Abstract:
A hard copy recording device for transferring images to media, the hard copy recording device including an engine, a controller, a first non-volatile memory, and a second non-volatile memory. The engine transfers images to the media in response to control signals. The controller provides the control signals to the engine based upon image data and a first non-volatile memory stores recording device system data accessible by processes executing at the controller. The second non-volatile memory stores a copy of selected portions of the recording device system data, the second non-volatile memory being detachably coupled to the hard copy recording device and capable of being coupled to a second hard copy recording device for downloading the selected portions of the recording device system data to the second hard copy recording device.

Description:
RELATED APPLICATIONS 
   This application is a continuation application of U.S. patent application Ser. No. 11/521,267, filed Sep. 14, 2006, now abandoned which is a divisional application of U.S. patent application Ser. No. 10/998,870, filed Nov. 29, 2004, now U.S. Pat. No. 7,116,343, which is a divisional application of U.S. patent application Ser. No. 09/995,385, filed Nov. 26, 2001, now U.S. Pat. No. 6,825,864. 

   BACKGROUND 
   1. Field of the Invention 
   Embodiments of the present invention are directed to printing systems. In particular, embodiments of the present are directed to printing systems capable of transferring images to different types of media. 
   2. Related Art 
   High quality imaging for precision applications such as medical diagnostics typically require the use of large and expensive photographic equipment. This equipment is typically large, bulky and expensive. Additionally, such photographic equipment is difficult and costly to maintain. 
   Advancements in printer technology have enabled the use of stand-alone printers to provide high quality printing. Such printer technology has eliminated the need for costly and inconvenient photographic laboratories. Printing systems can perform precision imaging using processes such as direct thermal imaging or dye diffusion imaging on opaque media or transparent film. Unfortunately, typical systems for performing dye diffusion or direct thermal printing to provide image quality suitable for medical diagnostics are very costly. Additionally, these printers are typically bulky and occupy valuable space in a work environment. Furthermore, an operation which relies on precision requiring direct thermal and dye diffusion printer capabilities, such as a medical diagnostic center, typically needs to purchase and maintain two separate printers, one for direct thermal imaging and one for dye diffusion printing. The purchase and maintenance of multiple printers further contributes to high costs and inconvenience associated with typical printing systems used in environments requiring precision imaging. 
   There is, therefore, a need for simpler and more cost effective alternative for providing precision imaging capabilities to enterprises. 
   SUMMARY 
   An object of an embodiment of the present invention is a system and method of providing precision image quality suitable for medical diagnostics in a cost effective manner. 
   Another object of an embodiment of the present invention is to provide a system and method of transferring images to media sheets of varying sizes. 
   Another object of an embodiment of the present invention is to provide images on media with image quality suitable medical diagnostics or other high precision application from a system which does not occupy a large amount of space. 
   It is yet another object of an embodiment of the present invention to eliminate the need for multiple printers for performing different types of image transfer processes. 
   Briefly, an embodiment of the present invention is directed to a printer which is capable of performing either direct thermal imaging or dye diffusion imaging from a single printhead and through a single media path. Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example various features of embodiments of the invention. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  shows a perspective view of a multi-media printer according to an embodiment of the present invention with a top panel of the printer removed to expose a picker assembly. 
       FIG. 2  shows an exploded view of the multi-media printer exposing a chassis behind housing panels. 
       FIG. 3A  shows a view of the multi-media printer with a top panel of the enclosure removed and exposing a picker assembly. 
       FIGS. 3B and 3C  show an alternative embodiment for a picker assembly. 
       FIG. 3D  shows a side view of a picker arm in a lowered position. 
       FIG. 4  shows a view of the multi-media printer exposing picker assemblies associated with media tray cavities. 
       FIG. 5  shows a view of the multi-media printer exposing a mechanism for driving the picker assemblies illustrated in  FIG. 4 . 
       FIG. 6  shows a view of the multi-media printer behind a side panel of the enclosure exposing a drive mechanism. 
       FIG. 7  shows a rear view of the multi-media printer illustrating external vents in the enclosure thereof. 
       FIG. 8  shows a frontal perspective view of the multi-media printer with enclosure panels removed. 
       FIG. 9A  shows a view of the multi-media printer with a side panel of the enclosure removed to expose a mechanism for applying torque to a platen roller from a stepper motor. 
       FIG. 9B  shows a capstan and pinch roller combination according to an embodiment of the multi-media printer. 
       FIG. 9C  shows an embodiment of a spring loaded pinch arm for securing a pinch roller against a fixed capstan roller. 
       FIG. 9D  shows an embodiment of media tray sensors for detecting the presence or absence of media in media trays. 
       FIG. 9E  shows an embodiment of a mechanism for moving the pinch roller around the fixed capstan roller. 
       FIG. 10A  illustrates a drive mechanism for moving a bar code scanner according to an embodiment. 
       FIGS. 10B and 10C  show front and side views, respectively, of an embodiment of the bar code scanner illustrated in  FIG. 10A . 
       FIGS. 10D and 10E  show side and perspective views, respectively, of an embodiment of a removable output tray with kicker assemblies. 
       FIG. 11A  illustrates holes in a chassis wall of the media printer for securing the drive shafts of the platen and capstan rollers according to an embodiment. 
       FIG. 11B  illustrates the orientation of the platen, and capstan as being secured in the holes in a chassis wall of the embodiment of  FIG. 11A . 
       FIG. 11C  illustrates forces acting on the platen and capstan roller shafts for securing the position of the shafts against the “V” blocks of the holes of the chassis wall illustrated in  FIGS. 11A and 11B . 
       FIG. 12  shows a view of the multi-media printer exposing a media wall as part of an input path for receiving media sheets dispensed from media trays. 
       FIG. 13  shows a view of the multi-media printer illustrating the position of the power supply with respect to the printhead according to an embodiment. 
       FIG. 14  shows a side view of the chassis of a multi-media printer according to an embodiment. 
       FIG. 15A  illustrates an embodiment of the movement of the printhead and donor carriage when transitioning between direct thermal and dye diffusion according to an embodiment of the multi-media printer. 
       FIG. 15B  depicts a mechanism that may be used to drive a donor ribbon take-up spool according to an embodiment of the invention. 
       FIG. 16  shows a cross-sectional view of the multi-media printer illustrating an input path for transferring media sheets from media trays to a print station according to an embodiment. 
       FIG. 17A  shows an enlarged view of the print station of  FIG. 16  with an anti-vibration surface according to an embodiment. 
       FIG. 17B  shows an alternative embodiment of the printhead assembly that employs a movable bracket assembly for securing the printhead heat sink to the torque tube housing. 
       FIG. 17C  shows an enlargement of the movable bracket assembly illustrated in  FIG. 17B . 
       FIG. 18  shows a view of the multi-media printer illustrating an output diverter according to an embodiment. 
       FIG. 19  shows a printhead assembly according to an embodiment. 
       FIG. 20  shows an enlarged view of the printhead assembly according to an embodiment. 
       FIG. 21  shows an enlarged view of the printhead assembly illustrating a sealed channel for providing external air to the heat sink of the printhead according to an embodiment. 
       FIG. 22  is shows a view of the multi-media printer illustrating a kicker assembly associated with the removable output tray illustrated in  FIGS. 11D and 11E . 
       FIG. 23  shows an embodiment of the side edge sensors according to an embodiment. 
       FIG. 24  shows an embodiment of a donor ribbon having a side bar code according to an embodiment. 
       FIG. 25  shows an embodiment of a printhead bead having an imaging surface geometry suitable for either direct thermal or dye diffusion printing. 
       FIGS. 26 and 27  show an embodiment of a “U” shaped structure for thermal elements in a printhead and a bead geometry achievable from same. 
   

   DETAILED DESCRIPTION 
   Embodiments of the present invention are directed to a multi-media printer capable of transferring images to media using either direct thermal or dye diffusion imaging process. Multiple media trays are adapted to dispense media sheets to a single input path. The media trays may dispense different sizes and types of media for direct thermal or dye diffusion printing. A print station including a printhead receives media sheets from the input path fed by multiple media input trays. The print station may be configurable in real-time to transfer images to media using either the direct thermal or dye diffusion imaging process. In embodiments of the invention, a single motor may drive a capstan roller, a platen roller and kicker assemblies for output trays. This allows for a reduced size and cost while providing superior image quality suitable for medical imaging. Other embodiments described herein are directed to providing additional cost and size advantages, as well as improvements in media selection and identification capabilities and image quality using the direct thermal and dye diffusion imaging processes. 
   Embodiments of the multi-media printer described herein are capable of dispensing media sheets from anyone of a plurality of media input trays. The media trays may hold stacks of media sheets of different sizes (e.g., 8.0×10 inches, 8.5×11 inches, 14×17 inches, etc.) and/or different media types (e.g., opaque media for direct thermal imaging, opaque media for dye diffusion imaging, transparent film for direct thermal imaging and transparent media for dye diffusion printing). Thus, each media input tray may hold a stack of media sheets of an associated media size and media type. The media printer may include a separate picker assembly associated with each of the input trays for individually dispensing media sheets to a common input path. 
   The print station includes a platen roller and a printhead which is capable of transferring an image to media sheets dispensed from the input trays using either a dye diffusion or direct thermal printing process. When employing the dye diffusion process, a donor carriage may provide a multi-colored dye diffusion donor ribbon between the printhead  151  (in  FIG. 11C ) and a sheet of receiving media. The donor ribbon may provide any one of several color combinations such as cyan, magenta and yellow (CMY); CMY and black; and CMY and laminate. When the printer performs direct thermal imaging onto a subsequent media sheet, the donor ribbon may be removed so that the printing is applied directly to the subsequent media sheet. Accordingly, the multi-media printer of the illustrated embodiment can perform either dye diffusion or direct thermal imaging from a single print station that receives media sheets from a single input path. A capstan and pinch roller combination may translate the imaged media through a common discharge path. The media may then be diverted to anyone of a plurality of output trays. 
     FIG. 1  shows a perspective view of an embodiment of the multi-media printer. Input media cavities  6  may be adapted to receive input media trays (not shown) as described in U.S. patent application Ser. No. 08/979,683, filed on Nov. 26, 1997, entitled “System and Method for Dispensing Media for Capturing Images,” assigned to Codonics Inc., and incorporated herein by reference. The multi-media printer may include compartments for housing various electro-mechanical systems for controlling the printer. For example, compartment  2  may include a central printer controller such as a 600 megahertz Pentium printer controller (not shown), which may be used as a printer controller among other functions, and which may be combined with a motor control board (not shown). Alternatively, the printer controller and motor control board may be separated in a motherboard/daughterboard combination. 
     FIG. 2  shows a perspective view of the multi-media printer with enclosure components removed exposing a chassis thereof. The chassis includes side walls  10 . As shown in  FIG. 9A , the chassis may further include a base  75  and a cross chassis  73  forming a back portion, a bottom portion coupled to the base  75  and side portions coupled to each of the sides  10 . The compartment  2  may include a bay for securing a removable memory device  8  (e.g., a high density disk drive, such as a Zip drive sold by Iomega). 
     FIG. 3A  shows an embodiment of the multi-media printer with a top panel of the enclosure removed while exposing a picker assembly  12 . In the illustrated embodiment, each of the media input cavities  6  is associated with a separate picker assembly  12 . Each of the picker assemblies  12  includes two picker tires  13  to provide a lateral force to the top sheet in a stack of media disposed within the respective media tray when the tires are rotated. In response to the lateral force, the top sheet is translated, causing the top sheet to be dispensed from the media tray through a media input path to a print station. As discussed below, each of the picker assemblies  12  receives a source of torque from a single source of torque at DC servo motor  30  (shown in  FIG. 4 ). The DC servo motor  30  may receive signals from the printer controller to control the speed and rotational displacement of the DC servo motor. The DC servo motor  30  may include an encoder to directly or indirectly measure its rotational displacement, speed, etc. The DC servo motor  30  may also include one or more optically detectable flags and a sensor for detecting the flag to provide a feedback signal to the printer controller for controlling the speed and displacement. 
   This structure eliminates the need for having a separate picker motor for each of the picker assemblies  12 , permitting a reduced size and cost for the printer. The single source of torque causes the picker tires  13  of each of the picker assemblies  12  to rotate simultaneously. When a particular media tray is selected to dispense its top media sheet, the picker tires  13  of the corresponding picker assembly may be lowered to the top sheet of the selected media tray to provide the aforementioned lateral force until the leading edge of the dispensed media sheet reaches the print station. After such time the picker tires  13  may be lifted from the stack of media sheets. In the embodiment shown in  FIG. 3A , the picker tires  13  are rotated using a side belt drive  16 . 
     FIGS. 3B ,  3 C and  3 D illustrate an alternative embodiment of the picker assembly  12  in which the picker tires  13  are rotated in response to a torque applied by a center belt  222  located between the picker tire  13 . A picker drive shaft  223  receives a torque from the center belt  222  for rotating the picker tire  13 . The picker drive shaft  223  is fixed at a pivot point  228  such that the picker drive shaft  223  can rotate in directions (illustrated by arrows  230 ) in a plane substantially normal to the top sheet and the media stack. As illustrated, the pivot point  228  may be a pivot bushing joining two separate shafts to form the picker drive shaft  223 . By having a center belt  222  and allowing the picker tires to move in the direction  230  along with the drive shafts  223 , the force applied by the picker tires  13  to the top sheet of media is substantially evenly distributed between the picker tires  13 . This prevents skewing of the media sheets while being dispensed from the media trays when a greater lateral force is being applied to the media sheet by one of the picker tires  13 . 
     FIGS. 3C and 3D  show a side view of a picker arm  231  in a raised and lowered position, respectively, according to an embodiment of the invention. In the embodiment of the invention shown in  FIG. 3B , a picker assembly  12  may have a picker arm  231  on each side of the center belt drive  222 . The picker arm  231  may include a diagonal slot  226  which receives the drive shaft  223 . When the picker arm  231  is in the lowered position to apply a lateral force to the top media sheet from the picker tire  13 , the diagonal slot  226  may be aligned so as to be substantially vertical to the bottom media sheet. The length of the diagonal slot may thus serve to limit the range of movement of the picker arm  13  in the direction normal to the top sheet (shown by arrows  230 ). When the picker arm  231  is in a position such that the picker tires  13  are not touching the bottom sheet of a stack of media or the bottom of the media tray, the diagonal slot creates a lifting force vector. This creates a negative feedback so one tire does not grab more than the other, by allowing the shaft  223  to move in the vertical direction (i.e., direction  230 ) to balance the forces on the media sheet applied by the two picker tires  13 . In the illustrated embodiment, picker tires  13  may be made of a spongy rubber composition having a width of up to 1½″ and a diameter of about ⅝″ to provide optimal traction to many different types of media to be dispensed from the media trays. 
   Returning to an embodiment in which side drive belts  16  are used,  FIG. 4  illustrates a mechanism for raising and lowering the picker assemblies  12 . Each of the picker assemblies  12  is coupled to a torque shaft  32  for driving the side drive belts  16  to rotate the picker tires  13  in response to the DC servo motor  30 . Each of the picker assemblies  12  includes a sheet metal arm  17  that may be rotated to raise and lower the picker tires  13 . Torsion springs  34  apply torque through members  19  to each of the sheet metal arms  17  in a direction that raises the picker assembly  12 . Torque springs  36  apply a torque to the sheet metal arms  17  in the opposite direction of the torque of torsion springs  34 . If the torque applied by torsion springs  34  is greater than the torque applied by torsion springs  36 , the picker assemblies  12  are maintained in a position such that the picker tires  13  are raised above the top sheet in the media tray. 
   As discussed below, a motor  30  raises and lowers a bar code scanner for reading a bar code on the side of media trays as illustrated on the aforementioned U.S. patent application Ser. No. 08/979,683. As the bar code scanner moves to a media tray position, the corresponding torsion spring  34  is pulled back, reducing its torque on the sheet metal arm  17  of the selected picker assembly  12 , to allow the corresponding torsion spring  36  on the same sheet metal arm  17  to lower the picker tires  13 . The torque translates to the lateral force of the picker tires  13  of the lowered picker assembly  12  against the top media sheet in the selected tray to translate the top sheet through the input path. 
     FIG. 6  shows a perspective view of the multi-media printer with all enclosures removed. A donor lift motor  38  may provide torque to a jack shaft  40  to move timing belts  42  to raise or lower a donor donor spool (not shown) attached to the timing belts  42  at each end. The timing belts  42  may raise or lower the donor spool depending upon whether the multi-media printer is to imprint an image on the media using a direct thermal or dye diffusion process. If the printer is to use a direct thermal process, the timing belts  42  may raise the donor spool to remove the donor ribbon from between the printhead  151  (in  FIG. 11C ) and the media receiving the image. If the printer is using a dye diffusion process, the timing belts  42  may conversely lower the donor spool to extend the donor ribbon between the printhead  151  (in  FIG. 11C ) and the receiving media. A five-phase stepper motor  44  may provide a belt-driven torque to a capstan shaft  52  using a belt tension idler  46 . A platen shaft  54  may be selectively clutched with the capstan shaft  52  to drive a platen as discussed below with reference to  FIG. 9 . The five-phase stepper motor enables the printer controller to accurately control the rotations of the capstan roller and platen using pulse encoded signals. 
   A worm gear (not shown) enclosed within worm gear housing  56  is driven by worm gear motor  58  to control the torque applied by a torque arm to the printhead  151  (in  FIG. 11C ) as discussed below with reference to  FIGS. 15 and 20  in response to control signals from the printer controller. 
     FIG. 7  shows a rear view of the multi-media printer which may include vents for cooling a power supply  138  ( FIG. 13 ), a printhead  151  (in  FIG. 11C ), and a printer controller and other electronics disposed within the compartment  2  ( FIG. 1 ). In the illustrated embodiment, these vents allow air to circulate about the heat sink, power supply and electronics disposed within the compartment  2  while remaining insulated from the print station. This reduces the amount of dust and particulates that may interfere with the direct thermal or dye diffusion processes occurring at the printhead  151  (in  FIG. 11C ) resulting in artifacts. Intake vent  70  and exhaust vent  72  allow external air to circulate through to the power supply  138  under the power of a fan (not shown). Similarly, printhead vents  62  and  63  allow air to circulate to a heat sink of the printhead  151  (in  FIG. 11C ) under the power of one or more fans (not shown). Printhead vents  62  and  63  each have eight vertically arranged horizontal slits. The lower five slits of the printhead vents  62  and  63  provide intakes and the upper three slits of printhead vents  62  and  63  provide exhausts. Again, as illustrated below with reference to  FIG. 21 , the air circulated through the vents  62  and  63  is insulated from the print station. Vents  66  and  68  permit air to circulate through to the printer controller and other electronics while maintaining insulated from the print station under the power of a fan. Vent  66  provides an intake while vent  69  provides an exhaust. 
     FIG. 8  shows a perspective view of the multi-media printer with the enclosure pieces removed so as to illustrate components of an output diversion mechanism discussed more thoroughly below with respect to  FIG. 18 . 
     FIG. 9A  shows another perspective view of the multi-media printer with the enclosure covers removed. A pinch roller  77  is in contact with a capstan roller  79  which receives media sheets receiving printed images from the printer (not shown). Capstan drive  80  receives a torque from stepper motor  44  ( FIG. 6 ) through a compliant belt as discussed above. A platen gear  82  may be moved inward or outward by an arm  84  to form a clutch mechanism for applying and removing torque to the platen shaft  54  ( FIG. 6 ). This clutch mechanism receives torque from the capstan gear  86  to rotate the platen roller  76 . The capstan drive  80  also engages a compliant belt drive  90  for transferring torque to output kickers after the media passes the print station to be dispense into an output tray  113  ( FIG. 22 ). Accordingly, a five-phase stepper motor  44  may provide a single source of torque for rotating the capstan drive  80  which may be engaged with the clutch to rotate the platen roller  76  and transfers torque to output kickers through belt drive  90 . 
     FIG. 9B  shows a pinch and capstan roller combination in which a pinch roller  77  is composed of a soft, elastic (e.g., spongy) substance and the roller  79  is rigid and substantially non-deformable. The capstan roller  79  may be coated to provide a high coefficient of static fraction when in contact with the media sheets. This combination provides a substantial surface area of contact of the media sheet with the pinch and capstan rollers  77  and  79 , and prevents slippage of the media with respect to the capstan roller  79 . Accordingly, the surface speed of the capstan roller  79  and the surface speed of the media sheet are substantially the same. The surface of the capstan roller  79  may be formed (e.g., by coating) to provide sufficient traction for multiple dye diffusion passes without marring imaged or unimaged film, transparency or other media. In one embodiment, the outer surface of the capstan roller  79  may be coated with a plasma substance to provide the necessary traction for dye diffusion printing while not marring scratchable film or transparencies. 
     FIG. 9C  shows an enlarged view of the pinch arm  98  that forces the pinch roller  77  against the capstan roller  79 . The pinch arm  98  includes a slot  101  for securing the shaft of the pinch roller  77 . Hole  100  provides a pivot point while hole  99  receives a force from spring  96  ( FIG. 9A ). While  FIG. 9A  only shows one pinch arm  98  at one side of the pinch roller  77 , it will be understood that a similar pinch arm  98 , while not shown, exists at the opposite side of the pinch roller  77 . A rod  89  fits in each of the holes  99  of the two pinch arms. The rod  89  may be moved in a direction opposite to the desired direction of movement of the pinch roller to rotate the pinch arms  98  about their respective pivot holes  100  to force the pinch roller  77  against the capstan roller  79 . 
   As shown in  FIG. 9E , two gear driven arms  314  position the pinch roller  77  radially with respect to the capstan roller  79 . These arms are driven by a gear train  316 . A DC servo motor  315  with a built in position encoder may supply the torque to drive the gear train  316 . In embodiments of the invention, the gear train  316  may be driven by the same DC servo motor  30  that is used to rotate the picker tires  13  of the picker assemblies  12 . 
     FIG. 9A  shows an embodiment of the present invention in which sources  102  and sensors  103  are located on each side of the media tray cavities. A source  102  and sensor  103  pair on opposite sides of the media tray cavities is associated with each media tray  87 .  FIG. 9D  illustrates how the sources  102  and sensors  103  may be used to detect whether a media tray  87  is empty. A source  102  transmits light to the top sheet  83  of a stack of media in a media tray  87 . The corresponding sensor  103  receives light reflected from the top sheet  83 . A bottom surface  81  of the media tray  87  does not reflect light from the transmitting source  102  to the receiving sensor  103 . This can be accomplished by, among other things, providing a rough, deflected or non-reflective surface on the bottom  81  facing upwards. As long as there are media sheets in the media tray  87 , the receiving sensor  103  may receive a reflection of the light transmitted by the transmitting source  102 . When the receiving sensor  102  no longer receives a reflection, it may be determined that the media tray  87  is empty. Therefore, when the information gathered from the aforementioned optical system is used in conjunction with bar code scanning information received from the bar scan coder described in the aforementioned U.S. patent application Ser. No. 08/979,683 and below, the printer controller in the media printer can determine the type and size of media in each tray loaded to the printer, and whether any of these trays are empty. The optical system described is also advantageous because its components are not embedded in the media tray  87 . 
   In embodiments in which optical components are embedded in the media tray  87 , the media tray  87  may be inserted into the media tray cavity so as to engage an electrical connector so that the signal from the embedded component may be transmitted to the printer controller. In such embodiments in which opaque or translucent media are used, the source  102  may be located above the media stack and the sensor may be located in the bottom surface of the media tray (or vice versa). A significant increase in the amount of light received by the sensor may indicate that the tray is empty. 
   Furthermore, in embodiments of the invention, a sensor  103  may extend laterally downward and may be comprised of multiple optically-sensitive areas. In such embodiments, the location at which the light from the source  102  is received by the sensor  103  may indicate the height of the media stack. This information may be used by the printer controller to indicate to a user when the media stack should be replenished. 
   Moreover, in the embodiment of the present invention shown in  FIG. 9D , the light from the source  102  may be relatively unfocused so that it is received by the sensor  103  regardless of the height of the media stack. For example, the source  102  may be a bulb or lamp. Alternatively, the source may be a focused or coherent source and may be moved so that the direction at which light is emitted may be changed until light reflected from the top sheet  83  is received by the sensor  103 . In such embodiments, the direction at which the source  102  emits light may be used by the printer controller to determine the height of the media stack, so that the user may be warned when the media stack should be replenished. 
     FIG. 9A  also shows holes  104  on opposite sides of output trays  113  ( FIG. 22 ) which provide electric eyes across each output tray  113 . The electric eyes detect when a corresponding output tray  113  is full. 
     FIG. 10A  shows a perspective view of the multi-media printer with enclosure panels removed to illustrate the belt drive to the capstan and a bar code scanner for the media trays. The five-phase stepper motor  44  drives a compliant belt  126  through a belt tension idler  46 . Knob  128  may provide a manual override for raising and lowering the printhead  151  (in  FIG. 11C ). 
   Bar code scanner  110  is raised and lowered by a drive mechanism  114 . When a media tray is inserted into the printer, drive mechanism  114  moves bar code scanner  110  in position to read a bar code on the side of the inserted media tray. This bar code identifies the size and type of the media loaded therein. Mechanism  114  is driven by the DC servo motor  30  which is also used for lowering the picker tires  13  of the picker assemblies  12  ( FIG. 4 ). A catch attached to the drive mechanism  114  at about the bar code scanner  110  provides an opposing force to the torsion springs  34  as the bar code scanner is positioned to read the bar code of associated media tray. This opposing force on the associated torsion spring  34  allows the torsion spring  36  to lower the picker tires  13  onto the top sheet of the media tray. 
   Mechanism  116  locks a top donor door (not shown). When the mechanism  114  raises the bar code scanner  110  to the top in contact with the mechanism  116 , the mechanism  116  unlocks the donor door. 
     FIGS. 10B and 10C  are directed to an embodiment of the bar code scanner  110  for identifying the contents of the individual media holders (e.g., media size, type and lot number). Media holders  220   a ,  220   b , and  220   c , each include a bar code label  222   a ,  222   b , and  222   c  respectively. The bar code labels  222   a ,  222   b , and  222   c  are preferably located on a side perpendicular to the front wall portion of the media holder on a portion which is inserted into the printer for use and represent at least 80 bits of information. 
   A vertical track  230  ( FIG. 10A ) positions a movable optical system included in an elevator housing  234  to position optical elements therein to selectively read from any of the individual bar code labels  222   a ,  222   b , or  222   c .  FIG. 10C  shows the assembly of the optical elements disposed within the elevator housing  234  which include a bar code scanner element  224  and a mirror  232 . According to an embodiment, the drive mechanism  114  ( FIG. 10A ) can selectively position the elevator housing  234  to receive an optical signature from any of the bar code labels  222   a ,  222   b , or  222   c.    
   The bar code scanner element  224  may be a commercially-available LM 500 plus scanner. Alternatively, other bar code scanning systems may be used. The elevator housing  234  may also include a small infrared sensor (not shown) for detecting an optical flag (not shown) on the side of the media trays  220   a ,  220   b  and  220   c . As the elevator housing  234  travels vertically, detections from the infrared sensor may initiate feed-back signals back to a circuit (not shown) for controlling the motor  30  and drive mechanism  114  which drives the elevator housing  234  to accurately position the optical elements to read the bar code labels. Alternatively, position can be determined by a built in optical position encoder on the DC servo motor  30 . In other embodiments of the invention, the position of the elevator housing may be determined by changes in readings taken by the bar code scanner element  224 . In such embodiments, the bar code labels  222   a - 222   c  may have a readable mark on a leading edge (or some other known location thereon). 
   The bar code labels  222   a ,  222   b , and  222   c , may be used to support various automation features of the printer. For example, the media trays may be for a single use only. Thus, the manufacturer may provide the customer with sealed media trays as illustrated in  FIG. 24  of the aforementioned U.S. patent application Ser. No. 08/979,683. Each of the media trays would then have a bar code label with a unique code. When the media tray is then inserted into the printer for a first use, the printer positions the optical elements within the elevator housing  234  to read the bar code from the bar code label of the newly inserted media tray. The printer controller maintains a record of all media trays which have been inserted into the printer. Thus, if the bar code of an inserted media tray, as read from the bar code scanner  224 , corresponds with a pre-stored bar code signature of a previously inserted media tray, the printer will not dispense media sheets from the newly inserted media tray and provide an error signal to the user. 
   Additionally, the bar code may include information which identifies the type of media (e.g., transmissive or reflective) stored therein and the size. Thus, whenever a media tray is inserted into the printer, the printer may position the optical elements within the elevator housing  234  to read the bar code of the media tray to determine the size and type of media sheets therein. In this manner, the printer can determine which pick roller assemblies  12  to lower for dispensing the desired size and type of media sheet to the input path. Based upon information relating to size, type and lot information of the media sheets in an associated input tray from a bar code label  222   a ,  222   b  or  222   c , the printer controller can control the picker assemblies  12  to optimize feeding of the media sheets into the input path. For example, the printer controller may apply an optimum speed and duration of application of the picker tires  13  based upon size and media type as indicated in the bar code labels  222   a - 222   c . Alternatively, the bar code labels  222   a - 222   c  may have information directly specifying the picker speed and duration for applying to media sheets in the associated media tray. 
   By having a single optical system disposed within a movable elevator housing  234 , the bar code labels from multiple trays can be read with only a single optical system. This reduces manufacturing costs by only requiring a single optical system rather than multiple optical systems. 
   Conventional apparatuses for dispensing media may have a system for reading an optical signature on a media tray as it is inserted. In these systems, the motion of the media tray as it is inserted moves the optical signature past the optical system to effect a scan of the optical signature. Thus, if the optical system cannot read (or misreads) the optical signature when the media tray is inserted, the media tray must typically be manually removed and reinserted so that the optical signature can be re-scanned over the optical system. Additionally, if the optical signature is scratched or distorted where the optical system is directed, the optical system cannot read the optical signature even if other undistorted portions of the optical signature have all of the desired information. 
   In the embodiment of  FIGS. 10B and 10C , on the other hand, the optical elements within the elevator housing  234  may read any of the bar code labels  222   a ,  222   b  and  222   c  while the corresponding media holders  220   a ,  220   b  and  220   c  are stationary. Thus, if the optical elements do not read (or misread) any of the bar code labels  222   a ,  222   b  or  222   c  on a first scan, the optical elements can re-scan the bar code label without moving the media holder  220   a ,  220   b  or  220   c . According to an embodiment, the optical elements within the optical housing  234  periodically scan each of the bar code labels  222  of each of the inserted media holders  220 . Additionally, if one portion of a bar code label  222  is scratched or distorted, the bar code scanner  224  can be vertically adjusted to read from an undistorted and unscratched portion of the bar code label  222  to extract the desired information. 
     FIG. 10A  shows a notch  122  adapted to receive an output tray assembly which includes three output trays  113  ( FIG. 22 ) and a hide track  117  ( FIGS. 10D and 10E ). A sensor  120  detects whether or not the output tray assembly is installed. The hide track  117  receives media sheets during intermediate passes of dye diffusion processing. A compliant belt  92  may transfer torque from the capstan shaft  80  to a kicker drive  90  ( FIG. 9A ) to drives a gear drive  118 . The compliant belt  92  may also dampen vibrations from the output kicker tires  121  ( FIG. 10E ). The gear drive  118  drives the kicker assemblies on the output tray assembly.  FIG. 10D  shows an expanded view of the output trays  113  in conjunction with the capstan drive  80 . Here, the belt  92  transfers torque from the capstan drive  80  to provide torque to the gear drive  118 . The gear drive  118  then provides torque to each of the kicker assemblies associated with each of the output trays  113 .  FIG. 10E  shows a perspective view illustrating how the kicker shafts  119  may all be driven by the torque applied to the gear drive  118  from the capstan drive  80 . Hide track  117  may be sealed from the output trays  113  and the exterior of the media printer to reduce the incidence of dust at the print station, which can cause artifacts in the image, in subsequent passes of the dye diffusion process. 
     FIG. 11A  shows perspective view of the multi-media printer with the media trays  87 , picker assemblies  12 , bar code scanner apparatus  110 , etc. removed to expose the assembly for moving the printhead  151  ( FIG. 11C ). As discussed above, a mechanism  116  may release the donor doors when the bar code scanner apparatus  110  is raised to the top of the media printer. Drive  132  may apply a torque to the torque arm (not shown) attached to the printhead  151  in response to the worm gear  56  driven by the motor  58  ( FIG. 6 ). Fans  134  may be attached to vents  62  and  63  ( FIG. 7 ) to circulate air through the printhead heat sink (not shown). Holes  130  may secure the shafts for the platen, capstan, and pinch rollers. 
     FIG. 11B  shows an enlarged view of the holes  130  for securing the platen shaft  135 , capstan shaft  137  and pinch roller shaft  139 . The hole  130  for securing the platen shaft  135  and the capstan shaft  137  are formed in a chassis wall  10 . The hole  130  for securing the pinch roller shaft  139  (which may be the same as slot  101  in  FIG. 9E ) is formed in the pinch arm  98 . Each of the holes  130  includes a rounded portion  133  and a “V” block section  131 . The rounded portions  133  may be adapted to be packed with bearings and the V block sections  131  may secure the respective shafts  135 ,  137  and  139  in place in response to an opposing force. For example, when the printhead  151  is engaged with the platen, the printhead  151  may force the platen shaft  135  against the V block section  131  to prevent movement of the platen shaft  135  in any direction. Similarly, the pinch roller  77  and capstan roller  79  may apply opposing forces to one another ( FIG. 9B ), causing the pinch shaft  139  and capstan shaft  137  to be pushed into their respective V blocks portions  131 . This essentially prevents movement of the capstan shafts  137  and pinch shaft  139 . The pinch and capstan rollers may not move relative to one another. Nor will the platen move relative to the printhead  151  (in  FIG. 11C ). 
     FIG. 11C  shows a printhead assembly including a printhead  151  and a heat sink  150  in a print position. The arrows extending from the printhead  151  illustrate the forces acting upon the platen shaft  135 , the capstan shaft  137  and pinch shaft  139  which maintains these members in position against the V block portions  131  of their respective holes  130 . The printhead assembly may also include a printhead alignment tab  204  that serves to position the printhead  151  with respect to the media sheet and the ends of the platen roller  76 . The position of the printhead  151  may be changed from a print position, in which the printhead  151  and the platen roller  76  may sandwich the media sheet, by moving the torsion arm  170 . 
     FIG. 12  shows a media wall  136 , which may be placed to guide media dispensed from the input trays directly to the print station (not shown), without the use of any intermediate rollers. 
     FIG. 13  shows a perspective view of the interior of the multi-media printer which illustrates the location of a power supply  138  with respect to the printhead which is to receive power from the power supply  138 . The power supply  138  provides DC power to the printer controller through cable  141  and provides DC power to the printhead through cable  144 . The placement of the power supply  138  with respect to the printhead (as shown in  FIG. 15A ) reduces the inherent parasitic resistance associated with the power cable  144  and that of thermal elements of the printhead, resulting in very low power loss. However, in alternative embodiments of the invention, the power supply  138  may be located elsewhere based on space/interference, heat or other considerations. 
   Sensors  142  position the donor spool of the donor carriage as it travels vertically with the timing belt  42  ( FIG. 6 ). A sensor  148  detects when the printhead reaches a home position. 
     FIG. 15A  shows a cross-sectional view of the multi-media printer including a media input path to a print station including a printhead  151  and platen roller  76 . Printhead  151  may be coupled to a printhead heat sink  150 , which may be rotatable about the torsion arm  170  between a print position (as shown) and a retracted position in which the printhead assembly is rotated upwards in the direction  172  until a printhead home position sensor  154  is tripped. A ball joint  152  enables the printhead  151  and heat sink  150  to float on the platen surface to substantially distribute the load of the thermal elements of the printhead along the platen roller  76 . 
   A donor spool  161  is moveable in the vertical direction and extends a donor ribbon between the printhead  151  and the platen roller  76  (or a media sheet in contact with the platen roller  76 ) when performing dye diffusion imaging. A take-up spool  160  remains stationary. The donor spool  161  is snapped into a position  162  while direct thermal imaging is performed. When transitioning to dye diffusion printing, the torsion arm  170  retracts the printhead assembly in the direction  172 , and the timing belt  42  releases the donor spool  161  from the snapped position  162  and lowers the donor spool  161  to extend the donor ribbon across the platen roller  76 . The torsion arm  170  then returns the printhead assembly to the printing position with the printhead  151  against the extended donor ribbon, media sheet and platen roller  76 . When the media printer transitions from performing imaging using the dye diffusion process to the direct thermal imaging process, the printhead assembly moves in the direction  172  to the retracted position with the heat sink  150  meeting the stop  164 . The timing belt  42  then lifts the donor spool  161  while rotating the take up spool  162  to remove the donor ribbon from the print station, moving the donor spool  161  into the snapped position  162 . The printhead assembly then returns to the print position with the printhead  151  meeting the platen roller  76 . In alternative embodiments of the invention, the donor spool  161  may remain fixed in position and the take-up spool  160  may be moved from a first position to a second position so as to place the donor ribbon between the printhead  151  and a media sheet and the platen  76 . 
   Media sheets fed through the input path to the print station meet the capstan and pinch roller combination  77  and  79 . The capstan roller  79  rotates to translate the media sheets from the print station through an output path. An output diverter  156  receives media sheets from the output path and diverts these media sheets to one of the output trays  113  (if there is no further processing to be done on the image) or to the hide track  117  if the media sheet is in an intermediate stage of a dye diffusion printing process ( FIG. 4D ). The output diverter  156  rotates about the arch  158  into position for placing a imaged media sheet into a pre-selected output tray  113  or a media sheet during an intermediate dye diffusion color pass into the hide track  117  ( FIGS. 10D and 10E ). 
   Each of the media trays may dispense media sheets to the print station formed by the platen roller  76  and printhead  151  through a single input path against the media wall  136 . In embodiments of the invention, there may be no intermediate rollers used in the transfer of media sheets from the media trays to the print station as media sheets are translated along the surface  136  by the picker assemblies  12 . Diverters  174  may include a lower surface  167  and an upper surface  169  for guiding media sheets from the media trays against the media wall  136  and preventing media sheets from reentering the media trays after being dispensed through the print station. By not having a separate motor for driving each of the picker assemblies  12 , the lowest media tray may be placed substantially near the print station to eliminate the need for using an intermediate roller. As media sheets are being dispensed from either of the two lowest media trays, the lower surface  167  and upper surface  169  may guide the leading edge of the media sheet through the input path against the media wall  136 . 
   While dye diffusion printing is performed, media sheets may be translated back and forth through the print station such that the trailing edge of the media sheet at times travels backwards towards the media trays along the media wall  136  between intermediate color passes. The surfaces  169  of the diverters  174  may prevent the trailing edge of the media sheets from reentering either of the two lower media trays when translated backwards during these transitions between intermediate color passes. 
     FIG. 16  shows a view of the print station including the printhead  151  and platen roller  76 . A printhead shield  180  may protect bond wires as well as some integrated circuits that are on a printed circuit board (not shown) of the printhead assembly. The printhead shield  180  may also serve as a mechanism for feeding media as it approaches the print station. A leading edge sensor  186  detects a leading edge of the media sheet as it is translated between the print station and the pinch and capstan roller combinations  77  and  79 . 
   The printhead assembly may include an internal portion  285  with a ball joint  152  (shown as  283  in  FIG. 16 ). The ball joint  152  may allow the printhead  151  and heat sink  150  to rotate in one dimension. The internal portion  285  may be enclosed within a ventilation channel formed by sealing member  187 . The sealing member  187  may be coupled to the printhead heat sink  150  by a flexible seal  189  that allows movement of the printhead heat sink  150  with respect to the internal portion  285 . This may allow further freedom of the thermal elements of the printhead  151  to uniformly distribute the load of the printhead  151  against the platen roller  76 . Alternatively, a flexible sealed  291  may be provided at the base of the internal portion  285  to allow similar movement. 
     FIG. 17A  shows an enlarged portion of the print station, which may include the platen roller  76  and the printhead  151 . In addition to protecting bond wires and integrated circuits of the printhead  151 , the printhead shield  180  also diverts the media through the input path in a manner that minimizes vibrations causing artifacts. The print station may include an area of inflexion  188 , which is proximate the platen roller  76 . This area of inflexion may dampen the trailing edge of the media sheet as it is dispensed through the print station between the platen rollers  76  and the printhead  151 . Accordingly, vibrations caused by feeding the trailing edge through the print stations are reduced to result in fewer artifacts in the image. 
   Regarding the path of the media from the platen roller  76  to the capstan and pinch roller combination  77  and  79 , the media may exit the print station from point  190 , the point where the printer applies force to the platen roller  76 , and travels from a point of substantial tangency with the platen roller  76  to point  191  between the capstan and pinch rollers  77 . This reduces the incidences of media curling when, for example, performing direct thermal imaging on film using a smaller diameter platen roller  76  yields suitable imaging results. 
     FIGS. 17B and 17C  show an alternative embodiment for a pivot point  152  ( FIG. 15A ) for allowing the printhead heat sink  150  to move relative to the torsion bar  170 . Bracket  301  is disposed between portions of the air channel for drawing air to the printhead heat sink  150  as illustrated below with reference to  FIG. 21 . Bracket  301  includes a first member  303  that couples to event housing  307 . The event housing may be useful in directing later scenes from a movie. It includes a torsion bar  170 . The second member  305 , couples to the printhead heat sink  150 . Members  305  and  303  are permitted to move relative to one another to allow the thermal elements of the printhead  151  to have uniform load distributed across the platen  76 . As discussed above, the ball joint  152  in the embodiment of  FIG. 15A  allows the printhead  151  and heat sink  15  to rotate in a single plane. The bracket  301 , on the other hand, allows movement of the printhead  151  and heat sink  150  with additional degrees of freedom, enabling greater flexibility to uniformly distribute the load of the printhead  151  on the platen roller  76  among the thermal element of the printhead  151 . 
     FIG. 18  shows a perspective view of the internal works of the media printer including the output diverter  156 .  FIG. 19  shows a cross-section of the printhead assembly. 
     FIG. 20  shows an enlargement of embodiment of the printhead assembly including a printhead alignment tab  204  and a ventilation channel  212 , which may include an intake path  208  and an exhaust path  206 .  FIG. 21  shows a perspective view of the printhead assembly shown in  FIG. 20 .  FIG. 21  shows the bracket assembly  301  ( FIGS. 17B and 17C ) being disposed between ventilation channel members  213  for transporting external air to the heat sink  15  through external vents  62  and  63  ( FIG. 7 ). 
     FIG. 22  shows an external view of the multi-media printer illustrating kicker tires  216  for a top output tray  113 . As discussed above, similar kicker tires may be similarly placed to guide media sheets to the lower two output trays  113 . 
   Returning to  FIG. 17A , a portion of the media sheets during direct thermal imaging does not receive an image. This includes borders at the leading and trailing edges of the media sheet and at the sides of the media sheet. According to the embodiment, these areas may be blackened during the direct thermal processing. Here, the printhead may blacken the border at the leading edge up until the desired image portion begins. This may be accomplished by engaging the platen roller  76  with the clutch members  82  and  84  to pull the leading edge past the printhead  151  until the pinch and capstan rollers can grab the leading edge to commence translating the media sheet. After the border of the leading edge is blackened by the printhead  151 , the clutch members  82  and  84  disengage the platen roller  76  from the capstan drive  80  to allow the capstan and pinch rollers  79  and  77  to pull the media sheet through the print station for transferring the desired image portion to the sheet. While transferring the desired image portion between the borders at the lending and trailing edges, the printhead  151  may also blacken the borders at the side edges. After the desired image portion is transferred to the media sheet, the platen roller  76  capstan and pinch roller may pull the trailing edge of the media sheet past the printhead  151  to be blackened. 
   The size of the borders at the side edges of the media sheet may be determined based upon the positioning of the media sheet relative to the printhead  151 . A side edge sensor system may be located at one of the sides of the media sheet in the discharge path (and positioned relative to the printhead  151 ) to determine the lateral positioning of the media sheet with respect to the printhead  151 . By knowing the lateral positioning of the media sheet, the location of the side edge borders in the media sheet can be precisely determined. This allows the printer controller to control the printhead  151  to blacken the side borders without marring the desired image received in the area of the media sheet within the side borders. 
   According to an embodiment, the printhead  151  may have a length greater than the widest media sheet used in the media printer. This may enable the printhead  151  to transfer an image to any portion of the imaging surface of the media sheet, regardless of the lateral alignment of the media sheet in the print station. Therefore, upon detection of the lateral alignment of the media sheet at the side edge sensors, the printer controller can control the printhead to blacken the borders at the side edges while transferring the desired image portion onto the media sheet between the borders at the side edges. 
     FIG. 23  shows an embodiment of the sensor for detecting the side edge of the media sheet in the discharge path. The transmitter  322  may be placed at one side of the discharge path over or above a space where a side of the media sheet is to travel. A corresponding receiver portion  320  may be placed on the same side of the media sheet opposite the transmitter  322  to detect light energy emitted by the transmitter  322 . Transmitter  322  may includes several LED lights or other light sources such as bulbs or lamps for providing a light source. A linear wave polarizer and quarter wave retarding filter  324  may be disposed over the transmitter  322  to provide a polarized light source directed to the receiver  320 . 
   The receiver  320  may include an array of light detecting elements formed in a charge coupled device (CCD). A second linear polarizer may be disposed over the CCD which is eighty degrees (80°) out of phase from the linear polarizer of the transmitter  322 . A second quarter wave retarding filter may be disposed over the second linear polarizer. Therefore, the CCD detecting elements may receive approximately 20% of the energy from the transmitter  322  when no media is present. Opaque media blocks all light. Therefore, for opaque media, the absence of energy at a pixel element in the receiver  320  that is adjacent to a pixel element detecting energy, processing may indicate that this point of change is the side edge of the media sheet. 
   Since the receiver  320  is capable of detecting changes in phase, the side edge detectors may detect edges not only for opaque media, but also for transparent media which have defraction properties introducing phase changes detectable at the pixel elements of receiver  320 . Energy in excess of 20% may be transmitted when transparent plastic media are in the input path. Therefore, for transparent media, the detection of a high energy at a pixel element in the receiver  320  that is adjacent to a pixel element detecting no energy may indicate that the point of change is the side edge of the media sheet. 
   In addition to using the side edge sensor for blackening the borders of the sides of the media during direct thermal imagining, information from the side edge sensors may be used to calibrate the positioning of the printhead  151  in the lateral dimension. Given the exact placement of the side edge sensor with respect to the printhead  151 , the lateral placement of the media sheet with respect to the printhead  151  can be precisely determined. 
     FIG. 24  illustrates a donor ribbon  346  that may be used in conjunction with the donor carriage including the donor spool  161  and the take up spool  162  ( FIG. 15A ). In the illustrated embodiment, the donor ribbon  346  provides for four-color dye diffusion printing having color sections for the following colors: cyan; magenta; yellow; and black. In the dye diffusion process, the media sheet is translated to the print station between the platen roller  76  and the donor ribbon  346  in multiple passes, each pass transferring a corresponding color component of the image onto the media sheet.  FIG. 24  shows a yellow color section  342  and a magenta color section  344 . Although only two color sections are shown, it will be understood that the illustrated embodiment may include color sections of four different colors for each of the aforementioned colors in the process. The color sections of donor ribbon  346  may repeat any given pattern such that each set of four consecutive color sections may span the four colors used in the dye diffusion process. Donor ribbon  346  may also includes a bar code portion  340  that extends along side of all of the color sections. This bar code information may indicate a specific lot number associated with the donor ribbon  346  and other manufacturer designated information. Additionally, in the illustrated embodiment, the bar code information at bar code portion  340  may indicate the specific linear location on the donor ribbon  346 . For example, the bar code portion  340  at a particular location on the donor ribbon  346  may indicate the particular color associated with the adjacent color section. Additionally, the bar code portion  340  may indicate when a transition occurs between adjacent color sections. For example, as shown in  FIG. 24 , point  338  of the bar code portion  340  may indicate that the position of the donor ribbon  346  corresponding to point  338  is the border between the yellow color section  342  and the magenta color section  344 . Accordingly, the media printer may use a single sensor to extract information about the particular lot of the donor ribbon and locations of transition between color sections. 
   Returning to  FIG. 18 , an embodiment of a sensor for reading the bar code  340  on the side of the donor ribbon  346  is shown. An emitter  159  may generate light that is reflected from reflecting piece  157  onto the bar code portion  340 . A sensor  155  then receives the reflected bar code signature to decode. The printer controller can then determine the lot number and other manufacturing information and detect transitions between color sections in the donor ribbon  346 . 
   Returning to  FIG. 16 , an embodiment of the present invention is directed to aligning a media sheet as it is translated to the print station. As discussed above, the picker assemblies  12  may be selectable for translating a top media sheet in a corresponding media tray against a guide surface  181 . The leading edge of each top sheet in each of the media trays may be at a known distance from its position in the media tray to the print station where the printhead  151  meets the platen roller  76 . The DC servo motor with encoder  30 , the source of torque which drives the picker assemblies  12 , may respond to a set number of encoded pulse signals that indicates that a particular top media sheet has traveled a particular distance. In other words, depending upon which media tray a top sheet is being dispensed from, the DC servo motor with encoder  30  receives a discrete number of encoded pulses to translate the leading edge of the top sheet to the print station where the platen roller  76  meets the printhead  151 . This discrete number of encoded pulses may depend upon the size of the media sheet in a tray. 
   The torsion bar  170  may place the printhead assembly in any one of four positions: a retracted position; a load position; a feed position and a print position. In the retracted position the printhead assembly is retracted back until a head home position sensor  154  is tripped. In the print position, the printhead  151  is pressed against the platen roller  76  with a force sufficient for printing. In the load position, the printhead  151  is raised off of the platen roller  76  slightly, allowing a media sheet to be pulled through the print station by rotating the platen roller  76 . In the feed position, the printhead is brought into contact with the platen  76 , but with less force than in the print position. In the feed position, a media sheet may be translated over the printhead by rotating the platen roller  76 . 
   As the leading edge of the media sheet approaches the print station, the printhead  151  is in the feed position against the platen roller  76 , preventing the leading edge of the media sheet from passing through. A nip is formed between the printhead  151  and the platen roller  76  when the printhead is in the feed position. The DC servo motor  30  may drive the picker assembly  12  until the leading edge of the media sheet is received at the nip. Under the control of the printer controller, the DC servo motor  30  may continue to drive the picker assembly  12  to slightly buckle the media sheet proximate the leading edge thereof to align the leading edge of the media sheet in the nip. As the leading edge aligns in the nip between the printhead  151  and the platen roller  76 , the printhead  151  may be raised to the load position momentarily and then to the feed position. The platen  76  may then be engaged to rotate (via the clutch members  82  and  84 ) to translate the media sheet a certain distance further. The media sheet then meets the capstan and pinch roller combination  79  and  77  to be further translated through the print station as the clutch  82  disengages the platen roller  76  from the capstan shaft  80 . The printhead  151  then moves from the load position to the print position against the platen  76  to commence printing. 
   The media wall  136  ( FIG. 15A ) is shaped to support media sheets to maintain longitudinal rigidity to prevent buckling except at the leading edge when aligning the media sheet in the nip performed at the capstan and pinch roller combination  79  and  77 . Accordingly, no intermediate rollers are required between the media trays and the print station. 
   In another embodiment, the media printer includes a leading edge detection sensor  186  ( FIGS. 16 and 17A ) for detecting a leading edge of a media sheet being dispensed during the input path. Upon detection of the leading edge of a media sheet by the leading edge sensor  186 , the printer controller may be able to determine how many additional encoded pulses should be transmitted to the DC servo motor  30  to rotate the picker tires  13  until the leading edge of the media sheet reaches the nip where the platen roller  76  meets the printhead  151 . 
   In addition to controlling whether the printhead  151  is in either a retracted position, load position, feed position or print position, the printhead assembly may be adjusted to provide a controllable force at many levels to the platen  76  to support several different imaging techniques. This is enabled by the worm gear  56  and motor  58 , which control the torque applied to the torsion arm with great precision in response to signals from the printer controller. This enables the media printer to provide the appropriate force of the thermal elements of the printhead  151  against the platen roller  76  depending upon whether the intended printing process is dye diffusion or direct thermal printing. Also, the force of the printhead  151  against the platen roller  76  may be adjusted based upon the width of the media sheet being imaged. The force of the printhead  151  against the platen roller  76 , therefore, may be controlled by the printer controller by providing control signals to the motor  58  for application to the worm gear  56 . 
   One embodiment of the present invention employs media trays as described in the aforementioned U.S. patent application Ser. No. 08/979,683 incorporated herein by reference. In particular, the media trays may be vacuum formed from a thermoplastic sheet and have internal dimensions that are formed to the specific size of media to be dispensed from the tray. In one embodiment, the media trays are intended to be disposable. Therefore, each media tray may be specifically formed to dispense media sheets of a particular type and size. 
   The top media sheet in each media tray may adhere to the media sheet immediately below the top media sheet with some retention force. The picker tires  13  may apply a lateral force to the top sheet which exceeds the retention force, causing the top sheet to translate forward while a nail in the media tray fixes the leading edge in the media tray, causing the top sheet to buckle until the leading edge flips over the tray and into the input path. According to an embodiment, each media tray may be specially formed (e.g., by varying the angles of the front nail which secures the leading edge of the top sheet while the trailing edge is translated forward) based upon the specific media type (and retention force associated therefore) and media size. 
   In the illustrated embodiment, the thermal elements of the printhead  151  are adapted for thermal imaging using either a direct thermal or dye diffusion process. Thermal elements in a printhead are typically formed by a resistive heating element(s) coated with a ceramic bead to provide an imaging surface. For dye diffusion printing, the optimum printhead geometry is typically provided by a thermal imaging surface in the form of a rounded bead. On the other hand, the optimal printhead geometry for direct thermal imaging is typically a flatter imaging surface.  FIG. 25  shows a thermal element printhead geometry  350  which is optimized for either direct thermal or dye diffusion processing according to an embodiment of the printhead  151 . The dimension shown are in inches. 
   As discussed above, embodiments of the present invention are directed to a multi-media printer which is capable of interchangeably using a direct thermal or dye diffusion process. Direct thermal printing and dye diffusion printing each have different requirements for heating the printhead. Each process has an associated subimaging temperature. Maintaining a printhead at a subimaging temperature between prints allows the printer to quickly raise the temperature of the thermal elements as required to transfer an image to the media using either process. In an illustrated embodiment, the media printer maintains the thermal elements of the printhead at the lowest subimaging temperature supported by the media printer. Therefore, the imaging surfaces of the thermal elements can be raised to a temperature suitable for imaging in any of the imaging methods employed by the media printer. 
   The printhead  151  of the illustrated embodiment receives a series of voltage pulses at a set pulse width and a set duty cycle to provide certain levels of intensity or gray to a pixel in the image. While for any particular media type there may be a set pulse profile for each desired level of intensity or gray, media sheets of the same type from different manufacturing lots may have different responses to the same pulse profile. For example, a first lot of media may require fifteen pulses at 15 volts to provide a level of gray or intensity of 2.0. On the other hand, a different lot may require fifteen pulses at 15.6 volts to achieve the same level of gray or intensity. As discussed above with reference to  FIGS. 10A through 10C , a bar code scanner  110  reads a bar code on the side of each media tray as inserted into the media printer. In addition to identifying the media type and size associated with the media sheets disposed therein, this bar code may also identify a particular manufacturing lot associated with the media in the media tray. Therefore, the printer controller can, upon associating a media type and manufacturing lot number with the media sheet to receive the image, change the voltage of the pulses applied to the thermal elements to provide the desired level of intensity or gray at points in the image. Additionally, the voltages can be further modified based upon a parasitic resistance which results from the combination of the resistance of the power cable from the power supply  144  ( FIG. 13 ) and the known resistances of the thermal elements which may be measured according to techniques described in U.S. patent application Ser. No. 09/262,988, filed on Mar. 5, 1999 entitled “System for Printhead Pixel Heat Compensation,” assigned to Codonics, Inc., and incorporated herein by reference. 
   The different sensors in the media printer, including the side edge sensor, leading edge sensor and bar code sensor for the donor ribbon, may rely on a light emitting diode (LED) source for light. Over time, LEDs such as those employed in the media printer for the various sensors, typically decrease in brightness. According to an embodiment, a printer controller includes logic for compensating for the decreases in the brightness of the LEDs by recalibrating the sensors periodically. This may increases the life of a sensor by keeping it from going out of adjustment from changes in the intensity of light emitted by the LEDs. 
   Returning to  FIG. 15A , the take-up spool  162  of the donor carriage may be driven by gears with a clutch. The gears may be sized to provide enough drag on the donor roll  161  without introducing any artifacts. A gear casing  159  houses the drive mechanism of the take up spool  160 . As shown in  FIG. 15B , a built-in slip clutch, comprised of a pressure plate  308 , friction disc  310 , spring member  309 , adjustment nut  312  and drive gear  311 , decouples the motor  314  and pinion gear  313  noise and provides for an even pull on the donor ribbon. 
   Embodiments of the media printer may include a densitometer located in the discharge path on the opposite side of the print station from the input path. As known to those of ordinary skill in the art, a densitometer includes a sensor system for determining the image density in a particular portion of an image transferred onto media. If this is on a known portion of the image with a corresponding desired image density represented in image data at the printer controller, the printer controller can determine whether the printed image, in general, has an image density which accurately reflects the image data of the desired image. As discussed above, embodiments of the media printer may adjust the voltages applied to the printhead elements based upon a media type and the lot number detected from the bar coder  110 . The voltages of the pulses applied to the printhead may be further modified based upon the densitometer readings to provide an even more accurate image density by taking into consideration not only media type and specific lot number, but also the unique characteristics of the print station of the printer as measured by the densitometer. 
   In another embodiment of the present invention, a smart card or removal memory is provided as an adjunct to a nonvolatile memory of the print controller which includes information stored in the print controller such as gamma contrast, license keys, Postscript settings, a TCP/IP address associated with the printer, and the like. When the printer is not in service or is malfunctioning, this memory may be removed and inserted into a functioning printer so that the new printer does not need to be reprogrammed to the settings of the malfunctioning computer. The malfunctioning printer may then be shipped off site for repair. 
   As discussed above, in one embodiment of the present invention the top and bottom and side borders of the image may be blackened during direct thermal imaging. This is particularly useful in applications where direct thermal imaging is used on film for medical diagnostic imaging such as x-ray images. In an alternative embodiment, the media sheets may have perforations on top and bottom and sides so that the unprinted borders can be easily removed and the imaged media sheets can be used in medical analysis in the normal fashion. 
   Embodiments of the multi-media printer are directed to allowing the user easy access to areas of the multi-media printer for removal of jammed media sheets and cleaning. Referring to  FIGS. 3A and 4 , the user may remove jammed paper in the input path by removing a media tray from its media input cavity  6  and rotating the sheet metal arm  17  of the associated picker assembly  12  upward. The sheet metal arm  17  is rotatable upward by manually lifting to apply a torque against the torsion spring  36  of the associated picker assembly  12 . 
   Additionally, the user may have unobstructed access to the discharge path following the capstan and pinch roller combination  79  and  77 .  FIGS. 8 and 18  illustrate an output media guide  360  which may be manually rotated about a point  372  to allow access to the capstan and pinch rollers when the output media tray and kicker assembly (shown  FIGS. 10D and 10E ) are removed. In the illustrated embodiment, the output media guide  360  may rotated in a direction  366  about point  372  to place the output media guide  360  in an open position. When the output media guide  360  is in the closed position (as shown in  FIG. 18 ), the output media guide  360  is secured at clips  362  on opposite sides of the media printer. When the user moves the output media guide  360  from the closed to the open position, the user detaches the output media guide  360  from the clips  362 , rotates the upward media guide  360  in the direction  366 , and attaches the output media guide to clips  364  ( FIG. 4 ). Accordingly, the user can gain unobstructed access to the pinch and capstan roller combination  77  and  79  at the discharge path by first removing the output tray assembly shown in  FIGS. 10D and 10E  and then moving the output media guide  360  in the open position to be secured at clips  364 . 
     FIGS. 4 ,  8  and  18  show that the output diverter  156  is coupled to the output media guide  360  so that it is rotated upward in the direction  366  when the output media guide  360  is rotated in the direction  366  from the closed to the open position. The user may also gain unobstructed access to the capstan and pinch roller combination  77  and  79  through the discharge path by manually positioning the output diverter  156  while the output media guide remains in the closed position. 
   In another embodiment, the output diverter  156  may include a lower portion  370  and an upper portion  368 . The user may manually separate the lower portion  370  from the upper portion  368  by rotating the upper portion  368  in a direction  372 . 
     FIG. 26  shows an embodiment of the printhead  151 , which includes an array of thermal elements  372 . Each thermal element  372  has a “U” shaped structure having a common lead  378  and an individual lead  376 . Each of the thermal elements may include a bridge  380  coupled at a first end to the associated common lead  378  and coupled at a second end to the associated individual lead  376 . The first and second ends of the bridge  380  may be coupled to the associated individual lead  376  and common lead  378  through a resistive element  374 . The common leads  378  of the thermal elements  372  may be coupled to a common fixed voltage or ground while a signal having a pulse profile is applied to the individual lead  376  for imaging. By having two resistive elements  374  for each thermal element  372  aligned in line with the linear array of thermal elements, the imaging surface of the thermal element  372  may be concentrated over a smaller area. This allows placement of the imaging surface of the printhead  151  (i.e., the ceramic printhead bead) closer to the edge of the printhead  151  toward the pinch and capstan roller combination  77  and  79  as shown in  FIG. 27 .  FIG. 27  shows an alternative geometry of a printhead bead which is placed near the edge of the printhead  151  so as to minimize the size of the borders at the leading and trailing edges of the media sheet which cannot receive portions of the desired image during direct thermal imaging. 
     FIGS. 17 and 18  show that the printhead shield  180  may include a leading edge portion  390  which is in contact with the donor ribbon (not shown) during dye diffusion printing. FIG.  16  shows the printhead assembly in a preprint position. During printing, the torsion arm  170  may apply an increased level of torque such that the printhead assembly bends at ball joint  152 . This positions the lending edge portion  390  to guide the donor ribbon between the supply and take up spools. 
     FIG. 15A  shows a donor ribbon supply carriage  394  which may hold the take up spool at a location  159  and includes a snap portion  162  for removably receiving the donor roll  161 . A donor access door  392  is adapted to receive the donor ribbon supply cartridge  394  when the donor roll  161  is removed and inserted from the snap position  162 . In the illustrated embodiment, when the printhead assembly is in a retracted position applying a force to stop portion  164  of the donor ribbon supply cartridge  394 , the donor roll  161  may be pulled out of the snap position at  162  while the printhead assembly maintains force against the portion  164  (while the printhead assembly is in the retracted position). 
   While there has been illustrated and described what are presently considered to be the preferred embodiments of the present invention, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from the true scope of the invention. Additionally, many modifications may be made to adapt a particular situation to the teachings of the present invention without departing from the central inventive concept described herein. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the invention include all embodiments falling within the scope of the appended claims.