JPH10228207A - Image forming device and electric conduction controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly and accurately perform an electric conduction control. SOLUTION: Electrical energy is converted into heat energy by a halogen heater 2. The halogen heater 2 is energized by a heater control circuit 6 so as to control the generation of the heat energy. A toner image formed on a photoreceptor drum based on an image signal is melted by the heat energy and fixed to a recording material through a fixing roller 1. A thermistor 6 arranged opposite to the fixing roller 1 is provided with impedance characteristics corresponding to a temperature. By having a constitution of a disconnection detection resistance 7, a high temperature detection resistance 8, switches 9 and 10, voltages V1 and V2 corresponding to the impedance of the thermistor 5 are generated. The voltages V1 and V2 are compared with reference voltages Vref1 and Vref2 from a disconnection comparison voltage supply 14 and a high temperature comparison voltage supply 13 by a high temperature comparator 11 and a disconnection comparator 12. In accordance with the comparison results, the electric conduction to the halogen heater 2 by the heat control circuit 6 is controlled by a system control microcomputer 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an energization control device, and more particularly, to an image forming apparatus and an energization control device for performing energization control for applying heat energy to a fixing roller for fixing a toner image onto a recording material. It is about.

[0002]

2. Description of the Related Art Conventionally, a heater for converting electric energy into heat energy, heat generation control means for controlling the generation of heat energy by energizing the heater, and forming an electrostatic latent image based on an image signal by developing with toner. 2. Description of the Related Art An image forming apparatus including a fixing roller for melting a toner image formed on a rotating photoconductor by heat energy and fixing the toner image on a recording material is well known. In this image forming apparatus, the temperature of the fixing roller is controlled, and as a safety mechanism for preventing the temperature of the fixing roller from exceeding a set value, an additional thermistor for detecting a high temperature in addition to the temperature control thermistor, a heater, or the like is used. A power control device has been used in which a temperature switch or the like is provided in series with the power supply and a power supply to the heater is stopped when an unexpected temperature is reached.

[0003]

However, in a conventional power supply control device for an image forming apparatus, if a safety mechanism is provided by operating a temperature switch when a temperature control thermistor mechanism malfunctions, a temperature switch And the like have a problem that since the operation speed is slower than that of the thermistor, heat history is left on the fixing roller to cause trouble in image formation.

There is also used a mechanism in which the temperature control thermistor mechanism itself detects that the temperature does not rise in response to the heater energization signal, and stops the energization of the heater as an abnormal temperature detection operation. However, even in this mechanism, there is a problem that an error in the detected temperature increases due to foreign matter entering between the thermistor for temperature control and the fixing roller, and a heat history is left on the fixing roller to cause a problem in image formation. Was.

Accordingly, the present invention has been made in view of the above points, and has as its object to provide an image forming apparatus and an energization control apparatus which solve the above-mentioned problems.

[0006]

According to a first aspect of the present invention, there is provided a heat energy generating means for converting electric energy into heat energy, and a power supply to the heat energy generating means. An image forming apparatus comprising: a heat generation control means for controlling generation of the heat energy; and a fixing roller for melting the toner image formed on the rotating body based on the image signal by the heat energy and fixing the toner image on a recording material. In the device, a variable impedance element having an impedance characteristic according to the temperature, disposed opposite to the fixing roller, and a parameter generating means for generating an electrical parameter according to the impedance of the variable impedance element,
And an energization control unit that compares the electric parameter with a predetermined reference value and controls energization by the heat generation control unit in accordance with the comparison result.

Here, the variable impedance element is a thermistor having a negative temperature coefficient, and the parameter generating means includes first and second constant impedance elements having different impedances, the variable impedance element, and the first and second constant impedance elements. And a switch means for switching and connecting one of the second constant impedance elements and the variable impedance element. When the power is supplied, the first and second electric parameters corresponding to the switching state of the switch means are set. The power supply control unit generates the first electrical parameter with a first reference value indicating a temperature abnormality of the fixing roller; and the second electrical parameter is variable. Second comparing means for comparing with a second reference value indicating an abnormality of the impedance element, and the first and second comparing means; Comparison result by may consist of a current stop means for controlling to stop the power supply to said heat energy generating means by the heat generation control means.

Here, the variable impedance element includes:
The recording material is disposed at a position where the temperature changes according to a position where the recording material passes through the fixing roller, and the first reference value is changed according to a size of the recording material in an axial direction of the fixing roller. There may be provided a reference value changing means for increasing the first reference value when the size is small compared to when the size is large.

Further, the variable impedance element includes:
The recording material is disposed at a position where the temperature changes according to the position where the recording material passes through the fixing roller, and the first reference value is changed according to the number of the recording materials passing through the fixing roller within a predetermined time. It is also possible to provide a reference value changing means for increasing the first reference value when the number of passages is large as compared with when the number of passages is small.

In this case, the parameter generating means includes the variable impedance element and the switch means connected in series to the power supply, and the first and second constant impedance elements and the variable impedance element are connected to each other. A first detection voltage as the first electric parameter corresponding to a first voltage division ratio based on an impedance of the variable impedance element and the impedance of the first constant impedance element, wherein the power is alternately supplied to a series circuit; And a second detection voltage as the second electric parameter according to a second voltage division ratio based on the impedance of the variable impedance element and the second constant impedance element. When the first detection voltage is higher than the first reference value, and when the second detection voltage is higher than the second reference value. The power supply to said heat energy generating means can be stopped when remote small.

[0011] Further, the parameter generating means may be such that the variable impedance element and the switch means are connected in parallel to the power supply, and the first or second constant impedance element and the variable impedance element are connected in parallel. A first detection current as the first electric parameter corresponding to a first shunt ratio by the impedance of the variable impedance element and the first constant impedance element, wherein the power is alternately supplied to a circuit; The second constant-current ratio according to a second shunt ratio based on the impedance of the variable impedance element and the second constant impedance element;
And a second detection current as an electrical parameter of the second detection current, and the power supply stopping means determines whether the second detection current is greater than the first detection current when the first detection current is greater than the first reference value. When the value is smaller than the reference value of 2, the power supply to the thermal energy generating means can be stopped.

In order to achieve the above object, an apparatus according to the present invention converts electric energy into heat energy and converts a toner image formed on a rotating body based on an image signal onto a recording material. In an energization control device comprising: a heat energy generating unit that applies the heat energy to a fixing roller to be fixed; and a heat generation control unit that controls the generation of the heat energy by energizing the heat energy generation unit. A variable impedance element having characteristics and disposed opposite to the fixing roller; a parameter generating means for generating an electrical parameter corresponding to the impedance of the variable impedance element; and a predetermined reference value for the electrical parameter. And an energization control unit for controlling energization by the heat generation control unit in accordance with the comparison result.

Here, the variable impedance element is a thermistor having a negative temperature coefficient, and the parameter generating means includes first and second constant impedance elements having different impedances, the variable impedance element, and the first and second constant impedance elements. And a switch means for switching and connecting one of the second constant impedance elements and the variable impedance element. When the power is supplied, the first and second electric parameters corresponding to the switching state of the switch means are set. The power supply control unit generates the first electrical parameter with a first reference value indicating a temperature abnormality of the fixing roller; and the second electrical parameter is variable. Second comparing means for comparing with a second reference value indicating an abnormality of the impedance element, and the first and second comparing means; Comparison result by may consist of a current stop means for controlling to stop the power supply to said heat energy generating means by the heat generation control means.

Here, the variable impedance element includes:
The recording material is disposed at a position where the temperature changes according to a position where the recording material passes through the fixing roller, and the first reference value is changed according to a size of the recording material in an axial direction of the fixing roller. There may be provided a reference value changing means for increasing the first reference value when the size is small compared to when the size is large.

Further, the variable impedance element includes:
The recording material is disposed at a position where the temperature changes according to the position where the recording material passes through the fixing roller, and the first reference value is changed according to the number of the recording materials passing through the fixing roller within a predetermined time. It is also possible to provide a reference value changing means for increasing the first reference value when the number of passages is large as compared with when the number of passages is small.

Here, the parameter generating means includes the variable impedance element and the switch means which are connected in series to the power source, and wherein both the first or second constant impedance element and the variable impedance element are connected. The power supply is alternately supplied to a series circuit, and a first detection voltage as a first electric parameter corresponding to a first voltage division ratio by an impedance of the variable impedance element and the first constant impedance element is provided. A second voltage division ratio corresponding to a second voltage division ratio based on the impedance of the variable impedance element and the second constant impedance element.
And a second detection voltage as an electrical parameter of the second detection voltage, and the power supply stopping means determines whether the second detection voltage is higher than the first detection voltage when the first detection voltage is higher than the first reference value. When the value is smaller than the reference value of 2, the power supply to the thermal energy generating means can be stopped.

[0017] Further, the parameter generating means may be such that the variable impedance element and the switch means are connected in parallel to the power supply, and the first or second constant impedance element and the variable impedance element are connected in parallel. A first detection current as the first electric parameter corresponding to a first shunt ratio by the impedance of the variable impedance element and the first constant impedance element, wherein the power is alternately supplied to a circuit; The second constant-current ratio according to a second shunt ratio based on the impedance of the variable impedance element and the second constant impedance element;
And a second detection current as an electrical parameter of the second detection current, and the power supply stopping means determines whether the second detection current is greater than the first detection current when the first detection current is greater than the first reference value. When the value is smaller than the reference value of 2, the power supply to the thermal energy generating means can be stopped.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram showing an image forming apparatus according to a first embodiment of the present invention. Although omitted in FIG. 1, a charging device, a photosensitive drum, a toner developing device, a recording material conveying device, and the like are provided.

1 is a fixing roller, 2 is a fixing roller 1
In the halogen heater. Reference numeral 3 denotes a temperature switch, which is connected to the heater control circuit 6 in series with the halogen heater 2. Reference numeral 4 denotes a temperature control thermistor, which is disposed near and in the vicinity of the center of the fixing roller 1. The thermistor 4 detects the temperature of the fixing roller 1 and sends the detected temperature signal to the heater control circuit 6. The heater control circuit 6 controls the energization of the halogen heater 2 based on the detected temperature signal so that the temperature becomes suitable for fixing the toner. The above configuration is a conventional general temperature controller.

The thermistor 5, which is a novel configuration of the present invention, is provided at a predetermined distance from the fixing roller 1 so as to face a non-sheet passing portion near the right end of the fixing roller 1 in the drawing. The recording material does not pass through the non-sheet passing portion, but passes through a portion near the center. The temperature of the non-sheet passing portion changes depending on the dimension of the recording material passing through the fixing roller 1 for fixing in the fixing roller axial direction, that is, the passing position. The thermistor 5 includes the fixing roller 1
This is for safety measures to detect abnormal high temperature of the thermistor 5 and abnormality of the thermistor 5 itself. As is well known, the impedance of the thermistor 5 is a variable impedance element having a negative temperature coefficient and having impedance characteristics according to temperature. One end of the thermistor 5 is connected to a common connection point, which is the upper end of each of the switches 9 and 10, and the other end is connected to one end of a voltage source (not shown).

The switch (SW) 9 is used for disconnection switching.
The lower end is connected to the disconnection detection resistor 7. Switch (SW)
Reference numeral 10 denotes a high-temperature detection switch, and is connected to the high-temperature detection resistor 8. The two resistors are constant impedance elements having different impedances, and the lower ends thereof are connected to the other end of the voltage source, and are disposed at a position that is hardly affected by a temperature change of the fixing roller 1. The temperature coefficient is a slight positive value. The switches 9 and 10 are connected to the system control microcomputer 15
The opening / closing timing is controlled by the switching signal from the controller, and the switching is alternately turned on / off as shown in the timing chart of FIG.

Thus, the thermistor 5 and the switch 9 or 10 are alternately connected in series to the power supply, and the power supply is alternately supplied to both series circuits of the detection resistor 7 or 8 and the thermistor 5 so that the thermistor 5 And high temperature detection resistor 8
, A detection voltage V1 as a first electric parameter corresponding to a first voltage division ratio, a thermistor 5, and a disconnection detection resistor 7
And a detection voltage V2 as a second electric parameter corresponding to the second voltage division ratio. The detection voltage V1 is shown in FIG.
During the switch 10 ON period T1, the detection voltage V2 is generated alternately during the switch 9 ON period T2. In the period T1, an abnormally high temperature of the fixing roller 1 is detected based on the detection voltage V1, and in the period T2, an abnormality due to the disconnection of the thermistor 5 is detected based on the detection voltage V2.

That is, during the abnormal high temperature inspection period T1, the detection voltage V1 and the reference voltage Vre from the high temperature comparison voltage source 13 are output.
f1 is compared by the high temperature comparator 11. In the disconnection inspection period T2, the detection voltage V2 and the reference voltage Vref2 from the disconnection comparison voltage source 14 are compared by the disconnection comparator 12. The reference voltages Vref1 and Vref2 are predetermined values. When the detection voltage V1 is higher than the reference voltage Vref1, the thermistor 5 has a low impedance due to abnormally high temperature. When the detection voltage V2 is lower than the reference voltage Vref2. The thermistor 5 is disconnected at high impedance.

The result of comparison between the comparators 11 and 12 is input to the system control microcomputer 15. The system control microcomputer 15 controls the heater control circuit 6 to stop energizing the temperature switch 3 and the series circuit of the halogen heater 2 when detecting disconnection of the thermistor 5 and detecting abnormally high temperature of the fixing roller 1. I do.

As described above, according to the present embodiment, in addition to the thermistor 3 for temperature control, the thermistor 5
The temperature of the end of the fixing roller 1 is measured by detecting a change in impedance of the thermistor 5 from the detection voltage, and it is checked whether the thermistor 5 itself is disconnected. The detection of the high temperature of the fixing roller due to the temperature control abnormality is reliably performed. Although it is disadvantageous for controlling the temperature of the fixing roller 1, the temperature is detected at the non-sheet passing portion to protect a delicate thermistor, and the temperature detection of the fixing roller 1 and the disconnection detection of the thermistor 5 are alternately and continuously performed. In this case, the temperature switch 3 is operated in response to a malfunction or abnormally high temperature of the temperature control thermistor 4 of the fixing roller 1.
(Or thermal fuse) can be controlled so that the heater energization is stopped in a short time more quickly than in the case of a thermal fuse.

(Second Embodiment) FIG. 3 is a block diagram showing an image forming apparatus according to a second embodiment of the present invention. Although not shown in FIG. 3, a charging device, a photosensitive drum, a toner developing device, a conveying device for a recording material, and the like are provided. In addition to the configuration in FIG. Accordingly, a signal line L1 for changing the output reference voltage Vref1 of the high-temperature comparison voltage source 13 under the control of the system control microcomputer 15 is newly added.

Thus, during the high-temperature inspection period T1 in which the high-temperature changeover switch 10 is closed, the output reference of the high-temperature comparison voltage source 13 is compared with the detection voltage V1 determined by the division ratio between the high-temperature detection resistor 8 and the thermistor 5. The voltage Vref1 is increased or decreased.

FIG. 4 is a characteristic diagram showing the surface temperature distribution of the fixing roller 1 according to the dimension of the recording material in the fixing roller axial direction.

That is, according to the temperature distribution of the large-sized paper in FIG. 4, when the axial size of the fixing paper is large, there is no temperature rise at the end, so that the reference voltage Vref1 is set to be lowered. When the dimension of the fixing paper in the axial direction is small, the temperature rise at the end is remarkable, so that the reference voltage Vref1 is set to be increased.

As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained. In addition, the fixing roller that controls the temperature by changing the reference voltage Vref1 according to the size of the fixing paper can be obtained. The temperature difference between the center of the fixing roller and the end of the fixing roller is corrected to prevent erroneous detection due to an increase in the end temperature when fixing small paper despite the normal image forming operation. Accuracy can be increased.

(Third Embodiment) FIG. 5 is a block diagram showing an image forming apparatus according to a third embodiment of the present invention. Although not shown in FIG. 5, a charging device, a photosensitive drum, a toner developing device, a conveying device for a recording material, and the like are provided. In addition to the configuration shown in FIG. Another signal line L2 for changing the output reference voltage Vref1 of the high-temperature comparison voltage source 13 under the control of the system control microcomputer 15 according to the number of passages is newly added.

Thus, during the high-temperature inspection period T1 in which the high-temperature changeover switch 10 is closed, the output reference of the high-temperature comparison voltage source 13 is compared with the detection voltage v1 determined by the division ratio between the high-temperature detection resistor 8 and the thermistor 5. The voltage Vref1 is increased or decreased.

FIG. 6 is a characteristic diagram showing the surface temperature distribution of the fixing roller 1 according to the number of times the recording material passes through the fixing roller within a predetermined time.

That is, according to the temperature distribution of the large-sized paper shown in FIG. 6, when the number of passing fixing papers is small, the temperature rise at the end of the fixing roller is slight, while the number of large number of papers within a predetermined time is small. At this time, the temperature rise at the end of the fixing roller becomes remarkable. Therefore, when the number of sheets is large, the output reference voltage Vref1 of the high-temperature comparison voltage source 13 is set to be higher than when the number of sheets is small.

As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained, and the influence of the size of the recording material varies depending on the number of sheets continuously fixed within a predetermined time. Can be corrected, and erroneous temperature detection due to a rise in end temperature when a small recording material is fixed can be accurately prevented.

In each of the above embodiments, the detection voltage V
Although V1 and V2 are generated by the voltage division by the thermistor 5 and the resistors 7 and 8, the current may be detected according to the impedance change of the thermistor 5.
For example, a thermistor 5 and switches 9 and 10 are connected in parallel to a current source, a constant impedance element is connected to both switches, and a current is alternately supplied from the current source to both parallel circuits of the thermistor 5 and the constant impedance element. A first detection current as a first electrical parameter corresponding to a first shunt ratio based on the impedance of the thermistor 5 and the first constant impedance element, and a second detection current as an impedance of the thermistor 5 and the second constant impedance element. And a second detected current as a second electric parameter corresponding to the shunt ratio may be generated, and both detected currents may be compared with a reference value.

[0038]

As described above, according to the present invention, a toner image having an impedance characteristic corresponding to a temperature and formed on a rotating body based on an image signal is melted by thermal energy to form a recording material. A variable impedance element disposed opposite to the fixing roller to be fixed, a parameter generating means for generating an electric parameter corresponding to the impedance of the variable impedance element, and comparing the electric parameter with a predetermined reference value. A heating control means for controlling the generation of heat energy by energizing a heat energy generating means for converting electric energy into heat energy in accordance with the result; If there is an abnormality in the variable impedance element itself, the energization by the heat control means can be stopped,
There is an effect that the power can be quickly and quickly controlled in response to an abnormality, there is no error in detecting a temperature abnormality, and there is no trouble in image formation without leaving a heat history on the fixing roller.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a first embodiment of an image forming apparatus to which the present invention has been applied.

FIG. 2 is a timing chart of a disconnection inspection and a high-temperature inspection according to the embodiment of the present invention.

FIG. 3 is a block diagram illustrating a second embodiment of the image forming apparatus to which the present invention has been applied.

FIG. 4 is a characteristic diagram illustrating a surface temperature distribution of the fixing roller 1 according to a dimension of a recording material in an axial direction of the fixing roller.

FIG. 5 is a block diagram illustrating a third embodiment of the image forming apparatus to which the present invention has been applied.

FIG. 6 is a characteristic diagram illustrating a surface temperature distribution of the fixing roller 1 according to the number of times the recording material passes through the fixing roller within a predetermined time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Halogen heater 3 Temperature switch 4, 5 Thermistor 6 Heater control circuit 7 Disconnection detection resistance 8 High temperature detection resistance 9, 10 Switch 11 High temperature comparator 12 Disconnection comparator 13 High temperature comparison voltage source 14 Disconnection comparison voltage source 15 System control Microcomputer

Claims (12)

[Claims] 1. A heat energy generating means for converting electric energy into heat energy, a heat generation control means for controlling the generation of the heat energy by energizing the heat energy generating means, and a rotation formed based on an image signal. An image forming apparatus including a fixing roller for melting a toner image on a body by the thermal energy and fixing the toner image on a recording material, wherein the image forming apparatus has an impedance characteristic corresponding to a temperature, and is disposed to face the fixing roller. A variable impedance element, parameter generation means for generating an electrical parameter according to the impedance of the variable impedance element, comparing the electrical parameter with a predetermined reference value, and energizing the heat generation control means according to the comparison result. An image forming apparatus comprising: an energization control unit that controls the power supply. 2. The variable impedance element according to claim 1, wherein the variable impedance element is a thermistor having a negative temperature coefficient, and wherein the parameter generation means includes first and second constant impedance elements having different impedances, and the variable impedance element. And a switch means for switching and connecting one of the first and second constant impedance elements to the variable impedance element. The first and second constant current elements are supplied with power and the first and second elements correspond to the switching state of the switch means. An electrical parameter generating unit, the energization control unit compares the first electrical parameter with a first reference value indicating an abnormal temperature of the fixing roller, and the second electrical unit Second comparing means for comparing a parameter with a second reference value indicating an abnormality of the variable impedance element; An image forming apparatus comprising: a power supply stopping means for controlling the heat generation means to stop supplying power to the thermal energy generating means based on a comparison result of the second comparing means. 3. The fixing roller according to claim 1, wherein the variable impedance element is disposed at a position where a temperature changes according to a position at which the recording material passes through the fixing roller. The first according to the axial dimension
An image forming apparatus comprising: a reference value changing unit that changes a reference value of the first reference value and increases the first reference value when the size is small compared to when the size is large. 4. The variable impedance element according to claim 1, wherein the variable impedance element is disposed at a position where a temperature changes according to a position at which the recording material passes through the fixing roller, and wherein the recording is performed within a predetermined time. A reference value changing unit that changes the first reference value in accordance with the number of sheets passing through the fixing roller, and increases the first reference value when the number of passages is large as compared with when the number is small. Image forming device. 5. The parameter generating means according to claim 2, wherein said variable impedance element and said switch means are connected in series to said power supply, and said first or second constant impedance The power is alternately supplied to both series circuits of the element and the variable impedance element, and the first electric circuit according to a first voltage division ratio by the impedance of the variable impedance element and the first constant impedance element. A first detection voltage is generated as a parameter, and a second detection voltage is generated as the second electric parameter according to a second voltage division ratio based on the impedance of the variable impedance element and the second constant impedance element. When the first detection voltage is higher than the first reference value, the power supply stopping means determines that the second detection has been completed. Said voltage second
An image forming apparatus, wherein the power supply to the thermal energy generating means is stopped when the reference value is smaller than the reference value. 6. The parameter generating means according to claim 2, wherein said variable impedance element and said switch means are connected in parallel to said power supply, and said first or second constant impedance The power is supplied alternately to both parallel circuits of the element and the variable impedance element, and the first electrical circuit according to a first shunt ratio by the impedance of the variable impedance element and the first constant impedance element. A first detection current as a parameter and a second detection current as a second electric parameter according to a second shunt ratio based on the impedance of the variable impedance element and the second constant impedance element are generated. The energization stopping means determines whether the first detection current is larger than the first reference value and the second detection current. Image forming apparatus characterized by detecting current stops energization of the thermal energy generating means when less than said second reference value. 7. A heat energy generating means for converting electric energy into heat energy and applying the heat energy to a fixing roller for fixing a toner image formed on a rotating body based on an image signal to a recording material; An electricity supply control device comprising: a heat generation control means for controlling the generation of the heat energy by energizing the heat energy generation means, wherein the variable impedance has an impedance characteristic corresponding to a temperature and is disposed opposite to the fixing roller. An element, parameter generation means for generating an electrical parameter according to the impedance of the variable impedance element, comparing the electrical parameter with a predetermined reference value, and controlling energization by the heat generation control means according to the comparison result And an energization control device. 8. The variable impedance element according to claim 7, wherein the variable impedance element is a thermistor having a negative temperature coefficient, and wherein the parameter generating means includes: first and second constant impedance elements having different impedances; And a switch means for switching and connecting one of the first and second constant impedance elements to the variable impedance element. The first and second constant current elements are supplied with power and the first and second elements correspond to the switching state of the switch means. An electrical parameter generating unit, the energization control unit compares the first electrical parameter with a first reference value indicating an abnormal temperature of the fixing roller, and the second electrical unit Second comparing means for comparing a parameter with a second reference value indicating an abnormality of the variable impedance element; An energization control device, comprising: an energization stop unit that controls the heat generation unit to stop energization of the thermal energy generation unit based on a comparison result of the second comparison unit. 9. The fixing roller according to claim 7, wherein the variable impedance element is disposed at a position where the temperature changes according to a position at which the recording material passes through the fixing roller. The first according to the axial dimension
And a reference value changing means for changing the first reference value when the size is small and making the first reference value larger than when the size is large. 10. The variable impedance element according to claim 7, wherein the variable impedance element is disposed at a position where the temperature changes in accordance with a position at which the recording material passes through the fixing roller, and the recording within a predetermined time period. A reference value changing unit that changes the first reference value in accordance with the number of sheets passing through the fixing roller, and increases the first reference value when the number of passages is large as compared with when the number is small. Energization control device. 11. The parameter generator according to claim 8, wherein said variable impedance element and said switch are connected in series to said power supply, and said first or second constant impedance The power is alternately supplied to both series circuits of the element and the variable impedance element, and the first electric circuit according to a first voltage division ratio by the impedance of the variable impedance element and the first constant impedance element. A first detection voltage is generated as a parameter, and a second detection voltage is generated as the second electric parameter according to a second voltage division ratio based on the impedance of the variable impedance element and the second constant impedance element. When the first detection voltage is higher than the first reference value, Energization control apparatus 2 of the detected voltage is equal to or stopping the energization of the thermal energy generating means when less than said second reference value. 12. The parameter generation means according to claim 8, wherein said variable impedance element and said switch means are connected in parallel to said power supply, and said first or second constant impedance The power is supplied alternately to both parallel circuits of the element and the variable impedance element, and the first electrical circuit according to a first shunt ratio by the impedance of the variable impedance element and the first constant impedance element. A first detection current as a parameter and a second detection current as a second electric parameter according to a second shunt ratio based on the impedance of the variable impedance element and the second constant impedance element are generated. When the first detection current is greater than the first reference value, Energization control apparatus 2 of the detected current is equal to or stopping the energization of the thermal energy generating means when less than said second reference value.