Image formation device

Abstract

To determine the cause of any abnormal high temperature of a heating body.SOLUTION: When it is determined that a temperature rise of a heater 201 is abnormal (YES in S1205) with a triac 308 in a non-conduction state (S1203) and a relay 303 in a connected state (S1201), an engine controller 304 brings the relay 303 into a cut-off state (S1207). After the lapse of a predetermined first time T1 (S1208), the engine controller 304 brings the relay 303 into a connected state (S1209), and then determines the cause of the abnormal temperature rise (S1211, S1212, S1214) on the basis of a result of comparison of a first temperature a1 of the heater 201 detected by a thermistor 202 (S1210) with a predetermined abnormal temperature threshold c1.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including an image heating device as an image fixing means.

Background Art

[0002] As an AC waveform supplied to an image forming apparatus or the like, a sine wave of a rated power supply voltage and frequency defined by the standards of each country is supplied. On the other hand, as an auxiliary power supply used when the AC power supply fails, a square wave synchronized with the AC power supply is used, for example, as described in Patent Document 1. When a power failure occurs in a facility where such an uninterruptible power supply is installed, the AC waveform supplied to the image forming apparatus is switched from a sine wave to a square wave.

[0003] In an image forming apparatus that operates by supplying an AC waveform, a heating element drive circuit for thermally fixing a toner image transferred onto a recording paper generally has the following configuration. A drive circuit that controls the heating element drives a photo-triac coupler based on the output signal of a temperature detection element by a CPU. Next, when the triac becomes conductive, power is supplied to the heating element, and the heating element is heated. At this time, a drive signal is output from the CPU, and a relay connected in series with the heating element and the triac is driven, so that power is supplied to the heating element. If the relay is not driven, even if the triac is driven, the circuit is interrupted by the relay contacts, so power is not supplied to the heating element. In such an image forming apparatus, as a configuration for detecting an abnormally high temperature (runaway) of the heating element due to an abnormality in the heating element drive circuit or the like, when the heating element reaches a predetermined temperature (abnormally high temperature detection temperature), there is a configuration that stops driving the triac and the relay. With this configuration, the power supply to the heating element is interrupted. Further, as another method for detecting an abnormally high temperature of the heating element, for example, there is a method of interrupting the power supply to the heater according to the temperature rise gradient per unit time detected by the temperature detection element, as shown in Patent Document 2.

Prior Art Documents

Patent Document

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional example, when an AC power supply generated by an uninterruptible power supply is supplied to an image forming apparatus, the supplied AC power supply becomes a square wave. Therefore, since the slopes of the current and voltage waveforms applied to the triac become steep, due to the structure of the triac, after the triac is turned on once, there is a case where it falls into a commutation failure state in which the supplied current cannot be turned off at the zero-crossing point. When the triac falls into this commutation failure state, temperature control of the heating element by the triac becomes impossible, and the power of the uninterruptible power supply connected to the image forming apparatus is directly supplied to the heating element, and the heating element becomes abnormally hot. Also, similarly, even when a heating element drive circuit including a triac experiences a short circuit failure, temperature control of the heating element by the triac becomes impossible, and the power of the power supply connected to the image forming apparatus is directly supplied to the heating element, and the heating element becomes abnormally hot. That is, the cause of the abnormally high temperature is either due to an abnormality in the voltage waveform or due to a failure of the heating element drive circuit including the triac. As a method for detecting an abnormally high temperature of the heating element, when the detected temperature of the temperature detection element reaches the abnormally high temperature detection temperature, or when the temperature increase gradient per unit time becomes equal to or greater than a certain value, the driving of the triac and the relay is stopped, and there is a method of cutting off the power supply to the heating element. In the case where the cause is a short circuit failure or the like of the heating element drive circuit including the triac, it is necessary to replace the substrate on which the heating element drive circuit is provided. When the square wave generated by the uninterruptible power supply is input and the triac enters the commutation failure state, if the waveform of the input AC voltage returns to a sine wave, normal operation can be restored. However, there is a possibility that the separation cannot be made and unnecessary substrate replacement may occur by a service technician or the like. For this reason, there is a demand for an image forming apparatus that can determine the cause after an abnormally high temperature has occurred.

[0006] The present invention has been made under such circumstances, and an object thereof is to determine the cause when the heating element becomes abnormally hot.

Means for Solving the Problems

[0007] In order to solve the above-described problems, the present invention has the following configuration.

[0008] (1) An image forming apparatus comprising: heating means having a heating element; temperature detection means for detecting the temperature of the heating means; a switching element connected to one end of an AC power supply and configured to be in a conductive state for supplying power from the AC power supply to the heating means or a non-conductive state for not supplying power, and controlling the temperature of the heating means to a target temperature; a cutoff element connected to the other end of the AC power supply and configured to be in a connected state for connecting the heating means and the AC power supply or a cutoff state for cutting off the connection between the heating means and the AC power supply; and control means for controlling the switching element and the cutoff element based on the temperature information of the heating means detected by the temperature detection means. In the image forming apparatus, when the control means determines that the temperature rise of the heating means is abnormal in a state where the switching element is in the non-conductive state and the cutoff element is in the connected state, the control means sets the cutoff element to the cutoff state, and after a predetermined time has elapsed, based on the result of comparing the detected temperature of the heating means detected by the temperature detection means with a predetermined specified value after setting the cutoff element to the connected state, the control means determines the cause of the abnormal temperature rise.

[0009] (2) A heating means having a heating element, a temperature detection means for detecting the temperature of the heating means, a switching element connected to one end of an AC power supply for supplying power from the AC power supply to the heating means in a conductive state or not supplying power in a non-conductive state to control the temperature of the heating means to a target temperature, a cutoff element connected to the other end of the AC power supply for establishing a connection state between the heating means and the AC power supply or a cutoff state for cutting off the connection between the heating means and the AC power supply, and a control means for determining the control of the switching element and the cutoff element based on the temperature information of the heating means detected by the temperature detection means. In the image forming apparatus, when the control means determines that the temperature rise of the heating means is abnormal with the switching element in the non-conductive state and the cutoff element in the connected state, the cutoff element is set to the cutoff state, and after a predetermined time has elapsed, based on the comparison between the temperature gradient based on the detected temperature of the heating means detected by the temperature detection means after setting the cutoff element to the connected state and a predetermined temperature gradient standard value, the cause of the abnormal temperature rise is determined. The image forming apparatus is characterized by this.

Advantages of the Invention

[0010] According to the present invention, when the heating element reaches an abnormally high temperature, the cause can be determined.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

Examples

[0012] The specific configuration of the present invention for solving the above-described problems will be described below based on examples. Note that the examples shown below are merely examples and are not intended to limit the technical scope of this invention thereto.

[0013] (Image forming apparatus) FIG. 1 is a cross-sectional view of an image forming apparatus 100 using electrophotographic recording technology. When a print signal is generated, the scanner unit 101 emits a laser beam modulated according to image information, and scans the photosensitive drum 103 charged to a predetermined polarity by the charging roller 102. As a result, an electrostatic latent image is formed on the photosensitive drum 103. Toner is supplied to this electrostatic latent image from the developing device 104, and a toner image corresponding to the image information is formed on the photosensitive drum 103. On the other hand, the recording paper P, which is a recording material loaded in the paper feed cassette 105, is fed one by one by the pickup roller 106 and conveyed by the roller 107 toward the registration roller 108. Further, the recording paper P is conveyed from the registration roller 108 to the transfer position at the timing when the toner image on the photosensitive drum 103 reaches the transfer position formed by the photosensitive drum 103 and the transfer roller 109. During the process in which the recording paper P passes through the transfer position, the toner image on the photosensitive drum 103 is transferred to the recording paper P. Thereafter, the recording paper P is heated by the heater 201 in the image heating device 200, and the unfixed toner image is heat-fixed to the recording paper P. The recording paper P carrying the fixed toner image is discharged to the tray above the image forming apparatus 100 by the rollers 110 and 111.

[0014] Note that the cleaner 112 cleans the photosensitive drum 103, and the paper feed tray (manual feed tray) 114 is a tray having a pair of recording paper regulating plates whose width can be adjusted according to the size of the recording paper P. The paper feed tray 114 is provided to accommodate recording paper P of sizes other than standard sizes. The pickup roller 115 feeds the recording paper P from the paper feed tray 114. The motor 116 is a motor that drives the image heating device 200 and the like. Electric power is supplied from the control board 300 connected to the AC power supply 117 to the motor 116. Electric power is supplied to the heater 201 in the image heating device 200 under the control of the power supply unit 301 (see FIG. 3) connected to the AC power supply 117. The photosensitive drum 103, the charging roller 102, the scanner unit 101, the developing device 104, and the transfer roller 109, which are described above, constitute an image forming means for forming an unfixed image on the recording paper P. Note that the image forming apparatus to which the present invention is applicable is not limited to the image forming apparatus 100 having the configuration shown in FIG. 1.

[0015] (such as a heating device) FIG. 2 is a cross-sectional view of the image heating device 200 in Example 1. The image heating device 200 includes an endless belt (hereinafter described as a film) 203, a heater 201 as a heating means, a pressure roller (nip portion forming member) 208, and a thermistor 202 as temperature detection means. The film 203 is an endless belt, that is, a cylindrical film. The heater 201 has a heating element and contacts the inner surface of the film 203. Note that the heater 201 may have one heating element, or may have a plurality of heating elements having different lengths in the width direction orthogonal to the conveyance direction of the recording material P. The pressure roller 208 forms a fixing nip portion N together with the heater 201 via the film 203. The thermistor 202 detects the temperature of the heater 201.

[0016] The material of the base layer of the film 203 is a heat-resistant resin such as polyimide or a metal such as stainless steel. An elastic layer such as heat-resistant rubber may be provided on the surface layer of the film 203. The pressure roller 208 has a core metal 209 made of a material such as iron or aluminum and an elastic layer 210 made of a material such as silicone rubber. The heater 201 is held by a heat-resistant resin holding member 205. The holding member 205 also has a guide function for guiding the rotation of the film 203. The stay 204 is provided to apply the pressure of a spring (not shown) to the holding member 205 and is made of metal. The pressure roller 208 receives power from a motor (not shown) and rotates in the direction of the arrow. When the pressure roller 208 rotates, the film 203 is driven to rotate. The recording paper P carrying the unfixed toner image is heated, pressurized, and fixed while being sandwiched and conveyed at the fixing nip portion N.

[0017] (Heater drive circuit) FIG. 3 shows a control board 300 that controls the power supply from the AC power supply 117 to the image heating device 200 in Example 1. The control board 300 includes a power supply unit 301, a zero-cross detection circuit 400, a power supply voltage generation unit 302, a relay 303, and a power control unit 304 (hereinafter referred to as an engine controller 304).

[0018] The power supply unit 301 includes a transistor 306, a bidirectional thyristor (hereinafter referred to as a triac) 308, a photo triac coupler 307, and resistors 309, 310, 311. The power supply unit 301 is connected to one (one end) of the AC power supply 117 and is connected to the image heating device 200 via the connection terminal 305b in the AC connector 305. The relay 303 is connected to the other end of the AC power supply 117 and is a cutoff element that can be in a connection state connecting the heater 201 and the AC power supply 117 or a cutoff state cutting off the connection between the heater 201 and the AC power supply 117.

[0019] In the first embodiment, the heater 201 has, for example, two heating elements 201a and 201b, and the heating element 201a and the heating element 201b are connected in series. The AC connector 305 has connection terminals 305a and 305b. One end of the connection terminal 305a is connected to the relay 303, and the other end is connected to the heating element 201a. One end of the connection terminal 305b is connected to the power supply unit 301, and the other end is connected to the heating element 201b. One end of the thermistor 202 is connected to the connection terminal 312a of the connector 312, and the connection terminal 312a is connected to the engine controller 304 to output a signal TH corresponding to temperature information. The other end of the thermistor 202 is connected to the connection terminal 312b of the connector 312, and the connection terminal 312b is grounded (GND).

[0020] The engine controller 304 functions as control means for controlling the triac 308 and the relay 303 based on the temperature information of the heater 201 detected by the thermistor 202. A current flows through the optotriac coupler 307 via the transistor 306 turned on by the heater drive signal ON1 output from the engine controller 304. As a result, a current flows through the gate of the triac 308 and the triac 308 becomes an ON state. The triac 308 serves as a switching element for controlling the power supplied to the heater 201. When the triac 308 becomes an ON state, a current flows through the heater 201 and the heater 201 generates heat. The triac 308 is connected to one end of the AC power supply 117 and is a switching element for controlling to be in a conductive state of supplying power from the AC power supply 117 to the heater 201 or a non-conductive state of not supplying power so that the temperature of the heater 201 becomes the target temperature.

[0021] The zero-cross detection circuit 400 and the power supply voltage generation unit 302 are both connected to the AC power supply 117. The zero-cross detection circuit 400 outputs a zero-cross signal ZEROX indicating the zero-cross point of the waveform of the AC voltage of the AC power supply 117 (hereinafter referred to as the AC waveform) to the engine controller 304. Note that the zero-cross point is the timing at which the AC waveform changes from positive to negative or from negative to positive.

[0022] The power supply voltage generation unit 302 generates the power supply voltage VIN necessary for the operation of the engine controller 304 and other parts from the AC waveform. The engine controller 304 serves as the control unit of the image forming apparatus 100. Based on the temperature information (signal TH) sent from the thermistor 202 inside the image heating device 200 via the DC bus line 313, the engine controller 304 controls the power supply unit 301 via the heater drive signal ON1 so that the detected temperature becomes a predetermined temperature. Further, when the engine controller 304 detects an abnormal temperature rise of the heater 201 from the temperature information sent from the thermistor 202, it shuts off the relay 303 as a cutoff element to prevent the heater 201 from generating heat. The engine controller 304 connects or disconnects the relay 303 by outputting the signal RLON.

[0023] (Description of the zero - cross circuit) FIG. 4 shows the zero - cross detection circuit 400 in the first embodiment. During the period when the voltage is applied from the AC power supply 117 in the direction of C1 (hereinafter, this direction is defined as positive (+)), the current flows through the pull - down resistor 401 and then flows into the diode 402d of the photocoupler 402. As a result, the transistor 402t on the secondary side turns ON, and the current flowing through the pull - down resistor 403 flows between the collector and the emitter, so that the zero - cross signal ZEROX outputs a low level (hereinafter, referred to as L) (the same level as GND).

[0024] On the other hand, during the period when the voltage is applied from the AC power supply 117 in the direction of C2 (hereinafter, this direction is defined as negative (-)), since a reverse voltage is applied to the diode 402d of the photocoupler 402, no current flows. Since the transistor 402t on the secondary side also turns OFF, the zero - cross signal ZEROX outputs a high level (hereinafter, referred to as H) from 3.3V through the pull - down resistor 403.

[0025] Through the operation as described above, the rising edge of the zero-cross signal ZEROX from the low level to the high level synchronizes with the zero-cross point where the voltage of the AC power supply 117 changes from positive to negative. Also, the falling edge of the zero-cross signal ZEROX from the high level to the low level can synchronize with the zero-cross point where the voltage of the AC power supply 117 changes from negative to positive.

[0026] (Normal operation of the heater drive circuit) FIG. 5 shows the relationship of the input voltage, zero-cross signal ZEROX, heater drive signal ON1, and heater current flowing through the heater 201 with respect to each time when a sinusoidal AC voltage is applied from the AC power supply 117 to the normal control board 300 without a failure. FIG. 5(i) is a graph showing the waveform of the AC voltage, (ii) is a graph showing the ZEROX signal, (iii) is a graph showing the heater drive signal ON1 which is the drive signal of the heater 201, and (iv) shows the current flowing through the heater 201. In (iii), the heater drive signal ON1 is set to ON (high level) when current flows through the heater 201.

[0027] The engine controller 304 calculates the power to be supplied to the heater 201 based on, for example, PI control, based on the set temperature (target temperature) of the heater 201 and the detected temperature of the thermistor 202. The engine controller 304 converts it into a control level of a frequency corresponding to the supplied power based on the zero-cross point of the AC power supply 117 detected by the zero-cross detection circuit 400. Then, the engine controller 304 issues a heater drive signal ON1 according to the converted control condition (control level) to control the triac 308. As a result, a heater current is applied to the heater 201. This control is called temperature control of the heater 201.

[0028] (Temperature change of the heater in normal temperature control) FIG. 6(a) is a graph showing the relationship between the elapsed time from the start of temperature control in normal printing operation and the detected temperature of the thermistor 202. In FIG. 6(a), the target temperature (set temperature) of the heater 201 and the abnormal temperature threshold c2 are indicated by broken lines. t1 to t3 indicate each timing.

[0029] After the temperature control is started at timing t1, the temperature detected by the thermistor 202 changes near the target temperature of the heater 201, and it can be seen that the temperature of the thermistor 202 decreases after timing t2 when the temperature control ends. Here, let the abnormal temperature threshold for detecting that the heater 201 shows an abnormal temperature rise be c2. In FIG. 6(a), the detected temperature of the thermistor 202 does not exceed the abnormal temperature threshold c2. Therefore, the engine controller 304 can determine that no abnormal temperature rise has occurred in the heater 201, and at timing t3, the image forming apparatus 100 can be determined to be in a normal state.

[0030] (Explanation of the cause of the abnormal temperature of the heater 201) When the input voltage of the AC power supply 117 changes from a sine wave to a square wave, or when the triac 308 has a short circuit failure, an abnormal temperature rise occurs in the heater 201. FIG. 6(b) is a graph showing the relationship between the elapsed time from the start of temperature control and the detected temperature of the thermistor 202 when it is detected that the heater 201 has a temperature rise at a timing when it should not have a temperature rise, and it is the same graph as FIG. 6(a). t11 to t13 indicate each timing. Timing t11 is the same as timing t1, the timing of starting temperature control, and timing t12 is the same as timing t2, the timing of ending temperature control.

[0031] The engine controller 304 determines that the detected temperature of the thermistor 202 exceeds the abnormal temperature threshold c2 at the timing t13 after the temperature control ends at the timing t12. In this case, the engine controller 304 determines that an abnormal temperature rise of the heater 201 has occurred. Therefore, the engine controller 304 shuts off the relay 303 at the timing t13. By shutting off the relay 303 to cut off the current flowing through the heater 201, the temperature rise of the thermistor 202 can be stopped. However, with only this control, the engine controller 304 cannot determine the cause of the abnormal temperature rise of the heater 201.

[0032] (Two causes of abnormal temperature rise of the heater) There are two cases where an abnormal temperature rise of the heater 201 occurs even though the temperature control of the image heating device 200 has ended. The first case is when the voltage waveform of the AC power supply 117 changes from a sine wave to a square wave. Fig. 7(a) shows the relationship of each waveform over time when the voltage applied from the AC power supply 117 changes from a sine wave to a square wave at the timing Ta while the heater 201 is being powered, and it is the same figure as Fig. 5.

[0033] The input voltage changes from a sine wave to a square wave at timing Ta. Once the triac 308 is turned on, if the temperature of the triac 308 itself is rising and the slopes of the current and voltage applied to the triac 308 suddenly change, it will enter a commutation failure state where it cannot turn off the supplied current. In Fig. 7(a), at the timing Ta when the voltage changes from a sine wave to a square wave, the triac 308 enters a commutation failure state. As a result, after timing Ta, even though the heater drive signal ON1 is in the OFF state (iii), current continues to flow through the heater 201 (iv). Consequently, an abnormal temperature rise of the heater 201 occurs. In this case, the cause of the abnormality is due to the voltage waveform of the AC power supply 117. Since there is no abnormality in the control board 300 itself, there is no need to replace the board of the control board 300. Here, if it is erroneously determined that an abnormality has occurred in the control board 300, unnecessary board replacement will be carried out, resulting in loss of time and cost until the image forming apparatus 100 is restored, which is disadvantageous to the user.

[0034] The second case where an abnormal temperature rise of the heater 201 occurs is when the triac 308 on the control board 300 has a short circuit failure. In Fig. 7(b), the voltage applied from the AC power supply 117 is a sine wave, and it shows the relationship of each waveform over time when the triac 308 has a short circuit failure at the timing Ta at the end of temperature control, and it is the same figure as Fig. 5.

[0035] When the triac 308 has a short circuit failure, after timing Ta, even though the heater drive signal ON1 is in the OFF state (iii), current continues to flow through the heater 201 (iv). As a result, an abnormal temperature rise of the heater 201 occurs. In this case, since the triac 308 itself on the control board 300 is faulty, the image forming apparatus 100 cannot be restored unless the board of the control board 300 is replaced. From the above, in order to reduce the loss time until the restoration of the image forming apparatus 100, when an abnormal temperature rise of the heater 201 occurs, the cause should be grasped as described below and the necessity of replacing the board of the control board 300 should be determined.

[0036] (Method for grasping failure cause) (When the square wave is the cause) FIG. 8(a) is a graph showing the relationship between the elapsed time from the start of temperature control and the detected temperature of the thermistor 202 when the cause of the abnormal temperature rise of the heater 201 in Example 1 was that the voltage waveform of the AC power supply 117 changed from a sine wave to a square wave. FIG. 8(a) is the same graph as FIG. 6(a). Note that below the graph of FIG. 8(a), the state of the AC voltage waveform (sine wave, square wave) and the state of temperature control (during temperature control, temperature control OFF) are also shown. t21 to t25 indicate each timing.

[0037] When temperature control is started at timing t21 and the detected temperature of the thermistor 202 reaches that temperature after temperature control ends at timing t22, the temperature detected as abnormal is set as the abnormal temperature threshold c2 as a predetermined second specified value. When an abnormal temperature rise occurs, the engine controller 304 shuts off the relay 303 once at timing t23 and then turns on the relay 303 again at timing t24. The temperature detected as abnormal when the detected temperature of the thermistor 202 reaches that temperature after timing t24 is set as the abnormal temperature threshold c1 as a predetermined first specified value (specified value). Note that the abnormal temperature threshold c1 is lower than the abnormal temperature threshold c2 (c1 < c2).

[0038] After the timing t22 when temperature control ends, the engine controller 304 monitors the detected temperature of the thermistor 202 as the second temperature a2. When the engine controller 304 detects that the second temperature a2 is equal to or higher than a predetermined abnormal temperature threshold c2 (equal to or higher than the second specified value), it determines that an abnormal temperature rise of the heater 201 has occurred (the temperature rise is abnormal). Then, the engine controller 304 turns off the relay 303 at timing t23.

[0039] Note that the engine controller 304 turns off the relay 303 at the timing t23 when the second temperature a2 is equal to or higher than the abnormal temperature threshold c2. However, the timing for turning off the relay 303 may be within the first hour T1 (predetermined time) from the timing t23. By turning off the relay 303 within the predetermined first hour T1, the engine controller 304 not only prevents the temperature rise of the triac 308 due to power supply, but also cools the temperature inside the image heating device 200 and prevents the film 203 from sticking to the pressure roller 208.

[0040] At the timing t24 when the first hour T1 has elapsed since the relay 303 was turned off, the engine controller 304 turns on the relay 303. Here, in Fig. 8(a), since there is no failure in the control board 300 (the heater drive signal is OFF), just turning on the relay 303 does not cause current to flow through the heater 201. Also, since the temperature of the triac 308 has dropped sufficiently, the triac 308 does not enter a commutation failure state where it cannot turn off the current it is supplying.

[0041] Therefore, when the detected temperature of the thermistor 202 is monitored as the first temperature a1, the first temperature a1 in this case is less than the abnormal temperature threshold c1 (less than the first specified value). From the above control, the engine controller 304 turns off the relay 303 once, turns it on again, and then detects the first temperature a1 by the thermistor 202. Then, if the detected first temperature a1 is equal to or lower than the predetermined abnormal temperature threshold c1, the engine controller 304 can determine that the cause of the abnormal temperature rise of the heater 201 is that the voltage waveform of the AC power supply 117 has changed from a sine wave to a square wave.

[0042] (When caused by a triac) FIG. 8(b) is a graph showing the relationship between the elapsed time since the start of temperature control and the detected temperature of the thermistor 202 when the cause of the abnormal temperature rise of the heater 201 in Example 1 was a short circuit failure of the triac 308, and it is the same graph as FIG. 6(a). Note that below the graph of FIG. 8(b), the state of the triac 308 (normal, short circuit failure) and the state of temperature control (during temperature control, temperature control OFF) are also shown. t31 to t35 indicate each timing.

[0043] Similar to FIG. 8(a), when the detected temperature of the thermistor 202 reaches that temperature after starting temperature control at timing t31 and ending temperature control at timing t32, the temperature detected as an abnormality is set to a predetermined abnormal temperature threshold value c2. The engine controller 304 shuts off the relay 303 once at timing t33 and then turns on the relay 303 again at timing t34. Then, when the detected temperature of the thermistor 202 reaches that temperature after timing t34, the temperature detected as an abnormality is set to a predetermined abnormal temperature threshold value c1.

[0044] The engine controller 304 monitors the detected temperature of the thermistor 202 as the second temperature a2 after the temperature control ends at timing t32. When the engine controller 304 detects that the detected second temperature a2 is equal to or higher than a predetermined abnormal temperature threshold value c2, it determines that an abnormal temperature rise of the heater 201 has occurred and turns off the relay 303 at timing t33.

[0045] Similar to FIG. 8(a), the engine controller 304 cools the temperature inside the image heating device 200 by turning off the relay 303 after determining an abnormality, thereby preventing the film 203 from sticking to the pressure roller 208. The engine controller 304 turns on the relay 303 at timing t34 when the first hour T1 has elapsed from timing t33 when the relay 303 was turned off.

[0046] Here, in FIG. 8(b), since a short circuit failure of the triac 308 has occurred, when the relay 303 is turned ON, current flows through the heater 201, and the detected temperature of the thermistor 202 rises. Therefore, when the detected temperature of the thermistor 202 is monitored as the first temperature a1, the first temperature a1 becomes equal to or higher than the abnormal temperature threshold value c1 (equal to or higher than the first specified value). If the first temperature a1 detected by the thermistor 202 after the timing t34 is equal to or higher than the predetermined abnormal temperature threshold value c1, the engine controller 304 can determine that the cause of the abnormal temperature rise of the heater 201 is due to the short circuit failure of the triac 308.

[0047] As described above, when an abnormal temperature rise of the heater 201 occurs, the engine controller 304 turns OFF the relay 303. After a certain period of time has elapsed since the engine controller 304 turned OFF the relay 303, the engine controller 304 turns ON the relay 303 and detects the temperature with the thermistor 202. The engine controller 304 can determine the cause of the abnormal temperature rise of the heater 201 based on the state of the detected temperature by the thermistor 202.

[0048] (Flowchart for judging the cause of temperature rise) FIG. 9 shows a flowchart of the operation of the image forming apparatus 100 in the first embodiment. In step (hereinafter referred to as S) 1201, the engine controller 304 sets the relay 303 to a driving state (ON) as a normal image forming operation. In S1202, the engine controller 304 starts temperature control of the heater 201. In S1203, the engine controller 304 ends the temperature control of the heater 201 and sets the triac 308 to a non-driving state (non-conducting state). In S1204, the engine controller 304 monitors the detected temperature of the thermistor 202 as the second temperature a2.

[0049] At S1205, the engine controller 304 determines whether the second temperature a2 detected at S1204 is equal to or higher than the abnormal temperature threshold value c2. If, at S1205, the engine controller 304 determines that the second temperature a2 is not equal to or higher than the abnormal temperature threshold value c2, the process proceeds to S1206. At S1206, the engine controller 304 determines that no abnormal temperature rise of the heater 201 has occurred, and ends the process. If, at S1205, the engine controller 304 determines that the second temperature a2 is equal to or higher than the abnormal temperature threshold value c2, the process proceeds to S1207.

[0050] In this case, the engine controller 304 determines that an abnormal temperature rise of the heater 201 has occurred, and at S1207, shuts off (turns OFF) the relay 303 in order to prevent the film 203 and the pressure roller 208 in the image heating device 200 from sticking. At the stage of S1207, it is impossible to determine whether the cause of the abnormal temperature rise of the heater 201 is that the voltage waveform of the AC power supply 117 has changed from a sine wave to a square wave (Fig. 8(a)), or that the triac 308 of the control board 300 has short-circuited (Fig. 8(b)).

[0051] In order to make this determination, at S1208, after the first time T1 has elapsed, the engine controller 304 turns ON the relay 303 at S1209. Note that the engine controller 304 has a timer (not shown) and measures the elapsed time since the relay 303 was turned OFF at S1207. At S1210, the engine controller 304 monitors the detected temperature of the thermistor 202 as the first temperature a1.

[0052] In S1211, the engine controller 304 determines whether the first temperature a1 detected in S1201 is equal to or higher than the abnormal temperature threshold value c1. If, in S1211, the engine controller 304 determines that the first temperature a1 is equal to or higher than the abnormal temperature threshold value c1, the process proceeds to S1212. In S1212, the engine controller 304 determines that the triac 308 has a short circuit failure, and the process proceeds to S1213. In S1213, the engine controller 304 shuts off (turns OFF) the relay 303 to prevent the film 203 and the pressure roller 208 in the image heating device 200 from sticking together, and ends the process.

[0053] If, in S1211, the engine controller 304 determines that the first temperature a1 is not equal to or higher than the abnormal temperature threshold value c1, the process proceeds to S1214. In S1214, the engine controller 304 determines that the voltage waveform of the AC power supply 117 has changed from a sine wave to a square wave, shuts off (turns OFF) the relay 303 in S1213, and ends the process.

[0054] Thus, when the engine controller 304 determines that the temperature rise of the heater 201 is abnormal with the triac 308 in the non-conducting state and the relay 303 in the connected state, the engine controller 304 controls as follows. The engine controller 304 sets the relay 303 to the cut-off state, and after a predetermined time has elapsed, sets the relay 303 to the connected state and then compares the detected temperature of the heater 201 detected by the thermistor 202 with a predetermined specified value. Then, based on the comparison result, the engine controller 304 determines the cause of the abnormal temperature rise.

[0055] According to the flowchart shown above, it is possible to distinguish whether the cause of the abnormal temperature rise of the heater is that the voltage waveform of the AC power supply 117 has changed from a sine wave to a square wave, or that the triac 308 of the control board 300 has short-circuited. In the first embodiment, the values of the abnormal temperature threshold c1 and the abnormal temperature threshold c2 are different, but they may also be the same value. Further, when the image forming apparatus 100 includes a display unit, the engine controller 304 may display the determination result of S1212 or S1214 on the display unit to notify the user.

[0056] As described above, according to the first embodiment, when the heating element becomes abnormally hot, the cause can be determined.

Embodiment

[0057] (Method for grasping the cause of failure) (When the square wave is the cause) In the second embodiment, a control method for detecting an abnormal temperature rise of the heater 201 from the temperature gradient of the heater 201 obtained from the temperature detected by the thermistor 202 and the elapsed time is shown. FIG. 10(a) is a graph showing the relationship between the elapsed time from the start of temperature control and the detected temperature of the thermistor 202 when the cause of the abnormal temperature rise of the heater 201 in the second embodiment is that the voltage waveform of the AC power supply 117 has changed from a sine wave to a square wave. FIG. 10(a) is the same graph as FIG. 8(a). t41 to t45 indicate each timing.

[0058] After the start of temperature control at timing t41 until after the end of temperature control at timing t42, the engine controller 304 detects the third temperature a3 by the thermistor 202, and detects the fourth temperature a4 by the thermistor 202 at timing t43 when the second time T2 (third time) has elapsed. The engine controller 304 calculates the temperature gradient of the heater 201 (referred to as the second temperature gradient) from the third temperature a3, the fourth temperature a4, and the second time T2. Here, the engine controller 304 compares the calculated second temperature gradient (temperature gradient) of the heater 201 with a previously defined second temperature gradient standard value d2 (temperature gradient standard value) of the heater 201. The second temperature gradient standard value d2 defines the time for detecting the temperature gradient, the differential temperature, and the number of times. For example, a standard value such as "detecting a 10°C rise twice in 5 seconds" is defined.

[0059] When the engine controller 304 detects that the second temperature gradient exceeds the second temperature gradient standard value d2 and the heater 201 is experiencing a temperature rise, it determines that an abnormal temperature rise of the heater 201 has occurred and turns off the relay 303 at timing t43. Note that timing t43 may be within the first time T1. Thereby, in addition to cooling the temperature inside the image heating device 200 and preventing the film 203 from sticking to the pressure roller 208, it also prevents the temperature rise of the triac 308 due to power supply. The engine controller 304 turns on the relay 303 at timing t44 when the first time T1 (predetermined time) has elapsed.

[0060] In FIG. 10(a), since no failure has occurred in the control board 300, no current flows through the heater 201 even when the relay 303 is turned on at timing t44. Also, since the temperature of the triac 308 has sufficiently dropped, the triac 308 does not fall into a commutation failure state where it cannot turn off the current supplied by the power supply. That is, even when the relay 303 is turned on, no current flows through the heater 201, and the detected temperature of the thermistor 202 does not rise.

[0061] The engine controller 304 turns on the relay 303 at timing t44. The engine controller 304 detects the fifth temperature a5 (first temperature) detected again by the thermistor 202, and detects the sixth temperature a6 (second temperature) by the thermistor 202 at timing t45 when the third hour T3 (second hour) has elapsed. The engine controller 304 calculates the first temperature gradient of the heater 201 from the fifth temperature a5, the sixth temperature a6, and the third hour T3. When the engine controller 304 detects that the calculated first temperature gradient is equal to or less than the predetermined first temperature gradient standard value d1 of the heater 201, it can be determined that the cause of the abnormal temperature rise of the heater 201 is due to the abnormality of the voltage waveform of the AC power supply 117.

[0062] (When it is caused by a triac) FIG. 10(b) is a graph showing the relationship between the elapsed time from the start of temperature control and the detected temperature of the thermistor 202 when the triac 308 has a short circuit failure in the second embodiment, and is the same graph as FIG. 8(b). t51 to t55 indicate each timing.

[0063] After the temperature control start at timing t51 to the end of temperature control at timing t52, the engine controller 304 detects the third temperature a3 by the thermistor 202, and detects the fourth temperature a4 by the thermistor 202 at timing t53 when the second hour T2 has elapsed. The engine controller 304 calculates the second temperature gradient of the heater 201 from the third temperature a3, the fourth temperature a4, and the second hour T2. When the second temperature gradient of the heater 201 calculated here exceeds the predetermined second temperature gradient standard value d2 of the heater 201, the engine controller 304 detects that an abnormal temperature rise of the heater 201 has occurred.

[0064] The engine controller 304 cools the temperature inside the image heating device 200 by turning off the relay 303 at timing t53, preventing the film 203 from sticking to the pressure roller 208. The engine controller 304 turns on the relay 303 at timing t54 when the first time T1 has elapsed. At this time, in Fig. 10(b), since the triac 308 on the control board 300 has a short circuit failure, current flows through the heater 201, and the detected temperature of the thermistor 202 rises.

[0065] At timing t54, the engine controller 304 detects the fifth temperature a5 by the thermistor 202, and at timing t55 when the third time T3 has elapsed, the engine controller 304 detects the sixth temperature a6 by the thermistor 202 again. The engine controller 304 calculates the first temperature gradient of the heater 201 from the fifth temperature a5, the sixth temperature a6, and the third time T3. The engine controller 304 can detect that the calculated first temperature gradient exceeds the first temperature gradient standard value d1 of the heater 201 set in advance. From the above control, when the first temperature gradient at the third time T3 is equal to or greater than the first temperature gradient standard value d1, the image forming apparatus 100 can determine that the cause of the abnormal temperature rise of the heater 201 is that the triac 308 on the control board 300 has a short circuit failure.

[0066] (Flowchart for judging the cause of temperature rise) Fig. 11 shows a flowchart of the determination process in the second embodiment. Since the processes of S1501 to S1503 are the same as the processes of S1201 to S1203 in Fig. 9, the description thereof is omitted.

[0067] At S1504, the engine controller 304 holds the detected temperature by the thermistor 202 as the third temperature a3. At S1505, after the second time T2 has elapsed, the engine controller 304 holds the detected temperature by the thermistor 202 as the fourth temperature a4 at S1506. At S1507, the engine controller 304 calculates the second temperature gradient from the third temperature a3, the fourth temperature a4, and the second time T2. The engine controller 304 determines whether the calculated second temperature gradient exceeds the second temperature gradient standard value d2.

[0068] When the engine controller 304 determines at S1507 that the second temperature gradient does not exceed the second temperature gradient standard value d2, the process proceeds to S1508. Note that the process of S1508 is the same as the process of S1206 in FIG. 9, and the description thereof is omitted. When the engine controller 304 determines at S1507 that the second temperature gradient exceeds the second temperature gradient standard value d2, it determines that an abnormal temperature rise of the heater 201 has occurred, and the process proceeds to S1509.

[0069] At S1509, the engine controller 304 turns off the relay 303. At S1510, the engine controller 304 cools the temperature inside the image heating device 200 and waits for the elapse of the first time T1 to prevent the film 203 from sticking to the pressure roller 208. At S1511, the engine controller 304 holds the detected temperature by the thermistor 202 as the fifth temperature a5. At the stage of S1511, it is impossible to distinguish whether the cause of the abnormal high temperature of the heater 201 is that the voltage waveform of the AC power supply 117 has changed from a sine wave to a square wave, or that the triac 308 of the control board 300 has a short circuit failure. To make this distinction, at S1512, the engine controller 304 turns on the relay 303. At S1513, after the elapse of the third time T3, the engine controller 304 holds the detected temperature by the thermistor 202 as the sixth temperature a6 at S1514.

[0070] At S1515, the engine controller 304 calculates the first temperature gradient from the fifth temperature a5, the sixth temperature a6, and the third time T3. The engine controller 304 determines whether the calculated first temperature gradient exceeds the first temperature gradient standard value d1. When the engine controller 304 determines at S1515 that the first temperature gradient exceeds the first temperature gradient standard value d1, the process proceeds to S1516. When the engine controller 304 determines at S1515 that the first temperature gradient does not exceed the first temperature gradient standard value d1, the process proceeds to S1518. Note that the processes of S1516 to S1518 are the same as the processes of S1212 to S1214 in FIG. 9, and the description thereof is omitted.

[0071] If the above control is implemented, it is possible to determine whether the cause of the abnormal temperature rise of the heater 201 is that the voltage waveform of the AC power supply 117 has changed from a sine wave to a square wave, or that the triac 308 of the control board 300 has short-circuited. In the second embodiment, the values of the first temperature gradient standard value d1 and the second temperature gradient standard value d2 are different values, but they may be the same value.

[0072] As described above, according to the second embodiment, when the heating element becomes abnormally hot, the cause can be determined.

[0073] (Proper use of the method for determining abnormal temperature rise) Whether to use the method for detecting the abnormal temperature rise of the heater 201 as the abnormal temperature threshold shown in the first embodiment or the abnormal temperature gradient shown in the second embodiment can be selected, for example, based on whether the film 203 and the pressure roller 208 are rotating or stopped. FIG. 12 shows a graph representing the relationship between the elapsed time from the start of temperature control and the detected temperature of the thermistor 202, with the state where the film 203 and the pressure roller 208 are rotating shown by a dashed line and the stopped state shown by a solid line. t61, t62, T5, T4, and T6 indicate each timing. The timing t61 is the timing when the temperature control is started, and the timing t62 is the timing when the temperature control ends.

[0074] When an abnormal temperature rise occurs in the heater 201 while the film 203 and the pressure roller 208 are stopped, as shown by the solid line graph in FIG. 12, the thermistor 202 rises in temperature in a short time. When detecting the occurrence of an abnormal temperature rise using the abnormal temperature threshold, the relay 303 is cut off at T4, which is the timing when the seventh temperature a7 becomes equal to or higher than the abnormal temperature threshold c2.

[0075] On the other hand, when an abnormal temperature rise is detected at the second temperature gradient standard value d2, in order to capture that the heater 201 has increased its temperature within a certain continuous time, the temperature at which the abnormality is detected becomes lower than the eighth temperature a8, and the timing at which the relay 303 is cut off becomes T5. In this case, by the control of the second embodiment, an abnormal temperature rise of the heater 201 can be detected in a time shorter than T4 (at an earlier timing), and sticking between the film 203 and the pressure roller 208 can be prevented.

[0076] On the other hand, when an abnormal temperature rise occurs in the heater 201 while the film 203 and the pressure roller 208 are rotating, as shown by the broken-line graph in FIG. 12, the thermistor 202 rises in temperature over a long period of time. In this case, if an attempt is made to detect an abnormal temperature rise based on the temperature gradient, the temperature rise will not meet the set temperature gradient standard value. Therefore, in such a case, the engine controller 304 cannot detect an abnormal temperature rise of the heater 201.

[0077] Therefore, when the film 203 and the pressure roller 208 are rotating, if the detection based on the abnormal temperature threshold value described in the first embodiment is performed, the relay 303 is cut off at T6, which is the timing when the seventh temperature a7 of the thermistor 202 exceeds the abnormal temperature threshold value c1. In this case, the time until the relay 303 is cut off becomes longer, but since the film 203 and the pressure roller 208 are rotating, sticking does not occur.

[0078] As described above, when the film 203 and the pressure roller 208 as rotating bodies are stopped, the method of the second embodiment may be used, and when the film 203 and the pressure roller 208 are rotating, the method of the first embodiment may be used. As described above, the method of detecting an abnormal temperature rise of the heater 201 may be properly selected according to the operating state such as the stopped state or the rotating state of the rotating body of the image heating device 200 (fixing device).

[0079] <Other Embodiments> The present invention can also be realized by supplying a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and causing one or more processors in a computer of the system or apparatus to read and execute the program. Further, it can also be realized by a circuit (for example, ASIC) that implements one or more functions.

[0080] The disclosure of this embodiment includes the following configurations. (Configuration 1) Heating means having a heating element, Temperature detection means for detecting the temperature of the heating means, A switching element that is connected to one end of an AC power supply and controls the heating means to be in a conductive state for supplying power from the AC power supply or a non-conductive state for not supplying power so that the temperature of the heating means becomes a target temperature, A cutoff element that is connected to the other end of the AC power supply and is in a connection state for connecting the heating means and the AC power supply or a cutoff state for cutting off the connection between the heating means and the AC power supply, Control means for controlling the switching element and the cutoff element based on the temperature information of the heating means detected by the temperature detection means, In an image forming apparatus comprising: When the control means determines that the temperature rise of the heating means is abnormal in a state where the switching element is in the non-conductive state and the cutoff element is in the connection state, the control means sets the cutoff element to the cutoff state, and after a predetermined time has elapsed, based on the result of comparing the detected temperature of the heating means detected by the temperature detection means with a predetermined specified value after setting the cutoff element to the connection state, the image forming apparatus is characterized in that it determines the cause of the abnormal temperature rise. (Configuration 2) When the detected temperature is a first temperature and the specified value is a first specified value, The control means determines that the temperature rise is abnormal when the second temperature detected by the temperature detection means is equal to or higher than a predetermined second specified value in a state where the switching element is in the non-conducting state and the blocking element is in the connected state. The image forming apparatus according to Configuration 1 is characterized in that. (Configuration 3) When the first temperature is less than the first specified value, the control means determines that the cause of the abnormal temperature rise is an abnormality in the waveform of the AC voltage applied to the heating means. The image forming apparatus according to Configuration 2 is characterized in that. (Configuration 4) When the first temperature is equal to or higher than the first specified value, the control means determines that the cause of the abnormal temperature rise is an abnormality in the switching element. The image forming apparatus according to Configuration 2 or Configuration 3 is characterized in that. (Configuration 5) The heating means has a rotating body, The control means determines the cause of the temperature rise in a state where the rotating body is rotating. The image forming apparatus according to any one of Configurations 1 to 4 is characterized in that. (Configuration 6) A heating means having a heating element, Temperature detection means for detecting the temperature of the heating means, A switching element connected to one end of an AC power supply and configured to supply power from the AC power supply to the heating means in a conducting state or to control the temperature of the heating means to a target temperature in a non-conducting state where power is not supplied, A blocking element connected to the other end of the AC power supply and configured to connect the heating means to the AC power supply in a connected state or to block the connection between the heating means and the AC power supply in a blocking state, Control means for determining the control of the switching element and the blocking element based on the temperature information of the heating means detected by the temperature detection means, In an image forming apparatus comprising: When the control means determines that the temperature rise of the heating means is abnormal in a state where the switching element is in the non-conducting state and the blocking element is in the connected state, the control means sets the blocking element to the blocking state. After a predetermined time has elapsed, based on the result of comparing the temperature gradient based on the detected temperature of the heating means detected by the temperature detection means after setting the blocking element to the connected state with a predetermined temperature gradient standard value, the control means determines the cause of the abnormal temperature rise. The image forming apparatus is characterized by this. (Configuration 7) When the predetermined time is set as the first time, After the first time has elapsed, the control means sets the blocking element to the connected state, detects a first temperature by the temperature detection means, and when a second time has elapsed after detecting the first temperature, detects a second temperature by the temperature detection means. The image forming apparatus according to Configuration 6 is characterized by obtaining the temperature gradient from the first temperature, the second time, and the second temperature. (Configuration 8) When the temperature gradient is set as the first temperature gradient and the temperature gradient standard value is set as the first temperature gradient standard value, The control means detects a third temperature by the temperature detection means in a state where the switching element is in the non-conducting state and the blocking element is in the connected state, detects a fourth temperature by the temperature detection means when a third time has elapsed, and determines that the temperature rise is abnormal when a second temperature gradient obtained from the third temperature, the third time, and the fourth temperature exceeds a predetermined second temperature gradient standard value. The image forming apparatus according to Configuration 7 is characterized by this. (Configuration 9) When the first temperature gradient is less than or equal to the first temperature gradient standard value, the control means determines that the cause of the abnormal temperature rise is an abnormality in the waveform of the AC voltage applied to the heating means. The image forming apparatus according to Configuration 8 is characterized by this. (Configuration 10) When the first temperature gradient exceeds the first temperature gradient standard value, the control means determines that the cause of the abnormal temperature rise is an abnormality in the switching element, according to the image forming apparatus described in Configuration 8 or Configuration 9. (Configuration 11) The heating means has a rotating body. The control means determines the cause of the temperature rise in a state where the rotation of the rotating body has stopped, according to the image forming apparatus described in any one of Configurations 6 to 10. (Configuration 12) An image forming means for forming a toner image on a recording material is provided. The heating means heats, presses, and fixes an unfixed toner image formed on the recording material, according to the image forming apparatus described in any one of Configurations 1 to 11.

Explanation of reference numerals

[0081] 201 Heater 202 Thermistor 303 Relay 304 Engine controller 308 Triac

Claims

1. heating means having a heating element; temperature detection means for detecting the temperature of the heating means; a switching element connected to one end of an AC power supply and configured to supply power from the AC power supply to the heating means in a conductive state or not supply power in a non-conductive state, and to control the temperature of the heating means to a target temperature; a cutoff element connected to the other end of the AC power supply and configured to connect the heating means to the AC power supply in a connected state or disconnect the connection between the heating means and the AC power supply in a cutoff state; control means for controlling the switching element and the cutoff element based on the temperature information of the heating means detected by the temperature detection means; In an image forming apparatus comprising: when the control means determines that the temperature rise of the heating means is abnormal with the switching element in the non-conductive state and the cutoff element in the connected state, the control means sets the cutoff element to the cutoff state, and after a predetermined time has elapsed, based on the result of comparing the detected temperature of the heating means detected by the temperature detection means with a predetermined specified value after setting the cutoff element to the connected state, the control means determines the cause of the abnormal temperature rise. An image forming apparatus characterized by this.

2. When the detected temperature is a first temperature and the specified value is a first specified value, the control means determines that the temperature rise is abnormal when a second temperature detected by the temperature detection means is equal to or higher than a predetermined second specified value in a state where the switching element is in the non-conductive state and the cutoff element is in the connected state. The image forming apparatus according to claim 1, characterized by this.

3. When the first temperature is less than the first specified value, the control means determines that the cause of the abnormal temperature rise is an abnormality in the waveform of the AC voltage applied to the heating means. The image forming apparatus according to claim 2, characterized by this.

4. When the first temperature is equal to or higher than the first specified value, the control means determines that the cause of the abnormal temperature rise is an abnormality in the switching element. The image forming apparatus according to claim 2, characterized by this.

5. the heating means has a rotating body, the control means determines the cause of the temperature rise in a state where the rotating body is rotating. The image forming apparatus according to any one of claims 1 to 4, characterized by this.

6. heating means having a heating element, temperature detection means for detecting the temperature of the heating means, a switching element connected to one end of an AC power supply and configured to control the temperature of the heating means to a target temperature by entering a conductive state in which power from the AC power supply is supplied to the heating means or a non-conductive state in which power is not supplied, a cutoff element connected to the other end of the AC power supply and configured to enter a connection state in which the heating means and the AC power supply are connected or a cutoff state in which the connection between the heating means and the AC power supply is cut off, control means for determining control of the switching element and the cutoff element based on the temperature information of the heating means detected by the temperature detection means, in an image forming apparatus comprising: when the control means determines that the temperature rise of the heating means is abnormal with the switching element in the non-conductive state and the cutoff element in the connected state, the control means sets the cutoff element to the cutoff state, and after a predetermined time has elapsed, based on a comparison between a temperature gradient based on the detected temperature of the heating means detected by the temperature detection means after setting the cutoff element to the connected state and a predetermined temperature gradient standard value, the control means determines the cause of the abnormal temperature rise. The image forming apparatus is characterized by this.

7. when the predetermined time is a first time, the control means sets the cutoff element to the connected state after the first time has elapsed, detects a first temperature by the temperature detection means, detects a second temperature by the temperature detection means when a second time has elapsed after detecting the first temperature, and obtains the temperature gradient from the first temperature, the second time, and the second temperature. The image forming apparatus according to claim 6 is characterized by this.

8. when the temperature gradient is a first temperature gradient and the temperature gradient standard value is a first temperature gradient standard value, the control means detects a third temperature by the temperature detection means with the switching element in the non-conductive state and the cutoff element in the connected state, detects a fourth temperature by the temperature detection means when a third time has elapsed, and determines that the temperature rise is abnormal when a second temperature gradient obtained from the third temperature, the third time, and the fourth temperature exceeds a predetermined second temperature gradient standard value. The image forming apparatus according to claim 7 is characterized by this.

9. The control means determines that when the first temperature gradient is less than or equal to the first temperature gradient standard value, the cause of the abnormal temperature rise is an abnormality in the waveform of the alternating voltage applied to the heating means. The image forming apparatus according to claim 8, characterized in that.

10. The control means determines that when the first temperature gradient exceeds the first temperature gradient standard value, the cause of the abnormal temperature rise is an abnormality in the switching element. The image forming apparatus according to claim 8, characterized in that.

11. The heating means has a rotating body, The control means determines the cause of the temperature rise in a state where the rotation of the rotating body has stopped. The image forming apparatus according to any one of claims 6 to 10, characterized in that.

12. An image forming means for forming a toner image on a recording material is provided, The heating means heats, presses, and fixes an unfixed toner image formed on the recording material. The image forming apparatus according to any one of claims 1 to 4, claims 6 to 10, characterized in that.

Images