Optimal Vertical Position Control of a Near-Surface Remotely Operated Vehicle in Regular Waves

Precise vertical positioning has a very significant impact on the accuracy and reliability of the Remotely Operated Vehicle (ROV) working process. This paper establishes an experimental system which is capable of controlling and measuring the vertical position of ROV. The control signal output system is developed by integrating certain modules such as video recording, image-analog-digital signal converting, timing depth calculating and force signal outputting modules. The effects of Proportional-Integral-Derivative (PID) method on ROV depth control in still water and under various regular waves was tested and compared. The causes of difference of control effect between in still water and in waves were analyzed. Giving insight into the hydrodynamic characteristics and consequent movement of ROV, a practical underwater vehicle maneuvering mathematical model was established. The space motion equations were set up to solve the underwater vehicle maneuvering problem. The effects acted on the carrier by the waves were analyzed in order to develop a feasible control strategy that is applicable to the practical operation. Unsatisfactory effects of thrust output are optimized with MATLAB simulation based on ITAE criterion, using the simplex method for re-tuning PID parameters. Experimental results show that the system for measuring and controlling the vertical position of the ROV is successful. With an appropriate time interval for data collecting, the ROV model’s vertical depth can be effectively determined by the program written in VB language in the still water and small wave height situation. While the wave height increases or the wave period changes, the program needs to be adjusted. Simulation results also show that the wave frequency response abates as the wave period decreases. Compared to the original PID parameters, the new ones can rapidly give response to the vertical position change and guarantee the stability of ROV depth controlling. It is of obvious importance to actual control of the underwater vehicles’ vertical movement with the help of mathematical optimization method for the controller parameters. The proposed controlling algorithm can be an alternative for other similar working conditions.