Patent Publication Number: US-2022236675-A1

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an image forming apparatus, such as a printer and a copier, using an electrophotographic system. The present invention also relates to an image heating apparatus, such as a glossing apparatus, that improves a gloss value of a toner image, by reheating the toner image fixed to a fixing unit equipped in the image forming apparatus, or to a recording material. 
     Description of the Related Art 
     In order to implement both reducing higher harmonic waves generated from the electric current applied from a commercial AC power supply to a fixing apparatus (image heating apparatus) and decreasing flickers in the image heating apparatus, controlling a waveform pattern of an electric current that flows through the heating elements of a heater has been performed. For example, Japanese Patent Application Publication No. 2003-123941 discloses a control in which: a phase control is used for at least one half wave out of a control cycle, which is a multiple of one half wave of a commercial frequency; and a wave number control is used for the other half wave, where power is supplied continuously or not supplied at all. 
     SUMMARY OF THE INVENTION 
     In a case where overvoltage outside the rating is applied to an image heating apparatus equipped in the image forming apparatus under a conventional heating element control system, overvoltage may be applied to the heating elements inside the image heating apparatus. Therefore sufficient countermeasures must be taken to prevent damage to the heating elements. 
     It is an object of the present invention to provide a technique to suppress overvoltage applied to the heating elements. 
     To solve this problem, an image forming apparatus of the present invention includes: 
     an image forming portion that forms an image on a recording material; 
     a heating portion that includes a heating element which is heated by power supplied from a commercial AC power supply and heats an image formed by the image forming portion: 
     a temperature detecting portion that detects temperature of the heating portion; and 
     a power control portion that controls power supplied from the commercial AC power supply to the heating element based on temperature information detected by the temperature detecting portion, wherein 
     the image forming apparatus further comprises a detecting portion that detects whether voltage applied from the commercial AC power supply exceeds a rated value, wherein 
     in a case where the detecting portion detects that the voltage applied from the commercial AC power supply exceeds the rated value, the power control portion controls the power supply such that a waveform pattern of an electric current flowing to the heating element in one control cycle becomes a waveform pattern of phase control, where power supplying time to the heating element in one half wave becomes a predetermined time or less. 
     As described above, according to the present invention, overvoltage applied to the heating elements can be suppressed, hence damage to the heating element can be avoided. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an image forming apparatus of Embodiment 1: 
         FIGS. 2A to 2C  are schematic diagrams of an image heating apparatus of Embodiment 1; 
         FIG. 3  is a control circuit diagram according to Embodiment 1; 
         FIG. 4  is a diagram for describing a peak voltage detecting portion according to Embodiment 1; 
         FIG. 5  is a diagram for describing a supply power pattern according to Embodiment 1: 
         FIGS. 6A and 6B  are diagrams for describing the circuit operation and supply power pattern according to Embodiment 1: 
         FIG. 7  is a control flow chart according to Embodiment 1; 
         FIG. 8  is a control circuit diagram according to Embodiment 2; 
         FIG. 9  is a diagram for describing a peak voltage detecting portion according to Embodiment 2; and 
         FIG. 10  is a control flow chart according to Embodiment 2. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a description will be given, with reference to the drawings, of embodiments (examples) of the present invention. However, the sizes, materials, shapes, their relative arrangements, or the like of constituents described in the embodiments may be appropriately changed according to the configurations, various conditions, or the like of apparatuses to which the invention is applied. Therefore, the sizes, materials, shapes, their relative arrangements, or the like of the constituents described in the embodiments do not intend to limit the scope of the invention to the following embodiments. 
     Embodiment 1 
       FIG. 1  is a schematic cross-sectional view of an image forming apparatus  100  using an electrophotographic recording system according to an embodiment of the present invention. Image forming apparatuses to which the present invention is applicable are a copier and a printer that use an electrophotographic system or an electrostatic recording system, and a case of applying the present invention to a laser printer, which forms an image on a recording paper P (recording material) using the electrophotographic system, will be described. 
     The image forming apparatus  100  includes a video controller  120  and a control portion  113 . As an acquisition portion that acquires information on an image to be formed on the recording material, the video controller  120  receives and processes image information and print instructions which are sent from such an external device as a personal computer. The control portion  113  is connected with the video controller  120 , and controls each composing element constituting the image forming apparatus  100 , in accordance with an instruction from the video controller  120 . When the video controller  120  receives a print instruction from an external device, the following operation to form an image is executed. 
     When an image forming apparatus main body  100  receives a print signal, a scanner unit  21  emits a laser beam, which has been modulated in accordance with the image information, and scans the surface of a photosensitive drum  19 , which has been charged to a predetermined polarity by a charging roller  16 , with the laser light. Thereby an electrostatic latent image is formed on the photosensitive drum  19 . When toner is supplied from a developing roller  17  to this electrostatic latent image on the photosensitive drum  19 , the electrostatic latent image is developed as a toner image. On the other hand, recording materials (recording paper) P loaded on a paper feeding cassette  11  are fed one by one by a pickup roller  12 , and are conveyed toward a resist roller pair  14  by a conveying roller pair  13 . At a timing when the toner image on the photosensitive drum  19  reaches a transfer position, constituted of the photosensitive drum  19  and a transfer roller  20 , the recording material P is conveyed from the resist roller pair  14  to the transfer position. While the recording material P passes through the transfer position, the toner image on the photosensitive drum  19  is transferred to the recording material P. Then the recording material P is heated by a fixing apparatus (fixing portion)  200 , which is an image heating apparatus (image heating portion), whereby the toner image is heat-fixed to the recording material P. The recording material P bearing the fixed toner image is discharged to a tray, which is located on the upper part of the image forming apparatus  100 , by a conveying roller pair  26  and  27 . A drum cleaner  18  cleans toner remaining on the photosensitive drum  19 . A paper feeding tray  28  (manual feeding tray), which is a pair of recording material restriction plates and of which width can be adjusted in accordance with the size of the recording material P, is disposed to support a recording material P of which size is substandard. A pickup roller  29  feeds the recording material P from the paper feeding tray  28 . The image forming apparatus main body  100  includes a motor  30  that dives the fixing apparatus  200  and the like. 
     A control circuit  300 , which is a power control portion connected to a commercial AC power supply  301 , supplies power to the fixing apparatus  200 . The above mentioned photosensitive drum  19 , charging roller  16 , scanner unit  21 , developing roller  17  and transfer roller  20  constitute an image forming portion that forms an unfixed image on a recording material P. In Embodiment 1, a developing unit including the photosensitive drum  19 , the charging roller  16  and the developing roller  17 , and a cleaning unit including the drum cleaner  18 , are configured as a process cartridge  15 , which is attachable to/detachable from the apparatus main body of the image forming apparatus  100 . The fixing apparatus  200  is also configured to be attachable to/detachable from the image forming apparatus  100 . 
       FIG. 2A  is a schematic cross-sectional view of the fixing apparatus  200 , which is the image heating apparatus of Embodiment 1. The fixing apparatus  200  includes a fixing film (hereafter referred to as “film”)  202 , which is an endless belt, a heater  203  which contacts with the inner surface of the film  202 , a pressure roller  208  which is press-contacted to the heater  203  via the film  202 , and a metal stay  204 . The pressure roller (nip forming member)  208  is press-contacted to the outer surface of the film  202 , and the pressure roller  208  and the heater  203  form a fixing nip N. 
     The film  202  is a cylindrical multilayer heat resistant film, and the material of the base layer is a heat resistant resin (e.g. polyimide), or a metal (e.g. stainless steel). An elastic layer (e.g. heat resistant rubber) may be disposed on the surface layer of the film  202 . A temperature detecting portion  212  (e.g. thermistor) contacts with the heater  203 . The pressure roller  208  includes a core metal  209  (e.g. iron, aluminum) and an elastic layer  210  (e.g. silicon rubber). The heater  203  is held on the inner side of the film  202  by a holding member  201  made of heat resistant resin. The holding member  201  also has a guide function to guide the rotation of the film  202 . The metal stay  204  is configured to apply pressure of a spring (not illustrated) to the holding member  201 . The heater  203 , the holding member  201  and the stay  204  constitute a heater unit  211 . Such a member as a heat transfer member may be disposed between the film  202  and the heater  203 . The pressure roller  208  rotates in the arrow direction by power received from the motor  30 . The film  202  is rotated by the rotation of the pressure roller  208 . The recording paper P bearing an unfixed toner image is held and conveyed by the fixing nip N, during which heating and fixing processing are performed. 
       FIG. 2B  indicates an example of the heater  203 , and is heated by heating elements (heating resistors)  202   a  and  202   b  disposed on a ceramic substrate. The power supplied from the later mentioned C 1  and C 2  of the control circuit  300  is supplied to the heating elements  202   a  and  202   b  via the electrodes E 1  and E 2  and the conductor  213  disposed on the ceramic heater. 
       FIG. 2C  also indicates an example of the heater  203 . Heating elements  202   a  and  202   b  disposed on a ceramic substrate are divided into heating element  202   a - 1  to heating element  202   a - 7 , and heating element  202   b - 1  to heating element  202   b - 7  respectively in the longitudinal direction. Thereby a heating zone of the respective heating elements can be controlled in accordance with the paper size of the recording paper P in the longitudinal direction of the ceramic heater. Each of E 3 - 1  to E 3 - 7  disposed on each of conductors  203 - 1  to  203 - 7  is an electrode of each heating element, and power is supplied to each heating element by supplying power to the electrode of each heating element and the electrodes E 4  and E 5  disposed between a conductor  201   a  and a conductor  201   b.    
       FIG. 3  indicates the control circuit  300  according to Embodiment 1, that supplies power from the commercial AC power supply  301  to the fixing apparatus  200 . The control circuit  300  is constituted of a power supply portion  302 , a zero-cross detecting circuit portion  313 , a peak voltage detecting portion  400 , a relay  312 , and a power control portion  314  (hereafter referred to as “engine controller  314 ”). The power supply portion  302  is connected to one side of the commercial power supply  301 , and is connected to the fixing apparatus  200  via a connection terminal C 2 . The electric current flows to a photo triac coupler  307  via a transistor  311  by an ON 1  signal outputted from the engine controller  314 . As a result, the electric current flows into a gate of the triac  303 , whereby the triac is turned ON and the electric current flows to the triac  303 . The zero-cross detecting circuit portion  313  and the peak voltage detecting portion  400  are both connected to the commercial AC power supply  301 . The zero-cross detecting circuit portion  313  outputs a zero-cross signal, which indicates a zero-cross point of the commercial AC waveform, to the engine controller  314 . The peak voltage detecting portion  400  outputs the information VIN on the peak voltage of the commercial AC waveform to the engine controller  314 . Based on the temperature information sent from the temperature detecting portion  212  inside the fixing apparatus  200 , the engine controller  314  controls the power supply portion  302  via the ON 1  signal, so that the detected temperature becomes a predetermined temperature. 
       FIG. 4  indicates a circuit diagram of the peak voltage detecting portion  400  according to Embodiment 1, which is a first peak voltage detecting portion.  FIG. 4  indicates a part of a switching power supply device where an active clamp system is used for an insulating type convertor using a fly-back transfer, so as to convert the AC power, supplied from the commercial AC power supply  301  to DC power, and supply the power to the image forming apparatus. The commercial AC power supply  301 , outputs AC voltage, and voltage rectified by a bridge diode  402  (full wave rectifving unit) is inputted to a switching power supply circuit  401 . A smoothing capacitor  403  is used as a smoothing unit to smooth the rectified voltage, and the lower side potential of the smoothing capacitor  403  is denoted with DCL, and the higher side potential thereof is denoted with DCH. The switching power supply circuit  401  outputs the power supply voltage, such as a constant voltage V 11  (e.g. 5V), from the input peak voltage charged in the smoothing capacitor C 3  to an insulating secondary side. The switching power supply circuit  401  includes an insulating type transformer T 1 , which includes a primary coil P 1  and an auxiliary coil P 2  on the primary side and a secondary coil S 1  on the secondary side. By the switching operation of an FET  404  and an FET  405  controlled by a primary side control portion  419 , energy is supplied from the primary coil P 1  to the secondary coil S 1  in the transformer T 1 . The capacitor  406  used for clamping the voltage and the FET  404 , which are connected in series, are connected to the primary coil P 1  of the transformer T 1  in parallel. The capacitor C 1  for resonating the voltage, which is connected in parallel with the FET  405 , is disposed to reduce loss of the FET  404  and the FET  405  when the switch is turned OFF. A resistor  407  is a current detecting resistor, and supplies voltage IA, which corresponds to a current load value, to the primary side control portion  419 . The auxiliary coil P 2  of the transformer T 1  rectifies and smooths the forward voltage of the input peak voltage that is applied to the primary coil P 1 , using a diode  408 , a resistor  409  and a capacitor  410 , and this voltage is divided using a resistor  411  and a resistor  412 , is smoothed by a capacitor  413 , and is inputted to the primary side control portion  419  as a voltage ACV. The voltage of the ACV is a voltage that is in proportion to the input peak voltage. The primary side control portion  419  outputs a PWM signal generated by converting the voltage value of the ACV into a pulse width, and inputs it to the gate of the FET  415  via a resistor  414 . Electric current is supplied to a photocoupler  416  via a resistor  417  in accordance with the switching of the FET  415 . The pulse signal transferred to the secondary side via the photocoupler  416  is smoothed via a resistor  418 , a resistor  421  and a capacitor  420 , and is supplied to the engine controller  314  as a VIN signal. 
     As described above, the peak voltage detecting portion  400  according to Embodiment 1 converts the voltage, which is in proportion to the input peak voltage detected via the auxiliary coil P 2  (a part of the switching power supply device  401 ), into a pulse signal, transfers the pulse signal to the secondary side, and smooths the pulse signal using the resistor  418  and the capacitor  420 , whereby the VIN signal is transferred to the engine controller  314 . Then the engine controller  314  can recognize the input voltage value by converting the VIN signal into the input peak voltage. 
       FIG. 5  is a diagram indicating supply power patterns  501  that flow into the fixing apparatus  200  via the triac  303  when the engine controller  314  of Embodiment 1 supplies an ON 1  signal to the power supply portion  302 . Each supply power pattern  501  is based on the assumption that the power flowing into the fixing apparatus  200  is updated every four cycles (four full waves) of the commercial AC power supply, and  FIG. 5  indicates the supply power patterns  501  when four full waves comprise one cycle of a control cycle (one control cycle). In a supply power pattern  501 , when the power to be supplied to the fixing apparatus  200  is 0 to 25%, the first full wave is a wave number control (OFF), the second full wave is a phase control, the third full wave is a wave number control (OFF), and the fourth full wave is a wave number control (OFF), that is, in this control waveform, the wave number control (OFF) and the phase control are mixed in the four full waves. In the control waveform of the supply power pattern  501 , when the power to be supplied to the fixing apparatus  200  is 25 to 100% as well, the wave number control (ON/OFF) and the phase control are mixed in the four full waves. Hereafter, the control waveform, in which the wave number control and the phase control are mixed, is referred to as “hybrid control”. In Embodiment 1, the temperature control system of the power supply portion  302  via the ON 1  signal supplied by the engine controller  314  is hybrid control as a standard, in which the wave number control and the phase control are mixed, as described in  FIG. 5 . In other words, in one control cycle, power is supplied by one of the waveform pattern of the wave number control; the waveform pattern of the phase control; and the control pattern combining the wave number control and the phase control. 
       FIG. 6A  is a diagram indicting the transition of the waveform of the peak voltage detecting portion VIN described in  FIG. 4  and the transition of the supply power pattern  501 , which characterizes Embodiment 1, in a case where the input voltage changes from the normal voltage to overvoltage.  FIG. 6B  indicates a method for controlling the supply power pattern  501  in a case where the engine controller  314 , which is a detecting portion to detect whether the voltage applied from the commercial AC power supply exceeds a rated value or not, detected overvoltage. In  FIG. 6A , the input voltage changes from a normal voltage to the overvoltage at timing A, since voltage exceeding the rated value was applied from the commercial AC power supply. In other words, the VIN signal of the peak voltage detecting portion  400  gradually increases from the timing A at a speed of the charges that are stored in the smoothing capacitor  403 , and the voltage of the VIN signal saturates as the charges in the smoothing capacitor  403  saturate. The engine controller  314  judges an overvoltage when the voltage of VIN exceeds a predetermined voltage Vth (predetermined threshold). In  FIGS. 6A and 6B , the timing when VIN exceeded the predetermined voltage Vth is the timing B. At the timing B when overvoltage was determined, the engine controller  314  immediately changes the supply power pattern  501  from the hybrid control described in  FIG. 5  to the phase control waveforms alone. In  FIG. 6B , ±Vbreak indicates the voltage threshold to prevent damage to the heating elements. The engine controller  314  stores a predetermined ON time tmax with which the supply power pattern  501  does not exceed ±Vbreak voltage, whereby the supply power pattern  501  is controlled such that the ON time of the ON 1  signal does not exceed the time of tmax. The supply power pattern  501  indicated in  FIG. 6B  is an example of a waveform pattern of the phase control where in one full wave of one control cycle, the time when power is supplied to the heating elements in one half wave is within a predetermined time. 
       FIG. 7  is a control flow chart of the engine controller  314  according to Embodiment 1. In S 1 , in a case where a printer request was received from a user, the engine controller  314  starts the request to supply power. In S 2 , processing advances to S 3  if the VIN signal detected by the peak voltage detecting portion  400  exceeds the predetermined voltage Vth, or advances to S 6  if the VIN signal is the predetermined voltage Vth or less. In S 3 , the engine controller  314  selects the phase control for the temperature control and starts supplying power. At this time, the tmax time is set for the ON 1  signal, and the temperature control is started with the ON time which is tmax or less. In S 4 , when the temperature detected by the temperature detecting portion  212  reaches a target temperature T, the engine controller  314  starts feeding paper from the paper feeding cassette  11 . In S 5 , it takes time to control the temperature to the target temperature since the power supplied to the fixing apparatus  200  is limited by the tmax time of the ON 1  signal. Therefore a control, to set the paper feeding interval after the second paper to Amm, is executed. In other words, images are formed continuously on a plurality of recording materials, and the conveying intervals of the plurality of recording materials are set longer when continuous paper feeding, to heat the images continuously, is performed. Thereby power required for the fixing apparatus  200  to fix the images is decreased. Then processing advances to S 13 . 
     In S 6 , the engine controller  314  selects the standard hybrid control for the temperature control, and starts supplying power. In S 7 , when the temperature detected by the temperature detecting portion  212  reaches the target temperature T, the engine controller  314  starts feeding paper from the paper feeding cassette  11 . In S 8 , control, to set the paper feeding interval after the second paper to standard Bmm, is executed. In S 9 , it is detected whether the VIN signal exceeded a predetermined voltage Vth during paper feeding, and processing advances to S 10  if exceeded, or to S 12  if not. In S 10 , the engine controller  314  shifts the standard hybrid control to the phase control if the VIN signal&gt;voltage Vth is detected for E seconds. E seconds is a chattering time. In S 11 , the engine controller  314  executes a control to set the paper interval to Amm if VIN signal&gt;voltage Vth is detected for F seconds, and processing advances to S 13 . F seconds is a chattering time. When the engine controller  314  determines to stop printing in S 12 , the temperature control and the print control are stopped, and processing is ended. Processing returns to S 9  if the stop request is not received. In S 13 , it is detected whether the VIN signal dropped to a predetermined voltage Vth 2  or less during paper feeding, and processing advances to S 14  is dropped, or to S 16  is not. For the voltage of Vth 2 , a hysteresis relationship of Vth 1 ≥Vth 2  may be set to stabilize control. In S 14 , the engine controller  314  shifts the phase control to the standard hybrid control if VIN signal&lt;voltage Vth 2  is detected for C seconds. C seconds is a chattering time. In S 15 , the engine controller  314  shifts to a control to set a paper interval to standard Bmm if VIN signal&lt;voltage Vth 2  is detected for D seconds. When the engine controller  314  determines to stop printing in S 16 , the temperature control and the print control are stopped, and processing is ended. Processing returns to S 9  if the stop request is not received. 
     As described above, the sequence to control the overvoltage applied to the heating elements of Embodiment 1 has the following characteristics.
         When the peak voltage exceeds a predetermined voltage, the temperature control is changed to the phase control.   At this time, it is controlled such that the ON 1  signal, to drive the triac  303 , does not become ON for a predetermined time or longer.   The paper interval is set to Amm which is wider than the standard Bmm (A&gt;B).       

     According to Embodiment 1, the overvoltage applied to the heating elements can be suppressed, hence damage to the heating elements can be easily avoided. 
     Embodiment 2 
       FIG. 8  indicates a control circuit  800  according to Embodiment 2 that supplies power from the commercial AC power supply  301  to the fixing apparatus  200 . The control circuit  800  is constituted of the power supply portion  302 , the zero-cross detecting circuit portion  313 , a peak voltage detecting portion  801 , the relay  312  and the engine controller  314 , and here the peak voltage detecting portion  801 , which is a characteristic of Embodiment 2, will be described. One side of the peak voltage detecting portion  801  is connected with the commercial power supply  301  at a location N 1 , and the other side is electrically connected with the image heating apparatus at a location N 2 , so that the peak voltage detecting portion  801  detects voltage applied to the fixing apparatus  200 . 
       FIG. 9  indicates a circuit diagram of the peak voltage detecting portion  801  according to Embodiment 2, which is a second peak voltage detecting portion. The voltages supplied from N 1  and N 2 , which are connected to the fixing apparatus  200 , are rectified by a diode array  900 . The rectified voltage is divided by the resistors  901  and  902 , and are applied to a Zener diode  903 . The threshold Vth of the peak voltage that is applied to the image heating apparatus is determined by the divided voltage values of the resistors  901  and  902  and the voltage of the Zener diode. If voltage exceeding the Zener voltage is applied to the resistor  902 , voltage is applied to a base of a transistor  904  and a base resistor  905 , and the transistor  904  is turned ON. When the transistor  904  turns ON, electric current limited by a resistor  907  flows into a primary side LED of a photocoupler  906 , and a secondary side transistor turns ON. As a result, the VIN 2  signal, inputted to the engine controller  314 , changes from HIGH to LOW. 
     As described above, the peak voltage detecting portion  801 , according to Embodiment 2, sets the voltage threshold to prevent damage to the heating elements using the divided voltages of the resistors  901  and  902  and the voltage of the Zener diode  903 , and transfers the binary information, indicating whether each threshold is exceeded or not, to the engine controller  314 . 
       FIG. 10  is a control flow chart of the engine controller  314  according to Embodiment 2. In T 1 , the engine controller  314  starts a request to supply power if a print request is received from a user. In T 2 , the engine controller  314  selects the standard hybrid control for the temperature control, and starts supplying power. In T 3 , the engine controller  314  determines whether the VIN 2  signal detected by the peak voltage detecting portion  801  is LOW, and processing advances to T 4  if the VIN 2  signal is LOW, or advances to T 7  if the VIN 2  signal is HIGH. In T 4 , the engine controller  314  selects the phase control for the temperature control and continues supplying power if LOW of the VIN 2  signal is detected for E seconds. E seconds is a chattering time. Then the engine controller  314  gradually decreases the power supplying time of the triac  303  by the ON 1  signal, and stores the time when VIN 2 =L changed to H as tmax. In other words, the engine controller  314  acquires tmax, which is a predetermined power supplying time at which the peak voltage, detected by the peak voltage detecting portion  801 , becomes a second predetermined threshold or less in order to prevent applying overvoltage. In T 5 , the temperature control by the phase control is continued so that the ON 1  signal does not exceed tmax. In T 6 , the engine controller  314  starts a control to set paper interval to Amm if LOW of the VIN 2  signal is detected for F seconds. F seconds is a chattering time. When the engine controller  314  determines to stop printing in T 7 , the temperature control and the print control are stopped, and processing is ended. Processing returns to T 3  if the stop request is not received. 
     As described above, the sequence to suppress the overvoltage applied to the heating elements of Embodiment 2 has the following characteristics.
         The peak voltage detecting portion  801  detects voltage that is applied to the heating elements.   The ON time of the ON 1  signal, where overvoltage is not applied to the heating elements, is detected, and after the ON time is detected, the ON 1  signal is limited so as not to exceed the ON time.       

     According to Embodiment 2, the overvoltage applied to the heating elements can be directly detected and suppressed, hence damage to the heating elements can be avoided with more accuracy than Embodiment 1. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2021-009483, filed on Jan. 25, 2021, which is hereby incorporated by reference herein in its entirety.