Abstract:
A folding knife includes a handle defining a knife receiving chamber and including first and second inner plates disposed in spaced relation between a pair of outer plates. The folding knife also supports a blade having a tip end and a tang end that is pivotally attached to the handle and is pivotable between a retracted position where the blade is disposed in the knife receiving chamber and an extended position where the blade resides outside of the handle. The first inner plate has a slot formed therein so as to define a lock member that has a locking edge that is biased inwardly towards the blade and having an extension projecting outwardly from the locking edge. When the blade is in the extended position, the locking edge moves into a locking arrangement abutting against the tang end of the blade, with the extension being constructed to prevent the locking edge from inadvertently slipping from its abutting relationship with the tang end of the blade to ensure that the blade is securely held open in the extended position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This present application is a continuation of U.S. patent application Ser. No. 10/459,053 filed on Jun. 10, 2003, now U.S. Pat. No. 7,080,457, issued Jul. 25, 2006, and which claims the benefit of U.S. Provisional Patent Application No. 60/387,658, filed Jun. 10, 2002, both of which are hereby incorporated by reference in their entirety. 

   TECHNICAL FIELD 
   This invention generally relates to folding knives, and more particularly, to folding knives that include an internal spring bias for assisting in the opening of the knife blade. 
   BACKGROUND 
   So-called spring-assisted foldable knives have been around at least since the early 1800&#39;s. These knives generally include a handle and a pivotally attached knife blade. A spring mechanism is attached between the handle and the knife blade so that the knife blade is biased to an open position. A locking mechanism is positioned within the handle portion and is designed to selectively engage the knife blade so that the blade may be held in a closed position, safely within the handle and against the action of the spring mechanism until it is needed. In use, an operator of the knife merely has to release the locking mechanism to cause the spring to force the blade to pivot to its open position. Once open, the locking mechanism typically engages the blade to hold it in its open position. 
   To close this prior art spring-assisted folding blade, the operator must first disengage the locking mechanism and then manually pivot the blade, against the action of the spring to its closed and again locked position. Some types of knives provide spring assist for both opening and closing the blade action. 
   U.S. Pat. Nos. 5,802,722 and 6,145,202 both of Onion both disclose a spring-assisted foldable knife assembly that includes a handle portion, a knife blade that is pivotally attached to the handle and operates within a knife plane. A torsion bar positioned within the handle and adjacent to the knife plane is attached between the handle and the knife blade. The torsion bar creates a “balanced” spring bias that applies either an opening force or a closing force depending on the angular position of the knife blade with respect to the handle. 
   In use, the operator of this type of knife pivots the blade towards its open position against the closing action of the torsion bar. When the blade is pivoted past a point of equilibrium, the spring bias of the torsion bar begins to apply an opening force to the blade and forces the blade to quickly pivot to its fully open position. To close the blade, the user first releases a locking mechanism and then forces the blade against the spring bias of the torsion bar, again until the blade passes the point of equilibrium, at which point the torsion bar pulls the blade to its closed position, safely within the handle. 
   SUMMARY 
   According to one aspect, a folding knife includes a handle defining a knife receiving chamber and including first and second inner plates disposed in spaced relation between a pair of outer plates. The handle supports a pivot pin. The folding knife also supports a blade having a tip end and a tang end that is pivotally attached to the handle about the pivot pin and is pivotable between a retracted position where the blade is disposed in the knife receiving chamber and an extended position where the blade resides outside of the handle. 
   The first inner plate has a slot formed therein so as to define a lock member that has a locking edge that is biased inwardly towards the blade and having an extension projecting outwardly from the locking edge. In addition, a recess is formed in the outer plate adjacent the first inner plat. When the blade is in the extended position, the locking edge moves into a locking arrangement abutting against the tang end of the blade and when the blade is in the retracted position, the extension is received in the recess. The extension is constructed to prevent the locking edge from inadvertently slipping from its abutting relationship with the tang end of the blade to ensure that the blade is securely held open in the extended position. 
   The lock member of the present invention ensures that when the blade is in the extended position, the blade is securely held and maintained in this position by the lock member. 
   In one exemplary embodiment, the lock member is a flexible member that can flex so that it lies outside of a plane containing the rest of the first inner plate and the extension is angled relative to the locking edge (e.g., at an angle other than 90 degrees). The extension extends outwardly in an opposite direction relative to the biasing direction of the lock member. 
   Other features and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the following drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The foregoing and other features of the present invention will be more readily apparent from the following detailed description and drawings of illustrative embodiments of the invention in which: 
       FIG. 1  is a side view of a folding knife, according to a first embodiment of the invention; 
       FIG. 2  is a front view of the folding knife of  FIG. 1 , according to the first embodiment of the invention; 
       FIG. 3  is a side view of a knife blade, according to the first embodiment of the invention; 
       FIG. 4  is a bottom view of the knife blade of  FIG. 3 , showing details of a tang recess, according to the first embodiment of the invention; 
       FIG. 5  is a sectional view of the knife blade of  FIG. 3 , taken along the lines  5 - 5 , according to the first embodiment of the invention; 
       FIG. 6  is a side view of the folding knife similar to the one shown in  FIG. 1 , shown without a handle plate or a liner plate, revealing details of a spring-assisted opening mechanism, according to the first embodiment of the invention; 
       FIG. 7   a  is a front assembly view of the knife, according to the first embodiment of the invention, showing details of the blade, its tang recess, liner plates, and handle plates, and a rod; 
       FIG. 7   b  is a front view of the knife, according to the first embodiment of the invention, showing an assembled knife; 
       FIG. 8  is a side view of a spring housing block, according to the first embodiment of the invention; 
       FIG. 9  is a top view of the spring housing block of  FIG. 8 , showing details of rod-access slot, according to the first embodiment of the invention; 
       FIG. 10  is a front view of the spring housing block, according to the first embodiment of the invention; 
       FIG. 11  is a top view of a linkage element, showing details of pivot pins, according to the first embodiment of the invention; 
       FIG. 12  is a sectional view of the linkage element of  FIG. 11 , taken along the lines  12 - 12 , showing details of front and rear vertical slots, according to the first embodiment of the invention; 
       FIG. 13  is a front view of the linkage element of  FIG. 12 , showing details of the front vertical slot, according to the invention; 
       FIG. 14  is an assembly view of the spring assisted mechanism, showing details of the blade, the rod, the spring housing block, the linkage, and a spring, according to the first embodiment of the invention; 
       FIG. 15  is a partial enlarged sectional side view of the knife, according to the first embodiment of the invention, showing details of the rod attached to the tang of the blade within the tang recess, the linkage, and the spring located within the spring housing block; 
       FIG. 16  is a concept side view of the knife of  FIG. 6  (shown without a liner plate and a housing plate to reveal details of the spring-assisted opening mechanism), shown with the blade in a partially opened position wherein the rod is located on the line of equilibrium, according the first embodiment of the invention; 
       FIG. 17  is a concept side view of the knife of  FIG. 16 , wherein the blade is opened to a further position wherein rod is located beyond the line of equilibrium, according to the first embodiment of the invention; 
       FIG. 18  is a concept side view of the knife of  FIG. 16 , wherein the blade is in a fully opened position, according to the first embodiment of the invention; 
       FIG. 19  is a side view of a blade according to a second embodiment of the invention, showing details of a split-pin pivoting assembly; 
       FIG. 20  is a bottom view of the blade of  FIG. 19 , showing details of a split-pin pivoting assembly, according to a second embodiment of the invention; 
       FIG. 21  is a rear sectional view of the blade of  FIG. 19 , taken along the line  19 - 19 , showing details of a split-pin pivoting assembly, according to a second embodiment of the invention; 
       FIG. 22  is an assembly view of a knife, according to the second embodiment of the invention, showing details of the blade of  FIG. 19 , liner plates, handle plates, a straight rod, a spring housing block, securing bolts, and a pivot pin; 
       FIG. 23  is a sectional view of the knife of  FIG. 25 , taken along the lines  23 - 23 , showing details of the blade pivotally attached to liner plates, housing plates, using securing bolts, according to the second embodiment of the invention; 
       FIG. 24  is an end view of the knife of  FIG. 23 , showing one handle plate in section to reveal a recess formed therein sized and positioned to accommodate the head of a securing bolt, according to the second embodiment of the invention; 
       FIG. 25  is a side view of the knife, according to the second embodiment of the invention; 
       FIG. 26  is a concept view of the knife of  FIG. 25 , shown without a liner plate or a handle plate to reveal details of the spring assisted opening mechanism, according to the second embodiment of the invention; 
       FIG. 27  is a rear view of a clip, according to a third embodiment of the invention; 
       FIG. 28  is a side view of the clip of  FIG. 27 , according to the third embodiment of the invention; 
       FIG. 29  is a front view of the clip of  FIG. 27 , according to the third embodiment of the invention; 
       FIG. 30  is a side view of the clip of  FIG. 27 , shown pivotally attached to a knife and positioned in an unlocked position (the blade of the knife is revealed to explain the operation of the clip), according to the third embodiment of the invention; 
       FIG. 31  is a side view of the clip of  FIG. 27 , shown pivotally attached to a knife and positioned in an unlocked position, according to the third embodiment of the invention; 
       FIG. 32  is a top view of the knife of  FIG. 31 , showing a blade located within a blade cavity and details of a loop of the clip in an unlocked position, according to the third embodiment of the invention; 
       FIG. 33  is a side view of the clip of  FIG. 27 , shown pivotally attached to a knife and positioned in a safety position (the blade of the knife is revealed to explain the operation of the clip), according to the third embodiment of the invention; 
       FIG. 34  is a side view of the clip of  FIG. 27 , shown pivotally attached to a knife and positioned in a safety position, according to the third embodiment of the invention; 
       FIG. 35  is a top view of the knife of  FIG. 31 , showing a blade located within a blade cavity and details of a loop of the clip in a safety position preventing the removal of the blade from the blade cavity, according to the third embodiment of the invention; 
       FIG. 36  is a side view of a knife, (shown without a liner plate or a handle plate) showing details of a spring assisted opening mechanism, according to a fourth embodiment of the invention; 
       FIG. 37  is a side view of a liner plate, according to the invention; 
       FIG. 38  is a side view of a locking liner plate, according to the invention, showing details of a locking tab; 
       FIG. 39  is an end view of the liner plate of  FIG. 38 , showing the thickness of the liner plates, according to the invention; 
       FIG. 40  is a top view of a knife, showing a blade in an open position, a locking liner plate with its locking tab in a locked position against the tang of the blade, according to the invention; 
       FIG. 41  is an assembly top view of the locking liner plate and a handle plate, according to the invention; 
       FIG. 42  is an assembly top view of a non-locking liner plate and a handle plate, according to the invention; 
       FIG. 43  is top view of the locking liner plate, according to the invention, showing details of an angle extension; 
       FIG. 44  is a side view of the locking liner plate of  FIG. 43 , according to the invention; 
       FIG. 45  is a front view of the locking liner plate of  FIG. 44 , showing details of the angle extension, according to the invention; 
       FIG. 46  is a rear view of the locking liner plate of  FIG. 44 , showing details of the angle extension, according to the invention; 
       FIG. 47  is a partial top view of a locking tab, showing details of the angle extension, according to the invention; 
       FIG. 48  is a top view of a knife showing a blade in a fully open position and a locking tab positioned in a locked position abutting the tang of the blade, and further showing (in phantom) a recess formed in a handle plate used to accommodate the angle extension when positioned in a stowed, unlocked position, according to the invention; 
       FIG. 49  is a top view of a knife showing a blade in a closed position and a locking tab positioned in the stowed, unlocked position with the angle extension positioned within the recess formed within the handle plate, according to the invention; 
       FIG. 50  is a side view of a knife, according to yet another embodiment of the invention, showing details of an accessible lever arm (shown in an unlocked position) and a blade located in a closed position; 
       FIG. 51  is a side view of the knife of  FIG. 50 , shown without a liner plate or a handle plate, thereby revealing details of a blade locking mechanism (shown located in an unlocked position), according to the invention; 
       FIG. 52  is a side view of the knife of  FIG. 50  showing the blade in a fully position and showing the lever arm in a locked position, according to the invention; 
       FIG. 53  is a side view of the knife of  FIG. 51 , shown without a liner plate or a handle plate, thereby revealing details of the blade locking mechanism (shown in a locked position, engaged with a linkage), according to the invention; 
       FIG. 54  is a top view of a non-locking liner plate, according to the invention; 
       FIG. 55  is a side front view of the non-locking liner plate, according to the invention; 
       FIG. 56  is a front view of the non-locking liner plate, according to the invention; 
       FIG. 57  is a rear view of the non-locking liner plate, according to the invention; 
       FIG. 58  is a side view of a knife, according to yet another embodiment of the invention (shown without a liner plate or a handle plate thereby revealing details of a spring assisted mechanism), including a spring located within a curved spring recess, wherein the blade of the knife is in a closed position; and 
       FIG. 59  is a side view of the knife of  FIG. 58 , wherein the knife blade is positioned outside a blade receiving cavity, yet is not at its fully opened position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 through 5 , a knife  10 , according to the invention, includes a knife blade  12 , two parallel liner plates  14 , two handle plates  16 , a thumb pin  18 , and a spring housing block  20 . Blade  12  includes a tip  22 , a cutting edge  24 , a spine  26  (or an opposing second cutting edge, depending on the type of knife), a pivot opening  28 , and a tang  30 . Tang  30  includes a recess  34 , as shown in  FIGS. 4 and 5 . 
   As shown in  FIGS. 1-7   b , blade  12  is pivotally attached between the two liner plates  14  by pivot pin  36 , along pivot axis  38 . Pivot pin  36  is sized and shaped to snugly fit within pivot opening  28  and is preferably a threaded fastener (e.g., a bolt) which may engage into aligned threaded openings formed within each respective liner plate  14 , as is understood by those skilled in the art. 
   As shown in  FIGS. 3 ,  4 ,  5 , and  6 , blade  12  is pivotal between a closed position, ( FIG. 6 ), wherein blade  12  rests between liner plates  14  and cutting edge  24  is inaccessible and shielded, and a fully open position ( FIG. 7 ), wherein blade tip  22  is positioned remote from liner plates  14  and cutting edge  24  is exposed and usable. 
   Referring now to  FIGS. 2 ,  6 ,  8 ,  9 , and  10 , spring housing block  20  is positioned between liner plates  14 , generally opposite spine  26  of blade  12  (when the blade is in its closed position within handle plates  16 ), and includes an upper surface  40 , two side walls  42  (which make contact with an inside surface of each respective liner plate  14 ), a lower surface  44  (which is preferably shaped to follow the general contours of the handle plates  16  and liner plates  14 ), a rear surface  46  (which also is preferably shaped to follow the general contours of handle and liner plates  16 , and  14 , respectively), a front end surface  48 , a longitudinally disposed spring recess  50 , and several laterally directed bores  52 . Bores  52  are sized and shaped to receive mechanical fasteners, such as bolts (not shown), which are used to secure liner plates  14  on either side of spring housing block  20  (abutting each respective side walls  42 ). As is generally understood by those skilled in the art, bores  52 , and their respective receiving bolts (not shown) may be equally substituted with projecting pins which align with openings formed within each liner plate  14 . These projecting pins may be integrally formed with the spring housing block  20 . 
   Positioned on upper surface  40  and adjacent to front end surface  48  is a rod-access slot  54  which provides selective access to within spring recess  50 , as described below. Spring recess  50  preferably includes at least an open side window  56  within one side wall  42 , as shown in  FIG. 8 . Side window  56  and spring recess  50  are sized and shaped to accommodate a spring  62 . Front end surface  48  further includes a pin-recess  58  which is sized and shaped to receive a stop-pin  60  (described below, and shown in  FIG. 2 ). 
   Referring to  FIG. 6 , spring  62  is positioned within spring recess  50  and includes rear-hook (or loop)  64 , and a front hook (or loop)  66 . A lateral anchor pin  68  is positioned at a rear end of spring recess  50  and is secured to at least one liner plate  14 . Lateral anchor pin  68  is sized and shaped to receive rear-hook  64  of spring  62  and effectively anchor the rear portion of spring  62  to the body of the knife. 
   Referring to  FIGS. 6 ,  11 ,  12 ,  13 , and  15 , positioned within spring recess  50 , adjacent to the front end surface  48  is a linkage  70 , which is generally block-rectangular in shape (resembling a link of a bicycle chain) and includes a bearing surface  72 . Linkage  70  is sized and shaped to snugly fit and slide (longitudinally) within spring recess  50 . Linkage  70  includes a front vertical slot  76  and a rear vertical slot  74 , and two lateral bores  78 , which are sized and shaped to receive two lateral pins  80 , respectively, as shown in  FIG. 11 . Linkage  70 , is preferably wide enough to extend within the plane of each respective liner plate  14  so that the strong liner plate  14  can function as a guide to linkage  70  as linkage  70  moves. In such instance, liner plates  14  much include an appropriate slot which is sized and shaped to accommodate the linkage  70 . 
   Front hook  66  of spring  62  is positioned within rear vertical slot  74  of linkage  70  and secured therein by lateral pin  80 , as shown in  FIGS. 6 and 15  so that movement of linkage  70  is influenced by the bias of spring  62 . Spring  62  is preferably a coil type spring that applies a pulling force to linkage  70  so that linkage  70  is pulled rearwardly at all times, during the opening and closing of blade  12  from knife  10 . 
   As shown in  FIGS. 2 ,  6 ,  14 , and  15 , a connecting rod (or linkage)  82  connects tang  30  of blade  12  to linkage  70 . According to one preferred embodiment, rod  82  is shaped similar to a little question mark (like this one—?—but bigger), including a straight lower end  86 , an upper end  88 , and a curve  90  formed near upper end  88 . Rod  82  includes a lower pin-receiving bore  92  at lower end  86 , and an upper pin-receiving bore  94  at upper end  88 . As shown in  FIG. 15 , lower end  86  of rod  82  is slidably positioned within rod-access slot  54  and pivotally attached to linkage  70  at pivot point  84 . Rod  82  is attached to linkage  70  within front vertical slot  76  by pin  80 . Upper end  88  of rod  82  is pivotally attached to tang  30  of blade  12  within recess  34 , using pin  96 . Pin  96  is preferably attached to tang  30  within bores  98  of blade  12  (rod  82  pivots about rod-pivot axis  100  (see  FIG. 2 ). Rod  82  is preferably made from a strong rigid material (such as spring steel or tempered steel), and is sized to fit within recess  34  without friction or interference. 
   The exact shape of rod  82 , its length, its exact connection point at tang  30  and the length and strength of spring  62  are critical parameters which will dictate the performance and operation of the opening and closing process of blade  12  from knife  10 . To aid in explaining these critical parameters, a line of equilibrium  102  is provided (see  FIG. 15 ), and is defined herein as the line intersecting both pivot axis  38  and pivot point  84  (where rod  82  pivotally connects with linkage  70 ). An important aspect of the present invention is that when blade  12  is in its fully closed position (as shown in  FIGS. 1 ,  2 , and  6 ), rod-pivot axis  100  is positioned above pin  36  and behind (i.e., rear of) line of equilibrium  102  (preferably around a 1 o&#39;clock position where the “clock” is centered about pivot axis  38 ). In this arrangement, the pulling action of spring  62  applies a rearwardly directed spring bias to linkage  70 , which, in turn, causes rod  82  to force blade  12  to rotate counterclockwise towards its fully closed position (as shown in  FIG. 6 ). The end result is that the blade of the present knife will be held in its fully closed position by spring  62 , until a user starts to open the blade. 
   Referring to  FIGS. 6 ,  16 ,  17 , and  18 , as blade  12  is manually rotated about pivot axis  38  (against the action of spring  62 , described above), rod-pivot axis  100  will also rotate about pivot axis  38 , advancing towards line of equilibrium  102 , until it resides on line of equilibrium  102 , as shown in  FIG. 16 . This is a “turning point”, after which spring  62  will no long cause blade  12  to rotate counterclockwise, but will instead, cause blade  12  to rotate clockwise (as shown in  FIG. 17 ), until it locks at its fully open position, (shown in  FIG. 18 ). As blade  12  rotates about pivot axis  38 , linkage  70  will slide within rod-access slot  54  and spring recess  50  as necessary to accommodate movement of rod  82  (this is illustrated in  FIGS. 6 ,  16 ,  17  and  18 ). 
   In use, an operator holds the present knife  10  in one hand, and uses his thumb and thumb pin  18  to rotate blade  12  from its fully closed position within protective liner plates  14  against the relatively mild closing action created by spring  62 . The force of the closing action will diminish as blade  12  is opened further until the “turning point” at which the rod-pivot axis  100  passes in front of the line of equilibrium  102 . Once the blade reaches the turning point, any further clockwise of blade  12  will cause spring  62  to create a bias that encourages blade  12  to quickly rotate to the blade&#39;s fully open position (shown in  FIG. 18 ). 
   Once blade  12  reaches the fully open position, any appropriate locking mechanism can be used to hold the blade at the fully open position, as understood by those skilled in the art. Although many different locking mechanisms can be employed without departing from the gist of the invention, a liner-lock mechanism is preferred, as described in greater detail below. The spring action and the use of a “line of equilibrium” attachment allows single-handed operation to open the blade, and, as described below, to further close the blade. 
   To close blade  12 , the user first disengages the blade locking mechanism (which ever type is used), and, using the forefinger of the hand holding the knife (or any appropriate surface, or the user&#39;s other hand) rotates blade  12  counterclockwise about pivot axis  38  and against the relatively strong opening bias of spring  62  until rod-pivot axis  100  again crosses the line of equilibrium  102 , at which point, the pulling force of spring  62  will be redirected so that blade  12  is forced back to its fully closed position within liner plates  14  and handle plates  16 . 
   An important feature of the present invention is that blade  12  is connected to spring  62  by rod  82  wherein both rod and spring are positioned and operate within the same plane as blade  12 . Although prior art spring-assisted knives of the type that provide a line of equilibrium (wherein a spring bias forces a blade both closed and open depending on the angular displacement of the blade with respect to the knife) use a rod connecting the spring with the tang of the blade, the rod is offset with respect to the plane of the blade. The present knife includes recess (or slot)  34  which allows rod  82  to be attached to blade  12  within the plane of the blade  12 . Some early knife designs of the prior art use a spring to open the blade wherein the spring and the attachment to the blade is positioned within the plane of the blade. In these prior art knives, however, there is no line of equilibrium used so the spring bias never causes the blade to rotate to its closed position. 
   In contrast, the present knife creates a slot within the tang  30  of blade  12  towards tip  22  past the line of equilibrium (which is generally past the pivot axis  38 ). 
   The slot or recess  34  is preferably formed by machining into tang  30  of blade  12  during the manufacture of blade  12 , but can be formed using any other appropriate method, as understood by those skilled in the art. 
   Rod  82  is preferably made from a strong rigid material such as tempered or spring steel. 
   Spring housing block  20  is preferably made injection molding a strong (possibly fiber reinforced) plastic, but also may be made by machining an appropriate metal, such as steel or aluminum. Spring housing block  20  is shaped according to the particular desired shape and size of knife  10 . Spring recess may be either straight (as shown in  FIG. 16 , for example) or curved (not shown) depending on the particular shape and size of knife  10 . 
   Liner plates  14  are preferably made from tempered steel plate, as well as blade  12 , as is understood by those skilled in the art. 
   Blade  12  may be shaped appropriately and may include any type and shape of cutting edge, including a jagged edge and a double cutting edge. 
   Linkage  70  is preferably made from a strong material, such as tempered steel or reinforced plastic. 
   Spring  62  is preferably a coil-type tension spring that is sized and shaped to fit within spring recess  50  of spring housing block  20  and includes two integrally formed end hooks, as described above. The strength of spring  62  depends on the size, weight, and materials used for blade  12 , linkage  70  and rod  82 , as well as the relative locations of pivot axis  38  and rod-pivot axis  100 , and the size and shape of linkage  70 . Depending on the handle design and size, a different arrangement of spring may be necessary, including the use of two or more tension type springs, or an arrangement of other types of springs (including torsion members). 
   As described above, and shown in the accompanying figures, blade  12  is preferably pivotally attached to and positioned between liner plates  14 . An appropriate bolt or pivot pin  36  is preferably used to pivotally secure knife blade  12  to liner plates  14 . In such instance, rod  82  must include curve  90  to accommodate pin (or bolt)  36  and position the effective attaching point of spring  62  to blade  12  rear of the line of equilibrium  102  (as shown in  FIG. 15 ) when blade  12  is at or near its closing position. According to another embodiment of the invention, referring to  FIGS. 19-26 , blade  12  includes opposing integrally formed pin-halves  104 , each projecting outwardly from blade  12 , as shown in  FIGS. 20 and 21 . Neither pin half  104  extends into recess  34  so that rod  82  may move freely within recess  34  between pin halves  104 . With this arrangement, a straight rod  106  (similar to rod  82 , described above, but without curve  90 ) connects blade  12  and linkage  70  at a connection point  108 . The knife shown in  FIGS. 19-26  operates in a similar manner to the knife described above, and shown in  FIG. 6 . When blade  12  of the knife shown in  FIGS. 19-26  is in its fully closed position and connection point  108  is positioned behind (closer to the rear portion of the knife) the line of equilibrium  102 , spring  62  applies a pulling force on blade  12  so that blade  12  is drawn into its closed position and held there by the bias of spring  62  until it is needed. As in the previously described embodiment (see  FIG. 6 ), when a user pivots blade  12  from its rest and fully closed position, eventually point of connection  108  will cross over the line of equilibrium  102  and spring  62  will then bias blade  12  to angularly displace clockwise. The end result is that once the user moves blade  12  past a certain point (using thumb pin  18 , for example), the blade will automatically and relatively quickly pivot to its fully open position. The exact location of the line of equilibrium in any embodiment of this invention will dictate how far the user must open the blade against the action of spring  62  until spring  62  will force the blade open. 
   With this arrangement, recess  34  effectively extends within tang  30  past pivot axis  38  without obstruction so that rod  82  does not need to include curve  90  and may be made straight (also, a flexible cable can be used in this “split-pin” arrangement). It should be noted, however, that with this split-pin arrangement, additional reinforcement of and/or securement between liner plates may be necessary to ensure that blade  12  is suitably secured to liner plates  14 . This may require that each pin section be welded to or otherwise integrally formed with blade  12 , as shown in  FIGS. 19-26 . 
   According to yet another embodiment of the invention, spring  62  is connected directly to tang  30  of blade  12  using either the split-pin arrangement (wherein spring  62  may include a relatively straight connection portion  63 , as shown in  FIG. 36 . If the full-pin version is used (as in  FIGS. 6 ,  7   a , and  7   b ), connection portion  63  may also include a curved portion (similar to curve  90 —see  FIG. 6 ) to accommodate the full pivot pin  36 . With this arrangement, linkage  70  and rod  82  may be eliminated, and the cost of manufacture thereby reduced owing to the simple construction requiring fewer parts. 
   In either case, spring  62 , linkage  70 , rod  82  (or  104 ) and the point where the rod connects with blade  12  as well as the relative location of pivot axis  38  are preferably designed so that blade  12  is forced into its fully closed position sufficiently to prevent, or at least discourage accidental opening of blade  12 , should knife  10  be thrown or dropped. Referring to  FIGS. 27-35 , to help ensure that blade  12  does not accidentally open either while the knife  10  is being stored, shipped, or worn by a user, a clip  110  is provided. Clip  110  includes a first U-shaped hanging loop  112 , a second U-shaped hanging loop  114  connected to the first loop  112  at a connecting axis  116 , and two opposing pivot pins  118  positioned along connecting axis  116  and inwardly directed. Clip  110  is preferably made from a strong material such as steel or a very strong plastic. Clip  110  is pivotally secured to knife  10  by at an appropriate opening  120  positioning each pin half  118  in opening  120  on each respective side of knife  10 , as shown in  FIGS. 30-35 . Clip  110  is preferably resilient and therefore allows a slight give in its shape so that pin halves  118  can be separated from each other sufficiently to allow knife  10  to fit therebetween. Once pin halves  118  are aligned with opening  120 , the resiliency of the material used to make clip  110  will cause the clip to return to its original shape and thereby cause pin halves  118  to “snap” into opening  120  so that clip  110  becomes pivotally attached to knife  10 . 
   Clip  110  is pivotal between an unlocked position, shown in  FIGS. 30-32 , and a safety position, shown in  FIGS. 33-35 . Loop  112  is preferably angularly offset from loop  114  by about 130 arc degrees (although any offset angle may be used depending on the particular shape of knife  10  and blade  12 ). When clip  110  is positioned in its unlocked position, as shown in  FIG. 30 , loop  112  is arranged in a general vertical position (away from knife  10 ) and is accessible to be used to secure knife  10  to a hanging tether (not shown). In this unlocked position, loop  114  resides against the back side of knife  10  (opposite the blade access side), as shown in  FIGS. 30-32 . In the unlocked position, clip  110  does not interfere with the pivotal movement of blade  12  and blade  12  may be opened without rotating clip  110 . 
   When clip  110  is moved to its safety position, shown in  FIGS. 33-35 , loop  114  is now positioned generally vertical (away from knife  10 ) and may therefore be used to secure knife  10  to a hanging tether (not shown). Loop  112  is positioned across the path of blade  12  so that blade  12  is prevented from pivoting from its fully closed position to an open position. The weight of knife  10  hung from tether (not shown) encourages clip  110  to maintain its safety position. To further encourage clip  110  to hold its position (either unlocked or safety), appropriate grooves  122  are provided within knife handle plate  16 , as shown in  FIGS. 31 and 34 . Each groove  122  is sized and positioned to snugly receive either loop  112  or loop  114  (depending on the position of clip  110 ). As clip  110  rotates about opening  120 , loop  112  or loop  114  will eventually align with groove  122 . The resiliency of clip  110  will cause loop  112 ,  114  to snap into groove  122  when in alignment. Groove  122  functions somewhat as a position stop for clip  110 . 
   Locking Mechanisms 
   The present invention may use any of a variety of locking systems known in the prior art, such as a liner-type locking system. Referring to  FIGS. 37 ,  38  and  39 , handle plates  16  are shown having an integrally formed liner-lock tab  130  in one handle plate  14 . Liner-lock tab  130  is formed in one handle plate  16  by cutting shaped slot  132 , thereby defining a locking edge  134 . As is understood by those skilled in the art, tab  130  is bent so that locking edge  134  becomes spring biased inwardly against knife blade  12  (towards the opposing liner plate  14 ). In normal operation, when the blade of a knife is opened, locking edge  134  of liner plate  14  moves into a locking arrangement abutting tightly against the back edge of the blade. However, a concern arises in the present invention since tang  30  of the present knife  10  is slotted (forming recess  34 ). Locking edge  134  is thin enough to inadvertently slip into recess  34  and thereby fail to hold blade  12  in its fully open position. 
   Referring to  FIGS. 40 ,  41 , and  42 , an angle-extension  136  is provided to overcome this potential problem. By effectively widening locking edge  134  of tab  130  (at least wider than the width of recess  34 ), locking edge  134  cannot enter recess  34  and the liner-locking system will not fail. Referring to  FIGS. 47 ,  48 , and  49 , to accommodate the angle extension  136  of liner lock tab  130 , a recess  138  is formed within the adjacent handle plate  16 , as shown in  FIGS. 48 and 49 . Angle extension  136  is preferably formed integrally with the formation of tab  130 , by forming a bend near the locking edge  134 , as shown in  FIGS. 43-46 , but may also be attached to tab  130  as a separate element. Also, angle extension  136  may be strengthened by welding the inside corner of the angle extension  136  against tab  130 . 
   As suggested by  FIGS. 47 ,  48 , and  49 , in accordance with another embodiment of the invention, angle extension  136  may be provided on the tab portion of any liner lock system for any type of folding knife, regardless if the tang of the blade is slotted or remains solid. Angle extension  136  will help prevent the locking edge of any prior art liner lock from slipping from its abutted position. 
   Referring now to  FIGS. 50 ,  51 ,  52 , and  53 , a knife locking system according to yet another embodiment of the invention, includes a pivotal locking element  140  which is arranged to selectively engage a portion of linkage  70  when blade  12  reaches its fully open position. Locking element  140  is preferably positioned between a handle plate  16  and a liner plate  14  (an appropriate recess (not shown) is formed within handle plate  16  to accommodate locking element  140 ). Locking element  140  includes an engaging edge  142  and a pivot opening  144 . An accessible lever arm  146  is provided on an outside surface  148  of handle plate  16 , as shown in  FIGS. 50 and 52 . A pivot pin  146  is provided to mechanically connect accessible lever arm  146  and locking element  140 . An appropriate spring (not shown) is used to exert a counterclockwise bias to both locking element  140  and lever arm  146 . When knife blade  12  is in any position except its fully open position, the counterclockwise bias causes locking element  140  to effectively engage an upper surface of linkage  70 . As blade  12  is rotated from its fully closed position to its fully open position, linkage  70  will linearly displace within spring recess  50 , as described above. When blade  12  reaches the fully open position, as shown in  FIG. 53 , linkage  70  reaches a point that allows locking element  140  to rotate into engagement with a front surface  150  of linkage  70 . This engagement prevents any return, forward movement of linkage  70  within spring recess  50 , thereby effectively locking blade  12  in its fully open position. A user merely has to rotate the accessible lever arm  146  clockwise to angularly displace locking element  140  from its engagement with linkage  70 . This action thereby releases the lock to linkage  70  and blade  12  so that blade  12  can thereafter be returned to its closed position, shown in  FIG. 50 . Applicant prefers that a locking element  140  is provided on both sides of blade  12  and either operate together or separately (separately operating locking elements  140  will provide a locking system that is less likely to accidentally release). In order for locking elements  140  to engage with linkage  70 , linkage  70  must be made sufficiently wide so that at least a portion of linkage  70  extends past liner plate  14  (or both plates  14 ) and into the handle plate  16  (within a recess formed within handle plate  16 , not shown). 
   Applicant has provided the above locking systems as suggestions. Of course, other locking arrangements may be implemented without departing from the invention, such as locking systems that use aligned slots formed within the liner plates and a particularly shaped rod to provide an effectively lock to the blade. Such a system is shown in U.S. Pat. No. 6,079,106 of Vallotton and its entire content is hereby incorporated by reference. 
   Although preferred embodiments of this invention have been disclosed, it will be appreciated that further variations and modifications may be made thereto without departing from the scope of the invention.