数控机床主轴可靠性加速试验基础问题研究

The spindle system of the advanced CNC machine tools is the complex hydromechatronic system which plays an most important role in the reliability. Under the circumstance that complex load conditions of the spindle can be simulated by spindle reliability accelerated test benches, it is an urgent need to establish theories and methods for the spindle reliability system accelerated tests. This project uses the methods of weight of maximum entropy model and feature vector to establish a weight model corresponding to different kinds of stress loads (including axial static and dynamic cutting force, static and dynamic radial cutting force, cutting torque and speed, etc.) and an spindle test program spectrum which can provide loading basis for the spindle reliability accelerated test under integrated stress. Bootstrap and Monte Carlo sampling methods are integrated into the optimization method of the spindle stress accelerated tests；based on the Arrhenius and inverse power law hybrid algorithm，the napping relation between the reliability under accelerated stress level and the reliability under regular stress level is researched. In addition，the accelerated model and acceleration coefficient are also determined. Interval estimate method can be given based on the simulated generation method for failure time and Bootstrap method, which is used to estimate the level of reliability under complex stresses accelerated test appropriately. A new theory and method of the spindle system reliability acceleration test for the CNC machine tool will be got, which has an important academic significance and engineering value.

数控机床的主轴是影响其可靠性的最重要的机电复杂系统，在研制出能够模拟主轴复杂载荷工况的可靠性台架加速试验装备的情况下，急需建立能够指导主轴系统可靠性加速试验的理论与方法。本项目采用熵法和特征向量法建立不同载荷（含轴向静动态切削力、径向静动态切削力、切削扭矩和转速等）的权重模型，建立主轴复杂应力的程序试验谱，为可靠性加速试验提供加载依据；融合Bootstrap抽样和蒙特卡洛方法，研究提出主轴复杂应力下加速试验方案的优化设计方法；采用Arrhenius和逆幂律混合算法，研究加速应力下的可靠性与常规应力下的可靠性之间的映射关系，建立可靠性加速模型并确定加速系数；研究故障时间模拟生成方法和利用Bootstrap抽样技术进行主轴可靠性评价的区间估计方法，实现在复杂应力加速试验环境下对可靠性水平的正确评价。通过上述研究形成数控机床主轴系统可靠性加速试验的理论与方法，具有重要的学术意义和工程应用价值。

数控机床主轴是影响机床整机可靠性的关键功能部件，在具备能够模拟主轴复杂载荷工况的可靠性台架加速试验装备的情况下，研究能够指导主轴可靠性加速试验理论与技术具有重要意义。.（1）建立了主轴的可靠性加速试验程序试验谱.以模拟主轴的真实工况为主要目标，开展了主轴加载试验谱的编制方法研究。首先考虑到不同加工方式下的载荷数量和载荷特点均不同（即切削力特性不同），采用载荷循环计数法分别编制了机床的铣削加载谱、钻削加载谱和镗削加载谱；之后将编制的三个加载谱合成为主轴的总加载试验谱，为主轴的可靠性台架试验提供了载荷模拟加载依据。为便于工程推广和应用，形成了程序试验谱的外推技术和编制软件。.（2）提出了主轴可靠性加速试验方案的优化设计方法.为了在短时间内获得足够多的主轴可靠性信息，通过施加高应力水平的可靠性加速试验加快主轴的性能退化。以转速和径向力载荷为主轴的加速应力，开展了主轴的可靠性加速退化试验。综合考虑试验成本和退化试验数据的精度，以正常应力水平下的主轴伪故障时间估计值的渐进方差为目标函数，以应力水平、样本量、各应力水平下的性能检测间隔和检测次数、截尾时间、试验成本为优化变量，单个试验样品价格、单次性能测量费用、人力成本及设备折旧费为费用约束条件，建立了主轴的加速试验方案优化模型。采用遗传算法对优化模型进行了求解，得到了优化后的主轴可靠性加速试验方案。.（3）建立了主轴可靠性加速模型.考虑维修对主轴可靠性的随机和不可预测性的影响，基于加速应力水平必须保证故障机理和故障模式不变的原则，基于逆幂律关系模型建立了基于切削力单应力的主轴可靠性加速模型；假定主轴的各应力载荷相互独立，基于多项式加速模型建立了考虑多应力的主轴加速模型，采用最小二乘法对单应力和多应力的加速模型进行了求解。.（4）提出了主轴可靠性特征量的区间估计方法.研究了非齐次泊松过程的故障时间模拟生成方法，利用Bootstrap抽样技术实现了主轴可靠性特征量的区间估计方法，提高了可靠性评估的准确性，完善了可靠性评估体系。