Abstract:
A hydraulically driven extending clamp is disclosed having a pivoting main body which includes an extendable clamping rod disposed therein. The clamping rod extends above the pivot and is extended by air pressure and retracted by a spring internal to the clamping rod. A retaining member extends through a slot in the clamping rod and forms a travel limit stop as well as a retraction spring contact point. A hydraulic cylinder pivots the main body in seesaw-like fashion to apply clamping forces.

Description:
This application claims priority from Provisional application Ser. No. 60/215,263,filed Jun. 30, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to fluid pressure driven clamps and particularly to such clamps which include an extendable clamping member. 
     Extending clamps generally comprise a clamping member which can be moved away from a clamping area and which can return to the clamping area to apply clamping forces to an object placed in the clamping area. Such clamps are useful in present day industrial environments, particularly where successive parts are to be appropriately placed before the clamp and then clamped. It is desirable to have a clamp with a relatively long extension which can apply large clamping forces with minimum power required both for extension and clamping. These goals have not been achieved with known clamps. Clamps which are capable of large clamping forces tend to be physically large and have limited extension. Conversely, clamps which have long possible extension typically are not capable of large clamping forces. 
     SUMMARY OF THE INVENTION 
     These limitations in prior extending clamps are overcome in accordance with the embodiments herein which describe a compact extending clamp capable of relatively long extension and large clamping forces. The clamp of the embodiment includes a main clamping block which incorporates most of the active parts of the extending clamp assembly. The main block is pivotably mounted to a stationary mounting plate which is affixed to a surface against which clamping is to occur. The main block of the embodiment is constructed of a solid metal block into which openings are formed to convey control fluids and to retain the moving parts of the assembly. The clamping end of the main block is referred to as the outward end. A pressure cylinder is disposed within the moving block at the other end, called the inward end, of the main block so that the pivoting of the main block results in a seesaw motion of the inward and outward ends of the main block. The clamping cylinder may, for example, be a hydraulic cylinder which receives fluid under pressure from an inlet at the inward end of the main block. Advantageously, the clamping cylinder is disposed near the pivot at an outward angle to increase the lever arm available for clamping forces. The outward end of the main block is raised in the absence of hydraulic pressure in the cylinder by a spring on the outward side of the pivot. 
     The clamping forces are applied to objects to be clamped by the clamping rod which is slidably disposed within the main block. The clamping rod in its retracted state extends from the outward end of the main block, crossing above the pivot and ending on the inward side of the pivot. An air cylinder is disposed within the main block to extend the clamping rod by means of compressed air applied at an inlet connected to the inward end of the main block. The clamping rod has a slot along its length which, in conjunction with a retaining member of the main block performs a number of significant functions. The retaining member extends through the slot in sliding contact therewith. An outward end of the slot contacts the retaining member to define the maximum retraction of the clamping rod. Similarly, an inward end of the slot contacts the retaining member to define the maximum extension of the clamping rod. The retaining member, by extending through the slot also serves to keep the clamping rod from rotating and thus keeps the clamping surface of the clamping rod in a downward position. Advantageously, the embodiment shows a clamping rod retraction spring disposed within a central bore formed within the clamping rod. The spring provides retraction forces by urging against an inward end of the clamping rod bore and against the retaining member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a ,  1   b  and  1   c  are perspective views of an extending clamp in rest, extended and extended with clamping positions respectively; 
     FIG. 2 is a transparent perspective view of the main block of the extending clamp; and 
     FIG. 3 is a cross-sectional view of the clamp along the section line  3 — 3  of FIG. 1 a.   
    
    
     DESCRIPTION 
     FIGS. 1 a ,  1   b  and  1   c  show a perspective view of three different operational states of an extending clamp. The clamp includes a stationary mounting plate  101  which is affixed by means of fasteners through holes  102  to a surface (not shown) against which clamping force is to be applied. Mounting plate  101  comprises a pivot assembly  104  which preferably mounts a pivoting main block  106  by means of a pivot  108 . Pivot  108  may comprise, in part, a Teflon® coated metal bushing. Main block  106  includes a clamping rod  110  which can be extended from the main block  106  as shown in FIG. 1 b  and retracted as shown in FIG. 1 a.    
     Pivoting main block  106  also comprises a hydraulic cylinder  112  having a relatively movable contact point  114  in abutting contact with the stationary main plate  101  at a contact point  116 . The piston  118  of clamp cylinder  112  is hydraulically driven by hydraulic fluid introduced into the main block  106  to pivot the main block  106  in the direction shown by arrow  120  (FIG. 1 c ). When the hydraulic pressure is reduced, a pivot return spring  122  returns the main block  106  in the direction shown by arrow  124  to the rest position shown in FIG. 1 a . The rest position is limited by an abutment  127  of the main block  106  which contacts a stop  126  of the mounting plate  101  to complete rotation in the direction shown in by arrow  124 . 
     The clamping rod  110  may be driven outwardly (FIG. 1 c ) by air pressure supplied at an inlet  128  and retracted to the position shown in FIG. 1 a  by an internal spring  305  shown in FIG.  3 . The hydraulic fluid pressure to forcefully rotate the main block  106  in the direction shown by arrow  120  is provided via inlet  130 . 
     FIG. 3 is a cross section of the clamp taken vertically from section line  3 — 3  shown in FIG. 1 a . In FIG. 3 a clamping anvil  301  is shown attached to clamping rod  110  by a bolt  303  through the clamping rod near its outward end. When the clamping rod  110  is extended, the clamping anvil  301  extends with it. The main block  106  includes a clamp rod bore  321  which is produced by machining or other processes. The clamping rod  110  is inserted into the bore  321 . The clamping rod  110  includes an inward end  317  which forms a piston for movement in response to air pressure from inlet  128  in fluid communication with a chamber  325  via a conduit (not shown). Air pressure introduced into chamber  325  works against piston end  327  to apply extension force to the clamping rod  110 . The piston  317  of clamping rod  110  also includes a seal  319  which may comprise an O-ring seal to retard the leakage of air pressure past the piston  317 . 
     Internal to clamping rod  110  is a central bore  329  which extends from the outward end of the clamping rod to the piston  317 . A spring  305  is disposed within the bore  329  and extends from an inward end  334  of the bore to a bolt  307 . The clamping rod  110  also comprises a slot  323  having an inward end  313  and an outward end  315  shown in FIG. 5 abutting the bolt  307 . As the clamping rod is driven outwardly by an increase in air pressure in chamber  325 , spring  305  is compressed between bolt  307  and bore end  334 . This compression returns the clamping rod to the rest position shown in FIG. 3 when the air pressure in chamber  325  is released. 
     An extending clamp, by its very nature, applies clamping forces by means of a movable clamping rod. In order to provide a good product lifetime using affordable parts, it has been recognized that a significant portion of the clamping rod  110  should remain within the main body  106  at the time of clamping. The present embodiment provides the axis of motion of the clamping rod  110  over the top of the pivot from the outward to the inward end of the main block. This permits a relatively long clamping rod and thus allows a significant amount of the clamping rod to remain within the main block at clamping. Additionally, the long clamping rod discussed allows the use of a long return spring  305 . 
     Bolt  307  is disposed through a hole  309  which extends from the top of main block  106 , through the slot  323  in the clamping rod  110 , and into a threaded fitting at  311 . The placement of bolt  307  with respect to the main block  106  and the clamping rod  110  is also shown in FIG.  2 . The maximum and minimum extension of the clamping rod  110  are determined by the length and positioning of the slot  323 . In the retracted (rest) position, the spring forces the clamping rod inwardly until the slot end  315  contacts the bolt  307 . When air pressure in chamber  325  acting against piston face  327  overcomes the spring  305  forces, the clamping rod extends to its outward position in which slot end  313  is driven into contact with bolt  307 . 
     Main block  106  also includes a cylindrical opening  331  which receives a portion of pivot return spring  122 . The opening  331  includes an end  333  which captures spring  122  between itself and a block  335  of stationary mounting plate  101 . When hydraulic fluid pressure rises in a chamber  337 , from inlet  130 , a piston  339  is driven downwardly against stop  116  which rotates the main block  106  against the spring  122 . Similarly, when hydraulic pressure drops, the spring  122  forces rotation of main block  106  to the rest position of FIG.  3 . In the present embodiment, cylinder  112  is disposed at an angle away from vertical. The orientation of the cylinder  112 , and contact point  116  is such that, at the position of main block  106  during maximum clamping forces, a line, e.g.  160  (FIG. 1 c ) drawn through the axis of pivot  108  intersects a line, e.g.  161 , along the axis of cylinder  112  at a 90° angle. This orientation reduces greatly the abrasive forces between contact point  116  and movable contact point  114 , providing an improved product lifetime. 
     In use, an item to be clamped is moved to a position predetermined by the placement of mounting plate  101 , the position of bolt  307  and the length of slot  323 . Initially, both air pressure and hydraulic pressures are below the point at which spring forces from springs  122  and  305  control. Thus, the clamping rod  110  is withdrawn and the main block  106  is in the rest position. This selection is shown in FIG. 1 a . After placement of the item to be clamped, air pressure is increased to extend clamping rod  110  until surface  313  of slot  323  meets the bolt  307  (FIG. 1 b ). At this time hydraulic pressure is increased to a predetermined amount to apply clamping forces by the outward end, e.g.  301 , of clamping rod  110  to the item to be clamped (FIG. 1 c ). At the completion of clamping, hydraulic pressure is decreased, followed by a decrease of air pressure so that the clamp again assumes the rest position shown by FIG. 1 a.    
     While there have been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the scope of the present invention.