Evaluation of system models for an endoscopic fringe projection system

To be able to perform inline inspection of complex geometries, which exhibit for example undercuts or internal structures, a new endoscopic micro fringe projection system has been developed. It is designed to perform areal measurements for tool inspection inside the limited space of metal forming presses by employing flexible image fibers to couple the measurement system’s camera and projector to a compact sensor head. The projector features a laser light source and a digital micro-mirror device to generate high-contrast fringe patterns. To increase the depth of field of the sensor heads, custom gradient-index lenses have been designed as an approximation to the Scheimpflug principle. Challenges arise for both calibration and phase measuring algorithms from the optics, as well as from the reduction in resolution introduced by the fiber bundles. This paper presents an evaluation of two different system models for the endoscopic fringe projection system, which are based on the pinhole camera model and a black box model. An automated calibration process, which gathers the calibration data for two calibration algorithms that are robust to artifacts introduced by the optical path, is demonstrated. Based on a comparison of measurements, differences between the two modeling approaches are discussed. Finally, results of measurements of a demonstrational metal forming tool are shown as an application example.     

抗(耐)震压力表液压伺服脉动校验装置应用研究

执行SY/T 6817—2010《抗(耐)震压力表校准方法》对抗(耐)震压力表进行校验时,需要在量程的30%～40%之间的一个检验点上施加正弦波脉动压力,其幅度不大于该点压力值的10%,脉动频率为（60±5）次/min。为了获得这样的脉动压力源,采取气驱液泵预压产生检验点基准值,及利用液驱液增压缸产生10%增幅的高压值,通过伺服液压控制增压缸活塞的往复运动产生波动范围在基准值和高压值之间的正弦脉动。研制的校验装置脉动频率和幅度设定方便、环境参数影响小,通过工控机采集卡控制,显示界面明晰、控制精度高,适合于试验室、检定室校验抗(耐)震压力表使用等。     

嵌入式标定平台控制系统设计

通过对交流伺服控制系统进行研究,成功将UC/OS-II实时多任务操作系统移植到STM32微控制器上,设计了一种基于STM32的实时控制系统,使得标定平台能够满足海流传感器检测性能要求。在伺服电机控制方面采用开环和闭环控制相结合的方式,不仅提高了平台的定位精度,还减轻了处理器的运算压力,提高了软件的实时性;上位机采用基于Lab VIEW的界面设计,直观监测标定平台的运行状态,并后台存储重要的数据信息。通过实验验证该控制系统满足标定平台速度稳定、定位精度高和低速运行的要求。     

重型商用车转向节臂疲劳试验研究

转向节臂是重型商用车转向节的关键零部件,其疲劳性能直接影响整车的可靠性和安全性。对转向节臂疲劳试验输入载荷谱的确定和台架试验进行了研究。通过标定转向直拉杆和采集典型转向工况实车载荷谱确定了转向节臂疲劳试验的输入载荷。根据采集到的载荷谱和疲劳累积损伤等效原则制定了转向节臂疲劳试验输入载荷谱,并据此进行了转向节臂的疲劳性能验证试验。疲劳试验有效验证了转向节臂的疲劳性能,找出了可能出现失效的部位,为转向节臂的改进提供了依据。最后对改进过的转向节臂进行了疲劳性能的台架试验验证。     

粉末冶金真空炉专用新型热电偶与在线原位校准

从粉末冶金行业的精确生产与优质高效的战略出发,简述粉末冶金行业用钨铼热电偶的特点、分类与使用。详细论述粉末冶金真空炉专用超高真空(10~5 Pa)、超高压(15 MPa)密封式热电偶及炉温均匀性测试等新型传感器。详细探讨真空炉测温准确度的影响因素:真空度、发射率、热导率、热响应时间及热电偶的插入深度、热电偶保护管的选择等;简介进口真空炉专用热电偶国产化研究,国内外温度传感器性能对比及替代进口真空炉热电偶的成功业绩。目前,对测温系统的检定,多采用分立元件法,即对构成测温系统的元件及仪表分别进行检定。此种检定方法是离线的。本文简述离线式检定方法的诸多弊端以及美国宇航标准(AMS 2750E)中,有关系统准确度校准的特点及要求。详细论述在线原位校准的最新理念,最佳的系统准确度校准方案,并开发出与其配套、行之有效的带有校准孔的热电偶及便携式在线校准仪。为了提高测温系统的准确度,建议采用在线原位校准,方便易行,现已在国内推广应用。     

A novel approach based on artificial neural network for calibration of multi-hole pressure probes

Imperfections in the manufacturing process of flow measuring probes affect their measuring behavior. Nevertheless, in order to provide the highest possible accuracy, each individual multi-hole pressure probe has to be calibrated before using them in turbomachinery. This paper presents a novel method based on artificial neural networks (ANN) to predict the flow parameters of multi-hole pressure probes. A two-stage ANN approach using multilayer perceptron (MLP) is proposed in this study. The two-stage prediction approach involves two MLP networks, which represent the calibration data and the prediction error. For a given set of inputs, outputs from both networks are combined to estimate the measured value. The calibration data of a 5-hole probe at RWTH Aachen was used to develop and validate the proposed ANN models and two-stage prediction approach. The results showed that the ANN can predict the flow parameters with high accuracy. Using the two-stage approach, the prediction accuracy was further improved compared to polynomial functions, i.e. a commonly used method in probe calibration. Furthermore, the proposed approach offers high interpolation capabilities while preventing overfitting (i.e. failure to fit new data). Unlike polynomials, it is shown that the ANN based method can provide accurate predictions at intermediate points without large oscillations.     

A comparison of methods for measuring the induction time for bubble–particle attachment

Froth flotation is an exceedingly complex physicochemical process. The convenience of distilling much of the complexity of the particle–bubble interactions into a single parameter has led to the continuing popularity of the classical ‘induction time’ to quantify the threshold for particle–bubble attachment to occur. Despite this popularity and the simplicity of the concept, there is no single universal method of evaluating the induction period.In this paper, we begin with a critical review of the available techniques for estimating the induction period. These are: back-calculation from experimental (micro)flotation tests; pushing a particle toward a stationary bubble (or vice versa) using an atomic force microscope (AFM); pushing a bubble toward a stationary bed of particles in the ‘Induction Timer’; pushing a bubble toward a stationary solid surface using the ‘integrated thin film drainage apparatus’ (ITFDA); and dropping particles onto a submerged stationary bubble using the ‘Milli-Timer’ device. Each one of these methods has advantages and disadvantages, and the best choice depends on the application.In the experimental section, we present quantitative comparison of the induction periods estimated using two different techniques, namely the Induction Timer and the Milli-Timer. The same particles were tested in each device, under the same conditions. It was found that by tuning the operation of the particle pick-up device, similar estimates of induction period could be obtained to the estimates made by direct observation with the Milli-Timer. In the former device a bubble is driven toward a particle bed at a controlled rate, whereas in the latter a particle’s motion is governed by the hydrodynamics. The potential to match these presents an intriguing prospect for better understanding the bubble–particle interaction, and the possibility to ‘calibrate’ the simpler Induction Timer against direct observations.     

A compilation of patents related to mechanical metrology standards and high-precision measurement of mechanical quantities

The paper aims to provide a source of information regarding the measurement of physical quantities, specifically those related to mechanical metrology. Since there is a lack of literature reviews referencing patents as a way of gathering useful information, we performed a systematic search for patents that could solve practical problems in this field. The methodology used focused on one of the most comprehensive patent database, Orbit.com, covering about 70,000,000 documents. This text gives a quick look at the fundamentals of the measurement literature and then points out the state-of-the-art concerning patents in the area of study. Additionally, data analysis shows the trends in the last five decades of patents about the subject. In total, 5686 documents are found and we compiled 10 examples of relevant patents for the quantities Length, Temperature and Mass, making this article a source of information for both scientific and non-scientific metrology community.     

Four-year study of roughness patterns using weekly calibrations

In order to evaluate the stability and reproducibility of roughness measurements, calibrations of the same roughness standard were held over four years. Calibrations were performed in the Laboratório de Medição de Superfícies Ópticas (LMSO), on Mondays, between late January to early December every year. Here are presented and analyzed the calibration results and also the measurements of lab temperature and relative humid, at the time of calibration, in order to assess if there is any correlation between these influence factors in the obtained results. The LMSO lab is accredited by INMETRO (Brazilian NMI).