JP2004206137A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of shortening the period of time needed for density correction and reducing the consumption of a toner used for the correction while keeping the density output of the whole image constant according to the kind of an image such as a solid image, a line image, and a half-tone image. <P>SOLUTION: In the image forming apparatus, an image density correcting means of corrects half-tone density by forming a plurality of toner pattern for half-tone density detection which vary in density level from a low-density area to right before a high-density area and compares them with a half-tone density reference value, and also corrects a detected value of the low-density area with a value obtained by deleting detected values less than a previously set low-density area deletion reference value and performing approximation processing by using a plurality of remaining detected values, so the time can greatly be shortened as compared with the generation of a density conversion table covering all gradations by complementary processing. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, and a facsimile apparatus using an electrophotographic method.

  As shown in FIG. 2, which is an explanatory view of the present invention, the color electrophotographic apparatus includes a plurality of photoreceptor drums 1 rotatably supported, and each of the photoreceptor drums 1 is driven by a driving device in a direction indicated by an arrow. It is designed to be driven to rotate.

  Further, around the photosensitive drum 1, a charging device 2 for uniformly charging the surface of the photosensitive drum 1, an exposing unit 3 for exposing the surface of the photosensitive drum 1 to form a latent image, and A developing device 4 for developing an image to form a toner image, a transfer device 5 for transferring the toner image to a transfer material, and a cleaning device 6 for cleaning toner remaining on the surface of the photosensitive drum 1 are arranged.

  On the other hand, the four photosensitive drums 1 are arranged in series, and each has a developing tank containing toner of Y (yellow), M (magenta), C (cyan), and Bk (black).

  The transfer device 5 includes a transfer belt 7 that runs while being stretched between a driving pulley and a driven pulley, and the transfer belt 7 runs in the direction of the arrow. The recording medium as a transfer material is electrostatically held on the transfer belt 7 and conveyed.

  Inside the loop of the transfer belt 7, transfer chargers 8 are arranged at positions facing the respective photosensitive drums 1, and these transfer chargers 8 are formed on the respective photosensitive drums 1. The toner image is transferred.

  Further, the recording medium that has passed through the four photosensitive drums 1 on the transfer belt 7 passes through the fixing device 9 and the toner image is fixed.

  In an electrophotographic apparatus such as a color electrophotographic apparatus, the density characteristics fluctuate with respect to an applied voltage or temperature rise in charging, exposure, development, and the like in an electrophotographic process. It is common to output data after correcting the density characteristics of the data.

  That is, a plurality of toner patterns corresponding to a predetermined density are formed on the photosensitive drum 1 when the power is turned on or every time a predetermined number of sheets are output. Next, the density of the toner pattern is measured by a sensor, and a difference between the measured density and a most desirable density, that is, a preset reference value is obtained, and a density conversion table is created based on the difference. Thereafter, the density of the input image data is corrected based on the density conversion table, and the image is output.

  Incidentally, image output in an image forming apparatus such as an electrophotographic apparatus includes types such as solid, line, and halftone. Because these images change under the influence of the various factors of charging, exposure, development, transfer and fixing in the electrophotographic process, it is necessary to maintain the density of the output image constant without performing density correction on the image. Is impossible. In addition, since the degree of influence on each variable factor of the electrophotographic process differs depending on the type of image, it is necessary to change the control of density correction depending on the type of image.

  However, in the above-described conventional image forming apparatus, since the solid image density or the toner adhesion amount is detected to control the toner adhesion amount on the photosensitive drum 1, the density output of the entire image is output according to the type of the image. There is a problem that it cannot be fixed.

  In order to solve this problem, for example, there is an image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 8-265571 (Patent Document 1).

  In this image forming apparatus, in order to make the density of the entire image including the halftone and the like appropriate, the developing bias is changed so that the toner pattern for the high density detection and the toner pattern for the halftone density detection are formed on the photosensitive drum. Two types of density detection toner patterns are formed.

  The maximum amount of toner adhering to the photosensitive drum is controlled by the density correction unit by detecting the toner pattern for high density detection by the toner amount detection unit including a reflection sensor, and the toner amount detection unit is controlled by the toner amount detection unit. By detecting the halftone density detecting toner pattern, the density correction means controls the amount of toner adhering to the halftone density portion on the photosensitive drum. By controlling the maximum amount of toner attached to the high density detection toner pattern and controlling the amount of toner attached to the halftone density portion using the halftone density detection toner pattern, the density of the entire image is kept constant. I have.

  Specifically, the density correction unit detects high density from the toner pattern for high density detection by the toner amount detection unit, compares the high density with the high density reference value, and determines whether a deviation from the high density reference value has occurred. Performs high density correction. Further, the density correction unit detects the halftone density from the halftone density detection toner pattern by the toner detection unit under the condition that the high density image adjustment is guaranteed, and compares the halftone density with the reference value by comparing with the halftone density reference value. If there is a shift, halftone density correction is performed.

  Japanese Patent Application Laid-Open No. 8-289148 (Patent Document 2) discloses a halftone density correction method in which a halftone toner pattern in which the pulse width of a laser is modulated during exposure in the course of charging, exposure, development, and transfer is transferred. A plurality of each color is formed on the belt, these patterns are sequentially measured by a density detection sensor, and the optical density is detected from each measurement result.

Next, the halftone table is corrected by comparing with a plurality of target density values of each color stored in advance, calculating the amounts of change between the target value and the current value, respectively.
JP-A-8-265571 (published October 11, 1996) JP-A-8-289148 (published on November 1, 1996)

  By the way, as described above, the density correction using the toner pattern is executed by forming a plurality of toner patterns each time the power is turned on or every time a predetermined number of sheets are output.

  Therefore, in the above-described conventional image forming apparatus, since not only high density correction but also halftone density adjustment is performed, it takes much time. As a result, the user has to wait more than the high-density correction alone, which causes a problem that the usability is rather poor.

  Further, since not only high-density correction but also half-tone density adjustment is performed each time, there is a problem that the amount of toner consumed for forming a toner pattern due to the half-tone density adjustment increases, resulting in an increase in cost.

  Here, with respect to the halftone density correction method, the technique of Japanese Patent Application Laid-Open No. 8-289148 will be described in more detail. First, a first density conversion table as a reference is created at the time of maintenance. Next, when actually outputting an image, a toner pattern is output every predetermined number of copies, the density is measured, and the measured density is used as a second density conversion table. Next, a new density conversion table to be actually used is created based on the first density conversion table and the second density conversion table. In other words, in the middle density area, the internal density results of the first density conversion table and the second density conversion table are used. Table values are set in a straight line having

  However, in general, in order to generate a toner pattern and measure its density, it is necessary to perform various processes in a photoreceptor, a developing unit, a transfer unit sensor, and the like. Noise may be included for various reasons. In such a case, if the density conversion table is created on the assumption that the density of the detected toner pattern is always correct, an output image having an incorrect gradation density will be generated. Further, the number of toner patterns is generally smaller than the number of gradations of the output image density, and a density conversion table covering all the gradations is created by various interpolation processes. However, if an erroneous density conversion table is created in this interpolation process, an output image having an erroneous tone density will be generated.

  In addition, if the interpolation processing is performed precisely, there is a problem that a great amount of processing time is required and it is not practical.

  On the other hand, since a multi-color image is formed by superimposing a single-color image, as in the conventional method, if the determination is made based on the density change of only one of the colors, the entire multi-color image is determined. There is a problem that it is difficult to determine a change in color balance.

  That is, since the color balance of the entire color image greatly changes due to the ambient temperature, humidity, and the life change of members related to image formation, it is not possible to judge such a change in the color balance of the entire color image and perform correction. Indispensable for expressing images.

  In addition, the image density also varies depending on the above-mentioned variation factors regardless of the high-density area and the half-tone density area, and the variation often greatly differs depending on each color.

  On the other hand, in the prior art, as shown in FIG. 12, when the difference from each color reference density exceeds a certain value, that is, when the image density exceeds the shaded area A and exists in the area B, the density is reduced. In this method, the presence or absence of a correction operation is determined based on a change of only one color, that is, correction is performed.

  However, if the density change occurs from the density curve before the member replacement indicated by the dashed line to the density curve after the member replacement indicated by the two-dot chain line as shown in FIG. Changes in the color balance of natural images cannot be determined.

  In other words, although the density change of only one color is shown in the figure, in practice, each color changes variously depending on the ambient temperature, humidity and life characteristics of the member. Regarding the density change of each color, even if the difference from each reference density is slight, by superimposing toner images for expressing a multi-color image, the color balance of the color image can be improved. Changes often occur.

  As a result, the method of determining the presence or absence of the correction operation based on only one color change as shown in FIG. 12 cannot accurately determine a change in a color image.

  The present invention has been made in view of the above-described conventional problems, and has as its object to perform density correction while maintaining a constant density output of the entire image according to the type of image such as solid, line, or halftone. It is an object of the present invention to provide an image forming apparatus capable of shortening the time required for the image formation and reducing the consumption of toner used at the time of correction.

  In order to solve the above problem, the image forming apparatus of the present invention forms a predetermined high-density detection toner pattern on a photoreceptor, and sets the high-density detection toner pattern to a value detected by a reflective sensor. A high density correction amount is determined by comparing with a density reference value, and a predetermined halftone density detection toner pattern is formed on the photoreceptor. In the image forming apparatus having the image density correcting means for comparing the detected value with the halftone density reference value to determine the correction amount of the halftone density, the image density correcting means performs the correction of the halftone density. In performing the correction, a plurality of halftone density detecting toner patterns having different density levels from the low density area to the front of the high density area are formed and compared with the halftone density reference value, and the correction is performed. Remove the low density area deleting reference value following the detection value set in advance for the detection value, it is characterized by performing the correction by linear approximated processed value using the remaining plurality of detection values.

  According to the invention, the image density correcting means forms a plurality of halftone density detecting toner patterns having different density levels from the low density area to the front of the high density area when correcting the halftone density. The correction value is compared with the reference density reference value, and the detection value of the low-density area is deleted by using a detection value equal to or less than the preset low-density area deletion reference value. Is corrected by the value approximated to the above.

  That is, when performing correction by comparing with the halftone density reference value, a plurality of halftone density detection toner patterns having different density levels from the low density area to the front of the high density area are formed, and these are detected. Then, for example, the correction is made by a value approximated linearly.

  Here, the detection value of the low-density area is generally disturbed in numerical values, and it is difficult to perform linear approximation processing. Therefore, in the present invention, at the time of the approximation processing, for the detection value of the low-density area, a detection value that is equal to or less than a preset low-density area deletion reference value is deleted, and for example, linear detection is performed using the remaining plurality of detection values. Is used.

  As a result, a detection value that is equal to or less than the preset low-density area deletion reference value can be deleted, and an appropriate detection value can be used to perform the approximation processing, thereby improving the accuracy of the approximation processing.

  Further, since the approximated value is used, it is possible to prevent an erroneous density conversion table from being created.

  Further, the time can be greatly reduced as compared with the case where the density conversion table covering all gradations is created by performing the complementing process.

  Accordingly, the time required for density correction can be shortened while the density output of the entire image is reliably and accurately maintained at a constant level in accordance with the type of the image such as solid, line, or halftone, and a high-quality image is output. It is possible to provide an image forming apparatus capable of reducing the amount of toner used sometimes.

  In order to solve the above problem, in the image forming apparatus according to the present invention, in the above image forming apparatus, the image density correction unit outputs a laser output as a low density region deletion reference value when approximating the low density region. It is characterized in that an inflection point of the detected value when the time is changed from the low side to the high side sequentially is adopted.

  That is, how to set a low-density area deletion reference value in order to use a detection value appropriate for the approximation process is a problem.

  However, according to the present invention, the image density correction unit is used to change the laser output from the low side to the high side sequentially as the low density area deletion reference value for the low density area, for example, when performing linear approximation processing. The inflection point of the detection value in is adopted. Specifically, a point where the detection value starts to continuously increase in a color image is adopted, while a point where the detection value starts to continuously decrease in a monochrome image is adopted.

  As a result, it is possible to reliably delete the detection value that is difficult to perform the approximation processing in the low-density region, and to leave as many detection values appropriate for the approximation processing as possible.

  As a result, the time required for density correction while maintaining the density output of the entire image efficiently, reliably and accurately according to the type of image such as solid, line, and halftone, and outputting a high-quality image. Can be provided, and the amount of toner used for correction can be reduced.

  In order to solve the above-described problems, the image forming apparatus according to the present invention, in the above-described image forming apparatus, wherein the image density correction unit compares the high density reference value with the result of the high density correction, and determines the difference. 2. The image forming apparatus according to claim 1, wherein the halftone density is continuously corrected only when the difference is equal to or larger than a preset difference reference value.

  According to the invention described above, the image density correction unit compares the high density reference value with the result of the high density correction, and continues to adjust the halftone density only when the difference is equal to or larger than a preset difference reference value. Make corrections.

  That is, the correction of the halftone density is not performed every time the high density correction is performed, but the high density reference value is compared with the result of the high density correction, and the difference is equal to or larger than the preset difference reference value. It only happens when.

  Therefore, the presence or absence of the halftone density correction operation is determined from the result of the high density correction, and the halftone density correction operation is performed based on the result, which leads to a reduction in the density correction time and a reduction in toner consumption during the density correction.

  The presence or absence of the halftone density correction operation is determined by comparing the high density reference value with the result of the current high density correction, and determining whether the difference is equal to or greater than a preset difference reference value.

  Therefore, the halftone density correction is performed only when there is a large deviation from the high density reference value. Therefore, since the halftone density correction is performed only when it is really necessary, the efficiency is high.

  Further, when the high-density reference value is not changed, the input image is charged based on the initially set high-density reference value of the toner, corresponding to a change in density characteristics due to an applied voltage such as charging, exposure, and development, or a rise in temperature. The data density characteristics are corrected and output.

  Therefore, the density characteristics of the input image data can be corrected and output in accordance with the ideal density characteristics.

  As a result, the time required for density correction can be shortened, and the amount of toner used for correction can be reduced while the density output of the entire image is kept constant according to the type of image such as solid, line, or halftone. An image forming apparatus can be provided.

  As described above, in the image forming apparatus according to the present invention, the image density correction unit detects a plurality of halftone densities having different density levels from the low density area to the front of the high density area when correcting the halftone density. While forming a toner pattern and comparing it with a halftone density reference value for correction, the detection value of the low density area is deleted with a detection value equal to or less than a preset low density area deletion reference value, and the remaining plural values are deleted. The correction is performed using a value that is linearly approximated using the detected value.

  Therefore, the detection value of the low-density area is generally disturbed in numerical values, and it is difficult to perform linear approximation processing. Uses a value obtained by deleting a detection value equal to or less than a preset low-density area deletion reference value, and linearly approximating the remaining plurality of detection values.

  As a result, it is possible to delete a detection value equal to or less than the preset low-density area deletion reference value and use an appropriate detection value for performing the linear approximation process, thereby improving the accuracy of the approximation process.

  Further, since a value approximated linearly is used, it is possible to prevent creation of an erroneous density conversion table.

  Further, the time can be greatly reduced as compared with the case where the density conversion table covering all gradations is created by performing the complementing process.

  Accordingly, the time required for density correction can be shortened while the density output of the entire image is reliably and accurately maintained at a constant level in accordance with the type of the image such as solid, line, or halftone, and a high-quality image is output. There is an effect that it is possible to provide an image forming apparatus that can reduce the amount of toner used sometimes.

  As described above, in the image forming apparatus according to the present invention, in the above-described image forming apparatus, the image density correction unit includes, as a low-density area deletion reference value when linearly approximating the low-density area, The inflection point of the detected value when the laser output is changed from the low side to the high side sequentially is adopted. Specifically, a point where the detected value starts to continuously increase in a color image is adopted, while a point where the detected value starts to continuously decrease in a monochrome image is adopted.

  Therefore, it is possible to reliably remove the detection value that is difficult to perform the linear approximation process in the low-density region, and to leave as many detection values appropriate for the linear approximation process as possible.

  As a result, the time required for density correction while maintaining the density output of the entire image efficiently, reliably and accurately according to the type of image such as solid, line, and halftone, and outputting a high-quality image. And an image forming apparatus capable of reducing the consumption of toner used at the time of correction can be provided.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS. In this embodiment, a color electrophotographic apparatus as an image forming apparatus will be described. However, the present invention is not limited to this, and may be a simple electrophotographic apparatus as an image forming apparatus. Further, the present invention can be applied to other image forming apparatuses such as a copying machine, a laser beam printer, and a facsimile machine using an electrophotographic method.

  As shown in FIG. 2, the color electrophotographic apparatus according to the present embodiment includes a plurality of photoconductor drums 1 rotatably supported as photoconductors, and each photoconductor drum 1 is driven by a driving device. It is designed to be driven to rotate in the direction of the arrow.

  A charging device 2 for uniformly charging the surface of the photosensitive drum 1, an exposure device 3 for exposing the surface of the photosensitive drum 1 to form a latent image, and an A developing device 4 for developing an image to form a toner image, a transfer device 5 for transferring the toner image to a transfer material, and a cleaning device 6 for cleaning toner remaining on the surface of the photosensitive drum 1 are arranged.

  On the other hand, the four photosensitive drums 1 are arranged in series, and each has a developing tank containing toners of Y (yellow), M (magenta), C (cyan), and Bk (black).

  The transfer device 5 includes a transfer belt 7 that runs while being stretched between a driving pulley and a driven pulley, and the transfer belt 7 runs in the direction of the arrow. Therefore, the recording medium as the transfer material is electrostatically held on the transfer belt 7 and conveyed.

  Inside the loop of the transfer belt 7, transfer chargers 8 are arranged at positions facing the respective photosensitive drums 1, and the transfer chargers 8 are formed of toners formed on the respective photosensitive drums 1. The image is transferred to the transfer belt 7. In addition, inside and outside the loop of the transfer belt 7, a cleaning member (not shown) and a charge removing member (not shown) for removing charges accumulated in the transfer belt 7 are arranged.

  The recording medium on which the toner images passing through the four photosensitive drums 1 are transferred on the transfer belt 7 passes through the fixing device 9 so that the toner images are fixed.

  On the other hand, in the color electrophotographic apparatus of the present embodiment, as shown in the figure, the density detecting sensor 10 as the toner amount detecting means is opposed to the transfer belt 7 at an appropriate position below the transfer belt 7. Is provided.

  The above-mentioned density detection sensor 10 is a reflection type sensor, and has a light-emitting element 11, a diffuse reflection light-receiving element 12, and a regular reflection light-receiving element 13 as shown in FIG. And both can be detected.

  That is, when performing color density detection, light irregularly reflected by a toner image such as a toner pattern emitted from the light emitting element 11 and transferred to the transfer belt 7 is received by the irregular reflection light receiving element 12, and the light is reflected in accordance with the amount of light. Generates voltage.

  When black density detection is performed, light that is emitted from the light emitting element 11 and is regularly reflected by a toner image including the toner pattern on the transfer belt 7 is received by the regular reflection light receiving element 13 and a voltage corresponding to the light amount is received. Occurs.

  Here, the transfer belt 7 uses a modified polyimide as a material for greatly changing the reflectance of the toner, and has a specular reflectance of 10% or more by finishing the surface to a mirror surface.

  By the way, in the color electrophotographic apparatus of the present embodiment, in order to properly correct the image density at the time of image output, the developing bias is changed and the high-density detecting toner pattern and the halftone Two types of density detection toner patterns including a density detection toner pattern are formed. Each of the high-density detection toner pattern and the halftone density detection toner pattern includes a pattern formed as a reference value and a pattern formed as needed when an image is formed.

  The high-density detection toner pattern and the halftone density detection toner pattern are formed in the non-image forming area of the photosensitive drum 1.

  The high-density detection toner pattern is formed as a solid image. As a result, it is possible to perform control to make the maximum toner adhesion amount appropriate.

  On the other hand, a plurality of halftone density detecting toner patterns of, for example, a 3 × 3 pixel matrix are formed by changing the density. In other words, by forming a predetermined number of dots in a certain area of a 3 × 3 pixel matrix with toner, the predetermined number is sequentially increased, and the high density area becomes a solid image from the low density area. A toner pattern having a plurality of levels of density is formed in the intermediate density area up to this point. This makes it possible to control the amount of toner attached to the intermediate density region.

  Therefore, by using both the high-density detection toner pattern and the halftone density detection toner pattern, it is possible to maintain the density of the entire image at a constant level and output the image properly.

  The image density correction performed by the image density correction means (not shown) in the color electrophotographic apparatus having the above configuration will be specifically described based on the process control flowchart shown in FIG.

  As shown in the figure, first, it is determined whether or not the condition for executing the image density correction is determined (S1). If the condition for executing the image density correction is satisfied, the calibration of the density detection sensor 10 is performed. (S2) High density correction is performed (S3).

  This high density correction will be described in detail.

  First, the photosensitive drum 1 is charged, exposed, and developed. At this time, a predetermined high-density detecting toner pattern of each color described later is formed on each of the photosensitive drums 1 by changing a developing bias. The formed plurality of high density detection toner patterns of each color are transferred to the transfer belt 7. These high-density detection toner patterns are sequentially measured by the density detection sensor 10 to determine a correction amount.

  Here, at the time of color high-density correction, the following three types of 100% solid patterns are formed on the transfer belt 7 by changing the developing bias through charging, exposure, development, and transfer processes. You.

v1: Low voltage (becomes -50 V with respect to the previously set developing bias)
v2: Reference voltage (development bias set last time)
v3: High voltage (+50 V with respect to the previously set developing bias)
Next, these high-density detecting toner patterns are sequentially measured by the density detecting sensor 10, and the optical density is detected from each measurement result. Then, as shown in FIG. 4A, a developing bias which connects three points with a straight line and intersects with the reference sensor value is employed. In FIG. 7A, the reference sensor value is, for example, 2.4V. In FIG. 9A, the reference voltage as a reference value of the developing bias set last time is -300V.

  Next, at the time of black high-density correction, an 80% solid pattern is formed on the transfer belt 7 through charging, exposure, development, and transfer by changing the developing bias as described below. The reason why the 80% solid pattern is used is that the reflected light is weakened with the 100% solid pattern and cannot be detected.

v1 ': Low voltage (becomes -50 V with respect to the previously set developing bias)
v2 ': reference voltage (development bias set last time)
v3 ': High voltage (+50 V with respect to the previously set developing bias)
Next, these toner patterns are sequentially measured by the density detection sensor 10, and the optical density is detected from each measurement result by the following equation (1).

Density = Reflectance of toner pattern / Reflectance on transfer belt (1)
Then, as shown in FIG. 4 (b), the three points are connected by a straight line, and here a developing bias having a value obtained by dividing the developing bias crossing the reference sensor value of 1V by 0.8 is used as a certain value. . By using the above equation (1), the reflectance of the transfer belt 7 is standardized, and the density can be read stably.

  Next, in the present embodiment, the halftone density correction is not always performed when the high density correction is performed, but the execution condition determination of the halftone density correction is performed as shown in FIG. 1 (S4). ), Halftone density correction is performed only when this execution condition is met.

  The reason for this is that the halftone density correction requires forming a plurality of halftone density detection toner patterns for each color, and the correction time and toner consumption are problematic, so the number of operations and timing are important.

  In the present embodiment, as shown in FIG. 1, halftone density correction is executed only when the difference between the development bias set at the time of the previous high density correction and the development bias set this time exceeds the difference reference value. I have to.

  That is, in this embodiment, the result of the current high-density correction, that is, the developing bias voltage value determined by the current high-density correction, and the result of the previous high-density correction, that is, the developing bias voltage determined by the previous high-density correction The voltage value is compared, and the halftone density is continuously corrected only when the difference is equal to or greater than a preset difference reference value.

  Further, in the present embodiment, for example, a developing bias of ± 50 V is used as the difference reference value, and the halftone density correction is performed only when the developing bias becomes ± 50 V or more. When the difference reference value is equal to or more than ± 50 V, it is based on the determination that it is appropriate to perform the halftone density correction together with the high density correction, but is not necessarily limited to ± 50 V.

  In the above-mentioned halftone density correction, as shown in FIG. 1, in the course of charging, exposure, development and transfer, a plurality of halftone density detections having different densities are performed by modulating the pulse width of a laser at the time of exposure. The toner pattern for each color is formed on the transfer belt 7 for each color (S5), and these toner patterns for halftone density detection are sequentially measured by the density detection sensor 10 (S6), and the laser PMW (Pulse (Wave Modulation) value is calculated and the optical density is detected (S7). The detection method is the same as the detection method used for the high density correction described above.

  Next, a comparison is made with a plurality of pre-set and stored halftone density reference values, the amount of change between the halftone density reference value and the current value is calculated, and the halftone density correction table is corrected (S8). . The halftone density is corrected based on the halftone density correction table. The table of the halftone density reference values is created at the time of maintenance.

  More specifically, as shown in FIG. 5, when the laser duty is a laser output, the detection value of the density detection sensor 10 is A ', and the halftone density reference value is B. When で, the laser duty A is changed to the laser duty B to secure the halftone density reference value B 'as a sensor value and maintain the image density.

  As a result, the image density can be kept constant even for the halftone density.

  In the determination of the execution condition of the intermediate correction density in S4, when the difference reference value is less than 50 V, the image is output without performing the halftone correction.

  The timing for performing the high density correction and the halftone density correction will be described with reference to FIG.

  First, in FIG. 6, when the color electrophotographic apparatus is started, the initial high density reference value has a developing bias voltage value of -300V.

  Here, at time t1, high density correction was performed, and the correction result was a developing bias voltage value of -320V. At this time, ΔV is 20 V with respect to the previous development density voltage value of −300 V, which is the high density reference value, and the halftone density correction is not performed because the difference reference value of 50 V or more is not satisfied.

  Next, at time t2, high density correction was performed again. As a result, the developing bias voltage value was -260 V, and the previous correction result was adopted as the high density reference value, and the developing bias voltage value was -60 V with respect to the developing bias voltage value of -320 V as the high density reference value.

  For this reason, since the increase satisfies the condition that the difference reference value is 50 V or more, halftone density correction is performed.

  Next, at time t3, high density correction was performed again. However, at this time, the developing bias voltage value is -270 V, which is .DELTA.10 V with respect to the developing bias voltage value of -260 V, which is the previous high density reference value, and the difference reference value of 50 V or more is not satisfied. No correction was made.

  Next, at time t4, high density correction was performed again. As a result, the developing bias voltage value became -320 V, and became? 50 V with respect to the developing bias voltage value of -270 V which was the previous high density reference value. For this reason, since the increase satisfies the condition that the difference reference value is 50 V or more, halftone density correction is performed.

  As described above, the above-described correction method focuses on a point that when the density characteristic with respect to the developing bias largely changes, the density characteristic with respect to the laser output is also likely to change.

  As a result, the density of the entire image can be always kept constant by automatically correcting the halftone density while keeping the high density constant. Further, by determining the presence or absence of the halftone density correction operation from the result of the maximum density correction, the halftone density correction operation can be performed effectively and without waste, so that the density correction time can be shortened and the toner consumption during the density correction can be reduced. It leads to reduction.

  Further, when correcting the density of a color image, in the present embodiment, the high density reference value is compared with the result of the current high density correction, and only when the difference is equal to or greater than the difference reference value for at least one color, The halftone density of the color is corrected.

  Therefore, even when halftone density correction is required for only one color, it is possible to accurately maintain color balance by correcting all halftone densities.

  As described above, in the color electrophotographic apparatus of the present embodiment, in order to maintain a constant image density, a predetermined high-density detection is performed while changing the developing bias on the photosensitive drum 1 to perform high-density correction. A toner pattern is formed. Then, the value detected by the density detection sensor 10 for the high density detection toner pattern is compared with a high density reference value to determine a high density correction amount. Further, a predetermined halftone density detecting toner pattern is formed on the photosensitive drum 1 while changing the developing bias in order to correct the halftone density. The correction value of the halftone density is determined by comparing the detected value with the halftone density reference value. Further, these operations are performed by an image density correction unit (not shown).

  As a result, the density of the entire image can be always kept constant by automatically correcting the halftone density while keeping the high density constant.

  Here, the image density correction means adopts the result of the previous high density correction as the high density reference value, compares the high density reference value with the result of the current high density correction, and sets the difference in advance. Only when the difference is equal to or greater than the difference reference value, the laser output at the time of exposure is adjusted to raise or lower the surface potential of the photosensitive drum 1 to correct the halftone density.

  That is, each time the high density correction is performed, the high density reference value is updated to the result of the high density correction. Then, the result of the current high density correction is compared with the updated high density reference value.

  On the other hand, the correction of the halftone density is not performed every time the high density correction is performed, but the updated high density reference value is compared with the result of the current high density correction, and the difference is set as a predetermined difference reference. It continues only when the value is greater than or equal to the value.

  As a result, the presence or absence of the halftone density correction operation is determined from the result of the high density correction, and the halftone density correction operation is performed based on the result, leading to a reduction in the density correction time and a reduction in toner consumption during the density correction. .

  The presence or absence of the halftone density correction operation is determined by comparing the updated high density reference value with the result of the current high density correction and determining whether the difference is equal to or greater than a preset difference reference value.

  Therefore, the halftone density correction is performed only when there is a large deviation from the updated high density reference value. Therefore, since the halftone density correction is performed only when it is really necessary, the efficiency is high.

  Further, since the high density reference value is updated each time high density correction is performed, the input image can be changed in response to a change in density characteristics in the current situation due to an applied voltage such as charging, exposure, and development in an electrophotographic process or a rise in temperature. Data density characteristics can be corrected and output.

  As a result, the time required for density correction can be shortened, and the amount of toner used for correction can be reduced while the density output of the entire image is kept constant according to the type of image such as solid, line, or halftone. An image forming apparatus can be provided.

  On the other hand, in the case of a color image, since there are Y (yellow), M (magenta), C (cyan), and Bk (black) color toners, halftone density correction is performed every time high density correction is performed. If the processing is executed, the time is significantly increased as compared with the monochrome density correction time. For this reason, the user is further waited, which causes a problem that the usability is not good.

  However, in the present embodiment, when the density correction of the color image is performed, the image density correction unit compares the high density reference value with the result of the current high density correction, and determines that at least one color has a difference reference value or more. Only after that, the correction of the halftone density of all the colors is continuously performed.

  Therefore, since the correction of the halftone density of all the colors is continuously performed only when the difference is equal to or more than the difference reference value for at least one color, the density correction time is shortened and the toner consumption is reduced.

  Further, image density correction in a multicolor image forming apparatus plays an important role in determining color balance. Therefore, even when halftone density correction is required for only one color, it is possible to accurately maintain color balance by correcting all halftone densities.

  As a result, in a color image, the time required for density correction can be reduced while the density output of the entire image is kept constant according to the type of the image such as solid, line, or halftone, and the amount of toner consumed during correction is reduced. And an image forming apparatus capable of reducing image quality.

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIGS. For convenience of description, members having the same functions as those shown in the drawings of the first embodiment are given the same reference numerals, and descriptions thereof will be omitted.

  In the color electrophotographic apparatus according to the present embodiment, as in the first embodiment, whether or not to perform the halftone density correction operation is determined based on the result of the maximum density correction. The method is different from that of the first embodiment.

  That is, in the color electrophotographic apparatus of the present embodiment, the result of the high density correction when the halftone density correction is executed last is set as the high density reference value, and the high density reference value and the result of the current high density correction are used. , And the halftone density is continuously corrected only when the difference is equal to or larger than a preset difference reference value.

  The image density correction in the color electrophotographic apparatus having the above configuration will be specifically described based on a process control flowchart shown in FIG. The same steps as those in FIG. 1 of the first embodiment are denoted by the same step numbers, and description thereof is omitted.

  As shown in the figure, first, after executing the high-density correction (S3), a determination is made as to whether or not to execute the half-tone density correction (S14).

  In the present embodiment, as a condition for executing the halftone density, the high density developing bias voltage value set at the previous halftone density correction is used as the high density reference value, and the difference between the high density reference value and the currently set developing bias value is set. Is adjusted to be equal to or greater than the difference reference value (± 50 V in this case).

  The subsequent halftone density correction method is the same as the flowchart shown in FIG.

  This makes it possible to keep the density of the entire image constant by automatically correcting the halftone density while keeping the high density constant. Further, by determining the presence or absence of the halftone density correction operation from the result of the maximum density correction, the halftone density correction operation can be performed effectively and without waste, so that the density correction time can be shortened and the toner consumption during the density correction can be reduced. It leads to reduction.

  A specific example of the timing of the high density correction and the halftone density correction will be described with reference to FIG.

  First, in FIG. 8, at the first time t0 when the color electrophotographic apparatus is started, the developing bias voltage value of the high density reference value is -300V. In this case, since this is the initial state, halftone density correction is also performed.

  Next, at times t1, t2, t3, and t4, high density correction was performed, and the high density reference values were set to developing bias voltage values of -320V, -310V, -330V, and -340V, respectively. However, in these cases, the value is less than Δ50 V with respect to the developing bias voltage value of −300 V, which is the initial high density reference value, and does not satisfy the condition that the difference reference value is 50 V or more. Therefore, no halftone density correction is performed.

  Next, at time t5, high-density correction was performed again. As a result, the developing bias voltage value became -350 V, which was equal to or more than [Delta] 50 V with respect to the initial high-density reference value of -300 V. For this reason, since the increase satisfies the condition that the difference reference value is 50 V or more, halftone density correction is performed.

  Next, at times t6 and t7, the high density correction is performed again. In this case, the developing bias voltage value -350V, which is the high density reference value when the last halftone density is corrected (time t5). Is less than Δ50 V, and does not satisfy the condition that the difference reference value is 50 V or more. Therefore, no halftone density correction is performed.

  Next, at time t8, high density correction was performed again. As a result, the developing bias voltage value becomes -290 V, and the correction result when the last halftone density is corrected (time t5) becomes the high density reference value. It became Δ60V. Therefore, since the increase satisfies the condition that the difference reference value is 50 V or more, the halftone density correction is performed.

  As described above, in the color electrophotographic apparatus of the present embodiment, the image density correction unit compares the high density reference value with the result of the current high density correction, and determines that the difference is equal to or larger than the preset difference reference value. Then, the correction of the halftone density is continuously performed only when the threshold value is reached.

  That is, the correction of the halftone density is not performed each time the high density correction is performed, but the high density reference value set initially and the result of the current high density correction are compared, and the difference is set in advance. It is continued only when the difference reference value is exceeded.

  Therefore, the presence or absence of the halftone density correction operation is determined from the result of the high density correction, and the halftone density correction operation is performed based on the result, which leads to a reduction in the density correction time and a reduction in toner consumption during the density correction.

  The presence or absence of the halftone density correction operation is determined by comparing the high density reference value with the result of the current high density correction, and determining whether the difference is equal to or greater than a preset difference reference value.

  Therefore, the halftone density correction is performed only when there is a large deviation from the high density reference value. Therefore, since the halftone density correction is performed only when it is really necessary, the efficiency is high.

  Furthermore, when the initially set high density reference value is to be used thereafter without changing the high density reference value, charging, exposure, application voltage for development, etc. based on the initially set high density reference value for the toner, The density characteristic of the input image data is corrected and output according to the change in the density characteristic due to the temperature rise.

  Therefore, the density characteristics of the input image data can be corrected and output in accordance with the ideal density characteristics.

  As a result, the time required for density correction can be shortened, and the amount of toner used for correction can be reduced while the density output of the entire image is kept constant according to the type of image such as solid, line, or halftone. An image forming apparatus can be provided.

  Further, in the color electrophotographic apparatus according to the present embodiment, the image density correction unit adopts the result of the high density correction when the halftone density correction was executed last as the high density reference value, and The result of the high-density correction is compared with the result of the present high-density correction, and the correction of the halftone density is continuously performed only when the difference is equal to or larger than a preset difference reference value.

  That is, the result of the current high-density correction is compared with the high-density reference value that is the result of the high-density correction when the halftone density correction was executed last.

  In addition, the correction of the halftone density is not performed every time the high density correction is performed, but the high density reference value which is the result of the high density correction when the halftone density correction is executed last and the current high density correction. The comparison is made with the result, and only when the difference is equal to or larger than the preset difference reference value, the operation is continued.

  Therefore, the presence or absence of the halftone density correction operation is determined from the result of the high density correction, and the halftone density correction operation is performed based on the result, which leads to a reduction in the density correction time and a reduction in toner consumption during the density correction.

  Also, the presence or absence of the halftone density correction operation is determined by comparing the high density reference value, which is the result of the high density correction when the halftone density correction was executed last, with the result of the current high density correction. The determination is made based on whether the difference is equal to or larger than a preset difference reference value.

  Therefore, the halftone density correction is performed only when there is a large deviation from the high density reference value. Therefore, since the halftone density correction is performed only when it is really necessary, the efficiency is high.

  Further, since the high density reference value is updated to the result of the high density correction when the halftone density correction was executed last, even if the toner has deteriorated, it is determined in the electrophotographic process according to the deterioration state of the toner. The density characteristics of the input image data can be corrected and output in response to fluctuations in the density characteristics due to an applied voltage such as charging, exposure, and development or a rise in temperature.

  As a result, the time required for density correction can be shortened, and the amount of toner used for correction can be reduced while the density output of the entire image is kept constant according to the type of image such as solid, line, or halftone. An image forming apparatus can be provided.

  Also, in the color electrophotographic apparatus of the present embodiment, when correcting the density of a color image, the high density reference value is compared with the result of the current high density correction, and at least one color has a difference reference value or more. Only when is the correction of the halftone density of all colors continued.

  Therefore, since the correction of the halftone density of all the colors is continuously performed only when the difference is equal to or more than the difference reference value for at least one color, the density correction time is shortened and the toner consumption is reduced.

  Further, image density correction in a multicolor image forming apparatus plays an important role in determining color balance. Therefore, even when halftone density correction is required for only one color, it is possible to accurately maintain color balance by correcting all halftone densities.

  As a result, in a color image, the time required for density correction can be reduced while the density output of the entire image is kept constant according to the type of the image such as solid, line, or halftone, and the amount of toner consumed during correction is reduced. And an image forming apparatus capable of reducing image quality.

[Embodiment 3]
The following will describe another embodiment of the present invention with reference to FIGS. For convenience of explanation, members having the same functions as those shown in the drawings of Embodiments 1 and 2 are given the same reference numerals, and descriptions thereof are omitted.

  In the present embodiment, a method of correcting a halftone density will be described in detail.

  First, the halftone density correction includes two steps, a first step and a second step. The first step is mainly for obtaining a low-density rising point and a high-density saturation point, and the second step is for obtaining detailed data of the points in order to perform an approximation process.

  In the first step, through the charging, exposure, development, and transfer processes, five types of halftone density detection toner patterns having different densities are formed on the transfer belt 7 while varying the laser duty of the exposure device 3. The values of the laser duty are, for example, 31, 47, 63, 79, 255. The laser duty has a value of 0 to 255.

  Next, these halftone density detection toner patterns are sequentially measured by the density detection sensor 10, and as shown in FIG. 9, a low density rising point and a high density saturation point are calculated from each measurement result.

  The calculation of the low concentration rising point and the high concentration saturation point is performed as follows.

  First, in the figure, a straight line Y = a passing through the output ratio a of the density detection sensor 10 at which the laser duty becomes 0, a straight line Y = b passing through the output ratio b of the density detection sensor 10 at which the laser duty becomes 255, For example, y = cx + d is obtained by approximating the four points 31, 47, 63, and 79 by the least square method.

  Note that the output ratio a of the density detection sensor 10 at which the laser duty becomes 0 is a fixed value that can be obtained without collecting data.

  Next, an intersection between the straight line Y = a and the straight line y = cx + d is set as a low density rising point, and an intersection between the straight line Y = b and the straight line y = cx + d is set as a high density saturation point.

  Next, a second step is performed.

  In the second step, 16 types of halftone density detection toner patterns are continuously formed on the transfer belt 7, and detailed data of the points obtained in the first step is obtained. For example, between the straight line Y = a and the straight line Y = b, data is collected for each laser duty 6. Therefore, these 16 types may be different from the laser duties 31, 47, 63, 79, 255 obtained in the first step, or may be common. In the vicinity of the inflection point between the low-density rising point and the high-density saturation point obtained in the first step, the pitch of the laser duty is reduced.

  Then, in the second step, as shown in FIG. 10, approximation processing is performed for each of two regions, a low-density region and a middle-high-density region, and these are connected later. Note that, here, the low density region is, for example, up to 40% of the density detection sensor output ratio, and the higher density region is a middle and high density region. However, it is not necessarily limited to this.

  Here, in the present embodiment, for example, 5% is set as a reference value in the low density region in order to prevent the instability of the sensor value near the low density rising point from affecting the output image. The approximation processing is performed by deleting the data of the toner pattern for halftone density detection of 5% or less.

  Therefore, in the present embodiment, the approximation process is performed only with the data of the toner pattern for halftone density detection from the point where the sensor value of the density detection sensor 10 starts to increase continuously, thereby further reducing the variation of the approximation line. Let me.

  Next, the halftone density curve obtained in this manner is compared with the target (initial) curve shown in FIG. 5 to calculate a correction amount, thereby correcting the halftone table.

  As a result, it is possible to output a high-quality image by correcting the halftone density in a short time.

  9 and 10 show the relationship between the laser duty in the color image and the output ratio of the irregularly-reflected sensor 10 in the color image. 4B, the detected value is a specularly reflected detection value from the density detection sensor 10, and as shown in FIG.

  As described above, in the color electrophotographic apparatus according to the present embodiment, the image density correction means detects a plurality of halftone density detections having different density levels from the low density area to the front of the high density area when correcting the halftone density. For the detection value of the low-density area, a detection value equal to or less than a preset low-density area deletion reference value is deleted, and the remaining plural values are deleted. Is corrected using a value that is linearly approximated using the detected value of.

  That is, when performing correction by comparing with the halftone density reference value, a plurality of halftone density detection toner patterns having different density levels from the low density area to the front of the high density area are formed, and these are detected. Is corrected by the value approximated linearly.

  Here, the detection value of the low-density area is generally disturbed in numerical values, and it is difficult to perform linear approximation processing. Therefore, in the present embodiment, at the time of the approximation processing, the detection value of the low-density area detection value that is equal to or less than the preset low-density area deletion reference value is deleted, and the linear detection is performed using the remaining plurality of detection values. Use the value approximated in general.

  As a result, it is possible to delete a detection value equal to or less than the preset low-density area deletion reference value and use an appropriate detection value for performing the linear approximation process, thereby improving the accuracy of the approximation process.

  Further, since a value approximated linearly is used, it is possible to prevent creation of an erroneous density conversion table.

  Further, the time can be greatly reduced as compared with the case where the density conversion table covering all gradations is created by performing the complementing process.

  Accordingly, the time required for density correction can be shortened while the density output of the entire image is reliably and accurately maintained at a constant level in accordance with the type of the image such as solid, line, or halftone, and a high-quality image is output. It is possible to provide an image forming apparatus capable of reducing the amount of toner used sometimes.

  On the other hand, how to set a low-density area deletion reference value in order to use an appropriate detection value for performing a linear approximation process is a problem.

  However, in the present embodiment, an inflection point of the detected value when the laser output is changed from the low side to the high side in a sequential manner is adopted. Specifically, a point where the detection value starts to continuously increase in a color image is adopted, while a point where the detection value starts to continuously decrease in a monochrome image is adopted.

  As a result, it is possible to reliably delete the detection value that is difficult to perform the linear approximation process in the low-density area, and to leave as many detection values appropriate for the linear approximation process as possible.

  As a result, the time required for density correction while maintaining the density output of the entire image efficiently, reliably and accurately according to the type of image such as solid, line, and halftone, and outputting a high-quality image. Can be provided, and the amount of toner used for correction can be reduced.

[Embodiment 4]
The following is a description of still another embodiment of the present invention. For convenience of explanation, members having the same functions as those shown in the drawings of the first to third embodiments are denoted by the same reference numerals, and description thereof is omitted.

  In the color electrophotographic apparatus according to the present embodiment, the image density correction unit (not shown) compares the result of the current high density correction with the high density reference value for each color, and the sum of all the differences is set in advance. The halftone density is continuously corrected only when the difference becomes equal to or more than the total difference reference value.

  That is, for each of the colors Y, M, C, and Bk, as shown in FIGS. 4A and 4B, high density correction is performed to correct the developing bias potential. Here, the high density reference value of the developing bias potential of each color is set to 300V.

  In this embodiment, the total difference reference value, which is the sum of the four colors of the difference between the correction result of the developing bias and the high density reference value, is set to 100 V, and the halftone density correction is performed at 100 V or more. It is supposed to be done.

  For example, in the current high-density correction, when the correction result of the developing bias potential is Y = 325 V, M = 345 V, C = 320 V, and Bk = 315 V, the difference from the high-density reference value is 25 V, respectively. 45V, 20V and 15V. At this time, it is considered that the color balance of the image has changed, and halftone correction is required.

  By the way, conventionally, when the difference between the correction result of the developing bias and the high density reference value exceeds 50 V even for one color, the halftone correction operation is performed.

  However, in the above example, the correction operation is not performed in the conventional method because the difference is 50 V or less for each color.

  On the other hand, in the present embodiment, in the above example, the total sum of the differences of the four colors is 105 V, and the total sum of the differences of the four colors is equal to or more than the total difference reference value of 100 V, so that the halftone density correction of each color is operated.

  Accordingly, when the presence or absence of the halftone density correction operation is determined by summing the correction amounts of the high density correction of each color, it is possible to more accurately determine when the color balance of the image is changing.

  As described above, in the color electrophotographic apparatus according to the present embodiment, the image density correction unit (not shown) compares the result of the current high density correction with the high density reference value for each color, and sums the differences for all colors. Is continuously corrected only when is equal to or larger than a preset total difference reference value.

  For this reason, the density of the entire image can always be kept constant by automatically correcting the halftone density while keeping the high density constant.

  In addition, by determining the presence or absence of the halftone density correction operation by summing up the correction amount of the high density correction of each color, it is possible to change the color balance of the image, instead of the change of the halftone density of a single color, for a multicolor image. You can judge more accurately when you are.

  As a result, the halftone density correction operation can be performed effectively and without waste in consideration of all colors, so that it is possible to shorten the density correction time and reduce toner consumption during the density correction while improving the image quality. it can.

[Embodiment 5]
The following is a description of still another embodiment of the present invention. For convenience of explanation, members having the same functions as those shown in the drawings of the above-described first to fourth embodiments are given the same reference numerals, and descriptions thereof are omitted.

  In the color electrophotographic apparatus according to the present embodiment, the image density correction unit (not shown) compares the result of the current high density correction with the high density reference value for each color, and only one monochrome color has a monochrome difference reference value or more. The correction of the halftone density is continued only when the color difference other than monochrome is reached or when the sum of the differences between the respective colors other than monochrome is equal to or greater than a preset color sum difference reference value. .

  That is, for each of the colors Y, M, C, and Bk, as shown in FIGS. 4A and 4B, high density correction is performed to correct the developing bias potential. Here, the high density reference value of the developing bias potential of each color is set to 300V.

  In the present embodiment, the difference between the correction result of the developing bias and the high density reference value is Bk, and the monochrome difference reference value is 40 V or the color sum of three colors is 80 V or more. Halftone density correction is performed.

  For example, assuming that the correction result of the developing bias potential becomes Y = 325 V, M = 345 V, C = 320 V, and Bk = 315 V by the high density correction, the difference between the high density reference value of Bk and the high density reference value is 15 V, and three colors are used. Is 90V.

  Accordingly, since only the total sum of the three colors exceeds the total color difference reference value of 80 V, the halftone density correction is performed only for the three colors.

  As described above, in the color electrophotographic apparatus according to the present embodiment, the image density correction unit (not shown) compares the result of the current high density correction with the high density reference value for each color, and determines that only one monochrome color has the monochrome difference reference value. The correction of the halftone density is continued only when the value is equal to or more than the value, or when the sum of the difference between each color except monochrome is equal to or more than the preset color sum difference reference value.

  For this reason, the density of the entire image can always be kept constant by automatically correcting the halftone density while keeping the high density constant.

  Also, the presence or absence of the halftone density correction operation is determined separately for monochrome and color colors other than monochrome, and then the halftone density correction operation is performed. The correction can be performed individually when the halftone density of the monochrome image changes.

  This makes it possible to perform the halftone density correction operation effectively and wastefully in consideration of monochrome or all colors other than monochrome when correction of only one of the color colors other than monochrome is required. In addition, it is possible to shorten the density correction time and reduce toner consumption during the density correction while improving the image quality.

[Embodiment 6]
Another embodiment of the present invention will be described below with reference to FIG. For convenience of explanation, members having the same functions as those shown in the drawings of the above-described first to fifth embodiments are denoted by the same reference numerals, and description thereof is omitted.

  In the color electrophotographic apparatus according to the present embodiment, the image density correction unit (not shown) compares the result of the current high density correction with the high density reference value for each color, and calculates the absolute value of the difference between each color. The halftone density is continuously corrected only when the sum is equal to or larger than a preset absolute value sum difference reference value.

  That is, for each of the colors Y, M, C, and Bk, as shown in FIGS. 4A and 4B, high density correction is performed to correct the developing bias potential. Here, the high density reference value of the developing bias potential of each color is set to 300V.

  In the present embodiment, the halftone density correction is performed when the sum of the four colors of the absolute value of the difference between the correction result of the developing bias and the reference value is equal to or greater than the absolute value total difference reference value 100 V.

  For example, when the correction result of the developing bias potential becomes Y = 325 V, M = 345 V, C = 280 V, and Bk = 285 V by the high density correction, the differences from the high density reference value are 25 V, 45 V, and −20 V, respectively. -15V.

  At this time, a change in the density of the entire image is predicted as shown in FIG. When the summation is performed as described in the fourth embodiment, the sum is 35 V, and the halftone correction operation is not performed.

  On the other hand, in the present embodiment, when the sum of the differences from the high-density reference value is set as the absolute value, the sum is 105 V. Therefore, since the sum of the absolute values of the four colors is equal to or more than the absolute value sum difference reference value 100 V, the halftone density correction of each color is operated.

  As described above, in the color electrophotographic apparatus according to the present embodiment, the image density correction unit (not shown) compares the result of the current high density correction with the high density reference value for each color, and calculates the absolute value of the difference between the colors. The halftone density correction is continued only when the total sum of all the colors is equal to or larger than the preset absolute value total difference reference value.

  For this reason, the density of the entire image can always be kept constant by automatically correcting the halftone density while keeping the high density constant.

  In addition, when the correction amount of the high-density correction is summed for each color, even if the correction result differs for each color in the positive direction and the negative direction with respect to the high-density reference value, the difference between each high-density reference value and By summing the absolute values, it is possible to accurately determine when the color balance of the multicolor image has changed.

  As a result, the halftone density correction operation can be performed effectively and without waste in consideration of all colors, so that it is possible to shorten the density correction time and reduce toner consumption during the density correction while improving the image quality. it can.

  The present invention can be configured as follows.

  A predetermined high-density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the high-density detection toner pattern is compared with a high-density reference value to determine a high-density correction amount. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the halftone density detection toner pattern is compared with a halftone density reference value. In an image forming apparatus having an image density correcting means for determining a correction amount of a halftone density, the image density correcting means adopts a result of the previous high density correction as a high density reference value, and An image forming apparatus characterized in that the result of the high density correction is compared with the current result, and the halftone density is continuously corrected only when the difference is equal to or greater than a preset difference reference value.

  According to the above-described invention, a predetermined high-density detection toner pattern is formed on the photoconductor in order to perform high-density correction in order to maintain a constant image density. Then, the value detected by the reflection type sensor for the high density detection toner pattern is compared with a high density reference value to determine a high density correction amount. In addition, a predetermined halftone density detection toner pattern is formed on the photoreceptor to correct the halftone density, and the halftone density detection toner pattern is detected by a reflection type sensor and the halftone density reference value. And the correction amount of the halftone density is determined. Further, these operations are performed by an image density correction unit.

  As a result, the density of the entire image can be always kept constant by automatically correcting the halftone density while keeping the high density constant.

  Here, the image density correction means adopts the result of the previous high density correction as the high density reference value, compares the high density reference value with the result of the current high density correction, and sets the difference in advance. The correction of the halftone density is continuously performed only when the difference is equal to or larger than the difference reference value.

  That is, each time the high density correction is performed, the high density reference value is updated to the result of the high density correction. Then, the result of the current high density correction is compared with the updated high density reference value.

  On the other hand, the correction of the halftone density is not performed every time the high density correction is performed, but the updated high density reference value is compared with the result of the current high density correction, and the difference is set as a predetermined difference reference. It continues only when the value is greater than or equal to the value.

  As a result, the presence or absence of the halftone density correction operation is determined from the result of the high density correction, and the halftone density correction operation is performed based on the result, leading to a reduction in the density correction time and a reduction in toner consumption during the density correction. .

  The presence or absence of the halftone density correction operation is determined by comparing the updated high density reference value with the result of the current high density correction and determining whether the difference is equal to or greater than a preset difference reference value.

  Therefore, the halftone density correction is performed only when there is a large deviation from the updated high density reference value. Therefore, since the halftone density correction is performed only when it is really necessary, the efficiency is high.

  Further, since the high density reference value is updated each time high density correction is performed, the input image can be changed in response to a change in density characteristics in the current situation due to an applied voltage such as charging, exposure, and development in an electrophotographic process or a rise in temperature. Data density characteristics can be corrected and output.

  As a result, the time required for density correction can be shortened, and the amount of toner used for correction can be reduced while the density output of the entire image is kept constant according to the type of image such as solid, line, or halftone. An image forming apparatus can be provided.

  In the above-described image forming apparatus, the image density correction unit adopts a result of the high density correction when the halftone density correction is executed last as a high density reference value, and determines the high density reference value and the current high density reference value. The result of the density correction may be compared, and the halftone density may be continuously corrected only when the difference is equal to or greater than a preset difference reference value.

  According to the above invention, the image density correction means adopts the result of the high density correction when the halftone density correction was executed last as the high density reference value, and uses the high density reference value and the current high density correction value. The results are compared with each other, and the correction of the halftone density is continuously performed only when the difference is equal to or larger than a preset difference reference value.

  That is, the result of the current high-density correction is compared with the high-density reference value that is the result of the high-density correction when the halftone density correction was executed last.

  In addition, the correction of the halftone density is not performed every time the high density correction is performed, but the high density reference value which is the result of the high density correction when the halftone density correction is executed last and the current high density correction. The comparison is made with the result, and only when the difference is equal to or larger than the preset difference reference value, the operation is continued.

  Therefore, the presence or absence of the halftone density correction operation is determined from the result of the high density correction, and the halftone density correction operation is performed based on the result, which leads to a reduction in the density correction time and a reduction in toner consumption during the density correction.

  Also, the presence or absence of the halftone density correction operation is determined by comparing the high density reference value, which is the result of the high density correction when the halftone density correction was executed last, with the result of the current high density correction. The determination is made based on whether the difference is equal to or larger than a preset difference reference value.

  Therefore, the halftone density correction is performed only when there is a large deviation from the high density reference value. Therefore, since the halftone density correction is performed only when it is really necessary, the efficiency is high.

  Further, since the high density reference value is updated to the result of the high density correction when the halftone density correction was executed last, even if the toner has deteriorated, it is determined in the electrophotographic process according to the deterioration state of the toner. The density characteristics of the input image data can be corrected and output in response to fluctuations in the density characteristics due to an applied voltage such as charging, exposure, and development or a rise in temperature.

  As a result, the time required for density correction can be shortened, and the amount of toner used for correction can be reduced while the density output of the entire image is kept constant according to the type of image such as solid, line, or halftone. An image forming apparatus can be provided.

  In the image forming apparatus described above, the image density correction unit compares a high density reference value with a result of the current high density correction when density correction of a color image is performed. The correction of the halftone density of all the colors may be continuously performed only when it becomes true.

  That is, in the case of a color image, since there are toners of Y (yellow), M (magenta), C (cyan), and Bk (black), halftone density correction is performed every time high density correction is performed. If the processing is executed, the time greatly increases as compared with the monochrome density correction time. For this reason, the user is further waited, which causes a problem that the usability is not good.

  However, the image density correction means compares the high density reference value with the result of the current high density correction when density correction of a color image is performed. The halftone density of the color is corrected.

  Therefore, since the correction of the halftone density of all the colors is continuously performed only when the difference reference value is equal to or more than at least one color, the time required for the density correction in the color image is shortened and the toner consumption is reduced.

  Further, image density correction in a multicolor image forming apparatus plays an important role in determining color balance. Therefore, even when halftone density correction is required for only one color, it is possible to accurately maintain color balance by correcting all halftone densities.

  As a result, in a color image, the time required for density correction can be reduced while the density output of the entire image is kept constant according to the type of the image such as solid, line, or halftone, and the amount of toner consumed during correction is reduced. And an image forming apparatus capable of reducing image quality.

  A predetermined high-density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the high-density detection toner pattern is compared with a high-density reference value to determine a high-density correction amount. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the halftone density detection toner pattern is compared with a halftone density reference value. In an image forming apparatus having an image density correction unit for determining a correction amount of a halftone density, the image density correction unit compares a result of the current high density correction with a high density reference value for each color, and calculates a difference between the results. Wherein the halftone density is continuously corrected only when the total sum of all the colors is equal to or greater than a preset total difference reference value.

  According to the invention described above, the image density correction unit compares the result of the current high density correction with the high density reference value for each color, and determines that the sum of all the differences is equal to or greater than a preset total sum difference reference value. Then, the correction of the halftone density is continuously performed only when the threshold value is reached.

  For this reason, the density of the entire image can always be kept constant by automatically correcting the halftone density while keeping the high density constant.

  In addition, by determining the presence or absence of the halftone density correction operation by summing up the correction amount of the high density correction of each color, it is possible to change the color balance of the image, instead of the change of the halftone density of a single color, for a multicolor image. You can judge more accurately when you are.

  As a result, the halftone density correction operation can be performed effectively and without waste in consideration of all colors, so that it is possible to shorten the density correction time and reduce toner consumption during the density correction while improving the image quality. it can.

  A predetermined high-density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the high-density detection toner pattern is compared with a high-density reference value to determine a high-density correction amount. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the halftone density detection toner pattern is compared with a halftone density reference value. In an image forming apparatus having an image density correction unit that determines a correction amount of a halftone density, the image density correction unit compares a result of the current high density correction with a high density reference value for each color to obtain a monochrome monochromatic image. Only when the color difference is equal to or greater than the monochrome difference reference value, or when the sum with the difference of each color other than monochrome is equal to or greater than the preset color sum difference reference value. Image forming apparatus is characterized by performing correction between tone density.

  According to the above invention, the image density correction unit compares the result of the current high density correction with the high density reference value for each color, and determines whether only one monochrome has a monochrome difference reference value or more, or The halftone density correction is continued only when one of the sums of the differences between the respective colors except for the color difference exceeds a preset color sum difference reference value.

  For this reason, the density of the entire image can always be kept constant by automatically correcting the halftone density while keeping the high density constant.

  Also, the presence or absence of the halftone density correction operation is determined separately for monochrome and color colors other than monochrome, and then the halftone density correction operation is performed. The correction can be performed individually when the halftone density of the monochrome image changes.

  This makes it possible to perform the halftone density correction operation effectively and wastefully in consideration of monochrome or all colors other than monochrome when correction of only one of the color colors other than monochrome is required. In addition, it is possible to shorten the density correction time and reduce toner consumption during the density correction while improving the image quality.

  A predetermined high-density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the high-density detection toner pattern is compared with a high-density reference value to determine a high-density correction amount. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the halftone density detection toner pattern is compared with a halftone density reference value. In an image forming apparatus having an image density correction unit that determines a correction amount of a halftone density, the image density correction unit compares the result of the current high density correction with a high density reference value for each color, and An image forming apparatus characterized in that the halftone density is continuously corrected only when the sum of all the colors at the absolute value of the difference is equal to or greater than a preset absolute value sum difference reference value.

  According to the above invention, the image density correction means compares the result of the current high density correction with the high density reference value for each color, and the total sum of all colors at the absolute value of the difference between the colors is set in advance. The correction of the halftone density is continuously performed only when the difference is equal to or larger than the value sum difference reference value.

  For this reason, the density of the entire image can always be kept constant by automatically correcting the halftone density while keeping the high density constant.

  In addition, when the correction amount of the high-density correction is summed for each color, even if the correction result differs for each color in the positive direction and the negative direction with respect to the high-density reference value, the difference between each high-density reference value and By summing the absolute values, it is possible to accurately determine when the color balance of the multicolor image has changed.

  As a result, the halftone density correction operation can be performed effectively and without waste in consideration of all colors, so that it is possible to shorten the density correction time and reduce toner consumption during the density correction while improving the image quality. it can.

FIG. 3 shows an embodiment of a color electrophotographic apparatus according to the present invention, in which the result of the previous high-density correction is adopted as a high-density reference value, and the high-density reference value is compared with the result of the present high-density correction. 9 is a flowchart showing an operation of continuously correcting the halftone density only when the difference is equal to or larger than a preset difference reference value. FIG. 2 is a configuration diagram illustrating an outline of an image processing unit in the color electrophotographic apparatus. FIG. 3 is a configuration diagram illustrating a density detection sensor for detecting a high density detection toner pattern or a halftone density detection toner pattern in the color electrophotographic apparatus. FIGS. 4A and 4B show a state in which density correction is performed by a density detection sensor in the color electrophotographic apparatus, wherein FIG. 4A is an explanatory diagram for correcting a color image to high density, and FIG. FIG. FIG. 3 is an explanatory diagram illustrating a state in which halftone correction is performed in the color electrophotographic apparatus. FIG. 3 is an explanatory diagram showing timings at which high density correction and halftone density correction are performed in the color electrophotographic apparatus. FIG. 14 shows another embodiment of the color electrophotographic apparatus according to the present invention, in which the result of the high density correction when the halftone density correction is executed last is adopted as the high density reference value, and the high density reference value is used. 9 is a flowchart illustrating an operation of comparing the result of the high-density correction and the result of the current high-density correction, and continuously correcting the halftone density only when the difference is equal to or greater than a preset difference reference value. FIG. 3 is an explanatory diagram showing timings at which high density correction and halftone density correction are performed in the color electrophotographic apparatus. FIG. 9 shows still another embodiment of the color electrophotographic apparatus according to the present invention. In correcting a halftone density, as a first step, five types of toner patterns for halftone density detection are formed to reduce the density. FIG. 9 is an explanatory diagram illustrating a state in which a density rising point and a high density saturation point are calculated. In the above color electrophotographic apparatus, when correcting the halftone density, as a second step, 16 types of halftone density detection toner patterns are formed in order to perform an approximate process of the halftone density by the least square method. FIG. 4 is an explanatory diagram illustrating a state in which data is collected. FIG. 13 shows still another embodiment of the color electrophotographic apparatus according to the present invention, which is used only when the sum of all colors at the absolute value of the difference between the respective colors is equal to or larger than a preset absolute value sum difference reference value. FIG. 9 is an explanatory diagram showing a change in density (ID: image density) of each color when the halftone density is subsequently corrected. FIG. 9 is a conceptual diagram illustrating a conventional color electrophotographic apparatus and illustrating a density correction operation determination. FIG. 4 is an explanatory diagram showing a change in a density curve due to replacement of a member in the color electrophotographic apparatus.

Explanation of reference numerals

1 Photoconductor drum (photoconductor)
4 Developing device 7 Transfer belt 10 Density detection sensor (reflective sensor)
11 light emitting element 12 diffuse reflection light receiving element 13 regular reflection light receiving element

Claims (4)

A predetermined high-density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the high-density detection toner pattern is compared with a high-density reference value to determine a high-density correction amount. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoreceptor, and a value detected by the reflection type sensor for the halftone density detection toner pattern is compared with a halftone density reference value. In an image forming apparatus having an image density correction unit that determines a correction amount of a halftone density,
The image density correcting means forms a plurality of halftone density detecting toner patterns having different density levels from the low density area to the front of the high density area and corrects the halftone density reference value when correcting the halftone density. On the other hand, the detection value of the low-density area is deleted by comparing the detection value that is equal to or less than the preset low-density area deletion reference value, and the correction is performed using a value obtained by performing an approximation process using the remaining plurality of detection values. An image forming apparatus comprising:   The image density correction unit employs an inflection point of a detection value when the laser output is sequentially changed from a low side to a high side as a low-density area deletion reference value when performing approximation processing on the low-density area. The image forming apparatus according to claim 1, wherein:   The image density correction means compares the high density reference value with the result of the high density correction, and performs the halftone density correction only when the difference is equal to or greater than a preset difference reference value. The image forming apparatus according to claim 1, wherein: 2. The image forming apparatus according to claim 1, wherein the image density correction unit performs the correction using a value approximated linearly.

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