Improving the performance of an AUV hovering system by introducing low-cost flow rate control into water hydraulic variable ballast system

Combined Depth Control Strategy for Low-Speed and Long-Range Autonomous Underwater Vehicles

“…A typical configuration of an AUV equipped with VBS, and bow and stern fins is given in Figure 1. The schematic diagram of the on-off type VBS, which uses a single speed motor, a fixed displacement pump and four fast-response direct-acting solenoid valves, is shown in Figure 2 [13]. Suppose the AUV is designed to have passive stability in both roll and pitch directions, and the ballast tank is configured to have the center at the origin of the body-fixed coordinate system.…”

“…With the increasingly wide activities in deep-sea exploration and exploitation, underwater vehicles of various types have become indispensable tools for scientists, researchers and engineers to conduct ocean research and perform underwater tasks [1][2][3][4][5][6][7][8][9][10][11][12]. Among them, autonomous underwater vehicles (AUVs), which are developed to provide high automation, cost-effectiveness, and medium and long-range capability to execute underwater missions without placing human lives at risk [13], are increasingly being used in highly detailed survey and inspection applications including the exploration of unknown environments [14], oceanographic observations [15], the inspection of underwater structures [16] and so on. In such scenarios, AUVs are expected to be capable of both satisfactory hovering and low-speed and energy-efficient cruising for high-quality data gathering and long-duration missions.…”

“…Variable ballast systems (VBSs), which change the masses of underwater vehicles, mainly fall into three types, i.e., water hydraulics that pump seawater between ballast tanks and the surroundings [18], compressed air that is blown/vented to/from ballast tanks [25], and the hybrid method, using both water hydraulics and compressed air [26]. With its advantages of ease in construction, sealing and disposal of working media and environmental friendliness, the water hydraulic VBS is the most popular and competitive mechanism for hovering control of AUVs [13,28].…”

“…Although both simulations and water trials have demonstrated the effectiveness of this on-off type VBS and controller design, the hovering performance needs to be improved. Three kinds of novel VBSs-continuous type VBSs, which support the valve controlled mode via pulse width modulation (PWM) controlled solenoid valves or pump controlled mode via a servo motor to control the flowrate of ballast water-are proposed to improve the performance of an AUV hovering system [13]. Both the valve-controlled mode and pump-controlled mode, however, impose more complicated problems, to establish the mathematical models of the flowrate control means, compared to on-off type VBS.…”

“…Both the valve-controlled mode and pump-controlled mode, however, impose more complicated problems, to establish the mathematical models of the flowrate control means, compared to on-off type VBS. It is noteworthy that in order to realize the valve-controlled mode for continuous flowrate control [13], the electric valves (usually with a 3 s response time) used in the on-off type VBS [18] are replaced by four fast-response direct-acting solenoid valves (within milliseconds of response time), which greatly shortens the response delay of the VBS.…”