JPH052352A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent wrinkle or jitter and to improve fixing performance by constituting a fixing roller device of a pair of heating rollers and a pair of pressuring rollers and arranging a nipping position for a recording medium along a nearly linear carrying path. CONSTITUTION:A fixing device 9 is formed of two pairs of fixing roller devices 33 and 36 which are constituted by pairing the heating rollers 31 and 34 and the pressuring rollers 32 and 35 which mutually press-contact. The respective fixing roller devices 33 and 36 are arranged so that the respective nipping position and the carrying path of the recording medium 2 from a transfer position of a photosensitive body may be nearly linear Therefore, even when the pressuring force of the pressuring roller is made weak so as to prevent the occurrence of the wrinkle on the recording medium 2 such as an envelope, fixing is performed twice by the fixing roller and the fixing performance is made excellent. Besides to that, the recording medium 2 passes through two fixing rollers in a nearly linear state, so that the recording medium is prevented from being bent or being butted. Furthermore, a control circuit is simplified by using a self temperature control heating element as a heat source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an image forming apparatus such as a printer, a copying machine and a facsimile.

[0002]

2. Description of the Related Art In an image forming apparatus such as a printer,
It is widely practiced to fix a toner image transferred on a recording medium by a fixing device having a heating roller and a pressure roller.

It is desired to increase the pressure applied between the heating roller and the pressure roller in order to improve the fixing property.
When the applied pressure is increased, wrinkles occur on the recording medium. In particular, wrinkles are likely to occur in a recording medium such as an envelope.

When the recording medium is an envelope, for example, in order to fix the recording medium without wrinkling, the pressure of the pressure roller is reduced to 1/2 to 1/5 of that of plain paper. There is a need to. If the pressure applied to the pressure roller is reduced in order to prevent the occurrence of wrinkles, insufficient fixing will occur.

In order to reduce the applied pressure and prevent insufficient fixing, two pressure rollers are arranged for one fixing roller, and the recording medium is pressed twice by the pressure roller. It is considered to solve the lack of fixing due to the shortage. A fixing device in which two pressure rollers are arranged with respect to one fixing roller is known, for example, from Japanese Utility Model Publication No. 58-26058 and Japanese Utility Model Publication No. 59-66256.

In the conventional fixing device using two pressure rollers, since the recording medium passes through the nip position of one pressure roller and moves toward the next pressure roller, the conveying path is curved, The leading end of the recording medium hits the second pressure roller and is guided to the rear nip position. Since the pressure force of the pressure roller is low, when the leading edge of the recording medium hits the second pressure roller, the recording medium slips with respect to the first pressure roller and causes a jitter in that portion. There is a problem.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a good fixing property without causing wrinkles or jitter on a recording medium such as an envelope. An object is to provide a fixing device that can be obtained.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-described problems by providing a fixing device of an image forming apparatus for transferring and fixing a toner image on a recording medium, which includes a heating roller and a pressure roller which are in pressure contact with each other. The fixing device is characterized in that two pairs of fixing roller devices are arranged so that their respective nip positions are located along a substantially linear conveying path of the recording medium.

[0009]

According to the present invention, since two sets of fixing roller devices are arranged in the substantially linear conveying path of the recording medium, even if the pressure of the pressure roller with respect to the heating roller is reduced to the extent that wrinkles are not generated, the fixing roller is fixed. Will be fixed twice by
The fixability is good. Moreover, the recording medium can be linearly guided from the nip position of the pair of fixing rollers to the nip position of the next fixing roller, and the leading end of the recording medium can be nipped without hitting the fixing roller. , The shock acting on the portion nipped by the first fixing roller is eliminated. Therefore, the occurrence of jitter is also prevented.

By using a self-temperature control heating element, for example, a heating element such as a ceramic heater whose electric resistance decreases as the temperature rises, as the heat source for at least one heating roller of the two fixing rollers, By heating the heating roller with one common heat source, for example, a heat source arranged between both heating rollers, the heat source can be simplified and the cost can be reduced by saving energy.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on the embodiments shown in the drawings.

In FIG. 1, which shows a laser beam printer as an example of an image forming apparatus, a recording medium (for example, transfer paper) 2 fed from a paper feeding device 1 in a pair of registration rollers.
Is conveyed to the latent image carrier composed of the drum-shaped photoconductor 4 at a timed timing by the registration roller pair 3.
The photoconductor 4 is rotationally driven in the counterclockwise direction, the surface of the photoconductor 4 is charged by the charging charger 5, and the laser light from the laser optical system 6 is irradiated to form an electrostatic latent image on the photoconductor. This latent image is visualized by toner as it passes through the developing device 7, and this visible image is transferred by the transfer charger 8 onto the sheet (recording medium) 2 conveyed to the photoconductor 4 and transferred onto the recording medium. The visible image of is fixed by the fixing device 9. On the other hand, the residual toner is removed from the photoreceptor 4 after the transfer of the visible image by a cleaning device having the cleaning blade 12. The toner particles removed from the photoconductor are collected in the toner collecting tank 13.

The recording paper discharged from the fixing device 9 is rotated by a double-sided entrance guide 17 and a pair of double-sided conveyance rollers 18 is provided.
Be led to. The recording paper 2 is conveyed to the reversing roller pair 19 rotating clockwise by the double-sided conveying roller pair 18 and passes through the reversing sensor 20. After the recording medium 2 passes the reversing sensor 20 for a predetermined time, the reversing roller pair 19 changes its rotation direction counterclockwise, and the rotatable reversing guide 21 conveys the recording medium 2 in the registration roller pair 3 direction. The recording medium 2 fed again to the registration roller pair 3 is timed by the registration roller pair 3 and the photosensitive member 4
Then, the toner is fixed on the recording medium through the same procedure as above. At this time, since the surface opposite to that when the paper is fed from the paper feeding device 1 contacts the photoconductor 4, double-sided recording is performed on the recording medium 2. After passing through the fixing device 9, the double-sided recording medium 2 passes through the double-sided entrance guide 17 and is discharged to the paper discharge tray 21 by the paper discharge roller device 11 to be stored therein.

While the fixing device 9 is shown in FIG. 1 as a conventional structure, it is constructed as shown in FIG. 2 in the present invention. A first fixing roller device 33 is formed by a pair of rollers including a first heating roller 31 and a first pressure roller 32 that is in pressure contact with the first heating roller 31, and a second heating roller 34 and the second heating roller 34. A second fixing roller device 36 is formed by a pair of rollers including a second pressure roller 35 that is pressed against the heating roller 34. The first fixing roller device 33 and the second fixing roller device 36 are arranged such that the respective nip positions are such that the conveyance path of the recording medium from the transfer position of the photoconductor 4 is substantially linear. That is, the two sets of roller devices 33, 3 are arranged so that the respective nip positions are present along the substantially linear transport path.
6 is arranged.

First heating roller 31 and second heating roller 34
Can be configured to be heated by separate heat sources respectively contained therein, in which case one or both, for example only the heat source of the second heating roller 34 or both the heat sources of the first heating roller 31 and the second heating roller 34 can be heated. For example, a self-temperature control heating element such as a positive temperature coefficient thermistor or a ceramic heater, for example, a self-controlled heating element whose electric resistance decreases as the temperature rises and which maintains a substantially constant temperature can be used.

FIG. 3A shows a heating circuit diagram in which self-temperature control heating elements are used for the heat sources 31a and 34a of both heating rollers 31 and 34, and an abnormal temperature rise prevention thermostat 37 is connected, and FIG. 3B shows the second heating. The heat source 34 a of the roller 34 uses a self-temperature control heating element, and the heat source 3 of the first heating roller 31
Reference numeral 4a indicates a circuit to which a switch 38, for example, a triac is connected, and the switch 38 is ON / OFF controlled by the control circuit 40 based on the detection information from the thermistor 39.

A heat source for the heating rollers 31 and 34 is shown in FIG.
It is possible to use one common heat source 41 as shown in FIG. The heat source 41 includes the first heating roller 31 and the second heating roller 3.
It is possible to dispose the heating roller 31 and the second heating roller 34 on the outer side of the first heating roller 31 and the second heating roller 34 at the same position from the outer sides of the heating roller 31. A reflector 42 is provided for the heat source 41 to direct the heat radiated outward to the heating rollers 31 and 34, respectively, to improve the heating efficiency.

The second heating roller 34 is provided with a separating claw 43 so as to surely separate the recording medium after fixing.
The temperature of the second heating roller 34 is detected by the thermistor 39 to enable ON / OFF control of the heat source 41, and detected by the thermostat 37 to prevent abnormal temperature rise. The control circuit for the heat source 41 can be configured as shown in FIG. Precise temperature control can be performed by controlling the heat source 41 to be turned on and off.

[0019]

According to the present invention, the recording medium can pass through the two fixing rollers in a substantially straight line, and the recording medium is not bent or abutted, so that it is possible to prevent wrinkles and jitter. Since two fixing rollers are used, even if the pressure applied to each of the fixing rollers is low, a sufficient pressure can be obtained by fixing with both fixing rollers, and the fixability is improved.

According to the present invention, the self-temperature control heating element can be used as the heat source, or the heating can be performed by one common heat source, the control circuit can be simplified, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of a printer.

FIG. 2 is a schematic explanatory view of a fixing device according to the present invention.

FIG. 3 is a control circuit diagram of a heat source of a heating roller, where A is 2
FIG. 3B is a control circuit diagram in the case where two heat sources are formed by self-controlled heat generating elements, and B is a control circuit diagram in the case where one is formed by a self-controlled heating element.

FIG. 4 is a control circuit diagram when one common heating element is used.

[Explanation of symbols]

2 recording media 9 Fixing device 31 First Pressure Roller 32 First pressure roller 33 First fixing roller device 34 Second pressure roller 35 Second Pressure Roller 36 Second Fixing Roller Device 31a heat source 34a heat source 38 switch 39 Thermistor 40 control circuit

Claims (3)

[Claims] 1. In a fixing device of an image forming apparatus for transferring and fixing a toner image onto a recording medium, two sets of fixing roller devices each having a heating roller and a pressure roller pressed against each other are provided. A fixing device, wherein the nip position is arranged along a substantially linear conveying path of a recording medium. 2. The fixing device according to claim 1, wherein at least one of the heat sources provided to the heating rollers of the two fixing roller devices is formed by a self-temperature control heating element. 3. The fixing device according to claim 1, wherein the heating rollers of the two sets of fixing roller devices are heated by one common heat source.