JPH1145026A - Fixing-temperature controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing-temperature controller which reduces the possibility of malfunction of a comparator-using excessive-temperature-increase- prevention circuit by altering the reference value of the comparator-using excessive-temperature-increase-prevention circuit according to an amount of correction in the case a fixing temperature is corrected by the controller. SOLUTION: A relay 4 is controlled through the relay 4 and switching element 5 for controlling the energization of a fixing heater 2, a detection means 9 for detecting the temperature of a fixing roller, and a comparison means 11 for comparing the comparison voltage of a resistor 10 connected to the detection means 9 in series with a reference voltage obtained by two resistors 13 and 15 in series. Using the fixing-temperature controller 1 which compares the comparison voltage with the predetermined reference value and controls the switching element 5 and relay 4, voltages which are applied to the resistors are selectively set according to the amount of the alteration of the reference value.

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]

2. Description of the Related Art Conventionally, a fixing temperature control device of a copying machine of this type has been provided with an excessive temperature rise prevention device for preventing smoke, ignition and the like of a fixing portion. One of them is (1) that detects an excessive temperature rise using a comparator 11 as shown in FIG. This is achieved by comparing the resistance value of the thermistor 9 having a negative characteristic with the divided voltage of the resistor 10 connected in series with the reference voltage obtained by the divided voltage of the two resistors 13 and 15 by the comparator 11. As a result, 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 relay coil 8, which controls the energization to the fixing heater, The transistor 22 that controls the voltage supply to the photo triac 7 is turned off, and the relay coil 8
No voltage is supplied to the phototriac 7, the relay 4 and the triac 6, which are magnetically coupled to the relay coil 8, are turned off, and the power to the fixing heater 2 is stopped. (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) Next, a circuit in which a control circuit using a control element such as a CPU is added to the over-temperature prevention circuit using a comparator based on data stored in a non-volatile memory in order to perform software-based control. A fixing temperature control circuit for maintaining the fixing roller temperature at a predetermined fixing temperature in advance based on software control will be considered.

[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 resistor connected in series to the temperature detecting means, two resistors, a resistor on the voltage source side and a resistor on the ground side, connected in series between the terminals of the voltage source; Voltage comparing means for comparing the voltage obtained by the resistor with the voltage obtained by the two resistors connected in series between the terminals of the voltage source; and applying the power supply voltage to the relay coil based on the comparison result of the voltage comparing means. Controls on / off of the switching element and the relay based on a comparison result between a driver to be controlled, a voltage obtained by the temperature detecting means and a resistor connected in series thereto, and a predetermined reference value. The fixing temperature control device, wherein the reference value can be set and changed, a plurality of the voltage sources are installed, and the resistance of the voltage source side connected in series according to the change amount of the reference value. A voltage to be applied to two resistors, a resistor on the ground side and a resistor on the ground side, can be selectively set from the voltage sources.

According to a second aspect of the present invention, there is provided a relay and a switching element for controlling energization of a fixing heater, a resistor connected in series to a temperature detecting means for detecting a fixing roller temperature, and a series connection between terminals of a current source. And a resistor connected in series between a terminal of a current source and a voltage obtained by a temperature detecting means and a resistor connected in series to the two resistors, a resistor on the current source side and a resistor on the ground side. Voltage comparison means for comparing the voltages obtained by the two resistors, a driver for controlling the application of the power supply voltage to the relay coil based on the comparison result of the voltage comparison means, and temperature detection means and a resistor connected in series with the driver. A fixing device for controlling the on / off of the switching element and the relay based on a comparison result between the voltage and a predetermined reference value, wherein the reference value can be set and changed; In the degree control device, a plurality of the current sources are provided, and a current flowing through two resistors, a current source-side resistor and a ground-side resistor, connected in series according to a change amount of a reference value, is supplied to the current source. And a configuration that can be selectively set from the following.

According to a third aspect of the present invention, in the first or second aspect, a gate based on a power-on reset signal is provided between the voltage comparison means and a driver for controlling the application of a power supply voltage to the relay coil. It is characterized by having been provided.

[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 resistors 13 and 15 connected in series 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 supplied from the Q terminal 21 to the base of the driver 22. It is connected to the. The low-voltage side 7-2 of the phototriac and the relay coil 8 are connected in parallel to the emitter side of the driver 22.
(Not shown).

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 does not reach the fixing target temperature upper limit Tb.
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 reaches the fixing target temperature upper limit Tb, so that the phototriac 7 is turned 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 has decreased to the fixing target temperature lower limit Ta. The photo triac 7 is turned on. By performing this control, the fixing temperature T is set to Ta <T.
It can be controlled in the range of <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 fixing high temperature abnormal reference value (divided by the resistors 13 and 15) Hard) The voltage Vd 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 the divided voltage Vx is higher than the fixing high temperature abnormality reference value (hard) voltage Vd, so that the output of the comparator 11 is “H”. The relationship between the reference value voltage Vd and the fixing high temperature abnormality reference value (soft) Vc is set to Vc> Vd. 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 turned on due to runaway of the CPU and the fixing temperature T becomes higher than the fixing high temperature abnormality reference value (hard) Td, the comparator 11
Changes from “H” to “L”. In response to this
The output of the R 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 relay coil 8 and the low voltage side 7-2 of the phototriac are connected. Is shut 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. The output Q of the SR latch 17 at this time is the output “Qo = Qo = R0” in the state of R and S immediately before both R and S become “H”.
Therefore, even if the fixing temperature T falls below the fixing high temperature abnormality reference value (hard) Td, the fixing heater 2 is not turned on unless the power-on reset signal becomes "L". In other words, unless you turn the power off and on again,
The fixing heater 2 will not be turned on.

In this embodiment, the resistors 15 and 13 described above are used.
Transistors 14 connected in series to 14-1, 14-2,
14-n so that the voltage applied to the resistors 13 and 15 can be selectively set. In the soft overheating prevention performed by the CPU, the vertical axis indicates the partial pressure value Va at the lower limit of the fixing target temperature, as shown in FIG. When the fixing temperature Ta is taken on the horizontal axis below the intersection with and the temperature is changed from Ta to Ta ', and similarly, when the fixing temperature is changed from Tb to Tb',
The fixing temperature Tc may be increased (Tc → Tc ′). However, in order to prevent the hardware from excessively rising, the fixing high temperature abnormal reference value (hard) Td is determined by the resistance 13 and the resistance 15, so that the CPU control is performed. Cannot be changed by T
The difference between b ′ and the fixing high temperature abnormality reference value (hard) Td becomes small, and the hardware-based excessive temperature rise prevention means malfunctions due to noise or the like at normal times, and the fixing heater may be always turned off. Therefore, in the present invention, the voltage applied to the resistors 13 and 15 for producing the reference voltage is V, and
Transistor 14 connected in series with 13 is connected to 14-1, 14-
2, 14-n, and the respective voltage sources corresponding to the respective transistors can be selectively set as V-1, V-2, V-n. The same voltage value as the voltage V applied to the resistors 13 and 15 for generating the reference voltage is used, and the voltage from the voltage source V-2 to the voltage source V-n is
The value is smaller than the voltage source V-1. Therefore, if a voltage source from the voltage source V-2 to the voltage source Vn is selected, the reference voltage Vd can be reduced. If the fixing control temperature range is increased, the fixing high temperature abnormal reference value (hard) Td is selected by selecting a voltage source from the voltage source V-2 to the voltage source V-n according to the amount of change. Since it can be changed, malfunction due to noise or the like can be prevented.

In the second embodiment shown in FIG. 3, the current sources I-1 to In can be selectively set instead of the voltage sources V-1 to V-n of the first embodiment. Things. Therefore, in the present invention, the current flowing through the resistors 13 and 15 for generating the reference voltage is defined as I, and the transistors 14 connected in series to the resistor 13 as shown in FIG. , And the respective current sources corresponding to the respective transistors can be selectively set as I-1, I-2, In, so that the current source I-1 is used to generate a reference voltage. Resistance 1
The current value of the current source I−
The current from 2 to the current source In is set to a value smaller than the current source I-1. Therefore, if the current sources from the current sources I-2 to In are selected, the reference voltage Vd can be reduced. If the fixing control temperature range is increased, the fixing high temperature abnormality reference value (hard) Td is also selected by selecting the current sources from the current sources I-2 to In according to the amount of change. Since it can be changed, malfunction due to noise or the like can be prevented, and a plurality of voltage sources are not required, which contributes to downsizing of the device. Other operations are the same as those of the first embodiment, and the description is omitted.

In the third embodiment, an AND gate 24 shown in FIG. 4 is provided between the SR latch 17 and the driver 22 of the first embodiment shown in FIG.
21 and the input terminal 25 of the AND gate,
20 and the S input terminal 19 of the SR latch 17 are connected to the input terminal 26 of the AND gate, and the output terminal 27 is connected to the base side of the driver 22. Here, the same operations as those of the first embodiment will not be described, 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, when the CPU determines the reference voltage corresponding to the reference temperature in the over-temperature prevention circuit using the comparator, it does not provide a measure against runaway of the CPU. Therefore, in the present invention, the output signal of the SR latch 17 and the power-on reset signal of the reset unit 20 are input to the AND gate 24 as shown in FIG. 4, so that the power-on reset signal is "L" when the CPU goes out of control. Therefore, the input of the driver 22 becomes "L", and the relay 4 and the triac 6 are turned off, so that even when the CPU goes out of control, the fixing temperature can be prevented from rising excessively and the equipment can be prevented from being damaged.

In the fourth embodiment, the output terminal of the comparator 11 of the second embodiment shown in FIG. 3 is provided with an AND gate 24 shown in FIG. 4, and the output terminal of the comparator 11 is connected to the R input terminal 18 of the SR latch 17. , The Q terminal 21 of the SR latch 17 is connected to the input terminal 25 of the AND gate 24, and the S input terminal 19 and the reset unit 20 of the SR latch 17 are connected to the input terminal of the AND gate.
26, and the output terminal 27 is connected to the base side of the driver 22. The operation is the same as in the third embodiment, and a description thereof will be omitted.

[0023]

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.

The second aspect of the present invention eliminates the need for a plurality of voltage sources, and has the effect of reducing the number of parts and reducing the size and cost of the device.

According to the third aspect of the present invention, since the heater can be forcibly turned off when the CPU runs away, an excessive rise in the fixing temperature of the fixing device can be prevented, 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 a constant current source according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing an AND gate according to third and fourth embodiments 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 element 10, 13, 15 Resistance 11 Comparator 20 Reset part 22 Driver 24 Gate

Claims (3)

[Claims] 1. A voltage source connected in series between a relay and a switching element for controlling energization of a fixing heater, a resistor connected in series to temperature detecting means for detecting a fixing roller temperature, and a terminal of a voltage source. And a resistor on the ground side, a voltage obtained by a temperature detecting means and a resistor connected in series with the temperature detecting means, and the two resistors connected in series between terminals of a voltage source. A voltage comparison unit that compares the voltage to be applied to the relay coil, and a driver that controls application of a power supply voltage to the relay coil based on a comparison result of the voltage comparison unit.
Control means for controlling on / off of the switching element and the relay based on a comparison result between the temperature detection means and a voltage obtained by a resistor connected in series thereto and a predetermined reference value, wherein the reference value is set. In the fixing temperature control device that can be changed, a plurality of the voltage sources are provided, and two resistors, a resistor on the voltage source side and a resistor on the ground side, which are connected in series to the voltage source according to the amount of change of the reference value. A fixing temperature control device, wherein a voltage applied to a resistor can be selectively set from among the voltage sources. 2. A current source connected in series between a relay and a switching element for controlling energization of a fixing heater, a resistor connected in series to a temperature detecting means for detecting a fixing roller temperature, and a terminal of the current source. And a ground-side resistor, a voltage obtained by a temperature detecting means and a resistor connected in series with the temperature detecting means, and a voltage obtained by the two resistors connected in series between terminals of a current source. A voltage comparing means for comparing the voltage with the voltage, 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, and a voltage obtained by the temperature detecting means and a resistor connected in series with the temperature detecting means. A fixing unit that controls on / off of the switching element and the relay according to the comparison result with the reference value, and the reference value is settable and changeable. A plurality of the current sources are installed, and a current flowing through two resistors, a current source-side resistor and a ground-side resistor, connected in series to the current source according to the amount of change in the reference value is supplied to the current source. A fixing temperature control device characterized in that the fixing temperature control device can be selectively set from the following. 3. The fixing temperature according to claim 1, wherein a gate based on a power-on reset signal is provided between the voltage comparison unit and a driver that controls application of a power supply voltage to the relay coil. Control device.