Patent Publication Number: US-8971770-B2

Title: Developer-agitating transporter, developing device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2013-001618 filed Jan. 9, 2013. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a developer-agitating transporter, a developing device, and an image forming apparatus. 
     (ii) Related Art 
     Image forming apparatuses, such as a photocopier or a printer, include a developing device for developing electrostatic latent images formed on a photoconductor. The developing device includes a development roller disposed opposite the photoconductor. In the developing device, for example, a two-component developer containing a magnetic carrier and toner mostly made of resin is agitated by a developer-agitating transporter and supplied to the development roller via a developer-supplying transporter. 
     SUMMARY 
     According to an aspect of the invention, a developer-agitating transporter includes multiple helical blades that helically extend around a rotation shaft, the helical blades being arranged at different positions in a direction perpendicular to a longitudinal direction of the rotation shaft; and a gap portion that divides each of the helical blades into a first blade portion and a second blade portion so that the helical blade is discontinuous in a direction in which the helical blade extends, the first blade portion and the second blade portion opposing each other across the gap portion, wherein the gap portion causes the first blade portion and the second blade portion to be arranged at a certain angular interval in a circumferential direction of the rotation shaft, and wherein at least one surface of adjacent ones of the helical blades that are adjacent in the circumferential direction of the rotation shaft has a sloped area that is sloped at an angle that changes with respect to an axial direction of the rotation shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  schematically illustrates a configuration of an image forming apparatus according to an exemplary embodiment; 
         FIG. 2  schematically illustrates a developing device according to an exemplary embodiment; 
         FIGS. 3A and 3B  schematically illustrate a developer-agitating transporter according to an exemplary embodiment and  FIG. 3C  is a diagram in which the circumferential surface of the developer-agitating transporter is unfolded; 
         FIGS. 4A to 4D  schematically illustrate the developer-agitating transporter according to the exemplary embodiment; and 
         FIG. 5  schematically illustrates cross sections of the developer-agitating transporter according to the exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary Embodiment 
     Hereinbelow, an exemplary embodiment of the present invention will be described with reference to the drawings.  FIG. 1  schematically illustrates the configuration of an image forming apparatus  1  according to an exemplary embodiment including a developer-agitating transporter  42  and a developing device  40 . The image forming apparatus  1  according to the exemplary embodiment includes a controller  2 , a photoconductor  10 , a charging unit  20 , an exposing unit  30 , a developing device  40 , a transfer unit  50 , a fixing unit  60 , a cleaning unit  70 , and a sheet storage  80 . The image forming apparatus  1  forms an image on a sheet P, which serves as a recording medium, or on other types of media on the basis of image data supplied thereto. 
     The controller  2  includes an arithmetic unit such as a central processing unit (CPU) and a memory to control operations of components of the image forming apparatus  1 . 
     The photoconductor  10  is a cylindrical rotating body that rotates in a direction of the arrow of  FIG. 1  and that has a photosensitive layer made of an organic photosensitive material to hold an image. 
     The charging unit  20  applies a predetermined charging voltage to the surface of the photoconductor  10  using, for example, a charging roller that rotates while coming into contact with the surface of the photoconductor  10 . The charging unit  20  may be a contact-type charging unit that charges the photoconductor  10  while coming into contact with the photoconductor  10  using a brush or may be a non-contact-type charging unit that charges the photoconductor  10  using a corona discharge. 
     The exposure unit  30  emits light based on image data to the surface of the photoconductor  10  charged by the charging unit  20  and forms an electrostatic latent image having a latent image potential by using a potential difference. As the photoconductor  10  rotates, the electrostatic latent image moves to a position at which the developing device  40  is disposed. 
     The developing device  40  has a rotatable developing roller  41  and toner adhering to the developing roller  41  transfers to the photoconductor  10 . Specifically, the toner transfers to the surface of the photoconductor  10  due to there being a potential difference between the charged toner and the electrostatic latent image formed on the photoconductor  10 . Consequently, a toner image is formed on the photoconductor  10 . The toner image moves to a position at which the transfer unit  50  is disposed as the photoconductor  10  rotates. 
     Inside the developing device  40 , a developer-agitating transporter  42  that agitates toner T and developer D, a developer-supplying transporter  43  that supplies the developer D to the development roller  41 , a partitioning portion  44 , and a replenishing unit  45  that supplies the toner T to the developer-agitating transporter  42  are provided. Detailed description of the developing device  40  and the developer-agitating transporter  42  will be described below. 
     The transfer unit  50  transfers a toner image formed on the photoconductor  10  to a sheet P that has been transported thereto by transportation rollers  91 . The sheet P to which the toner image has been transferred is transported to the fixing unit  60  by transportation rollers  91 . 
     The fixing unit  60  includes a fixing roller  61 , which includes a heat source, and a pressing roller  62 , which is disposed opposite the fixing roller  61 . The fixing roller  61  is pressed by the pressing roller  62 . The fixing unit  60  fixes an unfixed toner image formed on a sheet P to the sheet P by heating and pressing the toner image. The sheet P to which the toner image has been fixed by the fixing unit  60  is transported by transportation rollers  91  and then ejected to the outside. 
     The cleaning unit  70  removes remnants such as toner remaining on the surface of the photoconductor  10  after the toner image has been transferred to the sheet P. Multiple sheets P are stored in the sheet storage  80 . The sheets P are picked up by a pick-up roller  90  from the sheet storage  80  and transported to the transfer unit  50  by the transportation rollers  91 . 
     Now, the developing device  40  according to the exemplary embodiment will be described.  FIG. 2  is a schematic diagram of the inside of the developing device  40  illustrated in  FIG. 1 . As described above, the developing device  40  includes the development roller  41 , the developer-agitating transporter  42 , the developer-supplying transporter  43 , the partitioning portion  44 , and the replenishing unit  45 . 
     The development roller  41  is disposed opposite the photoconductor  10  illustrated in  FIG. 1 , the photoconductor  10  rotating while carrying an electrostatic latent image. The development roller  41  holds developer D and develops the electrostatic latent image held by the photoconductor  10  with the developer D. The developer-agitating transporter  42  agitates the developer D and toner T added to the developer D. 
     The developer-agitating transporter  42  includes a shaft  42   a , serving as a rotation shaft, and a double-helix blade  42   b  including two helical blades  42   b   1  and  42   b   2  that helically extend around the circumferential surface of the shaft  42   a . The two helical blades  42   b   1  and  42   b   2  are arranged at different positions in a direction perpendicular to a longitudinal direction of the rotation shaft  42   a . Specifically, the double-helix blade  42   b  includes two helical blades  42   b   1  and  42   b   2 , which are arranged at an angular interval of approximately 180° in the circumferential direction of the shaft  42   a.    
     Each of the helical blades  42   b   1  and  42   b   2  includes multiple gap portions FR and multiple blade portions BR, which are separated by the gap portions FR. The gap portions FR make the helical blades  42   b   1  and  42   b   2  discontinuous in the longitudinal direction. The multiple blade portions BR include a first blade portion and a second blade portion, which oppose each other across a gap portion FR. Each gap portion FR causes adjacent blade portions BR, which are a first blade portion and a second blade portion, to be arranged at a certain angular interval in the circumferential direction of the shaft  42   a . The details of the developer-agitating transporter  42  according to the exemplary embodiment will be described below. 
     The developer-supplying transporter  43  transports the developer D agitated by and supplied from the developer-agitating transporter  42  to the development roller  41 . The developer-supplying transporter  43  includes a rotatable shaft  43   a  and a helical blade  43   b  mounted on the shaft  43   a.    
     The partitioning portion  44  is disposed between the developer-agitating transporter  42  and the developer-supplying transporter  43  so as to separate these transporters  42  and  43  from each other. The partitioning portion  44  does not fully extend throughout the length of a container so that the developer D is circulated through the openings on both sides of the partitioning portion  44 . 
     The replenishing unit  45  supplies the toner T to an upstream-side end portion of the developer-agitating transporter  42  from the side of or above the developer-agitating transporter  42 . The toner T supplied from the replenishing unit  45  and the circulating developer D are mixed by being agitated by the developer-agitating transporter  42  disposed downstream from the replenishing unit  45 . The developer mixed with the toner is supplied to the development roller  41  via the developer-supplying transporter  43  and held by the development roller  41 . 
     The toner T contained in the developer D supplied to the development roller  41  is consumed by being used for development. The toner T for compensating for the consumed toner T is supplied to the developer-agitating transporter  42  from the side of or above the developer-agitating transporter  42  and added to the circulating developer D. 
     Referring now to  FIG. 3 , the developer-agitating transporter  42  according to the exemplary embodiment will be described.  FIG. 3A  is a perspective view of the developer-agitating transporter  42 .  FIG. 3B  is an enlarged view of the developer-agitating transporter  42  illustrated in  FIG. 3A .  FIG. 3C  is a diagram in which the circumferential surface of the developer-agitating transporter  42  is unfolded. 
     An upstream-side portion of the helical blade  42   b   1  illustrated in  FIG. 3A  transports the toner T supplied from the replenishing unit  45  illustrated in  FIGS. 1 and 2  to the downstream side. In a portion downstream from the upstream-side portion of the helical blade  42   b   1 , the helical blade  42   b   1  and the helical blade  42   b   2  are disposed so as to be superposed with each other in the axial direction of the shaft  42   a.    
     In the portion in which the helical blade  42   b   1  and the helical blade  42   b   2  are superposed with each other in the axial direction, multiple gap portions FR are cyclically formed such that each of the helical blade  42   b   1  and the helical blade  42   b   2  is discontinuous. Portions of each of the helical blades  42   b   1  and  42   b   2  divided by the gap portions FR serve as multiple blade portions BR. 
       FIG. 3B  is an enlarged view of a portion in which the helical blade  42   b   1  and the helical blade  42   b   2  illustrated in  FIG. 3A  are positioned closer to each other in the axial direction of the shaft  42   a . As illustrated in  FIG. 3B , the developer D that has been transported to each gap portion FR by rotation of the helical blade  42   b   1  and the helical blade  42   b   2  is divided into two parts in the gap portion FR. 
     A developer portion D 1 , which is one of the divided parts of the developer D, is transported so as to become separated from a blade portion BR and is transported by the helical blade  42   b   1  and the helical blade  42   b   2  as illustrated in  FIG. 3B . The developer portion D 1  thus transported delays one cycle by being separated from the blade portion BR. 
     A developer portion D 2 , which is another one of the divided parts of the developer D, is transported by the blade portion BR and further transported by the helical blade  42   b   1  and the helical blade  42   b   2  as illustrated in FIG.  3 B. The developer portion D 2  thus transported merges with developer D that has previously been separated from the blade portion BR one cycle ago. 
     As illustrated in  FIG. 3B , it is preferable that an end surface DM of each blade portion BR that is adjacent to the gap portion FR have a base substantially parallel to the axial direction of the shaft  42   a . Thus, the force in the circumferential direction is applicable to the developer D by the end surface DM of the blade portion BR, thereby improving the agitating efficiency. 
       FIG. 3C  is an unfolded diagram of the circumferential surface of the shaft to show the relationship between the helical blade  42   b   1  and the helical blade  42   b   2 . The vertical axis indicates the angles from 0 to 360 degrees in the circumferential direction of the shaft  42   a  and the horizontal axis indicates the positions of the helical blades  42   b   1  and  42   b   2  within the portion in which the helical blade  42   b   1  and the helical blade  42   b   2  are superposed in the axial direction from the upstream side to the downstream side. 
     As illustrated in  FIG. 3C , in the gap portion FR, an upstream-side end T 1  of a blade portion BR and a downstream-side end T 2  of an adjacent blade portion BR are arranged at a certain angular interval in the circumferential direction of the shaft  42   a . Specifically, as illustrated in  FIG. 3C , an angle K 1 , which is an angle between a direction in which the blade portion BR is wound and the axial direction of the shaft  42   a , and an angle K 2 , which is an angle between the longitudinal direction of the gap portion FR and the axial direction of the shaft  42   a , are different from each other. In the exemplary embodiment, the angle K 2  is set so as to be a substantially right angle. The angle K 1  and the angle K 2  may be optimally selected in relation to agitation and transportation of the developer. 
     Referring now to  FIGS. 4A to 4D , the blade portions BR of the developer-agitating transporter  42  will be described.  FIG. 4A  is a perspective view of the developer-agitating transporter  42 .  FIG. 4B  schematically illustrates cross sections of the blade portions BR of  FIG. 4A .  FIG. 4C  schematically illustrates the flow of the developer.  FIG. 4D  schematically illustrates movement of the developer D in a portion in which the helical blade  42   b   1  and the helical blade  42   b   2  are positioned closer to each other in the axial direction of the shaft  42   a.    
     As illustrated in  FIG. 4A , each blade portion BR of the helical blade  42   b   1  and the helical blade  42   b   2  of the developer-agitating transporter  42  includes a first area R 1  on a side surface. The first area R 1  is, for example, a convexly sloped area. Specifically, the first area R 1 , which is a sloped area, is formed on at least one surface of the blade portion BR that opposes an adjacent blade portion BR that is adjacent in the circumferential direction of the rotation axis of the shaft  42   a  such that the angle of the first area R 1  with respect to the axial direction of the rotation shaft changes. The first area R 1  is formed in a portion of each blade portion BR that is superposed with another blade portion BR in the axial direction of the shaft  42   a  such that the portion of the blade portion BR corresponding to the first area R 1  has a bottom face that comes into contact with the shaft  42   a , the bottom face having a dimension in the axial direction that increases and decreases continuously. Thus, the first area R 1  and an opposing surface of an adjacent blade portion BR that is adjacent in the circumferential direction of the shaft  42   a  define a narrow region. 
       FIG. 4B  illustrates cross sections of portions of a blade portion BR taken in parallel to the shaft  42   a  to explain a width H 1  of a portion of the blade portion BR corresponding to the first area R 1 , which is a sloped area as described above, and a width H 2  of a portion of the blade portion BR corresponding to a second area R 2 . In the exemplary embodiment, as illustrated in  FIG. 4B , the width H 1  of the portion of the blade portion BR corresponding to the first area R 1  and the width H 2  of the portion of the blade portion BR corresponding to the second area R 2  have a relationship satisfying H 1 ≧H 2 . 
       FIG. 4C  illustrates an example in which the developer D flows into a gap portion FR and then is divided into a developer portion D 1  and a developer portion D 2 . Before flowing into the gap portion FR, the developer D passes the first area R 1  and the second area R 2 . 
       FIG. 4D  illustrates the directions in which the developer in a portion in which the helical blade  42   b   1  and the helical blade  42   b   2  are positioned closer to each other in the axial direction moves. As illustrated in  FIG. 4D , in a narrow portion of the passage in the portion in which the helical blade  42   b   1  and the helical blade  42   b   2  are positioned closer to each other in the axial direction, for example, in a portion sandwiched between the first area R 1 , which is a sloped area, and the opposing surface, the developer D flows turbulently and thus is prevented from adhering or being stagnated. Specifically, the developer D is allowed to flow further turbulently in the vicinity of the first area R 1  than in other portions because the direction of force that the developer D receives from the helical blades  42   b   1  and  42   b   2  changes. 
     Specifically, in a portion in which adjacent two blade portions BR are positioned closer to each other in the axial direction of the shaft  42   a , each blade portion BR has a first area R 1  and a second area R 2  as illustrated in  FIG. 4D  so as to increase the dimension in the axial direction of the shaft  42   a.    
       FIG. 5  schematically illustrates a cross section of the developer-agitating transporter  42 .  FIG. 5  illustrates an end a of a first blade portion BR, which is a helical blade  42   b   1 , on the same plane as the cross section of the shaft  42   a  and an end b of a second blade portion BR, which is a helical blade  42   b   1 , that opposes the first blade portion BR with a gap portion FR interposed therebetween.  FIG. 5  also illustrates an end c of a third blade portion BR, which is a helical blade  42   b   2 , on the same plane as the cross section of the shaft  42   a  and an end d of a fourth blade portion BR, which is a helical blade  42   b   2 , that opposes the third blade portion BR with another gap portion FR interposed therebetween. 
     As illustrated in  FIG. 5 , when an angle between a line extending from the end a to the center of the shaft  42   a  and a line extending from the end b to the center of the shaft  42   a  is defined as an angle A and an angle between a line extending from the end b to the center of the shaft  42   a  and a line extending from the end c to the center of the shaft  42   a  is defined as an angle B, the relationship B=180°−A is satisfied in the exemplary embodiment. The angle A is a passage in the gap portion FR over which the developer D is transported and the angle B is a space in which two blade portions BR are positioned closer to each other in the axial direction. 
     Specifically, it is preferable that the angle of an gap formed between first areas R 1  of adjacent blades B at the center of the shaft  42   a  be smaller than the angle B. With this configuration, at least one of opposing surfaces of two blade portions BR that form the angle B has a first area R 1 . 
     Since the developer-agitating transporter  42  according to the exemplary embodiment includes the double-helix blade  42   b , the developer-agitating transporter  42  has a larger area on the surface on which the developer D is transported and a higher transporting efficiency in the axial direction than in the case of a configuration having a single-helix blade. The double-helix blade  42   b  has portions in which multiple pairs of blades, each pair having a helical blades  42   b   1  and a helical blades  42   b   2  that define a narrow portion, exist in the circumferential direction. 
     In each portion in which multiple pairs of blades, each pair having a helical blades  42   b   1  and a helical blades  42   b   2  that define a narrow portion, exist in the circumferential direction, each of the helical blades  42   b   1  and  42   b   2  has at least one portion having a bottom face whose dimension in the axial direction continuously changes. In this configuration, during agitation of the developer D, wall surfaces of the helical blades  42   b   1  and  42   b   2  continuously change the direction in which the developer D is pressed and thus the developer D turbulently flows, thereby preventing the developer D from adhering or being stagnated. 
     Other Exemplary Embodiment 
     The developer-agitating transporter  42 , the developing device  40 , and the image forming apparatus  1  according to the exemplary embodiment have been described thus far. The present invention, however, is not limited to the above-described exemplary embodiment and other exemplary embodiments are also conceivable. Now, other exemplary embodiments will be described. 
     The developer-agitating transporter  42  according to the exemplary embodiment includes a double-helix blade, but the preset invention is not limited to this. For example, the developer-agitating transporter  42  may include a multi-helix blade such as triple-helix or more-helix blades. A developer-agitating transporter including such a multi-helix blade has a larger area on the surface on which the developer is transported and a higher transporting efficiency in the axial direction. 
     The first area R 1  formed on the side surface of the blade portion BR may be a concavely sloped area. Even when the first area R 1  is a concavely sloped area, the developer is transported in different directions due to the surface being sloped and flows turbulently. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various exemplary embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.