JP6341104B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for coping with a power supply abnormality of a heating apparatus for fixing an image formed on a sheet by heat.

  2. Description of the Related Art Conventionally, there is an image forming apparatus that generates a zero cross signal synchronized with the zero cross timing of an AC power source and controls the energization time of a heater based on the generated zero cross signal (for example, Patent Document 1). In this image forming apparatus, the triac is used for controlling the energization time of the heater. However, in the case of a power supply abnormality, for example, when a square wave AC voltage is input instead of a sine wave AC voltage, the AC voltage If the voltage change rate (dv / dt) at the zero cross point exceeds the allowable characteristic value of the triac, there is a possibility that the triac cannot be turned off. If the heater is continuously energized without being able to turn off the triac, a failure may occur. Further, when an AC voltage having a large voltage change rate is input, it becomes difficult for the image forming apparatus to generate a zero cross signal synchronized with the zero cross timing and to control energization based on the generated zero cross signal. For this reason, in the image forming apparatus disclosed in Patent Document 1, energization of the heater is interrupted when a rectangular wave AC voltage is input.

JP 2011-113807 A

  By the way, in an inexpensive uninterruptible power supply (UPS), for example, the waveform of the generated AC voltage may be closer to a rectangular wave than a sine wave. In an image forming apparatus connected to such a UPS, when an instantaneous interruption of the commercial power supply occurs, the power supply is switched to the UPS, and a rectangular wave AC voltage is temporarily input. In this case, in the image forming apparatus described above, when it is determined that the input voltage is a rectangular wave based on the voltage change rate, the printing operation is stopped.

  However, some of the input voltages that are determined to be rectangular waves, such as the AC voltage output from the UPS, actually operate effectively with the TRIAC OFF control without causing the TRIAC to fail. There is a possibility that the printing operation can be continued. Therefore, stopping the printing operation until such a triac operates effectively leads to a decrease in productivity.

  The technology disclosed in the present application has been proposed in view of the above problems. An object of the present invention is to provide an image forming apparatus capable of maintaining a continuation of operation without stopping as much as possible when a power supply abnormality occurs.

  In order to solve the above problems, an image forming apparatus of the present invention includes a heater connected to an AC power supply, a temperature detection sensor that detects the temperature of the heater, a changeover switch provided between the AC power supply and the heater, An energization time adjustment element provided between the AC power source and the heater, a zero cross signal generation circuit that generates a zero cross signal synchronized with the zero cross timing of the AC voltage from the AC power source, and a control device, the control device, The adjustment process for adjusting the energization time from the AC power supply to the heater by adjusting the ON period of the energization time adjustment element based on the zero-cross signal, and whether the voltage change rate of the AC voltage at the zero-cross timing is greater than or equal to the allowable value In response to determining that the voltage change rate is greater than or equal to an allowable value in the first determination process and the first determination process. In response to an upper limit temperature reduction process for lowering the upper limit temperature for determining propriety from the first upper limit temperature to the second upper limit temperature, and the detected temperature of the heater detected by the temperature detection sensor being equal to or higher than the second upper limit temperature. And an energization stop process for controlling energization from the AC power source to the heater by controlling the changeover switch.

  In the image forming apparatus, when it is determined that the voltage change rate is equal to or higher than an allowable value, the upper limit temperature used for determining whether or not to operate the heater is changed from the first upper limit temperature to the first upper limit temperature. The temperature is lowered to the second upper limit temperature which is lower than that of. In the image forming apparatus, for example, when a rectangular wave AC voltage is input and the off-control of the energizing time adjusting element (for example, triac) does not function and the heater temperature rises, the upper limit temperature is set low. Thus, the temperature detected by the temperature detection sensor easily exceeds the upper limit temperature. Therefore, the image forming apparatus can stop the heater at a safer stage as compared with the case where the operation is continued with the first upper limit temperature before the change. Further, in the conventional image forming apparatus, when the voltage change rate exceeds an allowable value, the operation is immediately stopped. On the other hand, in the image forming apparatus, since the printing operation is continued while lowering the upper limit temperature and ensuring safety, the alternating current in which the off-control of the energization time adjusting element functions effectively is not a normal sine wave alternating voltage. When the voltage is input, the printing operation is continued without stopping the activation, and the productivity of the printing process can be improved.

  In the image forming apparatus of the present invention, an image forming unit that forms an image on a recording medium based on image data, and a fixing roller that is heated by a heater and fixes the image formed by the image forming unit on the recording medium The control device may be configured to execute a target temperature reduction process for reducing the print target temperature when the fixing roller is heated by the heater in response to determining that the voltage change rate is equal to or greater than an allowable value. Good.

  In the image forming apparatus, a print target temperature is set and the fixing roller is heated to the print target temperature. When the print target temperature is higher than the second upper limit temperature after the upper limit temperature reduction process, when the heater is heated to the print target temperature after the upper limit temperature reduction process, the temperature detected by the temperature detection sensor exceeds the second upper limit temperature. The energization operation to the heater is stopped. For this reason, in the image forming apparatus, it is possible to prevent the above-described problem from occurring by lowering the print target temperature in accordance with the lowering of the upper limit temperature.

  In the image forming apparatus of the present invention, an image forming unit that forms an image on a recording medium based on image data, and a fixing roller that is heated by a heater and fixes the image formed by the image forming unit on the recording medium And the control device executes a sheet passing speed reduction process for reducing the sheet passing speed of the fixing roller that transports the recording medium in response to determining that the voltage change rate is equal to or greater than an allowable value. Also good.

  A part of the heat amount of the fixing roller heated by the heater is taken when the image is fixed on the recording medium. For this reason, the amount of heat taken by the fixing roller increases as the number of recording media to be printed per unit time increases. Therefore, in the image forming apparatus, the printing operation is continued even when the upper limit temperature and the print target temperature are lowered by slowing the sheet passing speed and reducing the amount of heat consumed per unit time compared to the normal control. It becomes possible.

  Further, in the image forming apparatus of the present invention, the control device, prior to the sheet passing speed reduction process, in response to the detection temperature of the temperature detection sensor being equal to or higher than the temperature upper limit lower than the second upper limit temperature by a predetermined temperature A configuration may be adopted in which a heater cooling process for controlling the changeover switch to temporarily stop energization of the heater and lower the temperature of the heater is executed.

  When the printing operation is started at a lower paper feeding speed, if the detected temperature is already equal to or higher than the second upper limit temperature or equal to or higher than the temperature upper limit close to the second upper limit temperature, the detected temperature is increased when printing is started. Immediately after the second upper limit temperature is exceeded, the energization operation to the heater is stopped. For this reason, in the image forming apparatus, first, when the detected temperature is equal to or higher than the temperature upper limit lower than the second upper limit temperature by a predetermined temperature, the energization is temporarily stopped to cool the heater, and then the change is made. By performing the printing operation at the sheet passing speed, it is possible to prevent the occurrence of the above-described problems.

  In the image forming apparatus of the present invention, the control device may be configured to execute the upper limit temperature reduction process in response to the detected temperature of the temperature detection sensor being equal to or lower than the second upper limit temperature.

  In the image forming apparatus, since the upper limit temperature reduction process is not executed unless the temperature detected by the temperature detection sensor is equal to or lower than the second upper limit temperature, there is a situation in which the detected temperature exceeds the second upper limit temperature immediately after the upper limit temperature is changed. It becomes possible to prevent more reliably.

  Further, in the image forming apparatus of the present invention, the control device decreases the sheet passing speed by the sheet passing speed reduction process, and then the energization stop process is performed in response to the detected temperature of the temperature detection sensor being equal to or higher than the second upper limit temperature. It is good also as a structure which performs.

  In the image forming apparatus, if the detected temperature exceeds the second upper limit temperature even when the printing operation is performed with the sheet passing speed reduced and the amount of heat consumed per unit time being reduced, the energization time adjusting element Since there is a high possibility that a failure or continuous power failure has occurred, the heater is turned off to ensure safety.

  In the image forming apparatus of the present invention, the control device controls the changeover switch to stop energizing the heater in response to determining that the voltage change rate is equal to or greater than the allowable value during the printing operation. A configuration may be adopted in which the paper passing speed reduction process is executed after the recording medium being printed is discharged.

  For example, if the sheet passing speed is changed while the recording medium is being conveyed by the fixing roller, unevenness or the like may occur in the image being printed. Therefore, when the image forming apparatus determines that the voltage change rate is equal to or higher than the allowable value during the printing operation, the energization to the heater is stopped. The image forming apparatus fixes the image to the recording medium being printed by residual heat, discharges the recording medium after fixing, and then slows the sheet passing speed. Thereby, it is possible to prevent image unevenness and the like.

  In the image forming apparatus of the present invention, the control device may be configured to determine the voltage change rate based on the pulse width of the zero cross signal in the first determination process.

  In the image forming apparatus, by determining the voltage change rate based on the pulse width of the zero-cross signal, for example, when the pulse width is equal to or less than a predetermined width, the case where an AC voltage of a rectangular wave is input from the AC power supply It becomes possible to detect. Further, for example, in the method of determining the voltage change rate based on the cycle of the zero cross signal, the cycle is measured from the input interval of the pulse signal. Therefore, the voltage change rate cannot be determined unless at least two pulse signals are input. On the other hand, in the image forming apparatus, since the voltage change rate is determined based on the pulse width, it is possible to determine from one pulse signal, and it is possible to perform a quicker determination as compared with the determination based on the period.

  In the image forming apparatus of the present invention, the control device detects the pulse width of the zero cross signal in the first determination process in the first pulse width comparison process for comparing the pulse width with the first threshold value and in the first pulse width comparison process. A second pulse width comparison process that compares the pulse width of the zero-cross signal with a second threshold value that is smaller than the first threshold value in response to the reduced pulse width being smaller than the first threshold value. Also good.

  In the image forming apparatus, the voltage change rate is determined based on the pulse width of the zero cross signal. For example, when a direct current (DC) voltage is input from an AC power source due to some abnormality, the zero cross timing does not occur, and the zero cross signal is generated. No pulse width is detected. Therefore, in the image forming apparatus, it is first determined based on the first threshold value whether or not the AC voltage input from the AC power source is an AC voltage to continue the operation. Since the above-described DC voltage is included in the AC voltage that is determined to have a pulse width smaller than the first threshold value, the image forming apparatus determines the pulse width using the smaller second threshold value. To do. As a result, in the image forming apparatus, for example, when the pulse width is smaller than the second threshold, it is possible to perform the energization stop process as a power supply abnormality without performing the determination to continue the operation, It is possible to quickly deal with an abnormal input such as a DC voltage that does not cause zero crossing.

  In the image forming apparatus of the present invention, the control device sets abnormality information indicating a temperature abnormality when the temperature detected by the temperature detection sensor exceeds at least one of the first upper limit temperature and the second upper limit temperature. An abnormality information setting process to be performed and a failure determination process to determine whether the energization time adjustment element is normal or not according to the fact that the abnormality information is set at the time of activation may be configured.

  When the energization stop process is performed when the detected temperature exceeds at least one of the first upper limit temperature and the second upper limit temperature, the energization time adjustment element may be broken due to a short circuit or the like. Therefore, in the image forming apparatus, when abnormality information is set at the time of activation and it is detected that an abnormal end has occurred during the previous operation, it is determined whether the energization time adjustment element has already failed. As a result, for example, when it is determined that a failure has occurred, it is possible to perform appropriate processing such as notifying the user of an error without starting the printing operation.

  In the image forming apparatus of the present invention, the control device permits the voltage change rate in the second determination process for determining whether the voltage change rate of the AC voltage at the zero-cross timing is equal to or less than the allowable value, and in the second determination process. In response to the determination that the value is equal to or less than the value, a return process that restores the setting changed according to the determination result of the first determination process may be executed.

  In the image forming apparatus, when it is determined that the voltage change rate is less than the allowable value and the power supply has returned to the normal state, the changed settings (upper limit temperature, print target temperature, sheet passing speed, etc.) are restored to normal operation. It becomes possible to start.

  In the image forming apparatus and the like described in the present invention, when a power supply abnormality occurs, it is possible to maintain a continuous operation state without stopping as much as possible.

It is sectional drawing of the laser printer which concerns on one Embodiment of this invention. It is a block diagram which shows the schematic structure of a heating apparatus. It is a circuit diagram of a fixing drive circuit. It is a time chart of the signal concerning energization control. It is a flowchart for demonstrating energization control processing. It is a flowchart for demonstrating energization control processing. 6 is a flowchart for explaining fixing drive circuit failure determination processing. It is a flowchart for demonstrating rectangular wave detection control. It is a figure which shows the relationship between the various setting temperature which concerns on normal control and rectangular wave detection control. It is a time chart which shows the relationship between the input voltage in the case of becoming an error state, and a zero cross pulse signal. It is a time chart which shows the relationship between input electric power in the case of becoming an error state, and a zero cross pulse signal. It is a time chart which shows the relationship between input electric power in the case of transfering to rectangular wave detection control, and a zero cross pulse signal. It is a flowchart for demonstrating the electricity supply control process of another example.

  Hereinafter, an embodiment of the present application will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a monochrome laser printer 1 which is an embodiment of an image forming apparatus according to the present application. A monochrome laser printer (hereinafter simply referred to as a “printer”) 1 uses a toner image formed in an image forming unit 5 on a sheet (paper, OHP sheet, etc.) supplied from a tray 4 disposed in a lower part of a main body casing 2. After the toner image is formed, the toner image is heated by the fixing device 7 to perform fixing processing, and finally the sheet is discharged to a paper discharge tray 9 located at the upper portion of the main body casing 2. In FIG. 1, the right side of the page is defined as the front side of the device, and when the device is viewed from the front side, the side that comes to the left hand (the front side of the page) is defined as the left side. To do.

  The image forming unit 5 includes a scanner unit 11, a developing cartridge 13, a photosensitive drum 17, a charger 18, a transfer roller 19, and the like. The scanner unit 11 is disposed in the upper part of the main body casing 2, and laser light emitted from a laser light emitting unit (not shown) is applied to the surface of the photosensitive drum 17 via a polygon mirror, a reflecting mirror, a lens, and the like. Irradiate with high-speed scanning.

  The developing cartridge 13 is configured to be detachable from the main body of the printer 1, and contains toner therein. Further, a developing roller 21 and a supply roller 23 are provided at the toner supply port of the developing cartridge 13 so as to face each other in the front-rear direction. The developing roller 21 is disposed in a state of facing the photosensitive drum 17 in the front-rear direction. The toner in the developing cartridge 13 is supplied to the developing roller 21 by the rotation of the supply roller 23 and is carried on the developing roller 21.

  Above the rear side of the photosensitive drum 17, a charger 18 is disposed at an interval. A transfer roller 19 is disposed below the photosensitive drum 17 so as to face the photosensitive drum 17. The surface of the photosensitive drum 17 is uniformly charged by the charger 18 to, for example, positive polarity while rotating. Next, an electrostatic latent image is formed on the surface of the photosensitive drum 17 by the laser light from the scanner unit 11. Thereafter, the toner carried on the developing roller 21 rotating in contact with the photosensitive drum 17 is supplied to and carried on the electrostatic latent image on the surface of the photosensitive drum 17, thereby causing the toner on the surface of the photosensitive drum 17 to be carried. A toner image is formed. The formed toner image is transferred to the sheet by a transfer bias applied to the transfer roller 19 while the sheet passes between the photosensitive drum 17 and the transfer roller 19.

  The fixing device 7 is disposed downstream of the image forming unit 5 in the sheet conveyance direction (rear side in the printer 1), and includes a fixing roller 27, a pressure roller 29 that presses the fixing roller 27, and the fixing roller 27. Including a halogen heater 31 and the like. The fixing roller 27 rotates in accordance with the driving of the electric motor 28 controlled by the control unit 33 shown in FIG. 2, and applies a conveying force to the sheet while heating the toner transferred to the sheet. On the other hand, the pressure roller 29 is driven to rotate while pressing the sheet toward the fixing roller 27. Therefore, the control unit 33 can control the sheet passing speed at which the sheet of the fixing device 7 (the fixing roller 27 and the pressure roller 29) is conveyed by controlling the electric motor 28. The halogen heater 31 is energized and controlled by the controller 33 of the heating device 30 shown in FIG.

  FIG. 2 is a block diagram illustrating a schematic configuration of the heating device 30. The heating device 30 includes a halogen heater 31, a control unit 33, a low voltage power supply circuit (AC-DC converter) 35, a zero cross generation circuit 37, a fixing drive circuit 41, a fixing relay 39, and the like.

  The halogen heater 31 generates heat in response to energization of the AC power source 101. The temperature sensor 31A provided in the vicinity of the halogen heater 31 outputs the detected temperature of the halogen heater 31 to the control unit 33 as a temperature detection signal Sa. For example, the low-voltage power supply circuit 35 converts an AC voltage of 100 V into a DC voltage of 24 V and 3.3 V, and supplies the DC voltage to each unit including the control unit 33.

  The zero-cross generation circuit 37 includes a full-wave rectification bridge circuit 51 that full-wave rectifies the input voltage V supplied from the AC power supply 101, a light-emitting diode 53 connected to the full-wave rectification bridge circuit 51, and a photocoupler 55 together with the light-emitting diode 53. A phototransistor 57, a resistor R2, an inverter 59, and the like are included. The input voltage V of the AC power supply 101 is input to the full-wave rectification bridge circuit 51 via the resistor R1. A voltage that has been full-wave rectified by the full-wave rectification bridge circuit 51 is applied to the light emitting diode 53.

  The phototransistor 57 has an emitter connected to the ground and a collector connected to the DC power supply line Vcc via the resistor R2. The inverter 59 is connected to the collector of the phototransistor 57 and inverts and outputs the voltage level (High / Low) of the collector. In the zero-cross generation circuit 37 having such a configuration, when the input voltage V of the AC power supply 101 decreases, the light emission amount of the light emitting diode 53 decreases, and the current Ic flowing through the phototransistor 57 decreases. The input voltage Vin of the inverter 59 increases as the current Ic decreases. Therefore, for example, as shown in FIG. 4, when the absolute value of the input voltage V of the AC power supply 101 falls below the threshold value Vt, the input voltage Vin becomes high level, and the zero cross pulse signal Sr that is the output signal of the inverter 59 becomes low level. It becomes.

  On the other hand, when the input voltage V of the AC power supply 101 increases, the light emission amount of the light emitting diode 53 increases and the current Ic flowing through the phototransistor 57 also increases. As the current Ic increases, the input voltage Vin of the inverter 59 decreases. Therefore, for example, as shown in FIG. 4, when the absolute value of the input voltage V of the AC power supply 101 exceeds the threshold value Vt, the input voltage Vin becomes low level, and the zero cross pulse signal Sr becomes high level. Therefore, the zero-cross generation circuit 37 outputs the low-level zero-cross pulse signal Sr only during the period (pulse width K1) in which the input voltage V of the AC power supply 101 is in the zero-cross detection range U defined by positive and negative Vt. .

  Further, as shown in FIG. 2, the zero cross pulse signal Sr output from the zero cross generation circuit 37 is input to the control unit 33. Therefore, the control unit 33 can detect the rising and falling edges of the zero cross pulse signal Sr by determining the voltage level of the zero cross pulse signal Sr. For example, the control unit 33 may be configured mainly by a program operating on the CPU. Alternatively, the control unit 33 may be configured by dedicated hardware such as ASIC, for example. In addition, the control unit 33 may be configured to operate using, for example, software processing and hardware processing together. The control unit 33 includes a memory 33A for storing information related to control and processing such as RAM, ROM, and flash memory.

  The controller 33 adjusts the energization time of the input voltage V to the halogen heater 31 using the zero cross pulse signal Sr. Specifically, the control unit 33 generates the trigger pulse signal Sb corresponding to the zero cross point ZC (see FIG. 4) by using the falling timing of the zero cross pulse signal Sr as a reference. The control unit 33 outputs the generated trigger pulse signal Sb to the fixing drive circuit 41. As shown in FIG. 3, the fixing drive circuit 41 includes a triac 43, a phototriac coupler 45, a drive transistor 47, and the like. The drive transistor 47 turns on / off the phototriac coupler 45 in accordance with the trigger pulse signal Sb input from the control unit 33. The triac 43 is turned on in response to the phototriac coupler 45 being turned on, and is turned off when a reverse voltage is applied or the current becomes zero. The halogen heater 31 is energized with the input voltage V for a predetermined energization time. The predetermined energization time is from the rising timing of the trigger pulse signal Sb to the zero cross timing of the input voltage V as shown by the heater voltage waveform in FIG. The control unit 33 controls the temperature of the halogen heater 31 by changing the period Tw (see FIG. 4) from the falling timing of the zero cross pulse signal Sr to the rising timing of the trigger pulse signal Sb.

  As shown in FIG. 2, the fixing relay 39 is connected between the input voltage V and the halogen heater 31. The controller 33 controls on / off of the fixing relay 39 to turn on / off the input voltage V to the halogen heater 31. For example, when the input voltage V having a steep voltage change rate (dv / dt) such as a rectangular wave is input, the control unit 33 turns off the fixing relay 39 and supplies power to the halogen heater 31 and the triac 43. Stop supplying. The fixing relay 39 is, for example, a semiconductor switch such as a transistor or a mechanical switch such as a relay.

  The control unit 33 determines the detected temperature based on the temperature detection signal Sa output from the temperature sensor 31A provided in the halogen heater 31, and controls the temperature by, for example, controlling the energization time for the halogen heater 31 based on the phase. Adjust. The control based on this phase is not to manage the energization time of the halogen heater 31 by the wave number, but to control by the conduction phase angle (also called the ignition angle) α. The conduction phase angle α is a phase at which conduction of the triac 43 is started. The method for controlling the energization time of the halogen heater 31 is not limited to the control by the phase, and wave number control managed in units of the wave number of the input voltage V may be performed.

  Next, energization control of the halogen heater 31 by the control unit 33 will be described with reference to FIGS. For example, when the power of the printer 1 is turned on by the user, or when the printer 33 returns from the sleep mode in which it waits for an operation from the user or reception of print data, the control unit 33 sets the halogen heater 31 according to a predetermined program. Start energization control. For example, the predetermined program is stored in the ROM of the memory 33A (see FIG. 2).

  First, in step (hereinafter, simply referred to as “S”) 11 in FIG. 5, the control unit 33 determines whether or not it has been terminated due to an abnormality at the previous activation. The abnormal end mentioned here means a state in which the operation is ended, for example, when the high temperature of the halogen heater 31 is detected by the temperature detection signal Sa of the temperature sensor 31A or when the triac 43 becomes uncontrollable. In the case of abnormal termination, the control unit 33 sets a flag indicating abnormality in S77 of FIG. And the control part 33 can determine whether it ended abnormally by detecting whether this flag is set at the time of starting.

  When it is determined that the control unit 33 has ended abnormally (S11: YES), the control unit 33 executes a failure determination process for the fixing drive circuit 41 (S13). As shown in FIG. 7, when the failure determination process is started, the control unit 33 first determines whether the temperature detected by the temperature sensor 31A exceeds the upper limit temperature B (S51).

  FIG. 9 shows the relationship between various set temperatures used during normal control and during rectangular wave detection control described later. The print target temperature shown in FIG. 9 is a target temperature when the halogen heater 31 is heated in the printing operation. The control unit 33 controls the fixing drive circuit 41 so that the temperature detected by the temperature sensor 31A becomes the print target temperature. The upper limit of the normal temperature is an upper limit temperature that may overshoot the target temperature when the halogen heater 31 is heated and controlled so as to reach the print target temperature. The thermostat operating temperature is a set temperature of a temperature fuse (not shown) that is blown when the temperature of the halogen heater 31 exceeds the upper limit of the normal temperature. This thermal fuse is connected between, for example, the halogen heater 31 and the fixing drive circuit 41 or on the gate side of the triac 43, and is blown when the halogen heater 31 is abnormally heated to stop energization. It is. The upper limit temperature is a temperature for determining whether or not to turn off the fixing relay 39 when the halogen heater 31 is abnormally heated due to a failure of the triac 43 or the like. Further, in the printer 1 of the present embodiment, when the input voltage V that may cause a rectangular wave is detected, the rectangular wave detection control that continues the operation while lowering the set temperature is executed. Accordingly, various set temperatures (such as the upper limit temperature B) in the rectangular wave detection control are lower than the set temperatures during normal control. The fixing device melting temperature is a temperature at which a part of the roller portion of the fixing roller 27 and the pressure roller 29 is melted.

  Returning to the description of FIG. 7, for example, when the power is turned on immediately after the previous abnormal end and the temperature of the halogen heater 31 exceeds the upper limit temperature B (upper limit temperature of the rectangular wave detection control) due to residual heat, The temperature of the heater 31 is set to the upper limit temperature B or lower. In S51, when the detected temperature of the temperature sensor 31A exceeds the upper limit temperature B (S51: NO), the control unit 33 temporarily enters a standby state until the detected temperature becomes equal to or lower than the upper limit temperature B (S53). When the detected temperature becomes equal to or lower than the upper limit temperature B, the control unit 33 starts the processes after S52.

  On the other hand, when the temperature detected by the temperature sensor 31A is equal to or lower than the upper limit temperature B (S51: YES), the control unit 33 turns on (connects) the fixing relay 39 (S52), and the temperature of the temperature sensor 31A increases. That is, it is determined whether the temperature of the fixing device 7 is increased (S55). Under normal conditions, when the trigger pulse signal Sb is not supplied to the fixing drive circuit 41 (the fixing device 7 is in the OFF state), the electric power is not supplied to the halogen heater 31 and the temperature rises only by turning on the fixing relay 39. Never do. However, when the fixing relay 39 is turned on, for example, when the triac 43 shown in FIG. 3 has failed and shorted, the halogen heater 31 is turned on regardless of the control of the control unit 33 (whether or not the trigger pulse signal Sb is supplied). The temperature rises. Therefore, the control unit 33 determines that the fixing drive circuit 41 or the like is faulty when the temperature rises only by turning on the fixing relay 39.

  If the detected temperature rises after the fixing relay 39 is turned on (S52) (S55: YES), the control unit 33 determines that the fixing drive circuit 41 is in failure (S57) and ends the failure determination processing. To do. On the other hand, when the detected temperature does not increase (S55: NO), the control unit 33 determines that the fixing drive circuit 41 is normal (S58) and ends the failure determination process.

  Returning to the description of FIG. 5, when the failure determination in S <b> 13 ends, the control unit 33 performs processing according to the result of the failure determination (S <b> 15). When it is determined that the fixing drive circuit 41 is abnormal (S15: YES), the control unit 33 turns off the fixing relay 39, stops input of the input voltage V to the halogen heater 31, and notifies the user of the error. To stop the operation (S43 in FIG. 6). The method of notifying an error to the user can be changed as appropriate. For example, the error content may be displayed on a display unit (not shown) of the printer 1.

  On the other hand, when it is determined that the fixing drive circuit 41 is normal (S15: NO), the control unit 33 uses the first mask Zmk1 (FIG. 10) as a zero cross pulse width mask (hereinafter sometimes simply referred to as “mask”). (See) is set (S17), and the zero cross pulse signal Sr detection process is started. Here, the “zero cross pulse width mask” is a value for determining whether or not the pulse width K1 of the zero cross pulse signal Sr shown in FIG. 4 is normal.

  Here, when an abnormal input voltage V, for example, a rectangular wave input voltage V, is input, the voltage change rate (dv / dt) of the input voltage V increases. When the voltage change rate of the input voltage V becomes large (the slope of the waveform is steep), the pulse width K1 of the zero-cross pulse signal Sr output from the zero-cross generation circuit 37 becomes extremely short or zero. In this case, the control unit 33 cannot accurately detect the falling timing of the zero cross pulse signal Sr based on the zero cross pulse signal Sr.

  Therefore, the control unit 33 determines whether or not an abnormal input voltage V such as a rectangular wave has been input, for example, a pulse width K1 that is a time from the falling edge to the rising edge of the zero cross pulse signal Sr is a predetermined width (first mask). It is determined by whether or not it is less than Zmk1). When it is determined that the pulse width K1 is less than the first mask Zmk1, the control unit 33 determines that an abnormal input voltage V may have been input.

  In S11 of FIG. 5, if the control unit 33 determines that the previous abnormal termination has not occurred (S11: NO), the fixing relay 39 is turned on (S14), and the first mask Zmk1 is set (S17). ).

  Next, after setting the first mask Zmk1 (for example, 100 μs) as the mask value in S17, the control unit 33 determines that the zero cross pulse signal Sr falls, that is, the zero cross pulse signal Sr becomes low level. As an opportunity, the time during which the zero cross pulse signal Sr is at a low level is counted, and whether or not the pulse width K1 is less than the first mask Zmk1, that is, whether or not the count value is less than the first mask Zmk1. Determine (S23). When the period count of the first mask Zmk1 continues and it is determined that the pulse width K1 is not less than the first mask Zmk1 (S23: NO), the control unit 33 has the pulse width K1 greater than or equal to the mask upper limit value Zmkmax (for example, 200 μs). It is determined whether or not the count is continued for the period of the mask upper limit Zmkmax (S25).

  If the pulse width K1 is equal to or larger than the first mask Zmk1, it is considered that the input is normal. For example, if the pulse width K1 is too large compared to the first mask Zmk1, that is, the voltage change rate is too small. Is also envisaged. FIG. 10 shows a time chart when the voltage change rate of the input voltage V decreases from the normal state. As shown in FIG. 10, when the voltage change rate of the input voltage V is normal, the pulse width K1 is within the range between the first mask Zmk1 and the mask upper limit value Zmkmax (timing T0 in FIG. 10). ). However, when the voltage change rate of the input voltage V decreases, the pulse width K1 becomes larger than the mask upper limit value Zmkmax (timing T1 in FIG. 10). In this case, the controller 33 may not be able to generate an appropriate trigger pulse signal Sb based on the zero cross pulse signal Sr. As a result, the temperature of the halogen heater 31 may not be properly controlled. Therefore, when it is determined that the count continues for the period of the mask upper limit value Zmkmax and the pulse width K1 has become equal to or larger than the mask upper limit value Zmkmax (S25: YES), the control unit 33 performs error stop (FIG. 6). S43, timing T1 in FIG. On the other hand, when the control unit 33 determines that the zero-cross pulse signal Sr rises to a high level before the period of the mask upper limit value Zmkmax elapses and the count ends, and the pulse width K1 does not become the mask upper limit value Zmkmax or more. (S25: NO), the normal control (printing process etc.) is continued (S27), and the processing from S23 is executed again. In the example shown in FIG. 10, the controller 33 immediately performs error processing when the control unit 33 determines that the pulse width K1 is equal to or larger than the mask upper limit value Zmkmax. Then, error processing may be performed after continuously determining that the pulse width K1 is equal to or greater than the mask upper limit value Zmkmax. Further, the controller 33 may perform error processing after repeatedly determining for a predetermined time that the pulse width K1 is equal to or greater than the mask upper limit value Zmkmax.

  Further, when it is determined in S23 that the zero cross pulse signal Sr rises and becomes a high level before the period of the first mask Zmk1 elapses and the count ends, and the pulse width K1 is determined to be less than the first mask Zmk1 (S23). : YES), the control unit 33 ignores the low-level zero-cross pulse signal Sr that is the target of counting of the pulse width K1, ignores it, and continues the processing after the next S31 (S29). Here, “not to be processed” means, for example, that when the process of S23 is performed again after the process of S31 described later, it is not to be compared with the first mask Zmk1. That is, when S23 is performed again, the next pulse and later are targeted. Further, the control unit 33 determines whether or not the pulse width K1 is continuously determined for a predetermined time (for example, several hundreds of milliseconds) when the pulse width K1 is less than the first mask Zmk1 (S31). Note that the processing in S31 may not be based on the duration time, and for example, it may be determined whether the pulse width K1 is repeatedly determined repeatedly for a plurality of times that the pulse width K1 is less than the first mask Zmk1. In S31, the control unit 33 does not repeatedly determine that the pulse width K1 is less than the first mask Zmk1 for a predetermined time, that is, the predetermined time has elapsed if the pulse width K1 is greater than or equal to the first mask Zmk1. If it is determined before performing (S31: NO), the processing from S23 is executed again.

  For example, when the input voltage V of a rectangular wave is input and the control unit 33 repeatedly determines that the pulse width K1 is less than the first mask Zmk1 for a predetermined time (S31: YES), the control unit 33 uses the first as a mask. A second mask Zmk2 (for example, 10 μs) having a smaller width (shorter time) than the mask Zmk1 is set (S33 in FIG. 6). FIG. 11 shows a time chart when an input voltage V that is less than the second mask Zmk2 is input. As shown in FIG. 11, after timing T3 when the input voltage V becomes a rectangular wave, the control unit 33 continuously repeats for a predetermined time from timing T3 to timing T4 when the pulse width K1 is less than the first mask Zmk1. When it is determined, at timing T4, the mask is changed from the first mask Zmk1 to the second mask Zmk2. The control unit 33 determines whether the pulse width K1 is less than the second mask Zmk2, that is, whether the count value is less than the second mask Zmk2 (S37). When the zero-cross pulse signal Sr rises and becomes high level before the period of the second mask Zmk2 elapses and the count ends, and it is determined that the pulse width K1 is less than the second mask Zmk2 (S37: YES), the pulse A process of ignoring the low-level zero-cross pulse signal Sr that is the count target of the width K1 is performed (S39), and the control unit 33 continuously and repeatedly determines that the pulse width K1 is less than the second mask Zmk2. It is determined whether or not (S41). It may be determined whether the pulse width K1 is less than the second mask Zmk2 and whether or not the determination is continuously repeated a plurality of times.

  If the control unit 33 determines in S41 that the pulse width K1 is less than the second mask Zmk2 and has not repeatedly determined for a predetermined time (S41: NO), it executes the processing from S37 again. On the other hand, when the control unit 33 determines in S41 that the pulse width K1 is less than the second mask Zmk2 and continuously determines for a predetermined time (S41: YES), the control unit 33 performs error stop (S43, FIG. 11). Timing T5). Here, the case where the pulse width K1 is repeatedly determined to be continuously less than the second mask Zmk2 smaller than the first mask Zmk1 for a predetermined time is, as shown in FIG. 11, a pulse width K1 like a rectangular wave. Is extremely short or becomes zero, and the input of the input voltage V in which the pulse width K1 becomes shorter than the second mask Zmk2 is continued for a predetermined time from timing T4 to timing T5. Alternatively, for example, a case where a direct current (DC) input voltage V is input due to some abnormality of the AC power supply 101 and the zero cross pulse signal Sr cannot be detected for a predetermined time. Such an abnormal input voltage V cannot be used for energization control, and it is necessary to immediately stop the supply of the input voltage V to the halogen heater 31. Therefore, processing of rectangular wave detection control (see FIG. 8) described later is performed. The control unit 33 stops the error without setting the target.

  On the other hand, in S37, the control unit 33 determines that the period count of the second mask Zmk2 continues and the pulse width K1 is not less than the second mask Zmk2, that is, second mask Zmk2 ≦ pulse width K1 <first mask Zmk1. If it is determined (S37: NO), rectangular wave detection control is executed (S45). FIG. 12 shows a time chart when the input voltage V satisfying the second mask Zmk2 ≦ pulse width K1 <first mask Zmk1 is input. As shown in FIG. 12, after timing T7 when the input voltage V becomes a rectangular wave, the controller 33 continuously repeats for a predetermined time from timing T7 to timing T8 when the pulse width K1 is less than the first mask Zmk1. If determined, the mask is changed from the first mask Zmk1 to the second mask Zmk2 (timing T8). Thereafter, when the second mask Zmk2 ≦ pulse width K1 <first mask Zmk1, the control unit 33 shifts from the normal mode to the rectangular wave detection control mode (timing T9). In the control unit 33 of the present embodiment, when the second mask Zmk2 ≦ pulse width K1 <the first mask Zmk1, it is assumed that the off control of the triac 43 operates effectively and is set to continue the printing operation. For this reason, the set value of the second mask Zmk2 can be set, for example, based on the allowable range of the voltage change rate at which the used triac 43 operates effectively.

  As shown in FIG. 8, in the rectangular wave detection control, the control unit 33 first determines whether or not a printing operation is being performed (S61). When the printing operation is being performed (S61: YES), the control unit 33 turns off the fixing relay 39, stops the supply of the trigger pulse signal Sb to the fixing driving circuit 41 (fixing unit 7 OFF), and also performs printing. Printing of only the sheet is completed (S65). The control unit 33 rotates the fixing roller 27 of the fixing device 7 to heat and melt the toner transferred to the sheet with residual heat to fix the toner on the sheet, and to convey the sheet to the downstream side of the conveyance path and from the discharge tray 9. Discharge.

  The controller 33 compares the detected temperature of the temperature sensor 31A with the normal temperature upper limit B after discharging the sheet being printed (S65) or when the printing operation is not being performed (S61: NO) (S63). . In the control unit 33 of the present embodiment, when it is determined that the pulse width K1 falls within the predetermined mask value range, it is possible that the printing operation can be continued. In addition, the sheet feeding speed of the fixing device 7 is lowered to continue the printing operation. This is because the heat amount of the fixing device 7 taken by the sheet per unit time can be reduced by reducing the sheet passing speed, and the heat amount (temperature) necessary for the fixing device 7 can be suppressed. It is.

  As shown in FIG. 9, various set temperatures (normal temperature upper limit B etc.) in the rectangular wave detection control are lower than the set temperatures during normal control. The control unit 33 lowers various set temperatures in the next S67 described later. Prior to that, first, it is necessary to determine whether the current temperature is equal to or lower than the changed normal temperature upper limit B. This is because if the normal temperature upper limit B is exceeded at the time of the change, if the halogen heater 31 is heated, the detected temperature will immediately exceed the upper limit temperature B, resulting in an error stop. . For this reason, when the control unit 33 determines in S63 that the current detected temperature exceeds the changed normal temperature upper limit B (S63: NO), the fixing relay 39 is turned off, and the detected temperature is set to the normal temperature upper limit. It waits temporarily until it becomes below B (S69). When the detected temperature becomes equal to or lower than the upper limit temperature B, the control unit 33 starts the processes after S67.

  In addition, when the control unit 33 determines that the detected temperature is equal to or lower than the normal temperature upper limit B (S63: YES), the control unit 33 controls the electric motor 28 (see FIG. 2) to reduce the sheet passing speed and various set temperatures. The control for lowering A from B to A is executed (S67). For example, the control unit 33 reduces the conveyance speed for conveying the sheet to half the speed during normal control. For example, the control unit 33 lowers the upper limit temperature from the upper limit temperature A (230 ° C.) to the upper limit temperature B (185 ° C.). For example, the control unit 33 decreases the print target temperature from the print target temperature A (191 ° C.) to the print target temperature B (150 ° C.). Then, the control unit 33 turns on the fixing relay 39 with the sheet passing speed and various set temperatures lowered (S67). The control unit 33 executes a printing operation when there is a print job or the like. As shown in FIG. 9, in the rectangular wave detection control, since the upper limit temperature B is lower than the fixing device melting temperature, the printing operation is continued while preventing the fixing roller 27 of the fixing device 7 from being melted. It is possible.

  Next, the control unit 33 determines whether the temperature detected by the temperature sensor 31A is equal to or lower than the upper limit temperature B (S71). When the detected temperature is equal to or lower than the upper limit temperature B (S71: YES), the controller 33 counts the pulse width K1 and the period C1 (see FIG. 4) of the zero cross pulse signal Sr (S73). If the control unit 33 determines that at least one of the pulse width K1 and the period C1 is outside the allowable normal range (S75: NO), the control unit 33 continues the rectangular wave detection control (S79), and performs the printing operation while performing S71. The process from is executed again.

  If the controller 33 determines in S71 that the detected temperature exceeds the upper limit temperature B (S71: NO), the controller 33 sets a flag indicating failure (S77) and stops the error (S43 in FIG. 6). ). Specifically, the control unit 33 sets a status indicating a register abnormality, for example. Or the control part 33 may preserve | save the information (bit value) which shows abnormality in the non-volatile memory (flash memory etc.) of the memory 33A (refer FIG. 2). When an abnormality is detected at this time, there are various cases such as an abnormality due to a rectangular wave or a failure of the fixing drive circuit 41. Therefore, the control unit 33 sets a flag, and the next activation as described above. Sometimes failure determination is performed (see FIG. 7).

  In S75, when the state where the pulse width K1 is within the normal range and the period C1 is within the normal range continues for a predetermined number of times or for a predetermined time (S75: YES), the control unit 33 determines that the input voltage V is normal. It determines with having returned, and the process which returns a paper passing speed and various setting temperature to the thing at the time of normal control (upper limit temperature A etc.) is performed (S81). And the control part 33 performs the process from S17 of FIG. 5 again. Note that the control unit 33 determines whether or not the printing operation is being performed in the same manner as S61 and S65 when returning the sheet passing speed or the like in S81, and if necessary, ON / OFF of the fixing relay 39 or printing is performed. The middle sheet discharge process may be executed.

  In addition, in the determination process for returning to normal in S75, the control unit 33 determines whether the cycle C1 is normal in addition to the pulse width K1. When the zero-cross generation circuit 37 receives an input voltage V having a steep waveform such as a rectangular wave, there is a possibility that the zero-cross pulse signal Sr cannot be generated in synchronization with the zero-cross timing. Therefore, for example, even when the pulse width K1 is larger than the second mask Zmk2, the zero-cross pulse generation circuit 37 cannot successfully generate the zero-cross pulse signal Sr if the cycle C1 of the zero-cross pulse signal Sr is too long. Can be considered. For this reason, in the control part 33 of this embodiment, compared with the determination condition which transfers to rectangular wave detection control, the determination condition which transfers to normal control is made severer, and the determination by the period C1 is also implemented. In addition, in the other determination processes (S23, S25, S37, etc.), the control unit 33 may perform the determination based on the period C1 in addition to the determination of the pulse width K1, or instead of the determination of the pulse width K1. You may implement determination by the period C1.

  Incidentally, the halogen heater 31 is an example of a heater. The temperature sensor 31A is an example of a temperature detection sensor. The control unit 33 is an example of a control device. The fixing relay 39 is an example of a changeover switch. The triac 43 is an example of an energization time adjustment element. The zero cross pulse signal Sr is an example of a zero cross signal. The upper limit temperature A is an example of a first upper limit temperature. The upper limit temperature B is an example of a second upper limit temperature. The input voltage V is an example of an AC voltage. The process of S23 is an example of a first determination process. The process of S43 is an example of an energization stop process. The process of S67 is an example of an upper limit temperature reduction process, a target temperature reduction process, and a sheet passing speed reduction process. The process of S75 is an example of a second determination process. The process of S77 is an example of an abnormality information setting process. The process of S81 is an example of a return process. The first mask Zmk1 is an example of a first threshold value. The second mask Zmk2 is an example of a second threshold value.

As mentioned above, according to above-mentioned embodiment, there exist the following effects.
<Effect 1> When the control unit 33 determines that the pulse width K1 is less than the first mask Zmk1 (S23 in FIG. 5: YES), the upper limit temperature is changed from the upper limit temperature A to the upper limit temperature when a predetermined condition is satisfied. Lower to B (S67). As a result, in the printer 1 of the present embodiment, when the temperature of the halogen heater 31 rises due to the input of the rectangular wave input voltage V and the OFF control of the triac 43 does not function, the upper limit temperature at which the temperature detected by the temperature sensor 31A is lowered. B is easily exceeded. Therefore, the control unit 33 can stop the halogen heater 31 at a safer stage as compared with the case where the operation is continued with the upper limit temperature A before the change. Further, the control unit 33 does not stop immediately even if a rectangular wave is detected, and continues the printing operation while lowering the upper limit temperature and ensuring safety. As a result, the control unit 33 continues the printing operation without stopping the start-up when the input voltage V which is not a normal sine wave input voltage V but the triac 43 is effectively turned off is input. It is possible to improve the productivity of the printing process.

<Effect 2> Further, in S67, the control unit 33 executes a process of lowering the print target temperature when the fixing roller 27 is heated by the halogen heater 31 from the print target temperature A to the print target temperature B. As a result, the control unit 33 can prevent the problem that the operation stops when the print target temperature after the change exceeds the upper limit temperature by lowering the print target temperature as the upper limit temperature is lowered. It has become.

<Effect 3> Further, in S67, the control unit 33 reduces the sheet passing speed of the fixing unit 7 and reduces the heat amount of the fixing unit 7 taken by the sheet per unit time, whereby the upper limit temperature and the print target temperature are set. Even if the value is lowered, the printing operation can be continued.

<Effect 4> If the control unit 33 determines in S63 before changing the sheet passing speed in S67 that the current detected temperature exceeds the normal temperature upper limit B after the change (S63: NO), fixing The relay 39 is turned off, and a temporary standby is performed until the detected temperature becomes equal to or lower than the normal temperature upper limit B (S69). This can prevent the detected temperature from exceeding the upper limit temperature B (S71: NO) and causing an error stop (S43 in FIG. 6) when the printing operation is started at a reduced sheet passing speed. It has become.

<Effect 5> If the control unit 33 determines that the detected temperature exceeds the upper limit temperature B even if the printing operation is performed in a state where the sheet passing speed is lowered (S71: NO), such as a failure of the triac 43, etc. Since there is a high possibility, an error is stopped (S43) to ensure safety.

<Effect 6> When the rectangular wave detection control shown in FIG. 8 is started and the printing operation is being performed (S61: YES), the control unit 33 turns off the fixing relay 39 and prints only the sheet being printed. Is completed (S65). Thereby, since the sheet passing speed is not changed during the printing operation, it is possible to prevent the occurrence of unevenness in the image being printed and maintain the printing accuracy.

<Effect 7> The control unit 33 determines the voltage change rate based on the pulse width K1 of the zero cross pulse signal Sr. When the second mask Zmk2 ≦ pulse width K1 <the first mask Zmk1 is satisfied, rectangular wave detection is performed. Control is being executed. As a result, when the control unit 33 determines that the pulse width K1 is less than the second mask Zmk2 and continuously determines for a predetermined time (S41: YES in FIG. 6), the control unit 33 performs error stop (S43, By the timing T5) in FIG. 11, it is possible to quickly cope with an abnormal input such as a DC voltage that does not cause zero crossing.

<Effect 8> When the control unit 33 determines in S71 of FIG. 8 that the detected temperature exceeds the upper limit temperature B, the control unit 33 sets a flag indicating failure in the register and ends (S77). Further, when the abnormality flag is set at the next startup (S11 in FIG. 5: YES), the control unit 33 executes a process of determining a failure of the fixing drive circuit 41 (S13). If the control unit 33 determines that a failure has occurred (S57 in FIG. 7), the control unit 33 does not start the printing operation and notifies the user of an error and prompts appropriate processing (FIG. 7). 6 S43).

<Effect 9> In S75, when the state where the pulse width K1 is within the normal range and the period C1 is within the normal range continues for a predetermined number of times or for a predetermined time (S75: YES), the control unit 33 determines that the input voltage V is It is possible to determine that it has returned to normal and to automatically return the sheet passing speed and various set temperatures to those during normal control (such as the upper limit temperature A) (S81).

In addition, this invention is not limited to the said embodiment, It is possible to implement in the various aspect which gave various change and improvement based on the knowledge of those skilled in the art.
For example, the processing content of the flowcharts shown in FIGS. 5 to 8 in the above embodiment is an example, and can be changed as appropriate. For example, you may perform the process in S31 of FIG. 5 using the period C1 of the zero cross pulse signal Sr. In S31 of FIG. 5, it is determined whether or not the pulse width K1 less than the first mask Zmk1 continues for a predetermined time. On the other hand, as shown in FIG. 13, it may be determined whether or not the cycle C1 of the zero cross pulse signal Sr exceeds a predetermined upper limit value (S91). In the following description, the same reference numerals are assigned to the same processes as those in the above embodiment, and the description thereof is omitted as appropriate.

  As illustrated in FIG. 13, when the control unit 33 determines that the pulse width K1 is less than the first mask Zmk1 (S23: YES), the control unit 33 ignores the low-level zero-cross pulse signal Sr that is a target for counting the pulse width K1. Then, the process is continued (S29). In this case, if the period C1 (see FIG. 4) from the rising edge of the zero cross pulse signal Sr to the next rising edge is counted, the pulse width K1 becomes a high level from the low level zero cross pulse signal Sr that is less than the first mask Zmk1. Since the rise to the zero cross pulse signal Sr is ignored, the count value of the cycle C1 continues to increase gradually. Therefore, the control unit 33 continues to input the low-level zero-cross pulse signal Sr that makes the pulse width K1 less than the first mask Zmk1 by determining whether or not the counted cycle C1 exceeds a predetermined upper limit value. It is possible to determine whether or not Even in such a configuration, it is possible to obtain the same effect as in the above embodiment.

  Similarly, another process, for example, the process in S25, may be determined by the cycle C1 of the zero cross pulse signal Sr. Moreover, you may determine each above-described process using both pulse width K1 and the period C1. For example, although it determined using both pulse width K1 and period C1 in S75 shown in FIG. 8, you may determine either.

  In the above embodiment, when it is determined that the detected temperature exceeds the upper limit temperature B in the rectangular wave detection control shown in FIG. 8 (S71: NO), a failure flag is set (S77). A failure flag may be set when an abnormality is detected during operation and the process ends. For example, in S25 of FIG. 13, when the pulse width K1 does not become the mask upper limit Zmkmax or more (S25: NO), the control unit 33 executes S93. When it is determined in S93 that the detected temperature exceeds the upper limit temperature A for a predetermined time (S93: YES), the control unit 33 sets a failure flag (S95) and stops in error (S43 in FIG. 6). ). In such a configuration, for example, when the triac 43 fails during normal operation and ends abnormally, the failure determination process shown in FIG.

In the above-described embodiment, the control unit 33 executes the process of reducing the sheet passing speed and various set temperatures in S67. However, the present invention is not limited to this. For example, only the process of reducing the upper limit temperature from the upper limit temperature A to the upper limit temperature B. May be executed.
Moreover, in the said embodiment, although the heating apparatus 30 was the structure provided with only one halogen heater 31, the structure provided with the some halogen heater 31 may be sufficient. In this case, for example, in the rectangular wave detection control, only the upper limit temperature is lowered without reducing the sheet passing speed, and the printing operation is continued while suppressing the temperature rise of each heater by driving a plurality of heaters. It is possible to prevent a decrease in productivity.

Further, the control unit 33 confirms the temperature of the halogen heater 31 prior to the process of S67, and executes a process of cooling the halogen heater 31 if necessary. S67 may be executed.
In addition, when the printing operation is being performed when the rectangular wave detection control is started (S61: YES), the control unit 33 executes a process of discharging the sheet being printed. However, a process for reducing the sheet passing speed may be executed.
Moreover, although the control part 33 determined the pulse width K1 using two types of masks, the 1st mask Zmk1 and the 2nd mask Zmk2, it is not restricted to this, You may determine only with one type of mask.
Further, when the control unit 33 determines in S75 that the pulse width K1 is within the normal range (S75: YES), the control unit 33 automatically returns the sheet passing speed or the like. You may perform the process which alert | reports that to a user, without returning.

In the above embodiment, the control unit 33 uses the falling edge of the zero cross pulse signal Sr as a reference for starting the period Tw. The timing may be used as a reference.
Moreover, in the said embodiment, the signal which becomes active low in the zero cross detection range U was illustrated as an example of the zero cross pulse signal Sr. However, the zero cross pulse signal Sr may be a signal that is synchronized with the zero cross timing of the input voltage V, and may be a signal that becomes active high, for example.
In addition, the heater in the present application is not limited to the halogen heater 31 but may be another element or device that generates heat by energization control based on the zero cross pulse signal Sr.

  In the above embodiment, the monochrome laser printer 1 has been described as an example of the image forming apparatus of the present application, but the present invention is not limited to this. For example, the image forming apparatus may be a color laser printer capable of color printing, a color LED printer, or a multifunction machine having a FAX function in addition to an image forming function.

  DESCRIPTION OF SYMBOLS 1 Monochrome laser printer (image forming apparatus), 5 Image forming part, 27 Fixing roller, 31 Halogen heater, 31A Temperature sensor, 33 Control part, 37 Zero cross production circuit, 39 Fixing relay, 43 Triac, 101 AC power supply, Sr Zero cross pulse Signal, mk1 first mask Z, mk2 second mask Z.

Claims (11)

A heater connected to an AC power source;
A temperature detection sensor for detecting the temperature of the heater;
A changeover switch provided between the AC power source and the heater;
An energization time adjusting element provided between the AC power source and the heater;
A zero-cross signal generation circuit that generates a zero-cross signal synchronized with the zero-cross timing of the AC voltage from the AC power supply;
A control device,
The controller is
An adjustment process for adjusting an energization time from the AC power source to the heater by adjusting an ON period of the energization time adjustment element with the zero cross signal as a reference,
A first determination process for determining whether or not a voltage change rate of the AC voltage at the zero-cross timing is greater than or equal to an allowable value;
In response to determining that the voltage change rate is equal to or greater than the allowable value in the first determination process, an upper limit temperature for determining whether the heater can be operated is set from a first upper limit temperature to a second upper limit temperature. Lowering the upper temperature limit,
Stop energization to control energization from the AC power source to the heater by controlling the changeover switch in response to the detected temperature of the heater detected by the temperature detection sensor being equal to or higher than the second upper limit temperature. And an image forming apparatus. An image forming unit that forms an image on a recording medium based on the image data;
A fixing roller heated by the heater and fixing the image formed by the image forming unit on the recording medium,
The control device executes a target temperature reduction process for reducing a print target temperature when the fixing roller is heated by the heater in response to determining that the voltage change rate is equal to or greater than the allowable value. The image forming apparatus according to claim 1. An image forming unit that forms an image on a recording medium based on the image data;
A fixing roller heated by the heater and fixing the image formed by the image forming unit on the recording medium,
In response to determining that the voltage change rate is equal to or greater than the allowable value, the control device performs a sheet passing speed reduction process for decreasing the sheet passing speed of the fixing roller that transports the recording medium. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   Prior to the sheet passing speed reduction process, the control device controls the changeover switch according to a detection temperature of the temperature detection sensor being equal to or higher than a temperature upper limit lower than the second upper limit temperature by a predetermined temperature. The image forming apparatus according to claim 3, wherein a heater cooling process for temporarily stopping energization of the heater and lowering the temperature of the heater is performed.   The image forming apparatus according to claim 4, wherein the control device performs the upper limit temperature reduction process in response to a temperature detected by the temperature detection sensor being equal to or lower than the second upper limit temperature.   The control device executes the energization stop process in response to the temperature detected by the temperature detection sensor being equal to or higher than the second upper limit temperature after the sheet passing speed is reduced by the sheet passing speed reduction process. The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus.   In response to determining that the voltage change rate is equal to or greater than the allowable value during a printing operation, the control device controls the changeover switch to stop energization of the heater, and to The image forming apparatus according to claim 3, wherein the sheet passing speed reduction process is executed after the recording medium is discharged.   The image forming apparatus according to claim 1, wherein the control device determines the voltage change rate based on a pulse width of the zero-cross signal in the first determination process. . In the first determination process, the control device includes:
A first pulse width comparison process for comparing the pulse width of the zero-cross signal with a first threshold;
In the first pulse width comparison process, in response to the detected pulse width being smaller than the first threshold, the pulse width of the zero cross signal is compared with a second threshold that is smaller than the first threshold. The image forming apparatus according to claim 8, wherein the second pulse width comparison process is executed. The controller is
An abnormality information setting process for setting abnormality information indicating a temperature abnormality in response to detection temperature of the temperature detection sensor exceeding at least one of the first upper limit temperature and the second upper limit temperature;
A failure determination process for determining whether or not the energization time adjustment element is normal is executed according to the fact that the abnormality information is set at the time of startup. Item 12. The image forming apparatus according to Item 9. The controller is
A second determination process for determining whether a voltage change rate of the AC voltage at the zero-cross timing is equal to or less than the allowable value;
In response to determining that the voltage change rate is equal to or less than the allowable value in the second determination process, a return process for restoring the setting changed according to the determination result of the first determination process is executed. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images