JPH10333481A - Fixing temperature controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the possibility of the malfunction of a temperature overrising preventing circuit using a comparator by making the resistance value of one of two resistors connected in series between constant voltage terminals selectively settable in accordance with a variation in a reference value. SOLUTION: A fixing high-temperature abnormal reference value for preventing, as hardware, the overrising of temp. is set by resistors 13 and 15, without being controlled by a CPU, so that there is a possibility that during the normal operation, a fixing heater is always turned off because a temperature overrising preventing means as hardware malfunctions because of noise, etc. In such a case, the resistor 15 can be selectively set and a resistor 15-1 has the same resistance value as that of the resistor 15. The resistance values of resistors 15-2-15-n are set smaller than that of the resistor 15. When these resistors are selected, a reference voltage can be made low. When a fixing control temperature range is made high, the resistors 15-2-15-n are selected in accordance with the variation in the fixing control temperature range, so that the fixing high-temperature abnormal reference value can be changed as well to prevent the malfunction caused by the noise, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing temperature control device for a copying machine, and more particularly to a fixing temperature control device characterized by a method for detecting an abnormally high fixing temperature.

[0002]

[Prior art]

(1) Conventionally, a fixing temperature control device of a copying machine of this type is provided with an overheating prevention device for preventing smoke, ignition and the like of a fixing portion. One of them is to detect an excessive temperature rise using a comparator 11 as shown in FIG. This is because the voltage divided by the resistance value of the thermistor 9 having a negative characteristic and the resistor 10 connected in series with the resistance value of the thermistor 9 and the two resistors 1
The reference voltage obtained by the voltage division of 3 and 15 is compared with the comparator 11
As a result of the comparison, when the partial pressure value on the thermistor side is lower than the reference value (when the fixing temperature is higher than the reference temperature), the output of the comparator 11 becomes “L” and the power supply to the fixing heater is controlled. The transistor 22 that controls the voltage supply to the relay coil 8 and the phototriac 7 is turned off, and no voltage is supplied to the relay coil 8 and the phototriac 7, and the relay coil 8 and the phototriac 7 are magnetically coupled. Relay 4 and triac 6 are turned off,
The power supply to the fixing heater 2 is eliminated. (2) Further, the fixing temperature control device disclosed in Japanese Patent Laid-Open No. 4-34485 discloses a fixing roller based on data stored in a non-volatile memory for various error factors generated when a fixing temperature is detected by a thermistor. Is controlled to maintain the temperature at a predetermined fixing temperature. (3) A fixing temperature control device in which the configuration disclosed in JP-A-4-34485 of (2) is added to the overheating prevention circuit using the above-mentioned comparator is conceivable. In this case, control for maintaining the fixing roller temperature at a predetermined fixing temperature in advance is performed based on the data stored in the nonvolatile memory.

[0003]

However, since the fixing temperature is detected by the thermistor in the method (1), the difference between the error factor in the detection and the temperature obtained by actually heating the fixing roller is determined. It has to be corrected by adjusting the volume, which is complicated. In the method (2), an error between the detected temperature of the fixing temperature measured by the thermistor and the detected temperature obtained by actually heating the fixing roller is determined by determining the fixing roller temperature based on data stored in a nonvolatile memory. Although the adjustment work becomes unnecessary by controlling the fixing temperature, there is a problem that if the CPU performing this control runs away, it is not sufficient to ensure safety. In the method (3), since the correlation between the thermistor for measuring the fixing temperature and the voltage obtained by the resistance differs depending on each fixing device, the fixing temperature measured by the thermistor is corrected or the measured value is read. It is necessary to perform correction from the software side on the reference value to be compared with.
Also, in the case of the predetermined correction from the software side, it is not possible to perform the correction on the hardware side necessary for the actual reference voltage of each fixing device, and an error occurs between the corrections of the two sides. This causes a problem of causing malfunction.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the conventional overheat prevention circuit, and when the fixing temperature is corrected on the control device side, a comparator is provided in accordance with the correction amount. Another object of the present invention is to provide a fixing temperature control device capable of reducing the possibility of malfunction of the over-temperature prevention circuit using a comparator by changing the reference voltage of the over-temperature prevention circuit using the same.

[0005]

In order to achieve the above object, according to the present invention, a relay and a switching element for controlling energization to a fixing heater and a temperature of a fixing roller are detected. A temperature detection unit, a resistor connected in series with the temperature detection unit, two resistors connected in series between the constant voltage terminals, a voltage obtained by the temperature detection unit and a resistor connected in series thereto, Voltage comparing means for comparing a voltage obtained by two resistors connected in series between constant voltage terminals, a driver for controlling application of a power supply voltage to a relay coil based on a comparison result of the voltage comparing means, and temperature detecting means And a control means for controlling on / off of the switching element and the relay according to a comparison result between a voltage obtained by a resistor connected in series with the switching element and a predetermined reference value. In the fixing temperature control device in which the reference value can be changed, at least one resistance value of two resistors connected in series between the constant voltage terminals is selectively selected according to the change amount of the reference value. It is characterized in that it can be set.

According to a second aspect of the present invention, in the first aspect of the invention, at least one of two resistors connected in series between the constant voltage terminals is provided with an electronic volume. is there.

According to a third aspect of the present invention, in the first aspect, a voltage obtained by the temperature detecting means and a resistor connected in series to the temperature detecting means and two resistors connected in series between the constant voltage terminals are provided. A gate provided by a power-on reset signal is provided between the output of the voltage comparing means for comparing the voltages obtained by the above and a driver for controlling the application of the power supply voltage to the relay coil based on the comparison result of the voltage comparing means. Is what you do.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiments shown in the drawings, the same reference numerals are given to the same parts, and the description of the common parts in each embodiment is omitted in the same manner, and mainly different parts will be described. And FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In this embodiment, reference numeral 1 denotes a fixing temperature control device. The fixing heater 2 has one end connected to a relay 4 connected via an AC power supply 3 and the other end connected to a switching element 5. In FIG. 1, a triac 6 is used as the switching element 5. The triac 6 has one end connected to the fixing heater 2 and the other end connected to the relay 4.
In addition, it is connected to the high voltage side 7-1 of the photo triac 7. The high pressure side 7-1 of this phototriac and CP
The low-voltage side 7-2 of the phototriac connected to U (not shown) is photoelectrically connected to the phototriac, and forms separate circuits from the relay coil 8 that controls the energization of the relay 4.

The voltage divided by the resistor of the thermistor 9 connected to the A / D input and the resistor 10 connected in series to the A / D input is applied to the non-inverting input terminal 12 of the comparator 11. The voltage divided by the selection resistor 15 via the transistor 14 in series with the comparator 11 is applied to the inverting input terminal 16 of the comparator 11. The output of the comparator 11 is connected to the R input terminal 18 of the SR latch 17, the reset unit 20 is connected to the S input terminal 19 of the SR latch 17, and the output of the SR latch 17 is connected to the Q terminal 21.
It is further connected to the base of the driver 22. Driver 22
The low-voltage side 7-2 of the phototriac and the relay coil 8 are connected in parallel to the emitter side, and each is connected to a CPU (not shown) of control means.

In the first embodiment having the above configuration,
Both the relay 4 and the triac 6 can turn on and off the power supply to the fixing heater 2. However, when the temperature control during the power supply is performed, the relay 4 is always on and the triac 6 is turned on and off. Phototriac low pressure side 7-
2. It is performed by the driver 22 connected to the relay coil 8. The fixing roller 23 has a built-in fixing heater 2, and a temperature detecting element for detecting the temperature is arranged near the fixing roller. Here, a thermistor 9 having a negative characteristic is used as the temperature detecting element. The voltage obtained by the voltage division of the thermistor 9 and the resistor 10 connected in series is output to the CPU and the voltage comparing means.

Next, in order to explain the operation of the fixing temperature control, items of a fixing temperature, a thermistor resistance value, a divided voltage value of the thermistor and a resistor, an A / D conversion result of the divided voltage value, and a role in control are described. Table 1 shows the correspondence between the codes. Hereinafter, description will be made using this code.

[0012]

[Table 1]

The voltage output to the CPU is first A / D converted by the CPU, and the result is compared with a predetermined reference value b. Since the thermistor 9 used here has a negative characteristic, as the temperature rises, the resistance value decreases and the divided voltage also decreases. During a period in which the fixing temperature is low and the A / D conversion result is larger than the reference value b, the fixing temperature T becomes the upper limit temperature Tb.
Since it has not reached, the photo triac 7 is turned on. When the fixing temperature rises and the A / D conversion result becomes smaller than the reference value b, the fixing temperature T has reached Tb.
Turn photo triac 7 off. When the triac 6 is turned off, the fixing temperature decreases, and the A / D conversion result becomes larger than the reference value a (a> b), the fixing temperature T becomes Ta.
The photo triac 7 is turned on again. By performing this control, the fixing temperature T
Can be controlled in the range of Ta <T <Tb.

The A / D conversion result is always compared with a reference value c (c <b) to prevent the fixing temperature from rising excessively. A
When the / D conversion result is smaller than c, the output of the relay driver 22 is turned off and the relay 4 is turned off. As a result, even if the driver 22 on the low voltage side 7-2 of the photo triac is damaged and the triac 6 becomes conductive, it is possible to prevent the fixing temperature from rising excessively. However, all of the temperature control including the above-mentioned temperature rise prevention control is C
Since the operation is performed by the PU, if the CPU runs away, the fixing temperature cannot be controlled. In order to prevent this, the comparator 11, the SR latch 17, and the driver 22 prevent the temperature from excessively rising in hardware without using software.

The divided voltage Vx obtained by dividing the voltage by the thermistor 9 and the resistor 10 is output to the non-inverting input terminal 12 of the comparator 11, and the voltage Vd divided by the resistor 13 and the selection resistor 15 is obtained. The signal is output to the inverting input terminal 16 of the comparator 11, and the two values are compared. Normally, the fixing temperature is low and Vx is higher than Vd, so that the output of the comparator 11 is "H". The reference voltage Vd is V
c> Vd is set. An SR latch 17 is connected to the next stage of the comparator 11, and the operation of the SR latch 17 is as shown in Table 2.

[0016]

[Table 2]

The output of the comparator 11 is R
A power-on reset signal, which is reset for a certain period after power-on, is input to the S input terminal 19 from the reset unit 20 to the S input terminal 19. Comparator 11
Is normally "H", and the power-on reset signal is "L" for a certain period of time after the power is turned on, and then becomes "H". Therefore, the output Q is R, immediately before R and S both become "H". “Qo = H” which is the output in the state of S.

When the relay 4 and the triac 6 are always on due to runaway of the CPU and the fixing temperature Tx becomes higher than Td, the output of the comparator 11 changes from "H" to "L". In response to this, the output of the SR latch 17 also becomes “H”, the output Q becomes “L”, the driver 22 connected to the next stage of the SR latch 17 is turned off, and the low voltage side of the relay coil 8 and the phototriac is turned off. The voltage supply to 7-2 is cut off. Even if the CPU goes out of control because the voltage supply is cut off and the relay coil 8 and the driver 22 of the low voltage side 7-2 of the phototriac are always turned on, these relays are forcibly relayed regardless of the control signal. 4. The triac 6 can be turned off. At this time, the output Q of the SR latch 17 holds the output “Qo = L” in the state of R and S immediately before both of R and S become “H”, so that the fixing temperature becomes Td.
The fixing heater 2 does not turn on unless the power-on reset signal becomes "L" even if the temperature decreases. That is, unless the power is turned off and then turned on again, the fixing heater 2 is not turned on.

A transistor is connected in series with the voltage dividing resistor 13 described above.
The selection resistor 15 connected via 14 is capable of selectively setting a resistance value. This is because, in the soft overheating prevention performed by the CPU, as shown in FIG.
Take Ta on the horizontal axis below the intersection with the line at that time,
If it is changed to → Ta ′, and similarly to Tb → Tb ′, Tc may be increased (Tc → Tc ′). Cannot be changed by the control of the CPU, the difference between Tb 'and Td becomes small, and the hardware overheat prevention means malfunctions due to noise or the like at normal times, and the fixing heater is always turned off. There is a possibility of becoming. Therefore, in the present invention, the resistor 15 can be selectively set as shown in FIG. 1, and the resistor 15-1 has the same resistance value as the resistor 15,
The resistances from the resistance 15-2 to the resistance 15-n are smaller than the resistance 15. Therefore, the resistor 15-2
If a resistor up to 15-n is selected, the reference voltage Vd can be reduced. If the fixing control temperature range is increased, Td can be changed by selecting the resistors from the resistors 15-2 to 15-n according to the amount of change, so that malfunction due to noise or the like can be prevented. .

In the second embodiment shown in FIG. 3, the selection resistor 15 of the first embodiment is replaced by an electronic volume 24, which changes the resistance value between the electronic volume terminals by a signal. Since the other operations are the same as those of the first embodiment, description thereof will be omitted.

FIG. 4 shows a third embodiment in which an AND gate 25 is provided between the SR latch 17 and the driver 22. The description of the same operations as those of the first embodiment will be omitted, and only different points will be described. The over-temperature prevention circuit using the comparator 11 is characterized in that even if the CPU goes out of control, the relay 4 and the triac 6 can be forcibly turned off because the over-temperature is detected only by hardware. However, the reference voltage corresponding to the reference temperature in the over-temperature prevention circuit using the comparator is C
When determined by the PU, it does not provide a measure against runaway of the CPU. Therefore, according to the present invention, as shown in FIG. 5, the output signal of the SR latch 17 and the power-on reset signal of
Since the power-on reset signal is "L" at the time of runaway, the input of the driver 22 becomes "L" and the relay 4 and the triac 6 are turned off.

[0022]

According to the first aspect of the present invention, there is an effect that a noise margin can be secured and a malfunction can be prevented even when the fixing set temperature is raised.

According to the second aspect of the present invention, the number of components can be reduced, the resolution can be increased, and the cost, the mounting area on the substrate, and the accuracy can be improved.

According to the third aspect of the present invention, since the heater can be forcibly turned off when the CPU goes out of control, the fixing temperature of the fixing device can be prevented from rising excessively, and the device can be prevented from being damaged.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a fixing temperature and a divided voltage value of a thermistor resistance.

FIG. 3 is a circuit diagram showing an electronic volume according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing an AND gate according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a conventional overheat prevention circuit of the same type as the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing temperature control device 2 Fixing heater 4 Relay 5 Switching element 8 Relay coil 9 Temperature detecting means 10, 13 Voltage dividing resistor 11 Comparator 20 Reset part 22 Driver 24 Electronic volume 25 Gate

Claims (3)

[Claims] 1. A relay and a switching element for controlling energization of a fixing heater, a temperature detecting means for detecting a fixing roller temperature, a resistor connected in series with the temperature detecting means, and a serial connection between a constant voltage terminal. Two connected resistors,
Voltage comparison means for comparing the voltage obtained by the temperature detection means and the resistance connected in series with the voltage obtained by the two resistances connected in series between the constant voltage terminals, and the comparison result of the voltage comparison means A driver for controlling the application of a power supply voltage to the relay coil, and a switching element and a relay are turned on and off based on a comparison result between a voltage obtained by a temperature detection unit and a resistor connected in series with a predetermined reference value. A fixing means for controlling the reference value, wherein the reference value can be set and changed, wherein at least one of two resistors connected in series between the constant voltage terminals according to the change amount of the reference value. A fixing temperature control device, characterized in that the two resistance values can be selectively set. 2. The fixing temperature control device according to claim 1, wherein an electronic volume is provided on at least one of the two resistors connected in series between the constant voltage terminals. 3. An output of voltage comparing means for comparing a voltage obtained by the temperature detecting means and a resistor connected in series with the voltage and a voltage obtained by two resistors connected in series between the constant voltage terminals; 2. The fixing temperature control device according to claim 1, wherein a gate based on a power-on reset signal is provided between a driver that controls application of a power supply voltage to the relay coil based on a comparison result of the voltage comparison unit.