振动激励下枣树力传递效果室内模拟试验

为了提高林果振动采收的作业效率,根据果品在振动过程中瞬时加速度的变化,研究其振动采收时力的传递效果,降低激振功耗.该文以红枣振动采收为研究对象,建立红枣"枝-柄-果"的双摆振动模型,分析系统振动过程中的固有频率,获得系统的固有振动频率为14.69、17.26Hz;利用振动试验测试系统,进行扫频试验,测得枣树发生共振频率的范围集中出现在12~24Hz;当振幅分别为3、5、7mm时,频率在12~24Hz时进行枣树的定频振动试验,通过DHDAS分析软件分析,获得枣树的振动频率和瞬时加速度的关系;对受迫振动的红枣采用3D高速摄像技术进行运动分析,获得红枣在空间的最大瞬时加速度值,通过统计计算分析,红枣的最大瞬时惯性力值均大于果柄最大拉断力6N.试验表明在振幅为7mm、频率为17Hz时,红枣振动采收过程中,力的传递效果较好.该研究可为红枣收获机激振系统的设计提供理论依据和技术参考.

Simulation experiment in lab on force transfer effect of jujube under vibration excitation

Abstract: In recent years, jujube planting area in Xinjiang has been increasing, and jujube harvest depends entirely on manual work that is characterized by low efficiency and high cost, which has become the bottleneck of the sustainable development of Xinjiang jujube industry. Therefore, mechanized operation is in urgent need. In order to improve the efficiency of vibration harvesting for fruits to reduce power consumption in excitation, the effect of force transfer in vibration harvesting was studied based on the changes in instantaneous acceleration of fruits in vibration,. Aimed to vibration harvesting of jujube, the preset study analyzed natural frequencies in system vibration through simplifying "branch-stalk-fruit" of jujube to a double-pendulum vibration model firstly, and then constructed Lagrange''s double-pendulum multi-degree-of-freedom vibration equation, and the natural vibration frequencies of the system were obtained (14.69 and 17.26 Hz respectively). Based on electrodynamic vibration test stands, experiment of frequencies scanning was conducted for the whole jujube tree. In the resonance, with the gradual increase of the distance to excitation source, resonance frequency increased gradually. The resonant frequency of 3 test points in each path ranged from 12 to 24 Hz, which provided reference for constant frequency test. In order to investigate the effect of vibration frequency and amplitude on instantaneous acceleration of each branch of the sample tree, vibration test for constant frequency of jujube was carried out at the amplitude of 3, 5 and 7 mm, respectively, and the frequency of 12-24 Hz. DHDAS analysis showed a correlation between vibration frequency and instantaneous acceleration of jujube. The longer the distance to excitation source, the greater the change of instantaneous acceleration in resonance. Instantaneous acceleration showed no obvious changes with the increase of amplitude. The bifurcation point and diameter of the tree had great influence on the resonance amplitude; and the more the bifurcation points of the path, the smaller the change of instantaneous acceleration. The motion of jujube under forced vibration was analyzed using 3D (three-dimensional) high-speed camera technology to reveal the maximum instantaneous acceleration value of jujube in space. Statistical analysis demonstrated that the maximum instantaneous inertia force of jujube was greater than the maximum breaking load of fruit stalk (6 N). With the increase of amplitude, the maximum instantaneous acceleration of jujube increased gradually, and its variation coefficient did not change obviously. That was, within the range of the amplitude of the sample jujube tree, the maximum acceleration value of each jujube was relatively large and jujube was more likely to fall with the increase of amplitude. With the same amplitude and different paths, the larger the mass of jujube, the larger the instantaneous acceleration of jujube vibration, suggesting that large mass of jujube is correlated with easy falling in vibration. With different amplitudes and the same path, the smaller the trunk diameter of each path of the sample tree, the larger the average value of vibration acceleration of jujube, which suggested that trunk diameter was also one of the main factors affecting jujube vibration harvest. This study can provide a theoretical basis and technical reference for the design of the excitation system for jujube harvest.