Patent Application
20130293653
The present disclosure relates to an apparatus for and method of transporting sheets of substrate media through a marking zone along an air bearing support rail.
Achieving high image quality in a printing assembly requires overcoming variants in static co-efficients and dynamic co-efficients of friction within a system. Controlling friction results in a precisely controlled speed, which is an important element of fine pixel placement. Also, pixel placement is a component of the media velocity as a marking element is placed on the sheet. Thus, it is desirable to control both the static and dynamic co-efficients of friction that are often associated with stick-slip, common to roller bearing systems.
Additionally, contemporary systems that exclusively use roller bearing elements for media carts are subject to wear and tear which further propagates miscalculations of velocity and/or position between the marking systems and the sheet to be marked. In this way, contemporary bearing surfaces and roller bearing assemblies make the repeatability of machine performance less consistent. Additionally, the wear and tear can increase the print head gap between print head surfaces and the substrate media sheet. When using inkjet technology, the downward spray of ink can fan out further than intended as a consequence of an increased print head gap, thus decreasing precision in the marking engine.
Additionally, contemporary roller bearing cart assemblies exhibit irregularities of positioning in a cross-process direction as well. Cart motion through a print zone is often accompanied by a cyclical back and forth motion across the marking zone resulting in nonlinear trajectory for the media cart and the sheet carrier thereon. Such a nonlinear trajectory can further diminish accuracy when attempting to mark the substrate media sheet.
Accordingly, it would be desirable to provide a media transport system and method for efficiently moving media through a print zone to permit high quality outputs and that overcomes other shortcomings of the prior art.
According to aspects described herein, there is disclosed an apparatus transporting a sheet of substrate media along a process path through a marking zone. The apparatus includes a marking zone, an air bearing support rail and a media cart. The marking zone for marking a sheet of substrate media. The air bearing support rail extending from a first location upstream of the marking zone to a second location downstream of the marking zone. The media cart for conveying the sheet along the process path. The media cart including a platen for holding the sheet thereon as the media cart translates through the marking zone. The media cart supported along the process path between the first and second locations by the air bearing support rail. The air bearing support rail including a gaseous layer providing a non-contact bearing support between an outer surface of the air bearing support rail and a non-contact support surface of the media cart.
Additionally, the air bearing support rail can include a porous support surface over which the non-contact support surface moves. The gaseous layer can be formed by a gas emitted through the porous support surface. The gas can substantially includes air passing through the porous support surface. The air bearing support rail can include a horizontal support surface and a vertical bearing wall. The vertical bearing wall can include the gaseous layer formed thereon. The vertical bearing wall can guide lateral movement of the media cart. The marking zone can include a printing assembly. The printing assembly can be moveable laterally across at least a portion of the process path. The printing assembly is an inkjet assembly which can mark the sheet with no more than a single lateral pass. The media cart can include a contact bearing element. The contact bearing element can support the media cart in bearing engagement with the process pass upstream of the first location. The support track can provide an upstream path portion of the process path for the media cart. The upstream path can extend from a pre-marking zone location upstream of the first location at least to the first location. The contact bearing element can be in direct engagement with the support track as the media cart moves along the upstream path. The contact bearing element can include a set of support wheels. The direct engagement of the contact bearing element can be a rolling engagement. The transition ramp can switch the media cart between using the contact bearing element and the non-contact support surface. The transition ramp can be disposed on the process path between the upstream path and the first location.
According to further aspects described herein, there is disclosed method of conveying sheets of substrate media through a marking zone. The method including loading a substrate media sheet onto a media cart. The media cart including a platen for holding the substrate media sheet. The method also including conveying the media cart with the substrate media sheet thereon along an air bearing support rail extending from a first location upstream of a marking zone to a second location downstream of the marking zone. The air bearing support rail including a gaseous layer providing a non-contact bearing support between an outer surface of the air bearing support rail and a non-contact support surface of the media cart. The method further including marking the substrate media sheet as it passes the marking zone.
Additionally, the air bearing support rail can include a porous support surface over which the non-contact support surface moves. The gaseous layer can be formed by a gas emitted through the porous support surface. Forcing air to pass through a porous support surface of the air bearing support rail for forming the gaseous layer. The non-contact support surface of the media cart can move over the porous support surface with the gaseous layer there between. Controlling lateral movement of the media cart using a vertical bearing wall. The vertical bearing wall can prevent movement of the media cart in a cross-process direction. The gaseous layer can be formed on the vertical bearing wall disposed between the vertical bearing wall and a non-contact lateral control surface of the cart. Moving a print assembly laterally across a portion of the process path in the marking zone. The printing assembly is an inkjet assembly marking the substrate media sheet with no more than a single lateral pass. Conveying the media cart along a process path downstream of the second location. The air bearing support rail can not extend downstream beyond the second location. A contact bearing support surface of the media cart can engage a support track as the media cart is conveyed downstream beyond the second location. The media cart can move up a transition ramp at the second location. The contact bearing support surface can directly engage the support track as the media cart is conveyed downstream of the second location. The contact bearing element can include a set of support wheels. The direct engagement of the contact bearing element can be a rolling engagement. Conveying the media cart along the process path from an upstream location to the first location. The air bearing support rail can not extend upstream beyond the first location. The contact bearing support surface of the media cart can engage the support track as the media cart is conveyed from the upstream location to the first location.
Describing now in further detail these exemplary embodiments with reference to the Figures. The disclosed technologies improve image quality for large format print jobs, while providing an efficient sheet handling system that can improve productivity. The apparatus and methods disclosed herein can be used in a select location or multiple locations of a marking device path that includes a media cart made to ride on a track. Thus, only a portion of an exemplary substrate media handling path is illustrated herein.
As used herein, “substrate media sheet”, “substrate media” or “sheet” refers to a substrate onto which an image can be imparted. Such substrates may include, paper, transparencies, parchment, film, fabric, plastic, photo-finishing papers, corrugated board, or other coated or non-coated substrate media upon which information or markings can be visualized and/or reproduced. 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 a process direction.
As used herein, “marking zone” refers to the location in a substrate media processing path in which the substrate media is altered by a “marking device.” Marking devices as used herein include a printer, a printing assembly or printing system. Such marking devices can use digital copying, bookmaking, folding, stamping, facsimile, multi-function machine, and similar technologies. Particularly those that perform a print outputting function for any purpose.
Particular marking devices include printers, printing assemblies or printing systems, which can use an “electrostatographic process” to generate printouts, which refers to forming an image on a substrate by using electrostatic charged patterns to record and reproduce information, a “xerographic process”, which refers to the use of a resinous powder on an electrically charged plate record and reproduce information, or other suitable processes for generating printouts, such as an ink jet process, a liquid ink process, a solid ink process, and the like. Also, a printing system can print and/or handle either monochrome or color image data.
As used herein, the terms “process” and “process direction” refer to a process of moving, transporting and/or handling a substrate media sheet. The process direction substantially coincides with a direction of a flow path P along which a portion of the media cart moves and/or which the image or substrate media is primarily moved within the media handling assembly. Such a flow path P is said to flow from upstream to downstream. Accordingly, cross-process, lateral and transverse directions refers to movements or directions perpendicular to the process direction and generally along a common planar extent thereof.
As used herein, “cart” or “media cart” refers to a media transport device translatable along a process path for conveying a substrate media sheet. Such a media transport device includes a frame holding a platen for directly supporting the substrate media sheet thereon. A cart or media cart as described herein can include a sled running on rails, a conveyance having wheels in rolling engagement with a track, other moveable carriage structure and/or any combination thereof.
An air bearing substrate media transport is disclosed which transports a sheet of substrate media along a process path through a marking zone with precision. The disclosed apparatus employs air bearings, referred to herein as “air bars,” to aid in the positioning and orientation of the substrate media sheet as it passes through a marking zone. By providing precision motion quality, a marking device, such as an inkjet printing system, can accurately lay down an image on the substrate media. The substrate media sheet is conveyed on a platen mounted on a media cart that moves along a track defining the process path. The media cart includes rolling bearing wheels that roll along bearing surfaces on portions of the track. Also, the media cart includes non-contact bearing surfaces that allow the cart to float across air bars on other portions of the track, particularly across the marking zone. The media cart transitions from the rolling bearing support to the non-contact bearing support by way of a transition ramp that makes the media cart descend, allowing the air bars to take-over support of the cart on a thin layer cushion of air. Once the media cart is supported by the air bars, it glides along in a virtually frictionless manner through the marking zone.
The process path 40 is formed by a set of tracks along which the media cart 80 is adapted to travel.
The air bearing support rails 42 (also referred to herein as “air bars”) provide non-contact bearing support surfaces over which the media cart 80 can glide across the marking zone 20. Unlike contact-roller bearings such as wheels that ride on a smooth low-friction rigid surface, air bars 42 utilize a thin film of pressurized air to provide an exceedingly low friction load-bearing interface between the track 40 and the media cart 80. A thin gaseous layer of air is formed over the air bars 42 over which non-contact bearing surfaces of the cart 80 can ride without touching the air bars 42 themselves. Being non-contact, air bars 42 avoid friction, wear, problems with particulates on the track and the need for lubricants. What is more, air bars 42 provide precision in positioning and are particularly suited for high-speed application. An example of air bearing technology is disclosed in U.S. Pat. No. 7,607,647 to Zhao et al., the disclosure of which is incorporated herein by reference.
The use of air bars 40 provides enhanced image quality by effectively overcoming the variance in static co-efficient and dynamic co-efficient of friction within the system. This reduced friction environment results in more precisely controlled speed and position of the transported substrate media sheet. Therefore this would provide improved pixel placement, particularly in an inkjet environment. Air bearing assemblies are particularly advantageous since both the static and dynamic coefficients of friction are equalized. This allows for the elimination of stick-slip that is generally associated with roller bearing systems. Particularly, by reducing static friction to virtually zero, it is possible to achieve higher resolution and repeatability. Also, with the elimination of contact bearing surfaces between moving elements, the reduction of wear and tear further eliminates the propagation of additional errors in marking accuracy. Further, by eliminating the contact surfaces, particularly in the marking zone, the system can see reduced maintenance costs and labor, considering no lubricants (or at least less lubricants) are needed for the system. Air bearings are also advantageous in that they are self-purging, with constant air exiting the surface, which blows fibers and contaminants from the process path. Also, the non-contact surface eliminates variations associated with surface finish or irregularities of a stick-slip system. Using a non-contact bearing surface averages out surface profiles and results in a straighter trajectory of motion. Also, the air bars 42 provide repeatability and accuracy of the print head gap as discussed further below.
As shown in
As the cart 80 approaches the marking zone 20, the carts rolling bearing wheels ride down a transition ramp 60 that causes the cart 80 and particularly the cart wheels to descend lower than the upper surface of the bearing track 50. As the cart 80 descends down the transition ramp 60, non-contact bearing surfaces 90 of the media cart 80 take over the bearing support of the cart 80. Thereafter, the cart 80 is conveyed along the air bars 42 while the wheels no longer engage a bearing surface. In this way, the media cart 80 glides along a gaseous layer of the air bars 42, providing a virtually frictionless motion as the cart 80 moves across the marking zone 20. In this way, the apparatus 100 exquisitely controls the velocity and position of the substrate media sheet 5.
In accordance with an aspect of the disclosed technologies, within the marking zone 20, an image is imparted to the substrate media sheet 5 by an inkjet printing system 30.
As the target substrate media 5 is carried by the media cart 80 in the marking zone, the velocity of the media cart 80 is tightly controlled. Nonetheless, the printing system, such as the inkjet assembly 30, must target the substrate media 5 as it passes. While the air bearings assist in positional precision of the target substrate media, a further aspect of the disclosed technologies applies the ink jet marking using a cross-process movement of the inkjet assembly 30. As the media cart passes through the marking zone 20, the inkjet heads of the inkjet assembly 30 are made to move across the substrate media sheet 5 as it passes. The inkjet assembly 30 thus moves in a cross-process direction CP, which extends laterally relative to the process direction P. In accordance with one aspect of the disclosed technology, the inkjet assembly 30 marks the substrate media sheet 5 with a single lateral pass in the cross-process direction CP. Providing a single pass architecture further minimizes variations in sheet registration which can occur trying to target the sheet again on a second or subsequent pass. Nonetheless, it should be understood that while an inkjet system is illustrated and described herein, a variety of devices for generating an image could be alternatively and/or additionally used. For example, xerographic, flexographic or lithographic image transfer systems could be employed.
The media cart 80 includes a pair of front rolling bearing wheels 84 and rear bearing wheels 86. The front and rear bearing wheels 84, 86 are intended to ride along the bearing track 50. It should be further noted that the front bearing wheels 84 are disposed further towards the opposed lateral edges of the track 40, while the rear rolling bearing wheels 86 are slightly inset, relative to the front bearing wheels 84. This offset design between the front and rear rolling bearing wheels 84, 86 enables the platen 82 to remain level horizontally, as the cart moves across each transition ramp 60 on opposed sides of the marking zone 20. As shown in
The transition ramp(s) 60 are used to move the media cart 80 from the bearing track 50 onto the air bars 42 and then from the air bars 42 back onto further bearing track 50 on the downstream side of the marking zone 20. Thus, the rolling bearing wheels 84, 86 carry the media cart 80 along the bearing track 50 from an upstream position 26 to a first pair of opposed transition ramps 60 (one ramp on each lateral side of the track, aligned with sections of bearing track). Initially while moving along the transition ramp (as shown in
Additionally,
Additionally, in order to maintain lateral position control, the media cart 80 includes lateral spring loaded wheels 94, 96 on the lower portion of the cart. Those lateral spring loaded wheels 94, 96 provide a generalized lateral control along the process path 40. While riding the segments of bearing track 50, the lateral spring loaded wheels 94, 96 can engage lateral side walls of the track, such as lateral wall 51 shown upstream and downstream of the marking zone 20 in
In accordance with aspects of the disclosed technologies, the media cart 80, the printing system 30 or other parts of the apparatus 100 can be operated by a controller (not shown). The controller may also control any number of functions and systems within the overall apparatus 100. The controller may include one or more processors and software capable of generating control signals. Through the coordinated control of the apparatus sub-elements, including the cart movement and the printing systems, the substrate media sheet 5 may be efficiently handled and marked. For example, the media cart 80 can be made to accelerate, decelerate or even stop at various locations along the process path. Similarly, the timing and speed of the printing system 30 can be controlled to maintain improved image quality.
It will be appreciated that variations of the above-disclosed and other features and functions, or alternative thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. In addition, the claims can encompass embodiments in hardware, software, or a combination thereof.
