JPS624715B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for preventing excessive rise in fixing temperature in a copying machine or the like.

Generally, in a copying machine or the like, a fixing heater in a fixing section flashes on and off to keep the fixing temperature approximately constant. Therefore, if the fuser heater is turned on continuously, accidents such as fire may occur due to excessive temperature rise, so in order to prevent this, conventionally, an overtemperature rise prevention element is connected in series with the fuser heater. It is something that exists. In this case, a temperature fuse is often used as a temperature overrise prevention element, and when the temperature rises excessively due to continuous lighting, the temperature fuse is blown out to prevent ignition. When a temperature fuse is used in this way, as the temperature fuse blows out due to its operation, the temperature fuse cannot be used again and the parts must be replaced, resulting in wasted costs and time required for replacement. It is what it is.

The present invention has been made in view of the above points, and is designed to shut off the fuser heater using a relatively simple circuit before the overtemperature rise prevention element operates when an excessive temperature rise occurs due to continuous lighting of the fuser heater. The purpose of the present invention is to provide a fixing temperature over-rise prevention circuit that can eliminate the waste of cost and time due to discarding of over-temperature-rise prevention elements and replacing parts that would otherwise cause the fuser to burn out. .

The present invention connects an energization control circuit to which a fuser heater, a temperature overrise prevention element, and a temperature control circuit are connected, and a cutoff contact in series to a power source, measures the lighting time of the fuser heater, and measures the lighting time. A timer circuit is connected to the control circuit and generates an output when the temperature exceeds a predetermined time due to continuous lighting, and the cutoff contact is opened by the output of the timer circuit. The feature is that a circuit is provided. Therefore, by providing a timer circuit that generates an output at a predetermined timing, as well as a cutoff contact and a cutoff circuit, if the fixing heater is turned on continuously and causes an excessive temperature rise, it is possible to prevent the overtemperature rise prevention element from operating. It is possible to reliably turn off the fuser heater, thereby eliminating waste of money and time due to discarding overtemperature protection elements and replacing parts.
Further, even if the energization control circuit fails, the fixing heater is configured to reliably prevent an excessive rise in temperature.

A first embodiment of the present invention will be explained based on FIGS. 1 to 4. First, to explain the schematic circuit configuration with reference to FIG. 1, in the fixing unit, a fixing heater 2, a temperature fuse 3 which is an element for preventing excessive temperature rise, and a power supply control circuit are connected to a power supply 1 of AC100V.
A series circuit of an AC driver 4 is connected, and a relay contact 5 serving as a breaking contact is connected in series to this series circuit. Here, the AC driver 4 turns the fixing heater 2 on and off based on the output of a temperature control circuit 6 which receives a signal from a temperature detection element such as a thermistor. A timer circuit 7 is provided to measure the lighting time of the fixing heater 2 based on the output of the temperature control circuit 6.
A cutoff circuit 8 is provided to open the circuit.

Here, the setting of the time constant for producing an output from the timer circuit 7 will be considered. Generally, a fixing section is provided with a temperature control circuit 6 for maintaining the fixing temperature determined by a temperature detection element such as a thermistor, and the output of this temperature control circuit 6 is shown in FIG. 2a. It becomes a pulse signal that repeats H level and L level. In this case, the time during which the H level signal is generated is the time until the fixing temperature by the fixing heater 2 reaches a predetermined temperature, so it is not infinitely long. Therefore,
In principle, the timer circuit 7 measures the H level output time of the temperature control circuit 6 corresponding to the lighting time of the fixing heater 2, and when this measured time exceeds a certain fixed time, the timer circuit 7 generates an output. When the cutoff circuit 8 is operated, the relay contact 5 is opened, so that the fixing heater 2 can be turned off. However, if it is only to prevent dangers such as ignition due to continuous lighting of the fuser heater 2 for a certain period of time or more, the fuser heater 2 will go out due to melting of the temperature fuse 3, so a preventive measure using the temperature fuse 3 is necessary. It's a good thing.
Therefore, it is necessary to set a time constant so that the timing at which the timer circuit 7 generates an output occurs after a certain period of time and before the temperature fuse 3 operates.

Further consideration shows that when the main switch of the copying machine is turned on, the output time of the H level from the temperature control circuit 6 is long because it continues until the fixing temperature is reached, but after that, the repetition of the H level and L level is short. As a result, the fixing temperature is maintained (see curve A in FIG. 3). Therefore, the time constant of the timer circuit 7 is set to be a little longer than the H level output time when the main switch of the copying machine is turned on, and the temperature fuse 3 is prevented from operating within that time. That is, the time constant T of the timer circuit 7 is set to correspond to the point A on the curve B in FIG. 3, which shows the characteristics when the fixing heater 2 is continuously lit. In this case, the temperature fuse 3 is a preventive means to prevent ignition, so the time it takes for the temperature fuse 3 to operate, that is, the operating point, is relatively similar to point B on the curve B in Figure 3. It is something you can choose freely. Thereby, the timer circuit 7 produces an output when its measured time reaches the time constant T.

The specific circuit configuration of the circuit shown in FIG. 1 is as shown in FIG. 4. That is, as the AC driver 4, a solid state relay SSR is used which turns on the fixing heater 2 in response to an H level signal from the temperature control circuit 6. Further, as the timer circuit 7, a capacitor C1 is provided, which is charged by the H level signal from the temperature control circuit ₆ through a resistor _R1 , and a diode _D1 for discharging the capacitor _C1 and a resistor _{R2 are} connected to the capacitor C1.
and is connected along with this capacitor C ₁
A Zener diode ZD ₁ is connected together with the diode D ₂ to compare the base potential of the transistor 9 with a predetermined value. The cutoff circuit 8 is provided with a transistor 10 that becomes conductive when the transistor 9 is made conductive, and a transistor 11 that is cut off when the transistor 10 becomes conductive.
It is connected with D ₃ .

In such a configuration, when looking at the lighting cycle of the fixing heater 2 under normal conditions, as shown in FIG.
The light goes out repeatedly (see the waveform of , in Figure 2). That is, upon receiving the H level signal from the temperature control circuit 6, the AC driver 4 turns on the fixing heater 2.
It lights up. At this time, the H level signal from the temperature control circuit 6 is charged into the capacitor _C1 through the resistor _R1 , and the H level energization time, that is, the lighting time of the fixing heater 2 is measured. Here, the cycle shown in Figure 2,
In this case, it is normal and the fuser heater 2 does not light up continuously, so the transistor 9 is connected to the capacitor _C1.
The base potential of never reaches the reference potential determined by the Zener diode _ZD1 . This results in
Transistor 9 remains in the cut-off state, no output is produced from timer circuit 7, cut-off circuit 8 also does not operate, and relay 12 remains energized. The charge stored in the capacitor C ₁ is then discharged by the diode D ₁ and the resistor D ₂ in each cycle.

When the fixing heater 2 is turned on continuously as shown in the cycle in FIG. 2, the temperature control circuit 6
The charging potential of the capacitor _C1 rises due to the continuous H level output signal from the transistor 9, and the base potential of the transistor 9 reaches the reference potential of the Zener diode _ZD1 . The time required to reach this reference potential corresponds to the time constant T as described above. As a result, transistor 9 becomes conductive and an output is generated from timer circuit 7, transistor 10 becomes conductive, transistor 11 is cut off, and the input to relay 12 is cut off. Then,
A relay contact 5 connected in series with the fixing heater 2 is opened, and the fixing heater 2 is turned off. Here, since such an operation is performed before the operation of the temperature fuse 3, the temperature fuse 3 is not blown out, and after the fixing temperature is recovered, it is possible to continue without replacing the temperature fuse 3. can.

Regarding the circuit configuration, a copying machine is usually provided with a temperature control circuit 6, and at the same time, a cutoff circuit 8 is often provided, for example, to prevent abnormal lighting of the exposure lamp. Since the temperature control circuit 6 and the cutoff circuit 8 can be used, this embodiment has a simple circuit configuration by adding the timer circuit 7.

Next, a second embodiment of the present invention will be described with reference to FIGS. 5 and 6. The same parts as those shown in the previous embodiment are given the same reference numerals, and the explanation will be omitted.
This embodiment utilizes the terminal voltage of the fixing heater 2 as an input to a timer circuit 7 that measures the lighting time of the fixing heater 2, and is provided with an AC/DC conversion circuit 13 that converts this terminal voltage into direct current. . Here, as shown in FIG. 6, the specific configuration of this AC/DC conversion circuit 13 includes Zener diodes ZD ₂ , ZD ₃ , resistor R ₃ , diode D ₄ and A light emitting section ₁₄ consisting of a photodiode _D5 connected in parallel to the diode D4, a diode _D6 and a transistor 1 that operate upon receiving light from the photodiode _D5 .
5 and a transistor 17 that charges the capacitor _C1 by making the transistor 15 conductive. Note that in FIG. 6, the temperature control circuit 6 for operating the AC driver 4 is omitted.

In such a configuration, the terminal voltage generated when the fixing heater 2 is turned on is converted into direct current by the AC/DC conversion circuit 13 and charges the capacitor _C1 . Here, since the signal based on the terminal voltage of the fixing heater 2 matches the signal from the temperature control circuit 6 shown in FIG. 2a, the subsequent operations are performed in the same manner as in the previous embodiment.

Therefore, in the case of this embodiment, a simple circuit configuration in which the AC/DC conversion circuit 13 is added together with the timer circuit 7 is sufficient.

As described above, the present invention includes a timer circuit that generates an output at a predetermined timing in response to continuous lighting of the fixing heater, and the output of this timer circuit controls the operation of the cut-off circuit for the cut-off contact. If the fuser heater lights up and causes an over-temperature rise, it is possible to ensure that the fuser heater is turned off before the over-temperature rise prevention element operates, thereby reducing the cost of discarding the over-temperature rise prevention element and replacing parts.
To eliminate wasted time, to reliably prevent an excessive rise in temperature of a fixing heater even if the energization control circuit breaks down, and at the same time to perform such operations under a simple circuit configuration. It has the following effects:

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the first embodiment of the present invention, Fig. 2 is a waveform diagram, Fig. 3 is a characteristic diagram, Fig. 4 is a specific circuit diagram, and Fig. 5 is a second embodiment of the present invention. FIG. 6 is a block diagram showing an embodiment of the present invention, and FIG. 6 is a specific circuit diagram thereof. 1...Power source, 2...Fusing heater, 3...Temperature fuse (temperature overrise prevention element), 4...AC driver (energization control circuit), 5...Relay contact (cutoff contact), 7...Timer circuit , 8... Breaking circuit.

Claims (1)

[Claims] 1 Connect the fuser heater, the overtemperature preventive element, the temperature control circuit, the energization control circuit, and the cutoff contact in series to the power supply, measure the lighting time of the fuser heater, and determine the continuous lighting time. A timer circuit is connected to the control circuit and generates an output when a predetermined period of time has elapsed due to lighting, and before the overtemperature rise prevention element operates, and a cutoff circuit is provided that opens the cutoff contact by the output of the timer circuit. A fusing temperature over-rise prevention circuit.