Laser Triangulation Research Articles

Blade tip clearance measurement method based on blade tip timing without the once per revolution sensor

Abstract The rotor blade tip clearance (BTC) of an aeroengine is a critical parameter that significantly impacts its performance and safety. Accurately determining dynamic BTC has been a focal point of research in experimental testing. Among the effective measurement methods for dynamic BTC, the laser triangulation method based on blade tip timing (BTT) stands out. However, this method typically relies on an once-per-revolution (OPR) sensor for rotor speed and blade serial number information during measurement, leading to increased installation and maintenance costs as well as additional measurement uncertainties. In response to this challenge, this paper presents two signal processing method that eliminate the need for an OPR sensor. The first method, referred to as "none OPR method 1," closely follows the measurement principles of the traditional method but employs a skewed dual light probe (SDLP) signal to extract rotational speed information, thus obviating the need for an OPR sensor. The second method, "none OPR method 2," introduces a novel data processing approach that enables BTC determination without any source of rotor speed information. Both methods utilize dynamic and static BTC matching techniques to identify blade serial numbers and achieve BTC measurement without an OPR sensor on a simulated rotor experimental bench. Comparative analysis with traditional method BTC measurements reveals that, under stable rotor speeds, all methods achieve similar levels of accuracy and repeatability errors within 0.025mm. However, when dealing with variable speed conditions, the traditional method's accuracy is significantly affected. None OPR method 1 mitigates the impact of rotor speed changes to some extent, while none OPR method 2 remains unaffected by such changes. Importantly, both none OPR methods demonstrate the capability to measure blade-by-blade tip clearances akin to the traditional method.

Study on the polymerization shrinkage and mechanical-physical properties of dental resin composite modified by polyurethane dimechacrylate and glass flake fillers

ObjectivesWe intend to explore the polymerization shrinkage and mechanical-physical properties of the dental resin composite modified by polyurethane oligomer PU-MA and glass flakes fillers, and provide some experimental information for developing new dental materials. MethodsBased on Bis-GMA/TEGDMA, the new dental resin composite was hand fabricated by combining PU-MA with different content (65 wt% ∼ 75 wt%) of glass flakes/Si-Al-borosilicate glass mixed fillers. The kinetics of polymerization shrinkage was investigated by using an experimental set-up based on laser triangulation. The mechanical-physical properties of specimens after 60 days water immersion and 5000 times thermo-cycles were measured by three-point bending test and micro vickers hardness tester. Data were submitted to one-way ANOVA/LSD-test (α = 0.05). Independent sample T test was used to analyze the data before and after aging. Two-way ANOVA was adopted to analyze the effect of composition and aging condition on the mechanical-physical properties (α = 0.05). ResultsPU-PG-75 % performs lower volume shrinkage (1.35%). As the increase of filler content, the water sorption and solubility increased and the depth of cure decreased significantly (P < 0.05). After aging, the flexural strength, elasticity modulus and vickers hardness of commercial products dropped obviously and PU-PG-75wt% was relatively stable. Conclusions20 wt% PU-MA could decrease the volume shrinkage of dental resin composite effectively. 60 days water immersion and 5000 times thermal cycles simultaneously resulted in a significant reduction in the flexural properties for experimental materials. PU-PG-75 % may have the potential to be taken as a low shrinkage dental resin composite with good mechanical properties. Clinical SignificanceThis new synthesized composite could perform low polymerization shrinkage and better mechanical resistance, which may provide a new idea for improving the lifespan of direct restoration.

A novel wafer defocus measurement method for spot-scanning imaging system using laser triangulation

Abstract For spot scanning dark-field scattering technology, the defocus caused by the change in wafer surface height decreases the defect detection rate and size measurement repeatability. The demand for accurately and rapidly measuring the wafer surface height online is becoming increasingly urgent. The defect detection system integrates scattering, reflection, film thickness, and topography defect detection channels. The integration of laser-triangulation-based defocus measurement into the bright-field optical path is proposed. The laser beam is directed onto the surface of the wafer, and the reflected light is transmitted through a lens onto the photosensitive surface of a four-quadrant detector. This detector captures both the strength and position of the reflected signal simultaneously. In this paper, a triangulation-modified model is established to obtain the height of each inspection spot on the wafer surface through the position signal of the reflected image. When the signal-to-noise ratio of the simulated reflection image position is 20 dB, the signal-to-noise ratio of the height measurement resolved by the triangulation-modified model is 41 dB, and the measurement error is less than 0.2 μm, indicating that the model has a noise suppression effect. The spot-scanning imaging system is established, and the height measurement results of the triangulation measurement model are verified using a laser interferometer. Within the travel range of 69 μm, the system has a measurement accuracy better than ±1 μm and a measurement repeatability better than ±0.2 μm, which meet the measurement requirements of the spot-scanning imaging system. The system is utilized for defect detection and defocus measurement of the wafer surface, along with the motion mechanism, to accurately and rapidly obtain the height distribution of the wafer surface.

Laser Scan Compression for Rail Inspection

The automation of rail track inspection addresses key issues in railway transportation, notably reducing maintenance costs and improving safety. However, it presents numerous technical challenges, including sensor selection, calibration, data acquisition, defect detection, and storage. This paper introduces a compression method tailored for laser triangulation scanners, which are crucial for scanning the entire rail track, including the rails, rail fasteners, sleepers, and ballast, and capturing rail profiles for geometry measurement. The compression technique capitalizes on the regularity of rail track data and the sensors’ limited measurement range and resolution. By transforming scans, they can be stored using widely available image compression formats, such as PNG. This method achieved a compression ratio of 7.5 for rail scans used in the rail geometry computation and maintained rail gauge reproducibility. For the scans employed in defect detection, a compression ratio of 5.6 was attained without visibly compromising the scan quality. Lossless compression resulted in compression ratios of 5.1 for the rail geometry computation scans and 3.8 for the rail track inspection scans.

First step toward designing effective real-time control systems in laser directed energy deposition

In-process monitoring and control are essential for quality assurance and consistency of laser-based directed energy deposition processes. Detection of irregularities during deposition in terms of defects or flaws is based on in situ monitoring of output process parameters such as temperature, melt-pool geometry, or deposition height. The real-time feedback of these output parameters allows the development of control strategies for real-time adjustment of input process parameters, such as laser power or scanning speed, to correct detected deviations from the desired output process parameters. Therefore, criteria such as sensitivity, stability, correlation, trends, and interactions of the input-output process parameters have a direct impact on controller design, establishing, for example, control limits or tolerance ranges of the output parameters. This paper focuses on the study of the characteristics of output process parameters to input process parameters. This research involves analyzing and comparing the deposition of single tracks under various input process parameters, including laser power and scanning speed. Melt-pool geometry and temperature are estimated from a visual camera and a hyperspectral line camera, whereas the final deposition geometry is obtained from a laser triangulation scanner. The results show the linearity between input and output process parameters, the steadiness of the output process parameters, the relation between melt-pool and final deposition, and offer insights to design effective in-process control systems.

An evaluation of six techniques for measuring porosity of ribbons produced by roller compaction

Ribbon porosity is a critical parameter to monitor in the roller compaction process. In this study, six techniques for measuring the porosity of solid compacts, i.e., manually by caliper (Caliper), X-ray microtomography (µCT), off-line near-infrared spectroscopy (NIR), laser triangulation (Laser), mercury intrusion porosimetry (MIP), and GeoPyc, were compared using a set of rectangular ribblets of microcrystalline cellulose (MCC). These ribblets, which were compressed at 8–––130 MPa on a compaction simulator, exhibited porosities over the range of 0.09 – 0.52. Subsequently, porosities of MCC ribbons made on a roller compactor at specific roll forces of 1.8 kN/cm and 8.8 kN/cm were measured. The Caliper method is convenient for samples with a simple shape but not suitable for real ribbons. The accuracy of GeoPyc measurement relies on accurate conversion factor (unit in cm3/mm), sample shape and size, and sufficient sample volume percentage in the medium. The µCT data is more accurate at lower porosities (< 0.2), while the MIP data is more accurate at higher porosities (> 0.4). The Laser method has good accuracy and is more reproducible compared to other methods in the ribblets measurement. The NIR method is fast, which makes it suitable for in-line monitoring of changes in ribbon quality, but porosity quantification is sensitive to sample presentation, such as surface curvature and roughness. These insights could assist in the choice of the most appropriate method for monitoring ribbon porosity to guide the development and optimization of a roller compaction process for a given formulation.

Optical Surface Roughness Estimation Using Artificial Intelligence

ABSTRACTA system for analysing steel plates is presented for an application in the wind power industry. The objective of the system is to assess the surface roughness as a preliminary step for the application of an anti‐corrosion coating. A number of noncontact sensor systems were considered, with the laser triangulation scanner proving to be the optimal solution. The samples are analysed in a test stand and the roughness is measured with this optical system. At the same time, the surface is recorded with a CMOS camera. An AI model is created from the sensor fusion of both systems, which can classify individual segments of the surface as well or poorly blasted. In the following step, the surface roughness is estimated as the Rz parameter by another AI model. An error of less than 6 μm is achieved.

Automatic optimization design of laser triangulation ranging sensors using an improved genetic algorithm

Optical system parameter design is of great importance to ensure the accuracy of asymmetry systems such as laser triangulation ranging systems. However, the system parameter determination often depends on the experience and manual attempts of designers, which is not only time-consuming but also inevitable to introduce human errors. Therefore, in this paper an automatic optimization design method based on nonlinear programming genetic algorithm with elitism strategy (E-NPGA) is proposed, to accurately and fast determine the optimal system parameters of laser triangulation ranging systems assisting in improving the measurement accuracy. Firstly, an optimization model of system parameters is developed under the Scheimpflug rule establishing the constraints for various measurement resolutions and ranges. An image size constraint is constructed for the first time to improve and evaluate the parameter optimization. Secondly, the E-NPGA is proposed with nonlinear optimization and elitism strategy, which can determine the optimal system parameters in 15 iterations avoiding local extremum. In design examples, using the E-NPGA determined system parameters ZEMAX simulation and experimental results of the parameters depended image spot size show a slight relative difference below 0.6%. Moreover, the experiment results demonstrate the sensor system designed by using the E-NPGA enables a distance measurement with submicron absolute error and 10−4 relative uncertainty. The automatic optimization method proposed in this paper is compared with the conventional GA method and PSO method, and it is validated that the convergence accuracy of the proposed method is much higher than the conventional ones.

High-precision docking of wheelchair/beds through LIDAR and visual information.

To address the low docking accuracy of existing robotic wheelchair/beds, this study proposes an automatic docking framework integrating light detection and ranging (LIDAR), visual positioning, and laser ranging. First, a mobile chassis was designed for an intelligent wheelchair/bed with independent four-wheel steering. In the remote guidance phase, the simultaneous localization and mapping (SLAM) algorithm was employed to construct an environment map, achieving remote guidance and obstacle avoidance through the integration of LIDAR, inertial measurement unit (IMU), and an improved A* algorithm. In the mid-range pose determination and positioning phase, the IMU module and vision system on the wheelchair/bed collected coordinate and path information marked by quick response (QR) code labels to adjust the relative pose between the wheelchair/bed and bed frame. Finally, in the short-range precise docking phase, laser triangulation ranging was utilized to achieve precise automatic docking between the wheelchair/bed and the bed frame. The results of multiple experiments show that the proposed method significantly improves the docking accuracy of the intelligent wheelchair/bed.

Effect of Mechanical Compression on Ionic Conductivity of PEO-LiTFSI Solid Polymer Electrolytes

In the field of energy storage materials, the development of robust solid polymer electrolytes for lithium-ion batteries necessitates an understanding of ionic conductivity when subjected to mechanical stress. Accurate determination of ionic conductivity requires knowing the electrolyte thickness, which is subject to volumetric changes during charging and discharging of solid-state batteries. However, compressive stress reduces the thickness of the electrolyte by an indeterminate amount.This work presents experimental measurements of ionic conductivity as a function of compressive stress, using poly(ethylene oxide) and with bis(trifluoromethane) sulfonimide (PEO-LiTFSI). In this study, we not only measure the stress-strain response of the electrolytes directly, but also monitor the extent of compression during electrochemical impedance spectroscopy (EIS). Compression was applied up to 50% strain for three consecutive cycles, and the typical thickness for the fabricated electrolytes was ~50 µm. EIS testing was performed by using an impedance analyzer, with the electrolyte placed between stainless steel blocking electrodes. Bulk resistance was determined by equivalent circuit modeling of impedance between 100 Hz and 2 MHz. Ionic conductivity κ was calculated from bulk resistance Rb , electrolyte thickness h, and cross-sectional area A, according to the equation κ = h/(Rb·A).In order to measure both stress and deformation simultaneously, a custom positioning stage was engineered to apply prescribed compression. The apparatus has an in-line load cell for force measurements and a laser triangulation sensor for position tracking with submicron resolution. We found that the bulk resistance at room temperature decreases exponentially, with magnitude reduced by approximately five-fold when subjected to compressive stress up to 10 MPa. Beyond ~7 MPa, bulk resistance values were no longer dependent on the amount of applied compression.In addition to mechanical measurements, changes in crystalline and amorphous regions were correlated to the magnitude of compressive stress and the measured ionic conductivity of the electrolyte. For optical imaging with simultaneous EIS measurements, glass slides coated with an indium tin oxide (ITO) film were used instead of stainless steel disks. The extent of crystallinity was visualized by optical microscopy of spherulites through a viewing window when compressed between rigid plates.Figure 1. Apparatus (left) and representative ionic conductivity vs. compressive stress (right) data for a PEO-LiTFSI polymer electrolyte. Figure 1

Error-controlled adaptive machining of aeronautical cabin structures by laser triangulation on-machine measurement.

Laser Triangulation On-Machine Measurement (LTOMM) is being implemented increasingly to inspect aeronautical components accurately and efficiently, with its enhanced application in adaptive machining. This work proposes an error compensation and controlling method for measuring the typical features of steps, holes, and freeform surfaces to improve accuracy. Then, the global path to inspect the cabin's structures is planned by introducing optimization algorithms, thus providing an appropriate sequence to shorten the traveling length. After these, the test piece was designed, measured, and manufactured using the adaptive machining process that integrates the LTOMM. The results show that the measurement errors of steps, holes, and freeform surfaces are +0.0092, -0.006, and +0.0406mm, respectively, and further reduced to +0.0013, -0.0019, and +0.0083mm after error controlling. The cabin's freeform surface was fabricated with the maximum positive and minimum negative errors of +0.184 and -0.123mm, which is evaluated by the mechanical probe. The measured data-driven machining process can guarantee that the error satisfies the required tolerance, promoting the application of the LTOMM process in aeronautical intelligent manufacturing.

Application of a Laser Profile Sensor for the Full-Field Measurement of the Continuous Icing Process of Rotating Blades.

With the advancing energy transition, icing is a growing problem in the wind turbine sector. The development of systems to detect and mitigate icing makes it necessary to understand its basic behavior and characteristics. This paper proposes a method for the continuous and full-field measurement of the icing process of rotating blades, using a single line laser profile scanner. Inside of a climate chamber, a rotor is driven by a motor, while a system of nozzles provides a fine water dust, which leads to ice accumulating on simple NACA blades, which in turn is measured by a triangulation laser. The measurement data are cleared from outliers and presented as a surface in 3D space. An alpha shape is used to reconstruct and extract the volume of the ice between a reference and a measurement surface, using the corresponding Matlab function. Appropriate input parameters for the function and offsetting of the reference surface to improve the results are compared and discussed. The resulting system is able to detect small changes in the ice layer thickness in the sub-millimeter range.

Rail Flatness Measurement Based on Dual Laser Triangulation

Rail Flatness Measurement Based on Dual Laser Triangulation

Online monitoring of the size distribution of lime nodules in a full-scale operated lime kiln using an in-situ laser triangulation camera

To maximize efficiency of the recausticizing process in a pulp mill, producing a reburned lime with high and consistent reactivity is process critical. Prior investigations have demonstrated a correlation between the reactivity of lime and its nodule size, as well as the dusting behavior of the kiln. Therefore, monitoring the nodule size produced in the lime kiln could be a promising indirect method to measure the performance of the lime kiln. The objective of this investigation was to evaluate the utility of a laser triangulation camera for online monitoring of nodule size distribution for the lime kiln. A series of full-scale trials were performed in a lime kiln of a kraft pulp mill in which a camera was installed at the exit conveyor to analyze the lime discharging from the kiln. The nodule size distribution was analyzed for correlation with the lime temperature, flue gas temperature, and rotational speed of the kiln. The monitoring demonstrated temporal stability, and the results showed that the lime temperature had the most significant effect on the nodule size. The rotational speed of the lime kiln and the flue gas temperature showed limited effect on nodule size, but they had significant impact on the specific energy demand. The overall conclusion of the study is that the camera methodology effectively correlates lime temperature with nodule size distribution, and it advocates for the methods of implementation in automating lime temperature control, facilitating the production of consistently reactive lime at a lower specific energy consumption.

Procedure for the Orientation of Laser Triangulation Sensors to a Stereo Camera System for the Inline Measurement of Rubber Extrudate

Abstract. Rubber production is a labour-intensive process. In order to reduce the needed number of workers and the waste of material, the level of digitalisation should be increased. One part of the production is the extrusion to produce gaskets and similar objects. An automated observation of the continuous rubber extrudate enables an early intervention in the production process. In addition to chemical monitoring, the geometrical observation of the extrudate is an important aspect of the quality control. For this purpose, we use laser triangulation sensors (LTS) at the beginning and the end of the cooling phase of the extrudate after the extrusion. The LTS acquire two-dimensional profiles at a constant frequency. To combine these profiles into a three-dimensional model of the extrudate, the movement of the extrudate has to be tracked. Since the extrudate is moved over a conveyor belt, the conveyor belt can be tracked by a stereo camera system to deduce the movement of the extrudate. For the correct usage of the tracking, the orientation between the LTS and the stereo camera system needs to be known. A calibration object that considers the different data from the LTS and the camera system was developed to determine the orientation. Afterwards, the orientation can be used to combine arbitrary profiles. The measurement setup, consisting of the LTS, the stereo camera system and the conveyor belt, is explained. The development of the calibration object, the algorithm for evaluating the orientation data and the combination of the LTS profiles are described. Finally, experiments with real extrusion data are presented to validate the results and compare three variations of data evaluation. Two use the calculated orientation, but have different tracking approaches and one without any orientation necessary.

On-Machine LTS Integration for Layer-Wise Surface Quality Characterization in MEX/P.

Material Extrusion (MEX) currently stands as the most widespread Additive Manufacturing (AM) process, but part quality deficiencies remain a barrier to its generalized industrial adoption. Quality control in MEX is a complex task as extrusion performance impacts the consistency of mechanical properties and the surface finish, dimensional accuracy, and geometric precision of manufactured parts. Recognizing the need for early-stage process monitoring, this study explores the potential of integrating Laser Triangulation Sensors (LTS) into MEX/P manufacturing equipment for layer-wise 3D inspections. Using a double-bridge architecture, an LTS-based sub-micrometric inspection system operates independently from the manufacturing process, enabling comprehensive digitization and autonomous reconstruction of the target layer's topography. Surface texture is then computed using standardized indicators and a new approach that provides insight into layer quality uniformity. A case study evaluating two alternative extruder head designs demonstrates the efficacy of this integrated approach for layer quality characterization. Implementing a generalized layer-wise procedure based on this integration can significantly mitigate quality issues in MEX manufacturing and optimize process parameter configurations for enhanced performance.

Case study using APDMS and RPEMS for SAWL pipes and benefits for offshore pipelay

This paper reviews an Automatic Pipe Dimension Measurement System (APDMS) and a Robotic Pipe End Measurement System (RPEMS) which can measure 19 and 9 parameters with the help of 72 and 6 measurement sensors respectively. APDMS and RPEMS are integrated into one optical measurement system, using laser triangulation, coupled with Systems, Applications and Products in Data Processing (SAP) integration and its own calibration modulus which provides an accurate solution to all pipe measurements. Two longitudinal submerged arc welded offshore projects were executed for an offshore pipe lay with close dimensional tolerances measured using the APDMS for one project and RPEMS for the other project. The radii data, assessed from the newly calculated common centre of all cross-sectional data, was used to line up the two adjacent pipes in a faster and more accurate way. By knowing the shape of the pipe ends based on this radii data, the best relative rotation of these two pipes can be determined and any misalignment will be verified and will stay within the requirements. The extensive database available for each pipe helped to match the line pipes with similar or close out-of-roundness at pipe ends resulting in good fitment of the pipes and ultimately quality welds, together with more pipe joints per day, resulting in a faster completion of the project. This paper shows the significance of using both systems.

Real-time uncertainty reduction in laser triangulation via dynamic speckle correlation

The speckle-induced measurement uncertainty is one of the major bottlenecks to achieve high measurement accuracy in laser triangulation sensors (LTS). Conventional methods for improving uncertainty focus on suppressing speckles and refining centroid extraction algorithms, overlooking the potential information about object motion that speckles inherently contain. To address this deficiency, a dynamic speckle correlation (DSC) method is proposed to reduce speckle-induced measurement uncertainty in laser triangulation systems. This method uses the correlation between speckle patterns and the movement of the object being measured, thereby enabling real-time error compensation without any speckle reduction mechanisms. To verify the effectiveness of the DSC method, we have designed a compact LTS based on oblique incident laser. Extensive experiments demonstrate that, for displacement measurement of objects with surface roughness ranging from Ra0.4 to Ra3.2, the DSC method can effectively reduce the root mean square (RMS) measurement error to 3∼5μm. Compared with using the traditional grayscale centroid method alone, the measurement accuracy after DSC compensation is improved by at least 20%.

Pipe Organ Design Including the Passive Haptic Feedback Technology and Measurement Analysis of Key Displacement, Pressure Force and Sound Organ Pipe

In this work, an organ pipe instrument with a mechatronic control system including the Passive Haptic Feedback technology is implemented. The test bed consists of a motorized positioning stage mounted to a brace that is attached to a bridge on a platform. A simple pneumatic mechanism is designed and realized to achieve the same dynamics pressure for each measurement attempt on the keyboard. This system contain pipes, an air compressor, valves, and a piston connected to applied force pressure on the keyboard of the organ pipe. The pneumatic components, like valves and pressure regulators, mounted on the profile plate are connected to the main air supply line via flexible tubing or hoses to the air compressor and mechanical trucker. The pneumatic system has many types of valves that regulate the air speed, air flow, and power. The combination of valves and air compressor control the air flow and the mechanism of piston and pressure on the keyboard. The mechanical actuator presses the key to be tested, and a load cell detects the applied key force. A laser triangulation measurement system based on a Laser Displacement Sensor measures the displacement of the key during the key depression. The velocity of the key motion is controlled by the pneumatic actuator. A miniature-sized strain gauge load cell, which is mounted on a musical keyboard key, measures the contact force between the probe and the key. In addition, the quality of the audio signal generated by the organ instrument is estimated using the Hilbert transform.

Using a Slit to Suppress Optical Aberrations in Laser Triangulation Sensors.

In this paper, we present a laser triangulation sensor to measure the distance between the sensor and an object without contact using a diffraction slit rather than a traditional lens. We show that by replacing the lens with a slit, we can exploit the resulting diffraction pattern to have finer and yet simpler image analysis, yielding better estimation of the distance to the object. To test our hypothesis, we build a precision position table and a laser triangulation sensor, generate large data sets to test different estimation algorithms on various materials, and compare data acquisition using a traditional lens versus using a slit. We show that position estimation when using a slit is both more precise and more accurate than comparable methods using a lens.