Laser Triangulation Research Articles

Shaping and Geometrical Analysis of the Ring-type Test Samples Used in Dimensional Measurements by a Bench-Type Multisensor CMM

The routine measurements of various geometrical quantities in industrial applications are realized by use of a range of optical methods. Optical metrology is a dynamically developing area of the modern science and technology using a hardware solution from simple sensors to advanced computer-controlled measurement systems. In many specific applications dedicated measurement systems are required, which are characterized by much better metrological parameters and wider measuring capabilities than typical systems. Testing of such systems must be carried out on objects with similar properties as the actual objects produced in industrial conditions. The hybrid system for non-contact simultaneous assessment of the surface texture and dimension developed in Koszalin University of Technology (Koszalin, Poland) specially produced sets of ring-type samples with a variable external diameter φz=20.5-30±0.2 mm. This paper presents theprogress of works related to the design, production and analysis of the geometrical dimensions of such sets of test samples prepared for dimensional assessment by using laser triangulation methods. All the stages of this work are all so described and detailed in this paper. These stages included: the determination of assumptions for the preparation of samples, the choosing and characterising of the materials used for samples, the machiningwith a specialized bench-type lathe SK-1, as well as the dimensional measurements used by simple hand measuring instruments and the advanced bench-type coordinate measuring machine Video-Check®-IP 250 produced by Werth Messtechnik GmbH. The results obtained, which were presented in the form of bar diagrams and detailing already discussed, confirmed the dimensional correctness of the machining that was carried out.

Laser triangulation as a fast and reliable method for determining ribbon solid fraction; focus on accuracy, precision, and measurement time

Roller compaction and dry granulation represent well-established unit operations in the pharmaceutical industry. The ribbon solid fraction is classified as a critical quality attribute, that directly impacts final product quality and performance. The development and evaluation of novel methods measuring ribbon solid fraction represent a subject of current research, since novel analyses strategies need to be established for at-, on–, or in-line process monitoring to overcome limitations of end product testing and to set the course for continuous manufacturing. In this study, a novel analytical device, using the principle of laser triangulation, was investigated to asses its potential being used as at-line process analytical technology tool during a roller compaction process. To this end, the laser triangulation device was compared with X-ray micro-computed tomography and powder based volume displacement measurement techniques using different statistical evaluation methods. Special focus was given to accuracy, precision, and total measurement time. The laser triangulation device was confirmed as highly accurate and precise, enabling the shortest total measurement time compared to the other methods. The findings of this study support the idea of implementing the laser triangulation device as a novel at-line process analytical technology tool into a roller compaction process.

Development of automatic inspection device for pipe inner surface

Aiming at the problem of 3D measurement of the inner surface of pipe, this paper develops a new structure of pipe inspection device inside the pipe based on the principle of laser triangulation. The device is composed of motion mechanism and image acquisition system. The three-dimensional shape of the inner surface is reconstructed the image pixel offset. The detection device driven by the motion mechanism can realize the automatic detection of different positions. The experiment shows the steps of the three-dimensional measurement of the inner surface of the pipe, verifies the feasibility of this method.

Improved laser measurement using advanced techniques: A review

AbstractLaser measurement technique has been widely explored and applied in various fields in recent years due to its advantages of high measurement precision and resolution. However, applications in frontier fields such as MEMS motion measurement and robotics control pose have requirement for higher precision and resolution, which promote further studies in improving the performance of this technique. Many advanced techniques have been proposed and applied in the laser measurement system to optimize its performance, and the optimized measurement system has found its way in state‐of‐the‐art applications. In this invited paper, we focus on the latest investigations and new applications of the improved laser measurement methods, especially present recent research works regarding the laser triangulation measurement and the laser heterodyne vibration measurement. At the end, we have discussed further developments and challenges of laser measurement technique.

Underwater fuel assembly deformation measurement with multisensor dual-line structured light.

The fuel assembly is the core component of the nuclear energy system, and its excessive deformation will affect the normal insertion of the fuel rod and endanger safe operation of the reactor. In this paper, we present an underwater fuel assembly deformation measurement system based on 10 sets of visual measurement units. Benefitting from the waterproof design, the shielding-radiation design, the reflective structure design, the dual-optical line laser triangulation principle, and the underwater multilayer refractive geometry, the measurement system has shorter measurement time, higher measurement accuracy, and better environmental adaptability. Through the underwater field measurement and verification of the standard rod and fuel assembly, the bow deformation measurement accuracy of the measurement system is better than 0.3 mm, and the twist deformation measurement accuracy of the system is better than 0.15°. The proposed method allows transient and high-precision measurement in a certain irradiation dose and certain depth water, which provides a strong guarantee for measurement of fuel assembly deformation parameters in deep water and high radiation.

Simple Modification of a Commercial Laser Triangulation Sensor for Distance Measurement of Slot and Bore Side Surfaces.

The aim of the research is to analyze the possibility of the development and realization of a common laser triangulation sensor arrangement-based probe for the measurement of slots and bore sides with the help of a mirror attachment. The analysis shows the feasibility and limits of the solution with respect to the maximum measurement depth and surface distance measurement working range. We propose two possible solutions: one for maximizing the ratio of the measurement depth to the measured bore size and the second for maximizing the total depth, intended for the measurement of slots and large bore sizes. We analyzed measurement error sources. We found that the errors related to the reflection mirror misalignment can be fully compensated. We proved the validity of the proposed solution with the realization of a commercial laser triangulation sensor-based probe and demonstrated a slot side and a bore side surface distance scanning measurement. The probe working range was assessed with regard to the obscuration effect of optical beams.

Wake Shape and Height Profile Measurements in a Concave Open Channel Flow regarding the Target in DONES

Wakes appearing downstream of disturbances on the surface of a water flow in a concave open channel were examined experimentally. The investigated channel geometry was similar to the liquid lithium target in DONES (Demonstration fusion power plant Oriented NEutron Source). The objective of the measurements was to analyze the effect of a disturbance on the downstream layer thickness. For measuring the height profiles in the channel, an optical measurement system based on laser triangulation was developed. It was shown that the wake of the undisturbed flow emerged from the nozzle corner, which was in accordance with analytical solutions. For sufficiently large disturbances at the nozzle edge, the height profiles located downstream showed symmetrical minima and maxima on both sides of the disturbance. The wake depth strongly depended on the diameter and penetration depth of the disturbance, as well as the circumferential position in the channel, which yields to a critical wake depth of one millimeter for the lithium target in DONES.

Process parameter study for enhancement of directed energy deposition powder efficiency based on single-track geometry evaluation

Directed energy deposition (DED) is a widespread laser additive manufacturing process characterized by the simultaneous laser and powder delivery. During the layerwise bounding of the material, many complex interconnected physical phenomena take place in a very short time. Presently, one of the main challenges faced by DED is to enhance the powder deposition efficiency. It is defined as the ratio of powder that has been effectively solidified in the part over the total amount of powder that flowed through the nozzle while the laser was on during the deposition process. Increasing the powder efficiency would allow us to minimize the powder waste, minimize the overall costs of the DED process, and therefore reduce the printed part cost. The present work, therefore, proposes to study the influence of laser beam diameter, stand-off distance, and gas/powder settings on the DED powder efficiency. The considered gas/powder settings are carrier and shielding gas volumetric flow rate, powder mass flow rate, and particle diameter. The efficiency is computed by means of the geometry of 316L stainless steel single-track deposits. The track geometries are evaluated based on the deposition width, deposition height, and area of deposition, all extracted from the deposition profiles measured by means of laser triangulation. Optical micrographs of the single-track transversal cross sections are linked to the obtained powder efficiencies. The final aim is to get insight into the effect of process parameters on the powder efficiency and print quality and to identify the optimal process parameter combination in order to maximize the powder efficiency.

Feasibility analysis of using machinable glass ceramics to manufacture non-contact measurement approach metrological artefacts

Rather than measurement contact methods, non-contact ones are more desirable in case of on-machine and in-process measurement due to their great accessibility and high acquisition rates. Nevertheless, it is well known that these methods commonly present different issues related to the surface properties of the digitized material and other external factors. Thus, an important characterization work must be carried out by exposing each non-contact technique to different conditions. For this characterization work, the use of metrological gage artefacts is mandatory. These artefacts must be made of materials on which non-contact methods will work properly. Therefore, the analysis of new materials is still an important issue nowadays. Among the current possible materials, those that can be easily formed in typical artefact geometries stand out, while maintaining the required properties such as low thermal expansion, high hardness, etc. In this work the feasibility of a machinable glass ceramic named Macor® to produce a metrological artefact to be used with a non-contact digitizing sensor is analysed. Once stated the benefits of this material and proposed some machining conditions, an artefact is manufactured and digitized with a non-contact laser triangulation sensor, comparing its results regarding to a widely used metrological reference system.

Validation of the sandblasting process in the manufacturing of precision spheres for non-contact metrology

In order to ensure the measurements that can be made with non-contact metrology technologies, it is necessary to use verification and calibration procedures using precision artefacts as reference elements. In this environment, the need for increasingly accurate but also more cost-effective calibration artefacts is a clear demand in industry. The aim of this work is to demonstrate the feasibility of using low-cost precision spheres as reference artefacts in calibration and verification procedures of non-contact metrological equipment. Specifically, low-cost precision stainless steel spheres are used as reference artefacts. Obviously, in order for such spheres to be used as standard artefacts, it is necessary to change their optical behaviour by removing their high brightness. For this purpose, the spheres are subjected to a manual sandblasting process, which is also a very low-cost process. The equipment used to validate the experiment is a laser triangulation sensor mounted on a Coordinate Measuring Machine (CMM). The CMM touch probe, which is much more accurate, will be used as a device for measuring the influence of sandblasting on the spheres. Subsequently, the influence of this post-processing is also checked with the laser triangulation sensor. Ultimately, the improvement in the quality of the point clouds captured by the laser sensor will be tested after removing the brightness, which distorts and reduces the quantity of points as well as the quality of the point clouds. In addition to the number of points obtained, the parameters used to study the effect of sandblasting on each sphere, both in contact probing and laser scanning, are the measured diameter form error, as well as the standard deviation of the point cloud regarding the best-fit sphere.

Laser pointing error analysis and compensation method of low-power laser diode source applied to triangulation ranging system.

The pointing drift and dither of the light source greatly reduces the measurement accuracy of the laser triangulation ranging system. In particular, for the low-power laser diode (LD) source, the temperature drift and the dither of the LD itself are more obvious. In this paper, the influence factors on the laser pointing error were analyzed by experiments and simulations based on the triangulation ranging system, and a combined optimization algorithm was proposed to compensate the pointing error. First, we built a platform for testing the directivity of low-power LD and analyzed the directivity drifting error caused by the change in LD temperature, the dithering error of the LD at constant temperature. In addition, the measurement error caused by the thermal deformation of the focusing lens was also analyzed in ZEMAX. Second, polynomial fitting was adapted to preliminarily correct the LD temperature drifting error, and the Kalman filter was introduced to further optimize the measurement results with the aim of improving both the absolute accuracy and repeatability of the laser triangulation ranging system. The experimental results showed that the measurement root mean square error was 0.91 µm and the repeatability was 0.61 µm after the pointing error was compensated by the method we proposed.

A Calibration Method of Inner Bore Profile Detecting on Electromagnetic Railgun

When the electromagnetic rail gun accelerates the armature, the rail is in a harsh condition of high temperature, high pressure and powerful current which will cause a series of grooving phenomenon. In order to detect the inner bore profile, we developed a measuring device using laser triangulation method and basically realized the measurement of the inner bore profile measurement. However, except for the translation and deflection errors, we found that the actual measurement cross-section would be rotated due to the unsteady movement compared with the ideal section. In addition, the previous calibration needs a high-resolution image sensor to get deflection information, it means high cost. In this paper, we analyzed the 3 kinds of deviations and provide a method to calibrate the rotation error using a calibration block. An improved calibration system was designed in low cost and experiment verified the feasibility of the calibration method. The calibration system can be divided into 3 parts, the outside global laser light provides a constant central position, a distance detecting device with a cone laser generator and an inside calibration block. After experiment, the calibration method was effective and the deviation of the profile can be corrected.

Testing the Sandblasting Process in the Manufacturing of Reference Spheres for Non-Contact Metrology Applications

To ensure that measurements can be made with non-contact metrology technologies, it is necessary to use verification and calibration procedures using precision artefacts as reference elements. In this environment, the need for increasingly accurate but also more cost-effective calibration artefacts is a clear demand in industry. The aim of this work is to demonstrate the feasibility of using low-cost precision spheres as reference artefacts in calibration and verification procedures of non-contact metrological equipment. Specifically, low-cost precision stainless steel spheres are used as reference artefacts. Obviously, for such spheres to be used as standard artefacts, it is necessary to change their optical behavior by removing their high brightness. For this purpose, the spheres are subjected to a manual sandblasting process, which is also a very low-cost process. The equipment used to validate the experiment is a laser triangulation sensor mounted on a Coordinate Measuring Machine (CMM). The CMM touch probe, which is much more accurate, will be used as a device for measuring the influence of sandblasting on the spheres. Subsequently, the influence of this post-processing is also checked with the laser triangulation sensor. Ultimately, the improvement in the quality of the point clouds captured by the laser sensor will be tested after removing the brightness, which distorts and reduces the quantity of points as well as the quality of the point clouds. In addition to the number of points obtained, the parameters used to study the effect of sandblasting on each sphere, both in contact probing and laser scanning, are the measured diameter, the form error, as well as the standard deviation of the point cloud regarding the best-fit sphere.

Weld defect inspection based on machine vision and weak magnetic technology

This study proposes a weld defect inspection method based on a combination of machine vision and weak magnetic technology to inspect the quality of weld formation comprehensively. In accordance with the principle of laser triangulation, surface information about the weldment is obtained, the weld area is extracted using mutation characteristics of the weld edge and an algorithm for identifying defects with abnormal average height in the weld surface is proposed. Subsequently, a welding seam inspection process is developed and implemented, which is composed of a camera, a structured light sensor, a magnetic sensor and a motion control system. Inspection results from an austenitic stainless steel weldment show that the method combining machine vision and magnetism can identify defect locations accurately. Comprehensive analysis of the test results can effectively classify surface and internal defects, estimate the equivalent sizes of defects and evaluate the quality of weld formation in multiple dimensions.

Closed-loop control of medium-thickness plate arc welding based on weld-face vision sensing

In one-side welding with full penetration, the use of backing strips helps support molten weld metals, but increases manufacturing cycle time and cost. The backing-free welding technology is under investigation for medium-thickness structural components in the aerospace industry. Its crucial challenge is ensuring complete joint penetration and maintaining a suitable and stable backside bead width. This paper presents an innovative method of controlling weld formation based on weld-face vision sensing in arc welding. A standard laser triangulation setup is used to obtain images of weld pool, and a new weld-face feature ‘depression degree of the weld pool’ is proposed. An image processing procedure is developed to extract the depression degree of the weld pool from images in real-time. The depression degree of the weld pool is found to correlate closely with the backside bead width, and is a better indicator of the backside bead width than the weld pool width, with a higher consistency and a smaller time lag. Employing the depression degree as a feedback signal, a backside bead width control method is developed and implemented. Welding experiments on 6-mm-thick aluminum alloy 2219 plates show that the presented method is remarkably effective in achieving full penetration and keeping backside bead width constant.

STRICT GEOMETRIC CALIBRATION OF AN UNDERWATER LASER TRIANGULATION SYSTEM

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

Displacement Measurement in the Vertical Axis of the Measuring Microscope using Laser Triangulation Sensor

The article deals with assessment of the suitability of using a laser triangulation sensor to measure the displacement in vertical axis of a measuring microscope. Data obtained from sensor calibration are used for determination of measuring range in which the smallest measurement error occurs. Linear approximation of the inverse calibration function is applied to correct systematic errors in reduced measuring range of the sensor. Residual measurement errors of corrected sensor output can be applied in uncertainty calculation for sensor future measurements.

Vibration Measurement Using Laser Triangulation for Applications in Wind Turbine Blades

The blades in a wind turbine are currently manufactured with flexible and light materials, which make them more susceptible to the effects of vibrations when the wind speed is high enough, causing fatigue damage, affecting the functionality of its structure and aerodynamic efficiency. This work presents a comparison of the modal vibration parameters, applied to a cantilever beam, determined with two experimental methods—the use of accelerometers and a proposed optical non-contact method—based on the principle of laser triangulation and photogrammetry techniques. This technique uses the geometric symmetry of the equidistant displacements along the z axis of the beam to obtain the amplitude data. Parameters such as natural frequency and modal form are obtained by fitting the data to a nonlinear equation with a solution which is an exponential/harmonic equation. Also, analytically, these parameters are determined, and a comparison is made between the experimental methods. The result shows that the relative error of the first-order natural vibration frequency is below 1%. The proposed method is simple, efficient, reliable, and it is also a method that has not been applied to the test of wind turbine blades, so its implementation as this type of wind turbine component is an area of opportunity for the validation of modal vibration parameters in the wind industry. An analysis of results is presented showing benefits of the proposed method and its limitations.

Correction to: Measuring the supporting slats of laser cutting machines using laser triangulation

Correction to: Measuring the supporting slats of laser cutting machines using laser triangulation

Development of a small-size laser triangulation displacement sensor and temperature drift compensation method

In practical applications, some special working scenarios need to take into account both narrow space and extreme temperature, which puts more strict requirements on the size and temperature adaptability of the laser triangulation displacement sensor (LTDS). In this paper, a small-size LTDS was developed and the measurement error caused by temperature drift of the sensor was corrected. Firstly, based on direct projection laser triangulation imaging with a reflector unit, a mathematical model of the compact geometry optical structure was established; then, an optimization process of the optical parameters was formulated, and the sensor was assembled. Secondly, a temperature drift error database was built by an extreme temperature experiment, and a general regression neural network model was constructed for error compensation. In addition, root mean square error and execution time were used to evaluate and compare different regression methods. Finally, the experimental results showed that the repeatability accuracy of the proposed sensor was ±2.3 µm, and the temperature linearity was 0.001% F.S. °C−1.