Abstract:
Alignment nip regulation may be implemented by controlling the approach of media to an alignment nip. Where media is fed from a plurality of sources and from a plurality of approach angles through a common alignment nip, nip entry may be controlled by focusing the media through a diverter or a jog in an existing path to alter the course followed by the media sheets. The diverter may be configured to direct the media sheets to a contact point at or near the alignment nip, such as on a roller that forms the alignment nip. Alternatively, media sheets arriving at the nip from separate conduits may be separately directed to a common contact point near the alignment nip. In either case, one or more sensors may detect the approach of the media sheets at a time when the sheets are a common, predetermined distance away from the alignment nip.

Description:
BACKGROUND 
   A persistent goal of many image forming devices is precise registration of images formed on media sheets. This may be particularly true of color printers using multiple color cartridges to create a single color image. In an effort to improve image registration, many image forming devices use an alignment mechanism to control the position and timing of media sheets traveling from various media sources, through the media path, and to the image forming location within the device. Thus, the image forming device relies on the alignment mechanism, which may include a variety of optical, electrical, or mechanical sensors, to know precisely where to form an image on the sheet. 
   As image forming devices are incorporated in smaller packages, rigid space constraints on the media transport components within the device create problems for devices having multiple feed sources. One example of this type of device is a laser printer with multiple media trays, a duplex path, and perhaps a manual feed path. Devices such as these may route media sheets from each of these sources through a common media path. As these devices become smaller, so too does the internal space used to align media fed from the multiple sources into the common media path. 
   A disadvantage of smaller device packaging is that, in general, more space and longer paths are desirable to accurately direct media sheets that are fed from multiple sources toward a common alignment point. Where sufficient space is available, the various media paths can be gradually merged to a common path so that sheets traveling in this common path may then repeatably arrive at a common alignment point. Further, with sufficient spacing, sheets arriving at this common alignment point may be sensed using a single leading edge sensor or other equivalent sensor. Thus, the timing of image processing and media transport events may be predictably determined. Thus, given sufficient space, the fact that media sheets arrive at the common alignment point from media paths converging from different directions and different approach angles may be nearly irrelevant. 
   Unfortunately, as image forming devices get smaller, alignment nips, rollers, and other alignment points move closer to the various media sources. Consequently, the distances previously relied on to align media from different sources get smaller and it has become increasingly difficult to provide consistent media sheet entry into these alignment points. Other factors such as media curl, media weight, and environmental conditions make it even more difficult to reliably control where the leading edge of a media sheet contacts the alignment point. For example, in an alignment nip formed at the contact surface between two registration rollers, the above factors may contribute to the leading edge of media sheets unpredictably striking either roll or both rolls simultaneously, leading to feed reliability problems such as skew, folding, or treeing. 
   Furthermore, the timings for each media source may not be consistent. With the sheets approaching the alignment point from varying angles and the leading edge of the sheets contacting the alignment point at different locations, the time that elapses between sensing a leading edge approaching the alignment point and passing of the leading edge through the alignment point may vary drastically. Thus, transport and image processing algorithms must accommodate this variation by implementing different feed times for the different sources or implementing large delay windows to account for the various feed times, neither of which is optimal. 
   SUMMARY 
   Embodiments of the present invention relate to controlling the approach and entry of media to an alignment nip as may be formed between alignment or registration rollers. Media sheet approach may be controlled with a conduit through which media sheets originating from a plurality of sources pass. The conduit may be positioned adjacent and upstream of an alignment nip. The conduit may comprise a diverting path or jog to alter the course followed by the media sheets passing through the conduit to focus the approach of the media sheets toward the alignment nip. The diverting path may alter an angle of approach of the media sheets to the alignment nip. The diverting path may also improve the likelihood that media sheets from the various sources contact the alignment nip at a repeatable point. In an exemplary system where the alignment nip comprises a contact area between a driven roller and a drive roller, the diverting path may be configured to direct the media sheets to a contact point at the alignment nip or to a point on the drive or driven rollers. 
   Other embodiments comprise separate conduits through which media sheets pass in approaching the alignment nip. The separate conduit may also be configured to direct media sheets to a common contact point near the alignment nip. The alignment nip may also have an associated media sensor associated with each media sheet path. The sensor, an example of which is a leading edge sensor, may be adapted to trigger when a leading edge of a media sheet traveling through either the media sheet paths passes a substantially common distance away from the common point at the alignment nip. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an image forming device according to one embodiment of the present invention; 
       FIG. 2  is a schematic illustration of media feed paths in the vicinity of an alignment nip according to one embodiment of the present invention; 
       FIG. 3  is a schematic illustration of media feed paths in the vicinity of an alignment nip according to one embodiment of the present invention; 
       FIG. 4  is a schematic illustration of a media feed sensor in the vicinity of an alignment nip according to one embodiment of the present invention; and 
       FIG. 5  is a schematic illustration of a media feed sensor in the vicinity of an alignment nip according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Embodiments of the present invention are directed to media alignment in an image forming apparatus. One application of the embodiments disclosed herein is for moving media sheets from a plurality of sources into an image forming path within an image forming apparatus as generally illustrated in  FIG. 1 .  FIG. 1  illustrates a representative image forming device, such as a printer, according to one embodiment of the present invention and is indicated generally by the numeral  10 . The exemplary image forming device  10  comprises a main body  12 , at least one media input section  13  holding a print media tray  14 , a pick mechanism  16 , registration rollers  39 , 40 , a media transport belt  20 , a printhead  22 , a plurality of image forming stations  100 , a fuser roller  24 , exit rollers  26 , an output tray  28 , and a duplex path  30 . The components and operation of image forming device  10  are conventionally known; however, a brief discussion is included below for clarity. 
   The image forming device  10  of  FIG. 1  includes a first input section  13 , a manual input section  32 , and optionally, a second input section  50 . Multiple input sections allow for storing or introducing multiple types and sizes of media that may be picked and fed into the media path  21  as required. The input sections may also be sized to hold a large capacity of media sheets. The first input section  13  includes a media tray  14  with a pick mechanism  16  to introduce media sheets into the media path  21  responsive to the receipt of a pick command. The manual input section  32  may also be located in a main body  12  to introduce media sheets into the media path  21 . Manual input section  32  includes an associated pick mechanism  17  to feed media sheets introduced by a user from outside the body  12  of image forming device  10 . A second input section  50  is located in or adjacent to the main body  12  below the first media tray  14 . The second input section  50  includes a third pick mechanism  51 , including pick roller  53 , that picks sheets from input tray  59 . In one embodiment, the input tray  59  has a larger capacity than tray  14  to hold a greater number of sheets. For example, input tray  59  may have a capacity of 500 sheets versus 250 sheets for tray  14 . Feed rollers  55  are located downstream from the pick mechanism  51  to receive the sheets and forward them through input path  54  towards the media path  21 . The media trays  14 ,  59  may be removable as indicated by arrows P and S for refilling, and located on a lower section of the device  10 . 
   From the various input sections  13 ,  32 ,  50  and their associated media paths, media sheets are fed into the media path  21 . One or more registration rollers  39 ,  40  disposed along the media path  21  align the media sheet and precisely control its further movement. A media transport belt  20  forms a section of the media path  21  for moving the media sheets past a plurality of image forming units  100 . In a typical color electrophotographic printer such as exemplary device  10 , three or four colors of toner—cyan, yellow, magenta, and optionally black—are applied successively to a print media sheet to create a color image. Correspondingly, the embodiment of  FIG. 1  depicts four image formation stations  100  arrayed along a media transport belt  20 . The transport belt  20  carries the media sheet successively past the image formation stations  100 . At each station  100 , imaging device  22  forms a latent image onto an associated photoconductive member or PC drum. The latent image is then developed by applying toner to the PC drum. The toner is subsequently deposited on the media sheet as it is conveyed past the image formation station  100 . 
   Once the media sheet moves past the image forming stations  100 , a fuser  24  thermally fuses the loose toner to the media sheet. The sheet then passes through reversible exit rollers  26  to the output stack  28  formed on the exterior body  12  of image forming device  10 . Alternatively, the exit rollers  26  may reverse motion after the trailing edge of the media sheet has passed the entrance to a duplex path  38 , thus directing the media sheet through the duplex path  30  and again into media path  21  to print a duplex image on the opposite side of the media sheet. It should be understood that while the foregoing description relates to a color electrophotographic printer as shown in  FIG. 1 , the present invention is not limited to color printers, but may be advantageously applied to other types of image forming devices  10 , including but not limited to, single-color laser printers and inkjet printers. 
   Referring to  FIGS. 1 and 2 , the registration rollers  39 ,  40  may advantageously perform an alignment process whereby the leading edge of a media sheet is generally held in a fixed location for a predetermined period of time before passing the media sheet through the rollers  39 ,  40  toward the media path  21  and transport belt  20 . The rollers  39 ,  40  form a nip  42 , shown specifically in  FIG. 2 , at the contact area between the rollers that is sometimes referred to as an alignment nip, metering nip, or registration nip as representative of this process. The media alignment may consist of a bump alignment process, which forms a buckle in the media sheet immediately upstream of the alignment nip  42 . During simplex printing (e.g., printing on a first side of a sheet fed from input sections  13 ,  32 ,  50 ), a media sheet is moved by a pick roller  16 ,  17  or a feed-through roller  55  to the alignment nip  42 . In duplex printing, media sheet is moved through duplex path  30  to the alignment nip  42 . For either case, the registration rollers  39 ,  40  rotate in a reverse direction as the leading edge of the media sheet reaches the rollers  39 ,  40 . This reverse rotation laterally aligns the media sheet relative to the alignment nip  42  prior to passing the sheet to media path  21  for image formation. The pick roller  16 ,  17 , drive through roller  55 , or duplex path  30  rollers, however, continue to feed the media sheet towards the alignment nip  42 . As a result, a “buckle” forms in the sheet as the leading edge of the sheet bumps up against the alignment nip  42 . After a predetermined time, the registration rollers  39 ,  40  reverse and begin to rotate in a forward direction to convey the sheet to the media path  21 . 
     FIG. 2  shows a more detailed schematic of various feed paths  60 - 63  approaching registration rollers  39 ,  40  and alignment nip  42 . In the illustrated embodiment, feed path  60  is followed by media fed to alignment nip  42  by pick roller  16  in the primary input source  13 . Feed path  61  is followed by media fed to alignment nip  42  through media path  54  from the second input source  50  (see  FIG. 1 ). Feed path  62  is followed by media fed to alignment nip  42  by pick roller  17  from the manual input source  32 . Feed path  63  is followed by media fed to alignment nip  42  through the duplex path  30 . 
   In one embodiment, the registration rollers  39 ,  40  are comprised of a drive roller  40  and a backup roller  39 . The drive roller  40  is rotated by a drive motor and, optionally, an associated drive mechanism (not shown). The backup roller  39  may also be rotated by a drive motor, but is more advantageously rotated by frictional forces created by contact with the drive roller  40  at the nip  42 . Thus, backup roller  39  operates as a follower roller that rotates in a direction opposite to that of drive roller  40 . Friction between the rollers  39 ,  40  may be increased by incorporating a material having a high coefficient of friction on one or both of the outer surfaces  46 ,  44  of the rollers  39 ,  40 . In addition, the nip force between the rollers  39 ,  40  may be increased with a bias member such as a spring. For reasons discussed in greater detail below, the outer surface  46  of backup roller  39  is preferably comprised of a wear-resistant material such as a hardened resin, composite, steel, or other metal. 
   In the exemplary embodiment, media sheets traveling along feed paths  60 - 62 , which originate from widely different directions, are routed through a common channel or conduit  64  prior to reaching alignment nip  42 . Routing these feed paths in a converging manner like this improves the likelihood that media following these paths will reach a common point at the alignment nip  42 , such as focal point  70  on backup wheel  39  (or on drive wheel  40  or at the nip  42 ). A diversion or jog  66  in the conduit  64  further diverts the sheets traveling through the conduit  64  so that the leading edge of sheets following paths  60 - 62  contacts focal point  70 . Diversion  66  tends to harmonize the direction from which the media paths  60 - 62  approach the focal point  70  in addition to normalizing the point of contact  70  at or near the alignment nip  42 . In the absence of conduit  64  and diversion  66 , the media paths  60 - 62  are more likely to contact other areas around alignment nip  42 , including on drive wheel  40  or at the nip  42  itself. The diversion  66  and conduit  64  also advantageously operate to prevent media sheets from missing the nip altogether, as would happen, for example, if a leading edge of a media sheet were to contact a right side of backup wheel  39  shown in  FIG. 2 . 
   In the exemplary embodiment, diversion  66  may alter the direction followed by heavy-weight sheets fed from pick roller  16  along path  60 . Diversion  66  may also alter the direction followed by media sheets on paths  61 - 62  to more closely follow that of path  60 . For example, in  FIG. 2 , diversion  66  may alter the paths  61 - 62  towards the left, perhaps even to the left of focal point  70 . This is not to say that media paths  60 - 62  are always identical between the diversion  66  and focal point  70 , though they may be. It is more likely that, because of the inherent beam stiffness and weight in media, media paths  60 - 62  will follow a different course between the diversion  66  and the focal point  70 . For instance, in one embodiment, sheets following media path  62  contact the various media guides between pick roller  17  and backup roller  39  at four contact points  90 ,  94 ,  96 , and diversion  66 . Thus, sheets following media path  62  may conform to a four (or more)-point spline curve in the vicinity of conduit  64 . A media sheet moving along path  61  also encounters multiple contact surfaces including diversion  66 , and points  94 ,  96 . Likewise, path  60  encounters points  92 ,  94 , and  96 . 
   With the media constrained as described along paths  60 - 62 , individual sheets may also be ironed out in a widthwise (or perpendicular to the direction of travel) direction. In one embodiment, the media sheets may be intentionally directed at contact point  96  immediately prior to contacting the alignment roller  39  to eliminate leading edge curl effects such as dog ears, treeing, nip stubs and the like. 
   In addition to media paths  60 - 62  converging at focal point  70 , media path  63  from duplex path  30  also advantageously converges at the focal point. In certain document handling devices, such as the exemplary embodiment shown, space constraints may prevent certain feed paths from being routed through a common conduit  64 . As an alternate or parallel solution to the inherent problem of alignment nip  42  approach, certain paths may be directed individually or in groups to a common focus point  42 . Thus, in the embodiment provided, whereas three feed paths  60 - 62  are diverted through conduit  64  and past diversion  66 , one feed path  63  is routed to focal point  70  outside of conduit  64  and diversion  66 . For instance, with sufficient space, duplex path  30  and paper path  63  may also be routed through conduit  64 . Alternatively, paths  62 ,  63  might be combined and routed to focal point  70  independent of paths  60 ,  61 . Certainly other combinations of individual or grouped media paths may be utilized depending on the particular application. 
   As alluded to above, the focal point  70  in the present embodiment is positioned on a surface  46  of roller  39 . The focal point  70  may also be positioned at other locations in the vicinity of the nip  42 , such as on drive wheel  40 , as shown in  FIG. 3 , or at the nip  42 . Also discussed above was that the outer surface  44 ,  46  of one or both the drive wheel  40  and backup wheel  39  may be covered with a high-friction surface to induce rotation in a non-driven, follower wheel such as backup wheel  39 . With wear considerations in mind, the surface  46  on which the focal point  70  is located, may advantageously be constructed of a wear resistant material, such as steel, steel alloy, or other hardened material. Thus, persistent contact of the leading edge of sheets at the focal point  70  will not prematurely lead to dimples or scratches on the surface  46  of backup roller  39 . 
   A sensor  72 , shown in  FIG. 2  and more clearly in  FIG. 4 , may be associated with the alignment nip  42  to sense the approach of media traveling along media paths  60 - 63 . The sensor  72  advantageously informs the image forming device  10  of the presence of an approaching media sheet to begin a timing sequence used in controlling further transport and image processing. The exemplary sensor  72 , which comprises a mechanical arm rotatable about pivot  74 , is shown in three positions. The solid line view of sensor  72  represents a triggered position. The hidden line views of the sensor  72  represent a closed, non-triggered position where no paper is present and an open position showing how the sensor moves out of the way to allow the media to pass. In one embodiment, the sensor  72  is spring biased to the closed position. During operation, a leading edge of a media sheet traveling along paths  60 - 63  contacts and displaces the sensor  72  to the triggered position where the sensor activates a switch, which may be optical, electrical, or mechanical in nature. In one embodiment, the switch is a mechanical switch  78  that is activated by a leaf spring contact  76 . In another embodiment, sensor  72  may be rotated into or out of the path of a photointerrupter (not shown) to detect the position of sensor  72 . The sensor  72  may also be configured to sense a condition when media traveling along all media paths  60 - 63  is a common distance R away from the focal point  70 . Thus, the various timing events may advantageously begin at a similar starting point, regardless of whether media arrives from conduit  64  or duplex path  30 . 
   In an alternative embodiment shown in  FIG. 5 , the mechanical sensor  72  may be replaced with one or more optical sensors  80 ,  82 . As with the embodiment shown in  FIG. 4 , the sensors  80 ,  82  are positioned to trigger when media reaches a common distance R away from the focal point  70 . The sensor  80 ,  82  may be discrete sensors with sensor  80  detecting the presence of media following paths  60 - 62  and sensor  82  detecting the presence of media following path  63 . Alternatively, the sensors  80 ,  82  may be components of a single, integrated sensor. For instance, sensor  80  may be an optical, magnetic, or acoustical transmitter and sensor  82  may be a corresponding receiver (or vice-versa). Thus, the trigger points for media following paths  60 - 62 ,  63  would exist along a straight line between emitter  80  and receiver  82  and may still suitably approximate a common time of leading edge approach to focal point  70 . 
   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. For instance, the embodiments described have been depicted in use with a diversion  66  within an elongated media conduit  64 . The diversion  66  and conduit  64  may also be integrated into a short guide through which media passes. It is also possible to implement one-sided deflecting plate as a suitable diverting jog. Still another possibility is the use of a series of jogs to achieve the intended diversion. 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.