JP2010061080A - Image forming apparatus - Google Patents

Abstract

Deterioration of a fixing device and peripheral parts of the fixing device is prevented when a failure of a chain element or the like occurs.
A fixing device, a heating unit that heats the fixing device by energization, an energization interruption unit that interrupts energization of an external AC power source to the heating unit, and an energization control that controls energization of the external AC power source to the heating unit. A control means comprising: a means; a control means for controlling the operation of the energization cutoff means and the energization control means; and further determining a failure of the energization cutoff means; and a pulse generation means for generating a pulse synchronized with the external AC power supply, Based on the width of the output pulse of the pulse generation means after a predetermined time has elapsed since the interruption instruction to the energization interruption means, a failure of the energization interruption means is determined (S104).
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, and a facsimile, and more particularly to prevention of deterioration of a fixing device and peripheral components of the fixing device when a toner image fixing device fails.

  Here, the toner image fixing device forms and carries an unfixed toner image corresponding to the target image information on the surface of the transfer material by the image forming process means, and carries the unfixed toner image. This is a heat-fixing device of a type in which heat-fixing processing is performed on the transfer material surface. The image forming process means is electrophotography, electrostatic recording, magnetic recording, etc., and uses toner made of heat-meltable resin, etc., and the transfer material is paper, printing paper, transfer material sheet, OHT sheet, gloss Paper, glossy film, etc. The transfer method is a direct transfer or indirect transfer method.

  In recent years, colorization has progressed in image forming apparatuses such as printers and copiers. Such a color image forming apparatus is required to have higher specifications year by year in terms of printing speed, image quality, and the like. As a fixing device to be used, a configuration of a heat roller fixing or a film fixing having an elastic layer on a fixing member is used. Many have been taken. FIG. 14 shows a conventional example of a fixing device using a fixing film having such an elastic layer.

In this fixing device, a thin fixing film 18 is sandwiched between a fixing heater 16 (hereinafter referred to as a fixing heater) as a heating means fixedly supported by a heater holder 17 and an elastic pressure roller 19 to fix the fixing nip. Part N is formed.
Then, the fixing film 18 is slid to the surface of the fixing heater 16, and the transfer material P carrying the toner image t is nipped and conveyed between the fixing film 18 and the pressure roller 19 in the fixing nip N to fix the fixing film 18. The toner image on the transfer material P is heated by the heat from the fixing heater 16 via the. When the unfixed toner image t on the transfer material P passes through the fixing nip portion N, it receives heat and pressure and is fixed on the transfer material P as a completed fixed image.

  In the fixing nip portion N, an elastic layer is provided on the side of the fixing film 18 that is a fixing member in contact with the unfixed toner t. The reason is to fix the toner image surface as uniformly as possible.

  By providing an elastic layer on the fixing film 18 side, the elastic layer is deformed along the toner layer when the toner image t passes through the fixing nip N. As a result, the toner that is unevenly placed on the image is encased by the elastic layer and uniformly heated, thereby achieving uniform fixing.

  The fixing film 18 is formed by forming a silicone rubber layer as an elastic layer on an endless film formed of a polyimide resin in a cylindrical shape with a thickness of 50 μm by a ring coating method, and coating a PFA resin tube with a thickness of 30 μm. .

The fixing heater 16 is formed by forming a resistance heating element on a ceramic substrate. An example of energizing the fixing heater 16 will be described with reference to FIG.
In FIG. 15, 27 is a commercial AC power source, 28 is a bidirectional three-terminal thyristor (also referred to as a triac, hereinafter referred to as a bidirectional three-terminal thyristor) which is an energization control means for the fixing heater, and 26 is an engine control unit (which is a control means). CPU) (hereinafter referred to as an engine control unit), 46 is a bidirectional three-terminal thyristor drive circuit, 29 is a relay (hereinafter referred to as a relay) as an energization cutoff means, and 47 is a relay drive circuit. Reference numeral 30 denotes a DC power line, which is a line for supplying the same 24V voltage as that of the motor of the apparatus main body and the power source of the high voltage power source. Reference numeral 32 denotes a temperature protection element, and a temperature fuse or a thermo switch is used.

  When energizing the fixing heater 16, the relay 29 is first energized, and then the bidirectional heater 3 is controlled to control the bidirectional heater 3. When power is supplied to the fixing heater 16, a temperature detection element 25 (hereinafter referred to as a thermistor) that is in contact with the fixing film 18 detects the temperature of the fixing heater 16 and is fixed by an engine control unit (CPU) 26. Temperature control is performed so that the temperature of the heater 16 becomes a desired temperature. When the energization of the fixing heater 16 is stopped, the bidirectional three-terminal thyristor 28 is turned off and then the relay 29 is turned off.

  The reason why the relay 29 is used is to shut off the fixing heater 16 so as to prevent the energization at all times when the bidirectional three-terminal thyristor 28 is short-circuited due to a failure or the like.

  However, when the relay 29 itself fails due to contact welding or the like (short-circuit failure), there is a problem that the function of cutting off the power supply to the fixing heater 16 cannot be achieved.

Therefore, in order to solve this problem, Patent Document 1 or 2 performs processing for detecting a short circuit failure of the relay 29 by devising a circuit configuration with the engine control unit (CPU) 26.
Specifically, as shown in FIG. 16, one end of the AC power supply 27 is connected to the relay 29, the other end of the AC power supply 27 is connected to the pulse generating means 33 (hereinafter referred to as a ZEROX detection circuit), and the other end of the ZEROX detection circuit 33. Is connected to the other end of the relay 29, the engine control unit 26 outputs a relay-off signal to shut off the relay 29. At this time, if the relay 29 is normal and is cut off by the relay-off signal, the AC power supply 27 is not connected to the ZEROX detection circuit 33. Therefore, a pulse waveform synchronized with the ZEROX point of the AC power supply 27 (hereinafter referred to as ZEROX). (Referred to as a waveform) is not output. However, when the contact of the relay 29 is short-circuited, the AC power supply 27 is connected to the ZEROX detection circuit 33 regardless of the relay-off signal of the engine control unit (CPU) 26. Therefore, a ZEROX waveform is output. In Patent Document 1 or 2, if a ZEROX waveform is output when this relay-off signal is output, a short-circuit failure of the relay 29 is assumed.
JP 2002-214965 A JP 2002-296955 A

  However, the above-described conventional example has the following problems.

In Patent Documents 1 and 2, a spark killer 45 (hereinafter referred to as a spark killer) which is a noise suppression element configured by directly connecting a resistor and a capacitor to both ends of a bidirectional three-terminal thyristor as shown in FIG. The ZEROX detection circuit 33 is connected to one end of the relay 29, and the other end of the ZEROX detection circuit 33 is connected to the negative output terminal of the rectifier diode bridge 44. Even if it is normal, when the relay 29 is turned off, a ZEROX waveform is output.
The reason for this will be described with reference to the waveform diagram (B) of FIG. As shown in (c), a case is considered in which a negative voltage is applied from the AC power supply 27 in the state where the relay 29 is turned off, as shown in FIG. A part). Line 1 and Line 2 shown in the circuit diagram are connected to the AC power supply 27, and the solid line waveform in (a) indicates the potential of Line 1 with respect to the potential of Line 2. In this case, as indicated by the solid line A in the circuit diagram, a current flows through the path of the AC power supply 27 → the spark killer 45 → the fixing heater 16 → the ZEROX detection circuit 33 → the rectifier diode bridge 44 → the AC power supply 27. At this time, the voltage across the spark killer 45 has a voltage waveform that is charged to a negative voltage as shown in a section C of the waveform diagram (a). Next, when a positive voltage is applied from the AC power source 27 (B portion of the waveform diagram), as indicated by a broken line B in the circuit diagram, the AC power source 27 → the rectifier diode bridge 44 → the ZEROX detection circuit 33 → the fixing heater. Current flows through a route of 16 → spark killer 45 → AC power supply 27. At this time, the voltage across the spark killer 45 has a voltage waveform in which a negative voltage is discharged as shown in a section D of the waveform diagram (a). By repeating this, the spark killer 45 is repeatedly charged and discharged, and is saturated at a certain voltage. In this state, when the potential of Line 1 of the AC power supply 27 is lower than the potential of Line 2, the point E when the negative terminal of the rectifier diode bridge 44 is used as a reference is the waveform shown in the waveform diagram, and the amplitude exceeds 0 volt. . If this voltage is higher than the threshold voltage at which the transistor 53 in the ZEROX detection circuit 33 is turned on, the transistor 53 is turned on and Hi is output from the ZEROX waveform as shown in the waveform diagram (b). On the other hand, when the potential of Line 1 of the AC power supply 27 is higher than the potential of Line 2, a current flows through a broken line path ahead of the circuit diagram. Therefore, the transistor 53 is not turned on, and the ZEROX waveform is output as shown in the waveform diagram (b).
In this case, since a ZEROX waveform is output, a short circuit failure of the relay 29 cannot be detected by the conventional detection method. Therefore, if the relay 29 is short-circuited and the bidirectional three-terminal thyristor 28 is short-circuited, the fixing heater 16 is always energized. In this case, the temperature of the fixing device rises until the temperature protection element 32 such as a thermo switch is activated, and the fixing is caused by melting of the heater holder 17 and damage due to heat of the fixing film 18 and the elastic layer of the pressure roller 19. There is a possibility that the life of the apparatus may be reduced and the image may be affected.

  The present invention has been made under such circumstances, and provides an image forming apparatus capable of preventing deterioration of a fixing device and peripheral parts of the fixing device when a rare occurrence of a chained element or the like occurs. It is to be an issue.

  In order to solve the above problems, in the present invention, the image forming apparatus is configured as described in the following (1), (2), and (3).

(1) a fixing device that fixes and conveys the image onto the transfer material by sandwiching and conveying the transfer material carrying the image at a nip formed by the first fixing member and the second fixing member, and heating and pressurizing the transfer material;
A heating unit provided on at least one of the first fixing member or the second fixing member and energized and heated by an external AC power source;
Energization interruption means for interrupting energization from the external AC power source to the heating means;
Energization control means for controlling energization from the external AC power source to the heating means;
A noise suppression element including a capacitor connected in parallel to the energization control means to suppress noise generated from the energization control means;
Control means for controlling the operation of the energization cut-off means and the energization control means, and further determining a failure of the energization cut-off means;
A rectifier diode bridge connected to the external AC power source;
Pulse generating means for generating a pulse synchronized with the output of the external AC power supply;
With
One end of the energization cutoff means is connected to one end of the external AC power source, and the heating means and the energization control means are connected in series between the other end of the energization cutoff means and the other end of the external AC power source. And
One end on the input side of the pulse generation means is connected to the other end of the energization cutoff means via a diode, and the other end on the input side of the pulse generation means is connected to the negative output end of the rectifier diode bridge, A resistor is connected in parallel to the diode,
The image forming apparatus, wherein the control unit determines a failure of the energization interruption unit based on a width of an output pulse of the pulse generation unit after a predetermined time has elapsed since the interruption instruction to the energization interruption unit.

(2) a fixing device that fixes and conveys the image onto the transfer material by nipping and conveying the transfer material carrying the image at a nip formed by the first fixing member and the second fixing member, and heating and pressurizing the transfer material;
A heating unit provided on at least one of the first fixing member or the second fixing member and energized and heated by an external AC power source;
Energization interruption means for interrupting energization from an external AC power source to the heating means;
Energization control means for controlling energization from the external AC power source to the heating means;
A noise suppression element including a capacitor connected in parallel to the energization control means to suppress noise generated from the energization control means;
Control means for controlling the operation of the energization cut-off means and the energization control means, and further determining a failure of the energization cut-off means;
A rectifier diode bridge connected to the external AC power source;
Pulse generating means for generating a pulse synchronized with the output of the external AC power supply,
One end of the energization cutoff means is connected to one end of the external AC power source, and the heating means and the energization control means are connected in series between the other end of the energization cutoff means and the other end of the external AC power source. And
One end on the input side of the pulse generation means is connected to the other end of the energization cutoff means via a diode, and the other end on the input side of the pulse generation means is connected to the negative output end of the rectifier diode bridge,
The image forming apparatus that determines a failure of the energization interruption unit based on the presence / absence of an output pulse of the pulse generation unit after a predetermined time has passed since the interruption instruction to the energization interruption unit.

(3) a fixing device that nipping and conveying a transfer material carrying an image at a nip formed by a first fixing member and a second fixing member, heating and pressing the image, and fixing the image on the transfer material;
A heating unit provided on at least one of the first fixing member or the second fixing member and energized and heated by an external AC power source;
Energization interruption means for interrupting energization from an external AC power source to the heating means;
Energization control means for controlling energization from the external AC power source to the heating means;
A noise suppression element including a capacitor connected in parallel to the energization control means to suppress noise generated from the energization control means;
Control means for controlling the operation of the energization cut-off means and the energization control means, and further determining a failure of the energization cut-off means;
A rectifier diode bridge connected to the external AC power source;
Pulse generating means for generating a pulse synchronized with the output of the external AC power supply,
One end of the energization cutoff means is connected to one end of the external AC power source, and the heating means and the energization control means are connected in series between the other end of the energization cutoff means and the other end of the external AC power source. And
One end on the input side of the pulse generation means is connected to the other end of the energization cutoff means, and the other end on the input side of the pulse generation means is connected to the negative output end of the rectifier diode bridge,
The image forming apparatus, wherein the control unit determines a failure of the energization cutoff unit based on a cycle of an output pulse of the pulse generation unit after instructing the energization cutoff unit.

  According to the present invention, it is possible to prevent deterioration of the fixing device and its peripheral components at the time of occurrence of breakage of a rare chain element or the like by an inexpensive method.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  A “color image forming apparatus” that is Embodiment 1 will be described in detail with reference to the drawings. The description will be made in the order of the entire image forming apparatus, the heat fixing unit, the heating control unit, and the failure detection sequence of the relay or relay drive transistor.

(Image forming device)
FIG. 2 is a schematic sectional view of a color image forming apparatus according to this embodiment. The color image forming apparatus of this embodiment is an image forming apparatus that obtains a full color image by superimposing toner images (developer images) of four colors of yellow, cyan, magenta, and black using an electrophotographic system.

Y, C, M, and Bk are four process cartridges that respectively form yellow, cyan, magenta, and black color toner images, which are arranged in order from the bottom to the top. Each process cartridge Y, C, M, and Bk uses a so-called all-in-one cartridge in which the following means are collected in one container.
That is, the all-in-one cartridge is composed of photosensitive drums 1bk, 1m, 1c, and 1y as image carriers, charging rollers 2bk, 2m, 2c, and 2y as charging means, and developing means 3bk and 3m for developing an electrostatic latent image. 3c, 3y. Further, it has cleaning means 4bk, 4m, 4c, 4y, etc. for the photosensitive drums 1bk, 1m, 1c, 1y. The developing means 3y of the yellow process cartridge Y is filled with yellow toner, and the developing means 3c of the cyan process cartridge C is filled with cyan toner. The developing means 3m of the magenta process cartridge M is filled with magenta toner, and the developing means 3bk of the black process cartridge Bk is filled with black toner.

  An optical system 5 that forms an electrostatic latent image by exposing the photosensitive drums 1bk, 1m, 1c, and 1y is provided corresponding to the four color process cartridges Y, C, M, and Bk. As the optical system 5, a laser scanning exposure optical system is used.

  In each of the process cartridges Y, C, M, and Bk, the optical system 5 performs scanning exposure based on the image data on the photosensitive drums 1bk, 1m, 1c, and 1y uniformly charged by the charging roller 2. The As a result, electrostatic latent images corresponding to the image data are formed on the surfaces of the photosensitive drums 1bk, 1m, 1c, and 1y. The developing bias applied to the developing rollers of the developing units 3bk, 3m, 3c, and 3y from a bias power supply unit (not shown) is set to an appropriate value between the charged potential and the latent image (exposed portion) potential. As a result, the negatively charged toner is normally electrostatically attracted to the electrostatic latent images on the photosensitive drums 1bk, 1m, 1c, and 1y, and the electrostatic latent images on the photosensitive drums 1bk, 1m, 1c, and 1y. Is developed.

  That is, a yellow toner image is formed on the photosensitive drum 1y of the yellow process cartridge Y, and a cyan toner image is formed on the photosensitive drum 1c of the cyan process cartridge C. A magenta toner image is formed on the photosensitive drum 1m of the magenta process cartridge M, and a black toner image is formed on the photosensitive drum 1bk of the black process cartridge Bk.

  The single-color toner image developed and formed on the photosensitive drums 1 of the process cartridges Y, C, M, and Bk is an intermediate transfer belt that rotates at a substantially constant speed in synchronization with the rotation of the photosensitive drums 1. 6 are first transferred and superposed in order in a predetermined alignment state. As a result, a full-color toner image is synthesized and formed on the intermediate transfer belt 6.

  In this embodiment, an endless intermediate transfer belt is used as an intermediate transfer member, and is suspended and stretched around three rollers, a driving roller 7, a secondary transfer roller facing roller 14, and a tension roller 8. Driven by the driving roller 7. Hereinafter, the intermediate transfer member 6 is referred to as an intermediate transfer belt 6.

The primary transfer rollers 9bk, 9m, 9c, and 9y are used as primary transfer means for the toner image from the photosensitive drums 1bk, 1m, 1c, and 1y of the process cartridges Y, C, M, and Bk to the intermediate transfer belt 6. Is used. A primary transfer bias having a polarity opposite to that of toner (usually positive polarity) is applied to the primary transfer rollers 9bk, 9m, 9c, and 9y from a bias power source (not shown). As a result, the toner images are primarily transferred from the photosensitive drums 1 of the process cartridges Y, C, M, and Bk to the intermediate transfer belt 6.
After the primary transfer from the photosensitive drum 1 to the intermediate transfer belt 6 in each of the process cartridges Y, C, M, and Bk, the toner remaining as a transfer residue on the photosensitive drum 1 is cleaned by the cleaning units 4bk, 4m, 4c, and 4y. Removed. In this embodiment, cleaning for contact removal using a urethane blade is performed as the cleaning means 4bk, 4m, 4c, 4y.

  On the other hand, the transfer material P set in the transfer material cassette 10 serving as the transfer material supply unit is fed by the feed roller 11. Then, it is conveyed by the registration roller 12 to a nip portion between the intermediate transfer belt 6 suspended from the secondary transfer roller facing roller 14 and the secondary transfer roller 13 as the secondary transfer means at a predetermined control timing.

  The primary transfer toner image formed on the intermediate transfer belt 6 is collectively transferred onto the transfer material P by a bias having a polarity opposite to that of a toner applied from a bias power supply unit (not shown) to the secondary transfer roller 13 serving as a secondary transfer unit. Transcribed.

  The secondary transfer residual toner remaining on the intermediate transfer belt 6 after the secondary transfer is removed by the intermediate transfer belt cleaning means 15. In the present embodiment, the intermediate transfer belt is cleaned with a urethane blade in the same manner as the cleaning means 4bk, 4m, 4c, and 4y for the photosensitive drums 1bk, 1m, 1c, and 1y.

  The above process is performed in the process cartridges Y, C, M, and Bk for yellow, cyan, magenta, and black in synchronization with the rotation of the intermediate transfer belt 6, and the primary transfer toner for each color is transferred onto the intermediate transfer belt 6. The images are formed one after another. At the time of monochrome image formation (monochrome mode), the process is performed only for a target color.

  The toner image that has been secondarily transferred onto the transfer material P passes through a fixing device F as a fixing means, and is melted and fixed onto the transfer material P. Then, the toner image is conveyed to a discharge tray through a discharge path to form an image. This is the output image of the device.

(Fixing device F)
FIG. 3 is a schematic sectional view of the fixing device F in this embodiment. The fixing device F of the present embodiment is a fixing film type and pressure rotating body driving type (tensionless type) device.

  Reference numeral 18 denotes a fixing film as a first fixing member, which is a cylindrical (endless film-like) member in which an elastic layer is provided on the film-like member. Reference numeral 19 denotes a pressure roller as a second fixing member. Reference numeral 16 denotes a heating means (hereinafter referred to as a fixing heater), and reference numeral 17 denotes a heater holder having a substantially semi-circular arc shape in cross section and having heat resistance and rigidity. The fixing heater 16 is disposed on the lower surface of the heater holder 17 along the length of the holder. The fixing film 18 is loosely fitted on the heater holder 17.

  The heater holder 17 is formed of a liquid crystal polymer resin having high heat resistance, plays a role of holding the fixing heater 16 and guiding the fixing film 18. In this example, Zenite (registered trademark) 7755 manufactured by DuPont was used as the liquid crystal polymer. The maximum usable temperature of Zenite® 7755 is about 270 ° C.

  The pressure roller 19 is disposed such that both ends of the core metal are rotatably supported by bearings between a back plate and a front plate of a fixing device frame (not shown). On the upper side of the pressure roller 19, the heating assembly including the fixing heater 16, the heater holder 17, the fixing film 18 and the like is arranged in parallel to the pressure roller 19 with the fixing heater 16 facing downward. Both ends of the heater holder 17 are 98N (10 kgf) on one side and a total pressure of 196 N (20 kgf) by a pressurizing mechanism comprising a pressurizing stay 21 provided inside the heater holder 17 and a pressurizing spring 22 provided on both ends of the pressurizing stay 21. Is urged in the axial direction of the pressure roller 19 by the force of. As a result, the downward surface of the fixing heater 16 is applied to the elastic layer of the pressure roller 19 (corresponding to the second fixing member in the claims) via the fixing film 18 (corresponding to the first fixing member in the claims). A fixing nip portion N having a predetermined width necessary for heat fixing is formed by pressing with a predetermined pressing force against the elasticity of the elastic layer. Further, the pressure mechanism has a pressure release mechanism (not shown), and is configured to release the pressure and remove the transfer material P at the time of jam processing or the like.

  The pressure roller 19 is rotationally driven in a counterclockwise direction indicated by an arrow A at a predetermined peripheral speed by a driving unit (not shown). A rotational force acts on the cylindrical fixing film 18 by the pressure friction force at the fixing nip portion N between the outer surface of the pressure roller 19 and the fixing film 18 by the rotational driving of the pressure roller 19. As a result, the fixing film 18 is rotated in the clockwise direction indicated by the arrow B around the outer periphery of the heater holder 17 while the inner surface thereof is in close contact with the downward surface of the fixing heater 16 and slides. Grease (not shown) is applied to the inner surface of the fixing film 18, and the sliding property between the heater holder 17 and the inner surface of the fixing film 18 is ensured by the grease.

  The pressure roller 19 is rotationally driven, and accordingly, the cylindrical fixing film 18 is driven and rotated, and the fixing heater 16 is energized. The fixing heater 16 is heated up to a predetermined temperature, and the temperature is adjusted. It will be in the state. In the temperature-controlled state, the transfer material P carrying the unfixed toner image t is guided and introduced along the entrance guide 23 between the fixing film 18 and the pressure roller 19 in the fixing nip N. . Then, the toner image carrying surface side of the transfer material P is in close contact with the outer surface of the fixing film 18 in the fixing nip portion N, and the fixing nip portion N is nipped and conveyed together with the fixing film 18. In this nipping and conveying process, the heat of the fixing heater 16 is applied to the transfer material P through the fixing film 18, and the unfixed toner image t on the transfer material P is heated and pressurized on the transfer material P to be melted and fixed. The The transfer material P that has passed through the fixing nip N is separated from the fixing film 18 by the curvature, and is discharged by the fixing discharge roller 24.

  In normal use, as the pressure roller 19 of the fixing device F starts to rotate, the rotation of the fixing film 18 starts. As the temperature of the fixing heater 16 increases, the inner surface temperature of the fixing film 18 also increases. In energization of the fixing heater 16, the input power is controlled so that the temperature detected by the thermistor 25 becomes a target temperature (eg, 195 ° C.).

(Heating control means)
Next, a circuit configuration as a heating control means for the fixing heater 16 in this embodiment will be described with reference to FIG.
Reference numeral 27 denotes an AC power source (corresponding to an external AC power source in the claims) connected to the image forming apparatus. The image forming apparatus supplies the AC power source 27 to the fixing heater 16 through the AC filter 34 to thereby fix the fixing heater 16. Energize. The power supply to the fixing heater 16 is controlled by energizing and shutting off the bidirectional three-terminal thyristor 28. The connection relationship between the fixing heater 16 and the bidirectional three-terminal thyristor 28 corresponds to “the heating unit and the energization control unit are connected in series” in the claims. A spark killer 45 in which a resistor and a capacitor are connected in series is connected to both ends of the bidirectional 3-terminal thyristor in order to suppress noise normally generated when the bidirectional 3-terminal thyristor is turned on / off. The resistors 35 and 36 are bias resistors for the bidirectional three-terminal thyristor 28, and the phototriac coupler 37 (a type of photosensitive thyristor coupler) is a device for ensuring a creepage distance between the primary and secondary. By energizing the light emitting diode of the phototriac coupler 37, the bidirectional three-terminal thyristor 28 is energized. The resistor 38 is a limiting resistor for limiting the current of the light emitting diode of the phototriac coupler 37, and turns on / off the phototriac coupler 37 by the phototriac drive transistor 39.

  The phototriac drive transistor 39 operates in accordance with an on / off signal from the engine control unit (CPU) 26 via the resistor 40. The AC power supply 27 can be cut off by the relay 29 via the AC filter 34, and the relay drive transistor 41 controls the energization / cutoff of the relay 29. The relay drive transistor 41 operates according to an on / off signal from an engine control unit (CPU) 26 via a resistor 42. When energizing the fixing heater 16, the relay 29 is first energized, and then the bidirectional 3-terminal thyristor 28 is controlled to energize the fixing heater 16. When the energization of the fixing heater 16 is stopped during power off, sleep, jam, or the like, the bidirectional three-terminal thyristor 28 is turned off and the relay 29 is turned off.

  The AC power supply 27 branches before the relay 29 and is connected to the DC / DC converter 31 via the rectifier diode bridge 44. The capacitor 59 is a smoothing capacitor that constitutes a full-wave rectifier circuit.

  Between the relay 29 and the fixing heater 16 and between the resistance 50 of the ZEROX detection circuit 33, a diode 48 and a high resistance 49 for suppressing discharge connected in parallel to the diode 48 are connected. The common connection point of the resistor 50 and the resistor 49 corresponds to “one end on the input side of the pulse generation means” in the claims. One of the features of this embodiment is that the diode 48 and the high resistance 49 for suppressing discharge are connected. These functions will be described later. On the other hand, the emitter of the transistor 53 in the ZEROX detection circuit 33 is connected to the negative terminal of the rectifier diode bridge 44. Therefore, the AC power supply 27 is always input to the ZEROX detection circuit 33 via the relay 29.

  Here, the operation of the ZEROX detection circuit 33 when the relay is on, that is, when the temperature control is executed will be described. When the potential of Line 1 of the AC power supply 27 is higher than the potential of Line 2, the AC power supply 27 is applied to the ZEROX detection circuit 33 via the relay 29 and the diode 48. Thereafter, the voltage divided by the resistors 50 and 51 is input to the base of the transistor 53. The capacitor 52 constitutes a filter for the transistor 53 together with the resistor 50, and removes noise from the input. When the voltage applied to the base of the transistor 53 becomes equal to or higher than a predetermined threshold voltage, the transistor 53 is turned on, and the collector current is DC obtained by an auxiliary winding of a power transformer (not shown) in the DC / DC converter 31. The current flows from the power source 54 through the current limiting resistor 55. Therefore, the internal photodiode of the photocoupler 56 is cut off from current supply and does not emit light, the internal phototransistor of the photocoupler 56 is turned off, and Hi is output to the engine control unit (CPU) 26. The resistor 57 is a current limiting resistor from the secondary side DC power source 58.

  On the other hand, when the potential of Line 1 of the AC power supply 27 is lower than the potential of Line 2, the potential difference between the negative terminal of the rectifier diode bridge 44 and the point E in FIG. Therefore, the voltage applied to the base of the transistor 53 becomes lower than the threshold voltage, and the transistor 53 is turned off, so that no collector current flows, and this time current flows to the internal photodiode of the photocoupler 56 and light is emitted. As a result, the internal phototransistor of the photocoupler 56 is turned on, and Lo is output to the engine control unit (CPU) 26.

By repeating this, the ZEROX detection circuit 33 outputs a ZEROX waveform to the engine control unit (CPU) 26.
The engine control unit (CPU) 26 detects the edge of the pulse of the ZEROX waveform and controls the bidirectional three-terminal thyristor 28 on / off by phase control or wave number control.

Further, in order to detect the temperature of the fixing film 18, a voltage obtained by dividing the reference voltage (Vref) by the thermistor 25 and the voltage dividing resistor 43 is used as a temperature detection signal (hereinafter referred to as TH signal), and an engine control unit (CPU). 26 is A / D input.
The temperature of the fixing film 18 is monitored by the engine control unit (CPU) 26 as a TH signal, and the target temperature set inside the engine control unit (CPU) 26 is compared with the average fixing film temperature based on the TH signal. Then, the electric power to be supplied to the fixing heater 16 is calculated, converted into a phase angle (phase control) or wave number (wave number control) corresponding to the supplied electric power, and the engine control unit (CPU) 26 performs a photo according to the control conditions. An ON signal is sent to the triac drive transistor 39.

  When supplying power to the fixing heater 16, if the power supply control means breaks down and the fixing heater 16 reaches a thermal runaway, an excessive temperature rise prevention means 32 is provided on the fixing heater as one means for preventing excessive temperature rise. It is arranged in. The excessive temperature rise prevention means 32 is, for example, a thermal fuse or a thermo switch. When the fixing heater 16 reaches a thermal runaway due to a failure of the power supply control means and the overheat prevention means 32 exceeds a predetermined temperature, the overheat prevention means 32 is disconnected if it is a thermal fuse, and OPEN if it is a thermo switch. The energization to the fixing heater 16 is cut off.

(Failure detection sequence of relay or relay drive transistor)
Next, the failure detection sequence of the relay 29 or the relay drive transistor 41 in this embodiment and the reason why the failure can be detected will be described.
The failure detection sequence will be described based on the flowchart of FIG. First, the relay-off timing due to initial end, job end, jam, etc. comes (S100). Next, the engine control unit (CPU) 26 outputs an OFF signal to the relay drive transistor 41 in order to place the relay 29 in the cutoff state (S101, corresponding to the cutoff instruction in the claims). Next, the engine control unit (CPU) 26 starts a timer (S102). Next, the engine control unit (CPU) 26 stands by until a predetermined time elapses (S103). After a predetermined time has elapsed, the engine control unit (CPU) 26 monitors the ZEROX waveform in order to check whether the relay 29 is in the cut-off state, and corresponds to the pulse width of the ZEROX waveform (corresponding to the output pulse width in the claims). ) Is less than or equal to a predetermined pulse width (S104). If the pulse width of the ZEROX waveform is equal to or smaller than the predetermined pulse width, it is determined that the relay 29 and the relay drive transistor 41 are normal and in the cutoff state, and the process proceeds to the next sequence (S105).
If the pulse width of the ZEROX waveform is not less than or equal to the predetermined pulse width, it is determined that the relay 29 or the relay drive transistor 41 is out of order (S106), and a failure error is reported to the outside via a display unit (S107).

Next, the reason why it is possible to determine that the relay 29 or the relay drive transistor 41 has failed based on the pulse width of the ZEROX waveform in S104 will be described with reference to FIG.
When the relay 29 and the relay drive transistor 41 are normal in the circuit configuration of the present embodiment, the pulse width of the ZEROX waveform after a predetermined time has elapsed after the relay 29 is output and the relay 29 is shut off, It becomes shorter than the pulse width of the ZEROX waveform. That is, as shown in FIG. 5A, the pulse width changes depending on whether the relay 29 is turned on or off. The reason why the pulse width of the ZEROX waveform changes immediately after the relay is turned off will be described later.
On the other hand, if the relay 29 remains energized due to a failure of the relay 29 or the relay drive transistor 41, the energization cannot be interrupted even if the relay off signal is output, and the pulse width of the ZEROX waveform is It does not change. That is, as shown in FIG. 5B, the pulse width does not change regardless of whether the relay 29 is on or off.
By detecting this difference by the engine control unit (CPU) 26, it is possible to determine a failure.

The reason why the pulse width of the ZEROX waveform changes when the relay 29 is in the cut-off state in the circuit configuration of this embodiment will be described with reference to FIG.
Also in the circuit configuration of the present embodiment, the spark killer 45 charges and discharges in the same way as described in the conventional problem when the relay is off. However, the difference from the conventional example is that the ZEROX detection circuit is connected between the relay 29 and the fixing heater 16 shown in the circuit diagram (A) of FIG. 6 via a diode 48 and a discharge suppressing high resistance 49 connected in parallel to the diode 48. It is a point connected to. In the case of this configuration, when the spark killer 45 is charged when the relay is off, as shown by the solid line path A in the circuit diagram (A), the current flows through the diode 48 and is charged, whereas the discharge is discharged. As shown by the broken line path B in the circuit diagram (A), a current flows through the discharge suppressing high resistance 49 and discharges. Therefore, the amount of discharge is smaller than the amount of charge because the impedance of the discharge route of the broken line route B is higher. That is, the charge amount and discharge amount of the spark killer 45 can be differentiated by the diode 48 and the discharge suppressing high resistance 49. By setting the resistance value of the discharge suppressing high resistance 49 to a predetermined value, the voltage across the spark killer 45 (the voltage at the point I on the basis of the point H in the circuit diagram, hereinafter referred to as Vhi) is shown in FIG. Saturates near the peak of the negative voltage of the AC power supply 27.
At this time, when an AC voltage in which the potential of Line 1 of the AC power supply 27 is lower than the potential of Line 2 as shown in (a), the voltage at the point E on the negative terminal of the rectifier diode bridge 44 (hereinafter referred to as Ve) is A potential difference (hereinafter referred to as Vi) between the point I which is one end of the spark killer 45 and the negative terminal of the rectifier diode bridge 44 is substantially applied. The spark killer 45 is charged and Vhi is a voltage near the peak of the negative voltage of the AC power supply 27 as shown by the broken line in the waveform diagram (a), and the potential difference from the negative terminal of the rectifier diode bridge 44 is reduced. Since this potential difference is almost applied to Ve, the period exceeding 0 volt is smaller than that when the relay is turned on, as shown by the one-dot broken line in the waveform diagram (a). Therefore, the period exceeding the threshold voltage of the transistor 53 is shortened, and the pulse width is shortened. This ZEROX waveform is output to the engine control unit (CPU) 26.
Also, as shown in FIG. 7, when the relay 29 is cut off at a timing when no charge is charged at both ends of the spark killer 45, the pulse width of the ZEROX waveform is as shown in (b) until Vhi is saturated. Widely, when it is saturated, the pulse width gradually decreases, and when it is saturated, the pulse width becomes constant. Therefore, as shown by S103 in FIG. 1, a sequence for waiting for the time until the voltage charged at both ends of the spark killer 45 is saturated is performed.

Here, depending on the constant of the high resistance 49 for suppressing discharge, the value at which Vhi saturates changes, so the period in which Ve exceeds 0 volts also changes. Therefore, it is necessary to select the constant of the high resistance 49 for suppressing discharge so that the voltage is higher than the threshold voltage at which the transistor 53 is turned on and the pulse width of the ZEROX waveform is shortened. In this example, 1 MΩ was used.
In the circuit configuration of the conventional example, since the charging path and the discharging path are substantially the same path, the negative voltage at which Vhi is saturated is not so high. Therefore, since the pulse width of the ZEROX waveform at the time of relay ON and at the time of relay OFF has a slight difference as shown in FIG. 17B, it may be difficult to determine the difference in pulse width. In contrast, by making a difference between the charge amount and the discharge amount of the spark killer 45 by the diode 48 and the discharge suppressing high resistance 49, the change in the pulse width of the ZEROX waveform can be made remarkable, and the relay 29 or It is possible to determine whether the relay drive transistor 41 is normal or malfunctioning.

  In this embodiment, an example in which the engine control unit (CPU) 26 detects the energization and cut-off state of the relay 29 based on the ZEROX waveform from the ZEROX detection circuit 33 connected as shown in FIG. However, it is also possible to detect the energized state of the relay 29 by providing a circuit for detecting the pulse width of the ZEROX waveform separately.

  Although an example using a ceramic heater is shown here, the heat source may of course be induction heating or a halogen heater.

  As described above, according to the present embodiment, it is possible to accurately determine whether the relay 29 or the relay drive transistor 41 is normal or malfunctioning.

An “image forming apparatus” that is Embodiment 2 will be described.
The overall configuration and image forming operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, the same functional parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted here, and only the parts peculiar to this embodiment are described.

In the first embodiment, a diode 48 and a discharge suppressing high resistance 49 connected in parallel with each other are connected between the relay 29 and the fixing heater 16 and the resistor 50 of the ZEROX detection circuit 33 in the circuit configuration. Further, the failure detection of the relay 29 or the relay drive transistor 41 is determined based on whether the pulse width of the ZEROX waveform is equal to or smaller than a predetermined pulse width.
On the other hand, the circuit configuration of the present embodiment is different in that the discharge suppressing high resistance 49 of the first embodiment is not connected. Further, the second embodiment is different from the first embodiment in that the failure of the relay 29 or the relay driving transistor 41 is waited for a predetermined time after the relay is turned off, and then the failure is detected by checking the presence or absence of the ZEROX waveform.

A circuit configuration in this embodiment will be described with reference to FIG.
A diode 48 is connected between the relay 29 and the fixing heater 16 and between the resistor 50 of the ZEROX detection circuit 33. It is one of the features of this embodiment that this diode 48 is connected. This function will be described later. On the other hand, the emitter of the transistor 53 in the ZEROX detection circuit 33 is connected to the negative terminal of the rectifier diode bridge 44.
Since the operation of the ZEROX detection circuit 33 in the relay-on state is the same as that of the first embodiment, a description thereof will be omitted.

(Failure detection sequence of relay or relay drive transistor)
The failure detection sequence of the relay 29 or relay drive transistor 41 in this embodiment will be described with reference to FIG.
First, the relay-off timing due to initial end, job end, jam, etc. comes (S900). Next, the engine control unit (CPU) 26 outputs an off signal to the relay drive transistor 41 in order to place the relay 29 in the cut-off state (S901). Next, the engine control unit (CPU) 26 starts a timer (S902). Next, the engine control unit (CPU) 26 stands by until a predetermined time elapses (S903). After a predetermined time has elapsed, the engine control unit (CPU) 26 monitors the ZEROX waveform to check whether or not there is a falling edge in the ZEROX waveform in order to check whether the relay 29 is in the cut-off state (S904). If there is a falling edge of the ZEROX waveform, it is determined that the relay 29 and the relay drive transistor 41 are normal and in a cut-off state, and the process proceeds to the next sequence (S905).
If there is no falling edge of the ZEROX waveform, it is determined that the relay 29 or the relay drive transistor 41 is out of order (S906), and a failure error is reported to the outside through a display or the like. (S907).

Next, the reason why the failure of the relay 29 or the relay drive transistor 41 can be determined based on the presence or absence of the falling edge of the ZEROX waveform in S904 will be described with reference to FIG.
When the relay 29 and the relay drive transistor 41 are normal in the circuit configuration of the present embodiment, a signal for turning off the relay 29 is output, and the ZEROX waveform is not output after a predetermined time has elapsed after the relay 29 is shut off. On the other hand, if the relay 29 remains energized due to a failure of the relay 29 or the relay drive transistor 41, the energization cannot be cut off even if a signal for turning off the relay 29 is output, and the ZEROX waveform Will be output.
Therefore, it is possible to determine the failure by detecting whether or not the ZEROX waveform is output after the relay off signal is output by the engine control unit (CPU) 26.

The reason why the ZEROX waveform is not output when the relay 29 and the relay drive transistor 41 are normal and the relay 29 is in the cut-off state will be described.
Also in the circuit configuration of the present embodiment, the spark killer 45 charges and discharges as in the first embodiment. However, the difference from the first embodiment is that the discharge suppressing high resistance 49 connected in parallel to the diode 48 is eliminated as shown in the circuit diagram (A) of FIG. In the case of this configuration, when the spark killer 45 is charged when the relay is off, as shown by the solid line path A in the circuit diagram (A), the current flows through the diode 48 and is charged, whereas the discharge is discharged. As shown by the broken line path B in the circuit diagram (A), no current flows because the diode 48 is connected. Therefore, the charge charged in the spark killer 45 cannot be discharged, and the voltage Vhi across the spark killer 45 is charged to the negative voltage peak of the AC power supply 27 shown in the waveform diagram (a).
Here, if a diode 48 having a large reverse current is used, the spark killer 45 discharges, and therefore, it is necessary to use a diode having a small reverse current. In this embodiment, a reverse current of 20 μA or less is selected.
At this time, when an AC voltage whose Line 1 potential of the AC power supply 27 is lower than the Line 2 potential is applied, the Ve is almost the peak voltage of the negative voltage of the AC power supply 27 in the spark killer 45. As shown by the one-dot broken line in a), it does not exceed 0 volts. Therefore, the transistor 53 is turned off and the ZEROX waveform is not output.
When the relay 29 is cut off at a timing when no charge is charged at both ends of the spark killer 45, the ZEROX waveform is output until Vhi is saturated as in the first embodiment. It gradually becomes shorter and will eventually not be output. Therefore, as shown by S103 in FIG. 9, a sequence for waiting the time until the voltage charged at both ends of the spark killer 45 is saturated is performed.

  As described above, according to the present embodiment, since it is only necessary to check the presence or absence of the ZEROX waveform, it is possible to more accurately determine whether the relay 29 or the relay drive transistor 41 is normal or malfunctioning. . In addition, it is possible to reduce one part from the circuit configuration of the first embodiment, and it is possible to prevent deterioration of the fixing device with minimal cost.

An “image forming apparatus” that is Embodiment 3 will be described.
The overall configuration and image forming operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, the same functional parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted here, and only the parts peculiar to this embodiment are described.

  In the circuit configuration of this embodiment, as shown in FIG. 11, the diode 48 and the discharge suppressing high resistance 49 are not connected between the relay 29 and the fixing heater 16 and the resistor 50 of the ZEROX detection circuit 33. The first embodiment differs from the first and second embodiments in that the circuit configuration is the same as that of the conventional example. Further, the first embodiment is different from the first and second embodiments in that the failure of the relay 29 or the relay drive transistor 41 is detected from the difference in the timing of the falling edge of the ZEROX waveform immediately after the relay is turned off.

(Failure detection sequence of relay or relay drive transistor)
A failure detection sequence of the relay 29 or the relay drive transistor 41 in this embodiment will be described with reference to FIG.
First, the relay-off timing due to initial end, job end, jam, etc. comes (S1200). Next, the engine control unit (CPU) 26 detects the falling edge of the ZEROX waveform (S1201). After detection, the engine control unit (CPU) 26 starts a timer (S102). Next, the engine control unit (CPU) 26 outputs an OFF signal to the relay drive transistor 41 in order to put the relay 29 in the cut-off state (S1203), and detects the ZERO fall immediately after the relay OFF signal is output (S1204). Next, the engine control unit (CPU) 26 calculates the time from the fall of the ZERO waveform immediately before the relay is turned off to the fall of the ZERO waveform after the relay is turned off (S1205). It is confirmed whether the calculation time is within the range of the predetermined time T1 to T2 (S1206). Here, T1 and T2 are set so as to be in a range having a little margin with respect to the zero-crossing period detected before the relay is turned off. If the falling time interval of the ZEROX waveform before and after the relay is off is within the range of the predetermined time T1 to T2, it is determined that the relay 29 and the relay driving transistor 41 are normal and in the cut-off state, and the process proceeds to the next sequence (S1207).
If the falling time interval of the ZEROX waveform before and after the relay is off is not within the range of the predetermined time T1 to T2, it is determined that the relay 29 or the relay drive transistor 41 is out of order (S1208). To do. (S1209).

Next, the reason why the failure of the relay 29 or the relay drive transistor 41 can be determined based on the falling time interval of the ZEROX waveform before and after the relay is turned off in S1206 will be described with reference to FIG.
When the relay 29 and the relay drive transistor 41 are normal in the circuit configuration of the present embodiment, the current path to the ZEROX detection circuit 33 when the relay is on is the solid line path of A in FIG. 13 (A), and the potential of Line 1 is A ZEROX waveform is output when the potential is higher than Line2. On the other hand, the current path to the ZEROX detection circuit 33 when the relay is OFF is a broken line path B in FIG. 13, and a ZEROX waveform is output when the potential of Line1 is lower than the potential of Line2.
Therefore, as shown in the waveform diagram (B), the ZEROX waveform changes immediately after the relay 29 off signal is output and the relay 29 is cut off. As shown in the figure, the falling period of the ZEROX waveform changes between the period Ton when the relay is on and the period Toff immediately after the relay is off.
If the relay 29 remains energized due to a failure of the relay 29 or the relay drive transistor 41, the energization cannot be cut off even if a signal for turning off the relay 29 is output, and the ZEROX waveform Is output as usual. Therefore, the interval between the falling edges is substantially synchronized with the ZEROX point of the AC power supply 27.
In this manner, the engine control unit (CPU) 26 detects that the falling edge intervals of the ZEROX waveform before and after the relay-off signal output are different, so that a failure can be determined.

  As described above, according to the present embodiment, the relay 29 or the relay drive transistor 41 is normal or failed even in the ZEROX circuit configuration in which the failure could not be detected in the conventional example without adding parts. It is possible to determine whether or not

7 is a flowchart showing a failure detection sequence of the relay or relay drive transistor in the first embodiment. Sectional drawing which shows schematic structure of the image forming apparatus of Example 1. FIG. Sectional drawing which shows schematic structure of the fixing apparatus in Example 1. FIG. Electric circuit diagram in Example 1 Explanatory drawing of the ZEROX waveform at the time of abnormality and failure of the relay and relay drive transistor in Example 1 Explanatory drawing of the waveform of the electric circuit at the time of relay OFF in Example 1 Explanatory drawing of ZEROX waveform immediately after relay-off in Example 1 Electric circuit diagram in Example 2 7 is a flowchart showing a failure detection sequence of a relay or relay drive transistor in the second embodiment. Explanatory drawing of the ZEROX waveform at the time of abnormality and failure of the relay and relay drive transistor in Example 2 Electric circuit diagram in Example 3 9 is a flowchart showing a failure detection sequence of the relay or relay drive transistor in the third embodiment. Explanatory drawing of the ZEROX waveform at the time of abnormality and failure of the relay and relay drive transistor in Example 3 Sectional drawing which shows schematic structure of the fixing device in a prior art example Block diagram of an electric circuit in a conventional example Block diagrams of electric circuits in Patent Documents 2 and 3 Explanatory drawing of ZEROX waveform at the time of relay OFF in the electric circuits of Patent Documents 2 and 3

Explanation of symbols

16 Fixing heater 19 Pressure roller 26 Engine control unit (CPU)
27 AC power supply 28 Bidirectional three-terminal thyristor 29 Relay 33 ZEROX detection circuit 41 Relay drive transistor 44 Rectifier diode bridge 45 Spark killer 48 Diode 49 High resistance for suppressing discharge F Fixing device N Fixing nip P Transfer material

Claims (3)

A fixing device that fixes and conveys the image onto the transfer material by nipping and conveying the transfer material carrying the image at a nip formed by the first fixing member and the second fixing member, and heating and pressurizing the transfer material;
A heating unit provided on at least one of the first fixing member or the second fixing member and energized and heated by an external AC power source;
Energization interruption means for interrupting energization from the external AC power source to the heating means;
Energization control means for controlling energization from the external AC power source to the heating means;
A noise suppression element including a capacitor connected in parallel to the energization control means to suppress noise generated from the energization control means;
Control means for controlling the operation of the energization cut-off means and the energization control means, and further determining a failure of the energization cut-off means;
A rectifier diode bridge connected to the external AC power source;
Pulse generating means for generating a pulse synchronized with the output of the external AC power supply;
With
One end of the energization cutoff means is connected to one end of the external AC power source, and the heating means and the energization control means are connected in series between the other end of the energization cutoff means and the other end of the external AC power source. And
One end on the input side of the pulse generation means is connected to the other end of the energization cutoff means via a diode, and the other end on the input side of the pulse generation means is connected to the negative output end of the rectifier diode bridge, A resistor is connected in parallel to the diode,
The control means discriminates a failure of the energization interruption means based on a width of an output pulse of the pulse generation means after a predetermined time has elapsed since the interruption instruction to the energization interruption means. Image forming apparatus. A fixing device that fixes and conveys the image onto the transfer material by nipping and conveying the transfer material carrying the image at a nip formed by the first fixing member and the second fixing member, and heating and pressurizing the transfer material;
A heating unit provided on at least one of the first fixing member or the second fixing member and energized and heated by an external AC power source;
Energization interruption means for interrupting energization from an external AC power source to the heating means;
Energization control means for controlling energization from the external AC power source to the heating means;
A noise suppression element including a capacitor connected in parallel to the energization control means to suppress noise generated from the energization control means;
Control means for controlling the operation of the energization cut-off means and the energization control means, and further determining a failure of the energization cut-off means;
A rectifier diode bridge connected to the external AC power source;
Pulse generating means for generating a pulse synchronized with the output of the external AC power supply,
One end of the energization cutoff means is connected to one end of the external AC power source, and the heating means and the energization control means are connected in series between the other end of the energization cutoff means and the other end of the external AC power source. And
One end on the input side of the pulse generation means is connected to the other end of the energization cutoff means via a diode, and the other end on the input side of the pulse generation means is connected to the negative output end of the rectifier diode bridge,
The control means discriminates a failure of the energization interruption means based on the presence or absence of an output pulse of the pulse generation means after a predetermined time has elapsed since the interruption instruction to the energization interruption means. Image forming apparatus. A fixing device that fixes and conveys the image onto the transfer material by nipping and conveying the transfer material carrying the image at a nip formed by the first fixing member and the second fixing member, and heating and pressurizing the transfer material;
A heating unit provided on at least one of the first fixing member or the second fixing member and energized and heated by an external AC power source;
Energization interruption means for interrupting energization from an external AC power source to the heating means;
Energization control means for controlling energization from the external AC power source to the heating means;
A noise suppression element including a capacitor connected in parallel to the energization control means to suppress noise generated from the energization control means;
Control means for controlling the operation of the energization cut-off means and the energization control means, and further determining a failure of the energization cut-off means;
A rectifier diode bridge connected to the external AC power source;
Pulse generating means for generating a pulse synchronized with the output of the external AC power supply,
One end of the energization cutoff means is connected to one end of the external AC power source, and the heating means and the energization control means are connected in series between the other end of the energization cutoff means and the other end of the external AC power source. And
One end on the input side of the pulse generation means is connected to the other end of the energization cutoff means, and the other end on the input side of the pulse generation means is connected to the negative output end of the rectifier diode bridge,
The image forming apparatus according to claim 1, wherein the control unit determines a failure of the energization interruption unit based on a cycle of an output pulse of the pulse generation unit after instructing the energization interruption unit.

Images