Patent Publication Number: US-9904203-B2

Title: Image forming apparatus and image forming method for charging image carrier

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2015-194322 filed on Sep. 30, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to an image forming apparatus and an image forming method that are capable of forming an image in an electrophotographic manner. 
     In image forming apparatuses such as a printer capable of forming an image in an electrophotographic manner, the surface of an image carrier such as a photosensitive drum is charged and an electrostatic latent image is formed on the surface of the image carrier. For example, this type of image forming apparatus is provided with a charging member for charging the surface of the image carrier by DC voltage applied from a power supply. 
     By the way, in the image forming apparatus, the DC voltage applied to the charging member might pulsate. For example, in the image forming apparatus, in the case where superimposition voltage obtained by superimposing DC voltage and AC voltage is applied to a development member for developing an electrostatic latent image formed on the surface of the image carrier, the DC voltage applied to the charging member interferes with the superimposition voltage and thereby pulsates. If the DC voltage applied to the charging member pulsates, variations occur in the surface potential of the image carrier, whereby density unevenness occurs in an image formed on the surface of the image carrier. In this regard, technology of suppressing pulsation of DC voltage applied to the charging member, by connecting a capacitor connected to the ground, to the charging member, is known. 
     SUMMARY 
     An image forming apparatus according to one aspect of the present disclosure includes an image carrier, a charging member, a capacitor, a voltage control portion, and a current conduction control portion. The charging member is configured to charge the image carrier. The capacitor is connected on a current conduction path connecting the charging member and a ground. The voltage control portion is configured to control whether or not to apply DC voltage to the charging member. The current conduction control portion is configured to make the current conduction path conductive after DC voltage is applied by the voltage control portion, and to disconnect the current conduction path before application of DC voltage by the voltage control portion is stopped. 
     An image forming method according to another aspect of the present disclosure is executed by a processor provided in an image forming apparatus including: an image carrier; a charging member configured to charge the image carrier; and a capacitor connected on a current conduction path connecting the charging member and a ground. The image forming method includes a first step and a second step. In the first step, whether or not to apply DC voltage to the charging member is controlled. In the second step, the current conduction path is made conductive after DC voltage is applied in the first step, and the current conduction path is disconnected before application of DC voltage in the first step is stopped. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the configuration of an image forming apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a block diagram showing the system configuration of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG. 3  is a diagram showing the configuration of a power supply portion of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG. 4  is a flowchart showing an example of a second voltage control process executed by the image forming apparatus according to the embodiment of the present disclosure. 
         FIG. 5  is a flowchart showing an example of a first voltage control process executed by the image forming apparatus according to the embodiment of the present disclosure. 
         FIG. 6  is a diagram showing output timings of control signals outputted from a control portion of the image forming apparatus according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, with reference to the accompanying drawings, embodiments of the present disclosure will be described for understanding of the present disclosure. It is noted that the following embodiments are examples in which the present disclosure is embodied, and do not limit the technical scope of the present disclosure. 
     [Schematic Configuration of Image Forming Apparatus  10 ] 
     First, with reference to  FIG. 1  and  FIG. 2 , the schematic configuration of an image forming apparatus  10  according to an embodiment of the present disclosure will be described. Here,  FIG. 1  is a schematic sectional view showing the configuration of the image forming apparatus  10 . 
     As shown in  FIG. 1  and  FIG. 2 , the image forming apparatus  10  includes an ADF  1 , an image reading portion  2 , an image forming portion  3 , a sheet feed portion  4 , a control portion  5 , an operation display portion  6 , and a power supply portion  7 . The image forming apparatus  10  is a multifunction peripheral having a plurality of functions such as a facsimile function or a copy function as well as a scan function of reading image data from a document and a print function of forming an image on the basis of the image data. In addition, the present disclosure is applicable to image forming apparatuses such as a printer device, a facsimile device, and a copy machine. 
     The ADF  1  includes a document set portion, a plurality of conveyance rollers, a document holder, and a sheet discharge portion, and is an automatic document feeder which conveys a document to be read by the image reading portion  2 . The image reading portion  2  includes a document table, a light source, a plurality of mirrors, an optical lens, and a CCD (Charge Coupled Device), and is capable of reading image data from a document. 
     The control portion  5  includes control devices such as a CPU, a ROM, a RAM, and an EEPROM (registered trademark), which are not shown. The CPU is a processor which executes various calculation processes. The ROM is a nonvolatile storage portion in which information such as a control program for causing the CPU to execute various processes is stored in advance. The RAM is a volatile storage portion used as a temporary storage memory (working area) for various processes to be executed by the CPU. The EEPROM is a nonvolatile storage portion. In the control portion  5 , various control programs stored in advance in the ROM are executed by the CPU. Thus, the image forming apparatus  10  is comprehensively controlled by the control portion  5 . It is noted that the control portion  5  may be configured from an electronic circuit such as an integrated circuit (ASIC), or may be a control portion provided separately from a main control portion for comprehensively controlling the image forming apparatus  10 . 
     The operation display portion  6  has: a display portion such as a liquid crystal display which displays various information in accordance with a control command from the control portion  5 ; and an operation portion such as an operation key or a touch panel for inputting various information to the control portion  5  in accordance with a user&#39;s operation. 
     The image forming portion  3  is capable of executing an image forming process (printing process) for forming an image in an electrophotographic manner on the basis of image data read by the image reading portion  2  or image data inputted from an information processing device such as an external personal computer. 
     Specifically, as shown in  FIG. 1 , the image forming portion  3  includes a photosensitive drum  31 , a charging member  32 , a light scanning unit  33 , a developing device  34 , a transfer roller  35 , a cleaning device  36 , an electricity removing device  37 , a fixing device  38 , and a sheet discharge tray  39 . 
     The photosensitive drum  31  allows an electrostatic latent image to be formed on the surface thereof. For example, the photosensitive drum  31  is formed by coating the surface of an element tube made of aluminum, with an organic photosensitive material composed of an organic compound that improves electric conductivity when being irradiated with light. Here, the photosensitive drum  31  is an example of an image carrier in the present disclosure. 
     The charging member  32  charges the surface of the photosensitive drum  31 . For example, the charging member  32  is a roller member provided in contact with the surface of the photosensitive drum  31 . DC voltage is applied to the charging member  32  from a first power supply portion  71  described later. Thus, discharge occurs between the charging member  32  and the photosensitive drum  31 , whereby the surface of the photosensitive drum  31  is charged. It is noted that the charging member  32  may be a member provided in a contactless manner with the surface of the photosensitive drum  31 . 
     The light scanning unit  33  forms an electrostatic latent image on the surface of the photosensitive drum  31 . Specifically, the light scanning unit  33  applies light based on image data to the surface of the photosensitive drum  31  charged by the charging member  32 . 
     The developing device  34  develops the electrostatic latent image formed on the surface of the photosensitive drum  31 , using toner. Specifically, the developing device  34  includes a development member  341  which supplies toner to the surface of the photosensitive drum  31 . For example, the development member  341  is cylindrical shape and rotatable a roller member provided away from the surface of the photosensitive drum  31 . Superimposition voltage obtained by superimposing DC voltage and AC voltage is applied to the development member  341  from a second power supply portion  72  described later. Thus, an electric field is formed between the development member  341  and the photosensitive drum  31 , and toner is supplied from the development member  341  to the surface of the photosensitive drum  31 . It is noted that the developing device  34  is supplied with toner (developer) from a toner container  34 A attachable to and detachable from the image forming portion  3 . 
     The transfer roller  35  transfers a toner image formed on the surface of the photosensitive drum  31  by the developing device  34 , to a sheet fed from the sheet feed portion  4 . The superimposition voltage obtained by superimposing DC voltage and AC voltage is applied to the transfer roller  35  from a power supply device (not shown). Thus, an electric field is formed between the transfer roller  35  and the photosensitive drum  31 , and the toner image formed on the surface of the photosensitive drum  31  is transferred to the sheet. 
     The cleaning device  36  cleans the surface of the photosensitive drum  31  after the toner image is transferred by the transfer roller  35 . For example, the cleaning device  36  includes: a blade-like cleaning member which removes the remaining toner on the surface of the photosensitive drum  31 ; and a conveyance screw which conveys the toner removed by the cleaning member to a toner storage case (not shown). 
     The electricity removing device  37  applies light to the surface of the photosensitive drum  31 , to remove the remaining charge on the surface of the photosensitive drum  31 . 
     The fixing device  38  melts and fixes, on the sheet, the toner image transferred to the sheet by the transfer roller  35 . For example, the fixing device  38  includes a fixing roller  381  and a pressure roller  382 . The fixing roller  381  is provided in contact with the pressure roller  382 , and heats the toner image transferred to the sheet, to fix the toner image on the sheet. The pressure roller  382  pressurizes the sheet passing through a contact part formed between the pressure roller  382  and the fixing roller  381 . 
     The sheet on which the toner image is fixed by the fixing device  38  is discharged to the sheet discharge tray  39 . 
     In the image forming portion  3 , an image is formed on a sheet fed from a sheet feed cassette attachable to and detachable from the sheet feed portion  4 , through the following procedure, and the sheet after the image formation is discharged to the sheet discharge tray  39 . It is noted that the sheet is a sheet material such as paper, coated paper, a postcard, an envelope, or an OHP sheet. 
     First, the surface of the photosensitive drum  31  is uniformly charged at a predetermined potential by the charging member  32 . Next, the light scanning unit  33  applies light based on image data to the surface of the photosensitive drum  31 . Thus, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum  31 . Then, the electrostatic latent image on the photosensitive drum  31  is developed (visualized) as a toner image with toner supplied from the development member  341  of the developing device  34 . 
     Subsequently, the toner image formed on the photosensitive drum  31  is transferred to the sheet by the transfer roller  35 . Thereafter, the toner image transferred to the sheet is heated by the fixing roller  381  to be melted and fixed, while the sheet is passing between the fixing roller  381  and the pressure roller  382  of the fixing device  38 . It is noted that the remaining toner on the surface of the photosensitive drum  31  is removed by the cleaning device  36 . In addition, the remaining charge on the surface of the photosensitive drum  31  is removed by light applied from the electricity removing device  37 . 
     By the way, DC voltage applied to the charging member  32  might pulsate. For example, the DC voltage applied to the charging member  32  interferes with the superimposition voltage applied to the development member  341  and thereby pulsates. If the DC voltage applied to the charging member  32  pulsates, variations occur in the surface potential of the photosensitive drum  31 , whereby density unevenness occurs in an image formed on the surface of the photosensitive drum  31 . In this regard, technology of suppressing pulsation of the DC voltage applied to the charging member  32 , by connecting a capacitor connected to the ground, to the charging member  32 , is known. 
     However, in the above technology, even if DC voltage is applied to the charging member  32 , charging by the charging member  32  is not performed until the capacitor is charged, and thus start of the printing process might be delayed. In addition, in the above technology, even if application of DC voltage to the charging member  32  is stopped, charging by the charging member  32  continues until discharge from the capacitor is finished, and thus deterioration of the photosensitive drum  31  progresses. On the other hand, the image forming apparatus  10  according to the embodiment of the present disclosure can suppress delay of start of the printing process and suppress deterioration of the photosensitive drum  31 , as described below. 
     Hereinafter, with reference to  FIG. 2  and  FIG. 3 , the power supply portion  7  will be described.  FIG. 3  is a block diagram showing the configuration of the power supply portion  7 . 
     As shown in  FIG. 3 , the power supply portion  7  includes a first power supply portion  71 , a second power supply portion  72 , a changeover switch  73 , and a capacitor  74 . 
     The first power supply portion  71  is a voltage source for applying DC voltage to the charging member  32 . The first power supply portion  71  applies DC voltage to the charging member  32  in accordance with a control signal A 1  (see  FIG. 3 ) inputted from the control portion  5 . For example, the first power supply portion  71  includes an amplification circuit, a step-up circuit, a rectification circuit, and the like, and generates DC voltage to be applied to the charging member  32 , on the basis of the control signal A 1 . 
     The second power supply portion  72  is a voltage source for applying the superimposition voltage obtained by superimposing DC voltage and AC voltage, to the development member  341 . The second power supply portion  72  applies the superimposition voltage to the development member  341  in accordance with a control signal A 2  (see  FIG. 3 ) inputted from the control portion  5 . For example, the second power supply portion  72  includes an amplification circuit, a step-up circuit, a rectification circuit, and the like, and generates the DC voltage on the basis of the control signal A 2 . The second power supply portion  72  superimposes the generated DC voltage and AC voltage generated by an AC voltage source, to generate the superimposition voltage. 
     As shown in  FIG. 3 , the capacitor  74  is connected on a current conduction path connecting the charging member  32  and the ground. The capacitor  74  absorbs, through charging and discharging, pulsation of DC voltage applied to the charging member  32  by the first power supply portion  71 . For example, DC voltage applied to the charging member  32  by the first power supply portion  71  interferes with the superimposition voltage applied to the development member  341  and thereby pulsates. In addition, it is also conceivable that DC voltage applied to the charging member  32  by the first power supply portion  71  interferes with the superimposition voltage applied to the transfer roller  35  and thereby pulsates. 
     As shown in  FIG. 3 , the changeover switch  73  is provided on the current conduction path connecting the charging member  32  and the ground, and can switch the current conduction path between a conductive state and a nonconductive state. For example, the changeover switch  73  is a transistor switch which makes the current conduction path conductive in accordance with the control signal A 3  inputted from the control portion  5 . It is noted that the changeover switch  73  may be a relay circuit or the like. 
     In the ROM of the control portion  5 , a voltage control program for causing the CPU to execute a second voltage control process (see flowchart in  FIG. 4 ) and a first voltage control process (see flowchart in  FIG. 5 ) described later is stored in advance. It is noted that the voltage control program may be stored in a non-transitory computer-readable storage medium such as a CD, a DVD, or a flash memory, and may be read from the storage medium, to be installed onto the storage portion such as the EEPROM in the control portion  5 . 
     As shown in  FIG. 2 , the control portion  5  includes a first voltage control portion  51 , a second voltage control portion  52 , a superimposition voltage control portion  53 , and a current conduction control portion  54 . Specifically, the control portion  5  executes the voltage control program stored in the ROM, using the CPU. Thus, the control portion  5  functions as the first voltage control portion  51 , the second voltage control portion  52 , the superimposition voltage control portion  53 , and the current conduction control portion  54 . 
     The first voltage control portion  51  applies DC voltage to the charging member  32  when the printing process is executed in the image forming apparatus  10 . Specifically, the first voltage control portion  51  inputs the control signal A 1  to the first power supply portion  71  to cause the first power supply portion  71  to start application of DC voltage to the charging member  32 . In addition, the first voltage control portion  51  stops input of the control signal A 1  to the first power supply portion  71  to cause the first power supply portion  71  to stop application of DC voltage to the charging member  32 . 
     The second voltage control portion  52  applies DC voltage to the charging member  32  at a predetermined timing except when the printing process is executed in the image forming apparatus  10 . For example, the predetermined timing is a time at which the image forming apparatus  10  is powered on, a time at which the image forming apparatus  10  returns to a normal operation state from a sleep state in which a part of the function thereof is stopped, a time at which a predetermined time has elapsed since the last printing process has finished, or the like. 
     Specifically, the second voltage control portion  52  controls whether or not to apply DC voltage to the charging member  32  by the first power supply portion  71 , using the control signal A 1 , as in the first voltage control portion  51 . Here, the first voltage control portion  51  and the second voltage control portion  52  are an example of a voltage control portion in the present disclosure. 
     The superimposition voltage control portion  53  applies the superimposition voltage obtained by superimposing DC voltage and AC voltage, to the development member  341 , after DC voltage is applied to the charging member  32  by the first voltage control portion  51 . Specifically, the superimposition voltage control portion  53  inputs the control signal A 2  to the second power supply portion  72  to cause the second power supply portion  72  to start application of the superimposition voltage to the development member  341 . In addition, the superimposition voltage control portion  53  stops input of the control signal A 2  to the second power supply portion  72  to cause the second power supply portion  72  to stop application of the superimposition voltage to the development member  341 . 
     In the case where DC voltage is applied by the first voltage control portion  51 , the current conduction control portion  54  causes the current conduction path connecting the charging member  32  and the ground to be conductive after DC voltage is applied by the first voltage control portion  51 , and disconnects the current conduction path before application of DC voltage by the first voltage control portion  51  is stopped. 
     On the other hand, in the case where DC voltage is applied by the second voltage control portion  52 , the current conduction control portion  54  makes the current conduction path conductive before DC voltage is applied by the second voltage control portion  52 , and disconnects the current conduction path before application of DC voltage by the second voltage control portion  52  is stopped. 
     In addition, the current conduction control portion  54  makes the current conduction path conductive before the superimposition voltage is applied by the superimposition voltage control portion  53 . 
     Specifically, the current conduction control portion  54  inputs the control signal A 3  to the changeover switch  73  to cause the changeover switch  73  to make the current conduction path conductive. In addition, the current conduction control portion  54  stops input of the control signal A 3  to the changeover switch  73  to cause the changeover switch  73  to disconnect the current conduction path. 
     In the image forming apparatus  10 , the second voltage control process described below is executed, whereby the capacitor  74  is charged in advance before execution of the printing process. In addition, in the image forming apparatus  10 , the first voltage control process described later is executed, whereby discharge of the capacitor  74  upon finish of the printing process is restricted. 
     [Second Voltage Control Process] 
     Next, with reference to  FIG. 4 , an example of the procedure of the second voltage control process executed by the control portion  5  in the image forming apparatus  10  will be described. Here, steps S 11 , S 12 , . . . denote the numbers of steps in the processing procedure executed by the control portion  5 . 
     &lt;Step S 11 &gt; 
     First, in step S 11 , the control portion  5  determines whether or not the predetermined timing has come. 
     Here, if the control portion  5  determines that the predetermined timing has come (Yes in S 11 ), the control portion  5  shifts the process to step S 12 . In addition, if the predetermined timing has not come yet (No in S 11 ), the control portion  5  waits until the predetermined timing comes in step S 11 . 
     &lt;Step S 12 &gt; 
     In step S 12 , the control portion  5  causes the current conduction path connecting the charging member  32  and the ground to be conductive. Specifically, the control portion  5  inputs the control signal A 3  to the changeover switch  73  to cause the changeover switch  73  to make the current conduction path conductive. Here, the processing of step S 12  is executed by the current conduction control portion  54  of the control portion  5 . 
     &lt;Step S 13 &gt; 
     In step S 13 , the control portion  5  applies DC voltage to the charging member  32 . Specifically, the control portion  5  inputs the control signal A 1  to the first power supply portion  71  to cause the first power supply portion  71  to start application of DC voltage to the charging member  32 . Here, the processing of step S 13  is executed by the second voltage control portion  52  of the control portion  5 . 
     Here, in the second voltage control process, the current conduction path is made conductive before the DC voltage is applied to the charging member  32 . Thus, it becomes possible to avoid occurrence of unnecessary discharge between the charging member  32  and the photosensitive drum  31 . It is noted that, in the second voltage control process, the processing order of step S 12  and step S 13  may be reversed. In this case, it is conceivable that, while the photosensitive drum  31  is rotated, the electricity removing device  37  is lit to remove the charge accumulated on the surface of the photosensitive drum  31  due to discharge occurring between the charging member  32  and the photosensitive drum  31 . 
     &lt;Step S 14 &gt; 
     In step S 14 , the control portion  5  determines whether or not a predetermined charge time has elapsed since application of DC voltage to the charging member  32  has been started in step S 13 . Here, the charge time is a time needed for charging the capacitor  74  with current supplied from the first power supply portion  71 . 
     Here, if the control portion  5  determines that the charge time has elapsed since the application of DC voltage to the charging member  32  has been started in step S 13  (Yes in S 14 ), the control portion  5  shifts the process to step S 15 . On the other hand, if the charge time has not elapsed yet (No in S 14 ), the control portion  5  waits until the charge time elapses in step S 14 . 
     &lt;Step S 15 &gt; 
     In step S 15 , the control portion  5  disconnects the current conduction path. Specifically, the control portion  5  stops input of the control signal A 3  to the changeover switch  73  to cause the changeover switch  73  to disconnect the current conduction path. Here, the processing of step S 15  is executed by the current conduction control portion  54  of the control portion  5 . 
     &lt;Step S 16 &gt; 
     In step S 16 , the control portion  5  stops application of DC voltage to the charging member  32 . Specifically, the control portion  5  stops input of the control signal A 1  to the first power supply portion  71  to cause the first power supply portion  71  to stop application of DC voltage to the charging member  32 . Here, the processing of step S 16  is executed by the second voltage control portion  52  of the control portion  5 . 
     Here, in the second voltage control process, the current conduction path is disconnected before application of DC voltage to the charging member  32  is stopped. Thus, discharge of the capacitor  74  to be caused after application of DC voltage to the charging member  32  is stopped is restricted. 
     [First Voltage Control Process] 
     Next, with reference to  FIG. 5  and  FIG. 6 , an example of the procedure of the first voltage control process executed by the control portion  5  in the image forming apparatus  10  will be described.  FIG. 6  is a timing chart showing output timings of the control signals A 1  to S 3  to be outputted from the control portion  5  in execution of each step in the first voltage control process. Here, the first voltage control process is executed together with the printing process in the case where the printing process is executed in the image forming apparatus  10 . 
     &lt;Step S 21 &gt; 
     In step S 21 , the control portion  5  applies DC voltage to the charging member  32 . Specifically, the control portion  5  outputs the control signal A 1  to cause the first power supply portion  71  to start application of the DC voltage to the charging member  32 . Here, the processing of step S 21  is executed by the first voltage control portion  51  of the control portion  5 . 
     &lt;Step S 22 &gt; 
     In step S 22 , the control portion  5  causes the current conduction path connecting the charging member  32  and the ground to be conductive. Specifically, the control portion  5  outputs the control signal A 3  to cause the changeover switch  73  to make the current conduction path conductive. Here, the processing of step S 22  is executed by the current conduction control portion  54  of the control portion  5 . 
     Here, in the image forming apparatus  10 , the second voltage control process is executed before execution of the printing process, whereby the capacitor  74  is charged in advance. Therefore, even if the current conduction path is made conductive, the amount of current supplied from the first power supply portion  71  to the charging member  32  does not decrease. 
     &lt;Step S 23 &gt; 
     In step S 23 , the control portion  5  applies the superimposition voltage to the development member  341 . Specifically, the control portion  5  outputs the control signal A 2  to cause the second power supply portion  72  to start application of the superimposition voltage to the development member  341 . Here, the processing of step S 23  is executed by the superimposition voltage control portion  53  of the control portion  5 . 
     Here, in the image forming apparatus  10 , the current conduction path is made conductive before the superimposition voltage is applied to the development member  341 . Thus, even if the DC voltage applied to the charging member  32  by the first power supply portion  71  interferes with the superimposition voltage applied to the development member  341  and thereby pulsates, the pulsation is absorbed by the capacitor  74 . 
     &lt;Step S 24 &gt; 
     In step S 24 , the control portion  5  determines whether or not the printing process has finished. 
     Here, if the control portion  5  determines that the printing process has finished (Yes in S 24 ), the control portion  5  shifts the process to step S 25 . On the other hand, if the printing process has not finished yet (No in S 24 ), the control portion  5  waits until the printing process finishes in step S 24 . 
     &lt;Step S 25 &gt; 
     In step S 25 , the control portion  5  stops application of the superimposition voltage to the development member  341 . Specifically, the control portion  5  stops output of the control signal A 2  to cause the second power supply portion  72  to stop application of the superimposition voltage to the development member  341 . Here, the processing of step S 25  is executed by the superimposition voltage control portion  53  of the control portion  5 . 
     &lt;Step S 26 &gt; 
     In step S 26 , the control portion  5  disconnects the current conduction path. Specifically, the control portion  5  stops output of the control signal A 3  to cause the changeover switch  73  to disconnect the current conduction path. Here, the processing of step S 22  and step S 26  is an example of a second step in the present disclosure, and is executed by the current conduction control portion  54  of the control portion  5 . 
     &lt;Step S 27 &gt; 
     In step S 27 , the control portion  5  stops application of DC voltage to the charging member  32 . Specifically, the control portion  5  stops output of the control signal A 1  to cause the first power supply portion  71  to stop application of DC voltage to the charging member  32 . Here, the processing of step S 21  and step S 27  is an example of a first step in the present disclosure, and is executed by the first voltage control portion  51  of the control portion  5 . 
     Here, in the first voltage control process, the current conduction path is disconnected before application of DC voltage to the charging member  32  is stopped, as in the second voltage control process. Thus, discharge of the capacitor  74  to be caused after application of DC voltage to the charging member  32  is stopped is restricted. 
     Thus, in the image forming apparatus  10 , the first voltage control process is executed, whereby discharge of the capacitor  74  upon finish of the printing process is restricted. Thus, deterioration of the photosensitive drum  31  due to discharge of the capacitor  74  to be caused upon finish of the printing process is suppressed. In addition, a charging process for the capacitor  74  at the start of the printing process is omitted, whereby delay of start of the printing process is suppressed. 
     In addition, in the image forming apparatus  10 , the second voltage control process is executed, whereby the capacitor  74  is charged in advance before execution of the printing process. Thus, in the printing process to be executed for the first time after the image forming apparatus  10  is powered on, after the image forming apparatus  10  returns to a normal operation state from a sleep state in which a part of the function thereof is stopped, or after a predetermined time has elapsed since the last printing process has finished, the charging process for the capacitor  74  is omitted, whereby delay of start of the printing process is suppressed. 
     It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.