Image forming apparatus and control program

Abstract

This prevents image quality from becoming unstable when the development coverage changes. [Solution] The image forming apparatus has multiple developing units containing developers of the same toner color, and an image forming unit that forms an image on a recording medium based on image data, The system includes an image processing control unit 111 that selects a developer from among several developer units to be used for image processing, based on the original document coverage determined by the image data.

Description

Technical Field

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[0001] The present invention relates to an image forming apparatus and a control program.

Background Art

[0007] The present invention has been made in view of the above circumstances, and aims to provide an image forming apparatus that prevents image quality from becoming unstable when the development coverage changes, by selecting an appropriate developer according to the original coverage. [Means for solving the problem]

[0008] The above objectives of the present invention are achieved by the following means.

[0009] (1) An image forming unit having multiple developing units containing the same color toner and forming an image on a recording medium based on image data, An image forming apparatus comprising: an image forming control unit that selects a developer from among a plurality of developer units to be used for image formation according to the original coverage based on image data.

[0010] (2) Each of the above-mentioned multiple developing units has a pre-set range for the use of original document coverage. The image forming apparatus according to (1) above, wherein the image forming control unit selects a developer whose original coverage value corresponds to the usage range.

[0011] (3) Connected to a print controller having a coverage calculation unit that calculates the original coverage using the image data, The image forming apparatus according to (2) above, wherein the image forming control unit selects the developer to be used for image formation according to the original document coverage obtained from the print controller.

[0012] (4) The image forming apparatus according to (3) above, wherein the image forming control unit selects a developer to be used for image formation for a single print job, a page included in the print job, or a plurality of pages in which images are formed consecutively, using the original coverage calculated by the coverage calculation unit.

[0013] (5) The coverage calculation unit calculates in advance the progress of the original document coverage for each page in a single print job, The image forming apparatus according to (3) above, wherein the image forming control unit determines a page break where the original coverage crosses the boundary of the usage range, divides the print job into multiple sections according to the page break, and predetermines the developer to be used for image formation in each section.

[0014] (6) The coverage calculation unit calculates in advance the progress of the original document coverage for each page in a single print job, The image forming apparatus according to (3) above, wherein the image forming control unit determines a page break where the moving average of the original coverage in a predetermined number of pages crosses the boundary of the usage range, divides the print job into multiple sections according to the page break, and predetermines the developer to be used for image formation in each section.

[0015] (7) The image forming unit is The system comprises multiple image-forming units, each having one of the aforementioned developing units and photoreceptors, and an intermediate transfer body. The image forming apparatus according to (2) above, wherein, in the direction of movement of the intermediate transfer body, the range of original document coverage set in the developer of the imaging unit located upstream is set to have lower coverage than the range of original document coverage set in the developer of the imaging unit located downstream.

[0016] (8) The image forming apparatus according to (2) above, wherein, among the plurality of developing units, the amount of developer stored in the developing unit set to high coverage as the usage range is greater than the amount of developer stored in the developing unit set to low coverage.

[0017] (9) A toner supply unit comprising a toner bottle, a toner hopper for temporarily storing the toner supplied from the toner bottle, and a toner supply unit for supplying the toner in the toner hopper to a developer, The aforementioned multiple developing units use a common toner hopper, The image forming apparatus according to (2) above, wherein the toner supply unit comprises a plurality of units, each of which transports toner from the toner hopper to its respective developer, and the amount of toner supplied per unit time by the toner supply unit to the developer is set to be greater for the developer supply unit set to high coverage than for the supply unit for the developer supply unit set to low coverage as an operating range.

[0018] (10) The image forming apparatus according to (2) above, wherein the image forming parameters for each of the plurality of developing units are linked to each of the developing units.

[0019] (11) Of the image-forming parameters, with respect to the fixing conditions of the paper on which the toner image has been transferred, The image forming apparatus described in (10) above, wherein, among the plurality of developing units, the fixing conditions when image formation is performed using a developing unit set to high coverage as its operating range are set to conditions that result in higher fixing force than the fixing conditions when image formation is performed using a developing unit set to low coverage.

[0020] (12) Of the image-forming parameters, with respect to the primary transfer bias applied to the primary transfer section when transferring the toner image formed on the photoreceptor by the developer to the intermediate transfer body, The image forming apparatus described in (10) above, wherein, among the plurality of developing units, the primary transfer bias when image formation is performed using a developing unit set to high coverage as its operating range is set to a higher condition than the primary transfer bias when image formation is performed using a developing unit set to low coverage.

[0021] (13) In the image stabilization control for forming a patch image by the developing device and setting the image forming parameters based on the detected density of the patch image in order to keep the density constant, In the image forming apparatus according to (10) above, the patch images of each of the plurality of developing devices are set to a size that covers the coverage within the range of the original coverage of each developing device.

[0022] (14) When the original coverage is a high coverage of a predetermined value or more, In the image forming apparatus according to (1) or (2) above, the image forming control unit divides an image of one page and forms the image of one page by dispersing it among a plurality of developing devices of the same color.

[0023] (15) A control program for controlling an image forming apparatus including an image forming unit that forms an image on a recording medium based on image data and has a plurality of developing devices storing developers of the same toner color, A control program for causing the image forming apparatus to execute a selection process of selecting a developing device to be used for image formation from among the plurality of developing devices according to the original coverage based on the image data.

[0024] (16) In each of the plurality of developing devices, a usage range of the original coverage is set in advance, In the selection process according to the control program described in (15) above, a developing device corresponding to the usage range of the original coverage value is selected.

Advantages of the Invention

[0025] According to the present invention, an image forming apparatus includes an image forming unit that forms an image on a recording medium based on image data and has a plurality of developing devices storing developers of the same toner color, and an image forming control unit that selects a developing device to be used for image formation from among the plurality of developing devices according to the original coverage based on the image data. By doing so, by selecting an appropriate developing device according to the original coverage, it is possible to prevent the image quality from becoming unstable even if the developing coverage changes.

Brief Description of the Drawings

[0026] The advantages and features provided by one or more embodiments of the present invention will be better understood from the following detailed description and accompanying drawings. However, these are for illustrative purposes only and are not intended to limit the present invention. [Figure 1] This figure shows a schematic configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a block diagram showing the main components of an image forming apparatus. [Figure 3] This is an example of a mapping table showing the settings for the developing unit and the range of coverage used for the original document. [Figure 4] This is a functional block diagram showing the schematic configuration of the image forming apparatus and print controller. [Figure 5] This is a schematic diagram illustrating an image forming apparatus according to another embodiment. [Figure 6] This table shows the trends for each characteristic in the cases of low coverage and high coverage. [Figure 7] This graph shows the changes in each characteristic when there is a rapid shift from high coverage to low coverage. [Figure 8A] This is a flowchart showing the printing process in the first embodiment. [Figure 8B] This graph shows the original document coverage and selected developer for each print job. [Figure 9A] This is a flowchart showing the printing process in the second embodiment. [Figure 9B] This graph shows the original document coverage and the selected developer for a single print job. [Figure 10A] This is a flowchart illustrating the printing process in the third embodiment. [Figure 10B] This graph shows the original document coverage and selected developer for a single print job. [Figure 11] This is a table showing the conditions set for each developer for low to high coverage in the fourth embodiment. [Figure 12] This is a table showing the conditions set for each developer for low to high coverage in the fifth embodiment. [Figure 13] This is a diagram illustrating the size of the patch image in the sixth embodiment. [Figure 14] This figure illustrates the process in the seventh embodiment for distributing and printing a one-page high-coverage image using multiple developer units. [Modes for carrying out the invention]

[0027] Embodiments of the present invention will be described below with reference to the attached drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios. In this embodiment, the recording medium includes paper and various films. Paper includes thin paper, plain paper, thick paper, recycled paper, and coated paper. To simplify the explanation, the following description will be given using the case where the recording medium is paper as an example.

[0028] Figure 1 is a diagram showing the schematic configuration of the image forming apparatus 100 according to this embodiment. Figure 2 is a block diagram mainly showing the main configuration of the image forming apparatus 100. As shown in Figures 1 and 2, the image forming apparatus 100 includes a control unit 11, a storage unit 12, a paper feed and transport unit 13, an operation display unit 14, a patch density sensor 15, an image forming unit 30, and a toner supply unit 50, which are interconnected by signal lines. A print controller 200 is also connected to the image forming apparatus 100. The print controller 200 has a communication function and receives print jobs from an external device, such as a PC (personal computer). A print job consists of original image data (hereinafter also simply referred to as image data) and a job setting that describes the paper size, double-sided / single-sided setting, number of copies to print, etc. The print controller 200 may be built into the image forming apparatus 100, or it may be configured as a separate unit. The print controller 200 may also be included in the image forming apparatus 100.

[0029] The control unit 11 is equipped with a CPU, RAM, ROM, etc., and performs various controls on the entire image forming apparatus 100 by having the CPU execute control programs stored in the memory unit 12. Details of the functions of the control unit 11 will be described later (Figure 4, etc.).

[0030] (Storage unit 12) The storage unit 12 consists of an auxiliary storage unit such as a hard disk or SSD for storing various programs and data. The storage unit 12 stores a control table (hereinafter also simply called the mapping table) that sets the correspondence between the usage range of the original coverage and the developing unit, and image production parameters. The mapping table will be described later (Figure 3 below). Image production parameters include fixing control parameters, transfer control parameters, transport / feed control parameters, and image parameters. Fixing control parameters include the fixing control temperature and fixing pressure settings. Image parameters include the development bias applied to the developing roller and the transfer bias applied to the primary transfer roller 32. Image production parameters are determined by the control unit 11 based on paper characteristics, ambient environment information (temperature and humidity), double-sided / single-sided settings, etc. In particular, image production parameters are set in conjunction with the image production unit 31 to the developing unit 312, which will be described later (details will be described later).

[0031] (Image forming unit 30) The image forming unit 30 forms an image on the paper 90 by an electrophotographic process. The image forming unit 30 has a plurality of image forming units 31A, 31B, and 31C. All image forming units 31A, 31b, and 31C correspond to the same color toner, for example, black (K: Black). Hereinafter, when referring to them collectively, they will simply be called image forming units 31 (the same applies to the developer unit 312 described later). In this embodiment, an intermediate transfer belt type image forming apparatus is illustrated, in which toner images from multiple developers are transferred to an intermediate transfer belt and then transferred to the paper 90 all at once. However, it is not limited to this, and an image forming apparatus of the direct transfer type may also be used, in which the image is transferred directly from the photoreceptor drum to the paper 90 without an intermediate transfer belt.

[0032] The image forming unit 30 has primary transfer rollers 32A, 32B, and 32C, which correspond to the respective image forming units 31A, 31B, and 31C. The image forming unit 30 also has an intermediate transfer belt 33, a secondary transfer roller 34, a fixing device 35, and the like.

[0033] (Image-making unit 31) The image-forming units 31A, 31B, and 31C are arranged in this order in the direction of movement of the intermediate transfer belt 33. Aside from their different positions, the mechanical configurations of the image-forming units 31A, 31B, and 31C are the same, and the following description will use image-forming unit 31A as a representative example. The developer toners stored in the developer units 312A, 312B, and 312C are all the same color, for example, black. Image-forming unit 31A includes a photoreceptor drum 313A, a strip electrode, an exposure unit 311A, a developer unit 312A, a cleaning unit, etc. (some components are omitted from the illustration).

[0034] The photoreceptor drum 313A is made of an organic photoreceptor, for example, in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer surface of a drum-shaped metal substrate. The photoreceptor drum 313A rotates counterclockwise as shown by the arrow in Figure 1. After the surface of the photoreceptor drum 313A is charged substantially uniformly by a band electrode, the exposure unit 311A ​​exposes it pixel by pixel based on image data, and an electrostatic latent image is formed on its surface. The electrostatic latent image is developed by the developer unit 312A to form a toner image. The developer unit 312A has a developing roller positioned opposite the photoreceptor drum 313A. The developer unit 312A contains a two-component developer consisting of, for example, small-particle black toner and a carrier.

[0035] (Intermediate transfer belt 33, fixing device 35, etc.) The intermediate transfer belt 33 is rotatably stretched by a plurality of internally inscribed rollers and rotates clockwise as shown by the arrows in Figure 1. On the inner circumferential surface (back side) of the intermediate transfer belt 33, a plurality of primary transfer rollers 32 (also called the primary transfer section) are arranged facing the photoreceptor drum 313. During transfer, a primary transfer bias is applied to the primary transfer rollers 32 by a high-voltage power supply. The toner images formed on each photoreceptor drum 313 (313A to 313C) are sequentially transferred onto the intermediate transfer belt 33 by each primary transfer roller 32, and then transferred to the transported paper 90 by the secondary transfer rollers 34. The paper 90 on which the superimposed or sequentially transferred toner images have been transferred is transported to the downstream fuser 35, where it is heated and pressurized to form an image on the paper 90.

[0036] The fixing device 35 has a pressure roller and a heating roller, and the heating roller is controlled by a heater inside to reach a predetermined fixing control temperature. By passing the paper 90 through the fixing nip formed by both rollers, the paper 90 is subjected to heating and pressurizing treatment. In addition, the fixing device 35 is equipped with a pressure variable mechanism on the rotation axis of either the heating roller or the pressure roller, and the fixing pressure is increased or decreased by changing the distance between the two roller axes.

[0037] (Matching table) Figure 3 shows an example of a mapping table that indicates the settings for the developing unit and the coverage range of the original document. The mapping table also has image processing parameters linked to it. This is an example of a mapping table. The mapping table is pre-configured and stored in the storage unit 12.

[0038] In this embodiment, as described above, each developer unit 312A to 312C of the image-making units 31A to 31C contains a two-component developer composed of the same black toner. The use of each developer unit 312A to C is as follows. In the following, the developer units 312A to C may be referred to as developer unit A, B, and C, respectively, and the image-making units 31A to C may be referred to as image-making unit A, B, and C, respectively.

[0039] Image processing unit A (developer A) is for low coverage and is selected when the original document coverage is 0% or more and less than 5%. Image processing unit C (developer C) is for high coverage and is selected when the original document coverage is 30% or more and 100%. Image processing unit B (developer B) is for intermediate coverage and is selected when the original document coverage is 5% or more and less than 30%. Here, the original document coverage is calculated by the print controller 200 and sent to the control unit 11. In the examples shown in Figures 1 and 3, three developers 312 using the same color toner are shown, but this is not limited to this, and two or four developers 312 using the same color toner may also be used. The mapping table may also be a mapping table for two or four developers, depending on the number of developers. Furthermore, the range of original document coverage used may be changed as appropriate. For example, the settings may be configured by the user via the operation display unit 14. Also, although the developing units A, B, and C are arranged in this order in the rotational direction of the intermediate transfer belt 33, they are not limited to this and may be arranged in other orders.

[0040] (Patch concentration sensor 15) The patch density sensor 15 has a light-emitting element and a light-receiving element, and optically detects the density of patch-shaped toner images (hereinafter referred to as patch images) formed on the intermediate transfer belt 33 using each developer 312. The control unit 11 performs image stabilization control to adjust the image formation parameters based on the density detection value of the patch image. The adjusted image formation parameters are stored in the storage unit 12. The image formation parameters are also stored linked to the developer 312 in the mapping table.

[0041] (Toner supply unit 50) The toner supply unit 50 comprises a toner bottle 51, a toner hopper 52, and three toner supply units 53. The toner bottle 51 is detachable. The toner bottle 51 is loaded into the receiving unit of the main body in a new state with toner already filled inside. When the toner bottle 51 is completely used up, the user replaces it with a new one. The toner T supplied from the toner bottle 51 is temporarily stored in the toner hopper 52 below. The liquid level of the toner T in the toner hopper is detected by a detection sensor (not shown), and if the liquid level of the toner T falls below a predetermined height, the toner bottle 51 rotates and toner is supplied to the toner hopper 52 until the liquid level reaches the predetermined height. Each of the three toner supply units 53 consists of a transport screw and a toner transport path surrounding it. Each of the three toner supply units 53 is connected to one of the developers 312A, 312B, or 312C.

[0042] In the embodiment shown in Figure 1, multiple developer units 312 share a single toner hopper 52. By sharing the toner bottles 51 and toner hopper 52 among the multiple developer units 312, cost reduction and a reduction in the number of parts can be achieved. Toner is then supplied from the single toner hopper 52 to each developer unit 312A, 312B, and 312C by their respective toner supply units 53. Each developer unit 312 is equipped with a toner density sensor, and the supply by the toner supply unit 53 is controlled so that the toner density remains at a constant control density. The supply performance of the three toner supply units 53 is the same, but is not limited to this, and may be set to different supply performances (see Figure 11 below). Here, supply performance refers to the amount of toner supplied per unit time (g / sec) to the developer unit 312 by the toner supply unit 53.

[0043] (Functions of the control unit 11 and the print controller 200) The functions of the control unit 11 and the print controller 200 will be described below with reference to Figures 2 and 4. Figure 4 is a functional block diagram showing the schematic configuration of the image forming apparatus 100 and the print controller.

[0044] The control unit 11 functions as an image-making control unit 111 and also has a page memory inside. The print controller 200 functions as a coverage calculation unit 201.

[0045] The print controller 200 receives print jobs from a PC or the like via the communication unit. As described above, the received print job includes print data (mainly in PDL format) which is the source of image data, and print job information which describes print settings such as the type of paper to be used. Based on the print settings, the print controller 200 performs rasterization (RIP) processing to convert the print data into page-level bitmap data. The RIP image after rasterization is temporarily stored in the image memory inside the print controller 200 and then sent to the control unit 11. The control unit 11 of the image forming apparatus 100 temporarily stores the received RIP image in the compressed memory area of ​​the page memory. During normal printing, the RIP image stored in the compressed memory area is decompressed by the compression / decompression IC and sent as the original image to the exposure unit 311 of the image forming unit 31 via the writing processing unit, where exposure and other image formation processes are performed.

[0046] The coverage calculation unit 201 of the print controller 200 calculates the original document coverage for each page of the original image (the original image printed on one sheet of paper 90) based on the print data of the received print job. The calculated original document coverage information is sent to the image control unit 111 of the control unit 11. The image control unit 111 selects the developer unit 312 or image unit 31 to be used for image formation from among multiple developer units A to C (312A to 312C) that contain developer for the same color toner, according to the page-by-page original document coverage information received from the print controller 200. In this process, the image control unit 111 uses a mapping table.

[0047] The image processing control unit 111 refers to a mapping table as shown in Figure 3, and for example, if the original coverage of the first page is 10%, it selects the image processing unit B (developer B) for medium coverage. The image processing control unit 111 then sends a selection instruction to the page memory and the image processing unit. As a result, the RIP image stored in the page memory is sent as the original image to the exposure unit 311B of the selected image processing unit 31B, and image processing such as exposure is performed. The image processing control unit 111 also sends the image processing parameters associated with the selected image processing unit B to the image processing unit B. The image processing unit B performs image processing using the sent image processing parameters (condition 2).

[0048] (Image forming apparatus 100b of another embodiment) Figure 5 is a schematic diagram illustrating the general configuration of an image forming apparatus 100b according to another embodiment. The image forming apparatus 100x shown on the left side of Figure 5 is a comparative example. The image forming apparatus 100x comprises four imaging units 31Y, 31M, 31Cy, and 31K. Each imaging unit's developer contains a developer composed of toners of different colors corresponding to Y (yellow), M (magenta), Cy (cyan), and K (black). The toner images formed in these developers are superimposed on an intermediate transfer belt, transferred onto paper 90, and fixed to form a full-color image on the paper 90.

[0049] The image forming apparatus 100b, shown on the right side of Figure 5, is an image forming apparatus 100x with a modified toner color. Specifically, the toner color of the developing units 31M and 31Cy, and the toner color filled in the corresponding toner bottles of the toner supply unit 50, have been changed from magenta or cyan to black (K). In image forming apparatus 100b, the image forming units for colored toners (magenta, cyan) are repurposed as image forming units for black. Aside from the difference in toner color used, the substantial mechanical configuration of image forming apparatus 100b and image forming apparatus 100x is the same. The yellow (Y) image forming unit is not used and has been removed (indicated by a dashed line). However, the mechanical configuration may remain in the apparatus.

[0050] In this image forming apparatus 100b, the three imaging units 31A, 31B, and 31C function in the same way as in the image forming apparatus 100 shown in Figure 1.

[0051] (Problems caused by rapid changes in manuscript coverage) Next, with reference to Figures 6 and 7, the new problems identified by the present inventor will be explained.

[0052] Figure 6 is a table summarizing the relationship between document coverage and the properties of the developer and image output characteristics. If the document coverage changes rapidly during continuous printing of a single print job or between consecutive print jobs, the toner concentration and toner charge amount of the developer in the developer unit 312 change rapidly. The image forming apparatus 100 responds to this change by performing image stabilization control to keep the image density constant and by adjusting the image formation parameters.

[0053] As shown in Figure 6, this table illustrates the trends of each characteristic until convergence, under two conditions: when high coverage is continuous and when low coverage is continuous. In the case of high coverage, the band toner charge remains high, and the toner density remains low. The image density obtained with this characteristic remains low. To bring this image density to the target density, the image stabilization control adjusts the image parameters in a direction that increases developability. Conversely, in the case of low coverage, the band toner charge remains low, and the toner density remains high. The image density obtained with this characteristic remains high. To bring this image density to the target density, the image stabilization control adjusts the image parameters in a direction that decreases developability.

[0054] Figure 7 is a graph showing the changes in each characteristic when there is a rapid change from high coverage to low coverage. In Figure 7, the vertical axis represents the high or low level of each characteristic, and the horizontal axis represents the number of pages. At page x0, the coverage changes from high to low. Pages x1, x2, x3, and x4 are the timings for changing the image-making parameters due to image stabilization control. Image stabilization control here is performed by detecting patch images formed between page images (between sheets of paper) during continuous printing using the patch density sensor 15. Patch images are formed every predetermined number of pages, for example, from a few pages to several tens of pages, for example, every 30 pages. That is, the interval between pages x1 and x2, and the interval between pages x2 and x3, correspond to this predetermined number of pages (30 pages). The predetermined number of pages cannot be less than this due to constraints with other controls.

[0055] In Figure 7, as explained with reference to the table in Figure 6, due to the rapid change from high coverage to low coverage, the toner charge decreases and the toner density decreases from page x0 onwards. The image density temporarily remains high. Image stabilization control is performed on pages x1, x2, etc., but the image stabilization control cannot adequately follow the changes in density, and the density becomes temporarily unstable (within the dashed rectangle in the graph).

[0056] Conversely, when the original coverage of a continuous print changes from low coverage to high coverage, a large amount of toner is supplied to the developer in the developer unit, which had been maintaining a low charge level due to the low coverage. This causes a sudden increase in charge level, and consequently, the image density temporarily decreases. Similarly, since image stabilization control is performed at predetermined intervals of pages, it cannot adequately track changes in density, resulting in temporary density instability.

[0057] In this embodiment, as shown in the correspondence table in Figure 3, multiple developers A to C, each containing a developer for the same color toner, are selected according to their intended use, such as for low coverage, medium coverage, and high coverage. As a result, abrupt changes in coverage do not occur in each developer A to C, and the phenomenon of temporarily unstable density, as shown in Figure 7, can be suppressed.

[0058] (Selection and control of the developing unit according to the original document coverage) Next, each embodiment will be described with reference to Figures 8A to 14.

[0059] (First embodiment) Figure 8A is a flowchart showing the printing process in the first embodiment. Figure 8B is a graph showing the original document coverage and selected developer for each print job.

[0060] (Step S11) Here, the print controller 200 and the image forming apparatus 100 accept print jobs.

[0061] (Step S12) The print controller 200 analyzes the print data included in the print job and calculates the document coverage. The calculated document coverage is sent to the image forming control unit 111 of the image forming apparatus 100.

[0062] (Step S13) The image processing control unit 111 refers to the mapping table shown in Figure 3 and performs the following processing according to the range of document coverage received in step S12. If the document coverage is less than 5%, the image processing control unit 11 proceeds to step S14; if it is 5% or more but less than 30%, the processing proceeds to step S15; and if it is 30% or more, the processing proceeds to step S16.

[0063] (Step S14) Here, the image-forming control unit 111 selects developer unit A. In this case, the image-forming control unit 11 stops developers B and C. Stopping in this case means stopping the operation of the exposure unit 311, developer unit 312 (developers B and C), and photoreceptor drum 313 with respect to image-forming units B and C (the same applies hereafter).

[0064] (Step S15) The image processing control unit 111 selects developer unit B. In this case, the image processing control unit 11 stops developers units A and C.

[0065] (Step S16) The image processing control unit 111 selects developer unit C. In this case, the image processing control unit 11 stops developers units A and B.

[0066] (Step S17) The image forming unit 30 uses the developer 312 selected in any of steps S14 to S16 to create an image and form an image on the paper (end).

[0067] Refer to Figure 8B. If the original coverage remains below 5% for a single print job or for consecutive pages, as in print job 1, the image is formed using the selected low-coverage developer A. If the original coverage remains between 5% and 30% for a single print job, as in print job 2, the image is formed using the selected medium-coverage developer B. If the original coverage remains above 30% for a single print job, as in print job 3, the image is formed using the selected high-coverage developer C.

[0068] Thus, in the first embodiment, the image forming apparatus comprises an image forming unit having a plurality of developers containing the same color toner, and an image forming control unit that selects a developer from the plurality of developers to be used for image formation according to the original coverage based on the image data. This prevents unstable image quality by selecting the appropriate developer based on the original coverage information. In particular, in the first embodiment, the usage range of the original coverage is set in advance for each developer as shown in the correspondence table. Then, by selecting each developer according to its application using this, even if the development coverage changes between print jobs, it is possible to prevent the phenomenon of temporarily unstable density without causing abrupt changes in coverage in each developer.

[0069] (Second embodiment) Figure 9A is a flowchart showing the printing process in the second embodiment. Figure 9B is a graph showing the original document coverage and selected developer for one print job.

[0070] (Steps S21, S22) The processing here is the same as steps S11 and S12 shown in Figure 8A, so the explanation is omitted. The document coverage information acquired by the image control unit 111 is information about multiple pages.

[0071] (Step S23) The image processing control unit 111 extracts page breaks that straddle the boundaries of the usage range. In the example of the mapping table shown in Figure 3, the document coverage at the boundaries is 5% and 30%. The image is then divided into multiple sections before and after the page break.

[0072] In the example shown in Figure 9B, the image control unit 111 determines that page x11 corresponds to a page break where it crosses 5% (or 30%) of the boundary, and divides the pages up to this point into section 1 and the pages after it into section 2. The image control unit 111 then determines that the developer to be used for section 1 is developer A, and the developer to be used for section 2 is developer C. It is preferable to perform this step S23 before executing the print job, but it may also be performed while the print job is being executed (the same applies to step S34 in other embodiments described later). For example, once the page range for section 1 and the developer to be used have been determined, the printing of section 1 is started and executed while the page break determination process for section 2 and beyond in step S23 is performed in parallel.

[0073] (Step S24) The image forming apparatus 100 starts printing the print job received in step S21.

[0074] (Steps S25, S26) The image processing control unit 111 performs image processing using the developer determined for each section. Thereafter, the process in step S25 is repeated until the print job is completed (S26: NO), and when the print job is completed (S26: YES), the process is terminated (end).

[0075] Thus, in the second embodiment, the image forming control unit of the image forming apparatus determines the page breaks where the original coverage crosses the boundaries of the usable range, divides the print job into multiple sections based on the page breaks, and pre-determines the developer to be used for image formation in each section. This provides the same effect as in the first embodiment. That is, by selecting an appropriate developer based on the original coverage information, it is possible to prevent image quality from becoming unstable even if the development coverage changes during a single print job.

[0076] (Third embodiment) Figure 10A is a flowchart of the printing process in the third embodiment. Figure 10B is a graph showing the original document coverage and selected developer for one print job. In the third embodiment described below, the original document coverage is subjected to a moving average process.

[0077] (Steps S31, S32) The processing here is the same as steps S21 and S22 shown in Figure 9A, so the explanation is omitted. The document coverage information acquired by the image control unit 111 is information about multiple pages.

[0078] (Step S33) The image processing control unit 111 performs moving average processing of the original document coverage. For example, for the original document coverage information for each page, it calculates the average of the original document coverage for the window size (the most recent predetermined number of pages) as the moving average for that page. The window size is, for example, 5 pages, and the average value of the 5 pages including the page in question is used as the moving average. For initial pages that do not fit within the window size, the original document coverage of the pages up to that page may be averaged. For example, for page n, which does not fit within the window size of 5 pages, the average value of the original document coverage of pages 1 to n is used as the moving average for that page n.

[0079] (Step S34) The image processing control unit 111 extracts page breaks that straddle the boundaries of the usage range. This differs from step S23 in that it uses the original document coverage after moving average processing, but otherwise the process is the same. In the example of the mapping table shown in Figure 3, the original document coverage at the boundaries is 5% and 30%. The image is then divided into multiple sections before and after the page break.

[0080] In the example shown in Figure 10B, the image processing control unit 111 determines that page x22 corresponds to a page break that crosses 5% of the boundary, and divides the pages up to this point into section 1 and the pages after this point into section 2. The image processing control unit 111 then determines that the developer to be used for section 1 is developer A, and the developer to be used for section 2 is developer B, which corresponds to medium coverage.

[0081] (Steps S35-S37) Here, the developing unit determined in step S34 is used to create images for each section and execute the print job. Steps S35 to S37 are the same as steps S24 to S26 in Figure 9A, and their explanation is omitted.

[0082] Thus, in the third embodiment, the image forming apparatus comprises an image forming unit having a plurality of developers containing developers of the same toner color, and an image forming control unit that selects a developer from the plurality of developers to be used for image formation according to the original coverage based on the image data. The image forming control unit also determines a page break where the moving average of the original coverage in a predetermined number of pages crosses the boundary of the usage range, divides the print job into multiple sections by the page break, and predetermines the developer to be used for image formation in each section. In this way, the same effects as in the first and second embodiments can be obtained, and the following effects can be obtained by using the moving averaged original coverage. If the change in original coverage frequently crosses the boundary, the developer used for image formation will have to be switched frequently during the print job. When switching developers, processing such as starting up the stopped developer and stopping the operating developer is required, which reduces productivity. By using the moving averaged original coverage, it is possible to reduce the frequency of crossing the boundary, and thus the decrease in productivity can be suppressed. For example, in the example shown in Figure 10B, it is possible to suppress the occurrence of developer switching on pages x21, x23, x24, etc.

[0083] (Fourth embodiment) Figure 11 is a table showing the conditions set for each developer for low to high coverage in the fourth embodiment.

[0084] (4-1) Placement position In the fourth embodiment, regarding the arrangement, a developer 312 for low coverage is placed upstream in the direction of movement of the intermediate transfer belt 33, and a developer 312 for high coverage is placed downstream. Specifically, as shown in Figure 1, the developer A (image unit A) for low coverage is placed at the uppermost position, the developer B (image unit B) for medium coverage is placed in the middle position, and the developer C (image unit C) for high coverage is placed at the lowermost position. This is to take into account the effect of reverse transfer. Reverse transfer is a phenomenon in which a portion of the toner that has been primary transferred to the intermediate transfer belt 33 by the upstream image unit 31 returns to the surface of the downstream photoreceptor drum 313 in the primary transfer further downstream. Reverse transfer reduces the transfer rate in the upstream image unit. If the high-coverage developer 312 is placed upstream, the amount of toner returning to the downstream photoreceptor drum 313 due to the reverse transfer phenomenon will also increase in order to always produce images with high coverage. If the developability is increased to compensate for the amount of toner returning to maintain image density, the amount of toner will increase accordingly due to the higher coverage. To avoid this, a lower-coverage developer is placed upstream.

[0085] Furthermore, in a low-coverage developer, as explained with reference to Figure 6, the toner charge is lower and the toner density remains higher. Therefore, in a low-coverage developer, toner is prone to scattering (scattering due to the rotation of the developing roller), and the scattered toner accumulates on the surrounding components of the developer, and there is a high possibility that it will fall downwards. Even in such cases, by positioning the low-coverage developer at the uppermost position (upward in the direction of gravity), even if toner falls, it will adhere to the developer below, thus preventing it from falling onto the paper 90 or the transport path of the paper 90. In other words, quality defects caused by adhesion to the paper 90 can be prevented.

[0086] (4-2) Developer storage capacity In the fourth embodiment, regarding the amount of developer stored, the amount of developer stored in the low-coverage developer is reduced, and the amount of developer stored in the high-coverage developer is increased. Specifically, as shown in the table in Figure 11, the amount of developer stored in the low-coverage developer A is the smallest, the amount of developer stored in the medium-coverage developer B is an intermediate amount, and the amount of developer stored in the high-coverage developer C is the largest. For example, there may be a 20-30% difference between the minimum and maximum amount of developer stored. In this case, even if the size of the slot (space) in which each developer is loaded is the same, the internal volume may be changed by changing the shape of the inside of the developer, so that the volume differs according to the amount of developer stored.

[0087] At low coverage, toner consumption is low, so the toner resides in the developer for a longer time (average residence time), which makes the toner more prone to degradation. Toner degradation here refers to, for example, the embedding or detachment of the extrusion agent added to the toner due to prolonged residence. By reducing the amount of developer, the toner resides for a shorter time, and toner degradation can be suppressed. On the other hand, in developers for high coverage, toner consumption is high, so keeping up with image density and ensuring sufficient toner agitation time become issues. To address these issues, increasing the amount of developer can be expected to improve both image density keeping and toner agitation time.

[0088] (Toner supply performance of toner supply unit 50) High-coverage developers consume a large amount of toner, requiring a higher toner supply rate from the toner replenishment unit 50 per unit time. However, if this increased toner supply is used to replenish a low-coverage developer, it can result in over-supply (overshoot), potentially leading to unstable toner density fluctuations.

[0089] Therefore, in the fourth embodiment, the amount of toner supplied from the toner hopper 52 to each developer 312 by the toner supply unit 53 is varied. Specifically, the amount of toner supplied to the developer 312 for high coverage is set to be greater than the amount supplied to the developer 312 for low coverage. The amount of toner supplied can be set by the pitch, outer diameter, or rotational speed (rpm) of the drive motor of the transport screw of the toner supply unit 53.

[0090] (Fifth embodiment) Figure 12 is a table showing the conditions set for each developer for low to high coverage in the fifth embodiment.

[0091] (5-1) Conditions for retention In the case of high coverage, the amount of toner on the paper is large, so the fixing force of the fuser unit 35 needs to be high. For example, to increase the fixing force, at least one of a high fixing temperature (fixing control temperature) and a high fixing pressure is required. On the other hand, if the same fixing force is applied to low coverage, the fixing force will be excessive, resulting in excessive paper curling and wasted power. For this reason, in the case of low coverage, since the amount of toner on the paper is small, neither a high fixing temperature nor a high fixing pressure is necessary, and a low fixing force is sufficient.

[0092] For these reasons, in the fifth embodiment, with respect to the fixing conditions of the fixing device 35, the fixing force (also called fixing performance) when using a high-coverage developer is set higher than the fixing force (also called fixing performance) when using a low-coverage developer. By doing so, it is possible to prevent the supply of more power than necessary, and to avoid using rollers (pressure rollers / heating rollers) at a fixing pressure that is greater than necessary, thereby saving energy and suppressing a decrease in fixing durability.

[0093] (5-2) Primary Transcription Conditions In a low-coverage developer, toner consumption is low, resulting in a longer toner residence time (average residence time) within the developer, which makes the toner more prone to degradation. Consequently, the toner's charge level is low. On the other hand, in a high-coverage developer, toner consumption is high, resulting in a shorter toner residence time within the developer, which prevents toner degradation and results in a higher toner charge level. For these reasons, the appropriate value of the primary transfer bias applied to the primary transfer roller 32 differs. Therefore, in the fifth embodiment, the output of the primary transfer bias is set lower when imaging with a low-coverage developer and higher when imaging with a high-coverage developer. This allows for the application of the optimal primary transfer bias for each toner charge level, thereby improving transfer efficiency.

[0094] (Sixth embodiment) Figure 13 is a diagram illustrating the size of the patch image in the sixth embodiment. In Figure 13, the notation for the imaging unit 31, etc., is omitted.

[0095] The developer in the developer unit 312 for high to low coverage is in the state of the developer used when imaging for each respective original coverage range. The imaging parameters are then adjusted so that a constant image density is achieved in that developer state.

[0096] As described above, in image stabilization control, an image patch is created for detection by the patch density sensor 15. The image patch created at this time is usually sized to correspond to the detection area of ​​the patch density sensor 15, so the amount of toner in the patch image is low when converted to coverage.

[0097] In the example shown in Figure 13, the size of the patch image for developer A, which is designed for low coverage, is small, corresponding to the detection range of the patch density sensor 15. The amount of toner in the patch image of this size corresponds to the low coverage range (0-5%).

[0098] If image stabilization control is performed on developer C, which is designed for high coverage, using a patch image of this size as is, the image will be produced with low coverage outside the usable range of the original document coverage while the image stabilization control is active, and the state of the developer will change.

[0099] Therefore, in the sixth embodiment, in order to minimize changes in the state of the developer, the size of the image patch is set so that the amount of toner in the image patch created by image stabilization control corresponds to the usable range of the original coverage of each developer. In the example shown in Figure 13, the size of the patch image for developer C, which is for high coverage, is set to be between 30% and 100% in terms of original coverage. In this way, changes in the state of the developer due to the formation of the patch image can be suppressed.

[0100] (Seventh Embodiment) Figure 14 illustrates the process of printing a high-coverage image on one page distributed across multiple developing units in the seventh embodiment. Figure 14(a) is a schematic diagram showing the image data of one page of the original document and its distribution, and Figure 14(b) is a table showing the allocation of the original document coverage distributed across developing units A to C.

[0101] In the first to sixth embodiments described so far, when the original document coverage was 60%, developer unit C for high coverage was selected, and imaging was performed using only developer unit C. However, continuously imaging such high original document coverage with a single developer unit places a heavy load on the unit. Therefore, when the original document coverage is above a predetermined value, for example, 60% or more, the imaging control unit 111 distributes the image to developer unit A for 5%, developer unit B for 20%, and developer unit C for the remaining 35%. The image is then distributed and processed in each developer unit A to C (imaging units A to C), and combined on the intermediate transfer belt 33 to form an image for one page. Figures 14(a) and (b) show the state in which the image has been formed by distributing it in developer units A to C in this way. Here, the distribution to each developer unit may be done by simply dividing one page by area, or it may be done by distributing it according to the objects of the text image and graphic image such as a photograph. For example, text images are processed in developer unit A, while graphic images are divided among developer units B and C depending on their size. This prevents the load from being concentrated on a single developer unit C, which is used for high coverage.

[0102] The configuration of the image forming apparatus 100 described above is intended to illustrate the main features of the above embodiment, and is not limited to the above configuration. Various modifications can be made within the scope of the claims. Furthermore, it does not preclude configurations that are common to general image forming apparatuses.

[0103] For example, each embodiment may be combined and implemented, or only some of the configurations may be implemented. For example, the first to third embodiments may be combined with the fourth to seventh embodiments. Also, the fourth to seventh embodiments may be combined with each other. Furthermore, in the fourth embodiment, instead of applying all of (4-1) placement position, (4-2) developer storage amount, and (4-3) toner supply amount, at least one of them may be applied. Similarly, in the fifth embodiment, instead of applying both (5-1) fixing conditions and (5-2) primary transfer conditions, only one of them may be applied.

[0104] Furthermore, the means and methods for performing various processing in the image forming apparatus 100 according to the above embodiment can be implemented by either a dedicated hardware circuit or a programmed computer. The program may be provided, for example, on a computer-readable recording medium such as a USB memory stick or a DVD (Digital Versatile Disc)-ROM, or it may be provided online via a network such as the Internet. In this case, the program recorded on the computer-readable recording medium is usually transferred to and stored in a storage unit such as a hard disk. The program may also be provided as a standalone application software, or it may be incorporated into the software of the apparatus as a function of the apparatus.

[0105] While embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are for illustrative purposes only and are not limiting. The scope of the present invention should be interpreted in accordance with the language of the appended claims.

[0106] The means and methods for performing various processing operations in the image forming apparatus according to the above embodiment can be implemented by either a dedicated hardware circuit or a programmed computer. The program may be provided, for example, on a computer-readable recording medium such as a USB memory stick or a DVD (Digital Versatile Disc)-ROM, or it may be provided online via a network such as the Internet. In this case, the control program recorded on the computer-readable recording medium is usually transferred to and stored in a storage unit such as a hard disk.

[0107] While embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are for illustrative purposes only and are not limiting. The scope of the present invention should be interpreted in accordance with the language of the appended claims. [Explanation of Symbols]

[0108] 100 Image forming apparatus 11 Control Unit 111 Image Forming Control Unit 12 Storage section 13 Paper feeding and transport section 14 Operation display section 15 Patch concentration sensor 30 Image forming unit 31, 31A, 31B, 31C Image-making units 311, 311A, 311B, 311C Exposure section 312, 312A, 312B, 312C developer 313, 313A, 313B, 313C Photoconductor Drum 32, 32A, 32B, 33C Primary Transfer Rollers 33 Intermediate transfer belt 34 Secondary transfer roller 35 Fixing device 50 Toner Refill Unit 51 Toner Bottles 52 Toner Hopper 53 Toner supply unit 200 Print Controllers 201 Coverage Calculation Unit

Claims

1. An image forming unit having multiple developing units containing the same color toner and forming an image on a recording medium based on image data, An imaging control unit that selects from among the plurality of developing units to be used for imaging according to the original coverage based on image data, An image forming apparatus comprising:

2. Each of the aforementioned multiple developing units has a pre-set range for the use of original document coverage. The image forming apparatus according to claim 1, wherein the image forming control unit selects a developer whose original coverage value corresponds to the usage range.

3. It is connected to a print controller having a coverage calculation unit that calculates the document coverage using the aforementioned image data. The image forming apparatus according to claim 2, wherein the image forming control unit selects the developer to be used for image formation according to the original coverage obtained from the print controller.

4. The image forming apparatus according to claim 3, wherein the image forming control unit selects a developer to be used for image formation for a single print job, a page included in the print job, or a plurality of pages in which images are formed consecutively, using the original coverage calculated by the coverage calculation unit.

5. The coverage calculation unit calculates the progression of page-by-page document coverage in advance for a single print job. The image forming apparatus according to claim 3, wherein the image forming control unit determines a page break where the document coverage crosses the boundary of the usage range, divides the print job into a plurality of sections according to the page break, and predetermines a developer to be used for image formation in each section.

6. The coverage calculation unit calculates the progression of page-by-page document coverage in advance for a single print job. The image forming apparatus according to claim 3, wherein the image forming control unit determines a page break where the moving average of the original coverage in a predetermined number of pages crosses the boundary of the usage range, divides the print job into a plurality of sections according to the page break, and predetermines the developer to be used for image formation in each section.

7. The image forming unit is The system comprises multiple image-forming units, each having one of the aforementioned developing units and photoreceptors, and an intermediate transfer body. The image forming apparatus according to claim 2, wherein, in the direction of movement of the intermediate transfer body, the range of original document coverage set in the developer of the imaging unit located upstream is set to have lower coverage than the range of original document coverage set in the developer of the imaging unit located downstream.

8. The image forming apparatus according to claim 2, wherein, among the plurality of developing units, the amount of developer stored in the developing unit set to high coverage as the operating range is greater than the amount of developer stored in the developing unit set to low coverage.

9. The toner supply unit includes a toner bottle, a toner hopper for temporarily storing the toner supplied from the toner bottle, and a toner supply unit for supplying the toner in the toner hopper to a developer. The aforementioned multiple developing units use a common toner hopper, The image forming apparatus according to claim 2, wherein the toner supply unit comprises a plurality of units, each of which transports toner from the toner hopper to its respective developer, and the amount of toner supplied per unit time to the developer by the toner supply unit is set to be greater for the developer supply unit set to high coverage than for the supply unit set to low coverage as the operating range.

10. The image forming apparatus according to claim 2, wherein the image forming parameters for each of the plurality of developing units are linked to each of the developing units.

11. Of the aforementioned image-forming parameters, regarding the fixing conditions for the paper on which the toner image has been transferred, The image forming apparatus according to claim 10, wherein, among the plurality of developing units, the fixing conditions when image formation is performed using a developing unit set to high coverage as its operating range are set to conditions that result in higher fixing force than the fixing conditions when image formation is performed using a developing unit set to low coverage.

12. Of the aforementioned image-forming parameters, with respect to the primary transfer bias applied to the primary transfer section when transferring the toner image formed on the photoreceptor by the developing unit to the intermediate transfer unit, The image forming apparatus according to claim 10, wherein, among the plurality of developing units, the primary transfer bias when image formation is performed using a developing unit set to high coverage as its operating range is set to a higher condition than the primary transfer bias when image formation is performed using a developing unit set to low coverage.

13. In image stabilization control, in which a patch image is formed by the developer in order to maintain a constant density, and the image-forming parameters are set based on the detected density of the patch image, The image forming apparatus according to claim 10, wherein the patch image of each of the multiple developing units is set to a size that results in coverage within the original coverage range of each developing unit.

14. If the manuscript coverage is higher than the specified level, The image forming apparatus according to claim 1 or claim 2, wherein the image forming control unit divides an image of one page and forms images of the image of one page by distributing them using a plurality of the same color developing units.

15. A control program for controlling an image forming apparatus that has multiple developing units containing developers of the same toner color, and an image forming unit that forms an image on a recording medium based on image data, A control program for causing an image forming apparatus to perform a selection process to select one of the multiple developing units to be used for image formation, based on the original coverage determined by the image data.

16. Each of the aforementioned multiple developing units has a pre-set range for the use of original document coverage. The control program according to claim 15, wherein the selection process selects a developer corresponding to the usage range based on the value of the original document coverage.

Images