船舶系码头或船舶间转接装卸货时，船舶与码头或船舶之间会出现纵向位移变化，传统方式通过调节缆绳完成补偿。本文将船舶与码头间相对位移量输入PLC控制系统，将计算结果输入液压系统，通过液压臂的行程油缸伸缩的方式，补偿船舶纵向位移的改变。

When the transfer loading and unloading of the ship， the longitudinal displacement between the ship and the dock or between the ship is changed. The traditional method is to compensate for the change of displacement by adjusting the cable. In this thesis， the author a compensation method that the relative displacement between the ship and the dock as the input quantity， calculates the control quantity of the hydraulic system through the PLC control system， and compensates the change of the ship's longitudinal displacement by the way of the stroke cylinder expansion of the hydraulic arm.