Abstract:
A roller ball pen ( 2 ) that permits a user to adjust the bias force that biases a roller ball cartridge ( 4 ) out of the pen ( 2 ) to suit the user&#39;s particular writing style. The pen ( 2 ) has a body ( 8 ) having distal and proximal ends, a roller ball cartridge ( 4 ) disposed in the body ( 8 ), a cap ( 10 ) removably disposed on the proximal end of the body ( 8 ), a control member ( 14 ) slidingly disposed in the cap ( 10 ), a spring ( 18 ) attached to the distal side of the control member ( 14 ) and abutting the roller ball cartridge ( 4 ), and a drive rod ( 16 ) engaged with the control member ( 14 ). Rotation of the drive rod ( 16 ) moves the control member ( 14 ) distally or proximally, thereby adjusting the bias force applied by the spring ( 18 ) to the roller ball cartridge ( 14 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a continuation of application Ser. No. 09/493,922, filed Jan. 28, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to pens with replaceable roller ball cartridges.  
         BACKGROUND OF THE INVENTION  
         [0003]    In general roller ball pens have a pen body into which a replaceable roller ball cartridge is held in place such that a user may write with the pen. The roller ball cartridge has a writing tip and a butt end. Usually the pen body has two pieces detachably held together by threads, for example. In order to replace the roller ball cartridge the two pieces are separated and the spent roller ball cartridge is removed and a replacement roller ball cartridge is inserted into one of the two pieces and the other piece is attached back into place. In some cases a spring or other biasing element abuts the butt end of the roller ball cartridge at one end and the inside of the body at the other end, such that the spring biases the writing tip out of the pen body. The spring or biasing element also provides a certain feel to the user, because, depending on the biasing force, the roller ball cartridge will have a certain recoil within the body while the user is writing with the pen. The prior art pens only provide one tension, which is set by design, and a user must be satisfied with the feel of the particular pen chosen. Therefore, there is a need in the art for a roller ball pen for which the user can set the biasing force to meet the user&#39;s particular needs.  
         SUMMARY OF THE INVENTION  
         [0004]    A preferred embodiment of roller ball pen includes a pen body with distal and proximal ends, a roller ball cartridge inserted into the pen body (with the writing end extending at least partially out of the distal end of the pen body), a cap detachably attached to the proximal end of the pen body, a drive rod rotatably fixed to the cap, a control member, such as a nut, and a biasing element (preferably a spring) attached to the nut and abutting the butt end of the roller ball cartridge. Preferably, the control member, such as a nut, is slidingly disposed within the cap such that it may move distally or proximally, but may not substantially rotate therein. The drive rod extends at least partially into the cap and is rotatably fixed thereto such that it may not substantially move distally or proximally. The distal end of the drive rod engages the control member, such as a nut, so that rotation of the drive rod will move the nut distally or proximally, thereby changing the biasing force of the spring against the roller ball cartridge. Preferably there is a drive knob fixed to the proximal end of the drive rod and the drive knob is rotatable to rotate the drive rod. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a roller ball cartridge pen with adjustable spring tension in accordance with an embodiment of the present invention;  
         [0006]    [0006]FIG. 2 is a cross-section of the proximal end of the pen of FIG. 1;  
         [0007]    [0007]FIG. 3 is a cross-section of a cap of the pen of FIG. 1;  
         [0008]    [0008]FIG. 4 is a cross-section of a nut of the pen of FIG. 1;  
         [0009]    [0009]FIG. 5 is a cross-section of a drive rod of the pen of FIG. 1;  
         [0010]    [0010]FIG. 6 is a cross-section of a drive knob of the pen of FIG. 1; and  
         [0011]    [0011]FIG. 7 is a cross-section of another embodiment of the proximal end of the pen of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    Referring to FIG. 1 there is shown a pen  2  in accordance with an embodiment of the present invention. Pen  2  has roller ball cartridge  4 , pen top  6 , body portion  8  (also referred to herein as first part of the body and distal part of the writing instrument), cap  10  (also referred to herein as second part of the body and proximal part of the writing instrument), drive knob  12 , control member or nut  14 , drive rod  16  and spring  18 . Bushing  20  is threaded and fixed into distal end  22  of cap  10 . Proximal end  24  of body portion  8  is removably secured to cap  10  using bushing  20 . Thus, a user may replace roller ball cartridge  4  by unscrewing body portion  8  from cap  10 , removing the spent cartridge, inserting a new cartridge and screwing body portion  8  back to cap  10 .  
         [0013]    Referring to FIGS. 2 and 3, cap  10  preferably has a tapered cylindrical exterior shape with a straight cylindrical ring  26  at its proximal end  28 , which has a smaller outer diameter than cap  10 . The interior of cap  10  has first hollow section  30 , second hollow section  32 , cylindrical cavity  34 , and hole  36 . First hollow section  30  is configured to fit over butt end  33  of roller ball cartridge  4  and has threads  34  configured to mate with bushing  20 , as described above. Second hollow section  32  is configured to receive and engage engagement portion  40  of nut  14 , such that nut  14  will not rotate relative to cap  10  and such that nut  14  may move longitudinally within second hollow section  32 . Preferably second hollow section  32  has eight sides (not shown) and slidingly receives and mates with nut  14 , as described more fully below. A skilled artisan will readily recognize that many shapes other than the preferred eight-sided shape for second hollow section  32  may be used without exceeding the scope of the present invention. For example, and without limitation, any number-sided shape may be used, even as few as a two sided shape. Cylindrical cavity  34  has a smaller diameter than the nominal diameter of second hollow section  32 , and a larger diameter than hole  36 . The difference in diameters between cylindrical cavity  34  and hole  36  defines shoulder  38 .  
         [0014]    Referring to FIGS. 2 and 4, control member or nut  14  has engagement portion  40  and hollow cylinder  42 . The exterior of engagement portion  40  is configured to engage second hollow section  32  of cap  10 ; preferably it has an octagonal shape as described above. Engagement portion  40  also has a hole  44  therethrough that has threads  46  configured to engage threads  48  of drive rod  16 , as more fully described below. Hollow cylinder  42  of nut  14  is attached to or integral with distal side  50  of engagement portion  40 . The outer diameter of hollow cylinder  42  is smaller than the nominal outer diameter of engagement portion  40 , and the inner diameter is larger than the diameter of hole  44 , thereby defining spring cavity  52  with spring abutment  54 . Spring cavity  52  is configured to receive and secure spring  18  against spring abutment  54 . Preferably, the diameter of spring  18  is slightly larger than the inner diameter of hollow cylinder  42  and spring  18  is secured therein by friction. A skilled artisan will readily recognize other ways to secure spring  18  to nut  14 .  
         [0015]    Referring to FIGS. 2 and 5, drive rod  16  has threaded portion  56 , ring  58 , ledge  60  and attachment section  62 . Threaded portion  56 , as shown, has threads  48  and stop  64 . Prior to assembly of pen  2 , stop  64  is a straight cylindrical portion  66 , as shown in phantom. Once drive rod  16  is installed, straight cylindrical portion  66  is deformed to form stop  64 , which prevents drive rod  16  from being completely removed from nut  14 .  
         [0016]    Referring to FIGS. 2 and 6, drive knob  12  has first cavity  68  and second cavity  70 . First cavity  68  has a slightly smaller diameter than the diameter of attachment section  62  of drive rod  16  and at least the same length. Attachment section  62  is jammed into first cavity  68  of drive knob  12 , thereby creating a friction connection between the two pieces. Preferably the surface of attachment section  62  is roughened to provide a better attachment. A skilled artisan will recognize many ways to attach drive knob  12  to drive rod  16 , such as, and without limitation, threads  80 ,  82 , as shown in FIG. 7, or adhesive. Second cavity  70  has an inside diameter that is larger than the outside diameter of straight cylindrical ring  26  of cap  10 . Second cavity  70  fits over straight cylindrical ring  26  and is held in place by virtue of the attachment of drive knob  12  to drive rod  16 , as further discussed below. The exterior of drive knob  12  is preferably tapered to follow the contours of the exterior of cap  10 .  
         [0017]    Referring to FIG. 2, first circular washer  72 , spacer washer  74 , and second circular washer  76  are inserted into cap  10 , and abut against shoulder  38  of cap  10 . Preferably spacer washer  74  is not a flat washer, but rather one with an undulating surface that provides some longitudinal movement when compressed. Attachment section  62  of drive rod  16  is inserted through and out of hole  36  of cap  10 , and drive knob  12  is attached thereto, such that ring  58  of drive rod  16  abuts second circular washer  76 . In this manner drive knob  12  and drive rod  16  are secured to cap  10 . It should be noted that drive knob  12 , while secured to cap  10 , may freely rotate about its longitudinal axis. After drive rod  16  is installed, engagement portion  40  of nut  14  is inserted, such that the exterior of engagement portion  40  mates with second hollow section  32  of cap  10 , as described above. Drive knob  12  is rotated to engage threads  46  of nut  14 , thereby advancing nut  14  over drive rod  16  and into cap  10  in the proximal direction. Straight cylindrical portion  66  (shown in phantom) is deformed to create stop  64  that prevents nut  14  from coming off of drive rod  16  during use of the pen. Spring  18  is inserted over drive rod  16  and into hollow cylinder  42  of nut  14 , and is secured thereto as described above. With roller ball cartridge  4  in place, cap  10  is attached to body portion  8 , and spring  18  biases roller ball cartridge  4  in the distal direction. A user may adjust the biasing force by turning drive knob  12  in one direction or the other, which rotates drive rod  16 , and moves nut  14  either distally or proximally. This movement causes spring  18  to compress or decompress, thereby varying the biasing force exerted by spring  18  against roller ball cartridge  4  in accordance with a user&#39;s preferred feel.  
         [0018]    The skilled artisan will readily recognize that ways other than using drive rod  16  in combination with nut  14  to adjust the tension of spring  18  may be used without exceeding the scope of the present invention. For example, and without limitation, drive knob  12  may be secured directly to cap  10 , and have threads to engage with drive rod  16  such that rotation of drive knob  12  would cause drive rod  16  to move within cap  10 . Another example would be a ratchet type mechanism.  
         [0019]    The materials used to construct roller ball pens are well known in the art. In the present invention it is preferred to use plastic for body portion  8 , and brass for cap  10 , drive rod  16  and nut  14 . As for the other parts of the present invention any suitable material known to those skilled in the art will suffice. Although various embodiments of the present invention have been described, the descriptions are intended to be merely illustrative. Thus, it will be apparent to the skilled artisan that modifications may be made to the embodiments as described without departing from the scope of the claims set forth below.