Image forming device

Abstract

To solve the problem in which: taking measures against adhesion of ejected sheets may unnecessarily reduce the productivity of printing.SOLUTION: An image forming apparatus has: a first loading unit on which a sheet conveyed through a first conveyance path through which a printed sheet is conveyed is loaded; a second loading unit on which a sheet conveyed through a second conveyance path is loaded; and a control unit that can control printing means to perform a first printing operation to continuously form images on a plurality of sheets, and subsequently perform a second printing operation to continuously form images on a plurality of sheets, wherein the number of printings per unit time is smaller than the first printing operation. The control unit changes the timing to start the second printing operation or the number of printings per unit time in the second printing operation between a case where a sheet is conveyed through the first conveyance path and a case where a sheet is conveyed through the second sheet conveyance path.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet. [Background technology]

[0002] Conventionally, in electrophotographic image forming devices, an electrostatic latent image formed on a photosensitive member is developed with toner, and this toner image is then transferred and fixed onto recording paper. The fixing device performs the fixing process by heating the toner image to fix the image onto the sheet. After fixing, the sheet is discharged by a discharge section and stacked on a stacking section.

[0003] Immediately after passing through the fixing unit, the sheet is at a temperature above the melting point of the toner. When hot sheets come into contact with each other, the toner melts and the sheets stick together (hereafter referred to as discharge adhesion) in the stacking area.

[0004] In order to prevent discharged sheets from adhering, a technique has been proposed in which discharged sheets are delayed to allow heat to be dissipated from the sheets, thereby preventing discharged sheets from adhering. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-248349 Summary of the Invention [Problem to be solved by the invention]

[0006] In Japanese Patent Application Laid-Open No. 2003-248349, adhesion of discharged sheets is prevented by delaying the discharge of the sheets, but delaying the discharge of the sheets results in a decrease in productivity.

[0007] Image forming apparatuses equipped with a first stacking section and a second stacking section on which discharged sheets are stacked are known. In such cases, the temperature of a sheet passing through a transport path leading to the first stacking section may differ from that of a sheet passing through a transport path leading to the second stacking section. For example, a sheet passing through a transport path with a longer distance to the stacking section is cooler than a sheet passing through a shorter transport path, making it less likely to experience discharge adhesion. This is because the temperature of the sheet decreases during transport from the fixing unit to the stacking section. Furthermore, a sheet passing through a transport path cooled by a cooling device such as a blower fan is cooled by the fan, making it less likely to experience discharge adhesion.

[0008] The present invention has been made under such circumstances, and an object thereof is to prevent adhesion of discharged sheets and a decrease in productivity in an image forming apparatus having a plurality of stacking units. [Means for solving the problem]

[0009] The image forming apparatus of the present invention includes a printing means for printing an image on a sheet, including a fixing means for fixing an image on a sheet using heat, a first transport path along which sheets on which an image has been printed by the printing means are transported, a first stacking section on which sheets transported along the first transport path are stacked, a second transport path along which sheets on which an image has been printed by the printing means are transported, and a second stacking section on which sheets transported along the second transport path are stacked, and a control unit that can control the printing means to perform a first printing operation in which an image is formed on a plurality of sheets in succession, and then a second printing operation in which an image is formed on a plurality of sheets in succession with a smaller number of sheets printed per unit time than the first printing operation, and is characterized in that the control unit changes the timing of starting the second printing operation after performing the first printing operation or the number of sheets printed per unit time in the second printing operation between when sheets are transported through the first transport path to the first stacking section and when sheets are transported through the second transport path to the second stacking section. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent adhesion of discharged sheets and also to prevent a decrease in productivity. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 2] FIG. 1 is a block diagram showing a system configuration of an image forming apparatus. [Figure 3] 1 is a diagram showing the structure of each page information. [Figure 4] 10 shows the number of sheets loaded at which the discharged paper adhesion countermeasure for each discharged paper tray is started and the productivity when the discharged paper adhesion countermeasure for each discharged paper tray is implemented according to the first embodiment. [Figure 5] 10 shows the number of sheets loaded at which the discharged paper adhesion measure for each discharged paper tray is started to be implemented and the heat radiation time when the discharged paper adhesion measure for each discharged paper tray is implemented according to the second embodiment. [Figure 6] 1 is a flowchart of a main operation. [Figure 7] 6 is a flowchart of a process for determining whether to implement a discharged paper adhesion countermeasure and a countermeasure operation according to the first embodiment. [Figure 8] 10 is a flowchart of a process for determining whether to implement a discharged paper adhesion countermeasure and a countermeasure operation according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, the components described in the embodiments are merely examples and are not intended to limit the scope of the present invention.

[0013] (First embodiment) <Image forming device> 1 is a cross-sectional view of an image forming apparatus 1. The image forming apparatus 1 forms an image on a sheet using an electrophotographic image forming process. Examples of the image forming apparatus 1 include electrophotographic copiers (e.g., digital copiers), electrophotographic printers (e.g., color laser beam printers, color LED printers, etc.), MFPs (multi-function peripherals), and facsimile machines.

[0014] Although the image forming apparatus 1 forms monochrome images, the present invention is not limited to this, and the image forming apparatus 1 may also form color images. The recording paper sheet is a transfer material on which an image is formed by the image forming apparatus 1, and may be, for example, paper, an overhead projector sheet, or cloth. The image forming apparatus 1 is provided with an image reading unit 191 that reads an image from a document. However, the image forming apparatus 1 does not necessarily need to be provided with the image reading unit 191. The image forming apparatus 1 may also be provided with a paper discharge unit 2, such as a post-processing device (paper discharge unit) that performs post-processing on the sheet P. In this embodiment, the paper discharge unit 2 is a so-called optional device. In other words, the paper discharge unit 2 is detachable from the main body of the image forming apparatus 1. The image forming apparatus 1 can operate even when the paper discharge unit 2 is detached. While the paper discharge unit 2 is an optional device as exemplified here, the paper discharge unit 2 may also be built into the image forming apparatus 1.

[0015] The image forming apparatus 1 has an image forming unit 220 as an image forming means for forming an image on a sheet P. The image forming unit 220 has a photosensitive drum (image carrier) 120 as a photosensitive member. Around the photosensitive drum 120, a charging device 123, an exposure device 124, a developing device 121, and a transfer roller 122 as a transfer device are arranged. The transfer roller 122 is arranged opposite the photosensitive drum 120 to form a transfer unit TP. The charging device 123 uniformly charges the surface of the photosensitive drum 120. The exposure device 124 emits a light beam modulated according to image data onto the uniformly charged surface of the photosensitive drum 120 to form an electrostatic latent image on the surface of the photosensitive drum 120. The developing device 121 develops the electrostatic latent image with toner to form a toner image.

[0016] At the bottom of the image forming apparatus 1, a feeding cassette 100 for storing sheets P is disposed.

[0017] The image forming apparatus 1 includes a conveying unit 250 for conveying sheets stored in a feeding cassette 100. The conveying unit 250, which constitutes a printing unit together with the image forming unit 220, includes a pickup roller 102, a feeding roller 104, a retard roller 103, a registration roller 110, and a drive motor for driving each roller. The conveying unit 250 further includes a first paper discharge roller 142, a reversing roller 180, a conveying roller 183 arranged in a double-sided conveying path 181, and a drive motor for driving each roller.

[0018] A pickup roller 102 picks up a sheet P from the feed cassette 100. The sheets P picked up by the pickup roller 102 are separated one by one by a feed roller 104 and a retard roller 103 and fed. The sheet P fed by the feed roller 104 is abutted against a stationary registration roller 110, where skew is corrected. The registration roller 110 starts rotating so that the leading edge of the sheet P coincides with the leading edge of the toner image on the photosensitive drum 120 at the transfer portion TP, and transports the sheet P to the transfer portion TP through a substantially vertical transport path 125. A transfer roller 122 transfers the toner image on the photosensitive drum 120 to the sheet P. A fixing roller 130 serving as a fixing portion is disposed downstream of the transfer portion TP in the transport direction of the sheet P. The fixing roller 130 applies heat and pressure to the toner image on the sheet P to fix the toner image to the sheet P, thereby forming an image on the sheet P.

[0019] The image forming apparatus 1 is provided with a first tray 160 as a first stacking section. The paper discharge unit 2 is provided with a second tray 161 as a second stacking section. As shown in FIG. 1 , a sheet P on which an image has been formed is discharged to the first tray 160 and stacked on the first tray 160, or is discharged to the second tray 161 and stacked on the second tray 161.

[0020] <Paper ejection unit> 1, the paper discharge unit 2 is attached to the top of the image forming apparatus 1. In this embodiment, the paper discharge unit 2 is disposed between the image forming apparatus 1 and the image reading unit 191. The image reading unit 191 is disposed above the paper discharge unit 2.

[0021] The paper discharge unit 2 has a second tray 161 onto which the sheet P on which an image has been formed is discharged, and a second conveyance path 152 through which the sheet passes when heading towards the second tray 161 after the image has been formed on the sheet by the image forming section 220. The second conveyance path 152 is provided with an entrance roller 150 that receives the sheet P from the image forming apparatus 1, and a second paper discharge roller 151 that discharges the sheet P from the second conveyance path 152 to the second tray 161.

[0022] The paper discharge unit 2 has a double-sided reversing guide (hereinafter referred to as a second reversing guide) 170 into which the sheet P temporarily enters as it is conveyed by a reversing roller 180 serving as a double-sided reversing means for reversing the front and back sides of the sheet P. The paper discharge unit 2 has a fan 171 serving as a blowing means for blowing air into the paper discharge unit 2. The paper discharge unit 2 is provided with a post-processing section 231 for post-processing the sheet on which an image has been formed.

[0023] The post-processing unit 231 is a paper discharge unit 2 that can align sheets and sort them by set as post-processing. That is, the paper discharge unit 2 can perform post-processing by shifting the sheets P left and right using a shift mechanism (not shown) and discharging them to the second tray 161. Note that the post-processing of the post-processing unit 231 may also include punching and binding processes for the sheets. Note that the paper discharge unit 2 shown here has the function of performing post-processing. However, the paper discharge unit 2 may also have only the function of discharging the sheets P without having post-processing.

[0024] <Transportation route> The transport path of the sheet P in the image forming apparatus 1 will be described below with reference to Fig. 1. When the sheet P is discharged to the first tray 160, the discharge flapper 141 rotates upward as indicated by the solid line in Fig. 1, and the sheet P is discharged to the first tray 160 by first discharge rollers 142 through a discharge transport path (hereinafter referred to as the first transport path) 143. When the sheet P is discharged to the second tray 161, the discharge flapper 141 rotates downward as indicated by the dashed line in Fig. 1, and the sheet P is discharged to the second tray 161 by second discharge rollers 151 through a second transport path 152. Here, the path length of the first transport path 143 through which the sheet discharged to the first tray 160 passes is shorter than the path length of the second transport path 152 through which the sheet discharged to the second tray 161 passes.

[0025] When double-sided printing is performed with the discharge unit 2 attached to the image forming apparatus 1, the double-sided flapper 140 rotates downward as shown by the dashed line in FIG. 1, and the sheet P, on which an image has been formed on its first side (front side), is conveyed to the reversing rollers 180. The reversing rollers 180 rotate forward and convey the sheet P to the second reversing guide 170 of the discharge unit 2. The reversing rollers 180 rotate reversely and convey the sheet P from the second reversing guide 170 to a double-sided conveying path 181 provided in the image forming apparatus 1. This reverses the front and back sides of the sheet P. The sheet P passes through the double-sided conveying path 181 by the conveying rollers 183 and is conveyed to the transfer unit TP by the registration rollers 110. An image is formed on the second side (back side) of the sheet P by the image forming unit 220, and the sheet P is then discharged to the first tray 160 or the second tray 161.

[0026] <Control System> A control system for controlling the image forming apparatus 1 will be described below with reference to FIG. 2. FIG. 2 is a block diagram of the control system for controlling the image forming apparatus 1. The control system includes a central processing unit (hereinafter referred to as CPU) 200, a read-only memory (hereinafter referred to as ROM) 201, and a random access memory (hereinafter referred to as RAM) 202. The CPU 200, which serves as a control unit, is connected to an external device 210, such as a personal computer, via an external interface (hereinafter referred to as external I / F) 211, such as a USB cable. The CPU 200 is connected to the paper discharge unit 2 via a paper discharge unit interface (hereinafter referred to as paper discharge unit I / F) 230. The CPU 200 is also electrically connected to the image forming unit 220, the conveying unit 250, the operation and display unit 190, the image reading unit 191, and the temperature and humidity sensor 221. The CPU 200 is connected to the conveying unit 250 and controls the conveyance of sheets.

[0027] The CPU 200 acquires information (hereinafter referred to as print information) related to image formation on a sheet P from the external device 210 via the external I / F 211, and starts the print process (image forming operation). Also, when a user operates the operation display unit 190 to perform a copy operation using the image reading unit 191, the CPU 200 acquires the print information from the operation display unit 190 and the image reading unit 191, and starts the print process. The CPU 200 executes the print process of the image forming apparatus 1 using the print information in accordance with a control program stored in the ROM 201. The CPU 200 writes processing data for the print process to the RAM 202, and also reads the processing data from the RAM 202.

[0028] The CPU 200 controls the image forming unit 220 to form a toner image on the photosensitive drum 120, transfer the toner image onto the sheet P by the transfer roller 122, and fix the toner image onto the sheet P by the fixing roller 130. The CPU 200 controls the reversing roller 180 of the conveying unit 250 to reverse the sheet P on which the image has been formed on the front side, and form an image on the back side.

[0029] The CPU 200 acquires user operation information from the operation display unit 190. The CPU 200 also displays information related to image formation (print information), warnings, and the like on the operation display unit 190 as a display unit. The CPU 200 controls the image reading unit 191 to read an image of a document. The user operation information from the operation display unit 190 as a setting unit includes setting information on whether to discharge a sheet to the first tray 160 or the second tray 161, i.e., setting information on the discharge destination.

[0030] A temperature and humidity sensor (temperature and humidity detector) 221 serving as an environmental sensor detects the temperature and humidity around the image forming apparatus 1. The CPU 200 stores the temperature and humidity detected by the temperature and humidity sensor 221 in a RAM (storage unit) 202. The CPU 200 drives a fan 171 provided in the paper discharge unit 2 via a paper discharge unit I / F 230. The CPU 200 drives a post-processing unit 231 provided in the paper discharge unit 2 via the paper discharge unit I / F 230.

[0031] <Basic operations of image forming devices> Next, with reference to Figures 1 and 2, a basic operation of the image forming apparatus 1 when the paper discharge unit 2 is attached to the image forming apparatus 1 will be described. When the CPU 200 acquires print information from the external device 210, it starts the print process. Here, with reference to Figure 3, the print information will be described. Figure 3 is a diagram showing print information 310. The print information 310 is created for each page. The print information 310 includes a sheet ID 300, feed port data 301, paper discharge port data 302, and image data 303. The CPU 200 saves the print information 310 in the RAM 202, and reads the print information 310 from the RAM 202 during the print process.

[0032] The sheet ID 300 is information for identifying the type of sheet and is assigned to each sheet. The feed slot data 301 is information for specifying the feed slot through which the sheet on which an image is to be formed is fed. In this embodiment, the feed slot data 301 specifies the feed cassette 100 or the duplex conveying path 181. The discharge slot data 302 is information for specifying the discharge slot through which the sheet on which an image is formed is discharged. In other words, the discharge slot data 302 includes data indicating whether the sheet is to be discharged to the first tray 160 or the second tray 161. More specifically, the discharge slot data 302 specifies the first tray 160, the second tray 161, or the duplex conveying path 181. In the case of double-sided printing, the sheet ID of the printing information for the first side and the sheet ID 300 of the printing information for the second side specify the same sheet type, and the discharge slot data 302 of the printing information for the first side and the feed slot data 301 of the printing information for the second side specify the duplex conveying path 181. The image data 303 is data of an image to be formed on the sheet P.

[0033] When the feed port data 301 specifies the feed cassette 100 based on the printing information 310, the CPU 200 starts feeding the sheet P from the feed cassette 100 using the pickup roller 102. The CPU 200 separates the sheets P one by one using the feed roller 104 and the retard roller 103, and feeds them to the registration roller 110. The CPU 200 detects the presence or absence of the sheet P in the feed cassette 100 using the sheet sensor 101. The CPU 200 starts rotating the registration roller 110 in synchronization with the toner image formed on the photosensitive drum 120 by the developing device 121, and transports the sheet P to the transfer unit TP. The CPU 200 transfers the toner image on the photosensitive drum 120 to the sheet P using the transfer roller 122. The CPU 200 transports the sheet P to the fixing roller 130 using the transfer roller 122. The CPU 200 applies heat and pressure to the toner image using the fixing roller 130, fixing the toner image to the sheet P.

[0034] When the fixing sensor 131 detects the leading edge of the sheet P on which an image has been formed, the CPU 200 switches the orientation of the duplex flapper 140 and the discharge flapper 141 in accordance with the discharge port data 302. If the discharge port data 302 specifies the first tray 160, the CPU 200 switches the duplex flapper 140 to the orientation shown by the solid line in Fig. 1 and the discharge flapper 141 to the orientation shown by the solid line in Fig. 1. The sheet P is conveyed to the first discharge rollers 142. The CPU 200 discharges the sheet P to the first tray 160 by the first discharge rollers 142 with the side on which the image has been formed (printed side) facing downward.

[0035] When the paper discharge port data 302 specifies the second tray 161, the CPU 200 switches the duplex flapper 140 to the orientation shown by the solid line in FIG. 1 and the paper discharge flapper 141 to the orientation shown by the dashed line in FIG. 1. The sheet P is conveyed to the inlet rollers 150 of the paper discharge unit 2. The CPU 200 drives the post-processing section 231 of the paper discharge unit 2 via the paper discharge unit I / F 230, and the inlet rollers 150 convey the sheet P to the second paper discharge rollers 151 through the second conveyance path 152. The CPU 200 discharges the sheet P to the second tray 161 by the second paper discharge rollers 151 with the side on which the image of the sheet P is formed (printed side) facing downward.

[0036] When the paper discharge port data 302 specifies the duplex conveying path 181, the CPU 200 switches the duplex flapper 140 to the orientation shown by the dashed line in FIG. 1. The sheet P is conveyed to the reversing roller 180. The CPU 200 rotates the reversing roller 180 forward to convey the sheet P to the second reversing guide 170. When a predetermined time has elapsed since the fixing sensor 131 detected the trailing edge of the sheet P, the CPU 200 switches the duplex flapper 140 to the orientation shown by the solid line in FIG. 1 and simultaneously rotates the reversing roller 180 in the reverse direction to change the conveying direction of the sheet P to the opposite direction. The CPU 200 conveys the sheet P to the registration roller 110 through the duplex conveying path 181 by the conveying roller 183. The CPU 200 starts the rotation of the registration roller 110 in synchronization with the toner image of the second side being formed on the photosensitive drum 120, and conveys the sheet P to the transfer unit TP. The subsequent operation is the same as that for forming the image on the first side, and the image on the second side is formed on the back side of the sheet P, opposite to the front side on which the image on the first side has been formed. In this way, double-sided printing is performed on the sheet P. The sheet P on which double-sided printing has been performed is discharged with the second side facing downwards to the first tray 160 or the second tray 161 in accordance with the paper discharge port data 302. Note that the configuration and operation of the image forming apparatus 1 described above are merely an example, and the present invention is not limited to the configuration and operation described above.

[0037] <Measures to prevent adhesive discharge> (1) Overview of paper discharge adhesion measures As a result of experiments, it has been found that in the image forming apparatus 1 of this embodiment, when the temperature of the sheets P stacked on the first tray 160 or the second tray 161 exceeds 85°C, discharge adhesion occurs, causing the discharged sheets to stick together.

[0038] The CPU 200 of the image forming apparatus 1 determines whether or not an operation to avoid adhesion of discharged sheets is necessary based on the number of sheets continuously stacked on the first tray 160 or the second tray to which the sheet P is discharged.

[0039] Therefore, when the CPU 200 determines that it is necessary to avoid discharge adhesion, it performs a discharge adhesion avoidance operation so that the next sheet is discharged after the temperature of the sheet P stacked on the first tray 160 or the second tray 161 has dropped. By performing the avoidance operation, the temperature of the sheet P does not reach 85°C, thereby preventing discharge adhesion from occurring.

[0040] In the operation to avoid adhesive discharge, continuous printing is performed with reduced productivity by widening the discharge interval when discharging sheets P to the first tray 160 or the second tray 161. Here, productivity refers to the number of printed sheets per unit time. The number of printed sheets refers to the number of sheets discharged to the first tray 160 or the second tray 161 after printing. While productivity is reduced (while the operation to avoid adhesive discharge is being performed), the sheet P is naturally cooled, making it possible to prevent adhesive discharge. Note that while the operation to avoid adhesive discharge is being performed, the start of image creation processing for the next sheet P is also delayed in order to reduce productivity.

[0041] By the operation of avoiding adhesive discharge, the sheets P stacked on the first tray 160 or the second tray 161 are naturally cooled, making it possible to prevent adhesive discharge from occurring.

[0042] (2) Tendency of adhesive discharge depending on the length of the transport path The longer the conveying distance from the fixing roller 130 to the sheet discharge tray, the more heat the sheet P radiates, and the slower the temperature rise until it reaches the temperature at which discharge adhesion occurs.

[0043] When the sheet P is discharged to the second tray 161, the transport distance from the fixing roller 130 to the sheet discharge tray is longer than when the sheet P is discharged to the first tray 160, and therefore the temperature rises more slowly than when the sheet P is discharged to the first tray 160.

[0044] (3) Tendency of adhesive discharge caused by fans If there is a fan that generates an air current in the conveying path, the sheet P is cooled during conveyance, and the temperature rise becomes even more gradual. Inside the paper discharge unit 2, a fan 171 that blows air into the second conveying path 152 is installed.

[0045] Therefore, when the sheet P is discharged onto the second tray 161, the temperature rise until it reaches the temperature at which discharged sheet adhesion occurs is more gradual than that of the first tray 160.

[0046] (4) Productivity trends due to the implementation of measures to improve adhesiveness of discharged paper relative to the length of the transport path The longer the transport distance from the fixing roller 130 to the paper discharge outlet, the longer the heat dissipation time until the sheet P is discharged, and the more gradually the temperature rise when the sheet P is stacked on the tray. If the temperature rise is gentler, the heat dissipation time of the sheets stacked on the paper discharge tray can be shortened, and the decrease in productivity when the sheet P is discharged can be minimized.

[0047] When the sheet P is discharged to the second tray 161, the conveyance distance from the fixing roller 130 to the sheet stacking on the discharge tray is longer than when the sheet P is discharged to the first tray 160, and the temperature rise is slower than when the sheet P is discharged to the first tray 160. Therefore, when the sheet P is discharged to the second tray 161, the decrease in productivity when the sheet P is discharged to the first tray 160 can be made smaller.

[0048] (5) Productivity trends due to the implementation of fan-based paper discharge adhesive measures If there is a fan that blows air through the conveyance path, the sheets P are cooled during conveyance, so the temperature rise when the sheets P are stacked on the tray is gradual. If the temperature rise is gradual, the heat dissipation time of the sheets stacked on the paper output tray can be shortened, and the decrease in productivity when the sheets P are ejected can be minimized.

[0049] A fan 171 that blows air is installed inside the paper discharge unit 2. Therefore, when the sheets P are discharged to the second tray 161, the temperature rise when the sheets P are stacked on the tray is more gradual than in the first tray 160, so that the decrease in productivity when the sheets P are discharged can be minimized.

[0050] (6) Regarding the relationship between the discharge destination and the avoidance operation of discharge adhesive, In consideration of the above trends (2) to (5), in this embodiment, the productivity when the operation to avoid adhesive discharge is being performed is set according to the destination to which the sheet P is discharged, as shown in Fig. 4. In addition, in this embodiment, the timing to start the operation to avoid adhesive discharge is determined according to the destination to which the sheet P is discharged, as shown in Fig. 4.

[0051] The "number of printed sheets" in FIG. 4 refers to the number of sheets printed consecutively in a normal printing operation, that is, the number of sheets printed before the avoidance operation is initiated (number of sheets at which the discharge adhesive prevention measures are initiated). The normal printing operation as the first printing operation is the printing operation that is performed before the discharge adhesive prevention operation as the second printing operation is initiated. That is, in this embodiment, if the discharge destination is set to the first tray 160, the discharge adhesive prevention operation is initiated when 70 sheets printed consecutively in a normal printing operation are discharged to the first tray 160. If the discharge destination is set to the second tray 161, the discharge adhesive prevention operation is initiated when 85 sheets printed consecutively in a normal printing operation are discharged to the second tray 161.

[0052] In FIG. 4, "Productivity when measures are implemented" indicates the percentage of productivity when the operation to avoid adhesive discharge is being implemented, with normal printing operation being taken as 100 percent. In this embodiment, during normal printing, the number of printed sheets per minute is 60 regardless of whether the discharge destination is the first tray 160 or the second tray 161. Therefore, when the discharge destination is set to the first tray 160, the number of printed sheets per minute when the operation to avoid adhesive discharge is being implemented is 30. When the discharge destination is set to the second tray 161, the number of printed sheets per minute when the operation to avoid adhesive discharge is being implemented is 45.

[0053] As described above, in this embodiment, the timing to start the operation to avoid adhesive discharge and the productivity of the operation to avoid adhesive discharge are determined depending on the output tray to which the paper is discharged. Therefore, in this embodiment, it is possible to prevent adhesive discharge while minimizing the rate of decrease in productivity.

[0054] <Flowchart (main)> Next, the main operation of the CPU 200 in this embodiment will be described with reference to Fig. 6. The control described below with reference to Fig. 6 is executed by the CPU 200 based on a program stored in the ROM 201, using the RAM 202 as a work area.

[0055] When the image forming apparatus is powered on, the CPU 200 first initializes the RAM 202 (S801). The CPU 200 then accesses the paper discharge unit I / F 230 to check whether the paper discharge unit 2 is connected (S802). If the CPU 200 can confirm that the paper discharge unit 2 is connected (S802: YES), the CPU 200 starts driving the fan 171 via the paper discharge unit I / F 230 as an initial operation (S803). If the CPU 200 cannot confirm that the paper discharge unit 2 is connected (S802: NO), the CPU 200 ends the initial operation.

[0056] After the initial operation is complete, the user starts printing based on print information 310 (see FIG. 3) from an external device 210 such as a personal computer, or starts copying using the image reading unit 191 from the operation display unit 190. The CPU 200 determines that the print information has been acquired (S804: YES). Then, based on the print information acquired in S805, the CPU 200 stores the print information in the RAM 202 in S805 (S805) and executes printing (S806). After each sheet of printing is completed, the CPU 200 checks whether it is necessary to avoid ejected paper adhesion, as described below, and executes a countermeasure operation for ejected paper adhesion (an operation to avoid ejected paper adhesion) if necessary (S807). After checking the ejected paper adhesion, the CPU 200 checks whether there are any more pages to print (S808). If the CPU 200 determines that there are still pages to print (S808: YES), the CPU 200 continues executing the print process (S806). If the CPU 200 determines that there are no pages left to print (S808: NO), the CPU 200 ends the printing process and returns to the standby state.

[0057] The CPU 200 checks whether the power has been turned off (S809). If the CPU 200 determines that the power has not been turned off (S809: NO), the CPU 200 then checks whether print information has been received from the external device 210 or the image reading unit 191 (S804). If the CPU 200 determines that the power has been turned off (S809: YES), the CPU 200 performs a process to stop each function. If the CPU 200 determines that the paper discharge unit 2 is connected (S810: YES), the CPU 200 stops the fan 171 (S811), performs a process to stop each function of the image forming apparatus 1, and then ends the process. If the CPU 200 determines that the paper discharge unit 2 is not connected (S810: NO), the CPU 200 performs a process to stop each function of the image forming apparatus 1, and then ends the process.

[0058] <Flowchart (Avoiding adhesive discharge)> Next, with reference to FIG. 7, the process of determining whether or not to implement discharged paper adhesion measures, which is executed in S806 of FIG. 6, and the operation performed when it is determined that discharged paper adhesion measures are necessary will be described.

[0059] First, the CPU 200 acquires the number of printed sheets at which to start a paper discharge adhesive countermeasure (hereinafter referred to as the paper discharge adhesive countermeasure start number) corresponding to the paper discharge tray of the discharge destination shown in FIG. 4 (S901). The CPU 200 acquires the temperature from the temperature and humidity sensor 221 (S902) and updates the number of consecutively printed sheets printed in normal operation (S903). The CPU 200 checks whether the number of consecutively printed sheets has reached the paper discharge adhesive countermeasure start number (S904). In this embodiment, when the discharge destination is the first tray 160, the CPU 200 determines that the paper discharge adhesive countermeasure start number has been reached when 70 sheets have been printed in succession in normal printing operation and the sheets have been discharged to the first tray 160. When the discharge destination is the second tray 161, the CPU 200 determines that the paper discharge adhesive countermeasure start number has been reached when 85 sheets have been printed in succession in normal printing operation and the sheets have been discharged to the second tray 161.

[0060] If the CPU 200 determines that the number of consecutively printed sheets has not reached the number of sheets required to start the discharged paper adhesion countermeasure (S904: NO), the discharged paper adhesion countermeasure operation is not required, so the CPU 200 checks the next printing process from the printing information stored in the RAM 202.

[0061] If the CPU 200 determines that the number of continuously printed sheets has reached the discharge adhesive countermeasure start count (S904: YES), the CPU 200 acquires the productivity value for when it is necessary to avoid discharge adhesive, corresponding to the discharge tray that is the discharge destination shown in FIG. 4 (S905). The CPU 200 determines the productivity for subsequent sheets P (S906). Then, the CPU 200 checks whether there are pages to print (S907). If there are pages to print (S907: YES), the CPU 200 accepts the next print information and operates at the low productivity determined in S906. In this manner, printing on consecutive sheets at low productivity is a countermeasure operation (avoidance operation) for discharge adhesive. As described with reference to FIG. 4, in this embodiment, when the discharge destination is the first tray 160, printing is performed at 50% of the productivity of normal printing operation during the discharge adhesive countermeasure operation. Also, when the discharge destination is the second tray 161, printing is performed at 75% of the productivity of normal printing operation during the discharge adhesive countermeasure operation.

[0062] If the CPU 200 determines that there are no pages to print (S907: NO), there is no need to reduce productivity, so the CPU 200 restores the reduced productivity (S908) and initializes the number of sheets to be discharged (number of sheets to be continuously printed) corresponding to the tray set as the discharge destination (S909).Then, the image forming apparatus 1 prepares for the next print process.

[0063] In the first embodiment, whether or not it is necessary to avoid adhesive discharge is determined based on the number of sheets that must be discharged before adhesive discharge countermeasures can be initiated. However, whether or not it is necessary to avoid adhesive discharge may also be determined based on the printing time corresponding to the number of sheets that must be discharged before adhesive discharge countermeasures can be initiated. In other words, a timer may be used to measure the time during which normal printing is being performed, and when the measured time reaches a time that is predetermined for each discharge destination, the operation to avoid adhesive discharge may be initiated.

[0064] This determination may be made by estimating the temperature for each paper output tray from the temperature set for the fixing roller 130 or the temperature of the temperature and humidity sensor 221. For example, the number of sheets to start a paper output adhesion countermeasure or the printing time determined for each paper output tray may be corrected based on the temperature set for the fixing roller 130 or the temperature and humidity sensor 221.

[0065] In the first embodiment, the operation to prevent adhesive discharge of sheets is to widen the gap between sheets (the gap from the rear edge of the preceding sheet to the front edge of the following sheet) to reduce productivity, thereby preventing adhesive discharge of sheets. Another method of reducing productivity is to reduce the discharge speed to a value set for each discharge tray.

[0066] As described above, according to the first embodiment, the number of printed sheets (number of stacked sheets) is determined for each tray to be discharged until the discharge adhesive measure is implemented. This allows for a longer period to determine whether productivity has decreased due to the discharge adhesive measure. Furthermore, it is possible to reduce the rate of productivity decrease due to the discharge adhesive measure.

[0067] In the above-described embodiment, an example was given in which both the number of prints before the discharge adhesive avoidance operation is performed and the productivity during the discharge adhesive avoidance operation are changed depending on the discharge destination. However, only one of the number of prints before the discharge adhesive avoidance operation is performed or the productivity during the discharge adhesive avoidance operation may be changed depending on the discharge destination. In other words, the number of prints before the discharge adhesive avoidance operation is performed may be changed depending on the discharge destination, while the productivity during the discharge adhesive avoidance operation may be the same regardless of the discharge destination. Alternatively, the number of prints before the discharge adhesive avoidance operation is performed may remain the same regardless of the discharge destination, and the productivity during the discharge adhesive avoidance operation may be changed depending on the discharge destination.

[0068] Note that normal printing operations may be resumed after a predetermined recovery time has elapsed since the start of the countermeasure operation (avoidance operation) for adhesive discharged sheets. The predetermined recovery time here is a time set so that adhesive discharged sheets will not occur even if normal printing operations are resumed. In this case, it is recommended that the countermeasure operation (avoidance operation) for adhesive discharged sheets be executed again after a predetermined number of sheets determined for each output destination have been printed during the resumed normal printing operations (or after a predetermined time has elapsed).

[0069] (Second embodiment) In the first embodiment, productivity was reduced when continuously printing sheets as a countermeasure against adhesive discharge. In the second embodiment, printing is temporarily suspended as a countermeasure against adhesive discharge. In the following, explanations of the configuration and control similar to those of the first embodiment will be omitted, and only the configuration and control different from those of the first embodiment will be described in detail.

[0070] In the second embodiment, the tendency of the temperature rise of the sheet P relative to the transport distance from the fixing roller 130 to being stacked on each of the discharge trays 160 and 161, and the tendency of the temperature rise of the sheet P relative to the presence or absence of a fan blowing air through the transport path, are the same as those in the first embodiment.

[0071] Specifically, in this embodiment, if it is determined that it is necessary to avoid discharge adhesion, the printing operation for the next sheet P is temporarily suspended and a post-rotation operation is performed. Then, after a predetermined suspension time has elapsed, the printing operation is resumed. While the printing operation is suspended, the sheets P stacked on the first tray 160 or the second tray 161 are naturally cooled, and by lowering the temperature inside the machine, discharge adhesion can be prevented.

[0072] While printing is suspended, the temperature inside the machine drops depending on the transport distance from the fixing roller 130 to the paper output tray and whether or not there is a fan blowing air through the transport path. By reflecting the effects on the temperature inside the machine of the transport distance and the presence or absence of a fan in the specified time for printing suspension, it is possible to take measures appropriate for each paper output tray.

[0073] In this embodiment, the time to suspend the printing operation to avoid adhesive discharge is set according to the discharge destination to which the sheet P is discharged, as shown in Fig. 5. Also, in this embodiment, the timing to start suspending printing as an operation to avoid adhesive discharge is determined according to the discharge destination to which the sheet P is discharged, as shown in Fig. 5.

[0074] The "number of printed sheets" in FIG. 5 refers to the number of sheets printed consecutively in a normal printing operation, and is the number of sheets printed before printing is suspended as a preventive operation (number of sheets at which measures to prevent adhesive discharged sheets begin). Note that a normal printing operation is a printing operation that is performed before the printing operation is suspended to prevent adhesive discharged sheets. That is, in this embodiment, if the discharge destination is set to the first tray 160, the printing operation is suspended when 70 consecutive printed sheets have been discharged to the first tray 160. If the discharge destination is set to the second tray 161, the printing operation is suspended when 85 consecutive printed sheets have been discharged to the second tray 161.

[0075] In FIG. 5, the "interruption time when countermeasures are implemented" indicates the length of time (interruption time) that printing operations are interrupted to avoid adhesive discharge. In this embodiment, during normal printing operations, the number of printed sheets per minute is 60, regardless of whether the discharge destination is the first tray 160 or the second tray 161. Therefore, during normal printing operations, the sheet discharge interval is one second, meaning that sheets are discharged approximately every second. Here, if the first tray 160 is set as the discharge destination, printing is interrupted for 20 seconds to avoid adhesive discharge. If the second tray 161 is set as the discharge destination, printing to avoid adhesive discharge is interrupted for 15 seconds. Whether the discharge destination is the first or second tray 161, the length of time that printing operations are interrupted to avoid adhesive discharge is longer than the one-second sheet discharge interval during normal printing operations.

[0076] <Flowchart> The main operation of the CPU 200 in this embodiment is the same as that in the first embodiment shown in Fig. 6. The process of determining whether to implement discharged paper adhesion measures and the timing of operation when it is determined that discharged paper adhesion measures are necessary are also the same as those in the first embodiment, and are executed in S806 in Fig. 6.

[0077] Next, the process of determining whether or not to implement a discharged sheet adhesion countermeasure in the second embodiment and the operation performed when it is determined that a discharged sheet adhesion countermeasure is necessary will be described with reference to FIG.

[0078] First, the number of printed sheets at which to start a paper discharge adhesive countermeasure (hereinafter referred to as the paper discharge adhesive countermeasure start number) corresponding to the paper discharge tray of the paper discharge destination shown in FIG. 5 is obtained (S1001). The CPU 200 obtains the temperature from the temperature and humidity sensor 221 (S1002) and updates the number of consecutively printed sheets actually printed in normal operation (S1003). The CPU 200 checks whether the number of consecutively printed sheets has reached the paper discharge adhesive countermeasure start number (S1004). In this embodiment, when the discharge destination is the first tray 160, the CPU 200 determines that the paper discharge adhesive countermeasure start number has been reached when 70 sheets have been printed in succession in normal printing operation and discharged to the first tray 160. When the discharge destination is the second tray 161, the CPU 200 determines that the paper discharge adhesive countermeasure start number has been reached when 85 sheets have been printed in succession in normal printing operation and discharged to the second tray 161.

[0079] If the CPU 200 determines that the number of consecutively printed sheets has not reached the number of sheets required to start the discharged paper adhesion countermeasure (S1004: NO), the discharged paper adhesion countermeasure operation is not required, so the CPU 200 checks the next printing process from the printing information stored in the RAM 202.

[0080] If the CPU 200 determines that the number of consecutively printed sheets has reached the ejection adhesive countermeasure start number (S1004: YES), the CPU 200 acquires the current timer value from a timer function (not shown) and stores it in RAM 202 as the ejection time of the last sheet (S1005). The CPU 200 acquires the stop time (the time required for heat dissipation to prevent ejection adhesive) corresponding to the ejection tray shown in FIG. 5 (S1006) and executes a post-rotation operation to interrupt printing (S1007). The CPU 200 acquires the current timer value to calculate the elapsed time since printing (S1008) and calculates the elapsed time from the difference between the current timer value and the ejection time of the last sheet stored in RAM 202 (S1009). The CPU 200 repeats acquiring the timer value and calculating the elapsed time until the elapsed time calculated in S1009 reaches the stop time (the time required for heat dissipation) acquired in S1006 (S1010: NO).

[0081] If the CPU 200 determines that the elapsed time has reached the stop time (the time required for heat dissipation) obtained based on FIG. 5 (S1010: YES), it determines that the sheet P has sufficiently dissipated heat, and performs initialization operations for the next print. Specifically, the CPU 200 initializes the number of stacked sheets (S1011) and initializes the last paper ejection time saved in the RAM 202 (S1012). After completing the initialization operations, the CPU 200 performs pre-rotation, which is a print preparation operation (S1013), to prepare for the next print process. Thereafter, the process returns to S808 of FIG. 6, and if the CPU 200 determines that there is a next sheet to be printed, the CPU 200 resumes the suspended print operation in S806.

[0082] In the second embodiment, whether or not it is necessary to avoid adhesive discharge is determined based on the number of printed sheets (number of sheets at which adhesive discharge countermeasures are initiated). However, whether or not it is necessary to avoid adhesive discharge may also be determined based on the printing time corresponding to the number of printed sheets. In other words, a timer may be used to measure the time during which normal printing is performed, and printing may be interrupted (stopped) when the measured time reaches a time predetermined for each output destination.

[0083] Furthermore, the determination may be made by estimating the temperature for each paper output tray from the temperature set for the fixing roller 130 or the temperature of the temperature and humidity sensor 221. For example, the number of sheets at which to start taking adhesive measures against discharged paper and the interruption time determined for each paper output tray may be corrected based on the temperature set for the fixing roller 130 and the temperature and humidity sensor 221.

[0084] As described above, according to the second embodiment, the number of prints until the countermeasure operation for discharging paper is performed is determined for each discharge destination. This makes it possible to suppress printing interruptions due to the countermeasure operation for discharging paper. Furthermore, by setting the printing interruption time due to the countermeasure operation for discharging paper for each discharge destination, it is possible to reduce the rate of productivity loss due to the countermeasure operation for discharging paper.

[0085] In the second embodiment, both the number of prints and the interruption time before printing is interrupted to avoid ejection paper adhesion are changed depending on the ejection destination. However, only one of the number of prints or the interruption time before printing is interrupted may be changed depending on the ejection destination. In other words, the number of prints before printing is interrupted to avoid ejection paper adhesion may be changed depending on the ejection destination, and the interruption time may be the same regardless of the ejection destination. Alternatively, the number of prints before printing is interrupted may not be changed depending on the ejection destination, but the interruption time may be changed depending on the ejection destination.

[0086] In each of the above embodiments, the fan 171 blows air onto the sheet on the second conveying path 152, through which the sheet passes toward the second tray. However, the fan 171 is not necessarily required. Even in this case, the conveyance distance of the sheet is longer when the sheet is discharged to the second tray 161 via the second conveying path 152 than when the sheet is discharged to the first tray 160 via the first conveying path 143. The cooling conditions for the sheet when the discharge destination is the first tray 160 are conditions under which the sheet is not cooled as much as when the discharge destination is the second tray 161. Therefore, when the discharge destination is the second tray 161, discharge adhesion is less likely to occur than when the discharge destination is the first tray 160.

[0087] In addition, in each of the above embodiments, the conveyance distance of the sheet is longer when the sheet is discharged to the second tray 161 via the second conveyance path 152 than when the sheet is discharged to the first tray 160 via the first conveyance path 143. However, the conveyance distance of the sheet may be the same when the sheet is discharged to the second tray 161 via the second conveyance path 152 than when the sheet is discharged to the first tray 160 via the first conveyance path 143. For example, the conveyance distance of the sheet may be slightly shorter when the sheet is discharged to the second tray 161 via the second conveyance path 152 than when the sheet is discharged to the first tray 160 via the first conveyance path 143. In either case, the sheet on the second conveyance path 152, through which the sheet bound for the second tray passes, is cooled by air blown by the fan 171. The cooling conditions for the sheet when the discharge destination is the first tray 160 are conditions under which the sheet is not cooled as much as the cooling conditions when the discharge destination is the second tray 161. Therefore, discharge adhesion is less likely to occur than when the discharge destination is the first tray 160. Note that the fan 171 that blows air toward the sheets on the second conveying path 152 (generating an airflow toward the sheets) has been exemplified as the cooling means for cooling the sheets discharged onto the second tray 161. However, the cooling means may be a fan that generates an airflow that exhausts (wastes heat) from the second conveying path 152 to cool the sheets. Also, the cooling means for cooling the sheets may be a fan that blows air toward the sheets stacked on the second tray 161. [Explanation of symbols]

[0088] 2 Paper output unit 130 Fuser roller 143 First conveying route 152 Second transport route 160 1st Tray 161 Second Tray 171 fans 221 Temperature and humidity sensor

Claims

1. a printing means for printing an image on the sheet, the printing means including a fixing means for fixing the image on the sheet using heat; a first conveying path along which a sheet on which an image is printed by the printing means is conveyed; a first stacking section on which the sheets conveyed through the first conveying path are stacked; a second conveying path along which a sheet on which an image is printed by the printing means is conveyed; a second stacking section on which the sheets conveyed through the second conveying path are stacked; a control unit that can control the printing means to perform a first printing operation in which images are formed continuously on a plurality of sheets, and then a second printing operation in which images are formed continuously on a plurality of sheets, the number of sheets printed per unit time being smaller than that of the first printing operation; The image forming apparatus is characterized in that the control unit changes the timing at which the second printing operation is started after the first printing operation is executed, or the number of printed sheets per unit time in the second printing operation, between when the sheet is transported through the first transport path to the first stacking section and when the sheet is transported through the second transport path to the second stacking section.

2. The image forming apparatus according to claim 1, characterized in that the control unit changes the timing of starting the second printing operation and the number of printed sheets per unit time in the second printing operation when the sheet is transported to the first stacking section by passing through the first transport path and when the sheet is transported to the second stacking section by passing through the second transport path.

3. a path length of the sheet when conveyed through the first conveying path is shorter than a path length of the sheet when conveyed through the second conveying path; The image forming apparatus of claim 2, characterized in that when the control unit transports a sheet through the first transport path to the first stacking section, it starts the second printing operation earlier and reduces the number of printed sheets per unit time in the second printing operation than when the control unit transports a sheet through the second transport path to the second stacking section.

4. a fan that generates an airflow in the second transport path; The image forming apparatus of claim 2, characterized in that when the control unit transports a sheet through the first transport path to the first stacking section, it starts the second printing operation earlier and reduces the number of printed sheets per unit time in the second printing operation than when the control unit transports a sheet through the second transport path to the second stacking section.

5. An image forming apparatus as described in any one of claims 1 to 4, characterized in that when a sheet is transported through the first transport path to the first stacking section, the control unit controls the timing of starting the second printing operation to be earlier by reducing the number of sheets printed in the first printing operation before starting the second printing operation compared to when a sheet is transported through the second transport path to the second stacking section.

6. An image forming apparatus as described in any one of claims 1 to 4, characterized in that when the sheet is transported to the first stacking section by passing through the first transport path, the control unit controls the timing of starting the second printing operation to be earlier by shortening the time from starting the first printing operation to starting the second printing operation compared to when the sheet is transported to the second stacking section by passing through the second transport path.

7. An image forming apparatus according to any one of claims 1 to 6, characterized in that the cooling conditions for the sheet transported through the first transport path and loaded onto the first stacking section are conditions under which the sheet is cooled less than the cooling conditions for the sheet transported through the second transport path and loaded onto the second stacking section.

8. 8. The image forming apparatus according to claim 1, wherein a path length of the sheet when transported through the first transport path is shorter than a path length of the sheet when transported through the second transport path.

Images