Optimization Design and Testing of Under-actuated Tea Harvesting End-effector

LIN Guichao, ZHENG Xiaoxin, ZENG Wenyong, HE Zijian, LI Wangheng, ZHU Lixue

Abstract

Aiming at the problem of low success rate of the end-effector of famous tea picking, an under-actuated end-effector was optimized. Taking Yinghong 9 as the object, the physical and mechanical properties of its buds were measured. The structure and working principle of the end-effector were analyzed. According to the geometric relationship of the rod length under the three working conditions of initial, shearing and post-throwing, several equations and inequality constraints were established. Taking the sum of the rod lengths as the objective function, the total rod length was shortened by 25.33% by using the trust region optimization algorithm. The static analysis of the end effector showed that the shear force generated was 7.0 N, which was greater than the ultimate shear force required to cut the stem.Single-factor tests were conducted on key variables, including clamping position, growth angle, and the presence of multiple leaves per bud. The results indicated that the picking success rate of the optimized end-effector was increased by 17.47 percentage points to 25.83 percentage points and 11.67 percentage points to 13.33 percentage points in the two single-factor experiments concerning clamping position and growth angle, respectively. The end-effector operated optimally with a clamping position ranged from 4 mm to 8 mm, a growth angle between 70 degrees and 90 degrees, and when the picking object was either a single bud or one bud with one leaf, achieving a success rate of 93.30% to 95% and an average picking time of 0.64 s, both of which were commendable. Following optimization, the success rate of picking operation of the end-effector was significantly enhanced, and the body shape was obviously reduced, providing a technological foundation for the efficient and intelligent mechanized harvesting of premium teas.

 

Keywords: tea picking robot, end-effector, under-actuated mechanism, optimal design, field test

 

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