Patent Publication Number: US-7216791-B1

Title: Spring energized stapler lever fulcrum in low position

Description:
FIELD OF THE INVENTION 
   The present relates to desktop staplers. More precisely the present invention relates to geometry of a pivotal mounting of an actuating lever within a spring-powered stapler. 
   BACKGROUND OF THE INVENTION 
   In a common spring powered stapler a handle is linked to a rear end of a lever, and the front end of the lever is linked to a striker. Pressing the handle causes the lever to pivot about a lever fulcrum. According to one design the front end of the lever moves upward in an arcing motion so that the lever moves rearward as the lever front end approaches its upper limit. At a predetermined position of the lever the striker is disengaged from the lever. The striker then moves downward from the bias of a power spring to eject a staple from the stapler. 
   U.S. Pat. No. 5,988,478 (Marks) shows a lever and a power spring where each respective component has a separate and distinct fulcrum. U.S. Pat. No. 6,145,728 (Marks) shows a staple gun where a power spring and a lever share a common fulcrum. The lever is a “U” channel design and the power spring is an elongated flat spring. The shared fulcrum provides minimal net force on the fulcrum and thus internal forces since the lever and spring press with approximately equal and opposite forces on the fulcrum. Especially when plastic material is used it is desirable to limit internal forces in the stapler to minimize distortion of the housing. U.S. Patent Application Publication US2004/0232192 (Marks) shows a further design where the power spring is a dual, co-axial, coiled torsion spring and the lever is a vertically flat metal form. In these references the lever releasably engages an opening in the striker. The lever front end includes an upper position near the top of the housing body. The lever fulcrum is lower than this upper position end position; therefore the lever front end will move in an arcing motion rearward to pull out of the opening in the striker and disengage the striker. This action comprises the release action. At the upper position of the striker a staple on a guide track advances to be under the striker. The power spring forces the striker downward to eject the staple under the striker. 
   In these designs it is important that the release action occurs at a consistent position of the lever. If the release is too early the striker will not raise high enough to allow the staple to advance. If the release is too late it may not occur at all, the striker will reach its upper limit before the lever moves rearward out of engagement with the striker. To provide a reliable release point the lever fulcrum should be well below the upper most position of the lever front end. The resulting geometry provides a relatively large rearward motion of the lever at the release point with respect to the upward motion. With a large rearward motion the design will not be overly sensitive to manufacturing variations; the release occurs within a small vertical range of motion of the striker. 
   In a vertically compact design the power spring and lever must be as near as possible to each other vertically. Further the total vertical motion of the striker will be limited. When the lever and spring share a fulcrum the spring is under the fulcrum since the spring presses upward. In the Marks &#39;728 patent, the fulcrum is a round post. A flat power spring presses the post tangentially under the post. The lever pivots around the center of this post. The lever pivot location is therefore spaced above the spring by the radius of the post. 
   SUMMARY OF THE INVENTION 
   In the present invention a lever pivots about a lowest possible fulcrum position so that the lever front end is as high as possible above the fulcrum when the lever is at the release point. As discussed above, this design tends toward a reliable release condition. According to the invention a lever and flat power spring share a fulcrum post. The fulcrum post includes a flat rear face that extends down to be adjacent to the power spring. Near the release point the lever presses this flat face at a location immediately adjacent to the spring. The lever pivot is then in the lowest possible position. 
   According to one embodiment the lever fulcrum is partly cylindrical and partly flat. The flat portion extends away from the cylindrical portion to form an extended cam. The lever fulcrum fits in a notch of the lever. The lever pivots at the notch about a central axis of the cylindrical part of the fulcrum through a lower range of motion of the lever. As the lever moves upward, at the lever front end, to approach the release point the notch moves to press the extended cam of the flat portion. The lever then moves more quickly rearward to reliably disengage from the striker. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side, rear perspective view of selected components of a stapler according to the invention, with the illustrated parts in an initial position. 
       FIG. 2  is the stapler of  FIG. 1  with the components in a release point position. 
       FIG. 3  is a side elevation of the stapler of  FIG. 1 . 
       FIG. 4  is a detail view of the fulcrum area of the stapler of  FIG. 3 . 
       FIG. 5  is a detail view of the striker and lever engagement area of the stapler of  FIG. 3 . 
       FIG. 6  is a side elevation of the stapler of  FIG. 2 . 
       FIG. 7  is a detail view of the fulcrum area of the stapler of  FIG. 6 . 
       FIG. 8  is a detail view of the striker and lever engagement area of the stapler of  FIG. 6 . 
       FIG. 9  is a detail view of the front portion of a lever. 
       FIG. 10  is an end view of a post sleeve. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the Figures only selected parts of a stapler are shown for clarity. These include left housing half  10 , handle  20 , lever  40 , fulcrum sleeve  30 , power spring  70 , wheel  90 , and striker  100 . Striker  100  is vertically movable within housing  10 .  FIGS. 1 and 3  show these components of the stapler in an initial rest position. Handle  20  is linked to lever  40  through optional low friction wheel  90 . As handle  20  is pressed the mechanism approaches the configuration of  FIGS. 2 and 6 . Lever  40  is forced to rotate counterclockwise so that release end  41  of the lever moves upward. Power spring  70  engages an opening, not shown, in striker  100  at spring tip  71 ,  FIGS. 5 and 8 . Power spring  70  deflects about fulcrum sleeve  30 . Fulcrum sleeve  30  surrounds fulcrum post  14  of housing  10 . A “lever fulcrum” refers generally to the fulcrum position defined by the location on fulcrum sleeve  30  that lever  40  pivots. Lever release end  41  moves in an arcing motion about the lever fulcrum. As the lever rises above the lever fulcrum, release end  41  retracts rearward out of slot  108  of striker  100  as a result of the arcing motion. At a predetermined rearward position of lever release end  41  the lever will disengage from the striker and the striker will be driven downward from the urging of power spring  70 . This predetermined position is the release point shown in  FIGS. 2 ,  6  and  8 . In  FIG. 8  it is visible that lever release end  41  has moved rearward to release striker  100 . The space between release end  41  and striker  100  is exaggerated for clarity. 
   At a selected vertical position of striker  100  the upward speed of the striker corresponds to a rearward speed of retraction of the lever. A faster retraction speed makes the release point less sensitive to the vertical position of striker  100 . The retraction speed becomes faster as the lever front end, including release end  41 , rises higher above the lever fulcrum as a result of the tangent direction of the arc described by the motion of lever end  41 . However if the retraction speed is excessive there will be more sliding and friction than necessary between lever  40  and striker  100  as lever release end  41  pulls out from slot  108 . Therefore there should be just enough retraction speed to match the release sensitivity to the manufacturing tolerances of the stapler. 
   In the illustrated stapler the very compact design includes a geometry of the lever and power spring such that fulcrum post  14  has an axial center vertically close to lever release end  41 . If the lever fulcrum is at this axial center the release end will not be as high as possible above the lever fulcrum. Then the retraction speed may not be fast enough for a reliable release. It is desirable to have the lever fulcrum at a lower position. In  FIG. 4  it is seen that lever notch  42  rotates about the axial center, or more precisely the cylindrical portion, of fulcrum sleeve  30 . The structure of the lever fulcrum may not include a precisely cylindrical portion; “axial center” may refer to a general center of a fulcrum structure. The axial center is spaced above the power spring with a substantial portion of the fulcrum structure between the axial center and the power spring. This axial center corresponds to notch center  43  of lever  40 ,  FIG. 9 . In  FIG. 9  radial line  43   a  connects notch center  43  to release end  41 . Tangent angle line  43   b  is perpendicular to radial line  43   a . Tangent line  43   b  describes the direction of travel of release end  41  for a particular angular position of lever  40  when the lever fulcrum is at notch center  43 . 
   In  FIG. 7  corner  44  of notch  42  is pressing rearward facing flat  32  of fulcrum sleeve  30  at a position below the axial center. From this engagement the lever fulcrum has traveled from notch center  43  to notch corner  44 ,  FIG. 9 . Radial line  44   a  connects notch corner  44  to release end  41 . Tangent line  44   b  is perpendicular to radial line  44   a . In  FIG. 9  it is seen that tangent line  44   b  is angled more rearward than tangent line  43   b , with the difference noted as “tangent angle”. Release end  41  therefore has a stronger rearward component to its direction when the lever fulcrum is at notch corner  44 . In  FIG. 7  notch corner  44  and the corresponding lever fulcrum are nearly adjacent to power spring  70 , while notch center  43  is spaced further above the power spring. Flat  32  extends downward to be adjacent to power spring  70 . 
   The structures of fulcrum post  14  and fulcrum sleeve  30  are large enough to secure lever  40  through its pivoting motion. However according to the invention it is not required that the lever always pivot about the axis described by the generally cylindrical shape of fulcrum sleeve  30 . Rather the lever pivots about a rear, generally flat, face of the fulcrum sleeve for at least some positions of the lever. In this manner the lever can pivot as low as possible, immediately near the power spring at the bottom of the structure of the fulcrum post and sleeve. When notch corner  44  presses forward on flat  32  of fulcrum sleeve  30 , the lever is urged rearward to quickly retract from striker  100 . 
   In the illustrated embodiment the lever engages the fulcrum sleeve in two ways. A first pivot point is substantially downward about the cylindrical axis of fulcrum sleeve  30  for an initial range of motion of the lever. Near the release point the pivot location is at a lower position pressing forward against flat  32 . Optionally notch corner  44  may press flat  32  through most or all of the range of motion of the lever. In either case, at or near the release point, the lever pivots about a lowest possible position adjacent to power spring  70 .