Thermal characteristics of a CNC feed system under varying operating conditions

In high-speed and high-precision feed systems, thermal positioning errors are mainly caused by the non-uniform temperature variations and resulting time-varying thermal deformations under different operating conditions. The research presented here ultimately aims to develop a generic method capable of evaluating the thermal characteristics (such as temperature rise of heat sources, thermal positioning error) of the feed system induced by varying operating conditions (feed speed, cutting load and preload of ball screw). The thermal contact resistance between the balls and the inner and outer rings of supporting bearing is calculated using the Hertzian theory and JHM method. Experiments were carried out on a high-speed feed system experimental bench, and the influences of operating conditions on temperature rises of supporting bearings and ball screw nut were analyzed. Based on a WNN-NARMAL2 model, the relationship between temperature rise of supporting bearings and operating conditions was established. Furthermore, with the temperature of the ball screw nut set to be a moving heat source load, the temperature and thermal deformation distributions of the ball screw were simulated. The work described lays a solid foundation for thermal error prediction and compensation of a feed system under varying operating conditions.     

长跨距滚珠丝杠辅助支撑装置

介绍了一种数控机床长跨距滚珠丝杠使用的辅助支撑装置,该辅助支撑装置是一种可以与滚珠丝杠螺母一起随动的动态滚珠丝杠辅助支撑装置,它能有效解决长跨距滚珠丝杠自重下垂变形以及旋转抖动问题,延长了长跨距滚珠丝杠及其支撑轴承的使用寿命,提高了机床运动精度和加工精度,降低了机床运动噪声.     

基于RBF神经网络的丝杠热误差模型研究

数控机床的定位精度是反映机床性能的一项重要指标,由丝杠和螺母相对运动产生的热变形严重影响定位精度。结合丝杠热变形的非线性等特点,采用径向基函数神经网络方法建立丝杠热变形误差模型。同时在XHFA2420大型仿形定梁龙门加工中心,对模型进行了实验验证。     

钢球全表面展开原理及方法

针对轴承用钢球表面缺陷检测的生产需求,以实现球面全展开为目标,提出球面螺旋线运动展开原理。首先,设计实现钢球全表面展开的倾斜轴锥面驱动体,并建立其锥面模型;分析展开过程中球面上一点的运动参数,建立钢球和驱动体的接触约束模型,采用迭代法求解拟合出驱动体锥面上接触点的运动轨迹模型;为保证钢球全表面展开,进一步分析球面上接触轨迹,利用弧长积分得到展开过程中球面上的接触轨迹曲线模型;最后通过仿真技术和物理样机试验对钢球展开过程进行分析测试,验证了理论分析结果的正确性。提出的球面展开理论及方法可以应用到高精密轴承球类滚动体的表面缺陷检测设备,也可对其他球类物体的检测提供理论参考。     

Hybrid dynamic modeling and analysis of a ball-screw-drive spindle system

We propose a comprehensive modeling approach to investigate the rigid-flexible coupling vibration of a Ball-screw-drive spindle system (BSDSS). Taking into account the rigid-flexible coupling between the ball screw and rigid components, a hybrid dynamic model for the BSDSS is established. The ball screw shaft was modeled by a flexible beam with axial, torsional, and transverse deformations, and the Ritz series expansion was used to approximate the continuous deformations. The motion equations were obtained using the Lagrange method. The analytical solution was derived and verified. According to the proposed model, the dynamic behavior of the system for various operating conditions was simulated and discussed. The numerical simulation result is useful for the controller design or tuning and the stiffness matching design of ball screw drives.     

Design of high-precision ball screw based on small-ball concept

This paper addresses a design method of ball screws for high-precision feed drives of machine tools. The torque fluctuation of a ball screw influences position deviation, which deteriorates the contorting accuracy. The torque fluctuation comes from the load change of the contacting balls between the nut and the screw shaft during ball circulation. In order to decrease the load change, a ball screw that employs smaller balls was designed and evaluated in the measurement tests. The experimental results showed that the designed ball screw could decrease both the torque fluctuation and position deviation.     

考虑三维运动和相对滑动的滚动球轴承局部表面损伤动力学建模研究

滚动体通过局部表面损伤时轴承的运动参数及动力学响应是轴承疲劳损伤分析和故障诊断的有效输入和重要依据。基于GUPTA轴承模型构建具有局部表面损伤的滚动球轴承的完整动力学模型。该模型中每个轴承元件(滚球、内圈及外圈)具有6个自由度,并且考虑了元件之间的相对滑动和润滑牵引特性。在对局部表面损伤进行建模时,完整考虑了损伤出现后由于材料缺失而引入的额外间隙,以及损伤对赫兹接触刚度及接触载荷作用方向的影响。研究滚球在通过局部表面损伤时轴承的加速度与滚球/损伤之间冲击力的对应关系,以及轴承转速和损伤宽度对轴承振动响应的影响规律。仿真结果表明,由于考虑了相对滑动和滚球/损伤之间冲击力的影响,本模型能够对具有局部表面损伤的球轴承进行更为合理的动力学特性分析,可为滚动球轴承的疲劳损伤分析和故障定量诊断提供一定的理论依据。     

An ultraprecision positioning system using a twist-roller friction drive

For ultraprecision positioning, the use of the twist-roller friction drive is proposed. To improve the positioning accuracy of conventional twist-roller friction drives, the proposed design has two features: (1) the twist angle between the driving shaft and the driven rollers is very small, and (2) the driven rollers are supported by hydrostatic bearings. The twist-roller friction drive is mechanically a kind of lead screw, and the small twist angle makes the lead of the friction drive less than 0.1 mm. The use of hydrostatic bearing is effective for improving the rotational accuracy of the driven rollers and for eliminating the influence of the fluctuation in roller rotation on positioning accuracy. It has been shown by experiments that the resolution of positioning can be less than 10 nm, and the twist-roller friction drive is suitable for an ultraprecision positioning system.     

Experimental Study of Four-Point Contact Ball Bearing with Deformable Rings

When a ball bearing is designed with thin rings or is mounted in a flexible housing, the assumption of rigid rings is not true anymore. In this article, an experimental study is presented and a comparison with a numerical model is performed. The numerical approach is based on the coupling between a semi-analytical code and a finite element (FE) model that computes the deformation of the rings and housings. The numerical model accounts for ring ovalization, raceway opening, change of conformity, and structural displacements of the whole assembly. The experimental setup allows investigation of the load–displacement behavior of a four-point contact ball bearing submitted to a static thrust loading. Displacements are measured by an optical method (stereo-correlation) that enables comparison of the surface deformation of the two tested bearings and computation of the rigid-body displacement of the inner ring with respect to the outer ring. A comparison between experimental results, numerical results, with and without consideration of ring and housing stiffness, is presented. The numerical results show the importance of the housing stiffness in the modeling, even with standard ball bearings with relatively large and thick rings. Good agreement between measured quantities and numerical results was found. This permits the prediction of the real nonlinear bearing stiffness (load–displacement curve) with a reasonable margin of error.     

高速滚珠丝杠进给驱动系统机械模型的仿真研究

建立了高速滚珠丝杠进给系统的机械模型。重点分析了机械系统对整个进给驱动系统的影响,并利用MATLAB进行计算机仿真分析与研究。同时指出在高速加工过程中屈服形变引起的轨迹误差,并通过反复修改参数得到优化结果,从而找出进一步改进的措施。