基于激光和视频的桥梁挠度测量新系统

短期和长期的挠度/位移变化是评估桥梁安全的一个重要指标.为了精确测量桥梁挠度,提出了一种基于激光和视频的桥梁二维挠度/位移测量新系统,该系统经过对相关视频数据进行采集、颜色识别、阈值判定、图像滤波、激光光斑中心拟合的方式达到测量目的,系统具有精度高、成本低、适合连续在线监测等优点.讨论了系统的一些结构性误差及其应对措施,分析了系统的时间开销和测量精度.实验结果验证了系统性能.目前,该系统已经在两座实际大桥的挠度/位移在线监测上得到了应用.     

面向特大型齿轮的激光跟踪多站位定位

提出了面向特大型齿轮的激光跟踪多站位定位测量方法以提高特大型齿轮激光跟踪在位测量系统的齿轮定位精度并精确确定测量仪器与被测齿轮位置与姿态的关系。根据激光跟踪仪多站位测量提供的冗余数据优化求解空间两点间共线方程,建立了特大型齿轮激光跟踪多站位测量模型。然后,提出了利用奇异值分解修正多站位测量模型解析矩阵条件数的方法。 实验结果表明,使用多站位测量模型求得的不同站位待测点间距离的标准差的均值为0.008 mm,明显小于直接在不同站位下测量的标准差均值0.024 mm,表明多站位测量模型具有良好精度控制效果。本文的研究提高了齿轮定位时所需测量点的三维测量精度,为特大型齿轮激光跟踪多站位测量系统建立齿轮坐标模型提供了可靠的数据来源。     

提高工业视觉测量系统精度的途径

介绍了工业视觉测量系统的测量原理,分析了影响系统测量精度的各种因素及提高测量精度的途径,并给出了空间点位置测量实例。     

CNC 大型内齿轮在机测量系统研究

针对大型齿轮的特点和在机测量的难点,研究开发了大型内齿轮在机测量的相关技术,建立了可测量大型内齿轮齿形、齿向及齿距误差的ＣＮＣ大型内齿轮在机测量系统。     

逆向工程中基于线结构光视觉传感器的光学坐标测量系统研究

研究了将线结构光学视传感器作为三坐标测量机的光学测头,开发非接触式光学测量系统及其在逆向工程中应用的有关技术问题,主要内容包括线结构光视觉传感器与ＣＭＭ集成测量模型的建立与标定技术,测量视角的规划技术,多视角测量数据的配准与拼接技术等。实验结果与本文开发的光学坐标测量系统是有效的。     

Calibration and analysis of eccentric error of the laser rotary-scanning measurement system

A laser rotary-scanning measurement system was developed for the reverse engineering of 360° objects. The system is constructed by an optical head and a rotary indexing. The optical head is composed of a laser diode strip-light projector and dual CCD cameras. Based on the principle of structured-light triangulation, a laser line is projected onto the object upon which the distorted line is captured by dual CCD cameras from left and right simultaneously. By processing a series of line fittings from the discrete angular positions of an object, the entire 3D profile can be reconstructed. Since the actual space coordinates of the object are computed according to the geometric relationship between the coordinate of optical head system and the coordinate of the rotary indexing systems, if these two coordinate systems are not in good alignment, errors in the computed coordinates will be introduced.This paper describes the influences of the alignment and eccentricity errors of the laser rotary-scanning measurement system on the computed geometrical profile. Calibration procedures are then proposed to adjust the alignment to avoid image distortions and thus enhance the system accuracy. Experimental results show that this easy-to-use calibration procedure can significantly improve the accuracy of the system.     

Multi-beam laser probe for measuring position and orientation of freeform surface

This study develops a novel optical non-contact probe that measures the position and orientation (normal vector) of a freeform surface. The probe system comprises a five-laser-beam projector and a charge-coupled device (CCD) camera. The probe is integrated on a three-axis platform. Five designed laser beams project onto a measuring surface, where five light spots are observed. The CCD captures the image of this surface and processes it. The 3D coordinates of the five light spots can be then computed. The normal direction at the central spot on the measuring surface is determined from two crossed curves through the coordinates of these five light spots. Two crossed curves are constructed using the Bezier method. The normal vector is the cross-product of two tangent vectors to the two crossed curves at central spot. A scheme for calibrating and making measurements using this five-laser-beam probe is proposed and verified experimentally. Experimental results demonstrate that this five-laser-beam probe system can measure the position and orientation of a freeform surface. The range of depths that can be measured using this probe is 2.4 mm and the range of angles is 40°. The positional measuring accuracy of the complete system is approximately 30 μm while the orientational accuracy is 1.8°.     

Measuring large 3D structures using four portable tracking laser interferometers

A new concept that allows measuring 1D–3D objects in the range of several centimeters to 5 m × 5 m × 5 m is presented. In general terms the concept can be seen as a task specific correction of geometrical errors of coordinate measuring machines (CMMs). The developed system comprises a commercial CMM, its measurement and its evaluation software and a set of at least four high accurate tracking laser interferometers. The CMM is simply used as a mover which allows to capture points on the surface of a measuring object. In parallel the tracking laser interferometers follow a retro-reflector located close to the stylus tip of the tactile probe of the CMM. Based on a multi-lateration algorithm 3D-positions are calculated from the measured interferometric distances. Finally, two sets of coordinates emerged, namely, one by the CMM and the second from the metrological frame of the tracking laser interferometers. The interferometrically measured positions are usually more precise than the positions measured by the CMM. This is due to the high accuracy of the interferometric system and also due to the fact that the measurement positions are taken in a manner which almost avoids Abbe errors. Because of that, the measurement positions of the CMM are substituted with the more accurate measurement points calculated from distance measurements of the tracking interferometers. The position coordinates thus obtained are used for the further computerized evaluations, which yield the geometric parameters of the object measured. First measurements under laboratory condition show very promising results. It has been demonstrated that the concept is suitable for the high precision calibration of large workpieces with small tolerances, for instance, for the calibration of large gears for the windmill industry.     

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.     

飞机强度试验舵面偏角测量方法的研究

为满足飞机结构强度试验中舵面偏角测量的要求,提出了一种基于位移测量的舵面偏角测量方法.该方法通过安装于舵面悬挂支臂上的两个拉线式位移传感器,测量相对于舵面悬挂接头上同一个测量点的位移,利用三角公式进行计算,得到舵面的偏转角度.对比验证试验表明,该方法的测量性能指标满足飞机结构强度试验要求,解决了传统利用倾角传感器无法测...     

An active MEMS probe for fine position and force measurements

This paper deals with the development and calibration of a single degree-of-freedom probe that is capable of regulating an input position and measuring force or applying a constant input force and measuring deflection. Such a probe is useful in making sensitive measurements on thin films, nano- and microstructures, and fluids. The probe is actuated by an electrostatic comb drive with an integrated capacitive sensor. COTS electronics and a capacitance-to-voltage IC are used to develop a closed-loop controller for the system, capable of regulating position over a range of about 40 μm to within a 5 nm resolution and controlling forces up to 300 μN with a resolution of 25 nN. The design and fabrication of the probe are discussed. The calibration of the device is performed using multiple methods to cross check each other. The use of the probe is demonstrated in the measurement of surface tension and probing the response of a soft polymer to small forces.     

Principle, theory and software for a new method of screw thread measurement by optical coordinate measuring systems

A new method is explained for optical thread measurement by means of two or three coordinate measuring instruments with a rigid microscope aligned perpendicular to the measuring plane. Measuring points of the flanks are taken in an extra-axial plane above or below of the axial plane respectively. Computer controlled measurement and evaluation of measuring points are carried out by a special evaluation program.     

Measurement of deflections in buried flexible pipes by close range digital photogrammetry

In this study, the monitoring of the load–deflection behavior of buried flexible pipes by digital close range photogrammetry was described. Experimental investigations were performed in a test box made of steel, with a Plexiglas front wall. An online vision system with three CCD cameras was developed to measure automatically the deflections of pipes during load tests. The system can also correct image distortions caused by refraction of light rays passing through different medias. The computational approach involves first determining camera calibration parameters, then calculating of object coordinates of targets placed on pipe wall section after each load step using the results of the calibration process. In loading tests, LVDTs were also used to measure the changes in vertical diameters of the pipes. The comparison of results obtained from both measurement systems indicated that photogrammetric system is reliable and accurate to monitor deflection behavior of pipes under loading conditions.     

Dimensional and angular measurements using least squares and neural networks

In this study a machine vision approach is developed for dimensional and angular measurements of manufactured components comprising straight line segments. We aim at the measurements of distance between two parallel lines and angle between two intersecting lines using both least mean square (LMS) and artificial neural network (ANN) techniques. LMS models estimate the line parameters based on the sum of squared perpendicular distances, rather than the vertical distances, between the observed data points and the line. A set of 23 gauge blocks of varying sizes is used to evaluate the performance of the LMS line estimators. Experimental results show that the measurement errors of the LMS models are affected by the line length and orientation of digital images. ANN techniques are, therefore, used to adjust the measurement errors resulting from the LMS models. Two back-propagation neural networks are developed, one for measuring the distance between two parallel lines, and the other for measuring the angle between two intersecting lines. Experimental results show that the ANNs are very effective for correcting the measurement errors regardless of line lengths and orientations of digital images. A 90% improvement in measurement accuracy for the ANN compared to the LMS was achieved. By using the ANNs, the measurement accuracy and flexibility in manufacturing applications can be significantly improved.     

Piezoelectric based resonant mass sensor using phase measurement

The paper presents design, development and testing of a resonant sensor to measure mass in the range of 0-12 g. The sensor is built using cantilever structure with piezoelectric excitation, sensing and microcontroller based closed loop electronics. The sensor measures the unknown mass by measuring the shift in resonance frequency of the cantilever beam. The shift in resonance frequency for a change in mass is detected by measuring the phase difference between the piezoelectric sensor output and actuator input using microcontroller. The proposed measurement system is simple and accuracy is found to be ±1.2% of full scale deflection.     

一种激光挠测量系统的实现

本文介绍了一种用于大型土木工程结构的投影式光学挠度测量系统。系统由激光器、光接收器件及其外围信号采集处理电路组成。光接收部分采用特殊的光电接收器件取代传统的CCD或PSD,使测量范围得到扩大;外围电路部分采用现场可编程逻辑阵列FPGA器件作为核心。通过这种设计,系统的量程和可扩展性得到改善,实现了通道复用。实验室证明,系统的测量范围可以达到210mm,分辨率达到0.005mm,可完成结构的静态及动态挠度测量。     

基于三维测量扫描线点云的表面重建

由结构光测量系统获得扫描线点云，通过剔除测量方向部分冗余数据点和插补扫描方向的稀疏数据，对物体表面原始三维数据密度进行适当调整。采用基于局部切平面簇的方法对调整后的数据点云进行表面重建，建立优化函数简化网格，并采用Loop细分法平滑网格，获得描述物体表面特征的重建表面。该方法解决了由扫描线点云重建物体表面的问题。     

Scaling of resistance standards in the Primary Electromagnetic Laboratory of Croatia

One of the main tasks of Primary Electromagnetic Laboratory (PEL) in Croatia is to ensure a system of international traceability for its standards. PEL has established resistance traceability for the group of resistance standards in the range of 1 mΩ to 100 MΩ. The preferred way of resistance standard calibration at PEL is self-developed method using two digital voltmeters, which are measuring voltage drops on serially connected standard resistors. The method is also used for calibration purposes of all types of resistors, decades, shunts and resistance measuring devices. Another method for calibrating high-ohm resistance standards is currently being developed to extend the resistance measuring capability of PEL to the TΩ range.     

An improved online dimensional measurement method of large hot cylindrical forging

The dimensional measurement of large forgings under high temperature plays an important role in product control. Cylindrical forgings belong to the important products in the forging workshop. In this paper, an improved online measurement method based on binocular vision for the dimensions of hot cylindrical forgings is proposed. Firstly, images of hot cylindrical forgings are captured by two CCD cameras, and the distorted light stripes projected onto hot cylindrical forgings can be resolved from the image by the deviated stripe model. Then, an accurate sub-pixel extraction algorithm of center points of the light stripes is developed for making the extraction of center points of the lights stripes more accurate. Moreover, for changing the field of view of cameras to measure different sections of forgings in the process of manufacturing, the fundamental matrix F is automatically calculated by matching the intersecting points of the projected light stripes in different images, without interrupting the forging process. Finally, experiments on measuring the diameters of hot cylindrical forgings in the workshop are conducted, and the experimental results indicate that the proposed measurement method is effective. Besides, an additional experiment in the laboratory verifies that the relative error of measuring diameters by the presented method is less than 0.7%.     

Distance measurement based on pixel variation of CCD images

This paper presents a distance measurement method based on pixel number variation of CCD images by referencing to two arbitrarily designated points in the image frames. By establishing a relationship between the displacement of the camera movement along the photographing direction and the difference in pixel count between reference points in the images, the distance from an object can be calculated via the proposed method. To integrate the measuring functions into digital cameras, a circuit design implementing the proposed measuring system in selecting reference points, measuring distance, and displaying measurement results on CCD panel of the digital camera is proposed in this paper. In comparison to pattern recognition or image analysis methods, the proposed measuring approach is simple and straightforward for practical implementation into digital cameras. To validate the performance of the proposed method, measurement results using the proposed method and ultrasonic rangefinders are also presented in this paper.