JP5510305B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of printing a toner image on both sides of a print medium.

  In an image forming apparatus capable of printing a toner image on both sides of a sheet, the sheet on which the toner image is printed is conveyed to a reversing path, and the traveling direction of the sheet is reversed in the reversing path. As a result, the front and back of the paper are reversed, and a toner image is printed on the back of the paper.

  By the way, in the image forming apparatus, when toner images are continuously printed on both surfaces of a plurality of sheets, there is a possibility that a paper jam (hereinafter referred to as a jam) occurs in the reverse path. More specifically, the image forming apparatus is provided with a fixing device for fixing a toner image on a sheet. The fixing device includes a heating roller and a pressure roller, and performs heat treatment and pressure treatment on a sheet passing between the heat roller and the pressure roller.

  Here, when the sheet passes between the heating roller and the pressure roller, heat conduction from the heating roller to the pressure roller is blocked by the sheet. Therefore, the heat of the pressure roller is taken away by the sheet, and the temperature of the pressure roller is lowered. When the paper continuously passes through the fixing device, the temperature of the pressure roller decreases significantly. Therefore, the temperature of the sheet surface facing the pressure roller is significantly lower than the temperature of the sheet surface facing the heating roller. As a result, the moisture on the surface of the sheet facing the heating roller evaporates more than the moisture on the surface of the sheet facing the pressure roller. As a result, the paper curls so as to be wound around the heating roller. Further, since the heat of the pressure roller is taken away by the paper while the paper is passing through the fixing device, the trailing edge of the paper is higher than the temperature of the pressure roller when the front edge of the paper is passing through the fixing device. When the toner is passing through the fixing device, the temperature of the pressure roller becomes lower. For this reason, curling occurs more significantly at the trailing edge than at the leading edge of the paper.

  As described above, when the conveyance direction of the sheet is reversed by the reversing path in a state where the curl is generated at the trailing edge of the sheet, the curled portion of the sheet becomes the leading edge of the sheet in the conveyance direction. For this reason, the curled portion of the paper is caught by the conveyance path switching member and the guide member. As a result, in the image shape apparatus, a jam occurs in the inversion path.

  Thus, for example, an image forming apparatus described in Patent Document 1 has been proposed as an image forming apparatus that reduces the occurrence of curling. In the image forming apparatus described in Patent Document 1, the time for which the heating roller and the pressure roller are in contact with each other is increased by increasing the interval between the preceding sheet and the succeeding sheet, thereby increasing the temperature of the pressure roller. Is suppressed.

  However, in the image forming apparatus described in Patent Document 1, since the interval between sheets is increased, the number of printed sheets per unit time is reduced.

JP 2006-106686 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of jam while suppressing a decrease in the number of printed sheets per unit time when printing toner images on both sides.

  An image forming apparatus according to an aspect of the present invention includes a first conveyance path through which a print medium is conveyed, a registration roller pair provided in the first conveyance path, and the registration roller in the first conveyance path. An image forming unit that is provided on the downstream side of the pair of rollers and forms a toner image on the print medium, and fixing that fixes the toner image on the print medium by performing a heat treatment on the print medium A second transport path connected between the first transport path and a downstream side of the fixing section of the first transport path and an upstream side of the registration roller pair of the first transport path, A plurality of print media, a second transport path for reversing the front and back of the print medium to enter the first transport path by reversing the transport direction of the print medium having a toner image fixed on the surface thereof; Toner on both sides When the image is printed, the first print medium on which the toner image is printed on the back surface, and the first print medium are conveyed along the first conveyance path, and the toner image is printed on the front surface. A first gap between the second print medium and the second print medium, the third print medium having a toner image printed on a surface thereof, the first print path following the third print medium, and And causing the pair of registration rollers to convey the second print medium and the fourth print medium so as to be larger than the second interval with the fourth print medium on which the toner image is printed on the back surface. And a control unit.

  According to the present invention, when a toner image is printed on both sides, it is possible to suppress the occurrence of jam while suppressing a decrease in the number of printed sheets per unit time.

1 is a diagram illustrating an overall configuration of an image forming apparatus. 6 is a time chart showing timing when a sheet passes a predetermined position. 6 is a time chart showing timing when a sheet passes a predetermined position in an image forming apparatus according to a modification.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described.

(Configuration of image forming apparatus)
Hereinafter, an image forming apparatus including a developing device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating the overall configuration of the image forming apparatuses 1 and 1a. In the following, the left-right direction in FIG. 1 is defined as the front-back direction, the up-down direction in FIG. 1 is defined as the up-down direction, and the vertical direction in FIG. 1 is defined as the left-right direction.

  The image forming apparatus 1 is an electrophotographic color printer, and is configured to synthesize images of four colors (Y: yellow, M: magenta, C: cyan, K: black) in a so-called tandem system. . The image forming apparatus 1 has a function of printing an image on a sheet based on image data read by a scanner. As shown in FIG. 1, a printing unit (image forming unit) 2, a paper feeding unit 15, a resist A roller pair 19, a fixing device 20, a paper discharge roller pair 21, a paper discharge tray 23, transport roller pairs 24a to 24e, a reverse roller pair 25, a control unit 30, a switching member 32, a sensor 33, and transport paths R10 and R20 are provided. Yes.

  The control unit 30 controls the entire image forming apparatus 1 and is configured by, for example, a CPU.

  The paper supply unit 15 serves to supply paper (print medium) P one by one, and includes a paper tray 16 and a paper supply roller 17. A plurality of sheets of paper P in a state before printing are stacked on the paper tray 16. The paper feed roller 17 takes out the paper P placed on the paper tray 16 one by one.

  The transport roller pair 24a transports the paper P taken out by the paper feed roller 17 upward. The registration roller pair 19 conveys the paper P upward while adjusting the timing so that the toner image is secondarily transferred in the printing unit 2 to the paper P conveyed by the paper supply roller 17 and the conveyance roller 24a.

  The printing unit 2 forms a toner image on the paper supplied from the paper supply unit 15, and the optical scanning device 6 (6 </ b> Y, 6 </ b> M, 6 </ b> C, 6 </ b> K), the intermediate transfer belt 11, the driving roller 12, the driven rollers 13, 2. The image forming unit 22 (22Y, 22M, 22C, 22K) is included. The image forming unit 22 (22Y, 22M, 22C, 22K) includes a photosensitive drum 4 (4Y, 4M, 4C, 4K).

  The photosensitive drum 4 (4Y, 4M, 4C, 4K) has a cylindrical shape. An electrostatic latent image is formed on the peripheral surface of the photosensitive drum 4 by the optical scanning device 6 (6Y, 6M, 6C, 6K), and then a toner image based on the electrostatic latent image is developed by a developing device (not shown). The Since the formation of the electrostatic latent image and the development of the toner image are general processes, a detailed description thereof will be omitted.

  The intermediate transfer belt 11 is stretched between the driving roller 12 and the driven roller 13. The toner image developed on the photosensitive drum 4 is primarily transferred to the intermediate transfer belt 11. The driving roller 12 is rotated by an intermediate transfer belt driving unit (not shown in FIG. 1), thereby driving the intermediate transfer belt 11 in the direction of arrow α. As a result, the intermediate transfer belt 11 conveys the toner image to the secondary transfer roller 14.

  The secondary transfer roller 14 faces the intermediate transfer belt 11 and has a drum shape. The secondary transfer roller 14 secondarily transfers the toner image carried by the intermediate transfer belt 11 to the paper P passing between the secondary transfer roller 14 and the intermediate transfer belt 11 by applying a transfer voltage. .

  The sheet P on which the toner image is secondarily transferred is conveyed to the fixing device 20. The fixing device 20 includes a heating roller 20a and a pressure roller 20b, which heat-treats and pressurizes the paper P to fix the toner image on the paper. The heating roller 20a incorporates a heater and is in pressure contact with the pressure roller 20b from the front side. As the paper P passes between the heating roller 20a and the pressure roller 20b, the heat treatment and the pressure treatment are performed on the paper P.

  The transport roller pair 24 b transports the paper P that has passed through the fixing device 20 to the paper discharge roller pair 21. The paper discharge roller pair 21 outputs the paper P on the paper discharge tray 23.

  Here, the image forming apparatus 1 has a configuration capable of duplex printing on the paper P. That is, the image forming apparatus 1 can perform printing on the back surface of the paper P by inverting the front and back of the paper P after printing on the front surface of the paper P. Hereinafter, in the state of being stacked on the paper feed tray 16, the upper surface of the paper P is referred to as the front surface, and the lower surface of the paper P is referred to as the back surface.

  In the image forming apparatus 1, the transport path R <b> 10 is a path from the paper feeding unit 15 to the paper discharge roller pair 21, and is configured by transport paths R <b> 1 and R <b> 2. The transport path R10 is configured by a guide (not shown), and the paper P is transported. On the transport path R10, a transport roller pair 24a, a registration roller pair 19, a printing unit 2, a fixing device 20, a transport roller pair 24b, and a paper discharge roller pair 21 are arranged in this order from the upstream side to the downstream side in the transport direction. It is provided as follows. That is, the printing unit 2 is provided downstream of the registration roller pair 19 in the transport direction.

  The conveyance path R20 is connected between the downstream side in the conveyance direction with respect to the fixing device 20 of the conveyance path R10 and the upstream side in the conveyance direction with respect to the registration roller pair 19, and the sheet having the toner image fixed on the surface thereof is connected. By reversing the transport direction, the front and back of the sheet are reversed and entered the transport path R10. The conveyance path R20 is constituted by conveyance paths R3 and R4, and is constituted by a guide (not shown).

  The conveyance path R1 constitutes a path from the paper feeding unit 15 to the branch portion B on the downstream side in the conveyance direction of the conveyance roller pair 24b. The conveyance paths R2 and R3 are branched into two at the branch portion B.

  The conveyance path R <b> 2 constitutes a path from the branch portion B to the paper discharge roller pair 21. A paper discharge roller pair 21 is provided on the transport path R2.

  The transport route R3 branches at the branch portion B above the transport route R2. A reverse roller pair 25 is provided on the transport path R3. The reverse roller pair 25 transports the paper P transported from the transport path R1 into the transport path R3, then reverses the transport direction of the paper P and transports the paper P to the transport path R4.

  The transport path R4 is connected to the transport path R3, and is connected to the transport path R1 on the upstream side of the registration roller pair 19 in the transport direction. More specifically, the transport path R4 branches off from the transport path R3 in the reverse roller pair 25. On the transport path R4, transport roller pairs 24c to 24e are provided in this order from the upstream side to the downstream side in the transport direction. The transport roller pairs 24c to 24e transport the paper P to the transport path R1.

  The switching member 32 is provided at the branch portion B of the transport paths R2 and R3, and switches the transport destination of the paper P transported from the transport path R1 to the transport path R2 or the transport path R3.

  The sensor 33 detects the paper P. More specifically, the sensor 33 detects that the trailing edge of the paper P has reached a predetermined position Pa (see FIG. 1) in the transport path R1. The predetermined position Pa is located on the downstream side in the conveying direction of the registration roller pair 19. The control unit 30 causes the registration roller pair 19 to convey the paper P based on the output from the sensor 33.

(Operation of image forming apparatus)
The operation of the image forming apparatus 1 when printing toner images continuously on both sides of a plurality of sheets P (P1, P2,...) Will be described below. FIG. 2 is a time chart showing the timing at which the paper P passes the predetermined position Pa.

  First, the image forming apparatus 1 prints toner images on the surfaces of the sheets P1 to P3. At this time, as shown in FIG. 2, the control unit 30 causes the registration roller pair 19 to convey the sheets P1 to P3 so that the interval between the sheets P1 to P3 becomes the interval x at the predetermined position Pa. The interval x is set equal to the interval between the preceding paper P and the succeeding paper P when a toner image is printed on the surface of the plurality of papers P.

  The sheets P1 to P3 on which the toner images are printed are transported to the transport path R20. Then, as shown in FIG. 1, the paper P1 enters the transport path R10 with its front and back reversed in the transport path R20. The image forming apparatus 1 prints a toner image on the back surface of the paper P1.

  The controller 30 causes the registration roller pair 19 to carry the paper P4 when a predetermined time T1 has elapsed since the sensor 33 detected the trailing edge of the paper P1. The predetermined time T1 is a time when the interval between the rear end of the paper P1 and the front end of the paper P4 is the interval x + α. Thereby, as shown in FIG. 2, the interval between the paper P1 and the paper P4 is controlled to the interval x + α. The interval x + α is set to a length that does not cause curling at the trailing edge of the paper P4. Thereafter, a toner image is printed on the back surface of the paper P1, and a toner image is printed on the front surface of the paper P4.

  Next, the control unit 30 causes the registration roller pair 19 to carry the paper P2 when a predetermined time T2 has elapsed since the sensor 33 detected the trailing edge of the paper P4. The predetermined time T2 is a time when the interval between the trailing edge of the paper P4 and the leading edge of the paper P2 is the interval x. Thereby, as shown in FIG. 2, the interval between the paper P4 and the paper P2 is controlled to the interval x. Thereafter, a toner image is printed on the back surface of the paper P2. The image forming apparatus 1 repeats the operations performed on the back surface of the paper P1, the front surface of the paper P4, and the front surface of the paper P2, and prints toner images on both surfaces of the plurality of paper P.

  As described above, in the image forming apparatus 1, when the toner images are printed on both sides of the plurality of sheets P, the control unit 30 applies the rear end of the sheet P1 on which the toner images are printed on the back side and the sheet P1. Subsequently, the distance x + α from the leading edge of the paper P4 on which the toner image is printed on the front surface is transported along the transport path R10, and the trailing edge of the paper P4 on which the toner image is printed on the front surface and the paper P4. The pair of registration rollers 19 conveys the sheets P2 and P4 so that the distance x is larger than the distance x from the leading end of the sheet P2 on which the toner image is printed on the back surface.

(effect)
According to the image forming apparatus 1 configured as described above, occurrence of jam can be suppressed. More specifically, in the image forming apparatus 1, the interval between the rear end of the paper P1 on which the toner image is printed on the back surface and the front end of the paper P4 on which the toner image is printed on the front surface is a relatively large interval x + α. Is set. Thereby, when the paper P4 on which the toner image is formed passes through the fixing device 20, the pressure roller 20b is sufficiently heated by the heating roller 20a. For this reason, curling is unlikely to occur at the trailing edge of the paper P4, and even when the transport direction of the paper P4 is reversed in the transport path R20, occurrence of a jam in the transport path R20 is suppressed.

  Further, according to the image forming apparatus 1, it is possible to suppress a decrease in the number of printed sheets per unit time. More specifically, the paper P2 on which the toner image is formed on the back surface is output to the paper discharge tray 23 by the paper discharge roller pair 21 without entering the transport path R20 after the toner image is formed. Therefore, even if curling occurs at the rear end of the paper P2 on which the toner image is formed on the back surface, it is difficult to cause a jam. Therefore, in the image forming apparatus 1, the interval between the rear end of the paper P4 on which the toner image is printed on the front surface and the front end of the paper P2 on which the toner image is printed on the back surface is set to a relatively small interval x. . As a result, the interval between the trailing edge of the paper P4 and the leading edge of the paper P2 is reduced, and it is possible to suppress a decrease in the number of printed sheets per unit time.

(Modification)
Hereinafter, an image forming apparatus 1a according to a modification will be described with reference to the drawings. FIG. 3 is a time chart showing the timing at which the paper P passes the predetermined position Pa in the image forming apparatus 1a according to the modification.

  As shown in FIG. 3, in the image forming apparatus 1a, the rear end of the paper P4 on which the toner image is printed on the front surface, the transport path R10 following the paper P4, and the toner image are printed on the back surface. The distance from the leading edge of the paper P2 may be an interval x−α smaller than the interval x. As a result, according to the image forming apparatus 1a, it is possible to more effectively suppress a decrease in the number of printed sheets per unit time.

  INDUSTRIAL APPLICABILITY The present invention is useful for an image forming apparatus, and particularly excellent in that jamming can be suppressed while suppressing a decrease in the number of printed sheets per unit time when printing toner images on both sides. .

R1 to R4, R10, R20 Conveyance path 1, 1a Image forming apparatus 20 Fixing apparatus 20a Heating roller 20b Pressure roller 30 Control unit 33 Sensor

Claims (5)

A first transport path through which the print medium is transported;
A pair of registration rollers provided in the first conveyance path;
An image forming unit that is provided on the downstream side of the pair of registration rollers in the first transport path and that forms a toner image on the print medium;
A fixing unit that fixes a toner image on the print medium by performing a heat treatment on the print medium;
A second transport path connected between the downstream side of the fixing section of the first transport path and the upstream side of the pair of registration rollers of the first transport path, the surface having toner A second transport path for reversing the front and back of the print medium and entering the first transport path by reversing the transport direction of the print medium on which the image is fixed;
When toner images are printed on both sides of the plurality of print media, the first print medium on which the toner images are printed on the back surface and the first print medium are conveyed along the first conveyance path. And a first interval between the second print medium on which the toner image is printed on the surface, a third print medium on which the toner image is printed on the surface, and the third print medium following the third print medium. The second print medium and the second print medium are placed on the pair of registration rollers so as to be larger than the second interval with the fourth print medium that is transported through one transport path and has a toner image printed on the back surface. A control unit for transporting the print medium of 4;
Having
An image forming apparatus. The first interval is larger than the third interval between the preceding fifth print medium and the subsequent sixth print medium when toner images are printed on the surfaces of the plurality of print media;
The image forming apparatus according to claim 1. The second interval is equal to the third interval;
The image forming apparatus according to claim 2. The second interval is smaller than the third interval;
The image forming apparatus according to claim 2. The interval between the print media is an interval between the trailing edge of the preceding printing medium and the leading edge of the succeeding printing medium;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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