JP2014056077A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device with high durability capable of detecting abnormal temperature rise of a fixing member in a quick and accurate manner with a relatively simpler configuration than before, and an image forming apparatus including the fixing device.SOLUTION: A fixing device includes a fixing belt 121, a heater 123, a heat transfer suppressing member 128, and a temperature sensor 129; and the heat transfer suppressing member 128 is arranged between the heater 123 and the fixing belt 121 so that a heat transfer suppression area is located in the vicinity of a non-heat transfer suppression area. A position of the heat transfer suppressing member 128 is switched depending on a paper width such as a large paper width and a small paper width of recording paper by an actuator of the fixing device so as to change a position relative to the fixing belt in the heat transfer suppression area.

Description

  The present invention relates to a fixing device that fixes an unfixed image on a recording medium and an image forming apparatus including the same.

  Generally, a fixing device used in an image forming apparatus such as a copying machine, a facsimile machine, or a printer includes a fixing roller that is heated by an internal heat source and a pressure roller that presses the fixing roller. A recording medium on which an unfixed image is formed passes through a nip formed between the fixing roller and the pressure roller. The unfixed image on the recording medium is heated by the fixing roller and pressed by the pressure roller when passing through the nip portion, and is fixed on the recording medium.

  In recent years, market demands for energy saving and high speed image formation have been increasing for image forming apparatuses such as copiers, facsimile machines, and printers in which such a fixing device is used. As a fixing device corresponding to such energy saving and high speed, fixing devices that heat by a contact heating method such as a heat roller method, a film heating method, and an electromagnetic induction heating method are widely adopted.

As this type of fixing device, an unfixed image on a recording medium is fixed by passing a recording medium on which an unfixed image is formed through a nip formed between a fixing belt and a pressure roller. Is known (see, for example, Patent Document 1).
The fixing belt of this fixing device is wound around a heating roller and a nip forming member, and heats an unfixed image on a recording medium and pressurizes it with a pressure roller.
In this fixing device, the fixing belt is thinned to have a low heat capacity, thereby shortening the warm-up time and reducing the power consumption.

  However, in such a fixing device composed of a fixing belt, it is necessary to shorten the warm-up time, which is the time required from a normal temperature state to a predetermined temperature at which printing is possible, that is, the reload temperature, such as when the power is turned on. ing. Another problem is to shorten the first print time, which is the time from when a print request is received to when a print operation is performed after the print request is received and the recording medium is discharged to the tray and the printing is completed. In addition, as the speed of image forming apparatuses increases, the number of sheets that pass through the recording medium per unit time increases, and the required amount of heat increases, so that the amount of heat is insufficient, particularly at the beginning of continuous printing. The lack of heat during high-speed rotation is also an issue.

In order to solve these problems, a fixing device that can heat the entire fixing belt has been proposed (see, for example, Patent Document 2).
The fixing device includes an endless fixing belt, a pipe-shaped metal heat conductor, a heat source including a heater, and a pressure roller that forms a nip portion in contact with the metal heat conductor via the fixing belt. And have. In this fixing device, a metal heat conductor is provided inside the fixing belt so as to be able to guide the movement of the fixing belt, and a heat source is provided inside the metal heat conductor. Is heated by. The fixing belt is moved in the circumferential direction so as to be rotated by rotation of the pressure roller.
With this configuration, the entire fixing belt can be warmed, the first print time from the heating standby time can be shortened, and the lack of heat during high-speed rotation can be solved.

However, in order to further save energy and improve the first print time, it is necessary to further reduce the heat capacity of the fixing belt. In order to further reduce the heat capacity of the fixing belt, the fixing belt may be configured to be directly heated without using the metal heat conductor from the structure in which the fixing belt is indirectly heated through the metal heat conductor. Conceivable.
In this configuration, power consumption is reduced by significantly reducing the heat capacity, and the first print time can be further shortened by rapidly raising the temperature of the fixing belt during heating. In addition, a metal heat conductor is not necessary, and the cost can be reduced.

However, in such a fixing device constituted by a fixing belt having a direct heating structure, the temperature of the fixing belt increases in a so-called non-sheet passing region where the recording medium does not pass, and the durability of the fixing belt is increased. There is a problem that it decreases.
That is, when the recording medium passes through the nip portion, the entire fixing belt is heated so as to reach a fixing temperature for fixing the unfixed image in the entire sheet passing area through which the recording medium passes. On the other hand, when the entire fixing belt is heated, the temperature of the fixing belt is lowered by the recording medium passing in the paper passing area, but the temperature of the fixing belt becomes high in the non-paper passing area because the recording medium does not pass. As a result, the fixing belt may be damaged. For this reason, in the non-sheet passing region, there is a problem that it is required to suppress the heating of the fixing belt by the heat source.

In order to solve this problem, a method of installing a heat transfer suppression member that suppresses heat transfer from a heat source to a fixing belt in a non-sheet passing region has been proposed.
In this regard, there is a fixing device that includes a rotation light shielding member as a heat transfer suppression member that is rotatably disposed outside the heat source, and is capable of adjusting the length of the heating roll in the axial direction (for example, Patent Documents). 3). Further, the fixing device includes a heating belt wound around a pair of rollers on the heating side and a pressure belt wound around the pair of rollers on the pressing side, and reflects the light irradiated from the heater lamp to the heating belt. There exists a thing which has a board and the light-shielding plate as a heat-transfer suppression member which interrupts light (for example, refer patent document 4).
Further, in the fixing device, a cylindrical fixing roller, a rod-shaped heater provided inside the fixing roller, and both ends in the axial direction of the fixing roller are provided between the fixing roller and the heater and are freely movable in the axial direction. There is one having a pair of shielding members as a heat transfer suppression member that moves to (see, for example, Patent Document 5).

However, in the fixing devices described in Patent Documents 3 to 5, although it is possible to prevent a high temperature from occurring in a non-sheet passing region where the recording medium does not pass through the fixing roller, abnormal heating of the fixing device causes abnormal heating. When this occurs, there is a problem that the fixing device may not be damaged. In particular, the fixing device described in Patent Document 4 has a problem that the configuration becomes complicated.
In the fixing device including the heat transfer suppression member described in Patent Document 3 to Patent Document 5, even when abnormal heating occurs while the recording medium passes through the nip portion, the recording medium passing through the sheet passing area is not affected. The temperature of the fixing belt decreases due to heat transfer. In the non-sheet passing region, the heat transfer from the heat source to the fixing belt is suppressed by the heat transfer suppressing member, so that the fixing belt temperature does not increase. As a result, although the surface temperature in the sheet passing area and the non-sheet passing area of the fixing belt is maintained within the normal range, the heat from the heat source accumulates in the peripheral components other than the fixing belt, resulting in a high temperature. As a result, there is a problem that the fixing device is damaged.

  In order to solve this problem, temperature sensors are attached to peripheral components other than the fixing belt whose temperature fluctuates due to heat transfer from the heat source, and the temperatures of these peripheral components are detected to detect the fixing device. A method for discriminating abnormal operation can be considered. However, in the case of such an abnormal operation determination method, the operation control of the heat source for maintaining the fixing belt for heating the recording medium at a predetermined fixing temperature is performed by detecting the temperature of the surface of the fixing belt, and the abnormal operation is performed. The presence / absence determination is performed by detecting an abnormal temperature rise in surrounding components.

  Therefore, there is a problem that temperature detection means such as a temperature sensor is separately provided, and the configuration becomes complicated. In addition, the control of the fixing temperature on the surface of the fixing belt and the control for determining the presence or absence of abnormal operation of the fixing device are performed separately, making the control complicated and controlling based on the temperature detected by separate temperature detection means There is a problem that it is difficult to ensure the accuracy of control.

  The present invention has been made to solve such a problem, and can detect an abnormal temperature rise of the fixing member quickly with high accuracy with a relatively simple configuration compared to the conventional one, and has high durability. It is an object of the present invention to provide a fixing device and an image forming apparatus including the same.

  In order to solve the above problems, a fixing device according to the present invention is configured to be rotatable and fix an unfixed image on a recording medium, a heat source provided inside the fixing member and heating the fixing member, A temperature sensor that detects the temperature of the surface of the predetermined region of the fixing member; and a heat transfer suppression member that suppresses heat transfer from the heat source to the specific region of the fixing member. The heat transfer suppression member is disposed between the heat source and the fixing member so as to be positioned in the vicinity of the predetermined region in the axial direction.

  According to the present invention, it is possible to quickly detect an abnormal temperature rise of a fixing member with high accuracy with a relatively simple configuration compared to the conventional one, and to provide a highly durable fixing device and an image forming apparatus including the same. can do.

1 is a schematic diagram showing a cross section of a color image forming apparatus including a fixing device according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view showing a fixing belt and a pressure roller of the fixing device according to the first embodiment of the present invention. FIG. 5 is an explanatory diagram illustrating a heat transfer suppression region and a heat transfer target region of a heat transfer suppression member with respect to the fixing belt of the fixing device according to the first embodiment of the present invention. The relationship between the position of the fixing belt and the surface temperature in the structure in which the heat transfer suppressing member is removed and the structure in which the heat transfer suppressing member is attached in the fixing device according to the first embodiment of the present invention is shown. It is a graph which shows suppression of the belt surface temperature outside a range. 6 is a graph showing the position of the fixing belt and the temperature distribution during normal heating and abnormal heating in the structure in which the heat transfer suppressing member is mounted in the fixing device according to the first embodiment of the present invention. FIG. 6 is a cross-sectional view illustrating a fixing belt and a pressure roller of a fixing device according to a second embodiment of the present invention. 7A and 7B are a perspective view and a partial enlarged cross-sectional view of a fixing device according to a second embodiment of the present invention, in which FIG. 9A shows the position of a heat transfer suppressing member corresponding to a recording paper having a large paper width, and FIG. The position of the heat transfer suppression member corresponding to a small recording paper is shown. FIG. 5 is an explanatory diagram illustrating a heat transfer suppression region and a heat transfer target region of a heat transfer suppression member with respect to the fixing belt of the fixing device according to the first embodiment of the present invention. FIG. 5 is an explanatory diagram illustrating a heat transfer suppression region and a heat transfer target region of a heat transfer suppression member with respect to the fixing belt of the fixing device according to the first embodiment of the present invention. FIG. 3 is a development view illustrating a heat transfer suppression region and a heat transfer target region of a heat transfer suppression member with respect to the fixing belt of the fixing device according to the first embodiment of the present invention.

  A first embodiment and a second embodiment in which an image forming apparatus including a fixing device according to the present invention is applied to a color image forming apparatus 1 will be described.

(First embodiment)
As shown in FIG. 1, a color image forming apparatus 1 according to the first embodiment includes an apparatus main body 2, an optical writing device 3, a process unit 4, a transfer device 5, a belt cleaning device 6, a sheet feeding device. A feeding device 7, a paper discharge tray 8, a registration roller 9, and a fixing device 10 are included.
The color image forming apparatus 1 includes a photoconductor including an image carrier that forms an image corresponding to each color separated into yellow (Y), cyan (C), magenta (M), and black (Bk). It has a tandem structure with drums arranged side by side.
The image forming apparatus according to the present invention is not limited to the tandem structure, and may have another structure. The image forming apparatus according to the present invention is not limited to the color image forming apparatus 1 and may be another image forming apparatus. For example, a copying machine or a facsimile machine may be used.

The apparatus main body 2 is composed of a casing that accommodates each component, and a conveyance path R that conveys a recording sheet S as a recording medium accommodated in the sheet feeding apparatus 7 is formed inside the casing. .
To the lower part of the paper discharge tray 8 of the apparatus main body 2, toner bottles 2aY, 2aC, 2aM, 2aBk filled with toners of yellow, cyan, magenta and black are detachably mounted. Further, a waste toner container (not shown) is provided inside the apparatus main body 2, and a toner transfer hose is connected to the entrance of the apparatus main body 2 so that waste toner entering from the toner transfer hose is stored. ing.

The optical writing device 3 includes a semiconductor laser (not shown) as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, and a rotating polygon mirror.
The optical writing device 3 is configured to form an electrostatic latent image on the process unit 4 by irradiating the process unit 4 with writing light Lb corresponding to each color. The image information included in the irradiated laser light is composed of single-color image information obtained by separating a desired full-color image into each color information of yellow, cyan, magenta, and black.

  The process unit 4 includes four process units 4Y, 4C, 4M, and 4Bk. The process unit 4Y includes a photosensitive drum 4d, a charging roller 4r, a developing device 4g, and a cleaning blade 4b. The process unit 4Y is configured such that charging, optical writing, development, transfer, cleaning, and charge removal are sequentially performed.

  In the process unit 4Y, first, the charging roller 4r is charged to accumulate static electricity on the photosensitive drum 4d, and optical writing is performed by the optical writing device 3 on the surface of the charged photosensitive drum 4d, whereby the photosensitive drum 4d. An electrostatic latent image consisting of an electrostatic pattern is formed on the surface. Then, the developing device 4g attaches yellow toner to the electrostatic latent image on the photosensitive drum 4d, that is, develops the toner image to form a toner image, and transfers the toner image to the transfer device 5. In preparation for the next transfer, the toner remaining on the photosensitive drum 4d is removed by the cleaning blade 4b, and the static electricity remaining on the photosensitive drum 4d is removed.

The photoconductor drum 4d has a photosensitive layer made of an inorganic or organic photoconductor on a cylindrical surface, and the charging roller 4r is disposed in the vicinity of the photoconductor drum 4d and between the photoconductor drum 4d. The photosensitive drum 4d is charged by this discharge.
The developing device 4g includes a supply portion for supplying yellow toner and a developing portion for attaching the yellow toner to the photosensitive drum 4d. The cleaning blade 4b has an elastic band member such as rubber and a toner removing member such as a brush. The developing device 4g is detachably accommodated in the apparatus main body 2.
The process units 4C, 4M, and 4Bk are also configured in the same manner as the process unit 4Y. The process unit 4C has a cyan toner image, the process unit 4M has a magenta toner image, and the process unit 4Bk has a black toner image. Each toner image is transferred to the transfer device 5.

The transfer device 5 includes a transfer belt 5a, a driving roller 5b, a driven roller 5c, a primary transfer roller 5d, and a secondary transfer roller 5e.
The transfer belt 5a is a so-called endless belt without a terminal, and is stretched between the driving roller 5b and the driven roller 5c in a tensioned state. Further, the transfer belt 5a is configured to be rotatable in the direction of the arrow A1 in the drawing, that is, to be able to run around by the driving roller 5b and the driven roller 5c.

The primary transfer roller 5d includes a primary transfer roller 5dY that presses the photosensitive drum 4d of the process unit 4Y via the transfer belt 5a, and a primary transfer roller 5dC and 5dM that similarly presses the photosensitive drum 4d of the process units 4C, 4M, and 4Bk. 5 dBk. Primary transfer nips are respectively formed at contact portions between the process units 4Y, 4C, 4M, and 4Bk and the pressed transfer belt 5a.
The secondary transfer roller 5e presses the drive roller 5b by pressing through the outer peripheral surface of the transfer belt 5a, and a secondary transfer nip is formed at the contact portion between the secondary transfer roller 5e and the transfer belt 5a. Yes.

  The belt cleaning device 6 is disposed between the secondary transfer nip and the process unit 4Y. The belt cleaning device 6 includes a toner removal member (not shown) that removes toner remaining on the outer peripheral surface of the transfer belt 5a during transfer at the secondary transfer nip, and toner that transfers the removed waste toner to a waste toner container. And a transfer hose.

  The sheet feeding device 7 is disposed at the lower part of the apparatus main body 2 and includes a paper feed cassette 7a for storing the recording paper S and a paper feed roller 7b. In the sheet feeding device 7, the recording paper S is taken out from the paper feeding cassette 7a one by one by the paper feeding roller 7b and sent out to the conveying path R.

The paper discharge tray 8 is disposed above the apparatus main body 2 above the optical writing device 3, and includes a tray 8a for storing the recorded recording paper S and a pair of paper discharge rollers 8b. .
In the paper discharge tray 8, the recording sheets S discharged from the transport path R by the pair of paper discharge rollers 8b are sequentially stacked and stacked one by one on the tray 8a.

The registration roller 9 has a pair of rollers, and is configured to adjust the conveyance of the recording sheet S that is fed by the sheet feeding roller 7 b of the sheet feeding device 7 and is in the conveyance path R.
A registration sensor (not shown) is disposed in the apparatus main body 2 between the registration roller 9 and the paper feed roller 7b on the transport path R so that the passage of the leading end portion of the recording paper S is detected. After a predetermined time elapses after the registration sensor detects the passage of the leading edge of the recording paper S, the recording paper S is abutted against the registration roller 9 and stops once. The registration roller 9 sandwiches and rotates the abutted recording sheet S at a predetermined timing, and conveys it to the secondary transfer nip. Examples of the predetermined timing include a time when the toner image superimposed in full color by the rotation of the transfer belt 5a is conveyed to the position of the secondary transfer nip.

  As shown in FIG. 2, the fixing device 10 includes a fixing belt 21, a pressure roller 22, a heater 23, a nip forming member 24, a support member 25, a holding member 26, a reflecting member 27, and heat transfer. The suppressing member 28 and the temperature sensor 29 are included. The fixing device 10 includes a control unit (not shown) that executes temperature control such as fixing temperature in components such as the fixing belt 21.

  In the fixing device 10, the recording sheet S on which the toner image is transferred is heated and pressed while passing through the nip portion N formed between the fixing belt 21 and the pressure roller 22, thereby recording the toner image. It is fixed on the paper S. The recording sheet S is separated from the fixing belt 21 when discharged from the nip portion N, and is conveyed toward the sheet discharge roller 8b through the conveyance path R.

The fixing belt 21 includes a belt base material 21a, an elastic layer 21b formed on the outer peripheral surface of the belt base material 21a, and a release layer 21c formed on the outer peripheral surface of the elastic layer 21b.
The fixing belt 21 is formed with a thickness of about 1 mm and has flexibility. The fixing belt 21 is elongated in the width direction of the recording sheet S passing through the outer peripheral surface, and is formed in an annular shape so that a cross section perpendicular to the width direction has a diameter of about 25 mm.

The fixing belt 21 may have a structure without the elastic layer 21b. When the elastic layer 21b is not provided, the heat capacity of the fixing belt 21 is reduced, and the thermal response and energy saving performance can be improved. The above-described diameter of the fixing belt 21 is appropriately selected within a range of about 15 to 120 mm in accordance with setting parameters of the fixing device 10.
The fixing belt 21 rotates in the arrow B2 direction as the pressure roller 22 rotates in the arrow B1 direction. That is, the fixing belt 21 uses the pressure roller 22 as a drive source. With the rotation of the fixing belt 21 and the pressure roller 22, the recording paper S enters the nip portion N in the direction of arrow B 3 and is discharged from the nip portion N.

  The belt substrate 21a is made of a material having a required mechanical strength, for example, a metal material such as nickel (Ni) or stainless steel (SUS), or a resin material such as polyimide (Polyimide), and has a thickness of 20 to 100 μm. It has a thickness of about. That is, it is formed of a thin metal film or resin film.

The elastic layer 21b is formed of a rubber material such as silicone rubber (Q) or fluorine rubber (FKM), and has a thickness of about 20 to 900 μm. When this elastic layer 21 b is provided, when heat and pressure are applied to the recording paper S passing through the nip portion N, pressure and heat conduction due to irregularities on the surfaces of the recording paper S and the fixing belt 21. The non-uniformity is improved.
That is, when the unfixed image on the recording paper S is crushed and fixed on the recording paper S, minute irregularities on the belt surface are transferred to the image, and a glossy uneven surface (skin-skin image) on the solid portion of the image. There may be a problem that remains. For example, when the elastic layer 21b is provided with a thickness of 100 μm or more, fine irregularities are absorbed by the deformation of the elastic layer 21b, and such a problem of the skin image can be solved.

  The release layer 21c is a material that has a high releasability from the recording paper S and the toner image, that is, a property that prevents the counterpart material from sticking to or sticking to the surface of the product such as a toner or a mold, so-called release. It is made of a material with good properties. Specific examples of materials that have good releasability include PFA (Tetra Fluoro ethylene-perfluoro Alkyl vinyl ether copolymer), PTFE (Poly Tetra Fluoro Ethylene), PEI (Poly Ether Imide), and PES (Poly Ether Sulphone). Resin material is mentioned. The release layer 21c is formed with a thickness of 1 to 200 μm.

The pressure roller 22 includes a roller 22a made of a mandrel, an elastic layer 22b formed on the outer peripheral surface of the roller 22a, and a release layer 22c formed on the outer peripheral surface of the elastic layer 22b.
The pressure roller 22 is configured to rotate by a driving force output from a driving mechanism (not shown) provided in the apparatus main body 2. This drive mechanism is comprised by drive parts, such as a motor, and deceleration parts, such as a reduction gear, for example. The pressure roller 22 is pressed against the fixing belt 21 by a pressure member (not shown), and the elastic layer 22b is crushed and elastically deformed to constitute a part of the nip portion N.

  The roller 22a is made of a metal material such as a carbon steel material (for example, SC, STKM) or an aluminum material (Al) having a required mechanical strength and good thermal conductivity, and is formed in a solid cylindrical shape. Yes. The roller 22a is formed in a hollow cylindrical shape, and is provided with a heat source such as a halogen heater inside. The recording paper is passing through the nip portion N via the roller 22a, the elastic layer 22b, and the release layer 22c. You may comprise so that S may be heated.

  Similar to the elastic layer 21b of the fixing belt 21, the elastic layer 22b is formed of a synthetic rubber such as silicone rubber (Q) or fluorine rubber (FKM). This synthetic rubber is made of so-called solid rubber that is relatively hard and not foamed. In the case where the roller 22a has a structure in which no heat source is provided, the synthetic rubber may be made of foamed elastic rubber layer so-called sponge rubber. Since this sponge rubber has bubbles inside, the heat insulation is improved, and the heat of the heated fixing belt 21 is not easily transferred to the pressure roller 22, that is, the heat is not easily taken away. Can be further improved.

  Similar to the elastic layer 21b of the fixing belt 21, the release layer 22c has a function of improving the so-called release property and enhancing the durability of the elastic layer 22b, and has a high thermal conductivity and high durability. It is formed. For example, the thing which apply | coated the fluororesin coating material which consists of PFA, PFA, or PTFE, or the thing which formed the silicone rubber layer or the fluororubber layer is used.

  The heater 23 is fixed to the apparatus main body 2 at a position separated from the fixing belt 21 on the inner peripheral side of the fixing belt 21. The heater 23 is composed of a known heat source having a single light emitting region so as to directly heat the fixing belt 21 with radiant heat. This heat source is composed of a so-called radiant heater, for example, a halogen heater that directly uses the radiant heat of a halogen lamp, a carbon heater that is composed of a quartz tube in which carbon fiber is enclosed in an inert gas, and is embedded in the ceramic. A ceramic heater composed of a resistance wiring can be mentioned. Control of energization and de-energization of the heater 23 is performed by the control unit described above.

  In addition, you may make it comprise the heater 23 with heat sources other than the well-known heat source which has a single light emission area | region. For example, the heater 23 may be a known electromagnetic induction heater that generates heat using the principle of electromagnetic induction. Examples of the electromagnetic induction heater include a heating device described in International Publication No. 2005/38533 and a heating device described in Japanese Patent Application Laid-Open No. 2007-334205. Specifically, these heating devices are arranged on the outer peripheral side of the fixing belt, and are arranged on the inner peripheral side of the fixing belt and the exciting device consisting of an exciting coil and a ferrite core, and sandwich the fixing belt. An opposing core that faces the core and a control unit that controls the excitation device are provided.

  In this electromagnetic induction heater, when a high frequency alternating current is passed through the exciting coil by the control unit, a magnetic field is formed around the exciting coil, and an eddy current is generated in the belt base material 21a made of metal of the fixing belt 21. Arise. When an eddy current is generated, Joule heat is generated by the electric resistance of the belt base material 21a itself, and heat is generated by so-called mutual induction heating. Therefore, in this case, the belt base material 21a becomes a so-called heat generation layer. The heat generating layer is preferably formed with a thickness of about 10 μm, for example, and is made of relatively efficient copper (Cu). The entire belt base material 21a is heated by the Joule heat. The fixing device 10 composed of the electromagnetic induction heater can raise the surface temperature of the fixing belt 21, that is, the fixing temperature to a desired temperature with less energy consumption and a short start-up time.

  The nip forming member 24 is formed to be elongated in the width direction of the recording paper S passing through the nip portion N, and the cross section orthogonal to the width direction is formed in a substantially rectangular shape, and a sliding surface portion 24a on which the fixing belt 21 slides. And a connecting portion 24b connected to the support member 25. The nip forming member 24 is disposed on the inner peripheral side of the fixing belt 21 and is fixed to the apparatus main body 2.

The sliding surface portion 24 a has a flat surface formed on the side facing the pressure roller 22 with the fixing belt 21 interposed therebetween. The fixing belt 21 comes into contact with the flat surface by the pressure of the pressure roller 22. In addition, when the pressure roller 22 presses the fixing belt 21, the elastic layer 22b is mainly crushed and deformed flat according to the flat surface of the sliding surface portion 24a.
A portion where the pressure roller 22 is deformed flat, that is, a nip portion N having a predetermined nip width is formed.

In addition, although the sliding surface part 24a is comprised with the structure which has a flat surface, you may make it comprise with structures other than a flat surface. For example, the sliding surface portion 24a may be configured with a curved surface formed to be recessed toward the fixing belt 21 when viewed from the pressure roller 22.
In the case of the structure having such a curved surface, the discharge direction of the leading edge of the recording paper S passing through the nip portion N is inclined toward the pressure roller 22, so that the recording paper S is easily separated from the fixing belt 21. The occurrence of so-called jams that are clogged during transport is suppressed.

Similar to the nip forming member 24, the support member 25 is elongated in the width direction of the recording paper S, and a cross section perpendicular to the width direction is formed by a groove that opens to the heater 23 side. And a housing portion 25b for housing the heater 23 and the reflecting member 27. The support portion 25 a is connected to the connection portion 24 b of the nip forming member 24, and supports the nip forming member 24 so as not to bend in the paper width direction by the pressure applied by the pressure roller 22. That is, a uniform nip width in the width direction of the recording paper S can be obtained.
Similarly to the nip forming member 24, the support member 25 is disposed on the inner peripheral side of the fixing belt 21 and is fixed to the apparatus main body 2.

The holding member 26 is disposed on the outer peripheral side of the fixing belt 21 and is fixed to the apparatus main body 2.
The holding member 26 has a holding function for holding both ends of the support member 25 in the paper width direction and a positioning function for determining the position of the support member 25 with respect to the apparatus main body 2. The holding member 26 also has a function as a travel guide that guides both ends of the fixing belt 21 in the paper width direction so that the fixing belt 21 that rotates is not displaced in the paper width direction.

  The reflection member 27 includes a fixed portion 27 a fixed to the apparatus main body 2, a reflection surface portion 27 b that reflects light emitted from the heater 23 toward the inner peripheral side of the fixing belt 21, and a cover portion 27 c that covers the support member 25. have. The fixing portions 27a are formed at both ends in the paper width direction, and are fixed to the apparatus main body 2 at both ends. The reflection surface portion 27 b is located between the support member 25 and the heater 23 and has a curved surface that is curved so as to surround the heater 23 on the side facing the heater 23.

  The cover portion 27c is configured to cover substantially the entire paper width direction of the opening portion opened on the opposite side of the support portion 25a of the support member 25. The reflection member 27 suppresses useless energy consumption due to the support member 25 being heated by radiation heat from the heater 23 or the like. Note that the same reflection effect can be obtained by performing a mirror surface treatment on the inner peripheral surface of the accommodating portion 25b of the support member 25 instead of including the reflection member 27. Further, even if the inner peripheral surface side of the accommodating portion 25b of the support member 25 is formed of a heat insulating material that insulates heat transmitted from the heater 23, the heat insulating effect of the heater 23 can be obtained.

  Similar to the reflection member 27, the heat transfer suppression member 28 is formed in an elongated shape in the width direction of the recording paper S, that is, in the axial direction, and is formed by a curved groove whose cross section perpendicular to the axial direction opens to the heater 23 side. . In addition, the heat transfer suppression member 28 is supported by the apparatus main body 2 by a guide (not shown) at one end and the other end in the width direction. The material and shape of the heat transfer suppressing member 28 are appropriately selected from metal materials and resin materials according to design specifications such as optical characteristics for blocking light from the halogen lamp and thermal characteristics capable of withstanding the fixing temperature. The

  The heat transfer suppression member 28 is provided between the fixing belt 21 and the heater 23, a heat transfer suppression region 28 a that suppresses heat transfer from the heater 23 to the fixing belt 21, and the heater 23 to the fixing belt 21. And a heat transfer target region 28b as a non-heat transfer suppression region that does not suppress heat transfer to the heat. The heat transfer suppression area 28a according to the first embodiment corresponds to a specific area according to the fixing device of the present invention, and the heat transfer target area 28b corresponds to a predetermined area according to the fixing device of the present invention.

As shown in FIG. 3, when a so-called paper passing area including the paper width of the recording paper S passing through the nip portion N is W0, the area of the paper passing area W0 and the broken line a from the paper passing area W0 are indicated. A region indicated by a broken line b from the region and the sheet passing region W0 is a region where the fixing belt 21 is heated so as to fix the unfixed image on the recording paper S, and is a heat transfer target region 28b. A temperature detection range T by the temperature sensor 29 is set in an area indicated by a broken line a from the sheet passing area W0.
Further, a region on the side separated from the paper passing area W0 from the broken line a and a region on the side separated from the paper passing area W0 from the broken line b are the heat transfer suppression area 28a.

When the fixing belt 21 is heated by the heater 23, the temperature of the fixing belt 21 at both ends of the heating portion is changed from the center of the heating portion due to heat radiation characteristics from the heater 23 and heat transfer to the non-heating portion of the fixing belt 21. So-called end temperature sagging occurs.
Since the temperature of the fixing belt 21 greatly affects the fixability of the unfixed image to be passed, the temperature in the entire sheet passing range of the fixing belt 21 is surely within the range of the fixing temperature at which the unfixed image can be normally fixed. It is necessary to keep it. Therefore, the heating range indicated by the broken line a to the broken line b is wider than the sheet passing area W 0 of the fixing belt 21.

The temperature sensor 29 is a sensor that detects the temperature of the surface of the fixing belt 21, for example,
It consists of a sensor element such as a contact thermistor. In addition, you may be comprised with the non-contact-type sensor provided with the thermistor and the thermopile.
The temperature sensor 29 is attached to the fixing device 10 so as to detect the surface temperature of the fixing belt 21 in the temperature detection range T shown in FIG.

This temperature detection range T is located in the heat transfer target region 28 b of the heat transfer suppressing member 28, and is a range in which the heat of the heater 23 is directly transferred to the fixing belt 21. That is, the temperature detection range T can accurately detect the temperature of the surface of the fixing belt 21 in contact with the recording paper S because heat transfer from the heater 23 is not suppressed by the heat transfer suppression member 28.
In addition, when the temperature detection range T is as small as possible, the heat transfer target area 28b can be reduced, so that the average temperature of the entire fixing belt 21 when the fixing device 10 operates normally can be reduced. It is desirable that the temperature of the fixing belt 21 be kept as low as possible even in the range of the heat resistant temperature or less because the deterioration of the fixing belt 21 is small. In general, a contact-type temperature sensor can realize a configuration having a smaller temperature detection range T at a lower cost than a non-contact-type temperature sensor. For this reason, the temperature sensor 29 used in the first embodiment is preferably a contact sensor. In the use of the contact type sensor, it is necessary to pay attention to the fact that the fixing property of the sheet passing image is affected by the wear of the fixing belt 21 at the contact point due to the rotational sliding of the fixing belt 21, and in the first embodiment, The temperature detection range T of the contact-type sensor is set outside the sheet-passable range of the fixing belt 21.

The basic operation of the color image forming apparatus 1 will be described below with reference to FIG.
When the image forming operation of the color image forming apparatus 1 is started, the photosensitive drums 4d of the process units 4Y, 4C, 4M, and 4Bk are rotated in the clockwise direction in the drawing by a driving device (not shown) to The surface of the drum 4d is uniformly charged to a predetermined polarity by the charging roller 4r. The surface of the charged photosensitive drum 4d is irradiated with laser light from the optical writing device 3, and an electrostatic latent image is formed on the surface of each photosensitive drum 4d. At this time, the image information to be optically written on each photosensitive drum 4d is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. The electrostatic latent image is visualized as a toner image (developer image) by supplying toner to the electrostatic latent image formed on the photosensitive drum 4d in this way by each developing device 4g. .

  When the drive roller 5b is driven to rotate counterclockwise in the figure, the transfer belt 5a is driven to travel in the direction indicated by the arrow in the figure. Further, a constant voltage or a constant current controlled voltage having a characteristic opposite to the toner charging polarity is applied to each primary transfer roller 5d. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 5d and each photosensitive drum 4d. Then, the toner images of the respective colors formed on the photosensitive drums 4d of the process units 4Y, 4C, 4M, and 4Bk are sequentially superimposed and transferred onto the transfer belt 5a by the transfer electric field formed in the primary transfer nip. . In this way, the transfer belt 5a carries a full-color toner image on its surface.

  Further, residual toner adhering to the surface of each photosensitive drum 4d after the toner image is transferred is removed by the cleaning blade 4b, and then the charge on the surface of each photosensitive drum 4d is gradually not shown. The surface potential is initialized by being subjected to a so-called slow current action that is removed by the electric device, and is prepared for the next image formation.

  Further, when an image forming operation for forming a toner image by causing toner to adhere to the formed electrostatic latent images on the respective photosensitive drums 4d by a developing unit is started, When the paper roller 7 b is driven to rotate, the recording paper S accommodated in the sheet feeding device 7 for the recording paper S is sent out to the transport path R. The recording sheet S sent to the conveyance path R is timed by the registration roller 9 and sent to the secondary transfer nip between the secondary transfer roller 5e and the driving roller 5b facing it. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the transfer belt 5a is applied to the secondary transfer roller 5e, thereby forming a transfer electric field in the secondary transfer nip.

  Then, the toner images on the transfer belt 5a are collectively transferred onto the recording paper S by the transfer electric field formed in the secondary transfer nip. The recording sheet S on which the toner image has been transferred is conveyed to the fixing device 10, and the recording sheet S is heated and pressed by the fixing belt 21 and the pressure roller 22 to fix the toner image. When the recording paper S is conveyed to the fixing device 10, heat transfer from the heater 23 is suppressed in the heat transfer suppression area 28a of the heat transfer suppression member 28, and from the heater 23 in the area of the heat transfer target area 28b. Is directly transferred to the fixing belt 21.

  The recording sheet S on which the toner image is fixed is separated from the fixing belt 21 by a separation mechanism (not shown), and is discharged to the tray 8a of the discharge tray 8 by the discharge roller 8b. Further, the toner remaining on the transfer belt 5a after the transfer is removed by the belt cleaning device 6, and the removed toner is conveyed to a waste toner container and collected.

  The above description is an image forming operation when a full color image is formed on the recording paper S. A single color image is formed using any one of the four process units 4Y, 4C, 4M, and 4Bk. Alternatively, two or three process units can be used to form a two or three color image.

Since the fixing device 10 according to the first embodiment is configured as described above, the following effects can be obtained.
That is, the fixing device 10 according to the first embodiment includes a fixing belt 21, a heater 23, a heat transfer suppression member 28, and a temperature sensor 29, and the heat transfer suppression region 28a is in the vicinity of the heat transfer target region 28b. The heat transfer suppressing member 28 is disposed between the heater 23 and the fixing belt 21 so as to be positioned at the position. And the heat-transfer suppression area | region 28a and the heat-transfer object area | region 28b become a structure which can be set by selecting the shape of the heat-transfer suppression member 28 suitably.
The heat transfer suppression area 28a is set at a position that is separated from the paper-passable area of the recording paper S. In addition, the temperature detection range T detected by the temperature sensor 29 is set at a position separated from the paper passing area, and is always set in the heat transfer target area 28b regardless of the change of the heat transfer suppression area 28a. ing. The temperature sensor 29 is provided in contact with the surface of the fixing belt 21 in the heat transfer target region 28b. The heater 23 is composed of either a radiant heat heater or an electromagnetic induction heater.

With such a configuration, the fixing device 10 according to the first embodiment can detect an abnormal temperature rise of the fixing belt 21 quickly with high accuracy with a relatively simple configuration compared to the conventional one, and has improved durability. The effect of being obtained.
Specifically, the following problems are solved and the durability of the fixing device 10 is improved.
That is, when the fixing device is configured with a structure in which the heat transfer suppressing member 28 is not mounted, the recording paper S of the fixing belt 21 passes through like the surface temperature distribution of the fixing belt 21 indicated by the broken line in FIG. The surface temperature of the fixing belt 21 outside the paper range is higher than the heat resistance temperature of the fixing belt 21 in the region of both end portions in the paper width direction.

  When the fixing device is configured with the heat transfer suppressing member 28 as in the fixing device 10 according to the first embodiment, the surface temperature of the fixing belt 21 indicated by the solid curve in FIG. It is set so that the heat resistance temperature of the fixing belt 21 does not exceed the region outside the paper range, and the predetermined fixing temperature is set in the region within the paper passing range.

As shown by the solid line in FIG. 5, when the fixing device 10 is operating normally and is normally heated, the surface temperature of the fixing belt 21 is set to a predetermined fixing temperature in an area within the sheet passing range. Is set.
In the area within the sheet passing range of the fixing belt 21, the recording sheet S passing through the nip N and the fixing belt 21 are in close contact with each other, so that the heat of the fixing belt 21 is transmitted to the recording sheet S and the surface temperature of the fixing belt 21. Will fall. As indicated by the dashed curve in FIG. 5, the fixing device 10 does not operate normally for some reason, and the heat resistance temperature of the fixing belt 21 is not exceeded even when abnormal heating occurs.

Therefore, in the case of the fixing device 10 according to the first embodiment, since the heat transfer suppressing member 28 is mounted, the following effects can be obtained. That is, even when the fixing device 10 is not only in normal heating but also in abnormal heating, as shown in FIGS. 4 and 5, the surface temperature of the fixing belt 21 is in a region other than the sheet passing range. Thus, in the heat transfer suppression area 28a, the heat transfer from the heater 23 is suppressed, so the fixing temperature exceeds the heat resistance temperature of the fixing belt 21 but does not exceed.
The heat transfer suppression member 28 has an effect that the heat transfer suppression region 28a and the heat transfer target region 28b can be easily and accurately set according to the shape thereof.
In the fixing device 10 according to the first embodiment, the fixing device 10 is not affected by how to use continuous paper passing, and the problem of damage to the fixing device 10 is solved, and the durability of the fixing device 10 is improved.

  Further, since the temperature detection range T shown in FIG. 3 is set in the heat transfer target area 28 b of the fixing belt 21, the surface temperature does not drop due to the recording paper S passing through the nip portion N. As a result, the normality in the temperature detection range T provided outside the paper passing range is larger than the temperature difference between the surface temperature of the fixing belt 21 during normal operation and the surface temperature of the fixing belt 21 during abnormal operation within the paper passing range. The temperature difference between the surface temperature of the fixing belt 21 during operation and the surface temperature of the fixing belt 21 during abnormal operation becomes larger. Therefore, an effect that the detection accuracy is improved in the temperature detection in the heat transfer target region 28b outside the sheet passing range is more than in the temperature detection in the sheet passing range. That is, the surface temperature of the fixing belt 21 varies depending on the heat storage state of the fixing device 10 and the heat transfer characteristics of the recording paper S. Therefore, when the surface temperature of the fixing belt 21 is detected by the temperature sensor 29, a small temperature difference is caused. It is difficult to determine whether the fixing device 10 is operating normally or abnormally. On the other hand, in the case of the fixing device 10 according to the first embodiment, as described above, the temperature difference between the normal operation and the abnormal operation of the detected temperature is larger. It is possible to determine whether the operation is abnormal or not. As a result, the abnormal operation of the fixing device 10 is quickly determined, and damage to the fixing device 10 due to the abnormal operation can be prevented in advance.

  In the fixing device 10 according to the first embodiment, the heat transfer region from the heater 23 to the fixing belt 21 can be simply set by simply mounting the heat transfer suppressing member 28 having a single structure between the heater 23 and the fixing belt 21. Can be set. That is, the heat transfer area to the fixing belt 21 is changed by changing the shape of the heat transfer suppressing member 28 in accordance with the size of the recording paper S passing through the nip portion N with a relatively simple configuration. Can do. Further, the temperature sensor 29 only needs to be provided on the surface of the fixing belt 21, and does not need to be provided on the components around the fixing belt 21. That is, since temperature detection is accurately performed by the single temperature sensor 29, temperature control can be executed easily and quickly.

Further, a temperature detection range T in which the temperature sensor 29 detects the surface temperature of the fixing belt 21 is provided in contact with the surface of the fixing belt 21 in the heat transfer target region 28b outside the sheet passing range. As a result, even if the surface of the fixing belt 21 is damaged by the temperature sensor 29 that comes into contact, the image on the recording paper S that passes through the nip portion N is not affected at all.
Further, since the heater 23 is composed of either a radiant heat heater or an electromagnetic induction heater, the fixing belt 21 can be directly heated. As a result, the heat capacity of the fixing device 10 can be greatly reduced, power consumption can be reduced, and the temperature of the fixing belt 21 can be increased rapidly during heating, further reducing the so-called first print time. It becomes possible.

(Second Embodiment)
Next, the fixing device 50 according to the second embodiment will be described with reference to the drawings.

  In the fixing device 50 according to the second embodiment, the heat transfer suppression member 28 of the fixing device 10 according to the first embodiment and the components around the heat transfer suppression member 28 are different, but the other components are the same. It is configured. Therefore, the same components will be described using the same reference numerals as those of the first embodiment shown in FIGS. 1 to 5, and only differences will be described in detail.

  The color image forming apparatus 1 according to the second embodiment is configured in the same manner as in the first embodiment, except for the fixing device 50.

  As shown in FIG. 6, the fixing device 50 includes a fixing belt 121, a pressure roller 122, a heater 123, a nip forming member 124, a support member 125, a holding member 126, a reflecting member 127, and heat transfer. The suppressing member 128 is configured to include a temperature sensor 129 and an actuator (not shown). As in the first embodiment, the fixing device 50 includes a control unit (not shown) that performs temperature control such as fixing temperature on components such as the fixing belt 121.

  As in the first embodiment, the fixing belt 121 includes a belt base 121a, an elastic layer 121b formed on the outer peripheral surface of the belt base 121a, and a release layer 121c formed on the outer peripheral surface of the elastic layer 121b. Have. As in the first embodiment, the fixing belt 121 is formed with a thickness of about 1 mm and has flexibility. The fixing belt 121 is elongated in the width direction of the recording paper S passing through the outer peripheral surface, and is formed in an annular shape so that a cross section perpendicular to the width direction has a diameter of about 25 mm.

The fixing belt 121 may also have a structure without the elastic layer 121b. When the elastic layer 121b is not provided, the heat capacity of the fixing belt 121 is reduced, and the fixing property can be improved. The above-described diameter of the fixing belt 121 is appropriately selected in a range of about 15 to 120 mm in accordance with setting parameters of the fixing device 50.
The fixing belt 121 rotates in the arrow B2 direction as the pressure roller 122 rotates in the arrow B1 direction. That is, the fixing belt 121 uses the pressure roller 122 as a drive source. With the rotation of the fixing belt 121 and the pressure roller 122, the recording paper S enters the nip portion N in the direction of arrow B 3 and is discharged from the nip portion N.
The belt base 121a, the elastic layer 121b, and the release layer 121c are formed in the same manner as in the first embodiment.

  As in the first embodiment, the pressure roller 122 includes a roller 122a made of a mandrel, an elastic layer 122b formed on the outer peripheral surface of the roller 122a, and a release layer 22c formed on the outer peripheral surface of the elastic layer 122b. Have. The pressure roller 122 is configured to rotate by the driving force output from the driving mechanism as in the first embodiment (not shown) provided in the apparatus main body 2. The pressure roller 122 is pressed against the fixing belt 121 by a pressure member (not shown), and the elastic layer 122b is crushed and elastically deformed to constitute a part of the nip portion N. The roller 22a, the elastic layer 22b, and the release layer 22c are formed in the same manner as in the first embodiment.

  The heater 123 includes a heater case 123 a and a pair of halogen lamps, and is fixed to the apparatus main body 2 on the inner peripheral side of the fixing belt 121 and at a position separated from the fixing belt 121. The heater 123 is composed of a heat source similar to that of the first embodiment so as to directly heat the fixing belt 121 with radiant heat. The heat source is a so-called radiant heater or electromagnetic induction heater.

The nip forming member 124 is formed to be elongated in the width direction of the recording paper S passing through the nip portion N, and the cross section orthogonal to the width direction is formed in a substantially rectangular shape, and a sliding surface portion 124a on which the fixing belt 121 slides. The connecting member 124b is connected to the support member 125.
The nip forming member 124 is disposed on the inner peripheral side of the fixing belt 121 and is fixed to the apparatus main body 2.
Similarly to the first embodiment, the sliding surface portion 124a is formed on the side facing the pressure roller 122 with the fixing belt 121 interposed therebetween, and has a flat surface on which the nip portion N is formed.

Similar to the nip forming member 124, the support member 125 is formed to be elongated in the width direction of the recording paper S, and has a support portion 125 a that supports the nip forming member 124.
The support part 125 a is connected to the connection part 124 b of the nip forming member 124, and supports the nip forming member 124 so as not to bend in the paper width direction by the pressure applied by the pressure roller 122. That is, a uniform nip width in the width direction of the recording paper S can be obtained.
Like the nip forming member 124, the support member 125 is disposed on the inner peripheral side of the fixing belt 121 and is fixed to the apparatus main body 2.

The holding member 126 is disposed on the outer peripheral side of the fixing belt 121 and is fixed to the apparatus main body 2. The holding member 126 has a holding function for holding both ends of the support member 125 in the paper width direction and a positioning function for determining the position of the support member 125 with respect to the apparatus main body 2.
The holding member 126 also has a function as a travel guide that guides both ends of the fixing belt 121 in the paper width direction so that the fixing belt 121 that rotates and moves in the paper width direction does not occur.

The reflecting member 127 includes a fixing portion 127 a that is fixed to the apparatus main body 2, a reflecting surface portion 127 b that reflects light emitted from the heater 123 toward the inner peripheral side of the fixing belt 121, and a cover portion 127 c that covers the support member 125. have.
The fixing portions 127a are formed at both ends in the paper width direction, and are fixed to the apparatus main body 2 at both ends. The reflection surface portion 127 b is located between the support member 125 and the heater 123 and has a recess formed to be recessed so as to surround the heater 123 on the side facing the heater 123.

  The cover portion 127c is configured to cover almost the entire sheet in the paper width direction on the opposite side of the support member 125 from the support portion 125a. The reflection member 127 suppresses useless energy consumption due to the support member 125 being heated by radiation heat from the heater 123 or the like.

  Similar to the reflection member 127, the heat transfer suppressing member 128 is formed in a curved groove that is elongated in the width direction of the recording sheet S, that is, in the axial direction, and a cross section orthogonal to the axial direction opens to the heater 123 side. . Further, the heat transfer suppressing member 128 is connected to an actuator (not shown) provided in the apparatus main body 2 at one end in the width direction, and is rotated without contact by the actuator. The other end in the width direction is rotatably supported by the apparatus main body 2 by a guide (not shown).

  As shown in FIG. 7A, the heat transfer suppression member 128 does not suppress heat transfer from the heater 123 by the actuator when the width of the recording sheet S is large, for example, when the recording paper S is A3 size. A non-contact and rotated state can be taken at the position of the heat transfer target area 128b as the non-heat transfer suppression area. Further, as shown in FIG. 7B, when the width of the recording paper S is small, for example, in the case of a postcard size, the actuator is placed at the position of the heat transfer suppression region 128a that suppresses heat transfer from the heater 123 by the actuator. It can take the state of rotating without contact.

  The material and shape of the heat transfer suppressing member 128 are the same as in the first embodiment, depending on the design parameters such as the optical characteristics for blocking light from the halogen lamp and the thermal characteristics that can withstand the fixing temperature. It is appropriately selected from materials.

The heat transfer suppression member 128 is provided between the fixing belt 121 and the heater 123. The heat transfer suppression region 128 a that suppresses heat transfer from the heater 123 and the heat transfer from the heater 123 are suppressed. And a heat transfer target area 128b.
In the heat transfer suppression member 128, the actuator rotates according to the width of the recording paper S passing through the nip portion N, and the size of each of the heat transfer suppression area 128a and the heat transfer target area 128b is determined. It is designed to switch. Note that the heat transfer suppression area 128a according to the second embodiment corresponds to a specific area according to the fixing device of the present invention, and the heat transfer target area 128b corresponds to a predetermined area according to the fixing device of the present invention.

  As shown in FIG. 8, when the paper width of the recording paper S is relatively large W1, areas indicated by broken lines c and d are areas where the fixing belt 121 is heated to fix the unfixed image on the recording paper S. It becomes the heat transfer object area | region 128b. In a region other than the paper width W1 of the recording paper S, the temperature detection range T by the temperature sensor 129 becomes the heat transfer target region 128b, and the region separated from the broken line a from the temperature detection range T by the temperature sensor 129 is the heat transfer suppression region 128a. It has become. Moreover, the area | region of the side separated from the broken line b is the heat-transfer suppression area | region 128a.

  As in the first embodiment, when the fixing belt 121 is heated by the heater 123, the fixing belt 121 at both ends of the heating portion is heated due to heat radiation characteristics from the heater 123 and heat transfer to the non-heating portion of the fixing belt 121. A so-called end temperature sag occurs in which the temperature is lower than the center of the heated portion. Since the temperature of the fixing belt 121 greatly affects the fixability of an unfixed image to be passed, the temperature in the entire sheet passing range of the fixing belt 121 is surely within the range of the fixing temperature at which the unfixed image can be normally fixed. It is necessary to keep it. For this reason, the heating range is wider than the sheet passing range of the fixing belt 121. That is, it is set so as to be wider than the paper width of the recording paper S passing therethrough.

As shown in FIG. 9, when the paper width of the recording paper S is relatively small W2, areas indicated by broken lines e and f are areas to be heated so as to fix the unfixed image on the recording paper S, and the heat transfer target area. 128b. In a region other than the paper width W2 of the recording paper S, the temperature detection range T by the temperature sensor 129 becomes the heat transfer target region 128b, and the region between the temperature detection range T by the temperature sensor 129 and the broken line c is the heat transfer suppression region 128a. It has become. Further, a region on the side separated from the broken line d in the direction opposite to the temperature detection range T by the temperature sensor 129 is a heat transfer suppression region 128a.
The paper widths W1 and W2 are substantially equal to the passable area where the recording paper S may pass through the nip portion N, or the paper widths W1 and W2 are slightly smaller than the passable area.

  In FIG. 9, the heat transfer suppression area 128 a is set so that the temperature of the fixing belt 121 near the temperature detection range T is equal to that in FIG. 8. As a result, the temperature sensor 129 can accurately determine the abnormal operation of the fixing device 50 regardless of the rotation state of the heat transfer suppression member 128.

FIG. 10 shows a developed view of the heat transfer suppression region 128a and the heat transfer target region 128b of the heat transfer suppression member 128. FIG. FIG. 10 shows the heat transfer suppression area 128 a and the heat transfer target area 128 b and the heat transfer area 128 c of the heater 123 in the paper width W 1 and the paper width W 2 of the recording paper S.
As shown in FIG. 10, when the upper portion of the development view is the paper width W1 of the recording paper S, the lower portion is the paper width W2 of the recording paper S, and the heat transfer suppression member 128 in the direction of the arrow g is shown. The paper width W2 is switched to the paper width W1 by the rotation, and the paper width W1 is switched to the paper width W2 by the rotation of the heat transfer suppressing member 128 in the direction opposite to the arrow e.
In other words, the heat transfer suppression area 128a in the axial direction of the fixing belt 121 can be changed according to the paper width of the recording paper S. The heat transfer suppression region 128 a is formed according to the shape of the heat transfer suppression member 128.

Similar to the first embodiment, the temperature sensor 129 includes a sensor that detects the temperature of the surface of the fixing belt 121.
The temperature sensor 129 is attached to the fixing device 50 so as to detect the surface temperature of the fixing belt 121 in the temperature detection range T shown in FIGS.
This temperature detection range T is located in the heat transfer target region 128 b of the heat transfer suppressing member 128 and is a range in which the heat of the heater 123 is directly transferred to the fixing belt 121. That is, the temperature detection range T can accurately detect the temperature of the surface of the fixing belt 121 in contact with the recording paper S because the heat transfer from the heater 123 is not suppressed by the heat transfer suppressing member 128.

Note that the color image forming apparatus 1 according to the second embodiment operates in the same manner as in the first embodiment.
In the fixing device 50 according to the second embodiment, unlike the fixing device 10 according to the first embodiment, the heat transfer suppression member 128 rotates according to the size of the recording paper S, and the heat transfer suppression region 128a and The heat transfer target area 128b is switched. That is, an actuator (not shown) operates according to detection information of a sensor that detects the paper width of the recording paper S, and when the width of the recording paper S is large as shown in FIG. It rotates in a non-contact manner to the position of the heat transfer target region 128b that does not suppress the heat transfer from 123. On the other hand, as shown in FIG. 7B, when the width of the recording sheet S is small, for example, when the postcard size is used, the actuator is placed at the position of the heat transfer suppression region 128a that suppresses heat transfer from the heater 123 by the actuator. It rotates without contact.

Since the fixing device 50 according to the second embodiment is configured as described above, the following effects can be obtained.
That is, the fixing device 50 according to the second embodiment includes a fixing belt 121, a heater 123, a heat transfer suppression member 128, and a temperature sensor 129, and the heat transfer suppression region 128a is in the vicinity of the heat transfer target region 128b. The heat transfer suppressing member 128 is disposed between the heater 123 and the fixing belt 121 so as to be positioned at the position. Then, the position of the heat transfer suppression region 128a with respect to the fixing belt 121 is changed by switching the position of the heat transfer suppression member 128 according to the paper width such as the large paper width W1 or the small paper width W2 of the recording paper S by the actuator of the fixing device 50. It is configured to be able to. And the heat-transfer suppression area | region 128a and the heat-transfer object area | region 128b become a structure which can be set by selecting the shape of the heat-transfer suppression member 128 suitably.

  Further, the heat transfer suppression area 128 a is set at a position separated from the paper passing area of the recording paper S. Further, the temperature detection range T detected by the temperature sensor 129 is set at a position separated from the paper passing area, and is always set in the heat transfer target area 128b regardless of the change of the heat transfer suppression area 128a. ing. The temperature sensor 129 is provided in contact with the surface of the fixing belt 121 in the heat transfer target region 128b. The heater 123 is configured by either a radiant heat heater or an electromagnetic induction heater.

  With such a configuration, the fixing device 50 according to the second embodiment can detect an abnormal temperature rise of the fixing belt 121 quickly with high accuracy with a relatively simple configuration compared to the related art, and has improved durability. The effect of being obtained.

Specifically, the following problems are solved and the durability of the fixing device 50 is improved.
That is, as in the first embodiment, when the fixing device is configured with a structure in which the heat transfer suppressing member 128 is not mounted, the fixing belt 121 is like a surface temperature distribution of the fixing belt 121 indicated by a broken line in FIG. The surface temperature of the fixing belt 121 is higher than the heat resistance temperature of the fixing belt 121 in the region of both end portions in the paper width direction of the fixing belt 121 outside the sheet passing range through which the recording paper S passes.

  When the fixing device is configured with the structure in which the heat transfer suppressing member 128 is mounted as in the fixing device 50 according to the second embodiment, the surface temperature of the fixing belt 121 indicated by the solid line curve in FIG. The heat resistance temperature of the fixing belt 121 is not exceeded in the area other than the paper range, and the predetermined fixing temperature is set in the area within the paper passing range.

As indicated by the solid line in FIG. 5, when the fixing device 50 is operating normally and is normally heated, the surface temperature of the fixing belt 121 is set to a predetermined fixing temperature in an area within the sheet passing range. Is set.
In the area within the sheet passing range of the fixing belt 121, the recording paper S passing through the nip portion N and the fixing belt 121 are in close contact with each other, so that the heat of the fixing belt 121 is transmitted to the recording paper S and the surface temperature of the fixing belt 121. Will fall. As indicated by the dashed curve in FIG. 5, the fixing device 50 does not operate normally for some reason, and the heat resistance temperature of the fixing belt 121 does not exceed even when abnormal heating occurs.
The heat transfer suppressing member 128 has an effect that the heat transfer suppressing region 128a and the heat transfer target region 128b can be easily and accurately set according to the shape thereof.
In the fixing device 50 according to the second embodiment, the fixing device 50 is not affected by the usage of continuous paper passing, and the problem of damage to the fixing device 50 is solved even during abnormal heating, and the durability of the fixing device 50 is improved. Enhanced.

  Similarly to the first embodiment, the temperature detection range T shown in FIGS. 8 and 9 is set in the heat transfer target area 128 b of the fixing belt 121, so that the recording paper S that passes through the nip part N The surface temperature does not drop. As a result, the temperature difference between the surface temperature of the fixing belt 121 during normal operation and the surface temperature of the fixing belt 121 during abnormal operation within the sheet passing range is normal in the temperature detection range T provided outside the sheet passing range. The temperature difference between the surface temperature of the fixing belt 121 during operation and the surface temperature of the fixing belt 121 during abnormal operation becomes larger. Therefore, the detection accuracy is improved in the temperature detection in the heat transfer target region 128b outside the sheet passing range, compared to the temperature detection in the sheet passing range.

  That is, since the surface temperature of the fixing belt 121 changes depending on the heat storage state of the fixing device 50, the heat transfer characteristics of the recording paper S, and the like, when the surface temperature of the fixing belt 121 is detected by the temperature sensor 129, a small temperature difference is caused. It is difficult to determine whether the fixing device 50 is operating normally or abnormally. On the other hand, in the case of the fixing device 50 according to the second embodiment, the temperature difference between the normal operation and the abnormal operation of the detected temperature is larger as described above. There is an effect that it is possible to determine which of the abnormal operation is performed. As a result, the abnormal operation of the fixing device 50 is quickly determined, and damage to the fixing device 50 due to the abnormal operation can be prevented in advance.

In the fixing device 50 according to the second embodiment, the heat transfer region from the heater 23 to the fixing belt 21 can be simply set by simply mounting the heat transfer suppressing member 128 having a single structure between the heater 123 and the fixing belt 121. Can be changed. That is, the heat transfer area can be quickly changed according to the size of the recording paper S passing through the nip portion N with a relatively simple configuration as compared with the related art.
With this configuration, when a plurality of patterns of heat transfer suppression areas are provided corresponding to the sheet width to be passed, the number of temperature sensors 129 for determining abnormal operation of the fixing device 50 is the number of patterns of the heat transfer suppression areas. It becomes possible to reduce more. Further, the temperature sensor 129 may be provided only on the surface of the fixing belt 121, and it is not necessary to provide the temperature sensor 129 on components around the fixing belt 121. That is, since temperature detection is accurately performed by the single temperature sensor 129, temperature control can be executed easily and quickly.

  Further, a temperature detection range T in which the temperature sensor 129 detects the surface temperature of the fixing belt 121 is provided in the heat transfer target region 128 b outside the sheet passing range so as to be in contact with the surface of the fixing belt 121. As a result, even if the surface of the fixing belt 121 is damaged by the contacting temperature sensor 129, the image on the recording sheet S passing through the nip portion N is not affected at all.

  Further, similarly to the first embodiment, the heater 123 is configured by either a radiant heat heater or an electromagnetic induction heater, so that the fixing belt 121 can be directly heated. As a result, the heat capacity of the fixing device 50 can be significantly reduced, power consumption can be reduced, and the temperature of the fixing belt 21 can be increased rapidly during heating, further reducing the so-called first print time. It becomes possible.

1 Color image forming device (image forming device)
10, 50 Fixing device 21, 121 Fixing belt (fixing member)
22, 122 Pressure roller (pressure member)
23, 123 Heater (heat source)
28, 128 Heat transfer suppression member 28a, 128a Heat transfer suppression region (specific region)
28b, 128b Heat transfer target area (non-heat transfer suppression area, predetermined area)
29, 129 Temperature sensor N Nip part S Recording paper (recording medium)
T Temperature detection range W1, W2 Paper width (paper passable area)

JP 2004-286922 A JP 2007-334205 A JP 2006-267420 A JP 2009-258203 A Japanese Patent Laid-Open No. 06-138789

Claims (10)

A fixing member configured to be rotatable and fixing an unfixed image of the recording medium;
A heat source provided inside the fixing member for heating the fixing member;
A temperature sensor for detecting the temperature of the surface of the predetermined region of the fixing member;
A heat transfer suppression member that suppresses heat transfer from the heat source to a specific region of the fixing member,
The fixing device, wherein the heat transfer suppression member is disposed between the heat source and the fixing member so that the specific region is positioned in the vicinity of the predetermined region in the axial direction of the fixing member.   The predetermined region is a non-heat transfer suppression region where heat transfer from the heat source is not suppressed, and the specific region is a heat transfer suppression region where heat transfer from the heat source is suppressed. The fixing device according to 1.   3. The heat transfer suppression area is configured to change the position of the fixing member in the axial direction according to the size of the width in the axial direction of a pre-recording medium. The fixing device described.   The fixing device according to claim 2, wherein the heat transfer suppression region is formed in accordance with a shape of the heat transfer suppression member.   The fixing device according to any one of claims 2 to 4, wherein the heat transfer suppression region is changed by movement of a position of the heat transfer suppression member.   6. The temperature detection range detected by the temperature sensor is always in a region where heat transfer from the heat source is not suppressed regardless of a change in the heat transfer suppression region. The fixing device according to any one of claims.   The fixing device according to any one of claims 1 to 6, wherein the temperature sensor is in contact with the surface of the fixing member in the non-heat transfer suppression region.   The fixing member has a paper-passable area through which the pre-recording medium may pass at the center in the axial direction, and the temperature detection range in which the temperature sensor detects the surface temperature of the fixing member is the axis. The fixing device according to any one of claims 1 to 7, wherein the fixing device is located at a position separated from the sheet passing area in a direction.   9. The heat source according to claim 1, wherein the heat source is configured by any one of a radiant heat heater that heats the fixing member by radiant heat and an electromagnetic induction heater that heats the fixing member by electromagnetic induction. A fixing device according to claim 1.   An image forming apparatus comprising the fixing device according to any one of claims 1 to 9.

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