六杆式西兰花采收末端执行机构优化设计与试验

Optimization Design and Experiment on Six-bar End Effector for Broccoli Harvesting

摘要:

针对目前西兰花采收末端执行机构存在结构尺寸大和质量大的问题，本文设计了一种结构紧凑、运动空间小、质量小的六杆式西兰花采收末端执行机构。测量西兰花物理特性，对西兰花茎秆组织的切割力进行评价，设定刀具入切角为90°、刀具切割力为100N。根据西兰花物理参数和生长状态确定六杆式采收末端执行机构方案，建立末端六杆机构运动学与动态静力数学模型，采用遗传算法以外部驱动力最小和理论轨迹实际轨迹差值最小为目标对末端执行机构参数进行双目标优化，优化后得到六杆结构杆长及末端六杆机构最小驱动力矩，其扭矩为1.37N·m，得出优化后刀具切割轨迹且轨迹优化差值为1.29mm，其单侧刀具与最大花球距离为25mm。最后，根据优化结果选定额定功率为400W伺服电机作为动力源，以优化后机构参数设计验证了样机并开展了采收末端执行机构试验。试验结果表明，末端执行机构试验采收成功率为92.5%，验证了六杆式西兰花采收末端执行机构具有良好的采收性能。

Abstract:

With regard to the drawbacks of large structural dimensions and heavy weights in the current end-effectors for broccoli harvesting, a six-bar end effector for broccoli harvesting was designed, which was compact in structure, small in motion space and light in mass. Initially, the physical features of broccoli were measured, and the cutting force of broccoli stem tissues was evaluated and analyzed. Then, the incipient cutting angle of the cutter was set as 90°, and the cutting force of the cutter was specified as 100N. Afterwards, based on the physical parameters and growth situations of broccoli, the plan of the six-bar end-effector for harvesting was settled. The kinematic and dynamic-static mathematical models of the end six-bar mechanism were erected. By applying the genetic algorithm and taking the minimization of the external driving force and the minimization of the difference between the theoretical track and the actual track as the goals, the parameters of the end effector were optimized via a dual-objective optimization method. After optimization, the results of the bar lengths of the six-bar structure and the minimum driving torque of the end six-bar mechanism were achieved, with the torque being 1.37N·m. The optimized cutting track of the cutter was procured, and the optimization difference of the track was 1.29mm. The distance between the unilateral cutter and the largest flower cluster was 25mm. Finally, according to the optimized results, a servo motor with a rated power of 400W was picked as the power supply. A prototype was designed and produced following the optimized mechanism parameters, and experimental researches on the harvesting end effector were performed. The success rate of the harvesting trials of the end effector was 92.5%. The experimental outcomes demonstrated that the six-bar end effector for broccoli harvesting had a good harvesting performance.