Abstract:
A hand tool—typically embodied as a knife—incorporates a blade or implement lock mechanism for securely locking the implement such as a blade in the open position. The lock mechanism locks the blade in the open position and allows it to be released so that the blade may be folded back into the closed position. The locking mechanism incorporates a safety mechanism that prevents the blade engaging lock from becoming unintentionally disengaged.

Description:
FIELD OF THE INVENTION 
   This invention relates to hand tools such as knives and multi tools that incorporate folding implements, and more specifically to a blade or implement locking mechanism for use in such tools that facilitates secure locking of the implement in the open or extended position. The lock mechanism incorporates a safety mechanism. 
   BACKGROUND 
   Many types of hand tools such as knives and multi tools incorporate folding mechanisms that allow an implement to be moved between a folded position in which the implement is safely stowed in the tool handle, and an extended position in which the implement is ready for work. One typical example of such a folding tool is a knife having a folding blade. The knife handle typically has two opposed handle portions defining a blade-receiving groove. A blade pivots on a shaft attached to the handle such that in a folded position the blade is stowed with the cutting portion of the blade retained safely in the groove, and such that in an extended position the blade is extended away from the handle, ready for use. 
   To increase the safety of folding tools such as knives, many such tools incorporate locking mechanisms of one type or another. When the knife blade pivots into the open position, it&#39;s pivotal movement is stopped with a blocking mechanism such as a transverse blade stop pin housed in the handle. Many kinds of knives include a locking mechanism that prevents the blade from unintentionally pivoting back from the open into the closed position. 
   There are many types of locking mechanisms. One common type is a “liner lock.” This kind of mechanism relies upon a resilient lever formed as part of a handle liner. When the blade is pivoted to the open or extended position, the resilient lever engages a cooperatively formed shoulder on the blade and thereby locks the blade in the open position. 
   There are other types of blade locks in addition to the liner locking mechanisms just described but there is a need therefore for improved locking mechanisms for folding hand tools. 
   The present invention relates to a hand tool—typically embodied as a knife—that incorporates a lock mechanism for securely locking the implement such as a blade in the open position, and for releasing the lock to allow the implement to be folded back into the closed position. The locking mechanism incorporates a safety mechanism that prevents the blade engaging lock from becoming disengaged unintentionally. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and its numerous objects and advantages will be apparent by reference to the following detailed description of the invention when taken in conjunction with the following drawings. 
       FIG. 1  is a perspective view of a hand tool—in this case a knife—incorporating a locking mechanism according to the present invention. In  FIG. 1  the knife blade is stowed in the closed or folded position. 
       FIG. 2  is a perspective view of body the knife shown in  FIG. 1  and a portion of the blade shown in the fully extended or open position to illustrate the locking mechanism engaging the rear of the tang of the blade and the lock safety mechanism. 
       FIG. 3  is a side elevation view of the knife shown in  FIG. 1  with the handle half on the near side removed to expose and illustrate the locking mechanism and the safety mechanism. In  FIG. 3 , the blade is in the open position, the lock is in the locked position and the lock safety mechanism is in the locked or engaged position. 
       FIG. 4  is a side elevation view similar to the illustration of  FIG. 3 , but in which the safety mechanism is in the released or unlocked position so that the locking mechanism may be unlocked. 
       FIG. 5  is a side elevation view similar to the illustration of  FIG. 4 , showing the blade being partially rotated toward the closed position in which the blade is stowed in the handle. 
       FIG. 6  is a side elevation view similar to the illustration of  FIG. 5 , showing the blade being fully rotated into the closed position in which the blade is stowed in the handle. 
       FIG. 7  is a sectional view taken along the line  7 - 7  of  FIG. 3 . 
       FIG. 8  is an exploded perspective view of the knife shown in  FIG. 1 , illustrating some of the component parts  FIG. 9  is a perspective view showing in isolation the cam wheel used with the safety mechanism. 
       FIG. 10  is a cutaway view of a portion of the knife handle, illustrating the cavity formed in the knife handle for receiving a portion of the cam wheel shown in  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A preferred embodiment of a hand tool  10  incorporating a locking mechanism and safety mechanism in accordance with the illustrated invention is shown in the figures. Although the invention is described with respect to its embodiment in a particular type of tool—a knife—it will be appreciated that references to this type of a knife, and indeed this particular type of hand tool, are for illustrative purposes to describe the invention. Those of ordinary skill in the art will appreciate that the invention claimed herein is not limited to knives, but instead extends to any hand tool having the features claimed herein. 
   With particular reference now to  FIGS. 1 and 2 , knife  10  includes a handle  12  with a blade  14  pivotally attached to one end of the handle at a blade pivot shaft  16 . Handle  12  comprises three primary structural components, a first handle half or side wall  18 , a second handle half or side wall  20 , and a spacer  22  that is fixed therebetween when the knife is assembled (see, e.g.,  FIGS. 3 ,  8 ). Spacer  22  holds the handle halves  18  and  20  in a spaced apart orientation to define a blade-receiving groove or slot  24  between the halves. When the blade is in the closed position, the working portion  26  of blade  14  is safely stowed in slot  24 . Blade  14  is pivotally movable about pivot shaft  16  between the fully closed position ( FIG. 1 ) and the fully open position ( FIG. 2 ). 
   With reference now to  FIG. 8 , additional structural parts of knife  10  will be identified beginning with blade  14 , which includes a tang  28  having a bore  30  through which pivot shaft  16  extends. Specifically, pivot shaft  16  comprises a cylindrical bushing  32  that fits into bore  30  and has outer cylindrical portions  34  on both lateral sides that have stepped-down diameters relative to the central portion of bushing  32 , and which are received into bores  37  formed in handles  18  and  20  in the assembled knife  10  (only one bore  37  is shown). Pivot shaft  16  includes a threaded screw  36  that extends through bushing  32  and engages a nut (not shown) to secure the blade to the handle  12 . Blade  14  preferably includes a thumb lug  27  to assist with opening and closing the blade. The rearward end of tang  28  is formed into a flattened section  44 , which as detailed below cooperates with a spring member to lock the blade in the open position. 
   The handle halves  18  and  20  are assembled with the blade  14  as just described. Spacer  22  is held in place with plural screws  38 , which as shown best in  FIG. 8 , engage threaded openings  42  in spacer  22 . It will be appreciated that the structural peculiarities such as number of screws  38  is not particularly important so long as the knife  10  is securely assembled. Some of the screws  38  may attach plates  40  to recesses  42  formed in the handle halves for added structural strength and/or aesthetics, and of course the screws  38  may thread completely through both handle halves and the spacer if desired. Screw  39  ( FIGS. 3 through 7 ) acts as a blade stop pin, preventing rotation of the blade beyond the fully open position shown in  FIG. 2 . 
   The blade locking mechanism, identified generally with reference number  50 , will now be described in detail. Handle half  20  is preferably made of a resilient material such as a variety metals and alloys. Handle half  20  comprises an integrally formed, bifurcated sheet comprising a base  52  having an elongate, L-shaped slot  54  extending from a relatively thinner wall section  56  in a forward direction and turning at a 90° angle and extending through the edge of the handle half at exit point  58 . The elongate slot  54  defines a spring arm  60  having a free end  62  at the forward end of the spring arm, and an elongate fixed body portion  55  opposite of slot  54  from spring arm  60 . The slot  54  further defines a base end  64  at a thinner wall section  56  near the rearward, terminal end of slot  54 . A bore  65  may optionally be formed at the rearward, terminal end of slot  54  to provide more resiliency to the spring arm  60 . The forward end of free end  62  of spring arm  60  is flattened to define a flattened face  66 . 
   It will be appreciated that base end  64  extends integrally from base  52  in a one-piece construction. During fabrication of handle half  20 , spring arm  60  is pre-stressed so that the spring arm is given an initial bias inwardly in the direction toward the blade-receiving slot  24 —that is, generally into the plane of the paper in  FIG. 1 . The relatively thinner wall section  56  aids in facilitating the initial inward bias, but should be seen as optional. The inward bias is preferably sufficiently strong that the free end  62  of spring arm  60  will normally continue to be biased under spring pressure inwardly in the direction toward slot  24  until constrained against further movement by another structural component of the knife. 
   With reference to  FIG. 1 , blade  14  is in the closed position. In this position, the free end  62  of spring arm  60  is pressing inwardly against the blade and applying force thereto. The spring force applied against the blade in this manner helps retain the blade in the closed position. 
   The blade  14  is shown in the open position in  FIG. 2 . Here, blade  14  has rotated to the point where the flattened face  66  of free end  62  of spring arm  60  snaps behind the flattened portion  44  of tang  28  and blade stop pin  39  abuts an upper portion of tang  28 . The spring force applied to spring arm  60  maintains the spring arm in this locking position, wherein the blade cannot be rotated from the open to the closed position because the free end  62  of the spring arm  60  is in an abutting relationship with the flattened portion  44  of tang  28 . Preferably, the respective mating faces of flattened portion  44  and flattened face  66  of free end  62  may be cooperatively sloped in opposite directions relative to one another, in the manner of a conventional liner lock, to assist with the locking engagement between these two structures. 
   It will be appreciated that both handle halves may preferably be fabricated from the same type of material. Alternately, while handle half  20 , which comprises locking mechanism  50 , must be a resilient material, handle half  18  may be made of a different material if desired. 
   As noted above, the locking mechanism  50  of knife  10  includes a safety mechanism, which is identified generally with reference number  80 . As detailed herein, safety mechanism  80  is operable to secure the locking mechanism  50  in the locked position of  FIG. 2  to thereby prevent unintentional unlocking of blade  14  where it could inadvertently close, and also to prevent spring arm  60  from being forced so far in the unlocking direction when the blade is unlocked such that the spring arm could be damaged. Safety mechanism  80  further is operable to prevent spring arm  60  from moving in the direction transverse to the direction of the spring force, which further minimizes potential damage to the spring arm. 
   With reference to  FIGS. 1 and 2 , safety mechanism  80  comprises a semi-circular cam wheel or disk  82  rotatably attached with a screw  84  to a cooperatively sized, semi-circular cavity  86  formed near free end  62  of spring arm  60 . Screw  84  is threaded into a cooperatively threaded opening  85  in the spring arm  60 . The cam wheel  82  is shown in isolation in  FIG. 9 . In  FIG. 9  it may be seen that the cam wheel includes a flattened portion  90  that bisects part of the generally circular cam and which extends across the cam toward a tab  92  that is formed opposite the flattened portion  90 . A ramped or sloping section  94  extends annularly from tab  92  around a peripheral section that preferably measures between about 90° to about 160° along the peripheral edge of the cam wheel. Ramped portion  94  is defined by the cam wheel being milled so that the ramped portion is relatively thinnest near tab  92 , and the thickness of the ramped portion gradually increasing along the length of the ramped portion until the terminal end  96  of the ramped portion, where the thickness of the ramped portion is the same as the thickness of the cam wheel. The cam wheel  82  includes a knurled peripheral edge portion  98  between the terminal end  96  and the flattened portion  90 . The knurled peripheral edge allows the cam to be conveniently gripped by the user during operation of the cam wheel. 
   Cam wheel  82  is rotatably attached to spring arm  60  with a screw  84  as indicated in  FIGS. 1 ,  2  and  8  in a cavity  86  milled into the spring arm. The cavity  86  is generally cylindrical so that it accepts cam wheel  82  and allows the cam wheel to rotate in the cavity. The radius of cam wheel  82  measured from its center to knurled edge portion  98  is greater than the distance from opening  85  in spring arm  60  to the exposed edge  100  of the spring arm. As such, when the cam wheel is attached to the spring arm as shown in the drawings, the knurled portion is exposed so that a user may conveniently rotate the cam wheel with one finger, as best illustrated in  FIGS. 1 and 2 . 
   With specific reference to  FIGS. 8 and 10 , and as described below, a cooperatively formed notch or cavity  110  is milled or otherwise formed in fixed body portion  55  in a location so that portions of cam wheel  82  spans or extends across slot  54  and engage the cavity  110  as the cam wheel  82  as it is rotated. Cavity  110  is semi-circular in shape and is formed so that it has an annular ramped portion  112  that is cooperatively formed and oppositely sloped relative to ramped portion  94  of cam wheel  82 . 
   When cam wheel  82  is assembled as shown in  FIGS. 1 and 2  it may be rotated in the clockwise and counter clockwise directions between two ending positions. In the first position, shown in  FIG. 1  where blade  14  is in the closed position, cam wheel  82  is rotated fully counter clockwise (from the perspective of the viewer in the drawing). In this position, flattened portion  90  of cam wheel  82  is parallel to and abuts flattened surface  102  of elongate body  55  in slot  54 , thereby preventing further rotation of the cam wheel in the counterclockwise direction. This position of the cam wheel  82  is referred to as the open or unlocked position, and is also shown in  FIGS. 4 ,  5  and  6 , wherein it may be seen that tab  92  extends across slot  54  so that the tab extends at least partially into cavity  110 . 
   Referring now to  FIGS. 2 and 3 , blade  14  is shown in the fully open position and locked in that position by the locking engagement described above between flattened face  66  of spring arm  60  and rearward flattened portion  44  of tang  28 . Spring arm  60  may be safely locked in this locking position by rotation of cam wheel  82  fully in the clockwise direction in FIG.  2 —this position of the cam wheel is referred to as the locked position. This same position is shown in  FIG. 3 , but because  FIG. 3  shows the opposite side of knife  10  from the view of  FIG. 2 , the rotational direction of cam wheel  82 , as shown by arrow A, is reversed and thus counter clockwise. 
   In this position, annular ramped portion  94  of cam wheel  82  engages the oppositely sloped ramped portion  112  of cavity  110 . Accordingly, as cam wheel  82  is rotated toward the locked position, the ramped portion  94  on cam wheel  82  engages and abuts the ramped portion  112  of cavity  110 . As the wheel is rotated, the abutting, oppositely sloped ramped portions  110  and  112  bear against and thus exert pressure against one another, with the result being that pressure is exerted by cam wheel  82  on elongate body portion  55 . This inwardly directed pressure (i.e., toward the blade receiving groove  24 ) further drives and urges spring arm  60  toward the locked position, in addition to the normal spring force that drives the spring arm toward the locked position. The cam wheel  82  is retained in this position by virtue of the frictional contact between ramped portions  94  and  112 . The blade is thus safely locked in the fully open position, and the spring arm  60  cannot be moved to the unlocking position because cam wheel  82  is engaging the elongate body portion  55 . 
   Moreover, with cam wheel  82  in the locked position shown in  FIG. 3 , the outer peripheral annular edge of the cam wheel at ramped portion  94  lies in close tolerance proximity to the annular border of cavity  110 . As a result, the free end  62  of spring arm  60  cannot move in the direction toward elongate body portion  55 . Stated another way, slot  54  is wide enough that absent cam wheel  82 , the free end  62  could be deflected slightly in the direction toward spacer  22 . This movement can cause wear between the abutting surfaces at  66  and  44  when the blade is in the open position. Wear on these surfaces could loosen the locking relationship. However, because the outer periphery of the cam wheel is in close tolerance to the wall of cavity  110 , movement of the spring arm in this direction is eliminated, thus eliminating wear on the surfaces at  66  and  44 . 
   The procedure for unlocking the knife will now be described with reference to  FIGS. 4 and 5 . With blade  14  in the open position the blade locked by virtue of blade lock mechanism  50  ( FIG. 2 ), and with safety mechanism  80  in the locked position, cam wheel  82  is rotated in the direction of arrow B in  FIG. 4  (clockwise in  FIG. 4 , which correlates to counter clockwise in  FIG. 1 ). The cam wheel is rotated until flattened section  90  abuts surface  102 , thereby stopping rotation of the cam wheel. As noted above, in this position, tab  92  spans slot  54  and extends into cavity  110 . However, as noted the cam wheel  82  is relatively thinnest at tab  92 . This, combined with the fact that body  55  is relatively thinner at cavity  110  allows the free end  62  of spring arm  60  to move outwardly, out of the locking position a sufficient distance so that the blade may be disengaged from the lock-that is, the flattened face  66  of spring arm  60  may be disengaged from the flattened portion  44  of tang  28 . Once the locking engagement between the blade tang and the spring arm is disengaged, blade  14  is free to be rotated toward the closed position, as shown in  FIG. 5 . 
   Because the tab  92  extends across the slot  54  and into the cavity  110 , free end  62  of spring arm  60  is prevented from moving outwardly, i.e., away from blade  14 , more than is necessary to allow the blade to be closed. Stated another way, with cam wheel  82  in the position shown in  FIGS. 1 ,  4 ,  5  and  6 , when the free end  62  of spring arm  60  is moved outwardly, away from blade  14 , the tab  92  engages or contacts body  55  in cavity  110 , limiting movement of the free end in the direction away from the blade, thereby preventing movement of the free end beyond the position where the tab contacts the wall of the cavity. There is a sufficient amount of movement of free end  62  to disengage the locking mechanism, but the amount of movement is limited, which prevents the spring arm from being “hyper extended” in the outward direction, against the spring force of the spring arm, which could damage the spring arm and render it inoperable for its locking functionality, or diminish the functionality of the locking mechanism. 
   It will be appreciated by those of ordinary skill in the art that various modifications may be made to the mechanisms described above without departing from the scope of the invention defined in the claims. For example, the safety mechanism  80  may be fabricated with a longitudinally slidable button attached to the spring arm and slidable in a direction generally transverse to the longitudinal axis of the handle toward and into cooperatively formed slot in the fixed body portion, the button and the fixed body portion preferably having cooperatively and oppositely sloped mating surfaces. Similarly, although the cam wheel  82  and the slidable button just described preferably include cooperatively sloped mating surfaces so that the spring arm is driven toward the locked position, an equivalent safety mechanism may be made without the sloping surfaces. 
   The length of the spring arm, and also the relative biasing strength of the spring arm, may be varied widely by varying the length of slot  54 . 
   Furthermore, the tab  92  may be eliminated from cam wheel  82 . Although removal of tab  92  will allow spring arm  60  to be moved outwardly and hyper extended as described above, the safety mechanism  80  remains functional to secure the locking mechanism  50  in the locked position. Finally, the safety mechanism defined by cam wheel  82  may be reversed from the position shown in the drawings. 
   While the present invention has been described in terms of a preferred embodiment, it will be appreciated by one of ordinary skill that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.