JPH0527614A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent or suppress the rise in the temperature of a transfer roller and a toner image carrier, to maintain stable image quality over a long period, to prevent the slight staining of a transfer material and, in addition, to obtain the satisfactory property for passing through the transfer material in an image forming device which transfers a toner image formed on a toner image carrier on the transfer material by passing the transfer material between the image carrier and the transfer roller. CONSTITUTION:This image forming device is provided with an arm 180 which supports the two transfer rollers 19 and 20 so that either one of them is selectively arranged in a transfer position, a motor (m) which drives the arm 180, thermistors 25 and 26 which detect the temperature of the transfer roller arranged in the transfer position out of the transfer rollers 19 and 20 and a control part which controls the operation of the motor (m) so that the used transfer roller is replaced with the other one when the temperature detected by the thermistors exceeds the predetermined temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer for transferring a toner image formed on a toner image carrier such as a photoconductor onto a transfer material.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, a toner image formed on a toner image carrier such as a photoconductor is transferred onto a transfer material by a transfer device. Transfer devices that have been proposed and put into practical use include a corona transfer system and a roller transfer system. Recently, the transfer roller method has been reconsidered in that it can realize low ozone and that transfer deviation is small.

FIG. 6 is an explanatory view of an example of an electrophotographic apparatus using a conventional transfer roller. In this device, the photoconductor 1A
Is charged by the charging roller 2A and is exposed by the exposure unit 3A by an optical system (not shown) to form an electrostatic latent image. This latent image is developed by the developing unit 4A. On the other hand, the transfer sheet S sent from the sheet feeding cassette 9A by the action of the separating roller 10A and the separating plate 11A reaches the timing roller 12A, and from there, is sent to the transfer section in synchronization with the toner image on the photoconductor, and thus The toner image is transferred onto the transfer paper S by the transfer roller 5A. At this time, a bias having a polarity opposite to that of the toner is applied to the transfer roller 5A. The transfer sheet S is separated from the photoconductor 1A by its own stiffness, discharged by the charge elimination needle 6A, guided by the guide 13A to the fixing device 15A, where the toner image is fixed, and then the outside of the machine. Is discharged to. The photoconductor 1A is cleaned of residual toner by the cleaner 7A and erased of residual charge by the eraser 8A, and the same process is repeated again.

In this case, since the transfer roller 5A is always in contact with the photoconductor 1A, the fog toner on the photoconductor 1A in the non-image area adheres to the transfer roller 5A.
Conventionally, as a cleaning method for a transfer roller in this type of electrophotographic apparatus, there is a cleaning method in which the polarity of the bias voltage of the transfer roller is reversed at the time of non-transfer and the toner attached to the transfer roller is returned to the photoconductor. Are known.

However, according to this method, when the bias voltage of the transfer roller is switched from the transfer polarity to the reverse polarity,
Since a large amount of toner is returned to the photoconductor in a short period of time, the cleaner of the photoconductor is overloaded, and insufficient cleaning of the photoconductor is likely to occur. Therefore, generally, the transfer roller is cleaned with a brush or a blade.

[0006]

By the way, in a device capable of double-sided copying (printing) or composite copying (printing), when double-sided copying (printing) or composite copying (printing) is continuously performed, the transfer paper is temporarily As the temperature of the transfer roller passes through the fixing device and becomes higher, the transfer roller again passes through the transfer roller again, which increases the surface temperature of the transfer roller. When the surface temperature of the transfer roller rises,
The viscoelastic property of the toner attached to the transfer roller is changed, and the cleaning by the brush or blade is not carried out. As a result, the back surface of the transfer material is smeared or, in the worst case, JAM is generated. To do.

Further, as an adverse effect when continuous double-sided copying (printing) or composite copying (printing) is performed by an electrophotographic apparatus using a transfer roller, there is a change in sensitivity due to a temperature rise of a photoconductor. This is because the use of the transfer roller improves the adhesion between the transfer material and the photoconductor. When the sensitivity of the photoconductor changes, the charging potential of the charging device fluctuates, which leads to image defects.

Therefore, an object of the present invention is to transfer a toner image formed on a toner image carrier in an image forming apparatus in which a transfer material is passed between the carrier and a transfer roller and transferred onto the transfer material. By preventing or suppressing the temperature rise of the roller and the toner image bearing member, the problems associated with the temperature rise are solved,
It is to maintain stable image quality for a long period of time, prevent back smearing of the transfer material, and obtain good transfer material passage property.

[0009]

According to the present invention, in accordance with the above object, a toner image formed on a toner image carrier is transferred onto the transfer material by passing a transfer material between the carrier and a transfer roller. In the image forming apparatus, a plurality of the transfer rollers, a means for supporting any of the plurality of transfer rollers so that they can be selectively placed at a transfer position, a means for driving the supporting means, the plurality of transfer rollers Of these, at least the means for detecting the temperature of the transfer roller arranged at the transfer position, and the drive means for replacing the used transfer roller when the temperature detected by the temperature detecting means is equal to or higher than a predetermined temperature. An image forming apparatus is provided with a control unit for controlling the operation of the above.

The means for detecting the temperature of the transfer roller may be a direct means such as a thermistor which is in contact with or close to the roller, or the temperature rise of the roller is estimated from the number of continuous copies and / or time. In addition, it may be an indirect one using it as the detected temperature.

[0011]

According to the image forming apparatus of the present invention, one of the transfer rollers supported by the transfer roller supporting means is arranged at the transfer position facing the toner image carrier under the drive of the supporting means by the driving means. The toner image is transferred onto a transfer material passing between the roller and the toner image carrier. The temperature of the transfer roller, which is involved in transfer due to repeated double-sided copy (print) and composite copy (print), and other causes
When the temperature exceeds a predetermined temperature, this temperature information is input to the control means, and the control means issues an instruction to the drive means of the transfer roller supporting means, and the drive means moves the transfer roller currently in use to the transfer position. The transfer roller having a low surface temperature is placed at the transfer position while being evacuated, and is used for transfer.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic cross section of a copying machine which is an embodiment. This copying machine can perform double-sided copying and composite copying in addition to normal single-sided copying. This copying machine has a photosensitive drum 1 on its upper part, and a charging charger 31, a developing device 32, a transfer device 2, and a cleaner 33 around the photosensitive drum 1.
And an eraser 34.

An optical system 7 for scanning a document image and exposing the image on the photosensitive member 1 is arranged above the photosensitive member 1. An automatic document feeder 71 is provided on the optical system 7. A timing roller 8 is provided on the left side of the transfer device 2, and a sheet is fed from the manual feed tray T1 or from the lower duplex unit 5, the upper sheet feeding cassette 6 or the lower sheet feeding cassette 7 to the timing roller 8. There is.

On the right side of the transfer device 2, a guide 81 for guiding the sheet after transfer, a fixing roller 82, a paper discharge roller 83, and a paper discharge tray 84 are sequentially arranged. Paper ejection roller 83
A switching claw 85 that selectively guides the paper output from the fixing roller 82 to the paper discharge roller 83 or the duplex unit 5 is provided on the upstream side of the. Duplex unit 5
Has an upper passage 51 and a lower passage 52, a switching pawl 53 at the entrance of these passages, and a feed roller 54 capable of moving up and down at the exit.

In the case of double-sided copying, the sheet that has come out of the fixing roller 82 is guided to the unit 5 by the switching claw 85, and the switching claw 53.
Is guided to the upper path and further passes under the paper feed roller 54 at the raised position, and is placed in the lower path 52 with the first image surface facing up. ,
It is sent to the timing roller 8 again. At the time of composite copying, the sheet guided to the unit 5 is
The sheet is guided to the lower passage with the first image surface facing downward, and is fed again to the timing roller 8 by the paper feed roller 54.

Both the upper and lower paper feed cassettes 6 and 7 can be taken in and out of the main body of the copying machine.
Is fed to the timing roller 8 by the feeding roller 61, and the sheet S in the lower cassette is fed to the timing roller 8 by the feeding roller 71. As shown in FIG. 2, the transfer device 2 is provided with two transfer rollers 19 and 20, and these rollers support the fulcrum 2
The rollers 1 and 22 are rotatably supported by both ends of the roller support arm 180. Each of the rollers 19 and 20 is formed by coating a core metal with silicon rubber, and the electric resistance value of the roller is adjusted by dispersing carbon in the silicon rubber. The arm 180 is rotatably supported by the shaft 18,
The rollers 19 or 20 may be selectively placed in the transfer position.
The transfer roller arranged at the transfer position can be driven and rotated while passing a sheet between the transfer roller and the photoconductor 1.

A box 17 for collecting toner, paper dust and the like is fixed to the arm 180, and has an opening 171 for receiving the toner or the like from the roller 19 and an opening 172 for receiving the toner or the like from the roller 20. 171 is a blade 23 rotatably provided on the box,
The blades 72 are opened and closed by blades 24 rotatably provided on the box. The blade 23 closes the opening 171 by turning off the solenoid SOL1 of the spring offset type when the transfer roller 19 is out of the transfer position, and when the transfer roller 19 is in the transfer position, the solenoid SOL.
When 1 is turned on, the opening 171 is opened and the roller 19
To scrape off the toner and paper dust on it, opening 1
Drop to 71. Similarly, the blade 24 closes the opening 172 when the solenoid SOL2 is turned off, and opens it so that the toner and the paper dust on the roller 20 are scraped when SOL2 is turned on.

The box 17 is also equipped with thermistors 25 and 26 as temperature detectors. The thermistor 25 detects the surface temperature of the roller 19 and the thermistor 26 roller 20. FIG. 3 shows the control circuit of the copying machine shown in FIG. 1 focusing on the part that controls the transfer device 2.

That is, a microcomputer CPU (hereinafter, "microcomputer CPU") for controlling the operation of the entire copying machine.
), And the outputs from the thermistors 25 and 26 are input to the temperature detection circuit 27 as temperature information. A transfer roller control circuit 28 is connected to the microcomputer CPU, and the control circuit 23 of the arm 180, that is, the operation control circuit 23 of the motor m for driving the arm is connected to the circuit, and the transfer roller 19 or A power source HV for applying a transfer bias to 20 and solenoids SOL1 and SOL2 for driving the blades 23 and 24.
Is connected to the control circuit 29.

A copying machine operation panel 30 is connected to the microcomputer CPU, and from this, a single-sided copy mode, a double-sided copy mode, a composite copy mode, the number of copies to be set with the numeric keypad, a copy start command with the print key, and the like. The photoconductor drum 1 and other parts operate according to instructions from the microcomputer CPU. According to the copying machine described above, the photoconductor 1 has the charging charger 3
At 1, the surface is charged and an electrostatic latent image is formed by image exposure. This latent image is developed by the developing device 32 to become a toner image, which is directed to the transfer device 2. On the other hand, the paper S is sent from the manual feed tray T1, the upper paper feed cassette 6 or the lower paper feed cassette 7 to the timing roller 8, and the timing roller 8 synchronizes the paper S with the toner image on the photoconductor. Send to 2.

Thus, the toner image on the photoconductor 1 is transferred onto the paper S by the transfer device 2 and subsequently fixed on the paper by the fixing roller 82. If the single-sided copy mode is selected for the sheet on which the toner image has been fixed, the sheet is directly output to the discharge tray 84.
However, in the double-sided copy mode or the composite copy mode, it is sent to the duplex unit 5, and then sent again to the transfer device 2 via the timing roller, where the second image is formed, After being fixed by the fixing roller 82, the sheet is discharged to the sheet discharge tray 84.

The microcomputer CPU in the control circuit executes the transfer roller selection subroutine shown in FIG. 4 in the double-sided copying or the composite copying mode. That is, in step S1, it is determined whether the mode is the double-sided mode or the composite mode, and if "NO", that is, the normal single-sided copy mode, the process directly returns to the main routine.
If “YES”, in step S2, the surface temperature T ₁ of the transfer roller 19 or 20 at the transfer position is obtained, and then in step S3, whether the temperature is equal to or higher than a predetermined temperature (50 ° C. in this example) or not. To judge. This reference temperature 50 ℃
Is determined below the glass transition temperature of the toner. If "NO" in the step S3, the process returns to the main routine, but if "YES", it is determined in a step S4 whether or not there is a sheet at the copy position. The presence / absence of this sheet is determined by a sheet passing sensor (not shown) provided at or near the transfer position. It should be noted that this determination may be performed by other means such as determination based on the passage of time after the operation of the timing roller or the like is started.

In step S4, if "paper is present", the process directly returns to the main routine, but if "paper is not present", in step S5 the currently used transfer roller 19 (or 20) is moved to the lower position. The transfer roller 20 (or 19) having a low surface temperature, which has been retracted until now, is arranged at the transfer position by driving the motor m. By alternately using the transfer rollers in this way, the surface temperature of the transfer roller used rises even when the sheet heated by the fixing roller 82 repeatedly passes through the transfer device 2 in the double-sided or composite mode. As a result, it is possible to prevent toner and paper dust from sticking to the roller, which prevents the backside of the paper from being smeared and provides good paper-passing properties. Further, it is prevented or suppressed that the temperature of the photoconductor 1 rises and its sensitivity is changed, whereby the photoconductor sensitivity is stabilized and the image is well stabilized.

After the transfer roller replacement instruction is given in step S5, in step S6, the blade drive solenoid SOL1 (or SOL2) is turned off, and the retracted blade 23 (or 24) closes the corresponding box opening and the solenoid SOL2. (Or SOL1) is turned on, the blade 24 (or 23) newly placed at the transfer position is brought into contact with the transfer roller, and the box opening corresponding to the blade is opened.

A cooling fan (not shown) may be provided for the transfer device 2 and the fan may be rotated for a fixed time T _F when the transfer roller is switched. The transfer roller selection routine of the microcomputer CPU at this time is as shown in FIG. When continuous copying was performed in the double-sided / composite mode at a speed of 35 sheets per minute with the copying machine described above, no particular problem occurred. On the other hand, when continuous copying was performed under the same conditions as in this experimental example without changing the transfer roller, backside smearing of the paper occurred. The surface temperature of the roller at this time was about 55 ° C.

In the embodiment described above, even if double-sided / composite copying is performed using the transfer roller, it is possible to secure the image formation without noise and the sheet passing stability. Further, as another effect, it was possible to suppress the temperature rise on the surface of the photoconductor and reduce the amount of change in image quality due to the change in sensitivity of the photoconductor.

[0027]

As described above, according to the present invention, an image in which a toner image formed on a toner image carrier is transferred onto the transfer material by passing a transfer material between the carrier and a transfer roller. In a forming apparatus, it is possible to prevent or suppress the temperature rise of a transfer roller or a toner image carrier, maintain stable image quality for a long period of time, prevent back smearing of a transfer material, and obtain better transfer material passing property. You can

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention.

FIG. 2 is an enlarged side view of a transfer device.

FIG. 3 is a block diagram centering on a transfer device control portion of a control circuit.

FIG. 4 is a flowchart showing a transfer roller selection routine in a microcomputer operation in a control circuit.

FIG. 5 is a flowchart of a transfer roller selection routine according to another embodiment of the present invention.

FIG. 6 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 1 Photoconductor 2 Transfer Device 17 Toner Collection Box 180 Transfer Roller Support Arm 19, 20 Transfer Roller 23, 24 Blade 25, 26 Thermistor SOL1, SOL2 Blade Drive Solenoid CPU Microcomputer 27 Temperature Detection Circuit 28 Transfer Roller Control Circuit 29 Blade Control Circuit 30 Operation panel m Arm drive motor HV Transfer bias power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Yamada 2-3-13 Azuchi-cho, Chuo-ku, Osaka, Osaka International Building Minolta Camera Co., Ltd. (72) Yoshinobu Hara 2-chome, Azuchi-cho, Chuo-ku, Osaka No. 13 Osaka International Building Minolta Camera Co., Ltd. (72) Inventor Daisuke Nagao 2-33 Azuchicho, Chuo-ku, Osaka City Osaka International Building Minolta Camera Co., Ltd.

Claims (1)

Claim: What is claimed is: 1. An image forming apparatus for transferring a toner image formed on a toner image carrier onto the transfer material by passing a transfer material between the carrier and a transfer roller. At least transfer of the plurality of transfer rollers, means for supporting any one of the plurality of transfer rollers so that the transfer roller can be selectively arranged at a transfer position, means for driving the supporting means, and transfer roller of the plurality of transfer rollers Means for detecting the temperature of the transfer roller arranged at the position, and when the temperature detected by the temperature detecting means becomes a predetermined temperature or higher, the operation of the driving means is controlled so as to replace the transfer roller used. An image forming apparatus comprising a control unit.