欠驱动式茶叶采摘末端执行器优化设计与试验

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

摘要:

针对名优茶采摘末端执行器作业成功率低的问题，对一款欠驱动式末端执行器进行优化设计。以英红九号为对象，对其嫩芽的物理和力学特性进行测定；分析末端执行器的结构及工作原理，根据末端执行器在初始、剪切和后抛等3个工作状态下的杆长几何关系建立多个等式和不等式约束条件，以杆长之和最小作为目标函数，运用信赖域寻优算法将总杆长缩短25.33%；对末端执行器进行静力学分析，解得所产生的剪切力为7.0 N，大于剪断茎秆所需的极限剪切力。对夹持位置、生长角度和一芽多叶等关键因素开展单因素试验，结果表明：当夹持位置为4~8 mm、生长角度为70°~90°、采摘对象为单芽或一芽一叶时，末端执行器作业效果达到最佳，成功率为93.30%~95.00%，平均采摘时间为0.64 s，均优于优化前末端执行器。优化后末端执行器作业成功率得到明显提高，体型明显减小。

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.