JPH0362207A - Abnormality detecting method for temperature controller of object to be heated - Google Patents

Abstract

PURPOSE:To detect the abnormality with no occurrence of malfunctions, etc., by stopping the abnormality detecting action for a prescribed time after changing the abnormality detecting reference temperature in response to the switch to a control target temperature. CONSTITUTION:The voltage levels corresponding to a weight temperature Sw and a fixing target temperature St are stored as the control target temperatures together with the voltage levels corresponding to the reference temperatures T1t and T1w for detection of the over-temperature control in both fixing and weight action stages, and the voltage levels corresponding to the reference temperatures T2t and T2w for detection of short circuits (of a detection means 2) respectively. The corresponding control target temperatures can be sent to a temperature control means 3 based on both fixing action start and end signals. At the same time, the abnormality detecting reference temperatures T1 and T2 can be sent to an abnormality detection means 5. Then the abnormality detecting reference temperature is changed in response to the change to the control target temperature. Then the abnormality detecting action is stopped for a prescribed time. Thus the abnormality can be detected with high efficiency with no occurrence of malfunctions even while an object to be heated is changed to another control target temperature.

Description

Detailed Description of the Invention "Industrial use!?" The present invention provides a temperature control device for use in a heat fixing device that heat-fixes an unfixed toner image. has a second control target temperature lower than the first control target temperature;
The present invention relates to an abnormality detection method in a temperature control device for a heated object configured to control the temperature of the heated object while switching between the two control target 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 Sv 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
Then, at the same time as the fixing operation ends, the weight temperature is again shifted to the weight temperature Sw, and the above-mentioned control operation is repeated thereafter.

Now, in a temperature control device having such a configuration, in order to prevent heat damage due to abnormal temperature rise due to failure of control parts in the device, the fixing roller has an abnormal rise in temperature to a predetermined temperature (standard temperature T for abnormality detection). (downward), the heater is forcibly cut off to protect the circuit.

"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 that takes into account the appeasement 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 and The temperature difference between the reference temperatures T for abnormality detection becomes quite large, and as a result, if an abnormality occurs during weight control, a detection delay will inevitably occur, especially in the case of an abnormality caused by overcurrent in the control circuit, etc. The internal circuit may be destroyed due to the time delay.

In view of the shortcomings of the prior art, the present invention provides a temperature control device configured to control the temperature of a heated object while switching the control target temperature, which smoothly detects an abnormality in any of the temperature control states described above. It is an object of the present invention to provide an abnormality detection method that can accurately detect an abnormality without causing any malfunction even when the temperature of the heated body is being shifted to another control target temperature.

"Means to solve problems" The process that led to the present invention will be explained.

First, in order to eliminate the above-mentioned drawbacks, the weight temperature S
A plurality of abnormality detection reference temperatures TI and T2 are also prepared in correspondence with the control target temperatures of the control target temperatures Sw and St, and the abnormality detection reference temperatures are set in correspondence with the switching operations of the control target temperatures Sw and St. It is conceivable that TI and T2 may also be configured to be switchable.

However, if the abnormality detection reference temperature T1 and T2 are switched in conjunction with the switching operation of the control target temperatures Sw and St,
Since the temperature of the object to be heated 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, the detected temperature However, immediately after switching, the reference temperature for abnormality detection may become lower than T2, resulting in a malfunction. Therefore, in the invention set forth in claim 1), the switching of the reference temperature for abnormality detection is controlled. Target temperature? 1 o'clock T2
This feature is characterized in that the abnormality detection operation is performed in conjunction with the switching operation, and that the abnormality detection operation is stopped for a predetermined period of time after the switching.

Further, in the invention described in claim JJ'+ 2), at least when switching the weight control target temperature lower than the fixing control target temperature to 71 dT2, the abnormality detection reference temperature is switched in conjunction with the target temperature. Instead, the switching timing is delayed by a predetermined period of time.

Note that the time it takes for the fixing roller temperature to actually shift to the weight control target temperature after switching the target temperature varies somewhat depending on the state of the heat load immediately before the end of the fixing operation. Therefore, in order to shorten the predetermined time and reduce the variation, the fixing roller temperature is quickly shifted to the weight control target temperature by cooling the fixing roller using an exhaust fan or other forced cooling means. It is preferable to do so.

That is, by using the forced cooling means, it is possible to suppress variations in the time required to reach the weight control target temperature. Therefore, by effectively combining the forced cooling, accurate abnormality detection is possible.

The invention described in claim 3) has been made by paying attention to this point, that is, in correspondence with the switching operation to the control target temperature 〒1-4T2, the forced cooling means is switched at the same time as the abnormality detection reference temperature is switched. cooling the object to be heated for a predetermined period of time, and determining an abnormality if the object to be heated does not drop below a reference temperature for abnormality detection at least within the predetermined cooling time. ``Embodiments'' Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described in this example are unless otherwise specified.

This is not intended to limit the scope of the invention, but is merely an illustrative example.

FIG. 1 is a schematic block diagram showing a temperature control circuit of a heat fixing device according to an embodiment of the present invention. To briefly explain the configuration, 1 is a pressure roller lb and a heating roller la that rotate in synchronization with each other. This thermal fixing device has a heater lO built in along the axial direction inside the heating roller 1a.

Further, a temperature detection means 2 is disposed close to the surface of the roller 1a, and a detection voltage corresponding to the detected temperature t from the detection means 2 is inputted to the temperature control means 3 and the abnormality detection means 5, respectively.

The temperature control means 3 uses the detection voltage and temperature switching control means 11.
This is a circuit that inputs a reference voltage corresponding to the fixing or weight temperature from the input terminal and generates a pulse signal or a level signal whose pulse width etc. are changed proportionally based on the voltage difference between the two signals. and is transmitted to the energizing means 5SR4 to control the heating of the heater lO.

The temperature switching control means 11 stores reference voltage circuits (not shown) corresponding to the following temperatures, and adjusts the corresponding reference voltages based on a fixing operation start signal and a fixing operation end signal from the CPU control section 8. can be transferred to the temperature control means 3 and the abnormality detection means 5, respectively.

That is, over-temperature detection (due to failure of various control parts) during fixing operation and weight operation is performed using each voltage corresponding to weight temperature Sv and fixing target temperature St as control target temperature and as reference temperature for abnormality detection. Reference temperature for? 1
t, T1w and the reference temperature T for short circuit detection (of the detection means 2)
Each voltage corresponding to 2t and T2w is stored,
As described above, based on the fixing operation start signal and the fixing operation end signal, the corresponding control target temperature can be transferred to the temperature control means 3, and the reference temperature TI for abnormality detection, 〒2, can be transferred to the abnormality detection means 5, respectively. It consists of The reference temperature for abnormality detection is the reference temperature 〒1. In addition to ↑2, there is a reference temperature 〒3 for wire breakage detection (of the detection means 2), but this reference temperature is kept constant due to its nature.

The abnormality detection means 5 uses a detection voltage corresponding to the detected temperature t from the temperature detection means 2 and a reference temperature for abnormality detection Tl, T273.
When the detected temperature t is equal to or higher than the abnormality detection reference temperature TI, T273, the heater 10 is forcibly cut off via the relay 9, and the alarm 13 is set.
sounds.

Reference numerals 8a and 8b are first and second timers installed in the CPU control section 8, which temporarily store timer data counted from the CPU fIiI section 8 when a timer start signal arrives, and are activated by the clock. It measures time based on the data and outputs a count-up signal to the CPU control section 8 when the time measurement ends.

Reference numeral 7 denotes an exhaust fan drive circuit, which drives and controls the exhaust fan 14 for an arbitrary set time based on a signal from a CPU control section 8, which will be described later.

The exhaust fan 14 is disposed substantially on an axial extension of the heating roller la, and is normally driven during the fixing operation to avoid an increase in internal environmental temperature. .

Next, the operating procedure based on this embodiment is shown in FIGS. 2(a) and (b).
) and the temperature graph in FIG. 3.

First, when the fixing operation is completed while the exhaust fan 14 is rotating, the CPU control section 8 sends a fixing operation end signal to the temperature switching control means 11, thereby changing the control target temperature to the weight temperature Sw and detecting an abnormality. The reference temperature for the weight operation is switched to the reference temperature for the weight operation and is transferred to the temperature control means 3 and the abnormality detection means 5, respectively (STEP 1).
) Outputting timer data A and B to the first timer 6a and second timer 6b, respectively, to start clock counting, and stopping the abnormality detection operation of the abnormality detection means 5 while the first timer 8a is counting. (STEP 2)
Immediately after the control target temperature is switched, the detected temperature t of the fixing roller la is often higher than the short circuit detection temperature 71w, which is the higher abnormality detection temperature, and therefore the detected temperature t is the short circuit detection temperature. The time when the power becomes 71w or less is set as timer data A, taking into account the error. During this time, since the exhaust fan 14 is rotating, malfunctions due to external environmental temperature are eliminated as much as possible.

In addition, as shown in the dotted line flow, the above operation is performed without switching the reference temperature for abnormality detection to the reference temperature during the wait operation while the first timer 6a is counting based on the timer data A, and detects the abnormality after counting up. (STEP
2°), and after the first timer 6a counts up, the detected temperature t in the abnormality detection means 5 becomes the short circuit detection temperature 7.
It is determined whether the temperature is below 1W, and if it is above, it is judged that there is a short circuit in the temperature detection means, and the power is forcibly cut off and an alarm is sounded (STEP 3).On the other hand, if it is below, overtemperature is detected. and the detected temperature t
If the overtemperature is 72W or higher, the process is repeated until the timer data B counts up, and if the overtemperature is still abnormal even after the count-up, it is determined that the control parts etc. are abnormal and the power is forcibly cut off. (STEP 4) If the detected temperature t falls below the overtemperature before the timer data B counts up, the drive of the exhaust fan 14 is stopped (STEP 5), and the timer data C is set to the first timer 8a. The timer data C is outputted to start counting, and the drive of the exhaust fan 14 is stopped until the timer data C counts up. (STEP 6) After that, output the timer data D to the second timer 6b,
The exhaust fan 14 is driven until the timer data D counts up. (STEP?) That is, exhaust fan 1
4 performs intermittent operation at timer data C/D intervals during wait control.

On the other hand, if the detected temperature t becomes equal to or higher than the overtemperature element 2w while the timer data C is counting, the timer data C is canceled and the timer data E is outputted to the first timer 6a. (STEP 8) Then, even if the timer data E counts up, if the detected temperature t is still higher than the overtemperature 72W (STEP 9), the timer data F is set to the second
The exhaust fan 14 is driven until the timer 6b is output and the timer data F is counted up, and the fixing roller l is
A is forcedly cooled to lower the supertemperature to 72W or less.
(STEP 10) If it does not drop, it is determined that there is an abnormality, and the power is forcibly cut off and an alarm is sounded. (STEP 10)
11) "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, malfunctions, etc. can be prevented not only while maintaining each control target temperature but also during transition. It is possible to detect an abnormality with high accuracy without occurrence of such occurrence, and in particular, in claim 3), by adding a forced cooling means, it is possible to detect an abnormality with even higher accuracy.

It has various effects such as

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing the overall configuration of a temperature control device according to an embodiment of the present invention, FIGS. 2(a) and (b) are flowcharts thereof, and FIG. 3 is for explaining the operation of FIG. 2. FIG.

Claims (1)

[Claims] 1) It has a first control target temperature and a second control target temperature lower than the first control target temperature, and the temperature of the heated object is controlled while mutually switching between the two control target temperatures. In a temperature control device for a heated object configured to perform control, a plurality of reference temperatures for abnormality detection are set corresponding to each of the control target temperatures, and at least the first control target temperature to the second control target temperature are set. An abnormality detection method 2 in a temperature control device for a heated object, characterized in that the one or more reference temperatures for abnormality detection are switched in response to the switching operation, and the abnormality detection operation is stopped for a predetermined period of time after the switching. ) has a first control target temperature and a second control target temperature lower than the first control target temperature, and is configured to control the temperature of the heated object while switching between the two control target temperatures. In the temperature control device for a heated object, a plurality of reference temperatures for abnormality detection are set in correspondence with each of the control target temperatures, and at least a corresponding one is set when switching from the first control target temperature to the second control target temperature. An abnormality detection method in a temperature control device for a heated object characterized by delaying the switching timing of the reference temperature for abnormality detection by a predetermined time 3) A first control target temperature and a first control target temperature lower than the first control target temperature. In a temperature control device for a heated object, which has two control target temperatures and is configured to control the temperature of the heated object while switching between the two control target temperatures, Alternatively, a plurality of reference temperatures for abnormality detection are set, and at least corresponding to the switching operation from the first control target temperature to the second control target temperature, forced cooling is performed at the same time as the one or more reference temperatures for abnormality detection are switched. The object to be heated is cooled by means for a predetermined period of time, and an abnormality is determined if the object to be heated does not fall below a reference temperature for abnormality detection within the predetermined cooling time. Abnormality detection method in heating element temperature control device