JP2001249569A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of surely heating unfixed toner regardless of the thickness of a sheet even though heat generating temperature and paper passing speed are not varied. SOLUTION: This fixing device is equipped with a fixing roller 12, a pressure roller 14 rolling in contact with the roller 12 with specified pressure, a heating roller 16 disposed to separate from the roller 12, a fixing belt 20 endlessly laid over the rollers 16 and 12, and a halogen lamp 18 making the belt 20 generate heat so as to heat the unfixed toner on the sheet passing through the rolling part between the rollers 12 and 14, and the unfixed toner is fixed on the sheet by making the sheet on whose surface the unfixed toner is carried pass through the rolling part in one direction. Nip width in a sheet carrying direction at the rolling part is varied.

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 a copying machine, a printer, a facsimile, or the like, for melting and pressing unfixed toner on a recording medium and fixing the toner on the recording medium.

[0002]

2. Description of the Related Art Recently, in a fixing device for an electrophotographic apparatus, as shown in FIG. 4, a fixing roller R1 and a heating / tension roller (hereinafter simply referred to as "heating roller") R.
A technique has been developed that combines a belt fixing method in which a fixing belt B is stretched between the three and a pressing roller R2 that presses from below through the fixing belt B and preheating of the recording medium D. Thereby, the temperature of the nip portion can be set low by preheating, and by using the fixing belt B having a small heat capacity, the temperature of the fixing belt B is rapidly cooled when passing through the nip portion, and the fixing belt B is separated from the fixing belt B at the exit of the nip portion. By increasing the cohesive force of the toner, the releasability between the fixing belt B and the toner is enhanced, and a clear fixed image with no offset can be obtained even when no oil is applied or only a small amount of oil is applied. This device is known as a fixing device that solves the problems of releasability and oil application that could not be solved by the heating roller method.

The configuration of this conventional fixing device will be briefly described below. The fixing device includes a fixing roller R1, a pressure roller R2 disposed immediately below the fixing roller R1, and a side of the fixing roller R1 (an upstream side along a recording medium conveyance direction).
And a heating roller R3 disposed in the fixing roller R1.
A fixing belt B is stretched between the heating roller R3 and the heating roller R3.

An oil application roller R4 is provided above the fixing belt B. Further, a guide plate G as a recording medium support is provided with a gap below the fixing belt B.
And a heating path P for the recording medium is formed between the lower portion of the fixing belt B and the guide plate G. The fixing belt B is
The heating roller R3 is pressed by the pressing lever U in a direction separating from the fixing roller R1 to obtain a desired tension, and is driven by the fixing roller R1 to rotate stably without slipping or loosening. Can be done.

On the other hand, inside the heating roller R3, a heating heater H is provided as a heating source. Also, the heating roller R
3, a thermistor S is provided for measuring the surface temperature. Since the thermistor S measures the temperature of the test portion in the contact state, it is not preferable to make the thermistor S contact the paper passing area of the fixing belt B. Therefore, the thermistor S is brought into contact with the non-paper passing area of the fixing belt B.

[0006]

In the conventional fixing device having the above structure, the nip width of the nip formed between the fixing roller R1 and the pressure roller R2 is unchanged, and the nip width passing through the nip is undetermined. The amount of heat supplied to the recording medium was kept constant. As a result, the heating temperature of the recording medium differs between a thick recording medium having a large heat capacity and a thin recording medium having a relatively small heat capacity. There is a problem that the fixing property cannot be kept constant.

[0007] For this reason, conventionally, a set temperature for fixing is changed according to the thickness of the recording medium to control the amount of heat generation and supply to an unfixed recording medium so as to maintain the fixing property. A method to control the amount of heat, a method to control the amount of heat supplied to the unfixed recording medium so as to keep the fixing property constant by changing the paper passing speed of the recording medium, controlling the passage time in the nip part, etc. Has been developed and put into practical use.

However, in the conventional method in which the amount of current supplied to the heater H is changed, the thicker the recording medium is,
This increases the amount of power supply, increases the heat generation temperature, and may shorten the life of the fixing belt due to thermal influence, which is not preferable. On the other hand, in the conventional method in which the paper passing speed is changed, the thicker the recording medium, the lower the paper passing speed, and the lower the printing speed, which is also undesirable.

[0009] For this reason, the nip width of the nip portion is widened,
Even when a thick recording medium is passed, it is conceivable to heat the unfixed toner without fail so that the fixability is not impaired.

In this case, it is true that the problem can be solved from the viewpoint of heating the unfixed toner on the recording medium. Another problem that the paper curl increases and the high-temperature offset easily occurs is unfavorably generated.

As described above, there is a demand for a fixing device that can reliably heat the unfixed toner on the recording medium even when the thickness of the recording medium is different, and that does not cause the above-mentioned another problem. This problem is caused not only by the thickness of the recording medium but also by the type of the recording medium, for example, the degree of heat absorption differs between the recording medium made of paper and the OHP recording medium. There is a need for a solution as well.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and a main object of the present invention is to provide a recording apparatus which does not change a set temperature for fixing and a paper feeding speed regardless of the thickness of a recording medium. An object of the present invention is to provide a fixing device capable of reliably heating unfixed toner on a medium.

Another object of the present invention is to provide a fixing device capable of reliably heating unfixed toner on a recording medium irrespective of the thickness of the recording medium and free of paper wrinkles. That is.

Another object of the present invention is to provide a fixing device capable of reliably heating unfixed toner on a recording medium irrespective of the material of the recording medium without changing the heat generation temperature or the sheet passing speed. It is to provide.

A further object of the present invention is to provide a fixing device capable of reliably heating unfixed toner on a recording medium irrespective of the material of the recording medium and free of paper wrinkles. It is.

[0016]

Means for Solving the Problems To solve the above-mentioned problems,
In order to achieve the object, according to the first aspect of the present invention, a fixing device includes a fixing roller, a pressing roller that rolls in contact with the fixing roller at a predetermined pressure, and a distance from the fixing roller. A fixing belt provided endlessly around the supporting roller and the fixing roller; causing the fixing belt to generate heat; A heat generating means for heating the unfixed toner, wherein the recording medium having the unfixed toner carried on its surface passes through the rolling contact portion along one direction, so that the unfixed toner is transferred onto the recording medium. The nip width along the transport direction of the recording medium at the rolling contact portion is made variable.

According to a second aspect of the present invention, in the fixing device, the nip width is changed by changing a pressure between the fixing roller and the pressure roller. I have.

According to a third aspect of the present invention, the fixing device is characterized in that the nip width is changed according to the type of the recording medium.

According to a fourth aspect of the present invention, in the fixing device, the nip width when the recording medium is made of paper is larger than the nip width when the recording medium is made of an OHP film. Is also characterized by a narrow setting.

According to a fifth aspect of the present invention, in the fixing device, the nip width is changed according to the thickness of the recording medium.

According to a sixth aspect of the present invention, in the fixing device, the nip width is set wider as the thickness of the recording medium increases.

In the fixing device according to the present invention, the center distance between the fixing roller and the pressure roller is variably set, and the center distance is set to be variable. The fixing roller and the pressure roller are separated from each other when set to the maximum.

Further, according to the fixing device according to the present invention, the heat generating means is built in the supporting roller.

According to a ninth aspect of the present invention, the fixing device is characterized in that the fixing belt is driven to run by at least the support roller.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an embodiment of a fixing device according to the present invention will be described below in detail with reference to the accompanying drawings.

First, as shown in FIG. 1, the fixing device 10 of this embodiment has a housing structure, which is fixed to an electronic image forming apparatus (not shown), for example, a frame of an electronic printer. The housing (not shown) is provided.

Further, the fixing device 10 has a roller configuration, in which a fixing roller 12 is rotatably supported on a housing (not shown) around a fixed axis, and substantially below (specifically, obliquely below) the fixing roller 12. In a state where it is transferred to this,
A pressure roller 14 rotatably supported around a movable axis set in parallel with a fixed axis of the fixing roller 12;
A supporting roller 16 is attached to a swing lever (not shown) in a state substantially above the fixing roller 12, and is supported rotatably about its own central axis.

The fixing device 10 includes a support roller 1
6, a heating source 18 such as a halogen lamp, and a fixing belt (heat transfer belt) 20 endlessly wound around the fixing roller 12 and the support roller 16.
And further provided. That is, in this embodiment, the support roller 16 functions as a heating roller in which the halogen lamp 18 as a heating source is built. In the following description, the support roller 16 will be described as a heating roller.

Here, although the details will be described later, the fixing roller 1
2 is configured as an elastic roller, while the pressure roller 14
Are configured as rollers having a higher on-roller hardness than the elastic roller.

The fixing device 10 includes a fixing belt 2
And an oil applying roller 22 for applying a silicone oil to the outer surface of the fixing belt 20 and cleaning the outer surface of the fixing belt 20. hand,
An urging member (not shown) for applying a predetermined tension to the fixing belt 20 is connected.

The nip portion (contact portion) formed between the fixing roller 12 and the pressure roller 14 is located at the position adjacent to the right side in the drawing (ie, the position adjacent to the upstream side in the recording medium conveyance direction). A guide plate 24 for guiding the unfixed recording medium having the toner carried on the upper surface toward the nip portion is attached.

Here, the guide plate 24 is attached in such a manner as to be inclined upward and diagonally to the left in the figure so that its height increases as it approaches the nip portion. The leading end of the guide plate 24, that is, the upper left end in the figure, is positioned so as to face the nip between the fixing roller 12 and the pressure roller 14.

In the fixing device 10 having such a schematic configuration, the unfixed recording medium S conveyed onto the guide plate 24 via a conveying mechanism (not shown) guides the lower surface on which the unfixed toner is not adhered. The fixing roller 12 is guided and directed toward a rolling contact portion (nip portion) between the fixing roller 12 and the pressure roller 14 around which the fixing belt 20 is wound. By being inserted in this state, the unfixed toner on the recording medium is thermocompression-bonded and fixed on the recording medium. Less than,
The various components described above will be sequentially described individually.

{Description of Fixing Roller 12} The above-described fixing roller 12 includes a core 12A rotatably supported by a side plate 16 via a bearing (not shown), and a core 12A.
And a roller main body 12B around which the fixing belt 20 is wound. The roller outer diameter is set to 30.0 mm in this embodiment. Here, in this embodiment, the core bar 12A has a diameter of 22 mm.
roller body 12B
Is formed of a silicone rubber heat-resistant elastic body (specifically, 15 degrees in JIS A hardness on a roller) attached to the outer periphery of the cored bar 12A with a thickness of 4 mm.

{Description of Pressure Roller 14} The pressure roller 14 described above is composed of a core 14A rotatably supported by a swing arm 32 of a nip width variable mechanism 30 described later, and a core 14A. Roller body 14B coaxially arranged on the outer periphery of
And the roller outer diameter is set to 30 mm. Here, in this embodiment, the core metal part 14A
Is formed from an iron pipe having an inner diameter of 20 mm and an outer diameter of 27 mm, and the roller body 14B is a silicone rubber heat-resistant elastic body attached at a thickness of 1.5 mm to the outer periphery of the cored bar 14A.
(Specifically, a roller having a JIS A hardness of 25 degrees on a roller harder than the fixing roller 12 described above).

A bearing 34 is fitted to a shaft 14C coaxially attached to one end of the core 14A, and is rotatably supported. The pressure roller 14 is axially viewed rotatably by a swing arm 32 of the nip width variable mechanism 30 described later via the bearing 34.

{Description of Heating Roller 16} In this embodiment, the heating roller 16 having the above-described heating source 18 is provided with a 20 mm-thick aluminum pipe core having a diameter of 30 mm and a thickness of 1.5 mm. A PTFE covering layer is coated, and a collar (not shown) made of heat-resistant resin, polyetheretherketone (PEEK), having an outer diameter of 36 mm is inserted into the bearings at both ends. 20 meandering and leaning are prevented.

The heating source 16 is provided inside the heating roller 16.
In this embodiment, the heating source 18 is a halogen lamp 18 having a maximum output of 1 kW.
It is composed of

Although not shown, the heating roller 16
A shaft is integrally formed at one end of the shaft, and a driven gear is coaxially fixed to the shaft to rotatably drive the heating roller 16. Although not shown, a drive gear constituting a drive force transmission mechanism is meshed with the driven gear. That is, in this embodiment, the fixing belt 2
The heating roller 16 is set as a main drive for driving the traveling roller at 0. In other words, the fixing belt 20 is set to be driven to run by at least the heating roller 16.

As described above, since the heating roller 16 is set as the main drive for driving the fixing belt 20 to travel,
The fixing roller 12 is controlled via a nip width varying mechanism 30 described later.
Even if the nip width between the fixing roller 20 and the pressure roller 14 is changed, the traveling speed of the fixing belt 20, that is, the traveling speed of the unfixed sheet (the so-called linear speed) does not change, and a constant speed is maintained. Can be done.

In other words, in a configuration in which at least one of the fixing roller 12 and the pressure roller 14 is driven to rotate to convey an unfixed sheet, the elastic deformation of the elastic portion in the nip portion is caused by a change in the nip width. This causes the outer diameter of the roller at the nip to change. As described above, when the outer diameter of the driving roller changes, the peripheral speed changes in accordance with the change of the outer diameter, and it is apparent that the running speed of the fixing belt 20 changes. On the other hand, in this embodiment, since the fixing belt 20 driven and driven by the heating roller 16 is employed, the rotation speeds of the fixing roller 12 and the pressure roller 14 are defined by the fixing belt 20. Therefore, a specific effect that a constant linear velocity is always achieved is achieved.

{Description of Fixing Belt 20} The fixing belt 20 described above can fix the unfixed toner on the unfixed recording medium S without applying an excessive amount of heat to the fixing temperature.
The heat capacity per square cm of the fixing belt 20 is
Those in the range of 0.002 cal / ° C to 0.025 cal / ° C are preferred. For this reason, in this embodiment, the fixing belt 20 has an inner diameter of 55 mm and a thickness of 40 μm, an endless nickel-electroformed belt substrate, and a 200 μm thick outer peripheral surface (surface layer) of the belt substrate.
And a heat-resistant elastic release layer made of silicone rubber coated with a silicone rubber.

Next, the above-described variable nip width mechanism 30 will be described. As shown in the figure, the variable nip width mechanism 30 includes a swing arm 32 pivotally supported at one end (left end in the drawing) around a support shaft 36.
At the other end (right end in the figure) of the shaft 14C of the pressure roller 14.
Recess 3 for removably receiving bearing 34 fitted in
2A is formed. That is, in a state where the shaft portion 14 </ b> C is received in the recess 32 </ b> A of the swing arm 32 via the bearing 34, the pressure roller 14 applies a force to the fixing roller 12 in accordance with the swing of the swing arm 32. The pressing force can be changed, in other words, the nip width of the nip between the fixing roller 12 and the fixing roller 12 can be changed.

On the other hand, in order to drive the swing arm 32 to swing, an eccentric disk cam 38 is provided below the swing arm 32.
, And is in rolling contact with the lower surface of the swing arm 32 from below. The eccentric disk cam 38 has a rotation center eccentric from the center of the disk, and a drive shaft 42 that is rotationally driven by a drive motor 40 is integrally connected to the rotation center.

The drive motor 40 is connected to a control device (not shown), and is driven and controlled in accordance with the control procedure of the control device.
An OHP mode for fixing unfixed toner carried on an OHP film as shown in FIG. 1 and an unfixed toner carried on color paper (for example, 80 g / m 2 paper) as shown in FIG. In the color paper mode for fixing the toner, the pressing roller 14 is connected to the fixing roller 12 as shown in FIG.
, And is set to be switchable from three modes of the pressure release mode for releasing the pressure between the two modes to an arbitrary mode.

In the state in which the OHP mode is set, as shown in FIG. 1, the eccentric disk cam 38 has a longest cam surface whose distance from the center of rotation is the longest. The swing arm 32 is set to be displaced to the uppermost position. In the state where the OHP mode is set as described above, the nip pressure is 25 k on one side.
gf and the nip width nw based on this nip pressure
Is set to be 7.6 mm in arc distance.

In the state where the color paper mode is set, as shown in FIG. 2, the eccentric disk cam 38 has an intermediate cam surface at an intermediate distance from the center of rotation.
, And the swing arm 32 is set to be displaced to a lower position than in the OHP mode.
In the state where the color paper mode is set as described above,
The nip pressure is set to 20 kgf on one side, and the nip width nw based on this nip pressure is set to be 6.9 mm in arc distance.

In the state where the pressure release mode is set, as shown in FIG. 3, the eccentric disk cam 38 has the shortest cam surface whose distance from the center of rotation is the shortest.
From below, and the swing arm 32 is
4 is set to allow the fixing roller 4 to be separated downward from the fixing roller 12. In the state where the pressure release mode is set as described above, the pressing roller 14 and the fixing roller 1
2, the nip pressure is 0 kgf and the nip width nw is also 0 mm.

In this pressure release mode, the pressure roller 14 is separated from the fixing roller 12 without fail.
A coil spring 44 for urging the swing arm 32 downward is connected to the other end of the swing arm 32.

The fixing device 10 configured as described above is mounted on a printer (trade name: Pretail 550) manufactured by Ricoh Company, where an unfixed toner image is transferred to color paper and an OHP film. The unfixed recording medium carrying the toner is fixed to the fixing device 10 at a fixing temperature of 165 ° C., and the paper passing speed (passing speed of the nip portion) is set to 90.
The fixing operation was performed at mm / sec.

Here, when the OHP film is passed, the OHP mode is set as shown in FIG. 1, the fixing pressure is set to 25 kgf / one side, and the nip width is set to 7.6 mm. As a result, the unfixed toner image on the OHP film was fixed by the fixing device 10 in the OHP mode. As a result, no problem occurred in the fixing property.

On the other hand, when the color paper is passed, the color paper mode is set as shown in FIG.
5. Set to 0 kgf / one side, thereby setting the nip width to 6.
9 mm. As a result, the unfixed toner image on the color paper is fixed by the fixing device 10 in the color paper mode.
No problem occurred in the fixing property.

As described above in detail, in this embodiment, even when the fixing temperature in the nip portion is fixedly set at 165 ° C., the fixing is performed in a state unique to each of the OHP mode and the color paper mode. 25kg pressure
f / one side, and 20 kgf / one side. By setting the nip width to 7.6 mm and 6.9 mm, respectively, in the OHP film and the color paper,
The unfixed toner image is reliably fixed.

As described above, since the sheet passing speed is not changed, the number of printed sheets is not reduced by changing the sheet passing speed as before, and the fixing temperature is not changed. Changing the fixing temperature does not cause a reduction in the life of the fixing belt due to thermal effects, and it is possible to achieve reliable fixing by selecting the optimal nip width according to the material of each recording medium. As a result, a good fixing device free from defects can be achieved from the viewpoint of the structure of the fixing device and the life.

Further, in this embodiment, since the pressure release mode is set, for example, even when a paper jam occurs in the fixing device 10, the pressure release mode is set so that the fixing roller 12 and the fixing roller 12 are connected. The recording medium is immediately separated from the pressure roller 14, and the jammed recording medium can be easily removed. In this way, the fixing device 10 is very easy to use against paper jams.

Further, by setting the pressure release mode corresponding to the power-off, when the fixing device 10 is not used, the fixing roller 12 and the pressure roller 14 are separated from each other, and no pressure contact force is generated. State. As a result, even if the non-use state of the fixing device 10 is extended for a long period of time, since the pressing roller 14 is separated from the fixing roller 12, the outer peripheral surface of the fixing roller 12 is dented by the pressing roller 14. Is reliably avoided, and the fixing roller 12
The occurrence of a defective fixed image due to the depression on the outer peripheral surface of the above-mentioned is effectively prevented.

{Verification of Fixing Temperature} In the present invention, the nip width is changed in accordance with the material of the recording medium while the fixing temperature is kept constant, so that a good quality matching the material of the recording medium is obtained. An important point here is that by changing the nip width in this way, a fixing temperature common to the recording medium materials that achieves the fixing property can be achieved because the fixing property is achieved. is there. Therefore, in the configuration of the above-described embodiment, the fixing pressure is set to 10 kgf / one side,
Five types of 5 kgf / one side, 20 kgf / one side, 25 kgf / one side, 30 kgf / one side are set (accordingly, the nip width is 5.2 mm, 6.2 mm, 6.9 mm, and 7.
6 mm and 8.1 mm), and the fixing temperature range was verified for each of the color paper and the OHP film. The paper passing conditions are the same as those in the above-described embodiment except for the nip width. The results are shown in Table 1 below.

[0058]

[Table 1]

As is apparent from Table 1, when the fixing temperature is set in the range of 160 ° C. to 165 ° C., the nip width of the OHP film is from 7.6 mm to 8.1 m.
m, and in the case of color paper,
Nip width from 5.2mm to 8.1mm (ie full range)
It was found that good fixing performance was attained by setting.

Therefore, in the above-described embodiment, the nip width is set to 7.6 mm in the OHP mode and 6.9 mm in the color paper mode, so that the fixing temperature is fixed. That good fixing performance was achieved was also supported by data.

[0061]

DESCRIPTION OF OTHER EMBODIMENTS It goes without saying that the present invention is not limited to the configuration of the above-described embodiment, but can be variously modified without departing from the gist of the present invention.

For example, in the above-described embodiments, the nip width has been described as being adaptable to two types of the OHP film and the color paper. However, the present invention is not limited to such a configuration. For example, even when the material of the recording medium is paper, the nip width may be changed according to the thickness of the recording medium.

That is, in the fixing device of another embodiment,
Since the above-described color paper can be regarded as thick paper, a thick paper mode for fixing thick paper, a plain paper mode for fixing plain paper (64 g / sq. M), and a thin paper (52 g / sq. The three fixing modes, i.e., the thin paper mode for fixing m), can be switched and set.

Here, as in the above-described embodiment, the results of verifying the common fixing temperature in these three modes are shown in Table 2 below.

[0065]

[Table 2]

As is apparent from Table 2, the fixing temperature was 1
By setting the temperature to 65 ° C., the optimum nip width can be set for each of the three modes.

In particular, in the case of thin paper, the nip width can be set narrow, that is, the fixing pressure can be set weak, so that the effect of effectively suppressing the occurrence of paper wrinkles can be achieved. Will be done.

Further, in the above-described embodiment, the coil spring 44 for urging the swing arm 32 so as to pull the swing arm 32 downward has been described. Even if such a coil spring 44 is not provided, the structure may be such that the swing arm is naturally lowered by its own weight.

In the above-described embodiment, the fixing pressure is changed by using a configuration in which the swing arm 32 and the eccentric cam 38 are combined and the eccentric cam 38 is directly brought into contact with the swing arm 32. However, the present invention is not limited to such a configuration, and a spring is interposed between the swing arm 32 and the eccentric cam 38, and the spring force is changed by rotating the eccentric cam 38. Alternatively, the fixing pressure may be changed.
In short, any structure can be used as long as the fixing pressure can be changed.

[0070]

As described above in detail, according to the present invention, the unfixed toner on the recording medium can be obtained regardless of the thickness of the recording medium without changing the set temperature for fixing or the paper feeding speed. Is provided, which can reliably heat the fixing device.

According to the present invention, there is provided a fixing device capable of reliably heating unfixed toner on a recording medium regardless of the thickness of the recording medium and free of paper wrinkles. become.

Further, according to the present invention, there is provided a fixing device capable of reliably heating unfixed toner on a recording medium irrespective of the material of the recording medium without changing the heat generation temperature or the sheet passing speed. Will be done.

Further, according to the present invention, it is possible to provide a fixing device which can surely heat unfixed toner on a recording medium irrespective of the material of the recording medium and which does not generate paper wrinkles. Become.

[Brief description of the drawings]

FIG. 1 is a front view schematically showing a configuration of an embodiment of a fixing device according to the present invention in a state where an OHP mode is set.

FIG. 2 is a front view schematically showing a configuration of an embodiment of a fixing device according to the present invention in a state where a color paper mode is set.

FIG. 3 is a front view schematically showing a configuration of one embodiment of a fixing device according to the present invention in a state where a pressure release mode is set.

FIG. 4 is a diagram schematically showing a configuration of a conventional belt-type fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fixing apparatus 12 Fixing roller 12A Core part 12B Roller body 14 Pressure roller 14A Core part 14B Roller body 14C Shaft part 16 Heating roller 18 Heat source (halogen lamp) 20 Fixing belt 22 Oil application roller 24 Guide plate 30 Nip width Variable mechanism 32 Swing arm 34 Bearing 36 Support shaft 38 Eccentric disk cam 40 Drive motor 42 Drive shaft 44 Coil spring

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H033 AA06 BA11 BA26 BB01 BB12 BB17 BB33 BB35 CA16 CA39 3F049 AA10 BB07 CA32 CA33 DA04 DA19 EA21 LA02 LA05 LA07 LB03 3J103 AA02 AA85 BA02 BA43 FA01 GA57 GA58 GA60

Claims (9)

[Claims] An image forming apparatus comprising: a fixing roller; a pressure roller that rolls in contact with the fixing roller at a predetermined pressure; a support roller disposed apart from the fixing roller; And a heat generating means for heating the unfixed toner on the recording medium passing through the rolling contact portion of the fixing roller and the pressure roller. The recording medium carried by the fixing device fixes the unfixed toner on the recording medium by passing the contact portion along one direction, in the conveying direction of the recording medium in the contact portion A fixing device characterized by having a variable nip width along the same. 2. The fixing device according to claim 1, wherein the nip width is changed by changing a pressure between the fixing roller and the pressure roller. 3. The fixing device according to claim 1, wherein the nip width is changed according to a type of a recording medium. 4. The nip width when the recording medium is made of paper is set to be narrower than the nip width when the recording medium is made of an OHP film. Fixing device. 5. The fixing device according to claim 1, wherein the nip width is changed according to the thickness of the recording medium. 6. The fixing device according to claim 5, wherein the nip width is set wider as the thickness of the recording medium increases. 7. The fixing roller and the pressure roller have a variable center-to-center distance, and when the center-to-center distance is set to a maximum, the fixing roller and the pressure roller are separated from each other. The fixing device according to claim 1, wherein the fixing devices are separated from each other. 8. The fixing device according to claim 1, wherein said heat generating means is incorporated in said support roller. 9. The fixing device according to claim 1, wherein the fixing belt is driven to run by at least the support roller.