JPH05323827A - Fixing device of electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent occurrence of malfunctions such as contact defect at a sensor attaching part and to perform temperature detection of a rear side electrically conductive coating film with high accuracy. CONSTITUTION:The device is provided on a printer by which a toner image developed on a photosensitive body drum is transferred to transfer paper 13 and an image is formed. The toner image transferred to the transfer paper 13 is held between pressure rollers via a heat resistant belt and is heat-melted by the surface electrically conductive coating film which is formed on a surface of a heating member 21 to fix it to the transfer paper 13. The rear side electrically conductive coating film 39 which has the length at least more than two times the length between both tip parts in the longitudinal direction of the surface electrically conductive coating film and varies the resistance dependent upon temperature, is provided on the rear surface of the heating member 21. A CPU 15 detecting the resistance value of the rear side electrically conductive coating film 39 and the CPU 15 performing temperature control of the rear side electrically conductive coating film 39 based on the output of the CPU 15 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device of an electrophotographic apparatus for fixing a toner image transferred from a photoconductor to a transfer paper.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic apparatus such as a printer, as a method for fixing toner particles transferred onto a transfer paper, a method has been adopted in which a pressure roller made of a heat-resistant elastic member and a heating roller having a heating means therein are provided. In addition, a method of fixing the transfer paper by pinching and conveying the transfer paper has been adopted.

However, in this type of fixing device, it takes time to reach a predetermined temperature because the heat capacity of the heating roller is large. Since a heating body having a large heat capacity is required, heat is radiated to the printer body severely, and there is a problem that the temperature rise of the printer body becomes remarkable.

As a method for solving these problems, JP-A-1-
There are those disclosed in Japanese Patent No. 263678 and Japanese Patent Laid-Open No. 1-263683.

In these prior arts, as shown in FIG. 10, in a fixing device 51, a toner image formed on the surface of a transfer paper 52 is fed through a take-up type fixing belt 53 to generate a sheet-like heat instead of a heating roller. By applying pressure and heat between the body 54 and the pressure roller 55, the toner image formed on the surface of the transfer paper 52 is fixed. Also,
The temperature control of the sheet heating element 54 is performed by providing a sensor such as a thermocouple on the back surface of the sheet heating element 54.

As a result, the heating element becomes smaller, and the problem of the above-mentioned heat capacity is solved.

[0007]

However, in the above-described conventional printer fixing device 51, a sensor such as a thermocouple is provided on the back surface of the sheet heating element 54. Therefore,
Since the rigidity of the planar heating element 54 having a small heat capacity is insufficient, there is a problem that malfunctions are likely to occur due to contact failure or the like at the sensor mounting portion due to external factors such as vibration. ing.

Further, since there is a distance between the front surface and the back surface of the planar heating element 54, there is a problem that the heater surface temperature of the planar heating element 54 and the temperature detected by the sensor are different. There is.

That is, as shown in FIG. 11, in the initial stage of heating, the temperature characteristic of the sheet heating element 54 is indicated by a solid line, while the temperature detected by the sensor is indicated by a broken line in the figure. As a result, assuming that the temperature detected by the sensor reaches the temperature T ₁ after the lapse of t ₁ time, the actual planar heating element 54 is higher than the temperature T ₁ by the temperature difference ΔT.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to prevent the occurrence of malfunction such as poor contact at the mounting portion of the sensor, while at the same time, the planar heating element in the initial stage of heating. It is an object of the present invention to provide a fixing device for an electrophotographic apparatus, which can prevent a temperature difference between the sensor detection temperature and the sensor detection temperature.

[0011]

In order to solve the above-mentioned problems, a fixing device for an electrophotographic apparatus according to the present invention transfers a toner image developed on a photoreceptor to a transfer paper to form an image. The toner image transferred to the transfer paper is held between the pressure roller and the fixing belt, and is heated and melted by the planar heating member formed on the surface of the heating element. In a fixing device of an electrophotographic apparatus for fixing to a transfer paper by means of a fixing member, the back surface of the heating element has a length of at least twice as long as both ends of the planar heating member in the longitudinal direction, and the resistance of the heating member varies depending on the temperature. While a conductive member that changes is provided, a resistance detection unit that detects the resistance value of the conductive member and a temperature control unit that controls the temperature of the planar heating member based on the output of the resistance detection unit are provided. It is characterized by being.

According to a second aspect of the invention, there is provided a fixing device for an electrophotographic apparatus according to the first aspect of the invention, in which the conductive member itself is a conductive member. It is characterized in that a heating means for heating is provided.

According to a third aspect of the present invention, there is provided a fixing device for an electrophotographic apparatus, wherein, in order to solve the above-mentioned problems, in the fixing device for an electrophotographic apparatus according to the first aspect, at least one electrode connected to a conductive member. However, the conductive member is movably provided.

[0014]

According to the structure of claim 1, on the back surface of the heating element,
At least 2 between both ends in the longitudinal direction of the planar heating member
A conductive member having a length that is at least twice the length and whose resistance changes with temperature is provided. Then, while the resistance detection means detects the resistance value of the conductive member, the temperature control means controls the temperature of the planar heating member based on the output of the resistance detection means. For this reason, unlike a sensor such as a conventional thermocouple, since the mounting surface is formed wide, it is possible to prevent malfunction such as poor contact at the sensor mounting portion.

Further, the conductive member has a length of at least twice the length between both ends of the planar heating member in the longitudinal direction. Therefore, it becomes possible to detect the temperature of the planar heating member more accurately. That is, if the length of the conductive member is one time between both ends in the longitudinal direction of the planar heating member, the electric resistance is small because the length is short, and as a result, the change of the electric resistance with respect to the temperature change. Is also small, making it difficult to detect resistance changes. The length of the conductive member is, for example, 1.
If it is 5 times, deviation occurs in the accuracy of the resistance value.

Further, according to the second aspect of the invention, since the heating means heats the conductive member itself, at the time of initial heating, the heating of the planar heating member formed on the surface of the heating element is accompanied by heating. The conductive member provided on the back surface of the is also heated for several seconds, for example. Therefore, even when the temperature of the sheet heating element rises rapidly in the initial stage of heating, the conductive member is also heated to follow the rapid temperature rise of the sheet heating element, and the sheet heating element and the sensor detection in the initial stage of heating. It is possible to prevent a temperature difference from the temperature.

According to the third aspect of the invention, since at least one of the electrodes connected to the conductive member is provided so that the conductive member can move, the distance between the electrodes of the conductive member is changed. be able to. As a result, it is possible to change the initial temperature resistance (resistance at room temperature) of the conductive member, which makes it possible to change the set value of the control temperature. It is possible to prevent a temperature difference from

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. 1 to 9.

As shown in FIG. 2, for example, a printer as an electrophotographic apparatus of the present embodiment is provided with a photosensitive drum 1 as a cylindrical photosensitive member rotatable in the direction A in the apparatus. Around the photosensitive drum 1, a charger 2, LE
A D (Light Emitting Diode) array 3, a developing device 4, a transfer device 5, a cleaner 6 and the like are provided.

On the paper feed side of the photosensitive drum 1, a paper feed tray 8 for containing the transfer paper 13 and a paper feed device 7 are provided. Further, the fixing device 9 is provided on the paper output side of the transfer device 5.
On the other hand, a paper discharge tray 10 is provided on the paper output side of the fixing device 9. Paper detection switches 11 and 12 for detecting the passage of the transfer paper 13 are provided on the paper output side of the paper supply device 7 and the paper supply side of the paper discharge tray 10, respectively.

As shown in FIG. 3, the fixing device 9 has a heat resistance as an endless fixing belt formed of a film mainly composed of, for example, a polyimide resin and wound between a driving roller 23 and a driven roller 24. The belt 22, the heating device 20 that heats the heat-resistant belt 22 from the inside, and the heating device 20 that is provided at a position opposite to the heating device 20, sandwiches and presses the heat-resistant belt 22 and the transfer paper 13 between the heating device 20 and the heating device 20. The pressure roller 25 and the belt meandering prevention mechanism 14 that detects the meandering of the heat resistant belt 22 by the meandering sensor 26 and pulls the driven roller 24 to prevent the heat resistant belt 22 from meandering.

The heating device 20 comprises a heating member 21 as a heating element made of, for example, a ceramic heater, and a heat insulating material 19 for holding the heating member 21 and preventing heat diffusion to the side opposite to the heat resistant belt 22. Is becoming Then, the heating device 20 is fixed by attaching the heat insulating material 19 to a mounting plate (not shown) fixed to the printer body.

The heating member 21 is, as shown in FIG.
Electrically insulating plate 38 having heat resistance, such as ceramics
A surface conductive coating film 36 having a small heat capacity such as MoSi ₂ as a heater surface is applied to the surface in a rectangular shape on the surface of the heater surface. A surface protective layer 37 made of, for example, glass is coated while leaving the electrode portion. The surface conductive coating film 36 and the surface protective layer 37 are directed toward the heat resistant belt 22.

On the other hand, the back surface of the heating member 21 is coated with a back surface conductive coating film 39 as a belt-shaped conductive member as shown in FIGS. The back surface conductive coating film 39 is formed by meandering in three lines so as to have a length three times as long as the length of the front surface conductive coating film 36. Then, the back surface conductive coating film 39 is made of the same material as the front surface conductive coating film 36 as the sensor surface, and the resistance thereof changes depending on the temperature. Here, the reason why the back surface conductive coating film 39 has a length which is three times the length of the front surface conductive coating film 36 in the longitudinal direction will be described.

First, in the case where the back surface conductive coating film 39 has a length which is one time the longitudinal length of the surface conductive coating film 36, that is, the same length as the surface conductive coating film 36, the back surface conductive coating film 39. This is because the electric resistance is small due to the short length, and the change in the electric resistance with respect to the temperature change is also small, which makes it difficult to detect the resistance change. Then, if the back surface conductive coating film 39 is 1 time or more and less than 2 times the front surface conductive coating film 36, in addition to the above-mentioned problem, a problem that the detection error becomes larger occurs. That is, as shown in FIG. 7, the back surface conductive coating film 39 is 1.5 times the front surface conductive coating film 36.
In the case of double, it means that the temperature in the right side area is twice as long as that in the left side area, and the temperature in the right side area is twice weighted compared to the left side area. This is because the detection result will be shown. As a method of reducing this error, the error can be reduced by making the length of the back surface conductive coating film 39 twice or more.

On the other hand, as shown in FIG. 1, a back surface protective layer 40 is coated on the back surface conductive coating film 39, leaving electrode portions at both ends of the back surface conductive coating film 39.
This electrode portion serves as a fixed electrode surface 39a whose one end is formed short, and the other end has a length of, for example, 2/3 of the length of the surface conductive coating film 36 in the longitudinal direction. It is formed as the electrode surface 39b. The fixed electrode surface 39a is connected to the fixed electrode 16 connected to the CPU 15 as a resistance detecting means, and the sliding electrode surface 39b is connected to the sliding electrode 17 as an electrode connected to the CPU 15. It is connected and the sliding electrode 17 is slidable on the sliding electrode surface 39b.

The front surface conductive coating film 36 is connected to the power source 18 through the heater power supply control circuit 41, while the back surface conductive coating film 39 is applied from both ends to the sensor power supply control circuit 27 as a heating means. It is connected to the power source 18 via.

The heater power supply control circuit 41 and the sensor power supply control circuit 27 are respectively connected to the CPU 15 as a temperature control means, and in response to a heating control signal from the CPU 15, each heater power supply circuit 17 and the sensor power supply circuit. The power supply control circuit 27 is adapted to be turned on / off.

That is, in the sensor power supply control circuit 27, as shown in FIG. 8, the power supply 18 is directly connected to the fixed electrode 16 of the back surface conductive coating film 39, while the power supply 1 is connected.
It is connected from the terminal 28 of No. 8 through the triac 29 to the connecting portion 30 at the other end of the back surface conductive coating film (sensor portion) 39. Also, from the terminal 28 of the power source 18 to the resistor R1
Also, it is connected to the gate electrode 32 of the triac 29 through the photo diac 31. Further, a resistor R2 is connected between the gate terminal 32 and the connecting portion 30 of the back surface conductive coating film 39. On the other hand, a circuit in which a resistor R3 and a photodiode 33 are connected in series is connected to the CPU 15. And the photodiode 3
3 forms a photo coupler with the photo diac 31 so that signals can be transmitted and received. The CPU 15 is connected to the sliding electrode 17 provided on the back surface conductive coating film 39 via the diode 34, and is also connected to the fixed electrode 16 of the back surface conductive coating film 39.

The operation of the printer having the above configuration will be described.

As shown in FIG. 2, the photosensitive drum 1 charged by the charger 2 is exposed with an image pattern by an LED (Light Emitting Diode) array 3 to remove the charged electric charge in the exposed portion to expose the photosensitive drum 1. An electrostatic latent image is formed on the body drum 1. In the developing device 4, a toner having the same polarity as the charge on the photoconductor drum 1 is attached to the portion of the photoconductor drum 1 from which the charge has been removed to form a toner image as a visible image. This toner image is overlapped with the transfer paper 13 fed from the paper feeding device 7, and is transferred by the transfer device 5 to the transfer paper 1.
A voltage having a polarity opposite to that of the toner is applied from the back side of 3 to electrostatically attract the toner image on the surface of the photosensitive drum 1 to transfer it to the transfer paper 13. After that, the transfer paper 13 on which the toner image is transferred is introduced into the fixing device 9. Fixing device 9
Then, the toner image formed on the surface of the transfer paper 13 is formed on the surface of the transfer paper 13 by applying pressure and heat between the sheet heating element 21 and the pressure roller 25 via the heat resistant belt 22. To fix the toner image. Then, transfer paper 13
Is separated from the heat resistant belt 22 and discharged to the paper discharge tray 10.

Next, the temperature control of the fixing device will be described.

First, since the heating member 21 used has a small heat capacity, when the surface conductive coating 36 on the heater surface is heated, the back conductive coating 39 on the sensor surface is also heated. As a result, the electric resistance of the back surface conductive coating film 39 provided on the sensor surface changes. Since the resistance of the substance changes in proportion to the temperature, the temperature of the back surface conductive coating film 39 can be specified by detecting the electric resistance. By feeding back this information to the voltage applied to the heater surface, the temperature of the heating member 21 can be controlled.

In the temperature control as described above, the resistance value of the front surface conductive coating film 36 on the heater surface and the resistance value of the back surface conductive coating film 39 have different initial temperature resistances (resistance values at room temperature). Therefore, the resistance value is different even at the temperature to be controlled. In addition, the surface conductive coating film 3
Even though both 6 and the back surface conductive coating film 39 have small heat capacities, immediately after energization of the surface conductive coating film 36 on the heater surface, between the front surface conductive coating film 36 and the back surface conductive coating film 39. Temperature difference occurs.

In order to solve such a problem, in the fixing device of this embodiment, since the back surface conductive coating film 39 can be heated, the back surface conductive coating film 39 is energized immediately after energization for several seconds. Thereby, the temperature difference between the front surface conductive coating film 36 and the back surface conductive coating film 39 can be reduced. Then, after that, the back surface conductive coating film 39 is switched from the heat generation mode to the sensor mode, whereby the temperature can be accurately controlled.

Further, in the fixing device of this embodiment, as shown in FIG. 1, the sliding electrode 17 is slidably connected to one sliding electrode surface 39b of the back surface conductive coating film 39, The distance between the fixed electrode 16 and the sliding electrode 17 can be changed. Therefore, since the resistance of the back surface conductive coating film 39 changes in proportion to the length, it becomes possible to change the temperature set value to be controlled by changing the initial temperature resistance. Further, it is possible to eliminate the difference in initial temperature resistance between the back surface conductive coating film 39 and the front surface conductive coating film 36.

Here, the temperature control of the fixing device will be described with reference to FIG.
It will be described in detail based on the flowchart of FIG.

First, when the paper detection switch 11 provided on the paper output side of the paper supply device 7 detects the insertion of the transfer paper 13 (S1), the heater surface (surface conductive coating 36 ) And the sensor surface (back surface conductive coating film 39) are applied with voltage and heated (S2). Then, after several seconds have passed, the heating of the heater surface is continued, the heating of the sensor surface is stopped, and the operation is switched to the temperature detection operation (S3). Next, it is determined whether the detected temperature of the sensor surface is the temperature T ₁ or higher (S4). If the detected temperature of the sensor surface is the temperature T ₁ or higher, the heating of the heater surface is stopped (S5).
If the detected temperature of the sensor surface is not higher than the temperature T ₁ , heating of the heater surface is continued (S6) and the process returns to S4.

After S5, it is judged whether or not the fixing is started (S7). If the fixing is not started, the process returns to S4. When the fixing is started in S7, it is judged whether the detected temperature of the sensor surface is the temperature T ₁ or higher (S8). If the detected temperature of the sensor surface is the temperature T ₁ or higher, the heating of the heater surface is performed. It is stopped (S9), and then it is determined whether the fixing is completed (S10). If the detected temperature of the sensor surface is not higher than the temperature T _{1 in} S8, the heating voltage is turned on to the heater surface (S11), and the process proceeds to S10.

If the fixing is completed in S10, the process is ended (S12), and if the fixing is not completed, the process returns to S8.

As described above, in the fixing device 9 of the printer of this embodiment, the surface conductive coating film 36 is formed on the back surface of the heating member 21.
A back surface conductive coating film 39 having a length at least twice as long as both ends in the longitudinal direction and having a resistance that changes with temperature is provided. Then, the CPU 1 as the resistance detecting means
5 detects the resistance value of the back surface conductive coating film 39, while the CPU 15 as the temperature control means detects C as the resistance detection means.
The temperature of the surface conductive coating film 36 is controlled based on the output of the PU 15. For this reason, unlike a sensor such as a conventional thermocouple, since the mounting surface is formed wide, it is possible to prevent malfunction such as poor contact at the sensor mounting portion.

Further, the back surface conductive coating film 39 has a length of at least twice as large as the distance between both ends in the longitudinal direction of the front surface conductive coating film 36. Therefore, it becomes possible to detect the temperature of the surface conductive coating film 36 more accurately.

Further, since the sensor power supply control circuit 27 heats the back surface conductive coating film 39, at the time of initial heating, the front surface conductive coating film 36 formed on the surface of the heating member 21 is heated and the back surface conductive coating film 39 is heated. The characteristic coating film 39 is also heated, for example, for several seconds. Therefore, even when the temperature of the front surface conductive coating film 36 rapidly rises in the initial stage of heating, the back surface conductive coating film 39 is also heated in order to follow the rapid temperature rise of the front surface conductive coating film 36. It is possible to prevent a temperature difference between the surface conductive coating film 36 and the sensor detection temperature.

Since at least one of the sliding electrodes 17 connected to the back surface conductive coating film 39 is movably provided on the back surface conductive coating film 39, the distance between the electrodes of the back surface conductive coating film 39 is reduced. Can be changed. As a result, it is possible to change the initial temperature resistance of the back surface conductive coating film 39, and thereby the set value of the control temperature can be changed, so that the front surface conductive coating film 36 and the sensor detection temperature at the initial heating stage. It is possible to prevent a temperature difference from

[0045]

As described above, in the fixing device of the electrophotographic apparatus according to the first aspect of the present invention, the back surface of the heating element has at least twice as much space between the longitudinal ends of the sheet heating member. A conductive member having a length and whose resistance changes with temperature is provided, while resistance detecting means for detecting the resistance value of the conductive member and the temperature of the planar heating member based on the output of the resistance detecting means. The temperature control means for controlling is provided.

As a result, unlike the conventional sensor such as a thermocouple, since the mounting surface is formed wide, it is possible to prevent malfunction such as contact failure at the sensor mounting portion.

Further, since the conductive member has a length which is at least twice as large as the length between both ends of the sheet heating member in the longitudinal direction, the temperature of the sheet heating member can be detected more accurately. It will be possible.

As described above, the fixing device for an electrophotographic apparatus according to a second aspect of the present invention is the fixing device for an electrophotographic apparatus according to the first aspect, wherein the conductive member is a heating means for heating the conductive member itself. Is provided.

Thus, in addition to the effect of the present invention as set forth in claim 1, even when the temperature of the sheet heating element is rapidly increased in the initial stage of heating, the conductive member is required to follow the rapid temperature rise of the sheet heating element. It is also possible to prevent the occurrence of a temperature difference between the sheet heating element and the sensor detection temperature in the early stage of heating.

According to the fixing device of the electrophotographic apparatus of the third aspect of the invention, as described above, in the fixing device of the electrophotographic apparatus of the first aspect, at least one electrode connected to the conductive member is conductive. This is a configuration in which the member is movably provided.

As a result, in addition to the effect of the first aspect of the invention, the initial temperature resistance of the conductive member can be changed, and the set value of the control temperature can be changed. It is possible to prevent the occurrence of a temperature difference between the heating element and the sensor detection temperature.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a heating device in a fixing device of a printer according to an embodiment of the present invention.

FIG. 2 is a schematic overall configuration diagram showing various components of the printer.

FIG. 3 is an enlarged configuration diagram of a main part showing an enlarged view of the fixing device.

FIG. 4 is a perspective view showing a heating member provided in the fixing device.

FIG. 5 is a plan view showing a back surface conductive coating film provided on the back surface of a heating member provided in the fixing device.

FIG. 6 is a vertical cross section of FIG. 5, in which (a) is X-.
X-ray vertical sectional view, (b) is a YY line vertical sectional view.

FIG. 7 shows a comparative example of a heating member provided in the fixing device, and is an explanatory view showing a heating member in which a back surface conductive coating film has a length 1.5 times that of a front surface conductive coating film. is there.

FIG. 8 is a circuit diagram showing a sensor control circuit in the fixing device.

FIG. 9 is a flowchart showing a temperature control operation in the fixing device.

FIG. 10 is a schematic configuration diagram showing a fixing device of a conventional printer.

FIG. 11 is a graph showing a temperature difference between the front surface and the back surface of the heating member in the fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum (photoconductor) 2 Charging device 5 Transfer device 9 Fixing device 13 Transfer paper 15 CPU (resistance detection means, temperature control means) 16 Fixed electrode 17 Sliding electrode (electrode) 18 Power supply 19 Heat insulating material 20 Heating device 21 Heating member (heating element) 22 Heat-resistant belt (fixing belt) 25 Pressure roller 27 Power supply control circuit for sensor (heating means) 29 Fixed electrode 36 Surface conductive coating film (planar heating member) 38 Electrical insulating plate 39 Backside conductivity Coating (conductive member) 39a Fixed electrode surface 39b Sliding electrode surface 40 Back surface protective layer 41 Heater power supply control circuit

Claims (3)

[Claims] 1. An electrophotographic apparatus for forming an image by transferring a toner image developed on a photoconductor onto a transfer paper, wherein the toner image transferred onto the transfer paper is supplied to a pressure roller via a fixing belt. In the fixing device of the electrophotographic apparatus, which is sandwiched between the heating elements and is heated and melted by the sheet heating member formed on the surface of the heating element to fix the sheet onto the transfer paper. A conductive member having a length at least twice as long as both ends in the longitudinal direction and whose resistance changes with temperature is provided. On the other hand, resistance detecting means for detecting the resistance value of the conductive member, and this resistance detection. And a temperature control means for controlling the temperature of the sheet heating member based on the output of the means. 2. An electrophotographic apparatus for forming an image by transferring a toner image developed on a photoconductor onto a transfer paper, wherein the toner image transferred onto the transfer paper is transferred to a pressure roller via a fixing belt. In the fixing device of the electrophotographic apparatus, which is sandwiched between the heating elements and is heated and melted by the sheet heating member formed on the surface of the heating element to fix the sheet onto the transfer paper. A conductive member having a length at least twice as long as both ends in the longitudinal direction and whose resistance changes with temperature is provided. On the other hand, resistance detecting means for detecting the resistance value of the conductive member, and this resistance detection. Temperature control means for controlling the temperature of the planar heating member based on the output of the means, and further, the conductive member is provided with heating means for heating the conductive member itself. Fixing of electrophotographic device Location. 3. An electrophotographic apparatus for forming an image by transferring a toner image developed on a photoconductor onto a transfer paper, wherein the toner image transferred onto the transfer paper is transferred to a pressure roller via a fixing belt. In the fixing device of the electrophotographic apparatus, which is sandwiched between the heating elements and is heated and melted by the sheet heating member formed on the surface of the heating element to fix the sheet onto the transfer paper. A conductive member having a length at least twice as long as both ends in the longitudinal direction and whose resistance changes with temperature is provided. On the other hand, resistance detecting means for detecting the resistance value of the conductive member, and this resistance detection. Temperature control means for controlling the temperature of the planar heating member based on the output of the means, and at least one electrode connected to the conductive member is provided so that the conductive member can move. Is characterized by The fixing device of the child photographic apparatus.