三爪卡盘机构及其夹紧力模型分析

Model analysis of three-jaw chuck mechanism and its clamping force

三爪卡盘的夹紧可靠特性和夹紧力大小与其机构及结构参数有关。通过对三爪卡盘机构组成、传动原理及夹持特性的分析,分别采用几何法和数值计算法来建立端面螺纹的几何模型、螺旋线方程和夹持力模型,研究影响卡盘夹紧力与夹持可靠性的结构因素和相关参数,探讨其关键问题。结果表明,利用阿基米德螺旋线的等速性设计卡盘机构的三爪来实现对工件的自定心夹紧在理论上具有合理性;低速和高速卡盘夹紧力的计算分别按静态力和动态静力平衡法建立模型比较可靠,夹持可靠性的关键是满足自锁条件,即螺旋升角小于最小摩擦角(λ<φmin),螺旋副导程与螺纹直径之比应满足S/d<πμmin;卡盘结构参数对夹紧力影响相对较小,高速时的惯性力使卡盘的实际夹紧力减小、可靠性降低。改善螺旋副表面质量和润滑条件可增大夹紧力,适当增大预夹紧力可减小惯性力的影响和提高夹持可靠性。

The clamping reliability and clamping force of three-jaw chuck are related to its mechanism and structural parameters.Through the analysis of the composition,transmission principle and clamping characteristics of the three-jaw chuck,the geometric model,helical equation and clamping force model of the end thread are established by using geometric method and numerical method,the structural factors and related parameters that affect the clamping force and clamping reliability of the chuck are studied,and the key problems are discussed.The results show that it is reasonable in theory to use the constant velocity of Archimedes helix to design the three jaw of the chuck mechanism to realize the self-centering clamping of the workpiece.The calculation of low speed and high speed chuck clamping force according to the static force and dynamic static equilibrium method to establish the model is relatively reliable,the key to the clamping reliability is to meet the self-locking condition,that is,the spiral rising angle is less than the minimum friction angle(λ<?min),the ratio of screw pair lead and thread diameter should meet S/d<πμmin.The effect of chuck structure parameters on clamping force is relatively small,and the inertia force at high speed reduces the actual clamping force and reliability of chuck.The clamping force can be increased by improving the surface quality and lubrication condition of screw pair,and the effect of inertia force can be reduced and the clamping reliability can be improved by appropriately increasing the preclamping force.