Inverse dynamics control of a bio-inspired robotic-fish underwater vehicle propulsion based on Lighthill slender body theory

A 2-joint, 3-link multibody vehicle model biologically inspired by a Body Caudal Fin (BCF) carangiform fish propulsion mechanism in fluid environment is presented in this paper. Under the Lighthill (LH) mathematical slender body theory different mathematical propulsive waveforms are developed to generate robotic fish locomotion. LH Cubic function is found to be 16.32 % efficient than a non-LH function. We develop the dynamic motion control strategy of the robotic fish based on two different control schemes, the CTM (Computed-Torque Method) and the FF (Feed-Forward) controller both with dynamic PD compensation. An inverse dynamic control method based on non-linear state function model including hydrodynamics is proposed to improve tracking performance. CTM control generates a feedback loop for linearization and decoupling robot dynamic model with a shorter response time while a dynamic PD compensation in the feed-forward path is employed by FF scheme through the desired trajectories. This model based strategy results in an improved tracking. Overall results indicate that control designs based on the inverse dynamic model are useful for robotic fish motion tracking.