Application of higher order spectral features and support vector machines for bearing faults classification

Condition monitoring and fault diagnosis of rolling element bearings timely and accurately are very important to ensure the reliability of rotating machinery. This paper presents a novel pattern classification approach for bearings diagnostics, which combines the higher order spectra analysis features and support vector machine classifier. The use of non-linear features motivated by the higher order spectra has been reported to be a promising approach to analyze the non-linear and non-Gaussian characteristics of the mechanical vibration signals. The vibration bi-spectrum (third order spectrum) patterns are extracted as the feature vectors presenting different bearing faults. The extracted bi-spectrum features are subjected to principal component analysis for dimensionality reduction. These principal components were fed to support vector machine to distinguish four kinds of bearing faults covering different levels of severity for each fault type, which were measured in the experimental test bench running under different working conditions. In order to find the optimal parameters for the multi-class support vector machine model, a grid-search method in combination with 10-fold cross-validation has been used. Based on the correct classification of bearing patterns in the test set, in each fold the performance measures are computed. The average of these performance measures is computed to report the overall performance of the support vector machine classifier. In addition, in fault detection problems, the performance of a detection algorithm usually depends on the trade-off between robustness and sensitivity. The sensitivity and robustness of the proposed method are explored by running a series of experiments. A receiver operating characteristic (ROC) curve made the results more convincing. The results indicated that the proposed method can reliably identify different fault patterns of rolling element bearings based on vibration signals.     

Effect of turbulence on the static performance of a misaligned externally adjustable fluid film bearing lubricated with couple stress fluids

Static analysis of a misaligned externally adjustable fluid-film bearing is carried out thereby including turbulence and couple-stress effects in lubricants blended with polymer additives. A modified form of Reynolds equation, incorporated with the theory of micro-continuum and the concept of adjustability, is solved numerically, for various simulated operating conditions. The effects of turbulence and couple-stress on key performance parameters are presented.This study predicts that, an externally adjustable fluid-film journal bearing operating with negative adjustment configuration and lubricants with couple-stress, results in superior load carrying capacity with reduced friction and end leakage, as compared to a conventional partial arc bearing.     

Condition monitoring studies on spindle bearing of a lathe

In modern industry, machinery must become increasingly flexible and automatic. In order to increase productivity, enhance quality and reduce cost, machine tools have to work free of any failure. When a failure occurs in a machine tool, it is necessary to identify the causes as early as possible. Machine tool condition monitoring is very important to achieve this goal. Condition monitoring is generally used on the critical subsystem of any machine tool. This paper endeavors to focus on the condition monitoring aspects on the machine tool element. In the present study, a critical subsystem has been identified based on the failure data analysis. Condition monitoring techniques like vibration monitoring, acoustic emission, Shock Pulse Method (SPM) and surface roughness have been successfully used for fault identification.     

Experimental investigation of the effect of lead errors on helical gear and bearing vibration transmission characteristics

The characteristics of gear meshing vibration undesgo change as the vibration is transmitted from the gear to the housing. Therefore, vibration transmission characteristics of helical gear systems must be understood before the effective methods of reducing gear noise can be found. In this work, using a helical gear with different lead errors, the gear vibration in the rotational direction and the bearing vibration are measured. The frequency characteristics of gear and bearing vibration are investigated and a comparson is also provided.     

某卫星液体火箭发动机推力偏心测试技术研究

卫星火箭发动机推力矢量测试,是一项高新技术火箭测试技术.根据某卫星液体火箭发动机推力矢量的特点和测量要求,阐述了待测推力矢量参数的定义,然后对转台测试原理和计算方法进行了简单的介绍.     

Method of machine technical state assessment on the basis of joint signal analysis

Joint analysis of two signals which are observed during machine operation allows us to acquire information on such phenomena occurring within the machine which cannot be obtained as the results of an analysis of single signals. This knowledge makes it purposeful to assume that the joint analysis of a major number of signals allows us also to acquire new information on the machine state. In this paper the concept of joint signal analysis based on a signal analysis in both “micro” and “macro” time domains was described. In order to calculate values of joint features of signals and determine the machine state on the basis of the joint analysis results the generalized data window was introduced. In order to limit a number of simultaneously considered signals and determine a relation between signal feature values and machine states, the procedure based on an application of additional virtual signals was proposed. In order to verify the elaborated method an active diagnostic experiment was carried out. The experiment result was a set of learning data, which enables us to construct a diagnostic classifier. Exemplary results of classification of technical state of a machine were also presented.     

The use of SESK as a trend parameter for localized bearing fault diagnosis in induction machines

A critical work of bearing fault diagnosis is locating the optimum frequency band that contains faulty bearing signal, which is usually buried in the noise background. Now, envelope analysis is commonly used to obtain the bearing defect harmonics from the envelope signal spectrum analysis and has shown fine results in identifying incipient failures occurring in the different parts of a bearing. However, the main step in implementing envelope analysis is to determine a frequency band that contains faulty bearing signal component with the highest signal noise level. Conventionally, the choice of the band is made by manual spectrum comparison via identifying the resonance frequency where the largest change occurred. In this paper, we present a squared envelope based spectral kurtosis method to determine optimum envelope analysis parameters including the filtering band and center frequency through a short time Fourier transform. We have verified the potential of the spectral kurtosis diagnostic strategy in performance improvements for single-defect diagnosis using real laboratory-collected vibration data sets.     

前帮机轨迹涂胶系统设计

针对传统前帮机鞋底上胶存在较大误差的问题,研制了一种以轨迹控制技术为基础的前帮机自动上胶系统,提出了一种同步双喷嘴机构,并对其进行了运动控制。最后,给出了系统的软件设计流程图。实验结果表明,采用自动轨迹涂胶控制的前帮机完成的上胶效果更好,能制作的鞋型种类更丰富,生产效率更高。     

Measurement method and pipe wall misalignment adjustment algorithm of the pipe butting machine

This paper presents a runout measurement method and a novel finite grouping method to predict and optimize the rotational angle and translational displacement of butting pipes to minimize pipe wall misalignment (PWM). This study develops a method to minimize the PWM of the pipes excluding the positions of welding seams. In this method, the measurement data are divided into finite groups and the criteria are created to identify the positions of welding seams and eliminate the effect of the welding seams. Finally, the rotational angle and translational displacement of the butting pipes are optimized to minimize the PWM. A butting machine is designed to implement this method. The machine is benchmarked by a standard smooth pipe to minimize system errors. Three butting experiments have been performed with welded pipes of diameter 406 mm. The comparison shows that the computation results agree with the experimental results very well. The maximum PWMs in three experiments are less than 1.87 mm, which satisfies the butting requirements, that is, a PWM of less than 2.0 mm. Then, the uncertainties of the measurement results are discussed.     

The influence of bearing misalignment on the performance of helicopter gear boxes

The misalignments in the bearings of a gear box affect the life of the bearings and the deflection of the tooth contact points of the gears and consequently the performance of the gear box as a whole. Owing to the interaction of the deflections of all component parts of a gear box such as gears, shafts, bearings, spacers etc. it is necessary to consider these in combination rather than individually. A computer program was developed for analysing typical helicopter gear boxes with cantilevered housings in which the gear shafts are supported by taper roller bearings. In this program such factors as the misalignment of the bearings, the torque transmitted, the bearing preload, the rigidity of the casing and shaft complete with the bearing spacer, the spacing between the bearings, the location of the external load and the elements of elastic deformations in the bearings are considered. The particular assembly used in this paper is based on a Wessex tail rotor gear box, although the program developed is of a general nature.The influence of the misalignments between the bearing races that may be present before the application of an external load is investigated in this paper. The effect of crowning of the rollers or race tracks, to reduce the edge loading, on the deflection components of the gear tooth contact points is also included in the investigation.     

数控转塔冲床转盘振动分析和结构改进

数控转塔冲床转盘是冲床的核心部件,转盘在旋转和冲裁周期作用力的作用下,产生旋转振动和纵向振动。以转盘为研究对象,建立转盘旋转振动模型,分析转盘在旋转过程中偏心距、阻尼比等对振动的影响,利用ANSYS软件进行谐响应分析,找出转盘的薄弱环境,并针对转盘的振动提出两种改进方案,对改进结构进行分析和对比。     

基于往复压缩机轴心轨迹特征的故障诊断方法研究

往复压缩机的故障诊断一直以来都是研究工作的重点问题,对其关键运动部件的监测诊断更是研究的热点之一.当往复压缩机发生运动部件磨损、撞缸等故障时,活塞杆的运行状态会发生改变,进而引起活塞杆轴心轨迹的变化.因此,提出了一种基于活塞杆轴心轨迹的往复压缩机智能诊断方法.首先,文章利用改进的离散点轮廓包络方法提取活塞杆轴心轨迹特征...     

基于iSIGHT的陶瓷轴承优化设计

以陶瓷轴承内部结构参数优化为目标,建立了其优化设计的数学模型.在此基础上,利用iSIGHT优化设计软件实现了优化过程.结果表明所建立的优化模型对陶瓷轴承的设计有一定的指导作用.     

滚动轴承的正确使用与维护

滚动轴承是机械中最常用到的标准零件之一,常用来承受转轴上的负荷,也是易损元件之一.文章从安装、使用、维护等方面提出了如何正确使用和维护滚动轴承.     

基于DMC的机器人轨迹规划研究与实现

在分析6自由度机器人运动控制系统架构的基础上,提出基于DMC(digital motion controller)的开放式运动控制系统的6自由度机器人轨迹插补算法.主要研究在笛卡尔空间规划中直线的插补算法.同时介绍了插补算法在DMC上的具体实现方式.实验证明了控制器能可靠精确地实现机器人轨迹运动.     

基于电机转矩曲线下码垛机器人轨迹函数的优化研究

针对工程实际中由于机器人电机速度滞后于关节速度带来的振动问题,首先,对机器人关节进行了轨迹函数的规划和关节运动方程的分析,建立了电机转矩与轨迹函数之间的关系,应用Solidworks和Matlab软件,绘制出了机器人运动关节轨迹函数的速度—转矩曲线。其次,参考伺服电机速度—转矩特性曲线,分析了关节最大转矩与电机转矩之间的相互影响。最后,提出了一种基于电机转矩曲线下优化轨迹函数的简单方法,推导出了轨迹函数中与关节最大转矩相关的变量,进行了轨迹函数的优化,并利用机器人实验平台进行了轨迹函数优化后的测试。研究结果表明,通过该方法调整轨迹函数后,码垛速度从4.5 s/包提高到3.96 s/包,并且在相同速度下,调整后的关节没有产生冲击,验证了该方法在优化轨迹函数方面的合理性。     

Application of an envelope technique in the detection of ball bearing defects in a laboratory experiment

To judge the diagnostic capabilities of an envelope technique, based on enveloping the resonance frequency of a transducer,

1 Bearcon Signature™, Carl Schenck AG, Germany

artificially damaged ball bearings (SKF 6207) were run under oil lubrication at different radial loads and speeds in a laboratory experiment. Damage to the outer race, inner race and ball of different magnitudes was introduced by spark erosion and the response of the measurement system was analysed. The results showed that vibration spectrum components of outer race defects showed up in the envelope spectra of undamaged bearings, and that the detectability of defects was primarily limited by the speed of the bearing; on occasion the automatic scaling facility of the analyser was a limiting factor. Inner race and ball defects showed the well-known effects of load modulation in the defect contact zone, which can become dominant in the envelope spectra at high loads and speeds. This phenomenon could be confirmed by computer simulation. The detection of ball damage was hampered by the fact that overrolling of the defect in purely radially loaded bearings takes place incidentally. This drawback could be mitigated by applying a trigger technique to the envelope signal.     

新型偏心静压向心轴承的性能研究

提出一种组合油腔结构的新型偏心静压向心轴承，通过数值计算给出矩形腔、岛式腔和组合腔结构的轴承性能比较，表明新型组合腔结构轴承的承载能力和刚度系数均最高。     

A study on the prevention of cracks on the trepan area of motor bearing

Trepan prevents the wear of the inside part of a bearing when the initial shaft rotates. It continuously contacts with the eccentric part of the shaft in rotation and is loaded repeatedly. Therefore, even if an early crack of a trepan part is small, the crack may progress by the repeated load. If the crack progresses, very small chips come out. This is put in the rotor and prevents the rotation of the compressor. There can be leaks in a microgroove and extreme wear can occur due to lack of oil on the surface contact part. Therefore, this study was carried out to compare and investigate the trepan strength and deflection characteristics between trepan locations and dimension changes using the finite element method and search a motor bearing for a model with bigger stiffness of a trepan part and the same deflection.     

Influence of operational variables in a hydrodynamic bearing on the generation of acoustic emission

Detecting mechanical faults of rotating machines particularly in hydrodynamic bearings has been recognised as important for preventing sudden shut downs. This technical note presents an experimental investigation that is aimed at understanding the influence of operational variables (speed, load, etc) on generation of acoustic emission in a hydrodynamic bearing. It is concluded that the power losses of the bearing are directly correlated with acoustic emission levels.