Design And Experiment Of A Uniform Diameter Roller Screening Machine For Fresh Tea Leaves

Fresh tea leaves screening machine is one of the important equipment which can improve upon the throughput and the quality of the tea product. The existing screening machine has low productivity, screening rate, and performs poorly over a wide range of fresh tea leaves. Furthermore, there is limited data on optimization of screening parameters. Therefore, both the design and development a new kind of screening machine and the research on the relationship between the screening rate and screening parameters have important theoretical value and practical significance. The influence of screening parameter on screening performance was studied, so as to optional the screening parameter. Finally, the control system of screening machine was developed. The main research contents and findings are as follows.(1) Design of uniform diameter roller screening machine for fresh tea leavesThrough the analysis of the structure and performance of the roller screening machine found the roller diameter, roller inclination, roller rotating speed and feeding rate were the main design parameters of the screening machine for fresh tea leaves. A uniform diameter roller screening machine was designed with adjustable structural and working parameters, which including roller, frame and regulating mechanism of roller inclination and feeding rate and etc. The diameter of the roller was 0.8 m and has a length of 3 m. The rotating speed ranges from 0 to 24 r/min and has the inclination ranging from 4° to 16°. The feed rate ranges from 0 to 3.5 kg/min.(2) Studying and optimizing the parameters of screening fresh tea leavesThe influenced of roller, rotating speed and feeding rate on total-screening rate were analyzed, by the developed screening machine of fresh tea leaves, and finding the optimal parameters’ combination of screening parameter, in spring and summer. Results suggested that:(1) The influence of roller rotating rate on total-screening rate for fresh tea leaves in spring was higher than roller inclination and the influence of roller inclination was also higher than the feed rate. The maximum screening rate was reached when roller inclination was 6°, the rotation rate of 8 r/min and the feed rate was 2.0 kg/min in spring. The analysis of variance at 5 % significant level in spring showed that the roller inclination and rotation rate had significant impact(P < 0.05) on the total-screening rate.(2) The influence of roller inclination on total-screening rate for fresh tea leaves in summer was higher than the feed rate and the influence of feed rate was also higher than the roller rotation rate. The maximum screening rate was reached when roller inclination was 6°, rotation rate was 16 r/min and feed rate was 1.5 kg/min in summer. The analysis of variance at 1 % significant level in summer showed that the roller inclination had significant impact(P < 0.01) on the total-screening rate.(3) The screening output and screening rate became higher when roller inclination was 6°, rotation rate was 8 r/min and feeding rate was 3.0 kg/min for the spring tea leaves. However, the screening output and the screening rate reached higher when the roller inclination was 6°, rotation rate was 16 r/min and feeding rate was 3.0 kg/min.(4) The movement speed of the fresh tea leaves in the axial direction of the roller was a linear combination of the inclination and the rotation rate of the roller.(3) The control system development of the screening machine for fresh tea leavesIntegrated Mitsubishi FX2N-32MR-001 PLC, TK6102 i touch panel, LCA318T-30 angle sensor, and NJK-5001 C NPN normally open type Hall sensor with three lines to build a control system of screening machine for fresh tea leaves. The roller rotation rate, roller inclination and feeding rate could be adjusted by itself when the parameters are assigned. Changing the rotation direction of drive motor of regulating mechanism changes the height of roller’s feeding port. This helps to achieve the optimal value of adjusting inclination of the roller. Changing the frequency of the output current of the CNT800 converter changes the output rotation rate of the motors. This enables the rotation rate and feeding rate to be adjusted to the assigned values. The control of screening parameters can be automatically and manually realized.Running test on adjusting the roller inclination from 6° to 12° resulted in an average absolute error of about +0.18° or +0.14° and adjusting the rotating speed from 6 to 24 r/min resulted in an average absolute error of 0.06 r/min.The innovation of this research is the designed and developed set of equal-diameter roller screening machine and its control system for fresh tea leaves. Subsequently, the parameters of the machine were optimized so as to provide technical support for the automatic screening of fresh tea leaves in spring and summer.