JPS61196276A - Detecting device for temperature abnormality of part to be heated - Google Patents

Abstract

PURPOSE:To prevent damage by detecting the rate of variation in the output of a temperature sensor before a heated part attains to set temperature and suppressing the heated part from being overheated. CONSTITUTION:A potential V1 as the output signal of the temperature sensor RS is inputted to a differentiator DIF. Its variation rate, i.e. tangential gradient is inputted as an output voltage V4 to a comparator COM 2. The comparator COM 2 compares potentials V4 and V3 and outputs a signal I2. Namely, the comparator outputs a signal H when the potential V4 is higher than the potential V3 and a signal L when not. The potential V3 gives the lower-limit value of the proper temperature rise gradient of the heated part AA and the output I2 of the comparator COM 2 is inverted from H to L when the actual temperature rise gradient V4 (variation rate of potential V1) detected by the temperature sensor RS decreased below its lower-limit value V3, thereby detecting temperature abnormality.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an apparatus having a heating mechanism, for example, a temperature abnormality detection apparatus for a heated part of a copying machine or the like.

<Prior art and its drawbacks> Conventionally, temperature abnormality detection in the fusing unit of a copying machine (a mechanism that heats and presses the transferred copy paper to fix it) has been carried out by detecting the output of a temperature sensor after a certain period of time has elapsed since the heating device was turned on. This was done by outputting an abnormal signal when the temperature did not show a constant temperature.

However, such a detection method has the following problems: For example, if the ambient temperature is too low, such as in a cold region, the predetermined temperature cannot be reached within the initially set time. An abnormal signal was sometimes generated even though there was no abnormality in the heating device. When the setting time was increased to solve this problem, the following problem occurred. In other words, if some force is applied to a part of the temperature sensor, the sensor may become detached from the contact surface in the case of a contact type sensor, or the sensor may shift from its original measurement position in the case of a non-contact type sensor.
Since the accurate temperature of the heated part cannot be detected, the detected temperature is slightly too low, and heating continues until the set time is reached, resulting in excessive heating and damage to the device.

<Object of the Invention> The object of the present invention is to prevent damage to the heated part and perform proper heating by detecting the rate of change in the temperature sensor output until the heated part reaches a set temperature. An object of the present invention is to provide a device for detecting temperature abnormality of a heated part.

<Structure of the Invention> In order to achieve the above object, a temperature abnormality detection device according to the present invention includes a heated part heated by a heater, a temperature sensor that detects the temperature of the heated part, and this temperature sensor. and a differentiator for detecting the rate of change of the output signal of the heating element, and when the output of the differentiator exceeds a certain level, an abnormality in temperature of the heated portion is detected.

<Embodiment> Hereinafter, an embodiment of the temperature abnormality detection device for a heated part according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a control circuit diagram of the temperature abnormality detection device. In the figure, HT is the power supply AC
This heater HT is a heater driven by a heater HT that heats a heated part AA such as a fixing part of a copying machine. A temperature sensor R3 is arranged at a specific position of the heated portion AA. As shown in FIG. 2, this temperature sensor R3 preferably has a resistance value that is linear with respect to temperature. Of course, the temperature sensor does not have to have linear characteristics, but may be a temperature sensor that has been corrected to have linear characteristics by an attached circuit.

Temperature sensor R3 is connected in series with resistor R1, and resistors R2, R3 and resistors R4 and R5 are connected in parallel. A voltage VC is applied to the circuit, and the circuit is driven. The midpoint between sensor R3 and resistor R1, the midpoint between resistor R2 and resistor R3, and the resistor R4 and resistor R
The potentials at the midpoints of 5 are Vl, V2 and v3, respectively.
is given by

Potential v1 and potential ■2 which are the output signals of temperature sensor R3
is input to the comparator C0M1. The comparator C0M1 compares the potential ■1 with the potential v2 and outputs a signal ■1. That is, when the potential v1 is higher than the potential v2, the signal 'HJ' is output, and when the potential v1 is lower than the potential 2, the signal 'LJ' is output. To explain in more detail, comparator C0
M1 is a heated part A detected by temperature sensor R3
It is determined whether the temperature of A has reached a predetermined temperature given by potential v2. That is, as the temperature rises, the resistance value of the sensor R3 decreases, and as a result, the potential (1) gradually increases, and when it exceeds the potential (2), it is determined that the heated part AA has reached the predetermined temperature, and the comparator C0M1 Output ■1 is 'LJ
From 'HJ' to 'HJ'.

On the other hand, the potential V1, which is the output signal of the temperature sensor R3, is input to the differentiator DIF, and its rate of change, that is, the tangential slope, is input to the comparator C0M2 as the output voltage v4. Comparator C
0M2 compares the potential v4 with the potential V3 and outputs a signal 2. That is, if the potential (4) becomes larger than the potential (v3), the signal 'HJ' is output, and if the potential (v4) becomes smaller than the potential (3), the signal 'LJ' is output. , which is detected by temperature sensor R3.

When the temperature increase gradient V4 (rate of change in potential v1) falls below its lower limit value v3, the output I2 of the comparator C0M2 is changed from 'HJ to'LJ to detect a temperature abnormality.

As shown in the flow chart described later, when the signal 11 is in the 'LJ state (the heated part AA has not reached the predetermined temperature), the signal I2 is in the "L" state (the temperature increase gradient ■4 is the lower limit value). (2) If the heating output signal 01 becomes lower than 3), control is performed to change the heating output signal 01 from 'HJ to rL' and shut off the heater HT. The output signal 01 is voltage-divided by a resistor R6 and a resistor R7, and is inputted to the base terminal of the transistor Tr. Therefore, when the output signal 01 is 'HJ, the potential of the base terminal rises, the transistor Tr becomes conductive, and the relay Ryl to which the voltage VB is applied is turned on. This closes the movable contact Ryc, and the power source AC heats the heater HT. Conversely, when the output signal 01 is 'LJ', the transistor Tr is cut off and the relay R
yl is turned off and the movable contact RyC is closed. In other words, the heater HT is cut off.

FIG. 3 shows a time chart of the signals vi, v4 and ■2 which clearly shows the above-mentioned conditions. When the power is turned on and heating starts at time t1, the sensor output v1 increases linearly. In reality, there is a delay time during which the temperature is conducted to the sensor after the heating command is output, so the differentiator output v4 exceeds the slope reference value V3 at time t2,
The gradient comparison output I2 changes from "rl" to rH. However, it is assumed that the heater HT is disconnected or the temperature sensor R8 moves during the process, so that the temperature increase rate of the sensor output v1 decreases, and the slope decreases like a broken line at time t3. Then, the differentiator output v4 becomes the slope reference value ■3 at time t4.
As a result, output 2 changes from rH to ``LJ.'' This ``L'' signal causes the CPU to change output 01 to ``HJ.''
to 'LJ' and shut off the heater HT as described above. On the other hand, the state indicated by the dotted line indicates a case where there is no abnormality at all during the process, and the sensor output (1) reaches the predetermined temperature at time t5, and heating is stopped at time t6.

FIG. 4 shows a flowchart of the above embodiment.

First, when the main unit is powered on, step nl (
The process proceeds to step ni (hereinafter simply referred to as ni), where it is determined whether the temperature comparison signal 11 is "L", and since the predetermined temperature has not yet been reached, the process proceeds to R2. Heating output signal 01 is “L”
”, so proceed to R3, set the signal 01 to 'HJ', and turn on the heater HT. Next, use R4 to cent the timer,
Set the time lag time from turning on the heater HT until heat is conducted to the sensor. After this, temperature comparison signal ■1 becomes 'H'
Determine whether it has reached J (R5), return to R2 again, and if the set time does not exceed (R6), R2,
Heating is continued by repeating each cycle of R6 and R5.

If the signal 11 becomes rH within the set time (R5), R7
At this point, the heating output signal 01 is set to rL to turn off the heater HT and reset the timer.

Next, if the signal (1) does not become rH within the set time, it is determined in R8 whether the slope comparison signal (2) is 'HJ'. If signal I2 becomes 'LJ', turn off the power.
9),) Display that there was a trouble (n 10).

Reset the timer at the same time you turn off the heater (
R7). As long as the heating continues smoothly even after the set time has elapsed, the signal I2 remains 'HJ', and each cycle of R2, R6, R8 and R5 is repeated to continue heating until the signal TI becomes 'H'.

In the above embodiment, damage caused by excessive heating can be prevented by detecting the temperature gradient until the predetermined temperature is reached. In addition, when the temperature gradient rapidly increases due to rapid heating, damage can be prevented by setting an upper limit value and stopping the heating when the upper limit value is exceeded.

<Effects of the Invention> As described in detail above, the present invention detects the rate of change in the temperature sensor output until the heated part reaches the set temperature, suppresses excessive heating of the heated part, and prevents it from occurring. It has the advantage of being able to prevent damage.

[Brief explanation of drawings]

FIG. 1 is a control circuit diagram of an embodiment of the present invention, FIG. 2 is a linear characteristic diagram of a temperature sensor, FIG. 3 is a time chart of each signal, and FIG. 4 is a flow chart showing the operation of the embodiment. AA-overheated part, DrF-differentiator, HT-heater, R3-temperature sensor, vl-temperature sensor output signal, VS-constant level.

Claims (3)

[Claims] (1) It is equipped with a heated part heated by a heater, a temperature sensor that detects the temperature of this heated part, and a differentiator that detects the rate of change of the output signal of this temperature sensor. A temperature abnormality detection device for a heated part that detects a temperature abnormality in the heated part when the output of the heated part reaches a certain level. (2) A temperature abnormality detection device for a heated part according to claim 1, which detects an abnormality when the output of the differentiator falls below a certain level before the temperature of the heated part reaches a predetermined temperature. (3) The temperature abnormality detection device for a heated part according to claim 1 or 2, wherein the heated part is a fixing part of a copying machine.