Patent Publication Number: US-7587158-B2

Title: Second transfer area for an image forming device and methods of use

Description:
BACKGROUND 
   The present application is directed to a second transfer system for transferring a toner image from an intermediate member to a media sheet and, more particularly, to aspects of the second transfer system that provide good toner transfer and higher quality images. 
   Image forming devices may include one or more image forming units for forming a toner image. The toner image is transferred to an intermediate member as it moves past the image forming unit. The intermediate member than moves the toner image to a second transfer area where the image is transferred to a media sheet. Good print quality results when the toner image accurately transfers to the media sheet. 
   A second transfer roller may be positioned at the second transfer area where the toner image is transferred to the media sheet. The intermediate member should be oriented to contact the second transfer roller and the media sheets at predetermined locations. 
   The image forming device should also be constructed in a manner to facilitate maintenance and repair. Many of the elements within the device may wear out or otherwise become exhausted through use requiring that they be removed and replaced. The device should be constructed such that the removal and replacement occurs in a straight-forward manner, and that print quality remains adequate. Further, the device may be constructed to be as small as possible. This sizing allows the device to be positioned in a variety of different locations within a workplace. A small overall size is often a key factor when a user is making a purchasing decision. 
   SUMMARY 
   The present application is directed to second transfer areas and methods of transferring toner images from an intermediate member to a media sheet. In one embodiment, a tension roller directs the intermediate member into a second transfer nip formed between a second transfer roller and a back-up roller. The tension roller positions the intermediate member to form a soft nip where the intermediate member contacts the second transfer roller but not the back-up roller. A hard nip may also be formed where the intermediate member contacts both the second transfer roller and the back-up roller. The pressure exerted at the second transfer nip may also result in good transfer of the toner images. In one embodiment, the combination of the length of the soft nip and the pressure at the second transfer nip results in good toner transfer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of an image forming device according to one embodiment. 
       FIG. 2  is a schematic view of a section of the intermediate transfer member according to one embodiment. 
       FIG. 3  is a schematic view of a tension roller and a section of the intermediate transfer member according to one embodiment. 
       FIG. 4  is a perspective view of the second transfer area according to one embodiment. 
   

   DETAILED DESCRIPTION 
   The present application is directed to second transfer areas and methods of transferring toner images from an intermediate member to a media sheet. The second transfer area comprises a second transfer nip formed between a second transfer roller and a back-up roller. The media path moves through this nip with the media sheets moving along the path and receiving the toner image from the intermediate member. The amount of force applied by the second transfer roller may affect the transferability of the toner images to the media sheet. Further, the intermediate member may contact the second transfer roller at soft nip and hard nip locations. The lengths of these nips may also affect the transferability of the toner images. 
   The image forming device may include a laser printer (mono or color), facsimile, copier, or combination of two or more of these devices which is often referred to as an all-in-one device. The device may be sized to fit on a workspace, such as a desktop. The device may further include accessible work areas for the user to insert and remove media sheets, replace components within the device, and clear media jams from within the device. 
     FIG. 1  illustrates one embodiment of an image forming device, generally illustrated as  10 . The device  10  includes a media input tray  68  positioned in a lower section of a body  12 . The tray  68  is sized to contain a stack of media sheets that will receive color and/or monochrome images. The media input tray  68  is preferably removable for refilling. Therefore, in this embodiment, a user may insert and remove the media input tray  68  from the device  10  through a front  13  of the body  12 . A control panel  14  may be located on the front  13  of the body  12 . Using the control panel  14 , the user is able to enter commands and generally control the operation of the image-forming device  10 . For example, the user may enter commands to switch modes (e.g., color mode, monochrome mode), view the number of images printed, take the device  10  on/off line to perform periodic maintenance, and the like. 
   A first toner transfer area  30  includes one or more imaging units  31  that are aligned horizontally extending from the front  13  to a back  15  of the body  12 . Each imaging unit  31  includes a charging roll  32 , a developer roll  33 , and a rotating photoconductive (PC) drum  34 . The charging roll  32  forms a nip with the PC drum  34 , and charges the surface of the PC drum  34  to a specified voltage such as −1000 volts, for example. A laser beam from a printhead  36  contacts the surface of the PC drum  34  and discharges those areas it contacts to form a latent image. In one embodiment, areas on the PC drum  34  illuminated by the laser beam are discharged to approximately −300 volts. The developer roll  33 , which also forms a nip with the PC drum  34 , then transfers toner particles from a toner reservoir  37  to the PC drum  34  to form a toner image. The toner particles are attracted to the areas of the PC drum  34  surface discharged by the laser beam  35 . 
   The toner reservoir  37  is operatively connected to each of the imaging units  31 . The toner reservoirs  37  are sized to contain toner that is transferred to the imaging units  31  for image formation. The toner reservoirs  37  may be mounted and removed from the device  10  independently from the imaging units  31 . In one embodiment, the toner reservoirs  37  each contain one of black, magenta, cyan, or yellow toner. Each of toner reservoirs  37  may be substantially the same, or one or more of the toner reservoirs  37  may hold different toner capacities. In one specific embodiment, the black toner reservoir has a higher capacity than the others. The toner reservoirs  37  may mount from a top  16  of the device  10 , and may detach during removal with the imaging units  31  remaining within the device  10 . 
   An intermediate transfer mechanism (ITM)  60  is disposed adjacent to each of the imaging units  31 . In this embodiment, the ITM  60  is formed as an endless belt trained about support roller  29 , tension roller  21  and back-up roller  22 . The belt may be constructed from a variety of materials including polyimide, Ethylene TetrafluoroEthylene (ETFE), nylon, thermoplastic elastomers (TPE), polyamide-imid, and polycarbonate alloy. During image forming operations, the ITM  60  moves past the imaging units  31  in a clockwise direction as viewed in  FIG. 1 . One or more of the PC drums  34  apply toner images in their respective colors to the ITM  60 . In one embodiment, a positive voltage field attracts the toner image from the PC drums  34  to the surface of the moving ITM  60 . 
   The ITM  60  rotates and collects the one or more toner images from the imaging units  31  and then conveys the toner images to a media sheet at a second transfer area. The second transfer area includes a second transfer nip  40  formed between the back-up roller  22  and a second transfer roller  41 . 
   A media path  44  extends through the device  10  for moving the media sheets through the imaging process. Media sheets are initially stored in the input tray  68  or introduced into the body  12  through a manual feed  48 . The sheets in the input tray  68  are picked by a pick mechanism  67  and moved into the media path  44 . In this embodiment, the pick mechanism  67  includes a roller positioned at the end of a pivoting arm. The roller rotates to move the media sheets from input tray  68  towards the second transfer area. In one embodiment, the pick mechanism  67  is positioned in proximity (i.e., less than a length of a media sheet) to the second transfer area with the pick mechanism  67  moving the media sheets directly from the input tray  68  into the second transfer nip  40 . For sheets entering through the manual feed  48 , one or more rollers are positioned to move the sheet into the second transfer nip  40 . 
   The media sheet receives the toner image from the ITM  60  as it moves through the second transfer nip  40 . The media sheets with toner images are then moved along the media path  44  and into a fuser area  70 . Fuser area  70  includes fusing rollers or belts  71  that form a nip to adhere the toner image to the media sheet. The fused media sheets then pass through exit rollers  45  that are located downstream from the fuser area  70 . Exit rollers  45  may be rotated in either forward or reverse directions. In a forward direction, the exit rollers  45  move the media sheet from the media path  44  to an output area  47 . In a reverse direction, the exit rollers  45  move the media sheet into a duplex path  46  for image formation on a second side of the media sheet. 
     FIG. 2  illustrates the ITM  60  as it moves in a clockwise direction past the tension roller  21  and through the nip  40  at the second transfer area formed between the second transfer roller  41  and the back-up roller  22 . The tension roller  21  is mounted on a pivoting arm  24  and positioned to direct the ITM  60  into contact with the second transfer roller  41  prior to contacting the back-up roller  22 . The tension roller  21  is positioned in close proximity to the back-up roller  22  to reduce the overall height of the device  10 . In one embodiment, the center  28  of the tension roller  21  is positioned within about 30 mm of the second transfer nip  40 . In another embodiment, this distance is within about 20 mm of the second transfer nip  40 . 
   The ITM  60  first contacts the second transfer roller  41  before contacting the back-up roller  22 . The first contact area, referred to as the soft nip  23   a,  is where the ITM  60  begins to wrap onto the second transfer roller  41  prior to contacting the back-up roller  22 . A second contact area, referred to as the hard nip  23   b,  is where the ITM  60  is also supported by the back-up roller  22 . The ITM  60  is in contact with both rollers  22 ,  41  in the hard nip  23   b.  As the media sheets move along the media path  44 , the sheets first contact the soft nip  23   a  of the second transfer roller  41  and then proceed to the hard nip  23   b.  It has been determined that a greater soft nip  23   a  and hard nip  23   b  produce higher quality printed images. 
   The soft nip  23   a  may have a variety of lengths ranging from about 1.0 mm to about 4.8 mm. In one embodiment, the soft nip  23   a  has a length of about 1.7 mm. Other embodiments include a soft nip  23   a  of about 1.25 mm and about 2.6 mm. The hard nip  23   b  may also have a variety of lengths. In one embodiment, the hard nip  23   b  is about 4.0 mm. 
   The tension roller  21  is mounted on the end of the arm  24  and pivots about point  25 . As illustrated in  FIG. 3 , a tensioner  26  is attached to the arm  24 . Tensioner  26  positions the arm  24  and tension roller  21  to provide a predetermined amount of tension to the ITM  60 .  FIG. 3  illustrates one embodiment of the tensioner  26  that includes a bellcrank  102  and torsion spring  103 . The tensioner  26  maintains a tension on the arm  24  to position the tension roller  21  and thus the belt  60  within a predetermined area. The arm  24  and tension roller  21  may pivot about point  25  during run-out of any or all of the rollers  21 ,  22 ,  29  that support the ITM  60 . Pivoting movement causes the position of the arm  24  and tension roller  21  to move relative to the second transfer roller  41 . This movement is illustrated by the solid and dashed lines indicated in  FIG. 2 . This motion causes the movement of the tension roller  21  to be largely in a direction tangent to the path of the ITM  60 . Thus, the contact point between the ITM  60  and the second transfer roller  41  does not substantially change during movement of the arm  24 . 
   As illustrated in  FIG. 3 , a line A extends through the arm  24  and the center of pivot  25  and the center  28  of the tension roller  21 . In one embodiment, an angle α formed between line A and the path of the ITM  60  is about 90°. In other embodiments, the angle α formed between the line A and the ITM  60  is between about 70-110°. In still another embodiment, the angle α is between about 75-105°. These angles are determined when the arm  24  is at a normal, home position. The angles will change during the pivoting motion of the arm  24 . 
   The size and positioning of the second transfer roller  41  within the main body  12  accommodates a larger roller than with previous devices. In one embodiment, the second transfer roller  41  has a diameter of about 25 mm. 
     FIG. 4  illustrates the second transfer nip  40  formed between the second transfer roller  41  and the back-up roller  22 . For purposes of clarity, the ITM  60  that runs through the nip  40  is not illustrated. The second transfer roller  41  is mounted within arms  42  that extend along each axial end. A biasing mechanism  43  on each of the arms  42  attach to a shaft  49  that extends through the roller  41 . The biasing mechanisms  43  force the roller  41  into the back-up roller  22 . The backup roller  22  may be fixedly positioned within the body  12 , or may be positioned to allow a slight amount of movement. In one embodiment, the second transfer roller  41  is softer causing it to deform when forced into contact with the back-up roller  22 . 
   The amount of force applied by the second transfer roller  41  further affects the transfer of the toner image to the media sheet at the second transfer area  40 . In one embodiment, the amount of force applied by the second transfer roller  41  is greater than about 9 g/mm. Specific embodiments include the amount of force applied by the second transfer roller  41  to be about 15 g/mm, and about 25 g/mm. In yet another embodiment, the force is about 35 g/mm. This force causes a transfer nip pressure to transfer the toner image from the ITM  60  to the media sheet. In one embodiment, the transfer nip pressure is about 0.045 N/mm 2 . 
   The combination of the length of the soft nip  23   a  and the force at the second transfer nip  40  greatly affects the transfer of the toner image from the ITM  60  to the media sheet. In one embodiment, a soft nip of about 1.25 mm and a second transfer force of greater than about 15 g/mm results in good image transfer. In one embodiment, the force was about 15 g/mm. In another embodiment, the force was about 25 g/mm. In yet another embodiment, the force was about 35 g/mm. 
   In one embodiment, an ITM unit  80  is a replaceable component that may be removed from the body  12  and replaced with a new component. The ITM unit  80  includes the ITM  60 , interior rollers  21 ,  22 , and  29 , and the second transfer roller  41 . Removal and replacement of the second transfer roller  41  with the back-up roller  22  ensures that the pressure at the second transfer nip  40  is accurate upon replacement of the ITM unit. 
   In the embodiment described above, a force is applied to the second transfer roller  41  to form the pressure in the second transfer nip  40 . In another embodiment, the force is applied through the back-up roller  22  with the second transfer roller  41  remaining relatively stationary. In another embodiment, a force is applied through both rollers to obtain the necessary nip pressure. 
   Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
   As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
   The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. In one embodiment, the back-up roller  22  is deformed due to contact with the second transfer roller  41 . In another embodiment, neither of the rollers  22 ,  41  deform. In yet another embodiment, both rollers  22 ,  41  deform. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.