US2819113A - Clamps with composite flexible grab arms - Google Patents

Description

Jan 7, 1958 c. H. PHILLIPS 2,819,113

CLAMPS WITH COMPOSITE FLEXIBLE GRAB ARMS Filed 001;. 8, 1953 2 Sheets-Sheet l INVENTOR CLIFTON H. PBILLIPS HIS ATTORNEY Jan. 7, 1958 c. H. PHILLIPS 2,819,113

CLAMPS WITH COMPOSITE FLEXIBLE GRAB ARMS Filed Oct. 8, 1953 2 Sheets-Sheet 2 CLIFTON H. PH ILLIPS BY: HS ATTORNEY United States CLAMPS WITH COMPOSITE FLEXIBLE GRAB ARMS Application October 8, 1953, Serial N 0. 384,867 1 Claim. (Cl. 29487) This invention relates to clamps having a pair of grab or gripper arms that extend forwardly in spaced relation from a pair of supporting, relatively shiftable clamp brackets such as are used, for example, in industrial lift trucks having side-shifting clamps. More particularly, the invention relates to clamps the arms of which are flexible to adapt them for engaging objects of different shapes or outlines, for gripping such objects by frictional forces that are distributed over the areas of contact.

For convenience, the invention will be described with reference to a specific embodiment applied to an industrial lift truck having side-shifting clamp brackets and grab arms that extend horizontally forwards from the clamp brackets and have substantiallly vertical, opposed articleengaging faces. The choice of such an embodiment is, however, arbitrary and it should be understood that the improved clamp may be used in other positions or inclinations and need not be used on industrial trucks with side-shifting clamps. It is, therefore, evident that such expressions as horizontal and vertical are used in the description and claims to indicate relative dispositions of parts of the clamp as shown on the appended drawing and are not restrictive of the directions of the parts of the clamp in actual use.

A drum, keg or the like is both a convexly curved object and a flat-ended object in that it has parallel, more or less fiat ends, even when provided with chimes. For brevity, in the following description, unless the contrary appears, reference to the clamping of a drum or the like is intended to refer to engagement by the grab arms of the convex surfaces of the drum and not to engagement of the ends of the drum.

The elimination of pallets by the use of clamps usually makes it desirable to employ the same clamp arms for handling articles of different types, e. g., flat-ended objects, such as cartons and boxes, and convexly curved objects, such as cylindrical drums or kegs. Such dual use was not feasible with prior clamps and it was necessary to change the grab arms for different types of loads. For example, the usual grab arms with essentially parallel article-engaging faces, suitable for flat-ended objects, are not Well suited for clamping the convex parts of drums because of the danger of forward slippage of the drums, e. g., in the case of rigid arms due to forward inertia of the drum when the clamp is suddenly accelerated rearwardly (as when a forwardly moving lift truck on which the clamp is mounted is stopped suddenly) and due to spreading of the front parts of the arms in relation to the rear parts incident to deflection caused by the clamping action, especially when less rigid arms are used. This further makes it impracticable to clamp more than one drum with the flat, parallel-sided clamps heretofore in use. On the other hand, when the article-engaging faces of rigid or relatively unflexible arms are shaped concavely to conform to the contour of the drum or the like or have toe-in or inwardly directed projections at the front ends to retain drums, they are not well suited to clamp objects having other shapes, particularly flat-ended objects, be-

OfiFice Patented Jan. 7, llifih cause the pressure is not applied evenly to the ends of such object; this is highly objectionable especially in the case of fragile containers, such as cartons. Such concavely shaped rigid arms, moreover, permit the drums to be picked up in only one predetermined position relative to the clamp and result in a construction of the arms that is thick, thereby restricting the use of the clamp to places where there is ample clearance between the object to be clamped and a nearby wall or other objects; this wastes warehouse and freight space.

In my copending U. S. patent application Serial No. 328,301, filed December 19, 1952, there is disclosed an improved clamp with grab arms of laminar construction that are thin and have at least the front parts thereof convergent for retaining convexly curved objects against forward slippage, the arms having suflicient lateral flexibility to permit them to assume essentially parallel positions when engaged against the faces of a flat-ended object to apply a suitably distributed or even pressure against such faces throughout different parts thereof at varying distances from the clamp brackets. The lateral flexibility of the arms is not uniform along the length but is relatively greater at the forward parts thereof, so that the frictional forces by which a flat-ended object is gripped is properly distributed, while permitting the clamp to serve also for clamping convexly curved objects. The distribution of the lateral flexibility along the lengths of the arms will differ among arms designed for different types of loads, e. g., arms designed to engage only one drum or arms intended to engage two drums, one near the clamp bracket and another farther forward. The preferred curvatures of the arms for such diverse loads are described in the said patent application and need not be repeated herein.

According to a construction described in the aforesaid patent application the lateral flexibility is made different at difierent distances out from the clamp brackets by interconnecting the laminations of the same grab arm directly, e. g., by welds, and providing such connections at different densities at different portions of the arms.

Now, according to the instant invention, there is provided a clamp wherein the lateral flexibility of the arm is increased in relation to that possible by directly fixing together two contiguous metal plates. While the grab arms according to this invention can be made of heavy material to carry loads comparable to those carried by the arms of the said prior patent application, the instant arms are particularly adapted to lighter construction, and permit a relatively greater lateral flexure of the arms under loads without buckling the plates.

In summary, according to the instant invention, the clamp has arms each comprising a pair of elastic, essentially vertical and parallel plates, the rear parts of which are fixed against relative longitudinal sliding movement and the front parts of which are spaced apart and interconnected by an elastic corrugated spacer in engagement with both plates along substantially vertical lines corresponding to the rugations thereof and fixed to the plates at a plurality of points along said lines of contact; the spacer may be fixed, e. g., by welding, riveting, etc. The density of the connections may be varied to control the flexibility of the composite arm and an infinite number of points may in certain instances be used, i. e., there may be a continuous weld along some of the lines of contact.

The arms may be given any of the shapes described in the said earlier patent application, e. g., to provide convergence between at least the front parts of the arms; thus, the arms, when unstressed, may be substantially parallel or only slightly convergent at their rear parts and curved inwardly at the front parts to provide all or the greater part of the convergence, or the arms may be flat and fixed to the clamp brackets so as to be forwardly convergent throughout their lengths. Moreover, the essentially vertical arms may be mounted with their upper and lower portions equidistant or. the lower portions may be closer together to give camberto the arms, as described in my copending U. S. patent application- Serial No. 328,303, tiled December 29, 195 2.

The invention will be further described by reference to the accompanying drawings forming a part of this specification and showing one preferred embodimentby way of illustration, wherein:

Figure 1 is a' side elevation view .ofanindustrial lift truck with a side-shifting clamp having grab arms. aceording to the invention used on a drum;

' Figur'e'2 is a horizontal sect-ion takenon line22 =of Figure 1; i

Figure 3 is a plan view of the clamp usedtoengagea box;

Figure 4 is a plan view ofthe clamp, on an enlarged scale, part of the bracket structure being shown in section; and' Figure 5 is a side elevation of the clamp.

Referring to the drawings in detail, the clamp is illustrated as applied to a conventional industrial truck having wheels21, a steering wheel2 2 and the usual accesseries, including (not shown) a hydraulicreservoir,pump and controls for actuating the eleyatorptilting controller, clamps, etc. The truck carries vertical guide columns 23 and 23a which provide vertical tracks for an elevator 24 which is vertically movable on the tracks. The guide columns may be mounted for pivotal motion about ,a transverse pin 25 that is fixed to the truck chassis, tilting being effected by actuation of tilting levers 26 that '-a 1 'e connected to the guide column by pivoted links 27. The elevator 24and levers 26 are actuatedby suitable-motors controlled from the truck, such as hydraulic motors. Such motors and controls and the elevatorbeing all wellknown in the art, they are not further described herein.

Two laterally movable, telescoping clamp slides or clamp brackets 28 and 29 are slidably mounted for horizontal translatory motion by means of a hollow support bracket 30 that is fixed to the elevator. Each clamp bracket has a plurality of rectangular slide bars indicated at 28a and 29a having a sliding support in the bracket 30 so as to resist relative rotation about .a vertical axis such as would be induced by the spreading tendency of the front parts of the grab arms, to be described, when an article is clamped. These slide bars are further mounted to prevent rotation of the brackets about a transverse horizontal axis, such as would be induced by the weight of a load supported by the arms. The clamp brackets are provided with a suitable motor of any type, ,such as a hydraulic motor including a plurality of hydraulic cylinders, of which only the cylinder 31 is indicated in Figure 4; the cylinders have the pistons thereof connected by rods 32, 32a to the brackets. These cylinders are supplied through flexible hoses (not shown) with pressure fluid from -a pump driven by the truck engine and controlled by the operator on the truck for translating the clamp brackets telescopically apart and together. The specific construction of the clamp brackets and their mounting on the elevatoras well as the actuating motor and control device thereof are all known and form no part of the invention; further description thereof is, therefore, unnecessary and the invention is not restricted to the specific arrangement illustrated.

Each clamp bracket carries an essentially vertical grab or gripper arm 33 or 34 that is rigidly secured to the lateral end of the bracket by any suitable means, such as welding or bolting by the countersunk, flat head screws 35. Each grab arm is assembled from a pair of elastic leaves or plates, such as steel plates 36 and 37 that may be made of resilient, spring stock and may be pre-shaped according to any of the shapes as described in the aforesaid prior patent application. The two plates 36-and 37 are spaced apart in substantially parallel relation, the rear parts thereof being spaced by a metal spacer block 38 in the shape of a vertical bar and secured against relative motion by the screws 35 and, preferably, additionally by weldments 39 and 40, between the block 38 and the plates 36 and 37, respectively. A corrugated spacer.41 of elastic material, such as thin sheet steel, is situated between the front parts of the plates with the rugat-ions extending substantially vertically and in engagement with the plates along lines of contact. Thespacer 41 has the outline; of the parts of the plates forward from the block 38. It is evident that the rugati onsin engagement with: the plate 36 are staggered in relation to the rugations in engagement with the plate 37. The corrugated spacer is fixed to each of the plates along the said lines of contact by any suitable connector members or means, such as rivets or welds,

- welds being preferred. The welding can in some instances be continuous;-however, in most cases it is advantageous to use spot welds-as shown at 42 in Figure 5.

'It is an important featureof this inventionthat the degree to which the corrugated spacer is fixed to the plates along any particular line of contactcan be varied to provide the degree of lateral flexibility desired at any part'of the-arm. In the case of rivets or ,spot welds this is conveniently achieved by-varying the; number of rivets or spot welds along any given line; when continuous welds are used they can be interrupted at intervals to produce a similar effect. As shown in the drawing, 'the first row of welds A at the rear of the arm contains many welds and the next two rows B contain a smaller but still high number of welds, whereby the arm is generally stiff at the rear. In the regions C and D the number of welds per line is progressively smaller to make the arms more flexible toward the f ront,'while the number of welds is again increased somewhat in the rows E and F. It will ,be understood that this particular distribution of the vdensity of the welds was chosen merely for purposes 10f illustration and that other arrangements may be used to adapt the arms to particular types of loads. It will be also understood that the corugated spacer is similarly welded to the inner plate 36 along the staggered lines of contact and that the distribution of the density of the welds will usually follow the same pattern as that used for the outer plate 37.

The plates 36 and 37 and the spacer 41 are shaped to provide in the composite arm a horizontal slot 43, open to the front and extending back a suitable distance in accordance with the intended use for the clamp, e. g., slightly in excess of one-half the length of the arm, as shown, for loads as indicated in Figures 1 andZ, orin excess of three-fourths of the length when two drums at diflferent distances from the supporting bracket are to be engaged by the same arm. This slot serves the dual purpose of 1) facilitating insertion of the grab arm into a gap between a wall and a stack of drums or between two stacks of drums that have no clearance between rolling hoops or withdrawal of the arms from such gaps, and (2) providing added security in supporting the load in that the rolling hoops or other convexly curved parts or other protuberances on the clamped object can project outwardly into the slot to receive vertical ,support. The vertical extent of the slot 43 should not, however, be made greater than necessary to achieve these purposes because the fiexible grab arms according to the invention are made thin and should be of sufficient vertical extent to perform their function without buckling or permanent deformation. In general, it is preferred that the height of the slot be onl a minor pa o theheight of the grab arm, advantageously not greater than the height of either the part of the arm above the slot or the part below the slot.

As was indicated above, the plates 36 and 37 may but need not be prestressed. In the latter case they are given the shapes shown in Figure 4, or any other desired shape, such as flat, and connected to the spacers while unstressed. It is, however, also possible to employ the technique disclosed in the aforesaid earlier patent application Serial No. 328,301. In brief, according to such a technique the plates 36 and 37 are first assembled to the spacer block 38 by the welds 39 and 40 and the corrugated spacer 41 is inserted; if desired the terminal line of contact A may be connected. The plates are then both bent elastically toward the exposed face of plate 36 and secured temporarily by any suitable jig or clamp in deflected position; the corrugated spacer is then fixed to both plates at the desired points, after which the plates are released. The corrugated spacer will now resist the tendency of the plates to return to their normal, unstressed condition, whereby the inner plate 36 will be permanently under longitudinal tensile stress and the outer plate is permanently under longitudinal compressive stress, so long as the arm is not stressed by engagement to a load.

After completion of the above assembly operations the inner faces of the arms, i. e., the exposed faces of the plates 36, are advantageously covered with a suitable resilient material 44 having a high coeflicient of friction, such as rubber facing, expanded metal, mesh, or a combination of these or similar materials. A similar covering 45 may be applied to the front face of the bracket 30.

It is evident that when the arms are clamped to a load by approach movement of the brackets 28 and 29 the arms are subjected to cantilever stresses such that the front ends are urged apart. This stresses the corrugated spacer 41 to impose tensile stress on the traverses of the spacer that are inclined forwardly and outwardly toward the plate 37, as indicated at 41a, and to impose compressive stress on the traverses that are inclined forwardly and inwardly toward the plate 36, as indicated at 41b. The corrugated spacer will be elastically deformed to permit the arms to flex. In sections where relatively fewer connections between the spacer and the plates occur, e. g., at the lines of contact D, the corrugated spacer is less effective to oppose the deflection of the plates, whereby the arms have a relatively greater flexibility than in sections, e. g., at the lines of contact B, where relatively more numerous connections occur.

When using the truck for lifting objects with rounded outlines, such as oil drum 46 standing on end and having peripheral rolling hoops 47 (Figures 1 and 2) the clamp brackets are moved apart and the truck 20 is maneuvered into position to embrace the drum, the elevator being previously moved if necessary to position the slot 43 at the level of one of the rolling hoops. When the clamp brackets are brought together, the rolling hoops opposite the slot 43-the lower hoop in the case illustrated-projects through the said slot and the other rolling hoop extends laterally outwards from the grab arm-over the upper edge in this instance. Each of the parts of the grab arm above and below the slot applies a clamping force to the drum at the smooth, cylindrical portions thereof. The front parts of the arms remain toed-in and the drum is thereby secured against forward slippage despite deflection of the rear parts of the arms due to the application of a strong clamping force by the clamp brackets or the sudden stopping of the truck 20 when in forward motion. In fact, the clamp can securely clamp two upright drums disposed side by side, with one drum in engagement with only the arm 33 and the other drum in engagement with only the arm 34. The convergence of the flexible, front parts of the arms prevents forward slippage also with such a load. With longer arms a greater number of upright drums, arranged in two rows parallel to the arms, can be clamped.

When used to clamp flat-ended objects, such as a carton or box 48 (Figure 3) or a cylindrical drum with the parallel ends in engagement with the grab arms, the truck is similarly maneuvered to embrace the box or similar object. When the clamp brackets are moved together the box is engaged first at the front parts of the grab arms. These parts are sufficiently flexible to straighten elastically, thereby engaging the ends of the box resiliently along the length of the arms, and affording a dependable clamping action despite the outward bending deflection of the rear parts of the arms, whereby the bending moment is greatest. The arms, accordingly, assume the shapes shown in Figure 3 and a substantially even pressure is applied against the box. Moreover, the flexibility of the arms also permits the arms to adapt themselves to boxes the ends of which are not truly parallel and makes it possible to clamp securely a plurality of boxes situated not only across the breadth of the clamp but also at various points along the lengths of the arms. The flexibility further facilitates clamping boxes of light construction with reduced danger of crushing them.

An important advantage of the construction is that it permits the arms to be made relatively thin and with outer and inner surfaces that are free from protuberances, whereby the arms can be inserted into narrow gaps or withdrawn therefrom.

It is evident that changes in the details and dimensions, as well as in the shapes, curvatures and inclinations of the essentially parallel plates may be made without departing from the spirit of the invention as defined in the appended claim. For example, while the plates are shown to be truly parallel throughout their entire lengths, it is not necessary that they be exactly parallel, and the front edges thereof may be converged or even touching. Also, it should be noted that the curvature and convergence of the arms, as well as the thickness of the arms in relation to the over-all size of the clamp were exaggerated somewhat in the drawing for clarity.

-I claim as my invention:

In a clamp adapted to handle flat-ended objects and convexly curved objects the combination of: a support structure, a pair of clamp brackets attached to said support structure, means for moving said brackets laterally relative to each other, a pair of thin substantially vertical grab arms extending longitudinally forwardly from said clamp brackets, each of said grab arms being rigidly attached to one of said clamp brackets, each of said grab arms comprising a pair of substantially parallel elastic metal plates having rear parts and front parts that are spaced apart, a spaced block positioned between the rear parts of said plates to hold the plates in spaced relationship, means rigidly securing the rear parts of said plates and said spaced block to the clamp bracket, a corrugated elastic metal sheet situated between said front parts and having the rugations thereof extending substantially vertically, said corrugated metal sheet being in engagement with both said plates along a plurality of lines of contact at progressively different distances forwardly from the clamp bracket corresponding to the location of said rugations whereby the lines of contact on one plate are staggered in relation to the lines of contact on the other plate and a plurality of connector members fixing each plate to the corrugated sheet along the said lines of contact.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,694 Ehmann Aug. 4, 1953 2,423,870 *Blessing July 15, 1947 2,645,372 Broersma July 14, 1953 2,727,779 Phillips Dec. 20, 1955 2,739,009 Phillips Mar. 20, 1956 2,746,139 Van Pappelendam May 22, 1956

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