Laser-based Measurement System Research Articles

Panoramic three-dimensional optical digitization system assisted by a bi-mirror.

The digitization of objects' full surfaces finds widespread applications in fields such as virtual reality, art and design, and medical and biological sciences. For the realization of three-dimensional full-surface digitization of objects within complex sceneries, we propose a straightforward, efficient, and robust panoramic three-dimensional optical digitization system. This system contains a laser-based optical three-dimensional measurement system and a bi-mirror. By integrating mirrors into the system, we enable the illumination of the object from all angles using the projected laser beam in a single scanning process. Moreover, the main camera employed in the system can acquire three-dimensional information of the object from several different viewpoints. The rotational scanning method enhances the efficiency and applicability of the three-dimensional scanning process, enabling the acquisition of surface information of large-scale objects. After obtaining the three-dimensional data of the sample from different viewpoints using laser triangulation, mirror reflection transformation was employed to obtain the full-surface three-dimensional data of the object in the global coordinate system. The proposed method has been subjected to precision and validity experiments using samples with different surface characteristics and sizes, resulting in the demonstration of its capability for achieving correct three-dimensional digitization of the entire surface in diverse complex sceneries.

Laser Sensing System for Contactless Detection of Subsurface Defects in Concrete Tunnel Lining

Regular inspections of underground infrastructure are mandatory to maintain structural integrity and traffic safety. Standard procedures rely on visual inspection, complemented by testing for internal defects of the tunnel lining with the hammering method. This testing method uses manual excitation with a hammer and interpretation of the perceived sound by an engineer or technician. Result quality is based on the experience of the executing personal and thus highly subjective. The presented project aims at the automation of this procedure to enable a fast and objective inspection covering the whole tunnel lining. To achieve this, a new laser-based measurement system for detecting near surface defects in large concrete structures is developed. Surface vibrations are induced with plasma ignition and measured with a Doppler Vibrometer. The system has motorized mirror adjustment and can thus obtain fast-paced measurements on a grid. We present the experimental setup, the measurements performed on a concrete test block with artificial defects and the algorithms for automated defect detection. From the measured eigenfrequencies, we derive the size and location of defects. Computer vision techniques are adapted to make the system resilient against variable environmental conditions, like noise and temperature, or changes in construction material and age. These sophisticated signal processing methods are applied to extract relevant information from the measurements and are combined with topological data to provide service personnel with detailed maps for maintenance work.

The research of laser-based rapid measurement system for scintillator neutron detectors arrays

Scintillator Neutron Detectors Arrays (SNDA) were successfully installed at General Purpose Powder Diffractometer (GPPD) at the China Spallation Neutron Source (CSNS). The inhomogeneity of the detection efficiency in each detector module, which caused by the gain nonuniformity of the multi-anode photo-multiplier tubes (MA-PMTs) and the inconsistency of the wave-length shifting fibers in collecting scintillation photons, need to be mitigated before the installation. An automated rapid measurement system based on the blue laser and the two-dimensional mobile platform was developed to calibrate the light response of each channel in detector modules. According to the test results of this system, the electronics threshold of each channel of the SNDA is adjusted. Before the installation of the all 40 SNDA modules in GPPD, the electronics thresholds of each channel are adjusted according to the measurement results of this rapid measurement system. Compared with the unadjusted detector module, the adjusted one obtained a better uniformity of the neutron detection efficiency. The inhomogeneity of the detection efficiency is improved from 27.4% to 10.9%. The test result of the diffraction peak of the standard sample Si showed that the adjusted SNDA works well in GPPD.

Laser-based precise measurement of tailor welded blanks: a case study

Precise measurement of tailor-welded blanks is crucial for quality control of laser welding. The difficulty in measuring the seam profile of similar gage tailor–welded blanks lies in lacking of solutions to locate their feature points such as those representing the laser stripe. A laser sensor–based method is proposed to measure tailor-welded blanks based on its laser stripe and texture features, from which the proposed algorithm is employed to extract the feature points for seam profile assessment. The algorithm is evaluated on a laser-based weld seam measurement system, the experiment results show that the proposed method measures the tailor-welded blanks with high accuracy and is suitable for online inspection.

A Review of Diameter Measurement and a Proposal for the Improvement Thereof

In order to establish traceability of area of pressure measurement, piston–cylinder assemblies are characterized dimensionally. Piston, cylinder and master ring gauges demand diameter measurement uncertainty of about 30 nm. As focused efforts to achieve the requisite uncertainty, most of the trendy diameter measuring machines, used and available across the globe, are studied for their designs and performance. Conceptually, the uncompensated systematic error contributes significantly to the uncertainty of the measurements. In order to understand the magnitudes of the various errors, some of the key comparison reports are also studied. Based on the analysis of the review, laser-based displacement interferometer measurement systems are proposed. Theoretically, the proposed models reduce the Abbe’s error.

Development of a laser-based line scan measurement system for the surface characterization of reinforcing steel

Abstract The fatigue behavior of reinforcing bars is mainly influenced by their surface properties. Massive ribs and sharp notches provoke failure in fatigue. For the current research, it was necessary to develop a measurement system in order to allow for the highly precise measurement of the surface of fair sized fatigue specimens. The paper presents the boundary conditions at the beginning of the research project and gives a short overview of the measuring techniques currently used. It presents the development of a laser-based line scan (LLS) measuring system which applies the principle of laser-triangulation. The high accuracy and precision of the system of measurement was quantified in several investigations.

Limiting Uncertainty Relations in Laser-Based Measurements of Position and Velocity Due to Quantum Shot Noise.

With the ongoing progress of optoelectronic components, laser-based measurement systems allow measurements of position as well as displacement, strain and velocity with unbeatable speed and low measurement uncertainty. The performance limit is often studied for a single measurement setup, but a fundamental comparison of different measurement principles with respect to the ultimate limit due to quantum shot noise is rare. For this purpose, the Cramér-Rao bound is described as a universal information theoretic tool to calculate the minimal achievable measurement uncertainty for different measurement techniques, and a review of the respective lower bounds for laser-based measurements of position, displacement, strain and velocity at particles and surfaces is presented. As a result, the calculated Cramér-Rao bounds of different measurement principles have similar forms for each measurand including an indirect proportionality with respect to the number of photons and, in case of the position measurement for instance, the wave number squared. Furthermore, an uncertainty principle between the position uncertainty and the wave vector uncertainty was identified, i.e., the measurement uncertainty is minimized by maximizing the wave vector uncertainty. Additionally, physically complementary measurement approaches such as interferometry and time-of-flight positions measurements as well as time-of-flight and Doppler particle velocity measurements are shown to attain the same fundamental limit. Since most of the laser-based measurements perform similar with respect to the quantum shot noise, the realized measurement systems behave differently only due to the available optoelectronic components for the concrete measurement task.

Laser-based measurement for micro-unbalance of cylindrical rollers of the high-speed precision rolling bearings

It is a stringent requirement for China to develop the technology on the measurement for the unavoidable micro residual unbalance of tiny cylindrical rollers of the high-speed precision bearings, which are widely equipped on high-end advanced equipment. During the measurement process, the vibration response excited by micro unbalance, which is easy to be messed up with background noise, is hard to be detected and a soft support mounting bracket is proposed to enhance the amplitude of vibration response, while maintaining the steady rotation of test roller. Accordingly, a dynamic model of both test roller and mounting bracket is constructed to analyze and simulate the vibration response. Furthermore, a μm level high precision laser-based non-contact measurement system consisting of a roller rotation drive system and a vibration signal acquisition system is developed to measure the synchronized vibration of the unbalance. Finally, by comparing experiment results of a standard roller with a special prepared unbalanced roller and comparing experiment results with simulated results, the validity of the proposed measurement method is verified.

Novel method for rail wear inspection based on the sparse iterative closest point method

As trains become progressively faster, it is becoming imperative to automatically and precisely inspect the rail profile of high-speed railways to ensure their safety and reliability. To realize this, a new method based on the sparse iterative closest point method is proposed in this study. Moreover, the noncontact method is mainly used for convenience and practicality. First, a line laser-based measurement system is constructed, and the position of the line laser is calculated to ensure that both the top and sides of the rail are in range of the line laser. Then, the measured data of the rail profile are separated into a baseline part and worn part. The baseline is involved in registering the measured data and reference profile by the sparse iterative closest point method. The worn part is then transformed by the same matrix of the baseline part. Finally, the Hausdorff distance is introduced to measure the distance between the wear model and reference model. The experimental results demonstrate the effectiveness and efficiency of the proposed method.

Spiral-shaped SU-8 cantilevers for monitoring mechanical response of cardiomyocytes treated with cardiac drugs

In this paper, a spiral-shaped SU-8 cantilever with biocompatibility was proposed to monitor the changes of cardiac contraction in response to injection of drug in real time. The cantilever comprises a thick quadrate body and a filmy spiral cantilever with micro-grooves and gold patterns on the top of its surface. The longitudinally patterned micro-grooves facilitate the aligned growth of cardiomyocytes in order to increase the contraction force. In addition, the spiral shape increases the cantilever’s effective length and decreases its spring constant, which means its bending displacement can be increased for the same force as compared to that observed in a conventional rectangular cantilever. The bending displacement of the spiral SU-8 cantilever induced by the contraction of cardiomyocytes can be precisely measured at the nanoscale using a homemade laser-based measurement system. The displacement in the spiral SU-8 cantilever without micro-grooves was much greater than that in the case of traditional rectangular SU-8 cantilevers. The displacement produced by the spiral cantilever with grooves is 240% greater than that without grooves. Following preliminary experiments, cardiac drugs including Verapamil, Quinidine, Lidocaine, E-4031, and Bay K 8644 were used to evaluate their side effects on cardiomyocytes. Quantitative analysis of measurements shows that not only Verapamil and Quinidine but also Lidocaine and E-4031 treatment can decrease the cell beating frequency, and both the Verapamil and Lidocaine treatment can decrease the cell contraction force. Furthermore, Bay K 8644 assay results indicate that it can decrease the contraction force and increase the beating frequency of cardiomyocytes.

Transmissivity testing of multilayer insulation at cryogenic temperatures

The problem of degraded emissivity of thin films at low temperatures has been a long observed phenomena. Previous efforts at measuring properties have suggested that transmission of energy through the films may play a key role in the thermal performance of multilayer insulation systems at low temperatures. Similarly, recent testing on tank applied systems has suggested a radiative degradation at low temperatures. Two different approaches were used to attempt to measure the transmission of energy through MLI at low temperatures. A laser based measurement system was set up to directly measure transmittance and a calorimetric based measurement system was used to measure relative emittance of a single layer between aluminum foil and double aluminized Mylar. Minimal transmission at long wavelengths were observed through standard MLI blanket materials at deposition thicknesses of even 35nm. Where transmission was measured, it was too low to effect the performance of a multilayers system. Similarly, the calorimeter showed similar increases of emissivity for both standard blanket materials and aluminum foils. Multiple different methodologies of measurement have all yielded the same result: that there is no transmission through standard MLI blanket materials at wavelengths associated with temperatures as low as 2K.

Laser-based water depth measurement system deployed via unmanned aerial vehicle

We introduced a laser-based noncontact shallow water depth measurement technique from a flying unmanned aerial vehicle (UAV). The water depth is measured by imaging two laser beam spots scattered from the surface and bottom of the water. The effect of water surface waves and UAV tilt angles to the depth measurement has been studied for practical applications. We have further developed this laser-based detection system consisting of a green laser, a global positioning system, a camera with a narrow field of view lens, a laser range finder, and a single-board computer. The measurement system onboard of a UAV flying over a small lake has demonstrated satisfactory water depth measurement capability. The low-cost light weight UAV-based water depth measurement should benefit water depth monitoring, mapping, and reporting in a hazardous environment offering flexibility, mobility, and remote control safe operation.

Methodological Comparison between a Novel Automatic Sampling System for Gas Chromatography versus Photoacoustic Spectroscopy for Measuring Greenhouse Gas Emissions under Field Conditions.

Trace gases such as nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) are climate-related gases, and their emissions from agricultural livestock barns are not negligible. Conventional measurement systems in the field (Fourier transform infrared spectroscopy (FTIR); photoacoustic system (PAS)) are not sufficiently sensitive to N2O. Laser-based measurement systems are highly accurate, but they are very expensive to purchase and maintain. One cost-effective alternative is gas chromatography (GC) with electron capture detection (ECD), but this is not suitable for field applications due to radiation. Measuring samples collected automatically under field conditions in the laboratory at a subsequent time presents many challenges. This study presents a sampling designed to promote laboratory analysis of N2O concentrations sampled under field conditions. Analyses were carried out using PAS in the field (online system) and GC in the laboratory (offline system). Both measurement systems showed a good correlation for CH4 and CO2 concentrations. Measured N2O concentrations were near the detection limit for PAS. GC achieved more reliable results for N2O in very low concentration ranges.

Work-hardening and ductility of artificially aged AA6060 aluminium alloy

The work-hardening and ductility of an artificially aged AA6060 aluminium alloy were studied based on tensile tests of smooth and notched cylindrical samples. The alloy was tested after three processing steps, each followed by artificial aging. These processing steps were casting and homogenization, extrusion, and cold rolling and heat treatment to obtain a recrystallized grain structure. Subsequent to each of these processing steps, the material was tested after artificial aging to underaged, peak aged and overaged conditions. The true stress–strain curve to failure was determined by use of a laser-based measurement system. The Bridgman correction was applied to estimate the equivalent stress–strain curves, and the work-hardening behaviour was analysed using an extended Voce approach. Fractography was applied to study the failure mechanisms for material exposed to the different processing steps and temper treatments. To evaluate the use of the Bridgman correction and to study the notch strengthening effect observed experimentally, finite element simulations were performed using the Gurson model. The experimental study demonstrates the effects of thermomechanical processing and artificial aging on the stress–strain behaviour and the tensile failure strain of the alloy.

Surface-patterned SU-8 cantilever arrays for preliminary screening of cardiac toxicity

Arrays of a μgrooved SU-8 cantilever were utilized to analyze changes in the contraction force and beating frequency of cardiomyocytes in vitro. The longitudinally patterned μgrooves facilitates alignment of cardiomyocytes on top of the SU-8 cantilever, which increases the contraction force of cardiomyocytes by a factor of about 2.5. The bending displacement of the SU-8 cantilever was precisely measured in nanoscale using a laser-based measurement system combined with a motorized xyz stage. The cantilever displacement due to contraction of the cardiomyocytes showed the maximum on day 8 after their cultivation. Following preliminary experiments, Isoproterenol, Verapamil, and Astemizole were used to investigate the effect of drug toxicity on the physiology of cardiomyocytes. The experimental results indicated that 1µM of Isoproterenol treatment increased contraction force and beating frequencies of cardiomyocytes by 30% and 200%, respectively, whereas 500nM of Verapamil treatment decreased contraction force and beating frequencies of cardiomyocytes by 56% and 42%, respectively. A concentration of less than 5nM of the hERG channel suppression drug Astemizole did not change the contraction forces in the displacement but slightly decreased the beating frequencies. However, irregular or abnormal heartbeats were observed at Astemizole concentrations of 5nM and higher. We experimentally conformed that the proposed SU-8 cantilever arrays combined with the laser-based measurement systems has the great potential for a high-throughput drug toxicity screening system in future.

A laser-based machine vision measurement system for laser forming

Laser forming continues to be a promising technology in manufacturing due to its fast speed, flexibility, and low-cost. Measurement of deformation after laser forming is widely needed to verify its convergence to the intended shape in academic research. With the development of laser forming, high requirements on the measurement of the deformed work-piece have been sought such as a 3D profile of the deformed surface, a large measuring range, and measuring convenience. In this paper, a laser-based machine vision measurement system was developed to measure the 3D profile of deformed surface by a one-off scanning process. Based on the 3D profile data, the vertical displacement of the deformed plate was calculated for bending analysis. In addition, as one of the important feature parameters, transverse shrinkage was automatically determined through a novel image-based method during the scanning process. A measuring accuracy of 0.03mm for vertical displacement measurement and 0.0125mm for transverse shrinkage were achieved in the developed measurement system. This measurement performance is acceptable in most of the laser forming processes currently studied.

Development of high throughput Dual Laser system incorporating CCD-based multichannel Czerny – Turner spectrometer for real-time qPCR fluorescence intensity measurements

In this article, the development of a commercial high throughput system incorporating a multichannel CCD-based Czerny – Turner spectrometer for real-time fluorescence quantitative polymerase chain reaction (qPCR) measurements is described. The system employs two 20 mW lasers (532 ± 1 nm and 637 ± 3 nm) 2.5× Galilean beam expander-focuser, 5×4-200 μm core diameter fiber-optic bundle and a two-axis galvanometer for exciting fluorescent dyes. Further, the optical measurement system can detect twenty reaction vessels in asynchronous manner and up to five different fluorescent dyes (5-plex) at 1 nM dye concentration in each of the reaction vessels simultaneously. Moreover, PCR curves obtained using the optical measurement system for a genomic deoxyribonucleic acid (DNA) template containing three fluorescent generic binding dyes (FAM, Q670 and CRF610) is discussed. The measurement system repeatability is <1% CV (coefficient of variance). Finally, a performance comparison between the reported qPCR laser-based measurement system and an LED-based qPCR measurement system described by the author in ref. 14 is provided.

基于激光扫描的大尺寸圆锥体几何测量系统

基于激光扫描的大尺寸圆锥体几何测量系统

Evaluation of Aerial Spray Technologies for Adult Mosquito Control Applications

Abstract Spray droplet size has long been recognized as an important variable that applicators of vector control sprays must be aware of to make the most effective spray applications. Researchers and applicators have several different techniques available to assess spray droplet size from spray nozzles. The objective of this study was to compare the droplet size spectrum produced by three nozzles commonly used in vector control in a high-speed wind tunnel, when characterized using three different laser-based droplet size measurement systems. Three droplet sizing systems: Malvern Spraytec laser diffraction, Sympatec HELOS laser diffraction, and TSI Phase Doppler Particle Analyzer (PDPA), were simultaneously operated, but under different operating conditions, to measure the spray droplet size-spectra for three spray nozzles. The three atomizers: a TeeJet® 8001E even flat fan nozzle, a BETE® PJ high pressure fog nozzles, and a Micronair ® AU5000 rotary atomizer were evaluated in a high speed wind tunnel at airspeeds of 53 and 62 m/s (120 and 140 mph). Based on the results of this work, only the BETE® PJ high pressure fog nozzles met the label requirements for both Fyfanon® and Anvil®. While the other nozzle might met the Dv0.5 (VMD - volume median diameter) requirement for Fyfanon®, the resulting Dv0.9 values exceeded labeled size restrictions. When applying Anvil with the BETE PJ high pressure fog nozzles, it is important to use the smaller two orifice sizes. The larger sizes tended to result in Dv0.9 values that exceeded label recommendations

ACCURATE DETERMINATION OF TORSION AND PURE BENDING MOMENT FOR VISCOELASTIC MEASUREMENTS

Measurements of time-dependent material properties in the context of linear viscoelasticity, at a given frequency and temperature, require accurate determination of both loading and deformation that are subjected to the testing materials. A pendulum-type viscoelastic spectroscopy is developed to experimentally measure loss tangent and the magnitude of dynamic modulus of solid materials. The mechanical system of the device is based on the behavior of the cantilever beam, and torsion and pure bending moment are generated from the interaction between a permanent magnet and the Helmholtz coils. The strength of the magnetic interactions may be determined with a material with known mechanical properties, such as aluminum 6061T4 alloy. The sensitivity of the torque measurement is on the order of one micro N-m level. With the high accurate torque measurement and deformation detection from a laser-based displacement measurement system, viscoelastic properties of materials can be experimentally measured in different frequency regimes. Sinusoidal driving signals are adopted for measuring complex modulus in the sub-resonant regime, and dc bias driving for creep tests in the low frequency limit. At structural resonant frequencies, the full-width-at-half-maximum (FWHM) method or Lorentzian curve fitting method is adopted to extract material properties. The completion of determining material properties in the wide frequency spectrum may help to identify the deformation mechanisms of the material and to create better models for simulation work.