JPH04235612A - Temperature controller for calorific body - Google Patents

Abstract

PURPOSE:To surely detect the abnormality of the control system of a calorific body whose temperature is controlled regardless of the level of power voltage by controlling an electric heater. CONSTITUTION:The voltage of an AC power supply 12 which is applied to a halogen heater 10a for heating a fixing roller 10 is detected by a voltage detector 23. An abnormality detecting pert 22a of a control part 22 is provided with a function which changes the detecting time for the abnormality of a control system based on the voltage level detected by the detector 23. Thus the abnormality of the control system is surely detected from the detecting time accordant with the voltage of the supply 12.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device for a heating element such as a fixing roller used in an image forming apparatus such as a copying machine.

0002

2. Description of the Related Art A fixing device is used to fix a toner image carried on a transfer paper onto the transfer paper as a permanent image, and conventionally, a heat roller type fixing device is often used.

An example of such a heat roller type fixing device will be described with reference to FIG. 7. The fixing device rotates in the direction of arrow A in the figure and includes a fixing roller 10 having a halogen heater 10a as a heat source inside, and the fixing roller 10. The toner image is heated and pressurized by passing a transfer paper carrying the toner image between the fixing rollers 10 and 11. This is fixed by melting it onto the transfer paper.

The fixing roller 10 is heated by a halogen heater 10a, and the surface temperature of the fixing roller 10 is detected by a thermistor 20 and controlled to a temperature suitable for fixing (hereinafter referred to as fixing temperature T0). That is, the signal from the thermistor 20 is input to the control section 22 via the A/D converter 21, and if the fixing roller 10 is below the fixing temperature T0, the control section 22 inputs the signal from the AC power source 12 via the heater drive circuit 23. The halogen heater 10a is then energized, and when the fixing roller 10 reaches the fixing temperature T0 or higher, the halogen heater 10a is stopped from being energized from the AC power source 12 via the heater drive circuit 23.

FIG. 8 shows the change in the surface temperature of the fixing roller 10 from the time of start-up of the fixing device, and from this figure, from the time of start-up until the fixing roller 10 reaches the fixing temperature T0, the halogen heater 10a is continuously operated. It can be seen that when the fixing roller 10 reaches the fixing temperature T0, the halogen heater 10a is turned ON/OFF. In addition, the solid line in the figure is when the voltage of the AC power supply 12 is 100Vrms, and the broken line is when the voltage is 200Vrms.
The case is shown below.

Here, thermistor 20 and thermistor 2
If there is a failure such as a disconnection in the wiring from the A/D converter 21 to the control unit 22, the surface temperature of the fixing roller 10 will not be accurately transmitted to the control unit 22 etc. via the thermistor 20, and the fixing roller 10 It becomes impossible to control the temperature of the fixing roller 10, resulting in abnormal heating of the fixing roller 10. This inconvenience causes damage to the bearings of the pressure roller 11 and the fixing roller 10. This damage not only deteriorates image quality but also damages parts other than the fixing device.

Therefore, an abnormality detection means for detecting abnormality in the control system is provided in the control unit 22, and as shown in FIG.
Afterwards, the surface temperature T1 of the fixing roller 10 (voltage is 100 Vr)
The abnormality detection means detects whether or not the control unit 22 recognizes the error (in the case of ms) via the thermistor 20,
If the control unit 22 does not recognize the surface temperature T1 or a value close to it, it is assumed that there is an abnormality in the control system, and safety measures are taken such as stopping the power supply to the halogen heater 10a.

[0008]

[Problems to be Solved by the Invention] However, although a general commercial power source is used as the AC power source 12 that supplies power to the halogen heater 10a, the voltage of the commercial power source is
There are various types such as 0Vrms and 200Vrms, and the amount of heat generated by the halogen heater 10a differs depending on the voltage of the commercial power supply. 1
At 00 Vrms, the surface temperature of the fixing roller 10 becomes T1 as shown by the solid line, but at 200 Vrms it becomes T2 (T2>T1) as shown by the broken line.

Therefore, depending on how the detection time t0 is taken, the surface temperature of the fixing roller 10 after the detection time T0 may exceed the fixing temperature t0, which causes the problem that the abnormality detection means cannot effectively perform its function sufficiently. was there.

The present invention has been made in view of the above problems, and its purpose is to provide a temperature control device for a heating element that can reliably detect abnormalities in the control system regardless of the magnitude of the power supply voltage. There is something to do.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention controls an electric heater in the heating element via a signal from a temperature detection means of the heating element, controls the temperature of the heating element, and controls the temperature of the heating element at a predetermined level. In a temperature control device for a heating element, the heating element temperature control device is equipped with a control system abnormality detection means for detecting an abnormality in the control system through a detection time of , and preventing abnormal heating of the heating element.
A function of providing voltage detection means for detecting the magnitude of the power supply voltage applied to the electric heater of the heating element, and changing the detection time of the abnormality detection means of the control system according to the magnitude of the detected voltage from the voltage detection means. It is characterized in that it provides reliable detection of abnormalities in the control system.

0012

[Operation] For example, if the heating element is the fixing roller of the fixing device,
The abnormality detection means of the control system detects that there is an abnormality in the control system if the temperature signal of the fixing roller sent from the control system after the elapse of the detection time at startup has not reached the signal value of the predetermined temperature.

However, if the power supply voltage applied to the electric heater that heats the fixing roller becomes higher than normal, and there is an abnormality in the control system, the fixing roller may be abnormally heated after the detection time elapses. .

[0014] Therefore, the function of detecting the power supply voltage applied to the electric heater for heating the heating element by the voltage detecting means and changing the detection time based on the voltage value detected by the voltage detecting means is used to detect an abnormality in the control system. As a means, abnormalities in the control system are detected using a detection time commensurate with the power supply voltage.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings.

First, a first embodiment of the present invention will be explained with reference to FIGS. 1 to 4.

FIG. 1 shows a heating means for a fixing roller 10 of a fixing device and a temperature control device for controlling the heating means. The heating means is composed of a halogen heater 10a that is a heat source disposed inside the fixing roller 10, and an AC power source 12 that supplies power to the halogen heater 10a.The halogen heater 10a is operated via the AC power source 12. By this, the fixing roller 10 reaches a predetermined fixing temperature T.
heated to 0. In addition to the fixing roller 10, the fixing device also includes a pressure roller and the like to fix the toner image on the transfer paper as a permanent image, but since the explanation was given in the prior art section, it is omitted here. do.

The temperature control means includes a thermistor 20 for detecting the surface temperature of the fixing roller 10, an A/D converter 21 for A/D converting the signal from the thermistor 20, and an A/D converter 21 for A/D converting the signal from the thermistor 20.
An abnormality detection unit 22a that recognizes the surface temperature of the fixing roller 10 based on a signal from the thermistor 20 via the D converter 21, controls the surface temperature to the fixing temperature T0, and detects an abnormality in the control system of the fixing device. A control unit 22 equipped with a control unit 22 turns on/off the power supply from the AC power supply 12 to the halogen heater 10a according to a signal from the control unit 22.
OFF control heater drive circuit 23 and AC
It is comprised of a voltage detector 24 and the like that detects the voltage value of the power source 12 and transmits the type to the control unit 22.

The thermistor 20 measures the surface temperature of the fixing roller 10 as a change in electrical resistance value, and outputs this change in resistance value as a change in voltage value (thermistor voltage).

[0020] Here, the normal operation of the above temperature control device will be explained when the AC power supply 12 is 100V (in the case of the solid line in FIGS. 2 and 3). When the fixing device starts operating,
The fixing roller 10 is heated by the halogen heater 10a, and the surface temperature of the fixing roller 10 is raised all at once from room temperature to the fixing temperature T0, as shown by the straight line in FIG. In this case, the surface temperature of the fixing roller 10 is determined by the thermistor 20.
, the AC power 12 is constantly recognized by the control section 22 via the A/D converter 21, and is supplied to the halogen heater 10a via the heater drive circuit 23 controlled by the control section 22.

When the fixing roller 10 reaches the fixing temperature T0, the control section 22 stops supplying electricity to the halogen heater 10a via the heater drive circuit 23, but after that, the fixing roller 10 is cooled naturally or by the fixing operation. Every time a temperature drop occurs, the halogen heater 10 is turned on by the control unit 22 or the like.
The ON/OFF operation of a is performed, and the temperature of the fixing roller 10 is maintained at a substantially constant value, as shown by the dotted line in FIG.

In the above case, as shown in FIG. 3, the thermistor voltage decreases slowly when the temperature of the fixing roller 10 is low, but if the fixing roller 10 is heated to a certain extent and its temperature rises, it changes greatly and the fixing When the roller 10 reaches the fixing temperature T0, the temperature changes as shown by the dotted line.

Next, abnormality detection in the control system, which is a characteristic feature of the present invention, will be explained. For example, if there is a disconnection in the thermistor 20 and the thermistor 20 does not transmit the correct temperature (thermistor voltage) of the fixing roller 10 to the control unit 22, the fixing roller 10 will be heated to an abnormally high temperature by the halogen heater 10a. may occur. For this reason, the control section 22 is provided with an abnormality detection section 22a that detects abnormalities in the control system, so that the above-mentioned troubles can be prevented from occurring. The abnormality detection unit 22a detects a predetermined detection time t from the start-up of the fixing roller 10.
After the elapsed time, it is checked whether the thermistor voltage transmitted to the control unit 22 via the thermistor 20 is the expected thermistor voltage or a value close to this, and if this thermistor voltage is significantly different from the expected value, the halogen heater is 1
This is to stop the power supply to 0a.

Here, since a general commercial power source is used as the AC power source 12 that supplies power to the halogen heater 10a,
The voltage value is not only 100Vrms (100~120V) but also 200Vrms (220~240V)
may be used. Therefore, as shown by the broken line in FIG. 2, the voltage of the AC power supply 12 is 200Vrms.
In this case, the temperature of the fixing roller 10 rises faster than in the case of 100 Vrms shown by the solid line. Therefore, if the detection time t is constant, in the case of 200 Vrms, the expected surface temperature of the fixing roller 10 increases, and the fixing temperature There may be cases where T0 is exceeded.

Therefore, the voltage detector 24 detects the AC power source 1.
As shown in Figure 2, this voltage is 100
Vrms, the detection time t is t1, and 200Vr
ms, this is set as t2, and t1>t2, and the surface temperatures of the fixing roller 10 after time t1 and time t2 are approximately the same. In this way, it is possible to suppress the expected surface temperature T1 of the fixing roller 10 after the detection time t has elapsed, and it is also possible to prevent this from changing greatly depending on the voltage value of the AC power source 12. In this case, the expected value of the thermistor voltage, which is the output from the thermistor 20, is V1 for the detection time t1 and V2 for the detection time t2, as shown in FIG.

The operation of detecting an abnormality in the control system by the voltage detector 24 and the abnormality detecting section 22a of the control section 22 will be described below with reference to the flowchart shown in FIG.

It is determined whether the CPU of the control unit 22 has been reset or whether the fixing device has been energized via the AC power supply 12 (step 1). YES if it has been done
Therefore, the voltage value of the AC power supply 12 detected by the voltage detector 24 is either L (100Vrms) or H (200Vrms).
ms ) is determined (step 2). Voltage detector 2
If the output signal of step 4 is L (100 Vrms), the detection time t1 is set in the timer (step 3), the halogen heater 10a of the fixing roller 10 is energized from the AC power supply 12 (step 4), and the detection time t1 is set in the timer (step 3). It is determined whether or not the period has elapsed (step 5).

[0028] Then, if the detection time t1 has not elapsed, N
If the detection time t1 has elapsed, the result becomes YES and it is determined whether the thermistor voltage from the thermistor 20 has reached the expected voltage V1 (step 6). If the thermistor voltage from the thermistor 20 is not equal to the expected voltage V1 or a value close to it, the result is NO, and it is assumed that there is an abnormality in the control system (for example, there is a disconnection in the thermistor 20), and the energization to the halogen heater 10a is stopped (step 7), a message indicating that there is an abnormality in the control system of the fixing device is displayed, and the operation of the entire device is stopped (step 8). If the thermistor voltage is the expected voltage V1 or a value close to it in step 6, then Y
ES, the detection program ends as there is no abnormality in the control system.

Furthermore, in step 2, the voltage detector 24
If the output signal is H (200 Vrms), the detection time t2 is set in the timer (step 9), the halogen heater 10a of the fixing roller 10 is energized from the AC power supply 12 (step 10), and the detection time t2 is set in the timer (step 9). t
It is determined whether or not 2 has elapsed (step 11). If the detection time t2 has not elapsed, the answer is NO and returns to step 10, and if the detection time t2 has elapsed, the answer is Y.
S, the process moves to step 6, where it is determined whether the thermistor voltage from the thermistor 20 is the expected voltage V2 or a value close to it, and the process proceeds in the same manner as in the above case.

As described above, if the voltage value of the AC power supply 12 is large, the detection time t for detecting abnormality in the control system is made small, and conversely, if the voltage value is small, this detection time t is made large. , the thermistor voltage becomes smaller than the predetermined value after the detection time t has elapsed, and the surface temperature of the fixing roller 10 does not become higher than the fixing temperature T0. Another advantage is that the surface temperature of the fixing roller 10 can be made substantially the same, and abnormalities in the control system can be detected with substantially the same precision.

Next, a second embodiment of the present invention will be described with reference to FIGS. 5 and 6.
This is explained by: Components having the same functions as those in the first embodiment are designated by the same reference numerals, and their explanations will be omitted.

In the first embodiment, abnormality detection in the control system at startup of the fixing device was explained, but in this embodiment, control after the surface temperature of the fixing roller 10 is maintained at a constant value (fixing temperature T0) is explained. System abnormality detection will be explained.

FIG. 5 shows that the voltage of the AC power supply 12 is 100Vrm.
The state of change in the surface temperature of the fixing roller 10 in the case of s and the corresponding ON/OFF status of the halogen heater 10a
6 shows the state of change in the surface temperature of the fixing roller 10 when the voltage of the AC power supply 12 is 200 Vrms, and the corresponding state of the change in the surface temperature of the halogen heater 10a.
Indicates the ON/OFF time status. It is understood from FIGS. 5 and 6 that the fixing roller 10 is heated periodically.

In this case, the amount of heating to the fixing roller 10 is proportional to the power consumption of the halogen heater 10a, and the voltages VA, VB applied from the AC power supply 12 to the halogen heater 10a
and the corresponding power consumption WA of the halogen heater,
Since the relationship with WB is empirically expressed as WB = (VB /VA)1.54·WA, the ON time of the halogen heater 10a in FIG. 5(a) is equal to the ON time of the halogen heater 10a in FIG. 6(a). ON
This is approximately three times the time.

Therefore, once the fixing roller 10 reaches the fixing temperature T0, an abnormality in the control system is detected when the ON time of the halogen heater 10a is set to the warning value (1.3 to 1.3 of the normal ON time).
1.5 times).

Therefore, the abnormality detection section 22a of the control section 22 is equipped with a halogen heater 10a corresponding to the voltage value of the AC power source 12.
ON time warning value (for example, tA for 100V)
, tB for 200V) is stored, the voltage value of the AC power supply 12 is determined based on the signal from the voltage detector 24, and the actual halogen heater 10a is determined based on the voltage value.
The ON time of the halogen heater 10a is compared with the warning value, and if the ON time exceeds the warning value, the energization to the halogen heater 10a is stopped.

As described above, in this embodiment as well, abnormalities in the control system can be accurately detected depending on the difference in the voltage applied to the halogen heater 10a.

Although the fixing roller 10 has been described as the heating element in the first and second embodiments above, the present invention is of course applicable to other heating elements used in the image forming apparatus. .

[0039]

As is clear from the above description, according to the present invention, the voltage applied from the power supply to the electric heater of the heating element is detected by the voltage detection means, and an abnormality in the control system is detected based on the magnitude of the applied voltage. Since the detection time for the control system is changed appropriately, it is possible to reliably detect an abnormality in the control system regardless of the magnitude of the power supply voltage.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a heating means and a temperature control device for a fixing roller of a fixing device according to a first embodiment.

FIG. 2 is a diagram showing temperature changes of a fixing roller of the fixing device.

FIG. 3 is a diagram showing changes in the thermistor voltage, which is the thermistor output of the fixing device.

FIG. 4 is a flowchart showing a method for detecting an abnormality in the temperature control system of the fixing roller of the fixing device.

FIG. 5 is a diagram showing the temperature of the fixing roller and the ON/OFF operating state of the halogen heater of the fixing device according to the second embodiment.

FIG. 6 is a diagram showing the temperature of the fixing roller and the ON/OFF operating state of the halogen heater of the fixing device according to the second embodiment.

FIG. 7 is an explanatory diagram of a fixing device for explaining the prior art.

FIG. 8 is a diagram showing a temperature change of a fixing roller of a fixing device for explaining the prior art.

[Explanation of symbols]

10 Fixing roller (heating element) 10a
Halogen lamp (electric heater) 20
Thermistor (temperature detection means) 22a
Abnormality detection section (abnormality detection means) 23 Voltage detector (voltage detection means) t1, t2 Detection time

Claims (1)

[Claims] 1. Controlling an electric heater in the heating element through a signal from a temperature detection means of the heating element, controlling the temperature of the heating element, and detecting an abnormality in the control system through a predetermined detection time, In a temperature control device for a heating element, which includes an abnormality detection means for a control system to prevent abnormal heating of the heating element, a voltage detection means for detecting the magnitude of a power supply voltage applied to an electric heater of the heating element is provided; The temperature of the heating element is characterized in that the abnormality detection means of the control system has a function of changing the detection time depending on the magnitude of the detected voltage from the voltage detection means, thereby making it possible to reliably detect abnormalities in the control system. Control device.