JP2007292855A - Image correcting method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image correcting method which can precisely correct image forming conditions by forming a standard pattern matching the actual use and detecting the toner density, and to provide an image forming apparatus using this image correcting method. <P>SOLUTION: This image correcting method corrects images by detecting an amount of toner for the test pattern formed to correct the image on the photoreceptor drum 11. It formes a reference position mark 17d readable by the density sensor 1 on the toner image transfer surface 17c of the transfer belt 17, and detects the reflected light quantity with the sensor 1 all around the toner image transfer surface 17c to store as the base data to transfer the toner image. Then, it formes a test pattern at the position not synchronizing with the reference position mark 17d for the process control on the toner image transfer surface 17c, and corrects the amount of toner based on the reflected light quantity of the test pattern detected by the sensor 1 and the base data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image correction method and an image forming apparatus for correcting an image output by a copying machine, a facsimile, a printer, or the like.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, or a printer is required to have gradation reproducibility that faithfully reproduces gradation from highlight to shadow of a reproduced image. However, the gradation of the formed image fluctuates due to changes in the density of the toner that is the developer, changes in the setting conditions of the image forming process, and the like.

  Therefore, as a means for improving the gradation reproducibility, a method of performing gradation correction (γ correction) processing at a predetermined timing is adopted. This gradation correction process is for faithfully reproducing the gradation of an image to be a document, and is performed as follows.

  First, a plurality of test pattern (reference pattern) latent images corresponding to different predetermined densities are formed on the photosensitive member at predetermined intervals in the paper conveyance direction. Next, these test pattern latent images are developed in a state where the linear velocity of the developing roller is constant. Then, the toner density of each developed test pattern image is detected, and a gradation correction curve is created based on the detected toner density data.

  The current test pattern (gradation pattern) is usually composed of patches with different gradations of about 3 to 10, and the size of each patch is formed to some extent in consideration of machine fluctuations and the like. Yes.

  However, in such a conventional test pattern (reference pattern), density unevenness may occur in the patch due to mechanical variation or the like. For this reason, density measurement measures a certain area within the patch. For this reason, there are problems that it takes time to measure the density and the toner consumption is large.

  In view of this, an image forming apparatus is proposed in which the developing bias is continuously changed within one test pattern area to reduce the entire test pattern area, thereby reducing toner consumption and shortening the measurement time. (See Patent Document 1).

In this image forming apparatus, in order to avoid instability of the toner density when the developing bias is changed stepwise, the photosensitive member charging potential and the developing bias are continuously changed in the paper transport direction (main scanning direction). One test pattern with continuously changing gradation is created.
This achieves the above purpose, that is, reduction of toner consumption and measurement time.

Further, in order to perform more accurate image correction, there has been proposed an apparatus in which the toner density is corrected according to a partial density change on the surface of the image carrier on which the toner image is formed (Patent Document 2). reference).
Japanese Patent Application Laid-Open No. 8-21722 Japanese Patent Laid-Open No. 11-295941

  By the way, in the above-mentioned Patent Document 1, one test pattern with continuously changing gradation is created, and the density of this test pattern is measured to correct the image forming conditions.

However, when an image forming process is actually performed, the image forming apparatus does not change the photosensitive member charging potential or the developing bias to produce the image density, but the photosensitive member charging potential or the developing bias is fixed to an appropriate value. Then, the light and darkness of the image is obtained by the light amount control by the light writing means.
For this reason, there is a problem that even if the image forming conditions are corrected as in the above-mentioned Patent Document 1, it is not always possible to correct appropriately according to the actual use state.

  In Patent Document 2, the image forming conditions are corrected by measuring the density of the test pattern formed on the image carrier, but the toner image is indirectly transferred to the recording medium using an intermediate transfer member. In the case of an image forming apparatus configured to form, since the toner image formed on the image carrier is transferred to the recording medium via the intermediate transfer member, the toner adhesion amount transferred affects the intermediate transfer member. Therefore, there is a problem that it is difficult to perform image correction with high accuracy.

Further, in order to improve the accuracy of the conventional process control as described above, the surface of the image carrier before the test pattern formation is read with an optical reflection sensor for detecting the toner adhesion amount, and is used as the background data, and then the test is performed. There is a case where a method of removing the influence of the background by the background data is used for the toner adhesion amount data detected by reading the pattern.
Here, in order to avoid the problem that the detection system drifts due to the drift of the drive current of the LED of the illumination light source, and the background condition fluctuates depending on the position of the image carrier, the reflection sensor has background data when executing process control. And a test pattern is created at the position where the background data is read to detect the toner adhesion amount, and there is a problem that it takes time to move the image carrier one or more times.

  The present invention has been made in view of conventional problems, and it is possible to correct image forming conditions with high accuracy by creating a reference pattern in accordance with an actual use state and detecting toner density. An object of the present invention is to provide an image correction method and an image forming apparatus that implements the image correction method.

An image correction method according to the present invention for solving the above-described problems and an image forming apparatus that implements the image correction method are as follows.
The image correction method according to claim 1, wherein the image carrier is uniformly charged and then exposed to form an electrostatic latent image, and toner is attached to the electrostatic latent image on the image carrier by a developing device. The image is formed by developing, and an electrostatic latent image of a reference pattern is formed with toner on the image carrier, the reference pattern is developed by the developing device, and the developed reference pattern is attached to the toner. In an image correction method for detecting an amount and correcting an image based on a detection result of the toner adhesion amount, toner on an endless intermediate transfer body onto which a toner image formed on the image carrier is temporarily transferred A reference position mark detectable by a reflection sensor is formed on the image transfer surface, and the toner image is transferred by detecting the amount of reflected light on the toner image transfer surface by the reflection sensor over the entire circumference of the toner image transfer surface. Save as background data A reference pattern for process control is formed at a position asynchronous with the reference position mark on the toner image transfer surface, and the toner adhesion amount is corrected based on the amount of reflected light of the reference pattern detected by the reflection sensor and the background data. It is characterized by doing.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the reference sensor is used as a reference pattern expressed by gradation with black toner, and the reflection sensor is used to detect regular reflection. This is a specular reflection sensor.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the invention, the amount of reflected light on the toner image transfer surface by the reflection sensor is detected during warm-up after the power is turned on. It is characterized by.

  According to a fourth aspect of the present invention, there is provided an image bearing member on which an electrostatic latent image is formed after being uniformly charged and then exposed, and a toner attached to the electrostatic latent image on the image bearing member. A developing device that forms an image, a reference pattern writing unit that forms an electrostatic latent image of a reference pattern on the image carrier, and an endless shape to which a toner image formed on the image carrier is temporarily transferred An image correction method comprising: an intermediate transfer member; and a toner density detecting unit that detects a toner density of a reference pattern visualized by toner in the developing device, and performing image correction based on a detection result by the toner density detecting unit 4. The image forming apparatus according to claim 1, wherein a specular reflection sensor is used as the toner density detection unit, and the image correction method according to claim 1 is performed as the image correction method. Be Than is.

  According to the first aspect of the present invention, the image carrier is uniformly charged and then exposed to form an electrostatic latent image, and toner is attached to the electrostatic latent image on the image carrier by a developing device. The image is formed by developing, and an electrostatic latent image of a reference pattern is formed with toner on the image carrier, the reference pattern is developed by the developing device, and the developed reference pattern is attached to the toner. In an image correction method for detecting an amount and correcting an image based on a detection result of the toner adhesion amount, toner on an endless intermediate transfer body onto which a toner image formed on the image carrier is temporarily transferred A reference position mark detectable by a reflection sensor is formed on the image transfer surface, and the toner image is transferred by detecting the amount of reflected light on the toner image transfer surface by the reflection sensor over the entire circumference of the toner image transfer surface. Save as background data, A reference pattern for process control is formed at a position asynchronous with the reference position mark on the toner image transfer surface, and the toner adhesion amount is corrected based on the reflected light amount of the reference pattern detected by the reflection sensor and the background data. As a result, the toner image immediately before transfer to the recording medium, that is, the reference pattern on the intermediate transfer member is detected to correct the toner adhesion amount, so that the toner density in accordance with the actual use state can be obtained. Therefore, it is possible to realize correction of image forming conditions with high accuracy.

Moreover, according to the invention of Claim 2 and 3, in addition to the said common effect obtained by the invention of Claim 1, the following effect can be acquired.
That is, according to the second aspect of the present invention, the reference pattern is a reference pattern expressed by gradation with black toner, and the reflection sensor is a regular reflection sensor that detects regular reflection. Even when the printing process speed, for example, the printing speed for monochrome image output and the printing speed for color image output are different, the optimum image forming conditions can be corrected according to the printing process speed.

  According to the third aspect of the present invention, in addition to the effect obtained by the first or second aspect of the invention, the reflection sensor detects the amount of reflected light on the toner image transfer surface during warm-up after turning on the power. By doing so, the image correction can be performed efficiently by effectively utilizing the operation time at the start of the apparatus.

  According to the fourth aspect of the present invention, the toner is attached to the image carrier on which the electrostatic latent image is formed by being uniformly charged and then exposed to light, and the electrostatic latent image on the image carrier. A developing device that visualizes the image, a reference pattern writing unit that forms an electrostatic latent image of a reference pattern on the image carrier, and an endless image on which the toner image formed on the image carrier is temporarily transferred An intermediate transfer member, and a toner concentration detection unit that detects the toner concentration of a reference pattern developed with toner by the developing device, and performs image correction based on the detection result of the toner concentration detection unit In the image forming apparatus that performs the correction method, a regular reflection sensor is used as the toner density detection unit, and the image correction method according to any one of claims 1 to 3 is performed as the image correction method. And record Highly accurate image formation because the toner image just before transferring to the body, that is, the reference pattern on the intermediate transfer body can be detected to correct the toner adhesion amount and obtain the toner density according to the actual use state An image forming apparatus capable of outputting a high-quality image by correcting the conditions can be realized.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing the configuration of an image forming unit of a digital color copying machine which is an image forming apparatus in which the image correction method of the present invention is executed.
It should be noted that the present invention can be similarly applied to other image forming apparatuses such as printers and facsimile apparatuses that perform electrophotographic image formation other than digital color copying machines.

  The digital color copying machine reads a color image from an original in a scanner unit, performs predetermined image processing, supplies it to the image forming unit 10 as image data, and reproduces the color image read from the original on a recording medium such as paper. To do.

  The image forming unit 10 of the digital color copying machine includes a transfer conveyance belt (intermediate transfer member) 17 that is stretched in a state where a horizontal portion is formed between two rollers 17a and 17b and rotates in the direction of arrow A. ing. The transfer conveyance belt 17 conveys the sheet placed on the upper surface while sequentially facing the plurality of image forming stations 10a to 10d by rotation in the arrow A direction while being positioned in the upper horizontal portion. Each of the image forming stations 10a to 10d performs electrophotographic image formation using toner of three primary colors (cyan, magenta, and yellow) of black and subtractive color mixture.

  The transfer conveyance belt 17 faces the density detection sensor (reflection sensor) 1 while being positioned in the lower horizontal portion. Further, a reference position mark 17d that can be detected by the density detection sensor 1 is formed in one portion on a part of the toner image transfer surface 17c on which the toner image is formed on the transfer conveyance belt 17.

  Further, a fixing device 18 is disposed on the downstream side of one roller 17 a of the transfer conveyance belt 17. The fixing device 18 includes a pair of rollers, and heats and pressurizes the paper that has passed through each of the image forming stations 10a to 10d, and melts and fixes the toner image transferred on the paper to the surface of the paper.

  Each of the image forming stations 10a to 10d has the same configuration except for the toner storage amount. As an example, the image forming station 10a includes a charger 12a, an exposure unit 13a, a developing unit 14a, a transfer unit around a photosensitive drum 11a that rotates in the direction of arrow B by forming a photosensitive layer on the surface of a cylindrical conductive substrate. The container 15a and the cleaner 16a are arranged in this order.

The charger 12a uniformly charges the surface of the photosensitive drum 11a with a predetermined polarity.
The exposure unit 13a exposes the surface of the photosensitive drum 11a with image light to form an electrostatic latent image.
The developing unit 14a supplies the toner stored therein to the surface of the photosensitive drum 11a, and visualizes the electrostatic latent image into a toner image.
The transfer unit 15 a faces the peripheral surface of the photosensitive drum 11 a with the transfer conveyance belt 17 interposed therebetween, and a toner image carried on the surface of the photosensitive drum 11 a is transferred to a sheet of paper placed on the transfer conveyance belt 17. Transfer to the surface.
The cleaner 16 removes the toner remaining on the peripheral surface of the photosensitive drum 11a after the transfer process.

  The developing unit 14a includes a developing roller (not shown) that rotates to face the peripheral surface of the photosensitive drum 11a. The developing roller supplies toner carried on the surface by rotation to the peripheral surface of the photosensitive drum 11a. By changing the peripheral speed of the developing roller, that is, the rotational speed, the amount of toner supplied to the peripheral surface of the photosensitive drum 11a can be increased or decreased, and the density of the toner image can be adjusted.

  Each of the exposure units 12a to 12d provided in the image forming stations 10a to 10d is supplied with image data of each color of black, cyan, magenta and yellow, and each of the developing units 14a to 14d is black, cyan. , Magenta and yellow toners are stored. Accordingly, in each of the image forming stations 10a to 10d, black, cyan, magenta, and yellow toner images are sequentially transferred onto the paper, and full color is obtained by subtractive color mixing of the toner images of each color on the paper that has passed through the fixing device 18. An image is formed.

  The density detection sensor 1 includes a light emitting element 2 and a light receiving element 3, and a toner image transfer surface of a transfer conveyance belt 17 on which a correction test pattern (reference pattern) is formed with black toner formed during image correction processing described later. The surface of 17c is irradiated with light from the light emitting element 2, and the reflected light that is specularly reflected is received by the light receiving element 3, and an electrical signal corresponding to the amount of received light is output as a toner density detection signal.

  The correction test pattern formed on the surface of the transfer conveyance belt 17 is removed from the surface of the transfer conveyance belt 17 by a cleaning unit (not shown) after facing the density detection sensor 1.

  Further, in each of the image forming stations 10a to 10d, the density detection sensor 1 is disposed at a position facing the surface of the photosensitive drum 11 after the development process is completed, and the correction test pattern before being transferred to the transfer conveyance belt 17 is displayed. The present invention can be similarly implemented when detecting the concentration.

  In this embodiment, the density detection sensor 1 receives (detects) reflected light in a state where no toner image is formed on the toner image transfer surface 17c of the transfer conveyance belt 17, and the detected toner image transfer surface 17c. Is stored in the image data input unit 40 as background data.

Next, an image processing unit constituting the digital color copying machine according to the present embodiment will be described with reference to the drawings.
FIG. 2 is a block diagram showing the configuration of the image processing unit of the digital color copying machine according to this embodiment.

  The image processing unit 20 of the digital color copying machine includes an image data input unit 40, an image data processing unit 41, an image data output unit 42, a gradation correction unit 46, a density recognition unit 47, a memory 49, and a CPU 44.

The image data input unit 40 converts the read signals for the three additive primary colors (RGB system) read from the color image of the document by the scanner unit into digital data.
The image data processing unit 41 generates subtractive mixed three primary colors and black (YMCK) image data from RGB image data, and performs zoom processing and the like according to the set copy magnification.

The gradation correction unit 46 performs gradation correction processing described later on the YMCK image data.
The image data output unit 42 outputs drive data generated based on the YMCK image data subjected to the gradation correction processing to the exposure units 13a to 13d.

  The memory 49 stores data for forming test patterns (correction test patterns (reference patterns) and preliminary test patterns, which will be described later) on the surface of the transfer conveyance belt 17 during image correction processing which will be described later. This data is supplied to the image data output unit 42 by the CPU 44 during the image forming process. The density recognition unit 47 recognizes the density signal output from the density detection sensor 1.

  The operation of each unit in the image processing unit 20 is controlled by the CPU 44 in an integrated manner. The CPU 44 controls the operation of the photosensitive drum 11 and the like in the image forming unit 10 in synchronization with the operation of the image data output unit 42. Further, the CPU 44 optimizes the correction condition in the gradation correction unit 46 and the process condition in the image forming unit 10 based on the density signal of the test pattern for correction recognized by the density recognition unit 47 during the image correction process. .

  With the above configuration, when the copy image or the correction test pattern is formed in the image forming unit 10, in order to reproduce the density of the image according to the image data, the circumference of the photosensitive drum 11 is passed through the exposure unit 13. It is necessary to form an electrostatic latent image that reproduces the density of image data on the surface. As the method, there are a pulse width modulation (PWM) method, a power modulation method, an area gradation method (dithering), and the like.

In the pulse width modulation method, the on / off time (pulse width) of the laser beam emitted from the exposure unit 13 is controlled according to the image density.
In the power modulation method, the intensity of the laser beam emitted from the exposure unit 13 is controlled in accordance with the image density. The area gradation method is a method in which black and white is generated based on a certain rule according to the gradation of pixels of the original image, and halftones are expressed by the appearance frequency of black and white.

In the image data input unit 40, high density correction processing and gradation correction processing are sequentially performed on each of the YMCK image data during the image correction processing.
Hereinafter, each correction process will be described.

  Here, as shown in FIG. 2, data input from the image data input unit 40 to the gradation correction unit 46 via the image data processing unit 41 is image input data, and from the gradation correction unit 46 to the image data output unit. The data output to 42 is image output data, and when the correction test pattern is formed, the data read from the memory 49 by the CPU 44 and supplied to the image data output unit 42 is recognized by the test pattern data and density recognition unit 47. The obtained data is referred to as detection data.

First, a reference example of high density correction processing in the digital color copying machine according to the present embodiment will be described.
The high density correction process is performed in order to suppress fluctuations in the overall density of the image to be subjected to the image forming process. In the high density correction process, the test pattern data for forming one test pattern (preliminary test pattern) whose gradation changes continuously among the test pattern data stored in the memory 49 is displayed by the CPU 44. It is read out and supplied to the image data output unit 42. As a result, one test pattern that changes in a series from high density to low density is formed on the surface of each of the photosensitive drums 11a to 11d.

  For each electrostatic latent image formed for each of the photosensitive drums 11a to 11d in this way, the CPU 44 rotates the developing rollers in the developing units 14a to 14d at different rotational speeds so that a visible image appears on the toner image. Turn into. Therefore, the electrostatic latent images formed on the surfaces of the photosensitive drums 11a to 11d under the same exposure conditions are developed with different toner densities.

  The test pattern toner images formed on the surfaces of the photoconductor drums 11a to 11d are transferred to the surface of the transfer and transport belt 17 by the transfer units 15a to 15d, and then the toner density is detected by the density detection sensor 1 to recognize the density. The detected toner density is recognized by the unit 47. The CPU 44 compares the target value of the toner density for the high-density test pattern stored in advance in the memory 49 with the toner density recognized from the correction test pattern actually formed by the density recognition unit 44, and sets the target value. The developing condition (rotational speed of the developing roller) of the correction test pattern in which the toner density closest to is detected is set as the developing condition in the subsequent image forming process.

Here, high density correction using the correction test pattern in the present embodiment will be described with reference to the drawings.
FIG. 3A is an explanatory view showing a correction test pattern formed in the image forming unit of the digital color copying machine according to the present embodiment, and FIG. 3B is a sensor of a density detection sensor for detecting the correction test pattern. It is a graph which shows the relationship between an output and developing bias potential.

  As an example, as shown in FIG. 3A, first, the laser PWM duty is fixed to 100%, the grid voltage (Vg) is fixed to −600V, and the developing bias (Vb) is −275V, −325V, − Switching to 375 V, correction test patterns TP1, TP2, and TP3 with three black toners are created.

  Then, the reflected light (regular reflected light) of the respective correction test patterns TP1, TP2, and TP3 is read by the density detection sensor 1, and the reflected light detected by the density detection sensor 1 is read as shown in FIG. The sensor outputs I1, 12, and 13 based on the amount of light are plotted on a graph showing the relationship between the sensor output (Is) and the developing bias potential (Vb), and are connected by a straight line.

  Then, a linear approximation expression of the sensor output of the density detection sensor 1 corresponding to the straight line L1 and the development bias potential is derived, and from this, the development bias Vb0 that obtains the sensor output I0 that becomes the reference toner density is obtained. Then, the developing bias is set to Vb0 (for example, −310 V), and the developing bias correction is completed.

  Here, when the potential difference between the developing potential difference (cleaning field) and the grid electrode bias Vg and the developing bias Vb0 for preventing toner fogging on the white background is smaller than 150V and Vg−Vd0> −150V, Vg = Vd0−150V. Change to finish high density correction.

  In this way, when the next high density correction is performed, three correction test patterns of Vb0 + 50V, Vb0, Vb0-50V are created on the basis of the developing bias Vb0 obtained immediately before, and the above-described correction pattern is generated. The development bias is corrected in the same manner as the contents.

Next, gradation correction processing in the digital color copying machine according to the present embodiment will be described.
The gradation correction process is performed in order to faithfully reproduce the gradation of the original image in the copy image by suppressing the variation in gradation of the toner image.
In the gradation correction process, the CPU 44 reads out data for forming a plurality of test patterns (correction test patterns) having different gradations from the test pattern data stored in the memory 49, and the image data output unit 42. To supply. Thereby, electrostatic latent images of a test pattern for correction in which the PWM duty of the laser diode is switched are formed on the photosensitive drums 11a to 11d.

The CPU 44 develops the electrostatic latent images of the correction test patterns formed on the photoconductor drums 11a to 11d in this manner under the preset development conditions (rotation speed of the development roller).
The toner image of the test pattern for correction formed on each of the photosensitive drums 11a to 11d is transferred to the surface of the transfer conveyance belt 17 by the transfer units 15a to 15d, and then the toner by the density detection sensor 1 and the density recognition unit 47. Receives concentration detection and recognition.

  The CPU 44 compares the target density of the gradation test pattern stored in advance in the memory 49 with the toner density recognized from the correction test pattern actually formed by the density recognition unit 47, and based on the comparison result. Create a tone correction table.

  Here, the gradation correction table is a reference for performing appropriate gradation correction in the gradation correction unit 46 on the image input data, and the image input data and the image output data are one-to-one. It corresponds to.

  In the present embodiment, as shown in FIG. 4B, the gradation correction table (number of gradations-laser PWM duty table) A has a horizontal axis as the density of image input data (input gradation data) and a vertical axis. It is expressed as a curve on the coordinates with the density of the image output data (specifically, the laser PWM duty of the exposure unit). The tone correction table A is stored in the memory 49 as a look-up table, and is corrected renewably in, for example, halftone process control. The halftone process control is a well-known technique (see, for example, Japanese Patent Application Laid-Open No. 2001-309178), and thus detailed description thereof is omitted here.

Here, gradation correction using the correction test pattern in the present embodiment will be described with reference to the drawings.
FIG. 4A is an explanatory view showing a correction test pattern formed by the image forming unit according to the present embodiment, and FIG. 4B is a graph showing the relationship between the number of gradations of the correction test pattern and the laser PWM duty. It is.

  As an example, referring to a gradation correction table (number of gradations-laser PWM duty table) A shown in FIG. 4B, as shown in FIG. 4A, for example, steps from gradation numbers D1 to D16 are performed. Test patterns TP101 to TP116 for correction using black toner that changes with time are created.

  Then, the density detection sensor 1 reads the reflected light (regular reflection light) of the respective correction test patterns TP101 to TP116, and sensor outputs I101, I102... I116 based on the amount of reflected light detected by the density detection sensor 1. Each toner density (toner adhesion amount) is measured based on the above.

  Then, a gradation correction table (number of gradations—laser PWM duty table) B is obtained as shown in FIG. 4B by connecting 16 measurement points by the correction test patterns TP101 to TP116 with lines. When the next gradation correction process is performed, the gradation correction table B obtained this time is used as the next correction table A.

Next, image correction in the digital color copying machine according to the present embodiment will be described with reference to a flowchart.
FIG. 5 is a flowchart showing a procedure for performing image correction in the digital color copying machine according to the embodiment.

The process control in the following description means the high density correction in the present embodiment described with reference to FIG. 3 and the gradation correction table update process described with reference to FIG. 4. It is preferable to update the gradation correction table after the value is fixed. Further, depending on the process control repetition interval, the update of the high density value or the gradation correction table may be omitted.
In the flowchart of FIG. 5, process control is abbreviated as “procone”.

In the present embodiment, the printing process speed is set at a high speed VH of 350 mm / sec during mono black printing, and at a medium speed VM of 225 mm / sec during full color printing.
As shown in FIG. 5, in the image correction in the present embodiment, when the power is turned on (step S1), the printing process speed is executed at the medium speed VM (step S2), and then the high speed is set. A process control in VH is performed (step S3), and a difference table between image correction tables at high speed VH and medium speed VM is created (step S4).

  If there is a print request from the outside or the user, an image output process is performed (step S5), and if there is no print request, the process returns to step S2.

  In step S5, image output processing has been performed, whether the total number of prints has exceeded 100 sheets (step S6), whether the temperature change has exceeded 5 ° C. (step S7), or has the humidity change exceeded 5% (step S7). If step S8) is determined and each exceeds a predetermined numerical value, the process proceeds to step S9 to confirm the print request.

  On the other hand, if each of the steps S6, S7, S8 has not reached the predetermined numerical value, the process returns to step S5 to confirm the print request again.

  In step S9, if there is a print request at the high-speed VH repeatedly at the print process speed, the process control at the high-speed VH is performed (step S10), and the print request (request JOB) is processed based on the created image correction table. (Step S11). Then, an image correction table for the medium speed VM is created based on the image correction table for the high speed VH (step S12).

  On the other hand, if the print process speed is not a print request at the high speed VH in step S9, the process control at the medium speed VM is performed (step S13), and the print request is processed based on the created image correction table (step S14). ). Then, an image correction table at high speed VH is created based on the image correction table at medium speed VM (step S15).

  The image correction table TBM at the medium speed VM and the image correction table TBH at the high speed VH are obtained from the image correction table TBM at the medium speed VM and the image correction table TBH at the high speed VH, as shown in part C of FIG. The conversion table TBO is created based on the image correction table at the opposite process speed.

Further, in the present embodiment, image correction is performed based on the background data of the toner image transfer surface 17c of the transfer conveyance belt 17 detected by the density detection sensor 1.
The characteristic image correction method of the present invention based on the background data on the toner image transfer surface 17c of the transfer conveyance belt 17 in the digital color copying machine will be described below with reference to flowcharts.
FIG. 6 is a flowchart showing a procedure for performing image correction based on the background data on the toner image transfer surface of the transfer conveyance belt constituting the digital color copying machine according to the embodiment.

The image correction based on the background data of the transfer conveyance belt 17 in this embodiment is 1 over the entire circumference of the transfer conveyance belt 17 by the density detection sensor 1 when the power is turned on (step S21) as shown in FIG. The background data of the toner image transfer surface 17c for a week, that is, the amount of reflected light from the toner image transfer surface 17c in a state where the toner image is not transferred, is detected and stored as background data in the image data input unit 40 (step S22). ).
Detection of background data on the toner image transfer surface 17c by the density detection sensor 1 is performed during warm-up during the preparation operation of the apparatus.

  Then, the conveyance of the transfer conveyance belt 17 is stopped (step S23), and the stop timing of the transfer conveyance belt 17 at this time is stored (step S24). This stop timing is calculated from the position data of the reference position mark 17d. Then, a process control for image correction is performed (step S25).

  First, the background data of the toner image transfer surface 17c detected by the density detection sensor 1 at an arbitrary timing T1 is set as U1 (step S26), and the corresponding background data, that is, detected by the density detection sensor 1 and stored. The background data U0 at the arbitrary timing T1 in the background data is read (step S27), and a background correction coefficient α (α = U1 / U0) for correcting the background data is determined (step S28).

  Then, a correction test pattern (reference pattern) for measuring the toner adhesion amount at any timing Tn (arbitrary position Pn on the transfer conveyance belt 17) without adjusting the timing with respect to the timing T1 is created, and the density The reflected light amount In of the correction test pattern created at an arbitrary timing Tn is detected by the detection sensor 1 (step S29). Of the stored background data, the background data Un at an arbitrary timing Tn when the correction test pattern is generated is read, and the background data Un is multiplied by the background correction coefficient α to obtain the background data correction value Un ′ (Un ′ = Un • Find α). (Step S30).

  Then, the reflected light amount In ′ (In ′ = In / Un ′) of the test pattern for correction from which the influence of the background (toner image transfer surface 17c) is removed, and an image correction table is created based on the corrected reflected light amount In ′. Then, image correction is performed based on the created image correction table (step S31).

As described above, according to the present embodiment, as an image correction method, the reflected light from the toner image transfer surface 17c of the transfer conveyance belt 17 is detected by the density detection sensor 1 and is applied to the toner image transfer surface 17c as background data. Since the toner adhesion amount of the transferred correction test pattern is corrected based on the background data, the correction test pattern corrected without affecting the surface state (reflection state) of the toner image transfer surface 17c is highly accurate. Image correction can be performed.
By adopting the above-described image correction method in a digital color copying machine, high-quality image output can be realized.

In addition, according to the present embodiment, the reference pattern expressed by gradation with black toner is formed as the correction test pattern, and the regular reflection sensor is used as the density detection sensor 1 for reading the correction test pattern. Even when image formation is performed at a plurality of process speeds during mono black printing and during medium-speed full-color printing, high-accuracy image correction can be performed using a test pattern for correction corresponding to each process speed.
Note that the processing for removing the background influence in the present embodiment is effective for both the high density correction processing and the gradation correction processing.

1 is a schematic diagram illustrating a configuration of an image forming unit of a digital color copying machine which is an image forming apparatus in which an image correction method of the present invention is executed. FIG. 2 is a block diagram showing a configuration of an image processing unit of the digital color copying machine. (A) is an explanatory view showing a test pattern for correction formed in the image forming unit of the digital color copying machine, and (b) is a diagram showing the relationship between the sensor output of the density detection sensor for detecting the test pattern for correction and the developing bias potential. It is a graph to show. (A) is explanatory drawing which shows the test pattern for correction | amendment formed in the image formation part which concerns on this embodiment, (b) is a graph which shows the relationship between the number of gradations of the said test pattern for correction | amendment, and a laser PWM duty. 3 is a flowchart showing a procedure for performing image correction in the digital color copying machine. 3 is a flowchart showing a procedure for performing image correction based on background data on a toner image transfer surface of a transfer conveyance belt constituting the digital color copying machine.

Explanation of symbols

1 Concentration detection sensor (reflection sensor)
2 Light emitting element 3 Light receiving element 10 Image forming unit 10a to 10d Image forming station 11, 11a to 11d Photosensitive drum (image carrier)
14a Development unit (developing device)
17 transfer conveyance belt 17c toner image transfer surface 17d reference position mark 40 image data input unit 41 image data processing unit 42 image data output unit 44 density recognition unit 46 gradation correction unit 47 density recognition unit 49 memory Is, I0, I1, 12 , 13, I101 to I116 Sensor output TB0 conversion table TBH Image correction table TBM Image correction table TP1, TP2, TP3
TP101 to TP116 Correction test pattern (reference pattern)
Vb, Vb0 Development bias VH High speed VM Medium speed

Claims (4)

The image carrier is uniformly charged and then exposed to form an electrostatic latent image, and a developing device is used to create an image by attaching toner to the electrostatic latent image on the image carrier and developing it. Forming an electrostatic latent image of a reference pattern with toner on the image carrier, developing the reference pattern with the developing device, detecting the toner adhesion amount of the developed reference pattern, and detecting the toner adhesion amount In an image correction method for performing image correction based on a result,
Forming a reference position mark detectable by a reflection sensor on a toner image transfer surface of an endless intermediate transfer member to which a toner image formed on the image carrier is temporarily transferred;
The reflected light amount of the toner image transfer surface is detected by the reflection sensor over the entire circumference of the toner image transfer surface and stored as background data on which the toner image is transferred.
Forming a reference pattern for process control at a position asynchronous with the reference position mark on the toner image transfer surface;
An image correction method for correcting a toner adhesion amount based on a reflected light amount of the reference pattern detected by the reflection sensor and the background data. The reference pattern is a reference pattern expressed in gradation by black toner,
The image correction method according to claim 1, wherein the reflection sensor is a regular reflection sensor that detects regular reflection.   3. The image correction method according to claim 1, wherein the amount of reflected light on the toner image transfer surface by the reflection sensor is detected during warm-up after power-on. 4. An image carrier on which an electrostatic latent image is formed by being uniformly charged and then exposed, a developing device for developing toner by attaching toner to the electrostatic latent image on the image carrier, and the image carrier A reference pattern writing unit for forming an electrostatic latent image of a reference pattern thereon, an endless intermediate transfer member onto which a toner image formed on the image carrier is temporarily transferred, and toner in the developing device In an image forming apparatus, comprising: a toner density detecting unit that detects a toner density of a visualized reference pattern, and performing an image correction method that performs image correction based on a detection result by the toner density detecting unit;
A reflection sensor is used as the toner concentration detection means,
An image forming apparatus, wherein the image correcting method according to claim 1 is performed as the image correcting method.

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