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机械采收是林果收获最有效的方法,在受迫振动下果实的掉落不仅受到激振振幅、频率和持续时间的影响,还与果树自身的生长形态和固有频谱特性有关。为了研究银杏树的频谱特性与振动响应之间的关系以及振动响应在不同方向上的差异性,该文在室内冲击激振下测试了一棵Y型银杏树不同方向的频谱特性。然后,通过频谱曲线中峰值点和谷值点所在的频率对果树树干进行简谐激振获得空间加速度响应。结果显示频谱特性与振动响应之间存在一定的对应关系,基频以及10.00 Hz以下的激振频率无法激发起很大的振动响应。共振频率能够引起极大的振动响应,但是加速度幅值在低频下较小并且随着激振频率的增加而增大。当频率高于25.00 Hz时并不能再次引起较强的加速度响应,样品树的最佳激振频率为23.75 Hz。在同一个测试位置,3个方向的振动响应呈现出相似的特性但振幅不同。随着测试位置逐渐远离激振点,沿着果树生长方向的加速度幅值显著增加,并且该方向是振动响应传递过程的主导方向。结果表明在机械采收林果时,可以首先测试果树的频谱来获得共振频率,然后在特定的共振频率下对果树进行激振来获得较强的振动响应,更高的激振频率并不一定引起更强烈的振动响应。同一个测试位置不同方向之间存在差异性,不同位置的果实可以被不同方向的惯性力移除。
Mechanical harvesting is the most effective method for fruit harvesting. Fruit drop under forced vibration is not only affected by amplitude, frequency and duration of excitation, but also related to fruit tree’s own growth pattern and inherent frequency spectrum. In order to study the relationship between spectral characteristics and vibration response of ginkgo trees and the difference of vibration responses in different directions, the spectrum characteristics of different directions of a Y-ginkgo tree were tested under indoor impact excitation. Then, the spatial acceleration response was obtained by simple harmonic excitation of the tree trunk through the frequency of the peak point and the valley point in the spectral curve. The results show that there is a certain relationship between the spectral characteristics and the vibration response. The fundamental frequency and the excitation frequency below 10.00 Hz can not stimulate a large vibration response. The resonant frequency can cause a very large vibration response, but the acceleration amplitude is small at low frequencies and increases with increasing excitation frequency. When the frequency is higher than 25.00 Hz, it can not cause strong acceleration response again. The best exciting frequency of sample tree is 23.75 Hz. At the same test position, the vibration responses in three directions show similar characteristics but different amplitudes. As the test position gradually moves away from the excitation point, the amplitude of acceleration along the growth direction of the fruit tree increases significantly, and this direction is the dominant direction of the vibration response transfer process. The results show that in the mechanical harvesting of fruit, you can first test the frequency spectrum of fruit trees to obtain the resonant frequency, and then at a specific resonant frequency of the fruit trees to obtain a strong vibration response, the higher the excitation frequency is not certain Cause a more intense vibration response. There is a difference between different directions in the same test position. Fruits in different positions can be removed by inertial forces in different directions.