Research Progress of Key Technology of High-Speed and High Precision Motorized Spindles

High speed machining and high precision machining are two tendencies of themanufacturing technology worldwide. The motorized spindle is the core component of the machine toolsfor achieving the high speed and high precise machining, which affects the general developmentlevel of the machine tools to a great extent. Progress of the key techniques is reviewed in thispaper, in which the high speed and high precision spindle bearings, the dynamical and thermalcharacteristics of spindles, the design technique of the high frequency motors and the drivers, theanti-electromagnetic damage technique of the motors, and the machining and assembling technique areinvolved. Finally, tha development tendencies of the motorized spindles are presented.

Model of Rotation Accuracy of High-Speed Spindles on Ball Bearings

For the purpose to improve a design quality of high-speed spindle units, we have developed mathematical models and software to simulate a rotation accuracy of spindles running on ball bearings. In order to better understand the mechanics of ball bearings, the dynamic interaction of ball bearings and spindle unit, and the influence of the bearing imperfections on the spindle rotation accuracy, we have carried out computer aided analysis and experimental studies. When doing this, we have found that the spindle rotation accuracy can vary drastically with rotational speed. The influence of bearing preload has a secondary importance. Comparison of the results of these studies has demonstrated adequacy of the models developed to the real spindle units.

MECHANICAL-ELECTRIC COUPLING DYNAMICAL CHARACTERISTICS OF AN ULTRA-HIGH SPEED GRINDING MOTORIZED SPINDLE SYSTEM

On the basis of the traditional mechanical model of a grinding wheel rotor and the mechanical-electric coupling model with ideal sinusoidal supply, taking high-frequency converting current of inverter power switches into further consideration, a modified mechanical-electric coupling model is created. The created model consists of an inverter, a motorized spindle, a grinding wheel and grinding loads. Some typical non-stationary processes of the grinding system with two different supplies, including the starting, the speed rising and the break in grinding loads, are compared by making use of the created model. One supply is an ideal sinusoidal voltage source, the other is an inverter. The theoretical analysis of the high-order harmonic is also compared with the experimental result. The material strategy of suppressing high-order harmonic mechanical-electric coupling vibration by optimizing inverter operating parameters is proposed.

Optimization of Bearing Locations for Maximizing First Mode Natural Frequency of Motorized Spindle-Bearing Systems Using a Genetic Algorithm

This paper has developed a genetic algorithm (GA) optimization approach to search for the optimal locations to install bearings on the motorized spindle shaft to maximize its first-mode natural frequency (FMNF). First, a finite element method (FEM) dynamic model of the spindle-bearing system is formulated, and by solving the eigenvalue problem derived from the equations of motion, the natural frequencies of the spindle system can be acquired. Next, the mathematical model is built, which includes the objective function to maximize FMNF and the constraints to limit the locations of the bearings with respect to the geometrical boundaries of the segments they located and the spacings between adjacent bearings. Then, the Sequential Decoding Process (SDP) GA is designed to accommodate the dependent characteristics of the constraints in the mathematical model. To verify the proposed SDP-GA optimization approach, a four-bearing installation optimazation problem of an illustrative spindle system is investigated. The results show that the SDP-GA provides well convergence for the optimization searching process. By applying design of experiments and analysis of variance, the optimal values of GA parameters are determined under a certain number restriction in executing the eigenvalue calculation subroutine. A linear regression equation is derived also to estimate necessary calculation efforts with respect to the specific quality of the optimization solution. From the results of this illustrative example, we can conclude that the proposed SDP-GA optimization approach is effective and efficient.

Thermal Model of High-Speed Spindle Units

For the purpose to facilitate development of high-speed Spindle Units (SUs) running on rolling bearings, we have developed a beam element model, algorithms, and software for computer analysis of thermal characteristics of SUs. The thermal model incorporates a model of heat generation in rolling bearings, a model of heat transfer from bearings, and models for estimation of temperature and temperature deformations of SU elements. We have carried out experimental test and made quantitative evaluation of the effect of operation conditions on friction and thermal characteristics of the SUs of grinding and turning machines of typical structures. It is found that the operation conditions make stronger effect on SU temperatures when rpm increases. A comparison between the results of analysis and experiment proves their good mutual correspondence and allows us to recommend application of the models and software developed for design and research of high-speed SUs running on rolling bearings.

Electromagnetic Analysis and Optimization of High-speed Maglev Linear Synchronous Motor Based on Field-circuit Coupling

High speed maglev train has become a new non-contact transportation mode mainly studied in recent years because of its non-sticking and high speed characteristics.Firstly,the finite element model of the long stator linear synchronous motor(LSM)is established based on the structure of the test prototype.After calculation,it is compared with the experimental data and verified.On this basis,a field-circuit coupling model based on inverter circuit is established,and the influence of carrier wave ratio change on the output characteristics of LSM is calculated and analyzed.Finally,the filter circuit is introduced into the field-circuit coupling model,and the influence of the filter circuit on the output characteristics of the LSM is compared and analyzed.

Optimization Design of High-speed Interior Permanent Magnet Motor with High Torque Performance Based on Multiple Surrogate Models

In order to obtain better torque performance of high-speed interior permanent magnet motor(HSIPMM) and solve the problem that electromagnetic optimization design is seriously limited by its mechanical strength, a complete optimization design method is proposed in this paper. The object of optimization design is a 15 kW、20000 r/min HSIPMM whose permanent magnets in rotor is segmented. Eight structural dimensions are selected as its optimization variables. After design of experiment(DOE), multiple surrogate models are fitted, a set of surrogate models with minimum error is selected by using error evaluation indexes to optimize, the NSGA-II algorithm is used to get the optimal solution. The optimal solution is verified by load test on a 15 kW, 20000 r/min HSIPMM prototype. This paper can be used as a reference for the optimization design of HSIPMM.

Dynamic Response Analysis of Motorized Spindle System

As to motorized spindle system, this paper builds a simplified 3D model of spindle and bearing, performs structure modal analysis, reveals its dynamic characteristics under the free model; furthermore, modifies bearing radial stiffness and number of model and studies the change of modal parameters. On this basis, through the harmonic response analysis of the finite element model, dy- namic response characteristic caused by imbalance of monitored spindle system and law of vibration response to different amount of unbalance is analyzed.

Analysis of Thermal Characteristics for a High Speed Motorized Spindle Based on the ANSYS Workbench

The high-speed motorized spindle, as the key component of machining centers and other high-end CNC machine tools, has performance directly affecting machining accuracy. According to the internal motor character- istics of the high speed motorized spindle in the paper, two major heat sources are analyzed and quantity of heat is calculated. The finite element analysis model of motorized spindle thermal characteristics is built through ap- plying the ANSYS Workbench. The thermal steady state, heat-structure coupling characteristics is carried out based on the cooling coefficient of thermal boundary conditions, and taking heating value of the bearing and mo- tor as thermal load, the temperature field distribution and thermal deformation of the spindle system are obtained, which prepare fox＂ the next thermal error modeling

Analysis of Temperature Rise in High-Speed Permanent Magnet Synchronous Traction Motors by Coupling the Equivalent Thermal Circuit Method and Computational Fluid Dynamics

To solve the problem of temperature rise caused by the high power density of high-speed permanent magnet synchronous traction motors,the temperature rise of various components in the motor is analyzed by coupling the equivalent thermal circuit method and computational fluid dynamics.Also,a cooling strategy is proposed to solve the problem of temperature rise,which is expected to prolong the service life of these devices.First,the theoretical bases of the approaches used to study heat transfer and fluid mechanics are discussed,then the fluid flow for the considered motor is analyzed,and the equivalent thermal circuit method is introduced for the calculation of the temperature rise.Finally,the stator,rotor loss,motor temperature rise,and the proposed cooling method are also explored through experiments.According to the results,the stator temperature at 50,000 r/min and 60,000 r/min at no-load operation is 68℃ and 76℃,respectively.By monitoring the temperature of the air outlets inside and outside the motor at different speeds,it is also found that the motor reaches a stable temperature rise after 65 min of operation.Coupling of the thermal circuit method and computational fluid dynamics is a strategy that can provide the average temperature rise of each component and can also comprehensively calculate the temperature of each local point.We conclude that a hybrid cooling strategy based on axial air cooling of the inner air duct of the motor and water cooling of the stator can meet the design requirements for the ventilation and cooling of this type of motors.

Dynamic Analysis of Axial Magnetic Forces for DVD Spindle Motors

The axial magnetic force, induced by the complicated flux linkage distribution from rotor magnet and stator slotted, is constructed by different relative heights and calculated by 3D finite element method (FEM) to analyze the dynamic characteristics for a DVD spindle motor. The axial magnetic force is designed to provide an axial stiffness, and govern the natural frequency of the dynamic performance. According to the simulation results and experimental measurements, the dynamic behaviors are significantly improved with a variation of relative height of rotor magnet and stator slotted on a DVD spindle motor.

Integration of bio-inspired limb-like structure damping into motor suspension of high-speed trains to enhance bogie hunting stability

Hunting stability is an important performance criterion in railway vehicles.This study proposes an incorporation of a bio-inspired limb-like structure(LLS)-based nonlinear damping into the motor suspension system for traction units to improve the nonlinear critical speed and hunting stability of high-speed trains(HSTs).Initially,a vibration transmission analysis is conducted on a HST vehicle and a metro vehicle that suffered from hunting motion to explore the effect of different motor suspension systems from on-track tests.Subsequently,a simplified lateral dynamics model of an HST bogie is established to investigate the influence of the motor suspension on the bogie hunting behavior.The bifurcation analysis is applied to optimize the motor suspension parameters for high critical speed.Then,the nonlinear damping of the bio-inspired LLS,which has a positive correlation with the relative displacement,can further improve the modal damping of hunting motion and nonlinear critical speed compared with the linear motor suspension system.Furthermore,a comprehensive numerical model of a high-speed train,considering all nonlinearities,is established to investigate the influence of different types of motor suspension.The simulation results are well consistent with the theoretical analysis.The benefits of employing nonlinear damping of the bio-inspired LLS into the motor suspension of HSTs to enhance bogie hunting stability are thoroughly validated.

喷嘴位置对轴承腔内油气润滑两相流的影响

基于气液两相流理论,采用多重坐标系法构建角接触球轴承数值计算模型,分析不同喷嘴位置和转速下轴承腔内油相体积分数、保持架表面及轴承内外圈的油气分布特性。结果表明:在轴承低转速下,正面供油时轴承腔内油相体积分数及其周向分布的波动大于背面供油;正面供油时保持架下表面会产生润滑油的积聚,造成润滑油无法及时通过出口排出,而背面供油时润滑油在保持架表面的油相分布更均匀;正面供油时内圈左面油相体积分数较高,外圈油相分布变化较大,而背面供油时内圈右面、中间面及外圈中间面油相体积分数较高。不同转速下喷嘴位置对腔内油相分布的影响也不同,低转速下正面供油时腔内油相体积分数更高,高转速下喷嘴位置对轴承腔内油相分布的影响较小,润滑油在轴承腔内分布较为均匀,保持架下侧未见明显的润滑油积聚。

考虑热误差的电主轴建模与可靠性全局灵敏度分析

以数控机床电主轴为研究对象,旨在分析其轴向热伸长量对电主轴可靠性的影响.采用Svenska Kullager-Fabriken(SKF)摩擦力矩模型对轴承生热量进行分析,设定对流换热系数为边界散热条件,建立了热分析有限元耦合模型,求解电主轴的温度以及轴向热伸长分布.将有限元模型与实验结果进行对比,验证了建立的有限元模型的准确性.考虑随机因素的影响,建立电主轴热变形可靠性分析模型,并采用Kriging模型进行可靠性求解.对电主轴热误差可靠性全局灵敏度进行分析,结果表明,转速和冷却水流量对可靠度影响较大,轴向力和径向力对可靠度影响较小.

电主轴热补偿及轴承故障检测在热辐射测温方面的研究

针对电主轴轴体的热变形以及重要零部件轴承在加工中心上的常见故障,提出基于收集电主轴温度变化的热误差实时补偿计算方法与轴承常见故障的诊断方法。热误差补偿方法可以通过对轴体上测温点数据的处理对电主轴单元进行实时的热误差补偿提高加工精度。故障诊断方法是对不同的温度节点设置不同的阈值,阈值对应着电主轴单元内部某些重要零件的故障特征,当节点温度变化超出阈值即进行报警以诊断具体零件的故障。促进了电主轴的智能化进程,为接下来的研究打下基础。

面向电主轴热误差预测建模分析的改进IGWO-LSTM算法

针对电主轴复杂运行工况下的热误差建模问题,提出一种基于改进灰狼优化算法(IGWO)的LSTM神经网络参数预测模型IGWO-LSTM。通过对灰狼算法收敛因子a计算方法进行优化来提高算法寻优性能;通过IGWO算法的适应度函数与LSTM隐含层节点数组成的IGWO-LSTM闭环系统对电主轴热误差预测模型进行训练和预测,避免陷入局部最优,同时提升模型预测精度。为了验证该算法性能,将它与改进前的算法进行对比,通过求取平均绝对误差、平均绝对百分比误差以及均方根误差对这两种神经网络进行评价,结果显示:文中算法的3种指标均优于改进前的LSTM模型,具有更好的热误差预测准确性和全局搜索能力。

模糊自整定PID的液压马达驱动机床主轴速度控制研究

液压马达驱动机床主轴系统具有参数时变和高度非线性,传统PID控制器控制精度不高。针对液压马达驱动机床主轴系统速度控制问题,采用模糊自整定PID控制器实现液压马达驱动机床主轴系统的有效控制,并对控制效果进行仿真验证。构造了液压马达驱动机床主轴系统模型简图,建立了液压马达驱动机床主轴系统数学模型。对传统PID控制器参数,用模糊控制器进行实时整定,开发了模糊自整定PID控制器。最后,采用MATLAB对液压马达驱动机床主轴系统进行仿真。同时,与传统PID控制器的计算结果进行对比和分析。仿真结果显示:采用模糊自整定PID控制器的液压马达驱动机床主轴转速超调量小,具有更快的响应时间,跟踪精度高,同时系统能耗减少20%左右;即使受到较大随机干扰,模糊自整定PID控制器也能快速消除干扰,使机床主轴转速处于受控状态。采用模糊自整定PID控制器可以有效提高液压马达驱动机床主轴系统的动态稳定性以及抗干扰能力。

基于主轴电机电流信号的表面粗糙度检测

针对表面粗糙度不能及时检测造成的工件浪费问题,首次提出根据主轴电机电流信号进行表面粗糙度检测分类。通过实验采集不同表面粗糙度加工时的主轴电机电流信号,采用小波包分解将电流信号分解成不同频段,借助能量特征和裕度因子对不同频段电流信号进行评估,过滤低相关性频段,再通过随机森林筛选特征,降低特征的冗余性。总谐波失真特征实现了积屑瘤检测,仅依赖构建的电流信号特征工程表面粗糙度检测准确率高达95%以上,并且检测时间在2 s以内,基本实现了工件表面粗糙度的快速准确检测。

基于ANSYS Workbench的磨削用电主轴转子动力学特性研究

电主轴是将电机与主轴融为一体的新技术,相比传统主轴它具有更高的精度、转速与功率。为了开发性能更加优良的电主轴,在设计环节需要通过转子动力学方法验算出极限转速,从而提高其寿命和加工性能。目前行业上广泛采用的是刚性梁假设的转子动力学方程组,来求解轴系的动态特性,该方法未能充分考虑到模型的所有自由度导致不能充分测算出主轴的性能。针对于此,本文提出了一种采用仿真软件结合轴承理论的方法,在ANSYS Workbench软件中搭建主轴的网格模型,分析了主轴的刚度、极限转速与模态频率,并与试验结果进行验证。结果表明,仿真结果误差较小,该方法具有有效性与实用性。