Study of artificial fish bladder system for robot fish

The robot fish, with straight and turn movement, is undertaken by the waving of body combined with caudal fins. In heaving motion, fish robot is propelled and controlled by pectoral fins or a changing system like the bladder in real fish. In this paper, the adjusting gravitation method was chosen to change the depth of sinking and make robot fish floating. Using this method, the mechanical structure of robotic fish is simple, easy to design a changing gravitation system, especially that it can sink vertically in water without any locomotion. A servomotor, a transmission device and a piston with cylinder are employed for a proposed design. The bladder system is an apparatus that can realize diving and floating control. It was inspired by biologic fish's bladder principle, so it named artificial fish bladder system. An analytic structure of fish bladder design were established and based on kinematic and dynamic analysis, affected to the gravity and buoyancy on robot fish. In addition, the research on the effect of bladder system for fish robot was confirmed by experimental results.