Internal actuation of underwater robots using Control Moment Gyros

Abstract

A novel control scheme based on internal actuation using Control Moment Gyros (CMGs) is proposed as the basis of an unrestricted attitude control system suitable for application to Autonomous Underwater Vehicles (AUVs). The coupled dynamic equations of a CMG actuated underwater robot are derived, taking into account interactions with the fluid environment. A nonlinear feedback control law is developed based on energy considerations of the coupled system. Singularities, redundancy and null motion are discussed in the context of CMGs and a mathematical escapability condition is developed based on the differential geometry of null motion. A geometric study of a CMG pyramid's singularities forms the basis of a global steering law that guarantees real-time singularity avoidance whilst maintaining exactness in some constrained workspace. The practical design considerations of a CMG pyramid developed for a laboratory scale underwater robot are discussed. Finally the results of practical experiments using the CMG pyramid are presented to demonstrate the steering and control performance of the system.