芒果采收车机械臂运动特性分析及试验

为提高芒果采收车机械化采摘的适应性，该研究采用多体动力学理论方法对其机械臂的运动特性进行分析。首先，结合芒果生长和农艺特征及采摘机械臂几何构型与向量特性，运用D-H法建立了机械臂运动学模型以探索其运动特性，并进行末端执行器运动轨迹规划。轨迹规划结果表明末端执行器运动平稳，满足芒果采摘运动要求。进一步地，利用拉格朗日法构建了机械臂的动力学模型，对其进行了正逆动力学仿真验证，以深入了解机械臂的关节运动特性。动力学分析结果表明，在恒力矩工况下，伸缩装置和摆动装置的运动呈现一定的周期性，摆动装置、旋转装置角加速度和伸缩装置加速度均约在1.25、2.3、4.15 s达到阶段峰值；在仅做摆动周期运动的情况下，旋转装置、摆动装置所受驱动力矩均近似呈周期性变化，峰值分别为72.5与52 N·mm，且在一个运动周期内，均有两个极大值点。对机械臂结构进行仿真模态计算和模态试验，结果表明前六阶固有频率误差在5%以内，验证了芒果采收车机械臂多体动力学仿真建模的准确性。研究结果可为保证有效实现机械臂的采摘效果及提高其可靠性与稳定性提供依据。

Analysis and test of the kinematics characteristics of the roboticarm for a mango harvesting vehicle

Motion characteristics of the robotic arm can dominate the performance of mango harvesting vehicles during picking. In this study, the kinematics analysis was carried out using the multi-body dynamics theory. An initiative was first undertaken to conceptualize and engineer a mango harvesting vehicle. The higher efficiency and labor-saving harvesting was achieved within tropical agricultural regions, compared with the manual. The equipment was designed with walking, lifting, and harvesting functions that were tailored to the Hainan mango planting environment, growth and harvesting agronomy. The core components of the vehicle included a hexapod bionic walking device, a robotic arm, and an end-effector. However, the harvested mangoes were of a modest size within the available operational range, resulting in a low load on the harvesting vehicle. The kinematics model of the robotic arm was established using the Denavit-Hartenberg (D-H), according to the growth of mangoes, the geometric and vector configuration of the robotic arm. The variable separation was employed to conduct the inverse kinematics on the joint variables of the robotic arm. The end-effector motion space planning was also conducted to systematically clarify the motion. The trajectory planning showed that the stability of end-effector motion fully met the motion requirements of the robotic arm during picking. The dynamic model of the robotic arm was constructed by the Lagrangian method. The forward and inverse dynamics simulation was carried out on the joint motion of the robotic arm under constant torque and only periodic swing using Adams software. The dynamic analysis showed that there was a certain periodicity movement under the constant torque in the telescopic and swing devices. The peak of the stage reached about 1.25, 2.3, and 4.15 s. In the case of only oscillating periodic motion, the driving torques of the rotating and oscillating device were approximately cyclically changed, with the peak values of 72.5, and 52 N·mm, respectively, indicating two maximum values in one motion cycle. A vibration analysis was also performed to determine the dynamic performance of the robotic arm. The feasibility of the multi-body dynamics model was verified using linear modal calculations and experiments. A vibration element was then created at the bottom of the robotic arm, in order to explore the effect of the bottom vibration excitation on the motion of the end-effector. The frequency response curve showed that the end-effector was subject to the greatest vibration in the y-direction during the operation of the robotic arm, leading to the overall vibration. Moreover, there was a relatively gentle amplitude in the y-direction between 0-10 Hz. Parametric calculations were then performed, where the y direction of the end-effector was defined as the target for optimization. The maximum response value of the robotic arm was 0.1665, indicating the minimal vibration to fully meet the specified smooth operation. In conclusion, the mango harvesting vehicle can be an effective solution to the challenges posed by manual mango picking in tropical agricultural areas. The trajectory planning shared the efficient and precise movement of the end-effector, meeting the requirements of mango harvesting. The multi-body dynamics model of the mango-picking robotic arm was verified by experiments. The findings can provide a strong reference for the picking performance of the robot arm for its high reliability and stability.