针对海上舷梯末端点位置镇定控制问题，通过运动学反解，计算出补偿海浪引起的船舶摇荡运动对舷梯末端点位置的扰动、保证舷梯末端点位置在惯性坐标系下保持不变的舷梯关节期望位置；综合考虑舷梯动力学模型参数不确定及海浪引起的船舶摇荡运动对舷梯的扰动力，构造扩张状态观测器（ESO），估计由参数不确定及海浪引起的船舶摇荡运动对舷梯的扰动力组成的总扰动；进一步，设计基于ESO的终端滑模关节位置跟踪控制律，保证舷梯的关节位置跟踪其期望位置。理论分析证明了所构造的ESO的状态估计误差有界和所设计的基于ESO的终端滑模控制律使舷梯的关节位置跟踪误差在有限时间内收敛到零，从而保证舷梯末端点位置在惯性坐标系下保持不变.仿真结果验证了所设计控制律的有效性。

Aiming at the position stabilization control problem of the offshore gangway tip, the expected joint trajectories of the gangway were calculated by inverse kinematics solution to compensate the disturbances of the gangway tip position caused by the ship motions under the waves, and ensure the gangway tip position unchangeable in the inertial coordinate system. Considering the parameter uncertainties and the generalized disturbance forces of the gangway caused by ship motions under waves in the gangway dynamics model, the extended state observer (ESO) was constructed to estimate the total disturbance composed of the parameter uncertainties and the generalized disturbance forces of the gangway caused by ship motions under waves. Furthermore, a terminal sliding mode trajectory tracking control law based on the ESO was designed to ensure the joint trajectories of the gangway tracking the expected trajectories. Theoretical analysis shows that the state estimation error of the constructed ESO is bounded, and the designed ESO based terminal sliding mode control law converges to zero in finite time for the joint position tracking error of the gangway, thereby ensuring that the end point position of the gangway remains unchanged in the inertial coordinate system. Simulation results verify the effectiveness of the designed control law.