JP6376018B2 - 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 having a pulse signal synchronized with the zero cross timing of an AC power source, and controls the energization time of a heater based on the generated pulse signal of the 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, the triac may not 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 is difficult for the image forming apparatus to generate a pulse signal synchronized with the zero cross timing and to control energization based on the generated pulse signal. For this reason, in the image forming apparatus disclosed in Patent Document 1, when it is detected that the voltage change rate is equal to or greater than an allowable value, the energization of the heater is cut off assuming that a rectangular wave AC voltage is input.

JP 2011-113807 A

  By the way, in this type of image forming apparatus, for example, the zero cross pulse width, which is the time during which pulse signals are continuously generated, is counted, and the voltage change rate exceeds the allowable value when the zero cross pulse width is smaller than a predetermined value. When the method of determining that the signal is detected is adopted, when an AC voltage having a maximum amplitude smaller than a reference value for generating a pulse signal (hereinafter simply referred to as “low voltage”) is input, Since the pulse signal is continuously generated during a certain period, the zero cross pulse width may be larger than a predetermined value. In this case, since energization to the heater is not cut off, if the input low voltage AC voltage is a rectangular wave, the triac cannot be turned off and the heater may fail. Therefore, in consideration of safety, it is conceivable to cut off the power supply to the heater when a low-voltage AC voltage is input. However, even when a low-voltage AC voltage is input, for example, when a sinusoidal AC voltage is input, the triac can be effectively controlled and the printing operation may be continued.

  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 achieving both safety and printing productivity.

  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, When the energization time adjusting element provided between the AC power source and the heater and the voltage value of the AC voltage from the AC power source are larger than the threshold value, a first level zero cross signal is generated, and the voltage value is equal to or lower than the threshold value. A zero-cross signal generation circuit for generating a second-level zero-cross signal different from the first level, and a control device. The control device turns on the energization time adjustment element with reference to the second-level zero-cross signal. An adjustment process for adjusting the energization time from the AC power supply to the heater by adjusting the period, a first determination process for determining whether or not the maximum value of the voltage value is equal to or less than a threshold value, and a first determination An upper limit temperature reduction process for reducing the upper limit temperature for determining whether or not the heater can be operated from the first upper limit temperature to the second upper limit temperature in response to the determination that the maximum value of the voltage value is equal to or less than the threshold value. 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, an energization stop process for controlling the changeover switch to stop energization from the AC power supply to the heater is executed. It is characterized by doing.

  In the image forming apparatus, when it is determined that the maximum value of the voltage value of the AC voltage is equal to or less than the threshold value, that is, when a low voltage AC voltage is input, it is determined whether or not the heater should be operated. The upper limit temperature used in the above is lowered from the first upper limit temperature to the second upper limit temperature which is lower than the first upper limit temperature. In the image forming apparatus, for example, when a low-voltage and rectangular-wave AC voltage is input and the off time control of the energization time adjustment element (for example, triac) does not function and the heater temperature rises, the upper limit temperature is set low. By doing so, 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. Furthermore, compared to a configuration in which the operation is uniformly stopped when a low-voltage AC voltage is input, the image forming apparatus has a low voltage because the printing operation is continued while lowering the upper limit temperature and ensuring safety. However, when an AC voltage that can effectively control the energization time adjusting element is input, the printing operation is continued without stopping the operation, 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 And the control device reduces the sheet passing speed of the fixing roller that transports the recording medium to the first sheet passing speed in response to determining that the maximum voltage value is equal to or less than the threshold value. A configuration for executing the paper speed reduction processing may be adopted.

  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, it is possible to continue the printing operation even if the upper limit temperature is lowered compared with the normal control by reducing the heat consumption per unit time by reducing the sheet passing speed. Become.

  In the image forming apparatus of the present invention, the control device determines that the maximum value of the voltage value is equal to or less than the threshold value when only the second level zero cross signal is input from the zero cross signal generation circuit in the first determination processing. It is good also as composition to do.

  In the image forming apparatus, when the maximum value of the voltage value of the AC voltage supplied from the AC power supply becomes larger than the threshold value, the level of the zero cross signal changes from the second level to the first level. For this reason, the control device can determine that a low-voltage AC voltage has been input when only the second-level zero-cross signal is input.

  In the image forming apparatus according to the aspect of the invention, the control device may have the maximum voltage value when the second level zero cross signal is continuously input from the zero cross signal generation circuit for the first reference time or more in the first determination process. It is good also as a structure which determines with a value being below a threshold value.

  In the image forming apparatus, the control device determines that the low-voltage AC voltage has been input by comparing the time during which the second-level zero-cross signal is continuously input with the first reference time. It becomes possible.

  In the image forming apparatus of the present invention, the control device includes a second determination process that determines whether or not the first-level zero-cross signal is continuously input for the second reference time or more, and the second determination process. The first error processing may be performed in response to the determination that the one-level zero-cross signal has been continuously input for the second reference time or longer.

  For example, when a DC voltage or a voltage close to DC is input due to an abnormality in the AC power supply, a zero-cross signal of the first level is continuously input to the control device. Therefore, in the image forming apparatus, when the first level zero-cross signal is continuously input for the second reference time or longer, it is possible to perform appropriate measures such as first error processing, for example, error stop.

  In the image forming apparatus of the present invention, the control device determines that the maximum value of the voltage value is equal to or less than the threshold when the temperature change rate of the detected temperature is equal to or less than the reference change rate in the first determination process. It is good.

  The heater and the AC power source are connected, and the power supplied to the heater decreases as the maximum value of the AC voltage decreases. Further, the change rate of the heater temperature is proportional to the change rate of the supplied power. For example, when a low-voltage AC voltage is continuously input in a state where the heater temperature is lowered, the rate of change in the heater temperature becomes small. Therefore, the control device can determine that a low-voltage AC voltage has been input by comparing the temperature change rate of the temperature detected by the temperature detection sensor with a predetermined reference change rate.

  In the image forming apparatus according to the aspect of the invention, the control device determines whether the heater is operable in response to determining that the maximum voltage value is equal to or less than the threshold value in the first determination process. The lower limit temperature reduction process for lowering the first lower limit temperature to the second lower limit temperature, and whether or not the detected temperature is lower than the second lower limit temperature after a predetermined time has elapsed since the start of energization from the AC power source to the heater. Third determination processing to be determined, second error processing in response to determining that the detected temperature is lower than the second lower limit temperature in the third determination processing, and a second level zero cross signal from the zero cross signal generation circuit are the first And a fourth determination process for determining whether or not the input is continuously performed for less than a third reference time that is smaller than the reference time, and in the fourth determination process, the second level zero cross signal is less than the third reference time. Continuous In response to determining not inputted Te, it may be configured to perform a first determination process.

  The control device of the image forming apparatus compares the heater temperature and the first lower limit temperature. For example, if the heater temperature is lower than the first lower limit temperature, a failure of the heater is considered, and error processing is performed. . The control device lowers the lower limit temperature from the first lower limit temperature to the second lower limit temperature when the maximum voltage value is equal to or lower than the threshold value, that is, when a low-voltage AC voltage is input. When the controller starts energizing the heater in a low voltage state and performs a printing operation or the like, the heater temperature becomes lower than the second lower limit temperature after a predetermined time has elapsed since the heater was driven. , Error handling. In such a configuration, by lowering the lower limit temperature for determining whether or not the heater can be operated, it is possible to suppress the error processing from being started immediately by the lower limit temperature after the start of the low voltage operation, and continue the printing operation and the like. By doing so, it is possible to achieve both safety and printing productivity.

  The zero-cross signal generation circuit generates a zero-cross signal having a short second continuous time when an AC voltage such as a rectangular wave having a large voltage change rate is input. Therefore, the control device determines an AC voltage such as a rectangular wave depending on whether or not the second level zero cross signal is continuously input for the third reference time. And a control device performs the 1st judgment processing, when AC voltage, such as a rectangular wave, is not inputted. As a result, it is possible to perform processing or the like when a low voltage AC voltage is input by excluding an AC voltage having a large voltage change rate from the processing target.

  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 determines the first paper passing speed of the fixing roller that transports the recording medium in response to the determination that the maximum voltage value is equal to or less than the threshold value in the first determination process. In the first adjustment process for executing at least one of the process for setting the speed and the process for setting the ON period of the energization time adjustment element to the first ON period, and the fourth determination process, the second level zero-cross signal is the third reference time. In response to determining that the input has been continuously less than the second sheet passing speed, which is faster than the first sheet passing speed, and the second period in which the on period is shorter than the first on period. ON period A second adjusting process for performing at least one of the processing may be configured to run.

  When each of the AC voltage of the sine wave and the AC voltage of the rectangular wave having the same maximum voltage value and period is applied to the heater, the AC voltage of the rectangular wave is the AC voltage of the sine wave. It is considered that the total power supplied to the heater is larger than that of. For this reason, if a rectangular wave AC voltage is applied, the heater is heated more than when a sine wave AC voltage is applied. For example, when a low-voltage sine wave AC voltage is input, the amount of heat consumed by the heater is lower than when a square-wave AC voltage is input, or if the heater is not heated more, the heater operation There is a risk of an error stop depending on the lower limit temperature for determining whether or not this is possible. Further, the heat amount of the fixing roller heated by the heater is consumed as the number of recording media to be printed per unit time increases.

  Therefore, in the image forming apparatus, the first paper passing speed in the first adjustment processing when a low-voltage sine wave AC voltage is input, and the AC voltage having a large voltage change rate such as a rectangular wave is input. By making the speed slower than the second sheet passing speed in the second adjustment process, it is possible to reduce the amount of heat consumed per unit time by the heater, and to suppress error stoppage due to the lower limit temperature. Similarly, in the image forming apparatus, the first on-period in the first adjustment process is made longer than the second on-period in the second adjustment process, so that the heater is heated more and error stoppage due to the lower limit temperature is performed. It becomes possible to suppress.

  In the image forming apparatus and the like described in the present invention, it is possible to achieve both safety and printing productivity.

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 timing chart of the signal concerning energization control. It is a flowchart for demonstrating energization control processing. It is a flowchart for demonstrating rectangular wave detection control. It is a flowchart for demonstrating low voltage detection control. It is a figure for demonstrating the various setting temperature at the time of normal printing processing, rectangular wave detection control, and low voltage detection control. It is a timing chart of the signal concerning energization control when the input voltage of a rectangular wave is inputted. It is a timing chart of each signal when an input voltage changes from a normal state to a low voltage state. It is a timing chart of each signal when input voltage changes from the normal state to the state of DC voltage.

  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 signal SR that is the output signal of the inverter 59 is low level ( An example of “second level”.

  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 a low level, and the zero cross signal SR is an example of a high level (an example of “first level”). ) Therefore, the zero cross generation circuit 37 outputs the zero cross pulse signal SP that makes the zero cross signal SR low level only during the period in which the input voltage V of the AC power supply 101 is in the zero cross detection range U defined by the positive / negative threshold Vt. To do.

  As shown in FIG. 2, the zero cross 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 SP by determining the voltage level of the zero cross 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 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 SP 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 the phototriac coupler 45 on and off according to 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 supplied with the input voltage V only during the ON period TN shown in FIG. The on period TN 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 waveform of the heater voltage HV in FIG. The controller 33 changes the ON period TN by changing the period TW (see FIG. 4) from the falling timing of the zero cross pulse signal SP to the rising timing of the trigger pulse signal SB, and the temperature of the halogen heater 31 is changed. To control.

  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 of the DC voltage is input due to some abnormality of the AC power supply 101, the control unit 33 turns off the fixing relay 39 and stops the power supply to the halogen heater 31 and the triac 43. 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 ON period TN of the halogen heater 31 based on the phase, for example. Adjust the temperature. The control based on this phase is not to manage the on-period TN 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 on-period TN 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.

  The control unit 33 can supply the trigger pulse signal SB to the fixing drive circuit 41 even when only the low-level zero cross signal SR is input and the zero cross pulse signal SP cannot be detected. Specifically, when an input voltage V having a smaller maximum amplitude than the threshold value Vt at which the zero cross pulse signal SP is generated (hereinafter, sometimes referred to as “low voltage input voltage V”) is input from the inverter 59. The zero-cross signal SR that is generated maintains a low level and does not transition to a high level. Therefore, the control unit 33 cannot generate the trigger pulse signal SB based on the zero cross pulse signal SP. However, among the low-voltage input voltages V that fall within the zero-cross detection range U, there are input voltages V that can effectively control the heater voltage HV and the triac 43. Further, with this low input voltage V, an operable drive voltage may be supplied to the control unit 33 without stopping the oscillation on the secondary side of the transformer connected to the switching circuit of the low-voltage power supply circuit 35. is there. Therefore, in the state where the zero-cross pulse signal SP is not input and the drive voltage is supplied from the low-voltage power supply circuit 35, the control unit 33, for example, a period set before the input of the zero-cross pulse signal SP is stopped. A trigger pulse signal SB is artificially generated at the same cycle as TW (see FIG. 4) and supplied to the fixing drive circuit 41 to drive the halogen heater 31 to continue the printing operation (FIG. 10). reference).

  Next, energization control of the halogen heater 31 by the control unit 33 will be described with reference to FIGS. In the following description, as shown in FIG. 4, the pulse width corresponding to the time when the low-level zero-cross signal SR is continuously input from the zero-cross generation circuit 37 to the control unit 33, that is, the zero-cross pulse signal SP The pulse width is referred to as zero cross pulse width ZL. A cycle in which the zero cross pulse signal SP of the zero cross signal SR is generated is referred to as a cycle PZ. The above definition of the zero cross pulse width ZL is an example. For example, the zero-cross pulse width ZL is not limited to the time when only the low-level zero-cross signal SR is input, but as the time when the low-level zero-cross signal SR continues with a short high-level time shorter than a predetermined time. It may be defined.

  The control unit 33 determines whether the input voltage V is abnormal based on the zero cross pulse width ZL and the period PZ, and performs processing according to each aspect of the input voltage V. Although details will be described later, when the period PZ is abnormal (step shown in FIG. 5 (hereinafter simply referred to as “S”) 29: YES), the control unit 33 performs error processing (S31). In addition, when the input voltage V (hereinafter referred to as “rectangular wave or the like”) having a steep voltage change rate (dv / dt) such as a rectangular wave is input (S33: YES), the control unit 33 detects the rectangular wave. Control is executed (S35, see FIG. 6). Moreover, the control part 33 performs low voltage detection control (process after S53), when the low voltage input voltage V is input (S51 of FIG. 7: YES). Moreover, the control part 33 performs an error process, when the input voltage V of DC voltage is input (S51: NO) (S31).

  First, 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 performs a halogen heater according to a predetermined program. 31 energization control is started. For example, the predetermined program is stored in the ROM of the memory 33A (see FIG. 2).

  In S <b> 11 of FIG. 5, the control unit 33 turns on the fixing relay 39 and starts inputting the input voltage V to the halogen heater 31. Next, the control unit 33 starts detection processing of the zero cross pulse signal SP, and whether or not the zero cross pulse width ZL shown in FIG. 4 is equal to or greater than the reference time T1 and the cycle PZ of the zero cross signal SR is smaller than the cycle threshold value TP. And whether or not the input voltage V is normal is determined (S13).

  Here, the “reference time T1” is a reference time for determining whether or not the input voltage V has a normal waveform by comparing with the zero cross pulse width ZL. For example, as will be described later, when the zero-cross pulse width ZL is shorter than the reference time T1, the control unit 33 determines that the input voltage V is a rectangular wave or the like (S33: YES), and executes rectangular wave detection control. (See FIG. 6). The “cycle threshold TP” is an upper limit value indicating whether or not the cycle PZ is within a normal range. For example, when the period PZ is equal to or greater than the period threshold TP, the value of the period threshold value TP is changed to the trigger period signal SB based on the zero cross pulse signal SP by the control unit 33 and the on period TN (see FIG. 4) is changed. However, a value at which the halogen heater 31 cannot be heated to a desired fixing temperature can be set. The desired fixing temperature is, for example, a lower limit temperature (see FIG. 8) that determines whether a printing operation described later is possible.

  When the zero cross signal SR falls, that is, when the zero cross pulse signal SP is generated and the zero cross signal SR becomes low level, the control unit 33 takes the time that the zero cross signal SR is low level (zero cross pulse SR). Width ZL) is counted, and it is determined whether or not the zero cross pulse width ZL is equal to or greater than the reference time T1 (S13). Further, the control unit 33 counts the time interval at which the zero cross pulse signal SP is generated, and determines whether or not the period PZ is smaller than the period threshold value TP (S13). Although the details will be described later, when the input voltage V of the DC voltage is input, the control unit 33 cannot detect the zero cross pulse signal SP, cannot count the zero cross pulse width ZL and the period PZ, and has a high level. The zero cross signal SR is continuously input.

  When the zero cross pulse width ZL is equal to or longer than the reference time T1 and the period PZ is smaller than the period threshold value TP (S13: YES), it is considered that the input voltage V is a normal sine wave AC voltage that can be printed. Since there is no problem even if the process is executed, the control unit 33 determines whether there is a print job (S19). When there is a print job (S19: YES), the control unit 33 starts normal print processing (S21). As will be described later, when the input voltage V is a rectangular wave or the like or a low voltage, the control unit 33 according to the present embodiment starts print processing after changing various settings (such as the upper limit temperature in FIG. 8). To do. In this printing process of S21, since the control unit 33 determines that the normal sine wave input voltage V is input in the determination of S13, the normal printing is performed without changing various settings such as the upper limit temperature. Execute the process.

  In S13, when the controller 33 determines once that the zero cross pulse width ZL is equal to or greater than the reference time T1 and the period PZ is smaller than the period threshold value TP, the control unit 33 immediately executes the processes after S19. For example, when the determination is made continuously a plurality of times, a setting for executing the processing after S19 may be used. Alternatively, the control unit 33 may be configured to execute the processing after S19 when it is repeatedly determined for a predetermined time that the zero cross pulse width ZL is equal to or greater than the reference time T1 and the period PZ is smaller than the period threshold value TP.

  Next, after starting printing, the control unit 33 determines whether or not the temperature detected by the temperature sensor 31A exceeds the upper limit temperature (S23). FIG. 8 shows the relationship between various set temperatures used during normal printing processing and during rectangular wave detection control and low voltage detection control described later. The print target temperature shown in FIG. 8 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. The lower limit temperature is a temperature for determining whether or not to turn off the fixing relay 39 when the temperature of the halogen heater 31 does not rise to a desired temperature due to a failure of the triac 43 or the like. For example, during the normal printing process described above, the control unit 33 does not turn off the fixing relay 39 while the temperature detected by the temperature sensor 31A is within the range of the lower limit temperature A ≦ the detected temperature ≦ the upper limit temperature A. Then, the control of the halogen heater 31 by the triac 43 is executed.

  In addition, when the control unit 33 according to the present embodiment detects an input voltage V that may be a rectangular wave or the like, the control unit 33 performs rectangular wave detection control that continues the operation while lowering the set temperature. Further, when detecting the input voltage V that may cause a low voltage, the control unit 33 executes low voltage detection control that continues the operation while lowering the set temperature. Therefore, as shown in FIG. 8, various set temperatures (upper limit temperature B and the like) in the rectangular wave detection control and the low voltage detection control are set lower than the set temperatures in the normal control. In the rectangular wave detection control and the low voltage detection control, various set temperatures may be different temperatures. 8 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 FIG. 5, the control unit 33 starts the normal printing process (S21), and if the detected temperature of the temperature sensor 31A becomes higher than the upper limit temperature A (S23: NO), or the detected temperature is the lower limit. When the temperature is lower than the temperature B (S25: NO), error processing is performed (S31).

  When the temperature detected by the temperature sensor 31A is within the range of the lower limit temperature A ≦ the detected temperature ≦ the upper limit temperature A (S23: YES, S25: YES), there is another print job to be executed. It is determined whether or not (S27). When there is another print job to be executed (S27: NO), the control unit 33 performs the processing from S13 again. Note that the control unit 33 may perform the processing from S13 again when the print job being executed does not end even after a predetermined time has elapsed even if there is no other print job in S27. As a result, the control unit 33 repeatedly executes the processing from S13 every predetermined time, not in units of print jobs.

  On the other hand, when there is no other print job to be executed (S27: YES), the control unit 33 ends the process. If there is no print job to be executed in S19 (S19: NO), the control unit 33 ends the process.

  In S13, when the zero cross pulse width ZL is at least one of a state where the zero cross pulse width ZL is smaller than the reference time T1 and a state where the period PZ is equal to or greater than the period threshold value TP (S13: NO), the control unit 33 It is determined whether or not PZ is greater than or equal to the cycle threshold value TP (S29). When the period PZ is greater than or equal to the period threshold value TP (S29: YES), the control unit 33 performs error processing (S31). The control unit 33 turns off the fixing relay 39, stops input of the input voltage V to the halogen heater 31, and stops each drive source such as the electric motor 28 (S31). Moreover, the control part 33 displays an error on a display part (not shown), for example, notifies a user, and complete | finishes a process. Note that the controller 33 determines in S13 that the zero cross pulse width ZL is greater than or equal to the reference time T1 and the period PZ is greater than or equal to the period threshold TP (S13: NO), that is, only the period PZ is abnormal. Therefore, it is preferable to omit the process of S29 and start the processes after S31.

  Here, in S29, when it is determined that the period PZ is not equal to or greater than the period threshold TP (S29: NO), the input voltage V corresponds to either a rectangular wave or the like, a low voltage, or a DC voltage. FIG. 9 shows a timing chart of signals related to energization control when a rectangular wave input voltage V is input. As shown in FIG. 9, when 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 zero cross pulse width ZL of the zero cross pulse signal SP output from the zero cross generation circuit 37 becomes short. If the zero cross pulse width ZL becomes too short, the triac 43 cannot be turned off, and the halogen heater 31 may be energized continuously. On the other hand, even in the case of a rectangular wave, the control unit 33 can detect the rising edge of the zero cross pulse signal SP if the zero cross pulse width ZL has a constant width.

  Therefore, when an input voltage V such as a rectangular wave is input, the control unit 33 reduces the upper limit temperature shown in FIG. 8 to the lower limit temperature B, and executes the printing process while ensuring safety. Further, the control unit 33 determines whether or not the input voltage V such as a rectangular wave has been input based on whether or not the zero cross pulse width ZL of the zero cross pulse signal SP is 0 <zero cross pulse width ZL <reference time T1. (S33).

  When 0 <zero cross pulse width ZL <reference time T1 (S33: YES), the control unit 33 executes rectangular wave detection control (S35). As shown in FIG. 6, in the rectangular wave detection control, the control unit 33 first determines whether or not a printing operation is being performed (S41). When the printing operation is being performed (S41: 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 (turns off the fixing device 7), and prints. Printing of only the middle sheet is completed (S43). 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 (S43) or when the printing operation is not being performed (S41: NO) (S45). . In the control unit 33 according to the present embodiment, when it is determined that 0 <zero cross pulse width ZL <reference time T1, it is possible that the printing operation can be continued. The sheet feeding speed of the fixing device 7 is decreased from the normal sheet feeding speed VP to the sheet feeding speed VP1, and the printing operation is continued. This is because by reducing the sheet passing speed VP, the heat amount of the fixing device 7 taken by the sheet per unit time can be reduced, and the heat amount (temperature) necessary for the fixing device 7 can be suppressed. Because. The sheet passing speed VP can be defined as the number of sheets conveyed per unit time, for example.

  As shown in FIG. 8, various set temperatures (normal temperature upper limit B and the like) 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 step S49 described later, but prior to that, it is necessary to first determine whether or not 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 it is determined in S45 that the current detected temperature exceeds the changed normal temperature upper limit B (S45: NO), the control unit 33 turns off the fixing relay 39, and the detected temperature is the normal temperature upper limit. It waits temporarily until it becomes below B (S47). When the detected temperature becomes equal to or lower than the upper limit temperature B, the control unit 33 starts the processing after S49.

  Further, when the control unit 33 determines that the detected temperature is equal to or lower than the normal temperature upper limit B (S45: YES), the control unit 33 controls the electric motor 28 (see FIG. 2) and the like to slow down the sheet passing speed VP to the sheet passing speed VP1. At the same time, control is performed to lower the various set temperatures from A to B (S49). For example, the control unit 33 decreases the sheet passing speed VP to a sheet passing speed VP1 that is half the speed during normal control. For example, the control unit 33 lowers the upper limit temperature from the upper limit temperature A (for example, 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 in a state where the sheet passing speed VP and various set temperatures are lowered (S49). The control unit 33 ends the rectangular wave detection control, and performs the processes after S19 shown in FIG. When there is a print job (S19: YES), the control unit 33 executes a printing process based on various changed set temperatures (upper limit temperature B, lower limit temperature B, etc.) (S21, S23, S25). As shown in FIG. 8, 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 suppressing the melting of the fixing roller 27 of the fixing device 7 and the like. It is possible.

  Further, in S33 of FIG. 5, when 0 <zero cross pulse width ZL <reference time T1 is not satisfied (S33: NO), the controller 33 determines whether the zero cross pulse width ZL is equal to or greater than the reference time T2, as shown in FIG. It is determined whether or not (S51). The “reference time T2” here is a reference time for determining whether or not the input voltage V is a low voltage by comparing with the zero cross pulse width ZL.

  FIG. 10 shows a timing chart of each signal when the input voltage V changes from the normal state to the low voltage state. The input voltage V shown in FIG. 10 is a low input voltage V after time TM3. At time (time TM1, TM2) before time TM3, the input voltage V has an absolute value equal to or less than the threshold value Vt at time TM1 and an absolute value equal to or greater than the threshold value Vt at time TM2. The zero cross pulse width ZL of the zero cross pulse signal SP falls within the range of reference time T1 ≦ zero cross pulse width ZL <reference time T2.

  Further, after time TM3, when the absolute value of the input voltage V becomes smaller than Vt, the low-level zero cross signal SR is continuously input to the control unit 33. For this reason, when the count value of the zero cross pulse width ZL is equal to or greater than the reference time T2 (S51: YES), the input voltage V is considered to be a low voltage, so the control unit 33 starts the low voltage detection control ( S53). Since the zero cross signal SR does not rise to the high level after time TM3, the control unit 33 cannot detect the period PZ.

  On the other hand, when the count value of the zero cross pulse width ZL is smaller than the reference time T2 (S51: NO), the zero cross pulse width ZL is equal to the reference time T1 <zero cross pulse width ZL <reference time T2 or “0” (cannot be detected). State). When the reference time T1 <zero cross pulse width ZL <reference time T2, the input voltage V is considered to have a normal waveform. In this case, the period PZ is smaller than the period threshold value TP. That is, the control unit 33 determines that the input voltage V is normal (S13: YES) in S13 of FIG. For this reason, when the zero cross pulse width ZL is smaller than the reference time T2 in S51 (S51: NO), it is considered that the zero cross pulse width ZL = 0 and the input voltage V of the DC voltage is input. Since the control based on the zero cross signal SR becomes impossible, the control unit 33 performs error processing (see S31 in FIG. 5).

  Further, when the low voltage detection control is started (S53), the control unit 33 first determines whether or not a printing operation is being performed (S57). In the following description, the description of the same processing as the rectangular wave detection control is omitted as appropriate. If the printing operation is being performed (S57: YES), the control unit 33 turns off the fixing relay 39 and the fixing device 7 and completes printing of only the sheet being printed (S58). 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 (S58) or when the printing operation is not being performed (S57: NO) (S59). .

  The controller 33 determines whether or not the current temperature is equal to or lower than the changed normal temperature upper limit B before lowering the various set temperatures in S63. When the control unit 33 determines in S59 that the current detected temperature exceeds the changed normal temperature upper limit B (S59: NO), the control unit 33 turns off the fixing relay 39, and the detected temperature becomes the normal temperature upper limit B or less. It waits temporarily until it becomes (S61). When the detected temperature becomes equal to or lower than the upper limit temperature B, the control unit 33 starts the processing after S63.

  Further, when the control unit 33 determines that the detected temperature is equal to or lower than the normal temperature upper limit B (S59: YES), it lowers various temperatures (such as the upper limit temperature) (S63) and continues the printing operation (FIG. 5). Process after S19). Further, the control unit 33 slows the sheet passing speed of the fixing device 7 from the normal sheet passing speed VP to the sheet passing speed VP2. The sheet passing speed VP2 is preferably slower than the sheet passing speed VP1 (see S49 in FIG. 6) during the rectangular wave detection control.

  More specifically, when a sinusoidal input voltage V and a rectangular wave input voltage V having the same maximum value and cycle as the input voltage V are applied to the halogen heater 31 as the heater voltage HV, the rectangular wave The total power of the input voltage V is larger than that of the sine wave input voltage V. For example, as shown in the hatched area AR in FIG. 10, the rectangular wave input voltage V is increased by the power corresponding to the portion indicated by the area AR as compared to the sine wave input voltage V. For this reason, when the rectangular wave input voltage V is applied, the halogen heater 31 is heated more than when the sine wave input voltage V is applied. Therefore, the control unit 33 according to the present embodiment slows the sheet passing speed VP2 when the low voltage sine wave input voltage V is input as compared with the sheet passing speed VP1 when the input voltage V is a rectangular wave or the like. The amount of heat consumed per unit time by the halogen heater 31 is reduced, and the error processing (see S31 in FIG. 5) is suppressed from starting below the lower limit temperature B.

  Note that the control unit 33 is not limited to the method of reducing the amount of heat consumed by the halogen heater 31 by providing a difference in the above-described sheet passing speed VP. For example, the control unit 33 increases the ON period TN (see FIG. 4) to the halogen heater 31. The amount of heat may be increased by increasing the length and heating the halogen heater 31 more. For example, the control unit 33 changes the length of the period TW (see FIG. 4) and compares it with the on period TN (an example of the second on period) in the printing process (see S21 in FIG. 5) after the rectangular wave detection control. Thus, the ON period TN (an example of the first ON period) in the printing process (S21) after the low voltage detection control may be lengthened and the halogen heater 31 may be further heated for adjustment. Alternatively, the control unit 33 may perform adjustment using both the sheet passing speed VP and the ON period TN.

  Then, the control unit 33 turns on the fixing relay 39 in a state where the sheet passing speed VP and various set temperatures are lowered (S63). The control unit 33 ends the low voltage detection control, and starts the processing after S19 shown in FIG.

  Further, in the printing process (see S21 in FIG. 5), as described above, the control unit 33 generates the trigger pulse signal SB in a pseudo manner even when the input voltage V is low and the zero cross pulse signal SP cannot be detected. Generated and supplied to the fixing drive circuit 41. For example, as shown in FIG. 10, after the trigger pulse signal SB is output, the control unit 33 does not receive the zero-cross pulse signal SP, so that the time during which the trigger pulse signal SB of the next cycle cannot be generated is only the upper limit period TW1. When the time elapses (see time TM4), the trigger pulse signal SB is generated and output to the fixing drive circuit 41 regardless of whether the zero cross pulse signal SP is input. Further, the control unit 33 uses the time TM4 when the trigger pulse signal SB is output as a reference, and the trigger pulse signal after the next cycle in the same period as the period TW set before the input of the zero cross pulse signal SP is stopped. SB is generated in a pseudo manner and supplied to the fixing drive circuit 41. As a result, the control unit 33 can control the temperature of the halogen heater 31 even when the low input voltage V is input.

  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 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 lower limit temperature A is an example of a first lower limit temperature. The lower limit temperature B is an example of a second lower limit temperature. The input voltage V is an example of an AC voltage. The reference time T1 is an example of a third reference time. The reference time T2 is an example of a first reference time. The sheet passing speed VP1 is an example of a second sheet passing speed. The sheet passing speed VP1 is an example of a second sheet passing speed. The process of S21 is an example of an adjustment process. The process of S23 and S31 is an example of an energization stop process. The process of S25 is an example of a third determination process. The process of S31 is an example of a second error process. The process of S33 is an example of a fourth determination process. S49 is an example of a second adjustment process. The process of S51 is an example of a first determination process. The process of S63 is an example of an upper limit temperature reduction process, a first sheet passing speed reduction process, a lower limit temperature reduction process, and a first adjustment process.

As mentioned above, according to above-mentioned embodiment, there exist the following effects.
<Effect 1> When the low input voltage V is input (S51 in FIG. 7: YES), the control unit 33 changes the upper limit temperature for determining whether or not the halogen heater 31 is operable from the upper limit temperature A to the upper limit temperature B. (S63, see FIG. 8). As a result, the control unit 33 can stop the halogen heater 31 at a safer stage as compared with the case where the printing operation is continued with the upper limit temperature A without changing the upper limit temperature. Furthermore, since the control unit 33 continues the printing operation while lowering the upper limit temperature and ensuring safety, the operation is stopped when an input voltage V that can effectively control the triac 43 is input although the voltage is low. Thus, the printing operation can be continued without making it possible to improve the productivity of the printing process.

<Effect 2> In S63, the control unit 33 slows the sheet passing speed VP of the fixing unit 7 to the sheet passing speed VP2, and reduces the heat amount of the fixing unit 7 taken by the sheet per unit time. Even if the upper limit temperature is lowered to the upper limit temperature B, the printing operation can be continued.

<Effect 3> In S51, the control unit 33 compares the time during which the low-level zero cross signal SR is continuously input (zero cross pulse width ZL) with the reference time T2 (an example of the first reference time). Thus, it is possible to determine that the low input voltage V has been input.

<Effect 4> The control unit 33 lowers the lower limit temperature from the lower limit temperature A to the lower limit temperature B in the low voltage detection control shown in FIG. 7 (S63). When the temperature is lower than B (S25: NO in FIG. 4), error processing is performed (S31). As a result, the control unit 33 suppresses the error processing (S31) from being started immediately by the lower limit temperature after starting the printing operation, and continues the printing operation and the like. It is possible to achieve both.

  Further, the control unit 33 determines whether or not the input voltage V such as a rectangular wave is input depending on whether or not the low-level zero-cross signal SR is continuously input for the reference time T1 (an example of the third reference time). If the input voltage V such as a rectangular wave is not input (S33: NO), it is determined whether or not the rectangular wave detection control is executed (S51 in FIG. 7). Thereby, the control part 33 can exclude the input voltage V with a large voltage change rate from the process target of low voltage detection control.

<Effect 5> In S63, the control unit 33 decreases the sheet passing speed from the normal sheet passing speed VP to the sheet passing speed VP2. The sheet passing speed VP2 is slower than the sheet passing speed VP1 during the rectangular wave detection control. Thereby, the heat consumption of the halogen heater 31 in the low voltage detection control is reduced as compared with the rectangular wave detection control, and the error process (S31) is prevented from starting below the lower limit temperature B.

<Effect 6> In S49 and S63, 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 7> When the control unit 33 determines in S59 before changing the sheet passing speed VP or the like in S63 that the current detected temperature exceeds the changed normal temperature upper limit B (S59: NO), The fixing relay 39 is turned off, and a temporary waiting is performed until the detected temperature becomes equal to or lower than the normal temperature upper limit B (S61). This prevents the detected temperature from exceeding the upper limit temperature B (S23: NO in FIG. 5) and causing an error stop (S31) when the printing operation is started with the sheet passing speed VP being reduced. It is possible.

<Effect 8> When the control unit 33 starts the low voltage detection control shown in FIG. 7 (S53) and the printing operation is being performed (S57: YES), the fixing relay 39 is turned off, and only the sheet being printed is displayed. Is completed (S58). Thereby, since the sheet passing speed VP 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.

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, in the above-described embodiment, the control unit 33 determines the low voltage and the DC voltage by determining whether or not the zero cross pulse width ZL is equal to or greater than the reference time T2 in S51. It is not limited. For example, the control unit 33 may determine the low voltage and the DC voltage (an example of a second determination process) based on the time during which the high-level zero cross signal SR is continuously input in S51. FIG. 11 shows a timing chart when the input voltage V of the DC voltage is input. For example, when the input voltage V becomes a DC voltage at time TM6, a high level zero-cross signal SR is continuously input to the control unit 33. For this reason, when the high-level zero-cross signal SR is continuously input for a predetermined time, for example, the reference time T3 (an example of the second reference time), it can be considered that the input voltage V of the DC voltage is input. .

  As shown in FIG. 11, the control unit 33 uses a halogen of the input voltage V in order to ensure safety at a time TM7 in which the time during which the high-level zero-cross signal SR is continuously input is equal to or longer than the reference time T3. Error processing (see S31 in FIG. 5) such as stopping input to the heater 31 is executed. At time TM7, the heater voltage HV supplied to the halogen heater 31 is stopped. This error processing is an example of the “first error processing” in the present application. In S51 of FIG. 7, when the time during which the high-level zero-cross signal SR is continuously input is shorter than the reference time T3, it is considered that the low-voltage input voltage V is input. 33 executes low voltage detection control. Even when the control based on the reference time T3 is executed, it is possible to obtain the same effect as the control based on the reference time T2 in the embodiment. The reference time T3 (an example of the second reference time) may be the same length as the reference time T2 (first reference time) or may be a different length of time.

  In S51, the control unit 33 may determine the low voltage and the DC voltage based on the temperature change rate of the temperature detected by the temperature sensor 31A. The temperature change rate of the halogen heater 31 is proportional to the power supplied from the AC power supply 101 (see FIG. 2), that is, the change rate of the input voltage V. For example, when the low voltage input voltage V is continuously input while the temperature of the halogen heater 31 is lowered, the temperature change rate of the halogen heater 31 is reduced. Therefore, for example, the control unit 33 calculates the temperature change rate from the temperature detected by the temperature sensor 31A, and when the calculated temperature change rate is equal to or less than the reference change rate, the low voltage input voltage V is input. You may judge. Even if the comparison between the temperature change rate and the reference change rate is executed, it is possible to obtain the same effect as the control by the reference time T2 in the above embodiment.

In addition, the control unit 33 executes the process of lowering the sheet passing speed VP and various set temperatures in S49 and S63. However, the present invention is not limited to this, and for example, only the process of lowering the upper limit temperature may be executed.
Moreover, although the control part 33 determined the waveform of the input voltage V using the zero cross pulse width ZL and the period PZ, you may determine using either one. For example, a value or range for determining each of a normal sine wave such as a DC voltage, a rectangular wave, and a low voltage may be defined only by the zero cross pulse width ZL.
In the above embodiment, a difference is provided between the paper passing speed VP1 for the rectangular wave detection control and the paper passing speed VP2 for the low voltage detection control. However, both speeds may be the same speed.

  Further, when the low voltage detection control is started and the printing operation is being performed (S57: YES), the control unit 33 performs the process of discharging the sheet being printed (S58). Alternatively, a process for reducing the sheet passing speed VP may be executed while printing.

In the above embodiment, the control unit 33 uses the falling edge of the zero cross pulse signal SP as a reference for starting the period TW. However, other timing, for example, the rising edge of the zero cross pulse signal SP, or between the rising edge and the falling edge, is used. 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 SP. However, the zero cross pulse signal SP may be a signal 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, and may be another element or device that generates heat by energization control based on the zero cross signal SR.
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 low voltage detection control, only the upper limit temperature is lowered without lowering the sheet passing speed VP, and a plurality of heaters are driven to suppress the temperature rise of each heater and continue the printing operation. The decrease in productivity may be suppressed.

  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, 5 Image formation 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 signal, V input voltage, Vt threshold, VP paper feed speed, TN on period.

Claims (8)

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;
When the voltage value of the AC voltage from the AC power supply is larger than a threshold value, a first level zero cross signal is generated. When the voltage value is equal to or lower than the threshold value, the second level is different from the first level. A zero cross signal generation circuit for generating a zero cross signal;
A control device,
The controller is
An adjustment process for adjusting an energization time from the AC power supply to the heater by adjusting an ON period of the energization time adjustment element with reference to the second level zero cross signal;
A first determination process for determining whether a maximum value of the voltage value is equal to or less than the threshold;
In response to determining that the maximum value of the voltage value is equal to or less than the threshold value in the first determination process, the upper limit temperature for determining whether the heater can be operated is changed from the first upper limit temperature to the second upper limit temperature. An upper temperature reduction process to lower
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,
In response to determining that the maximum value of the voltage value is equal to or less than the threshold, the control device reduces the sheet passing speed of the fixing roller that transports the recording medium to a first sheet passing speed. The image forming apparatus according to claim 1, wherein a paper speed reduction process is executed.   In the first determination process, the control device determines that the maximum value of the voltage value is equal to or less than the threshold when only the second level zero cross signal is input from the zero cross signal generation circuit. The image forming apparatus according to claim 1 or 2.   In the first determination process, when the second-level zero-cross signal is continuously input from the zero-cross signal generation circuit for a first reference time or more in the first determination process, the maximum voltage value is equal to or less than the threshold value. The image forming apparatus according to claim 3, wherein it is determined that The controller is
A second determination process for determining whether or not the first level zero-cross signal is continuously input for a second reference time or more;
The first error processing is executed in response to the determination that the first level zero-cross signal is continuously input for the second reference time or longer in the second determination processing. The image forming apparatus according to claim 4.   The said control apparatus determines that the maximum value of the said voltage value is below the said threshold value when the temperature change rate of the said detected temperature is below a reference change rate in the said 1st determination process. The image forming apparatus according to claim 1. The controller is
In the first determination process, in response to determining that the maximum value of the voltage value is equal to or less than the threshold value, a lower limit temperature for determining whether the heater can be operated is changed from the first lower limit temperature to the second lower limit temperature. Lower limit temperature reduction processing to lower the temperature,
A third determination process for determining whether or not the detected temperature is less than the second lower limit temperature after a predetermined time has elapsed from the start of energization of the heater from the AC power supply;
A second error process in response to determining that the detected temperature is lower than the second lower limit temperature in the third determination process;
Performing a fourth determination process for determining whether or not the second-level zero-cross signal is continuously input from the zero-cross signal generation circuit for less than a third reference time that is smaller than the first reference time;
5. The fourth determination process, wherein the first determination process is executed in response to determining that the second level zero cross signal is not continuously input for less than the third reference time. The image forming apparatus described in 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,
The controller is
A process in which, in the first determination process, when the maximum value of the voltage value is determined to be equal to or less than the threshold, the sheet passing speed of the fixing roller that transports the recording medium is set to the first sheet passing speed. And a first adjustment process for executing at least one of processes for setting the ON period of the energization time adjustment element to a first ON period;
In the fourth determination process, in response to determining that the second-level zero-cross signal is continuously input for less than the third reference time, the sheet passing speed is higher than the first sheet passing speed. And a second adjustment process for executing at least one of a process of setting a two-sheet passing speed and a process of setting the on period to a second on period shorter than the first on period. Item 8. The image forming apparatus according to Item 7.

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