CAD-DIRECTED INSPECTION PLANNING FOR FREEFORM SURFACE USING CONTACT PROBES

A methodology for CAD-directed measurement of freeform surface using a coordinate measuring machine equipped with a touch-trigger probe is presented,mainly including adaptive sampling of measurement points and registration of freeform surface.The proposed sampling method follows four steps: Freeform surface is fitted by bi-cubic B-spline; Curvedness measure of the surface is computed; Given a number of sampling points,an iterative algorithm is constructed for selecting a set of measurement points by employing the curvedness information; The measurement points is regularized for tradeoff between maximizing the measurement accuracy and minimizing the sampling time and cost.The aforesaid algorithm is demonstrated in term of a marine propeller blade.An offset surface registration method is presented to improve alignment accuracy of freeform objects,and Monte Carlo simulation is conducted to verify the effectiveness of the method.     

基于超声测距的自由曲面数字化方法研究

对数学模型未知的自由曲面进行超声仿形测量时，必须事先估算各采样点的位置和法矢。针对此问题，提出了一种两次采样的数字化方法：首先采用双曲线外插方法对曲面进行特征线采样，生成初始曲面；然后采用B样条节点插入算法对初始曲面进行递归分割，生成基于给定采样精度的自适应采样路径。实例表明，该方法能较好地提高自由曲面超声测量的效率。     

激光跟踪扫描曲面测量的自适应算法研究

针对自由曲面壳体的测量问题,研究了非接触测量时激光束跟踪测量高精度自由曲面壳体的一种自适应测量算法。从测量速度和精度两方面考虑,提出采用圆弧切线外插算法控制激光束跟踪扫描,实现曲面的自适应跟踪测量。采用该算法在三坐标测量机上用激光束跟踪快速扫描测量电力安全帽实物样件,并对其进行实物原型的数字化处理,完成了电力安全帽反求工程测量任务。测量实验表明采用该算法跟踪和测量精度高,测量速度快。     

Location tracking scanning method based on multi-focus in confocal coordinate measurement system

Confocal microscopy is high precision and widely used method for topography measurement. The surface height information is obtained by peak extraction of the axial response signal (ARS) which axial tomography of the surface is required. Therefore, when scanning large-diameter surfaces with a confocal coordinate measuring system (CCMS), the relative horizontal scanning trajectory (RHST) between the confocal sensor and surface is repeated and time-consuming step motion, which greatly increases the measurement time. To improve the scanning measurement efficiency of CCMS, we propose a new location tracking scanning (LTS) method based on multi-focus. In the LTS method, the RHST is a continuous linear motion during the process of axial tomography, and the horizontal motional surface is located and tracked through a series of focuses to restore the ARS. A generatrix profile of a spherical surface is measured to verify the effectiveness of the proposed method, and the results show that the scanning measurement time can be reduced by more than 90% without loss of accuracy of the profile measurement.     

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。     

Adaptive sampling method for inspection planning on CMM for free-form surfaces

Coordinate measurement machines (CMMs) have been widely used in inspecting mechanical parts with higher accuracy. Both the distribution and the number of the sampled points on measurand have an important effect on the efficiency and quality of the measurement of CMMs. In this paper, an adaptive sampling method is proposed for inspection planning on CMM for free-form surface. The points are iteratively sampled from a form error model, which is constructed by superimposing appropriate form errors on the nominal data. Moreover, a modified algorithm is introduced to determine the deviation of two point sets for the improvement of the inspecting accuracy, and the inspection uncertainty is also analyzed. A comparison is performed between the proposed method and the two well-known sampling methods, which are the equi-parametric method and the patch mean Gaussian curvature-based method, both simulated and experiment results show the effectiveness and robustness of this method.     

Adaptive sampling point planning for free-form surface inspection under multi-geometric constraints

Free-form surfaces have been widely used in aerospace, automotive and other fields. Due to its complex geometry, free-form surface inspection is generally conducted by touch-trigger or measuring probe-based Coordinate Measurement Machines or On-machine Measurement. Sampling strategy plays a decisive role in improving both measurement accuracy and efficiency, which is determined by sample size and distribution of sample points. However, it is difficult to simultaneously take the surface curvature, sampling density and approximation error into account, considering the complexity of surface geometry. In this paper, triangle mesh simplification is innovatively adopted in sampling planning to achieve multi-geometric constraints. As triangle mesh has outstanding advantages in representing the surface features, strong stability and is easy to modify its structure, free-form surface is converted to a dense triangle mesh. Triangle mesh simplification is implemented by iteratively contracting triangle edges. An improved quadric error metric is established to decide contraction order and optimal target vertices under discrete curvature constraint. Sampling density is controlled by limiting the triangle edge length. Detailed adaptive sampling algorithm under multi-geometric constraints is then developed. Both simulation and experiment are conducted to validate feasibility and robustness of the proposed method. The results are compared with uniform sampling and existing adaptive sampling strategy to show that the proposed method can prominently reduce sampling error when sample size is small.     

基于双拟合优化的聚焦深度三维形貌测量方法

聚焦深度法广泛地应用于小尺寸零构件的三维形貌测量。 针对聚焦评价曲线多存在噪声导致三维形貌测量的精度下 降,且效率受图像序列数目和聚焦评价算法限制的难题,通过结合双拟合优化理论与聚焦单峰性评价指标提出了一种基于自适 应权重的聚焦极值搜寻方法,并进一步基于三次多项式二次插值算法和多级中值混合滤波优化深度信息。 实验结果表明,方法 对仿真图像数据的均方根误差(RMSE)较高斯拟合和多项式拟合分别降低了 19. 08% 、17. 32% , 对球栅阵列封装 (BGA) 图像 中受噪声干扰较大的区域仍具三维分辨能力,同时对钻削刀具进行了测量,提出的方法在 50% 的图像序列数目和图像分辨下 RMSE 仍降低了 77. 8% 、62. 6% ,有效减少了聚焦曲线噪声对测量结果影响的同时提升了三维测量的效率。     

波长轮换与相移扫描相结合的表面形貌测量系统

用光学显微干涉法进行表面形貌测量时其深度测量范围的扩大和形貌测量精度的提高是一对矛盾。为此,本文设计出了一种基于波长轮换与相移扫描相结合的三波长表面形貌测量系统,并提出了一种基于椭圆拟合与相位差大小尺度相结合的相位提取与识别算法。将这种算法运用于多波长干涉图像的数据处理,有效地提高了形貌的整体测量精度,并拓展了深度测量范围。实验结果表明:在深度测量范围扩大近15倍的条件下,采用粗糙度国家基准校准的方波多刻线样板得到的表面粗糙度数据与校准数据的相对误差仅为4.12%,表明该系统在一定的深度范围内能够实现表面形貌的高精度测量。另外,针对该系统设计的多波长相位识别算法对环境噪声要求不高,可以支持系统的高噪声或在线测量。     

基于脉冲星信号的自适应同步采样方法

基于传统GPS/北斗信号的广域同步测量技术易受到恶意网络攻击,可靠性难以得到保障。为解决这一问题,本文利用脉冲星信号周期脉冲精度高、免疫于现有网络攻击的特性,提出一种新型自适应同步采样方法:首先对射电望远镜接收到的脉冲星信号进行多相滤波、消色散和周期折叠处理,得到脉冲轮廓;然后采用最小二乘法监测本地晶体振荡器频率,动态调整定时控制间隔实现自适应同步采样。为验证算法的有效性,本文采用脉冲星J0437-4715的观测数据生成同步信号,实现电网信号的同步测量,利用递归离散傅里叶变换算法计算采样数据的相角和频率,得到相角和频率平均测量误差分别为-9.75×10~(-5)°和9.83×10~(-7) Hz,验证了所提自适应同步采样方法的有效性。     

截面测量数据的B样条曲面拟合

针对激光扫描仪测量得到的截面型数据,提出了对截面线重新采样的方法,分析了重采样数据拟合曲线的误差,及平方误差随重采样比例变化的规律,从而通过控制误差来确定重采样数目.构造插值于截面数据点的非均匀B样条,再对其进行相同数目的采样,得到了呈矩形分布的点阵,采用双向平均积累弦长参数化方法确定、方向节点矢量,用插值的方法进行曲面拟合.此种方法不仅避免了对轮廓线进行相容性的处理,而且减少了模型数据量,提高了曲面重构的效率.     

A practical sampling method for profile measurement of complex blades

Blade is one of the most important parts in turbine machinery. The complex geometry of blades not only makes them difficult to fabricate, but also leads them difficult to inspect. Typically, the surface of blades is measured by using coordinate measuring machine (CMM). Since the measurement time and cost increase proportionally as the increase of measurement points, it is essential to sample measurement points which can represent entire blade with sufficient confidence and accuracy. In order to achieve a certain allowable deviation with a suitable set of points, a practical sampling method for surface measurement of blades was studied. Firstly, the leading edge curve and trailing edge curve were supposed to represent the twisted and bend information of blades. A sampling method based on maximum chordal deviation for leading edge curve and trailing edge curve was researched. Further, a fusion approach for sampling points on both edge curves, which determine the cross-sections, was proposed. Secondly, the inspection points sampling method for sectional curves were investigated. Finally, two simulation and one experimental examples were used to demonstrate the sampling methodology. The results indicated that the approach of this study can ensure the measurement precision at high curvature potion by measuring a small number of points.     

测量强反射自由曲面的测头设计

分析了利用三角法测量强反射表面时存在的问题。基于多目视觉测量 ,根据偏振特性 ,开发了由三个摄像机组成的测头系统。在建立几何模型的基础上 ,分析了各项结构参数对系统纵向分辨率的影响 ,对结构参数进行了优化 ,为实现自由曲面的高精度在线检测提供了理论依据。本系统与三坐标测量机相结合 ,能够测量金属强反射表面 ,具有高精度、高效率的特点。     

超声波传输时间精密测量方法及应用研究

根据超声波回波信号是一个变幅周期性信号这一特点,提出一种用数字细分来精密测量超声波传输时间的方法,阐明了超声波换能器驱动电路原理及利用FPGA电路和高分辨率A/D电路通过高频采样来实现这一方法的原理,并采用该方法和电路设计了超声波流量计。指出超声波传输时间测量的分辨率取决于超声波信号的频率和A/D电路的分辨率,为保证测量精度,应尽可能采用较高的采样频率。超声波传输时间的测量综合了全部回波信号采样数据,有很好的可靠性和很强的抗干扰能力。     

基于散乱数据的罐车曲面重建与容积检定系统

针对目前铁路罐车容积测量技术在可操作性、准确性等方面存在的问题,提出一种简捷、准确的罐车容积检定方法。该方法通过罐车序列图像三维重构,获取罐车表面测量数据。进而借助提出的散乱数据序化方法,构造罐车的系列截面轮廓线,并以蒙皮操作为基础实现罐车曲面的精确重建。最后利用参数曲面的离散表达,完成罐车容积的快速检定。对比试验表明,所提检定方法的结果符合"JJ140-1998铁路罐车容积"中"铁路罐车容积扩展不确定度小于0.4%(k=2)"的要求。     

Development of surface reconstruction algorithms for optical interferometric measurement

Optical interferometry is a powerful tool for measuring and characterizing areal surface topography in precision manufacturing. A variety of instruments based on optical interferometry have been developed to meet the measurement needs in various applications, but the existing techniques are simply not enough to meet the ever-increasing requirements in terms of accuracy, speed, robustness, and dynamic range, especially in on-line or on-machine conditions. This paper provides an in-depth perspective of surface topography reconstruction for optical interferometric measurements. Principles, configurations, and applications of typical optical interferometers with different capabilities and limitations are presented. Theoretical background and recent advances of fringe analysis algorithms, including coherence peak sensing and phase-shifting algorithm, are summarized. The new developments in measurement accuracy and repeatability, noise resistance, self-calibration ability, and computational efficiency are discussed. This paper also presents the new challenges that optical interferometry techniques are facing in surface topography measurement. To address these challenges, advanced techniques in image stitching, on-machine measurement, intelligent sampling, parallel computing, and deep learning are explored to improve the functional performance of optical interferometry in future manufacturing metrology.     

基于数字微镜器件的并行彩色共聚焦测量系统

彩色共聚焦技术因其高分辨率、高测速的特点,在表面形貌测量领域备受关注,然而现有的彩色共聚焦技术多为单点测量,一定程度上限制了测量效率。本文在彩色共聚焦技术的基础上,以DMD作为光分束器件,结合自主研发的大口径色散管镜,利用面阵彩色相机作为光电接收器件,研究和建立了基于数字微镜器件的并行彩色共聚焦实验平台,实现了对被测物面上多个探测点的并行图像处理。最终,利用所搭建的并行彩色共聚焦测量系统,对50μm高的台阶和自制台阶进行了测量,并对硬币的表面形貌进行了三维恢复。实验结果表明,该测量系统的轴向测量范围为300μm,测量精度达到微米级;同时,能够较好地恢复硬币的表面形貌特征,具有较好的测量效率与可靠性。     

Efficient analysis-suitable T-spline fitting for freeform surface reconstruction and intelligent sampling

Optical scanning instruments require sampling and reconstruction with high accuracy and low computational cost. T-splines have recently been developed that allow significant reductions in the number of control parameters by overcoming some of the topological constraints of B-splines and NURBS. As a subset of T-splines, analysis-suitable T-splines (ASTS) show promise due to the linear independence and partition of unity of their basis functions. In this paper, a computationally efficient ASTS fitting algorithm for freeform surface reconstruction is proposed. This algorithm starts with adaptive construction of an initial analysis-suitable T-mesh according to the distribution of high-curvature feature points. A local refinement and local optimisation algorithm of the analysis-suitable T-mesh is then iteratively performed until a preset accuracy condition is satisfied. Our experimental results show that the proposed ASTS fitting can produce over 50% root-mean-square reconstruction error reduction compared to NURBS fitting, with the same number of control parameters. The computing efficiency of the proposed algorithm is equivalent to or higher than that for simple T-spline fitting. Fast derivative analysis of the ASTS has also been carried out, where two automatic intelligent sampling design methods have been developed, namely element area sampling and element curvature sampling. Up to 50% reconstruction error reduction is observed when compared to uniform and statistically optimised sampling designs. With the novel reconstruction and compatible intelligent sampling design techniques, freeform surface measurement accuracy and efficiency could be effectively improved using coordinate measuring machines.     

基于E-SPCM的直线电机动子位置高精度测量方法研究

针对直线电机动子位置测量,引入一种基于扩展采样相位相关法(E-SPCM)的亚像素位移图像检测方法,以提高测量精度和抗干扰性。首先建立了直线电机位置检测系统,通过高速相机实时采集条纹图像序列;其次对条纹图像进行边缘特征提取,利用相位相关得到相邻条纹图像的互功率谱,即动子位置的整像素位移;进而对整像素邻域的互功率谱进行上采样相位相关计算,实现高精度的亚像素位移测量,进一步由系统标定得到实际位移值。对比传统相位相关算法,所采用的方法能够提高测量精度且有很好的噪声抑制性能,最后搭建了实验检测平台,验证了算法的有效性。     

Isoplanar-based adaptive sampling for model-unknown sculptured surface coordinate metrology using non-contact probe

Optimizing sampling size and point distribution is a difficult issue for sculptured surface measurement. Highly curved areas should be sampled densely and vice versa. To achieve this goal, an adaptive sampling using point laser sensor has been further researched based on isoplanar method for model-unknown surface coordinate metrology. Sampling control points must be previously predicted using the measured data. Therefore, a reference needs to be initially established, and then dynamically updated during sampling process. Isoplanar line method has been employed to plan sampling movement. Curvature-based adaptive step adjustment method and hybrid extrapolation mode have been developed and further employed to calculate the two control increments in both feeding direction and side direction. A group of planar curves, which are utilized as an initial reference for scanning, are primarily sampled in slow tracking stage. As a result, a guide path can be estimated to direct fast scanning for the next path. The surface measurement algorithm was designed and programmed on an open CNC platform. Finally, with the help of linear interpolation technique and macro variables, a practical application has been implemented to verify the proposed fast sampling approach.