Leveling Sling

Abstract

A sling for carrying a load includes a frame with a gripper mounted thereon and a cable extends across the gripper and is held thereby against movement when the load is lifted. The ends of the cable are doubled back toward the frame and connected with each other by a chain to form two elongated loop portions which are disposed on opposite sides of the frame and function as the two legs of the sling. The chain is trained across a drive sprocket which is mounted on the frame vertically of the gripper and is driven by a motor to draw the chain across the frame from one side to the other and thereby selectively shorten one loop portion while lengthening the other loop portion to adjust the load to a precise attitude after the load has been lifted.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to slings used in conjunction with a hoist for lifting a load and, more particularly, to the type of sling having adjustable legs for leveling the load.

SUMMARY OF THE INVENTION

The general object of the present invention is to provide a novel sling which can be used to precisely level the load much more quickly and easily than is possible with prior slings of the same general character.

A more detailed object is to provide a sling in which the legs are adjusted roughly for length preparatory to lifting the load with further small adjustments in the length of the legs being made for precise leveling once the load is lifted.

A further object is to make small adjustments in the length of the legs by shortening one leg while at the same time lengthening the other leg and to do so after the load is lifted and without releasing the legs from their roughly adjusted position.

These and other objects and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sling embodying the novel features of the present invention.

FIG. 2 is an enlarged fragmentary elevational view of the sling.

FIG. 3 is a cross-sectional view taken substantially along line 3--3 of FIG. 2.

FIG. 4 is a cross-sectional view taken substantially along line 4--4 of FIG. 3.

FIGS. 5a and 5b are schematic views of the operation of the sling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the drawings for purposes of illustration, the present invention is embodied in a sling 10 adapted for use with a hoist (not shown) to lift a load 11. Herein, the sling (FIG. 1) includes a frame 13 supporting a bail 14 having a center opening into which a crane hook 15 suspended on the lower end of hoist cables 16 is inserted to carry the sling for lifting purposes. More particularly, the load is carried on the ends of two sling legs 17 each of which includes two cables 19 extending through the frame to exit on opposite sides of the upper end portion of the frame. The cables are attached to the load at horizontally spaced positions as shown in FIG. 1 and serve to carry the load at a selected attitude after being lifted.

Connected to the bail and mounted within the upper end portion of the frame 13 is a saddle-shaped gripper 20 (FIGS. 2 and 4) which serves to support and grip the cables 19 within the frame to prevent slippage of the load once lifted. In addition, the gripper acts as a guide when under no load to permit the frame to be slid along the cables prior to lifting the load in order to make a general adjustment in the length of the sling legs and thereby select the general attitude at which the load is to be carried. The particular construction and use of a sling which includes such grippers is well known in the art. One particular arrangement is described in Caldwell U.S. Pat. No. 2,919,949, and therefore will be described only briefly herein.

With reference to FIGS. 2, 3, and 4, the gripper 20 includes two semi-circular wedge plates 21 spaced from each other on either side of the bail 14. The curved edges of the wedge plates are directed upwardly to define a saddle for carrying one of the two cables 19 on each side of the bail. Inwardly tapered annular shoulders 23 formed on the inside wall and along the curved upper edge of each wedge plate define a V-groove 24 between each plate and the bail. It is within this groove that the cables wedge against movement when under load. When under no load, vertically movable rollers 25 (FIG. 4) are urged by springs 26 into raised positions to lift the cables out of the grooves and allow the frame 13 to be slid along the cables to simultaneously shorten one while lengthening the other of the sling legs 17 in order to adjust the legs for picking up the load at a selected general attitude.

Usually it is desired that the load 11 be carried in a level attitude, and to do this it is necessary to locate the frame 13 over the center of gravity of the load. Loads having symmetrical configurations or points of attachment equally spaced from the center of gravity of the load present little problem in achieving a close approximation to the center of gravity of the load by eye. Other types of loads such as those which must be lowered into place at some exact attitude whether level or not and those loads lacking attachment points which are evenly spaced from the center of gravity (see FIG. 1) present more difficult problems in adjusting the length of the sling legs 17 so as to lift the load at the exact desired attitude.

In accordance with the primary aspect of the present invention, provision is made in the sling 10 for very quick and easy adjustment of the length of the sling legs 17 to position the load 11 at the exact desired attitude while lifted. For this purpose, each of the cables 19 forming the two sling legs is doubled back to make an elongated loop and the ends of the two cables are supported by and connected together across the frame 13. With this arrangement, the sling legs may be lengthened and shortened as desired to precisely adjust the attitude of the load simply by selectively drawing a portion of cable from one loop and feeding it across the frame to enlarge the other loop thus greatly simplifying and speeding up delicate loading operations.

In the present instance, a double block 27 and hook 29 (FIG. 1) is carried within the looped end of each of the legs 17 with each of the two cables 19 being trained around one pulley section of the double block to adapt each leg for attachment to the load 11. Connected between each leg is a length of roller chain 30 which is trained across a power driven sprocket 31 (FIG. 4) mounted in the frame 13 directly beneath the gripper 20. MOre particularly, the ends of the two cables forming each leg are fastened together on an eye 33 (see FIG. 2) and each eye is linked with a shackle 34 connected to the end of the roller chain. Thus, the chain serves to connect one leg with the other in effect, creating a large single loop across the frame. Consequently, when the power driven sprocket is rotated, the chain is moved selectively from one leg to the other thereby to lengthen and shorten the sling legs one at the expense of the other.

In use, the legs 17 of the sling 10 are hooked to the load 11 at spaced positions (see FIG. 1), preferably such that when the load is lifted, the included angle a between the two legs is approximately 90.degree. or less, so that substantial portions of the cables 19 are wedged tightly within the gripper 20 (FIG. 2) to prevent slippage. Before lifting the load, rough attitude adjustment is accomplished by shifting the frame 13 one way or the other along the cables to position the frame on the cables and over the load so that when the load is lifted it will assume the approximate attitude desired.

To precisely adjust load 11 after it has been lifted, a motor 35 connected wit the drive sprocket 31 is actuated to turn the sprocket selectively in the desired direction to shorten one sling leg 17 and lengthen the other sling leg. As the sprocket rotates, the chain 30 is fed through the frame 13 pulling the double block 27 and hook 29 up on the one leg along the portion of the cables 19 leading from the block to the gripper 20 while at the same time lowering the block 27 and hook 29 on the other leg along a similar portion of the cables (see FIGS. 5a and 5b). Thus, the looped ends of the legs are raised and lowered as desired to raise and lower opposite ends of the load and, in effect, shift the load beneath the frame 13 until the center of gravity of the load is located directly below the center vertical axis of the frame to hold the load exactly level. Thus, it is seen that after the load has been lifted by the sling 10, the legs can be shortened and lengthened quickly and easily to selectively tilt or level the load precisely into the desired attitude.

To support the chain 30 and the drive sprocket 31, the frame 13 includes two generally rectangular plates 36 and 37 (FIG. 3) bolted respectively to the front and back sides of the bail 14. Four block spacers 39 (FIG. 4) are held by the bolts between the two plates and the bail with one spacer being positioned at each of the upper end corners of each plate and adjacent the curved upper edge of the gripper 20. The blocks serve to further separate the plates from each other and act as guides to prevent the cables 19 from jumping out of the V-groove 24 formed along the top edge of the gripper. Additional bolts 40 extend through and are fastened to the plates intermediate their upper and lower ends to hold the plates together. Tubular spacers 41 (FIG. 3) telescoped around each of the bolts between the plates serve to support the plates rigidly in their spaced relationship. Supporting the drive sprocket 31 between the two plates and below the gripper is an axle 43 which is mounted on the vertical center line of the frame and is journaled to both plates with one end of the axle projecting through the front plate 36. Mounted below and adjacent each side of the drive sprocket in the same vertical plane are two small idler sprockets 44 (FIG. 4) supported on shafts 45 journaled at each of their ends to the sides of the plates. The chain 30 is threaded through the frame between the two plates along the underside of each of the idler sprockets with the portion of chain extending between the idler sprockets looped up over the drive sprocket 31 thereby to vertically support the chain in the frame. Thus, the idler sprockets act to guide the chain over a substantial contact area on the drive sprocket to prevent slippage of the chain when the drive sprocket is rotated.

Power is supplied to turn the drive sprocket 31 by a power train including the motor 35, a speed reducer 46 and a double reduction, chain-driven, gear arrangement 47 which is connected between the reducer and drive sprocket. The entire power train is mounted on the frame 13 with the motor carried on the back plate 37 and a motor drive shaft 49 extending through both the plates 36 and 37 to drive the speed reducer and gear arrangement. Both the reducer and gear arrangement are carried on the front plate 36 to balance the sling 10 against tilting on the crane hook 15 and thereby prevent the cables 19 or chain 30 from binding against the sides of the frame. An output shaft 50 from the reducer is connected by chains through two lower intermediate sprockets 51 and 53 and a large sprocket 54 which is fastened to the projected end of the drive sprocket axle 43. This defines the double reduction, chain-driven, gear arrangement 47 which herein results in approximately a one thousand to one reduction of speed and a comparable reduction in the torque required of the motor. Advantageously, this arrangement allows for a comparatively small motor 35 to be used to rotate the drive sprocket 31 to draw the chain 30 from one side of the frame to the other when adjusting the attitude of the load. Moreover, the speed reducer is of the worm and worm gear type and also acts as a brake to prevent the drive sprocket from turning under the weight of the load when no power is being supplied by the motor.

Herein, the motor 35 is carried on a L-shaped mounting bracket 55 and four bolts 56 extend through the bracket and the back plate 37 to mount the bracket on the back plate and flexible couplings 58 permit relative vertical adjustment between the motor and the reducer 46. Supporting the reducer on the front plate 36 is a reducer carrier 57 which includes a back piece 59 engaging the lower surface of the front plate and a vertical front piece 60 connected to and spaced from the back piece by side and bottom members 61 and 63 (FIG. 2). An idler shaft 64 is journaled between the two pieces and carries the intermediate sprockets 51 and 53 of the gear arrangement. Four bolts 65 fasten the back piece to the front plate of the frame and extend through elongated slots 66 in the back piece to permit vertical adjustment of the intermediate sprockets to adjust the tension in the chain leading to the large sprocket 54. Slidably mounted on the front piece of the carrier is a brace 67 supporting the reducer 46. Additional bolts 68 also extend through vertically elongated openings 69 to permit vertical adjustment of the reducer relative to the intermediate sprockets and thus the tension in the chain connecting the gear arrangement with the output shaft 50 of the reducer.

From the foregoing, it will be apparent that the present invention provides a unique sling 10 which may be used to very quickly and easily adjust a load such as 11 for carriage at a precise attitude. This is accomplished through the novel construction of the sling legs 17 as adjustable interconnected loops each of which carries a block 27 and hook 29 for attachment to the load. Before the load is lifted, the sling frame 13 may be slid along the top portion of the looped legs to selectively lengthen and shorten the legs by enlarging one loop at the expense of the other. When the load is lifted, the gripper 20 holds the frame against sliding on the top portion of the cables 19 to prevent the load from tilting out of the previously selected general attitude. Then while the load remains lifted, the lower portions of the looped legs are shortened and lengthened selectively by rotating the drive sprocket 31 to drive the chain 30 across the frame thereby to lengthen one leg at the expense of the other. As the legs are being shortened and lengthened the blocks carrying the hooks ride up and down on the cables to respectively raise and lower opposite ends of the load to position to the load precisely at the desired attitude as shown in FIGS. 5a and 5b.

Claims

I claim as my invention:

1. A sling for carrying a load comprising a liftable, load-bearing frame, a releasable gripper mounted on said frame, two sling legs depending from the sides of said frame opposite each other and being defined by a cable having an intermediate end portion trained across said gripper and an end doubled back and connected with said frame to form an elongated loop, said legs having free ends adapted for attachment to the load, said gripper serving to hold said frame against sliding on the intermediate end portion of the cable when under load, mechanism for releasing said gripper from the cable when under no load so that said gripper may be slid with said frame across the cable to lengthen one of the legs by enlarging the loop forming that leg while shortening the other leg thereby to select the general attitude at which said load is to be lifted, and means connected to the doubled back end of said cable and selectively operable to lengthen and shorten said one loop after said load is lifted to move said load into a precise attitude for carriage by said sling.

2. A sling for carrying a load comprising a liftable, load-bearing frame, a releasable gripper mounted on said frame, two sling legs depending from opposite sides of the frame and formed as elongated loops defined by a cable having an intermediate end portion trained across said gripper and end portions doubled back and connected with said frame, said loops having free ends adapted for attachment to the load, said gripper serving to hold said frame against sliding on the intermediate end portion of the cable when under load, mechanism for releasing said gripper from the cable when under no load so that said gripper may be slid with said frame across the cable to lengthen one of the legs by enlarging the loop forming that leg while shortening the other leg thereby to select the general attitude at which said load is to be lifted, and power means connected between said two loop portions and being selectively operable to lengthen one of said loops while shortening the other of said loops after said load is lifted to move said load into a precise attitude for carriage by said sling.

3. A sling as defined by claim 2 wherein said power means includes a motor mounted on said frame, a drive sprocket mounted on said frame vertically of said gripper and connected to said motor for selective rotation thereby, and a chain connected to and extending between the doubled back ends of said loop portions and trained across said sprocket for selective movement thereby from one side of said frame to the other side to shorten one of said loop portions while lengthening the other of said loop portions when said motor is actuated to rotate the sprocket.

4. A sling as defined by claim 3 wherein said power means further includes a power reducer mounted on said frame opposite said motor and connected between said motor and said sprocket to act as a brake and thereby prevent movement of said chain without actuation of said motor.

5. A sling as defined by claim 4 including two idler sprockets mounted on said frame vertically of said drive sprocket, said idler sprockets being spaced from each other at opposite ends of said drive sprocket, said chain being threaded around said idler sprockets to guide the chain over a predetermined length on the circumference of said drive sprocket notwithstanding differences in the included angle between said sling legs.

6. A sling as defined by claim 5 including a block and hook mounted on the looped end of each of said legs for attachment to the load and for riding within said loop portions as said legs are lengthened and shortened to adjust the attitude of said load.

7. A sling for carrying a load comprising a liftable, load-bearing frame, a releasable gripper mounted on said frame, two sling legs depending from opposite sides of the frame and formed as elongated loops defined by a cable having an intermediate end portion trained across said gripper and end portions doubled back toward said frame, and connected to each other, said loops having free ends adapted for attachment to the load, said gripper serving to hold said frame against sliding on the intermediate end portion of the cable when under load, mechanism for releasing said gripper from the cable when under no load so that said gripper may be slid with said frame across the cable to lengthen one of the legs by enlarging the loop forming that leg while shortening the other leg thereby to select the general attitude at which said load is to be lifted, power means being operable to move the connected end portions of said cable back and forth selectively to lengthen one of said loops while shortening the other of said loops after said load is lifted to move said load into a precise attitude for carriage by said sling.