JP2018066921A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress an increase in temperature inside the apparatus during double-sided printing.SOLUTION: An image forming apparatus comprises: transfer means that transfers a toner image held on an image holding body to a sheet; fixing means that fixes the toner image to the sheet; inversion conveyance means that turns over the sheet on which the image is formed and conveys the turned-over sheet toward the transfer means; a first conveyance path that is in proximity with the image holding body to guide the sheet toward the transfer means; a second conveyance path that is separated from the image holding body to guide the sheet toward the transfer means; and switching means that switches between the first conveyance path and second conveyance path.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus.

  An image forming unit that forms an image on the conveyed paper, a fixing unit that heats and melts the image formed on the paper, and a reverse conveying unit that reverses and conveys the paper on which the image is fixed by the fixing unit. There is known an image forming apparatus including a first transport path and a second transport path for transporting a sheet that has passed through a fixing unit reversed by a reversing transport unit so as to be switchable to the image forming unit. (Patent Document 1).

  A pair of conveyance rollers for conveying the recording material, a transfer unit for transferring an image onto the recording material, a fixing device for fixing an unfixed image, a pair of discharge rollers for discharging the recording material on which the image is fixed, and a conveyance roller In an image forming apparatus having a double-sided printing mechanism that includes a main conveyance path of a recording material that connects a pair, a transfer unit, and a fixing device, and a reverse path, a fan is provided between the main conveyance path and the reverse path, When a recording material having an unfixed image is conveyed through the main conveyance path, the fan is rotated so that the air inside the apparatus main body is discharged to the outside of the apparatus main body, and the recording material having an unfixed image is main conveyed. An image forming apparatus that rotates a fan so that air is sucked into the apparatus main body from the outside of the apparatus main body when the path is not conveyed is also known (Patent Document 2).

JP 2009-265349 A JP 2010-39116 A

  An object of the present invention is to provide an image forming apparatus capable of suppressing a temperature rise inside the apparatus during double-sided printing.

In order to solve the above-mentioned problem, an image forming apparatus according to claim 1,
Transfer means for transferring the toner image held on the image carrier to paper;
Fixing means for fixing the toner image on a sheet;
Reversing and conveying means for reversing the front and back of the paper on which the image is formed, and for conveying the paper with the front and back reversed to the transfer means;
A first conveyance path for guiding the sheet toward the transfer means in the vicinity of the image carrier;
A second conveyance path that guides the sheet toward the transfer unit apart from the image carrier;
Switching means for switching between the first transport path and the second transport path,
It is characterized by that.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
The switching means switches to the second transport path when at least the paper is transported by the reverse transport means;
It is characterized by that.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
The switching means switches between the first transport path and the second transport path according to at least one of the number of continuously printed sheets, the printing speed, and the outside temperature.
It is characterized by that.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
The switching means is a gate claw that swings around a rotation support shaft.
It is characterized by that.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect,
A blower fan that blows air toward the second transport path;
It is characterized by that.

The invention according to claim 6 is the image forming apparatus according to claim 5,
The blower fan stops blowing when the paper is transported through the first transport path;
It is characterized by that.

The invention according to claim 7 is the image forming apparatus according to claim 5 or 6,
The blower fan changes the air volume according to the heat capacity of the paper.
It is characterized by that.

The invention according to claim 8 is the image forming apparatus according to claim 5 or 6,
The blower fan changes the air volume according to at least one of the number of continuously printed sheets, the printing speed, and the outside temperature.
It is characterized by that.

  According to the first aspect of the present invention, both sides of the first conveyance path close to the image holding body and the second conveyance path spaced apart from the image holding body can be switched. An increase in temperature inside the apparatus during printing can be suppressed.

  According to the second aspect of the present invention, it is possible to make it difficult for the heat of the paper during double-sided printing to be transmitted to the image holding member, and to suppress an increase in temperature inside the apparatus.

  According to the invention described in claim 3, it is possible to suppress a decrease in printing speed.

  According to invention of Claim 4, a 1st conveyance path and a 2nd conveyance path can be switched reliably with a simple mechanism.

  According to the fifth aspect of the present invention, it is possible to further cool the paper during double-sided printing.

  According to the invention described in claim 6, flapping of the paper passing through the first conveyance path can be suppressed.

  According to the seventh aspect of the present invention, flapping of the conveyed paper can be suppressed.

  According to the eighth aspect of the present invention, it is possible to suppress an increase in noise and power consumption.

2 is a schematic vertical sectional view showing an internal configuration of the image forming apparatus. FIG. It is a cross-sectional schematic diagram of a paper transport unit. FIG. 5 is a schematic cross-sectional view illustrating an internal configuration of a paper transport unit switched to a first transport path and paper transport. FIG. 6 is a schematic cross-sectional view illustrating an internal configuration of a paper transport unit switched to a second transport path and paper transport. 6 is a flowchart illustrating a flow of a switching operation between a first conveyance path and a second conveyance path in a sheet conveyance unit. It is a cross-sectional schematic diagram which shows the internal structure and paper conveyance of the paper conveyance part which concern on 2nd Embodiment. It is a flowchart which shows the flow of operation | movement of the switching of the 1st conveyance path and the 2nd conveyance path, and the ventilation fan in the paper conveyance part which concerns on 2nd Embodiment. It is a timing chart which shows rotation drive control of a ventilation fan. 10 is a flowchart showing a flow of rotational drive control of a blower fan in Modification 2.

Next, the present invention will be described in more detail with reference to the drawings with reference to embodiments and specific examples. However, the present invention is not limited to these embodiments and specific examples.
Also, in the description using the following drawings, it should be noted that the drawings are schematic and the ratio of each dimension and the like are different from the actual ones, and are necessary for the description for easy understanding. Illustrations other than the members are omitted as appropriate.
In order to facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, and the up-down direction is the Z-axis direction.

“First Embodiment”
(1) Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic longitudinal sectional view showing the internal configuration of the image forming apparatus 1 according to this embodiment.
Hereinafter, the overall configuration and operation of the image forming apparatus 1 will be described with reference to the drawings.

  The image forming apparatus 1 includes a control device 10, a paper feeding device 20, a photosensitive unit 30, a developing unit 40, a transfer unit 50, a paper transport unit 60, a fixing unit 70, and the like. On the upper surface (Z direction) of the image forming apparatus 1, there is formed a discharge tray portion T1 for discharging and storing a sheet on which an image is recorded. Further, on the side surface (−X direction) of the image forming apparatus 1, an opening / closing door 110 that opens the inside of the image forming apparatus 1 is rotatably supported when removing or inspecting when the paper P is jammed. Has been.

  The control device 10 includes an image forming device control unit 11 that controls the operation of the image forming device 1, a controller unit 12 that prepares image data according to a print processing request, an exposure control unit 13 that controls lighting of the exposure head LH, It has a power supply device 14 and the like. The power supply device 14 applies a high voltage to a charging roller 32, a developing roller 42, a primary transfer roller 52, a secondary transfer roller 62 and the like, which will be described later, and includes an exposure head LH, a paper feeding device 20, a fixing unit 70, and the like. Power is supplied to each sensor.

  The controller unit 12 converts print information input from an external information transmitting apparatus (for example, a personal computer) into image information for forming a latent image and outputs a drive signal to the exposure head LH at a preset timing. . The exposure head LH of the present embodiment is configured by an LED head in which a plurality of light emitting elements (LEDs) are linearly arranged along the main scanning direction.

  A paper feeding device 20 is provided at the bottom of the image forming apparatus 1. The sheet feeding device 20 includes a sheet stacking plate 21, and a large number of sheets P are stacked on the upper surface of the sheet stacking plate 21. The sheets P stacked on the sheet stacking plate 21 are pulled out side by side (−X direction) by the sheet pull-out section 22 one by one from the upper side, and then the nip portion of the registration roller pair 25 through the sheet guide guide 23. It is conveyed to.

  The photosensitive unit 30 is provided in parallel above the sheet feeding device 20 (Z direction) and includes a photosensitive drum 31. Around the photosensitive drum 31, a charging roller 32, an exposure head LH, a developing unit 40, a primary transfer roller 52, and a cleaning blade 33 are arranged along the rotation direction.

The developing unit 40 has a developing housing 41 in which a developer is accommodated. In the developing housing 41, a developing roller 42 disposed to face the photosensitive drum 31, and a pair of augers 44 that stir and convey the developer to the developing roller 42 side obliquely below the back side of the developing roller 42, 45 is arranged.
Each of the developing units 40 is configured in substantially the same manner except for the developer contained in the developing housing 41, and each forms a toner image of yellow (Y), magenta (M), cyan (C), and black (K). To do.

  The surface of the rotating photosensitive drum 31 is charged by the charging roller 32, and an electrostatic latent image is formed by the latent image forming light emitted from the exposure head LH. The electrostatic latent image formed on the photosensitive drum 31 is developed as a toner image by the developing roller 42.

  The transfer unit 50 includes an intermediate transfer belt 51 to which each color toner image formed on the photoconductive drum 31 of each photoconductor unit 30 is transferred, and each color toner image formed on each photoconductor unit 30 to the intermediate transfer belt. A primary transfer roller 52 that sequentially transfers (primary transfer) to 51 is provided. Further, an intermediate transfer belt cleaner 54 that removes residual toner adhering to the intermediate transfer belt 51 is provided.

  The paper transport unit 60 corrects the posture of the paper P fed from the paper feeding device 20 and sends the paper P to the secondary transfer portion TR in accordance with the secondary transfer timing, and a driven roller 25b of the registration roller pair 25, A secondary transfer roller 62 is provided that collectively transfers (secondary transfer) each color toner image transferred onto the intermediate transfer belt 51 onto a sheet P as a recording medium. Further, the sheet P on which the transferred toner image is held is guided to the fixing nip portion NP of the fixing unit 70 via the conveyance guide 65.

  Each color toner image formed on the photosensitive drum 31 of each photosensitive unit 30 is transferred to an intermediate transfer belt by a primary transfer roller 52 to which a predetermined transfer voltage is applied from a power supply device 14 or the like controlled by the image forming apparatus control unit 11. Electrostatic transfer (primary transfer) is sequentially performed on 51, and a superimposed toner image in which toners of respective colors are superimposed is formed.

The superimposed toner image on the intermediate transfer belt 51 is conveyed to the secondary transfer unit TR as the intermediate transfer belt 51 moves. When the superimposed toner image is conveyed to the secondary transfer unit TR, the paper P is supplied from the registration roller pair 25 to the secondary transfer unit TR in accordance with the timing.
A predetermined transfer voltage is applied to the secondary transfer roller 62 from the power supply device 14 controlled by the image forming apparatus control unit 11, and the sheet P sent from the registration roller pair 25 is multiplexed on the intermediate transfer belt 51. The toner image is batch transferred.

  Residual toner on the surface of the photosensitive drum 31 is removed by the cleaning blade 33 and collected in a waste toner collection container (not shown). The surface of the photosensitive drum 31 is recharged by the charging roller 32.

  The fixing unit 70 includes a heating module 71 and a pressure module 72, and a fixing nip portion NP (fixing area) is formed by a pressure contact area between the heating module 71 and the pressure module 72. The sheet P on which the toner image is transferred in the secondary transfer unit TR is transported to the fixing unit 70 via the transport guide 65 in a state where the toner image is not fixed. The toner image is fixed on the sheet P conveyed to the fixing unit 70 by a pair of heating module 71 and pressure module 72 by the action of heating and pressure bonding.

  The paper P on which the fixing toner image is formed is discharged from the discharge roller pair 79 to the discharge tray portion T1 on the upper surface of the image forming apparatus 1 via the conveyance roller pair 78. In the case of duplex printing, when the rear end of the sheet P on which the surface is fixed passes through the transport roller pair 78, the discharge roller pair 79 is driven reversely so that the reverse transport formed in the open / close door 110 is reversed. From the path, the sheet is conveyed to the registration roller pair 25 and image formation is performed on the back surface.

(2) Configuration and Operation of the Paper Conveying Unit FIG. 2 is a schematic cross-sectional view of the paper conveying unit. FIG. FIG. 5 is a schematic cross-sectional view showing the internal configuration of the paper transport unit switched to the second transport path and the paper transport. FIG. 5 shows the flow of the switching operation between the first transport path and the second transport path in the paper transport unit. It is a flowchart.
Hereinafter, the configuration and operation of the paper transport unit of the image forming apparatus 1 will be described with reference to the drawings.

  The paper transport unit includes an opening / closing door 110 and a paper transport unit 60.

(2.1) Opening / Closing Door The opening / closing door 110 rotates and supports the paper transport unit 60 inside, and the rotation axis 111 is supported by the casing 100 to close the opening and the opening to close the opening of the casing 100. Rotate and move between the open position to open.
On the inner surface of the opening / closing door 110 facing the housing 100, the outer side which is one of the reverse conveyance paths through which the paper P whose conveyance direction has been reversed after the surface has been fixed passes again before joining the registration roller pair 25 again. A conveyance guide 113 is formed.

The outer transport guide 113 forms a reverse transport path by holding a predetermined gap with the inner transport guide 631 formed in the paper transport unit 60.
A plurality of conveyance roller pairs 120 (shown in FIG. 1), 130, and 140 are disposed in the reverse conveyance path, and the outer conveyance guide 113 includes drive-side conveyance rollers 120a that constitute the conveyance roller pairs 120, 130, and 140. 130a and 140a are arranged.

(2.2) Paper Transport Unit The paper transport unit 60 includes a registration unit unit 610, a secondary transfer unit unit 620, and a duplex unit unit 630.

  The registration unit 610 includes a first sheet guide 611, a driven roller 25b of the registration roller pair 25, and a second sheet guide guide 612 as a second transport path. The driving roller 25a of the registration roller pair 25 is disposed on the apparatus main body side.

The first sheet guide 611 guides the sheet P fed from the sheet feeding device 20 and the sheet P conveyed through the duplex unit 630 to the nip portion of the registration roller pair 25.
The second sheet guide 612 guides the sheet P, which is separated from the intermediate transfer belt 51 as an example of the image carrier and is sent out with the posture corrected from the registration roller pair 25, to the secondary transfer unit TR.

  As shown in FIG. 3 (broken arrows in the figure indicate the flow of the paper P), a first transport path is provided on the downstream side of the registration roller pair 25 in the paper transport direction so as to face the second paper guide guide 612. The sheet guide 26 is provided in the vicinity of the intermediate transfer belt 51. The paper guide 26 guides the paper P, which is sent out by correcting the posture from the registration roller pair 25, to the secondary transfer unit TR.

Between the paper guide 26 and the second paper guide 612, a gate claw 27 as an example of a switching unit is disposed.
As shown in FIG. 3, the gate claw 27 has a first position for guiding the paper P to the paper guide 26, and as shown in FIG. 4 (broken arrows indicate the flow of the paper P). It is rotatably supported by the rotation support shaft 28 so as to take the second position leading to the two-sheet guide guide 612.

The gate claw 27 has a first guide surface 27a and a second guide surface 27b. The first guide surface 27a passes the sheet P conveyed through the registration roller pair 25 through the sheet guide guide 26 and the secondary transfer portion. A first transport path for guiding to the TR is formed.
The second guide surface 27b forms a second transport path for guiding the paper P transported through the registration roller pair 25 to the secondary transfer unit TR through the second paper guide guide 612.

  The secondary transfer unit section 620 includes a secondary transfer roller 62 and a conveyance guide 65, and a secondary transfer roller that is urged toward the intermediate transfer belt 51 to the sheet P that is fed in accordance with the secondary transfer timing. At 62, the toner image held on the intermediate transfer belt 51 is batch transferred (secondary transfer). The sheet P on which the toner image is transferred is guided to the fixing nip portion NP of the fixing unit 70 via the conveyance guide 65.

The double-sided unit 630 has an inner conveyance guide 631 that constitutes the other surface side of the reverse conveyance path so as to face the outer conveyance guide 113 formed on the inner surface side of the opening / closing door 110, and the sheet P to be printed on both sides. It is conveyed to the registration roller pair 25.
The inner conveyance guide 631 includes a pinch roller 130b and a pinch roller 140b that are rotatably arranged, and constitutes drive-side conveyance rollers 130a and 140a and conveyance roller pairs 120, 130, and 140 disposed on the outer conveyance guide 113. ing.

(2.3) Sheet conveyance in the sheet conveyance unit The image forming apparatus 1 performs sheet conveyance by switching the sheet conveyance path in the sheet conveyance unit according to the print mode.

(2.3.1) Single-sided printing At the time of single-sided printing, as shown in FIG. 3, the paper P sent out from the paper feeding device 20 is stopped by a pair of conveying rollers 24 via a paper guide guide 23. It is conveyed to the nip portion of the pair 25. The sheet P on which a loop is formed by the stopped registration roller pair 25 is sent from the registration roller pair 25 to the secondary transfer portion TR in a state where skew feeding is corrected as the registration roller pair 25 rotates.

Prior to the rotation of the registration roller pair 25, the gate claw 27 rotates to the first position for guiding the paper P to the paper guide 26, and the paper P fed from the registration roller pair 25 is fed to the first guide surface 27a of the gate claw 27. , The sheet is conveyed toward the sheet guide guide 26 and is fed along the sheet guide guide 26 to the secondary transfer portion TR.
In such single-sided printing, the temperature of the sheet P conveyed along the sheet guide guide 26 is substantially the same as the temperature inside the apparatus loaded on the sheet feeding device 20. The temperature of the secondary transfer part TR including 51 does not rise excessively.

(2.3.2) Double-sided printing When double-sided printing is performed, the conveyance roller pair 78 and the discharge roller pair 79 are downstream until the trailing edge of the paper P on which one side has been recorded passes through the conveyance roller pair 78. Conveyed to the side. When the trailing edge of the sheet P passes through the conveyance roller pair 78, the discharge roller pair 79 rotates in the reverse direction and is conveyed toward the reverse conveyance path.

  As shown in FIG. 4, the reversed paper P is transported by the transport roller pairs 120, 130, and 140 in the reverse transport path formed by the outer transport guide 113 and the inner transport guide 631, and the first paper guide guide 611. , Merged with the paper guide 23, and conveyed to the registration roller pair 25 with the front and back reversed.

  Then, the gate claw 27 rotates to the second position for guiding the paper P to the second paper guide guide 612, and the paper P fed from the registration roller pair 25 is guided to the second guide surface 27b of the gate claw 27 while being intermediate. The sheet is fed along the second sheet guide guide 612 separated from the transfer belt 51 to the secondary transfer unit TR, and the image is transferred onto the second surface of the sheet P in the secondary transfer unit TR.

When duplex printing is performed, the sheet conveyance path from the registration roller pair 25 to the secondary transfer unit TR is switched from the first conveyance path to the second conveyance path according to the flowchart shown in FIG.
First, when the image forming apparatus 1 receives a print job, the image forming apparatus control unit 11 determines whether or not double-sided printing is performed in a state where the gate claw 27 is rotated to the first position and switched to the first transport path (S101). Is determined (S102).

If it is determined that the printing is duplex printing (S102: Yes), it is next determined whether or not the continuous printing number N in the job is equal to or larger than a predetermined number Nth (S103). Here, an example of the predetermined number Nth is about 100.
If the number of continuous prints is equal to or greater than Nth (S103: Yes), it is further determined whether or not the print speed V is equal to or higher than a predetermined print speed V1 (S104). Here, an example of the predetermined printing speed V1 is a printing speed that is ½ of the maximum process speed of the apparatus.

  When the printing speed V is equal to or higher than the predetermined printing speed V1 (S104: Yes), it is determined whether the outside temperature T is equal to or higher than the predetermined temperature Tth (S105). Here, the outside temperature T is a temperature that is provided at the bottom of the open / close door 110 away from the fixing unit 70 that generates heat, the power supply device 14 and the like, and detects the outside temperature that affects the image formation of the image forming apparatus 1. An example of the predetermined temperature Tth detected by the sensor ST1 (see FIG. 1) is 10 ° C.

  If the outside temperature T is equal to or higher than the predetermined temperature Tth (S105: Yes), printing is started (S107), and it is determined whether or not the next printing surface is the front surface (S108). When the next printing surface is the front surface (S108: Yes), the first transport path is switched (S109), and one surface is printed (S111). When the next printing surface is the back surface (S108: No), the second printing path is switched (S110), and printing of one surface is executed (S112).

As described above, during duplex printing, the continuous printing number N is equal to or greater than the predetermined number Nth, the printing speed V is equal to or higher than the predetermined printing speed V1, and the outside temperature T is equal to or higher than the predetermined temperature Tth. When the next printing surface is the back surface, the second transfer path is switched (S110).
As a result, the paper P that is heated by the fixing unit 70, reversed, and fed again from the reverse conveyance path is transferred from the intermediate transfer belt 51 that is switched by the gate claw 27 from the registration roller pair 25 to the secondary transfer portion TR. An increase in temperature of the secondary transfer portion TR including the intermediate transfer belt 51 that is conveyed along the separated second sheet guide guide 612 is suppressed.

Also, when the continuous printing number N is smaller than the predetermined number Nth, when the printing speed V is lower than the predetermined printing speed V1, or when the outside temperature T is lower than the predetermined temperature Tth In any case, printing is started as it is (S106).
As a result, an excessive temperature rise in the secondary transfer unit TR including the intermediate transfer belt 51 is suppressed, and the secondary transfer unit TR is transported along the first transport path having a shorter transport path than the second transport path. Reduction is suppressed.

"Second embodiment"
FIG. 6 is a schematic cross-sectional view showing the internal configuration and paper conveyance of the paper conveyance unit according to the second embodiment, and FIG. 7 is a switching between the first conveyance path and the second conveyance path in the paper conveyance unit according to the second embodiment. 8 is a timing chart showing the rotational drive control of the blower fan 80, and FIG. 9 is a flowchart showing the flow of the rotational drive control of the blower fan 80 in the second modification.
Hereinafter, the sheet conveyance in the sheet conveyance unit of the image forming apparatus 1 </ b> A and the flow of air by the blower fan will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same component as the image forming apparatus 1 which concerns on 1st Embodiment, and the detailed description is abbreviate | omitted.

(1) Configuration of Paper Conveying Unit As shown in FIG. 6 (the arrow indicates the flow of air in the figure), the image forming apparatus 1A has a blower fan 80 disposed above the paper drawer 22 (see FIG. 1). ing. A ventilation duct 81 is provided on the downstream side of the blower fan 80 to guide the air sent from the blower fan 80 toward the back side of the paper guide 26A.
A vent hole 26Aa is formed in the paper guide 26A, and the air sent out from the air duct 81 is blown to the paper transport portion between the registration roller pair 25 and the secondary transfer portion TR.

Since the blower fan 80 is disposed above the sheet drawer portion 22 away from the fixing unit 70 that generates heat, the power supply device 14 and the like, the second blower fan 80 draws air near the temperature outside the apparatus and blows it. The sheet P conveyed along the sheet guide guide 612 is directly cooled.
In addition, the blower fan 80 always blows air to the sheet conveyance unit between the registration roller pair 25 and the secondary transfer unit TR except when the sheet P is conveyed through the first conveyance path. The second sheet guide guide 612 that guides the sheet P that is heated and re-conveyed by the fixing unit 70 is cooled.

(2) Paper transport in the paper transport unit The image forming apparatus 1A performs paper transport by switching the paper transport path in the paper transport unit according to the printing mode, and blows air on the paper P that is transported again during duplex printing. P is cooled to suppress an increase in temperature of the secondary transfer portion TR including the intermediate transfer belt 51.

  As shown in the flowchart of FIG. 7, when the image forming apparatus 1A receives a print job, the image forming apparatus control is performed in a state where the gate claw 27 is rotated to the first position and switched to the first transport path (S201). It is determined in section 11 whether double-sided printing is performed (S202).

If it is determined that the printing is duplex printing (S202: Yes), it is then determined whether or not the continuous printing number N in the job is equal to or greater than a predetermined number Nth (S203).
If the continuous printing number N is equal to or greater than Nth (S203: Yes), it is further determined whether or not the printing speed V is equal to or higher than a predetermined printing speed V1 (S204).
When the printing speed V is equal to or higher than the predetermined printing speed V1 (S204: Yes), it is determined whether the outside temperature T is equal to or higher than the predetermined temperature Tth (S205).

  When the outside temperature T is equal to or higher than a predetermined temperature Tth (S205: Yes), printing is started (S207), and it is determined whether or not the next printing surface is the front surface (S208). When the next printing surface is the front surface (S208: Yes), the first transport path is switched (S209), and one surface is printed (S212). When the next printing surface is the back surface (S208: No), switching to the second transport path (S210), rotating the blower fan 80 (S211), printing on one surface is performed (S212). ).

  As described above, during double-sided printing, when the continuous print number N is equal to or greater than the predetermined number Nth, the print speed V is equal to or greater than the predetermined print speed V1, and the outside temperature T is equal to or greater than the predetermined temperature Tth. Switching to the second transport path (S209), rotating the blower fan 80 (S211), blowing air directly onto the paper P transported toward the secondary transfer unit TR, and heating the paper P heated by the fixing unit 70. Cooling.

When rotating the blower fan 80, as shown in the time chart of FIG. 8, after the registration roller pair 25 is stopped and a registration loop is formed, the secondary transfer portion TR starts the second rotation from the timing (a) when the rotation is started. The rotation of the blower fan 80 is stopped only until the timing (d) when the next transfer bias is turned off.
As a result, except when the paper P is transported through the first transport path, air is always blown to the paper transporting portion between the registration roller pair 25 and the secondary transfer portion TR. When the sheet is not conveyed, the second sheet guide guide 612 can be cooled to further decrease the sheet temperature before the back surface transfer.

  As a result, the paper P that is heated by the fixing unit 70, reversed, and fed again from the reverse conveyance path is separated from the intermediate transfer belt 51 while air is blown from the registration roller pair 25 to the secondary transfer portion TR. The sheet is transported along the second sheet guide guide 612 while preventing the sheet from rising, and the temperature increase of the secondary transfer unit TR including the intermediate transfer belt 51 is further suppressed.

Also, when the continuous printing number N is smaller than the predetermined number Nth, when the printing speed V is lower than the predetermined printing speed V1, or when the outside temperature T is lower than the predetermined temperature Tth , Printing is started as it is (S206).
As a result, an excessive temperature rise in the secondary transfer unit TR including the intermediate transfer belt 51 is suppressed, and the secondary transfer unit TR is transported along the first transport path having a shorter transport path than the second transport path. Reduction is suppressed.

"Modification 1"
The image forming apparatus 1 </ b> A changes the air volume according to at least one of the continuous printing number N of double-sided printing, the printing speed V, and the outside temperature T.
Specifically, as shown in the flowchart of FIG. 7, when the continuous printing number N is smaller than the predetermined number Nth (S203: No), the printing speed V is lower than the predetermined printing speed V1. In the case (S204: No), when the outside temperature T is lower than the predetermined temperature Tth (S205: No), the rotation of the blower fan 80 is switched to the low speed rotation.
As a result, an excessive temperature rise in the secondary transfer portion TR including the intermediate transfer belt 51 is suppressed, and an increase in noise and power consumption can be suppressed.

"Modification 2"
The image forming apparatus 1 </ b> A changes the air volume according to the heat capacity of the paper P. Since the heat capacity of the paper P differs depending on the type of paper (for example, the thickness or basis weight of the paper), the amount of heat supplied by the fixing unit 70 is also different, and the type of the paper P that is reversed and re-conveyed (that is, The number of rotations of the blower fan 80 required for cooling is changed according to the heat capacity.

Specifically, instead of step 211 in the flowchart of FIG. 7, as shown in FIG. 9, the thickness information of the paper P in the print job is acquired (S302), and the paper P is a thick paper (S303: A). ) Increases the amount of air blown by driving the blower fan 80 at high speed rotation, thereby preventing the paper P from being lifted and improving the cooling efficiency.
On the other hand, when the paper P is thin (S303: B), the air blower 80 is driven at a low speed to reduce the amount of air blown, and the secondary transfer portion TR including the intermediate transfer belt 51 is excessively heated. While the rise is suppressed, the flapping of the paper P is suppressed.

  Here, examples of the thick paper include 120 gsm or more, examples of the thin paper include 60 gsm or less, and examples of the plain paper include the range of 70 to 110 gsm. Etc.).

DESCRIPTION OF SYMBOLS 1, 1A ... Image forming apparatus 10 ... Control apparatus 20 ... Paper feed apparatus 25 ... Registration roller pair 26 ... Paper guide guide 27 ... Gate claw 30 ... Photoconductor unit 40 ... Development unit 50 ... Transfer unit 60 ... Paper transport unit 610 ... Registration unit 611 ... First paper guide guide 612 ... Second paper guide guide 620 ... Secondary transfer Unit unit 630... Double-sided unit unit 631 .. Inner conveyance guide 62... Secondary transfer roller 70... Fixing unit 80. ..Outside conveyance guide

Claims (8)

Transfer means for transferring the toner image held on the image carrier to paper;
Fixing means for fixing the toner image on a sheet;
Reversing and conveying means for reversing the front and back of the paper on which the image is formed, and for conveying the paper with the front and back reversed to the transfer means;
A first conveyance path for guiding the sheet toward the transfer means in the vicinity of the image carrier;
A second conveyance path that guides the sheet toward the transfer unit apart from the image carrier;
Switching means for switching between the first transport path and the second transport path,
An image forming apparatus. The switching means switches to the second transport path when at least the paper is transported by the reverse transport means;
The image forming apparatus according to claim 1. The switching means switches between the first transport path and the second transport path according to at least one of the number of continuously printed sheets, the printing speed, and the outside temperature.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The switching means is a gate claw that swings around a rotation support shaft.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A blower fan that blows air toward the second transport path;
The image forming apparatus according to claim 1. The blower fan stops blowing when the paper is transported through the first transport path;
The image forming apparatus according to claim 5. The blower fan changes the air volume according to the heat capacity of the paper.
It is characterized by
The image forming apparatus according to claim 5, wherein the image forming apparatus is an image forming apparatus. The blower fan changes the air volume according to at least one of the number of continuously printed sheets, the printing speed, and the outside temperature.
The image forming apparatus according to claim 5, wherein the image forming apparatus is an image forming apparatus.

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