US3387822A - Electrically operated hoists or pulley blocks - Google Patents

Description

June 11, 1968 A. T. c. BuRRows 3,387,822

ELECTRICALLY OPERATED HOISTS OR PULLEY BLOCKS Filed Feb. 9, 1967 2 Sheets-Sheet l Junell, 1968 A. T. c. BURRows 3,387,822

v ELECTRICALLY OPERATED HOISTS OR PULLEY BLOCKS Filed Feb. 9, 1967 2 Sheets-Sheet 2 3,387,822 ELECTRICALLY OPERATED HOISTS R PULLEY BLOCKS Arthur Thomas Charles Burrows, Hertfordshire, Engl land, assignor to Geo. W. King Limited, Stevenage, "Hertfordshire, England, a British company Filed Feb. 9, 1967, Ser. No. 614,978 Claims priority, application Great Britain, Feb. 11, 1966, 6,247/66 3 Claims. (Cl. 254-174) ABSTRACT 0F THE DISCLOSURE In an electrically operated hoist or pulley block incorporating a slipping clutch between the motor and the sprocket or winding drum the provision of at least one latch or pawl device capable of movement into and out of an operative position wherein it will .positively -lock the sprocket or drum against rotation. Means are provided for controlling the latch or pawl device so that while during a normal lifting or lowering movement it will be retained inoperative, approach to the limit of travel of the hoist chain or cable in one direction or the other will result in movement of said latch or pawl device into its operative position. Resilient means are provided for minimizing the shock on the hoist chain or cable as a result of locking of the sprocket or drum.

This invention is concerned with electrically operated hoists or pulley blocks and more particularly to such apparatus incorporating a load limiting or so-called slip- .ping clutch between the drive motor and the load sprocket or winding drum. The employment of a slipping clutch has the advantages that the electrical control system of the block can be simplied since it is no longer necessary to provide top and bottom limit switches. Moreover a block so equipped is safer in use since it is impossible to lift much more than the set working load and if the -load hook becomes caught up in any way during a lifting operation the clutch will slip. Again shock caused by careless operation of the block will also be limited.

While the incorporation of a slipping clutch in a chain hoist or pulley block results, as indicated above, in a number of advantages there is one disadvantage and that is that the load chain or cable has to withstand at least twice the working load when the chain or cable is lowered to its fullest extent and the slack end of the chain has to withstand the working load plus the force due to the slipping of the clutch. This is quite a serious matter since it means that the load chain has to be appreciably larger than that required with earlier control systems, i.e., the blocks having no slipping clutch and incorporating top and bottom limit switches.

It is the primary object of the present invention to provide a mechanism which Will be effective to limit the maximum load in the chain so that it will not materially exceed the set working load at any time during a lowering operation. lt may be mentioned here that while that is a primary object, the invention is however not limited solely to the control of lowering operations but may well be employed for controlling lifting operations.

According to the present invention it is proposed in an electrically operated hoist or pulley Iblock incorporan ing a slipping clutch between the driving motor and the load sprocket or winding drum, to provide means adapted to be actuated as a result of a predetermined travel of the hoist chain or a predetermined winding of rope or cable oil or on the drum, positively to engage the sprocket, drum or an element associated therewith thereby to lock said sprocket or drum against further rotation.

States Patent The means may include one or a pair of pawls or like devices which, or each of which is adapted to cooperate with a slot or recess in the load sprocket, drum or an element associated therewith, the arrangement being such that while during normal operation the pawl (or both pawls where two are present) will be in an inoperative or disengaged position, approach to the limit of travel of the chain in one or either direction (or winding on or ott of a predetermined amount of rope or cable) will result in movement of the pawl, or the appropriate one of such pawls into a position wherein it will engage the slot or recess in the sprocket drum or element associated therewith.

In order that the said invention may be clearly understood and readily carried into elect reference will now be made to the accompanying drawings in which:

FIGURE 1 shows in section a known type of electrically operated chain hoist or pulley block to which the invention is to be applied,

FIGURE 2 is a diagrammatic view illustrating the mechanism for limiting the downward travel of the chain of a chain hoist, and

FIGURE 3 is a diagrammatic view illustrating a mechanism for limiting the upward travel of the chain of a chain hoist.

Referring now to FlGURE l, 10 denotes a load or chain sprocket which is driven by an electric motor 11 via a slipping clutch 12, a shaft 14 and gearing designated generally by 15. As is usual with hoists of this kind a brake assembly 16 is also incorporated.

As hereinbefore indicated the hoist illustrated in FIG- URE l is of a known type and is shown merely as indicating one type of hoist to which the mechanism according to the invention may be applied.

Referring now to FIGURE 2, 10 again denotes the load or chain sprocket of a hoist or pulley block which in this case is provided, for example, by milling with a groove or recess 17 with which a sliding pawl 18 is adapted to cooperate. In FIGURE l a possible positioning of the groove or recess 17 and of the pawl 18 is shown in dotted lines. In FIGURE 2 the pawl 18 is shown in engagement with the groove or recess 17 but during a normal lowering operation it will be displaced to the right and will be clear of said groove or recess. The pawl 18 is located between guides 19 so as to be capable of free sliding movement which is imparted thereto by means of a sliding cam or actuating member 20. The member 20 which cooperates with an inclined slot 18a in the pawl 18 is formed with an angled portion 20a, the arrangement being such that when the mechanism is in the actuated position, as shown, and said member 20 is in its uppermost position, the pawl 18 will be in engagement with the recess 17 in the sprocket 10 while when said member 20 is in a -lowered position, as it will be the Case during normal lowering operation, said pawl 18 will, as a result of the shape of the member 20, be displaced to the right out of engagement with the recess 17. The member 20 is slidably supported in guides 21 and is urged downwardly by a spring 22 which bears against a stationary abutment 23. At its lower end the member 20 is provided with a pair of depending forks or extensions 24 between which a bobbin like member 25 is freely rotatably supported. Also rigidly attached to the main frame of the pulley block is a guide member 26 which serves to support a resilient'ly mounted chain anchoring device 27 the latter being provided with a rod 28 which is slidably journalled within the member 26 and with a spring 29. A possible position for the parts constituting the chain anchoring means is also indicated in dotted lines in FIGURE 1.

The load chain which is designated by 30 is anchored to the device 27 and normally either hangs slackly between said device and the sprocket or rests in a chain collecting bucket not shown.

During normal operation of the pulley block there will be slack chain between the anchoring device 27 and the sprocket 10 and said chain will be out of contact with the bobbin like member 25. At this stage the slide member Ztl will be maintained in the lowermost position by the spring 22 and the pawl 18 will be displaced to the right out of engagement with the recess 17 in the sprocket so that the latter will be free to rotate in a clockwise direction as shown in the drawing. As load hook approaches its uily lowered position, the amount of slack chain between the anchoring device 27 and the sprocket 10 will decrease progressively to such an extent that said chain will engage the bobbin like member 25 and will force the member 20 upwardly against the action of its spring 22 until the position illustrated in the drawing is attained. In this position, the pawl 18 will have been moved into engagement with the recess 17 in the sprocket 16 and will thus positively lock the latter against further rotation in the direction to cause Vfurther lowering of the load hook. The resilient mounting of the anchoring device 27 will ensure that the load on that portion of the chain between the sprocket 10 and said device will be very small when the sprocket is so locked.

It will be appreciated that by forming the sprocket with a further recess which is similar to the recess 17 it is possible to provide a pawl somewhat similar to the pawl 18 and adapted to limit the travel of the chain in the upwards direction. A possible arrangement is illustrated in FIG- URE 3 wherein the load sprocket 10 is provided with a recess 31 with which. a pawl 32 is adapted to cooperate. The pawl is supported for sliding movement in suitable guides 33 and is normally urged into an inoperative position shown in dotted lines by means of a spring 34. The chain 30 is arranged to pass through a slot or aperture in the pawl 32 and the arrangement is such that during a normal lifting or lowering motion of the chain said pawl will be maintained in its inoperative or off position. However during a lifting operation when the chain approaches the upward limit of its travel, the block normally supporting the load hook or other load supporting means will contact the pawl 32 and move the same against the action of the spring 34 into its operative or engaged position as shown in full lines thereby positively to lock. the sprocket 10. In FIGURE 3 the aforesaid block is indicated diagrammatically at 35. The spring 34 will effectively serve to minimize the shock to the load chain which would otherwise occur, when the load chain reaches its highest position. The magnitude of such a shock would of course be related to the setting of the slipping clutch between, the sprocket 10 and the drive motor of the hoist.

An arrangement such as is shown in FIGURE 3 could well be adapted for limiting downward travel of the chain rather than the mechanism shown in FIGURE 2.

In the foregoing, reference has been made solely to the application of the invention to electrically operated chain pulley blocks but in fact the mechanism above described could readily be adapted for use with an electrically operated wire rope pulley block wherein the wire or cable is wound on a drum such cable serving to support a bottom pulley block carrying the load hook. With such wire rope pulley blocks, it is common practice to employ a rope guide which is adapted to move axially of the drum in one direction or the other depending upon whether the rope is being wound on or ofi the drum. Such a rope guide could be employed to operate pawls arranged to engage the drum when the bottom block was at either of its two extremes of travel. In other words as the bottom block approached one extreme position which would also correspond with the rope guide approaching one limiting position, a rope guide would actuate the pawl to lock the drum while as the bottom block approached its other extreme position with consequent approach of said guide to its other extreme position said guide would then actuate the second pawl to again lock said drum. The introduction of such pawls would result in a marked improvement in operation of such a pulley block, since:

(i) When lifting, the bottom block can be stopped just clear of the wire rope guide so that it will not, as has happened heretofore, hit the rope guide or the drum.

(2) On lowering when reaching the extremity of downward travel the pawl may be caused to engage the drum while the statutory two dead turns are still wound on said drum. Heretofore this condition (i.e. the presence of the two dead turns) has been ensured by switching off the motor and applying the brake but with the arrangement now envisaged such an electrical control may be eliminated.

It will be appreciated that should the bottom block not be required to travel to the very highest or very lowest positions, intermediate stopping points would readily be arranged simply by adjusting the means controlled by the wire rope guide in order that the pawls would be actuated earlier in the axial travel of said guide i.e. before the latter approached either of its extreme positions.

I claim:

1. In a chain hoist wherein a chain is anchored at one end to a hoist body and passes over a chain sprocket which is driven by an electric motor through the intermediary of a slipping clutch, an improvement comprising two pawl devices each movable into and out of an operative position wherein it Will lock the chain sprocket against rotation, an actuating member movable between first and second positions and engaging one of said pawl devices to effect movement thereof between inoperative and operative positions coresponcling to the first and second positions of said actuating member, resilient means acting on said actuating member to urge the same into its first position, means associated with said actuating member so that as the chain approaches the lower limit of its travel, that portion of the chain between the sprocket and the anchor point will be effective to cause displacement of the actuating member to its second position with resultant movement of said one pawl device into its operative position, resilient means associated with the second pawl device and normally effective to maintain the same in an inoperative position, and means including an abutment carried by said chain for contacting said second pawl device to move the same against the action of the associated resilient means into its operative position as the chain approaches the upper limit.

2. The improvement as claimed in claim 1 comprising means resiliently anchoring said one end of the chain to the hoist body.

3. The improvement as claimed in claim 1 wherein said one pawl device is provided with an angled slot, said actuating member extending through said angled slot and being slidable in said slot between said iirst and second positions, said actuating member including an angled portion which engages said one pawl device in the angled slot thereof to move said one pawl device between the inoperative and operative positions as the actuating member is moved back and forth between said first and second positions.

References Cited UNITED STATES PATENTS 2,053,976 9/1936 Stahl 254--173 3,261,589 7/1966 Neumeier 254-173 3,290,012 12/1966 Matthews 254-187 FOREIGN PATENTS 1,116,364 11/1961 Germany.

EVON C. BLUNK, Primary Examiner.

H. C. HORNSBY, Assistant Examiner.

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