The invention relates to an improved hoisting apparatus that, through the use of a dual diameter or tapered drums and opposite direction wire rope wrapping, reduces the shaft torque required to lift a load with respect to that seen in conventional hoisting systems.
Figs 2 and 3
With differing drum diameter sections, the shaft torque for the same operation may be positive, zero or negative. This improved design, besides allowing for smaller drum rotating mechanical equipment, has wide applications in the hoisting and craning industry. One of the applications is for use as a container crane’s trim, list, skew and snag protection system (TLSS).
Container cranes typically hoist containers with four individual wire ropes. For the purposes of simplification in explanation, each wire rope runs to a corner of a lift beam connected to the container. By controlled take up and let out of these four wire ropes the operator of the crane can force a container to tilt in the x axis, the y axis or yaw about a vertical z axis.
In the craning industry these motions are called list, trim, and skew. In aircraft terms, these would be termed limited roll right and left, limited pitch nose and tail, and limited yaw clockwise and counterclockwise (TLS). By adjusting these motions a suspended container can be forced to align better as it is moved on and off a ship and on or off a truck.
A snag occurs when a hoist is lifting a lift beam at high speed and the lift beam hangs up in a ship’s hold, or alternatively, when the lift beam fails to stop when it reaches the underside of the hoist trolley. Although there is a significant amount of stretch in long wire ropes, once a snag occurs, if the upward lift of the crane is not stopped, damage will occur. Stopping the upward motion of the lift beam is not immediate as the hoist machinery keeps turning by virtue of its own flywheel inertia.
The rotating kinetic energy associated with that flywheel inertia must be converted to heat, elastic strain or deformation. A typical snag event only lasts about 0.3 seconds. For this reason container cranes must be equipped with a fast-acting snag system.
Most previous art systems incorporate hydraulic cylinders in some manner. The most popular system combines four individual cylinders to serve all four functions. With this type
of system, the same cylinder that can adjust wire rope length to perform one or more TLS functions can also release the wire rope in a controlled manner when needed for snag events. As a cylinder releases the wire rope, hydraulic oil flows through a metered orifice heating the oil and thereby absorbing much of the hoist flywheel energy.
One problem with such prior art systems, is that while a small cylindrical stroke is enough for TLS adjustment, snag compensation requires a large cylinder stroke. The control sensitivity for combining these large and small strokes on the same cylinder results in a poorly operating system for all four functions. Even the speed for trim and list is incompatible with the super sensitivity needed to control skew.
For that reason crane operators prefer to separate TLS systems from snag systems and want adjustable speeds for the TLS features. A secondary problem with such prior art systems is hydraulic oil. Hydraulic systems usually leak and require a considerable amount of maintenance.
Stand alone mechanical TLS systems are already available, but are more expensive than hydraulic systems that can serve the same function. The combination of mechanical TLS and hydraulic snag is a solution, but is too costly to be popular.
The present invention is a TLSS system that incorporates a drum with
at least two different diameter sections upon which the different ends of a lifting wire rope simultaneously spool on and off of as a function of counterclockwise and clockwise drum rotation.
The wire rope rides around an equalising sheave which is rotatably connected to another equalising sheave around which one of the main crane wire ropes ride. Altering the drum wire rope length moves the duo sheave assembly and causes the main crane wire rope’s vertical length to be altered. The differing TLSS drum diameters act to alter the amount of shaft torque required to adjust the main crane wire rope length and increases the number of drum rotations required to do so. By using various combinations of multiple drum regions with different drum diameters, a precise, fast-acting mechanical TLSS system using conventional electric motors can be designed for a crane’s specific configuration.
Henceforth, a tapered TLSS drum and opposite direction wire rope wrapping would fulfill a long felt need in the hoisting industry. This new invention utilises and combines known and new technologies in a unique and novel configuration to overcome the aforementioned problems and accomplish this.
Reduced torque
The general purpose of the present invention is to provide a crane apparatus that operates with an adjustable, reduced torque load over that of conventional assemblies.
It claims to have many advantages and many novel features that result in a new crane trim, list, skew and snag protection apparatus which is not anticipated, rendered obvious, suggested, or even implied by any of the prior art, either alone or in any combination thereof, it claims.
In accordance with the invention, an object of the present invention is to provide an improved system for altering the tilt, list and skew lifting functions of a container crane.
It is another object of this invention to provide an improved system capable of meeting or exceeding current remedial action response times for a crane snag.
It is a further object of this invention to provide an improved system that is adapted for finer control over the tilt, list and skew lifting functions of a container crane.
It is still a further object of this invention to provide for a TLSS drum designed with multiple, different diameter sections that may be designed, built and operated in conformity with a specific crane’s trim, list, skew and snag protection (TLSS) needs.
Additionally, it is an object of the invention to provide a safer and quicker responding snag protection system with emergency torque reversal for snag events that exceed the normal demand of wire rope extension.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organisation and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.
Other objects, features and aspects of the present invention are discussed in greater detail below.
Technical illustrations
Referring to Fig 1, it can be seen that the prior art hoist drum and wire rope arrangement has both ends of the wire rope (4) wound in the same direction at opposite sides of a constant diameter drum (2). In this manner, any rotation of the drum retracts or pays out the same amount of wire rope from either side of the drum. Here the amount of shaft torque (Y) (denoted by arrow 6) required to raise a load is the lifting force or sum of all the tensions multiplied by the drum radius (R).
Container cranes are commonly found in harbours where the loading and unloading of large containers from ships, rail cars and transport trucks occurs. Fig 2 depicts a simplified perspective view of the main hoist reeving of a typical container crane. The container crane has two main crane lifting wire ropes (16) that are spooled out or in from two main crane drums (18). These two main wire ropes (16) each traverse around the four main wire rope sheaves (20) and are arranged in four separate wire rope lifting loops (22) that hang in a vertical orientation and which attach to the four corners of the container (24) via a lifting beam (beam not illustrated).
A wire rope from the TLSS system (25) runs about a TLSS sheave (26) which is mechanically affixed to one of the four main wire rope sheaves (20). When raising a container (24), the vertical length of the lifting loops (22)
is adjusted by the rotation of the two main crane drums (18). When making a TLS adjustment, one or a combination of TLSS drums is rotated to spool in or out TLSS wire rope (28) so as to adjust the horizontal position of one or more of the main crane sheaves (20).
This main crane sheave movement adjusts slightly the vertical length of one or more of the lifting loops so as
to tilt, list or skew the container lifting beam. There are four TLSS systems (25) required to enable all possible tilt, list and skew configurations.
Fig 3 depicts a simplified perspective view of the reeving of a typical container crane with a variation on the TLSS system location and arrangement. Here an additional four main crane sheaves (20) have been utilised so as to allow the TLSS
system (25) to be physically located elsewhere. The operation is otherwise, functionally identically.
Looking at Figs 4 and 5, views of the TLSS system dual diameter, opposite wire rope wrapped drum with dual transitional tapers (44), the remaining elements that comprise the TLSS system (25) can best be seen. Drum
44 is mounted upon axle 72 that has bearings (74) affixed at or near the axle’s distal and proximate ends. The bearings reside in pillow block assemblies (76) rigidly attached mechanically to a mountable base (78). One end of the axle 72 is connected to a gearbox (82).
In conclusion
The patent concludes: “There are numerous variations and modifications that will also remain readily apparent to others skilled in the art, now that the general principles of the present invention have been disclosed. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilised as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.”
