JP2012018199A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy in correcting gradation while suppressing drastic variation of density.SOLUTION: An image forming apparatus performs: forming a gradation-pattern image including a plurality of different density patches for every cycle of gradation pattern image-forming; detecting density of each patch included in the formed gradation pattern images. Where "A0" is defined as an initial value of a ratio A of the present density value, the apparatus increases the ratio A of the present density value by a predetermined value B for every cycle of a correction curve update (where [cycle of correction curve update]<[cycle of gradation pattern image-forming]), calculates a weighted average of the present density value and the previous density value with a ratio of A to (1-A), and updates a correction curve used in correcting a gradation characteristic of an image forming section of the apparatus based on the result of weighted average. After a ratio A of the present density value reaches "1", the apparatus lets the ratio A stay at "1" until the next cycle of forming a gradation pattern image and detecting density of each patch.

Description

  The present invention relates to an image forming apparatus.

  In general, gradation stability is very important for a printer. Conventionally, in an electrophotographic image forming apparatus, a gradation pattern image including a plurality of density patches is formed on an image carrier or paper at predetermined intervals, and the density of each patch is measured by a density sensor. The gradation stability of the printer is ensured by correcting the printer gradation based on the measurement result.

  At this time, the density may change abruptly before and after the correction due to the state of the image forming apparatus or environmental changes. In order to prevent this, there has been proposed an image forming apparatus in which a past density value and a current density value are weighted and averaged at a predetermined ratio, and gradation correction is performed based on the weighted average density value (Patent Document 1). , See Patent Document 2).

JP 2004-245943 A JP 2010-50867 A

  However, even when gradation correction is performed using a plurality of density values as in the prior art described above, the correction curve used for correcting the gradation characteristics is not recalculated. Only the timing according to the formation of the tone pattern image and the density measurement). That is, the same correction curve has been used until the next correction timing. For this reason, when the ratio of the current density value when weighted average of density values for a plurality of times is increased, there is a possibility that an abrupt density change may occur. On the other hand, when the ratio of the density values in the past is increased, the gradation correction is based on considerably old data near the next correction timing, and the correction accuracy is poor.

  The present invention has been made in view of the above-described problems in the prior art, and an object thereof is to improve the accuracy of gradation correction while suppressing a rapid density change.

  In order to solve the above problems, the invention according to claim 1 is characterized in that the image forming unit, the density sensor, and the image forming unit each time image formation of a predetermined number of faces is performed in the image forming unit. And a control unit that controls the density sensor to form a gradation pattern image including a plurality of patches having different densities, and causes the density sensor to detect the density of each patch included in the formed gradation pattern image, The control unit detects by the density sensor during the period from the formation of the gradation pattern image and the density detection of each patch to the next formation of the gradation pattern image and the density detection of each patch. The weighting ratio between the current density value and the previous density value is changed stepwise to take a weighted average of the two density values, and based on the weighted average result, the gradation characteristics of the image forming unit When correcting The process of updating the correction curve used multiple times, an image forming apparatus.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control unit increases the weighting ratio of the current density value stepwise when the correction curve is updated.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the control unit changes the weighting ratio based on the difference between the current density value and the previous density value. decide.

  A fourth aspect of the present invention is the image forming apparatus according to any one of the first to third aspects, further comprising an operation unit for designating the predetermined number of surfaces, wherein the control unit A method for changing the weighting ratio is determined based on the designated number of faces.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the control unit determines a method for changing the weighting ratio for each color.

  According to the first aspect of the invention, it is possible to improve the accuracy of gradation correction while suppressing a rapid density change.

  According to the second aspect of the present invention, since the weighting ratio of the current density value is increased stepwise, the accuracy of gradation correction can be improved while suppressing a rapid density change.

  According to the third aspect of the present invention, the weighting ratio can be changed according to the difference between the current density value and the previous density value.

  According to the invention described in claim 4, the weighting ratio can be changed according to the designated number of faces.

  According to invention of Claim 5, a weighting ratio can be changed according to a color.

1 is a block diagram illustrating a functional configuration of an image forming apparatus according to a first embodiment. It is a figure which shows the internal structure of an image formation part. It is a figure which shows the example of a gradation pattern image. It is a figure which shows the example of a correction curve. It is a figure for demonstrating how to change the ratio of the density value this time. It is a figure which shows the example of a change of the ratio of the density value of this time from which a change rate differs. 3 is a flowchart illustrating processing executed in the image forming apparatus according to the first embodiment. It is a figure which shows the example of how to change the ratio of this density value according to the difference of this density value and the last density value in 2nd Embodiment. It is a figure which shows the example of how to change the ratio of the density value this time according to the gradation pattern image formation interval in 3rd Embodiment. It is a figure which shows the example of how to change the ratio of the density value of this time for every color in 4th Embodiment.

[First Embodiment]
First, a first embodiment of the present invention will be described.
FIG. 1 shows a functional configuration of an image forming apparatus 100 according to the first embodiment. The image forming apparatus 100 is a multifunction machine having a copy function, an image reading function, and a printer function, and is an electrophotographic color image forming apparatus.

  As shown in FIG. 1, the image forming apparatus 100 includes a control unit 10, an operation display unit 20, a scanner unit 30, an image processing unit 40, an image forming unit 50, a density sensor 70, a storage unit 80, a communication unit 90, and the like. Each part is connected by a bus.

  The control unit 10 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. In response to an operation signal input from the operation display unit 20 or an instruction signal received by the communication unit 90, the CPU reads the system program and various processing programs stored in the ROM, expands them in the RAM, and expands them. The operation of each part of the image forming apparatus 100 is centrally controlled according to the program.

  The operation display unit 20 is configured by an LCD (Liquid Crystal Display), and displays various operation buttons, device status display, operation status of each function, and the like on the display screen according to instructions of a display signal input from the control unit 10. Do. The LCD display screen is covered with a pressure-sensitive (resistive film pressure) touch panel that consists of transparent electrodes arranged in a grid, and detects the position coordinates pressed by a finger or touch pen as a voltage value. The detected position signal is output to the control unit 10 as an operation signal. The operation display unit 20 includes various operation buttons such as a numeric button and a start button, and outputs an operation signal generated by the button operation to the control unit 10. For example, the operation display unit 20 is used when a gradation pattern image formation interval to be described later is designated.

  The scanner unit 30 includes a scanner below a contact glass on which a document is placed, and reads an image of the document. The scanner includes a light source, a CCD (Charge Coupled Device) image sensor, an A / D converter, and the like, and forms an image of reflected light of light scanned from the light source onto the document and photoelectrically converts the image of the document to RGB. The signal is read as a signal, and the read image is A / D converted and output to the image processing unit 40.

  The image processing unit 40 performs tone correction processing and halftone processing for correcting the tone characteristics of the image forming unit 50 with respect to image data obtained by reading by the scanner unit 30 and image data received by the communication unit 90. The image processing such as the above is performed and output to the image forming unit 50. The image processing unit 40 is realized by software processing in cooperation with the CPU of the control unit 10 and a program stored in the ROM.

The image forming unit 50 prints an image on a sheet based on yellow (Y), magenta (M), cyan (C), and black (K) image data output from the image processing unit 40 by electrophotography. Form and output.
FIG. 2 shows an internal configuration of the image forming unit 50. As shown in FIG. 2, the image forming unit 50 includes Y, M, C, and K photoconductive drums 51Y, 51M, 51C, and 51K, developing units 52Y, 52M, 52C, and 52K, and charging units 53Y and 53M. , 53C, 53K, cleaners 54Y, 54M, 54C, 54K, primary transfer rollers 55Y, 55M, 55C, 55K, intermediate transfer belt 56, roller 57, registration roller 58, and secondary transfer roller 59 The fixing unit 60 and a paper discharge roller 61 are provided.

Here, image formation in the image forming unit 50 will be described.
The photosensitive drum 51Y rotates, the surface thereof is charged by the charger 53Y, and a latent image of an image of Y data input from the image processing unit 40 is formed on the charged portion by exposure with a laser light source (not shown). Then, a yellow toner image is formed on the latent image portion by the developing device 52Y. The toner image is transferred to the intermediate transfer belt 56 by the pressure contact of the primary transfer roller 55Y. The toner image is a yellow image corresponding to the image data to be output. The toner that has not been transferred is removed by the cleaner 54Y.
Magenta, cyan, and black toner images are formed and transferred in the same manner.

  The intermediate transfer belt 56 is rotated by the rotation of the roller 57 and the primary transfer rollers 55Y, 55M, 55C, and 55K, and the YMCK toner images are sequentially superimposed and transferred on the intermediate transfer belt 56. In addition, the sheet is conveyed from a paper feed tray (not shown) to the secondary transfer roller 59 by the rotation of the registration roller 58.

  As the registration roller 58 and the secondary transfer roller 59 rotate, the sheet passes through the pressure contact portion of the secondary transfer roller 59, whereby the YMCK toner image on the intermediate transfer belt 56 is transferred to the sheet. The sheet on which the YMCK toner image is transferred passes through the fixing unit 60. By the pressurization and heating of the fixing unit 60, the YMCK toner image is fixed on the paper to form a color image. The paper on which the image has been formed is conveyed by a paper discharge roller 61 to a paper discharge tray (not shown).

  In addition, when performing duplex printing, a secondary transfer roller is formed by a registration roller 58 so that a sheet on which an image is formed on one side is reversed by a duplex conveyance unit (not shown) and an image is formed again on a surface on which no image is formed. It is conveyed to 59.

  The density sensor 70 outputs a voltage value corresponding to the density of each patch of the gradation pattern image on the fixed paper on which the image is formed by the image forming unit 50 to the control unit 10. The density sensor 70 includes an LED (Light Emitting Diode), a lens, a light receiving element, and the like. The density sensor 70 irradiates each patch on the paper on which the gradation pattern image is formed with light from the LED, and the reflected light is received by the light receiving element through the lens. Then, the light receiving element outputs a voltage value corresponding to the reflected light to the control unit 10.

  The storage unit 80 is configured by a hard disk, a flash memory, or the like, and stores various data. The storage unit 80 includes a gradation pattern image storage unit 81, a density detection result storage unit 82, a correction curve storage unit 83, a counter value storage unit 84, and the like.

  The gradation pattern image storage unit 81 stores YMCK data for forming a gradation pattern image including a plurality of patches having different densities.

  In the present embodiment, as shown in FIG. 3, four gradation pattern images G1, G2, G3, and G4 are used for one correction. Each gradation pattern image G1, G2, G3, G4 is different, and each gradation pattern image G1, G2, G3, G4 has a minimum density (gradation value 0) to a maximum density (gradation value 255). Includes patches of multiple densities in the range. For example, the gradation values of the patches of each color included in the gradation pattern image G1 are 0, 32, 65, 98, 131, 164, 197, and 230, respectively, and the patches of the respective colors included in the gradation pattern image G2 are. The gradation values are 8, 41, 74, 106, 139, 172, 205, and 238, respectively. The gradation values of the patches of each color included in the gradation pattern image G3 are 16, 49, 82, 115, and respectively. 148, 180, 213, and 246, and the gradation values of the patches of each color included in the gradation pattern image G4 are 24, 57, 90, 123, 156, 189, 222, and 255, respectively.

  The density detection result storage unit 82 stores the current density value and the previous density value of each patch detected by the density sensor 70. These values are updated each time the gradation pattern images G1, G2, G3, and G4 are formed and the density of each patch is detected.

  In the correction curve storage unit 83, correction curve data used for correcting the gradation characteristics of the image forming unit 50 is stored for each of Y, M, C, and K colors. The correction curve is for performing gradation conversion such that the output density becomes linear with respect to the input value, and the input value and the output value are associated with each other as shown in FIG. The correction curve may be stored in the form of an arithmetic expression for the input value, or may be stored in the form of an LUT (Look Up Table) in which the input value and the output value are associated with each other.

  The counter value storage unit 84 stores the value of a counter that counts the number of image forming surfaces in the image forming unit 50. In the case of single-sided printing, the counter value increases by “1” for one sheet output, and in the case of double-sided printing, the counter value increases by “2” for one sheet of output.

  The communication unit 90 includes a modem, a LAN (Local Area Network) adapter, a router, a TA (Terminal Adapter), and the like, and performs communication control with each device connected to the network N.

  The control unit 10 stores the level stored in the gradation pattern image storage unit 81 every time image formation of a predetermined number of faces (hereinafter referred to as gradation pattern image formation interval) is performed in the image forming unit 50. The tone pattern image is read, the image forming unit 50 is controlled to form a gradation pattern image including a plurality of patches having different densities, and the density of each patch included in the formed gradation pattern image is stored in the density sensor 70. Let it be detected.

  The control unit 10 is detected by the density sensor 70 after the gradation pattern image is formed and the density of each patch is detected until the next gradation pattern image is formed and the density of each patch is detected. The weighting ratio between the current density value and the previous density value is changed stepwise to obtain a weighted average of both density values, and the gradation characteristics of the image forming unit 50 are corrected based on the weighted average result. The process of updating the correction curve used when performing the process is performed a plurality of times. Specifically, the control unit 10 includes an image forming unit from the time when the gradation pattern image is formed and the density of each patch is detected until the next gradation pattern image is formed and the density of each patch is detected. Each time an image with a predetermined number of faces (hereinafter referred to as a correction curve update interval) is formed at 50, the correction curve is changed while gradually changing the weighting ratio between the current density value and the previous density value. Recalculate. Note that the value of the correction curve update interval is smaller than the value of the gradation pattern image formation interval.

  When the control unit 10 updates the correction curve between the time when the gradation pattern image is formed and the density of each patch is detected until the time when the next gradation pattern image is formed and the density of each patch is detected. In addition, the weighting ratio of the current density value is increased step by step.

  FIG. 5 shows an example of how to change the ratio A (0 ≦ A ≦ 1) of the current density value when taking the weighted average of the current density value and the previous density value. The horizontal axis is the number of image forming surfaces in the image forming unit 50, and the vertical axis is the value of the ratio A of the current density value. The initial value of the current density value ratio A is A0, and the current density value ratio A is increased by a predetermined value B determined in advance every correction curve update interval. After the current density value ratio A reaches 1, the current density value ratio A remains 1 until the next gradation pattern image is formed and the density of each patch is detected. Then, when forming the next gradation pattern image and detecting the density of each patch, the density value ratio A of this time is set as the initial value A0 again.

  As shown in FIG. 6, when the rate of change of the density value ratio A this time (predetermined value B with respect to the correction curve update interval) is large, the density of the printed material while the ratio A of the current density value is being changed. Change will also increase. On the other hand, when the change rate of the current density value ratio A is small, the density change of the printed matter accompanying the change of the current density value ratio A becomes gradual. The initial value and the change rate of the density value ratio A this time may be fixed values or set by the user. Further, at least one of the correction curve update interval and the predetermined value B may be set by the user. In FIG. 6, the current density value ratio A is described so as to be continuously (linearly) changed with respect to the number of image forming planes. It is changed stepwise for each of a plurality of image forming surfaces (correction curve update interval).

Next, the operation will be described.
FIG. 7 is a flowchart illustrating processing executed in the image forming apparatus 100 according to the first embodiment. This process is realized by software processing in cooperation with the CPU of the control unit 10 and the program stored in the ROM.

  First, the control unit 10 acquires the value of the counter stored in the counter value storage unit 84, and determines whether it is the formation timing of the gradation pattern image (step S1). Specifically, the control unit 10 forms the gradation pattern image from the previous gradation pattern image formation (and density detection of each patch) based on the number of image forming surfaces in the image forming unit 50 indicated by the counter value. It is determined whether or not image formation for the interval has been performed.

  When it is the formation timing of the gradation pattern image (step S1; YES), the control unit 10 reads the gradation pattern image from the gradation pattern image storage unit 81, and the image forming unit 50 is controlled to read the gradation pattern image. The output gradation pattern image is formed on the paper (step S2). Next, the control unit 10 detects the density of each patch included in the gradation pattern image formed on the sheet based on the voltage value output from the density sensor 70, and stores the density detection result for each patch. The current density value and the previous density value of the part 82 are updated (step S3). Next, the control unit 10 initializes the current density value ratio A (step S4).

  Next, the control unit 10 takes a weighted average of the current density value and the previous density value at a ratio of A: (1-A) for each patch (step S5). Next, the control unit 10 calculates a correction curve for each color of Y, M, C, and K based on the weighted average result for each patch (step S6). The calculated correction curve is stored in the correction curve storage unit 83 by the control unit 10. Next, the control unit 10 adds a predetermined value B to the current density value ratio A (step S7). Since the upper limit of the density value ratio A this time is 1, if the predetermined value B is added to 1 or more, it is set to 1.

  Next, the image processing unit 40 performs image processing such as gradation correction processing based on the correction curve stored in the correction curve storage unit 83 on the image data, and forms an image according to the control of the control unit 10. Printing is executed by the unit 50 (step S8). Then, the control unit 10 increments the counter stored in the counter value storage unit 84 (step S9). In the case of single-sided printing, the counter value increases by “1”, and in the case of double-sided printing, the counter value increases by “2”. After step S9, the process returns to step S1 and the process is repeated.

  In step S1, if it is not the formation timing of the gradation pattern image (step S1; NO), the control unit 10 performs the correction curve update timing based on the counter value stored in the counter value storage unit 84. It is determined whether or not there is (step S10). Specifically, based on the number of image forming surfaces in the image forming unit 50 indicated by the counter value, the control unit 10 determines whether or not image formation for the correction curve update interval has been performed since the previous correction curve calculation. To be judged.

  When it is time to update the correction curve (step S10; YES), the control unit 10 determines whether or not the current density value ratio A is less than 1 (step S11). If the current density value ratio A is less than 1 (step S11; YES), the process proceeds to step S5.

  If it is not the correction curve update timing in step S10 (step S10; NO), or if the current density value ratio A is not less than 1 in step S11 (step S11; NO), the process proceeds to step S8. .

  In this way, the correction curve is recalculated for each predetermined number of image forming surfaces (correction curve update interval), and the current density value ratio A is 1 (the current density value is 100%). After that, the correction curve is fixed and output until the next gradation pattern image is formed and the density of each patch is detected.

  As described above, according to the image forming apparatus 100 in the first embodiment, after the gradation pattern image is formed and the density of each patch is detected, the next gradation pattern image is formed and each patch is detected. Until the density detection is performed, the weighting ratio between the current density value and the previous density value is changed in stages, so that the accuracy of gradation correction can be improved while suppressing a sudden density change. .

  Further, since the weighting ratio of the current density value is increased step by step, the density value used for the correction curve (the weighted average value of the current density value and the previous density value) gradually becomes the ideal in the current image forming apparatus 100. As the value approaches the value (current density value), the accuracy of gradation correction can be improved while suppressing a rapid density change.

[Second Embodiment]
Next, a second embodiment to which the present invention is applied will be described.
Since the image forming apparatus according to the second embodiment has the same configuration as that of the image forming apparatus 100 according to the first embodiment, FIG. 1 and FIG. 2 are used, and description of the configuration is omitted. . Hereinafter, a characteristic configuration of the second embodiment will be described.

  When the difference between the current density value and the previous density value is large, the density change becomes large if the ratio of the current density value and the previous density value is high when the weighted average is taken. Therefore, the control unit 10 determines a method of changing the weighting ratio when taking the weighted average of both density values based on the difference between the current density value and the previous density value. As the difference between the current density value and the previous density value, for example, an average value of absolute values of differences between both density values in each patch is used.

  FIG. 8 shows an example of how to change the ratio A of the current density value according to the difference between the current density value and the previous density value. As shown in FIG. 8, the larger the difference between the current density value and the previous density value, the smaller the initial value and change rate of the ratio A of the current density value, and the difference between the current density value and the previous density value becomes smaller. The smaller the value is, the larger the initial value and change rate of the current density value ratio A are. That is, the larger the difference between the current density value and the previous density value, the smaller the initial value A0 of the current density value ratio A shown in FIG. 5, and the predetermined value added at each correction curve update interval. Decrease the value of B. In FIG. 8, the current density value ratio A is described so as to be continuously changed with respect to the number of image forming surfaces, but actually, as in FIG. 5, one or a plurality of image forming surfaces. Change in steps for each number.

  The processing in the image forming apparatus according to the second embodiment is the same as the processing (see FIG. 7) shown in the first embodiment, and thus description thereof is omitted.

  As described above, according to the image forming apparatus of the second embodiment, in addition to the same effects as those of the first embodiment, the weighting ratio is set according to the difference between the current density value and the previous density value. Can be changed. For example, as the difference between the current density value and the previous density value is larger, the initial value of the ratio A of the current density value is decreased, so that the pattern immediately after the gradation pattern image is formed and the density of each patch is detected. Concentration change can be suppressed. In addition, by decreasing the change rate of the ratio A of the current density value as the difference between the current density value and the previous density value is larger, the density change when changing the ratio A of the current density value is suppressed. be able to.

[Third Embodiment]
Next, a third embodiment to which the present invention is applied will be described.
Since the image forming apparatus according to the third embodiment has the same configuration as that of the image forming apparatus 100 according to the first embodiment, FIG. 1 and FIG. 2 are used, and description of the configuration is omitted. . Hereinafter, a characteristic configuration of the third embodiment will be described.

  Based on the gradation pattern image formation interval designated from the operation display unit 20, the control unit 10 determines a method for changing the weighting ratio when taking a weighted average for the current density value and the previous density value.

  FIGS. 9A and 9B show an example of how to change the ratio A of the current density value according to the gradation pattern image formation interval. As shown in FIG. 9A, when the gradation pattern image formation interval is equal to or smaller than a predetermined value (for example, 500; hereinafter referred to as the reference plane number), the formation of the next gradation pattern image and The rate of change is determined so that the current density value ratio A is 1 when the density of each patch is detected. As shown in FIG. 9B, when the gradation pattern image formation interval is larger than the reference plane number, the density value ratio A of this time becomes 1 when image formation is performed for the reference plane number. Determine the rate of change. In FIGS. 9A and 9B, the current density value ratio A is described so as to be continuously changed with respect to the number of image forming surfaces, but in reality, as in FIG. The number of image forming surfaces is changed stepwise for each one or a plurality of image forming surfaces.

  The initial value of the density value ratio A may be changed based on the gradation pattern image formation interval.

  The processing in the image forming apparatus of the third embodiment is the same as the processing shown in the first embodiment (see FIG. 7), and thus the description thereof is omitted.

  As described above, according to the image forming apparatus of the third embodiment, in addition to the same effects as those of the first embodiment, the weighting ratio can be changed according to the gradation pattern image forming interval. it can. For example, when the gradation pattern image formation interval is equal to or less than the reference number of planes, the current density value ratio A is gradually brought close to 1 over the gradation pattern image formation interval, thereby suppressing a rapid density change. However, the accuracy of gradation correction can be improved. Further, when the gradation pattern image formation interval is larger than the reference plane number, the density value ratio A is set to 1 when image formation is performed for the reference plane number. After the ratio A reaches 1, gradation correction based on the latest density value can be performed.

[Fourth Embodiment]
Next, a fourth embodiment to which the present invention is applied will be described.
Since the image forming apparatus in the fourth embodiment has the same configuration as that of the image forming apparatus 100 shown in the first embodiment, FIG. 1 and FIG. 2 are used, and description of the configuration is omitted. . Hereinafter, a characteristic configuration of the fourth embodiment will be described.

  The control unit 10 determines, for each color, a method of changing the weighting ratio when taking a weighted average for the current density value and the previous density value.

  FIG. 10 shows an example of how to change the ratio of the current density value for each color. Among the colors of YMCK, black (K) has little effect on the color tone such as gray balance even if the density change is relatively large. Therefore, as shown in FIG. The rate is set to be larger than the rate of change of the ratio A of the current density value of YMC. Also, the initial value of the density value ratio A this time may be changed for each color. In FIG. 10, the density value ratio A of this time is described so as to be continuously changed with respect to the number of image forming surfaces, but actually, as in FIG. 5, one or a plurality of image forming surfaces. Change in steps for each number.

  In addition, when outputting a printed matter that emphasizes gradation such as a photographic image with a single black color, the change rate of the ratio A of the current density value may be set smaller for black.

  Since the processing in the image forming apparatus of the fourth embodiment is the same as the processing (see FIG. 7) shown in the first embodiment, description thereof is omitted.

  As described above, according to the image forming apparatus of the fourth embodiment, in addition to the same effects as those of the first embodiment, the weighting ratio can be changed according to the color.

  The description in each of the above embodiments is an example of the image forming apparatus according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of each part of the image forming apparatus can be changed as appropriate without departing from the spirit of the present invention.

  For example, in each of the above embodiments, the example in which the density sensor 70 is provided in the subsequent stage of the fixing unit 60 has been described. However, the density sensor is provided in a position facing the gradation pattern image formed on the intermediate transfer belt 56. It is good also as being done. In this case, the density sensor outputs a voltage value corresponding to the density of each patch of the gradation pattern image formed on the intermediate transfer belt 56 to the control unit 10.

  Also, a weighting ratio changing method based on the difference between the current density value and the previous density value (see the second embodiment), and a weighting ratio changing method based on the gradation pattern image formation interval (third embodiment). The weighting ratio changing method may be determined by combining two or more methods among the weighting ratio changing methods (see the fourth embodiment) different for each color.

  In the above description, an example in which a ROM is used as a computer-readable medium storing a program for executing each process is disclosed, but the present invention is not limited to this example. As other computer-readable media, a non-volatile memory such as a flash memory and a portable recording medium such as a CD-ROM can be applied. A carrier wave may be applied as a medium for providing program data via a communication line.

DESCRIPTION OF SYMBOLS 10 Control part 20 Operation display part 30 Scanner part 40 Image processing part 50 Image formation part 51Y, 51M, 51C, 51K Photosensitive drum 52Y, 52M, 52C, 52K Developing device 53Y, 53M, 53C, 53K Charger 54Y, 54M, 54C, 54K Cleaners 55Y, 55M, 55C, 55K Primary transfer roller 56 Intermediate transfer belt 57 Roller 58 Registration roller 59 Secondary transfer roller 60 Fixing unit 61 Paper discharge roller 70 Density sensor 80 Storage unit 81 Gradation pattern image storage unit 82 Density detection result storage unit 83 Correction curve storage unit 84 Counter value storage unit 90 Communication unit 100 Image forming apparatus G1, G2, G3, G4 Tone pattern image N network

Claims (5)

An image forming unit;
A concentration sensor;
Each time image formation of a predetermined number of faces is performed in the image forming unit, the image forming unit is controlled to form a gradation pattern image including a plurality of patches having different densities, and the formed gradation A control unit that causes the density sensor to detect the density of each patch included in the pattern image;
With
The controller controls the density sensor between the time when the gradation pattern image is formed and the density of each patch is detected until the time when the next gradation pattern image is formed and the density of each patch is detected. The weighting ratio between the detected current density value and the previous density value is changed stepwise to take a weighted average of the two density values, and based on the weighted average result, the gradation of the image forming unit The process of updating the correction curve used when correcting the characteristics is performed multiple times.
Image forming apparatus. The control unit, when updating the correction curve, gradually increases the weighting ratio of the current density value,
The image forming apparatus according to claim 1. The control unit determines a method of changing the weighting ratio based on the difference between the current density value and the previous density value.
The image forming apparatus according to claim 1. An operation unit for designating the predetermined number of faces;
The control unit determines a method of changing the weighting ratio based on the designated number of faces.
The image forming apparatus according to claim 1. The control unit determines a method for changing the weighting ratio for each color.
The image forming apparatus according to claim 1.

Images