Two-dimensional Laser Scanner Research Articles

Design of two-dimensional piezoelectric laser scanner system for precision laser beam steering.

In this work, a large aperture two-dimensional (2D) piezoelectric laser scanner system with an onboard sensor to detect the scanner's deflection angle has been designed and prototyped. The proposed 2D laser scanner is driven using three amplified piezoelectric actuators assembled in an equilateral triangle configuration to provide structural stability and compactness. To overcome the nonlinearity that derives from the hysteresis effect of the piezoelectric actuators, the tip-tilt principle and the control schemes of the 2D scanner are analyzed and compared. Thanks to the combination of onboard sensing of the deflection angle of the scanner with the closed-loop control capability, this 2D scanner's features include a large aperture and high accuracy. The experimental results demonstrate that closed-loop control achieves higher control accuracy than the open-loop control approach, leading to a reduction in the relative error from 2%-4% to ∼0.5%, while the deflection angle tracking accuracy lies approximately within the 40 μrad range.

Investigating the use of two-dimensional OSL laser scanning instruments and energy-dispersive x-ray spectroscopy for OSL exposure dating

Optically Stimulated Luminescence (OSL) depth profiles can be used to extrapolate rock surface exposure ages by understanding a sample's light attenuation and OSL bleaching behaviors. However, the current measuring procedure for producing depth profiles, by measuring the luminescence of millimeter slices from surface core samples, offers limited resolution data, limiting parameter extrapolative precision. The use of OSL laser scanning measuring protocols on transverse core slices has potential for improving the data resolution of OSL depth profiles from core samples. An 11-year exposed rock surface was parameterized for light attenuation and luminescence bleaching rates using depth profile data from four surface cores collected via wafer and scan measuring techniques, to show the potential of OSL laser scanning to improve depth profile dataset resolutions and parameter extrapolative precision. Additionally, non-quartz OSL anomalies were filtered from scan datasets to determine if non-quartz mineral filtering can further improve the resolution and parameterization of depth profile datasets. OSL scanning measures improved the resolution of depth profiles over wafer derived depth profiles for the measured samples, and in comparing absolute uncertainties of parameters, broadly improved parameter precision using maximum likelihood estimate fitting protocols. Non-test dose corrected spatially resolved data error bounds were generally larger than from wafer derived data. When compared to unfiltered spatially resolved depth profile data, OSL anomaly filtered scanned depth profiles improved error bounds of anomaly affected data, and improved parameter extrapolative precision with roughly a similar effect as using non-filtered scan data. The absolute uncertainty in parameterization was impacted by scatter prevalent from scan datasets, which is caused by low OSL sensitivity from samples, the potential recording of remnant OSL, the lack of regenerative dose normalization applied to the scan dataset, as well as other scanning instrument measuring limitations. Still, these influences can be mitigated with optimized instrumentation and scanning protocols.

Reference Modulation for High-Quality Scan Images of 2-D Laser Scanner Systems

For laser scanner systems, the most critical issue for high-quality images is the linearity of the slow axis. The laser scanner systems have various disturbances and uncertainties, such as manufacturing tolerances, structure vibrations, and parameter uncertainties. Further, there are vertical and horizontal resonance modes that hinder controller design. In this letter, we propose a reference modulation technique to enhance the vertical angle linearity of the slow axis for two-dimensional laser scanner systems. First, the laser scanner system is mathematically modeled in the state-space form. Then, the reference modulation is designed to boost the loop gain over the desired frequency range. The reference modulation can guarantee high-quality scan images by redesigning the desired reference based on the output feedback. The current tracking controller was then implemented with virtual references for the states. We investigated its tracking performance via sensitivity function analysis against the disturbances. Experiments were performed to evaluate the effectiveness of the proposed method using four different laser scanners. We confirmed that the proposed method achieved up to 48% improvement in the angle tracking error from the experimental results.

The Research and Application of System for Paper Surface Morphology Stereoscopic Observation and Characterization

The work aims to explore a microscopic observation system of paper surface and achieve high-precision stereoscopic observation with detail characterization of paper surface morphology. Based on the DT-400E precision program-controlled three-dimensional translation stage and KEYENCE LJV-7200 two-dimensional laser scanner, the hardware parts of our own system are developed to scan and transmit point cloud data of paper surface morphology to the computer. The corresponding system software will automatically process the point cloud data acquired from the laser scanner and generate the corresponding vivid 3D model and height histogram. This system scans and characterizes four different types of paper samples, allowing the human eye to visually distinguish the differences in surface morphology as well as automatically calculate the numerical differences in paper surface morphology parameters. The results of the applicability test show that the system is highly efficient in acquiring, observing, and evaluating the topography of the paper surface. The system can not only predict the paper surface quality of printed paper, but can also be extended to the evaluation of 3D printed surfaces.

Two-dimensional laser scanner based coal mine shaft guide deformation detection device

Two-dimensional laser scanner based coal mine shaft guide deformation detection device

Detection algorithm of shaft guide based on two-dimensional laser scanning technology

Detection algorithm of shaft guide based on two-dimensional laser scanning technology

低成本二维激光扫描投影技术

低成本二维激光扫描投影技术

Submap-Based Indoor Navigation System for the Fetch Robot

In this paper, we present a novel navigation framework for the Fetch robot in a large-scale environment based on submapping techniques. This indoor navigation system is divided into a submap mapping part and an on-line localization part. For the mapping part, in order to deal with large environments or multi-story buildings, a submap mapping framework fusing two-dimensional (2D) laser scan and 3D point cloud from RGBD sensor is proposed using Google Cartographer. Meanwhile, several image datasets with corresponding poses are created from the RGBD sensor. Thanks to the submap framework, the error is limited corresponding to the size of the map, thus localization accuracy will be improved. For the on-line localization, so as to switch the submaps, the on-line images from the RGBD sensor are used to match the database images using DeepLCD, a deep learning based library for loop closure. Based on the information from DeepLCD and odometry, adaptive Monte Carlo localization (AMCL) is reinitialized to finish the localization task. In order to validate the result accuracy, reflectors and a motion capture system are used to compute the absolute trajectory error (ATE) and the relative pose error (RPE) based on the Gaussian-Newton (GN) algorithm. Finally, the proposed framework is tested on the Fetch simulator and the real Fetch robot, including both submap mapping and on-line localization.

Underwater De-scattering Imaging by Laser Field Synchronous Scanning

A novel underwater optical imaging method is proposed to improve the quality of images which suffer from poor visibility due to underwater scattering and signal attenuation under artificial illumination. A high sensitive sCMOS video camera was designed to operate in rolling shutter mode which formed a narrow field-of-view (FOV) during the exposure process. Meanwhile, a MEMS-based two-dimensional laser scanning light source only illuminated the camera's narrow FOV. Thus the backscatter caused by the FOV intersection of the camera with the light source was reduced. Since the laser scanning route of the method is a field instead of a line, we named it Laser Field synchronous Scanning (thereafter LFS). A modified off-the-shelf laser scanning projector with green laser diode driving signal extracted was employed as the two-dimensional laser scanning light source, and the driving signal was received by the sCMOS video camera to synchronize the rolling shutter. The experiment was conducted by utilizing contrast ratio and contrast signal-to-noise ratio (CSNR) to compare the images captured using an LED light source and LFS under different water turbidity. The experimental results show that LFS has much better contrast and CSNR performance compared to the LED light source, and the peak contrast improvement is 8.77 times (under 29.17 FTU) and the peak CSNR improvement is 1.87 times (under 17.72 FTU). The experiment results demonstrate that LFS imaging method can significantly reduce the backscatter effect caused by water and suspending particles under artificial illumination.

Two-Dimensional Laser Scanning Utilizing Inclined Rolling of an Ellipsoidal Reflector

Compact light detection and ranging (LIDAR) with wide scanning angle is required for the environment monitoring of automobile. We have developed a two-dimensional (2D) laser scanner for the LIDAR system with the horizontal scanning angle of 360 degrees. The scanner is composed of an inclined rolling ellipsoidal reflector equipped with a permanent magnet at the center, a ferromagnetic steel pillar, and six electromagnets. The reflector is attached on top of the pillar by magnetic force; the reflector is translationally-fixed but free in rotational motion. The electromagnets are arranged in a circular pattern under the reflector. Applying current pulses to the electromagnets subsequently, the reflector is rotated by the electromagnetic force. The maximum rotational speed of 85 rps (revolutions per second) was achieved with an elliptical reflector (major axis: 22 mm, minor axis: 18.2 mm, thickness: 0.2 mm) and a permanent magnet (diameter: 4 mm, thickness: 2 mm) at an applied current 28 mA to the electromagnets. We successfully demonstrated 2D laser scan with the horizontal scanning angles of 360 degrees, the vertical scanning angle of 18 degrees, and the rotational speed of 70 rps.

A Novel Real-Time Moving Target Tracking and Path Planning System for a Quadrotor UAV in Unknown Unstructured Outdoor Scenes

A quadrotor unmanned aerial vehicle (UAV) should have the ability to perform real-time target tracking and path planning simultaneously even when the target enters unstructured scenes, such as groves or forests. To accomplish this task, a novel system framework is designed and proposed to accomplish simultaneous moving target tracking and path planning by a quadrotor UAV with an onboard embedded computer, vision sensors, and a two-dimensional laser scanner. A support vector machine-based target screening algorithm is deployed to select the correct target from multiple candidates detected by single shot multibox detector. Furthermore, a new tracker named TLD-KCF is presented in this paper, in which a conditional scale adaptive algorithm is adopted to improve the tracking performance for a quadrotor UAV in cluttered outdoor environments. According to distance and position estimation for a moving target, our quadrotor UAV can acquire a control point to guide its fight. To reduce the computational burden, a fast path planning algorithm is proposed based on elliptical tangent model. A series of experiments are conducted on our quadrotor UAV platform DJI M100. Experimental video and comparison results among four kinds of target tracking algorithms are given to show the validity and practicality of the proposed approach.

An Extensive Approach to Features Detection and Description for 2-D Range Data Using Active B-splines

This letter presents three novel contributions for the two-dimensional laser scan data. First, a low-level point feature detector for stable interest point detection. Second, an approach for high-level B-splines features extraction, and finally, a local descriptor for the interest points based on the shape context representation of the uniformly distributed points on the B-splines features. The clues of stable interest points obtained from the detector are used in the B-splines features extraction from the scan data, which enables lightweight and accurate mapping of the environment using fewer control points instead of scan data points. This letter also proposes benchmark metrics to evaluate the performance of the extracted high-level features approach in comparison with the state-of-the-art methodology. A robust descriptor for the interest points offers an efficient association and correspondence matching. Consistent results compared with the state-of-the-art FALKO-BSC and FLIRT- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">β</i> -Grid features in experiments with standard datasets prove the stability of our proposed interest point detector and the proficiency of the descriptor. The results of efficient localization using the pair are also presented.

Development of two-dimensional piezoelectric laser scanner with large steering angle and fast response characteristics.

We describe a two-dimensional piezoelectric laser scanner designed and tested to obtain a large steering angle of 1° and fast response characteristics of 200 Hz. To overcome the relatively small expansion capability of piezoelectric actuators, the displacement amplification mechanisms with two levers in series are employed to magnify the end tip of the lever which is connected to a 0.5-in. glass mirror. For fast response characteristics, the natural frequencies of the hinge mechanisms were calculated by using the finite element analysis technique. In order to evaluate the performance of the proposed scanner, the hinge mechanism has been manufactured of titanium alloy and the natural frequencies of the hinge mechanism have been measured by sine sweep test. Also, the actual machining test on the burning paper has been done by using a high power laser, and it is shown that the proposed laser scanner is capable of steering the laser beam 1° with a frequency of 200 Hz.

Two-dimensional environment reconstruction based on the absolute local deflection angle of laser scanning data

Successive edge following (SEF) is extensively used to extract environment characteristics from two-dimensional laser scanning data given its simplicity. Conventional SEF compares the Euclidean distance between two adjacent points to either a fixed or an adaptive threshold. However, the segmentation accuracy is low and information loss occurs during processing of planes with a large deflection angle with respect to the laser sensor because the distance estimation is sensitive to this angle. Moreover, available SEF algorithms cannot suitably determine corners in the environment. To address these problems, we propose an extended SEF algorithm based on the absolute local deflection angle of laser scanning points. The proposed algorithm determines the local deflection angle between target and reference points, and an adaptive threshold is calculated based on the range precision of the laser sensor. Furthermore, corners are efficiently estimated and noise is mitigated by using three constraints. An experiment on two-dimensional environment reconstruction of an underground parking lot verifies the accuracy and capability of the proposed algorithm to reconstruct the lines and corners representing the environment.

Automated low-cost terrestrial laser scanner for measuring diameters at breast height and heights of plantation trees.

A terrestrial laser scanner is a fast, high-precision data acquisition device, which has been applied more and more to the research area of forest inventory. In this study, a type of automated low-cost terrestrial laser scanner was designed and implemented based on a SICK LMS-511 two-dimensional laser scanning sensor and a stepper motor. The new scanner was named BEE(developed by the department of Electronic Engineering, Beijing Forestry University), which can scan the forest trees in three dimensions. The BEE scanner and its supporting software are specifically designed for forest inventory. The specific software was developed to smoothly control the BEE scanner and to acquire the data, including the angular data, range data, and intensity data, and the data acquired by the BEE scanner could be processed into point cloud data, a range map, and an intensity map. Based on the point cloud data, the trees were detected by a single slice of the single scan in a plot, and the local ground plane was fitted for each detected tree. Then the diameter at breast height (DBH), tree height, and tree position could be estimated automatically by using the specific software. The experiments have been performed by using the BEE scanner in an artificial ginkgo forest which was located in the Haidian District of Beijing. Four 10 m × 10 m square plots were selected for the experiments. The BEE scanner scanned in the four plots and acquired the single-scan data, respectively. The DBH, tree height, and tree position of the trees in the four plots were estimated and analyzed. For comparison, manually-measured data was also collected in the four plots. The trunk detection rate for all four plots was 92.75%; the root mean square error of the DBH estimation was 1.27 cm; the root mean square error of the tree height estimation was 0.24 m; and the tree position estimation was in line with the actual position. The scanner also was tested in more natural forest in the JiuFeng Forest Park. Two plots with a radius of 5 meters were scanned. Eleven trees in the plot with a flat ground were detected and DBH were estimated. But tree detection was failed in the other plot because of the undulating ground. Experimental results show that the BEE scanner can efficiently estimate the structure parameters of plantation trees and has good potential in practical applications of forest inventory.

Two-dimensional environment reconstruction based on absolute local deflection angle of laser scanning data. Reconstruction of the spatial environment in two-dimensional laser scanning, using data on the absolute value of the local angle of deviation

Two-dimensional environment reconstruction based on absolute local deflection angle of laser scanning data. Reconstruction of the spatial environment in two-dimensional laser scanning, using data on the absolute value of the local angle of deviation

Rail wear inspection based on computer-aided design model and point cloud data

Railway transportation demands more efficient and accurate rail wear inspection systems to ensure the train operation safety. To obtain continuous three-dimensional data, a structured light rail wear inspection system is developed in this article, and the data processing method for aligning the point cloud from structured light scanning to the nominal computer-aided design model of the rail is investigated. For further data registration, the point cloud of the computer-aided design model is generated and the normal vectors of these points are calculated. In the coarse registration, conformal geometric algebra is applied to align the segmented point clouds by intuitive geometric calculations to those from the computer-aided design model. In the fine registration, the accurate alignment of the point clouds is implemented by the iterative closest point algorithm. The vertical and lateral wear amounts are obtained on the cross section by slicing the aligned three-dimensional point clouds data. Finally, the proposed system and method are validated by comparing the vertical wear amounts with the two-dimensional laser scanning and contact measurement results.

Open-sector rapid-reactive collision avoidance: Application in aerial robot navigation through outdoor unstructured environments

A new reactive collision avoidance method for navigation of aerial robots (such as unmanned aerial vehicles (UAVs)) in unstructured urban/suburban environments is presented. Small form-factor aerial robots, such as quadcopters, often have limited payload capacity, flight time, processing power, and sensing capabilities. To enhance the capabilities of such vehicles without increasing weight or computing power, a reactive collision avoidance method based on open sectors is described. The method utilizes information from a two-dimensional laser scan of the environment and a short-term memory of past actions and can rapidly circumvent obstacles in outdoor urban/suburban environments. With no map required, the method enables the robot to react quickly and navigate even when the enivornment changes. Furthermore, the low computational requirement of the method allows the robot to quickly react to unknown obstacles that may be poorly represented in the scan, such as trees with branches and leaves. The method is validated in simulation results and through physical experiments on a prototype quadcopter system, where results show the robot flying smoothly around obstacles at a relatively high speed (3 m/s).

Micro air vehicle local pose estimation with a two-dimensional laser scanner: A case study for electric tower inspection

Automation of inspection tasks is crucial for the development of the power industry, where micro air vehicles have shown a great potential. Self-localization in this context remains a key issue and is the main subject of this work. This article presents a methodology to obtain complete three-dimensional local pose estimates in electric tower inspection tasks with micro air vehicles, using an on-board sensor set-up consisting of a two-dimensional light detection and ranging, a barometer sensor and an inertial measurement unit. First, we present a method to track the tower’s cross-sections in the laser scans and give insights on how this can be used to model electric towers. Then, we show how the popular iterative closest point algorithm, that is typically limited to indoor navigation, can be adapted to this scenario and propose two different implementations to retrieve pose information. This is complemented with attitude estimates from the inertial measurement unit measurements, based on a gain-scheduled non-linear observer formulation. An altitude observer to compensate for barometer drift is also presented. Finally, we address velocity estimation with views to feedback position control. Validations based on simulations and experimental data are presented.

A 3D Polymer Based Printed Two-Dimensional Laser Scanner

A two-dimensional (2D) polymer based scanning mirror with magnetic actuation is developed for imaging applications. Proposed device consists of a circular suspension holding a rectangular mirror and can generate a 2D scan pattern. Three dimensional (3D) printing technology which is used for implementation of the device, offers added flexibility in controlling the cross-sectional profile as well as the stress distribution compared to the traditional planar process technologies. The mirror device is developed to meet a portable, miniaturized confocal microscope application in mind, delivering 4.5 and 4.8 degrees of optical scan angles at 111 and 267 Hz, respectively. As a result of this mechanical performance, the resulting microscope incorporating the mirror is estimated to accomplish a field of view (FOV) of 350 µm × 350 µm.