JP4040632B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus to which an electrophotographic system such as a copying machine or a printer is applied. In particular, the density correction execution condition is detected during image formation (printing), and the density correction is performed when the condition is satisfied. The present invention relates to a color image forming apparatus to be implemented.

  In an image forming apparatus to which an electrophotographic system is applied, the image quality (density) of a printed matter varies with changes in the apparatus over time, such as deterioration of a photoreceptor. For this reason, in the image forming apparatus, in order to continue printing with a constant image quality, it is necessary to appropriately perform density correction processing. This density correction processing is usually performed by changing image forming conditions such as a developing bias voltage and a charging bias voltage.

  In order to perform such density correction, the image forming apparatus monitors whether or not a predetermined density correction execution condition is satisfied, and performs density correction processing when it is determined that the density correction execution condition is satisfied. To do. An example of a case where it is determined that the density correction execution condition is satisfied is, for example, when the image forming apparatus is turned on, when the toner cartridge is replaced, or when reaching every predetermined number of output sheets.

  On the other hand, a recent image forming apparatus has an image memory capable of storing a plurality of jobs, and when printing of another job is requested while printing a certain job, the job related to the new printing request Is stored in the image memory. The jobs stored in the image memory are printed in the order stored in the image memory.

  The job printed by the image forming apparatus may be data obtained by reading an original with an image reading apparatus, or data sent from a computer connected to the image forming apparatus via a network. However, the input data is printed after being subjected to image processing such as γ processing and screen processing.

Further, in the image forming apparatus, a job stored in the image memory and waiting for printing is subjected to these image processing (γ processing and screen processing) so that printing can be performed quickly when the printing order is reached. And stored in the image memory (see Patent Document 1).
JP 11-289436 A (publication date October 19, 1999)

  However, the above-described conventional configuration causes the following problems when the density correction execution condition is satisfied during the printing operation.

  That is, during the printing operation of a certain job, the number of printed sheets from the previous density correction may reach a predetermined number and the density correction execution condition may be satisfied. At this time, if the job being printed is interrupted and the density correction process is performed, the image forming conditions change in the middle of the same job, so the image quality of the printed matter changes in the middle of the job. .

  On the other hand, if there is a job that is being printed when the density correction execution condition is satisfied, it is possible to execute the density correction processing after the printing of the job is completed. However, in this case, if another job is stored in the image memory when the density correction execution condition is satisfied, an appropriate image forming condition for the job stored in the image memory is used. There is a problem that printing is not possible.

  This is a problem caused by a mismatch between image processing (γ processing or screen processing) performed on a job and image forming conditions at the time of printing for the job. In other words, jobs stored in the image memory are stored in the image memory after being subjected to γ processing and screen processing image processing before printing, and these image processing is based on image forming conditions at the time of printing. Since there is a correlation, an appropriate image quality may not be obtained unless the image processing applied to the job matches the image forming conditions at the time of printing.

  Therefore, if the density correction process is performed with the image processed job stored in the image memory and the image forming conditions change, the image processing applied to the job matches the image forming conditions at the time of printing. Therefore, there is a problem that printing is not performed under appropriate image forming conditions. This problem is particularly noticeable when printing a color image.

  In order to avoid the above problem, it is conceivable to perform density correction processing when printing of all jobs stored in the image memory is completed. However, in this case, although the density correction execution condition is satisfied, the density correction process may be postponed and printing of many jobs may be continued without performing the density correction process. . In particular, if there are many job print requests to the image forming apparatus and the jobs stored in the image memory do not disappear for a long time, it is inappropriate to perform density correction processing for many jobs. Printing may continue for a long time.

  Alternatively, if there is a job stored in the image memory when the density correction execution condition is satisfied, the density correction process is performed before the printing process for the job, and then the density correction is performed on the job. It is also possible to redo image processing (γ processing or screen processing) that matches the image forming conditions after processing. However, in this case, there is a problem that the burden on the image processing unit in the image forming apparatus is increased by performing image processing again on the job stored in the image memory.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to perform density correction processing quickly and to perform appropriate printing for all jobs stored in the image memory. An object of the present invention is to realize an image forming apparatus capable of performing the above.

  In order to solve the above problems, an image forming apparatus according to the present invention includes an image memory capable of storing image data corresponding to a plurality of jobs, and an output in an image forming apparatus having an image forming unit to which an electrophotographic method is applied. An image processing unit that performs image processing on image data to be processed, and image formation of the image forming unit to perform density correction processing in the image forming unit when the image forming unit satisfies a density correction execution condition A density correction unit that changes conditions, and the image data waiting for printing stored in the image memory is stored in a state in which at least a part of the image processing performed in the image processing unit has been performed. If the density correction execution condition of the image forming unit is satisfied during printing of a job, the job stored in the image memory at that time is printed. Were classified into color jobs and monochrome job, performs a density correction process color job after printing with priority, it is characterized by printing a monochrome job after the density correction process.

  According to the above configuration, by performing density correction after processing a color job first, with respect to a color job, image processing performed on the job and image forming conditions at the time of printing for the job are determined. Can be matched. Thus, in a color job, it is possible to reliably avoid significant image quality degradation when the image processing performed on the job does not match the image forming conditions at the time of printing for the job.

  For monochrome jobs, even if the image processing performed on the job and the image forming conditions for printing the job do not match, no significant image quality degradation occurs. By performing the process after the density correction process, it is possible to prevent the execution of density correction from being postponed more than necessary, and to ensure long-term image quality stability.

  In the image forming apparatus, the image forming condition can be a developing bias voltage or a charging bias voltage. According to the above configuration, the density correction process can be easily performed.

  As described above, the image forming apparatus according to the present invention includes an image memory that can store image data corresponding to a plurality of jobs, an image processing unit that performs image processing on image data to be output, and the image forming unit. A density correction unit that changes the image forming condition of the image forming unit in order to perform density correction processing in the image forming unit when the unit satisfies the density correction execution condition, and is stored in the image memory The waiting image data is stored in a state where at least a part of the image processing performed in the image processing unit has been performed, and during the printing of a certain job, When the density correction execution conditions are satisfied, the jobs stored in the image memory at that time are classified into color jobs and monochrome jobs, and color jobs are printed with priority. Performs density correction process, is configured to print a monochrome job after the density correction process.

  Therefore, with respect to a color job, it is possible to match the image processing performed on the job with the image forming conditions at the time of printing for the job, and it is possible to avoid significant image quality deterioration. .

  In addition, for monochrome jobs, even if the image processing applied to the job and the image forming conditions at the time of printing for the job do not match, noticeable image quality degradation does not occur. By doing so, it is possible to prevent the density correction from being postponed more than necessary, and to ensure long-term image quality stability.

  An embodiment of the present invention will be described below with reference to FIGS. First, a schematic configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG.

  FIG. 2 shows a color copying machine 2 which is one of image forming apparatuses. The color copying machine 2 includes a document feeding unit 3, an image reading unit 4, a paper feeding unit 5, an image forming unit 6, and a fixing unit 7.

  The document feeder 3 places a double-sided automatic document feeder 8 (abbreviated as RADF: Reversing Automatic Document Feeder) for feeding a document to be copied and a document fed from the RADF 8 at a predetermined position. A document table 9 and a document receiving tray 10 are included. The RADF 8 has a predetermined positional relationship with the document table 9 and is supported in an openable / closable state. The RADF 8 feeds the original so that one side of the original is placed at a predetermined position of the original table 9 and opposed to the image reading unit 4, and the image reading on one side is completed. Then, the document is reversely transferred so that the other surface is placed at a predetermined position on the document table 9 and opposed to the image reading unit 4, and when the image reading on the other surface is completed, the document is removed. The document is discharged to the document receiving tray 10. Such document feeding and front / back reversing operations are controlled in relation to the overall operation of the copying machine 2. When only one side of the original is copied, the reverse transfer of the original is not executed.

  The image reading unit 4 is disposed below the document table 9, performs an operation of reading an image of the document fed to the document table 9 by the RADF 8, and reciprocally moves in parallel along the lower surface of the document table 9. Second scanning units 11 and 12, an optical lens 13, and a CCD (Charge Coupled Device) line sensor 14 that is a photoelectric conversion element are included.

  The first scanning unit 11 includes an exposure lamp 15 that exposes the surface of a document image to be read and a first mirror 16 that deflects a reflected light image from the document in a predetermined direction, and is constant with respect to the lower surface of the document table 9. While reciprocating at a predetermined scanning speed. The second scanning unit 12 includes second and third mirrors 17 and 18 that further deflect the reflected light image deflected by the first mirror 16 of the first scanning unit 11 in a predetermined direction. And reciprocally move in parallel along the lower surface of the document table 9 while maintaining a constant speed relationship.

  The optical lens 13 reduces the reflected light image deflected by the third mirror 18 of the second scanning unit 12 and forms an image at a predetermined position of the CCD line sensor 14. The CCD line sensor 14 is a three-line color CCD that can read a black-and-white image or a color image and output line data that is color-separated into red (R), green (G), and blue (B) color components. The reflected light image formed by the optical lens 13 is photoelectrically converted in sequence to output an electrical signal. Document image information output as an electrical signal from the CCD line sensor 14 is input to the image forming unit 6.

  The paper feeding unit 5 is disposed at the lowermost part of the copier 2 and has a paper tray 19 on which recording paper P as a recording medium is stacked and separated, and a separation roller that separates and feeds the recording paper P in the paper tray 19 one by one. 20 and a paper feed roller 21, and supplies the recording paper P as a recording medium to the image forming unit 6. The recording paper P separated and supplied one by one from the paper supply unit 5 is transported to the front of the image forming unit 6 by transport rollers 22 provided in various transport paths of the recording paper P, and is provided in front of the image forming unit 6. The sheet feeding timing is controlled by the pair of registration rollers 23 and is supplied to the image forming unit 6.

  The image forming unit 6 is disposed between the image reading unit 4 and the paper feeding unit 5, and includes a laser beam scanner unit 24, an image forming station 25, and a transfer conveyance belt mechanism 26. The transfer / conveying belt mechanism 26 is disposed below the image forming unit 6, and has a driving roller 27, a driven roller 28, an endless belt 29 stretched between the driving roller 27 and the driven roller 28, and a surface of the endless belt 29. An adsorption charger 30 for charging and adsorbing the recording paper P and a static eliminator 31 for separating the recording paper P adsorbed on the endless belt 29 are provided.

  The endless belt 29 is driven in the direction of the arrow 32 by rotation around the axis of the drive roller 27. The recording paper P supplied with timing control by the registration roller 23 is electrostatically attracted to the surface-charged endless belt 29 by the suction charger 30 and conveyed in the direction of the arrow 32 described above. An image is transferred to the recording paper P in the process of being conveyed in the direction of the arrow 32 by the endless belt 29. It is conveyed. Paper feed timing control by the registration roller 23 is detected by a sensor (not shown) provided in the transport path of the recording paper P in the transport direction, and is executed according to the detection output of the sensor.

  Since the copying machine 2 is a color copying machine, four sets of the laser beam scanner unit 24 and the image forming station 25 are provided corresponding to each color of black, cyan, magenta, and yellow. Each of the laser beam scanner units 24 and the image forming station 25 has a pixel signal corresponding to a black component image of the image original information that the color of toner used for development is different from black, cyan, magenta, and yellow. Since the pixel signal corresponding to the cyan color component image, the pixel signal corresponding to the magenta color component image, and the pixel signal corresponding to the yellow color component image are the same, the configuration is the same. The unit 24 and the image forming station 25 will be described as representative examples, and the description of the other will be omitted. When the laser beam scanner unit 24 and the image forming station 25 corresponding to each color are individually shown, alphabetic suffixes: b (black), c (cyan), m (magenta), y (yellow) This is indicated with

  The laser beam scanner unit 24b deflects a laser beam from the semiconductor laser element (not shown) that emits dot light modulated according to image document information input from the image reading unit 4 and a laser beam from the semiconductor laser element in the main scanning direction. A polygon mirror 33b, fθ lenses 34b and 35b for imaging a laser beam deflected by the polygon mirror 33b on the surface of an electrophotographic photoreceptor 40b (hereinafter simply referred to as a photoreceptor), and reflection mirrors 36b, 37b and 38b. Is provided. The laser beam reflected by the reflecting mirror 38b exposes the surface of the photoreceptor 40b of the image forming station 25b, and forms an electrostatic latent image.

  The image forming station 25b is exposed with a photosensitive member 40b that is rotatably supported in the direction of the arrow F around the axis 39b, and the following equipment arranged along the circumferential surface of the photosensitive member 40b, that is, the laser beam described above. The electrostatic latent image formed on the surface of the photosensitive member 40b by developing the charger 41b for uniformly charging the surface of the photosensitive member 40b and the exposure of the laser beam output from the laser beam scanner unit 24b is developed. A developing device 42b for visualizing the image, a transfer discharge device 43b for transferring the developed image, which is provided opposite to the photoreceptor 40b via the endless belt 29, onto the recording paper P on the endless belt 29, and an electrostatic latent image. And a cleaning unit 44b that removes and collects toner remaining on the surface of the photoreceptor 40b after the developing process. The charger 41b, the developing unit 42b, the transfer discharger 43b, and the cleaning unit 44b are provided in this order from the upstream side to the downstream side in the rotation direction indicated by the arrow F.

  The charger 41b uniformly charges the surface of the photoreceptor 40b by discharging. The surface of the uniformly charged photoreceptor 40b is exposed by the laser beam from the laser beam scanner unit 24b corresponding to the image document information, and the charged amount of the exposed portion and the charged amount of the unexposed portion are changed. Differences occur and an electrostatic latent image is formed.

  The developing device 42b can freely rotate a developing roller 45b provided to face the photoreceptor 40b, a developer conveying roller 46b that supplies a developer containing toner to the developing roller 45b, a developing roller 45b, and a developer conveying roller 46b. And a casing 47b for accommodating the developer in the internal space. The developer is supplied from the developing roller 45b of the developing device 42b to the surface of the photoreceptor 40b on which the electrostatic latent image is formed, whereby the electrostatic latent image is developed and visualized. The visualized image is transferred to the recording paper P on the endless belt 29 by the transfer discharger 43b as described above.

  The recording paper P on which the black image is transferred is conveyed in the direction of the arrow 32 while being adsorbed by the endless belt 29, and is provided in the following order from the upstream side to the downstream side in the conveyance direction. When passing through the yellow laser beam scanner units 24c, 24m, and 24y and the image forming stations 25c, 25m, and 25y, the cyan, magenta, and yellow images are sequentially changed in the same manner as the black image described above. Transcribed. In this way, a full color image is formed on the recording paper P. The recording paper P on which the full-color image is formed is peeled off from the endless belt 29 by the static eliminator 31 and fed to the fixing unit 7.

  The fixing unit 7 includes a heating roller 48 that includes a heating unit (not shown), and a pressure roller 49 that is provided to face the heating roller 48 and that is pressed by the heating roller 48 to form a so-called nip portion 50. The recording paper P supplied to the fixing unit 7 is heated and pressurized when passing through the nip part 50, and the developer on the recording paper P is fixed to form a robust image.

  When the recording paper P fixed by the fixing unit 7 forms an image only on one surface, or when the image is formed on the other surface after being reversed after forming the image on one surface, the switching gate 51 operates. The paper is fed upward, and is further discharged to a paper discharge tray 53 by a discharge roller 52. When an image is formed on one surface of the recording paper P and then further on the other surface, the recording paper P is fed downward by the operation of the switching gate 51, and the switchback transport path 54. Then, the image is reversed and then conveyed again to the image forming unit 6. An image is formed on the recording paper P fed to the image forming unit 6 in the same manner as described above.

  The configuration of the image forming apparatus shown in FIG. 2 is merely an example, and does not limit the present invention. The image forming apparatus according to the present invention may be a copying machine or a printer, or may be a complex machine having functions in both.

  An image forming apparatus according to the present invention forms an image by an electrophotographic system and has an image memory capable of storing a plurality of jobs. As an embodiment of the image forming apparatus to which the present invention is applied, the configuration of a digital color copying machine is shown in FIG. As shown in FIG. 3, the digital color copying machine includes an image input device 60 and an image output device 70.

  The image input device 60 is composed of a scanner unit having, for example, a CCD (Charge Coupled Device), and the reflected light image from the original is converted into an analog signal of RGB (R: red, G: green, B: blue) by the CCD. This is read and input to the image output device 70. The image output device 70 performs predetermined image processing on the image data input from the image input device 60, and outputs the image data subjected to the image processing onto a recording medium (for example, paper). Image formation is performed by a photographic method. The image input unit 60 is not included in the image forming apparatus of the present invention and may be connected to the outside. The image input unit 60 is not limited to a scanner, and may be an information processing apparatus that inputs image data to the image output apparatus 70 via a network, such as a personal computer.

  The image output device 70 includes an image processing unit 71, an image memory 72, a correction amount storage unit 73, an image output unit 74, and a density correction unit 75. The above-described units of the image output device 70 are controlled by a control unit (not shown).

  The image processing unit 71 performs image processing including γ processing and screen processing on the image data input from the image input device 60 and outputs the processed image data to the image output unit 74. A more specific configuration example of the image processing unit 71 is shown in FIG.

  That is, the image processing unit 71 performs smoothing processing, sharpening processing, and scaling processing on the image data input from the image input device 60 by the shading correction unit 711, and outputs an image by the γ adjustment processing unit 712. Γ processing such as luminance / density conversion and copy density correction in accordance with the gradation characteristics of the unit 74 is performed, color conversion processing from RGB to CMYK is performed by the color conversion processing unit 713, and dither processing and error are performed by the intermediate processing unit 714 Apply diffusion treatment. Then, the compression / decompression unit 715 compresses the image data, and the image data is stored in the image memory 72 under the control of the control unit.

  When there is an instruction to output image data from the control unit, the image processing unit 71 reads the image data from the image memory 72 and decompresses it by the compression / decompression unit 715. The read image data is subjected to screen processing such as pulse width modulation for each of the image data CMYK by the screen processing unit 716 and output to the image output unit 74. As described above, the basic processing contents of the image processing unit 71 are color conversion processing, γ processing, and screen processing. In the configuration example of FIG. 4, the image data before the screen processing is stored in the image memory 72, but the image data after the screen processing is stored in the image memory 72 may be used. Good.

  The image memory 72 temporarily stores image data input from the image input device 60, that is, a print request job. Since the image forming apparatus has the image memory 72, when printing of another job is requested during printing of a certain job, the job relating to the new printing request is stored in the image memory 72. A plurality of jobs can be stored.

  Next, density correction processing in the image output unit 74 will be described. The density correction processing in the image forming apparatus is performed by the density correction unit 75 changing the image forming conditions of the image output unit 74.

  That is, the density correction process is performed by, for example, actually creating a toner image on a photosensitive member or a transfer material conveying belt before normal image formation, and detecting optical characteristics such as a reflected light amount of the toner image, etc. It means obtaining image forming conditions for obtaining a desired density.

  Such density correction processing is performed when the power is turned on, when the toner cartridge is replaced, or whenever a predetermined number of sheets are output, and a plurality of patch images corresponding to a predetermined density are formed on the photosensitive drum. Next, the patch image is transferred onto a transfer material conveyance belt through exposure, development, and transfer. Then, the density of the patch image transferred onto the transfer material conveying belt is measured by a density detection sensor.

  The density of the patch image measured by the density detection sensor is sent to the density correction unit 75 and compared with the density reference value. The density correction unit 75 performs density correction when the density of the patch image is deviated from the density reference value, that is, the image output unit so that the density of the patch image matches the density reference value. The image forming conditions 74 are changed. Density correction methods include (1) a method for changing the developing bias voltage, (2) a method for changing the charging potential by irradiation with the maximum exposure amount, and (3) a method for changing the peripheral speed ratio of the developing sleeve. Conceivable. In other words, the image forming condition obtained by the density correction unit 75 during the density correction process is stored in the correction amount storage unit 73 as a correction amount such as a developing bias voltage or a charging potential.

  The density correction process is performed for each color image forming unit because the image forming apparatus forms a color image.

  Further, the density correction unit 75 can perform a high density correction process and a halftone density correction process as the density correction process. That is, in the high density correction process, when the toner amount detection means detects a high density from the high density detection toner pattern and compares it with the high density reference value, a deviation from the high density reference value occurs. Performs high density correction. Further, in the halftone density correction process, the halftone density is detected from the toner pattern for halftone density detection by the toner detecting means under the condition that high-density image adjustment is guaranteed, and the reference is obtained by comparing with the halftone density reference value. If there is a deviation from the value, halftone density correction is performed.

  In the image forming apparatus according to the present embodiment, when the density correction execution condition is satisfied during printing of a certain job and the image memory 72 has image data waiting to be printed at that time, the density correction processing is performed quickly. It is also intended to enable appropriate printing for all jobs stored in the image memory 72.

  For this reason, in the image forming apparatus, when the density correction execution condition is satisfied and the density correction process is performed by interrupting the printing job, the γ process and the screen process are already finished and stored in the image memory 72. With respect to the print waiting job, the job output order is changed so that the processing is different between the color job and the monochrome job.

  For example, as shown in FIG. 1, when the jobs A to E are stored in the image memory 72 and the density correction execution condition is satisfied while the job A is being printed, the jobs B to E that are waiting for printing at that time are displayed. Are classified into color jobs and monochrome jobs, and the job output order is switched. Specifically, the output order of jobs B, C, and E, which are color jobs, is first, and the output order of job D, which is a monochrome job, is later.

  The color job is printed before the density correction process, and the density correction process is performed immediately after the color job is printed. Thereafter, a monochrome job is printed.

  As described above, when it is time to execute the density correction process during the printing of the job, before executing the density correction process, among the jobs waiting for printing stored in the image memory 72 at that time, the color correction process is performed. Print only the job first. As a result, for color jobs, the image processing (γ processing or screen processing) applied to the job at the time of storage in the image memory 72 can be matched with the image forming conditions at the time of printing for the job. it can.

  That is, if the image processing performed for a job and the image forming conditions at the time of printing for the job do not match, appropriate density correction cannot be performed, and there is some deviation from the original density of the image. Give rise to In a color job, such a density shift occurs for each basic color (for example, C, M, Y). Therefore, these shifts may combine with each other to impair the color of the image and cause a significant deterioration in image quality. is there. For this reason, the above-described method can reliably avoid such image quality deterioration in the color job.

  On the other hand, in a monochrome job, the image processing applied to the job and the image forming conditions at the time of printing for the job do not match, and even if there is a slight deviation from the original density of the image, The shift does not impair the color of the image and the like, and no significant image quality deterioration occurs.

  For this reason, with respect to a monochrome job waiting for printing at the time of execution of the density correction process, the printing process is performed after the density correction process, and the density correction process is performed first. That is, by performing the density correction process before printing monochrome data, it is possible to prevent the density correction from being postponed more than necessary, and to ensure long-term image quality stability.

  In an electrophotographic color image forming apparatus, density correction processing can be performed quickly and appropriate printing can be performed for all jobs, which can be applied to applications such as color copying machines and color printers.

FIG. 2 is a diagram illustrating a relationship between density correction processing and job printing in an image forming apparatus according to an exemplary embodiment of the present invention. It is sectional drawing which shows schematic structure of the said image forming apparatus. FIG. 2 is a block diagram illustrating a main configuration of the image forming apparatus. It is sectional drawing which shows schematic structure of the image process part in the said image forming apparatus.

Explanation of symbols

60 Image input device 70 Image output device 71 Image processing unit 72 Image memory 73 Correction amount storage unit (density correction unit)
74 Image output unit (image forming unit)
75 Density correction unit

Claims (3)

In an image forming apparatus having an image forming unit to which an electrophotographic method is applied,
An image memory capable of storing image data corresponding to a plurality of jobs;
An image processing unit that performs image processing on image data to be output;
A density correction unit that changes the image forming conditions of the image forming unit in order to perform density correction processing in the image forming unit when the image forming unit satisfies a density correction execution condition;
The image data waiting for printing stored in the image memory is stored in a state where γ processing or γ processing and screen processing are performed among the image processing performed in the image processing unit,
If the density correction execution condition of the image forming unit is satisfied during printing of a certain job, the job stored in the image memory at that time is classified into a color job and a monochrome job, and the color job is An image forming apparatus, wherein density correction processing is performed after priority printing, and a monochrome job is printed after density correction processing.   The image forming apparatus according to claim 1, wherein the image forming condition is a developing bias voltage.   The image forming apparatus according to claim 1, wherein the image forming condition is a charging bias voltage.

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