GB2183595A - Lifting apparatus - Google Patents

Abstract

A tongs type grab has jaws 17,18 with a member 31 engageable with a load on descent of the grab to release a locking arm 25 so that on raising of the grab the jaws can close. Between the member 31 and a further member which acts on the locking arm are a pair of cams, lost motion between which is taken up by a pair of keys. Raising and lowering of the grab cause the locking arm to be moved between its operative and inoperate positions via the cams and keys. <IMAGE>

Description

SPECIFICATION Lifting apparatus This invention relates to lifting apparatus.

According to the invention a grab comprises jaws movable between open and closed positions, means engageable with a load to be lifted and operably connected to cam means, said cam means comprising cooperablefirst and second cams, means biassing the first and second cams into operative relationship, means for holding the jaws open, said engageable means being effective to release the holding means on lowering of the grab so thaton raising of the grab the jaws close and the load is lifted and on subsequent lowering ofthe grab engagement of the load with a support operates the engageable means and the jaws open to release the load.

The invention may be performed in various ways and one specific embodiment with possible modifications will now be described by way of example with reference to the accompanying drawings, in which: Figure lisa front view of a grab in fullyopen position; Figure2 is a side view of Figure 1; Figure3is a section on the line A-A of Figure 1; Figure 4 is a side view of a cam; Figure 5 is an end view from the right of Figure 4; Figure 6is a plan view of Figure 4; Figure 7is a developed viewofthe cam of Figure4; Figure 8 is a side view of anothercam; Figure9is an end view from the right ofFigure8; Figure 10 is a plan view of Figure 8;; Figure 11 is a developed view ofthe cam of Figure 8;and Figure 12 to 16 show schematic views of the cams in various positions during operation ofthe grab.

The grab or lifting apparatus 10 has atop lifting eye 11 to the front of which is secured a vertical hollow element 12 in which is slidable a guide bar 13 having at its lower end a housing 14for a pivot pin 15 held bya spring pin 16. Two grab jaws 17, 18 can pivot on the pin 15. Each jaw comprises two spaced jaw elements 17,18. Each jaw element 18 has fixed to itastop 19 having aface 19a engaged bythe respective jaw element 17 in the fully open (full line) position of the jaws.

The upper ends of the jaw elements 17,18 are respectively pivoted at 20,21 to links 22,23 the upper ends of which can pivot on pin 24 mounted in the lower end ofthe eye 11 to form a lazytongs arrangement.

Movementoftheguide 13 up and down will move the jaws between the open position and a grabbing or lifting position, one of which is shown in chain-dotted lines (Figure 1) in which the jaws are gripping a fuel pin 25 for a nuclear reactor, although the grab can be used in lifting other articles.

When not in use the grab is stored in the open, but locked, position. An arm 25 can pivot on pin 20 and includesformation 26 which in the locked position engages pin 21 to prevent closing movementofthe jaws 17, 18,further opening movement being prevented by the stops 19. A pad or locating member 30 includes downwardly diverging arms 31 and is held in the lower end of a vertical shaft 32 buy a bolt33 and is biassed downwards by spring 34 around the shaft between the member30 and a housing 35 of operating mechanism 36.

The pivot pin 15 has an enlarged central position 37 forming the lower part of housing 35 and an upper housing part 38 rests on an outward flange 39 of a slotted bush 40 on the inside of housing parts 38,37.

The shaft 32 can move in a bush 41 in the housing 37 and a shaft 42 of an upper cam 43 can move in bush 44 in housing 38 and is biassed down by spring 45 on shaft 42 in housing 38. The upper end of shaft 32 carries lower cam 46.

Two flat movable keys 50,51 are located in slots in the bush 40and in keyways52 inthecam 46and serveto operatively connect the cams as described later.

The upper end of shaft42 carries an axially adjustable stop 53.

Figure 12 shows the grab in the locked, open, condition. Cam 46 is resting on the lower end of housing 37, the lower ends of keys 50,51 extend part way into keyways 52 and cam 43 is seated on top of the keys. To pick up a load, the grab is lowered until the arms 31 contact the load 25. In this position stop 53 engages beneath the bar 25. On continued lowering,the spring 34 is compressed and shaft42 is moved upwards,this lifting bar25 and removing stop formation 26 from the pin 21.Lowering is continued until the shaft 42 is fully extended upwards (Figure 13) in which position the keys 50,51 have largely passed through the keyways 52 and the cam 43 can index angularly so thatthe cam surfaces 43a, 46a abut and the cam 43 passes overthe tops of the keys so that itisiocked against return movement underthe effect of spring 45 and thus bar25cannot re-engage on pin 21.

The grab is now raised by, for example, a hoist.

Cam 46 slides axially down the keys 50,51 (Figure 14) and when thecam 46 is belowthetops ofthekeysthe cam 43 continues to index (leftwards in Figure 14) and comes to rest on the top of the keys at cam positions 2,4. The spring 34 pushes the arms 31 downwards to the extended position whereafterthe claws or jaws start to close and closing continues until parts 1 9b of stops 19 engages claws 17.

Afurthersmallvertical movement of the eye 11 engages the load 25 in the claws 17, 18 and the load is raised by further raising ofthe hoist. Itwili be understood that the load 25 could be a barto which a further load is secured.

When the grab with load is lowered, the load first engages the set-down level and then the cam 46 is raised, sliding up the keys, which raises cam 43.

When cam 43 is abovethe level ofthetopsofthe keys it indexes angularlyfurtheruntil it again contacts surfaces 46a (Figure 15); on further lowering the jaws open.

If the hoist is now raised, astheweight is taken by the hoist spring 34 extends, pushing the arms 31 to the extended position and shaft 42 to retract downwards relative to housing 36, allowing the bar 25 to reengage on the pin 21 and lockthe grab open.

The cam 46 slides down the keys 50,51 and once cam 43 is below the level of the top ofthe keys, cam 43 will complete its angularindexing motion and cometo rest with positions 3,4 on top of the keys (Figure 16).

Thus in one complete cycle the keys have moved from positions 1,3 in cam 43 to positions 3,1 respectively.

Claims (4)

1. A grab comprising jaws movable between open and closed positions, means engageable with a load to be lifted and operably connected to cam means, said cam means comprising cooperable first and second cams, means biassingthefirstand second cams into operative relationship, means four holding the jaws open, said engageable means being effective to release the holding means on lowering of the grab so that on raising ofthegrabthe jaws close and the load is lifted and on subsequent lowering ofthe grab engagement ofthe load with a support operates the engageable means and the jaws open to release the load.

2. A grab as claimed in Claim 1, including a lost motion connection between the first and second cams.

3. A grab as claimed in Claim 2, in which the lost motion connection comprises key means operably connecting the first and second cams, said first cam being slidable with respect to the key means.

4. A grab substantially as hereinbefore described with reference to and as shown in the accompanying drawings.