Abstract:
A retractable writing instrument has a push-to-extend, push-to-retract operating mechanism assembled for life as a single module which is removeable from a body of the writing instrument. A prehensile member is connected to the operating mechanism and is moveable axially for displacing the writing tip of the cartridge between its extended and retracted positions. The prehensile member has resilient parts adapted for grasping the end of the cartridge inserted through an aperture in the operating mechanism module and pressed into a cavity in the prehensile member, thereby allowing users to readily replace the cartridge without the risk of releasing small easily-lost components of the operating mechanism.

Description:
TECHNICAL FIELD 
     The present invention relates to writing instruments having a cartridge with a writing tip which may be retracted within the body of the instrument, and particularly to writing instruments having a push-to-extend, push-to-retract operating mechanism. 
     BACKGROUND OF THE INVENTION 
     Replacing an ink cartridge (or a pencil cartridge) in a retractable writing instrument having push-to-extend, push-to-retract operating mechanism typically involves unscrewing the two parts forming the body of the pen for access to the cartridge enclosed therein. A number of small components, such as a plunger, rotary ratchet and a helical compression spring, typically come loose or must be removed during this operation. The compression spring may be mounted about the cartridge, with opposing ends abutting a stop on the cartridge and the body respectively, requiring it to be placed about the replacement cartridge, before the rest of the components are carefully re-installed. U.S. Pat. No. 4,991,988 describes a pen with these features. It will therefore be understood that there is a need for an improved retractable writing instrument of this type, which allows users to more readily replace the cartridge without the risk of releasing small easily-lost components. It is an object of the present invention address this need or more generally to provide an improved retractable writing instrument. 
     DISCLOSURE OF THE INVENTION 
     According to one aspect of the present invention there is provided a writing instrument for receiving an elongate cartridge having a writing tip at a first end thereof and an opposing second end, the writing instrument comprising: 
     first and second retainers that are mutually connected to define a chamber having a longitudinal axis; 
     at least one axially-extending rib disposed on the first retainer, the rib terminating in a tip; 
     an axially-aligned aperture in the second retainer that is sized for withdrawing and inserting the cartridge therethrough; 
     a plunger disposed for axial sliding movement in the chamber; 
     a groove in the plunger, the groove receiving the rib for preventing rotation of the plunger; 
     a plurality of plunger teeth on the plunger; 
     a rotary ratchet disposed in the chamber for rotation about the longitudinal axis and sliding movement parallel to the longitudinal axis; 
     a plurality of ratchet teeth on the ratchet, the ratchet teeth cooperating with and opposing the plunger teeth and rib tip so as to impel rotation of the ratchet about the longitudinal axis when the stem is pressed and released; 
     a concavity between two of the ratchet teeth; 
     a longitudinal channel in the ratchet; 
     a compression spring disposed in the chamber, the compression spring urging the rotary ratchet toward the tip of the rib such that the tip is received in the concavity when the ratchet is in an extended position and the rib is received in the channel when the ratchet is in a retracted position, and 
     prehensile means having a cavity complementary to the second end of the cartridge for grasping the cartridge such that the prehensile means and attached cartridge are moved longitudinally with the rotary ratchet between the extended and retracted positions. 
     By placing the plunger, rotary ratchet and compression spring within the retainers and providing prehensile means in the manner described, replacement of the cartridge can be performed by simply grasping the cartridge adjacent the writing tip and withdrawing the cartridge from engagement with the prehensile means and then pulling it axially out through the aperture in the second retainer, before inserting a replacement in the reverse manner. 
     Preferably the prehensile means comprises one or more resilient members disposed about the cavity. Most preferably the prehensile means comprises a resilient sleeve having a longitudinal slot therein. Alternatively, for instance, the prehensile means may comprise one or more fingers circumferentially spaced about the cavity. In this manner the one or more resilient members provide clamping action firmly holding the cartridge. Optionally the prehensile means may be integral with the rotary ratchet. Preferably the mouth of the cavity or the second end of the cartridge are tapered to assist entry of the second end into the cavity. 
     Preferably the first and second retainers are substantially tubular, the second retainer being received within an inner end of the first retainer and wherein first and second internal abutment faces are disposed on the first and second retainers respectively, opposing ends of the compression spring abutting the first internal abutment face and the resilient sleeve to thereby urge the resilient sleeve against the rotary ratchet. 
     Preferably the writing instrument further includes a hollow body having a first opening for receiving the writing tip and a second opening for receiving the first and second retainers therethrough. Preferably the hollow body comprises two shells joined at a longitudinal plane, each shell having a recess therein, an insert fixed in the recesses, the insert having an internal screw-thread and wherein the inner end of the first retainer has a screw thread complementary to the thread on the insert for securing the first retainer within the body. 
     This invention provides a writing instrument which is effective and efficient in operational use, and which has an overall simple design which minimizes manufacturing costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
         FIG. 1  is an exploded view of a first embodiment of a pen according to the invention; 
         FIG. 2  is a schematic longitudinal sectional view through a second embodiment of a pen of the invention when assembled; 
         FIG. 3  is a part-sectional side view of the first retainer of the pen of  FIG. 1 ; 
         FIG. 4   a  is a pictorial view of the plunger of the pen of  FIG. 1 ; 
         FIG. 4   b  is an end view of the plunger of  FIG. 4   a;    
         FIG. 5   a  is a pictorial view of the rotary ratchet of the pen of  FIG. 1 ; 
         FIG. 5   b  is an end view of the rotary ratchet of  FIG. 5   a;    
         FIG. 6  is a pictorial view of the prehensile member of the pen of  FIG. 1 ; 
         FIG. 7  is a pictorial view of the second retainer of the pen of  FIG. 1 ; 
         FIG. 8  is a pictorial view of the cartridge of the pen of  FIG. 1 , and 
         FIG. 9  is a plan view of one of the shells making up the body of the pen of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 and 2 , a retractable writing instrument or pen  10  generally includes a push-to-extend, push-to-retract retractor mechanism  11  and a replaceable ink cartridge  12  held within a body  13 . The pen  10  is substantially elongate having a longitudinal axis  71 . The writing tip  53  of the ink cartridge  12  projects from the inner end of the pen  10 , while the cap  14  by which it is retracted and extended projects from the outer end. The first and second embodiments of  FIGS. 1 and 2  differ only in respect of the design of the cap  14 , which in the first embodiment includes a decorative cap of threads. As used herein, the term “axial” refers to a direction substantially parallel to the longitudinal axis  71 . The term “radial” refers to a direction substantially orthogonal to the longitudinal axis  71 . The term “circumferential” refers to the direction of a circular arc having a radius substantially orthogonal to the longitudinal axis  71 . 
     The retractor mechanism  11  is a module that includes a plunger  15 , rotary ratchet  16 , a prehensile member  17  and a helical compression spring  18  which are generally received within a first retainer  19  and held therein by a second retainer  20 . 
     The first retainer  19 , shown in  FIG. 3 , is moulded from polymer and has a tubular form with an external screw thread  21  at its inner end. Adjacent the inner end are diametrically opposing square-section openings  22  extending transversely through the side walls. Proximate the outer end an integral annular flange  23  projects inwardly from the cylindrical inner wall  27  and has in inwardly facing abutment face  24 . Integral axially-aligned ribs  25  also project inwardly from the cylindrical inner wall  27 . Each rib  25  terminates in a tapered tip  26  at its inner end. 
       FIGS. 4   a  and  4   b  show the plunger  15 , which is also a moulded polymeric component. The plunger  15  is axially elongated having a stem  28  at its outer end with a generally cylindrical surface upon which parallel flats  29  are formed. Facing inwardly and disposed at the inner end of the plunger  15  are a plurality of pointed plunger teeth  30 . The teeth  30  are circumferentially spaced apart and each has a partly-cylindrical facet  33  complementary to the inner wall  27 . A plurality of faces  61  are aligned in a radial plane. Also formed on the plunger  15  are axially-aligned grooves  31  sized to receive respective ribs  25  in a sliding fit for preventing rotation of the plunger  25  about the axis  71 . A blind hole  34  extends axially from the inner end of the plunger  15 . 
     The rotary ratchet  16  is shown in  FIGS. 5   a  and  5   b  and includes an axial shaft portion  35  received in a sliding fit in the blind hole  34  so as to assist in supporting the rotary ratchet  16  for rotation about the axis  71  and sliding movement parallel to the axis  71 . Three projections  36  project radially outward from a cylindrical, axially aligned face  37 , each projection  36  defining two tapered ratchet teeth  38  with a an outwardly-opening concavity  39  therebetween. The ratchet teeth  38  face the outer end of the rotary ratchet  16  such that they are opposing the plunger teeth  30 . The ratchet teeth  38  are asymmetrical to rotate unidirectionally. Channels  40  in the rotary ratchet  16  are angularly spaced from the ratchet teeth  38  and sized to receive the ribs  25  in a sliding fit. Each projection  36  has a partly-cylindrical facet  41  complementary to the inner wall  27  for supporting the rotary ratchet  16 . An aperture  42  extends axially through the rotary ratchet  16 . 
     The prehensile member  17  comprises with a sleeve of resilient polymer having a partly-cylindrical face  43  complementary to the inner wall  27 . A slot  44  extends axially through one wall of the sleeve. The through-extending cavity  46  has mouth portions  45  at axially opposing ends, the mouth portions tapering radially inwardly toward the centre of the sleeve. 
     The second retainer  18  is generally tubular, having an axially-aligned aperture  47  sized for withdrawing and inserting the cartridge  48  therethrough. The outer cylindrical surface  49  is complementary to the inner wall  27  and projecting from it are diametrically opposite lugs  50  sized to be received in the square section openings  22  in the first retainer  19 . The second retainer  18  includes an annular abutment face  51 . 
     A first end of the cartridge  12  includes a writing tip  53  holding a ball point (not shown) and a reservoir tube  52  fixed to the writing tip  53 . The second end  54  has a cylindrical outer surface sized to be received in the cavity  46 . 
     The hollow body  13  comprises two shells  55  joined at a central longitudinal plane, each shell  55  having a recess  56  therein defined by ribs  57 . Openings  58 ,  59  are formed at axially-opposing ends of the shells, the opening  58  is sized for receiving the writing tip  53 , while the opening  59  is sized for receiving the retractor mechanism  11  therethrough. An insert  60  fixed in the recesses  56  has an internal screw-thread  61  complementary to the thread  21  on the first retainer  19 . The decorative cap  14  includes a hub  66  with an opening  67  sized to receive the stem  28 , the opening including corresponding flats for engaging the flats  29  to prevent relative rotation about axis  71  between the hub  66  and plunger  15 . Permanently fixed to the hub  66  is a bunch  68  of multi-coloured elastic strings. The hub  66  itself is also permanently fixed to the stem  28 , as by an interference fit. 
     The first retainer  19  bounds a chamber  62  in which at least part of the plunger  15 , rotary ratchet  16 , prehensile member  17  and helical compression spring  18  are received and retained. In assembly, the plunger  15  is inserted through the inner end  70  into the chamber  62 , the faces  61  abutting the abutment face  24  to retain the plunger  15 . This is followed successively by the rotary ratchet  16 , prehensile member  17  and helical compression spring  18  before the second retainer  20  is fixed in the inner end  70 . In this manner opposing ends of the compression spring  18  abut the abutment face  51  and the prehensile member  17 . The first and second retainers are flexible and resilient allowing them to deflect as the second retainer  18  is inserted into the inner end  70  and they are thus connected as the lugs  50  are received in the openings  22 . The resulting module or retractor mechanism  11  is assembled for the life of the pen and can be used with cartridges and writing instrument bodies of many different types. 
     The outer end  54  of the cartridge  12  is inserted through the aperture  47  into the cavity  46  in the prehensile member  17 . The tapered mouth  45  assists entry of the end  54  into the cavity and further insertion along the tapered mouth  45  resiliently deforms the sleeve thereby providing a clamping action or interference fit firmly holding the cartridge  12 . The spring  18  urges the prehensile member  17  against the rotary ratchet  16  with radially-aligned faces on each abutting. In this manner the prehensile member  17  follows the axial movement of the rotary ratchet  16  between retracted position (shown in  FIG. 2 ) and an extended position (not shown), but is not restrained to rotate with the rotary ratchet  16 . Correspondingly, the cartridge  12  can be readily removed by withdrawing the cartridge from engagement with the prehensile member  17  and then pulling it axially out through the aperture  47 . The retractor mechanism  11  and attached cartridge  12  are then inserted into the body  13 , while engaging the screw threads  21 ,  61 . 
     In operation, the cap  65  is toggled (alternately pushed, then released) to extend and retract the cartridge  12  in the well-known manner. In the retracted position shown in  FIG. 2  the rotary ratchet teeth  38  are held in engagement with the plunger teeth  30 , the faces  61  abutting the abutment face  24 , and the rib  25  is received in the channel  31 . In the extended position the rotary ratchet  16  is urged by the spring  18  into engagement with the rib  25 , with the tip  26  of the rib  25  received in the concavity  39 . The ratchet teeth  38  cooperate with the plunger teeth  30  and rib tip  26  so as to impel a first small rotation of the rotary ratchet  16  when the cap is pressed and a second small rotation when the cap is released. 
     Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.