JPH0346528A - Detecting circuit for fault of temperature sensor - Google Patents

Abstract

PURPOSE:To exactly execute the detection without being influenced by a variance of a constant and a change with the lapse of time by providing a comparing circuit for outputs of a model circuit and a temperature sensor, and always using the output of the temperature sensor as a value to be compared at the time of starting to detect a fault. CONSTITUTION:A desired value set by a desired value circuit 1 and an output of a temperature sensor 2 are inputted and added 3, and an output of a proportional circuit 4 for inputting it is inputted to a heat roll 5. Subsequently, an output of the roll 5 is detected by the sensor 2 and brought to feedback. In this case, to a model circuit 6 having an input/output characteristic being approximate to a transfer function, the output of the sensor 2 is inputted as an initial value. Next, the outputs of the circuit 6 and the sensor 2 are compared 7, and based thereon, an alarm processing 8 is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a temperature sensor failure detection circuit in an electrophotographic printing device, and in particular, to a failure detection circuit for a temperature sensor that detects the temperature of a heat roll that is fixing toner. Regarding circuits.

[Conventional technology]

Conventionally, this type of temperature sensor failure detection circuit compares the output of the temperature sensor and the output of the comparison value generation circuit.
It is configured to perform alarm processing.

FIG. 2 is a block diagram of a temperature sensor failure detection circuit showing an example of such conventional technology.

As shown in FIG. 2, the conventional detection circuit includes a target value circuit 1, a temperature sensor 2, an adder 3 which uses the output of the target value circuit 1 as an addition input and the output of the temperature sensor 2 as a subtraction input.
A proportional circuit 4 which receives the output of the adder 3 as an input, a heat roll 5 which receives the output of the proportional circuit 4 as an input, a comparison value generation circuit 9, and the output of the temperature sensor 2 and the output of the comparison value generation circuit 9. It has a comparison circuit 7 as an input, and an alarm processing circuit 8 that receives the output of the comparison circuit 7 as an input.

Next, the operation of such a temperature sensor failure detection circuit will be explained.

First, target value circuit 1. Temperature sensor 2. The adder 3, the proportional circuit 4, and the heat roll 5 have a configuration generally known as a feedback control system, and make the surface temperature of the heat roll 50 coincide with the output of the target value circuit 1 with a certain degree of steady-state deviation.

On the other hand, as the temperature sensor 2, a thermistor having negative temperature characteristics is generally widely used. If this thermistor breaks, the lead wire breaks, or the connector is incorrectly inserted, an incorrect output value indicating that the surface temperature of the heat roll 5 is low will be generated, and the feedback control system will limit the heat roll 5 to its limit. The fixing unit continues to heat up, resulting in burnout of the fixing unit.

However, the comparison value generation circuit 9 has a resistance value equivalent to the resistance value of the temperature sensor 2 in which the temperature sensor 2 described above has failed,
This value is output to the comparison circuit 7. Therefore, when the output of the temperature sensor 2 shows a resistance value higher than the resistance value of the comparison value generation circuit 9, the comparison circuit 7 determines that there is a failure and notifies the alarm processing circuit 8. Therefore, the alarm processing circuit 8 inputs the signal from the comparison circuit 7, determines that the temperature sensor 2 is malfunctioning, and stops heating the thermo roll 5.

[Problem to be solved by the invention]

The conventional temperature sensor failure detection circuit described above requires adjustment for each temperature sensor in order to distinguish between failure and when the surface temperature of the thermo roll is actually low due to variations in the constants of the thermistors used as temperature sensors. is required,
This has the disadvantage of requiring an increase in the number of adjustment steps.

Furthermore, there is also the drawback that erroneous detection may occur as the temperature sensor changes over time, leading to a decrease in the reliability of the device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a temperature sensor failure detection circuit that is not affected by such temperature sensor constant variations or changes over time.

[Means to solve the problem]

The temperature sensor failure detection circuit of the present invention includes a target value circuit that sets a target value, a temperature sensor, an adder that receives the output of the target value circuit and the output of the temperature sensor, and an adder that receives the output of the adder. In a temperature sensor failure detection circuit that has a proportional circuit as an input, a controlled object that receives the output of the proportional circuit as an input, and constitutes a feedback control system in which the temperature sensor detects the output of the controlled object, the temperature sensor failure detection circuit has a transfer function. a model circuit that has similar input/output characteristics and inputs the output of the temperature sensor as its initial value; a comparison circuit that compares the output of the model circuit and the output of the temperature sensor; and an alarm based on the output of the comparison circuit. and an alarm processing circuit that performs processing.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a temperature sensor failure detection circuit showing one embodiment of the present invention.

As shown in FIG. 1, this embodiment includes a target value circuit 1, a temperature sensor 2, an adder 3 that receives the outputs of the target value setting circuit 1 and the temperature sensor 2, and an adder 3 that receives the output of the adder 3. A proportional circuit 4 whose output is taken as input, a heat roll 5 whose output is input, a model circuit 6 whose input is the output of the target value circuit 1 and the temperature sensor 2, and whose input is the output of the model circuit 6 and the temperature sensor 2. It has a proportional circuit 7 and an alarm processing circuit 8 whose output is input.

Next, the operation of such a temperature sensor failure detection circuit will be explained.

First, target value circuit 1. Temperature sensor 2. The components of the adder 3, the proportional circuit 4, and the heat roll 5 operate in the same manner as in the conventional example described above.

Here, if the output of the target value circuit 1 is U1, the gain of the temperature sensor 2 is KS, its output is Y, the proportional gain of the proportional circuit 4 is KP, the time constant of the heat roll 50 is 1M, and the gain is KM, then the feedback control system The transfer function of is expressed by the following equation (1).

That is, the model circuit 6 calculates the state transition method of the following equation (2) using a microcomputer so that it has an input/output characteristic approximated to the input/output characteristic of the equation (1). still,
In equation (2), T represents the sample time for calculation by the microcomputer, and U (N, T); Y (N, T
) represent the values of the above-mentioned U;Y at the time of N samples, respectively.

(2) Here, the value of the temperature sensor 2 is used as the initial value Y (0, T) at the start of calculation. Also, Y(N+1.T
) changes with the transition of U (N, T), and outputs an approximate value of the output of the temperature sensor 2.

On the other hand, the comparison circuit 7 inputs and stores the output value of the temperature sensor 2 at the start of failure detection, and compares it with the output value of the model circuit 6 after an arbitrary number of samples to determine the failure of the temperature sensor 2. In this case, the alarm processing circuit 8 is notified.

〔Effect of the invention〕

As explained above, the temperature sensor failure detection circuit of the present invention includes a model circuit that approximates the input/output characteristics of the feedback control system and a comparison circuit that compares the output of this model circuit and the output of the temperature sensor, and starts failure detection. By always using the output of the temperature sensor as the value to be compared, there is an effect that a failure of the temperature sensor can be accurately detected without being affected by variations in constants of the temperature sensor or changes over time.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a temperature sensor failure detection circuit showing an embodiment of the present invention, and FIG. 2 is a block diagram of a temperature sensor failure detection circuit showing a conventional example. 1... Target value circuit, 2... Temperature sensor, 3... Adder, 4... Proportional circuit, 5...
...Heat roll, 6...Model circuit, 7.
... Comparison circuit, 8 ... Alarm processing circuit.

Claims (1)

[Claims] a target value circuit for setting a target value, a temperature sensor, an adder that receives the output of the target value circuit and the output of the temperature sensor as input, a proportional circuit that receives the output of the adder as input, and the proportional circuit. has a controlled object whose input is the output of
In a temperature sensor failure detection circuit that constitutes a feedback control system in which the output of the controlled object is detected by the temperature sensor, a model that has an input/output characteristic that approximates a transfer function and inputs the output of the temperature sensor as its initial value. A temperature sensor failure detection circuit comprising: a comparison circuit that compares an output of the model circuit with an output of the temperature sensor; and an alarm processing circuit that performs alarm processing based on the output of the comparison circuit.