Pool Section 29 Regulation 3.2(2) AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: CLAMPING DEVICE FOR LIFTING SLAB, PANEL, OR SHEET MATERIAL The following statement is a full description of this invention, including the best method of performing it known to us: 1 CLAMPING DEVICE FOR LIFTING SLAB, PANEL, OR SHEET MATERIAL FIELD OF THE INVENTION 5 The present invention relates to clamping devices that may find use in hoisting and handling heavy slab, panel or sheet materials such as stone, masonry, concrete, marble, metal and the like materials. Specifically, the invention relates to an improvement for lifting clamps of the type having a rigid frame having a fixed jaw plate that provides a first clamping surface, a movable 10 jaw plate that provides a second clamping surface and which is supported at the frame for reciprocating movement towards and away from the fixed jaw plate, and an actuating mechanism to bias the movable jaw plate towards the fixed jaw plate whereby the respective clamping surfaces abut onto opposite faces of the sheet material and frictionally clamp same against displacement. 15 BACKGROUND OF THE INVENTION Heavy slabs and sheets of material are usually stored and stacked upright standing or in slightly inclined orientation. Handling of this type of materials often entails use of lifting clamps that grip the sheet (hereinafter used generically to 20 also encompass slabs and other planar objects) at its upper edge for hoisting. Consequently, it is convenient in the following description of known devices and the lifting device in accordance with the present invention to use reference terminology such as 'vertical', 'horizontal', 'upper', 'lower' and similar when describing operation and components of such clamping devices, bearing in mind 25 that these devices may also be used in a 'horizontal' or other orientation, eg as a simple clamp or a haulage attachment. Thus, unless otherwise clear in the context, such reference terms are not to be interpreted as a limitation. A lifting clamp of the type with which the present invention is conceded is known from US Patent 5,893,595 (Corbett). The lifting device includes a rigid 30 frame comprising vertical, parallel spaced apart side plates, the upper ends of which are rigidly secured together by four tubular cross-members. The lower portion of one of the side plates is angled away in downward orientation from the other side plate, the latter providing a fixed clamping jaw of the device. A 2 vertically extending plate is mounted for horizontal sliding movement on the cross-members between the side plates and provides a movable jaw of the device. An actuator carriage which is disposed for guided vertical up and down movement is located between the movable jaw and the lower, angled portion of 5 the frame side plate, whereby a set of rollers of the carriage respectively engage the facing surfaces of the movable jaw plate and the angled portion of the frame side plate. The carriage is connected to a strip member that extends beyond the upper end of the frame and has a lifting lug to which is attachable a lifting cable or chain. In order to lift (or otherwise handle) sheet material, the device is placed 10 over the upper edge of the sheet so that it is received between the fixed and movable jaw plates, the carriage is raised by lifting the strip member through pulling the lifting cable upwards, whereby the carriage travels on the angled frame side plate portion and displaces the movable jaw horizontally until it abuts on the facing surface of the sheet material. Upon increasing the upward pulling force, the 15 sheet material is frictionally clamped sufficiently tightly for it to be lifted with the device. In essence, clamping of the sheet material between the plate jaws is achieved by wedging the carriage between the frame side plate and the movable jaw, and the clamping force is maintained for as long as there is upward force being on the lifting cable. 20 A lifting clamp of similar design to that of Corbett is disclosed in German patent publication DE 199 23 788 Al (Scheibenbogen GmbH & Co KG), where, however, the mechanism employed to move the movable jaw into gripping engagement with the sheet material comprises, a cam pulley instead of a wedging carriage. The pulley is mounted on the movable jaw plate with its axis of 25 rotation perpendicular to the plane of the movable jaw plate, four rollers serving to support the pulley in parallel relationship at the facing jaw surface. Two cams are arranged on the opposite face of the pulley, concentrically with and symmetrical about the rotation axis. The cams extend equiradially over a sector of the of the pulley circumference. The hight of the cams increase from near the pulley face to 30 a maximum hight that is dictated by the maximum spacing between the fixed and movable jaws of the clamp in their fully spaced apart position. The cams thus provide sloping guide and bearing surfaces for respective actuator rollers that are secured in fixed relationship on the frame plate of the device that faces the pulley.
3 An actuator cable that is secured to the pulley perimeter is used to rotate the pulley, the actuator cable advantageously terminating in a hoop on which a hoisting cable or chain may be attached. In operation of the clamp, when a pulling force is exerted on the actuator cable, rotation of the pulley causes the actuator 5 rollers to travel along the inclined (or curved) bearing surfaces of the cams, thereby displacing the movable jaw away from the facing frame plate towards the fixed jaw and clamping sheet material received between the jaws. One disadvantage that has been observed with lifting clamps made in accordance with Corbett as well as Scheibenbogen is the tendency of the clamp 10 frame, on lifting of in particular thin sheet material from the ground, of rotating into a different spatial attitude from the initially given "no load" attitude, the later being characterised by the substantially vertical orientation of the clamping surfaces of the jaws when these are clamped onto a sheet of material resting upright on the ground. This rotation induces swaying and swinging of the sheet material at the 15 lifting cable that makes precise hoisting difficult, and increases breakage risk upon hitting against objects in the vicinity of the sheet. The moment that causes this rotation is induced by the presence of an out-of-alignment force pair on initial lifting off of the sheet attached to the clamp frame (upward directed lifting force vs downward directed weight of sheet material and clamp). This movement inducing 20 moment decreases and ceases as the clamp frame and the sheet material rotate into and eventually assume a final, slightly inclined orientation with respect to the vertical, as the respective centres of gravity of the clamp and the sheet material seek to and ultimately align themselves along the same (vertical) line along which the lifting force is being exerted. 25 This problem stems from the lay-out of the clamp as such, ie due to the presence of a fixed clamp against which a single movable clamping jaw plate is forced. With such lay out, the line along which gravity force acts on the upright sheet material locates within the clamp frame at different traverse locations, depending on the thickness of the sheet, and does not align with the point at 30 which the upward directed hoisting force acts on the clamp frame, notwithstanding the lifting force ultimately acts on the carriage or cam pulley of the clamp actuating mechanism in close vicinity of the secured sheet material.
4 Equally, whilst the cam pulley clamping mechanism of Scheibenbogen has the advantage over Corbett's of providing a more even distribution of clamping pressure onto the sheet material, the Scheibenbogen lifting clamp has a more pronounced tendency of swaying under load, which results in difficulties in 5 controlling movement of sheet material during transport. One object of the present invention is to provide a lifting device of the aforementioned type in which the tendency of the clamp of swaying into an inclined position during lifting of sheet material is minimised. 10 SUMMARY OF THE INVENTION In accordance with one aspect of the invention there is provided a clamping device suitable for lifting and handling of sheet like-objects, having a rigid frame with a fixed jaw that provides a first clamping surface, a movable jaw that provides a second clamping surface that is substantially parallel to the first 15 clamping surface, the movable jaw being supported at the frame for reciprocating, linear movement towards and away from the fixed jaw, and an operating mechanism arranged to bias the movable jaw towards the fixed jaw in response to an actuating force being exerted on a tensile force transmitting member of the operating mechanism, thereby to abut the respective clamping surfaces onto 20 opposite faces of an object received between the jaws and frictionally clamping same against displacement, characterised in that the movable jaw comprises a sliding plate on which the second clamping surface is provided, the sliding plate being inclined at an angle of about 8 to 12 degrees with respect to the first and second clamping surfaces and being supported at the frame to maintain said 25 angle during movement to and from the fixed jaw, and in that the tensile force transmitting member is guided and supported at an upper location of the sliding plate that substantially aligns with or overhangs the second clamping surface. It has been found that the inclined arrangement of the sliding plate and location of the force transmitting member reaction point at the sliding plate have 30 positive effects in minimising the presence of swing-inducing moments when a slab or sheet material of relatively small thickness is hoisted with the clamp, as the reaction point of the lifting force at the sliding plate is brought in closer alignment with the line along which gravity exerts force on the sheet material. An 5 inclination angle of the sliding plate of about 11 degrees renders particularly good results in minimising the gravity and lifting force induced moment at the clamp frame, providing thus better lift / hoisting control. Advantageously, the operating mechanism of the lifting clamp comprises a 5 cam pulley system whose operating principle (but not necessarily its constructional layout) is similar to the one described in above mentioned German document, the contents of which is incorporated herein by way of cross reference. Such actuating system provides for a more uniform and even clamping load distribution as compared to the solution of Corbett. 10 Accordingly, in accordance with a preferred implementation of the invention, the operating mechanism includes a drive pulley that is mounted on the sliding plate of the movable jaw with its axis of rotation perpendicular to the plate plane, a plurality (preferably four or more) of bearing rollers arranged to support the pulley in parallel relationship at the facing sliding plate surface, at least one, 15 preferably two actuating cams protruding from the pulley surface that faces away from the sliding plate, the actuating cams being symmetrically disposed about the rotation axis of the pulley and extending along an arc sector radially inwards of the pulley circumference, the cams having a hight that increases from near the pulley face to a maximum hight that is related to the maximum spacing between 20 the fixed and movable jaws of the clamp in their fully spaced apart position, the cams each defining a sloped guide and bearing surface for respective actuator rollers that are secured in fixed relationship on a stationary part of the clamp frame that faces the pulley, the arrangement being such that upon rotation of the pulley, the actuator rollers travel along the guide and bearing surfaces of the 25 cams thereby displacing the pulley and therewith associated sliding plate along the axis of rotation of the pulley relative to the stationary clamp frame part. The tensile force transmitting member used to rotate the pulley is preferably an actuator cable that is suitably secured to the pulley perimeter and partially wound on and running in a peripheral groove of the pulley. The actuator 30 cable may advantageously terminate at its other, free end in a hoop on which a hoisting cable or chain may be attached. In operation of the clamp, when a pulling force is exerted on the actuator cable, eg when hoisting a slab, rotation of the pulley causes the actuator rollers to 6 travel along the bearing surfaces of the cams. The hight increase of the cams can be constant, progressive or decreasing, ie the contour of the bearing surfaces can be rectilinear, curved or otherwise shaped, thereby to achieve a desired displacement movement of the sliding plate away from the stationary frame part, 5 eg a frame plate, towards the fixed jaw. The sheet material received between the jaws is thus clamped with a force that is a function of the pulley diameter, the distance of the arc-shaped cams from the axis of rotation of the pulley, and the weight of the material being hoisted with the clamp. When employing such cam pulley operating mechanism, the rigid frame 10 may preferably be an assembly consisting of a side plate that provides the fixed jaw, a substantially rectangular parallelepiped shaped housing part with an open side disposed to face the side plate, whereby a bottom wall or side walls of the housing may provide the stationary frame part that supports and locates the actuating rollers that engage the cam pulley, and a plurality of (preferably four) 15 cross struts rigidly joining the side plate and the housing part in spaced apart relation ship at upper ends thereof, the housing part having a cavity in which the cam pulley of the operating mechanism locates when the clamp is in a fully open state, eg non-clamping state, in which the movable sliding plate comes to rest adjacent the housing part and covers the open side face. The partially encased 20 operating mechanism is thus protected from damage to its moving parts. In a further preferred embodiment, the clamping device may incorporate a locking mechanism that is arranged to lock the cam pulley against rotation. The locking mechanism may be designed to be engageable only when the movable jaw is in its non-clamping position, or in any position. 25 One embodiment of the locking mechanism includes a rotatable locking plate attached to or otherwise operably connected to a handle, knob or other manual actuating member, the locking plate being supported at the housing part in a location where it can be rotated or displaced in and out of engagement with a locking receptacle provided either on the cam pulley or a support shaft thereof. A 30 spring-loaded actuator rod that acts on the latch mechanism, located at the housing part front or side wall, is preferred.
7 A preferred embodiment of a clamping device as used for lifting slab materials in accordance with the present invention, and further features and advantages of the invention, will be described with the accompanying drawing. 5 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an isometric, disassembled view of clamping device for hoisting slab materials in accordance with a first embodiment of the invention, showing its main subassemblies; Fig. 2 is an isometric view of the clamping device of fig. 1, from an 10 opposite side perspective and showing the component parts of the subassemblies of the clamp; Figs. 3a to 3 c are schematic and simplified longitudinal sections of the clamping device of fig. 1, illustrating operation of the clamp from a rest position to two different engaged positions; and 15 Fig. 4 is a schematic and simplified longitudinal section similar to fig. 3a of a further embodiment of a hoisting clamping device in accordance with the invention. DESCRIPTION OF PREFERRED EMBODIMENTS 20 in the following description, reference terms such as 'upper', 'lower', 'vertical', 'horizontal', 'left' and 'right' are chosen with regard to the drawing plane of the relevant figures and to aid in referencing clamp components with respect to one another. Referring first to figs 1 and 2, there is shown a clamping device 10 in 25 accordance with a preferred embodiment of the present invention as devised for lifting and hoisting sheet-like materials of substantial planar dimensions and weight. The expression "sheet materials" is here generically used to describe slabs of stone, marble, sheet or sheets of metal tightly bundled into a stack, or the like. 30 The lifting clamp 10, shown schematically also in longitudinal section in figs 3a to 3c, comprises essentially four subassemblies or components, a stationary jaw 20, a movable jaw 22, a housing frame assembly 24, and an actuator carriage assembly 26. The latter serves to move the movable jaw part 22 8 with respect to the stationary jaw 20 and housing assembly 24 in between which the movable jaw 22 is received, and to apply a clamping force to retain sheet material (not shown) securely clamped between the fixed and movable jaws 20 and 22 within the device 10 5 Stationary jaw part 20 and housing part 24 define a rigid clamp frame and are joined together at an upper end in spaced-apart relationship by means of two pairs of parallel tubular cross bars 28 which have terminal ends that are secured by screws 30 in receptacle bores (not shown) at the housing member 24 and whose opposite terminal ends are rigidly fixed to stationary jaw part 20 using 10 screws 32 that extend through bores 34 as is evident from fig. 2 and fig 3. Stationary jaw part 20 is comprised of a substantially rectangular steel plate 35 with the four bores 34 disposed at an upper end. A rubber glove 36 is fitted to the lower portion of steel plate 35, and has a trapezoidal cross-section with a lower portion that is angled slightly inwardly to allow for easy manoeuvring 15 of the jaw part 20 over the slab and minimising risk of edge breakage. Glove 36 provides a high friction material clamping surface 37 at stationary jaw 20 against which the sheet material to be clamped will be pressed during lifting, to prevent the sheet from slipping or being damaged during lifting operation. The movable jaw part 22 consists of a generally rectangular steel plate 38, 20 carrying on one surface a pair of steel ramp blocks 40 that are spaced-apart across the width of plate 38. The steel ramp blocks 40 are welded or otherwise fastened to plate 38, but may also be integrally cast with the plate 38. These ramp blocks 40 define a contoured track surface 42 the purpose of which is described below. On the surface opposite that on which blocks 40 are carried, a 25 rubber material or other high friction pad 48 is secured (eg by gluing) to plate 38, thus providing a second clamping surface 49 for engagement with the sheet material during lifting operations which minimises slippage risk during hoisting. A pair of link arms 50 serve to mount and pivot the movable jaw 22 to the housing frame part 24 which is described in greater detail below. The upper 30 terminal ends of link arms 50 are secured by way of mounting screws 51 and washers 52 into respective mounting recesses 54 provided at width-wise opposite sides in an upper portion of the housing frame part 24 (see fig 2) to allow rotational movement of the arms about an axis A that extends traverse to 9 longitudinal axis L of the device 10. The lower terminal ends of link arms 50 are secured by way of mounting screws 53 and washers 54 to the width-wise outward facing side of the ramp blocks 40, which to this end are provided at a lower end with threaded mounting bores 55, see fig 1. Sleeves or bushes 56 ensure that 5 movable jaw 22 is free to pivot about an axis B that extends traverse to longitudinal axis L of the device 10. The link arm mounting arrangement chosen enables the movable jaw 22 as a whole to be displaced towards and away from the stationary jaw 20 as well as housing frame part 24, the length of the arms ensuring that pivot axis B 10 performs only a shallow arcuate path about pivot axis A that causes the lower terminal edge of movable jaw 22 to move slightly vertically up and down during such pivoting, as well as enabling the movable jaw 22 itself to pivot about axis B. The latter enables the clamping surface 49 of movable jaw 22 to cater for lack of complete parallel arrangement of the surfaces of sheet material to be clamped 15 between the movable and stationary jaws 22 and 20. As best seen in fig 2, housing frame 24 includes a substantially rectangular parallelepiped shaped housing box part 60, which has a solid material upper portion 62 and a lower portion 64. The upper portion 62 has formed therein four bores of stepped diameter that serve to form-fittingly receive the terminal ends of 20 cross rods 28 and secure same against displacement therein using screws 30. Lower portion 64 includes an open cavity 66 bordered by opposing width-wise disposed side walls 68, a lower-end bottom wall 69, a planar base wall 70 and said upper solid material portion 62. An inclined surface 72 sloping towards the upper end of frame part 24 defines the transition between the vertical inner 25 surface 71 of planar base wall 70 and upper portion 62, as is best seen in figs 3a to 3c. As noted above, recesses 54 are formed in the solid material portion 62 for receiving and securing the upper ends of linkage arms 50. Carriage assembly 26 includes a vertically extending metal strip bar 80 carrying at its upper terminal end a connection ear or lug 82 with an eye 84 that is 30 adapted to receive a hook or shackle or directly a tension cable by way of which the entire device 10 may be lifted and the clamping action effected. At its lower end, strip bar 82 is.bifurcated and defines two mounting flanges 86 which serve to secure a roller axle 88 which in turn carries a first roller 90 that is located between 10 the mounting flanges 86, and a pair of follower rollers 92 disposed at axially opposite ends of the axle 88 outside the respectively adjoining flanges 86. Axle 88 is secured in known manner against removal from its mounting at flanges 86. Rollers 90 and 92 define together with the lower part of bar 80 an actuator 5 carriage that serves the purpose of displacing / moving movable jaw 22 in relation to the two stationary frame parts 20 and 24. Strip bar 80 is of a width that enables close but friction-free guidance thereof between the traverse cross-member pairs during upward and downward movement thereof. It will be appreciated by the skilled worker that when the clamping device 10 10 is suspended from lug 82, the entire actuator carriage assembly 26 will wish to move in upward direction, whereby the central roller 90 will be maintained in engagement with and roll up first along the vertical inner surface 71 and then along the inclined upper surface 72; these surfaces 71, 72 thus provide track segments which the central carriage roller 90 will follow. 15 To secure the actuator carriage assembly 26 in the lower most, inoperative position, a simple locking device 100 is provided, consisting of a spring-loaded hook lever 102 pivoted between pedestal supports 104 formed or fastened at the outside upper end of frame housing part 24. Finally, as best seen in figs. 2 and 4, a set of four tension springs 96are 20 located between the movable jaw plate 48 and the housing box part 60 such as to bias the movable jaw 22 towards the frame housing 24 and cover cavity 66. This position represents the fully open clamp jaws position, and depending on the spring constants of the tension springs employed, an additional locking member, not illustrated, may be required to secure the open position. For symmetry 25 reasons, four tension springs are used, located and secured in appropriate manner using screws 97 at the respective corners of movable jaw plate 48 and housing box part 60. A slightly modified embodiment of such lifting clamp 10' is shown in fig. 4. The main difference in comparison to the embodiment illustrated in figs. 1 to 3 30 resides in the shortened linkage arms 50', the consequential need for pivoting these near an upper portion of the movable jaw plate 38 instead of at a middle or lower part, as well as a modified track profile 44' and 46' at the ramp blocks 40', in that two inclined track surface portions are provided instead of one inclined 46 11 and one vertically 44 extending section as seen in figs. 3a to 3c in particular. The clamp 10' of fig 4 has a smaller jaw opening width capability, and is thus more suited for clamping and lifting thicker sheet materials. Operation of the clamp device will now be described with reference to figs 5 3a to 3c. As noted above, the entire device 10 may be hoisted through use of a suitable hoisting cable that is secured to lug 82 at the upper terminal end of the carriage assembly's pull rod (bar) 80. The lifting force exerted by the hoisting cable will cause actuator carriage 26 move upwards, and in absence of any sheet material being received between movable jaw 22 and stationary jaw 20 move 10 from the rest position illustrated in fig 3a at the bottom of the housing frame cavity 66 into a position past the one illustrated in fig 3c, where the clamping surfaces 37 and 49 of the jaw members 20 and 22 may come into abutting stop. As noted above, locking mechanism 100 may be employed in order to arrest upward movement of actuator carriage 26 with respect to housing part 24, so that the 15 lifting clamp 10 may be hoisted in its non-operational rest position. During upward movement of carriage 26, its follower rolls 92 will roll on the track surfaces 46 and 44 defined at ramp blocks 40, without coming into engagement with the inner surface 71 of the bottom wall 71 of frame housing part 24. Rather, the central roller 90 (which is not visible in figs. 3a-c) will perform 20 guidance and reaction of the actuator carriage 26 at the stationary frame housing 24 as it rolls first along vertical section 71 and then inclined track section 72. During upward movement of carriage 26, pivot axis B, at which the movable jaw 22 is supported on the linkage arms 50, will move slightly upwards and be displaced in horizontal direction towards the stationary jaw part 20, as 25 schematically indicated in fig. 3c. All along such movement pattern, the movable jaw 22 may freely pivot about axis B unless otherwise restrained from doing so, eg by a sheet material received in the gap between jaw members 20 and 22. The parallel arrangement of linkage arm pivot axis A and B enables the movable jaw plate to maintain an upright orientation parallel with the longitudinal axis L of the 30 device 10, and if required attain an inclined orientation to adapt to a non plane parallel surfaced sheet material, eg where there is a slight taper in the sheet thickness.
12 It will be appreciated that the specific geometries, dimensions and relative spacing of linkage pivot axes A and B, linkage arms, angle of inclination of the inclined tracking surfaces 46, 72 for the actuator carriage rollers 90 and 92 and other components that define the specific kinematics of movement of the movable 5 jaw member 22 may be varied to suit requirements. Of course, modifications such as the profile shape of the track surface for the actuator carriage, number and location of ramp blocks, the number and locations of the tension springs, the size and cross-sectional shape of the cross bars, the material of the various components of the lifting device to form a light 10 weight, yet strong clamping lifting device that will withstand heavy duty use, etc. are all within the scope contemplated by the disclosed invention.