Custom TFT-LCD for avionics applications: Environmental tests and optical measurements

Avionics represents of the most important industrial sector where innovation is a key issue. In order to guarantee that any new device introduced onboard has an adequate quality and reliability level, testing activity is fundamental to help engineers and technicians to verify their designs and prevent any safety critical failures. National regulatory agencies and standards organizations, such as, the European Union Authority for aviation safety (European Aviation Safety Agency – EASA), the United States defense standard, often called military standard (MIL-STD) carried out by the U.S. Department of Defense or the Radio Technical Commission for Aeronautics (RTCA), have developed several test procedures that have to manage with the customer requirements. This paper is focused on the experimental results related to the validation process of a custom TFT-LCD for avionics applications. Environmental tests and, in particular, optical measurements will be described in detail in order to underline the key role that test plannig and measurements represent in aerospace applications.     

Thermal sensor for in situ flying height measurements of optical flying heads

The application of flying head technology in optical recording promises a considerable increase in recording density. It may be used for both far field and near field recording. For dynamic in situ flying height and flight attitude measurements, a prototype of a thermal test head has been developed. It takes advantage of the heat transfer in sub-micrometer air bearings as well as its dependence from the air gap width. Such a test head has a slider with a similar air bearing surface as the recording head, but with thermo-resistive sensors that are energized by Joule's heat and embedded at each of the four corners. The paper describes the head design and the fabrication technology and provides first experimental test results as well.     

Feature selection for surface defect classification of extruded aluminum profiles

This research investigates detection and classification of two types of the surface defects in extruded aluminium profiles; blisters and scratches. An experimental system is used to capture images and appropriate statistical features from a novel technique based on gradient-only co-occurrence matrices (GOCM) are proposed to detect and classify three distinct classes; non-defective, blisters and scratches. The developed methodology makes use of the Sobel edge detector to obtain the gradient magnitude of the image (GOCM). A comparison is made between the statistical features extracted from the original image (GLCM) and those extracted from the gradient magnitude (GOCM). This paper describes in detail every step of the image processing with example pictures illustrating the methodology. The features extracted from the image processing are classified by a two-layer feed-forward artificial neural network. The artificial neural network training is tested using different combinations of statistical features with different topologies. Features are compared individually and grouped. Results are discussed, achieving up to 98.6 % total testing accuracy.     

Study on one-step simulation for the bending process of extruded profiles

Traditional one-step approaches are either based on the membrane element in which bending effects cannot be considered or based on the simplified shell element in which the initial blank is flat and the curvatures are kept unchanged in the one-step iterative computation. They are not suitable for the bending process of extruded profiles. In order to inspect the formability and possible forming defects in profile bending for preliminary designs quickly and to provide an efficient finite element computation for process analysis, a new one-step approach is presented. In this approach, instead of the traditional simplified shell element, the rotation-free basic shell triangular element is introduced to consider bending effects and make the new one-step approach suited to the simulation of profile bending. On the basis of the presented one-step approach, an in-house program named profile bending simulation-one step (PBS-ONESTEP) has been developed to simulate stretch bending of aluminum extrusions and three-point bending of stainless steel extrusions. The algorithm for initial guess solution of extruded profiles is described. Sliding constraint and the penalty method are adopted to treat contacts for the two numerical examples, respectively. The numerical results of PBS-ONESTEP simulation are compared with those of ABAQUS/EXPLICIT incremental analyses and experiments.     

Digital processing of images of extruded rubber profiles for process control MRI

Magnetic resonance imaging (MRI) is a powerful technique in materials science, in particular for the analysis of polymer and rubber materials. So far the use of this technique for quality control has not been fully explored mainly because of the prohibitive costs and maintenance associated with conventional MRI tomography systems. This constraint has been removed recently since robust and mobile desktop tomographs with permanent magnets have become available at reduced cost. In this work we apply an image processing chain algorithm to MR images of rubber profiles recorded with a desktop MRI scanner. Although the nominal spatial resolution of MR images is inherently lower than that of optical methods, we demonstrate that the digital resolution achieved after the image processing steps allows one to determine the spatial positions of the inner and outer contours with 50 μm precision. Using this information it is then possible to measure structural dimensions of the rubber profiles, such as wall thickness or internal voids, with precisions that are of the same order of magnitude as those observed with CT or camera imaging.     

Application of optical velocity measurements including a novel calibration technique for micron-resolution to investigate the gas flow in a model experiment for crystal growth

An important step in the fabrication of many modern semiconductor materials and devices is the crystal growth process. These processes take place in high-temperature furnaces using inert gas and other atmospheres. The flow in the gas phase influences the transport of crystal components, dopants and impurities and hence has a significant impact on the grown crystals. In this work, we study the flow in a simplified model of a crystal growth furnace. This model is made of PMMA filled with a Diesel mixture as a model fluid to match the refractive index of PMMA and to allow for measurements in the complex geometry. The comparability to the flow in a real furnace is ensured by matching the Reynolds number. Two optical measurement methods, Particle Image Velocimetry (PIV) and the Laser Doppler Velocity Profile Sensor (LDV-PS) are used to investigate the global flow field as well as the small-scale flow structures. A calibration model is developed for the LDV-PS to reduce systematic measurement errors caused by the refractive index of the model fluid from up to 1% to less than 0,1%. The results obtained in this study improve the understanding of the gas flow behavior inside a crystal growth furnace and provide reference data for simulation. The first analysis shows a highly unsteady flow with unexpected flow direction along the crystal and melt surfaces. The near-surface flow patterns are of particular relevance in crystal growth because of their large influence on the local heat and mass transport during the crystallization process.     

Compact high-aperture interferometer with a diffractive reference wave for high-precision referenceless aberration measurements of optical elements and systems

We present the optical layout and actual design of a compact high-aperture referenceless point diffraction interferometer with a diffraction reference wave. The basic concept of this interferometer is based on a single-mode optical fibre with a subwave output aperture, which is used as a source of spherical reference waves. The interferometer is designed for high-precision measurements of the surface shape and aberrations of optical elements. It makes use of a diffraction reference wave and is developed for mass industrial applications. The proposed design does not require the involvement of special external conditions, and reduces the need for calibrated reference surfaces. We evaluate the performance of our interferometer for highprecision measurements and demonstrate its use by presenting results obtained from measuring the shapes of spherical references from various manufacturers and the aberration of a five lens objective.     

River velocity measurements using optical flow algorithm and unoccupied aerial vehicles: A case study

Accurate and reliable measurements of river flow are critical for a multitude of hydrologic engineering applications. However, flow rate measurements using in-situ sensors are uncertain in many applications and physical measurements of velocity may not be practical due to inaccessible sites or flood conditions. Recent advances in remote sensing using unoccupied aerial vehicles have overcome these limitations through non-contact measurements of river velocities; however, existing approaches have several shortcomings, including the need for artificial tracers in the absence of debris and prior knowledge of tracer size, shape, and flow direction. This case study seeks to overcome these shortcomings through the development of a system that utilizes drones, video imaging, and state-of-the-art optical flow algorithms to measure velocity in rivers. This system was applied along Menomonee River in Wauwatosa, WI. To remotely sense river flow, a DJI Matrice 210 RTK drone equipped with a Zenmuse X5S camera was used to capture video. The video data from the drone was analyzed using optical flow algorithms to generate velocity estimations. River velocity was measured directly at point locations using a hand-held velocimeter. Results indicate that the optical flow algorithms estimate the magnitude of surface velocity to within 13–27% of hand-held measurements without the use of artificial seeding. These outcomes suggest that this system could be used as a possible method to measure velocities in rivers.     

Tunable optical tweezers for wavelength-dependent measurements

Optical trapping forces depend on the difference between the trap wavelength and the extinction resonances of trapped particles. This leads to a wavelength-dependent trapping force, which should allow for the optimization of optical tweezers systems, simply by choosing the best trapping wavelength for a given application. Here we present an optical tweezer system with wavelength tunability, for the study of resonance effects. With this system, the optical trap stiffness is measured for single trapped particles that exhibit either single or multiple extinction resonances. We include discussions of wavelength-dependent effects, such as changes in temperature, and how to measure them.     

高精度光学表面磁流变修形技术研究

作为一种确定性子孔径的光学加工方法,磁流变抛光具有高精度、高效率、高表面质量以及无亚表面损伤的特点,有能力对各种形状的光学零件进行加工。本文系统的介绍了磁流变抛光高精度光学表面的关键技术,并采用自研的KDMRF－1000磁流变抛光机床和KDMRW-1水基磁流变抛光液对直径100mm的K4材料平面反射镜和直径200mm的K9材料球面反射镜进行加工实验。样件一面形收敛到PV值55.3nm,面形RMS值5.5nm;样件二面形收敛到PV值40.5nm,面形RMS值5nm。样件的表面粗糙度均有显著改善。     

Dedicated optical instruments for ultrasonic welder inspection and control

Two different optical instruments for real-time vibration measurements, inspection and control of ultrasonic welders were designed, realized and characterized: a self-mixing laser interferometer and an optical triangulator, both studied for achieving high bandwidth and very good resolution within a short dynamic range. The implemented instruments can solve the problem of measurement and control of ultrasonic welders that until now has no low-cost solutions available on the market. The performance of the two developed instruments was compared in order to assess which is the most appropriate for this specific application. Finally, results of the real-time characterization of an ultrasonic welder are given and discussed.     

Design of an optical probe for testing surface roughness and micro-displacement

This paper presents a practical monitoring tool for measurements of surface roughness and micro-displacement. An optical probe of the methods based on light scattering for measuring surface roughness and optical triangulation for measuring micro-displacement is described. The proposed technique allows evaluation of surface roughness and micro-displacement of specimen by using just one device. The theoretical models of surface roughness and micro-displacement measurements have been established for the probe. The measuring principles applied in the design are described in detail and the validity of the design is demonstrated by experimental evaluations. The experimental results show that, for specimens with surface roughnesses R_a in the range from 0.005μm to 0.1 μm, micro-displacement measurements in the linear range of ± 300μm can be obtained.     

Near-field scanning optical microscopy studies of L-alpha-dipalmitoylphosphatidylcholine monolayers at the air-liquid interface

The phase structure in L-alpha-dipalmitoylphosphatidylcholine-20 mol% fluorescent 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate Langmuir monolayers dispersed on a 2 M sucrose solution subphase is studied with near-field scanning optical microscopy (NSOM). Cantilevered NSOM probes operating in a tapping-mode feedback or an optical interferometric feedback mode are capable of tracking the air-sucrose solution interface. At the micrometre scale, the NSOM fluorescence images reveal lipid domain features similar to those observed previously in supported Langmuir-Blodgett (LB) monolayers. At the submicrometre scale, the small nanometric lipid islands seen in LB films are not observed at the air-sucrose interface. This supports a mechanism in which domain formation in LB films can be induced by means of the transfer process onto the solid support. Progress towards extending these studies to films at the air-water interface using the optical interferometric feedback method is also discussed.     

Analysis of optical linear encoders’ errors under vibration at different mounting conditions

The optical linear encoders are the preferred choice sensors for positioning machine tools’ moveable parts. Machine tools’ errors have been traditionally focused on the analysis and performance of the machine tool structure until recent works have treated the encoder itself as a source of error. Encoder error quantification has been done for several mounting conditions in static situations, but there is a lack of information regarding the performance of the encoder under dynamic solicitations. The aim of this work is to analyze the loss of accuracy of the sensor because of vibration for different mounting conditions. A finite element model of encoder has been developed and experimental results have been analyzed using this model.     

Video camera calibration for optical densitometry

An efficient technique for calibrating video cameras to record optical density (OD) from microscopic images is described. The method corrects for variation over the field of the brightfield and darkfield intensities, does not assume a linear response of the camera to the incident intensity and requires a single calibration filter.     

智能光纤液位检测系统

本文介绍了一种光纤液位检测系统。给出了系统检测原理、数据采集及信号处理，并说明了本系统具有防爆等特点。     

X-ray reflectometer for optical efficiency and scatter measurements

An instrument has been developed to determine the reflection efficiency and scatter characteristics of optical samples at x-ray wavelengths from 1.5 to 113 A. The reflectometer operates in an oil-free vacuum chamber and measures the reflection efficiency and scatter characteristics as a function of the angle of incidence. The reflection efficiency is given for lambda=8.34 A incident on a fused silica sample finished to a flatness of lambda/10. The experimental reflection efficiency is compared to the theoretical data. The scatter curves are given for the direct x-ray beam and for the beam reflected from the fused silica sample at theta=50 arc minutes. The full-width-at-half-maximum (FWHM) resolution of the instrument is approximately 13 arc seconds as determined by a least-squares smoothing of the experimental data.     

Optical probe for local void fraction and interface velocity measurements

In view of the importance of obtaining unsteady local void fraction and interface velocities in liquid-vapor two-phase flows, an optical probe with a controlled tip geometry was developed and is described. In order to minimize the disturbances caused to the flow field by the presence of the probe, its dimensions have been miniaturized. The electronic and hydrodynamic responses of the probe were investigated experimentally. The probe was found to be sensitive to both the interface velocities and the phase present at the probe tip. A possible explanation for the behavior of the probe is presented. Within the velocity range checked and with proper calibration, the optical probe described can be used to determine both local void fractions and interface velocities.     

Lensed optical fiber sensors for on-line measurement of flow

This paper describes a system using lensed optical fiber sensors that are arranged in the form of two orthogonal projections. The sensors are placed around a process vessel for upstream and downstream measurements. The purpose of the system is for on-line monitoring of particles and droplets being conveyed by a fluid. The lenses were constructed using a custom heating fixture. The fixture enables the lenses to be constructed with similar radii resulting in identical characteristics with minimum differences in transmitted intensity and emission angle. By collimating radiation from two halogen bulbs, radiation can be obtained by the sensors with radiation intensity related to the nature of the media. Each sensor interrogates a finite section of the measurement section. Each sensor provides a view. Parallel sensors provide a projection. Signal processing is carried out on the measured data in the time and frequency domains to investigate the latent information present in the flow signals.     

光开关技术及其控制系统

光开关是全光网络中的关键器件.介绍光开关在光传输交换中的功能,分析光开关的性能要求与指标参数.基于不同工作原理,介绍了典型光开关及其技术特点与性能.最后分析光开关控制系统,将其分为控制单元、驱动单元、执行单元和反馈单元四部分.