Abstract:
A printer and method for operating a printer are provided. The printer has a printhead adapted to heat a thermal donor medium to transfer donor material from a donor web to a receiver medium; a receiver medium path having guides shaped to direct receiver medium along a receiver medium travel path to and from a position in registration with the printhead with said receiver medium path having at least one change of receiver medium direction therein causing said receiver medium to bend; and a motorized platen for moving receiver medium through the receiver medium path, wherein said receiver medium path is further shaped so that the change in receiver medium direction occurs in a portion of the receiver medium path that takes the receiver medium from a position in registration with the printhead.

Description:
FIELD OF THE INVENTION 
   This invention relates in general to printers and methods of printing and in particular to methods of borderless printing. 
   BACKGROUND OF THE INVENTION 
   A key component of a conventional thermal dye transfer printer is the thermal printhead. In many thermal printers, the thermal printhead has a ceramic substrate side and a circuit board side bonded together to an aluminum backer plate. The ceramic substrate side has a plurality of heating elements (heater line) for transferring dye from a ribbon onto paper. The circuit board has integrated circuits laterally spaced from the ceramic substrate on the bottom and connectors on the top to supply power and data for selectively operating the heating elements. In some printers, the integrated circuit is enclosed in a protective housing that has two walls and a cover between the walls, with one wall distal from the ceramic substrate and transverse to the substrate and the other wall proximate to the ceramic substrate and varying in height from a minimal level proximate the level of the substrate to a maximum level of the cover. Alternatively, in other printers the integrated circuit is covered by a junction coated resin to protect the integrated circuit. 
   In a conventional thermal printer, a receiver medium  12 , such as a paper, fabric, film, or other web or sheet type material, is clamped between a capstan roller and a pinch roller and pulled through a nip between the thermal printhead and the platen. The capstan and pinch rollers are driven by a stepper motor that provides both precise movement and control of the paper sheet. The printhead and platen capture a web of donor material with dye and press it against the paper. In some printers the platen spins freely while the web and receiver are pulled past the printhead and in other printers the platen is driven. Heat from the thermal head transfers dye from the donor web onto the receiver medium to create an image. 
   Using this process, thermal dye transfer printers create continuous tones of specific colors not unlike those of traditional color photo prints. Whereas traditional color photos use dyes and fine grains of silver salts, chemically processed to produce an image, thermal printers achieve continuous tones by laying their cyan, yellow and magenta dyes on top of each other with repeated passes of the paper past the printhead. (Some thermal printers also add black dye to the final process). Thermal dye transfer printers also have the capacity to use their heat provided by the printhead to seal a clear plastic layer over the completed print giving the final product an estimated 100-year lifespan. 
   An example of a conventional thermal dye transfer printer that provides monotone, multi-tone or full color printing is shown in  FIG. 1 . Conventional printer  10  has a sheet of receiver medium  12  that is driven along a print path  14  by capstan roller  16  and pinch roller  18 . A printhead  20  is opposite a free spinning platen  22 . Donor supply roller  24  and donor take up roller  26  support a web  28  of thermal dye donor material. A bias spring  30  presses printhead  20  against donor web  28  that contacts receiver medium  12 . A pinch spring  32  urges pinch roller  18  against capstan roller  16 . Capstan roller  16  is turned by a stepper motor  34 . A belt  36  connects the capstan roller  16  to stepper motor  34 . A leading edge of the receiver medium  12  is fed through a feed nip  38  between capstan roller  16  and pinch roller  18  so that receiver medium  12  and donor web  28  are pulled past the printhead  20  and platen  22  where donor material is transferred to receiver medium  12 . 
   As illustrated, conventional printer  10  has printhead  20  normally positioned with an integrated circuit cover  40  extending into the plane of the print path. As such, receiver medium  12  must be turned to bend beneath integrated circuit cover  40 . Whenever receiver medium  12  is deflected from a straight path and must be curved or bent to travel along a bent path, there is a higher likelihood that receiver medium  12  will be diverted from the precise alignment required of a receiver medium  12  during thermal printing. This can cause variations in registration that can create unwanted image artifacts. Thus, what is needed is a thermal printer having more easily established registration. 
   SUMMARY OF THE INVENTION 
   In various aspects of the invention, a method for printing and a printer are provided. 
   In one aspect of the invention, a method for operating a printer is provided. The printer has a printhead moveable toward and away from a platen. The printhead comprises a ceramic substrate for holding a plurality of heating elements and, an integrated circuit laterally spaced from the ceramic substrate and connected to the heating elements for selectively operating the heating elements. In accordance with the method, the receiver medium is moved along the path toward the printhead and the platen; the printhead is moved toward the donor web to clamp the receiver medium between the donor web and the platen and the platen is moved with respect to the printhead to advance the receiver medium and the donor web past the printhead in a direction where the donor web and receiver medium pass the ceramic substrate and thereafter pass the integrated circuit. Portions of the printhead are selectively energized to transfer donor material from the donor web to the receiver medium during the movement. 
   In another aspect of the invention, a printer is provided having a printhead moveable toward and away from a platen. The printhead comprises a ceramic substrate for holding a plurality of heating elements and, an integrated circuit laterally spaced from the ceramic substrate and connected to the heating elements for selectively operating the heating elements; a platen for receiving and carrying a receiver medium past the printhead; a donor web disposed between the printhead and the receiver medium; a sheet feeder for moving the receiver medium toward the platen to register the receiver medium with the donor web; and a motor coupled to the platen for operating the platen to drive the receiver medium and the donor web during printing in a direction from the ceramic substrate toward the integrated circuit. 
   In yet another aspect of the invention, a printer is provided having a printhead moveable toward and away from a platen. The printhead comprises a ceramic substrate for holding a plurality of heating elements and an integrated circuit laterally spaced from the ceramic substrate and connected to the heating elements for selectively operating the heating elements. A donor web is disposed between the printhead and the receiver medium. A transport path is shaped to guide receiver medium toward the platen to register the receiver medium with the donor web A movable platen advances the receiver medium and the donor web along the transport path during printing in a direction from the ceramic substrate toward the integrated circuit. 
   In still another aspect of the invention, a thermal printer is provided. The thermal printer comprises: a printhead adapted to heat a thermal donor medium to transfer donor material from a donor web to a receiver medium; a receiver medium path having guides shaped to direct receiver medium along a receiver medium travel path to and from a position in registration with the printhead with the receiver medium path having at least one change of receiver medium direction therein causing the receiver medium to bend; and a motorized platen for moving receiver medium through the receiver medium path, wherein the receiver medium path is further shaped so that the change in receiver medium direction occurs in a portion of the receiver medium path that takes the receiver medium from a position in registration with the printhead. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a mechanical schematic of a conventional thermal printer with capstan/pinch drive rollers; 
       FIG. 2  is a mechanical schematic view of a thermal printhead; 
       FIG. 3  is a mechanical schematic of a thermal printer showing the reversed direction of paper flow with regard to the printhead of  FIG. 1 ; 
       FIG. 4  is a mechanical schematic view of the printing apparatus with reversed flow direction; and 
       FIG. 5  is a mechanical schematic view of another embodiment of a printer having a printhead with resin encased integrated circuits and reversed flow direction. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIGS. 2 ,  3  and  4 , there is shown a borderless thermal dye thermal printer  50  for printing images along the width and length of a receiver medium  12 , such as for example, a paper, fabric or film. Printer  50  has a thermal printhead  52 . Printhead  52  has a ceramic substrate  54  with a linear array of heating elements  56 . An aluminum backer plate  58  is on the upper side of ceramic substrate  54  for dissipating heat generated in heating elements  56 . In various embodiments, backer plate  58  can comprise a heat sink or can be connected to convey heat to a separate heat sink (not shown). Heating elements  56  are arranged along what is commonly known as a heat line HL or print line. The terms “linear array of heating elements”, “heat line HL”, and “print line” are used interchangeably in this patent and refer to any form or arrangement of heating elements  56  that extend generally across a printable area of receiver medium  12  as receiver medium  12  is moved past printhead  52 . 
   Next to ceramic substrate  54  is a circuit board  60 . On one side of circuit board  60  is a connector  62  for receiving power and data signals and on the other side an integrated circuit  64  that controls power to heating elements  56 . Integrated circuit  64  is enclosed in a protective housing  66  that has a first end wall  68  and a second end wall  70 , with a cover  72  between end walls  68  and  70 , and two sidewalls (not shown). First end wall  68  is proximate ceramic substrate  54  and has a sloped surface that extends from ceramic substrate  54  to a height above integrated circuit  64 . Second end wall  70  extends substantially transverse to circuit board  60 . Cover  72  extends between end walls  68  and  70  and the sidewalls. 
   Thermal printhead  52  is oriented with ceramic substrate  54  facing toward the leading edge of receiver medium  12  as receiver medium  12  is moved during a printing operation. In the rest or non-printing position, substrate  54  and receiver medium  12  are arranged in substantially parallel, spaced-apart planes. During a printing operation thermal printhead  52  is moved relative to receiver medium  12  so that ceramic substrate  54  will cover and rest on top of web  28  of thermal dye transfer donor material and receiver medium  12 . 
   A donor supply roller  24  on one side of thermal printhead  52  provides web  28  of thermal dye transfer donor material that travels across the linear array of heat elements  56  and is wound on a donor take-up roller  26 . Web  28  of donor material can comprise a single color for monotone printing, but it typically comprises at least three sequential sections of different colors in order to provide full-color print and a clear section for applying a protective cover on the print. Beneath printhead  52  is a cylindrical platen  22 . Platen  22  is coupled to a platen stepper motor  74  by a suitable platen transmission  76  such as a belt. Those skilled in the art understand that  FIGS. 2-4  are schematic in nature and other suitable means are possible for connecting the platen stepper motor  74  to cylindrical platen  22  in order to turn platen  22 . Such other means include and are not limited to gear trains. Thermal printhead  52  is coupled to control circuit  80 . Control circuit  80  is coupled to a printhead actuator (not shown), such as a motor or solenoid and appropriate transmission that controls the position of thermal printhead  52  relative to platen  22 . In operation, control circuit  80  operates the printhead actuator (not shown) in order to move thermal printhead  52  along the axis shown by arrow  82  so as to increase or decrease the size of a printing nip area  57 . 
   In the embodiment of  FIGS. 2-4 , receiver medium  12  is stored in a hopper  84 . The top sheet of receiver medium  12  from hopper  84  is removed from hopper  84  by a suitable pick roller  85 . This receiver medium  12  travels along a heating first printer path  86  that leads it to guide rollers  88 ,  90 , between surface guides  92 ,  94 , past edge sensor  96 , through printing nip area  57 , past heat line HL to exit urge rollers  98 ,  100 , exit guides  102 ,  104  and into exit hopper  106 . Control circuit  80  is connected to the moveable and operative elements of printer  50  for controlling their individual and coordinated operation. Those skilled in the art understand that control circuit  80  is a schematic representation for a hard-wired controller or a processor controlled system that uses hardware and optionally software to control and operate printer  50  and its components. 
   Edge sensor  96  is any suitable sensor for identifying the leading edge of a receiver medium  12 . Edge sensor  96  can be an optical, mechanical, or a combination optical/mechanical device that senses the leading edges of the receiver medium  12 . Such sensors are well-known in printers and photocopiers and any suitable, conventional sensor may be used. In addition, edge sensor  96  may be combined with a suitable gate (not shown). 
   Those skilled in the art understand that when receiver medium  12  reaches edge sensor  96 , receiver medium  12  has its lateral sides aligned and deskewed so that the leading edge of receiver medium  12  is transverse to heating first printer path of travel  86  and is substantially aligned parallel to the linear array of heating elements  56 . Edge sensor  96  thus senses the position of the leading edge of receiver medium  12  at the location of edge sensor  96 . 
   Edge sensor  96  is disposed at a known distance from heat line HL. Edge sensor  96  is coupled to control circuit  80 . In response to edge sensor  96  detecting the leading edge of receiver medium  12 , control circuit  80  drives urge stepper motor  34  a predetermined number of steps in order to move receiver medium  12  toward heating elements  56  and to stop receiver medium  12  with the leading edge at a distance D from heat line HL. The initial position is a distance D just short of the heat line HL and is close enough to the heat line HL that the lead edge of receiver medium  12  will be captured in the nip between web  28  and platen  22 . 
   In the embodiment illustrated in  FIGS. 2-4 , receiver medium  12  is staged under the ceramic substrate  54  of thermal printhead  52  which has the advantage of allowing receiver medium  12  to traverse a relatively straight receiver medium path before it enters the printing nip  57  between printhead  52  and platen  22 . A straight receiver medium path allows easier registration of receiver medium  12  during printing. 
   Receiver medium  12  is precisely positioned and repositioned by one or more of the stepper motors that operate the pairs of guide rollers  88 ,  90 , and exit urge rollers  98 ,  100  and platen  22 . In one embodiment, only platen  22  or one of the pairs of guide rollers  88 ,  90  move receiver medium  12  at any one time. Thus, the first pair of guide rollers,  88 ,  90 , control movement of receiver medium  12  past edge sensor  96  to the initial position. Platen  22  then controls movement of receiver medium  12  beneath heating elements  56 . Exit urge rollers  98 ,  100  control return of receiver medium  12  toward its initial position and its final discharge from printer  50 . Exit urge rollers  98 ,  100  release control of receiver medium  12  after receiver medium  12  has been moved by a predetermined distance after printing is complete. Then exit urge rollers  98 ,  100  resume control to precisely reposition receiver medium  12  at the initial position that is within the distance D of heat line HL. 
   Control circuit  80  operates guide rollers  88 ,  90  to move the leading edge of receiver medium  12  into printing nip  57  between thermal printhead  52  and platen  22 . Guide rollers  88 ,  90  can be permanently engaged or can be selectively engaged. To selectively engage guide rollers  88 ,  90 , upper roller  88  can be spring biased away from guide roller  90  and an actuator (not shown) controlled by control circuit  80  is operable to move guide roller  88  into or out of engagement with guide roller  90 . Exit urge rollers  98 ,  100  can be similarly constructed. If the guide rollers  88 ,  90  and exit urge rollers  98 ,  100  are permanently engaged, then they will be actuated as described above. 
   As discussed above, guide rollers  88 ,  90  drive receiver medium  12  to the initial position where a leading edge of receiver medium  12  is positioned at a distance D from the from heat line HL. After receiver medium  12  is in the initial position, control circuit  80  drives thermal printhead  52  downward in the direction of arrow  82  in order to clamp receiver medium  12  between printhead  52  and platen  22 . With receiver medium  12  in place, control circuit  80  causes platen stepper motor  74  and thermal printhead  52  and its linear array of heating elements  56  to be selectively operated to transfer donor material, in particular thermal-dye transfer material, from donor web  28  to receiver medium  12 . 
   After printing, the direction of donor web  28  and receiver medium  12  are sharply altered to separate donor web  28  from receiver medium  12 . Receiver medium  12  continues to travel between exit guides  102 ,  104  and into the nip of exit urge rollers  98 ,  100 . Exit urge rollers  98 ,  100  are likewise under control of control circuit  80 . Exit urge rollers  98 ,  100  are optionally operable to rewind and feed receiver medium  12  back toward platen  22 . Receiver medium  12  is rewound and fed back during multicolor printing. After a color or clear laminate is transferred to receiver medium  12 , control circuit  80  stops receiver medium  12  at a position just past heating element  56 . Control circuit  80  turns off heating elements  56  and causes printhead actuator (not shown) to raise thermal printhead  52  to release receiver medium  12  from printing nip area  57  between printhead  52  and platen  22 . Next, control circuit  80  turns on exit urge rollers  98 ,  100  to drive receiver medium  12  back toward the printing nip area  57 , or following the application of the last color or laminate, toward exit hopper  106 . 
   Donor web  28  has multiple, sequential sections of different colors or a clear laminate and the single printing cycle described above is repeated for each color and for the clear laminate. A typical color print operation includes serial printing from section of yellow, magenta, cyan dyes and then transferring a clear, protective layer on receiver medium  12 . After each color or clear section is printed, receiver medium  12  is returned to its initial position for printing the next color from the donor web. After multicolor printing is completed, exit urge rollers  98 ,  100  discharge receiver medium  12  into exit hopper  106 . 
   It is valuable in a printer to be able to re-register receiver medium  12  between the printing of different colors. A receiver medium path which is straight and free of disruptions is desirable. 
   Accordingly, various embodiments of printer  50  achieve borderless printing on a single sheet by precisely locating the leading edge of receiver medium  12  and, in particular, locating the leading edge precisely between heating elements  56  and platen  22  both initially and at the beginning of printing of each new color if any. Edge sensor  96  senses the leading edge during the location process. Stepper motors precisely drive sets of guide rollers  88 ,  90  and platen  22  to precisely position receiver medium  12  at its initial position for each printing cycle. In this way, thermal-dye transfer material may be transferred from the leading edge of receiver medium  12  to the trailing edge of the paper, thereby eliminating any border on the leading and trailing edges. 
   As is illustrated in  FIG. 5 , in certain embodiments, printer  50  can have a printhead  52  with an integrated circuit  64  positioned on an outside of printhead  52 , but protected by a deposit  108  of a protective material, such as a coating of resin. As can be seen in  FIG. 5 , printer  50  provides a generally a straight and unbent heating first printer path  86  leading to heating elements  56 . 
   Accordingly, a printer is provided that reverses the direction of receiver medium movement past printhead  52  from the conventional direction (from circuit board to ceramic head) to the reversed direction (from ceramic head to circuit board) in order to reduce any bends in the path of the receiver medium in advance of printing. In particular, a leading edge of receiver medium  12  passes the heat line HL before passing the integrated circuit  64  and any protective structure associated therein, such as housing  66 , or deposit  108 . This removes the integrated circuit and such protective structure from the path of the leading edge of the unprinted receiver medium  12  to provide an uninterrupted path as receiver medium  12  travels to the heat line HL. 
   The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
   PARTS LIST 
   
       
         10  conventional printer 
         12  receiver medium 
         14  print path 
         16  capstan roller 
         18  pinch roller 
         20  printhead 
         22  platen 
         24  donor supply roller 
         26  donor take up roller 
         28  donor web 
         30  bias spring 
         32  pinch spring 
         34  stepper motor 
         36  belt 
         38  nip 
         40  cover 
         50  printer 
         52  thermal printhead 
         54  ceramic substrate 
         56  heating elements 
         57  printing nip area 
         58  backer plate 
         60  circuit board 
         62  connector 
         64  integrated circuit 
         66  housing 
         68  first end wall 
         70  second end wall 
         72  cover 
         74  platen stepper motor 
         76  platen belt 
         80  control circuit 
         82  arrow 
         84  hopper 
         85  pick roller 
         86  heating first printer path 
         88  guide roller 
         90  guide roller 
         92  surface guide 
         94  surface guide 
         96  edge sensor 
         98  exit urge roller 
         100  exit urge roller 
         102  exit guide 
         104  exit guide 
         106  exit hopper 
         108  deposit 
       D distance 
       HL heat line