FIELD OF THE INVENTION
The present invention generally relates to sheet discharge systems, particularly sheet discharge systems for automatic document feeding apparatuses.
BACKGROUND
Many multifunction printers, copying machines and stand-alone scanners are provided with an automatic document feeder (ADF) for automatically transporting individual sheets from a stack of media sheets to an image reading region, and then ejecting and restacking the sheets automatically onto an output tray. It is desirable to neatly restack the media sheets as the sheets exit the ADF. However, this may be difficult to achieve. The incoming ejected sheet tends to slide across the previously ejected sheet. The friction between the sheets may lead to incomplete ejection or skewing of the sheets relative to each other. Known solutions for this problem include modifying the geometry of the output tray to achieve proper stacking, such as inclining the output tray at a steep angle or placing several edge guides on the output tray. These known solutions either produce an unattractive output design or add cost to the ADF. There remains a need for improving the stacking of ejected sheets in ADF devices without adding special features to the output tray or modifying the geometry of the output tray.
SUMMARY
The present invention provides a sheet discharge roller assembly that can improve stacking of media sheets at the output area of an automatic document feeder without adding special features to the output area. In one embodiment, the sheet discharge roller assembly includes an upper cylindrical exit roller mounted on a rotatable drive shaft and a lower cylindrical pinch roller having a wheel attached to one end. The pinch roller has a length that is longer than the length of the exit roller and is moveable into contact with the exit roller so as to form a nip for gripping a print media to be discharged. The wheel has a diameter that is larger than that of the pinch roller and an outer circumferential edge composed of a plurality of protruding contact portions arranged in a radial pattern. The wheel is positioned so that the wheel can contact the media sheet being gripped and cause the sheet to deform temporarily, thereby making the sheet more rigid.
The objects and advantages of the present invention will become apparent from the detailed description when read in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view showing an exemplary automatic document feeder which incorporates a sheet discharge roller assembly according to an embodiment of the present invention.
FIG. 2 is an isometric view showing the main components of the sheet discharge roller assembly according to an embodiment of the present invention
FIG. 3 is an isometric view showing a lower pinch roller, which is part of the sheet discharge roller assembly shown in FIG. 2.
DETAILED DESCRIPTION
FIG. 1 shows an exemplary automatic document feeder (ADF) 10 which incorporates a sheet discharge roller assembly 16 according to an embodiment of the present invention. The ADF 10 includes a sheet supply tray 11 for holding a stack of media sheets (hereinafter, simply referred to as “media stack”), a pickup unit 12, a set of de-skew rollers 13, a plurality of transport rollers 14 and 15, a sheet discharge roller assembly 16, and an output tray 17. The ADF 10 includes a substantially U-shaped, main media path P1 for guiding the media sheet from the pickup unit 12 to the output tray 17. An optical window W and an image reader R, e.g. an optical scanner, are arranged along the media path P1 so that the image data on one side of the media sheet can be read through the optical window W by the image reader R. As such, the region above the optical window W defines a scanning region of the ADF 10. The pickup unit 12 includes a pick roller 12a operable to pull (i.e., “pick”) the uppermost sheet from the media stack and a feed roller 12b operable to advance the uppermost sheet toward the de-skew rollers 13. The de-skew rollers 13 are operable to perform skew correaction of the media sheet and to advance the same sheet along the main media path P1 toward the transport rollers 14. The transport rollers 14 are designed to advance the media sheet further downstream toward the scanning region where the optical window W is located. The transport rollers 15 are configured to advance the media sheet from the image reading position toward the sheet discharge roller assembly 16. The sheet discharge roller assembly 16 is configured to discharge the scanned media sheet to the output tray 17. The ADF 10 also includes a switch-back path P2 that extends from the sheet discharge roller assembly 16 to the de-skew rollers 13 so that the media sheet may be re-introduced into the main media path P1 for scanning on the opposite side. The ADF 10 is operable in a simplex mode, in which one side of a document is scanned, or a duplex mode, in which both sides of a document are scanned.
Referring to FIG. 2, the sheet discharge roller assembly 16 includes two pairs of rollers (21, 22) arranged along the width of the media path, each pair including an upper cylindrical exit roller 21 cooperating with a lower cylindrical pinch roller 22. The exit rollers 21 are fixedly mounted to a drive shaft 23, which is operatively connected to a media motor (not shown) such that the exit rollers 21 can be driven to rotate by a drive force from the media motor. The pinch rollers 22 are rotatably mounted to a housing 24 and are moveable relative to the exit rollers 21. One end of the pinch roller 22 is attached to a wheel 22a with scalloped circumferential edge. The pinch rollers 22 are arranged so that the ends without the wheels are facing one another, and the distance between the wheels 22a is greater than the combined lengths of the two exit rollers 21 plus the distance between the two exit rollers 21. As shown in FIG. 2, the scalloped circumferential edge of wheel 22a has a plurality of protruding contacting portions alternating with a series of small curves, which define the non-contacting portions. Although a scalloped edge design is shown, it should be understood that other circumferential edge designs are possible as long as there are a plurality of protruding contacting portions arranged in a radial pattern at a predetermined pitch. For example, the circumferential edge of wheel 22a may take the form of a serrated edge, i.e. an edge with a plurality of tips like the edge of a saw. The wheel 22a has a diameter that is larger than the diameter of the pinch roller 22. The length of the pinch roller 22 is longer than that of the exit roller 21. The pinch rollers 22 are spaced so that the wheels 22a can contact the media sheet near the side edges thereof.
FIG. 3 shows an unobstructed view of one of the lower pinch rollers 22 rotatably mounted to housing 24. The housing 24 is movable relative to the exit rollers 21 to cause the pinch rollers 22 to be in nipping contact with or out of contact with the exit rollers 21. As shown in FIG. 3, the housing 24 has slots 24s for receiving the axles 22b of each pinch roller 22. A substantially U-shaped, wire spring 25 is mounted to the housing 24 so as to be pivotable about axis X with the free ends of the spring in contact with and under the axles 22b of the pinch roller 22 as shown in FIG. 3. By this arrangement, the pinch roller 22 may be spring biased upward against the exit roller 21 via wire spring 25 to form a nip for nipping the media sheet. The wire spring provides the required nipping force while allowing the axles 22b of the pinch roller 22 to be moveable within the slots 24s in a direction substantially orthogonal to the axis of the axles 22 so as to accommodate various media thicknesses.
During the process of discharging a media sheet to the output tray, the pinch rollers 22 are biased against the corresponding exit rollers 21 so as to define a nip that grips the media sheet being discharged, and the pinch rollers 22 rotate in synchronism with the rotation of the exit rollers 21 to move the media sheet toward the output tray. The wheels 22a attached to pinch rollers 22 cause the nipped media sheet to be deformed temporarily, thereby making the sheet more rigid. This deformation results in less droop and drag of the media sheet as the sheet exits the ADF, thereby resulting in a more orderly media stacking. Furthermore, the scalloped edge design gently pushes the trailing edge of the exiting media sheet past the exit rollers 21, thereby preventing incomplete ejection and clinging of the media sheet at the output area of the ADF.
While particular embodiments of the present invention have been described, it will be understood by those skilled in the art that modifications and substitutions can be made without departing from the scope of the invention as set forth in the following claims.
Patent Application
20080265485
