JPH02222013A - Abnormality detecting circuit and protecting circuit for heat using equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a heater that is controlled to be energized based on a temperature detected by a temperature detection means, such as a heat fixing device that heat-fixes an unfixed toner image. This invention relates to abnormality detection circuits and protection circuits for heat utilization equipment with built-in heat utilization equipment.

``Prior art'' Conventionally, image fixation has been carried out by inserting transfer paper carrying an unfixed toner image between a pair of rollers, including a fixing roller with a built-in heater and a pressure roller that rotates synchronously while being in pressure contact with the fixing roller. In the heat fixing device, a temperature control circuit is installed to maintain the roller surface temperature at a target temperature by controlling the energization of the heater using known control means such as proportional control or ON/OFF control. ing.

This type of control circuit uses multiple control methods through program control to quickly raise the control target temperature and to prevent temperature fluctuations as much as possible even when 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 terms of hardware and software, and as a result, thermal runaway is likely to occur due to, for example, a CPU programming error or deterioration of the resistor or diode that sets the reference temperature. Thermal deterioration and damage occur to members with low heat resistance.

For this reason, conventional temperature control circuits are provided with a protection circuit that forcibly turns off the heater when the surface temperature of the fixing roller rises above a certain temperature.

However, due to a delay in the response of the temperature detection element that detects the surface temperature of the fixing roller and residual heating after the heater is turned off, overshoot inevitably occurs when the heater is raised to the control target temperature after the power is turned on. It was necessary to set the set temperature of the protection circuit to a high value in consideration of overshoot.

However, in recent years, in order to downsize the equipment, the diameter of the fixing roller has been reduced, or in other words, the heat capacity has been reduced, while large heaters have been used to minimize the waiting time during startup. However, overshoot inevitably tends to be large, and therefore, if the set temperature takes such overshoot into account, the set temperature may reach near the critical heat resistance of thermally degraded parts after transition to a steady state, and the parts may There is a risk of heat damage.

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

In order to eliminate this drawback, for example, in the case of ON/OFF control, the number of pulses corresponding to the energization time to the heater or the energization time after passing a predetermined temperature is detected, and these values are set as a reference time that is set in advance. (Pulse) Technology that cuts off the heater power or outputs an abnormal signal when the pulse is exceeded (Special Publication No. 58-55504, Special Publication No. 5B-28288
(Japanese Patent Publication No. 5B-29273), a technology that integrates electrical signals from temperature detection elements, measures temperature increase rate at the time of startup, and detects abnormalities based on these values. has also been proposed. (Japanese Patent Publication No. 5B-28288, Japanese Patent Publication No. 55-78371, etc.) "Problems to be Solved by the Invention" The above-mentioned conventional technologies do not only detect instantaneous temperature, but also measure values that take time into account. In principle, changes in the rising temperature gradient, energization time, detection voltage (signal)
It is understood by replacing it with changes in the integrated sum or differential amount, etc., and then compared with the reference value.

However, the temperature increase gradient is easily influenced by the environmental temperature at the time of start-up, and the environmental temperature may differ by 30 degrees or more, especially in winter and summer. However, the above-mentioned prior art technique of determining the temperature itself still has problems.

For this reason, there is a technique for appropriately changing the reference temperature in accordance with the environmental temperature, but if such a configuration is adopted, the circuit configuration becomes complicated both in terms of software and hardware.

In view of the shortcomings of the prior art, the present invention has been developed to quickly and quickly prevent thermal damage to heat-degraded parts when a temperature control circuit attached to a heat utilization device with a built-in heater, such as the heat fixing device, goes out of control for some reason. In particular, the present invention is characterized by providing an abnormality detection circuit and a protection circuit that can reliably protect these. It is an object of the present invention to provide an abnormality detection circuit and a protection circuit that can accurately and reliably protect the thermally degraded components even when a set temperature is uniquely determined without considering the above.

"Means for Solving the Problem" In order to achieve the technical problem, the present invention first proposes an abnormality detection circuit in claim 1), which is characterized by: - At least heat utilization equipment In other words, more specifically, the reference temperature is lower than the overshoot temperature at the time of steady startup as shown in Fig. 2. , and is preferably set to a value higher than the upper limit temperature of the variation in temperature fluctuation during steady state after transition to the control target temperature.

■A counting means is provided to count the number of times the temperature detected by the temperature detection means has passed the reference temperature.The number of times the temperature has passed includes both cases where the temperature has passed due to a rise in temperature and cases where it has passed due to a fall in temperature. , or both may be selected as necessary.

(2) Abnormality is determined based on whether or not the count value of the counting means reaches a reference count value.

In addition, claim 3) proposes a protection circuit, which is characterized in that, in addition to the temperature setting means described in (1) above and the counting means described in (2) above, a) the temperature detected by the temperature detection means is Based on a signal from the switching means or other means, the heater is equipped with an ON/OFF switching means that turns off the energization of the heater when the temperature exceeds the reference temperature or returns the energization when the temperature falls below the reference temperature. The number of times the detected temperature passes the reference temperature is counted by the counting means, and when the count value reaches a preset count value.

The configuration is such that the power supply to the heater is forcibly cut off. It is in.

"Operation" According to the abnormality detection circuit according to claim 1), according to this technical means, heater power is cut off or abnormality is detected based on a time-series temperature change situation such as an instantaneous detected temperature change or a temperature increase gradient. It is not a device that performs detection, but rather a device that counts the number of times the temperature detected by the temperature detection means passes the reference temperature and compares this count value with the reference count value to detect abnormalities. Even if there are steady fluctuations in the overshoot temperature or variations in the temperature rise gradient due to It can be detected.

On the other hand, according to the protection circuit according to claim 3), when the detected temperature becomes equal to or higher than the reference temperature during normal operation due to overshoot or other reasons, even if the detected temperature is in a proportional control operation, for example, it is independent of the control operation. Turn off the power to the heater L,
The temperature is quickly lowered to below the reference temperature, and when the detected temperature becomes below the reference temperature, the energization is restored to maintain the control target temperature based on a predetermined proportional control operation.

If the above-mentioned reference temperature or higher occurs again or multiple times even after transition to steady control operation other than overshoot, it is an abnormality caused by a CPU program error or deterioration of the resistance or diode in the control circuit. 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 power supply to the heater is forcibly cut off. As a result, the heat utilization equipment is protected.

In other words, the present invention simply temporarily stops heating the heater when the detected temperature exceeds the reference temperature, prompting the temperature to return to below the reference temperature, and only when the detected temperature remains above the reference temperature for some time. It operates a double protection mechanism that completely stops the heater.

Incidentally, like a heat fixing device used in an electrophotographic device.

Some devices temporarily lower the control target temperature to a preheating temperature when the transfer paper insertion process is completed, and wait while maintaining the preheating temperature until the next transfer paper insertion process starts. Overshoot occurs every time the transfer sheet insertion step is restarted, and the count value accumulates, making it impossible to determine whether there is an abnormality.

Therefore, in such a case, as described in claims 2) and 4), each time the detected temperature drops to a preheating temperature lower than the control target temperature, in other words, each time the transfer paper insertion process is restarted, It is sufficient to provide a reset means for clearing the count value of the counting means.

``Example'' A preferred embodiment of the present invention will be described in detail below by way of example with reference to one drawing. 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 circuit configuration diagram showing a heating control circuit of a thermal fixing device according to an embodiment of the present invention, in which 1 is a heater built into a fixing roller IO, a temperature fuse 11, and a relay switch 1.
2 and a solid state relay SSR. And the relay switch 12 is
The O of the heater is determined based on the energization and de-energization of the relay coil 15 connected in series with the switching transistors 13 and 14.
Performs N/OFF control.

2 is a thermistor that is placed close to the surface of the fixing roller lO and measures the roller surface temperature; 3 is a thermistor that converts the roller surface temperature into the fixing temperature TI (control target temperature) or preheating temperature based on the voltage detected by the thermistor 2; This is a temperature control circuit for maintaining and controlling the temperature of the heater 1, and the heating control of the heater 1 is performed without ON/OFF control of the solid state relay SSR based on the electric signal from the control circuit 3.

4A and 4B are reference voltage generators consisting of voltage dividing resistors R1-R2 and R3-R4, respectively, and the - generator 4A is a reference voltage generator consisting of voltage dividing resistors R1-R2 and R3-R4.
Standard protection temperature located in a higher temperature range ■a! A first reference voltage corresponding to is set, and this reference voltage is applied to the comparison terminal side of the negative comparator 5A. Also another generator 4B
sets a reference voltage corresponding to a second reference temperature (hereinafter referred to as reset temperature ↑r) located in a temperature range between fixing temperature 〒1 and preheating temperature T2, and compares this reference voltage with another comparator 5B. It is applied to the terminal side.

- The comparator 5A compares the roller surface temperature with the reference protection temperature T.
max, and when the roller surface temperature exceeds the reference protection temperature ↑wax, which is higher than the fixing temperature TI, an OFF signal is output to the base side of the negative transistor 13 and the counter circuit 8, and the negative transistor 13 is At the same time, the relay switch 12 is turned off through the relay switch 12, and the count value in the counter circuit 6 is updated.

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

At this time, since the output signal from the counter circuit B continues to be output until the count value is cleared by the signal from the reset circuit 8, even if the roller surface temperature falls below the reference protection temperature Tmax, In other words, even if the negative transistor 13 is turned on, the relay switch 12
will never return.

Now, the other comparator 5B outputs a signal to the reset circuit 8 when the roller surface temperature falls below the reset temperature which is lower than the fixing temperature 〒1, in other words, every time the transfer sheet insertion process is completed, and outputs a signal to the counter circuit 8. This clears the count value.

Next, the operation of this embodiment will be briefly explained based on FIG. A in FIG. 2 is the temperature distribution during normal operation, and B is the temperature distribution during abnormal operation.

First, turn on the power to energize Beef 1, and then fix roller 1.
0 to the fixing temperature T1, and when an overshoot occurs and the roller surface temperature exceeds the reference protection temperature Tlaf, the signal from the comparator 5B is reversed to an OFF signal, and the counter circuit B counts 1. In addition, transistor 13. Heater 1 via relay switch 12
Power is cut off.

Thereafter, when the roller surface temperature falls below the reference protection temperature Tmax, the signal from the comparator 5B is turned ON again. When the heater 1 is energized again according to the operation procedure described above, the temperature control circuit The maintenance control of the fixing temperature element 1 is performed based on the signal from 3. When the transfer paper insertion process is completed and the roller surface temperature drops to the preheating temperature, the reset circuit 9 is activated based on the output signal from the comparator 5B.
The count value of the counter circuit 8 is cleared via , and the above operation is repeated thereafter.

On the other hand, due to CPU and other abnormalities, the roller surface temperature once again dropped to the standard protection temperature ↑■a! If the above is repeated - or multiple times, the count value in the counter circuit 6 is updated accordingly, and when the count value reaches a preset count value, the output from the counter circuit 8 is Based on the signal, an abnormality display is displayed on the abnormality display 7, and the transistor 14 is turned off, thereby forcibly cutting off the electricity to the heater 1, thereby protecting the heat fixing device.

"Effects of the Invention" As described above, according to the present invention, even if the temperature control circuit 3 attached to the heat utilization equipment including the heater 1, such as the heat fixing device, goes out of control for some reason, the thermally deteriorated parts It is possible to quickly and reliably protect them or detect abnormalities without causing thermal damage to them.

Further, the present invention can accurately and reliably protect or protect the thermally degraded parts even when the set temperature is uniquely determined without considering variations in overshoot temperature or temperature increase gradient caused by changes in environmental temperature, etc. It is possible to detect anomalies.

In particular, in the invention described in claim 3), the first protection means temporarily stops the heating of the heater 1 when the roller surface temperature reaches or exceeds the reference protection temperature 7181; Protection temperature child ■a! The safety is extremely high because it provides a double protection system that completely stops the heater 1 when the above occurs.

It has various effects such as

[Brief explanation of the drawing]

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

Claims (1)

[Claims] 1) In an abnormality detection circuit for a heat utilization device incorporating a heater whose energization is controlled based on a temperature detected by a temperature detection means, a reference temperature is set in a temperature range higher than a control target temperature of the heat utilization device. a temperature setting means for setting, and a counting means for counting the number of times the temperature detected by the temperature sensing means has passed the reference temperature, and whether or not the count value of the counting means has reached a preset count value. 2) An abnormality detection circuit for heat utilization equipment, characterized in that it is configured to determine whether or not there is an abnormality based on Claim 1) characterized in that a reset means for resetting the count value is provided.
Abnormality detection circuit for heat utilization equipment described in 3) In the protection circuit for heat utilization equipment containing a built-in heater whose energization is controlled based on the temperature detected by the temperature detection means,
temperature setting means for setting a reference temperature in a temperature range higher than at least the control target temperature of the heat utilization equipment; ON/OFF switching means for restoring the energization when the temperature drops below a reference temperature; and counting means for counting the number of times the detected temperature passes the reference temperature based on a signal from the switching means or other means. A protection circuit for heat utilization equipment, characterized in that the circuit is configured to forcibly cut off electricity to the heater when the count value of the counting means reaches a preset count value.