JPH09265244A - Heat fixing device - Google Patents

Abstract

(57) [Abstract] (Correction) [Problem] Since the heating source inside the heat roller is arranged at the center of rotation, the entire heat roller is heated uniformly,
When it is detected by the detection element that detects the surface temperature of the heat roller, it is heated by receiving the radiant heat from the heating source, and the accurate surface temperature cannot be detected. A sheet 2 carrying a toner image is guided to a heat roller 11 side by a guide member 3 so that the sheet 2 is preheated and guided to a contact portion A to melt the toner. It is fixed on 2. At this time, the heat roller 11 is detected at a position apart from the pressure roller 12 by the temperature detection element 17, but can be accurately detected without being affected by the radiant heat from the halogen lamp 15, and based on this temperature detection Then, the amount of electric power to the halogen lamp 15 is controlled via the temperature control circuit 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an unfixed image carried on a sheet, for example, a toner image as a permanent image in an image forming apparatus utilizing an electrophotographic system, particularly in a copying apparatus, a printer, a facsimile and the like. The present invention relates to a heat fixing device that melts the toner and fixes it on a sheet for fixing.

[0002]

2. Description of the Related Art In an image forming apparatus utilizing an electrophotographic system, a toner image is formed on a photosensitive member which is a recording medium, and the toner image is transferred onto a sheet such as plain paper and the toner image on the sheet is transferred. A heating and fixing device that fuses toner and fixes it by applying pressure is generally known and provided in order to hold it on a sheet as a permanent image.

This heating and fixing device is provided with a pressure roller which is brought into pressure contact with a heat roller having a heating source such as a heater lamp, for example, a halogen lamp, with an appropriate pressure, and the temperature of the surface of the heat roller. Is detected by the temperature detecting element to drive and control the heating source, and thereby the temperature of the surface of the heat roller is maintained so that the toner can be melted and heated and fixed.

In such a structure, the pressure roller, which is pressed against the heat roller, rotates when the operation for fixing the heat is started, and thus takes a large amount of heat from the heat roller. That is, although the pressure roller is heated at the contact portion with the heat roller, the non-contact peripheral surface comes into contact with the heat roller due to rotation, so the heat of the heat roller is taken by the pressure roller. Therefore, at the beginning of the process, the surface temperature of the heat roller is lowered to the set temperature or lower, so that the heat source is controlled to supply a larger amount of heat than the heat source.

[0005]

However, in the conventional heat fixing device in the image forming apparatus, the heat source, which is a heater lamp, is arranged at the center of the heat roller, and the entire heat roller (entire circumference) is radiated. It is heated evenly. Then, in order to control the surface temperature of the heat roller to a predetermined temperature, a temperature detection element such as a thermistor is pressed against the heat roller, and the detection signal from this temperature detection element is fed back to control the drive of the heating source. It is carried out.

Since the heat source inside the heat roller is arranged in the central portion, radiant heat is uniformly heated from the inside of the heat roller, and the heat roller surface is heated and controlled so as to reach the set temperature. . Therefore, when the heat roller is in contact with the pressure roller and the sheet carrying the toner image to fix the heat roller, a large amount of heat is removed including the sheet conveyed at the start of the heat roller. The surface temperature drops sharply.

At this time, when the heat roller is released from the contact state with the pressure roller and is rotated to the position where the temperature detecting element is arranged, when the heat roller is uniformly heated by the heating source and is lowered. The current situation is that the temperature state of the heat roller cannot be detected. That is, after the heat roller is separated from the pressure roller and before reaching the temperature detection element, the surface temperature rises above the surface temperature when separated from the pressure roller due to the influence of radiant heat from the heating source. Cannot be accurately detected.

As a result, even if a large temperature change occurs when the heat roller surface temperature comes into contact with the sheet and the pressure roller, if this state is not accurately detected, the toner image on the sheet is melted and fixed. A sufficient amount of heat cannot be replenished via the heating source.

Therefore, in anticipation of the heat to be taken by the pressure roller, the start of image formation is delayed and the image forming operation is temporarily put on standby. First, the heat roller and pressure roller of the heat fixing device are rotated to sufficiently apply heat. It has been considered that the image forming operation is started when the pressure roller is heated and heat is not absorbed by the pressure roller. With such a configuration, even if the problem of defective fixing can be solved, the start of the first image forming operation is delayed.

In view of this, Japanese Patent Laid-Open No. 5-217660 proposes a device in which the temperature of the heat fixing device is detected at the final stage of the fixing operation. For example, as shown in FIG. 6, a pressure roller 8 that applies pressure from the back surface to the sheet P carrying the toner image t,
The contact portion (nip portion N) is configured by the endless film 7 on the side facing the toner image t on the sheet P, and is opposite to the back surface of the endless film 7, that is, the side in contact with the toner image t. A heating source 9 is provided in contact with the surface, and a temperature detecting element 10 for detecting the film temperature is provided immediately after the heating source 9 to form a heat fixing device.
In the figure, “a” indicates the transport direction of the film 7, and “b” indicates the rotation direction of the pressure roller 8.

In this way, in order to detect the temperature of the film 7 for melting and fixing the toner image t at the position where the pressure roller 8 and the sheet P come into contact with each other, the temperature state of the film 7 during fixing is almost reached. Can be detected. However, since this temperature detection detects the surface opposite to the fixing surface of the film 7, the actual surface temperature state of directly heating and fixing the toner image on the film 7 is not accurately detected.

Further, according to the heat fixing device as shown in FIG. 6, the film 7 is a heat-resistant thin film, and a thermal heater is used as the heating source 9, resulting in high cost. In addition, the temperature detecting element 10 needs to be arranged at a limited position near the heating source, which makes positioning extremely difficult, and assembly and position adjustment thereof are very troublesome. Furthermore, since the temperature detecting element 10 is located in the vicinity of the heating source 9, it is necessary to prevent thermal deterioration and heat from the heating source 10 from being detected. It becomes very troublesome to design.

As described above, the heat roller system should be used.
Even with the fixing method using the film shown in FIG. 6, it is very important to detect the surface temperature of the member heated by the heating source and perform the detection. If the detection of the surface temperature is not accurate, the surface temperature of the heat roller or the like when the heating source is driven and controlled cannot be maintained at a predetermined fixing set temperature. Moreover, the amount of electric power is wastefully supplied to the heating source, resulting in a waste of power consumption.

According to the present invention, in a heat fixing apparatus of a heat roller type, which has been used more frequently than ever before and is inexpensive, the heat from a heating source for heating the heat roller is efficiently used to supply electric power to the heating source. The purpose of this is to reduce the temperature and to accurately detect the temperature of the heat roller surface.

A particular object of the present invention is to provide a heat fixing device which enables highly reliable temperature control by accurately detecting the surface temperature of the heat roller.

[0016]

In order to achieve the above-mentioned object according to the present invention, a pressing member for forming a contact portion is pressed against a heat roller having a heating source therein at an appropriate pressure. And controlling the surface temperature of the heat roller based on a detection signal from a temperature detection element to control the amount of electric power supplied to the heating source, thereby controlling the surface temperature of the heat roller to a predetermined temperature. A heating and fixing device including a circuit disposes the heating source not at the center of rotation of the heat roller but at a position biased to the upstream side from the contact portion with the pressing member, and presses the temperature detection element. It is characterized in that it is arranged so as to be in pressure contact with the surface of the heat roller on the downstream side away from the member.

In such a structure, the heating source can concentrate and heat the upstream side of the contact portion between the heat roller and the pressure member, so that the sheet carrying the toner image is heated before being guided to the contact portion. It is preheated by the heat roller.
Therefore, the toner can be effectively melted at the contact portion, and the range of the contact portion can be reduced. As a result, the amount of heat taken to the pressure member is reduced, and the radiant heat from the heating source can be used efficiently, so that the amount of power consumed by the heating source can be reduced and the effect of preventing the sheet from curling can be obtained. is there. Further, since the temperature detecting element is arranged on the downstream side of the contact portion, the surface temperature of the heat roller due to the amount of heat taken by the pressure member or the like can be accurately detected, and the surface temperature of the heat roller can be controlled more accurately. .

Therefore, the heating source may be arranged such that a reflecting plate that reflects the heat radiated in the opposite direction facing the upstream side of the contact portion with the pressing member to the upstream side of the contact portion faces the heating source. For example, the effect of preheating the sheet can be promoted, and at the same time, the heat roller separated from the pressure member is not heated by the effect of the radiant heat from the heating source, so the temperature detection element can detect the temperature more accurately. Is possible.

Further, if the heating sources are arranged so as to concentrate and heat just before the contact portion with the pressing member, the preheating effect of the sheet before being guided to the contact portion is enhanced. To be

In order to more accurately detect the surface temperature of the heat roller according to the present invention, the heat roller provided with a heat source inside the heat roller is pressed and contacted with an appropriate pressure. The surface temperature of the heat roller can be determined by controlling the amount of power supplied to the heating source based on a detection signal from a temperature detection element, which is provided with a pressure member for forming a section. In the heat fixing device having a temperature control circuit for controlling the temperature, the temperature detecting element provided on the elastic plate in the vicinity of the heat roller away from the pressure member is brought into pressure contact with the surface of the heat roller. It is characterized by being placed in.

With this structure, it is not necessary to separately provide the temperature detecting element with the biasing means and press the temperature detecting element into contact with the surface of the heat roller, so that the surface temperature in the vicinity of the heat roller separated from the pressing member can be detected. Therefore, the state where the temperature of the heat roller is lowered by the heat taken by the pressure member or the like can be immediately and accurately detected without being affected by the radiant heat from the heating source.

Therefore, the heating sources are arranged so as to concentrate and heat the upstream side in contact with the pressure member, or
Alternatively, when a reflecting plate is provided together with a heating source so as to intensively heat the upstream side, the influence of radiant heat is almost eliminated, especially when the heat roller is separated from the pressing member, and a more accurate The temperature can be detected.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing a heat fixing device according to a first embodiment of the present invention. The heating and fixing device 1 melts the toner carried on the sheet 2 and heats and fixes it on the sheet 2 while conveying the sheet 2 carrying an image, especially a toner image on its surface. is there.

Although not shown, the sheet 2 passes through an image forming process section, whereby a toner image is electrostatically transferred onto the surface thereof. This toner image is formed by a recording medium, which is a photoconductor, passing through each process of charging, exposure, and development. That is, the recording medium that is rotationally driven is first uniformly charged by the charging process, and is moved to the exposure process so that a light image is emitted according to the image. By irradiating this light image, an electrostatic latent image is formed on the surface of the photoconductor, and then toner is attached to the electrostatic latent image in the developing process to develop it as a visible image. The development image (toner image) formed by the toner thus formed is electrostatically transferred onto the sheet 2 which is driven and controlled to be transferred to the transfer area in synchronization with the rotation of the recording medium. A toner image is carried on.

The sheet 2 bearing the toner image on the surface (upper surface) is separated from the recording medium and guided to the heat fixing device 1 shown in FIG. 1 through the guide member 3. The guide member 3 is arranged in such an angled state that the leading end of the sheet 2 is first guided to the surface of the heat roller 11 constituting the heat fixing device 1. In this way, the sheet 2 is attached to the heat roller 1
By guiding the sheet to the first surface, it is possible to prevent the sheet from wrinkling at the pressure contact portion.

(First Embodiment) Next, the structure of the heat fixing apparatus 1 according to the first embodiment of the present invention will be described in detail.

The heat fixing device 1 is provided with the heat roller 11 for fixing the toner image carried on the sheet 2 as described above, and the pressure roller is pressed against the heat roller by a necessary pressing force. 12 are provided. The heat roller 11 has a cylindrical roll surface formed of a metal material having a high thermal conductivity such as aluminum as a base material, and has polyterafluoroethylene (polyterafluoroethylene: polyterafluoroethylene) which is a fluororesin having releasability for toner. It is formed by coating with PTFE) or parafluoroalcoxy (PEA). Although not shown, both ends of the heat roller 11 are rotatably supported by a frame or the like constituting the heat fixing device 1 via bearings and the like, and a driven gear fixed to one end thereof. , Meshes with the drive gear to which the rotational force from the drive motor is transmitted, and is rotationally driven in the direction of the arrow in the figure.

The pressure roller 12 pressed against the heat roller 11 is pressed against the heat roller 11 on the rotary shaft 13 so that a nip portion A, which is a contact portion pressed against each other, can be formed. It is constituted by covering an elastic member such as silicone rubber or sponge having good releasability.
Both ends of the rotating shaft 13 are rotatably supported, and are rotated in the direction of the arrow as the heat roller 11 rotates. Further, since the pressure roller 12 is pressed against the heat roller 11 with a predetermined pressure, a spring or the like is provided in a portion that supports the rotary shaft 13, and the biasing force of the spring is used to move the heat roller 11 toward the heat roller 11. It is provided to pressurize. In this pressing structure, the pressure roller 12 is biased to press the heat roller 11 side, but the heat roller 11 side may be biased to the pressure roller 12 side. However, if the heat roller 11 is on the drive side, in order to perform good meshing with the drive gear, the pressure roller 12 side opposite to the driven side may be biased.

Instead of the pressure roller 12 which is a pressure member that is pressed against the heat roller 11, a pressure pad 12a may be provided as a pressure member as shown in FIG. Since the pressure pad 12a is provided in a fixed state on the support member 14 attached to the frame or the like,
It is preferable to provide a surface of silicon rubber, sponge or the like coated with a member or the like that is slippery on the sheet 2. Also in this configuration, similarly to the pressure roller 12, the support member 14 is configured to press the pressure pad 12a toward the heat roller 11 side by a biasing means such as a spring so as to configure the nip portion A. There is.

On the other hand, inside the heat roller 11, a halogen lamp 15, which is a heating source for heating the heat roller 11, is provided. This halogen lamp 15
Are arranged eccentrically toward the side where the sheet 2 is conveyed, without being arranged at the center of rotation of the heat roller 11. That is, the halogen lamp 15 is arranged in a biased manner on the upstream side of the heat roller 11 so as to concentrate and heat the upstream side of the contact portion (A) between the heat roller 11 and the pressure roller 12. Therefore, the heat roller 1
In No. 1, the amount of heat heated by the halogen lamp 15 is large on the side where the sheet 2 is guided by the guide member 3, and the amount of heat due to radiant heat that heats the opposite side is small.

Further, a part of the radiant heat from the halogen lamp 15, that is, the radiant heat directed to the opposite side of the contact portion (A) from the upstream side of the heat roller 11 can further heat the above-mentioned upstream side of the heat roller 11. In addition, a reflector 16 is provided. In addition to the radiant heat by which the halogen lamp 15 directly heats the heat roller 11 by the reflecting plate 16, the heat radiated to the opposite side is also directed to the upstream side. As a result, the heat roller 11 is intensively heated on the upstream side. Therefore, the sheet 2 is first guided to the heat roller 11 to be preheated by the above-described amount of radiant heat, and thereafter, the contact portion (yup) between the heat roller 11 and the pressure roller 12 or the pressure pad 12a. Width A)
The toner image 3 on the sheet 2 is efficiently heated and fixed.

Then, a temperature detecting element 17 including a thermistor for detecting the surface temperature of the heat roller 11
Is provided on the downstream side immediately after passing through the contact portion (A) between the heat roller 11 and the pressure roller 12, in a state of being pressed against the surface of the heat roller 11. The temperature detecting element 17
The temperature (detection signal) detected by the temperature control circuit 18
To the halogen lamp 1 in the temperature control circuit 18.
The power supplied to 5 is controlled. That is, if the temperature detected by the temperature detecting element 17 is equal to or lower than the predetermined temperature, the temperature control circuit 18 increases the amount of electric power supplied to the halogen lamp 15 in order to raise the temperature of the surface of the heat roller 11. Control. As a result, the heat roller 11
It is controlled so that a predetermined toner can be maintained at a set temperature at which the toner can be melted and fixed by heating.

According to the heat fixing device having the above-mentioned structure, the halogen lamp 15 is not arranged at the rotation center position inside the heat roller 11, but is located in front of the contact portion for heat fixing the toner image on the sheet 2. Since it is arranged near the upstream side, the amount of radiant heat in the vicinity of the contact portion increases. Moreover, by providing the reflection plate 16, the area of the heat roller 11 near the contact portion is concentrated and heated. As a result, the sheet 2 is guided to the heat roller 11 and preheated in this region. After being preheated, the sheet 2 is heated by the heat roller 11
Is guided to the contact portion (nip portion A) between the pressure roller 12 (or the pressure pad 12a) and the toner image on the sheet 2 is
The pressure roller 12 is melted by the heat of the heat roller 11.
It is fixed on the sheet by the pressure.

At this time, since the sheet 2 is preheated, a large amount of heat of the heat roller 11 is not taken at the contact portion, and the toner is efficiently melted. Then, the surface temperature of the heat roller 11 is immediately detected by the temperature detecting element 17 on the downstream side of the contact portion. Therefore, although the surface temperature of the heat roller 11 decreases according to the amount of heat taken by the contact portion, the decreased temperature is detected by the temperature detecting element 1.
7 detects it and feeds it back to the temperature control circuit 18, so that the power supplied to the halogen lamp 15 can be replenished and controlled in order to compensate for the insufficient amount of heat.

Here, the radiant heat of the halogen lamp 15 acts so as to efficiently heat the upstream side of the contact portion of the heat roller 11, so that the heat roller 11 region on the downstream side that leaves the contact portion is heated. Will be reduced. Therefore, the temperature detecting element 17 can accurately detect the temperature of the surface of the heat roller 11 without being affected by the radiant heat from the halogen lamp 15. Therefore, since the temperature control circuit 18 can accurately control the power supply to the halogen lamp 15 without waste, the temperature of the surface of the heat roller 11 can be accurately maintained at the set temperature.

In addition, the heat roller 11 efficiently heats the upstream side of the contact portion with the pressure roller 12, and the sheet 2
Since the preliminary heating can be effectively performed, wasteful heat removal in the fixing area at the contact portion with the pressure roller 12 is also reduced. Therefore, the radiant heat from the halogen lamp 15 can be used effectively and efficiently, and the power consumption supplied to the halogen lamp 15 can be reduced.

Further, by preheating, it is not necessary to spend time for fixing the toner image at the contact portion, and the width of the nip portion A can be shortened without making it longer than necessary. This also has the effect of reducing the amount of heat that the heat roller 11 is deprived of by a pressure member such as the pressure roller 12, and the radiant heat from the halogen lamp 15 can be used more efficiently.

Further, the sheet 2 does not curl along the outer peripheral surface of the heat roller 11. That is, the nip portion A along the outer periphery of the heat roller 11 is not arcuate,
This is because the state becomes almost linear. In addition, since the sheet 2 is linear, the sheet 2 is easily separated from the heat roller 11, and the jam around the heat roller 11 can be eliminated.

As a heating source for heating the heat roller 11, a heating source such as a nichrome wire lamp may be used instead of the halogen lamp 15. In addition, the temperature sensing element 1
7 is pressed against the surface of the heat roller 11 and wrapped with heat-resistant sponge except for the surface in contact with the heat roller 11 so as not to absorb a large amount of heat, and the surface in contact with the heat roller 11 has heat resistance and wear resistance. It is covered with a fluororesin film or the like. As a result, damage to the surface of the heat roller 11 and the temperature detecting element 17 is prevented, and the surface of the heat roller 11 is pressed with an appropriate pressure contact force.

(Second Embodiment) In the above, the halogen lamp 15 as a heating source for heating the heat roller 11 is arranged at a position biased to the upstream side of the contact portion (A) in contact with the pressure roller 12, The heat roller 11 in front of the contact portion is efficiently heated.

Further, an embodiment of a heat fixing device for improving heating efficiency will be described below. An example of the heat fixing device 1 according to the second embodiment of the present invention is shown in FIG.
As shown in (3), the vicinity of the contact portion between the heat roller 11 and the pressure roller 12 is concentratedly heated.

The heat fixing device 1 shown in FIG. 3 is the same as the heat fixing device 1 shown in FIG. 1 except that the position where the halogen lamp 15 is provided is slightly different, and other configurations are the same, and the details thereof are omitted.

In FIG. 3, the halogen lamp 15 is
The heat roller 11 and the pressure roller 12 are arranged in the vicinity of the contact portion in a biased state, and the halogen lamp 1 is also arranged so as to intensively heat the reflection plate 16 in front of the contact portion.
It is arranged so as to reflect radiant heat directed to the side opposite to 5 and heat the front side of the contact portion. The reflecting plate 16 directs the radiant heat from the halogen lamp 11 so as to intensively heat a part of the heat roller 11.

In this structure, especially the heat roller 1
At the same time as the sheet 2 guided toward 1 is preheated, the sheet 2 is concentrated and preheated before the contact portion with the pressure roller 12, that is, immediately before entering the contact portion. Therefore, the toner on the sheet 2 can be melted and fixed by pressing the contact portion. Therefore, the width of the nip portion A, which is a contact portion with the pressure roller 12, can be reduced, and the amount of heat taken to the pressure roller 12 can be further reduced, so that the utilization efficiency of heat can be further improved and the power consumption can be reduced. Can be possible.

(Third Embodiment) The above-mentioned first and second embodiments
According to the embodiment of the present invention, the heat roller 11 is replaced by the pressure roller 1.
In this example, the heating source is arranged so as to heat intensively on the upstream side of the contact portion with 2, particularly immediately before.

On the other hand, in the third embodiment,
A temperature detection element 17 is arranged immediately before the downstream side of the contact portion between the heat roller 11 and the pressure roller 12 to detect the surface temperature of the heat roller 1 more accurately and accurately, and to supply the electric power to the halogen lamp 15. By eliminating the waste of heat, the temperature efficiency can be improved and the temperature can be controlled with high reliability.

FIG. 4 shows an example of detecting the temperature of the heat roller 11 more accurately and accurately. In particular, the temperature detecting element 17 is made to come into pressure contact with the surface of the heat roller 11 using an elastic plate made of stainless steel or the like. With this configuration, the temperature detecting element 17 can be effectively brought into pressure contact with the heat roller 11, and it is not necessary to provide any special biasing means.

In particular, in FIG. 5, the temperature detecting element 17 is shown in detail. The temperature detecting element 17 is fixed to the stainless (SUS) plate 5 with an adhesive or the like and comes into contact with the heat roller 11. A polyimide sheet 6 having a very strong abrasion resistance and a thickness of about 0.02 mm is attached to the side surface,
At the same time as protecting the temperature detecting element 17, the heat roller 1
1 It is designed to prevent damage to the surface.

By holding the temperature detecting element 17 in this way, a special biasing means for the heat roller 11 is not required, and it is compact and space can be saved. Therefore, the heat roller 11 immediately after being separated from the pressure roller 12 in the vicinity of the contact portion between the heat roller 11 and the pressure roller 12.
This is particularly effective when detecting the surface temperature of the. That is, by providing it on the stainless steel plate 5 which is also an elastic plate that also serves as the urging means, it becomes possible to press-contact the area of the heat roller 11 immediately after separating from the pressure roller 12.

By doing so, in the first and second embodiments, the surface temperature of the heat roller 11 lowered by the heat taken by the pressure roller 12 and the sheet 2 can be detected more accurately and accurately. In particular, even if the halogen lamp 15 is arranged at the center of rotation, the surface temperature of the heat roller 11 can be detected with high accuracy without being significantly affected by the radiant heat from the halogen lamp 15. As a result, the amount of electric power supplied to the halogen lamp 15 via the temperature control circuit 18 can be controlled without waste, and the surface temperature can be maintained and controlled with high reliability.

Moreover, as shown in FIGS. 1 and 3, the halogen lamps 15 are arranged in a biased position so that the vicinity of the contact portion with the pressure roller 12 is concentratedly heated, or the reflector 16 is also provided. By including and heating the vicinity of the contact portion in a concentrated manner, it is possible to prevent the radiant heat from the halogen lamp 15 from heating the area of the heat roller 11 particularly away from the contact portion. Therefore, the temperature detection element 17 can be expected to detect the surface temperature of the heat roller 11 with higher accuracy.

The temperature detecting element 17 is connected to the heat roller 1
One end of the stainless steel plate 5 to be pressed against 1 is fixed to a frame or the like for supporting the heat roller 11 or the like. In this case, it may be fixed to the frame or the like via a heat insulating material so that heat does not escape to the frame or the like.

[0053]

As described above, according to the heat fixing device of the present invention, the heat roller centrally heats the upstream side in contact with the pressure member, particularly the vicinity immediately before the contact portion, by the heating source. By doing so, the sheet is effectively preheated before being guided to the contact portion, and thereby the efficiency of melting and fixing the toner image at the contact portion can be increased.

Therefore, the contact portion (nip portion) with the pressurizing member can be made small, and the amount of heat taken to the pressurizing member can be reduced, so that the radiant heat from the heating source can be efficiently used and the heat utilization efficiency can be improved. The amount that can be improved can reduce the amount of electric power supplied to the heating source. Moreover, since the contact portion can be made small, the effect of preventing the sheet from curling is enhanced.

By disposing the temperature detecting element at a position where the heat roller and the pressing member are separated from each other, the surface temperature lowered by the heat taken by the heat roller can be accurately detected with high accuracy, and the surface of the heat roller can be detected. When controlling the temperature to the set temperature, highly reliable control can be enabled. In particular, since the radiant heat of the heating source can be concentrated and heated in front of the contact portion by the reflecting plate or the like, there is no need to detect the temperature due to the effect of the radiant heat from the heating source on the heat roller separated from the pressurizing member. It enables highly accurate detection of surface temperature.

Moreover, by supporting the temperature detecting element on the elastic plate and pressing it against the heat roller, it is possible to detect the heat roller surface temperature in the vicinity where the heat roller is separated from the pressing member, and more accurate temperature detection is possible. Becomes

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a heat fixing device for explaining a first embodiment according to the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of a pressure member that is pressed against a heat roller in the heat fixing device in FIG.

FIG. 3 is a cross-sectional view showing a structure of a heat fixing device for explaining a second embodiment of the present invention.

FIG. 4 is a cross-sectional view showing the structure of a heat fixing device for explaining a third embodiment of the present invention.

5 is a cross-sectional view showing details of a pressure contact state of the temperature detecting element of FIG. 4 with a heat roller.

FIG. 6 is a sectional view showing an example of a conventional heat fixing device.

[Explanation of symbols]

 1 Heat Fixing Device 11 Heat Roller 12 Pressure Roller (Pressure Member) 12a Pressure Pad (Pressure Member) 15 Halogen Lamp (Heating Source) 16 Reflector 17 Temperature Detection Element 18 Temperature Control Circuit 2 Sheet 3 Guide Member 5 Stainless Steel Plate (elastic plate)

Claims (5)

[Claims] 1. A pressure member for pressurizing a heat roller having a heating source therein at an appropriate pressure to form a contact portion, and detecting the surface temperature of the heat roller from a temperature detecting element. A heating and fixing device comprising a temperature control circuit configured to control the surface temperature of the heat roller to a predetermined temperature by controlling the amount of electric power supplied to the heat source based on a signal. Not at the center of rotation, but at a position biased to the upstream side from the contact portion with the pressure member, and the temperature detection element is arranged in pressure contact with the surface of the heat roller on the downstream side away from the pressure member. A heating and fixing device characterized by the above. 2. A reflecting plate, which reflects heat radiated in the opposite direction facing the upstream side of the contact portion with the pressure member to the upstream side of the contact portion, is arranged facing the heating source. The heat fixing device according to claim 1, wherein 3. The heating and fixing device according to claim 1, wherein the heating sources are arranged so as to concentrate and heat particularly immediately before a contact portion with the pressing member. 4. A pressure member for pressing a heat roller having a heating source therein at an appropriate pressure to form a contact portion, and detecting the surface temperature of the heat roller from a temperature detecting element. In a heat fixing device including a temperature control circuit that controls the surface temperature of the heat roller to a predetermined temperature by controlling the amount of electric power supplied to the heating source based on a signal, A heating and fixing device characterized in that a temperature detection element provided on an elastic plate in the vicinity of the pressure member is arranged in a state of being in pressure contact with the surface of the heat roller. 5. The heating source is arranged so as to concentrate and heat the upstream side in contact with the pressure member, or a reflector is provided together with the heating source to concentrate and heat the upstream side. The heat fixing device according to claim 4.