MATERIAL HANDLING SYSTEMS

Abstract: A material handling system of the kind incorporating a bucket elevator (BE) pivotable from the vertical incorporates a position transducer (PT) control means (CD, DU) responsive thereto for adjusting the speed of the elevator in dependence upon its angular position so as to maintain the rate of feed of the material approximately constant.

Description: This invention relates to material handling systems of the kind incorporating a bucket elevator movable along a path which can be pivoted to some extent from the vertical. Such material handling systems are commonly used, for example, for unloading loose material, which may be either non- or free-flowing, such as coal, iron ore, phosphates, grain and so on from the holds of barges and ships, or from storage containers, stockyards and the like. In use of such systems the bucket elevator is usually carried by an elevator leg which depends from a supporting boom, the leg being pivotable inwards and outwards with respect to the boom to a limited extent, in order to enable the elevator to reach different parts of a hold, container, stockyard or the like, such movement being generally referred to as kicking. One difficulty experienced with such bucket elevators is that the quantity of material which the buckets can contain depends on the angle and direction in which the elevator has been kicked, and if the elevator is driven at a constant speed the feed rate of the material being handled will vary in dependence upon the position of the elevator. According therefore to the invention, a material handling system of the kind referred to incorporates a transducer for monitoring the angular position of the elevator, and arranged to generate an output signal for automatically adjusting the speed at which the elevator is driven so as to maintain the rate of feed of the material approximately constant. By this means it is possible to ensure an optimum rate of discharge of material over the full operating range of kicking movement of the elevator. One bucket elevator system in accordance with the invention employed in a continuous ship unloader will now be described by way of example with reference to Figures 1 to 4 of the accompanying schematic drawings, in which Figure 1 represents a side view of the ship unloader in diagrammatic form, Figures 2 and 3 illustrate the manner of operation of the elevator, and Figure 4 illustrates an alternative form of ship unloader embodying the invention. Referring first to Figure 1, the ship unloader comprises a main luffing boom A mounted, intermediate its end on a support frame R by means of a horizontally extending pivot V, the frame being carried by a main support structure S relative to which it is free to slew about a vertical axis. A marine leg B, accommodating a bucket elevator BE (Figure 2), depends downwards from one end of the luffing boom A, being mounted on a transversely-extending pivot pin MP which allows the leg to be "kicked" inwards and outwards to a limited extent from the vertical. The opposite end of the luffing boom A carries a fixed ballast D and a rocking ballast E, the latter being mounted at the upper end of a support frame K which is pivoted at its lower end to the luffing boom, and is coupled at its upper end to the upper end of the marine leg B, which projects above the luffing boom A, via links G, F and a bell crank lever C. A hydraulic ram J acts between the frame R and the rearwardly projecting arm M of the bell crank lever C for pivoting the latter about its axis, this resulting in the marine leg being kicked in or out, and at the same time producing a simultaneous movement of the rocking ballast E such as to compensate for changes in the position of the centre of gravity of the marine leg B relative to the luffing boom A, as described in co-pending Patent Application No. 8609497. The bucket elevator BE is driven in use by a variable speed electric or hydraulic drive motor DM located at the top of the marine leg B. It will be noted that the amount of material carried by the elevator buckets BT (only some of which are shown) is at its lowest when the marine leg is kicked-out through its maximum angle +α° as at BEO, and is greatest when it is kicked in through its greatest angle -α° as at BEI. This is shown more clearly with reference to Figure 3, in which 3(a) shows a bucket BT with the marine leg B kicked-out at an angle +α°, the surcharge angle of material (shown shaded) within the bucket being below the edges BTE of the bucket sides. Figure 3(b) shows a bucket with the marine leg in the vertical position, the surcharge relative to the bucket being increased, and Figure 3(c) shows a bucket with the marine leg kicked-in at an angle -α°, giving a maximum bucket fill, with the surcharge well above the bucket edges BTE. A position transducer PT of any convenient kind monitors the movement of the bell crank lever C and hence the angle of kick of the marine leg B, and a control device CD responsive to the position transducer PT generates an output signal which is fed to a drive control unit DU which controls the speed of the electric or hydraulic motor DM driving the bucket elevator the speed being increased when the leg B is kicked-out, and decreased when it is kicked-in, by amounts depending upon the angle of kick, such as to maintain the rate of feed of the material approximately constant. Furthermore it will be noted with reference to Figure 2 that with the marine leg B kicked-in and the bucket elevator running at its lowest speed, the trajectory of materials from head of elevator will be low, allowing material to flow down the discharge chute DC at a steep angle, whereas with the marine leg kicked-out and the elevator running at its highest speed the trajectory of material will be high, allowing material to flow down discharge chute at a flatter angle, the angle of the chute varying with the angular setting of the marine leg in an appropriate manner to allow for the changes in trajectory. In the ship unloader illustrated the transfer ashore is on the opposite side of the elevator head to the discharge, but it will be appreciated that the invention and the principles contained therein apply also to installations in which the transfer is on the same side as the discharge. The position transducer, instead of monitoring the position of the marine leg B indirectly, as illustrated in Figure 1, may be located directly between the leg and the boom as in the modified arrangement shown in Figure 4, the control in this case being arranged to include a correction for variations in boom angle.

Claims: 1. A material handling system of the kind referred to incorporating a transducer for monitoring the angular position of the elevator, and arranged to generate an output signal for automatically adjusting the speed at which the elevator is driven so as to maintain the rate of feed of the material approximately constant. 2. A material handling system according to Claim 1, wherein the bucket elevator forms part of an elevator leg which is supported for pivotal movement in a vertical plane by a nominally horizontal boom, the boom is itself mounted on, and is arranged to luff about a horizontal axis to a limited extent relative to, a main support structure, and wherein the support structure carries a bell crank lever, also pivotable about said horizontal boom axis, and actuating means linked to the bell crank lever for producing a pivoting movement thereof, the bell crank lever being linked to the elevator leg for transmitting the motion of the actuator to the leg, which linkage is such that the angular setting of the leg remains substantially constant over a range of different luffing positions of the boom, and the transducer being arranged to monitor the position of the bell crank lever and hence the angular setting of the elevator leg. 3. A material handling system according to Claim 1, wherein the bucket elevator forms part of an elevator leg which is supported for pivotal movement in a vertical plane by a nominally horizontal boom, the boom is itself mounted on, and is arranged to luff about a horizontal axis relative to, a main support structure, the transducer being arranged to monitor the position of the elevator leg relative to the boom, and a further transducer means being provided for monitoring the position of the boom relative to the support, and the system including control means for adjusting the speed of the elevator in dependence upon the outputs of both transducer means. 4. A material handling system according to Claim 1, 2 or 3 wherein the bucket elevator is driven by an electric motor, and the system incorporates a control circuit for controlling the speed of the motor in dependence upon the output of the transducer. 5. A material handling system according to Claim 1, 2 or 3 wherein the bucket elevator is driven by an hydraulic motor, and the system incorporates means for controlling the speed of the motor in dependence upon the output of the transducer. 6. A material handling system according to any preceding Claim wherein the elevator incorporates a discharge chute at the top of the elevator for feeding material discharged from the buckets of the elevator on to a conveyor belt carried by the boom, the angle of the chute relative to the vertical varying with the angular setting of the elevator leg. 7. A material handling system according to any preceding Claim in which the elevator head chute is shaped and positioned to ensure efficient discharge within the range of kick angles and belt speed and the resultant discharge trajectory of the material from the elevator buckets.

Inventors: ADDICOTT, DONALD WILLIAM RUSSELL
Applicants: GEC ALSTHOM MECH HANDLING LTD
Application year: 1987
Main classification: B65G67
IPC codes: B65G67