Multi-objective Targeted Quality Bulk Tea Pre-treating Key Technologies Research And Equipment Development

Bulk tea is a kind of goods which is produced massively. Mechanized harvesting, large-scale, continuous and automatic processing is the current trend of bulk tea. The source material of bulk tea is machine plucked, which have different lengths and with varied tenderness. The quality of such kind of tea is not guaranteed since different constituents are processed altogether. On the other hand, the existing tea production lines are generally tailored according to customer’s demands which make their flexibility poor, resulting in limited tea kinds. How to improve the quality of bulk tea and make its flavor diversified with new technology, new idea, and new equipment has always been a hot topic and tough issue in the tea processing field. It is of great significance for the sustainable development and virtuous cycle of the tea industry to solve this problem. Sponsored by the "twelfth five year" science and technology program, in order to improve the quality and diversity of bulk tea, this paper is focused on the research of multi-objective targeted pre-treating technologies of fresh tea leaves, which will lay the foundation for the construction of multi-purpose tea production line. The chapters are as follows:In chapter1, the research background and significance of the subject is introduced briefly. On the basis of technical status analysis of tea industry and tea processing machinery, a multi-objective targeted tea production line is proposed, and a review on the research status of pre-treating key technologies are presented, including quality-targeted technologies:grading level evaluation of fresh tea materials, grading and classification of fresh tea leaves, fresh tea leaf and stalk separation, and flavor-targeted technology:preprocessing of fresh tea leaves. Based on this, scientific issues are proposed which will be tackled later in the paper.In chapter2, on the basis of analysis and summarization of quality bulk tea’s feature in color, geometry, and mechanical property, the possibility of identifying fresh tea’s quality level by image processing and the work scheme of fresh tea grading, leaf and stalk separation are evaluated, besides, the preprocessing methods of different kinds of tea are compared and their common problems are summarized, which paves the way for the research of quality and flavor targeted pre-treating key technologies for quality bulk tea.In chapter3, the quality-targeted grading evaluation of quality bulk tea materials is studied. With the introduction of constrained Delaunay triangulation, the geometric parameter recognition of fresh tea with different orientations is solved, and a method based on the quantity statistics of tea sprouts and leaves is proposed to determine the quality level of fresh tea materials. Then a geometric feature index concerning the oldness of fresh tea is proposed, which is a combination of fresh tea leaves’average length, width, area and distance between petioles. It can be used to subdivide fresh tea materials’ grading level further. The purpose is to make the grading level quantified and make it associate with optimal parameters, thus facilitating parameter selection and avoid subjective.In chapter4, the quality-targeted throw grading technique of quality bulk tea materials is studied. Through theoretical analysis and simulation, the motion of throw grader and the influence of mechanical parameters to its performance are studied. At the same time, the motion of materials on the vibrating trough is investigated, including throw condition, throw stroke and its control. Finally, a solution concerning automatic lifting platform and leaf sweeping chain is proposed to remove tea materials blocked in sieves during grading and corresponding grader is developed.In chapter5, the quality-targeted coarse tea leaf and stalk separation technique is studied. The direction recognition problem of fresh tea in tilt chute is studied with feature size and local extreme points which provides technical support for the orientation of fresh tea. Meanwhile, the clamping of small object like tea stalk is studied and a self-locking gripper is designed to clamp a column of tea stalk and its mathematical model is also established. Based on this, the squeeze-cut style fresh tea leaf and stalk separator was designed, and the clamp and cut function was proved to be viable.In chapter6, the flavor-targeted preprocessing technique of quality bulk tea materials is studied. To achieve the green-making effect of oolong tea, mechanical simulation technique is studied. To ensure uniformity of air flow and temperature inside the machine, layered heating, layered ventilation and multiple branch pipes are considered. To adjust the humidity inside, high pressure low flow pump and tiny nozzles are used. Based on this, a multi-functional fresh tea leaf preprocessing machine is developed which can realize the spreading of green tea, withering of black tea, and green-making of oolong tea. Processing equipment will be simplified dramatically if it is adopted in multi-objective targeted tea processing line. In chapter7, the main work of this thesis, research findings and innovations are summarized, and some future work is suggested.