JPH06180540A - Image forming device - Google Patents

Abstract

PURPOSE:To keep the temperature of a heating element constant without using a temperature control circuit by arranging a heating resistor on the heating surface being the front surface of the heating element and providing a temperature limiting and current limiting element on a non-heating surface being the back surface of the heating element. CONSTITUTION:The heating resistor 14 is arranged on the heating surface being the front surface of the heating element 9 used as a heat source for a fixing device, and a PTC thermistor 14 being the temperature limiting and current limiting element is provided on the non-heating surface being the back surface thereof. The resistor 14 and the thermistor 15 are connected in series, and further a power source 16 and a switch 17 are also connected in series, then a current is supplied to the resistor 14 from the power source 16 when the switch 17 is turned on. When the temperature of the resistor 111 attains the specified temperature, the current supplied to the thermistor 14 is suddenly limited by the temperature limiting and current limiting characteristic of the thermistor 15. As a result, the temperature of the resistor 14 is kept nearly constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms an unfixed toner image by toner on an image carrier by an electrophotographic method, and transfers the toner image to a print medium via a transfer fixing belt to fix the toner image. The present invention relates to an image forming apparatus that forms an image by means of.

[0002]

2. Description of the Related Art FIG. 8 is a perspective view showing a heating element of an example of a conventional image forming apparatus, (a) showing a heating surface, (b) showing a surface opposite to the heating surface, and FIG. 8 is a circuit diagram showing electrical connection of the example of FIG. 8, and FIG. 10 is a characteristic diagram showing temperature characteristics and current characteristics of the example of FIG.

A conventional image in which an image is formed by forming an unfixed toner image with toner on an image carrier by an electrophotographic method, and transferring the toner image to a print medium via a transfer fixing belt and fixing the toner image. The forming device is shown in FIG.
As shown in FIG. 9, the heating element 49 is provided with a heating resistor 44 and a temperature sensor 48, and in order to control the temperature inside the apparatus,
As shown in, the heating resistor 44 and the temperature sensor 48 are connected to the temperature control circuit 50, and a current is supplied to the temperature control circuit 50 from the power supply 46 via the switch 51.

The current characteristic of the heating element 49 of the conventional image forming apparatus thus configured is continuously supplied until the heating element temperature reaches a predetermined temperature T, as shown by the current waveform 53 in FIG. The temperature characteristic is linearly increased until reaching a predetermined temperature T as shown in the temperature waveform 52 of FIG. Draw a curve of up and down.

[0005]

As described above, the conventional image forming apparatus has a temperature sensor for detecting the temperature of the heating element and a temperature control for controlling the temperature inside the apparatus by a signal from the temperature sensor. Since the circuit is required, there is a problem that a space for installing the electronic component and the circuit is required. Further, there is a drawback that the temperature fluctuation after reaching a predetermined temperature is large and a large current constantly flows, resulting in a large power consumption.

[0006]

In a first image forming apparatus of the present invention, a toner image is formed on the surface of the photoconductor by a charging device, an exposing device, a developing device, and a photoconductor, and the toner image is formed by a transfer device. To the transfer fixing belt,
In an image forming apparatus for transferring and fixing the toner image transferred to the transfer fixing belt onto a medium by a sheet-like heating element and a pressure roll, a heating resistor is provided on a heating surface of the heating element, and the heating element is provided. One temperature limiting current limiting element is provided on the non-heating surface, and the heating resistor, the temperature limiting current limiting element, and the power source are connected in series.

In a second image forming apparatus of the present invention, a toner image is formed on the surface of the photoconductor by a charging device, an exposing device, a developing device and a photoconductor, and the toner image is transferred to a transfer fixing belt by a transfer device. Then, in the image forming apparatus for transferring and fixing the toner image transferred to the transfer fixing belt onto a medium by a planar heating element and a pressure roll, a heating resistor is provided on a heating surface of the heating element, A plurality of temperature limiting current limiting elements are provided on the non-heating surface of the heating element, a plurality of the temperature limiting current limiting elements are connected in parallel, and a plurality of the temperature limiting current limiting elements are connected in parallel with the heating resistor. An element and a power source are connected in series, and any one of the plurality of temperature limiting current limiting elements can be selected by a switch.

[0008]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 7 is a front view showing a first embodiment of the present invention, and FIG. 1 is a perspective view showing a heating element of the embodiment of FIG.
(A) is a diagram showing a heating surface, (b) is a diagram showing a surface opposite to the heating surface, FIG. 2 is a circuit diagram showing electrical connection of the embodiment of FIG. 7, and FIG. 3 is a diagram of the embodiment of FIG. It is a characteristic view which shows a temperature characteristic and a current characteristic.

In FIG. 7, the charging device 1, the exposing device 2, the developing device 3 and the photoconductor 4 form a toner image on the surface of the photoconductor 4 by a well-known electrophotographic method. The toner image formed on the surface of the photoconductor 4 is transferred by the transfer unit 5 to the transfer and fixing belt 12 which makes a circular motion in synchronization with the rotational motion of the photoconductor 4 by the driving roll 7, the driven roll 6, and the tension roll 8. Transcribed.

The toner image transferred to the transfer / fixing belt 12 has a sheet-like heating element 9 and a pressure roller 1 made of elastic rubber which is pressed against the heating element 9 by a spring 11.
At the contact portion (Nip portion) with 0, it is transferred and fixed on the medium 13 supplied in synchronization with the transfer fixing belt 12.

Since the surface of the transfer / fixing belt 12 is subjected to a surface treatment such as fluorine treatment, it has a high releasability, and the toner image on the transfer / fixing belt 12 is efficiently transferred to the medium 13 to form a good image. Is obtained.

A heating element 9 used as a heat source for the fixing device.
As shown in FIG. 1, the heating resistor 14
And a PTC thermistor 15 which is a temperature limiting current limiting element is provided on the non-heat generating surface on the back side.

Heating resistor 14 and PTC thermistor 15
As shown in FIG. 2, the power source 16 and the switch 17 are connected in series, and the switch 17 is turned on so that the power source 16 supplies a current to the heating resistor 14. Is configured.

As shown in FIG. 3, when the temperature of the heating resistor 14 reaches a predetermined temperature T, the temperature limiting current limiting characteristic of the PTC thermistor 15 causes the heating resistor 14 to reach the heating resistor 14 as shown by a current waveform 23. The current supplied by the device is sharply limited. As a result, the temperature of the heating resistor 14 is kept substantially constant as shown by the temperature waveform 22.

FIG. 4 is a perspective view showing a heating element of a second embodiment of the present invention, (a) showing a heating surface, (b) showing a surface opposite to the heating surface, and FIG. 4 is a circuit diagram showing electrical connection of the embodiment of FIG. 4, FIG. 6 is a characteristic diagram showing temperature characteristics and current characteristics of the embodiment of FIG. 4, and FIG. 6A shows characteristics when one PTC thermistor is operated. Figure (b) shows the other P
It is a figure which shows the characteristic at the time of operating a TC thermistor.

As shown in FIG. 4, the heating element 29 in this embodiment has a heating resistor 24 on the front heating surface and two PTC thermistors 25a and 25 on the back non-heating surface.
b is provided. PTC thermistor 25a and PT
The C thermistor 25b has a different temperature limiting current limiting characteristic.

Heating resistor 24 and PTC thermistor 25a
And 25b are connected in series as shown in FIG. 5, and the PTC thermistor 25a and the PTC thermistor 25 are connected.
b is connected in parallel. Furthermore, the heating resistor 24
A switch 27, a power supply 26, and a switch 28 are connected in series between the and PTC thermistors 25a and 25b. Switch 28 is a PTC thermistor 2
Either 5a or 25b is connected to the power supply 26.
By turning on the switch 27, a current is supplied from the power supply 26 to the heating resistor 24.

The PTC thermistor 2 by the switch 28.
When the switch 27 is turned on with 5a connected to the power supply 26, as shown in FIG. 6 (a), when the temperature of the heating resistor 24 reaches a predetermined temperature T ₁ , the PTC thermistor 25
Due to the temperature limiting current limiting characteristic of a, the current supplied to the heating resistor 24 is sharply limited as shown by the current waveform 33a. As a result, the temperature of the heating resistor 24 is
As shown by the temperature waveform 32a, the temperature T ₁ is maintained at a substantially constant temperature.

The PTC thermistor 2 is provided by the switch 28.
When the switch 27 is turned on with 5b connected to the power supply 26, as shown in FIG. 6B, when the temperature of the heating resistor 24 reaches a predetermined temperature T ₂ , the PTC thermistor 25
Due to the temperature limiting current limiting characteristic of b, the current supplied to the heating resistor 24 is sharply limited as shown by the current waveform 33b, and the temperature of the heating resistor 24 changes to the temperature waveform 32
As shown in b, the temperature T ₂ is kept substantially constant. Energy saving can be achieved by using two PTC thermistors having different characteristics as described above and selecting them according to the situation.

[0021]

As described above, in the image forming apparatus of the present invention, the heating resistor is disposed on the heating surface of the heating element, and the temperature limiting current limiting element is provided on the non-heating surface of the back surface. There is an effect that it is possible to maintain the temperature of the heating element substantially constant without using a temperature control circuit. Therefore, the structure can be simplified and the cost can be reduced, and the device can be downsized. There is.

[Brief description of drawings]

1 is a perspective view showing a heating element of the embodiment of FIG. 7, (a)
Is a diagram showing a heat-generating surface, and (b) is a diagram showing a surface opposite the heat-generating surface.

FIG. 2 is a circuit diagram showing an electrical connection of the embodiment shown in FIG.

FIG. 3 is a characteristic diagram showing temperature characteristics and current characteristics of the embodiment of FIG.

FIG. 4 is a perspective view showing a heating element according to a second embodiment of the present invention, (a) showing a heating surface, and (b) showing a surface opposite to the heating surface.

5 is a circuit diagram showing an electrical connection of the embodiment of FIG.

6 is a characteristic diagram showing temperature characteristics and current characteristics of the embodiment of FIG. 4, (a) shows a characteristic when one PTC thermistor is operated, and (b) shows another PTC thermistor. It is a figure which shows the characteristic at the time of operating.

FIG. 7 is a front view showing the first embodiment of the present invention.

FIG. 8 is a perspective view showing a heating element of an example of a conventional image forming apparatus, (a) showing a heating surface and (b) showing a surface opposite to the heating surface.

9 is a circuit diagram showing an electrical connection of the example of FIG.

10 is a characteristic diagram showing temperature characteristics and current characteristics of the example of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charging device 2 Exposure device 3 Developing device 4 Photoconductor 5 Transfer device 6 Follower roll 7 Driving roll 8 Tension roll 9 ・ 29 ・ 49 Heating element 10 Pressure roll 11 Spring 12 Transfer fixing belt 13 Medium 14 ・ 24 ・ 44 Heating resistance Body 15 ・ 25a ・ 25b PTC thermistor 16 ・ 26 ・ 46 Power supply 17 ・ 27 ・ 28 ・ 51 Switch 22 ・ 32a ・ 32b ・ 52 Temperature waveform 23 ・ 33a ・ 33b ・ 53 Current waveform 48 Temperature sensor 50 Temperature control circuit

Claims (2)

[Claims] 1. A toner image is formed on the surface of the photoconductor by a charging device, an exposing device, a developing device, and a photoconductor, and the toner image is transferred to a transfix belt by a transfer device and transferred to the transfix belt. In an image forming apparatus for transferring and fixing the toner image on a medium by a sheet-like heating element and a pressure roll, a heating resistor is provided on the heating surface of the heating element, and one heating element is provided on the non-heating surface of the heating element. The image forming apparatus, wherein the temperature limiting current limiting element is provided, and the heating resistor, the temperature limiting current limiting element, and a power source are connected in series. 2. A toner image is formed on the surface of the photoconductor by a charging device, an exposing device, a developing device, and a photoconductor, and the toner image is transferred to a transfix belt by a transfer device and transferred to the transfix belt. In an image forming apparatus for transferring and fixing the toner image onto a medium by a sheet-like heating element and a pressure roll, a heating resistor is provided on the heating surface of the heating element, and a plurality of heating resistors are provided on the non-heating surface of the heating element. A temperature limiting current limiting element is provided, a plurality of the temperature limiting current limiting elements are connected in parallel, and a plurality of the temperature limiting current limiting elements connected in parallel with the heating resistor and a power source are connected in series. An image forming apparatus, wherein any one of the plurality of temperature limiting current limiting elements can be selected by a switch.