Laser Triangulation Measurement Research Articles

Kinetics of elastic recovery in roll compaction

Elastic recovery (ER) has been investigated and discussed extensively in the field of tableting. However, until now only limited data is available regarding ER in roll compaction. Therefore, a previously established in-line measurement technique was rolled out to further investigate the kinetics of ER in roll compaction and the effects of specific compaction force (SCF) and roll speed (RS). In-line laser triangulation measurements at different positions within a roll rotation as well as measurement over time after the process has been stopped were utilized. Pure microcrystalline cellulose (MCC) and two placebo powder blend formulations were analysed. Successful fit of the contained ER profiles emphasized that the ER on the roll surface is build out of two exponential kinetics. Starting with a dominating fast ER (ERA), characterized by a high increase of the ribbon thickness after passing the gap width, followed by a slower ER (ERB). Sigma minus plot analysis showed that increasing RS led to an accelerated ERA and ERB which was related to the viscoelastic behaviour of MCC. The SCF only had an effect on the kinetics of ER if a brittle filler was added to the mixture. The conducted study established the first approach in literature to characterize the kinetics of ER in roll compaction. It supports the understanding and characterization of relaxation times and the effect of the RS and SCF in roll compaction.

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.

Laser Triangulation Measurements on Moving Samples With Reduced Lateral Feature Uncertainty

Laser Triangulation Measurements on Moving Samples With Reduced Lateral Feature Uncertainty

Laser Triangulation Based In-Line Elastic Recovery Measurement for the Determination of Ribbon Solid Fraction in Roll Compaction

Process Analytical Technology (PAT) plays a crucial role in the design of today's manufacturing lines as continuous manufacturing becomes more important. Until now PAT tools to measure the ribbon solid fraction (SFribbon) in-line are not commonly used in roll compaction. The aim of this study was therefore to establish a new approach as PAT for in-line ribbon solid fraction determination. Different placebo formulations with different binders and one formulation containing active pharmaceutical ingredient were investigated using in-line laser triangulation measurement to detect the ribbon thickness after compaction. With this the ribbon elastic recovery was determined in-line (ERin−line) while the ribbons are attached to the roll surface. It was found that the ratio (ERratio) between the total elastic recovery and ERin−line is formulation specific and not influenced by any process parameters. This enables ERratio as prediction tool for SFribbon, if the solid fraction at gap (SFgap) width is known. SFgap was determined with ribbon mass flow measurement or based on the Midoux model, a simplified Johanson model, gaining two prediction models for SFribbon. Both models showed good agreement of the predicted SFribbon and the measured one.

Laser triangulation measurement of blade oscillation in a transonic compressor cascade

The paper describes a method for optical measurement of oscillation of blades in a linear cascade designed for flutter research. The method uses laser triangulation, which measures the distance between the sensor and the oscillation object. The distance can be recalculated to angular displacement of the blade. However, the relation is nonlinear due to the curvature of the blade. The nonlinear dependence between the distance and angular displacement is derived and quantified analytically. The paper further analyzes the influence of light refraction in the optical window, surface quality and sensor inclination. A procedure for the nonlinear calibration is proposed and used during wind tunnel measurements in a blade cascade with forced oscillation of the middle blade.

МЕТОД ТЕХНІЧНОГО ДІАГНОСТУВАННЯ КАНАЛІВ СТВОЛІВ ВОГНЕПАЛЬНОЇ ЗБРОЇ НА ОСНОВІ ВИЗНАЧЕННЯ ЇХНІХ ГЕОМЕТРИЧНИХ ХАРАКТЕРИСТИК

The work is devoted to the justification of the method of technical diagnosing of the bores of firearms, which is based on determining their geometric characteristics using a laser triangulation measurement tool and creating a detailed image of the surface in a cylindrical coordinate system. An analysis of modern methods of technical diagnosing of the bores of firearms was carried out, and the contradiction between their capabilities and the growing needs of practice was determined. The need to create a diagnostic method and tool that would ensure obtaining a detailed image of the inner surface of the bore and identifying both the type of defect and the degree of its manifestation is substantiated. The detailed image of the inner surface of the bore should be presented in the form of a data array containing the spatial coordinates of the points on its inner surface and the corresponding values of the radius of the bore. It is shown that it is most expedient to diagnose the bore using the laser triangulation method, which makes it possible to determine their geometric characteristics and create tables of coordinates of surface points in a cylindrical coordinate system with a given step. The number of points at which measurements are made in each of the sections is chosen depending on the purpose of the research and the requirements for detailing the technical condition of the surface of the bore. The general principle of measurement based on the application of the triangulation method of determining distances to the controlled surface of the object, as well as the structure of the sensor and the features of its integration with the measuring probe and the positioning module, are considered. An approach to determining the required amount of measurement information and the number of control points is proposed. The method of grouping the measurement results into the given options for their presentation for the next analysis is defined.

Laser triangulation measurement system with Scheimpflug calibration based on the Monte Carlo optimization strategy.

We propose a linear laser triangulation measurement system using Scheimpflug calibration based on the Monte Carlo optimization strategy. A Scheimpflug inclination camera calibration model is introduced in the measurement system for improving the image definition in small-range measurements with a large depth-of-field. To address the nonlinear optimization problem between the instrument resolution and measurement range, the Monte Carlo method is adopted to determine the optimal optical parameters (scattering angle, Scheimpflug angle, and focus length) in a practical measurement system. Furthermore, we experimentally constructed the measurement system to demonstrate the measurement precision by measuring a standard step block (measurement range 15 mm). The performance parameters of the maximum measurement error, maximum standard deviation, and linearity are obtained as ±7 μm, 0.225 μm, and 0.046%, respectively. Finally, the proposed measurement system based on the Monte Carlo optimization strategy is promising for high-precision measurements in industrial applications and provides guidance for optimizing the design parameters of ranging measurement sensors.

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.

A Smartphone Integrated Hand-Held Gap and Flush Measurement System for in Line Quality Control of Car Body Assembly.

This paper presents the design and the characterization of a portable laser triangulation measurement system for measuring gap and flush in the car body assembly process. Targeting Human in the Loop (HILT) operations in the manufacturing sector, and in line with the vision of human empowerment with Industry 4.0 technologies, the instrument embeds features to ease operators’ activity and compensate possible misuse that could affect the robustness and the quality of data acquired. The device is based on a smartphone integrated with a miniaturized laser triangulation system installed in a cover. The device embodies additional sensors and control systems in order to guarantee operators’ safety (switching on and off the laser line based on specific conditions), support operators during the measurement execution task, and optimize the image acquisition process for minimizing the uncertainty associated to the measurement. The smartphone performs on-board processing and allows Wi-Fi communication with the plant IT infrastructure. Compliance to Industry 4.0 requirements is guaranteed using OPC-UA (Open Platform Communications—Unified Architecture) communication protocol enabling the exchange of live data with the plant middleware. The smartphone provides also an advanced high-resolution color display and well proven and ergonomic human–machine interfaces, which have been fully exploited in the design. The paper introduces the system optical layout and then presents the algorithms implemented to realize the gap and flush measurement. The paper finally presents the calibration of the instrument and estimates its calibration uncertainty in laboratory conditions. Then it discusses how performance decays when the operator handles the instrument on a reference car body. Finally, it shows the analysis of uncertainty when the device is used on real car bodies of different colors in a production line. It is observed that the measurement uncertainty of the whole measurement chain (measurand + instrument + operator + uncontrolled environmental conditions) is larger than the instrument calibration uncertainty because the measurement process is affected by the operator and the variable conditions of the production line.

Sensor-Realistic Simulations for Evaluation and Planning of Optical Measurement Systems With an Application to Laser Triangulation

Image acquisition plays a central role in optical measurement systems. To configure machine vision setups, engineers often go through some empirical best practices to evaluate the measurement in different geometrical and optical configurations. This approach turns out to be expensive, tedious, and sometimes even unsuitable for nontrivial tasks. To automate this process, realistic synthetic images allow us to evaluate and optimize imaging setups without employing physical parts and sensors. Available computer graphics rendering techniques can be very beneficial for realistic simulation of images in machine vision systems. Simulating optical measurement systems, however, requires taking extra simulation components into account, including the wave optics effects and realistic spectral response and stochastic noise of the digital sensor. In this article, we focus on physical simulation of optical measurement systems and further propose and verify a sensor-realistic simulation framework for this purpose. We demonstrate the results in different steps for a laser triangulation measurement system, and verify them against experimental images, both qualitatively and quantitatively. The measurement with a laser light source results in wave optics effects which cannot be modeled by conventional ray-tracing methods. The concepts of this article are, however, general to many optical systems with both coherent and/or incoherent light sources. The agreement of simulations with reality is a promising proof of concept for machine vision experts, to move towards automating the setup planning process by means of sensor-realistic simulations.

Experiments on High-Temperature Hypersonic Fluid–Structure Interaction with Plastic Deformation

This study provides experimental results on hypersonic fluid structure interaction (FSI) with focus on high thermal loads and plastic deformation designed for validation of coupled simulations. We conducted experiments with thin panels in a high enthalpy flow environment in the arc-heated wind tunnel L3K. Time-resolved surface deformation and temperature fields were measured. The challenging digital image correlation (DIC) measurements through the flow field were validated by comparison to internal laser triangulation measurements. The resulting data set allows a detailed analysis of the coupling between thermal loads and structural deformation. We obtained severe localized heating and resulting deformations of more than 12 times the panel thickness. In addition to single exposure measurements, the effects of repeated load cycles were investigated.

Weld Quality Verification by Using Laser Triangulation Measurement

Adaptive welding parameter control and robotic workpiece positioning feedback control impose a strict requirement on the dimensional measurement of the workpieces and fittings. Laser triangulation-based vision systems are commonly used to measure and compensate for the workpiece positioning inaccuracies as well as the inconsistencies of the weld seam. In this study, the laser triangulation system’s accuracy and reliability for welding quality control, workpiece positioning and welding parameter control are analyzed. The combined accuracy of both applied laser sensor and robot are analyzed and compared with the welding requirements. The study shows that the measurement and positioning accuracy of the robot is sufficient on reliable welding torch positioning for reaching and fulfilling the requirements of ISO 5817 level B class weld consistently. The measurement accuracy of the presented system and repeatability of the robot is well within the suitable measurement window for achieving consistent weld quality.

Novel laser triangulation measurement method for screw rotor profile under multi-factor constraints

In order to achieve optimal control of the screw rotor process, a novel measurement method using laser triangulation under multi-factor constraints was introduced to achieve online measurement of the screw rotor profile. This method involved the integration of a 4-axis motion system, which is used to adjust the laser probe, with a laser displacement sensor (LDS), which is used to measure the screw rotor profile. Firstly, the effect of laser beam positioning on measurement accuracy was analyzed experimentally in conjunction with an improved LDS error compensation model. Then, according to the characteristics of rotor profiles, a laser-measurement trajectory planning algorithm for the rotor profile under multi-factor constraints was developed. Finally, the comparison study between the traditional contact measurement (P65) and the proposed measurement demonstrates that the proposed method has not only kept the advantages of traditional contact measurement, but also shown good performances and high measuring precision.

Particle Filter With Unknown Statistics to Estimate Liquid Level in the Silicon Single-Crystal Growth

In the process of silicon single-crystal growth, the detection of melt level is an important step to ensure that the grown silicon single crystal is of high quality. Since there exist many mechanical motions, chemical interactions, thermal convection, and so on, it is extremely difficult to obtain the noise statistics of the liquid-level data. To attain a high-accuracy detection of liquid level with unknown noise statistics, we present an extended set-membership-based particle filter (PF). The key points are as follows. We construct a nonlinear state-space model for liquid-level detection system based on the kinematic principle and laser triangulation measurement principle and cast the detection problem of the liquid level into a state estimation problem. Based on this model, we use the extended set-membership estimation theory to generate an ellipsoid set that contains the true value of the liquid-level state. To overcome the difficulty of drawing particles under the case of unknown statistics noise, we draw particles from a Gaussian distribution in the obtained ellipsoidal set. In order to resample particles when the measurement noise statistic is unknown, we introduce a cost function to obtain the weights of the particles, and the ultimate estimation of liquid level is calculated by the weighted particles after the resampling procedure. Comparing with the extended Kalman PF (EPF) and the cost-reference PF (CRPF), the proposed algorithm has higher estimation accuracy. Some simulation and experiment results are presented to illustrate the effectiveness of the proposed method.

Gear Tooth Profile Reconstruction via Geometrically Compensated Laser Triangulation Measurements.

Precision modeling of the hydraulic gear pump pressure dynamics depends on the accurate prediction of volumetric displacement in the inter-tooth spaces of the gear. By accurate reconstruction of the gear profile, detailed transient volumetric information can be determined. Therefore, this paper reports a non-contact gear measurement device using two opposing laser triangulation sensors, and the key geometrical models to reconstruct the profile with geometrical error compensation. An optimization-based key parameter calculation method is also proposed to find the unknown orientation of the sensor. Finally, an experimental setup is established, the performance of the device is tested and the geometric model is validated. Initial results showed that the method is able to reconstruct the target tooth profile and compensated results can reduce the geometrical error by up to 98% compared to the uncalibrated ones.

Laser triangulation measurement model based on least square polynomial fitting method

Laser triangulation measurement model based on least square polynomial fitting method

Full simulation model for laser triangulation measurement in an inhomogeneous refractive index field

The optical inspection of wrought hot workpieces between subsequent forming steps of a multistage process chain can yield diverse advantages. Deficient components can be detected in an early forming stage. Moreover, the eliminated cooling economizes heating energy. The present workpiece temperature can be exploited in the following chain steps. Challenges arise due to the heat input into the air surrounding the workpiece, as triangulation techniques rely on homogeneous optical conditions. The effect of an inhomogeneous refractive index field (RIF) in air on a 3-D geometry measurement by optical triangulation is modeled exemplary by a virtual measurement of a hot cylinder. To our knowledge, this is the first simulation approach that fully considers both light deflection from the illumination unit to object and from object to camera. Simulated measurement results in a homogeneous and an inhomogeneous RIF are compared. The presented approach predicts measurement deviations in inhomogeneous optical media and can help to design actuated or computer-assisted compensation routines in order to reduce deflection effects when measuring hot objects.

Error analysis and correction for color in laser triangulation measurement

With the aim to improve the accuracy of laser triangulation measurements, this paper proposes to analyze the error caused by different colors of a measurand surface and proposes a compensation method. By investigating the fundamentals of laser triangulation, the color error is obtained via the Phong model, while the relationship between the measurement error and color is obtained through experiments. Based on the above results, a color error compensation method is proposed, which produces a color-error library according to the error of the different colors. Thus, the correlation between the error and color of the measurand surface is also calculated. The experimental data demonstrates that this method can reduce the error to 10% and maintain the color measurement error to within 90 μm. Moreover, this technique is of great significance to measure a measurand surface with different colors.

Melt level measurement for the CZ crystal growth using an improved laser triangulation system

Abstract An improved image-based laser-triangulation measurement system is proposed in this paper to measure the melt level in CZ crystal pullers. The system uses a line laser to overcome the deficiency of the traditional laser-triangulation system caused by the heat shield. The laser line projected to the melt surface and the bottom of the heat shield generates two scattered bars, which are captured by the camera. The relationship between the pixel distance of the two bars and the melt level is studied. An optimized adaptive laser bar detection approach is applied to measure the melt level quickly and accurately. Three experiments have been made to demonstrate the advantages of the system. The calibration experiment shows the system has a measurement resolution of 0.0755 mm. The accuracy experiment proves the system has a precise measurement performance and the robustness experiment demonstrates the system using a truncated mean filter is reliable and robust.

Spectral selective and difference imaging laser triangulation measurement system for on line measurement of large hot workpieces in precision open die forging

This paper presents the development of a measuring system for on line measurement of large hot workpieces in precision open die forging. The major advantage of the system is in achieving more accurate final dimensions of workpieces, reduction of finish allowance and reduced losses of workpiece material due to additional milling. Workpiece cross section is measured based on laser triangulation principle. A novelty in the developed measuring system is in avoiding light interferences from a hot glowing workpiece and workshop environment based on operation in green light spectrum and the use of difference imaging principle supported by laser switching. Workpiece dimensions are determined from the geometry primitives interpolated to the measured cross section. Measuring uncertainty, spatial resolution and environmental disturbances are analysed.