JPH05210335A - Safety protective device - Google Patents

Abstract

PURPOSE:To reduce the loss of power consumption in terms of insuring safety of the safety protective device of a fixing device, etc., and to rapidly interrupt the supply of a current by constituting an element which generates heat in a moment and an element which interrupts the conduction of a current supply circuit of the fixing device, etc., by the generated heat as separate circuits and housing them in one package. CONSTITUTION:A heating element 7 and an interrupting element (temperature fuse) 8 which is disposed near the element 7 and interrupts the current supply circuit for a fixing heater 3 are housed in the same package 9, and the heating element 7 and the interrupting element 8 are connected to a DC power source 13 and an AC power source 11, respectively, and constituted as the separate circuits. In the case of judging that a solid state relay SSR 10 is not normally actuated, a control part 12 actuates(turns on) a switching transistor 14, the current is supplied to the resistance R of the heating element 7 from the power source 13 so as to generate the heat. The temperature fuse of the interrupting element 8 is fused instantaneously by the heat generated by the heating element 7 and the supply of the current from the power source 11 is interrupted, then the abnormal heating of the heat roller 2 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety protection device such as a fixing device in an image forming apparatus such as a printer or a copying machine.

[0002]

2. Description of the Related Art An example of a fixing device of an image forming apparatus is composed of a heat roller containing a fixing heater and a pressure roller in contact with the heat roller.

The surface temperature of the heat roller is a temperature detecting element which is provided in the vicinity of the heat roller in a contact or non-contact state.
The temperature of the heat roller surface is detected by (for example, a thermistor). The detection voltage of this temperature detection element is
The D / D conversion is compared with the preset temperature setting value, and the control unit controls the solid state relay to reach the predetermined temperature.
(Hereinafter, referred to as SSR) is turned on / off to control the current supply to the fixing heater.

[0004]

As a safety protection device for a current supply circuit to the fixing heater, a heating element for detecting an abnormal temperature is conventionally provided in series with the fixing heater to detect the abnormal temperature of the heating element. An abnormal temperature detecting unit such as a fuse detects the temperature, and the fuse is blown to stop the current supply to the fixing heater.

When a heating element for detecting an abnormal temperature is provided in series with such a fixing heater, there is a problem in that there is always a power loss for detection and power consumption increases.

As another safety protection device, there is one in which a temperature fuse is connected in series with a fixing heater of a fixing device, but there is a problem that it takes time for the temperature fuse to melt.

In view of such circumstances, it is an object of the present invention to quickly cut off the current supply circuit in a safety protection device such as a fixing device by reducing the loss of power consumption for ensuring safety. To do.

[0008]

According to a first aspect of the present invention, in a protective device such as a fixing device of an image forming apparatus, an element which is supplied with an electric current for detection and instantaneously generates heat, and the heating element. The element for interrupting the conduction of the current supply circuit such as the fixing device due to the heat generation of 1 is constituted by a separate circuit, and the heat generating element and the cutoff element are located in the vicinity where the heat generated by the heat generating element is sensitively reflected by the cutoff element. It is characterized in that they are accommodated in the same package.

According to a second aspect of the present invention, in a protection device such as a fixing device of an image forming apparatus, an element that is instantaneously heated by current being supplied due to a failure or the like and a current supply of the fixing device or the like. The element for interrupting the continuity of the circuit is characterized in that the operating elements are arranged in the respective current supply circuits of the heat generating element and the interrupting element so that they can be simultaneously operated separately when an abnormality occurs.

[0010]

According to the present invention, an element which is supplied with a current for detection and generates heat instantaneously and an element which cuts off the conduction of a current supply circuit such as a fixing device due to the heat generated by the heating element are provided in separate circuits. The SSR that is configured and accommodated in one package supplies a current to the heating element only when a failure occurs in the SSR that turns on / off the current supply circuit to perform a detection operation. Since the heat generating element and the cutoff element are accommodated in the same package with no loss, the operation is performed immediately.

Further, when an abnormality occurs, the heat generating element and the cutoff element are separately operated at the same time to facilitate compliance with safety standards.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit configuration diagram of an embodiment according to claim 1 of the present invention, which is a case where it is applied to a fixing device of an image forming apparatus. In the figure, 1 is a fixing device, and a heat roller 2
A built-in fixing heater 3 for heating the heat roller from the inside; a thermistor (A) 4 for detecting the surface temperature of the heat roller in contact with or not in contact with the heat roller; And a thermistor (B) 5 for detecting. 6 is a safety protection device according to the present invention, which is a heating element 7
(For example, a resistor R) and a cutoff element 8 (for example, a thermal fuse) that cuts off a current supply circuit to the heater 3 arranged in the vicinity of the heating element are housed in the same package 9. The heat generating element 7 is composed of a DC power source 13 and the cutoff element 8 is composed of an AC power source 11 by separate circuits. A solid-state relay (SSR) 10 turns ON / OFF the current supply from the AC power supply 11 to the fixing heater 3, and this is controlled by a control signal from the control unit 12. Reference numeral 14 is a switching transistor (Tr) for the heating element 7.

The operation will now be described. In normal control, the SSR 10 is turned on / off by a control signal from the control section 12.
The power is turned off, and the current supply from the AC power supply 11 to the fixing heater 3 is turned on (lighted) / off (lighted off). Thermistor (A) 4
Detects the surface temperature of the heat roller 2 and inputs it to the control unit 12, A / D-converts it by the control unit 12, compares it with a predetermined temperature set value, and turns on the SSR10 so as to reach a predetermined temperature.
N / OFF.

In this case, when the SSR 10 fails for some reason, the safety protection device 6 of the present invention operates. That is,
When the control unit 12 determines that the SSR 10 does not operate normally,
The switching transistor (Tr) 14 is operated (ON),
A current is supplied from the DC power source 13 to the resistance R of the heating element 7 to generate heat. Due to the heat generated by the heating element 7, the temperature fuse of the cutoff element 8 is immediately blown, and the current supply from the AC power source 11 is cut off, preventing abnormal heating of the heat roller 2.

That is, since the safety protection device 6 supplies current to the heating element 7 and melts the cutoff element 8 only when the SSR does not operate due to a failure or the like, the power loss can be remarkably reduced as compared with the conventional case.

The operating temperature of the safety protection device 6 is usually
It is preferable that the temperature is not less than the operating temperature of the machine plus the temperature rise in the fixing device 1 and the storage temperature, but when a thermal fuse is used as the blocking element 8, the temperature of the heating element 7 is set to the temperature at which the thermal fuse is blown. There is no problem if the temperature is set.

Further, when the SSR10 fails, the thermistor
In addition to the detection temperature of (A) 4, the detection temperature of the fixing device 1 of the thermistor (B) 5 is added, and the control unit 12 controls the switching transistor (Tr) 14 to control the temperature of the heating element 7.
By controlling the current supply from the C power supply 13 to operate the interruption element 8, it is possible to operate as a more precise safety protection device 6.

2 and 3 show examples of the safety protection device 6 shown in FIG. 1. In FIG. 2, a bimetal 8a is used as a breaking element 8 for the heating element 7a (heater) to cut off the AC power supply circuit. This is the case.

FIG. 3 shows a case where the shape memory alloy 8b is used as the breaking element 8 for the heating element 7b (lamp) to cut off the AC power supply circuit. In both cases of FIG. 2 and FIG. 3, it can be used again because it is restored after a predetermined time has elapsed.

The lower the operating temperature of the breaking element 8 of the safety protection device 6 shown in FIGS. 1 to 3, the faster the operation of the safety protection device and the earlier the abnormal state can be prevented.

FIG. 4 is a circuit diagram of an embodiment according to claim 2 of the present invention, in which the heating element 7 and the cutoff element 8 of the safety protection device 6 are supplied with current from the same AC power source 11 Between the elements 7 and 8 and the AC power source 11, the respective SSR10-2, S
It has an SR 10-1 and is configured to be ON / OFF controlled by the control unit 12.

According to this configuration, when a failure or the like occurs in the SSR 10-1 for some reason, the control unit 12 causes the SSR 10-2 to operate.
Is turned on (ON), the heating element 7 is heated by the AC from the AC power supply 11, and the cutoff element 8 can be cut off. As described above, since the heating element 7 is caused to generate heat by AC, there is an advantage that the safety standard can be easily met.

A means for monitoring the energization of the fixing heater 3 (CT transformer or the like) may be provided to monitor the energization control of the SSR, and the safety protection device 6 may be operated by the control section 12 when an abnormality occurs. Good.

[0024]

As described above, the safety protection device of the present invention can be operated promptly and at low cost without wasting electric power.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment according to claim 1 of the present invention.

FIG. 2 is a diagram showing an example of the safety protection device 6 of FIG.

3 is a diagram showing an example of the safety protection device 6 of FIG.

FIG. 4 is a circuit configuration diagram of an embodiment according to claim 2 of the present invention.

[Explanation of symbols]

1 ... Fixing device, 2 ... Heat roller, 3 ... Fixing heater,
4 ... Thermistor (A), 5 ... Thermistor (B), 6 ... Safety protection device, 7, 7a, 7b ... Heating element, 8 ... Breaking element, 8a ... Bimetal, 8b ... Shape memory alloy, 9 ...
Package, 10, 10-1, 10-2 ... Solid state relay (SSR), 11 ... AC power supply, 12 ... Control section, 13 ... D
C power supply, 14 ... Transistor (Tr).

Claims (2)

[Claims] 1. In a protection device such as a fixing device of an image forming apparatus, an element which is supplied with a current for detection and generates heat instantaneously, and the heat generation of the heating element interrupts conduction between a current supply circuit such as a fixing device. The heat generating element and the cutoff element are housed in the same package so that they are located in the vicinity of where heat generated by the heat generating element is sensitively reflected by the cutoff element. Safety protection device. 2. In a protection device such as a fixing device of an image forming apparatus, an element which is instantaneously heated by an electric current due to a failure or the like and an element which interrupts conduction of a current supply circuit of the fixing device are abnormal. A safety protection device, wherein operating elements are provided in the respective current supply circuits of the heat generating element and the interrupting element so that they are simultaneously activated when they occur.