双丝杠驱动进给单元轴向刚度模型及影响因素分析

The model and influencing factors analysis of axial stiffness of dual ball screw driving feed unit

双丝杠驱动进给单元在高性能数控机床中的应用较为广泛,研究其动态特性对于提高数控机床的加工性能具有重要的意义。文章基于关键滚动功能部件结合面刚度各个方向耦合的影响,围绕双丝杠驱动进给单元轴向刚度进行了研究分析,通过研究双丝杠驱动进给单元的轴向刚度模型,结合动力学和Hertz接触理论的相关知识,推导其各组成部分的刚度计算公式,探索其主要影响因素及关系曲线。结果表明:双丝杠驱动进给单元的轴向刚度主要受到滚珠丝杠副、支承轴承的结构参数,螺母位置以及两根丝杠跨距的影响;支承轴承结构参数的变化,会引起进给单元轴向刚度的明显变化;螺母位置是进给单元轴向刚度的主要影响因素,在两端固定的方式下其轴向刚度中间最小,在机床加工过程中,应尽量避免在丝杠的中间位置进行操作。

Dual ball screw driving feed unit has been used increasingly in the high performance CNC machine tool, so it is very significant to study the dynamic characteristics of dual ball screw driving feed unit for improving the processing performance of NC machine tool. Considering the coupled influence of the stiffness of key roiling joint surface, the research on axial stiffness of dual ball screw driving feed unit is carried on. An axial stiffness model of dual ball screw driving feed unit is built, stiffness calculation equations of each component are deduced based on dynamics and Hertz contact theory and its main influencing factors and their relationship curves are obtained. The results show that the axial stiffness of dual ball screw driving feed unit changes slightly with the structural parameters of ball screw pair, but changes obviously with the structural parameters of ball bearing. Ball screw span makes the axial stiffness linearly increase. Torsion angle makes the axial stiffness nonlinearly increase. The influence of nut position is related to its support mode. Through calculation of stiffness proportion, nut position is the main influence factor on the axial stiffness： under both ends fixed, the axial stiffness is the largest at both ends and smallest at mid position. As a result, during machining process of CNC, operation at middle position need to be avoided.