WO1995021722A1

WO1995021722A1 - Self-equalizing clamp

Info

Publication number: WO1995021722A1
Application number: PCT/US1995/001862
Authority: WO
Inventors: John S. Ausilio
Original assignee: Ausilio John S
Priority date: 1994-02-14
Filing date: 1995-02-14
Publication date: 1995-08-17

Abstract

A self-equalizing clamp (10) brings one of a pair of clamp arms (60, 62) into engagement with a workpiece (20) at the actual position of the workpiece (20). In one embodiment, one end (66, 92) of each clamp arm (60, 62) is pivotally connected to a drive cylinder (26) and to a piston rod (27) of the cylinder (26), respectively, for pivoting the opposite ends (64, 90) of the clamp arms between a first, spaced apart position and a second workpiece engaging position. Adjustment of clamp arm (62) causes the opposite clamp arm (60) to correspondingly move. Alternatively, a biasing member (168) disposed between a pair of slidable plates (136) automatically adjusts the positional relationship of the plates (136). Alternately, a clamp (170) is adjustable relative to a fixed support by adjustment screws in displaceable plates (172, 176).

Description

SELF EQUALIZING CLAMP BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates, in general, to clamps and, more specifically, to pivotal clamps for holding a workpiece during manufacturing operations. Background Description:

Clamps are widely employed to hold two or more parts together during a manufacturing operation. In automotive assembly plants, for example, clamps are used to hold two or more metal sheets or parts together under pressure and at a predetermined coordinate position during welding, piercing, hemming and other manufacturing operations.

Typically, such clamps include a riser which is mounted via a mounting plate to a tool base. A clamp with at least one pivotal clamp arm is mounted on the upper end of the riser and is movable between an open position and a closed, workpiece engaging position, either manually or under power by means of a fluid cylinder, for example. In such a clamp, two pressure feet or N/C blocks are respectively mounted on one end of the clamp arm through a clamp nose member attached to the pivotal clamp arm and to the upper end of the riser to establish a predetermined coordinate position therebetween when the clamp arm is moved to the closed position bringing the pressure feet into engagement with a workpiece disposed therebetween. Due to the close tolerances reguired for accurate automobile assembly as well as other manufacturing operations, the pressure feet, clamp arm and risers, etc., are specifically designed to predetermined dimensions and tolerances for each application.

The workpiece engaging surfaces of the pressure feet mounted on the end of a clamp arm and on the riser, or on the ends of two opposed, pivotal clamp arms in an alternate clamp assembly, are designed to close together into secure engagement with a workpiece, typically a stack of two or more metal sheets. The closed position of the workpiece engaging surfaces of the pressure feet and/or riser is precisely located at the time of design and installation of the clamp.

However, it is well known that workpiece dimensions, shapes and flange positions vary from production run to production run of workpieces. Thus, the position of the metal sheets forming the workpiece which are to be held together by the clamp may vary by a few to many thousandths of an inch.

At extreme variations in the actual position of the metal stack, the high closing force of the clamp can actually deform the edges of the metal sheets resulting in subseguent problems in assembly operations or, at the least, a disfigured workpiece. In order to accommodate such variations, shims and L-brackets are provided in a typical clamp assembly and are added to or removed from the pressure foot mount on the clamp to adjust the position of the metal contact surfaces of each pressure foot. This entails partial disassembly of the clamp and potentially an interruption of production.

Thus, it would be desirable to provide a clamp which securely clamps a workpiece in a fixed position regardless of variations between the actual position of the workpiece and a predetermined design position. It would also be desirable to provide a clamp for clamping a workpiece over a range of positions of the workpiece. It would also be desirable to provide a clamp which achieves these features while having a simple construction for an economical manufacturing cost. Finally, it would be desirable to provide a clamp which is easily adjusted for use in clamping other workpieces or repositioned workpieces. SUMMARY OF THE INVENTION The present invention is a self equalizing clamp which securely clamps a workpiece in a fixed position regardless of the actual position of the workpiece with respect to the clamp.

In one embodiment, the present self equalizing clamp includes a support mounted on a base. First and second clamp arms, each having first and second spaced ends and an intermediate portion disposed between the first and second ends, are pivotally mounted to the support at the intermediate portion. Pivot means are coupled to the second ends of the first and second clamp arms for pivoting the first ends of the first and second clamp arms between a first spaced apart position and a second closely spaced position engaging a workpiece therebetween. A pressure foot is mounted on the first end of each of the first and second clamp arms.

Adjustably positioning means are coupled between the support and the second clamp arm for adjustably positioning the first end of the second clamp arm to supportingly engage a workpiece disposed between the spaced apart first ends of the first and second clamp arms at any position of the workpiece. Due to the self- equalizing arrangement of the first and second clamp arms, any adjustments to the position of the second clamp arm cause a like adjustment in the position of the first clamp arm relative to the second clamp arm to insure that the first end of the first clamp arm securely closes on the workpiece when the first clamp arm is moved to the second, closed position.

In a preferred embodiment, the adjustable positioning means includes a set screw threadingly extendible and retractable in a bore on the second clamp arm. The head of the set screw is disposed in engagement with the clamp arm support such that any extension or retraction of the head of the set screw with respect to the second clamp arm causes an automatic repositioning of the first clamp arm through the interconnected second ends of the first and second clamp arms and the pivotal mounting of the clamp arms on the support.

The pivot means preferably comprises a fluid operated cylinder having a reciprocal, extensible and retractable piston rod extending therefrom. Means are provided for pivotally connecting the second end of the first clamp arm to the reciprocal piston rod and for pivotally connecting the second end of the second clamp arm to the cylinder.

In a second embodiment, the self equalizing clamp includes a support member and a clamp support. A clamp having at least one pivotal clamp arm movable between open and closed positions with respect to a second clamp arm is mounted on the clamp support. Pivot means are connected to the clamp arm to pivot the clamp arm between the open and closed positions with respect to an opposed clamp arm. Means are provided for slidingly attaching the clamp support to the support member. Means are coupled between the attaching means and the clamp support for equalizing the position of the first and second clamp arms with respect to the actual position of the workpiece disposed therebetween.

In the second embodiment, the attaching means preferably comprises a first plate attached to the clamp support and a second plate slidingly mounted within the first plate, the second plate being fixedly connected to the support member. The equalizing means preferably comprises a biasing means mounted between the first and second plates for automatically adjusting the position of the first plate with respect to the position of the first and second clamp arms. The biasing means preferably comprises a pair of coil springs each mounted between a portion of the first plate and opposite surfaces of the second plate.

In yet another embodiment, the clamp includes a support member and a clamp support. At least one pivotal clamp arm is mounted on the clamp support and is movable between open and closed positions with respect to an opposed second clamp arm. Pivot means are connected to the clamp arm to pivot the first clamp arm between the first and second positions with respect to the other clamp arm. Means are provided for slidably attaching the clamp support to the support member. Means are provided for fixedly attaching the clamp support to the support member in a desired position. In this embodiment, the slidably attaching means comprises first and second plates, with the first plate having opposed, outwardly extending flanges disposed in a spaced apart position from opposite sides of the second plate. Adjusting means are connected to and extend through the first and second flanges in the first plate into engagement with the opposed sides of the second plate to reciprocally adjust the position of the first plate with respect to the second plate.

The self equalizing clamp of the present invention overcomes many of the deficiencies found with previously devised clamps which will deform a workpiece if the portions of the workpiece engaged by the clamp vary significantly in actual position from a predetermined normal or design position. The clamp of the present invention uniquely equalizes the position of the clamp arms such that adjustment of the position of one of the clamp arms into engagement with a workpiece disposed out of its normal or design position will cause a corresponding adjustment in the opposite clamp arm such that the opposite clamp arm still moves into the desired closed position with respect to the workpiece, despite the variation in the position of the workpiece from a normal or design position. This eliminates the need for the addition or removal of shims and L-brackets to the clamp as extensively required in prior clamps. In addition, the clamp of the present invention may be easily reused without major modification on different or redesigned workpieces since only the workpiece engaging members need be replaced for major workpiece modifications. The clamp is constructed of standard components for an economical manufacturing cost. BRIEF DESCRIPTION OF THE DRAWING

The various features, advantages and other uses of the present invention will become more apparent by referring to the following detailed description and drawing in which: Figure 1 is a side elevational view of a self equalizing clamp according to one embodiment of the present invention;

Figure 2 is an exploded, partial, perspective view depicting the major components of the clamp shown in Figure 1;

Figure 3 is an enlarged, partial, side elevational view showing the adjustable positioning and the equalizing operation of the clamp arms of the clamp shown in Figure 1; Figure 4 is a side elevational view of a second embodiment of a self equalizing clamp according to the present invention;

Figure 5 is a cross sectional view generally taken along line 5-5 in Figure 4; Figure 6 is a side elevational view of a third embodiment of a clamp according to the present invention; and

Figure 7 is an exploded, perspective view showing the interconnection of the first and second plates of the third embodiment of the clamp shown in Figure 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a self equalizing clamp which is adjustable to the position of a workpiece, i.e., a metal stack, regardless of the position of the workpiece to securely clamp the workpiece in a fixed position. As shown in Figure 1, the clamp 10 in a first embodiment of the present invention includes a riser 12 which has any predetermined height to mount the clamp 10 at a predetermined position with respect to an underlying base or support, not shown. The riser 12 includes a lower mounting base 14, an elongated tubular member or weldment 16 of any desired height, and an upper mounting base 18 which is fixedly connected to the tubular member 16. The riser 12 is mounted to an underlying base or support, such as a tool, stand, etc., not shown, to position the clamp 10 at the desired position with respect to a workpiece denoted generally by reference number 20. By way of example only, and not limitation, the workpiece 20 is depicted as being a metal stack formed of a plurality of overlaying metal sheets, such as an upper sheet 22 and a lower sheet 24. As is conventional, the workpiece 20 is designed to be disposed in a predetermined normal or design dimensional position for precise manufacturing operations on the workpiece 20. The clamp 10 is also specifically designed to clamp the workpiece 20 in the normal position.

As shown in Figure 1, the clamp 10 includes a pivot means for pivoting the movable clamp arms, described hereafter, between open and closed positions. The pivot or drive means 26 preferably comprises a fluid operated cylinder, such as an air or hydraulic operated cylinder. As is conventional, the fluid operated cylinder 26 includes a tubular housing 28 which is mounted between a first end cap 30 and a second end cap 32. The end caps 30 and 32 are connected together by elongated rods 34 and nuts.

The cylinder 26 includes an internal, reciprocally movable piston, not shown, which drives an extensible and retractable piston rod 27 bi-directionally in a reciprocal manner with respect to the tubular housing 28 of the cylinder 26. As shown in Figure 1, and in greater detail in Figure 2, the clamp 10 includes a clamp arm support denoted generally by reference number 36. The clamp arm support 36 includes a mounting base 38 which is fixedly connected by suitable fasteners extendible through apertures 40 to the upper base 18 of the riser 12. A pair of spaced clamp support legs 42 and 44 of any desired shape are mounted on and fixedly secured to the upper surface of the base 38. The legs 42 and 44 may be welded to the base 38. Aligned apertures 43 and 45 are formed in an upper portion of each of the legs 42 and 44, respectively, and slidably receive a pivot pin 46 therethrough. A clip 48 engages a notch 50 formed in the pivot pin 46 to secure the pivot pin 46 in position through the aligned apertures 43 and 45 in the clamp support legs 42 and 44, respectively.

Each of the clamp support legs 42 and 44 is provided with a first outwardly extending flange 52 and an opposed outwardly extending second flange 54, the purpose of which will be described in greater detail hereafter. A transverse bar 55 is fixedly joined to and extends between a lower portion of the second flanges 54 as shown in Figure 2.

The clamp 10 includes first and second pivotal clamp arms 60 and 62, respectively. The first or upper clamp arm 60 includes a first end 64, an opposed second end 66 and an intermediate portion 68 disposed therebetween. An aperture 70 is formed in the intermediate portion 68 for mounting the first or upper clamp arm 60 pivotally about the pivot pin 46 as described hereafter. Similarly, an aperture 72 is formed in the second end 66 of the first clamp arm 60 for pivotally mounting the first clamp arm 60 to the drive cylinder rod 27, as also described hereafter. An insert 74 is fixedly attached to the first end 64 of the first clamp arm 60. The insert 74 is in the form of a clamp nose 76 having a slot 78 extending inward from one end thereof adapted to slidably engage the first end 64 of the first clamp arm 60. A set screw 80 extends through one of the legs of the clamp nose 76 bounding the slot 78 to engage the first end 64 of the first clamp arm 60 when the insert 74 is mounted thereon to temporarily secure the insert 74 on the first clamp arm 60. When the insert 74 has been positioned relative to the first clamp arm 60 in its desired final position with respect to the first clamp arm 60 and the workpiece 20, the insert 74 may then be welded or otherwise securely and fixedly connected to the first end 64 of the first clamp arm 60.

A through bore 82 is formed in one end of the clamp nose 76 and receives a suitable fastener, not shown, which extends through the bore 82 into a corresponding bore 84 formed in a pressure foot or NC block 86. The pressure foot 86 has a workpiece engaging surface 88 conformed to the shape of the workpiece 20, such as the shape of the upper sheet 22 of the workpiece 20 shown in Figure 1, by way of example only. Further details regarding the slip plane positioning of the insert 74 and the pressure foot 86 with respect to the associated first clamp arm 60 and the workpiece 20 may be had by referring to United States Patent No. 5,226,638, entitled "Clamp Arm with Slip Plane Positioning", issued July 13, 1993 in the name of the present inventor, John S. Ausilio, the contents of which are incorporated herein by reference.

The second clamp arm 62 also has a first end 90 and an opposed second end 92. An intermediate portion in the form of a pair of spaced arms 94 is provided between the first and second ends 90 and 92. A pair of aligned apertures 96 are formed in the intermediate arms 94 of the second clamp arm 62 and slidably receive the pivot pin 46 therebetween. The arms 94 are spaced apart a predetermined distance to pivotally receive the intermediate portion 68 of the first clamp arm 60 therebetween, with the pivot pin 46 extending through the aligned aperture 96 in the arms 94 of the second clamp arm 62 and the aperture 70 in the first clamp arm 60 to pivotally interconnect the first and second clamp arms 60 and 62 at their respective intermediate portions 68 and 94.

The second end 92 of the second clamp arm 62 is formed in a yoke with first and second spaced legs 93A and 93B as shown in Figure 2. Aligned apertures 95 are formed in each of the legs 93A and 93B for pivotally attaching the second end 92 of the second clamp arm 62 to the first end plate 30 of the drive cylinder 26, as described hereafter.

An insert 100 in the form of a clamp nose is provided with a bore 102 extending inward from one end which slidably engages the first end 90 of the second clamp arm 62. A set screw 104 extends through one of the legs of the clamp nose 100 bounding the slot 102 to temporarily attach the clamp nose or insert 100 to the first end 90 of the second clamp arm 62 in the same manner as described above for the insert 74 on the first clamp arm 60. A pressure foot or NC block 106 is fixedly connected to one end of the insert 100 and has a workpiece engaging surface 108 adapted to engage the bottom sheet 24 of the workpiece 20 shown in Figure 1.

Adjustable positioning means are coupled between the clamp arm support 26 and the second clamp arm 62 to adjustably position the first end 92 of the second clamp arm 62 in supporting engagement with the workpiece 20 at the actual position of the workpiece 20. The adjustable positioning means preferably includes a set screw 112 which is mounted in threaded bore 113 in the second clamp arm 62 adjacent the intermediate portion 94 of the second clamp arm 62. The set screw 112 engages the bar 55 extending between the flanges 54 on the clamp support legs 42 and 44. A lock nut 111 is mounted on the set screw 112 to lock the set screw 112 in any desired lengthwise extending position with respect to the second clamp arm 62.

In assembling the clamp 10 of the present invention, the intermediate portion 68 of the first clamp arm 60 is inserted into the spaced legs 94 of the intermediate portion of the second clamp arm 62. Both of the first and second clamp arms 60 and 62 are then slidably inserted between the spaced clamp support legs 42 and 44 before the pivot pin 46 is inserted through the aligned apertures 43 and 45 in the clamp support legs 42 and 44 and the aligned apertures 70 and 96 in the first and second clamp arms 60 and 62, respectively to pivotally mount the first and second clamp arms 60 and 62 in the clamp support legs 42 and 44. The first end 64 of the first clamp arm 60 is pivotally connected to an outer end of the drive cylinder rod 27 by means of a pivot pin inserted through the aperture 72 in the first end 64 of the first clamp arm 60 and the spaced legs of a cap 116 fixedly mounted on the outer end of the cylinder rod 27.

Similarly, pivot pins 118 are inserted through the apertures 95 in the legs 93A and 93B of the second end 92 of the second clamp arm 62 into aligned bores formed in the first end cap 30 of the drive cylinder 26 to pivotally connect the second end 92 of the second clamp arm 62 to the drive cylinder 26.

The drive cylinder 26, with the rod 27 fully retracted, is configured to normally position the first clamp arm 60 in a first, normally open or spaced apart position with respect to the workpiece 20 and the second clamp arm 62, as shown in phantom in Figure 1. However, when the cylinder 26 is activated by supplying fluid under pressure to one side of the internal piston, the piston rod 27 extends outward from the cylinder 26 pivoting the second end 66 of the first clamp arm 60 about the intermediately disposed pivot pin 46 to bring the pressure foot 86 mounted through the insert 74 to the first end 64 of the first clamp arm 60 into a closed or workpiece engaging position as shown in solid in Figure 1. In this closed position, the pressure feet 86 and 106 on the first and second clamp arms 60 and 62, respectively, securely engage the workpiece 20 under pressure to hold the workpiece 20 in a fixed position. Retraction of the piston rod 27 will cause a reverse movement or opening of the first clamp arm 60 back to the position shown in phantom in Figure 1. A situation may arise, however, where the workpiece 20 varies from its normal position to a different position due to material tolerance, variations in material thickness or the location of the flange or end surface of the workpiece 20 which is engaged on the clamp 10. As shown in Figure 3, such a varied position of the workpiece 20 is shown in phantom, with the normal or design position of the workpiece 20 depicted in solid lines. Despite this variation in the actual position of the workpiece 20, the self equalizing clamp 10 still functions to securely engage the workpiece 20 in its actual position without deforming or moving the workpiece 20 and without requiring the use of additional shims, L- brackets or the need to machine the surface of the pressure foot 106. This is achieved through the pivotal connection of the second end 66 of the first clamp arm 60 to the end cap 116 on the piston rod 27 and the second end 92 of the second clamp arm 62 to the first end plate 30 on the drive cylinder 26, the pivotal mounting of the intermediate portions of the first and second clamp arms 60 and 62 to the clamp support 36, and the provision of the adjustable positioning means 112.

Assuming that the workpiece 20 has varied from its normal position to a higher position, as shown in phantom in Figure 3, with respect to a normal or ideal position, the lock nut 110 is released and the set screw rotated in a clockwise direction to retract the head of the set screw 112 toward the second clamp arm 62 in the direction of arrow 114 in Figure 3. Due to the weight of the cylinder 26 on the second end 92 of the second clamp arm 62, the second clamp arm 62 will pivot about the pivot pin 46 thereby resulting in a counterclockwise or upward movement of the first end 90 of the second clamp arm 62 in the direction of arrow 115 until the set screw 112 engages the bar 55. When the set screw 112 is properly adjusted the pressure foot 106 mounted on the first end 90 of the second clamp arm 62 will supportingly engage the bottom sheet 24 of the workpiece 20. At the same time, the pivotal movement of the second clamp arm 62 in the direction of arrow 115 causes a similar pivotal movement of the first clamp arm 60 about the pivot pin 46 to the position shown in phantom in Figure 3 due to the interconnection of the second ends of the first and second clamp arms 60 and 62 with the cylinder 26 and piston rod 27. In this manner, the first claim arm 60 still moves through the same arcuate length of travel upon energization of the cylinder 26 to engage the workpiece 20 at the actual position of the workpiece 20.

Similarly, if the position of the workpiece 20 varies below the normal position shown in solid lines in Figure 3, the set screw 112 can be rotated to extend further out from the second clamp arm 62 and cause the pressure foot 106 on the second clamp arm 62 to move below the normal position shown in Figure 3 in a direction opposite to arrow 115. The first clamp arm 60 likewise pivots to a corresponding position from its normal first, open position shown in solid in Figure 3. Referring now to Figures 4 and 5, there is depicted a second embodiment of a self equalizing clamp according to the present invention. In this embodiment, the self equalizing clamp 130 includes a riser 132 which is depicted in the form of a weldment of several plates. A lower mounting base is provided at one end of the riser 132 for mounting the riser 132 to an underlying tool or support. A clamp support in the form of a pair of spaced plates 136, only one of which is visible in Figure 4, are mounted to a mounting plate 138. The mounting plate 138 is fixedly connected to a first end cap 140 of a drive means, such as a fluid operated cylinder 142 having a reciprocal, extensible and retractable piston rod, not shown, extending outward from one end thereof.

A first pivotal clamp arm 144 is pivotally connected by means of a pivot pin 146 to the spaced clamp support legs 138 and is coupled to the piston rod for pivotal movement between an open position shown in Figure 4 and a closed position with respect to an opposed second clamp arm 146. In the exemplary embodiment shown in Figure 4, the second clamp arm 146 is stationarily attached to the spaced clamp support plates 136. It will be understood, however, that the second clamp arm 146 may also be pivotal between open and closed positions.

Means are provided for equalizing the position of the first and second clamp arms 144 and 146 with respect to a workpiece 20 disposed therebetween, regardless of the actual position of the workpiece 20. The equalizing means preferably comprises a first plate 150 and a second plate 152 which are slidably disposed with respect to each other. The second plate 152, as shown in Figure 5, is stationarily attached to the riser 132, such as by welds, etc. The first plate 150 is secured by suitable fasteners 154 to a plate 156 which is in turn secured by fasteners 158 to the spaced clamp support plates 136, as shown in Figure 4. A bearing 160, such as a THK bearing, is fixedly connected to the second plate 152, as shown in Figure 5, and provides a sliding surface between opposed legs 162 and 163 of the first plate 150 and the second plate 152. In this manner, the pivotal clamp arms 144 and 146 and the drive cylinder 142 are slidably mounted on the stationarily fixed riser 132.

As shown in Figure 4, a pair of opposed first and second flanges 164 and 166 are connected to and extend outward from opposite ends of the first plate 150. The flanges 164 and 166 overlay opposed ends of the second plate 152 and are spaced therefrom. Biasing means 168, preferably in the form of a coil spring, is seated within and disposed between the first flange 164 and the adjacent surface of the second plate 152 as well as between the second flange 166 and the adjacent surface of the second plate 152 to biasingly mount the first plate 150 and the attached clamp arms 144 and 146 and drive cylinder 142 to the stationary second plate 152. The biasing means 168 equalizes the position of the clamp arms 144 and 146 with respect to the workpiece 20 regardless of the actual position of the workpiece 20.

For example, if the workpiece 20 is spaced from its normal design position, one of the clamp arms 144 and 146, such as the first clamp arm 144, will engage the workpiece 20 before the opposed clamp arm 146. The resistance exerted by the workpiece 20 on the first clamp arm 144 will be transmitted through the first clamp arm 144 and the clamp support plates 136 to the first plate 150. This force will cause the first and second flanges 164 and 166 on the first plate 150 to move with respect to the opposed edges of the second plate through the biasing springs 168 and cause the second flange 166 to move toward the opposed surface of the second plate 152 to bring the second clamp arm 146 into engagement with the workpiece 20 at the actual position of the workpiece.

The drive cylinder 142 functions in a normal manner to move the clamp arm 144 between open and closed positions with respect to a workpiece 20 and the stationary clamp art 146. The equalizing means automatically positions the clamp arms 144 and 146 in a workpiece engaging position at the actual position of the workpiece and compensates for any variation between the actual position of the workpiece 20 and its normal design position. Another embodiment of the present invention is shown in Figures 6 and 7. The clamp 170 shown in Figures 6 and 7 is easily repositionable to engage new workpieces, redesigned workpieces or merely repositioned workpieces as such changes are made to the workpieces. The clamp 170 is similar to that described above and shown in Figure 4 and like reference numbers have been used for like components. Thus, a drive cylinder 142 is fixedly mounted to a pair of spaced clamp support plates 136. A first pivotal clamp arm 144 and a stationary second clamp arm 146 are mounted between the clamp support plates 136. At least the first clamp arm 144 is pivotal with respect to the opposed second clamp arm 146 by means of a driving connection with the piston rod of the drive cylinder 142.

In this embodiment, a first plate 172 is fixedly connected by means of fasteners 158 to a mounting portion on the clamp support legs 136. A pair of spaced bores 174 are formed in the plate 172. A second plate 176 is fixedly connected to and extends outward from a riser 132. Elongated slots 178 are formed in the second plate 176 and are alignable with the bores 174 in the first plate 172. Fasteners, such as bolts 180, extend through a precision weld washer 182 into the slots 178 and the bores 174 to fixedly mount the first plate 172 to the second plate 176.

Adjustment means for adjusting the position of the first plate 172 with respect to the second plate 176 is provided by means of a pair of substantially L-shaped flanges 184 and 186 which are mounted on and extend outward from opposite sides of the first plate 172. The outer end portions of the flanges 184 and 186 overlay opposed edges of the second plate 176, as shown in Figure 6. Adjusting screws 188, such as set screws, extend through apertures formed in the flanges 184 and 186 into engagement with the opposed edges of the second plate 176. It can be seen that loosening of the bolts 180 and adjusting the fasteners 188 partially withdraw by the fastener 188 with respect to the flange 184 and advancing the opposite fastener 188 through the flange 186 will cause the first plate 172 to be urged in an upward direction with respect to the second plate 176 in the orientation shown in Figures 6 and 7. An opposite movement of the fasteners 188 will cause the first plate 172 to be urged in a downward direction with respect to the second plate 176.

When the first plate 172 has been adjusted to its desired position with respect to the second plate 176 so as to bring the pressure feet attached to the end of the clamp arms 144 and 146 into a desired position with respect to a workpiece 20 when the clamp arms 144 and 146 are in the closed position, the fasteners 180 are threaded into secure engagement with the bores 174 in the first plate 172 and the weld washers 182 are tack welded to the second plate 176 to thereby securely position the first and second plates 172 and 176 together.

The clamp 170 may be readjusted in position at any time by merely breaking the welds on the weld washers 182 and loosening the bolts 180. Adjustment via the fasteners 188 is then used to reposition the first plate 172 and the attached clamp arms 144 and 146 to the new position.

In summary, there has been disclosed a unique self equalizing clamp which automatically positions pressure feet attached to the ends of first and second pivotal clamp arms to the actual position of a workpiece despite any variations in the actual position of the workpiece from its normal, design position. This is achieved without any deformation or damage to the workpiece as is common with conventional clamps. The self equalizing clamp of the present invention is constructed of conventional components for an economical manufacturing cost. Further, the clamp may be reused in subsequent model programs, new workpieces, or with minor design modifications to existing workpieces by merely attaching a new pressure foot onto the ends of the clamp arms. The present clamp also eliminates the need to redesign the entire clamp assembly for a new application or for minor modifications to the shape of an existing workpiece.

Claims

What is Claimed is:

1. A self equalizing clamp comprising: a support; first and second clamp arms, each having first and second spaced ends and an intermediate portion between the first and second ends, the intermediate portion of the first and second clamp arms being rotatably attached to the support; pivot means, extensibly connected to the second end of the first clamp arm and to the second end of the second clamp arm, for moving the second ends of the first and second clamp arms relative to each other upon extension and retraction of the pivot means to pivot the first ends of the first and second clamp arms relative to each other between a first spaced apart position and a second closely spaced position engaging a workpiece therebetween; a pressure foot mounted on the first end of each of the first and second clamp arms; and means, coupled between the support and the second clamp arm, for adjustably positioning the first end of the second clamp arm to supportably engage a workpiece disposed between the first ends of the first and second clamp arms when the first and second clamp arms are in the first, spaced apart position; the first and second clamp arms being arranged such that adjustment of the position of the first end of the second clamp arm by the adjustably positioning means into supporting engagement with a workpiece causes a corresponding adjustment of the position of the first end of the first clamp arm relative to the first end of the second clamp arm through the pivot means such that the first end of the first clamp arm pivots about the intermediate portion thereof upon extension of the pivot means to bring the pressure foot on the first end to the first clamp arm into engagement with a workpiece at the second, closely spaced position with respect to the first end of the second clamp arm at any adjustably selected position of the first end of the second clamp arm.

2. The self equalizing clamp of Claim 1 wherein the pivot means comprises: a fluid operating cylinder having a reciprocally extensible and retractable piston rod extending therefrom; means for pivotally connecting the second end of the first clamp arm to the piston rod; and means for pivotally connecting the second end of the second clamp arm to the cylinder.

3. The self equalizing clamp of Claim 1 further comprising: a first insert carrying variably positionably mounted on the first end of the first clamp arm, the first insert carrying the pressure foot; and a second insert variably positionably mounted on the second end of the second clamp arm, the second insert carrying the pressure foot.

4. The self equalizing clamp of claim 1 wherein the adjustably positioning means comprises: a variably extendible set screw mounted in one of the support and the second clamp arm between the intermediate portion and the first end thereof and extensibly adjustably engagable with the other of the support and the second clamp arm.

5. The self equalizing claim of Claim 4 further comprising: a pivot pin mounted in one end of the support and rotatably connecting the first and second clamp arms to the one end of the support; and a flange extending outward from the one end of the support; the set screw extensibly mounted on the second clamp arm and engagable with the flange.

6. The self equalizing clamp of Claim 1 further comprising: a base, the support mounted on the base.

7. A self equalizing clamp comprising: a support; first and second clamp arms, each having first and second spaced ends and an intermediate portion between the first and second ends, the intermediate portion of the first and second clamp arms being rotatably attached to the support; pivot means, including a fluid-operated cylinder rotatably connected to the second end of the second clamp arm, the cylinder having a reciprocally extendible and retractable piston rod rotatably connected to the second end of the first clamp arm, for moving the second ends of the first and second clamp arms relative to each other upon extension and retraction of the pivot means to pivot the first ends of the first and second clamp arms relative to each other between a first spaced apart position and a second closely spaced position engaging a workpiece therebetween; a pressure foot mounted on the first end of each of the first and second clamp arms; and means, coupled between the support and the second clamp arm, for adjustably positioning the first end of the second clamp arm to supportably engage a workpiece disposed between the first ends of the first and second clamp arms when the first and second clamp arms are in the first, spaced apart position, the adjustably positioning means including a variably extendible set screw mounted in one of the support and the second clamp arm between the intermediate portion and the first end thereof and extensibly adjustably engagable with the other of the support and the second clamp arm; the first and second clamp arms being arranged such that adjustment of the position of the first end of the second clamp arm by the adjustably positioning means into supporting engagement with a workpiece causes a corresponding adjustment of the position of the first end of the first clamp arm relative to the first end of the second clamp arm through the pivot means such that the first end of the first clamp arm pivots about the intermediate portion thereof upon extension of the pivot means to bring the pressure foot on the first end to the first clamp arm into engagement with a workpiece at the second, closely spaced position with respect to the first end of the second clamp arm at any adjustably selected position of the first end of the second clamp arm.

8. A self equalizing clamp comprising: a support member; a clamp support; first and second clamp arms mounted in the clamp support and movable between open and closed positions with respect to each other; drive means, connected to at least one of the first and second clamp arms, for pivoting the at least one clamp arm between first and second positions with respect to the other clamp arm; means for slidably attaching the clamp support to the support member; and means, coupled between the support member and the clamp support, for equalizing the position of the first and second clamp arms with respect to the position of a workpiece disposed therebetween.

9. The self equalizing clamp of Claim 8 wherein the attaching means comprises: a first plate fixedly attached to the clamp support; and a second plate slidably mounted within the first plate and fixedly connected to the support member.

10. The self equalizing clamp of Claim 9 further comprising equalizing means for automatically adjusting the position of the first plate with respect to the second plate upon initial engagement of one of the first and second clamp arms with a workpiece.

11. The self equalizing clamp of Claim 10 wherein: the first plate includes: first and second flanges extending outward from opposite sides of the first plate and spaced from opposite edges, respectively, of the second plate; and the equalizing means including: biasing means mounted between the first and second flanges and the opposite edges of the second plate.

12. A clamp comprising: a support member; a clamp support; first and second clamp arms mounted in the clamp support and movable between open and closed positions with respect to each other; drive means, connected to at least one of the first and second clamp arms, for pivoting the at least one clamp arm between first and second positions with respect to the other clamp arm; means for slidably attaching the clamp support to the support member; and means for fixedly attaching the clamp support to the support member in a position for the first and second clamp arm to engage a workpiece in the closed position.

13. The clamp of Claim 12 further comprising: a first plate attached to the clamp support; a second plate attached to the support member; first and second flanges mounted on the first plate and extending therefrom in spaced relationship to the second plate; and adjusting means, connected to and extending through the first and second flanges into engagement with opposed edges, respectively, of the second plate to reciprocally adjust the position of the first plate with respect to the second plate.

14. The clamp of Claim 13 further comprising: bores formed in the first plate; slots formed in the second plate; and fasteners extendable through the slots in the second plate into the bores in the first plate to fixedly connect the first and second plates together.