Abstract
The development of a control system for the dive plane control of non-linear biorobotic autonomous underwater vehicles, equipped with pectoral-like fins, is the subject of this paper. Marine animals use pectoral fins for swimming smoothly. The fins are assumed to be oscillating with a combined pitch and heave motion and therefore produce unsteady control forces. The objective is to control the depth of the vehicle. The mean angle of pitch motion of the fin is used as a control variable. A computational-fluid-dynamics-based parameterisation of the fin forces is used for control system design. A robust servo regulator for the control of the depth of the vehicle, based on the non-linear internal model principle, is derived. For the control law derivation, an exosystem of third order is introduced, and the non-linear time-varying biorobotic autonomous underwater vehicle model, including the fin forces, is represented as a non-linear autonomous system in an extended state space. The control system includes the internal model of ak-fold exosystem, wherekis a positive integer chosen by the designer. It is shown that in the closed-loop system, all the harmonic components of order up tokof the tracking error are suppressed. Simulation results are presented which show that the servo regulator accomplishes accurate depth control despite uncertainties in the model parameters.
Highlights
Aquatic animals swim smoothly through water using a variety of- oscillating fins, and birds and insects fly using flapping wings (Azuma 1992; Luca 1999; Sfakiotakis et al 1999; Fish 2004; Lauder and Drucker 2004; Kato and Kamimura 2008)
The extraordinary maneuverability of marine animals, birds and insects is the result of their ability to generate and control large forces from unsteady hydrodynamics and aerodynamics, respectively
Researchers are involved in developing biorobotic autonomous underwater vehicles (BAUVs) which have the ability to swim like marine animals (Bandyopadhyay 2005)
Summary
Aquatic animals swim smoothly through water using a variety of- oscillating fins, and birds and insects fly using flapping wings (Azuma 1992; Luca 1999; Sfakiotakis et al 1999; Fish 2004; Lauder and Drucker 2004; Kato and Kamimura 2008). The control system designed based on the time-invariant average model ignores the effect of time-varying fin forces on the vehicle motion As such in the closed-loop system, the tracking error responses exhibit fluctuations caused by the harmonic components of the fin forces in the steady state. Exact discretisation is not possible for non-linear models of BAUVs. discrete-time controllers can give zero tracking error only at the sampling instants, and in the closed-loop system, large inter-sample excursions may exist. It is shown that the controller, including the internal model in the loop, suppresses harmonic fluctuations of degree up to k in the tracking error responses This desirable closed-loop property is not possible using the method of averaging (Luca 1999) or discretisation (Singh et al 2004; Narasimhan et al 2006; Naik and Singh 2007). Simulation results are presented which show that the servo regulator accomplishes set point control of the depth precisely in spite of large parameter uncertainties in fin forces
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