JPH10293490A - Fixing device - Google Patents

Abstract

[PROBLEMS] To provide a fixing device that has a short rise time and can suppress a temperature rise in a non-sheet passing area. SOLUTION: A heating layer 3 is laminated on an inner surface of a metal base 1 of a fixing roller 100 to be a main heat source. On the other hand, an auxiliary heater 13 having a heat generation width corresponding to the small-size paper passing width is provided in the fixing roller. When the large-size sheet is passed, only the main heat source 3 is energized to maintain the fixing roller temperature. When the small-size sheet is continuously fed, the auxiliary heater 13 is continuously energized and the main heat source 3 is energized (mainly). By maintaining the fixing roller temperature in the paper passing area (by reducing the amount of electricity to the heat source),
Prevents excessive rise in the temperature of the fixing roller end.

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 image forming apparatus such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile or the like using an electrophotographic system, a transfer paper,
BACKGROUND ART A heat fixing device is widely used as a fixing device for fixing an unfixed image (toner image) transferred onto a recording material such as an OHP film to the recording material. Conventionally, as a heat fixing device, a heat roller system in which a pressure roller is pressed against a fixing roller heated by a heater, and an unfixed toner image is fixed by heat and pressure while nipping and conveying the recording material between both rollers. Things are heavily used. In such a fixing device, in order to keep the fixing quality constant, it is necessary to keep the surface temperature of the fixing roller constant within the fixable temperature.

[0003] In recent years, with the increasing awareness of environmental regulations and environmental protection, it has been required to reduce the power consumption of various image forming apparatuses. One of the measures is to fix the fixing apparatus only when the paper is passed during which the fixing operation is performed. An on-demand system has been proposed in which the heater is energized and the heater is not energized at other times (preheating is not performed). Alternatively, it has been proposed that the fixing heater, which is turned off when not in use, is energized by detecting the approach of the user by a sensor to increase the temperature of the fixing heater.

In such a power saving type image forming apparatus,
It is necessary that the surface temperature of the fixing roller immediately reaches a set temperature (control temperature) during image formation, and a fast (fast) startup of the fixing device is required.

In the conventional fixing roller, a heater such as a halogen lamp is installed inside a hollow pipe-shaped metal roller, and the halogen heater generates heat to heat the entire roller. In order to enable rapid temperature rise with this type of fixing roller, the thickness of the fixing roller base is reduced to 1 mm or less.

On the other hand, as another measure for satisfying the requirement of a high-speed start-up of the fixing device, a heating layer such as an electric resistor is provided on the outer peripheral surface or the inner peripheral surface of the roller, and the roller is heated directly. It has been proposed to use a heat-generating fixing roller. This direct heating type fixing roller
It has high heating efficiency and is suitable for energy saving.However, in order to raise the temperature immediately when the user uses it without preheating, it is possible to achieve rapid temperature rise by combining with the technology of thinning the fixing roller base. I'm trying.

[0007]

However, in a heat roller type fixing device, a portion through which a sheet (recording material) passes passes through the roller surface where heat is taken away by the sheet, but a portion without the sheet (a non-sheet passing area). Since there is no heat loss, when small-sized paper (for example, B5 portrait) is continuously passed, the roller temperature in the non-paper passing area may rise beyond an allowable range. In a normal, center-based apparatus, the temperature at the roller end of the fixing roller is too high, and there is a problem that the life of the roller and the life of the bearing are shortened. With the thin fixing roller as described above, the heat conduction in the roller axis direction is reduced, so that the temperature rise in the non-sheet passing area during continuous sheet passing becomes very remarkable.

An object of the present invention is to solve the above-mentioned problems in the conventional fixing device, and to provide a fixing device which has a short rise time and can suppress a rise in temperature in a non-sheet passing area.

[0009]

SUMMARY OF THE INVENTION According to the present invention, there is provided a recording apparatus comprising a fixing roller which is driven to rotate, and a pressing roller which is in pressure contact with the fixing roller. In a heat fixing device for fixing an unfixed image to recording paper by passing the paper, the fixing roller is made of a thin hollow cylindrical metal substrate, and an electrical insulating layer and a heat generating layer are formed on the inner or outer surface of the hollow cylindrical metal substrate. And a supplementary heat source having a heat generation width corresponding to the paper passing width of the small-sized recording paper.

According to the present invention, in order to solve the above-mentioned problems, the auxiliary heat source has a low capacity such that the auxiliary heat source alone does not maintain the fixing roller set temperature when the small size paper is continuously passed. It is proposed to control the surface temperature of the fixing roller by continuously energizing the auxiliary heat source during continuous paper feeding and controlling the energization of only the main heat source.

Further, in order to solve the above-mentioned problem, the present invention proposes that the auxiliary heat source is installed inside the fixing roller. Further, the present invention proposes that the auxiliary heat source is a nichrome wire heater in order to solve the above-mentioned problem.

Further, according to the present invention, in order to solve the above-mentioned problems, the fixing roller has an electric insulating layer and a heat generating layer laminated on an inner surface of a cylindrical metal base, and a roller cross section is formed at both ends of the heat generating layer on the inner surface of the fixing roller. A power receiving electrode having a disc-shaped portion in the direction is provided, and a power supply member is brought into contact with the disc-shaped portion of the power receiving electrode as a sliding surface, and the auxiliary heat source is provided between the pair of power receiving electrodes at the center of the disc-shaped portion. It is suggested to fix and arrange.

Further, in order to solve the above-mentioned problems, the present invention proposes that a disk-shaped reinforcing member which engages with the inner wall of the fixing roller is mounted on the auxiliary heat source.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to an embodiment of the present invention. In the fixing device shown in this figure, a pressure roller 200 is pressed against a fixing roller 100 with a constant pressing force by an urging means (not shown). The fixing roller 100 is supported by the fixing side plates 7a and 7b via heat insulating bushes 5a and 5b and bearings 6a and 6b. A driving gear 8 is provided at one end of the fixing roller 100.
The gear 8 is engaged with a driving mechanism (not shown) to rotate the fixing roller.

As shown in the partially enlarged view of the hollow pipe-shaped fixing roller 100, an insulating layer 2 and a resistance heating layer 3 are laminated on an inner surface (inner peripheral surface) of a thin metal base 1, and an outer surface (outer peripheral surface). 3), a release layer 4 is formed. On the inner peripheral surface of the fixing roller 100, power receiving electrodes 9a and 9b are fixedly provided at both ends of the resistance heating layer 3. The receiving electrodes 9a, b
The power supply electrodes 11a and 11b are pressed by the leaf springs 10 attached to the support plates 12a and 12b, and power is supplied to the resistance heating layer 3, which is the main heat source.

A nichrome wire heater 13 as an auxiliary heat source is provided inside the fixing roller 100. The heater 13 supported by the support plates 12a and 12b has a heat generation distribution corresponding to the width of the transfer paper of a small size. Further, the rating of the heater 13 is such that the heater 13 has a low capacity which is less than the electric power required to maintain the temperature of the fixing roller 100 at a set temperature (control temperature) only by the heater 13 when continuously passing small-sized paper. It is. As the heater 13 as the auxiliary heat source, for example, a halogen lamp or a ceramic heater other than the nichrome wire heater can be used. In the fixing device of the present embodiment, the center is based on paper passing, and the heat generating area of the heater 13 as an auxiliary heat source is provided in the center of the fixing roller 100. The heat generating region of the heat source can be provided close to either end of the fixing roller.

A temperature sensor 14 is in contact with the outer peripheral surface of the fixing roller 100. The signal detected by the temperature sensor 14 is sent to the CPU 300 via the input circuit 301.
The CPU 300 detects the fixing roller 10
Based on the temperature of 0, the power supply to the resistance heating layer 3 and the nichrome wire heater 13 as the main heat source and the auxiliary heat source is controlled via the drivers 302a and 302b. The portions related to the energization control can be provided in the image forming apparatus main body to which the fixing device is attached.

In the fixing device configured as described above,
At the time of continuous passing of small-size paper, power is supplied to the nichrome wire heater 13 which is an auxiliary heat source, and the amount of power supplied to the resistance heating layer 3 which is a main heat source is reduced. And the temperature rise at the roller end can be prevented.

FIG. 2 is a timing chart showing how the energization of the main heat source and the auxiliary heat source is controlled in this embodiment. As shown in this chart, when a large-size transfer paper is passed, the heater 13 is turned off, the temperature of the fixing roller 100 is kept constant only by the resistance heating layer 3, and a small-size transfer paper (for example, B5 portrait) is printed. Heater 13 when passing paper
ON (continuous energization) to control only the amount of energization to the resistance heating layer 3 to keep the fixing roller temperature in the paper passing area constant. In the present embodiment, the control of the main heat source is ON / OFF control, and the interval between the ON and the ON of the main heat source at the time of small-size paper passing is made longer than at the time of large-size paper passing (small-size paper passing). Off time of the main heat source is longer than when large-size paper is passed). Note that the control of the main heat source may be phase control. By such power supply control, the amount of power supply to the main heat source (resistance heating layer 3) during small-size paper passing can be reduced, and as a result, the temperature rise at the end of the fixing roller 100 can be suppressed.

FIG. 3 is a flowchart showing the energization control in this embodiment. That is, Step 1 (hereinafter, referred to as Step 1)
Step S is abbreviated as S) to determine the transfer paper size, and if the transfer paper is of a small size (if it is smaller than a predetermined size)
The auxiliary heat source is turned on (S2). And the temperature sensor 14
Is read (S3), and the value is compared with the set temperature to control the main heat source (S4). On the other hand, if the size of the transfer sheet is large (larger than a predetermined size), the main heat source is controlled by the value of the temperature sensor without turning on the auxiliary heat source.

As can be seen from this flowchart, the control is simple simply by turning on the auxiliary heat source when the small-size transfer paper is passed, and the load on the software processing is very small. Transfer paper size recognition, for example,
The determination can be made by setting a paper size input key provided on an operation unit (operation panel) of the image forming apparatus to which the fixing device is attached. Alternatively, the determination may be made based on a value set in advance by a paper size switch or the like provided in a paper feed cassette or the like of the image forming apparatus.

FIG. 4 is a graph showing the temperature of the fixing roller when the small size paper is continuously passed in the fixing device of the present embodiment in comparison with the conventional example. In this graph, as shown by the thick solid line, the temperature at the center of the fixing roller 100 (small size paper passing area) is maintained within a predetermined range around the set temperature. Further, the temperature rise of the fixing roller end portion temperature in the present embodiment is suppressed to a minimum as shown as the case with the auxiliary heat source. On the other hand, in the case of the conventional example having no auxiliary heat source, the temperature of the end portion of the fixing roller is remarkably increased as shown by the dashed line as the case without the auxiliary heat source.

As described above, according to the fixing device of the present embodiment, by providing the auxiliary heat source corresponding to the paper passing area of the small size paper, it is possible to reduce the cost of the end of the fixing roller with a relatively simple structure without increasing the cost. Temperature rise can be prevented. Accordingly, even with a thin fixing roller having a small heat capacity and a fast rise, a uniform fixing roller temperature can be obtained regardless of the size of the transfer sheet. Further, the control is simple, and the cost can be reduced in software.

Incidentally, a thin fixing roller having a small heat capacity tends to have a large temperature ripple.
Generally, a fast-response halogen lamp is used as a heat source of the fixing device, and a nichrome wire heater having a poor response is not suitable for performing fine control. However, in the present embodiment, as described with reference to FIG. 2, the auxiliary heat source is continuously energized when small-sized paper is passed, and does not require detailed control. Therefore, a nichrome wire heater with poor response can be used as an auxiliary heat source. Unlike a halogen lamp, a nichrome wire heater does not require gas filling or the like and is inexpensive, and thus has the effect of reducing the cost of the fixing device as compared with the case where a halogen lamp is used.

Next, as another example of this embodiment, an example in which an auxiliary heat source is provided outside the fixing roller will be described. FIG. 5 is a side view showing a main part of a fixing device in which a ceramic heater 20 as an auxiliary heat source is provided outside the fixing roller 101. The rating of the ceramic heater 20 is
When the small-size paper is continuously fed, the fixing roller 101 has a low capacity that is less than the electric power required to maintain the temperature of the fixing roller 101 at a set temperature (control temperature) using only the heater 20. In this figure, as shown in a partially enlarged view, a hollow pipe-shaped fixing roller 101 has an insulating layer 2 and a resistance heating layer 3 laminated on an outer surface (outer peripheral surface) of a thin metal base 1, and a mold release thereon. Layer 4 is formed. Power receiving electrodes 19 a and 19 b are fixedly provided at both ends of the fixing roller 101 and at the ends of the resistance heating layer 3. The support plates 22a, 22a
b, the feed electrodes 11a, 11b
, And power is supplied to the resistance heating layer 3 which is the main heat source. The fixing roller 101 is connected to the fixing side plate 7 via heat insulating bushes 15a and 15b and bearings 16a and 16b.
a, b are supported. The configurations of the temperature sensor 14 and the power supply controller are the same as those of the fixing device shown in FIG.

The control of energizing the main heat source and the auxiliary heat source in this embodiment is the same as the timing chart of FIG. 2 and the flowchart of FIG. Further, as shown in FIG. 4, when the small-size paper is continuously fed, the temperature of the fixing roller at the end of the fixing roller is suppressed from rising, and the end temperature does not rise as in the conventional example.

In this embodiment, the auxiliary heat source 20 is provided outside the fixing roller 101. In this case, the length of the entire auxiliary heat source (length in the axial direction of the fixing roller) is reduced. Can be. That is, the heat generation area of the auxiliary heat source need only have a width (length in the axial direction of the fixing roller) corresponding to a small-sized sheet. However, as in the fixing device shown in FIG. In this case, since the heat generation area needs to be supported inside the fixing roller, even if the heat generation width is reduced, the width of the entire auxiliary heat source does not become short. Therefore, when the auxiliary heat source is provided outside the fixing roller, there is an advantage that the width of the entire auxiliary heat source can be reduced. This is not limited to the ceramic heater, but also when a nichrome wire heater or a halogen lamp is used as an auxiliary heat source.

FIG. 6 shows another embodiment of the present invention.
FIG. 3 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to an embodiment of the present invention). In the fixing device shown in this figure, a ceramic heater 30 as an auxiliary heat source is disposed inside a hollow pipe-shaped fixing roller 100. Ceramic heater 30
Has a length (length in the roller axis direction) corresponding to the small-size sheet passing area, and is set at a position corresponding to the small-size sheet passing area. Further, the rating of the heater 30 is such that the fixing roller 100
Has a low capacity that is less than the electric power necessary to maintain the temperature at the set temperature (control temperature) only by the heater 30. The configuration of the fixing roller temperature detecting unit and the power supply control unit and the control of the power supply to the main heat source and the auxiliary heat source in this fixing device are the same as those in the embodiment shown in FIGS.

When the auxiliary heat source is provided inside the fixing roller as in the fixing device of the present embodiment, the auxiliary heat source 30 is disposed outside the fixing roller 100 as shown in FIG. The heat of the auxiliary heat source 30 can be efficiently transmitted to the fixing roller 100 without the heat of the auxiliary heat source 30 escaping. Further, the empty space inside the fixing roller 100 can be effectively used, and the space of the fixing device can be reduced.

Next, still another embodiment of the present invention (an embodiment according to claim 5) will be described. In the fixing device of the present embodiment shown in FIG. 8, the hollow pipe-shaped fixing roller 100 includes an insulating layer 2 and a resistance heating layer 3 on the inner surface (inner peripheral surface) of the thin metal base 1 as shown in a partially enlarged view.
Are laminated, and a release layer 4 is formed on the outer surface (outer peripheral surface). On the inner peripheral surface of the fixing roller 100, power receiving electrodes 49 a and 49 b are fixed to both ends of the resistance heating layer 3. The power receiving electrodes 49a and 49b are attached to the power feeding electrodes 41a and 41b by the leaf springs 40 attached to the support plates 12a and 12b.
, And power is supplied to the resistance heating layer 3.

Further, inside the fixing roller 100, a nichrome wire heater 13 is provided as an auxiliary heat source. The heater 13 has a heat generation distribution corresponding to the width of a small-sized transfer sheet. Further, the rating of the heater 13 is such that the temperature of the fixing roller 100 is controlled when the small-size paper is continuously passed.
It has a low capacity that is less than the power required to maintain the set temperature (control temperature) alone. As the heater 13 as the auxiliary heat source, for example, a halogen lamp or a ceramic heater other than the nichrome wire heater can be used.

The power receiving electrodes 49a and 49b have a disc-shaped portion in the roller cross-sectional direction, and the nichrome wire heater 13 has left and right power receiving electrodes 49a at the center of the disc-shaped portion.
a and b are fixedly arranged. Therefore, the receiving electrode 49
The nichrome wire heater 13 as an auxiliary heat source supported by a and b rotates integrally with the fixing roller 100. Both ends of the nichrome wire heater 13 are configured as power receiving electrodes, and power is supplied from power supply electrodes 43a and 43b supported by the support plates 12a and 12b via a leaf spring 42. It goes without saying that the power receiving electrode portion of the heater 13 is electrically insulated from the power receiving electrodes 49a and 49b of the main heat source. The configurations of the temperature detection unit and the power supply control unit of the fixing roller and the power supply control of the main heat source and the auxiliary heat source are the same as those in the embodiment shown in FIGS.

In the present embodiment, the power supply electrodes 41a, 41b to the resistance heating layer 3, which is the main heat source, are
The portions 9a and 9b are in sliding contact with the disc-shaped portions in the roller cross-sectional direction, not the portions in the roller inner surface direction (portions extending in the roller axis direction). That is, by bringing the sliding portion (sliding contact portion) between the power supply electrode and the power receiving electrode close to the center of the fixing roller, the sliding speed of the two can be reduced, and wear of the power supply portion due to sliding friction can be prevented. .

In addition, since the power receiving electrode has a disk-shaped portion in the roller cross-sectional direction, the thin fixing roller 100 having a small mechanical strength is reinforced, and the flattening of the fixing roller in the cross-sectional direction and the deflection of the roller are prevented. it can. In the present embodiment, the auxiliary heat source 13 is fixedly arranged between the pair of power receiving electrodes 49a and 49b provided at both ends of the fixing roller, and the auxiliary heat source 13 functions as a bar for the power receiving electrodes 49a and 49b. Thereby, the power receiving electrodes 49a and 49b do not shift to the inside of the roller, and
a and b press the power receiving electrodes 49a and 49b,
9a and 9b do not shift from a predetermined position.

In this embodiment, the auxiliary heat source 13 is provided inside the fixing roller 100, and the auxiliary heat source is
9a and 9b are fixed at the center of the disk-shaped portion. However, when the auxiliary heat source is provided outside the fixing roller as a ceramic heater, for example, and the heat generating layer of the fixing roller is provided on the inner surface of the roller, the central portion of the power receiving electrode 49 is formed. It is also possible to slide the power supply electrode at a time. That is, when the auxiliary heat source is provided outside the fixing roller, it is not necessary to fix the auxiliary heat source to the center of the disk-shaped portion of the main heat source power receiving electrode, and the center of the disk-shaped portion is used as a sliding surface with the power supply electrode. Because you can do it. In such a configuration, the sliding friction of the power supply unit to the main heat source can be further reduced, and the wear can be further reduced.

Next, still another embodiment of the present invention (an embodiment according to the sixth aspect of the present invention) will be described. The basic configuration of the fixing device of this embodiment is the same as that of the embodiment shown in FIG. 8, and different portions will be mainly described.

In the fixing device of this embodiment shown in FIG. 9, the fixing roller 102 has insulating reinforcing members 50a and 50b inside. The reinforcing members 50 a and 50 b have a disk shape and are engaged with the inner wall of the fixing roller 102. The reinforcing member 50 is not limited to a dish-shaped disk, and may be a disk having radially arranged columns. The nichrome wire heater 53 as an auxiliary heat source includes two reinforcing members 50a and 50b.
It is fixed in between. A communication member 54 is fixed between each of the reinforcing members 50a, 50b and the power receiving electrodes 49a, 49b. A conductive member (not shown) for supplying electric power to the heater 53 is provided in the communication member 54. Alternatively, the communication member 54 itself may be formed of a conductive material. The communication member 54 may be formed separately from the heater 53 or may be formed integrally with the heater 53. The rating of the heater 53 is
When the small-size paper is continuously passed, the fixing roller 102 has a low capacity that is less than the electric power required to maintain the temperature of the fixing roller 102 at a set temperature (control temperature) only by the heater 53.

In this embodiment, in addition to the power receiving electrodes 49a and 49b having a disc-shaped portion, two reinforcing members 50a and 50b are provided.
Is provided, the mechanical strength of the fixing roller can be more firmly increased. Further, the supporting strength of the heater 53 as the auxiliary heat source can be increased, and the fixing of the power receiving electrodes 49a and 49b can be further strengthened.

Further, by reducing the width (length in the axial direction) of the auxiliary heater 53 itself and disposing the connecting members 54 on both sides thereof (on one side of the auxiliary heater when the paper passing reference is one-sided), the strength is improved. And in terms of cost. That is, since a material having higher strength and / or a lower cost than the heater 53 can be used as the connecting member 54, it is more advantageous than forming the whole between the pair of power receiving electrodes 49a and 49b as a heater. It is.

[0040]

As described above, according to the fixing device of the present invention, by providing the auxiliary heat source corresponding to the paper passing area of the small-sized paper, the fixing roller can be formed with a relatively simple structure without increasing the cost. It is possible to prevent a rise in the temperature of the end portion, so that a uniform fixing roller temperature can be obtained regardless of the size of the transfer paper even with a thin fixing roller having a small heat capacity.

According to the configuration of the second aspect, the control for preventing the end portion temperature from excessively rising is very simple, and the cost can be reduced in terms of software. By providing the auxiliary heat source inside the fixing roller, the heat of the auxiliary heat source can be efficiently transmitted to the fixing roller, and the space of the fixing device can be reduced.

According to the fourth aspect of the present invention, the cost of the fixing device can be reduced by using an inexpensive nichrome wire heater as an auxiliary heat source. According to the fifth aspect of the present invention, a disk-shaped portion is provided on the power receiving electrode, and a sliding portion (sliding contact portion) between the power receiving electrode and the power supply member is brought closer to the center of the fixing roller, thereby reducing abrasion of the power supply portion due to sliding friction. be able to. In addition, the thin fixing roller is reinforced by the disc-shaped portion of the power receiving electrode, and it is possible to prevent the fixing roller from being crushed in the cross-sectional direction and the roller from being bent. Then, the auxiliary heat source functions as a stick of the power receiving electrode, thereby preventing the positional deviation of the power receiving electrode.

According to the configuration of the sixth aspect, the fixing roller can be reinforced by the disk-shaped reinforcing member, and the auxiliary heat source and the power receiving electrode can be more firmly fixed to obtain high reliability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to an embodiment of the present invention.

FIG. 2 is a timing chart showing a state of controlling energization of a main heat source and an auxiliary heat source in the embodiment.

FIG. 3 is a flowchart illustrating energization control according to the embodiment.

FIG. 4 is a graph showing a fixing roller temperature when small-size paper is continuously passed in the fixing device of the present embodiment in comparison with a conventional example.

FIG. 5 is a side view showing a main part of a fixing device in which an auxiliary heat source is provided outside a fixing roller as another example of the embodiment.

FIG. 6 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to another embodiment of the present invention.

FIG. 7 is a cross-sectional configuration diagram illustrating an example in which an auxiliary heat source is disposed outside a fixing roller.

FIG. 8 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to still another embodiment of the present invention.

FIG. 9 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller base 2 Insulating layer 3 Heat generation layer 9a, b Power receiving electrode 11a, b Power supply electrode (power supply brush) 13, 20, 30, 53 Auxiliary heat source 14 Temperature sensor 19a, b Power reception electrode 41a, b Power supply electrode (power supply brush) 49a, b Power receiving electrode 50a, b Reinforcing member 100, 101, 102 Fixing roller 200 Pressure roller

Claims (6)

[Claims] An image forming apparatus comprising: a fixing roller that is driven to rotate; and a pressure roller that is pressed against the fixing roller. In the heat fixing device for fixing, the fixing roller is made of a thin hollow cylindrical metal base,
A fixing device comprising: a main heat source in which an electric insulating layer and a heat generating layer are laminated on an inner surface or an outer surface of the hollow cylindrical metal base; and an auxiliary heat source having a heat generating width corresponding to a paper passing width of a small-sized recording paper. apparatus. 2. The auxiliary heat source has a low capacity so that the fixing heat source alone does not maintain the set temperature of the fixing roller when the small-size paper is continuously passed, and the auxiliary heat source is continuously energized when the small-size paper is continuously passed. 2. The fixing device according to claim 1, wherein the fixing roller surface temperature is controlled by controlling the energization of only the main heat source. 3. 3. The fixing device according to claim 1, wherein the auxiliary heat source is provided inside the fixing roller. 4. The fixing device according to claim 3, wherein the auxiliary heat source is a nichrome wire heater. 5. The fixing roller according to claim 1, wherein an electrical insulating layer and a heat generating layer are laminated on an inner surface of the cylindrical metal base, and a power receiving electrode having a disk-shaped portion in a roller cross-sectional direction is provided at both ends of the heat generating layer on the inner surface of the fixing roller. A power supply member is brought into contact with the disc-shaped portion of the power receiving electrode as a sliding surface, and the auxiliary heat source is fixedly arranged at the center of the disc-shaped portion between the pair of power receiving electrodes. Item 5. The fixing device according to item 3 or 4. 6. The fixing device according to claim 5, wherein a disk-shaped reinforcing member that engages with the inner wall of the fixing roller is mounted on the auxiliary heat source.