JPH0580672A - Fixing device - Google Patents

Abstract

PURPOSE:To provide a fixing device whose cost is low, which has a simple constitution and in which fixing ability to comply with an OHP sheet, etc., enough can be obtained without changing an electrophotographic process speed. CONSTITUTION:The device is provided with a fixing roller in which a heating roller 21a and a pressure roller 21b press-contacting to the heating roller 21a are equipped and a toner image is heated to be fixed on a paper by making the paper having the toner image adhering pass between both rollers 21a, 21b, carrying rollers 23, 26 carrying the paper fed from the fixing roller, and a controller to control the turning of each roller; the controller makes the turning of the fixing roller and the carrying roller 23 reverse before the trailing edge of the paper separates from between the fixing rollers after the area of the paper where the toner image is transferred passes through the fixing roller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device in an electrophotographic apparatus such as an electrophotographic copying machine or a laser printer.

[0002]

2. Description of the Related Art In this type of electrophotographic apparatus, a toner image is formed on a rotating photosensitive drum (or photosensitive belt) by an electrophotographic process, and a cut sheet (sheet) stored in a sheet feeding cassette is fed by a sheet feeding roller. Extract and adjust the posture and the conveyance timing with the registration roller so that the sheet at the transfer position matches the toner image on the photosensitive drum,
The sheet on which the toner image has been transferred is passed through a fixing device to fix the toner image on the sheet, and the sheet that has passed through the fixing device is discharged onto a discharge tray outside the main body by a conveyance roller. ing.

The fixing device for fixing the toner image includes a xenon flash system utilizing radiant heat transfer and a planar heater system utilizing convective heat transfer, but at present, thermal efficiency is good and operating temperature is 180 ° C. Many of them are of the heating roller type, which has a relatively low degree of safety and is excellent in safety, and also has both a fixing function and a sheet conveying function.

In recent printers, in addition to conventional black printing and multicolor printing, there is a tendency for full-color printers that print images of a large number of colors to increase.

Further, the type of paper used is also a general PPC.
Including paper, bond paper, postcards, envelopes, OHP sheets, etc.

However, it is difficult for the above-mentioned heating roller type fixing device to obtain the fixing performance that works optimally in common on these various types of paper. That is, in the heating roller type fixing device, a sheet is passed between a heating roller having a heater at the center and a fixing roller in which a pressure roller having a silicon rubber layer or the like formed on the surface thereof is arranged in pressure contact with each other, and The toner image is heated and pressed to fix it on the paper.
The fixing energy E is expressed by the following equation as a function of the heating temperature T, the nip width W formed by the pressure contact force between the heating roller and the pressure roller, and the sheet conveying speed V.

E∝T · W · V Here, in a general small color laser printer (printing capacity of about 8 to 10 sheets / minute on A4 size paper), T = 16
The limit values are about 0 to 200 ° C. and W = 3 to 5 mm, and in order to obtain a larger fixing energy, a method such as installing a heater on the pressure roller side or slowing the entire process speed is used. However, the cost will increase, the printing capacity will decrease, and in order to raise the heating temperature, the structure will be able to withstand higher temperatures, materials, safety measures, etc. It contains many problems in practice.

In particular, in printing a full-color image on an OHP sheet, which is frequently used in conferences and presentations, in order to project a color toner image on the OHP sheet as a color image on a screen by a projector, the toner image is at least 50%. It is necessary to fix it so that it has a light transmissivity higher than a certain level. For this purpose, it is necessary to fix more smoothly than fixing to general PPC paper, a large fixing force is required, and a fixing device of a color printer configured for use of general PPC paper is required. It is difficult to obtain such fixing power.

In order to obtain a high fixing performance in a fixing device constructed by using general PPC paper as a standard, Japanese Patent Laid-Open No.
The fixing device described in Japanese Patent Laid-Open No. 121474 proposes a configuration in which the sheet is passed through the fixing roller and then the fixing roller is rotated in the reverse direction so that the sheet is passed through the fixing roller again. However, the paper that has passed through the fixing roller is thermally deformed, and it is difficult to accurately supply the paper that has left the fixing roller to the fixing roller again, which causes troubles such as wrinkles and jams. Become. Further, as described in JP-A-60-86574 and JP-A-60-211483, when fixing a toner image on an OHP sheet, a fixing device that slows down the fixing speed is an OHP sheet.
The sheet itself has a drawback that it is largely deformed by giving excessive heat energy, and the electrophotographic process speed must be slowed down, so that the control becomes complicated in order to perform the optimum electrophotographic process. There are drawbacks.

[0010]

As described above, when it is attempted to improve the fixing ability of the fixing device in the conventional electrophotographic apparatus, paper is wrinkled or jammed.
There is a problem that complicated control for changing the electrophotographic process speed is required.

An object of the present invention is to provide an OHP with low cost and simple structure without changing the electrophotographic process speed.
An object of the present invention is to provide a fixing device capable of sufficiently fixing a sheet or the like.

[0012]

SUMMARY OF THE INVENTION According to the present invention, a heating roller and a pressure roller pressed against the heating roller are provided, and a sheet having a toner image attached thereto is passed between the rollers to form a toner image on the sheet. A fixing device comprising a fixing roller for heating and fixing, a conveying roller for conveying a sheet sent from the fixing roller, and a control device for controlling rotation of each roller, wherein the control device is a toner image of the sheet. After the transfer area has passed the fixing roller and before the trailing edge of the sheet leaves the fixing rollers, a control function of reversing the rotation of the fixing roller and the conveying roller is provided.

[0013]

To fix a toner image on a sheet that requires a large amount of fixing energy, the sheet on which the toner image has been transferred is reciprocated between fixing rollers to give a large amount of fixing energy. After the toner image transfer area of the sheet passes between the fixing rollers when the sheet moves to, the rotation direction of the fixing roller is reversed before the rear end of the sheet leaves the fixing rollers. The cause of occurrence is reduced. Moreover, since the fixing speed does not change during the forward fixing, the electrophotographic process is stable at a constant execution speed, and the thermal deformation of the paper is reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a vertical sectional side view of a compact color laser printer according to the present invention. The rotating photosensitive belt 1 is uniformly charged by a charger 2 and then the photosensitive belt 1 is exposed by an exposure device 3. This is a structure in which an electrostatic latent image is formed, and the electrostatic latent image is converted into a color toner image by selectively using the four-color developing device 4 to develop the electrostatic latent image. This toner image is rotated with the photosensitive belt 1 and transferred onto the transfer drum 5. The exposure device 3 exposes the photosensitive belt 1 by generating a blinking laser beam in accordance with a video signal provided by a higher-level information processing device, and is a static image formed by exposing a color image to be printed with a color-separated video signal. The electrostatic latent image is developed by selectively using the developing device 4 of the corresponding color, the toner image formed by the development is transferred to the transfer drum 5, and the required color is repeated to form a color toner image on the transfer drum 5. Is formed.

The paper 11 on which the color toner image is retransferred is contained in a paper feed cassette 12, and the paper 11 is extracted by a paper feed roller 13 and conveyed to a registration roller 14. The registration roller 14 is used to convey the paper 11 that has been conveyed.
The transfer timing is adjusted so that the toner image is received and shaped, and is aligned with the toner image on the transfer drum 5. The sheet 11 sent from the registration roller 14 is the transfer drum 5
The transfer device 15 electrostatically transfers the toner image on the transfer drum 5 to the paper 11 by applying transfer charges to the back surface of the paper 11 while moving in contact with.

The sheet 11 separated from the transfer drum 5 after the toner image has been transferred is fixed by a fixing device 21 and then discharged as a printed matter onto an upper discharge tray 24 by a discharge guide 22 and a conveyance roller 23 (one-way fixing). ), Or after reciprocal fixing, the switching discharge guide 25 and the transport roller 2
The sheet 6 is ejected as a printed matter to the side sheet ejection tray 27 (reciprocal fixing).

The control unit 28 executes electrophotographic process control, paper feed control, fixing control and conveyance control.

Next, the fixing device 21 will be described in detail with reference to FIG. The fixing device 21 passes the paper 11 between a fixing roller composed of a heating roller 21a and a pressure roller 21b arranged in pressure contact with each other so that the unfixed toner image adhering to the paper 11 is transferred onto the paper 11. Heat fixing to. The heating roller 21a has a structure in which a surface of a metal roller made of aluminum is coated with Teflon or a silicon rubber layer is molded, and is heated to about 150 to 200 ° C. by an internal heater 21c in an ordinary small color laser printer. Further, the pressure roller 21b has a configuration in which a silicon rubber layer is molded on a core metal, and in the above-mentioned ordinary small-sized color laser printer, the pressure roller 21b is pressed against the heating roller 21a so that the nip width becomes about 2 to 5 mm. The pressure roller 21b is driven by the frictional force with the heating roller 21a.
The cores of the heating roller 21a and the pressure roller 21b may be gear-coupled and driven.

The fixing device 21 having the above-described structure allows one-way fixing of general PPC paper or the like, passes the paper, and discharges it as it is onto the upper paper discharge tray 24 through the paper discharge guide 22 and the conveying roller 23. , OHP sheet, etc.
When reciprocally fixing a sheet that requires a larger amount of fixing energy than a PC sheet, the toner image transfer area (printing area) on the sheet is fixed and then fixed, and then the heating roller 21a, the pressure roller 21b, and the conveying roller 23 are used. Stop turning,
Heating roller 21a, pressure roller 21b, and conveyance roller 2
3 is reversed to convey the sheet in the reverse direction, and the toner image transfer area is again passed between the heating roller 21a and the pressure roller 21b to be re-fixed, and the switching sheet ejection guide 25 and the conveyance roller 26 are provided. The sheet is discharged onto the side discharge tray 27 by.

At this time, if the heating roller 21a is stopped in the toner image transfer area, excessive heating causes fixing failure, so that after the toner image transfer area passes through the nip portion, the trailing end of the sheet is moved to the nip portion. The heating roller 21a is stopped and held in the state of being held in the reverse direction.

The heating roller 2 for such reciprocal fixing
The control device 28 controls the rotation of the 1a and the conveyance rollers 23 and 26. However, the conventional paper conveyance management data is used or a paper trailing edge detector is arranged in front of the fixing device 21, Get control timing. Further, whether or not the paper 11 to be used is an OHP sheet that requires reciprocal fixing (recognition of paper type) is based on paper information provided from a switch provided in a higher-level information processing apparatus or the laser printer, As shown in FIG. 5, according to the detection signal of the transmission type detector 29 arranged in the sheet conveying path, a general PP is used.
One-way fixing control is performed on the C sheet, and reciprocal fixing control is performed on the OHP sheet.

As described above, when an OHP sheet or the like is used as the paper 11, the toner image on the paper 11 can be provided with twice as much fixing energy as usual by fixing the OHP sheet and the like in a reciprocal manner. Greatly improved.

The fixing device 2 for performing such reciprocal fixing
If the drive system for 1 and the transport rollers 23, 26 is independent of the drive system for other paper feeding system or electrophotographic process system, the fixing device 2
While 1 is reciprocally fixed, it is possible to shift to paper feeding and execution of an electrophotographic process for printing on the next paper 11, and the reciprocal fixing is realized with almost no decrease in the overall process speed. It is possible to For example, in a printer that prints on A4 size paper at an electrophotographic process speed of about 75 mm / s, before the next paper 11 reaches the fixing device 21, it depends on the length of the paper transport path from paper feeding to fixing. In addition, the reciprocal fixing of the paper 11 can be completed, there is no need to slow down the electrophotographic process speed, and the performance does not deteriorate. Further, by making the drive speed of the fixing device 21 changeable as appropriate, the fixing speed is slowed only when the paper is fed backward (during backward fixing) in consideration of the electrophotographic process speed, so that the fixing property is further improved. It is also possible to do so.

During reciprocal fixing, when the fixing device 21 is reversed and the paper 11 is returning, the switching conveyance guide 6 in front of the fixing device 21 feeds the moved paper 11 to the side discharge tray 27. Switch the transport path so that the paper is discharged upward.

For this reason, the switching discharge guide 25 is
As shown in FIG. 3, both end support portions 25a and 25b are rotatably held, and are positioned in the state shown by the solid line in FIG. 1 by weight balance or by a weak spring force. Then, when the sheet 11 separated and conveyed from the transfer drum 5 is conveyed to the fixing device 21, the sheet 11 is conveyed.
When the leading edge of the sheet hits the lower surface of the switching discharge guide 25, the switching discharge guide 25 is pushed up to the position shown by the alternate long and short dash line, and the sheet 11 is allowed to be conveyed toward the fixing device 21. When the paper is fed back (returned) from the fixing device 21, the paper 11 is guided along the upper surface of the switching paper discharge guide 25 in the direction of the transport roller 26 and discharged onto the side paper discharge tray 27. The configuration. Then, the switching paper ejection guide 25 is configured such that the paper 11 is switched to the switching paper ejection guide 25.
When the sheet is pushed up to move toward the fixing device 21, the tip of the sheet 11 is prevented from being scratched and the path is not obstructed, so that the sheet has a comb shape to reduce the mass and the material has a small specific gravity. It is better to use plastic or the like. As a result, the moment required to push up the switching sheet ejection guide 25 can be set to several gmm to several tens of gmm, and the above object can be achieved.

[0027]

As described above, according to the present invention, in fixing a toner image to a sheet requiring a large fixing energy such as an OHP sheet, the sheet on which the toner image is transferred is reciprocated between fixing rollers. Gives a large amount of fixing energy,
Rotation of the fixing roller after the toner image transfer area of the sheet passes between the fixing rollers and before the trailing edge of the sheet leaves between the fixing rollers when the sheet moves from the forward movement to the backward movement. The reverse causes the occurrence factor of jam to decrease. Moreover, since the fixing speed does not change during the forward movement, the electrophotographic process is stable at a constant execution speed, and the thermal deformation of the paper is reduced.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view of a fixing device and a paper discharge unit according to the present invention.

FIG. 2 is a perspective view of a paper type detector.

FIG. 3 is a perspective view of a switching discharge guide.

FIG. 4 is a vertical sectional side view of the color laser printer according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive belt 3 Exposure device 4 Developing device 5 Transfer drum 11 Paper 21 Fixing device 21a Heating roller 21b Pressure roller 23,26 Conveying roller 25 Switching paper ejection guide 24 Upper paper ejection tray 27 Side paper ejection tray 28 Control device

Claims (4)

[Claims] 1. A fixing roller which comprises a heating roller and a pressure roller which is in pressure contact with the heating roller, and heats and fixes the toner image on the paper by passing the paper on which the toner image adheres between the rollers. In a fixing device including a conveyance roller that conveys a sheet sent from a fixing roller, and a control device that controls the rotation of each of the rollers, the control device is configured such that a toner image transfer area of the sheet passes the fixing roller. A fixing device having a control function of reversing the rotation of the fixing roller and the conveying roller before the trailing edge of the sheet leaves the fixing rollers. 2. The fixing device according to claim 1, wherein the control device controls the rotation of the fixing roller and the conveying roller according to the type of paper. 3. A fixing roller which comprises a heating roller and a pressure roller which is in pressure contact with the heating roller, and which heats and fixes the toner image on the paper by passing the paper on which the toner image adheres between the rollers. In a fixing device including a conveyance roller group that conveys a sheet sent from a fixing roller, and a control device that controls rotation of each of the rollers, the control device is configured such that a toner image transfer area of the sheet is the fixing roller. A control function is provided to reverse the fixing roller and the conveying roller group before the trailing edge of the sheet has passed between the fixing rollers after passing the fixing roller. A fixing device comprising: a first conveying roller that conveys the sheet returned from the fixing roller to a second sheet discharging tray; and a second conveying roller that conveys the sheet returned from the fixing roller to the second sheet discharging tray. 4. The fixing device according to claim 2, wherein the control device controls the rotation of the fixing roller and the conveyance roller group according to the type of paper.