US3302437A - Tension control - Google Patents

Description

Feb.

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United States Patent 3,302,437 TENSION CONTROL Stanley M. Dolney, Pal-ma, Ohio, assignor to The Cyril Bath Company, Solon, Ohio, a corporation of Ohio Filed June 22, 1964, Ser. No. 376,751 4 Claims. (Cl. 72-296) This invention relates to a prestretch fixture on a combination of such fixtures with a draw die press, particularly to a tension control for controlling the tension applied to the stock by the stretching fixtures.

The present invention is an improvement on the structure shown in US. Letters Patent No. 3,116,780, issued January 7, 1964, Cyril J. Bath, inventor.

The object of the invention is to provide means for measuring the tension being applied to the stock during the combined stretching operation and drawing of the stock by closure of the dies.

Further objects and advantages will become apparent from the following description wherein reference is made to the drawings, in which FIGURE 1 is a front elevation of a draw die press with pre-stretch fixtures of the present invention installed therein;

FIG. 2 is a fragmentary top plan view of one end of the prestretch fixtures partly in section;

FIG. 3 is a vertical sectional view of the structure of FIG. 2, and is taken on the line 3-3 in FIGURES 2 and 4, part thereof being shown in section for clearness in illustration;

FIG. 4 is a horizontal sectional view of part of the structure illustrated in FIGURE 3, taken as indicated by the line 44 in FIG. 3;

FIG. 5 is a vertical sectional view of the structure illustrated in FIG. 3, taken on line 5-5 thereof;

FIG. 6 is an enlarged fragmentary sectional view of part of the structure illustrated in FIG. 5; and

FIG. 7 is a schematic hydraulic and wiring diagram showing the control of the press and the control of the stretch heads and the relation of the tension control means thereto.

Referring to the drawing, the invention is shown as incorporated in a conventional hydraulic press, indicated generally at 1, comprising a bed 2 with upright guide posts 3 arranged at the corners and guiding a ram 4 for vertical movement toward and away from the bed. The bed 2 supports a male drawing die 5 and the ram supports a complementary female drawing die 6. The dies 5 and 6 are conventional drawing dies which define, when closed, a concavo-convex pattern or patterns into which the metal is drawn by the closure of the dies.

The ram is driven on its forming and return strokes by means of a hydraulic piston and cylinder assemblage indicated generally at 7, comprising cylinders 8 with pistons 9 therein and having piston rods 10 secured to the ram. Mounted on the bed 2 is a prestretch fixture, indicated generally at 11, which comprises two units 12 arranged on the bed 2 between the post 3, one unit at each end of the male die 5. Since the units are the same in form and function, only one unit 12 will be described in detail.

Referring particularly to FIGS. 2 through 6, each unit comprises a base plate 13 on the ends of which are mounted guide supports 14 which support upright guides 15. Each guide 15 has upright slide surfaces 16 facing inwardly of the unit in a direction forwardly and rearwardly of the bed, and upright guide faces 17 at right angles to the surfaces 16. Mounted for vertical reciprocation in the slideways is a stretch head elevator 20 which is guided thereby for movement upwardly and downwardly while the elevator itself remains parallel to its starting position.

For moving the elevator 20 upwardly and downwardly, suitable piston and cylinder assemblages 21 are provided, one at each end of the elevator. Each assembladge comprises a cylinder 22 mounted in fixed position on the sup port 14. A piston 23 is reciprocable in the cylinder and has a piston rod 24 which is connected to a plate 25 on the elevator 20. Thus, upon introduction of the hydraulic pressure fluid to the head ends of the assemblages 21, they move the elevator 20 upwardly, and by introduction of the fluid to the rod end of the cylinders, they pull the elevator 2t) downwardly. These movements are under yieldable hydraulic pressure and controllable independently of the operation and control of the ram piston and cylinder assemblages 7.

In order to stretch the stock into -a range above its elastic limit independently of the dies, suitable gripper heads 30 are provided, one for each unit 11. Each head comprises an elongated body 31 which, endwise, extends forwardly and rearwardly of the press bed, and thus transversely of the direction in which the stock is to be tensioned. Each head has complementary gripping jaws 32 and 320 which are cooperable with cam surfaces 33 and 33a, respectively, so that when the jaws are moved toward the dies they grip the stock firmly. Each pair of jaws extends substantialy the full length of the head.

In order to close its jaws, each head is provided with a plurality of cylinders 36 in which pistons 37, having piston rods 38, are reciprocable. The rods 38 are connected by enlarged heads 39 to the jaws 32 and 32a for causing them to move along the cam surfaces 33 and 33a toward and away from the dies for opening and closing the jaws. A plurality of such piston and cylinder assemblages are provided, six being employed in the form illustrated. A common manifold 41 is connected by individual ducts 42 to the rod ends of the cylinders 36, by individual ducts 43 through suitable connections 44 to the head ends of the cylinders 36. Thus all jaw operating piston and cylinder assemblages can be operated concurrently.

As mentioned hereinbefore, it is desirable that each head 30 be arranged so that it can move toward and away from the dies under the yieldable resistance of the hydraulic stretch forming pressure, without binding and with a minimum or negligible amount of frictional stresses. For this purpose, each head 30 is mounted on a carriage 50 which is mounted on the elevator 20 for movement relative tothe elevator toward and away from the adjacent ends of the dies in a horizontal path.

In order to so mount the carriage 50 on the elevator 20 while maintaining it under the yieldable restraint of the hydraulic stretch forming pressure, a stretch forming assemblage 52 is mounted on the elevator 20. The assemblage 52 is shown as a bank of cylinders 53. The cylinders 53 are supported by trunnions 54 for rocking about a horizontal axis extending lengthwise of the gripper head. The trunnions 54 are rockably supported in suitable bearings 55 which are rigid with the elevator 20.

Each cylinder 53 carries a piston 60 with a piston rod 61. The rods extend generally horizontally and each has an eye 62 at its outer end by which the rod is pivotally connected by a pivot 63 to an associated rocking link 64, three of which are used with six cylinders 53. The links 64 are arranged approximately upright and at their lower ends are provided with pivots 65. The pivots are mounted in suitable bearings 66 on the elevator 20, for rocking about a common pivotal axis. As mentioned, in the form illustrated, three links are provided for each unit.

At their upper ends, the links 64 carry pivots 67 by which they are connected to suit-able bearing portions on the carriage 50 for rocking relative thereto. The pivots 63, 65 and 67, and also the trunnions 54, are horizontal and parallel to each other.

At that edge of the elevator 20 adjacent the dies, the elevator is provided with upwardly facing horizontal trackways 70. The trackways extend toward and away from the dies. The carriage 50 is provided with rollers 71 which normally rest on the trackways 70, respectively.

The carriage 50 is free to rock about the axis of the pivots 67.

In addition to the foregoing structure, which is described in the above identified Bath patent, an additional pair of piston and cylinder assemblages 75 are provided. Each assemblage 75 includes a cylinder 76 in which is reciprocal a piston 77, having a rod 78. The rods 78 are connected to the carriage 50 and are operable by operation of the assemblages to urge the carriage downwardly on tracks, or to rock the carriage upwardly about the axis of the pivot 67 when such appears desirable in forming the stock.

Thus the assemblages 75 can control the rocked position of the carriage about the axis of the pivot 67 above horizontal at all times.

In the Bath patent, the gripper head was mounted on the carriage in fixed position relative thereto for movement with the carriage.

The structure thus far described is disclosed in the patent and does not embody the present invention.

In accordance with the present invention, and as best illustrated in FIGURE 6, the gripper head 30 is mounted on the carriage for limited horizontal movement relative thereto toward and away from the dies. For this purpose the gripper head 30 is mounted on a base 80 which, in the form illustrated, is composed of two plates 80a and 80b. The base 80 is held in position on the carriage 50 by means of a series of bolts 81 and carries spool keepers 82. The bolts extend through bores 83 in the base 80. The spools 82 fit the bores 83 with slight radial clearance and thus permit the base 80, and thereby the head 30, to move a small fraction of an inch along the top of the carriage 50 toward and away from the dies. The base 80 is also connected to the carriage 50 with similar bolts 84 and spools 85 arranged at the forward end to the carriage 50. These spools likewise permit a slight movement of the base 80 toward and away from the dies along the carriage 50 and prevent the forward end of the base from lifting upwardly relative to the carriage 50.

In order to assure that the base can move freely on the upper face of the carriage 50, front and rear sets 86 of recirculating roller bearings are provided. These sets are arranged in two rows, one near the rear of the carriage 50 and one near the front or die side of the carriage.

Brackets 87 are mounted on the carriage 50 at the pposite end thereof from the gripping jaws. Brackets 88 are mounted on the gripper head 30 for movement therewith and with the base 80. A tension bar 89 is connected by pivots 90 and 91, respectively, to the brackets 87 and 88. The tension bar has a portion intermediate its ends which is thinner than the end portions and by which tension is measured. Sensing devices 92, in the form of strain gauges, are mounted on the tension bar for measuring the tension, which is a function of the elastic elongation of the bar. Two such tension bars 89 are connected to the head 30 and are arranged at opposite sides of the center line of the head, each preferably midway between the nearest end of the head, forwardly and rearwardly of the press, and the centerline of the head.

Generally the heaviest tension is applied by the head 30 at the beginning of the operation while the head holds the sheet in horizontal position between and clear of the dies. In such position the small fraction of an inch which the gripper head 30 moves relative to the carriage 50 is horizontal and free from any substantial friction, because the longitudinal axis of the tension bar, indicated at xx is at a level between the gripping faces of the jaws. Accordingly, the tension bar can reflect the actual tension applied to the stock. On the other hand, if the stock should slope upwardly from the gripping jaws in a direction toward the dies as the elevator is being lowered during forming the stock around one end of the die, the entire carriage 50 swings upwardly about the pivot 67 so that the tension applied by the head 30 on the bar 89 is still parallel to the upper surface of the support and parallel to the axis xx of the tension bars. Consequently, the tension is accurately reflected by the strain gauges. The weight of the base 80 and the gripping head 30 carried thereon can affect the result very slightly and usually this is not sufficient to be serious except when very great downward components are necessary for wrapping the stock around one end of the male die. Even in such cases, this effect can be offset by actuating the assemblages 75 for the proper inclining of the carriage in the direction of tension and the direct line pull on the stock.

In order to assure that the elevator 20 retains the same level at both ends, a suitable shaft 94 is mounted on the machine frame and carries gears 95 at its ends. The gears 95 are in mesh with racks 96 on the opposite ends of the elevator, so that the shaft 94 is constrained to rotate the same at both ends, thus assuring that the elevator rises and falls the same distance at each end.

Referring next to FIGURE 7, the strain gauges 92 are connected to an amplifier 97, which in turn is connected across the power source L1-L2. The amplifier 97 operates a control 98 which controls a reversible electric motor '99. The motor drives an adjustable pressure relief valve 100 according to the setting of the control 98, and thus controls the pressure in the stretch assemblies in accordance with the elastic elongation of the tension bar.

The terms Upright and horizontal where used herein and in the claims are used in a relative sense for briefness in defining relative positions and movement of various parts, and not as absolutes. The valve 100 is operated to increase the pressure to the stretching assemblage for stretching when the tension is below a predetermined amount, and to reduce the pressure when the tension rises above a predetermined amount. Valve 100 is in the pressure feed line at the reversing and stop valve of the stretch assemblies 52. Thus the tension applied by the stretch assemblages is regulated by the tension bar 89 acting through the strain gauges 92.

If desired, a strain gauge 101 may be provided on the tension bar 89 and connected through the amplifier 97 to a voltmeter 102 calibrated in total stretch forming tension applied to the bar 89. The strain gauges may be such as disclosed in US. Letters Patent No. 2,292,549, issued August 11, 1942. The circuitry for use of signals from such strain gauges is well known and is here shown broadly diagrammatically. A more detailed description may be found in US. Letters Patent No. 2,849,048, issued August 26, 1958. The important feature of the present invention is the combining of the tension bars with stretch units of a stretch-draw press.

Referring to FIG. 7, the ram piston and cylinder assemblages may be supplied with pressure fluid from a pump 104, driven by a motor 105, through a solenoid operated, spring restored, cutoff and reversing valve 106.

The other piston and cylinder assemblages may be supplied by a pump 107 driven by a motor 108. The supply to the elevator assemblages 21 is through a spring return solenoid operated cutoff and reversing valve 109, and that to the gripper cylinder 36 through a like valve 110, The supply to the stretch forming assemblage 52 is through a solenoid operated spring return cutoff reversing valve The relief valve 100, for controlling the applied tension is connected between the pump and valve 111. Pressure fluid is supplied to the assemblages 75 from the pump 107 through a spring return reversible cutofl? valve 112.

A flow regulator 113, controlled by a motor 114, is interposed between the pump 107 and the valve 199, as also is a pressure regulator 115 driven by a motor 116.

correspondingly, a flow regulator 117 driven by a motor 118, and a pressure regulator 119 driven by a motor 120 are interposed between the pump 107 and valve 112.

The stretch units being duplicates, like circuits are provided for each.

It is apparent from the foregoing description that the enefits of the desired movements and operation of the stretch heads 30 can be maintained while obtaining a signal which reflects the actual tension on the sheet, regardless of any frictional forces in the power mechanisms, carriage 50, and elevator 29. Such forces can affect the tension on the sheet and such tension is the algebraic resultant of all forces acting in the tensioning direction and this alone is reflected by the tension bars 89.

The movement of the base 80 relative to the carriage 50 is very slight with the friction free connection described and the direct tension is lengthwise of the bar at all times. Consequently no appreciable frictional forces are introduced between the sheet and tension bar.

The various flow controls, relief valves, and pressure controls can readily be adjusted and coordinated and remotely controlled automatically by control of their motors in response to the signals from the tension bars 89.

Having thus described my invention, I claim:

1. A prestretch fixture comprising a frame, a stretch head including a jaw for gripping the margin of a length of metal to be stretched, a carriage for the head, means supporting the carriage for movement in opposite directions in generally upright paths and for movement, concurrently with the movement in said generally upright paths, in opposite directions in generally horizontal paths in all positions of the carriage along said upright path, power means operable to cause said concurrent movements of the carriage, means connecting the head to the carriage for substantially free movement of the head relative to the carriage in said opposite directions in said generally horizontal paths, said power means including stretch forming power means yieldably urging the carriage in one of said directions in said generally horizontal path, and stress measuring tension =bar means interconnecting the carriage and head and extending in said one direction from the head to the carriage and operative for restraining said movement of the head relative to the carriage and for concurrently transmitting between the head and carriage the tensioning forces imposed by the stretch forming power means.

2. An apparatus according to claim 1 wherein the head and the carriage are elongated horizontally transversely to the direction of movement of the head for applying tension, and the stress measuring tension bar means comprise a plurality of tension bars spaced from each other laterally lengthwise of the head and carriage, and each bar interconnecting the carriage and head.

3. An apparatus according to claim 1 wherein the carriage is connected to the supporting means for swinging upwardly about a horizontal axis during movements of the carriage along said generally horizontal and upright paths, and supplemental power operable means are provided and interconnect the supporting means and carriage and are operable for swinging the carriage about said horizontal axis during said movements.

4. An apparatus according to claim 3 wherein means are provided to lock the supplemental power operable means for holding the carriage in different swing positions, selectively.

References Cited by the Examiner UNlT ED STATES PATENTS 2,974,708 3/1961 Perkins 7220 3,113,607 12/1963 Maize 72-296 3,116,780 1/1964 Bath a 72297 CHARLES \V. LANHAM, Primary Examiner.

L. A. LARSON, Assistant Examiner.

Claims (1)

1. A PRESTRETCH FIXTURE COMPRISING A FRAME, A STRETCH HEAD INCLUDING A JAW FOR GRIPPING THE MARGIN OF A LENGTH OF METAL TO BE STRETCHED, A CARRIAGE FOR THE HEAD, MEANS SUPPORTING THE CARRIAGE FOR MOVEMENT IN OPPOSITE DIRECTIONS IN GENERALLY UPRIGHT PATHS AND FOR MOVEMENT, CONCURRENTLY WITH THE MOVEMENT IN SAID GENERALLY UPRIGHT PATHS, IN OPPOSITE DIRECTIONS IN GENERALLY HORIZONTAL PATHS IN ALL POSITIONS OF THE CARRIAGE ALONG SAID UPRIGHT PATH, POWER MEANS OPERABLE TO CAUSE SAID CONCURRENT MOVEMENTS OF THE CARRIAGE, MEANS CONNECTING THE HEAD TO THE CARRIAGE FOR SUBSTANTIALLY FREE MOVEMENT OF THE HEAD RELATIVE TO THE CARRIAGE IN SAID OPPOSITE DIRECTIONS IN SAID GENERALLY HORIZONTAL PATHS, SAID POWER MEANS INCLUDING STRETCH FORMING POWER MEANS YIELDABLY URGING THE CARRIAGE IN ONE OF SAID DIRECTIONS IN SAID GENERALLY HORIZONTAL PATH, AND STRESS MEASURING TENSION BAR MEANS INTERCONNECTING THE CARRIAGE AND HEAD AND EXTENDING IN SAID ONE DIRECTION FROM THE HEAD TO THE CARRIAGE AND OPERATIVE FOR RESTRAINING SAID MOVEMENT OF THE HEAD RELATIVE TO THE CARRIAGE AND FOR CONCURRENTLY TRANSMITTING BETWEEN THE HEAD AND CARRIAGE THE TENSIONING FORCES IMPOSED BY THE STRETCH FORMING POWER MEANS.

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