Study and implementation of station-holding performance on a fish robot in adverse unsteady flow

In the present work we study the station-holding performance exhibited by real fish and implement the similar performance onto a biomimetic fish robot. The aim is to make the swimming of a fish robot capable of holding its station in one-dimensional unsteady adverse flow, i.e. to obtain adaptation to the variations of flow rate. With the sensory feedbacks including water environment information and the displacement of fish robot, a closed-loop swimming control scheme is developed. Firstly, inspired by a real carp fish swimming in adverse flow, control laws that regulate the tail beat frequency and amplitude of fish robots are formulated. A non-linear oscillator is applied to model the periodic swimming gaits. As controlling parameters of the oscillator, frequency and amplitude are dynamically tuned by the feedback control laws. The output of the oscillator that generates the adaptive swimming gaits is adjusted accordingly. The control method is verified through simulation and experiments on a BCF type fish robot.