JPH01229280A - Temperature control circuit for heat fixing device - Google Patents

Abstract

PURPOSE:To perform efficient temperature control by providing three high, intermediate, and low stages of reference temperature, and selecting the high or intermediate reference temperature according to whether the detected temperature of a temperature sensor is high or not and then driving the heat fixing device. CONSTITUTION:Comparators 6a-6c input reference voltages corresponding to the three stages Ta-Tc of reference temperature (Ta>Tb>Tc). A FF 13 opens a gate 12b when a comparison result indicating that the detected temperature of the thermistor 1 is lower than the temperature Tc from the comparator 6c is obtained. A SSR 8, therefore, inputs the outputs of the comparator 6c through the gate 12b and performs on-off control at the temperature Tb. When a comparison result of the comparator 6a which indicates that the detected temperature of the thermistor 1 reaches the temperature Ta is obtained, the FF 13 opens the gate 12a and performs on-off control at the temperature Ta. Consequently, temperature control which has an extremely small overshoot at the time of a temperature rise is realized.

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a temperature control circuit for a heat fixing device for preventing accidents such as damage to the heat fixing device due to overheating. (Prior art) For example, in a recording device that performs recording using an electrophotographic recording method, the temperature of the thermal fixing device that thermally fixes the toner image transferred to the recording paper in the transfer process in the fixing process falls within a certain range. Generally, a temperature control circuit is provided to control the temperature. FIG. 3 is a circuit diagram showing a depiction of the temperature control circuit of this type of conventional thermally constant F4 device, in which 1 is a thermistor, 2.3.4
．． 5 is a resistor, 6 is a comparator, 7 is an inverter, 8 is a solid state relay (hereinafter referred to as SSR), 9
9 is a heat fixing device, 9a is a heater, 10 is an AC power source, and 11 is a temperature sensor. In FIG. 3, the thermistor 1 is for detecting the temperature of the thermal fixing device 9, and is disposed in the vicinity thereof. In actual operation, the temperature of the thermal fixing device 9 is detected as a voltage change of the thermistor 1, and this voltage change is divided by the resistor 2 and inputted to the comparison value input (-) terminal of the comparator 6. . On the other hand, a predetermined voltage corresponding to a set temperature, for example Ta, is inputted to the reference value human power (10) terminal of the comparator 6 by dividing the voltage between the resistors 3 and 4. Next, the comparator 6 detects whether the temperature detected by the thermistor 1 is higher than the set temperature Ta by comparing the corresponding voltages. The output of the comparator 6 corresponding to this comparison result is input to the SSR8 through the inverter 7. Here, 5SR8 is an AC converter for the output of comparator 6 when the temperature detected by thermistor 1 is lower than the set temperature Ta.
It operates to energize the heater 9a of the thermal fixing device 9 from the power source 10. On the other hand, 5SR8 stops the power supply from the AC voltage source 10 to the heater 9a of the thermal fixing device 9 in response to the output of the comparator 6 when the temperature detected by the thermistor 1 is higher than the set temperature Ta. Operate. In this way, by turning the drive of the heat fixing device 9 ON and OFF depending on whether the humidity of the heat fixing device 9 exceeds the set temperature Ta, it is possible to prevent accidents such as scratches on the heater 9a due to overheating. can. Here, the resistor 5 is a resistor to provide a hysteresis characteristic to the operation of the comparator 6 related to ON/OFF control of the heat fixing device 9, and the temperature heater 11 runs M despite the above-mentioned temperature control. Heater 9a
The heat fixing device 9 is operated to protect the thermal fixing device 9 by forcibly stopping the power supply to the heat fixing device 9. As a result of such control, when the temperature of the heat fixer 9 suddenly changes from normal temperature, such as when starting up the heat fixer 9, the drive of the heat fixer 9 should be turned off at the set temperature -ra. However, in actual operation, the temperature of the thermal fixing device 9 is turned off after the temperature of the thermal fixing device 9 rises considerably above the set temperature Ta due to the operation delay of the thermistor 1 and the thermal fixing device 9. This situation can be seen in the temperature characteristic diagram of FIG. 4 regarding control described in section 2.
The difference between the temperatures F and T0 is shown by the extremely large Operjou 1 to T0. This kind of phenomenon called overcrowding 1~ becomes more pronounced as the start-up operation of the thermal fixing device (temperature rise of the thermal fixing device 9) is steeper, and it may shorten the life of the thermal fixing device 9 or cause the temperature fuse to rise. This has an unfavorable effect on temperature control by causing the 11 to malfunction. In addition, as part of measures to eliminate this effect, in order to prevent malfunction of the temperature fuse 11, it is necessary to set its operating temperature higher by the amount of overage coating, which reduces the safety of the thermal fixing device. Even the inconvenience is inno [
I decided to issue it. (Problem to be Solved by the Invention) As described above, in the temperature control circuit of the conventional heat fixing device, the ON/OFF control of the heat fixing device is controlled by one setting - I&
- Since the process was performed using temperature, the

[Due to sudden temperature changes in the heat fixing device, an overage coat occurs that causes a large difference between the temperature and the set temperature.
The problem is that it is not possible to perform temperature control efficiently enough to reliably protect the thermal fixing device, such as shortening the life of the thermal fixing device, malfunctioning of the temperature fuse, or reducing safety. was there. The present invention has been made in view of the above-mentioned circumstances, and is an object of the present invention to reduce as much as possible the overshoot that occurs when the temperature of the heat fixing device suddenly changes when the heat fixing device starts operating, and to reliably protect the heat fixing device. It is an object of the present invention to provide a temperature control circuit for a heat fixing device that can perform sufficiently efficient temperature control. [Structure of the Invention] (Means for Solving the Problems) The temperature control circuit of the heat fixing device of the present invention includes a temperature sensor that detects the temperature of the heat fixing device, and a comparison between the detected temperature of the temperature sensor and a reference temperature. a drive control section -C)- that controls the drive of the heat fixing device based on the result; a first temperature setting means that sets a first reference temperature to be given to the drive control section; - a second temperature setting means for setting a second reference temperature lower than the first reference temperature to be set for the second temperature; and a third reference temperature lower than the first temperature for the second temperature. , the detected temperature of the temperature sensor day no is the third group? the first group or the second group depending on whether the temperature is higher than the It temperature or not? The reference temperature selection means is configured to selectively set one of the back It temperatures to the drive control section. (Function) The temperature control circuit of the heat fixing device of the present invention appropriately controls the actual temperature of the heat fixing device detected by the temperature sensor when there is a sudden temperature change in the heat fixing device when the heat fixing device starts operating. A second reference temperature that is lower than the first reference humidity Jζ between the set third sub-temperature and the first reference temperature to be used for temperature control after operation stabilization is set as the set temperature. The above objective is achieved by controlling the temperature in advance by turning off the drive of the heat fixing device in anticipation of an overheating period of 1 to 10 minutes. (Example) Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of the temperature control circuit of the heat fixing device according to the present invention, and the conventional heat fixing device shown in FIG. ? Components of the M4 component of the temperature control circuit of the apparatus and those that perform the same functions are designated by the same reference numerals (J l.). d) New configuration for the temperature control circuit of the heat fixing apparatus of the present invention A comparator 6a is connected between the thermistor 1 and 5SR8 via an inverter 7a1 and a gate 12a. Similarly, the comparator 6b is connected between the thermistor 1 and 5SR8 via the inverter 7b and the gate 12b. Further, the comparator 6c is connected to the flip-flop 13 via an inverter 7c.
The Q and σ output terminals of No. 3 are connected to the gate 12a and Goo 1 to 12b, respectively. Further, the output of the inverter 7a is connected to the clock input terminal 9;1: of the flip-flop 13 via an OR gate 14, and a monomultivibrator 15 is connected to the other input terminal of this OR gate 1-14. There is. This seven-normal voltage vibrator 15 is provided to generate a signal for optimizing the output of the flip-flop 13 upon power-on. Note that resistors 3a and 4a, resistors 3b and 4b, and resistors 3C and 4C are connected to the reference value input (+) terminals of each of the aforementioned comparators 6a, 6b, and 6c, respectively. The reference voltage determined by the voltage is manually determined. This reference voltage is at the reference temperature T a shown in FIG. The comparators 6a, 6b, and 6c are set to have larger values in the order of Tb and Tc, respectively. Further, a resistor 5 is connected between the reference value human power (10) terminal and the output of each of the comparators 6a, 6b, and 6c.
A, 5b, and 5c are hysteresis resistors that perform the same function as the resistor 5 in the conventional circuit. Next, the operation of the temperature control circuit of this heat fixing device will be described in detail. First, the electric ratio detected by the thermistor 1 corresponding to the temperature of the thermal fixing device 9 is divided by the resistor 2 and inputted to the comparison value input (-) terminals of the comparators 6a, 6b, and 6c, respectively. Here each of these comparators 6a, 6b. Input basic value of 6C (+)! ! For the i5i child, the resistors 3a and 4a, the resistors 3b and 4b, and
Reference temperature Ta determined by the partial pressure between resistors 3C and 4C
, Tb, Tc (Ta>Tb>1'-c) are input. Of these, the comparator 6a detects whether or not the detected temperature of the Mr. 1 is higher than the reference temperature Ta by comparing the corresponding voltages, and outputs the comparison result to the 5SR8 through the inverter 7a. Similarly, the comparator 6b determines whether the temperature detected by the thermistor 1 is 1. Whether or not the temperature is higher than -[b is detected by comparing the corresponding voltages, and the comparison result is output to 5SR8 through inverter 7b. Further, the comparator 6C detects whether the temperature detected by the thermistor 1 is higher than the reference temperature TcJ by comparing the corresponding voltages, and outputs the comparison result to the flip-flop 13 through the inverter 7C. do. Then, based on this output, the flip-flop 13 generates an output Q and a strawberry between either of the goo h12aA3 and the goo1-12b. That is, here, the flip-flop 13 is operated by the comparator 6C according to the predetermined operating conditions →)--
As long as the comparison result that the detected temperature of Mister 1 is lower than the reference temperature C is selected, the control operates to open the gate 12b. Therefore, at this time, the output of the comparator 6b is input to the 5SR8 through the Moeki games 1 to 12b. As a result, the 5SR8 energizes the heater 9a of the thermal fixing device 9 from the AC power source 10 when the temperature detected by the thermistor 1 is lower than the reference temperature Tb based on the comparison result of the comparator 6b; When the detected temperature i becomes higher than the base culm temperature -2b, the AC power source 10 is operated to stop supplying electricity to the heater 9a of the thermal fixing device 9. On the other hand, the temperature detected by the thermistor 1 is changed to the +-temperature T by the 2] temperature sensor 6C.
temperature is higher than c, and =] temperature is increased by temperature °
When the comparison result indicating that Ia has been reached is 1q, it operates to perform control between Goo 1 and 12a. Therefore, at this time, the output of the comparator 6a is input to 5SR8 through the gate 12a. Accordingly, based on the comparison result of the comparator 6a, when the temperature detected by the thermistor 1 is lower than the base temperature Ta, the 5SR8 outputs a signal from the AC power source 10 to the heater 9a of the heat stabilizer 9.
On the contrary, when the temperature detected by the thermistor 1 becomes higher than the reference temperature Ta, the AC power supply 10 stops supplying power to the heater 9a of the thermal fixing device 9. As a result of such control, if the temperature of the thermal fixing device 9 suddenly changes from normal temperature, such as when the thermal fixing device starts operating, and the temperature detected by the thermistor 1 is lower than the reference temperature TCJζ, this thermal fixing device 9 is controlled to turn ON and OFF based on the reference temperature Tb, which is lower than temperature a, and only when the temperature detected by the thermistor 1 becomes n than the reference temperature Tc and reaches temperature Ta. The drive of the heat fixing device 9 is controlled to be turned on and off based on the base temperature Ta. Therefore, when the heat fixing device starts operating, the temperature of the heat fixing device 9 is If the reference temperatures Tc and Tb are set appropriately by taking into consideration the operation delay of the heat fixing device 9 and thermistor 1, etc., the target control temperature is 1 degree. Temperature control with very little overshoot 1~ can be realized. Figure 2 shows a temperature characteristic diagram regarding temperature control in the temperature control circuit of the heat fixing device of the present invention. At the stage where the reference temperature Ta is first set via the reference humidity Tb, the overshoot has already been removed, and the temperature continues to change stably thereafter. Although only an example of control using three reference temperatures has been described in order to prevent overshoot of the control temperature when increasing the temperature, it is of course possible to prepare more reference temperatures and perform more fine-grained temperature control. [Effects of the Invention] As explained above, according to the temperature control circuit of the heat fixing device of the present invention, the actual temperature of the heat fixing device can be adjusted even when the temperature of the heat fixing device changes suddenly when the heat fixing device starts operating. By setting the reference temperature lower than the reference temperature as the set temperature and turning off the drive of the thermal fixing device until the temperature reaches the reference temperature that should be used for temperature control after the operation has stabilized, the over-secondary temperature can be set in advance for 1 minute. Since temperature control is performed in advance, overshoeing, which can shorten the life of the heat fuser, cause malfunction of the temperature sensor, or reduce safety, can be minimized. The superior advantage of being able to provide efficient temperature control sufficient to reliably protect the fusing device is annoying.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the temperature control circuit of the heat fixing device according to the present invention, and FIG. 2 shows an example of the control temperature characteristics of the heat fixing device by the temperature control circuit of the heat fixing device of the present invention. FIG. 3 is a circuit diagram showing the configuration of a temperature control circuit of a conventional heat fixing device, and FIG. 4 shows an example of control temperature characteristics of the heat fixing device by the temperature control circuit of a conventional heat fixing device. It is a diagram. 1...Thermistor, 2, 3, 4.3a~3c, 4a~
4C...Resistance, 5,5a~5c...Hysterosis resistance, 6.6a~6c...Comparator, 7,7a~
7C...Inverter, 8...Solid stay 1~Relay (SSR), 9-Heat fixing device, 9-a/e-Even, 1
0... AC power supply, 11... Temperature hikozu, 12a. 12b...Gate, 13...Flip-flop, 1
4...OR gate, 15...Monomal Divibrator representative patent attorney Nori Chika Yushu Yamashita -

Claims (1)

[Scope of Claims] A temperature sensor that detects the temperature of a heat fixing device, a drive control unit that controls driving of the heat fixing device based on a comparison result between the temperature detected by the temperature sensor and a reference temperature, and the drive. a first temperature setting means for setting a first reference temperature to be given to the control section; and a second temperature setting means for setting a second reference temperature lower than the first reference temperature to be given to the drive control section. temperature setting means, and a third reference temperature lower than the second reference temperature, and the temperature setting means has a third reference temperature lower than the second reference temperature, and the first or the third reference temperature is determined depending on whether the detected temperature of the temperature sensor is higher than the third reference temperature. 1. A temperature control circuit for a thermal fixing device, comprising: reference temperature selection means for selectively applying one of two reference temperatures to the drive control section.