Biology-inspired adaptive and nonlinear robust control of BAUV using pectoral-like fins

Aquatic animals have splendid ability to move smoothly through water using variety of oscillating fins. Presently researchers are involved in developing biorobotic autonomous underwater vehicles (BAUVs) which have the ability to swim like marine animals. Multiple oscillating fins (dorsal, caudal, pectoral, pelvic, etc.) can be mounted on BAUVs to generate control forces for propulsion and maneuvering. In this research work, control of the BAUVs using pectoral fins alone is considered. The oscillating pectoral fins produce unsteady periodic forces. The control of motion of a BAUV in yaw and dive planes are considered.;We first design an adaptive controller for controlling the heading angle of a BAUV in the yaw plane. The fins are assumed to be oscillating with a combined sway and yaw motion. The bias angle of the angular motion of the fin is used as the control input. The yaw angle is considered as the output variable. The adaptive controller requires the tuning of a single gain and uses only the yaw angle and its derivative for feedback.;Then, a robust servoregulator for the control of BAUVs based on the nonlinear internal model principle is designed. This design methodology is applied to control of BAUV both in the dive plane and yaw plane. In the dive plane, the fins attached to the vehicle have oscillatory pitching and heaving motion. The pitch bias angle of the fin is taken as the control input. The depth is taken as the output variable. In the yaw plane, the yaw angle command tracking of the BAUV is desired. In both the cases, the same design strategy is adopted. For the control law derivation, an exosystem of third-order is introduced, and the nonlinear time-varying BAUV model, including the fin forces, is represented as a nonlinear autonomous system in an extended state space. Based on this representation, a nonlinear robust regulator for the set point control of the depth is derived. The control system includes the internal model of a k-fold exosystem, where k is a positive integer chosen by the designer. It is shown that the control system suppresses all the harmonic components of order up to k of the tracking error.;Finally, the servoregulation of BAUVs in the dive plane using indirect adaptive output feedback control is considered. It is assumed that the physical vehicle parameters, hydrodynamic coefficients, fin forces and fin moments are unknown. This entails the design of a parameter identifier to estimate the nonlinear BAUV system parameters. A sampled-data control system is designed for the reference trajectory tracking using output feedback. The design of a stabilizing control law requires an internal model of the exosignals. The constant reference signal and also the constant disturbance input together are taken as the exosignals. The closed-loop indirect adaptive feedback control law derived is applicable to both minimum phase and non-minimum phase BAUV systems.;Simulation results show that in spite of uncertainties in the system parameters, precise tracking of the BAUV is achieved for the various control design methods indicated.