Abstract:
A method of aligning the edge of an elongated printable media on the web handling assembly of a printer is disclosed. The method includes the steps of projecting an alignment marker onto at least a portion of the web handling assembly, passing the elongated printable media through the web handling assembly, and aligning the edge of the elongated printable media with the alignment marker such that the edge is substantially co-linear with the alignment marker. An apparatus for aligning an elongated printable media on the web handling assembly of a printer is also disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/227,083, filed Aug. 22, 2000, now abandoned, which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of large format printing, and more particularly to an apparatus and method for aligning an image receiving substrate material on the web handling assembly of a large format printer. 
     2. Technical Background 
     There are several systems commercially available today that employ a plurality of piezoelectric print heads to transfer ink to a large scale image receiving substrate or web material to produce graphic products with multicolored or enhanced graphic images for signs, large banners, billboards, and the like. The web material used in such systems is typically supplied in a roll and is typically constructed of vinyl, some other polymeric material, or specialty paper. Generally speaking a computer system is employed to format a selected graphic target image such that it can be reproduced in the desired enlarged size and location on the web material by the piezoelectric print heads as the web material is advanced through a plurality of rollers in the printer. A carriage housing the piezoelectric print heads is typically moved across the web material at a controlled rate of speed while ink is delivered from the heads to the web material. Generally speaking the ink is typically delivered during a number of passes across the web material so that the graphic image created on the web material resembles the target image entered in the computer as closely as possible. 
     Printing with such commercially available systems is extremely difficult and time consuming. Because such systems generally deliver only four colors of ink, preferably, cyan, magenta, yellow, and black, reproducing an acceptable likeness of the target image requires precise synchronization of the web advancement and ink delivery. Any misalignment of the web material, change in the advancement rate of the web material, clogging of the print heads, misfires of the ink jet nozzles, improper impact of the ink droplets on the web material, or other misstep in the process can result in poor color quality, improper shading, an effect commonly known in the art as “banding”, poor resolution, or other defect in the graphic image transferred to the web material. Moreover, because the graphic image transferred to the web material occupies such a large surface area, small mistakes in the process are magnified and are generally readily apparent to the naked eye. 
     An important aspect of large format printing is the alignment of the web material with respect to the print heads. If the web material, which is generally supplied in a roll having a diameter of up to approximately 16 inches, is not properly loaded into the printer, any initial misalignment, however small, will result in a significant shift in alignment of the web material as the web material approaches the end of the roll. This phenomena, known as “walking” will significantly impact printing quality, and if severe enough, can inhibit printing altogether. In most commercially available large format printers, loading of the web material is still a manual process and requires an operator to advance the web material several meters in a dry run to determine if the web material walks. Others have attempted to position reference marks on the web material rollers to facilitate proper alignment during loading, but this approach has had little success as the web material cores often cover the reference marks or the reference marks become inadvertently covered with ink so that they are no longer visible after a relatively short period of time. As a result, determining whether the web material is loaded square or straight in the printer has been a difficult task. 
     What is needed therefore, but currently unavailable in the art, is an improved large format printer incorporating an alignment apparatus and method for facilitating proper loading of web material onto the web handling assembly rollers of the printer. The apparatus and method should be easy to maintain, provide quick and accurate web material alignment, and facilitate proper incremental advancement of the web material during printing operations. Moreover, such a device should facilitate efficient loading and unloading of web material rolls and provide large format graphic images of higher resolution and clarity than other large format printers known in the art, while at the same time increasing print speeds. The alignment apparatus should also be inexpensive to manufacture and maintain and should be efficient in operation. It is to the provision of such an apparatus and method that the present invention is primarily directed. 
     SUMMARY OF THE INVENTION 
     Accordingly, one aspect of the present invention relates to a method of aligning the edge of an elongated printable media on the web handling assembly of a printer. The method includes the steps of projecting an alignment marker onto at least a portion of the web handling assembly, passing the elongated printable media through the web handling assembly, and aligning the edge of the elongated printable media with the alignment marker so that the edge is substantially co-linear with the alignment marker. 
     In another aspect of the present invention is directed to an elongated printable media alignment apparatus for aligning the elongated printable media on the web handling assembly of a printer. The apparatus includes a light source constructed and arranged to project a substantially linear alignment marker onto at least a portion of the web handling assembly, and an adjustable support structure for securing a light source to the printer such that the light source is sufficiently remote from the printer. 
     An additional aspect of the present invention relates to a method of aligning an edge of an elongated printable media on a printer web handling assembly incorporating a supply roller and take-up roller. The method includes the steps of loading a roll of elongated printable media onto the supply roller, projecting an alignment marker onto at least a portion of the web handling assembly, and moving the roll of elongated printable media toward the alignment marker to align the edge of the media with the alignment marker. The elongated printable media is extracted from the roll to pass the elongated printable media through the web handling assembly, and the edge of the elongated printable media is aligned with the alignment marker as the elongated printable media is brought into engagement with the take-up roller. Once the edge of the elongated printable media is aligned with the alignment marker, the elongated printable media is secured to the take-up roller. 
     The web material alignment apparatus and method of the present invention results in a number of advantages over other grand format printers and methods of printing large scale graphics commonly known in the art. For example, the web material alignment apparatus of the present invention significantly reduces web material misalignments during web material loading. In addition, the present invention obviates the need for complex and inaccurate web material and alignment procedures and facilitates the rapid loading and unloading of web material rolls. 
     In addition to the advantages set forth above, the web material alignment apparatus and method of the present invention significantly reduces the occurrence of web material wrinkling during web advancement and printing operations. Moreover, web material “walking” on the take-up roller during web advancement and printing is substantially prevented. As a result, far less time is spent repeating the same print job using the improved grand format printer of the present invention. 
     Additional features and advantages of the present invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described herein. 
    
    
     It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide further understanding of the invention, illustrate various embodiments in the invention, and together with the description serve to explain the principles and operation of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of an improved grand format printer in accordance with the present invention. 
     FIG. 2 is a rear perspective view of the improved grand format printer depicted in FIG.  1 . 
     FIG. 3 is a detailed perspective view of a preferred web material alignment assembly taken from the rear of the improved grand format printer of the present invention with certain portions of the improved grand format printer being shown using phantom lines for the sake of clarity. 
     FIG. 4 is an exploded perspective view of a preferred laser assembly in accordance with the present invention. 
     FIG. 5 is a side elevational view of the laser assembly depicted in FIG. 4 with the front shield removed. 
     FIG. 6 is a cut-away perspective view of the improved grand format printer depicted in FIG. 2 showing the operation of the web material alignment apparatus of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawing figures. Wherever possible, the same reference characters will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the improved grand format printer of the present invention is shown in FIG. 1, and is designated generally throughout by reference numeral  10 . 
     In accordance with the invention and as shown in FIG. 1, improved grand format printer  10  is preferably supported by a frame  12  preferably constructed of tubular metal and having welded connections. Broadly speaking, improved grand format printer  10  incorporates an ink delivery system (not shown), a data processing system (not shown), a heating zone  14  including a web material pre-heating platen  16  and an ink drying heater such as dry heater  18 , and a lighting system  20 . Improved grand format printer  10  may also preferably include a color management system (not shown), which among other things, minimizes banding and otherwise improves the resolution and quality of a graphic image transferred to a web material by the ink delivery system (not shown). In addition, and as depicted in FIG. 2, improved grand format printer  10  preferably includes a web handling assembly  22  and a web material alignment assembly  24 , which, among other things, facilitates accurate alignment of a web material  26  within improved grand format printer  10  during web loading. As used herein, “web handling assembly  22 ” includes, but is not limited to, a supply roller, redirect roller, a directional roller, and a take-up roller, among other things. Each of the above-mentioned systems and assemblies cooperate to permit the expedient and efficient printing of large format graphics onto web material  26  being fed through improved grand format printer  10 . 
     As depicted in FIG. 3, web material alignment assembly  24  preferably includes a laser line generator  28  which may be supported within a first mounting block  30 , removably attached to a support frame  32 . Although support frame  32  may be constructed from any rigid material and may take on any number of shapes, support frame  32  is preferably constructed from aluminum or some other light weight metal. In addition, support frame  32  preferably includes a substantially horizontal support arm  34  connected to a substantially upright support arm  36  at a joint. Although not critical to the operation of the present invention, horizontal support arm  34  is preferably joined with upright support arm  36  such that the support arms form a substantially right angle. The end of upright support arm  36  remote from horizontal support arm  34  is preferably supported within a pivot assembly  38 , which is fastened to a second mounting block  40 , which may be affixed to frame  12  or some other portion of improved grand format printer  10 . 
     A preferred laser assembly  42  in accordance with the present invention can be more clearly described with reference to the exploded perspective view depicted in FIG.  4 . In accordance with a preferred embodiment of the present invention, first mounting block  30  is preferably constructed to include a horizontal support arm aperture  44  for axially receiving horizontal support arm  34 , and a laser mounting bore  46  for axially receiving a laser line generator  28 . As preferably arranged, horizontal support arm  34  and laser line generator  28  are received within their respective aperture and mounting bore in directions substantially orthogonal to one another. First mounting block  30  may be secured to horizontal support arm  34  by reducing the diameter of horizontal support arm aperture  44  by, for example, tightening a screw (not shown) within horizontal support arm adjustment aperture  48  in order to prevent rotation of first mounting block  30  on horizontal support arm  34 . Likewise, the diameter of laser mounting bore  46  can be controlled by tightening or loosening a screw  49  within laser adjustment bore  50  to fixedly secure laser line generator  28  within first mounting block  30 . 
     In a preferred embodiment, first mounting block  30  is preferably fitted with a front shield  52  and a rear shield  54 , which, among other things, prevents an individual from moving closer than a distance of 20 cm from the laser aperture of laser line generator  28 , as required by governmental regulations. As shown in FIG. 4, each shield  52  and  54  may be secured along the sides of first mounting block  30  by aligning shield apertures  56  with laser adjustment bore  50  and mounting block bores  58  located on the side of first mounting block  30 . Screws  60  or other fasteners may then be passed through shield apertures  56  and threadably received within mounting block bores  58  to fixedly secure front shield  52  and rear shield  54  to the sides of mounting block  30 . As will be recognized by one of ordinary skill in the art, screw  49  received within laser adjustment bore  50  serves the purpose of controlling the diameter size of laser mounting bore  46 . 
     The characteristics and operation of laser assembly  42  may be more clearly described with reference to the portion of the laser assembly  42  depicted in FIG. 5 with front shield  52  removed. Laser line generator  28  is preferably a diode laser requiring low power such as Model No. ULL5-3.5G-635-90 Line Generator Diode Module, manufactured by World Star Technologies, Inc., Toronto, Ont., Canada. This particular laser line generator operates at a wavelength of approximately 635 nm, has a maximum peak radiant power of 3.5 mW, has a fan angle of 90°, a line thickness of less than 1 mm, has an operating voltage of 5 volts, and is classified as a Continuous Wave (CW) class II laser. In a preferred embodiment, laser line generator  28  is housed within an anodized aluminum casing which includes a rotatable adjustment bezel  62 . When necessary, adjustment bezel  62  may be rotated by a user to rotate laser line  64  along a central axis  66  passing axially through the center of laser line generator  28 . Laser line generator  28  is preferably powered by a conventional power source (not shown) along electric leads  68 . Although not shown in the drawing figures, laser line  64  continues beyond the bottom  70  of rear shield  54  to impinge upon the web material during web material alignment as will be described in greater detail below. Moreover, it will be understood by those skilled in the art that although a particular laser line generator  28  has been described in detail above, other types of laser line generators having various other operating characteristics may be used in accordance with the present invention. 
     In Operation 
     Generally speaking, web material alignment assembly  24  and laser line generator  28  are calibrated at the factory and laser alignment or reference marks are provided on frame  12  to facilitate assembly and mounting of the web material alignment assembly  24  in the field. With web material alignment assembly  24  properly mounted on frame  12 , laser line generator  28  is activated to emit a narrow beam of light which should impinge upon the frame markings indicating that the generated beam is in proper alignment. With the laser line generator  28  active, a supply roll  72  of web material  26  is positioned on a supply roller  74  of web handling assembly  22 . Supply roll  72  should be slidably received onto supply roller  74  until a supply roll web material edge  76  is aligned with the laser line projected on supply roller  74 . Generally speaking, the supply roll core  78  will extend beyond the web material on supply roll  72  and the laser line. Web material  26  is then extracted from supply roll  72  and passed under a redirect roller  80  over platens  16  and dry heater  18  (FIG.  1 ), passed back over a directional roller  82  located above the printing area and extended towards a take-up roller  84  located at the rear of improved grand format printer  10 . A take-up web material core  86  is typically pre-positioned on take-up roller  84  and web material  26  is preferably positioned on take-up web material core  86  such that web material edge  88  is aligned with laser line  90 . Likewise, web material edge  80  may also be aligned with laser line  90  at the location of take-up roller  84 . Web material  26  is then fastened to take-up web material core  86 , preferably with tape or some other suitable fastener to secure web material  26  to the take-up web material core  86 . Thus configured, an operator can easily and immediately visually inspect the loaded web handling assembly  22  to ensure that web material  26  is properly aligned for printing operations. Once properly aligned, printing may begin and web material  26  will be collected to form a take-up roll of web material which can be removed after printing operations are complete. 
     Web material  26  will generally be cut after one or more print runs to remove the printed web material collected on take-up roll  94  from take-up roller  84 . Generally speaking, a new take-up web material core  86  will then be placed on take-up roller  84  and the web material  26  will again be affixed to take-up web material core  86  as described above. Over time, however, web material alignment assembly  24  and/or laser line generator  28  may fall out of alignment. Generally speaking, this will be noted by the operator once printing operations begin by, among other things, the web material not tracking correctly, the web material walking on take-up roll  94 , or wrinkling of web material  26 . 
     At this point, printing operations should be terminated and web material alignment assembly  24  should be adjusted to align laser line  90  with the reference points on the frame. To effect this alignment, horizontal support arm  34  should first be checked to ensure that it is level with redirect roller  80 . Thereafter adjustment bezel  62  at the end of laser line generator  28  may be rotated to rotate laser line  90  along central axis  66  until laser line  90  is aligned with both reference points. If, however, laser line  90  appears convex or concave rather than linear, an additional adjustment can be made to web material alignment assembly  24 . Second mounting block  40  is provided with an adjustment mechanism that enables web material alignment assembly  24  to be pivoted laterally with respect to the path of travel of web material  26  during printing operations. In a preferred embodiment, second mounting block  40  incorporates an adjustment screw  96  that allows the web material alignment assembly  24  to be pivoted to the left or right as required to correct for either a convex or a concave laser line  90 . In a preferred embodiment, if the line appears concave, adjustment screw  96  should be loosened. If, however, the line appears convex, the adjustment screw  96  should be tightened so that the proper upright support arm  36  position can be achieved. Either one or both of these operations should be sufficient to bring web material alignment assembly  24  back into proper alignment. 
     If, however, the above-mentioned operations do not correct the problem, or if web material alignment assembly  24  has not been properly factory calibrated, laser line  90  may be calibrated for alignment by the following method. A level reading of redirect roller  80  is first taken and transferred to horizontal support arm  34  of web material alignment assembly  24  by making the necessary adjustments at the joint between horizontal support arm  34  and upright support arm  36 . With laser line generator  28  in the on position, adjustment bezel  62  of laser line generator  28  may then be turned to rotate laser line  90  so that laser line  90  appears to be visually straight and aligned to the operator. A sheet of non-vinyl printer paper having a minimum width of two (2) feet and being of a sufficient length should then be loaded from a take-up web material core  86  positioned on take-up roller  84 , under redirect roller  80 , over platens  16  and dry heater  18 , over directional roller  82  at the top of the printer, and back to the take-up web material core  86  such that the sheet overlaps on the core. While applying even pressure to both ends of the sheet, the overlapped edges of the sheet should be aligned so that the sheet edge will be square in the printer. While continuing to apply pressure to the sheet, the sheet may be taped, paper to paper, at the core in order to make a loop. First mounting block  30  may then be moved laterally along horizontal support arm  34  and adjustment bezel  62  may be rotated with respect to laser line generator  28  so that laser line  90  is as close as possible to parallel with the edge of the sheet. If laser line  90  appears concave or convex, adjustment screw  96  may be loosened or tightened, respectively, to adjust upright support arm  36  so that laser line  90  becomes straight. If laser line  90  is to one side of the sheet edge at redirect roller  80  and on the other side of the sheet edge at take-up roller  84 , then adjustment bezel  62  should be rotated to rotate laser line  90  into alignment with the edge. Thereafter, the paper can be removed from the printer and new reference marks can be positioned where laser line  90  impinges on the horizontal material rack brace  98  and the frame member  99  (FIG. 2) below dry heater  18 . Following either or both of these procedures should correct any web material  26  alignment problems and permit proper alignment for continued printing operations. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. For example, in a preferred embodiment, web material  26  edge  88  will be aligned with laser line  90  at each of the supply roller  74 , redirect roller  80 , directional roller  82 , and take-up roller  84  during the web material  26  alignment process as discussed above. Thus, it is intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents.