| 摘要 |
A heave motion compensation appartus is used to move a load from a supply ship in heavy seas to a platform on an oil rig. A main load line extending down from a point of a crane boom mounted on the oil rig is driven by a pair of hydraulic main hoist drum motors. One of the motors is a variable displacement swash-plate type motor. The motors are driven through a hydrostatic transmission by a pair of variable displacement hydraulic pumps. A signal line running over the boom point is attached to the supply vessel and maintained taut. Sensor and control means reading movement of the signal line with respect to the first platform is used to control the displacement of one of the main hoist pumps to cause an outer end of the main hoist line to move up and down with the supply vessel. The other pump is controlled to raise and lower the outer end of the main load line. The main load line is attached to the load. A signal is generated by the sensor and control means to indicate upward movement of the outer end of the main load line, and this signal is used to generate a signal representative of the rate of change of the speed of the outer load line and the load attached thereto. On demand by the operator, the control means determines when the supply vessel is moving up with respect to the oil rig and the rate of change of velocity is zero. The control means then moves the variable displacement main hoist drum motor and the two variable displacement main hoist pumps to maximum displacement to cause the main load line to pick the load from the supply vessel.
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