WO2009020429A1

WO2009020429A1 - Gantry crane with multiple hoists

Info

Publication number: WO2009020429A1
Application number: PCT/SG2007/000234
Authority: WO
Inventors: Brian Chang
Original assignee: Yantai Raffles Shipyard Limited
Priority date: 2007-08-03
Filing date: 2007-08-03
Publication date: 2009-02-12
Also published as: BRPI0707970B1; BRPI0707970A2

Abstract

The present invention provides a gantry crane with multiple hoists for hauling a structural load (L). The structural load (L) has two parallel load beams (40a, 40b). The hoisting system (10) includes a fixed girdle (12), a parallel girdle (16) moveable in a gantry direction, a plurality of hoist units (20) on each girdle (12,16) and a plurality of load connectors (34) engageable on one load beam and another plurality of load connectors (34) engageable on the other load beam. A load distribution is determined and the plurality of load connectors (34) is grouped so that each group has a target load and the centre of gravity falls within the selected group of hoist units (20) and associated load connectors (34). During hoisting up/down operation, safety checks on hoist components, tension/position of each rope (28) and imbalance of the load (L) is monitored.

Description

Gantry Crane With Multiple Hoists

Field of Invention

[0001] The present invention relates to a gantry crane with multiple hoists for hoisting and lowering a structural member. In particular, the invention relates to a system and method for synchronizing a plurality of independent hoists of a gantry crane in order to raise and lower a suspended load safely.

Background

[0002] Marine or offshore structures are generally huge and heavy. Often, a crane with a single hoist is not sufficient to hoist such a huge marine or offshore structure. As a result, shipyards have resorted to building modules of such marine structures and then assembling the modules on a floating dock. For example, a semi-submersible platform has a hull and a deck. The hull is made up of two pontoons and a number of vertical columns on each pontoon. The pontoons and vertical columns are typically built with steel plates and bulkheads to form a number of internal compartments or ballast tanks. The platform is also built with plates and bulkheads. Water is pumped into or out of the ballast tanks to adjust the buoyancy of the hull and/or platform during fabrication, or the entire semi-submersible platform during operation.

[0003] The sizes and weights of such modules of a marine or fabricated structure are usually limited by the capacity and working height of available crane facility. The partially completed pontoon, column or platform with usable ballast tanks or compartments are often floated in the sea instead of being handled by land-based cranes. For example, a partially completed platform may be floated above a submerged hull; the submerged hull is then floated to lift the partially completed platform above water level so that further work on the platform is completed on the sea. Such fabrication of structures in the open is dependent on weather conditions and available crane barges. This makes fabrication of such structures expensive and risky. [0004] These marine structures are typically made of steel and require periodic maintenance. Often, after a service life of about 10-20 years, it is more economical to refurbish a marine structure instead of building a new one. In order to hoist such a marine structure by an overhead crane, the bulkheads must be connected and designed for overhead lifting. Different parts of the structure may have different weights. A crane with multiple independent hoists is therefore desired; a method of controlling the crane with a plurality of hoists for safe operation is therefore required.

Summary

[0005] The following presents a simplified summary to provide a basic understanding of the present invention. This summary is not an extensive overview of the invention, and is not intended to identify key features of the invention. Rather, it is to present some of the inventive concepts of this invention in a generalised form as a prelude to the detailed description that is to follow.

[0006] In one embodiment, the present invention provides a hoisting system having a plurality of independent hoist drum units disposed on each of two spaced apart girdles. The hoisting system comprises: a load connector operable to connect to a rope associated with each respective hoist drum; and a load having two enlongate load beams, which are spaced apart to substantially the same dimension as the spaced apart girdles; wherein the load connector is operable to connect with the elongate load beams and the load itself synchronises the independent hoist drums hoisting up/down operation.

[0007] In another embodiment, the present invention provides a control method for the above hoisting system. The control method comprises: determining the load distribution with respect to two girdles; grouping the hoist units and associated load connectors into one or more groups so that the centre of gravity falls within the one group, between two groups or within the groups; establishing a target load for each of the one or more grouping of hoist units and associated load connectors; and incrementing the load a predetermined step, such as 10%, up to the target load during operation whilst checking the hoisting system for safety; tension, displacement and speed of each rope; and imbalance in the load.

Brief Description of the Drawings

[0008] This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which:

[0009] FIG. IA illustrates a double girdle gantry crane according to an embodiment of the present invention;

FIG. IB illustrates the use of load connectors and load-bearing beams for hoisting up/down a load with the crane shown in FIG. IA;

FIG. 1C illustrates a load connector shown in FIGs. IA and IB;

FIG. ID illustrates a hoist unit shown in FIGs. IA and IB; and

FIG. IE illustrates an arrangement of the rope sheaves shown in FIGs. IA and IB.

[0010] FIG. 2 illustrates a flow chart for safe operation of the crane shown in FIG. IA according to another embodiment of the present invention; and

[0011] FIGs. 3A-3E illustrate hoist groupings for synchronizing separate hoist units and levelling control of a load according to yet another embodiment of the present invention.

Detailed Description

[0012] One or more specific and alternative embodiments of the present invention will now be described with reference to the attached drawings. It shall be apparent to one skilled in the art, however, that this invention may be practised without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, common reference numerals or series of numerals will be used throughout the figures when referring to the same or similar features common to the figures.

[0013] FIG. IA shows a hoisting system 10 according to an embodiment of the present invention. As shown in FIG. IA the hoisting system 10 includes a fixed overhead girdle 12 and a gantry overhead girdle 16 for holding a load L. The fixed overhead girdle 12 spans across the top of two columns 13 whilst the gantry girdle 16 spans across the top of two lower columns 17. Although the fixed girdle 12 and gantry girdle 16 are at different heights, they are substantially parallel to each other. On each of the girdles 12, 16, there are six hoist units 20a, 20b...2Of. As shown in FIGs. IA, ID and IE, each hoist unit 20a, 20b ... 2Of includes a drum 22, a hoist motor-gear set 24, a set of hoist brakes 26a, 26b... etc, an encoder 27, a rope 28 and rope sheaves 30 and a load cell 29. The rope sheaves 30 includes a set of fixed sheaves 31 and a set of load connectors 34 connected to a set of travelling sheaves 32 for cooperation with the set of fixed sheaves 31, and a fleet-angle pulley 36.

[0014] As shown in FIG. IA, the fixed sheaves 31a, 31b ...etc are connected to a lower edge of each girdle 12, 16 in a staggered manner along the longitudinal axis of the respective girdle and are uniformly spaced apart. The travelling sheaves 32a, 32b... etc at the load connectors 34 are equally and uniformly spaced apart by pivoted link bars 38a, 38b, 38c. In use, the load connectors 34 are connected to an elongate load-bearing beam 40 on the load L. As shown in FIGs. IA and IB, there are two spaced apart load- bearing beams 40a, 40b. The gantry overhead girdle 16 is moved apart from the fixed overhead girdle 12 to substantially the same dimension between the spaced apart load- bearing beams 40a,40b.

[0015] The hoisting system 10 also includes a control panel 50 but is not shown in FIG. IA. The control panel 50 includes at least a programmable logic controller (PLC) 52, driver/inverter 54 for each hoist motor, an alarm/buzzer 56, an emergency stop button 58 and a central control console 60. The PLC 52 is programmed to allow manual and automatic control of individual hoist unit 20 or group(s) of hoist units. The central control console 60 includes at least a display/touch screen panel 62, control stick 64a, 64b ...etc for each hoist unit, indicator lights 66, alarm/buzzer 56 and emergency stop 58.

[0016] With the present invention, the tension transmitted from each hoist unit 20a, 20b... etc is uniformly distributed by the respective sets of fixed sheaves 30 and travelling sheaves 32 to the respective load connectors 34 and load-bearing beams 40a,40b. The load transmitted to different hoist units or group(s) of hoists may be different depending on the centre of gravity of the load L.

[0017] Operation of the hoisting system 10 includes executing the following functions:

1. safety checks;

2. pretension and calibration;

3. level control; and

4. synchronized hoist group operation.

FIG. 2 shows a flow-chart 200 for safe operation of the hoisting system 10 according to another embodiment of the present invention. As shown in FIG. 2, the hoisting system operation 200 starts from step 205. In step 205, power is supplied to the control panel 50, central control console 60 and lights/flood-lights 70.

[0018] A decision is then made in step 210 whether the hoist grouping is correctly selected considering the weight of the load L and its centre of gravity. If the hoist grouping is not correctly made and the decision in step 210 is negative, the system operation 200 is aborted. If the decision in step 210 is positive, the system operation 200 proceeds to step 215.

[0019] In step 215, electric power is supplied to the hoist motor-gear set 24 and all the other hoisting system 10 components.

[0020] A decision in then made in step 220 whether any safety interlock is activated. A safety interlock includes activating an emergency stop button 58 and/or switching the system operation to repair/maintenance mode, programming mode or calibration mode. If any safety interlock is activated, the system operation is reset in step 222. If no safety interlock is activated, the system operation proceeds to step 225. [0021] In step 225, each hoist motor inverter /driver 54 is checked whether it is normal. If the check in step 225 is negative, i.e. a hoist motor inverter/driver may be faulty, the system operation is aborted; a signal is then sent to the central control console 60 and the relevant indicator light 66 is illuminated to indicate the fault. If the check in step 225 is positive, the system operation proceeds to step 230.

[0022] In step 230, a decision is made whether any of the hoist motor 24 is overheated. If the decision in step 230 is positive, the relevant indicator light 66 at the central control console 60 is illuminated, such as a repair indication in step 238. Hoist motor over-heating may be due to fan malfunction 232, thermistor malfunction 234, exceeding maintenance period 236, overloading, etc. Once the hoist motor fault is rectified, the repair indication is reset in step 238. The system operation then checks, in step 240, whether repair/reset has been carried out. If repair/reset is carried out, for example, after a predetermined time interval, the system operation is aborted in step 227. If repair/reset is carried out, the system operation loops back to step 230 and hoist motor overheating condition is checked again. When all the hoist motors 24 are in normal running condition, the system operation proceeds to step 245.

[0023] In step 245, a decision is made whether each hoist encoder 27 is in normal working condition. In normal working condition, the position of each encoder 27 indicates the pay out length of rope from the respective hoist drum 22, which is calculated to indicate the vertical position of the load L. At the same time, the rotation per unit time is calculated to indicate the speed of the hoist drum 22. If the decision in step 245 is negative, i.e. a hoist encoder 27 is malfunctioning, the system operation stops and executes, in step 295, a fault monitoring program to identify/report the faulty condition, for example by illuminating the relevant indicator light 66. If the decision in step 245 is positive, the system operation proceeds to step 250.

[0024] In step 250, each hoist brake 26a,26b...etc is checked whether it is in working order. If a hoist brake 26a,26b ...etc is not in working order, the system operation stops and executes, in step 295, the fault monitoring program to identify the faulty/report the faulty condition. If all the hoist brakes 26a,26b ...etc are in working condition, the system operation proceeds to step 255.

[0025] In step 255, each brake pad is checked whether it is in normal condition. If any of the brake pad is worn out and the associated brake actuator is near its limit of travel, the system operation stops and executes, in step 295, the fault monitoring/reporting program. If all the brake pads are still in working condition, the system operation proceeds to step 257.

[0026] In step 257, the speed of each hoist drum 22 in the selected hoist group made in step 210 is incremented by 10%, before operation of the hoisting system proceeds to step 260.

[0027] In step 260, each hoist drum speed is checked whether it is normal. If a hoist drum speed is too fast, there may be a slack or break in the associated rope 28. In addition or alternatively, the associated hoist brake 26 or gear unit 24 may fail. If a hoist drum is too slow, it may be overloaded. If the check in step 260 determines that the hoist drum speed is abnormal, the system operation stops and executes the fault monitoring/reporting program in step 295. If the hoist speeds of all the hoist units 24 are normal, the system operation proceeds to step 270.

[0028] In step 270, each load cell 29 associated with a hoist unit 24 is checked whether it is over-loaded. If a load cell 29 is overloaded, the load cell condition is checked again in step 272 after an elapsed of a predetermined time period. If the check in step 272 is again positive, the system operation stops and executes, in step 295, the fault monitoring/reporting program. If none of the hoist unit is overloaded in step 270 or the overload condition in step 272 has recovered, the system proceeds to step 275.

[0029] In step 275, the system 200 allows an operator to operate the hoist units 24 up or down according to the operator command. At the same time, the system operation continues to check the system for any safety breaches. [0030] In step 280, dynamic tension and displacement of each rope associated with each hoist unit is checked whether they are normal. If the tension and displacement are abnormal, for example due to slack or break in a rope, the system operation stops and executes the fault monitoring/reporting program in step 295. If the tension and displacement of all the ropes are normal, the system operation proceeds to step 285.

[0031] In step 285, the hoist units 24 are checked whether they are synchronized. If the difference in speed of any one of the hoist units 24 exceeds a predetermined percentage of the difference in speed among all the hoist units, the system operation stops and executes the fault monitoring/reporting program in step 295. If the differences in hoist speed among all the hoist units are consistent with the change in the number of rope layers on the hoist drum 22, the system operation continues to step 290.

[0032] In step 290, any imbalance of the load L is again checked. Imbalance of the load L may be due to improper selection of hoist grouping. If such imbalance happens, and the predetermined percentage difference in rope tensions and displacements in step 280 is not detected, or synchronization of the hoist units in step 285 is not detected, the system operation stops and executes the fault monitoring/reporting program in step 295. If no imbalance of the load L is detected, the system 200 proceeds to step 292.

[0033] In step 292, the system 200 checks whether full speed of each selected hoist drum 22 has attained its full speed. If the decision in step 272 is negative, the system 200 loops back to step 257 and the hoist speed is increased by increments of 10% of the full speed. With each increment in hoist speed, the system 200 loops through step 260 to step 290, and a decision is made again in step 292. If the decision in step 292 is positive, meaning that the relevant hoist drum 22 has attained its full speed, the system 200 jumps back to node 273 and continues to check each hoist unit from step 272 through to step 292 for safe operation.

[0034] The load L envisaged in the present invention is typically heavy and expansive; as a result, the centre of gravity is typically not at the geometric centre. Thus, lifting the load L must be planned such that the centre of gravity of the load is within the envelope defined by the load connectors 34; this is to ensure that the load does not over-turn during hoisting or lowering. This problem is complicated in the present invention because all the hoist-gear sets 24 are not mechanically synchronised. The problem encountered in the present invention is overcome by benefiting from the rigidity of the load L acting as a synchronising mechanism. At the same time, tensions and speeds of the ropes 28 are monitored so that the load L remains level during hoisting or lowering.

[0035] FIGs. 3A-3E illustrate various groupings of the hoist units 24 for safe operation of the hoisting system 200 according to the present invention. As shown in FIG. 3 A₅ some of the hoists on both girdles 12, 16 are operated in one group such that the centre of gravity falls within the envelope defined by the one group of hoists. If the rope tension in any hoist unit in the group of selected hoists exceeds its safe working load, hoisting operation is stopped and the fault monitoring program would prompt the operator to re-group the hoist units for safe operation.

[0036] FIG. 3 A illustrates a grouping of the hoist units 24 on each of the two girdles in addition to a third grouping spanning both girdles. FIG. 3 B illustrates a grouping of the hoist units 24 on a girdle and another two groupings on the second girdle. FIG. 3C illustrates a U-grouping of the hoists that spans both girdles. FIG. 3D illustrates a grouping of the hoist units 24 on each of the two girdles 12,16. FIG. 3E illustrates a grouping of the hoist units 24 on a girdle and an L-grouping spanning two girdles. In these possible hoists grouping configurations, the centre of gravity fall within a large envelope defined by the grouping of hoists. During hoisting up or down of the load L, the rope tension and speed associated with each hoist unit 24 are continuously monitored, i.e. the rope tensions are kept within safe working load to ensure safe operation; at the same time, the system 200 ensures differences in rope speeds does not exceed the predetermined percentage speed difference so that all the hoist-gear sets 24 are substantially synchronized and the load L remains substantially level.

[0037] Once all the safety checks in steps 210-255 are complete and the rope/cable tensions and displacements, together with the percentage differences, are within design limits, hoisting up/down operation in step 275 continues. During startup, for example during initial system setup or after maintenance, the hoist operation step 275 includes a pretensioning and calibration step 277 and a load leveling step 278. In one embodiment, pretensioning is done by hoisting up each set of the travelling sheave blocks 32 and load connectors 34 at a slow speed such that any rope slack is taken up. When there is no more rope slack, reading of each load cell 29 at the central control console 60 associated with each hoist unit 20 is zeroed and the control stick 64 position readout is re-set.

[0038] In load leveling step 278, a test load is connected to two or more groups of hoist units 20 and the test load is hoisted up at a predetermined constant speed. During each load leveling test, the position and speed of each hoist unit 20 are recorded by a data logger connected to the PLC 52. The vertical position of the test load and speed of the hoist units are analysed; for example, from the change in height and the corresponding speed, the hoist with the lowest speed is chosen as a reference hoist, whose position and speed are used as reference data for the positions and speeds of all the other hoist units 20. In other words, automatic calibration of the positions and hoist speeds are executed; manual and automatic compensation are then made possible. In addition, the load cells 29 are calibrated. The system 200 also provides for manual and automatic operation of the entire crane.

[0039] Once pretensioning, calibration and automatic leveling of the hoist system are done, the hoisting system 10 is ready for use. As shown in FIG. 2, the hoisting system 10 continues to monitor the tension and displacement in all the ropes 28 in step 280. In addition, the hoisting system 10 also continues to monitor level control of the load L by checking the synchronization of all the hoist units 20 in step 285 and checking for any imbalance in step 290.

[0040] In implementing the group hoisting according to the present invention, the mass and centre of gravity of different modules making up the load L are determined. A load distribution is determined and a selection of the hoist grouping(s) is then made with each group having a target load. During a hoist up/down operation, the target load is increased by increments of 10% over a predetermined period of time. During each load increment, all the safety checks from step 220 through to step 272, tension/displacement in step 280 and load imbalance in steps 285 and 290 are made. If any imbalance in the load occurs, the hoist grouping(s) is/are re-defined and the system operation 200 is carried out again.

[0041] While specific embodiments have been described and illustrated, it is understood that many changes, modifications, variations and combinations thereof could be made to the present invention without departing from the scope of the invention. For example, a gantry crane with multiple hoists on more than two girdles may be used.

Claims

CLAIMS:

1. A hoisting system having a plurality of independent hoist drum units disposed on each of two spaced apart girdles, the system comprising; a load connector operable to connect to a rope associated with each respective hoist drum; and a load having two enlongate load beams, which are spaced apart to substantially the same dimension as the spaced apart girdles; wherein the load connector is operable to connect with the elongate load beams and the load itself synchronises the independent hoist drums hoisting up/down operation.

2. A hoisting system according to claim 1, wherein the load connector is connected to a travelling sheave block whilst a fixed sheave block is disposed on the relevant girdle.

3. A control method for the hoisting system according to claim 1 or 2, the method comprising: determining the load distribution with respect to two girdles; grouping the hoist units and associated load connectors into one or more groups so that the centre of gravity falls within the one group, between two groups or within the groups; establishing a target load for each of the one or more grouping of hoist units and associated load connectors; and incrementing the load by a predetermined step up to the target load during operation whilst checking the hoisting system for safety; tension, displacement and speed of each rope; and imbalance in the load.

4. A control method according to claim 3, wherein the predetermined step is 10% of the target load.

5. A control method according to claim 3 or 4, wherein imbalance in the load occurs when the percentage change in the tension, displacement or speed of a hoist unit exceeds a predetermined percentage change.

6. A control method according to any one of claims 3-5, further comprising: pretensioning of each rope and calibrating the load cell associated therewith; and load leveling.

7. A control method according to claim 6, wherein after carrying out load leveling, the hoist with the lowest speed is used as a reference hoist to which the displacement or speed of other hoists are referred to.