Media hold-down for printing system

A media hold down apparatus including a media transport including a transport surface having a plurality of vacuum openings formed therein in fluid communication with a vacuum source. The media transport is adapted to move substrate media in a process direction past a print zone. The transport surface includes a first recess extending in a cross-process direction along a portion of a width of a first sheet of substrate media transport. The recess is disposed on the media transport such that the recess lies beneath one of a leading or trailing edge portion of the first sheet of substrate media. The recess is in communication with the vacuum source, wherein the vacuum urges the one of a leading or trailing edge portion toward the recess on to the transport surface.

TECHNICAL FIELD

This disclosure relates to an apparatus for securing a sheet of substrate media during transport, and more particularly to an apparatus and system for securely holding a sheet including the leading and trailing edges during transport through a printing system.

BACKGROUND

Printing on sheets of substrate media by direct marking is a rapidly expanding marking technology due to low run-costs and overall simplicity. Direct marking printing includes printing systems using inkjet technology where one or more print heads are located proximate to the sheet surface. As resolutions improve, many believe that direct marking will make inroads relative to markets where xerographic systems currently dominate. Three challenges with direct to paper marking systems include; achieving good marking quality of the media, holding the media away from the print-heads to prevent burnishing or clogging of the print head nozzles, and achieving sufficiently high resolution with a single pass at low costs.

In such systems it is important to consistently hold the sheets flat as they pass by the print heads. If the portion of the sheet onto which an image is to be printed is not flat, the image quality will suffer. Moreover, if the edges or any part of the sheet project upwardly, they can engage the print heads causing damage. In order to hold the sheet flat, media vacuum hold-down drums or plates have been used. Such drums/plates typically enable good marking quality and enable multi-pass printing which requires fewer print heads and saves cost.

However, a drum/plate increases the challenge of holding the media away from the print heads with upcurled sheet leading and trailing edges becoming especially challenging. As shown inFIG. 1, in prior art systems with vacuum drum4having a smooth drum surface6, the bending moment exerted by the vacuum on the sheet8becomes very small as you get closer to the edge of the media10(and eventually becomes zero). This makes it very difficult to hold the edge tightly to the drum and a gap12can exist.

Accordingly, it would be desirable to provide a media hold-down apparatus and system which improves hold down performance of the leading and trailing edges of substrate media.

SUMMARY

According to aspects described herein, there is disclosed a media hold down apparatus including a media transport including a transport surface having a plurality of vacuum openings formed therein in fluid communication with a vacuum source. The media transport is adapted to move substrate media in a process direction past a print zone. The transport surface includes a first recess extending in a cross-process direction along a portion of a width of a first sheet of substrate media transport. The recess is disposed on the media transport such that the recess lies beneath a leading edge portion of the first sheet of substrate media. The recess is in communication with the vacuum source, wherein the vacuum urges the leading edge toward the recess on to the transport surface.

According to other aspects described herein, there is provided a direct marking system including a media transport including a transport surface having a plurality of openings formed therein in fluid communication with a vacuum source to constrain media through the application of a vacuum force. The outer surface includes a first recess extending in a cross-process direction along a portion of a width of the media transport. The first recess is disposed on the media transport such that it lies beneath a leading edge portion of the media, the first recess being in communication with the vacuum source, wherein the leading edge is pulled down by the vacuum toward the first recess on to the transport surface. An image marking system marks the media when passing through a print zone, wherein the media transport moves the media in a process direction past the image marking system.

According to still other aspects described herein, there is provided a method of holding and transporting a sheet of media including delivering a sheet of substrate media having a leading edge to a media transport. The media transport includes a transport surface having a plurality of vacuum openings formed therein in fluid communication with a vacuum source. The media transport is adapted to move substrate media in a process direction past a print zone. The outer surface including a first recess extending in a cross-process direction along a portion of a width of a first sheet of substrate media transport. The recess is in operative communication with the vacuum source. The method further including positioning the leading end of the media at least partially over the first recess; applying a vacuum through the transport surface to draw the sheet of media toward the transport surface; and applying a vacuum through the recess to draw the leading edge toward the transport surface.

DETAILED DESCRIPTION

Describing now in further detail these exemplary embodiments with reference to the Figures, as described above the media hold down is typically used in a select location or locations of the paper path or paths of various conventional media handling assemblies. Thus, only a portion of an exemplary media handling assembly path is illustrated herein.

As used herein, a “printer,” “printing assembly” or “printing system” refers to one or more devices used to generate “printouts” or a print outputting function, which refers to the reproduction of information on “substrate media” for any purpose. A “printer,” “printing assembly” or “printing system” as used herein encompasses any apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, etc. which performs a print outputting function.

As used herein, “substrate media” refers to, for example, paper, transparencies, parchment, film, fabric, plastic, photo-finishing papers or other coated or non-coated substrates on which information can be reproduced, preferably in the form of a sheet or web. While specific reference herein is made to a sheet or paper, it should be understood that any substrate media in the form of a sheet amounts to a reasonable equivalent thereto. Also, the “leading edge” of a substrate media refers to an edge of the sheet that is furthest downstream in the process direction. The “trail edge” or trailing edge of the substrate media refers to an edge of the sheet that is furthest upstream in the process direction, and the lateral edge or edges refer to one or more of the opposed side edges of the sheet, extending substantially in the process direction.

As used herein, the terms “process” and “process direction” refer to a process of moving, transporting and/or handling a substrate media. The process direction is a flow path (also described as a transport path) the substrate media moves in during the process. A “cross-process direction” is perpendicular to the process direction and generally extends parallel to the width of the substrate media.

As used herein, the term “media transport” refers to an apparatus for transporting a sheet of media in a printing system. A media transport can be in the form of a rotating drum or translating sled. The media transport may have a transport surface upon which the media is supported.

As used herein, the term “image marking system” refers to an apparatus for imparting an image on to substrate media.

As used herein, the term “media hold-down” refers to a device for securing a sheet of substrate media to a transport surface of the media transport.

As used herein, the term “recess” refers to a depression, slot, indentation, gap, or the like which forms an interruption in a surface.

With reference toFIG. 2, a printing system20including a media transport22and image marking system24is shown. The media transport22moves a sheet of substrate media26in a process direction past a print zone25of the image marking system24. The image marking system24may include one or more print heads28which permit for direct marking of the media26to form an image thereon. The media transport22may receive the media from a pair of upstream transfer nips30wherein the media26is captured by the media transport22as it is released from the transfer nips.

The media transport22includes a media hold-down32for securing a sheet of media26to a transport surface34of the media transport. The media hold-down32applies a hold-down force that is selectively engagable to allow the media26to be selectively secured and released from the media transport. The media hold-down may include a vacuum system36wherein the transport surface34includes a plurality of openings38(FIG. 5) formed therein which are in fluid communication with a vacuum source40. In one embodiment, the media transport may be in the form of a vacuum drum42having an inner plenum44region operably connected to the vacuum source40. The vacuum plenum44communicates with the surface openings38may be arranged such that various sections of transport surface34may be selectively and independently subjected to a vacuum. It is within the contemplation of the present invention that the media hold-down32may include other known manners of securing a sheet to a transport surface, including, for example, electrostatic hold-down force or a combination of vacuum and electrostatic force.

The vacuum flow may be regulated by a controller46which generates a signal to turn the vacuum on and off at predetermined times. For example, when the media26is first received by the media transport22, the vacuum may be applied so that the media is drawn to the transport surface thereby allowing rotary motion of the vacuum drum to transport the media sheet past the print heads28. After the media has been marked with an image, the vacuum may be removed so that the media can be removed from the media transport and travel further down the transport path in the process direction P. A positive pressure may be applied to the media to help separate it from the transport surface. The controller46may include one or more vacuum control valves and a control circuit for operating the valves.

With reference toFIGS. 3,4and5when a hold-down force is applied to the media26, the media tends to conform to the transport surface34. It is desirable that the entire sheet of media lies flat against the transport surface both to avoid media engagement with the print heads28, and to keep a uniform distance between the media and the print head which enables a uniformly high image quality across the media. However, the media edges, such as the leading50and trailing edges52, may be more difficult to hold down. This is especially true if the edges have an upcurl. In order to assist in holding the edges flat against the transport surface34, the transport surface may include a first recess60extending along a cross-process direction CP along with the width of the vacuum drum42. The first recess60may be in the form of a slot having a base62joined by upwardly extending side walls64which engage the top portion of the transport surface. The engagement of the wall and the top portion of the transport surface form a recess edge65. In one embodiment, shown inFIG. 3, the oppose side walls may engage the top portion of the transport surface at generally a right angle, such that the recess60has a generally rectangular cross-sectional profile. Another embodiment show inFIG. 4, it is contemplated that the side walls64may form an obtuse angle with the transport surface with the wall extend in a more gradual sloping manner toward the outer transport surface. The first recess may have a generally rectangular in shape; however, it is also contemplated that the recess could be formed in different shapes. These recesses move the bending point of the media farther away from the leading edge or trailing edge of the sheet, which enables the vacuum force to more effectively deflect the leading or trailing edge of the sheet toward the transport surface34.

The first recess60may be located on the media transport at a location which corresponds to the media leading edge50. The recess base62may include a plurality of vacuum openings38such that vacuum may be generated over the recess region of the media transport. The first recess60may have a length extending in the cross-process direction in an amount equal or greater than the width of the media. Accordingly, the recess60extends over the entire width of sheet of media.

With reference toFIG. 4, the media transport22may include a second recess70spaced a distance from the first recess60. The second recess70is preferably formed in a manner similar to the first recess60. The distance between the first and second recess traveling along the transport surface is dependent on the length of the sheet of media which the media transport is intended to secure and transport. Accordingly, the second recess70may be disposed at a location on the media transport surface such that it is aligned with the sheet of media trailing edge52.

With reference toFIGS. 3 and 3A, when a sheet of media26is delivered to the media transport, the leading edge50overhangs the first recess60. In situations where the leading edge50has an upward curl, this leading edge will be spaced a distance X above the base of the recess. When a vacuum is applied, the overhanging cantilevered sheet edge portion76having a length Y creates a moment arm which is rotated about the recess edge65by the vacuum force F. The recess edge acts like a fulcrum or bending point with the media cantilevered portion providing the moment arm. The cantilevered edge portion will keep moving downward unimpeded by the transport surface since the media deflects into the recess. In addition, as the media portion75is urged down to the transport surface34, the length Y of the moment arm remains substantially the same. Therefore, the torque exited by the vacuum force does not diminish as the media edge portion76moves to the transport surface34. This allows for a significant torque to urge the leading edge downward toward flat against the transport surface,FIG. 4. The mechanism acting on the sheet would be the same for the second recess70which is positioned adjacent to the media trailing edge52.

In one embodiment, the recess may be positioned so that the end of the media would fall within the recess. The recess may be relatively shallow in the range of 50-200 microns in depth and between 10 and 50 millimeters in width in the process direction. The size of the recess may depend on the weight of the media with the larger recesses of 200 microns or greater being used with heavier weight media. The recess depth would minimize image quality problems, but permit a moment to be created to assist in deflecting leading edge of the media down toward the transport surface. Since the recess is relatively shallow and close to the end of the sheet, image defects due to changes and print head gap are not significant. In another embodiment, the recess may be positioned such that the media would completely span the width of the recess and the very end of the media would lie on the transport surface.

In an alternative embodiment shown inFIG. 6, the first and second recesses,60and70respectively, may be located slightly back, approximately 2 to 10 mm, from the leading50and trailing52edges. Therefore, the distance between the first and second recesses is less than the length of the media26. This provides the benefit of increasing the bending moment since the recess edge65forming the bend point or fulcrum is disposed back further from the edge of the sheet. In this way, the width of the recesses60,70may be kept relatively small. In this embodiment, recess in the order of 50 to 75 microns deep may be desirable. The sheet deflection into the recess would near the sheet edges. This would help reduce any issues of compromised image quality.

With reference toFIGS. 1,5, and7, it is also contemplated that additional recesses80may be formed in the transport surface34, in order to accommodate sheets26having different lengths. The vacuum to the various recesses can be selectively turned on and off by the controller46(FIG. 1) such that only the recesses which are disposed adjacent to the leading and trailing edges of the substrate media are subjected to vacuum. Any recesses disposed beneath the media26that are not adjacent to the leading or trailing edges would have the vacuum turned off. This would help prevent distortions in the medial portions of the substrate media which could affect image quality. The controller46may be operably connected to a media length input82so that the controller may apply vacuum to the recess responsive to the media length. The media length input may be a sensor disposed in the travel path of the substrate media or it may be an input selected by an operator.

As shown inFIGS. 7 and 7A, multiple sets of recesses may be formed in the transport surface34in order to allow the media transport to carry a plurality of media sheets26at a time. For example,FIG. 7shows two sheets26being transported andFIG. 7Ashows three sheets being transported. It is also contemplated that a media transport could be configured with multiple sets of recesses to secure more than three sheets. Sheets26may be transported with a recess60and70being disposed adjacent the leading50and trailing52edges for each sheet. In order to permit multiple sheets of different lengths to be accommodated, additional recess80may be formed on the transport surface34. As set forth above, the recesses not located near the edge of given size media could optionally have their vacuum turned off by the controller46to minimize any deflection of the mid span of the sheets. With no vacuum in a “center span slot” and slot widths of an inch or less, the sheets spanning the slot will roughly follow the curvature of the drum.

In an alternative embodiment shown inFIGS. 8 and 9, the media transport may be in the form of a sled90having a generally planar transport surface92. The sled90may be translated back and forth in the process direction P. The sled carries one or more sheets26through the print zone25and under the print heads28for receiving an image. The sled90may be transported on a linear guide91in a manner known in the art. The transport surface92may include a first and second recess94and96generally aligned with the leading50and trailing52edges of the media. The recesses may be formed in a manner similar to the recesses described above in the drum embodiment. Additional recesses80may be formed therein in order to accommodate sheets at different lengths and/or multiple sheets. For example, the sled90ofFIG. 9is shown carrying 2 sheets26. The transport surface92may include a plurality of vacuum openings98which are in fluid communication with a vacuum source40. The sled90may include a generally hollow vacuum plenum93connected to the vacuum source40. The plenum93communicates with the surface vacuum openings98may be arranged such that various sections of transport surface34may be selectively and independently subjected to a vacuum. The controller46may selectively control the application of vacuum to various recesses96,94and80of the transport surface as desired. Accordingly, certain recesses of the transport surface may be subjected to vacuum while others may not.

With reference toFIGS. 1 and 5, operation of the media transport will now be described. The media transport may energize a set of transport rollers30which drive a sheet of media26in the process direction P and deliver the sheet to the media transport22. The media transport22includes a transport surface34having a plurality of vacuum openings38formed therein in fluid communication with a vacuum source40. The sheet of media26is positioned on the transport surface34such that the media leading edge50is at least partially disposed over the first recess60. Vacuum is applied through the transport surface to draw the sheet of media toward the transport surface. The media transport22moves the substrate media in the process direction past a print zone25. In the embodiment wherein the media transport is a drum42, the drum rotates the media past the print zone25. In the embodiment shown inFIGS. 8 and 9wherein the media transport is in the form of a sled90, the sled translates the media past the print zone25. After the image has been imparted on the media26, the media is released from the media transport surface34. The media may be released by terminating the vacuum and exposing the vacuum openings38to atmosphere. Alternatively, the controller46could cause a positive pressure to be applied to help separate the media26from the transport surface34. The media transport may keep cycling by repeatedly picking out sheets of media and securing the sheet to the transport surface, moving them past the print zone, and releasing the sheets in order to move media through the printing system20.