JPH0243588A - Detection of abnormality in temperature detecting means - Google Patents

Abstract

PURPOSE:To prevent a heated body and various parts arranged around the heated body from being deteriorated and thermally destructed by detecting the abnormality of a temperature detecting means without supplying current to a heater. CONSTITUTION:The existence of a state change in a control signal before and after the passage of a prescribed time is detected under the stopped state of current supply to the heater 1C, and when the signal state is changed, the normality of the temperature detecting means 2 is decided, and no change is decided as abnormality. Thereby, the existence of abnormality in a temperature control device including the means 2 can be accurately detected without supplying current to the heater 1C. Consequently, the heated body and various parts arranged around the heated body can be prevented from being deteriorated or thermally destructed.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a method for detecting an abnormality in a temperature detection means or a temperature control device in which the temperature detection means is incorporated, and particularly relates to a method for detecting an abnormality in a temperature detection means or a temperature control device in which the temperature detection means is incorporated. The present invention relates to an abnormality detection method that can easily detect abnormalities such as disconnection of temperature detection means.

"Prior Art" Conventionally, temperature control has been performed in which an energization control signal is changed based on temperature information from a temperature detection means that detects the heating temperature of a heated object, and heat generation of a heater is controlled based on the changed control signal. The device is publicly known, and in this type of device, if the temperature detecting means is disconnected or short-circuited, it is possible to detect the current temperature state of the heated object or a change in the heating temperature that changes due to heating of the heater. As a result, erroneously continuing heating even though the heated object has reached the control target temperature not only causes thermal destruction and thermal deterioration of the heated object and various parts located around it. In the worst case, a fire accident may occur.

For this reason, in conventional devices, before performing a heating operation, the temperature detection means is energized and the output voltage is compared with a reference voltage for abnormality detection to determine a disconnection or short circuit. Immediately after the voltage is applied to the circuit, the voltage may not be constant and a transient voltage with a large peak value may be applied, so the output voltage from the detection means will inevitably become large, resulting in disconnection of the thermistor or Even though no short circuit has occurred, there is a risk that the voltage will exceed the reference voltage, resulting in a problem of lack of accuracy.

In order to eliminate this drawback, the heater is energized for a certain period of time to bring the temperature of the heated object to a range that does not cause the malfunction.
A detection method has been proposed in which the output voltage from the temperature detection means is compared with a reference voltage after the resistance of the thermistor is reduced to a certain level. (Unexamined Japanese Patent Publication No. 58-
5EiO08) ``Problem to be Solved by the Invention'' However, in such a device, an abnormality is detected after the heater is energized for a certain period of time, regardless of the current temperature of the heated object, so that the heated object has already reached the control target value. If the temperature is high before the heater is energized, such as when the power is temporarily turned off and then turned on again, the heating temperature after the heater is energized will be much higher than the control standard temperature. Particularly in the case of a member having low heat resistance and whose upper limit temperature at which it can be heated is strictly regulated, it may easily be thermally destroyed by the energization.

Furthermore, even if such thermal breakdown does not occur, forced energization of an object to be heated that is already in a high temperature range is likely to cause deterioration of various parts constituting the heating device.

Furthermore, in recent heating control devices, the control signal for controlling the energization of the heater is changed continuously and/or discontinuously based on the temperature information from the temperature detection means, thereby accurately and quickly. Various control devices have been proposed that adopt an on-off control method or a proportional control method to shift to a control target value, but in such control methods, the control state changes depending on the heating temperature state of the heated object. Therefore, the above-mentioned detection method of uniformly performing forced conduction while ignoring the heating temperature state is unreasonable and tends to cause erroneous control operations. It is possible to accurately detect the presence or absence of an abnormality in the temperature control device including the temperature detection means,
It is an object of the present invention to provide an abnormality detection method that can completely prevent deterioration and thermal destruction of a heated object and various parts arranged around it.

Another object of the present invention is to provide an abnormality detection method that is extremely suitable for a control device that employs an on-off control method or a proportional control method in which the control state changes depending on the heating temperature state of the heated object. purpose.

[Means for Solving the Problems] First, before explaining the present invention, the process that led to the present invention will be explained.

Generally, if a thermistor constituting the temperature detection means is disconnected or short-circuited, the detected voltage from the temperature detection means, which is output as a partial voltage of the thermistor, will change even if the external environment temperature is in the room temperature range. Regardless of this, a detection voltage of the same level as temperature information when the heated object is in a high temperature range (or extremely low temperature range) is output.

Therefore, in a device that changes the type of control signal output from the control device based on the temperature information before and after reaching a predetermined temperature range, such as a temperature control device that uses a so-called proportional control method or an on-off control method, In other words, the signal type is determined to be a signal type other than normal temperature by determining the signal type to which temperature range the control signal output corresponding to the temperature information corresponds, regardless of whether or not the heater is energized/blacked out. In this case, it is possible to determine that there is a possibility that the temperature detecting means or the like is abnormal. (Hereinafter, such determination means will be referred to as the first determination means.) However, even if the temperature control device including the temperature detection means is operating normally, the heater may There are cases where the detected temperature of the heated object before energization is higher than the ambient environment temperature, and therefore, using only the above-mentioned determination method, there is a risk that in such a case, it will be erroneously determined to be abnormal.

Therefore, in the above case, if the temperature of the heated object is higher than the ambient environment temperature, the temperature of the heated object will change toward the ambient environment temperature as time passes, so as long as the temperature control device is operating normally. In response to this, switching of the control signal type or a change in the signal state occurs based on the temperature information, but conversely, for example, if the temperature detection means is disconnected, there is no change in the temperature of the heated object. However, since this cannot be detected by the detection means, its output voltage remains constant, and the type of control signal or signal state cannot change in response to the voltage.

Therefore, even if the signal type etc. is a signal type other than room temperature, without immediately determining it as abnormal,
A second determination is made after a predetermined period of time has elapsed, and if there is a change in the control signal type νJ or a change in the signal state between the first and second determinations, it is determined that the temperature detection means etc. are normal. If there is no change, it is determined that there is an abnormality (hereinafter referred to as "I determination means second determination means"), so-called two-stage determination is possible, and this makes it possible to conduct a so-called two-stage determination. A vehicle can be created that accurately determines the presence or absence of an abnormality in the temperature detection means, etc. without causing any damage, and as a result, it is possible to completely prevent deterioration and thermal destruction of various parts constituting the heating device, as well as the risk of fire.

The invention described in claim 2) is a combination of the first and second determining means, and in particular, as in the so-called proportional control method, when a predetermined heating temperature range sandwiching the control target value is reached. It is suitably applied to a device that switches the type of signal output from the control device side before and after.
The feature is that after confirming whether the control signal is a signal type in any heating temperature range, if the control signal is a signal type other than the normal temperature range, after a predetermined period of time has elapsed, The vehicle is configured to check the difference in signal type or change in the signal, and detect whether or not there is an abnormality in the temperature detection means based on the difference or change in the signal type.

Now, especially when it is clear in advance that the temperature of the heated object is different from the ambient environment temperature, such as when the power supply is temporarily interrupted, the first determining means can be omitted.

Therefore, in claim 1), the patent claims that the second determination means alone attempts to detect the presence or absence of an abnormality in the temperature detection means or the like.

The invention described in claim 1) is not limited to devices in which the signal changes over a predetermined temperature range, such as the above-mentioned proportional control or on-off control, but also in devices in which the control signal changes continuously over the entire temperature range. It can also be effectively applied to equipment that uses In particular, in such a device, the signal type is the same in all temperature ranges, including in the case of an abnormality, so it may be difficult to practically employ the first determination means. It is better to apply it partially.

"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.

1 and 2 are a schematic block diagram and a detailed circuit block diagram showing the overall configuration of a heat fixing device incorporated in an electrophotographic printer according to an embodiment of the present invention.The overall configuration will be briefly explained as follows. 1 is a heating fixing device consisting of a pressure roller 1b that rotates in synchronization with each other and a fixing roller la containing a heater lc; a temperature detecting means 2 is disposed close to the surface of the fixing roller 1a; After outputting a signal controlled based on the temperature information from pulse width modulation circuit 3 to a control circuit 6 composed of a microcomputer, the control circuit 6 generates a heater on/off signal corresponding to the control signal. On/off control of the AC power supply 8, which supplies power to the heater lc, is performed while operating the solid state relay SSR based on the on/off signal.

On the other hand, in an electrophotographic printer incorporating such a heat fixing device, the temperature detecting means 2 detects the temperature of the fixing roller 1a whose temperature fluctuates rapidly due to repeated fixing and non-fixing operations.
Since the temperature detecting means 2 is arranged nearby, the thermistor 2a constituting the temperature detecting means 2 is likely to be disconnected.

Therefore, in this embodiment, a measure is taken to easily detect the disconnection of the thermistor 2a without energizing the heater lc.

Next, the configuration of various members constituting this means will be explained in detail.

The temperature detection means 2 consists of a thermistor 2a that divides the reference circuit voltage Vc and a fixed resistor 2b, and when the thermistor 2a is disconnected, the detection output (voltage) from the temperature detection means 2 becomes -E (at least The detection output is configured to change in direct proportion to the temperature rise of the fixing roller 1d so that the voltage corresponds to a high temperature range below a lower limit reference temperature Tu (to be described later).

In other words, since the temperature-resistance distribution of the thermistor 2a shown in 11η generally increases or decreases in inverse proportion, in this embodiment, as shown in FIG. The partial pressure output of the sensor is configured to be taken out as a detection output, thereby making it possible to change the detection output in direct proportion to temperature information.

As is well known, the pulse modulation circuit 3 uses a "threshold generation circuit" to generate the respective reference voltages To and Tu corresponding to the lower and upper reference temperatures provided on both sides of the target voltage ↑a corresponding to the fixing temperature. ”4, and the reference voltages To, T
u and the detection output S, and if the detection output S is below the lower limit reference voltage TO, an ON signal is continuously transmitted to the control circuit 6 side until the lower limit reference voltage TO is reached, and the detection output S After reaching the lower limit reference voltage TO, the pulse width was varied in proportion to the difference between the target voltage ↑a and the detection output S. In other words, as the target voltage Ta approaches, the pulse width (ON width) is changed by changing the clock A control pulse signal proportionally reduced based on the clock period oscillated by the generation circuit 5 is transmitted to the control circuit 6 side.

On the other hand, if the detection output S exceeds the upper limit reference voltage Tu due to overshoot or the like, an off signal is continuously sent to the control circuit 6 until the upper limit reference voltage Tu is reached, and then the detection After the output S reaches the upper limit reference voltage Tu, the pulse width is varied in proportion to the difference between the target voltage Ta and the detected output S. In other words, as the output S approaches the target voltage Ta, the off width is changed in the same manner as the clock generation circuit. A control pulse signal proportionally reduced based on the clock period oscillated by the control circuit 5 is transmitted to the control circuit 6 side.

(The signals output from these pulse width modulation circuits 3 are collectively referred to as control signals.) The control circuit 6 is composed of a microcomputer, and has a built-in predetermined program that performs the abnormality detection function described later in addition to the temperature control. A timer 8 is provided to measure a predetermined time based on a command from a microcomputer, and in this embodiment in particular, the timer 8 is used to perform a second determination after the first determination as shown in the operation described later. setting a time interval width necessary for determining whether the control signal is an off signal, an on signal, or a pulse signal; and setting a time width necessary for determining whether the control signal is an off signal, an on signal, or a pulse signal, and the pulse signal. Reference numeral 7 designates an alarm generation circuit for setting the time width necessary to check whether there is a change in the pulse width.

Next, an abnormality detection operation based on this embodiment will be explained based on FIG. 3.

When a fixing operation start command is issued by the power switch, first the heater is turned on/off from the output port of the control circuit 6.
While the output of the off signal is stopped and the heater is maintained in a non-energized state (STEP 1), a reference circuit voltage Vc is applied to the temperature detection stage f side to obtain its detection output S. Then, within the pulse width modulation circuit a, the detection output S and the reference voltages To, Tu
A control signal corresponding to the detection output S is output to the control circuit B side. (STEP 2) On the control circuit B side, after the control signal is read by the microcomputer (STEP 3), it is determined whether the signal is on, off, or a pulse signal. (STEP 4) At this time, if the thermistor 2d is disconnected, the detection output is configured to be a voltage that corresponds to a high temperature range that is higher than the upper and lower limit reference temperature To. If the signal is on, determine that there is no disconnection (STEP 5). Based on this determination, the output stop of the heater on/off signal is canceled and normal heating control is performed (STEP 8), and the temperature control is then completed. Continue this operation until (STEP 7) If the signal type read by the microcomputer is an off or pulse signal, start the timer (STEP 8)
), the timer is stopped when a predetermined period of time has elapsed (
STEP 9) Read the signal again (STEP
O) Next, after determining whether or not the signal type has changed before and after the elapse of the predetermined time (STEPll), if it has changed, it is determined that there is no disconnection and the process described in step 5 is performed.
Predetermined heating control of TEP8-7 is started.

Note that if the signal type is at the off level, the heating state of the heater is also off before the power is turned on, so the temperature is decreasing, and therefore the predetermined time after the power is turned on again is delayed. The control signal is quickly switched from the OFF state to the pulse signal state without any delay.

However, when the signal type is in the pulse signal state, the heating state of the heater before the power is turned on is a proportional heating state, so even if the heater is turned on by VJ in that state, for example, the rotation of the fixing roller may stop. Due to the balance between the reduction of the heat load of the heater and the residual heat of the heater, the temperature may rise or the temperature may remain in equilibrium. Therefore, in order to switch from the pulse signal state to the on signal state in this state, it is necessary to extend the predetermined time after the power is turned on again.

Therefore, in this embodiment, we focused on the fact that when the detection output changes, the pulse width of the pulse signal changes correspondingly, and when the signal is not switched (S
Even in TEP12), if the pulse width changes before and after a predetermined time has passed (STIEP13), this is detected in the control circuit 6, and if it changes, it is determined that there is no disconnection.
EP 5) Start predetermined heating control of the above 5TEPθ to 7.

It is determined that there is a disconnection only when the above-mentioned change does not occur. (STEP 14) Thereby, disconnection of the thermistor constituting the temperature detection means can be easily and quickly detected.

"Effects" As described above, according to the present invention, since an abnormality in the temperature detection means is detected without energizing the heater, deterioration and thermal damage of the heated object and various parts arranged around it can be achieved. 5 Furthermore, fire accidents can be completely prevented.

In particular, according to the invention described in claim 2), the temperature control operation of the control device that adopts an on-off control method or a proportional control method in which the control state changes depending on the heating temperature state of the heated object is effectively utilized. In order to perform the detection operation, a single circuit configuration and the detection operation are simplified, and there is no room for erroneous control operation, allowing accurate and reliable detection.

Furthermore, according to claim 1), when the power is temporarily turned off and then turned on again when the heating is controlled to a predetermined heating temperature, such as in the case of a jam in a heat fixing device, the heater is turned on by '1111!'. Since it is possible to detect anomalies without the need for heating, it is possible to completely prevent deterioration and thermal destruction of the heated object and various parts placed around it, as well as fire accidents.

It has various effects such as

[Brief explanation of the drawing]

1 to 3 show a heat fixing device according to an embodiment of the present invention, FIG. 1 is a schematic block diagram showing the overall configuration of the heat fixing bag applied to the present invention, and FIG. 2 is a detailed circuit block thereof. In the figure, FIG. 3 is a flowchart showing the operating procedure.

Claims (1)

[Scope of Claims] 1) An abnormality detection method for a temperature control device in which a control signal for controlling heat generation of a heater is configured to be changeable based on temperature information of a heated object from a temperature detection means, which includes: Abnormality detection characterized by detecting the presence or absence of a change in the state of the control signal before and after the elapse of a predetermined time in a stopped state, and detecting an abnormality in the temperature control device including the temperature detection means based on the presence or absence of the change. Method 2) Compare the temperature information from the temperature detection means that detects the heating temperature state of the heated object with one or more reference temperatures preset in the temperature control device, and determine when the temperature information reaches the reference temperature. In a method for detecting an abnormality in a temperature control device, the control state is switched and different types of control signals are output before and after the control state is reached. After confirming whether the control signal is a signal type or not, if the control signal is a signal type outside a predetermined reference temperature range, confirming the signal type and/or a change in the signal state after a predetermined time elapses;
An abnormality detection method characterized by detecting an abnormality in a temperature control device including the temperature detection means based on the change.