Laser Measurement System Research Articles

Model for surface topography prediction in the ultra-precision grinding of silicon wafers considering volumetric errors

Ultra-precision grinding machine is widely used for thinning silicon wafers. The wafer surface quality is considerably affected by volumetric errors at the functional point of the ultra-precision grinding machine. Therefore, a volumetric error model is established based on the homogeneous transformation matrix (HTM) method. The model is, then, optimized by considering Abbe and Bryan errors induced volumetric errors during the error measurements process. A prediction model for the wafer surface topography is established by combining the manufacturing mechanism of the ultra-precision grinding and the optimized volumetric error model of the ultra-precision grinding machine. Volumetric errors are detected using an author’s group developed laser measurement system and a commercial spindle error analyzer. The model enables to predict the topography and total thickness variation (TTV) of the wafer surface. A group of grinding experiments are performed to verify the effectiveness of the proposed models.

Application of mobile laser measurement system in railway inspection

Abstract Given the time constraints and demanding precision requirements of railway measurements, traditional measurement methods struggle to meet the inspection needs for the future expansion and renovation of extensive rail networks. This paper presents a railway data collection and processing system developed by using mobile laser scanning technology. To address the issue of error accumulation exceeding predefined limits in the positioning algorithm, we conducted a comprehensive study and utilized smoothing algorithms to correct acceleration and attitude angles. This optimization process not only enhances trajectory data but also improves the accuracy of the point cloud. The results indicate that this system holds significant importance in the realms of railway digital survey and design, as well as digital renovation and related areas.

Efficient Method for Identifying Key Errors Based on 21-Geometric-Error Measurement of Three Linear Axes of Machine Tools

Key errors of machine tools have a significant impact on their accuracy, however accurately and quickly measuring the geometric errors of machine tools is essential for key error identification. Fortunately, a quick and direct laser measurement method and system for 21 geometric errors of three linear axes of machine tools were proposed previously, which enables the measurement of all 21 geometric errors via a one-step installation and a three-step automated measurement process. Based on this, to efficiently identify the key error factors, this paper first utilizes the 21 geometric errors obtained from the proposed measurement system to evaluate the contribution of each error to the volumetric errors of machine tools, leading to the building of a 21-geometric-error sensitivity analysis model. Then, experiments are carried out on the vertical machining tool TH5656, and all 21 geometric errors are obtained in 5 min. After this, the volumetric error distribution in the machining workspace is mapped according to the relationship between the geometric errors and the machining errors, and the key error factors affecting the manufacturing and machining accuracy of the TH5656 are ultimately determined. Thus, this new method provides a way to quickly identify key errors of the three linear axes of machine tools, and offers guidance for the machine tool configuration design, machining technology determination, and geometric error compensation.

Fabrication and Characterization of Diaphragm Headphones Based on Graphene Nanocomposites.

The goal of this paper is to fabricate innovative diaphragm headphones using graphene oxide paper (GOP) and GOP/epoxy nanocomposites (GOPC). Initially, graphene oxide suspension is fabricated, and the vacuum filtration method is adopted to make GOP. Then, vacuum bag molding is used to fabricate GOPC from GOP. Hot pressing and associated molds are adopted to fabricate line-indented (GOPC-L) or curve-indented patterns (GOPC-C) on the GOPC. The performances of one kind of GOP and three kinds of GOPC diaphragm headphones are analyzed based on their sound pressure level (SPL) curves achieved by the Soundcheck measurement system. There are four important processing parameters that will influence the performance of the diaphragm, including material type GOP versus GOPC, indented pattern type, sonication time on suspension, and graphene weight fraction in suspension. Compliances of various diaphragms are measured by the Klippel LPM laser measurement system. The results indicate that effects of sonication time and graphene weight fraction on SPL of GOP and GOPC headphones are in reverse, and this is associated with their difference on compliance (modulus), mass, damping ratio, and microstructure uniformity. Either GOPC-L or GOPC-C seems to improve the microstructure of the GOPC, and leads to better SPL performance. The correlation between the previous four factors and SPLs of four kinds of diaphragm headphones is proposed by using scanning electron microscope (SEM) to examine the microstructure of these diaphragms.

Omnidirectional Sensor Design for Distributed Laser Measurement Systems

Distributed laser measurement systems, widely used in high-end equipment such as airplanes, ships, and other manufacturing fields, face challenges in large spatial measurements due to laser plane obstructions and weak intersections. This paper introduces a novel omnidirectional sensor with enhanced adaptability to complex environments and improved measurement accuracy. Initially, an integrated omnidirectional measurement model is established, followed by the analysis of the optical path of the front-end detector, and the design of a signal-conditioning circuit for the photoelectric conversion of the front-end laser signal, Subsequently, a circuit testing platform is established to validate the detection functionality, and the corresponding results indicate that the symmetry of the output waveform is under 10 ns, the response time is under 100 ns, and the maximum detection distance is 22 m. Further, experimental results demonstrate the superiority of omnidirectional sensors over planar ones in complex environments, successfully receiving 360° laser signals. The positional accuracy of the common point to be measured on the top of the omnidirectional sensor is confirmed to exceed 0.05 mm, and the accuracy of the angle of attitude exceeds 0.04°. Using the laser tracker, the measurement accuracy of the system is verified to be better than 0.3 mm. When rotating in the horizontal and pitch directions, the measurement accuracy is better than 0.35 mm and 0.47 mm, respectively, fulfilling the sub-millimeter precision requirement and expanding the application scope of distributed laser measurement systems.

Modeling and analysis of radial throw of micro-milling tool based on tool-attachment errors in high-speed rotating

In the process of micro-milling complex structures, radial throw is likely to cause lower dimensional/form accuracy, which will severely affect the performance of the components. Therefore, it is necessary to investigate the source contributing to the radial throw. According to the kinematic process of the radial throw arising from the attachment errors of the micro milling cutters, a mathematical model considered the attachment errors and the variable section geometry of the micro milling cutters was established to predict the radial throw on the basis of the principle of minimum total potential energy and the Timoshenko beam theory. In comparison to the mathematical model, the proposed finite element model (FEM) presetting the attachment errors shows the effect of modal vibration and the variation of radial throw with attachment errors. To further investigate the environmental factors influencing the radial throw, a measurement method based on the laser measurement system is presented to achieve the on-machine measurement of runout, and a specific extraction method of attachment errors was proposed to help validate the mathematical model. The difference between the results of the mathematical model, FEM, and the experiment is not exceeding 10 % within 3 μm of the maximum runout. Radial throw varies strongly with attachment errors, and the high rotation speed will aggravate the system instability caused by the attachment errors. The main contributor among experimental factors to the variation of runout is the form accuracy of micro milling cutters, accounting for 4.7 % at the highest. This method can provide a theoretical basis for the sources of unbalanced cutting force analysis and the improvement of dimensional/form accuracy.

Measuring the Roller Skew Angle in the Loading Zone of a Cylindrical Roller Bearing With Strain Gauges for Long-Term Monitoring

Abstract Roller skew in roller bearings can cause heat generation in roller–race and roller–rib contacts, thus reducing bearing life. It is significant to obtain the roller skew angle in situ for guiding the bearing design and adjusting the operating conditions. In this study, a method for measuring the roller skew angle in the loading zone of a cylindrical roller bearing with strain gauges is presented. The measurement principle is that the roller skew angle is related to the movement of the contact line between the roller and raceway. The strain gauge array on the outer surface of the outer ring shows temporally separated responses when roller skew occurs. An experimental system is developed to validate the effectiveness of the proposed method for cylindrical roller bearing measurements. A laser measurement system is incorporated into the experimental system to detect the horizontal displacement of the reflected spot using a high-speed camera, which is then converted into the roller skew angle. The calculated roller skew angle from the time shift of the strain response agrees well with the value of a specially modified roller independently measured with the laser detection system. Compared with other measurement methods, the proposed method provides a potential way to achieve the nondestructive measurement of the roller skew angle in actual service for long-term purposes.

Spot Invalid Point Repair Algorithm of Detector Array Measurement System Based on Image Correlation Coefficient

The detector array method has been widely used in the field of high-energy laser far-field spot parameter measurement due to its ability to directly measure the far-field spot of high-energy lasers, wide dynamic range of the detectors, high system sampling frequency, good real-time performance, and suitability for various testing environment requirements. However, during the measurement process, the irradiation of strong lasers or damage to other hardware systems can result in invalid points in the acquired spot images, thereby reducing the measurement accuracy of the system. In order to achieve accurate measurement of laser far-field spot parameters, this paper establishes an experimental model based on the analysis of the sampling spacing of the detector array target and proposes a laser far-field spot invalid point repair algorithm based on image correlation coefficient. Experimental results demonstrate that the algorithm proposed in this paper effectively reduces the impact of invalid points in the measurement system on the measurement accuracy, and achieves accurate measurement of high-energy laser measurement systems.

Laser Beam Quality of Airy Beam in the Jet Engine Exhaust Induced Turbulence

Theoretical predictions of laser beam interactions with jet-engine-exhaust-induced turbulence are of importance for optimization of various optical systems, including LIDARs and airborne laser measurement systems. This paper is based on the extended Huygens–Fresnel diffraction integral and the Wigner distribution function, combined with the recently proposed power spectral density function of atmospheric turbulence induced by jet engine exhaust, to derive the formula for the quality factor of a partially coherent Airy beam in turbulent media induced by jet engine exhaust. Numerical calculations based on the analytical formula show that the smaller the structure constant and outer scale of the atmospheric turbulence induced by jet engine exhaust, the smaller the quality factor of a partially coherent Airy beam, indicating better laser beam quality. At the same time, the larger the generalized parameter and inner scale of the jet-engine-exhaust-induced turbulence and the longer the wavelength of the laser beam, the smaller the corresponding quality factor. The numerical results also show that reducing the coherence length of a partially coherent Airy beam and increasing its characteristic width are beneficial for reducing the quality factor in the atmospheric turbulence induced by jet engines. However, the numerical results show that increasing the coherence length of a partially coherent Airy beam and reducing its characteristic width are beneficial for reducing the quality factor in vacuum. This situation demonstrates significant differences between the interaction mechanisms of an Airy beam in vacuum and in the jet-engine-exhaust-induced turbulence. The results of our discussion contribute to clarifying the mechanism of interaction between an Airy laser beam and random media, as well as the application of a curved Airy laser beam in practical situations.

Application of laser cable measuring systems in production

In order to meet the need of testing cable quality parameters during the production process and make the cable parameters reach the allowable error of the national standard, a design scheme of a laser cable measurement system is proposed. The laser cable measurement system consists of the laser measurement system and data processing system. With ARM as the core controller, the laser and linear CCD sensor are used for online detection and data processing of the cable outer diameter, and the cable outer diameter can be accurately measured without contact. The laser cable measurement system can be directly applied to the cable production line to measure the cable in real time. Under the working conditions of the production line, the system has a simple structure, high precision and good application prospect.

Near-zero beam drift laser tracking and measurement system with two-stage compression structures.

This paper introduces a scheme of near-zero beam drift tracking technology with two-stage compression structures for the coordinate accuracy measurement of a laser tracker. The Galileo telescope system, with a magnification of 21.43, is designed to compress the beam drift in a dual-frequency interferometer. The azimuth and pitch of the beam drift are compressed to 2.41in. and 2.92in., and the compression rates are 95.0% and 91.9%, respectively. The improved four degrees of freedom position-sensitive detector system is used to further compress the beam drift. The peak-to-peak value of the beam drift is 0.9in. in the azimuth direction and 2.1in. in the pitch direction. The standard deviation of azimuth is within 0.15in, and the pitch is within 0.43in. The coordinate accuracy of the laser tracker can be improved 6.85 parts per million by simulation. The developed two-stage compression near-zero beam drift system can be used in the laser tracker to realize large-scale precision instrument geometric measurement.

Wireless Piezoelectric Motor Drive

Nanopositioners with embedded piezoelectric motors are used in a variety of industries, from microscopy to laser processing or measurement systems. A concrete example would be fine-tuning of multiple mirror or lens units in a system. After fine adjustment of a mirror or lens, its position is expected to be maintained when the system is not energized. Features such as small size, direct drive, and maintaining position with high rigidity at power off make inertia-type piezoelectric motors suitable for such “set and go”-type applications. However, wiring with dedicated control electronics for each positioner can increase system complexity. In this study, a wireless driving method for piezoelectric inertia-type motors is introduced for the first time, to the best of our knowledge. In our approach, sawtooth signals for driving a two-phase piezoelectric inertia motor are converted into two complementary pulse-width-modulated (PWM) signals at 1.0 MHz and amplified by class-D amplifier topology, in which GaN transistors are implemented. The amplified complementary PWM signals are applied to a transmitter coil. A receiver coil, which forms an LC network with the capacitances of the piezoelectric multilayer actuators, picks up the driving signals. The filtered voltage waveform by the receiver coil is converted into a modified sawtooth signal, which can operate the piezoelectric inertia-type motor wirelessly. Initial measurements revealed that even a single driving pulse can be transmitted to the receiver coil and precise movements of the slider can be obtained. Mean step sizes for single pulse drive are 140 nm in one direction and 125 nm in the reverse direction.

An improved method to determine the minimum extinguishing concentrations of ultrafine dry powder agents: Taking NaHCO3 and KHCO3 as examples

Ultrafine dry powder agents (UDPAs) are the most potential Halon substitutes due to the high extinguishing effectiveness and excellent environmental friendliness. Nevertheless, the method for obtaining minimum extinguishing concentration (MEC) is flawed and inaccurate. An improved method is proposed by developing the special laser measurement system without powder contamination, the concentration calibration test bench and the cup burner with uniform aerosol generating. The results show that the optimum calibration position is 0.35–0.65 m from the inlet in the y-axis coordinate. More accurate mathematical relationships between the transmittance of the laser measurement system and the NaHCO3 and KHCO3 powders are established, with the errors less than 12%. Upon reaching MECs in the modified cup burner, the flames pulsate, then fade and eventually die. Based on the phenomenon of the sudden change in the transmittance of the laser measurement system at the moment of flame extinguishment, i.e. the “step shape” curve, a more accurate critical criterion point for the MEC is proposed. The measured MECs for methane flames by NaHCO3 (32.2 g/m3) are approximately 4 times that of KHCO3 (8.2 g/m3), consistent with previous studies. The obtained MECs of NaHCO3 and KHCO3 for kerosene flame are verified by 1 m3 total flooding fire extinguishing experiments. The improved method may guide the design of industry fire protection systems based on UDPAs to achieve process safety.

Measurements of Droplet Size and Velocity Distributions During Rod Bundle Core Reflood

As part of the Organisation for Economic Co-operation and Development/Nuclear Energy Agency Rod Bundle Heat Transfer (RBHT) project, an experimental study was performed to investigate the entrained droplet sizes and velocities in a rod bundle under reflood conditions. Experimental results were obtained from the U.S. Nuclear Regulatory Commission/The Pennsylvania State University RBHT test facility using advanced dual laser measurement systems that allow for the simultaneous measurement of droplet behaviors at two axial locations during reflood transients. The RBHT facility is highly instrumented and contains a 7×7 electrically heated bundle with dimensions matching those in commercial pressurized water reactors. The combination of the measurement capabilities of the RBHT facility and the choice of appropriate experimental conditions allows for the measurement of unique droplet size and velocity distributions under different transient reflood conditions.

Matrix data analysis methods for applications in laser beam position measurement modules

This paper addresses the problem of selecting an optimal algorithm suitable for real-time processing of matrix sensor data in laser beam positioning applications. We compare four different algorithms and prove that the chosen one provides the same results in time by several orders of magnitude lower and with negligible memory consumption, making it suitable for use in microcontroller-based sensing modules. Full Text: PDF ReferencesS. Donati, Electro-Optical Instrumentation-Sensing and Measuring with Lasers (Prentice Hall, Upper Saddle River, NJ, 2004). DirectLink K.N. Joo, J.D. Ellis, E.S. Buice, J.W. Spronck, R.H. Munning Schmidt, "High resolution heterodyne interferometer without detectable periodic nonlinearity", Optics Expr. 18(2), 1159 (2010). CrossRef G. Budzyń, J. Rzepka, "Study on Noises Influencing the Accuracy of CNC Machine Straightness Measurements Methods Based on Beam Position Detection", J. Machine Engin. 20(3), 76 (2020). CrossRef Reference materials for PSD and CMOS sensors, , referenced 7-11-2022 CrossRef S. Das, A. Saha, "Laser Beam Position-Dependent PSD-Based Calibrated Self-Vibration Compensated Noncontact Vibration Measurement System", IEEE Trans. Instr. Meas. 68(9), 3308 (2019). CrossRef P. Zhang, J. Liu, H. Yang, L. Yu, "Position Measurement of Laser Center by Using 2-D PSD and Fixed-Axis Rotating Device", IEEE Access 7, 140319 (2019). CrossRef J. Rzepka, G. Budzyn, "Laser measurement system for machine tools", Proc. SPIE 5144, 840 (2003). CrossRef S. Xiang, H. Li, M. Deng et al., "Geometric error identification and compensation for non-orthogonal five-axis machine tools", Int. J. Adv. Manuf. Technol. 96, 2915 (2018). CrossRef N. Hagen, E. Dereniak, "Gaussian profile estimation in two dimensions", App. Opt. 47(36), 6842 (2008). CrossRef S.M. Ross, Introduction to Probability and Statistics for Engineers and Scientists (Academic Press 2014). CrossRef

Research on laser spot location accuracy of low-power laser diode source applied to high precision laser measurement system

The results of laser spot location have an important influence on the accuracy of a laser measurement system. Laser diode (LD) sources have been widely used in recent years because of its low cost and easy integration. Based on the low-power LD source, a conventional laser spot location system was built to study the factors that affect the accuracy of location. We analyzed the influencing factors on laser spot location from two aspects of LD driven and charge coupled device (CCD) imaging, and experiments were conducted to further obtain quantitative analysis results and laws on different influencing factors, including the LD temperature, LD injection current, the size of imaging laser spot and its intensity fluctuation. The drifting RMS and the dithering range R were adapted to evaluate the drift and dither of the laser spot respectively, and the influence laws of location error were discussed. Finally, laser triangulation displacement sensor was taken as an optimization design example when considering the influencing factors studied in this paper. As a result, the RMS accuracy of the design example was 3.6 μm and its repeatability was 2.17 μm. The experimental results provided guidance for the optimization design of laser spot location measurement system.

Die permanente dreidimensionale Datenerfassung geotechnischer Strukturen mittels webbasierter Anwendung terrestrischer LiDAR‐Sensorik

AbstractAs part of the i2MON research project, an integrated monitoring service was developed for the identification and evaluation of soil and slope movements in the context of coal mining. The focus was on the correct integration (to give reliability, accuracy and integrity) of a long‐range laser scanner into a web‐based monitoring system from an engineering geodetic point of view. A web‐based application of terrestrial laser scanners has been developed by cooperation between DMT GmbH & Co. KG and RIEGL Laser Measurement Systems GmbH.The system allows a high temporal and spatial resolution for measured value acquisition by means of permanent installation in the vicinity of a monitored object. This article shows how the laser scanner can be remotely controlled within a web‐based monitoring platform. In addition, the integration of various sensors (including total station, GNSS, geotechnical sensors) within a project into a uniform monitoring platform based on a web interface and the corresponding data analysis (including the automatic detection of geomorphological processes) will be described.

3D Point Cloud Generation Based on Multi-Sensor Fusion

Traditional precise engineering surveys adopt manual static, discrete observation, which cannot meet the dynamic, continuous, high-precision and holographic fine measurements required for large-scale infrastructure construction, operation and maintenance, where mobile laser scanning technology is becoming popular. However, in environments without GNSS signals, it is difficult to use mobile laser scanning technology to obtain 3D data. We fused a scanner with an inertial navigation system, odometer and inclinometer to establish and track mobile laser measurement systems. The control point constraints and Rauch-Tung-Striebel filter smoothing were fused, and a 3D point cloud generation method based on multi-sensor fusion was proposed. We verified the method based on the experimental data; the average deviation of positioning errors in the horizontal and elevation directions were 0.04 m and 0.037 m, respectively. Compared with the stop-and-go mode of the Amberg GRP series trolley, this method greatly improved scanning efficiency; compared with the method of generating a point cloud in an absolute coordinate system based on tunnel design data conversion, this method improved data accuracy. It effectively avoided the deformation of the tunnel, the sharp increase of errors and more accurately and quickly processed the tunnel point cloud data. This method provided better data support for subsequent tunnel analysis such as 3D display, as-built surveying and disease system management of rail transit tunnels.

Investigation on deformation of composite multi-bolted joints considering influences of hole-location errors and installation sequence

In this paper, deformation of composite multi-bolted joints considering hole-location error and installation sequence was investigated. Experiments were conduct to examine deformation and damage of joints with different hole-location error and installation sequence. Deformation of joints was measured by laser measurement system. Bolt-composite interfaces were examined microscopically to reveal damage caused by forced installation. Results showed that hole-location error caused vertical deformation of composite joint. Non-uniform extrusion of up and down hole was caused by forced installation. Besides, deformation mode of hole exit was dominated by deformation asymmetry. Damage distribution was influenced by radial extrusion direction of up and down holes. Thus, damage was distributed no-uniformly along depth of holes. During forced installation, deformation accumulation of multi-bolted joints was generating. Different installation sequences caused various deformation distribution of composite joints. Average deformation were reduced by more than 70% after changing the installation sequence. Conclusions of this paper are of significance for developing deformation model and deformation reduction of composite multi-bolted joints assembly.

Top Surface Roughness Modeling for Robotic Wire Arc Additive Manufacturing

Wire Arc Additive Manufacturing (WAAM) has many applications in fabricating complex metal parts. However, controlling surface roughness is very challenging in WAAM processes. Typically, machining methods are applied to reduce the surface roughness after a part is fabricated, which is costly and ineffective. Therefore, controlling the WAAM process parameters to achieve better surface roughness is important. This paper proposes a machine learning method based on Gaussian Process Regression to construct a model between the WAAM process parameters and top surface roughness. In order to measure the top surface roughness of a manufactured part, a 3D laser measurement system is developed. The experimental datasets are collected and then divided into training and testing datasets. A top surface roughness model is then constructed using the training datasets and verified using the testing datasets. Experimental results demonstrate that the proposed method achieves less than 50 μm accuracy in surface roughness prediction.