Sampling error in ad conversion of the surface profile signal

A fundamental problem in a/d conversion of a measurment signal of surface profile id discussed from the viewpoint of a limit of sampling error in the time domain. A comparison is also made of the results of autocorrelation function, power spectrum and profile parameters such as R_max, R_a etc, obtained from the sampled surface profile in the time domain and in the longitudinal domain. It is suggested that the minimization of sampling error may be attained by the use of a digital displacement transducer attached to the usual surface measurement instrument.     

Towards a rational surface profile characterization system

Approaches to surface profile characterization are first discussed and the superiority of a suitable statistical approach based on a set of ‘primary’ parameters suggested. The selection of such a set is considered with reference to recent publications on parameter inter-relationships and approaches to spatial characterization of profiles containing both random and periodic components, and a primary parameter set then proposed. The estimation of other surface finish parameters from those in the primary set is considered and illustrated for profiles from a number of machining processes.     

实时调整表面粗糙度计算机辅助测量中的采样间隔

现有的表面粗糙度计算机辅助测量系统中,采样间隔一般需由人工凭经验设定,难以做到使之与被测表面相适应,本文以被测表面的统计特性为依据,提出一种采样间隔实时调整的算法,它能根据不同表面自身的物理特点,确定合适的采样间隔,简化了操作。     

三维表面粗糙度测量方法综述

表面粗糙度测量是评估零件表面特性的重要手段。经过二十多年的发展,三维表面粗糙度逐渐成为反映工件表面特性的重要指标。本文总结并比较了多种三维表面粗糙度的测量方法及特点,根据测量过程是否接触被测表面,将三维表面粗糙度测量方法分为接触式测量法与非接触式测量法。接触式测量法主要包括触针扫描法;非接触式测量法主要包括光学法(相移干涉显微法、相干扫描干涉法、数字全息法、共聚焦显微法、共聚焦色差显微法、点自动对焦法、变焦法、激光三角法和光切法)和电镜法(扫描电子显微法、扫描隧道显微法、扫描近场光学显微法和原子力显微法)。针对每种测量方法的发展现状,本文讨论了其适用范围及局限性,并指出未来的发展方向。     

抽样定理在周期性非连续信号的压电泵气穴现象中的应用方法

抽样时间间隔由抽样定理来决定.压电泵气穴现象所摄取的连续画像也应遵从该定理来抽取得到不连续的静止画像.可是,作为由振动形式驱动的压电泵,气穴现象只发生在吸入工程,了解其气穴现象统计特性时,如果按着抽样定理,在吐出工程的半周期,即使是不发生气穴现象也必须依次抽样.若利用这样的数据系统,数据的样本将过大,对其解析的时间性与经济性均不利.而且,在吐出工程的半周期,是与气穴无关系的信号.因此对于气穴现象数据系统,可以说是输入了错误情报信号.为此,开发了适用于压电泵气穴现象周期性非连续信号的抽样定理的方法;同时,利用这个方法,以有阀压电泵为例,调查了该泵的气穴现象特性之一的中心多发性,发现里利用新方法测得的中心多发几率高于原方法.     

The fibre optic sensor in the in-process measurement of surface roughness

In the paper, a NFF type fibre optic displacement sensor is proposed, which now has been adopted to measure surface roughness. The system with this sensor is designed to be suitable for in-process measurement, in which a Z8 single-chip microcomputer is matched. The whole system is supported by assembly programs and is automatic, intelligent and flexible. The output changes of the sensor are discussed respectively for several special cases, and some necessary measures are described for the real operational environments.     

Measurement and control of surface finish in manufacture

The topography of technical surfaces and the reasons for their assessment in the fields of process control and precision engineering are reviewed. Alternative approaches to surface characterization and the range of instrumentation currently available for measuring surface texture are discussed. Particular reference is made to digital profiling instruments based on microprocessors and to the extended range of parameters these instruments can provide. Throughout, discussion is linked to the contents of Australian Standard AS2536     

基于坐标测量机的自由曲面检测采样策略

为了实现自由曲面快速精确的检测和评定,研究了检测过程涉及的采样策略。提出采用随机Hamersley采样、简单随机采样和列系统采样3种方法设置自由曲面上的测量点。采用拟粒子群算法优化变换参数,实现被测曲面与设计曲面之间的定位,采用曲面细分法搜索设计模型上与被测点距离最近点以计算自由曲面轮廓度误差。为了对基于坐标测量机(CMM)在不同采样策略下的检测结果进行比较,采用非均匀有理B样条生成零件设计模型,选择相同的加工工艺在不同的加工中心加工多个零件得到粗糙度不同的自由曲面。最后,使用CMM在所设计的采样策略下实测零件,用提出的方法计算零件的轮廓度误差,并与CMM内置软件的计算结果进行比较。实验结果显示:选择随机Hammersley采样法和中等采样点数的采样策略检测效果最佳,不仅测量精度高,而且耗时少、成本低。应用提出的方法计算自由曲面轮廓度误差时,其精度比由CMM内置软件计算结果高10%~22%,表明提出的方法适用于自由曲面零件轮廓度误差的快速精确检测与评定。     

自由曲面自适应采样测量方法的研究现状

介绍了自适应采样测量方法的原理,分别对CAD模型己知与未知时自由曲面测量的国内外研究现状进行了综合评述,并展望了今后的研究方向。     

Finite difference spectral moment estimation for profiles the effect of sample spacing and quantization error

The mean square slope m₂ and curvature m₄ of surface profiles are characteristics that depend upon the frequency content of the roughness. Together with the mean square profile height m₀ they determine the microgeometrical behaviour of contacting rough surfaces. It is shown that in the absence of quantization error, the error due to finite sample spacing in estimating these spectral moments for a sinusoid is negligible when more than 8 points per cycle are used. In the presence of quantization error, large potential overestimates of m₂ and m₄ can occur. The error decreases initially with increased sample spacing and then increases. The severity of the distortion is shown to increase as the peak-to-peak range of the sine wave decreases relative to the full range of the a/d converter used in the digitization process.     

Non-contact profile measurement of a reflecting diaphragm surface

An interference pattern produced by a simple optical set-up irradiating a curved surface with coherent light is presented. The pattern is formed where reflected light beams intersect, even far from the curved surface. This reflected light pattern can be used for measuring curved diaphragm profiles which are expressed by mathematical functions with points of infection.     

利用声发射信号时频特征在线监测慢走丝线切割加工表面粗糙度

针对慢走丝线切割加工(WEDM-LS)时因温度高、切缝窄等因素造成的加工过程难以监测的问题,利用声发射检测技术对占空比可调脉冲的慢走丝线切割加工过程进行在线监测。首先利用小波包能谱算法将AE信号分解到8个独立的频段上:分别为W1~W8,且频率依次降低;然后提取各频段上的能量特征,研究其与加工工件表面粗糙度值之间的相关性。试验结果表明:W8频段的能量与表面粗糙度值之间具有较高的相关性,该频段的能量与脉冲放电能量均随着脉冲信号占空比的增大而增大,且加工表面粗糙度值也随之逐渐增大。最后通过回归分析得到了反应材料表面粗糙度值与W8频段能量占比关系的数学预测模型,该模型的预测结果与实际测得的表面粗糙度值误差仅为3.51%。说明该模型具有较高的预测精度,可用于加工表面粗糙度的在线监测。     

化学刻蚀的光学元件面形修复

采用化学加工方法对光学元器件进行面形加工,可以避免传统的抛光工艺带来的亚表面缺陷和表面污染。实验中利用Marangoni界面效应有效控制化学液的驻留时间和驻留面积,并通过数控系统实现编程控制加工,进行了面形修复实验,利用轮廓仪测量了加工前后的表面粗糙度。结果表明,采用拼接小去除量多次加工的方法,有效地降低了面形误差,面形值由1.32 λ(λ=632 nm)减少到0.66 λ,粗糙度基本维持不变。利用此实验装置使基片面形得到修复,避免了传统加工方式带来的亚表面缺陷等问题,有利于强激光系统的使用。     

基于自适应采样的曲面加工误差 在机测量方法

基于模具在机测量的自适应采样结果,提出一种新的获取自由曲面加工误差的方法。该方法首先基于自适应采样获取加工曲面上少量测点的坐标数据,利用NURBS曲面重构来拟合加工曲面;然后基于广义牛顿法计算重构的实际曲面和理论曲面的法向距离,获得自由曲面的加工误差,并对实验加工的模具模型曲面的轮廓度误差进行分析。实验结果表明,基于自适应采样的加工曲面重构方法能够在机测量且有效地获得自由曲面加工误差。     

表面微观轮廓的高分辨率光学测量方法

较全面地介绍了用于表面微观轮廓测量的几种高分辨率甚至可达亚纳米的光学测量方法及其最新进展.文中重点描述了以扫描共焦显微检测法、离焦误差检测法为代表的光触针法,以TOPO轮廓仪、Nomarski显微镜、外差干涉轮廓仪、双焦干涉轮廓仪和同轴干涉轮廓仪为代表的干涉测量法和以扫描近场光学显微镜及光子扫描隧道显微镜为代表的近场光学法三种适用于表面微观轮廓测量的光学测量方法,分别介绍了其工作原理、特性、发展现状及存在问题,通过对这些方法的对比和总结,阐述了表面微观轮廓纳米级光学测量的发展趋势.     

Accurate evaluation of free-form surface profile error based on quasi particle swarm optimization algorithm and surface subdivision

Although significant progress has been made in precision machining of free-form surfaces recently, inspection of such surfaces remains a difficult problem. In order to solve the problem that no specific standards for the verification of free-form surface profile are available, the profile parameters of free-form surface are proposed by referring to ISO standards regarding form tolerances and considering its complexity and non-rotational symmetry. Non-uniform rational basis spline(NURBS) for describing free-form surface is formulated. Crucial issues in surface inspection and profile error verification are localization between the design coordinate system(DCS) and measurement coordinate system(MCS) for searching the closest points on the design model corresponding to measured points. A quasi particle swarm optimization(QPSO) is proposed to search the transformation parameters to implement localization between DCS and MCS. Surface subdivide method which does the searching in a recursively reduced range of the parameters u and v of the NURBS design model is developed to find the closest points. In order to verify the effectiveness of the proposed methods, the design model is generated by NURBS and the measurement data of simulation example are generated by transforming the design model to arbitrary position and orientation, and the parts are machined based on the design model and are measured on CMM. The profile errors of simulation example and actual parts are calculated by the proposed method. The results verify that the evaluation precision of freeform surface profile error by the proposed method is higher 10%-22% than that by CMM software. The proposed method deals with the hard problem that it has a lower precision in profile error evaluation of free-form surface.     

A new stylus instrument with a wide dynamic range for use in surface metrology

An instrument has been developed which can measure not only radius of curvature but also form deviation and surface texture at the same time. A computer is used to mathematically separate the form from the texture. The technique can be applied to the measurement of cross track curvature of bearing raceways and to other precision components whose form is defined as a circular arc, or a straight line, in which case angle will be measured instead of radius. The measurement of other forms such as parabolic, elliptical, hyperbolic and aspheric are the subject of continuing development. The instrument provides a distinctive and useful advance in measurement by the stylus method, offering possible solutions to many obdurate problems in the field of surface metrology     

抽样点对基于Zernike多项式曲面拟合精度的影响

在光学测量中,常以Zernike多项式作为基底函数对测量得到的离散数据进行拟合,把实际波面或面形表示为Zernike多项式各项的线性组合,用拟合得到的曲面方程去反应实际波面或面形的属性。现研究了用不同精度的测量设备得到的抽样数据进行基于Zernike多项式的曲面拟合,研究了测量设备精度和抽样点数目对拟合精度的影响,得出通过增加抽样点可以对由较低精度设备测得的抽样数据进行较高精度拟合的结论。     

散射法表面粗糙度测量

介绍了标量和矢量两种散射理论,并用软X射线反射率对超光滑表面进行散射测量,同时应用这两种理论计算了超光滑表面粗度均方根值,从计算结果来看,两种理论所得结果与WYKO测量结果吻合较好。     

The significance of surface topography in engineering

All machining processes leave characteristic topographic features on the surfaces of components. This paper reviews a wide range of examples in which the surface topography of a component has been found to bear a significant effect on its function. Problems in manufacture which are related to surface roughness requirements are also disccused.