JP2007256583A - Belt-fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt-fixing device having another fixing means independent of a heat source incorporated in a heat roller, wherein stable temperature control is made possible. <P>SOLUTION: The belt-fixing device 1 has an internal heat roller 6 and an internal heater lamp 6a in a hollow formed inside a fixing belt 2, and the surface of a fixing roller 3 is heated. A non-contact type thermistor 12 is disposed outside of and near the fixing belt 2, and at a position on the upstream side of a nip area N in the rotating direction x of the fixing belt 2. The fixing roller 3 has a diameter equal to or larger than that of the heat roller 5. The non-contact type thermistor 12 is disposed, at a position so that the angle α between a line AB, extending from the center A of the fixing roller 3 to the center B of the heat roller 5 and a line AC, extending from the center A to the center C of the non-contact type thermister 12 is 90° or larger. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device using a fixing belt used in an image forming apparatus such as a color laser printer.

  An image forming apparatus such as a color laser printer generally includes a fixing device for fixing a toner image on a sheet-like medium on which a toner image as an image to be fixed is formed. As a fixing device, there are a wide range of heat roller types that have a fixing roller (with a built-in heat source) and a pressure roller, and fix the toner image by heating and pressing at a nip formed by both rollers. Generally known.

  When the color toner is fixed using the above-mentioned heat roller pair type fixing device, a sufficient nip width is necessary for sufficiently melting and mixing the color toners and discharging them without winding around the fixing roller. Therefore, measures have been taken to provide a thick elastic layer on the fixing roller and the pressure roller. However, the heating by the heat source built in the fixing roller raises the temperature of the elastic layer at the core metal interface of the fixing roller, which causes hardening and liquefaction of the elastic layer, resulting in a short life of the fixing roller. It was.

  Therefore, a fixing belt consisting of an endless belt having a thin and low heat capacity is provided between a heating roller (with a built-in heat source) and a fixing roller (without a built-in heat source), and is heated by the heating roller. A belt fixing device has been proposed in which a toner image is heated and melted and fixed at a nip portion where a fixing belt is formed by a fixing roller and a pressure roller.

  When the belt fixing device is used, problems such as curing deterioration and liquefaction of the elastic layer of the fixing roller are solved. Further, since the nip shape can be made an upward convex shape by the thickness and hardness of the elastic layer of the fixing roller and the pressure roller, a good paper discharge property can be obtained.

  Also in the belt fixing device, similarly to the heat roller pair type fixing device, the toner image is fixed to the sheet-like medium by melting by heating, and therefore temperature control is very important. In the belt fixing device, in order to perform stable temperature control, it is desirable to detect a temperature close to the temperature at the nip portion of the surface of the fixing belt that directly relates to the fixing of the toner image. Further, in order not to cause the problem of skewing and durability of the fixing belt, a non-contact type is often used as the temperature detecting means.

  By the way, in the conventional belt fixing device, when performing high-speed fixing of 40 sheets per minute or when fixing thick paper continuously at high speed, a heating roller transfer portion is provided to increase the rotation speed of the fixing belt. There is a problem that the passing time is short and it is difficult to supply the amount of heat necessary for fixing. Therefore, it has been proposed to add a new heating means separately from the heat source built in the heating roller.

For example, Patent Literature 1 includes a fixing belt that is an endless belt that is stretched between a fixing roller and a support roller, and a nip portion is formed by the fixing roller and the pressure roller via the fixing belt. In the fixing device, it has been proposed to arrange a heating roller in contact with a position outside the fixing belt and upstream of a nip portion in the rotation direction of the fixing belt.
JP 2005-99104 A

  However, in the belt fixing device described in Patent Document 1, when the heating roller is disposed in the vicinity of the nip portion, it is difficult to dispose the non-contact type temperature detecting means in the vicinity of the nip portion. For this reason, it is difficult to detect a temperature close to the temperature at the nip portion of the surface of the fixing belt that directly relates to the fixing of the toner image, and it becomes difficult to perform stable temperature control.

  In view of the above problems, an object of the present invention is to provide a belt fixing device capable of stable temperature control in a belt fixing device having a new heating means separately from a heat source built in a heating roller. And

  In the present invention, the belt fixing device is a pair of fixing rollers and a pressure roller arranged opposite to each other, a heating roller containing a heat source, and an endless belt that is spanned between the fixing roller and the heating roller. A fixing belt comprising a belt, and a heating unit for heating the surface of the fixing roller in a hollow portion formed inside the fixing belt, wherein the fixing belt is formed by pressure contact between the fixing roller and the pressure roller. In the belt fixing device for fixing the toner image on the sheet-like medium by heating and melting at the nip portion, the outer side and the vicinity of the fixing belt and upstream of the nip portion in the rotation direction of the fixing belt. A non-contact type belt temperature detecting means is provided at the position.

  According to this, the belt fixing device of the present invention is provided with a heating means for heating the surface of the fixing roller in a hollow portion formed inside the fixing belt, and further, on the outer side and in the vicinity of the fixing belt, in the rotation direction of the fixing belt Non-contact type belt temperature detecting means is provided at a position upstream of the nip portion. Here, since the belt temperature detecting means is disposed outside and in the vicinity of the fixing belt, it detects the temperature of the surface of the fixing belt directly related to the fixing of the toner image. Further, since the belt temperature detecting means is disposed at a position upstream of the nip portion in the rotation direction of the fixing belt, it detects the temperature of the surface of the fixing belt before heat is taken away by fixing of the toner image. It will be. Therefore, not only the heat from the heating roller but also the heat via the fixing roller surface from the heating means is transmitted to the fixing belt, the temperature control of the belt fixing device is performed at the nip portion of the fixing belt surface directly related to the fixing of the toner image. It can be performed using a temperature close to the temperature. Further, since the belt temperature detecting means is a non-contact type, there is no problem of skewing and durability of the fixing belt. Therefore, even when a large amount of heat is required, such as high-speed output or thick paper fixing, the fixing belt can be heated sufficiently without unevenness, and there is no problem with skewing and durability of the fixing belt, and the belt fixing device with reduced cost. In addition, a belt fixing device capable of stable temperature control is obtained.

  In the present invention, in the belt fixing device having the above-described configuration, the fixing roller has a diameter larger than that of the heating roller, and includes a belt temperature detecting unit, and a cross section perpendicular to the rotation axis of the fixing roller and the heating roller. The angle between the line segment from the center of the fixing roller toward the center of the heating roller and the line segment toward the center of the belt temperature detecting means is preferably 90 degrees or more.

  According to this, the fixing roller has a diameter larger than that of the heating roller, and includes a belt temperature detection unit, and includes a belt temperature detection unit, and the section is perpendicular to the rotation axis of the fixing roller and the heating roller. The angle formed by the line segment and the line segment toward the center of the belt temperature detecting means is 90 degrees or more. In other words, the center of the belt temperature detecting means faces the portion of the fixing roller surface where the fixing belt is wound (contacted). For this reason, the belt temperature detecting means detects the temperature of the surface of the fixing belt in the portion where the fixing belt is wound around the fixing roller. In the belt fixing device of the present invention, the heat passing from the heating means through the surface of the fixing roller is also transmitted to the fixing belt. Therefore, by detecting the temperature of the surface of the fixing belt at the portion where the fixing belt wraps around the fixing roller, the belt The temperature control of the fixing device can be performed by using a temperature very close to the temperature at the nip portion of the surface of the fixing belt directly related to the fixing of the toner image.

  According to the present invention, in the belt fixing device having the above-described configuration, the center of the nip portion from the center of the fixing roller in a cross section perpendicular to the rotation axis of the fixing roller and the pressure roller, including the belt temperature detecting unit. It is desirable that the angle formed by the line segment toward the center and the line segment toward the center of the belt temperature detecting means is 45 degrees or more.

  According to this, in a cross section perpendicular to the rotation axis of the fixing roller and the pressure roller including the belt temperature detecting means, a line segment from the center of the fixing roller to the center of the nip portion and the center of the belt temperature detecting means. The angle formed by the line segment is 45 degrees or more. In other words, the position where the belt temperature detecting means is disposed is away from the conveyance path of the sheet-like medium on which the toner image is formed, and does not hinder the conveyance of the sheet-like medium.

  In the present invention, the belt fixing device having the above-described configuration may include a contact-type temperature detection unit that contacts the heating roller or a non-contact type temperature detection unit disposed in the vicinity of the heating roller. .

  According to this, since the contact type temperature detection means that contacts the heating roller or the non-contact type temperature detection means disposed in the vicinity of the heating roller is provided, the temperature of the heating roller can also be used for temperature control. Furthermore, stable and advanced temperature control becomes possible. Here, when the contact type temperature detecting means that can directly detect the temperature of the heating roller is used, the time until the temperature control is stabilized can be shortened. When the non-contact type temperature detecting means is used, There are no durability issues. Moreover, of course, temperature control which complements each other using both of these is also possible.

  In the present invention, the belt fixing device having the above-described configuration may include a contact-type temperature detection unit that contacts the heating unit or a non-contact type temperature detection unit disposed in the vicinity of the heating unit. .

  According to this, since the contact-type temperature detection means that contacts the heating means or the non-contact type temperature detection means disposed in the vicinity of the heating means is provided, the temperature of the heating means can also be used for temperature control. Furthermore, stable and advanced temperature control becomes possible. Here, when a contact-type temperature detection means that can directly detect the temperature of the heating means is used, the time until temperature control is stabilized can be shortened. When a non-contact-type temperature detection means is used, the heating means There are no durability issues. Moreover, of course, temperature control which complements each other using both of these is also possible.

  In the present invention, the belt fixing device having the above-described configuration may include an external heating unit that heats the surface of the pressure roller.

  According to this, an external heating means for heating the pressure roller surface is used as a means for increasing the temperature of the pressure roller surface, which requires a certain temperature in order to improve toner fixability. This eliminates the need to heat the pressure roller with a built-in heat source, eliminating the problems of hardening and liquefaction of the elastic layer at the core metal interface of the pressure roller, resulting in shortening the life of the pressure roller. it can.

  In the present invention, the belt fixing device having the above-described configuration includes a contact-type temperature detection unit that contacts the external heating unit or a non-contact type temperature detection unit disposed in the vicinity of the external heating unit. Also good.

  According to this, it is equipped with a contact-type temperature detection means that contacts the external heating means or a non-contact type temperature detection means arranged in the vicinity of the external heating means, so the temperature of the external heating means is also used for temperature control. As a result, more stable and advanced temperature control is possible. Here, when a contact-type temperature detection means that can directly detect the temperature of the external heating means is used, the time until stabilization of temperature control can be shortened, and when a non-contact-type temperature detection means is used, external heating is performed. The problem of durability of the means does not occur. Moreover, of course, temperature control which complements each other using both of these is also possible.

  According to the present invention, there is provided a belt fixing device capable of stable temperature control in a belt fixing device having a new heating means separately from a heat source incorporated in a heating roller.

  The best mode for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing a schematic configuration of a belt fixing device 1 according to the first embodiment of the present invention. The belt fixing device 1 is installed in a color copying machine (not shown). A color copying machine (not shown) reads an original image by a reading unit, forms a toner image corresponding to the original image on an image forming unit, transfers the image to a sheet, and fixes the toner image transferred to the sheet. The belt fixing device 1 is used when fixing a toner image.

  The belt fixing device 1 according to this embodiment includes a fixing belt 2, a fixing roller 3, a pressure roller 4, a heating roller 5, an internal heating roller 6, and an external heating roller 7. A heater lamp 5 a (heat source) is disposed in the hollow of the heating roller 5, an internal heater lamp 6 a is disposed in the hollow of the internal heating roller 6, and an external heater lamp 7 a is disposed in the hollow of the external heating roller 7. It is installed.

  The belt fixing device 1 includes a non-contact thermistor 12 (belt temperature detecting means), a contact thermistor 15 (temperature detecting means) that contacts the heating roller 5, and a contact thermistor 16 (contacts the internal heating roller 6). Temperature detecting means) and a contact thermistor 17 (temperature detecting means) that contacts the external heating roller 7. The details of the position where the non-contact thermistor 12 is disposed will be described later.

  The belt fixing device 1 has a pre-fixing guide 21, a post-fixing guide 22, and a pair of conveying rollers 23 a and 23 b around the fixing belt 2.

  The fixing belt 2 is wound around the fixing roller 3 and the heating roller 5 and is driven by the fixing roller 3 in the arrow x direction. The fixing belt 2 is an endless belt made of a nickel thin plate having a thickness of 40 μm, and has an outer peripheral surface coated with an offset preventive agent such as a silicon rubber film.

  The fixing roller 3 and the pressure roller 4 are rubber rollers arranged so as to face each other. The pressure roller 4 is pressed toward the center of the fixing roller 3 via the fixing belt 2, so that the nip portion N is formed. Form. The heating roller 5 applies tension to the fixing belt 2 and is made of a cylindrical aluminum tube having a constant thickness in the axial direction. Then, heat from the heater lamp 5a disposed in the hollow of the heating roller 5 is transmitted to the fixing belt 2 through the heating roller 5, and the fixing belt 2 is heated. Note that the fixing roller 3 is set to have a diameter larger than that of the heating roller 5.

  Further, the belt fixing device 1 has an internal heating roller 6 pressed against the fixing roller 3 in a hollow portion formed inside the endless fixing belt 2, and the internal heating roller 6 is driven by the rotation of the fixing roller 3. Then rotate. The heat transmitted from the internal heater lamp 6 a disposed in the hollow of the internal heating roller 6 to the surface of the fixing roller 3 through the internal heating roller 6 is transmitted to the fixing belt 2. That is, the internal heating roller 6 and the internal heater lamp 6a constitute a heating unit that heats the surface of the fixing roller 3. And the heating by this heating means prevents the fixing temperature from being lowered at the time of high-speed fixing of 40 sheets or more per minute.

  Further, the belt fixing device 1 has an external heating roller 7 pressed against the pressure roller 4, and the external heating roller 7 rotates following the rotation of the pressure roller 4. Then, heat is transmitted from the external heater lamp 7 a disposed in the hollow of the external heating roller 7 to the surface of the pressure roller 4 through the external heating roller 7. That is, the external heating roller 7 and the external heater lamp 7a constitute an external heating means for heating the surface of the pressure roller 4. The surface of the pressure roller 4 needs a certain temperature to improve the toner fixing property. However, by using this external heating means, it is not necessary to heat the pressure roller 4 with a built-in heat source. The problem of hardening deterioration and liquefaction of the elastic layer at the core metal interface of the pressure roller 4 and the resulting shortening of the life of the pressure roller 4 can be solved.

  In the belt fixing device 1 having the above-described configuration, the sheet S (sheet-like medium) after the toner image T is formed is conveyed in the direction of the arrow y by the pre-fixing guide 21 and is heated and pressurized in the nip portion N, whereby toner The image T is fixed. Thereafter, the sheet S is discharged to a tray provided outside the color copying machine by the post-fixing guide 22 and the transport rollers 23a and 23b.

  Next, details of the position where the non-contact thermistor 12 is disposed will be described. The non-contact thermistor 12 is disposed outside and in the vicinity of the fixing belt 2 and upstream of the nip portion N in the rotation direction x of the fixing belt 2.

  When the non-contact type thermistor 12 is disposed at the above position, the non-contact type thermistor 12 has a temperature on the surface of the fixing belt 2 directly related to fixing of the toner image T before heat is taken away by fixing of the toner image T. Will be detected. Therefore, the belt fixing device 1 can perform temperature control using a temperature close to the temperature at the nip portion N on the surface of the fixing belt 2 directly related to the fixing of the toner image T. Further, since the non-contact type thermistor 12 detects the temperature of the surface of the fixing belt 2 in a non-contact manner, there is no problem of skewing or durability of the fixing belt 2.

  Further, the position where the angle α formed by the line segment AB from the center A of the fixing roller 3 toward the center B of the heating roller 5 and the line segment AC toward the center C of the non-contact thermistor 12 is 90 degrees or more. In addition, a non-contact type thermistor 12 is disposed.

  When the non-contact type thermistor 12 is disposed at the above position, the fixing roller 3 has a diameter larger than that of the heating roller 5, so that the center C of the non-contact type thermistor 12 is the fixing belt on the surface of the fixing roller 3. It will face the part where 2 is wound (contacted). Therefore, the non-contact type thermistor 12 detects the temperature of the surface of the fixing belt 2 at the portion where the fixing belt 2 is wound around the fixing roller 3.

  In the belt fixing device 1, the heat transferred from the internal heater lamp 6 a disposed in the hollow of the internal heating roller 6 to the surface of the fixing roller 3 through the internal heating roller 6 is transferred to the fixing belt 2. By detecting the temperature of the surface of the fixing belt 2 at the portion where the fixing belt 2 is wound around the fixing roller 3, the temperature control of the belt fixing device 1 is performed so that the nip portion N of the surface of the fixing belt 2 directly related to the fixing of the toner image is controlled. Can be performed using a temperature very close to the temperature at.

  Further, a position where an angle β formed by a line segment AD from the center A of the fixing roller 3 toward the center D of the nip portion N and a line segment AC toward the center C of the non-contact thermistor 12 is 45 degrees or more. In addition, a non-contact type thermistor 12 is disposed.

  When the non-contact type thermistor 12 is disposed at the above position, the position at which the non-contact type thermistor 12 is disposed moves away from the conveyance path of the paper S on which the toner image T is formed and obstructs the conveyance of the paper S. do not become.

  The belt fixing device 1 includes a contact thermistor 15 that contacts the heating roller 5, a contact thermistor 16 that contacts the internal heating roller 6, and a contact thermistor 17 that contacts the external heating roller 7. . Therefore, the temperature of the heating roller 5, the temperature of the internal heating roller 6, and the temperature of the external heating roller 7 can be used for temperature control, and more stable and advanced temperature control is possible. In the present embodiment, a contact thermistor that can directly detect the temperature of the roller is used as the temperature detecting means of the heating roller 5, the internal heating roller 6, and the external heating roller 7. Therefore, a non-contact type thermistor is used. Compared to the case of using it, the time until the temperature control is stabilized can be shortened.

(Second Embodiment)
FIG. 2 is a cross-sectional view showing a schematic configuration of a belt fixing device 1 according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the part which is common in the belt fixing device 1 which concerns on 1st Embodiment, and description is abbreviate | omitted. The belt fixing device 1 according to the present embodiment has a planar heating element 30 (heating means) in a hollow portion formed inside the fixing belt 2, and the planar heating element 30 is in pressure contact with the fixing roller 3. Further, the belt fixing device 1 has a contact thermistor 31 (temperature detection means) that contacts the planar heating element 30.

  FIG. 3 is a cross-sectional view showing a schematic configuration of the planar heating element 30. As shown in FIG. 3, the sheet heating element 30 has a surface on one side of the substrate 30a as a surface on the film sliding side, and is electrically connected with TA2N, silver palladium, or the like along the surface longitudinal direction at a substantially central portion of the surface. This is a resistance heating element having a planar low-heat capacity resistance heating element layer 30b coated with a resistance material. Further, it has a glass layer 30c and is in pressure contact with the fixing roller 3 on the surface on the glass layer 30c side.

  According to the above configuration, the sheet heating element 30 provided in the hollow portion formed inside the fixing belt 2 constitutes a heating means for heating the surface of the fixing roller 3, so that the internal heating roller 6 and the internal heater lamp Compared with the case where 6a is used as a heating means, the belt fixing device 1 has a simple configuration, and the cost can be reduced. Further, since the contact type thermistor 31 that contacts the planar heating element 30 is provided, the temperature of the on-surface heating element 30 can also be used for temperature control, and more stable and advanced temperature control is possible. In this embodiment, the contact thermistor 31 that can directly detect the temperature of the on-surface heating element 30 is used as the temperature detecting means of the on-surface heating element 30, and therefore, a non-contact type thermistor is used. In comparison, the time until the temperature control is stabilized can be shortened.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, a contact type thermistor is used as the temperature detecting means of the heating roller 5, the internal heating roller 6, the external heating roller 7, and the sheet heating element 30, but a non-contact type thermistor is used. It is also possible to use it. When a non-contact thermistor is used, the time until the temperature control is stabilized increases as compared with the case where a contact thermistor is used, but the heating roller 5, the internal heating roller 6, the external heating roller 7, The durability problem of the planar heating element 30 does not occur.

  Further, both a contact type thermistor and a non-contact type thermistor can be used as temperature detecting means for the heating roller 5, the internal heating roller 6, the external heating roller 7, and the sheet heating element 30. In this case, for example, the contact type thermistor is disposed at a position corresponding to the non-sheet passing region of the heating roller 5, the internal heating roller 6, the external heating roller 7, and the sheet heating element 30, and the non-contact type thermistor is passed through the sheet region. Until the heating roller 5, the internal heating roller 6, the external heating roller 7, and the sheet heating element 30 reach a predetermined temperature, the temperature is detected using a contact type thermistor, and the heating roller 5. After the internal heating roller 6, the external heating roller 7, and the sheet heating element 30 reach a predetermined temperature, it may be possible to detect the temperature using a non-contact thermistor.

  With such a configuration, the contact type thermistor is disposed at a position corresponding to the non-sheet passing region, so that the durability problem of the heating roller 5, the internal heating roller 6, the external heating roller 7, and the planar heating element 30. In addition, after the heating roller 5, the internal heating roller 6, the external heating roller 7, and the sheet heating element 30 reach a predetermined temperature, temperature detection is performed using a non-contact thermistor, so that non-contact The length of time to stabilize the type thermistor is not a problem. That is, it is possible to perform temperature control that complements the weak points of the contact thermistor and the non-contact thermistor.

  The present invention relates to a fixing device using a fixing belt, and can be used for an image forming apparatus such as a color laser printer.

1 is a cross-sectional view illustrating a schematic configuration of a belt fixing device according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the outline of the belt fixing device which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the structure of the outline of the planar heating element which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Belt fixing device 2 Fixing belt 3 Fixing roller 4 Pressure roller 5 Heating roller 5a Heater lamp (heat source)
6 Internal heating roller 6a Internal heater lamp 7 External heating roller 7a External heater lamp 12 Non-contact thermistor (belt temperature detection means)
15 Contact type thermistor (temperature detection means)
16 Contact type thermistor (temperature detection means)
17 Contact type thermistor (temperature detection means)
30 Planar heating element (heating means)
31 Contact type thermistor (temperature detection means)
A Center of fixing roller B Center of heating roller C Center of non-contact thermistor (center of belt temperature detection means)
D Center of nip N Nip S S Paper (sheet medium)
T Toner image x Fixing belt rotation direction

Claims (7)

A pair of fixing rollers and a pressure roller disposed opposite to each other;
A heating roller with a built-in heat source;
A fixing belt comprising an endless belt that is stretched between the fixing roller and the heating roller;
A heating unit for heating the surface of the fixing roller in a hollow portion formed inside the fixing belt;
In the belt fixing device in which the fixing belt heats and melts a toner image on a sheet-like medium at a nip portion formed by pressure contact between the fixing roller and the pressure roller.
A belt fixing device comprising: a non-contact type belt temperature detecting means outside and in the vicinity of the fixing belt and upstream of the nip portion in the rotation direction of the fixing belt. The fixing roller has a diameter larger than that of the heating roller;
In a cross section perpendicular to the rotation axis of the fixing roller and the heating roller, including the belt temperature detection unit, a line segment from the center of the fixing roller to the center of the heating roller and the center of the belt temperature detection unit The belt fixing device according to claim 1, wherein an angle formed by a line segment to be directed is 90 degrees or more.   In the cross section perpendicular to the rotation axis of the fixing roller and the pressure roller, including the belt temperature detecting means, a line segment from the center of the fixing roller to the center of the nip portion, and the center of the belt temperature detecting means The belt fixing device according to claim 1 or 2, wherein an angle formed by a line segment toward the head is 45 degrees or more.   4. The belt fixing according to claim 1, further comprising a contact-type temperature detection unit that contacts the heating roller or a non-contact type temperature detection unit disposed in the vicinity of the heating roller. vessel.   5. The belt fixing according to claim 1, further comprising a contact-type temperature detection unit that contacts the heating unit or a non-contact type temperature detection unit disposed in the vicinity of the heating unit. vessel.   6. The belt fixing device according to claim 1, further comprising an external heating unit that heats the surface of the pressure roller.   The belt fixing device according to claim 6, further comprising a contact-type temperature detection unit that contacts the external heating unit or a non-contact type temperature detection unit disposed in the vicinity of the external heating unit.

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