Depth control of robotic fish propelled by oscillating paired pectoral fins

The double-closed loop depth control method based on expert PID and fuzzy control was proposed, which was used to realize the depth control of robotic fish propelled by oscillating pectoral fins. The pitching moment acting on the robotic fish was produced by the oscillating angle control of the robotic fish's tail rudder. Then the pitch attitude of the robotic fish was changed, and it could achieve the up-and-down motion. Related depth control experiments of the robotic fish were also carried out. The reason that initial ranges of pitching angle under different target depth are different was analyzed. The experimental results show that the proposed depth control method can make the robotic fish reach the target depth accurately. After the robotic fish arrives in the target depth, the proposed method can also improve the pitching stability when the robotic fish swims in the target depth. The proposed control method can better realize the depth control of the robotic fish.