JP4517635B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a technique for correcting the density of an image formed in an image forming apparatus.

  In a tandem-type multicolor (color) image forming apparatus equipped with a plurality of image forming engines, an image formed on a recording sheet due to a change in usage environment such as temperature and humidity, or deterioration of components and toner over time. Concentration varies. Therefore, in this type of color image forming apparatus, density correction processing for correcting the image density to an appropriate value is appropriately executed, and a typical process is called calibration. It has been known. In this calibration, a number of reference patch images (hereinafter simply referred to as reference patches) having a uniform density are formed on a recording paper, a photoreceptor or an intermediate transfer belt, and the density of the formed reference patches is measured. The image forming conditions for forming an image are corrected based on the comparison result.

  Such calibration is often performed between the image forming process for one page and the image forming process for the next page (so-called inter-image), which hinders the productivity of these image forming processes. It is desirable to complete the execution in as short a time as possible. In view of such circumstances, for example, in the technique described in Patent Document 1, reference patches of Y (yellow), M (magenta), C (cyan), and K (black) are simultaneously created, and the intermediate transfer belt is simultaneously created. By transferring it to the image, the time required from the creation of the reference patch to the measurement of the density is reduced.

  Here, FIG. 7 is a diagram showing the order in which the reference patches of each color are created in each image forming engine and the positional relationship of the reference patches transferred to the intermediate transfer belt. “Y engine”, “M engine”, “C engine”, and “K engine” shown in FIG. 7 mean image forming engines that form Y, M, C, and K images, respectively. When the intermediate transfer belt moves from upstream to downstream, the order of arrangement of these image forming engines is “Y engine”, “M engine”, “C engine”, “K engine” from upstream to downstream. . In the drawing, the horizontal axes corresponding to “Y engine”, “M engine”, “C engine”, and “K engine” are obtained by developing the circumferential surface of the photosensitive drum included in each engine into a flat surface. Represents the position. It means that an image located on the horizontal axis from the left side to the right side of the paper is an image formed on the circumferential surface of the photosensitive drum at a later timing. Also, the horizontal axis corresponding to the “intermediate transfer belt” in the figure represents the position on the intermediate transfer belt, and the image located on the horizontal axis from the right side to the left side of the sheet moves in the direction of movement of the intermediate transfer belt. It means that the image is transferred to the leading side (downstream side).

  As described above, when the Y, M, C, and K image forming engines simultaneously create the reference patches of the respective colors and transfer them to the intermediate transfer belt at the same time, the sequence shown in FIG. The reference patches for each color are lined up. That is, the K reference patch Pk formed by the K engine located on the most downstream side is disposed at the head (most downstream side) in the moving direction of the intermediate transfer belt, and subsequently the C reference patches Pc and M reference patches. The Pm and Y reference patches Py are arranged in this order. That is, the order of the colors of the image forming engines arranged from the upstream to the downstream and the order of the colors of the reference patches arranged from the downstream to the upstream in the intermediate transfer belt are completely reversed.

  However, when the reference patches are arranged in the above arrangement, there are the following two problems. For example, as shown in FIG. 8, it is assumed that a reference patch is created between the image forming process for the Nth page and the image forming process for the (N + 1) th page. In this case, the image forming process for the Nth sheet is performed immediately before the process of creating the reference patch. Therefore, in order to simultaneously create the four color reference patches, the Y engine, the M engine, and the C engine need to wait until the N-th image forming process by the K engine located on the most downstream side is completed. That is, the Y engine, the M engine, and the C engine should be able to start the reference patch creation process as soon as the Nth image formation process is completed. It is necessary to wait until the image forming process by the K engine is completed. Therefore, when the process described in Patent Document 1 is applied to an inter image, the processing time is not shortened so much. This is the first problem.

  Further, in a color image forming apparatus, there are a case where image forming conditions in all image forming engines are simultaneously corrected in image units for one page, and a case where image forming conditions are corrected independently for each image forming engine. is there. The former is a case where image forming conditions with high responsiveness are corrected. For example, image forming conditions relating to latent image formation such as charging conditions and exposure conditions, and image forming conditions such as gradation control of image signals are corrected. This is the case. When this type of image forming condition is changed, the changed content is immediately reflected in the density of the image on the recording paper. Therefore, when this type of image forming condition is corrected for only a specific color, Y for one page is corrected. , M, C, K color images, only the density of the color changes abruptly, and as a result, the overall color balance may be lost. Accordingly, the image forming conditions as described above must be adjusted simultaneously for all the colors Y, M, C, and K for one page. On the other hand, the latter is a case where an image forming condition with low responsiveness is corrected. For example, the image density is corrected in a darker direction by newly supplying toner. When this type of image forming condition is corrected, the correction result is not immediately reflected in the density of the image formed on the recording paper. Therefore, even if each image forming engine is used independently, the color balance is lost. The problem you did not occur.

  As shown in FIG. 8, the density sensor for reading the density of the reference patch is generally arranged on the most downstream side of the intermediate transfer belt. Therefore, the density of each reference patch is the leading side in the moving direction of the intermediate transfer belt. Measurement is performed in the order of Pk, Pc, Pm, and Py from the (downstream side), and the image forming conditions are corrected in the order of measurement (that is, the order of K, C, M, and Y). Therefore, the density measurement process is the last for the reference patch Py arranged on the rear side (upstream side) of the intermediate transfer belt in the moving direction, whereas the image forming process for each color of the (N + 1) th sheet is Y. Therefore, there is a possibility that the correction of the Y image forming condition may not be in time before the start of the process of forming the (N + 1) th Y image. In the example shown in FIG. 8, for K and C, the correction of the image forming condition is in time until the formation processing of the (N + 1) th image is started (“◯” in the figure), but for Y and M, In this example, the correction of the image forming condition is not in time until the formation processing of the (N + 1) th image is started (“×” in the figure). As described above, considering the color balance of the image, the image forming conditions must be simultaneously corrected in image units for one page, so that the image forming conditions are corrected based on the density of the reference patch for each color. As shown in FIG. 9, this is from the (N + 2) th image. This makes it impossible to correct the image density quickly. This is the second problem.

JP 2002-139877 A

  From the above, the technique described in Patent Document 1 is a case where image forming conditions are corrected independently by each image forming engine, for example, density correction processing by toner replenishment, and a reference patch is created. Only when an image is not formed immediately before, can the time reduction that is the original purpose be realized. Therefore, the present invention does not impair the productivity of the image forming process even when the image forming conditions of each color are corrected simultaneously in image units for one page in the interval between image forming processes (inter-image). An object is to complete the density correction processing in a shorter time.

In order to solve the above-described problems, the present invention provides a yellow, which is arranged in a predetermined color order from an upstream side to a downstream side along an intermediate transfer body or a recording material transport body that is moved from upstream to downstream. A plurality of image forming means corresponding to four colors of magenta, cyan, and black, each color image is formed on each image holding body based on image forming conditions determined for each color, and each color image formed For each color by using a plurality of image forming means for superimposing one page at a time and transferring it onto the intermediate transfer body, the recording material transport body, or a recording material on the transport body, and each of the image forming means. A reference patch creating means for forming a reference patch image of each color at a determined timing, and transferring the formed reference patch image to the intermediate transfer member, the recording material transport member or the recording material; Patch density measurement that measures the density of a reference patch image that is disposed near the downstream side of the intermediate transfer body or the recording material transport body and transferred to the intermediate transfer body or the recording material transport body or the recording material on the transport body And image density control means for correcting the image forming conditions of each color in image units for one page based on the density measured by the patch density measuring means, each image of the plurality of image forming means Among the holders, the diameter of the image holder of the black image forming unit is different from the diameter of the image holder of each of the yellow, magenta, and cyan image forming units, and the reference patch creating unit performs the transfer. The yellow, magenta, and cyan reference patterns in the traveling direction in which the intermediate transfer member, the recording material transport member, or the recording material moves from the upstream side to the downstream side. With respect to the H image, the reference patch image of each color is transferred to each of the image forming means at a timing such that the order of the colors of the reference patch images arranged in order from the head in the traveling direction is the same as the predetermined color order. For the black reference patch image, the color order of the black reference patch image with respect to the yellow, magenta, and cyan reference patch images is not the same as the predetermined color order , and the head in the traveling direction side in becoming not timing, an image forming apparatus for forming on said image forming means each reference patch images of each color.

  In another preferred embodiment, the reference patch creation means may be a period from when each of the image forming means performs an image forming process for one page until an image forming process for the next page is started. Alternatively, after each image forming unit finishes the image forming process for the last page, the image forming unit forms a reference patch image at the timing. From the viewpoint of not hindering the productivity of the image forming process, if the reference patch is created in the above case, the present invention has a remarkable effect.

  In another preferred embodiment, the reference patch creating unit causes each of the image forming units to form a plurality of reference patch images having different image forming conditions, and the image density control unit includes the patch density measuring unit. The image forming conditions are corrected based on the density of the plurality of patch images measured by the means.

  Preferably, the reference patch creating unit has a length shorter than a distance between transfer positions at which each of the image forming units transfers an image to the intermediate transfer member, the recording material transport member, or the recording material. The reference patch image is formed on the image forming means.

Embodiments of the present invention will be described below.
A: Apparatus Configuration FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 includes image forming engines 10Y, 10M, 10C, and 10K that respectively form yellow (Y), magenta (M), cyan (C), and black (K) toner images. The intermediate transfer belt 20 that is stretched over a plurality of rolls 22 and 23 and moved from upstream to downstream (direction of arrow A) and primary transfer from the image forming engines 10Y, 10M, 10C, and 10K to the intermediate transfer belt 20. A secondary transfer roll 15 for secondary transfer of the toner image onto the recording paper P, and a fixing device (not shown) for fixing the toner image transferred onto the paper P on the paper P by heating and pressing. Yes.

  Each of the image forming engines 10Y, 10M, 10C, and 10K includes photosensitive drums 1Y, 1M, 1C, and 1K that are image carriers, and charging devices 2Y, 2M, and 2C that charge the photosensitive drums 1Y, 1M, 1C, and 1K. , 2K, and charged photosensitive drums 1Y, 1M, 1C, and 1K are irradiated with light modulated based on image signals corresponding to the colors Y, M, C, and K to form an electrostatic latent image on the drum surface. Exposure devices 3Y, 3M, 3C, and 3K to be formed, and developing devices 4Y, 4M, 4C, and 4K that form toner images by supplying toners of colors Y, M, C, and K to the electrostatic latent image, And a cleaning device (not shown) for cleaning toner remaining on the photosensitive drums 1Y, 1M, 1C, and 1K after the toner image is primarily transferred. To the developing devices 4Y, 4M, 4C, and 4K, toner boxes 7Y, 7M, 7C, and 7K are connected via pipes with built-in augers. The amount of toner supplied from the toner boxes 7Y, 7M, 7C, 7K to the developing devices 4Y, 4M, 4C, 4K is adjusted by the rotation time of the dispense motors 9Y, 9M, 9C, 9K. The developing machines 4Y, 4M, 4C, and 4K are provided with ATC sensors 8Y, 8M, 8C, and 8K that measure the toner density, respectively.

  Further, the image forming apparatus 100 includes an image reading unit (IIT) 30 that reads a document image, an image processing unit 31 that generates image data by performing screen processing on an image signal output from the image reading unit 30, and image processing. A controller 32 that performs color conversion processing on the image data output from the unit 31 or the image data output by the external device 40 such as a personal computer to separate the color data into Y, M, C, and K colors and perform pulse width modulation. A pixel counter 33 that calculates the image density by counting the number of pixels of the image data, an image control unit 34 that controls the operation of each of the image forming engines 10Y, 10M, 10C, and 10K, and a dispense motor 9Y, 9M, 9C. , And a TC control unit 35 for controlling 9K rotation. The Y, M, C, and K image data pulse-width modulated by the controller 32 are supplied to the exposure devices 3Y, 3M, 3C, and 3K via the image control unit 34, and laser light corresponding to these image data is exposed. The photosensitive drums 1Y, 1M, 1C, and 1K are irradiated from the devices 3Y, 3M, 3C, and 3K, respectively.

  A density sensor 25 for measuring the density of the reference patch is provided on the downstream side of the image forming engine 10K and in the vicinity of the intermediate transfer belt 20 and facing the outer peripheral surface of the belt. In the vicinity thereof, a temperature sensor 26 that measures the temperature inside the image forming apparatus 100 and a humidity sensor 27 that measures humidity are provided. The output values of the ATC sensors 8Y, 8M, 8C, and 8K, the temperature sensor 26 and the humidity sensor 27, and the image density calculated by the pixel counter 33 are supplied to the TC control unit 35. The TC control unit 35 dispenses based on the predicted toner consumption calculated from the image density counted by the pixel counter 33 and the output values of the ATC sensors 8Y, 8M, 8C, and 8K, the temperature sensor 26, and the humidity sensor 27. The rotation times of the motors 9Y, 9M, 9C, and 9K are integrated, and the dispense motors 9Y, 9M, 9C, and 9K are rotated by the rotation time based on a predetermined logic from the integration result. As a result, an appropriate amount of toner is supplied from the toner boxes 7Y, 7M, 7C, and 7K to the developing devices 4Y, 4M, 4C, and 4K.

  A user interface (UI) 36 including a display unit and an operation unit is provided on the upper surface of the casing of the image forming apparatus 100. The display unit includes a liquid crystal panel, and various information is displayed by driving the panel. Further, the liquid crystal panel of the display unit also functions as a touch panel, and the operator can perform various operations using the liquid crystal panel in addition to the operation unit.

  The image control unit 34 includes an image density control unit 70. The image density control unit 70 corrects the density of the image formed on the recording paper by correcting the image forming conditions that the image forming engines 10Y, 10M, 10C, and 10K should follow. Here, FIG. 2 is a diagram showing a configuration of the image density control unit 70, and the same components as those in FIG. As shown in FIG. 2, the image density control unit 70 includes a calculation unit 71, engine control units 72Y, 72M, 72C, 72K corresponding to the colors Y, M, C, and K, and Y, M, C, K. Are provided with reference patch creation sections 73Y, 73M, 73C, 73K corresponding to the respective colors. The engine control units 72Y, 72M, 72C, 72K, based on instructions from the calculation unit 71, image forming conditions (here, charging potentials in the charging devices 2Y, 2M, 2C, 2K, and exposure devices 3Y, 3M, 3C, 3K). And the set image forming conditions are instructed to the charging devices 2Y, 2M, 2C, and 2K and the exposure devices 3Y, 3M, 3C, and 3K, respectively. Each of the image forming engines 10Y, 10M, 10C, and 10K forms an image according to the instructed image forming conditions.

  The calculation unit 71 creates a reference patch for each color at a timing as described later when the image forming apparatus 100 is turned on and whenever an image of a predetermined number of pages is formed after the power is turned on. The reference patch creation units 73Y, 73M, 73C, and 73K are instructed. In response to this instruction, the reference patch creation units 73Y, 73M, 73C, and 73K set the light amount level of light emitted by the exposure devices 3Y, 3M, 3C, and 3K, and the set contents are set as the exposure devices 3Y, 3M, and 3K. Instruct 3C and 3K to irradiate. An electrostatic latent image of a reference patch is formed on each photosensitive drum 1Y, 1M, 1C, 1K irradiated with light, and these electrostatic latent images are developed by the developing devices 4Y, 4M, 4C, 4K, A toner image of a reference patch for each color is formed. The toner images of these reference patches are respectively transferred to the intermediate transfer belt 20 by the primary transfer rolls 5Y, 5M, 5C, and 5K.

  The density of the reference patch of each color transferred onto the intermediate transfer belt 20 is measured by the density sensor 25, and the measurement result is output to the calculation unit 71. The computing unit 71 compares the density indicated by the output value with a predetermined target value, and sets the image forming condition (charging of the charging devices 2Y, 2M, 2C, and 2K so that the density of the reference patch matches the target value. The correction amount of the potential and the light amount level of the exposure devices 3Y, 3M, 3C, and 3K is calculated. Thereafter, the calculation unit 71 sets the image forming conditions for each color in image units for one page in each of the image forming engines 10Y, 10M, 10C, and 10K by adding the correction amount to the image data supplied from the controller 32. To do.

B: Method for Creating Reference Patch Next, some specific examples of the method for creating the reference patch for each color will be described.
B-1: Creation method 1
FIG. 3 is a diagram showing the order in which the images of the respective colors are formed in the image forming engines 10Y, 10M, 10C, and 10K and the positional relationship between the reference patches Py, Pm, Pc, and Pk transferred to the intermediate transfer belt 20. It is. As shown in FIG. 3, the reference patches Py, Pm, Pc, and Pk for each color are transferred so as to be arranged in the color order of Y, M, C, and K from the head (downstream side) of the intermediate transfer belt 20 in the moving direction. Is done. This color order is the same as the color order of the image forming engines 10Y, 10M, 10C, and 10K arranged along the intermediate transfer belt 20 from upstream to downstream. In order to realize such an arrangement, the calculation unit 71 of the image density control unit 70 uses the same color order of the reference patches on the intermediate transfer belt 20 as the color order of the image forming engines 10Y, 10M, 10C, and 10K. The reference patch creation units 73Y, 73M, 73C, and 73K may be instructed to form the reference patches of the respective colors at such timing.

  As shown in FIG. 3, the image forming process for the (N + 1) th page in each image forming engine is started first from the image forming engine 10Y arranged on the most upstream side. The reference patch Py formed by the image forming engine 10Y is arranged at the head (downstream side) of the intermediate transfer belt 20 in the moving direction, and the density of the reference patch Py is measured by the density sensor 25 earliest. Therefore, the correction of the image forming condition according to the density measurement result of the reference patch Py is in time for the (N + 1) th Y image formation. Similarly, the correction of the image forming conditions according to the measurement results of the densities of the reference patches Pm, Pc, and Pk is in time for the N + 1th M, C, and K image formation, respectively. Therefore, the result of the image density correction based on the reference patch creation process performed between the Nth page and the N + 1th page is reflected from the time of the image formation process on the (N + 1) th page immediately after the creation of the reference patch. Is possible.

B-2: Creation method 2
After forming the reference patch of each color, it is transferred to the intermediate transfer belt 20, and the image forming conditions are corrected based on the density of the transferred reference patch. Whether it takes a certain amount of time depends on various conditions. The conditions include, for example, the length and number of each reference patch, the distance between the image forming engines 10Y, 10M, 10C, and 10K, the moving speed of the intermediate transfer belt 20, the 10Y, For example, a distance between an image for one page and an image for the next page on the peripheral surfaces of 10M, 10C, and 10K. Depending on the contents of such conditions, it may not be necessary to consider the arrangement of reference patches of all colors as in the above-described creation method 1.

  As described above, since the image forming process for the (N + 1) th sheet is first started by the image forming engine 10Y arranged on the most upstream side, at least the reference patch Py of the image forming engine 10Y is the most on the intermediate transfer belt 20. As long as they are arranged on the leading side (the most downstream side) in the moving direction, the image density correction processing for M, C, and K other than Y is in time for the (N + 1) th image forming processing for each M, C, and K. There are cases like this. For example, in the example shown in FIG. 4, the respective reference patches are arranged in the order of Py, Pk, Pc, and Pm from the downstream side, but between the Nth page image and the N + 1th page image. Since the distance is relatively large and there is time allowance, the correction of the image forming conditions in accordance with the measurement results of the density of the reference patches for all colors is in time for the (N + 1) th image forming process. In order to realize such an arrangement, the calculation unit 71 of the image density control unit 70 performs an intermediate transfer after the reference patch Py formed by the image forming engine 10Y arranged on the most upstream side is transferred. What is necessary is just to instruct | indicate to the reference patch preparation part 73Y the timing which is transcribe | transferred most downstream in a belt.

B-3: Creation method 3
In the creation methods 1 and 2, the case where one reference patch is created for each color has been described. However, the present invention is not limited to this, and a plurality of reference patches may be created for each color. For example, FIG. 5 shows a case where two reference patches are created for each color. In this case, for example, the Y reference patch Py1 is an image having a density of 50%, and the reference patch Py2 is an image having a density of 100%. Further, when a plurality of reference patches are created in this way, as described in the creation method 1, the color order of the reference patches on the intermediate transfer belt 20 and the color order of the image forming engines 10Y, 10M, 10C, and 10K. May be the same (this is the case shown in FIG. 5). Further, as described in the creation method 2, at least the reference patches Py1 and Py2 of the image forming engine 10Y may be arranged at the head (downstream side) in the moving direction of the intermediate transfer belt 20.

C: Other Creation Methods In the creation methods described above, the lengths of the reference patches for each color (the total length of the reference patches for a plurality of colors) are determined by the respective image forming engines 10Y, 10M, 10C, and 10K. It is desirable that the distance be less than the distance between the transfer positions. Here, “the transfer positions of the image forming engines 10Y, 10M, 10C, and 10K” means that the images of the respective colors are intermediate from the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming engines 10Y, 10M, 10C, and 10K. This is the position where the image is transferred to the transfer belt 20. Therefore, the “distance between transfer positions” corresponds to the distance L shown in FIG.

  Here, FIG. 6 shows a case where the length l when two reference patches of each color are connected is larger than the distance between the transfer positions of the image forming engines 10Y, 10M, 10C, and 10K. Note that Lym in the drawing means the distance between the transfer positions of the image forming engine 10Y and the image forming engine 10M. In FIG. 6, since the length l of two reference patches connected in series is larger than the distance L between the transfer positions, the timing at which the density of the reference patch is measured by the density sensor 25 is arranged rearward (upstream) in the movement direction. It will be very slow. In the example shown in FIG. 6, the density measurement is in time for the Y, M, and C reference patches until the image forming process for the (N + 1) th page, but for the K reference patch, the image forming process for the (N + 1) th page. The case where it is not in time is shown. Considering the color balance of the image, the image forming conditions must be corrected simultaneously in image units for one page. In FIG. 6, the image forming conditions are corrected based on the density of the reference patch for each color. , It becomes from the (N + 2) th image. Therefore, if the distance between the image for one page and the image for one page is increased in each of the image forming engines 10Y, 10M, 10C, and 10K, the above inconvenience can be solved. In this case, since the time interval of the image forming process for each page is widened, the productivity of the image forming process (the number of page images that can be formed per unit time) is lowered.

  In order to eliminate such inconvenience, the length 1 of each color reference patch (the total length of a plurality of consecutive reference patches when there are a plurality of colors) is determined by the transfer position of each image forming engine 10Y, 10M, 10C, 10K. It is desirable that the distance L is less than or equal to In this way, the difference in timing for measuring the density of the reference patch for each color by the density sensor 25 is less than the difference in timing for starting the image forming process for each color in each of the image forming engines 10Y, 10M, 10C, and 10K. Therefore, the timing for measuring the density of the reference patch does not fall short of the timing for starting the image forming process.

  The image forming engine 10K that forms an image of K is an image forming engine 10Y, 10M, or 10M that forms images of other colors in order to maintain the reliability when forming a black and white image and the durability of the engine itself. A photoconductive drum having a diameter different from that of 10C may be used. Thus, if only the photosensitive drum 1K of the image forming engine 10K has a different diameter, it may be difficult to arrange the four-color reference patches including the K as intended. Since K does not directly affect the overall color balance, in an image forming apparatus equipped with four color image forming engines of Y, M, C, and K, at least for three colors of Y, M, and C Considering the arrangement of the reference patches as described above, a certain effect can be obtained.

  Further, according to the present invention, a reference patch is created between image forming processes (inter-image) as shown in FIGS. 3 to 5 rather than a case where a reference patch is created prior to an original page unit image forming process. In this case, the effect of shortening the time can be obtained more significantly. Furthermore, in the present invention, as long as the image forming process is executed immediately before creating the reference patch, the effect of time reduction can be expected. Therefore, the image forming engines 10Y, 10M, 10C, The reference patch may be created after 10K has completed the image forming process for the last page.

  Further, although the configuration of the image forming apparatus of the present embodiment has been described using an image forming apparatus having a tandem configuration using an intermediate transfer belt, the image forming apparatus is not limited to the intermediate transfer belt, and may be an intermediate transfer drum. Further, the method is not limited to the intermediate transfer method, and may be a method of transferring directly to a recording material carried on a paper conveyance belt or a recording material conveyed by a paper conveyance drum. In this case, the density sensor 25 is provided at a position facing the paper transport belt or the paper transport drum. Further, a method may be used in which a reference patch is transferred to a recording material conveyed by the recording material conveyance body, and the density of the reference patch is measured. In this case, the density sensor 25 may be provided at a position facing the recording material on the recording material conveyance body.

  In the so-called tandem type image forming apparatus, a single color reference patch is created by one rotation of the photosensitive drum, and a four-color exposure apparatus is common. Because of such a premise, when the present invention is applied to a tandem type image forming apparatus, an expected effect can be obtained. On the other hand, even if the present invention is applied to a so-called four-cycle image forming apparatus, the effect of reducing the influence on the productivity of the image forming process cannot be obtained.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of an image density control unit provided in the image forming apparatus. FIG. 6 is a diagram illustrating an order in which images of each color are formed in each image forming engine and a positional relationship between reference patches of each color transferred to an intermediate transfer belt. FIG. 4 is a diagram illustrating an order in which images of respective colors are formed and positions of reference patches of the respective colors transferred to the intermediate transfer belt. FIG. 3 is a diagram illustrating the order in which each color image is formed in each image forming engine and the positional relationship between the reference patches of each color transferred to the intermediate transfer belt 20. FIG. 3 is a diagram illustrating the order in which each color image is formed in each image forming engine and the positional relationship between the reference patches of each color transferred to the intermediate transfer belt 20. FIG. 5 is a diagram illustrating the order in which each color image is formed in each image forming engine and the positional relationship of each color reference patch transferred to an intermediate transfer belt. FIG. 7 is a diagram illustrating the order in which images of respective colors are formed in each image forming engine and the positional relationship of reference patches of each color transferred to an intermediate transfer belt in an inter image. FIG. 7 is a diagram illustrating the order in which images of respective colors are formed in each image forming engine and the positional relationship of reference patches of each color transferred to an intermediate transfer belt in an inter image.

Explanation of symbols

1Y, 1M, 1C, 1K ... photosensitive drum, 2Y, 2M, 2C, 2K ... charging device, 3Y, 3M, 3C, 3K ... exposure device, 4Y, 4M, 4C, 4K ... Developing device, 5Y, 5M, 5C, 5K ... primary transfer roll, 10Y, 10M, 10C, 10K ... image forming engine, 20 ... intermediate transfer belt, 25 ... density sensor, 34 ... Image control unit, 70 ... Image density control unit, 71 ... Calculation unit, 72Y, 72M, 72C, 72K ... Engine control unit, 73Y, 73M, 73C, 73K ... Reference patch creation unit.

Claims (4)

Corresponding to four colors of yellow, magenta, cyan, and black arranged in a predetermined color order from the upstream side to the downstream side along the intermediate transfer member or the recording material transport member moved from upstream to downstream. A plurality of image forming means for forming an image of each color on each image holding body based on an image forming condition determined for each color, and superimposing the formed images of each color for one page, the intermediate transfer A plurality of image forming means for transferring the recording material or the recording material conveying member or the recording material on the conveying member;
By using each of the image forming means, a reference patch image of each color is formed at a timing determined for each color, and the formed reference patch image is applied to the intermediate transfer body, the recording material transport body, or the recording material. A reference patch creating means to be transferred;
Patch density for measuring the density of a reference patch image that is disposed near the downstream side of the intermediate transfer body or the recording material transport body and transferred to the intermediate transfer body, the recording material transport body, or a recording material on the transport body Measuring means;
Image density control means for correcting the image forming conditions of each color in image units for one page based on the density measured by the patch density measuring means,
Of the image holding members of the plurality of image forming units, the diameter of the image holding member of the black image forming unit is different from the diameter of the image holding member of each of the image forming units of yellow, magenta, and cyan,
The reference patch creating means includes yellow, magenta, and cyan reference patches with respect to a traveling direction in which the intermediate transfer member, the recording material transport member, or the recording material after the transfer is moved from upstream to downstream. For images, the reference patch images of the respective colors are formed in the respective image forming means at a timing such that the order of the colors of the reference patch images arranged in order from the head in the traveling direction is the same as the predetermined color order. With respect to the black reference patch image, the color order of the black reference patch image with respect to the yellow, magenta, and cyan reference patch images is not the same as the predetermined color order , and is at the head in the traveling direction side. An image forming apparatus in which a reference patch image of each color is formed on each of the image forming units at a timing that does not occur.   The reference patch creating unit may be a period from when each image forming unit performs image forming processing for one page until image forming processing for the next page is started, or each image forming unit. The image forming apparatus according to claim 1, wherein after the image forming process for the last page is completed, the image forming unit forms a reference patch image at the timing. The reference patch creating unit causes each of the image forming units to form a plurality of reference patch images having different image forming conditions,
The image forming apparatus according to claim 1, wherein the image density control unit corrects an image forming condition based on the densities of a plurality of patch images measured by the patch density measuring unit.   The reference patch creating means generates a reference patch image having a length shorter than a distance between transfer positions at which each of the image forming means transfers an image to the intermediate transfer body, the recording material transport body, or the recording material. The image forming apparatus according to claim 1, wherein the image forming unit forms the image forming unit.

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