Implementation of control techniques for a semi-autonomous underwater vehicle

Abstract

As technology advances and becomes more affordable, Remotely Operated Vehicles (ROVs) are becoming more accessible to the general public than ever before. They can be adapted for a wide range of applications varying from recreational use to maintenance, construction and military missions. The ROV consists of several subsystems that need to be designed with the intended underwater operation in mind. A crucial aspect of the design is the propulsion system that often consists of several motors that need to be operated at the same time in order to command the desired ROV trajectory. To manually control the trajectory in an underwater environment is challenging for the remote operator especially if no automation support is provided. This has led to a growth in research on developing semi-autonomous control techniques for manoeuvring such ROVs. This dissertation studies the design and implementation of semi-autonomous control systems for an underwater ROV. This included linearisation of a mathematical model that enables the use of linear control techniques on a nonlinear system, application of cascaded PID control techniques for the control of the ROV, discretisation of the continuous-time controller and software algorithm implementation. Simulation testing of the cascaded PID control system designed in this project yielded performance results which indicate that the linear control technique is effectively able to control the ROV’s motion. This proves that despite their simplicity, linear PID controllers are robust and suitable for many different practical applications. Such controllers could also be designed for nonlinear systems, thereby simplifying the need for designing more complex nonlinear control systems.