US2943666A - Gripper devices - Google Patents

Description

July 5, 1960 T. a. HAWKES GRIPPER DEVICES Original Filed April 1, 1953 3 SheetsSheet 1 v S M mm 3 R m mm N A k QN Wm H m, QV m R m n um N H w mm mw & m w E Q M r M r: 1% uw m 7 z w\ Julyf5', 1960- 'r. B. HAWKES GRIPPER mavr czs 3 Sheets-Sheet 2 Original Filed April 1, 1953 INVENTOR. THU/MS BLAIR HAWKES y -196 T. B. HAwkEs 2,943,666

GRIPPER DEVICES Original Filed April 1, 1953 r v v 3 Sheets-Sheet 3 INVENTOR. 77/0MA5 BLAIR HAWKES BY WV United States Patent UfiFice 2,943,666 Patented July 5, 1960 GRIPPER DEVICES Thomas Blair Hawkes, '315 Trumbull Road, Manhasset, N.Y.

Original application Apr. 1, 1953, Ser. No. 346,164. Dligided and this application Sept. 27, 1956, Ser. No. '6 ,536

'3 Claims. (Cl. 153-48) blank or shape must be gripped so that the metal therebetween can be tensioned sufiiciently to elongate the material beyond its elastic limit, thereby imparting a permanent set thereto. In one form of stretching machine,

two sets of gripper devices adapted to clamp the ends of a the metal sheet are disposed on either side of a central table for the forming die. The table is carried on hydraulic rams Whose rise and fall are under the control of the operator. Provision is made to hold the sheet tan-. gentially to the curvature of the die and to stretch the sheet to a degree approaching the yield point on the material whereby upon release of the gripper devices the work retains the shape of the die. There are other forms of such machines, and a stretcher leveler also requires the use of gripper.

Gripper devices are usually constituted by opposing jaws which serve to clamp the end of the metal blank. When the workpieces are of Widely varying shape and size, conventional gripper devices are incapable of conforming to the contour of the workpiece, as a result of which the gripping action is uneven and certain portions of the workpiece are inadequately clamped.

Another difficulty experienced with conventional gripping devices arises from the fact that the pull of the workpiece, in the course of stretching, exerts a lateral force on the jaws, thereby tending to shift the upper jaw relative to the lower jaw. This displacement produces a mismatch of the jaws and hampers the gripping action. Furthermore, when the pressure exerted downwardly on the upper jaw is by means of a hydraulic piston operating within a cylinder, the lateral forces produced by the pull of the workpiece tend to displace the piston from its axial position within the cylinder. This displacement is injurious to the mechanism of the hydraulic apparatus and acts to score and otherwise mar the cylinder wall and the surface of the piston.

Wedge type grippers using a wedge angle adequate for good holding power, require long linear motion of the wedges. This makes a bulky, inconvenient, arrangement. The present invention provides a more compact form with the same or greater holding power.

In view of the foregoing, it is an object of this invention to provide an improved gripper device having jaws adapted efliciently to grasp bars or sheets of varying size and shape.

More particularly, it is an object of the invention to provide a gripper device constituted by an upper jaw which cooperates with a lower jaw and is adapted to assume a profile conforming to the upper surface of a metal., bla nk having a non-uniform thickness. A significant per device operates efiectively with sheets tapering in thickness from one side to the other, or whose edges are warped and buckled. Prior art wedge or toggle type grippers do not provide a large enough jaw opening in such cases.

Yet another object of the invention is to provide a gripper device having interengaging upper and lower jaws adapted to resist lateral stresses tending to displace the jaws. Another salient feature of the invention is that the jaw construction is such as to isolate the verticallyoperating hydraulic system from lateral forces whereby the axial position of the piston is maintained under exceedingly heavy workpiece tension conditions.

For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description to be read in connection with the accompanying drawings wherein like components in the several views are identified by like reference numerals.

In the drawings:

Fig. 1 is an elevational view of a stretch-forming main which a modified form of gripper device is shown;

feature of the invention resides in the fact that the grip- Fig. 6 is an elevational view, partly broken away and partly in section of the gripper device of Fig. 5;

Fig. 7 is an enlarged detail view, shown in elevation,

partly in section, of the lower hydraulic piston and its pivotal connection to the upper movable jaw of the modified form; I

Fig. 8 is a detail view in elevation of the lower portion of the lower piston of the modified form; and

Fig. 9 is a side elevation of Fig. 8. Referring now to the drawings and more particularly to Fig. 1, a stretch press including gripper devices in accordance with the invention comprises a die table 10 for supporting a die 11 of suitable shape. Table 10 may be raised or lowered in position by means including a hydraulic ram, reciprocal in a cylinder 12 and controlled by an operator from an instrument console.

The table 10 is located between two gripper devices,

generally designated by numerals 13 and 14, and'includ ing hydraulic cylinders 15 and 16, the devices being designed to engage and hold opposite ends of a workpiece. Gripper devices 13 and 14 are mounted on carriages 17 and 18, and are tiltable thereon about respective pivot pins 19 and '20 by means of tilting motors 21 and 22. Also provided for the carriages are lead screws 23 and 24 for adjusting the position of the gripper devices longitudinally with respect to the die table. Other arrangements may be used, such as hydraulic cylinders.

In operation, a workpiece is supported over the die 11 and held along its opposite side edges by gripper devices 13 and 14. This workpiece is pulled and set permanently in its desired shape by applying tension increasing to a point where at least portions of the material are under tensile stresses between its yield point and its ultimate breaking point. This operative condition is achieved by restraining or holding the opposite edges of the workpiece, or pulling on said edges in opposing directions through the powered movement of the gripper de-.

it to swing 'vertically about the axis .of ther.pin which is;

parallelito. thel'gripper jaws.:-

Seated;on' .anvil 1.26 Z'is a lower fixed. jawpiece 27. in. theform of'racontinuous banext'ending substantially the. 1 The front face of jaw piece.

full length of the anvil. 27- is 'aligned-iwithmthelfront. face ofv anvil' 26 .but .the width of the jaw piece is smallerthan that. of the anvil whereby a channel. 28;is defined between the rear. face of jaw piece 27 and the. adjacentwallof jaw head 25. To secure the jaw piece against displacement with respect to anvilr'26,'. .the:under.:snrface ()fithfl jaw piece and .the upper surface .:of .the;.anvil;.'are'= provided :with. complementary serrations: The lower jaw27 isv affixed to. anvil.

26 by means such: as screws 29.

Formed in-jawrpiece 27 is a recess extending the full length thereof for: accommodating .a series of wearplate inserts :30 at equally spaced positions .therealong. Co-:

operatively arranged with respect to the lower jaw piece 27 is a movable upper jaw piece 31 in the form. of..a continuous bar extending the full length of jaw head 25 and provided with 'a longitudinally extending recess 32 for accommodating a series of aligned wear plate .inserts 33 at positions corresponding to that of inserts 31 in the lower jaw'piece and cooperating therewith to grip the margin of a workpiece W-Pto be stretched and shaped over the die. This workpiece may be in-the form of a metal sheet or bar of uniform or varying shape and contourv asheretofore explained. The'upper inserts 33 are retained in the upper jaw piece by means such as:

screws 34. 1

The movable upper jaw piece 31 is provided with a lip 35 depending downwardlytherefrom and dimensioned for insertion in the channel 28 behind the lower jaw piece, whereby the. front'face of the lip abuts the rear face of the lower jaw piece 27. Lip 35 serves as a guide and stopfor aligning-the edge of the workpiece 33 or any other workpiece to be gripped and stretched. The lip functions s also to prevent relative. stress and lateral movement in-the direction ofpull during the stretching operation as-between the upper and lower jaws.

To effect downward movement of the upper jaw 31 so as to clampthe workpiece for stretch-forming, and subsequent upward movement'to release the stretched workpiece, a row or bank of main hydraulic pistons 36'is provided, each of which is reciprocable in respective cylinders 37 bored in jaw head 25.

The upper jaw piece 31 is secured to the lower end or stem of the main pistons and against the rear face of a shoulder 38depending therefrom by means of studs 39. These studs pass through oversize holes 40 in'said shoulder 'and are threadedly received in the upper jaw piece. T heupper-jaw piece-31 is of deformable metal and r the holes:40 are somewhat larger in diameter than the studs-39ythus affording the necessary clearance for relative movement or: playbetweenzthe jaw piece and the pistons. It :is important to'tnote .that the. lip 35 which engages the'arear face of the lowerjaw 27 not only acts to-'prevent=-relative movement of the jaw piece but also functions to avoid "lateral displacement of the pistons against the wall-of the cylinder; Thus the lateral pull pressed..npon.the.. dependingv .lip, but. is kept. away. .from

the cylinder, which effect materially improves the hydraulic action. This lip also acts as a locator when inserting sheet or bar stock.

To hold the workpiece W-P tangentially to the sides of the die as it is being stretched and shaped, there is connected to the jawhead 25 a nose-piece 41 extending substantially the full length' thereof. Nose-piece 41 is attached to jawhead '25. 'by means such as threaded studs 42. Nose-piece 41 presents a convexly curved surface 43 under and ,against whichthe workpiece is placed, the .nose-pie'ce .serving 'as a guide to' the .metal .blank while it is brought to position. It may either be-in-the form of a single continuous bar, as shown, extending substantially the fullJ-length of. the jaw head, or it may be of sectionalized construction consisting of a series of pieces which are arranged end to end in interconnection or articulated.

A row or bank of,hydraulic point units are associated with the upper jaw 31 of the gripper device, each unit including, as, already indicated, a main piston 36 reciprocable in a cylinder bore 31 formed injaw head 25. In accordance with the invention these power units are designed to be hydraulically actuated in a manner whereby initially a relatively lowpressure is applied and'thereafter, a much higher or intensified pressure is applied to develop the necessary gripping forces.

For this purpose, each of cylindrical bores 37 is enclosed at its upper end by a cylinder head 44 which in turn is surmounted by an intensifier cylinder 45 in axial alignment with the lower cylinder bore. Intensifier cylinder 45 is closed at its top by a second cylinder head 46. Cylinder head 44 and intensifier cylinder 45 are connected together and to jaw head 25 by studs 47.

Cylinder head 44 defines a hydraulic pressure chamber 48 enclosed by the top of main piston 36 and the side wall of the cylinder. Cylinder head 44 has a bore therethrough for the reciprocation therein of an intensifier piston rod 49, the lower end of which has a cylindrical flange 50 extending into a counterbore 51in the piston 36 for reciprocating movement therein. of piston rod 49 is connected to an intensifier piston 52 reciprocable in intensifier cylinder 45. The upper end of counterbore 51 is partially enclosed by a cap 53 secured to main piston 36 to provide an abutment for the intensifier piston flange 50 by which'said flange is able to lift the main piston and thereby lift the upper jaw 31 during certain phases of operation.

Flange 50 is smaller in diameter than counterbore 51 to define an annular passage 54 for the escape of working liquid therethrough. The hole in the cap 53 through which the intensifier rod 49 passes is slightly larger in diameter than said rod, thus providing annular clearance 55 around said rod for flow communication with the interior-of counterbore 51 and hydraulic pressure chamber 37. Means including pipe 56 are provided to feed fluid into the intensifier chamber above the intensifier piston 51. Means including pipes 57 are provided to feed fluid below intensifier piston 52 in the intensifier chamber. Means including pipe 58 are provided to feed fluid above main piston 36 in the main hydraulic chamber.

Asdisclosed in greater detail in the copending application, the main and intensifier cylinders act in conjunction with a hydraulic fluid reservoir and valve system whereby the main cylinder functions to move the upper jaw into engagement with the lower jaw to grip the workpiece. Means are provided which automatically are operable when the movement of the main piston is arrested upon engagement of the movable jaw with the workpiece for intensifying the hydraulic pressureacting on the main piston to enhance the gripping force of the jaws.

In the embodiment of the invention shown in Figs. 5 to 9, the hydraulic actuation system for the jaws may be substantially identical to that shown in Fig. 1, savefor The upper end the structure of the main piston. Hence this hydraulic system is omitted in Figs. 5 to 9 except for the main piston and its linkage to the upper jaw of the grippers. Basically the difference between the gripping devices in Figs. 1 and 5 is that in the latter the upper jaw structure is sectionalized.

Referring now to Figs. 5 to 9, each of the gripper devices is provided, as in the case of Fig. 1, with a jaw head 25 from which projects an anvil 26 on which is seated a lower fixed jaw piece 27 in the form of a continuous bar extending the full length of the anvil and coated thereto by means of serrations. Screws 29 serve to hold the lower jaw piece 27 in firmly locked relation with the anvil 26.

In place of the spaced inserts shown in the embodiment of Fig. 1, there is provided a continuous bar or wearplate 60 extending along the full length of the low jaw piece, the wearplate being secured to the jaw piece by screws 61. The wearplate has its gripping surface roughened or serrated as at 62 to afford a more positive grip on the blank W-P.

The upper jaw structure is constituted by an assemblage of movable upper jaw sections 63. The movable upper jaw sections receive the motive power from a row of hydraulic main pistons 64, each piston having an upper jaw section 63 depending therefrom. The upper jaw sections are pivotally mounted on the lower end of the pistons in a manner affording enough play or free swinging movement to effect alignment with respect to that part of the marginal surface which is to be gripped. Each of the upper jaw sections are hydraulically and separately actuated so as to give a uniform and direct gripping pressure between the upper and lower gripping jaws, even though the workpiece is tapered, bent or irregular along its marginal surface to be gripped. In other words, the sectionalized upper jaw is caused generally to assume the configuration of the marginal surface of the workpiece.

The main piston 64 is reciprocal in the hydraulic cylinders 37 formed in the jaw head 25. The upper jaw sections 63 which constituted the upper jaw assembly extend substantially along the full length of the jaw head 25.

The upper jaw sections 63 of each gripper device are pivotally secured to the lower ends of the pistons 64 by headed steel pins 65. The piston 64 is provided at its lower end with a centrally located arcuate projection or rib 66, the rib being dimensioned so as to fit freely into a similarly shaped recess formed in the upper jaw section to provide a seat 67. The seat 67 is flanked by a pair of ears 68 and 69, each car being apertured to receive the shank of a stud pin 65 which also passes through an oversized hole 70 in the rib 66. The aperture in car 69 is threaded to receive the threaded end of the pin 65. The arcuate rib 66 and the arcuate seat 67 are of the same radii and are adapted for sliding engagement, thereby coating with the loose-fitting hole to provide a loose pivotal connection.

In order to reduce friction during the gripping action between the rib 66 and its mating seat 67, the center portion of the rib is relieved centrally, leaving two spaced arcuate lands 71 and 72 to bear on the seat. From this arrangement it will be evident that the pressure transmitted to the upper jaw section and its serrated insert 73 will be through the arcuate seat. The function of stud pin 65 is for the purpose of retracting the upper jaw sections upon opening the grip of the jaws and to permit the loose pivotal movement of the upper jaw section. To permit this movement, operating clearances 74 are left between adjacent jaw sections.

The gripping inserts 73 are received in recesses in the lower surface of each of the upper jaws and are held therein by screws 75. Each upper jaw section has a depending lip portion 76 which is received in a channel behind the low jaw piece and operates to keep all of the sections in alignment. The lip portions, as previously described, prevent lateral displacement of the jaws.

While there has been shown what is considered to be a preferred embodiment of the invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims to cover all such changes and modifications as fall within the true scope of the invention.

I claim:

1. In a power press for stretch forming metal blanks of widely varying shape and size, a gripper device for clamping one edge of said blank and comprising a pair of cooperating jaw structures for holding the blank therebetween, one of said structures being movable relative to the other and being constituted by a continuous rectilinear bar of resilient material adapted when clamped on the metal blank to flex so as to assume a profile conforming to the surface of the blank engaged thereby, said movable jaw structure being provided at its rear side with a depending lip portion adapted to set down in back of the other structure to resist displacement of said jaws when said blank is subjected to stretching forces; and apparatus for applying gripping pressure to said movable structure comprising a row of independent power units formed by hydraulic mechanisms and extending along said movable jaw structure, and means loosely coupling each unit to said movable jaw structure to permit said structure to assume the desired profile when pressure is applied thereto.

2. In a power press for stretch forming metal blanks I of widely varying shape and size, a gripper device for clamping one edge of said blank and comprising a pair of cooperating jaw structures for holding the blank therebetween, one of said structures being movable relative to the other and constituted by a continuous rectilinear bar of resilient material adapted when clamped on the metal blank to flex so as to assume a profile conforming to the surface of the blank engaged thereby, said movable jaw structure being provided at its rear side with a depending lip portion adapted to set down in back of the other structure to resist displacement of said jaws when said blank is subjected to stretching forces, and apparatus for applying gripping pressure to said movable structure comprising a row of hydraulic cylinders extending along said movable structure, a piston reciprocable in each cylinder and having a shoulder projecting longitudinally from one end thereof, said bar being seated against the end of said pistons and laterally against the shoulders thereof, and means loosely coupling said bar to said shoulders to permit said bar to flex with respect to said shoulders and into conformity with the surface of the blank engaged thereby.

3. In a power press as set forth in claim 2 wherein said loose coupling means are constituted by studs conmeeting said shoulders to said bar, said studs passing through oversize bores in said shoulders, whereby said bores provide clearance permitting relative movement between the bar and the shoulders.

References Cited in the file of this patent UNITED STATES PATENTS 153,133 Van Wagoner July 14, 1874 656,966 Gregory Aug. 28, 1900 878,491 Barker Feb. 11, 1908 2,218,503 Brooks et al. Oct. 22, 1940 2,342,437 Summers Feb. 22, 1944 2,378,413 Lermont et al. June 19, 1945 2,379,658 Saunders July 3, 1945 2,437,105 Lindsey Mar. 2, 1948 2,692,633 Green Oct. 26, 1954 2,696,241 Larsen Dec. 7, 1954 FOREIGN PATENTS 432,766 Great Britain Aug. 1, 1935

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