番木瓜摘取的接触力学模型构建与试验

Design and test of a contact mechanics model for papaya picking

【目的】实现番木瓜稳定无损伤摘取。【方法】采用三指对称夹持后扭断的摘取方案,构建摘取接触力平衡方程,依据三指内力汇交原理进行抓取稳定性分析,制定摘取接触力学模型求解方案,并对番木瓜进行摘取试验。【结果】样本表面无明显变形、压痕与裂纹,夹持处果肉室温静置24 h后无明显的颜色变化和伤痕,最大夹持力远小于成熟番木瓜横径方向受压弹性变形阶段压力极限值;质量和摘取扭转力矩与横径、纵径、果柄长度、果柄扭断直径有密切依存关系,质量多元线性回归达极显著水平,扭转力矩多元线性回归达显著水平;依据接触力学模型和回归模型计算的理论夹持力与测量夹持力对比,测量夹持力均高于理论夹持力,两者最大偏差小于20%,两者在趋势上具有较好一致性。【结论】摘取方案能稳定无损伤摘取番木瓜,摘取接触力学模型具有正确性与实用性,可为番木瓜摘取末端执行机构设计与力度控制提供依据。

【Objective】 For stably picking papaya without damage.【Method】 A clamping plan of papaya was designed by means of three-finger clamping symmetrically and wringing,and the equilibrium equation of contact force was constructed. On the basis of force screw theory, the clamping stability was analyzed. The picking contact mechanics model was formulated, and a picking test for papaya was conducted. 【Result】 There were no obvious deformation, crack or indentation on the surfaces of papaya samples. The pulp at the clamping position had no obvious color change or bruise after leaving for 24 hours at room temperature. The maximum clamping force was far less than the pressure limit on the transverse diameter of ripe papaya at the elastic deformation stage. Papaya mass and torque moment were correlated closely with transverse diameter, vertical diameter, stalk length and diameter of the twisted stalk. Mass multiple linear regression analysis achieved extremely significant level, and twist torque linear regression analysis reached significant level. There were good trend consistency between theoretical clamping forces and the measured clamping forces. The measured clamping forces were higher than theoretical values, but the maximum deviation was less than 20%. 【Conclusion】 The picking scheme can stably clamp papaya without mechanical damage. The papaya picking contact mechanics model is correct and practical. The research can provide a basis for designing papaya picking end-effector and controlling clamping force.