JPS60205562A - Safety device in fixing device - Google Patents

Abstract

PURPOSE:To prevent damaging of a fixing device and to improve reliability by providing a means for shutting off a heat source by the detection signal for an abnormal temp. from a detecting circuit provided separately from a temp. control system. CONSTITUTION:The temp. of a fixing device is judged to be abnormal if the voltages VT, VF in a measuring circuit 10 for the temp. of the fixing device and an upper limit circuit 12 for the fixing device are VT>=VF. A CPU4 makes the signal to a firing element 7 non-active in this stage and therefore the abnormal temp. rise does not arise if the element 7 is normal. The damage of the fixing device is prevented even when the element 7 is broken by a short circuit mode or when the CPU4 is abnormal. More specifically, a system for another comparator 13 is provided in addition to the control system for the CPU4 so that a relay 14 turns on and the power source for a lamp 6 is interrupted from the source when the temp. of the fixing device attains the abnormal temp. limit VF in the period after lapse of the time until overshoot settles down.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a safety device against temperature abnormalities in a fixing device using a heat fixing method.

[Prior art]

Conventionally, fixing devices that use heat to fix the object to be fixed have been widely used as fixing devices used in the fixing process of electronic copying machines and the like. Temperature control is required to control the temperature to the required temperature.

By the way, in recent years, the reliability of this type of fixing device control has been improved by the use of microprocessors compared to the past. Regarding 5, it is insufficient to prevent troubles caused by abnormalities in drivers such as ignition elements for power control, and there is a lack of ensuring safety. In other words, if a microprocessor goes out of control or its heat source driver short-circuits, it will become difficult to control, causing an abnormal temperature rise, and even if the thermostat is activated, normally by that point, the The situation has become such that a large number of parts need to be replaced for repair.

[Purpose of the invention]

In view of the above points, it is an object of the present invention to provide a safety device capable of dealing with an uncontrollable situation that causes an abnormal temperature rise as described above in this type of fixing device, and to prevent damage to the fixing device from occurring. The purpose is to prevent such problems and improve reliability.

[Structure of the invention]

In order to achieve the above object, the present invention uses a detection circuit to detect that the temperature of the fixing unit has reached an abnormal temperature, in addition to a temperature control system that controls the temperature to a desired level depending on the temperature. A system that uses that signal to cut off the power to the heat source (
A control system is provided to perform the following:

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram of a temperature control system of a fixing device to which the present invention can be applied, in which (1) is a device for measuring the temperature of the fixing device, and (2) is a device for controlling the temperature of the fixing device to a desired control temperature. The reference circuit (3) is an A/D converter for obtaining a reference signal that serves as a reference for comparison in the case where the outputs of the fuser temperature measuring device (1) and the reference circuit (2) are A/D converted. , one-chip C as a microprocessor
P U (given as data to 41, this CP, ,
A control signal is sent from U+41 to lower the temperature of the fixing device when it is lower than the control temperature, and to raise it when it is higher. c.
The control signal from pU (41) is passed through the drive circuit (5),
Ignition element (S) for the drive of the lamp (6) as a heat source
S R) added to +71. This ignition element (7)
is provided in the power supply path of the lamp (6) together with the thermostat (8), and is connected to the AC100V commercial power supply (9).
The electric power supplied to the lamp (6) is controlled by using the electric power to the lamp (6), and the temperature of the fixing device is thereby controlled.

FIG. 2 shows a circuit configuration of an embodiment of the present invention used in a temperature control device for a fixing device using the above-mentioned lamp (6) as a heat source.

The fuser temperature measuring circuit 0■ is a circuit that converts the temperature detected by the sensor that measures the temperature of the fuser into voltage or current so that the temperature can be controlled when controlling the temperature of the fuser. In this example, the temperature of the fixing device is detected using a thermistor RT, and the detected temperature is converted into voltage so that it can be extracted.

In other words, a thermistor RT is connected between the operating power supply VCO and ground.
It is equipped with a voltage dividing circuit in which the resistance value R and the resistance value R are connected in series, so that the voltage VT taken out from both ends of the resistance R as the resistance value of the thermistor RT changes becomes a parameter indicating the temperature of the fuser. .

The control temperature reference circuit 01) also has a voltage dividing circuit with a resistor RctR, but the resistance value of the resistor Re is the resistance value that the thermistor RT would show if the temperature of the fixing device was the control temperature Tc. r. is set to . In other words, this means that the control temperature TC of the fuser is set to the voltage V. According to the resistance value t of the thermistor RT at the control temperature Tc,
Control temperature T. is being simulated. In addition to these, a circuit (12) is provided that converts the abnormal temperature of the fixing unit into a voltage vF so that it can be expressed as a voltage value, and this is also connected to the control temperature reference circuit (111). The resistance value of the resistor RF is set using the same selection method as the abnormal temperature limit TF of the fuser.
It is possible to simulate the resistance value r of the thermistor RT at the time.

Each of the above circuits (voltages V, VC,
V.

The respective output signals of
The two output signals of the voltages V and V are given to the CPU (41), and it is determined whether or not the temperature of the fixing unit is higher than the abnormal temperature by comparing the two output signals. is added to the comparator α3). The control system of the A/D converter (3) and CPU (41) determines whether the voltage VT is different from the voltages vc and vF, and if vT<vc, the temperature of the fixing unit is has not reached the control temperature T., and ■vT=
If vc, the temperature of the fuser matches the control temperature vc, and if vP<VT>vo, the temperature of the fuser exceeds the control temperature TC but has not yet reached an abnormal temperature. First, if vT≧vF, it is determined that the temperature of the fixing device has reached an abnormal temperature, and the ignition element (7) is controlled in accordance with each case.

The comparator (13101) is provided separately from such a control system to detect that the temperature of the fixing unit has reached an abnormal temperature, and if vT≧V in (■) above,
In the case of F, the configuration is such that, for example, an H level detection output is obtained as the output. The relay contact α4 is inserted into the power supply circuit of the lamp (6), and the detection output of the above-mentioned comparator (13+) is used to turn on the power to the lamp (6) when the fuser temperature is abnormal. However, in this embodiment, an AND circuit 05) is provided to bypass temporary temperature abnormalities due to overshoot when the power is turned on, and its output controls the relay (141). It has become.

That is, in the fuser, if the main switch (16) is turned on and power is applied when the fuser is cooled down, overshoot will occur as shown in Figure 3, so one input of the AND circuit (15) will As shown in Fig. 4 (bl), the output of the comparator (13) is given, and as the other input, as shown in Fig. 4 (c), after the main switch α6 is turned on, until the time t1 when the overshoot subsides, A timer circuit signal that is at L level and then becomes H level is added, and in the case shown, such a timer circuit signal is obtained by using the timer circuit built into the CPU +41.

According to the above-mentioned embodiment device, in the case of vT≧vF mentioned above, when CPU+41 determines that there is an abnormality, the ignition element (
Since the signal to 7) is made inactive, the ignition element (
If 7) is also normal, it will not cause an abnormal temperature rise. Furthermore, even when the ignition element +71 is broken in short-circuit mode or when the CPU (41) becomes abnormal, damage to the fuser can be prevented. In other words, even when the CPU (41) becomes abnormal.
In addition to the control system, a separate system for comparator 03) is provided, so that, as shown in FIG. Temperature of the device or abnormal temperature limit T
When it reaches F, the relay circle is turned on as shown in FIG. 3(d), and the power to the lamp (6) can be cut off from the beginning.

Therefore, if the ignition element (7) is short-circuited or the C
When the PU (41) goes out of control, the temperature of the fuser rises uncontrollably, and the temperature rises until the thermostat (8) is activated, and as mentioned above, usually +1 - Mostat (8)
When the fuser is in operation, a situation in which a large number of parts are required to be replaced for repair does not occur, and such a situation can be avoided, thereby eliminating damage to the fuser. In this way, by providing two systems, the control system for the CPU (41) and the control system for the comparator (13), it is possible to obtain a reliable safety device that is twice as reliable as the conventional system. Unlike the temperature control of the CPU (4) system, it is only necessary to control whether power is supplied or cut off, so it can be constructed at low cost.

In the configuration shown in FIG. 2, the overshoot time t1 is bypassed by the CPU +41, but in a fixing device where the overshoot time t1 is relatively short,
Instead of bypassing the overshoot time t1, the power supply may be cut off when the time during which the abnormal temperature is reached is longer than a certain period of time.

〔Effect of the invention〕

As described above, the present invention can provide an inexpensive and reliable safety device that can cope with uncontrollable uncontrollable situations, prevent damage and ensure safety. It has features such as being able to achieve

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a temperature control system of a fixing device to which this invention can be applied, FIG. 2 is a circuit diagram showing a circuit configuration of an embodiment of this invention, and FIG. An explanatory diagram of temperature overshoot, Figure 4 shows the normal temperature of the fixing unit,
FIG. 3 is an explanatory diagram illustrating the operation of the circuit in FIG. 2 during an abnormality. Code explanation (4)...CPU (61...Lamp (7)...
Ignition element α0)...Fuser temperature measurement circuit (17J...Fuser upper limit circuit αJ...Comparator circle...Relay patent applicant Fuji Xerox Co., Ltd. Agent Tomohiro Nakamura, Patent Attorney Dojo Seiji Katsuo Ise

Claims (1)

[Claims] In a fixing device that has a control system that controls temperature by controlling power supplied to a heat source for heat fixing, a fixing device is provided separately from the control system to detect when the temperature of the fixing device has reached an abnormal temperature. 1. A safety device for a fixing device, comprising: a detection circuit; and means for cutting off power to the heat source based on a detection signal from the detection circuit.