JPS59226910A - Temperature controller - Google Patents

Abstract

PURPOSE:To perform highly safe temperature control by switching a power-on time to be detected through a temperature controller which performs power-on control over the heater of a copying machine, etc., according to the state of the heater. CONSTITUTION:The time of feeding to the heater H1 is monitored to detect abnormality of the heater H1. The time of feeding to the heater H1 is monitored by different timers in power-on operation, stand-by state, and in copying operation. This results from that it takes about 20sec to raise the surface temperature of a roller from room temperature (about 20 deg.C) to temperature in stand-by state (about 180 deg.C) while it takes about 1sec to enter the stand-by state in the stand- by mode or copying operation after the heater H1 is turned off. For the purposes, two timers are used. Further, the signal from a thermistor Th1 which monitors the surface temperature of the roller is detected and a judgement of abnormality is made when the surface temperature exceeds a specific value to blow a fuse resistance R38.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a temperature control device for controlling energization of a heater in a copying machine or the like.

BACKGROUND ART Conventionally, as a measure against runaway of the heater in a heat-fixing device of a copying machine, for example, a temperature fuse is provided in series with the heater, and the fuse is placed near the fixing roller of the heat fixing device.
They were able to detect an abnormal temperature rise at Kinbutsu and cut the fuse.

However, with such a tube bottom alone, there will be variations in the fuse disconnection time between the first M power turn on and the normal copy, including the thermal response of the fuse. The difference becomes noticeable when .

Therefore, in some cases, damage may occur to the fixing device (for example, deformation of the fixing roller, deformation of the separating claw, etc.), and depending on the degree, it is often impossible to reuse the device.

Therefore, various abnormality countermeasures, such as measures against disconnection of the temperature measuring element (for example, thermistor) for temperature control of the heater, have been taken to prevent the heater from running out of control. If the heater goes out of control due to a short-circuit accident or damage to the elements constituting the triac trigger circuit, it is necessary to rely on the temperature fuse described above. A method is also being considered to detect that the heater is energized for more than a certain period of time (an abnormality in energization) and stop the heater from running out of control. In this case, the energization time for determining that energization is abnormal is set, for example, to the time T1 from when the heater cools down to room temperature to when the heater reaches standby temperature (for example, 180° C.). If the heater is energized for a period of time T1 or longer, it is determined that some abnormality has occurred, but the value Tl is extremely large compared to the heater energization time T2 during standby or copying. For example, during the normal time T1, if a heater energization error occurs during 20 bytes or during copying, the heater temperature will rise abnormally, posing the risk of damaging the apparatus.

Purpose The present invention has been made in consideration of the above points, and an object of the present invention is to provide a highly safe temperature control device.

Example Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a control circuit block diagram of the temperature control device in this practical example, and FIG. 2 shows it in more detail. Here, Fl is a temperature fuse, Hl is a fixing heater,
K1 is a power relay, Q6゜Q8 is a triac, Th
Reference numeral 1 indicates a thermistor that detects the surface temperature of a constant magnification roller (not shown) heated by the fixing heater H1&C, and 1 controls opening/closing of the triac Q8 via the triac drive circuit 2 in accordance with the detection result of thermistor Th1. 3 is a power relay that controls 1. A second control circuit is used. Ql, Q5, and Q7 are photocouplers. Q2 to Q
4 is a comparator, R1-13B is a resistor, D1-D13
is a diode, ZDl~ZD3 are Zener diodes,
Q9 to Q12 are transistors, 01 to C8 are capacitors, 11. I2 is an inverter, Pl is an AC power supply, Ml is a main motor, and Vc is a 24V power supply voltage.

The fixing heater H1 is connected to the Act line via a relay 1 and a triac Q8. Therefore, the fixing heater H1 is turned on when the relay 1 is closed and the triac Q8 is turned on.

In this circuit, before the power is turned on, the relay 1 contact is in an open state, and even after the power is turned on, unless current flows to the relay 1 coil side, the relay will not be set to 1. That is, after the power is turned on, when current flows from the power supply Vc to the fill of relay 1 through the fuse resistor R38, the relay 1 enters the cent state.

Further, the first control circuit 1 is composed of, for example, a microcomputer, and controls the triac Q8 by a signal from a thermistor Th1 that monitors the surface temperature of a roller (not shown). Incidentally, since the first control circuit 1 is well known, a detailed explanation thereof will be omitted.

In addition, in this circuit, as a safety measure in case of abnormal fogging of the fixing heater H1 built into the roller, the secondary side of the relay Kl is disconnected by a second control circuit B provided separately from the first control circuit 1. This opens contact 1 of the relay to prevent abnormal heating.In other words, in this circuit, a fuse resistor is used for R38, and the circuit is configured to turn off the fuse resistor in the event of an abnormality. Therefore, if an abnormality occurs, the relay will not be turned on until the fuse resistor is replaced.

Next, a method for detecting abnormal runaway of the heater H1 in this embodiment will be explained.

This circuit detects normal energization of the heater Hi by changing the energization time to the heater H1, and also detects abnormal temperature rise of the roller based on a signal from the thermistor Thi. First, a method for detecting an abnormality in energization of the heater H1 will be described. The energization time to the heater H1 is monitored by different timers when the power is turned on, during standby, and during copying.

As shown in Figure 6, when the surface temperature of the roller is at room temperature (approximately 20°C), it usually takes approximately 20 seconds to bring it up to the standby temperature (approximately 180°C).
This is because after the heater H1 is once turned off during the standby time or copying time, it takes about 1eθC to rise again to the standby temperature.In other words, when these characteristics are taken into account, Even if an attempt is made to detect an abnormality in energization with one timer, the time K required for the temperature to rise to the standby state varies considerably depending on the state of the device, so it is impossible (for example, the heater H1 heats up too much).

Therefore, in this embodiment, sufficient safety measures are taken by using two timers. In addition, by using different timers for standby and copying, it is possible to detect abnormalities in power supply even more effectively.

Also, to explain the method of detecting abnormal temperature rise of the roller (heater H1), this circuit detects a signal from the thermistor Th1, and when this reaches a predetermined value or more, it is determined that there is an abnormality.

Next, fuse resistance R3 at the time of abnormal runaway of heater H1
The cutting method No. 8 will be explained in detail using the circuit shown in FIG.

(1) In case of abnormal temperature rise, thermistor Th1 (?14i sensor) is connected to comparator Q.
By using the characteristic of the thermistor Th1 whose resistance value decreases as the temperature rises, the output of the comparator Q4 is set to H level G (Shi, When driver Q12 is turned on, a current exceeding the rated value flows through fuse resistor R3B, so fuse resistor R118 is cut off.

That is, when abnormal temperature rise is detected by thermistor Th1, fuse resistor R38 is disconnected, the contacts of power relay Ki become open, and heater J
'The power supply to ' will be stopped. This state is shown by fracture ia in FIG. In the figure, the horizontal axis indicates time (Ct), and the vertical axis indicates the surface temperature ('C) of the roller. Incidentally, the energization time of the heater at this time is represented by ■.

(2) In case of energization abnormality, temperature fuse F1 and heater H1,! The signal from both ends connecting J series 1 is Tochiak Q 8 d! When in the on state, full-wave rectification is performed by the diodes D1 to D4, and the secondary side of the photocoupler Q1 becomes in the on state. As a result, the transistor Q 11 Fl turns off, and the abnormality timer described later operates. Also, when the triac Q8 is off, there is no power supply to the diodes D1 to D4, so the secondary side of the photocoupler Q1 is turned off. . However, the transistor Q11 does not turn on at the same time as the photocoupler Q1 turns off.
)'ZDi, resistor R4 and capacitor C2Kj: Charging of capacitor C2 is performed when heater H1 is off on the negative side. This is because when the heater H1 is off, the transistor Q11 is immediately turned on and an abnormality occurs. This is because if the heater is configured to be reset, the heater will turn off for a moment and then turn on again, causing problems such as the heater heating up too much if it is left on for a long time without a flange. Therefore, heater H
When Q1 is in the off state, the transistor Qll is not turned on for a certain predetermined time (determined by R4 and 1G2). In other words, even if the heater H1 is turned off, the abnormality type is not reset for a predetermined period of time.

Next, we will explain the abnormality timer.The collector side of transistor Q11 is connected to resistor R7゜capacitor C3 and resistors R7 and R8 (connected in parallel with R7 and R8).
, stb, with two types of abnormalities of capacitor C3. For a predetermined period of time after the power is turned on, an abnormality in the conduction is detected by the abnormality timer of the resistor R7 and capacitor C3. This predetermined time is the time from when the power is turned on until the output of the comparator Q2 reaches the L level (for example, 455 ec
). In other words, this predetermined time is when the output of the timer made up of resistor R21 and capacitor C5 exceeds the reference voltage, the timer circuit made up of resistors R7, R8, and capacitor C6 switches, and an abnormality in energization is detected. 0 to be done
These two abnormality timer circuits are connected to the input terminal of the comparator Q3, and when the reference voltage of the comparator Q3 is exceeded, it is determined that an abnormal state has occurred.
The output of transistor Q changes to H level.
12 is turned on, and the fuse resistor H38 is cut off as in the case of abnormal temperature rise.

The surface temperature of the roller in the above-mentioned abnormal state is represented by the two-dot chain line (a) and the one-dot chain line (d) in FIG.

The two-point chain ib is connected to the first timer (resistor R7, capacitor 03
) indicates the temperature state of the loaf when an abnormality in energization is detected when the power is turned on, and the energization time at this time is represented by ■ (approximately 65 seconds).

Also, in the single-point chain, @a is the second timer (resistors R7, R8').

This indicates the temperature state of the roller when an abnormality in power supply during standby or during copying is detected by capacitor C3), and in this circuit, if a current of 1488C or more is applied during standby or during copying, it is considered abnormal. Note that C indicates the temperature state of the normal roller, and approximately 9 seconds is the maximum energization time of the heater in normal conditions.
In addition to the first control circuit that controls the heater according to the detection results of It is something that allows you to fully maintain your sexuality.

Furthermore, since this circuit simultaneously detects abnormal temperature rise and abnormal energization, it is possible to always accurately detect the abnormal state of the heater.

In this embodiment, the power relay 1 is used, but other opening/closing means such as a triac, a thyristor, etc. may be used.

Further, a fuse breaker or the like may be used instead of the fuse resistor R5B. Further, the second control circuit 3 may be implemented by a microcomputer, and may be configured to detect abnormal energization and abnormal temperature rise independently of the first control circuit 1. Further, the timer time and thermistor detection temperature described above are not limited to these, and may be determined as appropriate. Alternatively, the temperature at power-on may be detected and the abnormality timer at power-on may be switched depending on the temperature.

Effects As detailed above, according to the present invention, a highly safe temperature control device can be obtained. Furthermore, damage to the device due to abnormal heating of the heater can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the restraining circuit in this embodiment, Fig. 2 is a detailed circuit diagram of Fig. 1, Fig. 6 is a diagram showing changes in the surface temperature of the roller under normal conditions, and Fig. 4 is an abnormality. It is a figure which shows the surface temperature change of the roller in a state. Here, Fl is a temperature fuse, Hl is a heater, K1 is a power transistor, rh1 is a thermistor, and Q8 is a triac.

Claims (1)

[Claims] A connoisseur of heaters? In a temperature control device that detects an abnormality in energization of the heater by detecting a time. A temperature control device characterized in that the energization time to be detected is switched depending on the state of the heater.