Traversing hoists – Having means to prevent or dampen load oscillations – Antisway
Reexamination Certificate
2002-02-28
2003-11-11
Ullis, Eileen D. (Department: 3652)
Traversing hoists
Having means to prevent or dampen load oscillations
Antisway
C414S733000
Reexamination Certificate
active
06644486
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a system for stabilizing and controlling a hoisted load. The invention relates more specifically to a system for stabilizing and controlling in six degrees of freedom the movement of a hoisted load. The invention relates even more specifically to a system which can both be adapted to existing single point lift mechanisms, and constrain the load in all six degrees of freedom.
2. Description of Related Art
As discussed in U.S. Pat. No. 4,883,184, lifting platforms are commonly attached to cranes, such as overhead tower-type cranes having a horizontal boom and boom-type cranes having a diagonal boom. Applications for these lifting platforms can include transporting cargo on and off ships, and relocating necessary equipment and materials on a construction site.
The potential motions of a hoisted object can best be envisioned by means of a Cartesian coordinate system in which the z-axis is in the vertical direction, and the x and y axes form the horizontal plane. The rotation of the hoisted object about the z-axis is therefore defined as yaw, rotation about the x-axis is defined as pitch, and rotation about the y-axis is defined as roll.
In typical load transporting applications, a crane will have a single lifting cable. In these applications, the lifting cable is stable only in the z direction. Under any external influence from the sides, the load will either roll, pitch, or yaw, or will sway in the x and y directions.
The prior art has long recognized the need to compensate for these motions, and as a result, various conventional devices exist for attempting to stabilize a hoisted load. For example, U.S. Pat. No. 4,171,053 describes a crane for overcoming the undesirable effects of cargo pendulation. The crane consists of conventional booms, vertical hoist lines, and a hook member for engaging the cargo to be lifted and lowered. The crane also consists of a horizontal beam located at the base of the boom. The major portion of the hoist lines remains in substantially a vertical plane as a result of lines which extend from a guide means at the bottom of the hoist lines to the horizontal beam.
U.S. Pat. No. 4,883,184 describes a cable arrangement and lifting platform for lifting a load in a stabilized manner. The lifting platform secures loads to a securing device and the platform is able to be suspended from a crane by an attachment carriage. The attachment carriage includes a cable winch onto which six cables suspend and attach to the lifting platform. The attachment carriage also includes cable guides which guide the six cables away from the winch in three cable pairs, preferably equidistantly-spaced. In order to secure the cables to the lifting platform, the platform includes an attachment frame having three cable attachment points, preferably spaced equidistantly apart with respect to each other. The lifting platform helps stabilize the lifting of loads by sensing the load's imbalance relative to the center of mass of the platform and repositioning the load to correct for the imbalance.
U.S. Pat. No. 4,932,541 describes a stabilized cargo-handling system using means for stabilizing suspended cargo in all six degrees of freedom using six individually controlled cables in tension in a kinematic arrangement. Inertial and distance sensors, coupled with high-performance cable drives, provide the means to control the multi-cabled crane automatically. The distance sensors are used to track the target container or lighter vessel during the pickup and setdown modes of operation; the inertial sensors are used to prevent pendulation during transfer of the cargo from the seagoing cargo ship to the vicinity of the receiving lighter.
U.S. Pat. No. 5,507,596 describes an underwater work platform supported by a plurality of cables connected between a support structure and the work platform. Motions of the support structure in the body of water are sensed, and the length of the cables is adjusted in response to the sensed motion of the support structure so that the work platform can be maintained in a stationary position even when the support structure is subjected to wave forces and currents.
In the late 1980's the National Institute of Standards and Technology (“NIST”) developed a concept known as RoboCrane based on a Stewart platform geometry parallel link manipulator, but which uses cables as the parallel links and winches as the actuators.
NIST also developed a version of the RoboCrane known as TETRA for testing long cable suspensions. TETRA includes winches mounted on the work platform as opposed to the supporting structure. TETRA's relatively light duty winch cables are used to augment existing heavy duty lift equipment (such as cranes) by attaching to the suspended load and then using RoboCrane control programs to provide intuitive load control in six degrees of freedom.
Single point lift mechanisms, such as boom-type cranes, typically include a base, a boom, and a heavy duty hoist system including a winch and block and tackle. As indicated above, however, load pendulation is a basic problem typical of such cranes since they can only control the vertical axis. Attempts at controlling load pendulation have included control programs that maneuver the lift point to stay above the load. Others attempts have included the use of reeving (like the RoboCrane) and vertical motion compensation.
A vessel known as a Tactical Auxiliary Crane Ship (“T-ACS”) includes a system called the Rider Block Tagline System (“RBTS”) that attempts to stabilize a load by pulling on taglines to prevent large pendulations. The RBTS, however, affords limited control of the spreader/cargo sway, and no rotational control of the spreader/cargo. Additionally, the RBTS introduces complex load motions that are difficult to dampen, so that operators often disable the system. Furthermore, the RBTS hinders performance and safety as a result of depth perception and line of sight occlusion, and requires the presence of ground personnel with taglines in hazardous areas to guide the load. Routine RBTS operations, therefore, require precision boom control and a highly trained operator. Finally, the RBTS does not control the load in all six degrees of freedom.
While the aforementioned conventional devices may therefore provide varying degrees of control of a hoisted load, not all of these devices can control all six degrees of freedom, and none can both be adapted to existing single point lift mechanisms, and constrain the load in all six degrees of freedom, thus satisfying a long-felt need in this environment.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a system which can both be adapted to existing single point lift mechanisms, and constrain a hoisted load in all six degrees of freedom.
Accordingly, the present invention advantageously relates to a system for stabilizing and controlling in six degrees of freedom the movement of a hoisted load. The system comprises a suspension point, an assembly, a lateral tension lines member, and a control system. In a first embodiment, the assembly comprises a first platform for positioning the assembly; a second platform disposed below the first platform; first, second, third, fourth, fifth, and sixth, control lines having a first end and a second end, with the control lines disposed between first platform and the second platform; an assembly hoist, which comprises first, second, and third assembly hoist lines in communication with a corresponding one of each of first, second, and third assembly hoist line length adjusters; and a load hoist which comprises a load hoist line and a load hoist connector, with the load hoist line in communication with a load hoist line length adjuster.
The first platform comprises a first platform upper surface, a first platform lower surface, a first platform outer edge, load hoist line guides in slidable communication with the load hoist line, and a plurality of lateral tension line connectors for engaging a plurality of lat
Albus James Sacra
Bostelman Roger Vernon
Jacoff Adam Stephan
Johnson R. B.
Stevens Davis Miller & Mosher L.L.P.
The United States of America as represented by the Secretary of
Ullis Eileen D.
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