JPH0792852A - Fixing device for image forming device - Google Patents

Abstract

PURPOSE:To reduce variance in temperature in the axial direction on the surface of a fixing roller and to preclude a partial defect in fixation, a high-temperature offset, and gloss unevenness by placing the heat generation part of one heater on the heat non-generation part of the other heater. CONSTITUTION:The heaters are fitted to the fixing device so that the heat generation part of one heater 19 is put on the heat non-geneartion part of the other heater 20. In this case, the heat generation distribution of the heater 19 is shown by a broken line B and the heat generation distribution of the heater 20 is shown by a broken line C; and the heaters 19 and 20 have large heat generation ripples in the axial direction respectively, but the heat generation part and heat nongeneration part are put one over the other to obtain heat generation distribution characteristics a shown by a solid line D. When the temperature of the fixing roller is controlled by using the couple of heaters, the surface temperature distribution of the fixing roller shown by a solid line D is obtained the axial temperature ripples can be made small. Further, when the axial temperature ripples of the fixing roller become small, the partial defect in fixation, high-temperature offset, and gloss unevenness can be prevented.

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 a copying machine, a printer or an image forming apparatus which uses electrophotography.

[0002]

2. Description of the Related Art An example of a conventional fixing device using a thin fixing roller is shown in FIG. In FIG. 5, 1 is a fixing roller,
It is made of aluminum having an outer diameter of 30 mm and a wall thickness of 1 mm, and the surface layer is coated with a release layer of fluororesin. The fixing roller 1 is rotationally driven in the direction of arrow a while being heated by the heaters 3 and 4, and the paper 6 on which the unfixed toner image 7 is placed in the fixing nip N formed with the pressure roller 2.
To obtain a permanently fixed image.

To control the temperature of the fixing roller 1, the heaters 3 and 4 are turned on by the heater driving circuits 9 and 10 based on the temperatures measured by the temperature detecting element (thermistor) 5 and the temperature measuring means 8.
・ Perform by turning off. The relationship between the temperature and the ON / OFF timing is as follows: CPU 11, I / O 12, memory 1
3. Determined by a control system including the bus line 14.

Here, the reason why two heaters, which are heat sources, are used will be described. Since the fixing device shown here uses a thin fixing roller, the temperature response of the surface of the fixing roller to ON / OFF of the heater is good. As a result, the temperature ripple of the fixing roller during temperature control during printing becomes large, and there are some areas where the proper temperature cannot be applied. In some cases, the toner was melted more than necessary due to the excessive supply of toner, and a high-temperature offset that adheres to the fixing roller occurred. In order to reduce this temporal temperature ripple, it is necessary to reduce the heater output to reduce the temperature change of the fixing roller. However, if the heater output is simply reduced, the time from turning on the power until reaching the standby state is reduced. Wait time becomes long. Therefore, in order to prevent this, a fixing device using a conventional thin-walled fixing roller is provided with a heater that is used only during the weighting so that the temperature ripple in the steady state is reduced while shortening the weighting time. Is.

Explaining with the example shown in FIG. 5, first, when the power is turned on, the heaters 3 and 4 are turned on to warm the fixing roller 1. When the fixing roller 1 reaches the controlled temperature, the drive circuit 10 of the heater 4 does not operate and the heater 3 turns ON / O.
The FF alone operates to keep the temperature of the fixing roller at the controlled temperature. Here, the input voltage of the apparatus is 100V, and the heaters 3 and 4 are also driven by this voltage.

FIG. 6 shows the structure of a conventionally used heater. The heaters 3 and 4 shown in FIG. 6 are the same and are composed of insulator 15, tungsten wire 18, and quartz tube 17. A portion around which the tungsten wire 18 is wound is called a segment 16, and heat is mainly generated in this portion. If the same heater is used, the segments 16 will overlap in the axial direction as shown in FIG.

[0007]

However, according to the above-mentioned conventional example, the segment 1 which is the heat generating portion of the heater is used.
Since 6 overlaps in the axial direction, the ability to warm the fixing roller 1 in the axial direction varies in the axial direction, and the temperature ripple in the axial direction occurs in the fixing roller 1 as shown in FIG.

If such a temperature distribution occurs in the fixing roller, partial fixing failure, high temperature offset, and difference in surface property of the fixing toner may occur on the paper surface in a direction perpendicular to the paper traveling direction. There is a problem that uneven gloss or the like occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a fixing device capable of preventing temperature ripple in the axial direction of the fixing roller due to overlapping of heater segments.

[0010]

SUMMARY OF THE INVENTION According to the present invention, the above object is to provide a hollow fixing roller, a heating roller which is disposed inside the fixing roller, and which heats the fixing roller. While having a plurality of heaters whose portions are alternately arranged in the axial direction and a pressure roller that is pressed against the fixing roller, the powder developer on the recording material is heated and melted and fixed on the recording material. In a fixing device of an image forming apparatus which conveys a recording material, it is achieved by arranging a portion of one heater having a large heat generation amount so as to overlap an other heater having a small heat generation amount in the axial direction. .

[0011]

According to the present invention, the heat generating portion and the non-heat generating portion of the heater each having a large heat generating ripple in the axial direction are overlapped with each other to smooth the heat generating distribution characteristic in the axial direction and reduce the temperature ripple in the axial direction. .

[0012]

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

<Embodiment 1> First, Embodiment 1 of the present invention will be described with reference to FIGS. 1, 2 in FIG.
Reference numeral 0 denotes a heater, which is attached to the fixing device so that the heat generating portion of one heater 19 overlaps the non-heat generating portion of the other heater 20. The input voltage of the device is 100V, heater 1
9 and 20 are also driven by this voltage. The heaters 19 and 20 are 400 W each.

The temperature of the fixing roller 1 is controlled by measuring the temperature of the fixing roller 1 with the thermistor 5 and the temperature measuring means 8.
CPU 11, I / O 12, memory 13, bus line 14
Heater drive circuits 9 and 10 under the control of a control system including
Is performed by turning on / off the heaters 19 and 20. The actual heater control is as follows.

[Wait] Both the heaters 19 and 20 are continuously turned on until the surface of the fixing roller reaches the controlled temperature.

[During Standby and Printing] In the conventional example, the temperature is controlled by only one of the heaters, but in the present embodiment, the temperature of the fixing roller is controlled by alternately turning on and off one by one. The ON / OFF timing is a simple one in which the heater is turned on when the surface temperature of the fixing roller is below the temperature control temperature and turned off when the surface temperature of the fixing roller is below the temperature control temperature.

FIG. 2 shows the positional relationship between the two heaters, the heat generation distribution, and the temperature distribution on the surface of the fixing roller. Heater 1
The heat generation distribution of 9 is a broken line B, and the heat generation distribution of the heater 20 is a broken line C
Is. Although each heater has a large heat generation ripple in the axial direction, the heat generation distribution characteristics as shown by the solid line D can be obtained by overlapping the heat generation portion and the non-heat generation portion as in this embodiment. When the temperature of the fixing roller is adjusted by using this heater pair, the surface temperature distribution of the fixing roller becomes like the solid line D, and the temperature ripple in the axial direction can be reduced.

Further, if the temperature ripple in the axial direction of the fixing roller is reduced, it is possible to prevent partial fixing failure, high temperature offset, and uneven gloss.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, a case of a fixing device compatible with small-size paper passing will be described. It is generally known that fixing a small size paper sheet using a thin fixing roller causes a problem of temperature rise in a non-sheet passing portion. This causes an inconvenience that the temperature of the fixing roller in the non-sheet passing portion rises and the fluororesin or the like on the surface of the fixing roller deteriorates.

In order to prevent the temperature rise of the non-sheet passing portion, the heaters used in the case of changing the heat generation distribution of the two heaters to pass the medium-sized sheet and the sheet of the small-sized sheet. Is changing.

In this case, one of the heaters used is for small size paper, and the heat distribution is such that only the width of the small size paper is warmed. The other heater is a heater that generates a large amount of heat outside the paper passing area for small size paper.

When printing on a plain paper size, the temperature is controlled by two heaters, and on the small size plain paper, the temperature is controlled by a heater for the small size paper. The present invention is also effective in such a fixing device.

FIG. 3 shows a second embodiment of the present invention. In FIG. 3, F is a plain paper width, and G is a small size paper width. Reference numeral 21 is a heater for small size paper, and heat generating portions are arranged at equal intervals in the paper passing area, and the heat generation distribution of the heater is H-shaped. Reference numeral 22 is a heater used in combination with the heater 21 in the case of plain paper passing, and is mainly used for warming the outside of the small size paper passing area, and its heat generation distribution is as shown in I.

The heaters 21 and 22 are arranged such that the heat-generating portions divided into short sections are arranged at equal intervals in the small-size paper passing area, but here, in this area, the heat-generating portion of one heater is not the other heater. Each heater is arranged so as to overlap the heat generating portion.

When printing on plain paper size paper, the heaters 21 and 22 are alternately turned on and off to control the temperature.
In this case, the temperature distribution on the surface of the fixing roller is as shown by the solid line J, and the heat generating portions of the heater are alternately arranged to reduce the temperature ripple in the axial direction at the small-size paper passing portion.

Here, in the case of passing small size paper, the heater 2
If the temperature is controlled only by the heater 21 without turning on 2, the temperature distribution on the fixing roller will have a large ripple as indicated by the one-dot chain line L, and the above-mentioned problem will occur.

Therefore, when fixing small-sized paper, the ON / OFF interval between the heater 21 and the heater 22 is changed to perform temperature control. Specifically, the ratio of the lighting times of the heaters 21 and 22 that are alternately turned on and off

Heater 22: Heater 21 = 1: 2

When the heater 22 is turned on, the heater is turned off even if the fixing roller temperature does not reach the controlled temperature.

By doing so, the temperature distribution on the fixing roller becomes like the broken line K. In this case, the ripple in the small-size paper passing area is smaller than that when the temperature is adjusted only by the heater 21, and it can be set to a level at which there is no practical problem.

Therefore, while using the thin fixing roller, the temperature rise at the edge of the small size paper is suppressed and the temperature ripple of the paper passing part is also reduced to cause partial fixing failure, high temperature offset and uneven gloss. Can be prevented.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment, the configuration in which the input voltage of the device is constant has been described, but here, the case of the device corresponding to a plurality of input voltage levels will be described.

For example, in the case of an apparatus that accepts an input voltage of 120V to 85V, the heater of the fixing device must be set according to the higher voltage. This is because if the heater is used at a voltage higher than the rating, an overcurrent will flow and it will be damaged.

In this case, if the device is used at a low voltage, the heater will be driven at a low voltage. Then, since the amount of heat generated per unit time becomes small, the ON time of the heater for one time becomes long, and temperature nonuniformity corresponding to the heat generation distribution of the heater occurs on the fixing roller. In order to prevent this, the present embodiment has a configuration as shown in FIG.

In FIG. 4, reference numerals 23 and 24 denote temperature detecting elements (thermistors) which are set at positions corresponding to the heat generating portions (segments) of the heaters 19 and 20, and the surface temperature of the fixing roller 1 at the positions corresponding to the respective segments. Can be measured. Reference numerals 25 and 26 are respective temperature measuring means.

In operation, first, one of the heaters (for example, the heater 19) is turned on, and when the temperature of the fixing roller surface reaches the controlled temperature, the heater is turned off. Next, when the temperature of the fixing roller falls, the heater 20 is turned on to warm the fixing roller.
By repeating this, the temperature of the fixing roller 1 is adjusted. In this operation, when the temperature difference between the thermistors 23 and 24 is within a certain temperature (for example, 5 ° C. or less), the lower temperature of the two thermistors is prioritized as the temperature control temperature.

Further, when the temperature difference between the two thermistors exceeds a certain temperature, the heater which is turned on is replaced. For example, even if the heater 19 is ON, when the temperature of the thermistor 24 becomes 5 ° C. lower than the temperature of the thermistor 23, the heater 19 is turned off and the heater 20 is turned on. When the surface temperature of the fixing roller 1 reaches the controlled temperature, turn off the heater,
When the fixing roller cools and the next heater ON timing comes, the heater 20 is turned ON first.

With the above-described structure, even when the input voltage of the apparatus is lower than the rated voltage of the heater and the ON time of the heater is long, the temperature variation in the axial direction of the fixing roller surface is within a certain temperature. It is possible to prevent partial fixing failure, high temperature offset, and uneven gloss.

[0041]

As described above, according to the present invention,
When a plurality of heaters used for the thin fixing roller are divided into a heat generating portion and a non-heat generating portion in the fixing roller heating area,
By overlapping the heat-generating part of one heater with the non-heat-generating part of the other heater, the temperature variation in the axial direction of the fixing roller surface can be reduced to prevent partial fixing failure, high temperature offset, and uneven gloss. It is a thing.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a fixing device according to a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the arrangement of heat generating portions of the heater according to the first embodiment of the present invention, the heat generation distribution of the heater, and the surface temperature distribution of the fixing roller.

FIG. 3 is a diagram showing a relationship between the arrangement of heat generating portions of a heater according to the second embodiment of the present invention, heater heat distribution, surface temperature distribution of a fixing roller, and sheet passing width.

FIG. 4 illustrates a configuration of a fixing device according to a third exemplary embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional fixing device.

FIG. 6 is a diagram showing a configuration of a conventional fixing device.

FIG. 7 is a diagram showing a surface temperature of a fixing roller of a conventional fixing device.

[Explanation of symbols]

 1 Fixing Roller 2 Pressurizing Roller 16 Segment (Heating Part) 19, 20, 21, 22 Heater

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Norio Hashimoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Masaharu Okubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Hiroto Hasegawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kazuro Ono 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. A hollow fixing roller, and a plurality of heaters disposed inside the fixing roller, in which a portion having a large heat generation amount and a portion having a small heat generation amount are alternately arranged in an axial direction in a region for heating the fixing roller. And a pressure roller that is in pressure contact with the fixing roller, wherein the powder developer on the recording material is heated and melted on the recording material to be fixed while the recording material is conveyed. A fixing device of an image forming apparatus, wherein one heater has a large heat generation amount and another heater has a small heat generation amount so as to overlap in an axial direction. 2. The fixing device according to claim 1, wherein the thickness of the fixing roller is 1.2 mm or less.