精密滚珠丝杠副非赫兹接触磨损分布模型与精度加速退化试验研究

Precision ball screw is the key functional component which manifests high speed and precision characteristics of NC machine tools. Under high speed condition, the large inertia load and poor lubricating lead to severe wear and accuracy degradation. At present, its wear failure mechanism research is far from perfect. Many related studies can not accurately reveal wear mechanism owing to ignoring the ball-raceway contact does not satisfy the Hertzian contact hypothesis and the wear of the raceway is not uniform distribution. This project will build the contact stress model using Non-Herzian contact theory suitable for the general contact condition and complex relationship of relative motion, and obtain the stress distribution and the relative sliding velocity distribution of the ball-raceway contact region combined with the kinematics analysis and mechanical analysis. Furtherly, the contact surface of the raceway will be discretized, and the wear distribution model will be established based on the elastic-plastic model of the asperity and 3D fractal model considering the surface micro morphology of the raceway . The accuracy degradation mechanism of the precision ball screw can be accurately constructed based on the wear distribution model. For increasing the efficiency of the experimental study, the physical model of the accelerated test for the wear will be established to optimize the design of the accelerated test. Then, the accelerated test of the accuracy degradation of the precision ball screw will be implemented combined with theoretical analysis to reveal the mechanism of the accuracy performance degradation and predict the accuracy life rapidly. This project will clarify the characteristics of the ball-raceway contact and accuracy degradation mechanism of precision ball screw, put forward the growth strategy of the accuracy stability, and has scientific significance and engineering value for promoting the accuracy stability of modern NC machine tools.

精密滚珠丝杠副彰显数控机床高速精密特征，但其高速工况惯性负载大，润滑条件易破坏，磨损加剧导致精度退化。目前其磨损机理研究尚不完善，忽略了滚珠滚道接触不满足赫兹接触假设条件和滚道磨损分布非均匀性等问题，难于准确揭示其精度退化机理。本项目将采用适用一般条件的非赫兹接触理论建立考虑多种复杂相对运动关系的滚珠滚道接触分析模型，并结合运动学和力学建模准确揭示接触面接触应力和相对滑动速度分布规律。进一步考虑滚道磨损非均匀性而离散化接触区，并采用微凸体弹塑模型和三维分形模型考虑滚道微观形貌特征构建滚道三维分形磨损分布模型，为精密滚珠丝杠副精度退化机理研究奠定基础。进一步基于物理仿真模型优化设计精度加速退化试验，加速试验结合理论模型，揭示精度退化机理并实现精度寿命快速预测。项目预期探清滚珠滚道接触特性，阐明精密滚珠丝杠副精度退化机理，提出精度保持性增长策略，对提高数控机床精度保持性具有科学意义和工程价值。

课题建立了精密滚珠丝杠副匀速和加速工况下运动学模型，给出了滑滚比计算方法，探清了滚珠丝杠副滚珠、丝杠和螺母三者间的相对运动关系；提出采用最小余能原理建立滚珠丝杠副非赫兹接触模型，精确计算滚珠滚道接触应力和接触变形，避免了滚道接触区非对称性和存在切向摩擦力导致的计算误差；建立了考虑切向接触应力、滚珠惯性力矩、陀螺力矩等因素的滚珠丝杠副匀速和加速工况下运动力学模型和摩擦力矩计算模型，分析了接触角、螺旋升角、丝杠加速度和轴向载荷对滚珠滚道接触点滑滚比的影响规律，为滚珠丝杠副复杂运动状态下精度保持性分析和预测提供理论依据；采用三维分形磨损模型和微凸体接触模型建立了滚道法向磨损深度计算模型和摩擦力矩、预紧力物理仿真模型，实现了滚珠丝杠副预紧力和精度保持性退化的理论数值仿真。同时，建立了加速退化试验方法和试验装置，开展了精度加速退化试验研究，验证所建立理论模型的正确性，并在物理仿真模型的基础上提出了了小子样条件下滚珠丝杠副精度退化和精度寿命快速测评新方法，降低了试验成本、缩减了测评时间，并制定了相关试验规范。最后，在理论分析和试验研究的基础上，从滚珠丝杠副结构优化设计、制造工艺及运行控制方面提出了多种滚珠丝杠副精度保持性增长措施。