Abstract:
A writing instrument includes a barrel, a refill assembly, and a refill plug assembly that is quick to release from the barrel and quick to re-attach to the barrel when changing a refill assembly. The refill plug assembly is quickly secured to the barrel of the writing instrument and quickly released from the barrel of the writing instrument through a twisting and/or pushing action that may require less than one full turn to disengage from the barrel and to re-attach to the barrel, thus expediting replacement of the refill assembly.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The invention generally relates to a refill plug assembly for accessing a refill assembly of a writing instrument and more specifically to a refill plug assembly that is quickly secured to the barrel of the writing instrument and quickly released from the barrel of the writing instrument through a twisting and/or pushing action. 
         [0003]    2. Related Technology 
         [0004]    Some conventional writing instruments have a replaceable refill assembly for replacing ink when ink in one refill assembly is depleted. Typically, the refill assembly is longitudinally disposed within a hollow center of a barrel of the writing instrument. The hollow center of the barrel may be accessed by removing a front portion (or ferrule portion) of the writing instrument, or the hollow center portion may be accessed by removing a cap on an end of the barrel opposite the writing point. The refill assemblies may include an ink reservoir and a writing point that is fluidly connected to the ink reservoir so that replacing the refill assembly also includes replacing the writing point. Other refill assemblies may not include a writing point and such refill assemblies may be fluidly connected to the writing point during insertion of the refill assembly into the barrel. 
         [0005]    When accessing the hollow portion of the barrel, from either end, the cap or the ferrule is typically attached to the barrel with a threaded connection. To remove the cap or the ferrule, the cap or the ferrule must be rotated through several complete turns before the threads disengage. As a result, changing the refill assembly is time consuming because removing the ferrule or the cap and re-attaching the ferrule and cap are both time consuming operations. 
       SUMMARY 
       [0006]    A writing instrument includes a barrel and a refill plug assembly that is quickly released from the barrel and quickly re-attached to the barrel when changing a refill assembly. In one embodiment, the refill plug assembly requires less than one full turn to disengage from the barrel and to re-attach to the barrel, thus expediting replacement of the refill assembly. 
         [0007]    In another embodiment, a refill plug assembly includes a button having a button first end, a button second end, and a hollow bore, the hollow bore having an opening proximate the first button end. A sheath is operatively connected to the button, the sheath having a first sheath end, a second sheath end, a through-bore, and external turn threads disposed on an outer surface proximate the first sheath end. A plunger is slidably disposed within the through-bore of the sheath. 
         [0008]    In another embodiment, a refill plug assembly includes a button having a button first end, a button second end, and a hollow bore, the hollow bore having an opening proximate the first button end. A sheath is operatively connected to the button, the sheath having a first sheath end, a second sheath end, and a through-bore. A plunger is slidably disposed within the through-bore of the sheath so that the plunger is displaceable between a first extended position in which a first plunger end is proximate the second sheath end and a second retracted position in which the first plunger end is proximate the button second end. One or more posts extend outward from the sheath, the posts being sized and shaped to cooperate with a cam channel on a cam liner to releasably secure the refill plug assembly to a barrel of a writing instrument. 
         [0009]    In yet another embodiment, a refill plug assembly includes a button having a button first end, a button second end, and a hollow bore, the hollow bore having an opening proximate the first button end. A sheath is operatively connected to the button, the sheath having a first sheath end, a second sheath end, and a through-bore. A plunger is slidably disposed within the through-bore of the sheath so that the plunger is displaceable between a first extended position in which a first plunger end is proximate the second sheath end and a second retracted position in which the first plunger end is proximate the button second end. One or more posts extend radially outward from a free end of a flexible arm on the sheath The flexible arm is disposed between two legs of a channel and the one or more posts cooperate with a cam groove on a cam liner to releasably secure the refill plug assembly to a barrel of a writing instrument. 
         [0010]    In another embodiment, a writing instrument having a refill plug assembly includes a barrel having a hollow central bore. A refill assembly including an ink reservoir that is fluidly connected to a writing point is removably disposed within the hollow central bore of the barrel. A refill plug assembly is disposed at one end of the hollow central bore, the refill plug assembly including a button having a first button end, a second button end, and a hollow bore, the hollow bore having an opening proximate the first button end. A sheath is operatively connected to the button, the sheath having a first sheath end, a second sheath end, and a through-bore, and a plunger is slidably disposed within the through-bore of the sheath so that the plunger is displaceable between a first extended position in which a first plunger end is proximate the second sheath end and a second retracted position in which the first plunger end is proximate the button second end. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Further features and advantages of the invention can be gathered from the claims, the following description, and the attached diagrammatic drawings, wherein: 
           [0012]      FIG. 1  is a longitudinal cross-sectional view of a writing instrument with a refill plug assembly; 
           [0013]      FIG. 2  is a longitudinal cross-sectional view of the writing instrument of  FIG. 1  with the refill plug assembly and a refill assembly partially removed from a barrel of the writing instrument; 
           [0014]      FIG. 3  is a longitudinal cross-sectional view of the writing instrument of  FIG. 1  with the refill plug assembly removed from the barrel; 
           [0015]      FIG. 4  is a side view of the refill plug assembly of the writing instrument of  FIG. 1 ; 
           [0016]      FIG. 5  is a longitudinal cross-sectional view of a writing instrument with an alternate embodiment of a refill plug assembly; 
           [0017]      FIG. 6  is a side view of a button, a sheath, and a plunger of the refill plug assembly of the writing instrument of  FIG. 5 ; 
           [0018]      FIG. 7  is a side view of a liner of the refill plug assembly of the writing instrument of  FIG. 5 ; 
           [0019]      FIG. 8  is a close up view of the refill plug assembly of the writing instrument of  FIG. 5  in an unlocked position with the barrel of the writing instrument being partially removed; 
           [0020]      FIG. 9  is a close up view of the refill plug assembly of the writing instrument of  FIG. 5  in a first intermediate position between an unlocked position and a locked position with the barrel of the writing instrument being partially removed; 
           [0021]      FIG. 10  is a close up view of the refill plug assembly of the writing instrument of  FIG. 5  in a second intermediate position between an unlocked position and a locked position with the barrel of the writing instrument being partially removed; 
           [0022]      FIG. 11  is a close up view of the refill plug assembly of the writing instrument of  FIG. 5  in a locked position with the barrel of the writing instrument being partially removed; 
           [0023]      FIG. 12  is a close up cross-sectional view of a portion of the refill plug assembly and a portion of the refill assembly; 
           [0024]      FIG. 13  is a longitudinal cross-sectional view of a writing instrument with yet another alternate embodiment of a refill plug assembly; 
           [0025]      FIG. 14  is a side view of a sheath of the refill plug assembly of  FIG. 13 , the sheath having a flexible arm; 
           [0026]      FIG. 15  is a side view of a cam liner of the refill plug assembly of  FIG. 13 ; 
           [0027]      FIG. 16  is a side view of the refill plug assembly of  FIG. 13  in an unlocked position with the barrel of the writing instrument being partially removed; and 
           [0028]      FIG. 17  is a side view of the refill plug assembly of  FIG. 13  in a locked position with the barrel of the writing instrument being partially removed. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The disclosed refill plug assembly allows a user quick and easy access to a hollow portion of a barrel for replacement of an ink refill assembly. The refill plug assembly may be releasably secured to the barrel with a connection that engages or disengages the barrel with a twist and/or a push of the refill plug assembly. 
         [0030]    The writing instrument  10  exemplified in the drawings has a writing tip comprising an extruded plastic nib, however, other writing points including, but not limited to ball points, porous plastic nibs, fountain pen nibs, and felt tip pen nibs can be used. In addition to writing instruments, other fluid application devices could also be made in accordance with the teachings of the disclosure by selection of appropriate components. 
         [0031]    Turning now to  FIGS. 1-4 , the writing instrument  10  includes a barrel  12  having a first barrel end  14 , a second barrel end  16 , and a hollow central bore  18 . A ferrule section  20  may extend from the first barrel end  14 . In some embodiments, the ferrule section  20  and the barrel  12  may be separate components; in others, the ferrule section  20  may be integrally formed with the barrel  12 . 
         [0032]    A refill assembly  22  may be disposed within the hollow central bore  18 . The refill assembly  22  may include an ink reservoir  24  that is fluidly connected to a writing point  26 . In some embodiments, an ink feedstick  28  may be fluidly connected to both the ink reservoir  24  and to the writing point  26  to facilitate delivery of ink from the ink reservoir  24  to the writing point  26 . The ink feedstick  28  may be an extruded feedstick or a fibrous feedstick, for example. Alternatively, the ink reservoir  24  can be fluidly connected to the writing point  26  via a lumen. In some embodiments the ink reservoir  24  may be a fibrous reservoir and in other embodiments the ink reservoir  24  may be a free ink reservoir. 
         [0033]    A refill plug assembly  40  may be releasably secured to the barrel  12  at the second barrel end  16 . The refill plug assembly  40  prevents the ink refill assembly  22  from unintentionally becoming dislodged from the hollow central bore  18  and maintains the ink refill assembly  22  in its proper position within the barrel  12 . The refill plug assembly  40  may be quickly and easily removed to access the ink refill assembly  22 . For example, in one exemplary embodiment, the refill plug assembly  40  may be rotated through less than one full turn to release the refill plug assembly  40  from the barrel  12 . 
         [0034]    The refill plug assembly  40  may include a button  42 , a sheath  52 , and a plunger  62 . The button  42  may have a first button end  44  and a second button end  46 . The button  42  may also include a hollow bore  48  having an opening  50  proximate the second button end  46 . The sheath  52  may include a first sheath end  54 , a second sheath end  56 , and a through bore  58 . A first sheath portion  60  may be operatively connected to the button  42  and a second sheath portion  64  may extend away from the button  42 . The first sheath portion  60  may have an inner diameter that is larger than an inner diameter of the second sheath portion  64 . An angled portion  66  may connect the first sheath portion  60  to the second sheath portion  64 . 
         [0035]    The plunger  62  may be slidably attached to the second sheath portion  64 . So that the plunger is displaceable between a first extended position in which a first body end  70  is proximate the second sheath end  56  and a second retracted position in which the first body end  70  is proximate the button second end  46 . The plunger may include a plunger body  68  having the first body end  70  and a second body end  72 . At least a portion of the plunger body  68  may be disposed within the through bore  58  of the sheath  52 . The plunger body  68  may be displaceable longitudinally within the through bore  58  substantially parallel to a longitudinal axis A of the sheath  52 . In some embodiments, the through bore  58  and the plunger body  68  may be substantially cylindrical in shape. In other embodiments, the through bore  58  and the plunger body  68  may take on other shapes as long as the plunger body  68  has a shape that fits within the through bore  58 . In preferred embodiments, the plunger body  68  has an outer shape that is complimentary to the inner shape of the through bore  58 . 
         [0036]    The second portion  64  of the sheath  52  may include an inner annular flange  74  extending inwardly from an inner surface  73  of the through bore  58  proximate the first sheath end  56 . The inner annular flange  74  may be sized and shaped to retain at least a portion of the plunger  62  within the through bore  58 . Similarly, the plunger  62  may include an outer annular flange  76  proximate the first body end  70 , the outer annular flange  76  being sized and shaped to retain the plunger  62  at least partially within the through bore  58 . In one embodiment, the outer annular flange  76  may cooperate with the inner annular flange  74  to prevent the plunger  62  from moving completely out of the through bore  58 . The inner annular flange  74  may act as a stop for the outer annular flange  76 , thus preventing further longitudinal movement of the plunger  62  away from the sheath  52 . 
         [0037]    A retaining element  77  may be located proximate the second body end  72 . The retaining element  77  may cooperate with the refill assembly  22  to releasably secure the plunger  62  to the refill assembly  22  to facilitate removal of the refill assembly  22  from the barrel  12 . In one embodiment, the retaining element  77  may have the shape of an annular ring with an annular opening facing the refill assembly  22 . The annular ring may be sized to releasably receive a portion of the refill assembly  22 . More specifically, the annular ring may be sized to receive an annular wall  75  of the refill assembly  22  that may be formed at least in part by an annular channel  78 . 
         [0038]    In one embodiment the sheath  52  may include external threads  80  disposed on an outer surface of the first portion  60  of the sheath  52 . The external threads  80  may cooperate with internal threads  82  disposed on an inner surface of the barrel  12  to releasably secure the refill plug assembly  40  in the barrel  12 . The external threads  80  and the internal threads  82  may form a threaded connection that may be engaged or released with less than a full turn of the refill plug assembly  40 . In some embodiments, the threaded connection may engage or release with approximately a ¼ turn of the refill plug assembly  40 . For example, a first short thread that extends around a quarter of the circumference of the outer surface of the sheath  52  and a second short thread that extends around a quarter of the inner surface of the barrel  12  may cooperate to produce a threaded connection that releases and/or engages in approximately ¼ turn of the refill plug assembly  40 . One of the first and second short threads may include a stopping surface or ridge at one end thereof to prevent the refill plug assembly  40  from turning more than approximately ¼ turn when the threads are engaged. In yet other embodiments, a bayonet connection may be used instead of a threaded connection. 
         [0039]    Turning now more specifically to  FIG. 4 , the button  42  includes an outwardly extending circumferential wall  84 . The circumferential wall  84  includes an annular wall recess  86  that retains an annular ring  88 . In one embodiment the annular ring  88  may be an elastomeric o-ring. When the refill plug assembly  40  is releasably secured to the barrel  12  proximate the first barrel end  16 , the circumferential wall  84  and the annular ring  88  cooperate with an inner surface of the barrel  12  to seal the refill assembly  22  within the barrel  12  to protect the refill assembly  22  from environmental factors or damage. 
         [0040]    A spring  92  ( FIG. 1 ) is disposed within the refill plug assembly  40  to bias the refill plug assembly  40  away from the refill assembly  22 , which facilitates removal of the refill plug assembly  40  when the refill assembly  22  is changed. More specifically, the spring  92  has a first spring end  94  and a second spring end  96 . The first spring end  94  is seated against a tapered surface  90  in the hollow bore  48  of the button  42  and the second spring end  96  is seated against the plunger  62 , thus biasing the plunger  62  away from the button  42 . 
         [0041]    When the refill plug assembly  40  is released from the barrel  12 , the spring  92  causes the button  42  to move away from the plunger  62 , which is releasably connected to the refill assembly  22 . As the button  42  moves away from the plunger  62 , the button  42  extends beyond the first barrel end  16 , which makes the button  42  easy to grasp. A user then may pull the button  42  away from the first barrel end  16 , which causes sheath  52  to slide away from the first barrel end  16  with the button  42  until the outer annular flange  76  on the plunger  62  engages the inner annular flange  74  on the sheath  52 . Once the outer annular flange  76  engages the inner annular flange  74 , any further movement of the button  42  away from the barrel  12  causes the refill assembly  22  to move with the refill plug assembly  40  because the retaining element  77  is releasably engaged with the refill assembly  22  via the annular wall  75 . 
         [0042]    When securing the refill plug assembly  40  to the barrel  12  after replacing the refill assembly  22 , the refill plug assembly  40  is inserted at least partially into the hollow central bore  18  of the barrel  12 . As the refill plug assembly  40  is moved into the hollow central bore  18 , the retaining element  77  will eventually contact the refill assembly  22  and the retaining element will releasably engage the annular wall  75 . As the refill plug assembly  40  continues to move into the hollow central bore  18 , the spring  92  will keep the plunger  62  biased towards the refill assembly  22 . The second end  72  of the plunger  62  is received at least partially by a blind bore  98  in the refill assembly  22 . Eventually the second end  72  of the plunger  62  will bottom out in the blind bore  98 . At that point, the first end  70  of the plunger  62  will slide within the second portion  64  of the sheath  52  as the bias produced by the spring  92  is overcome. Finally, the external threads  80  will engage the internal threads  82  and a turn of less than one complete revolution of the refill plug assembly  40  releasably secures the refill plug assembly  40  within the barrel  12 . 
         [0043]    A writing instrument  110  with a second embodiment of a refill plug assembly  140  is illustrated in  FIGS. 5-12 . Elements of the writing instrument  110  that are similar to the elements of the writing instrument  10  of  FIGS. 1-4  are given similar reference numerals, but increased by 100. 
         [0044]    The writing instrument  110  illustrated in  FIGS. 5-12  includes a barrel  112  having a first barrel end  114 , a second barrel end  116 , and a hollow central bore  118 . A ferrule section  120  may extend from the first barrel end  114 . In some embodiments, the ferrule section  120  and the barrel  112  may be separate components; in others, the ferrule section  120  may be integrally formed with the barrel  112 . 
         [0045]    A refill assembly  122  may be disposed within the hollow central bore  118 . The refill assembly  122  may include an ink reservoir  124  that is fluidly connected to a writing point  126 . In some embodiments, an ink feedstick  128  may be fluidly connected to both the ink reservoir  124  and to the writing point  126  to facilitate delivery of ink from the ink reservoir  124  to the writing point  126 . The ink feedstick  128  may be an extruded feedstick or a fibrous feedstick, for example. Alternatively, the ink reservoir  124  can be fluidly connected to the writing point  126  via a lumen. In some embodiments the ink reservoir  124  may be a fibrous reservoir and in other embodiments the ink reservoir  124  may be a free ink reservoir. 
         [0046]    A refill plug assembly  140  may be releasably secured to the barrel  112  at the second barrel end  116 . The refill plug assembly  140  prevents the ink refill assembly  122  from unintentionally becoming dislodged from the hollow central bore  118  and maintains the ink refill assembly  122  in its proper position within the barrel  112 . The refill plug assembly  140  may be quickly and easily removed to access the ink refill assembly  122 . For example, the refill plug assembly  140  may be rotated through less than one full turn (approximately ¼ turn) to release the refill plug assembly  140  from the barrel  112 . 
         [0047]    The refill plug assembly  140  may include a button  142 , a sheath  152 , and a plunger  162 . The button  142  may have a first button end  144  and a second button end  146 . The button  142  may also include a hollow bore  148  having an opening  150  proximate the second button end  146 , similar to the embodiment of  FIGS. 1-4 . 
         [0048]    The sheath  152  may include a first sheath end  154 , a second sheath end  156 , and a through bore  158 . A first sheath portion  160  may be operatively connected to the button  142  and a second sheath portion  164  may extend away from the button  142 . The first sheath portion  160  may have an inner diameter that is larger than an inner diameter of the second sheath portion  164 . An angled portion  166  may connect the first sheath portion  160  to the second sheath portion  164 . The sheath  152  may include one or more bayonets or posts  147  that extend radially outward from an outer surface  149  of the sheath  152 . In one embodiment, the posts  147  may be shaped as cylinders, as illustrated in  FIG. 6 . In other embodiments, the posts  147  may have other shapes, such as cubes or pyramids. Furthermore, the refill plug assembly  140  may include two posts  147 , as illustrated in  FIG. 6 . In other embodiments, the refill plug assembly  140  may include one, three, four, five, six, or more posts  147 . 
         [0049]    The plunger  162  may be slidably attached to the second sheath portion  164 . The plunger  162  may include a plunger body  168  having a first body end  170  and a second body end  172 . At least a portion of the plunger body  168  may be disposed within the through bore  158  of the sheath  152 . The plunger body  168  may be displaceable longitudinally within the through bore  158  substantially parallel to a longitudinal axis A of the sheath  152 . The plunger  162  may be displaceable between a first extended position in which the first plunger end  170  is proximate the second sheath end  156  and a second retracted position in which the first plunger end  170  is proximate the second button end  146 . In some embodiments, the through bore  158  and the plunger body  168  may be substantially cylindrical in shape. In other embodiments, the through bore  158  and the plunger body  168  may take on other shapes as long as the plunger body  168  has a shape that fits within the through bore  158 . In preferred embodiments, the plunger body  168  has an outer shape that is complimentary to the inner shape of the through bore  158 . 
         [0050]    A retaining element  177  ( FIG. 6 ) may be located proximate the second body end  172 . The retaining element  177  may cooperate with the refill assembly  122  to releasably secure the plunger  162  to the refill assembly  122  to facilitate removal of the refill assembly  122  from the barrel  112 . In one embodiment, the retaining element  177  may have the shape of an annular ring  179  attached to a hollow tube  181 . The hollow tube  181  may be sized to fit within a blind bore  198  ( FIG. 5 ) in the refill assembly  122 . The hollow tube  181  and the blind bore  198  may form an interference fit that releasably retains the refill assembly  122  on the refill plug assembly  140 . 
         [0051]    A cam liner  130  ( FIG. 7 ) may be disposed between the refill plug assembly  140  and the barrel  112 . The cam liner  130  may include a cylindrical outer wall  131  that fits within the hollow bore  118  of the barrel  112 . A cam channel  132  may be formed in the cylindrical outer wall  131 . The cam channel  132  may include a first leg  133  oriented longitudinally, substantially parallel to the longitudinal axis A and a second leg  134  that is oriented circumferentially around a portion of the cylindrical outer wall  131 . The second leg  134  may include a locking recess  135  that is oriented substantially longitudinally, similarly to the first leg  133 . The locking recess  135  may be sized and shaped to receive a portion of the post  147 . 
         [0052]    Turning now to  FIGS. 8-11 , the posts  147  cooperate with the cam liner  130  to releasably retain the refill plug assembly  140  in the barrel  112 . Initially, when securing the refill plug assembly  140  to the barrel  112 , the posts  147  are aligned with the cam channel  132 . As the refill plug assembly  140  is pushed towards the cam liner  130 , the posts  147  travel into the first leg  133  of the cam channel  132 . The refill plug assembly  140  travels longitudinally along axis A until the posts  147  reach the end of the first leg  133  of the cam channel  132 . At this point, the posts  147  contact an edge of the cam channel  132 , which prevents further longitudinal movement of the refill plug assembly  140  towards the cam liner  130 . The refill plug assembly  140  is then rotated (preferably less than ¼ of a turn) and the posts  147  travel along the second leg  134  of the cam channel  132 . Upon reaching an end of the second leg  134  ( FIG. 10 ), the spring  192  ( FIG. 5 ) biases the button  142  away from the cam liner  130 , which forces the posts  147  to move into the locking recess  135 , thereby securing the refill plug assembly  140  within the barrel  112 . 
         [0053]    In other embodiments, the bayonets or posts  147  may be formed on an inner surface of the cam liner  130  and the cam channel  132  may be formed on the outer surface  149  of the sheath  152 . In yet other embodiments, the cam liner  130  may be integrally formed with the barrel  112 . 
         [0054]    Turning now to  FIG. 12 , the connection between the retaining element  177  and the refill assembly  122  is illustrated in greater detail. The hollow tube  181  forms an interference fit with the blind bore  198  in the refill assembly. The hollow tube  181  may include a central bore  183  sized to receive a portion of the plunger body  168  so that the plunger body  168  may compress into the blind bore  198  (at least partially) as the refill plug assembly  140  is secured to the refill assembly  122 . In some embodiments the retaining element  177  may be made from an elastomeric material while an end cap  185  of the refill assembly  122  may be made from a thermoplastic material. The retaining element  177  may be soft enough to be squeezed into the blind bore  198  (and at least partially into the annular channel  178 ) to enhance the releasable connection between the refill plug assembly  140  and the refill assembly  122 . In other embodiments, the end cap  185  may be made from polyethylene, polypropylene, silicone, aluminum, brass, stainless steel, or any combination thereof. 
         [0055]    A third embodiment of a writing instrument  210  with a refill plug assembly is illustrated in  FIGS. 13-17 . Elements of the writing instrument  210  that are similar to the elements of the writing instruments  10  and  110  of  FIGS. 1-12  are given similar reference numerals, but increased by 100 over the writing instrument  110  of  FIGS. 5-12  and by 200 over the writing instrument  10  of  FIGS. 1-4 . 
         [0056]    The writing instrument  210  illustrated in  FIGS. 13-17  includes a barrel  212  having a first barrel end  214 , a second barrel end  216 , and a hollow central bore  218 . A ferrule section  220  may extend from the first barrel end  214 . In some embodiments, the ferrule section  220  and the barrel  212  may be separate components; in others, the ferrule section  220  may be integrally formed with the barrel  212 . 
         [0057]    A refill assembly  222  may be disposed within the hollow central bore  218 . The refill assembly  222  may include an ink reservoir  224  that is fluidly connected to a writing point  226 . In some embodiments, an ink feedstick  228  may be fluidly connected to both the ink reservoir  224  and to the writing point  226  to facilitate delivery of ink from the ink reservoir  224  to the writing point  226 . The ink feedstick  228  may be an extruded feedstick or a fibrous feedstick, for example. Alternatively, the ink reservoir  224  can be fluidly connected to the writing point  226  via a lumen. In some embodiments the ink reservoir  224  may be a fibrous reservoir and in other embodiments the ink reservoir  124  may be a free ink reservoir. 
         [0058]    A refill plug assembly  240  may be releasably secured to the barrel  212  at the second barrel end  216 . The refill plug assembly  240  prevents the ink refill assembly  222  from unintentionally becoming dislodged from the hollow central bore  218  and maintains the ink refill assembly  222  in its proper position within the barrel  212 . The refill plug assembly  240  may be quickly and easily removed to access the ink refill assembly  222 . For example, the refill plug assembly  240  may be longitudinally moved along axis A to successively release and secure the refill plug assembly  240  from the barrel  212 . 
         [0059]    The refill plug assembly  240  may include a button  242 , a sheath  252 , and a plunger  262 . The button  242  may have a first button end  244  and a second button end  246 . The button  242  may also include a hollow bore  248  having an opening  250  proximate the second button end  246 , similar to the embodiments of  FIGS. 1-4  and  FIGS. 5-12 . 
         [0060]    The sheath  252  may include a first sheath end  254 , a second sheath end  256 , and a through bore  258 . The sheath may include a flexible arm  253  ( FIG. 14 ) located between two legs of a channel  255 . At a free end of the flexible arm  253 , a protrusion or post  247  extends radially outward. The flexible arm  253  may be displaced laterally, generally perpendicular to the longitudinal axis A to allow the post  247  to move within a cam channel, as discussed below. 
         [0061]    The plunger  262  may be slidably attached to the sheath  252 . The plunger  262  may include a plunger body  268  having a first body end  270  and a second body end  272 . At least a portion of the plunger body  268  may be disposed within the through bore  258  of the sheath  252 . The plunger body  268  may be displaceable longitudinally within the through bore  258  substantially parallel to the longitudinal axis A. In some embodiments, the through bore  258  and the plunger body  268  may be substantially cylindrical in shape. In other embodiments, the through bore  258  and the plunger body  268  may take on other shapes as long as the plunger body  268  has a shape that fits within the through bore  258 . In preferred embodiments, the plunger body  268  has an outer shape that is complimentary to the inner shape of the through bore  258 . 
         [0062]    The sheath  252  may be at least partially disposed within a hollow bore  229  ( FIG. 15 ) of a cam liner  230 . The cam liner  230  has a cam groove  232  formed on an inner surface thereof. In the embodiment illustrated in  FIGS. 13-17 , the cam groove  232  does not extend completely through the cam liner  230 . In other embodiments the cam groove  232  may extend completely through the cam liner  230 . The cam groove  232  includes a first leg  233  that extends substantially parallel to the longitudinal axis A and a second leg  234  that extends circumferentially, substantially perpendicularly to the longitudinal axis A. The second leg  234  also includes a locking recess  235  that is sized and shaped to receive at least a portion of the post  247 . 
         [0063]    As illustrated in  FIGS. 16 and 17 , the posts  247  cooperate with the cam liner  230  to releasably retain the refill plug assembly  240  in the barrel  212 . Initially, when securing the refill plug assembly  240  to the barrel  212 , the posts  247  are aligned with the cam groove  232 . As the refill plug assembly  240  is pushed towards the cam liner  230 , a first cam surface  237  forces the posts  247  circumferentially into the first leg  233  of the cam groove  232 . Once the posts  247  clear the first cam surface  237 , the flexible arm  253  returns to a neutral position, where the flexible arm  253  is generally aligned with the longitudinal axis A, thereby bringing the posts  247  into the second leg  234  of the cam groove  232 . The spring  292  ( FIG. 13 ) biases the refill plug assembly  240  away from the cam liner  230 , which causes the posts  247  to move into the locking recess  235 . 
         [0064]    To release the refill plug assembly  240 , the refill plug assembly  240  is moved longitudinally, towards the cam liner  230 . Once the posts  247  clear the locking recess  235 , the button  242  may be rotated (preferably less than ¼ turn) until the posts  247  align with the cam groove  232 . Thereafter, the spring  292  biases the refill plug assembly  240  away from the cam liner  230  and the refill plug assembly  240  and the refill assembly  222  may be removed from the barrel  212 . 
         [0065]    Elements of any of the disclosed embodiments may be combined with any of the other disclosed embodiments. For example, any of the various disclosed retaining elements may be used with any of the disclosed plungers. Similarly, any of the disclosed plungers may be used with any of the disclosed refill plug assemblies. 
         [0066]    The disclosure is not limited to a writing instrument with an extruded plastic writing point. The disclosure could be applied to virtually any writing instrument, such as markers, ball point pens, fibrous pens, etc. The features of the invention disclosed in the description, drawings and claims can be individually or in various combinations for the implementation of the different embodiments of the invention.