JP6051747B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus. More specifically, a copying machine that performs color stabilization processing for stabilizing the color of an output image by correcting the image forming condition of the image forming means based on the result of colorimetry of the output multi-color toner image The present invention relates to image forming apparatuses such as facsimiles and printers.

  In an image forming apparatus that forms an image by an electrophotographic method, when a continuous printing operation is performed, there is a risk of causing uneven development density due to a large change in the charge amount of the toner contained in the developer contained in the developing device. is there.

  Specifically, a developing device that replenishes a developer contained in a developing device using a two-component developer composed of toner and a carrier according to a decrease in the amount of toner accompanying development, thereby developing the developing device. The toner density of the developer is maintained within a certain range. The toner replenished in the developing device gradually increases the charge amount as it is mixed and stirred with the carrier particles in the developer, but immediately after being replenished, the toner is not sufficiently charged. ing.

  For this reason, when a large amount of toner is supplied to the developing device in a short time, such as when printing images with a high image area ratio, the charge amount (Q / M) per unit weight of toner in the developer is compared. Become smaller. As a result, the amount of toner particles adhering to the electrostatic latent image at a predetermined potential on the latent image carrier increases, and the development density increases.

  On the other hand, when a state where only a small amount of toner is replenished to the developing device continues for a long time, such as when continuously printing images with a low image area ratio, most of the toner in the developer is stirred in the developing device for a long time. It will be in a state of staying. As a result, the charge amount (Q / M) of the toner in the developer becomes relatively large, and the amount of toner particles adhering to the electrostatic latent image at a predetermined potential on the latent image carrier is reduced. , Development density decreases. The increase / decrease in the development density as described above causes development density unevenness.

  Therefore, Patent Document 1 discloses an image forming apparatus that suppresses uneven development density by performing toner replenishment processing and adhesion amount stabilization processing. In the toner replenishment process of Patent Document 1, toner is replenished to the developing device according to the difference between the result of detecting the toner concentration of the developer in the developing device by the toner concentration sensor and a predetermined control target value. This process stabilizes the toner density within a certain range near a predetermined control target value.

  In addition, the adhesion amount stabilization process is performed in parallel with the toner replenishment process, and each time a predetermined number of print outputs are performed during a continuous print operation, a test image is applied to the photoreceptor as a latent image carrier. A toner image is formed, and the toner adhesion amount per unit area with respect to the toner image is detected by an optical sensor.

  When the detection result is larger than the predetermined target adhesion amount, that is, when the development density is higher than the target, the toner density control target value of the developer is corrected to a smaller value to lower the toner density. . As a result, the carrier particles are more actively rubbed against the individual toner particles to increase the toner charge amount (Q / M), thereby lowering the development density to approach the target image density.

  On the other hand, when the detection result is smaller than the target adhesion amount, that is, when the development density is lower than the target, the control target value of the developer toner density is corrected to a larger value to increase the toner density. . As a result, the amount of carrier particles rubbed against individual toner particles is reduced to reduce the toner charge amount (Q / M), thereby increasing the development density to approach the target image density. By carrying out such an adhesion amount stabilization process, uneven development density can be reduced.

  Further, in a color image forming apparatus including a plurality of developing devices that perform development using toners of different colors, the toner image of each color is stabilized by stabilizing the toner adhesion amount by the above-described adhesion amount stabilization process for each color. Can be output stably without greatly changing the density of the. By stabilizing the toner adhesion amount in this way, it is possible to stabilize the color of the output image. The control for stabilizing the output image is not limited to the control for correcting the control target value of the toner density in the developing device, such as the value of the developing bias and the intensity of the exposure light for writing the latent image on the surface of the photoconductor. Control for correcting other image forming conditions may be used.

  However, in the above-described adhesion amount stabilization process, toner must be used to form a test toner image, and as a result, there is a problem that the unit price per printed sheet increases. In addition, when a test toner image is formed, a user image formed based on image information input by a user operation cannot be formed. Therefore, an adhesion amount stabilization process is performed to suppress a decrease in productivity. There was a problem that it was not possible to carry out the operation frequently.

  Therefore, Patent Document 2 discloses a user image formed on a recording medium such as recording paper as control for stabilizing the color of an output image without forming the test toner image for the adhesion amount stabilization process described above. Control for correcting the image forming condition based on the result of the color measurement is disclosed.

  If the control is to measure the color of such a user image and correct the image formation condition based on the color measurement result, it is not necessary to form a test toner image, so the image is created based on the color measurement result of the user image. By combining the control for correcting the image condition and the above-described adhesion amount stabilization process, the color of the output image can be stabilized while suppressing the frequency of the adhesion amount stabilization process.

  Further, by suppressing the frequency of the adhesion amount stabilization processing, it is possible to suppress the productivity from being lowered when the image forming conditions are corrected. Here, if the output image color can be stabilized only by the control for correcting the image forming condition based on the colorimetric result of the user image without performing the above-described adhesion amount stabilizing process, the image forming condition is corrected. It is possible to further suppress a decrease in productivity when performing the process.

  The colors expressed by the color image forming apparatus are roughly classified into primary colors and multi-order colors. The primary color is a color expressed by only one type of toner. For example, in a configuration using four types of toners of yellow (Y), magenta (M), cyan (C), and black (K), it is expressed by only one of Y, M, C, and K toners. The color that is to be processed is the primary color. On the other hand, the multi-order color is a color expressed using two or more kinds of toners.

  In addition, many color image forming apparatuses express multi-order colors by mixing primary colors such as yellow (Y), magenta (M), cyan (C), and black (K). Adjusts the development density of each color by manipulating the primary color image forming conditions. However, since many user images are often composed of multi-colors rather than primary colors, it is difficult to directly know the development density of the primary color to be adjusted by control from the user image.

  For this reason, in the conventional color image forming apparatus that performs control for correcting the image forming condition based on the colorimetric result of the user image, the following control is performed. That is, a user image formed of a multi-order color toner image formed on a recording medium is color-measured, and obtained by measuring the color information of a target multi-order color (hereinafter referred to as a target color) obtained in advance. Compare the color information of the multi-order color. Then, the imaging condition of the primary color toner image of each color forming the multi-order color toner image is corrected so that the color of the user image composed of the multi-order colors approaches the target color.

  Thus, in the control for comparing multi-order colors, the image forming condition of the primary color to be corrected for the combination of color information for comparing the measured color information with the color information of the target color. Therefore, it is difficult to correct the user image color so that it closely approaches the target color. This is due to the following reason.

That is, when comparing multi-order colors, it is not possible to simply compare one color as if it is darker or lighter than the other color. As a method of comparing multi-order colors, for example, there is a method of comparing two multi-order colors such that the closer the color difference is, the closer the color difference is in the color system of L ^* a ^* b ^*. .

By using the color system of L ^* a ^* b ^*, the color difference between the measured color and the target color can be obtained, but how is the image forming condition of each primary color for the measured color? It cannot be determined whether the target color can be approximated by correction. The same applies to the case of using other color systems, and it is not possible to determine how the image forming conditions should be corrected.

  Therefore, in order to bring the color of the user image closer to the target color, how should the image forming conditions for each primary color be corrected when a certain color measurement result is output for the certain target color, It is necessary to input a combination of information in advance. In order to correct the color of the user image close to the target color with high accuracy, it is necessary to input a large number of combinations of information such as image forming conditions in advance. To obtain such a combination of information It is necessary to conduct an experiment in advance, and an increase in the number of combinations leads to high costs.

  Furthermore, even if the above-described combination of information can be given as a table or model, the validity of the information used for the control is lowered unless the previously input information is calibrated. In this calibration process, it is generally necessary to output a large number of patch images, which causes a problem that a large amount of toner is consumed. Furthermore, there is a problem that this calibration process takes a long time. For this reason, in the control for comparing multi-order colors, it is difficult to realize accurate correction of image forming conditions.

  Further, for example, when an RGB scanner is used as a colorimeter, the color measurement result is a ternary value of R value, G value, and B value. In general, there are four primary colors (cyan) from these three values. , Magenta, yellow, black) is difficult to estimate. As a specific example, there is a case where 3C gray and black obtained by mixing three colors of cyan, magenta, and yellow at an equal ratio cannot be distinguished.

  In other words, for example, even if a quaternary color measurement result that is too light is obtained, it is because the density of all three colors of cyan, magenta, and yellow is low, or only the density of black is low. There is a problem (hereinafter referred to as “black redundancy problem”) in which it is not possible to determine whether this is due to a low density of all primary colors or not. This is due to the fact that when equal amounts of cyan, magenta, and yellow are mixed, the color becomes almost achromatic and exhibits the same characteristics as black. The spectrometer and the human eye can distinguish between the two, but it is difficult to distinguish with a general RGB scanner.

  The present invention has been made in view of the above problems, and the image forming conditions under which a primary color toner image is formed on a latent image carrier are determined from multi-order color information acquired based on output image information. An object of the present invention is to provide an image forming apparatus capable of further stabilizing the color of an output image by performing correction with high accuracy.

In order to achieve such an object, an image forming apparatus according to the present invention includes, based on input image information, an image forming unit that forms a primary color toner image, which is a toner image of a different primary color, on a latent image carrier, Transfer means for forming a primary color toner image formed by superimposing the primary color toner images formed on the latent image carrier on the recording medium, and colorimetric measurement of the multicolor toner image formed on the recording medium Output image colorimetric means for acquiring output image information, color information acquisition means for acquiring color information of a multi-order color based on the output image information, and the multi-color based on the color information of the multi-order color. Based on color information estimation means for estimating the color information of each primary color of the color information of the primary color toner image constituting the primary color toner image, the color information of the primary color, and the input image information, The density level of the primary color toner image constituting the multi-order color toner image. And the concentration level determination means for determining the Le, the multi-color toner color number of primary colors constituting the image, and on the basis of the respective primary color dot percentage of validity as the number of colors of the primary colors is increased Color information that verifies that the color information of the primary color is low and that the color information of the primary color is verified to be low when it includes a primary color whose halftone dot ratio of the primary color is less than a predetermined value. Verification means; and image forming condition control means for correcting an image forming condition for forming the primary color toner image on the latent image carrier based on the density level of the primary color toner image and the validity. When the color information verification unit verifies that the color information of the primary color is low, the image formation condition control unit reduces the correction amount of the image formation condition.

  According to the present invention, according to the present invention, image formation for correcting an image forming condition for forming a primary color toner image on a latent image carrier from multi-color information acquired based on output image information. It is possible to further stabilize the color of the output image by performing accurate correction with the apparatus.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus. FIG. 3 is an enlarged configuration diagram illustrating an enlarged main part in a housing of a printer unit. FIG. 3 is an enlarged configuration diagram illustrating two adjacent image forming units in a printer unit. It is an exploded top view showing a developing device of an image forming unit. FIG. 3 is a plan view showing an intermediate transfer belt and an optical sensor unit in a printer unit. It is an enlarged block diagram which shows the 1st optical sensor in an optical sensor unit. It is an enlarged block diagram which shows the 2nd optical sensor in an optical sensor unit. FIG. 3 is a block diagram illustrating electrical connection of each unit in the image forming apparatus. 6 is a flowchart of color stabilization processing executed in the image forming apparatus. It is explanatory drawing explaining the relationship between a laser intensity | strength and a halftone dot rate. It is the schematic diagram of a control chart and an evaluation chart, and the processing flow of an Example. It is an estimation result of the halftone dot ratio of each primary color (comparative example). It is a transition of the color difference of the 55% 4C gray patch which is an observation color (comparative example). It is a transition of the color difference of each primary color obtained by measuring the evaluation chart (comparative example). It is an estimation result of the halftone dot rate of each primary color (Example). It is a transition of the color difference of the 55% 4C gray patch which is an observation color (Example). It is a transition of the color difference of each primary color obtained by measuring the evaluation chart (Example).

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

  The image forming apparatus according to the present embodiment forms image forming means (latent image toner) that forms a primary color toner image, which is a toner image having different primary colors, on a latent image carrier (photoconductor 20) based on input image information. The image writing unit 21 and the four image forming units 18 (Y, C, M, K)) and the toner image formed on the latent image carrier are directly or via an intermediate transfer member (intermediate transfer belt 10). Transfer means (primary transfer rollers 62, 2) for forming on the recording medium a multi-color toner image formed by superimposing the primary color toner images formed on the latent image carrier by transferring to the recording medium (recording paper P). Secondary transfer roller 24, etc.), output image colorimetric means (control scanner 900) for measuring output of the multi-order color toner image formed on the recording medium and obtaining output image information, and multi-order color of the output image Color information acquisition means for acquiring the color information of the (control The color which estimates the color information of each primary color of the color information of the primary color toner image constituting the multi-order color toner image based on the color information of the multi-order color acquired by the scanner 900) and the color information acquisition means Based on color information and input image information of the primary color estimated by the information estimation means (main control unit 500) and the color information estimation means, the density level of the primary color toner image constituting the multi-color toner image is determined. Density level determination means (main control section 500), color information verification means (main control section 500) for verifying the validity of the color information of the primary color estimated by the color information estimation means, and density level determination means An image forming condition control means for correcting an image forming condition for forming a primary color toner image on the latent image carrier based on the density level of the primary toner image and the validity verified by the color information verifying means. And (main controller 500), and has a. In addition, the code | symbol in embodiment and the example of application are shown in a parenthesis.

  Hereinafter, an electrophotographic color copying machine (hereinafter simply referred to as a copying machine 600) will be described as an embodiment of a color image forming apparatus to which the present invention is applied.

  First, the basic configuration of the copying machine 600 will be described. FIG. 1 is a schematic configuration diagram showing a copying machine 600 according to the present embodiment. The copier 600 includes a printer unit 100 that forms an image, a paper feeding device 200 that supplies a recording paper P that is a recording medium to the printer unit 100, a scanner 300 mounted on the printer unit 100, and this And an automatic document feeder (hereinafter referred to as ADF 400) mounted on the scanner 300.

  The printer unit 100 includes a manual feed tray 6 for manually feeding the recording paper P, a paper discharge tray 7 for stacking the image-formed recording paper P discharged from the housing of the printer unit 100, and the like. To do.

  When copying a document in the copying machine 600, first, a bundle of documents that are not bound is set on the document table 30 of the ADF 400. In the case of a bound document, it is set on the contact glass 31 of the scanner 300 instead of setting it on the ADF 400.

  At this time, the ADF 400 is opened to expose the contact glass 31, and a document is placed thereon, then the ADF 400 is closed and the document is pressed with it. Thereafter, when the user presses a start switch (not shown), the copying operation starts. When the document is set on the ADF 400, the document is automatically conveyed to the automatic reading unit 401 provided on the left side of the contact glass 31, The document that has passed through the automatic reading unit 401 is conveyed to the document discharge tray 30a.

  When the copy operation starts, when a document is set on the contact glass 31, the scanner 300 drives the first traveling body 33, and the light emitted from the light source on the first traveling body 33 is reflected on the document surface on the contact glass 31. Reflect. When the document is set on the ADF 400, the scanner 300 stops the first traveling body 33 below the automatic reading unit 401, and the light emitted from the light source on the first traveling body 33 passes through the automatic reading unit 401. Reflect it on the original surface of the original.

  The scanner 300 reflects the reflected light reflected on the document surface by the mirror of the second traveling body 34 and guides it to the reading sensor 36 through the imaging lens 35. In this way, the image information of the original is read. The obtained image information is sent to the printer unit 100. The printer unit 100 prints an image based on image information obtained by reading a document by the scanner 300. The printer unit 100 of the copier 600 can also form an image based on image information sent from an external device such as a personal computer in addition to image information obtained by reading an original by the scanner 300.

  The paper feeding device 200 includes a plurality of paper feeding cassettes 44 for storing the recording paper P, a paper feeding roller 42 and a separation roller 45 for feeding the recording paper P stored in the paper feeding cassette 44 one by one, and the sent recording. It is composed of a transport roller 47 that transports the paper P along the paper feed path 46. The paper feed path 46 is connected to the transport path 48 of the printer unit 100. When a user presses a start switch (not shown) or image information is sent from an external device, the paper feeding device 200 feeds a paper feed cassette 44 that accommodates the recording paper P selected by the user. The paper roller 42 rotates and the recording paper P is sent out from one of the paper feed cassettes 44. The fed recording paper P is separated into one sheet by the separation roller 45 and enters the paper feed path 46, and is conveyed to the conveyance path 48 in the printer unit 100 by the conveyance roller 47.

  FIG. 2 is an enlarged configuration diagram illustrating a main part in the casing of the printer unit 100 in an enlarged manner. The printer unit 100 is provided with an endless intermediate transfer belt 10 as an intermediate transfer member. An example of the base material of the intermediate transfer belt 10 is PI (polyimide), which is a material that is capable of suppressing misalignment due to belt elongation and has excellent mechanical strength. Carbon is dispersed in the base material of the intermediate transfer belt 10 as a resistance adjusting agent so that stable transfer performance is always obtained regardless of the temperature and humidity environment. Therefore, the intermediate transfer belt 10 is black. In order to reduce costs, PVDF (polyvinylidene fluoride) that does not disperse carbon can be used as a material for the base material of the intermediate transfer belt 10.

  The intermediate transfer belt 10 has a plurality of stretching members such as a first support roller 14, a second support roller 15, and a third support roller 16 disposed on the inner side of the loop. It is stretched in a posture that takes the shape of a substantially horizontal triangle. Hereinafter, the stretched surface forming a substantially horizontal side of the upper part of the triangle is referred to as a horizontal stretched surface. The intermediate transfer belt 10 is endlessly moved in the clockwise direction in FIG. 1 and FIG. 2 (in the direction of arrow A in the figure) when at least one of the three support rollers (14, 15, 16) is rotationally driven. To do.

  Above the intermediate transfer belt 10, four image forming units 18 (Y, C, Y) for individually forming yellow (Y), cyan (C), magenta (M), and black (K) toner images, respectively. M, K) are arranged along the horizontal stretched surface of the intermediate transfer belt 10. As shown in FIG. 1, a latent image writing unit 21 is disposed further above the image forming units 18 (Y, C, M, K).

  The latent image writing unit 21 receives image information obtained by reading a document by the scanner 300 or image information sent from an external device at its own writing control unit. Based on the image information, Y, C, M, and K semiconductor lasers (not shown) are driven to generate Y, C, M, and K writing lights. Then, the photoconductor 20 (Y, C, M, K) of the image forming unit 18 (Y, C, M, K) is optically scanned by the writing light, and the photoconductor 20 (Y, C, M, K) is scanned. Write an electrostatic latent image to K). Note that the light source of the writing light is not limited to a laser semiconductor, and an LED or the like may be employed.

  FIG. 3 is an enlarged configuration diagram showing two adjacent image forming units 18 among the four image forming units 18 (Y, C, M, K). In FIG. 3, the symbols Y, M, C, and K are omitted. As shown in FIG. 3, the image forming unit 18 includes a charging device 60, a developing device 61, a photoconductor cleaning device 63, a charge removal device 64, and the like around the drum-shaped photoconductor 20.

  The charging device 60 uniformly charges the surface of the photoreceptor 20 that is driven to rotate counterclockwise in FIG. 3 to the same polarity as the charging polarity of the toner. In the example shown in the drawing, a charging bias is applied to a charging roller that is brought close to the photosensitive member 20 in a non-contact manner, and a discharge is generated between the photosensitive member 20 and the charging roller, whereby the photosensitive member 20 is moved. It shows a method of uniformly charging. Instead of such a charging roller system, a non-contact charging system using a non-contact scorotron charger or the like may be employed.

  FIG. 4 is a top view of the developing device 61 with the upper portion of the casing removed. The developing device 61 develops the electrostatic latent image on the photoconductor 20 using a developer containing a magnetic carrier and a nonmagnetic toner. The developing device 61 is roughly divided into a stirring unit 66 and a developing unit 67.

  The stirring unit 66 includes two conveying screws 68 that are arranged in parallel to each other. These two conveying screws 68 are provided in a partition space that is individually partitioned by a partition wall 69. The partition wall 69 interposed between these partition spaces has notches at both ends in the screw longitudinal direction.

  Due to the notches, the two partition spaces that individually accommodate the two conveying screws 68 communicate with each other at both ends in the screw longitudinal direction. Of these two partition spaces, the partition space adjacent to the developing unit 67 described later is a supply chamber for supplying developer to the developing sleeve 65 in the developing unit 67.

  The other partition space is a return chamber in which the developer received from the supply chamber on one end side in the longitudinal direction of the screw is transported to the other end side and returned to the supply chamber. The transport screw 68 in the supply chamber and the transport screw 68 in the return chamber are designed to transport the developer in the opposite direction as they are driven to rotate, and the developer transported to the vicinity of the end in the screw longitudinal direction. Is fed into the other chamber through the aforementioned notch.

  As a result, as indicated by an arrow in FIG. 4, the developer in the developing device 61 is circulated and conveyed between the supply chamber and the return chamber. As shown in FIG. 3, a toner concentration sensor 71 for detecting the toner concentration of the developer is attached to the bottom of the supply chamber in the stirring unit 66.

  As shown in FIG. 4, a toner replenishing port 61a is formed above a notch that communicates the downstream end in the transport direction in the supply chamber and the upstream end in the transport direction in the return chamber.

  The developing unit 67 accommodates a developing sleeve 65 made of a nonmagnetic cylindrical member that can be driven to rotate. Inside the developing sleeve 65, a magnet roller having a plurality of magnetic poles arranged in the circumferential direction is fixed so as not to rotate with the developing sleeve 65. In the supply chamber of the stirring unit 66 described above, the toner density is detected by the toner density sensor 71 while the developer is being conveyed in the direction indicated by the arrow B in FIG.

  Then, a part thereof is pumped up to the developing sleeve 65 by the magnetic force generated by the magnetic pole of the magnet roller. The developer drawn up on the surface of the developing sleeve 65 is transported toward the developing region where the developing sleeve 65 and the photosensitive member 20 face each other as the developing sleeve 65 rotates.

  At this time, the layer thickness of the developer on the surface of the developing sleeve 65 on the surface of the developing sleeve 65 is regulated by the doctor blade 73 before reaching the developing region. The developer that has reached the development area after this regulation has a development potential that is a potential difference between the development sleeve 65 to which a development bias having the same polarity as the charging polarity of the toner is applied and the electrostatic latent image on the photoreceptor 20. By the action, the toner particles are separated from the magnetic carrier and transferred to the electrostatic latent image. Thereby, the electrostatic latent image on the photoconductor 20 is developed.

  When the developer containing toner particles not transferred to the photoconductor 20 in the development region passes through the development region as the development sleeve 65 rotates and is conveyed to the position of the repulsive magnetic pole in the magnet roller, the surface of the development sleeve 65 is reached. And is returned to the supply chamber of the stirring unit 66. In the supply chamber, when the toner concentration of the developer decreases as the developer contributing to the development is returned, this is detected by the toner concentration sensor 71, and an appropriate amount of toner is supplied from the toner supply port 61a. Such toner replenishment control based on the detection result of the toner density sensor 71 is executed for each sheet passing.

  Inside the loop of the intermediate transfer belt 10, four primary transfer rollers 62 that sandwich the intermediate transfer belt 10 between the four photoreceptors 20 are disposed. Each primary transfer roller 62 presses the front surface of the intermediate transfer belt 10 toward each photoconductor 20, thereby forming four primary transfer nips where the belt front surface and the photoconductor 20 abut. Has been. A primary transfer bias having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 62. Thereby, in the primary transfer nip, a primary transfer electric field is formed in which the toner moves from the photoconductor 20 side to the primary transfer roller 62 side, and the toner image on the surface of the photoconductor 20 is formed on the front surface of the intermediate transfer belt 10. Primary transcription. Instead of the primary transfer roller 62, a transfer brush, a non-contact corona charger, or the like may be employed as a primary transfer unit that primarily transfers the toner image on the photoreceptor 20 to the front surface of the intermediate transfer belt 10. .

  Untransferred toner that has not been primarily transferred to the intermediate transfer belt 10 adheres to the surface of the photoreceptor 20 after passing through the primary transfer nip. This transfer residual toner is removed from the surface of the photoconductor 20 by the photoconductor cleaning device 63. The photoconductor cleaning device 63 supports a polyurethane rubber cleaning blade 75 in a cantilevered manner, with its free end abutting against the surface of the photoconductor 20 and scraping off transfer residual toner on the surface. The transfer residual toner on the surface of the photoconductor 20 is also removed by a conductive fur brush 76 that rotates while contacting the photoconductor 20. The toner removed from the photoconductor 20 by the cleaning blade 75 and the fur brush 76 is accommodated in the photoconductor cleaning device 63.

  The surface of the photoconductor 20 from which the transfer residual toner has been removed by the photoconductor cleaning device 63 is neutralized by light irradiation of the neutralization device 64. Thereby, the surface potential of the photoconductor 20 is initialized. Thereafter, the toner is uniformly charged to the same polarity as the charging polarity of the toner by the charging device 60, and then the surface potential is detected by the potential sensor 320.

  The photoconductor 20 of the present embodiment is a drum-shaped member having a diameter of 60 [mm], and is driven to rotate counterclockwise in the drawing at a linear velocity of 282 [mm / sec]. The developing sleeve 65 of the present embodiment is a cylindrical member having a diameter of 25 [mm], and is driven to rotate at a linear speed of 564 [mm / sec]. In the developing device 61 of the present embodiment, the charge amount of the toner in the developer supplied to the developing area is in the range of about 10 to 30 [−μC / g]. The thickness of the photosensitive layer of the photoconductor 20 is 30 [μm], the beam spot diameter of the optical system of the latent image writing unit 21 is 50 × 60 [μm], and the amount of light is about 0.47 [mW]. ]. The surface of the photoconductor 20 is uniformly charged to, for example, 700 [-V] by the charging device 60, and the potential of the electrostatic latent image portion irradiated with the laser by the latent image writing unit 21 is 120 [-V]. . The developing bias applied to the developing sleeve 65 is 470 [−V], and thus a developing potential of 350 [−V] acts on the toner on the electrostatic latent image on the photoconductor 20.

  In the image forming unit 18 having the above configuration, as the photoconductor 20 is rotationally driven, it is first uniformly charged by the charging device 60 and then subjected to optical scanning by the latent image writing unit 21 to receive the electrostatic latent image. Carry an image. The optical scanning is performed based on image information read by the scanner 300 or image information sent from an external device.

  The electrostatic latent image on the photoreceptor 20 is developed by the developing device 61 to become a toner image. This toner image is primarily transferred onto the intermediate transfer belt 10 by a primary transfer electric field formed between the photoreceptor 20 and the primary transfer roller 62. The transfer residual toner remaining on the surface of the photoconductor 20 after the primary transfer is removed by the photoconductor cleaning device 63, and thereafter, the surface of the photoconductor 20 is discharged by the charge removal device 64 and used for the next image formation.

  As shown in FIG. 2, a secondary transfer roller 24 is disposed outside the loop of the intermediate transfer belt 10, and the intermediate transfer belt 10 is sandwiched between the third support roller 16 inside the belt loop. It is out. When the third support roller 16 presses the intermediate transfer belt 10 toward the secondary transfer roller 24, a secondary transfer nip where the front surface of the belt and the secondary transfer roller 24 abut is formed.

  When a start switch (not shown) is pressed by the user, a drive motor (not shown) is driven, and one of the three support rollers (14, 15, 16) is rotationally driven, so that the intermediate transfer belt 10 is rotated. Rotating drive. At the same time, the photosensitive members (Y, C, M, K) of the image forming unit 18 (Y, C, M, K) are also rotationally driven.

  Thereafter, based on the image information read by the reading sensor 36 of the scanner 300, the latent image writing unit 21 transfers the photosensitive member 20 (Y, C, M, K) of the image forming unit 18 (Y, C, M, K). ) Is irradiated with writing light. As a result, electrostatic latent images are formed on the photoreceptors 20 (Y, C, M, K), respectively, and are visualized by the developing devices 61 (Y, C, M, K). Thereby, Y, C, M, and K toner images are formed on the photoreceptor 20 (Y, C, M, and K). The Y, C, M, and K toner images formed in this way are superimposed and transferred onto the intermediate transfer belt 10 at the primary transfer nips for Y, C, M, and K. As a result, a four-color superimposed toner image in which the toner images of the respective colors are overlapped is formed on the intermediate transfer belt 10.

  The recording paper P delivered from the paper feeding device 200 described above enters the conveyance path 48 of the printer unit 100 and then stops when it strikes the registration roller pair 49. The registration roller pair 49 sends the recording paper P received in the conveyance path 48 to the secondary transfer nip at a timing that can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 10.

  On the recording paper P fed to the secondary transfer nip, recording is performed by the action of the secondary transfer electric field formed between the secondary transfer roller 24 to which the secondary transfer bias is applied and the third support roller 16. Secondary transfer is performed on the paper P at once. The four-color superimposed toner image is combined with the white color of the recording paper P to become a full-color toner image.

  Thereafter, the recording paper P is transported to the fixing device 25, and the fixing device 25 is heated and pressed to perform a fixing process for the full-color toner image. The conveyance direction of the recording paper P that has passed through the fixing device 25 is switched between a direction toward the paper reversing device 93 and a direction toward the paper discharge roller pair 56 shown in FIG. When the recording paper P is fed into the paper reversing device 93, the upper and lower surfaces are reversed and then fed again to the registration roller pair 49 so that a full color image is formed on the other surface. Further, when the paper is fed to the paper discharge roller pair 56, it is stacked on the paper discharge tray 7 outside the apparatus.

  In addition to the secondary transfer roller 24, a transfer charger may be employed as the secondary transfer unit that secondary-transfers the four-color superimposed toner image on the intermediate transfer belt 10 to the recording paper P. A roller cleaning unit 91 that cleans toner adhering to the secondary transfer roller 24 is in contact with the secondary transfer roller 24 of the present embodiment.

  A belt cleaning device 17 is in contact with a portion where the intermediate transfer belt 10 is wound around the second support roller 15 in the circumferential direction. The belt cleaning device 17 cleans the transfer residual toner adhering to the intermediate transfer belt 10 after passing through the secondary transfer nip.

  The printer unit 100 is provided with a manual paper feed path 41 that joins from the manual feed tray 6 to the conveyance path 48. On the upstream side of the manual paper feed path 41, a manual paper feed roller 601 and a manual separation roller 602 for feeding the recording paper P set on the manual feed tray 6 one by one are provided.

  As shown in FIG. 1, a control RGB scanner 900 (to be referred to as a control scanner 900 hereinafter), which will be described in detail later, is disposed above the paper discharge tray 7. The copying machine 600 can measure the color of the image formed on the recording paper P discharged onto the paper discharge tray 7 by the control scanner 900. The control scanner 900 detects RGB values on the recording paper P. A range from 0 [mm] to 210 [mm] in the main scanning direction when the front end in the main scanning direction in the region through which the recording paper P of the minimum size can pass is 0 [mm]. Thus, the RGB values can be detected at 22 locations every 10 [mm].

  Further, the control scanner 900 detects the sub-scanning direction (the conveyance direction of the recording paper P) by dividing it every 10 [mm], and at 22 points in the main scanning direction for detecting the spectral reflectance distribution, 10 is detected. Color measurement is performed on a square area of [mm] × 10 [mm]. The detected RGB value is an average value of the colorimetric values in this square area.

  Further, as shown in FIGS. 1 and 2, outside the loop of the intermediate transfer belt 10, the optical sensor unit 310 is opposed to the belt-wrapped portion of the first support roller 14 with a predetermined gap. It is arranged.

  FIG. 5 is a top view showing the horizontal stretched surface of the intermediate transfer belt 10 and the optical sensor unit 310. As shown in FIG. 5, the optical sensor unit 310 includes a first optical sensor 311 and a second optical sensor 312 that are arranged in the belt width direction (front-back direction in FIGS. 1 and 2 and up and down direction in FIG. 5). have. The second optical sensor 312 is disposed at a position closer to the center of the belt than the first optical sensor 311. The position near the center of the belt is in the developer conveyance direction (in the direction of arrow B in FIG. 4) by the conveyance screw 68 in the supply chamber development region for supplying the developer to the developing sleeve 65 in the developing unit 67 of the developing device 61. It corresponds to the position on the more upstream side.

  Due to the configuration of the developing device 61, the image density tends to be higher on the upstream side in the developer transport direction of the supply chamber developing region than on the downstream side. This is because there is a distribution in the charge amount of the toner, toner having a relatively low charge amount is developed on the upstream side, and the developer volume is higher on the upstream side than on the downstream side.

  That is, even if the patch image is formed under the same conditions, the amount of attachment varies depending on the position of the developing sleeve 65 in the main scanning direction. The reason why the second optical sensor 312 is disposed at a position closer to the center of the belt than the first optical sensor 311 is because it is important where the position in the main scanning direction to be controlled is set.

  For example, when a sensor is arranged upstream in the developer conveyance direction of the supply chamber development region, the dark patch is controlled, and the development density is higher than the measurement point in other places (downstream from the measurement point). getting thin. A problem that is more likely to occur in electrophotographic imaging systems is that the development density is too high (the toner charge is too low) and the toner scatters in the machine, making it dirty or not developing. There is a problem that toner adheres.

  In order to prevent this problem, it is preferable to perform measurement upstream where the problem is likely to occur. However, the toner on the upstream side is not sufficiently stable because the developer is not sufficiently stirred, the charge amount distribution is wide, and there is a high possibility that weakly charged toner is present. It is highly possible that the measurement is unstable. Therefore, it is desirable to measure the patch image as upstream as possible in the downstream region where the charge amount of the toner is relatively stable. Since the black toner is more stable than the other color toners, the second optical sensor 312 that measures the color patch image is disposed at a position closer to the center of the belt, which is a more suitable position for measuring the patch image. ing.

  FIG. 6 is an enlarged configuration diagram showing the first optical sensor 311, and FIG. 7 is an enlarged configuration diagram showing the second optical sensor 312.

  The first optical sensor 311 detects the toner adhesion amount per unit area with respect to the K toner patch image Pk formed on the intermediate transfer belt 10 in the adhesion amount stabilization process described later. As shown in FIG. 6, the first optical sensor 311 receives a first sensor light source 311 a that is an LED that emits light toward the intermediate transfer belt 10, and regular reflection light that is specularly reflected on the intermediate transfer belt 10. And a first sensor regular reflection light receiving element 311b.

  The second optical sensor 312 detects toner adhesion amounts per unit area for Y, C, and M toner patch images Py, Pc, and Pm formed on the intermediate transfer belt 10 in the adhesion amount stabilization process described later. It is. As shown in FIG. 7, the second optical sensor 312 receives the second sensor light source 312 a that is an LED that emits light toward the intermediate transfer belt 10 and the specularly reflected light that is specularly reflected on the intermediate transfer belt 10. A second sensor regular reflection light receiving element 312b and a second sensor diffuse reflection light receiving element 312c for receiving diffuse reflection light diffusely reflected on the intermediate transfer belt 10 are provided.

  As each of the first sensor light source 311a and the second sensor light source 312a, a GaAs infrared light emitting diode having a peak emission wavelength λp = 950 [nm] is used. As the light receiving elements used for the first sensor regular reflection light receiving element 311b, the second sensor regular reflection light receiving element 312b, and the second sensor diffuse reflection light receiving element 312c, Si phototransistors having a peak light receiving wavelength of 800 [nm] are used. Yes. In addition, the distance (detection distance) between each optical sensor and the intermediate transfer belt 10 that is the detection target surface is set to 5 [mm]. In addition to these optical sensors, the optical sensor unit 310 is also provided with a sensor memory 313.

  FIG. 8 is a block diagram showing the electrical connection of each part in the copying machine 600. The copying machine 600 includes a main control unit 500, and the main control unit 500 controls driving of each unit. The main control unit 500 functions as a ROM 503 that stores in advance fixed data such as a computer program and a work area that stores various data in a rewritable manner via a bus line 502 to a CPU 501 that executes various arithmetic processes and drive control of each unit. RAM 504 to be connected.

  The main control unit 500 is connected to each unit of the printer unit 100, the paper feeding device 200, the scanner 300, and the ADF 400. Here, the optical sensor unit 310 and the control scanner 900 of the printer unit 100 send the detected information to the main control unit 500.

  The main controller 500 can perform the following adhesion amount stabilization process. That is, first, as shown in FIG. 5, Y, C, M, and K toner patch images Py, Pc, Pm, and Pk are formed on the intermediate transfer belt 10. Then, based on the output from the optical sensor when the toner patch image passes directly under the optical sensor, the Y, C, M, K toner patch images Py, Pc are applied by the optical sensor unit 310 as the adhesion amount detection means. , Pm, and Pk, Y, C, M, and K toner adhesion amounts per unit area are obtained.

  Then, the calculated value of the Y toner adhesion amount is compared with the Y toner adhesion amount target value. If the former is smaller than the latter, the Y toner density control target value used in the toner replenishment control is made larger. When the former is larger than the latter, the Y toner density control target value is made smaller.

  Similarly, the C, M, and K toner density control target values are corrected based on the comparison result between the calculated values of the C, M, and K toner adhesion amounts and the C, M, and K toner adhesion amount target values. By such adhesion amount stabilization processing, the toner adhesion amount per unit area for the Y, C, M, and K toner images is stabilized, so that the color tone of the full-color image can be stabilized.

  However, in the adhesion amount stabilization process described above, toner must be used to form a test toner image, resulting in an increase in the unit price per printed sheet. Furthermore, when a test toner image is formed, a user image formed based on image information input by a user operation cannot be formed. For this reason, in order to suppress the fall of productivity, adhesion amount stabilization processing cannot be implemented with high frequency.

  As control for stabilizing the color of the output image without forming a test toner image, output image information is obtained from a full-color user image formed on the intermediate transfer belt 10 and the image information used for image formation In comparison, it is conceivable to control the image forming condition so that the value obtained from the image information of the user image approaches the target value obtained from the image forming image information used for image formation.

However, since the toner image on the intermediate transfer belt 10 is an unfixed toner image, the color information of the image finally output from the printer unit 100 cannot be obtained. In addition, since the full-color toner image on the intermediate transfer belt 10 is in a state where only the unfixed primary color toner image is superimposed, it is possible to obtain information on the toner adhesion amount, but it is finally output. It is impossible to obtain color information of a multi-order color image, such as L ^* a ^* b ^* values.

As described above, since only information on the amount of toner adhesion can be detected on the intermediate transfer belt 10, the color of the toner image fixed on the recording paper P based on the information obtained from the toner image on the intermediate transfer belt 10. It is difficult to stabilize (for example, L ^* a ^* b ^* value) to an arbitrary target value.

  As described above, it is difficult to stabilize the color of the toner image fixed on the recording paper P based on the information obtained from the toner image on the intermediate transfer belt 10. The configuration is not limited to a configuration in which the toner image is a user image. A similar problem occurs even in a configuration in which a test toner image is formed as in the above-described adhesion amount stabilization process.

  As a method for solving such a problem, there is a method for acquiring output image information from a toner image fixed on the recording paper P, instead of acquiring output image information from a state before the generated toner image is fixed. is there. Color measurement is possible with the toner image fixed on the recording paper P in this way, and the result of color measurement can be used for control.

  There are roughly two methods for measuring the color of the toner image fixed on the recording paper P. One is a method for measuring the color by forming a patch image on the recording paper P, and the other is a method for measuring the color. In this method, a user image is formed on recording paper P and colorimetric is performed.

  The former method needs to print a patch image separately from the user image, and thus has a demerit that it leads to a decrease in toner yield and a decrease in productivity as in the above-described adhesion amount stabilization processing. Further, since an image other than the user image is formed on the recording paper P, a waste paper is generated, and a mechanism for sorting the recording paper P on which the patch image is formed and the recording paper P on which the user image is formed is necessary. There is a demerit that it becomes. However, there is an advantage that an arbitrary toner image including a color to be measured for control can be formed on the recording paper P, and color measurement used for control becomes easy.

  On the other hand, the latter method does not have the disadvantages of the former described above, but an arbitrary toner image including a color to be measured for control cannot be formed. Therefore, whether or not the color to be measured for control can be measured is determined by the user image. Strongly depends on.

  In practice, it is very important to suppress the increase in cost and productivity, so it is not practical to use only patch images, and it is not possible to use user images together or use only user images. I do not get.

  The copying machine 600, which is an image forming apparatus to which the configuration of the present invention is applied, predicts the development density of the primary color from the colorimetric result of the multi-order color user image formed on the recording paper P, thereby enabling the patch as much as possible. This is intended to stabilize the color of the output image without outputting the image. Hereinafter, the control for stabilizing the color of the output image based on the color measurement result of the multi-order color user image in the copying machine 600 is referred to as color stabilization processing.

  Next, a characteristic configuration of the copying machine 600 according to the present embodiment will be described. In the copying machine 600, in the color stabilization process, the main control unit 500 performs color information based on the color information of the multi-color user image acquired by the control scanner 900 which is an output image colorimetric unit and a color information acquisition unit. As estimation means, color information of primary colors of the primary color toner images of Y, M, C, and K constituting the multi-order color toner image is estimated.

  In addition, the main control unit 500 serves as a density level determination unit that determines the density level of the primary color toner image constituting the multi-color toner image based on the estimated primary color information and input image information. As information verification means, the validity of the color information of the estimated primary color is verified.

  Further, the main control unit 500 serves as image forming condition control means based on the estimated color information of the primary colors of Y, M, C, and K, the density level of the primary color toner image, and the validity of the color information of the primary color. The control parameters of the image forming conditions in the image forming units 18 (Y, C, M, K) and the latent image writing unit 21 for forming the primary color toner image are corrected. Here, the control parameters to be corrected include the toner density control target value in the developing device 61, the developing bias, the intensity of the writing light that the latent image writing unit 21 irradiates on the surface of the photoconductor 20.

  Hereinafter, the color stabilization process in the copying machine 600 will be described in detail.

  FIG. 9 is a flowchart of the color stabilization process executed by the copying machine 600. In the color stabilization process, the main control unit 500 first acquires image information sent from an external device or image information obtained by the scanner 300 as input image information. This input image information includes pixel values representing the brightness of monochromatic components of R (red), G (green), and B (blue) for a plurality of pixels arranged in a matrix that form an image. . The main control unit 500 converts the input image information into image forming image information having pixel values representing the lightness of single color components of C (cyan), M (magenta), Y (yellow), and K (black). Conversion is performed (S1).

  After conversion to image forming image information, the following two processes are performed simultaneously. One is an image forming process (S2) and a transfer process (S3) as a printing process, and the other is a colorimetric area determining process (S4). Determine the color area.

  As the image forming process (S2), based on the image forming image information, as described above, the photoreceptors 20 (Y, C, M, and K) of the four image forming units 18 (Y, C, M, and K), respectively. K) A primary color toner image is formed on the image, and the primary color toner image is superimposed on the intermediate transfer belt 10 to form a multi-color toner image. In the transfer process (S3), the multi-color toner image formed on the intermediate transfer belt 10 as described above is transferred onto the recording paper P at the secondary transfer nip. Thereafter, the recording paper P on which the multi-color toner image is fixed by the fixing device 25 is conveyed toward the paper discharge tray 7.

  On the other hand, as the colorimetric region determination process (S4), the main control unit 500 serves as a colorimetric region determining unit, which region among all the regions of the image indicated by the image forming image information is the colorimetric region to be measured. Decide what to do.

  After the printing process (S2 and S3) and the colorimetric area determination process (S4) are executed, the colorimetric process (S5) is executed. In the color measurement process (S5), it corresponds to the color measurement area determined in the color measurement area determination process (S4) out of all image areas of the multi-color toner image on the recording paper P passing under the control scanner 900. Measure the area to be measured.

  In the copying machine 600 of the present embodiment, a part of the entire image area is set as a colorimetric area, and the colorimetry of the colorimetric area and the operation of comparing the output image information of the colorimetry result with the image forming image information are performed. Is going. As described above, the image information is not limited to comparing a part of the entire image area as a colorimetric area and comparing image information. If possible, the entire image area is divided into several colorimetric areas. The color measurement and the comparison of image information may be performed for the entire image area.

  However, when color measurement and comparison between image information are performed for the entire image area, the amount of information to be processed becomes very large, and if the CPU does not have a high processing speed, the productivity of the apparatus decreases. Higher CPU speed leads to higher costs. For this reason, in the present embodiment, the copier 600 uses a part of the entire image area as a colorimetric area, and performs colorimetry and comparison between image information for the colorimetric area.

  Further, the colorimetric region is preferably a region in which the change in hue in the region is as small as possible (the color flatness is high) when performing highly accurate colorimetry. Therefore, the main control unit 500 performs a process of searching for an area having high color flatness and suitable for color measurement based on the image forming image information.

  After this search, when the recording paper P on which the image is formed by the printer unit 100 is discharged onto the paper discharge tray 7, the colorimetric region is measured by the control scanner 900. Thereafter, the color information obtained from the color measurement result is compared with the color information of the color measurement region obtained from the image forming image information.

  The search for the colorimetric area is performed as follows. That is, a pixel at a predetermined position in the pixel matrix represented by the image forming image information is set as a target pixel, and a region having a predetermined size centered on the target pixel is extracted as a partial region. For example, in the first extraction, the pixel in the 51st column and the 51st row from the upper left in the pixel matrix is the pixel of interest, and a rectangular area (about 4 [mm] square) of 101 pixels × 101 pixels centered on this pixel of interest. Are extracted as partial areas. Then, the flatness indicating the flatness of the hue of the entire partial area is calculated while referring to the pixel values (C, M, Y, K) of each pixel in the extracted partial area. As the flatness, those obtained by various calculation methods can be used.

  As a first example of flatness, one obtained by the following calculation method can be cited. That is, first, the variance of each pixel is obtained for C, M, Y, and K, respectively. Next, a value obtained by adding a negative sign to the sum of the variances is obtained as the flatness in the partial region.

  As a second example of flatness, one obtained by using a determinant of a variance-covariance matrix can be cited. Specifically, for C, M, Y, and K, the variance and covariance at each pixel in the partial area are obtained. Next, a 4 × 4 variance-covariance matrix is constructed in which variance is arranged in the diagonal component and covariance is arranged in the non-diagonal component, and the determinant is calculated. Then, a value obtained by adding a negative sign to the value of the determinant may be obtained as the flatness. This is because the spread of the distribution in the CMYK space can be evaluated by using the determinant of the variance-covariance matrix. Compared to the flatness of the first example described above, the color spread between different components can be evaluated.

  Further, as a third example of flatness, one using the frequency characteristics of color can be cited. Specifically, the Fourier transform is performed using each pixel value in the partial region, and the sum of the squares of the absolute values of the Fourier coefficients of the specific frequency is obtained. A flatness is obtained by adding a negative sign to this sum. A plurality of frequencies can be used for the specific frequency. In the flatness of the first example, there is a case where a flat region cannot be identified for an image subjected to halftone processing due to the influence of the pattern of halftone processing. On the other hand, in the flatness of the third example, the flatness excluding the influence of halftone processing can be calculated by using the sum of the squares of the absolute values of the Fourier coefficients of the specific frequency.

  The flatness is not limited to the first to third examples described so far, and a known flatness calculation technique can be used.

  When the flatness of the extracted partial areas is obtained, it is next determined whether or not all partial areas have been extracted (whether or not extraction of partial areas has been completed for all areas of the image). If it is determined that there is a partial area that has not yet been extracted, the position of the target pixel is shifted by one pixel in the right direction, and the pixels in the 52nd column and the 51st row from the upper left are used as the target pixel. A rectangular area of 101 pixels × 101 pixels centering on is extracted as a partial area. Similarly, the flatness of the color of the extracted partial area is calculated. Thereafter, when extracting the third, fourth, fifth,..., Nth partial area, the position of the target pixel is shifted by one pixel to the right. Then, after shifting the position in the column direction of the target pixel from the right end of the matrix to the 51st position, the position in the column direction of the target pixel is returned from the left end of the matrix to the right to the 51st position. At the same time, the position in the row direction is shifted downward by one pixel. Thereafter, the process of shifting the position of the target pixel to the right by one pixel is repeated. As described above, the position of the target pixel is sequentially shifted like raster scanning to cover the entire area of the image.

  As described above, the method for extracting the partial areas for the entire area of the image is not limited to the method of shifting the target pixel by one pixel, and each partial area is extracted so that the edges of the extracted partial areas do not overlap each other. May be. For example, after extracting a partial region having a size of 101 pixels × 101 pixels centered on the pixel of interest in the 51st column and the 51st row, 101 pixels × centering on the pixel of interest in the 152th column and the 51st row A partial region having a size of 101 pixels is extracted.

  When the main control unit 500 extracts partial areas from the entire area of the image and calculates the flatness, the main control section 500 identifies the best flatness among all the partial areas, and determines the flatness in advance. It is determined whether or not the predetermined reference flatness is superior. If it is excellent, the partial area is set as a colorimetric area suitable for colorimetry. On the other hand, if the flatness of the specified partial area is inferior to a predetermined reference flatness, it is determined that the user image output at that time does not have a colorimetric area suitable for colorimetry.

  If a colorimetric region suitable for colorimetry is not found based on the image information, a conventionally known adhesion amount stabilization process described above is performed. Although this adhesion amount stabilization processing cannot accurately match the output of the multi-color to the original color, it can be stabilized at a value slightly deviated from the original color. A large disturbance in the color tone of the image can be avoided. In other words, if a colorimetric area suitable for colorimetry is not found in the user image, the adhesion amount stabilization process is performed instead of the color stabilization process described later, thereby preventing the occurrence of large color tone disturbances. can do.

  Next, the main control unit 500 serves as a color information estimation unit, and the primary color colors constituting the multi-color toner image based on the multi-color information acquired from the colorimetric output image information. A color separation process (S6) for estimating information is performed. A specific example of this estimation method will be described later.

  The main control unit 500 also serves as a density level determination unit that compares color information of each estimated primary color with color information on control of each primary color that is a target value acquired from input image information. Comparison processing (S7) is performed.

  Further, the main control unit 500 determines a correction amount for the control parameter as image forming condition control means, and executes a correction process (S8).

  The control parameters to be corrected here are the laser intensity (LDP) of the latent image writing unit 21, the charging application voltage (Cdc) of the charging device 60, and the developing bias (Vb) of the developing device 61. In addition to this, the toner density of the developer stored in the developing device 61 can be adopted as the control parameter.

  Next, a primary color information estimation method (color separation process) based on multi-order color information acquired from colorimetric output image information will be described. In the present embodiment, as the color information of the primary color, an apparent average halftone dot rate (hereinafter simply referred to as an output halftone dot rate) when a toner image when output in the primary color is measured is estimated.

  Here, the relationship between the dot ratio and the laser intensity of the latent image writing unit 21 will be described. FIG. 10 is an explanatory diagram for explaining the relationship between the laser intensity and the dot ratio.

  Parameters that can adjust the laser output of the latent image writing unit 21 include LD-Power (LDP) and LD-Duty (LDD). LDP is the laser intensity of the writing light, and LDD is the ratio of the time for writing per unit time. The halftone dot ratio is a ratio of an area where a toner image per unit area on the surface of the recording paper P is formed, and this is a latent image per unit area on the surface of the photoreceptor 20. It is the area ratio. Therefore, for example, a halftone dot ratio of 50 [%] means that LDD is 50 [%].

  As shown in FIG. 10, the larger the LDP value and the LDD value, the larger the amount of toner supplied on the surface of the photoconductor 20 and the higher the image density. Also, the LDP value and the LDD value can be changed independently, and the image density can be changed by changing the LDP or the LDD. For this reason, even if the LDP value is the same, the larger the LDD value, the darker the image density, and even if the LDD value is the same, the larger the LDP value, the darker the image density. . However, as a control of the image density, a method of changing the LDD so as not to change the gradation is common. The LDP generally has a configuration in which the solid image (the darkest image) is adjusted to a predetermined density when the LDD is 100 [%]. In the copying machine 600, as a control parameter, In this configuration, the value of LDP is actively moved.

  In the copying machine 600, the LDP value can be adjusted as necessary with a value lower than the strongest laser intensity (for example, 70 [%]) as an initial value. When the control parameter is not corrected, the laser intensity is fixed, and the control halftone dot ratio (hereinafter referred to as the control halftone dot ratio) is set so that the desired image density is obtained with the fixed laser intensity. The

  Here, as an example, let us consider a case where the primary color image forming conditions are a laser intensity of 70 [%] and a control dot ratio of 40 [%].

  When a desired image is formed under these conditions, a toner adhesion amount per pixel corresponding to a laser intensity of 70 [%] on the recording paper P is 40 per unit area on the surface of the recording paper P. A toner image is formed in the area of [%]. The output dot ratio when such a toner image is output is 40 [%]. On the other hand, when the toner adhesion amount per pixel is reduced despite the image formation under the same conditions, the toner image is formed in an area of 40 [%] per unit area on the surface of the recording paper P. In other words, it looks thinner than the toner image on which the desired image is formed. When such a toner image is output, the output halftone dot ratio is smaller than 40 [%].

  In this way, the control halftone dot ratio is compared with the output halftone dot percentage. If the output halftone dot percentage is smaller than the control halftone dot percentage, the amount of toner adhesion is increased by increasing the laser intensity. Correct the control parameters. On the contrary, when the output halftone ratio is larger than the control halftone ratio, the control parameter is corrected so that the toner adhesion amount is reduced.

  Here, assuming that the control halftone ratio is a target value, if the output halftone ratio is known, the color information (output halftone ratio) of each primary color constituting the multi-color toner image, and image forming image information It is possible to compare with the color information (control halftone dot ratio) on the control of each primary color, which is the target value obtained from.

  However, the toner image formed on the recording paper P has a multi-order color, and the output halftone ratio, which is color information of the primary color, cannot be directly measured. For this reason, the main controller 500 estimates the output halftone ratio of each primary color based on the output image information of the multi-order color toner image measured by the control scanner 900, and controls the halftone dot ratio for each primary color. Is compared with the estimated output halftone dot ratio (hereinafter referred to as an output halftone dot ratio estimated value) to determine a correction amount for the control parameter.

  Thereafter, the correction amount for the control parameter is determined using the correction amount for the determined control parameter, and the control parameters (laser intensity, charging applied voltage, development bias) are set to values that reflect the correction amount.

  A method for estimating the output dot ratio estimated value of the primary color from the color measurement result of the multi-order color toner image will be described. First, a primary color data table used for estimation will be described.

  In the algorithm for estimating the estimated output dot ratio of the primary color employed in the copying machine 600, the spectral reflectance distribution cyan (kc, λ), magenta of each primary color at the dot ratio in the vicinity of the control dot ratio is used as prior information. (Km, λ), yellow (ky, λ), and black (kk, λ) are required. However, since it is generally difficult to prepare data for arbitrary halftone dot ratios kc, km, ky, kk, for example, each of the ten halftone dot ratios kc1 to kc10, km1 discretized in increments of 10 [%]. Only the data of the spectral reflectance distribution of the primary colors for .about.km10, ky1 to ky10, and kk1 to kk10 are stored in the primary color data table. In the primary color data table, a halftone dot ratio for each color and spectral reflectance distribution data that is a colorimetric result of the primary color toner image formed at the halftone dot ratio are stored in the ROM 503 of the main control unit 500. .

  Next, an algorithm for estimating the output dot ratio estimated value of the primary color will be described. First, a candidate for an estimated output dot ratio (a combination of dot ratios close to the control dot ratio) is generated from the control dot ratio that is the dot ratio of the colorimetric region obtained from the image information.

  Next, candidates for the output halftone dot rate estimation value that may reduce the reliability of the estimation result due to the black redundancy problem are deleted. The candidates for the estimated output halftone dot ratio to be deleted are selected by the following method. First, the control dot ratio is subtracted from the output dot ratio estimate for each primary color candidate for each output dot ratio estimate (hereinafter, the result obtained here is referred to as an estimated dot ratio deviation (density deviation)). Call).

  For example, the control dot ratio is (C, M, Y, K) = (50, 50, 50, 50), and the output dot ratio estimate is (C, M, Y, K) = (55, 40, 50). 52), the estimated halftone dot rate deviation is (C, M, Y, K) = (5, −10, 0, 2). Next, the sign of each element of the estimated halftone dot rate deviation is confirmed. If C, M, and Y have the same sign and K has a different sign from C, M, and Y, they are deleted. For example, (C, M, Y, K) = (1, 10, 5, -2), (3, -2, 0, 5), (-4, -5, -1, 4), (4, When four estimated halftone dot ratio deviations of 3, 0, −1) are given, the first and third are to be deleted.

  Next, a spectral reflectance distribution of each primary color corresponding to the output dot ratio estimated value candidate is generated from the primary color data table. For example, when the control halftone dot ratio of a certain color is 55 [%], the spectral reflectance distribution when the halftone dot ratio is 50 [%] or 60 [%], which is a neighboring value, is the primary color of the color. Generate from the data table.

Next, the obtained spectral reflectance distribution of each primary color is converted into an L ^* a ^* b ^* value to obtain an estimated L ^* a ^* b ^* of each primary color.

Then, by converting the RGB values of the multi-color toner image measured by the control scanner 900 in ^L * ^a * ^{b *} values to obtain an observation ^L * ^a * ^{b *} values.

Finally, a color difference (CIEDE94) between the estimated L ^* a ^* b ^* value and the observed L ^* a ^* b ^* value is calculated, and a combination of output halftone dot rate estimation values that minimize the value is searched for and estimated results And

In this embodiment, CIDEDE94 is adopted as a color difference formula for calculating the color difference between the estimated L ^* a ^* b ^* value and the observed L ^* a ^* b ^* value. However, other color difference formulas such as CIEDE2000 are adopted. It is also possible to do.

  Here, generation of an output halftone dot rate estimation value candidate will be described with an example. An image of a red toner image having a control dot ratio of 50 [%] and an image having a predicted spectral reflectance distribution given by red (0.5, λ) is generally magenta (0.5, λ) and yellow. It is made by superimposing (0.5, λ). Therefore, color separation as shown in Equation 1 can be considered.

However, in practice, such a decomposition cannot always minimize the color difference between the estimated L ^* a ^* b ^* value and the observed L ^* a ^* b ^* value. There may be multiple causes, but for example, the primary color characteristics change due to changes in the image forming engine characteristics such as changes in development capability, resulting in deviations from the characteristics stored in the primary color data table. This contributes to this. Therefore, it is not determined that the control halftone ratio obtained from the image information is directly reflected as the output halftone dot ratio, and a value near the control halftone dot ratio is generated as a candidate for the output halftone dot ratio estimated value. .

  For example, when decomposing a colorimetric result of a toner image in which an image is formed with a control dot ratio of 50 [%] and a predicted spectral reflectance distribution is given by red (0.5, λ), Magenta and As combinations with Yellow, a total of nine candidates are generated as shown in Equation 2.

  Here, for simplification of explanation, nine types of candidates are described. However, more combinations may be generated as combinations of candidates for the output halftone dot rate estimation value.

  Further, when data not registered in the primary color data table is necessary, it is obtained by interpolating the registered data. For example, as described above, the primary color data table stores spectral reflectances corresponding to 10 halftone dot ratios of halftone dot ratios kc1 to kc10. For 1 ≦ n ≦ 9, when a spectral reflectance distribution cyan (kc ′, λ) corresponding to kc ′ satisfying kcn <kc ′ <kc (n + 1) is required, it is given by Equation 3.

  Next, a method for correcting control parameters (laser intensity, charging applied voltage, developing bias) will be described. First, a potential table used for control parameter correction will be described. A set of table values and control parameters is stored in the potential table, and is created such that the smaller the table value, the lower the development density, and the higher the table value, the higher the development density.

  The control dot ratio obtained from the image information is compared with the output dot ratio estimate, and if the control dot ratio is larger than the output dot ratio estimate, the table value is increased and the output dot ratio is increased. If the control dot ratio is smaller than the estimated value, the table value is decreased. Then, a control parameter corresponding to the increased / decreased table value is searched from the potential table, weighted as will be described later, and set as an image forming condition for the corresponding image forming unit 18 and latent image writing unit 21.

  The weighting at the time of setting the control parameter will be described. As the number of primary colors constituting the multi-order color increases, the number of candidates for the output halftone dot ratio estimated value increases, and the amount of calculation required to estimate the primary color from the multi-order color increases. However, since the allowable calculation time is limited, as a result, the primary color is estimated from a multi-order color having a large number of colors than the multi-order color having a small number of colors. However, rough candidate generation is performed, leading to a decrease in estimation accuracy.

  In addition, it is difficult to estimate the color information of the primary color of the low halftone dot from the multi-color including the primary color of the low halftone dot because the SN of the color information deteriorates. In addition, with respect to a primary color with a too high halftone dot ratio, signal saturation occurs, so that the estimation accuracy decreases.

  As described above, the reliability of the primary color estimation result varies depending on the number of primary colors constituting the observed multi-order color and the halftone dot ratio. Therefore, in the present embodiment, when the number of primary colors constituting the observed multi-order color is one, two are 0.9, three are 0.8, and four are 0.7. Set the value obtained by multiplying the amount of change in the control parameter by rounding to an integer. If the observed multi-order color includes a primary color of less than 15% of the halftone dot ratio, a value multiplied by 0.5 is set. Thereby, when a highly reliable estimation result is obtained, strong control is performed, and when it is not, relatively weak control is performed, thereby suppressing extreme deterioration of control performance.

  In this embodiment, when the reliability of the estimation result is low, a method of reducing the amount to change the control parameter to be set is used, but when the control can be performed relatively frequently, such as when the control cycle is short. It may be advantageous not to change the control parameters. Moreover, you may switch both adaptively according to a control period.

  In the configuration described above, when comparing the color information of the primary color estimated based on the color measurement result and the color information of the target color of the primary color, the halftone dot ratio is used as the color information to be compared. That is, the output halftone dot estimated value is the color information of the primary color estimated, and the control halftone dot ratio is the color information of the target color of the primary color.

  As described above, the color information for comparing the color information of the estimated primary color and the color information of the target color is not limited to the halftone dot rate.

Since the spectral reflectance distribution for each halftone dot ratio is stored in the primary color data table, the spectral reflectance distribution for the output halftone dot estimated value and the control halftone dot ratio can be calculated. If the spectral reflectance distribution is known, the L ^* a ^* b ^* value can be calculated by a known method. The L ^* a ^* b ^* value corresponding to the output halftone dot estimated value is used as the estimated primary color color information, and the L ^* a ^* corresponding to the control halftone dot color information is used as the primary color target color information ^. The b ^* value may be used to compare the L ^* a ^* b ^* values with each other to control the primary color that forms the output toner image closer to the target color.

When comparing L ^* a ^* b ^* values, one of the three components “L ^* ”, “a ^* ”, and “b ^* ” has the highest sensitivity to the change in toner adhesion amount for each color. You may compare only. When comparing multiple colors, even if the value of “L ^* ” is the same, the values of “a ^* ” and “b ^* ” may be different. On the other hand, when comparing the primary colors, it is dark or light, so when the value of one component is determined, the values of the other two components are also dependently determined, and the value of “L ^* ” is Even if they are the same, the values of “a ^* ” and “b ^* ” are not different.

For this reason, cyan compares the value of “L ^* ”, magenta compares the value of “a ^* ”, and yellow compares the value of “b ^* ” to form the output multi-color toner image. It can be determined whether each primary color toner is dark or light with respect to each target color.

  The copying machine 600 includes a plurality of photoreceptors 20 that are latent image carriers, creates a primary color toner image on each photoreceptor 20, performs primary transfer so as to overlap the intermediate transfer belt 10, and performs intermediate transfer. 2 is an image forming apparatus that secondary-transfers a multi-color toner image formed on the transfer belt 10 onto a recording paper P. FIG. Based on the color information of the multi-order color, which is a feature of the present invention, the color information of each primary color of the primary color toner image constituting the multi-color toner image is estimated, and the color of each estimated primary color The image forming apparatus to which the configuration for correcting the image forming condition of the primary color toner image based on the information is applicable is not limited to this.

  An image forming apparatus that forms images on a plurality of latent image carriers is not limited to a configuration including an intermediate transfer belt, and each primary color toner is directly transferred from a latent image carrier to a recording medium. The present invention is also applicable to an image forming apparatus that forms a multi-color toner image by superimposing images.

  Further, not only a configuration including a plurality of latent image carriers, but also a configuration in which an image is formed with one latent image carrier can be applied. The configuration in which an image is formed on one latent image carrier can also be applied to an image forming apparatus in which a plurality of developing devices are arranged on the surface of one latent image carrier.

  In this image forming apparatus, the primary color toner image formed on the latent image carrier is transferred onto the intermediate transfer member, and the primary color toner image previously transferred to the intermediate transfer member is newly added onto the latent image carrier. The primary color toner image thus formed is transferred in a superimposed manner, a multi-color toner image is formed on the intermediate transfer member, and transferred onto a recording sheet. Further, in the configuration in which an image is formed on one latent image carrier, a toner image formed earlier is configured in which a combination of a plurality of charging devices, exposure devices, and developing devices is arranged on one latent image carrier. It can also be applied to an image forming apparatus that charges, exposes, and develops the surface of a latent image carrier that carries

As described above, any image forming apparatus that forms a multi-color toner image on which a primary color toner image is superimposed on a recording medium can be applied.

  As described above, the copying machine 600 of the present embodiment includes the four image forming units 18 (Y, C, M, K) and the latent image writing unit 21, the intermediate transfer belt 10, the secondary transfer roller 24, and the control scanner. 900 and a main control unit 500. The latent image writing unit 21 and the four image forming units 18 (Y, C, M, and K) respectively store primary color toner images, which are toner images composed of different primary colors (yellow, cyan, magenta, and black). An image forming means is formed on the photosensitive member 20 (Y, C, M, K) which is a latent image carrier provided in the image forming unit 18 (Y, C, M, K). The intermediate transfer belt 10 and the secondary transfer roller 24 are used to record toner images formed on the photoconductors 20 (Y, C, M, and K) as recording media that are recording media via the intermediate transfer belt 10 that is an intermediate transfer body. A transfer means for transferring to P is configured. In the copying machine 600, the primary color toner images formed on the photoreceptors 20 (Y, C, M, and K) are transferred onto the recording paper P by superimposing the primary color toner images on the intermediate transfer belt 10. A multi-order toner image on which the toner images are superimposed is formed on the recording paper P. The control scanner 900 measures the multi-order color toner image formed on the recording paper P and obtains the RGB value of the multi-order color toner image as the multi-order color information of the output image. And color information acquisition means. The main controller 500 is image forming condition control means for controlling the image forming conditions of the primary color toner image by the latent image writing unit 21 and each image forming unit 18.

  In such a copier 600, the main control unit 500 serves as color information estimation means based on the RGB values acquired by the control scanner 900, and the primary colors of the primary color toner images constituting the multi-color toner image. As the color information, the estimated output halftone dot ratio of each color is estimated.

  Further, the main control unit 500 corrects the image forming condition of the primary color toner image as image forming condition control means based on the estimated output halftone dot ratio of each primary color. Therefore, by setting the control dot ratio as the color information as the target color for each primary color, the output dot ratio estimated value estimated based on the colorimetric result for each primary color and the primary color The control halftone dot ratio can be compared.

  The control halftone dot rate as color information of the target color of the primary color in the copying machine 600 is color information of the primary color toner image used when forming the primary color toner image based on the input image information. Since the dot ratios of the same primary colors are compared, it is a simple comparison of how dark or light one color is with respect to the other color.

  For this reason, if the estimated primary color is lighter than the target color, the image forming condition is corrected so that the developing density becomes dark, and if the estimated primary color is dark, the image forming condition is corrected so that the developing density becomes light. For this reason, for each primary color, it is necessary to input in advance correction information for appropriate image forming conditions for the density difference between the primary color corresponding to the output halftone dot estimated value and the target color corresponding to the control halftone dot rate. Good.

Therefore, if the configuration is such that the halftone dot ratios of the primary colors are compared as in the copying machine 600, the amount of information that must be input in advance, which is necessary for accurate correction, is determined between the conventional multi-order colors. Can be significantly reduced as compared with the configuration for comparing. By remarkably reducing the amount of information to be input in advance, it is possible to perform correction with high accuracy based on the result of colorimetry of the output multi-color toner image. The color information for comparing the estimated primary color with the target color is not limited to the halftone dot ratio, but may be other comparable color information such as L ^* a ^* b ^* values obtained from the spectral reflectance distribution. Good. The copier 600 is an image forming apparatus that corrects the image forming conditions of the image forming means based on the result of colorimetry of the output multi-color toner image, and further corrects the color of the output image by performing accurate correction. Can be achieved.

  In the copying machine 600, the color information of the multi-order color acquired by the control scanner 900 is the RGB value of the multi-order color toner image, and the main control unit 500 serving as the color information estimating means has a plurality of colors for each primary color. A ROM 503 which is a primary color spectral reflectance distribution storage unit in which information of spectral reflectance distribution of the toner image at the halftone dot ratio is input in advance.

  Based on the input image information, the main control unit 500 as color information estimation means estimates an output halftone rate that is an estimated value of the output halftone rate that is the apparent halftone rate of the primary color that is the color information of the primary color. Generate multiple value candidates. Then, candidates whose reliability may be lowered due to the black redundancy problem are excluded. Thereafter, an estimated spectral reflectance distribution that is a spectral reflectance distribution corresponding to the output halftone dot ratio estimated value candidate is generated based on the information input to the ROM 503.

Then, the product of the spectral reflectance distributions of all the primary colors forming the multi-order toner image (“cyan (kc, λ) × magenta (km, λ) × yellow (ky, λ) × black (kk, λ)) )) Is converted into an L ^* a ^* b ^* value and the RGB value of the multi-order color toner image acquired by the control scanner 900, and the output dot ratio estimated value candidates for which the color difference is as small as possible are obtained for each primary. Search for colors one by one. The value obtained by this search is used as the estimated output halftone dot ratio for each primary color.

  The main control unit 500 as color information estimation means of the copying machine 600 sets a control halftone dot rate as a halftone dot rate target value, which is a halftone dot rate that is a target value for each primary color, based on the input image information. When the estimated output halftone dot ratio is smaller than the target halftone dot ratio for each primary color, the development density is higher than the image forming conditions for forming the multi-color toner image when the estimated output halftone dot ratio is obtained. If the output halftone dot ratio estimated value is larger than the halftone dot ratio target value, the image forming condition is corrected as described above. The image forming conditions are corrected so that the development density becomes light. In this way, by comparing the control halftone dot rate and the output halftone dot rate for each primary color, it becomes possible to compare the color information between the primary colors, compared to the control that compares the color information between the multi-colors. Therefore, it is possible to correct the imaging conditions with high accuracy.

  The main control unit 500 of the copier 600 determines, as a colorimetric area determination unit, a colorimetric area in which the control scanner 900 performs colorimetry as a part of the image area of the output image. When color measurement and comparison between image information are performed for the entire image area, the amount of information to be processed becomes very large, and if a CPU with a high processing speed is not provided, the productivity of the apparatus decreases. Higher speed leads to higher costs. On the other hand, as in the copying machine 600, a part of the entire image area is set as a colorimetric area, and the colorimetric area is compared with comparison of image information with respect to the colorimetric area, thereby maintaining the productivity of the apparatus. However, it is possible to prevent an increase in cost associated with an increase in CPU speed.

  The main control unit 500 of the copying machine 600 determines a colorimetric region by searching for a region with high color flatness and suitable for colorimetry based on the input image information as a colorimetric region determining unit. An area with high color flatness has little change in hue within the area, and therefore, accurate color measurement can be performed.

  The image forming means composed of the latent image writing unit 21 and the image forming unit 18 includes at least a latent image writing unit 21 which is a latent image writing means for writing a latent image on the photosensitive member 20 which is a latent image carrier. And a developing device 61 as developing means for developing the latent image carried on the photoconductor 20 with toner.

  Further, as the latent image writing unit 21, a unit that writes an electrostatic latent image by performing optical scanning on the surface of the photoconductor 20 uniformly charged by a charging device 60 that is a charging unit is used. As the developing device 61, the toner in the developer on the developing sleeve 65 is transferred to the electrostatic latent image on the photoconductor 20 while applying a developing bias to the developing sleeve 65 that is a developer carrying member carrying the developer on the surface. Use a material that can be transferred to The main control unit 500 that is an image forming condition control means includes at least one of the charging intensity of the charging device 60, the optical writing intensity of the latent image writing unit 21, the developing bias, and the toner density of the developer as the image forming condition. A process of correcting any one is performed. With such a configuration, it is possible to realize control for correcting the image forming condition based on the result of comparing the color information of the primary colors.

  The copying machine 600 uses a developing device 61 that develops a latent image using a developer containing toner and carrier. Then, according to the difference between the result of detecting the toner density of the developer contained in the developing device 61 by the toner density sensor 71 and a predetermined density target value, the toner is supplied into the developing device 61 from the toner supply port 61a. Toner replenishing means (not shown) for replenishing is provided. The main control unit 500, which is an image forming condition control means, corrects the value of a predetermined density target value of the toner density of the developer on the basis of the result of comparing the color information of the primary colors. As a control parameter, control for correcting the toner density can be realized.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to these.

  An experiment was conducted to confirm the effect of the present invention on the black redundancy problem. In the experiment conducted, the color of a 4C gray patch with a halftone dot ratio of 55% was measured, and the result of color separation was compared with a predetermined primary color target value. The image forming conditions were set to be dark.

  In this embodiment, two types of charts are used. One is a control chart 700 and the other is an evaluation chart 701. In the control chart 700, nine 55% 4C gray patches are arranged to cancel the influence of the in-plane density deviation. A value obtained by averaging the nine color measurement results is adopted as the color measurement result. In the evaluation chart 701, patterns of a total of 16 gradations ranging from 6.25% to 100% in 6.25% increments are provided for each primary color. Further, for the same reason as in the control chart 700, each patch is arranged at nine points in the plane, and the average value is used as the colorimetric result of the patch.

  FIG. 11 shows a schematic diagram of a control chart 700 and an evaluation chart 701 and a processing flow of this embodiment. First, one control chart 700 is printed (S10). Next, the 55% 4C gray patch disposed in the control chart 700 is measured (S11). Next, the halftone dot ratio of the primary color is estimated from the obtained color measurement result and input image information (55% for each color in this example) (color separation, S12).

  Next, it is determined whether each primary color is dark or light from the color separation result and input image information, and image forming conditions are set so that the color becomes light if it is dark and dark if it is light (S13). Next, ten evaluation charts 701 are printed (S14). From the control chart printing to the evaluation chart printing described above as one set, a total of 30 sets are repeated.

  On the other hand, the result when no countermeasure is taken against the black redundancy problem is shown (comparative example). FIG. 12 shows the estimation results of the halftone dot ratio of each primary color (FIG. 12 (A) cyan, (B) magenta, (C) yellow, (D) black). It can be seen that C, M, and Y have almost the same increase / decrease tendency, and K shows the opposite tendency. That is, it is highly likely that the black redundancy problem has occurred.

  FIG. 13 shows the transition of the color difference of the 55% 4C gray patch that is the observed color. From FIG. 11, each primary color has a maximum dot variation of about 20%, but the observed color is not greatly affected. This is a characteristic characteristic of the black redundancy problem. Note that the color used as a reference in calculating the color difference was the colorimetric value of the control chart 700 printed immediately before the start of the experiment.

  FIG. 14 shows the transition of the color difference of each primary color obtained by measuring the evaluation chart 701 (FIG. 14 (A) cyan, (B) magenta, (C) yellow, (D) black). Although there are differences depending on the color, there are colors that greatly exceed the color difference 3, and considering a general sense, it is difficult to say that the results are very good. Note that the color used as a reference in calculating the color difference was the colorimetric value of the evaluation chart 701 printed immediately before the start of the experiment.

  Next, a result when measures against the black redundancy problem are taken is shown (Example). FIG. 15 shows the estimation results of the halftone dot ratio of each primary color (FIG. 15 (A) cyan, (B) magenta, (C) yellow, (D) black). The characteristic of the estimated halftone dot rate characteristic of the black redundancy problem is not recognized.

  FIG. 16 shows the transition of the color difference of the 55% 4C gray patch that is the observed color. The result is clearly better than that of FIG. The reason is that the primary color is appropriately estimated due to the absence of the black redundancy problem, and as a result, the control performance is improved.

  FIG. 17 shows the transition of the color difference of each primary color obtained by measuring the evaluation chart (FIG. 17 (A) cyan, (B) magenta, (C) yellow, (D) black). Compared with FIG. 14, the color difference can be clearly reduced.

  From the above embodiments, it was confirmed that the black redundancy problem has a great adverse effect on the control result, and that the present invention can avoid the black redundancy problem.

6 Manual feed tray 7 Paper discharge tray 10 Intermediate transfer belt 14 First support roller 15 Second support roller 16 Third support roller 17 Belt cleaning device 18 Image forming unit 20 Photoconductor 21 Latent image writing unit 24 Secondary transfer roller 25 Fixing Device 30 Document platen 30a Document discharge tray 31 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 36 Reading sensor 41 Manual paper feed path 42 Paper feed roller 44 Paper feed cassette 45 Separating roller 46 Paper feed path 47 Conveying roller 48 Conveying path 49 Registration roller pair 56 Discharging roller pair 60 Charging device 61 Developing device 61a Toner replenishment port 62 Primary transfer roller 63 Photoconductor cleaning device 64 Static eliminating device 65 Developing sleeve 66 Stirring unit 67 Developing unit 68 Conveying screw 69 Partition Wall 71 Toner concentration sensor 73 Doctor blur 75 Cleaning blade 76 Fur brush 91 Roller cleaning unit 93 Paper reversing device 100 Printer unit 200 Paper feeding device 300 Scanner 310 Optical sensor unit 311 First optical sensor 311a First sensor light source 311b First sensor regular reflection light receiving element 312 Second optical Sensor 312a Second sensor light source 312c Second sensor diffuse reflection light receiving element 312b Second sensor regular reflection light receiving element 313 Sensor memory 320 Potential sensor 400 Automatic document feeder (ADF)
401 Automatic Reading Unit 500 Main Control Unit 502 Bus Line 600 Copier 601 Manual Feed Roller 602 Manual Separation Roller 700 Control Chart 701 Evaluation Chart 900 Control RGB Scanner (Control Scanner)
P Recording paper

JP 2001-343827 A JP 2010-271595 A

Claims (4)

Image forming means for forming, on the latent image carrier, primary color toner images, which are different primary color toner images, based on input image information;
Transfer means for forming, on the recording medium, a multi-color toner image obtained by superimposing the primary color toner images formed on the latent image carrier;
Output image colorimetric means for measuring the multi-color toner image formed on the recording medium to obtain output image information;
Color information acquisition means for acquiring color information of multi-order colors based on the output image information;
Color information estimating means for estimating color information of each primary color of the color information of the primary color toner image constituting the multi-order color toner image based on the color information of the multi-order color;
A density level determination means for determining a density level of a primary color toner image constituting the multi-color toner image based on the color information of the primary color and the input image information;
Based on the number of primary colors constituting the multi-color toner image and the halftone dot ratio of each primary color, the validity is determined to be lower as the number of primary colors increases, and the primary color Color information verifying means for verifying the validity of the color information of the primary color , judging that the validity is low when including a primary color whose halftone dot ratio is less than a predetermined value ;
Image forming condition control means for correcting an image forming condition for forming the primary color toner image on a latent image carrier based on the density level of the primary color toner image and the validity, and
The image forming condition control unit reduces the correction amount of the image forming condition when the color information verifying unit verifies that the color information of the primary color is low. . The multi-color toner image is composed of cyan, magenta, yellow, and black,
The color information estimation unit generates a plurality of combinations of color information of the primary color toner images constituting the multi-color toner image, and one of the generated candidates is the color information of the primary color. When estimating as
Based on the input image information, the density deviation with respect to the density information of the primary color has the same sign for three colors of cyan, magenta, and yellow, and black is excluded from candidates having a different sign from these three colors. The image forming apparatus according to claim 1. When the color information verification means verifies that the color information of the primary color is low,
The image forming apparatus according to claim 1, wherein the image forming condition control unit does not correct the image forming condition. The color information obtaining means, the image forming apparatus according to any one of claims 1 to, characterized in that an RGB scanner to 3.