JP2006030794A - Image forming apparatus, image forming method, computer program and computer readable storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining an output image having excellent color balance while restraining the downtime of a printer and the increase of print cost to the utmost. <P>SOLUTION: The image forming apparatus has an image density control means which controls an image forming condition in accordance with the result of detection by extracting a prescribed image pattern included in a print image signal, and detecting the light reflection characteristic of a toner image on an image carrier or transfer material formed according to the prescribed image pattern by an optical sensor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, an image forming method, a computer program, and a computer-readable storage medium, and in particular, an image forming apparatus and an image forming method capable of obtaining an output image with good color balance, and a computer program and a computer. The present invention relates to a readable storage medium.

  In general, an image forming apparatus using an electrophotographic image forming process is likely to vary in image density depending on various conditions such as a use environment and the number of prints. In particular, in a color image forming apparatus that performs color printing by superimposing a plurality of color toner images, if the image density of each color fluctuates, the color balance (so-called color) fluctuates. It becomes an important issue.

  Therefore, many of recent color image forming apparatuses form a test toner image (toner patch) on an image carrier such as a photoreceptor or an intermediate transfer member on an experimental basis, and measure the toner amount of the toner patch with an optical sensor. The image density is controlled by feeding back the exposure amount, the developing bias, and the like based on the detection result to obtain a stable image. Such a color image forming apparatus is disclosed, for example, in JP-A-11-65237.

Another method is to create a test toner image (toner patch) on the transfer material (paper) and detect the toner density of the toner patch after fixing on the transfer material with an optical sensor. From the results, a control method has been proposed in which image density control is performed by feeding back the exposure amount, development bias, and the like. This method has been attracting attention in recent years because it provides superior density stability compared to a density control method that uses an unfixed toner patch on an image carrier. Such an image density control method is disclosed in, for example, Japanese Patent Laid-Open No. 2003-287934.
JP-A-11-65237 JP 2003-287934 A

  However, the conventional image forming apparatus described above has the following problems.

  In order to make the image density more stable, it is necessary to perform image density control at a high frequency. However, since control time is required for image density control, the more control is performed, the longer the print waiting time becomes, which leads to user discomfort. Furthermore, since dedicated toner image patches are printed at the time of image density control, the amount of toner consumption increases accordingly. That is, the printing cost is increased.

  Further, in an image forming apparatus that performs image density control using a detection toner image (toner patch) formed on a transfer material (paper), a control transfer material is also required. There is also an increase in printing costs.

  In addition, density fluctuations that occur in an electrophotographic image forming apparatus are influenced by various conditions such as the state of use environment and print image pattern. very difficult.

  Therefore, depending on the use conditions, there may be a case where the density fluctuation does not occur so much and a case where the density fluctuation significantly occurs. On the other hand, since it is necessary for the printer to always print at a stable density, it is necessary to perform image density control assuming a case in which the density fluctuation is the largest (abrupt). In this case, unnecessary control is performed under conditions where the concentration does not vary much. That is, an unnecessary print waiting time and an increase in printing cost are generated.

  The present invention has been made under such circumstances, and provides an image forming apparatus capable of obtaining an output image having a good color balance while suppressing an increase in printer downtime and printing cost as much as possible. It is.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a pattern extracting unit that extracts a specific image pattern included in a print image signal, and a toner on an image carrier formed according to the specific image pattern. The image processing apparatus includes: a detection unit that detects a light reflection characteristic of an image; and an image density control unit that determines an image forming condition according to a detection result of the detection unit and controls an image density.

  The image forming method according to the present invention also includes a pattern extracting step for extracting a specific image pattern included in a print image signal, and detecting a light reflection characteristic of a toner image on an image carrier formed according to the specific image pattern. And an image density control step of determining an image forming condition according to a detection result of the detection step and controlling an image density.

  As described above, according to the present invention, an output image with a good color balance can be obtained while suppressing an increase in printer downtime and printing cost as much as possible.

  Hereinafter, each embodiment will be described with reference to the drawings.

<First Embodiment>
In the present embodiment, a specific image pattern included in the print image signal is extracted, and the image density control is executed during printing using the specific image pattern formed on the image carrier, so that dedicated control is performed. A method of obtaining an output image with a good color balance without consuming time or control toner will be described.

  FIG. 1 is a cross-sectional view showing the overall configuration of the color image forming apparatus according to the first embodiment. As shown in the figure, this apparatus is a tandem color image forming apparatus that employs an intermediate transfer member 27 that is an example of an electrophotographic color image forming apparatus. The color image forming apparatus includes an image forming unit 20 and an image processing unit 10 shown in FIG.

  First, the operation of the image forming unit in the electrophotographic color image forming apparatus will be described with reference to FIG.

  First, in the image processing unit 10, image data input from the host computer 1 is input to the CPU via the interface 11, and predetermined image processing is performed as necessary. The image processing related to the present invention is related to density control processing. For example, in the density control process, a control program stored in the ROM 13 is read, and image data image-processed according to the program is temporarily stored in the RAM 14 as necessary. The image data for which the image processing has been completed is input to the PWM decoding processing unit 15 and subjected to PWM decoding. After the processing, the image data is input to the laser drivers 24Y, 24M, 24C, and 24K, and the process proceeds to the image forming process. Details of the density control process will be described later.

  The image forming unit 20 forms an electrostatic latent image with exposure light that is turned on based on the exposure time converted by the image processing unit, develops the electrostatic latent image to form a single color toner image, and the single color toner image Are superimposed on each other to form a multicolor toner image, the multicolor toner image is transferred to the transfer material 11, and the multicolor toner image on the transfer material 11 is fixed. Photoconductors (22Y, 22M, 22C, 22K) for each station, injection charging means (23Y, 23M, 23C, 23K) as primary charging means, toner cartridges (25Y, 25M, 25C, 25K), developing means (26Y) 26M, 26C, 26K), an intermediate transfer member 27, a transfer roller 28, a cleaning unit 29, a fixing unit 30, a density sensor 41, and a color sensor 42.

  The photosensitive drums (photoconductors) 22Y, 22M, 22C, and 22K are configured by applying an organic optical conductive layer to the outer periphery of an aluminum cylinder, and are rotated by the driving force of a driving motor (not shown) being transmitted. The photosensitive drums 22Y, 22M, 22C, and 22K are rotated counterclockwise according to the image forming operation.

  As the primary charging means, four injection chargers 23Y, 23M, 23C, and 23K for charging the yellow (Y), magenta (M), cyan (C), and black (K) photoreceptors are provided for each station. In configuration, each injection charger is provided with a sleeve 23YS, 23MS, 23CS, 23KS.

  Exposure light to the photosensitive drums 22Y, 22M, 22C, and 22K is sent from the scanner units 24Y, 24M, 24C, and 24K, and the electrostatic latent images are selectively exposed by exposing the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K. An image is formed.

  As developing means, in order to visualize the electrostatic latent image, four developing devices 26Y, 26M for developing yellow (Y), magenta (M), cyan (C), and black (K) for each station, Each developing device is provided with a sleeve 26YS, 26MS, 26CS, and 26KS. Each developing device is detachably attached.

  The intermediate transfer member 27 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, and rotates clockwise when forming a color image. The intermediate transfer member 27 rotates in accordance with the rotation of the photosensitive drums 22Y, 22M, 22C, and 22K. The toner image is transferred. Thereafter, a transfer roller 28 to be described later comes into contact with the intermediate transfer member 27 to sandwich and convey the transfer material 11, and the multicolor toner image on the intermediate transfer member 27 is transferred to the transfer material 11.

  The transfer roller 28 contacts the transfer material 11 at the position 28a while the multicolor toner image is transferred onto the transfer material 11, and is separated to the position 28b after the printing process.

  The fixing unit 30 melts and fixes the transferred multi-color toner image while conveying the transfer material 11, and as shown in FIG. 1, the fixing roller 31 for heating the transfer material 11 and the transfer material 11 are fixed to the fixing roller. A pressure roller 32 is provided for pressure contact with 31. The fixing roller 31 and the pressure roller 32 are formed in a hollow shape, and heaters 33 and 34 are incorporated therein, respectively. That is, the transfer material 11 holding the multicolor toner image is conveyed by the fixing roller 31 and the pressure roller 32, and heat and pressure are applied to fix the toner on the surface.

  After the toner image is fixed, the transfer material 11 is discharged to a discharge tray (not shown) by a discharge roller (not shown) and the image forming operation is finished.

  The cleaning unit 29 cleans the toner remaining on the intermediate transfer member 27. The waste toner after the four-color multicolor toner image formed on the intermediate transfer member 27 is transferred to the transfer material 11 is: Stored in a cleaner container.

  The density sensor 41 is an optical sensor for detecting the toner amount and is used for image density control. The density sensor 41 is disposed at the center position in the scanning direction toward the intermediate transfer member 27 in the color image forming apparatus of FIG. 1, and measures the density of the toner patch formed on the surface of the intermediate transfer member 27. An example of the configuration of the density sensor 41 is shown in FIG. An infrared light emitting element 51 such as an LED, a light receiving element 52 such as a photodiode, an IC (not shown) that processes received light data, and a holder (not shown) that accommodates these elements.

  The infrared light emitting element 51 is installed at an angle of 45 degrees with respect to the vertical direction of the intermediate transfer body 27 and irradiates the toner patch 64 on the intermediate transfer body 27 with infrared light. The light receiving element 52 is installed at a symmetrical position with respect to the light emitting element 51, and detects regular reflection light from the toner patch 64.

  An optical element such as a lens (not shown) may be used for coupling the light emitting element 51 and the light receiving element 52.

  In the first embodiment, the intermediate transfer member 27 is a polyimide single-layer resin belt having a circumference of 880 mm. In addition, an appropriate amount of carbon fine particles is dispersed in the resin for adjusting the resistance of the belt, and the surface color is black. Furthermore, the surface of the intermediate transfer member 27 is highly smooth and glossy.

  In the density sensor 41, when the surface of the intermediate transfer member 27 is exposed (toner amount is 0), the light receiving element 52 detects reflected light. The reason is that the surface of the intermediate transfer member 27 is glossy as described above. On the other hand, when a toner image is formed on the intermediate transfer member 27, the regular reflection output gradually decreases as the density (toner amount) of the toner image increases. This is because the regular reflected light from the belt surface is reduced by the toner covering the surface of the intermediate transfer member 27.

  FIG. 3 is a diagram illustrating the relationship between the detection value of the density sensor and the toner amount. In FIG. 3, the vertical axis represents the output voltage of the density sensor, and the horizontal axis represents the image density (corresponding to the toner amount). The concentration sensor used in this embodiment has a maximum output voltage of 5V. In FIG. 3, curve A shows the output characteristics when the density sensor is not soiled and the intermediate transfer member is free of soiling and gloss reduction. On the other hand, the curve B shows the output characteristics when the density sensor is dirty, and the output voltage is reduced compared to the curve A. Since the output voltage decreases when the density sensor becomes dirty, the image forming apparatus according to this embodiment performs output correction of the density sensor using the output value (background output value) of the intermediate transfer member in the absence of toner. ing. Specifically, the output value of the toner patch is normalized by the background output value of the intermediate transfer member (output value of density 0 in FIG. 3). (Toner patch output / background output). The sensor output characteristics after normalization are as shown in FIG. 4, and the output values match regardless of the density sensor contamination. The same correction can be made when the gloss of the intermediate transfer belt is lowered due to dirt, scratches, or the like. The above-described method for normalizing and correcting the toner patch output with the background output is a known method, and is used in many commercially available color image forming apparatuses.

  Next, image density control using a print image signal corresponding to an arbitrary image signal for which a print instruction has been issued from the host computer 1, which is a feature of this embodiment, will be described with reference to the flowchart of FIG. 5. Note that the image density control in the image forming apparatus of the present embodiment is image gradation control for adjusting the density gradation characteristics of the image. Further, the image density control of the first embodiment is executed simultaneously with normal printing. Accordingly, the control flow is also executed every time printing is performed.

  In step S101, an operation for extracting a specific image pattern of the print signal is executed. In step S102, it is determined whether a specific pattern that can be used for density control exists in the print signal. If there is a specific pattern, the process proceeds to step S103. If there is no specific pattern, the image density control operation itself ends. In the present embodiment, a monochrome pattern (monochromatic pattern of any one of C, M, Y, and K) having a printing rate of 25% to 75% in the detectable region of the density sensor (the central portion in the scanning direction, that is, the density sensor mounting portion). Is present in a measurable size and with a predetermined rate of change (uniformity), the pattern is used for density control. In the image forming apparatus, the measurable pattern size of the density sensor is 6 mm in the vertical direction and 4 mm in the horizontal direction. The predetermined change rate is assumed that the difference between the maximum value and the minimum value of the image data in the pattern area is within 2%. In order to cope with the data change (data variation) in the pattern, the density is measured, for example, five times at intervals of 0.5 mm in the vertical direction (paper transport direction) of the image pattern, and the average value is obtained from the image pattern. Concentration value. Here, the reason why the image pattern for density control is limited to 25% to 75% is that good gradation control cannot be performed with a pattern having a very light density or a dark density area. This value is preferably set to an optimum value in accordance with the characteristics of the image forming apparatus to which the present invention is applied.

  In step S103, the density sensor detects the amount of reflected light of a specific pattern formed on the intermediate transfer member.

  In step S104, the background measurement of the intermediate transfer member is executed. Note that the measurement is performed in a non-printing area outside the image area.

  In step S105, the density of the toner patch is calculated. Regarding the density calculation method, first, the output value of the toner image is normalized by the background output value of the intermediate transfer member (toner output / background output). Next, the normalized value is converted into a density value using a density conversion table. The density conversion table is stored in advance in a ROM (not shown) of the apparatus main body.

  In step S106, image gradation control (gradation correction) is executed. Hereinafter, image gradation control (gradation correction) will be described with reference to FIG. Here, only cyan tone correction will be described, but magenta, yellow, and black are also corrected in the same manner. In FIG. 6, the horizontal axis represents image data. The vertical axis represents the density detection value of the density sensor 41 (calculated in step S105). In FIG. 6, a circle mark P represents the detected density value of the density sensor 41.

  Next, a straight line T in FIG. 6 represents a target density gradation characteristic for image density control. In the present embodiment, the target density gradation characteristic T is determined so that the relationship between image data and density is proportional. A curve γ represents a density gradation characteristic in a state where density control (tone correction control) is not performed. It should be noted that the density of the gradation not forming the patch is calculated by performing spline interpolation so as to pass through the origin, P, and maximum density point. In this embodiment, an average solid density 1.2 in the image forming apparatus is given as a fixed value as the maximum density point.

  A curve D represents a gradation correction table calculated by this control, and is calculated by obtaining a symmetric point with respect to the target gradation characteristic T of the gradation characteristic γ before correction. The gradation correction table D is calculated by the CPU 12, and the calculated gradation correction table D is stored in the RAM 14 (nonvolatile memory). When the print image is formed, the target gradation characteristics can be obtained by correcting the image data with the gradation correction table D. The above gradation control is performed for each color from which a specific image pattern for density control is extracted. Thus, the exposure amount (image forming conditions) is determined based on the detection result of the specific pattern on the carrier, and the image density is controlled.

  The above is the description of the image density control (image gradation correction) in the present embodiment.

  In the first embodiment, one image pattern density is detected and image density measurement is performed. However, a plurality of image patterns may be extracted. Furthermore, image density control may be performed by extracting a plurality of image patterns from a plurality of prints (for example, several sheets) within a range in which density fluctuation hardly occurs. In this case, since the detection is performed at a printing rate with a wider width (step), the accuracy of gradation correction is improved.

  According to the first embodiment, a specific image pattern included in a print image signal is extracted, and image density control is executed during printing using the specific image pattern formed on the image carrier. Therefore, an output image with good color balance can be obtained without consuming dedicated control time or control toner.

<Second Embodiment>
In the second embodiment, a specific image pattern included in the print image signal is extracted, and a specific image pattern formed on the transfer material is used to execute image density control during printing. A method for obtaining an output image with a good color balance without consuming control time or control toner will be described.

  FIG. 7 is a cross-sectional view showing the overall configuration of the color image forming apparatus in the present embodiment. In the image forming apparatus of the present embodiment, a color sensor 42 is provided instead of the density sensor 41 provided in the image forming apparatus of the first embodiment. Other main parts of the overall configuration are the same as those of the image forming apparatus according to the first embodiment, and a description thereof will be omitted.

  The color sensor 42 is disposed at the center in the scanning direction toward the image forming surface of the transfer material 11 downstream from the fixing unit 30 in the transfer material conveyance path in the color image forming apparatus of FIG. An RGB output value for the formed toner patch after fixing is detected. By disposing the image inside the color image forming apparatus, it becomes possible to automatically detect the fixed image before discharging it to the paper discharge unit.

  FIG. 8 is a diagram illustrating the configuration of the color sensor 42. Here, the color sensor 42 includes a white LED 53 and a charge storage sensor 54a with an RGB on-chip filter. The white LED 53 is made incident on the transfer material 11 on which the patch 61 after fixing is formed at an angle of 45 degrees, and the intensity of diffuse reflected light in the 0 degree direction is detected by the charge storage sensor 54a with an RGB on-chip filter. The light receiving portion of the charge storage type sensor 54a with RGB on-chip filter is a pixel independent of RGB like 54b.

  The charge storage sensor of the RGB on-chip filter charge storage sensor 54 may be a photodiode. Several sets of three RGB pixels may be arranged. Further, a configuration in which the incident angle is 0 degree and the reflection angle is 45 degrees may be employed. Furthermore, you may comprise by LED which emits RGB three colors, and a sensor without a filter.

  The detection output value of the color sensor is maximum for both RGB in the absence of toner (white transfer material base), and has a complementary color relationship as the color toner (C, M, Y toner) on the transfer material increases. The output value of the light receiving unit decreases. For example, if a large amount of C toner is used, the complementary color R output decreases. Similarly, G output corresponds to M toner, and B output corresponds to Y toner. That is, by detecting the RGB output values, the toner amounts of the C, M, and Y color toners can be detected. In the case of K toner, since all RGB output values decrease, any received light output value may be used. In this image forming apparatus, the amount of K toner is calculated from the G output.

  As in the case of the density sensor described in the first embodiment, the detected output value from the toner image is normalized by the output value of the transfer material background, so that fluctuations in the received light output value such as sensor contamination can be corrected. .

  Next, image density control using a print signal, which is a feature of this embodiment, will be described with reference to the flowchart of FIG. Note that the image density control of the second embodiment is executed simultaneously with normal printing. Accordingly, the control flow is also executed every time printing is performed.

  In step S201, a specific pattern is extracted from the print signal. In step S202, it is determined whether or not the print signal has a specific image pattern that can be used for density control. If there is a specific pattern, the process proceeds to step S203, and if there is no specific pattern, an image density control operation is performed. In the present embodiment, a monochrome pattern (monochromatic pattern of any one of C, M, Y, and K) having a printing rate of 25% to 75% in the detectable region of the density sensor (the central portion in the scanning direction, that is, the density sensor mounting portion). Is present in a measurable size and with a predetermined rate of change (uniformity), the pattern is used for density control. In the image forming apparatus, the measurable pattern size of the density sensor is 6 mm in the vertical direction and 4 mm in the horizontal direction. The predetermined change rate is assumed that the difference between the maximum value and the minimum value of the image data in the pattern area is within 2%. In order to cope with the data change (data variation) in the pattern, the density is measured five times at 0.5 mm intervals in the vertical direction of the image pattern (paper transport direction), and the average value is the density of the image pattern. Value.

  In step S203, the color sensor detects the amount of reflected light of a specific pattern formed on the transfer material (on paper).

  In step S204, the background measurement of the transfer material is performed. Note that the measurement is performed in a blank portion which is a non-printing area of the transfer material.

  In step S205, the density of the toner patch is calculated. The density calculation method is the same as that of the density sensor described in the first embodiment.

  In step S206, image gradation control (gradation correction) is performed. The gradation correction method is the same as that in the first embodiment.

  The gradation correction control is performed for each color from which a specific image pattern for density control is extracted.

  As described above, according to the second embodiment, a specific image pattern included in the print image signal is extracted, and image density control is performed during printing using the specific image pattern formed on the transfer material. Since it is executed, an output image with a good color balance can be obtained without consuming dedicated control time or control toner.

<Third Embodiment>
In the third embodiment, a specific image pattern included in the print image signal is extracted, and the light reflection characteristic of the toner image formed according to the specific image pattern is detected by the optical sensor. Accordingly, a method for obtaining an output image with a good color balance while suppressing an increase in printer downtime and printing cost as much as possible by executing image density control will be described.

  The overall configuration of the color image forming apparatus and the configuration of the density sensor used in the present embodiment are the same as those of the color image forming apparatus described in the first embodiment, and a description thereof will be omitted.

  First, an image density control method according to this embodiment will be described with reference to the flowchart of FIG. Note that the image density control in the image forming apparatus of the present embodiment is image gradation control for adjusting the density gradation characteristics of the image. This image density control is performed when the power of the main body is turned on and when the developing device and the photoconductor are replaced, in which fluctuation of the image density is assumed. Furthermore, it is also executed when an image density control execution condition described later is satisfied during printing.

  In step S301, the background measurement of the intermediate transfer member is executed. The measurement position and the number of points are the same as those of the toner patch used for image density control.

  Here, FIG. 11 is a diagram showing a patch pattern formed on the intermediate transfer member, and 8 mm square patches are provided at intervals of 2 mm on the portion where the density sensor 41 is arranged, for each of Y, M, C, and K. In addition, the image printing rate (density gradation degree) is changed in 8 steps (8 patches for each color) to form a total of 32 images. The correspondence between each patch and the printing rate (gradation) is Y1, M1, C1, K1 = 12.5%, Y2, M2, C2, K2 = 25%, Y3, M3, C3, K3 = 37.5% Y4, M4, C4, K4 = 50%, Y5, M5, C5, K5 = 6. 5%, Y6, M6, C6, K6 = 75%, Y7, M7, C7, K7 = 87.5%, Y8, M8, C8, K8 = 100%. The background measurement of the intermediate transfer member is performed before the patch is formed (one round before the patch formation) at the location where the 32 patches are formed.

  In step S302, a toner patch is formed on the intermediate transfer member. Details of the patch are as described in FIG.

  In step S303, the density sensor detects the amount of light reflected from the toner patch.

  In step S304, the density of the toner patch is calculated. Hereinafter, since the calculation method of the density is the same as that in the first embodiment, the description is omitted here.

  In step S305, image gradation control (gradation correction) is performed. Hereinafter, image gradation control (gradation correction) will be described with reference to FIG. Here, only cyan tone correction will be described, but magenta, yellow, and black are also corrected in the same manner.

  In FIG. 12, the horizontal axis represents image data. The vertical axis represents the density detection value of the density sensor 41. Further, in the figure, circles indicate the detected density values of the density sensor 41 for C1, C, C3, C4, C5, C6, C7, and C8 patches. Next, a straight line T represents a target density gradation characteristic for image density control. In the present embodiment, the target density gradation characteristic T is determined so that the relationship between image data and density is proportional. A curve γ represents a density gradation characteristic in a state where density control (tone correction control) is not performed. It should be noted that the density of gradations not forming a patch is calculated by spline interpolation through C3, C4, C5, C6, C7, and C8 through the origin and C1 and C. A curve D represents a gradation correction table calculated by this control, and is calculated by obtaining a symmetric point with respect to the target gradation characteristic T of the gradation characteristic γ before correction. The gradation correction table D is calculated by the CPU 12, and the calculated gradation correction table D is stored in the RAM 14 (nonvolatile memory). When the print image is formed, the target gradation characteristics can be obtained by correcting the image data with the gradation correction table D.

  Next, an image density control execution determination method, which is a feature of the present embodiment, will be described with reference to the flowchart of FIG. Note that the execution determination of the image density control of the third embodiment is executed simultaneously with normal printing. Accordingly, the control flow is also executed every time printing is performed.

  In step S401, a specific pattern that can be used for determining density control is extracted from the print signal. In step S402, it is determined whether the pattern exists. In the present embodiment, a monochrome pattern (monochrome pattern of any one of C, M, Y, and K) having a printing rate of 30% to 70% in the detectable region of the density sensor (the central portion in the scanning direction, that is, the density sensor mounting portion). Is present, the pattern is used to determine execution of density control. Here, the reason why the image pattern used for the determination of execution of density control is limited to 30% to 70% is that a good determination cannot be made with a pattern of a very light density or a dark density area. This value is preferably set to an optimum value in accordance with the characteristics of the image forming apparatus to which the present invention is applied.

  In step S403, the density sensor detects the amount of reflected light of a specific pattern formed on the intermediate transfer member.

  In step S404, the background measurement of the intermediate transfer member is executed. Note that the measurement is performed in a non-printing area outside the image area.

  In step S405, the density of the toner pattern is calculated. In step S406, execution determination of image gradation control is performed. That is, in step S406, it is determined whether there is a color whose density has fluctuated greatly. If there is a color, the process proceeds to step S407, and if not, the process ends.

  Hereinafter, control execution determination will be described with reference to FIG. Here, only the determination of the cyan color will be described, but the same method is also used for magenta, yellow, and black.

  In FIG. 14, the horizontal axis represents image data, and the vertical axis represents the density detection value of the density sensor 41.

  A straight line T represents the target density gradation characteristic in the above-described image density control. The density gradation characteristic immediately after the image density control coincides with the straight line T, and when printing is performed thereafter, the density change gradually occurs and the density gradation characteristic moves away from the straight line T. The straight lines H and L represent the upper limit (straight line H) and the lower limit (straight line L) of the allowable range of density fluctuation. When the density gradation characteristics are outside this range, it is necessary to perform image density control. . In the present embodiment, the allowable range of density fluctuation is set to ± 10% with respect to the target gradation characteristics. This value may be set to an optimum value according to the characteristics and specifications of the image forming apparatus to which the present invention is applied. If the value of the toner pattern calculated in step S405 deviates from between the straight lines H and L (when a large density fluctuation occurs), it is determined to execute image density control. The above-described determination is performed for each color from which the specific image pattern is extracted. If it is determined that image density control is required even for one color, the image density control is performed.

  In step S407, an image density control sequence is executed. The image density control method is as described above.

  In step S408, if a specific pattern is not detected, it is further determined whether or not a density control execution determination is performed for a predetermined number or more. In step S408, if there is a color whose density variation is not determined, the process proceeds to step S407, and if not, the process ends. In other words, an image pattern that can be used for determination of image density control may not be extracted even though a large number of prints are performed. When the density control execution determination is not performed for a predetermined number of prints (1000 sheets in the present embodiment), it is determined that a large density variation may have already occurred, and image density control is performed. The predetermined number of sheets may be set to an optimum value according to the characteristics of the apparatus to which the present invention is applied.

  As described above, in the third embodiment, a specific image pattern included in a print image signal is extracted, and a light reflection characteristic of a toner image formed according to the specific image pattern is detected by the optical sensor. Then, image density control is executed according to the detection result. According to the third embodiment, the density control is performed only when the density fluctuation largely occurs, so that it is possible to eliminate control time and toner consumption required for unnecessary density control. On the other hand, since a dedicated pattern having a plurality of gradations is used for density control, density control with high detection accuracy can be performed. The third embodiment can also be applied to the image forming apparatus that detects the toner density on the transfer material described in the second embodiment.

  In the first to third embodiments, image gradation control for adjusting the density gradation characteristics of an image has been described as an example of the image density control method. However, the image density control method is another method. But it ’s okay. For example, after forming a plurality of toner patches by changing the developing bias value and the charging bias value, calculating the toner amount of those patches, and calculating the optimum developing bias value and charging bias value according to the values. The method of controlling the density may be used.

  In the first to third embodiments, the case where the density is used as the toner amount corresponding to the light reflection characteristic when the density sensor detects the toner patch is described as an example. However, the light reflection detected by the density sensor is used. The toner amount corresponding to the characteristic is not limited to this, and naturally, the toner weight itself may be used, and further, chromaticity may be used. That is, it goes without saying that the present invention is within the scope of the present invention as long as the optical sensor detects a physical quantity corresponding to the toner quantity converted based on the light reflection characteristic from the toner patch.

  According to the image forming apparatus according to each embodiment, a specific image pattern included in a print image signal is extracted, and a specific image pattern formed on an image carrier or a transfer material is used to print an image density during printing. By executing the control, it is possible to obtain an output image with a good color balance without consuming dedicated control time or control toner. In addition, a specific image pattern included in the print image signal is extracted, a light reflection characteristic of a toner image formed according to the specific image pattern is detected by the optical sensor, and an image density is determined according to the detection result. By executing the control, the density control is performed only when the density variation is large, so that it is possible to eliminate control time and toner consumption required for unnecessary density control.

  In the present invention, a storage medium in which a program code of software that realizes the functions of the embodiments is recorded is provided to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus is stored in the storage medium. It is also achieved by reading and executing the program code. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. As a storage medium for supplying such a program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM Etc. can be used.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) running on the computer based on the instruction of the program code Includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing.

  Furthermore, after the program code read from the storage medium is written to the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, the function is based on the instruction of the program code. This includes the case where the CPU of the expansion board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  Further, the program code of the software that realizes the functions of the above embodiments is distributed via a network, so that it can be stored in a storage means such as a hard disk or memory of a system or apparatus or a storage medium such as a CD-RW or CD-R Needless to say, this can also be achieved by the computer (or CPU or MPU) stored in the system or apparatus reading and executing the program code stored in the storage means or the storage medium.

1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus used in a first embodiment. 3 is a diagram illustrating a configuration of a density sensor 41. FIG. It is a figure for demonstrating a density sensor characteristic. It is a figure for demonstrating the normalization correction | amendment of a density sensor output. 5 is a flowchart for explaining an image density control method according to the first embodiment; FIG. 5 is a diagram for explaining a gradation control method according to the first embodiment. It is sectional drawing which shows the whole structure of the image forming apparatus used for 2nd Embodiment. 2 is a diagram illustrating a configuration of a color sensor 42. FIG. It is a flowchart for demonstrating the image density control method of 2nd Embodiment. It is a figure for demonstrating the image density control method of 3rd Embodiment. It is a figure for demonstrating the patch pattern on an intermediate transfer body. It is a figure for demonstrating the image gradation control of 3rd Embodiment. 12 is a flowchart for explaining image density control execution determination according to the third embodiment. It is a figure for demonstrating the image density control execution judgment of 3rd Embodiment.

Claims (14)

Pattern extraction means for extracting a specific image pattern included in the print image signal;
Detection means for detecting light reflection characteristics of a toner image on the image carrier formed according to the specific image pattern;
Image density control means for determining an image forming condition according to the detection result of the detection means and controlling the image density;
An image forming apparatus comprising: Pattern extraction means for extracting a specific image pattern included in the print image signal;
Detecting means for detecting light reflection characteristics of a toner image on a transfer material formed according to the specific image pattern;
Image density control means for determining an image forming condition according to the detection result of the detection means and controlling the image density;
An image forming apparatus comprising: Pattern extraction means for extracting a specific image pattern included in the print image signal;
Detection means for detecting light reflection characteristics of a toner image on the image carrier formed according to the specific image pattern;
Image density control determining means for determining whether to execute image density control according to the detection result of the detecting means;
An image forming apparatus comprising: Pattern extraction means for extracting a specific image pattern included in the print image signal;
Detecting means for detecting light reflection characteristics of a toner image on a transfer material formed according to the specific image pattern;
Image density control determining means for determining whether to execute image density control according to the detection result of the detecting means;
An image forming apparatus comprising: Furthermore, it comprises density variation determination means for determining whether or not there is a color that exceeds a predetermined range of density variation in the extracted specific image pattern,
5. The image forming apparatus according to claim 3, wherein the image density control determination unit determines whether to execute image density control according to a determination result of the density fluctuation determination unit. Furthermore, when the specific image pattern is not extracted by the pattern extraction unit, a density variation estimation unit that determines whether or not there is a color that has not been subjected to density variation determination more than a predetermined number of prints,
6. The image formation according to claim 3, wherein the image density control unit determines whether or not to execute the image density control according to a determination result of the density variation estimation unit. apparatus. A pattern extraction step of extracting a specific image pattern included in the print image signal;
A detection step of detecting light reflection characteristics of the toner image on the image carrier formed according to the specific image pattern;
An image density control step for determining image forming conditions according to the detection result of the detection step and controlling the image density;
An image forming method comprising: A pattern extraction step of extracting a specific image pattern included in the print image signal;
A detection step of detecting light reflection characteristics of a toner image on a transfer material formed according to the specific image pattern;
An image density control step for determining image forming conditions according to the detection result of the detection step and controlling the image density;
An image forming method comprising: A pattern extraction step of extracting a specific image pattern included in the print image signal;
A detection step of detecting light reflection characteristics of the toner image on the image carrier formed according to the specific image pattern;
An image density control determination step for determining whether to execute image density control according to the detection result of the detection step;
An image forming method comprising: A pattern extraction step of extracting a specific image pattern included in the print image signal;
A detection step of detecting light reflection characteristics of a toner image on a transfer material formed according to the specific image pattern;
An image density control determination step for determining whether to execute image density control according to the detection result of the detection step;
An image forming method comprising: And a density variation determination step for determining whether or not a color exceeding a predetermined range of density variation exists in the extracted specific image pattern,
11. The image forming method according to claim 9, wherein the image density control determination step determines whether or not to execute image density control according to a determination result of the density variation determination step. Furthermore, when the specific image pattern is not extracted in the pattern extraction step, a density variation estimation step for determining whether there is a color that has not been subjected to density variation determination for a predetermined number of prints or more is provided.
12. The image formation according to claim 9, wherein the image density control step determines whether or not to execute the image density control according to a determination result of the density variation estimation step. Method.   A computer program for executing the image forming method according to any one of claims 7 to 12. A computer-readable storage medium storing the computer program according to claim 13.

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