JP4008418B2 - Image forming apparatus - Google Patents

Description

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

  As shown in FIG. 2, which is an explanatory diagram of the present invention, the color electrophotographic apparatus includes a plurality of photosensitive drums 1 that are rotatably supported. Each photosensitive drum 1 is driven in the direction of an arrow by a driving device. Are driven to rotate.

  Further, around the photosensitive drum 1, in order, a charging device 2 that uniformly charges the surface of the photosensitive drum 1, an exposure unit 3 that exposes the surface of the photosensitive drum 1 to form a latent image, and a latent image thereof. A developing device 4 that develops an image to form a toner image, a transfer device 5 that transfers the toner image to a transfer material, and a cleaning device 6 that cleans the toner remaining on the surface of the photosensitive drum 1 are disposed.

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

  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, which is 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 such an electrophotographic apparatus such as a color electrophotographic apparatus, the density characteristics fluctuate with respect to the applied voltage and temperature rise in charging, exposure, development, etc. in the electrophotographic process. In general, the density characteristic of data is corrected and output.

  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 whenever 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 the 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 image output is performed.

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

  However, in the conventional image forming apparatus, since the solid image density or toner adhesion amount is detected and the toner adhesion amount on the photosensitive drum 1 is controlled, the density output of the entire image is output according to the type of image. There is a problem that it cannot be made constant.

  In order to solve this problem, for example, there is an image forming apparatus disclosed in JP-A-8-265571 (Patent Document 1).

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

  Then, by detecting the high density detection toner pattern by the toner amount detection means comprising a reflection type sensor, the density correction means controls the maximum toner adhesion amount on the photosensitive drum, and the toner amount detection means By detecting the halftone density detection toner pattern, the density correction unit adjusts and controls the toner adhesion amount on the photosensitive drum with respect to the halftone density portion. By combining the control of the maximum toner adhesion amount by the high density detection toner pattern and the toner adhesion amount control to the halftone density portion by the halftone density detection toner pattern, the density of the entire image is kept constant. Yes.

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

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

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

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

  Therefore, in the conventional image forming apparatus, not only high density correction but also halftone density adjustment is performed, so that much time is required. As a result, the user is awaited as compared with only the high density correction, and the problem is that the usability is not good.

  Further, since not only high density correction but also halftone density adjustment is performed every time, there is a problem in that the amount of toner consumption for forming a toner pattern accompanying halftone density adjustment increases and the cost increases.

  Here, regarding the halftone density correction method, the technique disclosed in Japanese Patent Laid-Open No. 8-289148 will be described in detail. First, a reference first density conversion table is created during maintenance. Next, when actually outputting an image, a toner pattern is output for each predetermined number of copies, the density is measured, and the measured density is used as the second density conversion table. Next, a new density conversion table that is actually used is created based on the first density conversion table and the second density conversion table. In other words, the internal density results of the first density conversion table and the second density conversion table are used for the medium density area, and the predetermined inclination is referred to the adjacent medium density areas for the low and high density areas. 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 the photoconductor, developing unit, transfer unit sensor, and the like. Noise may be included due to various causes. In such a case, if the density conversion table is created assuming that the density of the detected toner pattern is always correct, an output image having an incorrect gradation density is generated. Also, the number of toner patterns is usually smaller than the number of gradations of the output image density, and a density conversion table for all gradations is created by various interpolation processes. However, if an incorrect density conversion table is created in this interpolation process, an output image with an incorrect gradation density is also generated.

  Further, if the interpolation process is performed precisely, a great amount of processing time is required, and there is a problem that it cannot be put into practical use.

  On the other hand, since a multicolor image is formed by superimposing single-color images, it is possible to determine the density of only one color among the colors as in the conventional method. It has the problem that it is difficult to determine the change in color balance.

  In other words, since the color balance of the entire color image varies greatly depending on the ambient temperature, humidity, and life modification of the members related to image formation, it is important to determine the color balance change of the entire color image and perform correction. Indispensable for expressing images.

  In addition, the image density also changes depending on the above-described variation factors regardless of whether it is a high density area or a halftone density area, and the fluctuation is often greatly different for each color.

  On the other hand, in the prior art, as shown in FIG. 12, only when the difference from each color reference density exceeds a certain value, that is, when the image density exceeds area A indicated by hatching and exists in area B, This is a method for determining the presence or absence of a correction operation based on a change in only one color for correction.

  However, as shown in FIG. 13, when the density change occurs in the density curve after the member replacement shown by the two-dot chain line from the density curve before the member replacement shown by the one-dot chain line, as shown in FIG. Change in the color balance of an image cannot be judged.

  That is, in the same figure, the density change of only one color is shown, but in actuality, each color changes variously depending on the ambient temperature, humidity, and the life characteristics of the member. Regarding the density change of each color, even if the difference from each reference density is small, the toner image is superimposed to express the color image of multiple colors, so that the color balance of the color image is reduced. Changes often occur.

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

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

  In order to solve the above problems, the image forming apparatus of the present invention forms a predetermined high density detection toner pattern on a photoconductor, and the high density detection toner pattern is detected by a reflection type sensor. While comparing with the density reference value to determine the correction amount for high density, a predetermined halftone density detection toner pattern is formed on the photoconductor, and this halftone density detection toner pattern is used as a reflective sensor. In the image forming apparatus having the image density correction unit that compares the detected value with the halftone density reference value and determines the correction amount of the halftone density, the image density correction unit corrects the halftone density. When performing, 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 compared with the halftone density reference value for correction. 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 above invention, the image density correction unit forms a plurality of halftone density detection toner patterns having different density levels from the low density area to the high density area before the halftone density correction. Compared with the adjustment density reference value, the correction is made, while for the detection value of the low density area, the detection value equal to or lower than the preset low density area deletion reference value is deleted, and the remaining plurality of detection values are used for linear correction. Correction is performed using the value approximated to.

  That is, when correcting 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 detected. Thus, for example, the correction is performed using a linearly approximated value.

  Here, the detection values in the low density region are generally disturbed in numerical values, and it is difficult to approximate them linearly. Therefore, in the present invention, in the approximation process, for the detection value of the low density region, the detection value equal to or lower than the preset low density region deletion reference value is deleted, and the remaining plurality of detection values are used, for example, in a linear manner. A value approximated by is used.

  As a result, it is possible to delete a detection value equal to or lower than a preset low density region deletion reference value and use a detection value appropriate for the approximation process, thereby improving the accuracy of the approximation process.

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

  Furthermore, the time can be significantly shortened as compared with the case where the density conversion table for all gradations is created by performing the complementary processing.

  Therefore, the time required for density correction can be shortened while correcting the density output of the whole image reliably and accurately and according to the type of image, such as solid, line, halftone, etc., and outputting a high quality image. It is possible to provide an image forming apparatus capable of reducing the amount of toner consumed sometimes.

  In order to solve the above problems, the image forming apparatus of the present invention is characterized in that, in the above image forming apparatus, the image density correcting means outputs a laser output as a low density area deletion reference value when performing approximation processing on the low density area. A feature is that an inflection point of a detected value is adopted when it is sequentially changed from a low side to a high side.

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

  However, in the present invention, the image density correction unit is configured to gradually change the laser output from the low side to the high side as a low density region deletion reference value for, for example, linearly approximating the low density region. The inflection point of the detected value at is adopted. Specifically, the point where the detection value starts to rise continuously is adopted in the color image, while the point where the detection value starts to fall continuously is adopted in the monochrome image.

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

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

  In order to solve the above problems, the image forming apparatus of the present invention is configured such that, in the above image forming apparatus, the image density correcting unit compares the high density reference value with the result of the high density correction, and the difference is obtained. 2. The image forming apparatus according to claim 1, wherein the halftone density is continuously corrected only when the difference difference value exceeds a preset difference reference value.

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

  That is, halftone density correction is not performed every time high density correction is performed, but the difference between the high density reference value and the result of high density correction is equal to or greater than a preset difference reference value. Only when continued.

  Therefore, the presence / 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 shortening of the density correction time and toner consumption at the time of density correction.

  The presence / 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, halftone density correction is performed only when there is a large deviation from the high density reference value. Therefore, halftone density correction is performed only when it is really necessary, so that efficiency is good.

  In addition, when the high density reference value is not changed, the input image corresponding to fluctuations in density characteristics due to applied voltage and temperature rise such as charging, exposure, development, etc. based on the initially set high density reference value for the toner. Data density characteristics are corrected and output.

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

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

  In the image forming apparatus according to the present invention, as described above, the image density correction unit is configured to detect a plurality of halftone densities having different density levels from the low density area to the high density area before correcting the halftone density. A toner pattern is formed and compared with the halftone density reference value for correction. On the other hand, for the detection value of the low density area, the detection value equal to or lower than the preset low density area deletion reference value is deleted, and the remaining plural Correction is performed using a value approximated linearly using the detected value.

  Therefore, the numerical values of the detection values in the low density region are generally disturbed, and it is difficult to perform approximation processing linearly. However, in the present invention, the detection values in the low density region are determined in the approximation processing. Uses a value obtained by deleting a detection value equal to or lower than a preset low density region deletion reference value and linearly approximating it using a plurality of remaining detection values.

  As a result, it is possible to delete a detection value equal to or lower than a preset low density region deletion reference value and use a detection value appropriate for the approximation processing linearly, so that the accuracy of the approximation processing is improved.

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

  Furthermore, the time can be significantly shortened as compared with the case where the density conversion table for all gradations is created by performing the complementary processing.

  Therefore, the time required for density correction can be shortened while correcting the density output of the whole image reliably and accurately and according to the type of image, such as solid, line, halftone, etc., and outputting a high quality image. There is an effect that it is possible to provide an image forming apparatus that can reduce the amount of toner consumed sometimes.

  As described above, the image forming apparatus according to the present invention is the image forming apparatus described above, wherein the image density correction unit uses the 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 gradually from the low side to the high side is adopted. Specifically, the point where the detection value starts to rise continuously is adopted in the color image, while the point where the detection value starts to fall continuously is adopted in the monochrome image.

  Therefore, it is possible to reliably delete detection values that are difficult to approximate in a linear manner in a low density region, and to leave as many detection values as appropriate to perform approximation processing in a linear manner.

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

[Embodiment 1]
An embodiment of the present invention will be described with reference to FIGS. 1 to 6 as follows. In this embodiment, a color electrophotographic apparatus as an image forming apparatus is described. However, the present invention is not limited to this, and a simple electrophotographic apparatus as an image forming apparatus may be used. Further, the present invention can be applied to image forming apparatuses such as copying machines, laser beam printers, facsimile machines, and the like using other electrophotographic systems.

  As shown in FIG. 2, the color electrophotographic apparatus of the present embodiment includes a plurality of photosensitive drums 1 as photosensitive members that are rotatably supported. Each photosensitive drum 1 is driven by a driving device. It is driven to rotate in the direction of the arrow.

  Around the photosensitive drum 1, in order, a charging device 2 that uniformly charges the surface of the photosensitive drum 1, an exposure device 3 that exposes the surface of the photosensitive drum 1 to form a latent image, and a latent image thereof. A developing device 4 that develops an image to form a toner image, a transfer device 5 that transfers the toner image to a transfer material, and a cleaning device 6 that cleans the toner remaining on the surface of the photosensitive drum 1 are disposed.

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

  Further, 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 an arrow. Therefore, 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 each of the transfer chargers 8 is a toner formed on each photosensitive drum 1. The image is transferred to the transfer belt 7. Further, a cleaning member (not shown) and a charge eliminating member (not shown) for removing charges accumulated in the transfer belt 7 are arranged inside and outside the loop of the transfer belt 7.

  The recording medium on which the toner images that have passed through the four photosensitive drums 1 on the transfer belt 7 have been transferred passes through the fixing device 9 to be fixed.

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

  The density detection sensor 10 is a reflective sensor, and includes a light emitting element 11, an irregular reflection light receiving element 12, and a regular reflection light receiving element 13, as shown in FIG. 3, and detects color density and black density. Both can be detected.

  That is, when color density detection is performed, 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 according to the amount of light. Generate voltage.

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

  Here, the transfer belt 7 uses modified polyimide as a material in order to greatly change the reflectance of the toner, and has a regular reflectance of 10% or more by finishing the surface into a mirror surface.

  By the way, in the color electrophotographic apparatus of the present embodiment, in order to appropriately correct the image density at the time of image output, the developing bias is changed to change the high density detection toner pattern and the halftone on each of the photosensitive drums 1. Two types of density detection toner patterns are formed together with the density detection toner pattern. The high density detection toner pattern and the halftone density detection toner pattern include a pattern formed as a reference value and a pattern formed as needed when an image is formed.

  These high density detection toner pattern and 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 detection toner patterns, for example, those of a 3 × 3 pixel matrix are created with different densities. In other words, a predetermined number of dots formed with toner in a certain area of a 3 × 3 pixel matrix is gradually increased from the low density area to a high density area that becomes a solid image. A toner pattern having a plurality of levels of density is formed in the intermediate density region up to the front of the first density. Thereby, the toner adhesion amount for the intermediate density region can be controlled.

  Therefore, by using the high density detection toner pattern and the halftone density detection toner pattern in combination, the density of the entire image can be kept constant and the image can be output properly.

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

  As shown in the figure, first, it is determined whether or not the image density correction is executed (S1). If the image density correction is executed, the density detection sensor 10 is calibrated. (S2) High density correction is executed (S3).

  This high density correction will be described in detail.

  First, the photosensitive drum 1 is charged, exposed, and developed. At that time, a developing bias is changed to form a predetermined high-density detection toner pattern for each color, which will be described later, on each photosensitive drum 1. A plurality of high density detection toner patterns of each color formed are transferred to the transfer belt 7. These high density detection toner patterns are sequentially measured by the density detection sensor 10 to determine the correction amount.

  Here, at the time of high density correction of color, through the charging, exposure, development, and transfer processes, the development bias is changed, and three types of 100% solid patterns as shown below are formed on the transfer belt 7. The

v1: Low voltage (the voltage is -50V with respect to the previously set development bias)
v2: Reference voltage (previously set development bias)
v3: High voltage (+ 50V with respect to the previously set development bias)
Next, each of these high density detection toner patterns is sequentially measured by the density detection sensor 10, and the optical density is detected from each measurement result. Then, as shown in FIG. 4A, a developing bias that connects the three points with a straight line and intersects the reference sensor value is employed. In FIG. 5A, the reference sensor value is 2.4V, for example. In FIG. 9A, the reference voltage as the 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 by changing the development bias as shown below through charging, exposure, development and transfer. The reason why the 80% solid pattern is used is that the reflected light becomes weak and cannot be detected with the 100% solid pattern.

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

Density = Reflectance of toner pattern / Reflectivity on transfer belt (1)
Then, as shown in FIG. 4B, the three points are connected by a straight line, and a development bias having a value obtained by dividing the development bias intersecting with the reference sensor value of 1 V, for example, by 0.8 is adopted as a certain value here. . By using the above formula (1), the reflectance of the transfer belt 7 is normalized, and the density can be read stably.

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

  This is because 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 the 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 previous high density correction and the development bias set this time exceeds the difference reference value. I have to.

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

  In the present embodiment, for example, the developing bias ± 50 V is used as the difference reference value, and halftone density correction is performed only when the developing bias is ± 50 V or more. This difference reference value is based on the determination that it is appropriate to perform at least the high density correction and the halftone density correction when it becomes ± 50 V or more, but is not necessarily limited to ± 50 V.

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

  Next, comparison is made with a plurality of halftone density reference values set and stored in advance for each color, 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 halftone density reference value table is created during maintenance.

  Specifically, as shown in FIG. 5, the detection value of the density detection sensor 10 at the time of laser duty A, which is a laser output, is currently A ′, and the halftone density reference value is B, as shown in FIG. When “is”, the halftone density reference value B ′ is secured as the sensor value by changing the laser duty A to the laser duty B, and the image density is held.

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

  In the execution condition determination of the intermediate correction density in S4, when the difference reference value is less than 50V, the image is output without performing 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 up, the first 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, halftone density correction is not performed since ΔV is Δ20V with respect to the development bias voltage value −300V that is the previous high density reference value, and the condition that the difference reference value is 50V 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, which was Δ60 V with respect to the developing bias voltage value −320 V that is 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 Δ10 V with respect to the developing bias voltage value −260 V, which is the previous high density reference value, and does not satisfy the condition that the difference reference value is 50 V or more. No correction was made.

  Next, at time t4, high density correction was performed again. As a result, the developing bias voltage value was −320 V, which was Δ50 V with respect to the developing bias voltage value −270 V that is 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 correction method focuses on the fact that when the density characteristic with respect to the developing bias changes greatly, the density characteristic with respect to the laser output is likely to change.

  As a result, 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 halftone density correction operation from the result of maximum density correction, the halftone density correction operation can be performed effectively and without waste, so the density correction time can be shortened and the toner consumption during 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 at least one color becomes the difference reference value or more, Correction of the halftone density of the color is performed.

  For this reason, 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 high density correction amount is determined by comparing the value detected by the density detecting sensor 10 with the high density detection toner pattern and the high density reference value. Further, a predetermined halftone density detection toner pattern is formed on the photosensitive drum 1 while changing the developing bias so as to correct the halftone density, and this density detection sensor 10 uses the halftone density detection toner pattern. The halftone density correction amount is determined by comparing the detected value with the halftone density reference value. Further, these are performed by an image density correction means (not shown).

  As a result, the density of the entire image can always be 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 becomes equal to or larger than the reference difference 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, the high density reference value is updated to the result of the high density correction every time high density correction is performed. Then, the result of the current high density correction is compared with the updated high density reference value.

  On the other hand, halftone density correction is not performed every time 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 in advance as a difference standard. Continued only when the value is greater than or equal to.

  As a result, the presence / 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 shortening of the density correction time and toner consumption at the time of density correction. .

  Also, the presence / 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, halftone density correction is performed only when there is a large deviation from the updated high density reference value. Therefore, halftone density correction is performed only when it is really necessary, so that efficiency is good.

  In addition, since the high density reference value is updated every time high density correction is performed, the input image corresponding to fluctuations in current density characteristics due to applied voltage and temperature rise in charging, exposure, development, etc. in the electrophotographic process. Data density characteristics can be corrected and output.

  As a result, it is possible to reduce the time required for density correction while keeping the density output of the entire image constant according to the type of image such as solid, line, halftone, etc., and to reduce the amount of toner used for correction. 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) toners, halftone density correction is performed every time high density correction is performed for all colors. If it is executed, the time is significantly increased compared to the monochrome density correction time. For this reason, the user has to wait further, and this leads to a problem that the usability is not good.

  However, in the present embodiment, when correcting the density of a color image, the image density correction unit compares the high density reference value with the result of the current high density correction, and becomes at least the difference reference value for at least one color. Only occasionally, halftone densities of all colors are corrected.

  Accordingly, halftone density correction for all colors is continued only when the difference reference value is exceeded for at least one color, leading to a reduction in density correction time and a reduction in toner consumption.

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

  As a result, in color images, the time required for density correction can be shortened while maintaining the density output of the entire image constant according to the type of image such as solid, line, halftone, etc., and the amount of toner consumed for correction Can be provided.

[Embodiment 2]
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 the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

  In the color electrophotographic apparatus of the present embodiment, as in the first embodiment, whether or not to perform the halftone density correction operation is determined from the result of the maximum density correction, but the difference reference value is set. 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 The halftone density is continuously corrected only when the difference is equal to or greater than a preset difference reference value.

  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. In addition, the same step number is attached | subjected about the same part as FIG. 1 of Embodiment 1, and the description is abbreviate | omitted.

  As shown in the figure, first, after executing high density correction (S3), whether or not halftone density correction is to be executed is determined (S14).

  In the present embodiment, as the execution condition of the halftone density, the high density development bias voltage value set at the previous halftone density correction is set as the high density reference value, and the difference between the high density reference value and the currently set development bias value is set. The halftone density correction is executed only when the difference becomes equal to or greater than the difference reference value (± 50 V in this case).

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

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

  A specific example of the timing of the above high density correction and 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 up, the developing bias voltage value of the high density reference value is −300V. Further, 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 development bias voltage values of −320 V, −310 V, −330 V, and −340 V, respectively. However, in these cases, the development bias voltage value of −300 V, which is the initial high density reference value, is less than Δ50 V, and the condition that the difference reference value is 50 V or more is not satisfied. For this reason, halftone density correction is not performed.

  Next, the high density correction was performed again at time t5. As a result, the development bias voltage value was −350V, which was Δ50V or more with respect to the development bias voltage value −300V that is the initial 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 t6 and t7, the high density correction is executed again. At this time, the developing bias voltage value −350 V which is the high density reference value when the last halftone density is corrected (time t5). In contrast, it is less than Δ50V and does not satisfy the condition that the difference reference value is 50V or more. For this reason, halftone density correction is not performed.

  Next, at time t8, high density correction was performed again. As a result, the development bias voltage value becomes −290V, and the correction result when the last halftone density is corrected (time t5) becomes the high density reference value, and the development bias voltage value −350V which is the high density reference value is It became Δ60V. 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, 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 the difference is equal to or greater than the preset difference reference value. Only when this is the case, the halftone density is continuously corrected.

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

  Therefore, the presence / 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 shortening of the density correction time and toner consumption at the time of density correction.

  The presence / 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, halftone density correction is performed only when there is a large deviation from the high density reference value. Therefore, halftone density correction is performed only when it is really necessary, so that efficiency is good.

  Further, when the high density reference value set initially without changing the high density reference value is used thereafter, the applied voltage for charging, exposure, development, etc. based on the initially set high density reference value for the toner, Corresponding to the fluctuation of the density characteristic due to the temperature rise, the density characteristic of the input image data is corrected and output.

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

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

  Further, in the color electrophotographic apparatus of the present embodiment, the image density correction unit adopts the result of the high density correction when the halftone density correction is executed last as the high density reference value, and the high density reference value and The result of the high density correction this time is compared, and halftone density correction is continued only when the difference is equal to or greater than a preset difference reference value.

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

  The halftone density correction 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 at the last time and the current high density correction. The comparison with the result is continued only when the difference is equal to or larger than a preset difference reference value.

  Therefore, the presence / 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 shortening of the density correction time and toner consumption at the time of density correction.

  In addition, the presence or absence of the halftone density correction operation is performed by comparing the high density reference value, which is the result of the high density correction when the halftone density correction was last executed, with the result of the current high density correction. Judgment is made based on whether or not the difference reference value is greater than a preset value.

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

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

  As a result, it is possible to reduce the time required for density correction while keeping the density output of the entire image constant according to the type of image such as solid, line, halftone, etc., and to reduce the amount of toner used for correction. 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 the difference is equal to or greater than the difference reference value for at least one color. Only after that, the halftone density of all colors is corrected.

  Accordingly, halftone density correction for all colors is continued only when the difference reference value is exceeded for at least one color, leading to a reduction in density correction time and a reduction in toner consumption.

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

  As a result, in color images, the time required for density correction can be shortened while maintaining the density output of the entire image constant according to the type of image such as solid, line, halftone, etc., and the amount of toner consumed for correction Can be provided.

[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 Embodiment 1 and Embodiment 2 are given the same reference numerals, and the description thereof is omitted.

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

  First, halftone density correction is composed of two steps, a first step and a second step. The first step is mainly for obtaining a low concentration rising point and a high concentration saturation point, and the second step is for collecting detailed data of points to perform approximation processing.

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

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

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

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

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

  Next, the 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 the detailed data of the points obtained in the first step is taken. For example, data is taken for each laser duty 6 between the straight line Y = a and the straight line Y = b. Therefore, the 16 types may be different from or common to the laser duties 31, 47, 63, 79, and 255 obtained in the first step. Further, in the vicinity of the inflection point that becomes the low concentration rising point and the high concentration saturation point obtained in the first step, the pitch of the laser duty is made fine.

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

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

  Therefore, in the present embodiment, the approximation process is performed only with the data of the halftone density detection toner pattern from the point where the sensor value of the density detection sensor 10 starts to rise continuously, thereby further reducing the variation in the approximate line. I am letting.

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

  As a result, the halftone density can be corrected in a short time and a high-quality image can be output.

  9 and 10 show the relationship between the laser duty in the color image and the output ratio of the irregularly reflected light of the density detection sensor 10, so that the line is an upward straight line. Since the detected value is specularly reflected by the density detection sensor 10, the inclination is lowered to the right as shown in FIG. 4B.

  As described above, in the color electrophotographic apparatus according to the present embodiment, the image density correction unit detects a plurality of halftone densities having different density levels from the low density area to the high density area before correcting the halftone density. A toner pattern is formed and compared with the halftone density reference value for correction. On the other hand, for the detection value of the low density area, the detection value equal to or lower than the preset low density area deletion reference value is deleted, and the remaining plural Correction is performed using a value approximated linearly using the detected value.

  That is, when correcting 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 detected. It is corrected by the value approximated linearly.

  Here, the detection values in the low density region are generally disturbed in numerical values, and it is difficult to approximate them linearly. Therefore, in the present embodiment, in the approximation process, for the detection value of the low density region, the detection value equal to or lower than the preset low density region deletion reference value is deleted, and the remaining plurality of detection values are used for linear processing. The approximated value is used.

  As a result, it is possible to delete a detection value equal to or lower than a preset low density region deletion reference value and use a detection value appropriate for the approximation processing linearly, so that the accuracy of the approximation processing is improved.

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

  Furthermore, the time can be significantly shortened as compared with the case where the density conversion table for all gradations is created by performing the complementary processing.

  Therefore, the time required for density correction can be shortened while correcting the density output of the whole image reliably and accurately and according to the type of image, such as solid, line, halftone, etc., and outputting a high quality image. It is possible to provide an image forming apparatus capable of reducing the amount of toner consumed sometimes.

  On the other hand, there is a problem of how to set the low density region deletion reference value in order to use a detection value appropriate for approximation processing linearly.

  However, in the present embodiment, the inflection point of the detected value when the laser output is sequentially changed from the low side to the high side is adopted. Specifically, the point where the detection value starts to rise continuously is adopted in the color image, while the point where the detection value starts to fall continuously is adopted in the monochrome image.

  As a result, it is possible to reliably delete detection values that are difficult to approximate in a linear manner in a low-density region, and to leave as many detection values as appropriate to perform approximation processing in a linear manner as much as possible.

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

[Embodiment 4]
The following will describe still another embodiment of the present invention. For convenience of explanation, members having the same functions as those shown in the drawings of Embodiments 1 to 3 are given the same reference numerals, and descriptions thereof are omitted.

  In the color electrophotographic apparatus of the present embodiment, the image density correction means (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 colors of the differences is preset. Only when the sum difference reference value is exceeded, the halftone density is continuously corrected.

  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 sum difference reference value, which is the sum of the four colors of the difference between the development bias correction result and the high density reference value, is set to 100 V, and halftone density correction is performed at the sum difference reference value of 100 V or more. To do.

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

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

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

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

  Therefore, by determining the presence or absence of the halftone density correction operation by summing up the correction amounts of the high density correction for 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 of the present embodiment, the image density correction means (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 colors of the difference. The halftone density is continuously corrected only when becomes equal to or greater than a preset 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, by determining the presence or absence of halftone density correction operation by summing the correction amount of high density correction for each color, it is not a single-tone halftone density change but a change in image color balance for a multicolor image. You can judge when you are doing more accurately.

  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 density correction while improving the image quality. it can.

[Embodiment 5]
The following will describe still another embodiment of the present invention. For convenience of explanation, members having the same functions as those shown in the drawings of Embodiments 1 to 4 are given the same reference numerals, and descriptions thereof are omitted.

  In the color electrophotographic apparatus of the present embodiment, the image density correction means (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 is equal to or higher than the monochrome difference reference value. The halftone density is continuously corrected only when the sum of the differences between the colors other than monochrome exceeds 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 this embodiment, the difference between the development bias correction result and the high density reference value is Bk and the monochrome difference reference value is 40V or the color sum of the three colors is the color sum difference reference value of 80V or more. Halftone density correction is performed.

  For example, if the correction result of the development bias potential is Y = 325V, M = 345V, C = 320V, and Bk = 315V due to the high density correction, the difference from the high density reference value of Bk is 15V, and three colors. The sum of the differences is 90V.

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

  As described above, in the color electrophotographic apparatus of 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 monochrome one color is the monochrome difference reference. The halftone density is continuously corrected only when either the value becomes equal to or greater than the value or when the sum of the differences between the colors other than monochrome exceeds 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.

  In addition, the halftone density of the color image is changed by performing the halftone density correction operation after separately determining whether the halftone density correction operation is performed, and monochrome colors other than monochrome. The correction can be made individually when the halftone density of the monochrome image is changed.

  As a result, halftone density correction operation can be performed effectively and without waste in consideration of all colors except monochrome or monochrome when it is necessary to correct only one of monochrome colors except monochrome or monochrome. Thus, it is possible to shorten the density correction time and reduce toner consumption during density correction while improving the image quality.

[Embodiment 6]
The following will describe still another embodiment of the present invention with reference to FIG. For convenience of explanation, members having the same functions as those shown in the drawings of Embodiments 1 to 5 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 compares all the colors with the absolute value of the difference between the colors. The halftone density is continuously corrected only when the sum exceeds 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 this embodiment, halftone density correction is performed when the sum of the four colors of the absolute value of the difference between the development bias correction result and the reference value is 100 V or more as the absolute value sum difference reference value.

  For example, when the correction result of the development bias potential is Y = 325V, M = 345V, C = 280V, and Bk = 285V due to the high density correction, the difference from the high density reference value is 25V, 45V, and −20V, respectively. -15V.

  The change in density of the entire image at this time is predicted to vary as shown in FIG. If the sum is performed as described in the fourth embodiment, the sum is 35V, and the halftone correction operation is not performed.

  On the other hand, in the present embodiment, when the summation is performed with the difference from the high density reference value as an absolute value, the sum is 105V. Therefore, since the sum of the absolute values of the four colors is equal to or greater than the absolute value sum difference reference value of 100 V, halftone density correction for each color is operated.

  As described above, in the color electrophotographic apparatus of 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 uses the absolute value of the difference between the colors. The halftone density is continuously corrected only when the total sum of all the colors becomes equal to or larger than a preset absolute 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 up for each color, even if the correction result for each color is different between the positive direction and the negative direction with respect to the high density reference value, the difference between each high density reference value By summing up the absolute values, it is possible to accurately determine when the color balance of the multicolor image is changing.

  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 density correction while improving the image quality. it can.

  In addition, this invention can also be comprised as follows.

  A predetermined high density detection toner pattern is formed on the photoconductor, and the high density correction amount is determined by comparing the value detected by the reflective sensor with the high density reference value. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoconductor, and the halftone density detection toner pattern is compared with the halftone density reference value detected by the reflective sensor. In an image forming apparatus having an image density correction unit that determines a halftone density correction amount, the image density correction unit adopts the result of the previous high density correction as a high density reference value, and the high density reference value and An image forming apparatus characterized in that the halftone density is continuously corrected only when a difference between the current high density correction result and a difference difference value equal to or larger than a preset difference reference value is reached.

  According to the above invention, in order to keep the image density constant, a predetermined high density detection toner pattern is formed on the photoconductor to perform high density correction. Then, the high density correction amount is determined by comparing the value detected by the reflective sensor with the high density detection toner pattern and the high density reference value. In addition, a predetermined halftone density detection toner pattern is formed on the photosensitive member to correct the halftone density, and a value obtained by detecting the halftone density detection toner pattern with a reflective sensor and a halftone density reference value. And the halftone density correction amount is determined. Further, these are performed by image density correction means.

  As a result, the density of the entire image can always be 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 halftone density is continuously corrected only when the difference exceeds the reference value.

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

  On the other hand, halftone density correction is not performed every time 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 in advance as a difference standard. Continued only when the value is greater than or equal to.

  As a result, the presence / 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 shortening of the density correction time and toner consumption at the time of density correction. .

  Also, the presence / 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, halftone density correction is performed only when there is a large deviation from the updated high density reference value. Therefore, halftone density correction is performed only when it is really necessary, so that efficiency is good.

  In addition, since the high density reference value is updated every time high density correction is performed, the input image corresponding to fluctuations in current density characteristics due to applied voltage and temperature rise in charging, exposure, development, etc. in the electrophotographic process. Data density characteristics can be corrected and output.

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

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

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

  The halftone density correction 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 at the last time and the current high density correction. The comparison with the result is continued only when the difference is equal to or larger than a preset difference reference value.

  Therefore, the presence / 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 shortening of the density correction time and toner consumption at the time of density correction.

  In addition, the presence or absence of the halftone density correction operation is performed by comparing the high density reference value, which is the result of the high density correction when the halftone density correction was last executed, with the result of the current high density correction. Judgment is made based on whether or not the difference reference value is greater than a preset value.

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

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

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

  In the image forming apparatus described above, when correcting the density of a color image, 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 greater than the difference reference value for at least one color. The halftone density of all the colors may be corrected only when the color becomes the same.

  That is, in the case of a color image, since there are Y (yellow), M (magenta), C (cyan), and Bk (black) toners, halftone density correction is performed every time high density correction is performed for all colors. If it is executed, the time is significantly increased compared to the monochrome density correction time. For this reason, the user has to wait further, and this leads to a problem that the usability is not good.

  However, when correcting the density of a color image, the image density correction means compares the high density reference value with the result of the current high density correction, and continues only when at least one color becomes the difference reference value or more. The halftone density of the color is corrected.

  Therefore, halftone density correction for all colors is continued only when the difference reference value is exceeded for at least one color, leading to a reduction in density correction time in a color image and a reduction in toner consumption.

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

  As a result, in color images, the time required for density correction can be shortened while maintaining the density output of the entire image constant according to the type of image such as solid, line, halftone, etc., and the amount of toner consumed for correction Can be provided.

  A predetermined high density detection toner pattern is formed on the photoconductor, and the high density correction amount is determined by comparing the value detected by the reflective sensor with the high density reference value. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoconductor, and the halftone density detection toner pattern is compared with the halftone density reference value detected by the reflective sensor. In the image forming apparatus having the image density correction unit that determines the correction amount of the halftone density, the image density correction unit compares the result of the current high density correction with the high density reference value for each color, and the difference An image forming apparatus characterized in that halftone density correction is continued only when the total sum of all the colors becomes equal to or greater than a preset sum difference reference value.

  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 the sum of all the colors of the difference is equal to or greater than a preset sum difference reference value. Only when this is the case, the halftone density is continuously corrected.

  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, by determining the presence or absence of halftone density correction operation by summing the correction amount of high density correction for each color, it is not a single-tone halftone density change but a change in image color balance for a multicolor image. You can judge when you are doing more accurately.

  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 density correction while improving the image quality. it can.

  A predetermined high density detection toner pattern is formed on the photoconductor, and the high density correction amount is determined by comparing the value detected by the reflective sensor with the high density reference value. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoconductor, and the halftone density detection toner pattern is compared with the halftone density reference value detected by the reflective sensor. In the image forming apparatus having the image density correction unit for determining the halftone density correction amount, the image density correction unit compares the result of the current high density correction with the high density reference value for each color, Only when either becomes the monochrome difference reference value or more, or when the sum of the differences between the colors other than monochrome exceeds 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 means compares the result of the current high density correction with the high density reference value for each color, and when only one monochrome is equal to or higher than the monochrome difference reference value, or monochrome The halftone density is continuously corrected only in one of the cases where the sum of the differences between the colors except the color 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.

  In addition, the halftone density of the color image is changed by performing the halftone density correction operation after separately determining whether the halftone density correction operation is performed, and monochrome colors other than monochrome. The correction can be made individually when the halftone density of the monochrome image is changed.

  As a result, halftone density correction operation can be performed effectively and without waste in consideration of all colors except monochrome or monochrome when it is necessary to correct only one of monochrome colors except monochrome or monochrome. Thus, it is possible to shorten the density correction time and reduce toner consumption during density correction while improving the image quality.

  A predetermined high density detection toner pattern is formed on the photoconductor, and the high density correction amount is determined by comparing the value detected by the reflective sensor with the high density reference value. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoconductor, and the halftone density detection toner pattern is compared with the halftone density reference value detected by the reflective sensor. In an image forming apparatus having an image density correction unit that determines a halftone density correction amount, the image density correction unit compares the current high density correction result with a high density reference value for each color, An image forming apparatus characterized in that halftone density correction is continued only when the sum of all 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 absolute sum of all the colors with the absolute value of the difference between the colors is preset. The halftone density is continuously corrected only when the value sum difference difference reference value is exceeded.

  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 up for each color, even if the correction result for each color is different between the positive direction and the negative direction with respect to the high density reference value, the difference between each high density reference value By summing up the absolute values, it is possible to accurately determine when the color balance of the multicolor image is changing.

  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 density correction while improving the image quality. it can.

1 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 current high density correction. Then, it is a flowchart showing an operation of continuously correcting the halftone density only when the difference becomes equal to or larger than a preset difference reference value. It is a block diagram which shows the outline | summary of the image process part in the said color electrophotographic apparatus. FIG. 3 is a configuration diagram showing a density detection sensor for detecting a high density detection toner pattern or a halftone density detection toner pattern in the color electrophotographic apparatus. The color electrophotographic apparatus shows a state in which density correction is performed by a density detection sensor, (a) is an explanatory diagram for correcting a color image at a high density, and (b) is an explanation showing a state for correcting a monochrome image at a high density. FIG. It is explanatory drawing which shows the state which performs halftone correction in the said color electrophotographic apparatus. It is explanatory drawing which shows the timing which performs high density correction and halftone density correction in the said color electrophotographic apparatus. 7 shows another embodiment of the color electrophotographic apparatus according to the present invention, and adopts the result of the high density correction when the halftone density correction is finally performed as the high density reference value, and the high density reference value. 6 is a flowchart showing an operation of comparing halftone density correction only when the difference is equal to or larger than a preset difference reference value by comparing the current high density correction result with the current high density correction result. It is explanatory drawing which shows the timing which performs high density correction and halftone density correction in the said color electrophotographic apparatus. FIG. 6 shows still another embodiment of the color electrophotographic apparatus according to the present invention. When correcting halftone density, as a first step, five types of toner patterns for detecting halftone density are formed and reduced. It is explanatory drawing which shows the state which calculates a density | concentration rising point and a high density | concentration saturation point. In the color electrophotographic apparatus, when halftone density correction is performed, as a second step, 16 types of halftone density detection toner patterns are formed in order to perform halftone density approximation processing by the method of least squares. It is explanatory drawing which shows the state which takes data. FIG. 9 shows still another embodiment of the color electrophotographic apparatus according to the present invention, and is only when the sum of all colors in the absolute value of the difference of each color is equal to or greater than a preset absolute value sum difference reference value. It is explanatory drawing which shows the density | concentration (ID: image density) change of each color when correcting halftone density continuously. FIG. 9 is a conceptual diagram illustrating a conventional color electrophotographic apparatus and illustrating density correction operation determination. It is explanatory drawing which shows a change in the density curve by member replacement | exchange in the said color electrophotographic apparatus.

Explanation of symbols

1 Photoconductor drum (photoconductor)
4 Developing device 7 Transfer belt 10 Density detection sensor (reflection type sensor)
DESCRIPTION OF SYMBOLS 11 Light emitting element 12 Diffuse reflection light receiving element 13 Regular reflection light receiving element

Claims (3)

A predetermined high density detection toner pattern is formed on the photoconductor, and the high density correction amount is determined by comparing the value detected by the reflective sensor with the high density reference value. On the other hand, a predetermined halftone density detection toner pattern is formed on the photoconductor, and the halftone density detection toner pattern is compared with the halftone density reference value detected by the reflective sensor. In an image forming apparatus having an image density correction means for determining a halftone density correction amount,
When correcting the halftone density, the image density correcting unit forms a plurality of halftone density detection toner patterns having different density levels from the low density area to the high density area, and sets the halftone density reference value. While comparing and correcting, the detection value of the low density area is deleted by deleting the detection value below the preset low density area deletion reference value, and correction is performed with the approximate value using the remaining detection values. ,
The image density correction means compares the high density reference value with the result of the high density correction, and performs halftone density correction only when the difference is equal to or greater than a preset difference reference value. An image forming apparatus. The image density correction means adopts the inflection point of the detected value when the laser output is changed gradually from the low side to the high side as the low density region deletion reference value when the low density region is approximated. The image forming apparatus according to claim 1 . The image forming apparatus according to claim 1 , wherein the image density correction unit performs correction using a linearly approximated value.

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