JP2005091934A - Fixing control device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure safety even in the event that any one of CPUs runs away of control in the use of an induction heat system and a 2-CPU system. <P>SOLUTION: A fixing control device includes: a main relay 222 which is on/off controlled by the main body CPU 211 in the use of the induction heat system and 2-CPU system; a sub-relay 223 which is disposed in an AC power source supply path for an induction heat control circuit 215 so that the sub-relay 223 and the main relay 222 are in series, and which is on/off controlled by the CPU 216 for IH; a main body AC power source 227 which supplies DC power source to the CPU 216 for the IH without depending on ON/OFF of the main relay 222 and sub-relay 223. In terms of hardware, the main relay 222 and the sub-relay 223 can be off-controlled based on abnormally high temperature detected by an abnormally high temperature detection circuit 229. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing control device for an induction heating type fixing device, and to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile machine including such a fixing control device.

  In general, as a fixing device in this type of image forming apparatus, a sheet carrying an unfixed toner image is nipped and conveyed between a fixing roller for heating and a pressure roller to heat and press the unfixed toner image on the sheet. Heat roller type fixing devices for fixing on top are well known.

  In such a heat roller type fixing device, a halogen lamp as a heater is provided inside the fixing roller, and the inside of the fixing roller is heated by the halogen lamp.

  However, such a heating method using a heater such as a halogen lamp takes a long time to heat the fixing roller to a necessary temperature, and the loss of the heater itself is large. Therefore, there is a demand for a fixing device that is efficient and has a fast rise time.

  Under such circumstances, a fixing device using an induction heating (hereinafter referred to as “IH” as appropriate) method can instantaneously heat the fixing roller by eddy current due to electromagnetic induction. (For example, refer to Patent Document 1).

  Here, compared with the halogen heater method, the IH fixing method has a sharp temperature change, and thus requires precise control, which increases the control load on the central processing unit (CPU) that controls the control. In this regard, as a conventional method, the CPU that controls the entire image forming apparatus generally also serves as the IH control. However, the cost increases due to the high performance of the CPU, and the control software becomes complicated (according to this, a bug) Is also likely to come out). However, when IH control is unavoidably simplified by using a normal CPU, there is a problem that the original performance of the induction heating method cannot be achieved.

  In this regard, for example, Patent Document 2 proposes a 2-CPU system in which a separate and independent CPU is mounted in an induction heating control circuit in addition to a CPU that controls the entire image forming apparatus.

  In addition, an inverter circuit is generally used for power supply control to a heater (induction heating means) in this type of induction heating method. However, according to Patent Document 3, AC power supply on / off is controlled according to Patent Document 3. An on / off relay is provided on the main body side. Further, according to Patent Document 4, two switch means of a relay and a semiconductor switch are provided in series on an AC supply line to a heater, and these switch means are controlled by a fixing control unit. Further, according to Patent Document 5, it is shown that a relay for turning on and off the power supply to the heater driving inverter circuit is provided.

JP 2001-175118 A Japanese Patent No. 3400402 JP 2001-222191 A JP-A-9-319251 JP-A-10-063352

  Compared with the halogen heater method, the induction heating fixing method has a sharp temperature rise. Therefore, it is important to ensure more safety for temperature control when the CPU is out of control than the halogen heater method. In particular, in the 2-CPU system, it is important to ensure safety when each CPU runs away.

  In this regard, in the 2-CPU system as shown in Patent Document 2, it is necessary to consider safety measures in the case where the CPU runs away, but this point is not particularly considered in the past.

  For this reason, in the 2CPU system, for example, when the main body CPU of the main body control unit runs away or the relay is welded, the serial communication with the CPU on the inverter circuit side is interrupted and a system abnormal operation is detected. Have problems such as the relay cannot be turned off and safety cannot be ensured.

  An object of the present invention is to ensure safety in the case where any CPU runs away in using the induction heating method and the 2CPU method.

  According to a first aspect of the present invention, there is provided a fixing control device including a main body control circuit having a main central processing unit that controls the operation of the entire image forming apparatus, an exciting coil that receives a current supply and induction-heats a fixing member to be heated, An induction heating control circuit having a sub central processing unit independent of the main central processing unit and controlling the current supply to the exciting coil; and provided in an AC power supply path to the induction heating control circuit; A main-side relay that is on / off controlled by a central processing unit and an AC power supply path to the induction heating control circuit are provided in series with the main-side relay and are on / off controlled by the sub-central processing unit. A sub-side relay, and a main body DC power supply unit that supplies DC power to the sub-central processing unit without depending on on / off of the main-side relay and the sub-side relay.

  Therefore, for example, when there is an abnormality such as runaway of the main central processing unit of the main body control circuit or main relay relay welding, the main relay cannot be turned off, but the sub central processing unit of the induction heating control circuit is Safety can be ensured by turning off the relay to cut off the AC power supply. Conversely, if there is an abnormality such as a runaway of the sub-central processing unit of the induction heating control circuit or a secondary relay welding, or if a temperature abnormality or the like in the fixing device is detected on the main central processing unit side, When the central processing unit turns off the main relay to cut off the AC power supply, safety can be ensured. Furthermore, when the sub-central processing unit of the induction heating control circuit independently detects a temperature abnormality or the like, by independently turning off the sub-side relay and cutting off the AC power supply independently from the main body control circuit side , Can ensure safety.

  According to a second aspect of the present invention, in the fixing control device according to the first aspect, a temperature sensor that detects a temperature of the fixing member to be heated, and the fixing member to be heated based on temperature information acquired from the temperature sensor A high temperature abnormality detection circuit that detects the high temperature abnormality and forcibly turns off the main-side relay and the sub-side relay.

  Therefore, regardless of the software control by the main central processing unit or sub central processing unit, the high temperature abnormality of the heated member for fixing is constantly monitored by hardware using the high temperature abnormality detection circuit, and a high temperature abnormality is detected. In this case, by forcibly turning off the main-side relay and the sub-side relay, the current supply to the exciting coil can be quickly cut off to ensure safety and improve the reliability.

  According to a third aspect of the present invention, in the fixing control device according to the second aspect, when the main-side relay and the sub-side relay are turned off by the high temperature abnormality detection circuit, the main body DC power supply unit is not turned off once. Maintenance means for maintaining an OFF state of the relay is provided.

  In the control according to the second aspect of the present invention, when either the main central processing unit or the sub central processing unit is operating abnormally, the temperature of the heated member for fixing is lowered by forcibly turning off the hardware relay. However, when the detection of the high temperature abnormality by the high temperature abnormality detection circuit is cancelled, there is a risk that the relay is forcibly turned off and energized and heated again, but in the present invention, the high temperature abnormality detection circuit detects the high temperature abnormality. When the relay is forcibly turned off, safety can be ensured by maintaining the relay in the OFF state unless the main body DC power supply is turned off and then turned on again.

  According to a fourth aspect of the present invention, in the fixing control device according to the third aspect, the maintaining means includes a zero-cross detection circuit that detects an AC power supply state in the AC power supply path, and a zero-cross detection signal of the zero-cross detection circuit. And a latch circuit that is controlled based on the high temperature abnormality detection signal of the high temperature abnormality detection circuit.

  Therefore, the invention according to claim 3 can be easily realized by using the zero cross detection circuit and the latch circuit.

  According to a fifth aspect of the present invention, in the fixing control device according to any one of the first to fourth aspects, when the main-side relay or the sub-side relay is turned off, an informing means for informing an error is provided.

  According to a sixth aspect of the present invention, there is provided an image forming apparatus comprising: a fixing device having a fixing member to be heated that is heated by an induction heating method; a printer engine including a photosensitive member; and other electrophotographic process members; and the fixing member to be heated. And a fixing control device according to any one of claims 1 to 5.

  Therefore, the same operation and effect as the invention according to any one of claims 1 to 5 are provided.

  According to the present invention, when using any of the induction heating method and the 2CPU method, even if any CPU runs away, the current supply to the exciting coil can be quickly cut off to ensure safety. Reliability can be improved.

  The best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a schematic front view showing an example of an electrophotographic image forming apparatus to which the present invention is applied. This image forming apparatus is an image forming apparatus having a copying function and other functions such as a printer function and a facsimile function. The copying function, the printer function, and the facsimile function are sequentially switched by an application switching key of the operation unit. It is possible to select. The copy mode is selected when the copy function is selected, the print mode is selected when the printer function is selected, and the facsimile mode is selected when the facsimile mode is selected.

  First, in the copy mode, the operation is as follows. In an automatic document feeder (hereinafter referred to as ADF) 101, a document bundle on which a document is placed on a document table 102 is placed on the document table 102 when the start key on the operation unit is pressed. The paper is fed to a predetermined position on a document table 105 made of contact glass by a paper feed roller 103 and a feed belt 104. The ADF 101 has a count function that counts up the number of documents every time a document is fed. The document on the document table 105 is discharged onto a sheet discharge table 108 by a feeding belt 104 and a discharge roller 107 after image information is read by an image reading device 106 as an image input unit.

  When the document set detector 109 detects that the next document is present on the document table 102, the lowermost document on the document table 102 is similarly documented by the feed roller 103 and the feeding belt 104. The sheet is fed to a predetermined position on the table 105. After the image information is read by the image reading device 106, the document on the document table 105 is discharged onto the sheet discharge table 108 by the feeding belt 104 and the discharge roller 107. Here, the paper feed roller 103, the feed belt 104, and the discharge roller 107 are driven by a carry motor.

  The first paper feeding device 110, the second paper feeding device 111, and the third paper feeding device 112 as paper feeding means were loaded on the first tray 113, the second tray 114, and the third tray 115, respectively, when selected. A transfer sheet as a transfer material is fed, and the transfer sheet is conveyed to a position where it abuts on the photoconductor 117 by the vertical conveyance unit 116. The photoconductor 117 is a drum photoconductor and is driven to rotate by a main motor.

  Image data read from the original by the image reading device 106 is converted into optical information by a writing unit 118 as writing means via an image processing means (not shown), and the photoconductor 117 is uniformly charged by a charger (not shown). After that, it is exposed with light information from the writing unit 118 to form an electrostatic latent image. The electrostatic latent image on the photoconductor 117 is developed by the developing device 119 to become a toner image.

  The conveyance belt 120 serves as a sheet conveyance unit and a transfer unit, and a transfer bias is applied from a power source. The transfer belt 120 conveys the toner image on the photoconductor 117 while conveying the transfer paper from the vertical conveyance unit 116 at the same speed as the photoconductor 117. Transfer to transfer paper. The transfer paper is fixed with a toner image by a fixing device 121 and is discharged to a paper discharge tray 123 by a paper discharge unit 122. The photoreceptor 117 is cleaned by a cleaning device (not shown) after the toner image is transferred. Here, the photoconductor 117, the charger, the writing unit 118, the developing device 119, and the transfer unit constitute a printer engine that forms an image on transfer paper based on image data.

  The above operation is for copying an image on one side of a transfer sheet in the normal mode. When copying an image on both sides of a transfer sheet in the duplex mode, one of the paper feed trays 113 to 115 is copied. The transfer paper that is further fed and has an image formed thereon as described above is switched by the paper discharge unit 122 to the double-sided paper feed path 124 side instead of the paper discharge tray 123 side, and is switched back by the reversing unit 125. Then, the front and back sides are reversed and conveyed to the duplex conveying unit 126.

  The transfer paper transported to the double-sided transport unit 126 is transported to the vertical transport unit 116 by the double-sided transport unit 126, transported to a position where it abuts on the photoconductor 117 by the vertical transport unit 116, and on the photoconductor 117 as described above. The toner image formed on the back surface is transferred to the back surface and the toner image is fixed by the fixing device 121, whereby double-sided copying is performed. This double-sided copy is discharged to the paper discharge tray 123 by the paper discharge unit 122.

  Further, when the transfer paper is reversed and discharged, the transfer paper that is switched back by the reversing unit 125 and turned upside down is not conveyed to the duplex conveying unit 126 but is discharged via the reverse discharge conveyance path 127. The paper is discharged to the paper discharge tray 123 by the unit 122.

  In the print mode, image data from the outside is input to the writing unit 118 instead of the image data from the image processing means, and an image is formed on the transfer paper by the printer engine. Further, in the facsimile mode, the image data from the image reading means is transmitted to the other party by a facsimile transmission / reception unit (not shown), and the image data from the other party is received by the facsimile transmission / reception unit, instead of the image data from the image processing means. By inputting the data to the writing unit 118, an image is formed on the transfer paper by the printer engine described above.

  Next, a configuration example of the fixing device 121 will be described with reference to FIG. FIG. 2 is a front view illustrating a schematic configuration example of the fixing device 121. The fixing device 121 of the present embodiment is configured as an induction heating type fixing device. First, a fixing roller 201 for heating and dissolving the toner on the transfer paper on which the toner has been transferred and fixing the toner onto the transfer paper with respect to the transfer paper transport path in the same manner as a normal halogen heater method and the like. A pressure roller 202 is provided so as to face the transfer paper and fix the toner by applying pressure thereto. A heating roller 203 is provided at a position spaced from the fixing roller 201, and a fixing belt 204 is stretched between the heating roller 203 and the fixing roller 201. This fixing belt 204 is a heated member for fixing that is induction-heated by an exciting coil (hereinafter also referred to as an IH coil) 205, and has a multi-layer structure including a heated metal portion (metal conductor) and a non-heat conductive portion. Become. The exciting coil 205 is for inductively heating the fixing belt 204 with an eddy current. In this embodiment, the exciting coil 205 is an external heating method. The coil is wound around. Such an exciting coil 205 is energized with a current having an arbitrary frequency characteristic by an inverter circuit, which will be described later, and an eddy current flows through the heating roller 203 by receiving a magnetic flux generated by the current and is heated. The heat of the heating roller 203 is transmitted to the rotating fixing belt 204, and the heat and the nip pressure of the fixing roller 201 and the pressure roller 202 cause the heat on the transfer paper to move between the fixing roller 201 and the pressure roller 202 in the rotation direction. The toner is fixed on the transfer paper.

  Further, the temperature of the fixing belt 204 is always monitored by a thermistor (temperature sensor) 207 that is close thereto, and current supply to the exciting coil 205 is continued if the temperature is lower than the control temperature, and supply is stopped if the temperature is higher. Temperature control is performed by a main body control circuit, which will be described later, but a safety device that directly shuts off the power supply by the thermostat 208 is mounted when the temperature becomes too high due to control failure.

  The fixing roller 201 is rotationally driven by a power source such as a fixing motor 209, and the fixing belt 204 is moved and rotated by the power. The heating roller 203 is a driven roller that rotates by being suspended by the movement of the fixing belt 204.

  In addition, an encoder 210 that functions as a sensor for detecting that the fixing belt 204 is rotating is provided on the shaft of the heating roller 203, and the heating is performed despite the rotation of the fixing roller 201. When the roller 203 does not rotate, it is determined that the belt has run out or the belt has slipped, and the operation of the inverter circuit is interrupted to prevent burning of the exciting coil 205 due to abnormal belt temperature rise.

  However, the induction heating type fixing device 121 is not limited to the external heating method as shown in the figure, and may be, for example, an internal heating method of a type in which an exciting coil is built in a fixing roller.

  Next, a configuration example of a control system for the IH coil unit 213 including the fixing belt 204, the excitation coil 205 and the thermistor 213, that is, a fixing control device will be described with reference to a schematic block diagram shown in FIG. First, a main body as a main central processing unit that controls the entire image forming apparatus such as drive control of each drive source, peripheral device control, electrophotographic process control, energy saving control, etc. in addition to fixing control targeted in the present embodiment A main body control unit 212 on which the CPU 211 is mounted is provided. Here, the sensor signal of the thermistor 207 for detecting the temperature of the fixing belt 204 is input to the main body CPU 211, converted into analog to digital by the A / D converter, and used for taking in the temperature signal. In particular, the main body CPU 211 of the present embodiment is assigned a role of temperature control for controlling the temperature measured by the thermistor 207 to coincide with the target temperature for fixing control.

  In addition, an inverter unit (induction heating control circuit) 215 equipped with an inverter circuit 214 that functions as a power supply device for supplying a current to the IH coil unit 213 including the exciting coil 205 for induction heating the fixing belt 204 is provided. ing. The inverter circuit 214 performs full-wave rectification of the AC power supply, and then supplies a current that is high-frequency switched by a switching control element such as an IGBT or FET as a coil current to the exciting coil 205 and a capacitor (not shown) to resonate, thereby generating an AC magnetic field. And the fixing belt 204 is heated by eddy current. On the inverter unit 215, an IH CPU 216 is mounted as a sub-central processing unit that is independent from the main body CPU 211 described above. The main body CPU 211 determines the target power or the target temperature and instructs the IH CPU 216, but the target value varies depending on the paper size, paper type, environmental temperature, black and white / color, linear velocity, and the like. In any case, the main body CPU 211 simply instructs the target value to the IH CPU 216, and the IH CPU 216 controls and maintains the temperature to the target value. Thereby, the control load of the main body CPU 211 is remarkably reduced. Therefore, the IH CPU 216 receives a control instruction only by the power instruction signal transmitted from the main body CPU 211 through the signal line 217a, for example, and the inverter circuit 214 based on the power instruction signal and the detected current detection signal and voltage detection signal. It is responsible for the control operation of calculating the power control value for and outputting as an inverter control signal. This inverter control signal changes the duty of high-frequency switching in the inverter circuit 214, thereby changing the current flowing through the exciting coil 205 to control the amount of heat generation. In this embodiment, only the induction heating control is performed as the IH CPU 216. Therefore, a low-cost one-chip CPU that is lower in processing capacity than the main body CPU 211 can be used. In this case, the functions of the IH CPU 216 are preferably provided with A / D converter, interval timer, serial communication (UART), and I / O functions, and further those with a built-in ROM.

  In addition, since the IGBT used in the inverter circuit 214 is fragile, it is necessary to constantly monitor the input voltage and the input voltage so as not to break it. Therefore, a current detection signal and a voltage detection signal are used. These signals are converted from analog to digital by the A / D converter of the IH CPU 216 and processed in the IH CPU 216.

  Further, AC supply to the inverter circuit 214 for driving the excitation coil 205 is performed on the main side relay 222 in the power supply unit (PSU) 221 provided in the image forming apparatus main body and on the sub side provided on the inverter unit 215. An AC power supply path is set so as to be performed via the relay 223. The main relay 222 and the sub relay 223 are provided in series. Here, a main unit DC power source (DDC) 227 is provided in the power unit 221 via a main switch 224, a noise filter (NF) 225, and a full-wave rectifier circuit 226, and + 5V used in the main unit CPU 216, the IH CPU 216, and the like. It is configured to generate a + 24V power source used for a power source and a DC load. That is, DC power is supplied from the main body DC power supply (DDC) 227 to the main body CPU 216 and the IH CPU 216 without depending on on / off of the main relay 222 and the sub relay 223. . The + 24V power line is connected to an interlock switch 228 for turning off the + 24V for safety when the front door of the image forming apparatus is opened, and the main relay 222, Relay coils 222b and 223b for controlling opening and closing of the relay contacts 222a and 223a of the sub relay 223 are connected.

  On the other hand, in the main body control unit 212, the temperature signal from the thermistor 207 that detects the temperature of the fixing belt 204 is compared with a reference signal corresponding to a preset reference temperature by an analog comparator, and the temperature is equal to or higher than the reference temperature. In this case, a high temperature abnormality detection circuit 229 for outputting a high temperature abnormality detection signal for stopping the operation of the inverter circuit 214 is provided. The main body CPU 211 and the IH CPU 216 are also connected by a signal line 217b for communicating with each other in order to exchange various information. The main body CPU 211 is an IH CPU 216 as one of status exchanges. The IH CPU 216 is set to periodically receive a confirmation signal indicating that it is operating normally. Here, in the present embodiment, the main body CPU 211 detects the runaway of the IH CPU 216 based on the reception state of the confirmation signal, and outputs it as another error signal. An OR circuit 230 is provided to which a high temperature abnormality detection signal from the high temperature abnormality detection circuit 229 and other error signals from the main body CPU 211 are input. A relay coil 222b for forcibly opening the normally closed relay contact 222a is connected to the output side of the OR circuit 230. When a high temperature abnormality detection signal or other error signal is output, the relay circuit 222b is relayed. The contact 222a is forcibly opened and the power supply to the inverter circuit 214 side is forcibly cut off.

  Also on the inverter unit 215 side, an OR circuit 231 to which a high temperature abnormality detection signal from the high temperature abnormality detection circuit 229 and other error signals from the IH CPU 216 are input is provided. A relay coil 223b for forcibly opening the normally closed relay contact 223a is connected to the output side of the OR circuit 231, and when a high temperature abnormality detection signal or other error signal is output, a relay is provided. The contact 223a is forcibly opened to forcibly cut off the power supply to the inverter circuit 214 side.

  Next, as an example of operation control according to the present embodiment, an example of a power instruction signal output from the main body CPU 211 to the IH CPU 216 through the signal line 217a will be described with reference to a timing chart shown in FIG. Here, an example of a serial signal using a PWM (pulse width modulation) signal is shown, and the main body CPU 211 sends a PWM signal to the IH CPU 216 at a fixed period of 10 ms. Here, 10 ms means a cycle shorter than the control cycle (interrupt cycle) of the main body CPU 211, and the IH CPU 216 that can cope with the resolution of 10 ms is used. In this case, the update cycle of the power instruction signal (duty change cycle of the PWM signal) by the main body CPU 211 is not performed every 10 ms, but randomly occurs at intervals of 10 ms × n (n is an arbitrary integer). It is set to be. In the present embodiment, it is assumed that the power instruction is performed with the length of the variable-length L-level period shown in FIG. Therefore, when the output is turned off, it is fixed at the H level as shown in FIG. Also, as shown in FIG. 4 (c), the minimum power instruction is given when the minimum width is L level with respect to the cycle of 10 ms, and as shown in FIG. 4 (d), the maximum width of L level is set with respect to the cycle of 10 ms. Sometimes it is the maximum power indication. These minimum width and maximum width are determined according to the agreement between the main body CPU 211 and the IH CPU 216.

  However, the power instruction signal is not limited to a serial signal (including a PWM signal), but may be a signal that indicates a power control value in a combination of a plurality of bits, for example, 1200 W = 111, 1100 W = 110, 1000 W = 101. Good (see, for example, FIG. 2 in Patent Document 2). According to this, it becomes possible to simplify electric power control value control.

  In such a configuration, a basic fixing control operation example will be described with reference to a schematic flowchart shown in FIG. First, in the flow of the main routine, the main body CPU 211 detects temperature information of the fixing belt 204 from the thermistor 207 as shown in FIG. 5A (step M1). Then, the command power is determined based on the detected temperature information and the target temperature (step M2). Then, the duty of the PWM signal is determined according to the command power as described with reference to FIG. 4, and commanded as a power command signal to the IH CPU 216 through the signal line 217a (step M3).

  On the other hand, in the CPU 216 for IH, as shown in FIG. 5B, for example, the instruction output by the PWM signal from the main body CPU 211 is periodically sampled at 10 ms intervals as a control cycle (step S1). A power instruction signal is determined (step S2). In parallel with this, a current detection signal and a voltage detection signal are acquired (step S3). By calculation processing based on these power instruction signal, current detection signal, and voltage detection signal (step S4), the power control value for the inverter circuit 213 is calculated and determined (step S5), and the output voltage is determined based on the power control value. Generate (step S6). Specifically, a PWM signal is output to the inverter circuit 213, and the current flowing through the exciting coil 205 is varied according to the target value.

  Therefore, according to the present embodiment, when using the induction heating method and the two-CPU method, the main body CPU 211 that controls the entire image forming apparatus performs a control instruction to the IH CPU 216 using only the power instruction signal. The control load of the main body CPU 211 can be reduced, the control software can be prevented from becoming complicated, and precise control is also possible to take advantage of the inherent temperature followability of the induction heating method. Can be. In addition, the main body CPU 211 that actually controls the entire image forming operation directly monitors the temperature of the fixing belt 204 through the thermistor 207, and instructs power whenever necessary so that the output of the exciting coil 205 is optimized based on the temperature detection result. Since the IH CPU 216 is controlled using only the signal, precise fixing control according to the temperature detection state and the operation state of the image forming apparatus can be performed, which contributes to the improvement of the image quality.

  In such a configuration, the safety measure of the present embodiment will be described with reference to FIG. First, in this embodiment, relays 222 and 223 capable of controlling the AC power supply to the inverter circuit 214 are provided in both the PSU 221 and the inverter unit 215 belonging to the main body side. The main relay 222 is driven and controlled by the main body CPU 211, and the sub relay 223 is driven and controlled by the IH CPU 216, and DC power is supplied to the IH CPU 216 and the like in the inverter unit 215 in the PSU 221. The DC power supply unit 227 supplies power to the relay, and does not depend on whether the relays 222 and 223 are turned on or off. As a result, it is possible to improve safety against a wide range of malfunctions up to the IH coil unit 213 in addition to the safety of the inverter circuit 214 and the like, against both software and hardware malfunctions.

  For example, when serial communication with the IH CPU 216 is interrupted due to the runaway of the main body CPU 211 of the main body control unit 212 and a system abnormal operation is detected, the IH CPU 216 cannot turn off the main relay 222. In this regard, in this embodiment, in such a case, the relay trigger signal in the inverter unit 215 is controlled to be turned off by the IH CPU 216, and the relay contact 223b is opened by the relay coil 223b. The supply of power can be turned off to ensure safety. In this way, it is possible to stop the AC power supply from each of the CPUs 211 and 216 to the inverter unit 215 in response to a software malfunction, which is caused by a malfunction when compared with the conventional centralized (one-point relay) response. Improve safety.

  Further, when the abnormal temperature of the IH coil unit 213 is detected by the detection signal of the thermistor 207 by the main body CPU 211 in the main body control unit 212, an abnormal operation due to relay welding or the like is estimated. In this case, the relay trigger signal is turned off for the main relay 222 of the PSU 211 and the relay trigger signal for the IH CPU 216 is also turned off for the sub relay 223 of the inverter unit 215, whereby the main relay 222 and the inverter unit 215 in the PSU 211 are turned off. The AC power supply to the inverter circuit 214 can be stopped at any relay welding time of the sub-side relay 223.

  By the way, in this embodiment, hardware operation control is added to such software operation control. In the present embodiment, the temperature sensor signal from the thermistor 207 uses the characteristic that the resistance value changes with temperature, and the sensor output value is also input to the high temperature abnormality detection circuit 229 of the main body control unit 212. The high temperature abnormality detection circuit 229 uses a comparator, for example, to detect the presence or absence of a high temperature abnormality state based on a comparison result between the temperature signal level and the abnormal temperature level. Here, when the main body CPU 211 of the main body control unit 212 and the CPU 216 for IH in the inverter unit 215 run away softly, the heater malfunctions, and the sensor output voltage becomes smaller than the reference voltage indicating the high temperature state of the heater with a high temperature abnormality. The comparator output of the high temperature abnormality detection circuit 229 is inverted, and an OFF signal is output to the relay drive signal of the main body control unit 212 and the relay drive signal of the inverter unit 215 by this high temperature abnormality detection signal. Accordingly, the relay contacts 222a and 223a are forcibly turned off by the relay coils 222b and 223b. From such an off-operation, the AC power supply to the inverter unit 215 can be cut off without any software, and safety can be ensured.

  By the way, regarding such a hard forced off operation during a high temperature abnormal operation, the thermistor detection temperature is lowered by cutting off the AC power supply to the inverter unit 215 by the relay drive operation off signal, and the high temperature abnormality detection circuit 229 The high temperature abnormality detection signal is canceled. In this case, it is often the case that the factor that originally caused the abnormal operation has not been eliminated, and the heater is abnormally turned on again. Therefore, in the present embodiment, by providing a latch circuit 232 that latches the high temperature abnormality detection signal by the zero cross signal (zero cross detection circuit 233) by the AC power supply to be interrupted, the temperature reduction due to the relay-off operation is again performed. Prevents the relay from being turned on. The AC power supply is cut off when the relay is turned off, and the zero cross signal is not input. Therefore, even if the high temperature detection signal is released, the relay-off signal continues to be latched to prevent smoke and fire and ensure the safety of the device. Here, the latch circuit 232 and the zero-cross detection circuit 233 constitute a maintaining means.

  At this time, when the high temperature abnormality is detected by the high temperature abnormality detection circuit 229 and the relay contacts 222a and 223a are opened, or when the relay contact 222a is opened due to the runaway detection of the IH CPU 216, or the main body CPU 211 runs away. In any case where the relay contact 223a is opened by detection, an error signal is output from the OR circuit 230 to a display unit or the like of an operation panel (not shown) of the image forming apparatus, and the display unit or the like is used as a notification unit. It is desirable to notify that an abnormality has occurred with an error display (or error sound or the like). According to this, when the relay contact 223a or the relay contact 222a is turned off due to a high temperature abnormality, the main body CPU 211 or the IH CPU 216 runaway, etc., an error is notified by the notification means, so that the safety of the power source is ensured as described above. In addition, it is possible to make the user take appropriate measures.

1 is a schematic front view illustrating an example of an electrophotographic image forming apparatus to which the present invention is applied. FIG. 3 is a front view illustrating a schematic configuration example of a fixing device. 2 is a schematic block diagram illustrating a configuration example of a fixing control device. FIG. It is a timing chart which shows an example of an electric power directions signal. 3 is a schematic flowchart illustrating an example of a basic fixing control operation.

Explanation of symbols

117 Photoconductor 121 Fixing Device 204 Heating Member 205 for Fixing Excitation Coil 207 Temperature Sensor 211 Main Central Processing Unit 212 Main Control Circuit 215 Induction Heating Control Circuit 216 Sub Central Processing Unit 222 Main Side Relay 223 Sub Side Relay 227 Main Unit DC Power Supply 229 Abnormal temperature detection circuit 232 Latch circuit 233 Zero cross detection circuit

Claims (6)

A main body control circuit having a main central processing unit for controlling the operation of the entire image forming apparatus;
An exciting coil that receives current supply and induction-heats the fixing member to be heated;
An induction heating control circuit that has a sub-central processing unit independent of the main central processing unit and controls current supply to the excitation coil;
A main-side relay provided in the AC power supply path to the induction heating control circuit and controlled to be turned on and off by the main central processing unit;
A sub-side relay that is provided in series with the main-side relay in the AC power supply path to the induction heating control circuit and is controlled to be turned on and off by the sub-central processing unit;
A main body DC power supply unit that supplies DC power to the sub-central processing unit without depending on ON / OFF of these main-side relays and sub-side relays;
A fixing control device comprising: A temperature sensor for detecting the temperature of the fixing member to be heated;
A high temperature abnormality detection circuit that detects a high temperature abnormality of the heating member for fixing based on temperature information acquired from the temperature sensor and forcibly turns off the main-side relay and the sub-side relay;
The fixing control device according to claim 1, further comprising:   The maintenance means for maintaining the relay in the OFF state unless the main body DC power supply is turned off once when the main relay and the sub relay are turned off by the high temperature abnormality detection circuit. 3. The fixing control device according to 2. The maintaining means includes
A zero cross detection circuit for detecting the AC power supply state in the AC power supply path;
A latch circuit that is controlled based on the zero-cross detection signal of the zero-cross detection circuit and latches the high-temperature abnormality detection signal of the high-temperature abnormality detection circuit;
The fixing control device according to claim 3, further comprising:   5. The fixing control device according to claim 1, further comprising a notification unit configured to notify an error when the main relay or the sub relay is turned off. 6. A printer including a fixing device having a heated member for fixing heated by induction heating, a photoconductor, and other electrophotographic process members;
The fixing control device according to claim 1, wherein the fixing heated member is controlled.
An image forming apparatus comprising:

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