Patent Publication Number: US-11048186-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims priority rights from Japanese Patent Application No. 2019-115914, filed on Jun. 21, 2019, the entire disclosures of which are hereby incorporated by reference herein. 
     BACKGROUND 
     1. Field of the Present Disclosure 
     The present disclosure relates to an image forming apparatus. 
     2. Description of the Related Art 
     In an image forming apparatus of a two-component-developer type, when electric power is cut off, if potential of a development device decreases against a photoconductor drum that is in a charging status, then a carrier development (carrier jumping from the development device to the photoconductor drum) may occur. Therefore, when electric power is cut off, an image forming apparatus causes an exposure device to perform fully-continuous lighting and thereby reduces an electric charge amount on the photoconductor drum, and consequently restrains such carrier development. 
     However, even if such exposure is performed when electric power is cut off, a section from an exposure position (i.e. irradiation position) to a position with the shortest distance to the development device (i.e. development position) on a surface of the photoconductor drum is not exposed with exposure light, and consequently such carrier development may occur when this section reaches to the development position due to inertial rotation of the photo conductor drum. 
     SUMMARY 
     An image forming apparatus according to an aspect of the present disclosure includes a photoconductor drum, a charging device, an exposure device, a development device, and an exposure position changing unit. The charging device is configured to charge the photoconductor drum. The exposure device is configured to irradiate the photoconductor drum and thereby form an electrostatic latent image on the photoconductor drum. The development device is configured to cause toner to adhere to the electrostatic latent image on the photoconductor drum in a two-component-development manner. The exposure position changing unit is configured to change, on the photoconductor drum, an exposure position of the exposure device to a position getting close to the development device from an exposure position for print image development when electric power cutoff is detected. 
     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  shows a side view that indicates an internal mechanical configuration of an image forming apparatus in an embodiment according to the present disclosure; 
         FIG. 2  shows a block diagram that indicates an electronic configuration of the image forming apparatus shown in  FIG. 1 ; 
         FIG. 3  shows a diagram that indicates an example of an exposure position changing unit  23  shown in  FIG. 2 ; and 
         FIG. 4  shows a timing chart that explains a behavior of the image forming apparatus shown in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment according to an aspect of the present disclosure will be explained with reference to drawings. 
       FIG. 1  shows a side view that indicates an internal mechanical configuration of an image forming apparatus in an embodiment according to the present disclosure. The image forming apparatus shown in  FIG. 1  is an apparatus that has an electrophotographic printing function, such as a printer, a facsimile machine, a copier or a multi function peripheral. 
     The image forming apparatus includes a photoconductor drum  1 , a charging device  2 , an exposure device  3 , a development device  4 , a transportation belt  5 , a driving roller  6   a  and a driven roller  6   b , a transfer roller  7 , a cleaning device  8 , and a fuser device  9 . 
     The charging device  2  charges a surface of the photoconductor drum  1  so as to cause the surface to get a predetermined potential. 
     The exposure device  3  exposes the photoconductor drum using a light source  3   a , and thereby forms an electrostatic latent image on the photoconductor drum  1 . Here, the light source  3   a  is an LED (Light Emitting Diode) head, but alternatively may be an LSU (Laser Scanning Unit). 
     The development device  4  causes toner to adhere to the electrostatic latent image on the photoconductor drum in a two-component-development manner. For example, the development device  4  includes a development roller  4   a . The development roller  4   a  keeps two-component developer on a surface thereof. To the development roller  4   a , a predetermined voltage is applied as a development bias by a bias circuit (not shown). When applying a development bias for ordinary print image development, only toner in the two-component developer gets apart from the development roller  4   a  due to the development bias and adheres to the electrostatic latent image on the photoconductor drum  1 . When electric power is cut off, the development bias of the development roller  4  immediately changes to zero volt. 
     The transportation roller  5  rotates due to a driving force from the driving roller  6   a , and thereby transports a print sheet  101  to a position between the photoconductor drum  1  and the transfer roller  7 . 
     The transfer roller  7  makes the print sheet  101  contact to the photoconductor drum  1 , and transfers a toner image on the photoconductor drum  1  to the print sheet  101 . 
     The cleaning device  8  collects residual toner on the photoconductor drum  1  after transferring the toner image. For example, the cleaning device  8  causes a cleaning blade  8   a  to contact to the photoconductor drum  1 , and thereby removes and collects toner on the photoconductor drum  1 . 
     The fuser device  9  fixes the toner image on the print sheet  101 , for example, in a heating-and-pressurizing manner. 
       FIG. 2  shows a block diagram that indicates an electronic configuration of the image forming apparatus shown in  FIG. 1 . As shown in  FIG. 2 , the image forming apparatus in this embodiment includes a print engine  21 , a power supply circuit  22 , and an exposure position changing unit  23 . 
     The print engine  21  includes an ASIC (Application Specific Integrated Circuit) of a predetermined specific function, a micro computer, another electronic circuit, and/or the like, and controls the exposure device  3  and the like and thereby performs printing an image. The power supply circuit  22  supplies electric power to the print engine  21  and the like with a predetermined voltage (e.g. 24 volt) on the basis of electric power obtained from commercial power supply. 
     When electric power cutoff is detected by a power-supply-cutoff detecting circuit  34  mentioned below, the exposure position changing unit  23  changes on the photoconductor drum  1 , an exposure position of the exposure device  3  to a position getting close to the development device  4  from an exposure position for print image development. 
     In this embodiment, the exposure position changing unit  23  changes a position or a direction of the light source  3   a  of the exposure device  3 , and thereby changes the exposure position to a position getting close to the development device  4  from an exposure position for print image development. 
       FIG. 3  shows a diagram that indicates an example of an exposure position changing unit  23  shown in  FIG. 2 . 
     For example, as shown in  FIG. 3 , the exposure position changing unit  23  includes a rotation shaft  23   a  of the light source  3   a , a solenoid  23   b , and a spring  23   c . The solenoid  23   b  provides electromagnetic force to the light source  3   a  such that the direction of the light source  3   a  (i.e. its light emitting direction) gets a predetermined direction for print image development. Here, the light source  3   a  includes a member of a soft magnetic material (e.g. iron) at a position thereon facing to the solenoid  23   b . When the electric current to the solenoid  23   b  is stopped and the electromagnetic force of the solenoid  23   b  is removed, for example, as shown by a dashed line in  FIG. 3 , the spring  23   c  causes the light source  3   a  to rotate to the predetermined direction around the rotation shaft  23   a  as a center of the rotation using restoring force of the spring  23   c.    
     Thus, when developing a print image, the electric current is caused to flow through the solenoid  23   b  and thereby the direction of the light source  3   a  is set as a predetermined first direction, and consequently, light emitted from the light source  3   a  is incident to a predetermined position PE 0  on the photoconductor drum  1 . Contrarily, when electric power is cut off, the electric current flow through the solenoid  23   b  is immediately stopped and thereby the direction of the light source  3   a  is set as a predetermined second direction, and consequently, light emitted from the light source  3   a  is incident to a predetermined position PE 1  on the photoconductor drum  1  such that the position PE 1  gets close to the development position from the position PE 0 . 
     The print engine  21  includes driver circuits  31  and  32 , a controller  33 , and a power-supply-cutoff detecting circuit  34 . 
     The driver circuit  31  drives the light source  3   a  of the exposure device  3 . The driver circuit  32  drives the exposure position changing unit  23 . The controller  33  controls the driver circuits  31  and  32 . 
     Specifically, the controller  33  ( a ) provides an exposure switching control signal and thereby sets an ON status or an OFF status of the exposure of the exposure device  3  (i.e. light emitting of the light source  3   a ) to the driver circuit  31 , and (b) provides an exposure position control signal and thereby sets the exposure position of the exposure device  3  (i.e. a position on the photoconductor drum  1  where light emitted from the light source  3   a  is incident) to the driver circuit  32 . 
     If a power supply voltage of the power supply circuit gets less than a predetermined value, then the power-supply-cutoff detecting circuit  34  detects that power supply cutoff occurs. If the power-supply-cutoff detecting circuit  34  detects power supply cutoff, then the controller  33  sets the ON status of the exposure of the exposure device  3  to the driver circuit  31 . The driver circuit  31  turns the light source  3   a  on/off in accordance with the exposure switching control signal. Consequently, this exposure is performed onto a whole printable area. 
     For example, if the exposure position changing unit  23  is installed as shown in  FIG. 3 , then the controller  33  ( a ) causes electric current to flow through the solenoid  23   b  using the driver circuit  32  and thereby causes the solenoid  23   b  to provide electromagnetic force to the light source  3   a  such that the direction of the light source  3   a  gets the predetermined direction for print image development, and (b) when electric power cutoff is detected, immediately removes the electromagnetic force by stopping the electric current using the driver circuit  32  and thereby changes the direction of the light source and immediately causes the exposure position to get close to the development device  4 . 
     The following part explains a behavior of the aforementioned image forming apparatus.  FIG. 4  shows a timing chart that explains a behavior of the image forming apparatus shown in  FIGS. 1 and 2 . 
     At the time T 1 , if commercial AC power supply cutoff occurs, then an output voltage of the power supply circuit (i.e. DC (direct current) internal power supply voltage) gradually decreases, and when this output voltage gets less than a predetermined threshold value TH, the power-supply-cutoff detecting circuit  34  immediately detects power supply cutoff (at the time T 2 ), and changes a level of a power-supply-cutoff detection signal from HIGH to LOW. 
     It should be noted that a power supply voltage that enables each element in the print engine  21  (i.e. the controller  33  and the like) to act (e.g. 5 volt or 3.3 volt) is less than the output voltage of the power supply circuit (e.g. 24 volt), and therefore, even at this time point, the print engine  21  continues to act. Power supply for each element in the print engine  21  (i.e. the controller  33  and the like) is (a) power supply provided through voltage conversion from the output voltage of the power supply circuit  22 , (b) power supply provided by another power supply circuit, or the like. 
     If the power-supply-cutoff detection signal gets the LOW level, then the controller  33  activates the exposure position changing unit  23  using the driver circuit  32  and thereby causes the exposure position of the exposure device to get close to the development device  4  in a circumferential direction on a surface of the photoconductor drum  1 . 
     Further, the power-supply-cutoff detection signal gets the LOW level, then the controller  33  changes the exposure switching control signal from the HIGH level to the LOW level. If the exposure switching control signal gets the LOW level, then the driver circuit  31  causes the light source  3   a  of the exposure device  3  to perform continuous lighting. 
     Consequently, on the surface of the photoconductor drum  1 , this exposure at power supply cutoff reduces an unexposed area. In other words, compared with the exposure performed at the position PE 0  shown in  FIG. 3  when power supply is cut off, the exposure performed at the position PE 1  when power supply is cut off decreases a potential (absolute value) of the development position on the photoconductor drum  1  in the inertial rotation in a shorter time (e.g. until the development bias vanishes after the power supply cutoff). 
     As mentioned, in the aforementioned embodiment, the charging device  2  charges the photoconductor drum  1 . The exposure device  3  exposes the photoconductor drum  1  and thereby forms an electrostatic latent image on the photoconductor drum  1 . The development device  4  causes toner to adhere to the electrostatic latent image on the photoconductor drum in a two-component-development manner. When electric power cutoff is detected, the exposure position changing unit  23  changes on the photoconductor drum  1 , an exposure position of the exposure device  3  to a position getting close to the development device  4  from an exposure position for print image development. 
     Consequently, on the surface of the photoconductor drum  1 , an area without reducing an electric charge amount immediately after power supply cutoff hardly reaches to the development position, and therefore the carrier development is restrained in a short time immediately after the power supply cutoff. 
     It should be understood that various changes and modifications to the embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims. 
     For example, while the image forming apparatus of the aforementioned embodiment is a direct-transfer image forming apparatus, the feature of the present disclosure can also be applied to an indirect-transfer image forming apparatus. 
     Further, while the image forming apparatus in the aforementioned embodiment is a monochrome image forming apparatus, the feature of the present disclosure can also be applied to a color image forming apparatus. 
     Furthermore, in the aforementioned embodiment, the exposure position is changed by changing the position or the direction of the light source  3   a . Alternatively, the exposure position may be changed by inserting an optical system (mirror and/or the like) in an optical path between the light source  3   a  and the photoconductor drum  1  in order to change the optical path from the light source  3   a  to the photoconductor drum  1 .