Patent Publication Number: US-6215972-B1

Title: Apparatus for cleaning a squeeze roller of a liquid printer

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for cleaning a squeeze roller of a liquid printer, and more particularly, to an apparatus for cleaning a squeeze roller of a liquid printer in which the structure of a blade is improved to improve the efficiency in cleaning and extend the life span of the blade. 
     2. Description of the Related Art 
     A liquid electrophotographic printer prints an image by forming an electrostatic latent image by scanning a laser beam on a photosensitive medium, developing the image with a developer including toner of a predetermined color using a developing unit and transferring the developed image to a print medium. 
     The liquid electrophotographic printer, as shown in FIG. 1, includes a laser scanning unit (LSU) for forming an electrostatic latent image on a photosensitive medium  10  and a developing unit  20  for forming an image corresponding to the electrostatic latent image. 
     The developing unit  20  includes a developing vessel  21  and a developing roller  23  which is disposed to face the photosensitive medium  10  such that a predetermined gap G exists therebetween. The apparatus further includes a cleaning roller  25  for removing developer adhering to the outer circumferential surface of the developing roller  23  and an injector  27  for injecting developer containing toner and a carrier into the gap G is a squeeze roller  29  for separating the toner and the carrier by closely pressing the photosensitive medium  10 , and a squeeze roller cleaning apparatus  30  for cleaning off the developer adhering to the squeeze roller  29  when a drip-line is removed. 
     The conventional squeeze roller cleaning apparatus  30 , as shown in FIG. 2, includes a blade  31  contacting the outer circumferential surface of the squeeze roller  29  slanted at a predetermined angle. The apparatus further includes, a blade holder  33  fixedly holding the blade  31 , and a spanking mechanism  35  for removing a holding volume Vh of the developer remaining between the blade  31  and the squeeze roller  29  by allowing the blade holder  33  to repeatedly pivot a plurality of times. As shown in FIG. 3, the blade  31  is formed of a single rubber member. To prevent a phenomenon in which a surface of a leading edge  31   a  of the blade  31  contacts the squeeze roller  29  since the blade  31  bends excessively by the rotation of the squeeze roller  29  (hereinafter, referred to as the overturn of the blade), the blade  31  is disposed in a trailing direction with respect to the rotational direction of the squeeze roller  29  in a drip-line removing mode. 
     To embody the above squeeze roller cleaning apparatus, in the developing unit  20 , the pressing force and rotational direction of the squeeze roller  29  varies according to each of a home position, a development mode, and a drip-line removing mode. In the development mode, the pressing force between the squeeze roller  29  and a squeeze backup roller  29 ′ is greatest and the squeeze roller  29  rotates in the direction the photosensitive medium  10  rotates by being passively rotated by the photosensitive medium  10 . The squeeze roller  29  squeezes and separates most of the carrier from the developer adhering to the photosensitive medium  10  so as to form a film of the developer. In this mode, the blade  31  is disposed to be separated from the squeeze roller  29 . 
     In the drip-line removing mode, a relatively weak force is applied between the squeeze roller  29  and the squeeze backup roller  29 ′ compared to the development mode and the squeeze roller  29  rotates in a direction opposite to that which the photosensitive medium  10  proceeds. The blade  31  contacts the squeeze roller  29  and cleans the carrier adhering to the squeeze roller  29 . 
     The squeeze roller cleaning apparatus for the conventional liquid printer having the above structure has the following disadvantages. 
     First, since a rubber member vulnerable to abrasion is adopted, the blade requires replacement after printing about 10,000 sheets of paper. 
     Second, since the blade is disposed in the trailing direction to prevent the overturn of the blade, the holding volume is generated due to the developer remaining between the blade and the squeeze roller so that the efficiency in cleaning is lowered. 
     Third, since a spanking mechanism for removing the holding volume is needed, the number of parts and the number of assembly steps increases. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is an objective of the present invention to provide an apparatus for cleaning a squeeze roller of a liquid printer. The apparatus includes a blade having a structure which prevents overturn of a contact portion thereof when a squeeze roller rotates so that, by controlling the arrangement of the blade, the life span of the blade can be prolonged, formation of a holding volume can be prevented, and a spanking mechanism is not needed. 
     Accordingly, to achieve the above objective, there is provided an apparatus for cleaning a squeeze roller of a liquid printer by which developer adhering to an outer circumferential surface of the squeeze roller. The squeeze roller is used for forming a film of the developer formed of toner and liquid carrier by pressing the developer onto a photosensitive medium. The apparatus is comprised of a blade holder and a blade. The blade comprises a plate having predetermined rigidity and a cover member having a weaker rigidity than the plate and is coated on or adhering to an outer surface of the plate. One end of the blade being fixedly coupled to the blade holder and an opposite end thereof contacting the outer circumferential surface of the squeeze roller, wherein the blade is disposed to be slanted in a trail counter direction with respect to a rotational direction of the squeeze roller in a drip-line removing mode so that the developer adhering to the squeeze roller can be removed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
     FIG. 1 is a view showing a portion of a general liquid printer; 
     FIG. 2 is a side view of the apparatus for cleaning a squeeze roller for a conventional liquid printer; 
     FIG. 3 is a perspective view showing a portion of a blade of the apparatus for cleaning a squeeze roller for a conventional liquid printer; 
     FIG. 4 is a side view showing an apparatus for cleaning a squeeze roller for a liquid printer according to a preferred embodiment of the present invention; 
     FIG. 5 is a partially cut-away perspective view showing a portion of the blade of the apparatus for cleaning a squeeze roller of a liquid printer according to the present invention; 
     FIG. 6 is a graph indicating the efficiency and the torque of the squeeze roller according to changes in the amount of interference of the blade; 
     FIG. 7 is a graph showing the efficiency and torque of the squeeze roller according to changes in the length of a blade tension when the blade interference is 1.0 mm; and 
     FIG. 8 is a graph indicating the comparison results of the cleaning efficiency between the preferred embodiment and the comparison examples. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 4 shows an apparatus for cleaning a squeeze roller of a liquid printer according to a preferred embodiment of the present invention. Here, the elements having the same reference numerals as those shown in FIGS. 1 through 3 have the same functions. Referring to FIG. 4, an apparatus for cleaning a squeeze roller  40  of a liquid printer according to a preferred embodiment includes a blade holder  45  and a blade  41  fixedly coupled to the blade holder  45 . The apparatus for cleaning a squeeze roller  40  cleans developer D adhering to an outer circumferential surface of the squeeze roller  29  for forming a film of the developer formed of toner and a liquid carrier by pressing the developer onto a photosensitive medium  10 . 
     One end of the blade  41  is fixed to the blade holder  45  and the other end thereof contacts the outer surface of the squeeze roller  29 . The blade  41 , as shown in FIG. 5, includes a plate  42  exhibiting a predetermined rigidity and a cover member  44  formed surrounding the plate  42 . 
     The plate  42  is formed of an SUS-based material, for example, SUS304, whose rigidity is greater than that of the cover member  44  and elastically biases a leading edge  41   a  contacting the outer circumference of the squeeze roller  29 . The cover member  44  is formed on the outer circumference of the plate  42  by being coated thereon or adhering thereto and is formed of a material exhibiting a weaker rigidity than the plate  42 , for example, TEFLON. TEFLON (polytetrafluoroethylene) is synthetic resin resistant to heat and friction so noise generated due to the friction is reduced and overturn of the blade  41  is limited. Also, contamination due to fixation of developer D cleaned from the squeeze roller  29  is prevented. 
     The blade  41  having the above structure is disposed to be slanted in a direction of trail counter to the rotational direction of the squeeze roller  29 . That is, when the squeeze roller  29  is driven in reverse to remove a drip-line, the inclination of the leading edge  41   a  of the blade  41  is disposed in a direction reverse to the rotational direction of the squeeze roller  29  and removes developer D adhering to the outer circumferential surface of the squeeze roller  29 . In the present invention overturn of the blade  41  does not occur due to the rigidity of the plate  42  and the material properties of the cover member  44 . Thus, holding volume Vh of the developer is not generated thus a spanking mechanism to allow the blade holder  45  to reciprocate and pivot is not needed. 
     In the apparatus for cleaning a squeeze roller  40  having the above structure, in order to increase pressure applied to the outer circumferential surface of the squeeze roller  29  due to the elastic bias of the blade  41 , the blade  41  is preferably disposed to be bent while contacting the squeeze roller  29 . The degree to which the blade is bent can be expressed as the amount of blade interference (R−r). Here, R denotes the radius of the squeeze roller  29  and r denotes the distance between the center of the squeeze roller  29  and the leading edge  41   a  of the blade  41  when the elastic bias applied to the blade  41  has been removed as indicated by a dotted line shown in FIG.  4 . 
     FIG. 6 is a graph indicating the efficiency and the torque of the squeeze roller according to changes in the amount of interference of the blade. It is preferable that the amount of blade interference satisfies the below Equation 1 considering the cleaning efficiency and the torque of the squeeze roller. 
     
       
         0.5 mm&lt; R−r&lt; 2.5 mm  [Equation 1] 
       
     
     FIG. 7 is a graph indicating the efficiency in cleaning and the torque of the squeeze roller according to changes in the length of a blade tension when the amount of blade interference is 1.0 mm. 
     The length from the leading edge of the blade holder  45  to the leading edge of the blade  41  is defined as a and the length of the blade  41  fixedly inserted in the blade holder  45  is defined as b. 
     Considering the efficiency in cleaning and the torque of the squeeze roller  29  it is preferable that the tension length a satisfies Equation 2. 
     
       
         8 mm&lt;a&lt;15 mm  [Equation 2] 
       
     
     Preferably, the fixed length of the blade b satisfies Equation 3 to fixedly couple the blade  41  to the blade holder  45 . 
     
       
         2.0 mm&lt;b  [Equation 3] 
       
     
     Preferably, to define the tangential position of the leading edge of the blade  41 , a blade pressure angle θ between line segments {overscore (CP 2 +L )} and {overscore (CT)} satisfies the below equation 4. 
     
       
         5°&lt;θ&lt;30°  [Equation 4] 
       
     
     Here, C is the center of the squeeze roller  29 ; P 1  is a point where a definite straight line concurrently passing C and perpendicular to the proceeding direction of the photosensitive medium  10  meets with the center in a widthwise direction of the blade holder  45 , P 2  is a point of contact between the leading edge  41   a  of the blade  41  and the outer circumferential surface of the squeeze roller  29 ; T is a tangent point closer to P 2  among two tangent points made by the line segments passing through P 1  and contacting the outer circumference of the squeeze roller  29 . 
     FIG. 8 is a graph indicating the comparison results of the cleaning efficiency between the apparatus for cleaning a squeeze roller having the above structure according to a preferred embodiment of the present invention and the conventional cleaning apparatus described with reference to FIGS. 2 and 3. As indicated in the graph, when cleaning is performed by disposing the squeeze roller  29  in a trailing direction using the apparatus for cleaning a squeeze roller  40  according to the present invention, the cleaning efficiency is about 60% that of in the comparison examples. However, when the squeeze roller  29  disposed in the trail counter direction and the cleaning is performed, the cleaning efficiency is about 99%. 
     As described above, in the apparatus for cleaning a squeeze roller having the structure according to the present invention, since the blade is formed using the rigid plate and a cover member is made of a material such as TEFLON covering the plate, the durability of the blade is improved so as to be used semi-permanently, i.e., printing up to about 100,000 sheets of paper. Also, abrasion of the squeeze roller by the plate can be prevented so that the quality of image can be improved. 
     Further, the overturn of the blade generated due to the material properties of the cover member is fundamentally solved so that the blade can be disposed in the trail counter direction. Thus, holding volume is not generated and the generation of foreign material is restricted. Accordingly, the spanking mechanism for removing the holding volume is essentially not needed.