Valve-PWM control of integrated pump-valve propulsion systems for highly maneuverable underwater vehicles

Precision maneuvering is an important requirement for many underwater robotic applications such as inspecting infrastructure systems. Maneuvering, especially at low speeds, is complicated by the presence of nonlinearities such as asymmetries and dead zones. Current work at MIT´s d´Arbeloff Laboratory has focused on the development of a compact maneuvering system for underwater vehicles using centrifugal pumps and high speed Coanda effect valves. This paper describes the development of a novel Valve PWM orientation control strategy designed specifically for this new maneuvering system. Simulations are used to show that simple linear control approaches are insufficient due to the presence of a dead zone. The Valve PWM system exploits the high speed nature of the valve and modulates the output force in order to produce small forces in a repeatable and predictable manner. A simple, intuition based approach for determining the PWM frequency and voltage amplitude is outlined and several optimal formulations are presented. A set of optimal parameters is selected and full nonlinear simulations are used to illustrate the effectiveness of the Valve PWM control system. Finally, preliminary experimental closed loop control data is used to emphasize that these concepts are both practical and applicable to physical robot systems.