JP2011215516A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform control for stopping the supply of power to a heater of a fixing part when a CPU runs away by a comparatively simple constitution.SOLUTION: An engine CPU 15 of an image forming device 1 monitors a second signal (watchdog signal) SWD outputted from a sub-CPU 23, and the sub-CPU 23 monitors a first signal (watchdog signal) EWD outputted from the engine CPU 15. When the sub-CPU 23 runs away, the engine CPU 15 turns temperature control signals (HREN signal, HRON signal) of the heater into an L level and brings a switching unit 45 into an off-state. When the engine CPU 15 runs away, the sub-CPU 23 outputs a signal (ECPUEN signal of H level) actuating a forcibl-off circuit 43 to forcibly bring the switching unit 45 into the off-state.

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for cutting off power supply to a heater of a fixing unit when an arithmetic processing unit such as a CPU (Central Processing Unit) runs away.

  2. Description of the Related Art Conventionally, in an image forming apparatus, when a CPU that controls the image forming apparatus runs away due to heat, static electricity, or the like, a technique for cutting off power supply from a power source to a heater is known (see, for example, Patent Document 1).

  According to the technique of Patent Document 1, the main body CPU that controls the operation of the entire image forming apparatus and the IH CPU that controls the heater of the fixing unit are connected via a signal line so that they can communicate with each other. The CPU monitors the runaway of the other CPU, and if the other CPU runs away, one CPU controls to cut off the power supply from the power source to the heater.

  (1) The main body CPU monitors the runaway of the IH CPU by a confirmation signal periodically sent from the IH CPU, and when the runaway is detected, the first relay contact is opened to supply power from the power source to the heater. Shut off the supply.

  (2) The IH CPU is disconnected from the main body CPU due to a runaway of the main body CPU, and when an abnormality in the system is detected, the IH CPU opens the contact of the second relay and switches from the power source to the heater. Shut off the power supply.

Japanese Patent Laying-Open No. 2005-91934 (paragraphs 0045 and 0053, FIG. 3)

  In the technology of the above-mentioned Patent Document 1, when the main body CPU runs away and the IH CPU runs away, the power supply to the heater is cut off by a separate circuit and relay, respectively, so that the structure is relatively complicated.

  An object of the present invention is to provide an image forming apparatus capable of realizing, with a relatively simple configuration, control for cutting off power supply to a heater of a fixing unit when a CPU runs away.

  An image forming apparatus according to an aspect of the present invention that achieves the above object includes an image forming unit that forms a toner image on a sheet based on image data and a heater, and the toner image is heated by the heater. A fixing unit that fixes the sheet; a switching unit that can be switched between an on state in which power is supplied from a power source to the heater; and an off state in which power supply from the power source to the heater is cut off; and the switching unit A forced-off circuit unit that operates to forcibly turn off the signal, a first signal output unit that outputs a first signal that functions as a watchdog signal, and a second signal that functions as a watchdog signal A first control unit that includes a first monitoring unit that implements the first signal output unit and the first monitoring unit using a first CPU, and the first monitoring unit. A second signal output unit that outputs a second signal to be viewed, and a second monitoring unit that monitors the first signal output from the first signal output unit, and uses a second CPU And a second control unit in which the second signal output unit and the second monitoring unit are realized, and the first control unit includes a signal for turning on the switching unit, A signal for switching the output to the off state to control the heater temperature and to turn off the switching unit when the first monitoring unit fails to recognize the second signal The heater temperature control unit is realized using the first CPU, and the second control unit recognizes the first signal by the second monitoring unit. If this is not possible, the forced off circuit is activated. It includes a forced OFF signal output unit for outputting that signal, the forced OFF signal output unit using the second CPU is realized.

  According to the present invention, the first control unit monitors the runaway of the second CPU, the second control unit monitors the runaway of the first CPU, and if the second CPU runs away, the first control unit The power supply to the heater is cut off by the control of the control unit, and if the first CPU runs away, the power supply to the heater is cut off by the control of the second control unit. By sharing the forced-off circuit unit and the switching unit used for the blocking by the first and second control units, the blocking can be performed with a small number of parts. Therefore, according to the present invention, when the CPU runs away, control for cutting off the power supply to the heater can be realized with a relatively simple configuration.

  The said structure WHEREIN: The said forced off circuit part can contain the latch circuit which continues an operation state, when the said forced off circuit part operate | moves.

  According to this configuration, even if the second CPU runs away following the runaway of the first CPU, the power supply from the power source to the heater can be continuously cut off. Since the second CPU does not control the temperature of the heater, when the forced-off circuit unit is operated, the operation state is continued and the heater is surely turned off.

  In the above configuration, when the heater temperature control unit outputs a signal for turning off the switching unit because the first monitoring unit cannot recognize the second signal, the first control unit It is possible to control to stop the system of the image forming apparatus.

  According to this configuration, when the signal for turning off the switching unit is output, the first control unit performs control to stop the system of the image forming apparatus. Therefore, following the runaway of the second CPU, the system of the image forming apparatus can be stopped before the temperature control of the heater becomes impossible due to the runaway of the first CPU.

  According to the present invention, when the CPU runs away, control for cutting off the power supply to the heater of the fixing unit can be realized with a relatively simple configuration.

1 is a diagram illustrating an outline of an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus. It is a figure which shows an example of the functional block for performing control which interrupts | blocks the electric power supply to the heater of the fixing device which concerns on this embodiment. FIG. 4 is a functional block diagram of elements related to the cutoff control in the engine controller and engine sub-controller shown in FIG. 3. It is a figure which shows an example of the circuit which performs the function of the forced OFF circuit part which concerns on this embodiment. It is a logic table | surface which shows the state of engine CPU, sub CPU, and the state of each signal. It is a figure which shows the state of engine CPU, a sub CPU, and the waveform of each signal. It is a flowchart explaining the control which interrupts | blocks the electric power supply to the heater which concerns on this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an outline of the internal structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 can be applied to, for example, a digital multifunction machine having functions of a copy, a printer, a scanner, and a facsimile. The image forming apparatus 1 includes an apparatus main body 100, a document reading unit 200 disposed on the apparatus main body 100, a document feeding unit 300 disposed on the document reading unit 200, and an operation disposed on the upper front surface of the apparatus main body 100. Unit 400 and a sheet post-processing unit 500 disposed on the sheet carry-out side, for example, the left side of the apparatus main body 100.

  The document feeding unit 300 includes a document placement unit 301, a paper feed roller 303, a document transport unit 305, and a document discharge unit 307. A paper feed roller 303 feeds the originals set on the original placement unit 301 one by one. The document transport unit 305 transports the fed document to the document reading unit 200. The document is read by the document reading unit 200 and discharged to the document discharge unit 307. As described above, the document feeding unit 300 functions as an automatic document feeding device, and can continuously send a plurality of documents placed on the document placing unit 301 to the document reading unit 200.

  The document reading unit 200 includes a carriage 201 equipped with a CCD (Charge Coupled Device) sensor and an exposure lamp, a document table 203 made of a transparent member such as glass, and a document reading slit 205. When reading a document placed on the document table 203, the document is read by the CCD sensor while moving the carriage 201 in the longitudinal direction of the document table 203. On the other hand, when reading a document fed from the document feeding unit 300, the carriage 201 is moved to a position facing the document reading slit 205, and the document fed from the document feeding unit 300 is scanned. Reading is performed by the CCD sensor through the reading slit 205. The CCD sensor outputs the read original as image data.

  The apparatus main body 100 includes a sheet storage unit 101, an image forming unit 103, and a fixing unit 105. The sheet storage unit 101 is disposed at the lowermost part of the apparatus main body 100 and includes a sheet tray 107 that can store a bundle of sheets. In the stack of sheets stored in the sheet tray 107, the uppermost sheet is fed out toward the sheet conveying unit 111 by driving the pickup roller 109. The sheet is conveyed to the image forming unit 103 through the sheet conveying unit 111.

  The image forming unit 103 forms a toner image on the conveyed paper based on the image data. The image forming unit 103 includes a photosensitive drum 113, an exposure unit 115, a developing unit 117, and a transfer unit 119. The exposure unit 115 generates light corresponding to image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.), and is uniformly charged photosensitive drum. The peripheral surface 113 is irradiated. As a result, an electrostatic latent image corresponding to the image data is formed on the peripheral surface of the photosensitive drum 113. In this state, a toner image corresponding to image data is formed on the peripheral surface by supplying toner from the developing unit 117 to the peripheral surface of the photosensitive drum 113. This toner image is transferred by the transfer unit 119 to the sheet conveyed from the sheet storage unit 101 described above.

  The sheet on which the toner image is transferred is sent to the fixing unit 105. In the fixing unit 105, heat and pressure are applied to the toner image and the paper to fix the toner image on the paper. Thereby, the printing of the image on the paper is completed. When post-processing is performed on the printed paper, the printed paper is sent from the paper discharge port 121 of the apparatus main body 100 to the paper post-processing unit 500. On the other hand, when no post-processing is performed, the printed paper is discharged to the paper discharge tray 123.

  The paper post-processing unit 500 performs post-processing such as sorting, stapling, punching, and saddle stitching on the printed paper. The paper post-processing unit 500 includes a paper carry-in port 501, a paper transport unit 503, a paper carry-out port 505, a stack tray 507, and the like. The paper transport unit 503 sequentially transports the printed paper carried into the paper carry-in port 501 from the paper discharge port 121, and carries out the post-processed printed paper from the paper carry-out port 505 to the stack tray 507. The stack tray 507 has a configuration capable of moving up and down in the direction of the arrow in accordance with the number of sheets stacked from the paper exit 505.

  The operation unit 400 includes an operation key unit 401 and a display unit 403. The display unit 403 has a touch panel function, and displays a screen including soft keys. The user operates the soft keys while viewing the screen to make settings necessary for executing functions such as copying.

  The operation key unit 401 includes operation keys including hard keys. Specifically, the operation key unit 401 includes a help key 405, a start key 407, a numeric key 409, a function switching key 411, and the like. A help key 405 is a key for displaying a help screen on the display unit 403. The help screen is a screen on which operation methods relating to functions such as a scanner, a facsimile, a printer, and a copy are displayed.

  A start key 407 is a key for starting operations such as copying and facsimile transmission. A numeric keypad 409 is a key for inputting numbers such as the number of copies and a facsimile number.

  The function switching key 411 includes a copy key, a transmission key, and the like, and is a key for switching between a copy function, a transmission function, and the like. When the copy key is operated, an initial copy screen is displayed on the display unit 403. When the transmission key is operated, an initial screen for facsimile transmission and mail transmission is displayed on the display unit 403.

  FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 has a configuration in which an apparatus main body 100, a document reading unit 200, a document feeding unit 300, an operation unit 400, a sheet post-processing unit 500, a control unit 600, and a communication unit 700 are connected to each other via a bus. Since the apparatus main body 100, the document reading unit 200, the document feeding unit 300, the operation unit 400, and the sheet post-processing unit 500 have already been described, description thereof will be omitted.

  The control unit 600 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an image memory, and the like. The CPU executes control necessary for operating the image forming apparatus 1 on the hardware constituting the image forming apparatus 1. The ROM stores software necessary for controlling the operation of the image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. The image memory temporarily stores image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.).

  The communication unit 700 includes a facsimile communication unit 701 and a network I / F unit 703. The facsimile communication unit 701 includes an NCU (Network Control Unit) that controls connection of a telephone line with a destination facsimile and a modulation / demodulation circuit that modulates / demodulates a signal for facsimile communication. The facsimile communication unit 701 is connected to the telephone line 705.

  A network I / F unit 703 is connected to a LAN (Local Area Network) 707. A network I / F unit 703 is a communication interface circuit for executing communication with a terminal device such as a personal computer connected to the LAN 707.

  Next, a description will be given of the control for shutting off the power supply from the power source to the heater of the fixing unit 105 when one CPU runs away. FIG. 3 is a diagram illustrating an example of a functional block for executing the cutoff control. FIG. 4 is a functional block diagram of elements related to the shut-off control in the engine controller 11 and the engine sub-controller 13 shown in FIG.

  The engine controller 11 is an example of a first control unit, and controls the entire printer engine of the image forming apparatus 1. The printer engine executes physical printing processes such as paper feeding, exposure, development, transfer, and fixing. The engine controller 11 has a configuration in which an engine controller CPU (engine CPU 15), a memory 17, and an IO port 19 are connected to each other via a bus line 21. The engine CPU 15 is an example of a first CPU.

  The engine sub-controller 13 is an example of a second control unit, and controls some functions (for example, a developing unit) of the printer engine. The engine sub-controller 13 has a configuration in which an engine sub-controller CPU (sub CPU 23), a memory 25, and an IO port 27 are connected to each other via a bus line 29. The sub CPU 23 is an example of a second CPU.

  The engine CPU 15 generates and outputs a first signal (engine watchdog signal) EWD that functions as a watchdog signal. The watchdog signal is a signal periodically output from the CPU when the CPU is operating normally. When the CPU runs away, the watchdog signal output stops. The first signal EWD is transmitted from the IO port 19 to the IO port 27 through the bus line 21 and is input to the sub CPU 23 through the bus line 29.

  The sub CPU 23 generates and outputs a second signal (sub watch dog signal) SWD that functions as a watch dog signal. The second signal SWD is sent from the IO port 27 to the IO port 19 through the bus line 29 and input to the engine CPU 15 through the bus line 21.

  The engine controller 11 includes a first signal output unit 31, a first monitoring unit 33, and a heater temperature control unit 35. These functions are realized by the engine CPU 15 and the memory 17 of the engine controller 11. The first signal output unit 31 outputs a first signal EWD that functions as a watchdog signal at a predetermined interval. This can be realized, for example, by providing a main routine of a program for controlling the engine controller 11 stored in the memory 17 with processing for generating and outputting the first signal EWD periodically. The first monitoring unit 33 monitors the second signal SWD output from the second signal output unit 37.

  The heater temperature control unit 35 controls the temperature of the heater 47 by switching and outputting a signal for turning the switching unit 45 on and a signal for turning it off. Specifically, the heater temperature control unit 35 outputs an HREN signal (heater relay enable signal) for controlling the switching unit 45. The HREN signal in the active state (H level in the present embodiment) is a signal that turns on the switching unit 45. The HREN signal in an inactive state (L level in the present embodiment) is a signal that turns off the switching unit 45.

  In addition, when the first monitoring unit 33 cannot recognize the second signal SWD, the heater temperature control unit 35 outputs a signal for turning off the switching unit 45 (inactive HREN signal).

  The engine sub-controller 13 includes a second signal output unit 37, a second monitoring unit 39, and a forced off signal output unit 41. These functions are realized by the sub CPU 23 and the memory 25 of the engine sub controller 13.

  The second signal output unit 37 outputs a second signal SWD that functions as a watchdog signal at a predetermined interval. This can be realized, for example, by providing a main routine of a program for controlling the engine sub-controller 13 stored in the memory 25 to generate and output the second signal SWD periodically. The second signal SWD may be output regardless of the first signal EWD, or the second signal SWD may be output when the second monitoring unit 39 recognizes the first signal EWD. .

  The second monitoring unit 39 monitors the first signal EWD output from the first signal output unit 31.

  The forced-off signal output unit 41 outputs a signal for operating the forced-off circuit unit 43 when the second monitoring unit 39 cannot recognize the first signal EWD. This signal is a signal for forcibly turning off the switching unit 45 by operating the forced-off circuit unit 43. Specifically, the forced-off circuit unit 43 outputs an ECPUEN signal (engine CPU enable signal). The ECPUEN signal in the active state (H level in the present embodiment) is a signal that activates the forced-off circuit unit 43.

  The HREN signal output from the engine CPU 15 and the ECPUEN signal output from the sub CPU 23 are input to the forced-off circuit unit 43. An HRON signal (heater relay ON signal) is output from the forced-off circuit unit 43, and the on state and the off state of the switching unit 45 including a relay are controlled by the HRON signal. In the present embodiment, when the engine CPU 15 and the sub CPU 23 are normal, the HREN signal output from the heater temperature control unit 35 is the HRON signal. Therefore, if the HREN signal is in the active state (H level), the HRON signal is also in the active state (H level), so that the switching unit 45 is turned on and power is supplied to the heater 47. On the other hand, if the HREN signal is in an inactive state (L level), the HRON signal is also in an inactive state (L level), so that the switching unit 45 is turned off and power supply to the heater 47 is cut off. The

  The heater 47 of the fixing unit 105 is connected via a switching unit 45 to a power source 49 that supplies power for driving the heater 47 to the heater 47. The toner image formed on the paper by the image forming unit 103 shown in FIG. 1 is heated by the heater 47 and fixed on the paper.

  If the switching unit 45 is in the ON state, power is supplied from the power source 49 to the heater 47, the heater 47 is driven, and the temperature of the heater 47 rises. On the other hand, if the switching unit 45 is in the OFF state, the supply of power from the power source 49 to the heater 47 is interrupted, and the heater 47 is not driven.

  When the forced-off circuit unit 43 operates, the switching unit 45 is forcibly turned off. FIG. 5 is a diagram illustrating an example of a circuit that executes the function of the forced-off circuit unit 43. The forced-off circuit unit 43 receives the HREN signal and the ECPUEN signal and outputs the HRON signal from the output terminal 51.

  The forced-off circuit unit 43 forces the HRON signal to be in an inactive state (in this embodiment) regardless of whether the HREN signal is in an active state (H level in this embodiment) or inactive state (L level in this embodiment). (L level). As a result, even if the engine CPU 15 runs away and the HREN signal becomes active (a signal for turning on the switching unit 45), the HRON signal is made inactive (a signal for turning off the switching unit 45). Can do.

  The forced-off circuit unit 43 includes an OR circuit 53 and an npn bipolar transistor 55. One input terminal of the OR circuit 53 is grounded via a resistor R1 and receives an ECPUEN signal. A signal output from the output terminal of the OR circuit 53 is input to the other input terminal of the OR circuit 53. The output terminal of the OR circuit 53 is connected to the base B of the bipolar transistor 55 via the resistor R2. The emitter E of the bipolar transistor 55 is grounded. A resistor is provided between the base B and the emitter E. The collector C is connected to the output terminal 51 of the forced-off circuit unit 43.

  FIG. 6 is a logic table showing the states of the engine CPU 15 and the sub CPU 23 and the states of the signals. FIG. 7 is a diagram showing the states of the engine CPU 15 and the sub CPU 23 and the waveform of each signal.

(1) Both the engine CPU 15 and the sub CPU 23 are normal. If both the engine CPU 15 and the sub CPU 23 are not runaway and are normal, the engine CPU 15 outputs the first signal EWD, and the sub CPU 23 outputs the second signal SWD. Is output. If the first monitoring unit 33 can recognize the second signal SWD, the engine controller 11 determines that the sub CPU 23 is normal. Thus, the heater temperature control unit 35 performs normal control. That is, when the heater 47 is driven, the HREN signal is set in an active state (H level), and when the heater 47 is not driven, the HREN signal is set in an inactive state (L level).

  On the other hand, when the second monitoring unit 39 can recognize the first signal EWD, the engine sub-controller 13 determines that the engine CPU 15 is normal. As a result, the forced-off signal output unit 41 sets the ECPUEN signal to an inactive state (L level).

  The HREN signal and the ECPUEN signal are input to the forced-off circuit unit 43 shown in FIG. ECPUEN is input to one input terminal of the OR circuit 53. The other input terminal of the OR circuit 53 is inputted with an L level signal before the forced-off circuit unit 43 is activated. Since the ECPUEN signal is at the L level, the OR circuit 53 outputs an L level signal. Since the L level signal is inputted to the base B of the bipolar transistor 55, the bipolar transistor 55 is turned off. As a result, the forced-off circuit unit 43 is deactivated, and the HREN signal is output as it is as the HRON signal. Therefore, if the HREN signal is in the active state (H level), the HRON signal is also in the active state (H level), so that the switching unit 45 is turned on and power is supplied to the heater 47. On the other hand, if the HREN signal is in an inactive state (L level), the HRON signal is also in an inactive state (L level), so that the switching unit 45 is turned off and power supply to the heater 47 is cut off.

(2) Engine CPU 15 is normal, sub CPU 23 is abnormal (runaway)
If the engine CPU 15 is normal and the sub CPU 23 is abnormal (runaway), the engine controller 11 (engine CPU 15) controls the power supply from the power source 49 to the heater 47 as described below.

  Since the engine CPU 15 is normal, the engine CPU 15 outputs a first signal EWD. If the sub CPU 23 runs out of control, the sub CPU 23 stops outputting the second signal SWD. Since the first monitoring unit 33 cannot recognize the second signal SWD, the engine controller 11 determines that the sub CPU 23 is out of control (abnormal). As a result, the heater temperature control unit 35 sets the HREN signal to an inactive state (L level). This is a signal for turning off the switching unit 45.

  On the other hand, since the sub CPU 23 runs out of control, it is not determined whether the ECPUEN signal output from the forced-off signal output unit 41 is in an active state (H level) or an inactive state (L level).

  Since the HREN signal is at the L level, the HRON signal is at the L level regardless of whether the forced-off circuit unit 43 is in the operating state or the non-operating state. Therefore, since the switching unit 45 is turned off, power supply from the power source 49 to the heater 47 is interrupted.

(3) If the engine CPU 15 is abnormal (runaway) and the sub CPU 23 is normal. If the engine CPU 15 is abnormal (runaway) and the sub CPU 23 is normal, the power supply 49 is supplied by the engine sub controller 13 (sub CPU 23) as described below. The power supply to the heater 47 is cut off.

  Since the sub CPU 23 is normal, the second signal SWD is output from the sub CPU 23. If the engine CPU 15 runs away, the output of the first signal EWD from the engine CPU 15 stops. Since the second monitoring unit 39 cannot recognize the first signal EWD, the engine sub-controller 13 determines that the engine CPU 15 is out of control. As a result, the forced-off signal output unit 41 sets the ECPUEN signal to an active state (H level). On the other hand, since the engine CPU 15 is running away, it is not determined whether the HREN signal output from the heater temperature control unit 35 is in an active state (H level) or an inactive state (L level).

  Since the ECPUEN signal is changed from the L level to the H level, the forced-off circuit unit 43 is activated. More specifically, as shown in FIG. 5, since the ECPUEN signal is at the H level, the OR circuit 53 outputs an H level signal. As a result, the bipolar transistor 55 is turned on, and the output terminal 51 is at the ground level (L level). Therefore, the HRON signal becomes L level regardless of whether the HREN signal is L level or H level. As a result, since the switching unit 45 is turned off, power supply from the power source 49 to the heater 47 is interrupted.

  By outputting an H level signal from the OR circuit 53, this signal is input to the other input terminal of the OR circuit 53. Therefore, since an H level signal continues to be output from the output terminal of the OR circuit 53, the operation state of the forced-off circuit unit 43 is continued, that is, the supply of power from the power source 49 to the heater 47 is continued. As described above, the OR circuit 53 functions as a latch circuit, so that the power supply from the power source 49 to the heater 47 is continuously cut off even if the sub CPU 23 runs away following the runaway of the engine CPU 15. . If the engine CPU 15 runs out of control, it is considered that the sub CPU 23 may not run out of control. Since the sub CPU 23 does not control the temperature of the heater 47, the operation state is continued when the forced-off circuit unit 43 is operated, so that the heater 47 is reliably turned off.

(4) Engine CPU15 and sub CPU23 are abnormal simultaneously (runaway)
When the engine CPU 15 and the sub CPU 23 run away at the same time, it is impossible to execute control for cutting off the power supply from the power supply 49 to the heater 47, but it is extremely rare that the engine CPU 15 and the sub CPU 23 run away at the same time.

  Next, control of power supply to the heater 47 according to the present embodiment will be described with reference to the flowchart shown in FIG. The first signal output unit 31 of the engine controller 11 outputs a first signal EWD that is a watchdog signal at a predetermined interval. This can be realized, for example, by providing a process for generating and outputting the first signal EWD periodically in the main routine of the program for controlling the engine controller 11. If the engine CPU 15 runs out of control and, for example, it becomes impossible to escape from the subroutine of the program, the first signal EWD is not output.

  When the first signal output unit 31 outputs the first signal EWD (Yes in step S1), the first signal EWD is input to the engine sub-controller 13, and the input first signal EWD is the second signal EWD. Recognized by the monitoring unit 39, the engine sub-controller 13 determines that the engine CPU 15 is normal (step S3).

  Similar to the first signal output unit 31, the second signal output unit 37 outputs the second signal SWD at a predetermined interval. When the sub CPU 23 runs out of control, the sub CPU 23 does not function normally, and the second signal SWD is not output.

  When the second signal output unit 37 outputs the second signal SWD (Yes in step S5), the second signal SWD is output from the engine sub-controller 13 and input to the engine controller 11. The input second signal SWD is recognized by the first monitoring unit 33, and the engine controller 11 determines that the sub CPU 23 is normal (step S7). The engine controller 11 controls normal power supply by the process described in “(1) Both the engine CPU 15 and the sub CPU 23 are normal” (step S7). That is, the heater temperature control unit 35 sets the HREN signal to an active state (H level) when the heater 47 is driven, and sets the HREN signal to an inactive state (L level) when the heater 47 is not driven.

  On the other hand, if the second signal SWD is not output from the second signal output unit 37 due to the runaway of the sub CPU 23 (No in step S5), the first monitoring unit 33 cannot recognize the second signal SWD. The engine controller 11 determines that the sub CPU 23 is out of control (step S11). By the process described in “(2) Engine CPU 15 is normal and sub CPU 23 is abnormal”, the power supply from the power source 49 to the heater 47 is cut off by the engine controller 11 (engine CPU 15) (step S13).

  The engine controller 11 performs control to display an error message indicating that the sub CPU 23 is abnormal (runaway) on the display unit 403 in FIG. 1 and control to stop the printer engine system of the image forming apparatus 1 (step S15).

  If the first signal EWD is not output from the first signal output unit 31 due to the runaway of the engine CPU 15 (No in step S1), the second monitoring unit 39 of the engine sub-controller 13 receives the first signal. Since the EWD cannot be recognized, the engine sub-controller 13 determines that the engine CPU 15 is out of control (step S17). By the process described in “(3) Engine CPU 15 is abnormal and sub CPU 23 is normal”, the power supply from the power source 49 to the heater 47 is cut off by the engine sub controller 13 (sub CPU 23) (step S19).

  Subsequent to the runaway of the engine CPU 15, even if the sub CPU 23 runs away (step S 21), the power supply from the power source 49 to the heater 47 is continuously cut off (step S 23). This is because the OR circuit 53 described in “(3) Engine CPU 15 is abnormal and sub CPU 23 is normal” has a latch function.

  The main effects of this embodiment will be described.

  (1) In this embodiment, the engine controller 11 (engine CPU 15) monitors the runaway of the sub CPU 23, and the engine sub controller 13 (sub CPU 23) monitors the runaway of the engine CPU 15. If the sub CPU 23 runs away, the engine controller 11 (engine CPU 15) cuts off the power supply to the heater 47, and if the engine CPU 15 runs away, the engine sub controller 13 (sub CPU 23) cuts off the power supply to the heater 47. By sharing the forced-off circuit unit 43 and the switching unit 45 used for the shutoff by the engine controller 11 and the engine sub-controller 13, the shutoff can be performed with a small number of parts. Therefore, according to this embodiment, when the CPU runs away, control for cutting off the power supply to the heater 47 can be realized with a relatively simple configuration.

  (2) As described in step S23, the OR circuit 53 functions as a latch circuit, so that the power supply from the power source 49 to the heater 47 is cut off even if the sub CPU 23 runs away following the runaway of the engine CPU15. To be continued. Since the sub CPU 23 does not control the temperature of the heater 47, the operation state is continued when the forced-off circuit unit 43 is operated, so that the heater 47 is reliably turned off.

  (3) As described in steps S13 and S15, after the power supply from the power source 49 to the heater 47 is interrupted by the engine controller 11, the engine controller 11 performs control to stop the printer engine system of the image forming apparatus 1. do. As a result, the printer engine system of the image forming apparatus 1 is stopped before the temperature control of the heater 47 becomes impossible due to the engine CPU 15 running away following the runaway of the sub CPU 23.

  (4) According to the present embodiment, the engine controller 11 (engine CPU 15) monitors the runaway of the sub CPU 23, and the engine sub controller 13 (sub CPU 23) monitors the runaway of the engine CPU 15. This eliminates the need for an external watchdog timer circuit for the CPU that monitors the watchdog signal.

1 Image forming apparatus 11 Engine controller (an example of a first control unit)
13 Engine sub-controller (example of second control unit)
15 engine CPU (an example of a first CPU)
23 Sub CPU (an example of a second CPU)

Claims (3)

An image forming unit that forms a toner image on a sheet based on image data;
A fixing unit including a heater and heating the toner image by the heater to fix the toner image on the paper;
A switching unit that can be switched between an on state in which power is supplied from a power source to the heater and an off state in which power supply from the power source to the heater is interrupted;
A forced-off circuit unit that operates to forcibly turn off the switching unit; and
A first signal output unit that outputs a first signal that functions as a watchdog signal; and a first monitoring unit that monitors a second signal that functions as a watchdog signal, and uses the first CPU to A first control unit in which a first signal output unit and the first monitoring unit are realized;
A second signal output unit that outputs a second signal monitored by the first monitoring unit; and a second monitoring unit that monitors the first signal output from the first signal output unit. A second control unit in which the second signal output unit and the second monitoring unit are realized using a second CPU,
The first control unit controls the temperature of the heater by switching and outputting a signal for turning the switching unit on and a signal for turning off, and the second monitoring unit A heater temperature control unit that outputs a signal for turning off the switching unit when the signal cannot be recognized, and the heater temperature control unit is realized using the first CPU,
The second control unit includes a forced off signal output unit that outputs a signal for operating the forced off circuit unit when the second monitoring unit fails to recognize the first signal. An image forming apparatus in which the forced off signal output unit is realized using a CPU.   The image forming apparatus according to claim 1, wherein the forced-off circuit unit includes a latch circuit that continues an operation state when the forced-off circuit unit is activated.   When the heater temperature control unit outputs a signal for turning off the switching unit because the second signal cannot be recognized by the first monitoring unit, the first control unit performs the image formation. The image forming apparatus according to claim 1, wherein control is performed to stop the system of the apparatus.

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