Patent Publication Number: US-11048196-B2

Title: Image formation apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority based on 35 USC 119 from prior Japanese Patent Application No. 2019-101923 filed on May 31, 2019, entitled “IMAGE FORMATION APPARATUS”, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     This disclosure may relate to an image formation apparatus. 
     An electrophotographic image formation apparatus includes a fixation device including a heat roller which is heated by a heater. An energization of the heater is generally controlled by controlling a switching control element such as a triac so that the temperature of the heat roller reaches a desired temperature. 
     To activate the image formation apparatus, an alternating current (AC) power source for inputting AC power is needed. In order to operate the image formation apparatus even when a commercial power source goes out, an uninterruptible device may be located outside the image formation apparatus. 
     In a state where the commercial power source stably supplies AC electric power, the uninterruptable device supplies the electric power from the commercial power source to the image formation apparatus. When detecting that a stoppage of the electric power from the commercial power source due to a power outage, the uninterruptable device converts a stored direct current (DC) power into an AC power and supplies the converted AC power to the image formation apparatus. There may be no problem if the converted AC power supplied from the uninterruptible power supply is not an abnormal AC current. However, if the converted AC power is abnormal such as a square wave, a zero-cross point or timing of the AC power cannot be properly detected so that the heater cannot be properly controlled. 
     An image formation apparatus disclosed in Patent Document 1 (Japanese Patent Application Publication No. 2018-173529) does not turn on a triac when an abnormality occurs in detection of the zero-crossing point or timing, so as to prevent getting out of control. 
     SUMMARY 
     However, in a case where the AC input is changed to an abnormal waveform after the triac, which is a control element to switch energization of the heater, is once turned on, an energization of the triac cannot be turned off even if an energization control signal for the triac is turned off. Accordingly, when the AC input is changed to an abnormal waveform, the power supply to the heater cannot be turned off. 
     An object of an aspect of one or more embodiments of the disclosure is to safely shut off a power supply to a heater even when a waveform of an input alternative current becomes abnormal. 
     An aspect of one or more embodiments is an image formation apparatus that may include: a heater that heats a medium on which a developer image is formed; a controller that controls the heater; a first path through which an input voltage, which is an alternating current (AC) voltage input from an external power supply, is converted to a predetermined voltage, and the predetermined voltage is supplied to the controller; a second path which is branched from the first path and through which the input voltage is supplied to the heater; a control element which is connected to the second path and controls on/off switching of the heater in response to an instruction from the controller; and a disconnection part that disconnects the second path when the input voltage that has a square wave is input. 
     According to the aspect, even when a waveform of an input alternating current becomes abnormal, a power supply to a heater may be safely shut off. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a vertical sectional view of a configuration of an image formation apparatus. 
         FIG. 2  is a block diagram illustrating schematic configurations of a low voltage power supply part and a main controller of the image formation apparatus. 
         FIGS. 3A and 3B  are block diagrams of configurational examples of a hardware of a control-related configuration. 
         FIG. 4  is a circuit diagram of an example of an AC zero-cross circuit. 
         FIG. 5  is a circuit diagram illustrating an example of a protection operation part. 
         FIG. 6  is a circuit diagram illustrating an example of a heater protection part. 
         FIG. 7  is a schematic diagram for explaining a system of a commercial power supply connected to the image formation apparatus. 
         FIGS. 8A to 8C  are graphs for explaining a relationship between an AC power signal and a power supply waveform. 
         FIG. 9  is a flowchart illustrating an initialization operation of an input power failure judgement part. 
         FIG. 10  is a flowchart illustrating a timer interrupt operation. 
         FIG. 11  is a graph for explaining a timer interrupt. 
         FIG. 12  is a flowchart of an AC zero-cross interrupt operation. 
         FIG. 13  is a flowchart of a temperature control of the heater  22 . 
         FIG. 14  is a flowchart of an AC zero-cross process. 
         FIG. 15  is a graph illustrating a first example in which an AC input is changed from a normal sine wave to a square wave. 
         FIG. 16  is a graph illustrating a second example in which an AC input is changed from a normal sine wave to a square wave. 
         FIG. 17  is a graph illustrating a third example in which an AC input is changed from a normal sine wave to a square wave. 
     
    
    
     DETAILED DESCRIPTION 
     Descriptions are provided hereinbelow for embodiments based on the drawings. In the respective drawings referenced herein, the same constituents are designated by the same reference numerals and duplicate explanation concerning the same constituents is omitted. All of the drawings are provided to illustrate the respective examples only. 
       FIG. 1  is a schematic diagram illustrating a vertical sectional view of a configuration of an image formation apparatus  100  according to an embodiment. The image formation apparatus  100  according to an embodiment is a color image formation apparatus that prints a color image by superimposing toners of four colors of black, yellow, magenta, and cyan. However, the invention is not limited to this, and may be a black monochrome image formation apparatus, or a color image formation apparatus using other colors. 
     As illustrated in the figure, the image formation apparatus  100  includes photosensitive drums  2 K,  2 Y,  2 M, and  2 C, charging devices  3 K,  3 Y,  3 M, and  3 C, exposure devices  4 K,  4 Y,  4 M, and  4 C, and development devices  5 K,  5 Y,  5 M, and  5 C. The image formation apparatus  100  includes transfer rollers  6 K,  6 Y,  6 M, and  6 C, a transfer belt  8 , a drive roller  9 , an idle roller  10 , a fixation device  11 , a first conveyance roller  12 , a second conveyance roller  13 , a discharge roller  14 , a hopping roller  15 , a write sensor  16 , a discharge sensor  17 , a support plate member  18 , a spring  19 , and a display part  20 . Further, the image formation apparatus  100  includes a low voltage power supply part  110  and a main controller  180 . Note that hereinafter the main controller  180  may be merely referred to as the controller. 
     In  FIG. 1 , capital letters “K”, “Y”, “M”, and “C” means black, yellow, magenta, and cyan, respectively. Note that hereinafter, if there is no need to distinguish between these colors, the explanations are made with these capital letters omitted. 
     Each photosensitive drum  2  is configured to carries thereon an image which is to be transferred. Here the image to be transferred is a toner image serving as a developer image. Each charging device  3  negatively charges the corresponding one of the photosensitive drums  2 . Each exposure device  4  writes an electrostatic image to the corresponding one of the photosensitive drums  2 . Each development device  5  visualizes the electrostatic image on the corresponding one of the photosensitive drums  2  with the negatively charged toner. 
     The transfer rollers  6  are provided inside of the transfer belt  8  as an endless belt. Each transfer roller  6  is biased by a bias member such as a spring or the like so as to be pressed toward the corresponding one of the photosensitive drums  2  with the transfer belt  8  being sandwiched between the transfer roller  6  and the photosensitive drum  2 . 
     The transfer belt  8  is supported by the outer circumferential surfaces of the drive roller  9  and the idle roller  10 . The transfer belt  8  is stretched between the drive roller  9  and the idle roller  10 , so as to have a flat surface thereof in an area where the photosensitive drums  2  are in contact with the transfer belt  8 . 
     The drive roller  9  is connected to an unillustrated driving device and is to be rotated about an axis thereof. When the transfer belt  8  is moved along with the rotation of the drive roller  9 , the idle roller  10  rotates, along with the movement of the transfer belt  8 , in a direction same as the rotation direction of the drive roller  9 . 
     The fixation device  11  includes a fixation roller  11   a  having a heater  22  therein as a heat source, and a back-up roller  11   b  biased toward the fixation roller  11   a  by a bias member. The fixation device fixes the toner image transferred to a recording medium  21  by heat and pressure. The heater  22  is used to heat the recording medium having the toner image formed thereon. 
     The dashed line in  FIG. 1  indicates a conveyance path of the recording medium  21 , Along the conveyance path, the first conveyance roller  12 , the second conveyance roller  13 , and the write sensor  16  are arranged upstream of the transfer belt  8 , and the discharge sensor  17  and the discharge roller  14  are arranged downstream of the fixation device  11 . 
     When the recording medium  21  is conveyed along the conveyance path, the write sensor  16  and the discharge sensor  17  detect predetermined positions of the recording medium  21  (in this example, the write sensor  16  detects the leading end of the recording medium, and the discharge sensor  17  detects the tail end of the recording medium), and transmits the detection signals to the main controller  180 . 
     On the upper surface of the support plate member  18 , a stack of the recording media  21  is placed. Under the support plate member  18 , the spring  19  serving as a bias member is provided to lift up the support plate member  18 . The stacked recording media  21  placed on the support plate member  18  are pressed against the hopping roller  15  by the biasing force of the spring  19 . When the hopping roller  15  rotates in a direction to push the recording medium  21  into the conveyance path, the uppermost one of recording media  21  is fed one by one to the conveyance path. 
     Note that the photosensitive drum  2 , the hopping roller  15 , the first conveyance roller  12 , the second conveyance roller  13 , the drive roller  9 , the fixation device  11  (the fixation roller and the backup roller), and the discharge roller  14  are connected to the driving device such as a motor or the like, and the driving device is controlled by the main controller  180 . 
       FIG. 2  is a block diagram illustrating schematic configurations of the low voltage power supply part  110  and the main controller  180  of the image formation apparatus  100  according to an embodiment. In  FIG. 2 , parts related to features of the low voltage power supply part  110  and the main controller  180  according to an embodiment are excerpted and illustrated. 
     The power supply cord  101  is connected to a commercial power supply or source (AC power supply or source). The power supply cord  101  is connected to the AC inlet  102 , and the AC inlet  102  is connected to the AC input part  111  of the low voltage power supply part  110 . 
     A line side of the AC input part  111  is connected to a fuse A  112 . The fuse A  112  is connected to a filter A  113  and an IN 2  pin of an AC zero-cross circuit  130 . A neutral side of the AC input part  111  is connected to the filter A  113  and an IN 1  pin of the AC zero-cross circuit  130 . 
     The filter A  113  is connected to a fuse B  114  and an IN 2  pin of a heater protection part  138 . The fuse B  114  is connected to an input side of a rectification bridge  115 , and the filter A  113  is connected to the input side of the rectification bridge  115  and is connected to an IN 1  pin of the heater protection part  138 . 
     A positive electrode of an output side of the rectification bridge  115  is connected to a positive electrode of an electrolytic capacitor  116 , a resistor  117 , a primary side of a transformer  118 . A negative electrode of the output side of the rectification bridge  115  is connected to a negative electrode of the electrolytic capacitor  116 , a resistor  119 , a GND pin of a power supply control IC  120 , a negative electrode of the electrolytic capacitor  121 , a third winding side of the transformer  118 , and an emitter of a photocoupler  122 . 
     The resistor  117  is connected to a VIN pin of the power supply control IC  120 . A source of an FET  123  is connected to the primary side of the transformer  118 . A drain of the FET  123  is connected to the resistor  119 , an IS pin of the power supply control IC  120 . A gate of the FET  123  is connected to an OUT pin of the power supply control IC  120 . 
     The transformer  118  includes a first winding on the primary side, a second winding on the secondary side, and a third winding as an auxiliary winding used for controlling the primary side. The third winding side of the transformer  118  is connected to an anode of a diode  124 , and a cathode of the diode  124  is connected to the positive electrode of the electrolytic capacitor  121  and a VCC pin of the power supply control IC  120 . 
     A collector of the photocoupler  122  is connected to a FB pin of the power supply control IC  120 . The secondary side of the transformer  118  is connected to an anode of a diode  125 , and a cathode of the diode  125  is connected to a positive electrode of the electrolytic capacitor  126 , a resistor  127 , a resistor  128 , a +24V pin of a protection operation part  129  and a +24V output pin of the low voltage power supply part  110 . 
     The secondary side of the transformer  118  is connected to an anode of a variable shunt regulator  131 , a negative electrode of the electrolytic capacitor  126 , the a resistor  132 , a GND pin of the protection operation part  129 , and a GND output pin of the low voltage power supply part  110 . 
     An anode of the photocoupler  122  is connected to the resistor  127 . A cathode of the photocoupler  122  is connected to a cathode of the variable shunt regulator  131 . A reference pin of the variable shunt regulator  131  is connected to the resistor  128  and the resistor  132 . 
     A phototriac  133  is connected to a gate of a triac  134  and a resistor  135 . The resistor  135  is connected to the triac  134  and an AC output part  136  for heater. The triac  134  is connected to a resistor  137  and an OUT 1  pin of the heater protection part  138 . The phototriac  133  is connected to the resistor  137 . An OUT 2  pin of the heater protection part  138  is connected to the AC output part  136 . 
     The triac  134  is a control element that controls an on/off switching of the heater  22  according to instructions from the main controller  180 . 
     A GND pin of the AC zero-cross circuit  130  is connected to the GND output pin of the low voltage power supply part  110 . The OUT pin of the AC zero-cross circuit  130  outputs an AC zero-cross signal. The AC zero-cross signal is input through an ACZERO connector to the main controller  180 . Although not illustrated, to a +5V pin of the AC zero-cross circuit  130 , a +5V voltage is input, which is generated by a DC-DC converter converting a +24V voltage from a +24V power supply of the low voltage power supply part  110 . 
     The main controller  180  is a control circuit board that controls the image formation apparatus  100 . The main controller  180  functions as a controller that controls the heater  22 . Note that the main controller  180  exchanges signals with the low voltage power supply part  110  via an ACON connector, the ACZERO connector, and an ERR dtc connector, as illustrated in  FIG. 2 . Further, the main controller  180  receives the power supply from the low voltage power supply part  110  via the +24V input pin and the GND input pin. 
     A voltage conversion part  181  generates each power supply (3.3V, 1.8V, etc.) to be used in the logic of the control circuit board from the +24V voltage or the +5 V voltage using a DC-DC conversion circuit. A display controller  182  causes a display of a display part  20  to execute various displays. A non-volatile storage  183  is a storage that stores error information. 
     A print controller  184  controls printing in the image formation apparatus  100 . The print controller  184  includes a heater temperature controller  185 . The heater temperature controller  185  controls the triac  134  to cause the triac  134  to perform the on/off switching of the heater  22 , so as to control the temperature of the heater  22 . 
     An output of the heater temperature controller  185  is a heater ON signal. The heater ON signal is input into an input power failure judgement part  186  (or input power supply abnormality judgement part), and then input from the input power failure judgement part  186  through the ACON connector to the phototriac  133 . Note that the heater ON signal instructs, when the signal is at the high (H) level, to turn on the heater  22 , and instructs, when the signal is at the low (L) level, to turn off the heater  22 . 
     The input power failure judgement part  186  receives the AC zero-cross signal from the AC zero-cross circuit  130  via the ACZERO connector, and determines, based on the AC zero-cross signal, whether the waveform of the input voltage, which is an AC voltage input from the commercial power supply as an external power supply, is abnormal. 
     When the input power failure judgement part  186  determines that the waveform of the input voltage is abnormal in a state where the heater  22  is turned on based on the instruction from the heater temperature controller  185 , the input power failure judgement part  186  outputs an fuse cut signal through the ERR dtc connector, to instruct a fuse cut. The fuse cut signal is input to a dtcl pin of the protection operation part  129 . The fuse cut signal is to instruct not to perform the fuse cut when the signal is at the L level, and to perform the fuse cut when the signal is at the H level. 
     Note that the AC zero-cross signal is also supplied from the input power failure judgement part  186  to the print controller  184 , and the print controller  184  executes, based on the AC zero-cross signal, phase control of the timing that turns on the heater  22 , so as to suppress inrush current or the like. 
     Note that the wire connected to the IN 2  pin of the heater protection part  138  is connected to the wire between the filter A  113  and the fuse B 114 , and the wire connected to the IN 1  pin of the heater protection part  138  is connected to the wire between the filter A  113  and the rectification bridge  115 . These connection points are referred as to a branch point BP of the wires. In other words, the image formation apparatus  100  includes: a first path through which the input voltage, which is input to the AC inlet  102  from a commercial power supply, is converted to a desired voltage, and the desired voltage is supplied to the controller  180 ; and a second path which is branched from the first path at the branch point BP and through which the input voltage is supplied to the heater  22 . In the second path, the heater  22 , the triac  134 , and the heater protection part  138  are connected in series. 
     A part or all of the display controller  182 , the print controller  184 , and the input power failure judgement part  186  may be configured by a memory  30  that stores programs therein and a processor  31  such as a central processing unit (CPU) that executes the programs stored in the memory  30 , for example, as illustrated in  FIG. 3A . Such programs may be not be stored in the memory  30 . That is, such programs may be retrieved through the network from the outside of the image formation apparatus or such programs may be retrieved from a non-transitory tangible data recording medium that is provided outside of the image formation apparatus and stores therein the programs. In other words, such programs may be provided, for example, as a program product. 
     Further, a part or all of the display controller  182 , the print controller  184 , and the input power failure judgement part  186  may be composed of a processing circuit  32  such as a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA), for example, as illustrated in  FIG. 3B . Note that the non-volatile storage  183  may be composed of a non-volatile memory such as an electrically erasable programmable read-only memory (EEPROM), a flash memory, or the like. 
       FIG. 4  is a circuit diagram of an example of the AC zero-cross circuit  130  according to an embodiment. The AC zero-cross circuit  130  includes a resistor  130   a , a resistor  130   b , a resistor  130   c , a photocoupler  130   d , a resistor  130   e , a capacitor  130   f , and the digital transistor  130   g.    
     The resistor  130   a  is connected to the IN 1  pin of the AC zero-cross circuit  130 . The resistor  130   a  is connected to the resistor  130   b  and the photocoupler  130   d.    
     The photocoupler  130   d  is connected to the IN 2  pin of the AC zero-cross circuit  130 . The photocoupler  130   d  is connected to the resistor  130   e . The resistor  130   e  is connected to the +5V pin of the AC zero-cross circuit  130 . Further, the photocoupler  130   d  is connected to the capacitor  130   f  and a base of the digital transistor  130   g.    
     An emitter of the digital transistor  130   g  is connected to the GND pin of the AC zero-cross circuit  130 . A collector of the digital transistor  130   g  is connected to the OUT pin of the AC zero-cross circuit  130 . 
     Note that there are several AC zero-cross circuits whose circuit configurations are different from each other. Thus, the AC zero-cross circuit  130  in an embodiment may have a configuration different from the above described configuration. Note that the AC zero-cross circuit  130  functions as an AC zero-cross detector that detects the AC zero-cross points of the input AC voltage. 
       FIG. 5  is a circuit diagram illustrating an example of the protection operation part  129  according to an embodiment. The protection operation part  129  includes a relay coil part  129   a , a transistor  129   b , a resistor  129   c , and a diode  129   d . The relay coil part  129   a  is connected to a cathode of the diode  129   d , the +24V pin of the protection operation part  129 . The relay coil part  129   a  is connected to an anode of the diode  129   d  and a collector of the transistor  129   b.    
     A base of the transistor  129   b  is connected to the resistor  129   c . The resistor  129   c  is connected to the dtcl pin of the protection operation part  129 . An emitter of the transistor  129   b  is connected to the GND pin of the protection operation part  129 . 
       FIG. 6  is a circuit diagram illustrating an example of the heater protection part  138  according to an embodiment. The heater protection part  138  includes a fuse C  138   a , a varistor  138   b , and a relay contact point  138   c.    
     The fuse C  138   a  is connected to the varistor  138   b  and the OUT 1  pin of the heater protection part  138 . Further, the fuse C  138   a  is connected to a neutral illustrated in  FIG. 2 . The fuse C  138   a  is a disconnection part (a cutting part) for disconnecting (cutting) the second path as a supply path of the voltage to the heater  22 . 
     The varistor  138   b  is connected to the relay contact point  138   c . The relay contact point  138   c  is connected to the OUT 2  pin and the IN 2  pin of the heater protection part  138 . 
       FIG. 7  is a schematic diagram for explaining a system of a commercial power supply connected to the image formation apparatus  100 . An uninterruptable device  40  stores the commercial AC power drawn from the outdoor in a storage battery  41  as DC power. When the supply of the commercial AC power is stopped due to a power outage or the like, the uninterruptable device  40  generates AC power from the power stored in the storage battery  41  by an AC inverter  42  and outputs the AC power to the image formation apparatus  100 . 
       FIGS. 8A to 8C  are graphs for explaining a relationship between a power supply waveform and an AC zero-cross signal. In  FIGS. 8A to 8C , the vertical axis represents the voltage and the horizontal axis represents the time. 
     In  FIG. 8A , the reference numeral  50  represents a power supply waveform of a normal sine wave of AC 100V/50 Hz, and the reference numeral  51  represents an AC zero-cross signal thereof. As illustrated in  FIG. 8A , in the normal state, the H level of the AC zero-cross signal is output constantly at 10 ms (milliseconds) intervals. In other words, the cycle of the AC zero-cross signal is 10 ms. Note that when commercial AC is input, the constant of the AC zero-cross detection circuit is preset so that the pulse width is 500 μs to 1.5 ms. 
     In  FIG. 8B , the reference numeral  52  represents a power supply waveform that is changed from a normal sine wave of AC 100V/50 Hz to a square wave, and the reference numeral  53  represents an AC zero-cross signal thereof. When the power supply waveform is changed to the square wave, the pulse width of the AC zero-cross signal becomes shorter than that of the normal sine wave. Here, the pulse width of the AC zero-cross signal of the square wave power supply is less than 500 μs. 
     In  FIG. 8C , the reference numeral  54  represents a power supply waveform that is changed from a normal sine wave of AC 100V/50 Hz to a square wave, and the reference numeral  55  represents an AC zero-cross signal thereof. The quire wave of the power supply waveform  54  in  FIG. 8C  has the voltage change steeper than that of the square wave of the power supply waveform  52  in  FIG. 8B , and thus the AC zero-cross waveform  55  of the square wave of the power supply waveform  54  has no pulse being outputted. 
     Here, the pulse width of the AC zero-cross signal is a length of time when the AC zero-cross point is detected. When the time length (the pulse width) is shorter than a threshold, or the AC zero-cross point is not detected, it can be determined that the waveform of the input voltage is abnormal. 
       FIG. 9  is a flowchart illustrating an initialization operation of the input power failure judgement part  186 . First, the input power failure judgement part  186  starts an AC zero-cross monitoring timer, as an initialization operation (step S 10 ). Here, the AC zero-cross monitoring timer is a timer that monitors intervals of the AC zero-cross points. 
     Next, the input power failure judgement part  186  permits an AC zero-cross interrupt (step S 11 ). With this, the AC zero-cross interrupt, which is described later, is allowed. Next, the input power failure judgement part  186  clears a heater ON flag to be “0” (step S 12 ). The heater ON flag is a flag that indicates whether the heater  22  is turned on or not. When the heater ON flag is “1”, the heater  22  is on, and when the heater ON flag is “0”, the heater  22  is off. 
     Next, the input power failure judgement part  186  sets a heater ON permission flag to “1”, to permit the heater temperature controller  185  to execute a heater ON control (step S 13 ). The heater ON permission flag is a flag that indicates whether or not the heater  22  can be turned on. When the heater ON permission flag is “1”, the heater  22  is allowed to be turned on, and when the heater ON permission flag is “0”, the heater is not allowed to be turned on. 
     Then, the input power failure judgement part  186  starts the temperature control of the heater  22  by the heater temperature controller  185  (step S 14 ). 
       FIG. 10  is a flowchart illustrating a timer interrupt operation. The timer interrupt operation is an operation that is performed when an AC zero-cross point in the AC zero-cross signal input from the AC zero-cross circuit  130  is not detected for a predetermined period 
     For example, as illustrated in  FIG. 11 , the input power failure judgement part  186  clears the counter in response to the interrupt of the falling edge of the AC zero-cross signal  56 , and starts counting. When the interrupt of the falling edge of the AC zero-cross signal  56  is not entered in the predetermined period, the input power failure judgement part  186  determines that a counter overflow occurs, and performs AC zero-cross process in step S 20 . In an embodiment, a counter overflow setting as the predetermined period is set to 200 counts which corresponds to 20 ms. Note that the predetermined period is longer than one cycle of the AC zero-cross signal of the normal AC voltage, and is preferably not longer than two cycle of the AC zero-cross signal of the normal AC voltage. However, the predetermined period may be longer than two cycle of the AC zero-cross signal. 
     Here, the AC zero-cross process in step S 20  is a process that monitors the pulse width of the AC zero-cross signal, and determines whether the pulse width of the AC zero-cross signal is abnormal. The AC zero-cross process in step S 20  is described in detail later with reference to  FIG. 14 . 
     On the other hand, when the interrupt of the falling edge of the AC zero-cross signal  56  is entered in the predetermined period, the input power failure judgement part  186  does not perform the AC zero-cross process of step S 20 . 
       FIG. 12  is a flowchart of an operation of the AC zero-cross interrupt. The AC zero-cross interrupt is an operation that is performed when the interrupt of the falling edge of the AC zero-cross signal is detected within the predetermined period. When the interrupt of the falling edge of the AC zero-cross signal is detected within the predetermined period, the input power failure judgement part  186  executes the AC zero-cross process (step S 30 ). The AC zero-cross process in step S 30  is described in detail later with reference to  FIG. 14 . 
     Since the input power failure judgement part  186  detects the AC zero-cross interrupt, the input power failure judgement part  186  clears the zero-cross monitoring timer (step S 31 ). 
       FIG. 13  is a flowchart of the temperature control of the heater  22 . The input power failure judgement part  186  determines whether or not the heater ON permission flag is “1” (step S 40 ). When the heater ON permission flag is “1” (Yes in step S 40 ), the process proceeds to step S 41 , and when the heater ON permission flag is “0” (No in step S 40 ), the process proceeds to step S 44 . 
     In step S 41 , the input power failure judgement part  186  determines whether or not there is a heater ON request from the heater temperature controller  185 . For example, the heater temperature controller  185  specifies the temperature of the heater  22  based on the detected value from a temperature sensor (not shown), and when the temperature does not reach a target value, sets the heater ON signal to the H level, to supply the heater ON request to the input power failure judgement part  186 . When there is the heater ON request (Yes in step S 41 ), the process proceeds to step S 42 , whereas there is no heater ON request (No in step S 41 ), the process proceeds to step S 44 . 
     In step S 42 , the input power failure judgement part  186  sets, through the ACON connector, the heater ON signal to the H level, to turn on the heater  22  by means of the triac  134 . Then, the input power failure judgement part  186  sets the heater ON flag to “1” (step S 43 ). 
     On the other hand, in step S 43 , the input power failure judgement part  186  sets, through the ACON connector, the heater ON signal to the L level, to turn off the heater  22  by means of triac  134 . 
       FIG. 14  is a flowchart of the AC zero-cross process. First, the input power failure judgement part  186  determines whether the pulse width of the AC zero-cross signal transmitted from the AC zero-cross circuit  130  is abnormal or not (step S 50 ). For example, the input power failure judgement part  186  specifies the pulse width of the H level of the AC zero-cross signal, and when the pulse width is less than the predetermined threshold, determines that the pulse width is abnormal. Note that, when the input power failure judgement part  186  cannot specify the pulse width (see for example,  FIG. 8C ), the input power failure judgement part  186  determines that the pulse width is not abnormal. When the pulse width is not abnormal (No in step S 50 , the process proceeds to step S 51 , whereas when the pulse width is abnormal (Yes in step S 50 ), the process proceeds to step S 52 . 
     In step S 51 , the input power failure judgement part  186  determines whether there is a zero-cross monitoring timer error. For example, when the zero-cross monitoring timer has counted the predetermined period, the input power failure judgement part  186  determines that the zero-cross monitoring timer error is occurred. When the zero-cross monitoring timer error is occurred (Yes in step S 51 ), the process proceeds to step S 52 , whereas when there is no zero-cross monitoring timer error (No in step S 51 ), the process proceeds to step S 59 . 
     In step S 52 , the input power failure judgement part  186  determines whether the heater ON flag is “1” or not. When it is determined that the heater ON flag is “1” (Yes in step S 52 ), the process proceeds to step S 53 , whereas when it is determined that the heater ON flag is “0” (No in step S 52 ), the process proceeds to step S 56 . 
     In step S 53 , since it is determined in step S 52  that the input AC waveform is abnormal in the state where the heater  22  is on, the input power failure judgement part  186  instructs the fuse cut process, so as to cut the fuse C  138   a  illustrated in  FIG. 6 . For example, the input power failure judgement part  186  changes, through the ERRdtc connector, the fuse cut signal to the H level, so as to instruct the protection operation part  129  to execute the fuse cut process. 
     Then, the input power failure judgement part  186  stores predetermined error information in the non-volatile storage  183  (step S 54 ). The input power failure judgement part  186  instructs the display controller  182  to cause the display part  20  to display an error massage (step S 55 ). 
     On the other hand, in step S 56 , since it is determined in step S 52  that the input AC waveform is abnormal in the state where the heater  22  is off, the input power failure judgement part  186  sets the heater ON permission flag to “0” so that the heater  22  is not accidentally turned on. 
     Then, the input power failure judgement part  186  stores predetermined error information in the non-volatile storage  183  (step S 57 ). The input power failure judgement part  186  instructs the display controller  182  to cause the display part  20  to display an error massage (step S 58 ). 
     In step S 59 , since the input AC waveform is normal, the input power failure judgement part  186  determines whether the heater ON flag is “1” or not. When the heater ON flag is “1” (Yes in step S 59 ), the process proceeds to step S 60 . 
     In step S 60 , the input power failure judgement part  186  determines whether the heater  22  is off. When the heater  22  is off (Yes in step S 60 ), the process proceeds to step S 61 . 
     In step S 61 , the input power failure judgement part  186  sets the heater ON flag to “0”. 
     Hereinafter, specific examples of  FIGS. 15 to 17  are explained with reference to the flowcharts illustrated in  FIGS. 13 and 14 .  FIG. 15  is a graph for explaining a first example in which the AC input is changed from a normal sine wave to a square wave. In  FIG. 15 , the vertical axis represents the voltage and the horizontal axis represents the time. Further, in  FIG. 15 , the reference numeral  60  represents the power supply waveform, the reference numeral  61  represents the AC zero-cross signal, the reference numeral  62  represents the heater ON signal (H level/L level) output from the temperature control unit  185  to control the triac  134  to turn on and off the power supply to the heater  22 , the reference numeral  63  represents the heater ON flag, and the reference numeral  64  represents the fuse cut signal. Note that the first example illustrated in  FIG. 15  is an example in which after the AC input is changed to the abnormal square wave, the AC zero-cross interrupts are detected at the falling edges of the pulses of the zero-cross signal but the pulse width of the AC zero-cross signal becomes less than 500 us. 
     At time T 01 , if there is the heater ON request from the heater temperature controller  185  for the power supply waveform  60  in the heater temperature control (Yes in S 41  in  FIG. 13 ), the input power failure judgement part  186  turns on the heater  22  (step S 42  in  FIG. 13 ). At this time, the heater ON signal is transitioned to the H level (as indicated by the reference numeral  62  in  FIG. 15 ), and the heater ON flag is set to “1” (as indicated by the reference numeral  63  in  FIG. 15 ). 
     Next, at time T 02  when the AC zero-cross interrupt occurs, the determination step (step S 50  in  FIG. 14 ) of determining whether or not the pulse width is abnormal is first executed. In step S 50  in  FIG. 14 , it is determined that the pulse width is 1 ms and thus is not abnormal, and thus the process proceeds to step S 51  in  FIG. 14 . 
     In step S 51  in  FIG. 14 , since the AC zero-cross interrupt is input normally, the input power failure judgement part  186  determines no zero-cross monitoring timer error (No in step S 51 ), and thus the process proceeds to step S 59  in  FIG. 14 . 
     In step S 59  in  FIG. 14 , it is determined that the heater ON flag is “1” as illustrated by the heater ON flag  63  in  FIG. 15 . Then, in step S 60 , it is determined that the heater  22  is not turned off, and thus the heater  22  is kept on and then the zero-cross interrupt process is terminated. 
     At time T 03  when the next AC zero-cross interrupt occurs, it is determined that the pulse the pulse width is 500 μs and abnormal (step S 50  in  FIG. 14 ), and thus the process proceeds to step S 52 . 
     In step S 52  in  FIG. 14 , as illustrated by the heater ON flag  63  in  FIG. 15 , it is determined that the heater ON flag is “1”, and thus the process proceeds to step S 53 . In step S 53  in  FIG. 14 , the input power failure judgement part  186  sets the fuse cut signal  64  to the H level, to cause the protection operation part  129  to cut the fuse C  138   a.    
     Further, the input power failure judgement part  186  stores predetermined error information into the non-volatile storage  183  (step S 54  in  FIG. 14 ), and displays the error massage on the display part  20  (step S 55  in  FIG. 14 ). 
       FIG. 16  is a graph illustrating a second example in which the AC input is changed to from a normal sine wave to a square wave. In  FIG. 16 , the vertical axis represents the voltage and the horizontal axis represents the time. Further, in  FIG. 16 , the reference numeral  70  represents the power supply waveform, the reference numeral  71  represents the AC zero-cross signal, the reference numeral  72  represents the heater ON signal (H level/L level), the reference numeral  73  represents the heater ON flag, and the reference numeral  74  represents the fuse cut signal. Note that the second example illustrated in  FIG. 16  is an example in which after the heater  22  is turned off, the AC zero-cross interrupts are detected at the falling edges of the pulses of the zero-cross signal, but the pulse width becomes abnormal. 
     At time T 11 , if there is the heater ON request from the heater temperature controller  185  for the power supply waveform  70  in the heater temperature control (Yes in S 41  in  FIG. 13 ), the input power failure judgement part  186  turns on the heater (step S 42  in  FIG. 13 ). At this time, the heater ON signal is transitioned to the H level as indicated by the reference numeral  72  in  FIG. 16 , and the heater ON flag is set to “1” as indicated by the reference numeral  73  in  FIG. 16 . 
     Next, at time T 12  when the next AC zero-cross interrupt occurs, the determination step (step S 50  in  FIG. 14 ) of determining whether or not the pulse width is abnormal is first executed. In step  50  in  FIG. 14 , it is determined that the pulse width is 1 ms and thus is not abnormal (No in step S 50 ), and thus the process proceeds to step S 51  in  FIG. 14 . 
     In step S 51  in  FIG. 14 , since the AC zero-cross interrupt is input normally, the input power failure judgement part  186  determines no zero-cross monitoring timer error (No in step S 51 ), and thus the process proceeds to step S 59  in  FIG. 14 . 
     In step S 59  in  FIG. 14 , it is determined that the heater ON flag is “1” as indicated by the heater ON flag  73  in  FIG. 16 . In step S 60 , it is determined that the heater  22  is not turned off, and thus the heater  22  is kept on and then the zero-cross interrupt process is terminated. 
     At time T 13  when the next AC zero-cross interrupt occurs, it is determined that the pulse width is 1 ms and is not abnormal (step S 50  in  FIG. 14 ), and it is determined that there is no zero-cross monitoring timer error (step S 51  in  FIG. 14 ), and then the process proceeds to step S 59  in  FIG. 14 . 
     In step S 59  in  FIG. 14 , as indicated by the heater ON flag  73  in  FIG. 16 , it is determined that the heater ON flag is “1” (Yes in step S 59  in  FIG. 14 ). However, it is determined that the heater  22  is turned off (Yes in step S 60  in  FIG. 14 ), and thus, the heater ON flag is set to “0” (step S 61  in  FIG. 14 ) as indicated by the reference numeral  73  in  FIG. 16 . 
     At time T 14  when the next AC zero-cross interrupt occurs, in step S 50  in  FIG. 14 , it is determined that the pulse width is 500 μs and is abnormal, and thus the process proceeds to step S 52  in  FIG. 14 . 
     In step S 52  in  FIG. 14 , as illustrated by the heater ON flag  73  in  FIG. 15 , it is determined that the heater ON flag is “0”, the process proceeds to step S 56 . In step S 56  in  FIG. 14 , the input power failure judgement part  186  sets the heater ON permission flag to “0”, so as to prevent the heater  22  from being accidentally turned on. 
     Then, the input power failure judgement part  186  stores the error information into the non-volatile storage  183  (step S 57 ), and displays the error massage on the display part  20  (step S 58 ). In this case, the fuse cut signal is never turned on. 
       FIG. 17  is a graph illustrating a third example in which the AC input is changed from a normal sine wave to a square wave. In  FIG. 17 , the vertical axis represents the voltage and the horizontal axis represents the time. Further, in  FIG. 17 , the reference numeral  80  represents the power supply waveform, the reference numeral  81  represents the AC zero-cross signal, the reference numeral  82  represents the heater ON signal (H level/L level), the reference numeral  83  represents the heater ON flag, and the reference numeral  74  represents the fuse cut signal. Note that the third example illustrated in  FIG. 17  is an example in which after the AC input is changed to the abnormal square wave, the AC zero-cross interrupts are not detected. 
     At time T 21 , if there is the heater ON request from the heater temperature controller  185  for the power supply waveform  80  in the heater temperature control (Yes in S 41  in  FIG. 13 ), the input power failure judgement part  186  turns on the heater  22  (step S 42  in  FIG. 13 ). At this time, the heater ON signal is transitioned to the H level as indicated by the reference numeral  82  in  FIG. 17 , and the heater ON flag is set to “1” as indicated by the reference numeral  83  in  FIG. 17 . 
     At time T 22  when the next AC zero-cross interrupt occurs, the determination step (step S 50  in  FIG. 14 ) of determining whether or not the pulse width is abnormal is first executed. In step S 50  in  FIG. 40 , it is determined that the pulse width is 1 ms and not abnormal (No in step S 50 ), and thus the process proceeds to step S 51  in  FIG. 14 . 
     In step S 51  in  FIG. 14 , since the AC zero-cross interrupt is input normally, the input power failure judgement part  186  determines there is no zero-cross monitoring timer error (No in step S 51 ), and thus the process proceeds to Step S 59  in  FIG. 14 . 
     In step S 59  in  FIG. 14 , as indicated by the heater ON flag  83  in  FIG. 17 , it is determined that the heater ON flag is “1” (Yes in step S 59  in  FIG. 14 ). Then, in step S 60 , it is determined that the heater  22  is not turned off (No in step S 60 ), and thus the heater  22  is kept on and the zero-cross interrupt process is terminated. 
     After that, as illustrated in  FIG. 17 , the power supply waveform  80  is changed to a square wave and thus no zero-cross interrupt is entered. At time T 23 , the AC zero-cross process in step S 20  in  FIG. 10  is executed in response to the timer interrupt due to the overflow of the zero-cross monitoring timer. 
     In step S 50  in  FIG. 14  of determining whether or not the pulse width is abnormal, since no pulse width is detected, it is determined that the pulse width is not abnormal (No in step S 50 ), and thus the process proceeds to step S 51 . In step S 51  in  FIG. 14 , since there is the zero-cross monitoring timer error (Yes in step S 51 ), the process proceeds to step S 52 . 
     In step S 52  in  FIG. 14 , as illustrated by the heater ON flag  83  in  FIG. 17 , it is determined that the heater ON flag is “1” (Yes in step S 52 ), the process proceeds to step S 53 . In step S 53  in  FIG. 14 , the input power failure judgement part  186  sets the fuse cut signal  84  to the H level, to cause the protection operation part  129  to cut the fuse C  138   a.    
     Further, the input power failure judgement part  186  stores the predetermined error information into the non-volatile storage  183  (step S 54  in  FIG. 14 ), and displays the error massage on the display part  20  (step S 55  in  FIG. 14 ). 
     Note that the above described operation in the example where the AC zero-cross interrupts are not detected as illustrated in  FIG. 17  is applicable not only when a square wave is input, but also when a DC is input, or a DC and an AC superimposed on each other are input. 
     According to one or more embodiments described above, the fuse C  138   a  is cut off as long as the input AC voltage waveform becomes abnormal in the state where the heater  22  is turned on. Accordingly, this prevents the fuse C  138   a  from being unintentionally cut even though the operation of the triac  134  is turned off. Therefore, when the normal AC input is restored, the recovery becomes easier. Note that here it is determined that the waveform of the input AC voltage is abnormal when the input AC voltage become a square wave. 
     The above descried one or more embodiments are applicable to any apparatus including a fixation device such as a printer, a facsimile device, a multi-function printer, or the like. 
     Note that in a case of an apparatus in which a halogen lamp is used for the heater  22  of the fixation device  11 , a zero-cross detection circuit is used in the phase control with reference to an AC zero-cross signal thereof to suppress inrush currents, thus the AC zero-cross signal may be shared. 
     In one or more embodiments described above, when it is determined that the waveform of the input voltage is abnormal and the triac  134  turns on the heater  22 , the input power failure judgement part  186  instructs the protection operation part  129  to executes the fuse cut. However, the invention is not limited to this. For example, when it is determined that the waveform of the input voltage is abnormal, the input power failure judgement part  186  may instruct the protection operation part  129  to executes the fuse cut. 
     The invention includes other embodiments in addition to the above-described embodiments without departing from the spirit of the invention. The embodiments are to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. Hence, all configurations including the meaning and range within equivalent arrangements of the claims are intended to be embraced in the invention.