Automatic Control Technology Of Tea Water-Removing System

With the improvement of living standard, people demand the amount of tea and the quality of tea all increased. China is the world’s major tea producing country and consuming country. The proportion of green tea is the largest. And it is the leading product of tea production and consumption. Water-removing is the first procedure of green tea primary processing, and also is the key procedure, which is so critical to the quality of green tea. So it is important to analyze the water-removing principle and research the control technology of water-removing system.At present, the index of the control system of tea water-removing machine is temperature. It ensures the quality of tea water-removing by thermostatically control. However, the initial moisture content of fresh leaves are changing, thermostatically control may appear impervious phenomenon. Tea vanilla gas is heavy and lack of fruit flavor. It is difficult to ensure the quality of water-removing. After the analysis of working principle and water-removing principle, the double closed-loop tea water-removing control system based on PLC and fuzzy-PID was investigated in order to meet the requirements of tea water-removing. The main work of this paper are as follows.(1) The heat transfer process of tea water-removing system, the water-removing principle, the mechanical structure’s features of tea water-removing system and the working principle were analyzed. According to the theory of material drying, the tea water-removing process is mainly in the constant speed drying stage. And the relationship between the moisture content of water-removing leaves and temperature was built.(2) The control scheme was designed based on the above analysis. The first roller and the last roller were thermostatically control. It uses fuzzy-PID control algorithm to improve its dynamic performance. The middle roller takes the moisture content of water-removing leaves as the control index, together with changing the temperature of the middle roller to dominate the moisture content. In order to improve its control accuracy and response speed, a double closed-loop control system of moisture content and temperature based on fuzzy-PID control algorithm was designed.(3) The PID control algorithm and fuzzy control algorithms were analyzed. The fuzzy-PID controller was designed based on the theoretical analysis. And the tea water-removing control system was simulated by MATLAB/SIMULINK. The result shows that fuzzy-PID control algorithm applied to the tea water-removing control system is successful. The system’s dynamic performance has been greatly improved. And the static performance is also guaranteed.(4) The hardware design and software design of the tea water-removing control system were finished. Fuzzy-PID control algorithm was implemented based on the PLC. The distributed control system was realized by the configuration software. And the tea water-removing result was assessed by experiment. The result shows that it can well suited to the circumstances that tea moisture is changing based on the index of the moisture content of water-removing tea. And it can meet the needs of engineering practice.