JPS5853553Y2 - Protection circuit for heat fixing device in electronic copying machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for a heat fixing device in an electronic copying machine.

Generally, an electronic copying machine is provided with a heat fixing device for heating and fusing a toner image electrostatically transferred onto a transfer paper to form a permanently fixed image on the transfer paper.

The heat fixing device is configured such that its heating temperature is controlled to a predetermined temperature by a temperature control circuit including an appropriate heat-sensitive element, so that there is no risk of fire of the transfer paper or the like due to an excessive rise in the heating temperature.

However, if the heat-sensitive element malfunctions or an abnormal condition such as a short circuit or disconnection occurs in the wiring of the control circuit, or furthermore, if the heat-sensitive element is separated from the fixing device and cannot accurately detect the heating temperature, If the control circuit malfunctions,
The heating temperature of the fixing device is uncontrolled and rises excessively above the predetermined temperature, scorching the transfer paper or causing a fire, which not only adversely affects the copying machine but also poses an extremely dangerous situation for the copying machine operator. .

Therefore, the present invention is capable of detecting a failure or disconnection of the heat-sensitive element or control circuit as described above, and immediately deactivating the heater of the fixing device to stop heating the fixing device. An object of the present invention is to provide a protection circuit for a heat fixing device in an electronic copying machine.

Embodiments of the present invention will be described below with reference to the drawings.

As shown in Figure 1, when the temperature control device is operating normally, the heating temperature of the heating device increases once to a predetermined temperature t1 (period h1
), and then the heater is energized on and off at a substantially constant cycle (h2) by the action of the temperature control circuit to maintain the predetermined temperature.

As shown in FIG. 2, the temperature control circuit A has a thermistor 1 used as a heat-sensitive element. Change the resistance value.

The thermistor 1 consists of diodes 3 (
The anode is connected to the thermistor 1), the resistor 4, and the resistor 5, 6. An appropriate voltage is applied between the connection point and the connection point with 5.

Also, the connection point between diode 3 and resistor 4 is diode 8.
The anode of the diode 8 is connected to the connection point between the resistors 5 and 6, and then to the non-inverting terminal of the operational amplifier 9.

Furthermore, the connection point between the diode 3 and the resistor 4 is connected to the inverting terminal of the operational amplifier 9.

In such a configuration, when the temperature of the heat fixing device is below a predetermined temperature, that is, when the thermistor 1 shows a high resistance value, the output 10 of the operational amplifier 9 shows an H level, and conversely, when the temperature of the heat fixing device is lower than a predetermined temperature, the output 10 of the operational amplifier 9 shows an H level. When the thermistor 1 exhibits a low resistance value, the output 10 of the operational amplifier 9 exhibits an L level.

The output terminal of the operator Luanbu 9 is connected to the resistor 11.
The light emitting element 12a of the photothyristor 12 is connected to the collector of the transistor 14 via the light emitting diode 13, the emitter of the transistor 14 is grounded, and the base is connected to a timer circuit to be described later.

Since the transistor 14 is in a conductive state according to instructions from the timer circuit when the temperature control circuit is operating normally, the photothyristor 12 is turned on when the output 10 of the operational amplifier 9 reaches the H level. It is configured.

The photothyristor 12 is incorporated in a switch circuit B for energizing or deenergizing the heater of the heat fixing device.

Switch circuit B is a so-called zero crossing triac trigger circuit.

The heater 16 of the heat fixing device is connected to an AC power source 18 via a triac 17 and a normally closed switch 110a of a relay circuit 110, which will be described later, to form a closed circuit.When the triac 17 is on, the heater 16 is energized. and heated.

On the other hand, a rectifying bridge 30 is formed by the diodes 19, 20, 21.22, and the rectifying bridge 30 has the anode of the diode 19 connected to the cathode of the diode 20, the anode of the diode 20 connected to the anode of the diode 21, and the cathode of the diode 21 connected to the anode of the diode 21. The anode of diode 22 is connected to the cathode of diode 19, and the cathode of diode 22 is connected to the cathode of diode 19, respectively.

The connection point between diodes 19 and 20 is connected to the gate of triac 17 and connected to power supply 18 via resistor 15.
The connection point between the diodes 21 and 22 is connected to the connection point between the heater 16 and the triac 17.

On the other hand, the connection point between diodes 20 and 21 is connected to the anode of a Zener diode 24 via a resistor 23.
The cathode of Zener diode 24 is connected to the connection point of diodes 19 and 22 via a resistor 25.

Further, a connection point between the resistor 23 and the Zener diode 24 is connected to the base of an npn type transistor 26.

The collector of the I transistor 26 is the photothyristor 12
The emitter is connected to the connection point between the diodes 20 and 21.

Further, the connection point between the diodes 19 and 22 is connected to the anode of the light receiving element 12b of the photothyristor 12 via a resistor 27, and the cathode of the light receiving element 12b is connected to the diode 2.
0 and 21, and is also connected to the collector of a transistor 26 via a resistor 28.

In such a switch circuit B, a rectifier bridge 30 from the AC power supply 24 is connected to both ends of the Zener diode 24.
A rectified voltage is applied, and when the value becomes equal to or higher than the Zener voltage, it becomes conductive, and a voltage is generated across the resistor 23, making the transistor 26 conductive.

In this way, a pulsed voltage is applied to the gate of the light receiving element 12b of the photothyristor 12.

On the other hand, the photothyristor 12 becomes conductive only when the light emitting element 12a is in the on state and a predetermined voltage is applied to the gate of the light receiving element 12b. bridge 30
It is triggered when the output voltage from the zener diode 17 is higher than the zener voltage of the zener diode 17, so that a gate current flows to the triac 17 through the rectifier bridge 30, and the triac 17 is turned on.

As the triac 17 is made conductive in this manner, the heater 16 is energized and heated.

Furthermore, when the photothyristor 12 is in the off state, the triac 17 is in a non-conducting state, so the heater 16 is deenergized.

In this way, when the heating temperature of the heat fixing device is below a predetermined value, that is, when the output 10 of the operational amplifier 9 is at the H level, the heater 16 is energized and heated, and when the heating temperature is above the predetermined value, that is, when the output 10 of the operational amplifier 9 is at the H level, the heater 16 is heated. 9 output 1
When 0 is at L level, it is cut off and the heater 16 is deenergized.

By repeating this process, the heating temperature is maintained at a predetermined temperature.

On the other hand, the output 10 of the operational amplifier 9 is connected to the resistor 3
1 to the base of a pnp transistor 32 incorporated in the display circuit C, and the transistor 32
the emitter of is connected to a conductor 33 connected to a positive power supply;
The collector is connected to grounded conductor 34 via resistors 35,36.

Further, the connection point between the resistors 35 and 36 is connected to the gate of the thermistor 37, and the cathode of the thermistor 37 is connected to the conductor 34.
The anode is connected to the cathode of the light emitting diode 38.

The anode of the light emitting diode 38 is connected to the conductor 33 via a resistor 39, and the connection point between the light emitting diode 38 and the resistor 39 is connected to the conductor 33 via a capacitor 40.
It is connected to 4.

In such a configuration, when the output of the operational amplifier 9 is 10 or the H level ρ, the transistor 32 is in a non-conducting state, but when the output of the operational amplifier 9 reaches a level, that is, when the heating temperature reaches a predetermined temperature, the transistor 32 is turned off. It becomes conductive, a voltage is generated across the resistor 36, and a voltage is applied to the gate of the cyrisk 37.

In this way, the cynostar 38 becomes conductive, and the light emitting diode 38 lights up, indicating that the heating temperature has reached a temperature sufficient for fixing the heat fixing device or the fixing device.

In a heat fixing device that performs such temperature control, if an abnormal condition such as a disconnection or failure occurs in the control circuit A that performs temperature control and the output of the operational amplifier 9 continues to be maintained at the H level, the heater 16 continues to heat up, and as shown by the broken line in FIG. 1, the heating temperature of the fixing device overheats to a predetermined temperature 11 or higher, damaging the copying machine.

In order to prevent this overheating, in this invention, heater 1
The continuous energization time of the heater 16 (the time from the start of energization of the heater 16 to the first de-energization of the heater) is calculated based on the rise time h1 from the start of energization of No. 6 until reaching the predetermined temperature t1. When the continuous energization time exceeds the reference time h1, it is determined that there is an abnormal state and the heater 1 is
A first protection circuit is provided which forcibly de-energizes 6.

The first protection circuit includes a timer circuit that measures the rise time h1 from the start of heater energization, and a timer circuit that measures the rise time h1 from the start of heater energization.
and a comparator for comparing the continuous energization time and the continuous energization time.

As shown in FIG. 2, the transistor 3 of the display circuit C
A connection point a between the resistor 2 and the resistor 35 is connected to the anode of the diode 42 of the first protection circuit.

The cathode of diode 42 is coupled to the base of transistor 45 via resistors 43,44.

The connection point between the resistor 44 and the transistor 45 is the resistor 58.
It is connected to the conductor 34 via.

The cathode of the diode 46 is connected to the capacitor 47 and the resistor 4.
8 to the cathode of a Zener diode 49, and the anode of the Zener diode 49 is connected to the conductor 34.

The collector of transistor 45 is connected to the connection point between capacitor 47 and resistor 48, and the emitter is connected to conductor 34.

Further, the connection point between the capacitor 47 and the resistor 48 is connected to the conductor 34 via the capacitor 50, and is also connected to the inverting terminal of an operational amplifier 51 (comparator).

The non-inverting terminal of the operational amplifier 51 is a resistor 52
The output terminal is connected to a connection point between a resistor 48 and a diode 49 through a resistor 53 .

A connection point between resistor 48 and diode 49 is connected via a resistor 65 to a connection point between amplifier 51 and resistor 52.

The output terminal of the operational amplifier 51 is a resistor 54,
It is connected to the conductor 34 via a light emitting diode 55 and to the base of the transistor 14 of the switch circuit B via resistors 56,57.

On the other hand, the connection point between the light emitting diode 38 and the diode 37 is connected to the anode of the diode 60, and the cathode of the diode 60 is connected to the transistor 62 through the resistor 61.
is connected to the base of

The collector of transistor 62 is connected to the connection point between diode 46 and capacitor 47, and the emitter is connected to conductor 34.

The base of transistor 62 is also connected to conductor 34 via resistor 63.

In such a configuration, when the heating temperature of the heat fixing device is in the rising state h1 (see FIG. 1), the connection point between the transistor 32 and the resistor 35 of the display circuit C is at the L level, so the diode 42 is at the L level. A signal is sent, and the transistor 45 becomes non-conductive. On the other hand, since the connection point between the light emitting diode 38 and the diode 37 is at H level, an H level signal is sent to the diode 60, and the transistor 62 becomes conductive. Ru.

A timer circuit is thus formed by transistor 62, conductor 33, Zener diode 49, resistor 48 and capacitor 47.50.

Therefore, after the heater starts energizing, capacitors 47 and 5
During the time until 0 becomes saturated, the voltage applied to the non-inverting terminal of the operational amplifier 51 becomes approximately OV, and the operational amplifier 51 produces an H level output.

This H level output is the transistor 1 of switch circuit B.
The signal is sent to the base of transistor 4 to turn on transistor 14 and allow the switch circuit to operate normally.

On the other hand, when the capacitors 47 and 50 reach a saturated state, a positive voltage is applied to the non-inverting terminal of the operational amplifier 51, and the operational amplifier 51 generates an L-level output and turns the transistor 14 of the switch circuit B into a non-conducting state. Cut off switch circuit B.

Here, the term "blocking the switch circuit" refers to turning off the switch operation of the switch circuit to forcibly de-energize the heater.

In this way, the thyristor 12 of the switch circuit B is turned off, and the heater 16 is deenergized.

The time until the capacitors 47 and 50 are saturated is the rise time h of the heating temperature during normal operation of the control circuit.
The time is set to several minutes longer than 1.

In this example, the time required for the heating temperature of the fixing device to rise to the predetermined temperature t1 is approximately 2.5 minutes, and the time required for one cycle of the on-off operation of energizing or de-energizing the heater thereafter is approximately 3 minutes.
Since it is 0 seconds, the resistance value of resistor 48 and capacitor 4
The capacitances of capacitors 7 and 50 are set so that the time it takes for capacitor 47 to become saturated is about 6 minutes, and the time it takes for capacitor 5b to become saturated is about 40 seconds.

On the other hand, when the control circuit A is operating normally, when the heating temperature of the fixing device reaches the predetermined temperature t1, that is, at the rise time h1, the output of the operational amplifier 9 of the control circuit A changes from the H level to the L level. As a result, the transistor 32 and thyristor 37 of the display circuit C become conductive as described above, and therefore, an H level signal is sent to the diode 42 of the first protection circuit, and an L level signal is sent to the diode 60. Sent.

In this way, the transistor 45 becomes conductive, and the transistor 6
2 is made non-conducting, thus capacitors 47 and 50
The charges stored in the capacitors 47 and 50 are discharged through the transistor 45 before the operational amplifier 51 becomes saturated, so the timer is canceled and the operational amplifier 51
continues to produce an H level output.

When the control circuit A is functioning normally, the operational amplifier 51 continues to output an H level output, so the transistor 41 of the switch circuit B continues to be conductive, and the switch circuit B is functioning normally. do.

On the other hand, if a disconnection occurs in the thermistor 1 or the control circuit and the operational amplifier 9 continues to generate an H level signal (a signal instructing the heater to heat up) even after the predetermined rise time h1, the The timer of protection circuit 1 is activated and resistor 48, capacitor 47.
After the time set by 50, switch circuit B is shut off to de-energize heater 16.

Next, a case will be described in which a failure or disconnection occurs in the thermistor 1 or the control circuit A during the on-off operation of the heater after the heating temperature rise time.

As described above, the heater 16 is repeatedly energized and deenergized at a fairly constant period h2 to maintain the heating temperature at a predetermined temperature t1.

However, if a disconnection or the like occurs in the control circuit and the amplifier 9 continues to emit an H level signal, the heater will continue to be energized as described above, and the heating temperature will rise, resulting in a dangerous situation.

Therefore, in the present invention, when the heater is continuously energized for more than 12 periods of time, the switch circuit B is forcibly cut off to de-energize the heater.

As described above, after the rise time h1 of the heater, the signal sent to the diode 60 of the first protection circuit shifts from the H level to the L level and then remains at the L level, so the transistor 62 becomes non-conductive. Fixed in state.

On the other hand, when the heater is deenergized and the heating temperature falls below the predetermined temperature t1, the heater is energized again by the action of the control circuit A, and at the same time, a timer comprising a resistor 48 and a capacitor 50 is activated.

That is, the operational amplifier 51 outputs an H-level output to operate the switch circuit B normally until the capacitor 50 is saturated, and after the capacitor 50 reaches the saturated state, the operational amplifier 51 outputs an L-level output to operate the switch circuit 15. shut off and de-energize the heater.

In this way, if the heater continues to be energized due to a break in the thermistor or the control circuit, the heater is forcibly de-energized by the operation of the timer circuit.

On the other hand, if the control circuit A operates normally and issues an L level signal (signal instructing to de-energize the heater) when the heating temperature reaches a predetermined temperature, the transistor 45 is rendered conductive. Since the charge in the capacitor 50 is discharged, the operational amplifier 51 continues to output an H level output and the switch circuit B operates normally. The heater is forcibly de-energized.

However, in such a circuit, if the copier operator turns off the power switch (which turns on/off the heater and protection circuit) after an abnormal condition occurs, the output of the operational amplifier 51 will be transferred to the capacitor 47,
During the discharge time of 51, the discharge charge keeps it at L level, but when the power switch is turned on again after this discharge,
The heater is again energized for the time that capacitor 47.51 is charged.

Since the discharge time of the capacitors 47 and 51 is extremely short, in this example about 3 minutes, the heater is energized for an additional fixed period of time before the heating temperature is sufficiently lowered. rises significantly higher than the temperature,
There is a risk of damage to the machine.

Therefore, in the present invention, once an abnormality occurs in the control circuit and the heater is deenergized, the above-mentioned off-on operation of the power switch is performed at least until the heating temperature drops to the outside temperature. A second protection circuit (timer holding circuit) E is provided to hold the abnormal signal from the timer circuit so that the heater will not be energized again even if the above operation is performed.

As shown in FIG. 2, the output terminal of the operational amplifier 51 of the first protection circuit is connected to the base of the transistor 71 of the timer holding circuit E via a resistor 70.
The collector of transistor 71 is coupled to conductor 33 via resistor 73.

The connection point between the transistor 71 and the resistor 73 is connected to the conductor 72 via a diode 74, a resistor 75, and a capacitor 76.
Further, the connection point between the diode 74 and the resistor 75 is connected to the capacitor 4 via the diode 77 and the resistor 78.
7 and the operational amplifier 51, and is also connected to the conductor 72 via a normally open switch 79.

In such a circuit, when an abnormal state occurs in the control circuit and the operational amplifier 51 issues an L-level output, the transistor 71 changes from a conductive state to a non-conductive state, and the charge stored in the capacitor 76 is released. The signal is sent to the inverting terminal of the operational amplifier 51, and the output of the operational amplifier 51 is held at L level.

In this example, the discharge time of this capacitor 76 is about 30
The heating temperature is set to approximately 1 minute, which is sufficient time for the heating temperature to drop to the outside temperature.

In this way, even if the power switch is turned off and on as described above, the capacitor 47.50.

The heater is not energized again during the discharge time of 76, ie, until the heating temperature has decreased to ambient temperature.

This means that even if the copier operator were to turn on the heater again before the faulty control circuit is repaired, heating would only occur from the outside temperature during the timer operation. , the temperature never rises above the predetermined temperature 11, and abnormal overheating does not occur.

On the other hand, a detection circuit F for detecting disconnection of the thermistor 1 of the control circuit A is provided.

The connection point between thermistor 1 and diode 3 is connected to the inverting terminal of operational amplifier 81 via resistor 80, and the connection point between resistor 80 and diode 3 is connected to capacitor 82 and resistor 83 in parallel. conductor 72 through
is connected to.

The non-inverting terminal of the operational amplifier 81 is the resistor 86.
The output terminal is connected to the connection point between the diode 3 and the resistor 4 via the resistor 84 and the diode 85 to the inverting terminal of the operational amplifier 51 of the first protection circuit.

In this way, when the thermistor 1 is normal, the output of the operational amplifier 81 is kept at the L level, but if a disconnection occurs in the thermistor 1, the output of the operational amplifier 81 becomes the H level, so the first protection circuit is activated. The operational amplifier 51 immediately goes to L level regardless of the operation of the timer circuit, and cuts off the switch circuit B.
Turn off the heater.

Furthermore, in the present invention, if an abnormality occurs in switch circuit B and the heater continues to be energized even though control circuit A is working normally, this abnormal state is immediately detected and the heater is de-energized. A third protection circuit G is provided.

In the switch circuit B, a current pickup coil 91 is provided around or in close proximity to a conductor 90 that connects the connection point between the AC power source 18 and the resistor 15 and the triac 17, and the coil 91 allows current to flow through the conductor 90. An electromotive force is generated when the heater is energized.

One terminal of the coil 91 is connected to the conductor 34, and the other end is connected to a non-inverting terminal of an operational amplifier 94 via a capacitor 92 and a resistor 93.

A connection point between the capacitor 92 and the resistor 93 is connected to an inverting terminal of an operational amplifier 94, and is also connected to an output terminal of the amplifier 94 via a resistor 95.

Further, the non-inverting terminal of the operational amplifier 94 is connected to the conductor 33 through a resistor 96, and to the conductor 34 through a resistor 97.
The reference voltage is applied to the reference voltage.

On the other hand, the output terminal of the operational amplifier 94 is connected to the base of a transistor 101 via a capacitor 98, a diode 99, and a resistor 100.

The emitter of transistor 101 is coupled to conductor 33;
It is coupled to conductor 34 via collector resistor 102 .

The connection point C between the transistor 101 and the resistor 102 is NA
Connected to one terminal 103a of the ND circuit 103, NA
The other terminal 103b of the ND circuit 103 is connected to the inverter 10
Operational amplifier 9 of temperature control circuit A via 4
is connected to the output terminal of

The output of NAND circuit 103 is sent to relay circuit 110.

Relay circuit 110 is configured to operate and open switch 110A when the output of NAND circuit 103 is at L level, and close switch 110A when the output is at H level.

Now, let us consider a case where switch circuit B is operating normally.

When the amplifier 9 of the control circuit A is generating an H level output, the heater 16 of the switch circuit B is energized, that is, current flows through the conductor 91, so an electromotive force is generated in the coil 91 and applied to the operational amplifier 94. be done.

Therefore, an AC output at the power supply frequency is obtained as the output of the operational amplifier 91, which is rectified and smoothed by the diode 99 and the capacitor 105, and makes the transistor 101 conductive.

In this way, input terminal 103a becomes H level, and terminal 1
Since the signal 03b is at the L level, the output of the NAND circuit 103 is at the H level.

Conversely, when the amplifier 9 of the control circuit A is outputting an L level output, the input terminal 103a of the NAND circuit 103 is at the L level and the terminal 103b is at the H level, so the output of the NAND circuit 103 is at the H level.

Next, consider a case where switch circuit B has developed an abnormal state.

If the heater continues to be energized even though the amplifier 9 of the control circuit A is emitting an L level output, as described above, the terminal 103a of the NAND circuit 103 is at HL/bell, the terminal 103a is at the H level, Since the terminal 103b goes high, the output of the NAND circuit 103 goes low, indicating that an abnormal state has occurred.

The L level output of the NAND circuit 103 is sent to the relay circuit 11
0, and the relay circuit 110 is activated to open the switch 110a and cut off the power to the heater.

In this way, when an abnormal condition occurs in the switch circuit B, the power to the heater is immediately cut off, so that the heater will not be overheated.

As described above, according to the protection circuit of the present invention, when an abnormal condition occurs in the temperature control circuit or the switch circuit, the abnormal condition can be immediately detected and the heater of the fixing device can be deenergized. After the occurrence, the heater cannot be reenergized for a predetermined period of time to prevent damage to the copying machine.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in heating temperature of a heating device according to the present invention; FIG. 2 is a diagram showing a fixing device protection circuit according to the present invention. 1... Thermistor, 16... Heater, A... Temperature control circuit, B... Switch circuit, C... Display circuit, D・・・・・・First
protection circuit, E...Second protection circuit, F...
...Detection circuit, G...Third protection circuit.

Claims (1)

[Scope of utility model registration request] A temperature control circuit detects the heating temperature of the heater of the heat fixing device and generates an instruction signal to de-energize the heater when the heating temperature exceeds a set temperature, and is turned off by the instruction signal from the temperature control circuit. In a protection circuit of a heat fixing device of an electronic copying machine, which has a switch circuit for deenergizing the heater, when the continuous energization time of the heater is compared with a set reference time and the continuous energization time exceeds the reference time. a first protection circuit that generates a signal to turn off the switch circuit and de-energize the heater; and a first protection circuit that generates a signal continuously for a set time when the first protection circuit generates the signal. a second protection circuit that maintains the operation of the first protection circuit; and a second protection circuit that detects the state when the switch circuit is activated contrary to the instruction signal of the temperature control circuit and cuts off power to the heater. 3. A protection circuit for a heat fixing device of an electronic copying machine, characterized in that the protection circuit comprises the following protection circuit.