JP2004125990A - Image forming apparatus, image forming method and control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of highly accurately correcting the density of a color image. <P>SOLUTION: In the case of performing a density gradation correcting processing for forming visible images having several density gradations by an electrostatic image forming part by using exposing/scanning data related to several density gradations, and then, correcting the exposing/scanning data related to several density gradations to be used in the image forming part based on the density of the visible image having several density gradations measured by a prescribed measuring means, the density of the visible image having several density gradations measured by the prescribed measuring means is corrected based on the medium density measurement value which is obtained by measuring the density of the medium on which the visible image is formed by the prescribed measuring means, then, the exposing/scanning data related to several density gradations to be used by the image forming part is corrected. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a density adjustment technique in an electrophotographic image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus using an electrophotographic technology such as a copier, a printer, and a facsimile, an electrostatic latent image is formed on a photoconductor by image exposure, developed with toner, and then transferred onto a transfer sheet (recording paper). An image is formed on a transfer sheet by transferring, visualizing, and fixing. An electrophotographic image forming apparatus that forms a color image by using this toner in four colors of yellow, magenta, cyan, and black has been widely used.
[0003]
An electrophotographic printer that forms a color image includes one photoconductor and four developing units, and forms a color image on a transfer sheet by sequentially repeating formation and transfer of a toner image on one photoconductor for each color. One drum system and four drum systems each having four exposing devices such as a photoconductor and a laser, a developing device, and a transferring device, and sequentially transferring the toner images formed by the respective devices onto a transfer sheet to form a color image. is there. In the four-drum system, the transfer to the transfer sheet can be performed in one pass, so that the throughput of the color image can be increased as compared with the one-drum system.
[0004]
In both the one-drum and four-drum systems, a direct transfer system in which a toner image on a photoconductor is directly transferred to a transfer sheet, and a method in which a toner image is temporarily transferred from a photoconductor to an intermediate transfer body such as an intermediate transfer belt and then transferred to a transfer sheet An indirect transfer system for transferring is known. In general, the indirect transfer method is less likely to be affected by the surface shape of the transfer sheet, the water content, and the like, so that a more stable image can be obtained.
[0005]
However, in addition to the influence on the image due to the variation in the quality of the transfer sheet, the toner density varies due to changes in the photoreceptor surface characteristics, toner characteristics, and transfer characteristics due to environmental fluctuations and durability deterioration. Regardless of the drum method, it is necessary to suppress fluctuations in toner density in order to obtain a more stable image. In particular, when a color image is formed, a variation in the toner density of each color toner appears as a tint, which is likely to cause a problem.
[0006]
Conventionally, as a method of correcting the fluctuation of the toner density, a latent image characteristic and a development characteristic on the surface of the photoreceptor are detected by measuring the density using a density patch having a maximum density, and conditions relating to the characteristic are adjusted. Maximum density correction control, multiple density patches corresponding to multiple density gradations are formed for each color, and the density is measured to detect data corresponding to each density information when creating actual image data (For example, refer to Patent Document 1).
[0007]
In the maximum density correction control, variation in the density reproduction range for each color can be corrected by changing the image forming conditions of the image forming unit. In the density tone correction control, the difference in the density change curve for each density tone for each color can be corrected by correcting the image data.
[0008]
[Patent Document 1]
JP-A-07-020669
[0009]
[Problems to be solved by the invention]
However, there is a problem that the density correction cannot be performed accurately because the reading accuracy of the density patch is deteriorated depending on the state of the background of the density patch.
[0010]
In particular, when a density patch is formed on an intermediate transfer member, there are many factors that deteriorate the density correction accuracy, such as contamination of the intermediate transfer member, uneven rotation speed of the intermediate transfer member, and bending of the intermediate transfer member.
[0011]
The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus, an image forming method, and a control program that can perform density correction with high accuracy.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides an image forming apparatus having an electrophotographic image forming unit, wherein: a measuring unit for measuring at least the density of a visible image formed by the image forming unit; Forming a visible image of a plurality of density gradations by the image forming unit using the exposure scanning data according to the tone, and using the density of the visible image of the plurality of density gradations measured by the measurement unit. Density tone correction means for correcting exposure scanning data relating to a plurality of density gradations used in the image forming section, wherein the density tone correction means is capable of correcting the plurality of density gradations measured by the measurement means. The image forming apparatus is configured to correct exposure scanning data related to a plurality of density gradations used in the image forming unit based on a density of a visual image and a density of a medium on which the visible image is formed.
[0013]
Further, in the image forming method, the density gradation correcting unit may be configured to perform the image forming based on a density obtained by subtracting a density of the medium from a density of a visible image having a plurality of density gradations measured by the measuring unit. It is configured to correct exposure scanning data relating to a plurality of density gradations used in the section.
[0014]
In the image forming apparatus, the density of the visible image and the density of the medium used for correcting the exposure scanning data related to the plurality of density gradations are the densities corresponding to the corresponding positions of the medium.
[0015]
Further, the image forming apparatus is configured to perform a process of forming the visible image on the medium, subsequent to a process of measuring the density of the medium.
[0016]
Further, the image forming apparatus is configured such that the size of one visible image is determined in consideration of at least a margin of an edge portion and a response delay of the measuring unit.
[0017]
Further, in the image forming apparatus, the visible images of the plurality of density gradations are formed so as to be formed in the order of high or low density.
[0018]
In the image forming apparatus, the measuring unit is configured to measure the density of the intermediate transfer member and the density of the visible image formed on the intermediate transfer member.
[0019]
In the image forming apparatus, the measuring unit may measure a density of a photoconductor or a recording paper transport unit and a density of the visible image formed on the photoconductor or the recording paper transport unit. It is configured.
[0020]
In the image forming apparatus, the image forming unit is configured by a color image forming unit that forms an image related to a plurality of colors.
[0021]
In the image forming apparatus, the image forming section has a plurality of photoconductors.
[0022]
In the image forming apparatus, the image forming section has one photoconductor.
[0023]
Further, the image forming apparatus forms a visible image with the image forming unit using exposure scanning data relating to a maximum density, and uses the density of the visible image measured by the measuring unit to form the image forming unit. Having a density range adjusting means for adjusting the image forming conditions, based on the density of the visible image measured by the measuring means and the density of the medium on which the visible image is formed. The image forming unit is configured to adjust image forming conditions.
[0024]
Further, according to the present invention, in an image forming method using an electrophotographic image forming unit, a measuring step of measuring at least a density of a visible image formed in the image forming unit, and an exposure related to a plurality of density gradations The image forming unit forms a visible image of a plurality of density gradations using scanning data, and the image forming unit uses the densities of the visible images of the plurality of density gradations measured in the measurement step. A density gradation correction step of correcting exposure scanning data relating to a plurality of density gradations to be used, wherein the density gradation correction step includes the densities of the visible images of the plurality of density gradations measured in the measurement step. The apparatus is configured to correct exposure scanning data related to a plurality of density gradations used in the image forming unit based on the density of the medium on which the visible image is formed.
[0025]
Further, in the image forming method, the density gradation correction step includes the step of forming the image based on a density obtained by subtracting a density of the medium from a density of a visible image of a plurality of density gradations measured in the measurement step. It is configured to correct exposure scanning data relating to a plurality of density gradations used in the section.
[0026]
Further, in the image forming method, the density of the visible image and the density of the medium used for correcting the exposure scanning data related to the plurality of density gradations are the densities corresponding to the corresponding positions of the medium.
[0027]
Further, the image forming method is configured to perform a process of forming the visible image on the medium, following the process of measuring the density of the medium.
[0028]
Further, the image forming method is configured such that the size of one visible image is determined in consideration of at least a margin of an edge portion and a response delay of the measurement process.
[0029]
Further, in the image forming method, the visible images of the plurality of density gradations are configured to be formed in an order of higher or lower densities.
[0030]
In the image forming method, the measuring step is configured to measure a density of the intermediate transfer member and a density of the visible image formed on the intermediate transfer member.
[0031]
In the image forming method, the measuring step may include measuring a density of a photoconductor or a recording paper transport unit and a density of the visible image formed on the photoconductor or the recording paper transport unit. It is configured.
[0032]
Further, in the image forming method, the image forming unit includes a color image forming unit that forms an image related to a plurality of colors.
[0033]
In the image forming method, the image forming unit has a plurality of photoconductors.
[0034]
In the image forming method, the image forming unit has one photoconductor.
[0035]
Further, the image forming method forms a visible image by the image forming unit using exposure scanning data relating to a maximum density, and uses the density of the visible image measured in the measuring step to form the image forming unit. Having a density range adjusting step of adjusting the image forming conditions, based on the density of the visible image measured in the measuring step and the density of the medium on which the visible image is formed. The image forming unit is configured to adjust image forming conditions.
[0036]
According to another aspect of the present invention, there is provided a control program executed by an image forming apparatus having an electrophotographic image forming unit, wherein the image forming unit uses a plurality of density scans using exposure scan data related to the plurality of density gradations. Forming a visible image of the tone and correcting the exposure scanning data related to the plurality of density gradations used in the image forming unit using the densities of the visible images of the plurality of density gradations measured by the predetermined measuring means. When performing the density gradation compensation processing, the density of the visible image of the plurality of density gradations measured by the predetermined measurement means is changed to the density of the medium on which the visible image is formed by the predetermined measurement means. And the exposure scan data relating to a plurality of density gradations used in the image forming unit is corrected based on the density of the visible image according to the correction.
[0037]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an image forming apparatus according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. In each of the drawings, members denoted by the same reference numerals represent the same members, and redundant description will be omitted.
[0038]
FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus 50 according to the present invention. Reference numeral 200 denotes an image input unit. Reference numeral 201 denotes a platen glass as a document loading table. Reference numeral 202 denotes a scanner, which includes a document illumination lamp (not shown), scanning mirrors 204 to 206, a lens 207, an image sensor unit 208, and the like.
[0039]
When the image input processing is started, the scanning mirror 204 is reciprocally scanned in a predetermined direction when the image capturing processing is started, and the reflected light of the original is scanned by the CCD sensor in the image sensor unit 208 via the scanning mirrors 204 to 206 and the lens 207. 109 (see FIG. 3). In an actual product, an ADF (automatic document feeder) or a pressure plate cover is placed on the image input unit 200 (not shown).
[0040]
The image output unit 100 is roughly divided into an image forming unit 10 (four stations a, b, c, and d are arranged side by side and have the same configuration), a sheet feeding unit 20, an intermediate transfer unit 30, It comprises a fixing unit 40 and a control unit (not shown).
[0041]
The image forming unit 10 has the following configuration. That is, the photosensitive drums 11a, 11b, 11c, and 11d as image carriers are pivotally supported at their centers and are driven to rotate in the direction of the arrow. Opposite to the outer peripheral surfaces of the photosensitive drums 11a to 11d, along the rotation direction thereof, primary chargers 12a, 12b, 12c, 12d, optical systems 13a, 13b, 13c, 13d, developing devices 14a, 14b, 14c, 14d. And cleaning devices 15a, 15b, 15c and 15d. The developing devices 14a, 14b, 14c, and 14d have built-in developing slaves 16, 16b, 16c, and 16d for applying a developing bias potential to the developing devices 14a, 14b, 14c, and 14d, respectively.
[0042]
The primary chargers 12a to 12d apply charges of a uniform charge amount to the surfaces of the photosensitive drums 11a to 11d. Next, the optical systems 13a to 13d expose the photosensitive drums 11a to 11d with light beams such as laser beams modulated in accordance with the recording image signals, thereby forming electrostatic latent images at the exposed positions. Further, the electrostatic latent images are visualized by developing devices 14a to 14d each storing a developer (toner) of four colors such as yellow, cyan, magenta, and black. Then, the visualized visible image is transferred to the intermediate transfer body 30.
[0043]
On the downstream side of the image transfer areas Ta, Tb, Tc, and Td, the cleaning devices 15a, 15b, 15c, and 15d scrape off the toner remaining on the photosensitive drums 11a to 11d without being transferred onto the transfer material, thereby removing the drum surface. Cleaning is performed. According to the above-described process, image formation using the toners of each color is sequentially performed.
[0044]
The paper feed unit 20 includes cassettes 21a, 21bb and a manual tray 27 for storing the recording material P, pickup rollers 22a, 22b and 26 for feeding the recording material P one by one from the cassette or from the manual tray, and each pickup roller. Roller pair 23 and a paper feed guide 24 for conveying the recording material P sent from the printer to the registration rollers 25a and 25b, and the recording material P in the secondary transfer area Te in accordance with the image forming timing of the image forming unit 10. And registration rollers 25a and 25b for sending them out.
[0045]
The intermediate transfer unit 30 includes an intermediate transfer belt 31, a driving roller 32, a tension roller 33, a driven roller 34, and a secondary transfer roller 36. As a material of the intermediate transfer belt 31, for example, PET [polyethylene terephthalate], PVDF [polyvinylidene fluoride], or the like is used. The intermediate transfer belt 31 is wound around a driving roller 32, a tension roller 33, and a driven roller 34, and is rotated by the driving roller 32 in a state where an appropriate tension is applied by the tension roller 33.
[0046]
The drive roller 32 is driven to rotate by a pulse motor (not shown), and the surface of the metal roller is coated with rubber (urethane or chloroprene) having a thickness of several mm to prevent slippage with the belt. A primary transfer plane A is formed between the driving roller 32 and the tension roller 33. Primary transfer blades 35a to 35d are arranged behind the intermediate transfer belt 31 in primary transfer areas Ta to Td where the respective photosensitive drums 11a to 11d and the intermediate transfer belt 31 face each other.
[0047]
A secondary transfer roller 36 is arranged to face the driven roller 34, and a nip with the intermediate transfer belt 31 forms a secondary transfer area Te. The secondary transfer roller 36 is pressed against the intermediate transfer belt 31 with an appropriate pressure. Further, a cleaning device (not shown) for cleaning the image forming surface of the intermediate transfer belt 31 is disposed downstream of the secondary transfer area Te on the intermediate transfer belt 31. The cleaning device has a cleaner blade (not shown: polyurethane rubber or the like is used as a material) and a waste toner box (not shown) for storing waste toner.
[0048]
In FIG. 1, a toner image density sensor 77 located on the upper surface of the drive roller 32 and facing the surface of the intermediate transfer belt 31 is a toner image density sensor 77, and each color toner transferred in the primary transfer areas Ta, Tb, Tc, and Td, respectively. This is a sensor for measuring the density of an image.
[0049]
The control unit includes a control board (not shown) for controlling the operation of the mechanism in each unit, a motor drive board (not shown), and the like. The fixing unit 40 fixes the toner image on the recording material P by heating and pressing the recording material P on which the toner image has been secondarily transferred in the secondary transfer area Te.
[0050]
FIG. 2 is a block diagram illustrating a configuration of the control unit 1 of the image forming apparatus 50. A CPU 171 controls the overall operation of the image forming apparatus 50. The CPU 171 includes a ROM 174 in which a control program is written, a work RAM 175 for performing processing, an input / output port 173, and the like. Connected by
[0051]
The input / output port 173 is connected to various loads (not shown) such as a motor and a clutch for driving the image forming apparatus 50 and inputs (not shown) such as sensors for detecting the position of the paper. The CPU 171 controls input and output sequentially through the input / output port 173 and executes a series of image forming operations according to a control program stored in the ROM 174.
[0052]
An operation unit 600 is connected to the CPU 171, and controls display processing and key input processing on the operation unit 600. That is, the operator instructs the CPU 171 to perform an image forming operation mode, display switching, and the like via the keys of the operation unit 600, and the CPU 171 performs operation mode setting and display control on the operation unit 600 according to the instruction. I do. The CPU 171 is connected to an image processing unit 170 that processes a signal converted into an electric signal by the image sensor unit 109 and an image memory unit 3 that stores a processed image.
[0053]
Next, details of the image processing unit 170 will be described with reference to FIG. In FIG. 3, image light of a document formed on the CCD sensor 109 via the lens 207 is converted into an analog electric signal, and is input to the image processing unit 170 as luminance data. The analog luminance data is input to an analog signal processing unit (not shown), where sample & hold, dark level correction, and the like are performed. Then, the data is converted into digital luminance data by the A / D / SH unit 301 (A / D conversion), and shading correction (variation of a sensor for reading a document and correction of light distribution characteristics of a document illumination lamp) is performed. , And then sent to the log converter 302.
[0054]
The log conversion unit 302 has an LUT (Look Up Table) for converting the input luminance data into density data, and outputs a table value corresponding to the input data based on the LUT, thereby obtaining the luminance. Convert the data to concentration data. After that, the image is scaled to a desired magnification by the scaling processing unit 303 and input to the γ correction unit 304.
[0055]
When outputting density data, the γ correction unit 304 performs conversion using a γLUT (Look Up Table) in consideration of the characteristics of the printer unit 100, and adjusts output according to the density value set by the operation unit 600. (Γ correction). After that, the γ-corrected density data is sent to the binarization unit 305.
[0056]
The binarization unit 305 binarizes the multi-valued density data, and the density value becomes “0” or “255”. The 8-bit image data is binarized and converted into 1-bit image data of “0” or “1”, and the amount of image data stored in the image memory unit 3 is reduced. However, when the image is binarized, the number of gradations of the image is changed from 256 gradations to two gradations, so that image data having a large number of halftones such as a photographic image is significantly degraded in image quality.
[0057]
Therefore, it is necessary to perform pseudo halftone expression using binary data. Here, an error diffusion method is used as a method for pseudo-halftone expression using binary data. In this error diffusion method, when the density data of an image is larger than a certain threshold, the density data is determined to be “255”, and when the density data is equal to or smaller than the threshold, the density data is “0”. This is a method of distributing the difference between the quantified data to surrounding pixels as an error signal. The distribution of the error is performed by multiplying a weight coefficient on a matrix prepared in advance by the error generated by the binarization and adding the result to surrounding pixels. As a result, the density average value of the entire image is stored, and the halftone can be represented in a pseudo binary manner.
[0058]
The binarized image data is sent to the image memory unit 3 and accumulated. It should be noted that the image data from the computer is processed as binary image data by the external I / F processing unit 4 and is thus sent to the image memory unit 3 as it is.
[0059]
The image memory unit 3 has a high-speed page memory and a large-capacity memory (hard disk 404, see FIG. 4) capable of storing a plurality of page image data. The plurality of image data stored on the hard disk 404 are output in an order according to the editing mode specified by the operation unit 600 of the image forming apparatus 50. For example, in the case of sorting, the image data of the document once stored is read from the hard disk 404, and this is repeated a plurality of times and output. Thereby, the same function as a sorter having a plurality of bins can be performed.
[0060]
The image data output from the image memory unit 3 is sent to the smoothing unit 306 of the printer unit 100. The smoothing unit 306 interpolates the data so that the leading end of the binarized image becomes smooth, and outputs the result to the exposure control unit 120. The exposure controller 120 forms image data on transfer paper by the above-described processing.
[0061]
Next, details of the image memory unit 3 will be described with reference to FIG. The image memory unit 3 writes binary image data from the external I / F processing unit 4 and the image processing unit 170 into a page memory 401 composed of a memory such as a DRAM under the control of a memory controller 402. Processing such as transfer to the unit 100 and input / output to / from the hard disk 404 via the JPEG compression unit 403 is performed.
[0062]
The memory controller 402 generates a DRAM refresh signal for the page memory 401, and arbitrates access to the page memory 401 from the external I / F processing unit 4, image processing unit 170, and hard disk 404. Further, the memory controller 402 controls a write address to the page memory 401, a read address from the page memory unit 401, a read direction, and the like according to an instruction from the CPU 171. Under these controls, the memory controller 402 executes a function of arranging and laying out a plurality of document images in the page memory 401 and outputting them to the printer unit 10, a function of cutting out and outputting only a part of an image, and an image rotating function.
[0063]
Next, the external I / F processing unit 4 will be described in detail with reference to FIG. The external I / F processing unit 4 facsimile-transmits image data from the reader unit 200 stored in the image memory unit 3 and transmits the image data to the external computer 11, and receives image data received by facsimile and external computer The image data transferred from the printer 11 is stored in the image memory unit 3 so as to be printed by the printer unit 100.
[0064]
The external I / F processing unit 4 includes a core unit 506, a facsimile unit 501, a hard disk 502, a computer interface unit 503, a formatter unit 504, and an image memory unit 505, and the core unit 506 includes an external I / F processing unit. 4 is controlled.
[0065]
The facsimile unit 501 is connected to a public line via a modem (not shown), and receives facsimile communication data from the public line and transmits facsimile communication data to the public line. The facsimile unit 501 performs facsimile transmission / reception processing such as facsimile transmission of specified image data at a specified time and facsimile transmission of image data in response to an inquiry about a specified password from a partner. At this time, the facsimile unit 501 uses the hard disk 502 as a facsimile transmission / reception memory. Thus, after the image data from the reader unit 200 is read from the image memory unit 3 and stored in the hard disk 502, facsimile transmission can be performed without accessing the image memory unit 3.
[0066]
The computer interface unit 503 is an interface unit for performing data communication with the external computer 11 and the like, and includes a local area network (hereinafter, LAN), a serial I / F, a SCSI I / F, and a Centro I / F for data input of a printer. F and the like. Via this I / F, the statuses of the printer unit 100 and the reader unit 200 are notified to the external computer 11, the image data read by the reader unit 200 is transferred to the external computer 11, and the external computer 11 Receiving image data.
[0067]
Since the image data received from the external computer 11 via the computer interface unit 503 is described in a dedicated printer code based on a printer driver installed in the external computer 11, the formatter unit 504 It is converted into raster image data for forming an image. At this time, the formatter unit 504 develops the raster image data on the image memory unit 505.
[0068]
The image memory unit 505 is used as a memory for the formatter unit 504 to convert the image data into raster image data and sends image data from the reader unit 200 to the external computer 11 (image scanner function). It is also used as a memory for converting into a data format suitable for the external computer 11.
[0069]
The core unit 506 controls and manages data transfer among the facsimile unit 501, the computer interface unit 503, the formatter unit 504, the image memory unit 505, and the image memory unit 3. In other words, the core unit 506 performs exclusive control and priority control even when the external I / F processing unit 4 has a plurality of image output units and has only one image transfer path to the image memory unit 3. And input and output of image data properly.
[0070]
Next, details of the operation unit 600 will be described with reference to FIG. In FIG. 6, a power lamp 621 indicates that the power is turned on, and is turned on or off according to the ON / OFF operation of the power switch 613. Reference numeral 622 denotes a numeric keypad (registered trademark), which is used for setting the number of images to be formed and for inputting numerical values when setting a mode. Reference numeral 623 denotes a clear key, which is used when clearing the contents set by the ten keys 622. Reference numeral 616 denotes a reset key for returning the set number of images to be formed, the operation mode, the selected paper feed stage, and other modes to default values.
[0071]
A start key 614 starts an image forming operation when the start key 614 is pressed. At the center of the start key 614, there are red and green LEDs (not shown) indicating whether or not the start is possible. If the start is not possible, the red LED is lit, and if the start is possible, the green LED is lit. I do. A stop key 615 is used to stop the copying operation. Reference numeral 617 denotes a guide key. When another key is pressed after pressing the guide key 617, a description of a function that can be set by the other key is displayed on the display panel 620. To cancel the guide display, the guide key 617 is pressed again.
[0072]
Reference numeral 618 denotes a user setting key. By pressing the user setting key 618, a predetermined setting of the image forming apparatus 50 can be changed. The settings that can be changed include the time until the settings are automatically cleared, the timer setting time, the setting of the dedicated tray, and the like, settings common to printer copy, or general functions unique to each function.
[0073]
Reference numeral 619 denotes an interrupt key. For example, when the interrupt key 619 is pressed during an image forming operation, the image forming operation can be stopped and copying can be performed. Reference numeral 620 denotes a display panel composed of a liquid crystal or the like, and the display content changes according to the setting mode in order to facilitate detailed mode setting. Further, the surface of the display panel 620 is constituted by a touch sensor.
[0074]
The display panel 620 in FIG. 6 shows an example of a setting screen for the copy operation mode. In FIG. 6, keys 624 to 631 are displayed on display panel 620, and by touching the display positions of these keys 624 to 631, the corresponding mode is set.
[0075]
Reference numeral 627 denotes a paper stage selection key. When the paper stage selection key 627 is pressed, information indicating the cassettes 21 a and 21 b and the manual feed tray 27 is cyclically displayed on the display panel 620. 628 to 631 are keys for setting the copy magnification of the copy operation. Reference numeral 626 denotes an application mode setting key. When the application mode setting key 626 is pressed, a screen for setting an application function mode such as a reduced layout mode and a cover / insert mode is displayed on the display panel 620.
[0076]
Reference numeral 624 denotes a setting key for double-sided operation, for example, a “single-sided mode” for performing duplex output from a single-sided original, a “both-sided mode” for performing double-sided output from a double-sided original, and two-sided output for two-sided original It is possible to set three types of double-sided modes, “both-single mode”. Reference numeral 625 denotes a sort key. By using the sort key 625, an operation mode of a post-processing device (not shown) and an output paper sorting mode using the image memory unit 3 can be set.
[0077]
When the mode of the display key cannot be set in addition to the normal display, the display of the key in the display panel 620 is indicated by a dotted line (shaded) to indicate that the key cannot be operated. It has become. Further, in the example of FIG. 6, the display of the contents set for the copying operation and the current operation state are displayed on the upper part of the display panel 620.
[0078]
There is a key (not shown) that can be changed by the user next to the application mode key 626 in the display panel 620, and up to two function keys that can be set on the application mode setting screen can be registered. By displaying the application mode setting key 626 at the position shown in FIG. 6, it is possible to more easily set the mode related to the registered key.
[0079]
Reference numeral 632 denotes a proof print mode key. When a plurality of copies are output when the sort mode is set by the sort key 625, the print operation is temporarily stopped when one copy is output, and the user is allowed to confirm the finish. If OK, continue, and if NG, proof print mode is set so that cancellation can be selected.
[0080]
In FIG. 6, reference numerals 604 to 612 denote keys and LEDs for switching display contents (operation screens) of the display panel 620 in order to set each function of a copying operation and a system operation using the image forming apparatus 50. Reference numerals 604, 607, and 610 are keys for switching each function. These function switching keys 604, 607, and 610 are constituted by translucent key buttons, and internally provided with display lamps (not shown) such as LEDs. When these keys 604, 607, and 610 are pressed, only the display lamps in the pressed keys are exclusively turned on, and the display lamps in the two keys that are not pressed are turned off.
[0081]
Green LEDs 606, 609, and 612 are disposed on the right side of the function switching keys 604, 607, and 610, respectively. These green LEDs 606, 609, and 612 are used to indicate the operation status of each function. For example, the green LED 606 associated with the copy key 604 is turned off when the copy function is on standby, and blinks when the copy function is operating as in the example of FIG. The light is turned on when the image data to be copied is being stored in the hard disk 404 of the image memory unit 3 and a print operation for copying has not been performed yet.
[0082]
Red LEDs 605, 608, and 611 are arranged on the left side of the function switching keys 604, 607, and 610. These red LEDs 605, 608, and 611 are used to indicate that an abnormal situation of each function has occurred. Is done. For example, the red LED 605 related to the copy key 604 blinks when an abnormality such as out of paper or JAM occurs in the copy processing. By pressing the copy function key 604, the details of the abnormal situation can be displayed on the operation screen of the display panel 620.
[0083]
The function switching keys 604, 607, and 610 can be pressed at any time regardless of the operation status of each function, and the operation screen of the display panel 620 can be switched.
[0084]
Next, image density correction control (image density adjustment control) unique to the present invention will be described. The image density correction control according to the present invention is performed by two controls: Vcont control as maximum density correction control and γLUT control as density gradation correction control.
[0085]
FIG. 7 is a characteristic diagram showing the relationship between the potential of the photoconductor at the minimum density and the maximum density, and the potential of the developing device. The horizontal axis corresponds to the photosensitive drum charging bias, and the vertical axis represents the photosensitive drum surface potential. Corresponding to
[0086]
Vback is a value determined so that the developing bias characteristic Vdc has a prescribed relationship with respect to the Vd characteristic in the case of the output of “00h (0)” which is the minimum density.
[0087]
(Equation 1)
Vback = Vd-Vdc
In a relationship.
[0088]
Vcont is a value obtained from the developing bias characteristic Vdc obtained from the specified value of Vback and the Vl characteristic when "FFh (255)" which is the maximum density is output.
[0089]
(Equation 2)
Vcont = Vdc−Vl
In a relationship. Note that Vd and Vl are the surface potentials of the photosensitive drums 11a to 11d. In addition, those with h are expressed in hexadecimal notation, and those in parentheses are expressed in decimal notation.
[0090]
Next, the Vcont calculation will be described with reference to FIG. FIG. 8 is a diagram showing the principle of the maximum density correction control according to the present invention. The horizontal axis corresponds to Vcont + Vback shown in FIG. 7, and the vertical axis corresponds to the maximum density Dmax.
[0091]
As shown in FIG. 8, it is considered that the maximum density Dmax is proportional to (Vcont + Vback). For this reason, Vcont in the current environment (setting) is set to VcontEnv, the set target value of the maximum density is 1.8, the density detection data of the output data “FFh” read by the toner image density sensor 77, that is, the maximum density patch. Assuming that the density read value of ODff is ODff, VcontNew which is Vcont in the new environment is
[0092]
[Equation 3]
VcontNew = (VcontEnv + Vback) × 1.8 / ODff−Vback
Is calculated as
[0093]
The above processing is performed for each color, and high-voltage output is performed for Vcont using VcontNew to form an image. That is, based on the calculated VcontNew of each color, the output of the high-voltage transformer to the primary chargers 12a, 12b, 12c, and 12d is controlled (the surface potential of the photosensitive drums 11a, 11b, 11c, and 11d is controlled), and the developing device is controlled. The developing bias applied to the developing sleeves 14a, 14b, 14c, and 14d (developing sleeves 16a, 16b, 16c, and 16d) is controlled.
[0094]
FIG. 9 is a diagram illustrating the principle of γLUT correction, which is image density gradation correction control according to the present invention.
[0095]
The density data of the toner patch transferred onto the intermediate transfer belt 31 read by the toner image density sensor 77 is indicated by a dotted line. Ideally, the density output is a straight line connecting the origin 0 and points (density OD “255 (FFh)” and Signal “255 (FFh)”) as shown in FIG. For example, to output the density “80h”, a signal value of “80h” may be output.
[0096]
However, actually, the printer characteristic density read by the toner image density sensor 77 does not show a linear characteristic as shown by a dotted line, for example. In order to correct this state and obtain a desired density for the output data as a printer output image, a value having a large γLUT is output in a low density area, and a value of the γLUT is reduced in a high density area. Must be output to The curve of the γLUT is created so that the read density curve is symmetrical with respect to the ideal straight line (see the curve shown by the solid line in FIG. 9).
[0097]
The principles of the maximum density correction control (Dmax control) and the density gradation correction control (γLUT control) according to the present invention have been described above.
[0098]
Now, as described above, the significance of reading the density of the density patch formed on the intermediate transfer belt 31 by the toner image density sensor 77 is as follows. It is to detect how much toner has adhered.
[0099]
However, for example, if the density patch forming area on the intermediate transfer belt 31 is dirty, the toner image density sensor 77 reads the density of the density patch in a state in which the density of the dirt is taken into consideration, and a predetermined density data signal , That is, the density of the density patch cannot be accurately read. Therefore, it is necessary to accurately grasp the state of the intermediate transfer belt 31, which is the base, including the position.
[0100]
Therefore, in the present embodiment, prior to the transfer of the density patch to the intermediate transfer belt 31 and the measurement of the density of the density patch, the density (that is, the density of the base) of the intermediate transfer belt 31 one round before the density patch is transferred is determined. Are read at a predetermined sampling timing by the toner image density sensor 77, and are sequentially stored in the RAM 175.
[0101]
Next, the toner images of the density patches formed on the photosensitive drums 11a to 11d are transferred to the transfer belt 31, the density of the transferred density patches is read at a predetermined sampling timing by the toner image density sensor 77, and is sequentially stored in the RAM 175. save.
[0102]
Then, the density of the density patch corresponding to the output of the predetermined density data signal is obtained by subtracting and correcting the density of the background at the corresponding position from the read density of the density patch.
[0103]
Further, the density of the density patch according to this correction is set as a patch read value indicated by a curve indicated by a broken line in FIG. 9, and a γLUT corresponding to the curve indicated by a solid line in FIG. 9 is generated.
[0104]
The reason why the measurement of the background data and the formation and the density measurement of the density patch are performed continuously is that, first, after the background data is measured and before the density patch is formed, the situation such as the contamination of the background is measured. This is because it is possible to obtain the density of the density patch with respect to the output of the predetermined density data signal more accurately by avoiding the change of the density as much as possible.
[0105]
Second, there is no means for detecting the position of the intermediate transfer belt 31. If there is means for detecting the position of the intermediate transfer belt 31 such as a home position sensor, the desired position detection accuracy is not sufficient. This is not always the case.
[0106]
Next, the shape (length) of the density patch will be described with reference to FIG.
[0107]
FIG. 10 shows the output of the toner image density sensor 77 and the sampling timing of the sensor output in the sub-scanning direction of the density patch. Note that the width of the density patch in the main scanning direction only needs to be sufficient for the toner image density sensor 77 to read.
[0108]
Regarding the width of the density patch in the sub-scanning direction, first, since the edge portion of the density patch is unclear, the times of the “edge effect portions” a and d can be considered. b is the time of the response delay of the toner image density sensor 77, and c is the time of the data actually used. In the present embodiment, a = 15.4 ms, b = 30 ms, d = 15.4 ms, and the sampling period is 15.6 ms.
[0109]
The number of data to be used must be at least six. Further, the position of the density patch and the sampling period are not necessarily synchronized. That is, the ideal sampling timing for the density patch is the sampling timing A, but the case where the sampling timing is most shifted is the sampling timings B and C, each of which shifts less than 15.6 ms.
[0110]
In consideration of the above, among the sampling data 12 of the sensor output for the density patch, the effective data is the fifth to tenth data, and c = 15.6 ms × 7. If there is a restriction on the density patch forming operation, it is necessary to form the patch shape in consideration of the restriction.
[0111]
Next, the density gradation correction operation will be described in detail.
[0112]
First, the CPU 171 reads the density (base density) of the intermediate transfer belt 31 with the toner image density sensor 77 at a fixed cycle, and sequentially stores the density data of the base in the RAM 175. Next, when it is time to start forming density patches, density patches are formed on the intermediate transfer belt 31.
[0113]
FIG. 11 shows an example of the base and the formed density patch. In FIG. 11, density patches are formed in the order of black, yellow, magenta, and cyan subsequent to the base, and for each color, density patches are formed in order from high density patches to light density patches. The arrangement of the order and number of colors and the order and number of gradations are examples, and are not limited to these. That is, the density patches may be formed in order from a density patch having a low density to a density patch having a high density.
[0114]
Each density patch formed on the intermediate transfer belt 31 sequentially passes through the position of the toner image density sensor 77 as the intermediate transfer belt 31 is driven to rotate. , And density data of the density patch related to the reading is stored in the RAM 175.
[0115]
Then, when the density patch formed last (the density patch having the lowest density of cyan in the example of FIG. 11) has passed the position of the toner image density sensor 77, the sensor reading of the density patch is completed. Thus, the RAM 175 stores all of the background data and the density data of the density patch required in the present invention.
[0116]
Therefore, when the last formed density patch has passed the position of the toner image density sensor 77, the CPU 171 scans the sensor reading data area of the RAM 175 and detects the density data of the first density patch. This detection process is specifically performed by detecting a large change point (rising edge) of the density data.
[0117]
When the density data of the first density patch is detected, the background data immediately before the density data is subtracted from the density data, in other words, the correction is performed by subtracting the background data immediately below the density patch related to the density data. By doing so, an accurate density of the density patch for the output of the predetermined density data signal is obtained. Such correction processing based on the background data is performed on the density data relating to reading of all the density patches.
[0118]
Finally, based on the density of the density patch to be corrected, a γLUT such as a curve shown by a solid line in FIG. 9 is generated, thereby performing density gradation correction with high accuracy.
[0119]
Note that the present invention is not limited to the above-described embodiment, and can be applied to an image forming apparatus of a one-drum type other than the four-drum type, for example, if it is an electrophotographic image forming apparatus. . Further, the present invention can be applied to not only the density gradation correction processing but also the maximum density correction processing.
[0120]
Further, by providing a plurality of toner image density sensors for each color, it is possible to detect the toner density with high accuracy and perform the density adjustment processing with high accuracy. Further, the background data used for the correction process does not necessarily have to correspond exactly to the formation position of the density patch. If the reading position of the background data and the position of the density patch partially overlap, there is a slight shift. You may. Further, the intermediate transfer member may be an intermediate transfer drum.
[0121]
Further, the present invention is also applicable to a case where a toner image is directly transferred to recording paper without using an intermediate transfer member. In this case, since the density patch is formed on the photoconductor or the recording paper transport unit, the density of the photoconductor or the recording paper transport unit may be read in advance as background data.
[0122]
Further, an object of the present invention is to supply a storage medium (or a recording medium) in which program codes of software for realizing the functions of the above-described embodiments are recorded to a system or an apparatus, and to provide a computer (or a CPU or MPU) of the system or the apparatus. Needless to say, the above can also be achieved by reading and executing the program code stored in the storage medium.
[0123]
In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0124]
Further, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a 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 processing realizes the functions of the above-described embodiments. When the present invention is applied to the storage medium, the storage medium stores program codes for executing the above-described density gradation correction processing.
[0125]
Another object of the present invention is to supply a storage medium storing program codes of software for realizing the functions of the embodiments to a system or an apparatus, and a computer (or CPU, MPU, or the like) of the system or the apparatus stores the storage medium. It is also achieved by reading and executing the program code stored in the.
[0126]
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.
[0127]
Further, as a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, magneto-optical disk, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD -RW, DVD + RW, magnetic tape, nonvolatile memory card, ROM, and the like can be used.
[0128]
When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. This also includes a case where some or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0129]
Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This also includes the case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0130]
【The invention's effect】
As described above, according to the present invention, it is possible to realize an image forming apparatus, an image forming method, and a control program that can perform density correction with high accuracy.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of a control unit.
FIG. 3 is a block diagram illustrating a configuration of an image forming processing unit.
FIG. 4 is a block diagram illustrating a configuration of an image memory unit.
FIG. 5 is a block diagram illustrating a configuration of an external I / F processing unit.
FIG. 6 is a top view illustrating a configuration of an operation unit.
FIG. 7 is a characteristic diagram showing the relationship between the potential of the photoconductor at the minimum density and the maximum density and the potential of the developing device.
FIG. 8 is a diagram for explaining the principle of maximum density correction control.
FIG. 9 is a diagram for explaining the principle of image density gradation correction control.
FIG. 10 is a diagram for explaining how to determine the size of a density patch.
FIG. 11 is a diagram for explaining a formation position of a density patch.
[Explanation of symbols]
1: Control units 11a to 11d: photosensitive drums 12a to 12d: primary chargers 13a to 13d: optical systems 14a to 14d: developing devices 16a to 16d: developing slaves 31: intermediate transfer belt 77: toner image density sensor 50: image formation Apparatus 100: Printer section 170: Image processing section 171: CPU
174: ROM 175: RAM 304: γ correction unit

Claims (25)

In an image forming apparatus having an electrophotographic image forming unit,
Measuring means for measuring the density of at least the visible image formed by the image forming unit, and forming a visible image having a plurality of density gradations by the image forming unit using exposure scanning data relating to the plurality of density gradations. A density gradation correction unit that corrects exposure scanning data related to the plurality of density gradations used in the image forming unit using the densities of the visible images of the plurality of density gradations measured by the measurement unit. Have
The density gradation correction unit includes a plurality of density gradation correction units that are used in the image forming unit based on a density of a visible image of a plurality of density gradations measured by the measurement unit and a density of a medium on which the visible image is formed. An image forming apparatus that corrects exposure scanning data related to the density gradation. The density gradation correction means includes a plurality of density gradations used in the image forming unit based on densities obtained by subtracting the density of the medium from the densities of the plurality of density gradation visible images measured by the measurement means. 2. The image forming apparatus according to claim 1, wherein the exposure scan data according to claim 1 is corrected. The density of the visible image and the density of a medium used for correcting the exposure scanning data related to the plurality of density gradations are densities corresponding to corresponding positions of the medium. Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the process of forming the visible image on the medium is performed subsequent to the process of measuring the density of the medium. 5. The image forming apparatus according to claim 1, wherein the size of one visible image is determined in consideration of at least a margin of an edge portion and a response delay of the measuring unit. The image forming apparatus according to claim 1, wherein the visible images of the plurality of density gradations are formed in a descending order of the density or in a descending order of the density. The image forming apparatus according to claim 1, wherein the measuring unit measures a density of the intermediate transfer member and a density of the visible image formed on the intermediate transfer member. 7. The apparatus according to claim 1, wherein the measuring unit measures a density of a photoconductor or a recording paper transport unit and a density of the visible image formed on the photoconductor or the recording paper transport unit. The image forming apparatus according to any one of the above. The image forming apparatus according to claim 1, wherein the image forming unit is a color image forming unit that forms an image related to a plurality of colors. The image forming apparatus according to claim 1, wherein the image forming unit has a plurality of photoconductors. The image forming apparatus according to claim 1, wherein the image forming unit includes one photoconductor. A density for forming a visible image by the image forming unit using exposure scanning data relating to a maximum density, and adjusting an image forming condition of the image forming unit using the density of the visible image measured by the measuring unit. An image forming unit for forming an image based on a density of the visible image measured by the measuring unit and a density of a medium on which the visible image is formed; The image forming apparatus according to claim 1, wherein conditions are adjusted. In an image forming method using an electrophotographic image forming unit, a measuring step of measuring at least the density of a visible image formed in the image forming unit, and using the exposure scanning data according to a plurality of density gradations, A plurality of density gradation visible images are formed by the image forming unit, and the plurality of density gradations used in the image forming unit using the densities of the plurality of density gradation visible images measured in the measurement step. Density gradation correction step of correcting the exposure scan data according to,
The density gradation correction step includes: a plurality of density gradation correction steps based on a density of a plurality of density gradation visible images measured in the measurement step and a density of a medium on which the visible image is formed. An image forming method comprising: correcting exposure scanning data relating to a density gradation of (1). The density tone correction step includes: determining a plurality of density tones used in the image forming unit based on a density obtained by subtracting the density of the medium from the density of the visible image of the plurality of density tones measured in the measurement step 14. The image forming method according to claim 13, wherein the exposure scan data according to claim 13 is corrected. The density of the visible image and the density of the medium used for correcting the exposure scanning data related to the plurality of density gradations are the densities corresponding to the corresponding positions of the medium. Image forming method. The image forming method according to any one of claims 13 to 15, wherein a process of forming the visible image on the medium is performed subsequent to the process of measuring the density of the medium. 17. The image forming method according to claim 13, wherein a size of one visible image is determined in consideration of at least a margin of an edge portion and a response delay of the measurement process. 18. The image forming method according to claim 13, wherein the visible images of the plurality of density gradations are formed in an order of higher or lower density. 19. The image forming method according to claim 13, wherein in the measuring step, a density of the intermediate transfer member and a density of the visible image formed on the intermediate transfer member are measured. 19. The method according to claim 13, wherein the measuring includes measuring a density of a photoconductor or a recording paper transport unit and a density of the visible image formed on the photoconductor or the recording paper transport unit. The image forming method according to any one of the above. The image forming method according to claim 13, wherein the image forming unit is a color image forming unit that forms an image related to a plurality of colors. The image forming method according to claim 13, wherein the image forming unit has a plurality of photoconductors. The image forming method according to claim 13, wherein the image forming unit has one photoconductor. A density for forming a visible image by the image forming unit using exposure scanning data relating to a maximum density, and adjusting an image forming condition of the image forming unit using the density of the visible image measured in the measuring step. The image forming section includes a range adjusting step, wherein the density range adjusting step includes the steps of: The image forming method according to claim 13, wherein conditions are adjusted. A control program executed by an image forming apparatus having an electrophotographic image forming unit,
The image forming unit forms a visible image of a plurality of density gradations using the exposure scanning data related to the plurality of density gradations, and forms a visible image of the plurality of density gradations measured by a predetermined measuring unit. When performing density gradation supplementation processing for correcting exposure scanning data relating to a plurality of density gradations used in the image forming unit using the density, the plurality of density gradations measured by the predetermined measuring means are visible. The image density is corrected by a medium density measurement value obtained by measuring the density of a medium on which the visible image is formed by the predetermined measuring unit, and based on the density of the visible image related to the correction, the image forming unit A control program having contents for correcting exposure scanning data relating to a plurality of density gradations used in the above.

Images