Browsing by Author "Zavislak, Colin"

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    AUV Control with Hard and Soft Actuators
    (2021-04-28) Zavislak, Colin; Ghorbel, Fathi
    Autonomous underwater vehicles (AUVs) find many applications in oceanography, environmental research, and inspection and maintenance of subsea energy assets. Subsea resident AUVs remain in subsea for extended periods of time that can last for several months. Maintaining depth or orientation using traditional hard actuators (HAs) is very energy expensive. Mimicking aquatic creatures by using propulsion and buoyancy control, it is shown in this thesis that HAs and proposed soft actuators (SAs) can collaborate in a novel way. This collaboration can stabilize AUVs at any desired depth and orientation with minimum energy consumption at steady state. Additionally, once in the desired position the SAs can be used to precisely adjust the orientation of the system while maintaining depth by changing the system's center of buoyancy. This allows for the system to utilize tools, pick up parts, or perform other functions that would result in system mass change. This is demonstrated using a laboratory AUV for which a nonlinear dynamic model was developed that uses experimentally validated system parameters. The AUV uses HAs to quickly reach any desired depth or orientation while SAs generate volume change to adjust the system’s buoyancy to maintain neutral buoyancy at the desired depth. In the neutral buoyancy state, the HAs shut off while the SAs stabilize and maintain the position with virtually zero energy consumption. A control algorithm architecture is developed to manage the HA and SA collaboration. The HAs use a proportional controller with a dead-band, while the SAs use a proportional-derivative-acceleration (PDA) feedback controller. The ability of both types of actuators to mitigate disturbance forces and mass error are explored and analyzed. Simulation results show that SAs alone can reject small disturbances and adjust buoyancy to mitigate shift in system CM, while using both SAs and HAs in collaboration can reject large disturbances and errors. Simulation results demonstrate that combining traditional HAs with SAs leads to dynamic performance and very low energy consumption capabilities that cannot be achieved by either one alone.