Patent Publication Number: US-8122792-B2

Title: Self-adjusting locking pliers

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending, commonly owned U.S. patent application Ser. No. 11/552,552, as filed on Oct. 25, 2006 and entitled “Self-Adjusting Locking Pliers,” which is incorporated herein by reference in its entirety. 
     CROSS-REFERENCE TO RELATED APPLICATION 
     Applicants claim, under 35 U.S.C. §119(e), the benefit of priority of the filing date of Jun. 8, 2006 of U.S. Provisional Patent Application 60/811,870, filed Jun. 8, 2006, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to pliers, and more particularly, to self-adjusting locking pliers that enable the clamping force generated by the device to be pre-set. 
     Self-adjusting or auto-adjusting pliers are known. Such pliers have jaws which are self-adjusting accordingly to the size of the work piece to be grasped between the jaws. Examples of such self-adjusting pliers are disclosed in U.S. Pat. No. 6,065,376 and U.S. Pat. No. 6,279,431. 
     Also known are locking pliers which incorporate an over-center compound toggle locking mechanism or linkage whereby when the moveable jaw of the pliers is adjusted to seize a work piece firmly between the moveable and the fixed jaw and the handles are tightly compressed, the toggle mechanism locks the hand tool onto the work piece. Examples of this type of pliers are disclosed in U.S. Pat. No. 5,056,385 and U.S. Pat. No. 6,626,070 (locking pliers sold under the trademark VISE-GRIP). 
     Self-adjusting locking pliers are also known. Such pliers include jaws that are self-adjusting according to the size of the work piece to be clamped between the jaws and that use an over-center compound toggle locking mechanism to firmly clamp the work piece. One example of such a pliers is disclosed in U.S. Pat. No. 6,941,844. Another example of such a pliers is disclosed in U.S. Pat. No. 6,591,719. Self-adjusting locking pliers are not all capable of generating the high clamping forces that are expected of locking pliers and some designs are susceptible to back drive forces that can inadvertently force open the pliers under high loads. Thus, an improved self-adjusting locking pliers is desired. 
     SUMMARY OF THE INVENTION 
     In one embodiment the self-adjusting locking pliers of the present invention include a fixed assembly having a body that forms a fixed handle and a plate or fixed jaw supported at one end thereof. A lever or movable handle is pivotably connected to the body. A moveable jaw is pivotably supported on the body at a locking slidable pivot connection whereby the moveable jaw is permitted to close down on a work piece disposed between the jaws for providing self-adjustment of the jaws for different sized work pieces. 
     The locking slidable pivot connection includes a pawl secured to the moveable jaw by a first pivot where the pivot and pawl are moveable within a slot formed in the body. The pawl may be provided with forwardly facing teeth for engaging a rack of teeth on a front edge of the slot for providing selective engagement therebetween. The pawl is normally disengaged from the rack and engages the rack when the jaws contact a work piece. The rack of teeth may include a first set of teeth and a second set of teeth extending parallel to one another along the front edge of the slot. The first set of teeth and the second set of teeth may each be engaged by the pawl teeth. The teeth of the first set of teeth may be offset from the teeth of the second set of teeth by up to ½ of the pitch. As a result, the pitch of the rack of teeth is effectively reduced by one-half without making the teeth smaller or reducing the actual pitch of the teeth. 
     A linkage is provided that connects the movable jaw, operating lever and body so as to transmit a force applied to the handles of the pliers to the jaws and to lock the jaws in the clamping position on the work piece. The linkage allows the angle between the links to be preset to thereby control the clamping force applied to the work piece. The linkage also allows the preset clamping force to be maintained on different work pieces through repeated clamping and unclamping operations of the pliers. 
     The movable jaw is selectively attached to the linkage in one of two positions such that the jaw span may be adjusted to accommodate relatively larger or smaller work pieces. The jaw span is adjusted in a manner such that the operation of the linkage is not affected by the position of the movable jaw. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view in side elevation of the self-adjusting locking pliers of the present invention with the jaws shown in the fully open position; 
         FIG. 2  is a view in side elevation of the pliers shown in  FIG. 1  with the jaws in the fully closed and locked position; 
         FIG. 3  is a view in side elevation of the pliers shown in  FIG. 1  with the jaws closed and locked on a large object showing the linkage in greater detail; 
         FIG. 4  is a perspective view of the pliers shown in  FIG. 1  with the jaws open showing the linkage in greater detail; 
         FIG. 5  is a perspective views of the racks of the locking slidable pivot; and 
         FIG. 6  is a view in side elevation of the pliers similar to  FIG. 1  with the jaws open showing the linkage in greater detail. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Referring to  FIGS. 1 through 6 , one embodiment of the self-adjusting locking pliers  10  of the invention is shown comprising a fixed assembly including a body  12  having a fixed handle  14  at one end thereof. The other end  16  supports a fixed plate or jaw  18 . The fixed jaw  18  may be made integrally with the body  12  or may be a separate member rigidly connected with the body. In the illustrated embodiment the body  12  is shown as a separately identifiable element from fixed jaw  18 . Where the body  12  and fixed jaw  18  are formed integrally with one another, a clear line of demarcation may not be visible between these elements such that elements disclosed herein as being arranged on the body may in some embodiments be arranged on a portion of the jaw structure or on a transition area between the jaw and body. The mechanism described herein with reference to the Figures can be applied to tools such as clamps, pliers, long-nose pliers, specialty pliers or other clamping/torque producing devices and the jaws may have different configurations designed for the specific function. 
     A moveable jaw  20  is pivotably supported on body  12  via first pivot  22  which is comprised of a locking slidable pivot connection. An operating lever  40  is connected to the body  12  at a sliding pivot  44 . A three-link linkage or toggle mechanism comprising a front link  60 , a middle link  70  and a rear link  80  converts the movement of lever  40  into the opening and closing motion of jaw  20  and locks the jaw  20  in the clamping position relative to fixed jaw  18  as will hereinafter be described. 
     The locking slidable pivot connection  22  comprises a pawl structure  24  that is secured to moveable jaw  20  by pivot pin  28 . In one embodiment the pawl comprises a first pawl  24   a  that is located to one side of moveable jaw  20  and a second pawl  24   b  (shown in  FIG. 5 ) located on the opposite side of moveable jaw  20 . The pawl structure  24  is moveable within slot  30  that extends in body  12  generally transversely to the body  12  such that the pawl structure  24  can reciprocate in slot  30 . Pawls  24   a  are provided with forwardly facing teeth  32  for engaging racks of teeth  34   a  and  34   b  ( FIG. 5 ) formed on the front edge of slot  30 . Tension spring  36  is connected between movable jaw  20  and middle link  70  for biasing the movable jaw carrying pawl structure  24  away from racks  34   a  and  34   b  such that pawl teeth  32  are normally disengaged from racks of teeth  34   a  and  34   b . As lever  40  is moved towards body  12 , pawl structure  24  moves in the slot  30  to automatically space the movable jaw  20  the proper distance from fixed jaw  18  for the size of the work piece. Pawl structure  24  moves in slot  30  until moveable jaw  20  contacts the work piece. When movable jaw  20  contacts the work piece, continued movement of lever  40  moves movable jaw  20  to the left as viewed in  FIG. 1  such that the pawl teeth  32  on pawls  24   a  are forced into engagement with the racks of teeth  34   a  and  34   b  to “lock” the pawl  24  into position thereby fixing the location of pivot  28 . Once the pawls  24   a  and  24   b  engage the racks of teeth  34   a  and  34   b , pawl structure  24  cannot move in slot  30  such that further movement of operating lever  40  results in the rotation of movable jaw  20  about pivot pin  28  (clockwise as viewed in  FIG. 1 ). As greater force is applied to lever  40 , a larger clamping force is applied to the work piece by jaws  18  and  20 . 
     The size and pitch of the teeth determines the incremental distance between adjacent positions of the pawl structure  24  in slot  30 —the larger the pitch the greater the distance between adjacent pawl positions. Pitch being defined as the distance between adjacent teeth. Over the same distance, large teeth having a large pitch provide fewer, more widely spaced incremental positions than smaller teeth having a smaller pitch. The greater this incremental distance, the less precise the size adjustment of the jaws. For work pieces of the same size, when the pawl teeth  32  engage the rack of teeth  34   a , the pawl teeth may “catch” and seat in any one of two or three adjacent teeth on the rack. If the tooth pitch is large, the difference in the force applied by the jaws to a work piece due to the engagement of the pawl with one rack tooth versus an adjacent rack tooth is great. 
     One way to solve this problem is to use teeth that are relatively small where the tooth pitch is also relatively small. In such an arrangement the difference in jaw spacing due to the engagement of the pawl with one rack tooth versus an adjacent rack tooth is minimized. One problem with such an approach is that small teeth can be relatively difficult to manufacture. Another problem is that smaller teeth are relatively weaker than larger teeth and are more likely to fail under a load. Another problem with small teeth is that the teeth are more easily fouled with dirt and debris such that engagement of the teeth may become unreliable. 
     To avoid these problems, yet provide a small incremental distance between adjacent positions of the pawl on the rack, two racks of teeth  34   a  and  34   b  are used. Rack of teeth  34   a  rack of teeth  34   b  extend parallel to one another along the front edge of slot  30 . The set of teeth of rack  34   a  and the set of teeth of rack  34   b  may comprise relatively large teeth where and the teeth of each rack may be the same size and shape and have the same pitch. The teeth of the first rack  34   a  may be offset from the teeth of the second rack  34   b  by up to ½ of the pitch. Thus, in the illustrated embodiment the peaks of the teeth of rack  34   a  align with the valleys of the teeth of rack  34   b . The teeth of pawl  24   a  engage the teeth of rack  34   a  and the teeth of the other pawl engage the teeth of rack  34   b . Because the teeth of racks  34   a  and  34   b  are offset, the distance between adjacent positions of the pawl  24  is reduced by one half. As a result, the pitch of the rack of teeth is effectively reduced by one-half without making the teeth smaller or reducing the actual pitch of the teeth. There is enough play between pawls  24   a , pin  28  and jaw  20  to allow the pawls to seat in the offset teeth of both racks  34   a  and  34   b.    
     In an alternate embodiment, the pawl teeth and racks may be eliminated and the pawl structure  24  may be locked in position in slot  30  using a friction engagement between the edge of the slot and the pawls. Specifically, as the jaws contact a work piece the moveable jaw  20  is moved to the left as viewed in  FIG. 1  until the pawl structure contacts the front edges of slot  30 . When the pawls contact the front edges of slot  30  the pawl is rotated such that the opposite end of the pawl contacts the back edges of the slot  30 . By properly dimensioning the pawls, the pawls wedge themselves in slot  30  thereby fixing the position of pivot  28 . 
     Operating lever  40  is supported at its front end  42  on body  12  via a second sliding pivot  44  where a pivot pin  46  is slidably received within long slot  48  in body  12  and is connected to lever  40 . A shorter slot  49  is formed in lever  40  that also receives pin  46 . The use of two slots allows for the same amount of travel of the pin  46  as a single long slot but provides a more compact construction. One long slot may be used if desired. The rear end of operating lever  40  provides a moveable handle  52  such that a user can grip the stationary handle  14  and the moveable handle  52  in one hand and by squeezing the handles, close the jaws on a work piece and lock the jaws in the closed or clamping position. When the handles are squeezed, the pivot pin  46  may move in slots  48  and  49  as the handle  52  is pivoted. This sliding pivot connection allows the handles to be spaced closer together in the open position and creates more jaw movement per degree of rotation of lever  40  than if a stationary pivot connection were used thereby reducing the hand span and making it easier to grip and squeeze the handles  14  and  52  in one hand. Because the grip of the human hand is stronger when the fingers of the hand are not widely extended, the reduction of hand span allows greater force to be applied by the tool. 
     The locking toggle linkage includes a front link  60  having a front end  62  supported on moveable jaw  20  via third pivot  64 . A mid-point of the first link  60  is supported on operating lever  40  via fourth pivot  66  at an intermediate point along operating lever  40 . The rear end  67  of first link  60  extends beyond fourth pivot  66 . Middle link  70  is pivotably connected at a central portion to the rear end  67  of first link  60  at fifth pivot  72 . The rear end  74  of middle link  70  is pivotably connected to rear link  80  at sixth pivot  82 . The rear end  84  of rear link  80  is pivotably connected to stationary handle  14  via seventh pivot  86 . 
     Tension spring  36  is connected between the movable jaw  20  and the end of the middle link  70 . Spring  36  biases the movable jaw clockwise about third pivot  64  such that the pawl structure  24  is normally biased out of engagement with racks  34   a  and  34   b . Spring  36  also maintains the connection of the movable jaw  20  on third pivot  64 . Pivot  64  comprises a pin  89  mounted on first link  60 . Pin  89  is engageable with either slot  92  or slot  94  formed in movable jaw  20 . When pin  89  is engaged with slot  92  ( FIG. 2 ), the jaws are spaced relatively farther apart than when pin  90  is engaged with slot  94  ( FIG. 1 ). By moving the pin to one or the other of the slots  92  or  94 , the spacing between the jaws may be varied such that the pliers can clamp relatively larger or smaller work pieces, respectively. To select the slot, the movable jaw  20  is rotated clockwise as viewed in  FIG. 1  while link  60  is held stationary thereby overcoming the force of spring  36  until the pin  89  is removed from one of slots  92  or  94 . The pin  89  is then positioned adjacent to the other of the slots and the movable jaw  20  is released. When the movable jaw  20  is released, spring  36  pulls the pin  89  into engagement with the slot and maintains this engagement during operation of the pliers. The seats of the slots  92  and  94  are located on an arc of a circle centered on pivot  28  such that pin  89  when positioned in either slot  92  or slot  94  is located the same distance from pivot  28 . As a result, the position of first link  60  and the geometry of the toggle linkage is the same regardless of which slot is engaged by pin  89 . Thus, the geometry of the linkage does not change even as the jaw spacing is changed. 
     A toggle preset mechanism is provided for setting the angles of the toggle locking mechanism to control the force generated by the jaws on the work piece. The preset mechanism comprises a protrusion  88  provided on the front side of rear link  80 . A control actuator  100  is adjustably mounted on middle link  70  such that it can move relative to the middle link towards and away from the rear link  80 . The control actuator  100  may comprise a thumb screw  101  threadably mounted on a threaded member  103  on the middle link  70  such that rotation of the thumb screw causes it to move toward and away from the rear link  80 . The actuator  100  engages the protrusion  88  when the pliers are in the open position shown in  FIG. 1 . A torsion spring  102  is mounted between the body  12  and the rear link  80  such that it biases the rear link about seventh pivot  86  counterclockwise as viewed in the Figures. The rotation of rear link  80  about pivot  86  causes the middle link  70  to tend to rotate clockwise around sixth pivot  82  such that the actuator  100  is forced into engagement with the protrusion  88  when the pliers are in the open position ( FIG. 1 ). 
     By extending actuator  100  towards or retracting actuator  100  away from the rear link  80 , the “throw” of the linkage may be changed to thereby vary the amount of clamping force generated by the pliers. The “throw” of the linkage is the distance the linkage moves from the unlocked position to the locked over-center clamping position. Operation of the pliers to vary the gripping force will be explained with reference to Figs.  FIG. 6  shows the pliers in the unlocked position with the jaws fully open to receive a work piece. The links are at a predetermined angular relationship relative to one another based on the position of actuator  100 . To clamp a work piece, handles  14  and  52  are squeezed to move operating lever  40  towards body  12 . As lever  40  moves toward body  12 , moveable jaw  20  is moved towards the fixed jaw  18  with pawl structure  24  traversing slot  30 . Because spring  36  biases the movable jaw  20  and pawl structure  24  toward the rear of the pliers, the teeth of pawls  24   a  and  24   b  are disengaged from racks  34   a  and  34   b  and pawl structure  24  can move freely in the slot  30 . When the jaws  18  and  20  contact the work piece, moveable jaw  20  is pivoted slightly counterclockwise around third pivot  64  overcoming the counterforce of spring  36  until the teeth of pawls  32   a  and  32   b  engage racks  34   a  and  34   b . In a preferred operation, jaw  18  should contact the work piece before jaw  20 . As previously explained, the pawl structure  24  may first engage either rack  34   a  or rack  34   b . Once the pawl structure  24  engages engage either rack  34   a  or  34   b , movement of pawl structure  24  in slot  30  is stopped and further movement of lever  40  is translated into clockwise (as viewed in  FIG. 1 ) rotational movement of moveable jaw  20  around first pivot  28  to thereby apply increasing clamping force to the work piece positioned between the jaws. 
     As lever  40  moves towards body  12 , the locking toggle linkage is also moved towards body  12 . When the work piece is clamped between the jaws  18  and  20  and increasing force is applied to the handles  14  and  52 , the forces generated on the linkage cause middle link  70  to pivot away from rear link  80  such that actuator  100  begins to separate from protrusion  88 . As the middle link  70  separates from the rear link  80  the linkage begins to straighten and the effective length of the linkage between pivots  64  and  86  increases. As the effective length of the linkage increases, increasing force must be applied to the lever  40  to move the linkage to the over-center locked position. This force is transmitted through the pliers to the work piece to increase the clamping force generated by the jaws on the work piece. The force applied to the lever  40  also deforms the pliers such that the resiliency of the pliers stores some of the energy applied to lever  40  to maintain the clamping pressure on the work piece. The force applied to the work piece may also deform the work piece depending on the relative stiffness of the work piece. 
     As lever  40  is closed the force applied to the work piece increases until the linkage assumes a dead center position where pivot  64 , pivot  82  and pivot  86  are in a straight line (line A-A in  FIG. 2 ). In this position the linkage is at its greatest effective length (the distance between pivot  64  and pivot  86  is greatest) and the loading on the pliers and, therefore, the clamping force, is maximized. From this dead center position, the linkage will continue to move until pivot  82  is positioned slightly above ( FIG. 2 ) the line A-A between pivot  64  and pivot  86 . In other words the pivot  82  moves across dead center as the tool moves from the open position to the closed position. In this position the pliers are locked in an over-center clamping position where the tool will maintain the clamping force until a force is applied to the linkage forcing the linkage back over dead-center. The engagement of the forward end  90  of rear link  80  with the middle link  70  limits the distance the linkage can move beyond dead center. Limiting this distance maximizes the forces applied by the pliers yet still provides the over-center locking operation. 
     The amount of clamping force generated by the pliers of the invention is related to the angle between the middle link  70  and rear link  80  as controlled by the actuator  100 . The smaller the included angle α between the middle link  70  and rear link  80 , the greater the throw and the greater the force generated by the pliers on the work piece. For example, an angle α of 180 degrees would provide zero clamping force, as angle α decreases the clamping force increases. Conversely, the larger the angle between the middle link  70  and rear link  80 , the smaller the throw and the smaller the clamping force generated by the pliers on the work piece. Where this angle is relatively small the distance between pivot  64  and pivot  86  is relatively small and the distance between pivot  82  and the dead-center line A-A is relatively large. As a result the pivot points  64  and  86  must travel a relatively greater distance as they are pushed apart by the linkage to reach the over-center position. The greater this distance, the greater the force the tool can exert on the work piece. 
     Because this angle may be preset and controlled by the position of the actuator  100  the force exerted by the device may be preset and controlled before a clamping force is applied. Moreover, the force applied by the tool, once the preset angle is set, does not vary for work pieces of different sizes where the work pieces are of similar hardness. This functionality makes the pliers of the invention particularly well suited for repeated clamping operations as the pliers can be clamped to and removed from various work pieces while applying a substantially consistent clamping force to all of the work pieces without the need to manually readjust the device for each clamping action. 
     To use the pliers of the invention, the preset link angle is set by rotating actuator  100  until links  70  and  80  are at the desired angle relative to one another. The pliers are then applied to a work piece and a force is exerted on the lever  40  closing the jaws on the work piece. As the jaws close, pawl structure  24  moves in slot  30 . When the jaws contact the work piece, the pawls  24   a  and  24   b  engage racks  34   a  and  34   b  locking pawl relative to the body  12  to properly and automatically size the jaws. During this sizing operation the preset link angle is maintained. Continued application of force to lever  40  tightens the jaws on the work piece by rotating moveable jaw  20  about pivot  64  while simultaneously rotating the linkage toward the over-center locked position. As the linkage moves to the over-center position, the force on the work piece increases as the ends of the linkage extend away from one another forcing pivots  64  and  86  apart. As previously explained, the amount of force generated is a function of the amount of travel of the links that is controlled by the preset angle set by actuator  100 . The lever is moved until it reaches the over-center position where it locks the pliers in the clamped position. The jaws clamp the workpiece with the clamping force preset by actuator  100 . In this position the user does not have to continue to apply force to the pliers. Once the operation on the work pieces is finished the pliers are opened to release the work piece. 
     The pliers can then be applied to work pieces having a different size. Because the force that will be generated by the pliers has been preset by actuator  100 , the pliers clamp the work pieces without any further adjustment even if the span of the work piece is different. The pliers will function as described above to apply substantially the same amount of force to the work pieces without any readjustment of the pliers for work pieces having generally the same stiffness or hardness. This eliminates the need in the prior art self-adjusting locking pliers of having to tighten the locking pliers after the pliers are clamped on a device to control the clamping force. Because the pliers are self-adjusting the different spans of the work pieces are accommodated automatically by the movement of pawl structure  24  in slot  30  even while the jaws apply a substantially consistant clamping force. To apply a different clamping force the actuator  100  is moved to change the preset angle α between middle link  70  and rear link  80  as desired by the user. The pliers of the invention have utility in a wide variety of clamping and torque applying operations. 
     To release the pliers from the over-center locked position, the linkage must be forced back through the dead-center position to the open position of  FIG. 1 . This may be accomplished by pulling lever  40  away from body  12 . However, the pliers of the invention are able to generate high clamping forces such that it may be difficult in some applications to pull the lever away from body  12 . To lessen the force required to open the pliers, a slotted connection is used for the fourth pivot  66  as best shown in  FIGS. 3 and 4 . A slot  110  is formed in first link  60  and through which pivot pin  66  passes. The slot allows enough play in the system that a force applied to the lever  40  away from body  12  will readily open the pliers. 
     Specific embodiments of an invention are disclosed herein. One of ordinary skill in the art will recognize that the invention has other applications in other environments. Many embodiments are possible. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described above.