Image forming apparatus

Abstract

To prevent a reduction in image quality caused by unnecessary drive of a developing device.SOLUTION: An image forming apparatus comprises a printing unit, a post-processing unit, and a control unit. The printing unit has an image forming unit. The image forming unit includes image carriers and developing devices. When performing printing with post-processing continuously for a plurality of copies, the control unit stops the drive of developer carriers upon completion of developing processing for a preceding image to be printed on the last sheet in a preceding copy, and starts the drive of the developer carriers when executing developing processing for a next image to be printed on the first sheet in the next copy. The control unit sets, to a developing drive stop period, a period from the stopping of the drive of the developer carriers upon completion of the developing processing for the preceding image until the starting of the drive of the developer carriers for executing the developing processing for the next image, and maintains stoppage of the drive of the developer carriers during the developing drive stop period regardless of the length of the developing drive stop period.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] The image forming apparatus includes a developing device. The developing device contains a developer containing toner. The developing device agitates the toner and supplies it to an electrostatic latent image. In this way, the developing device develops the electrostatic latent image into a toner image. The image forming apparatus feeds a sheet and transfers (prints) the developed toner image onto the sheet. Such an image forming apparatus is disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-118760 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in a print job that requires post-processing, such as folding sheets, the time between the last sheet of a previous set and the first sheet of the next set is long. In other words, the non-processing period during which no development processing is performed by the developing device is long. If the developing device continues to operate unnecessarily during the non-processing period, the toner agitation time increases, causing toner degradation. This results in the inconvenience of reduced image quality.

[0005] The present invention has been made to solve the above-mentioned problems, and has an object to provide an image forming apparatus that can suppress deterioration in image quality caused by unnecessary driving of a developing device. [Means for solving the problem]

[0006] To achieve the above object, an image forming apparatus according to one aspect of the present invention includes a printing unit that transports sheets fed to a transport path and prints an image on the sheet as it is being transported, a post-processing unit that performs post-processing on the sheet transported from the printing unit, and a control unit. The printing unit has an image forming unit that forms an image to be printed on the sheet. The image forming unit includes a rotatably supported image carrier having an outer circumferential surface on which an electrostatic latent image is formed, and a developing device that has a developer carrier that rotates and carries a developer containing toner, and that performs a development process to form an image by supplying toner from the rotating developer carrier to the electrostatic latent image on the image carrier and developing it. When printing multiple copies consecutively with post-processing, the control unit stops driving the developer carrier when development processing for the preceding image to be printed on the last sheet of the preceding copy is completed, and starts driving the developer carrier when development processing for the next image to be printed on the first sheet of the next copy is performed. The control unit sets the development drive stop period as the period from when the drive of the developer carrier is stopped due to the completion of the development process for the preceding image to when the drive of the developer carrier is started to execute the development process for the next image, and keeps the drive of the developer carrier stopped during the development drive stop period regardless of the length of the development drive stop period. [Effects of the Invention]

[0007] In the present invention, it is possible to suppress deterioration in image quality caused by unnecessary driving of the developing device. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of an image forming unit according to an embodiment. [Figure 3] FIG. 2 is a schematic diagram of a post-processing unit according to an embodiment. [Figure 4] FIG. 1 is a block diagram of an image forming apparatus according to an embodiment. [Figure 5] 10A and 10B are diagrams showing development drive stop periods when single-sided printing is performed in a printing unit according to an embodiment. [Figure 6]10A and 10B are diagrams showing development drive suspension periods when double-sided printing is performed in a printing unit according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Configuration of image forming device> In this embodiment, as shown in FIG. 1, the image forming apparatus 100 includes a printing unit 10. The image forming apparatus 100 also includes a main transport path MP. The main transport path MP corresponds to a "transport path." The main transport path MP passes through a printing position and a fixing position in that order. A sheet cassette CA is detachably attached to the main body of the image forming apparatus 100. The sheet cassette CA stores sheets S.

[0010] During a print job, the printing unit 10 feeds a sheet S from a sheet cassette CA to a main transport path MP and transports the sheet S along the main transport path MP. The printing unit 10 also forms an image using toner. The printing unit 10 then prints the image on the sheet S being transported.

[0011] The printing unit 10 includes a feed roller FR as a feed unit that feeds the sheet S from the sheet cassette CA to the main transport path MP. The feed roller FR is positioned so that it can contact the sheet S in the sheet cassette CA from above. The feed roller FR is also rotatably supported. The feed roller FR is connected to a feed motor (not shown) and rotates when the driving force of the feed motor is transmitted to the feed roller FR. The feed roller FR comes into contact with the sheet S in the sheet cassette CA from above and rotates in that state. As a result, the feed roller FR pulls the sheet S out of the sheet cassette CA and sends it out to the main transport path MP.

[0012] The printing unit 10 includes an image forming unit 1. There are four image forming units 1. The four image forming units 1 correspond to the colors cyan, magenta, yellow, and black, respectively. Each of the four image forming units 1 forms an image (i.e., a toner image) using toner of the corresponding color. In monochrome printing, a black image (i.e., a monochrome image) is formed and printed on the sheet S. In color printing, a color image is formed by overlaying images of the colors cyan, magenta, yellow, and black on top of each other, and printed on the sheet S. In other words, each image forming unit 1 forms an image to be printed on the sheet S.

[0013] The following description focuses on one image forming unit 1 and explains its configuration, but the configurations of the four image forming units 1 are the same. Therefore, the following description will be used to cite the configurations of the other image forming units 1 and will not be explained.

[0014] As shown in Fig. 2, the image forming unit 1 includes a photosensitive drum 11, a charging device 12, an exposure device 13, a developing device 14, and a cleaning device 15. The photosensitive drum 11 corresponds to an "image carrier." For example, the photosensitive drum 11, the charging device 12, the developing device 14, and the cleaning device 15 form a single unit. The exposure device 13 is a separate unit from the single unit.

[0015] The photosensitive drum 11 is supported so as to be rotatable about an axis extending in one direction (a direction perpendicular to the plane of the paper in FIG. 2). The photosensitive drum 11 rotates while carrying a toner image on its outer circumferential surface.

[0016] The charging device 12 has a charging roller 120. The charging roller 120 comes into contact with the outer peripheral surface of the photosensitive drum 11. As a result, the charging roller 120 charges the outer peripheral surface of the photosensitive drum 11.

[0017] The exposure device 13 exposes the outer peripheral surface of the photosensitive drum 11 to light to attenuate the charge. The exposure device 13 exposes the outer peripheral surface of the photosensitive drum 11 to light to form an electrostatic latent image on the outer peripheral surface of the photosensitive drum 11.

[0018] The developing device 14 performs the development process. The developing device 14 contains a developer containing toner. The developer is a two-component developer containing toner and a carrier. The developing device 14 has a developing roller 140. The developing roller 140 corresponds to a "developer carrier." The developing device 14 also has a stirring screw 141.

[0019] The developing roller 140 is supported so as to be rotatable about an axis extending in one direction (a direction perpendicular to the plane of the paper in FIG. 2). The developing roller 140 carries a developer (i.e., toner) on its outer circumferential surface. A magnetic brush is formed on the outer circumferential surface of the developing roller 140.

[0020] As a development process, the developing device 14 performs a process of forming an image by supplying toner from the rotating developing roller 140 to the electrostatic latent image on the photosensitive drum 11 and developing the image. Specifically, the developing roller 140 rotates while bringing a magnetic brush into contact with the outer circumferential surface of the photosensitive drum 11. As a result, the toner adheres to the outer circumferential surface of the photosensitive drum 11, and a toner image is formed on the outer circumferential surface of the photosensitive drum 11.

[0021] The stirring screw 141 is supported so as to be rotatable about an axis extending in one direction (a direction perpendicular to the plane of the paper in FIG. 2). The stirring screw 141 stirs the developer contained in the developing device 14 by rotating. For example, the stirring screw 141 is rotated by a driving force from the same driving source (motor) as the developing roller 140. The stirring screw 141 rotates together with the developing roller 140. When the developing roller 140 stops rotating, the stirring screw 141 also stops rotating.

[0022] The cleaning device 15 removes residual toner from the photosensitive drum 11 downstream in the rotation direction of the photosensitive drum 11 from a contact position between the intermediate transfer belt 2 and the photosensitive drum 11, which will be described later. Note that toner that has not been transferred to the intermediate transfer belt 2 remains on the photosensitive drum 11.

[0023] As shown in FIG. 1, the printing unit 10 also includes an intermediate transfer belt 2. The intermediate transfer belt 2 corresponds to the "intermediate transfer body" and the "transfer receiving body." The intermediate transfer belt 2 is an endless belt. The intermediate transfer belt 2 is stretched and rotatably supported by multiple tension rollers, including a belt drive roller 20. In FIG. 1, the reference numerals of rollers other than the belt drive roller 20 among the multiple tension rollers are omitted.

[0024] The belt drive roller 20 is connected to a belt motor (not shown). The belt drive roller 20 rotates by receiving a driving force from the belt motor. The intermediate transfer belt 2 rotates in response to the rotation of the belt drive roller 20.

[0025] The printing unit 10 includes primary transfer rollers 3. There are four primary transfer rollers 3. One primary transfer roller 3 is assigned to each of the colors cyan, magenta, yellow, and black. Each primary transfer roller 3 is disposed on the inner circumferential side of the intermediate transfer belt 2. Each photosensitive drum 11 is disposed on the outer circumferential side of the intermediate transfer belt 2. Each primary transfer roller 3 is pressed against the photosensitive drum 11 carrying the toner image of the corresponding color via the intermediate transfer belt 2.

[0026] The printing unit 10 includes a secondary transfer roller 4. The secondary transfer roller 4 is in pressure contact with the outer circumferential surface of the intermediate transfer belt 2 at the printing position. The secondary transfer roller 4 sandwiches the intermediate transfer belt 2 between itself and the belt drive roller 20, forming a transfer nip between itself and the intermediate transfer belt 2. This forms a transfer nip at the printing position. The main transport path MP passes through the transfer nip.

[0027] The printing unit 10 includes a belt cleaning unit 200. The belt cleaning unit 200 cleans the outer peripheral surface of the intermediate transfer belt 2. The belt cleaning unit 200 removes toner remaining on the intermediate transfer belt 2 downstream of the printing position in the rotation direction of the intermediate transfer belt 2.

[0028] In a print job, the sheet S is transported toward the printing position (i.e., the transfer nip). During transport, the sheet S passes through the transfer nip. That is, the outer circumferential surface of the intermediate transfer belt 2 contacts the sheet S downstream of the contact position with each photosensitive drum 11 in the belt rotation direction.

[0029] Each image forming unit 1 forms a toner image using toner of the corresponding color. Each primary transfer roller 3 primarily transfers the toner image onto the outer circumferential surface of the intermediate transfer belt 2. The intermediate transfer belt 2 rotates while carrying the toner image. A secondary transfer roller 4 secondarily transfers the toner image onto the sheet S passing through the transfer nip.

[0030] In color printing, toner images are formed in all four image forming units 1. The toner images of each color are sequentially transferred (primary transfer) to the intermediate transfer belt 2 and then superimposed on each other. As a result, a full-color toner image is formed on the intermediate transfer belt 2. The full-color toner image is then secondarily transferred onto the sheet S.

[0031] In monochrome printing, toner images are not formed in the three image forming units 1 that use color toners (cyan, magenta, and yellow toners), but are formed in only one image forming unit 1 that uses black toner. As a result, a monochrome toner image is formed on the intermediate transfer belt 2. The monochrome toner image is secondarily transferred onto the sheet S.

[0032] The image forming apparatus 100 also includes a fixing unit 5. The fixing unit 5 includes a heating roller and a pressure roller. The fixing unit 5 is disposed at a fixing position. The heating roller has a built-in heater. The heating roller and the pressure roller are in pressure contact with each other to form a fixing nip at the fixing position.

[0033] During a print job, the sheet S passes through the fixing position. That is, the sheet S is sandwiched in the fixing nip. The fixing unit 5 heats the sheet S as it passes through the fixing position. Also, pressure is applied to the sheet S at the fixing position. The fixing unit 5 applies heat and pressure to the sheet S, thereby fixing the toner image to the sheet S.

[0034] The printing unit 10 includes a transport unit (not shown). The transport unit includes a plurality of transport roller pairs. Each transport roller pair includes a pair of rollers. The pair of rollers has a transport nip between them. Each transport roller pair rotates to transport the sheet S that has entered the transport nip.

[0035] The transport unit transports the sheet S along a main transport path MP, and also transports the sheet S along a double-sided printing transport path DP, which will be described later.

[0036] The printing unit 10 can execute a single-sided printing job in which an image is printed on only one side of a sheet S, as well as a double-sided printing job in which an image is printed on both sides of a sheet S. To execute a double-sided printing job, the image forming apparatus 100 is provided with a double-sided printing transport path DP.

[0037] The double-sided printing transport path DP branches off from the main transport path MP at a branching position downstream of the fixing position in the sheet transport direction, and merges with the main transport path MP at a merging position upstream of the printing position in the sheet transport direction.

[0038] When the job to be executed is a single-sided printing job, the sheet S passes through the transfer nip only once, and a single transfer process is performed on the sheet S while it is passing through the transfer nip. After the first transfer process, the sheet S is transported to the post-processing section 6, which will be described later.

[0039] If the job being executed is a double-sided printing job, the sheet S passes through the transfer nip twice, with one transfer process performed on each of the front and back sides of the sheet S. Specifically, the first time the sheet S passes through the transfer nip, the transfer process is performed on one side of the sheet S. After the first transfer process, the sheet S is switched back when the rear edge of the sheet S passes the branch position. This causes the rear edge of the sheet S to be drawn into the double-sided printing transport path DP.

[0040] Thereafter, the sheet S is transported along the double-sided printing transport path DP. Then, the sheet S on the double-sided printing transport path DP is returned to the main transport path MP from the junction position. The sheet S returned to the main transport path MP is transported along the main transport path MP and passes through the transfer nip again. At this time, the orientation of the front and back surfaces of the sheet S is reversed to the orientation when it passed through the transfer nip the previous time. As a result, when the sheet S passes through the transfer nip for the second time, the transfer process is performed on the other side of the sheet S, which is opposite to the one side.

[0041] The image forming apparatus 100 also includes a post-processing unit 6. The post-processing unit 6 performs post-processing on the sheets S carried in from the printing unit 10 (i.e., the sheets S on which an image has been printed). For example, the post-processing unit 6 is an optional device that is detachable from the main body of the image forming apparatus 100. In other words, a post-processing device is attached to the main body of the image forming apparatus 100, and the post-processing device functions as the post-processing unit 6.

[0042] 3, the post-processing unit 6 has an inlet 6A. The inlet 6A is provided on the side of the post-processing unit 6 that is connected to the main body of the image forming apparatus 100. The post-processing unit 6 receives the sheet S from the printing unit 10 through the inlet 6A.

[0043] The post-processing section 6 includes a first discharge tray TR1 and a second discharge tray TR2, as well as a first transport path Pa and a second transport path Pb.

[0044] The first discharge tray TR1 and the second discharge tray TR2 are provided on the side of the post-processing section 6 opposite to the side connected to the main body of the image forming apparatus 100. The first discharge tray TR1 is the main discharge tray. The second discharge tray TR2 is disposed above the first discharge tray TR1.

[0045] The first conveying path Pa is the main conveying path. The first conveying path Pa extends from the carry-in entrance 6A to an outlet (reference numeral omitted) for the sheet S onto the first discharge tray TR1. The second conveying path Pb branches off from the first conveying path Pa and extends to an outlet (reference numeral omitted) for the sheet S onto the second discharge tray TR2.

[0046] The post-processing section 6 includes a punch unit U1, a staple unit U2, and a booklet unit U3. The punch unit U1, the staple unit U2, and the booklet unit U3 perform post-processing. The post-processing section 6 also includes a folding unit 60 as a unit that performs post-processing.

[0047] The punch unit U1 is disposed on the conveyance path of the first conveyance path Pa. The punch unit U1 performs a punching process to form punch holes in the sheet S conveyed along the first conveyance path Pa as post-processing.

[0048] The staple unit U2 performs stapling, which binds a stack of sheets S with staples, as post-processing. When stapling is performed, the sheets S transported along the first transport path Pa are stacked on a processing tray (reference numeral omitted). Then, stapling is performed on the stack of sheets S on the processing tray, and the stack of sheets S is discharged to the first discharge tray TR1. Note that when stapling is not performed (including when only punching is performed), the sheets S can be discharged to the second discharge tray TR2. Even when stapling is not performed, the sheets S may be discharged to the first discharge tray TR1.

[0049] The booklet unit U3 performs booklet processing as post-processing. Specifically, the booklet unit U3 has a center stitching unit (reference numeral omitted) that staples the center of the stack of sheets S. The booklet unit U3 also has a center folding unit (reference numeral omitted) that folds the stack of sheets S in the middle.

[0050] For example, the post-processing section 6 includes a third transport path Pc that branches off from the first transport path Pa and extends downward. The third transport path Pc is connected to a booklet unit U3. When booklet processing is performed, the sheet S is transported to the booklet unit U3 via the third transport path Pc.

[0051] The post-processing section 6 is equipped with a discharge tray TR for booklets. The discharge tray TR is provided on the side of the post-processing section 6 opposite the side connected to the main body of the image forming apparatus 100. The discharge tray TR is disposed below the first discharge tray TR1. The booklet unit U3 discharges booklets obtained by the booklet process onto the discharge tray TR.

[0052] 4, the image forming apparatus 100 also includes a control unit 7. The control unit 7 includes processing circuits such as a CPU and an ASIC. The control unit 7 also includes storage devices such as a ROM and a RAM. The control unit 7 controls print jobs executed by the image forming apparatus 100.

[0053] The control unit 7 controls the feeding of the sheet S from the sheet cassette CA to the main transport path MP as part of the control of the print job. To this end, the control unit 7 controls the feed motor connected to the feed roller FR and other components. By controlling the feed motor, the control unit 7 switches the feed roller FR between rotating and stopping its rotation. In other words, the control unit 7 controls the feeding operation of the sheet S by the feed roller FR.

[0054] The control unit 7 controls image formation by the four image forming units 1. For example, the control unit 7 controls the rotation of rotating bodies such as the photosensitive drum 11 and the developing roller 140. In other words, the control unit 7 controls the motors that rotate the rotating bodies. The control unit 7 can switch between rotating and stopping the rotation of the developing roller 140.

[0055] The control unit 7 also controls the post-processing by the post-processing unit 6. A dedicated control unit (herein referred to as a post-processing control unit) for controlling the post-processing by the post-processing unit 6 may be provided separately. In this case, the control unit 7 communicates with the post-processing control unit and causes the post-processing control unit to control the post-processing by the post-processing unit 6.

[0056] The image forming apparatus 100 includes a communication unit 71. The communication unit 71 includes a communication circuit, a communication memory, a communication connector, and the like. The communication unit 71 is communicably connected to an external device via a network such as a LAN. An example of the external device is a user terminal. A personal computer (PC), a smartphone, a tablet computer, and the like can serve as the user terminal.

[0057] The control unit 7 communicates with an external device using the communication unit 71. For example, print data of a print job is transmitted from the external device (user terminal) to the image forming apparatus 100. The print data includes image data to be printed in the print job.

[0058] The control unit 7 adds a print job corresponding to the received print data to a queue. The control unit 7 executes the print jobs in the queue in the order in which they are received. If there are multiple print jobs in the queue, those multiple print jobs are executed consecutively.

[0059] The control unit 7 determines whether a print job in the queue is color printing or monochrome printing. When monochrome printing is performed, the control unit 7 causes the three image forming units 1 corresponding to the colors cyan, magenta, and yellow not to form images, and causes the image forming unit 1 corresponding to the color black to form images. On the other hand, when color printing is performed, the control unit 7 causes all image forming units 1 to form toner images.

[0060] The image forming apparatus 100 includes an operation unit 72. The operation unit 72 is an operation panel and includes a touch screen. The operation unit 72 receives instructions from a user to execute a print job, etc. The operation unit 72 is connected to the control unit 7. The control unit 7 detects the instructions, etc. received by the operation unit 72 from the user.

[0061] The image forming apparatus 100 also includes a voltage control unit 8, a charging voltage power supply 81, a developing voltage power supply 82, and a transfer voltage power supply 83. The voltage control unit 8 includes a voltage control circuit. The charging voltage power supply 81 applies a charging voltage to the charging roller 120. The developing voltage power supply 82 applies a developing voltage to the developing roller 140. The developing voltage is a voltage in which an AC voltage is superimposed on a DC voltage. The transfer voltage power supply 83 applies a transfer voltage to each of the primary transfer roller 3 and the secondary transfer roller 4. The transfer voltage is a voltage of opposite polarity to the polarity of the toner.

[0062] The voltage control unit 8 is connected to the control unit 7. The voltage control unit 8 controls the charging voltage power supply 81, the developing voltage power supply 82, and the transfer voltage power supply 83 based on control signals output from the control unit 7. In other words, the control unit 7 controls the charging voltage power supply 81, the developing voltage power supply 82, and the transfer voltage power supply 83. In yet other words, the control unit 7 controls the voltage application to each roller such as the developing roller 140.

[0063] <Sheet transport control> In a print job with multiple print sheets, multiple sheets S are transported continuously. When an instruction to execute a print job with multiple print sheets is received, the control unit 7 causes the feed roller FR to start a feed operation. The feed roller FR performs a paper feed operation by rotating while contacting the topmost sheet S in the sheet cassette CA from above. This starts feeding the sheet S. The sheet S then reaches the pair of transport rollers downstream of the feed roller FR in the sheet transport direction.

[0064] When a predetermined time has elapsed since the start of feeding of the sheet S, the control unit 7 stops the feeding operation of the feed roller FR. At this time, the sheet S has reached the pair of transport rollers downstream of the feed roller FR in the sheet transport direction. As a result, the sheet S continues to be transported even when the feeding operation of the feed roller FR stops. Thereafter, the control unit 7 causes the feed roller FR to repeatedly perform the feeding operation until the number of fed sheets S reaches the number of sheets to be printed.

[0065] Furthermore, in a print job with multiple copies to be printed, the time between copies between the preceding and following copies is adjusted depending on the type of post-processing performed in the post-processing unit 6. The time between copies is the time interval between the leading edge of the last sheet S of the preceding copy and the leading edge of the first sheet S of the following copy. In other words, the time between copies is the time from the start of feeding the last sheet S of the preceding copy to the start of feeding the first sheet S of the following copy.

[0066] For example, when post-processing including center folding is performed in the post-processing unit 6, the control unit 7 sets the time between sets to 4 to 5 seconds. When post-processing including saddle stitching is performed in the post-processing unit 6, the control unit 7 sets the time between sets to 5.5 to 6 seconds. When post-processing including tri-folding is performed in the post-processing unit 6, the control unit 7 sets the time between sets to 6 to 8 seconds.

[0067] <Developing roller drive timing> 5 and 6, the timing of driving the developing roller 140 when printing multiple copies in succession with post-processing is described below. Fig. 5 shows the timing when the job being executed is a single-sided print job, and Fig. 6 shows the timing when the job being executed is a double-sided print job.

[0068] 5 and 6, time T0 corresponds to the inter-printing time. Furthermore, in Fig. 5 and 6, development drive indicates the timings for driving (i.e., rotating) and stopping the development roller 140. Development processing indicates the timings for starting and ending the development processing.

[0069] When printing multiple copies in succession with post-processing, the control unit 7 stops driving the developing roller 140 when the development process for the preceding image to be printed on the last sheet S of the preceding copy is completed. Then, the control unit 7 starts driving the developing roller 140 when the development process for the next image to be printed on the first sheet S of the next copy is executed.

[0070] In other words, when printing multiple copies in succession with post-processing, the control unit 7 stops driving the developing roller 140 at a first time point P1 after the development process for the preceding image to be printed on the last sheet S of the preceding copy is completed. Then, the control unit 7 starts driving the developing roller 140 at a second time point P2 before the development process for the next image to be printed on the first sheet S of the next copy is started.

[0071] Here, since no development process is performed between the preceding and following copies, development drive is unnecessary. In other words, toner agitation by development drive between the preceding and following copies is unnecessary. The longer the toner agitation time, the more toner degradation progresses, and image quality degradation such as a decrease in density is more likely to occur. Therefore, it is preferable to stop development drive between the preceding and following copies.

[0072] Therefore, in this embodiment, the control unit 7 sets the development drive stop period to the period T from when the drive of the development roller 140 is stopped due to the completion of the development process for the preceding image to when the drive of the development roller 140 is started to execute the development process for the next image. In other words, the control unit 7 sets the development drive stop period to the period T from the first point in time P1 to the second point in time P2. Then, regardless of the length of the development drive stop period T, the control unit 7 maintains the drive of the development roller 140 stopped during the development drive stop period T.

[0073] As a result, in this embodiment, the time for which the driving of the developing roller 140 is stopped between the preceding and following portions can be extended. In other words, unnecessary development driving is suppressed. As a result, deterioration in image quality can be suppressed.

[0074] In this embodiment, the control unit 7 causes the multiple image forming units 1 to perform development processing in a predetermined order so that the images formed by the multiple image forming units 1 are superimposed on one another on the intermediate transfer belt 2. In this configuration, the control unit 7 sets a development drive stop period T for each of the multiple image forming units 1, and keeps the development roller 140 stopped during the development drive stop period T. This makes it possible to suppress unnecessary development drive in all of the developing devices 14.

[0075] Furthermore, in this embodiment, the control unit 7 stops applying AC voltage to the developing roller 140 during the development drive stop period T. This makes it possible to suppress, with simple control, toner scattering from the developing device 14 during the development drive stop period T. By reducing the amount of toner scattering, it is possible to suppress contamination caused by scattered toner.

[0076] Furthermore, in this embodiment, the control unit 7 calculates the length of the development drive stop period T (in other words, the time for which the development roller 140 is stopped) using different formulas when an image is printed on only one side of the sheet S and when an image is printed on both sides of the sheet S. The length T1 of the development drive stop period T when an image is printed on only one side of the sheet S is calculated using the following formula (1). On the other hand, the length T2 of the development drive stop period T when an image is printed on both sides of the sheet S is calculated using the following formula (2). T1=T0-ts-te-L1 / S (1) T2=T0-ts-te-(2×L1+L2) / S (2)

[0077] In equations (1) and (2), T0 is the time from when the last sheet S of the preceding copy starts to be fed to the main transport path MP until when the first sheet S of the next copy starts to be fed to the main transport path MP (i.e., the copy time). te is the time from when the development process for the preceding image ends until when the driving of the developing roller 140 stops. ts is the time from when the driving of the developing roller 140 starts to execute the development process for the next image until when the development process for the next image starts. L1 is the length in the transport direction of the sheet S transported along the main transport path MP. L2 is the length in the transport direction between the rear end of the preceding sheet S and the front end of the next sheet S within the same copy.

[0078] By using the formulas (1) and (2), the length of the development drive stop period T can be easily set appropriately.

[0079] Furthermore, in this embodiment, the time from the end of the development process for the preliminary image to the stop of driving of the developing roller 140 (i.e., the time te) is longer than the time from the end of the development process to the end of transfer of the image developed in that development process to the intermediate transfer belt 2 (corresponding to the "transfer receiving body"). This makes it possible to prevent the inconvenience of a deterioration in image quality due to vibrations that occur when the drive of the developing roller 140 is stopped.

[0080] Furthermore, in this embodiment, the time from when the development roller 140 starts to be driven to execute the development process for the next image until the development process for the next image starts (i.e., time ts) is longer than the time it takes for the development roller 140 to rotate twice. As a result, during the period until the development process for the next image starts, the toner on the development roller 140 is transferred to the photosensitive drum 11 and removed by the cleaning device 15. In other words, the toner that causes toner fogging is removed. As a result, deterioration in image quality can be further suppressed.

[0081] The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0082] 1 Image forming unit 2 Intermediate transfer belt (intermediate transfer body, transfer target body) 6 Post-processing section 7 Control Unit 10 Printing Department 11 Photosensitive drum (image carrier) 14 Developing device 82 Development voltage power supply 100 Image forming device 140 Developing roller (developer carrier) MP Main transport path (transport path) S seat

Claims

1. a printing unit that conveys the sheet fed to the conveying path and prints an image on the sheet while being conveyed; a post-processing unit that performs post-processing on the sheets conveyed from the printing unit; a control unit, the printing unit has an image forming unit that forms an image to be printed on a sheet, The image forming unit includes: an image carrier that is rotatably supported and has an outer peripheral surface on which an electrostatic latent image is formed; a developing device that has a developer carrier that carries a developer containing toner and rotates, and that performs a developing process to form an image by supplying toner from the rotating developer carrier to an electrostatic latent image on the image carrier and developing it, When printing a plurality of copies in succession with the post-processing, the control unit stops driving the developer carrier when the development process for the preceding image to be printed on the last sheet of the preceding copy is completed, and starts driving the developer carrier when the development process for the next image to be printed on the first sheet of the next copy is executed; The control unit sets the development drive stop period to be the period from when the driving of the developer carrier is stopped due to the completion of the development process for the preceding image to when the driving of the developer carrier is started to execute the development process for the next image, and maintains the driving of the developer carrier stopped during the development drive stop period regardless of the length of the development drive stop period.

2. The printing unit a plurality of image forming units that form images of different colors; an intermediate transfer body that is rotatably supported and onto which each image formed by the plurality of image forming units is primarily transferred, The image transferred to the intermediate transfer body is secondarily transferred to a sheet, thereby printing the image on the sheet; the control unit causes the plurality of image forming units to perform the developing process in a predetermined order so that the images formed by the plurality of image forming units are superimposed on one another on the intermediate transfer body; 2. The image forming apparatus according to claim 1, wherein the control unit sets the development drive stop period for each of the plurality of image forming units, and keeps the development drive stop period for each of the plurality of image forming units.

3. a developing voltage power supply that applies a developing voltage to the developer carrier when the developing device performs the developing process; the developing voltage is a voltage in which an AC voltage is superimposed on a DC voltage, The image forming apparatus according to claim 1 , wherein the control unit stops applying the AC voltage to the developer carrier during the development drive stop period.

4. The time from the start of feeding the last sheet of the preceding copy to the conveying path to the start of feeding the first sheet of the next copy to the conveying path is defined as T0, the time from the end of the development process for the preliminary image to the stop of driving of the developer carrier is defined as te; a time from when the driving of the developer carrier is started to execute the developing process for the next image until when the developing process for the next image is started is defined as ts; The linear velocity of the image carrier is S, The length of the sheet conveyed along the conveying path in the conveying direction is defined as L1, If the length in the conveying direction between the rear end of the preceding sheet and the front end of the next sheet in the same section is L2, The length T1 of the development drive stop period when an image is printed on only one side of a sheet is calculated by the following formula (1):

2. The image forming apparatus according to claim 1, wherein the length T2 of the development drive stop period when printing images on both sides of a sheet is calculated by the following formula (2): T1=T0-ts-te-L1 / S...(1) T2=T0-ts-te-(2×L1+L2) / S...(2)

5. 2. The image forming apparatus according to claim 1, wherein the time from the completion of the development process for the preliminary image to the stopping of driving of the developer carrier is longer than the time from the completion of the development process to the completion of transfer of the image developed in the development process to the transfer medium.

6. 2. The image forming apparatus according to claim 1, wherein the time from when the driving of the developer carrier is started to execute the development process for the next image to when the development process for the next image is started is longer than the time it takes for the developer carrier to rotate two times.

7. The image forming apparatus according to claim 1 , wherein the post-processing includes a process of folding the sheet.

Images