Experimental investigation of air spindle unit thermal characteristics

This paper presents a report on the first stage of a research on the thermal analysis of spindle units with aerostatic bearings and an experimental investigation of temperature distributions. The objective of the present paper is to provide background information for further analysis. A test machine was used running to a maximum rotational speed of 20000 min⁻¹ with a 60 mm diameter spindle supported by aerostatic journal bearings of 20 μm radial clearance, and the temperatures of the housing, bush and the interface between the bush and air film were measured. In addition, the inlet and outlet air temperatures, the air film pressures and the deformations of the housing and spindle were measured. The experimental results show that the heat flow pattern is essentially radial flow, although axial heat flow was observed. The circumferential temperature distribution can be considered to be uniform, and the temperatures are proportional to the square of the spindle speed.     

永磁同步型磨削电主轴偏心振动分析及实验*

电主轴是将旋转主轴与电机转子集成为一体的主轴单元,结构复杂,由于加工或装配误差等原因,电主轴转子会存在着一定的偏心量,为探求由于电主轴偏心所导致的转子振动特性,建立了电主轴转子偏心模型,采用Maxwell应力张量法计算了偏心造成的不平衡磁拉力(UMP),将UMP解析式代入Jeffcott转子模型,得到了转子偏心振动方程。以某磨床的永磁同步电主轴为研究对象,利用有限元方法分析了UMP,发现作用于转子的UMP始终指向气隙最小的方向,研究了不同转速下转子在质量偏心离心力和UMP作用下的振动响应。研究结果表明,电主轴在低速运行时,UMP为转子振动的主要来源;随着转速的增加,质量偏心离心力对转子振动的影响更加明显,而UMP大小保持不变,其频率随转速增加而增大,对转子振动的作用随之减弱。对某机床厂所研发永磁同步型磨削电主轴在试运行时产生的振动问题进行了实验,对主轴振动频谱分析后判断实验电主轴存在静态偏心,测得主轴轴心轨迹对前述分析进行了验证。     

高速主轴轴承油气润滑的应用试验

高速主轴轴承油气润滑技术在国外一些工业化国家早已得到广泛应用。本文对高速主轴轴承油气润滑技术的应用进行了比较系统的试验研究，并与油雾润滑进行了对比应用试验。     

球头铣刀高速铣削Cr12模具钢的振动特性分析

利用球头铣刀高速铣削Cr12模具钢,研究了切削速度、进给量和切削深度对主轴和刀具切削振动的影响变化规律,结果表明随着切削速度的增加,工件振动增加缓慢,而主轴的振动迅速增加,远超过工件的振动成为主振动,主轴进给方向的振动要小于非进给方向的振动。在小进给时,随着进给速度增加各向切削振动而迅速下降,在大进给速度时,各向振动随进给速度增加保持平稳;各通道的切削振动都随着切削深度的增大而增长,因此在高速铣削过程中,主轴振动为主振动,是影响加工表面质量的主要因素。     

精密车削LY12铝合金的振动特性分析

利用超精密车床精密车削LY12铝合金,研究了切削速度、进给量和切削深度对主轴和刀具切削振动的影响及变化规律。试验结果表明主轴的振动随切削速度的增加而平稳增加,在高速时成为主要振动,而刀具在低速时振动很大,随着切削速度的增加而迅速降低。因此在低速时,刀具的振动是影响加工质量的主要因素;在高速时,主轴振动对加工质量的影响愈来愈大;在小进给时,各向的振动随进给的增加而迅速减少,降到临界值后,各通道振动又随进给增加而保持平稳;主轴的振动随切深的增加变化很小,而刀具的振动随切深的增加而增加,但增加到临界值,刀具的振动也保持平稳。     

Dynamic analysis and fuzzy logic control for the vane-type air motor

Air motors are widely used in the automation industry with special requirements, such as park-prohibited environments, mining, chemical manufacturing, and so on. However, during the past only few literatures discussed the dynamics of air motors or their control strategies. The purpose of this paper is to analyze the dynamics of a vane-type air motor, and design a fuzzy logic controller. It is found that the rotational speed of the air motor is strongly affected by the pressure and flow rate of the compressed air. Further, due to the mechanical friction, the overall system is actually nonlinear with dead-zone and has hysteretic behavior. The performance of conventional PI controllers implemented on the air motor usually results in large overshoot, slow response and significant fluctuation errors. To cope with the nonlinear effects of dead-zone and hysteretic behavior, we developed a fuzzy logic controller to improve the performance. The experimental results show that the proposed controller can effectively control the system with a settling time within 0.2 second, the error fluctuation less than 0.5% for high speed operation and 1.5% for low speed operation, and without any overshoot.     

Robust rotor dynamics for high-speed air bearing spindles

For ultra-precision machining machine tool components need to operate outside critical frequencies of the machining system to avoid insufficient surface finish caused by vibrations. This particularly applies to tooling spindles as those are generally the component of a machine tool with low stiffness and damping values. Surface finish and shape of a machined part rely directly on the overall accuracy in motion of the tooling spindle over the entire machining parameter and speed range. Thus spindle designs for an operation outside critical frequencies combined with high stiffness and damping values are crucial for ultra-precision machining.For sufficient stiffness properties bearing gaps of gas bearings have to have a size of only a few microns and show a distinct sensitivity on temperature and for journal bearings also on speed. This again means that bearing properties change with temperature and speed. Considering a spindle system comprising a rigid shaft rotating in a radial/axial bearing system with changing stiffness and damping properties leads to a resonance speed map with changing rigid mode resonance speeds.This paper treats the influence of shaft speed and temperature on bearing gaps from which rigid mode resonance speeds for a shaft spinning in a bearing system are derived. The quoted influence of centrifugal load and temperature on bearing stiffness, damping and load capacity can be applied to any kind of gas bearing. Therefore the calculation of bearing stiffness, damping or load capacity is not treated in detail. The reader will be shown that there are simple design rules for air bearing systems and shafts of high-speed tooling spindles to avoid critical speeds through the entire speed range. Finally, methods of how to prove the initial design goals and how to verify dynamics of high-speed spindles in production will be presented to the reader. It will also be shown that there are production high-speed spindles available which do not include any critical speed within their speed range and thus show robust rotor dynamics with extremely low errors in motion.Procedures in design, validation and application treated in this paper shall give the reader not only design guidelines for spindles to avoid critical spindle speeds within its speed range, but also recommendations for machine tool builders and end-users for a machine operation taking machine and rotor dynamics into account. As the knowledge for this paper is predominantly based on the experience and work of the author himself only a few references are used. However presented testing results entirely confirm the approach presented in this paper.     

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.     

数控机床HSK刀柄和主轴在高速旋转下的连接性能分析

刀柄与主轴连接性能对数控机床的加工精度以及工作安全性影响显著。针对HSK刀柄在高速旋转过程中发生刀柄和主轴连接失效这一主要失效形式,应用弹性力学理论建立了任一转速下刀柄与主轴连接锥面的接触应力模型,且有限元分析结果与该理论模型有较好的一致性。在此基础上,综合考虑夹紧力以及刀柄、主轴配合过盈量的影响,建立了基于HSK刀柄与主轴连接的临界转速计算模型以及连接可靠性模型。根据临界转速模型可以从理论上计算出一定过盈量和夹紧力下的临界转速,分析夹紧力和过盈量对临界转速的影响。根据连接可靠性模型可以求解任一转速下刀柄和主轴连接的可靠度,并得到可靠度随转速的变化规律。这两个模型的建立对防止HSK刀柄、主轴连接的失效,保证高速切削加工的精度以及工作的安全性有重要意义,同时也为正确使用HSK刀柄以及刀柄尺寸结构进一步优化和可靠性设计提供了理论基础。
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Proposal of disturbance-compensating and energy-saving control method of air turbine spindle and evaluation of its energy consumption

This paper introduces a disturbance-compensating and energy-saving control method of an air turbine spindle equipped with a rotation control system designed for use in ultra-precision milling. As one of the key components, our proposed pneumatic regulating device, called a high-precision quick-response pneumatic pressure regulator (HPQR), is used to control the air supply pressure of the air turbine spindle precisely and quickly. The rotation feedback control system including the HPQR and a disturbance force observer, which avoids changes of rotation speed due to disturbance forces applied to the air turbine spindle, is explained. In addition, a pneumatic energy assessment method using a device called an “air power meter” is explained. The effectiveness of the proposed method is demonstrated through the experimental results.     

高速主轴/刀柄接口联结特性

高速数控机床主轴/刀柄接口的联结特性对机床精度和加工稳定性具有重要影响。以HSK-E63为研究对象,利用非线性有限元法分析高速数控机床主轴/刀柄的联结特性,系统地揭示出过盈量、夹紧力、转速对锥面接触应力及间隙的影响及其变化规律。研究结果为高速主轴/刀柄接口的设计和优化提供了理论依据。     

小孔节流深浅腔动静压气体轴承承载特性分析

以小孔节流深浅腔动静压气体轴承为研究对象,采用Fluent软件对轴承的承载特性进行分析,研究偏心率、供气压力、主轴转速、气膜厚度、浅腔深度比等因素对轴承承载力和刚度的影响。结果表明:小孔节流深浅腔动静压气体轴承浅腔区的平均压力大于深腔区的平均压力,压力最大区域出现在浅腔末端靠近轴承端面处;随着供气压力的增加,承载力逐渐增大,但供气压力不应超过0.95 MPa;当主轴转速在3×10~5 r/min以内时,承载力和刚度随着转速的增加呈线性增长规律,当主轴转速超过3×10~5 r/min继续增加时,承载力和刚度的增长趋势明显放缓;承载力与刚度随着浅腔深度比的增加先增大后减小,当浅腔深度是气膜厚度的1～1.5倍时,承载力与刚度接近最大值。     

金刚石飞切加工参数对单晶硅的脆-塑转变影响

针对切削深度、进给量、主轴转速三个因素制定了单因素试验方案,并进行了单晶硅片的金刚石飞切加工试验。通过对试验结果的电镜检测,得出了各因素对加工机理的影响规律。     

加工中心主轴转子临界转速分析

文章运用传递矩阵法对精密高速加工中心主轴动态特性进行了分析，用Matlab工具开发了一套具有自主知识产权的动态计算分析软件，并以某款精密高速加工中心主轴为对象，分析了主轴结构参数对主轴动态特性的影响。分析结果表明，该款主轴动态设计软件运行可靠、操作简便，可应用于加工中心主轴的动态设计与快速开发。     

Counterbalance of cutting force for advanced milling operations

The goal of this work is to concurrently counterbalance the dynamic cutting force and regulate the spindle position deviation under various milling conditions by integrating active magnetic bearing (AMB) technique, fuzzy logic algorithm and an adaptive self-tuning feedback loop. Since the dynamics of milling system is highly determined by a few operation conditions, such as speed of spindle, cut depth and feedrate, therefore the dynamic model for cutting process is more appropriate to be constructed by experiments, instead of using theoretical approach. The experimental data, either for idle or cutting, are utilized to establish the database of milling dynamics so that the system parameters can be on-line estimated by employing the proposed fuzzy logic algorithm as the cutting mission is engaged. Based on the estimated milling system model and preset operation conditions, i.e., spindle speed, cut depth and feedrate, the current cutting force can be numerically estimated. Once the current cutting force can be real-time estimated, the corresponding compensation force can be exerted by the equipped AMB to counterbalance the cutting force, in addition to the spindle position regulation by feedback of spindle position. On the other hand, for the magnetic force is nonlinear with respect to the applied electric current and air gap, the characteristics of the employed AMB is investigated also by experiments and a nonlinear mathematic model, in terms of air gap between spindle and electromagnetic pole and coil current, is developed. At the end, the experimental simulations on realistic milling are presented to verify the efficacy of the fuzzy controller for spindle position regulation and the capability of the dynamic cutting force counterbalance.     

HSK刀柄-主轴结合面接触特性及其影响分析

以HSK刀柄-主轴为研究对象,采用有限元方法对HSK-A63型刀柄-主轴结合面接触特性及主轴系统动态特性进行了仿真分析。分析结果表明：高转速条件下,转速对接触面积影响较大,接触面积随转速增大而减小。夹紧力对接触应力影响较大,在转速和过盈量一定时,接触应力随夹紧力增大而增大,且接触应力的分布情况会发生变化。刀柄-主轴结合面对主轴系统固有频率、振动幅值影响显著,考虑结合面影响后,主轴系统的固有频率降低,振动幅值增大。     

高速磨削用电主轴结构动态优选设计

考虑滚动轴承径向刚度随转速非线性变化，运用传递矩阵法对电主轴的临界转速和静刚度特性进行了系统的研究，用Matlab工具开发了一套具有自主知识产权的动态计算分析软件。以某款精密高速(51000r／min)磨削用电主轴为对象，分析了主轴结构参数与砂轮参数对主轴动态特性的影响，并对主轴结构进行了优选设计。结果表明，基于传递矩阵法编制的电主轴动态设计软件运行可靠、操作简便，可应用于电主轴的动态设计与快速开发。经优选设计后，电主轴的一阶临界转速和主轴端静刚度均有较大幅度的提高。     

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.     

高精度主轴回转精度的测试与研究

通过对锯齿形多槽式动静压气体润滑轴承［１］主轴回转精度的实验研究，采取一定的测试方法和分析手段，找出了产生回转误差的主要原因，提出了进一步提高回转精度的有效措施。     

基于高能量转换效率的旋转式气动发动机动力学分析

针对目前常用气动发动机能量转换效率低的现状,提出一种新型旋转凸轮活塞式气动发动机结构。根据气动发动机工作原理,针对旋转式气动发动机膨胀容积大,缸内高压气体压力直接推动凸轮活塞旋转对外做功的结构特点,分析缸内气体压力与输出扭矩之间的关系,建立动力学模型,并以此动力学模型为基础,利用Matlab/Simulink软件对该发动机单缸工作过程进行计算机仿真分析。仿真结果表明:旋转式气动发动机具有低速时有效扭矩大,能量转换效率高的优点。