JP2006330123A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute an image density compensation mode in a normal image forming system even when a void (firefly) is produced in a density detection mark due to some reason during execution of the image density compensation mode. <P>SOLUTION: The image forming apparatus is provided with an image density compensation mode and an image forming system recovery mode, image forming units 10Y, 10M, 10C and 10K forming the density detection marks for image density compensation on an intermediate transfer belt 6 through photoreceptor drums 1Y, 1M, 1C and 1K, an image density sensor 12 detecting a density detection mark Md formed on the intermediate transfer belt 6 by these units and a control means 15 judging the abnormality or normality by comparing an image density detected by the image density sensor 12 and a judging reference value for the image density and continuing the image density compensation mode based on the judged result or executing the image forming system recovery mode by interrupting the image density compensation mode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention has an image forming apparatus and an image suitable for being applied to a tandem type color printer or color copier having a photoconductive drum and an intermediate transfer belt and having an image density correction mode, a color complex machine thereof, and the like. The present invention relates to a forming method.

  In recent years, tandem type color printers, color copiers, and these color composite machines have been used in many cases. In these color image forming apparatuses, a laser writing unit, a developing unit, a photosensitive drum, an intermediate transfer belt, and a fixing device for yellow (Y), magenta (M), cyan (C), and black (BK) colors. It has.

  For example, a Y-color laser writing unit draws an electrostatic latent image on a photosensitive drum based on information for forming a color image. The developing unit forms a color toner image by attaching a Y-color toner agent to the electrostatic latent image drawn on the photosensitive drum. The photosensitive drum transfers the toner image to the intermediate transfer belt. Similar processing is performed for the other M, C, and BK colors. The color toner image transferred to the intermediate transfer belt is transferred to a sheet and then fixed by a fixing device.

  According to this image forming apparatus, in order to maintain optimum color image formation quality, yellow (Y), magenta (M), cyan (C), and black that reproduce the R, G, and B colors of the original image. It is essential to correct the image forming means so that a predetermined image density of (BK) color is obtained (hereinafter referred to as an image density correction mode). Regarding the image density correction mode, the density detection mark formed on the intermediate transfer belt or the conveyance material transfer belt is detected by a detection means for detecting the image density (hereinafter referred to as an image density sensor) such as a reflection type sensor, and for each color. The difference in image density of the density detection mark with respect to the reference image density (control target value) is calculated, and the image density is corrected by controlling the developing bias and the laser drive circuit so as to eliminate the image density difference. Made.

  With regard to this type of color image forming apparatus, Patent Document 1 describes a color image recording method and apparatus. According to this color image recording apparatus, at the time of color balance adjustment, an electrostatic latent image for YMC color is formed on the photosensitive drum, and the electrostatic latent image of each color is developed by the developing device for each color. The YMC color toner images are superposed on the drum, and the color toner image superposed thereon is detected by a toner density sensor. The color balance means inputs and compares the toner density detection value obtained from the toner density sensor and a preset image density reference value, and determines whether the image density is abnormal or normal. For the toner agent of the color determined to be abnormal by the color balance means, an electrostatic latent image for the corresponding color is forcibly formed on the photosensitive drum, and the electrostatic latent image is developed by the developer for the corresponding color. The toner of the corresponding color is consumed after development.

  When the color image recording apparatus is configured in this way, even when the toner density is almost a predetermined value, even when the image density is lowered between the color developers, the image density is appropriate and the color balance is maintained. It is possible to reproduce a good color image.

  Patent Document 2 discloses an electrophotographic image forming apparatus. According to this image forming apparatus, the control means for determining the size of the image ratio based on the image density information and for controlling the mode in which the toner agent is forcibly consumed based on this determination is provided. When such a control means is configured, a high-quality image can be output stably over a long period even when a large amount of an image with a small amount of toner consumption is output.

Japanese Patent Laid-Open No. 05-323780 (FIG. 1 on page 5) Japanese Patent Application Laid-Open No. 09-034243 (page 3 FIG. 1)

However, the color image forming apparatus according to the conventional example has the following problems.
i. In the case where the image density correction mode is executed by a color image recording apparatus such as that disclosed in Japanese Patent Application Laid-Open No. 2004-228688, when the density detection mark causes a white spot (firefly) phenomenon to occur, the image density is accurately determined. There is a risk of being unable to calculate. Here, the white spot phenomenon means that the image formation output with a low printing rate has continued, the toner in the developing device has deteriorated and changed its shape, or foreign matter has entered the developing device or toner bottle. As a cause, in the next charging / exposure / development / cleaning cycle, a small amount of residual toner agent, paper dust fine powder and the like are involved, thereby preventing normal exposure. As a result, a part of the density detection mark is developed in white.

  When the white portion of the density detection mark is detected by the image density sensor, an image density different from the reference image density at the time of designing the mark is detected. As a result, the density detection value includes an error, and an accurate image density difference value or the like may not be calculated.

  ii. According to Patent Document 2, the toner consumption amount is estimated by measuring the image data and the toner consumption ratio is predicted, and if it is determined that the consumption rate is low, the toner consumption mode is forcibly executed, so Is preventing. However, in the case of the conventional method, the problem i still remains for unexpected white spots such as contamination of foreign matter in the developing unit or toner bottle.

  Therefore, the present invention solves the above-described problems, and even when a white spot (firefly) occurs in a printed image for some reason when the image density correction mode is executed, a normal image forming system is used. An object of the present invention is to provide an image forming apparatus and an image forming method capable of executing an image density correction mode.

  In order to solve the above problems, an image forming apparatus according to claim 1 of the present invention is an image forming apparatus that forms a color image on an image carrier, and forms a print image for image density correction on the image carrier, The image density of the printed image is read, an image density difference with respect to the reference image density of the printed image is calculated, and an operation for correcting the image density based on the image density difference is set as an image density correction mode. Image forming means for forming a printed image for image density correction on the image carrier when the image forming system recovery mode is set to an operation for forming a printed image for correction and removing the printed image formed on the image carrier. An image detecting means for detecting an image density of a printed image formed on the image carrier by the image forming means, an image density of the printed image detected by the image detecting means, and a discrimination reference value for the image density. Compared to abnormal or Control means for discriminating normality and continuing the image density correction mode based on the discrimination result or canceling the image density correction mode and executing the image forming system recovery mode. .

  According to the image forming apparatus of the present invention, when a color image is formed on the image carrier and the image density correction mode is executed, the image forming means displays the image density correction printed image as the image carrier. Form on the body. The image detecting means detects the image density of the printed image formed on the image carrier by the image forming means. On the premise of this, the control means discriminates an abnormality by comparing the image density of the printed image detected by the image detection means with a preliminarily prepared image density discrimination reference value, and based on the discrimination result, the image The density correction mode is continued, or the image density correction mode is stopped and the image forming system recovery mode is executed.

  Accordingly, when the image density correction mode is executed, if it is determined as “abnormal”, the image density correction mode is stopped, and an image for image density correction is formed on the image carrier, and then the image density correction image is formed on the image carrier. By removing the image density correction image, the image forming means can be restored to a normal state.

  The image forming method according to claim 5 is an image forming method for forming a color image on an image carrier, wherein a print image for image density correction is formed on the image carrier, the image density of the print image is read, and the print image is printed. An image density difference with respect to a reference image density of an image is calculated, and an operation for correcting the image density based on the image density difference is set as an image density correction mode. A print image for image density correction is formed on the image carrier, and the image When the operation for removing the image density correction printed image formed on the carrier is set to the image forming system recovery mode, a step of forming the image density correction printed image on the image carrier and the image density correction image formed on the image carrier. A step of detecting the image density of the stamped image, a step of comparing the detected image density of the stamped image with a discrimination reference value of the image density, and determining abnormality or normality, and image density correction based on the discrimination result Continue mode or image density It is characterized in that a step of performing an image forming system restoration mode to cancel the positive mode.

  According to the image forming method of the present invention, when a color image is formed on the image carrier and it is determined as “abnormal” when the image density correction mode is executed, the image density correction mode is stopped. By forming an image density correction image on the image carrier and then removing the image density correction image formed on the image carrier, the image forming means can be restored to a normal state. .

  According to the image forming apparatus and the image forming method of the present invention, the image density of the printed image for image density correction is compared with an image density determination reference value prepared in advance to determine abnormality or normality. The image density correction mode is continued based on the result, or the image density correction mode is stopped and the image forming system recovery mode is executed.

  With this configuration, when the image density correction mode is determined to be “abnormal”, the image density correction mode is stopped and an image for image density correction is formed on the image carrier, and then the image carrier is subjected to the image density correction mode. By removing the formed image density correction image, the image forming means can be restored to a normal state. Therefore, even when the image density correction mode is executed, even if a white spot (firefly) occurs in the printed image for some reason, the image density correction mode is executed with the normal image forming means after the execution of the image forming system recovery mode. become able to.

  Hereinafter, an image forming apparatus and an image forming method according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram showing a configuration example of a color copying machine 100 as an embodiment of the present invention.
A color copying machine 100 shown in FIG. 1 constitutes an example of an image forming apparatus, and forms a color image by superimposing colors on an image carrier based on image information. In this example, the color copying machine 100 has an image density correction mode and an image forming system recovery mode. Here, the image density correction mode is an image density correction mark image (hereinafter referred to as density detection mark Md) formed on the image carrier, and the image density of the density detection mark Md is read to obtain a difference from the reference image density. Is calculated, and the image density is corrected based on the difference. The image forming system recovery mode is an operation of forming an image density correction image on the image carrier and removing the image density correction image formed on the image carrier.

  The color copying machine 100 includes a copying machine main body 101 and an image reading device 102. An image reading device 102 including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the copying machine main body 101. The document d placed on the document table of the automatic document feeder 201 is transported by a transport unit (not shown), and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 202. Incident light reflecting the image is read by the line image sensor CCD.

  The analog image signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing unit (not shown) to become digital image information. The image information is sent to the laser writing units 3Y, 3M, 3C, 3K constituting the image forming means.

  The copying machine main body 101 is called a tandem type color image forming apparatus. The image forming means includes a plurality of sets of image forming units (hereinafter also referred to as image forming system II) 10Y, 10M, 10C, and 10K each having an image carrier for each color, and an endless intermediate transfer belt 6 (hereinafter referred to as image transfer system I). And a sheet feeding / conveying means including a sheet re-feeding mechanism (ADU mechanism), and a fixing device 17 for fixing the toner image.

  In this example, the image forming unit 10Y includes a photosensitive drum 1Y, a charger 2Y, a laser writing unit 3Y, a developing unit 4Y, and a cleaning unit 8Y for an image forming body, and forms a yellow (Y) image. To be made. For example, the photosensitive drum 1Y is rotatably provided near the upper right portion of the intermediate transfer belt 6 so as to form a Y-color toner image. In this example, the photosensitive drum 1Y is rotated counterclockwise by a driving mechanism (not shown). A charger 2Y is provided on the lower right side of the photosensitive drum 1Y so as to charge the surface of the photosensitive drum 1Y to a predetermined potential.

  A laser writing unit 3Y is provided almost directly beside the photoconductor drum 1Y, and has a predetermined intensity based on the image data for Y color with respect to the precharged photoconductor drum 1Y. The laser beam light is scanned. This laser beam light is deflected and scanned, for example, by rotating a polygon mirror for Y color. This is so-called Y-color image data writing in the main scanning direction. The main scanning direction is a direction parallel to the rotation axis of the photosensitive drum 1Y. The photosensitive drum 1Y rotates in the sub-scanning direction. The sub-scanning direction is a direction orthogonal to the rotation axis of the photosensitive drum 1Y. The photosensitive drum 1Y rotates in the sub-scanning direction, and an electrostatic latent image for Y color is formed on the photosensitive drum 1Y by the deflection scanning of the laser beam light in the main scanning direction.

  A developing unit 4Y is provided above the laser writing unit 3Y, and operates to develop a Y-color electrostatic latent image formed on the photosensitive drum 1Y. The developing unit 4Y has a Y-color developing roller (not shown), and a magnet is disposed therein, and a two-component developer obtained by stirring the carrier and the Y-color toner in the developing unit 4Y. The toner is rotated and conveyed to the opposite portion of the photosensitive drum 1Y, and the electrostatic latent image is developed with a Y-color toner.

  A correction unit 5Y is connected to the developing unit 4Y, and the amount of toner agent attached to the photosensitive drum 1Y is adjusted based on a development correction signal Sy supplied from the control unit 15. For example, the bias voltage between the photosensitive drum 1Y and the developing unit 4Y is adjusted, and the two-component developer for Y color is conveyed and attached from the developing unit 4Y having the adjusted bias voltage to the photosensitive drum 1Y. To be made.

  The Y toner image formed on the photosensitive drum 1Y is transferred to the intermediate transfer belt 6 by operating the primary transfer roller 7Y (primary transfer). A cleaning unit 8Y is provided below the left side of the photosensitive drum 1Y so as to remove (clean) the toner remaining on the photosensitive drum 1Y in the previous writing.

  In this example, an image forming unit 10M is provided below the image forming unit 10Y. The image forming unit 10M includes a photosensitive drum 1M, a charger 2M, a laser writing unit 3M, a developing unit 4M, and an image forming member cleaning unit 8M, and forms a magenta (M) color image. The A correction unit 5M is connected to the developing unit 4M, and the amount of toner agent attached to the photosensitive drum 1M is adjusted based on a development correction signal Sm supplied from the control unit 15.

  An image forming unit 10C is provided below the image forming unit 10M. The image forming unit 10C includes a photosensitive drum 1C, a charger 2C, a laser writing unit 3C, a developing unit 4C, and an image forming body cleaning unit 8C, and forms a cyan (C) color image. The A correction unit 5C is connected to the developing unit 4C, and the amount of toner agent attached to the photosensitive drum 1C is adjusted based on a development correction signal Sc supplied from the control unit 15.

  An image forming unit 10K is provided below the image forming unit 10C. The image forming unit 10K includes a photosensitive drum 1K, a charger 2K, a laser writing unit 3K, a developing unit 4K, and a cleaning unit 8K for an image forming body, and forms a black (BK) color image. The A correction unit 5K is connected to the developing unit 4K, and the amount of toner agent attached to the photosensitive drum 1K is adjusted based on a development correction signal Sk supplied from the control unit 15. For the configurations and functions of the image forming units 10M to 10K and the correction units 5C to 5K therein, refer to the image forming unit 10Y.

  An organic photoconductor (OPC) drum is used as the above-mentioned photoconductor drums 1Y, 1M, 1C, and 1K. Scorotron band electrodes are used for the chargers 2Y, 2M, 2C, and 2K, and a DC voltage of several hundreds [V] units is applied. The primary transfer rollers 7Y, 7M, 7C, and 7K are applied with a primary transfer bias voltage having a polarity opposite to that of the toner agent to be used (positive polarity in this embodiment).

  The intermediate transfer belt 6 is an example of an image carrier, and forms a color toner image (color image) by polymerizing the toner images transferred by the primary transfer rollers 7Y, 7M, 7C, and 7K. The color image formed on the intermediate transfer belt 6 is conveyed toward the secondary transfer roller 7A as the intermediate transfer belt 6 rotates clockwise. The secondary transfer roller 7A is positioned below the intermediate transfer belt 6 and transfers the color toner image formed on the intermediate transfer belt 6 onto a sheet conveyed from a sheet feeding unit (not shown) ( Secondary transfer).

  A fixing device 17 is provided on the left side of the secondary transfer roller 7A to fix the paper on which the color image has been transferred. The fixing device 17 includes a fixing roller, a pressure roller, and a heater. In the fixing process, the paper is heated and pressed by passing the paper between a fixing roller and a pressure roller heated by a heater. The fixed sheet is sandwiched between the discharge rollers 25 and placed on the discharge tray 25 outside the apparatus.

  In this example, a cleaning unit 8A is provided on the upper left side of the intermediate transfer belt 6 and operates to clean the toner agent remaining on the intermediate transfer belt 6 after transfer. The cleaning unit 8 </ b> A has a neutralization unit that neutralizes charges on the intermediate transfer belt 6 and a pad that removes toner remaining on the intermediate transfer belt 6. The intermediate transfer belt 6 after the belt surface is cleaned by the cleaning unit 8A and discharged by the discharging unit enters the next image forming cycle.

  An image density sensor 12 as an example of an image detection unit is provided in an area where the upper surface of the intermediate transfer belt 6 can be seen on the upstream side of the cleaning unit 8A of the copying machine main body 101, and the image forming unit 10Y described above. , 10, 10C, and 10K, the density detection mark Md for image density correction for each color formed on the intermediate transfer belt 6 is detected.

  FIG. 2 is a perspective view showing an example of detection of the density detection mark Md by the image density sensor 12. The image density sensor 12 shown in FIG. 2 is an area where the surface of the intermediate transfer belt can be seen, and is provided on one end of the intermediate transfer belt 6, and when the image density correction mode is executed, the image forming units 10Y, 10M, The density detection marks Md formed on both sides of the intermediate transfer belt 6 are detected by 10C and 10K.

  In the image density correction mode, a plurality of density detection marks Md for image density correction are formed for each color on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, and 1K, and the density detection marks Md are displayed. The image density is read, a difference in image density of the density detection mark Md with respect to the reference image density is calculated, and the image density is corrected based on the difference.

  In this example, the image density sensor 12 detects the image density at a plurality of detection points for each density detection mark Md. The image density refers to the respective toner image adhesion amounts of Y color, M color, C color, BK color, etc. when a color image based on image data is reproduced on the intermediate transfer belt 6. This image density is corrected by adjusting the toner image adhesion amount on the photosensitive drums 1Y, 1M, 1C, and 1K.

  In the image forming system recovery mode (toner forced consumption mode), a toner image based on the density detection mark Md for image density correction is formed on the photosensitive drums 1Y, 1M, 1C, and 1K and the intermediate transfer belt 6, and the photosensitive drum The toner image for image density correction transferred from the body drums 1Y, 1M, 1C, 1K to the intermediate transfer belt 6 is removed by the cleaning means 8A.

  FIG. 3 is a block diagram showing a configuration example of the image transfer system I and the image forming system II of the color copying machine 100. In the color copying machine 100 shown in FIG. 2, the processing system including the intermediate transfer belt 6 and the image density sensor 12 shown in FIG. 1 is an image transfer system I, and the image forming units 10Y, 10M, 10C, and 10K are image forming systems. Extracted as II.

  In FIG. 3, the color copying machine 100 includes image forming units 10Y, 10M, 10C, and 10K, an image density sensor 12, a nonvolatile memory 14, a control unit 15, an operation unit 16, a display unit 18, and an image processing unit 70. Yes.

  The image density sensor 12 is connected to the control means 15, and when the image density correction mode is executed, the density detection mark Md formed on the intermediate transfer belt 6 is detected and a density detection signal S2 is output. As the image density sensor 12, a reflective optical sensor, an image sensor, or the like is used. These sensors include a light emitting element and a light receiving element. Light is emitted from the light emitting element to the density detection mark Md, and the reflected light is detected by the light receiving element.

  A control unit 15 is provided in the copying machine main body 101, and a density detection signal S2 detected by the image density sensor 12 is input. Based on the density detection signal S2, the image density of the density detection mark Md and the image are displayed. The density discrimination reference value Lth is compared to discriminate abnormality or normality. Here, the discrimination reference value Lth is a reference value for discriminating whether or not the image density level of the density detection mark Md includes an abnormal level (hereinafter referred to as a whiteout level) caused by whiteout. Say.

  In this example, the discrimination reference value Lth is obtained by adding a weighting factor α () to a difference (Lmax−Lmin) between the maximum value (Lmax) and the minimum value (Lmin) of the reference image density of the density detection mark Md for each color calibrated in advance. It is selected and set from a value Lth = α (Lmax−Lmin) obtained by calculating 0 <α <1).

  The control unit 15 samples the density detection signal S2 obtained from the image density sensor 12, and detects a level (hereinafter referred to as a patch detection level L1x) indicating the image density at a plurality of detection points in the density detection mark Md. Thereafter, a maximum value and a minimum value are detected from among a plurality of patch detection levels L1x (x = 1 to n) in the density detection mark Md. Then, a difference Lε between the maximum value Lmax and the minimum value Lmin in the density detection mark Md is calculated. The control means 15 compares the difference Lε with the determination reference value Lth to determine the magnitude relationship.

  For example, when the difference Lε exceeds the determination reference value Lth, it is determined that the density detection mark Md is abnormal. When the difference Lε is less than the determination reference value Lth, it is determined that the density detection mark Md is normal. The control unit 15 continues the image density correction mode based on the determination result of abnormality or normality by the comparison process, or stops the image density correction mode and executes the image forming system recovery mode (toner forced consumption mode). .

  When executing the image density correction mode, an average value of density detection values obtained by density detection at a plurality of detection points within the same density detection mark Md is calculated for each color, and this average value is calculated as the density value. The image density of the detection mark Md (patch detection level L1) is set.

  In the image density correction mode, the control unit 15 determines the toner agent adhesion amounts of the developing units 3Y, 3M, and 3C based on the image density data Dg after the analog / digital conversion of the density detection signal S2 obtained from the image density sensor 12. Control. An operation unit 16 is connected to the control unit 15, and operation data D31 such as an image forming condition is input by a user in a normal print mode. The operation is performed by the user. In addition to the operation means 16, the display means 18 is connected to the control means 15, and for example, the image density correction mode content is displayed based on the display data Dv. A liquid crystal display is used for the display means 18, and the liquid crystal display is used in combination with a touch panel (not shown) constituting the operation means 16.

  A non-volatile memory 14 is further connected to the control means 15 and stores a determination reference value Lth for reference when executing the image density correction mode. The nonvolatile memory 14 stores image density correction data Dε obtained when the image density correction mode is executed, in addition to the image density data Dg and the determination reference value Lth. A hard disk, an EEPROM, or the like is used for the nonvolatile memory 14.

  Image forming units 10Y, 10M, 10C, and 10K are connected to the control unit 15. In the image forming unit 10Y, the photosensitive drum 1Y is loaded based on Y-color write data Wy output from the image processing unit 70. Thus, a Y-color toner image is formed on the intermediate transfer belt 6. The write data Wy includes image data Dy in the normal image forming mode, image data Dy ′ for forming the density detection mark Md in the image density correction mode, and image data for correcting the image density in the image forming system recovery mode. Dy ″ is included. For the configurations and functions of the other image forming units 10M to 10K, refer to the image forming unit 10Y.

  The control means 15 includes image forming units 10Y, 10M, 10M, 10M, 10M, 10M, 10M, 10M, 10M, 10M, and 10D that form density detection marks Md having a predetermined image density for image density correction on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, 1K. 10C and 10K are controlled.

  Further, the control unit 15 controls the image density sensor 12 so as to detect the image density of the density detection mark Md formed on the intermediate transfer belt 6, and the image density of the density detection mark Md detected by the image density sensor 12. And the determination reference value, and if the image density is equal to or less than the determination reference value, the image density correction mode is continued.

  When the image density exceeds the determination reference value, the control unit 15 stops the image density correction mode and applies image density correction to the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1 + C, and 1K. A toner image is formed and an image forming system recovery mode is executed, and then an image density correction mode is executed.

  In the image forming system recovery mode, the control unit 15 forms toner images of all colors for image density correction on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, and 1K. The image forming units 10Y, 10M, 10C, and 10K are controlled so that the toner images of all the colors formed in the above are removed by the cleaning unit 8A. This control forcibly discharges (removes) foreign matter such as a small amount of toner remaining on the photosensitive drum and undesirably adhering paper dust during the previous charging, exposure, development, and cleaning cycle. The image transfer system I and the image forming system II can be restored to the normal state.

  The controller 15 is not limited to this, and the controller 15 determines, for example, only the Y color image for correcting the image density on the intermediate transfer belt 6 via the photosensitive drum 1Y, which is determined to be abnormal in the image forming system recovery mode. The image forming unit 10Y may be controlled such that the Y color image formed and formed on the intermediate transfer belt 6 is removed by the cleaning unit 8A. Similarly, when the image forming units 10M, 10C, or 10K for other colors are determined to be abnormal, the M and C colors for image density correction are applied to the intermediate transfer belt 6 via the photosensitive drums 1M, 1C, and 1K. Only the color or BK color image is formed, and the corresponding M, C, or BK color image formed on the intermediate transfer belt 6 via the photosensitive drums 1M, 1C, and 1K is removed by the cleaning unit 8A. Alternatively, the image forming units 10Y, 10M, 10C, and 10K may be controlled.

4 and 5 are diagrams showing examples (parts 1 and 2) of detection of the density detection mark Md by the image density sensor 12. FIG. FIG. 4A is a top view showing an example of detection when the density detection mark Md is normal.
The density detection mark Md shown in FIG. 4A passes under the arrangement area of the image density sensor 12 when the intermediate transfer belt 6 (not shown) is conveyed in the sub-scanning direction (from the right side to the left side of the paper). At this time, the density detection mark Md is read by the image density sensor 12. For example, light is emitted from the light emitting element of the image density sensor 12 to the density detection mark Md, and the reflected light is detected by the light receiving element.

  FIG. 4B is a diagram illustrating a waveform example of the density detection signal S2. In FIG. 4B, the vertical axis represents the amplitude level of the density detection signal S2 (hereinafter also referred to as density detection level). The horizontal axis is time (time) t. According to the density detection level shown in FIG. 4B, when the density detection mark Md is normally formed, the belt detection level L2 and the patch detection level L1 are clearly separated and detected. In particular, when a plurality of detection points are set and sampled in the same density detection mark Md and the density detection mark Md is normal, the belt detection level L2 or a level approximate to the belt detection level L2 is included in the patch detection level L1. Will not be mixed and detected.

  In this example, eight sample points are set in the concentration detection signal waveform shown in FIG. 4B, the control means 15 samples at a constant interval, and calculates the concentration detection level from the sampling result. 4B, data D1 indicating the patch detection level L11 is obtained at time t1, and similarly, data D2 to D8 indicating the patch detection levels L12 to L18 are obtained from time t2 to t8. When the average value (L11 + L12 + L13 + L14 + L15 + L16 + L17 + L18) / 8 of the patch detection levels L11 to L18 based on these data D1 to D8 is calculated, the image density level (= patch detection level L1) of the density detection mark Md can be obtained from this average value. .

  FIG. 5A is a diagram illustrating a detection example of the density detection mark Md ′ in which white spots have occurred. The density detection mark Md ′ shown in FIG. 5A is a portion where white spots are generated due to deterioration of the toner agent, contamination with foreign matter, or the like. When the density detection mark Md 'in which such a white portion is generated is detected by the image density sensor 12, a density detection signal S2' as shown in FIG. 5B is obtained.

  FIG. 5B is a diagram illustrating a waveform example of the density detection signal S2 '. According to the density detection level shown in FIG. 5B, if white spots occur in the density detection mark Md ′, the belt detection level L2 or the white spot level Lw approximate to the level L2 is detected in the patch detection level L1. .

  In this example, data D1 'to D4' indicating the patch detection levels L11 to L14 are obtained at times t1 to t4, and data D5 'indicating the blank level Lx is obtained at time t5. Thereafter, data D6 'to D8' indicating patch detection levels L16 to L18 are obtained at times t6 to t8. Based on the data D6 'to D8', the control means 15 determines whether or not the density detection mark Md 'includes the white pattern Lw. The control unit 15 continues the image density correction mode based on the abnormality or normal determination result by the determination process, or stops the image density correction mode and executes the image forming system recovery mode (toner forced consumption mode). .

  Next, an image density correction example of the color copying machine 100 will be described for the image forming method according to the present invention. FIG. 6 is a flowchart showing an example of image density correction in the color copying machine 100.

  In this embodiment, an image density correction mode and an image forming system recovery mode are provided, and density detection marks Md for image density correction are formed on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, and 1K. Then, the density detection mark Md formed on the intermediate transfer belt 6 is detected, and the image density of the density detection mark Md detected here is compared with a discrimination reference value prepared in advance to discriminate an abnormality. An example will be given in which the image density correction mode is continued based on the result, or the image density correction mode is stopped and the image forming system recovery mode is executed.

  In this example, when it is determined whether or not the density detection mark Md ′ includes the blank pattern Lw, the maximum reference image density of the density detection mark Md for each color calibrated in advance is used as the determination reference value Lth. The difference (Lmax−Lmin) between the value (Lmax) and the minimum value (Lmin) is selected and set from the value Lth = α (Lmax−Lmin) obtained by calculating the weighting coefficient α (0 <α <1). For example, 0.5 is selected for α.

  Using these as image forming conditions, the operation mode is set in step A1 of the flowchart shown in FIG. In this operation mode setting, an image density correction mode is set. Further, either the full image forming mode or the partial image forming mode in the image forming system recovery mode can be selected. In the all-image forming mode, in the image forming system recovery mode, toner images of all colors for image density correction are formed on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, and 1K. An operation of removing all the toner images formed on the transfer belt 6 by the cleaning means 8A.

  The partial image forming mode refers to only the Y, M, C, or BK colors determined to be abnormal on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, or 1K in the image forming system recovery mode. An operation of forming a toner image for image density correction and removing the toner image of the corresponding color (Y color, M color, C color or BK color) formed on the intermediate transfer belt 6. These operation modes are set using the operation means 16.

  Thereafter, the process proceeds to step A2, and the image forming units 10Y, 10M, 10C, and 10K create a density detection mark Md on the intermediate transfer belt 6. At this time, the image processing circuit 71 shown in FIG. 2 reads out image density correction image data Dy ′ from a memory (not shown) based on the image processing control signal S4 and outputs it to the Y-signal switching unit 72Y. The Y-signal switching unit 72Y selects the image data Dy 'based on the write selection signal S5, and outputs this image data Dy' to the laser writing unit 3Y.

  In the image forming unit 10Y, an electrostatic latent image for image density correction is formed on the photosensitive drum 1Y based on the Y color write data Wy output from the image processing means 70 = image data Dy ′. . This electrostatic latent image is developed by the developing unit 4Y. The Y-color image density correction toner image developed by the developing unit 4Y is transferred to the intermediate transfer belt 6 by operating the primary transfer roller 7Y (primary transfer). The image forming units 10M to 10K are processed in the same manner as the image forming unit 10Y.

  Thereafter, in step A3, the image density sensor 12 reads the density detection mark Md and outputs an image detection signal S2. At this time, the image density sensor 12 shown in FIG. 2 irradiates light from a light emitting element (not shown) onto the intermediate transfer belt 6 moving in the sub-scanning direction at a constant linear velocity, and is reflected from the density detection mark Md and the like. The reflected light is detected by the light receiving element. The image density sensor 12 detects the density detection mark Md on the intermediate transfer belt 6 and outputs a density detection signal S2. The density detection signal S2 is binarized by the control means 15 and becomes image density data Dg. The image density data Dg is stored in the nonvolatile memory 14 for use in determining abnormality of the density detection mark Md.

  In step A4, the control means 15 calculates the maximum-minimum difference in image density for all density detection marks Md for each color of Y, M, C, and BK. At this time, the control means 15 uses the image density data Dg obtained from the image density sensor 12 and, in the example shown in FIG. 5B, from the data D1 to D8, at eight detection points in the density detection mark Md. Detect the image density level. Then, the maximum value and the minimum value are detected from the eight patch detection levels L1x (x = 1 to 8) in the density detection mark Md. Then, a difference Lε between the maximum value Lmax and the minimum value Lmin in the density detection mark Md is calculated.

  Thereafter, in step A5, the control means 15 determines whether the image density of the density detection mark Md for each color of Y, M, C, or BK is abnormal or normal. At this time, the control means 15 compares the difference Lε with the determination reference value Lth to determine the magnitude relationship. For example, when the difference Lε calculated in the previous step A4 is below the determination reference value Lth, it is determined that the density detection mark Md is normal. If it is determined that the image densities of the density detection marks Md for the respective colors Y, M, C, and BK are all “normal” based on the determination result, the process proceeds to step A6 and the image density correction mode is continued. Therefore, these image densities are calculated.

  In step A6, the control means 15 determines whether or not the image density is within an allowable range. At this time, the control means 15 reads and compares the image density correction data Dε and the image density threshold data Dth (image density design allowable value) from the nonvolatile memory 14. If it is determined that the image density is within the allowable range, the image density correction data Dε is stored in step A12, and the image density correction mode is terminated.

  If it is determined in step A7 that the image density is outside the allowable range, reprocessing of the image density correction is necessary. Therefore, the process proceeds to step A8, and after setting the image density correction mode again, the step Returning to A2, the above-described image density correction processing is repeated.

  If the previously calculated difference Lε exceeds the determination reference value Lth, it is determined in step A5 that the density detection mark Md is abnormal. In this case, the image forming system recovery mode should be executed. The process proceeds to step A9. In step A9, the toner image of each color Y, M, C, BK of the intermediate transfer belt 6 created in the image density correction mode is removed by the cleaning means 8A. The Y color toner image remaining on the photosensitive drum 1Y is removed by the cleaning unit 8Y, and the M color toner image remaining on the photosensitive drum 1M is removed by the cleaning unit 8M and remains on the photosensitive drum 1C. The C color toner image thus removed is removed by the cleaning means 8C, and the BK color toner image remaining on the photosensitive drum 1K is removed by the cleaning means 8K.

  Thereafter, the process proceeds to step A10, and the control unit 15 branches the control based on the previously set operation mode. If the all image forming mode is set in step A10, the process proceeds to step A11 to execute the all image forming mode. In the all image forming mode, all toner images of Y, M, C, and BK for image density correction are formed on the intermediate transfer belt 6 through the photosensitive drums 1Y, 1M, 1C, and 1K.

  For example, the image processing circuit 71 shown in FIG. 2 reads out image density correction image data Dy ″ from a memory (not shown) based on the image processing control signal S4 and outputs it to the Y-signal switching unit 72Y. The signal switching unit 72Y selects the image data Dy ″ based on the write selection signal S5, and outputs this image data Dy ″ to the laser writing unit 3Y.

  In the image forming unit 10Y, an electrostatic latent image for image density correction is formed on the photosensitive drum 1Y based on the Y-color write data Wy = image data Dy ″ output from the image processing means 70. Since the subsequent processing conforms to the density detection mark Md in the image forming units 10Y, 10M, 10C, and 10K shown in step A2, refer to that.

  Thereafter, all of the Y, M, C, and BK toner images formed on the intermediate transfer belt 6 are removed by the cleaning means 8A. Of course, the Y-color toner image remaining on the photosensitive drum 1Y is removed by the cleaning means 8Y, and the M-color toner image remaining on the photosensitive drum 1M is removed by the cleaning means 8M and remains on the photosensitive drum 1C. The C color toner image thus removed is removed by the cleaning means 8C, and the BK color toner image remaining on the photosensitive drum 1K is removed by the cleaning means 8K. As a result, the cause of white spots and the like is removed, and all image forming systems for YMCK are restored to a normal state.

  If the partial image formation mode is set in step A10, the process proceeds to step A12 to execute the partial image formation mode. In the partial image forming mode, for example, Y for image density correction is applied to the intermediate transfer belt 6 via the Y-color photosensitive drum 1Y determined as “the image density of the Y-color density detection mark Md is abnormal”. Only a color toner image is formed. See step A2 for an explanation thereof.

  As a result, the cause of the occurrence of white spots or the like in the Y color image forming system is removed, and the Y color image forming system can be restored to a normal state. When it is determined that the image density of the density detection mark Md for the other color is abnormal, the same operation is performed, and the image forming system for other colors can be restored to the normal state. Thereafter, the process returns to step A2 to resume the image density correction mode.

  If it is determined in step A7 that the image density is within the allowable range, the process proceeds to step A12 where the image density correction data Dε is stored in the nonvolatile memory 14 and the image density correction process is terminated. In the normal image forming mode, the image density of the image data Dy, Dm, Dc, etc. is corrected based on the image density correction data Dε. Thereby, the image density can be adjusted for each color by the image forming units 10Y, 10M, 10C, and 10K.

  As described above, according to the color copying machine and the image forming method thereof according to the embodiment of the present invention, a color image is formed on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, and 1K. Thus, when executing the image density correction mode, the control means 15 compares the image density detected by the image density sensor 12 with the discrimination reference value Lth prepared in advance to discriminate abnormality, and determines the discrimination result. Based on this, the image density correction mode is continued, or the image density correction mode is stopped and the image forming system recovery mode is executed.

  Accordingly, when the image density correction mode is determined to be “abnormal”, the image density correction mode is stopped and the image density correction is applied to the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, and 1K. The toner images of all colors or the corresponding colors are formed, and then the toner images for image density correction formed on the intermediate transfer belt 6 and the like are removed, thereby removing the image forming units 10Y, 10M, 10C and 10K can be restored to a normal state.

  As a result, even when a white spot (firefly) occurs in the density detection mark Md for some reason when the image density correction mode is executed, the image density correction mode is resumed after the execution of the image forming system recovery mode. The image density correction mode can be executed in the normal image forming units 10Y, 10M, 10C, and 10K.

  The present invention is suitable for application to a tandem type color printer or color copying machine having a photosensitive drum and an intermediate transfer belt, and having an image density correction mode, and a color complex machine thereof.

1 is a conceptual diagram illustrating a configuration example of a color copying machine 100 as an embodiment of the present invention. It is a perspective view which shows the example of detection of the density | concentration detection mark Md by the image density sensor 12. FIG. 2 is a block diagram illustrating a configuration example of an image transfer system I and an image forming system II of the color copying machine 100. FIG. FIG. 5 is a diagram illustrating a detection example (No. 1) of a density detection mark Md by an image density sensor 12; FIG. 6 is a diagram illustrating a detection example (No. 2) of the density detection mark Md by the image density sensor 12; 3 is a flowchart illustrating an example of image density correction in the color copying machine 100.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum (image carrier)
3Y, 3M, 3C, 3K Laser writing unit 4Y, 4M, 4C, 4K Development unit 5Y, 5M, 5C, 5K Correction means 6 Intermediate transfer member (image transfer means)
10Y, 10M, 10C, 10K Image forming unit (image forming means)
12 Image density sensor (image detection means)
14 Non-volatile memory (storage means)
DESCRIPTION OF SYMBOLS 15 Control means 16 Operation means 18 Display means 100 Color copier 101 Copier main body 102 Image reading apparatus 201 Automatic document feeder 202 Document image scanning exposure apparatus

Claims (5)

In an image forming apparatus for forming a color image on an image carrier,
An image density correction printed image is formed on the image carrier, the image density of the printed image is read, an image density difference with respect to a reference image density of the printed image is calculated, and the image density is calculated based on the image density difference. The operation to correct is the image density correction mode,
When an image density correction printed image is formed on the image carrier and the operation of removing the printed image formed on the image carrier is an image forming system recovery mode,
Image forming means for forming a printed image for image density correction on the image carrier;
An image detecting means for detecting an image density of the printed image formed on the image carrier by the image forming means;
Comparing the image density of the printed image detected by the image detecting means and the determination reference value of the image density to determine abnormality or normality, and continuing the image density correction mode based on the determination result, or An image forming apparatus comprising: control means for canceling the image density correction mode and executing the image forming system recovery mode. The discrimination reference value is
The difference between the maximum value and the minimum value of the image density of the printed image for each color calibrated in advance is selected and set from a value obtained by calculating a weighting factor α (0 <α <1). Item 2. The image forming apparatus according to Item 1. The control means includes
In the image forming system recovery mode,
2. The image forming means is controlled to form all color images for image density correction on the image carrier and to remove all color images formed on the image carrier. And the image forming apparatus according to 2. The control means includes
In the image forming system recovery mode,
Forming a mark image for correcting the image density of only the color determined to be abnormal on the image carrier and controlling the image forming means to remove the image of the corresponding color formed on the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus includes: In an image forming method for forming a color image on an image carrier,
An image density correction printed image is formed on the image carrier, the image density of the printed image is read, an image density difference with respect to a reference image density of the printed image is calculated, and the image density is calculated based on the image density difference. The operation to correct is the image density correction mode,
When an image density correction printed image is formed on the image carrier and the image density correction printed image formed on the image carrier is removed in the image forming system recovery mode,
Forming a printed image for image density correction on an image carrier;
Detecting an image density of the mark image formed on the image carrier;
Comparing the detected image density of the mark image with a determination reference value of the image density to determine abnormality or normality;
An image forming method comprising: continuing the image density correction mode based on a determination result, or suspending the image density correction mode and executing the image forming system recovery mode.

Images