Underwater Robots : Motion and Force Control of Vehicle - Manipulator Systems

Many aerospace engineers with an expertise in flight control system design, if tasked with designing a guidance system for an underwater vehicle, would dismiss the problem as easily solvable. To aerospace engineers, underwater vehicles are thought to be nothing more than powered blimps, which have been flying since 1852, when Henri Giffard built the first powered airship, a 143-ft long, cigar-shaped, gas-filled bag with a propeller that was powered by a 3-hp steam engine. If we can control intrinsically unstable airplanes at speeds several times that of sound, how difficult can it be to design a guidance system for an underwater vehicle that travels at less than 1/100 of the speed of sound? Of course, the fact that the density of water is about 800 times that of the air is irrelevant! As one of those aerospace engineers, after spending the last ten years trying to design that guidance system, I can finally recognize how “little I knew,” and I thank Gianluca Antonelli for helping me understand the challenges that such a problem presents. In this book, the author goes beyond the problem of controlling a single underwater vehicle by addressing the control of underwater vehicle/manipulator systems (UVMs). These systems have been used for many years in teleoperated versions to inspect and repair underwater cables and pipes, in search and rescue missions, for underwater archeology, and anything else that requires going underwater and grabbing something. A few years ago an operator of one of these teleoperated UVMs explained to me that it is very difficult to control the entire system simultaneously, so much so that, in practice, at first the manipulator is locked in place and the vehicle is moved until the end effector gets close to the desired position, then the manipulator is controlled toward the final target while the vehicle is maintained as steady as possible. By splitting the problem into two simpler problems, operators, who must be highly trained and talented, are able to complete the task. What makes this problem so difficult is the complexity of UVM dynamics, which are often redundant and provide multiple possible solutions to the task and even more possible undesired outcomes. We also need to consider the difficulties related to limited communication with underwater systems, the hostility of the ocean environment, and the delays experienced in the control loops, just to mention a few. In an effort to overcome these difficulties, this book is aimed at control for autonomous UVMs. The author has done an excellent job addressing several of these challenges and providing possible solutions of increasing complexity as the book progresses. In this second edition, the author has addressed many comments made by readers and reviewers by streamlining and improving the content. He has also added a few chapters addressing the state of the art and additional challenges, such as fault tolerance and collaborative control.