JP2017102402A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that can improve usability of an image forming apparatus including a fixing device.SOLUTION: In an image forming apparatus comprising: fixing means 109 including a heating element 3 that generates heat with a power supplied from a commercial AC power source 1 and heating a developer image to be fixed to a recording material; temperature detection means 135 that detects the temperature of the heating element 3; power control means 126 that controls supply of power from the commercial AC power source 1 to the heating element 3; and first power supply interruption means 70 that, when the detection temperature detected by the temperature detection means 135 increases to a first threshold or more, interrupts supply of power from the commercial AC power source to the heating element 3, when the number of times the supply of power is interrupted by the first power supply interruption means 70 exceeds a predetermined number of times, the power control means 126 maintains the interruption of power supply.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus including a fixing device.

  A fixing device (also called an image heating device) mounted on an image forming apparatus such as an electrophotographic copying machine or a printer is controlled by a control device such as a triac from a commercial AC power supply to a heating element of a heater as a heating means. As a result, the desired temperature is controlled. When a failure occurs in the control device for some reason, the power supplied to the heating element cannot be controlled, and there is a concern that abnormal heat generation may occur. As a preventive measure, there is a protection means for detecting abnormal heat generation with a temperature detection element such as a thermistor, shutting off the drive of the control device and latching the state.

  When the power of the image forming apparatus main body is turned off by the user while the protection means is operating, the power supply voltage of the latch circuit unit included in the protection means is also turned off, so that the latch state is not maintained and is released. May be. When a permanent failure has occurred in the control device, when control of the heating element is started at the next power-on, abnormal power is supplied to the heating element again, and the protection means operates. If the power is turned off and off for a very short period of time, excessive power will be supplied again while the temperature of the heating element does not drop sufficiently, and if this state is repeated several times, heat will be generated. The body temperature gradually rises. In such an abnormal state, energization is surely interrupted by an excessive temperature rise prevention means such as a thermo switch installed in the vicinity of the heating element, and the heating element or other members formed around it may be damaged. I am trying not to. However, once the thermo switch is activated, it is difficult for the user to automatically return, and the usability is reduced. Therefore, before the thermo switch is activated, the energization is interrupted by a protection means composed of a temperature detection element such as a thermistor. The method of making it desirable is preferable.

  If the protection means is constituted by a latch circuit portion, the latch state is released when the image forming apparatus main body is turned off as described above. In Patent Document 1, a non-volatile memory or the like is used to monitor a power-off period, and energization of a heating element is not permitted when the next power-on is performed in a period shorter than a preset period. There has been proposed a control method.

JP-A-1-291309

  However, in the configuration described in Patent Document 1, it takes a long time to return to the controllable state because it takes time to discharge the error memory capacitor constituting the latch circuit once the protection means is activated. There is a concern that it will be necessary. In addition, when the CPU that controls the control device such as the triac malfunctions or the latch circuit unit itself malfunctions, the heating element is not energized even though the temperature of the heating element is sufficiently low. It is possible to be blocked. In this case as well, there is a concern that the user needs to wait for a long time until the next control can be started.

  SUMMARY An advantage of some aspects of the invention is that it provides a technique capable of improving the usability of an image forming apparatus including a fixing device.

In order to achieve the above object, an image forming apparatus of the present invention includes:
An image forming unit for forming a developer image on a recording material;
A fixing unit that has a heating element that generates heat by electric power supplied from a commercial AC power source, and heats the developer image to fix it on a recording material;
Temperature detecting means for detecting the temperature of the heating element;
Power control means for controlling power supply from a commercial AC power source to the heating element;
When the detected temperature detected by the temperature detection means is equal to or higher than a first threshold, first power supply cutoff means for cutting off power supply from a commercial AC power source to the heating element;
In an image forming apparatus comprising:
The power control unit maintains the subsequent power supply in a cut-off state when the number of times that the power supply is cut off by the first power supply cut-off unit exceeds a predetermined number of times.

  According to the present invention, it is possible to improve the usability of an image forming apparatus including a fixing device.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. Explanatory drawing of the drive circuit of the fixing control in Embodiment 1. Flowchart of fixing control in Embodiment 1. Schematic explanatory diagram of fixing control in Embodiment 1. FIG. 6 is a diagram of a fixing control driving circuit according to the second embodiment. Schematic explanatory diagram of fixing control in Embodiment 3. Flowchart of fixing control in Embodiment 3 Schematic explanatory diagram of fixing control in Embodiment 4.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

[Example 1]
FIG. 1 is a schematic configuration diagram of a laser printer as an example of an image forming apparatus according to this embodiment using an electrophotographic process. A laser printer main body 101 (hereinafter, main body 101) is provided with a cassette 102 for storing a recording paper S as a recording material, and a cassette presence sensor 103 for detecting the presence or absence of the recording paper S in the cassette 102. In addition, the main body 101 is provided with a cassette size sensor 104 that detects the size of the recording paper S of the cassette 102. The cassette size sensor 104 is composed of a number of micro switches. Further, the main body 101 is provided with a paper feed roller 105 that feeds the recording paper S from the cassette 102. A registration roller pair 106 that synchronously conveys the recording paper S is provided downstream of the paper supply roller 105. Further, an image forming unit 108 that forms a toner image on the recording paper S based on the laser beam from the laser scanner unit 107 is provided downstream of the registration roller pair 106. The laser scanner 107 emits a laser beam modulated based on an image signal (image signal VDO) sent from an external device 131 described later, and scans and exposes the surface of a photosensitive drum 117 described later. Further, a fixing device (fixing device) 109 is provided downstream of the image forming unit 108 as a fixing unit that thermally fixes the toner image (developer image) formed on the recording paper S. Further, downstream of the fixing device 109, a paper discharge sensor 110 that detects the conveyance state of the paper discharge unit, a paper discharge roller 111 that discharges the recording paper S, and a stacking tray 112 on which the recording paper S that has been recorded are stacked are provided. It has been. The conveyance reference of the recording paper S is set so as to be centered with respect to the length of the recording paper S in the direction orthogonal to the conveyance direction of the main body 101, that is, the width of the recording paper S.

  The main body 101 includes a photosensitive drum 117, a primary charging roller 119, a developing device 120, a transfer roller 121, a cleaner 122, and the like necessary for a known electrophotographic process. The fixing device 109 includes a fixing film 132, a pressure roller 133, a ceramic heater 134 disposed inside the fixing film 132, and a temperature detection element 135 such as a thermistor as temperature detection means for detecting the surface temperature of the ceramic heater 134. Has been. The engine controller 126 includes a CPU, an ASIC, a program ROM, a memory RAM, and the like. The engine controller 126 controls the electrophotographic process by the laser scanner 107, the image forming unit 108, and the fixing device 109, and controls the conveyance of the recording paper S in the main body 101. I do. The video controller 127 is connected to an external device 131 such as a personal computer via a general-purpose interface 130 (Centronics, RS232C, etc.). The video controller 127 expands the image information sent from the general-purpose interface 130 into bit data, and sends the bit data to the engine controller 126 as a VDO signal 128.

  FIG. 2 is a diagram showing a fixing control circuit of the fixing device 109 in the embodiment of the present invention. The heating element 3 (formed on the substrate) provided on the ceramic heater 134 included in the fixing device 109 is supplied with electric power from the commercial AC power source 1 via the AC filter 2, the relay 41, and the triac 4. Generate heat. When supplying power to the heating element 3, the engine controller 126 turns on the relay 41. Reference numeral 42 denotes a protection diode from the coil back electromotive force voltage of the relay 41, 43 denotes a transistor for driving the relay 41, and a base terminal is connected to the RLD terminal of the engine controller 126 via the bias resistor 44. Yes.

  The switch 11 that turns on and off in conjunction with a main power switch (not shown) of the main body 101 is controlled by the engine controller 126 either spontaneously or in response to a user operation. When the main power switch of the main body 101 is off, an off signal is output from the ON terminal of the engine controller 126 and the switch 11 is turned off. When the main power switch is on, an on signal is output from the ON terminal and the switch 11 is turned on. The That is, when the main power switch of the main body 101 is off, only the output Vin of the low-voltage power circuit 28 is supplied to the fixing control circuit, and when the main power switch is on, Vin and Vref are supplied to the fixing control circuit. When the main power switch of the main body 101 is on, all device configurations connected to Vin and Vref are in a power state in which they can normally operate (normal power state) except when a failure or the like has occurred. This is because when the main power switch of the main body 101 is off, power consumption by various circuit units (including the fixing control circuit) connected to Vref is suppressed to save power (power saving state). Power to the engine controller 126 is supplied from the VCC terminal and is connected to Vin. It is assumed that Vin is always output regardless of whether the main power switch of the main body 101 is off or on. That is, power is supplied to the engine controller 126 even when the main power switch is off and the main body 101 does not perform a printing operation.

  Supply of power to the heating element 3 is performed by controlling energization and shut-off of the triac 4 in accordance with an FSRON signal from the engine controller 126 as power control means. Reference numerals 5 and 6 denote bias resistors for driving the triac 4. The control circuit of the triac 4 is a phototriac coupler 7 that insulates the primary side from the secondary side, and 9 is a control transistor for the phototriac coupler 7, which is connected to the FSRON signal from the engine controller 126 via the bias resistor 10. Controlled based on. The phototriac coupler 7 is connected to the power supply Vref via the resistor 8 and the transistor 78.

Reference numeral 135 denotes a temperature detection element such as a thermistor for detecting the temperature on the ceramic heater 134, and the partial pressure value with the resistor 22 is input to the FSRTH terminal of the engine controller 126. The engine controller 126 converts the voltage value input to the FSRTH terminal into a temperature and uses it for temperature control.

  The amount of heat given to the fixing device 109 is calculated based on the temperature adjustment target temperature set by the engine controller 126 and the temperature detected by the temperature detection element 135. Reference numeral 12 denotes a zero cross generation circuit which generates a zero cross signal whose level changes every 0 V of the commercial frequency. The generated zero cross signal is input to the ZEROX terminal of the engine controller 126, and energization control is performed with this zero cross signal as the lower side. In addition, as a second power supply interrupting means and an excessive temperature rise preventing means, a thermo switch 137 is disposed on the insulating substrate surface or the protective layer surface of the ceramic heater 134 through an appropriate member. The thermo switch 137 is constituted by a fuse that melts and breaks when a current exceeding a predetermined amount flows, for example. When the temperature of the ceramic heater 134 becomes abnormal, the thermoswitch 137 is disconnected to cut off the energization to the ceramic heater 134.

  Reference numeral 70 denotes a temperature protection circuit unit based on the detection temperature result of the temperature detection element 135 as a first power supply interruption means. When the control to the ceramic heater 134 is normal, the output of the comparator 71 is at a high level. It is in. When an abnormality occurs in the triac 4 or the like and the ceramic heater 134 falls into an uncontrollable state, the temperature detected by the temperature detecting element 135 rises abnormally and becomes equal to or higher than the threshold temperature determined by the resistors 72 and 73, and the output of the comparator 71. Becomes Low level. The threshold temperature (first threshold) used here is set to a temperature higher than the temperature control temperature during printing. The output of the comparator 71 is input to the FSRSAFE1 terminal of the engine controller 126, and the number of operations of the temperature protection circuit unit 70 can be monitored. The output of the comparator 71 is also connected to the base terminal of the transistor 75, and the transistor 75 is turned off when the detected temperature of the temperature detecting element 135 becomes abnormal. In a state where the control of the ceramic heater 134 is not abnormal, the transistor 75 is in an on state with Vref supplied through the resistor 74. When the transistor 75 is turned off, the subsequent transistor 78 is turned off via the resistors 76 and 77, and the voltage supply to the phototriac coupler 7 is cut off. As a result, the triac 4 cannot be turned on, and the power supply to the ceramic heater 134 is cut off.

  Once the output of the temperature protection circuit unit 70 becomes low level, the engine controller 126 maintains the triac 4 in the off state until the Vref voltage is cut off. The output of Vref stops when the main power switch of the main body 101 is turned off. That is, once the temperature protection circuit unit 70 is operated, this state is maintained until the main power switch of the main body 101 is turned off by the user, and energization to the heating element 3 is prohibited. With such a circuit configuration, the latch state can be maintained. Reference numerals 47 to 50 denote diodes constituting a full-wave rectifier circuit, and the low-voltage power supply unit 28 is formed at the subsequent stage.

The control in this embodiment will be described with reference to the flowchart of FIG. When the main power switch of the main body 101 is turned on, the switch 11 is turned on and Vref is supplied to the fixing circuit unit 70, whereby a high level is input to the terminal voltage of FSRSAFE 1 of the engine controller 126. At that time, the engine controller 126 checks the number of operations of the protection circuit unit 70 (S1). In this embodiment, the determination is made based on whether or not the number of operations of the protection circuit unit 70 is three. This value was selected in consideration of the temperature rise of the heating element 3 when the user quickly turned off the main power supply and the set value (second threshold value) of the thermo switch 137. That is, no matter what time interval the main power switch is turned on / off every time the power supply to the heating element 3 is cut off by the temperature protection circuit unit 70, the detected temperature of the fuse of the thermo switch 137 It is the number of times that the temperature (second threshold value) that will be reached is not reached. Note that the setting value may be changed as appropriate in consideration of the configuration of the fixing device 109 and the like. If the number of operations of the protection circuit unit 70 is less than 3 in S1, it waits for the reception of the start process or the print process. After that, the engine controller 126 starts its operation when receiving the startup process or the print process (S2).

  The engine controller 126 outputs High to the RLD terminal, turns on the relay 41, and starts temperature control. The engine controller 126 determines a fixing target temperature from conditions such as the environment in which the main body 101 is placed, the history of previous printing, the size of paper to be passed, and the like, and detects the temperature of a thermistor or the like so as to reach a predetermined target temperature. Based on the information of the element 135, the triac 4 is controlled. During the startup process or the print process, the engine controller 126 detects whether the FSRSAFE1 terminal is at the low level, that is, whether an error has occurred (S3).

  If no error is detected, it is determined whether the start-up process or print process ends normally (S4). If the process ends normally, energization of the heating element 3 is ended and the number of operations of the protection circuit unit is reset. (S5). If not, the operation from S3 is repeated. Thereafter, it is determined whether or not an instruction to move to the next step is requested (S6). For example, when the start process is completed, it is determined whether there is a print request. When the print process is completed, it is determined whether there is a next print request. Thereafter, when the user does not give a work instruction to the main body 101, the main power switch of the main body 101 is turned off.

  If an error occurs in S3, it is determined that there is some abnormality in the energization system to the heating element 3, and the immediate energization is terminated (S7). At that time, the engine controller 126 keeps turning off the relay 41 and the triac 4, keeps the power supply to the heating element 3 off, and increments the number of times of the protection circuit operation by one (S8). At that time, the failure content is notified to the user via a display panel (not shown) mounted on the main body 101 (S9). The engine controller 126 resets the number of operation of the protection circuit in S5 or unless an unillustrated inlet cable connected to the main body 101 is inserted (unless power supply from the commercial power supply to the apparatus is completely interrupted). Can be retained. That is, the number of operations is stored and held even when the main power switch of the main body 101 is turned off.

  In S1, when the number of times of operation of the protection circuit is 3, the energization to the heating element 3 is kept off regardless of any processing received thereafter (S10). At that time, the failure content is notified to the user via a display panel (not shown) mounted on the main body 101 (S11). When the power switch is turned off, a series of main body operations are completed, but even if the main power switch of the main body 101 is next turned on by the user, the number of times the protective circuit operation is performed is not reset. The flow from S1 to S8 is repeated again. That is, the state where the heating element 3 cannot be energized continues regardless of whether the main power switch of the main body 101 is turned on or off. In order to cancel the above state and start energizing the heating element 3 again, it is necessary to insert and remove the inlet cable by the user.

In FIG. 4, the relationship between the temperature rise of the fixing device and the operation of the protection circuit unit in this embodiment will be described. A case where an abnormal operation occurs in the triac 4 will be described as an example. First, when the main power switch of the main body 101 is turned on and the startup process or the print process is received, the engine controller 126 turns on the relay 41. Under normal conditions, the engine controller 126 controls the triac 4 so as to obtain an appropriate input power based on the target temperature of the heating element 3 and the temperature detected by the temperature detection element 135 by PI control or the like. However, since it is assumed that the TRIAC 4 is operating abnormally, the TRIAC 4 may not be controlled and excessive power may be supplied to the heating element 3. In time, the temperature of the heating element 3 exceeds the threshold temperature of the temperature protection circuit unit 70, and the low level of the FSRSAFE 1 signal is input to the engine controller 126. The engine controller 126 determines that an abnormality has occurred in the fixing device 109 and puts the energization of the heating element 3 in a cut-off state. As an operation, the drive signals of the relay 41 and the triac 4 are turned off. At this time, since it is assumed that the triac 4 is operating abnormally, the relay 41 is turned off and the power supply to the heating element 3 is cut off. In addition, the engine controller 126 increments the protection circuit operation count N by one.

  When the activation process or the printing process is not performed again, the state where the power supply to the heating element 3 is cut off is continued, so that the temperature of the heating element 3 is eventually lowered to room temperature. However, when the main power supply of the main body 101 is turned off by the user, the starting process or the control of the printing process is started from the beginning, so that the relay 41 is turned on again while the triac 4 is operating abnormally. When the user turns off the main power switch of the main body 101 at a very fast timing, excess power is applied again without the temperature of the heating element 3 being sufficiently lowered. In many cases, the fixing film 132 and the pressure roller 133 that are heated by the heating element 3 are constituted by a heat storage member. Therefore, this series of operations is repeated, and as the number of times of turning on and off the main power switch of the main body 101 increases, the temperature rising speed at the time of turning on becomes larger and the temperature decreasing speed at the time of turning off becomes smaller. As a result, the temperature of the heating element 3 gradually increases, and the thermoswitch 137 eventually exceeds the operating temperature as shown by the dotted line waveform in FIG. The set temperature of the thermo switch 137 is set to a temperature that does not damage the heating element 3 itself and its peripheral members.

  In this embodiment, when the number N of protection circuit operations is detected and the predetermined number of operations (N = 3) is detected, the subsequent startup processing or print processing is not performed, that is, the relay 41 and the triac 4 are turned on. It is characterized by non-control. That is, when the protection circuit operation number N reaches 3, the power is not supplied to the heating element 3 thereafter. Therefore, the temperature of the heating element 3 can be lowered to a sufficiently low temperature as shown by the solid line waveform in FIG. 4 without operating the thermo switch 137 that cannot be automatically reset by the user once it is operated. Once the thermo switch 137 is operated, i.e., once the fuse is blown out, it is necessary to replace the thermo switch 137. From the viewpoint of cost and usability, it is desirable that the thermo switch 137 remain as inoperative as possible. It is a configuration. According to the present embodiment, for example, when the user ignores the warning and tries to continue the image forming operation by turning the main power switch on and off many times even though the triac 4 is out of order. , Before the thermo switch 137 is activated, it can be forcibly disabled. Thereby, it is possible to suppress the deterioration of the excessive temperature rise state and the operation of the dark thermo switch 137.

  In this embodiment, when the number N of protection circuit operations exceeds 3 and the main power switch of the main body 101 is turned off and cannot be started or printed, the user can recover by inserting and removing the inlet cable. is there. For example, a user's return operation such as temporarily disconnecting the connection between the apparatus and the commercial AC power source, such as disconnecting a power cable from an outlet. At this time, when the apparatus returns to a normal state, it is possible to perform a start-up process or a print process as usual. It is desirable that the set value of the protection circuit operation number N is determined in consideration of the actual heating rate of the heating element 3 and the set value of the excessive temperature rise prevention means 137.

  In this embodiment, even when the main power switch of the main body 101 is turned off, the voltage is input to the engine controller 126 such as a CPU and the mechanism for holding the number N of operation of the protection circuit is maintained. Is not to be done. For example, a nonvolatile memory such as an EEPROM may be used as the storage means. When the main power switch of the main body 101 is turned off, the number N of protection circuit operations is held in the nonvolatile memory, and the engine controller 126 such as a CPU started when the main power switch is turned on has the number N of protection circuit operations in the nonvolatile memory. A configuration in which information is acquired and used for control may be used.

As described above, the number of operations of the protection circuit unit is detected and the number of counts can be held during the power-off period, and the fixing device is controlled according to the number of detections. This is a characteristic configuration of this embodiment. According to such a configuration, it is possible to avoid falling into a state where the control of the image heating apparatus cannot be started immediately even though the heating element is at a sufficiently low temperature, and to prevent malfunction of the protection circuit unit due to noise application or the like. Can also be effective. Therefore, according to the present embodiment, it is possible to realize a heating apparatus with improved usability and an image forming apparatus having the same.

[Example 2]
FIG. 5 shows a fixing control circuit of the fixing device 109 according to the second embodiment of the present invention. The difference between the present embodiment and the first embodiment is that the temperature protection circuit unit 70 is provided with a latch function with a hardware configuration, the energization current value to the heating element 3 is detected, and energization is forced according to the detected current value. Current protection circuit section and its latch circuit section are provided. Since others are the same as those of the first embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The current passed through the heating element 3 is converted into a voltage by the current transformer 25 and input to the current detection circuit 27 via the bleeder resistor 30. The current detection circuit 27 converts the voltage-converted current waveform into an effective value or an average value, and inputs it to the A / D conversion port of the engine controller 126 as an HCRRT signal.

  Reference numeral 80 denotes a latch circuit unit of the temperature protection circuit unit 70 as a first latch circuit. When the output of the temperature protection circuit unit 70 becomes a low level, the latch state is maintained until the Vref voltage is cut off. The output of Vref stops when a main power switch (not shown) of the main body 101 is turned off. That is, once the temperature protection circuit unit 70 is operated, the state is maintained until the main power switch of the main body 101 is turned off by the user, and energization to the heating element 3 is prohibited. When the output of the temperature protection circuit 70 becomes a low level, the transistor 84 is turned on, and the voltage value of the inverting input terminal becomes higher than the non-inverting input terminal of the comparator 81 determined by the resistors 86 and 87. Reference numeral 85 denotes a resistor for limiting the collector current of the transistor 84.

  When the output of the temperature protection circuit 70 is at a high level, the comparator 81 has a higher voltage value at the non-inverting input terminal, and the output remains at the high level. When the voltage at the inverting input terminal of the comparator 81 becomes higher, the output becomes the Low level. Here, reference numeral 82 denotes a malfunction prevention capacitor, which can be ignored even if the output of the temperature protection circuit 70 is at a low level for a short period due to noise or the like. Reference numeral 83 denotes a resistor for discharging the capacitor 82. Once the comparator 81 becomes low level, the control state to the heating element 3 returns to normal and the output to the FSRSAFE terminal of the engine controller 126 is low level even if the output of the temperature protection circuit 70 returns to high level. Is maintained. With such a circuit configuration, the latch state can be maintained.

  In the present embodiment, in addition to the protection circuit unit 70 for interrupting the triac 4 in the abnormal state, the protection circuit unit 60 is also provided for the relay 41 as the third power supply interruption means. The CURLIM terminal of the current detection circuit 27 has the function. The current supplied to the heating element 3 is input to the current detection circuit 27 via the current transformer 25 and input to the engine controller 126 as an HCRRT signal. At the same time, the current detection circuit 27 has a function of setting the CURLIM terminal to Low when a current exceeding a preset threshold value is detected (not shown). The threshold current used here is set to a value higher than the current value at the time of print start-up, and does not exceed this threshold if the heating element 3 is normally controlled. If an abnormality occurs in the triac 4 or the like and the heating element 3 falls into an uncontrollable state, the current supplied to the heating element 3 becomes equal to or greater than the threshold value, and the CURLIM terminal becomes a low level. The CURLIM terminal is also connected to the base terminal of the transistor 65, and the transistor 65 is turned off when the detected current value of the current detection circuit 27 becomes abnormal.

  The transistor 65 is in an on state when Vref is supplied via the resistor 64 when the detected current value of the current detection circuit 27 is not abnormal. When the transistor 65 is turned off, the subsequent transistor 61 is turned off via the resistors 62 and 63, and the voltage supply to the relay 41 is cut off. As a result, the relay 41 cannot be turned on, and the power supply to the heating element 3 is interrupted. The CURLIM terminal is input to the FSRSAFE2 terminal of the engine controller 126, and the number of operations of the current protection circuit unit 60 can be monitored.

  Reference numeral 90 denotes a latch circuit section of the current protection circuit section 60 as a second latch circuit, and maintains the latched state until the Vref voltage is cut off when the CURLIM terminal of the current detection circuit 27 becomes low level. When the CURLIM terminal becomes low level, the transistor 94 is turned on, and the voltage value of the inverting input terminal becomes higher than the non-inverting input terminal of the comparator 91 determined by the resistors 96 and 97. Reference numeral 95 denotes a resistor for limiting the collector current of the transistor 94. When the voltage at the inverting input terminal of the comparator 91 becomes higher, the output becomes the Low level. Here, reference numeral 92 denotes a malfunction prevention capacitor, which can be ignored even if the CURLIM terminal is at a low level for a short period due to noise or the like. Reference numeral 93 denotes a resistor for discharging the capacitor 92. Once the comparator 91 becomes Low output, the control state of the heating element 3 returns to normal and the base terminal of the transistor 43 is maintained at Low level even when the CURLIM terminal returns to High level. With such a circuit configuration, the latch state can be maintained.

  The control of this embodiment can be explained by the flowchart of FIG. The determination of the error occurrence in S3 is determined by the FSRSAFE1 signal that is the output of the temperature protection circuit unit 70 in the first embodiment. However, in this embodiment, the determination is also made by the FSRFAFE2 signal that is the output of the current protection circuit unit 60. ing. That is, it is determined that an error has occurred when either the temperature protection circuit unit 70 or the current protection circuit unit 60 detects an abnormality. In addition, a latch circuit unit is provided in each of the temperature protection circuit unit 70 and the current protection circuit unit 60, and when it is detected that the temperature of the heating element 3 or the energization current value is abnormal, the main power source of the main body 101 is detected by the user. Until the switch is turned off, the energization of the heating element 3 is kept off. The total number of times of power supply interruption to the heating element 3 by the temperature protection circuit unit 70 and the number of interruptions of power supply to the heating element 3 by the current protection circuit unit 60 is a predetermined number (three times in this embodiment). If it exceeds, energization of the heating element 3 is prohibited until the user disconnects the inlet cable.

  According to the present embodiment, in addition to the same effects as those of the first embodiment, it is possible to further improve safety and reliability. That is, by forming a protection circuit unit in each of the relay 41 and the triac 4, even when a permanent failure occurs in one of the relays 41 and the triac 4, it is possible to reliably cut off the power supply to the heating element 3. Furthermore, by using a hardware configuration for the latch mechanism, it is possible to improve usability and improve safety and reliability.

[Example 3]
The third embodiment is different from the first embodiment in that once the protection circuit unit is operated, an interval period corresponding to the number N of protection circuit operations is provided until the next activation process or print process is permitted. In the meantime, the activation process or the print process is prohibited. That is, the power supply to the heating element is maintained in a blocked state until the interval period elapses. Since others are the same as those of the first embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 6 illustrates the relationship between the temperature rise of the fixing device and the operation of the protection circuit unit in this embodiment. The case where an abnormal operation occurs in the triac 4 as in the first embodiment will be described as an example. First, body 1
When the 01 main power switch is turned on and the startup process or print process is received, the engine controller 126 turns on the relay 41. At this time, since it is assumed that the triac 4 is operating abnormally, the triac 4 cannot be controlled, and excessive power may be supplied to the heating element 3 in some cases. In time, the temperature of the heating element 3 exceeds the threshold temperature of the temperature protection circuit unit 70, and the low level of the FSRSAFE 1 signal is input to the engine controller 126. The engine controller 126 determines that an abnormality has occurred in the fixing device, and cuts off the power supply to the heating element 3. As an operation, the drive signals of the relay 41 and the triac 4 are turned off.

  At this time, since it is assumed that the triac 4 is operating abnormally, the relay 41 is turned off and the power supply to the heating element 3 is cut off. In addition, the engine controller 126 increments the protection circuit operation count N by one. When the main power switch of the main body 101 is turned off and on by the user, the start process or print process control is started from the beginning, so that the relay 41 is turned on again while the triac 4 is operating abnormally. At this time, if the user turns off the main power switch of the main body 101 at a very fast timing, the start-up process or the print process is started again without the temperature of the heating element 3 sufficiently lowered, and excess power is turned on. There is a concern that it will be.

  In the present embodiment, an interval period is provided in the time from when the main power switch of the main body 101 is turned off until the start-up process or the print process is executed again in accordance with the number of detections of the protection circuit operation number N. And In many cases, the fixing film 132 and the pressure roller 133 that are heated by the heating element 3 are constituted by a heat storage member. Therefore, the fixing film 132 and the pressure roller 133 repeat the above-described series of operations, and as the number of times the main power switch of the main body 101 is turned on / off increases, the temperature rising speed at the time of turning on increases, and the temperature at the time of turning off The rate of decrease tends to decrease the slope. In this embodiment, the larger the number of detections of the protection circuit operation number N is, the longer the interval period is set, whereby the temperature of the heating element 3 can be further lowered, and a fixing device with improved safety can be provided.

  In FIG. 6, the interval period when the protection circuit operation number N is 1 is T1, the interval period when the protection circuit operation number N is 2 is T2, and the relationship of T1 <T2 is set. In the example of FIG. 6, when the number N of protection circuit operations is 1, the relationship of T1 <OFF is established. Therefore, when the main power switch of the main body 101 is turned on again, the activation process or the print process is immediately performed. This is executed, and excessive heat is supplied to the heating element 3 to abnormally raise the temperature. Thereafter, when the temperature exceeds the threshold temperature of the temperature protection circuit unit 70 again, the relay 41 is turned off, so that the power supply to the heating element 3 is interrupted. At this time, the protection circuit operation frequency N is incremented by 1 to 2 times. After that, when the main power switch of the main body 101 is quickly turned on by the user, since T2> OFF, even if the main power switch of the main body 101 is turned on, the activation process or the print process is immediately performed. Is not executed. Eventually, after the interval period T2 has elapsed, the start-up process or print process is started.

Also in this embodiment, similarly to the other embodiments, when the number N of protection circuit operations is detected and the predetermined number of operations (N = 3) is detected, the subsequent startup processing or print processing is not performed. Control is performed so that the relay 41 and the triac 4 are not turned on. Therefore, in this embodiment, an interval period corresponding to the number N of protection circuit operations is set until the number N of protection circuit operations reaches 3. Once operated, the temperature of the heating element 3 can be lowered to a sufficiently low temperature as shown by the solid line waveform in FIG. 6 without operating the thermo switch 137 that cannot be automatically reset by the user. In this embodiment, when the number N of protection circuit operations exceeds 3 and the main power switch of the main body 101 is turned off and cannot be started or printed, the user can recover by inserting and removing the inlet cable. is there. At this time, when the apparatus returns to a normal state, it is possible to perform a start-up process or a print process as usual. It is desirable that the set value of the protection circuit operation number N is determined in consideration of the actual heating rate of the heating element 3 and the set value of the excessive temperature rise prevention means 137.

  The control in this embodiment will be described with reference to the flowchart of FIG. The same control as that in the first embodiment will not be described. When the main power switch of the main body 101 is turned on, the engine controller 126 checks the number of operations of the protection circuit unit (S1), and then the elapsed time from the previous main power switch off operation of the main body 101 reaches the interval period T. It is determined whether it has reached (S101). If the elapsed time from when the main power switch is switched from on to off does not exceed the predetermined interval period T, the engine controller 126 starts the process even if it receives a start process or print process request do not do. After that, when the interval period T elapses, if an activation process or a print process request is received during the interval period T, the process immediately starts. If an activation process or print process request has not been received during the interval T, a process request is awaited.

  Further, as described above, the interval period T is set by the protection circuit operation number N, and the interval period T is set to be a longer value as the protection circuit operation number N becomes larger. If an error occurs in S3, it is determined that there is some abnormality in the energization system to the heating element 3, and the immediate energization is terminated (S7). The number of operations is incremented by 1 (S8). Then, the failure content is notified to the user via a display panel (not shown) mounted on the main body 101 (S9). Thereafter, the engine controller 126 sets an interval period T (S102). The interval period T set here is a time measured using the time point when the main power switch off of the main body 101 is detected next time as a start trigger. The engine controller 126 does not permit the start-up process or print process required when the main power switch of the main body 101 is turned on next time until the time set in the interval period T elapses. Even when the main power switch of the main body 101 is turned off, the engine controller 126 can measure whether or not the interval period T has elapsed.

  According to the present embodiment, by providing an interval period triggered by turning off the main power switch, in addition to the same effects as those of the first embodiment, it is possible to further improve safety and usability.

[Example 4]
This embodiment is different from the first embodiment in that a self-diagnosis of a fault location is performed according to the number N of protection circuit operations and the result can be notified to the user. In the flowchart of FIG. 3, the operations of S9 and S11 correspond to this embodiment. Since others are the same as those of the first embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 8 shows an example of information related to the state of the device that is notified to the user via the display panel 129 (see FIG. 1) mounted on the main body 101 as notification means. In this embodiment, the protection circuit operation frequency N is incremented by 1 in S8 of the flowchart of FIG. 3, and the failure status of the main body 101 is estimated based on the detection result of the protection circuit operation frequency N. Then, the notification content is changed according to the number N of protection circuit operations and displayed on the display panel 129.

  When the protection circuit operation number N is 1, it is possible that the engine controller 126 itself or the temperature protection circuit unit 70 has malfunctioned. At this time, the engine controller 126 displays an abnormally high temperature on the display panel 129 and requests the user to turn on and off a main power switch (not shown) mounted on the main body 101. If the main power switch is turned off and then returns to normal operation, the engine controller 126 resets the protection circuit operation count N.

  When the number N of protection circuit operations is detected, there is a possibility that some hardware configuration has failed. The engine controller 126 determines that there is a possibility that the fixing circuit unit including the relay 41 and the triac 4 has failed, and notifies the user of the abnormally high temperature and also the fixing circuit unit abnormality. In addition, since it is presumed that the temperature of the heating element 3 is actually abnormal, it is required to leave a certain time interval until the main power switch of the main body 101 is turned on next time.

  When the number N of protection circuit operations is detected, it is highly likely that some hardware configuration has failed. The engine controller 126 determines that there is a very high possibility that the fixing circuit unit composed of the relay 41 and the triac 4 has failed, notifies the user of an abnormally high temperature, and notifies the fixing circuit unit failure. In addition, since it is estimated that the temperature of the heating element 3 is actually abnormal, a request is made to prohibit the main power switch of the main body 101 from being turned on next time, and a service call is requested. In addition, when using online, a service call may be automatically sent to the manufacturer service department.

  According to the present embodiment, in addition to the same effects as in the first embodiment, by notifying the user of the failure status corresponding to the number of operation of the protection circuit, it is possible to identify the defective portion and promote appropriate measures by the user. Therefore, usability can be further improved.

  It should be noted that the above embodiments can be applied in combination with each other as much as possible.

  DESCRIPTION OF SYMBOLS 1 ... Commercial AC power source, 3 ... Heat generating body formed on ceramic heater, 4 ... Triac, 27 ... Current detection circuit, 41 ... Relay, 101 ... Laser beam printer main body, 109 ... Fixing device, 126 ... Engine controller, 134 ... Ceramic heater, 135 ... Temperature detection element (thermistor), 137 ... Over temperature rise prevention means (thermo switch)

Claims (11)

An image forming unit for forming a developer image on a recording material;
A fixing unit that has a heating element that generates heat by electric power supplied from a commercial AC power source, and heats the developer image to fix it on a recording material;
Temperature detecting means for detecting the temperature of the heating element;
Power control means for controlling power supply from a commercial AC power source to the heating element;
When the detected temperature detected by the temperature detection means is equal to or higher than a first threshold, first power supply cutoff means for cutting off power supply from a commercial AC power source to the heating element;
In an image forming apparatus comprising:
The power control means maintains the subsequent power supply in a cut-off state when the number of times that the power supply is cut off by the first power supply cut-off means exceeds a predetermined number of times. apparatus. The power supply from the commercial AC power supply to the image forming apparatus is maintained in a normal power state in which all the apparatus configurations can operate, at least the power control unit is operable, and at least the first power supply cutoff unit is An image forming apparatus that can be switched between a power saving state in which operation cannot be performed,
When the detected temperature is equal to or higher than a second threshold value that is higher than the first threshold value, the apparatus further comprises second power supply cutoff means for cutting off the power supply.
The predetermined number of times is equal to the normal value every time the power supply is cut off by the first power cut-off means until the power control means is in a state of maintaining the power supply in the cut-off state. The number of times that the detected temperature does not reach the second threshold value even when switching from the power state to the power saving state is performed. Image forming apparatus.   The image forming apparatus according to claim 2, wherein the second power supply cutoff unit is a fuse that is disconnected when the detected temperature becomes equal to or higher than the second threshold value.   4. The image forming apparatus according to claim 2, wherein the cutoff state by the first power supply cutoff unit is maintained until the normal power state is switched to the power saving state. 5.   5. The image forming apparatus according to claim 2, wherein the shut-off state by the power control unit is maintained until the connection between the apparatus and the commercial AC power supply is cut off.   Non-volatile storage means capable of continuously storing the number of times the power supply is cut off by the first power supply cutoff means in both the normal power state and the power saving state. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. Current detecting means for detecting a current flowing through the heating element;
When the detected current value detected by the current detection means is equal to or greater than a third threshold, third power supply cutoff means for cutting off the power supply;
Further comprising
When the total of the number of times of the interruption state by the first power supply interruption means and the number of times of the interruption state by the third power supply interruption means exceeds the predetermined number of times, the power control means The image forming apparatus according to claim 2, wherein the power supply is maintained in a cut-off state. A first latch circuit for latching the interruption state by the first power supply interruption means;
The image forming apparatus according to claim 7, further comprising: a second latch circuit for latching the cutoff state by the third power feeding cutoff unit.   The power control means is configured such that a predetermined interval period elapses from a time point when the normal power state is switched to the power saving state after the power supply is turned off by the first power supply cutoff means. The image forming apparatus according to claim 2, wherein the power supply is maintained in a cut-off state until the image forming operation is performed.   The image forming apparatus according to claim 9, wherein the predetermined interval period becomes longer as the number of times the power supply is turned off by the first power supply cutoff unit increases. When the power supply is cut off by the first power supply cut-off means, the apparatus further comprises notification means for notifying a user of information relating to the state of the apparatus,
The said notification means changes the content of the said information to alert | report according to the frequency | count that the said electric power supply was made into the interruption | blocking state by the said 1st electric power feeding interruption | blocking means, The any one of Claims 1-10 characterized by the above-mentioned. The image forming apparatus described in the item.

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