JPH0619363A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent high-temperature offset and the thermal degradation of parts by controlling energizing 1st and 2nd heaters after finishing fixing in accordance with the condition of energizing the 1st and the 2nd heaters at the time of fixing. CONSTITUTION:Two heaters 19 and 20 having different light distribution are housed inside a core bar 17, and the surface temperature of a fixing roller 15 is detected by a temperature detecting sensor 24 and a signal from the sensor 24 is read in a control circuit 13, thereby controlling the on/off timing of the respective heaters 19 and 20 having the different light distribution. Namely, at the beginning of standby after finishing the fixing of small-sized paper, the temperature is adjusted by the main heater 19 whose light distribution in the center part is higher than at the end part. Furthermore, the temperature of the fixing roller is controlled only by the main heater 19 for a specified time when the temperature distribution of the fixing roller is made uniform after shifting to a standby state, and then the temperature is adjusted only by the sub heater 20. By adjusting the temperature only by the heater 20 at the time of standby after finishing the consecutive fixing of large-sized paper, the temperature at both end parts of the fixing roller becomes high and the temperature distribution is made uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as a copying machine or a printer for fixing an unfixed image on a recording material.

[0002]

BACKGROUND ART As a fixing device for fixing an unfixed image,
The heat roller method is widely used in terms of efficiency and the like.

In this heat roller system, it has been attempted in recent years to reduce the heat capacity by thinning the core material of the heat roller in order to shorten the wait time.

However, when the core material is made thin, the heat conduction in the longitudinal direction of the roller is deteriorated and the temperature of the non-sheet passing portion easily rises, and it is difficult to obtain the temperature distribution corresponding to the recording materials of all sizes.

Therefore, it is conceivable to use two heaters having different light distributions and control the on / off timings of the heaters according to the recording material size to make the temperature in the roller longitudinal direction substantially uniform.

[0006]

Even in a device using a plurality of heaters having different light distributions as described above, a temperature distribution occurs in the longitudinal direction of the heat roller when the fixing operation is continuously performed.

This temperature distribution state varies depending on the energization conditions to the heater, and is in a state where the end portion is high or the central portion is high.

Therefore, even if the standby temperature control is performed after the continuous fixing is completed, the temperature of the high temperature portion does not immediately drop. Therefore, if the fixing operation is performed immediately after entering the standby, a high temperature offset may occur.

[0009]

According to the present invention for solving the above-mentioned problems,
The first and second heating members each have a second heater having a light distribution different from that of the first light distribution member, and a backup member forming a nip with the heating member. The nip holds a recording material supporting an unfixed image. A fixing device for carrying and fixing the toner has control means for controlling power supply to the first and second heaters after completion of the fixing in accordance with power supply conditions to the first and second heaters at the time of fixing. It is characterized by.

[0010]

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

FIG. 1 is a sectional view of an image forming apparatus using a fixing device according to an embodiment of the present invention.

As is well known, the area where the toner image is formed is such that the charging device 2, the image exposure 3,
A developing device 4, transfer / separation chargers 5 and 6, a cleaning device 7, and a pre-exposure light source 8 are arranged, and a toner image is formed on the photoconductor 1 by an electrophotographic method.

This toner image is transferred as an unfixed toner image onto a transfer material P (hereinafter abbreviated as paper) in a storage container 10 which stores a transfer material which is a recording material. After that, it is conveyed to the fixing device 9 and fixed as a permanent image.

The storage container 10 detachable from the main body of the apparatus is
A paper size identification button 11 is provided, and the size identification button 11 is read by a paper size detection sensor 12 provided on the apparatus body side.

Then, a paper size signal is sent from the sensor 12 to the control circuit 13.

The control circuit 13 also counts the number of continuous image formations.

FIG. 2 is an enlarged sectional view of the fixing device 9.

The transfer paper carrying the unfixed toner image is guided to the nip between the fixing roller 15 and the pressure roller 16 by the guide 14, and the toner image is heated and pressure-fixed on the transfer material while passing through the nip.

The fixing roller 15 is a hollow cylinder having a thickness of 0.7.
The core metal 17 is made of steel and has a release layer 18 made of fluororesin and provided on the core metal 17.

Inside the core metal 17, two heaters 19 and 20 having different heater light distributions, which are heating sources, are housed. The pressure roller 16 has a hollow cylindrical cored bar 21 on which an elastic silicone rubber layer 22 is mounted on the outer peripheral surface thereof, and a fluororesin layer 23 is further coated on the pressure roller 16 in order to improve releasability.

The surface temperature of the fixing roller is detected by the temperature detection sensor 24, and the signal is read by the control circuit 13 to control the ON / OFF timing of two heaters having different light distributions.

This temperature detecting sensor is provided in the sheet passing area of the recording material of the smallest size used in the apparatus.

Next, the light distribution of the heaters 19 and 20 will be described.

The image forming apparatus of this embodiment is a so-called center reference, in which the recording material is conveyed with the center as the reference, regardless of its size.

FIG. 3 shows a light distribution pattern of the heater 19 (hereinafter referred to as a main heater), in which the amount of light is concentrated in the central portion in the longitudinal direction of the fixing roller (the width of the central portion is the width of small size paper). According to). FIG. 4 shows the heater 2
0 (hereinafter referred to as sub-heater) light distribution pattern,
The amount of light is concentrated at the end in the longitudinal direction of the fixing roller. The electric power of the heater used here is 700 [W] for the main heater and 600 [W] for the sub heater.

Next, the on / off timing of these two heaters 19 and 20 will be described.

Here, the small size paper refers to a paper size of B4 size or less, and the large size paper refers to a paper size of B4 size or more.
In addition, the B4 size paper is vertically fed with the long direction aligned with the carrying direction.

When forming an image on a small size sheet, heat is mainly taken from the central portion of the fixing roller.
Only the light is turned on and the sub heater 20 is turned off.

FIG. 5 shows the temperature distribution of the fixing roller after continuous fixing of small size paper.

As described above, although the sub-heater 20 is off, the temperature of both ends of the fixing roller becomes high after continuous fixing.

When an image is formed on a large size sheet, heat is also taken from the end portion in the longitudinal direction of the fixing roller, so that the temperature of both ends is lowered and the fixing failure occurs only with the main heater. Therefore, the sub heater and the main heater are alternately turned on / off
(Time control) makes the temperature distribution in the longitudinal direction of the fixing roller uniform. In the case of the heater used here,
The ratio of lighting time of the main heater and the sub heater is 4:
When it was set to 1, a good temperature distribution could be obtained. In other words, while the control circuit 13 outputs a signal to turn on the heater, 0.5 seconds is set as one cycle, the main heater is turned on for 0.4 seconds, and then the sub heater is turned on for 0.1 second. There is.

FIG. 6 shows the temperature distribution of the fixing roller after the continuous fixing of large size paper.

Next, the temperature control of the fixing roller during standby after the fixing operation will be described.

After continuous copying of small size paper, the temperature distribution of the fixing roller is high at both ends as shown in FIG. Therefore, if the temperature is controlled using the sub-heater having a higher light distribution at the edges than in the central portion after the continuous fixing of small-size paper during standby, the temperatures at both edges do not easily drop.

Therefore, in this embodiment, the temperature is controlled by the main heater, which has a higher light distribution in the central part than in the end parts, in the initial stage of standby after the fixing of small size paper.

For this reason, when entering the standby state, the temperature of both ends is promptly lowered, and the temperature distribution of the fixing roller becomes uniform.

If the temperature control of only the main heater is continued even after the temperature distribution becomes uniform, the heat radiation at both ends of the fixing roller is large, and the temperature at both ends is lowered, so that fixing failure at the ends tends to occur. .

Therefore, in this embodiment, further, the temperature of the fixing roller is controlled only by the main heater for a predetermined time period when the temperature shifts to the standby state and the temperature distribution of the fixing roller becomes uniform.
After that, the temperature is adjusted only by the sub heater.

After the continuous fixing of the small size paper is completed, if the temperature is adjusted only by the main heater, the temperature distribution of the fixing roller becomes substantially uniform in about 1 minute.

Therefore, in the present embodiment, the temperature is controlled only by the main heater for 1 minute after the continuous fixing of the small size paper is completed, and the temperature is switched by the sub heater only after 1 minute.

Next, the case after continuous fixing of large size paper will be described.

As shown in FIG. 6, the temperature distribution of the fixing roller after the continuous fixing of the large size paper is higher at the central portion than at the end portions.

Therefore, after the continuous fixing of the large-sized paper is completed, the temperature of both ends of the fixing roller is quickly raised by adjusting the temperature by the sub-heater at the standby time, and the temperature distribution becomes uniform. Further, in this case, since the heat radiation at both ends of the fixing roller is large even after the temperature distribution becomes uniform, the temperature is adjusted by the sub heater so that the temperature distribution is maintained substantially uniform.

As described above, according to the present invention, the temperature distribution of the fixing roller is made substantially uniform from the end of fixing to prevent the high temperature offset, regardless of the energization condition to the heater at the time of fixing, and further the pressure roller and The thermal deterioration of the cleaning member can be prevented.

(Embodiment 2) As the sub-heater having a larger light distribution in the end portion than in the central portion, a sub-heater having a larger light distribution in the central portion than the end portion and a larger power than that of the large lung main heater is used.

After the large-size paper is continuously fixed, the temperature of the fixing roller becomes higher at the center than at the ends as shown in FIG.

When the temperature control is started only by the sub-heater after the fixing of the large-sized paper as in the above-mentioned embodiment, the electric power of the sub-heater is large, and the temperature of both ends rapidly rises, as shown in FIG. There is a recess between the ends and the center where the temperature does not rise. If fixing is performed in such a state, fixing failure occurs at a portion corresponding to the recessed portion. Therefore,
For a predetermined time after the completion of fixing, which is set in advance, the temperature is adjusted only by the sub heater and then the temperature is adjusted only by the main heater, and then the temperature is adjusted only by the sub heater.

Specifically, after the completion of fixing, the temperature is adjusted by the sub heater for 20 seconds and then by the main heater for 10 seconds. When the temperature is adjusted again using the sub-heater for 30 seconds thereafter, the temperature distribution of the fixing roller becomes substantially uniform. FIG. 8 shows the ON / OFF timing of the main heater and the sub heater for 30 seconds only at this time.
In this way, by controlling the temperature by alternately using the sub heater and the main heater for a fixed time of 1 minute after the completion of copying, the temperature distribution of the fixing roller can be made substantially uniform and the fixing failure can be prevented.

(Embodiment 3) When the electric power relation of the heater and the temperature distribution of the fixing roller after the fixing are the same as those of the embodiment 2, the temperature control is performed only by the sub-heater as described in the second embodiment. Doing so will cause indentation, resulting in poor fixing.

Therefore, in this embodiment, the main heater and the sub-heater are alternately turned on and off for a predetermined time after the completion of fixing to control the time.

Specifically, if the ratio of the time-controlled main heater to the sub-heater is set to 1: 5 and the time for controlling the time after completion of fixing is set to 1 minute, the temperature distribution of the fixing roller becomes substantially uniform, and the fixability is improved. You can prevent defects. FIG. 9 shows the ON / OFF timing for only 30 seconds when the temperature is controlled by the time control using the main heater and the sub heater at this time. As a time control, the control is performed with 4 seconds as one break.

[0052]

As described above, according to the present invention, the temperature distribution of the heat roller can be promptly made substantially uniform after completion of fixing, and high temperature offset and heat deterioration of parts can be prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an image forming apparatus using a fixing device according to an exemplary embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of the fixing device according to the exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a light distribution of a main heater.

FIG. 4 is a diagram showing a light distribution of a sub heater.

FIG. 5 is a diagram showing a temperature distribution of a fixing roller after continuously fixing small size paper.

FIG. 6 is a diagram showing a temperature distribution of a fixing roller after continuously fixing a large size paper.

FIG. 7 is a diagram showing a temperature distribution of a fixing roller for explaining a second embodiment.

FIG. 8 is a diagram showing an on state of a main heater and a sub heater.

FIG. 9 is a diagram showing an on state of a main heater and a sub heater.

[Explanation of symbols]

 12 Paper Size Detection Sensor 13 Control Circuit 15 Fixing Roller 16 Pressure Roller 19 Main Heater 20 Sub Heater 24 Temperature Sensor

Claims (3)

[Claims] 1. A first and a second having a light distribution different from the first
In a fixing device that has a heating member having a heater and a backup member that forms a nip with the heating member, and nips and conveys a recording material that supports an unfixed image at the nip to perform fixing, A fixing device comprising control means for controlling the energization of the first and second heaters after completion of fixing in accordance with the energization conditions of the first and second heaters. 2. The fixing device according to claim 1, wherein the control means selects a heater to be energized after the fixing is completed according to an energizing condition at the fixing. 3. The fixing device according to claim 1 or 2, wherein, after a lapse of a predetermined time after completion of fixing, current is supplied under the same current supply condition regardless of current supply conditions during fixing.