JPH0362206A - Method and device for detecting abnormality of temperature control system - Google Patents

Abstract

PURPOSE:To detect the abnormality with high accuracy by setting plural reference temperatures for detection of the abnormality in accordance with each control target temperature and shifting those reference temperatures with each other via a time series temperature changing curve. CONSTITUTION:The temperature control reference voltage VW set at the anode side of a voltage dividing resistance R4 is switched to the reference voltage Vt corresponding to the fixing control target temperature St. Then the shift control is carried out to the temperature St based on the signal received from a comparator 1. At the cathode side, the weight reference voltage V2 is shifted to the fixing abnormality detecting reference voltage V1 by the voltage discharge of a time constant circuit 5 via a time series voltage changing curve V3 (temperature curve T3) with gradual reduction of voltage carried out in response to an RC constant after the change of the reference voltage owing to the circuit 5 set between the cathode and a comparator 2. Thus it is possible to shift to a fixing action while performing a prescribed abnormality detecting action even in a shift mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is applicable to a temperature control system used in a thermal fixing device that thermally fixes an unfixed toner image. The present invention relates to an abnormality detection method in a temperature control system configured to be able to switch temperatures.

``Prior Art'' Conventionally, temperature control of a roller-type thermal fixing device consisting of a combination of a fixing roller with a built-in heater and a pressure roller has generally been performed using an 0N-OFF control method, a proportional control method, or a control method consisting of a combination of these. However, in this control method, in order to save power, improve the durability of heat-degraded parts, or quickly transition the fixing operation, it is necessary to adjust the temperature to the operating state of the thermal fixing device. first, after turning on the power, the temperature of the heated body is controlled at a weight control temperature Sw lower than the fixing target temperature St, and if a fixing start signal is received during that time, the weight temperature is From Sv to fixing target temperature St
The system is configured so that a predetermined fixing operation is performed, and then, at the same time as the fixing operation is completed, the weight temperature is shifted to Sv again, and the above-mentioned control operation is repeated thereafter.

Now, in a temperature control circuit having such a configuration, in order to prevent thermal damage due to abnormal temperature rise due to failure of control parts constituting the circuit, the fixing roller is at a predetermined temperature (standard temperature for abnormality detection T). A protection circuit is provided that forcibly turns off the heater when it rises (descends).

"Problem to be Solved by the Invention" The reference temperature T for abnormality detection is determined by taking into account the variation and overshoot amount in the temperature control, so that malfunction does not occur with these normal temperature fluctuations, and the time required for abnormality detection is determined. The fixing target temperature St is set to an arbitrary temperature range with a significant difference within a range where no delay occurs, but if the abnormality detection reference temperature T is set based on the fixing target temperature St in this way, the weight temperature Sw The temperature difference between T and the reference temperature for abnormality detection becomes quite large, and as a result, if an abnormality occurs during weight temperature control, a detection delay will inevitably occur, especially in the case of an abnormality caused by overcurrent in the control circuit, etc. In some cases, the internal circuit may be destroyed due to the time delay.

In order to eliminate this drawback, a plurality of reference temperatures T for abnormality detection are also prepared in correspondence with the control target temperatures of the weight temperature Sw and fixing target temperature St, and are made to correspond to the switching operation of the control target temperature. It is conceivable that the abnormality detection reference temperature T is also switchable.

However, as shown in FIG. 3(a), the abnormality detection reference temperature Tl-I? When switching between 2 and 2, the temperature of the heated object changes over time with a predetermined temperature decreasing (warming) curve without triggering a temperature change, especially when switching from the fixing operation to the wait time. is, the detected temperature is
Immediately after switching, the temperature may drop below the abnormality detection reference temperature T2, resulting in malfunction.

In order to eliminate this drawback, it is conceivable to switch the reference temperature for abnormality detection by delaying a predetermined time Δ as shown in FIG. 3(b), but even with this configuration, the other During the transition to the control target temperature, the relative temperature difference between the abnormality detection reference temperature T and the actual detected temperature becomes large, making it impossible to eliminate the detection delay when an abnormality occurs during the transition. .

In view of the shortcomings of the prior art, the present invention enables highly accurate abnormality detection without causing malfunctions or time delays in abnormality detection even during the transition of the detected temperature to another control target temperature. The purpose is to provide an anomaly detection method.

"Means for Solving the Problem" In order to achieve the technical problem, the present invention sets a plurality of abnormality detection reference temperatures TI, T2 corresponding to a plurality of control target temperatures St, Sv, and at least An abnormality detection method is proposed in which the transition from the abnormality detection reference temperatures TI and T2 of 1 to other reference temperatures is performed via a time-series temperature change curve 'tc.

Note that the abnormality detection reference temperatures TI and T2 do not refer only to the upper limit reference temperatures flu and T2u that are higher than the respective control target temperatures SL and Sw, but rather to the upper limit reference temperatures flu and T2u that are higher than the control target temperatures St and Sw, as shown in the examples below. Upper and lower reference temperatures TIL and T2L may be set on both sides thereof.

Then, such a reference temperature for abnormality detection is 〒1. In order to perform the transition between T2 via the time-series temperature change curve Tc, for example, a reference voltage setting means capable of switching the reference voltage by a switching signal, and an output voltage from the reference voltage setting means and the voltage of the heated object are provided. an abnormality determining means for determining an abnormality in the temperature control system based on a detected voltage corresponding to the detected temperature; a time constant circuit is interposed on the output side of the reference voltage setting means; The reference voltage may be configured to shift from one reference voltage to another via a time-series voltage change curve based on the time constant of the time constant circuit.

In addition, as shown in the second embodiment described later, the reference voltage setting means is used for controlling target temperatures St and Sv and for abnormality detection temperature TI,
Since the reference voltage setting means for T2 may be common,
It is not particularly limited to a reference voltage setting means for abnormality detection.

"Embodiments" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative arrangements of the components described in this example are not intended to limit the scope of this invention, but are merely illustrative examples. It's nothing more than that.

FIG. 1 is a block diagram showing the configuration of main parts of a temperature control system according to the basic configuration of the present invention, where 1 is a temperature control comparator that generates a heater heating signal, and 2 is a temperature control comparator that generates a signal for heating the heater, and 2 is a temperature control comparator that generates a temperature control signal that is caused by an abnormal temperature rise in the detected temperature. A comparator for determining abnormality, 3 is a negative characteristic thermistor R connected in series between a pair of fixed resistors R1 and R2.
s, the detected voltage on the anode side of the thermistor Rs is inputted to the temperature control comparator l, and the cathode side is inputted to the abnormality determination comparator 2, respectively.

4 is a reference voltage setting circuit, which is a voltage dividing resistor R located in the center among three voltage dividing resistors R3, R4, and R5 connected in series.
The reference voltage obtained from the 7 node side of 4 is input to the temperature control comparator l, and the reference voltage obtained from the cathode side is input to the abnormality determination comparator 2 via the time constant circuit 5, and the control target temperature [St , Sv and the abnormality detection reference temperatures TI, T2, and the voltage dividing resistor R.
The collector side of the transistor T1 is connected to the anode terminal of 4 through the branch resistor R8, and the branch resistor R is turned on based on the switching signal from the I10 port B.
EI is grounded, thereby making it possible to vary each reference voltage input to each of the comparators 1.2. Incidentally, the temperature change and the voltage change can be reversed in accordance with the negative characteristics of the thermist.

Next, the operation of this embodiment will be explained based on the temperature change graph of FIG. 4 in correspondence with the fixing operation.

First, when the power is turned on and no switching signal is output from I10 port B, the branch resistor R6 is not grounded, so the reference voltages Vw, V2 set only by the voltage dividing resistors R3, R4, and R5 are is output to each comparator 1.2 from the 7th node side and the cathode side of the voltage dividing resistor R4, and it is possible to perform predetermined weight control and abnormality detection corresponding to the weight control temperature Sw.

When a fixing operation command is input during the weight control, a switching signal is output from I10 (port) 8 and the transistor Tri is opened, so that the branch resistor Re and the voltage dividing resistor R4
, R5 are connected in parallel, so that the voltage dividing resistor R4 is
The temperature control reference voltage Vw on the node side is switched to the reference voltage Vt corresponding to the fixing control target temperature St, and the comparator l
Based on this signal, control for shifting to the fixing control target temperature St is performed.

On the other hand, on the cathode side, since a time constant circuit 5 is interposed between the comparator 2 and the reference voltage, when the reference voltage is switched, the voltage discharge of the time constant circuit 5 causes the weight reference voltage v2 to be changed to RC.
The voltage gradually decreases in accordance with a constant and shifts to the reference voltage v1 for detecting a serious fixing abnormality via a time-series voltage change curve V3 (temperature curve T3).

Thereby, even during the transition, it is possible to proceed to the fixing operation while performing predetermined abnormality detection. Thereafter, the operation opposite to the above is performed in response to the fixing operation end signal.

FIG. 2 shows another embodiment of the present invention applied to a temperature control system for a fixing device, in which 10 is a heater built into the fixing device (not shown), and 11 is a device for detecting the surface temperature of the fixing device. , temperature detection means including a thermistor with negative characteristics, 12 is CP
A control section consisting of u, 13 is a proportional control circuit, and a control clock! 4, the control pulse signal can be generated.

20 is for control target temperature St, Sv and abnormality detection reference temperature T
A reference voltage setting circuit for setting a common reference voltage for I and D2, which includes a pair of voltage dividing resistors R11 and R11 as in the previous embodiment.
It consists of R12, branch resistor R13, and transistor ↑r2.

3G is an abnormality detection circuit, which includes a time constant circuit 31 connected to the output side of the reference voltage setting circuit 20, an amplifier 32 consisting of an operational amplifier, and an abnormality detection reference voltage VIL for upper and lower limits.
, Vlu, V2L, V2u are set by the voltage divider 33 and the comparators 34 and 35 that perform abnormality determination for upper and lower limits. Reference numeral 40 denotes a detection voltage control clock 14 from the temperature detection means 30 amplified via an amplifier 41.
This is a pulse superimposition circuit that superimposes pulses based on signals from

Next, the control operation based on this embodiment will be explained based on FIG. 5.

First, when the power is turned on, the control unit 6
Since the switching signal is not output to the Tr2 side of the reference voltage setting circuit 2o, the reference voltage Vw corresponding to the control target temperature Sw for weight control set only by the voltage dividing resistors R11 and R12 is set to the proportional temperature control circuit. 13 and performs predetermined weight control, the reference voltage Vw is boosted by the amplifier 32 via the time constant circuit 5 to obtain the lower limit abnormality detection reference voltage V2L, and the voltage V2L is output to the voltage divider 3.
3 to obtain the upper limit abnormality detection reference voltage V2u, and input these reference voltages V2L V2u to the upper limit and lower limit abnormality determination comparators 34 and 35, respectively.

On the other hand, the detection voltage from the temperature detection means is passed through an amplifier 32 and a pulse superimposition circuit 40 to generate a pulse detection signal having a pulse period corresponding to the control clock 14, and this pulse detection signal is used for each abnormality judgment. Comparator 1.2
By inputting the signal into the sensor, it becomes possible to detect abnormalities such as abnormal temperature rise and abnormal temperature fall, and since the detection signal is vibrated in a minute pulse shape, the abnormality detection sensitivity increases accordingly.

If a fixing operation command is received during the weight control, a switching signal from the control section 8 is sent to the reference voltage setting circuit 2.
By outputting to 0, branch resistor R13 and voltage dividing resistor R
Fixing control target temperature S based on parallel connection of 11 and R12
By obtaining a reference voltage Vt corresponding to t and inputting the reference voltage Vt to the proportional control circuit 13, the fixing device temperature can be shifted to and maintained at the fixing control target temperature St.

On the other hand, the reference voltage Vt is simultaneously input to the abnormality detection circuit 30 side, and the time-series voltage curve obtained by the voltage discharge of the time constant circuit 5 is increased by the amplifier 32, and the lower limit abnormality detection is performed to shift to the fixing operation. Voltage curve V3L-V
IL is obtained, and the voltage V3L-VIL is divided by a voltage divider to obtain the upper limit abnormality detection reference voltage V3u-Vlu, and these reference voltages V3L-VIL V3u-
Vlu 7ft, input to comparators 34 and 35 for each 'A normal judgment for upper and lower limits.

Therefore, even in this embodiment, the fixing operation can be performed while detecting a predetermined abnormality during the transition. Thereafter, the operation opposite to the above is performed in response to the fixing operation end signal.

"Effects of the Invention" As described above, according to the present invention, even in a control system having a plurality of switchable control target temperatures, there is a time limit for detecting malfunctions and abnormalities not only while maintaining each control target temperature but also during transition. It is possible to accurately detect an abnormality without causing any delay, and especially in claim 2), since a time constant circuit is simply added to the conventional detection circuit, the configuration is simplified and the above-mentioned By changing the RC constant of the time constant circuit, it can be applied to any temperature detection system, and its practical effects are extremely large.

It has various effects such as

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing the main configuration of a temperature control system according to the basic configuration of the present invention, FIG. 2 is a circuit block diagram showing the overall configuration of a temperature control system according to another embodiment,
FIG. 3 is a temperature graph showing the relationship between each control target temperature and abnormality detection reference temperature for the conventional technology, FIG. 4 for the device shown in FIG. 1, and FIG. 5 for the device shown in FIG. 2. be.

Claims (1)

[Scope of Claims] 1) An abnormality detection method in a temperature control system configured to enable switching of control target temperatures in accordance with the operating state of a heated object, comprising:
An abnormality detection method characterized by setting a plurality of reference temperatures for abnormality detection and at least mutually transitioning between the reference temperatures for abnormality detection via a time-series temperature change curve 2) The operating state of the heated object In an abnormality detection device for a temperature control system configured to be able to switch control target temperatures in accordance with each other, a reference voltage setting means capable of switching a reference voltage by a switching signal, an output voltage from the reference voltage setting means and the heated object are provided. an abnormality determination means for determining an abnormality in the temperature control system based on a detected voltage corresponding to a detected temperature, and a time constant circuit is interposed at least on the output side of the reference voltage setting means to detect the abnormality. An abnormality detection device for a temperature control system, characterized in that the reference voltages for use in the temperature control system are configured to be able to shift between reference voltages while changing the reference voltages in a time-series manner based on the time constant of the time constant circuit.