JPS58159565A - Heating device - Google Patents

Abstract

PURPOSE:To improve thermal response and to prevent a heat source from rising in temperature excessively even when the heater is applied to a heat source which has a fast temperature rise rate, by preheating a temperature fuse at below its blowing temperature directly by a heating member in the power-on start of the heater. CONSTITUTION:A fixation roll 1 is heated by the heater 4 and its surface temperature is detected by a thermistor 15; and a switch 12 is turned on/off by a signal output from a temperature adjusting circuit 16 according to the detected temperature of the thermistor 15 and the surface of the roll 1 is held at specific temperature. When the heater 4 is powered on, a heating member 6 connected to the heater 4 in series also starts generating heat simultaneously to heat the temperature fuse 9 directly. Therefore, the starting of the temperature rise of the temperature fuse 9 itself is speeded up and even if the temperature of the fixation roll 1 exceeds a specific value owing to a fault of the temperature adjusting circuit 16, the time up to the fusion is shortened under the thermal influence to solve the abnormal state speedily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating device, and particularly to a heating device having an overheat protection function.

Hereinafter, a heat fixing device applied to an image forming apparatus such as a copying machine will be described as an example of a heating device.

A conventional heat fixing device detects the surface temperature of a heating element, such as a fixing roller, heated by a halogen heater as a heat source, using a temperature detection member that is in contact with the fixing roller, and a temperature control circuit that receives this detection signal. A switch inserted in the heater circuit is connected and disconnected to control the surface temperature of the fixing roller to be kept substantially constant.

However, if the switch is not turned on or off due to a malfunction in the temperature control circuit, the fixing roller may be heated to an abnormally high temperature. Therefore, in order to prevent this excessive temperature rise, a temperature fuse as a heat-responsive member is provided close to the fixing roller, and this temperature fuse is inserted in series with the heater circuit, so that the temperature fuse absorbs the heat from the fixing roller. By fusing the fixing roller in response to the heat, the temperature of the fixing roller is prevented from rising excessively.

However, as described above, although the temperature fuse is close to the fixing roller, it is provided at a position away from the circumferential surface of the fixing roller. If a fuse that turns off a large current is used, the heat capacity itself is large, and the thermal response (reaction time) is lower than that of a thermistor or other temperature detection means.
There was a problem that it was inferior.

SUMMARY OF THE INVENTION Therefore, the present invention provides a heating device that solves the above-mentioned problems of the conventional example, improves thermal responsiveness, and can also prevent excessive rise in temperature of a heating source with rapid temperature changes.

An embodiment of the present invention will be described below.

FIG. 1 is a side sectional view of a heat fixing roller of a copying machine to which an embodiment of the present invention is applied.

In the figure, reference numeral 1 denotes a fixing roller, which is an aluminum roller. The fixing roller 1 is rotatably held at both ends (the other end is not shown) by bearings 2 . The roller 1 is heated at a rate of 10 to 15 degrees Celsius per second by a halogen heater 4 provided over almost the entire width of the roller 1. This halogen heater 4 is supported approximately at the center of the roller 1 by an electrode 3 attached to a frame 7.
It is connected to a power source through this electrode 3 and is energized.

Reference numeral 5 denotes a temperature fuse holder having a heating member 6, in which a temperature fuse 9 as a thermally responsive member is supported in a recess 6a of the heating member via an electrically insulating member 8. This holder 5 has a mounting seat 5a fixed to a frame 10 with screws 11 to maintain a constant distance between the fixing roller 1 and the temperature fuse 9. 12 is a switch, and 13 is a power supply.

The heater 4, the heating section side 6, the temperature fuse 9, the switch 12, and the power source 13 are connected in series through lead wires 1, as shown in FIG. Further, a short circuit 14 is connected in parallel to the heating member 6 in case the resistance value increases due to the temperature rising to the Curie point or higher.

As the heating section 6, a positive temperature characteristic ceramic heater containing barium titanate as a main component and having a Curie point at a temperature below the melting temperature of the temperature fuse 9, for example around 120 DEG C., is used.

The embodiment of the present invention has the above configuration, and temperature control of the fixing roller 1 will be explained below.

First, the fixing roller 1 is heated by the heater 4 supported by the electrode 3. Then, depending on the temperature detected by the thermistor 15 as a temperature detection member that is in contact with the surface of the fixing roller 1, a signal from the temperature control circuit 16 is sent to the switch 12.
is controlled to keep the surface of the roller 1 at a constant temperature by turning on and off. At this time, the temperature control circuit 16 controls the halogen heater 4 to output the maximum rated output when raising the surface temperature of the roller 1 from room temperature to the temperature necessary for fixing, and once the temperature reaches the temperature necessary for fixing, After that, phase control is performed to output 1/2 the output.

When the heater 4 is energized, the heating member 6 connected in series with the heater also starts generating heat at the same time, and the temperature increases by 1-9.
heat directly. Therefore, the temperature 14-8 itself rises quickly, and since the heating temperature is lower than the melting temperature of the temperature 31-', the temperature Wts+→X is not melted.

Furthermore, since the heating member 6 is a ceramic heater having positive temperature characteristics with a Curie point below the melting temperature of the temperature fuse, the electrical resistance value increases rapidly when the temperature exceeds the Curie point. Heater current is short circuit 1
4, so there is no increase in power loss.

In the unlikely event that the fixing roller 1 generates heat exceeding the specified temperature due to a failure of the temperature control circuit 16, etc., the temperature m4-? Since the fuse has already been heated by the heating member as described above, the time required for it to melt due to the influence of heat from the fixing roller is shortened, and the thermal response of the temperature fuse is improved.

Therefore, even if a temperature fuse with poor thermal conductivity or a temperature fuse with a high heat capacity is applied to a heating element that exhibits extremely rapid temperature changes of 10 to 20 degrees Celsius per second, there will be no delay in overheating of the heating element. It is capable of quickly responding to fusing, and quickly resolving abnormal conditions.

FIG. 4 shows an example of fixing device #F using the above embodiment.

In the figure, reference numeral 17 denotes a pressure roller, which pinches and conveys the sheet P having an unfixed image 18 between it and the fixing roller 1. Then, the unfixed image 18 is heated and fixed onto the sheet P by heat from the fixing roller 1 heated by the heater 4 . In addition,
The pressure roller 17 has a core metal 17a covered with an elastic member 17b made of rubber or the like. The fixing roller 1 receives the driving force from the motor M from the chain 21 to the gear 2.
2 and 23 to rotate, and the pressure roller 7 rotates as a result of this fixing roller 1. Note that the driving force from the motor M may be transmitted to the pressure roller 17. In the drawings, the frame, side plates, bearings, etc. are omitted.

As described above, in the present invention, the temperature fuse is directly preheated to a temperature below the fusing temperature by the heating section in connection with the start of energization to the heater. Compared to the case where the temperature is raised by receiving heat, the temperature rises faster and the thermal response (reaction time) improves. As a result, even when applied to a heating source with a rapid temperature rise rate, the fixing roller is fused without any time delay when the temperature rises abnormally, and excessive rise in temperature of the fixing roller can be reliably prevented.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of the heat-fixing roller equipped with a temperature fuse, Figure 2 is its cross-sectional view, Figure 3 is a block diagram of the system that controls the temperature of the heat-fixing roller, and Figure 4 is a diagram of the fixing device. FIG. IVi fixing roller, 4 is a heater, 5 is a holder, 6 is a heating member, 9 is a temperature fuse, 12 is a switch, 13 is a power supply, 14 is a short circuit, 15 is a temperature detection member, 16 is a Vi temperature control circuit, 17 is a heating member. pressure roller. htsu toichi

Claims (2)

[Claims] (1) A heating source, a heating element that is heated by the heat from the heating source to heat the sheet, a thermally responsive member that responds to the heat from the heating element, and the heating source and the thermally responsive member. a switch provided in a thread path that connects the members in series to a power source; a temperature detection member that detects the surface temperature of the heating element;
a temperature control circuit that opens and closes the switch in response to the detection output of the temperature detection member to control the amount of heat generated by the heat generating element; A heating device comprising a heating member that directly heats a member to a temperature below its fusing temperature. (2) The heating device according to claim 1, wherein the heating member is a ceramic heater having positive temperature characteristics with a cue point below the melting temperature of the thermally responsive member.