Patent Publication Number: US-2012027489-A1

Title: Printer with coupled media feed and print head activation mechanism

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     This disclosure relates to a printer and, in particular, to a printer having a single gear train that drives various mechanisms of the printer. 
     Thermal transfer printers for tube media present unique demands in comparison to thermal transfer printers for flat media. As a flat printing surface on the tube media needs to be established, the tube media must be deformed, at least to some degree, during the printing process. In particular, the print media should be flattened proximate the print head and a corresponding platen roller, as it is at this location that the creation of a flat surface for printing is of the greatest importance. 
     In many tube media printers, the print head itself is used to apply and maintain this force to the tube media. To generate this force on the print head, many tube printers include a long lever connected to the print head that is manually activated by a user. This kind of mechanical lever, however, greatly increases the footprint of the tube printer and requires manual activation by the user. Although automatic print head activation mechanisms have been implemented in some tube printers, these mechanisms frequently complicate the structure of the tube printer and require multiple independent motors which add to the overall cost and maintenance of the system. 
     Hence, a need exists for an improved printer for tube media. In particular, there is a need for a printer that automatically applies the force necessary for print head activation without significantly increasing the footprint of the printer and, further, without adding significant cost or complexity to the printer. 
     SUMMARY OF THE INVENTION 
     A printer is disclosed for printing on media. The printer includes a platen roller, a print head, and a media feed roller. The print head is supported by an arm. The arm is actuatable between an activated position in which the print head is urged toward the platen roller to provide a force therebetween and a deactivated position in which the print head is moved away from the platen roller. A motor is coupled to the arm and the media feed roller. The motor selectively actuates the arm between the activated position and the deactivated position and further drives the media feed roller. 
     In many forms of the printer, the motor may be coupled to the arm and the media feed roller by a gear train. The gear train may include a delay gear that initially actuates the arm and, after a delay, drives the media feed roller. The delay gear may be configured to generate a delay having a duration that permits completion of an actuation of the arm before driving the media feed roller. 
     A rocker arm assembly may operably link the motor to a print head activation gear that actuates the arm. The rocker arm assembly may include a central gear that separately intermeshes with two satellite gears. Further, the rocker arm assembly may be pivotable between a forward feed position and a reverse feed position. In the forward feed position, a first gear of the two satellite gears may drive the print head activation gear to move the arm into the activated position and a second gear of the two satellite gears may engage and drive a ribbon spool. In the reverse feed position, the first gear of the two satellite gears may disengage the print head activation gear and the second gear of the two satellite gears may engage and drive the print head activation gear to move the arm into the deactivated position. 
     The print head activation gear may include a plurality of radially outward extending teeth located about a circumference of the gear. In one form, at least a portion of the circumference of the print head activation gear may not have teeth. The portion of the circumference of the print head activation gear that does not have teeth may be positioned such that, during activation of the arm, as the arm approaches the activated position, the first gear of the two satellite gears reaches the portion of the circumference of the print head activation gear that does not have teeth. When the first gear reaches this toothless region of the print head activation gear, the first gear may no longer be able to drive the print head activation gear, thereby preventing further forward driving of the print head activation gear by the first gear. Likewise, another toothless portion of the print head activation gear may exist proximate a circumferential region in which the second gear has driven the print head activation gear to a point in which the arm is in the deactivated position. 
     In some forms, the printer may further include a brake that engages the print head activation gear when the arm approaches the activated position. The print head activation gear may include an outwardly-facing non-toothed surface that engages the brake to maintain the print head activation gear in place. This prevents the portion of the circumference that does not have teeth from slipping and an end tooth on one side of the portion of the circumference does not have teeth from repetitively engaging the first gear of the two satellite gears and generating noise. 
     In one form of the printer, the rocker arm assembly may further include a stop and the print head activation gear may include an axially-facing lip. In this form, when the rocker arm assembly is moved to the forward feed position and the first gear drives the print head activation gear to actuate the arm to the activated position, the stop on the rocker arm assembly may be configured to engage the axially-facing lip on the print head activation gear. This engagement may maintain the position of an axis of rotation of the first gear of the two satellite gears relative to an axis of rotation of the print head activation gear. This has the effect of maintaining the meshing of the first gear with the print head activation gear. 
     The print head activation gear may also include a cam surface and the arm may also include a projection that contacts the cam surface. An interaction of the cam surface with the projection during rotation of the print head activation gear may cause actuation of the arm. The cam surface may have a profile that generates a dwell time during activation of the print head toward the platen roller in which the print head is held in position apart from the platen roller before activation is complete. During the dwell time, a ribbon drive may be rotated to take up slack in an ink ribbon. 
     In some forms, the platen roller of the printer may also be driven by the motor. 
     A method of operating a printer for printing on tube media is also disclosed. The method includes operating a motor that drives a gear train. An arm supporting a print head is actuated via the gear train. The arm is actuated between an activated position in which the print head is urged toward the platen roller to provide a force therebetween and a deactivated position in which the print head is moved away from the platen roller. A media feed roller is also driven via the gear train. 
     In one form of the method, a delay gear in the gear train first may drive actuation of the arm and, only after actuation of the arm is complete, does the delay gear in the gear train drive the media feed roller. 
     Thus, a printer for tube media is provided that both actuates a print head between activated and deactivated positions and, further, drives a media feed roller using a single motor. The functions are timed such that the feed mechanisms may not engage until activation or deactivation of the arm and the attached print head has been completed. The disclosed structure avoids the need for a large mechanical lever to apply print head force, which increases the footprint of the printer and presents usability issues. Moreover, as only a single motor is used to perform both functions, the cost and size of the tube printer is minimized. 
     These and still other advantages of the invention will be apparent from the detailed description and drawings. What follows is merely a description of a preferred embodiment of the present invention. To assess the full scope of the invention, the claims should be looked to as the preferred embodiment is not intended to be the only embodiment within the scope of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top side perspective view of a tube printer with the top cover removed; 
         FIG. 2  is a perspective view of a portion of the innards of the tube printer including a gear train and an arm that supports a print head; 
         FIGS. 3 through 7  are side views of the gear train which illustrate various sequential steps of the activation and deactivation of a print head at the end of the arm; 
         FIG. 8  is a perspective view of a rocker arm assembly separate from the gear train; 
         FIG. 9  is a top side perspective view of the print head activation gear illustrating a cam surface; and 
         FIG. 10  is a bottom side perspective view of the print head activation gear illustrating the axially-facing lip. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to  FIG. 1 , a tube printer  10  is shown for printing on tube media. The tube printer  10  includes a housing  12  that, as illustrated, receives a media cartridge  14  and a ribbon cartridge  16  on either side of a media path for the tube media. Proximate the exit end of the media cartridge  14 , a media feed roller  18  and a corresponding pressure roller  20  are positioned to pull the tube media from the media cartridge  14 . During loading of the media cartridge  14 , the pressure roller  20  may be actuated toward or away from the media feed roller  18  by actuation of a lever  22  which overcomes a biasing force (provided by a spring or the like) that tends to bias the pressure roller  20  toward the media feed roller  18 . After the tube media is directed through the media feed roller  18  and the pressure roller  20 , the tube media is then fed though an area between a print head  24  and a platen roller  26 . 
     The print head  24  is biased toward the platen roller  26  to apply pressure to the tube media and to pinch the tube media between the print head  24  and the platen roller  26 , thereby establishing a flat surface on the tube media for printing. In the form shown, the print head  24  is a thermal print head that heats an ink ribbon that is threaded between the print head  24  and the tube media. By selectively heating and cooling portions of the print head  24 , the print head  24  is able to print patterns including, for example, text and images onto the tube media as the tube media is fed through the print head  24  and the platen roller  26 . 
     Although not shown in  FIG. 1 , the tube printer  10  includes a cutting mechanism or the like downstream of the print head  24 . The cutting mechanism is used to sever a length of printed tube media from the length of unprinted tube media. 
     While  FIG. 1  illustrates the placement of a media cartridge  14  within the housing  12  of the tube printer  10 , other printing configurations may be used to print on bulk quantities of tube media. For example, to print on tubing from a large spool using the tube printer  10 , instead of loading a media cartridge  14  into the housing  12 , an end of the tube media may be inserted in a bulk opening  28  on the lateral side of the housing  12 . The inserted end of the tube media may then be routed through the media feed roller  18  and the pressure roller  20  and then past the print head  24  and the platen roller  26 . 
     Looking now at  FIGS. 2 through 7 , a gear train within the tube printer  10  is shown, albeit separate from the tube printer  10  to better display the various gears and components and their interaction with one another. 
     The gear train is constructed to both drive the media feed roller  18  and platen roller  26  as well as activate or deactivate an arm  30  that supports the print head  24  using a single motor  32 . In one operational direction of the motor  32 , the arm  30  is moved from the deactivated position in which the print head  24  is spaced from the platen roller  26  (as is illustrated in  FIG. 3 ) to the activated position in which the print head  24  is moved toward the platen roller  26  (as is illustrated in  FIG. 5 ) thereby providing a pressure between the print head  24  and the platen roller  26  that pinches the tube media and applies a sufficient pressure for thermal transfer printing. In the forward operational direction, the arm  30  is actuated to the activated position by the gear train and, only after the activation of the arm  30 , do the media feed roller  18  and the platen roller  26  begin to rotate. In the reverse operational direction, the arm  30  is moved from the activated position to the deactivated position and, after the arm  30  is deactivated, the media feed roller  18  and platen roller  26  are rotated in a reverse feed direction. 
     The gear train initially extends from a motor-driven gear  34  which is, as the name indicates, driven by the motor  32  to a delay gear  36 . At the delay gear  36 , the gear train splits into two legs. A first leg connects the delay gear  36  to a print head activation gear  38  and ribbon feed components. A second leg connects the delay gear  36  to the media feed roller  18  and the platen roller  26 . The delay gear  36  is configured to first cause the motor-driven gear  34  to effectuate rotation of the print head activation gear  38  to activate or deactivate the arm  30 . Then, after the delay is complete and the arm  30  is actuated, the delay gear  36  drives the media feed roller  18  and the platen roller  26  to feed the tube media in a forward or reverse direction. 
     The motor-driven gear  34  is coupled to the delay gear  36  by a first idler gear  40  and a second idler gear  42 . These idler gears  40  and  42  are each dual layer spur gears. When the motor  32  is operating, the teeth of the motor-driven gear  34  engage the teeth  39  on the layer of the first idler gear  40  having the larger diameter causing the rotation of the first idler gear  40  in a direction opposite the motor-driven gear  34 . The teeth  41  of the layer of the first idler gear  40  with the smaller diameter then engage the teeth  43  of the layer of the second idler gear  42  with the larger diameter to cause rotation of the second idler gear  42  in a direction opposite the first idler gear  40 , but in the same rotational direction as the motor-driven gear  34 . The teeth  45  of the layer of the second idler gear  42  with the smaller diameter then engage a direct-driven portion  44  of the delay gear  36 . 
     In the transfer of motion from the motor-driven gear  34  to the delay gear  36 , the above-described configuration of the idler gears  40  and  42  results in a reduction in the speed of the input from the motor-driven gear  34  to the delay gear  36 . However, by reduction of the gear speed, an increase in the torque is realized. 
     As mentioned above, upon driving of the delay gear  36 , part of the delay gear  36  immediately drives the leg of the gear train relating to the actuation of the arm  30  and, after a duration, another portion of the delay gear  36  drives the leg of the gear train relating to the rotation of the media feed roller  18  and the platen roller  26 . The delay gear  36  has a two-part structure including the above-mentioned direct-driven portion  44  that is driven by the motor  32  via the first and second idler gears  40  and  42  and a delayed portion  46  that will rotate with the direct-driven portion  44  after a predetermined amount of angular rotation of the direct-driven portion  44 . The direct-driven portion  44  and the delayed portion  46  have axes of rotation that are coaxial with one another and diameters that are equal to one another. 
     To create the delay, the axial faces of the direct-driven portion  44  and the delayed portion  46  that face one another have features that interact with one another, such as projections, tabs, and so forth. When the direct-driven portion  44  of the delay gear  36  is rotated, it will require some amount of angular rotation before the features on the axial faces interact with one another to cause the delayed portion  46  to begin rotating with the direct-driven portion  44 . When the direction of rotation of the direct-driven portion  44  is reversed, then the features on the axially facing surfaces will disengage one another and the delayed portion  46  will again not be driven until the direct-driven portion  44  of the delay gear  36  re-engages the delayed portion  46  after some amount of rotation in the other angular direction of rotation. It should be appreciated that the features of the delay gear  36  that interact between the direct-driven portion  44  and the delayed portion  46  need not necessarily be formed on the axial faces of the portions. For example, a projection on one of the portions could engage a slot extending through at least a segment of the other portion. 
     The teeth of the direct-driven portion  44  of the delay gear  36  also drive a rocker arm assembly  48 . As will be described in further detail below, the rocker arm assembly  48  pivots between two positions depending on the direction of operation of the motor  32  to selectively actuate the arm  30  and, in at least one of the two positions, drive the ribbon feed components. 
     The rocker arm assembly  48  is shown separate from the gear train and in more detail in  FIG. 8 . The rocker arm assembly  48  includes a bracket  50  that supports a central gear  52  which separately meshes with two satellite gears  54  and  56  about the circumference of the central gear  52  and with the two satellite gears  54  and  56  meshing with the central gear  52  at two different non-overlapping axial heights of the central gear  52 . The bracket  50  fixes the position of the rotational axes of the central gear  52  relative to the two satellite gears  54  and  56 . The rocker arm assembly  48  is capable of pivoting about the axis of rotation of the central gear  52  such that, when the rocker arm assembly  48  pivots about the axis of the central gear  52 , the satellite gears  54  and  56  rotate about the central gear  52 . 
     The bottom portion of the bracket  50  also includes a projection  58  proximate the rightmost satellite gear  56  (as viewed from the perspective of  FIGS. 3 through 7 ). The projection includes an upwardly extending stop  60  which selectively interacts with the print head activation gear  38  as will be described in further detail below. 
     The rocker arm assembly  48  brings the two satellite gears  54  and  56  into selective engagement with the print head activation gear  38  and a ribbon spool idler gear  62  that is coupled to a ribbon drive  64 . The engagement of the two satellite gears  54  and  56  with the print head activation gear  38  and the ribbon spool idler gear  62  depends on the pivotal position of the rocker arm assembly  48 . 
     To change the pivotal position of the rocker arm assembly  48 , the direct-driven portion  44  of the delay gear  36  drives the central gear  52  of the rocker arm assembly  48 . When the central gear  52  rotates, this can initially cause the rocker arm assembly  48  to pivot (depending on the initial position of the rocker arm assembly and the direction of rotation). When pivoted to one of its extremes, any additional rotation of the central gear  52  is then transmitted to the two satellite gears  54  and  56  to drive the rotation of the teeth of the two satellite gears  54  and  56 . 
     The rocker arm assembly  48  is pivotable between two positions, a forward feed position and a reverse feed position, which are both restricted by the locations of surrounding gears. In the forward feed position in which the rocker arm assembly  48  has been rotated clockwise, the rightmost satellite gear  56  engages the print head activation gear  38  while the leftmost satellite gear  54  engages the ribbon spool idler gear  62 . In the reverse feed position in which the rocker arm assembly  48  has been rotated counter-clockwise, the leftmost satellite gear  54  engages the print head activation gear  38  while the rightmost satellite gear  56  is cleared from engagement with other gears (except for the central gear  52  to which it is attached by the bracket  50 ). 
     When the motor-driven gear  34  is driven in the forward direction (which is the clockwise direction as viewed from the perspective of  FIGS. 3 through 7 ), this causes the central gear  52  to rotate clockwise, thereby pivoting the rocker arm assembly  48  to the forward feed position. In the forward feed position, the continued clockwise rotation of the central gear  52  causes the counter-clockwise rotation of the two satellite gears  54  and  56 , which results in the clockwise rotation of the print head activation gear  38  as well as the clockwise rotation of the ribbon spool idler gear  62  and the counter clockwise rotation of the ribbon drive  64 . 
     Conversely, when the motor-driven gear  34  is driven in a reverse direction (which is the counter-clockwise direction), this causes the central gear  52  to rotate counter-clockwise, thereby pivoting the rocker arm assembly  48  to the reverse feed position. After pivoting, the counter-clockwise rotation of the central gear  52  causes the clockwise rotation of the two satellite gears  54  and  56 . After pivoting to the reverse position, the leftmost satellite gear  54  contacts and drives another the print head activation gear  38  in a counter-clockwise direction. Although the central gear  52  continues to drive the rightmost satellite gear  56 , the rightmost satellite gear  56  does not mesh with any other gears as it has been swung away from the print head activation gear  38  and, accordingly, does not drive any other gears. 
     Referring now to  FIGS. 9 and 10 , the print head activation gear  38  is shown in more detail. On the top side of the print head activation gear  38 , a cam surface  66  is formed. This cam surface  66  protrudes from the axial surface of the print head activation gear  38  and forms a curved surface that extends from approximately the rotational center of the print head activation gear  38  to approximately an outer circumference  68  of the print head activation gear  38 . 
     This cam surface  66  engages a post  70  on the arm  30  to cause the actuation of the arm  30  and the print head  24  between the activated and deactivated positions. As best seen in  FIGS. 2 through 7 , the arm  30  has two guiding slots  72  and  74  which engage posts  76  and  78 , respectively. The two guiding slots  72  and  74  and the posts  76  and  78 , define a range of motion for the arm  30  between the activated and deactivated positions along which the arm  30  is translated and rotated. As the print head activation gear  38  rotates, the post  70  of the arm  30  engages the cam surface  66  thereby causing the arm  30  to move within the limits of the guiding slots  72  and  74 . 
     While the print head activation gear  38  has teeth that extend about the outer circumference  68 , an angular toothless section  80  of the outer circumference  68  lacks teeth. When the print head activation gear  38  is rotated to the point where the teeth of the rightmost satellite gear  56  reach the angular toothless section  80  of the print head activation gear  38 , the print head activation gear  38  no longer is able to be further rotated in that direction as the teeth of the rightmost satellite gear  56  have no teeth to engage on the print head activation gear  38  at this angular orientation, thereby preventing the further rotation of the print head activation gear  38  in that direction. This angular toothless section  80  is positioned such that the print head activation gear  38  does not over-actuate the arm  30  by engagement with the cam surface  66  and excessively jam the print head  24  into the platen roller  26 . 
     The print head activation gear  38  also includes an outwardly-facing non-toothed surface  82  that selectively engages a brake  84  to prevent the teeth of the rightmost satellite gear  56  from continually clipping on the last tooth of the print head activation gear  38 . During forward feeding, when the print head activation gear  38  is rotated to a point at which the rightmost satellite gear  56  approaches the angular toothless section  80 , the brake  84  engages the outwardly-facing non-toothed surface  82  to maintain the print head activation gear  38  in place, thereby retaining the arm  30  in the activated position. 
     In the form shown, the brake  84  is a flexible member having a convex surface  86  that faces the print head activation gear  38 . The outwardly-facing non-toothed surface  82  of the print head activation gear  38  has a concave surface  88  that generally corresponds to the convex surface  86  of the brake  84 . When the print head activation gear  38  is rotated to the point at which the teeth of the rightmost satellite gear  56  are approaching the angular toothless section  80  of the print head activation gear  38 , the brake  84  initially flexes outwardly away from the outwardly-facing non-toothed surface  82  of the print head activation gear  38 . Upon further rotation, the convex surface  86  of the brake  84  passes a point of maximum deflection away from the outwardly-facing non-toothed surface  82  and then, as the brake  84  attempts to return to a non-deflected state, begins to seat within the concave surface  88  of the outwardly-facing non-toothed surface  82 . This eventually forces the rotation of the print head activation gear  38  to a point at which the teeth of the rightmost satellite gear  56  will not engage the last tooth of the print head activation gear  38 . Accordingly, the point at which the convex surface  86  of the brake  84  is comfortably seated within the concave surface  88  of the outwardly-facing non-toothed surface  82  corresponds to this point of non-engagement of the rightmost satellite gear  56  and the print head activation gear  38 . 
     Further, looking at the bottom side of the print head activation gear  38  in  FIG. 10 , an axially-facing lip  90  extends outwardly from the print head activation gear  38 . During rotation of the print head activation gear  38 , the axially-facing lip  90  selectively engages the stop  60  on the rocker arm assembly  48  within a predetermined angular range of rotation to maintain contact between the teeth of the print head activation gear  38  and the rightmost satellite gear  56 . In the form shown, the axially-facing lip  90  will engage the stop  60  when the rocker arm assembly  48  has been moved to the forward feed position and has begun to drive the print head activation gear  38 . This maintains engagement of the rightmost satellite gear  56  and the print head activation gear  38  until the print head activation gear  38  is rotated to the activated position at which position the brake  84  engages the print head activation gear  38  and the teeth of the rightmost satellite gear  56  have reached the angular toothless section  80  of the print head activation gear  38 . The axially-facing lip  90  does not angularly extend into the angular toothless section  80  of the print head activation gear  38 , such that stop  60  does not prevent the rocker arm assembly  48  from pivoting from the forward feed position to the reverse feed position when the motor  32  begins to run in the reverse direction. 
     It should be appreciated that the delay gear  36  provides a sufficient amount of delay such that the arm  30  can be activated or deactivated without the delay gear  36  initiating the feeding via the media feed roller  18  or the platen roller  26 . Once the print head  24  has been moved, the delayed portion  46  of the delay gear  36  begins to drive the media feed roller  18  and the platen roller  26  by toothed sections at the ends thereof. In the form shown, in the forward direction, the delay gear  36  rotates counter-clockwise and, therefore, the media feed roller  18  (which is the upper roller of the media feed roller  18  and pressure roller  20  pair) rotates clockwise. An idler gear  92  connects the media feed roller  18  to the platen roller  26 , and the idler gear  92  ensures that the platen roller  26  is also rotated in the clockwise direction and at such a rate as to maintain a slight tension on the tube media between the media feed roller  18  and the platen roller  26 . 
     The gear train having been described, the general operation of the tube printer  10  can be traced with sequential reference to  FIGS. 3 through 7 . 
     For purposes of this operational description, the tube printer  10  is initially set to the position in  FIG. 3 . In  FIG. 3 , the arm  30  is deactivated so that the print head  24  is spaced from the platen roller  26  and the rocker arm assembly  48  is in the reverse feed position. This is the arrangement of the gear train components after the motor  32  has been run in reverse to, for example, remove and replace the media cartridge  14 . Accordingly, in  FIG. 2 , the post  70  of the arm  30  has engaged the cam surface  66  to move the post  70  away from the rotational axis of the print head activation gear  38  such that the arm  30  and the print head  24  are forced into the disengaged position against any biasing force on the arm  30 . 
     At this point, the motor  32  can be run in a forward direction which, as stated above, is in a clockwise direction. As indicated in  FIG. 4 , the forward operation of the motor  32  first has the effect of pivoting the rocker arm assembly  48  to the forward feed position in which the leftmost satellite gear  54  is brought into engagement with the ribbon spool idler gear  62  and the rightmost satellite gear  56  is brought into engagement with the print head activation gear  38 . At this point, the delay gear  36  only directs the forward motion of the motor  32  through the leg of the gear train directed at the actuation of the arm  30  and print head  24  via the direct-driven portion  44 . 
     As shown in  FIG. 5 , the further forward motion of the motor  32  causes the rightmost satellite gear  56  to drive the print head activation gear  38  clockwise. This clockwise rotation of the print head activation gear  38  and a biasing force on the arm  30  urges the print head  24  toward the platen roller  26  causing the post  70  to travel radially inwardly along the cam surface  66  toward the center of the print head activation gear  38  until the print head  24  is activated against the platen roller  26  (with tube media and an ink ribbon therebetween). 
     As noted above, when the arm  30  is moved to the activated position, the rightmost satellite gear  56  approaches the angular toothless section  80  of the print head activation gear  38  and the brake  84  engaging the outwardly-facing non-toothed surface  82  of the print head activation gear  38  to maintain the position of the print head activation gear  38 . At this point, no further forward motion is transferred to the print head activation gear  38 . 
     However, the continual forward motion of the motor  32  drives the other gear train components. The continual forward driving of the motor  32  drives the ribbon drive  64  counter-clockwise via the leftmost satellite gear  54  and the ribbon spool idler gear  62  to feed the ink ribbon. Further, after the delay on the delay gear  36  has elapsed, the delayed portion  46  of the delay gear  36  begins to drive the media feed roller  18  in a clockwise direction to feed the tube media between the media feed roller  18  and the pressure roller  20 . Moreover, the teeth on the axial end of the media feed roller  18  engages the idler gear  92  which also engages teeth on an axial end of the platen roller  26  to drive the platen roller  26  in clockwise direction. 
     It should be noted that during the movement of the arm  30  from the deactivated to the activated position, the print head activation gear  38  may attempt to backdrive the rocker arm assembly  48 . To avoid separation of the rightmost satellite gear  56  from the print head activation gear  38 , shortly after the rightmost satellite gear  56  begins to drive the print head activation gear  38 , the stop  60  of the rocker arm assembly  48  engages the axially-facing lip  90  on the print head activation gear  38 . This maintains engagement of the rightmost satellite gear  56  and the print head activation gear  38  for the majority of the forward rotation of the print head activation gear  38 . However, at the rotational angles of the print head activation gear  38  shown in  FIGS. 3 and 5 , the axially-facing lip  90  does not engage or restrict the stop  60 , such that the rocker arm assembly  48  may pivot relative to the print head activation gear  38  so that either of the two satellite gears  54  and  56  during a change in the direction of operation of the motor  32 . 
     It should also be appreciated that the cam surface  66  is formed with such a profile as to add a dwell time during the activation of the print head  24  toward the platen roller  26  and before the activation is complete. This dwell occurs over the span of the cam surface  66  that is of a generally constant radial distance from the axis of rotation of the print head activation gear  38 . By adding the dwell section, the print head  24  is initially moved part way toward the platen roller  36  and then held at this position for a length of time before the cam surface  66  further moves the print head  24  toward the platen roller  26 . During this period of dwell, the leftmost satellite gear  54  will continue to drive the ribbon spool idler gear  62  and the ribbon drive  64  to take up slack in the ink ribbon and/or to tighten the ink ribbon before the print head  24  is moved into place. Slack in the ink ribbon of this type may be generated due to operator mishandling of the cartridge or possibly during deactivation of the print head  24 . In any event, adding a dwell during activation of the print head  24  by shaping the cam surface  66  accordingly advantageously provides time to remove this slack before activation is complete. 
     As shown in  FIG. 6 , when the motor  32  is subsequently driven in a reverse feed direction, the rocker arm assembly  48  pivots to the reverse feed position by the counter-clockwise rotation of the central gear  52 . In this position, the rightmost satellite gear  56  is moved clear of the print head activation gear  38  and the leftmost satellite gear  54  engages a toothed portion of the print head activation gear  38 . While this pivoting occurs, the brake  84  holds the print head activation gear  38  in its rotational position as the two satellite gears  54  and  56  switch engagement with the print head activation gear  38 . 
     When the motor  32  continues to run in the reverse direction, this causes the leftmost satellite gear  54  to be rotated in a clockwise direction as shown in  FIG. 7 , which causes the print head activation gear  38  to rotate in a counter-clockwise direction. This counter-clockwise rotation causes the post  70  of the arm  30  to slide away from the rotational axis of the print head activation gear  38  as the post  70  engages the cam surface  66 . This movement of the post  70  ultimately moves the arm  30  and the print head  24  thereon to the disengaged position shown in  FIG. 3 . 
     As in the movement to the engaged position, the print head activation gear  38  may have a second angular toothless section  94  that prevents further backward driving of the print head activation gear  38  after the arm  30  has been actuated to the disengaged position. As seen in  FIGS. 8 through 10 , it can be seen that the two satellite gears  54  and  56  and the toothless sections  80  and  94  may be located on different levels such that different rotational stop positions may be defined based on the forward or backward direction of rotation (and the level of the satellite gear that engages the print head activation gear  38 ). 
     In the reverse direction, as with the forward direction, once the arm  30  actuation is complete (in the case of the reverse direction, the arm  30  is moved to the deactivated position), the delay gear  36  begins to drive the media feed roller  18  and the platen roller  26 , albeit in a reverse direction. In some configurations, the platen roller  26  may have a clutch installed therein so that the platen roller  26  does not rotate at a rate greater than the media feed roller  18  and in such a manner as to create bunching of the reverse fed tube media in the media path. 
     Thus, a tube printer is disclosed that first actuates the print head and then further operates the feed mechanism. All of this is done with a single motor that drives the disclosed gear train having two separate legs. 
     Many modifications and variations to this preferred embodiment will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiment. To ascertain the full scope of the invention, the following claims should be referenced.