Laser Line Scan Research Articles

Effect of Laser Pulse Overlap and Scanning Line Overlap on Femtosecond Laser-Structured Ti6Al4V Surfaces.

Surface structuring is a key factor for the tailoring of proper cell attachment and the improvement of the bone-implant interface anchorage. Femtosecond laser machining is especially suited to the structuring of implants due to the possibility of creating surfaces with a wide variety of nano- and microstructures. To achieve a desired surface topography, different laser structuring parameters can be adjusted. The scanning strategy, or rather the laser pulse overlap and scanning line overlap, affect the surface topography in an essential way, which is demonstrated in this study. Ti6Al4V samples were structured using a 300 fs laser source with a wavelength of 1030 nm. Laser pulse overlap and scanning line overlap were varied between 40% and 90% over a wide range of fluences (F from 0.49 to 12.28 J/cm²), respectively. Four different main types of surface structures were obtained depending on the applied laser parameters: femtosecond laser-induced periodic surface structures (FLIPSS), micrometric ripples (MR), micro-craters, and pillared microstructures. It could also be demonstrated that the exceedance of the strong ablation threshold of Ti6Al4V strongly depends on the scanning strategy. The formation of microstructures can be achieved at lower levels of laser pulse overlap compared to the corresponding value of scanning line overlap due to higher heat accumulation in the irradiated area during laser machining.

Detection System for U-Shaped Bellows Convolution Pitches Based on a Laser Line Scanner.

An expansion joint is mainly composed of bellows and other components; it is attached on a container shell or pipe to compensate for the additional stress caused by temperature differences and mechanical vibrations. In China, the expansion joint fatigue tests are often used to assess the quality of products. After fatigue tests, convolution pitch will be changed. The amount of change is an important index that can be used to evaluate bellows expansion joints. However, the convolution pitch detection is mainly done manually and randomly by inspection agencies before shipping to the end users. This common practice is not efficient and is often subjective. This paper introduced a novel method for automatically detecting the change of the convolution pitch based on a laser line scanner and data processing technology. The laser line scanner is combined with a precision motorized stage to obtain the point cloud data of the bellows. After denoising and fitting, a peak-finding algorithm is applied to search for the crest of a convolution. The method to find the convolution pitch and the decision that needs to be made to ensure product eligibility are described in detail. A DN500 expansion joint is used as a sample to illustrate the efficiency of the system. The application of the technique intuitively allows a higher precision and relative efficiency in quality inspection of bellows expansion joints. It has also been implemented in the Special Equipment Safety Supervision and Inspection Institute of Jiangsu province with great success.

Use of Miniature Step Gauges to Assess the Performance of 3D Optical Scanners and to Evaluate the Accuracy of a Novel Additive Manufacture Process.

In this work, we show how miniature step gauges featuring unidirectional and bidirectional lengths can be used to assess the performance of 3D optical scanners as well as the accuracy of novel Additive Manufacturing (AM) processes. A miniature step gauge made of black polyphenylene sulfide (PPS) was used for the performance verification of three different optical scanners: a structured light scanner (SLS), a laser line scanner (LLS), and a photogrammetry-based scanner (PSSRT), having comparable resolutions and working volumes. Results have shown a good agreement between the involved scanners, with errors below 5 μm and expanded uncertainties below 10 μm. The step gauge geometry due to the bidirectional lengths, highlights that there is a different interaction between the optical properties of the step gauge under measurement and each optical instrument involved and this aspect has to be considered in the uncertainty budget. The same geometry, due to its great significance in the detection of systematic errors, was used, as a novelty, to evaluate the accuracy of Lithography-based Ceramics Manufacturing (LCM), a proprietary additive manufacturing technology used for the fabrication of medical implants. In particular, two miniature step gauges made of Tricalcium Phosphate (TCP) were produced. Measurements conducted with the SLS scanner were characterized by a negligible error and by an uncertainty of about 5 μm. Deviations of the manufactured step gauges with respect to the Computer Aided Designed (CAD) model were comprised between ±50 μm, with positive deviations in the order of 100 μm on vertical sides. Differences in the order of 50 μm between the two step gauges were registered.

Remote Inspection of Internal Delamination in Wind Turbine Blades using Continuous Line Laser Scanning Thermography

This study proposes a continuous line laser scanning thermography (CLLST) system for remote inspection of internal delamination in wind turbine blades. The CLLST system offers the following advantages: (1) remote delamination inspection can be achieved by mechanically scanning a line laser beam and simultaneously capturing the corresponding thermal waves in nondestructive and noncontact manners; (2) internal delamination and surface damages can be classified by analyzing laser-induced thermal wave propagating patterns; (3) instantaneous delamination detection and quantification can be accomplished without using baseline data which is previously collected from the pristine condition of a target blade. To examine the feasibility of the CLLST system, laboratory and full-scale tests were performed using a carbon fiber reinforced polymer (CFRP) plate, a 10 kW glass fiber reinforced polymer (GFRP) wind turbine blade, and a 3 MW GFRP wind turbine blade. The test results demonstrated that the 10 mm diameter internal delamination located 1 mm underneath the blade surface was successfully detected even 10 m far from the target blade with a laser scanning speed of 2 mm/s.

Real-Time 3D Reconstruction of Thin Surface Based on Laser Line Scanner.

The truncated signed distance field (TSDF) has been applied as a fast, accurate, and flexible geometric fusion method in 3D reconstruction of industrial products based on a hand-held laser line scanner. However, this method has some problems for the surface reconstruction of thin products. The surface mesh will collapse to the interior of the model, resulting in some topological errors, such as overlap, intersections, or gaps. Meanwhile, the existing TSDF method ensures real-time performance through significant graphics processing unit (GPU) memory usage, which limits the scale of reconstruction scene. In this work, we propose three improvements to the existing TSDF methods, including: (i) a thin surface attribution judgment method in real-time processing that solves the problem of interference between the opposite sides of the thin surface; we distinguish measurements originating from different parts of a thin surface by the angle between the surface normal and the observation line of sight; (ii) a post-processing method to automatically detect and repair the topological errors in some areas where misjudgment of thin-surface attribution may occur; (iii) a framework that integrates the central processing unit (CPU) and GPU resources to implement our 3D reconstruction approach, which ensures real-time performance and reduces GPU memory usage. The proposed results show that this method can provide more accurate 3D reconstruction of a thin surface, which is similar to the state-of-the-art laser line scanners with 0.02 mm accuracy. In terms of performance, the algorithm can guarantee a frame rate of more than 60 frames per second (FPS) with the GPU memory footprint under 500 MB. In total, the proposed method can achieve a real-time and high-precision 3D reconstruction of a thin surface.

The influence of the skin tumors excision width in the postoperative facial asymmetry

Background/Aim. Planning an elliptical excision of the facial skin, caused by lines of minimum tension, is very important in order to achieve good aesthetic results. The width of the tumor excision affects the possibility of a direct closure of the post-excision defect. The aim of the study was to determine the minimum width of excision that does not affect postoperative symmetry of the face, in relation to the preoperative one, using an objective scanning method with a line laser scanner. Methods. The study included 50 patients of both sexes, older than 50 years, who had verified facial skin tumor and established medical indication for surgical elliptical excision and direct suture. All patients had laser scanning preoperatively, and then seven days and 90 days postoperatively, giving x, y, and z coordinates of 5 cephalometric points on the face, which determined the shape of the examined region. Patients were divided into three groups depending on the width of the excision (< 10 mm, 10?15 mm, > 15 mm). The shape of the examined region among different width of excision was compared, preoperatively, 7 days and 90 days postoperatively, using Procrustes analysis and analysis of the coordinates of cephalometric points. Results. Taking into account preoperative and postoperative x, y and z coordinates of the cephalometric points, statistically significant differences between the group of patients with the width excision < 10 mm and the other two groups (excision width 10?15 mm and > 15 mm) were found. Conclusion. The width of the skin tumors excision < 10 mm does not affect the postoperative facial asymmetry when a post-excisional defect is closed by direct suture.

Measuring rutting dimension and lateral position using 3D line scanning laser and inertial measuring unit

Pavement rutting caused by repeated traffic loads is a common type of structural damage to pavement. Rutting dimensions and lateral position are strongly related to traffic safety and ride comfort. However, in the field, rutting depth is usually measured by traditional methods, and rutting lateral position is ignored due to the limitations of data sources and algorithms. This study provides an automatic method for rutting dimension and lateral position measurement using a 3D line scanning laser system and Inertial Measuring Unit (IMU). Rutting dimensions (e.g., width, depth, depression area, wall slope and spacing between the inner and outer rutting) and locations (e.g., lateral position and rutting deviation away from lane center line) are measured by fusing multivariate data (e.g., 2D pavement images, transverse profiles and IMU data). In this study, two straight road sections located in Fuzhou, China, are chosen to validate the reliability and robustness of the proposed algorithm. Findings indicate that the measurement results from the new algorithm are highly correlated with the ground truths manually collected in the field. This study would benefit transportation agencies in traffic safety analysis, ride comfort evaluation and structural damage prediction based on the continuous pavement rutting dimension and its lateral positions.

Effects of laser-induced periodic surface structures on the superconducting properties of Niobium

It is well known that the use of ultrashort (fs) pulsed lasers can induce the generation of (quasi-) periodic nanostructures (LIPSS, ripples) on the surface of many materials. Such nanostructures have also been observed in sample’s surfaces irradiated with UV lasers with a pulse duration of 300 ps. In this work, we compare the characteristics of these nanostructures on 1-mm and on 25-μm thick niobium sheets induced by 30 fs n-IR and 300 ps UV pulsed lasers. In addition to conventional continuous or burst mode processing configurations, two-dimensional laser beam and line scanning modes have been investigated in this work. The latter allows the processing of large areas with a more uniform distribution of nanostructures at the surface. The influence of the generated nanostructures on the superconducting properties of niobium has also been explored. For this aim, magnetic hysteresis loops have been measured at different cryogenic temperatures to analyse how these laser treatments affect the flux pinning behaviour and, in consequence, the superconductor’s critical current values. It was observed that laser treatments are able to modify the superconducting properties of niobium samples.

Laser line scanning thermography for surface breaking crack detection : modeling and experimental study

Crack detection in metallic samples at high surface temperature, hostile and hazardous environments, etc. is a challenging situation in any manufacturing industries. Most of the present NDE methods are suitable only for lower surface temperatures, especially at room temperature. In this situation, we need a fast and non-contact NDT method which can be applied even in high sample surface temperature. Laser thermography is one of the techniques having a high potential in non-contact inspection. As a preliminary investigation, in this article, we have studied the potentiality of laser line thermography in crack detection at room temperature. In laser line thermography, a continuous wave (CW) laser is used to generate a laser line, which in turn is used to scan the metal surface. The heat distribution over the sample surface is recorded by an infrared thermal (IR) camera. Two different approaches are reported in this work. Firstly, a stationary laser line source and its interaction with cracks; secondly, moving laser line source scanning over a surface with crack. When the distance between crack centre to laser line centre increases, crack detectability will decrease; and when laser power increases, crack detectability will increase. A dedicated image processing algorithm was developed to improve the detectability of the cracks. To understand the heat transfer phenomenon, a simplified 3D model for laser thermography was developed for the heat distribution during laser heating and was validated with experimental results. Defects were incorporated as a thermally thin resistive layer (TTRL) in numerical modeling, and the effect of TTRL in heat conduction is compared with experimental results.

Трёхмерная визуализация в неразрушающем контроле

The article focuses on two 3D optical imaging technologies and the application of these technologies to nondestructive testing: laser line scanning and structured light. Both technologies determine depth based on triangulation between a light source, the object under inspection, and a camera sensor. Both technologies have demonstrated accuracy, precision, and probabilities of detection sufficient to meet the demands of nondestructive testing. The second part of the article focuses on the application of 3D imaging in the assessment of corrosion on pipelines. In this application, 3D imaging is used to identify areas of corrosion, determine the maximum amount of metal loss, extract the river bottom profile, and calculate the remaining strength of a pipeline.

Estimation of water film depth for rutting pavement using IMU and 3D laser imaging data

ABSTRACT Rutting is a kind of pavement structural damage caused by repeated traffic loads, which is served as ‘reservoir’ in rainy days, and ponding water would bring in potential hydroplaning issues. However, the widely used water film depth (WFD) prediction models are empirical models for the pavements without ruts. This study develops an analytic model for WFD estimation by simulating the dynamics of the sheet flow on rutting pavements. Precipitation, pavement texture, road alignment and pavement depression are considered as the intervening factors on WFD. Herein, precipitation is automatically and continuously measured by RLMI, and pavement properties are automatically and continuously measured by the 3D line scanning laser system. Based on the proposed algorithm the impacts of pavement swelling and centre deformation on rutting measurement are eliminated. The measured dimensions of rutting and estimated depth of sheet flow on the pavement surface are contributed for WFD calculation. A case study for WFD estimation on 1.4 km asphalt pavement section is provided. Finally, a validation test referred to the ground truth obtained by field manual measurment shows the proposed methods are accurate in WFD estimation for rutting pavement. Based on the method proposed in this study the hazardous locations with strict water logging can be identified, so engineers can take remedial measures to reduce traffic accidents.

Impact of Sparse Benthic Life on Seafloor Roughness and High-Frequency Acoustic Scatter

Quantitative acoustic marine habitat mapping needs to consider the impact ofmacrobenthic organisms on backscatter data. However, the sensitivity of hydroacoustic systems toepibenthic life is poorly constrained. This study explores the impact of a benthic community withsparse abundance on seafloor microroughness and acoustic backscatter at a sandy seafloor in theGerman North Sea. A multibeam echo sounder survey was ground-truthed by landermeasurements combining a laser line scanner with sub-mm resolution and broad-band acoustictransducers. Biotic and abiotic features and spatial roughness parameters were determined by thelaser line scanner. At the same locations, acoustic backscatter was measured and compared with anacoustic scatter model utilizing the small-roughness perturbation approximation. Results of thelander experiments show that a coverage with epibenthic features of 1.6% increases seafloorroughness at spatial wavelengths between 0.005–0.03 m, increasing both spectral slope andintercept. Despite the fact that a strong impact on backscatter was predicted by the acoustic modelbased on measured roughness parameters, only a minor (1.1 dB) change of backscatter was actuallyobserved during both the lander experiments and the ship-based acoustic survey. The results of thisstudy indicate that benthic coverage of less than 1.6% is insufficient to be detected by currentacoustic remote sensing.

Detecting device and technology of pavement texture depth based on high precision 3D laser scanning technology

The pavement means texture depth (MTD) is part of the most significant indexes to the characteristics of the pavement macrostructure. Traditional measuring MTD methods are easily impacted by the human factors with inefficiency and low-accuracy. In order to realize the automatic detection of the MTD, a high precision asphalt pavement MTD detection system is built based on three-dimensional line laser scanning, and a MTD calculation method based on the line laser three-dimensional (3-D) data is proposed. Firstly, the 3-D elevation data are extracted from the obtained linear structure light images. Secondly, a denoising algorithm based on two-way standard deviation filter is presented for the 3-D elevation data. Finally, a MTD calculation method based on the line laser 3-D elevation data is designed. The MTD of five asphalt specimens with different roughness was measured by the calculation method designed in this study and sand patch measurements, respectively, and the results were comparable. The research demonstrates that the error between the calculation result of this algorithm and that of sand patch measurements is not more than 5%, which further proves the feasibility of this algorithm.

Microfluidic Channels Fabrication Based on Underwater Superpolymphobic Microgrooves Produced by Femtosecond Laser Direct Writing.

A strategy is proposed here to fabricate microfluidic channels based on underwater superpolymphobic microgrooves with nanoscale rough surface structure on glass surface produced by femtosecond (fs) laser processing. The fs laser-induced micro/nanostructure on glass surface can repel liquid polydimethylsiloxane (PDMS) underwater, with the contact angle (CA) of 155.5 ± 2.5° and CA hysteresis of 2.7 ± 1.5° to a liquid PDMS droplet. Such a phenomenon is defined as the underwater “superpolymphobicity”. Microchannels as well as microfluidic systems are easily prepared and formed between the underwater superpolymphobic microgroove-textured glass substrate and the cured PDMS layer. Because the tracks of the laser scanning lines are programmable, arbitrary-shaped microchannels and complex microfluidic systems can be potentially designed and prepared through fs laser direct writing technology. The concept of “underwater superpolymphobicity” presented here offers us a new strategy for selectively avoiding the adhesion at the polymer/substrate interface and controlling the shape of cured polymers; none of these applications can find analogues in previously reported superwetting materials.

Nanocluster-ripple grating fabricated by high repetition femtosecond fiber laser

In this paper we studied the surface morphology of the grating fabricated on the soda-lime silicate glass using a 500 kHz, 1040 nm femtosecond laser. A nanocluster-ripple grating can be fabricated with proper processing parameters. Our results demonstrate that the scan line spacing plays an important role in the diffraction efficiency of the fabricated grating. Such gratings, used as a multi-beam splitter or a dispersion element, can be fabricated easily by changing the laser scan line spacing.

Enhanced self-bias magnetoelectric effect in locally heat-treated ME laminated composite

This study reports the improvement in the magnetoelectric (ME) coupling effect in a locally heat-treated FeBSi (Metglas)/Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 single crystal laminated composite under zero magnetic bias. The high-temperature pulse laser treatment could induce local crystallization along the laser scanning line, but adjacent domains remained still amorphous, which resulted in the thermal and lattice mismatch. Therefore, it could produce a residual stress between the crystalline and amorphous phases, which generated an internal bias field in the Metglas foil. The experimental results showed that the ME coefficient for the laser-treated laminate was enhanced to 1220 V/cm Oe at the resonance frequency of 23.32 kHz without a magnetic bias, which was two times higher than that of the untreated ME laminates. The induced ME voltage also showed a linear response to the applied AC magnetic field with an amplitude as low as 10−10 T at the resonance. The excellent ME performance could, therefore, serve as a promising and practicable application for highly sensitive magnetic field sensors under the zero bias field.

A Distortion Model of Laser Sheet for a Laser Line Scanner With Large Fan Angle

This article proposes an analytical method of computing distorted laser sheet of a laser line scanner and compensating it. In this article, a distortion model of laser sheet generated from a laser line scanner with large fan angle is derived from physical principles to achieve accurate depth perception even around its edges on which significant depth estimation errors occur in existing algorithms. From a laser beam incident obliquely on a contact surface of two cylindrical lenses, a curved laser sheet is expressed in terms of the nonzero incident angle by the laws of geometrical optics. From the mathematical model of the distorted laser sheet, the incident angle is estimated through an optimization technique and then its estimate is used for depth computation. It is shown through simulations and experiments that the proposed distortion model enables a proper compensation scheme and hence the distortion-compensated depth estimation errors are reduced all over the range of interest, specially much around the both side edges of the laser sheet. Quantitatively in comparison to the compensation-free method, the depth estimation error is improved from 225 to 28 mm on average and from 1781 to 187 mm for worst-case scenarios near edges of a laser sheet.

IR laser line scanning treatments to improve levitation forces in MgTi0.06B2 bulk materials

Infrared (IR) laser-line scanning has been widely used to induce different surface microstructures in a broad range of materials. In this work, this laser configuration was applied on the surface of MgTi0.06B2 bulk samples in order to ascertain its effects on their superconducting properties, particularly on the magnetic levitation forces. The microstructural changes produced by this type of laser treatment were investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). It was observed that the thermal treatment induced by the laser improves grain connectivity in a layer of material just below the irradiated surface, in agreement with the observed improvement in critical current density values, Jc, which were estimated from isothermal magnetic hysteresis loops. A significant increment of both vertical (Fz) and lateral (Fx) magnetic levitation forces was achieved. Numerical calculations were performed to understand the experimental behaviour and to clarify how an improvement of Jc near the surface can improve the magnetic levitation force of these materials. In addition, the same studies were carried out in similar bulk samples but with nano-sized silver particle additions of 3 and 6 wt %, in the outer ring of the bulk, observing also an improvement of the levitation forces, albeit less than in samples without Ag because of the better performance of the original samples after laser treatment. These results are relevant to those studying superconductor fabrication and material fabrication modelling, essential for the development of technological applications of superconductors, and are based on microstructure control via application of a recently developed laser-line scan method.

An Improved Low-Noise Processing Methodology Combined with PCL for Industry Inspection Based on Laser Line Scanner.

This paper introduces a three-dimensional (3D) point cloud data obtained method based on a laser line scanner and data processing technology via a PCL open project. This paper also provides a systematical analysis of the error types of laser line scanner and common error reducing solutions and calibration of the laser line scanner. The laser line scanner is combined with a precision motorized stage to obtain the 3D information of a measurand, and the format of point cloud data is converted via the set of x, y, and z coordinates. The original signal is processed according to the noise signal types of the raw point cloud data. This paper introduced a denoise process step by step combining various segmentation methods and a more optimized three-dimensional data model is obtained. A novel method for industry inspection based on the numerous point cloud for the dimensions evaluation via feature extraction and the deviation of complex surface between scanned point cloud and designed point cloud via registration algorithm is proposed. Measurement results demonstrate the good performance of the proposed methods. An obtained point cloud precision of ±10 μm is achieved, and the precision of dimension evaluation is less than ±40 μm. The results shown in the research demonstrated that the proposed method allows a higher precision and relative efficiency in measurement of dimensions and deviation of complex surfaces in industrial inspection.

Ellipsoidal droplet formation on anisotropic superhydrophobic copper surface

Superhydrophobic copper surfaces with contact angle (CA) as high as 158° are fabricated using the one-step process of femtosecond fiber laser writing. Low spacing between the laser scanning lines was chosen purposefully to observe the anisotropic surface structures on the copper surfaces. This resulted in the formation of an ellipsoidal water droplet with anisotropic CAs, which are different along the major and minor axes. We quantified an experimentally measured parameter that correlates the droplet anisotropy and is related to the one-dimensional root mean square surface height deviation (1D RMS SHD). Theoretical CAs prediction based on triple contact line (TCL) theory on an ellipsoidal droplet volume is formulated and the calculations are in excellent agreement with experimentally observed anisotropic CAs. We presented an analytical expression for effective volume function relating the anisotropic contact angles, height, and the three semi-major axes of the ellipsoidal droplet. These functional values and observed contact angles are falling within the experimental errors of less than 5%. This work strengthens the validity of TCL theory. Our method of fabrication, high CAs results, correlation with 1D RMS SHD and theoretical prediction of elliptical CAs on an anisotropic surface will guide to design surfaces for many future applications.