Patent Application
20090154976
The present invention relates to image producing machines that include a paper transport system such as solid inkjet printing machines and electrostatographic image producing machines and, more particularly, to such a machine including a method and apparatus for enhanced edge hold-down for sheets being imaged.
One type of electrostatographic reproducing machine is a xerographic copier or printer. In a typical xerographic copier or printer, a photoreceptor surface, for example that of a drum, is generally arranged to move in an endless path through the various processing stations of the xerographic process. As in most xerographic machines, a light image of an original document is projected or scanned onto a uniformly charged surface of a photoreceptor to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged powdered developing material called toner to form a toner image corresponding to the latent image on the photoreceptor surface. When the photoreceptor surface is reusable, the toner image is then electrostatically transferred to a recording medium, such as a sheet of paper, and the surface of the photoreceptor is cleaned and prepared to be used once again for the reproduction of a copy of an original. The sheet of paper with the powdered toner thereon in imagewise configuration is separated from the photoreceptor and moved through a fusing apparatus including a heated fusing member where the toner image thereon is heated and permanently fixed or fused to the sheet of paper.
Given the complexity of Xerox's printing products, it is always advantageous to simplify, merge and/or remove as many of the required processing steps as possible. Ink jet products have the ability to generate an image directly onto a sheet of paper, thus removing the intermediate transfer step currently used in some piezo-electric ink jet systems. To accomplish direct-to-paper printing the paper has to be carefully and accurately registered and held down so that it does not come in contact with the print-heads. Current paper hold-down concepts include; “mechanical grippers”, “electrostatics”, “vacuum hold” and combinations of these systems and devices. Some of the limitations and challenges of the vacuum hold systems are media weight, porosity and pressure loses at the edges. Gripper systems can reliably hold sheet edges down, however these are complex, expensive devices and issues exist if different length media are to be transported. It would be desirable to resolve the vacuum hold-down issues so that media edges could be reliably held down without the use of edge gripper systems. This present disclosure will focus on the enhancement of the vacuum hold method; however, the concept described herein can be applied to electrostatic or other paper holding methods.
This present disclosure describes a technique to improve the “vacuum hold” concept by means of pre-curling the entire paper to be held. An alternate method consists of pre-curling the paper lead edge (LE) and trail edge (TE) only.
There's strong indication that by pre-curling the paper, to a radius that is equal or less than the radius of the vacuum cylinder [or belt surface], the amount of pressure required at the edges is drastically reduced. That is, by pre-shaping the paper to match the curvature of the vacuum cylinder [drum] or to the flatness of the vacuum belt surface, the hold system performance will improve without increasing the suction pressure. Additionally, a de-curling system will be used to remove the paper curl or flatten after printing. Similarly, this concept can be implemented with other paper holding approaches such as with electrostatic systems.
In solid inkjet color image printing, multi-colored images are formed on an intermediate member, such as a drum. Using different colored crayon-like inks that are solid at room temperature but are molten in the printhead, an image-wise pattern is applied to the intermediate member using moving or stationary full width printheads. Special ink formulations have been developed that allow the ink to melt at very precise temperatures, and that solidify very quickly when their temperature drops below such melting temperature. In a solid inkjet printer, the image-wise pattern of solid ink on the intermediate member is then transferred and fused or transfused onto a copy sheet. The fusing or transfusing smoothens out the sheet surface and strengthens the bond between the ink and the sheet. An alternative to the above approach is to form the image directly onto the media, without the use of an intermediate member. This requires the media to be held tightly against an intermediate member so that no portion of the media contacts the printheads during printing. This is difficult to do, especially at the edges of the media. Yet another alternative is to print directly onto the media using UV curable inks. After printing the sheet is then transported through a UV curing station to cure or harden the ink into the sheet.
In accordance with the present disclosure, there has been provided a method of enhancing cut sheet edge hold-down on an imaging transport surface, the method comprising: (a) moving a cut sheet towards the sheet the imaging transport surface; (b) inducing a desired curl on the lead edge of the cut sheet before the cut sheet enters the imaging transport surface, inducing a desired curl comprises inducing into said cut sheet a curl tending into the surface of the imaging transport surface. An apparatus for enhancing cut sheet edge hold-down on an imaging transport surface, comprising: (a) means for moving a cut sheet towards the imaging transport surface; and (b) a sheet curling device positioned upstream of the imaging transport surface relative to movement of said cut sheet for inducing a desired pre-curl in said cut sheet before said cut sheet enters the imaging transport surface.
As illustrated in
In the examples provided, the image producing machine 200 is a multicolor image producing machine having an ink delivery system which includes four sources holding four different colors CYMK (cyan, yellow, magenta, black) of inks. The ink delivery system is suitable for supplying the ink in liquid form to a plurality of printheads 120, 130, 140, and 150 which eject the ink onto the sheet held against the receiving surface 14 when forming an image.
The image producing machine 200 also includes a substrate supply and handling system. The substrate supply and handling system can include a plurality of substrate supply source 50 of which supply source 50, for example, is a high capacity paper supply or feeder for storing and supplying image receiving substrates in the form of cut sheets. The substrate supply and handling system can include a fusing or fixing device 180. Further, the print media sources may be loaded with print media of different types. Each document feeder tray may include print media having different attributes such as roughness, coats, weights and the like.
The image producing machine 200 also includes an ink delivery system 100 (not shown) that has a source of at least one color ink.
Operation and control of the various subsystems, components and functions of the image producing machine 200 are performed with the aid of a controller 80. The controller 80 can be a self-contained, dedicated computer having a central processor unit (CPU), electronic storage, and a display or user interface (UI). The controller 80 can include sensor input and control means as well as a pixel placement and control means. The CPU reads, captures, prepares and manages the image data flow between image input sources such as the scanning system, or an online or a work station connection, and the printheads. As such, the controller 80 is the main multi-tasking processor for operating and controlling machine subsystems and functions, including the operation of the ink delivery system. Decisions about when to fill each printhead would be made by the controller 80 based on input from ink level sensors located in the individual printhead reservoirs.
In operation, image data for an image to be produced is sent to the controller 80 from, for example, the scanning system or via a work station network connection for processing and output to the printheads. Additionally, the controller 80 determines and/or accepts related subsystem and component controls, for example from operator inputs via the user interface 86, and accordingly executes such controls. As a result, appropriate color inks are delivered to the printheads 30. The cut sheet 48 (not labeled) is removed from imaging transport 110 by stripper 160. Then cut sheet 48 (not labeled) moves to UV cure station 180.
Now focusing on aspects of the present disclosure, cut sheet 48 enters sheet curling device 220 which includes means such as rollers 222, 224 for inducing into the cut sheet 48 the curl C3 tending as shown by the arrow in
Preferably, the curl C3 and C4 has a radius that is equal or less than the radius of the vacuum cylinder [or belt surface]. Applicants have found that in case of a vacuum cylinder that the amount of pressure required at the edges is drastically reduced. That is, by pre-shaping the paper to match the curvature of the vacuum cylinder [drum] or to the flatness of the vacuum belt surface, the hold system performance will improve without increasing the suction pressure.
A post fusing nip de-curling device 104 may be provided for selectively removing any detected undesirable curl from the sheet as shown in
The above descriptions have focused on a drum based architecture, however a similar approach could also be employed when marking directly onto sheets being transported using a relatively flat belt system as shown in
It should also be noted that amount of curl induced onto the sheet lead and/or trail edges can be controlled by measuring the curl on the sheet using optical sensors or other means.
The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
