JPH0916034A - Heater controller, thermal fixing device and image forming device - Google Patents

Abstract

PURPOSE: To reduce the number of parts, to miniaturize devices and to reduce the cost. CONSTITUTION: A circuit 6 is a main heater driver B. A T1 terminal of a triac 6a is connected to a rush current preventive resistor 9, and the T2 terminal is connected to a main heater 2, and further, a base of a transistor 6c is connected to a port PA2 of an MPU 1. When the MPU 1 makes the PA2 and 'H', the transistor 6c is turned on, and an LED inside of a phototriac coupler 6b is driven, and the triac inside of the phototriac is turned on, and succeedingly, the triac 6a is turned on, and AC is impressed to the main heater 2 through the rush current preventive resistor 9. When the MPU 1 makes a PA3 the 'H', the transistor 7c is turned on, and the LED inside of the phototriac coupler 7b is driven, and the triac inside of the phototriac is turned on, and succeedingly, the triac 7a is turned on, and the AC is impressed to a sub-heater 3 directly, and the sub-heater 3 is driven.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater control device, a heat fixing device and an image forming apparatus.

More specifically, the present invention is a heater control device applicable to a thermal fixing device using a plurality of heaters in an image forming device for forming an image on a recording medium, and
The present invention relates to a thermal fixing device and an image forming apparatus including the heater control device.

[0003]

2. Description of the Related Art Conventionally, as an image recording apparatus of this kind, a laser printer and a copying machine using an electrophotographic process have been known.

In an image forming apparatus using such an electrophotographic process, a heat roll fixing device is generally used as a fixing device for fixing toner on a recording sheet, in which heat is applied from a heat roller and pressure is applied to fuse the toner. Is used for.

In the heat roll fixing device, a halogen heater is installed inside a cylindrical roller and the heat roller heated to a predetermined temperature is formed of a material having heat resistance and predetermined elasticity such as silicon rubber. The pressure rollers are arranged in pressure contact with each other to form a fixing roller pair, and the recording paper on which the toner image is placed is passed between the fixing roller pairs to heat and pressurize and fix the toner on the recording paper. It is a thing.

In this type of heat roll fixing device, a plurality of halogen heaters having different light distributions are used in order to obtain a uniform heat roller temperature distribution corresponding to various recording paper widths. In order to shorten the rise time, some heaters use a plurality of heaters, such as one using a plurality of halogen heaters.

[0007]

However, the above-mentioned conventional apparatus having a plurality of heaters has the problems listed below.

(1) Since the inrush current preventing means for preventing the inrush current at the time of starting the heater driving is provided in the current path of each heater, it becomes a factor of increasing the size and cost of the device.

(2) Since failure detection means for detecting heater disconnection and open or short circuit failure of the heater drive circuit is provided for each heater, it becomes a factor of increasing the size and cost of the apparatus.

Therefore, the first object of the present invention is to provide a heater control device, a heat fixing device, and an image forming apparatus in which inrush current prevention means in the case of using a plurality of heaters are downsized and cost reduced. To provide.

The second object of the present invention is to:
It is an object of the present invention to provide a heater control device, a thermal fixing device, and an image forming apparatus, which are designed to reduce the size and cost of a detection unit for a heater disconnection and an open or short circuit failure of a heater driving circuit when a plurality of heaters are used.

[0012]

In order to achieve the above object, the heater control device according to the first invention has a plurality of heaters and a plurality of heater driving means for independently driving the plurality of heaters. The heater inrush current prevention means,
Alternatively, failure detection means or current interruption means is provided in the current path common to the plurality of heaters.

In the heater control device according to the second aspect of the present invention, there is provided inrush current prevention switching means for switching whether or not to supply current to each of the plurality of heaters via the inrush current prevention means.

In the heater control device according to the third aspect of the present invention, the inrush current prevention switching means alternately supplies current to each of the plurality of heaters via the inrush current prevention means.

In the heater control device according to the fourth aspect of the present invention, the drive start and stop timings of each of the plurality of heater driving means and the switching timing of the inrush current prevention switching means are set to separate timings.

In the heater control device according to the fifth aspect of the invention, the failure detection means includes current detection means for detecting the presence or absence of a passing current.

In the heater control device according to the sixth aspect of the present invention, a plurality of heaters are alternately driven, and the output state of the current detecting means at that time is detected to detect disconnection of the specific heater or open failure of the specific heater drive circuit. A detection means for detecting is provided.

In the heater control device according to the seventh aspect of the invention, when driving of all the heaters is stopped and the current detection means outputs current at that time, it is determined that one of the heater drive circuits is short-circuited.

In the heater control device according to the eighth aspect of the invention, the failure detection means includes total current detection means for obtaining a predetermined voltage output according to the total passing current value.

In the heater control device according to the ninth aspect of the present invention, the driving states of a plurality of heaters are compared with the output value of the current detecting means to determine whether a particular heater has a disconnection and an open circuit failure or a short circuit failure in the heater drive circuit. It has a means for detecting.

In the heater control device according to the tenth aspect of the invention, the failure detecting means has means for activating the current interruption means provided in the common path to interrupt the current supply to each heater when a failure occurs.

In the heater control device according to the eleventh aspect of the present invention, the on-timing shift amount of the inrush current prevention means is set to an AC half cycle or more.

A heat fixing device according to the twelfth invention comprises the above heater control device.

An image forming apparatus according to the thirteenth invention has the above-mentioned heat fixing device and reproduces an image according to an electrophotographic process.

[0025]

According to the first aspect of the present invention, a plurality of heater driving means for independently driving a plurality of heaters are provided, and the heater inrush current preventing means, the failure detecting means, or the current interrupting means is common to the plurality of heaters. By providing in the current path, the number of parts is reduced, and the size and cost are reduced.

A second invention according to the present application selects inrush current prevention for each heater by providing each of the plurality of heaters with inrush prevention switching means for switching whether or not to supply current through the inrush current prevention means. It is designed so that you can do it.

According to a third aspect of the present invention, the current capacity of the inrush current prevention means can be reduced by alternately supplying current to each of the plurality of heaters by the inrush current prevention switching means via the inrush current prevention means. Therefore, the inrush current prevention means is downsized and reduced in cost.

According to a fourth aspect of the present invention, the driving start and stop timings of the plurality of heater driving means and the switching timing of the inrush current prevention switching means are set to different timings so that a predetermined heater driving circuit can be separated. This is to prevent an abnormal current from flowing to the heater drive circuit.

According to a fifth aspect of the present invention, the failure detecting means includes a current detecting means for detecting the presence or absence of a passing current so that the currents of a plurality of heaters can be detected by a single current detecting means. It was made possible.

According to a sixth aspect of the present invention, a plurality of heaters are alternately driven and the output state of the current detecting means at that time is detected to detect disconnection of a specific heater or open failure of a specific heater drive circuit. It is possible to do.

A seventh invention according to the present application is a coat for judging that any of the heater driving circuits has a short circuit failure by stopping driving of all the heaters and detecting the output of the current detecting means at that time. Is made possible.

According to an eighth aspect of the present invention, the failure detecting means includes a total current detecting means for obtaining a predetermined voltage output according to a total passing current value, so that the currents of a plurality of heaters are changed to a single current. The detection means makes it possible to detect at the same time.

The ninth invention according to the present application makes it possible to detect the disconnection of a specific heater and the open failure or short failure of the heater drive circuit by comparing the driving states of a plurality of heaters with the output value of the current detecting means. It is the one.

According to a tenth aspect of the present invention, the failure detecting means is provided with means for activating the current interrupting means provided in the common path when a failure occurs to interrupt the current supply to each heater. It is possible to cut off the current when a heater driving circuit is abnormal by a single current breaking means.

The eleventh aspect of the present invention is such that the on-timing shift amount of the inrush current prevention means is set to half an AC cycle or more.

The twelfth invention of the present application comprises a heater control device to enable appropriate heat fixing.

A thirteenth invention related to the present application has a heat fixing device and performs image reproduction according to an electrophotographic process.

[0038]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a circuit diagram showing a heater control device of a heat roll fixing device to which the present invention is applied. In the figure, 1 is a microprocessor as a main control means (hereinafter referred to as MPU).
And contains a ROM, a RAM, a timer and the like. M
PU1 serves as an output terminal for ports PA0, PA1, PA
2, PA3, PA4, PA5, and a port PB0 as an input terminal, and an analog input terminal having an A / D function for converting an analog voltage into a digital value and detecting it.

Reference numeral 2 denotes a first roller arranged in the heat roller.
Is a halogen heater (hereinafter referred to as a main heater), and 3 is a second halogen heater (hereinafter referred to as a sub heater).

Reference numeral 4a denotes a thermistor arranged in contact with the heat roller, one of which is ground, the other of which is a pull-up resistor 4b and an analog input port ANO of the MPU 1.
The MPU detects the temperature of the heat roller.

Reference numeral 5 is a main heater driver A, which includes a triac 5a, a phototriac coupler 5b having a zero cross function, a transistor 5c, and a resistor 5.
It is composed of d, 5e and 5f.

The T1 terminal of the triac 5a is the AC power source 1
4, the T2 terminal is connected to the main heater 2, and the base of the transistor 5c is the port PA1 of the MPU1.
It is connected to the. When MPU1 sets PA1 to “H”, the transistor 5c turns on, the LED inside the phototriac coupler 5b is driven, the triac inside the phototriac turns on, and then the triac 5a turns on and the main heater 2 directly. It is driven by AC application.

Reference numeral 6 denotes a main heater driver B, which includes a triac 6a, a phototriac coupler 6b having a zero cross function, a transistor 6c, and a resistor 6.
It is composed of d, 6e and 6f.

The T1 terminal of the triac 6a is connected to the inrush current prevention resistor 9, the T2 terminal is connected to the main heater 2, and the base of the transistor 6c is connected to the port PA2 of the MPU1. When MPU1 sets PA2 to "H", the transistor 6c is turned on, the LED inside the phototriac coupler 6b is driven, the triac inside the phototriac is turned on, and then the triac 6a is turned on and plunges into the main heater 2. Current prevention resistor 9
AC is applied via.

A sub-heater driver A 7 includes a triac 7a, a phototriac coupler 7b having a zero cross function, a transistor 7c, and a resistor 7.
It is composed of d, 7e and 7f.

The AC power source 1 is connected to the T1 terminal of the triac 7a.
4, the T2 terminal is connected to the sub-heater 3, and the base of the transistor 7c is connected to the port PA3 of the MPU1. When MPU1 sets PA3 to "H",
The transistor 7c is turned on, the LED inside the phototriac coupler 7b is driven, the triac inside the phototriac is turned on, and then the triac 7a.
Is turned on and the sub-heater 3 is directly driven by AC application.

A sub-heater driver B 8 includes a triac 8a, a phototriac coupler 8b having a built-in zero-cross function, a transistor 8c, and a resistor 8.
It is composed of d, 8e, and 8f.

The T1 terminal of the triac 8a is connected to the inrush current prevention resistor 9, the T2 terminal is connected to the sub-heater 3, and the base of the transistor 8c is connected to the port PA4 of the MPU1.

When MPU1 sets PA3 to "H", the transistor 8c is turned on and the phototriac coupler 8 is turned on.
The LED inside b is driven, the triac inside the phototriac is turned on, and then the triac 8a is turned on to the main heater 2 via the inrush current prevention resistor 9
C is applied.

Reference numeral 9 is an inrush current prevention resistor. When AC power is supplied to the main and sub heaters via this resistor, the voltage applied to the heater is lowered, so that the inrush current is reduced. In addition, since the inrush current prevention resistor has a built-in temperature fuse, abnormal heat generation does not occur even if continuous energization occurs during an abnormality.

Reference numeral 10 is a relay, which is arranged in a common current path from the AC power source 14 to the main and sub heaters.
Further, 11a is a transistor for driving the relay,
Reference numeral 1b is a surge absorbing diode, and the base of the transistor 11a is connected to the port PA0 of the MPU1. When MPU1 sets PA0 to "H", the transistor 11a turns on and the relay is closed.
Is set to "L", the transistor 11a is turned off and the relay is opened. Normally, the relay is closed and opened when an error occurs.

Reference numeral 12 is a current transformer, the primary winding of which is connected to a common current path from the AC power source 14 to the main and sub heaters, and the secondary winding of which is a rectifying bridge 13a inside a current detection circuit 13 described later. It is connected to the.

Reference numeral 13 is a current detection circuit, which is composed of a rectifying bridge 13a, a smoothing capacitor 13b, a load resistor 13c, threshold voltage regulating resistors 13d and 13e, and a comparator 13f. When an AC current flows through the main heater or the sub heater, the same AC current flows through the primary winding of the current transformer, and a predetermined AC voltage is generated at the secondary winding.

The AC voltage is full-wave rectified by the rectifying bridge 13a, smoothed by the smoothing capacitor 13b and the load resistor 13c, and converted into a DC voltage corresponding to the AC voltage.

Then, the generated DC voltage is compared with the threshold voltage, and if it is equal to or higher than the threshold voltage, "H" is input to the input port PB0 of MPU1. The threshold value is defined by the threshold value defining resistors 13d and 13e, and the value is
The output of the comparator 13f is set to "H" when a current flows through either the sub heater or the main heater.

Reference numeral 14 is a commercial AC power source.

The DC power supply VCC is supplied from a low-voltage power supply (not shown) (obtaining DC power from a commercial AC power supply).

Next, the startup sequence of the main heater and sub-heater in this embodiment will be described with reference to the timing chart of FIG. 2 and the flowchart of FIG.

First, the timer is started (step S
1), the port PA2 is set to "H", the main heater driver B6 is turned on, and the AC voltage is applied to the main heater 2 through the inrush current prevention resistor 9 (step S2). At this time, the inrush current flowing through the main heater is reduced by the amount by which the AC voltage applied to the main heater is lowered by the inrush current prevention resistor. Next, it waits until the timer value reaches t21 (step S3), and when t21 elapses, sets the port PA1 to "H" to turn on the main heater driver A5 to directly apply the commercial AC voltage to the main heater (step S4). .

At this time, since the filament of the main heater has risen to a certain temperature, the inrush current flowing is sufficiently small.

After that, the timer is restarted (step S
5) Wait for the timer value to reach t22 (step S
6) After t22, the port PA2 is set to "L" (step S7), the main heater driver B6 is turned off, and the current path between the inrush current prevention resistor 9 and the main heater 2 is cut off. Both of the main heater drivers A and B are turned on during t22 in order to prevent the inrush current prevention effect from being impaired due to both off periods at the time of driver switching due to variations in zero-cross detection of each driver.

Then, the timer is restarted (step S8), and the timer value is waited for t23 (step S9). When t23 elapses, the port PA2 is set to "H" (step S10), and the sub heater driver B8 is set. Is turned on, and an AC voltage is applied to the sub-heater 3 via the inrush current prevention resistor 9. That is, after t23 has passed since the current path between the inrush current prevention resistor 9 and the main heater 2 was cut off,
By opening the current path between the inrush current prevention resistor 9 and the sub-heater 3, the sub-heater driver B8 moves from the main heater driver B6 to the main heater driver A.
The current is prevented from flowing into 5. When the triac is triggered once, it stays on for a maximum of half an AC cycle. Therefore, by setting t23 to more than an AC half cycle, it is possible to reliably prevent the current flow. On the other hand, t22
Can be less than half an AC cycle.

Further, by not using the inrush current prevention resistor 9 at the same time in the main heater 2 and the sub heater 3,
The inrush current prevention resistor 9 is designed to withstand the current of one heater.

Next, the same control as the main heater 2 is applied to the sub heater 3.

First, the timer is restarted (step S1
1) and waits until the timer value reaches t24 (step S
3) After t24, the port PA3 is set to "H", the sub heater driver A is turned on for 7 and the commercial AC voltage is directly applied to the main heater (step S13).

After that, the timer is restarted (step S
14) and waits until the timer value reaches t25 (step S15). When t25 elapses, the port PA2 is set to "L" (step S7), the sub heater driver B8 is turned off, and the rush current prevention resistor 9 and the sub heater 2 are connected. Shut off the current path.

The above is the sequence for starting up the main and sub heaters.

Next, the abnormality detection sequence in this embodiment will be described with reference to the flowchart of FIG. The abnormality detection of this embodiment is performed by alternately turning on and off the main heater drivers A and B and the sub heater drivers A and B in sequence.

First, the port PA0 is set to "H" to close the relay 10 (step S20), and the port P is set.
All of A1, PA2, PA3 and PA4 are set to "L" and all the heater drivers are turned off (step S21).
Then, it is determined whether or not the port PB0 is "H", that is, whether or not the heater current is flowing (step S22). If the port PB0 is "H", the main heater driver A,
It is judged that one of B and the sub-heater drivers A and B has a short circuit failure (step S23), the port PA0 is set to "L" to open the relay 10 (step S40), and the main heater 2 and the sub-heater 3 are connected. The current supply path is cut off and the abnormality detection sequence ends.

If the port PB0 is not "H" in step S22, the port PA1 is set to "H" (step S2).
4) The main heater driver A is turned on to drive the main heater. Then, it is determined whether or not the port PB0 is "H" (step S25), and if it is not "H", it is determined that the main heater 2 is broken or the main heater driver A5 is open failure (step S26), and the port PA0 is set "". The relay 10 is brought to the open state by setting "L" (step S40), the current supply path to the main heater 2 and the sub heater 3 is cut off, and the abnormality detection sequence ends. If the port PB0 is "H" in step S25, PA1 is set to "L" and the main heater driver A is turned off (step S27).

Next, the port PA2 is set to "H" (step S28), the main heater driver B is turned on, and the main heater is driven. Then, it is determined whether or not the port PB0 is "H" (step S29), and if it is not "H", it is determined that the main heater 2 is broken or the main heater driver B6 is open (step S30), and the port PA0 is set to "H". The relay 10 is brought to the open state by setting "L" (step S40), the current supply path to the main heater 2 and the sub heater 3 is cut off, and the abnormality detection sequence ends. If the port PB0 is "H" in step S29, PA2 is set to "L" and the main heater driver B is turned off (step S31).

Next, the port PA3 is set to "H" (step S32), the sub heater driver A is turned on, and the sub heater is driven. Then, it is determined whether the port PB0 is "H" (step S33), and if it is not "H", it is determined that the sub-heater 3 is broken or the sub-heater driver A7 is open (step S34), and the port PA0 is set to "L". To open the relay 10 (step S4
0), the current supply path to the main heater 2 and the sub heater 3 is cut off, and the abnormality detection sequence ends. If the port PB0 is "H" in step S33, PA3 is set to "L" and the sub heater driver A is turned off (step S35).

Next, the port PA4 is set to "H" (step S36), the sub heater driver B is turned on, and the sub heater is driven. Then, it is determined whether or not the port PB0 is "H" (step S33). If it is not "H", it is determined that the sub heater 3 is broken or the sub heater driver 8 is open (step S38), and the port PA0 is set to "L". ", The relay 10 is opened (step S40),
The current supply path to the main heater 2 and the sub heater 3 is cut off to end the abnormality detection sequence. Step S3
If the port PB0 is "H" at 7, the PA4 is set to "L" to turn off the sub heater driver B to end the abnormality detection sequence (step S39).

Embodiment 2 FIG. 5 is a circuit diagram showing another heater control device of the heat roll fixing device to which the present invention is applied. The difference between the first embodiment described above and the second embodiment described in detail below is in the current detection circuit.

In the first embodiment, the current detection circuit 13 digitally detects the presence / absence of a heater current. On the other hand, the second
The current detection circuit 15 in the embodiment is the rectification bridge 15
The voltage generated at both ends of the load resistance, which is composed of a, the smoothing capacitor 15b, and the load resistance 15c, is input to the analog port AN1 of the MPU1.

FIG. 6 shows the voltage value input to the analog port AN1 when each heater driver is turned on independently.

FIG. 7 is a timing chart showing changes in the voltage value input to AN1 when the main and sub-heater startup sequences are executed (the timing is the first
Same as the example).

FIG. 8 is a flow chart for obtaining the state of each heater driver and the theoretical value of the output voltage of the current detection circuit 15.

FIG. 9 is a flow chart for explaining the abnormality detection sequence according to this embodiment.

In this embodiment, as shown in FIG. 8, it is first determined whether the main heater driver A is on (step S4).
1), If it is on, the voltage theoretical value (initial value is 0V) is 2.0.
V is added (step S42). If it is off, it is determined whether the main heater driver B is on (step S4).
3) If it is on, 1.2 V is added to the theoretical voltage value (step S44).

Subsequently, it is determined whether the sub heater driver A is on (step S45), and if it is on, 1.8 V is added to the theoretical voltage value (step S46). If off,
It is determined whether the sub heater driver B is on (step S4
7) If on, 1.0 V is added to the theoretical voltage value (step S48). From the above, the theoretical value of the current detection voltage value can be obtained.

In the flowchart shown in FIG. 9, first, the error value is calculated by subtracting the detected value from the theoretical value (step S).
51). Next, if the error value is> 0 (step S5
2) It is determined that one of the drivers has a short circuit failure, and the short circuit location is specified. That is, it is determined whether or not the error value matches the voltage value shown in FIG. 6, and if they match, it is determined that the driver has a short circuit failure (steps S53-).
S60), if there is no corresponding value, it is determined to be a composite failure of short-circuiting or opening of any driver and disconnection of the heater (step S61).

If the error value is <0 (step S6)
3) It is determined whether any of the drivers has an open failure or the heater is broken, and the open portion is specified. That is, it is determined whether the error value matches the negative voltage value shown in FIG. 6, and if they match, it is determined that the driver has an open failure or the heater is broken (steps S64 to S7).
1).

If there is no corresponding value, it is determined to be a composite failure of short-circuiting or opening of any driver and disconnection of the heater (step S61).

In case of any failure, the port PA0 is set to "L".
Then, the relay 10 is opened and the current supply path to each heater is cut off (step S62).

If the error value = 0, it is judged to be normal (step S72).

Third Embodiment Next, a third embodiment of the present invention will be described.

The difference between the first embodiment and the third embodiment is that a power thermistor is used instead of the inrush current prevention resistor 9 as an inrush current prevention element.

As a result, when the main heater driver B or the sub heater driver B has a short circuit failure,
The power thermistor is self-heated and its resistance value does not drop and it is not damaged. Further, a short circuit failure of the driver can be detected.

[0091]

As described above, according to the first invention of the present application, a plurality of heater driving means for independently driving a plurality of heaters are provided, and a heater inrush current preventing means,
Alternatively, by providing the failure detection means or the current cutoff means in the current path common to the plurality of heaters, it is possible to reduce the number of parts, reduce the size, and reduce the cost.

According to the second invention of the present application, by providing the inrush prevention switching means for switching whether or not the current is supplied to each of the plurality of heaters through the inrush current prevention means, the inrush current prevention for each heater is prevented. Can be selectively performed.

According to the third invention of the present application, the current capacity of the inrush current prevention means is increased by alternately supplying the current to each of the plurality of heaters by the inrush current prevention switching means. Since the number can be reduced, the inrush current prevention unit can be reduced in size and cost.

According to the fourth invention of the present application, the driving start and stop timings of the plural heater driving means,
By setting the switching timings of the inrush current prevention switching means to different timings, it is possible to prevent an abnormal current from flowing from the predetermined heater driving circuit to another heater driving circuit.

According to the fifth invention of the present application, the failure detecting means includes the current detecting means for detecting the presence or absence of the passing current, so that the currents of the plurality of heaters are detected by the single current detecting means. It becomes possible.

According to the sixth invention of the present application, a plurality of heaters are alternately driven, and the output state of the current detecting means at that time is detected to disconnect the specific heater or open the specific heater drive circuit. Can be detected.

According to the seventh invention of the present application, it is determined that one of the heater drive circuits has a short circuit failure by stopping the driving of all the heaters and detecting the output of the current detecting means at that time. It becomes possible to do.

According to the eighth invention of the present application, the failure detecting means includes the total current detecting means for obtaining a predetermined voltage output according to the total passing current value.
It becomes possible to detect the currents of a plurality of heaters simultaneously with a single current detecting means.

According to the ninth invention of the present application, by detecting the drive state of a plurality of heaters and the output value of the current detecting means, the disconnection of a specific heater and the open failure or short circuit failure of the heater drive circuit are detected. Will be possible.

According to the tenth invention of the present application, the failure detecting means is provided with means for activating the current interrupting means provided in the common path when the failure occurs to interrupt the current supply to each heater. It becomes possible to cut off the current when each drive circuit of a plurality of heaters is abnormal by a single current cutoff means.

According to the eleventh invention of the present application, the on-timing shift amount of the inrush current prevention means can be set to half an AC cycle or more.

According to the twelfth invention of the present application, it is possible to obtain a thermal fixing device including the above heater control device.

According to the thirteenth invention of the present application, it is possible to perform the image reproduction according to the electrophotographic process by including the above-mentioned heat fixing device.

[Brief description of the drawings]

FIG. 1 is a diagram showing a heater control circuit according to a first embodiment.

FIG. 2 is a timing chart showing a heater start-up sequence of the first embodiment.

FIG. 3 is a flowchart showing a heater startup sequence of the first embodiment.

FIG. 4 is a flowchart showing an abnormality detection sequence of the first embodiment.

FIG. 5 is a diagram showing a heater control circuit according to a second embodiment.

FIG. 6 is a diagram showing the relationship between the heater drive circuit ON and the current detection voltage in the second embodiment.

FIG. 7 is a diagram showing a relationship between a heater start-up sequence and a current detection voltage according to the second embodiment.

FIG. 8 is a flowchart showing a method for calculating a theoretical value of a current detection voltage in the second embodiment.

FIG. 9 is a flowchart showing an abnormality detection sequence of the second embodiment.

[Explanation of symbols]

 1 MPU 2 Main Heater 3 Sub Heater 5 Main Heater Driver A 6 Main Heater Driver B 7 Sub Heater Driver A 8 Sub Heater Driver B 9 Inrush Current Prevention Resistor 10 Relay 12 Current Transformer

Claims (13)

[Claims] 1. A heater having a plurality of heaters and a plurality of heater driving means for independently driving the plurality of heaters, wherein a heater inrush current prevention means, a failure detection means, or a current interruption means is provided in the plurality of heaters. A heater control device provided in a current path common to heaters. 2. The heater control device according to claim 1, further comprising inrush current prevention switching means for switching whether or not to supply current to each of the plurality of heaters through the inrush current prevention means. 3. The heater control device according to claim 2, wherein the inrush current prevention switching means alternately supplies current to each of the plurality of heaters via the inrush current prevention means. 4. The heater control device according to claim 3, wherein the driving start and stop timings of each of the plurality of heater driving means and the switching timing of the inrush current prevention switching means are separate timings. 5. The heater control device according to claim 1, wherein the failure detection means includes current detection means for detecting the presence or absence of a passing current. 6. The detecting means according to claim 5, wherein a plurality of heaters are alternately driven, and the output state of the current detecting means at that time is detected to detect disconnection of the specific heater or open failure of the specific heater drive circuit. A heater control device comprising: 7. The heater according to claim 5, wherein when driving of all the heaters is stopped and the output of the current detecting means at that time has current, it is determined that one of the heater driving circuits has a short circuit failure. Heater control device. 8. The heater control device according to claim 1, wherein the failure detecting means includes a total current detecting means for obtaining a predetermined voltage output according to a total passing current value. 9. A means for detecting a disconnection of a specific heater and an open failure or a short failure of a heater drive circuit by comparing the drive states of a plurality of heaters with an output value of a current detection means. A heater control device having. 10. The failure detection means according to claim 1,
A heater control device comprising means for activating a current interruption means provided on a common path to interrupt the current supply to each heater when a failure occurs. 11. The heater control device according to claim 4, wherein the on-timing shift amount of the inrush current prevention means is set to be half an AC cycle or more. 12. A thermal fixing device comprising the heater control device according to any one of claims 1 to 11. 13. An image forming apparatus comprising the heat fixing device according to claim 12, and performing image reproduction according to an electrophotographic process.