Abstract:
A thermal label printer includes an actuation mechanism and follower for facilitating loading of stock (e.g., label stock). A pivotable printer head pressure plate includes the actuation mechanism which cooperates with the follower coupled to a peeler roller. As the pressure plate is moved from a closed position proximate a platen to an open position for loading of stock or for cleaning the printer head, the peeler roller is automatically translated from the platen. The resulting roller gap and displaced printer head provide unrestricted access for threading of the printer. The printer also includes a programmable device in the printer electronics for reconfiguring the printer to accommodate a variety of thermal print mechanisms.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of, and claims priority to, U.S. patent application Ser. No. 08/757,244, filed Nov. 27, 1996, now U.S. Pat. No. 6,261,009 the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to printers and, more specifically, to a mechanical arrangement for automatically displacing a roller from a platen upon opening a printer head pressure plate. The automatic displacement feature facilitates the loading of stock (e.g., label stock) in the printer. Other aspects of the invention include the ability of the printer to be readily and easily reconfigured to accommodate an optional thermal ribbon cartridge and a variety of thermal print mechanisms. 
     BACKGROUND 
     Thermal printers are used increasingly in retail, warehouse, and other locations to generate adhesive labels for marking goods to facilitate identification, tracking, and pricing. Due to the print quality, accuracy, and versatility of dot matrix or array type thermal print mechanisms, a wide variety of information can be produced quickly and inexpensively on the labels as the need arises. Lot sizes of labels can be as small as one or as large as several hundred or more, depending upon the particular application. Printer electronics integral with the printer may include a microprocessor, memory, and associated internal and external communications so that the printer can be used to create alphanumeric characters of varying size, font, and orientation, stylized graphical markings such as logotypes and trademarks, and machine readable indicia such as bar codes for the particular goods to be labeled. A variety of these characters, markings, and indicia can be printed in combination on a single label. 
     Thermal printers can print on thermal paper which darkens or changes color when heated above a threshold temperature by the thermal print mechanism or printer head. By selectively activating discrete thermal elements in the printer head array as the thermal paper passes by, the desired information can be reproduced on the thermal paper. To provide intimate, uniform contact between the printer head and the label, the label is passed typically through a nip formed by the printer head and a powered rubber platen roller. The platen may be used to drive the label through the nip. Instead of heating the label, a thermal transfer ribbon having a layer of dried ink on a thin backing sheet can be disposed between the printer head and a paper label on the platen. As the printer head is heated above the ribbon ink threshold temperature, the ink melts and is transferred to the label where it dries and forms an indelible marking of the desired information. 
     “Label stock” generally includes a series of printable surfaces of paper or other label material adhesively and releasably attached to a web carrier backing. The label stock typically is manufactured in roll form for continuous feeding through a thermal printer. “Linerless” label stock is also commercially available which is in the form of a roll of continuous adhesive strip. Special handling of this stock is required to prevent misfeeding and jamming of the thermal printer. For example, a silicone platen roller may be used to prevent adhesion of the stock thereto and a cutter mechanism may be provided to separate a printed label portion from the remaining roll. 
     In printers for printing on a series of labels adhered to a web, it may be desirable to dispense printed labels individually, wholly or partially delaminated from the web, to facilitate removal by an operator. By passing the web across a peeler bar at an acute angle after discharge from the nip formed between the printer head and platen, a leading edge of the label becomes delaminated or detached from the web. An additional roller may be provided biased against the platen or other roller to form a second nip through which solely the web passes. By keeping the web taut and maintaining close conformance of the web to the peeler bar, reliable dispensing of the printed labels may be ensured. 
     When initially threading the printer with the label stock, the stock must be passed through the printer head nip and, if the peeler bar is to be used, the web also must be passed through the roller nip. The web should be taut between the printer head nip and the roller nip to tightly conform the web to the peeler bar. Various arrangements are known for providing a gap between the printer head and platen to facilitate loading. For example, see U.S. Pat. Nos. 5,014,073 and 5,150,130. Known arrangements for providing a gap between a roller and a platen to facilitate removal of paper jams include the arrangement disclosed in U.S. Pat. No. 4,947,185. Arrangements that require manual actuation to provide a gap between the roller and the platen include a spring loaded roller with bi-stable positioning so that the roller is stable in positions both against the platen as well as spaced therefrom. Manual actuation is required both to displace the roller from the platen as well as return the roller to the contact position. Each of these arrangements entails separate apparatus for displacing a printer head and a roller from the platen. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a printer which has an improved stock (e.g., label stock) loading feature. 
     It is another object of the invention to provide a printer that is readily and easily reconfigurable to accommodate an optional thermal ribbon cartridge and a variety of thermal print mechanisms. 
     An improved printer and printer subassembly according to the invention are useful in a wide variety of applications including, but not limited to, thermal printing on label stock. The printer subassembly includes a powered platen having an axis of rotation. A thermal print mechanism, including a printer head, is aligned with and biased against the platen by a stacked assembly of a pressure plate and an alignment plate with springs disposed therebetween. The printer head is fixedly mounted on the alignment plate which is supported by the pressure plate using a pivot feature in combination with a centering feature ensuring proper alignment of the printer head relative to the platen. 
     The pressure plate is hinged about an axis along an edge perpendicular to the platen axis. A latch disposed along an opposite edge of the pressure plate maintains the plate in a closed position for printing. The latch may include a microswitch to signal a printer controller that the pressure plate is closed and printing can begin if the printer is otherwise ready. Releasing the latch permits the pressure plate to be swung open providing access to load label stock as well as clean or remove the printer head. 
     The pressure plate includes an actuation mechanism proximate the hinge axis which cooperates with a follower. The follower is coupled to a roller biased against the platen to effect translation of the roller as the follower is moved. The actuation mechanism may be a cam sector with a fixed radial dimension and a varying axial dimension. The follower may be a cantilevered arm with a pin for sliding contact on the sector. As the pressure plate is moved from a closed to an open position, the follower pin slides along the contoured surface of the cam sector, translating the roller from a position biased against the platen to a position spaced therefrom. Accordingly, with the pressure plate in an open position, a gap is formed between the roller and the platen. After passing the label stock over the platen and a peeler bar, the web may be passed through the gap and held taut. As the pressure plate is closed and latched, the label stock is captured between the printer head and the platen and the web is captured between the roller and the platen. The label stock may then be advanced automatically or manually to align a leading edge of a label with the printer head for printing. 
     A detent in the cam sector corresponding to a fully open position of the pressure plate may be provided for engagement with the follower pin to keep the pressure plate in the open position during label stock loading. To provide parallel translation of the roller relative to the platen, cam surfaces may be affixed to both ends of the roller. The follower may also include an optional extension for manual translation of the roller when the pressure plate remains in a closed position. A frame supporting the roller may include slots to limit manual translation of the roller within predetermined limits. 
     The modular design of the interface between the pressure plate and the alignment plate permits rapid manual replacement or swapping of thermal print mechanisms without the need for tools. Additionally, the printer may include an optional modular thermal transfer ribbon assembly for printing on plain paper labels. 
     The printer may also be provided with electronics reconfigurable to accommodate a variety of thermal print mechanisms and the optional thermal transfer ribbon. Configuration information may be stored in memory, read by a microprocessor, and used to configure a programmable device such a field programmable gate array (“FPGA”) to allow print data received by the microprocessor to pass through the FPGA and be printed by the print mechanism loading in the printer. Configuration information may include parameters such as printer model, which includes motor type and printer head type. 
     According to the invention, loading of stock is greatly facilitated. Further, the printer is readily reconfigurable to accommodate an optional thermal ribbon cartridge and a variety of thermal print mechanisms which are easily removed and replaced without the need for tools or special alignment techniques. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, in accordance with preferred and exemplary embodiments, together with further advantages thereof, is more particularly described in the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic perspective view of a thermal printer in accordance with an embodiment of the invention; 
     FIG. 2 is a schematic perspective exploded view of a subassembly of the printer depicted in FIG. 1; 
     FIG. 3 is a schematic perspective view of the subassembly depicted in FIG. 2 in an assembled state open position; 
     FIG. 4A is a schematic left side view of the subassembly depicted in FIG. 2 in an assembled state closed position; 
     FIG. 4B is a schematic left side view of the subassembly depicted in FIG. 4A in an open position; 
     FIG. 5A is a schematic right side view of the subassembly depicted in FIG. 2 in an assembled state closed position; 
     FIG. 5B is a schematic right side view of the subassembly depicted in FIG. 5A in an open position; 
     FIG. 6A is a schematic sectional view of a portion of the subassembly depicted in FIG. 3 in an assembled state open position taken along line  6 A— 6 A of FIG. 3; 
     FIG. 6B is a schematic sectional view of a portion of the subassembly depicted in FIG. 6A in a closed position; 
     FIG. 7 is a block diagram of printer electronics and connections thereto by other components of the printer in accordance with an embodiment of the present invention; 
     FIG. 8A is a flowchart of the operation of a printer operating system; 
     FIG. 8B is a flowchart of an initialization subroutine of the operating system depicted in FIG. 8A; 
     FIG. 8C is a flowchart of a maintenance subroutine of the operating system depicted in FIG. 8A; 
     FIG. 8D is a flowchart of a command interpreter subroutine of the operating system depicted in FIG. 8A; and 
     FIG. 8E is a flowchart of the print subroutine of the command interpreter subroutine depicted in FIG.  8 D. 
    
    
     DESCRIPTION 
     FIG. 1 shows a schematic perspective view of a thermal label printer  10  in accordance with an embodiment of the invention. The printer  10  includes a cover  12 , depicted in an open position to show the arrangement of the printer components. A storage well  14  is provided for a roll of stock (e.g., label stock). The stock is supported on edge guides  16  which slide on track  18 . The track  18  may include a centrally disposed, spring loaded pinion which cooperates with racks formed on the edge guides  16  to automatically center the roll of label stock without the need for manual adjustment. 
     The printer  10  includes a printer subassembly  20  for conveying, printing, and dispensing labels. The subassembly  20  includes an optional modular thermal transfer ribbon assembly  22 , solely the frame of which is depicted here. The ribbon assembly  22  includes a plurality of hooks  24  formed in a base portion thereof which interlock with mating tab features disposed in an upper surface of a pressure plate  26  to facilitate rapid installation and removal without the need for tools. As will be discussed in greater detail hereinbelow, the pressure plate  26  captures and supports one of a variety of thermal print mechanisms, not depicted in this view. 
     The subassembly  20  also includes a motor  28 , preferably a step motor, and associated gear train for driving the ribbon assembly  22  and a platen roller  30 . The platen roller  30  supports the stock during printing and may be covered with rubber to provide a resilient surface for label stock and a coefficient of friction sufficient to ensure positive tracking of the stock through the nip formed with a printer head of the thermal print mechanism. As used herein, the term “nip” refers to a pinch line through which label stock or web backing passes. The nip may be formed by a cylindrical roller, such as the platen  30 , and a stationary element, such as a printer head. Alternatively, the nip may be formed by a pair of cylindrical rollers. There may be rolling contact between the rollers or sliding contact between the roller and stationary element, or alternatively there may be a nominal clearance. A peeler bar  32  is provided close to and spaced from the platen  30  and generally aligned with an uppermost surface of the platen  30  in a parallel arrangement to facilitate delamination of labels from a web backing after printing. 
     Referring now to FIG. 2, the printer subassembly  20  is shown in an exploded perspective view without the ribbon assembly  22 . In this view, the tab features of the pressure plate  26  are apparent and may be apertures  34  sized to receive the hooks  24  of the ribbon assembly  22 . The hooks  24  are sized with an opening or throat substantially equivalent to the thickness of the pressure plate  26 . A registration feature such as a depression  36  may be provided to accommodate a protuberance on the ribbon assembly  22  so that the ribbon assembly snaps in place upon installation. 
     A thermal print mechanism alignment plate  38  is removably captured by the pressure plate  26  by a pivot feature which includes alignment plate hooks  40  and pressure plate tabs  42 . A rearwardly opening, centrally disposed “T” slot  44  on the alignment plate mates with a “T” on an underside of the pressure plate  26 . Plungers  46  and springs  48  are captured in mating recesses  50  in both the pressure plate  26  and the alignment plate  38  to resiliently bias the alignment plate  38  away from the pressure plate  26 . A thermal print mechanism or printer head  52  is fixedly attached to an underside of the alignment plate  38  remote from the pressure plate  26 , for example with machine screws. Accordingly, the alignment plate  38  and the printer head  52  remain centered relative to the pressure plate  26  and can pivot and translate, within limits, to ensure intimate contact between the printer head  52  and a label disposed on the platen  30  and consistent, high quality print resolution. The alignment plate  38  and printer head  52  may be readily installed in the pressure plate  26  by squeezing the plates  26 ,  38  together to compress the springs  48  and translating the alignment plate rearwardly toward the label stock roll. Removal of the alignment plate  38  is achieved by squeezing and translation in a forwardly direction toward the peeler bar  32 . 
     The pressure plate  26  is hinged along a side thereof to a base housing or frame  54  by a hinge pin  56  which passes through respective apertures  58 ,  60 . A longitudinal axis “A” of the hinge pin  56 , when installed, is substantially perpendicular to an axis of rotation “B” of the platen roller  30 . An opposite edge of the pressure plate  26  includes a hook  58  configured to mate with a spring loaded latch  60  slidably disposed in slot  62  in the frame  54 . Accordingly, the pressure plate  26  can be latched in a closed position with the printer head  52  resiliently biased against the platen  30 , forming a nip for printing. Translation of the latch  60  in a rearward direction releases the hook  58  and the pressure plate  26  can be rotated or swung upwardly to the left, as depicted in FIG. 3, so that label stock may be inserted or so that the printer head  52  can be cleaned, removed, or replaced. A contoured ramp  64  may be provided which is hinged on hinge pin  54  rearwardly of the platen roller  30  to ride above the label stock and ensure smooth entry of the label stock into the printer head nip. A sensor or switch such as microswitch  98  may be provided proximate the latch  60  in the subassembly  20  to sense whether the pressure plate  26  is in the closed or open position. 
     The peeler bar  32  is disposed forwardly of the platen  30  and provides a small radius contour around which the label stock can be turned at an acute angle to delaminate a leading edge of a printed label from the web backing. To maintain close conformance of the web to the peeler bar  32  and keep the web taut, a pinch or peeler roller  68  is provided. The peeler roller  68  has an axis of rotation “C” substantially parallel with the platen axis B and is biased against the platen  30  by a pair of flat springs  70  to form a second nip. Solely the web passes through the second nip since the printed labels become detached from the web as the web passes over the peeler bar  32 . 
     FIG. 3 is a schematic perspective view of the printer subassembly  20  depicted in FIG. 2 in an assembled state with the pressure plate  26  in a fully open position to facilitate threading of the label stock across the platen  30  and peeler bar  32 . To facilitate threading of the roller nip  66  with the web, an actuation mechanism  72  is provided on the pressure plate  26  and a cooperating follower  74  is coupled to the roller  68 . When the hook  58  is released from the latch  60 , pressure plate  26  is moved about hinge axis A from a closed position substantially parallel to the platen axis to an open position substantially perpendicular to the platen axis. The actuation mechanism  72  reacts against follower  74  to cause translation of the roller  68  away from the platen  30 . The label stock may be readily laid across the platen  30  and peeler bar  32  as shown by arrow  76  and the web thereafter passed through the gap created between the roller  68  and the platen  30  as will be discussed in greater detail hereinbelow. 
     As best seen in FIG. 2, the actuation mechanism  72  is a cam sector  78  of about 90 degrees corresponding to the 90 degree swing of the pressure plate  26 . Smaller or larger angles may be employed if desired, depending on a particular application. The sector  78  has a substantially constant radial dimension relative to hinge pin axis A and a varying axial dimension. The axial dimension varies smoothly as a function of angle and may include a discontinuity or detent  80  proximate an end of the sector  78  substantially corresponding to end of travel of the pressure plate  26  at the fully open position of about 90 degrees. The follower  74  includes an axially extending pin  82  for sliding contact on the sector  78  and for engagement with the detent  80  at full pressure plate travel. Accordingly, as the pressure plate  26  is rotated from closed to open positions, the sector  78  drives the pin  82  in a forward direction. 
     The follower  74  is coupled to a shaft  84  of the roller  68 , for example, with a mating “D” slot and flat to prevent relative rotation therebetween, although other techniques could be used including a key or spline connection. One or more cylindrical roller elements  86  with or without ridges or other surface features may be provided which freely rotate relative to the shaft  84 . The follower  74  also includes a cam surface  88   a  for reacting against proximate structure as will be discussed in greater detail hereinbelow. A matching cam surface  88   b  is provided at an opposite end of the roller  68  which is similarly coupled to the shaft  84  by a mating “D” slot and flat. Lastly, the follower  74  includes an extension  90  for manual translation of the roller  68  away from the platen  30  when the pressure plate  26  is closed and latched. The roller shaft  84  passes through a pair of elongated slots  92  to limit manual translation of the roller  68 . 
     FIGS. 4A and 4B depict schematic left side views of the subassembly  20  depicted in FIG. 2 in assembled state in closed and open positions, respectively. With the pressure plate  26  in the closed position shown in FIG. 4A, follower pin  82  is biased against a portion of the sector  78  having a minimum axial dimension and follower cam surface  88   a  is fully engaged with a bushing  94   a  which circumscribes a shaft  96  of the platen roller  30 . The pin  82  is substantially aligned at a common height with hinge pin axis A. As the pressure plate  26  is raised to the open position depicted in FIG. 4B, the pin  82  slides along sector  78  until engagement with detent  80 . The follower  74  becomes canted as the roller shaft  84  is rotated. The shaft  84  translates in slot  92  due to the reaction of cam surface  88   a  against bushing  94   a.    
     In order to effect substantially parallel translation of the roller  68  relative to the platen  30  upon movement of the follower  74 , a similar arrangement of cam surface  88   b  and bushing  94   b  are provided at the opposite end of shaft  84  as depicted in FIGS. 5A and 5B. With the pressure plate  26  in the closed position shown in FIG. 5A, the cam surface  88   b  is fully engaged with the bushing  94   b  which circumscribes platen roller shaft  96 . As the pressure plate  26  is raised to the open position depicted in FIG. 5B, the follower  74  rotates roller shaft  84  and this end of the roller shaft  84  translates in slot  92  due to the reaction of cam surface  88   b  against bushing  94   b.    
     FIGS. 6A is a schematic sectional view of a portion of the subassembly  20  depicted in FIG. 3 in the open position taken along line  6 A— 6 A thereof The roller  68  is spaced from the platen  30  leaving a gap  100  therebetween. The printer head  52  has been swung out of the way providing access to thread the label stock and web. FIG. 6B is a schematic sectional view of the portion of the subassembly  20  depicted in FIG. 6A in a closed position with a label stock and web path depicted. Label stock  102  enters a nip  104  formed by the printer head  52  and the platen  30 . After exiting the nip  104 , the label stock  102  passes around peeler bar  32  at an acute angle, delaminating a label  106  from the web carrier backing  108  which passes through the nip  66  formed by the roller  68  and platen  30 . 
     In an exemplary embodiment, the platen  30  may be manufactured as a rubber covered roller having a length of up to about 4.5 inches (11.4 cm) and a nominal diameter of about 0.687 inches (1.74 cm). The labels may vary in size from about 1.0 inches (2.5 cm) along a side, or less, to about 4.0 inches (10.2 cm), or more. Label thickness may range from about 0.002 inches (0.005 cm) or less to about 0.015 inches (0.038 cm) or more. The peeler bar  32  may be manufactured from stainless steel for corrosion resistance and be a cylindrical member having a nominal diameter of about 0.094 inches (0.24 cm). The roller  68  may include a stainless steel shaft  84  with three roller elements  86  manufactured from acetyl resin. The roller elements  86  may have a nominal diameter of about 0.25 inches (0.64 cm) and include a plurality of axially spaced circumferentially disposed ridges having a maximum diameter of about 0.28 inches (0.71 cm). 
     The actuation mechanism  72  on the pressure plate  26  may have a sector  78  with a radius “r” of about 0.375 inches (0.953 cm) as best seen in FIG.  3  and an axial dimension “1” of about 0.25 inches (0.64 cm) as best seen in FIG.  4 A. The follower pin  82  may have a nominal diameter of about 0.125 inches (0.318 cm) to match the contour of the detent  80  in the sector  78 . Distance between a centerline of the pin  82  and the axis of rotation C of roller  68  is about 0.75 inches (1.9 cm). For these dimensions, the gap  100  created by fully opening the pressure plate  26  and engaging the pin  82  with the detent  90  is about 0.10 inches (0.25 cm). Clearly, the dimensions of the actuation mechanism  72  and follower  74  may be changed to either increase or decrease the size of the gap  100 , as desired. By employing the actuation mechanism  72  and follower  74  according to the invention, a compact low profile configuration for automatically opening the roller nip  66  can be produced. The actuation mechanism  72  may be formed integrally with the pressure plate  26  from a polycarbonate resin such as LEXAN™ available from General Electric Company, Pittsfield, Mass. The follower  74  may also be manufactured from polycarbonate resin. Alternatively, the actuation mechanism  72  and follower  74  may be manufactured from reinforced glass filled polymers or metals such as aluminum or stainless steel to enhance strength and wear resistance. 
     FIG. 7 is a block diagram of printer electronics  108  and connections thereto by other components of the printer  10 . The electronics  108  include a microprocessor  110  coupled by a data/address bus to volatile memory  112  (preferably RAM), non-volatile memory  114  (e.g., ROM, flash memory, etc.), and a programmable device  116  such as a field programmable gate array (FPGA). The RAM  112  functions as a scratch pad memory, with data being written to it prior to printing of a label. The non-volatile memory  114  includes printer operating system and application software such as non-standard fonts, non-standard bar codes, and printer head variables. The non-volatile memory  114  also includes an FPGA configuration file having printer head connections and printer head parameters for a variety of physically interchangeable thermal print mechanisms  52 . The non-volatile memory  114  may be a user-accessible, replaceable printed circuit card to facilitate memory upgrade. While permanent memory such as flash memory is preferred for the non-volatile memory  114 , battery-backed RAM could be used if desired. 
     The FPGA  116  is connected to a serial EEPROM  148 , a motor drive circuit  150  for controlling step motor  28 , and one of a variety of thermal print mechanisms  52 . Configuration information such as printer model, which includes motor type and printer head type, may be stored in the serial EEPROM  148 . Printer head type may be, for example, a non-intelligent print mechanism or an intelligent print mechanism. A non-intelligent print mechanism may have a resolution of between about 200 dots per inch (“dpi”) (79 dots/cm) and 300 dpi (118 dots/cm) and the capability to print at about 2 inches per second (“ips”) (5 cm/sec) to about 3 ips (8 cm/sec). Alternatively, an intelligent print mechanism may have a resolution of about 200 dpi (79 dots/cm) but be capable of printing at speeds as high as 7 ips (18 cm/sec) or faster due to the inclusion of circuitry within the printer head as well as dot history control. An intelligent print mechanism is commercially available from Rohm Co., Ltd. of Kyoto, Japan. Depending on whether an intelligent or non-intelligent print mechanism is installed in the printer  10  configuration information for motor type may include parameters such as motor direction and speed data. These parameters may be set to correspond to different gear trains installed in the printer  10  between the motor  28  and platen  30  so that the platen  30  is driven at an optimum speed for the installed print mechanism  52 . 
     An optional cutter circuit  118  may also be connected to the bus to control an optional guillotine or rotary cutter disposed downstream of the printer head nip  104  for cutting variable length labels produced from linerless stock or other continuous label stock. 
     The microprocessor  110  communicates externally by means of a serial port  120 , parallel port  122 , or for non-cabled communications an optional infrared (“IR”) port  124  or an optional short range radio frequency (“SRRF”) port  126 . A display  128  is also provided and may be a digital format liquid crystal display (“LCD”) or a plurality of light emitting diodes (“LED”) corresponding to “power”, “label stock out”, “on line”, etc. A keypad  130  permits manual input by an operator and may be an alphanumeric pad or a series of discreet function switches such as “on/off”, “feed label stock”, “cut label stock”, etc. 
     An internal battery or external power supply  132  is provided to energize the electronics  108  which may include a regulator circuit  134  for conditioning the power to a nominal voltage, V cc , for example 5 volts, provided to. the various components of the electronics  108 . The electronics  108  also includes a multi-channel analog-to-digital (A/D) converter  136  in communication with the FPGA  116 . The A/D converter  136  is connected to a plurality of printer sensors such as printer head thermistor  138  for sensing printer head temperature, ribbon sensor  140  to detect the presence of thermal transfer ribbon, paper sensor  142  to detect label stock in the printer head nip  104 , peeler sensor  144  to detect a dispensed label not yet removed from the area of the peeler bar  32 , and a paper supply sensor  146  for detecting when a roll of label stock disposed in the well  14  on the edge guides  16  is low. Since less energy is required for printing with a thermal ribbon, print mechanism activation or strobe times are decreased relative to printing on thermal paper labels without the thermal ribbon. The ribbon sensor  140  may be disposed in any of a variety of locations in the printer  10 , for example on the ramp  64  or frame  54 , in order to detect presence or absence of thermal ribbon in the general area of the printer head nip  104 . 
     In an exemplary embodiment, the microprocessor  110  of the printer electronics  108  is a Motorola  68340  microprocessor, the RAM  112  is 512 k bytes of RAM, the non-volatile memory  114  is 256 k bytes of non-volatile flash memory, and the FPGA  116  is a Xylinx XC3020A chip. The sensors may be infrared diode (emitter) and detector pairs which go high if there exists reflection from a white surface such as a label or web. 
     FIG. 8A is a flowchart of a printer operating system operation  152  in accordance with an embodiment of the present invention. A first step  154  is an initialization subroutine which is shown in FIG.  8 B. Referring to FIG. 8B, the FPGA  116  is configured for the printer head  52  and step motor  28  installed in the printer  10 . Thereafter, the display  128  and keypad  130  are set up, timers reset, and communications ports such as the serial port  120 , parallel port  122  and optional IR and SRRF ports  124 ,  126  set. The flash program in the non-volatile memory  114  is checked and any boot files executed. By depressing a feed key on the keypad  130  when the printer is first powered on, the printer  10  enters a diagnostic mode during initialization in which a series of diagnostic tests are performed and a report printed. 
     Referring once again to FIG. 8A, once initialization has been completed, all communications ports and input devices, such as the keypad  130  or optionally a bar-code scanner, are checked for data or commands. If there is none, a maintenance function step  156  is performed. As shown in FIG. 8C, the maintenance subroutine includes checks of any internal batteries or external power supply  132  with appropriate flashing LED indication for low battery and shut down for discharge condition. The keypad  130  is also checked and the optional cutter energized if the cut key is pressed. A programmed function is run if the feed key is pressed. Depending on a particular application, the programmed function can include feeding the label stock  102 , reprinting the last label  106 , or taking no action. 
     Referring again to FIG. 8A, if data or a command is available from an input source, the data or command is retrieved and merges with selected local files if the printer  10  is in a merge mode. In the alternative, a command interpreter step  158  executes one of a variety of functions, as shown in FIG. 8D, such as define file, use file, reprogram, form, reconfigure, status, and print. In the define file function, a file name and the contents thereof are retrieved and the file saved. In the use file function, merge mode is entered and a local file selected. In the reprogram function, a new printer program is retrieved through either the serial port  120 , parallel port  122 , or optional IR or SRRF ports  124 ,  126 . The form function executes a form feed, for example, advancing the label stock for a predetermined time period, a preselected distance, or until a next label is registered for printing. The reconfigure function changes operation parameters of the printer  10  such as baud rate, serial number, memory size, etc. The status function reports printer status such as condition of the battery, label stock supply, latch microswitch position, printer head contrast, software version, serial number, label odometer, etc. 
     If a print command is received, the command interpreter  158  enters a print step  160  as depicted in FIG.  8 E. The motor  28  is energized and the label stock  102  feed through the printer head nip  104  at low speed. Sensors such as ribbon sensor  140  are read so that printer head activation time can be calculated. Activation time is a function of a number of parameters including contrast, tone, voltage, dot density, printer head temperature read from the printer head thermistor  138 , thermal transfer ribbon presence, and motor speed. The motor  28  is stepped until all dot lines for the label  106  have been printed. Thereafter, the software loops, as depicted in FIG. 8A, awaiting additional data or commands. 
     While there have been described herein what are to be considered exemplary and preferred embodiments of the present invention, other modifications of the invention will become apparent to those skilled in the art from the teachings herein. The particular methods of manufacture of discrete components and interconnections therebetween disclosed herein are exemplary in nature and not to be considered limiting. It is therefore desired to be secured in the appended claims all such modifications as fall within the spirit and scope of the invention. Accordingly, what is desired to be secured by Letters Patent is the invention as defined and differentiated in the following claims.