Motion compensation winch

In the past most hoisting devices used for lowering lifeboats and the like relied on a winch operator to lower a boat so that the boat reached the surface when the water level is rising rather than falling away. Otherwise the wave falls away under the boat so it is suspended by the cable again. It is also necessary to prevent slack occurring in the hoisting cable. If slack does occur, then when the wave falls away, the slack is taken up and a violent jerk occurs as the weight of the lifeboat is taken by the cable. This jerk action may cause undue stresses in the hoisting cable or in the hoisting connections to the lifeboat. Furthermore, such an action causes discomfort to passengers in a lifeboat.
Various types of winches have been devised to prevent the occurrence of slack in a cable and to prevent the jerk that occurs when the slack is taken up. One such hoisting device is disclosed in U.S. Pat. No. 4,928,925 which discloses a constant tension hoisting member with a separate cable tension sensing system. The hoisting device provides an automatic launching operation but not an automatic recovery arrangement. The winch disclosed in this patent utilizes a main motor and an auxiliary motor.
An aim of the present invention is to provide a winch for launching and recovering an object such as a boat from an active wave environment generally moving relative to a stationary or moving platform where the winch has a number of operational modes which operate separately from a manual operational mode. The operational modes include a launch mode, a motion compensation mode, a free wheel mode and a recovery mode.
These and other objects are achieved by providing a winch drum that is driven by a primary gear reduction and a secondary gear reduction from a single fixed displacement hydraulic motor. Primary and secondary clutches are provided, the primary clutch engages and disengages the motor drive shaft from an internal gear of the primary gear reduction on a connecting tube. When the primary clutch is engaged, the motor drive shaft and the connecting tube rotate as one and thus the primary reduction is eliminated. When the primary clutch is disengaged, the motor drive shaft drives both the primary gear reduction and the secondary gear reduction, thus the cable drum rotates at a slower speed with full torque to the cable drum.
When the winch is in a motion compensation mode and in a recovery mode, a rotational sensor senses when the winch drum is paying out or paying in and selects a preset high pressure hydraulic oil supply to the primary clutch when the winch drum is paying in, and a preset low pressure hydraulic oil supply to the primary clutch when the winch drum is paying out. Thus, the hydraulic motor, through the primary clutch drives the winch drum with the primary reduction eliminated in the pay in direction, and the load on the cable pulls the winch drum in pay out direction against the oil cooled shipping primary clutch.
Apart from the manual mode, there are four automatic operational modes for the winch. These will be explained in detail. The first mode is the launching mode. Before activating any of the automatic operational modes, the winch operator is able to operate the winch in the manual mode as a standard winch simply by leaving the power off and utilizing the hoist control lever 114 to raise or lower a boat from the platform of a ship or dock and position it over the water.
When the required conditions are in compliance with the logic program, secondary clutch release solenoid valve 130 shifts and opens the port to the hydraulic supply tank 136 allowing the secondary clutch 52 to apply while the primary clutch 64 keeps driving freely in hoisting direction through the sprag clutch 48 located between the connecting tube 46 and the secondary clutch hub 50. When the load is elevated by the wave to its maximum height, the secondary clutch 52 and the secondary sprag clutch 48 keeps the connecting tube 46 from rotating in the pay out direction. As a result, this activates the primary gear reduction providing full gear reduction through the secondary gear reduction to the cable drum 12. Not only can the load no longer pay out, but the winch is basically shifted into manual mode capable of lifting full rated load. Once the hydraulic motor pressure reaches 2300 psi the low pressure switch 132 shifts the pressure select valve 126 to low clutch pressure providing minimum friction ready to drive full speed in hoisting direction should a second wave occur. The load is now under the operator's control and it may be stopped any time by moving the winch control lever 114 into the neutral position.