JP3070048B2 - Temperature control device for fixing heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a temperature control device of the fixing heater, particularly comparator and resistor fixing heater with a simple configuration of a fixing heater and a temperature detector with temperature control using The present invention relates to an apparatus for detecting an abnormality of a thermistor.

[0002]

2. Description of the Related Art Conventionally, in laser printers, copiers and facsimile machines capable of high-speed printing, an electrostatic latent image is formed on a photosensitive drum, and toner adhered to the electrostatic latent image on the photosensitive drum is used. The toner is transferred to and adhered to the recording paper, and then the toner is heated by a fixing heater, so that a fixing process is performed on the recording paper. By the way, the temperature of the fixing heater is detected by a thermistor, and the divided voltage at a voltage dividing point of a resistance circuit in which the thermistor and the fixed resistor are connected in series is input to an A / D converter. The digital temperature signal output from the converter is configured to be read by the control device.

Here, the temperature of the fixing heater is set to, for example, a set temperature for fixing standby of “130 ° C.” in a standby state in which no fixing process is performed. Set temperature for “150 °
C ". The controller controls the power supply to the fixing heater by feedback control based on the read temperature signal so as to maintain the fixing standby set temperature or the fixing set temperature.

On the other hand, when the fixing heater is disconnected or a failure such as disconnection of the thermistor occurs, the internal resistance of the thermistor becomes abnormally large and the partial pressure at the voltage dividing point of the resistance circuit changes rapidly. Therefore, the control device detects an abrupt change in the temperature signal from the A / D converter, and detects an abnormality of at least one of the fixing heater and the thermistor.

[0005]

However, as described above, the temperature of the fixing heater and the abnormality of the fixing heater and the thermistor are detected based on the digital temperature signal output from the A / D converter. Therefore, it is necessary to provide an A / D converter.
The D converter requires the use of expensive one-chip IC elements or a large number of gates in the gate array, resulting in a problem that the cost of a laser printer, a copying machine, and the like increases. .

Therefore, the present inventors have omitted the expensive A / D converter, and have detected the resistance value of the thermistor, that is, the temperature, through a resistor circuit capable of switching the resistance value between the comparator and the resistance value. However, in this method, it is difficult to detect a rapid change in the resistance value of the thermistor, so that an abnormality detection method similar to the conventional digital method cannot be applied.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. In addition to controlling the temperature of a fixing heater using an inexpensive comparator, the present invention detects an abnormality in the fixing heater or thermistor. It is an object of the present invention to provide a temperature control device for a fixing heater that can be obtained.

[0008]

To SUMMARY OF THE INVENTION To achieve the above object, the temperature control device of the fixing heater 請 Motomeko 1, the temperature of the fixing heater for fixing by heat the toner adhering to the record medium A control device, comprising: a thermistor for detecting a temperature of a fixing heater; a comparison voltage input terminal connected to a power supply opposite terminal of the thermistor by a conductive wire; a reference voltage input terminal to which a reference voltage is input; and an output terminal. A resistor circuit interposed between the lead wire and the ground, and selectively switchable between a first resistance value, a second resistance value, and a third resistance value different from each other; and a resistance value of the resistance circuit. Switching means for selectively switching the resistance value of the resistance circuit by the switching means, a first set temperature for fixing corresponding to the first resistance value, and a temperature lower than the first set temperature and For the second resistance value A second set temperature for fixing stand for,
Lower than the second set temperature and fixing with the thermistor
Judge that at least one of the heaters is abnormal
A temperature setting means for selectively temperature setting and a third setting temperature corresponding to the third resistance value of order, receiving the output signal of the output terminal of the comparator, the energization control for controlling the energization of the fixing heater means, through the temperature setting means, during the fixing process execution
Alternatively, when the set temperature is temporarily switched from the first set temperature or the second set temperature to the third set temperature in the fixing standby state, and after the switch, the output signal of the comparator continues the signal instructing the energization, the thermistor And an abnormality detecting means for judging that at least one of the fixing heaters is abnormal.

[0009]

In the temperature control system of the fixing heater according to claim 1 having an upper Symbol Configuration [action], the power supply facing terminals of the thermistor for detecting the temperature of the fixing heater is connected to the comparison voltage input terminal of the comparator by a conductive wire, the Between the conductor and ground
A resistor circuit that can be selectively switched between a first resistance value, a second resistance value, and a third resistance value different from each other is provided.
Since switch means for selectively switching the resistance value of the resistance circuit is provided, first, the third
In order to selectively set the temperature from the set temperature to a second set temperature for fixing standby higher than the third set temperature, the resistance value of the resistor circuit corresponding to the third set temperature is set by a switch means using a third resistor. When the value is switched to the second resistance value corresponding to the second set temperature, a divided voltage based on the internal resistance value of the thermistor and the resistance value of the resistance circuit is input to the comparison voltage input terminal via the conducting wire.

That is, since the thermistor generally has a negative temperature coefficient, the internal resistance when the temperature is low is larger than the internal resistance when the temperature is high. Then, the divided voltage changed based on the above is input to the comparison voltage input terminal. As a result, the comparator outputs a signal indicating a result of comparison between the divided voltage input to the comparison voltage input terminal and the reference voltage input to the reference voltage input terminal from the output terminal. Then, the energization control means receives the output signal from the output terminal of the comparator and energizes the fixing heater.

In order to selectively set a temperature from a second set temperature for fixing standby to a first set temperature for fixing higher than the second set temperature by a temperature setting means, a resistance is set by a switch means. When the resistance of the circuit is switched from the second resistance corresponding to the second set temperature to the first resistance corresponding to the first set temperature, the change based on the internal resistance of the thermistor and the resistance of the resistor circuit is performed. The divided voltage is input to the comparison voltage input terminal via the conducting wire, and in the same manner as described above,
The comparator outputs a signal indicating a result of comparison between the divided voltage and the reference voltage from an output terminal. Then, the energization control means receives the output signal from the output terminal of the comparator and energizes the fixing heater.

On the other hand, the first temperature for fixing is set by the temperature setting means.
In order to selectively set the temperature from the set temperature to a second set temperature for fixing standby lower than the first set temperature, the resistance value of the resistor circuit is changed from the first resistance value to the second resistance value by the switch means. When the switching is performed, the changed voltage division based on the internal resistance value of the thermistor and the resistance value of the resistance circuit is input to the comparison voltage input terminal via the conducting wire. As a result, the comparator outputs a signal indicating a result of comparison between the divided voltage and the reference voltage from the output terminal. Then, the power supply control means receives the output signal from the output terminal of the comparator and cuts off the power supply to the fixing heater.

[0013] Similarly, the temperature setting means, in order to selectively temperature set to the third set temperature lower than the second set temperature of the second set temperature or Rako, the resistance value of the resistor circuit by the switching means Is switched from the second resistance value to the third resistance value, the changed divided voltage is input to the comparison voltage input terminal via the conducting wire, and the energization control means performs the same operation as described above from the output terminal of the comparator. Upon receiving the output signal, the power supply to the fixing heater is cut off.

On the other hand, the abnormality detecting means receives the output signal of the comparator and, via the temperature setting means, executes the fixing process or waits.
When the set temperature is temporarily changed from the first set temperature or the second set temperature to the third set temperature during the operation, and the output signal of the comparator continues the signal instructing the energization after the change,
It is determined that at least one of the thermistor and the fixing heater is abnormal.

Thus, the first set temperature for fixing, the second set temperature for fixing standby lower than this set temperature, and the third set temperature lower than this set temperature are input to the comparison voltage input terminal of the comparator. A voltage division based on the resistance value of the resistance circuit switched to set the temperature selectively to the set temperature and the internal resistance value of the thermistor is input. This voltage division is compared with the reference voltage, and the comparison result is obtained. , The energization of the fixing heater is controlled so as to be the first set temperature, the second set temperature, or the third set temperature, which is selectively set, so that an expensive A / D converter is used. It is possible to control the temperature of the fixing heater without providing the fixing heater. Furthermore, when the temperature is temporarily switched from the first set temperature or the second set temperature to the third set temperature, it is only necessary to determine whether or not the output signal of the comparator continues to be energized. Can be easily and reliably detected.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, the present invention is applied to a laser printer (laser facsimile apparatus) that receives print data from an external device, stores the print data in a memory, and prints the print data. First, a printing mechanism PM provided in the laser printer 1 will be briefly described with reference to FIG. The laser printer 1 includes a laser scanner device 10, a process cartridge 20, a transfer / separation device 25 including a transfer charger and a static elimination needle, and a fixing roller 3.
1, a fixing device 30 including a pressure roller 32 and the like, and a transport device 35 including a paper feed roller 36, a registration roller 37, a transport roller 38, a paper discharge roller 39, and the like.

The laser scanner device 10 includes a semiconductor laser 11, a hexahedral mirror 12, an imaging lens 13, a reflection mirror 14, a lens member 15 made of synthetic resin, and the like. Inside the process cartridge 20,
A photosensitive drum 21, a primary charger 22, a developing cylinder 23, an exposure lamp 24, and the like are incorporated therein. At the center of the fixing roller 31 of the fixing device 30, a fixing heater 33 composed of a halogen lamp is provided.
1, a thermistor 34 for detecting the temperature of the fixing roller 31 is provided.

The light emitted from the semiconductor laser 11
The laser beam LB that has entered the planar mirror 12 is deflected by a predetermined angle for each mirror surface of the hexahedral mirror 12 that rotates at a constant high speed, so that the laser beam LB is main-scanned over a predetermined angle range, and the imaging lens 13 is scanned. Then, the light is reflected downward by the reflection mirror 14 and is irradiated onto the rotating photosensitive drum 21 via the lens member 15 to form an electrostatic latent image. Photosensitive drum 21
The electrostatic latent image formed thereon is developed with toner supplied from the developing cylinder 23, and this visible image is transferred to the recording paper P transported by the transport device 35 from the paper feed cassette 5 and printed. The printed recording paper P is then conveyed onto the paper discharge tray 6 by the rollers 38 and 39 while the fixing device 30 fixes the toner on the recording paper P.

Next, the control system of the laser printer 1 will be described with reference to the block diagram of FIG. 2. Since this control system is basically the same as that of a general laser printer, it will be briefly described. And The video controller 50 of the laser printer 1 includes a CPU 51, a ROM 52 storing various control programs, and a reception buffer for receiving and storing transmission data transmitted from a data transmission device 62 such as a personal computer or a host computer. A RAM 60 provided with various memories;
A timing control circuit (TC) 53 for generating a timing signal for writing / reading transmission data as reception data in a reception buffer, and a serial interface (S) for receiving print data transmitted from an external data transmission device 62 (I / F) 54 and 2 of 4K bytes
A video interface (V.I / F) 55 having two scan buffers and sequentially outputting print information converted to bit image data to the DC controller 58, and a panel interface (P / I / F) for receiving a signal from the operation panel 57 F) 56, and these are buses 59
Are respectively connected to the CPU 51 via the.

Here, the printing mechanism PM includes the laser scanner device 10 and the process cartridge 2 as described above.
0, transfer / separation device 25, fixing device 30, transport device 35
Are provided, a main motor for driving the photosensitive drum 21 and the transport device 35, a fixing heater 33 for the fixing roller 31, a circuit for other electrical components, and the like are provided.
The DC controller circuit 58 is configured to drive and control a scanner motor that drives the semiconductor laser 11 and the hexahedral mirror 12 in addition to the main motor, the fixing heater 33, and various electric component circuits. Further, a temperature control circuit 70 unique to the present application is connected to the DC controller circuit 58, and the temperature control circuit 70
Are connected to a fixing heater 33 and a thermistor 34, respectively.

The ROM 52 includes a font memory, which stores printing dot pattern data relating to a large number of characters such as characters and symbols, in addition to various control programs provided in a normal laser facsimile apparatus.
A memory management program for managing a memory capacity and a head address of each memory such as a reception data buffer and a print image memory provided in the AM 60 and a control program for abnormality detection control, which will be described later, are stored in advance.

Next, the temperature control circuit 70 will be described with reference to FIG. One terminal of the thermistor 34 is +
The other terminal is connected to a comparison voltage input terminal 71a of a comparator (corresponding to a comparator) 71 via a conductor L1. A resistor R1 connected in series and an NPN transistor T1 are connected between the voltage dividing point P1 of the conductor L1 and the ground, and a resistor R2 connected in series and an NPN transistor T2 are connected. R3 is connected.

On the other hand, the reference voltage input terminal 71b of the comparator 71 is connected to a voltage dividing point P2 between the resistors R4 and R5 which are provided in series between the + 5V power supply and the ground. That is, since the resistance values of these two resistors R4 and R5 are equal, a reference voltage of about 2.5 V is supplied to the reference voltage input terminal 71b. The base of the transistor T1 is connected to the output port OP1 of the DC controller circuit 58, the base of the transistor T2 is connected to the output port OP2, and the output terminal 71c is connected to the input port IP.
Connected to 1.

[0024] Here, the resistance value of the resistor R3, the fixing heater 33 is set substantially equal to the internal resistance value r ₄₀ of the thermistor 34 when approximately 40 ° C. Further, the parallel resistance value PR ₁₃ when the resistor R1 and the resistor R3 are connected in parallel, the thermistor 3 when the fixing heater 33 is about 130 ° C
4 substantially equal to the internal resistance value r ₁₃₀ of the parallel resistance value PR when the further parallel connected three resistors R1, R2, R3
_123, to be substantially equal to the internal resistance value r _0.99 thermistor 34 when the fixing heater 33 is about 0.99 ° C, the resistance values of the three resistors R1, R2, R3 are respectively set. Then, the parallel resistance value PR ₂₃ when connected in parallel with the resistor R2 and the resistor R3 as a result, the fixing heater 33 is substantially equal to the internal resistance value r ₁₂₀ of the thermistor 34 when about 120 ° C. That is, the parallel resistance value PR ₁₂₃ <
The parallel resistance PR ₁₃ <the parallel resistance PR ₂₃ <the resistance of the resistor R3, and the internal resistance r of the thermistor 34
Is a negative temperature coefficient, the internal resistance value r ₁₅₀ <the internal resistance value r ₁₃₀ <the internal resistance value r ₁₂₀ <the internal resistance value r ₄₀ .

Next, the output terminal 71c of the comparator 71
And a power supply control circuit 73 for controlling power supply to the fixing heater 33 will be described. One input terminal of the AND gate 72 is connected to the output terminal 71c, and the other input terminal is connected to the output port OP3 of the DC controller circuit 58. The output terminal of the AND gate 72 is connected to the photodiode 74a of the photocoupler 74. And the cathode of the photodiode 74a is grounded. The collector of the phototransistor 74b of the photocoupler 74 is connected to the second anode of the triac 75 via a resistor R6 and a commercial power supply (AC100 V).
Are connected to one side respectively. Further, the emitter of the phototransistor 74b is connected to a first anode of the triac 75 via a conductor L2, and a resistor R7 is provided on the conductor L2. The gate of the triac 75 is connected to the voltage dividing point P3 of the conducting wire L2. The fixing heater 33 is connected to the other side of the commercial power supply and the first anode of the triac 75, respectively.

Next, the operation of the energization control circuit 73 will be described. When an "H" level signal is input from the output terminal 71c to the AND gate 72 and an "H" level is input from the output port OP3, the AND gate 72 72 outputs an “H” level signal, so that the photodiode 7
4a is turned on, and the phototransistor 74b is turned on.
Here, when the positive voltage of the commercial power supply is supplied to the resistor R6, the two resistors R6 and R7 of AC100 V are set at the voltage dividing point P3.
Is generated, and the divided voltage is supplied to the gate of the triac 75 as a trigger signal, so that the triac 75 conducts. As a result, 100 V AC is supplied to the fixing heater 33 through the triac 75, and the fixing roller 31 is heated by the heat generated by the fixing heater 33.

On the other hand, when one of the output terminal 71c and the output port OP3 becomes "L" level, the AND gate 72 outputs an "L" level signal, so that the photodiode 74a is turned off and the phototransistor is turned off. 74b is shut off. As a result, the partial pressure at the partial pressure point P3 becomes 0 V,
Since the gate voltage of the triac 75 becomes 0 V,
The triac 75 is cut off, and the supply of AC 100 V to the fixing heater 33 is stopped.

Next, the operation of the temperature control circuit 70 will be described. First, in order to set the fixing heater 33 to the fixing standby set temperature “130 ° C. (corresponding to the second set temperature)”, the “H” level is applied to the two output ports OP 1 and OP 3 of the DC controller circuit 58. When each signal is output, the "H" level signal of the output port OP1 is supplied to the base of the transistor T1, and the transistor T1 is turned on.
Thermistor 34 and two resistors R1, R
The current flows through the parallel circuit of No. 3 to the ground. Here, when the fixing heater 33 is not heated, the internal resistance value r of the thermistor 34 is about 1
Which is larger than the substantially equal parallel resistance value PR ₁₃ and the internal resistance value r ₁₃₀ of the thermistor 34 when the 30 ° C, the comparison voltage input terminal 71a of the comparator 71, about supplied to the reference voltage input terminal 71b 2.5 The voltage divided at the voltage dividing point P1 of the conducting wire L1 smaller than the reference voltage of V is input, and the “H” level signal is output from the output terminal 71c of the comparator 71.

As a result, two "H" level signals are input to the AND gate 72, and the AND gate 72 outputs an "H" level signal. That is, as described above, the triac 75 of the energization control circuit 73 is turned on, and the fixing heater 33 is supplied with AC 100 V through the triac 75.
, The fixing roller 31 is heated . When Fixing roller 31 is heated to about 130 ° C, the thermistor 34
Internal resistance value r ₁₃₀ is slightly greater than the parallel resistance value PR ₁₃ of
Ku becomes, the comparison voltage input terminal 71a, the AND gate 72 following voltage 2.5 V is supplied to output the "L" level signal. As a result, as described above, the triac 7
5 is shut off, and the power supply to the fixing heater 33 is stopped.

On the other hand, when the fixing process is started, in order to set the fixing heater 33 to the fixing temperature "150 ° C. (corresponding to the first set temperature)", three DC controller circuits 58 are used. "H" for output ports OP1 to OP3
When the level signals are output, these output ports OP1
, OP2, the "H" level signal of both transistors T1, T2
2 are turned on, and the thermistor 34 and 3
A current flows to the ground via a parallel circuit of the three resistors R1 to R3. In this case, the internal resistance value r ₁₃₀ of the thermistor 34 which is larger than the parallel resistance value PR _123, the comparison voltage input terminal 71a of the comparator 71, a small partial pressure than the reference voltage is supplied, an output terminal of the comparator 71 7
An "H" level signal is output from 1c. This allows
A is supplied to the fixing heater 33 through the triac 75.
C100 V is energized.

[0031] When the fixing roller 31 is heated to approximately 0.99 ° C, slightly larger than the internal resistance value r _0.99 is the parallel resistance value PR ₁₂₃ of the thermistor 34, the comparison voltage input terminal 71a, 2.5 V or less Is supplied and AND
Gate 72 outputs an “L” level signal. as a result,
As described above, the triac 75 is shut off, and the power supply to the fixing heater 33 is stopped.

By the way, in order to set the fixing heater 33 to the fixing temperature "130.degree. C." at the end of the fixing process, "H" is applied to the two output ports OP1 and OP3 of the DC controller circuit 58. When the respective level signals are output, as described above, the parallel resistance value PR ₁₃ becomes the thermistor 3
4 is larger than the internal resistance value r ₁₅₀ , the comparator 71 is supplied with a partial voltage larger than the reference voltage to the comparison voltage input terminal 71 a, and outputs an “L” level signal from the output terminal 71 c of the comparator 71. You. Thus, the power supply to the fixing heater 33 is stopped.

Further, when the temperature of the fixing heater 33 is temporarily set to “40 ° C.” while the set temperature for fixing standby is set to “130 ° C.”, only the output port OP3 is connected. "H" level signal is output and + 5V
A current flows from the power supply to the ground via the thermistor 34 and the resistor R3. At this time, the resistance value of the resistor R3 is
4 of greater than the internal resistance value r _130, the comparison voltage input terminal 71a of the comparator 71, the partial pressure greater than the reference voltage is input, the "L" level signal is output from the output terminal 71c of the comparator 71 You. Thus, the power supply to the fixing heater 33 is stopped.

Next, a routine of abnormality detection control performed by the video controller 50 of the laser printer 1 will be described with reference to the flowchart of FIG. In the figure, Si (i = 30, 31, 32,...) Indicates each step. However, this abnormality detection control is executed by interruption processing to the CPU 51 every minute time when the fixing heater 33 is set to the fixing standby set temperature “130 ° C.” where no fixing processing is performed. Is done.

This control is started by interrupt processing to the CPU 51. First, in order to temporarily set the fixing heater 33 to the set temperature “40 ° C.”, the output port OP1 is set.
At the output port OP3, and an "H" level signal is output only to the output port OP3 (S30). Next, when the input port IP1 is at "L" level,
When the "L" level signal is being output from the output terminal 71c of the first (S31: Yes), as described above, the resistance R
Resistance of 3 from greater than the internal resistance value r ₁₃₀ of the thermistor 34, the comparison voltage input terminal 71a of the comparator 71, the partial pressure greater than the reference voltage is input, "L from the output terminal 71c of the comparator 71 Since the level signal is output, the fixing heater 33 and the thermistor 34 are operating normally, and the output port OP
The "H" level is output to 1 (S32), this control ends, and the routine returns to the main routine.

By the way, when the set temperature is "130 °", the "L" level is output to the output port OP1 and when the set temperature is temporarily switched to "40 ° C."
When IP1 is at the "H" level, that is, when the "H" level signal, that is, the signal instructing the energization is output from the output terminal 71c of the comparator 71 (S31: No), as described above, the fixing heater 33 is turned on. Is applied, that is, the fixing heater 33 is in a disconnected state and does not generate heat, and the internal resistance value r of the thermistor 34 is equal to the resistance R.
3 or when the internal resistance r of the thermistor 34 is infinitely large due to a failure such as disconnection of the thermistor 34.
And an abnormal state of at least one of the fixing heater 33 is detected (S33), the "L" level is forcibly output to the output port OP3, and the power supply to the fixing heater 33 is stopped (S34). Abnormality notification processing such as displaying a warning message on the display of the operation panel 57 via 56 is executed (S35), this control is ended, and the routine returns to the main routine.

Here, when the fixing process is completed, the set temperature of the fixing heater 33 is changed to the fixed set temperature “1”.
Since the temperature is changed from 50 ° C. to the set temperature for fixing standby “130 ° C.”, when the set temperature for fixing standby is changed, an abnormality of the thermistor 34 and the fixing heater 33 is detected. Is also good. That is, as shown in FIG. 5, when the abnormality detection control at the time of changing to the fixing standby set temperature is started, first, when switching from the fixing set temperature to the fixing standby set temperature (S50: Yes), when the input port IP1 is at the "L" level, and the "L" level signal is output from the output terminal 71c of the comparator 71 (S51: Yes), as described above, the fixing heater 33 and the thermistor 34 is operating normally, this control ends, and the routine returns to the main routine.

However, when the input port IP1 is at the "H" level, the "H" level is output from the output terminal 71c of the comparator 71.
When the level signal, that is, the signal for instructing the energization is output (S51: No), as described above, when the fixing heater 33 is in a disconnected state and does not generate heat,
Or, when an abnormal condition such as disconnection of the thermistor 34 occurs, an abnormal condition of at least one of the thermistor 34 and the fixing heater 33 is detected (S52), and the "L" level is forcibly output to the output port OP3. Then, the power supply to the fixing heater 33 is stopped (S53), and the operation panel 5
Such as displaying a warning message on the display of 7,
An abnormality notification process is executed (S54), this control is terminated, and the routine returns to the main routine.

As described above, the comparative voltage input terminal 71a of the comparator 71 has the fixing temperature “15”.
0 ° ”, a fixing standby set temperature“ 130 ° ”lower than the set temperature, and a resistance circuit switched to selectively set the temperature to a set temperature“ 40 ° ”lower than the set temperature. Of the voltage dividing point P1 of the conducting wire L1 based on the parallel resistance value PR of the thermistor 34 and the internal resistance value r of the thermistor 34, the divided voltage is compared with the reference voltage, and the voltage is selected according to the comparison result. The energization to the fixing heater 33 is controlled so as to be a fixed fixing set temperature or a fixing standby set temperature, so that the fixing can be performed without providing an expensive A / D converter. The temperature of the heater 33 can be controlled. Further, when the temperature is temporarily switched from the set temperature for fixing or the set temperature for fixing standby to any lower set temperature, the output signal of the comparator 71 is an “H” level signal, and the energization is continued. It is possible to simply and reliably detect the abnormality of at least one of the thermistor 34 and the fixing heater 33 simply by detecting whether or not this is the case.

In the abnormality detection control, while the fixing process is being performed, the set temperature is changed to the set temperature for fixing “150 °”.
Is lower than the set temperature for fixing standby “130”.
° or the set temperature “40 °” to detect an abnormality of the thermistor 34 or the fixing heater 33. Note that the present invention is not limited to the resistor circuit including the three resistors R1 to R3, and a resistor that can be selectively switched to a resistance value corresponding to a set temperature by combining a plurality of resistors or using a single resistor. It is also possible to configure a circuit. It should be noted that various changes may be made to each device and control of the above-described embodiment based on existing technology or technology obvious to those skilled in the art within the scope of the technical idea of the present invention. Of course, the present invention can be applied to a temperature control device of various fixing heaters such as a copying machine and a facsimile which fix toner on a recording sheet by attaching toner to an electrostatic latent image formed on a photosensitive drum. It is.

[0041]

As described above, according to the temperature control device of the fixing heater of the first aspect , the thermistor, the comparator, the resistance circuit, the switch means, the temperature setting means,
The power supply control means and the abnormality detection means are further provided, and a first set temperature for fixing, a second set temperature for fixing standby lower than the set temperature, and a set A voltage division based on the resistance value of the resistance circuit and the internal resistance value of the thermistor switched to selectively set the temperature to the third set temperature lower than the temperature is input. comparing, in response to the comparison result, controls so as to have a selective first set temperature set or the second set temperature or the third set temperature, power supply to the fixing heater this
In addition, the temperature of the fixing heater can be controlled without providing an expensive A / D converter. Further, the set temperature is set to the first temperature during execution of the fixing process or during standby .
A third set temperature lower than the set temperature or the second set temperature (this is because the thermistor and the fixing heater
These are the temperatures for judging one of the abnormalities). <br/> When the temperature is temporarily switched, the output signal of the comparator only detects whether or not the energization is continued. Can be easily and reliably detected.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a laser printer according to an embodiment of the present invention .

FIG. 2 is a block diagram of a control system of the laser printer.

FIG. 3 is a diagram illustrating a circuit configuration of a temperature control circuit and a conduction control circuit.

FIG. 4 is a schematic flowchart of a routine of abnormality detection control.

FIG. 5 is a flowchart of abnormality detection control when changing to a fixing standby set temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser printer 33 Fixing heater 34 Thermistor T1 transistor T2 transistor 50 Video controller 51 CPU 52 ROM 60 RAM 71 Comparator 73 Power supply control circuit L1 Lead wire P Recording paper R1 Resistance R2 Resistance R3 Resistance

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/20

Claims (1)

(57) [Claims] 1. A temperature control device for a fixing heater for heating and fixing toner adhered to a recording medium, wherein the thermistor detects the temperature of the fixing heater, and is connected to a power supply opposite terminal of the thermistor by a conducting wire. A comparator having a reference voltage input terminal, a reference voltage input terminal to which a reference voltage is input, and an output terminal; a first voltage having a different value interposed between the conductor and ground.
A resistance circuit that can be selectively switched between a resistance value, a second resistance value, and a third resistance value; switch means for selectively switching the resistance value of the resistance circuit; and resistance of the resistance circuit by the switch means. By switching the values, a first set temperature for fixing corresponding to the first resistance value, a second set temperature for standby for fixing lower than the first set temperature and corresponding to the second resistance value, and 2 Lower than the set temperature and less of the thermistor and fixing heater
A temperature setting means for selectively setting a temperature to a third set temperature corresponding to a third resistance value for judging that one of them is abnormal; and receiving an output signal from an output terminal of the comparator, energizing control means for controlling the energization of the fixing heater, via a pre-Symbol temperature setting means, the fixing process executing current or fixing wait
When the set temperature is temporarily changed from the first set temperature or the second set temperature to the third set temperature at the time of operation, and the output signal of the comparator continues the signal instructing the energization after the change, the thermistor and An abnormality detecting means for determining that at least one of the fixing heaters is abnormal; and a temperature control device for the fixing heater.