Abstract:
A method and apparatus for clamping a work piece is disclosed. The apparatus generally includes a stationary jaw disposed on a bar and having a first clamping surface and a moveable jaw disposed on the bar and having a second clamping surface. The apparatus further comprises a drive handle which provides movement of the moveable jaw relative to the bar. The drive handle can be configured to move the second clamping surface at different rates and forces when operated.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     Embodiments of the present invention generally relate to a hand tool and more particularly to a clamp. More particularly still, embodiments of the invention relate to a bar clamp with improved performance and utility.  
         [0003]     2. Description of the Related Art  
         [0004]     Clamps are used in order to temporarily hold one or more objects so that work can be performed on them. Historically, clamps required two hands in order to work the clamp making it difficult to hold the work piece while clamping. A vast improvement to clamps was made about 15 years ago with the advent of the QUICK-GRIP™ bar clamp, disclosed in U.S. Pat. No. 5,009,134, and QUICK-ACTION™ bar clamp, disclosed in U.S. Pat. No. 4,926,722 to Joseph A. Sorensen and Dwight L. Gatzemeyer. The QUICK-GRIP™ bar clamp provides a single hand clamping tool that allows one free hand to support the work piece or hold other tools and/or materials while clamping the work piece. This is a major improvement over the traditional screw activated “C” clamps or “over center” type lever actuated bar clamps.  
         [0005]     However, several problems exist with the QUICK-GRIP™ bar clamp. The QUICK-GRIP™ clamp must balance between the amount of force required by the hand and the amount of movement of the clamp for each squeeze of the hand. The amount of force exerted on the work piece in relation to the force exerted by the hand is determined by the mechanical advantage ratio (MAR) of the mechanism. As the MAR is increased, the amount of force on the clamp is increased, and the amount of force required to squeeze the handle is decreased. However, in the current hand clamps, the distance the clamp travels with each squeeze (or bar index) decreases if the MAR is increased. Thus, the current clamps on the market compromise by providing a MAR of about 4.5:1 and an index distance of 0.2 inches/squeeze. As people get older, the amount of strength in the hand decreases drastically making it more difficult to operate the QUICK-GRIP™ bar clamp or similar products. As the population ages, it is necessary to provide for a clamp that can increase the MAR and the bar index while requiring minimal squeezing force by the operator.  
         [0006]     Therefore, a need exists for improved apparatus and methods of hand clamping that increase the force on the workpiece for a primary squeezing force, increase the travel of the clamp per squeeze, and decrease the manufacturing cost.  
       SUMMARY OF THE INVENTION  
       [0007]     Embodiments of the invention generally relate to methods and apparatus for clamping a work piece. A clamping apparatus generally includes a stationary jaw disposed on a bar and having a first clamping surface and a moveable jaw disposed on the bar and having a second clamping surface. The apparatus further comprises a drive handle that provides movement of the moveable jaw relative to the bar when operated. The drive handle can be configured to move the clamping surfaces at different rates and forces. For some embodiments, first and second portions of the drive handle pivot about first and second pivot diameters, respectively, such that the moveable jaw moves with different forces. The drive handle can include a drive pin in contact with drive links disposed around the bar to forceably grip and move the bar as the drive pin moves due to operation of the drive handle. In some embodiments, the drive links include a bend in a middle portion thereof so that a first portion above the bar is offset from a second portion below the bar when the drive link is in a non-rotated position with respect to the bar. For some embodiments, a rear handle opposes a force applied to the drive handle and selectively disengages the moveable jaw from the bar upon movement thereof. Further, a release lever can connect a housing of the stationary jaw to the first clamping surface to enable selective disengagement of the stationary jaw from the bar. A method of clamping the work piece comprises moving the drive handle through a first range of motion to move the movable jaw with a first force and moving the drive handle through a second range of motion to move the moveable jaw with a second force smaller than the first force.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0009]      FIG. 1  is a front view of the bar clamp in accordance with embodiments of the invention.  
         [0010]      FIG. 2  is a cross sectional view of the clamp.  
         [0011]      FIG. 3  is a front view of the clamp showing a final position of a drive handle.  
         [0012]      FIG. 4  is an isometric view of the clamp.  
         [0013]      FIG. 5  is a cross sectional view of a moveable jaw further detailing an operation of a drive link(s).  
         [0014]      FIG. 6  is an isometric view of an offset drive link. 
     
    
     DETAILED DESCRIPTION  
       [0015]      FIG. 1  illustrates a schematic front view of a hand clamp  100  having moveable and stationary jaw assemblies configured to incorporate embodiments of the invention. The hand clamp  100  includes a moveable jaw housing  10  having mating surfaces for a high reduction pivot diameter  2  and a low reduction pivot diameter  7  formed along one side of a drive handle  5 . A drive pin  1  disposed through an aperture of the drive handle  5  substantially on one side of the high and low reduction pivot diameters  2 ,  7  enables pivotal movement of the drive handle  5  with respect to the moveable jaw housing  10 . In addition, a rear handle/lock release  3  couples to the moveable jaw housing  10  for operating a locking link  6 .  
         [0016]     The hand clamp  100  further includes first and second clamp heads  9 ,  29  for gripping a work piece (not shown). Each clamp head  9 ,  29  includes first and second clamping surfaces  26 ,  27 , respectively. The first clamp head  9  couples to the moveable jaw housing  10  via an arm  30 . The second clamp head  29  couples to a stationary jaw housing  11  via a release lever  8 . A bar  4  that the jaw housings  10  and  11  are disposed on connects the stationary jaw housing  11  to the moveable jaw housing  10 .  
         [0017]      FIG. 2  shows a schematic cross sectional view of the hand clamp  100  with the stationary jaw pivot  14  that couples the stationary jaw housing  11  to the release lever  8 . A stationary jaw locking dog  15  pivots with the release lever  8  about the stationary jaw pivot  14  to selectively lock the release lever  8  and hence the stationary jaw housing  11  to the bar  4 . A biasing member or leaf spring  13  coupled to the release lever  8  contacts a portion of the stationary jaw housing  11  to urge the release lever  8  to rotate about the stationary jaw pivot  14  in a counter-clockwise direction. The rotation engages the locking dog  15  with a first notch  40  on the bar  4  to prevent the stationary jaw housing  11  from disengaging the bar  4 . With the stationary jaw housing prevented from movement along the length of the bar  4 , the position of the second head  29  is locked.  
         [0018]     The bar  4  includes the first notch  40  and a corresponding second notch  41  on an opposite end thereof for convenience in assembly and manufacturing. The first notch  40  on the bar  4  locks the release lever  8  and attached stationary jaw housing  11  to the bar  4  with the locking dog  15 . While the notch  41  is not needed for operation of the bar  4  with respect to the moveable jaw assembly, the notches  40 ,  41  are symmetrical to enable attachment of the stationary jaw housing  11  to either end of the bar  4  during assembly. This reduces manufacturing and assembly costs.  
         [0019]     In operation, a drive link spring  12  disposed within the moveable jaw housing  10  biases the drive handle  5  to remain in an open position with the high reduction pivot diameter  2  engaged with the moveable jaw housing  10  when no outside force is exerted on the drive handle  5 . A surface of the movable jaw housing  10  provides a backstop for the drive link spring  12  that acts on the drive handle  5  via drive links  16 , shown here as three links, although it should be appreciated there can be any number of links. The drive links  16  have an aperture  50  (visible in  FIG. 6 ) through which the bar  4  fits. The drive link spring  12  biases the drive links  16  substantially perpendicular to the bar  4  to enable the bar  4  to pass through the aperture  50  without gripping contact of the drive links  16  until force is exerted on the drive handle  5 . With force exerted on the drive handle  5  to rotate the drive handle along the pivot diameters  2 ,  7 , movement of the drive pin  1  pushes the lower end on the drive links  16  causing the drive links  16  to rotate counter-clockwise until respective bottom and top edges of the drive links  16  at the aperture  50  engage the bar  4 . Accordingly, the number of edges available to grip the bar  4  increases with an increase in the number of the drive links  16  utilized. Continued movement of the drive handle  5  moves the drive links  16  with the bar  4  causing the stationary jaw housing  11  and the moveable jaw housing  10  to approach one another.  
         [0020]     A locking link spring  17  disposed within the moveable jaw housing  10  such that the moveable jaw housing  10  provides a backstop for the locking link spring  17  exerts force on a center portion of the locking link  6 . The locking link spring  17  acts to rotate the locking link  6  in a clockwise direction due to a top edge of the locking link  6  being trapped by a cavity formed in the moveable jaw housing  10 . The rotation of the locking link  6  causes inside edges of the locking link  6  to normally engage the bar  4  and lock it into place to prevent relative movement between the bar  4  and the moveable jaw housing  10  that is coupled to the locking link  6 . Upon squeezing the drive handle  5 , the force exerted to move the bar  4  relative to the moveable jaw housing  10  by operation of the drive links  16  is enough to overcome the locking link spring  17  and enable the locking link  6  to release the bar  4 . Release of the locking link  6  occurs due to the locking link  6  rotating to a substantially perpendicular position with respect to the bar  4  since movement of the bar  4  with respect to the movable jaw housing  10  having the trapped top edge of the locking link  6  causes counter-clockwise rotation of the locking link  6  against the bias of the locking link spring  17 . When the drive handle  5  is released or force is otherwise no longer exerted by operation of the drive handle  5 , the locking link spring  17  causes locking link  6  to reengage the bar  4 .  
         [0021]     When force is first applied to the drive handle  5 , the high reduction pivot diameter  2  of the drive handle  5  engages with the moveable jaw housing  10 . The MAR is determined approximately by the distance from where the load is applied on the drive handle  5  to the pivot diameter divided by the vertical component of the distance from the drive pin  1  to the pivot diameter. The MAR when the high reduction pivot diameter  2  is engaged is high, for example, about 8:1. It should be appreciated that the arrangement of the drive handle  5 , the high reduction pivot diameter  2 , and the drive pin  1  can be modified in order to raise or lower the MAR to suit the consumer. The high reduction pivot diameter  2  engages with the drive handle  5  for about half of the full stroke of the drive handle  5 . The stroke length required to disengage the high reduction pivot diameter  2  can be modified for a given product. An average human hand produces the maximum squeezing force at the point where the stroke is one half complete. Thus, this embodiment gives the user the maximum clamping force by using a high MAR coupled with the maximum human squeezing force.  
         [0022]     In summary, the squeezing force from the user&#39;s hand is transmitted to the drive handle  5  to rotate the drive handle  5  about the pivot diameters  2 ,  7 , thereby moving the drive pin  1  which transfers force to the drive links  16  engaging the bar  4  to move the first clamp head  9  toward the second clamp head  29 . The drive links  16  have the aperture  50  just slightly larger than the height of the bar  4  to enable the bar  4  to pass through the drive links, as shown in  FIG. 4 . When the drive links  16  rotate counter clockwise due to loading from the drive pin  1 , the drive links  16  bind onto the bar  4  creating enough normal force at the binding points to transmit the squeezing force to the bar through friction.  
         [0023]     When the stroke of the drive handle  5  reaches about the half way point, the low reduction pivot diameter  7  of the drive handle  5  engages the moveable jaw housing  10 . The high reduction pivot diameter  2  then disengages, as shown in  FIG. 3 . With low reduction pivot diameter  7  engaged, the MAR decreases because the distance from the drive pin  1  to the low reduction pivot diameter  7  increases. As shown, the MAR is low, for example, approximately 3.75:1, although it should be appreciated that adjustment in location of components can increase or decrease the MAR as desired. With the low reduction pivot diameter  7  engaged, a relatively small angular rotation of the drive handle  5  translates into a large axial travel of the bar  4  relative to the moveable jaw housing  10 . This minimizes the number of squeezes required to engage the work piece.  
         [0024]     Once the hand clamp  100  engages the work piece, the locking link  6  holds substantial force in order to prevent the bar  4  from slipping and allowing the movable jaw housing  10  and the clamp head  9  to move away from the stationary jaw housing  11  and clamp head  29 . A release mechanism for the locking link  6  is incorporated into the rear handle/lock release  3 , as shown in  FIG. 3 . The rear handle/lock release  3  attaches to the moveable jaw housing  10  at a pivot pin  60  and includes a release pin  65 . The entire rear handle/lock release  3  pivots backwards about pivot pin  60  to move the release pin  65  in contact with a bottom portion of the locking link  6  in order to rotate the locking link  6  counter-clockwise and release the clamping pressure. This release mechanism provides a release with a long lever arm and an ergonomic handle shape, which helps the user operate the hand clamp  100  more efficiently. Thus, this release mechanism represents a substantial improvement over the prior art clamps which included releases made of flat sheet metal.  
         [0025]     To release the stationary jaw housing  11  from the bar  4 , the user grabs and rotates the release lever  8  clockwise against the bias of the leaf spring  13  to raise the locking dog  15  from the first notch  40 . Then, the stationary jaw housing  11  slides freely on the bar  4  to enable removal of the entire stationary jaw assembly. The stationary jaw housing  11  reattaches to the bar  4  by inserting the bar into an opening  42  in the stationary jaw housing  11 , as shown in  FIG. 4 , and sliding the stationary jaw housing  11  along the bar  4 . The leaf spring  13  causes the locking dog  15  to find the first notch  40  in the bar  4  and snap into place.  
         [0026]     For some embodiments, the hand clamp  100  can be used as a spreader with the clamping surfaces  26 ,  27  disposed within the work piece as is known in the art. Unlike the embodiments shown with the clamping surfaces  26 ,  27  facing one another, the clamping surfaces can accordingly be arranged to oppose one another to facilitate this spreader use of the clamp.  
         [0027]     In another embodiment, the drive links  16  can be modified in order to more effectively increase the MAR. In order to increase the MAR, it is necessary for the drive pin  1  to be relatively close to the high reduction pivot diameter  2 . This configuration requires the drive pin  1  to push on the drive links  16  at a relatively small distance from the edge of the bar  4 . At some minimum distance, the drive links  16  no longer have enough frictional force with the bar  4  to drive the bar. Therefore, drive link(s)  46  provide an improved design that includes offset edges, as shown in  FIGS. 5 and 6 . A first distance D 1 , defined as the distance along the length of the bar  4  between the top front edge and the back bottom edge of the drive link  46  where the bar  4  is engaged, is reduced by having the offset. This reduction increases the magnitude of forces R 1  and R 2  engaging these edges of the drive link  46  with the bar  4 . The forces R 1  and R 2  result from countering the moment created by driving force F 1  from the pin  1  in contact with the drive link  46  and a second distance D 2  defined as the distance from the bottom of the bar  4  to the location where the pin  1  contacts the drive link  46  to apply the driving force F 1 . This increase in the forces R 1  and R 2  permits the second distance D 2  to be shorter and enables a higher MAR.  
         [0028]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.