JPH08314298A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the fixability and the curl correction function at the time of double-sided printing of the image forming apparatus. In a double-sided printable image forming apparatus having a fixing device including a developing device and a pair of fixing rollers and a paper conveyance path for backside recording, a single transfer sheet for transfer paper is provided in the middle of the paper conveyance path for backside recording. A configuration is provided in which a curl correction roller is arranged, and a holding unit for bringing the roller into contact with one of the rollers of the fixing device and rotating the roller in a driven manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an apparatus having a double-sided printing function in an electrophotographic system.

[0002]

2. Description of the Related Art As a prior art, Japanese Patent Laid-Open No. 62-29064
Publication No. 0 will be described with reference to FIG. Three curling rollers 47 are attached to the re-feeding path, but these need to be provided because the re-feeding path is long. Further, since the reversed paper is put in the intermediate tray 48, it is not necessary to reverse the rotation of the rollers during the re-feeding conveyance path conveyance during the conveyance of the paper.
Reference numeral 49 is a switching claw for changing the paper route.

Further, another conventional example will be described with reference to FIG. A back side printing paper route is provided at the bottom of the printer, and the paper tray 56 can be housed on it. The paper fed from the paper tray 56 passes through the transport roller 51, is transferred by the drum 52, and passes through the fixing roller 53. Therefore, normally, the paper is conveyed upward and ejected, but a switching pawl 54 is provided in the paper path route after fixing, and the paper is guided to the route for backside printing by switching the pawl, and the paper is conveyed upward by the conveyance roller 55. After being sent out, it is returned to the inside of the printer again by switchback. A switching claw 59 is provided so that the switched-back paper does not return to the original route.

The switched-back paper is returned to the carrying roller 51 by the carrying roller 58 and printed on the back side.
The switching of the switching claw 54 is performed by a solenoid. The curl is corrected by corrugating the paper with a roller on the back side printing paper route.

[0005]

In the conventional apparatus, a very long conveyance path is required in the step of printing the back surface of the transfer paper for double-sided printing, and the space efficiency is very poor.

Further, as the conveying path becomes long, the frequency of paper jams inevitably increases.

Further, there has been a problem that the number of transport rollers and curl correction rollers increases, leading to an increase in cost.

[0008]

An image forming apparatus according to claim 1, wherein the transfer paper on which a toner image is formed by a developing device is passed through a fixing device composed of a pair of fixing rollers to fix the toner image on the transfer paper. In the image forming apparatus capable of recording on both front and back sides of the transfer sheet by reversing the front and back sides of the transfer sheet and again conveying the transfer sheet to the developing device through the sheet conveying path for back side recording. A single transfer paper curl correction roller is arranged in the middle of the back surface recording paper conveyance path, and holding means for contacting the roller with one roller of the fixing device to rotate the roller is provided. A characteristic image forming apparatus.

An image forming apparatus according to a second aspect of the present invention is characterized in that the holding means includes an adjusting means for adjusting a contact pressure of the curl correcting roller against the one fixing roller. It is a device.

An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the first aspect, wherein the curl correcting roller is provided with an overheating means inside.

An image forming apparatus according to a fourth aspect is provided with a cleaning roller which comes into contact with the curl correcting roller and is driven to rotate.

[0012]

According to the structure of claim 1, the curl can be conveyed again to the developing section on the back side during double-sided printing by a short route and the driving of one of the fixing rollers can be used. It is possible to easily carry out sheet conveyance also for correction without using a drive source, a gear, a belt or the like.

According to the second aspect of the invention, the contact pressure of the curl correcting roller with respect to the fixing roller can be arbitrarily changed, so that the curl can be corrected more accurately.

According to the third aspect of the present invention, the curl correction roller can be more surely corrected by providing the heating means inside the curl correction roller. Further, it is possible to prevent defective fixing due to the heat of the fixing roller being taken by the correction roller.

According to the fourth aspect of the present invention, the cleaning roll is arranged so as to come into contact with the correction roll, so that the correction roll can be prevented from being contaminated and the image printing surface can be prevented from being contaminated.

[0016]

Embodiments of the present invention will be described with reference to FIGS.

FIG. 1 is a schematic configuration diagram of a laser printer which is an embodiment of the present invention. This laser printer comprises a main body 1, a process kit 2 and a front door 3. The process kit 2 is a disposable kit containing the photoconductor drum 12, the main charger 15, and the cleaner unit 16 (including the waste toner box), and is detachable from the main body 1. The front door 3 is attached to the main body 1 so as to be swingable about a pin 3a. A fixing device 13 is built in the front door 3. A paper tray 10 is provided on the bottom surface of the main body 1. Further, the optical system 14 and the developing device 1 are provided around the photosensitive drum 12 on the main body 1 side.
1 is provided.

When transferring and fixing, the paper is conveyed vertically instead of horizontally. At the time of printing, the respective operation units operate in synchronization and the image forming process is executed. In synchronization with the rotation of the photoconductor drum 12, each process of charging by the main charger 15, exposure by the optical system 14, and development by the developing device 11 is executed. Further, in synchronization with this, the paper (paper) is conveyed from the paper tray 10.

When the paper IN sensor 5 is turned on and the leading edge of the paper comes to the carrying roller 4a and the driven roller 4b, the carrying roller is stopped for a moment and the paper is carried to carry the paper. A toner image is transferred onto the conveyed paper on the photosensitive drum 12. The paper on which the toner image is transferred is fixed to the fixing rollers 13a, 1
It is transported to 3b.

The sheet fixed by the fixing roller is 7a.
The paper guide is rotated (the paper guide is configured to rotate around 7c, and an actuator is attached to the tip of the paper guide, and the structure is such that the rotation of the actuator also turns on and off the paper sensor 18. The paper guide is pushed up to the position of 7b and is conveyed to the paper discharge rollers 9a and 9b along the paper guide of 17. The trailing edge of the paper passes the fixing roller, passes through the paper guide 7b and reaches the paper ejection rollers 9a and 9b, and the paper ejection roller 9a is rotated in the reverse direction to reverse the paper conveyance direction.

During this time, the paper sensor 18 turns off when the motor reverses when the leading edge of the paper is discharged to the discharge tray formed on the upper surface of the process kit 2.
When it reaches F (that is, the trailing edge of the paper passes through the paper guide 7a, stops for a while, and reverses when the next signal is detected). Here, when the rear end comes over the fixing cleaner 8, the paper is stopped, and at the next signal, the paper advances along the guide 19 and is guided to the back side printing paper path 20.

The back side printing paper path of 20 is provided in the vicinity of the side opposite to the frame 24 where the fixing roller is attached (near the fixing roller 13b). A paper path including a correction roller 40 and conveying rollers 6a and 6b is provided so as to rotate around the frame 24 at the shortest.

The paper is fed by the correction roller 40 and the conveyance rollers 6a and 6b, the paper is applied from above the paper guide 23, the paper IN sensor 5 is turned on, and the conveyance rollers 4a and
When the leading edge of the paper comes to the carrying rollers 4a and 4b that carry the paper to 4b, the rollers are momentarily stopped and the papers are aligned.

After this, through the same process steps as the surface printing, this time the paper is discharged to the paper discharge tray formed on the upper surface of the process kit 2 without the paper discharge roller being reversed. FIG. 2 shows a method of driving the rollers 9a and 6a which are conveyed for surface printing. The printer main body is driven by a discharge roller 9a in which the conveyance roller 4a, the photosensitive drum 12, and the fixing roller 13a are driven by a motor in the same drive system, and a rear surface printing conveyance roller 6a separately from the main body drive.
Install a motor.

Drive is transmitted from the motor 26 to the paper discharge roller 9a and the conveying roller 6a by belts 27 and 28 (transmission may be transmission of drive by gears). The motor for driving the main body is driven in one direction, and the back side conveyance roller drive motor 26 is synchronized with the timing of the process of the main body to move the C of the main body.
Controlled by PU.

First, the main body motor is driven to feed the paper to the paper guide 7a, and when the paper sensor 18 is turned on, the back surface motor 26 is driven so that the paper discharge roller 9a rotates in the A direction. As mentioned above, the rear edge of the paper is sensor 1.
When 8 is turned off, the operation is stopped, and the back surface motor 26 is rotated in the reverse direction by the next signal, and the discharge roller is rotated in the reverse direction (direction B).

When the paper passes through the back side printing path and the back side printing process is performed and the paper guide 7a is turned on again, the back side motor 26 is rotated in the A direction. The motor for the main body stops the drive of the main body when the motor 26 for the rear surface reverses in the B direction, and the paper passes through the rear surface path so that the paper is conveyed by the conveying roller 4a and the driven roller 4
Drive when it reaches b. After the rear end of the backside printing paper passes the paper IN sensor 5, the second sheet of paper is conveyed, and control is performed so that the paper interval between the backside printing paper and the next paper is shortened. This method enables printing on the front and back sides.

FIG. 3 is a view showing the contact pressure adjusting means of the curl correcting roller. The paper (paper) discharged by being sandwiched between 13a and 13b is curled along the R (circumference) of 13a. However, after switching back, the nip between 13b and 40 (in the opposite direction to the nip for one side) is heated and corrected while being conveyed in the opposite direction to the curl, so that the paper is effectively stretched to become a straight (non-curl) paper. Go to the next step.

The correction roller 40 can be made of metal,
It is advisable to use a heat-resistant and heat-insulating resin such as PPS in order to improve the fixability without releasing the heat of the fixing roller. Even when metal is used, the heater 4 is placed in the center as in the fixing upper roller 13a.
By adding 1 and adjusting the temperature, the fixability is further improved. Even in the case of metal, the same effect can be obtained by using the bearing 43 as a heat insulating member.

By adjusting the pressure of the correction roll with the leaf spring 45 or the like, the pressure of the pressure roll 13b is also changed in conjunction, and there is no problem of curl amount increase associated with the fixing property UP and the curl is well balanced. Be improved.

It is of course possible to move only the correction roll 40. (In this case, the curl due to the fixing unit does not increase.) 42 is a cleaning roller, which contacts the correction roller 40 and is driven to remove dirt on the correction roller 40.

The fixing upper roller 13a and the correction roller 40
A method of correcting the amount of curl correction based on the difference in curvature between and is also conceivable. This is because the smaller the curvature is, the larger the curl amount is, so that the correction roller 40 is larger than the fixing upper roller 13a.
This is a method of removing all curls attached at the time of fixing by making R smaller (if the same curl (R) and the same curl are attached, the fixing roller inevitably has a heating means. Larger curl than roller occurs). According to this method, the heating means for the correction roller 40, the contact pressure adjusting means, etc. are unnecessary, and the optimum curl correction can be performed with a simple configuration (only by changing the diameter ratio between the upper fixing roller and the correction roller).

[0033]

According to the first aspect of the present invention, since the back side at the time of double-sided printing can be conveyed to the developing section again by the short route and the driving of one of the fixing rollers is utilized,
It is possible to easily carry out the sheet conveyance that also serves as the curl correction without using a drive source, a gear or a belt, and the cost of the apparatus can be reduced.

According to the second aspect of the present invention, since the contact pressure of the curl correcting roller with respect to the fixing roller can be arbitrarily changed, the curl can be corrected more accurately and the double-sided recording with almost no curl can be achieved.

According to the third aspect of the present invention, the curl correction can be performed more reliably by providing the heating means inside the curl correction roller. Further, it is possible to prevent the fixing failure due to the heat of the fixing roller being taken by the correction roller, and it is possible to maintain high print quality.

According to the fourth aspect of the invention, since the cleaning roll is arranged so as to contact the correction roll,
It is possible to prevent the correction roll from being soiled and also to prevent the image printing surface from being soiled, so that high printing quality can be maintained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a printer device according to the present invention.

FIG. 2 is a diagram showing a driving method of a conveyance roller for back side printing.

FIG. 3 is a view showing a contact pressure adjusting means of a curl correcting roller.

FIG. 4 is a cross-sectional view of a conventional device.

FIG. 5 is a device cross-sectional view of another embodiment of the conventional device.

[Explanation of symbols]

 1 Printer Main Body 2 Process Kit 3 Front Door 3a Front Door Rotation Center 4a Conveyor Roller 4b Follower Roller 5 Paper IN Sensor 6a Backside Conveyor Roller 6b Backside Conveyor Roller (Follow) 7a Paper Guide 7b Paper Guide 7c Paper Guide Rotation Center 8 Cleaner 9a Paper Ejection Roller 9b Paper Ejection Driven Roller 10 Paper Tray 11 Developing Device 12 Photoreceptor Drum 13 Fixing Device 13a Upper Fixing Roller 13b Lower Fixing Roller 14 Optical System Unit 15 Main Charger 16 Cleaner Unit 17 Paper Guide 18 Paper Sensor 19 Paper Guide 20 Backside printing paper path 21 Conveying roller 22 Driven roller 23 Paper guide 24 Frame 26 Motor 27 Belt 28 Belt 30 Discharge roller 31a Driven roller 31b Moving roller 32 Paper guide 33 Paper guide 34 Backside printing paper path 35 One-way clutch 36 Pulley 37 Actuator 37a Actuator rotation center 38 Reversible paper guide 38a Retractable paper guide rotation center 39 Manual feed guide 40 Correction roller 41 Heater 42 Cleaning roller 43 Correction roller bearing 44 Pressing spring fulcrum 45 Correction roll pressing plate spring 46 Pressure adjusting screw 47 Curling roller 48 Intermediate tray 49 Switching claw 51 Conveying roller 52 Drum 53 Fixing roller 54 Switching claw 55 Conveying roller 56 Paper tray 58 Conveying Roller 59 switching claw

Claims (4)

[Claims] 1. A transfer paper on which a toner image is formed by a developing device is passed through a fixing device composed of a pair of fixing rollers to fix the toner image on the transfer paper, and then the front and back surfaces of the transfer paper are reversed to reverse the surface. In the image forming apparatus capable of recording on both the front and back sides of the transfer sheet by conveying the transfer sheet again to the developing device via the recording sheet conveyance path, a single sheet is provided in the middle of the back side recording sheet conveyance path. The image forming apparatus, wherein the curl correction roller for the transfer paper is arranged, and a holding means for contacting the roller with one roller of the fixing device and rotating the roller is provided. 2. The image forming apparatus according to claim 1, wherein the holding unit includes an adjusting unit that adjusts a contact pressure of the curl correcting roller against the one fixing roller. 3. The image forming apparatus according to claim 1, wherein the curl correction roller is provided with an overheating means therein. 4. The image forming apparatus according to claim 1, further comprising a cleaning roller that comes into contact with the curl correction roller and is driven to rotate.