JP2007286460A - Image correction method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image correction method capable of highly accurately correcting an image forming condition, reducing a time required for a process control, and suppressing the wearing of the surface of an image carrier, and to provide an image forming apparatus implementing the image correction method. <P>SOLUTION: Regarding the image correction method for detecting an amount of toner sticking to a reference pattern on a photoreceptor drum 11 and correcting the image formed at a plurality of process velocities, regular-reflected light from the reference pattern formed at the middle velocity VM is detected by a density detection sensor 1, and the amount of sticking toner is calculated based on the light quantity of the reflected light detected by the density detection sensor 1, and a density correction table TBM for the middle velocity VM is formed, and when the images are repeatedly formed at the high velocity VH, a density correction table is formed in accordance with the process velocity, and the density correction table TBM for the middle velocity VM is converted based on the density correction table TBH for the high velocity VH, and the density correction table TBM for the middle velocity VM is corrected. <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 fluctuations, etc., and therefore density measurement measures a certain region in 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 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 (sub-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.
Japanese Patent Application Laid-Open No. 8-21722

  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.

  Further, even if the conventional image forming apparatus has a plurality of process speeds, process control is performed at a predetermined process speed. For example, at a low speed (during full color printing). In an apparatus that performs process control, when operating at a high speed (during monochrome printing), it is necessary to reduce the process speed in order to perform process control. As a result, the time required for the process control becomes longer, and further, there is a problem that the surface of the photoreceptor is worn (slip) due to idling of the photoreceptor.

  The present invention has been made in view of the conventional problems, and by creating a reference pattern in accordance with an actual use state and detecting the toner density, the image forming conditions can be corrected with high accuracy. An object of the present invention is to provide an image correction method capable of reducing the time required for process control and suppressing the wear (film slippage) of the surface of the image carrier, and an image forming apparatus for executing the image correction method. And

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 created at a plurality of process speeds based on a detection result of the toner adhesion amount, the reference pattern is a plurality of reference patterns having different toner adhesion amounts depending on black toner. The reflected light regularly reflected by the reference pattern created at a predetermined process speed is detected by the regular reflection sensor, and the reference pattern is determined based on the amount of the reflected light detected by the regular reflection sensor. The toner adhesion amount is calculated to create density correction data at a predetermined process speed, and when image formation is repeatedly performed at a process speed different from the predetermined process speed, density correction data is generated according to different process speeds, The density correction data at the predetermined process speed is converted and corrected based on the density correction data at the different process speed.

  The plurality of process speeds in the present invention include a process speed during monochrome printing and a process speed during full-color printing.

  In the present invention, for example, when a predetermined process speed is a process speed for monochrome printing, a different process speed may be a process speed for full-color printing. Further, the process speed for monochrome printing and the process speed for full color printing described above may be reversed.

  An image forming apparatus according to a second aspect of the present invention includes an image carrier 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 carrier. 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 a toner density that detects the toner density of the reference pattern visualized by toner in the developing device A regular reflection sensor as the toner concentration detecting means in an image forming apparatus for performing an image correction method for correcting an image formed at a plurality of process speeds based on detection results by the toner concentration detecting means. The image correction method according to claim 1 is performed as the image correction method.

  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 created at a plurality of process speeds based on a detection result of the toner adhesion amount, the reference pattern is a plurality of reference patterns having different toner adhesion amounts depending on black toner. The reflected light specularly reflected by the reference pattern created at a predetermined process speed is detected by the regular reflection sensor, and the reference pattern is based on the amount of reflected light detected by the regular reflection sensor. A toner correction amount is calculated to create density correction data at a predetermined process speed. When repeated image formation is performed at a process speed different from the predetermined process speed, density correction data is generated according to different process speeds. By converting and correcting the density correction data of the predetermined process speed based on the density correction data of different process speeds, it is possible to perform high-accuracy correction according to the actual use state and a plurality of processes. Even when an image is formed at a high speed, the image correction data is generated by feeding back the image correction data according to each process speed, so that the process control (image quality adjustment) corresponding to the process speed is applied each time the process speed is changed. Reduces time and eliminates idling of the image carrier, and wear of the surface of the image carrier (film slippage) It can be suppressed.

  According to the second 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 for visualizing the image, reference pattern writing means for forming an electrostatic latent image of the reference pattern on the image carrier, and detecting the toner density of the reference pattern visualized with toner by the developing device. In the image forming apparatus for performing an image correction method for correcting an image formed at a plurality of process speeds based on detection results by the toner density detection unit, the toner density detection unit is a positive toner density detection unit. By using a reflection sensor and performing the image correction method according to claim 1 as the image correction method, it is possible to obtain a toner density according to an actual use state, so that high-precision image formation is achieved. High-quality image output is possible by correcting the number of processes, and even if images are formed at multiple process speeds, the process speed can be reduced by creating image correction data by feeding back image correction data at each process speed. Each time it is changed, the time required for process control (image quality adjustment) corresponding to the process speed can be reduced, and the wear of the surface of the image carrier (film slippage) can be suppressed by eliminating idling of the image carrier. An image forming apparatus 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 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. 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.

  Further, the transfer conveyance belt 17 faces the density detection sensor (regular reflection sensor) 1 while being positioned in the lower horizontal portion. 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 the light emitting element is formed on the surface of the transfer conveyance belt 17 on which a correction test pattern (reference pattern) is formed with black toner formed at the time of image correction processing described later. 2 is irradiated with light, and the regularly reflected reflected light is received by the light receiving element 3, and an electric 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.

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. Furthermore, the CPU 44 corrects the gradation correction unit 46 and the process conditions in the image forming unit 10 based on the density signal of the test pattern (correction test pattern) recognized by the density recognition unit 47 during the image correction process. To optimize.

With the above configuration, when reproducing a copy image or a test pattern in the image forming unit 10, in order to reproduce the density of the image according to the image data, the peripheral surface of the photosensitive drum 11 is provided via the exposure unit 13. It is necessary to form an electrostatic latent image that reproduces the density of image data. 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 processing 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 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 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 development potential difference (cleaning field) and the grid electrode bias Vg and the development bias Vb0 is less than 150V to prevent toner fogging on the white background, Vg = Vb0-150V when Vg−Vb0> −150V. Change to finish high density correction.

  Thus, when the next high density correction is performed, three test patterns of Vb0 + 50V, Vb0, Vb0-50V are created based on the development bias Vb0 obtained immediately before, and the above-described contents are obtained. Similarly, development bias correction is performed.

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 this embodiment, the printing process speed is set at a high speed VH of 350 mm / sec during monochrome 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.

  As described above, according to this embodiment, even when an image is formed at a plurality of process speeds during monochrome printing (high speed VH) and full color printing (medium speed VM), image correction at each process speed is performed. An image correction table is created by feeding back data, and the time required for the process control (image quality adjustment) corresponding to the process speed can be reduced every time the process speed is changed. Further, since it is not necessary to idle the photosensitive drum 11a when performing the process control, it is possible to suppress wear (film slippage) of the surface of the photosensitive drum 11a.

  In addition, according to the present embodiment, the image correction table TBM at the medium speed VM and the image correction table TBH at the high speed VH are created based on the image correction tables by the conversion table TB0. The image correction table TBH at the high speed VH or the image correction table TBM at the medium speed VM corresponding to the image correction table TBM at the time or the image correction table TBH at the high speed VH can be easily created.

  That is, when the repeated image forming process is performed, for example, when the print speed of the print request (request JOB) changes from the high speed VH to the medium speed VM, the density correction table TBH and the conversion table TBO at the previous print speed (high speed VH). Thus, the density correction table TBM corresponding to the printing speed (medium speed VM) requested for printing can be easily created.

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) Explanatory drawing which shows the reference example of the test pattern for a correction | amendment formed in the image formation part of the said digital color copying machine, (b) is a sensor output and developing bias potential of the density | concentration detection sensor which detects the said test pattern for a correction | amendment. It is a graph which shows the relationship. (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.

Explanation of symbols

1 Concentration detection sensor (regular 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 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 (image correction data)
TBM image correction table (image correction data)
TP1, TP2, TP3,
TP101 to TP116 Correction test pattern (reference pattern)
Vb, Vb0 Development bias VH High speed VM Medium speed

Claims (2)

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 correcting an image formed at a plurality of process speeds based on a result,
The reference patterns are a plurality of reference patterns having different toner adhesion amounts depending on black toner,
The reflected light regularly reflected by the reference pattern created at a predetermined process speed is detected by a regular reflection sensor, and the toner adhesion amount of the reference pattern is calculated based on the amount of reflected light detected by the regular reflection sensor. To create density correction data for a given process speed,
When repeated image formation is performed at a process speed different from the predetermined process speed, density correction data is generated according to the different process speed,
An image correction method, wherein the density correction data at the predetermined process speed is converted and corrected based on the density correction data at the different process speed. 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 means for forming an electrostatic latent image of the reference pattern thereon; and a toner density detecting means for detecting the toner density of the reference pattern visualized with toner by the developing device; In an image forming apparatus for performing an image correction method for correcting an image formed at a plurality of process speeds based on a detection result by
A regular reflection sensor is used as the toner concentration detecting means,
The image forming apparatus according to claim 1, wherein the image correcting method according to claim 1 is performed as the image correcting method.

Images