JP2003208058A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a structure for preventing fixing failure caused when heat is taken away by the contact with a toner image support. <P>SOLUTION: The image forming apparatus has a belt 4 which is trained around a pair of rollers 2 and 3 and heated by a heat source 3A incorporated in one roller 3 of the pair, and a pressure roller 5 which moves the belt 4 over part of its peripheral face along the periphery. When an image is fixed while the toner image support is transported while held between the rollers, the heat contraction of the width of a hollow portion 5C of the pressure roller 5 is detected by a change in an optical length with the use of an optical fiber 6, and the heating of the belt 4b is controlled to prevent a drop in fixing temperature. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile and a printer, and an image forming method.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a facsimile or an electrophotographic printer, a toner image is formed on a photosensitive member and the toner image is formed on a toner image support such as paper or an OHP sheet. The toner is electrostatically transferred, but the toner electrostatically transferred from the photoconductor to the toner image support easily peels off from the toner image support simply by being attached by electrostatic force. It is necessary to permanently affix it to the toner image support.
The step of permanently fixing the toner to the toner image support is called a fixing process.

There are various fixing methods for permanently fixing the toner to the toner image support. Among them, the heat roller fixing method is most widely used because of its high thermal efficiency and safety. In this heat roller fixing method, two rollers are brought into pressure contact with each other to heat at least one of them, and a toner image support carrying unfixed toner is passed through the pressure contact portion (nip portion) of these two rollers. In this method, the unfixed toner on the toner image support is heated and fixed on the toner image support.

In the heat roller fixing method, when one of the two rollers is heated, the roller to be heated is called a fixing roller and the other roller is called a pressure roller. A heat source such as a halogen lamp or an electric heater is provided inside the fixing roller in the axial direction of the fixing roller.

A temperature sensor for detecting the surface temperature of the fixing roller is attached to the outer surface of the fixing roller. Based on the output value of this temperature sensor, the surface temperature of the fixing roller in the nip portion is on the toner image support. The amount of current supplied to the heat source is controlled so as to be maintained at a temperature suitable for fixing the unfixed toner. The heat roller fixing type fixing device is
Since a roller structure having a relatively large heat capacity is used, the rise time until the surface of the fixing roller reaches a predetermined fixing temperature tends to be long, which is 5 to 20 minutes. It is known to be disadvantageous.

On the other hand, in view of the fact that the energy saving effect, which is a problem in the heat roller fixing method, is low, a belt fixing method using a belt having a smaller heat capacity than the roller as a heating member has been proposed (for example, Japanese Unexamined Patent Publication No. Hei 8 (1999) -811). −
286535).

The above publication discloses a structure in which a belt wound around a pair of rollers is heated in advance and a pressure roller is provided so as to face one of the rollers around which the belt is wound. There is.

In addition to the above publication, there is a construction disclosed in Japanese Patent Application Laid-Open No. 8-314303 as a construction using a belt. In the same publication, as in the above publication, a means for heating the toner support from the surface opposite to the toner support surface of the toner support is provided on one of the spreading surfaces of the belt that is heated around a pair of rollers. Configurations are disclosed.

In the structures disclosed in the above-mentioned publications, the belt having a smaller heat capacity than the roller is used, whereby the nip region for sandwiching and carrying the toner support can be lengthened, so that the rise to the fixing temperature can be accelerated. At the same time, by increasing the nip area, the heat receiving time for obtaining the amount of heat required for fixing can be lengthened, so that the heat source temperature tends to decrease, and as a result, the fixing time can be shortened and the power consumption can be reduced. The belt used in such a structure and the roller used in the heat roller fixing method have, as the surface structure, firstly, a structure in which an elastic release material layer such as silicone rubber is arranged, and secondly,
As an example, a structure in which a layer represented by a fluororesin such as tetrafluoroethylene perfluoroalkoxy vinyl ether polymer (hereinafter, referred to as PFA for convenience) is arranged (for example, JP-A-6-167900), the third
There is known a structure in which a fluororesin is laminated on a silicone rubber on an elastic release material. The first configuration is
Although an elastic body is used to secure the nip,
It is sticky and has problems in paper transportation, dust adhesion, and offset. The second configuration has a thin film thickness of about 40 μm, has insufficient elasticity, cannot open the nip, cannot sufficiently supply heat, and has insufficient fixing property. In the third structure, the elasticity is made of silicone and the releasability is made of a fluorine-based resin, and the above problem is temporarily solved.

[0010]

On the other hand, in the belt fixing system using the belt having the above structure, the temperature of the toner at the nip portion cannot be directly measured by the belt or the roller that comes into contact with the toner image. When a material to be heated (toner support such as paper) such as a support reaches the nip portion, heat is removed from the nip portion by the toner support, so that the temperature at the nip portion cannot be accurately measured. In particular, a member that is deprived of heat causes a temperature gradient when it comes into contact with the toner support, but it is difficult to directly measure the temperature decrease. Therefore, when the temperature in the nip portion is out of the value required for fixing, the fixing using the phenomenon of melting and softening of the toner image and the penetration into the support is obtained in an incomplete state, and the fixing failure occurs. There is a problem that it occurs.

The object of the present invention is to maintain the fixing temperature by directly measuring the problem in the above-mentioned conventional fixing device, especially the case where the temperature is lowered due to the contact with the toner support, thereby causing the fixing failure. An object of the present invention is to provide an image forming apparatus and an image forming method having a configuration capable of preventing the above.

[0012]

The invention according to claim 1 is
Toner provided with a belt that is wound around a pair of rollers and heated by a heat source built in one of the rollers, and a pressure roller that moves the belt in the circumferential direction on a part of the circumferential surface. In an image forming apparatus having a configuration for fixing the toner image while sandwiching and conveying the toner image support on which an image is carried by the belt and the pressure roller,
The pressure roller is a flexible elastic body having a light emitting portion and a light receiving portion made of an optical fiber,
A shaft core capable of reflecting the light from the light emitting portion, and having a hollow portion provided between the surface layer and the shaft core and expandable and contractable by heat are provided along the radial direction, and in the radial direction, It is characterized in that it comprises means for controlling heating of the belt when the width of the hollow portion reaches a certain width or less.

According to a second aspect of the present invention, a belt is wound around a pair of rollers and is heated by a heat source incorporated in one of the rollers, and the belt has a part of its peripheral surface along the circumferential direction. In an image forming apparatus having a configuration in which a toner image supporting body carrying a toner image is sandwiched and conveyed by the belt and the pressure roller to fix the toner image The pressure roller comprises an elastic body having a flexible surface layer having a light emitting portion and a light receiving portion made of optical fibers, a shaft core capable of reflecting light from the light emitting portion, the surface layer and the shaft core. And a heat-expandable hollow portion provided along the radial direction, and heating the pressure roller when the width of the hollow portion in the radial direction reaches a certain width or less. It is equipped with means for controlling It is characterized in.

According to a third aspect of the present invention, a belt is wound around a pair of rollers and is heated by a heat source incorporated in one of the rollers, and the belt has a part of its circumferential surface along the circumferential direction. In the image forming method, the toner image supporting member carrying a toner image is fixed while the toner image support carrying the toner image is nipped and conveyed by the belt and the pressure roller. In the roller, an elastic body having a flexible surface layer having a light emitting portion and a light receiving portion formed of an optical fiber, a shaft core capable of reflecting light from the light emitting portion, and a space between the surface layer and the shaft core. A heat-expandable hollow portion is provided along the radial direction, and at least when the width of the hollow portion in the radial direction reaches a certain width or less, at least the belt or the pressure roller is provided. Heating for one It is characterized by performing the control.

The invention according to claim 4 is the invention according to claim 1 or 2.
In addition to the invention described above, the hollow portion is characterized by being filled with an inert gas.

[0016]

1 is a schematic view showing an example of an image forming apparatus according to an embodiment for explaining an embodiment of the present invention, and the image forming apparatus shown in the drawing has a plurality of color separations. 1 illustrates a color printer capable of forming an image using toner corresponding to a color. The image forming apparatus 20 shown in FIG.
Color images are transferred by sequentially transferring images for each color separation onto a sheet-shaped recording medium such as paper, which corresponds to the toner image carrier, and superimposing images developed with complementary color toners corresponding to the color separation colors. A method of forming an image is used. Instead of such an image forming method, the toner images for each color separation are sequentially transferred to an intermediate transfer member by a primary transfer process, and the superimposed images are collectively transferred to a paper, which is a toner image support, by a secondary transfer process. It is also possible to use a transfer method. In addition to the above, the image forming apparatus includes a facsimile apparatus that can perform the same image forming processing as the above-described copying machine and printer based on the received image signal. Note that the image forming apparatus includes not only the above-described color image as a target but also a device as a single-color image as a target.

In FIG. 1, the image forming apparatus 20 is provided with the following respective devices. Image forming devices 21C, 21Y, 21M, and 21 that form images for each color according to the original image
Bk and each image forming device 21C, 21Y, 21M, 21Bk
Transfer device 22 using a belt having a stretchable portion that can move opposite to each other, and image forming devices 21C, 21Y, 21M, 2
1Bk and a transfer device 22 face each other in a transfer area, and a sheet feeding tray 23 capable of supplying various sheet-like media such as paper corresponding to a toner image support (hereinafter, the toner image support is referred to as a sheet-like medium) and a paper feed tray. The sheet cassettes 24, 24 and the sheet-shaped medium conveyed from the manual feed tray 23 or the sheet feed cassettes 24, 24 are image forming devices 21C, 21Y,
A registration roller 30 is supplied at the timing of image formation by 21M and 21Bk, and a fixing device 1 for fixing the sheet medium after transfer in the transfer area.

The image forming apparatus 20, which corresponds to a toner image support, is a plain paper generally used for copying or the like, an OHP sheet, a card, a postcard 90K.
Sheet-like recording medium such as paper, thick paper having a basis weight of approximately 100 g / m ² or more, or a so-called special sheet having a larger heat capacity than the sheet (hereinafter, the toner image support is referred to as a sheet-like recording medium for convenience). Can be used.

Image forming devices 21C, 21Y, 21M, 21
Bk develops each color of cyan, yellow, magenta, and black, and the colors of the toners used are different, but the configurations are the same, so the image forming device 21B
k of the image forming devices 21C, 21Y, 21M, 21
This will be described as a representative of Bk. The image forming device 21Bk has a photosensitive drum 25Bk as an electrostatic latent image carrier, a charging device 27Bk, a developing device 26Bk, and a cleaning device 28Bk which are sequentially arranged along the rotation direction A of the photosensitive drum 25Bk. Charging device 27Bk and developing device 26Bk
A well-known structure for receiving the exposure light from the writing device 29 between and is used. The electrostatic latent image carrier may have a belt shape in addition to the drum shape.

In the case of the present embodiment, the transfer device 22 uses a conveyor belt whose expansion surface facing the image forming devices 21C, 21Y, 21M, and 21Bk moves in the direction of the arrow shown in the figure. The upstream side in the direction, that is, the side into which the sheet-shaped recording medium enters can be brought into contact with and separated from the image forming device (a state shown by a solid line and a state shown by a chain double-dashed line). The transfer device 22 electrostatically transfers the image formed on the charging device that electrostatically attracts the sheet-shaped recording medium to the belt and the photoconductors 25Bk, 25Y, 25C, and 25M in each image forming device to the sheet-shaped recording medium. Each of the transfer devices is provided. The sheet-shaped recording medium to which the image is transferred by the transfer device 22 is discharged after the image is fixed by the fixing device 1 and is fed to the back surface of the image transfer surface to transfer the image again. When and are selected and the image is transferred to the back side, I will not explain in detail,
The sheet-shaped recording medium is conveyed toward the registration rollers 30 in a reversed state and is conveyed to a re-feed mechanism. The electrostatic latent image carrier may have a belt shape in addition to the drum shape. Image forming apparatus 20 shown in FIG.
Since the transfer device 22 extends obliquely, the space occupied by the transfer device 22 in the horizontal direction can be reduced.

FIG. 2 is a diagram showing an outline of the fixing device in the embodiment of the present invention. The first embodiment is an embodiment of the invention according to claims 1 and 2, and is an embodiment of an image forming apparatus including an electrophotographic apparatus using an image forming method including the electrophotographic forming method. In the first embodiment, the belt 4 is wound around the pair of rollers 2 and 3 and is heated by the heat source 3A built in the heating roller 3 constituted by one of them, and the belt 4 has a circumferential surface. And a pressure roller 5 that is movable in the circumferential direction by abutting on a part thereof. The pressure roller 5 is pressed against the belt 4 by an urging mechanism (not shown) and can rotate in cooperation with the belt 4.

The heating roller 3 also serves as a tension member for the belt 4, and the halogen lamp used as a built-in heat source 3A heats the belt 4 on the upstream side in the transport direction of the sheet-shaped recording medium. The halogen lamp 3A is arranged with a length substantially equal to the entire length of the heating roller 3, and performs uniform heating in the axial direction of the heating roller 3.

The other roller 2 around which the belt 4 is wound is used as a fixing roller arranged at a position where the belt 4 can be moved along the peripheral surface of the pressure roller 5, whereby The pressure roller 5 is a part of the belt 4.
It is possible to configure a nip portion (a portion for sandwiching and conveying the sheet-shaped recording medium) that moves along the peripheral surface of the sheet. In the configuration shown in FIG. 2, the pressure roller 5 is in contact with the belt 4 stretched between the fixing roller 2 and the heating roller 3, but the present invention is not limited to this configuration, and the belt 4 may be removed. It is also possible to dispose the pressure roller 5 at a position facing the fixing roller 2. In this case, the belt 4 is pressed against the peripheral surface of the fixing roller 2 by making the surface layer portion of the fixing roller 2 an elastic body, and compared with the case where the pressure roller 5 abuts on the expanded portion of the belt 4. It is possible to improve the heat transfer efficiency from the belt 4 to the toner image by increasing the holding pressure of the sheet-shaped recording medium.

FIG. 3 shows a cross section near the center of the pressure roller 5 used in the fixing device 1 in the first embodiment in the roller axis direction, which is perpendicular to the roller axis direction. The roller 5 includes a shaft core 5A made of a material capable of reflecting light, an elastic body 5B located outside the shaft core 5A and made of silicon rubber or the like forming a surface layer, and the elastic body 5B. Hollow part 5C formed between shaft 5A
Have and.

The inside of the hollow portion 5C is filled with an inert gas and is in contact with only the belt 4 when the belt 4 is set at the fixing temperature, in other words, the sheet recording medium is the belt 4. The hollow portion 5C can be expanded most in the radial direction of the pressure roller when it is not sandwiched between the pressure roller 5 and the pressure roller 5. As shown in FIG. 4, inside the hollow portion 5C, a spacer that can maintain this state when the state in which the hollow portion 5C is inflated the most is set as the initial state and that allows shrinkage deformation in the hollow portion 5C. A plurality of 7 are arranged along the circumferential direction. In this embodiment, a columnar elastically deformable sponge is used as the spacer.

Inside the elastic body 5B, as shown in FIG. 3 (B), an optical fiber 6 parallel to the diameter of the pressure roller 5 is provided along the circumferential direction.
Book emitting fiber 6A and a plurality of receiving fibers 6
B is provided in combination. The ends of the optical fiber 6 on the same side in the extending direction of the light emitting fiber 6A and the light receiving fiber 6B, in the present embodiment, the shaft core 5A.
LED on the side of the light emitting fiber 6A at the end opposite to
And a distance sensor on the side of the light receiving fiber 6B. Since the pressure roller 5 reaches a high temperature to some extent, the irradiation light from the LED at room temperature is introduced into the light emitting fiber 6A, and the light reflected on the surface of the shaft core 5A from the end opposite to the light source side is the light receiving fiber. It is introduced into the distance sensor via 6B. Inside the hollow portion 5C located at the end on the axial core 5A side in the extension direction of the optical fiber 6, a light shielding plate 8 having a light transmitting opening formed in a part thereof is arranged. Part of the light reflected by the core 5A can be transmitted to any of the light receiving fibers 6B.

The light emitted from the light emitting element is carried to the hollow portion 5C by the light emitting fiber 6A, and the light L1 from the light emitting fiber 6A passes through the hollow portion 5C and is reflected on the surface of the shaft core 5A. The light-receiving fiber 6B receives the reflected light L2 from the axis 5A through the light-transmitting opening of the light-shielding plate 8 and conveys it to the light-receiving element. The light-receiving element receives the light from the light-receiving optical fiber 6B, and the camera is automatically focused. The width of the hollow portion 5C (the length of the pressure roller 5 in the radial direction) is measured by using the triangulation method used in the above.

FIG. 5 shows the hollow portion 5 for the optical fiber 6.
FIG. 4 is a diagram for explaining the trend of the reflected light from C. FIG. 4A shows an initial state in which the belt 4 and the pressure roller 5 are in direct contact, and FIG. (During copy operation)
1 shows a state in which the sheet-shaped recording medium is introduced between the belt 4 and the pressure roller 5 and is nipped and conveyed. In FIG. 5A, the surface temperature of the belt 4 is set to the fixing temperature, the sheet-shaped recording medium does not exist in the nip portion formed by the belt 4 and the pressure roller 5, and the pressure roller 5 is set to the belt 4. When pressed against the hollow part 5C, the filling (inert gas) in the hollow part 5C expands most and the width of the hollow part 5C (the pressure roller 5
Has the largest radial dimension S) of the elastic body 5
The surface of B is the most tense. At this time, the plurality of light receiving fibers 6B receives the reflected light L2 entering from the shaft core 5A through the light transmitting opening of the light shielding plate 8 by the upper (upstream in the rotational direction) optical fiber.

During image formation, the pressure roller 5 is deprived of heat by the sheet-shaped recording medium, and the temperature of the pressure roller 5 gradually decreases. Then, the inert gas, which is the filling material in the hollow portion 5C, gradually heat-shrinks. When the filler in the hollow portion 5C thermally shrinks, the spacer 7 also shrinks and deforms, so that the width of the hollow portion 5C becomes shorter (S ′ <S), and as shown in FIG.
The optical path until the light L1 emitted from the light emitting fiber 6A reaches the light receiving fiber 6B is shortened. At this time, with respect to the plurality of light-receiving fibers 6B, the distance (the length of the reflected light path) between the light-receiving fibers 6B and the shaft core 5A, that is, the lower side (rotation The reflected light L2 ′ is incident in a state of moving to the downstream side).

The distance between the optical fiber 6 and the shaft core 5A (width of the hollow portion 5C) is changed by indexing the fiber among the plurality of light receiving fibers 6B into which the reflected light is incident according to the width of the hollow portion 5C. Can be detected. Therefore, the light emitting element, the optical fiber 6, the light shielding plate 8 and the light receiving element constitute a means for detecting the distance (width of the hollow portion 5C) between the optical fiber 6 and the shaft core 5A.

Information regarding the width of the hollow portion 5C is output to the heating lamp control unit 9 shown in FIG.
In FIG. 6, the heating lamp control section 9 receives the output signal of the above-mentioned light receiving section (for convenience, the light receiving fiber 6B of the optical fiber 6 is shown in FIG. 6) via a known means, and the optical fiber 6 and the axis A switch is provided which is turned on when the distance from the core 5A is reduced to a predetermined distance or less and the width of the hollow portion 5C becomes a predetermined width or less.

The belt 4 is provided on the output side of the heating lamp controller 9.
Is connected to a heat source 10 which is arranged in the vicinity of the heat roller 3 and is provided separately from the halogen lamp 3A which is a heat source on the heating roller 3 side, and when the switch is turned on, the heat source 10 is turned on to turn on the temperature on the belt 4 side. Is increased to raise the temperature of the pressure roller 5 which is in pressure contact with the belt 4. As a result, the belt 4 and the pressure roller 5
It is possible to correct the temperature decrease of the pressure roller 5 which occurs when the sheet-shaped recording medium is sandwiched in the nip portion constituted by and by correcting the temperature on the belt 4 side to prevent fixing failure.

In the present embodiment, the procedure for preventing the fixing failure will be described with reference to the flowchart shown in FIG. When the image forming operation (copy operation) as described above is started, the belt 4 and the pressure roller 5 are
When the sheet-shaped recording medium is introduced into the nip part of
1) When the temperature at the nip portion is reduced, the space (hollow portion 5C) of the pressure roller 5 is contracted to reduce the width (ST
2). When the change in the width of the hollow portion 5C is discriminated (ST3), and when it is discriminated that the hollow portion has contracted to a certain width or less, the switch is turned on by the output signal of the light receiving portion in the heating lamp control portion 9 to turn on the heat source (see FIG. 7). Then, for the sake of convenience, the heating lamp 10 is turned on (ST4). The lighting period of the heat source 10 is determined by the result of determining whether or not the width of the hollow portion 5C has been restored to a certain width or more (ST5). When the width of the hollow portion 5C has been restored to a certain width or more, the heat source (heating lamp) 10 Is turned off (ST6). This makes it possible to correct the temperature decrease of the pressure roller 5 caused by heat removal by the sheet-shaped recording medium by the temperature increase on the belt 4 side and maintain a predetermined fixing temperature. It is possible to prevent defective fixing of the toner image carried on the toner.

According to this embodiment, when the heat of the pressure roller is taken away by the contact of the sheet-shaped recording medium, the temperature on the belt 4 side can be maintained at the fixing temperature.
Even if the contact state between the belt 4 and the pressure roller 5 becomes temporarily unstable due to the contraction deformation of the pressure roller 5 side, and the heat transfer to the sheet-shaped recording medium is not performed well, the belt 4 side does not. It is possible to reliably prevent the fixing failure by setting the temperature.

Hollow portion 5 due to heat shrinkage on the pressure roller 5 side
As a configuration for preventing the fixing failure in response to the change of the width of C, the applicant of the present application filed Japanese Patent Application Laid-Open No. 2000-33881.
There is a configuration disclosed in Japanese Patent No. 4 publication. In the configuration disclosed in the above publication, a pressure roller is provided so as to face the fixing roller instead of the belt, and the pressure roller 5 is pressed against the fixing roller when the hollow portion 5C of the pressure roller becomes a certain width or less. It is designed to control the pressure. In the case of this configuration, there is no configuration that guarantees the temperature of the member facing the pressure roller 5 at the fixing temperature as in the present embodiment. Therefore, even if the pressure roller is brought into pressure contact with the fixing roller, the fixing temperature for the sheet-shaped recording medium is controlled only by the temperature on the fixing roller side, and therefore the fixing temperature cannot be temporarily lowered. Will increase the probability of fixing failure. In contrast to this configuration, in the present embodiment, the fixing temperature for the sheet-shaped recording medium can be corrected on the belt side according to the contraction amount of the width of the hollow portion 5C of the pressure roller 5, so that the sheet-shaped recording medium can be corrected. Since it is possible to prevent the shortage of the applied heat amount, it is possible to maintain a state in which fixing failure hardly occurs.

Next, another embodiment of the present invention will be described with reference to FIG. The embodiment shown in FIG. 8 is the heat source 10 shown in FIG.
Is arranged in the vicinity of the pressure roller 5 instead of on the belt 4 side to control the heat of the pressure roller 5. In FIG. 8, the same members as those shown in FIG. 6 are designated by the same reference numerals. In FIG. 8, the heat source 10 is connected to the output side of the heating lamp control unit 9, and the heating lamp control unit 9 changes the width of the hollow portion 5C of the pressure lamp 5, that is, in the same manner as the configuration shown in FIG. The heat source 10 is turned on when the width of the hollow portion 5C reaches a certain value or less. In this embodiment, the sheet-shaped recording medium is the pressure roller 5.
When the hollow portion 5C contracts due to heat being taken from the pressure roller 5 due to the contact with the heat roller 10, the heat source 10 is turned on when the width of the hollow portion 5C becomes a certain width or less due to the contraction. Since the heat source 10 heats the pressure roller 5, it is possible to increase the temperature of the pressure roller 5 and help the width of the hollow portion 5C to return to a certain width or more. As a result, it is possible to prevent the fixing failure due to the temperature decrease in the nip.

According to this embodiment, the temperature drop can be eliminated for the pressure roller 5 which is a direct member of which heat is taken away by the passage of the recording medium on the sheet, so that the temperature at the nip portion can be eliminated. It is possible to suppress the decrease and eliminate the temperature gradient between the pressure roller 5 and the side of the belt 4 contacting the pressure roller 5,
The temperature of the nip portion can always be maintained at a constant fixing temperature.

[0038]

According to the first aspect of the invention, the heating control for the belt is executed when the width of the hollow portion provided in the pressure roller reaches a certain width or less in the radial direction of the pressure roller. As a result, the amount of heat required for fixing the toner image can be secured by correcting the temperature decrease caused by the pressure roller on the belt side which is a member facing the pressure roller. As a result, it is possible to prevent a fixing failure by suppressing a decrease in the amount of heat applied to the toner image at the nip portion.

According to the second aspect of the present invention, the heating control for the pressure roller is executed when the width of the hollow portion provided in the pressure roller reaches a certain width or less in the radial direction of the pressure roller. Therefore, the temperature of the pressure roller, which is a direct member having the width of the hollow portion, can be increased to prevent the temperature from decreasing in the nip portion. As a result, it becomes possible to prevent the fixing failure due to the temperature decrease in the nip portion.

According to the third aspect of the present invention, heating control can be performed on at least one of the belt and the pressure roller when the width of the hollow portion of the pressure roller reaches a certain width or less. It is possible to prevent a temperature drop in the nip portion formed by the pressure roller and prevent occurrence of fixing failure due to insufficient heat quantity.

According to the fourth aspect of the invention, since the hollow portion of the pressure roller is filled with the inert gas, mechanical deterioration such as corrosion of the pressure roller is prevented even when the pressure roller is exposed to high temperature. As a result, the contact relationship between the belt and the pressure roller can be appropriately maintained, and the energy-saving effect can be favorably obtained when the belt is used.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a fixing device used in the image forming apparatus shown in FIG.

3A and 3B are diagrams showing a configuration of a pressure roller used in the fixing device shown in FIG. 2, where FIG. 3A is an axial sectional view and FIG.
[FIG. 7] is an enlarged view of a position indicated by a symbol (B) in (A).

FIG. 4 is a schematic diagram for explaining an internal structure of a hollow portion provided in the pressure roller shown in FIG.

5A and 5B are diagrams showing an installation state of an optical fiber provided on the pressure roller shown in FIG. 3, FIG. 5A showing an initial state in which a toner image support is not in contact, and FIG. Each of them shows a state in which the support comes into contact with the substrate to remove heat.

FIG. 6 is a block diagram for explaining a configuration used for heating control in the fixing device shown in FIG.

FIG. 7 is a flowchart for explaining a control procedure with the configuration shown in FIG.

FIG. 8 is a block diagram illustrating a configuration used for heating control of a fixing device according to another embodiment of the present invention.

[Explanation of symbols]

1 fixing device 2 fixing roller 3 heating roller 3A Halogen lamp that is the heat source of the heating roller 4 belts 5 pressure roller 5A shaft core 5B elastic body 5C hollow part 6 optical fiber 6A light emitting fiber 6B Receiving fiber 7 Spacer 8 light shield 9 Heating lamp control unit 10 heat sources

Claims (4)

[Claims] 1. A belt wound around a pair of rollers and heated by a heat source incorporated in one of the rollers,
A pressure roller that moves the belt along the circumferential direction on a part of the peripheral surface, and the toner image carrier on which a toner image is carried is nipped and conveyed by the belt and the pressure roller. In an image forming apparatus having a structure for fixing an image, the pressure roller includes an elastic body having a flexible surface layer having a light emitting portion and a light receiving portion formed of optical fibers,
A shaft core capable of reflecting the light from the light emitting portion, and having a hollow portion provided between the surface layer and the shaft core and expandable and contractable by heat are provided along the radial direction, and in the radial direction, An image forming apparatus comprising means for controlling heating of the belt when the width of the hollow portion reaches a certain width or less. 2. A belt wound around a pair of rollers and heated by a heat source incorporated in one of the rollers,
A pressure roller that moves the belt along the circumferential direction on a part of the peripheral surface, and the toner image carrier on which a toner image is carried is nipped and conveyed by the belt and the pressure roller. In an image forming apparatus having a structure for fixing an image, the pressure roller includes an elastic body having a flexible surface layer having a light emitting portion and a light receiving portion formed of optical fibers,
A shaft core capable of reflecting the light from the light emitting portion, and having a hollow portion provided between the surface layer and the shaft core and expandable and contractable by heat are provided along the radial direction, and in the radial direction, An image forming apparatus comprising means for controlling heating of the pressure roller when the width of the hollow portion reaches a predetermined width or less. 3. A belt wound around a pair of rollers and heated by a heat source incorporated in one of the rollers,
A pressure roller that moves the belt along the circumferential direction on a part of the peripheral surface, and the toner image carrier on which a toner image is carried is nipped and conveyed by the belt and the pressure roller. In the image forming method of fixing an image, the pressure roller is capable of reflecting light from the light emitting portion, and an elastic body having a flexible surface layer having a light emitting portion and a light receiving portion formed of an optical fiber. A shaft, a hollow portion that is provided between the surface layer and the shaft core and is expandable and contractable by heat are provided along the radial direction, and the width of the hollow portion in the radial direction is equal to or less than a certain width. An image forming method, wherein heating control is performed on at least one of the belt and the pressure roller when the temperature is reached. 4. The image forming apparatus according to claim 1 or 2, wherein the hollow portion is filled with an inert gas.