可调振幅单向拽振式林果采收机构参数优化

    Parameter optimization of stroke-adjustable and monodirectional pulling fruit harvester

    • 摘要: 为提高果园的采收作业效率,该文提出了一种振幅可连续调节的单向拽振式林果采收机构。该机构主要由输出直线往复振动激励的曲柄摇杆滑块机构和实现振幅调节功能的曲柄滑块机构组成。该文对振摇机构建立了运动学模型,推导得到机构行程与调幅量方程。在满足振摇幅度及调幅量要求的前提下,采用遗传算法对变幅振摇机构进行尺寸优化。根据优化结果建立了变幅振摇机构的三维模型,在ADAMS软件中对调幅曲柄和振摇曲柄同时转动时的振摇机构动力学特性进行仿真分析。在上述理论分析的基础上完成样机加工并开展8 a树龄矮化山核桃田间采收试验,结果表明当调幅曲柄转速为7 r/min,振摇曲柄转动频率在5~14 Hz范围内连续变化时,振幅可调的单向拽振式林果采收机构能够实现山核桃的采收,平均采收率为63.9%。

       

      Abstract: Abstract: The fruit harvester is one of the most common machines in orchards. However, current mechanical harvesters are not suitable for orchard harvesting due to fixed operating parameters, especially the frequency and amplitude. Therefore, a monodirectional pulling fruit harvester with adjustable stroke was proposed based on slider-crank mechanism to improve the harvesting efficiency. The harvester consisted mainly of the case, a steel cable, and a front actuator. In particular, the shaking mechanism in the case was composed of one crank-rocker-slider mechanism and one crank-slider mechanism. The former was used to generate linear reciprocating vibration and the latter to adjust stroke. The stroke changed with the angle of the stroke-adjusting crank. Furthermore,a kinematic model of the shaking mechanism was established to describe its stroke and range dynamics. In order to define the influence of linkage length on the stroke and range, a program was developed based on the displacement equation of the shaking mechanism. The calculation result indicated that the shaking crank had more influence on the stroke than the rocker and stroke-adjusting crank. In addition, the stroke increased with the length of the shaking crank, but decreased with the length of the rocker and stroke-adjusting crank. Range was significantly affected by those two cranks and increased significantly with them. To make the fruit harvester more compact and avoid interferences among all components, the dimension of the shaking mechanism was optimized based on a genetic algorithm. The acceleration curve of the actuator slider at various rotation angles of the stroke-adjusting crank was acquired by further calculations. Moreover, the three-dimensional model of the shaking mechanism was built according to the optimal parameters. The dynamics of the shaking mechanism were simulated in ADAMS software when the shaking crank and stroke-adjusting crank rotated. The rotation speeds of the shaking crank and the stroke-adjusting crank were set to 840 r/min and 7 r/min, respectively. Then the driving torque of those two cranks, the displacement and the acceleration of actuating slider were obtained. The simulation results showed that the driving torque of those two cranks fluctuated wildly while the mechanism generated a two-frequency, reciprocating movement. Finally, based on the kinematic analysis and dynamics simulations, a physical prototype was developed. After that, five Chinese hickory trees with similar age and height in the orchard were measured by digital dynamometer to obtain the average separating force of the fruit, and then the fruit was harvested by the stroke-adjustable fruit harvester to evaluate its performance. The results revealed that the average separating force of fruit was 7.3 N, and the average harvesting percentage was 63.9%, which demonstrated that this mechanical harvester can be used to harvest fruit. By further analysis of problems and causes in the experiment, the cantilever structure in this mechanism needs to be regulated; otherwise it would easily cause vibration when the machine runs at ordinary high speed. In addition, the impact of small branches on energy transmission should be fully considered because part of the fruit grew at the end of small branches.

       

    /

    返回文章
    返回