Patent Publication Number: US-6666602-B2

Title: Method and apparatus for controlling print media shape during media transport

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This is a continuation of copending application Ser. No. 09/584,022 filed on May 30, 2000, which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to print media transport systems and, more specifically, to a method and apparatus for transporting a sheet of print media through a hard copy apparatus transport path with limited surface contact to protect the printing or printed surface. 
     2. Description of Related Art 
     Many computer-controlled hard copy printing apparatus are commercially available. Some types are compatible with specially coated media; for example, ink-jet printers use special media to print photographic quality reproductions from digitized photographs. [The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the  Hewlett-Packard Journal,  Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43 No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in  Output Hardcopy [sic] Devices,  chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988). For convenience in describing the art and the present invention, all types of hard copy apparatus are sometimes hereinafter referred to as “printers;” all types, sizes, and compositions of print media are also referred to as “paper,” all compositions of colorants are sometimes referred to as “ink;” and all embodiments of an ink-jet writing instrument are simply referred to as a “pen;” no limitation on the scope of the invention is intended nor should any be implied. 
     In many printers, the input paper path—that is, the automated, paper-transport path between the input tray where the user stacks sheets of preferred paper for the next printing job and the printing station of the apparatus—is configured to be curvilinear in order to reduce the overall printer footprint. U.S. Pat. No. 5,481,408 (assigned to the common assignee herein and incorporated herein by reference) filed by Giles et al. on Apr. 30, 1993 for a DUAL FEED PAPER PATH FOR INK-JET PRINTER, FIG. 7, demonstrates such a typical system as would be found in a commercial DeskJet™ product by Hewlett-Packard Company. However, contact with stationary printer mechanisms such as guide surfaces in the transport path can damage coatings on the paper printing surface, thus affecting the quality of the printed image. Maintaining a substantially constant tension in a moving sheet of paper presents many problems and can require a complex drive system; see e.g., U.S. Pat. No. 5,495,276 filed on Apr. 18, 1994 by Mul et al. (assigned to the common assignee herein) for a UNIFORM MEDIA TENSIONING OF PRINT MEDIA DURING TRANSPORT IN LASER PRINTER. 
     A common solution in a curvilinear input paper path is to underdrive an upstream set of transport rollers and overdrive a downstream set of transport rollers to relieve the tension during the curved path segment with the sheet moving between guide frames. This type of subsystem adds mechanical and electrical complexity and increases cost of manufacture as separate motors and controls are required to appropriately bend or buckle the media to avoid printing surface contact with a guide frame. 
     Therefore, there is a need for improved methods and apparatus for moving special media through an input paper path between stationary guide frame members to avoid a friction producing contact between the printing surface of the media and the frame. 
     SUMMARY OF THE INVENTION 
     In its basic aspects, the present invention provides a print media transport device including: a curved frame defining a media path therein; mounted with respect to the path, a pair of upstream rollers and a pair of downstream rollers, the upstream pair having one driven roller; a flexible coupling between the one driven roller and a pulley roller of the downstream pair; and a selectively positionable mechanism for changing tension of the flexible coupling such that predetermined shaping and positioning of media is maintained in the path. 
     In another basic aspect, the present invention provides a method for guiding print media, having a coated printing surface and a non-printing reverse surface, through a curvilinear path without contacting the coated printing surface on stationary mechanisms. The method includes the steps of: receiving a leading edge of a sheet of the media in a nip between an actively driven roller of a first pair of media drive rollers at the ingress of the curvilinear path such that the reverse surface is guided along a curved surface defining the path; receiving the leading edge of the sheet in a nip between a second pair of media drive rollers at the egress of the curvilinear path; and upon receiving the leading edge in the nip between the second pair of media drive rollers, changing the tension of a drive belt to a pulley wheel coupled to the driven roller to underdrive the second pair of media drive rollers such that the sheet is buckled in order to pass through the path without contact of the coated printing surface with any upper curved surface defining the path. 
     In another basic aspect, the present invention provides a printer having a printing zone therein, including: a supply of sheets of print media; an ink-jet writing instrument mounted for depositing ink on a sheet in the printing zone; and a print media transport device for sequentially delivering picked sheets to the printing zone, the device including a first curved frame member and a second curved frame member defining a curvilinear print media path therebetween, a first set of media drive rollers having a first drive roller and a first pinch roller mounted upstream of the print media path, a second set of media drive rollers having a second drive roller and a second pinch roller mounted downstream of the print media path, a motor coupled one drive roller, a flexible coupling between the first drive roller and the second drive roller, and a selectively positionable mechanism for changing tension of the flexible coupling such that a predetermined buckling of a segment of the print media in the path between the first curved frame member and second curved frame member is maintained wherein there is no contact between a surface of the media to be printed and a surface of either curved frame member. 
     Some of the advantages of the present invention are: 
     it simplifies input paper path tension control; 
     it simplifies the electronic control requirements; 
     it reduces the number of drive motors required for paper tension control; 
     it reduces manufacturing complexity and costs; and 
     it is adaptable for use with a duplex path media paper source. 
     The foregoing summary and list of advantages is not intended by the inventor to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 (PRIOR ART) is a schematic illustration an ink-jet hard copy apparatus demonstrating a conventional, curvilinear transport path. 
     FIG. 2 is a schematic illustration of the present invention in elevation view. 
     FIG. 3 is a schematic illustration of the present invention as shown in FIG. 2 in perspective view. 
     FIG. 4 is a schematic illustration (elevation view) of the present invention as shown in FIGS. 2 and 3 with a tension governor in a toted position. 
     FIG. 5 is a schematic illustration (perspective view) of the present invention as shown in FIG. 4 of the tension governor in a translated position. 
     FIG. 6 is a perspective view of the present invention as illustrated in FIGS. 1 and 2 and depicting details of an alternate embodiment of the tension governor. 
    
    
     The drawings referred to in this specification should be understood as not being drawn to scale except if specifically annotated. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is made now in detail to a specific embodiment of the present invention, which illustrates the best mode presently contemplated by the inventor for practicing the invention. Alternative embodiments are also briefly described as applicable. 
     FIG. 1 (PRIOR ART) is a schematic depiction of an ink-jet printer apparatus  10 . The elements of the apparatus  10  typify an ink-jet printer with a curvilinear input paper path in which the present invention can be employed. Mounted on a rail  20 , a scanning ink-jet pen  12  is provided with a printhead  16  having drop generators including nozzles for ejecting ink droplets onto an adjacently positioned print medium, e.g., a sheet “S” of paper from an input tray stack  42  transported through a printing zone  14 . A pick roller  44  selects the top sheet “S” of the stack  42 . The pick roller  44  transports the sheet “S” until its leading edge is received in a nip between a pinch roller  46  and drive roller  30  of input transport mechanism  28 . The leading edge is directed through the nip and bent upwardly into a guide plate  32  wrapped about a segment of UV outer surface of the drive roller  30  where the sheet “S” is curved around to deliver the printing surface to the printing zone  14  adjacent the printhead  16 . In general, the drive roller  30  is driven by a stepper motor (not shown) that moves the sheet “S” in precise steps through the printing zone  14  such that the scanning pen  12  can print swaths of ink between steps when the sheet is stationary under the printhead  16 . Note that printing surface  48  of the sheet “S” would likely be buckled and have regions in contact with the surface of the guide frame  50  and the inner surface of the guide plate  32 . If special, coated paper is being used, surface  48  would likely be abraded and damaged, affecting final print quality. 
     FIGS. 2 and 3 depict an input paper path transport mechanism  200  in accordance with the present invention. It is assumed that a known manner pick mechanism is used in conjunction with a stack of paper in an input tray to select a sheet  201  and that the sheet is delivered along the paper path (represented by arrows  203 ) to the transport mechanism  200  in a manner that will not abrade the paper printing surface  201 ′ on which the ink drops will be deposited. The function of paper path drive elements of the transport mechanism  200  will be to ensure that the paper printing surface  201 ′ does not come into contact with a print media upper guide  205  (compare FIG. 1, guide  32 ) during the transport of the sheet  201  through the paper path  203  to a downstream printing zone (e.g., FIG. 1,  14 ). The upper guide  205  has a generally concave surface  205 ′ adjacent the paper path  203 . A print media lower guide  207  is positioned adjacently to the upper guide  205 . The lower guide  207  has a generally convex surface  207 ′ adjacent the paper path  203 . 
     Generally, the paper path drive elements consist of two pair of rollers utilizing a selectively positionable, flexible coupling, or link, such that only one motor-controlled driven roller is required. More specifically, a first drive roller  210  is paired with a first pinch roller  211  at the upstream extremity of the paper path  203  segment located between the upper and lower guides  205 ,  207 ; in other words, appropriately mounted to have roller surface periphery contact within the printer where the sheet  201  enters that path segment. A second drive roller  220  (or “pulley”) is paired with a second pinch roller  221  at the downstream extremity of the paper path  203  segment located between the upper and lower guides  205 ,  207 ; in other words, mounted in peripheral roller surface contact within the printer where the sheet  201  exits that path segment. It will be recognized by those skilled in the art that print media path directions are relative to a specific printer implementation; for the purpose of describing the present invention, the term “upstream” shall mean toward the paper supply and “downstream” shall mean toward the printing zone. No limitation on the scope of the invention is intended nor should any be implied. 
     The two drive rollers  210 ,  220  are coupled with a flexible link  223 —such as a belt, chain, or the like as would be known in the art—such that driving one drive roller with a motor  225  will automatically drive both. In this embodiment the motor  225  is connected to turn the upstream drive roller  210  clockwise. The downstream drive roller  220  is then a pulley wheel. The flexible link  223  is routed through a tension governor  227  device whereby the tension in the link can be selectively changed. The flexible link  223  is provided with extra length beyond that needed merely to couple the upstream drive roller  210  to the pulley-type drive roller  220 ; the extra length will provide the ability to vary the tension in the link between the two drive rollers  210 ,  220 . The link tension governor  227  has a moving tension governor carriage  229  suitably associated in a known manner to the lower guide  207 . One embodiment of link tension governor  227  has two tension rollers: upper tension roller  230  and lower tension roller  231 . While a linear motion carriage  229  is demonstrated, it will be recognized by those skilled in the art that a rotary motion or cammed motion implementation can be employed. The carriage  229  is connected  233  in a known mechanical or electro-mechanical manner to a device  235  for selectively positioning the carriage between a media “standard feed” position as shown in FIGS. 2 and 3 and a media “overfeed” position as illustrated in FIGS. 4 and 5. For example, a solenoid device  235  can be employed to select one or the other position. One or both tension rollers  230 ,  231  are spring-loaded so that as the carriage shifts between the two positions the link  223  will not slip on the driver rollers  210 ,  220 . 
     An alternative embodiment for a tension governor  227 ′ is shown in FIG.  6 . The shown position of a guide block  600  used to shift the link  223 —in this illustration, an endless loop belt—is substantially identical to that as illustrated in FIGS. 2 and 3. The flexible link  223  passes through an aperture  601  in the guide block  600 . A link tension bar  603  bridges the aperture  601 . A pair of spring-loaded mounts  605 ,  606  hold the tension bar  603  in a pair of grooves  607 ,  608  in the side faces of the guide block  600 . So mounted, the outer surface of the bar  603  is in contact with one outer surface of the belt loop as it passes through the aperture  601  while the opposite surface of the belt loop is guided across an opposing inner surface of the guide block  600  within the aperture. The link  223  is thus biased between the bar  603  and the guide block  600 . As the solenoid  235  as shown in FIGS. 2-5 shifts the guide block  600  from the first operative position in FIGS. 2,  3  and  6  to the second operative position as shown in FIGS. 4 and 5, the tension bar  603 , as biased by the spring-loaded mounts  605 ,  606 , maintains a force (determined by the spring constant) against the belt loop outer surface preventing any slippage of the link  223  between the belt drive rollers  210 ,  220  while shifting the added length of the link. FIG. 6 also demonstrates a preferred arrangement of the assemblies for print media  201  drive rollers  210 ,  220  and respective pinch rollers  211 ,  221 . 
     In operation, during the feed of a next sheet from an input stack (see e.g., FIG. 1) into the paper path  203  segment starting at the nip between the upstream pair of rollers  220 ,  221 , the governor carriage  229  is positioned as shown in FIGS. 2 and 3. Extra length of the link  223  is removed from the drive coupling between the drive rollers  210 ,  220  by the tensioning contact between the link and the lower tension roller  231  in this “standard feed” position. This will create a slight “underfeeding” of the paper sheet  201  such that the media is guided through the paper path  203  segment between the upper guide  205  and lower guide  207  with the non-printing side of the sheet in contact with the convex surface  207 ′ of the lower guide. This ensures that the printing surface  201 ′ of the sheet  201  does not contact the guides  205 ,  207  where surface abrasion of media special coatings could occur. 
     Once the leading edge  201 ″ of the sheet  201  is received in the nip between the downstream pair of rollers  220 ,  221 , a sensor  237  (such as an optical detector, a mechanical flag, a trip switch activated by the paper leading edge, or the like as would be known in the art) triggers the solenoid  235 . Via the solenoid  235  action, the governor carriage  229  is translated to a position as shown in FIGS. 4 and 5. In other words, the tensioning of the link  223  is moved from the lower tension roller  231  to the upper tension roller  230 . As the translation occurs, the extra link length is moved from the bottom of the link (as shown in FIGS. 2-3) to the top. The movement of the extra link length to the top slows the rotation of the downstream pair of rollers  220 ,  221  and therefore generates a buckle in the sheet  201 , positioning it to be substantially free of contact with either guide  205 ,  207 . In other words, the sheet now captured by both sets of rollers is slightly overfed into the paper path segment between the guides. Thus, it can be recognized that the extent of the buckling to achieve this positioning is a function of the amount of extra link length added by moving the tension governor  227  to the second position. 
     Once the trailing edge of the sheet is passed through the upstream roller pair nip, the tension governor carriage  229  can be returned to the firs position as demonstrated by FIGS. 2 and 3 as the weight of the paper will generally cause it to fall against the lower guide  207 . However, this would require a second sensor proximate the upstream roller pair nip. 
     The present invention this provides a method and apparatus for feeding a print media through a closed, curved pat such that any abrasion of any special coating on the printing surface of the media is prevented. A motor driven pulley subsystem bridging the entrance and exit of the path is selectively adjustable to change the positioning and shape of the media as it passes therethrough. 
     The foregoing description of the preferred embodiment of the present invention has been presented for purposes of illustration end description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. Similarly, any process steps described might be interchangeable with other steps in order to achieve the same result. The embodiment was chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents. Reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather means “one or more.” Moreover, no element, component, nor method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the following claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ”