JP2764088B2 - Abnormality detection circuit and protection circuit of heat utilization equipment - Google Patents

Description

The present invention relates to a heater which is energized and controlled based on a temperature detected by a temperature detecting means, such as a thermal fixing device for thermally fixing an unfixed toner image. The present invention relates to an abnormality detection circuit and a protection circuit of a heat utilization device incorporating a device.

2. Description of the Related Art Conventionally, image fixing is performed while a transfer paper carrying an unfixed toner image is inserted between a pair of a roller including a fixing roller having a built-in heater and a pressure roller that rotates in synchronization with the fixing roller. In the heat fixing device to be performed, a temperature control circuit for maintaining the roller-to-surface temperature at the target temperature while controlling the power supply to the heater by using known control means such as proportional control or ON / OFF control is provided. I have.

This type of control circuit quickly raises the temperature to the control target temperature, and uses a plurality of control methods by program control so that the temperature does not fluctuate as much as possible even when the transfer paper is intermittently inserted between the pair of rollers. Temperature control is often performed in combination.

For this reason, the temperature control circuit has a complicated configuration both in hardware and software, and therefore, thermal runaway is likely to occur due to, for example, a program error of the CPU or deterioration of a resistor or a diode for setting a reference temperature. Thermal degradation or damage of a member having low heat resistance occurs.

For this reason, a conventional temperature control circuit is provided with a protection circuit for forcibly turning off the heater when the surface temperature of the fixing roller rises above a certain temperature.

However, due to a response delay of the temperature detecting element for detecting the surface temperature of the fixing roller or residual heating after the heater is turned off, an overshoot is inevitably generated when the heater is raised to the control target temperature after the power is turned on. It is necessary to set the set temperature of the protection circuit higher in consideration of overshoot.

However, as in recent years, in order to reduce the size of the apparatus, the diameter of the fixing roller is reduced, in other words, while the heat capacity is reduced, a large heater is used to minimize the waiting time at the time of startup. However, the overshoot inevitably tends to be large, and therefore, at a set temperature that takes such overshoot into consideration, after the transition to the steady state, the set temperature may reach the heat-resistant component near the critical temperature limit. There is a risk of heat damage.

On the other hand, when the operation set temperature of the protection circuit is set low, the protection circuit malfunctions due to overshoot generated even during normal operation.

In order to solve such a drawback, for example, in the case of ON / OFF control, the number of pulses corresponding to the energizing time for energizing the heater or the energizing time after passing a predetermined temperature is detected, and these values are set to a preset reference time. (Pulse) or more,
Technology to output heater cutoff or abnormal signal (JP-B-58-55504, JP-B-56-28266, JP-B-56-2927)
No. 3), and a technology that integrates an electric signal from a temperature detecting element, measures a temperature increase rate at the time of startup, and performs abnormality detection based on these numerical values have also been proposed. (Problems to be Solved by the Invention) In each of the above-mentioned prior arts, not only the instantaneous detected temperature but also a measured value that takes time into account. If it is changed, the change in the rising temperature gradient is basically grasped by replacing it with the change in the energization time, the integrated sum of the detected voltage (signal), the differential amount, and the like, and compares this with the reference value.

However, the rising temperature gradient is easily influenced by the environmental temperature at the time of startup.Especially, there is a case where the environmental temperature differs by 30 ° or more in winter and summer, and in consideration of the variation of the rising temperature gradient based on the environmental temperature, the reference value is increased. Must be set, and there is still a problem, though not as much as in the prior art for grasping the temperature itself.

For this reason, there is a technique for appropriately changing the reference temperature in accordance with the environmental temperature. However, adopting such a configuration complicates the circuit configuration in software and hardware.

In view of the drawbacks of the prior art, the present invention provides a quick control without causing thermal damage to a thermally degraded component when a temperature control circuit attached to a heat utilization device having a built-in heater such as the thermal fuser runs away for some reason. It is another object of the present invention to provide an abnormality detection circuit and a protection circuit capable of reliably protecting them.

In particular, the present invention protects the thermally degraded component accurately and reliably even when the set temperature is uniquely determined without considering variations such as overshoot temperature and temperature rise gradient caused by fluctuations in the environmental temperature. It is an object of the present invention to provide an abnormality detection circuit and a protection circuit that can perform the operation.

"Means for Solving the Problems" In order to achieve such technical problems, the present invention first proposes an abnormality detection circuit in claim 1). A point in which temperature setting means for setting a reference temperature in a temperature range higher than the control target temperature is provided. More specifically, the reference temperature is lower than the overshoot temperature at the time of steady start-up as shown in FIG. It is preferable that the temperature is set to a value higher than the upper limit temperature of the variation of the temperature fluctuation in the steady state after shifting to the control target temperature.

A point provided with a counting means for counting the number of times the temperature detected by the temperature detecting means has passed the reference temperature.The number of times of passing includes both cases of passing due to temperature rise and cases of passing when falling, Alternatively, both may be selected as necessary.

A point configured to make an abnormality determination based on whether or not the count value of the counting means has reached a reference count value.If the detected temperature drops to a predetermined temperature lower than the control target temperature, the counting means The point is that reset means for resetting the count value is provided.

Claim 2) proposes a protection circuit. The feature of the protection circuit is that, together with the temperature setting means and the counting means described above, the temperature detected by the temperature detection means is the reference temperature. A switch provided with ON / OFF switching means for turning off the power supply to the heater when the temperature becomes equal to or higher than that and returning the power supply when the temperature becomes equal to or lower than the above, based on a signal from the switching means or other means; The number of times the detected temperature has passed the reference temperature is counted by the counting means, and when the count value reaches a preset count value, the power supply to the heater is forcibly cut off. And resetting means for resetting the count value of the counting means when the detected temperature drops to a predetermined temperature lower than the control target temperature.

According to the abnormality detecting circuit described in claim 1), according to the technical means, it is possible to turn off the heater or cause an abnormality based on a time-series temperature change state such as an instantaneous detected temperature change or a temperature rise gradient. It does not perform detection, but counts the number of times the temperature detected by the temperature detection means has passed the reference temperature, and compares the count value with the reference count value to perform abnormality detection. Even if there is a variation such as a steady fluctuation of the overshoot temperature or a temperature rise gradient due to the above, if there is an abnormality at the time of transition to the steady state after the overshoot, the abnormality is promptly and surely detected. Can be detected.

On the other hand, according to the protection circuit described in claim 2, when the detected temperature becomes equal to or higher than the reference temperature during normal operation due to overshoot or other reasons, for example, even during proportional control operation, regardless of the control operation, The energization of the heater is turned off, the temperature is immediately lowered to the reference temperature or lower, and when the detected temperature becomes lower than the reference temperature, the energization is returned to maintain the control target temperature based on a predetermined proportional control operation.

If the temperature rises above the reference temperature still occurs one or more times even after transition to the steady-state control operation other than the overshoot, an abnormality caused by a program error of the CPU, deterioration of the resistance or diode in the control circuit, or the like. Therefore, for example, the OFF signal from the switching means is counted by the counting means, and when the count value reaches a preset count value, the energization of the heater is forcibly cut off. As a result, the heat utilization equipment is protected.

That is, the present invention merely stops the heating of the heater temporarily when the detected temperature becomes equal to or higher than the reference temperature to encourage the heater to return to below the reference temperature, and only when the detected temperature becomes higher than the reference temperature again. It performs the double protection function of completely stopping the heater.

Note that, as in the case of a thermal fixing device used in an electrophotographic apparatus, the control target temperature is temporarily lowered to the preheating temperature when the transfer paper insertion step is completed, and the next transfer paper insertion step is started while maintaining the preheating temperature. However, in such an apparatus, an overshoot occurs each time the transfer paper insertion process is restarted, and the count value is accumulated, making it impossible to determine whether there is an abnormality.

Therefore, in such a case, as described in the above constitutional requirements or c, the counting means may be set each time the detected temperature is lower than the control target temperature, for example, a preheating temperature, in other words, each time the transfer paper insertion process is restarted. Reset means for clearing the count value of.

Hereinafter, preferred embodiments of the present invention will be illustratively described in detail with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. It's just

FIG. 1 is a circuit diagram showing a heating control circuit of a thermal fixing device according to an embodiment of the present invention. Reference numeral 1 denotes a heating heater incorporated in a fixing roller 10, which includes a temperature fuse 11, a relay switch 12, and a solid state relay. Connected to AC power via SSR. The relay switch 12 includes a relay coil 15 having switching transistors 13 and 14 connected in series.
ON / OFF control of the heater is performed based on the excitation and non-excitation of the heater.

Reference numeral 2 denotes a thermistor which is disposed close to the surface of the fixing roller 10 and measures the roller surface temperature. A temperature control circuit for maintaining and controlling the heating of the heater 1 while controlling ON / OFF of the solid state relay SSR based on an electric signal from the control circuit 3.

4A and 4B are reference voltage generators each composed of a voltage dividing resistor R1-R2, R3-R4, and one generator 4A is a first reference corresponding to a reference protection temperature Tmax located in a temperature range higher than the fixing temperature T1. The voltage is set, and the reference voltage is applied to the comparison terminal side of one comparator 5A. The other generator 4B has a fixing temperature T1 and a preheating temperature T2.
A reference voltage corresponding to a second reference temperature (hereinafter, referred to as a reset temperature Tr) located in the temperature range between is set, and the reference voltage is applied to the comparison terminal side of another comparator 5B.

One comparator 5A is provided with the roller surface temperature and the reference protection temperature Tm.
ax is compared, and when the roller surface temperature becomes equal to or higher than the reference protection temperature Tmax higher than the fixing temperature T1, an OFF signal is output to the base side of one transistor 13 and the counter circuit 6, and the OFF signal is output through the one transistor 13. Then, the relay switch 12 is turned off and the count value in the counter circuit 6 is updated.

When the count value in the counter circuit 6 becomes equal to or greater than a predetermined count value, the output signal from the counter circuit 6 is sent to the abnormality indicator 7 and the base side of another transistor 14 via the inverter 8. Output the transistor
The relay switch 12 is turned off via 14.

At this time, since the output signal from the counter circuit 6 is continuously output until the count value is cleared by the signal from the reset circuit 9, for example, when the roller surface temperature falls below the reference protection temperature Tmax, In other words, even when one transistor 13 is turned on, the relay switch 12 does not return.

The other comparator 5B outputs a signal to the reset circuit 9 when the roller surface temperature falls below the reset temperature lower than the fixing temperature T1, that is, every time the transfer paper insertion step is completed, and the counter circuit 6 counts. This is to clear the value.

Next, the operation of this embodiment will be briefly described with reference to FIG. A in FIG. 2 is a temperature distribution during normal operation, and B is a temperature distribution during abnormal operation.

First, the heater 1 is turned on by turning on the power, and the fixing roller is turned on.
When 10 is raised to the fixing temperature T1, an overshoot occurs and when the roller surface temperature becomes equal to or higher than the reference protection temperature Tmax, the signal from the comparator 5B is inverted to an OFF signal, and 1 is counted in the counter circuit 6. With the transistor
13. The power supply to the heater 1 is cut off via the relay switch 12.

Thereafter, when the roller surface temperature falls below the reference protection temperature Tmax, the signal from the comparator 5B is again inverted to ON. Fixing temperature based on signal from 3
Maintenance control of T1 is performed. When the transfer paper insertion process is completed and the roller surface temperature drops to the preheating temperature, the comparator
The count value of the counter circuit 6 is cleared via the reset circuit 9 based on the output signal from 5B, and the above operation is repeated thereafter.

On the other hand, when the roller surface temperature again becomes equal to or higher than the reference protection temperature Tmax one or more times due to an abnormality of the CPU or the like, the count value in the counter circuit 6 is updated correspondingly, and the count value is set in advance. When the set count value is reached, an abnormality is displayed on the abnormality indicator 7 based on the output signal from the counter circuit 6, and the transistor
When the switch 14 is turned off, the energization of the heater 1 is forcibly cut off, and the thermal fixing device can be protected.

[Effects of the Invention] As described above, according to the present invention, even when the temperature control circuit 3 attached to the heat utilization device having the heater 1 built therein as the thermal fixing device runs away for some reason, the heat degraded component thereof They can be quickly and reliably protected or abnormally detected without causing thermal damage to them.

Further, the present invention provides a method for accurately and reliably protecting or thermally protecting the thermally degraded components even when the set temperature is uniquely determined without considering a variation such as an overshoot temperature or a temperature rise gradient caused by a change in environmental temperature or the like. Anomaly detection can be performed.

In particular, in the invention described in claim 3), the first protection means for temporarily stopping the heating of the heater 1 only when the roller surface temperature becomes equal to or higher than the reference protection temperature Tmax; The safety is extremely high because the heater 1 performs the double protection function of completely stopping the heater 1 when the temperature becomes equal to or higher than the protection temperature Tmax.

 And so on.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a heating control circuit of a thermal fixing device according to an embodiment of the present invention, and FIG. 2 is a temperature distribution diagram showing its operation.

Claims (2)

(57) [Claims] An abnormality detection circuit for a heat utilization device having a built-in heater which is energized and controlled to a control target temperature based on a temperature detected by a temperature detection means, wherein a reference temperature is set to a temperature range higher than the control target temperature. Temperature setting means for setting the temperature, and counting means for counting the number of times the temperature detected by the temperature detecting means has passed the reference temperature, and whether the count value of the counting means has reached a preset count value. And a reset unit for resetting the count value of the counting unit when the detected temperature has dropped to a predetermined temperature lower than the control target temperature. Abnormality detection circuit for heat utilization equipment. 2. A protection circuit for a heat utilization device having a built-in heater which is energized and controlled to a control target temperature based on a temperature detected by a temperature detection means, wherein a reference temperature is set in a temperature range higher than the control target temperature. Temperature setting means to be set, and ON / OFF switching for turning off the power supply to the heater when the temperature detected by the temperature detecting means becomes higher than the reference temperature and returning the power supply when the temperature becomes lower than the reference temperature. Means, and counting means for counting the number of times the detected temperature has passed the reference temperature based on a signal from the switching means or another means, and the count value of the counting means reaches a preset count value. In such a case, the power supply to the heater is forcibly cut off, and when the detected temperature decreases to a predetermined temperature lower than the control target temperature, the count value of the counting means is reduced. Protection circuit of a heat utilizing device, characterized in that a reset means set to.