JPS63212976A - Temperature controller for fixing device - Google Patents

Abstract

PURPOSE:To prevent a fixing device from being overheated, by storing abnormality detecting information, when the abnormality of a temperature sensor is detected. CONSTITUTION:When a power source switch 5 is turned on, and power conduction is started, a warm-up timer 4 starts its operation, and until the warm-up time elapses, a 'H' signal is outputted to an AND circuit 7. The circuit 7 outputs a 'H' signal so as not to operate an abnormality detecting circuit, and inputs it to a temperature control circuit 8. The circuit 8 outputs a 'L' signal. In this case, since a timer 10 and a storage element 11 are not operating, an OR circuit 13 outputs 'L', and a solid-state relay 14 becomes on, therefore, a heat source 1 becomes on. Subsequently, when the abnormality of a temperature sensor is detected, the heat source 1 is turned off quickly, so that the heat source 1 is not turned on even by an operation such as returning-on etc. of the switch 5 and a door switch 6. Also, after the abnormality has been detected, when the cause of disconnection of a thermistor 2, etc. is eliminated, its abnormality detection is released automatically, when a prescribed time elapses. Also, a state of the abnormality detection is released by only depressing a prescribed key 15 without waiting for the prescribed time.

Description

[Detailed description of the invention] Industrial applications 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 equipped with a fixing roller having a heating roller with a built-in heat source, and a fixing device equipped with a temperature sensor installed near the heating roller. It is maintained constant by controlling the power input to the heat source. However, when an element such as a thermistor is used as a temperature sensor, the thermistor has a high resistance at low temperatures, making it difficult to detect whether the thermistor is disconnected. Therefore, the transistor,
An amplifier circuit using an operational amplifier or the like was installed to amplify the temperature sensor output value, so that the temperature sensor output value at low temperatures could also be detected, making it possible to detect disconnection of the temperature sensor.

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

In view of the above-mentioned problems, the present invention provides a temperature control device for a fixing device that has a simple configuration and detects an abnormality in a temperature sensor to prevent overheating of the fixing device.

Means for Solving the Problems In order to solve the above problems, the fixing device temperature control device of the present invention uses a temperature sensor installed near a heating roller with a built-in heat source and reads the output value of this temperature sensor. The apparatus includes an output detection means and a storage means for storing abnormality detection information when an abnormality is detected in the temperature sensor, turns on holding for a certain period of time in an initial state, and then changes the output value of the temperature sensor to the value at the fixing temperature. If the temperature is not reached, or if the output value of the temperature sensor changes from the value at the fixing temperature during temperature adjustment, it is determined that the temperature sensor is abnormal and the heat source is immediately turned off. It is equipped with a structure that records and stores abnormality detection information of the temperature sensor and keeps the memory for a certain period of time.

Operation The present invention has the above-described configuration, and when an abnormality in the temperature sensor is detected, the heat source is immediately turned off, and the heat source is not turned on within a certain period of time even if the power is turned on again or the door switch is turned on again. I have to.

EXAMPLE An example of the present invention is shown below. First, each circuit element shown in FIG. 1 will be explained.

1 is a heat source built into the heating roller of the fixing device.

2 is a temperature sensor element installed near the heat source 1, and in this embodiment a thermistor is used. Reference numeral 3 denotes a resistor connected in series with a constant voltage v0° and the thermistor 2 in order to replace the resistance value that changes according to the temperature change of the thermistor 2 with a voltage change. 4 is a warm-up timer that starts operating at 9 o'clock when the power is turned on, outputs "H" for a certain period of time, and outputs "L+1" at other times. Reset terminal R
When 5T is set to ++ I, ++, it becomes the initial state.

5 is a power switch, 6 is a door switch attached to the door of the main body of the copying machine, and 6 is normally in an on state. 7 is an AND circuit which outputs "H" regardless of the value of the temperature detection signal vTll of the thermistor 2 while the warm-up timer 4 is outputting "H", and the warm-up timer 4 outputs "H" which is related to the value of the temperature detection signal vTll of the thermistor 2.
+L When outputting +1, the values of M and H are output as they are. However, the output value of this H'' is as low as vo.

8 is a temperature control circuit that controls the heat source on and off according to the temperature detection signal V and y of the thermistor 2 so that the temperature inside the fixing unit becomes a constant value (usually around 200'). If you enter a lower value than the value (vo in Figure 2), H
", and if a high value is input, L" is output.

9, the output of the AND circuit 7 is V. . This is an abnormality detection circuit that outputs K"H" when the value of , and normally outputs +1 L ++. 1o, the output of the abnormality detection circuit 9 is from L'' to H
'', a short pulse of ``H'' is output, a certain period of time is counted from that point, and after a certain period of time ++ I, +
This is a timer that outputs a short + pulse. Reference numeral 11 denotes a memory element, which uses a rewritable 1-bit memory called RAM, and when ``++L'' is input, it becomes ``0''.
When "H" is input, "1'" is stored, and the previous state is continued to be stored as long as the input does not change. or,
When the reset terminal R8T is set to °'L", it is forced to "o"
12 is a battery for backing up the memory in the memory element 11 so that it is not cleared when the power is turned off.

13 is an OR circuit, which outputs 'H' if either temperature control circuit 8 or memory element 11 is H'', and outputs 'L' only when both 8 and 10 are +t L ++. The rad state relay is designed to energize the heat source 1 when the OR circuit 13 becomes L'', and cut off the heat source 1 when the OR circuit 13 becomes H''. 15 resets the warm-up timer 4 and the memory element 11. This is the key for

Next, the operation of the circuit shown in FIG. 1 will be explained. When the power switch 5 is turned on and power supply starts, the warm-up timer 4 starts operating and outputs "H" to the AND circuit 7 until the warm-up time up to Wx in FIG. 2 has elapsed. AND circuit 7 is vo so as not to activate the abnormality detection circuit. It outputs an H''' signal with a much lower value and inputs it to the temperature control circuit 8.8 outputs an L'' signal, and the timer 10. Since the memory element 11 is not operating, the output is re L 17, so the OR circuit 1
3 outputs L", and the solid state relay 14 turns on, so the heat source 1 turns on. As a result, the temperature inside the fixing unit gradually rises within the range of W as shown in FIG. 2, and the thermistor 2
As the resistance value decreases, VO gradually decreases as well. The warm-up time W is determined as the time required from turning on the heat source 1 when the internal temperature of the fixing device is at room temperature until reaching the set temperature T0. When the warm-up timer 4 outputs H'' at W8, the AND circuit 7 outputs the value of vTll, and the temperature control circuit 8 maintains the internal temperature of the fixing unit at the set temperature T0. When the temperature inside the fuser is around room temperature when the power is turned on, the resistance value of the thermistor is extremely large, reaching several hundred ohms, so
o. is almost equal to warm-up timer 4. If the AND circuit 7 is not used, the abnormality detection circuit 9 will fail even during normal operation.
will work. To prevent this, the warm-up timer 4 is activated when the power is turned on, and the abnormality detection circuit 9 is not activated during that time. A very low "H" is output from the AND circuit 7 to forcibly turn on the heat source 1, and temperature control is performed only after the value of the heat source becomes low.

When the thermistor 2 is suddenly disconnected for some reason during temperature control operation, let us assume that the disconnection occurs at the time Eo in FIG. Since the abnormality detection circuit 9 is activated, it outputs "II H" to the timer 10, and the timer 1
0 outputs II Hn, the memory element 11 stores "1", outputs "H", the OR circuit 13 outputs tt H12, and the heat source 1 is turned off.

When the time F has elapsed, the timer 10 outputs °L" again, so the memory element 11 stores "0" and outputs "L" so that the temperature control operation can be performed again. If the thermistor remains disconnected, the abnormality detection circuit 9 operates again and the heat source 1 continues to be turned off.

The off time F is set as the time for natural cooling until the internal temperature of the fixing unit does not exceed To when the heat source 1 is turned on again.If it is too long, the work efficiency will deteriorate, so set it to about 10 minutes. There is.

If the memory element 11 and battery 12 are not present, immediately after the thermistor 2 is disconnected, for example, at the time of Es in Fig. 2, the power including the constant voltage v0° of this circuit is turned off and immediately turned on again, or the power is turned off. If there is a momentary power outage, the circuit will be in its initial state and the heat source 1 will continue to be on during warm-up W, so the temperature inside the fixing device will become higher than To, and the fixing device will burn out. Therefore, after detecting a thermistor disconnection abnormality, the information is stored and retained for a certain period of time while the heat source 1 is forcibly turned off.

In addition, even if the thermistor 2 is disconnected before the power is turned on, the heat source 1 will be turned on during the warm-up period, but the abnormality detection circuit 9 will immediately operate after that and turn off the heat source 1, so the temperature inside the fuser will be higher than To. It is designed not to happen.

Furthermore, by connecting the key 15 to the warm-up timer 4 and R3T of the memory element 11, even if the timer 10 is in operation, turning on the key 16 forces the circuit to the initial state, thereby waiting for FT for a certain period of time. The heat source can be turned on again without any delay.

Effects of the Invention As detailed above, according to the present invention, it is possible to prevent the fixing heater from being damaged by overheating, regardless of the state of the thermistor of the temperature sensor.

In addition, after detecting a thermistor disconnection like in the past, the power is turned off,
Alternatively, if the power is turned off due to a momentary power outage or the like and then turned on again, it is possible to prevent a dangerous situation in which the fixing heater continues to be turned on again even if the interior of the fixing device is at a high temperature.

Furthermore, after an abnormality is detected in the fixing heater section, if the cause, such as a thermistor disconnection, is removed, the abnormality detection will be automatically canceled after a certain period of time has passed, so that the normal state can be restored without any troublesome operations.

Moreover, even if the user waits for the above-mentioned predetermined time, it is possible to cancel the abnormality detection state of the fixing heater section by simply pressing a predetermined key, thereby saving time.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing one embodiment of a temperature control device for a fixing device according to the present invention, and FIG. 2 is a graph showing changes in temperature inside the fixing device and changes in the temperature detection signal V□ of a temperature sensor. . 1...Heat source, 2...Thermistor, 3...
...Resistor, 4...Warm-up timer, 5...Power switch, 6...Door switch, 7...AND circuit, 8... ... Temperature control circuit, 9 ... Abnormality detection circuit, 10 ...
...Timer, 11...Memory element, 12...
... Battery, 13 ... OR circuit, 14
...Solid state relay, 15...
·Key.

Claims (4)

[Claims] (1) a temperature sensor installed near a heating roller having a heat source; an output detection means for reading the output value of the temperature sensor; a storage means for storing abnormality detection information when an abnormality is detected in the temperature sensor; If the heat source is turned on for a certain period of time in the state, and then the output value of the temperature sensor does not reach the value at the fixing temperature, or if the output value of the temperature sensor during temperature adjustment changes from the value at the fixing temperature. 1. A temperature control device for a fixing device, further comprising: a control means for turning off the heat source and storing abnormality detection information of the temperature sensor in the storage means. (2) A temperature control device for a fixing device according to claim 1, wherein the storage means includes a RAM element and a backup power source. (3) Temperature control of the fixing device according to claim 1, wherein the control means turns off the heat source, resets the temperature sensor abnormality detection information after a certain period of time has elapsed, and turns on the heat source again. Device. (4) The fixing device temperature control device according to claim 1, wherein the control means turns on the heat source again by inputting a predetermined key.