JP5963114B2 - Image forming apparatus, image forming system, and image processing program - Google Patents

Description

  The present invention relates to an image forming apparatus, an image forming system, and an image processing program.

  2. Description of the Related Art In recent years, electrophotographic image forming apparatuses such as color printers and color copiers have been required to improve the stability of image tone (density) that greatly affects the image quality of an output image.

  However, in the image forming apparatus, the color tone (density) of the obtained image fluctuates due to changes in the environment, changes in the apparatus over time, or variations in characteristics of the apparatus itself. In particular, in an electrophotographic image forming apparatus, it is important to ensure the stability of the color tone (density) because there is a possibility that the color balance may be lost even by a slight change in color tone (density).

  Therefore, in an image forming apparatus, a patch pattern for density detection is formed on an intermediate transfer member or a photosensitive drum with toner of each color so that a stable color tone can be obtained, and the density of the patch pattern by the toner is detected by an optical sensor. On the basis of the detection result, the density of the output image is controlled by applying feedback to the image forming conditions such as the exposure amount and the developing bias.

  Further, in order to cope with a change in the color balance of the image due to transfer and fixing to the paper, the density or color of the patch pattern transferred and fixed on the paper is detected, and the image forming conditions are controlled based on the detection result. In some cases.

  Further, the spectral reflection intensity of the image for one page printed in the printing apparatus is divided and detected without creating a patch pattern on the paper, and the spectral density value and the reference value obtained from the detected value are obtained. There is also a method of controlling the ink supply amount while comparing (see, for example, Patent Document 1).

JP 2001-18364 A

  An object of this invention is to provide the technique which can improve the stability of the color tone of an image.

In order to solve the above-described problem, the image forming apparatus according to the first aspect of the present invention includes a plurality of photoconductors and a first transfer for transferring each of the images formed on the plurality of photoconductors to an intermediate transfer member. Means, second transfer means for transferring the image transferred to the intermediate transfer member to a plurality of recording media, and fixing means for fixing the image transferred to the recording medium by the second transfer means; Detection means for detecting the color tone of the image fixed on the recording medium by the fixing means, measurement means for measuring the color tone of the image based on the detection result from the detection means, and measurement of the image measured by the measurement means Based on the specifying means for specifying the direction in which the color tone is deviated from the reference value and the result obtained by the specifying means, which part of the monochromatic and multi-color colors of the image is deviated from the reference value. Judgment to judge whether Possess a stage, and a control means for controlling a transfer voltage of the second transfer means to suit the monochromatic and direction deviating the multicolor it is determined by said determining means, said determining means, said tone It is characterized in that it is determined whether the deviation of the brightness direction is a single color or a multi-order color based on the image forming mode or color information of the image information .

  According to a second aspect of the present invention, in the first aspect of the invention, the reference value is obtained by detecting the color tone of an image fixed on a first recording medium of the plurality of recording media by the detecting unit. It is a value obtained by detection.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the control means transfers the transfer of the second transfer means when the amount of color shift exceeds a predetermined threshold value. The voltage is controlled.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the control means is a primary color resulting from control of a transfer voltage of the second transfer means. The variation in color tone is corrected by gradation correction.

According to a fifth aspect of the present invention, there is provided an image forming system according to any one of the first to fourth aspects, and an image data output device that outputs image data to the image forming apparatus. Are connected via a communication line, and the image forming apparatus performs an image forming process on the acquired image data.

According to a sixth aspect of the present invention, there is provided an image processing program for forming an image on each of a plurality of photoconductors, and transferring each image formed on the plurality of photoconductors to an intermediate transfer member. 1 transfer process, a second transfer process for transferring the image transferred to the intermediate transfer member to a plurality of recording media, and a fixing for fixing the image transferred to the recording medium by the second transfer process. A process for detecting the color tone of the image fixed on the recording medium by the fixing process, a measurement process for measuring the color tone of the image based on the detection result of the detection process, and the measurement process Based on the identification process for specifying the direction in which the color tone of the image is deviated from the reference value and the result obtained by the identification process, which part of the monochromatic and multi-color colors of the image is relative to the reference value To determine whether A determining step of, have a, and a control step of controlling the transfer voltage of the second transfer means to suit has been the single color and the direction of shift of multicolor determined by the determining step, in the determination process, the It is characterized in that it is determined on the basis of the image formation mode or color information of the image information whether the deviation of the lightness direction of the color tone is a single color or a multi-color .

According to the first aspect of the present invention, it is possible to improve the stability of the color tone of the image as compared with the case where the present invention is not applied.
According to the first aspect of the present invention, it is possible to improve the accuracy of color tone correction of an image.
Further, according to the first aspect of the present invention, the speed of the image forming process is improved as compared with the case where the determination of whether the shift in the lightness direction of the color tone is a single color or a multi-color is based on the detection result of the image. It becomes possible to make it.

  According to the second aspect of the present invention, it is possible to set a reference value for judging a color tone shift to a more suitable value.

According to the second aspect of the present invention, it is possible to improve the speed of the image forming process compared to the case where no threshold is provided.

According to the fourth aspect of the present invention, it is possible to suppress or prevent the variation in the color tone of the primary color caused by controlling the transfer voltage of the second transfer means to correct the variation in the color tone of the multi-order color. It becomes possible.

According to the fifth aspect of the present invention, it is possible to provide an image forming system capable of improving the stability of the color tone of an image as compared with the case where the present invention is not applied.

According to the sixth aspect of the present invention, it is possible to provide an image processing program capable of improving the stability of the color tone of an image as compared with the case where the present invention is not applied.

1 is a schematic configuration diagram of an image forming system according to a first embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a function level of the image forming system in FIG. 1. FIG. 2 is a schematic configuration diagram of a mechanism system of an image forming unit in the image forming apparatus of the image forming system in FIG. 1. FIG. 2 is a schematic configuration diagram of a toner amount sensor when a regular reflection method is applied to an image forming unit in the image forming apparatus of the image forming system in FIG. 1. FIG. 2 is a schematic configuration diagram of a toner amount sensor when a diffuse reflection method is applied to an image forming unit in the image forming apparatus of the image forming system in FIG. 1. FIG. 2 is a schematic configuration diagram of an inline sensor of an image forming unit in the image forming apparatus of the image forming system of FIG. 1. FIG. 6 is a graph showing the relationship between the number of sheets and secondary transfer efficiency when images are continuously formed on a plurality of sheets. FIG. 6 is a graph showing the relationship between secondary transfer voltage and secondary transfer efficiency for primary color, secondary color, and tertiary color. FIG. 3 is a flowchart of color tone control during image formation of the image forming apparatus according to the first exemplary embodiment of the present invention. It is a figure of the coordinate of the color space in a L ^* a ^* b ^* color system. It is a plan view of an example of a patch pattern used for sensitivity detection and gradation correction of secondary transfer voltages of L ^* , a ^* , and b ^* . (A)-(c) is the figure which showed the L ^* sensitivity, a ^* sensitivity, and b ^* sensitivity with respect to the secondary transfer voltage in the graph. It is a figure for demonstrating the creation example of the data of the conversion look-up table for general gradation correction | amendment. It is a figure for demonstrating the creation example of the data of the conversion look-up table for general gradation correction | amendment. FIG. 10 is a flowchart of color tone control during image formation of an image forming apparatus according to a second embodiment of the present invention. FIG. 6 is a graph showing a correspondence relationship between a lookup table (before conversion) and a secondary transfer voltage.

  Hereinafter, an embodiment as an example of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  (First embodiment)

  FIG. 1 is a schematic configuration diagram of an image forming system 1 according to a first embodiment of the present invention.

  The image forming system 1 includes an image forming apparatus 10 and a computer 20. The image forming apparatus 10 includes an image processing apparatus 100 and an image output apparatus 200. When print data is received from the computer 20, the image forming apparatus 10 performs image processing and image forming processing based on the print data.

  The image processing apparatus 100 includes a data reception unit 110, storage units 120 and 150, a PDL (Page Description Language: hereinafter referred to as PDL) interpretation unit 130, a drawing unit 140, an image data analysis unit 160, and an image processing unit (an example of a specifying unit). , An example of determination means) 170.

  The data receiving unit 110 stores print data received (acquired) from the computer 20 in the storage unit 120. This print data is described in, for example, a page description language (PDL).

The print data from the computer 20 is, for example, image data expressed in any one of the RGB color space, L ^* a ^* b ^* color space, CMY color space, and CMYK color space.

  The RGB color space means a color space composed of red, green, and blue colors.

The L ^* a ^* b ^* color space is a device-independent color space (uniform color space) such as an image output device, for example, a CIE (International Lighting Commission) L ^* a ^* b ^* color space. Means.

  The CMY color space means a color space composed of cyan, magenta, and yellow colors.

  The CMYK color space means a color space composed of cyan (C), magenta (M), yellow (Y), and black (K) colors.

  The PDL interpretation unit 130 interprets the PDL data stored in the storage unit 120 and outputs the interpretation result to the drawing unit 140.

  The drawing unit 140 performs drawing processing for each processing unit (for example, page) related to drawing based on the interpretation result of the received PDL data, and stores the result of the drawing processing in the storage unit 150. In addition, the drawing unit 140 notifies the image data analysis unit 160 and the image processing unit 170 that the drawing processing for each processing unit has been completed. Note that the drawing data resulting from the drawing processing by the drawing unit 140 is bitmap format (raster format) image data.

  The image processing unit 170 of the image processing apparatus 100 includes a color conversion unit (an example of a measurement unit and an identification unit) 171, a gradation correction unit 172, and a halftone dot generation unit 173, and accepts image data (drawing data). A color conversion process, a gradation correction process, and a halftone dot generation process are performed on the image.

  In addition, the image processing unit 170 outputs the image data that has been subjected to the image processing to the image output apparatus 200.

  The image output apparatus 200 includes an image output apparatus control unit (an example of a control unit) 210 and an image forming unit 220.

  The image output device control unit 210 outputs the image data from the image processing unit 170 to the image forming unit 220 and outputs a command to start the image forming process (image forming process start command) to the image forming unit 220. To do.

  The image output device control unit 210 also includes information on at least the surrounding environment (defined as environment information) of the image forming unit 220 that functions as an image forming unit that performs image forming processing, and image forming processing performed by the image forming unit 220. Information on paper quality (an example of a recording medium) on which the result of printing is printed (defined as paper information) and information on time-dependent characteristics of the image output apparatus 200 (specifically, information on time-dependent characteristics of the image forming unit 220: time-dependent characteristics) At least one piece of information (defined as information) is output to the image data analysis unit 160 of the image processing apparatus 100.

  The image forming unit 220 has a function of an image forming unit, executes an image forming process based on the received image data in accordance with the image forming process start command, and a print output result as a result of the image forming process (Paper on which the image is printed) is output.

  Next, FIG. 2 shows a schematic configuration of functional levels of the image forming system 1 of FIG.

  The image forming system 1 is configured by connecting an image forming apparatus 10 and a computer (an example of an image data output apparatus) 20 via a communication line 30.

  The computer 20 functions as a processing device (client device), such as a CPU (Central Processing Unit) 20C, a storage device 20M1 such as a hard disk, and a RAM (Random Access Memory). A memory 20M2 and a communication interface (hereinafter referred to as communication I / F) 20IF are provided.

  The storage device 20M1 stores various types of data such as application software that issues document generation and print requests, a printer driver, and print data (PDL data).

  The memory 20M2 stores programs and data read from the storage device 20M1.

  The communication I / F 20 IF is an interface that transmits and receives data to and from the image forming apparatus 10 via the communication line 30.

  The CPU 20C controls the entire computer 20, and reads and executes a printer driver from the storage device 20M1 to the memory 20M2, for example. As a result, print data (PDL data) is transmitted to the image forming apparatus 10.

  On the other hand, the image processing apparatus 100 of the image forming apparatus 10 includes a CPU 100C, a storage device 100M1, such as a hard disk, a RAM 100M2, a ROM 100M3, and a communication I / F 100IF.

  The storage device 100M1 stores various programs and data necessary for performing print processing, such as an image processing program (an example of an image processing program) PD that is software.

  The image processing program PD is stored in each of the PDL interpretation unit 130, the drawing unit 140, the image data analysis unit 160, and the image processing unit 170 (the color conversion unit 171, the gradation correction unit 172, and the halftone generation unit 173) illustrated in FIG. The program (software) for realizing the function of is included.

  The ROM 100M3 stores data necessary for image processing, such as default values of color parameters, gradation parameters, and halftone dot parameters, and color range information.

  The RAM 100M2 stores the image processing program PD read from the storage device 100M1, print data received via the communication I / F 100IF, and the like.

  In addition, at least the following storage areas (a) to (d) are allocated to the RAM 100M2.

  (A) A storage area (area for storing print data) that functions as the storage unit 120 in FIG.

  (B) A storage area (area for storing drawing data) that functions as the storage unit 150 in FIG.

  (C) A storage area functioning as a color parameter storage unit of the color conversion unit 171 in FIG. 1, a gradation parameter storage unit of the gradation correction unit 172, and a halftone dot parameter storage unit of the halftone generation unit 173 (respectively as default values) Parameter storage area). That is, it is a storage area for storing parameters as default values read from the ROM 100M3.

  (D) Storage areas required when the image processing unit 170 in FIG. 1 performs image processing (such as storage areas for storing color conversion processing, tone correction processing, screen processing processes and processing results) It is.

  The CPU 100C controls the entire image forming apparatus 10. For example, the CPU 100C reads the image processing program PD from the storage device 100M1 into the RAM 100M2 and executes it to generate high-quality image data and send it to the image output device 200. Output toward.

  The communication I / F 100IF is an interface that transmits / receives data to / from the computer 20 via the communication line 30. For example, the communication I / F 100IF receives print data transmitted from the computer 20.

  The communication line 30 includes a local area network (hereinafter abbreviated as “LAN”), a wired communication line such as a telephone line, a wireless communication line such as a wireless LAN, and a combination of these communication lines. Is mentioned.

  Here, a case has been described in which each function of the image processing apparatus 100 is realized and an image processing program including a program indicating the processing procedure of the image processing is recorded in a storage device such as a hard disk as a recording medium. A processing program may be provided as follows.

  That is, the image processing program may be stored in the ROM, and the CPU may load the program from the ROM to the main storage device and execute it.

  The image processing program may be stored and distributed in a computer-readable recording medium such as a DVD-ROM, CD-ROM, MO (magneto-optical disk), or flexible disk. In this case, after the image processing apparatus 100 installs the program recorded on the recording medium, the CPU executes the program. As an installation destination of this program, there is a memory such as a RAM or a storage device such as a hard disk. Then, the image processing apparatus 100 loads the program stored in the storage device to the main storage device and executes it as necessary.

  Further, the image processing apparatus 100 is connected to a computer such as a server apparatus or a host computer via a communication line (for example, the Internet), and the image processing apparatus 100 downloads the image processing program from the server apparatus or the computer. Later, this program may be executed. In this case, the download destination of the program includes a memory such as a RAM and a storage device (recording medium) such as a hard disk. Then, the image processing apparatus 100 loads the program stored in the storage device into the main storage device and executes it as necessary.

  Next, FIG. 3 shows a schematic configuration mainly of a mechanical system of the image forming unit 220 of the image output apparatus 200.

  The image forming unit 220 forms an image by a tandem intermediate transfer method, and a plurality of image forming units 40Y on which toner images (images) of respective color components are formed by an electrophotographic method (electrophotographic process). , 40M, 40C, 40K and intermediate transfer belts (intermediate transfer members) that circulate and drive (rotate) the toner images of the respective color components formed by the image forming units 40Y, 40M, 40C, 40K in the direction of arrow Z in the figure. An example) includes primary transfer portions (an example of first transfer means) 41Y, 41M, 41C, and 41K that sequentially transfer (primary transfer) to 50.

  The image forming unit 220 also transfers a toner image (superimposed toner image) transferred onto the intermediate transfer belt 50 to the sheet P in a batch (secondary transfer) (second transfer unit (an example of a second transfer unit)) 60. And a fixing device (an example of a fixing unit) 70 for fixing the secondary-transferred image on the paper P, and a plurality of unfixed patch patterns for gradation correction transferred onto the intermediate transfer belt 50 are optically A toner amount sensor (Auto Development Control: hereinafter abbreviated as ADC) 80 and an inline sensor (In Line Sensor: optically detecting an image fixed on the paper P and a plurality of patch patterns for gradation correction described above. Hereinafter, abbreviated as ILS: an example of detection means) 90.

  The image forming unit 40Y includes a photosensitive drum (an example of a photosensitive member) 42Y that rotates in the direction of arrow A in the drawing. Around the photosensitive drum 42Y, a charging device 43Y for charging the photosensitive drum 42Y along the rotation direction, and a laser exposure device 44Y for writing an electrostatic latent image on the photosensitive drum 42Y (in the drawing, an exposure beam) And a color component formed on the photosensitive drum 42Y, and a developing device 45Y that accommodates the toner of the corresponding color component and visualizes the electrostatic latent image on the photosensitive drum 42Y with the toner. An electrophotographic device such as a primary transfer roll 46Y for transferring the toner image to the intermediate transfer belt 50 and a drum cleaner 47Y for removing residual toner on the photosensitive drum 42Y are sequentially arranged. The image forming unit 40Y includes a toner cartridge (not shown) for supplying a developer to the developing device 45Y.

  Each of the image forming units 40M, 40C, and 40K has photosensitive drums 42M, 42C, and 42K similar to the photosensitive drum 42Y, and the photosensitive drums 42M, 42C, and 42K are surrounded by the photosensitive drums 42M, 42C, and 42K. Electrophotographic devices similar to the electrophotographic devices (charging device, laser exposure device, developing device, primary transfer roll, drum cleaner) corresponding to the body drum 42Y are sequentially arranged. The image forming units 40M, 40C, and 40K are provided with toner cartridges (not shown) for supplying developer to the developing devices 45M, 45C, and 45K.

  Each of the image forming units 40Y, 40M, 40C, and 40K described above is yellow (Y), magenta (M), cyan (C), black from the upstream side in the rotation direction of the intermediate transfer belt 50 (the arrow Z direction in the figure). They are arranged in the order of (K). Each of the photosensitive drums 42Y, 42M, 42C, and 42K is configured to be able to contact and separate from the intermediate transfer belt 50.

  The primary transfer roll 46Y is disposed at a position facing the photosensitive drum 42Y with the intermediate transfer belt 50 interposed therebetween. A primary transfer voltage source 48Y for supplying a primary transfer voltage (primary transfer potential) is connected to the primary transfer roll 46Y. The primary transfer roll 46Y and the primary transfer voltage source 48Y are components constituting the primary transfer portion 41Y.

  Similarly to the above, the primary transfer rolls 46M, 46C, and 46K corresponding to the photosensitive drums 42M, 42C, and 42K are located at positions facing the corresponding photosensitive drums 42M, 42C, and 42K with the intermediate transfer belt 50 interposed therebetween. Has been placed. Primary transfer voltage sources 48M, 48C, and 48K that apply primary transfer voltages (primary transfer potentials) are connected to the primary transfer rolls 46M, 46C, and 46K, respectively. The primary transfer roll and the primary transfer voltage source corresponding to each of the photosensitive drums 42M, 42C, and 42K are constituent elements that constitute the primary transfer units 41M, 41C, and 41K, respectively.

  Primary transfer voltages (primary transfer potentials) from primary transfer voltage sources 48Y, 48M, 48C, and 48K are applied to the primary transfer rolls 46Y, 46M, 46C, and 46K, and a primary transfer current is supplied. . The primary transfer rolls 46Y, 46M, 46C, 46K generate a primary transfer bias when a primary transfer current is supplied, and the photosensitive drums 42Y, 42M, 42C, 42K of the photosensitive drums 42Y, 42M, 42K. The toner images on 42M, 42C, and 42K are transferred to the intermediate transfer belt 50.

  The above-described intermediate transfer belt 50 is a member that sequentially transfers (primary transfer) toner images of the respective color components formed by the respective image forming units 40Y, 40M, 40C, and 40K. The intermediate transfer belt 50 is formed in an endless manner in a state of being laid over a plurality of support rolls and a backup roll 60a, and is rotated in the counterclockwise direction (the direction indicated by the arrow Z), and each image forming unit. The toner images of 40Y, 40M, 40C, and 40K are subjected to primary transfer.

  The secondary transfer unit 60 described above is a mechanism unit for forming a full-color image by batch transfer (secondary transfer) of the toner image transferred onto the intermediate transfer belt 50 onto the paper P or the like. A backup roll 60a and a secondary transfer roll 60b arranged in a state of being opposed to each other with respect to each other. In batch transfer, a secondary transfer voltage having the same polarity as the toner charging polarity is applied to the backup roll 60a, or a secondary transfer voltage having a polarity opposite to the toner charging polarity is applied to the secondary transfer roll 60b. As a result, a transfer electric field is formed between the backup roll 60a and the secondary transfer roll 60b, and the unfixed toner image held on the intermediate transfer belt 50 is transferred onto the paper P or the like.

  The fixing device 70 has a function of fixing the toner image to the paper P or the like by applying heat and pressure to the paper P or the like to which the toner image has been transferred. For example, the fixing device 70 has a function of fixing the toner image onto the paper P or the like. And a pressure roll 70b for pressing P.

  The charging process, the exposure process, and the development process of the electrophotographic process are realized by the image forming units 40Y, 40M, 40C, and 40K (actually, the charging process is performed by the charging devices 43Y, 43M, 43C, and 43K, and the exposure process is performed by the laser. With the exposure devices 44Y, 44M, 44C and 44K, the development process is realized with the development devices 45Y, 45M, 45C and 45K, respectively.) The transfer process is performed with the primary transfer portions 41Y, 41M, 41C and 41K and the secondary transfer. The fixing process is realized by the fixing device 70.

  The above-described ADC sensor 80 is a sensor that optically reads a plurality of patch patterns for gradation correction transferred to the intermediate transfer belt 50. The plurality of patch patterns for gradation correction at this stage are not yet fixed.

  The ADC sensor 80 extends from the last primary transfer position (primary transfer roll 46K) to the secondary transfer position (secondary transfer roll 60b) along the rotational direction of the intermediate transfer belt 50. The plurality of patch patterns for gradation correction transferred to the intermediate transfer belt 50 are arranged at positions where they can be read optically and stably.

  The optical signal detected by the ADC sensor 80 is converted into an electric signal, transmitted to the image processing unit 170 shown in FIG. 1, and used as data for gradation correction in the gradation correction unit 172. Yes.

  Here, FIG. 4 and FIG. 5 show a schematic configuration of an example of the ADC sensor 80 using both the regular reflection system (see FIG. 4) and the diffuse reflection system (see FIG. 5). The arrows in FIGS. 4 and 5 indicate the direction in which the light travels.

  The ADC sensor 80 includes a light emitting element 80LA for regular reflection, a light emitting element 80LB for diffuse reflection, a light receiving element 80LC for both regular reflection and diffuse reflection, a reflection reference plate 80RS, and a shutter 80S.

  The light emitting elements 80LA and LB are configured by, for example, a near infrared LED (Light Emitting Diode), and the light receiving element 80LC is configured by, for example, a photodiode.

  As shown in FIG. 4, the ADC sensor 80 uses a regular reflection method for black toner that hardly diffusely reflects, and as shown in FIG. 5, diffuse reflection that can be read up to a high density for color toner. The method is to be used.

  Here, the case where a plurality of tone correction patch patterns transferred onto the intermediate transfer belt 50 are detected by the ADC sensor 80 has been described. Instead, the photosensitive drums 42Y, 42M, 42C, and 42K are used. The plurality of patch patterns for gradation correction developed in the above may be detected by the ADC sensor 80.

  On the other hand, the ILS 90 shown in FIG. 3 is a sensor that optically reads an image transferred from the intermediate transfer belt 50 onto the paper P or the like and fixed by the fixing device 70 and the plurality of patch patterns for gradation correction.

  The ILS 90 is a discharge unit for the sheet P so that the image fixed on the sheet P and the plurality of patch patterns for gradation correction can be optically and stably read in the subsequent stage of the fixing device 70 (downstream of conveyance of the sheet P). It is arranged in the vicinity. In the vicinity of the discharge portion of the paper P, the curl of the paper P is removed and the posture of the paper P is stabilized, so that the density and position of the image fixed on the paper P can be read with high accuracy.

  The optical signal detected by the ILS 90 is converted into an electric signal and transmitted to the image processing unit 170 shown in FIG. 1, and is used as data in the color conversion unit 171 and the gradation correction unit 172. .

  Here, FIG. 6 shows a schematic configuration of an example of the ILS 90. The ILS 90 is a sensor for reading an image fixed on the sheet P being conveyed and extracting the image information. The ILS 90 is an irradiation unit 90A, a CCD (Charge Coupled Device) sensor 90B, an image forming unit 90C, and a sensor. And a calibration unit 90D.

  The irradiation unit 90A is a unit that irradiates light toward the paper P on which an image is recorded, and includes a pair of lamps 90A1 and 90A2. The pair of lamps 90 </ b> A <b> 1 and 90 </ b> A <b> 2 are configured by, for example, linear xenon lamps, and are disposed at positions facing the image forming surface of the paper P. The pair of lamps 90A1 and 90A2 is set such that the length of the irradiation range is larger than the width of the largest sheet P to be conveyed, and provides stable reading accuracy when the sheet P is traveling. A sufficient illumination depth is secured to obtain.

  The CCD sensor 90B is means for receiving the light irradiated from the irradiation unit 90A and reflected by the paper P, and detecting the image or the paper P itself based on the intensity of the received light. The light focused on the CCD sensor 90B is converted into an electrical signal corresponding to the image density, transmitted to the image processing unit 170 shown in FIG. 1, and used as data for gradation correction in the gradation correction unit 172. Is done.

  The imaging unit 90C is a unit that images the light emitted from the irradiation unit 90A and reflected by the paper P onto the CCD sensor 90B. The imaging unit 90C is configured by, for example, a reduction projection optical system without mechanical operation, and includes a plurality of reflecting mirrors 90C1, 90C2, 90C3 and a lens 90C4.

  The sensor calibration unit 90D is a means for setting various standards and the like when using the ILS 90 and at the time of calibration. For example, the sensor calibration unit 90D includes a polygonal cylindrical reference roll 90D1 in which eight or more surfaces are formed in the circumferential direction. . As a result, various inspection targets are mounted at the image reading position, and automatic calibration of the reading accuracy of the ILS 90 is performed to ensure the performance as a measuring device.

  Next, image color tone control in the image forming apparatus 10 will be described.

  First, FIG. 7 is a graph showing the relationship between the number of sheets and the secondary transfer efficiency when images are continuously formed on a plurality of sheets. The secondary transfer efficiency refers to a rate at which the toner of an image transferred onto the intermediate transfer belt 50 is transferred to a sheet or the like by secondary transfer.

  In the electrophotographic image forming apparatus 10 as described above, the secondary transfer efficiency varies depending on the change in the charge amount of toner during the continuous image formation, the characteristics of the paper (water content), and the like. In many cases, however, it decreases as the number of processed sheets increases. In addition, the secondary color CL2 and the tertiary color CL3, such as the multi-color, have a larger attenuation amount of the secondary transfer efficiency than the primary color CL1, and the variation in the color tone of the multi-color is the primary color. It turns out that it is more conspicuous than the fluctuation of the color tone.

  Next, FIG. 8 is a graph showing the relationship between the secondary transfer voltage and the secondary transfer efficiency for the primary color CL1, the secondary color CL2, and the tertiary color CL3.

  The secondary transfer voltage is a parameter when the toners of the primary color CL1, the secondary color CL2, and the tertiary color CL3 are collectively transferred from the intermediate transfer belt 50 onto the paper P. The primary color CL1, the secondary color. The optimum setting values V1, V2, and V3 are different for each CL2 and the tertiary color CL3.

  However, in general, in order to balance the primary color CL1, the secondary color CL2, and the tertiary color CL3, a value close to the set value V2 of the secondary color is set as the center value Vc. Note that the set values V1, V2, and V3 of the secondary transfer voltage are generally updated according to information on paper characteristics (basis weight, surface property, resistivity, etc.) that has been acquired in advance.

  Next, FIG. 9 is a flowchart of color tone control during image formation of the image forming apparatus 10 according to the first embodiment. Here, a case where images are continuously formed on a plurality of sheets P will be described. The symbol n indicates the number of sheets P.

  First, at the start of image formation (step 500 in FIG. 9), toner images (images) are formed on the photosensitive drums 42Y, 42M, 42C, and 42K of the image forming unit 220 (see FIG. 3), and the respective toners are formed. The image is transferred (primary transfer) to the intermediate transfer belt 50. Subsequently, the toner image transferred to the intermediate transfer belt 50 is collectively transferred (secondary transfer) to the paper P, and then the toner image transferred to the paper P is fixed by the fixing device 70.

Next, the toner image fixed on the paper P is optically read by the ILS 90 (step 501 in FIG. 9). The ILS 90 transmits the detected toner image detection data on the entire surface of the paper P to the color conversion unit 171 of the image processing apparatus 100. The color conversion unit 171 measures the average L ^* , a ^* , b ^* of the toner images on the entire surface of the paper P based on the detection data transmitted from the ILS 90 (step 502 in FIG. 9).

Here, it is determined whether or not the sheet P is the first sheet (step 503 in FIG. 9). In the case of the first sheet, the average L ^* , a ^* and b ^* of the toner images on the entire surface of the sheet P is used as a reference. The value is stored in the storage device 100M1 or the like (step 504 in FIG. 9). By using the average L ^* , a ^* , b ^* of the toner images on the entire surface of the first sheet P as a reference value, the reference value for judging a color tone deviation is set to a more suitable value. Thereby, the stability and reproducibility of the color tone of the toner image are further improved. However, past data (experience value) or a calculated value may be adopted as the reference value and set (stored) in the storage device 100M1 or the like in advance.

On the other hand, if it is determined in step 503 that the sheet P is the second sheet or later, the color conversion unit 171 determines the average L ^* , a ^* , b ^* of the toner images on the entire surface of the second sheet and subsequent sheets P; The average L ^* , a ^* , b ^* (reference value) of the toner images on the entire surface of the first sheet P is compared, and the color deviations ΔL ^* , Δa ^* , Δb ^* are calculated from the difference. In addition, the direction deviating from the reference value is specified (step 505 in FIG. 9).

Next, the secondary transfer voltage of the secondary transfer unit 60 is controlled so that the shift is corrected according to the shift direction of L ^* a ^* b ^* obtained in step 505. Thereby, the stability and reproducibility of the color tone of the toner image formed on the paper P are improved. Here, for example, in the L ^* a ^* b ^* color system, it is determined which of the primary color, the secondary color, and the tertiary color is deviated from the sign and absolute value of ΔL ^* , Δa ^* , Δb ^*. Then, the secondary transfer voltage of the secondary transfer unit 60 is controlled so as to correct the deviation in accordance with the direction in which the primary color, the secondary color, and the tertiary color are shifted (step 506 in FIG. 9). Thereby, the accuracy of color tone correction of the toner image is improved.

  In Patent Document 1, a sensor is moved to a certain part of an image for measurement, or a plurality of sensors are provided for measuring the entire area within one page. For this reason, it takes time to specify the location of an image and to average data from a plurality of sensors, and a response delay may occur when high-speed processing is supported. Therefore, it is conceivable to install a large-capacity memory for high-speed processing or to increase the data transfer speed, but this significantly increases the cost. On the other hand, in the present embodiment, it is only necessary to detect the image of the paper P by the ILS 90, so that the image processing time is shortened and a response delay when the high-speed processing is supported is avoided. In addition, since it is not necessary to install a large-capacity memory or increase the data transfer speed, an increase in cost of the image forming system 1 and the image forming apparatus 10 can be suppressed.

  Further, in Patent Document 1, since a printing press is premised and ink of each color is not overlapped, when applied to forming an image by overlapping toners of each color, the amount of color variation at the time of image transfer is not absorbed. , Leading to fluctuations in color tone (density). On the other hand, in the present embodiment, even when the toner of each color is overlapped to form an image and the overlapped toner image is collectively transferred to the paper P, as described above, according to the direction of color misregistration. By controlling the secondary transfer voltage so that the deviation is corrected, fluctuations in the color tone (density) of the toner image can be suppressed.

  After step 506 in FIG. 9, it is determined whether or not the image forming process is completed (step 507 in FIG. 9), and the above process is repeated until it is determined that the image forming is completed.

Next, an example of control of the secondary transfer voltage will be described with reference to FIG. FIG. 10 shows the coordinates of the color space in the L ^* a ^* b ^* color system.

The L ^* a ^* b ^* color system is a three-dimensional space in which all colors are equally divided based on the limit that humans can distinguish between colors, and is designed to approximate human vision. Yes.

The L ^* axis represents lightness, with 0 being the darkest, and the larger the value, the brighter the color. When a ^* and b ^* = 0, it represents gray from black to white.

The combination of a ^* axis and b ^* axis represents all hues. When L ^* is seen on the same surface, the center is achromatic (a ^* , b ^* = 0), and the more outward the color is, the brighter the color becomes.

a The positive side of the ^* axis represents the saturation of magenta (M color), and the negative side represents the saturation of green (G color). Further, the + side of the b ^* axis represents yellow (Y color) saturation, and the-side represents blue (B color) saturation.

Here, for example, the average L ^* , a ^* , b ^* of the toner images of the reference (first sheet) paper P is set to the reference value S = (60, 10, 5), and the toner image of the nth paper P is measured. The average L ^* , a ^* , b ^* is the measured value N = (62, 8, 10).

In this case, the toner image of the nth sheet P has ΔL ^* = 2 and the tertiary color is lighter than the reference value S. Further, when Δa ^* = − 2, the secondary color is darker than the reference value S, and the primary color is lighter than the reference value S. Further, when Δb ^* = 5, the secondary color is lighter than the reference value S, and the primary color is darker than the reference value S.

In total, the secondary color and the tertiary color become light when ΔL ^* = 2 and Δb ^* = 5, and the secondary color and the tertiary color become dark when Δa ^* = − 2. The secondary transfer voltage is controlled to increase. Thereby, the secondary transfer efficiency is improved. Accordingly, since the deviation of the color tone from the reference is reduced, the stability and reproducibility of the color tone of the toner image transferred to the paper P is improved.

  Next, the setting of the secondary transfer voltage of the secondary transfer unit 60 will be described.

  Secondary transfer voltage = Current secondary transfer voltage + ΔSecondary transfer voltage

Δsecondary transfer voltage = β * (ΔL ^* α (L) + Δa ^* α (a) + Δb ^* α (b)).

α (L), α (a), and α (b) are coefficients for converting the Δ secondary transfer voltage from ΔL ^* , Δa ^* , and Δb ^* . Further, β (0 <β) is a correction factor, and is obtained experimentally to balance a primary color look-up table (Look Up Table: hereinafter referred to as LUT) correction, which will be described later. Is.

Next, how to obtain α, which is a coefficient for converting the Δ2 secondary transfer voltage from ΔL ^* , Δa ^* , Δb ^* will be described.

The relationship between ΔL ^* , Δa ^* , Δb ^* and Δsecondary transfer voltage varies depending on the amount of toner transferred to the paper P, so the density of the toner image, that is, each L ^* , a ^* , b ^* It is necessary to convert by the average value of. A specific example will be described with reference to FIG.

FIG. 11 is a plan view of an example of a patch pattern PP used for sensitivity detection and gradation correction of the secondary transfer voltage of L ^* , a ^* , and b ^* . In FIG. 11, for easy understanding of the explanation, each patch pattern PP has characters (3C (gray), R, G, B, Y, M, C, K) indicating colors and images (network). A number (20%, 50%, 80%) indicating an area ratio (Coverage in: hereinafter referred to as Cin) is shown, but these are not transferred or fixed.

Here, a patch pattern for gradation correction of 3C, RGB, and YMCK in three stages of image data (Cin = 20%, 50%, 80%) is detected in advance by the ILS 90, and L ^* , a ^* , b ^*. Measure. In this measurement, the secondary transfer voltage of the secondary transfer unit 60 is changed, for example, in about 3 to 10 steps of a set center value ± 30%. The measurement results are shown in FIG.

12A to 12C show L ^* sensitivity, a ^* sensitivity, and b ^* sensitivity with respect to the secondary transfer voltage. In (a) to (c), Vc is a set center value of the secondary transfer voltage.

For each Cin (20%, 50%, 80%), as the primary color CL1, the average value of YMC and K are obtained for each L ^* , a ^* , b ^* sensitivity, and the inclination is converted into a conversion factor (α (L20 (Primary) / L50 (primary) / L80 (primary)), α (a20 (primary) / a50 (primary) / a80 (primary)), α (b20 (primary) / b50 (1 Next) / b80 (primary)).

As the secondary color CL2, the average value of RGB is obtained, and as the tertiary color, the slopes (conversion coefficients) of L ^* , a ^* , b ^* are obtained from the measured values of 3C. The reason why YMC and K are divided is that K is used as a single color mode.

Here, as the proper use of the slope (conversion coefficient) of each Cin (20%, 50%, 80%), data of L ^* <10 and Cin = 80% of the actually formed image, 10 ≦ L ^* < 40, Cin = 50% data, and L ^* ≦ 50, Cin = 20% data. Although the actual relationship between the toner density and L ^* is not uniquely determined, it can be divided into the above three to correspond to the correction of the secondary transfer voltage.

Further, whether the L ^* direction shift indicating the direction of lightness of the color tone is a tertiary color or K single color is determined by a color mode (full color mode or single color K mode) which is an example of an image formation mode of image information. Alternatively, the determination may be made based on information indicating which color of YMCK is an example of color information of image information. In this way, by determining whether the color is a tertiary color or K single color from the image information, the process for determining the image becomes easier than in the case of determining from the actual image detection result. Increases speed.

  As described above, the secondary transfer voltage that matches the actual toner density can be corrected.

  (Second Embodiment)

  As described above, since the change in the color tone of the multi-color is more conspicuous than the change in the color tone of the primary color, the correction of the change of the multi-color is prioritized in the color tone correction of the toner image. However, when the change in the color tone of the multi-color is corrected by controlling the secondary transfer voltage, the color tone of the primary color may change. Therefore, in the second embodiment, this is dealt with by correcting the gradation of the image data as correction for the change in the tone of the primary color.

  For gradation correction, a patch pattern PP (see FIG. 11) for gradation correction formed on the intermediate transfer belt 50 (or each of the photosensitive drums 42Y, 42M, 42C, and 42K) of the image forming unit 220 is used as an ADC sensor 80. Alternatively, the detection is performed by the ILS 90, and the LUT is corrected based on the detection result.

  Here, FIG. 13 and FIG. 14 are diagrams for explaining an example of creating data of a general gradation correction conversion LUT.

  In FIG. 13, the horizontal axis indicates Cin (%), and the vertical axis indicates the output image density. The gradation characteristic TL indicates a target gradation characteristic line, and the gradation characteristic ML is a patch pattern PP for gradation correction formed on the intermediate transfer belt 50 (or the photosensitive drums 42Y, 42M, 42C, and 42K). Is an actually measured gradation characteristic line of the image forming apparatus 10 created by detecting the image sensor by the ADC sensor 80 (or the ILS 90 or both of the ADC sensor 80 and the ILS 90).

  In this case, the Cin value is different between the target gradation characteristic TL and the actually detected gradation characteristic ML to obtain the same output image density D1. Therefore, as shown in FIG. 14, data LL of a conversion LUT for converting data is created so that the difference between the target gradation characteristic TL and the actually detected gradation characteristic ML is eliminated.

  In FIG. 14, the horizontal axis indicates Cin (%), and the vertical axis indicates corrected Cin (%). As shown in FIG. 13 and FIG. 14, the basic conversion LUT data LL is created by obtaining the symmetrical point of the actually detected gradation characteristic ML with the target gradation characteristic TL as the center line. .

  The conversion LUT is created by the CPU 100C (see FIG. 2) of the image processing apparatus 100, and the result is stored in the memory 100M2, the storage device 100M1, or the like.

  In the second embodiment, the change in the color tone of the primary color due to the secondary transfer voltage is reflected in the conversion LUT. In the image formation (printing), the target gradation characteristics are obtained by correcting the image data with the conversion LUT.

  Next, FIG. 15 is a flowchart of color tone control during image formation of the image forming apparatus 10 according to the second embodiment. In this case as well, a case where images are continuously formed on a plurality of sheets P will be described.

After going through steps 500 to 505 in the same manner as described in FIG. 9 of the first embodiment, for example, in the L ^* a ^* b ^* color system, the signs and absolute values of ΔL ^* , Δa ^* , and Δb ^* are absolute. From the value, it is determined how much of the primary color, the secondary color, and the tertiary color is present (step 506A in FIG. 15).

  Subsequently, the color misregistration amount determined in step 506A is compared with a predetermined threshold (for example, ΔE = 2), and it is determined whether the misregistration amount is equal to or greater than the threshold (step 600 in FIG. 15).

  If the color misregistration amount is lower than the threshold value in step 600, the secondary transfer voltage and the conversion LUT are not changed (step 601 in FIG. 15), and the process proceeds to step 507. In this manner, since it is not necessary to perform correction by the secondary transfer voltage until the color tone shift included in the error range, the speed of the image forming process is improved as compared with the case where no threshold is provided.

  On the other hand, if the amount of color misregistration is greater than or equal to the threshold value in step 600, it is determined whether the secondary color and the tertiary color are misaligned in the light direction (step 602 in FIG. 15).

  If the secondary color and the tertiary color are deviated in the light direction at step 602, the secondary transfer voltage of the secondary transfer unit 60 is changed to a higher direction and the conversion LUT is changed to a direction where the primary color becomes darker. Change (step 603 in FIG. 15) and proceed to step 507.

  On the other hand, when the secondary color and the tertiary color are not shifted in the light direction (that is, shifted in the dark direction) in step 602, the secondary transfer voltage of the secondary transfer unit 60 is changed to a lower direction. The conversion LUT is changed in the direction in which the primary color becomes lighter (step 604 in FIG. 15), and the process proceeds to step 507.

  In this way, the problem that the color tone of the primary color fluctuates as a result of correcting the change in the color tone of the secondary color and the tertiary color by controlling the secondary transfer voltage is suppressed or prevented.

  Next, FIG. 16 is a graph showing the correspondence between the LUT (before conversion) and the secondary transfer voltage.

The first quadrant shows the relationship between the secondary transfer voltage and the reflection density Dout (converted from L ^* , a ^* , b ^* measured by ILS90), and the second quadrant shows the relationship between the LUT and the reflection density Dout. ing. The characteristic line DL in the first quadrant indicates an actually measured characteristic line, and the gradation characteristic TL in the second quadrant indicates a target gradation characteristic line.

  When measuring the patch pattern of FIG. 11 in the setup (initial setting stage) of the image forming apparatus 10, the characteristic line DL in the first quadrant of FIG. 16 is obtained from the detection result of the ILS 90 and originally prepared for tone correction. The conversion LUT is created by correcting the LUT from the gradation characteristics TL in the second quadrant of FIG.

  For example, when the secondary color or tertiary color is lighter than the reference value and is darkened by the correction by the Δ secondary transfer voltage (ΔV), the LUT of each YMC color is set to the YMC common correction (Δ secondary). (ΔLUT converted from the transfer voltage) is corrected in the direction of increasing the primary color.

  ΔLUT (common to YMC) = ε * ΔLUT (corresponding to correction of secondary transfer voltage)

  ε is a correction rate, and is used, for example, when balancing with the correction of the secondary transfer voltage described above. As described above, β and ε are 0 <β and ε <1, and the primary color variation is less noticeable than the secondary and tertiary colors. Therefore, the correction of the secondary and tertiary colors has priority over the primary color. Let

  Although the invention made by the present inventor has been specifically described based on the embodiment, the embodiment disclosed in this specification is an example in all respects and is limited to the disclosed technology. Should not be considered. That is, the technical scope of the present invention should not be construed restrictively based on the description in the above-described embodiment, but should be construed according to the description of the scope of claims. All modifications are included without departing from the technical scope equivalent to the described technique and the gist of the claims.

For example, the L ^* a ^* b ^* color system is used as a color system that expresses colors (tones and chromaticities) as numerical values, but the present invention is not limited to this. For example, Hunter Lab color system or XYZ (Yxy) ) A color system may be used.

  In the above embodiment, the case where the recording medium is applied to paper has been described. However, the present invention is not limited to this. Also good.

  In the above description, the case where the present invention is applied to a printer has been described. However, the present invention may also be applied to other image forming apparatuses such as a copying machine, a facsimile, or an image forming apparatus having these functions.

DESCRIPTION OF SYMBOLS 1 Image forming system 10 Image forming apparatus 20 Computer 30 Communication line 41Y, 41M, 41C, 41K Primary transfer part 42Y, 42M, 42C, 42K Photosensitive drum 43Y, 43M, 43C, 43K Charging device 44Y, 44M, 44C, 44K Laser exposure devices 45Y, 45M, 45C, 45K Developing devices 46Y, 46M, 46C, 46K Primary transfer roll 50 Intermediate transfer belt 60 Secondary transfer unit 70 Fixing device 80 ADC sensor 90 ILS
100 Image processing apparatus 100C CPU
100M1 storage device 100M2 RAM
100M3 ROM
170 Image Processing Unit 171 Color Conversion Unit 172 Tone Correction Unit 200 Image Output Device 220 Image Forming Unit P Paper PD Image Processing Program PP Patch Pattern

Claims (6)

A plurality of photoreceptors;
A first transfer means for transferring each image formed on the plurality of photosensitive members to an intermediate transfer member;
A second transfer means for transferring the image transferred to the intermediate transfer member to a plurality of recording media;
Fixing means for fixing the image transferred to the recording medium by the second transfer means;
Detecting means for detecting the color tone of the image fixed on the recording medium by the fixing means;
Measurement means for measuring the color tone of the image based on the detection result from the detection means;
Specifying means for specifying the direction in which the color tone of the image measured by the measuring means is deviated from a reference value;
Determination means for determining which part of the single color and multi-color of the image is deviated from the reference value based on the result obtained by the specifying means;
Control means for controlling the transfer voltage of the second transfer means in accordance with the direction in which the single color and the multi-color are shifted determined by the determination means ;
I have a,
The determining means determines whether a deviation in the direction of brightness of the color tone is a single color or a multi-color based on an image formation mode or color information of image information;
An image forming apparatus.   2. The reference value according to claim 1, wherein the reference value is a value obtained by detecting a color tone of an image fixed on a first recording medium of the plurality of recording media by the detecting unit. Image forming apparatus. 3. The image forming apparatus according to claim 1, wherein the control unit controls a transfer voltage of the second transfer unit when the amount of color shift exceeds a predetermined threshold value. 4. The said control means correct | amends the fluctuation | variation of the color tone of the primary color resulting from control of the transfer voltage of the said 2nd transfer means by gradation correction, The any one of Claims 1-3 characterized by the above-mentioned. Image forming apparatus. And an image forming apparatus according to any one of claims 1 to 4, an image data output device for outputting the image data to the said image forming apparatus are connected via a communication line, wherein the image forming apparatus acquires An image forming system for performing image forming processing on the image data. Forming an image on each of a plurality of photoconductors;
A first transfer step of transferring each image formed on the plurality of photosensitive members to an intermediate transfer member;
A second transfer step of transferring the image transferred to the intermediate transfer member to a plurality of recording media;
A fixing step of fixing the image transferred to the recording medium by the second transfer step;
A detection process for detecting the color tone of the image fixed on the recording medium by the fixing process;
A measurement process for measuring the color tone of the image based on the detection result of the detection process;
A specifying process for specifying a direction in which the color tone of the image measured by the measuring process is shifted from a reference value;
A determination process for determining which part of the single color and multi-color of the image is deviated from the reference value based on the result obtained by the specifying process;
A control process for controlling a transfer voltage of the second transfer means in accordance with a direction in which the single color and the multi-color are determined by the determination process ;
I have a,
In the determination process, it is determined based on the image formation mode or color information of the image information whether the deviation of the lightness direction of the color tone is a single color or a multi-color.
An image processing program characterized by that.

Images