电主轴系统的最佳预紧力研究

高速电主轴是高性能机床的核心部件,它将主轴电动机内置于机床主轴中,两者"合二为一",因而具有结构紧凑、质量轻、惯性小、振动小、噪音低、响应快、易于实现主轴定位和准停等突出优点.新一代高速电主轴的工况特点是低速大转矩和高速大功率,预紧力可控是很有技术发展前途的新方向.确定最佳预紧力,实现电主轴在包含低速大转矩与高速大功率整个工作范围内动力学品质全局兼优是预紧力可控的基础.因此,本文对电主轴系统的最佳预紧力进行了研究.     

高速电主轴轴承的预紧

针对高速电主轴轴承的预紧,从轴承预紧方式的选择和预紧力大小的确定两个方面进行了分析研究.     

高速主轴轴承预紧力技术研究

高性能电主轴单元集合了精密主轴轴承技术、高速电机驱动与控制技术、油气润滑与冷却技术、高速主轴轴承预紧等相关技术,其中高速主轴轴承预紧技术是实现高性能电主轴的关键技术之一.论文着重阐述了高速主轴轴承预紧力研究的目的和意义、轴承预紧力的研究现状以及本实验室对轴承施加预紧力的研究.     

高速机床主轴轴承预紧力理论分析

预紧力的大小直接影响机床主轴动态特性,传统的定压预紧已不能满足现代高速化机床主轴的性能需要,预紧力可控成为主轴技术的重要发展方向.采用有限元法,完成了高速主轴系统温度场分析,给出了预紧力和轴承温升的对应关系,以推荐的轴承温升为控制目标,确定高速段轴承预紧力;以轴承的疲劳寿命为设计目标,获得低速段轴承预紧力.以某高速机床主轴为例,分析并计算了预紧力随转速变化的关系曲线,研究结果表明:高速机床主轴轴承预紧力理论分析方法可行,为机床主轴的预紧力控制提供了依据.     

基于双尺度调控的电主轴轴承预紧力优化方法

为研究复杂工况条件下运行激励引起高速电主轴轴承动力学变化对轴承预紧力的影响过程,建立了一种适用于全功能高变速域的高速电主轴角接触轴承预紧力、速度和疲劳寿命耦合优化模型.提出基于轴承疲劳寿命尺度和可靠性度尺度综合控制的轴承预紧力优化方法,构建考虑滚动体滑动、自旋转、陀螺运动的轴承动力学分析方法,研究轴承预紧力与轴承运行状态的动态定量映射关系,以高速电主轴运行过程中轴承疲劳寿命为优化目标,通过可靠性影响因子和疲劳寿命影响因子的双尺度调控,实现轴承预紧力动态优化分析.分析表明:速度激励条件下可通过预紧力动态优化来实现轴承动力学特性动态控制,采用疲劳寿命尺度和可靠度尺度综合调控,可实现轴承预紧力动态定量优化.     

基于双尺度调控的电主轴轴承预紧力优化方法

为研究复杂工况条件下运行激励引起高速电主轴轴承动力学变化对轴承预紧力的影响过程,建立了一种适用于全功能高变速域的高速电主轴角接触轴承预紧力、速度和疲劳寿命耦合优化模型.提出基于轴承疲劳寿命尺度和可靠性度尺度综合控制的轴承预紧力优化方法,构建考虑滚动体滑动、自旋转、陀螺运动的轴承动力学分析方法,研究轴承预紧力与轴承运行状态的动态定量映射关系,以高速电主轴运行过程中轴承疲劳寿命为优化目标,通过可靠性影响因子和疲劳寿命影响因子的双尺度调控,实现轴承预紧力动态优化分析.分析表明:速度激励条件下可通过预紧力动态优化来实现轴承动力学特性动态控制,采用疲劳寿命尺度和可靠度尺度综合调控,可实现轴承预紧力动态定量优化.     

电主轴滚动轴承轴向预紧技术综述

概述了角接触球轴承在电主轴中的应用现状,分析了电主轴预紧力与电主轴精度、转速、寿命等性能的相互影响关系;回顾了轴承定位预紧技术和定压预紧技术的原理及特点;分类评述了采用液压装置、形状记忆合金弹簧、双金属隔套、压电装置、电磁力装置、离心力装置等预紧方式的调压预紧技术和自动预紧技术的原理及效果;最后,对电主轴预紧技术的未来发展趋势进行了预测与展望。     

预紧力对轴承接触状态及电主轴回转性能的影响

高速电主轴角接触球轴承的性能由转速、支承刚度、旋转精度和摩擦生热等因素决定,这些因素都直接关系到轴承在轴向预紧力作用下的接触特性。研究了轴承滚动体与滚道在轴向预紧力变化下的接触特性。提出了一种利用开尔文四线法测定轴承不同轴向预紧力下接触电阻的新方法。结果表明,随着轴承轴向预紧力的增大,接触电阻呈非线性减小。对于角接触球轴承,当轴向预紧力大于一定值时,接触电阻趋向平稳,形成"L"型曲线。进一步研究了轴向预紧力对背靠背角接触球轴承对作为大型电主轴一端支撑的旋转精度的影响。研究表明,轴承外圈径向跳动随着轴向预紧载荷的增大呈现"降-升-降"的波动趋势,反映了径向游隙变化以及背对背轴承对隔离挡圈平行度误差对轴承外圈姿态变化的综合影响。本研究为角接触球轴承作为小型电主轴和大型电主轴的支撑进行轴向预紧时预紧载荷的优化提供了技术支撑。     

基于机床数控系统的电主轴控制技术

现代数控机床需要同时能够满足低速粗加工时的重切削、高速切削时的精加工要求,因此数控机床的电主轴应同时具备低速大扭矩、高速大功率的性能.高速电主轴的大功率化已经是国际机床产业的一个发展方向,为了实现电主轴能达到较高转速的性能和在低转速时大扭矩的特点,电主轴配置安装星角转换装置.主轴星型连接时,具备低速大扭矩的特性,电主轴...     

高速电主轴轴承预紧的分析研究

在高转速下,轴承预紧力的确定及施加方式对高速电主轴起着至关重要的作用。通过理论分析与生产实践经验相比较,确认轴承样本上推荐的轻预紧力并不完全适合电主轴轴承的实际工况。同时通过对轴承预紧力的施加方式进行优化,满足电主轴的高速动态性能。     

A comparative study on the dynamics of high speed spindles with respect to different preload mechanisms

This paper presents the effects of bearing preload mechanisms on the dynamic performance of high speed spindles. The comparisons of two main types of bearing preload????constant?? and ??rigid????mechanisms are provided using a mathematical model as well as experiments. Based on the Timoshenko beam element theory coupled with a nonlinear model of angular contact ball bearings, the dynamics of the spindle shaft, housing, and bearings system is modeled as a nonlinear function of preload mechanism and amplitude, spindle speed, and external cutting loads. The mathematical model of the spindle is experimentally validated by comparing the predicted and measured static displacements, mode shapes, frequency response functions, and natural frequencies under different conditions. The performance of spindles under rigid and constant force preload is investigated systematically using a mathematical model under various conditions. It is shown, among other things, that at high speeds and under cutting loads the rigid preload mechanism is more efficient in maintaining the dynamic stiffness of spindles than constant preload.     

A parametric study on oil/air lubrication of a high-speed spindle

The ball-bearing is widely used on many high-speed spindles due to its low starting friction and high load capacity. However, heat generation and dynamic loading caused by high-speed rotation have been obstacles for increasing the speed limit in many high-speed ball-bearing applications. Applying an appropriate lubrication and preload cannot be overemphasized. Recently, oil/air lubrication has been used on high-speed spindles because of its accuracy in oil quantity control and high cooling efficiency. However, an oil/air supply with inadequate parameters is undesirable. In this study, the performance of a high-speed spindle under different lubrication parameters and preloads was investigated. The Taguchi method was applied to study the effects of design parameters on the lubrication efficiency. This method can also be used to obtain the optimum lubrication conditions. The optimum operating conditions that create the smallest temperature increase were established. The effects of preload on the temperature increase, the thermal deformation and the static stiffness of an oil/air lubricated spindle were studied. The results provide a useful tool in designing a high-speed spindle with a small increase in temperature and sufficient static stiffness.     

高速电主轴动态非接触电磁加载研究

针对高速电主轴接触式加载存在结构复杂、磨损及振动大等问题,提出一种非接触式电磁加载方法。该方法中动态电磁力可模拟主轴实际切削力载荷,实现高速电主轴动态非接触加载。利用电磁理论建立了非接触电磁加载模型,分析了电磁力的影响因素。解决了实现电磁加载的关键技术,并完成加载实验台整体设计。在转速为9 000 r/min、励磁电流为40 mA的加载条件下,针对170MD18Y16型磨削电主轴进行了动态加载实验,并对比了励磁电流和转速变化时动态电磁力的理论和实测值。结果表明,动态加载理论值与实测值变化一致,二者误差较小,验证了动态非接触电磁加载方法的有效性,且改变励磁电流和转速可实现不同条件的加载。     

A speed-dependent variable preload system for high speed spindles

High speed machine tools are required to operate in a wide range of spindle rotational speeds with high stiffness and high accuracy. The stiffness of the spindle is largely dependent on the axial preload of the angular contact bearings. A large preload is required at lower range of speeds to provide sufficient stiffness for vibration-free heavy cutting. However, at higher speeds, it results in rapid temperature rise and reduces the life of the bearing. For optimum performance, it is essential that the bearing preload is reduced as the rotational speed increases. In this paper, an automatic variable preload system is proposed that changes the preload on the bearings as a function of rotational speed. This system is based on the use of centrifugal forces and requires little space inside the spindle. The performance of this mechanical system is determined using finite element modeling. A prototype of the system is fabricated and its performance is investigated using a specially devised test stand for direct measurement of the preload. The effectiveness of the proposed system in reducing the preload at higher speeds is demonstrated.     

Comprehensive measurement and evaluation system of high-speed motorized spindle

Reducing the manufacturing time is the trend of high-precision manufacturing, and the precision of a work-piece is very important for manufacturing industry. The high-speed motorized spindle is the most critical part and becoming more widely used in the machine tool at present, and its precision may affect the overall performance of high-speed cutting. Most of the studies on high-speed cutting are focused on the cutting force, the vibration of the spindle and effects of the spindle’s thermal deformations; hence, how to roundly measure and objectively evaluate high-speed spindle is an imminence question of it because the comprehensive dynamic properties and evaluation system of spindles directly affect the cutting ability of the whole machine tool before they are manufactured. This paper presents a comprehensive measurement and evaluation system of high-speed motorized spindle, which reflects the overall performance of motorized spindle and bases on international standard.     

Kinematical analyses and transmission efficiency of a preloaded ball screw operating at high rotational speeds

High rotational speeds in ball screws (greater than 1000 rpm) cause more slip motion between balls and raceways than slower speeds. This increase in the slip motion increases the friction at the contact area, thus increasing the driving torque required for a high-speed ball screw. Theoretical analyses of the kinematics of a preloaded single-nut, double-cycle ball screw operating at high rotational speeds are presented in this study. The mechanical efficiency obtained from the theoretical driving torque, axial load and the orbital angular speeds of the ball was confirmed with experimental data. The slipping-rolling behaviour of each contact area was well developed from the distribution of stagnation lines consisting of pure-rolling points. Increasing the initial contact angle can significantly reduce the distance between the pure-rolling point and contact centre and decrease the driving torque, especially when the operating axial load approaches the applied preload. The mechanical efficiency can thus be increased, and wear may also be avoided by reducing the slip motion occurring at contact areas between balls and raceways.     

Ultrasonic motorized spindle with hydrostatic bearings

Ultrasonic and acoustic axial spindle oscillations improve the productivity and product quality in machining, reduce the cutting forces, and increase the tool life in the grinding, milling, and boring of structural components, including those made from materials that are hard to machine. Industrial prototypes of motorized spindles with axial spindle oscillations have been developed by specialists at Siberian Federal University and AO NPP Radiosvyaz and patented in Russia. These spindle units include contactless hydrostatic bearings, a resonant-frequency generator (a piezo generator for ultrasonic spindles and a hydromechanical generator for acoustic spindles), and a local concentrator for the spindle’s longitudinal intrinsic waves.     

Dynamic design for motorized spindles based on an integrated model

With increasing popularity in high-speed machining for its high efficiency, motorized spindles have been widely utilized in modern production facilities. Due to the combination of tools and built-in motors, the dynamic characteristics of motorized spindles are more complex compared with conventional spindles, and it is becoming necessary for engineers to thoroughly realize the influences of the system parameters to the system dynamics with considering the multi-physics coupling property. This paper presents an integrated model to study the electro-thermo-mechanical dynamic behaviors of motorized spindles. The integrated model consists of four coupled submodels as follows: bearing, built-in motor, thermal, and shaft model. Based on the proposed model, a design flow chart is developed and six design parameters are identified. The integrated model is validated experimentally and a design sensitivity analysis of the six parameters is then conducted based on a 170MD15Y20 type spindle. The results show that the integrated model is capable of accurately predicting the dynamic characteristics of motorized spindles, and the sensitivities of the six design parameters to the nature frequencies of the spindle system are obtained with and without the influence of the multi-physics coupling property. The coupling relationship among the electrical, thermal, and mechanical behaviors of the spindle system becomes clear from the results.