JPS58176667A - Control device for heater temperature - Google Patents

Abstract

PURPOSE:To prevent overheating of a heater owing to the malfunction of a microcomputer, by providing a means of interrupting the supply of electric power to the heater in the stage of the malfunction of the microcomputer which controls the comparison and detection of the surface temp. of a fixing roll. CONSTITUTION:An AC power source 5 is connected from a capacitor C to the analog input terminal A1 of a microcomputer 6 and a zero cross wire is detected. The divided voltage from a thermistor 7 and a comparing resistor 8 which indicates the resistance value of the temp. of a heater 3 is inputted to the analog input terminal A2 of the microcomputer 6. The microcomputer 6 outputs an overheating signal from the terminal D1 when the heater temp. basing on the divided voltage is lower than the set voltage and outputs an enable signal from the terminal D2. An inverter 9, a triode AC switch 4 and the heater 3 are connected to the terminal D1, and an OR circuit 10 and a pulse detection circuit 11 are connected to the terminal D2 as well. Since the heater 3 is driven at the zero cross timing of the power source 5, whereby the rush current when the heater is on is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heater temperature control device, and more particularly to a heater temperature control device that prevents overheating of a heater in a fixing section for a copying machine or the like.

As a conventional heater temperature control device, for example, a set signal for detecting the printer temperature of a fuser unit for a copying machine and a set temperature signal according to the heater set temperature are input to a microcomputer, and a program stored in advance is used. It is possible to control the heater power supply so that the heater temperature reaches the set temperature by processing both signals based on the temperature.

According to this heater temperature control device, there is no fear that the response will be slow unlike the nine control devices that use a thermostat.
Heater temperature I1. ．． The meeting can be controlled accurately.

However, in conventional heater temperature control devices, the microcomputer may malfunction due to external noise, etc. For example, if a malfunction occurs while the fuser heater is being driven, this state may be maintained. Ninth, there is a risk of heater overheating.

The present invention has been made in view of the above, and provides a heater temperature control device that detects the malfunction and stops overheating of the heater when the malfunction occurs in order to prevent heater overheating due to microcomputer 0v14 operation.

The heater temperature control device according to the present invention will be explained in detail below.

Embodiment 1 of the present invention is shown in FIG. 1, in which a charging section, an exposure section 1, a developing section C, a transfer section D1, and a fixing section E are arranged around a photosensitive drum 1 of a copying machine. p, fixing part f8
The heater 3 of the heating roll 2 (shown outside the roll 2 in the drawing) receives power from the AC power supply 5 when the triac 4 is turned on. The analog input terminal AsK of the microcomputer 6 is detected via the AC power supply capacitor C, and the zero cross point is detected. A divided voltage determined by the thermistor 7 and comparison resistor 8 is input to the analog input terminal A of the microcomputer 6. The microcomputer 6 compares the set temperature (temperature setting part is omitted in the illustration) with the heater temperature based on the divided voltage, and if the heater temperature is lower than the set temperature, it outputs an overheating signal from its own output terminal, and , when the heating signal is output, output terminal D3) outputs an enable signal. An inverter 9 that inverts the heating signal is connected to the output terminal D1 of the microcomputer 6, and the output of the inverter 9 controls the triac 4, and at the same time, the output of the inverter 9 is sent to the pulse detection circuit via the OR circuit 10 together with the enable signal of the first output terminal. 11 (the explanation is omitted, but it consists of a one-shot multi-pipe rake layer as shown). The pulse detection circuit 11 is enabled (the terminal Σ is “
If "1" is added to 11), when no pulse is input from the output terminal pi for a predetermined period of time, a "0" sound is output and the microcomputer 6t is reset.

In the above configuration, the operation will be explained using the time chart of FIG. 2. The AC signal 5 is input to the analog input port of the microcomputer 6! When input to the microcomputer 6, the zero cross drive 2 is formed in the microcomputer 6 by detecting the zero cross.

On the other hand, the set temperature signal T and the heater temperature signal TH input to the analog input terminal 3 of the microcomputer 6 are digitally processed after being converted, and TII<TI is the output terminal D1]
A pulse heating signal DI is output. The signal D1 is inverted as the drive signal P by the inverter 9, and when the signal P is "1", the trier 4 is turned on and the heater 3 is turned on.
(zero cross drive), the heating roll 2 is heated. During normal operation, the microcomputer 6 outputs an enable signal Dst from its output terminal, and inputs this to the enable terminal of the pulse detection circuit 11 to enable it.
IK is held, the pulse heating signal Dtt is detected, and the reset terminal K rlJ is output to maintain the operation of the microcomputer 6. On the other hand, at time 1 (when the drive signal P is held at "1"), noise etc.
malfunctions, the pulse heating signal DI is output from the output terminal Dl.
At the ninth point when the power is no longer output, the drive signal P maintains "1" to continue supplying power to the heater 3.

The enable signal Ds becomes “0” due to a malfunction of the microcomputer 6.
However, since the drive signal P enables the pulse detection circuit lit through the OR circuit 101, the pulse heating signal D
It is detected that I is not output for a predetermined period of time, and a reset signal "0" is output at time t3. Reset signal l
" is input to the reset terminal of the microcomputer 6 for a predetermined time, the tl-microcomputer 6 is reset (time ts), the output terminal D1 becomes "1", and the drive signal P becomes rOJK&. In the above embodiments, in which the triac 4 is turned off and heating of the heater 30 is stopped, the heater 3 is driven at the timing of the zero cross of the AC power source 3, and the 2. Can prevent shcurrent.

As explained above, according to the heater temperature control device according to the present invention, heating of the heater is stopped when a malfunction of the microcomputer is detected, and heating of the heater due to the malfunction can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention. Figure 2 is the first
Figure time chart. Explanation of symbols 1...Photosensitive drum, 2...Heating rail, 3.
...Heater, 4...Trier, 5...
AC power supply, 6-microcomputer, 7-senna, l l
-pZ Luz detection circuit.

Claims (1)

[Claims] Equipped with a microcomputer that compares the predetermined set temperature and the surface temperature of the fixing four-ra detected by the sensor, and controls the power supply to the heater to control the second surface temperature of the fixing four-ra to the set temperature. The heater temperature control device further comprises means for cutting off the power supply when the microcomputer malfunctions.