Automatic container spreader
This invention relates to a spreader which is useful for hoisting a container, for example with a crane or hoist. 
     Containers which are made according to International Standard Organisation specifications have four lifting blocks of hollow construction, one at each corner, each lifting block having a rectangular opening in which a key end of a twist lock may be inserted, the twist lock having a rectangular section key on the end of a spindle which, upon insertion and rotation, engages the walls of the opening and allows a lifting force to be applied for lifting the container. 
     When a container is to be lifted. a spreader frame is used having respective twist locks at each of four corners, and the spreader frame is lifted by the hook of a crane which engages a central lifting location, thereby lifting the container without applying side forces to the twist locks. 
     The spreaders which are presently used are occasionally unreliable, in that a spreader can still accept the weight of a container even though all twist locks are not properly located within the receiving blocks, and the main object of this invention is to provide a spreader and twist lock assembly wherein the danger of malfunction is reduced. A second object is to provide means which will reduce the amount of labour requirement. 
     In this invention a spreader for transmitting a lifting force to twist lock blocks located at respective corners of a container when engaged by respective twist locks carried by the frame of the spreader, comprises a lifting member, lifting cables extending from the lifting member to the spreader frame, an indexing head on the spreader frame, spring means between the indexing head and the lifting member, coupling means coupling the indexing head to respective said twist locks arranged to rotate the twist locks simultaneously upon said lifting force being applied, and inhibit means operable between each respective said twist lock and the frame arranged such that if any one of the twist locks does not rotate to a locking position upon said lifting force being applied, the inhibit means inhibits movement of the coupling means which in turn disables the indexing head from rotation and thereby all other twist locks are prevented from rotation. 
     With this arrangement, every twist lock is in the same position of locking, and partial engagement of one only of the twist locks in its receiving aperture in its respective block is avoided. 
     While the invention provides a safe and more secure lifting device than has previously been available, it is nevertheless desirable that an operator should have visual means of ensuring that there has been no malfunction and in one embodimnt of this invention, each twist lock is associated with a visible pointer which indicates movement from an unlocked position to a locked position when the twist locks are rotated into their locked position, and vice versa. 
    
    
     An embodiment of the invention is described hereunder in some detail with reference to, and is illustrated in, the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a spreader, 
     FIG. 2 is a plan view, 
     FIG. 3 is a side elevation, 
     FIG. 4 is a fragmentary end elevation showing a twist-lock and its key means, and 
     FIG. 5 is an &#34;exploded&#34; perspective view of the indexing head. 
    
    
     In this embodiment, a spreader 10 comprises a frame 11 provided with a longitudinal frame member 12 and two transverse frame members 13 one at each end, and diagonal stiffeners 14 between the central portion of the longitudinal member and the ends of the transverse frame members. 
     Each end of each transverse frame member is provided with bearing means supporting a twist lock spindle 16, and a twist lock key 17 is located on the lower end of the spindle 16. 
     The central portion of the longitudinal frame member has an upstanding tube 19 containing a first tensioning spring 20 which is coupled to a hoisting loop 21 by means of a spring tensioning cable 22. The lower end of the tensioning spring has a flexible cable 23 coupled to it and this passes over pulley 24 and around an indexing head drum 25, terminating at its other end in a return spring 26 (which is a second tensioning spring), the other end of the return spring 26 being anchored to the longitudinal frame member 12. 
     The indexing head 30 is provided with a ratchet pawl 31 which alternately engages with a ratchet stop block of a pair of blocks 32 contained in an annular slot 33 in drum 25, the arrangement being such that when the drum 25 is caused to rotate under the force applied to it by the first tensioning spring 20 when the hoisting loop 21 is lifted, one of the stop blocks 32 abuts the end of pawl 31 and causes lower plate 35 to rotate, since pawl 31 co-operates with part ring 36 to form a subassembly contained in annular slot 37 in lower plate 35. This carries the crank pin 40 with it through 180° of movement, further movement being inhibited by protuberance 41 of drum engaging an abutment (not shown) on frame member 12. Pawl 31 is urged into engagement with stop blocks 32 by spring means (not shown), but can ride over ramp surfaces 42 thereof in the return direction of rotation. When protuberance 41 strikes its abutmnt, further lifting force applied to hoisting loop merely tensions spring 20 until the lifting cables 44 become tensioned, to lift the spreader 10 and the container to which it is coupled by the four keys 17 of the respective twist locks. The indexing head drum 25 and the lower plate 35 are both carried by an upper plate 45 which is fixed to the longitudinal frame member, on bearings 50 which surround a central spindle 51. 
     When the lifting force is relaxed, and cables 44 become slack, spring 20 contracts and the second spring (return spring 26) reverses rotation of drum 25, but this does not cause any rotation of lower plate 25, since pawl 31 rides over the relevant stop block 32, as said above. That is, the keys 17 remain engaged in their respective lifing blocks. However, upon again applying a lifting force, the indexing head drum again rotates 180° in a forward direction, moving lower plate 35, with its crank pin 40, also through 180° to rotate lock keys 17 back into their disengaging positions, so that the spreader 10 lifts clear of its container. 
     The mechanism for achieving this is described hereunder: 
     The crank pin 40 is journalled in small bearings in the inner ends of two link bars 46 which extend in respective opposite directions from the crank pin. 
     The outer end of each link bar 46 is coupled to one leg of a respective bell crank 47, each bell crank 47 being pivotted intermediate its ends to a transverse frame member 13, and the outer leg being coupled to a twist lock actuating bar 48. Each outer end of the twist lock actuating bar 48 is coupled directly to an arm 49 on a respective twist lock spindle 16 in such a way that the bar directly controls movement of the twist lock spindle 16 (through an angle of 90° of rotation). However this movement is normally inhibited by four inhibit plungers 52 each projecting downwardly from a respective twist lock frame 53, and each inhibit plunger 52 is urged downwardly by a spring 54 within the twist lock frame 53. When the spreader frame however is positioned over a container to be hoisted, the lower ends of the inhibit plungers 52 abut the hollow lifting blocks, and the inhibit plungers are urged upwardly against their springs 54. Each inhibit plunger 52 carries an annular boss 55 intermediate its ends, which engages in a part circular groove 56 in the side wall of an annular nut 57 on its spindle 16. Only after this upward movement does boss 55 move free of abutment surface of the groove 56 to allow rotation of spindle 16. If a crane then applies an upward lift on the hoisting loop 21, the indexing head drum 25 rotates 180° as said above, the lower plate with its crank pin 40 is thereby rotated by 180° and the link bars 46 move within the longitudinal frame member 12 of the spreader 10 to in turn move the respective actuating bars 48 in a direction which results in the twist locks being rotated. 
     In the event however that any one of the inhibit plungers does not move upwardly, the relevant twist lock will be prevented from rotation, and this disables the outer three twist locks because the indexing head is itself prevented from its rotation. In such an instance, the hoist needs to be lowered and the tensioning spring relaxed, and if the displaced twist lock is then properly placed, and hoisting effort is again applied to the tensioning spring, the indexing head is free to rotate since there is nothing at that stage which will prevent movement of the actuating bars and consequential movement of the link bars. The next rotation of the indexing head will return the twist locks to their former positions. 
     In order to provide visual means which indicate to an operator that all twist locks are properly located, each twist lock spindle 16 has secured to it a pointer arm 60 which either points towards an open position or a locked position. 
     Each spindle nut 57 contains two grooves, but only one is engagable by a boss 55. This provides a means whereby only one shape of nut 57 is required for left/right hand aspects. 
     The above description indicates the crank pin 40 depending from a lower plate 35, and the ratchet pawl 31 being carried by the lower plate 35 and engaging ratchet stop blocks 32 in the indexing head drum 25, but clearly rearrangement of these elements constitutes an obvious mechanical equivalent of the described structure. 
     A brief consideration of the above embodiment will indicate that the invention is very simple, but both reduces operator time and increases the safety associated with a spreader bar hoisting device. 
     The claims defining the invention are as follows: