Development and Control of Underwater Gliding Robots: A Review Jian Wang, Zhengxing Wu, Huijie Dong, Min Tan, and Junzhi Yu, Fellow, IEEE Abstract—As one of the most effective vehicles for ocean development and exploration, underwater gliding robots (UGRs) have the unique characteristics of low energy consumption and strong endurance. Moreover, by borrowing the motion principles of current underwater robots, a variety of novel UGRs have emerged with improving their maneuverability, concealment, and environmental friendliness, which significantly broadens the ocean applications. In this paper, we provide a comprehensive review of underwater gliding robots, including prototype design and their key technologies. From the perspective of motion characteristics, we categorize the underwater gliding robots in terms of traditional underwater gliders (UGs), hybrid-driven UGs, bio-inspired UGs, thermal UGs, and others. Correspon- dingly, their buoyancy driven system, dynamic and energy model, and motion control are concluded with detailed analysis. Finally, we have discussed the current critical issues and future development. This review offers valuable insight into the development of next-generation underwater robots well-suited for various oceanic applications, and aims to gain more attention of researchers and engineers to this growing field. Index Terms—Buoyancy driven, motion control, oceanic applic- ations, system development, underwater gliding robots.    I. Introduction T HE ocean occupies 71% of the earth surface area, and contains abundant biological resources, mineral resources, and vast space resources. Therefore, with the vigorous development of economy and technology, the ocean explora- tion has received widespread attention from all over the world. Nowadays, unmanned underwater vehicles (UUVs) are mainly used to conduct the ocean exploration, including autono- mous underwater vehicles (AUVs) and remote operated vehi- cles (ROVs) [1]. As an AUV with long endurance characteri- stics, the underwater glider (UG) is one of the most effective underwater unmanned platforms for ocean observation in recent years. Compared with other underwater vehicles, UG can achieve the gliding motion by changing net buoyancy. It has the advantages of low energy consumption, wide range of navigation, long endurance, and low noise. In 1989, Stommel, an American oceanographer, proposed the concept of an underwater glider [2]. On the basis of this concept, many scientific research institutions around the world have successively carried out the development of underwater gliders [3]–[7]. Traditional underwater gliders have the unique characteristics of low energy consumption and strong endur- ance. However, their maneuverability is obviously poor owing to insufficient drive force, which is an important factor hindering the ocean exploration. In response to the above problems, more and more new types of underwater gliders have been developed in recent years. In terms of energy use, in order to further improve the endurance, the thermal underwater glider (TUG) has received wide attention [8]. Different from the traditional buoyancy system, its main principle is to utilize the temperature difference at different depths of the ocean, resulting in the volume change of the phase change material [9]. With regard to drive form, the hybrid-driven underwater glider (HUG) has both the strong endurance and high-speed characteristics by combining the propeller of AUV and buoyancy system of UG [10]. However, although hybrid-driven underwater gliders have obvious thrust effects, they have low efficiency and poor concealment, and the produced wakes will cause greater damage to the aquatic environment. Therefore, in recent years, in response to the call for marine environmental protection, bio-inspired underwater gliders (BUGs) have attracted the interest of scientific researchers [11]. Through imitating the appearance and swimming mechanism of natural creatures, the bionic driving mechanisms are designed to replace the propeller driver. The BUG not only has the characteristics of high speed, high maneuverability, and strong endurance, but also owns the unique advantages of high efficiency swim- ming, low noise, and strong concealment, which is of great significance to practical applications. Furthermore, for body shape, some heterosexual underwater gliders have begun to appear, such as disc-type [12], flying wing-type underwater gliders, and the above bionic shapes. They are designed to reduce fluid resistance, and increase lift-to-drag ratio through shape design, thereby improving the efficiency of gliding. Since 1989, many scientists have carried out a lot of Manuscript received February 17, 2022; revised March 24, 2022; accepted April 24, 2022. This work was supported in part by the National Natural Science Foundation of China (61725305, 62033013, U1909206, T2121002). Recommended by Associate Editor Shuai Li. (Corresponding author: Junzhi Yu.) Citation: J. Wang, Z. X. Wu, H. J. Dong, M. Tan, and J. Z. Yu, “Development and control of underwater gliding robots: A review,” IEEE/CAA J. Autom. Sinica, vol. 9, no. 9, pp. 1543–1560, Sept. 2022. J. Wang, Z. X. Wu, H. J. Dong, and M. Tan are with the State Key Laboratory of Management and Control for Complex Systems, Institute of Automation, Chinese Academy of Sciences, Beijing 100190, and also with the School of Artificial Intelligence, University of Chinese Academy of Sciences, Beijing 100049, China (e-mail: jianwang@ia.ac.cn; zhengxing.wu@ ia.ac.cn; donghuijie2018@ia.ac.cn; min.tan@ia.ac.cn). J. Z. Yu is with the State Key Laboratory of Management and Control for Complex Systems, Institute of Automation, Chinese Academy of Sciences, Beijing 100190, and also with the State Key Laboratory for Turbulence and Complex System, Department of Mechanics and Engineering Science, BIC- ESAT, College of Engineering, Peking University, Beijing 100871, China (e-mail: junzhi.yu@ia.ac.cn). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JAS.2022.105671 IEEE/CAA JOURNAL OF AUTOMATICA SINICA, VOL. 9, NO. 9, SEPTEMBER 2022 1543