振动方式和频率对杏树振动采收响应的影响

为了研究受到不同振动激励后杏树的响应状态以及杏树最佳振动采收频率,该文建立了单偏心式和对称双偏心式振动激励下杏树响应模型以及杏树-采收机动力学模型;分析杏树受振动激励后,不同位置的振动响应状态。理论分析与试验表明,杏树受单偏心式振动激励时,主要表现为扭转振动,夹持位置运动轨迹为圆形;受对称双偏心式振动激励时,主要表现为弯曲振动,夹持位置在水平方向上做往复运动,运动轨迹为直线。利用LabView振动测试软件,通过沿杏树主干安装的加速度传感器,检测杏树不同位置振动加速度变化。分析表明,振动由夹持位置沿树干向上传递,同时获得不同位置的加速度振动响应曲线;通过MATLAB对达到振动稳态后0.1 s内数据进行傅里叶拟合分析表明,各级枝干检测点均做周期性简谐运动,得到不同位置加速度拟合曲线及振动响应函数;通过对0~50 Hz加速度频谱分析表明,杏树在11.56 Hz振动激励时,各检测点加速度值最大。该研究可为林果振动收获机械设计与优化提供参考。

Effects of vibration mode and frequency on vibration harvesting of apricot trees

Abstract: In order to study the response state of apricot after being stimulated by different vibrations and the optimal vibratory harvest frequency of apricot tree and provide a theoretical basis for the design of the vibration harvesting machinery of tree fruit, we established a response model of apricot tree excited by single eccentric and symmetrical double-eccentric vibration, and an apricot tree - harvester dynamics model for the main apricot variety "Kumati" in Xinjiang. The apricot tree was simplified into a fixed cantilever beam structure at one end. In this way, the apricot tree could be regarded as a system that could be discretely divided into a finite number of degrees of freedom. The trunk was regarded as an isometric, and uniform-section cylindrical beam. The apricot tree canopy was considered as a mass group and was located in a movable cylinder. We analyzed the vibration response status of apricot trees at different positions after being stimulated by the single eccentric vibration and the symmetric double eccentricity vibration. The theoretical analysis and experiments showed that when apricot trees were excited by a single eccentric vibration, they mainly showed a torsional vibration, and the clamping position trajectory was circular while the trunk trajectory was similar to an inverted cone. When they were excited by a symmetrical double-eccentric vibration, they mainly performed a bending vibration with the reciprocating movement of the clamping position in the horizontal direction, the trajectory of which was straight, and the trunk trajectory was similar to a sector. The data obtained from the accelerometers installed in the clamp positions of the trunk, in the x and y directions, showed that the theoretical motion trajectory of the trunk brace position was consistent with the actual motion trajectory. LabView vibration test software was used and acceleration sensors were installed along the main trunk of the apricot tree to detect the vibration acceleration data of the apricot tree clamping position, the secondary branches and the third-level branches. The vibration acceleration response curve showed that the vibration was transmitted along the trunk upward from the clamping position. The time from the bottom to the top of the vibration initiated by the single eccentric vibration was: 0.135, 0.181, and 0.191 s. The symmetrical double-eccentric was 0.052, 0.219, and 0.224 s. The Fourier fitting analysis of the data within 0.1 s after reaching the vibration steady state in MATLAB showed that the branches detection points at all levels were periodical harmonic motions, and the single eccentric vibrational excitation period was 0.05 s which varied from the bottom to the top. The R2 values were: 0.912 1, 0.928 6, and 0.981 9, respectively. The symmetric double-eccentric vibration period was 0.1 s, and the R2 values at different positions from the bottom to the top were: 0.906 2, 0.939 8, and 0.93, respectively. The above values indicated a higher degree of function fitting. At the same time, the acceleration fitting curves and vibration response formulas at different positions were obtained. The frequency spectrum analysis of 0-50 Hz acceleration showed that the acceleration value of each detection point was maximum when the apricot was excited by 11.56 Hz vibration, and the acceleration of the single eccentric vibration clamping position was greater than that of the branches at all levels. When the symmetrical double-eccentric vibration was transmitted to the third-level branch, the acceleration was higher than that of the clamping position. At the same frequency, the acceleration response of the branches at the symmetrical double-eccentric vibration was greater than that of the single eccentric vibration, which made the vibration recovery more conducive. The results of this study could provide references for the design and the optimization of harvesting machinery parameters for the apricot and other varieties of forest fruits.