JP2002123121A - Image fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image fixing device constituted so that the excessive rising of temperature at both ends on a fixing roller is restrained even in the case of consecutively processing paper whose width is smaller than heating width on the fixing roller by simple constitution. SOLUTION: In this image fixing device where a temperature uniformizing roller is disposed so that it can be in press-contact with the fixing roller and it can be released from the press-contact therewith, an angle formed by the shafts of the temperature uniformizing roller and the fixing roller is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image fixing device which can be used in an electrophotographic image forming apparatus such as a copying machine and a printer.

[0002]

2. Description of the Related Art A recording paper carrying a toner image (hereinafter, referred to as paper) is guided to an image fixing device called a heating roller type fixing device, and a rotatable fixing roller having a built-in heating source and the fixing roller are provided. 2. Description of the Related Art An image fixing apparatus is known which is configured to pass between a pressure roller and a rotating pressure roller while pressing the toner image, and to fix the toner image on the sheet by a pressure and a heating action applied by the two rollers.

Further, in the above-mentioned image fixing device, a temperature control technique for controlling the temperature of the surface of the fixing roller to be within a predetermined temperature range is also known.

[0004]

The above-mentioned image fixing device has good handleability and can be made compact.
It is extremely useful, for example, because of its high safety. It is incorporated in many image forming apparatuses and is still conveniently used today.

However, the roller core of the fixing roller is
For example, the following inconvenience arises when it is made of glass so as to enable quick warm-up.

That is, when a sheet having a width smaller than the heating width must be continuously processed, the roller core has a lower thermal conductivity than a roller using a metal core. Even if a good fixing process can be performed, the temperature outside the contact area with the sheet, in other words, the temperature at both ends of the heating width on the fixing roller excessively rises, and in this state, the sheet having a large width is increased. Is a problem that gloss unevenness is generated on the paper corresponding to the boundary between the temperatures. Although a technique of disposing a cooling fan in order to prevent a temperature rise at the end has been proposed, there is a problem that thermal efficiency is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and a main object of the present invention is to provide a simple configuration, even when a sheet having a width smaller than a heating width on a fixing roller is continuously processed. An object of the present invention is to provide an image fixing device configured to be able to suppress an excessive rise in temperature at both ends on a roller.

[0008]

The object of the present invention can be achieved by the following constitution.

In an image fixing apparatus provided with a temperature equalizing roller capable of pressing and releasing the fixing roller from the fixing roller, the angle between the axes of the temperature equalizing roller and the fixing roller can be changed. An image fixing device comprising:

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fixing device according to the present invention will be described below with reference to the drawings. Prior to this, the overall configuration of an image forming apparatus will be described. FIG.
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus including a color printer.

In FIG. 1, reference numeral 10 denotes a photosensitive drum (hereinafter, simply referred to as a drum) as an image forming body; 11, a scorotron charger as charging means for each color; and 12, exposure optics as image writing means for each color. Reference numeral 13 denotes a developing device that is a developing unit for each color, and 14 denotes a transfer belt.

The drum 10 is formed, for example, by forming a transparent conductive layer, an a-Si layer or an organic photosensitive layer (OPC) on the outer periphery of a cylindrical base formed of a transparent member such as optical glass or transparent acrylic resin. Photosensitive layer (also called photoconductive layer)
And rotated clockwise as indicated by the arrow with the conductive layer grounded.

The scorotron charger 11, the exposure optical system 12, and the developing device 13 form an image forming means for each of yellow (Y), magenta (M), cyan (C) and black (K). And four sets are arranged in the order of Y, M, C, and K with respect to the rotation direction of the photosensitive drum 10.

The scorotron charger 11 has a control grid maintained at a predetermined potential and a discharge electrode 11a composed of, for example, a saw-tooth electrode, and has a corona discharge having the same polarity as the toner (in this embodiment, Negative charge)
As a result, a uniform potential is applied to the photosensitive drum 10.

The exposure optical system 12 is disposed inside the drum 10 so as to be located on the downstream side in the rotation direction of the photosensitive drum 10 with respect to the scorotron charger 11 described above.

Each exposure optical system 12 has a linear exposure element 12a in which a plurality of LEDs (light emitting diodes) as light emitting elements of image exposure light arranged in the main scanning direction in parallel with the drum axis are arranged in an array. And a light converging light transmitter (trade name: Selfoc lens array) 12b as an imaging element
And a lens holder (not shown), which is attached to a holding member 120.

In addition to the exposure optical system 12 for each color, a transfer simultaneous exposure unit 12d and a uniform exposure unit 12e are attached to the holding member 120, and are integrally accommodated in the base of the drum 10.

The exposure optical system 12 performs image exposure of the photosensitive layer of the drum 10 from the back side in accordance with image data for each color read by a separate image reading device and stored in a memory. Form a latent image.

As the exposure element 12a, besides LED, F
It is also possible to use a plurality of light-emitting elements such as L (phosphor emission), EL (electroluminescence), and PL (plasma discharge) arranged in an array.

The emission wavelength of the exposure element is usually Y, M,
A toner having a high transmittance in the range of 780 to 900 nm for the C toner is used. However, in this embodiment, since the image is exposed from the back surface, the toner does not have sufficient transmittance for the color toner. 400-780 shorter than this
nm wavelength.

The developing unit 13 includes a developing sleeve 13 made of a non-magnetic stainless steel or aluminum material that rotates in the forward direction at the closest point to the rotation direction of the drum 10.
1 and a developing casing 138, in which a one-component or two-component developer of yellow (Y), magenta (M), cyan (C) and black (K) is accommodated, respectively. ing.

Each of the developing devices 13 is kept in a non-contact state with a predetermined gap from the drum 10. By applying a developing bias in which a DC voltage and an AC voltage are superimposed on the developing sleeve 131, Contact reversal development is performed to form a superimposed toner image on the drum 10.

Reference numerals 14a and 14b denote the transfer belt 14
The transfer belt 14a receives power from a drive source (not shown) and rotates the transfer belt in the direction of the arrow.

Reference numerals 15 and 16 denote transfer units and static eliminators, which are first and second transfer means disposed opposite to the drum 10 with the transfer belt 14 interposed therebetween, and 17 denotes the drum 10 after the transfer step. AC static eliminator for static elimination, 1
Reference numeral 8 denotes a cleaning device that cleans the drum surface after static elimination, and has a cleaning blade 180.

Reference numeral 20 denotes a cassette containing paper P for transferring a toner image formed on the drum 10, and reference numeral 25 denotes a paper feed roller.

A transport roller pair R1
R5, the transfer belt 14, an image fixing device (hereinafter simply referred to as a fixing device) 30, and the like.

Reference numeral 44 denotes an AC static eliminator for separating paper, which is disposed to face the roller 14a via the transfer belt 14.

As will be described in detail later, the fixing device 30 has a built-in halogen heater (halogen lamp) 300, and a fixing roller 305 that can rotate around the halogen heater. And a pressure roller 315 that can be used. T indicates a nip portion.

The roller core of the fixing roller 305 is made of a light-transmissive base material.
It was made of glass having a thickness of 1.6 mm.

In addition, on the outside (outer periphery) of the roller core,
A transparent silicon rubber layer is formed, and a heat-resistant tube made of PFA (perfluoroalkoxy) having a high light absorption by mixing carbon black or the like is covered on the outside thereof.

The pressure roller 315 has a silicone rubber surface provided on an appropriate roller core.

In the drawing, reference numeral 46 denotes a separating claw for reliably separating the sheet P after the transfer, which is fed integrally with the transfer belt 14, and has a leading end with respect to the surface of the transfer belt 14 on the roller 14a. It is positioned in close proximity.

The image forming process in the image forming apparatus having the above configuration is as follows.

At the start of image formation, a drum drive motor (not shown) is started, and the drum 10 is rotated clockwise as shown by the arrow in FIG. 1, and at the same time, the yellow (Y) scorotron charger 11 is operated to activate the drum 10 To a predetermined potential.

Subsequently, the image writing by the first color signal, ie, the electric signal corresponding to the Y image data is started via the Y exposure optical system 12, and the Y image of the original image is formed on the surface of the drum 10. A corresponding electrostatic latent image is formed.

The electrostatic latent image is reversely developed by the Y developing device 13 in a non-contact state, and a yellow (Y) toner image is formed on the drum 10.

Next, the magenta (M) scorotron charger 1 is applied to the drum 10 from above the Y toner image.
A potential is applied by the charging action of M, and the exposure optical system M of M
2, an electrostatic latent image corresponding to the M image is formed by image writing using an electrical signal corresponding to the second color signal, that is, M image data, and the non-contact reversal development by the M developing device 13 causes A magenta (M) toner image is formed over the yellow (Y) toner image.

By the same process, the cyan (C) toner image corresponding to the third color signal is superimposed by the cyan (C) scorotron charger 11, the exposure optical system 12 of C, and the developing device 13 of C. The black (K) toner image corresponding to the fourth color signal is sequentially superimposed thereon by a black (K) scorotron charger 11, a K exposure optical system 12, and a K developing device 13. A superposed color toner image of four colors of yellow (Y), magenta (M), cyan (C) and black (K) is formed on the peripheral surface within one rotation of the photosensitive drum 10. .

These Y, M, C and K exposure optical systems 1
2 for writing an image on the photosensitive layer of the drum 10
It is performed from the inside of the drum 10 through the above-mentioned translucent substrate.

Accordingly, the writing of the images corresponding to the second, third and fourth color signals is performed without any influence from the previously formed toner image, and corresponds to the first color signal. It is possible to form an electrostatic latent image equivalent to an image.

The drum 1 is formed by the above-described image forming process.
The superimposed color toner images formed on the sheet P are collectively transferred onto the sheet P by the transfer device 15.

At this time, the simultaneous exposure device 12d provided inside the drum 10 is energized to perform uniform exposure so that good transfer is performed.

The toner remaining on the peripheral surface of the drum 10 after the completion of the transfer process is subjected to a static elimination action by the AC static eliminator 17 and then cleaned by a cleaning device 18, whereby the surface of the drum 10 is moved to the next position. Provided for image formation.

In the embodiment, after the cleaning and before the next charging, the uniform exposure device 12e using, for example, a light emitting diode is operated to eliminate the history of the preceding image formation on the drum surface.

The paper P on which the color toner image has been formed (transferred) is separated from the transfer belt 14 by the static elimination action of the AC static eliminator 44 and the separation claw 46, and is conveyed to the fixing device 30 to be fixed. In the above, the toner image is fixed on the paper P.

The paper P on which the image has been recorded is sent upside down, and is discharged to a tray at the top of the apparatus via transport rollers R3, R4 and R5.

FIG. 2 is a schematic side sectional view for explaining the configuration of the fixing roller 305, the pressure roller 315, and the temperature equalizing roller 330, which are main elements of the fixing device 30.

In the figure, a fixing roller 305 is provided on a side which comes into contact with an unfixed toner image on a sheet of paper P (not shown). The fixing roller 305 and the pressure roller 315 are pressed (contacted) with a predetermined pressure, and rotate in the same direction at the contact portion (nip portion T) while maintaining the pressed state during operation.
The unfixed toner image is fixed by heating and pressing.

As described above, the fixing roller 305 is a roller core 30 made of a cylindrical light-transmitting substrate (such as glass).
7, a light-transmitting elastic layer (transparent silicon rubber layer) 308 provided outside (outer peripheral surface) of the roller core 307, and a heat ray absorbing layer (also a release layer for toner) 309 provided outside thereof. have.

The pressure roller 315 includes, for example, a cylindrical metal pipe 316 made of aluminum and a metal pipe 3.
For example, the outer peripheral surface of the roller 16 is formed as a soft roller in which a silicone rubber layer 317 is coated.

Temperature uniform roller 330 according to the present invention
Has a configuration in which a roller 332 and a shaft 331 are main elements, a temperature sensor TS is disposed on an outer peripheral surface of the roller unit 332, and a pressure is applied to the fixing roller 305 by an outer peripheral surface of the heat ray absorbing layer 309. I have. The temperature sensor TS detects the surface temperature of the roller section 332, and the detection information is used as information necessary for selecting the pressure equalization roller 330 to the fixing roller 305, the pressure release, and the selection of the angle. , Which are taken into the control unit of the image forming apparatus.

The light-transmissive substrate (roller core) 307 constituting the fixing roller 305 is not limited to glass, which is defined as an inorganic substance obtained by cooling and solidifying a melt without depositing crystals. Pyrex (registered trademark) glass, sapphire (Al ₂ O ₃ ), CaF that transmits light from an irradiation member such as a halogen heater 300 (halogen lamp)
_2, such as a transparent material using a ceramic material, polyimide, polyamide or the like, so as to efficiently absorb heat rays such as a halogen lamp or a xenon lamp disposed inside the roller core, Fluorine resin (PF) mixed with powder of carbon black, graphite, iron black (Fe ₃ O ₂ ), various ferrites, etc. outside the transparent silicon rubber layer
A) A tube can be provided to form the above-mentioned heat ray absorbing layer.

As another configuration of the fixing roller, a heat-ray-permeable rubber layer made of silicon rubber mixed with a powder of a metal oxide such as silica, alumina or magnesium oxide as a filler is provided outside the roller core as described above. A heat ray absorbing layer containing powders of carbon black, graphite, iron black, various ferrites and their compounds, copper oxide, cobalt oxide, red iron oxide, etc., and a fluororesin paint which also serves as a binder and a release agent. There is a wide range of design freedom related to the configuration of the fixing roller, for example, an integrated heat ray absorbing layer may be formed integrally with the mixed release layer.

FIG. 3 is a schematic view for explaining the structure of one of the pressure-compression and pressure-releasing mechanisms of the temperature equalizing roller according to the present invention, and FIG. 4 is a diagram in which the axes of the fixing roller and the temperature equalizing roller coincide with each other. And FIG. 5 is a schematic diagram showing a state of a gap when the fixing roller and the temperature equalizing roller are pressed against each other.

3 and 4, reference numeral 305 denotes a fixing roller, 315 denotes a pressure roller, and 330 denotes a temperature uniforming roller.

The configuration of the temperature equalizing roller 330 is similar to that of the shaft 33.
1 and the roller section 332 as main elements,
The left and right end portions 2 are formed with gentle curved surfaces so as not to cause mechanical damage to the fixing roller 305.

In this embodiment, the temperature equalizing roller 330 is formed by applying a fluorine coating to the surface of a solid roller (round bar) made of an aluminum material having an outer diameter of 10 mm. As described later, the temperature equalizing roller 330 in the embodiment requires particularly good heat conduction,
It is desirable to use a material having high thermal conductivity such as aluminum or copper. The application of a heat pipe is also effective.

The temperature equalizing roller 330 is a fixing roller 3
The fixing device 305 is configured to be able to rotate by following the fixing roller 305, and to release the pressure. In addition, the angle between the axis of the temperature equalizing roller 330 and the axis of the fixing roller 305 is variable.
It is possible to change the range in which a gap can be formed in the contact portion when the contact portion is pressed. By combining the change in the range with the pressing and releasing operations of the temperature equalizing roller 330, the object is to reduce unevenness of the temperature distribution on the fixing roller 305 as a result.

Reference numeral 334 denotes a movable side plate which is configured to be swingable about a fulcrum 336 fixed to a fixing device main body frame (not shown) as a rotation axis, and a hole provided at one end of the movable side plate 334. H1 has a groove G1 fitted to the fulcrum 336 and extending in the longitudinal direction at the other end. The shaft 331 of the temperature equalizing roller 330 is held by a bearing 333, and the bearing 333 is formed by a groove G1 of the movable side plate 334.
Is slidably mounted on. The bearing 333 is urged toward the fixing roller 305 by a spring SP. The shaft 331 is urged via the bearing 333, and as a result, the temperature equalizing roller 330 is fixed to the fixing roller 305.
Will be crimped.

Reference numeral 337 denotes a pressure release lever for releasing the pressure of the temperature equalizing roller 330 against the fixing roller 305. The pressure release lever 337 has, at its longitudinal end, a hole H2 rotatably fitted to a fulcrum 338 fixed to a fixing device body frame (not shown). It has a groove G2 extending in the direction.
One shaft 33 of the temperature equalizing roller 330 is provided in the groove G2.
1 is slidably fitted. Crimping release lever 33
7 receives a load against the load of the spring SP by a known means such as a motor, a solenoid, or a cam mechanism (not shown), and is urged in the direction of the arrow with the fulcrum 338 as a rotation axis. Roller 33
By pressing 0 away from the fixing roller 305, the pressure bonding is released.

As can be seen from FIG. 4, the pressing and releasing mechanism of the temperature equalizing roller 330 is substantially symmetric with respect to the fixing roller 305. The same reference numerals are given to those having the same structure on the left and right.

In the embodiment, the movable side plate 334 is
, And lifts only one shaft 331 of the temperature equalizing roller 330 in the direction of the arrow.
The fixed side plate 335 is fixed to a fixing device main body frame (not shown). That is, the fixed side plate 335 has the same outer shape and groove shape as the movable side plate 334, but the movable side plate 334.
Is fixed to a fulcrum 336, while the fixed side plate 335 is fixed to the fixing device body frame by screws (not shown). The other shaft (fixed-side shaft) 331 of the temperature equalizing roller 330 is, similarly to the one shaft 331, a bearing (fixed-side bearing) slidably disposed in a groove of the fixed side plate 335. 333. The predetermined pressure at which the temperature equalizing roller 330 is pressed against the fixing roller 305 is such that one end of each of the two left and right springs SP presses the two left and right bearings 333, and the temperature equalizing roller 330 is fixed via the shaft 331. It is obtained by crimping to 305.

The movable side plate 334 is set so that the center of rotation is
By rotating the motor in a direction indicated by an arrow (see FIG. 3), for example, using a motor (not shown) capable of reversible rotation as a driving source, the temperature equalizing roller 330 and the fixing roller 3 are rotated.
05 can be tilted by a certain angle (the position indicated by the two-dot chain line in FIG. 4). Further, by rotating the motor in the reverse direction, the fixing roller 3 before the temperature equalizing roller 330 is tilted.
It is also possible to return to a position parallel to 05 (hereinafter referred to as a reference position).

The drive control of the motor may be performed by rotating the motor forward or backward with the reference position of the temperature equalizing roller 330 as the origin. The drive time of the motor may be controlled by an appropriate drive control unit. it can. As a matter of course,
The drive control unit stores the position of the temperature equalizing roller 330, and includes an operation unit that determines whether the rotation of the motor is normal or reverse depending on the condition described later.

As shown in FIG. 5, when the temperature equalizing roller 330 is pressed against the fixing roller 305, the temperature equalizing roller 3 is pressed.
The characteristics of the gap formed by the fixing roller 30 and the fixing roller 305 will be described.

FIG. 5A is a schematic diagram showing a gap between the temperature equalizing roller 330 and the fixing roller 305 when the temperature equalizing roller 330 is at the reference position, and FIG.
FIG. 10 is a schematic diagram illustrating a gap between the shaft 331 of the fixing roller 305 and a shaft 331 of the fixing roller 305 at a maximum inclination.

In the drawing, a range indicated by reference numeral R is a heating area in which the fixing roller 305 can perform the fixing process (a maximum sheet width of a usable sheet in a direction perpendicular to the transport direction), and a range indicated by reference numeral S is 3 shows a heating area necessary for a small sheet of usable sheets.

In FIG. 5A, the temperature equalizing roller 3
Shafts 331 at both ends of 30 are springs SP (see FIG. 3) disposed on side plates 334 and 335 (see FIG. 4).
As a result, a predetermined load F1 is received through the bearing 333 (see FIG. 4). The temperature equalizing roller 330 receiving the load on the shafts 331 at both ends presses the fixing roller 305, but at the same time, receives the reaction force F2 from the fixing roller 305. As shown in the figure, the temperature equalizing roller 330 applies the reaction force F
2 and the load F1 to bend under a bending force,
At both ends, the fixing roller is strongly pressed, but at the center, a gap is formed apart from the fixing roller 305. Therefore, the contact area between the temperature equalizing roller 330 and the fixing roller 305 at the nip is larger at the end and smaller at the center.

At the reference position, a range (length in the axial direction of the fixing roller) T at which a gap is formed in the center portion is determined by the length and rigidity of the temperature equalizing roller 330, the elasticity of the rubber layer 308 of the fixing roller 305, and It changes depending on the value of the load of the spring SP and the like, and these values can be selected and appropriately determined.

The value of the range T where the gap can be formed is, for example,
By changing the load F1 of the spring SP so as to be substantially the same as the value of the required heating area S for the small paper among the usable papers, the temperature uniforming roller 330 The range of the contact portion coincides with the region of both ends of the fixing roller 305 which is excessively heated during the continuous fixing process of the small width paper, and the high heat at both ends is transferred to the temperature equalizing roller 330. become. As described above, the contact area between the temperature equalizing roller 330 and the fixing roller 305 increases toward the end and gradually decreases toward the center, so that the temperature distribution of the fixing roller 305 becomes gentle, and Even after fixing large-size paper, gloss unevenness can be reduced so as not to be visually recognized.

In FIG. 3, when the movable side plate 334 is rotated by the reversible motor (not shown), a temperature uniforming roller is formed via the groove G 1, the bearing 333, and the shaft 331 of the movable side plate 334. The angle formed by the axis of the fixing roller 305 and the axis of the fixing roller 305 can be changed (tilted from the reference position by a predetermined angle), whereby the value of the range T where the gap can be formed at the reference position can be changed. . That is, the temperature equalizing roller 330
Is at the reference position, the range T in which the gap is formed is the maximum, and as the movable side plate 334 is rotated, the range T in which the gap is formed becomes smaller accordingly. FIG. 5 (b)
When the movable side plate 334 is rotated to the maximum, the range where the gap can be formed becomes substantially zero, and the temperature uniforming roller 3
The surface of the contact portion of the fixing roller 30 extends over almost the entire area in the longitudinal direction.
FIG. 5 shows a state of being press-bonded to the outer peripheral surface of a part No. 05.

The temperature equalizing roller 330 is connected to the fixing roller 30.
5 is determined by the control of the control unit of the image forming apparatus based on information on the sheet width to be fixed next and information on the surface temperature of the temperature equalizing roller 330 at that time. That is, when the next sheet to be fixed has the maximum width, the temperature equalizing roller 330 is not pressed against the fixing roller 305,
In the case where sheets of small width continue continuously, pressure bonding is performed. When pressure is not applied (during preheating or when the width of the paper to be fixed next is the maximum), the pressure release lever 33 is used.
A command to release the pressure bonding is issued to a motor (not shown) that rotates the motor 7. In response to this command, the motor is turned to the pressure release lever 33
7, the temperature equalizing roller 330 is separated from the fixing roller 305. When crimping (when the paper width is small), since no command is issued from the control unit,
The pressure release lever 337 is not operated, and the temperature equalizing roller 330 is urged by the spring SP to press against the fixing roller 305.

When the number of fixed sheets of small width is small, for example, five or less, the pressure contact of the temperature equalizing roller 330 is released to reduce the heat flow to the temperature equalizing roller 330. Is also possible.

When a large number of sheets having a small width continue and the surface temperature of the temperature uniforming roller 330 continues to rise, both ends of the fixing roller 305 (from the inside of the maximum sheet width R to the outside of the small sheet width S). In this case, the relative angle is changed so that almost the entire area of the temperature equalizing roller 330 and the fixing roller 305 is in close contact with each other. That is,
When the temperature detected by the temperature sensor TS disposed on the outer peripheral surface of the temperature equalizing roller 330 exceeds a predetermined temperature, the temperature information from the temperature sensor TS and the paper size information to be used are transmitted to the image forming apparatus. After input and arithmetic processing by the control unit, the movable side plate 334 is rotated via the reversible motor by a command from the control unit, and the axes of the temperature equalizing roller 330 and the fixing roller 305 are aligned. Shift the angle to the maximum. By displacing the angle, there is no gap at the contact portion between the temperature equalizing roller 330 and the fixing roller 305 at the center, and the fixing roller 305 having low thermal conductivity is brought into close contact with almost the entire area in the longitudinal direction. The heat accumulated at both ends of the fixing roller 305 is transmitted to the central portion of the fixing roller 305 via the temperature uniforming roller 330 having high thermal conductivity, and the temperature distribution of the fixing roller 305 is equalized.

If the number of sheets subjected to the fixing process for a small width sheet is small, after the fixing process is completed, the temperature equalizing roller 33 is used.
0 is retracted to the pressure release position, and the accumulated heat is naturally radiated.

For the sake of simplicity, the above description is directed to two types of paper, the largest paper width used and the narrower paper used for the heating area where the fixing roller 305 can perform the fixing process. However, for example, by stopping the angle at which the temperature equalizing roller 330 is inclined at an arbitrary intermediate position from the reference position to the maximum angle, it is possible to control according to a sheet having an intermediate sheet width.

As for the pressure releasing mechanism of the temperature equalizing roller 330, a configuration in which only one axis is shifted has been described. However, it is needless to say that a configuration in which both axes are shifted in opposite directions is also possible.

Although the configuration in which the roller core of the fixing roller is a light-transmitting substrate such as glass has been described, the same effect can be obtained by using a thin metal pipe. However, in this case, it is necessary to secure the contact area of the temperature equalizing roller at the time of pressure bonding with the fixing roller, and it is desirable to provide an elastic layer such as silicon rubber on the surface.

The configurations of the fixing roller 305 and the temperature equalizing roller 330 are not limited to the embodiment, and the materials, dimensions, and the like are appropriately selected according to the fixing capability of the fixing device to be applied and the fixing temperature specification. it can. Although a solid roller is used as the temperature equalizing roller 330 in the embodiment, it goes without saying that a pipe material may be used.

Although the temperature control is not described, the temperature control of the fixing roller is performed by arranging a temperature detecting element near the surface of the fixing roller corresponding to the passage area of the sheet having a small width. A known method of turning on / off the power supply to the heating source based on the output information can be applied.

[0081]

With a very simple configuration, even if a large number of narrow sheets are continuously fixed, the temperature difference between the sheet passing area and the non-sheet passing area on the fixing roller can be suppressed. Therefore, even if a wide sheet of paper is used subsequent to the above, a stable fixing process can be performed with little difference in the glossiness of the toner image at the boundary between the two areas.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus including a color printer.

FIG. 2 is a schematic side cross-sectional view for explaining the configuration of a fixing roller, a pressure roller, and a temperature equalizing roller, which are main elements of the fixing device.

FIG. 3 is a schematic diagram for explaining the configuration of one pressure bonding and pressure release mechanism of the temperature equalizing roller according to the present invention.

FIG. 4 is a schematic diagram showing a state where the axes of a fixing roller and a temperature equalizing roller are aligned with each other, and when the roller is inclined by a certain angle.

FIG. 5 is a schematic diagram showing a state of a gap at the time of pressure bonding between a fixing roller and a temperature equalizing roller.

[Explanation of symbols]

 Reference Signs List 30 fixing device 300 halogen heater 305 fixing roller 315 pressure roller 330 temperature equalizing roller 331 shaft 332 roller unit

Claims (4)

[Claims] 1. An image fixing apparatus having a temperature equalizing roller capable of pressing and releasing pressure from a fixing roller, wherein an angle formed between the temperature equalizing roller and the fixing roller is variable. An image fixing device comprising: 2. The image fixing apparatus according to claim 1, wherein an angle formed between the axis of the temperature equalizing roller and the axis of the fixing roller can be controlled in accordance with the width of a recording sheet. 3. An apparatus according to claim 1, wherein an angle formed between said axis of said temperature equalizing roller and said fixing roller can be controlled in accordance with a temperature of said temperature equalizing roller.
3. The image fixing device according to claim 1. 4. The image fixing device according to claim 1, wherein the fixing roller has a light-transmitting substrate and a light-transmitting elastic layer.