木材抓具抓取安全性的分析研究

面对南方桉树人工林归楞作业所设计的木材抓具在进行木材抓取时,为保证抓具能够安全可靠的抓紧和提升木材,需对其进行木材抓取时的安全性进行分析论证。在进行木材抓取时,木材抓紧阶段木材受力是否封闭和木材提升阶段木材倾覆角是否合理是评价木材抓具抓取安全性的两个最关键指标。在木材抓紧阶段,对于单根木材,用公共摩擦锥证明了单根木材的三点夹持力封闭;对于木材整体,用三维空间夹持力封闭三条件证明了木材整体夹持力封闭。在木材提升阶段,通过对两种不同抓取位置的木材进行受力分析,得出在木材提升阶段木材重心在抓具外为一种危险工况。并根据危险工况下抓具的力学形变、各形变之间满足的几何关系及木材受力平衡等条件对提升阶段进行了力平衡建模。根据所建模型,在理论上分析讨论了各因素对木材倾覆角影响并对理论分析结果进行了实机验证,结果表明:由于没有考虑到木材变形,导致倾覆角实际测量值普遍小于理论计算值,但数值相差不大,结果可以接受,证明所建的木材抓具提升木材模型是可行的。

Analysis and Research on Grasping Safety of Wood Grab

In order to ensure that the wood grabber designed for the southern eucalyptus plantation can grasp and lift the timber safely and reliably,the security of the wood grabber should be analyzed and demonstrated. The closure of force on wood and the rationality of overturning angle are the two most important indexes to evaluate the security in the stage of wood grabbing and lifting. In the clamping stage,the three-point clamping force closure of a single piece of wood was proved by the common friction cone for a piece of wood;The three-dimensional clamping force closure was proved by the three-dimensional space clamping force closure for bunch of wood. In the stage of wood lifting,through the force analysis of the situations in which two different grasping positions were selected,we can conclude that it is dangerous to lift if not grabbing on the center of gravity. A model of wood lifting under dangerous condition was established according to the mechanical deformation of the gripper,the geometric relationship between the deformations and the force balance condition. Various factors influencing the wood overturning angle were analyzed and discussed in theory,and the theoretical results were verified by real machine. The results show that the actual measured overturning angle is generally smaller than the theoretical value,but the difference between them is small enough to accept the theoretical simulation,which proves that the model of wood grabber is feasible.