Clamping device
FIELD OF THE INVENTION 
     This invention relates to clamping devices such as vices for the clamping of workpieces between a pair of clamping jaws at a safe and comfortable height. 
     BACKGROUND OF THE INVENTION 
     The most common clamping device in current use is the vice having a fixed jaw and a moving jaw carried by a threaded support engaged by a correspondingly threaded shaft for advancing the moving jaw to clamp a workpiece between the two jaws. Most vices are made from machined cast steel and must be bolted to a work bench or other support. For this reason, most vices are not easily portable from one working site to another. 
     A number of portable clamping devices have been proposed to enable a workman or handyman to conveniently transport the device from one work site to another. One such proposal is shown in European Patent Publication 64883 (82302408.8). This clamping device has an adjustable jaw which is fixed during the clamping operation, and a moving or clamping jaw actuated by a foot operated lever which pivots the jaw from a released position to a clamping position via an overcentring linkage pivoted to the lever and to the moving jaw to lock the moving jaw in its fully clamped position. 
     While the arrangement described in the above document has the advantage of portability, it does not allow different appropriate clamping forces to be applied depending on the object being clamped and the clamping range is not quickly adjustable, some degree of trial and error being required. Thus, unless the operator&#39;s foot is kept on the pedal to apply variable clamping forces lower than that necessary to cause the locking linkage to overcentre, only one clamping force may be maintained on a clamped object using this device, and this force may in many instances be excessive and damage the object being clamped or inadequate and allow the object to slip while being worked on. 
     Another type of clamping device is described in U.K. Patent Application 2187411. In the device shown in FIGS. 25 to 29, a moving jaw is operated by a spring loaded foot lever to apply a clamping force dictated by the force applied by the operator&#39;s foot. However, the operator&#39;s foot must be kept on the lever otherwise the spring releases the clamping jaw. This arrangement seriously restricts the activities which may be performed by the operator on the clamped object. 
     Numerous foot operated vices or clamps are disclosed in the Patent literature. For example, U.S. Pat. Nos. 1,430,260 Bobo and 2,892,369 Millet disclose clamps or vices having a foot operated lever which causes a work piece to be clamped between a fixed jaw and a movable jaw. While in each of these devices, the force applied by the foot operated lever may be varied, each device includes a toothed latching means for locking the foot operated lever when the required force has been reached. Since toothed locking devices can only be operated when the latch is aligned with an inter-tooth space, the foot operated lever cannot be locked at the desired position since the lever must be moved in either direction from the desired position to achieve the required alignment of the locking device. Furthermore, release of such locking devices often requires the foot operated lever to be pushed past its locked position thereby increasing the clamping force and possibly damaging the clamped object. 
     STATEMENT OF INVENTION AND OBJECTS 
     It is an object of a first aspect of the present invention to provide an improved lever operated clamping device capable of being mounted on a portable support and which can be locked at any selected position applying any selected clamping force. 
     It is an object of a second aspect of the present invention to provide an improved mechanism for rapidly advancing the jaw or jaws to the clamping position and to provide automatic locking at that position. 
     It is an object of a third aspect of the present invention to provide a rigid supporting structure for a clamping workbench which may be collapsed into a form which is convenient for carrying or stowing. 
     According to a first aspect, the present invention provides a clamping device comprising a support structure carrying two adjustably spaced apart jaws, lever means pivotally connected to the support structure and operably engaging advancing means for moving one of the jaws relative to the other as the lever means is pivoted to a selected position to apply a selected clamping force to an object between said jaws determined by the force applied to the lever, and locking means for holding the two jaws in any selected position with said selected clamping force applied to the object, said locking means allowing the continuous and infinitely variable locking of said clamping device in any selected position and selected clamping force. 
     In a preferred form, the locking means comprises a first member adapted to frictionally engage a second member in an infinitely variable manner to hold the jaws in any selected position. 
     The locking means preferably allows relative movement of said second member in one direction relative to said first member and is operative to lock the lever means as soon as the lever has reached the selected position and ceases pivotal movement in the advancing direction thereby enabling `hand-free` locking of the clamping device. 
     In one preferred form, the lever has an operative end to which operating forces are applied, said locking means acting between said support structure and said lever at a position which is closer to said operative end of the lever than its pivotal connection to the support structure. 
     The locking means preferably includes lock releasing means co-operating with said locking means holding the locking means in its deactivated state to allow the lever means to be reciprocated to repeatedly actuate the advancing means to reduce the space between the jaws in a `hands-free` manner. 
     In its presently preferred form, the locking means comprises a plate pivoted to the support structure and having an aperture through which a rod connected to the lever means is free to pass when they are perpendicular to each other, said plate being normally spring biased to an angular position with respect to the rod, so that the edges of the aperture in the plate grip the rod when advancing movement of the lever ceases, to prevent return movement of the lever to thereby lock the advancing means and the moving jaw in any desired position, said locking means having associated means for releasing the locking means when clamping is no longer required. 
     The lock releasing means may comprise a secondary lever pivoted to the support structure and having an abutment means positioned to engage the plate of said locking means to hold said plate in an orientation substantially perpendicular to the rod to allow the rod to slide freely through the aperture. 
     In a particularly preferred form of the invention, the support structure comprises an elongate portion defining a track for slidably receiving said jaw(s), and three legs pivotally attached to the elongate portion and comprising two legs pivoted to the elongate portion at the front of the support portion and one leg pivotally mounted at the rear end of the support portion, and collapsible bracing struts extending between said front legs and between said front leg bracing strut and said rear leg to releasably retain said legs in their supporting positions, said front legs being collapsible to lie along either side of the elongate support and said rear leg, lever arm and pedal being collapsible to lie along the length of the support to facilitate collapsing of the support structure into an easily transportable or stowable form. 
     The front legs preferably have enlarged feet secured to their lower ends and to which the bracing struts are pivotably attached, said feet being positioned to enable the operator to stand on the feet to stabilise the support structure. 
     In a second aspect, the invention provides a clamping device comprising two adjustably spaced apart jaws carried by a support structure, pivoted lever means carrying advancing means for advancing at least one of said jaws relative to the other jaw, said advancing means including an advancing member having means to engage spaced apertures, teeth or abutments in an elongate back runner of one of said jaws, said advancing member being pivoted to the inner end of said lever means and being spring biased to cause arcuate movement of said advancing member towards the back runner to cause engagement between said engagement means and said spaced apertures, teeth or abutments when the lever means is pivoted in the operative direction, and an abutment finger carried by said support structure for engaging the rear end of said advancing member when the lever is in its retracted position to pivot the advancing member against the action of said spring biasing to position the engagement means clear of the back runner to facilitate free sliding movement of said one of said jaws with respect to said support structure. 
     In a third aspect, the invention provides a support structure for a clamping workbench, comprising an elongate support carrying two adjustably spaced apart jaws, foot operated lever means pivotally connected to said support and having a foot pedal, said lever means operably engaging advancing means for moving one jaw relative to the other two front support legs pivotally mounted to the elongate support at the one end of the support and one rear support leg pivotally mounted at the other end of the support, collapsible bracing struts extending between said front legs and between said front leg bracing strut and said rear leg to releasably brace said legs in their supporting positions, said front legs being collapsible to lie along either side of the elongate support and said rear leg, said lever arm and foot pedal being collapsible to lie along the length of the support to facilitate collapsing of the support structure into an easily transportable or stowable form. 
     In a preferred form of the third aspect, the invention provides a clamping workbench comprising a support structure carrying two adjustably spaced apart jaws, foot operated lever means pivotally connected to the support structure and having a foot pedal, said lever means operably engaging advancing means for moving one of the jaws to a selected position relative to the other as the lever means is pivoted to apply a selected clamping force to an object between said jaws determined by the force applied to the lever, and locking means for holding the lever means in any said selected position with said selected clamping force applied to the object, said locking means comprising a first member mounted on said support to lockably engage a second member on said lever, leg means foldably carried by said support structure for supporting said support structure in a stable manner at an elevated position relative to a supporting surface, said legs said lever and said foot pedal being collapsible so as to be positioned adjacent to and along said support structure to render the workbench readily portable or stowable, said second member of said locking means being pivoted to said lever means to allow said lever means to be collapsed without disconnecting said locking means. 
     The locking means preferably has lock releasing means comprising a lever pivoted to said fixed jaw and configured to enclose said first and second means within said support structure, said lever having an abutment which engages said first means to hold it in a released position relative to said second means to allow repeated `hands-free` actuation of said lever without locking. In this way the locking means is neatly enclosed by the support structure at the same time allowing collapsing of the clamping workbench for transport or storage. 
     The front legs preferably have enlarged feet secured to their lower ends and to which the bracing struts are pivotably attached, said feet being positioned to enable the operator to stand on the feet to stabilise the support structure. 
     In another aspect, the invention provides a locking device for an operating mechanism of a working device such as a clamping device, said operating mechanism including a reciprocatable rod and said locking device comprising a pivoted plate having an aperture through which said rod is free to pass when they are substantially perpendicular, said plate being spring biased to an angular position with respect to the rod in which the edges of the aperture in the plate grip the rod to prevent return movement of the rod when operative movement ceases, and lock releasing means comprising a pivoted lever having an abutment means positioned to engage the plate of said locking means to hold said plate in an orientation substantially perpendicular to the rod to allow the rod to slide freely through the aperture. 
    
    
     One presently preferred form of the invention will now be described with reference to the accompanying drawings in which: 
     FIG. 1 is a partially sectional side elevation of a clamping device embodying the invention; 
     FIG. 2 is a fragmentary sectional elevation of the device showing the locking and advancing mechanisms of the device; 
     FIG. 3 is a perspective view from the front of the device of FIG. 1 showing the collapsible supporting frame in greater detail, and 
     FIG. 4 is a perspective view of the device in the folded condition. 
    
    
     Referring first to FIG. 1, the device comprises a support structure 1 which incorporates an integral track 2 and a fixed jaw 3. The support structure 1 is supported by a foldable frame 4 (see FIG. 3 for greater detail). 
     The support structure track 2 is adapted to receive a back runner 5 having an integral moving jaw 6. The back runner is adapted to freely travel back and fourth along the track 2 and is also capable of complete removal and reversal thereby facilitating a very broad range of jaw openings. The vice operation of the jaws is in a positive direction with the back runner being engaged by an advancing member 8. The engagement of the back runner is effected by forward facing pawls 7 on the surface of the advancing member 8 which are specifically adapted through the bias of spring 15 to engage apertures 9 in the back runner 5. The apertures 9 in the back runner are adapted for bi-directional engagement to allow the runner to be reversed for extended jaw capacity, and in the present embodiment there are two rows of generally square apertures engaged by spaced pairs of pawls 7. 
     The operation of the advancing member 8 is effected by an articulated connection to a foot operated lever means 10. The lever has a front foot pedal 11 located at the operative end, and a rear pivot 12 to the support structure 1. The foot lever is terminated by a cranked lever 13 which is pivotally connected to the advancing member 8 by pivot 14 so as to effect an advancing action substantially parallel to the direction of travel of the back runner 5 in the track 2. The advancing member 8 is freely pivoted to the cranked lever 13 but is biased by a spring 15 which tilts the advancing member to effect engagement of the pawls to the apertures of the back runner. The action of the advancing member is further restrained by interaction with an abutment finger 16 (see FIG. 2) which is positioned to partially withdraw the advancing member against the bias of the spring upon release of the foot lever (see FIG. 3). This action allows the pawls 7 to disengage the apertures 9 of back runner 5 and facilitates rapid advancing, retraction, removal or the reversal of the back runner 5 and moving jaw 6. 
     Activation of the foot operated lever 10 causes the advancing member 8 to move forward, off the finger 16, and lift up by action of the spring 15 to engage the apertures 9 of the back runner 5. Further activation of the foot lever moves the advancing member 8 forward which causes the back runner 5 and moving jaw 6 to advance toward the fixed jaw 3. Once the full operating span is reached, the lever 10 is returned to its rest position by spring 30 (see FIG. 2) causing the advancing member to disengage the back runner (as previously described) and reverse back along the back runner, with the back runner remaining stationary due to friction, to a further point of engagement where another activating operation can further advance the moving jaw. This operation is repeated until the jaws engage the object to be secured. 
     Referring now to FIG. 2, the foot operated lever further incorporates a locking mechanism located near the front foot pedal 11. The locking mechanism is located near the pedal end of the foot lever 10 to minimise the forces required to lock the jaws at a given pressure. 
     The locking mechanism comprises a rod 17 pivotally attached to the foot lever 10 and passing through an aperture 22 in a locking plate 18 positioned to effect a substantially tangential movement of the rod relative to the pivoting action of the foot lever 10. The locking plate comprises a pivoting, hardened steel locking plate 18 having an aperture 22 of greater diameter than the rod (FIG. 2), through which the rod 17 passes. The locking plate 18 is pivoted to the support structure 1 at 18a and is biased by a spring 22(a) to the locking position shown in broken outline in FIG. 2 such that movement of the rod 17 through the aperture 22 is normally limited to one direction only, said direction following the activation direction of the lever arm. As such, the locking plate provides a locking mechanism allowing the continuous and infinitely variable locking of the lever at any desired position. The mechanical advantage of the lever 10 and the continuous nature of the locking action ensure exquisitely fine control over the clamping pressure of the jaws whilst the very same mechanical advantage facilitates the availability of very high clamping pressure, if such pressure is required. Furthermore, the action of the advancing member 8 allows repeated advancement of the jaw 6 to operate in the manner of a press to perform pressing, bending or cropping off operations. 
     The locking plate 18 is released by pivoting the locking plate 18 against the action of the biasing spring 22(a) to the position shown in solid outline in FIG. 2. A lock releasing plate 19 or lever is pivoted to support structure 1 and has an abutment 20 which engages the plate 18 to effect such release. The locking plate 18 is shaped to enable the abutment 20 to hold the plate 18 in the released position, as shown in solid outline in FIG. 2, to allow free travel of the rod and lever arm. 
     The foldable frame 4 includes foldable support legs as detailed in FIGS. 3 and 4 where two front legs 23 are pivotally connected to the support structure 1 and straddle either side of the support structure 1. The two front legs 23 are fixed into the erect position by a bracing strut 25 comprising two struts joined at the centre by a locating housing 28. The rear leg 24 is pivoted from the rear of the support structure and is adapted to rigidly support the rear of the device being located in the erect position by a rear bracing strut 26 having a two part hinged construction joining the rear leg and the locating housing 28 of the front bracing strut 25. The rear bracing strut is positioned by forcibly opening the hinge to establish full strut length thereby placing the three legs under tension and rigidly establishing a very sturdy erect structure. The front legs 23 have foot plates 29 at their lower ends, to which the struts 25 are pivoted, to allow the frame 4 to be additionally stabilized by the user standing on one of the plates 29, or on the struts 25 and 26. 
     In the foldable mode shown in FIG. 4, the front legs fold back along the sides of the support structure and the rear leg folds up to lie along the length of the support structure and the lever 10 is folded about a pivot connection 31 as shown, to also lie along the length of the support structure to effect a compact and readily transportable unit. 
     From the foregoing it can be seen that the instant invention provides a highly versatile clamping device incorporating a number of unique features. The device provides a very broad range of clamping capacities by virtue of the reversible jaws. The leverage mechanics offer a high mechanical advantage which supplements the power available by operation to provide a device capable of very substantial clamping pressure or pressing force. The locking mechanics allow a continuous and infinitely variable lock for the clamp which allows locking at any position. The result of this feature is that jaws may be quickly locked at any position and at any pressure. The collapsible legs offer the device a high degree of portability whilst having suitable bracing to ensure a very rigid structure upon erection. 
     The claims form part of the disclosure of this specification.