JP2017062375A - Image forming apparatus and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a change in image quality before and after switching between the operation of a single station and the operations of a plurality of stations.SOLUTION: A CPU 604 controls an image forming operation by selectively switching, as an image forming mode, between a single mode where a single station operates to form a monochrome image on a sheet, and a plurality mode where two or more stations operate in parallel to form images in the same color overlapped on a sheet. During the plurality mode, two or more stations 125 operate at an image density allotment ratio N set thereto, and the allotment ratio is changed for each of image pages.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a technique for improving image quality in an image forming apparatus having a plurality of stations for forming an image.

  Conventionally, an image forming apparatus having a plurality of stations for forming an image is known. For example, in an image forming apparatus that forms a full-color image, generally, an image of each color developed by a developer (toner) of each color of Y (yellow), M (magenta), C (cyan), and K (black) is superimposed. And formed on a sheet (recording material). Thereby, a full color image is formed. Here, the developer of each color of Y, M, C, and K is stored in an independent developer container. In the case of an electrophotographic full-color tandem image forming apparatus, a toner container, a developing device, and a photoreceptor necessary for development are provided independently for each of Y, M, C, and K colors. Here, a set of a toner container and a developing device (which may include a photoconductor) corresponding to each color is referred to as a station.

  In an image forming apparatus, there are cases where full color output is required, and there are cases where it is desired that a larger number of continuously printable sheets can be obtained with monochrome output. In order to realize the latter, there is a technique that uses the basic configuration of a full-color image forming apparatus and increases the number of continuously printable monochrome images. For example, as illustrated in FIG. 9, in this technique, K (black) toner is accommodated in a plurality of toner containers, and is operated as a monochrome image forming apparatus having a plurality of stations of the same color.

  Specifically, in the case where normal color image formation is performed in each of the Y, M, C, and K stations 124y, m, c, and k, the toners (y, m, c and k) are accommodated. On the other hand, when used as an image forming apparatus having four black monochrome stations, black toner (indicated by K1, K2, and K3) is also stored in the toner containers of the stations 124y, m, and c. If the toner in the toner container runs out during image formation selectively using a certain station, the station used for image formation is switched to another station containing toner and image formation is performed. continue. Thereby, in the image formation of the same color, the image forming operation can be continued without performing the operation of supplying the toner to the station where the toner has run out. This technique has the advantages of reducing downtime and increasing the number of continuously printable sheets.

JP 2002-351190 A

  However, since each station has various unique characteristic values, as in Patent Document 1, when the used station is switched to the next station when the toner runs out, the density is changed between the pages before and after the switching. A change in image quality such as a change may occur. Depending on the degree of the change, the image quality may be noticeable. For example, the image density changes immediately after switching the station to be used due to the electrostatic state (T / D ratio) of the toner and the gap between the developing device and the photosensitive member for each station. The difference in image quality may be noticeable.

  Note that Patent Document 1 also describes monochromatic image formation using a plurality of stations. In this case, a change in image quality may occur before and after switching between a single operation and a plurality of operations of the station.

  An object of the present invention is to suppress a change in image quality before and after switching between a single operation and a plurality of operations of a station.

  In order to achieve the above object, the present invention provides an image forming apparatus having a plurality of stations for forming an image of the same color, wherein a single station operates as the image forming mode. Selectively switching between a single mode in which a single color image is formed on a sheet and a plurality of modes in which two or more of the plurality of stations operate in parallel to form images on a sheet. Control means for controlling the image forming operation, and the control means controls the image density to be assigned to each of the two or more operating stations when the image forming operation is controlled in the plurality of modes. It is characterized by.

  According to the present invention, it is possible to suppress a change in image quality before and after switching between a single operation and a plurality of operations of a station.

1 is a cross-sectional view of an image forming apparatus. 2 is a block diagram illustrating a control mechanism of the image forming apparatus. FIG. It is a time chart which shows the outline | summary of the operation | movement in developing station automatic switching control. It is a figure which shows the transition (FIG. (A)) of the laser light quantity setting value and sharing rate at the time of several modes, a change of a sharing rate (FIG. (A)), and a change of the sharing rate at the time of a single use mode (FIG. (C)). is there. It is a time chart which shows the outline | summary of operation | movement at the time of a single use mode. It is a flowchart which shows the image formation process regarding a monochromatic image. FIG. 7 is a flowchart continued from FIG. 6. It is a figure which shows the example of the confirmation message displayed at the time of use-up mode transfer. It is a figure which shows a mode that a color image forming apparatus is operated as a monochrome image forming apparatus which has two or more stations of the same color.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 is an electrophotographic full color tandem image forming apparatus. The image forming apparatus 100 includes four developing stations 125 (125y, 125m, 125c, and 125k) for forming four-color images of yellow (Y), magenta (M), cyan (C), and black (K). Have.

  Each developing station 125 (hereinafter abbreviated as station 125) includes a process unit 101 (101y, 101m, 101c, 101k) and a laser exposure device 104 (104y, 104m, 104c, 104k). Each station 125 further includes a toner container 106 (106y, 106m, 106c, 106k). Each process unit 101 includes a developing device 105 (105y, 105m, 105c, 105k), a photosensitive drum 102 (102y, 102m, 102c, 102k), and a cleaner 103 (103y, 103m, 103c, 103k). Each toner container 106 stores toner of a color corresponding to each station 125. Each toner container 106 is also provided with a remaining toner storage unit 121 (121y, 121m, 121c, 121k) which is a nonvolatile memory (see FIG. 2). Primary transfer rollers 107 (107y, 107m, 107c, 107k) are disposed on the opposite side of each photosensitive drum 102 with the intermediate transfer belt 108 interposed therebetween.

  The toner image formed at each station 125 is superimposed on the intermediate transfer belt 108 and primarily transferred. The toner images superimposed on the intermediate transfer belt 108 are conveyed and transferred onto a synchronized sheet (paper) by a registration roller 115 on a nip where the driving roller 122 and the secondary transfer roller 110 abut.

  In the present embodiment, an example in which the image forming apparatus 100 is used as a monochrome image forming apparatus is illustrated. Specifically, black (K) toner is stored not only in the toner container 106k but also in the toner containers 106y, 106m, and 106c, and a single color (black) toner image is formed in the same manner as in the case of color image formation. Superimpose on the intermediate transfer belt 108. Then, the toner image on the intermediate transfer belt 108 is transferred to a sheet. Accordingly, each station 125 is a plurality of stations for forming the same color image. Since the positional relationship between the conveyed sheet and each station 125 is the same as that in the case of color image formation, the timing of image synchronization is as described above.

  FIG. 2 is a block diagram illustrating a control mechanism of the image forming apparatus 100. The control board 600 includes a CPU 604 that performs basic control of the image forming apparatus 100, a RAM 602 that functions as a work area for the control program, and a ROM 601 that stores the control program. Each of the four stations 125 and the primary transfer roller 107 corresponds to the image forming unit 608. The operation unit 603 is a touch panel that can accept key inputs and display control information. When printing is instructed from the operation unit 603, the CPU 604 controls the image forming unit 608, the motors 609 to 612, and the separation motor 613 according to the program stored in the ROM 601. A motor 612 is a motor that drives the photosensitive drum 102k and the developing unit 105k. Similarly to the motor 612, the motors 609, 610, and 611 are motors that drive the photosensitive drums 102y, 102m, and 102c and the developing units 105y, 105m, and 105c, respectively. The separation motor 613 is a motor that controls contact between the intermediate transfer belt 108 and each process unit 101.

  The image data management unit 700 includes an image data storage unit 701 that stores image data for image formation, and an image data processing unit 702 that performs calculations and operations related to image data. The image data storage unit 701 is connected to the laser exposure apparatus 104 via a data bus 703, and a desired image is obtained by sending image data to the laser exposure apparatus 104 via the data bus 703 during an image forming operation. The image data processing unit 702 is connected to the CPU 604 via the communication interface 704.

  The toner remaining amount storage unit 121 holds information on the weight of toner stored in the corresponding toner container 106 as the toner remaining amount. The mechanism is as follows. First, when the image forming apparatus 100 is shipped from the factory, the toner weight stored in the toner container 106 is stored in the toner remaining amount storage unit 121 as an initial value. During the image forming operation, in synchronization with the developing operation, the image data management unit 700 notifies the control program executed by the CPU 604 of the amount of toner consumed in the operating station 125. In response to this notification, the control program reads the remaining toner amount from the corresponding remaining toner storage unit 121 and overwrites the remaining toner storage unit 121 with the value reduced by the consumed toner amount. As a result, the remaining amount of toner is updated according to the image forming operation. If necessary, the CPU 604 can access the remaining toner storage unit 121 via the IO interface 605 and acquire the remaining toner. Therefore, the toner remaining amount detection by the CPU 604 is realized by reading the toner remaining amount from the toner remaining amount storage unit 121 in each toner container 106.

  Next, an image forming operation when the image forming apparatus 100 is used as a monochrome machine will be described with reference to FIGS. 1 and 2. As a representative of the four stations 125, a basic image forming operation related to the station 125k will be described.

  When an image formation start signal is issued, the separation motor 613 is driven, the intermediate transfer belt 108 comes into contact with the process unit 101k, and the photosensitive drum 102k that is driven to rotate at a predetermined process speed is charged to a negative polarity. Then, the laser exposure device 104k irradiates a laser beam corresponding to an image signal input from the image data management unit 700 via the data bus 703, thereby forming an electrostatic latent image on the photosensitive drum 102k.

  Then, a black toner is attached to the electrostatic latent image formed on the photosensitive drum 102k by the developing unit 105k to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 102k is applied, thereby forming a toner image. Visualized. In primary transfer, a primary transfer bias (opposite polarity (positive polarity) with respect to toner) is applied to the primary transfer roller 107k. At this time, the toner image on the photosensitive drum 102k is primarily transferred to the driven intermediate transfer belt 108 in a state where the primary transfer roller 107k is pressed against the photosensitive drum 102k via the intermediate transfer belt 108.

  The toner image on the intermediate transfer belt 108 is conveyed to a secondary transfer portion between the driving roller 122 and the secondary transfer roller 110 shown in FIG. The sheet fed by the feeding cassette 113 passes through a substantially vertical conveyance path in accordance with the timing at which the leading edge of the toner image moves to the secondary transfer unit, and is transferred to the secondary transfer unit by the registration roller 115. Be transported. The toner image is secondarily transferred collectively to the sheet conveyed to the secondary transfer unit by the secondary transfer roller 110 to which a secondary transfer bias (polarity opposite to the toner (positive polarity)) is applied. The residual toner remaining on the intermediate transfer belt 108 after the secondary transfer is scraped off by the transfer cleaning device 111, and is conveyed and collected as a collected toner.

  The recording medium on which the toner image is formed is conveyed to a fixing device 117 positioned downstream from the secondary transfer portion, and the toner image is heated and pressed at a fixing nip portion between the fixing roller 118 and the pressure roller 119. Then, the image is heat-fixed on the surface of the sheet, and a series of image forming operations is completed.

  For the other process units 101 (101y, 101m, 101c), after the intermediate transfer belt 108 contacts the process units 101y, 101m, 101c, an image forming operation is performed in the same manner as described above for the process unit 101k.

  Next, the image forming mode will be described. In this embodiment, in the image forming mode, a single station 125 operates to form a single color image on a sheet, and two or more stations 125 operate in parallel to generate the same color. There is a “multiple mode” in which images are superimposed and formed on a sheet. The “multiple mode” includes a “single use mode” as a predetermined mode. The single color or the same color here means black, but other colors may be used. The CPU 604 functions as a control unit that selectively switches the image forming mode to control the image forming operation. In image forming processing (FIGS. 6 and 7) described later, the processing in steps S104 to S108 corresponds to a single mode. Further, the processing in steps S115 to S119 corresponds to a mode that is not a single use mode among a plurality of modes, and the processing in steps S124 to S129 corresponds to a single use mode.

  FIG. 3 is a time chart showing an outline of the operation in the development station automatic switching control. FIG. 3 particularly shows a case of switching from single mode → multiple mode → single mode.

  In the present embodiment, when the remaining amount of toner in the station 125 operating during image formation in the single mode falls below the reference value T1, the image formation mode is switched to a plurality of modes, and the station 125 is the next in order. Shift to parallel operation. Here, the order of the next station 125 to be added to the operation when switching from the single mode to the plurality of modes is determined in advance, and the information is stored in the ROM 601 or the like. As an example of the order, the first station 125 is the station 125y, and then the stations 125m, 125c, and 125k. Note that the order is not limited to this example, and the CPU 604 may determine the order at the start of image formation.

  Hereinafter, one station 125 operating in the single mode is referred to as a first station S1. Of the two stations 125 operating in the plural mode, the station 125 added later is referred to as a second station S2.

  In the example shown in FIG. 3, image formation is started using the first station S1 in accordance with the print job. However, the toner in the toner container 106 of the first station S1 has decreased in the middle, so that the second station S2 is used. It is a situation that gradually switches to. That is, when a print job is input, image formation is started in a single mode using a single first station S1 at time t0. Then, it is assumed that the remaining toner amount Tr1 in the toner container 106 of the first station S1 becomes less than a reference value T1 (for example, 10 mg) at time t1.

  Assuming that the single mode is continued as it is, and after the toner in the first station S1 runs out, the station 125 to be used is switched to the next station 125 to form an image in the single mode. In this case, a change in image quality may be conspicuous on pages before and after switching between the first station S1 and the next station 125. Therefore, the CPU 604 once switches to a plurality of modes by the parallel operation of the stations S1 and S2.

  In the plural modes by the stations S1 and S2, the toner images formed by the stations S1 and S2 are respectively primary transferred onto the intermediate transfer belt 108, and the toner images superimposed on the intermediate transfer belt 108 are transferred onto the sheet by the secondary transfer roller 110. Is transcribed. These operations are performed at the timing of image synchronization of the stations S1 and S2. The time period from time t1 to time t2 is the control period in the multiple mode. After time t2, image formation in a single mode is performed using station 125 (which will be referred to as station S1), which was station S2 until then.

  Here, when the image forming operation is controlled in a plurality of modes, the CPU 604 sets an image density sharing ratio N (N1, N2) that is an image density ratio shared by each of the operating stations S1 and S2. Each image density sharing ratio N (hereinafter abbreviated as “sharing ratio N”) is set so as to gradually change during a control period in a plurality of modes, instead of suddenly switching when the image forming mode is switched.

  FIG. 4A is a diagram illustrating the transition of the sharing ratios N1 and N2 of the first and second stations S1 and S2 during the multi-mode operation period. At time t1 when the mode is switched from the single mode to the plurality of modes, the sharing ratio N1 of the first station S1 is 100%, and the sharing ratio N2 of the second station S2 is 0%. Thereafter, the CPU 604 subtracts the share rate increase / decrease value Cn (for example, Cn is a fixed value of 10%) from the share rate N1 for each page of the image, and adds the increase / decrease value Cn to the share rate N2. . At the time t2 when the mode is switched from the plurality of modes to the single mode, the sharing ratio N1 of the first station S1 is 0%, and the sharing ratio N2 of the second station S2 is 100%. In this way, the specific gravity of concentration sharing is gradually (stepwise) transferred from the first station S1 to the second station S2.

Here, the sharing ratio N is controlled by the amount of laser light emitted from each laser exposure apparatus 104 (laser light emission unit thereof). FIG. 4B shows the relationship between the laser light quantity setting value and the image density sharing ratio N. The larger the image density sharing ratio N, the larger the laser light quantity setting value. In order to calculate the laser light quantity from the sharing ratio N, the following equation is stored in the ROM 601.
[Equation 1]
Laser light quantity setting value = 255 × image density sharing ratio N

  The CPU 604 sets the laser light amount to a light amount setting circuit (not shown) in the laser exposure device 104 of the station 125 to be used based on the laser light amount setting value calculated by the equation 1. The CPU 604 irradiates the laser exposure device 104 with a laser beam having a light amount corresponding to the image signal input from the image data management unit 700 via the data bus 703 and the laser light amount setting value. Then, the CPU 604 controls to form an electrostatic latent image on the corresponding photosensitive drum 102 at a specified sharing ratio N.

  In the present embodiment, the sharing ratio N is controlled by the amount of laser light. However, the present invention is not limited to this. For example, the control may be performed according to the developing bias application voltage of the developing device 105. In addition, Equation 1 is used to set the sharing rate N, but the total of the sharing rate N1 and the sharing rate N2 may be almost 100%, and a table or the like may be used instead of an arithmetic expression. . Further, although all four stations 125 can be targets to operate in a single mode or a plurality of modes for monochromatic image formation, the number of stations 125 that can be targets may be two or three. Any combination is acceptable.

  FIG. 5 is a time chart showing an outline of the operation in the single-use mode in the development station automatic switching control. The single-use mode is a mode in which two or more stations 125 in which the remaining amount of toner does not fall below the limit value T0 among the plurality of stations 125 operate in parallel to form images of the same color on a sheet. In the present embodiment, when the remaining toner amount Tr of all four stations 125 is less than the reference value T1, the non-no-toner stations 125 are operated in parallel. During the use-up mode, each station 125 operates until the toner runs out, and uses up the toner as much as possible.

  In the example shown in FIG. 5, the toner remaining amount Tr of all four stations 125 is less than the reference value T1, and only two stations (referred to as the first station S1 and the second station S2) are used. This assumes that no toner is running out of toner. Here, the determination threshold value for the absence of toner is a limit value T0 (for example, 1 mg), and when the remaining amount of toner is less than the limit value T0, it is determined that there is no toner. In addition, the value of the limit value T0 is smaller than the reference value T1 and may be 0 or a value close to 0, and is not limited to 1 mg. The remaining amounts of toner in the toner containers 106 at the stations S1 and S2 are denoted by Tr1 and Tr2, respectively.

  If image formation is continued in the single mode by the first station S1, the first station S1 runs out of toner when the toner is consumed for Tr1, and it is necessary to suddenly switch to the second station S2. Thereafter, image formation is continued in a single mode by the second station S2, and when the toner is consumed for Tr2, the second station S2 becomes out of toner, and image formation is stopped. In such control, since station switching that does not go through parallel operation occurs once, there is a risk that image quality changes between pages before and after switching.

  Therefore, in this embodiment, the stations S1 and S2 are operated in parallel in the single-use mode, and at this time, the sharing ratio N is set according to the respective remaining toner amount Tr, so that the timing at which no toner is used is set. Match as much as possible. As a result, since the image formation can be continued until the toner of approximately Tr1 + Tr2 is consumed, the image formation continuation period of the same color can be lengthened. In addition, since station switching does not occur during that time, it is possible to suppress changes in image quality.

In the single use mode, the sharing ratio N of the operating stations 125 is calculated by the following formula 2. The order of the stations 125 whose toner remaining amount Tr is equal to or greater than the limit value T0 is determined according to a predetermined priority order. Of these, the sharing ratio of the i-th station 125 and the toner remaining amount Tr are denoted as Ni and Tri, respectively.
[Equation 2]
Ni = Tri / ΣTri

  Therefore, the station 125 with a larger amount of remaining toner Tri has a larger share ratio Ni. In the example shown in FIG. 5, it is assumed that Tr2 <Tr1. In this case, the magnitude relationship between the sharing ratios N1 and N2 of the stations S1 and S2 is N1> N2. In the single-use mode of the two stations S1 and S2, as shown in FIG. 4 (c), image formation is continued with a constant sharing rate, as long as there is no toner in either of the stations S1 and S2.

  FIG. 5 illustrates the case where there are two stations 125 in which the toner remaining amount Tr is less than the reference value T1 and the limit value T0. However, if there are three or four such stations 125, the straight lines shown at the top of FIG. 5 are three and four, respectively, and three or four share rates N are calculated.

  6 and 7 are flowcharts showing image forming processing relating to a single color image. This process is started by inputting a print job and executed by the CPU 604. First, in step S101, the CPU 604 substitutes 1 for the number S1 indicating the first station S1. Here, the numerical values assigned to the numbers S1 and S2 are determined in advance as described above, and the numbers 1, 2, 3, and 4 correspond to the stations 125y, 125m, 125c, and 125k, respectively. Therefore, S1 = 1 means that the first station S1 is the station 125y. S1 = 2 means that the first station S1 is the station 125m. Similarly, S2 = 2 means that the second station S2 is the station 125m.

  Next, in step S102, the CPU 604 detects the remaining toner amount Tr1 in the toner container 106 of the first station S1 by reading it from the remaining toner amount storage unit 121. Next, in step S103, the CPU 604 compares the remaining toner amount Tr1 with the reference value T1, and determines whether or not Tr1 ≧ T1 is satisfied. If Tr1 ≧ T1 is satisfied, the process proceeds to step S104. .

  In step S104, the CPU 604 sets the image forming mode to a single mode using the first station S1, and performs an image forming operation using the first station S1 in step S105. Next, the CPU 604 determines whether printing is completed, that is, whether processing of the print job is completed (step S106). As a result of the determination, the CPU 604 ends the processing of FIGS. 6 and 7 when the processing of the print job is completed, and detects the remaining toner Tr1 of the first station S1 when the processing is not completed. (Step S107).

  Next, in step S108, the CPU 604 compares the remaining toner amount Tr1 with the reference value T1, and determines whether Tr1 ≧ T1 is satisfied. If Tr1 ≧ T1 is satisfied as a result of the determination, the process returns to step S105 to continue image formation by the first station S1. On the other hand, if Tr1 ≧ T1 does not hold, the toner remaining amount Tr1 of the first station S1 has decreased, so the CPU 604 assigns the number S2 indicating the second station S2 to set the second station S2. S1 + 1 is substituted (step S109).

  Next, the CPU 604 determines whether or not S2> 4 is satisfied (step S110). As a result of the determination, if S2> 4 is satisfied, there is no station 125 that can be set as the second station S2, so the CPU 604 stops image formation (step S111), and performs the processing of FIGS. Terminate. On the other hand, if S2> 4 does not hold, the CPU 604 detects the remaining toner amount Tr2 in the toner container 106 of the second station S2 by reading it from the remaining toner amount storage unit 121 (step S113). Next, the CPU 604 compares the remaining toner amount Tr2 with the reference value T2, and determines whether or not Tr2 ≧ T2 is satisfied (step S114).

  Here, the reference value T2 is a predetermined toner amount, and as a condition at the time of station switching, the value of the reference value T2, which is a necessary remaining amount of toner that the switching destination station 125 should have, is based on the reference value T1. A large value, for example, 20 mg. This is set to a value (approximately twice) sufficiently larger than the T1 value in consideration of the necessity of further station switching after station switching. The reference value T2 and the reference value T1 may be the same value.

  If Tr2 ≧ T2 is not satisfied as a result of the determination in step S114, the second station S2 does not have much remaining toner Tr2, and is not suitable for use in a plurality of modes. Therefore, the CPU 604 substitutes S2 + 1 for the number S2 indicating the second station S2 in order to reset the second station S2 (step S112), and returns the process to step S110. On the other hand, when Tr2 ≧ T2 is established, it is appropriate to execute the plurality of modes using the currently set stations S1 and S2 in parallel. Therefore, the CPU 604 shifts the processing to the plurality of modes after step S115. Transition.

  In step S115, the CPU 604 sets the image forming mode to a plurality of modes, and sets the first station S1 and the second station S2 as the two stations 125 that operate. Further, the CPU 604 sets the sharing ratio N1 of the first station S1 to 100% and the sharing ratio N2 of the second station S2 to 0%. Next, the CPU 604 updates the sharing rate N1 by subtracting the increase / decrease value Cn from the sharing rate N1 (step S116), and determines whether N1 ≦ 0 is satisfied (step S117).

  If N1 ≦ 0 is not satisfied as a result of the determination, the CPU 604 updates the sharing rate N2 by setting the value obtained by N2 = 100−N1 to the sharing rate N2, and also uses a plurality of stations S1 and S2. Image formation by the mode is executed (step S118). Next, the CPU 604 determines whether printing has been completed, that is, whether processing of the print job has been completed (step S119). As a result of the determination, the CPU 604 ends the processing of FIGS. 6 and 7 when the processing of the print job is completed, and returns the processing to step S116 when the processing is not completed. By repeating steps S116 to S119, the sharing rate N1 decreases stepwise toward 0%, while the sharing rate N2 increases stepwise toward 100% (see FIG. 4A).

  On the other hand, if N1 ≦ 0 holds as a result of the determination in step S117, the first station S1 does not share the image density ratio. Therefore, the CPU 604 advances the process to step S120 to exclude the first station S1 from the operating station 125, substitutes the current number S2 for the number S1 indicating the first station S1, and returns the process to step S102. . As a result, what was previously the second station S2 becomes the new first station S1. Then, if the process proceeds to step S105, the process shifts to image formation in a single mode using the new first station S1. Therefore, the mode is switched from single mode → multiple mode → single mode. Compared to the case where the station 125 is simply switched in the single mode as in the prior art, the change in the image quality of the product can be made inconspicuous by going through the plurality of modes once.

  If Tr1 ≧ T1 is not satisfied as a result of the determination in step S103, the current first station S1 is not suitable for use in the single mode. Therefore, the CPU 604 substitutes S1 + 1 for the number S1 in order to set the next station 125 as the first station S1 (step S121 in FIG. 7). Then, the CPU 604 determines whether or not S1> 4 is satisfied (step S122). If S1> 4 is not satisfied, the process returns to step S102. As a result, the remaining toner amount of the station 125 newly set as the first station S1 is detected as the remaining toner amount Tr1.

  On the other hand, when S1> 4 is satisfied, the remaining amount of toner Tr is low (less than T1) in all the stations 125, and therefore there is a station 125 that can be set as the first station S1 in the single mode. do not do. In step S123, the CPU 604 determines whether the image formation to be executed is the first image formation after the print job is input (step S123). As a result of the determination, if the image formation to be executed is not the first image formation after the print job is input, it corresponds to the middle of the job processing. If the mode is uniformly switched to the single-use mode in the middle of job processing, image quality may change before and after switching. Therefore, the CPU 604 performs notification by displaying a confirmation message as illustrated in FIG. 8 (step S131). Next, the CPU 604 determines whether or not the instruction received from the user is to continue image formation (step S131).

  FIG. 8 is a diagram illustrating an example of a confirmation message displayed at the time of transition to the single use mode. The CPU 604 displays this confirmation message on the operation unit 603 and accepts permission from the user to continue image formation. The user can select whether to continue or stop image formation on the screen. Accordingly, it is possible to notify that there is a possibility that the image quality is changed during the job processing, and it is possible to avoid the image quality change during the job processing according to the user's intention.

  As a result of the determination in step S131, the CPU 604 terminates the processing of FIGS. 6 and 7 when the received instruction is not continuation of image formation but is stopped, and on the other hand, if the accepted instruction is continuation of image formation, Transition to the single-use mode after S124. In step S <b> 124, the CPU 604 switches the image forming mode to the full-use mode, and sets the station 125 that is not out of toner as the operating station 125. At that time, the CPU 604 refers to the remaining toner amount Tr (Tri) that has already been read from the remaining toner amount storage unit 121 of each of the stations 125, and the station 125 in which Tr ≧ T0 does not have no toner. Assume that it is a station 125.

  Next, the CPU 604 calculates the sharing ratio Ni of each of the operating stations 125 by the above-described equation 2 (step S125), and executes image formation by operating the plurality of stations 125 in parallel according to the calculated sharing ratio Ni (step S125). Step S126). Next, the CPU 604 again detects the remaining toner amount Tri of each operating station 125 (step S127), and whether or not all the remaining toner levels Tri of the operating station 125 are equal to or greater than the limit value T0. Is determined (step S128). As a result of the determination, if all the remaining toner amount Tri is equal to or greater than the limit value T0, the CPU 604 determines whether printing is completed, that is, whether processing of the print job is completed (step S129).

  As a result of the determination, if the processing of the print job is completed, the CPU 604 ends the processing of FIGS. 6 and 7, while if the processing is not completed, the processing returns to step S126 to continue image formation. . On the other hand, as a result of the determination in step S128, if any one of the operating stations 125 has a remaining toner Tri less than the limit value T0, image formation is stopped (step S111). Therefore, as long as any remaining toner amount Tri of the operating station 125 does not become less than the limit value T0, image formation is repeated at a constant sharing rate Ni until the completion of printing (see FIG. 4C).

  Note that, as a result of the determination in step S128, when a station 125 in which the remaining toner amount Tri is less than the limit value T0 is generated, the process may be returned to step S124. In this way, it is possible to execute the use-up mode by a new combination of a plurality of stations 125 in which the remaining toner amount Tri is not less than the limit value T0. In this case, it is assumed that image formation is stopped when there is no station 125 whose remaining toner amount Tri is equal to or greater than the limit value T0. This is useful when toner is not consumed according to the share Ni.

  According to the present embodiment, a single mode and a plurality of modes are provided, and in the plurality of modes, two or more stations 125 operate at the set image density sharing ratio N. Thereby, the change in image quality before and after switching between the single operation and the plurality of operations of the station 125 can be suppressed and made inconspicuous. In particular, in the multiple mode, since the sharing ratio N of the operating stations 125 is changed for each image page, the degree of image quality change can be reduced.

  Further, when the toner remaining amount Tr1 in the first station S1 operating in the single mode falls below the reference value T1, the mode is switched to a plurality of modes. However, image formation can be continued.

  Further, when the sharing ratio N1 of the first station S1 becomes 0 in the plurality of modes, the mode is switched to the single mode in which only the second station S2 is operated, so that the stations can be smoothly switched. Furthermore, since the sharing rate N1 is decreased and the sharing rate N2 is increased from the timing of switching from the single mode to the multiple mode to the timing of switching from the multiple mode to the single mode, The concentration can be kept almost constant.

  Further, when the remaining toner amount Tr in all the stations 125 falls below the reference value T1, the mode is switched to the single use mode, so that the image formation continuation period of the same color can be lengthened. Moreover, in the single use mode, the sharing rate Ni is set according to the remaining toner amount Tri of each station 125 that operates, and the higher the remaining toner amount Tri, the higher the sharing rate Ni. As a result, the timing at which the toner runs out can be matched as much as possible between the operating stations 125.

  In the present embodiment, the sharing ratios N1 and N2 of the stations S1 and S2 during the multiple mode period are gradually changed in multiple steps using the increase / decrease value Cn. However, the change in the sharing ratio N of the stations S1 and S2 during the multi-mode period may go through at least one stage. For example, a value other than 100% or 0% (for example, 50%) may be passed while the sharing ratios N1 and N2 transition between 100% and 0%.

  In the multiple mode, the sharing ratio N is changed for each page of the image, but may be changed for each of the plurality of pages. Note that the number of stations 125 operating in the plurality of modes may be two or more, and may be three or more.

  From the viewpoint of simplifying the control, each of the sharing rates of the stations 125 operating in the plurality of modes may be a fixed value.

  In the present embodiment, application to a tandem image forming apparatus is illustrated, but the present invention is not limited to this. For example, the present invention can be applied to an image forming apparatus having a configuration in which a plurality of (four) developing devices correspond to one photosensitive drum as disclosed in Patent Document 1. The station in that case can be considered as the one excluding the photosensitive drum.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included.

125 Development station 604 CPU
N Image density sharing rate

Claims (11)

An image forming apparatus having a plurality of stations for forming an image of the same color,
The image forming mode includes a single mode in which a single station among the plurality of stations operates to form a single color image on a sheet, and an image in which two or more of the plurality of stations operate in parallel. A plurality of modes for superimposing and forming on the sheet, and a control means for selectively switching between and controlling the image forming operation,
The image forming apparatus according to claim 1, wherein when the image forming operation is controlled in the plurality of modes, the control means controls each of the two or more operating stations to share the image density.   The image forming apparatus according to claim 1, wherein the control unit changes a sharing ratio that is an image density ratio shared by each operating station while controlling the image forming operation in the plurality of modes.   The image forming apparatus according to claim 2, wherein the control unit changes the sharing ratio of each operating station for each image page.   When the remaining amount of toner in the first station operating in the single mode falls below a reference value, the control unit switches the image forming mode to the plurality of modes, and sets the first station and the plurality of stations. The image forming apparatus according to claim 1, wherein the second station is operated in parallel.   When the sharing ratio, which is an image density ratio shared by the first station, becomes 0 during the operation of the first station and the second station in parallel in the plurality of modes, the control means becomes zero. 5. The image forming apparatus according to claim 4, wherein the image forming mode is switched to the single mode and only the second station is operated.   The control means reduces the sharing ratio of the first station from the timing of switching from the single mode to the plurality of modes to the timing of switching from the plurality of modes to the single mode. 6. The image forming apparatus according to claim 5, wherein a sharing ratio which is an image density ratio shared by the second station is increased. In the plurality of modes, there is a predetermined mode in which two or more stations in which the remaining amount of toner does not fall below a limit value among the plurality of stations operate in parallel to form images of the same color on a sheet,
The image forming apparatus according to claim 1, wherein the control unit switches an image forming mode to the predetermined mode when a remaining amount of toner in all of the plurality of stations falls below a reference value.   8. The control unit according to claim 7, wherein when the image forming operation is controlled in the predetermined mode, the sharing ratio of each station is set based on a remaining toner amount of each station that operates. Image forming apparatus.   When the image forming mode is switched to the predetermined mode, the control unit informs that the mode is switched to the predetermined mode when the next image formation is not the first image formation in the print job. The image forming apparatus according to claim 7 or 8.   The control unit, after notifying that the image forming mode is switched to the predetermined mode, switches the image forming mode to the predetermined mode on condition that the permission of switching is received from the user. Item 10. The image forming apparatus according to Item 9. A method for controlling an image forming apparatus having a plurality of stations for forming an image of the same color,
The image forming mode includes a single mode in which a single station among the plurality of stations operates to form a single color image on a sheet, and an image in which two or more of the plurality of stations operate in parallel. A plurality of modes for superimposing and forming on a sheet, and a control step for selectively switching between and controlling an image forming operation,
The method of controlling an image forming apparatus, wherein, when the image forming operation is controlled in the plurality of modes, the control step controls the image density to be assigned to each of the two or more operating stations.