JPS63161477A - Fixing device - Google Patents

Abstract

PURPOSE:To quicken the operation of a temperature fuse to prevent thermal deformation of structure members and fusing of wiring by controlling a device to such a state that heat is easily transmitted to the temperature fuse when excessive temperature rise or the excessive temperature rise expecting state is detected by a temperature detecting means. CONSTITUTION:A temperature fuse 4 has both ends in the lengthwise direction supported by side walls of a frame body 9 whose part corresponding to a heating roller 1A is opened. A shutter plate 10 provided on the upper face of the frame body 9 has one end pivotally supported by a connection rod 11, and this connection rod 11 has one end connected to a solenoid 12. If the detection temperature of a thermistor 3 reaches an abnormally high temperature higher than a set temperature, a solenoid 12 is excited, and then, the shutter plate 10 is turned by movement of the connection rod 11 to close the upper face, and the quantity of radiation heat received from the heating roller 1A by the temperature fuse 4 is increased. Thus, the time to fusing of the temperature fuse at the time of arrival at the abnormally high temperature is shortened to suppress thermal deformation of constituting members.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a fixing device, and particularly to a fixing device provided with a structure for preventing overheating of a heating element.

(Prior Art) Generally, an image transferred onto an image carrier such as recording paper by electrophotographic processing is heated and fixed.

One of the structures used for image fixing is a roller that has a heating element inside it, such as a resistance wire.

There is a structure in which the image bearing member is heated while being sandwiched and conveyed by configuring the rollers in a pair, which are positioned in the conveying path of the image bearing member.

By the way, in such a structure, the energization of the resistance wire is controlled so that the temperature of the roller surface becomes the temperature required for fixing, but in this energization control section, unexpected If this situation occurs, excessive current is applied to the resistance wire, causing excessive heat generation in the resistance wire, resulting in the temperature on the roller surface exceeding the fixing temperature, which may cause the image carrier in contact with the roller to catch fire. be.

Therefore, 1. Usually, a thermocouple is installed to detect the temperature of the heater in order to control the energization of the resistance wire (hereinafter referred to as the heater).
Depending on the temperature detected by this thermocouple, the bidirectional thyristor is controlled via a differential amplifier and conduction angle control circuit to adjust the voltage supplied to the heater, while preventing ignition due to an excessive rise in heater temperature. In order to do this, a differential amplifier in which a predetermined comparison reference value regarding temperature is set is connected to the thermocouple.

This differential amplifier is equipped with a structure in which a relay is connected to the heater via a transistor to turn on and off the power to the heater. There is a device in which the output of the amplifier is reversed to make the transistor conductive, and the power to the heater is dialyzed by a relay (for example, Japanese Patent Laid-Open No. 56-9
9372).

However, in general, heaters for fixing use apply extremely large currents, so the control structure including the relays for dialysis of such currents is quite large, and as a result, However, there is a problem in that the cost of the device itself increases.

Therefore, instead of the above-mentioned relay, a thermal fuse is used as a member to cut off the power supply to the heater.

A structure has been proposed in which this thermal fuse is arranged near the surface of the roller so that the thermal fuse is blown when the roller surface reaches an abnormal temperature.

By the way, when setting the melting temperature of the temperature heater used in such a structure, the influence from the outside air temperature, over-sheeting when starting up the heater, etc. are taken into account, and the set temperature is different from that of a normal heater. The temperature is set quite high, specifically 20 to 30 degrees higher than the above set temperature.
The temperature has been raised.

Therefore, although there is no risk of fire at the temperature at which the temperature fuse operates, that is, when it melts, there is a new risk of thermal deformation or wiring analysis in the members that make up the fixing device, and the risk of fire after the temperature fuse operates. There was a risk that these members could not be reused.

(Purpose) In view of the problems of conventional fixing devices equipped with an overheating prevention structure, an object of the present invention is to solve the following problem: It is an object of the present invention to provide a fixing device that can prevent thermal deformation of structural members and melting of wiring.

(Structure) In order to achieve this object, the present invention locates a temperature heater connected in series to the fixing heater in the vicinity of the fixing heater, and uses a temperature detecting means to detect the temperature of the heater to detect an overtemperature. Rising state or.

The present invention proposes to promote heat transfer from the fixing heater to the thermal fuse when an expected temperature over-rise state is detected.

Embodiments of the present invention will be described in detail with reference to FIGS. 1 to 9 below.

FIG. 1 is an external view of a fixing device according to an embodiment of the present invention, in which a pair of rollers designated by reference numeral 1 is composed of a heating roller IA and a pressure roller IB.

That is, the heating roller IA has, for example, an internal structure.

Equipped with a fixing heater 2 having a resistance wire extending in the axial direction, the image carrier such as recording paper is pinched and conveyed in cooperation with a pressure roller IB that contacts one circumferential surface via a drive mechanism (not shown). Rotate as far as you can.

A thermistor 3 serving as temperature detection means is brought into contact with the circumferential surface of the heating roller IA, and a lead wire of the thermistor 3 is connected to a heating control section for a fixing heater 2, which will be described later.

On the other hand, a temperature heater 4 is connected to one of the lead wires extending from the fixing heater 2 built into the heating roller IA, and the lead wire from the temperature heater 4 is connected to the fixing heater 2, which will be described later. It is connected to the heating control section for the

The thermal fuse 4 is positioned near the circumferential surface of the heating roller IA by a support structure described later.

Now, FIG. 2 is a block diagram showing the connection of the heating control section to the fixing heater 2. The fixing heater 2 is connected to a power source 6 via a temperature fuse 4 and a current control element 5. It is connected.

A current control element 5 connected to one side of the fixing heater 2
is composed of a well-known current control element using a semiconductor such as a bidirectional thyristor.

On the other hand, the thermistor 3 is connected to a temperature detection circuit 7, and this temperature detection circuit 7 is connected to the current control element 5 via a heater control circuit 8.

The temperature detection circuit 7 captures changes in the surface temperature of the heating roller IA as changes in the resistance value of the thermistor 3.

A command (C) to energize the fuser heater 2 is output so that the surface temperature of the heating roller IA becomes the set temperature for fixing, and a command (d) is issued to indicate that the temperature has become abnormally high above the set temperature for fixing. ).

That is, in the temperature detection circuit 7, as shown in the third diagram, when the set temperature of the fixing roller surface is Ts to T2, the upper limit (Tt) of the temperature range.

For example, at %S1 point while detecting the lower limit (T2).

A command (C) is output to start the current supply by the current control element 5, and to perform the current supply dialysis by the current control element 5 at three points.

For example, if an abnormally high temperature (T3) higher than the upper limit (T2) of the set temperature is detected, that is, 83 in FIG.
At point, the abnormal high temperature is output as a command (d).

Note that the symbols (a), (b), (f), and (h) shown in FIG.
) indicates the line in FIG.

On the other hand, the above-mentioned thermal fuse 4 is supported by a support structure shown in FIGS. 4 and 5 having a drive control section shown in FIG. 6.

That is, in FIG. 4, the thermal fuse 4 is supported at both ends in the longitudinal direction by side walls of a frame 9 which is open at the portion facing the heating roller IA.

This frame body 9 is provided with a shutter plate 10 that is rotatable about a support shaft 10a on its upper surface, on the opposite side of the position facing the swivel heating roller IA.

The shutter plate 10 is pivotally supported at one end by a connecting rod 11, and the connecting rod 11 is connected at one end to a solenoid 12 and at the other end to a tension spring IIA.

When the solenoid 12 is in a non-energized state, the connecting rod 11 moves in a direction in which the shutter plate 10 rotates counterclockwise in the figure due to the biasing force of the tension spring IIA, and is brought into a resting state. 10 is inserted into and supported by a side wall 13 of the frame body 9 by a locking mechanism (not shown).

That is, the frame body 13 has an open bottom surface in the drawings, which is a portion facing the heating roller IA, and a plurality of ventilation holes 13a are formed in a top plate located on the opposite top surface.

This frame body 13 has a support shaft 14a on one side wall thereof.
An operating arm 14 is pivotably supported around the
One end of this actuating arm 14 is connected to the solenoid 12.

A tension spring 15 is hung on the upper surface of one side wall of the frame 13, and when the solenoid 12 is not energized, the frame 13 keeps the thermal fuse 4 away from the surface of the heating roller IA, as shown by the solid line. .

On the other hand, the solenoid 12 is connected to a drive circuit shown in FIG.

That is, in FIG. 6, the solenoid 12 connects the collector of the switching transistor TR+ and the power supply (
+24V) and the transistor T
The pace of Rs is determined by the temperature detection circuit 70 command (d
) terminal.

Therefore, in the embodiment having such a structure, the detection output from the thermistor 3 shown in the second figure is taken into the temperature detection circuit 7, and the set temperatures T1 to T shown in the third figure are obtained.

The current supply to the fixing heater 2 is controlled via the current control element 5 so that the current range is within the range of .

At this time, frames 9 and 13 supporting the thermal fuse 4
Since the solenoid 12 is still not energized, the shutter plate 10 is rotated to open the top surface [1 (Fig. 4) and the thermal fuse 4 is moved away from the surface of the heating roller IA. state (fifth cause).

On the other hand, for example, due to a short circuit in the current control element 5 or a failure in the heater control circuit 8, the power supply to the fixing heater 2 is continued, and as a result, the temperature detected by the thermistor 3 is abnormally high, exceeding the set temperature shown in the third diagram. When the temperature reaches (T3), a command (d) indicating an abnormally high temperature is outputted to the temperature detection circuit 7.

In this state, the transistor TRI in the solenoid drive circuit shown in FIG. 6 is conductive.

Solenoid 12 is energized.

When the solenoid 12 is energized, the frames 9 and 13 move the shutter plate 1o through the movement of the connecting rod 11.
; b: rotated to close the upper surface (FIG. 4) and approach the surface of the heating roller IA through the rotation of one operating arm 140 (FIG. 5); The drive control section shown in FIG. 6 functions as means for causing a change in the amount of heat received by the thermal fuse 4.

Therefore, in this state, the amount of heat taken into the temperature fuse 4 increases rapidly compared to the normal state, and the time until the fuse 4 blows out is accelerated, and the current supply to the fixing heater 2 is cut off.

According to the above-described embodiments, the temperature heater supported by the frame is provided. By changing the amount of heat received through a simple structure of controlling the drive of a solenoid, it is possible to control the time until the temperature fuse blows out.

Next, another embodiment of the present invention will be described with reference to FIGS. 7 to 9.

Another embodiment of the present invention is characterized in that the amount of heat received by the temperature fuse is caused to change by changing the airflow within an image forming apparatus such as a copying machine.

That is, the apparatus shown in FIG. 7 is a laser printer, which is one type of image forming apparatus.

In this apparatus, a laser beam scanning device 17 is provided at the exposure section for the photoconductor drum 16, and an electrostatic latent image formed on the photoconductor drum 16 is transferred to the photoconductor drum 16 by image scanning by the laser beam scanning device 17. Visible slag is processed by a developing device 18 located around the area.

After this visible image is transferred to recording paper, the image on the recording paper is fixed by a fixing device 19.

In such a device, the cooling fan 2 inside the device
0 is attached to the side wall of the device.

In this case, the type of fixing device is the roller pair 1 shown in FIG. 1, and the positional relationship of the thermistor 3 and humidity fuse 4 with respect to the heating roller IA of the roller pair 1 is explained as being the same. do.

That is, with respect to the cooling fan 20. As shown in FIG. 8, the drive control circuit includes a first switching transistor TRt whose base is connected to the command (d) terminal of the 1m degree detection circuit 7, a pace connected to the collector of this transistor TRt, and a cooling circuit. It is configured in combination with a second switching transistor TR2 that performs switching of the fan 20.

In this embodiment having such a configuration.

If the temperature detected by the thermistor 3 reaches an abnormally high temperature (T3) higher than the set temperature shown in FIG. 3, the temperature detection circuit 7
An abnormally high temperature command (d') is output from.

In response to this output, the transistor TR1 becomes conductive, whereas the transistor TR2 becomes non-conductive, and the current supply to the cooling fan 20 is maintained at LZ.

Therefore, a forced air flow was generated within the device while the cooling fan 20 was operating.

Only natural convection occurs, resulting in a state where heat is trapped and the temperature rises rapidly.

In such a state, as shown by the arrow in FIG. The time required for the temperature fuse 4 to blow is shortened due to the accumulation of hot air.

According to this embodiment, with a simple structure that only controls the operation of an existing cooling fan, it is possible to control the time until the thermal fuse blows out when an abnormally high temperature is reached.

(Effects) As described above, according to the present invention, by simply controlling the amount of heat received by the temperature fuse connected in series with the fixing heater, it is possible to prevent the temperature fuse from blowing out when an abnormally high temperature is reached. The time can be shortened, and as a result, expensive components such as relays are not used, so the device can be made at a low cost.

It is also possible to prevent thermal deformation of the structural members caused by the temperature rise until the thermal fuse blows out, thereby making it possible to reuse these structural members.

[Brief explanation of the drawing]

1 is an external view of a fixing device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a heating control section of a fixing heater in the fixing device shown in FIG. 3 is a diagram showing the function of the block diagram shown in FIG. 2, FIGS. 4 and 5 are overall configuration diagrams for explaining the support structure of the thermal fuse, and FIG.゜Figure 5 is a solenoid drive control circuit diagram, Figure 7 is an overall configuration diagram of a laser printer to which another embodiment of the present invention is applied, and Figure 8 is a diagram of a cooling fan according to another embodiment of the present invention. A drive control circuit diagram, FIG. 9 is an overall configuration diagram for explaining the support structure of the temperature heater of the fixing device shown in FIG. 7. 2... Fixing heater, 3... Thermistor, 4...
Temperature heat, 5... Current control element, 7... Temperature detection circuit. 9.13.21...Support frame, 11...Connecting rod, 12
... Solenoid, 14... Operating arm, 20... Cooling fan, TR1*TRz... Transistor. Figure 1 Figure 2 Figure 3 Figure 6 Figure 7 Figure 8 Figure 7

Claims (1)

[Scope of Claims] A fixing heater, a current control element connected in series to the heater, a temperature detection means for detecting the temperature of the fixing heater, and a current control element connected in series to the fixing heater. In the fixing device, the fixing device has a temperature fuse, and controls the current control element to the fixing heater based on the detection output of the temperature detection means, the temperature fuse is located near the fixing heater, When the temperature detecting means detects a temperature over-rise state or an expected temperature over-rise state, the heat transfer state between the temperature fuse and the fixing heater is controlled to a state where heat is easily transferred to the temperature fuse. A fixing device characterized in that it is provided with a means for.