Patent Publication Number: US-8989650-B2

Title: Printing medium alignment device with rollers attached and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of U.S. application Ser. No. 12/098,682 filed on Apr. 7, 2008, which claims the benefit of Korean Patent Application Nos. 2007-58954 and 2007-77794, filed on Jun. 15, 2007 and Aug. 2, 2007, respectively, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Aspects of the present invention relates to an image forming apparatus, and more particularly, to a printing medium alignment device and an image forming apparatus having the same, which aligns a front end of a printing medium supplied to a printing unit. 
     2. Description of the Related Art 
     An image forming apparatus is an apparatus that prints a black and white image, or a color image, on a printing medium, e.g., paper, according to an image signal. An image forming apparatus can be, for example, a laser printer, an ink-jet printer, a copying machine, a multi-function printer, a fax machine, etc. An image forming apparatus can be classified as an electrophotographic type, in which a beam is scanned to a photosensitive body to form an electrostatic latent image and a developer is supplied to the electrostatic latent image to transfer the same onto a printing medium; or an ink-jet type, in which a liquid ink is ejected onto the surface of a printing medium, according to an image signal. 
     An image forming apparatus generally includes: a printing medium supply unit, which contains sheets of printing media, and supplies the printing medium sheet by sheet; a printing unit, which prints letters or pictures on the printing medium supplied from the printing medium supply unit; and a printing medium discharge unit, which discharges the printed printing medium. In the electrophotographic image forming apparatus, the printing unit includes: a photosensitive body, on which an electrostatic latent image is formed; an exposure unit that radiates light to the photosensitive body; a developing unit that supplies a developer to the electrostatic latent image formed on the photosensitive body, to form a visible image; a transfer unit that transfers the visible image to the printing medium; and a fusing unit that fuses the visible image to the printing medium, by applying heat and pressure to the printing medium. In the ink-jet image forming apparatus, the printing unit is provided with a print head that ejects an ink onto the surface of the printing medium, according to an image signal. 
     The both types of image forming apparatuses further include a printing medium alignment device, which is provided upstream from the printing unit (with respect to a paper transfer direction), to uniformly align the front end of the printing medium supplied from the printing medium supply unit. The printing medium supplied from the printing medium supply unit may get twisted/misaligned when it is fed to the printing unit. Such a misalignment may result in reduced printing quality. To prevent this problem, the printing medium alignment device aligns the printing medium, before the printing medium advances to the printing unit. 
     An example of a conventional printing medium alignment device is disclosed in Japanese Patent Laid-Open Publication No. 2004-26343 (published on Jan. 29, 2004). The disclosed printing medium alignment device includes: a register roller that rotates by receiving a driving force; an idle roller that contacts the register roller, and rotates together with the register roller; and a register shutter that is mounted so as to contact the front end of the printing medium, as the printing medium advances into a nip formed between the register roller and the idle roller. If the front end of the printing medium is properly aligned, the register shutter rotates to pass the printing medium. 
     The register shutter is provided with plural front-end touch parts, which contact the front end of the printing medium. When an external force, which is larger than a predetermined force, is applied, the register shutter is rotated. If the printing medium gets twisted, and thus, the front end of the printing medium does not contact all of the front-end touch parts, the pushing force is too weak to rotate the register shutter, so the register shutter continues to block the printing medium. If the printing medium is aligned, and thus, the front end of the printing medium contacts all the front-end touch parts, the register shutter rotates, and the printing medium progresses between the register roller and the idle roller. 
     For the register roller to align the front end of the printing medium, the front-end touch parts should be arranged in parallel, in a direction perpendicular to a feeding direction of the printing medium, and should not be bent nor deformed. In order to prevent wear and bending of the register shutter, the register shutter is typically made of a material mixed with a glass fiber. 
     However, because the register shutter successively contacts the printing medium, noise occurs when the printing medium pushes the register shutter and progresses. Further, the noise increases when the printing operation is performed at a high speed. 
     SUMMARY OF THE INVENTION 
     An aspect of the invention provides a printing medium alignment device and an image forming apparatus having the same, which can decrease noises that occur when a printing medium passes through a printing medium alignment device, and can decrease wear of a register shutter. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention. 
     In accordance with an aspect of the invention, there is provided an image forming apparatus comprising: a printing medium supply unit to supply a printing medium; a printing unit to print an image on the printing medium supplied from the printing medium supply unit; and a printing medium alignment device. The printing medium alignment device includes: a register roller; an idle roller to form a nip by contacting the register roller, and to feed the printing medium supplied from the printing medium supply unit to the printing unit; a register shutter to temporarily block a front end of the printing medium from proceeding toward the nip, to align the printing medium, and to rotate out of a feeding path of the printing medium, to pass the printing medium; and at least one shutter roller mounted in the register shutter. When the register shutter deviates from the feeding path, the shutter roller rolls while in contact with the printing medium, to decrease friction between the printing medium and the register shutter. 
     According to aspects of the present invention, the register shutter may include at least one front-end touch part having a front-end touch surface, which contacts the front end of the printing medium. The shutter roller may be mounted to a lower portion of the front-end touch surface. 
     According to aspects of the present invention, the shutter roller may be mounted such that an outer peripheral surface of the shutter roller, which contacts the printing medium, protrudes from the front-end touch surface. 
     According to aspects of the present invention, the register shutter may include a plurality of front-end touch parts, and a shutter roller may be mounted on each of the front-end touch parts. 
     According to aspects of the present invention, the front-end touch part may be coupled with a coupling shaft, to rotatably support the shutter roller. 
     In accordance with another aspect of the invention, there is provided a printing medium alignment device comprising: a register roller; an idle roller to contact the register roller, to form a nip with the register roller; a register shutter to selectively block a front end of the printing medium from proceeding toward the nip, to align the printing medium, and to rotate out of a feeding path of the printing medium to pass the printing medium; and at least one shutter roller mounted on the register shutter. When the register shutter deviates from the feeding path, the shutter roller rolls while in contact with the printing medium, to decrease friction between the printing medium and the register shutter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, of which: 
         FIG. 1  is a side-sectional view schematically illustrating an image forming apparatus, in accordance with aspects of the present invention; 
         FIG. 2  is a perspective view schematically illustrating a printing medium alignment device of the image forming apparatus, in accordance with aspects of the present invention; 
         FIG. 3  is an enlarged view illustrating a part of the printing medium alignment device depicted in  FIG. 2 ; and 
         FIGS. 4 and 5  are side views for explaining an operation of the printing medium alignment device, in accordance with aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The exemplary embodiments are described below, in order to explain the aspects of present invention, by referring to the figures. 
     As shown in  FIG. 1 , an image forming apparatus  100 , according to an exemplary embodiment of the present invention, is an electrophotographic image forming apparatus. The image forming apparatus  100  includes: a main body  11  that forms an external appearance; a printing medium supply unit  12  to supply a printing medium; a printing unit  13  to print an image on the printing medium; a printing medium discharge unit  14  to discharge the printing medium from the main body  11 ; and a printing medium alignment device  50  to align the printing medium supplied from the printing medium supply unit  12 . As referred to herein, the printing medium can be paper, transparency sheets, envelopes, or any suitable printable material. 
     The printing medium supply unit  12  includes a printing medium loading cassette  21  that contains sheets of printing media, a pickup roller  22  that picks up single sheets of the printing media from the loading cassette  21 , and rollers  23 ,  24 ,  25 , and  26  that are mounted in a feeding path P of the printing medium, to feed the printing medium toward the printing unit  13 . The rollers include a first feeding roller  23  mounted near the pickup roller  22 , a double-feed prevention roller  24  disposed in contact with the first feeding roller  23 , a second feeding roller  25  mounted downstream from the first feeding roller  23 , to rotate according to a driving force from a driving source (not shown), and an idle roller  26  to rotate with the first feeding roller  23  and the second feeding roller  25 , while contacting the second feeding roller  25 . If two or more sheets of printing media are picked up from the printing medium loading cassette  21 , the double-feed prevention roller  24  back feeds any of the printing medium that does not contact the first feeding roller  23 , to the printing medium loading cassette  21 . 
     The printing unit  13  includes: a photosensitive body  31  where an electrostatic latent image is formed; a charge roller  32  that charges the photosensitive body  31  with a predetermined electric potential; an exposure unit  33  that radiates light to the photosensitive body  31 , according to an image signal; a developing unit  34  that supplies a developer to the photosensitive body  31 , to form a visible image; a transfer roller  35  that transfers the visible image formed on the photosensitive body  31  onto the printing medium; and a fusing unit  36  that fuses the transferred visible image to the printing medium. 
     The printing medium discharge unit  14  includes a discharge roller  41  that discharges the printing medium to the exterior of the main body  11 , and a discharge tray  42  to receive the printing medium discharged from the main body  11 . The printing medium alignment device  50  is mounted between the printing medium supply unit  12  and the printing unit  13 . The printing medium alignment device  50  aligns the front end of the printing medium supplied from the printing medium supply unit  12 , and then feeds the printing medium to the printing unit  13 . 
     Although they are not illustrated in the drawings, a driving source is mounted inside the main body  11 , to generate a driving force used in the operation of the image forming apparatus. A control device (not shown) to control the overall operation of the image forming apparatus  100  may also be included. 
     If the printing operation of the image forming apparatus  100  is started, the pickup roller  22  picks up the printing medium from the printing medium loading cassette  21 , and feeds the printing medium to the printing medium alignment device  50 . The light generated from the exposure unit  33  is radiated onto the surface of the photosensitive body  31 , which is charged with a predetermined electric potential by the charge roller  32 , according to an image signal. An electrostatic latent image is thereby formed on the photosensitive body  31 . The developer is applied to the electrostatic latent image by the developing unit  34 , to form a visible image. The visible image is transferred onto the surface of the printing medium by the transfer roller  35 , and is fused to the printing medium when the printing medium passes through the fusing unit  36 . The printing medium, on which the image has been printed, is discharged to the discharge tray  42 , by the discharge roller  41 . 
     While printing an image on the printing medium, which is fed along the feeding path P that extends from the printing medium loading cassette  21  to the discharge tray  42 , the printing medium may get twisted/misaligned. If the misaligned printing medium passes between the photosensitive body  31  and the transfer roller  35 , the visible image cannot be properly transferred onto the printing medium, thereby resulting in poor printing quality. To prevent this problem, the printing medium alignment device  50 , which is mounted upstream from the printing unit  13 , aligns the front end of the printing medium, when the printing medium is fed toward the printing unit  13 , and then transfers the printing medium to the printing unit  13 . 
     As shown in  FIG. 2 , the printing medium alignment device  50  includes: a register roller  51  that is rotated by a driving source (not shown); an idle roller  53  that contacts the register roller  51 , and forms a nip N (see  FIG. 4 ) with the register roller  51 ; and a register shutter  55  that blocks the front end of the printing medium, as the printing medium is fed toward the nip N, to align the printing medium. If the printing medium is properly aligned, the register shutter  55  exits the feeding path P, to allow the printing medium to enter the nip N. 
     The register roller  51  is coupled to a rotating shaft  52  that is mounted inside the main body  11 . The shaft  52  is driven by the driving source (not shown). The idle roller  53  is rotatably coupled to a supporting shaft  54  that is fixed to the main body  11 , in parallel with the rotating shaft  52 . The idle roller  53  rotates on the supporting shaft  54 . The idle roller  53  has an inner diameter slightly larger than an outer diameter of the supporting shaft  54 . The register roller  51  and the idle roller  53  contact each other, to form the nip N therebetween. When the register roller  51  rotates, the idle roller  53  is thereby rotated in a direction opposite to the rotational direction of the register roller  51 . 
     The register shutter  55  is loosely coupled to the supporting shaft  54 , so as to rotate thereon at a predetermined angle. An elastic supporting member  59  is provided at one end of the register shutter  55 . One end of the elastic supporting member  59  is coupled to the register shutter  55  and the other end of the elastic supporting member  59  is fixed to the main body  11 , as shown in  FIG. 1 . As shown in  FIG. 2 , the elastic supporting member  59  positions the register shutter  55  in a first position, to block the printing medium from proceeding to the nip N, so long as an external force is not applied to the register shutter  55 . 
     The register shutter  55  includes front-end touch parts  56 . The front-end touch parts  56  are positioned between the rotating shaft  52  and the supporting shaft  54 , to block the printing medium. As shown in  FIG. 3 , each of the front-end touch parts  56  has a front-end touch surface  56   a  that is flat, to contact the front end of the printing medium. When the register shutter  55  is in the first position, the front-end touch surfaces  56   a  are substantially perpendicular to the feeding direction of the printing medium. Thus, when properly aligned, the front end of the fed printing medium comes into contact with all of the front-end touch surfaces  56   a  simultaneously. 
     When the printing medium is fed toward the nip N, the register shutter  55  temporarily blocks the front end of the printing medium, and aligns the printing medium. If the printing medium is properly aligned, the register shutter  55  is rotated by the printing medium, into a second position that positions the register shutter  55  out of the feeding path P. In detail, if the printing medium is misaligned when fed toward the register roller  51  and the idle roller  53 , the printing medium only contacts some of the front-end touch parts  56 . Thus, the pushing force of the printing medium on the register shutter  55  is not sufficient to move the register shutter  55 , and the printing medium is blocked from entering the nip N. Thereafter, if the printing medium becomes properly aligned, the printing medium comes into contact with all of the front-end touch parts  56 , and the printing medium can then rotate the register shutter  55  out of the feeding path P (into the second position). 
     Each of the front-end touch parts  56  is provided with a shutter roller  57 . One shutter roller  57  and touch part  56  are described here, for convenience. The shutter roller  57  is mounted on a lower portion of the front-end touch surface  56   a , such that an outer peripheral surface  57   a  of the shutter roller  57  protrudes from the front-end touch surface  56   a . The shutter roller  57  is coupled to a coupling shaft  58 , which is rotatably mounted to the front-end touch part  56 . 
     As shown in  FIG. 3 , the lower portion of the front-end touch surface  56   a  has a mounting recess  56   b  in which the shutter roller  57  is received, and a coupling hole  56   c  into which the coupling shaft  58  is rotatably inserted. A bushing  56   d  is mounted in the coupling hole  56   c , to decrease friction between the coupling hole  56   c  and the coupling shaft  58 , so that the coupling shaft  58  can rotate smoothly. If the register shutter  55  and the shutter roller  57  are made of a plastic material, and the coupling shaft  58  is made of a metal material, the coupling shaft  58  can rotate smoothly in the coupling hole  56   c , without the bushing  56   d.    
     When the printing medium comes into contact with the front-end touch surface  56   a  and rotates the register shutter  55 , the shutter roller  57  is rotated by the printing medium, as the printing medium is transferred. The rotation of the roller  57  considerably decreases friction between the printing medium and the register shutter  55 . Accordingly, noise due to friction between the printing medium and the register shutter  55 , when the printing medium passes between the register roller  51  and the idle roller  53 , is remarkably decreased, and wear to the register shutter  55  is also remarkably decreased. 
     Hereinafter, an operation of a printing medium alignment device  50  of an image forming apparatus, according to aspects of the present invention, will be described with reference to  FIGS. 4 and 5 . As shown in  FIG. 4 , the printing medium is picked up from the printing medium loading cassette  21  by the pickup roller  22 , and is fed down the feeding path P by the first feeding roller  23  and the second feeding roller  25 . After passing the second feeding roller  25 , the printing medium is guided toward the nip N, by a guide plate  27  mounted on the feeding path P upstream from the printing medium alignment device  50 . 
     The front end of the printing medium comes into contact with the front-end touch surfaces  56   a  of the register shutter  55 . If the printing medium is improperly aligned, the front end of the printing medium contacts only some of the front-end touch surfaces  56   a  of the register shutter  55 . In this case, the printing medium cannot apply sufficient force to rotate the register shutter  55 , because the applied force is smaller than the elastic force of the elastic supporting member  59 . Therefore, the register shutter  55  does not move, and blocks the front end of the printing medium. If the printing medium is aligned with the register shutter  55 , by the second feeding roller  25 , the front end of the printing medium comes into contact with all of the front-end touch surfaces  56   a.    
     As shown in  FIG. 5 , if the front end of the printing medium contacts all of the front-end touch surfaces  56   a , the pushing force of the printing medium on the register shutter  55  is sufficient to overcome the elastic force of the elastic supporting member  59 . The printing medium then rotates the register shutter  55  in the clockwise direction, and the front-end touch parts  56  exit the feeding path P. The printing medium slides past the front-end touch parts  56 , to pass between the register roller  51  and the idle roller  53 , and proceeds toward the printing unit  13 . While the printing medium slides past the front-end touch parts  56 , the printing medium contacts the outer peripheral surface  57   a  of the shutter rollers  57  protruding from each of the front-end touch parts  56 . The shutter rollers  57  rotate when in contact with the printing medium, thereby considerably decreasing the friction between the printing medium and the register shutter  55 . Accordingly, noise, due to friction between the printing medium and the register shutter  55 , is remarkably decreased, and wear to the register shutter  55  is also minimized. 
     In the above description, the image forming apparatus has been exemplified as an electrophotographic image forming apparatus. However, the present invention can also be applied to an ink-jet image forming apparatus, or other various image forming apparatuses, such as a photocopier, a multi-function printer, etc. 
     As is apparent from the above description, an image forming apparatus, according to aspects of the present invention, can remarkably decrease noise due to friction between the register shutter and the printing medium, and can reduce wear to the register shutter. The shutter rollers mounted on the register shutter considerably decrease friction between the printing medium and the register shutter, by rolling when in contact with the printing medium. Resistance to the feeding of the printing medium, due to friction with the register shutter, is reduced, and the printing medium can be fed smoothly toward the printing unit. 
     Although exemplary embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments, without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.