# The Evolution and Development Trends of LNG Loading and Unloading Arms
## 2 Development of Marine LNG Loading and Unloading Arms
### Marine Loading Arm Actuation and Its Intelligence and Automation  
In terms of power, most of the loading and unloading arms of FMC Corporation (Philadelphia, PA, USA) and SVT (Schwhelm, Germany) use hydraulic cylinder drives. The hydraulic cylinder drive can provide greater power and has a great advantage in long-distance transportation [26]. However, the company EMCO WHEATON (Kirchhain, Germany) has abandoned the traditional hydraulic cylinder drive mechanism and adopted a four-bar linkage drive mechanism to provide power for the loading arm, resulting in more stable movement. Currently, for most loading and unloading arms, according to different requirements such as the caliber, model, and load of the loading arm, manual operation or electro-hydraulic control can be selected, making the loading process more flexible and efficient. With the rapid development of the liquefied natural gas market, the pressure on LNG receiving terminals has increased sharply. The traditional manual docking method requires at least two or more operators, as shown in the Figure 6, and can no longer meet market demands. The intelligent control and automated docking of loading and unloading arms are an inevitable trend. Loading and unloading arms need to complete loading operations with swaying tankers. Their intelligent development direction focuses on the precise positioning and docking of flange ports, as well as the remote monitoring and control of loading and unloading arms. Automation aims to diminish reliance on human labor and enhance production efficiency [28]. To achieve rapid and automatic docking of LNG loading and unloading arms, the key issue is to achieve precise positioning of flange ports. Initially, most of the automatic positioning systems for large loading spouts on the market used image capture  
Figure 6: Working schematic diagram of LNG marine loading arm docking with LNG ship. 1—LNG marine loading arm control box; 2—LNG marine loading arm; 3—end joint of the LNG marine loading arm; 4—land operator; 5—wave; 6—LNG ship; 7—transportation pipe interface; 8—ship operator; 9—wind. Adapted from [27]. cards with PCI interfaces [29] and completed flange positioning with the assistance of computers. However, the transmission performance of PCI interfaces is relatively low, and the image resolution is poor, making it difficult to meet the positioning requirements of flange interfaces. With the development of computer technology, the realization of the automatic positioning function has gradually evolved to precisely locate the 3D [30] coordinates of the filling port through visual recognition technology. [PERSON] et al. [31] proposed a two-stage positioning target recognition mode. By collecting 3D point cloud images of the target flange and processing the images using algorithms such as the normal filtering algorithm, circle-center fitting filtering algorithm, and laser dimension-reduction weighted tracking algorithm, the dynamic recognition and positioning of the target flange can be achieved. Binocular stereo vision simulates human eyes and recognizes 3D objects based on the principle of triangulation, making it widely used in robot navigation [32; 33; 34]. [PERSON] [35] proposed a binocular stereo vision positioning algorithm. They used a joint algorithm based on clustering and regional growth methods to segment the target pipe accurately, and they obtained the three-dimensional coordinates and pose of the target flange through binocular stereo matching. [PERSON] et al. [36] applied the 3D laser point cloud technology to port loading and unloading arms and proposed an automatic docking recognition and positioning algorithm for port loading and unloading arms based on 3D laser point clouds. They used the RANsAC algorithm combined with the European clustering segmentation algorithm method after denoising of the point. On this basis, the centroid coordinates of the target flange were further obtained by using the PCL third-party library Eigen library.