Patent Publication Number: US-11656559-B2

Title: Image forming apparatus that stops voltage application to a charger based on a current flowing through an image carrier motor after execution of stop control

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2021-001945 filed on Jan. 8, 2021, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to an image forming apparatus. 
     An image forming apparatus such as a printer capable of forming an image by an electrophotographic method includes an image carrier, a charger, a developing member, and a motor. The image carrier is rotatably provided. The charger charges the image carrier to a predetermined first polarity by receiving application of a voltage of the first polarity. The developing member develops an electrostatic latent image formed on the image carrier, using the toner charged to the first polarity. The motor rotates the image carrier. 
     In the image forming apparatus, when stop control for stopping driving of the motor at the time of operation stop and application control for stopping voltage application to the charger are simultaneously executed, the following problems occur. That is, the image carrier rotates by inertia after execution of the stop control. After execution of the application control, the image carrier is conveyed by the inertial rotation to a region where a non-charged region faces the developing member. As a result, the toner is wastefully consumed. On the other hand, it is conceivable that the inertial rotation time of the image carrier is measured in advance, and the voltage application to the charger is stopped after a lapse of a specific time determined based on the measurement result from the execution of the stop control. 
     However, the inertial rotation time of the image carrier varies depending on the operation state of the image forming apparatus. Therefore, in the above-described configuration, an excess or deficiency occurs in the specific time. If the specific time is too short, toner is wastefully consumed. On the other hand, if the specific time is too long, charging by the charger is performed even after the rotation of the image carrier is stopped, and the image carrier is deteriorated. 
     An object of the present disclosure is to provide an image forming apparatus capable of suppressing deterioration of an image carrier while suppressing wasteful consumption of toner at the time of operation stop. 
     SUMMARY 
     An image forming apparatus according to an aspect of the present disclosure includes an image carrier, a charger, a developing member, a motor, a drive controller, and an application controller. The image carrier is rotatably provided. The charger charges the image carrier to a predetermined first polarity by receiving application of a voltage of the first polarity. The developing member develops an electrostatic latent image formed on the image carrier using the toner charged to the first polarity. The motor rotates the image carrier. The drive controller executes stop control for stopping driving of the motor. The application controller stops voltage application to the charger based on a current flowing through the motor after execution of the stop control. 
     These and other objects, features and advantages of the present disclosure will become more apparent upon reading of the following detailed description along with the accompanied drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a configuration of an image forming apparatus according to an embodiment of the present disclosure. 
         FIG.  2    is a block diagram illustrating configurations of a controller and a high-voltage power supply unit of an image forming apparatus according to an embodiment of the present disclosure. 
         FIG.  3    is a timing chart illustrating a processing procedure of an operation stop process executed by the image forming apparatus according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the following embodiments are examples that embody the present disclosure and do not limit the technical scope of the present disclosure. 
     [Configuration of Image Forming Apparatus  10 ] 
     First, a configuration of an image forming apparatus  10  according to an embodiment of the present disclosure will be described with reference to  FIGS.  1  and  2   .  FIG.  1    is a cross-sectional view showing a configuration of an image forming apparatus  10 . In  FIG.  2   , the controller  5  and the high-voltage power supply unit  6  are indicated by broken lines. 
     The image forming apparatus  10  is a multifunction peripheral having a plurality of functions such as a scan function of reading image data from a document, a print function of forming an image based on the image data, a facsimile function, and a copy function. The image forming apparatus  10  may be an electrophotographic printer apparatus, a facsimile apparatus, or a copying machine. 
     As shown in  FIGS.  1  and  2   , the image forming apparatus  10  includes an automatic document feeder (ADF)  1 , an image reading unit  2 , an image forming unit  3 , a sheet feeding unit  4 , a controller  5 , a high-voltage power supply unit  6 , and a drum motor  7 . 
     The ADF  1  conveys a document to be read by the scan function. The ADF  1  includes a document setting unit, a plurality of document conveying rollers, a document presser, a paper discharge unit, and the like. 
     The image reading unit  2  realizes the scan function. The image reading unit  2  includes a document table, a light source, a plurality of mirrors, an optical lens, and a charge coupled device (CCD). 
     The image forming unit  3  realizes the print function. As illustrated in  FIG.  1   , the image forming unit  3  includes a photosensitive drum  31 , a charging roller  32 , an optical scanning device  33 , a developing device  34 , a toner container  35 , a transfer roller  36 , a cleaning device  37 , a fixing device  38 , and a sheet discharge tray  39 . 
     The photosensitive drum  31  is rotatably provided. The charging roller  32  is provided in contact with the circumferential surface of the photosensitive drum  31  and charges the circumferential surface of the photosensitive drum  31 . For example, the charging roller  32  receives application of a voltage having a positive polarity (an example of a first polarity of the present disclosure) and charges the circumferential surface of the photosensitive drum  31  to the positive polarity. The optical scanning device  33  irradiates the circumferential surface of the photosensitive drum  31  charged by the charging roller  32  with light based on image data. An electrostatic latent image is formed on the circumferential surface of the photosensitive drum  31  by the optical scanning device  33 . The photosensitive drum  31  is an example of an image carrier of the present disclosure. The charging roller  32  is an example of a charger of the present disclosure. 
     The developing device  34  develops the electrostatic latent image formed on the circumferential surface of the photosensitive drum  31 . The developing device  34  stores developer including toner and carrier. The developing device  34  stirs the developer by a stirring member (not shown) to frictionally charge toner and carrier contained in the developer. For example, in the image forming apparatus  10 , the toner is charged to a positive polarity and the carrier is charged to a negative polarity (an example of a second polarity of the present disclosure). As shown in  FIG.  1   , the developing device  34  includes a developing roller  341 . 
     The developing roller  341  uses positively charged toner to develop an electrostatic latent image formed on the circumferential surface of the photosensitive drum  31 . The developing roller  341  is provided so as to face the circumferential surface of the photosensitive drum  31 . The developing roller  341  conveys positively charged toner and negatively charged carriers to a developing region A 10  (see  FIG.  1   ) where electrostatic latent images formed on the circumferential surface of the photosensitive drum  31  are developed. The developing region A 10  is a region where the circumferential surface of the photosensitive drum  31  and the developing roller  341  face each other. The developing roller  341  develops the electrostatic latent image formed on the circumferential surface of the photosensitive drum  31  by receiving application of a positive voltage. The developing roller  341  is an example of a developing member of the present disclosure. The developing roller  341  may convey only the toner out of the toner and the carriers to the developing region A 10 . 
     The toner container  35  supplies toner to the developing device  34 . The transfer roller  36  transfers an electrostatic latent image (toner image) developed by the developing device  34  onto a sheet fed by the sheet feeding unit  4 . The cleaning device  37  cleans the circumferential surface of the photosensitive drum  31  after the toner image is transferred by the transfer roller  36 . The fixing device  38  fixes the toner image transferred to the sheet by the transfer roller  36  to the sheet. The sheet on which the toner image is fixed by the fixing device  38  is discharged to the sheet discharge tray  39 . 
     The sheet feeding unit  4  feeds sheets to the image forming unit  3 . The sheet feeding unit  4  includes a sheet feeding cassette, a pickup roller, a sheet feeding roller, a plurality of sheet conveying rollers, and a registration roller. 
     The controller  5  controls each configuration of the image forming unit  3  and the sheet feeding unit  4 . As shown in  FIG.  2   , the controller  5  includes a CPU  51 , a D/A converter  52 , a D/A (digital/analog) converter  53 , a motor driver  54 , and a current detection unit  55 . Note that the controller  5  may be a main controller that comprehensively controls the image forming apparatus  10 . 
     The CPU  51  is a processor that executes various types of arithmetic processing. The CPU  51  controls each configuration of the image forming unit  3  and the sheet feeding unit  4  by executing a control program stored in a ROM (not shown). 
     The D/A converter  52  converts digital electric signals X 11  (see  FIG.  2   ) input from the CPU  51  into analog electric signals X 21  (see  FIG.  2   ) and outputs the analog electric signals X 21 . The D/A converter  53  converts digital electric signals X 12  (see  FIG.  2   ) input from the CPU  51  into analog electric signals X 22  (see  FIG.  2   ) and outputs the analog electric signals X 22 . 
     The motor driver  54  drives the drum motor  7  in accordance with a control instruction from the CPU  51 . The motor driver  54  applies a drive voltage X 23  to the drum motor  7  in accordance with driving signals input from the CPU  51 . Further, the motor driver  54  executes stop control for stopping the driving of the drum motor  7  in accordance with stop signals X 13  (see  FIG.  2   ) input from the CPU  51 . For example, in the stop control, application of the drive voltage X 23  is stopped. The motor driver  54  is an example of a drive controller of the present disclosure. The drum motor  7  is an example of a motor according to the present disclosure. 
     The high-voltage power supply unit  6  generates a high voltage to be applied to each configuration of the image forming unit  3 . As shown in  FIG.  2   , the high-voltage power supply unit  6  includes a first voltage applying unit  61  and a second voltage applying unit  62 . 
     The first voltage applying unit  61  applies a positive applied voltage X 31  (see  FIG.  2   ) to the charging roller  32 . To be more specific, the first voltage applying unit  61  boosts the voltage of the electric signals X 21  input from the D/A converter  52  to generate the applied voltage X 31 . For example, when the printing process using the image forming unit  3  is executed, the first voltage applying unit  61  outputs the applied voltage X 31  of 700 V. 
     The second voltage applying unit  62  applies a positive applied voltage X 32  (see  FIG.  2   ) to the developing roller  341 . To be more specific, the second voltage applying unit  62  boosts the voltage of the electric signals X 22  input from the D/A converter  53  to generate the applied voltage X 32 . For example, when the printing process is executed, the second voltage applying unit  62  outputs the applied voltage X 32  of 350 V. 
     The drum motor  7  rotates the photosensitive drum  31 . 
     In the conventional image forming apparatus, when the stop control and the stop of the voltage application to the charging roller  32  are simultaneously executed at the time of stopping the operation, the following problems occur. That is, due to the inertial rotation of the photosensitive drum  31  generated after the stop control is executed, the non-charged region generated on the circumferential surface of the photosensitive drum  31  by the stop of the voltage application to the charging roller  32  is conveyed to the developing region A 10 , and the toner is wastefully consumed. On the other hand, it is conceivable that the inertial rotation time of the photosensitive drum  31  is measured in advance, and the voltage application to the charging roller  32  is stopped after the elapse of a specific time determined based on the measurement result from the execution of the stop control. 
     However, the inertial rotation time of the photosensitive drum  31  varies depending on the operation state of the image forming apparatus. Therefore, in the above-described configuration, an excess or deficiency occurs in the specific time. If the specific time is too short, toner is wastefully consumed. On the other hand, if the specific time is too long, charging by the charging roller  32  is performed even after the rotation of the photosensitive drum  31  is stopped, and the photosensitive drum  31  is deteriorated. 
     On the other hand, in the image forming apparatus  10  according to the embodiment of the present disclosure, as described below, it is possible to suppress deterioration of the photosensitive drum  31  while suppressing wasteful consumption of toner when the operation is stopped. 
     When the motor current X 24  (see  FIG.  2   ) flowing through the drum motor  7  is equal to or less than a predetermined threshold value Y 12  (see  FIG.  3   ), the current detection unit  55  outputs a notification signal X 14  indicating that the motor current X 24  is equal to or less than the predetermined threshold value Y 12 . For example, the current detection unit  55  includes resistors provided on a current path through which the motor current X 24  flows and a comparator that compares a voltage applied to the resistors with a reference voltage corresponding to the threshold value Y 12 . 
     The CPU  51  stops the voltage application to the charging roller  32  based on the motor current X 24  flowing through the drum motor  7  after executing the stop control. The CPU  51  Is an example of an application controller of the present disclosure. 
     For example, when the motor current X 24  flowing through the drum motor  7  after the stop control is executed is equal to or less than the threshold value Y 12 , the CPU  51  stops the voltage application by the first voltage applying unit  61 . To be specific, when the notification signals X 14  are input from the current detection unit  55 , the CPU  51  stops voltage application by the first voltage applying unit  61 . 
     For example, the threshold value Y 12  is the same value as the motor current X 24  at the first timing at which the photosensitive drum  31  that inertially rotates stops after the stop control is executed. 
     Note that the threshold value Y 12  may be the same value as the motor current X 24  at the second timing before the photosensitive drum  31  that inertially rotates stops after the stop control is executed. In this case, the second timing is a timing at which the non-charged region generated on the circumferential surface of the photosensitive drum  31  is not conveyed to the developing region A 10  by stopping the voltage application by the first voltage applying unit  61  due to the inertial rotation of the photosensitive drum  31  from the second timing until the photosensitive drum  31  is stopped. Further, the threshold value Y 12  may be the same value as the motor current X 24  at the third timing immediately after the photosensitive drum  31  that inertially rotates is stopped after the stop control is executed. 
     Further, the CPU  51  may stop the voltage application by the first voltage applying unit  61  when a decrease amount per unit time of the motor current X 24  flowing through the drum motor  7  after the stop control is executed is equal to or less than a predetermined reference value. Further, the CPU  51  may determine the stop timing of the voltage application to the charging roller  32  based on the motor current X 24  flowing through the drum motor  7  after the stop control is executed. For example, the CPU  51  may stop the voltage application by the first voltage applying unit  61  at a timing when a predetermined time has elapsed after the motor current X 24  flowing through the drum motor  7  becomes equal to or less than the threshold value Y 12  after the stop control is executed. 
     Here, the CPU  51  stops the voltage application to the charging roller  32  after stopping the voltage application to the developing roller  341 . 
     For example, the CPU  51  gradually decreases the voltage X 32  applied by the second voltage applying unit  62  to stop the voltage application to the developing roller  341 , and gradually decreases the voltage X 31  applied by the first voltage applying unit  61 . 
     For example, when the printing process is completed, the CPU  51  gradually decreases the voltage X 32  applied by the second voltage applying unit  62  from 350 V to 0 V. For example, the CPU  51  gradually reduces the value of the electrical signals X 12 . As a result, the voltage of the electric signals X 22  output from the D/A converter  53  and the applied voltage X 32  by the second voltage applying unit  62  also decrease in a stepwise manner. 
     Further, when the printing process is completed, the CPU  51  decreases the applied voltage X 31  by the first voltage applying unit  61  from 700 V to 100 V in a stepwise manner. For example, the CPU  51  gradually reduces the value of the electrical signals X 11 . As a result, the voltage of the electric signals X 21  output from the D/A converter  52  and the applied voltage X 31  by the first voltage applying unit  61  also decrease in a stepwise manner. 
     The CPU  51  may continuously decrease the applied voltage X 32  by the second voltage applying unit  62  and the applied voltage X 31  by the first voltage applying unit  61 . 
     [Operation Stop Process] 
     Hereinafter, the operation stop process executed by the image forming apparatus  10  will be described with reference to  FIG.  3   .  FIG.  3    is a timing chart showing output timings of signals during the operation stop process, and changes in the motor current X 24 , the applied voltage X 31 , and the applied voltage X 32 . The operation stop process is executed when the print process is completed. 
     When the operation stop process is started, the CPU  51  starts a stepwise decrease of the applied voltage X 31  by the first voltage applying unit  61  (timing T 11  in  FIG.  3   ). 
     Next, the CPU  51  starts a stepwise decrease of the applied voltage X 32  by the second voltage applying unit  62  (timing T 12  in  FIG.  3   ). For example, the timing T 12  is a timing at which the charged region formed on the circumferential surface of the photosensitive drum  31  by the charging roller  32  at the timing T 11  reaches the developing region A 10 . 
     As shown in  FIG.  3   , CPU  51  decreases the applied voltage X 31  by the first voltage applying unit  61  in a stepwise manner so that the applied voltage X 31  decreases from 700 V to 100 V during a period from the timing T 11  to the timing T 13 . In addition, the CPU  51  decreases the applied voltage X 32  by the second voltage applying unit  62  in a stepwise manner such that the applied voltage X 32  decreases from 350 V to 0 V during a period from the timing T 12  to the timing T 13 . 
     As a result, it is possible to stop the voltage application by the second voltage applying unit  62  while avoiding the potential difference between the circumferential surface of the photosensitive drum  31  and the developing roller  341  in the developing region A 10  from being larger than that at the time of executing the printing process. Therefore, it is possible to suppress transfer of carriers from the developing roller  341  to the photosensitive drum  31 , which is caused by an increase in the potential difference between the circumferential surface of the photosensitive drum  31  and the developing roller  341  in the developing region A 10  compared to when the printing process is performed. 
     Next, CPU  51  asserts the stop signal X 13  input to the motor driver  54  (timing T 14  in  FIG.  3   ). The stop signals X 13  are signals in which a high level indicates invalidity and a low level indicates validity. Thus, the motor driver  54  executes the stop control. Therefore, as shown in  FIG.  3   , the motor current X 24  gradually decreases from the current value Y 11  (see  FIG.  3   ) at the time of executing the printing process. 
     When the motor current X 24  becomes equal to or less than the threshold value Y 12 , the current detection unit  55  asserts the notification signal X 14  to be input to CPU  51  (timing T 15  in  FIG.  3   ). The high level of the notification signals X 14  indicates invalidity, and the low level thereof indicates validity. As a result, the CPU  51  stops voltage application by the first voltage applying unit  61 . Thus, as shown in  FIG.  3   , the applied voltage X 31  drops from 100 V to 0 V. 
     As described above, in the operation stop process, the voltage application to the charging roller  32  is stopped based on the motor current X 24  flowing through the drum motor  7  after the stop control is executed. Here, it can be said that the motor current X 24  flowing through the drum motor  7  after the stop control is executed indicates the rotation state (rotation speed) due to the inertial rotation of the photosensitive drum  31  after the stop control is executed. That is, the image forming apparatus  10  can determine the stop timing of the voltage application to the charging roller  32  based on the rotation state due to the inertial rotation of the photosensitive drum  31  after the execution of the stop control. Therefore, it is possible to suppress deterioration of the photosensitive drum  31  while suppressing wasteful consumption of toner at the time of operation stop. 
     Further, in the operation stop process, after the voltage application by the second voltage applying unit  62  is stopped, the voltage application by the first voltage applying unit  61  is stopped. Thus, compared to a configuration in which voltage application by the second voltage applying unit  62  is not stopped before voltage application by the first voltage applying unit  61  is stopped, it is possible to suppress transfer of toner from the developing roller  341  to the photosensitive drum  31  when voltage application by the first voltage applying unit  61  is stopped.