Application of a fuzzy controller to depth control of a midwater trawl net

Abstract

A control system is presented that uses a fuzzy algorithm in controlling the depth of a midwater trawl net, and field experiments carried out on the training ship Kaya of Pukyong National University. The fuzzy controller calculates the length of the warp to be changed, based on the depth error between the desired depth and actual depth of the trawl net and the change ratio in the depth error. The error and the error change are calculated every sampling time. Then the control input (i.e. desirable length of the warp) is determined by inference from the linguistic control rules which an experienced captain or navigator uses in controlling the depth of the trawl net during manual operation. The control input is then transmitted to the trawl winch controller and the length of the warp is changed. The results of these field experiments indicate that this proposed fuzzy controller rapidly follows the desired depth without steady-state error although the desired depth was given in one step, and shows robustness properties against changes in the parameters such as the change of towing speed. The suitability to practical operation of the fuzzy controller designed in this study is fully proved throughout the sea trials.