Laser Line Scan Research Articles

A 3D Laser Scanner Setup for a Measuring of Geometrical Product Specifications

The laser line scanners are coming to be frequently used in a field of dimensional inspection process. There are several phenomena that make the data acquisition more difficult. Particularly secondary reflection, direct reflection, scan overlapping, outlying points. The effect of these phenomena can be minimised by optimal setting of scanning parameters stated in this paper. The parameters were determined from an experimental measurements of 50 various parts. Additionally a thermal stability effect was measured at two types of Nikon scanners. The stabilisation time and the systematic error were determined for the scanner LC15Dx: 45 min, 20μm and 30 min and 37 μm for the LC60Dx scanner. It should help to prevent the systematic errors during the measurement.

Porous microstructures induced by picosecond laser scanning irradiation on stainless steel surface

A study of porous surfaces having micropores significantly smaller than laser spot on the stainless steel 304L sample surface induced by a picosecond regenerative amplified laser, operating at 1064nm, is presented. Variations in the interaction regime of picosecond laser pulses with stainless steel surfaces at peak irradiation fluences(Fpk=0.378–4.496J/cm2) with scanning speeds(v=125–1000μm/s) and scan line spacings(s=0–50μm) have been observed and thoroughly investigated. It is observed that interactions within these parameters allows for the generation of well-defined structured surfaces. To investigate the formation mechanism of sub-focus micropores, the influence of key processing parameters has been analyzed using a pre-designed laser pulse scanning layout. Appearances of sub-focus ripples and micropores with the variation of laser peak fluence, scanning speed and scan line spacing have been observed. The dependencies of surface structures on these interaction parameters have been preliminarily verified. With the help of the experimental results obtained, interaction parameters for fabrication of large area homogeneous porous structures with the feature sizes in the range of 3–15μm are determined.

Determination of Aspect Ratio Limitations, Accuracy and Repeatability of a Laser Line Scanning CMM Probe

Coordinate measurement machine (CMM) probing techniques can involve direct mechanical contact (e.g., tactile probing) or diverse non-contact principles (e.g., laser line scan probing). For some applications, contact methods are not capable of measuring fast enough to ensure 100% quality controlled parts. A laser line scanning probe uses a laser triangulation-based method to acquire 3D measurement points on a workpiece relative to a sensor. Mounting the sensor in a 3D coordinate frame, e.g., in a CMM provides enough information to fully examine the workpiece. These techniques are most commonly exploited in medical industry and industries involving plate materials. A high data density and measurement speed are significant advantages when measuring free-form surfaces by laser line scanning, making the process much more time-efficient. However, high-precision geometrical features (such as cylinders, spheres, etc.) must be measured for locating and aligning the free-form shapes. The accuracy of the equipment therefore has to be assessed. Probe Maximum Permissible Error (MPEP) values below 10μm have been reported for cutting-edge laser line scanners. This paper compares the major influences on measurements on cylindrical features. First, the aspect-ratio limitations are considered by comparing two inherently different techniques. The stable inspection of reference features is important, while trying to maximize the spatial extent of the measured features. Second, the measurement method is analyzed in two ways: by using a limited sample of the features to increase stability and eliminate interference from neighboring features; by varying the number of scan tracks, which greatly affects the measurement time.

Model/data comparisons of high-frequency backscattering from well-characterized sand sediment

In the Spring of 2010, acoustic backscattering from an artificially-smoothed sand sediment was measured in the NSWC PCD test pond. The measurements were made at frequencies from 200 to 500 kHz as a function of grazing angle. The residual roughness of the smoothed surface was measured using a laser line scanner while the sediment parameters were determined through diver core analysis and sound speed and attenuation measurements. At the time of the experiment, it was not possible to characterize the volume heterogeneities within the sediment. Subsequent analysis of historic conductivity probe measurements collected in the same test pond under similar conditions has been used to fill this gap. With this additional dataset, the environmental characterization of the sediment places significant constraints on models of scattering from both the sediment roughness and the subsurface volume heterogeneities. Using the sediment parameters, the predictions of small perturbation roughness and volume scattering theories are compared to the data when the sediment is modeled as a fluid and as a poroelastic medium. The effect of the measured porosity fluctuations on sound propagation within the sediment is also examined using a recently developed scattering loss model. [Work supported by ONR.]

High-adhesion Cu patterns fabricated by nanosecond laser modification and electroless copper plating

Adhesion strength is a crucial factor for the performance and reliability of metallic patterns on insulator substrates. In this study, we present an efficient technique for selective metallization of alumina ceramic with high adhesion strength by using nanosecond laser modification and electroless copper plating. Specifically, a 355nm Nd:YVO4 ultraviolet (UV) laser was employed not only to decompose palladium chloride film locally for catalyzing the electroless reaction, but also to modify the ceramic surface directly using its high fluence. An orthogonal experiment was undertaken to study the effects of processing parameters including laser fluence, scanning speed and scanning line interval on adhesion strength. The adhesion strength was measured by pulling a metallic wire soldered into the copper coating perpendicular to the substrate using a pull tester. The results have shown that a strong adhesion between the copper coating and the alumina ceramic, higher than the tensile strength of tin-lead solder was obtained. Surface and interface characteristics were investigated to understand that, whose results have shown that the high-aspect-ratio microstructures formed by the laser modification is the major reason for the improvement of adhesion.

Line laser lock-in thermography for instantaneous imaging of cracks in semiconductor chips

This study proposes a new line laser lock-in thermography (LLT) technique for instantaneous inspection of surface cracks in semiconductor chips. First, a new line LLT system is developed by integrating a line scanning laser source, a high-speed infrared (IR) camera with a close-up lens, and a control computer. The proposed line LLT system scans a line laser beam onto a target semiconductor chip surface and measures the corresponding thermal wave propagation using an IR camera. A novel baseline-free crack visualization algorithm is then proposed so that heat blocking phenomena caused by crack formation can be automatically visualized and diagnosed without relying on the baseline data obtained from the pristine condition of a target semiconductor chip. The proposed inspection technique offers the following advantages over the existing semiconductor chip inspection techniques: (1) inspection is performed in a noncontact, nondestructive and nonintrusive manner; (2) the crack diagnosis can be accomplished using only current-state thermal images and thus past thermal images are unnecessary; and (3) crack detectability is significantly enhanced by achieving high spatial resolution for thermal images and removing undesired noise components from the measured thermal images. Validation tests are performed on two different types of semiconductor die chips with real micro-cracks produced during actual fabrication processes. The experiments demonstrate that the proposed line LLT technique can successfully visualize and detect semiconductor chip cracks with width of 28–54μm.

3-D ice shape measurements using mid-infrared laser scanning.

A general approach based on mid-infrared (MIR) laser scanning is proposed to measure the 3-D ice shape no matter whether the ice is composed of clear ice, rime ice, mixed ice, or even supercooled water droplets or films. This is possible because MIR radiation penetrates ice and water only within a depth of less than 10 micrometers. First, an MIR laser point scanning technique is implemented and verified on transparent glass and clear ice. Then, to improve efficiency, an MIR laser line scanning method is developed and validated on different models. At last, several sequential MIR laser line scans are applied to trace the 3-D shape evolution of the continuous ice accretion on an airfoil in an icing wind tunnel. The ice growth process can be well observed in the results. The MIR scan shows a good agreement with the traditional visible laser scan on a plastic replication of the final ice shape made by the mold and casting method.

Making Operational Strategies of Asphalt Teams Explicit to Reduce Process Variability

The on-site construction process undertaken by asphalt teams has a critical impact on pavement quality. Process improvement and learning require explicit information about the process. However, current on-site operational activities and key parameters are, in general, not systematically monitored and mapped. The lack of process information makes it difficult for contractors and asphalt teams to distinguish between good and poor practices and to improve. Although technologies to make the on-site process explicit are becoming widely available, their adoption has been slow. To overcome this knowledge gap regarding explicit information about the on-site construction process, this paper proposes a framework and utilizes technologies for the systematic monitoring and mapping of on-site activities and key parameters. Various technologies and sensors, such as a global positioning system (GPS), a laser linescanner, and infrared cameras, make it possible to track the on-site movements of machinery and asphalt temperatures during construction. This framework was applied and refined during 29 asphalting projects in the Netherlands, creating an extensive set of on-site process data. Considerable variability was found in the delivered asphalt temperatures, the asphalt cooling, the compaction process and density progression, and the movements of machinery. This variability offers opportunities where action could be taken to improve process quality by reducing process variability. The framework and explicit data can help asphalt teams to verbalize their tacit knowledge and make their own processes and choices transparent and further promotes learning processes. This paper contributes to a deeper understanding of the on-site construction process and highlights how to encourage technology adoption in construction

Rail Sensor: A Mobile Lidar System for 3D Archiving the Bas-reliefs in Angkor Wat

This paper presents a mobile Lidar system for efficiently and accurately capturing the 3D shape of the Bas-reliefs in Angkor Wat. The sensor system consists of two main components: 1) a panoramic camera and 2) a 2D 360-degree laser line scanner, which moves slowly on the rails parallel to the reliefs. In this paper, we first propose a new but simple method to accurately calibrate the panoramic camera to the 2D laser scan lines. Then the sensor motion can be estimated from the sensor-fused system using the 2D/3D features tracking method. Furthermore, to reduce the drifting error of sensor motion we adopt bundle adjustment to globally optimize and smooth the moving trajectories. In experiments, we demonstrate that our moving Lidar system achieves substantially better performance for accuracy and efficiency in comparison to the traditional stop-and-go methods.

基于激光线扫方式的点云数据精简表达及STL文件生成方法

基于激光线扫方式的点云数据精简表达及STL文件生成方法

Obstacle Detection in Hybrid Cross-Country Environment Based on Markov Random Field for Unmanned Ground Vehicle

In order to detect the obstacle from the large amount of 3D LIDAR data in hybrid cross-country environment for unmanned ground vehicle, a new graph approach based on Markov random field was presented. Firstly, the preprocessing method based on the maximum blurred line is applied to segment the projection of every laser scan line inx-yplane. Then, based onK-means clustering algorithm, the same properties of the line are combined. Secondly, line segment nodes are precisely positioned by using corner detection method, and the next step is to take advantage of line segment nodes to build an undirected graph for Markov random field. Lastly, the energy function is calculated by means of analyzing line segment features and solved by graph cut. Two types of line mark are finally classified into two categories: ground and obstacle. Experiments prove the feasibility of the approach and show that it has better performance and runs in real time.

Optimizing parameters of freeform surface reconstruction using CMM

In this paper, Design of Experiment (DOE) techniques are used to optimize parameters of surface reconstruction in Reverse Engineering technology for freeform surfaces. The input factors are noise reduction, number of points in (%), triangle counts in (%), and Sampling when the responses are the surface accuracy of the final reconstructed surface, computational time and the required space in computer memory. Accuracy of the model is measured in terms of the minimum standard deviation values. The proposed approach was confirmed through a case study carried out using a real metallic part. The case study involves two types of point cloud which have been obtained from both fixed CMM laser line scanner and portable CMM laser line scanner. The 3D CAD models of the selected part are developed based upon combination of parameters given by Taguchi L32 orthogonal array design for point cloud obtained from fixed CMM and Taguchi L16 orthogonal array for point cloud data obtained from portable CMM. This study also describes the development of predictive models for the given responses utilizing response surface methodology (RSM). The developed predictive models are manipulated using contours and response surfaces. It has been concluded that the final accuracy level of reverse engineered surfaces is depending on number of input points of point cloud data, number of triangles in polygon model and noise reduction.

Laser line scanning for fluorescence reflectance imaging: a phantom study and in vivo validation of the enhancement of contrast and resolution.

Intraoperative fluorescence imaging in reflectance geometry is an attractive imaging modality to noninvasively monitor fluorescence-targeted tumors. In some situations, this kind of imaging suffers from poor resolution due to the diffusive nature of photons in tissue. The objective of the proposed technique is to tackle this limitation. It relies on the scanning of the medium with a laser line illumination and the acquisition of images at each position of excitation. The detection scheme proposed takes advantage of the stack of images acquired to enhance the resolution and the contrast of the final image. The experimental protocol is described to fully understand why we overpass the classical limits and validate the scheme on tissue-like phantoms and in vivo with a preliminary testing. The results are compared with those obtained with a classical wide-field illumination.

Wettability of dentin after Yb:KYW thin-disk femtosecond ablation.

The aim of this study was to quantitatively evaluate the wettability of dentin after Yb:KYW thin-disk femtosecond-pulsed laser ablation by measuring the contact angle. Different laser parameters were used including different fluences (F), scanning speeds, and scanning line spacings. Crowns of 15 extracted human teeth were cut longitudinally into slices approximately 1.5-mm thick with a cutting instrument. The samples were randomly divided into ten groups (n = 3/group). Samples in groups 1-8 were irradiated with a femtosecond-pulsed laser. The dentin samples were fixed on a stage at the focal plane, and the laser beam irradiated the samples through a galvanometric scanning system so rectangular movement could be achieved. Samples in groups 9 and 10 were prepared with grinding instruments. Following ablation and preparation, the samples were examined for contact angle with an optical contact angle measuring instrument. The results showed that scanning speed and scanning line spacing had little influence on the wettability of dentin following femtosecond-pulsed laser ablation, except when F = 6J/cm(2). For six out of the eight laser ablation groups, when a lower fluence was used, the dentin contact angle was higher and vice versa. Most of the dentin which had been ablated using the femtosecond-pulsed laser had improved wettability compared to samples prepared with the grinding instruments. This study showed that various laser fluences, scanning speeds, and scanning line spacings can alter dentin wettability. Therefore, adequate parameters should be chosen to achieve proper therapeutic benefits.

3D color reconstruction based on underwater RGB laser line scanning system

Laser line scanning (LLS) as an optical 3D survey method is recently used for underwater 3D imaging. This paper presents an approach for both 3D reconstruction and color restoration based on the LLS system. The system is set up with RGB laser scanning components for acquiring 3D data and color data at the same time. Direct calibration algorithms and RGB additive color model are involved for processing 3D color data. The experiment result shows that underwater targets can be feasibly 3D reconstructed with color texture simultaneously, at millimeter scales.

The influence of surface topology on the quality of the point cloud data acquired with laser line scanning probe

Purpose – The purpose of this paper is to investigate the influence of surface topology on the performance of laser line scanning probe and to suggest methodology for 3D digitization of specular surfaces. Design/methodology/approach – Two different molds, one having milled surface and the other with polished surface, were used to identify effect of surface characteristics on the performance of laser line scanning probe mounted on bridge-type coordinate measuring machine. The point cloud data acquisition of two surfaces was carried out using different combinations of laser scanning parameters. The point cloud sets thus obtained were analyzed in terms of completeness, noise and accuracy. The polished mold which exhibited specular reflection was digitized at different scanning angles of laser line scanning probe using the best combination of scanning parameters. Findings – Results confirmed that surface characteristics play important role to determine quality of the reverse engineering (RE) process. The results in terms of completeness, accuracy and noise for point cloud sets have successfully been obtained for milled and polished surfaces. Three-dimensional (3D) comparison analysis suggested larger deviation in cases of polished surface as compared to milled surface. The point cloud set acquired with proposed approach was better in terms of both completeness and noise reduction. Originality/value – There has been an increased demand for measurement of metallic, polished and shiny surfaces in automotive, aerospace and medical industries. These surfaces are very difficult to scan because they exhibit specular reflection instead of diffuse reflection. Laser line scanning probe which is a non-contact method is in great demand for RE. This is due to the fact that it possesses very high data acquisition speed. However, laser scanning is hugely affected by surface characteristics which in turn govern specular reflection.In this paper, it has been shown that a surface that exhibits various degrees of specular reflection can be digitized efficiently if appropriate combination of scanning parameters and positions of laser line scanning probe are used. Also, this paper has attempted to offer a procedure to overcome incompleteness and noise in 3D data as obtained by the laser line scanning probe.

Rapid and accurate reverse engineering of geometry based on a multi-sensor system

The reduction of the lead time in measurement and reverse engineering, and the increased requirements in terms of accuracy and flexibility, have resulted in a great deal of research effort aimed at developing and implementing multi-sensor systems. This paper describes an effective competitive approach for using a tactile probe to compensate the data from a laser line scanner to perform accurate reverse engineering of geometric features. With the data acquired using laser scanning, intelligent feature recognition and segmentation algorithms can be exploited to extract the global surface information of the object. The tactile probe is used to re-measure the geometric features with a small number of sampling points and the obtained information can be subsequently used to compensate the point data patches which are measured by laser scanning system. Then, the compensated point data can be exploited for accurate reverse engineering of a CAD model. The limitations of each measurement system are compensated by the other. Experimental results on three parts validate the rapidity and accuracy of this multi-sensor data fusion approach.

Weighted data fusion for UAV-borne 3D mapping with camera and line laser scanner

Unmanned aerial vehicles (UAVs) equipped with adequate sensors have nowadays become a powerful tool for capturing spatial information. In this article, we introduce a concept for weighted data fusion in order to enable an improved UAV-borne 3D mapping with a camera and a lightweight line laser scanner. For this purpose, we carry out geometric camera calibration as well as lever-arm and bore-sight calibration and subsequently present a new methodology for incorporating camera images and laser scanner data into an adjustment process. This adjustment is based on the concept of variance components in order to obtain a reasonable weight ratio for data fusion and accurately estimate the poses of the sensors. We demonstrate the feasibility of the proposed approach and show that the consideration of range measurements clearly improves the pose estimation.

Supplying interpolation and continuity in surface modeling via Bezier networks and optical metrology

An automatic technique to provide interpolation and continuity in the object surface modeling via Bezier networks is presented. This technique generates the surface model via Bezier networks based on surface points, which are retrieved via laser line scanning. In this model, a Bezier function is added in the surface edge to provide continuity G1 and interpolation. Preserving these surface properties via network, the model accuracy and object representation are improved. Also, the surface model reduces operations and memory size to generate the object surface. This is because the model is implemented with fewer mathematical terms than the traditional models. The surface model is defined by means of network weights and the control points. The surface measurement is carried out by a Bezier network via line position to avoid external measurement errors. Thus, the computational model generates the object shape with high accuracy. This is because the network interpolates all points of the physical object. The contribution of the proposed technique is corroborated by an evaluation based on interpolation, continuity, memory size, and speed of the traditional models. The evaluation shows evidences of the viability of the proposed network.

Rough Terrain 3D Mapping and Navigation Using a Continuously Rotating 2D Laser Scanner

Mapping, real-time localization, and path planning are prerequisites for autonomous robot navigation. These functions also facilitate situation awareness of remote operators. In this paper, we propose methods for efficient 3D mapping and real-time 6D pose tracking of autonomous robots using a continuously rotating 2D laser scanner. We have developed our approach in the context of the DLR SpaceBot Cup robotics challenge. Multi-resolution surfel representations allow for compact maps and efficient registration of local maps. Real-time pose tracking is performed by a particle filter observing individual laser scan lines. Terrain drivability is assessed within a global environment map and used for planning feasible paths. Our approach is evaluated using challenging real environments.