Fuzzy depth control of an unmanned free-swimming submersible vehicle

Fuzzy control of depth for. an unmanned free-swimming submersible vehicle (UFSSH) is presented in the paper. The UFSSH can help avoid the perniciousness to explorers and research workers. Water flow through the UFSSH can generate a force to rise or submerge the vehicle by deflecting the pitch elevator surface. The fuzzy approach to controlling the UFSSH does not need the transfer function of the vehicle. Instead, it uses field experience and knowledge to design the fuzzy logic controller (FLC). The fuzzy approach is compared to traditional control approach. The pitch angle responses of the UFSSH by the fuzzy approach are much better in settling time and steady state error than those by the traditional approach. The fuzzy approach can use expertise, engineering experience and judgment into the design of knowledge base in the FLC. The supreme merits of an FLC are in its simplicity, understandability of fuzzy rules, and model-free approach by which a plant is viewed as a black box and only the plant output is needed to the FLC for observation. Excellent performance has been observed and the pitch response of the UFSSH is symmetrical to the neutral position of the pitch elevator surface.