Laser Triangulation System Research Articles

Automatic Detection of Ballast Unevenness Using Deep Neural Network

The amount of freight transported by rail and the number of passengers are increasing year by year. Any disruption to the passenger or freight transport stream can generate both financial and human losses. Such a disruption can be caused by the rail infrastructure being in poor condition. For this reason, the state of the infrastructure should be monitored periodically. One of the important elements of railroad infrastructure is the ballast. Its condition has a significant impact on the safety of rail traffic. The unevenness of the ballast surface is one of the indicators of its condition. For this reason, a regulation was introduced by Polish railway lines specifying the maximum threshold of ballast unevenness. This article presents an algorithm that allows for the detection of irregularities in the ballast. These irregularities are determined relative to the surface of the sleepers. The images used by the algorithm were captured by a laser triangulation system placed on a rail inspection vehicle managed by the Polish railway lines. The proposed solution has the following elements of novelty: (a) it presents a simple criterion for evaluating the condition of the ballast based on the measurement of its unevenness in relation to the level of the sleeper; (b) it treats ballast irregularity detection as an instance segmentation process and it compares two segmentation algorithms, Mask R-CNN and YOLACT, in terms of their application to ballast irregularity detection; and (c) it uses segmentation-related metrics—mAP (Mean Average Precision), IoU (Intersection over Union) and Pixel Accuracy—to evaluate the quality of the detection of ballast irregularity.

Development of track component health indices using image-based railway track inspection data

The primary role of the US Department of Transportation (USDOT) Federal Railroad Administration (FRA) is ensuring the safe operation of railway rolling stock and infrastructure by way of regulatory oversight. FRA regulations require US railroads to conduct visual track inspections as often as twice per week depending on a specific track segment’s FRA track class, which also governs maximum train operating speed. Such inspections are often subjective due to the inherent limitations of human visual inspection and cognition. Additionally, human visual inspections require some level of risk given the need for inspectors to be on track while also consuming valuable network capacity. As a result, and the desire to collect objective data to improve both safety and maintenance planning, railroads are pursuing new means and methods to assess track condition and evaluate track component health. This paper presents a numerical method to define track component health using field data collected on the High Tonnage Loop (HTL) at the Transportation Technology Center (TTC) in Pueblo, Colorado, USA. Line scan laser and image data of the track were captured using a 3D Laser Triangulation system and were subsequently processed using Deep Convolutional Neural Networks (DCNNs). The track heath quantification method proposed establishes benchmarks that were developed based on the understanding of railway track mechanics, high axle load (HAL) railroad engineering instructions, and FRA regulations. The novel metrics presented are referred to as Track Component Heath Indices (TCHIs) and are quantitative values that objectively assess track condition and provide a means to monitor condition change with time and tonnage. These data can be used in conjunction with traditional track geometry and other forms of track heath data (e.g. GPR and rail profile) to more holistically assess the condition of the track structure and its components and ultimately predict its future state.

Mathematical Analyzing of Laser Triangulation System without Scheimpflug Condition via C++ and Qt Framework

In this paper, the mathematical characteristics of a laser triangulation system has been analyzed without considering Scheimpflug condition. The system parameters have been investigated and detailed information about the behavior of the system due to the changing some initial parameters just before designing the profile measurement system have been obtained. To be able to evaluate the system, C++ and Qt framework have been used for calculation of multi-dimensional arrays and visualization of the results to investigate the system parameters. The characteristics of the triangulation systems (both for our model and the model that proposed by Lamott and Noll, 2011) and characteristics of laser beam (laser beam thickness change for given measurement field range) for different laser sources with different wavelengths have been investigated. After analyzing the parameters of the triangulation system successfully, an adjustable system will be built in the laboratory to be able to get a better understanding the usage of this system in both 2D and 3D laser cutting systems.

Methodology for the characterization and understanding of longitudinal wrinkling during calendering of lithium-ion and sodium-ion battery electrodes

The manufacturing of lithium-ion battery (LIB) cells is following a complex process chain in which the individual process steps influence the subsequent ones. Meanwhile, increasing requirements especially concerning the battery performance, sustainability and costs are forcing the development of innovative battery materials, production technologies and battery designs. The calendering process directly affects the volumetric energy density of an electrode and therefore of a battery cell. Calendering is still challenging as it causes high stresses in the electrode that lead to defects and thus increased rejection rates. The interaction between electrode material and process as well as the formation of defects is still not fully understood, especially when new material systems are used. In this context, the sodium-ion battery (SIB) is one post-lithium battery system that is a promising option to overcome the limitations of conventional LIBs. Therefore, this paper presents a first material and machine independent methodology to describe and understand the defect type longitudinal wrinkle, which mostly appears at the uncoated current collector edge of an electrode and in running direction. The aim is to systematically characterize the longitudinal wrinkles according to their geometry. The automatic data acquisition is carried out with a laser triangulation system and a 3D scanning system. The geometry values are calculated from the raw data and correlated to selected process parameters. The methodology is applicable regardless of the material as shown by exemplary results of NMC811 cathodes for LIB and hard carbon anodes for SIB. By using two different pilot calenders it is shown, that the data acquisition can be carried out independently of the machine. The presented methodology contributes to finding solutions for the avoidance of longitudinal wrinkling in any battery electrode and therefore to reducing the rejection rate.

A design of laser triangulation system with combined diffuse and specular reflection modes for dull and shiny surface measurements

Conventional laser triangulations are designed to measure the depth or height on a dull or rough surface. This can be done by projecting a light perpendicularly to the surface and capturing the spot of the diffuse reflection which is scattered from the surface. However, for a shiny or smooth surface, the specular reflection dominates, and it is difficult to detect diffuse reflection. We may modify the system setting to capture the specular reflection, with the cost of losing the diffuse reflection information. In this article, we proposed a design of dual diffuse and specular reflection mode of laser triangulation. The advantage is that there is no need to repeat alignment and calibration processes when we change the measuring mode, so we can easily select the measuring mode that is suitable for each surface. We have described the system setting and the calibration results where we can achieve the resolution of micrometre for both measuring modes.

SINGLE IMAGE LASER TRIANGULATION SYSTEM FOR 360° EXTERNAL INSPECTION OF CYLINDRICAL SHAPED OBJECTS USING INVERSE TRIANGULATION ALGORITHM

Abstract. This paper proposes a new Laser Triangulation System (LTS) that allows an 360° external inspection for each acquired image using two planar mirrors, one laser line projector, and one camera. The new measurement algorithm is based on the inverse triangulation in which the analysis is made from 3D object space to image space, the opposite of traditional LTS algorithms, with laser peak detection in favourable directions even in an image with multiple reflections of the object. Measurement system principle, calibration and metrological evaluation are described based on simulated experimental data and 3D reconstructions examples. Uncertainty for a 20 mm plain plug gauge measurement was ±0.07 mm for 95.45% confidence.

3D reconstruction of concrete defects using optical laser triangulation and modified spacetime analysis

Automated investigation of concrete defects has attracted attention with well-developed computer vision techniques. However, most studies in defect reconstruction mainly focus on identifying and measuring defects on a two-dimensional surface. Few progresses have been made to explore the 3D reconstruction of concrete defects. This study describes an affordable optical laser triangulation system fusing a linear laser ray generator and a sports camera to reconstruct the concrete defects. The proposed system adopts a modified spacetime analysis approach to solve two critical imaging errors in typical laser triangulation approaches. By comparing the outputs of the proposed system and two typical laser triangulation approaches, the results show that the proposed system can eliminate the imaging errors and generate 3D reconstruction models of concrete defects with acceptable accuracy.

STRICT GEOMETRIC CALIBRATION OF AN UNDERWATER LASER TRIANGULATION SYSTEM

Abstract. This paper will describe a novel approach for the calibration of an underwater laser triangulation system. Underwater triangulation systems, consisting of a line laser and a camera can be used to determine the geometry of submerged objects or the topography of a water body bottom. Placing camera and laser line projector inside a waterproof housing leads to refraction effects at the air-glass-water interfaces, both of the laser light-sheet and image rays. This implies a deformed laser plane in the water and a curved line on the object surface. The proposed approach strictly models the geometry between camera, laser and housing. First experiments show, that the calibration method can be applied for water depth measurements with accuracies of 0.2–0.3 mm at depths in the order of 100 mm.

Optical Setup for Error Compensation in a Laser Triangulation System.

Absolute distance measurement is a field of research with a large variety of applications. Laser triangulation is a well-tested and developed technique using geometric relations to calculate the absolute distance to an object. The advantages of laser triangulation include its simple and cost-effective setup with yet a high achievable accuracy and resolution in short distances. A main problem of the technology is that even small changes of the optomechanical setup, e.g., due to thermal expansion, lead to significant measurement errors. Therefore, in this work, we introduce an optical setup containing only a beam splitter and a mirror, which splits the laser into a measurement beam and a reference beam. The reference beam can then be used to compensate for different error sources, such as laser beam dithering or shifts of the measurement setup due to the thermal expansion of the components. The effectiveness of this setup is proven by extensive simulations and measurements. The compensation setup improves the deviation in static measurements by up to 75%, whereas the measurement uncertainty at a distance of 1 m can be reduced to 85 μm. Consequently, this compensation setup can improve the accuracy of classical laser triangulation devices and make them more robust against changes in environmental conditions.

SENSOR EVALUATION FOR CRACK DETECTION IN CONCRETE BRIDGES

Abstract. Bridges are one of the most critical traffic infrastructure objects, therefore it is necessary to monitor them at regular intervals. Nowadays, this monitoring is made manually by visual inspection. In recent projects, the authors are developing automated crack detection systems to support the inspector. In this pre-study, different sensors, like different camera systems for photogrammetry, a laser scanner, and a laser triangulation system are evaluated for crack detection based on a defined required minimum crack width of 0.2 mm. The used test object is a blasted concrete plate, sized 70 cm × 70 cm × 5 cm and placed in an outdoor environment. The results of the data acquisition with the different sensors are point clouds, which make the results comparable. The point cloud from the chosen laser scanner is not sufficient for the required crack width even at a low speed of 1 m/s. The RGB or intensity information of the photogrammetric point clouds, even based on a low-cost smartphone camera, contain the targeted cracks. The authors advise against using only the 3D information of the photogrammetric point clouds for crack detection due to noise. The laser triangulation system delivers the best results in both intensity and 3D information. The low weight of camera systems makes photogrammetry to the preferred method for an unmanned aerial vehicle (UAV). In the future, the authors aim for crack detection based on the 2D images, automated by using machine learning, and crack localisation by using structure from motion (SfM) or a positioning system.

A Smartphone Integrated Hand-Held Gap and Flush Measurement System for in Line Quality Control of Car Body Assembly.

This paper presents the design and the characterization of a portable laser triangulation measurement system for measuring gap and flush in the car body assembly process. Targeting Human in the Loop (HILT) operations in the manufacturing sector, and in line with the vision of human empowerment with Industry 4.0 technologies, the instrument embeds features to ease operators’ activity and compensate possible misuse that could affect the robustness and the quality of data acquired. The device is based on a smartphone integrated with a miniaturized laser triangulation system installed in a cover. The device embodies additional sensors and control systems in order to guarantee operators’ safety (switching on and off the laser line based on specific conditions), support operators during the measurement execution task, and optimize the image acquisition process for minimizing the uncertainty associated to the measurement. The smartphone performs on-board processing and allows Wi-Fi communication with the plant IT infrastructure. Compliance to Industry 4.0 requirements is guaranteed using OPC-UA (Open Platform Communications—Unified Architecture) communication protocol enabling the exchange of live data with the plant middleware. The smartphone provides also an advanced high-resolution color display and well proven and ergonomic human–machine interfaces, which have been fully exploited in the design. The paper introduces the system optical layout and then presents the algorithms implemented to realize the gap and flush measurement. The paper finally presents the calibration of the instrument and estimates its calibration uncertainty in laboratory conditions. Then it discusses how performance decays when the operator handles the instrument on a reference car body. Finally, it shows the analysis of uncertainty when the device is used on real car bodies of different colors in a production line. It is observed that the measurement uncertainty of the whole measurement chain (measurand + instrument + operator + uncontrolled environmental conditions) is larger than the instrument calibration uncertainty because the measurement process is affected by the operator and the variable conditions of the production line.

Measuring the supporting slats of laser cutting machines using laser triangulation

When automatically generating programs for flatbed laser cutting machines, it is advantageous to know the position of the supporting tips of the raw material. This allows the nesting layout and tool path to be adapted in an intelligent way. The problem of measuring the supporting tips of a laser cutting machine has not been considered in published literature before. We introduce possible methods first and choose a laser triangulation system. A novel setup, where none of the components is at a right angle to the measured surface, is proposed to account for the circumstances in a laser cutting machine. Its performance is investigated thoroughly with special regard to robustness and accuracy. In order to achieve very high accuracies, the setup is extrinsically calibrated on the measured object and different line extraction algorithms are tested for their effect on the measurement result. It is shown that the measurement setup is robust for different changes in the environment, such as different slat materials, bent supporting tips, and slagging. The measurement accuracy of the setup is calculated to be within ± 0.8 mm.

A Study on the Uncertainty of a Laser Triangulator Considering System Covariances

A laser triangulation system, which is composed of a camera and a laser, calculates distances between objects intersected by the laser plane. Even though there are commercial triangulation systems, developing a new system allows the design to be adapted to the needs, in addition to allowing dimensions or processing times to be optimized; however the disadvantage is that the real accuracy is not known. The aim of the research is to identify and discuss the relevance of the most significant error sources in laser triangulator systems, predicting their error contribution to the final joint measurement accuracy. Two main phases are considered in this study, namely the calibration and measurement processes. The main error sources are identified and characterized throughout both phases, and a synthetic error propagation methodology is proposed to study the measurement accuracy. As a novelty in uncertainty analysis, the present approach encompasses the covariances of correlated system variables, characterizing both phases for a laser triangulator. An experimental methodology is adopted to evaluate the measurement accuracy in a laser triangulator, comparing it with the values obtained with the synthetic error propagation methodology. The relevance of each error source is discussed, as well as the accuracy of the error propagation. A linearity value of 40 µm and maximum error of 0.6 mm are observed for a 100 mm measuring range, with the camera calibration phase being the main error contributor.

Weld Quality Verification by Using Laser Triangulation Measurement

Adaptive welding parameter control and robotic workpiece positioning feedback control impose a strict requirement on the dimensional measurement of the workpieces and fittings. Laser triangulation-based vision systems are commonly used to measure and compensate for the workpiece positioning inaccuracies as well as the inconsistencies of the weld seam. In this study, the laser triangulation system’s accuracy and reliability for welding quality control, workpiece positioning and welding parameter control are analyzed. The combined accuracy of both applied laser sensor and robot are analyzed and compared with the welding requirements. The study shows that the measurement and positioning accuracy of the robot is sufficient on reliable welding torch positioning for reaching and fulfilling the requirements of ISO 5817 level B class weld consistently. The measurement accuracy of the presented system and repeatability of the robot is well within the suitable measurement window for achieving consistent weld quality.

Geometrical Model of Laser Triangulation System Based on Synchronized Scanners

In traditional synchronized scanning system, the trajectory of the 3D scanning point is modeled as a circle when the thickness of rotated mirror is assumed to be zero. In this paper, a novel method to model the geometric measurement of synchronized scanning triangulation in the unfolded light path is proposed. Unlike most existing recent works, the 3D coordinate of the target is reasoned from the geometrical model, which includes all 14 system parameters. Further, the performance of the system precision can be analyzed and the importance of the thickness of rotated mirror is confirmed. In the experiment, a synchronized scanning system is developed. The experimental result demonstrates that the value of measurement uncertainty at a distance of 0.5m is 0.75mm and at a distance of 5m is 6.68mm. The standard deviations from the measurement point to the fitting plane at a distance of 0.5 m and 5 m are 1.10 mm and 19.73 mm, respectively.

IMPROVING IMAGE MATCHING BY REDUCING SURFACE REFLECTIONS USING POLARISING FILTER TECHNIQUES

Abstract. In dense stereo matching applications surface reflections may lead to incorrect measurements and blunders in the resulting point cloud. To overcome the problem of disturbing reflexions polarising filters can be mounted on the camera lens and light source. Reflections in the images can be suppressed by crossing the polarising direction of the filters leading to homogeneous illuminated images and better matching results. However, the filter may influence the camera’s orientation parameters as well as the measuring accuracy. To quantify these effects, a calibration and an accuracy analysis is conducted within a spatial test arrangement according to the German guideline VDI/VDE 2634.1 (2002) using a DSLR with and without polarising filter. In a second test, the interior orientation is analysed in more detail. The results do not show significant changes of the measuring accuracy in object space and only very small changes of the interior orientation (Δc ≤ 4 μm) with the polarising filter in use. Since in medical applications many tiny reflections are present and impede robust surface measurements, a prototypic trinocular endoscope is equipped with polarising technique. The interior and relative orientation is determined and analysed. The advantage of the polarising technique for medical image matching is shown in an experiment with a moistened pig kidney. The accuracy and completeness of the resulting point cloud can be improved clearly when using polarising filters. Furthermore, an accuracy analysis using a laser triangulation system is performed and the special reflection properties of metallic surfaces are presented.

基于远心镜头的激光三角测距系统研究与实现

基于远心镜头的激光三角测距系统研究与实现

An innovative high temperature solid particulate erosion testing system

A new high temperature solid particulate erosion test system has been designed and built to improve the quality of high temperature erosion tests. The new test system is designed to carry out experiments at temperatures up to 900°C and particle velocities up to 300ms−1. A key feature is the use of commercial “air torch” technology to provide the necessary high air flow rates at elevated temperature giving the whole system a relatively small footprint. Measurements of erosion rate are revolutionised by two different forms of in-line measurement of wear to the sample. This new technology largely replaces the need for interrupting the test, cooling the test samples, and weighing at periodic intervals which can mean that a test with a total exposure of 30min to erosion by particles at high temperature can take most of a week. The two new technologies employed use a high precision balance to measure the in situ weight of the samples whilst they are still at test temperature, and the use of a custom designed blue laser triangulation system to measure the shape of the wear scars in situ and at temperature.The use of the new test system is illustrated by preliminary results of experiments from coated and uncoated Nimonic 80A.

Melt level measurement for the CZ crystal growth using an improved laser triangulation system

Abstract An improved image-based laser-triangulation measurement system is proposed in this paper to measure the melt level in CZ crystal pullers. The system uses a line laser to overcome the deficiency of the traditional laser-triangulation system caused by the heat shield. The laser line projected to the melt surface and the bottom of the heat shield generates two scattered bars, which are captured by the camera. The relationship between the pixel distance of the two bars and the melt level is studied. An optimized adaptive laser bar detection approach is applied to measure the melt level quickly and accurately. Three experiments have been made to demonstrate the advantages of the system. The calibration experiment shows the system has a measurement resolution of 0.0755 mm. The accuracy experiment proves the system has a precise measurement performance and the robustness experiment demonstrates the system using a truncated mean filter is reliable and robust.

Proposal of a new method for the rapid assessment of wood machinability and cutting tool performance in peripheral milling

The quality evaluation of a wooden surface machined by peripheral milling can be achieved by means of the visual assessment or by surface roughness measurement. The method defined in this paper is a novel alternative to the state-of-the-art material machine-ability evaluation providing objective results acquired by an automatic system. Critical machining conditions and surface defects are stimulated by a purposely-designed circular sample. The approach proposed bases on a multi-sensor technology where a laser triangulation system reconstructs the 3D surface topography and a camera records the grayscale image of the same surface while the sample is rotated around a central axis. The dedicated software allows automated surface reconstruction, quality assessment and the detection of specific defects. The method is rapid and allows an easy comparison of different cutting conditions intended as a tool to rapidly determine optimal solutions.