Calibration Of Measurement System Research Articles

Three-dimensional shape measurement method and system calibration for an annular inner-wall.

In the field of industrial measurement, capturing a three-dimensional (3D) profile of an annular inner-wall has been a significant challenge. Current methods typically require multiple scans using a 3D scanner or circular structured light technique, which are inefficient and inconvenient to use. To address this issue, an off-axis measurement method and corresponding system has been proposed in this paper based on circular fringe projection. It can be used to reconstruct the 360° profile of an annular inner-wall in a single scan without any movement. Additionally, a full-field calibration method using ray-tracing for this system has also been presented. Compared to the traditional methods, this method features a simple calibration structure, convenient operation and no need for strict coaxial alignment, which enhances the flexibility of the proposed measurement system and contributes to its high efficiency and the integrity of its output data. Simulation and experimental results confirm the effectiveness and practicality of this measuring approach and system calibration method, providing an alternative solution for automated 3D profile measurement of annular inner-wall.

A stepwise parameter identification strategy for probe-based robot on-machine measurement system calibration based on sensitivity analysis

The probe-based measurement presents an economical and efficient on-machine measurement (OMM) method. However, the low position accuracy of robot presents significant challenges for probe-based robot OMM. To improve the measurement accuracy of robot OMM system, this paper calibrates the geometric parameters of robot OMM system through a closed-loop calibration method with sphere constraint. First, the geometric error model for robot OMM system is established. Given the difficulty in model parameter identification, this paper defines a new index, the relative distance sensitivity index (RDSI), to reveal the contribution of model parameter to relative distance accuracy. Subsequently, sensitivity analysis is conducted on model parameters based on RDSI and model parameters are grouped according to the analysis results. In parameter identification, parameters are identified step by step according to the grouping results. Experiment results show that after calibration, the max distance measurement error of robot OMM system is reduced from 0.54 mm to 0.12 mm.

Full-field three-dimensional system calibration for composite surfaces reconstruction

The accurate calibration of composite surface measurement systems for specular and diffused surface is of great importance in a number of industrial applications. This paper addresses the challenges in calibrating composite surface reconstruction by proposing a comprehensive full-field calibration method. The principal innovation is the construction of a comprehensive reference phase and the pixel-by-pixel calibration of system parameters within the same coordinate system. The details are as follows: (1) construct a complete reference phase for the composite surfaces through external parameter constraints phase fusion and interpolation; (2) calibrate the mapping relationship coefficients, compensate the accuracy degradation of the partial reflection. Experimental results validate the accuracy of the full-field calibration data, demonstrating the effectiveness and feasibility.

Improved calibration method based on phase-slope description in phase-shift deflectometry

Phase-shift deflectometry is a widely used high-precision gradient measurement method for assessing the topography of specular objects. The calibration of phase-shift deflectometry measurement systems involves establishing the phase-slope mapping relationship. This paper analyzes the causes of phase variations at different calibration points in existing phase-slope analysis models. Based on the fact that changes in height simultaneously produce phase variations in two perpendicular directions, a decoupling method is proposed to address the phase ambiguity problem to some extent. Through simulation, the variation in height phase and slope distribution were quantitatively analyzed for a unidirectional inclined plane to validate the proposed algorithm. Additionally, measurement experiments were performed on a unidirectional inclined plane with an inclination angle of −2.584° and a concave mirror with a curvature radius of 779.87 mm. Based on the findings, the decoupling method reduced the relative root-mean-square error of the gradient measurement for the inclined plane in the inclined direction by 2.206% and improved the error range of the curvature radius for the concave mirror from [0.55%, 4.1%] to [0.22%, 3.86%]. By comparing with the existed method, the decoupling method showed a certain advantage in practicality.

Accuracy calibration of the multi-light screen measurement system using array optical signal

Abstract The multi-light screen measurement systems must be calibrated before being come into use, and a calibration method using live-fire practice is generally adopted. However, this method has many shortcomings, such as high cost, high risk and poor efficiency. To effectively improve the measurement accuracy of a multi-light screen measurement system, we propose a calibration method based on array optical signal in the paper. According to the measurement principle of the system, the proposed calibration theory is systematically described. The aim is to map the given measurement results in the form of vector into the specified time sequence. Furthermore, we develop a calibration platform whose core components are an arbitrary waveform generator and a tunable laser, and thus it can generate a set of six optical signals with an exact sequential relationship. After receiving the optical signals, some measurement results with errors are obtained by the system. Many calibration operations are performed to obtain the systematic errors, which are the statistical average of the deviation between the given measurement results and those with errors. Finally, we use the proposed calibration method combined with the error tensor and the traditional one to carry out comparison experiments. The results show that the proposed calibration method is superior to the traditional method in terms of comprehensive performance. In addition, the proposed calibration method relative to the traditional ones has some advantages, such as high efficiency, safety and low cost.

Research on the Measurement System and Remote Calibration Technology of a Dual Linear Array Camera

Abstract In order to accurately measure the flight trajectory of the projectile in a long-distance target range, it is important to establish a vertical target measurement system with a two-line array camera at several positions along the range. In the present work, a calibration system using dual theodolites is proposed to calibrate the vertical target measurement system of a dual linear array camera at different positions along a long target range. The present study investigates the principle of intersection measurement in the vertical target measurement system with a double linear array camera and presents the projectile’s target coordinate measurement formula. The calibration method of the measurement system is developed based on an analysis of the parameters in the projectile coordinate measurement formula. The calibration method only requires calibration of the camera’s distortion coefficient, the optical axis angle, and the principal point, ensuring a simplified and expedited calibration process. After calibration, the vertical target measurement system with a 3 m × 3 m measurement area is simulated and analyzed, yielding an error distribution diagram and identifying the factors that influence the measurement accuracy of the projectile’s target coordinates.

Impact of iodinated oil in proton therapy on relative stopping power of liver post-cTACE

Objective. Conventional transarterial chemoembolization (cTACE) is a common treatment for hepatocellular carcinoma (HCC), often with unsatisfactory local controls. Combining cTACE with radiotherapy shows a promise for unresectable large HCC, with proton therapy preserving healthy liver tissue. However, the proton therapy benefits are subject to the accuracy of tissue relative stopping power (RSP) prediction. The RSP values are typically derived from computed tomography (CT) images using stoichiometric calibration. Lipiodol deposition significantly increases CT numbers in liver regions of post-cTACE. Hence, it is necessary to evaluate the accuracy of RSP in liver regions of post-cTACE. Approach. Liver, water, and iodinated oil samples were prepared. Some liver samples contained iodinated oil. The water equivalent path length (WEPL) of sample was measured through the pullbacks of spread-out Bragg peak (SOBP) depth-dose profiles scanned in a water tank with and without sample in the beam path. Measured RSP values were compared to estimated RSP values derived from the CT number based on the stoichiometric calibration method. Main results. The measured RSP of water was 0.991, confirming measurement system calibration. After removing the RSP contribution from container walls, the pure iodinated oil and liver samples had RSP values of 1.12 and 1.06, while the liver samples mixed with varying oil volumes (5 ml, 10 ml, 15 ml) showed RSP values of 1.05, 1.05 and 1.06. Using the stoichiometric calibration method, pure iodinated oil and liver samples had RSP values of 2.79 and 1.06. Liver samples mixed with iodinated oil (5 ml, 10 ml, 15 ml) had calculated RSP values of 1.21, 1.34, and 1.46. The RSP discrepancy reached 149.1% for pure iodinated oil. Significance. Iodinated oil notably raises CT numbers in liver tissue. However, there is almost no effect on its RSP value. Proton treatment of post-cTACE HCC patients can therefore be overshooting if no proper measures are taken against this specific effect.

Calibration of visual measurement system for excavator manipulator pose

The automatic control of excavator operation trajectories is a pivotal technology for autonomous excavators, with the essential prerequisite being the real-time measurement of manipulator poses. Given the complexity of the operating environment, traditional sensor-based measurement methods face limitations, whereas visual measurement emerges as a promising technique. Accurately measuring excavator manipulator poses involves a crucial aspect: mapping the relationship between image information and poses. First, to address the significant errors in pose prediction encountered with machine learning techniques like artificial neural networks, this work introduces a mathematical model for mapping this relationship, referred to as the pose mapping mathematical model, which includes calibrating model parameters. Second, to address the sensitivity of initial values in the calibration process, we propose a residual-guided initialization algorithm. This algorithm aims to ensure that initial values closely approximate the ground truth values, thus preventing matrix singularity at the source and avoiding parameter estimation divergence. Third, to tackle challenges such as unstable lighting conditions and discrepancies between the dataset and the mathematical model, we introduce the random sample consensus-driven Levenberg–Marquardt parameter optimization algorithm to enhance parameter estimation accuracy. Experiments with static and dynamic online measurement demonstrate that our method reduces pose measurement errors compared to existing methods. This research lays a solid foundation for developing visual measurement techniques for excavators and automated manipulator control based on visual measurements, also serving as a valuable reference for research on mechanical arms.

Distributed measurement system calibration method with automatic networking mechanism

This paper presents a new method that balances accuracy and efficiency in the process of coordinate unification for distributed measurement systems. The method unifies the local coordinate systems of any two measuring units by installing a measuring point on the unit as a marker point and measuring the marker points between them in the working area, combined with the distance between the marker points. Moreover, it enables automatic networking of newly added or moved measurement units with the original measurement network, thereby further improving the efficiency of the dynamic measurements made using the system. The key factors affecting the accuracy of calibration achieved using this method were analysed via simulations. The results indicate that the accuracy of length measurement using the proposed methods is within 0.1 mm m−1 when the measurement units are distributed among the four corners of a rectangle with an area of 50 m2 or more. The experiments indicate that four measurement units calibrated using this method over an area of 35 m2 achieve an accuracy of within 0.2 mm m−1 and 0.1 mm standard deviations for length and three-dimensional coordinate measurements, respectively. Compared with traditional coordinate-unification methods, the proposed method simplifies the calibration process, improves the calibration efficiency by more than ten times, and significantly reduces the calibration time. It is universally applicable in the calibration of large-space distributed measurement systems.

An improved method of concentric circle positioning in visual measurement

Target with concentric circles has been widely used in artificial target and camera calibration of visual measurement systems. The accuracy of concentric circle target directly affects the accuracy of vision measurement system. In this study, an improved method for accurate positioning of concentric circles projection center is proposed. Compared with similar methods, the proposed method has high accuracy and does not need to know the radius of the concentric circle in advance. The influence of inner and outer circle radius and rotation angle of concentric circles on the position error of circular projection center is analyzed by single camera experiment. The experimental results show that the position error of this method is lower than that of similar methods. The concentric circles calibration board is designed as an application to calibrate the binocular vision system. It is shown that the calibration results of the camera’s intrinsic parameters are almost the same as those of PPAGC. However, compared with PPAGC, the total projection error of the left camera is reduced by 30.77% and that of the right camera by 28.29%.

A method for correcting the high-frequency mechanical vibration effects in the dynamic calibration of pressure measurement systems using a shock tube

The extremely rapid reflection of a shock wave from the end wall generated in the shock tube, in addition to the high-frequency content of pressure, inevitably also excites mechanical vibrations. These can potentially produce acceleration-induced spurious signals as part of the dynamic output of the pressure measurement system being calibrated. This paper proposes and evaluates a method for correcting the frequency response of a pressure measurement system obtained with a calibration using a shock tube for the acceleration-induced errors due to vibrations. The proposed method is based on the predetermined frequency response of the pressure measurement system to the accelerations and simultaneous measurements of the vibration accelerations of the pressure sensor during its calibration in the shock tube. The acceleration-induced errors were corrected for a piezoelectric pressure measurement system calibrated in a diaphragmless shock tube developed at the National laboratory for pressure and vacuum at RISE Research Institutes of Sweden, where different vibrational conditions were induced by changing the initial driver pressure, while keeping the initial driven pressure constant. The uncertainty of the correction of the frequency response of the piezoelectric pressure measurement system being calibrated was determined by considering the uncertainty contributions of the measured acceleration frequency response of the pressure measurement system, the measured acceleration of the pressure sensor during its calibration in the shock tube, the generated reference end-wall step pressure and the repeatability of the correction. The results show that the proposed method effectively eliminates acceleration-induced errors in the sensitivity and phase frequency responses of an acceleration-sensitive piezoelectric pressure measurement system being calibrated with a shock tube.

Calibration of strapdown magnetic vector measurement systems based on a plane compression method

The strapdown magnetic vector measurement system, which can measure the magnetic vector and the attitude of a magnetometer simultaneously, has wide applications in geophysical prospecting, etc. Calibration of systematic errors, including magnetometer errors and misalignment errors, is essential for this system. Traditional methods calibrate these two errors separately, with the problem of cumbersome steps and being dependent on special data acquisition methods, such as rotation. An original method that combines a plane compression method with an ellipsoid fitting method is proposed in this paper, which can simultaneously complete the calibration calculation of magnetometer error and misalignment error in one experiment. The calculation can be performed using the spatial scatter point data required by the traditional attitude-independent magnetometer calibration method, and no additional mechanical equipment is required. A mathematical analysis of this method is performed to study the elements decreasing the measurement accuracy of the system, and numerical simulation and field experiments are performed to validate the analysis. The results indicate that the method can contribute to the accuracy improvement of magnetic vector measurement systems.

Installation error calibration for MEMS angular measurement system in hypersonic wind tunnel

The accuracy of model attitude measurement has an important impact on wind tunnel test results. Microelectromechanical System Inertial Measurement Unit (MEMS IMU) provides a feasible way to measure model attitudes with high accuracy. However, the installation error between MEMS IMU coordinate system and the body coordinate system of test models can make the accuracy of the model attitude measurement decrease. In wind tunnel tests, the installation error depends on the relationship between the IMU and the model mechanism before tests. Therefore, in-field calibration in wind tunnel tests is necessary to reduce installation errors. To improve attitude measurement accuracy, the least squares quaternion calibration method based on MEMS IMU and six-position calibration procedure are proposed. High-precision three-axis turntable tests are performed. The pitch accuracy after calibration is higher than that before calibration in the angle of attack sweeping tests. The Root-Mean-Square Errors (RMSE) in the roll and yaw are within 0.01°, which are smaller than those before calibration. In the roll sweeping tests, RMSE of three attitude angles decrease significantly. In hypersonic wind tunnel tests, the pitch errors before and after calibration are within 0.05° and 0.02° in the angle of attack sweeping tests without wind. In five angle of attack sweeping tests with wind, the deviation between the mean of the pitch and the pitch after the elastic angle correction is within 0.03° and the standard deviation of five tests is within 0.01°. The proposed method is confirmed to enhance the accuracy of attitude measurement effectively, which is convenient for engineering applications.

SINGLE IMAGE LASER TRIANGULATION SYSTEM FOR 360° EXTERNAL INSPECTION OF CYLINDRICAL SHAPED OBJECTS USING INVERSE TRIANGULATION ALGORITHM

Abstract. This paper proposes a new Laser Triangulation System (LTS) that allows an 360° external inspection for each acquired image using two planar mirrors, one laser line projector, and one camera. The new measurement algorithm is based on the inverse triangulation in which the analysis is made from 3D object space to image space, the opposite of traditional LTS algorithms, with laser peak detection in favourable directions even in an image with multiple reflections of the object. Measurement system principle, calibration and metrological evaluation are described based on simulated experimental data and 3D reconstructions examples. Uncertainty for a 20 mm plain plug gauge measurement was ±0.07 mm for 95.45% confidence.

Reference Standard for the Calibration of Transformer Loss Measurement System in China

Power loss is unavoidable for transformers due to the characteristics of the lossy electrical components and magnetic materials used for manufacturing them. Transformer loss can be roughly categorized into load loss and no-load loss. Fig. 1 illustrates the circuit model of the non-ideal transformer and the losses [1]. It is estimated that there are more than 1.7 million power transformers in China, and the energy loss of these transformers is approximately 250 TWh per year. Such energy loss not only raises the total cost of the utilities but also causes considerable impact to the environment.

Micromagnetic and Microstructural Characterization of Ferromagnetic Steels in Different Heat Treatment Conditions

The paper addresses the investigation of microstructures from AISI 52100 and AISI 4140 in hardened as well as in quenched and tempered conditions. The specimens are compared in terms of their magnetic hysteresis and their microstructural and mechanical properties. Material properties were determined by hardness, microhardness, and X-ray diffraction measurements. Two different approaches were used to characterize magnetic properties via a hysteresis frame device, aiming, on the one hand, to record the magnetic hysteresis with established proceedings by setting a constant magnetic flux and, on the other hand, by offsetting a constant field strength to facilitate reproducibility of the results with other micromagnetic measurement systems. Comparable differences in both the micromagnetic and the mechanical material properties could be determined and quantified for the specifically manufactured specimens. The sensitivity of the magnetic hysteresis and, determined from that, the relationship between magnetic flux and magnetic field strength were confirmed. It was shown that a consistent change in hysteresis shape from hardened to high temperature tempered material states develops and that this change allows the characterization of different materials without the need to adjust magnetization parameters. Repeatedly, an increase in remanence with decreasing hardness was found for both test approaches. Likewise, a decreasing coercivity and increasing maximum magnetic flux could be detected with decreasing retained austenite content. The investigated correlations should thus contribute to the calibration of comparable measurement systems through the holistic characterized specimens.

Polarization Measurement Method Based on Liquid Crystal Variable Retarder (LCVR) for Atomic Thin-Film Thickness

Atomic thickness thin films are critical functional materials and structures in atomic and close-to-atomic scale manufacturing. However, fast, facile, and highly sensitive precision measurement of atomic film thickness remains challenging. The reflected light has a dramatic phase change and extreme reflectivity considering the Brewster angle, indicating the high sensitivity of the optical signal to film thickness near this angle. Hence, the precision polarization measurement method focusing on Brewster angle is vital for the ultrahigh precision characterization of thin films. A precision polarization measurement method based on a liquid crystal variable retarder (LCVR) is proposed in this paper, and a measurement system with a high angular resolution is established. A comprehensive measurement system calibration scheme is also introduced to accommodate ultrahigh precision film thickness measurement. Repeatable measurement accuracy to the subnanometer level is achieved. Standard silicon oxide film samples of different thicknesses were measured around Brewster angle using the self-developed system and compared with a commercial ellipsometer to verify the measurement accuracy. The consistency of the thickness measurement results demonstrates the feasibility and robustness of the measurement method and calibration scheme. This study also demonstrates the remarkable potential of the LCVR-based polarization method for atomic film thickness measurement in ultraprecision manufacturing.

Loop Antennas for Accurate Calibration of OTA Measurement Systems: Review, Challenges, and Solutions

The E-field and H-field standard antennas are commonly used for calibration of measurement systems in various test applications. The standard H-field antenna is a horizontally polarized omnidirectional probe antenna, with its radiated electromagnetic field being like that of an ideal virtual magnetic dipole. A H-field antenna is physically realized by a consistent current loop fed through a coaxial cable, thus is often referred to loop antenna. This review paper offers a careful description of all aspects involved in the design of a loop calibration antenna; specifically, the concept of a calibration loop antenna is introduced, the state of the art and the recent advances of loop antenna designs and performances are reviewed. The design of a calibration loop antenna needs to take into account comprehensive indicators such as gain ripple, common mode current, cross polarization, impedance matching and radiation pattern. A design of this type of calibration antenna is a challenging task since all the above aspects need to be taken into account simultaneously to find the best trade-off among them. In the context of the example calibration loop antennas, the techniques to improve the bandwidth, the performance of omnidirectional radiation and the effects of suppressing common-mode current are discussed, which provides new ideas for the design of calibration loop antennas. Finally, the principles and steps of the horizontal polarization calibration in the multi-probe anechoic chamber is introduced and discussed; the errors caused by the common mode current to the calibration results are evaluated through calibration examples to demonstrate the relevant impact of a well-designed loop antenna for the accurate calibration of a multi-probe measurement system, and the subsequent precise evaluation of the performances of the antenna under test (AUT).

Binary Sequences for Online Electrochemical Impedance Spectroscopy of Battery Cells

Online diagnostic of lithium-ion battery (LIB) cells may have significant impact on chemical energy storage systems. Electrochemical impedance spectroscopy (EIS) is widely used for the characterization of LIBs and could be the most appropriate technique for online diagnostic, but its response time should be shortened. This work investigates the usage of multisine excitation to shorten the measurement time and simplify the hardware implementation for EIS of battery cells. Two types of multisine binary sequences are considered: sigma–delta modulated multisine sequences (SDMSs) and maximum length binary sequences (MLBSs). Their applicability to online and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> EIS monitoring is evaluated by designing a measurement architecture also suitable to be implemented in a system-on-chip. The calibrated measurement system is compared with a benchtop reference instrument, reporting an RMSE deviation smaller than 5% in the frequency range of interest 1–200 Hz. The realized system is then used for online monitoring of the discharge process of a commercial 18650 LIB cell. The two proposed sequences are compared in terms of accuracy using a digital battery emulator circuit. Both the sequences demonstrated to be suitable for fast measurement and simple hardware integration, enabling online <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> EIS monitoring at cell level.

Two-step calibration for vision measurement system with large field of view and high depth

Two-step calibration for vision measurement system with large field of view and high depth