JP2019133087A - Image formation device - Google Patents

Abstract

To provide an image formation device capable of switching selection between image quality maintenance and efficiency improvement according to a number of stations which are subjected to discharge control, for enhancing productivity.SOLUTION: A CPU forms an image on a recording sheet 110 in image formation time based on a printing job, and forms a discharge pattern and discharges a developer from a development counter 112 in discharge control time for consuming a deteriorated developer. The CPU controls a bias applied to a primary transfer roller 107 based on a variable number Color Cnt indicating a number of color for which discharge processing is required, and controls a formation start timing of an electrostatic image in discharge control time immediately after image formation based on the printing job. The CPU applies a second bias which has a reverse polarity of that of a positive bias (first bias) of the image formation when the variable number Color Cnt>prescribed number, and waits finish of formation of the electrostatic image in image formation time immediately before discharge control in all stations, and then starts the discharge control.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus using a dry two-component developing system.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus that employs a dry development method using a two-component developer composed of a toner and a carrier is known. In this apparatus, when a large number of images with a low printing rate are formed, the toner is excessively charged up by continuing to drive the developing device that does not consume and replenish the toner for a long time. As a result, there is a problem in that the amount of developer applied per unit area on the photoreceptor is reduced. Further, there is a problem that the external additive attached to the toner is peeled off due to rubbing with the carrier and the like, leading to a decrease in print quality.

  Therefore, when the number of pixels of the image information is integrated and a predetermined number of sheets or more are printed, if the value obtained from the integrated value exceeds a threshold value, an image forming apparatus that consumes toner in the developing device by forming a pattern image Has been proposed (Patent Document 1). In this apparatus, a pattern image (hereinafter referred to as a discharge pattern) formed on the photosensitive member is not transferred to a recording medium but is collected by a removing unit (cleaning unit) for removing toner on the photosensitive member. For this purpose, this apparatus has a bias (reverse bias) opposite to the bias (positive bias) for forming an image on the recording medium with a high pressure of primary transfer so that the toner image is not transferred from the photosensitive member to the intermediate transfer member. ).

JP 2007-264398 A JP 2017-15990 A

  In Patent Document 1, after the above-described ejection pattern is formed, the primary transfer bias is sequentially switched from the normal image forming state (positive bias) to the reverse bias at each station. When the bias is switched, the force acting on the intermediate transfer member changes, and the behavior in the direction (width direction) perpendicular to the conveyance direction of the intermediate transfer member becomes temporarily unstable. For example, in an image forming apparatus having four color stations, during the primary transfer of the preceding image at the third or fourth color station, or when the transfer starts from now, the switching to the reverse bias is performed at the first color station. Suppose that it has started. Then, there is a possibility that color misregistration occurs due to the transfer position deviating in the main scanning direction (width direction) between the stations. Also, at each station, when the primary transfer bias is sequentially returned from the reverse bias to the positive bias for the return to the normal image formation after the ejection pattern is formed, the intermediate transfer member is kept for a predetermined time after the return of the positive bias. The behavior of becomes unstable. For this reason, when the subsequent image is primarily transferred in an unstable state, there is a risk of color misregistration.

  As a countermeasure against the color misregistration, when forming the ejection pattern, it is necessary to wait until the transfer of the preceding image at all stations before the ejection pattern is formed (2001 in FIG. 5A). Further, when the subsequent image is formed after the ejection pattern is formed, it is necessary to wait until the primary transfer bias of each station returns to the positive bias and the behavior of the intermediate transfer member is stabilized (FIG. 5A). ) 2003, 2004). However, by implementing these measures, the standby time is significantly increased, and the productivity of image formation is reduced.

  On the other hand, an image forming apparatus having a removing unit for cleaning the toner on the intermediate transfer member at a transfer portion where the toner image is transferred from the intermediate transfer member to the recording medium has been proposed (Patent Document 2). In this apparatus, the toner on the intermediate transfer member is removed by a removing unit having a cleaner fur, a bias roller, a cleaner fur brush, and a cleaner blade.

  In the case where toner is consumed by using the method of transferring the ejection pattern of Patent Document 2 to the intermediate transfer member and then removing it by the removing means, there is no need to switch the primary transfer bias, so the color resulting from the primary transfer bias switching. The problem of misalignment does not occur. However, since there is a limit to the cleaning capability of the removal unit, when the discharge pattern superimposed at a plurality of stations is cleaned by the removal unit, the cleaning may not be completed if the amount of toner constituting the discharge pattern is too large. . If the toner remains on the intermediate transfer member, the remaining toner may adhere to the back of the paper transported to the transfer section, and so-called paper back dirt may occur.

  As described above, the method of removing toner by the removing unit on the photosensitive member as in Patent Document 1 and the method of removing toner by the removing unit on the intermediate transfer member as in Patent Document 2 have advantages and disadvantages. There is. Regardless of the number of stations used for toner consumption, if any one of the above methods is adopted, there may be a problem that productivity is lowered or image quality is lowered.

  It is an object of the present invention to switch between selection of image quality maintenance and efficiency improvement according to the number of stations to be controlled for ejection.

  In order to achieve the above object, the present invention provides a photoconductor, a forming unit for forming a toner image on the photoconductor using a developer, a first removing unit for removing the developer on the photoconductor, A plurality of stations, a transfer unit that transfers the toner image on the photosensitive member to an intermediate transfer member, a second removal unit that removes the toner image on the intermediate transfer member, and a deteriorated developer. During discharge control, image formation based on a print job is interrupted and a pattern image for discharge control is formed on the photoconductor to discharge developer from the forming unit. Acquisition means for acquiring the number of stations to be performed, and the control means controls the bias applied to the transfer means based on the number acquired by the acquisition means, and performs a print job. And controlling the formation start timing of the electrostatic image at the time of ejection control just after the image formation brute.

  According to the present invention, selection between image quality maintenance and efficiency improvement can be switched according to the number of stations to be controlled for ejection.

1 is a schematic sectional view of an image forming apparatus. It is a block diagram of a controller. It is an enlarged view near a secondary transfer part. It is a figure which shows the structure of an operation display apparatus. It is a time chart of a discharge sequence. 6 is a flowchart of print processing. It is a flowchart of a discharge implementation determination process. It is a flowchart of a discharge sequence process. It is a flowchart of an ejection pattern formation process. It is a flowchart of a discharge pattern station process.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 includes a housing 101 and an operation display device 180. The casing 101 houses each mechanism for configuring the engine unit. The image forming apparatus 100 is an electrophotographic color image forming apparatus that employs a dry development method using a two-component developer composed of a toner and a carrier.

  Y, M, C, and K used in the following are abbreviations of yellow, magenta, cyan, and black, respectively. The engine unit is provided with four stations 120, 121, 122, 123 corresponding to YMCK. Stations 120, 121, 122, and 123 are image forming units that transfer toner onto the recording paper 110 to form an image. Since each station is composed of almost common parts, the configuration of the station 120 will be described as a representative.

  A photosensitive drum 105 as a photosensitive member is charged to a uniform surface potential by a primary charger 111. The laser 108 and the developing device 112 correspond to forming means in the present invention. A latent image (electrostatic image) is formed on the photosensitive drum 105 by the laser light output from the laser 108. The developing device 112 develops an electrostatic image using a color material (toner) to form a toner image on the photosensitive drum 105 (on the photosensitive member). This toner image (visible image) is transferred onto an intermediate transfer belt 106 as an intermediate transfer member by a primary transfer roller 107 as a transfer unit. The visible image formed on the intermediate transfer belt 106 is transferred by the secondary transfer belt 114 to the recording paper 110 conveyed from the storage 113.

  The fixing processing mechanism includes a first fixing device 150 and a second fixing device 160, and heats and pressurizes the toner image transferred to the recording paper 110 to fix it on the recording paper 110. The first fixing device 150 includes a fixing roller 151 for applying heat to the recording paper 110, a pressure belt 152 for pressing the recording paper 110 against the fixing roller 151, and a first post-fixing sensor 153 for detecting completion of fixing. including. The fixing roller 151 is a hollow roller and has a heater inside. The second fixing device 160 is disposed downstream of the first fixing device 150 in the conveyance direction of the recording paper 110. The second fixing device 160 imparts gloss (gloss) to the toner image on the recording paper 110 fixed by the first fixing device 150 or secures fixing properties. Similar to the first fixing device 150, the second fixing device 160 has a fixing roller 161, a pressure roller 162, and a second post-fixing sensor 163. Depending on the type of recording paper 110, it is not necessary to pass through the second fixing device 160. In this case, the image forming apparatus 100 allows the recording paper 110 to pass through the conveyance path 130 without passing through the second fixing device 160 for the purpose of reducing energy consumption.

  For example, when setting is made to add a lot of gloss to the recording paper 110, or when the recording paper 110 requires a large amount of heat for fixing like a thick paper, the recording paper 110 that has passed through the first fixing device 150 is used. Is also conveyed to the second fixing device 160. On the other hand, when the recording paper 110 is plain paper or thin paper and the setting for adding a lot of gloss is not made, the recording paper 110 is transported through a transport path 130 that bypasses the second fixing device 160. Whether the recording paper 110 is conveyed to the second fixing device 160 or the recording paper 110 is conveyed bypassing the second fixing device 160 is switched by a flapper 131 controlled by a motor control unit 312 (FIG. 2) described later. Controlled by

  All of the flappers 132, 133, and 134 are conveyance path switching guide members controlled by the motor control unit 312. The flapper 132 guides the recording paper 110 to the discharge path 135 or guides the recording paper 110 to the discharge path 139 to the outside. The leading edge of the recording paper 110 guided to the discharge path 135 passes through the reversal sensor 137 and is conveyed to the reversing unit 136. When the reverse sensor 137 detects the trailing edge of the recording paper 110, the conveyance direction of the recording paper 110 is switched. The flapper 133 guides the recording paper 110 to the conveyance path 138 for double-sided image formation or guides it to the discharge path 135. The flapper 134 guides the recording paper 110 to the discharge path 139 to the outside. The recording paper 110 conveyed through the discharge path 139 is discharged outside the image forming apparatus 100.

  Next, the configuration of the controller that controls the entire image forming apparatus 100 will be described with reference to FIG. FIG. 2 is a block diagram of the controller. As shown in FIG. 2, the controller includes a CPU circuit unit 900, and the CPU circuit unit 900 includes a CPU 901, a ROM 902, and a RAM 903. The CPU 901 comprehensively controls the image control unit 922, the printer control unit 931, and the display control unit 941 by a control program stored in the ROM 902. The RAM 903 temporarily stores control data and is used as a work area for arithmetic processing accompanying control by the CPU 901.

  The image control unit 922 performs various processes on the digital image signal input from the computer 905 via the external I / F 904, converts the digital image signal into a video signal, and outputs the video signal to the printer control unit 931. The processing operation by the image control unit 922 is controlled by the CPU circuit unit 900. The CPU circuit unit 900 executes image formation and various adjustments to be described later via the printer control unit 931.

  The printer controller 931 includes a high voltage controller 311 for controlling various high voltages, a motor controller 312 for driving various motors, and an I / O for controlling I / O (input / output) of various sensors. A control unit 313 is connected. The high pressure controller 311 biases the primary transfer roller 107 of each station used in the image forming apparatus 100, the secondary transfer roller 1061 and the bias roller 1142 in the secondary transfer belt 114, and the like (described later in FIG. 3). The control to apply is performed. The motor control unit 312 controls a plurality of motors and flappers used in the image forming apparatus 100. Each motor is connected to a conveyance roller or the like. Sensors including a conveyance sensor are connected to the I / O control unit 313, and changes in sensor signals are notified to the CPU 901 via the I / O control unit 313 and the printer control unit 931.

  A predetermined bias is applied to the primary transfer roller 107 (FIG. 1) provided in each of the stations 120 to 123 by the high pressure controller 311. When a transfer current for transferring the toner image formed on the photosensitive drum 105 to the intermediate transfer belt 106 is supplied, the high voltage control unit 311 applies a positive bias (for example, about +2000 V) to the primary transfer roller 107. The toner image formed on the photosensitive drum 105 is transferred to the intermediate transfer belt 106 by the electrostatic force generated by the transfer current. The positive bias is the first bias for image formation.

  In the present embodiment, “ejection control” for consuming the developer by discharging the deteriorated developer is performed. The discharge control includes first discharge control and second discharge control. During the first and second ejection control, the CPU circuit unit 900 forms a ejection pattern, which is a pattern image for ejection control, on the photosensitive drum 105 as a toner image. In the first discharge control, the CPU circuit unit 900 controls to collect and remove the discharge pattern by the drum cleaner 109 (first removal unit) without transferring the discharge pattern on the photosensitive drum 105 to the intermediate transfer belt 106. To do. The discharge pattern remains on the photosensitive drum 105 without being transferred to the intermediate transfer belt 106, and the remaining discharge pattern is removed by the drum cleaner 109. For this purpose, the high voltage controller 311 applies a reverse bias (for example, about −500 V) to the primary transfer roller 107. This reverse bias is a second bias having a reverse polarity to the first bias for image formation.

  During the second discharge control, the CPU circuit unit 900 applies a first bias to the primary transfer roller 107 to transfer the discharge pattern on the photosensitive drum 105 to the intermediate transfer belt 106. The CPU circuit unit 900 controls the secondary transfer belt 114 to be removed by cleaning the secondary transfer belt 114 by a cleaning mechanism described later with reference to FIG. 3, thereby removing the ejection pattern on the secondary transfer belt 114 (on the intermediate transfer member).

  By the way, there is a limit to the density of the toner image on the secondary transfer belt 114 that can be cleaned by a cleaning mechanism described later in FIG. 3, and if the secondary transfer belt 114 is contaminated with the toner that cannot be removed, the back of the paper becomes dirty. Is likely to occur. In order to prevent this, the first discharge control is provided. On the other hand, in the first discharge control, there is a case where the discharge pattern cannot be completely removed by passing the drum cleaner 109 once. Therefore, the CPU circuit unit 900 does not rotate the photosensitive drum 105 once more until the next page. Control not to start image formation.

  FIG. 3 is an enlarged view of the vicinity of the secondary transfer portion. In the secondary transfer portion, the secondary transfer roller 1061 is inscribed in the intermediate transfer belt 106. A predetermined bias (for example, about −3000 V) is applied to the secondary transfer roller 1061. The secondary transfer belt 114 is inscribed with an outer roller 1143a and tension rollers 1143b, 1143c, and 1143d. The outer roller 1143a is electrically grounded. The outer roller 1143a is disposed to face the secondary transfer roller 1061 with the intermediate transfer belt 106 interposed therebetween. When a predetermined transfer current flows from the outer roller 1143 a to the secondary transfer roller 1061, the toner image on the intermediate transfer belt 106 (on the transfer body) is transferred to the recording paper 110 as a recording medium by electrostatic force.

  A cleaner fur 1141 is provided on the outer peripheral side of the secondary transfer belt 114. A bias roller 1142 is provided in contact with the cleaner fur 1141, and a cleaner blade 1145 is provided in contact with the bias roller 1142. A predetermined bias (for example, about +1000 V) is applied to the bias roller 1142. The cleaner fur 1141, the bias roller 1142, and the cleaner blade 1145 are cleaning mechanisms for collecting and removing the toner on the intermediate transfer belt 106 when the toner is transferred to the secondary transfer belt 114. As the toner on the intermediate transfer belt 106 here, in addition to the ejection pattern transferred from the photosensitive drum 105, the measurement image used for auto-registration control, and the intermediate transfer belt 106 cannot be transferred onto the recording paper 110 during image formation. The residual toner remaining on the top is included. The auto registration control is a control for adjusting the image writing timing shift and the image inclination of each station. Note that the CPU circuit unit 900 does not supply the recording paper 110 to the secondary transfer unit during the second ejection control.

  FIG. 4 is a diagram illustrating a configuration of the operation display device 180. The operation display device 180 is provided with a start key 602 for starting an image forming operation and a stop key 603 for interrupting the image forming operation. Further, the operation display device 180 is provided with numeric keys 604 to 612 and 614 for setting a numeric value and the like, an ID key 613, a clear key 615, a reset key 616, and the like. The operation display device 180 includes a display unit 620. A touch panel is formed on the upper part of the display unit 620, and soft keys can be created on the screen.

  The image forming apparatus 100 performs discharge control to temporarily stop image formation and consume and refresh the developer when the toner consumption in forming a predetermined number of images is low (low printing rate). To discharge the toner. For example, an image of a low printing rate pattern having a yellow printing rate of 2.0%, a magenta printing rate of 1.0%, a cyan printing rate of 1.5%, and a black printing rate of 6.0%. Assume that image formation is performed continuously. The image forming apparatus 100 performs discharge control for discharging the developer (toner) so that the average printing rate becomes 2.0% when the average printing rate is less than “2.0%” for each color. For example, in the above example, since the magenta printing rate is 1.0% and cyan is 1.5%, the image forming apparatus 100 is 1.0% for magenta and 0.5% for cyan. The toner is discharged. In other words, the image forming apparatus 100 discharges an amount of toner corresponding to the predetermined number of sheets × 1.0% from the magenta developing device, and an amount of toner corresponding to the predetermined number × 0.5% of the developing device of cyan. A discharge pattern is formed so as to be discharged. As a sequence of ejection control, the image forming apparatus 100 temporarily stops image formation, and ejects deteriorated toner by forming an ejection pattern by either the first ejection control or the second ejection control. As described above, the bias applied to the primary transfer roller 107 is the reverse bias (second bias) when the discharge control to be performed is the first discharge control, and the positive bias (first first) when the second discharge control is performed. Bias).

  Next, details of ejection control (toner ejection sequence) by the CPU 901 will be described with reference to the flowcharts of FIGS. 6 to 10 and FIG.

  5A, 5B, and 5C are time charts of the discharge sequence. In particular, FIG. 5A shows a discharge sequence during the first discharge control. FIG. 5B shows a conventional discharge sequence. FIG. 5C shows a discharge sequence during the second discharge control. In FIGS. 5B and 5C, the exposure operation of the station that does not form the discharge pattern is described as exposure (dummy) in the drawings.

  FIG. 6 is a flowchart of the printing process. The processing of this flowchart is realized by the CPU 901 reading the program stored in the ROM 902 into the RAM 903 and executing it. Whether or not to perform the discharge process is switched between page printing and page printing. In the processing of FIG. 6, the CPU 901 plays a role as a control unit and an acquisition unit in the present invention.

  First, in step S101, the CPU 901 waits for a page print request based on a print job (print job), that is, a print request, and if there is a print request, in step S102, a discharge execution determination process (described later) (FIG. 7). ). Note that image data is transferred to the CPU 901 from an external device (computer, server, scanner) together with a print job (print job). The image data includes, for example, data created in PDL (page description language). In the discharge execution determination process (FIG. 7), TRUE indicating that it is necessary to perform or FALSE indicating that it is not necessary is set in the variable FLAG indicating whether or not discharge control needs to be performed. The variable FLAG is stored in the RAM 903.

  In step S103, the CPU 901 determines whether or not the value of the variable FLAG is TRUE. If the value of the variable FLAG is not TRUE, the CPU 901 advances the process to step S106 because it is not necessary to perform discharge control. On the other hand, if the value of FLAG is TRUE, it is necessary to perform discharge control, and thus the CPU 901 advances the process to step S104. In step S104, the CPU 901 executes a discharge sequence process (FIG. 8) described later. In the discharge execution determination process (FIG. 7), a discharge amount integrated value that is a variable indicating a required discharge amount is calculated for each color and stored in the RAM 903. Since the CPU 901 performed the discharge control in step S104, in step S105, the integrated discharge values of all stations stored in the RAM 903 are cleared to zero. In step S106, the CPU 901 executes page print processing, and in step S107, the CPU 901 determines whether the print job processing is completed. The CPU 901 returns the process to step S101 if the print job processing has not ended, and ends the processing in FIG. 6 if the print job processing has ended.

  FIG. 7 is a flowchart of the discharge execution determination process executed in step S102 of FIG. In step S201, the CPU 901 initializes the value of the variable FLAG to FALSE. In step S202, the CPU 901 initializes the value of the variable color indicating the index of the color for which the ejection control is performed to 1. The variable color is arranged in the RAM 903. Here, it is assumed that color and color have a correspondence relationship such as 1: Y, 2: M, 3: C, and 4: K. For example, the initial value “1” of the variable color indicates yellow.

  In step S <b> 203, the CPU 901 initializes a variable colorCnt indicating the number of colors (stations) that need to be ejected to 0. The variable colorCnt is stored in the RAM 903. Next, in step S204, the CPU 901 acquires information related to an image for one page to be printed this time. Specifically, the CPU 901 determines information on the total number of pixels of an image for one page to be printed this time and the number of dots to be printed at each station (on dots) based on the analysis result of the image data, and the page Obtained as information (image data). It is assumed that the number of dots printed at each station is stored in an array type variable videoCnt [color] arranged on the RAM 903. Next, in step S205, the CPU 901 calculates the image density of the color specified by the variable color. The CPU 901 calculates the image density according to the following formula 1, and stores the calculated result in the RAM 903. This density [%] corresponds to the printing rate of an image for one page to be printed this time.

Density [%] = (videoCnt [color] × 100) / total number of pixels (Expression 1)
In step S206, the CPU 901 determines whether or not the threshold Th1 is equal to or higher than the density (printing rate) calculated in step S205 (threshold Th1 ≧ density). Here, the threshold value Th1 is set to a fixed value of a target printing rate “2.0%” as a target value. However, the threshold Th1 may be changed by a maintenance person or may be changed according to the installation environment. If the threshold value Th1 ≧ density is not established as a result of the determination in step S206, it is determined that it is not necessary to update the discharge amount integrated value for the station of the color whose density is calculated this time, so the CPU 901 proceeds to step S211. Proceed. On the other hand, if the threshold value Th1 ≧ density is established, it is determined that the discharge amount integrated value needs to be updated for the station of the color whose density is calculated this time, the CPU 901 advances the process to step S207.

  In step S207, the CPU 901 updates the discharge amount integrated value [color] by the following equation 2 based on the density (print rate) of the image for one page to be printed, and the updated discharge amount integrated value [color]. Stored in the RAM 903.

Discharge amount integrated value [color] = Discharge amount integrated value [color] + {(threshold Th1−density) × total number of pixels} / 100 (Expression 2)
The discharge amount integrated value [color] corresponds to the total number of pixels that are insufficient with respect to the target printing rate. In other words, the discharge amount integrated value [color] corresponds to a value obtained by integrating the difference between the number of pixels forming the electrostatic image per page and the target value. Here, “total number of pixels” refers to the total number of pixels of the current page.

  Next, in step S208, the CPU 901 determines whether or not the discharge amount integrated value [color] is equal to or greater than the threshold Th2 (threshold Th2 ≦ discharge amount integrated value [color]). Here, the threshold value Th2 is a value corresponding to the total number of pixels of the ejection pattern, and is a fixed value. The threshold Th2 may also be changed by the person in charge of maintenance or may be changed according to the installation environment. When the discharge amount integrated value from the previous discharge reaches the threshold Th2, it is determined that the developer has deteriorated. If the threshold value Th2 ≦ discharge amount integrated value [color] is not satisfied, the CPU 901 advances the process to step S211. On the other hand, if the threshold value Th2 ≦ discharge amount integrated value [color] is satisfied, the CPU 901 can determine that the developer has deteriorated, and thus the process proceeds to step S209. In step S209, the CPU 901 sets the value of the variable FLAG to TRUE. Accordingly, it is determined whether or not to execute the discharge control based on the discharge amount integrated value [color].

  Next, in step S210, the CPU 901 updates the variable colorCnt stored in the RAM 903 by adding 1. Next, in step S211, the CPU 901 adds 1 to the variable color in order to set the variable color to the value of the next color. Next, in step S212, the CPU 901 determines whether or not the variable color exceeds the number of stations. If the variable color does not exceed the number of stations, the CPU 901 returns the process to step S205 because there is an unprocessed station for the page to be printed this time. On the other hand, if the variable color exceeds the number of stations, the processing for all the stations for the page to be printed this time has been completed, so the CPU 901 ends the processing in FIG.

  FIG. 8 is a flowchart of the ejection sequence process executed in step S104 of FIG. Hereinafter, a page on which an image is formed immediately before a certain discharge control is referred to as a preceding page N, and a page on which an image is formed immediately after the discharge control is referred to as a subsequent page N + 1. Accordingly, ejection control is performed between the preceding page N and the succeeding page N + 1. Hereinafter, FIG. 5 is also referred to as appropriate.

  First, in step S301, the CPU 901 determines whether or not the variable colorCnt is larger than the number of colors that can be cleaned (predetermined number). Here, the number of colors that can be cleaned is the number of ejection pattern colors that can be cleaned (removable) by the cleaning mechanism (FIG. 3) in the secondary transfer portion. The number of colors that can be cleaned is 1 as an example, but may be 2 or more depending on the cleaning capability of the cleaning mechanism. The number of colors that can be cleaned indicates that the discharge pattern for one color can be removed by one cleaning, but the discharge patterns for two or more colors may not be removed.

  As a result of the determination in step S301, if the variable colorCnt is larger than the number of colors that can be cleaned, the CPU 901 advances the process to step S302. On the other hand, if the variable colorCnt is not larger than the number of colors that can be cleaned, the CPU 901 advances the process to step S306. In steps S302 to S305, a discharge sequence (FIG. 5A) by the first discharge control is executed. FIG. 5A illustrates the case where the number of colors for ejection control is four. However, even when the variable colorCnt is larger than a predetermined number (two colors, three colors), the sequence is as shown in FIG. It will be the same as shown. On the other hand, in steps S306 and S307, a discharge sequence (FIG. 5C) by the second discharge control is executed. As long as the blank (standby period) is inserted, the ejection sequence shown in FIG. 5A is common to the conventional sequence (FIG. 5B).

  In step S <b> 302, the CPU 901 waits until exposure by the laser 108 is completed in all stations (the black station 123 whose exposure operation order is the last in the present embodiment) for the preceding page N. As a result, as illustrated in FIG. 5A, prior image completion waiting 2001 is inserted as a blank before the ejection pattern is formed. When the exposure by the laser 108 at all stations is completed, the CPU 901 executes an ejection pattern forming process (FIG. 9) described later (step S303) and advances the process to step S304.

  Steps S304 and S305 are processing steps for providing a blank between the formation of the ejection pattern and the image formation of the subsequent page N + 1. Specifically, the CPU 901 performs control so that a transfer switching wait 2003 and a belt stabilization wait 2004 shown in FIG. That is, in step S304, the CPU 901 waits until completion of the later-described ejection pattern station process in the black station 123 (completion of step S507 of FIG. 10 in step S407 of FIG. 9). As a result, as illustrated in FIG. 5A, a cleaning wait 2002 and a transfer switching wait 2003 are inserted as blanks. When the ejection pattern station process at the black station 123 is completed, the CPU 901 waits for a predetermined stabilization waiting time T (for example, 2 seconds) (step S305). Thereby, as illustrated in FIG. 5A, the belt stabilization waiting 2004 is inserted as a blank. When the stabilization waiting time T elapses, the process in FIG. 8 ends.

  When the process proceeds from step S301 to step S306, since step S302 is not executed, the preceding image completion wait 2001 is not inserted. In step S306, the CPU 901 executes an ejection pattern formation process (FIG. 9) described later, and advances the process to step S307. In step S307, the CPU 901 waits for completion of the ejection pattern formation process (step S508 in FIG. 10 in step S401 in FIG. 9) in the yellow station 120 whose operation order is the first. When the discharge pattern formation process in the yellow station 120 is completed, the CPU 901 ends the process of FIG. As a result, as shown in FIG. 5C, blanks of the transfer switching wait 2003 and the transfer belt stabilization wait 2004 are not inserted, and image formation of the subsequent page N + 1 is started immediately.

  FIG. 9 is a flowchart of the ejection pattern forming process by each station. This process is executed in step S303 or S306 in FIG. First, in step S401, the CPU 901 starts the ejection pattern station process (FIG. 10) at the yellow station 120. Next, in step S402, the CPU 901 waits until the passing time between stations elapses. That is, the CPU 901 waits until the ejection pattern station processing start timing at the magenta station 121. Here, the inter-station passage time is calculated by the distance between adjacent stations / process speed time. For example, the inter-station passage time between Y and M is calculated by the inter-station distance between Y and M / process speed time.

  When the inter-station passage time between Y and M has elapsed, the CPU 901 starts the ejection pattern station process (FIG. 10) at the magenta station 121 in step S403. Next, in step S404, the CPU 901 waits until the passing time between stations between M and C elapses. When the inter-station passage time between M and C has elapsed, the CPU 901 starts the ejection pattern station process (FIG. 10) at the cyan station 122 in step S405. Next, in step S406, the CPU 901 waits until an inter-station passing time between C and K elapses. When the inter-station passage time between C and K has elapsed, the CPU 901 starts the ejection pattern station process (FIG. 10) at the black station 123 in step S407, and ends the process of FIG.

  FIG. 10 is a flowchart of discharge pattern station processing in one station, and includes steps for executing discharge pattern exposure, primary transfer, and cleaning processing in one station. This process is started in each of steps S401, S403, S405, and S407 of FIG. 9, and can be executed in parallel at four stations.

  In the description of FIG. 10, a station that forms a discharge pattern is referred to as a processing target station. In the process of FIG. 10, the operation at a station that is not a process target is “dummy exposure”. In that case, specifically, the CPU 901 performs an exposure operation based on image data corresponding to blank paper.

  First, in step S <b> 501, the CPU 901 starts exposure for forming a discharge pattern on the photosensitive drum 105. Next, in step S502, the CPU 901 waits until the leading end of the ejection pattern on the photosensitive drum 105 reaches the primary transfer position (position where the photosensitive drum 105 and the primary transfer roller 107 face each other). When the leading edge of the ejection pattern reaches the primary transfer position, the CPU 901 determines in step S503 whether the variable colorCnt is larger than the number of colors that can be cleaned. If the variable colorCnt is larger than the number of colors that can be cleaned, the current ejection pattern is formed by the first ejection control, and the process advances to step S504. On the other hand, if the variable colorCnt is not greater than the number of colors that can be cleaned, the current ejection pattern is formed by the second ejection control, and the process advances to step S508.

  In step S <b> 504, the CPU 901 controls the high pressure control unit 311 to apply a reverse bias to the primary transfer roller 107. As a result, the ejection pattern (toner image on the photosensitive drum 105) remains on the photosensitive drum 105 without being transferred to the intermediate transfer belt 106. Next, in step S505, the CPU 901 waits until the rear end of the ejection pattern on the photosensitive drum 105 passes the primary transfer position. When the rear end of the ejection pattern passes the primary transfer position, the process proceeds to step S506. In step S <b> 506, the CPU 901 waits until the photosensitive drum 105 rotates once to remove the toner remaining on the photosensitive drum 105 as an ejection pattern by the drum cleaner 109. If the CPU 901 detects that the photosensitive drum 105 has made one revolution, it can be determined that the residual toner has been removed, and the process advances to step S507. As a result, a cleaning wait 2002 is inserted as a blank. In step S304 of FIG. 8, the CPU 901 detects that the process of step S506 in the black station is completed, and is controlled to proceed to the next step.

  In step S507, the CPU 901 controls the high-pressure controller 311 to return the primary transfer roller 107 to the original state before the ejection pattern is formed, and applies a predetermined bias, that is, a first bias ( Apply a positive bias). Thereafter, the CPU 901 ends the process of FIG.

  In step S508, the CPU 901 controls the high-pressure controller 311 to apply a predetermined bias (positive bias) to the primary transfer roller 107, and ends the processing in FIG. When step S508 is executed, steps S504 to S507 are skipped, so that the bias switching process of the primary transfer roller 107 is skipped. Therefore, as shown in FIG. 5C, the cleaning wait 2002 is not inserted.

  FIG. 5C illustrates a case where the number of colors that can be cleaned is one. When the number of colors that can be cleaned is two, in FIG. 5C, the ejection pattern is formed in parallel at the two-color station.

  6 to 10 described so far will be described again with reference to FIGS. 5A, 5B, and 5C in terms of ejection control and image formation timing.

  First, the CPU 901 acquires a variable colorCnt in order to know the number of colors that require ejection processing. The CPU 901 controls the bias applied to the primary transfer roller 107 based on the acquired variable colorCnt and also controls the electrostatic image formation start timing at the time of ejection control immediately after image formation based on the print job.

  Specifically, if the variable colorCnt> the predetermined number, the CPU 901 applies a second bias having a polarity opposite to the positive bias (first bias) for image formation. At the same time, the CPU 901 waits for the electrostatic image formation at the time of image formation immediately before the discharge control to be completed in all the stations, and starts the discharge control (FIG. 5A).

  On the other hand, when the variable colorCnt ≦ the predetermined number, the CPU 901 applies the first bias and does not wait for the electrostatic image formation at the time of image formation immediately before the discharge control to end in all stations. Discharge control is started. That is, the discharge control start timing is the time when the formation of the electrostatic image at the first station at the time of image formation immediately before the discharge control is completed (FIG. 5C). As a result, the preceding image completion waiting 2001 is omitted, and the productivity is increased.

  Considering the preceding image completion waiting 2001 from the viewpoint of the interval between the ejection pattern and the image, it is as follows. In the discharge control, the CPU 901 reduces the interval between the image formed based on the print job and the subsequent discharge pattern when the variable colorCnt ≦ predetermined number, compared to the case where the variable colorCnt> predetermined number. Control is performed as shown in FIG. Even when the waiting for completion of preceding image 2001 is not provided, the time lag from the time when the electrostatic image formation on the preceding page N is completed at the first station 120 to the start timing of the ejection control at the first station 120. There may be.

  The CPU 901 controls the bias applied to the primary transfer roller 107 based on the acquired variable colorCnt, and also controls the electrostatic image formation start timing at the time of image formation based on the print job immediately after the ejection control.

  Specifically, the CPU 901 applies the second bias when the variable colorCnt> the predetermined number. At the same time, the CPU 901 waits for the switching of the applied bias from the second bias to the first bias to end in the first station immediately after the discharge control, and forms an electrostatic image at the time of image formation immediately after the discharge control. Start (FIG. 5A). In addition, after switching the bias, the CPU 901 waits for a predetermined time (stabilization waiting time T) to elapse and starts forming an electrostatic image on the subsequent page N + 1 immediately after the ejection control (FIG. 5A). . Accordingly, a transfer switching wait 2003 and a belt stabilization wait 2004 are provided between the ejection control and the subsequent page N + 1, and good image quality is maintained.

  On the other hand, when the variable colorCnt ≦ the predetermined number, the CPU 901 applies the first bias, and when the electrostatic image formation in the discharge control is completed in the first station, the CPU 901 performs the static in the image formation after the discharge control. The formation of the electric image is started (FIG. 5C). As a result, the waiting for cleaning 2002, waiting for transfer switching 2003 and waiting for belt stabilization 2004 are omitted, and productivity is increased.

  Considering the waits 2002 to 2004, which are blanks, from the viewpoint of the interval between the ejection pattern and the image, it is as follows. When the variable colorCnt ≦ the predetermined number, the CPU 901 performs control so as to reduce the interval between the ejection pattern and the subsequent image formed based on the print job, as compared with the case where the variable colorCnt> the predetermined number (FIG. 5 (c)). In this case, there may be a time lag between the time when the removal of the developer on the photosensitive drum 105 is completed at the first station 120 and the timing when the electrostatic image formation is started on the subsequent page N + 1.

  According to the present embodiment, the CPU 901 controls the bias applied to the primary transfer roller 107 based on the variable colorCnt, and sets the electrostatic image formation start timing at the time of ejection control immediately after image formation based on the print job. Control. Further, the CPU 901 controls the bias applied to the primary transfer roller 107 based on the variable colorCnt, and also controls the electrostatic image formation start timing at the time of image formation based on the print job immediately after the discharge control. As a result, selection between maintaining image quality and improving efficiency can be switched according to the number of stations to be controlled.

  In the control according to the present invention, the interval between the ejection pattern and the image formed based on the print job is an interval as a distance, but may be controlled by grasping it as a time interval.

  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.

106 Intermediate transfer belt 107 Primary transfer roller 108 Laser 109 Drum cleaner 112 Developer 120 to 123 Station 901 CPU
1061 Secondary transfer roller

Claims (14)

A plurality of stations each including a photoconductor, a forming unit that forms a toner image on the photoconductor using a developer, and a first removing unit that removes the developer on the photoconductor;
Transfer means for transferring the toner image on the photosensitive member to an intermediate transfer member;
A second removing means for removing the toner image on the intermediate transfer member;
Control means for discharging developer from the forming means by interrupting image formation based on a print job and forming a pattern image for discharge control on the photosensitive member at the time of discharge control for discharging the deteriorated developer;
An acquisition means for acquiring the number of stations for discharge control in performing discharge control;
The control unit controls a bias applied to the transfer unit based on the number acquired by the acquisition unit, and controls an electrostatic image formation start timing at the time of ejection control immediately after image formation based on a print job. An image forming apparatus.   When the acquired number is larger than the predetermined number, the control unit applies a second bias having a polarity opposite to the first bias for image formation to the transfer unit, and also the image immediately before the ejection control. The image forming apparatus according to claim 1, wherein the ejection control is started after the electrostatic image formation at the time of formation is completed in all stations.   When the acquired number is not larger than a predetermined number, the control unit applies a first bias for image formation to the transfer unit and forms an electrostatic image at the time of image formation immediately before the ejection control. 2. The image forming apparatus according to claim 1, wherein the ejection control is started without waiting for completion of the operation at all stations.   If the acquired number is not larger than the predetermined number, the control means determines when the electrostatic image formation at the time of image formation immediately before the discharge control is completed at the first station, the discharge control start timing. The image forming apparatus according to claim 3, wherein:   When the acquired number is not larger than the predetermined number, the control means is used for controlling the image formed on the basis of the print job and the subsequent ejection control as compared with the case where the acquired number is larger than the predetermined number. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled to reduce an interval between the pattern image and the pattern image.   6. The control unit controls an electrostatic image formation start timing at the time of image formation based on a print job immediately after the ejection control, based on the number acquired by the acquisition unit. The image forming apparatus according to any one of the above. A plurality of stations each including a photoconductor, a forming unit that forms a toner image on the photoconductor using a developer, and a first removing unit that removes the developer on the photoconductor;
Transfer means for transferring the toner image on the photosensitive member to an intermediate transfer member;
A second removing means for removing the toner image on the intermediate transfer member;
Control means for discharging developer from the forming means by interrupting image formation based on a print job and forming a pattern image for discharge control on the photosensitive member at the time of discharge control for discharging the deteriorated developer;
In performing the discharge control, an acquisition means for acquiring the number of stations for discharge control;
The control unit controls a bias applied to the transfer unit based on the number acquired by the acquisition unit, and sets an electrostatic image formation start timing at the time of image formation based on a print job immediately after the ejection control. An image forming apparatus that controls the image forming apparatus.   When the acquired number is greater than a predetermined number, the control unit applies a second bias having a polarity opposite to the first bias for image formation to the transfer unit, and immediately after the ejection control, Waiting for the switching of the bias applied to the transfer means from the second bias to the first bias to be completed at the first station, the formation of an electrostatic image at the time of image formation immediately after the ejection control is started. The image forming apparatus according to claim 7.   When the acquired number is greater than the predetermined number, the control unit immediately switches the bias applied to the transfer unit from the second bias to the first bias immediately after the ejection control. The image forming apparatus according to claim 8, wherein after completion of the station, the electrostatic image formation is started at the time of image formation immediately after the ejection control after waiting for a predetermined time.   When the acquired number is not larger than a predetermined number, the control unit applies a first bias for image formation to the transfer unit, and the electrostatic image formation in the discharge control is performed at the first station. 8. The image forming apparatus according to claim 7, wherein when the image forming process is completed, formation of an electrostatic image is started at the time of image formation after the ejection control.   If the acquired number is not greater than the predetermined number, the control means may compare the pattern image and the subsequent image formed based on the print job as compared to the case where the acquired number is greater than the predetermined number. The image forming apparatus according to claim 7, wherein the image forming apparatus is controlled to reduce a distance between the image forming apparatus and the image forming apparatus.   12. The electrostatic image formation start timing at the time of ejection control immediately after image formation based on a print job is controlled by the control unit based on the number acquired by the acquisition unit. The image forming apparatus according to claim 1. The control unit causes the forming unit to form the pattern image on the photoconductor, and causes the transfer unit to form the pattern image on the photoconductor during discharge control when the number of stations to be controlled is greater than a predetermined number. Without transferring the pattern image to the intermediate transfer member, the pattern image on the photosensitive member is removed by the first removing means,
The control unit causes the forming unit to form the pattern image on the photoconductor, and causes the transfer unit to form the pattern on the photoconductor during discharge control when the number of stations to be controlled to discharge is not greater than the predetermined number. The image formation according to claim 1, wherein the pattern image is transferred to the intermediate transfer member, and the pattern image on the intermediate transfer member is removed by the second removing unit. apparatus.   The control means determines the amount of developer to be ejected for each station based on a value obtained by integrating the difference between the number of pixels forming an electrostatic image per page and a target value. The image forming apparatus according to claim 1.

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