Abstract
Abstract: Trawl winch is the most important equipment of trawler fishing. In order to ensure safe dragging operations of fishing vessel equipment under the complex sea conditions as well as to realize the quick response and precise control of trawl winch, and keep net shape good, in this study, the trawl tension automatic control system was designed based on electro-hydraulic control technology. The systemmainly consisted of proportional directional valve, balance valve, overflow valve, pilot valve, oil pressure sensor, and electric control system. Through measured input and output pressure of motor, we calculated warp tension as the feedback signal and usedPLC (programmable logic controller) to control the pressure of pilot relief valve, whichwas used to adjust the left and right warp tension and position, to maintain the dynamic balance of system as well as to keep the net shape good. The man-machine interface and operation mode of automatic tension control was developed based on LabVIEW, of which its main function consisted of parameter set, information management, system monitor and data inquire. The system facilitated operator monitoring the running state of the various equipment, and management equipment operation. In order to verify the characteristic and practicability of tension control of the system, application test was carried on the East China Sea area in 2015. The experiment continued about 4.5 hours, including three stages: shooting net, dragging net, and heaving net, which tested speed control and tension control performance of the system under the corresponding operating conditions, and measured relevant data such as shoot depth, shoot length, shoot speed, heave speed, warp tension and winch working pressure. The test resultshowed that dragging stage was the longest, and in this process, the left warp and right warp were kept balance, warp tension was mainly affected by hydrodynamic, warp weight, and water resistance of fishing gear. Warp shoot length range was 350-490 m, warp tension range was 118 -148 kN, corresponding to the system pressure of 2.3-2.7 MPa, and the average trawling speed of fishing vessel was 5.6 kN. Although warp tension various with the shoot length and shoot depth change, the winch was in constant tension state at the most. Data showed that the system could adjust the warp tension well to ensure trawl warp tension maintained in a certain range through adjusting the speed of receiving or releasing net, which suppressed effectively the interference of the warp tension variation on the nets. In addition, experiment also recorded the chart of net shape by netsonde, calculated the net expansion parameter. It could be known that net mouth perimeter was equal before and after using the tension automatic control system by comparison data. The net mouth height and net mouth roundness increased and the net mouth area was expanded by 9.5% after using tension control system, which effectively adjusted the net mouth expansion and improving the fishing efficiency. During the different stage of experiment, the set pressure of overflow valve should be different correspondingly. At the beginning of shooting, the pressure value was small, which can maintain good net mouth shape and position. Due to net speed increased relative to water flow, warp tension was increased and the maximum value reached 208 kN. The set pressure of overflow valve should be large so that it could be used to effectively protect warp and net safety, provided a guarantee for the safe production of fishing vessel. The experiment process was basically consistent with the actual fishing conditions. We concluded that in the tension automatic control mode, the trawl winch can automatically adjust speed of heave and shoot according to the fishing vessel speed and water flow. Though the system could generate heat and result in power loss during uses, the warp tension control system still cab meet the requirements of warp speed and tension control in the different trawl condition.
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