Abstract:
A sensor apparatus for providing two sensing operations within a thermal printer includes a densitometer with at least one light source that discriminates color and that is positioned in a first position for sensing donor patches within the thermal printer; the densitometer while in a second position provides signals from printed receiver media for internal color calibration of the thermal printer. At least one reflector directs light from the light source to the densitometer through a donor web when the densitometer is in the first position; and a switchable device repositions the densitometer from either the first position or the second position.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to thermal printers that record images by transferring donor materials from a donor ribbon to a receiver medium. 
       BACKGROUND OF THE INVENTION 
       [0002]    In thermal printing, it is generally well known to render images by heating and pressing one or more donor materials such as dye, colorant or other coating against a receiver medium. The donor materials are provided in sized donor patches on a moveable web known as a donor ribbon. The donor patches are organized on the ribbon into donor patch sets, each donor patch set contains all of the donor patches that are to be used to record an image on the receiver medium. For full color images, multiple colored dye sets can be used, such as yellow, magenta and cyan donor dye patches. Arrangements of other color patches can be used in like fashion within a donor patch set. Additionally, each donor set can include an overcoat or sealant layer. 
         [0003]    It will be appreciated from this that it is necessary to neutrally calibrate the printer by methods known to those skilled in the art. This calibration is performed to ensure that the output performance of the thermal printer remains within tolerance from unit-to-unit and media set to media set. Such calibration can be done at the factory by means of multiple look-up-tables (LUTs), one for each color. Additionally, the thermal printhead voltage may be adjusted for the total range of printer operation. As this calibration is performed at the factory, there is no means to compensate for onsite variability involving printer usage, media changes and environmental conditions at the customer site. In some of these situations, better color adjustment is required to adjust the printer settings to compensate for these variables. 
       SUMMARY OF THE INVENTION 
       [0004]    Whereas an operator of a thermal printer may print and measure a neutral tone scale, calculate and download new LUTs into the thermal printer, it is desirable that the calibration measurement means be embedded within the printer, and the measurement operation be performed automatically with little or no operator intervention. This typically involves integration of an embedded color sensor, densitometer, calorimeter or spectrophotometer inside the printer to measure the reflection density of the multiple colors printed on the receiver. The reflection density of a neutral or color tone scale is typically measured. This data is used to make adjustments to the LUTs or other printing parameters to obtain optimum color rendition. 
         [0005]    Additionally, thermal color printers should preferably be able to distinguish the edges, position and color of the donor dye patches on the web. For donor webs with three-color dye patch sets, a three-color sensor is typically employed to sense the edges of said dye patches as the donor web is moving. This donor patch sensor assembly is in addition to and separate from the embedded reflection color sensor, densitometer, calorimeter or spectrophotometer (henceforth a reflection densitometer) inside the printer, which is used for the purposes of neutral or color calibration. 
         [0006]    According to the present invention, a thermal printer incorporating an embedded reflection densitometer used for the purpose of neutral or color calibration (henceforth calibration), has been designed to allow said embedded reflection densitometer to also sense donor patches while donor and receiver are moving, and therefore at a time when it is not needed to measure reflection density from a tone scale on printed receiver. This eliminates the requirement for a separate donor patch sensor assembly. While the specifications for the embedded densitometer are more stringent than for the donor patch sensor assembly, it is a device capable of discriminating color. This capability can be adapted and employed for the additional purpose of sensing color patch edges on moving donor and for positioning color patches for printing. 
         [0007]    In a first aspect of the invention, a sensor apparatus provides two sensing operations within a thermal printer. The sensor apparatus includes a densitometer, which discriminates color and is positioned in a first position for sensing donor patches within the thermal printer. When the single sensor is in a second position, it provides a signal for internal color calibration of a receiver media. A light source provides light to at least one reflector that directs the light towards the densitometer. A switchable device repositions the densitometer from either the first position or the second position. 
         [0008]    Repeatedly measuring the reflected color as the donor web is moving, allows detection of the color patch edges to be positioned for printing. The second position aims the densitometer aperture at the printed receiver, allowing reflection measurements on the printed receiver. A control system is provided to operate the mechanical articulation means, which may include a motor or a solenoid with a spring return, or other convenient method. The mechanical articulation means allow the spring to return the densitometer aperture to position  1  for normal operation including donor movement, and to drive the densitometer aperture to position  2  when required to reflectively measure the density of a completed print. 
         [0009]    In a second aspect of the invention, means can be provided to split the beam of light and use two mutually exclusive light sources to select between donor patch detection and reflection density measurement. The light sources can be monochromatic or multi-colored depending on the exact configuration desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a prior art thermal printer with a control system; 
           [0011]      FIG. 2  shows a bottom view of a typical thermal printhead used in the thermal printer of  FIG. 1 ; 
           [0012]      FIG. 3  shows a typical donor web with three color donor patches and one clear donor patch; 
           [0013]      FIG. 4  shows a thermal printhead, platen roller, donor web, and receiver medium during printing; 
           [0014]      FIG. 5  shows a thermal printhead, platen roller, donor web, and receiver medium during printing; 
           [0015]      FIG. 6  illustrates a thermal printer system of the present invention utilizing an articulating color sensor densitometer; 
           [0016]      FIG. 7  illustrates an example of a thermal printer system of the present invention utilizing a beam splitter; 
           [0017]      FIG. 8  illustrates an example of a color sensor (densitometer) enabled for a dual purpose by means of a beam splitter of the type used in  FIG. 7 ; 
           [0018]      FIG. 8A  illustrates another example of a color sensor (densitometer) enabled for a dual purpose by means of a beam splitter of the type used in  FIG. 7 ; 
           [0019]      FIG. 8B  illustrates an example of a reflection color sensor densitometer of the type used in  FIG. 6 ; and 
           [0020]      FIG. 9  illustrates an example of a calibration target with a corresponding plurality of dye patches constituting a tone scale. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  shows one embodiment of a conventional thermal printer of the prior art, 18. It shares many of the same features as that of the present invention. As shown in  FIG. 1 , thermal printer  18  has a printer controller  20  that causes printhead  22  to record images on a receiver medium  26  by applying heat and pressure to transfer material from a donor web  30  to receiver medium  26 . Printer controller  20  can include but is not limited to a programmable digital computer, a programmable microprocessor, a programmable logic controller, a series of electronic circuits, a series of electronic circuits reduced to the form of an integrated circuit, or a series of discrete components. In the embodiment of  FIG. 1 , printer controller  20  also controls a receiver medium take-up roller  42 , a receiver medium supply roller  44 , a donor web take-up roller  48  and a donor web supply roller  50 , which are each motorized for rotation on command of the printer controller  20  to effect movement of receiver medium  26  and donor web  30 . 
         [0022]      FIG. 2  shows a bottom view of an illustration of one embodiment of a conventional thermal printhead  22  with an array of thermal resistors  43  fabricated in a ceramic substrate  45 . A heat sink  47 , typically in the form of an aluminum backing plate, is fixed to a left side  49  of ceramic substrate  45 . Heat sink  47  rapidly dissipates heat generated by the thermal resistors  43  during printing. In the embodiment shown in  FIG. 2 , thermal resistors  43  are arranged in a linear array extending across platen roller  46  (shown in phantom). Such a linear arrangement of thermal resistors  43  is commonly known as a heat line or print line. However, other non-linear arrangements of thermal resistors  43  can be used. Further, it will be appreciated that there are a wide variety of other arrangements of thermal resistors  43  and thermal printhead  22  that can be used in conjunction with the present invention. 
         [0023]    Thermal resistors  43  are adapted to generate heat in proportion to an amount of electrical energy that passes through thermal resistors  43 . During printing, printer controller  20  transmits signals to a circuit board  51  to which thermal resistors  43  are connected causing different amounts of electrical energy to be applied to thermal resistors  43  so as to selectively heat donor web  30  in a manner that is intended to cause donor material from donor patch sets  32 . 1  and  32 . 2 , to be applied to receiver medium  26  in a desirable manner. 
         [0024]    As is shown in  FIG. 3 , donor web  30  comprises a first donor patch set  32 . 1  having a yellow donor patch  34 . 1 , a magenta donor patch  36 . 1 , a cyan donor patch  38 . 1  and a clear donor patch  40 . 1  and a second donor patch set  32 . 2  having a yellow donor patch  34 . 2 , a magenta donor patch  36 . 2 , a cyan donor patch  38 . 2  and a clear donor patch  40 . 2 . Each donor patch set  32 . 1  and  32 . 2  has a leading edge (L) and a trailing edge (T). In order to provide a full color image with a clear protective coating, the four patches of first donor patch set  32 . 1  and the second donor patch set  32 . 2 , etc. are printed, in registration with each other, onto a common image receiving area  52  of receiver medium  26  shown in  FIG. 4 . Circuit board  51  provides variable electrical signals to thermal resistors  43  in accordance with the signal from printer controller  20 . 
         [0025]    A first color is printed in the conventional direction, from right to left as seen by the viewer in  FIGS. 1 and 3 . During printing, printer controller  20  raises printhead  22  and actuates donor web supply roller  50  and donor web take-up roller  48  to advance a leading edge (L) of a first donor patch set  32 . 1  to printhead  22 . In the embodiment illustrated in  FIGS. 1 through 3 , leading edge (L) for first donor patch set  32 . 1  is defined by a leading edge of a yellow donor patch  34 . 1 . As will be discussed in greater detail below, the position of this leading edge (L) can be determined by using a position sensor of the prior art to detect a marking, indicia on donor web  30  that has a known position relative to the leading edge of yellow donor patch  34 . 1  or by directly detecting leading edge of yellow donor patch  34 . 1  as will be discussed in greater detail below. 
         [0026]    Printer controller  20  also actuates receiver medium take up roller  42  and receiver medium supply roller  44  so that image receiving area  52  of receiver medium  26  is positioned with respect to the printhead  22 . In the embodiment illustrated, image receiving area  52  is defined by a leading edge and a trailing edge on receiver medium  26 , (LER) and (TER), respectively. Donor web  30  and receiver medium  26  are positioned so that leading edge (L) of yellow donor patch  34 . 1  is registered at printhead  22  with leading edge (LER) of image receiving area  52 . Printer controller  20  then causes a motor or other conventional structure to (not shown) lower printhead  22  so that a lower surface of donor web  30  engages receiver medium  26 , which is supported by platen roller  46 . This creates a pressure holding donor web  30  against receiver medium  26 . 
         [0027]    Printer controller  20  then actuates receiver medium take-up roller  42 , receiver medium supply roller  44 , donor web take-up roller  48  and donor web supply roller  50  to move receiver medium  26  and donor web  30  together past the printhead  22 . Concurrently, printer controller  20  selectively operates heater elements in printhead  22  to transfer donor material yellow donor patch  34 . 1  to receiver medium  26 . 
         [0028]    As donor web  30  and receiver medium  26  leave the printhead  22 , a stripping plate  54  separates donor web  30  from receiver medium  26 . Donor web  30  continues over idler roller  56  toward the donor web take-up roller  48 . As shown in  FIG. 4 , the trailing edge receiver of image receiving area  52  (TER) of receiver medium  26  remains on platen roller  46 . Printer controller  20  then adjusts the position of donor web  30  and receiver medium  26  using a predefined pattern of donor web movement so that a leading edge of each of the remaining donor patches  36 . 1 ,  38 . 10 , and  40 . 1  in the first donor patch set  32 . 1  are brought into alignment with leading edge receiver of image receiving area  52  (LER) and the printing process is repeated to transfer further material as desired to complete image format. 
         [0029]    Printer controller  20  operates the thermal printer  18  based upon input signals from a user input system  62 , an output system  64 , a memory  68 , a communication system  74  and sensor system  80 . User input system  62  can comprise any form of transducer or other device capable of receiving an input from a user and converting this input into a form that can be used by printer controller  20 . For example, user input system  62  can comprise a touch screen input, a touch pad input, a 4-way switch, a 6-way switch, an 8-way switch, a stylus system, a trackball system, a joystick system, a voice recognition system, a gesture recognition system or other such systems. An output system  64 , such as a display, is optionally provided and can be used by printer controller  20  to provide human perceptible signals for feedback, informational or other purposes. 
         [0030]    Data including, but not limited to, control programs, digital images and metadata can also be stored in memory  68 . Memory  68  can take many forms and can include without limitation conventional memory devices including solid state, magnetic, optical or other data storage devices. In the embodiment of  FIG. 1 , memory  68  is shown having a removable memory interface  71  for communicating with removable memory (not shown) such as a magnetic, optical or magnetic disks. In the embodiment of  FIG. 1 , memory  68  is also shown having a hard drive  72  that is fixed with thermal printer  18  and a remote memory  76  that is external to printer controller  20  such as a personal computer, computer network or other imaging system. 
         [0031]    In the embodiment shown in  FIG. 1 , printer controller  20  has a communication system  74  for communicating external devices such as remote memory  76 . Communication system  74  can be for example, an optical, radio frequency circuit or other transducer that converts electronic signals representing an image and other data into a form that can be conveyed to a separate device by way of an optical signal, radio frequency signal or other form of signal. Communication system  74  can also be used to receive a digital image and other information from a host computer or network (not shown). Printer controller  20  can also receive information and instructions from signals received by communication system  74 . 
         [0032]    Sensor system  80  includes circuits and systems that are adapted to detect conditions within thermal printer  18  and, optionally, in the environment surrounding thermal printer  18  and to convert this information into a form that can be used by printer controller  20  in governing printing operations. Sensor system  80  can take a wide variety of forms depending on the type of media therein and the operating environment in which thermal printer  18  is to be used. 
         [0033]    In the embodiment of  FIG. 1 , sensor system  80  includes an optional donor position sensor  82  that is adapted to detect the position of donor web  30  and a receiver medium position sensor  84 . Printer controller  20  cooperates with donor position sensor  82  to monitor donor web  30  during movement thereof so that printer controller  20  can detect one or more conditions on donor web  30  that indicate a leading edge of a donor patch set. In this regard, a donor web  30  can be provided that has markings or other optically, magnetically or electronically sensible indicia between first donor patch set  32 . 1  and second patch set  32 . 2 . Where such markings or indicia are provided, donor position sensor  82  is provided to sense these markings or indicia and to provide signals to the printer controller  20 . Printer controller  20  can use these markings and indicia to determine when donor web  30  is positioned with the leading edge of the donor patch set at printhead  22 . In a similar way, printer controller  20  can use signals from receiver medium position sensor  84  to monitor the position of the receiver medium  26  to align receiver medium  26  during printing. Receiver medium position sensor  84  can be adapted to sense markings or other optically, magnetically or electronically sensible indicia between each image receiving area of receiver medium  26 . 
         [0034]    During a full image printing operation, printer controller  20  causes donor web  30  to be advanced in a predetermined pattern of distances so as to cause a leading edge of each of the first donor patches  34 . 1 ,  36 . 1 ,  38 . 1 , and  40 . 1  to be properly positioned relative to the first image receiving area  52 . 1  at the start each printing process. Printer controller  20  can optionally be adapted to achieve such positioning by precise control of the movement of donor web  30  using a stepper type motor for motorizing donor web take-up roller  48  or donor web supply roller  50  or by using a movement sensor  86  that can detect movement of donor web  30 . In one example, an arrangement using a movement receiver medium position sensor  84 , a follower wheel  88  is provided that engages donor web  30  and moves therewith. Follower wheel  88  can have surface features that are optically, magnetically or electronically sensed by movement sensor  86 . One example of this is a follower wheel  88  that has markings thereon indicative of an extent of movement of donor web  30  and a movement sensor  86  that has a light sensor that can sense light reflected by the markings. In other optional embodiments, perforations, cutouts or other routine and detectable indicia can be incorporated onto donor web  30  in a manner that enables movement receiver medium position sensor  84  to provide an indication of the extent of movement of the donor web  30 . 
         [0035]    Alternatively, donor position sensor  82  can also optionally be adapted to sense the color of donor patches on donor web  30  and can provide color signals to the printer controller  20 . In this alternative, printer controller  20  is programmed or otherwise adapted to detect a color that is known to be found in the first donor patch, e.g., yellow donor patch  34 . 1  in a donor patch set such as first donor patch set  32 . 1 . When the first color is detected, printer controller  20  can determine that donor web  30  is positioned proximate to the start of a donor patch set. 
         [0036]    In the prior art printer described above, and shown in  FIG. 1 , donor position sensor  82 , has only one function, which is to sense the color of donor patches on donor web to provide positioning information. In the present invention, this function is embodied in color sensor (e.g. densitometer)  486  and  486 . 1  shown in  FIGS. 6 and 7  respectively. Additionally, for this invention, color sensor densitometers  486  and  486 . 1  provide the second function for measuring the reflection density of the printed receiver. Thus, a single color sensor, in this case a densitometer, is enabled with dual functionality. 
         [0037]    The thermal printer schematic of the present invention  400  shown in  FIG. 6  includes a donor supply spool  410  for distributing a donor web  415 . A donor take-up spool  420  removes slack donor web  415 . A receiver medium  440  distributes receiver web  445 . Receiver web  445  and donor web  415  are merged together atop platen roller  450  and beneath a thermal ceramic printhead  460  that includes a peel bar member  470 . Subsequent to the thermal ceramic printhead  460  adhering donor material on the donor web  415  to the receiver web  445 , the peel bar member  470  separates the donor web  415  from the receiver web  445 . Donor web  415  continues to travel on to the donor take-up spool  420 , while the receiver web  445  travels between a pinch roller  480  and a micro-grip roller  485  that form a nip. 
         [0038]    Referring to  FIG. 6 , color sensor (densitometer)  486  can perform two functions, a donor position sensor when in position # 1  and a reflection densitometer when in position # 2 . The change in position means to move the color sensor (densitometer)  486  about pivot  487 . 
         [0039]    When color sensor (densitometer)  486  is acting as a donor position sensor, its color discrimination ability allows the donor patches to be identified by color and the donor patch edge position to be sensed by the printer controller  20 . Once the donor patch edge position is known by the controller, the beginning of said patch can be positioned for printing between the thermal ceramic printhead  460  and the platen roller  450 . Reference  FIG. 3  illustrates a representation of the donor patches: 34.1, 36.1, 38.1, 40.1 34.2, 36.2, 38.2, and 40.2. As the donor web  415  is transported through the printer, light from the color sensor (densitometer)  486  passes through the donor web  415  and reflects off reflector  488  and back into the color sensor (densitometer)  486 . In this manner, the position of the various donor patches, shown in  FIG. 3 :  34 . 1 ,  36 . 1 ,  38 . 1 ,  40 . 1 ,  34 . 2 ,  36 . 2 ,  38 . 2 , and  40 . 2 ; can be determined and positioned for printing between thermal ceramic printhead  460  and platen roller  450 . 
         [0040]    When printer calibration is required the color sensor (densitometer)  486  is switched to position # 2 , to measure the reflection density of the printed receiver. Referring to  FIG. 9 , a test target  700  is printed on the receiver web  445 . The test target contains a tone scale  701 , consisting of a plurality of discrete patches ranging from light to dark (low density to high density). Each patch is scanned by color sensor (densitometer)  486  as the printed receiver is passed under it to determine its reflection density. The density information is passed to a calibration algorithm in controller  489 , which can calculate new printing parameters to be utilized by controller  489  to make neutrally corrected and/or color corrected prints. Such calibration algorithms are known to those skilled in the art. 
         [0041]    Relating to the second aspect of this invention shown in  FIG. 7 , color sensor  486 . 1  provides dual functionality by a different mechanism. Instead of pivoting the color sensor between two positions to achieve the dual functionality, a beam splitter arrangement is utilized with two discrete light sources that are actuated from printer controller  20  in a mutually exclusive manner. Referring to  FIG. 8 , light source  501  is activated and light source  502  is deactivated to use color sensor (densitometer)  486 . 1  as a donor position sensor. As the donor web  415  is transported, light from the color sensor (densitometer)  486 . 1  passes through the donor web  415  and is reflected off reflector  488 . 1  and back into the color sensor (densitometer)  486 . 1 . In this manner, the position of the various donor patches, shown in  FIG. 3 :  34 . 1 ,  36 . 1 ,  38 . 1 ,  40 . 1 ,  34 . 2 ,  36 . 2 ,  38 . 2 , and  40 . 2 ; can be determined and positioned for printing between thermal ceramic printhead  460  and platen roller  450  in a similar fashion to that described above. 
         [0042]    When the color sensor (densitometer)  486 . 1  in  FIG. 8 , has light source  501  deactivated and light source  502  activated, the printed receiver density can be measured for the purpose of neutral or color calibration in a similar fashion to that described above. Referring to  FIG. 9 , a test target  700  is printed on the receiver web  445 . The test target contains a tone scale  701 , consisting of a plurality of discrete dye patches ranging from light to dark (low density to high density). Each patch is scanned by color sensor (densitometer)  486  as the printed receiver is passed under it to determine its reflection density. The density information is passed to a calibration algorithm in controller  489 , which can calculate new printing parameters to be utilized by controller  489  to make neutrally corrected and/or color corrected prints. Such calibration algorithms are known to those skilled in the art. 
         [0043]    An example of color sensor (densitometer)  486  is shown in  FIG. 8B , which contains sensor  492  and light source  491  reflecting off receiver medium  445 . Many such custom or commercially available densitometers can be utilized for this purpose, such as the X-Rite™ il®. 
         [0044]    Another embodiment of a color sensor (densitometer)  486 . 2  utilizing a beam splitter  503  and two light sources  601  is shown in  FIG. 8A , where the reflector has been eliminated in favor of placing the light source  601  on the opposite side of donor web, eliminating the need for a reflector  488 . 1  in  FIG. 8 . This will improve the signal to noise ratio at the sensor. 
         [0045]    The initial printer settings can be established for example during an initial set up phase at a manufacturer&#39;s facility or elsewhere. However, because many aspects of printing, particularly color printing, are influenced by environmental conditions, printing process variations, and donor and receiver material variations, it is understood that, from time to time, it may be useful to recalibrate the initial printer settings to ensure that the colors that are printed correspond to colors called for in the print data. Such times can be determined, for example, when a user makes a request that the printer settings be recalibrated. Alternatively, controller  489  ( FIGS. 6 and 7 ) can be adapted to perform calibration when a sensor (not shown) indicates that either receiver medium  440  or a donor material supply  410  has been changed or replenished, when a receiver medium or donor material type is changed, or when there has been a meaningfil shift in ambient temperature, humidity or other environmental conditions since a time of the last calibration. In still other alternative embodiments, controller  489  can monitor factors such as the number of prints since the last printer calibration of the printer settings and an amount of time since the last calibration to determine when printer settings should be recalibrated. In yet another embodiment, controller  489  can be adapted to determine that printer settings should be recalibrated on a periodic basis such as at a particular time of a day or week. In a further embodiment, controller  489  is adapted to print a calibration verification mark during the printing of images and to sense the color of the calibration verification mark, controller  489  can determine that a need for calibration of printer exists based upon whether the color of the calibration verification mark is within a range of acceptable colors. See, for example, the procedures described in U.S. Pat. No. 7,271,935, issued on Sep. 18, 2007, in the names of Coons et al. 
         [0046]    For all of the embodiments described above, practical specifications will put additional constraints on the color sensor to have it utilized as a reflection densitometer. Such a sensor, so configured as a reflection densitometer, can then be utilized as a donor position sensor. Additional sensor embodiments might be realized that maintain the spirit of this invention. 
         [0047]    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 
       [0000]    
       
           18  thermal printer 
           20  printer controller 
           22  printhead 
           26  receiver medium 
           30  donor web 
           32 . 1  first donor patch set ( 34 . 1 ,  36 . 1 ,  38 . 1 , and  40 . 1 ) 
           32 . 2  second donor patch set ( 34 . 2 ,  36 . 2 ,  38 . 2 , and  40 . 2 ) 
           34 . 1  yellow donor patch 
           34 . 2  yellow donor patch 
           36 . 1  magenta donor patch  036 . 2  magenta donor patch 
           38 . 1  cyan donor patch 
           38 . 2  cyan donor patch 
           40 . 1  clear donor patch 
           40 . 2  clear donor patch 
           42  receiver medium take-up roller 
           43  thermal resistors 
           44  receiver medium supply roller 
           45  ceramic substrate 
           46  platen roller 
           47  heat sink 
           48  donor web take-up roller 
           49  left side of ceramic substrate 
           50  donor web supply roller 
           51  circuit board 
           52  image receiving area 
           54  stripping plate 
           56  idler roller 
           62  user input system 
           64  output system 
           68  memory 
           71  removable memory interface 
           72  hard drive 
           74  communication system 
           76  remote memory 
         80 sensor system 
           82  donor position sensor 
           84  receiver medium position sensor 
           86  movement sensor 
           88  follower wheel 
           400  thermal printer schematic 
           410  donor supply spool 
           415  donor web 
           420  donor take-up spool 
           440  receiver medium 
           445  receiver medium 
           450  platen roller 
           460  thermal ceramic printhead 
           470  peel bar member 
           480  pinch roller 
           485  micro-grip roller 
           486  color sensor (densitometer) 
           486 . 1  color sensor (densitometer) 
           486 . 2  color sensor (densitometer) 
           487  pivot 
           488  reflector 
           488 . 1  reflector 
           489  controller 
           491  light source 
           492  sensor 
           501  light source (light source # 2 ) 
           502  light source (light source # 1 ) 
           503  beam splitter 
           601  light source 
           700  test target 
           701  tone scale 
         L leading edge 
         LER leading edge receiver 
         T trailing edge 
         TER trailing edge receiver