基于多柔体动力学的葡萄挑藤机构参数优化与试验

    Parameter optimization and experiment of grapevines picking-up mechanism using multi-flexible-body dynamics

    • 摘要: 针对目前中国北方露地葡萄栽培区缺乏春季葡萄藤上架作业机械的问题,该研究提出了曲柄摇杆式挑藤机构,该机构采用曲柄摇杆结构带动推藤杆和挑藤杆运动,推藤杆用于聚拢葡萄藤,挑藤杆按照既定轨迹进行挑藤。采用Matlab软件对挑藤杆的挑藤轨迹进行了参数优化,得到较优的挑藤轨迹。通过物理试验和计算确定了挑藤机构的弹簧预紧力、弹性系数等结构参数,分析了挑藤过程。其次,基于多柔体动力学(multi-flexible-body dynamics, MFBD)仿真技术建立了葡萄藤的柔性体模型与挑藤作业模型,以前进速度、弹簧预紧力和曲柄转速为试验因素,以平均挑藤角度和角度变异系数为评价指标,设计Box-Behnken仿真试验并进行回归分析。依据多目标优化原则,得到最佳参数组合;进一步基于土槽试验,验证曲柄摇杆式挑藤机构优化结果的准确性。仿真优化结果表明,当前进速度为0.2 m/s,弹簧预紧力为128 N,曲柄转速为67 r/min时,其平均挑藤角度最大、角度变异系数最小,分别为40.6°和6.0%。土槽试验的挑藤机构平均挑藤角度为43.2°,与仿真挑藤角度相对误差为6.4%,角度变异系数为14.8%。土槽试验结果表明仿真优化结果可靠,挑藤角度准确且挑藤均匀性较好,满足葡萄藤上架的角度要求。该研究可为后续葡萄藤挑藤绑藤一体机的研制提供参考。

       

      Abstract: Grapevine picking-up machinery is a high demand in the open-field grape-producing regions of northern China during spring. In this study, the grapevine picking-up mechanism was proposed for the lifting operation using a crank-rocker mechanism. The mechanism was mainly consisting of a frame, crank rocker structure, pushing bar, picking bar, spring, and vine fender. Grapevines were lifted from the ground to the given angle with a simple and reliable structure. The structure of crank rocker was used to constrain the movement trajectory of the picking bar. The pushing bar was used to gather the grapevines, and then the picking bar was lifted them. MATLAB software was also utilized to optimize the parameters of the trajectory curve. An optimal set of structural parameters was achieved for the picking bar. The length of the crank was 160 mm, the length of the link-rod was 480 mm, the length of the rocker was 340 mm, and the length of the base frame was 600 mm. The endpoint coordinates of picking bar were relative to the uBv coordinate system as (1 070 mm, -250 mm). According to multi-flexible-body dynamics (MFBD) simulation, the finite element (FE) flexible body model was established for the grapevines and picking-up operation. A Box-Behnken simulation experiment was designed to analyze the impact of three parameters (forward speed, spring preload force, and crank rotational speed) on the grapevine picking-up through the software RecurDyn. Regression significance analysis of the experimental data was conducted using Design-Expert software, with the average angle and the coefficient of angle variation as the evaluation indices. The results showed that all three test factors shared a significant effect on the average angle, while the forward speed posed a significant effect on the coefficient of angle variation. Among the interaction factors, the spring preload force and the crank rotation speed had a significant impact on the average angle, while the spring preload force and the crank rotational speed had a significant impact on the coefficient of angle variation. Among the quadratic factors, only the square of the forward speed and the crank rotational speed had a significant effect on the coefficient of angle variation, while the rest factors had no significant effect. The maximum average angle and the minimum coefficient of angle variation were obtained after optimization. Consequently, the best combination of working parameter was determined for the machine: the forward speed was 0.2 m/s, spring preload force was 128 N, and crank rotation speed was 67 r/min. As such, the average angle of grapevines was 40.6° in RecurDyn, and the coefficient of angle variation was 6.0%. Finally, the prototype was manufactured to conduct the soil bin tests. There was the essentially consistent data with the optimization. The relative error between soil bin tests and simulation was 6.4%, and the mean of the coefficient of angle variation was 14.8%, fully meeting the operational requirements for picking up grapevines. This finding can be expected to serve as a strong reference in the integrated machines for grapevine lifting and tying.

       

    /

    返回文章
    返回