Ring derrick with stationary counterweight
A ring derrick includes a carriage which moves on a fixed circular track around a stationary counterweight. A tension and compression column assembled from transportable tubular segments is affixed to the counterweight by a universal swivel joint. The back mast of the derrick is secured at its upper end to the tension column, while the main boom of the derrick extends radially away from the tension column. The main boom and back mast are hinged directly together at the carriage by massive hinge pins which pass through spherical bearings mounted on the carriage. The carriage's suspension distributes the load from the boom and mast to an array of trucks and has an automatic stabilizing system that compensates for uneven track.
1. A hoisting device comprising
a mobile slewing carriage constrained to move around a geographically fixed axis of revolution,
a geographically stationary counterweight lying on said axis of revolution,
a tension column, capable of withstanding substantial axial compression, connected to the counterweight and extending upward from said counterweight along said axis of revolution,
a swivel joint connecting the counterweight to the tension column, which permits the tension column to deviate slightly from vertical,
a back mast extending from said slewing carriage to the tension column, the back mast being connected to the slewing carriage at one end and to the tension column at its other end, and
a main boom pivotally connected to the slewing carriage and extending from the slewing carriage in a direction away from said tension column,
wherein both the main boom and the back mast are joined to the slewing carriage by hinges, each said hinge comprising a hinge pin supporting both the back mast and the main boom, and a spherical bearing affixed to the slewing carriage and supporting the hinge pin.
2. The invention of claim 1 , wherein substantially all of the counterweight is below ground level.
3. The invention of claim 1 , wherein the tension column swivel joint comprises a universal joint and a low friction thrust bearing supporting the universal joint.
4. The invention of claim 3 , wherein the universal joint comprises a cross journal having trunnions which are supported on bearings between an upper yoke connected to the tension column and a bottom yoke connected to the counterweight.
5. The invention of claim 1 , further comprising a stationary substantially circular track supporting the slewing carriage.
6. The invention of claim 5 , wherein the track comprises at least one rail running in a horizontal plane about said axis of revolution, and the slewing carriage has at least two wheels which run on the rail.
7. The invention of claim 6 , wherein the slewing carriage includes a dynamic leveling system for keeping the slewing carriage level despite deviations of the rail from the horizontal plane.
8. The invention of claim 5 , wherein the track comprises a pair of concentric rails, each running in a substantially horizontal plane at a constant radius around said axis of revolution.
9. The invention of claim 5 , wherein the slewing carriage has a plurality of trucks, each having plural wheels which run on the track, and a suspension which distributes loads from the boom and mast to the wheels.
10. The invention of claim 9 , wherein the suspension comprises at least one stabilizer bar, each bar being supported by at least two of said trucks, and having a pivot connection to the carriage.
11. The invention of claim 10 , wherein the suspension further comprises at least one articulating girder, each articulating girder being supported by at least two of said stabilizer bars, and having a pivot connection to the carriage.
12. The invention of claim 11 , further comprising hydraulic means for controlling the pivoting of the articulating girder.