JP3072439B2 - Thermal fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device for fixing a toner image by heat, which is used in an image forming section of a laser beam printer, a copying machine, a plain paper facsimile or the like.

[0002]

2. Description of the Related Art The recording apparatus disclosed in Japanese Patent Application Laid-Open No. Sho 62-75571 uses a current transformer, which is well known as a current detecting means, for a monitor circuit, and utilizes the result of this monitor circuit. A failure detection operation of an SSR (semiconductor relay) is disclosed.

FIGS. 5 and 6 are circuit diagrams of a heater control circuit used in a heat fixing device of a laser beam printer disclosed in the above-mentioned publication, wherein 1 is a heater (for example, a halogen lamp), and 2 is Thermistor, 3 is CPU, 4 is SSR,
5 is a power relay contact, 6 is a power relay coil, 7 is a voltage drop resistor, 8 and 12 are rectifiers, 9 is a photocoupler, 10 is a protection diode, 11 is a current transformer, and 13 is a capacitor.

The above-mentioned control circuit is intended to maintain a constant temperature by controlling ON / OFF of the halogen lamp 1 by the SSR 4 in accordance with the output of the thermistor 2 under the control of the CPU 3. Since the SSR4 has no mechanical contact and is much more durable than a relay with respect to the number of times of ON / OFF, it is adopted as a normal control element. However, since it is composed of a semiconductor, It is known that short-mode failure occurs when a momentary and large stress is applied due to lightning, excessive rush current, noise, or the like.

[0005] Therefore, the power relays 5 and 6 which are hard to fail due to such stress are provided, and if the SSR 4 fails, the halogen lamp 1 is turned off by the power relays 5 and 6 to prevent overheat runaway. Is being done.

[0006] In the example shown in FIG.
6 to monitor the voltage of the halogen lamp, and in the example of FIG. 6, monitor circuits 11 to 13 to monitor the current of the halogen lamp.

The control operation of the halogen lamp described above will be briefly described. ON / OFF control for maintaining the output result of the thermistor 2 at a specified value is realized by turning the halogen lamp 1 ON / OFF via the SSR 4. doing.

The output result of the thermistor 2 is
/ D converter input, digitized and converted to CP
Used for U processing. At present, such fixing temperature control using a one-chip microcomputer is most commonly used.

When the SSR 4 is OFF, the SSR is controlled according to the outputs of the monitor circuits 7 to 10 and 11 to 13 of the halogen lamp 1 described above.
A check is made to see if SR4 has failed.

[0010]

However, in the above prior art, the safety circuit is designed on the premise that the power relays 5 and 6 do not fail, so that the power relays 5 and 6 are in a failure state. In such a case, the protection function is completely lost.

However, when an overcurrent also flows through the power relays 5 and 6, the mechanical contacts to be interrupted may be melted or burned, and the interrupting function may be lost. Further, since the failure mode of the power relays 5 and 6 does not prevent normal operation, the failure is not detected even if a failure occurs.
SR4 can also cause a failure. in this case,
The protection described above is completely lost.

In a general heat fixing device, when a heater (halogen lamp) powered by an AC power supply is turned on when the device is in a cold state, the resistance value of the heater is reduced. Becomes very large. Therefore, a switching element such as an SSR for turning on / off the heater needs to use a switching element having a large rated current so as to be destroyed or not destroyed by the rush current.

SUMMARY OF THE INVENTION An object of the present invention is to provide a more secure heat fixing apparatus which prevents failure and destruction of constituent parts.

[0014]

To achieve the above object, a first means of the present invention is to fix a toner image by heat.
A fixing heater to be used in order, in the fixing heater
Turns on the power supply to the fixing heater by detecting the temperature.
An SSR for turning on / off, a power relay for turning off a driving power supply to the fixing heater when a failure is detected, a monitor circuit provided between the fixing heater and the power relay for monitoring a driving state of the fixing heater. In the thermal fixing device provided with the above, after turning off the SSR, the power relay
Means for performing a power relay check operation for executing a power relay control error process when a driving state is detected by the monitor circuit in a state where the power supply is turned off and the SSR is turned on .

The second means is characterized in that the power relay check operation in the first means is performed only after the fixing heater has reached a high temperature state.

The third means is to fix the toner image by heat.
Smoothing to suppress a fixing heater to be used in order, in the heat fixing device that includes a DC power supply for DC lighting the fixing heater, the inrush current is provided to the DC power supply section
Circuit, a heater lighting circuit for AC lighting the fixing heater, and a DC voltage for a predetermined time for lighting the fixing heater.
After the application , a control circuit for switching to AC lighting by the heater lighting circuit is provided.

Further, a fourth means is the third means, wherein a timer circuit for controlling a time for applying a DC voltage for a predetermined time, a control circuit for controlling a switching timing between the DC voltage and the AC voltage, and the control circuit. And a switch circuit that receives a signal from the control circuit and selects a DC voltage or an AC voltage.

[0018]

According to the first means, a power relay check operation function for detecting a failure of the power relay without applying a load to the contacts before the occurrence of an abnormal situation is provided.
Before the main control element such as the SSR fails, the situation where the safety device does not operate due to the seizure of the power relay can be avoided, and the safety is greatly enhanced.

According to the second means, the power relay is not opened or closed and the check operation is not performed when the power is applied, which places the greatest burden on the power relay. Therefore, the power relay is damaged by the check operation itself, or the power relay is damaged after the check. Since there is no danger that a failure of the power relay will occur, a quick and reliable operation of the power relay can be expected.

According to the third and fourth means, it is possible to turn on the AC lighting of the fixing heater in a state where the resistance value of the fixing heater itself is increased, so that the rush current value can be suppressed. the destruction of the switching element is proof Gukoto
In addition, a switching element having a small rated current value can be used.

[0021]

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

FIG. 1 is a flowchart showing the operation of the first embodiment of the present invention. The basic circuit configuration of the first embodiment is as follows.
The circuit is the same as that described with reference to FIGS.
ON of SSR4 and power relays 5 and 6 by PU3
/ OFF to perform the power relay check operation. As described above, the monitor circuit for monitoring the driving state of the halogen lamp 1 as a fixing heater is configured by the elements 7 to 10 in FIG. 5 and by the elements 11 to 13 in FIG.

In FIG. 1, it is necessary to open and close the power relays 5 and 6 in order to perform a power relay check.
SSR4 is always turned off before opening and closing (S1-1). Thereafter, the power relays 5 and 6 are turned off (S1-2), and the SSR
4 is turned ON (S1-3). If the monitor circuits 7 to 10 and 11 to 13 do not detect the energization of the halogen lamp 1 while the SSR 4 is ON and the contact 5 is open (S1-4).
NO), since it is normal, SSR4 is turned off (S1-
5) Turn on the power relays 5 and 6 (S1-6).

However, when the energization of the halogen lamp 1 is detected with the SSR 4 being ON and the contact 5 being open (S1-4)
YES), power relay control error processing E is performed, and S
SR4 is turned off (S1-7), the main functions such as the printing operation are prohibited (S1-8), and an error is notified by appropriate means (S1-9).
I do.

When switching the contacts, SSR4 is not necessarily turned off.
There is no need to F. For example, when the contact 5 is opened with the SSR 4 kept ON, if the progress of the deterioration of the contact 5 is detected based on the time until the energized state is cut off, the deterioration of the contact can be known at an early stage.

The contents of the power relay control error include turning off the halogen lamp, prohibiting a main function such as a printing operation, and reporting an error, but the present invention is not limited to this. In addition, since the release of the error is a failure related to safety, it is desirable to hold the error until it is completely repaired. For this reason, the occurrence of an error is recorded in a non-volatile recording device,
It is effective to take measures such as not releasing the CPU 3 at least until the power is turned off.

FIG. 2 is a flow chart for determining whether or not to perform the above-described power relay check operation. It is considered that a failure of the power relay often occurs due to an inrush current when the power is turned on. For this reason, in the present embodiment, the power relay check operation is performed when the temperature reaches the first temperature specified value after the power is turned on, so that a failure can be found early.

That is, in FIG. 2, when the power is turned on, the thermistor 2 detects the temperature of the halogen lamp 1.
(S2-1). When the temperature information from the thermistor 2 is sent to the CPU 3, the CPU 3 determines whether or not the temperature of the halogen lamp 1 is a specified value (S2-2). If it is determined that the value is equal to or less than the specified value (YES in S2-2), SSR4 is set to O.
An N signal is output (S2-3), and the halogen lamp 1 is energized. Whether or not the energization is performed is detected by the monitor circuits 7 to 10 and 11 to 13 (S2-4). If the power is on (YES in S2-4), it is normal, and
Return to (S2-1). Power is supplied to the halogen lamp 1 until the specified value is reached. If it is not in the energized state (NO in S2-4), it is obviously abnormal, so it enters the failure state and stops the device.
(S2-5).

If it is determined in step (S2-2) that the temperature of the halogen lamp 1 is equal to or higher than the specified value under the energized state (NO in S2-2), it is the first temperature specified after the power is turned on. It is determined whether or not the value has been reached (S2-6),
If it is the first arrival (YES in S2-6), the power relay check operation described in the first embodiment is performed (S2-7). However, if it is not the first arrival (NO in S2-6), a signal for turning off the SSR 4 is output (S2-8), and the halogen lamp 1 is turned off.
Turn off power to the Then, the energization is detected by the monitor circuits 7 to 13 in the same manner as in step (S2-4) (S2-9). Returning to S2-1), the energization of the halogen lamp 1 is stopped until the temperature of the halogen lamp 1 reaches a specified value. However, if it is determined that the power is on (YE in S2-9)
S) Since it is abnormal, a failure state is entered (S2-10). Further, if this state continues, there is a possibility of fire, so the contact 5 is disconnected (S2-11).

The present invention is not limited to this embodiment. The power relay check operation may be performed when a certain time has elapsed after the halogen lamp 1 is turned on, so that the halogen lamp 1 can be checked at a high temperature.

The power relays 5 and 6 are turned on / off.
In this embodiment, the check operation is performed only once after the power is turned on, since the failure is considered to be unlikely to occur at times other than F. However, the check operation is performed repeatedly at regular intervals or at regular intervals. You may.

According to the first embodiment, the power relays 5 and 6, which play a central role in the safety circuit, can confirm that the shutoff operation is always possible prior to the operation of the safety circuit. Provided is a halogen lamp drive circuit protection circuit that is surely shut off when the safety circuit is activated and prevents the fixing unit from overheating beforehand. .

The driving current of the halogen lamp 1 flows the largest when the halogen lamp 1 is in a cooling state due to the negative resistance characteristic. Especially when lighting at room temperature,
Since a rush current of 10 to 15 times the rated current flows, burn-in of the power relays 5 and 6 easily occurs when the power is turned on. However, in the present embodiment, by performing the power relay check operation while avoiding power-on, an abnormality after power-on is quickly detected, and unnecessary rush current is applied to the contact 5 of the power relay when performing the check operation. An effective power relay check operation that does not apply an unnecessary load to the contact 5 by not performing the contact opening / closing in the flowing state is proposed.

FIG. 3 is a circuit diagram showing the configuration of a second embodiment of the present invention. FIG. 4 is a circuit diagram of the switch control unit shown in FIG. 3. Reference numeral 20 denotes a DC (direct current) power supply unit via a main switch 21.
AC (alternating current) input terminal connected to 22, DC power supply 23
22, a smoothing circuit; 24, a main switch 21 and a fixing heater 25;
A heater lighting circuit provided therebetween, 26 is an engine control unit including a CPU 27 and a driver unit 28 for controlling and driving each unit of a device such as a copying machine, and 29 receives a control signal from the engine control unit 26, DC power supply section 22 and heater lighting circuit
A switch control unit that controls switches SW-1, SW-2, and SW-3 provided between the engine control unit 24 and the engine control unit 26 and the fixing heater 25.

In FIG. 4, the switch control section
29, a timer circuit 30 for performing time control for applying a DC voltage for a predetermined time, a control circuit 31 for controlling switching timing of DC voltage and AC voltage, a reset circuit 32 for initializing the control circuit 31, It comprises a switch circuit 33 comprising the switches SW-1 to SW-3 for receiving a signal from the control circuit 31 and selecting a DC voltage or an AC voltage.

In the second embodiment, the switch SW-1 is turned on while the main switch 21 is turned on.
A DC power supply voltage is applied to the fixing heater 25 to perform a preheating operation of the fixing heater 25 itself. At this time, another switch SW
-2 and SW-3 are turned off. At this time, D
Although an inrush current is also generated in the C circuit portion, the inrush current generated in the DC circuit portion can be suppressed since the DC power supply portion 22 has the smoothing circuit 23.

Next, after a certain period of time has passed by the timer circuit 30 in the switch control section 29, the switch SW-1 is turned off.
FF state, and switches SW-2 and SW-3 are set to O
It becomes N, and it becomes a lighting method by a normal AC voltage.

For this reason, when the main switch 21 is turned on, the resistance value of the fixing heater 25 in a cold state becomes small and the inrush current becomes large, and the overcurrent at this time may destroy the switching element. Is prevented.

[0039]

As described above, according to the first aspect of the present invention , a load is applied to the contacts before the occurrence of an abnormal situation.
Since a power relay check operation function for detecting a failure of the power relay is provided without providing the power relay, a situation in which the safety device does not operate can be avoided, and the safety can be greatly improved. Since there is no danger that the power relay is damaged by the checking operation itself or a failure of the power relay occurs after the check, a quick and reliable operation of the power relay can be expected. Further, according to the third and fourth means, , it is possible to suppress the inrush current, the breakdown of the switching element can proof Gukoto, also it is possible to use a smaller less expensive switching element having a rated current value, a failure of a component, the fracture to prevent Thus, a more secure heat fixing device can be provided.

[Brief description of the drawings]

FIG. 1 is a flowchart showing the operation of a first embodiment of the heat fixing device of the present invention.

FIG. 2 is a flowchart according to a first embodiment of determining whether to execute a power relay check operation.

FIG. 3 is a circuit diagram showing a configuration of a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a switch control unit shown in FIG. 3;

FIG. 5 is a circuit diagram illustrating an example of a heater control circuit.

FIG. 6 is a circuit diagram showing another example of the heater control circuit.

[Explanation of symbols]

1,25: fixing heater, 2: thermistor, 3,27 ...
CPU (Central Processing Unit), 4 ... SSR (Semiconductor Relay), 5, 6 ... Power Relay (Power Relay), 7-1
0, 11 to 13 monitor circuit, 20 AC input terminal, 22
DC power supply section, 24: heater lighting circuit, 29: switch control section, 30: timer circuit, 31: control circuit, 32: reset circuit, 33: switch circuit.

Continuation of the front page (56) References JP-A-62-236001 (JP, A) JP-A-1-131829 (JP, A) JP-A-63-131422 (JP, A) JP-A-62-2265 (JP) , U) Actually open 63-94464 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/20

Claims (4)

(57) [Claims] 1. A method for thermally fixing a toner image.
And a fixing heater that, in the temperature detection in the fixing heater
To turn on / off the power supply to the fixing heater.
A semiconductor relay element, a power relay for turning off a drive power supply to the fixing heater when a failure is detected, and a monitor circuit provided between the fixing heater and the power relay to monitor a driving state of the fixing heater. After the semiconductor relay element is turned off in the heat fixing device,
The appliance was turned off and the semiconductor relay element was turned on
And a means for performing a power relay check operation for executing power relay control error processing when the monitor circuit detects a driving state in the state. 2. The thermal fixing device according to claim 1, wherein the power relay check operation is performed only after the fixing heater has reached a high temperature state. 3. A method for thermally fixing a toner image.
That a fixing heater, in the thermal fixing device equipped with a DC power supply for DC lighting the fixing heater, wherein the DC power supply
A smoothing circuit for suppressing the rush current provided in the heater, a heater lighting circuit for AC lighting the fixing heater, and applying a DC voltage for lighting the fixing heater for a predetermined time, and then performing AC lighting by the heater lighting circuit. A thermal fixing device comprising a switching control circuit. 4. A timer circuit for controlling time for applying a DC voltage for a predetermined time, a control circuit for controlling switching timing between DC voltage and AC voltage, a reset circuit for initializing the control circuit, and a control circuit. 4. A heat fixing device according to claim 3, further comprising: a switch circuit that receives a signal from the controller and selects a DC voltage or an AC voltage.