Abstract:
Constant tension in the thermal printing ribbon is maintained in a loading drum placed after the thermal print head that directs the ribbon by means of a planetary pivotable support lever arm to define a loop, thereby maintaining constant tension throughout the printing stage to ensure operational quality. The printing method includes threading the thermal printing ribbon between the pivotable support lever arm and the cylindrical drum, and the mechanism retains the printing ribbon against the loading drum by a biasing force on the lever arm, the lever arm being kept in biasing mode during the printing operation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a National Phase application of PCT Application No. PCT/IB2006/003786, filed on 28 Dec. 2006 (published as WO 2007/077482), claiming priority of Spanish Application No. 2005-03251, filed on Dec. 30, 2005, and also is a continuation-in-part of pending U.S. patent application Ser. No. 10/986,991, filed Nov. 15, 2004, which claims foreign priority from Spanish Application No. 2003-02818 filed on Dec. 1, 2003, the entire specifications of each of the above referenced priority documents being incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a printing device for application in heat transfer printing machines, as well as to the printing method itself, and more specifically, to heat transfer printing machines in which the tape on which printing is performed is maintained in a range of tension while simultaneously registering the tape with the printing head. 
         [0004]    2. Background Art 
         [0005]    This invention is directed to a printing device that incorporates means to provide a constant tension of the printing ribbon. A loading drum placed immediately after the thermal print head that draws the ribbon towards itself, and thereby forming a loop, and so maintains a constant tension during the printing stage to ensure quality of the operation. 
         [0006]    Printing machines with a thermal head transfer the ink from a printing ribbon to the material to be printed by heating a number of points in the thermal print head to release the ink. 
         [0007]    In first generation printing machines of this type, the transfer ribbon transport means were driven by a motor in the take-up spool and were provided with various possible combinations of braking devices in the feed spool to control the amount of ribbon supplied. 
         [0008]    During the printing stage it is crucial that the tension of the transfer tape or ribbon be as constant as possible in order to obtain a high printing quality. To achieve a constant tension in the tape, some manufacturers have developed moving devices that move to maintain the ribbon tension constant, thereby resulting in a relative motion between the print head and the ribbon, with the feed spool and take-up spool still. 
         [0009]    This is the case in U.S. Pat. No. 5,975,777, which discloses an alternative method and printing apparatus incorporating a shuttle that constitutes the transport element of the ribbon with respect to the thermal head during printing, while at least one of the spools remains still. This complex shuttle system requires the tape to be spooled through multiple rollers to maintain tension by back and forth motion of the complete shuttle. 
         [0010]    Other prior art methods used to maintain a constant ribbon tension involve acting on the various speeds of the feed and take-up spool motors. For example, U.S. Pat. No. 5,873,662 utilizes a brake mechanism on a dancer arm that controls the amount of tension on the ribbon by braking or releasing the unwind or feed reel. Others of these tensioning techniques include complicated and redundant processes, sometimes requiring elaborate software used to theoretically calculate the amount of tension that should be on the loop of tape that are continually calculating and adjusting during the printing process. For example, U.S. Pat. No. 5,366,303 to Barrus et al. discloses a complicated set of stepper motors acting as feed and take up spool motors that are controlled by a controller. The controller, using a complicated algorithm, calculates and counts the number of zero crossings in an electrical waveform, thereby to determine the amount of needed tension in the tape. Others have proposed tape or ribbon tensioning apparatus for heat transfer printing, including U.S. Pat. No. 6,082,914 to Barrus et al., U.S. Pat. No. 6,247,859 to Butcher, U.S. Pat. No. 7,052,194 to Mills and U.S. Pat. No. 7,150,572 to McNestry et al. 
         [0011]    These systems result in complex and hard to manage mechanisms, having poor precision as well as speed-related limitations determined by the inertia of the mechanical devices when these are set in motion. Moreover, none of these proposals have provided an efficient manner to maintain tension that relies on a sensed tension mechanism that does not require continual calculations of the expected or theoretical diameter of the tape being wound or released form a spool. Development of a device to solve the above-described problems is desirable. 
       SUMMARY OF THE INVENTION 
       [0012]    What is disclosed and claimed herein is a heat transfer printing device comprising a thermal print head, a feed spool for printing ribbon driven by a motor, entry guide rollers that direct the printing ribbon arriving from the feed spool toward the printing area, the printing area having a printing roller for supporting the material to be printed, a take-up spool driven by a motor to which the printing ribbon is directed with the aid of guide rollers, and a tape tension mechanism for monitoring and actuating a tensioner to maintain the tension of the printing ribbon between the feed spool and the take-up spool, the tension mechanism including a cylindrical loading drum having a surface and a support lever arm configured to provide a rotary force to the printing ribbon when rotating, which is placed after the thermal print head to which the printing ribbon is attached, by forming a loop around the loading drum, and thereby to maintain the tension of the ribbon during printing. 
         [0013]    In an other embodiment, the heat transfer printing device comprises at least one input guide roller that guides a printing ribbon towards a drum placed after a thermal printing head and before output guide rollers, and further comprises a swivelling roller that turns about the drum with the printing ribbon located between them, forming a loop of printing ribbon on the drum that establishes a tension in the ribbon during printing. 
         [0014]    This invention is an alternative and improved method as used for the printing process and comprises maintaining the printing ribbon on a loading drum by spring tension; 
         [0015]    The heat transfer printing device solves the needs described above as it ensures a constant tension of the print head during the printing stage in a simple and elegant manner that is essentially instantaneously sensitive to perceived changes in the tape tension. Moreover, the sensing and instantaneous reactions occur in response to the tape tension, and do not require calculation or other data manipulations of, for example, the average diameter of the spools including the amount of tape remaining or taken in on the feed or supply and take-up spools  20 ,  22 , respectively. The inventive tape tensioning mechanism is based fundamentally on the incorporation of a loading drum which in conjunction with a support lever arm on which a rotating planetary guide roller  32  extends the printing ribbon  15  to its complete length and continues to monitor the tension so as to maintain the tension in a very tight range. The planetary guide roller  32  is preferably disposed between the thermal print head  12  ( FIG. 1 ) and the ribbon take-up spool  22 . The rotating planetary wheel is constrained to move in a partial orbit around a on which the ribbon adheres to form a loop that increases, tensioned, during the printing stage. 
         [0016]    In a main embodiment of the invention, the drum is adjacent to a support arm that includes a guide roller for guiding tape or ribbon by forming a loop. The tape or ribbon loop is formed by the planetary guide roller and drum acting in concert to retain the print ribbon against the drum surface while also taking up any slack and being capable of easily providing extra ribbon to relieve any tension caused by the sudden binding or other resistance caused in the course of the printing process. The ribbon is retained on the drum by the planetary guide roller which extends the ribbon in a loop with a variable length, determining a tension that is maintained constant during the printing process to provide greater printing quality. 
         [0017]    The force generated by the drum on the print ribbon will depend on the structural configuration of the planetary guide roller, the drum and the distance between them, as well as on the amount of biasing force that is provided to the planetary arm to retain it in an equilibrium position. The ribbon remains in tension during the printing stage, and printing will commence when the speed of the printing ribbon and that of the material to be printed are the same. 
         [0018]    The amount of ribbon transferred through the printing station is partially controlled by a rotation sensor associated to a guide roller. This rotation sensor controls the tangential speed of the associated roller and sends a signal correlating the amount of ribbon transferred to the printing station so as to facilitate regulation of the revolution parameters of the ribbon feed spool motor and take-up spool motor. 
         [0019]    The loop start and end generation and maintenance of an equilibrium position, and thus governing the tension and position, are determined by a number of factors, including the sensor values of the corresponding plurality of planetary lever arm sensors disposed in an area adjacent the loading drum. Ideally, the sensors are in a configuration that sense the position of the planetary lever arm and guide roller which immediately indicates to the spool motors whether additional slack or tightening of the tape is needed. Thus, when the ribbon reaches the position of the first sensor it will be detected and when printing begins the loop will be extended, while when the ribbon reaches the position of the second sensor it will be detected, activating the printed ribbon take-up system by the required amount. Although two sensors are shown in  FIG. 1 , additional sensors may be utilized at more extreme positions to provide more urgent signals for take-up or slackening of the spool motors by a more drastic amount, depending on the position of the lever arm. Alternatively, as shown in  FIGS. 5-7 , the sensor may be a dedicated mechanism for monitoring the exact position, including the most recent trends of the positions, to enable the sensor to anticipate the need to release or take up more ribbon. 
         [0020]    The loop is taken up in the required amount according to the size of the printing by a motor associated to the printing ribbon take-up spool. To facilitate the take-up of this loop, the ribbon may be further controlled by an optional brake placed before the take-up spool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will now be discussed in further detail below with reference to the accompanying drawing figures to provide a better understanding of the invention, the drawing figures provided being an integral part of the invention in which, for purposes of illustration and in a non-limiting sense, the following has been shown: 
           [0022]      FIG. 1  illustrates in a schematic outline the elements of a printing device according to the present invention immediately prior to the engagement of the thermal print head; 
           [0023]      FIGS. 2 to 4  show in several schematic views the transfer ribbon tensioning sequence in which a loop is formed by the invention of  FIG. 1 ; 
           [0024]      FIG. 5  illustrates in a detailed view of the loading drum with the associated planetary roller guide according to the preferred embodiment of the invention; 
           [0025]      FIG. 6  shows a perspective view of the sensor mounted on the rear wall of the housing of the device; 
           [0026]      FIG. 7  shows a cross-sectional view of the sensor and wall shown in  FIG. 6 , and illustrating the interrelationship of the elements of the invention; 
           [0027]      FIG. 8  is a perspective view of the preferred embodiment of the angular position indicator, monitoring and control mechanism for the thermal printing device of  FIG. 1 ; and 
           [0028]      FIG. 9  is a perspective view of a CPU controller of the show in a separate portion of the inventive device and including an embodiment of the operational indicator. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    Referring now to the schematic illustrations of  FIGS. 1-4 , the inventive heat transfer printing ribbon tensioning device  10  and its operation will be described. The heat printing ribbon tensioning printing device  10  should be considered as being a part of a heat transfer printing assembly, generally designated as  100 , that includes a thermal print head  12 , a feed spool  20  containing a roll of printing ribbon  15 , the spool  12  being driven by a motor (not shown), a plurality of entry guide rollers  14  that direct the printing ribbon  15  from the feed spool  20  toward a printing area adjacent a print head  12  and a take-up spool  22  onto which the heat transfer printing ribbon is wound after use. Associated with the heat transfer printing ribbon  15  and guide rollers  14 , is a rotation sensor  26  for sensing the direction and speed of rotation of at least one of the rollers  14 . The printing area, generally designated as being the area around the device  10 , includes a printing roller  26  on which the material to be printed  13  is transported. Associated with the take-up spool  22 , which is also driven by a motor (not shown), guide rollers  16  direct the printing ribbon  15  from the printing area toward take-up spool  22 , as shown. 
         [0030]    The printing ribbon tensioning device  10  may optionally include a brake  23  disposed between two of the guide rollers  16 ,  16  that partially brakes the printing ribbon  15  to simplify the subsequent loop take-up stage by actuating the take-up loop  22 , as shown in  FIGS. 1 and 4  and described below. No such brake mechanism is necessary for operation of the inventive and in the preferred embodiment of the inventive transfer printing ribbon tensioning device, no brake is present. 
         [0031]    Although shown in  FIG. 1 , two sensors A and B may correspond to the minimum and maximum positions between which the ribbon loop may run when the printing ribbon  15  is shown in the tensioning operation ( FIG. 3-4 ), and as is described and illustrated in the aforementioned parent of this invention, (U.S. patent Ser. No. 10/986,991, published as U.S. Pat. Pub. 2005-0117956), but the preferred method is to have the sensors mounted on the back of the device as is shown in  FIGS. 5-7 . The sensors A, B may be any of a number of sensors, and can comprise, for example, light or proximity sensors, or they may be more precise, as is described below with respect to the preferred embodiment of the position sensor of the support arm  30  ( FIG. 5 ) and tensioning planetary guide roller  32 . A guide  29  may be provided as shown in  FIG. 1  to guide the ribbon  15  into the area in which the tensioning mechanism  10  operates to provide constant tension to the ribbon  15 . The guide can be a rotating wheel, as are guides  14 ,  16 , or a stationary pin (not shown) that is attached to the wall support of the mechanism  10 . 
         [0032]    The inventive heat transfer printing ribbon tensioning device  10  comprises several elements that are essentially identical to those of the parent invention, (U.S. patent Ser. No. 10/986,991, published as U.S. Pat. Pub. 2005-0117956), and reference is made thereto for a more concise explanation of the structure and operation thereof. Where the elements are similar or identical, the description of the elements in the parent is incorporated as if fully described herein. To recapitulate, the printing mechanism comprises a printing head  12  attached to an actuated arm  36  that is in operational engagement with an actuator  38 , for example as solenoid. When the printer head  12  is commanded to print, the actuator  38  is actuated, thereby moving the printer head  12  in a downward direction toward the ribbon or tape  15 , until it meets the tape, and starts the printing operation, as shown in  FIGS. 3 and 4  to print on the material  13  that is being printed on. 
         [0033]    The heat transfer printing ribbon tensioning device  10  comprising the invention is shown schematically in greater detail as a sequence of stages in  FIGS. 2-4 , in which the mechanism utilized for maintaining the desired amount of tension in the printing ribbon is discussed. As shown,  FIGS. 2-4  show several stages of the printing process and tensioning mechanism  10  and the manner in which the tension is maintained in the ribbon during the printing operation. The stage before the printing operation is commenced is shown in  FIG. 1 , and the beginning stage is shown in  FIG. 2 , wherein the printer is not yet operational. The next stage shown in  FIG. 3  is one in which the printer has begun to print, and the last stage ( FIG. 4 ) shows the mechanism approaching its limit of accommodating excess ribbon  15  that must be taken in by operation of the motors that drive the take-up spool  22  and the feed spool  20 . 
         [0034]    Tape or ribbon  15  is drawn thorough the device  10  by dispensing the ribbon  15  from the feed spool  20  and extending it around the first set of guides  14  and past rotation sensor  26 . The ribbon  15  is passed through a space between the guide  28  and a ribbon loop drum  40  which provides a surface  42  upon which the tape or ribbon  15  forms a loop  17  ( FIGS. 3-4 ), as previously described. Loop  17  is formed automatically upon the printer head  12  commencing the printing operation, which begins by the actuator actuating the shaft  36  toward the ribbon  15 . As the printer head  12  engages the printing ribbon  15 , this causes the ribbon  15  to bend from a linear condition toward an angled position as shown in  FIG. 3 . Simultaneously, the planetary support lever arm  30 , including the rotating guide roller  32 , shifts position and becomes disposed at the first or initial position which is at a point along the crescent opening  44  about half way between the two end points  45  ( FIG. 1 ). At this position, the lever support arm  30  can move in one direction if the ribbon tension is too tight and in the other direction if too slack, so as to accommodate the variability caused by the friction of the printing head  12  coming into contact with ribbon  15 . 
         [0035]    The inventive tape tensioning mechanism incorporates a loading drum  40  which in conjunction with a support lever arm  30  on which a rotating planetary guide roller  32  is mounted, extends the printing ribbon  15  to its complete length without breaking it and continues to monitor the tension so as to maintain the ribbon tension in a very tight range. The planetary guide roller  32  is preferably disposed between the thermal print head  12  ( FIG. 1 ) and the ribbon take-up spool  22 . The rotating planetary guide roller  32  is constrained to move in a partial planetary orbit around the drum  40  so that the ribbon  15  forms a loop  17  that has an increase in tension or decrease in tension, as required, during the printing process. 
         [0036]    As shown most clearly in  FIG. 7 , a central rotating shaft  42  extends from and aperture in the housing of motor  48  to drum  40 , which itself extends through an aperture  49  in the wall  50  of a housing of the printer device  10 . The aperture  49  may be concentric or even coterminous with the crescent aperture  44  through which the planetary lever arm  30  partially revolves, but the aperture  49  should be large enough for passage of the drum  40  therethrough to permit easy installation in case of any needed repair. The motor  48  and shaft  42  combination only operates during and initial start up stage of the printing process, until an equilibrium position of the lever arm is established, and the drum  40  is then permitted to rotate freely in a limited range around that equilibrium position, as described below. 
         [0037]    An appropriate mounting scheme is necessary for mounting the motor  48 . As shown, the mount can comprise a bracket  52  that has a second aperture through which drive shaft  42  passes, the bracket  52  itself being mounted on the wall  50  by means of a spacer  54  that is connected by an appropriate connection, such as a plurality of bolts  56 , connecting the bracket  52  to the wall  50 . While this connection is shown as being a preferred method, other connection schemes, for example, an attached housing (not shown) dedicated to house and orient the motor  48 , may be more appropriate as the features of the invention are developed in the future. 
         [0038]    At this position, correlating essentially to position B ( FIG. 1 ) in relation to the previously described embodiment of the aforementioned parent invention (U.S. patent Ser. No. 10/986,991, published as U.S. Pat. Pub. 2005-0117956), the ribbon speed is preset by the position as last provided, if in the intermittent mode, and at the constant adjustable speed in the continuous mode. At this position, the lever support arm  30  is left to “float”, that is, it reaches an equilibrium position that is being biased by the biasing force (spring  210 ,  FIG. 7 ) against the tension created by the ribbon. If the equilibrium is upset so that it is forced in one direction for too long and too far from the equilibrium, then the controller is signaled to either increase or decrease the tape speed, as needed to revert the position of the planetary lever support arm  30  back to the equilibrium position. 
         [0039]    This concept of equilibrium of forces acting on the planetary lever support arm  30  and associated planetary guide roller  32  is a key feature of the invention. That is, the equilibrium is reached immediately upon the starting of the intermittent printing process, and the planetary guide roller  32  is positioned at a point approximately halfway between the two ends of the crescent shaped aperture  44 , which may translate to about sensor B in  FIG. 1 . At this point, the planetary guide roller  32  can move easily in either direction, that is, clockwise in the direction of arrow CW or counterclockwise in the direction of arrow CCW ( FIG. 5 ), depending on the forces acting on the ribbon  15  and causing tension thereon to be increased or decreased. As soon as the need to increase or decrease tension is sensed, then the controller will automatically increase or decrease the rotational speed of the spools  20 ,  22 , thereby affecting the forces on the ribbon  15  and bringing the planetary guide roller  32  back into an equilibrium condition. Depending on the sensor mechanism and the biasing force, the reaction time to provide the return to the equilibrium point is such as to maintain the position at or near equilibrium irrespective of the printing speeds, or of motion of the tape or ribbon  15 . 
         [0040]    This feature is shown in  FIGS. 4 and 5 , wherein the lever support arm  30 , including the planetary guide roller  32 , is at the “loose ribbon” position, and the spring  210  has biased the planetary guide roller  32  position almost to the terminal point of the crescent aperture  44 . At this position, if not before, the controller will assert its function and will provide a signal to the spools  20 ,  22  to speed up or slow down the take-up and feed in order to bring the tension of the ribbon  15  to a value that will bring the planetary guide roller  32  back to equilibrium. 
         [0041]    Referring now to  FIGS. 5 ,  6  and  7 , the preferred embodiment of the sensor configuration  10  is shown. As described above, the drum  40  is driven by a motor  48  only at initial stages of the loop loading mechanism. After the initial stage, the motor ceases to control the operation of drum  40 , which begins rotating only under the motive force provided by the frictional engagement of the surface of drum  40  with the tape or ribbon  15  as it is rotated around the drum  40 . The only control is provided by the driving mechanism of the two stepper motors  20 ,  22  as is described above. In operative effect, the motor only acts as a support for the spindle or shaft  42  following the initial stages of establishing the initial angular position of the lever arm  30 , and may provide a support for the concentric bushing ring  62 . 
         [0042]    The process control is preferably governed by a sensor and control system  300  ( FIG. 9 ) that is immediately responsive to the indication sensed that will provide a signal to the feed and take-up drive motors ( 20 ,  22   FIG. 1 ) that the ribbon speed must be increased or decreased to adjust the tension at the printing head  12 . The sensing operation may be any of a number of methods, and any type of sensor that is able to provide an immediate signal is available. For example, a series of LED lights (not shown) may provide information as a discrete signal of the angular position of the lever arm  30 . However, as shown in  FIGS. 6-7 , the lever arm  30  is attached by a cantilevered connection mechanism to an electronic sensor, such as sensor system  49 , which provides angular information of the lever arm  30  relative to the axis CL of rotation of the arm  30 . The axis of rotation of the CL of rotation of the arm  30  may be identical to the axis of rotation of shaft  42 . The sensor position is translated into a signal to the feed and take-up drive motors ( 20 ,  22 ,  FIG. 1 ) to immediately implement the required action in reaction to the sensed position. The sensing operation may be continuous, so that the signal to increase or decrease ribbon speed can be monitored with greater precision. 
         [0043]    During normal operation of the ribbon tensioning mechanism  10 , drum  40  is always rotating in the rotational directions as it is driven by the advance of the ribbon  15  along its path from the feed spool  20  toward take-up spool  22 . However, depending on the relative rotational speeds of the feed spool  20  and take-up spool  22 , the planetary lever arm  30  and other forces, for example frictional forces from the printer head, causes the loop  17  to be formed in a variable sized semicircle around drum  40 . When a signal reaches the controller that there is too large of a ribbon loop  17 , the loop must be reduced in size, and that is done by the take-up spool  22  being signalled to increase the speed of rotation so that it takes up more of the ribbon  15  than is being supplied by the feed spool  20 . Simultaneously, the feed spool may be signalled to slow down to supply ribbon at a slower rate and thus pulling back on the loop  17  and thereby reducing its length. Conversely, when the controller  300  recognizes that the ribbon  15  is under tension so that the loop  17  is too small, it signals the feed spool  20  to speed up and the take-up spool  22  to slow down so as to accommodate the condition of the loop  17  and return it to an equilibrium position. 
         [0044]    One method to achieve this close monitoring and control is by utilizing a sensor that utilizes a predictive controller as a sensing mechanism  60  ( FIGS. 7 ,  8 ). Such controllers are commercially available under the brand name Gear Motors from Brain Wave, located in Milan, Italy. The preferred sensor mechanism will now be described with reference to as shown in  FIGS. 5-8  of the drawings. The mechanism comprises a predictive controller mechanism  60  that is configured to sense the exact position of the lever arm  30 , and thus the tape loop  17 , at all times. 
         [0045]    In a preferred embodiment, the motor  48  works in conjunction with the sensing mechanism  60  to provide adequate, and essentially real time, control over the operation of arm  30  so as to provide a minimum reaction time of the arm  30  to sensed conditions. As shown in  FIG. 7 , the arm  30  pivots or rotates about a bushing ring  62  which rotates with the arm around the central axis CL. 
         [0046]    Referring now mostly to  FIGS. 6 and 7 , the sensing mechanism  60  may comprise a second, concentric ring bushing  62  that is disposed around the drum shaft  42  and which extends into the housing of the motor  48 . A portion of the planetary lever arm  30 , distal to the tape  15  ( FIGS. 1-4 ), is connected to the ring bushing  62  by an appropriate means, such as a bolt assembly  64 , so as to provide a unitary structure. Alternatively, the ring bushing  62  and arm  30  may be an integral component (not shown). The concentric ring bushing  62  may be mounted on a journalled bearing contained within the motor housing (not shown) so that the arm  30 , which rotates with the ring  62  can rotate within the arc defined by the aperture  44 . 
         [0047]    The concentric ring bushing  62  is manipulated by motion of the lever arm  30  to rotate about the axis CL, and the journal mount of the concentric ring bushing  62  constrains the motion of the lever arm  30  to the path described by the planetary half crescent aperture  44  shown in  FIG. 4 . That is, the rotation of the concentric ring bushing  62  permits the arm  30 , and the roller guide  32 , to travel only in approximately a half orbit around the cylindrically shaped drum  40  as shown by arrows CW and CCW in  FIG. 7 . The predictive controller mechanism  60  may include preferably electronic sensing components that are available in commercially available devices. Conversely, the sensors may be LED or other sensing devices, for example, motion or proximity detectors, etc., that are disposed at appropriate positions along the arc defined by the crescent aperture  44 , (See A, B in  FIG. 1 ). The significant feature of this invention however lies partly in the ability of the device to sense the tension in the tape or ribbon directly, as a result of the change in equilibrium position of the lever arm, and to send a signal to correct any over or under balance as soon as the movement from the equilibrium position is sensed. It is also important to note that no calculations of any parameter of the system are necessary, in that only the direct sensed signal is the triggering mechanism to activate the control to the spool motors. 
         [0048]    An equilibrium condition of the planetary support lever arm  30  is reached by a balanced opposition of forces arising from the tension of the ribbon  15  and the countervailing bias of the biasing force generated by a biasing means, such as spring  210  ( FIG. 7 ). The spring  210  ideally has a smooth or linear opposing force, irrespective of the amount of stretch that is in the spring at any particular position. The force provided by the biasing means is thus able to provide a constant bias of essentially equal magnitude throughout the rotation of the planetary support arm  30 , and this constant biasing force may be assisted by a cam or gear  46  that is attached to the lever arm  30 . Utilizing such a cam or grooved gear  46  is preferable because it can help provide some flexibility in the system and thereby avoid any sudden changes to the angular momentum of the arm  30  that may cause the loop  17  or ribbon  15  to either tangle or to break in the event that the printer head  12  generates too much frictional force to the tape or ribbon in the printing process. 
         [0049]    With this configuration, the heat transfer printing device is characterized in that it incorporates a cylindrical loading drum  40  disposed after the thermal print head  12  in relationship to the normal direction of travel of the printing ribbon  15 , onto which the printing ribbon  15  is directed and retained in conjunction with the roller guide  32  on the planetary lever support arm  30 . Thus, the constant bias on the planetary support arm  30  exerting a biasing force, maintains constant tension on the ribbon  15  during the printing process. 
         [0050]    Optionally, the heat transfer printing device  10  is provided with a rotation sensor  19  associated with one or more of the guide rollers  14  that indicates the amount of printing ribbon  15  that has already been transferred in order to control the actuation of the motors associated to the feed spool  20  and the take-up spool  22 . This also may provide an indication of the need to change the printing ribbon feed spool  20  as it nears depletion from continual use in the printing process. 
         [0051]    Referring now to  FIG. 8 , a perspective view of the preferred embodiment of the angular position indicator, monitoring and control mechanism  60  for the thermal printing device is shown. Since the connection and configuration of the support lever arm  30  and motor  48 , including the mounting mechanism are essentially the same as that shown in  FIGS. 6-7 , these will not be described in detail herein. The structure provides for an angular position indicator  262 , which is not incorporated into the motor housing  48 , but is located externally adjacent to the wall  50 . A plate, shown as disc  262  in  FIG. 8 , includes a plurality of substantially evenly spaced LED or other photosensors  264  that are disposed in a circumferential pattern adjacent the circumferential or semicircular edge of disc  262 . Photosensors  264  are capable of determining the position of the support lever arm  30  as it is rotated through the angular path defined by the aperture  44  ( FIG. 5 ). As the arm  30  is sensed by any one individual sensor  264 , the position of the arm  30 , and this of the roller guide  32 , is thereby recognized, and a corresponding reaction of the electronic controller, shown in  FIG. 8  as a Printed Circuit Board (PCB)  250 , and corresponding printed circuits  253  and associated leads  65 . The leads or other signal carriers  65  extending from the predictive controller mechanism  60  send the signal either to a CPU  300  ( FIG. 9 ) for processing or directly or indirectly connected to the feed and take-up drive stepper motors (not shown) which drive the take-up and feed spools  20 ,  22 , respectively ( FIG. 1 ), so as to adjust the motor speeds to accommodate the newly sensed conditions. 
         [0052]    Another feature related to the sensor  19  provides operational indicators of the status of the device  10  and the printing process as it proceeds. Referring now to  FIG. 9 , a central processing unit controller  300  is shown in schematic, which includes a number of connection points  302 ,  304  to provide electrical communication to the various elements of the printing device  10 , for example, to receive the lead wires  67  from the sensor  48  ( FIG. 7 ) or from optional sensor  19  ( FIG. 1 ). The signals received from these and other sensors may be utilized to monitor and indicate the status of the device  310  by any of a number visual or auditory or other indications to the operator that the device requires attention, or gives a warning signal that it may require attention in the near future. A recording device, such as a digital cassette tape recorder  306 , may keep a record of the signals received and any output signals that may be generated by the CPU controller  300 , whether automatically or by operation of the user. 
         [0053]    One port  304  of the CPU controller  300  is an output port to which lead wires  308  may be attached, and which at the other end of the lead wires  308  is attached a visual or light indicator  310 . The light indicator may be configured to show one of three system conditions, by flashing or otherwise indicating an indicator color at one of three lights, which are colored red light  312 , yellow light  314 , and green light  316 . The indicator for the green light  316  may signify that the system is in normal operation, for the red light that there is a system malfunction, for example, that the printer ribbon  15  is not traversing through the printer device  10 , or a yellow light  312  which may indicate that the condition is still operational but that attention will soon be required, for example to indicate that spools  20  and  22  will have to be replaced because they have been used up in the printing operation. Other condition indicators may be programmed into the CPU controller  300 , which will ultimately be determined by the requirement of the specific printer device  10 . 
         [0054]    The printing method used to keep constant the ribbon tension during the printing mainly consists of the following stages: 
         [0055]    Transferring the printing ribbon  15  supplied from the feed spool  20 ; 
         [0056]    Displacing the thermal print head  12  in a direction toward the printing ribbon  15 ; 
         [0057]    Holding the printing ribbon  15  against the outer surface  42  of the loading drum  40 , which revolves, and in conjunction with the planetary guide roller  32 , creating a ribbon loop that will determine an essentially constant tension in the printing ribbon  15  during the printing stage; and 
         [0058]    Collecting the loop formed on the loading drum  40  in the take-up spool  22 . 
         [0059]    In the preferred embodiment, the printing ribbon  15  is held against the loading drum  40  by the tension produced by the angular displacement of the planetary guide roller  32  and by the biasing force created by the biasing means  210 . 
         [0060]    The operation of the printing device can be summarized by the following operations: 
         [0061]    a) Detection of the instantaneous speed of the material to be printed by an external speed sensor in contact therewith; 
         [0062]    b) Delivery of a printing activation signal by an external signal (sensors or other devices) for the start of the printing operation; 
         [0063]    c) Activation of the thermal print head and engagement of the print head and the thermal printing ribbon with the material to be printed; 
         [0064]    d) Activation of the printing ribbon feed spool motor; 
         [0065]    e) Activation of a suitable mechanism, including the support lever arm  30 , by the controller  48  in order to load and attract the heat transfer ribbon on the loading drum to form the loop; 
         [0066]    f) Placing the thermal print head near the transfer ribbon and printing on the material to be printed; 
         [0067]    g) Activation of the printed transfer ribbon take-up spool to unload the loop formed on the loading drum, according to a sequence determined by the controller as it processes the signals received from a plurality of sensors; 
         [0068]    h) Rotation of the feed spool motor in the opposite sense to recover the transfer ribbon lost during the acceleration of the feed spool and approaching of the thermal print head motor to the material to be printed. 
         [0069]    An optional step of deactivation of the transfer ribbon take-up spool motor by the required amount according to the printing size is also considered. 
         [0070]    The invention can be used in both continuous mode and for intermittent mode printers, with appropriate parameters being set for either. 
         [0071]    The invention herein has been described and illustrated with reference to the embodiments of  FIGS. 1-9 , but it should be understood that the features and operation of the invention as described is susceptible to modification or alteration without departing significantly from the spirit of the invention. For example, the dimensions, size and shape of the various elements may be altered to fit specific applications. Other means of sensing may become available in the future that do not rely on the presently described mechanisms, but which would not be presently apparent to a person of ordinary skill. Accordingly, the specific embodiments illustrated and described herein are for illustrative purposes only and the invention is not limited except by the following claims.