Optimization and experiment of arc type reciprocating double-acting tea picking cutter

Abstract: Chinese high-quality tea can be specially required for the appearance quality of tea leaves. Particularly, every single tea bud should be intact with the uniform length of all buds. Chinese famous tea is still widely picked by hand, due to the high breakage of tea shoots that are plucked by machines even the state-of-the-art ones. However, manual harvesting cannot fully meet large-scale tea production in recent years, leading to high labor intensity with low efficiency. It is absolutely necessary and urgent to investigate the suitable plucking machines for Chinese high-quality tea at present. Among them, the commonly-used reciprocating-cutting-type cutter was the core reason for the high tea crushing rate in the bulk tea plucking machine. As a result, the machine cannot be suitable for the high-quality tea. In this study, an optimization experiment was carried out on the structure and parameters of the cutter, in order to develop an excellent plucking tool for the high-quality tea. Firstly, the specific structure of the cutter was introduced to analyze the motion characteristics of the blade. The cutter device consisted of two blades, a double eccentric cam shaft, a driving box, and some standard units. When actuated by the motor through the shaft, the motion of the blade approximated a sine function without considering the micro deformation. The cut diagram was then drawn to determine the main factors for the high crushing rate of the machine. The results show that the main factors influencing the picking quality included the machine moving speed, speed ratio between cutter and machine, reciprocating movement stroke, and cutter tooth height, referring to the moving speed, speed ratio, stroke, and tooth height, respectively. These resulting factors interacted with each other for the complex tea plucking. Hence, comprehensive optimization was very necessary to clarify the plucking effect of every single factor, rather than the cut diagram only. Secondly, an electrical test platform was designed with the rail-type tea plucking to permit the setting of exactly the velocity values of cutting and driving needed in the experiment within a certain range. The self-propelled tea plucking machine was also designed before. The high precision values were achieved in the 0.1 (r/min) and 0.01 (m), respectively. A quadratic regression orthogonal rotary center combination test was carried out on the test platform. The nine pairs of blades were produced with different structure parameters, according to the test scheme. Then, the parameter optimization model was established with the evaluation indexes (including the integrity percentage of sprout leaves, leakage rate, and complete rate stubble roughness). The improved model was solved with the genetic algorithm (GA). The best combination of parameters was obtained for the machine as follows: the blade speed was about 0.4 m/s, the speed ratio was 1.2, the stroke was 23 mm, and the tooth height was 25 mm. The calculated integrity rate of bud and leaf was 86.89% under these conditions. Finally, the new cutter blade was developed, according to the parameter optimization. The experimental verification was achieved as follows: the integrity rate of bud and leaf was 82.6%, the leakage rate was 0.24%, and the stubble roughness was 2.8 mm, indicating better consistency with the optimized test. The integrity rate of tea picking increased by more than 20% after optimization, indicating the significantly improved quality of tea plucking. The finding can lay a sound foundation for the efficient technology mode of "machine picking and grading" during high-quality tea harvesting. This improved mode can be expected as a broad application prospect in the tea industry. The adaptive optimization of tea varieties and the dynamic process can be used further to promote the plucking tea quality during the reciprocating cutting plucking.