A MOTION COMPENSATING SYSTEM FOR USE WITH A CRANE HOIST

摘要

A motion compensation system for a crane hoist serves to assist the crane operator in safely lifting loads from the deck of a heaving work boat. The crane hook follows the motion of the load because a level of pre-tension is maintained on the line by use of a counterweight connected to the reeving system. A hydraulic cylinder connected to the counterweight provides for locking movement of the counterweight and also provides a cushion at both ends of its travel. Movement of the piston in the cylinder is controlled by a system including a check valve controlling flow between opposite ends of the cylinder which permits the reeving system to take up line. A limit switch responds to movement of the piston and counterweight near the top of their travel to actuate a light to warn the operator of a need to pay out line. As the piston and counterweight approach the bottom of their travel which indicates the load is moving upward, another limit switch actuates a light to indicate time to lift the load. A relief valve in parallel with the operator-controlled switch responds to excessive load to permit more line to be paid out. A separate pressure-responsive switch responds to normal working pressure in the rod end of the cylinder to prevent line from being paid out even though the operator might inadvertently provide an input to the operator-controlled switch.