Elongated load cell and combination thereof with stretch forming machine



C. J. BATH Sept. 4, 1962 3,052,119 ELONGATED LOAD CELL AND COMBINATION THEREOF WITH STRETCH FORMING MACHINE 3 Sheets-Sheet 1 Filed Dec. 11, 1959 NN NN mN UN m mm 1 on N m r \.1 M r .u. .IIQ F I a .IL FL I 0 1 h J I Q MN NW N m? m\ QN RN a 0 W c. J. BATH 3,052,119 NGATED LOAD CELL AND COMBINATION THEREOF WITH STRETCH FORMING MACHINE 5 Sheets-Sheet 2 MN why QL M ELO Sept. 4, 1962 Filed Dec. 11, 1959 INV EN TOR. (YE/L J. BATH 44 TTOF/VEK Sept. 4, 1962 c. J. BATH 3,052,119 ELONGATED LOAD CELL AND COMBINATION THEREOF WITH STRETCH FORMING MACHINE Filed Dec( 11, 1959 :5 Sheets-Sheet 3 F Z Q5 :5 34 - INVENTOR. (we/1. 1 BATH United States Patent Ofiice Patented Sept. 4, 1962 ELONGATED LOAD CELL AND COMBINATION THEREQF WITH STRETCH FORMING MACHINE Cyril John Bath, Chagrin Falls, Ohio, assignor to The Cyril Bath Company, Solon, Ohio, a corporation of (Phio Filed Dec. 11, 1959, Ser. No. 858,967 3 Claims. (Cl. 73-141) This invention relates to a load cell and to an improved load cell and stretch forming machine combination. The copending application of Henry W. Hein, Serial No. 762,655, filed September 22, 1958, entitled Stretch Forming Machine, discloses a stretch forming machine including a rotary table and a stretch forming assemblage having an elongated arm mounted on a stretch forming carriage so as to swivel about an axis parallel to the axis of the turntable. The arm extends from its pivotal axis toward the turntable. The carriage is yieldably urged by hydraulic pressure means in a direction away from the table to impart a tensioning force to a length of stock which is connected at one of its ends to the free end of the arm and at the other of its ends to the table for rotation therewith. This elongated arm structure not only has advantages in connection with the stretch forming machines themselves but affords an opportunity for providing a load cell and stretch forming machine combination in which the load cell is subjected substantially only to tensioning forces applied endwise of the .arm in the various positions in which the arm happens to be swung about its pivotal axis during the stretch forming operation. To a limited extent, advantage was taken of this structure as more fully disclosed in a copending application of Perkins and DeMarco, Serial No. 858,376, filed December 9, 1959, and entitled Load Cell and Combination Thereof With a Stretch Forming Machine. In accordance with the present invention, such a stretch forming structure and a load cell are further modified and combined so that total elongation of the cell can be obtained which is so great in relation to the tension force applied to the stock that it can be reflected as an adequate electrical control signal by the conventional, relatively inexpensive, and less sensitive and delicate types of signal devices, such as a transducer, or as a more direct signal by fluid or hydraulic pressure generators operated directly by the load cell through mechanical connections thereof with the generator. In some cases, the signal is sufficiently large to be applied directly as the motivating force to servo-motors or control valves and the like of the stretch forming assemblages for operating them without the interposition of electrically operated amplifiers. Various other objects and advantages of the present invention will become apparent from the following description wherein reference is made to the drawings, in which: FIGS. 1 and 2 are a top plan view and a side elevation, respectively, of a load cell and stretch forming machine combination embodying the principles of the present invention; FIG. 3 is a side elevation of the load cell of the present invention; FIG. 4 is a horizontal sectional view taken on a line 44 in FIG. 3; FIG. 5 is a vertical sectional View taken on the line 5-5 in FIG. 4; and FIG. 6 is a combined hydraulic and control diagram of the present invention. As more fully described in the above identified copending applications, the machine comprises generally an elongated frame 1 on which a turntable 2 is mounted on a post or pedestal 3 for rotation about an upright axis. The table carries a ring gear 4 which is driven by a suitable pinion gear 5, the pinion gear 5- being driven, in turn, by a speed reducing gear transmission 6. The transmission 6 is driven by a hydraulic motor 7 .and to which pressure fluid is supplied by a hydraulic pump 8 driven by an electrical motor 9. Mounted on the frame 1 for movement relatively toward and away from the table is a stretch forming assemblage 10. The assemblage includes a carriage 11 which is supported by suitable rollers 12 and 13 on trackways 14 and 15 on the frame. Connected to the carriage for movement therewith is a hydraulic cylinder 16 in which a double-ended piston 17 is operable, the piston having rods 18 and 19, respectively, which are fixedly connected to the frame at opposite ends thereof. The cylinder 16 is connected to the carriage 11 for movement therewith endwise of the frame. Pressure fluid for operating the piston and cylinder assemblage so as to yieldably urge the carriage 11 in a direction away from the table at the required tensioning force is provided by a hydraulic pump 20 driven by an electric motor 21. The pressure side of the pump 20 is connectable to the ends of the cylinder 16, selectively, by a conventional valve 22, and the opposite end in each instance is connectable thereby to a sump. The valve 22 may be remotely controlled by a suitable solenoid 23, if desired. Mounted on the table 2 for rotation therewith is a side face die D about which the stock S is to be stretch formed. A clamp 24 is fixedly secured on the table in a position for movement with the table in fixed relation to the die and is adapted to grip one end of the length of the stock S for movement of that end with the table as the stock is wrapped onto the die. As described in the above entitled copending application of DeMarco and Perkins, the stretch forming assemblage 10 includes an elongated arm 25 which is connected at one end to a sleeve 26 in which an upright post 27 on the carriage is received for supporting the arm for swinging about an axis 28 parallel to the table axis. The arm 25 extends from its pivotal axis 28 toward the table 2 and is elongated toward the table. The free end of the arm, remote from the axis 28, rests on skid pads 29 arranged on the carriage and on the underside of the free end portion of the arm 25, respectively. Mounted on the free end of the arm 25 is a stretch forming head 30 adapted to grip the end of the length of stock S opposite from the end gripped by the clamp 24 for applying yieldable tensioning force to the stock, endwise of the stock, in opposition to the pull exerted by the table 2 during rotation of the table. The structure thus far described is essentially the structure described in the above copending application of DeMarco .and Perkins, the present invention residing principally in the type of load cell, the manner in which the arm 25 is connected thereto, and the manner in which the arm effects cooperation of the load cell with the machine so that the machine can be controlled more effectively. Referring to FIGS. 3 through 5, the arm 25 is composed of two relatively telescoped portions 32 and 33, respectively, so arranged that they can move endwise relative to each other to extended or retracted condition. All forces, except those tending to move the member 32 endwise lineally with respect to the member 33, are reduced to a minimum. This is partially accomplished by connecting the members 32 and 33 together for relative movement at remote points along their lengths, for example, near the front and rear ends of the member 32. The connection may comprise four bolts 34 and four bolts 35, arranged one of each near each of the corners of the member 32. Each bolt 34 is Connected in the same manner as each other bolt 34 and each bolt 35 is connected in the same manner as each other bolt 35, hence only one of each will be described. Referring to FIG. 5, specifically, the bolt 34 is provided at one end with a head 36 and at the other end 37 is threaded. The bolt 34 extends through a suitable passage 38 in the arm 32, through a passage 39 in the member 33 and another passage 40' in the lower passage of the member 32 and is screw threaded by its lower end 37 to the arm 33. This bolt is drawn tightly so that through the interposition of a washer 411 between the head 36 and the member 32, the member 32 is urged downwardly. Each bolt 35, on the other hand, is provided with a head 43 and extends through a suitable passage 44 in the upper portion of the member 33 and thence downwardly to the lower port-ion of the member 32 at which point the screw threaded end 45 of the bolt 35 is connected to the member 32. By virtue of engagement of the head 43 with an interposed washer 46 between it and the member 33 and the screw threaded engagement at the end 45 with the member 32, the bolt 35 yieldably urges the member 32 upwardly. Thus there are four bolts pulling the member 32 upwardly at its four corners with respect to the member 33 and there are four bolts also tending to pull the member downwardly relative to the member 33. Thus the member 32 is suspended by tension rods in telescoping relation to the member 33 but can move readily endwise a short distance while resisted only by transverse flexure of the bolts 34 and 35. As mentioned, it is desirable that the member 32 move axially only and be constrained from lateral movement and that the load cell be relieved from stresses directed laterally of the member 32. For this purpose, a plurality of tie rods 47 are connected to the member 32 and extend through the side walls of the member 33. These rods are drawn tightly so that the member 32 is constrained thereby from movement transversely relative to the member 33, as any force tending to pull the member 32 transversely of the member 33 is resisted by direct axial tension of the members 47. However, the member 32 can move endwise relative to the member 33 by transverse fiexure of the various supporting rods and tie rods. Since the movement of the member 32 is quite limited, these rods offer negligible resistance to the movement of the member 32 lengthwise relative to the member 33 within the limits in which the movement must take place. It is desirable to obtain a large signal and advantage is taken of the particular structure in which the arm is mounted to swing about the post 27 a remote distance from the head 30 and is elongated endwise. To take the full advantage of this arrangement, a load cell or strain element 50 is provided which extends substantially the full length of the arm 25. This load cell is connected at its forward end by a tie pin 51 to the member 32 and at its other end is connected by a tie pin 52 to the member 33. Thus, the strain element or load cell member 50' is the only structure affording resistance to the movement of the members 32 and 33 to relatively extended position with respect to each other except for the negligible resistance to movement imposed by the flexure of the rods. It is desirable that the member 50 be free from any contact with the members 32 and 33 except where it is connected to them at the ends, as otherwise highly concentrated binding forces would be developed. For this purpose, the member 32 has a central portion of a box like formation provided by cutting away a part of the web of the member 32 and connecting the severed portions by side plates 54 which are welded fixedly to opposite faces of the web of the member 32. Advantage thus is taken of the elongated arm and the combination of the stretch forming machine afforded thereby to use an exceedingly long tension element as a load cell 50. For example, in the form illustrated, the tension element may be thirty-two to thirty-six inches long even in a moderate size stretch forming machine, and have a sensing portion, of smaller cross section than the end portions, about twenty-nine to thirty-two inches long. Such a bar, for example, under the stresses to which it is to be subjected, can be elastically deformed .058 of an inch in elongation repeatedly without suffering any appreciable deterioration. Such a movement, however, affords a very broad signal, so broad, in fact, that the highly sensitive patch type strain gauges are not necessary. Instead, a relatively cheap and inexpensive transducer or air or hydraulic or electrical signal device may be used for obtaining a signal or for obtaining the necessary power to control the tension supplied to the stretch forming cylinder without the interposition of electrical amplifying equipment. Also, the resistance of the various rods 34, 35, and 47 in flexure is negligible within these limits of movement by elongation. In the form illustrated, a signalling device is indicated at 55. It may be a transducer of any of the well known types or a bellows which is extended or contracted in accordance with the extension and contraction of the tension element or load cell 5t Whichever type of signalling device is used, it requires relatively movable portions. In the example, two movable portions are used, one of which, indicated at 56, is anchored to the member 33 and the other of which, indicated at 57, is anchored to the member 32. Thus the extension of the members against the resistance of the load cell results in a movement between the portions 55 and 57. If these portions are connected to a bellows so as to extend the bellows upon extension of the members 32 and 33, or to a transducer in which the core is connected to the portion 57 and is withdrawn partially from a coil connected to the member 56 upon extension of the members 32 and 33, a signal is given which is adequate to control the tension. Referring to FIG. 6, it is assumed that the signal is provided by pressure supplied by a bellows. In such case, the bellows is connected by a suitable small diameter tube 58 to a hydraulically operated servo-motor 59. The servo-n1otor is connected to, and operates, a variable pressure relief valve 6% which is connected between the pump 22 and the end of the cylinder 16 which is to urge the carriage 11 in the direction away from the table for tensioning the stock. Thus the valve is operated by the pressure from the bellows. If the tension becomes too great, then the bellows is operated by the portions 56 and 57 to deliver a degree of hydraulic pressure, positive or negative, to the servo-m0tor 59 which thereby is operated and 0perates the 'valve 60- to reduce the stretch forming pressure in the cylinder 16. Conversely, if the tension becomes too low, the bellows returns to original position, causing the servo-motor to move the variable relief valve to a position to increase the stretch forming pressure. As in the above copending application of DeMarco and Perkins, a suitable valve 62, operated by solenoids 63 for purposes of remote control, is interposed between the pump 22 and the cylinder 16 with the pressure relief valve interposed between the valve 62 and the cylinder 16 so that, by manipulation of the valve 62, the cylinder 16 can be rendered operative to move the carriage 11 toward or away from the table or to lock the carriage in any position desired hydraulically. In case the signalling device 55 is a transducer, the core may be connected to the portion 57 and the coil connected to the portion 56 and a signal can be derived therefrom which, with little or no amplification, can be delivered to an electric control motor 59 which, in such case, would be responsive to the electrical signal thus provided by the transducer. The important feature of the invention resides in the arrangement by which an extremely long tension sensing element can be provided in a stretch forming machine while maintaining a proper relation of the operating parts in the machine and while reducing the stresses very great- 1y. While the members 32 and 33 forming the arm 25 are shown as connected together by the tension rods, they may be telescopically arranged with respect to each other in contact with fair results where too great an accuracy is not required. This is true because, due to their great length, the mechanical advantages of the tensioning forces over those resisting binding at the corners due to lateral deflection, are very great, thus greatly reducing the tensioning component of force required to overcome friction and swing the arm. The words horizontal, vertical, and the like are used in the description and claims as convenient reference planes for describing the relative positions of the parts, and not as absolutes. Having thus described my invention, I claim: 1. A load cell comprising a pair of elongated rigid arm members, tension isolation supporting means connecting the members together at spaced locations along their lengths in telescopic and laterally spaced parallel relation to each other and constraining the members from movement relative to each other in all directions transversely of the lengths of the members while permitting relatively free movement relative to each other for short distances, lengthwise of the members, an elastically deformable tension strain element operatively connected at its ends to the members, respectively, so as to be elastically deformed lengthwise of the members upon said movement of the members lengthwise in one direction, means at the ends of the members, respectively, for connecting the members to force applying members so as to urge the members lengthwise relative to each other in said one direction, said tension isolation supporting means comprising a plurality of elongated, relatively stiif, tensioning elements arranged in groups, one group near each end of the telescoped members, the elements of each group extending generally transversely of the length of the members, each element being operatively connected at one end to one of the members and at the other end to the other of the members, said elements being preloaded for applying axial tension directed transversely of the members in directions such that the components of tensioning force of the elements of each group hold the members in tensioned equilibrium transversely of their lengths in the laterally 5 spaced parallel relation of the members and constrain the members from substantial relative movement transversely of their length under components of force extraneously applied to one of the members transversely of the length of the members, each element having negligible resistance 10 to flexure a slight distance transversely of its axis, one end of the strain element being connected to that end of the first elongated arm member which is at one end of the support, the other end of the strain element being connected to that end of the second elongated arm member which is at the other end of the support, and a signal producing device responsive to the elastic deformation of the strain element endwise of the arm members. 2. A load cell according to claim 1 wherein the signal device has two relatively movable parts connected to the members, respectively, for movement therewith relative to each other and operable, when so moved, to generate a signal, and means for transmitting the signal to a control device. 3. A load cell according to claim 2 wherein the signal device is a transducer having one part connected to one of the members and the other part connected to the other of the members. References Cited in the file of this patent 3 UNITED STATES PATENTS 1,580,430 Gaines Apr. 13, 1926 2,844,027 Davie July 22, 1958 2,849,048 Curtner Aug. 26, 1958 FOREIGN PATENTS 887,695 France Aug. 16, 1943 74,057 Holland Feb. 15, 1954 OTHER REFERENCES Aircraft Engineering, January 1952, page 5. (Copy in 73-141.)



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    Publication numberPublication dateAssigneeTitle