Abstract:
An apparatus capable of performing pick operations on multiple sizes in a printing device is disclosed. This apparatus separates a media sheet from a stack and drives it along a media path. The apparatus also corrects any pick skew of the media sheet caused during the pick operation before the media sheet is transferred to the drive roller. By ensuring that the traversing media sheet has a leveled leading edge, the pick skew of the media sheet is substantially eliminated.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to media handling in printing devices. In particular, it relates to an apparatus and a method, capable of handling multiple media sizes, for picking a media sheet from a stack substantially squared to a media path and substantially eliminating the pick skew of the media sheet in the media path. 
     BACKGROUND OF THE INVENTION 
     Many different kinds of hardcopy printing devices are available commercially today, and these include copiers, faxes and printers. Ubiquitous hardcopy printing devices such as printers are commonly found in homes and offices. Since the evolution of office automation, printers have been integrally connected with other office automation equipment like computers, workstations, print servers, or networks to provide hardcopy printing capability. With the advent of increased CPU processing speed and power due to fast-paced technological advancement, better computers, workstations and servers have also come into being. Thus, that complementing equipment such as printers too must have increased throughput in order to contribute to the overall productivity of any office automation system is inevitable. 
     Printers commonly use printing paper of various sizes, transparencies, or even postcards as print media. These media sheets are fed sequentially into these printers to receive print markings. In doing so, the throughput of the printer is thus limited, in part, by the rate at which the printer receives the media sheets. Many known methods are currently implemented in commercially available printers to handle and provide media sheets efficiently to these printers for printing. 
     An example of the implementation of such known methods is the pick-and-feed operation of many ink jet printers. A pick operation entails picking a single media sheet from a stack of media sheets and moving it along a media path through the use of a pick roller. A drive roller and a pinch roller, which cooperate to perform a feed operation, controls the positioning of the media sheet with respect to a printing head for receiving print markings. In some ink jet printers, the pick-and-feed operation is performed by the same roller serving both the pick and drive functions for cost reasons. From the perspective of performance however, a pick roller would require a different type of material from that of a driver roller. For high pick reliability, the pick roller should be made of soft rubber with high friction coefficient. Conversely, the rubber used for the drive roller should be hard so that it does not deform easily and thus is able to control the feeding of the media sheet accurately. Therefore the implementation of a common roller to perform both operations may not meet the need for both reliable and accurate media handling. 
     Some ink jet printers, on the other hand, make use of separate pick and drive rollers to achieve reliable and accurate media handling. This type of implementation, however, can present its own set of problems, especially during the design of a pick system for resiliently handling various sizes of media sheets. This set of problems can exist because such a pick system for multiple sized media sheets is usually susceptible to the occurrence of pick skew of the different sizes of media sheets. If the media sheet is skewed, then the print markings received on the media sheet will not be square to the page and the result will be aesthetically displeasing. 
     The present invention is intended to provide a solution to various prior art deficiencies, which include those present with the existing printing devices such as copiers, faxes or printers, to provide a cost effective and reliable media sheet pick operation within a media handling system. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, the present invention provides an apparatus, capable of handling multiple media sizes, for picking a media sheet from a stack substantially squared to a media path and substantially eliminating the pick skew of the media sheet in the media path. The apparatus comprises a rotating pick roller, and the pick roller rotates in an axis substantially orthogonal to the media path. The apparatus also comprises a separator which is raised from the surface of the media path. Accordingly, the rotating pick roller and the separator cooperate to provide parallel and opposing forces to separate the media sheet from the stack and move the media sheet along the media path. The apparatus further comprises a novel series of raised leveling surfaces on the surface of the media path. The leveling surfaces help to eliminate the pick skew by raising and leveling the leading edge of the media sheet. 
     The present invention also provides a method, capable of handling multiple media sizes, for picking a media sheet from a stack squared to a media path and the elimination of the pick skew of the media sheet in the media path. The method comprises the step of cooperatively using the pick roller and separator to apply parallel and opposing forces to separate the media sheet from a stack. The method also comprises the step of leveling the leading edge of the media sheet to eliminate the pick skew. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of the preferred embodiment of the present invention. 
     FIG. 2 is a plan view of the embodiment in FIG. 1 for use with known postcard-size print media. 
     FIG. 3 is a plan view of the embodiment in FIG. 1 for use with known A-size print media. 
     FIG. 4 is a plan view of the embodiment in FIG. 1 for use with known A3-size print media. 
     FIG. 5 is a plan view of the embodiment in FIG. 1 for use with known Super B-size print media. 
     FIG. 6 is another plan view of the embodiment in FIG.  1 . 
     FIG. 7 is a cross sectional view of the embodiment in FIG. 1 performing the pick operation to separate the media sheet from the stack. 
     FIG. 8A is a modified cross sectional view of the embodiment in FIG. 1 driving the media sheet along the media path towards the drive roller and pinch roller. 
     FIG. 8B is a modified sectional view of the embodiment in FIG. 3, taken along line A-A′, driving the media sheet along the media path towards the drive roller and pinch roller. 
     FIG. 8C is a further modified sectional view of the embodiment in FIG. 3, taken along line A-A′, with the pair of idle rollers removed. 
     FIG. 8D is a modified sectional view of the embodiment in FIG. 5, taken along line B-B′, driving the media sheet along the media path towards the drive roller and pinch roller. 
     FIG. 8E is a further modified sectional view of the embodiment in FIG. 5, taken along line B-B′, with the series of leveling ribs removed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Overview 
     The main reason for using separate pick and drive rollers in a printing device is to increase the reliability of the pick operation of the printing device, as mentioned in a preceding section. In the following sections, a preferred embodiment of the invention shall be described, by way of an example, as an independent pick system for picking multiple sized media sheets for use in an ink jet printer. 
     In FIG. 1 the preferred embodiment, which is a pick system  11 , is essentially formed with a pick roller  12 , a separator  13  (partially hidden by pick roller  12 ), a shaft  14 , a pair of idle rollers  15 , a series of leveling ribs  16 , and a media path  17 . 
     The pick system  11  forms an integral part of the ink jet printer, which is partially shown in FIG. 1. A stack of media (not shown) to be used for printing is placed in an input tray  19  (partially shown). The stack of media is also squared to the media path  17  and aligned to a right datum  18  of the media path  17 . The media handling process begins with the pick system  11  picking media sheets (also not shown), one at a time, from the stack in the input tray  19  and moving the media sheet along the media path  17  to a drive roller-pinch roller entry point (not shown). The media sheets will subsequently be fed into position, by the drive roller and pinch roller, for receiving print markings. 
     The pick roller  12  is fixed to the shaft  14 , which drives and rotates it. The pair of idle rollers  15  are also spaced along and connected to the shaft  14 . However, the idle rollers  15  are connected such that they freely rotate about the shaft  14 , and thus are not driven by the shaft  14 . The shaft  14 , and thus the rotational axis of the pick roller  12  and the pair of idle rollers  15 , is placed perpendicular to the media path  17  and parallel to a leading edge of the media sheet. This arrangement is necessary because the pick roller  12  will initially come into contact with the leading edge of the media sheet and subsequently drive the media sheet, keeping it substantially squared, along the media path. 
     The separator  13  is found directly below the pick roller  12  along the media path  17 . This arrangement allows the separator  13  to cooperate with the pick roller  12  to pick a single sheet of media sheet from the stack. The series of leveling ribs  16  are found on the surfaces of the input tray  19  and media path  17 . These ribs  16  are strategically located adjacent to the separator  13  and beneath the length of the shaft  14  on the surface of media path  17 . Independently, the series of leveling ribs  16  and the pair of idle rollers  15  perform pick skew correction for the different sizes of media sheets. Details of this operation will be further explained in later sections. 
     In FIGS. 2 to  5 , which are the plan views of the embodiment in FIG. 1, demarcations for the different sizes of media sheets  29 ,  39 ,  49  and  59  used by the ink jet printer are shown. These demarcations are used to indicate the leading edges and part of the left edges of the different types of media sheets  29 ,  39 ,  49  and  59 , or stacks of them, when their right edges are aligned with the right data  28 ,  38 ,  48  and  58  respectively. Media sheet  29  is commonly known as postcard-size print media; media sheet  39  as A-size print media; media sheet  49  as A3-size print media; and media sheet  59  as Super-B size print media. The most important common feature among all of the views shown by FIGS. 2 to  5  is the position of the different media sheets  29 ,  39 ,  49  and  59 , or stacks of them, with reference to the respective media paths  27 ,  37 ,  47  and  57 . By aligning all the different sizes of media to the right of the media paths  27 ,  37 ,  47  and  57 , and thus against the right data  28 ,  38 ,  48  and  58  respectively, the use of a single pick roller-separator configuration for multiple sized media sheets pick operation is made possible. This economy of parts is usually a desired arrangement because of obvious cost advantages. This configuration, however, causes the media sheet  29 ,  39 ,  49  and  59  to rotate in an anti-clockwise direction due to imbalancing forces acting on it as it is pulled at the right leading edge by the pick rollers  22 ,  32 ,  42  and  52  during the pick operation. This behaviour is illustrated in FIG. 6, in which the media sheet  69  experiences a rotational force  60  as result of the imbalancing forces. The right datum  68  however, prevents the media sheet  69  from rotating and contributing to the pick skew, by providing an equal and opposite force to the rotational force. 
     During the pick operation, as shown in FIG. 7, the pick roller  72  will rotate and thus may draw up two or more media sheets  79 A due to the static between each of the media sheets  79 A, or some other reasons, and drive these media sheets  79 A forward along the media path  77 . This undesirable phenomenon is known as multiple picks, and if the pick system  71  has no means to separate the media sheets  79 A, the media sheets  79 A will be fed to the driver roller and pinch roller (not shown) and into the printing position to receive print markings. This process may result in the media sheets  79 A being jammed along the media path  77 , since the media path  77  is designed to allow only one sheet of media  79 A to traverse. For this reason, the separator  73  is placed right below the pick roller  72  to provide friction between the bottom surface of media sheet  79 C and the upper surface of the separator  73 . Since the friction between the media sheet  79 B and media sheet  79 C is less than the friction between media sheet  79 C and the separator  73 , the media sheet  79 B will slide over the media sheet  79 C while being driven forward by the pick roller  72 . This operation will ensure that only one of media sheets  79 A is fed into the printer each time. 
     To provide effective contact between the separator  73  and the bottom surface of the media sheet  79 C, the separator  73  must protrude sufficiently above the surface of the media path  77 . Since the separator  73  is located near the right edge of the media path  77 , it causes the leading edge of the media sheet  79 B to be raised unevenly while the media sheet  79 B is being driven forward along the media path  77 . Accordingly, the shape of the media sheet  79 B is also altered. Since the unleveled leading edge of the media sheet  79 B is not aligned to the drive roller-pinch roller entry point (not shown), further pick skew will occur as the media sheet  79 B is fed to the drive roller and pinch roller. Unless the shape of the media sheet  79 B is corrected prior to its entry at the drive roller and pinch roller, the media sheet  79 B will stay skewed to the media path  77  at the amount caused during the pick operation. 
     The amount of pick skew occurring during the pick operation depends very much on the shape of the media sheet  89  with respect to the right edge of the media sheet  89 , which is shown in FIG.  8 . If the leading edge of the media sheet  89  can be leveled with the right edge of the media sheet  89  before being fed into the drive roller-pinch roller entry point  80 , the pick skew will kept to a minimum. As such, the following measures have been adopted to level the leading edge of the media sheet  89  as it proceeds forward along the media path  87 . 
     Postcard-size and A-Size Media Sheets 
     Due to the stiffness of these types of print media, the left edge of the media sheet  89 , as shown in FIG. 8C, does not bend as much as the right edge of the media sheet  89  as it is picked and driven forward by the pick roller  82 . This uneven bending will result in the left leading edge of the media sheet  89  reaching the drive roller-pinch roller entry point  80  later than the right leading edge of the media sheet  89 . To correct the shape of the media sheet  89 , a pair of idle rollers  85 , each of which is strategically placed over the left edge of each of the postcard-size media sheet  89  or A-size media sheet  89  as shown in FIG. 8B, operate to conform the left edge of the media sheet  89  with the right edge by applying a downward force. As a result, the leading edge of the media sheet  89  is leveled before the media sheet  89  is fed to the drive roller-pinch roller entry point  80 . 
     A3-size and Super B-size Media Sheets 
     Conversely, due to the heavier weight of the A3-size media sheet  89  or Super B-size media sheet  89 , the left edge of media sheet  89 , as shown in FIG. 8E, bends more that the right edge of the media sheet  89  and thus rests on the surface of the media path  87 . This uneven bending will again result in the left leading edge of the media sheet  89  reaching the drive roller-pinch roller entry point  80  later than the right leading edge of the media sheet  89 . To correct this problem, the media path  87  under the left edge of each of the different types of media sheet  89  is raised to the same height as the separator  83 . A leveled plan is thus maintained on which the media sheet  89  moves in order to facilitate the leveling of the leading edge of the media sheet  89 . This is done with the help of the series of leveling ribs  86  as shown in FIG.  8 D. 
     The preferred embodiment of the present invention described is not to be construed as limitative. For example, the series of leveling ribs used to level the leading edge of the media sheet driven through the pick system can be substituted by a series of raised planar surfaces or a series of idle rollers disposed on the surface of the media path. In another example, the separator disposed directly below the pick roller may be replaced by a flap located on one of the leading corners of the media stack. The flap operates to provide an opposing force to cause the corner of the top media sheet to buckle while being driven forward by the pick roller. The media sheet thus separates itself from the underlying media sheet. The flap may be substantially raised from the surface of the media path and thus can cause the leading edge of the media sheet to be unleveled. The resultant shape of the media sheet can accordingly be corrected by the use of the series of leveling ribs or idle rollers.