Patent Publication Number: US-8978952-B2

Title: Power spring configurations for a fastening device

Description:
BACKGROUND 
     The present invention relates to spring energized fastening tools. More precisely, the present invention relates to improvements to the spring and release of a spring-actuated stapling device. 
     Spring powered staplers and staple guns operate by driving a striker with a power spring. The striker ejects a staple by impact blow. In a desktop stapler, the staple is ejected into an anvil of a pivotally attached base. In a staple gun, the fastener is normally installed directly into a work surface. Two general principles are used in either type device. In the first design, the striker has an initial position in front of a staple track. The striker is lifted against the force of the power spring to a position above the staple track. The striker is released to impact and eject the staple. This design may be referred to as a “low start” stapler. A second design uses a “high start” position. That is, the striker has an initial position above the staples loaded on the staple feed track. The power spring is deflected while the striker does not move. At a predetermined position of the power spring deflection, the striker is released to accelerate into and eject a staple. A handle normally serves as an energy input device although motorized versions need not have a handle. Spring energized staple gun tackers have traditionally used a low start configuration although high start type tackers are known. Spring energized desktop staplers of both types are currently available. 
     In both high and low start types, the power spring can be made of wire or have a flat metal shape. The flat metal types are normally elongated along a length of the body. Wire springs may be horizontally elongated or vertically oriented compression style. Modern designs tend toward the elongated type, for example a torsion spring with extended arms. 
     A limitation of conventional designs is the absence of simplified structures to preload a torsion spring in a high start type. Further, an improvement is called for in providing a more compact lever arrangement to operate with the simplified wire spring. 
     In comparing a flat spring to a wire spring design, the length tolerance of an elongated flat spring is relatively precise, being limited mostly by the precision of the blank cut out for it, in the case that the spring is of reasonably straight bend. For a wire spring, however, the arm length may be less precise since it depends on the manner in which the coil is wound among other factors. It is therefore desirable to have a release mechanism that is less sensitive to spring length with a high start type wire spring. 
     SUMMARY OF THE INVENTION 
     The present invention is preferably directed to a high start type stapler, although the improvements in part or whole may be applied to a low start type or other fastening devices. 
     In one exemplary embodiment the present invention, vertically co-incident arms extend forward from at least one coil of a torsion spring. Preferably two co-axial coils provide a base for four forward extending wire arms, where some portions of these wires are at least nearly coincident with respect to a side view. Normally a majority of energy is stored in the spring by deflection of the coil of the torsion spring. However, the arms are at least partially resilient so that the arms also may store some useful energy as well. A first pair of arms extend from the coil to the striker. A second pair of arms normally press the first pair in a rest condition, while the second pair may be forcibly deflected away from first arm pair as the spring is energized. The preferred embodiment improved structures preload the torsion spring arms in the rest condition. In particular, the arms cross to directly press each other at least at one crossing location or a small bridge connects them. 
     In one preferred embodiment, the power spring is a single-piece, dual torsion spring. In a further embodiment, the two coils are from separate, adjacent, opposed torsion springs. The springs according to the aforementioned constructions have been shown to be more efficient than conventional power spring designs. Advantages of increased efficiency are one or a combination of reduced handle travel for a lower or smaller grip, added performance, and reduced handle force. It follows that a smaller force spring can be used for a constant performance. For example, a 10% increase in efficiency can allow about a 10% lower force spring for a given application. This has a virtuous benefit that any friction in the system is also reduced by 10% since friction is a direct proportion to the force at a friction area. 
     The separate springs may be best suited for higher force or energy applications such as staple guns or high capacity staplers. In the case of separate springs, there is a tendency for the coils to twist away from each other from forces at the front as explained later. The coils spread apart to undesirably press and scrape the inner housing walls if not otherwise retained together. According to the preferred embodiment, a flanged mandrel retains the coils together wherein sliding friction at the coil area is substantially eliminated. The mandrel may therefore be of a simple, single-molded piece. 
     A lever pivots near the front of the stapler body near a location of the striker. The lever presses the first pair of wire arms to deflect the arms downward, as the second pair of arms remains restrained by engagement to the striker. The lever presses the arms directly. 
     In a further feature of the invention, an improved release mechanism is disclosed. A prior release design is disclosed in, for example, U.S. Pat. No. 7,708,179 (Marks), in FIGS. 21 to 23, and in another variation, U.S. Pat. No. 7,828,184 (Marks), both issued to the present inventor and both of which are incorporated herein by reference. In these designs, a power spring tip presses a latch to restrain the striker from moving as the spring is energized. At a pre-release position of the handle, a cam moves to allow the latch to pivot and free the striker to move downward. These designs include flat springs in the preferred embodiments, although wire springs can also be used and are contemplated. 
     In a preferred embodiment, a tab of the striker presses atop the latch. The power spring extends through both the striker and the latch, but is not restrained by the latch. A resulting advantage is the spring length, as defined by the position of the front tip, can vary without affecting the release action. By contrast, a latch engagement to the spring tip can be sensitive to the position of that tip. Further, a wire spring does not provide a well-defined flat release surface at its tip. In the preferred embodiment, the striker tab extends forward. Upon pressing the latch the tab creates a torque on the striker that biases the bottom of the striker forward. As discussed in detail later, when used with a dual thickness striker, this torque helps guide the striker in its motion. 
     These and other aspects, features, and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments which, taken in conjunction with the accompanying drawings, illustrate by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is side elevational view of a desktop stapler with a right housing omitted for clarity. The stapler is depicted in a rest condition. 
         FIG. 1A  is a detail view of a front upper area of the stapler of  FIG. 1 . 
         FIG. 2  is a detail view of the stapler of  FIG. 1 , in a pre-release condition. 
         FIG. 2A  is a cross-sectional view taken along line  2 A from  FIG. 2 , showing detail of a lever-to-handle link. 
         FIG. 3  is an exploded rear perspective view of a striker, latch, and latch holder from the stapler of  FIG. 1 . 
         FIG. 4  is the view of the stapler from  FIG. 2 , with the stapler in a post-release condition. 
         FIG. 5  is a rear lower perspective view of a lever from the stapler of  FIG. 1 . 
         FIG. 6  is a rear perspective view of a subassembly of a lever, power spring, striker, and re-set spring from the stapler of  FIG. 1  with the elements in a rest condition. 
         FIG. 7  is the subassembly of  FIG. 6  with the elements in a pre-release condition. 
         FIG. 8  is the subassembly of  FIG. 6  with the elements in a post-release condition. 
         FIG. 9  is a top plan view of the power spring from the subassembly of  FIG. 6 . 
         FIG. 10  is a right side, upper perspective view of the power spring of  FIG. 9  in a rest position. 
         FIG. 11  is the power spring of  FIG. 10  depicted in a free position. 
         FIG. 12  is the power spring of  FIG. 10  depicted in a pressed position corresponding to  FIG. 7 . 
         FIG. 13  is a side elevational view of an alternative embodiment power spring-lever subassembly, depicted in a rest position. 
         FIG. 14  is a front view of the subassembly of  FIG. 13 , absent the lever. 
         FIG. 15  is a rear upper perspective view of the subassembly of  FIG. 13  absent the lever. 
         FIG. 16  is the subassembly of  FIG. 15  in a pressed position. 
         FIG. 17  is the subassembly of  FIG. 13  moved to a pressed position. 
         FIG. 18  is perspective view of a mandrel from the subassembly of  FIG. 13 . 
         FIG. 19  is the subassembly of  FIG. 15  showing only two opposed power springs, spaced apart, in a free position. 
         FIG. 20  is a bridge from the subassembly of  FIG. 15 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 to 12  show a standard duty desktop stapler including a preferred embodiment of the power spring of the present invention. For example, preferred embodiment power spring  90  includes coil  98  with terminal arm  95  and loop arm  96  extending forward from the coil, as seen in  FIG. 9 . Identical opposed elements of the double torsion spring may be addressed herein equivalently and in the singular for brevity. It is understood that there are two of each such element, or two pairs, in the preferred embodiment. 
     The present invention is directed to a spring energized fastening device. In a desktop stapler form seen in  FIG. 1 , base  120  or its equivalent structure is optionally included. Track  180  is at a bottom of housing  10  and guides staples or other fasteners (not shown) to striker  100  at the front of the stapler. 
     In the power spring  90 , the respective arms  95  and  96  include a free condition as shown in  FIG. 11 . This is a shape of the power spring  90  as it is manufactured. The arms  95 ,  96  are joined at base coil  98 , where as illustrated each opposed coil has preferably about 2.5 revolutions or turns. More or fewer revolutions are contemplated. Terminal arm  95  includes bends  93  and  97  and terminal end  99 . Loop arm  96  includes loop  94  and loop base  91 . 
     The power spring  90  is preferably fabricated from spring steel that has been heat treated. One example of such steel is music wire. In a staple gun application, the wire is about 0.090-0.150″ diameter inclusive of all dimensions within the specified out limits, while in a standard office desktop stapler application, the wire is about 0.06 to 0.08″ diameter, inclusive of all dimensions within the specified outer limits. Other wire diameters or materials may be selected as required for specific applications; for example, a staple gun that is of heavier or lighter duty than provided by the stated wire types. 
       FIG. 10  shows a preloaded rest condition of exemplary power spring  90 . Terminal arm  95  is forced up against spring bias beside loop arm  96 , toward but not necessarily entirely to the condition of  FIG. 12 . The terminal arm  95  is then moved inward to overlie loop  94 . Upon removing the applied force, the resilient arms press each other with bend  93  dipping slightly into the loop or at least being within the area described by the loop. The arms are thus preloaded to the extent that they are pressing each other in the position of  FIG. 10 . This operation may be done to both opposed terminal arms  95  at the same time or in sequence. Once in the rest condition of  FIG. 10 , the spring  90  is sufficiently stable for subsequent assembly operations. Bend  93  is restrained from sliding off of loop  94  by being contained within or confined by the loop. Alternatively, loop  94  may include upward bends (not shown) to confine arm  95  wherein bend  93  would be optional. 
     According to the above-described structure, power spring  90  maintains a preload without any additional components. The power spring  90  is thus restrained in its preloaded condition by folding against or crisscrossing itself. Specifically, the arms directly press each other at an arm preload location in a stable manner, such location being at a crossing of the arms. 
     In  FIG. 12  a pressed position of power spring  90  is shown. This position does not normally occur to the isolated spring, but rather corresponds to the pre-release condition within the assemblies of  FIGS. 2 and 7 . The assembly of  FIG. 7  has various components not shown for clarity. 
     As best seen in  FIG. 9 , terminal arm  95  crosses from outside loop arm  96  to extend inside the loop arm. Therefore, each arm  95 ,  96  is alternately an inner and an outer arm depending on a selected location along the spring length. By passing over each other, the arms can press each other at a crossing location with no intervening parts. In this manner, the arms  95 ,  96  are substantially vertically coincident at the crossing locations. The terminal arm  95  crosses the loop arm  96  a second time at a front most part of the loop  94 . Preferably, loop  94  of arm  96  is wider than the arm  96  portions rearward. This helps maintain a larger radius for ease of manufacture and presents a larger area for bend  93  to descend into. Optionally, depending on the particular geometry, there may be only a single crossing. For example, if arm  95  at bend  93  is farther out, it may just overlie loop  94  and be considered a single crossing. 
     Regarding the assembly,  FIGS. 1 and 6  show power spring  90  in the rest position of the isolated spring of  FIG. 10 . Lever  40  provides a link between handle  30  and power spring  90 . As seen in  FIGS. 5-8 , lever  40  preferably has an inverted triangular shape with three vertices: one vertex is lever pivot point  42 , a second vertex is fulcrum  41 , and the third vertex is rear end  44  that engages the handle  30 . The lever pivot point  42  is at a end thereof and the lever pivots about that end, while the opposite end of the lever corresponds to the rear end  44 . As seen in  FIG. 1 , power spring  90  is pivotally mounted to housing  10  at post  12  of the housing. Rear end  44  is substantially aligned vertically with post  12  and coil  98 , post  12  being a location for a rotational base of power spring  90 . This relative position of lever rear  44  in housing  10  provides a practical travel of linked handle  30 , in particular the positions shown from  FIG. 1  to  FIG. 2 . In  FIGS. 2 and 4  it is seen that rear end  44  is close to coil  98  or post  12  in the lever lowest position. Optionally, arms  95  and  96  may be shorter or longer to not so closely coincide with post  12 . However too long arms may cause a too weak force at striker  100  from such a long torque arm as applied by a reasonably sized coil  98 . If the arms are too short the arc radius at striker  100  is too small. This leads to excess friction from sliding at spring end  99  in striker opening  103  and non-vertical forces at striker  100  against slot  11 . 
     Lever  40  presses the power spring  90  at fulcrum  41  of the lever near bend  91  of the power spring. This pressing point is between a location of striker  100  and post  12 . According to the preferred embodiment of the invention, the lever  40  presses the power spring wire at a location substantially rearward of lever pivot point  42  ( FIGS. 2 ,  4 ). In this manner, pressing the lever  40  at its rear end  44  creates mechanical advantage through the lever arm between lever pivot point  42  and fulcrum  41 . The lever  40  acts directly on the power spring wire rather than through a further effective lever or linkage. This reduces overall part count, simplifies assembly, and eliminates friction and drag in the system. In  FIG. 2 , lever  40  is seen passing downward past largely stationary arms  95 , thus becoming more deeply nested between the arms  95 , in the pre-release position. In this context, becoming nested can mean moving from not nested or moving to be further nested between the arms. Lever  40  may include a further extension  47 , discussed below, whereby the lever is normally nested within arms  96 . 
     The user presses on handle  30  to operate the stapler. Handle  30  includes cam area  31  that slides along rear end  44  of lever  40  ( FIG. 2 ). By pressing the lever  40  at progressively varying angles, handle  30  provides increasing leverage upon lever  40 . In this manner, the force upon handle  30  as perceived by the user may remain relatively constant as power spring  90  is deflected and further energized from the rest position,  FIG. 1 , to the pressed position,  FIG. 2 . 
     Optional reset spring  130  normally biases the components upward in a reset stroke. In particular, reset spring  130  biases power spring  90  to move from the post-release position of  FIG. 4  to the rest position of  FIG. 1 . However, under some conditions striker  100  may resist rising, for example, if a jam occurs. So lever  40  preferably includes a rib, recess, or tab  47  that underlies arm  96  ( FIG. 2 ). Tab  47  provides a tensile link between the power spring  90  and the lever  40  to pull the power spring  90  and striker  100  upward when reset spring  130  cannot by itself do so. Tab  47  may be installed through the wide portion of loop  94  and slid rearward or by spreading the loop wires apart. 
     A second tensile link is shown in a preferred embodiment of  FIG. 2A  between lever  40  and handle  30 . This second link completes the tensile connection through lever  40  between power spring  90  and handle  30 . Undercut tab  35 , also shown hidden in  FIG. 2 , extends under rib  49  of lever  40  for all operative handle positions. Pulling up upon the handle  30  causes these elements to bias the lever  40  upward as they engage by sliding. To assemble tab  35  under rib  49 , it is moved down along slot  46 ,  FIG. 6 , as handle  30  is manipulated during installation. Handle  30  is then moved rearward to its operative position at rear end pivot  32 ,  FIG. 1  whereby tab  35  also moves rearward to become under rib  49 . 
     To provide a compact form in a preferred embodiment, power spring  90  has arms  95  and  96  extending from coil  98  at an angle where the arms become coincident in a rest condition (as seen from the side views of  FIGS. 1 and 4 ). The arms  95 , then bend at  97  to continue to extend substantially coincident with respect to the side view. The power spring  90  thus includes a converging angled portion near the coil  98  and an extended, parallel and coincident forward portion. With this arrangement, the power spring  90  is compact vertically in the front area where the lever  40  and striker  100  interact with it. As shown bend  97  is in arm  95 ; optionally there may be an equivalent bend in arms  96  or in both pairs of arms. A low profile power spring allows the entire desktop stapler or staple gun, especially in a high start configuration, to have a low profile. A low profile desktop stapler is very attractive to consumers who want a sleek, unobtrusive office tool for use in the office, home, or school. A compact staple gun allows a comfortably small gripping distance around the spring location. 
     In power spring  90 , arms  95  extend past loop  94  to engage striker  100 . In  FIG. 4  it can be seen that arm  95  near end  99  rests on an optional shock absorber  61 . With loop  94  ending mostly rearward of absorber  61 , arms  95  are exposed from below and there is room for the absorber  61  to engage arms  95  over a length segment of the arms when striker  100  rapidly moves down in the firing stroke. Such engagement is required, for example, when the fastening device is fired empty and there are no fasteners to otherwise stop the downward motion. 
       FIGS. 13-20  show an alternative embodiment power spring  190 . Power spring  190  preferably has two separate identical opposed torsion springs, as seen in  FIG. 19 . As discussed earlier regarding power spring  90 , a singular reference in the description here to part of a spring shall include an opposed equivalent part. 
     In power spring  190  the opposed parts are proximate each other for preferably the full length of the spring. This provides a compact shape with respect to width. This may be useful when the stapling device is to be high energy, such as a staple gun or high capacity desktop stapler. For example, a staple gun using T-50 type staples or a desktop stapler of over 60-page capacity may be considered heavy-duty formats although such uses may include other formats. In a staple gun, the power spring should fit within a housing that is comfortable to grip; a desktop stapler should be reasonable size not to appear bulky. 
     In accordance with the above goals, one embodiment of inner arms  196  including ends  199  are spaced near to each other. With no loop at the end, the arms  196  at ends  199  can engage a striker or equivalent structure (not shown) through a small opening or openings of the striker. Outer arm  195  extends forward at an angle toward inner arm  196  in the side view of  FIG. 13 . After bend  197 , outer arm  195  extends to distal end  193  through portion  191  parallel, coincident, and adjacent to inner arm  196 . Optional bridge  200  retains the opposed springs in a preloaded rest condition. Hooked section  203  of bridge  200  partially surrounds arm portion  191  ( FIG. 14 ). Bridge  200  optionally includes central hump  205  ( FIG. 20 ) in a floor of the bridge to hold inner arms  196  in a close but spaced-apart relation. Cage  200  thus holds the outer arms  195  from outside and above and the inner arms  196  from below, as seen in  FIGS. 13-16 . 
     The wire of power spring  190  is relatively thick. In one example staple gun application, the wire is about 0.125-0.130″ diameter, and inclusive of all dimensions in between the outer limits. So it is desirable to have the forward portions of the arms be very nearly coincident with respect to the side view, such as  FIG. 13 . In this way, the power spring  190  remains vertically compact. If the arms  195 ,  196  are coincident vertically they must therefore be separated laterally as seen in  FIG. 14 . 
     Within bridge  200 , outer arm  195  is biased to rise relative to inner arm  196 . This can be seen by comparing the free position of  FIG. 19 . So due to internal spring resilience, arm  195  at portion  191  presses up on bridge  200  while arm  196  presses down. Since the arms are spaced laterally there will be a torque arm across this space, horizontally in  FIG. 14 , to create a twisting bias on the power spring  190 , tending to cause the left side coil  198  of  FIG. 14  to rotate counterclockwise and the opposed right coil  198  to rotate clockwise. If there are a large number of coils  198 , the twisting bias will have a reduced effect since the coils will be wide enough, horizontal direction in  FIG. 14 , to provide stability. However, such a spring or spring assembly will not be compact. Also, this effect is not a factor in the preceding single piece power spring  90 . In that case, the arms are substantially coincident laterally, vertical direction on the page in  FIG. 9 . So there is no torque arm to create a torsion bias on the coils. Further, loop  94  ties the two sides of the power spring  90  together to resist any twisting between the sides. 
     Without remedy, the coils  198  of compact power spring  190  tend to twist away from each other and may be unstable within a stapler housing (not shown). It will improve this twisting condition to include an optional mandrel  160  upon which coil  198  is guided ( FIGS. 13 , to  17 ). There should be free play between mandrel  160  and coil  198  up to the deflection shown in  FIG. 16  to prevent binding of the coil. Specifically, the coil  198  inner diameter remains greater than the mandrel outer diameter for all operative positions of the power spring  190 . So the twisting bias on the coil  198  will cause the coil to skew on the mandrel  160 . As the opposed coils spread apart accordingly, the assembled power spring  190  will become unnecessarily wide within the housing. Further, the coil will tend to wedge and bind on the mandrel in spite of the free play clearance causing excess friction at the coil as the spring deflects. 
     Preferably, mandrel  160  is a discrete component so that it may be part of a power spring sub-assembly. The mandrel  160  is then pivotable upon a post of the housing to better allow for rotational motion of the power spring  190 . Preferably, the mandrel is made from a low friction material such as acetal, nylon, polypropylene, PTFE, or similar. However, optionally, such a mandrel may be included as an element of or integral to housing  10  or other component. 
     A solution is to the skewing bias includes flange  162  on mandrel  160  ( FIGS. 14-16 ,  18 ). This flange  162  confines the outer coil  198  from moving axially on the mandrel  160 . To assemble the coil  198  upon the flanged mandrel  160 , the mandrel is preferably installed with spring  190  in the free condition of  FIG. 19 . In this condition, coil  198  is of a larger diameter than in the rest condition of  FIG. 15  where the coil is wrapped toward closed. Optionally, the arms  195 ,  196  of the free condition spring  190  may be lightly urged further open to provide additional inside diameter space to clear the flange  162 . The mandrel flange end can be slidably installed into the coil with no or minimal resistance. Empirical testing of working samples shows that either assembly method can work. The coils  198  are held securely between the flanges  162  when the power spring  190  is moved toward the rest or pressed conditions wherein the coil diameter decreases. Accordingly, the coil  198  is held more securely between the flanges as the deflection and spreading force increases since the coil inside diameter is substantially less than the flange diameter. Substantially less here means sufficient to reliably retain the coils from sliding out past the flanges. In all operative positions the central mandrel outer diameter, between flanges, is less than the coil inside diameter to prevent binding. Naturally, the flange  162  may in alternative embodiments have localized humps or protrusions rather than a full circumferential rim. According to one embodiment of the invention, the mandrel may thus be a single component where the flange is present as the power spring is installed over it. Optionally, mandrel  160  may have two spaced-apart or not spaced-apart halves joined by a rivet, for example (not shown). In this instance, a central part of the mandrel may be a narrow element of the rivet diameter. This alternative mandrel may have the spring assembled over the flange or the halves may be assembled about the spring coils. Optionally, the flanges may be discrete elements (not shown) held in place by the rivet. 
     It may be noted here that a torsion wire spring should operate to close the coil upon deflection. Alternatively, opening or unwinding the coil may energize the spring. However, this creates tensile stress on the inside of the coil wires and has inferior life properties so such applications are normally limited to low energy uses. 
     Alternatively to flanges  162 , a wire or equivalent tensile tie may span arms  195  near to coil  198  to hold the arms together. The coils are then similarly held from spreading. 
     To deflect and assemble power spring  190  to bridge  200  to arrive at its rest condition of  FIG. 15 , the two opposed power springs  190  are preferably positioned on a fixture (not shown) about mandrel  160  and deflected from the free condition,  FIG. 19 , to or toward the pressed condition,  FIG. 16 . Bridge  200  is installed into position. Mandrel  160  normally fits about a post of the housing (not shown). 
     Bridge  200  may include extension  201  ( FIG. 20 ) to provide some additional support to the forward portion of arm  196 . This helps engage a longer portion of spring material in the pre-load stress of the rest condition. 
     Empirical testing has shown a tendency for bridge  200  to slide rearward upon the spring in use. Therefore, there should be an optional crimp or other inhibiting structure to prevent such motion. For example, bridge  200  may be crimped at  206  ( FIG. 14 ) to extend over end  193  of the spring arm in  FIG. 14 . 
     As with single spring  90  above, arms  195  near end  199  extend past bridge  200  in power spring  190 . This exposed underside area of arms  195  provides a surface for an absorber (not shown) to stop the motion of the power spring  190  at the end of a firing stroke. 
       FIGS. 13 and 17  show lever  140  that operates similarly to lever  40 . Pivot  142  fits to the housing (not shown) while rear end  144  provides a cam interface for a handle (not shown). In the preferred embodiment, fulcrum  141  presses bridge  200 . Pressing the bridge provides a larger diameter object to engage verse the wire of the power spring  190 . Wear on lever  140  may thus be reduced. As illustrated in  FIG. 17 , lever  140  straddles inner arms  196  to extend below the inner arms in the pressed position. As discussed above for power spring  90 , power spring  140  includes at least one position where rear end  144  is substantially vertically aligned with coil  198 . Likewise, the lever lowest position in  FIG. 17  has lever rear end  144  close to coil  198 . 
     It has been described that power spring embodiment  190  is suited for staple guns or high capacity staplers. Naturally, the first embodiment single piece spring  90  may be scaled to serve in such devices if desired. Likewise the two-piece spring  190  may be used for a standard duty desktop stapler. Further, it may be desired that the opposed elements of either spring embodiment be not identically opposed if there is an advantage to fit a particular structure. For example, there may be extra or fewer bends on one side or the parts may be identical and not opposed, i.e. entirely identical. 
     In various alternative embodiments, it is also possible to use the power spring of the present invention as a single torsion spring. For example, in spring  90  loop  94  may terminate in a hook rather than a full loop (not shown). A single arm  95  corresponding to a single coil  98  could be moved to rest upon such hook. For spring  190 , flanges  162  of the mandrel could provide useful guidance to a single coil to hold the coil from becoming skewed in a device. 
     An improved release mechanism or latch means for a high start type stapler is shown in  FIGS. 1 to 4 . The release mechanism or latch means is used to hold the striker in position while the power spring is energized when the handle is pressed, and then releases the striker to expel a fastener from the stapler by impact blow. A prior release system or latch means is shown, for example, in U.S. Pat. No. 7,828,184 (Marks), the contents of which are incorporated by reference. As in the present invention, the Marks &#39;184 stapler includes a striker, a latch, and a latch holder. The latch holder operates similarly to the present latch holder  300 , shown in  FIG. 3 . Latch holder  300  is attached at lower end  301  in a receiving recess of housing  10 ,  FIG. 1A . Top end  303  normally is exposed in an opening atop the housing  10 . Serpentine section  308  ( FIG. 3 ) allows top end  303  to move resiliently toward lower end  301 . As handle  30  is pressed down, tab  33  engages top end  303  to depress the latch holder  300 . Top end  303  moves below shelf  13  of the housing ( FIG. 2 ) and the latch holder  300  is then free to move forward. 
     Striker  100  moves vertically in slot  11  of housing  10  in  FIG. 2 . The striker  100  includes forward extending tab  102  at its top. Tab  102  rests on edge  209  of latch  200 . Power spring  90  at ends  99  biases the striker  100  downward as the power spring is energized. Tab  102  extends at a slight upward angle whereby latch  200  is biased to slide forward under the tab as the tab is pressed. Latch holder  300  selectively prevents the latch  200  from moving as described above. 
     The forward direction of tab  102  provides a particular advantage when used with a dual thickness striker as shown. As seen in  FIG. 3 , striker  100  includes a thin lower portion  105  and a thicker upper portion  104 . The thin section fits a standard 0.020″ staple dimension. The thicker upper section provides additional strength at openings  103  where power spring  90  engages the striker  100 . However, in some low profile configurations there is no room for a structure to closely confine the striker from the rear at the lower portion. This is in the area of absorber  61  in  FIG. 2 . Rather thick upper portion  104  moves down to be near to track  180  in a striker lowest position,  FIG. 4 , leaving no room for any such rear guide surface for thin  105 . As a result, striker  100  can rattle slightly at the lower end. 
     It is preferred that the striker  100  does not tilt rearward (clockwise in the drawings) as the power spring  90  is released. Otherwise the striker  100  may impact track  180  or a staple rearward of slot  11 . One way to bias the striker  100  forward at the lower end is from the angle of power spring  90  at end  99 . As seen in  FIG. 1A , the power spring  90  will press on a rear edge of openings  103 . This creates a counterclockwise bias to the striker in the  FIG. 1A  view and will lightly hold the lower portion of striker  100  against a front guide feature of the housing. 
     However, optionally, to further ensure the striker is biased forward at its lower area, tab  102  provides an improvement. The distance between the opening  103  and tab  102  with respect to the length direction (horizontal in  FIG. 1A ) creates a torque arm on striker  100 . A net downward force at  103  and an upward force at  102  firmly hold the striker with its lower end forward as striker  100  is stationary in the upper position. Accordingly, a guide face or rib at the lower rear of striker  100  is not required for reliable guidance of the striker. 
     In a wire type torsion, spring a position of a terminal end, such as end  99 , will be less precise than for a flat metal type. The flat metal spring is approximately accurate within the tolerance of the punching operation that forms the flat shape. However, the coil winding process and arm angle tolerance in a wire spring means such springs have a wider arm length tolerance. So it is preferable to release from the striker as shown herein rather than from a tip of the spring as has been done before. Latch  200  extends downward adjacent to and in front of striker  100 . So to allow for arm length variations, latch  200  includes openings  207 , seen in  FIGS. 1A ,  3 . These openings  207  allow the spring tip to extend through a thickness of the latch  200 . In this way, the position and length of end  99  may vary from just within striker opening  103  to within latch opening  207 . To preserve the torque arm described above and reliability of the release action, it is preferable that the openings  207  in the latch not serve as a release edge. Rather, tab  102  shall have that function. So spring end  99  should not press within the opening  207 . To ensure this is the case, opening  207  is larger than opening  103 . As seen in  FIG. 3 , opening  207  is elongated for this reason. If a sufficiently precise length spring is used, then opening  207  may serve as a release feature instead of or in addition to tab  102 . 
     Although the present invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of the invention. Components and features of one embodiment may be combined with other embodiments. Accordingly, the scope of the invention is intended to be defined only by reference to the appended claims. While variations have been described and shown, it is to be understood that these variations are merely exemplary of the present invention and are by no means meant to be limiting.