JP6868179B2 - Image forming device - Google Patents

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 an inverted conveying unit that inverts the paper on which the image is fixed by the fixing unit and conveys the image. An image forming apparatus including a first transport path and a second transport path for transporting paper that has passed through a fixing portion inverted by the reverse transport unit to the image forming unit in a switchable manner is known. (Patent Document 1).

A transport roller pair for transporting the recording material, a transfer unit for transferring the image onto the recording material, a fixing device for fixing the unfixed image, a discharge roller pair for discharging the recording material on which the image is fixed, and a transport roller. In an image forming apparatus having a double-sided printing mechanism including a main transport path for recording material and a reversal path for connecting a pair, a transfer unit, and a fuser, a fan is provided between the main transport path and the reversal path. When the recording material having an unfixed image is transported in the main transport path, the fan is rotated so that the air inside the device body is discharged to the outside of the device body, and the recording material having the unfixed image is mainly transported. An image forming apparatus that rotates a fan so that air is sucked from the outside of the apparatus main body to the inside of the apparatus main body when the road is not conveyed is also known (Patent Document 2).

Japanese Unexamined Patent Publication No. 2009-265349 Japanese Unexamined Patent Publication No. 2010-39116

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 problems, the image forming apparatus according to claim 1 is used.
A transfer means for transferring the toner image held on the image holder to paper, and
A pair of resist rollers that correct the posture of the conveyed paper and feed the paper to the transfer means.
A fixing means for fixing the toner image on paper and
A reversing transporting means for inverting the front and back of the paper on which an image is formed and transporting the paper with the inverted front and back toward the transfer means.
A first transport path that guides the paper toward the transfer means in the vicinity of the image holder on the downstream side in the paper transport direction of the resist roller pair.
A second transport path that guides the paper toward the transfer means away from the image holder on the downstream side of the resist roller pair in the paper transport direction.
A means for switching the paper transport direction to the first transport path or the second transport path.
It is characterized by that.

The invention according to claim 2 is the image forming apparatus according to claim 1.
The switching means switches to the second transport path at least when the paper is transported by the reverse transport means.
It is characterized by that.

The invention according to claim 3 is the image forming apparatus according to claim 1 or 2.
The switching means switches between the first transport path and the second transport path according to at least one of the number of prints to be printed continuously, the print speed, and the outside temperature.
It is characterized by that.

The invention according to claim 4 is the image forming apparatus according to any one of claims 1 to 3.
The switching means is a gate claw that swings around a rotary support shaft.
It is characterized by that.

The invention according to claim 5 is the image forming apparatus according to claim 1.
Further equipped with a blower fan for blowing 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 conveyed 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 prints continuously printed, 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 invention do not have a configuration capable of switching between a first transport path close to the image holder and a second transport path separated from the image holder. It is possible to suppress the temperature rise inside the apparatus during printing.

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 transferred to the image holder and suppress the temperature rise inside the apparatus.

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

According to the fourth aspect of the invention, the first transport path and the second transport path can be reliably switched by a simple mechanism.

According to the invention of claim 5, the paper at the time of double-sided printing can be further cooled.

According to the invention of claim 6, it is possible to suppress the fluttering of the paper passing through the first transport path.

According to the invention of claim 7, it is possible to suppress the fluttering of the conveyed paper.

According to the invention of claim 8, it is possible to suppress an increase in noise and power consumption.

It is a vertical cross-sectional schematic diagram which shows the internal structure of an image forming apparatus. It is sectional drawing of the paper transport unit. It is sectional drawing which shows the internal structure of the paper transport part switched to the 1st transport path, and the paper transport. It is sectional drawing which shows the internal structure of the paper transport part switched to the 2nd transport path, and the paper transport. It is a flowchart which shows the flow of the switching operation of the 1st transport path and the 2nd transport path in the paper transport section. It is sectional drawing which shows the internal structure of the paper transport part which concerns on 2nd Embodiment, and the paper transport. It is a flowchart which shows the switching of the 1st transport path and the 2nd transport path, and the operation flow of the blower fan in the paper transport section which concerns on 2nd Embodiment. It is a timing chart which shows the rotation drive control of a blower fan. It is a flowchart which shows the flow of the rotation drive control of a blower fan in the modification 2.

Next, the present invention will be described in more detail with reference to the drawings below with reference to embodiments and specific examples, but the present invention is not limited to these embodiments and specific examples.
In addition, in the explanation using the following drawings, it should be noted that the drawings are schematic and the ratio of each dimension is different from the actual one, which is necessary for the explanation 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-back 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 the Image Forming Device FIG. 1 is a schematic vertical cross-sectional view showing the internal configuration of the image forming apparatus 1 according to the present 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 photoconductor 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, an ejection tray portion T1 for ejecting and accommodating paper on which an image is recorded is formed. 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 the paper P is removed or inspected when a paper jam occurs. Has been done.

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 in response to a print processing request, and an exposure control unit 13 that controls the 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 the charging roller 32, the developing roller 42, the primary transfer roller 52, the secondary transfer roller 62, etc., 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 and the like.

The controller unit 12 converts the print information input from an external information transmission device (for example, a personal computer or the like) 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 composed of an LED head in which a plurality of light emitting elements (LEDs: Light Emitting Diodes) are linearly arranged along the main scanning direction.

A paper feeding device 20 is provided at the bottom of the image forming device 1. The paper feeding device 20 includes a paper loading plate 21, and a large number of papers P are loaded on the upper surface of the paper loading plate 21. The paper P loaded on the paper loading plate 21 is pulled out side by side (-X direction) by the paper drawer portion 22 one by one from the upper side, and then the nip portion of the resist roller pair 25 via the paper guide guide 23. Will be transported to.

Each of the photoconductor units 30 is provided in parallel above the paper feeding device 20 (Z direction), and includes a photoconductor 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 around the photoconductor drum 31 along the rotation direction.

The developing unit 40 has a developing housing 41 in which a developing agent is housed. In the developing housing 41, a developing roller 42 arranged so as to face the photoconductor drum 31, and a pair of augers 44 that agitate and convey the developer to the developing roller 42 side diagonally downward on the back surface 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 housed in the developing housing 41, and each forms a yellow (Y), magenta (M), cyan (C), and black (K) toner image. To do.

The surface of the rotating photoconductor 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 photoconductor drum 31 is developed as a toner image by the developing roller 42.

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

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

Each color toner image formed on the photoconductor drum 31 of each photoconductor unit 30 is formed on 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 an image forming device control unit 11. Electrostatic transfer (primary transfer) is sequentially performed on the 51, and a superimposed toner image on which each color toner is 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 to the secondary transfer unit TR from the resist roller pair 25 in accordance with the timing.
Then, 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 paper P sent out from the resist roller pair 25 is multiplexed on the intermediate transfer belt 51. The toner image is collectively transferred.

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

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

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 transport roller pair 78. Further, in the case of double-sided printing, when the rear end of the paper P whose surface is fixed passes through the transfer roller pair 78, the discharge roller pair 79 is reverse-driven and the reverse transfer is formed in the opening / closing door 110. It is conveyed from the road to the resist roller pair 25 and an image is formed on the back surface.

(2) Configuration and operation of the paper transport unit FIG. 2 is a schematic cross-sectional view of the paper transport unit, and FIG. 3 is a schematic cross-sectional view showing the internal configuration and paper transport of the paper transport unit switched to the first transport path. Is a schematic cross-sectional view showing the internal configuration of the paper transport section switched to the second transport path and the paper transport, and FIG. 5 shows the flow of switching operation between the first transport path and the second transport path in the paper transport section. 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 rotating shaft 111 is supported by the housing 100 to provide a closed position and an opening for closing the opening of the housing 100. Rotates and moves between the open position and the open position.
On the inner surface of the opening / closing door 110 facing the housing 100, the outer side, which is one of the reversing transport paths through which the paper P whose transport direction is reversed after the surface is fixed, passes until it rejoins the resist roller pair 25. A transport guide 113 is formed.

The outer transport guide 113 holds a predetermined gap with the inner transport guide 631 formed in the paper transport unit 60 to form an inverted transport path.
A plurality of transport roller pairs 120 (shown in FIG. 1), 130, 140 are arranged in the reversing transport path, and the drive-side transport rollers 120a, which constitute the transport roller pairs 120, 130, 140, are arranged in the outer transport guide 113. 130a and 140a are arranged.

(2.2) Paper Transfer Unit The paper transfer unit 60 is composed of a cash register unit unit 610, a secondary transfer unit unit 620, and a double-sided unit unit 630.

The cash register unit unit 610 has a first paper guide guide 611, a driven roller 25b of a resist roller pair 25, and a second paper guide guide 612 as a second transport path. The drive roller 25a of the resist roller pair 25 is arranged on the apparatus main body side.

The first paper guide guide 611 guides the paper P fed from the paper feeding device 20 and the paper P conveyed via the double-sided unit unit 630 to the nip portion of the resist roller pair 25.
The second paper guide guide 612 guides the paper P, which is sent out from the resist roller pair 25 after correcting the posture, to the secondary transfer unit TR, away from the intermediate transfer belt 51 as an example of the image holder.

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

A gate claw 27 as an example of the switching means is arranged between the paper guide guide 26 and the second paper guide guide 612.
The gate claw 27 has a first position for guiding the paper P to the paper guide guide 26 as shown in FIG. 3, and the gate claw 27 has the paper P as shown in FIG. 4 (the broken line arrow in the figure indicates the flow of the paper P). 2 It is rotationally supported by the rotary support shaft 28 so as to take a second position leading to the paper guide guide 612.

The gate claw 27 has a first guide surface 27a and a second guide surface 27b, and the first guide surface 27a is a secondary transfer unit for the paper P conveyed via the resist roller pair 25 via the paper guide guide 26. It forms a first transport path that guides the TR.
The second guide surface 27b forms a second transport path that guides the paper P transported via the resist roller pair 25 to the secondary transfer unit TR via the second paper guide guide 612.

The secondary transfer unit unit 620 has a secondary transfer roller 62 and a transfer guide 65, and is urged toward the intermediate transfer belt 51 by the paper P fed at the timing of the secondary transfer. The toner image held on the intermediate transfer belt 51 at 62 is collectively transferred (secondary transfer). The paper P on which the toner image is transferred is guided to the fixing nip portion NP of the fixing unit 70 via the transport guide 65.

The double-sided unit portion 630 has an inner transport guide 631 that forms the other side of the reversing transport path facing the outer transport guide 113 formed on the inner surface side of the opening / closing door 110, and prints on both sides of the paper P. It is conveyed to the resist roller pair 25.
A pinch roller 130b and a pinch roller 140b are rotatably arranged on the inner transfer guide 631, respectively, and constitute a drive side transfer roller 130a, 140a and a transfer roller pair 120, 130, 140 arranged on the outer transfer guide 113, respectively. ing.

(2.3) Paper Transport in the Paper Transport Unit The image forming apparatus 1 switches the paper transport path in the paper transport unit to perform paper transport depending on 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 feed device 20 is stopped by the transport roller pair 24 via the paper guide guide 23. It is conveyed to the nip portion of pair 25. The paper P in which the loop is formed by the stopped resist rollers 25 is sent from the resist rollers 25 to the secondary transfer unit TR in a state where the skew is corrected as the resist rollers 25 rotate.

Prior to the rotation of the resist roller pair 25, the gate claw 27 rotates to the first position for guiding the paper P to the paper guide guide 26, and the paper P sent out from the resist roller pair 25 is the first guide surface 27a of the gate claw 27. It is conveyed toward the paper guide guide 26 while being guided by the paper guide 26, and is sent to the secondary transfer unit TR along the paper guide guide 26.
In the single-sided printing, the temperature of the paper P conveyed along the paper guide guide 26 is substantially the same as the temperature inside the machine loaded on the paper feeding device 20, and even if continuous printing is performed, the intermediate transfer belt The temperature of the secondary transfer unit TR including 51 does not rise excessively.

(2.3.2) Double-sided printing When double-sided printing is performed, the back edge of the paper P on which one side has been recorded is downstream by the transport rollers vs. 78 and the discharge rollers vs. 79 until the rear end passes through the transport rollers vs. 78. Transported to the side. When the rear end of the paper P passes through the transfer roller pair 78, the discharge roller pair 79 rotates in the reverse direction and is conveyed toward the reverse transfer path.

As shown in FIG. 4, the inverted paper P is conveyed by the transfer roller pairs 120, 130, and 140 in the inverted transfer path formed by the outer transfer guide 113 and the inner transfer guide 631, and is conveyed by the first sheet guide guide 611. It is guided to the paper guide guide 23, and is conveyed to the resist roller pair 25 in a state where the front and back sides are reversed.

Then, the gate claw 27 rotates to the second position that guides the paper P to the second paper guide guide 612, and the paper P sent out from the resist roller pair 25 is guided to the second guide surface 27b of the gate claw 27 and is intermediate. It is sent to the secondary transfer unit TR along the second paper guide guide 612 separated from the transfer belt 51, and the image is transferred to the second surface of the paper P in the secondary transfer unit TR.

When double-sided printing is performed, the paper transfer path from the resist roller pair 25 to the secondary transfer unit TR is switched from the first transfer path to the second transfer path according to the flowchart shown in FIG.
First, when the image forming apparatus 1 receives the print job, the image forming apparatus control unit 11 performs double-sided printing in a state (S101) in which the gate claw 27 is rotated to the first position and switched to the first transfer path. Is determined (S102).

When it is determined that double-sided printing is performed (S102: Yes), then it is determined whether or not the number of continuous prints N in the job is equal to or greater than a predetermined number Nth (S103). Here, as an example of the predetermined number of sheets Nth, about 100 sheets can be mentioned.
Then, when the number of continuous prints is Nth or more (S103: Yes), it is further determined whether or not the print speed V is a predetermined print speed V1 or more (S104). Here, as an example of the predetermined printing speed V1, a printing speed that is 1/2 of the maximum process speed of the apparatus can be mentioned.

When the printing speed V is equal to or higher than the predetermined printing speed V1 (S104: Yes), it is determined whether or not the outside temperature T is equal to or higher than the predetermined temperature Tth (S105). Here, the outside temperature T is provided at the bottom of the opening / closing door 110 away from the fixing unit 70 and the power supply device 14 that generate heat, and is a temperature for detecting the outside temperature that affects the image formation of the image forming apparatus 1. An example of a predetermined temperature Tth detected by the sensor ST1 (see FIG. 1) is 10 ° C.

When 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 to (S109), and one surface is printed (S111). When the next printing surface is the back surface (S108: No), the printing on the first surface is executed by switching to the second transport path (S110) (S112).

In this way, at the time of double-sided printing, when the continuous printing number N is a predetermined number Nth or more, the printing speed V is a predetermined printing speed V1 or more, and the outside temperature T is a predetermined temperature Tth or more. , Switch to the second transport path when the next printing surface is the back surface (S110).
As a result, the paper P, which is heated by the fixing unit 70, is inverted, and is fed again from the inverted transfer path, is transferred from the intermediate transfer belt 51 switched from the resist roller pair 25 to the secondary transfer unit TR by the gate claw 27. It is conveyed along the separated second paper guide guide 612, and the temperature rise of the secondary transfer unit TR including the intermediate transfer belt 51 is suppressed.

Further, when the number of continuous prints N is less than the predetermined number of sheets Nth, the print speed V is lower than the predetermined print speed V1, and the outside temperature T is lower than the predetermined temperature Tth. If any of the above, printing is started as it is (S106).
As a result, the excessive temperature rise of the secondary transfer unit TR including the intermediate transfer belt 51 is suppressed, and the secondary transfer unit TR is conveyed along the first transfer path, which is shorter than the second transfer path, and the printing speed is increased. The decrease is suppressed.

"Second embodiment"
FIG. 6 is a schematic cross-sectional view showing the internal configuration of the paper transport unit according to the second embodiment and paper transport, and FIG. 7 is a switching between a first transport path and a second transport path in the paper transport unit according to the second embodiment. FIG. 8 is a flowchart showing the flow of operation of the blower fan, FIG. 8 is a timing chart showing the rotation drive control of the blower fan 80, and FIG. 9 is a flowchart showing the flow of the rotation drive control of the blower fan 80 in the second modification.
Hereinafter, the paper transport in the paper transport section of the image forming apparatus 1A and the flow of wind by the blower fan will be described with reference to the drawings. The components common to the image forming apparatus 1 according to the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

(1) Configuration of Paper Conveying Unit In the image forming apparatus 1A, as shown in FIG. 6 (arrows in the figure indicate air flow), a blower fan 80 is arranged above the paper drawer unit 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 guide 26A.
A ventilation hole 26Aa is formed in the paper guide guide 26A, and the air sent out from the ventilation duct 81 is blown to the paper transport portion between the resist roller pair 25 and the secondary transfer portion TR.

Since the blower fan 80 is arranged above the paper drawer portion 22 away from the fixing unit 70 and the power supply device 14 that generate heat, the second fan 80 draws in air close to the temperature outside the machine and blows it. The paper P conveyed along the paper guide guide 612 is directly cooled.
Further, the blower fan 80 constantly blows air on the paper transport section between the resist roller pair 25 and the secondary transfer section TR except when the paper P is conveyed in the first transport path. The second paper guide guide 612 that guides the paper 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 switches the paper transport path in the paper transport unit to perform paper transport according to the print mode, and blows air onto the paper P to be re-conveyed during double-sided printing. P is cooled to suppress an increase in the temperature of the secondary transfer unit TR including the intermediate transfer belt 51.

As shown in the flowchart of FIG. 7, when the image forming apparatus 1A receives the print job, the image forming apparatus control is performed in a state (S201) in which the gate claw 27 is rotated to the first position and switched to the first transfer path. Part 11 determines whether or not double-sided printing is used (S202).

When it is determined that double-sided printing is performed (S202: Yes), then it is determined whether or not the number of continuous prints N in the job is equal to or greater than a predetermined number Nth (S203).
Then, when the number of continuous prints N is Nth or more (S203: Yes), it is further determined whether or not the print speed V is a predetermined print speed V1 or more (S204).
When the printing speed V is equal to or higher than the predetermined printing speed V1 (S204: Yes), it is determined whether or not 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 the 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 transfer path is switched to (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) is performed, the blower fan 80 is rotated (S211), and printing on one surface is executed (S212). ).

As described above, at the time of double-sided printing, when the continuous printing number N is a predetermined number Nth or more, the printing speed V is a predetermined printing speed V1 or more, and the outside temperature T is a predetermined temperature Tth or more. The paper P is switched to the second transport path (S209), the blower fan 80 is rotated (S211), and air is directly blown onto the paper P transported toward the secondary transfer unit TR to heat the paper P in the fixing unit 70. Cooling.

When rotating the blower fan 80, as shown in the time chart of FIG. 8, the secondary transfer unit TR starts the rotation from the timing (a) when the resist roller pair 25 stops to form a registration loop and then starts rotating. The rotation of the blower fan 80 is stopped only until the timing (d) when the next transfer bias is turned off, and the rotation is constantly controlled otherwise.
As a result, air is always blown to the paper transport section between the resist roller pair 25 and the secondary transfer section TR except when the paper P is transported through the first transport path, and the paper P is transferred. When not being conveyed, the second paper guide guide 612 can be cooled to further lower the paper temperature before backside transfer.

As a result, the paper P, which is heated by the fixing unit 70, is inverted, and is fed again from the inverted transfer path, is separated from the intermediate transfer belt 51 while being blown air from the resist roller pair 25 to the secondary transfer unit TR. It is conveyed along the second paper guide guide 612 while preventing floating, and the temperature rise of the secondary transfer unit TR including the intermediate transfer belt 51 is further suppressed.

Further, when the number of continuous prints N is less than the predetermined number of sheets Nth, the print speed V is lower than the predetermined print speed V1, and the outside temperature T is lower than the predetermined temperature Tth. If any of the above, printing is started as it is (S206).
As a result, the excessive temperature rise of the secondary transfer unit TR including the intermediate transfer belt 51 is suppressed, and the secondary transfer unit TR is conveyed along the first transfer path, which is shorter than the second transfer path, and the printing speed is increased. The decrease is suppressed.

"Modification example 1"
The image forming apparatus 1A 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 number of continuous prints N is less than the predetermined number of sheets Nth (S203: No), the print speed V is lower than the predetermined print speed V1. In any case (S204: No) or 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 of the secondary transfer unit TR including the intermediate transfer belt 51 can be suppressed, and an increase in noise and power consumption can be suppressed.

"Modification 2"
The image forming apparatus 1A 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 also differs, and the type of paper P that is inverted and reconveyed (that is, 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, when the thickness information of the paper P in the print job is acquired (S302), the paper P is a thick paper (S303: A). ), The blower fan 80 is driven at a high speed to increase the amount of air blown to prevent the paper P from floating and improve the cooling efficiency.
On the other hand, when the paper P is thin paper (S303: B), the blower fan 80 is driven at a low speed to reduce the amount of air blown, and the excessive temperature of the secondary transfer unit TR including the intermediate transfer belt 51 is reduced. While suppressing the rise, the fluttering of the paper P is suppressed.

Here, the thick paper is 120 gsm or more as an example, the thin paper is 60 gsm or less as an example, and the plain paper is 70 to 110 gsm as an example. Etc.) can be judged accordingly.

1, 1A ... Image forming device 10 ... Control device 20 ... Paper feeding device 25 ... Resist roller pair 26 ... Paper guide guide 27 ... Gate claw 30 ... Photoreceptor unit 40・ ・ ・ Development unit 50 ・ ・ ・ Transfer unit 60 ・ ・ ・ Paper transfer unit 610 ・ ・ ・ Registration unit 611 ・ ・ ・ First paper guide guide 612 ・ ・ ・ Second paper guide guide 620 ・ ・ ・ Secondary transfer Unit part 630 ・ ・ ・ Double-sided unit part 631 ・ ・ ・ Inner transfer guide 62 ・ ・ ・ Secondary transfer roller 70 ・ ・ ・ Fixing unit 80 ・ ・ ・ Blower fan 100 ・ ・ ・ Housing 110 ・ ・ ・ Opening and closing door 113 ・・ ・ Outer transport guide

Claims (8)

A transfer means for transferring the toner image held on the image holder to paper, and
A pair of resist rollers that correct the posture of the conveyed paper and feed the paper to the transfer means.
A fixing means for fixing the toner image on paper and
A reversing transporting means for inverting the front and back of the paper on which an image is formed and transporting the paper with the inverted front and back toward the transfer means.
A first transport path that guides the paper toward the transfer means in the vicinity of the image holder on the downstream side in the paper transport direction of the resist roller pair.
A second transport path that guides the paper toward the transfer means away from the image holder on the downstream side of the resist roller pair in the paper transport direction.
A means for switching the paper transport direction to the first transport path or the second transport path.
An image forming apparatus characterized in that. The switching means switches to the second transport path at least when 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 prints to be printed continuously, the print speed, and the outside temperature.
The image forming apparatus according to claim 1 or 2. The switching means is a gate claw that swings around a rotary support shaft.
The image forming apparatus according to any one of claims 1 to 3. Further equipped with a blower fan for blowing air toward the second transport path.
The image forming apparatus according to claim 1. The blower fan stops blowing when the paper is conveyed 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.
Characterized by
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 prints continuously printed, the printing speed, and the outside temperature.
The image forming apparatus according to claim 5 or 6.

Images