JP2007114595A - Image forming apparatus and toner consumption calculation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately calculate the amount of toner to be consumed for forming an image, in an image forming apparatus that forms images using the toner. <P>SOLUTION: Image data after color conversion are integrated by an accumulator 203, while referring to a correction table 201 and correcting the data. The integral value is multiplied by a coefficient, an offset value is added to this result, and the thus obtained value is assumed as toner consumption. A correction table 201 stores characteristics, acquired by subtracting the amount of contribution to the correlation between the amount that toner sticks to the surface of a recording medium and the density of an actual image from a correlation between input image data and the density of the actual image on the recording medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for calculating the amount of toner consumed to form an image in an image forming apparatus that forms an image using toner.

  In an electrophotographic image forming apparatus that uses toner to form an image, such as a printer, a copying machine, or a facsimile machine, it is necessary to grasp the amount of toner consumed or the remaining amount for the convenience of maintenance such as toner replenishment. Therefore, a technique for accurately obtaining the toner consumption amount (hereinafter referred to as “toner counting technique”) has been proposed. For example, in the toner consumption detection method described in Patent Document 1, the gradation values of the printed dots expressed in multiple gradations are integrated for one page, and the integrated value is multiplied by a predetermined coefficient and contributes to image formation. The amount of toner consumption is obtained by adding an offset amount corresponding to the amount of toner consumed.

JP 2002-162800 A (paragraph 0010)

  In general, this type of image forming apparatus performs data processing on input image data in order to obtain a predetermined image quality. Such data processing is performed for the purpose of controlling the density of the image finally formed on the recording medium to a desired density. On the other hand, it is known that there is a nonlinear correlation between the amount of toner constituting an image and the image density. For this reason, the relationship between the image data and the amount of toner constituting the image corresponding to the image data may also be nonlinear.

  In the case of the above prior art, since the gradation value given to each printing dot is adjusted to obtain the desired density on the recording medium, the nonlinearity as described above can be obtained. Considering it, it cannot be said that the print dot value and the toner consumption are proportional. However, the above-described prior art does not consider such non-linearity, and there remains room for improvement in terms of accuracy of toner consumption calculation.

  The present invention has been made in view of the above problems, and an object of the present invention is to accurately calculate the amount of toner consumed to form an image in an image forming apparatus that forms an image using toner.

  An image forming apparatus according to the present invention is an image forming apparatus that forms an image corresponding to input image data on a recording medium, and in order to achieve the above object, a target image density represented by the input image data; Data processing means for generating output image data by performing data processing on the input image data so as to obtain a predetermined first correlation with an actual image density of an image formed on the recording medium; , Image forming means for forming an image corresponding to the output image data on the recording medium, the input image data, and a second correlation between the input image data and the toner adhesion amount on the recording medium And a toner consumption amount calculating means for calculating the amount of toner consumed for image formation based on the characteristics.

  In the toner consumption calculation method according to the present invention, a predetermined first correlation is obtained between the target image density represented by the input image data and the actual image density of the image formed on the recording medium. As described above, in the image forming apparatus that performs data processing on the input image data to generate output image data and forms an image corresponding to the output image data on the recording medium, toner consumed for image formation In order to achieve the above object, a second correlation between the input image data and the input image data and the toner adhesion amount on the recording medium is achieved. Based on the above, the amount of toner consumed for image formation is calculated.

  In the invention configured as described above, an image is formed with an image density having a desired first correlation with the target image density indicated by the input image data, while the toner consumption amount is the same as that of the input image data. Since it is determined based on the second correlation with the toner adhesion amount, it is possible to accurately determine the toner consumption amount.

  For example, the toner consumption amount can be calculated from a value obtained by integrating the input image data while correcting based on the second correlation, or a value obtained by correcting the integrated value of the input image data based on the second correlation. .

  Here, the second correlation can be obtained by subtracting the third correlation between the toner adhesion amount and the actual image density in the image on the recording medium obtained in advance from the first correlation. The correlation between the toner adhesion amount on the recording medium and the image density is a relationship mainly determined by the physical properties of the toner. Therefore, the third correlation can be obtained experimentally in advance for the toner to be used. The first correlation is a known characteristic since it is a characteristic indicating what image density the image corresponding to the input image data is to be realized. The apparatus then combines the second correlation (between the input image data and the toner adhesion amount) with the third correlation (between the toner adhesion amount and the actual image density). Therefore, the second correlation is obtained by removing the influence of the third correlation from the first correlation.

  Note that the first correlation between the target image density and the actual image density indicated by the input image data is not necessarily unique. For example, when forming an image corresponding to the same input image data, the image is expressed with the contrast enhanced by the user's request or according to the content of the image, or expressed with emphasis on halftone reproducibility. There are cases. Due to such a difference in expression, the correspondence between the target image density and the actual image density, that is, the first correlation is naturally different. Therefore, the second correlation that is taken into account when calculating the toner consumption should also be determined according to the first correlation at that time.

  In the image forming apparatus according to the present invention, the image forming means is configured to transfer the image formed on the image carrier that temporarily carries the image onto the transfer medium, while the image carrier. A density detector for detecting the density of the patch image formed above may be further provided, and the second correlation may be acquired based on the detection result of the density detector. In this way, even when the second correlation changes due to changes in the surrounding environment of the apparatus or changes in characteristics over time, the toner consumption can be obtained with high accuracy. In particular, the data processing means performs the data processing including gamma correction processing for compensating the gamma characteristics of the image forming means based on the detection result of the density detection means on the input image data, and outputs the output image data. In the image forming apparatus configured to generate the image, the effect is remarkable.

  In the apparatus configured as described above, the second correlation may be acquired based on the correlation between the input image data and the output image data. This is because the second correlation can be estimated from the manner in which the image data changes before and after the gamma correction process.

  As a specific mode for correcting the input image data or the integrated value thereof based on the second correlation, for example, a correction table in which the second correlation is tabulated is provided, and correction is performed based on the correction table. Can do. In particular, the data processing means is configured to perform data processing including screen processing for obtaining output image data expressed in halftone by applying one selected from a plurality of processing screens prepared in advance. If so, it is desirable to provide a correction table corresponding to each of the plurality of processing screens. Even images corresponding to the same input image data are expressed differently if the processing screens to be applied are different. By using the correction table for each process, it is possible to always obtain the toner consumption accurately with any image.

  FIG. 1 is a diagram showing a configuration example of an image forming apparatus to which the present invention can be preferably applied. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus 1 forms a full color image by superposing four color toners (developers) of yellow (Y), cyan (C), magenta (M), and black (K), or black (K) toner. This is an image forming apparatus that forms a monochrome image using only the image forming apparatus. In the image forming apparatus 1, when an image signal is given to the main controller 11 from an external device such as a host computer, the engine controller 10 controls each part of the engine unit EG in accordance with a command from the main controller 11 to obtain a predetermined image. The forming operation is executed, and an image corresponding to the image signal is formed on the sheet S.

  In the engine unit EG, the photosensitive member 22 is provided to be rotatable in the arrow direction D1 in FIG. A charging unit 23, a rotary developing unit 4 and a cleaning unit 25 are arranged around the photosensitive member 22 along the rotation direction D1. The charging unit 23 is applied with a predetermined charging bias, and uniformly charges the outer peripheral surface of the photoconductor 22 to a predetermined surface potential. The cleaning unit 25 removes the toner remaining on the surface of the photosensitive member 22 after the primary transfer, and collects it in a waste toner tank provided inside. The photosensitive member 22, the charging unit 23, and the cleaning unit 25 integrally constitute the photosensitive member cartridge 2, and this photosensitive member cartridge 2 is detachably attached to the main body of the apparatus 1 as a whole.

  Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 22 charged by the charging unit 23. The exposure unit 6 exposes the light beam L onto the photosensitive member 22 in accordance with an image signal given from an external device, and forms an electrostatic latent image corresponding to the image signal.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, the developing unit 4 is configured as a support frame 40 that is rotatably provided about a rotation axis center orthogonal to the paper surface of FIG. A yellow developing device 4Y, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K are provided. The developing unit 4 is controlled by the engine controller 10. Based on the control command from the engine controller 10, the developing unit 4 is driven to rotate, and the developing units 4Y, 4C, 4M, and 4K selectively face the photoconductor 22 with a predetermined gap therebetween. When positioned at a predetermined development position, the toner is applied to the surface of the photosensitive member 22 from a metal developing roller 44 that is provided in the developing unit and carries a charged toner of a selected color and is applied with a predetermined development bias. Is granted. As a result, the electrostatic latent image on the photosensitive member 22 is visualized with the selected toner color.

  Each of the developing devices 4Y, 4C, 4M, and 4K is provided with non-volatile memories 91 to 94 for storing information related to the developing devices. One of the connectors 49Y, 49C, 49M, and 49K provided in each developing device is selected as necessary, and the connector 109 provided on the main body side is connected to each other, and the CPU 101 of the engine controller 10 and the memory Communication is performed with 91-94. In this way, information about each developing device is transmitted to the CPU 101, and information in each of the memories 91 to 94 is updated and stored. Note that the communication between the CPU 101 and each of the memories 91 to 94 is not limited to that performed by mechanical contact using a connector as described above, and may be non-contact communication means such as wireless communication.

  The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 stretched between a plurality of rollers 72 to 75, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction D2 by rotationally driving the roller 73. It has. When a color image is transferred to the sheet S, each color toner image formed on the photosensitive member 22 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 along the conveyance path F.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet S, the timing of feeding the sheet S to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. S is sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet S on which the color image is thus formed is conveyed to the discharge tray portion 89 provided on the upper surface portion of the apparatus main body via the fixing unit 9, the pre-discharge roller 82 and the discharge roller 83. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reversal position PR behind the pre-discharge roller 82. The rotation direction of the discharge roller 83 is reversed, whereby the sheet S is conveyed in the direction of the arrow D3 along the reverse conveyance path FR. Then, the sheet is again placed on the transport path F before the gate roller 81. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 71 in the secondary transfer region TR2 is first transferred. It is the opposite surface. In this way, images can be formed on both sides of the sheet S.

  Further, a density sensor 60 and a cleaner 76 are provided in the vicinity of the roller 75. The density sensor 60 optically detects the amount of toner constituting the toner image formed on the intermediate transfer belt 71 as necessary. That is, the density sensor 60 irradiates light toward the toner image, receives reflected light from the toner image, and outputs a signal corresponding to the reflected light amount. The cleaner 76 is configured to be able to come into contact with and separate from the intermediate transfer belt 71, and scrapes the residual toner on the belt 71 by contacting the intermediate transfer belt 71 as necessary.

  In addition, the apparatus 1 includes a display unit 12 controlled by the CPU 111 of the main controller 11 as shown in FIG. The display unit 12 is constituted by, for example, a liquid crystal display, and in accordance with a control command from the CPU 111, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, etc. A predetermined message for notification is displayed.

  In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112. Reference numeral 106 is a ROM for storing a calculation program executed by the CPU 101, control data for controlling the engine unit EG, and the like. Reference numeral 107 is a RAM for temporarily storing calculation results in the CPU 101 and other data. is there.

  FIG. 3 is a diagram showing signal processing blocks in this apparatus. In this image forming apparatus, when an image signal is input from an external device such as the host computer 100, the main controller 11 performs predetermined signal processing on the image signal. The main controller 11 includes functional blocks such as a color conversion unit 114, a gradation correction unit 115, a halftoning unit 116, a pulse modulation unit 117, a gradation correction table 118, and a correction table calculation unit 119.

  In addition to the CPU 101, ROM 106, and RAM 107 shown in FIG. 2, the engine controller 10 includes a laser driver 121 for driving a laser light source provided in the exposure unit 6 and a detection result of the engine unit EG based on the detection result of the density sensor 60. A gradation characteristic detecting unit 123 that detects a gradation characteristic indicating a gamma characteristic is provided.

  In the main controller 11 and the engine controller 10, these functional blocks may be configured by hardware, or may be realized by software executed by the CPUs 111 and 101.

  In the main controller 11 to which the image signal is given from the host computer 100, the color conversion unit 114 converts the RGB gradation data indicating the gradation level of the RGB component of each pixel in the image corresponding to the image signal into the corresponding CMYK. Conversion into CMYK gradation data indicating the gradation level of the component. In this color conversion unit 114, the input RGB gradation data is, for example, 8 bits per pixel per color component (that is, representing 256 gradations), and the output CMYK gradation data is similarly 8 bits per pixel per color component ( That is, it represents 256 gradations). The CMYK gradation data output from the color conversion unit 114 is input to the gradation correction unit 115.

  The gradation correction unit 115 performs gradation correction on the CMYK gradation data of each pixel input from the color conversion unit 114. That is, the gradation correction unit 115 refers to the gradation correction table 118 registered in advance in the nonvolatile memory, and in accordance with the gradation correction table 118, the input CMYK gradation data of each pixel from the color conversion unit 114. Is converted into corrected CMYK gradation data indicating the corrected gradation level. The purpose of the gradation correction is to compensate for the change in the gamma characteristic of the engine unit EG configured as described above, and to keep the overall gamma characteristic of the image forming apparatus always ideal.

  The corrected CMYK gradation data corrected in this way is input to the halftoning unit 116. The halftoning unit 116 performs halftoning processing such as an error diffusion method, a dither method, and a screen method, and inputs halftone CMYK gradation data of 8 bits per pixel to the pulse modulation unit 117. The content of the halftoning process varies depending on the type of image to be formed. That is, based on a determination criterion such as whether the image is a monochrome image, a color image, a line image, or a graphic image, the optimum processing content for the image is selected and executed.

  The CMYK gradation data after halftoning input to the pulse modulation unit 117 is a multi-value signal indicating the size and arrangement of print dots of each color of CMYK to be attached to each pixel. The unit 117 uses the halftone CMYK gradation data to create a video signal for pulse width modulating the exposure laser pulses of the CMYK color images of the engine unit EG, and the engine controller via a video interface (not shown) 10 is output. Upon receiving this video signal, the laser driver 121 controls ON / OFF of the semiconductor laser of the exposure unit 6 to form an electrostatic latent image of each color component on the photosensitive member 22. In this way, image formation corresponding to the image signal is performed.

  Further, in this type of image forming apparatus, the gamma characteristic of the apparatus changes for each apparatus and also in the same apparatus depending on the use situation. Therefore, in order to eliminate the influence of the variation in gamma characteristics on the image quality, a gradation control process is executed to update the contents of the gradation correction table 118 based on the actual measurement result of the image density at a predetermined timing. To do.

  In this gradation control process, for each toner color, a gradation patch gradation image prepared in advance for measuring the gamma characteristic is formed on the intermediate transfer belt 71 by the engine unit EG, and each gradation patch is obtained. The density sensor 60 reads the image density of the image, and the gradation characteristic detecting unit 123 based on the signal from the density sensor 60 determines the gradation characteristic (corresponding to the gradation level of each gradation patch image and the detected image density). The gamma characteristics of the engine unit EG are created and output to the correction table calculation unit 119 of the main controller 11. Then, the correction table calculation unit 119 compensates the actually measured gradation characteristic of the engine unit EG based on the gradation characteristic given from the gradation characteristic detection unit 123 to obtain an ideal gradation characteristic. The tone correction table data is calculated, and the content of the tone correction table 118 is updated to the calculation result. Thus, the gradation correction table 118 is changed and set. By doing so, this image forming apparatus can form an image with stable quality regardless of variations in gamma characteristics of the apparatus and changes over time.

  Next, the operation and configuration of the toner counter 200 that calculates the amount of toner consumed for image formation in the image forming apparatus configured as described above will be described. As shown in FIG. 3, in this image forming apparatus, the engine controller 10 is provided with a toner counter 200. The toner counter 200 calculates the amount of toner consumed for image formation for each color based on multi-tone data for each color of CMYK given from the color conversion unit 114 to the tone correction unit 115 in the main controller 10. To do.

  FIG. 4 is a diagram for explaining the principle of the toner counting technique. The CMYK gradation data after color conversion represents the target image density that the formed image should have. More specifically, the gradation value that each of the printing dots that make up the image should have is represented by CMYK gradation data for each color. On the other hand, the data sent to the engine unit EG is gradation data after processing in which necessary data processing is performed by the gradation correction unit 115 and the halftoning unit 116. Of these, the gradation correction unit 115 performs data processing that compensates for the gamma characteristics of the engine unit EG. That is, the data output from the gradation correction unit 115 has a characteristic corresponding to the inverse characteristic of the gamma characteristic with respect to the input CMYK gradation data. Further, in the halftoning unit 116, data processing is performed so that the output image has a desired gradation reproducibility.

  The density (actual image density) of the image formed by the engine unit EG and transferred and fixed on the sheet based on the image data after the data processing in this way is determined by the gamma characteristic of the engine unit EG and toner adhesion described later. Influenced by quantity vs. image density characteristics. In other words, a stable image quality can be obtained regardless of these characteristics. The halftoning unit can cancel the gamma characteristic and the toner amount vs. image density characteristic of the engine unit EG to obtain a desired image density. This is because the image data output from 116 has been processed.

  FIG. 5 is a diagram illustrating an example of the relationship between the input tone value and the image density. More specifically, the gradation value (input gradation value) of the CMYK gradation data after color conversion of the input image signal and the actual image density of the image formed based on the gradation data are calculated. It is a figure which shows a relationship. For example, for a need to faithfully represent a photographic image, it is preferable to have a relationship in which the input tone value and the actual image density are substantially linear as shown by curve (a). On the other hand, when it is desired to express the outline of a photographic image with emphasis, or when an image mainly composed of characters is formed, it is desirable to increase the contrast of the image by giving a relationship as shown by the curve (b). The halftoning unit 116 performs appropriate screen processing on the image data so that the correlation between the input tone value and the actual image density becomes a desired characteristic.

  Therefore, as long as the operating conditions of the apparatus are properly controlled, there is a certain correlation between the CMYK gradation data representing the target density of the image to be formed and the actual image density finally obtained on the sheet S. (First correlation) is maintained. On the other hand, as described below, there is a non-linear relationship (third correlation) between the actual image density and the amount of toner constituting the image.

  FIG. 6 is a diagram showing the relationship between the toner adhesion amount and the image density. Here, the characteristic indicated by the image density with respect to the toner adhesion amount is referred to as “toner amount versus image density characteristic”. As shown in FIG. 6, as the toner adhesion amount increases, the image density generally increases in proportion to this, but when the toner adhesion amount becomes larger than a certain level, the increase in the image density becomes dull and eventually becomes saturated. Almost no change. This is because when the surface of the sheet S is covered with toner, the image density in that portion is almost the color of the toner, and even if the amount of toner is increased further, the image density does not increase. Hereinafter, in the toner amount versus image density characteristic (FIG. 6), a region where the image density is substantially proportional to the toner adhesion amount is referred to as a “proportional region”, and a region where the image density does not change so much is referred to as a “saturation region”.

  In this type of image forming apparatus, the solid image density with a gradation value of 255 (100%), for example, becomes the value Dmax in FIG. 6 so that the toner adhesion amount when the gradation value is maximized falls within the saturation region. In addition, it is preferable to determine the operating conditions of the apparatus. By doing so, it is possible to prevent the variation in the toner adhesion amount from being noticed as density unevenness in a solid image or a character-based image. However, in this case, the toner adhesion amount and the image density are not necessarily proportional, and as shown in FIG. 6, the increase in the image density is small in a region where the toner adhesion amount is relatively large.

  FIG. 7 is a diagram showing the relationship between the input tone value, the toner adhesion amount, and the image density. When the CMYK gradation data after color conversion is used for image formation without being subjected to data processing, the toner adhesion amount (solid line) is substantially proportional to the input gradation value as shown in FIG. The image density (broken line) tends to saturate in the high gradation value range. In consideration of this point, when data processing is performed so that the image density is substantially proportional to the input tone value, the toner adhesion amount increases in the high tone value range as shown in FIG. 7B. growing. In other words, a non-linear correlation (second) as shown by the broken line in FIG. 7B between the CMYK gradation data immediately after the color conversion and the amount of toner consumed for forming the corresponding image. Correlation) is observed.

  What is required when obtaining the toner consumption based on the gradation data after color conversion is the correlation between the gradation data and the toner adhesion amount, that is, the second correlation shown by the broken line in FIG. That is, by obtaining the toner consumption amount based on the gradation data and the second correlation, the toner consumption amount can be obtained with high accuracy. Hereinafter, two embodiments of the toner counter for calculating the toner consumption amount based on the above-described principle will be sequentially described.

<First Embodiment>
In the first embodiment of the toner counter according to the present invention, the second correlation described above is obtained from known characteristics, and the value of the gradation value represented by the CMYK gradation data is based on the second correlation. Accumulate while correcting. The correlation (first correlation) between the input image data and the actual image density on the sheet S is naturally known because it is defined as the correlation that the apparatus should aim for. Further, the correlation (third correlation) between the toner adhesion amount and the image density is mainly determined by the physical properties of the toner, and can be determined in advance according to the toner to be used. The correlation between the image data and the actual image density (first correlation) includes the correlation between the image data and the toner adhesion amount (second correlation), the toner adhesion amount, and the actual image density. The second correlation is obtained by subtracting the contribution of the known third correlation from the known first correlation. (See FIG. 5). Here, since the first correlation is different for each type of screen applied in the halftoning unit 116, the second correlation needs to be determined for each type of screen.

  FIG. 8 is a diagram for explaining the principle of determining the second correlation. As shown by the solid line in FIG. 8A, when a screen (characterized as “Scr-a” in FIG. 8) having such a characteristic that the input gradation value and the actual image density are substantially proportional is used. In order to compensate for the density saturation in the high gradation value range, as shown by the solid line in FIG. 8B, the correlation (second correlation) of the toner adhesion amount with respect to the input gradation value has a slope in the high gradation value range. Increased form. Further, as shown by a broken line in FIG. 8A, when a screen that emphasizes contrast (indicated as “Scr-b” in FIG. 8) is used, the toner adhesion amount in the high gradation range is increased. Since the increase becomes more remarkable, the second correlation is as indicated by a broken line in FIG.

  FIG. 9 is a diagram showing the configuration of the toner counter according to the present invention. The toner counter 200 includes a data correction unit 202 that corrects gradation data sent from the color conversion unit 114 of the main controller 11 to the gradation correction unit 115 based on the correction table 201.

  FIG. 10 is a diagram showing correction characteristics of the correction table in the first embodiment. The correction table 201 stores the characteristics shown in FIG. This correction characteristic is nothing but a simplified curve showing the second correlation shown in FIG. That is, the characteristic shown in FIG. 8B in which the toner adhesion amount increases in the high gradation value range returns an output proportional to the input up to a certain input gradation value L1, while the maximum value is obtained for all inputs beyond that. Is approximated by the property of returning. That is, in the data correction unit 202, all the gradation value data up to the value L1 are output as they are, but all the gradation value data above the value L1 are corrected to the maximum value (255) and output. The That is, here, the data of the value L1 or more is the correction target. In this manner, by outputting a constant value for a certain value or more as it is until a certain value is maintained, the configuration of the table can be simplified and memory resources can be saved.

  FIG. 11 is a diagram showing the boundary of the correction target range. As shown in FIG. 11, the range to be corrected, that is, the value L1 is set individually for each toner color and each screen type. The difference in the value of L1 for each toner color reflects that the physical properties of the toner are different for each color and the type of screen applied for each color is different. Further, the value of L1 differs depending on the type of screen because the correction table 201 is a schematic representation of the second correlation, and as shown in FIG. 8B, the second correlation depends on the type of screen. Because it is different.

  Returning to FIG. 9, the description of the toner counter 200 will be continued. The value corrected by the data correction unit 202 is integrated by the accumulator 203. The accumulated value accumulated in a predetermined unit (for example, one page unit) is multiplied by a predetermined coefficient K0 corresponding to the toner adhesion amount per gradation value, and the toner consumed for image formation Is required.

  Further, an offset value Coff given from the CPU 101 is added to the product of the integrated value stored in the accumulator 203 and the coefficient K0. The offset value Coff is a value corresponding to the amount of toner consumed in a form that does not contribute to image formation corresponding to given image data. Such toner is separated from the developing roller 44 and adheres to the photosensitive member 22 to cause fogging or scatter inside the apparatus, or is consumed inside the apparatus in the control operation for maintaining the performance of the apparatus. Toner etc. This includes toner consumed for forming various patch images in this embodiment. Since the amount of toner consumed in this manner is correlated with the operation time of the apparatus, the number of images formed, the operation conditions of the apparatus, and the like, the toner in the period is based on these pieces of information managed by the engine controller 10. The consumption amount is estimated and set as an offset value Coff, and the sum of the toner consumption amount corresponding to the image data and the offset value is set as the toner consumption amount of the entire apparatus.

  The toner consumption thus obtained is managed by the CPU 101 provided in the engine controller 10 and stored in the RAM 107 or the memory 91 such as each developing device 4Y as necessary. Further, it is possible to estimate the toner remaining amount of each developing device from the obtained toner consumption value, and when it is determined that the toner remaining amount in the developing device has decreased to a predetermined value or less, the display unit 12 For example, a message prompting the developer to be replaced can be displayed, which can be useful for managing consumables of the apparatus.

  As described above, in the first embodiment of the toner counter according to the present invention, the characteristic representing the relationship (second correlation) between the image data after color conversion and the toner adhesion amount is represented by the relationship between the image data and the actual image density. Based on the relationship (first correlation) and the relationship between the toner adhesion amount and the actual image density (third correlation), a table is obtained in advance, and the image data is integrated while being corrected based on this table. The toner consumption is obtained based on the integrated value. As described above, by integrating the image data while correcting the image data based on the correction table provided for calculating the toner consumption amount, the toner consumption amount can be accurately obtained in this embodiment. Further, by changing the correction method for each toner color and for each screen, it is possible to always obtain the toner consumption with high accuracy regardless of the image to be formed and the content of data processing.

  In the above embodiment, the correction table is obtained by simplifying the relationship between the color-converted image data and the toner adhesion amount. However, the curve shown in FIG. I do not care.

Second Embodiment
In the first embodiment of the toner counter described above, the second correlation obtained in advance based on the known characteristics is tabulated, and the toner data is calculated by correcting the image data after color conversion based on the table. The accuracy is improved. On the other hand, in the second embodiment of the toner counter described below, the second correlation is obtained from the density detection result of the patch image, and the image data is corrected based on the obtained characteristics. Yes. The configuration of the toner counter of the second embodiment is the same as that of the first embodiment described above (FIG. 8), and only the contents of the correction table are different from the first embodiment. Therefore, the description of the same configuration as that of the first embodiment is omitted here, and the content of the correction table in the second embodiment will be mainly described.

  As described above, this image forming apparatus forms a gradation patch image and detects its density for the purpose of compensating the gamma characteristic of the apparatus. Using this result, a correction table can be set. A gradation patch image is an image formed while changing gradation values in multiple stages. Also, since the purpose is to obtain the “raw” gamma characteristics of the device, no special data processing has been applied to the image data corresponding to the gradation patch image. When an image is formed without data processing, the image density is obtained by combining the toner amount with which the image density is saturated in the high gradation region level area and the image density characteristic and the gamma characteristic of the apparatus as shown in FIG. Show the characteristics.

  FIG. 12 is a diagram showing an example of the density of the gradation patch image. If the density detection result of the gradation patch image has a characteristic as shown by a solid line in FIG. 12, for example, by performing a correction that gives the image data in advance a broken line characteristic corresponding to the reverse characteristic, The image density is linear with respect to the original input tone value. The characteristic indicated by the broken line corresponds to the relationship between the input gradation value and the toner adhesion amount shown in FIG. 7B, that is, the second correlation. Further, the characteristics of the broken line in FIG. 12 also indicate the relationship between the input tone value before gamma correction and the output tone value after gamma correction. Therefore, after the tone correction table 118 is updated based on the density detection result of the tone patch image, a value that is compared between the input data and the output data of the tone correction unit 115 is the second correlation to be obtained. It expresses sex.

  FIG. 13 is a diagram showing correction characteristics of the correction table in the second embodiment. Here, the second correlation indicated by the broken line in FIG. 12 is approximated to a broken line whose slope changes with the input gradation value Lk. This characteristic is tabulated and stored in the correction table 201 (FIG. 9), and the data correction unit 202 performs integration while correcting the image data based on this correction characteristic. As in the first embodiment, the toner consumption can be obtained with high accuracy.

  The correction characteristics shown in FIG. 13 correspond to the halftone-oriented screen (Scr-a) shown by the solid line in FIG. For the contrast-enhanced screen (Scr-b) shown by the broken line in FIG. 8A, the characteristic obtained by adding the characteristic of the broken line in FIG. 8A to the characteristic in FIG. It becomes.

  In this embodiment, the second correlation is approximated by a polygonal line having one inflection point. However, the correction characteristic may be approximated by a polygonal line having two or more inflection points or another function curve. . Further, the input gradation value may be divided into several areas to give a stepwise correction characteristic.

  As described above, in each of the above embodiments, the gradation correction unit 115 and the halftoning unit 116 of the processing blocks of the main controller 11 function as the “data processing unit” of the present invention. The engine unit EG functions as the “image forming unit” of the present invention, and the intermediate transfer belt 71 and the density sensor 60 correspond to the “image carrier” and the “density detection unit” of the present invention, respectively. In each of the above embodiments, the toner counter 200 functions as the “toner consumption calculation unit” of the present invention. Further, in each of the above embodiments, the image data after color conversion output from the color conversion unit 114 corresponds to “input image data” of the present invention, while the image data output from the halftoning unit 116 of the present invention. Corresponds to “output image data”.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in each of the above embodiments, the toner consumption amount is obtained based on image data after receiving RGB image data from the host computer and color-converting it to toner color (CMYK). When image data corresponding to the toner color is originally transmitted, such as when only the image data corresponding to the black color is transmitted, it is naturally possible to directly calculate the toner consumption without performing color conversion. it can.

  In each of the above-described embodiments, the toner consumption amount is calculated by integrating the image data while correcting the image data, regardless of the content of the image to be formed. The correction may be performed only when necessary. As described above, when emphasizing halftone reproducibility and forming an image so that the input tone value and the actual image density are proportional, if the gamma correction is performed properly, the input The relationship between the gradation value and the toner adhesion amount is also close to linear. In such a case, it is expected that the error does not increase so much even if the input tone values are integrated without correction.

  Further, the present invention is not limited to the configuration of the above-described embodiment. For example, an apparatus that includes only a developing device corresponding to black toner and forms a monochrome image, and an apparatus that includes a transfer medium (transfer drum, transfer sheet, etc.) other than the intermediate transfer belt. In addition, the present invention can be applied to other image forming apparatuses such as copying machines and facsimile machines.

1 is a diagram illustrating a configuration example of an image forming apparatus to which the present invention can be preferably applied. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. The figure which shows the signal processing block in this apparatus. The figure for demonstrating the principle of a toner count technique. The figure which shows the example of the relationship between an input gradation value and image density. FIG. 4 is a diagram illustrating a relationship between toner adhesion amount and image density. The figure which shows the relationship between an input gradation value, toner adhesion amount, and image density. The figure for demonstrating the principle of how to determine the 2nd correlation. FIG. 3 is a diagram illustrating a configuration of a toner counter according to the present invention. The figure which shows the correction characteristic of the table for correction | amendment in 1st Embodiment. The figure which shows the boundary of the correction | amendment object range. The figure which shows the example of the density | concentration of a gradation patch image. The figure which shows the correction characteristic of the table for correction | amendment in 2nd Embodiment.

Explanation of symbols

  60 ... density sensor (density detection means), 71 ... intermediate transfer belt (image carrier), 115 ... gradation correction section (data processing means), 116 ... half toning section (data processing means), 200 ... toner counter (toner) Consumption calculation means), EG ... engine unit (image forming means), S ... sheet (recording medium)

Claims (9)

In an image forming apparatus for forming an image corresponding to input image data on a recording medium,
Data processing is performed on the input image data so that a predetermined first correlation is obtained between the target image density represented by the input image data and the actual image density of the image formed on the recording medium. Data processing means for generating output image data by applying
Image forming means for forming an image corresponding to the output image data on the recording medium;
Toner consumption calculation for calculating the amount of toner consumed for image formation based on the input image data and a second correlation between the input image data and the toner adhesion amount on the recording medium And an image forming apparatus.   The toner consumption amount calculating means calculates the toner consumption amount based on a value integrated while correcting the input image data or a value obtained by correcting the integrated value of the input image data, and the correction is performed on the first image data. The image forming apparatus according to claim 1, which is performed based on two correlations.   2. The second correlation is obtained by subtracting a third correlation between a toner adhesion amount and an actual image density obtained in advance on an image on the recording medium from the first correlation. The image forming apparatus according to 2. The image forming means is configured to transfer an image formed on an image carrier that temporarily carries an image to the transfer medium,
Further comprising density detecting means for detecting the density of the patch image formed on the image carrier,
The image forming apparatus according to claim 1, wherein the toner consumption amount calculating unit acquires the second correlation based on a detection result of the density detecting unit.   The data processing unit performs the data processing including the gamma correction processing for compensating the gamma characteristic of the image forming unit on the input image data based on the detection result of the density detection unit to generate the output image data. The image forming apparatus according to claim 4. The image forming apparatus according to claim 5, wherein the toner consumption amount calculation unit acquires the second correlation based on a correlation between the input image data and the output image data.   The image forming apparatus according to claim 2, wherein the toner consumption amount calculation unit includes a correction table in which the second correlation is tabulated, and performs the correction based on the correction table. The data processing means performs the data processing including screen processing for obtaining the output image data expressed in halftone by applying one selected from a plurality of processing screens prepared in advance.
The image forming apparatus according to claim 7, wherein the toner consumption amount calculating unit includes a plurality of the correction tables corresponding to the plurality of processing screens. Data processing is performed on the input image data so that a predetermined first correlation is obtained between the target image density represented by the input image data and the actual image density of the image formed on the recording medium. In a toner consumption calculation method for calculating the amount of toner consumed for image formation in an image forming apparatus that generates output image data and forms an image corresponding to the output image data on the recording medium.
Calculating the amount of toner consumed for image formation based on the input image data and a second correlation between the input image data and the toner adhesion amount on the recording medium. Toner consumption calculation method.

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