JP2636231B2 - Fixing unit temperature controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature control device for a fixing device.

2. Description of the Related Art A conventional electrophotographic copying machine is provided with a fixing roller having a heating roller having a built-in heat source and a fixing device having a temperature sensor installed near the heating roller. It is kept constant by controlling the power applied to the heat source. However, when an element such as a thermistor is used for the temperature sensor, the thermistor has a high resistance at a low temperature, and it is difficult to detect whether or not the thermistor is disconnected. Therefore, an amplifier circuit such as a transistor and an operational amplifier is provided to amplify the output value of the temperature sensor, so that the output value of the temperature sensor at a low temperature can also be detected so that the disconnection of the temperature sensor can be detected.

Problems to be Solved by the Invention In the configuration as described above, an amplifier circuit such as an operational amplifier or a transistor is required to detect disconnection or abnormality of the temperature sensor, which increases the size and complexity of the device and increases the cost. Had disadvantages.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a fixing device temperature control device that detects an abnormality of a temperature sensor with a simple configuration and prevents overheating of the fixing device.

Means for Solving the Problems In order to solve the above problems, a temperature control device of a fixing device of the present invention reads a temperature sensor installed near a heating roller having a built-in heat source and an output value of the temperature sensor. Output detection means, and storage means for storing abnormality detection information when the temperature sensor detects an abnormality, and turns on the heat source for a certain period of time in an initial state, and then the output value of the temperature sensor becomes a value at the time of the fixing temperature. If not reached, or if the output value of the temperature sensor has changed from the value at the time of fixing temperature during temperature control, it is determined that the temperature sensor is abnormal, and the heat source is immediately turned off. It is provided with a configuration for storing the abnormality detection information of the temperature sensor and keeping the storage for a certain period of time.

Function The present invention, with the above-described configuration, turns off the heat source as soon as an abnormality of the temperature sensor is detected, and prevents the heat source from being turned on by an operation such as turning on the power again and turning on the door switch within a certain period of time. .

Example An example of the present invention will be described below. First, each circuit element in FIG. 1 will be described.

Reference numeral 1 denotes a heat source built in a heating roller of the fixing device. Reference numeral 2 denotes a temperature sensor element installed near the heat source 1, and in this embodiment, a thermistor is used. 3 is a resistor that with serially to a constant voltage V _CC and the thermistor 2 to replace the resistance value that varies in accordance with a change in temperature of the thermistor 2 to the voltage change. Reference numeral 4 denotes a warm-up timer which starts operating when the power is turned on, outputs "H" for a certain period of time, and outputs "L" otherwise. Reset terminal ▲ ▼
When “L” is set to “L”, an initial state is set.

5 is a power switch, 6 is a door switch attached to the door of the copier body, and 6 is normally on. Reference numeral 7 denotes an AND circuit that outputs "H" regardless of the value of the temperature detection signal _vTH of the thermistor 2 while the warm-up timer 4 outputs "H", and the warm-up timer 4 outputs "L". Sometimes the value of v _TH is output as it is. However, this "H" output value is lower than V _CC . 8 a heat source on a temperature control circuit for turning off controlled according to the temperature detection signal v _TH fuser temperature within a certain value (usually 200 ° C. so) thermistor 2 so as to become the value of v _TH at the set temperature (the 2
When a value lower than V _O ) is input, “H” is output, and when a higher value is input, “L” is output.

Reference numeral 9 denotes an abnormality detection circuit that outputs “H” when the output of the AND circuit 7 is at the value of V _CC and normally outputs “L”.
Numeral 10 outputs a short pulse of “H” when the output of the abnormality detection circuit 9 changes from “L” to “H”, counts a certain time from that point, and outputs a short pulse of “L” after a certain time Timer. Reference numeral 11 denotes a storage element, which uses a rewritable 1-bit memory called a RAM, which stores "0" when "L" is input and stores "1" when "H" is input. Then, the previous state is kept stored as long as the input does not change. When the reset terminal ▲ ▼ is set to “L”, “0” is forcibly stored. Reference numeral 12 denotes a battery for backing up the storage of the storage element 11 so as not to be cleared when the power is turned off.

An OR circuit 13 outputs "H" if either the temperature control circuit 8 or the storage element 11 is "H", and outputs "L" only when both 8 and 10 are "L". 14 is a solid state relay, and when the OR circuit 13 becomes “L”, the heat source 1 is energized.
When 13 is "H", the heat source 1 is shut off. Fifteen
Is a key for resetting the warm-up timer 4 and the storage element 11.

Next, the circuit operation of FIG. 1 will be described. The power switch 5 is turned on, the warm-up timer 4 when starting energization starts operating, warm-up time to W _E of FIG. 2 outputs "H" until passage to the AND circuit 7. AND circuit 7
Is “H” lower than V _CC so as not to activate the abnormality detection circuit
A signal is output and input to the temperature control circuit 8. 8 outputs "L", and since the timer 10 and the memory element 11 are not operating, the OR circuit 13 outputs "L" because the output is "L" and the solid state relay 14 is turned on. Turn on. As a result, the temperature inside the fixing unit gradually increases within the range of W as shown in FIG. 2, the resistance value of the thermistor 2 decreases, and v _TH
Also gradually declines. The warm-up time W is determined as the time required from turning on the heat source 1 when the temperature inside the fixing device is normal temperature to reaching the set temperature T _O. Now the warm-up timer 4 is to output "H" at the time of the W _E AND circuit 7 outputs a value of v _TH, coercive fuser temperature inside the set temperature T _O by a temperature control circuit 8 Control the temperature so that it drip. When the temperature inside the fuser at power-on is about room temperature, the resistance value of the thermistor is very large, several hundred kΩ.
Therefore, v _TH becomes almost equal to V _CC , and unless the warm-up timer 4 and the AND circuit 7 are used, the abnormality detection circuit 9 operates even in a normal state. To prevent this, the warm-up timer 4 is activated when the power is turned on.
An “H” lower than V _CC is output from the AND circuit 7 to forcibly turn on the heat source 1 so that the abnormality detection circuit 9 does not operate, and v _TH
The temperature control is performed after the value of has become low.

If the thermistor 2 suddenly breaks during the temperature control operation for some reason, and if it breaks at the point of E _O in FIG. 2, the value of v _TH suddenly becomes the value of V _CC . Then AND circuit 7
Outputs _Vcc , the abnormality detection circuit 9 operates, outputs "H" to the timer 10, the timer 10 outputs "H", the storage element 11 stores "1", and outputs "H". Then, the OR circuit 13 outputs “H” and the heat source 1 is turned off. When the time of F _T has elapsed, the timer 10 outputs “L” again, so that the storage element 11 stores “0”, outputs “L”, and the temperature control operation can be performed again. If the thermistor disconnection remains, the abnormality detection circuit 9 operates again, and the heat source 1 continues to be turned off. The OFF time _FT is determined when the temperature inside the fixing unit is reduced when the heat source 1 is turned on again.
The natural cooling time is set until the temperature does not exceed T _O, and if it is too long, the work efficiency will deteriorate, so it is set to about 10 minutes.

If Toka Without storage element 11 and the battery 12 thermistor 2 is immediately after disconnection, for example, and immediately turned on again when the power is turned off, including the constant voltage V _CC of the circuit at the time of the E _S of FIG. 2, or the power supply If a power failure occurs momentarily, the circuit will be in the initial state, so that the heat source 1 continues to be turned on during the warm-up W, so that the temperature inside the fixing device becomes higher than T _O and the fixing device is burned. Therefore, after detecting the thermistor disconnection abnormality, the information is stored, and the heat source 1 is forcibly turned off while storing the information for a certain period of time.

Further, even if the thermistor 2 is disconnected before the power is turned on, the heat source 1 is turned on during the warm-up time, but immediately after that, the abnormality detection circuit 9 is operated to turn off the heat source 1, so that the temperature in the fixing device is higher than T _O. It is not going to be high.

Further, key 15 is used for warm-up timer 4 and storage element
As the timer 10 can again turn on the heat source without waiting for a predetermined time F _T by force the circuit to the initial state by turning the key 15 even during operation by second only to 11 ▲ ▼ ing.

Effects of the Invention As described in detail above, according to the present invention, it is possible to prevent the fixing heater from being overheated and damaged regardless of the state of the thermistor of the temperature sensor. In addition, if the power is turned off after the thermistor disconnection is detected or the power is turned off after an instantaneous power failure or the like, and the power is turned on again, the fixing heater may continue to be turned on even if the temperature inside the fixing unit is high. Can be prevented.

Further, after detecting the fixing heater unit abnormality, if the cause such as thermistor disconnection is removed, the abnormality detection is automatically canceled after a certain period of time, so that the normal state is restored without performing any troublesome operation.

Further, the state of the fixing heater unit abnormality detection can be canceled by simply pressing a predetermined key without waiting for the predetermined time, so that a waste of time can be eliminated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a temperature control device for a fixing device of the present invention, and FIG. 2 is a graph showing a change in temperature in the fixing device and a change in a temperature detection signal _vTH of a temperature sensor. . 1 ... heat source, 2 ... thermistor, 3 ... resistance, 4 ... warm-up timer, 5 ... power switch, 6 ... door switch, 7 ... AND circuit, 8 ... temperature control circuit,
9: Abnormality detection circuit, 10: Timer, 11: Storage element, 12: Battery, 13: OR circuit, 14: Solid state relay, 15: Key.

Claims (1)

(57) [Claims] A temperature sensor installed near a heating roller having a heat source; output detection means for reading an output value of the temperature sensor; and storage means for storing abnormality detection information when abnormality of the temperature sensor is detected. When the heat source is turned on for a certain period of time in the initial state, and then the output value of the temperature sensor does not reach the value at the time of the fixing temperature, or the output value of the temperature sensor at the time of temperature control changes from the value at the fixing temperature. Control means for turning off the heat source and storing the abnormality detection information of the temperature sensor by the storage means, the control means automatically turning off the heat source after a lapse of a certain time after turning off the heat source. Resetting the abnormality detection information of the temperature sensor stored by means and turning on the heat source again.