 7).

  FIG. 12 is a characteristic conversion chart showing characteristics for reproducing the density of an original.

In the figure, the I area shows the characteristics of the color sensor 71 in which the document density is converted into a density signal, and the II area shows the characteristics of the LUT 407 for converting the density signal into a laser output signal. A region III indicates the characteristics of the printer unit 418 that converts the laser output signal into the output density. Further, the above-mentioned control for setting the maximum density higher than the final target value causes the printer unit characteristic diagram in the region III to be as indicated by a solid line J.

  If such control is not performed, there is a possibility that the printer unit characteristic does not reach the target density 1.6 as indicated by the broken line H. In the case of the printer unit characteristic indicated by the broken line H, no matter how the LUT 407 is set, the LUT 407 does not have the ability to increase the maximum density, so that the density between the density DH and 1.6 cannot be reproduced. Become. The IV region shows the relationship between the document density and the recording density, and this characteristic represents the overall gradation characteristic in the image forming apparatus 1 according to the present embodiment.

  Hereinafter, the role of the LUT 407 and a method for correcting the gradation will be described.

As shown in FIG. 12, in this image forming apparatus, in order to make the gradation characteristic of the IV region linear, the portion of the recording characteristic of the printer unit 418 in the III region is bent.
It is corrected by. The LUT 407 can be easily created simply by switching the input / output relationship of the characteristics of the region III.

  In the present embodiment, since the number of gradations is processed by an 8-bit digital signal, it is 256 gradations.

  Next, similarly to the output density measurement test print, the pattern generator 410 outputs pattern data to the printer unit 418 to output a gradation measurement test print (step S713 in FIG. 8).

  Note that, when outputting a test print for gradation measurement, the LUT 407 is not operated and image formation is performed.

  As shown in FIG. 13, the test print for gradation measurement is composed of a gradation patch group of 64 gradations for each of the colors Y, M, C, and K. The 64-gradation patches here are 256 floors in total. Of these, the low density area is assigned with priority. By performing processing in this way, it is possible to satisfactorily adjust the gradation characteristics in the highlight portion.

  In FIG. 13, reference numeral 1301 denotes a patch having a resolution of 200 lpi (lines / inch), 1302 denotes a 400 lpi patch, and 1303 denotes a patch group. Forming an image of each resolution can be realized by preparing a plurality of triangular wave cycles used for comparison with image data to be processed in each color pulse width modulator.

  Note that the image forming apparatus 1 according to the present embodiment creates a gradation image with a resolution of 200 lpi and a line image of characters and the like with a resolution of 400 lpi. Although the same gradation level pattern is output at these two types of resolution, if the gradation characteristics differ greatly due to the difference in resolution, it is more preferable to set the previous gradation level according to the resolution. .

  The output test print for gradation measurement follows the same procedure as the above-described maximum density measurement method.

  The reading of the patch on the tone measurement test print by the color sensor 71 is the same as the reading of the patch on the density measurement test print described above (steps S714 to S722 in FIG. 8).

  The density value read and corrected by the color sensor 71 associates the laser output level with the gradation pattern creation position, and captures data indicating the relationship between the laser output level and the density into a memory (not shown).

At this stage, the characteristics of the printer unit 418 shown in the area III of FIG. 12 can be obtained, and the LUT 407 of the printer unit 418 can be determined by switching the input / output relationship of the printer unit characteristics. Are created and set (step S723 in FIG. 8). Thereafter, this processing operation is terminated.

  When obtaining the LUT 407 by calculation, there is only data for the number of gradation patterns of the patch pattern, so that there is a shortage in the middle so that the laser output level can correspond to all levels 0 to 255 of the density signal. Data is generated by performing interpolation.

  A linear gradation characteristic can be obtained by the control.

  Maximum density and gradation are corrected by the density / gradation CAL.

  In the electrophotographic image forming apparatus 1 according to the present embodiment, the maximum change in density and the change in gradation characteristics do not occur similarly.

  As described above, the target value of the final maximum density is set to 1.6, but the target value of the control for adjusting the maximum density is set to 1.7 in anticipation of a margin of 0.1. is there. Thus, for example, the maximum density is substantially controlled in the vicinity of the target value by environment control for setting Vcont or the like in a standard state according to another environment, toner density control of developer, or the like.

  However, in the long term, there is a mismatch with the above other controls due to the deterioration of developer durability, mechanical changes of various units involved in the image forming process, or replacement of the developer or other units. And the target maximum density cannot be obtained. In such a case, the correction of the maximum density is effective.

  Also, the above-described gradation characteristics change substantially stably due to the above-described other control, etc., but the change is acceptable depending on abrupt changes in the environment, changes in the sensitivity of the light attenuation characteristics of the photosensitive drum, and the like. Cases that exceed the range may occur in the relatively short term for changes in the maximum concentration.

  In particular, in a color image forming apparatus typified by the image forming apparatus 1 according to the present embodiment, even a slight change in gradation characteristics causes the gray balance to be lost, and depending on the intended use, the image quality is insufficient. It is possible that In such a case, gradation correction is effective.

  Here, color adjustment and gradation correction using the multi-order color CAL and density / gradation CAL are performed according to the user's operation, but the present invention is not limited to this, It may be configured to automatically execute at the timing. That is, if it is known in advance that the color reproducibility of the image forming apparatus 1 is considered to be unstable, the control for automatically executing the multi-color CAL and density / gradation CAL may be performed at that timing.

  There are various possible causes for color reproducibility, such as maintenance when only one unit is replaced, power on (ON) when the unit has not been used for a long time, and deterioration of developer durability. . Therefore, here, the multi-order color CAL is automatically executed under the following conditions.

(1) When the power is turned on (2) After the 100th sheet is output after the power is turned on,
(3) When opening and closing the front door,
(4) Every 1K after 40K,
The multi-color CAL timing in the image forming apparatus 1 according to the present embodiment is not limited to the above four.

  Thus, by providing in advance a condition that makes color reproducibility unstable and automatically controlling it, the user's hand is not bothered, and the image forming apparatus 1 with further usability is provided. Can do.

  As described above, according to the image forming apparatus 1 according to the present embodiment, excellent color reproducibility can be realized by reading the chromaticity and density of the patch formed on the recording material with the color sensor 71. It is possible to output a high-quality image with little difference in color reproducibility between image forming apparatuses and little variation in chromaticity over time over a long period of time.

[Other embodiments]
Note that the present invention can be applied to a system (for example, a copier, a facsimile machine, etc.) including a single device even when applied to a system including a plurality of devices (for example, a host computer, interface device, reader, printer, etc.). It may be applied.

  Another object of the present invention is to supply a storage medium (or recording medium) on which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or apparatus, and a computer (or CPU) of the system or apparatus Needless to say, this can also be achieved by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like is used. it can.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) or the like running on the computer based on an instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  In addition, after the program code read from the storage medium is written in the memory of the function expansion card inserted into the computer or the function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the card or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  Further, the present invention is not limited to these embodiments, and any configuration can be used as long as the functions shown in the claims or the functions of the configurations of the embodiments can be achieved. Is also applicable.

1 is a side sectional view showing a schematic internal configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a diagram illustrating a configuration around a color sensor in the image forming apparatus according to the first embodiment. It is a figure which shows the relationship between the wavelength of LED in the image forming apparatus which concerns on 1st Embodiment, and a sensitivity. 1 is a block diagram illustrating a configuration of an image forming apparatus according to a first embodiment. 6 is a flowchart showing a flow of profile creation processing operation by multi-order color CAL in the image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating an example of a test pattern on a test print measured by a color sensor in the image forming apparatus according to the first embodiment. 6 is a flowchart illustrating a flow of density / gradation CAL processing operations in the image forming apparatus according to the first embodiment. 6 is a flowchart illustrating a flow of density / gradation CAL processing operations in the image forming apparatus according to the first embodiment. It is a figure which shows an example of the test pattern used in the image forming apparatus which concerns on 1st Embodiment. FIG. 3 is a diagram illustrating a relationship between a surface potential of a relative photosensitive drum and an image density obtained by calculation in the image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating a relationship between a grid potential and a surface potential of a relative photosensitive drum in the image forming apparatus according to the first embodiment. 3 is a characteristic conversion chart showing characteristics of reproducing the density of an original in the image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating an example of a gradation measurement test print in the image forming apparatus according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 1a Photoconductor drum 1b Photoconductor drum 1c Photoconductor drum 1d Photoconductor drum 2a Developer 2b Developer 2c Developer 2d Developer 3 Transfer part 3a Transfer charger 3b Transfer charger 3c Transfer Charging device 3d Transfer charger 4a Cleaner 4b Cleaner 4c Cleaner 4d Cleaner 5 Fixing means 31 Transfer belt 51 Fixing roller 52 Pressure roller 53 Release agent supply application means 60 Temperature adjusting means 61 Paper feed cassette 61a Manual feed tray 61 62 Conveying belt 63 Application amount control means 64 Speed control means 71 Color sensor 201 LED (light emitting diode)
202 LED (light emitting diode)
203 LED (light emitting diode)
204 LED (light emitting diode)
205 LED (light emitting diode)
206 LED (light emitting diode)
207 LED (Light Emitting Diode)
208 LED (light emitting diode)
209 Imaging lens 210 Light-receiving part 211 Measurement aperture 211n Normal of measurement aperture 212 Patch (including image)
213 White plate 400 Image processing unit 401 External input I / F (interface)
402 Input ICC profile storage unit 403 CMM (color management module)
404 Output ICC profile storage unit 405 Spatial filter 406 Image memory 407 LUT (look-up table)
408 Color sensor input ICC profile storage unit 409 Profile creation unit 410 Pattern generator 411 Optical density conversion unit 412 Contrast potential control unit 413 LUT creation unit 414 A (analog) / D (digital) conversion unit 415 Sensor control unit 416 CPU (center) Processing equipment)
417 Operation unit 418 Printer unit 419 Light reception signal 419a Light reception signal 420 Image data 421 CMYK (Cyan Magenta Yellow Black) signal (data)
422 RGB signal (data)
423 L * a * b * signal (data)
424 CMYK signal (data)
425 L * a * b * signal (data)
426 L * a * b * signal (data)
427 L * a * b * signal (data)
428 Image signal 429 Image data 430 CMYK signal (data)
600 test print 601 test pattern 901 pattern 902 patch pattern 903 test pattern 1301 patch 1302 with resolution 200 lpi (lines / inch) patch 1303 with 400 lpi patch group

Claims (9)

In the image forming apparatus that corrects the image forming conditions according to the detection result of the output image,
Image forming means for forming the image on a recording material based on the image forming conditions;
Detecting means for detecting the image and outputting the detection result;
Conveying means for conveying the recording material from the image forming means to the detecting means;
Correction means for correcting the image forming conditions according to the detection result of the detection means,
The image forming means forms a color pattern image using one color material alone and a color pattern image combining two or more color materials using a plurality of color materials forming the image,
The detection means receives a plurality of light sources that emit detection light in a wavelength region in which a light absorption amount changes at a predetermined rate according to the pattern image, and receives reflected light from the pattern image of the detection light. An image forming apparatus comprising: a light receiving unit that outputs a detection result.   The detection means includes at least three light sources having peaks in each wavelength region of at least blue (B), green (G), and red (R), and a light receiving unit having sensitivity in all visible light regions. The image forming apparatus according to claim 1.   The correction unit includes a first correction unit that adjusts the image forming condition based on a detection result obtained by detecting the density of the color pattern image by the detection unit, and the chromaticity of the color pattern image and the color pattern image. The image forming apparatus according to claim 2, further comprising: a second correcting unit that adjusts the image forming condition based on the detected detection result.   When the chromaticity is detected by the detection unit, the plurality of light sources are sequentially emitted, and the color pattern image and reflected light from the color pattern image are received by the light receiving unit. Item 4. The image forming apparatus according to Item 3.   The second correction means has chromaticity calculation means for calculating a chromaticity value from the color pattern image and the detection result of the color pattern image, and creates a color conversion profile based on the calculation result of the chromaticity calculation means The image forming apparatus according to claim 4, wherein color conversion of an output image is performed using the color conversion profile. The image forming unit uses yellow (Y), magenta (M), cyan (C) or yellow (Y), magenta (M), cyan (C), and black (K) as the plurality of color materials. Forming the image,
When the chromaticity is detected by the detection means, detection light having the B, G, and R wavelength regions corresponding to the Y, M, and C color materials is emitted, and the color pattern image The image forming apparatus according to claim 3, wherein the reflected light is received by the light receiving unit.   When detecting the color pattern image formed with the K color material, the detecting means emits one of the plurality of light sources and receives the reflected light from the pattern image at the light receiving unit. The image forming apparatus according to claim 6.   The second correction means includes density calculation means for calculating a density value of the color pattern image, creates a density conversion table based on the calculation result of the density calculation means, and outputs the density conversion table using the density conversion table. 8. The image forming apparatus according to claim 6, wherein the image density and gradation characteristics are controlled. In the image forming method for correcting the image forming condition according to the detection result of the output image,
An image forming step of forming the image on a recording material based on the image forming conditions;
A detection step of detecting the image and outputting the detection result;
A conveying step of conveying the recording material from the image forming step to the detecting step;
A correction step of correcting the image forming conditions according to the detection result of the detection step,
The image forming step forms a color pattern image using a single color material alone using a plurality of color materials forming the image and a color pattern image combining two or more color materials,
The detecting step receives a plurality of light sources that emit detection light in a wavelength region in which light absorption changes at a predetermined rate according to the pattern image, and receives reflected light from the pattern image of the detection light, and An image forming method comprising: detecting using a light receiving unit that outputs a detection result.

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