光学三维测量技术与应用

光学三维测量技术是一种可视化的测量技术,能完成复杂形体的点、面、形的三维测量,能实现非接触测量,在制造业和航空航天领域得到广泛应用。航空三维激光扫描与摄影测量技术利用激光测距原理和航空摄影测量原理,与基于全球定位系统(GPS)和惯性测量装置(IMU)的机载定位定向系统(POS)联接,可以快速获取大面积地球表面三维数据。本文对光学三维测量技术和航空三维激光扫描技术做一简单介绍,给出三维激光扫描技术在航空航天领域的几个应用。     

视觉测量技术及其在现代制造业中的应用

视觉测量技术 (或称数字近场摄影测量技术 )是一种立体视觉测量技术。讨论视觉测量系统的组成、关键技术、视觉测量技术在工业领域实时应用中亟待解决的问题 ,并给出组建视觉测量系统的具体策略。     

迎接制造技术变革的挑战──1982年芝加哥机床展览会印象记(二)

二、迅速发展中的集成测量技术 在测量技术已广泛用于制造过程的今天,为了正确表达它的涵义和避免长期以来在积极(过程中)测量与消极(过程后)测量概念上的混乱,开始有越来越多的人接受了“集成测量技术”(integra'ted gaging tech-nology)的概念。 集成测量基本上有三种形式(图7):(1)在加工工位上测量后再把工件取走;(2)在邻近的一个测量站上进行测量,并把结果反馈给机床进行尺寸控制;(3)就在机床边上进行测量,并把有关尺寸的信息反馈给机床控制装置。既可进行尺寸控制,又可监视与记录工件的加工质量。 由于集成测量方法能够及时提供工件尺…     

磁致伸缩效应原理及在工业测量中的应用

简述了材料的磁致伸缩效应及逆效应原理,详细介绍了磁致伸缩纵向效应(焦耳效应)、扭转效应(维德曼效应)的工程应用及常用的磁致伸缩材料,重点介绍了这两种效应在工业测量领域中(如液位测量、固体材料的弹性模量测量、液体密度、黏度测量等)的应用.     

基于SoC测控系统的齿轮测量中心软件架构设计

介绍了一种新的面向测量任务的齿轮测量中心软件架构.在该软件架构上开发新测量功能时,重点关注测量对象、测量项目的测量方法和误差计算,而齿轮测量中心的硬件控制等功能,则在SoC(System on Chip)专用测控系统中实现.     

双棒法测最大直径外锥体

大直径(大于150mm)而且锥体高度较小(小于50mm)的特殊外锥体(制件或塞规),如果在正弦尺上测量,一是不好装夹,二是由于太重,会使正弦尺所垫量块产生较大弹性变形,因而测量误差大,不能保证测量精度。如果用圆棒(或钢球)、千分尺,在0级平板上测量,由于锥体斜角α的公差较小,同样不能保证测量精度。我们采用了在测长机上用双棒法测量,不但能保证测量精度,而且能测量锥体的小头直径。     

钠流量测量分析

在核电厂正常运行过程中,流量测量(一回路、二回路)是确保核电站安全稳定运行所必须的一个重要参数.中国示范快堆CFR600以液态钠作为冷却剂,因此水堆核电站(一回路、二回路)常用的差压测量流量不能满足钠工艺的要求,因此必须有专门的钠流量测量仪表,确保冷却剂流量测量准确.本文简单介绍钠流量测量的基本原理,一二回路钠流量测量...     

H-15加工中心测量功能的扩展应用

一、H-15加工中心原有 的自动测量动能 H-15加工中心采用的是 MAZATOL CAMM-2控制系统,其自动测量功能有工件测量和刀具测量两部分。 1.刀具测量 利用床鞍上的刀具测量台(台式传感器),使装在主轴上的刀具的刀尖接触测量台活塞的端面并压缩活塞,测量和自动计算出该刀具的编程长度。刀具测量作用如下: (1)测量刀具长度可用自动或手动数据输入(MDI)方式进行,测量计算的长度值自动输入NC装置的刀具数据文件中。 (2)刀尖破损检查管理在自动加工循环中,程序M35代码指令控制自动测量一次被管理刀具的长度,并与刀具数据文件中的长度值进行比…     

固体电介质空间电荷与电流和电位的 同步联合测量系统

为了综合、全面地获取固体电介质的介电响应信息,准确表征固体电介质的介电性能,提出了一种基于“分区同时” 测量策略的空间电荷与电流以及空间电荷与开路电位的同步同时联合测量方案。 该联合测量方案基于现有的电流测量单 元、电位测量单元以及空间电荷测量单元,通过 T 型滤波器和阻交电感对测量单元进行合理组合,保证测量过程中各单元之 间无互相干扰,从而实现电流、开路电位和空间电荷的同步联合测量。 以碳化硅( SiC)掺杂的低密度聚乙烯( LDPE)试样的 电流、电位和空间电荷同步联合测量结果为基础,对测量系统进行了校验。 研究结果表明,电流测量基础噪声在 pA 数量级, 在 1 ~ 10 kV 电压测量效果良好,空间电荷测量精度并未受到影响。 联合测量方案在技术上简单易行,能够实现对固体电介 质的电流、电位和空间电荷同步同时联合测量,同时该联合测量系统具有进一步扩展的空间,为后续多种测量技术的同步联 合应用提供参考与基础。     

无心磨削时主动检测精度的提高

<正> 在无心磨床上使用自动主动测量仪可省去中间测量、消灭废品、提高精度的工艺储备。在生产中使用这种量仪组成的单点接触(一个测量头)测量系统不能充分提高测量精度,这是因为在单点测量系统中,检验的是测量触头与被测表面的接触点相对于测量装置基准面的     

Discharge prediction in flow measurement flumes with different downstream transition slopes

Experimental testing of 9 different rectangular compound cross-section flow measurement flumes with different downstream slopes was conducted to yield the coefficient of discharge and the approach velocity coefficient. The aim of the experimental research was the determination of stage–discharge relationship in compound cross-section flow measurement flumes with different downstream slopes. One empirical predictive model for each of the coefficient of discharge and the approach velocity coefficient for the 9 cross-sections have been derived using one dimensionless parameter for the coefficient of discharge and another one dimensionless parameter for the approach velocity coefficient as the single independent variable. This approach is preferred as it allows the estimation of discharge by only measuring the water depth at the head measurement section. All obtained predictive models statistics have indicated the high reliability of the derived models in estimating discharge in an open channel flume of a rectangular compound cross-section using the predicted coefficients.     

Approximate solution for discharge coefficient of the sonic nozzle with surface roughness

Sonic nozzle is widely used in the flow measurement and control. Nowadays, it has been applied to higher Reynolds number flow increasingly. The effect of surface roughness on discharge coefficient of the sonic nozzle should be discussed. An approximate analytic solution for discharge coefficient of the sonic nozzle with surface roughness was proposed in detail. The determination of this coefficient was based on universal logarithmic velocity-distribution law and the principle of equivalent velocity profile. Although there are some apparently approximations, this algebraic method accurately predicts the discharge coefficient of the sonic nozzle with surface roughness in Reynolds number range from 10⁴ to 10⁹, a relative equivalent roughness range of 10⁻⁶ to 10⁻². Some experiments of sonic nozzle conducted by others showed agreement with present algebraic method. Besides, the agreement between this method and the corresponding exact numerical calculation is also good. The present method provides an excellent tool to deeply investigate the roughness effect and promote further improvement of the standard.     

Experimental and theoretical modeling of a quarter-circular gate flow

Gates are important hydraulic structures and used for flow measurement, water delivery, and water level regulation in open channels and irrigation networks. In this study, the quarter-circular gate is introduced and investigated. The cross section of this gate consists of a quarter circular arc and the lip angle of the gate equals to zero. Discharge coefficient, variation of downstream flow depth, and velocity distribution at opening section of gate were experimentally measured. Using potential flow theory supported by dimensional analysis, equations for discharge coefficient and velocity distribution at gate opening section of quarter-circular gate were derived and then validated using experimental data. The mean percentage error (MPE) of obtained equation for discharge coefficient of quarter-circular gate was calculated as 2.24%, indicating the high precision of the proposed theory. Based on obtained results, downstream flow depth of quarter-circular gate is uniform. Also, velocity distribution at gate opening section is nearly uniform. Discharge coefficient of quarter-circular gate was averagely obtained 55% larger than that of sluice gate. It was also obtained larger than that of radial gate. Elimination of contraction section at downstream of gate opening, which is the main source for energy loss and therefore discharge capacity reduction, is the main reason for larger discharge coefficient of quarter-circular gate.     

Discharge formula for rectangular sharp-crested weirs

Sharp-crested rectangular weirs used for discharge measurement in channels and laboratories are experimentally investigated. Height and width of weir plate are the two parameters characterizing the head-discharge relationship. Laboratory experiments are conducted by measuring the discharge and the head over the weir for variable weir heights and widths. Applicability of various formulations for the discharge coefficient are investigated. Experiments indicate that discharge is independent of weir height, when the weir is operated within an appropriate discharge range. Average velocity over the weir plotted against the weir head displays universal characteristics such that it can be used in the expression of discharge over the weir, eliminating the need for a discharge coefficient. The head-discharge relationship for a rectangular weir has distinct features for the partially contracted weirs and for the fully contracted slit weirs.     

Application of artificial neural networks instead of the orifice plate discharge coefficient

Differential pressure flowmeters are very often used in many industries. Therefore, the improvement of this method of flow measurement is an important task of flow measurement and instrumentation. One of the important characteristics of differential pressure flowmeters is the discharge coefficient of the flow transducers. A large number of studies and publications were devoted to modeling this coefficient. Therefore, in the framework of this research, this coefficient is simulated using artificial neural networks. The neural representation of this characteristic is made in the form of a multilayer perceptron. In this paper, we replace the traditional equation for the discharge coefficient with an artificial neural network. The advantages and disadvantages of such application of neural networks as discharge coefficients are discussed. The analysis of the results of gas flow measurement, where the neural network is used instead of the traditional equation, is presented. The estimation of flow rate measurement errors with such an approach is made; the error of calculation of the discharge coefficient is estimated.     

Estimation of one-dimensional velocity distribution by measuring velocity at two points

The measurement of the velocity distribution and discharge in the open channels has always been an important issue in hydraulics. Unfortunately, flow measurement in the open channel is often expensive and sometimes produces poor results. There are many empirical methods to estimate the velocity distribution in a conduit, however, these methods are often applicable only to a narrow range of open channel conditions. In this paper, considering velocity as a random parameter, one-dimensional velocity distribution in open-channel has been derived based on the entropy concept and the principle of maximum entropy (POME). The entropy indexes (M, G, λ₂ and λ_*) are important parameters in entropy method to estimate velocity distribution and discharge in a conduit. A new approach is presented in this work for estimating the entropy parameters based on two-point velocity measurements. The approach for estimating the entropy parameters is tested for laboratory observations and velocity distribution and discharge are determined using Shannon, Renyi and Tsallis entropy methods. The present approach has shown good agreement with measured data. Also, the results showed that Tsallis entropy method is more accurate than other forms of entropy and the calculated values of NRMSE for estimated velocity profile and discharge are 7.86 and 8.8% respectively, showing a good simulation.     

Prediction of stage–discharge curves in open-channels using a fixed-point velocity measurement

The single-point measurement method for discharge estimation, which was first introduced by Maghrebi, can be implemented to obtain the discharge at different stages of a river during a flood event. As an advantage of this method, discharge can be estimated automatically with a fixed measurement location in the river section or on the water surface, which is associated with minimum energy and cost consumptions. For the proposed model, we determine the isovel contours in a normalized form for the cross section of the flow. To do so, we need to apply the field or experimental data, concerning the cross sectional geometry at different stages and its roughness variation along the wetted perimeter to the model. Then we collect the data of the single fixed-point of velocity measurement at the flow section using a velocity current meter. To validate the method, it is applied to a flume with different cases of roughened walls. The obtained results of stage–discharge curves using the single point of measurement in comparison to the observed experimental ones show that this method can quickly and accurately estimate the flood discharges. The maximum deviation between the observed and calculated discharges for most of observations is less than 5%.     

Weir velocity formulation for sharp-crested rectangular weirs

Discharge in open channels can be measured by sharp-crested rectangular weirs. Generally, measured head over the weir crest is substituted into an empirical formula derived from energy considerations to calculate the discharge. Assumptions made on the derivation are taken into account by defining a discharge coefficient that fits into the experimental data. In this study, a physical quantity, the average velocity over the weir section defined as ‘weir velocity’ is directly formulated as function of weir geometry and head over the weir. Weir velocity plotted against the weir head has a universal behavior for constant weir width to channel width ratio independent of the weir size. This unique behavior is described in terms of weir parameters to calculate the discharge without involving a discharge coefficient. Combining weir velocity data for variable weir widths provides a basis for direct formulation of discharge. The weir velocity exhibits simpler functional dependency on weir parameters in contrast to the discharge coefficient.     

Application of LSPIV to measure supercritical flow in steep channels with low relative submergence

Measuring flow discharge has always been one of the most important concerns of water experts. To measure discharge in streams using velocity-area method it is necessary to quantify average velocity of the flow. It is not feasible to measure velocity by contact approaches like current meters under certain conditions such as in flood periods or for very shallow flows. Flow surface image velocimetry methods as non-intrusive solutions have recently been widely utilized to measure discharge in open channels. One of these methods is a variety of PIV method named LSPIV which has been very popular due to the elimination of laser application. In this study, LSPIV was used to measure 2D velocity field over the surface of steep supercritical flow. The obtained surface velocity data were used to calculate Velocity Index (VI) which is multiplied by surface velocity to convert it to mean velocity and subsequently flow discharge. Also, a few relations were proposed to calculate the VI according to the slope and relative submergence. Since, Velocity Index has been so far mostly studied for subcritical conditions, results of this study may be applied for measuring supercritical flows. Eventually, the proposed method was verified to be used for discharge measurement and was proven quite precise in this regard.     

A method for correcting discharge of boat-mounted ADCP measurements

GPS data are usually used to measure boat velocity during boat-mounted acoustic Doppler current profiler (ADCP) measurements when bottom tracking is biased by moving bed. GPS cannot provide consistently accurate boat velocity reference because of multipath errors, satellite signal reception problems, and heading errors. In addition, the computation of water velocity from an ADCP mounted onto a moving boat is a vector-algebra problem, thus the discharge calculation is subject to the compass error when GPS is used for boat velocity reference. This paper proposes a method for correcting discharge based on the idea that the discharge calculation is independent of the boat path. The processing of two sets of boat-mounted ADCP measurements integrated with differential GPS and non-differential GPS was simulated to verify the method. The results show that the proposed method performs well in both differential and non-differential GPS conditions. The relative errors range from 0.1% to 1.5% for all measurements with the mean relative errors of 0.7%. Analytical assessment of the GPS errors shows the proposed method is insensitive to the positioning accuracy of GPS, but positioning error of non-differential GPS may induce relative discharge error of more than 1% when the river or stream is narrow. On the contrary, a relatively small compass or heading error can cause a significant error in water velocity and discharge when using GPS as the boat velocity reference. Therefore, integrating a differential GPS and maintaining a slow boat speed are best practices for discharge measurement, especially for narrow streams or short boat paths.