核桃机械振动采摘枝干能量传递特性研究

Energy Transfer Characteristics of Walnut Trunk and Branches in Mechanical Vibration Picking

摘要:

为研究核桃树受到外部振动激励载荷作用下枝干振动动态特性，揭示机械振动采摘能量传递规律，建立核桃树-采摘机振动系统动力学模型，采用对称双偏心式核桃采摘机夹持主干的作业方式，并按照规定的路径和监测点安装三轴振动监测传感器的方法进行田间振动能量传递试验，主干振动位移响应数据表明：受对称双偏心式激振时，核桃树主干运动过程发生摆动，沿夹持位置Z方向做往复运动。由三轴振动监测传感器获得的核桃树受迫振动枝干振动位移和动能幅值变化规律可知：核桃振动采摘过程中机械能转换为动能，从主干激振位置以能量波的形式向上枝条自由端传递，传递过程中各监测点处依次获得动能，传递距离越远，动能衰减越多。枝条在空间运动过程中发生摆动弯曲，使其在生长方向存在瞬间小范围可恢复性形变。由于枝组长度较短等因素的影响，其空间运动过程中上下摆动幅度大于左右摆动幅度，与枝条和侧枝空间摆动幅度规律相反。通过对激振频率13~30Hz作业下最远端枝条受迫振动动能均值分析表明，采摘机在激振频率23~25Hz作业时，试验核桃树最远端枝条所获动能均值最大。研究结果可为核桃主干振动式采摘机工作参数的选择和高效振动采摘关键技术提供理论基础。

Abstract:

In order to study the dynamic characteristics of thin bark walnut tree with obvious trunk after artificial pruning under external vibration excitation load, the energy transfer law of mechanical vibration picking was revealed. A dynamic model of the vibration system of walnut tree-picker was established, and the operation mode of the symmetrical double-eccentric walnut picker gripping the trunk was adopted. The field vibration energy transfer test was carried out by installing a three-axis vibration monitoring sensor according to the prescribed path and monitoring point. Combined with the vibration displacement response data of the trunk, the results showed that when stimulated by symmetrical double eccentric vibration, the movement process of the walnut trunk oscillated and reciprocated along the Z direction of the clamping position. According to the variation rules of vibration displacement and kinetic energy amplitude of the forced vibrating branches of walnut tree obtained by the three-axis vibration monitoring sensor, the mechanical energy was converted into kinetic energy during the picking process of walnut vibration, and transferred from the excitation position of the trunk to the free end of the branch in the form of energy waves. In the transmission process, kinetic energy was obtained at each monitoring point in turn, and the longer the transmission distance was, the more the kinetic energy attenuation was. In addition, the branch wobbled and bent in the process of spatial movement, resulting in a small range of instantaneous restorable deformation in the growth direction. Due to the influence of short branch length and other factors, the up and down swing amplitude was larger than the left and right swing amplitude, which was opposite to the spatial swing amplitude of branches and lateral branches. The analysis of the mean value of forced kinetic energy of the farthest branch under excitation frequency of 13~30Hz showed that when the picker operated at 23~25Hz excitation frequency, the mean value of kinetic energy obtained by the farthest branch of the test walnut tree was the largest.The research results can provide a theoretical basis for the selection of working parameters of the vibrating picker for walnut trunk.