JP2000250342A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the durability of a hard roller from being wastefully lowered while satisfying a fixing condition corresponding to the switching of the characteristics of an object to be fixed by switching and using the hard roller and a soft roller. SOLUTION: A paper sheet material to be processed 6 is passed by selecting one out of two nip parts 4 and 5 formed between a hard roller 1 and the first soft roller 2 positioned in this order and between the first soft roller 2 and the second soft roller 3, respectively, and is fixed by utilizing difference between the combinations of the rollers 1-3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device, and more particularly, to switching of characteristics affecting a fixing process on a fixing target side, for example, switching of types of sheets to be processed, such as paper and OHP resin sheets, and a method of changing a sheet material to be processed. The present invention relates to a fixing device suitable for a fixing process corresponding to switching of at least one kind of characteristic, such as switching of an image forming process when an image is formed with various kinds of toner, and switching of an image quality mode for an image formed by a fixing target. is there.

[0002]

2. Description of the Related Art Conventionally, a fixing device of an electrophotographic apparatus mainly for forming a black monochrome image has a so-called hard roller provided with a Teflon layer on the surface of a metal substrate because of its simple structure and low cost. Used as a fixing roller. However, in a fixing device of an electrophotographic apparatus that forms a color image using a plurality of color toners, hard rollers are hardly used because they are not satisfactory in terms of compatibility with toner characteristics and image quality. The use of a so-called soft roller having a thick surface layer has become the mainstream.

In a fixing process of a color image, about three layers of different color toner layers are overlapped, and it is necessary to sufficiently melt and synthesize the toner layers. Otherwise, the color will not develop enough. Further, since the toner layer is thick, it takes time to transfer heat from the surface layer to the interface with the image carrying paper.

Further, since a sharp-melt toner is used, the cohesive force of the toner is reduced in a molten state, and the toner cannot be released from the roller surface. For these reasons, it is necessary for the fixing device for fixing multiple color toners of a color image to have a sufficient heating time. It is necessary to increase the nip width of the fixing roller in order to take a sufficient heating time without lowering the sheet passing speed, which may be achieved by increasing the size of the fixing roller, increasing the thickness of the rubber layer, or increasing the pressure.

However, the nip width is used to increase the heating time while maintaining the balance between the size of the entire electrophotographic apparatus and the limitation of the warm-up time.

[0006] This soft roller becomes expensive in price,
And the life is short. Therefore, both the initial cost and the running cost are higher than a fixing device that fixes a single monochrome toner of a monochrome image.

Specifically, a fixing roller for a monochrome image generally has a structure in which a Teflon-based resin is baked on the surface of a pipe-shaped aluminum base material and a radiation heating source is provided inside the pipe-shaped base material. It is. Usually, this is used by pressing against each other in pairs with a pressure roller having an elastic layer on a substrate.

Further, the fixing roller for a color image is provided with a thick rubber layer on a pipe-like base material of good heat conductivity such as aluminum, and radiantly heats the inside of the pipe-like base material with a halogen heater to obtain the temperature of the base material. The rubber layer is heated by heat conduction to keep the surface at a high temperature, and it is used by pressing it against the same structure and using a sufficient nip while adjusting to the unevenness of the thick toner layer between the soft rollers. A sufficient heating time depending on the width can be secured. Furthermore, in order to prevent toner from adhering to the surface rubber, it has an affinity for rubber (wettability).
In general, the rubber is impregnated with oil having high toner release properties, and the oil is supplied from the outside by an oil application mechanism.

A monochrome image can be fixed by a fixing device for a color image without deteriorating the image quality. However, when a color image is fixed by a fixing device for a monochrome image, the melting characteristic of the color toner is set to a sharp melt for the purpose of coloring and transmitting light, and the viscosity at the time of melting is compared with that of the toner for a monochrome image. Since it is quite low, fusion to the surface layer occurs, causing an offset phenomenon, making it difficult to use properly.

Therefore, a soft roller is used as a fixing device in a general color image forming apparatus, and when the image forming process is switched to a mono-color mode (mainly a black image), the fixing temperature, pressure and paper passing speed are reduced. In order to cope with this, the reduction of the life of the soft roller at the time of monochrome image formation is reduced.

[0011]

However, the use of the soft roller for fixing a monochrome image also shortens the service life, and is particularly problematic when the frequency of use of the monochrome image is high.

The problem with soft rollers for color images is that the number of sheets that can be used is small, that is, the life is short, rather than the heat resistance and durability of rubber. To form a large nip, a large thickness of several millimeters is required, and due to the low thermal conductivity of rubber, if heat is removed from the surface by paper passing, the heat supply from the base material will not catch up and the surface will not catch up. , The fixing performance during continuous paper passing is lowered, and the gloss of the image at the trailing edge of the paper is lowered. In order to ensure releasability, a large amount of oil application is required, the oil application mechanism becomes complicated and expensive, and unevenness or dirt of oil application may easily occur on an image.

In order to increase the heat supply, it is necessary to mix a high thermal conductive inorganic filler into the rubber material, so that the rubber hardness increases and the pressing force increases to secure the nip width. It becomes necessary, deterioration of the roller rubber material due to stress and deflection of the roller occur, the nip width and the uniformity of the pressing force seen in the axial direction are impaired, and the paper passing property and image noise are deteriorated. It is not preferable from the viewpoint of increasing the load on the machine side.

An object of the present invention is to satisfy the fixing conditions according to the switching of the characteristics affecting the fixing process on the fixing target side, such as monochrome image formation and color image formation, by switching between the hard roller and the soft roller. Another object of the present invention is to provide a fixing device that can prevent the durability of the hard roller from being unnecessarily reduced.

[0015]

In order to achieve the above-mentioned object, a fixing device according to the present invention comprises a hard roller, a first roller and a first roller.
A soft roller and a second soft roller, in this order, between the hard roller and the first soft roller,
The main feature is that one of the two nips formed between the soft roller and the second soft roller is selected, the sheet material to be processed is passed, and the fixing process is performed.

In such a configuration, the fixing process is performed by passing the sheet material to be processed by using the hard roller and the first roller.
By selecting one of the two nips between the first soft roller and the second soft roller between the first soft roller and the second soft roller and passing the paper, the combination of the hard roller and the soft roller and the soft roller By using the difference between the combination of the soft rollers, the frequency of using expensive and short-lived soft rollers is minimized while satisfying the fixing processing conditions corresponding to the switching of the characteristics that affect the fixing processing on the fixing target side. It is possible to prevent the durability from being unnecessarily reduced.

The use of a hard roller in which a Teflon-based resin layer is formed on a metal substrate is suitable for obtaining sufficient releasability while securing roller rigidity without observing a reduction in life.

The selection of the nip is performed by switching the image forming process depending on the fixing target to the sheet material to be processed, switching the image quality mode, or switching the sheet material to be processed.
It is effective to perform switching in response to switching of at least one type of characteristic that affects the fixing process on the fixing target side, and it is preferable to perform switching in response to switching of the most complex type of characteristics as much as possible.

When the nip between the hard roller and the first soft roller is selected, the second soft roller is moved to the first soft roller.
When the first and second soft rollers having low durability are rotated by unnecessary pressure contact with each other, it is possible to prevent the life from being shortened.

If at least a heating source is provided inside the hard roller, heat is transferred to the first soft roller forming a nip between the hard roller and the first soft roller, and the heat is passed therethrough regardless of which of the two nips is used. The sheet to be processed can be fixed by heating the sheet material to be processed mainly from the hard roller side in one nip and mainly from the first soft roller side in the other nip. Can be omitted.

When the nip between the first and second soft rollers is selected, the hard roller and the first soft roller are rotated while being pressed against each other prior to the fixing process.
At the time when the sheet material to be processed is passed and the fixing process is performed, the heat on the hard roller side is already conducted to the first soft roller and also to the second soft roller through the first soft roller. Therefore, even if the first and second soft rollers do not have a heat source, it is possible to prevent a delay in heating and a decrease in fixing performance.

By controlling the power supply to the heating source inside the hard roller during paper passing, the temperature condition at a required position due to heat conduction from the hard roller can be kept constant, and the fixing performance becomes stable. If the power supply is controlled on the basis of the temperature detected by the first soft roller, it is possible to handle either of the two nips.

When the nip between the hard roller and the first soft roller is selected, by controlling the power supply to the internal heat source based on the result of detecting the temperature of the hard roller,
A stable fixing process can be performed while keeping the temperature condition of the hard roller constant.

When a heat source is provided at least inside the hard roller and inside the first soft roller, the nip between the hard roller and the first soft roller and the first and second soft rollers are provided.
When the nip between the soft rollers is selected, the fixing process can be performed quickly and stably by heating from both the hard roller and the first soft roller.

At the time of warm-up, power supply to the heating source inside the hard roller is performed prior to power supply to the first soft roller, and when the temperature of the hard roller reaches a certain temperature, the first soft roller When power is supplied to the internal heating source, first, while heating the hard roller by supplying power to the heating source of the hard roller, the heat is directly transmitted to the first soft roller and then to the second soft roller. Supplies heat to the heat source of the first soft roller from the time when the hard roller reaches a certain temperature while conducting heat conduction through the first soft roller to directly increase the temperature. , The second soft roller is heated by heat conduction from the first soft roller, and the power supply time of the heating source inside the first soft roller is shortened to save power. It will be able to reach a predetermined warm-up state to the manner the air.

In this case, when the temperature of the hard roller reaches a certain temperature, fixing can be performed at the nip between the hard roller and the first soft roller. When the temperature reaches a certain temperature at which the heating by the heating source of the first soft roller is started for the warm-up, the entire warm-up is still required and the hard roller and the first The fixing process at the nip with the soft roller is stable because the first and second soft rollers are warmed up to the temperature of the hard roller so that heat is not deprived by these. it can.

During the period from the start of warm-up until the first soft roller reaches a predetermined temperature, at least one of the hard roller and the first soft roller is pressed and rotated to rotate the hard roller and the first soft roller. Since any one of the soft rollers rotates the hard roller and the first and second soft rollers by driving and following, and the heat is easily distributed all around the respective rollers. Warm-up can be performed almost uniformly from around the outer circumference.

[0028] Further objects and features of the present invention will become apparent from the following detailed description and drawings. Each feature of the present invention can be used alone or in various combinations in combination as far as possible.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings together with examples to provide an understanding of the present invention.

In the present embodiment, a nip between a hard roller and a soft roller formed by three rollers and a pair of software are provided in accordance with switching of an image forming process between a monochrome image forming mode and a color image forming mode by an electrophotographic system. By selecting the two nips between the nip between the rollers and performing the fixing process, the frequency of using the soft rollers can be minimized while satisfying the appropriate fixing conditions according to the difference in the image forming process. This is an example of a case where the durability can be prevented from being wasted. However, the present invention is not limited to this, and is effective when applied to any case where a toner image of, for example, a powder or a liquid is transferred from another or printed directly on a sheet material to be processed to form an image. It is.

In this embodiment, as shown in the examples of FIGS. 1 to 3 and the example of FIG. 4, three fixing rollers, ie, a hard roller 1, a first soft roller 2, and a second soft roller 3 are arranged in this order in a vertical direction as in the respective embodiments of the drawings, for example, between the hard roller 1 and the first soft roller 2, the first soft roller 2 and the second soft roller 3. One of the two nips 4 and 5 formed therebetween is selected, and the sheet 6 to be processed is passed along the corresponding transport path 8 or 9 to perform the fixing process. The three fixing rollers 1 to 3 may be arranged side by side or obliquely in any direction according to the setting of the positions and directions of the transport paths 8 and 9, and are not necessarily arranged in a straight line as in each embodiment of the drawing. They may be arranged in the shape of a letter without the letter.

As shown in FIGS. 3 and 4, the hard roller 1 carries a monochrome image 7a made of black toner, which is an example of a fixing object 7 carried on a sheet material 6 to be processed by image transfer or direct printing. The monochrome image 7a is fixed to the sheet material 6 to be processed by heating and melting, and if necessary, applying pressure to the sheet material 6 with a predetermined nip width N1 between the first soft roller 2 and the first soft roller 2. . At this time, the hard roller 1 is heated and melted to produce a monochrome image 7.
A Teflon-based resin layer 1b is formed as thin as about several tens of μm on a metal substrate 1a for releasability from a.
It is designed to have a sufficient surface strength that the durability does not decrease while securing the releasability suitable for fixing a.

The first and second soft rollers 2 and 3 are provided with rubber layers 2b and 3b having a thickness of several mm on metal bases 2a and 3a, respectively, and have a nip 5 between them in a pressed state. Thus, a nip width N2 capable of securing a sufficient heating time necessary for the color image 7b is obtained.

When the sheet 6 to be processed carrying the object to be fixed 7 on the upper surface is passed between the fixing rollers to perform the fixing process, as described above, between the hard roller 1 and the first soft roller 2, By selecting one of the two nips 4 and 5 between the first soft roller 2 and the second soft roller 3 and passing the paper, the combination of the hard roller 1 and the first soft roller 2 can be achieved. By using the difference between the combinations of the soft rollers 2 and 3, the expensive and short-lived soft rollers 2 and 3 are satisfied while satisfying the fixing conditions corresponding to the switching of various characteristics affecting the fixing of the fixing target 7 side. The frequency of use of the combination can be minimized to prevent useless reduction in life.

The selection of the nips 4 and 5 is performed by switching the image forming process to the sheet material 6 to be processed, switching the image quality mode, or switching the sheet material 6 to be processed, etc. It is effective to perform at least one switching of various conditions. It is suitable to improve the image quality and to improve the durability of the entire fixing device including the first and second soft rollers 2 and 3 by performing the switching of the most complex conditions as much as possible. The sheet material 6 to be processed in the present embodiment is a transfer material that transfers and carries the monochrome image 7a and the color image 7b,
HP resin sheet and the like. In some cases, it also includes envelopes and postcards. In some cases, it also includes other sheet-like materials.

When the nip 4 between the hard roller 1 and the first soft roller 2 is selected as shown in FIG. 3, the second soft roller 3 is separated from the first soft roller 2. Thereby, the first and second parts having low durability are obtained.
It is possible to prevent the life of the soft rollers 2 and 3 from being shortened due to unnecessary press contact and rotation.

In the embodiment shown in FIGS. 1 to 3, a cleaning web 22 is pressed against the surface of the hard roller 1 by a cleaning mechanism 21. Cleaning mechanism 21
The cleaning web 22 fed from the web supply roller 23 is wound around the winding roller 25 while being pressed against the hard roller 1 by the web pressure roller 24 whose surface is made of sponge rubber.

An oil application roller 26 for applying a release agent such as oil is brought into contact with the surface of the first soft roller 2 so that the release agent is applied. The applied release agent mainly acts on the multiple different color toners forming the color image 7b carried on the sheet material 6 to be processed, which is passed through the nip 5 for the color image 7b, A color toner having high property is prevented from adhering to the surface of the first soft roller 2. However, if the release agent is applied to the first soft roller 2 at the timing when the paper is not passed through the nip 4 for the monochrome image 7a,
The release agent is transferred to the surface of the hard roller 1 to prevent the single monochrome toner forming the monochrome image 7 a from adhering to the hard roller 1 when the paper passes through the nip 4. Can be further promoted.

As shown in the embodiment shown in FIGS. 1 to 3, if at least a heating source 11 such as a halogen lamp is provided inside the hard roller 1, a first nip 4 is formed between the heating source 11 and the heating source. Whichever one of the two nips 4 and 5 is selected and used by conducting heat to the soft roller 2, the sheet material 6 to be processed is passed through the soft nip 2. In the nip 5, the fixing process is performed by heating mainly from the first soft roller 2 side, and the two soft rollers 2 and 3 can omit a heating source.

When the nip 5 between the first and second soft rollers 2 and 3 is selected, if the hard roller 1 and the first soft roller 2 are rotated while being pressed against each other prior to the fixing process, At the time when the target sheet material 6 is passed and the fixing process is performed, the heat of the hard roller 1 side is the first heat.
Of the first and second soft rollers 2 and 3 without a heat source because the heat is already conducted to the second soft roller 2 through the first soft roller 2 and also to the second soft roller 3. It is possible to prevent the fixing performance at the nip 5 from being lowered due to the delay of the heating.

During paper passing, the heating source 11 inside the hard roller 1
By controlling the power supply to the hard roller 1, the temperature condition at a required position due to the heat conduction from the hard roller 1 can be kept constant, so that the fixing performance is stabilized. If the determination is made based on the temperature detected by the soft roller 2, either of the two nips 4, 5 can be selected. When the nip 4 between the hard roller 1 and the first soft roller 2 is selected, by controlling the power supply to the internal heating source 11 based on the temperature detection result of the hard roller 1, the temperature condition of the hard roller 1 is controlled. And the fixing process can be performed stably. Therefore, a temperature sensor 31 such as a thermistor is applied to the surface of the hard roller 1. In addition, when the nip 5 is selected, the surface temperature of the first soft roller 2 needs to reach a predetermined temperature. Therefore, to detect whether the temperature has reached the predetermined temperature,
A temperature sensor 32 such as a thermistor is also applied to the surface of the first soft roller 2.

More specifically, the hard roller 1 is formed by firing a 30 μm-thick Teflon-based resin layer 1b on a metal base material 1a in the form of an aluminum roller having a diameter of 40 mm and provided inside. Radiation heating is performed from the heated heating source 11.

The first soft roller 2 has a thickness of 3 mm on an aluminum roller-shaped base material 2a having a diameter of 34 mm.
It has a rubber layer 2b as an elastic layer made of silicon rubber of mm. The rubber layer 2b may be an elastic layer formed by laminating a plurality of functional layers such as a base layer, an oil barrier layer, and a surface layer, if necessary.

The second soft roller 3 has a rubber layer 3b as an elastic layer of silicon rubber having a thickness of 1 mm on an aluminum roller base material 3a having a diameter of 38 mm. The rubber layer 3b may include a base layer, an oil barrier layer,
It may be an elastic layer formed by laminating a plurality of layers according to functions such as the surface layer, and the surface layer may be covered with a tube of a fluororesin or the like as necessary to prevent the effect of toner adhesion. Good.

The oil application roller 26 has an application surface layer 26a made of a porous material such as Teflon provided on an oil holding tank 26b made of an aluminum pipe, and the oil contained in the oil holding tank 26b is applied to the oil application tank 26b. The oil can be stably applied by utilizing the bleeding through a hole provided in the pipe so as to maintain the saturated state at 26a.

The first and second soft rollers 2 and 3 have the rubber layers 2b and 3b to form a nip 5 having a large nip width N2 suitable for fixing a color image. Elastic deformation and restoration of the elastic layers 2b and 3b when both rotate as much as the width N2 is repeated with complicated movements, which easily causes fatigue and greatly affects the life. Therefore, when the nip 4 is selected, the separation mechanism 35 shown in FIG. 1 is provided to separate the first and second soft rollers 2 and 3 so as to prevent unnecessary fatigue.

The separation mechanism 35 drives and controls various actuators 36 connected to the second soft roller 3 by a control means using a CPU 37 or the like so that the first soft roller 2 is separated from the first soft roller 2 by time. .

Since the first soft roller 2 uses the heat from the heat source 11 in the hard roller 1 for fixing heat even when the nip 5 is selected, the first soft roller 2 and the hard roller 1 are heat conductive. However, the nip 4 formed by the first soft roller 2 in contact with the hard roller 1 is for the monochrome image 7a, so that the nip width N1 may be small, and the nip 4 when both are rotated. Elastic layer 2b
The elastic deformation and restoration are repeated by simple movements without fatigue, and do not particularly affect the service life.

The CPU 37 may control the operation of an image forming apparatus (not shown) equipped with the fixing device shown in FIGS. 1 to 3 or another CP for performing such control.
Signals may be exchanged with U to perform related control.

Hereinafter, a specific control example of the fixing device will be described. During the warm-up period from when the power is turned on to when the fixing is possible, power is supplied to the heating source 11 inside the hard roller 1 via the driver 42 as shown in FIG. Is radiantly heated.
The hard roller 1, the first and second soft rollers 2, 3 are
The rollers are driven to rotate while being pressed against each other, and the heat of the hard roller 1 is conducted to the surfaces of the first and second soft rollers 2 and 3.

The surface temperature of the hard roller 1 is measured by a temperature sensor 3
The power supply to the heating source 11 is controlled by the CPU 37 so as to maintain about 180 ° C. in consideration of the heat resistance temperature of the oil and peripheral members. The temperature of the first soft roller 2 is detected by a temperature sensor 32,
, The fixing enable signal at the nips 4 and 5 is issued.

In the color image forming mode set by manual input from the operation panel 37a or the like connected to the CPU 37, the sheet material to be processed is placed on the fixing unit as shown in FIG. While the sheet 6 is conveyed and passed, the hard roller 1 and the first and second soft rollers 2 and 3 are driven to rotate in the direction shown by the arrow A, and the conveyed sheet material 6 to be processed is Between the first and second soft rollers 2 and 3 by selecting two transport paths 8 and 9 provided corresponding to the nips 4 and 5 and by switching the position of only one transport path (not shown). The color image 7b is passed through the nip 5 and is on the sheet material 6 to be processed.
Is fixed.

The sheet material 6 to be processed after the fixing process mainly depends on the curvature of the first soft roller 2 and the sheet material 6 to be processed.
Is separated from the first soft roller 2 and the second soft roller 3 depending on the rigidity of the first soft roller 2 and the second soft roller 3 and is discharged. In order to prevent the sheet material 6 to be processed from being wound around the first and second soft rollers 2 and 3, the separation claw 38 is used.
38 are provided.

The temperature of the first soft roller 2 is based on the temperature detected by the temperature sensor 32 and is used to supply power to the heating source 11 in the hard roller 1 and to rotate the first soft roller 2 and the hard roller 1. By controlling through the driver 42, it can be kept constant.

In the mode for forming the monochrome image 7a set by manual input from the operation panel 37a or the like connected to the CPU 37, the second soft roller 3 is moved by the separation mechanism 35 in accordance with the selection of the nip 4 side. While being separated from the second soft roller 3 and while the sheet material 6 to be processed is conveyed to the fixing unit and is passed through, the hard roller 1 and the first soft roller 2 are driven through the driver 42 as shown in FIG. The sheet material 6 to be processed, which is driven to rotate and is conveyed in the direction of the arrow B, selects one of the two conveyance paths 8 and 9 provided corresponding to the nips 4 and 5 according to the selection described above.
By switching the position of the only transport path, the paper is passed through the nip 4 between the hard roller 1 and the first soft roller 2, and the monochrome image 7a on the sheet material 6 to be processed is fixed.

The sheet material 6 to be processed after the fixing process is separated from the hard roller 1 mainly by the curvature of the hard roller 1 and the rigidity of the sheet material 6 to be processed, that is, the stiffness, and is discharged. Note that a separation claw 39 is provided to prevent the sheet material 6 to be processed from winding around the hard roller 1.

The temperature of the hard roller 1 is controlled based on the temperature detected by the temperature sensor 31 through the driver 42 to control the supply of electric power to the heating source 11 of the hard roller 1, so that the surface temperature is kept constant.

In the embodiment shown in FIG. 4, a heating source 41 is provided inside the first soft roller 2 in addition to the heating source 11 for the hard roller 1. Accordingly, even when the nip 4 between the hard roller 1 and the first soft roller 2 and the nip 5 between the first and second soft rollers 2 and 3 are selected, the hard roller 1 and the first soft roller 2 are selected. Soft Roller 2
Fast and stable fixing can be achieved by heating from both sides.

During warm-up, power supply to the heating source 11 inside the hard roller 1 is performed prior to power supply to the heating source 41 of the first soft roller 2 so that the temperature of the hard roller 1 reaches a certain temperature. Then, when power is supplied to the heating source 41 inside the first soft roller 2,
First, while raising the temperature of the hard roller 1 by supplying power to the heating source 11 of the hard roller 1, the heat is directly transmitted to the first soft roller 2, and the heat is transmitted to the second soft roller 3 via the first soft roller 2. While conducting heat to increase the temperature,
From the time when the hard roller 1 reaches a certain temperature, power is supplied to the heating source 41 of the first soft roller 2 so that the first soft roller 2 is directly transferred from the first soft roller 2 to the second soft roller 3. Each is heated by the heat conduction of
The power supply time of the heating source 41 inside the soft roller 2 can be shortened to save power while the whole can reach a predetermined warm-up state relatively early.

In this case, when the temperature of the hard roller 1 reaches a certain temperature, if the fixing can be performed at the nip 4 between the hard roller 1 and the first soft roller 2, the heating by the hard roller 1 is performed in the first and second directions. When the temperature of the first soft roller 2 reaches a certain temperature at which the heating by the heating source 41 is started for the warm-up while sharing the warm-up of the second soft rollers 2 and 3, the entire warm-up is still performed. However, if necessary, the hard roller 1 and the first soft roller 2
The fixing process in the nip 4 with the first and second soft rollers 2 and 3 is warmed up to an extent commensurate with the temperature of the hard roller 1 so that the heat is not deprived by these. Fixing process can be performed.

During the period from the start of the warm-up until the first soft roller 2 reaches a certain temperature, at least one of the hard roller 1 and the first soft roller 2 is pressed and rotated to rotate the hard roller 1. And the rotation of the first soft roller 2 causes the hard roller 1 and the first and second soft rollers 2 and 3 to rotate by driving and following, respectively, so that heat is uniformly distributed over the entire circumference. Therefore, the three fixing rollers 1 to 3 can be brought into a warm-up state substantially uniformly around their respective outer circumferences by heating with one hard roller 1.

[0062]

According to the present invention, as is apparent from the above description, various conditions of the sheet material to be processed are utilized by utilizing the difference between the combination of the hard roller and the soft roller and the combination of the soft rollers. While satisfying the processing conditions corresponding to the differences, the use frequency of the combination of the soft rollers satisfying the predetermined condition that is expensive and has a short life can be minimized to extend the life.

[Brief description of the drawings]

FIG. 1 is a side view of a fixing device showing a first example according to an embodiment of the present invention.

FIG. 2 is a side view showing a use state of the apparatus of FIG. 1 when fixing a color image.

FIG. 3 is a side view illustrating a use state of the apparatus of FIG. 1 when fixing a monochrome image.

FIG. 4 is a side view of a fixing device according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hard roller 2 1st soft roller 3 2nd soft roller 4, 5 nip 6 Sheet material to be processed 7 Fixing object 7a Monochrome image 7b Color image 11, 41 Heat source 31, 32 Temperature sensor 35 Separation mechanism 37 CPU 37a Operation Panel 42 Driver N1, N2 Nip width

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H027 DA50 DC02 EA18 EC20 ED25 EE07 EF06 EF09 FA30 2H030 AA06 AD04 AD06 AD07 2H033 AA11 AA47 AA49 BA02 BA08 BA25 BA26 BA32 BB03 BB04 BB18 BB21 CA30 BB30 CA33 BB33 CA33 CA40

Claims (15)

[Claims] 1. A hard roller, a first soft roller, and a second soft roller are provided in this order, between a hard roller and a first soft roller, and between a first soft roller and a second soft roller. Form 2
A fixing device characterized in that any one of the nips is selected, a sheet to be processed is passed through, and a fixing process is performed. 2. The fixing device according to claim 1, wherein the hard roller has a Teflon-based resin layer formed on a metal base material. 3. The fixing device according to claim 1, wherein the selection of the nip is performed in response to switching of an image forming process according to an object to be fixed to a sheet material to be processed. 4. The fixing device according to claim 1, wherein the selection of the nip is performed in response to switching of an image quality mode for an image formed by the fixing target. 5. The fixing device according to claim 1, wherein selection of the nip is performed in response to switching of a sheet material to be processed. 6. The fixing device according to claim 1, wherein when a nip between the hard roller and the first soft roller is selected, the second soft roller is separated from the first soft roller. apparatus. 7. The fixing device according to claim 1, wherein a heat source is provided at least inside the hard roller. 8. The fixing device according to claim 7, wherein when a nip between the first soft roller and the second soft roller is selected, the hard roller and the first soft roller are rotated while being pressed against each other prior to the fixing process. apparatus. 9. The fixing device according to claim 8, wherein power supply to a heating source inside the hard roller is controlled during paper passing. 10. The fixing device according to claim 9, wherein the control of the power supply is performed based on a temperature detected by the first soft roller. 11. The fixing device according to claim 7, wherein when a nip between the hard roller and the first soft roller is selected, power control to a heating source is performed based on a temperature detection result of the hard roller. 12. The fixing device according to claim 1, wherein a heating source is provided at least inside the hard roller and inside the first soft roller. 13. At the time of warm-up, power supply to a heating source inside the hard roller is performed prior to power supply to the first soft roller, and when the temperature of the hard roller reaches a certain temperature, the first power is supplied to the first soft roller. 13. The fixing device according to claim 12, wherein power is supplied to a heating source inside the soft roller. 14. The fixing device according to claim 13, wherein when the temperature of the hard roller reaches a predetermined temperature, fixing can be performed at a nip between the hard roller and the first soft roller. 15. The fixing device according to claim 13, wherein at least one of the hard roller and the first soft roller is rotationally driven while pressing the first soft roller until the first soft roller reaches a predetermined temperature after the start of warm-up. apparatus.